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Progress Report on Grant: F49620-03-1-0379 (09/30/04)

Start Date: 6-15-03

New Instrumentation for Nanoscale Subsurface Spectroscopy and Imaging

Lukas Novotny, University of Rochester, The Institute of Optics, Rochester, NY 14627.P. Scott Carney, University of Illinois at Urbana-Champaign, Department of Electrical and

Computer Engineering, Urbana, IL 61801.Bennett Goldberg, Boston University, Physics Department, Boston, MA 02215.

Kevin F. Kelly, Rice University, Dept. of Electrical Engineering, Houston, TX 77005.Stephan J. Stranick, National Institute of Standards and Technology, Gaithersburg, MD 20899.

Selim Ünlü, Boston University, Dept. of Electrical Engineering, Boston, MA 02215.Paul S. Weiss, Penn State Univ., Depts. of Chemistry and Physics, University Park, PA 16802.

The objective of this MURI project is the development of techniques for non-destructive,chemically specific, three-dimensional nanoscale characterization of subsurfacestructures. While nanoscale resolution is achieved through localization of electromagneticradiation using favorably designed structures (e.g. SIL, sharp probes), chemicalspecificity arises through electromagnetic spectroscopy. We are exploring interactionsover a broad spectral range; Kelly and Weiss are studying local interactions in themicrowave regime, Stranick and Unlu are covering the infrared regime, and Goldbergand Novotny are studying interactions at optical frequencies. The theory needed toreconstruct the measured object(s) from the recorded signals is being developed byCarney. The different investigators involved bring together complimentary expertise anda common goal: the development of a measurement platform for subsurface spectroscopyand three-dimensional object reconstruction. The group effort is coordinated by a part-time project administrator (Sylvia Schattschneider, schatts@optics.rochester.edu) whoalso maintains a dedicated website with information on research progress, meetings,personnel, and outreach (http://xray.optics.rochester.edu/muri03). The central vision ofthis project is that new scientific discoveries are often catalyzed by new instrumentation.

Figure 1: Schematic of the project.

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The project is subdivided into four tasks as schematically represented in Figure 1. Thegoal of the initial period of the project is the independent development and refinement oftechniques in the laboratories of the participating investigators. Since the last projectreport we have explored new approaches and strategies for subsurface imaging and wehave developed test samples to demonstrate the feasibility of different measurementmodalities, to assess their limitations, and to provide comparison with other, existingtechniques. During the last project period we generated various important milestones.Among the research highlights are (1) demonstration of sub-10nm near-field Ramanimaging of carbon nanotubes and first near-field Raman subsurface measurements, (2)first demonstration of a shear-force controlled microwave instrument operating up to 20Ghz, (3) experimental demonstration of inverse scattering applied to photon scanningtunneling microscopy, (4) direct observation and manipulation of subsurface hydrogen inPalladium{111}, (5) first application of the Numerical Aperture Increasing Lens (NAIL)to subsurface thermal emission microscopy, and (6) measurements of DNAconformations with sub-nanometer resolution using spectral self-interference microscopy.This list of highlights demonstrates that our MURI project is well underway and thatsignificant results are being produced.

Period Tasks Milestones

Year 1 I

II

III

IV

I - IV

Demonstrate near-field Raman and IR microscopy with sub-30nmresolution. Develop test samples with buried nanoscale structures.Develop near-field inversion accounting for polarization, boundaryconditions and tip models.Develop and test microwave STM. Nanofabrication of dopedsemiconductor samples.Develop SIL microscope. Study influence of gap-width and surfaceroughness on resolution. Build 4! detuned, widefield FSI microscope.Demonstrate multiple layer spectral imaging.Define common goals, collaborations, and design criteria.

Year 2 I, II

III

IV, II

I - IV

Maximize field enhancement through optimized geometries andmaterials. Experimental demonstration of subsurface imaging and 3Dobject reconstruction.Measurement of 2D test samples and molecular electronic devices.Determination of lateral resolution.Demonstration of thermal subsurface imaging and semiconductor failureanalysis using solid-immersion lens (SIL) microscopy. Demonstratefluorescence self-interference (FSI) microscopy operating in 3D.Application of tomographic algorithms to FSI microscopy.Discuss common measurement platform. Develop test samples andbench marks.

Table 1: Projected milestones for year one and two.

Our team began to plan the layout of a common measurement platform. In order to saveresources, it was decided to modify and extend the capabilities of on an existing near-

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field scanning optical microscope. An independent DURIP application has beensubmitted to AFOSR for the acquisition of a commercial instrument by the Germancompany WITec. It is planned that the instrument be located at the newly completednanoscience center at Boston University. The different MURI team members will designindependent measurement heads that are compatible with the acquired instrument. Theopen-platform of WITec’s AlphaSNOM instrument provides a variety of modalitiesalready built in, but more importantly, can be readily modified with extended modules,lenses, and scan heads of our MURI team’s design. Acquisition of this instrument willserve three critically important goals to the current MURI: (1) It will be a test-bed,allowing our MURI team to integrate multi-spectral, tomographic, and broadbandevanescent nanoscale imaging in the context of a commercial platform, paving the waytoward adoption and widespread use; (2) The instrument and the new nano-optics lab itwill be housed in will serve as a locus of activity for the MURI team members. TheBoston University group will provide travel support, a new laboratory, and extensiveadditional equipment to extend the range and work with the entire MURI team; (3) Bybuilding the prototype nanoscale imaging extensions onto a commercial instrument, wewill conform to a standard and hasten development and scientific advancement innanoscale imaging.

During the last funding period, together with Richard Saykally (Berkeley), we haveorganized a dedicated Symposium on Microscopy beyond the Diffraction Limit at theAnnual American Chemical Society Meeting in Anaheim, CA. This symposium featurednearly 50 speakers including our MURI team members and also members from otherMURI programs (e.g. Halas @ Rice). The meeting provided an open platform forassessing the current state-of-the-art in high-resolution optical imaging and to developnew strategies for future experiments.

The following sections describe our research progress in more detail. The current state isdescribed separately for each task outline in Table 1. This report concludes with asummary of future plans and with a list of AFOSR sponsored publications andpresentations.

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1. Progress and Activities:

1.1 NANOSCALE CHEMICAL ANALYSIS (TASK 1)

Novotny and Stranick study the interaction between a laser-irradiated local probe, such asa metal tip, and a sample placed in close proximity. Under certain conditions, the localprobe is able to confine and enhance the incoming radiation. For metal tips it has beentheoretically predicted that the intensity at a metal tip can be a factor 103 – 104 strongerthan the intensity of the incoming radiation. The enhanced field at the tip acts as a highlyconfined light source for a local, spectroscopic interaction with the sample surface. Thefield enhancement originates from a combination of electrostatic lightning-rod effect(quasi-singularity at the tip) and surface plasmon resonances which are strongly materialand geometry dependent. By moving the sample underneath the laser-irradiated metal tipand acquiring an optical response for different tip-sample positions we are able to recordan optical raster-scan image with a resolution that solely depends on the tip sharpness.The principle of this tip-enhanced spectroscopy is shown in Fig. 2.

Near-field Raman imaging and spectroscopy:

The strength of field enhancement at the metal tip depends critically on the tip materialand its geometry. The enhancement at the tip originates from a combination of theelectrostatic lightning-rod effect, which is due to the geometric singularity at the tip, andlocalized surface plasmon resonances which depend sensitively on the excitationwavelength. Our experiments indicate that the measured enhancement factors aresignificantly weaker than the theoretically predicted values and it is the focus of ourstudies to determine the parameters that allow us to increase the strength of enhancement.

Figure 2: Principle of the local field-enhancement technique. A laser-irradiated metal tip(polarization along tip axis) enhances the incident electric field near its apex thereby creating alocalized photon source. a) Schematic of the method. b) Practical implementation: a higher-orderlaser beam is focused on a sample surface and a sharply pointed metal tip is positioned into thelaser focus. The enhanced fields at the tip locally interact with the sample surface therebyexciting a spectroscopic response that is collected by the same objective and directed on adetector.

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Our current probes consist of sharply pointed gold tips produced by electrochemicaletching. Occasionally we sharpen the tips further by focused ion-beam (FIB) milling.External laser-irradiation polarized along the tip axis induces an oscillating surfacecharge density which is peaked at the end of the tip [1,2]. In order to achieve strongpolarization along the tip-axis in the on-axis illumination scheme shown in Fig. 2b weconvert the fundamental Gaussian laser beam into a radially polarized beam outside thelaser cavity [3].

Due to their one-dimensional structure and their small size, single-walled carbonnanotubes are ideal test samples for the characterization of the field enhancementstrength. A representative image recorded with near-field Raman microscopy is shown inFig. 3A. The contrast in the image corresponds to the strength of the G-line centered atv=1594cm-1. The spatial resolution of 15nm is determined by the tip sharpness and theuniform signal along the nanotube and the weak D-band signal at v ~1270cm-1 indicatesthat this chemical-vapor deposition (CVD) grown tube is free of defects. We have foundthat other growth methods produce significant amounts of defects which can be localizedand characterized with the near-field Raman technique [4,5]. Fig. 3B shows acharacteristic Raman scattering spectrum recorded on top of the nanotube. Thehighlighted spectral band corresponds to the signal that was used to form image (A). Fig.3C is the signal enhancement as a function of tip-sample distance. This curve has beenacquired for the G-line highlighted in (B). Considering the different areas probed by thenear-field and farfield we find an effective enhancement factor of ~100, much lower thanthe theoretically predicted enhancement factors. Furthermore, we find that theenhancement is not uniform for the different spectral lines.

Figure 3: Near-field Raman imaging of single-walled carbon nanotubes. The spatial resolution of15nm in (A) is entirely defined by the tip sharpness. This image has been recorded by raster-scanning the sample underneath the laser-irradiated metal tip and integrating, for each imagepixel, the photon counts that fall into a narrow spectral bandwidth centered around the G-line atv=1594cm-1 (indicated by the yellow stripe in B). (B) Raman scattering spectrum recorded on topof the nanotube, (C) Enhancement of the G-line signal as a function of tip-sample distance. Theyellow line is an exponential fit with a 13nm decay length.

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However, our work clearly demonstrates that near-field Raman scattering is a powerfultechnique for the characterization of defects and also dopants in nanotubes. There isevidence that the selective doping of nanotubes increases the hydrogen uptake makingnanotubes an attractive material for hydrogen storage devices. Our technique is able tolocalize these dopands and allows us to systematically study their influence. Sincevirtually every practical application of semiconductors relies on the effects of dopants ordefects it can be expected that defects and dopants will also have a strong influence onthe properties of future carbon nanotube devices.

Ultimately, we intend to study nanotubes embedded in a solid host material. This planrequires extending the capabilities of near-field Raman scattering to subsurface imaging.During the past funding period we have developed test samples for a systematicinvestigation of subsurface near-field Raman imaging. The topographic profile of oneparticular test sample is shown in Fig. 4A. It consists of individual carbon nanotubesdeposited on a glass surface and overcoated with a 10nm thick SiO2 layer. The latter hascircular holes which are formed by nanosphere lithography [6,7], i.e. latex spheres havebeen deposited on top of the carbon nanotube sample before SiO2 deposition. The latexspheres act as a shadowing mask and after removal, they leave areas behind that areunexposed of SiO2. The simultaneously recorded near-field Raman image is shown inFig. 4B. The thin solid lines indicate the contours of the deposited SiO2 patterns. Whileuncovered nanotubes are clearly resolved only a few covered nanotubes show up. In fact,because of the strong localization of the near-fields at the metal tip, the signal strength ata distance of 10nm is less than 30% of the maximum value (c.f. Fig. 3C).

Figure 4: (A) Topographic image of a carbon nanotube test sample used for subsurface imaging.10nm thick SiO2 features are deposited on top of a glass surface with isolated carbon nanotubes.The SiO2 features have been created with nanosphere lithography using latex spheres asshadowing masks. (B) Simultaneously recorded near-field Raman image. Uncovered nanotubesare clearly resolved whereas only a few covered nanotubes (presumably bundles) can be detectedwith reasonable signal-to-noise. The black contourlines indicate the outline of the SiO2 features.

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Thus, in order to resolve SiO2 covered nanotubes we need a high signal-to-noise ratio andhence a high field enhancement to begin with. As indicated by the arrow in Fig.4B we areable to resolve some covered nanotubes but we believe that these are nanotube bundlesthat provide a much stronger signal compared with single isolated nanotubes. The key toimprove subsurface imaging is an optimization of the field enhancement strength.

Fig. 5 shows a quantitative analysis of the spatial resolution attainable in subsurfaceimaging. The topographic map in (A) indicates that the sample is covered with someresidues originating from the removal process of the latex spheres. It shows a nanotubebundle that is partly covered with 10nm SiO2. The simultaneously recorded near-fieldRaman image is shown in (B). It is evident that the Raman signal is not uniform along thenanotube. This is characteristic for the arc-discharge nanotubes which usually exhibit ahigh level of defects. Fig. 5C shows cross-sections evaluated at the positions indicatedby the arrows in (B). One cross-section (blue curve) corresponds to an uncoverednanotube segment whereas the other cross-section (red curve) originates from a coverednanotube section. Both cross-sections are normalized to the same amplitude and fittedwith a Gaussian curve. The red curve had to be scaled by a factor of 3.2 in order toachieve same signal amplitudes. This is consistent with the approach curve shown in Fig.3C. Notice, that we subtracted the signal due to the halo around the nanotube in Fig. 5B.This halo originates from direct exposure of the sample to the focused laser beam (c.f.Fig. 2B) and constitutes the diffraction-limited signal obtainable by conventionalconfocal Raman microscopy. Thus, the image represents a simultaneous near-field andfarfield Raman image of a single nanotube bundle.

Evaluation of the full-widths at half maximum (FWHM) of the curves in Fig. 5C rendersthe values of 28nm (uncovered tube) and 64nm (covered tube). This decrease inresolution originates from the fact that the fields of a localized source spread out widthdistance, i.e. the field confinement becomes weaker as the distance to the source isincreased. A simple dipole model in which the tip is replaced by a radiating dipole is ableto account for the observed effects.

Figure 5: (A) Topographic image and (B) near-field Raman image of a nanotube-bundle partiallycovered with 10nm thick SiO2 layer. (C) shows cross-sections evaluated at the positions indicatedby the arrow in (B). The 10nm SiO2 layer attenuates the near-field signal by a factor of 3.2 anddeteriorates spatial resolution from 28nm to 64nm.

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Although we have clearly demonstrated near-field optical imaging based on local fieldenhancement, many fundamental issues related to the nature of the near-field interactionbetween tip and sample have yet to be studied and understood. For example, we find thatonly a few gold tips show the desired field enhancement effect. Based on our previousinvestigations, we believe that field enhancement is affected by the crystalline grainstructure of gold [8], by surface contamination, or by nonlocal effects. The latteroriginates from electron scattering at the surface of the tip [9,10]. In bulk materialselectrons loose their kinetic energy due to electron-phonon interactions. However, whenthe size of the material becomes comparable with the mean free path of the electrons,there is an increased probability that electrons also scatter at the surface. This leads toincreased dissipation and thus to additional damping [9]. Although these nonlocal effectscan be taken into account in a theoretical analysis [10,11] it is not possible to derivequantitative results because the nonlocal parameters are not known. Therefore,quantitative figures for the strength of the field enhancement of a particular structure relyon experimental methods.

Results from other groups also suggest that the field enhancement has to be viewed as anantenna effect and that the best performing tip material is a perfect conductor and notnecessarily a noble metal such as gold or silver [12]. The best available conductor atvisible frequencies is aluminum with a skin depth of ~6.5 nm. Aluminum has the furtheradvantage that it naturally forms an oxide surface which protects the metal from chemicalreactions. It is commonly observed that the fluorescence of single molecules is increasednear the edges of an aluminum aperture [13,14], - a clear signature of field-enhancement.Furthermore, results from other groups show that single molecule fluorescence is notseverely quenched by the proximity of an aluminum tip [12]. Based on this newexperimental evidence, we currently believe that the optimum conditions are reached fora finite-sized [15] aluminum tip with length ~ λ/2 which follows from simple antennatheory. Aluminum is also much more durable than noble metals and hence can withstandhigher interaction forces with the sample surface.

As shown in Fig. 6, we have started to fabricate so-called tip-on-aperture (TOA) probes[16]. A tip is directly grown onto the end-face of a standard fiber-optic aperture probe.Light that is emitted by the aperture directly couples to the tip and localizes the field atthe tip end. This approach overcomes the problem of the farfield background that is, forexample, responsible for the halo around the nanotube in Fig. 5B. We expect that theTOA approach will lead to a much higher signal-to-background ratio which will allow usto increase the measurement range in subsurface imaging.

The process employed to fabricate the TOA probes follows several steps. First, a single-mode glass fiber for a wavelength of λ = 633nm is etched in 40% hydrofluoric acid (HF)to form a tip with a small apex radius. A layer of mineral oil floating on top of the HFand solvent heating to 60oC ensures a smooth glass surface. Tips are usually formed in aself-terminating process within 2 hours. The etched fibers are then cleaned in purifiedwater and the still attached plastic jacket is softened in dichloroethane (99.9%) for 10minutes. After this procedure, the jacket can easily be stripped off with tweezers. In anext step, the sharpened fibers are coated with two metal layers in an e-beam evaporator

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system. A 1nm thick layer of titanium (0.1nm/s) serves as adhesion layer for a 200nmthick aluminum layer (1.5nm/s). After deposition of both metals, the ends of the tips areentirely overcoated. To form an aperture, we used an FIB (Ga) with a current of 10pA ata voltage of 30kV to slice away a section of 400nm from the tip end. We have used a FEIdual-beam System DB235. As shown in Fig. 6B, the tips have now a flat and well-defined end-face with a nearly circular aperture. In a next step, a SiOx pillar is grown atopof the aperture. This step is accomplished by injecting tetraethoxysilane (TEOS) into theFIB chamber (1-3E-5 mbar) and exposing the aperture to a focused electron beam. Usingan electron voltage of 15kV, the electron-beam assisted growth mechanism produces a200nm tall pillar within 1 second. Optionally, the SiOx pillars can be cut to the desiredsize with the FIB. In a final step, the entire TOA probe is overcoated with a 10nmaluminum layer from an oblique angle. Because of the shadowing effect of the pillars theoblique incidence guarantees that not the entire aperture becomes metal covered, and thatthere is a small slit through which the metal tip can be excited.

In the next funding period we plan to further develop and characterize the tip-on-aperturetechnique. We will explore different materials and different tip lengths. The goal is toincrease the field enhancement in order to increase the measurement sensitivity insubsurface near-field Raman imaging.

Figure 6: SEM images of a tip-on-aperture probe. Side view (A) and front view (B). The end-faceof a sharpened and aluminum coated fiber is first sliced with a focused ion beam (FIB) in orderto create a tiny aperture. A SiOx whisker is grown directly on the aperture by electron-beamassisted growth. The whisker is then cut to the desired length using FIB. The arrows in (B)indicate the position of the remaining tip and the fragment that has been cut off. In a final step,the tip and aperture are overcoated with aluminum.

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Near-field RF and Microwave measurements:

Stranick and Novotny are also working on extending the field enhancement technique tothe RF and microwave range for the purpose of nanoscale characterization of dielectricmaterials and components. The properties of these materials vary widely, from highpermittivity with low loss for resonator applications to low permittivity and low loss forradomes, while Radar Absorbing Materials (RAM) are required to have a very high loss.In all applications, design is greatly facilitated by an accurate knowledge of the complexpermittivity of the materials. One of the common characteristics of recently developed,advanced dielectric materials is that they possess critical dimensions on short lengthscales (sub-micrometer) and that the components with these dimensions must behomogeneous and of high quality (defect free) for the intended dielectric performance tobe achieved. Given that these critical dimensions are well below that of the radiationwavelength, analysis by conventional dielectric probes, which look at materials on amacroscopic dimension, is no longer sufficient. Alternatively, a near-field microscopetakes advantage of the non-propagating electromagnetic fields (evanescent fields) presentat a sample’s surface when exposed to an electromagnetic wave. This results in animprovement in the spatial resolution (below 100 nm). This resolution, unlike that ofconventional dielectric probes, is largely wavelength independent. Additionally, the tip(a sharpened metallic probe) turns the non-propagating fields into radiation that can thenbe detected and analyzed.

During this funding period, we have made strides toward development of a microwavenear-field probe that has both increased sensitivity and a compact architecture to allowfor eventual incorporation into a variety of microscope platforms. To this end, in ournear-field microwave probe, microwave radiation up to 20 GHz is coupled evanescentlyto the sample surface using a sharp proximal probe that is part of a transmission line,resonant cavity structure, see Fig. 7. Analysis of reflected and transmitted signals isperformed using an HP8510 C Network Analyzer allowing the extraction of permittivityand permeability information.

Figure 7: Schematic of the transmission line cavity structure used in the microwave evanescentprobe microscope. One end of the cavity is terminated by an SMA coaxial connector (lower left),and the other end with a sharp metal tip (upper right).

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The probe-sample separation is controlled using shear-force feedback giving themicroscope the ability to map out the topographic structure of the sample surfaceconcurrently. The importance of going to microwave frequencies (2 to 20 GHz) is togain access to information concerning the dielectric nature of materials at their intendedoperational frequency.

As mentioned above, cavity and transmission line structures are being fabricated andevaluated for their ability to achieve maximum sensitivity and frequency agility. Wehave recently fabricated and tested an improved probe structure that has a measuredquality factor (Q) approaching 104 with supported modes at various frequencies acrossthe range from 100 MHz to 20 GHz. Precise control over the frequency and the Q of thecavity is accomplished using a remotely tunable impedance mismatch. This Tunablemismatch or “load” is attached to the SMA termination of the microscope cavity. It isremotely tuned by adjusting the mechanical dimensions of an air filled capacitor with apiezoelectric element. The effect of tuning the mismatch and subsequently one of themodes of the cavity is shown in Fig.8. It should be pointed out that an infinite number offrequency steps is possible (but not practical) with this design. Additionally, we havecompleted the automation of data acquisition events that allows for a higher density ofmicrowave vector (spectra) as well as scalar (integrated spectra) measurements to bemade.

Figure 8: Shown are representative single port, network analyzer measurements of a proberesonator mode as the variable mismatch is tuned, see text.

At microwave frequencies, valid measurements of a dielectric response must take intoaccount the effects of sample geometry, organic contamination, and resonant effects (thesample acting as a resonant structure) which can mask the true dielectric properties of asample. These effects will be magnified when moving to smaller and smaller samplevolumes/sizes as is the case with advanced materials. An example of a geometric effectis shown in Fig. 9. The sample is a thin-film dielectric coating of doped bariumstrontium titanate (BST) on silicon, see photograph in Fig. 9a. The BST sample wasfabricated by a dual-target pulsed laser deposition methodology: one target is bariumtitanate and the other is strontium titanate. Using this sample preparation method, a

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compositional gradient is formed across the sample surface ranging from barium rich tostrontium rich. More importantly, this will result in a dielectric gradient. By monitoringthe magnitude and frequency of one of the microscope’s resonance modes as the tip isscanned across the surface, a dielectric response map of a sample can be acquired, asshown in Figs. 9b,c. In Fig. 9b the dielectric response of the sample is dominated bysample thickness variations. The color scale variations (dielectric response) have a directcorrelation to the sample thickness (see optical interference pattern present in thephotograph of the sample, Fig. 9a). By controlling experimental protocols these effectscan be accounted for and minimized to reveal the samples dielectric response due only tothe stochiometric variations, see Fig. 9b.

Figure 9: As shown in these images of BST film gradients on a silicon substrate, by measuringthe frequency shift (color scale bar) of the resonance mode, the dielectric response of a samplecan be mapped out. In (a) a photograph of the region of the BST sample mapped in figures (b)and (c). The lines on the photograph detail regions of constant thickness.

Preliminary measurements of nanoscale composites are currently underway. Thesenanoscale samples are geometry controlled which will provide a metric of our currentspatial resolution, sensitivity, and accuracy of dielectric constant determination.

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1.2 NEAR-FIELD TOMOGRAPHY (TASK 2)

The task of near-field tomography is pursued both experimentally and theoretically.Carney implemented and demonstrated inverse scattering applied to photon scanningtunneling microscopy (PSTM) [17]. This work validates the theoretical approachdeveloped before the start of this grant. Further progress has been made in theimplementation of a power-extinction based imaging approach, optical power extinctiontomography (OPET), that will provide three-dimensional imaging without the usual needfor phase measurements. On the theoretical front, the theoretical underpinnings of thepower-extinction based approach have been extended to samples situated in a half-space,a step needed to deal with the experimentally relevant situation that the object to beimaged rests on a known substrate.

Near-field Tomography (experiment):

PSTM is a variant of near-field scanning optical microscopy in which the sample isilluminated by an evanescent optical field. This field is generated at the surface of ahigh-index prism by means of total internal reflection (TIR). The sample acts to frustratethe TIR field and couple some of the light to propagating and non-propagating modes.The resultant scattered field is then detected by a sharp optical probe scanned in the planein near-contact with the sample. Because the illuminating field and scattered fieldoverlap, the resultant measured signal represents the near-field equivalent of an in-line, orGabor, hologram.

Figure 10: Data obtained from PSTM measurements of a single object, but with two differentilluminating fields, both at a scan height of 300 nm. The field of view in both cases is 3.4 micronsby 5 micron. The scale corresponds to normalized photocounts.

Thus the data are highly dependent not only on the sample structure, but the illuminatingfield as well. Direct interpretation of the acquired image is problematic at best since achange in the illuminating field may produce a markedly different image (c.f. Fig. 10).The problem is further exacerbated when the scanning probe is withdrawn some distancefrom the sample to avoid contact.

To resolve ambiguities in the images and to obtain quantitatively meaningful images it isdesirable to solve the so-called inverse problem and determine the underlying structure of

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the sample computationally. The analysis applied here is based on Maxwell's equationswith a linear constitutive relationship. Direct numerical solution is computationallyintractable. However, we were able to take advantage of recent analytical advances(please see the paper for details) to precompute an appropriate kernel. The resultingobject structure is shown in Fig. 11 along with an atomic force microscope (AFM) imageof the object. The sample was prepared to consist of small islands of gold on a glasssubstrate. The AFM image thus provide a means to validate the morphology of thecomputed image. The results may be seen to be in good morphological agreement withthe AFM. Moreover, the susceptibility of the central island is seen to be in goodagreement with published valules of the susceptibility of gold at the wavelength of lightused in the experiment (633 nm).

Figure 11: The top panel (c) shows the computed image of the sample. The scale indicatescomputed susceptibility. The bottom panel shows the AFM image of the same sample. The field ofvies is 3.4microns by 5 microns in both images.

This work provides a proof of principle for the inverse scattering approach. Since thescan was made at a height of 300 nm above the sample, we expect that a similar approachcould be applied to the case that these objects were buried beneath a substrate of amaterial of known index and thickness up to 300 nm. The holographic nature of theimages, which is usually a hindrance to interpretation was here used to our advantage todetermine the phase and amplitude of the scattered field in the course of computing theobject structure.

In an effort to circumvent the phase problem, Carney has been building a new instrumentat UIUC. The OPET project is design to take advantage of theoretical advances in ourunderstanding of the role of energy conservation in electromagnetic scattering. Theinstrument consists of two arms, one mounted on a precise rotation stage, the other fixed(see Fig. 12a). Light is launched down the arms and meets in the region of the sample.The sample is also mounted on a rotation stage. The power throughput of each arm ismonitored. The total power lost due to the presence to the scatterer is related to a Fouriercomponent of the absorption index of object. The argument of the Fourier component isdetermined by the relative angle between the beams and the angle of the smaple withrespect to the beams and the phase is determined by varying the relative phase betweenthe beams by means of a piezo stage in one of the arms. A test sample consisting of anamplitude grating of known spacing. The Fourier space image of such a sample isexpected to consist of two bright lines with sidelobes. A recently acquired data set isshown in Fig.12b. The greatest challenge we face at the moment is controlling the

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relative phase of the two beams. We are considering several course of action in thisregard.

Figure 12: (a) On the right, the basic OPET scheme is shown. On the left, data obtained with theinstrument for a sample consisting of an 8 line per mm grating. The data are expected to formtwo clear lines.

Near-field Tomography (theory):

The OPET experiment is based on a generalization of the optical theorem, developed byCarney, applicable to the scattering of arbitrary incident fields falling on a scatterer infree-space. To address the experimental reality that samples must be supported on someknown substrate, it is necessary to extend this work to include an interface in thescatterer-free problem and then compute the effects of the scattering body. We haveaddressed this in a just published article [18]. The older result related the powerextinguished from a scatterer to the angular correlation function of the scattered field indirections corresponding to the directions of the plane wave components of the incidentfield. The new results takes into account the effects of the boundary and shown that thepower extinguished may be related to the components of the scattered field in thedirections of the outgoing parts of the incident field, including the transmission andreflection of the incident field at the boundary. This work is particularly relevant to theimaging of embedded bodies.

In related work, Carney and co-authors presented an information theoretic analysis of thenear-field inverse scattering problem for two dimensional objects [19]. This work showedthat for photon-noise limited systems (the best case) the near-field effectively ends onewavelength away from the sample. That is, the fields measured within a wavelength ofthe sample may provide sub-wavelength structure via solution of the inverse scatteringproblem, but fields measured at greater distances practically do not. Carney is alsopursuing a novel imaging system that makes use of the field scattered from an object intotal internal reflection tomography (TIRM). This year he published a review of theconnection between object structure, in particular sub-wavelength structure, and TIRMdata [20].

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1.3 MICROWAVE STM AND ELECTRON SPIN SPECTROSCOPY (TASK 3)

In order to address material properties in the technologically relevant microwave regime,Weiss and Kelly are developing alternating-current scanning tunneling microscopy andexploring its capabilities and limitations. Subsurface characterization is the centralobjective of this project and in order to understand subsurface imaging by ACSTM, it isnecessary to understand the current limitations of subsurface imaging in traditionalscanning tunneling and atomic force microscopes. In this context, the Weiss group hasbeen examining H atoms on and under the Pd{111} surface. Using scanning tunnelingmicroscopy (STM) at 4 K, they have been able to observe directly and to manipulatesubsurface hydrogen in Pd{111}. They are able to control subsurface hydrogen atoms byapplying voltage pulses from a STM tip. The Pd{111} surface was pretreated withhydrogen at exposures of ~1000 Langmuir then cleaned in ultrahigh vacuum usingsputtering, annealing and oxygen treatments. The oxygen treatments and a final, shorthigh temperature anneal (~1200 K) remove hydrogen from the surface and topmost Pdlayers but leave small amounts of hydrogen throughout the bulk.

When this system is imaged at 4K, surface features due to subsurface hydrogen areformed by moving the tip over the surface at bias voltages of either polarity greater than0.5 V. It is not possible to create these features with bias pulses applied to the tip if thecrystal has not been pre-treated with hydrogen. Fig.13 shows two images of areas of thesurface where the tip has traced lines at a variety of currents and bias voltages.

Figure 13: A) STM image (700 Å x 700 Å) of four lines on a Pd{111} surface at 4 K (Vsample =-0.025 V, It = 50 pA). B) STM image (950 Å x 700 Å) of five lines on a Pd{111} surface at 4 K(Vsample = -0.025 V, It = 50 pA). The two insets are differential conductance images (30 Å x 30Å) showing atomic resolution on the Pd{111} surface (Vsample = -0.018 V, It = 200 pA). Thehexagonal array of surface Pd atoms over the feature is distorted when compared to thehexagonal pattern of the flat Pd{111} surface.

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When tunneling at biases in the ranges that populate subsurface sites with hydrogen (0.5to 1.0 V and -0.5 to -1.0 V), the mean free path of the electron in clean Pd is ~1500 Å.Weiss assumes that these tunneling electrons are propagating from the tip into the crystal,(or vice versa at negative sample bias) and scattering inelastically from hydrogen atomsin the bulk. Fig.14 illustrates the effect of populating subsurface sites with hydrogenatoms from the bulk. In light of these STM observations, the Weiss group can conjecturethat the role of subsurface hydrogen in Pd-catalyzed reactions can be the key step in theformation of the desired products. Subsurface hydrogen could potentially create surfaceperturbations that ultimately direct product formation. Therefore, an understanding of theeffects subsurface hydrogen in Pd{111} can have on adsorbates is essential for effectivecatalytic designs and applications.

In addition, the Weiss group has been exploring the microwave transmission/reflection oftheir ACSTM system, looking towards its adaptation in the final combined measurementplatform. A variety of modified geometries are being tested, studying both the amplitudeand phase behavior of the microwave signals up to 20 GHz.

The Kelly group has constructed 2 microwave-compatible STM systems, both of whichare currently undergoing testing and debugging. The first system is a replica of the Weisssystem designed to detect the difference frequency produced in the STM junction. Thisinstrument will be used to explore nanolithographically patterned silicon as well asnanoscale doping in carbon nanotubes. It will also be used to investigate if the electronspin resonance signal can be stimulated and detected by pumping the transition with anexterior microwave source.

Figure 14: Schematic illustrating the effect of populating subsurface sites with hydrogen atomsfrom the bulk. A) The surface and subsurface (SS) regions are free of hydrogen on the cleancrystal, whereas the bulk contains some residual hydrogen. B) After applying a bias pulse withthe tip, some of the bulk hydrogen segregates to more stable sites in the subsurface region. Thesurface Pd atoms relax upwards, changing the local topography, and there is a dipole createdthat leaves the surface Pd atoms electron deficient with respect to their surroundings.

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The second system is a hybrid of the Weiss-style microwave ACSTM but adapted toperform the Welland-Durkan electron-spin resonance (ESR) STM experiment on singlemolecules. This system has a tremendous advantage over the latter as the spin signalwhich is in the MHz regime is more efficiently coupled from the STM junction to thepreamplifier and spectrum analyzer. Whereas Durkan et al. were limited to tunnelingcurrents in the tens of nanoamps, we expect to detect signals on the picoamp or lowerscales.

The Kelly group is also continuing its scanning probe investigations of single-wall carbonnanotubes. Functionalized nanotubes are an ideal testbed for this instrument as they havechemical and electronic signals that vary at the nanometer level. Scanning tunnelingmicroscopy allows for characterization at the atomic-scale and can be combined withnear-field Raman microscopy (TASK 1). The wide variety of sidewall reactions beingperformed by Kelly’s collaborators at Rice allow for distinguishing contributions to thechemical and electronic signature that is not obvious by traditional scanning probemicroscopy. There is a great deal of interest in fluorinated single wall carbon nanotubesfor solvation, subsequent chemical reaction, or as a means of controlled cutting. Towardsthis end, the Kelly group studied the defluorination of nanotubes using variable-temperature STM. Defluorination of the nanotubes begins at 550 K when annealed inUHV and is illustrated in Fig.15A. After complete defluorination by annealing at 1000K,nanoscale defects are still apparent along the tubes as seen in Fig.15B. We believe thesedefects play a key role in the cutting of carbon nanotubes. We are also comparing andcontrasting this behavior with covalently bound hydrogen.

Figure 15. A. STM image of a nanotube partially defluorinated by annealing in UHV at 650 K. B.STM of a completely defluorinated tube by annealing at 1000 K in UHV. Nanoscale defects arenow apparent along the tubes. C. Alkyl-thiophene functionalized nanotubes self-assembled on agold surface pretreated with a hexanethiol self-assembled monolayer.

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In addition to atomic modification to nanotube sidewalls, the Kelly group is alsoinvestigating the electronic and chemical behaviour of various molecular sidegroups.Alkanethiol- and alkylthiophene-modified nanotubes are particularly interesting becauseof their potential for self-assembly on gold surfaces. We have just begun atomic-scalecharacterization of such systems. An STM of thiophene-derivatized tubes inserted into ahexanethiolate monolayer on a gold surface is shown in Fig. 15C. The self-assemblyaspect of these systems will allow for the controlled patterning of nanotubes on surfaces,beneficial for both this grant and future commercial applications.

1.4 LONG-RANGE SUBSURFACE IMAGING (TASK 4)

Goldberg and Unlu pursue two different approaches for resolving features that are manywavelengths below the surface of the test sample. In one approach, the numericalaperture (NA) of a conventional optical imaging system is increased by placing aminiature hemispherical lens on top of the sample of investigation. A second approach isbased on the localization of individual fluorophores using spectral self-interference.

Numerical Aperture Increasing Lens (NAIL):

Spatial resolution of diffraction-limited microscopy can be improved by reducing thewavelength or increasing the collected solid angle. Unlu and Goldberg have recentlydeveloped novel techniques based on a Numerical Aperture Increasing Lens (NAIL) tostudy semiconductors at very high spatial resolution [21]. The NAIL is placed on thesurface of a sample and its convex surface effectively transforms the NAIL and the planarsample into an integrated solid immersion lens increasing the NA by a factor of square ofthe index n, to a maximum of NA = n corresponding to NA=3.6 in Si.

Figure 16: (a) Signal and radiant exitance from a 0.8 µm wide Al line, as a function of lateraldistance, and (b) resulting line spread function of the NAIL microscope with a FWHM of 1.4 µm.

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An immediate impact can be expected in high-resolution imaging of semiconductordevices, defects, and quantum structures and metrology and failure analysis in thesemiconductor industry. This impact will continue over the next 5 years as newsemiconductor technology generations are introduced. Earlier, using an optimizedconfocal system we demonstrated lateral spatial resolution of approximately 200 nm. Thespatial resolution improvement laterally is about a factor of 4 while longitudinally it is atleast a factor of 12.5 corresponding to an overall reduction of the volume of interrogationby a factor of 50. One of the important features of NAIL microscopy is improved lightcollection efficiency (scales with the square of NA), particularly important in the study ofquantum dots as well as a variety of semiconductor failure analysis modalities includingthermal imaging [22,23]. Recently, Unlu and Goldberg focused on utilizing the NAILmicroscopy technique in thermal imaging as well as quantum dot spectroscopy.

During the past funding period, we have demonstrated the first application of the NAILtechnique to thermal emission microscopy resulting in significant improvements. Insubsurface thermal emission microscopy of Si integrated circuits we demonstratedimprovements in both the lateral and longitudinal spatial resolutions, well beyond thelimits of conventional thermal emission microscopy. We experimentally demonstrated alateral spatial resolution of 1.4 µm (see Fig.16) and a longitudinal spatial resolution of 7.4µm, for thermal imaging at free space wavelengths up to 5 µm [24]. Since the amount oflight collected is not adversely affected by NAIL microscopy while the resolution isimproved, we believe that this technique will be widely used in thermal emissionmicroscopy for semiconductor failure analysis. Current efforts on thermal imaging arefocused on utilizing a pulsed UV source to create a dynamic thermal signature on Sisubstrates. We have completed simulations and concluded that using a 2.5ns Nitrogenlaser, we will be able to generate submicron thermal features on Si substrates that willsubsequently serve as calibration standards for our thermal microscopy efforts.

We have also developed a new method for the fabrication of spherical lenses with verysmooth flat surface and filed a provisional patent application [25]. Conventional NAILand SIL manufacturing techniques are based on starting with a sphere andgrinding/polishing to form the planar surface.

Figure 17: Schematic representation of a lens directly fabricated on the back side of Si subtrate[26]. The dimensions are consistent with our aplanatic NAIL configuration [21].

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The flatness and smoothness are limited by the processing capabilities. The additionalhigh-precision grinding polishing step to form the flat surface is costly. Furthermore,since the starting object is a sphere, it is difficult or impossible to select a specificorientation (in case of crystalline materials) for the flat surface. Specific crystallineorientation can be crucial for application of NAIL/SIL in case of birefringent andanisotropic materials.

Our invention is a manufacturable process for fabrication of solid immersion lenses(SIL), numerical aperture increasing lenses (NAIL), and other plano-convex devices withhighly accurate dimensions (radius of curvature and thickness) and atomically smoothsurfaces. The basic concept is temporarily bonding two substrates together and cuttingcubes that contain a sacrificial layer in the middle. After polishing down to a sphere, thesacrificial layer is removed resulting in 2 hemispheres (or truncated spheres) withatomically smooth flat surfaces. We have experimented with Si substrates and photoresistas the sacrificial layer. The first attempt was partially successful where we were able tofabricate 6mm diameter hemispheres with extremely flat surfaces. Further efforts areunderway.

Our efforts have been focused on the development of NAIL technique based on aseparate lens that is placed on the back side of the substrate of the sample to be studied.While it is the only way to study already fabricated planar samples, this approach,however, any finite gap between the lens (NAIL) and the planar substrate limits thehighest achievable numerical aperture, thus the resolution. While we will continue withour existing efforts on combining lenses with substrates towards building an integratedcharacterization instrument we will also pursue a new approach of directly fabricatinglenses on the substrates. Recently, Koyama et al. at ULSI development center, MitsubishiElectric.Co. have developed a technique to eliminate the interface between lens and thesubstrate device, by “forming the Si substrate into SIL (FOSSIL)” [26]. As schematicallyshown in Fig.17, such an integrated lens completely eliminates the gap between the lensand the substrate.

Figure 18: SEM micrograph of a NAIL fabricated by FEI on a SI substrate. Currently under testin our laboratory.

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It is also crucial to develop US competence in technologies vital to the advancedsemiconductor processing. Fortunately, we have identified an ideal collaboration partner:FEI Company of Peabody, MA. We have met with Rich Aucoin of FEI and discussedtheir propriety technique of laser assisted etching to form micro lenses on Si. FEI agreesto provide NAIL samples to be used in development efforts under the proposed program.Fig. 18 shows an electron microscope image of a typical FEI lens. The forming process isvery rapid, versatile, and capable of making arrays of lenses. We are currently evaluatingarrays of lenses with varying dimensions fabricated by FEI. This collaboration willprovide a unique enabling technology to allow us quickly combine our NAIL techniquewith near-field and confocal scanning microscopy techniques.

Fluorescence Self-Interference (FSI):

A goal of this MURI program is to combine infrared (IR) near-field microscopy togetherwith a new type of interference microscopy, called spectral self-interference fluorescencemicroscopy (SFM), to allow co-location experiments in vivo. The IR tip-enhanced near-field can determine the position of important proteins and cellular membrane moleculesin an untagged cell. SFM can then be used to follow the trajectories of fluorescentlylabeled moeties as they move in the inter- or intracellular space and interact with the IR-located species. SFM is a new interferometric technique in fluorescent imaging that mapsthe spectral oscillations emitted by a fluorophore located a distance of severalwavelengths above a reflecting surface into a precise position determination. Analysis ofthe spectral oscillations due to the self-interference from the direct and reflected emissionyields the vertical position of that fluorophore to within a nanometer. Our efforts haveresolved the 5nm step between fluorophores atop the protein streptavidin from those on abare surface [27,28], providing resolution orders of magnitude better than confocal, two-photon, or other competing microscopies. Recent work has imaged the position offluorphores bound to the head groups of the top of a lipid bilayer with sub-nanometerprecision. We are in the process of developing the instrumentation necessary todemonstrate SFM in vivo subcellular microscopy at 10 nm resolution to determine theprecise three-dimensional localization of proteins within prokaryotic cells. Suchlocalization is key to many cellular functions, including cell cycle, DNA replication,development, motility, and adhesion.In recent work, Goldberg and coworkers studied the resolution of fluorophores in top andbottom layers of lipid membranes. Fig.19a shows the experimental arrangement of a lipidbilayer formed atop a silicon wafer with a thick SiO2 oxide (5µm). A typical spectrumfrom such a layer is shown in Fig.19b, where the difference between the fringes and themodel fit is ~10-3 as demonstrated in the plotted residue. Finally, the spectral fringescombined with the model yield the height, displayed in Fig.19c. Clearly resolved are thedifferent distances between the chip surface (determined by white light interference) andthe fluorphore positions in both the top and bottom lipid layer. The resolution of thesemeasurements is +/- 0.3nm. The most recent breakthrough has been to distinguisharbitrary vertical distributions by using the added information of the position of thestanding wave excitation field, and sophisticated forward modeling. Currently, we areable to distinguish single layers with +/- 0.3nm accuracy, and multi-layers with +/- 10nmaccuracy. This represents the best ever reported axial resolution for biological systems.

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Figure 19: (a) Lipid bilayers with fluorophores in both top and bottom layers. (b) Typical spectrawith fit and residue. (c) SFM is able to distinguish the different distances between fluorophores,surface, and top of lipids layer with sub-nanometer precision.

Measuring DNA conformation: Observation of formation of a molecular brush: DNAchip technology has become a widespread tool in biological research, and is a keyenabling technology for the future of personalized medicine. Huge markets like geneexpression screening, gene sequencing, and drug discovery have benefited greatly by thehighly parallel detection provided by DNA microarray technology. One of thecharacteristics of a DNA array is the availability of the single-stranded probes forhybridization with the target. The conformation (or molecular orientation) of DNAmolecules bound to the surface of an array significantly affects the efficiency ofhybridization (binding of the target to the probe DNA) and thus the overall effectivenessof the technique. For instance, immobilized molecules located farther away from the solidsupport are closer to the solution state and are more accessible for contact with dissolvedanalytes, while the surface, especially a hydrophobic one, acts as a shield for probespositioned close to it because of the associated steric factors, and lack of diffusion of thebound molecules. Recently, there has been a growing effort to physically characterize thestructure of bound probes by such optical or contact methods as ellipsometry, opticalreflectivity (haeberli, nat biotech.), surface plasmon resonance (SPR), and atomic forcemicroscopy (AFM). However, none of these approaches can measure the sensitivechanges in molecular conformation that our SFM approach has recently demonstrated(Langmuir, to be submitted [29]).

Two interferometric microscopy techniques are combined to determine DNA molecularconformation. White light interference (similar to ellipsometry) measures the opticalthickness of the transparent material on top of a mirror. In our case, this provides ameasure of the average optical density of the material. Self-interference of the emittedspectrum of a bound fluorophore provides precise information on the location of theemitting molecule, as described above. Thus when bound to a strand of DNA, the labeldetermines the average position of the free or bound end of the DNA moleculeimmobilized on the surface, really the extension of each molecular strand.

The basic experiments consist of covalently binding the end oligonucleotide of a strandof DNA to the surface. The strands are typically between 20 and 50 base pairs, or lengthsof about 7 to 12 nm in length when fully extended and a fluorophore can be bound toeither the proximal or distal end (next to the surface or distant, respectively). We measure

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the optical thickness with white light interferometry and the extension of the ssDNA withself-interference and discover the average density and height with sub-nanometerprecision. Following this, a second, complementary strand is hybridized to the first. Thesecond strand can also have fluorophores attached to either end, and we again measurethe optical thickness and extension of the double stranded array. Figure 20 displays ahistogram of measurements, demonstrating the precision. We have discovered thatwhereas a first, single strand can go down coiled on the surface, a second strand canmake the molecule rigid, lifting it up and creating a molecular brush.

Figure 20: Self-interference measurement of the position of a fluorophore bound to the proximal(3’) and distal (5’) end of a double stranded DNA 50-mer. The bottom of the strands aremeasured to be within 2nm of the surface, while the tops are 10.5nm from the surface, indicationa near-vertical orientation in the form of a molecular brush (see above).

4-! Interference Microscopy Platform: In the past several months we have put togetherthe interfeometric arm of the 4-pi instrument and are in the process of testing it. Inaddition, we have examined the complete optical transfer function for the 4-pi system,including the interferometric spectral components. Fourier analysis does have significantworth in Spectral Self Interference Fluorescence Microscopy. It can be applied byregarding the instrument as a collection of linear, shift-invariant systems each operatingat a different detection wavelength. The resulting Fourier analysis allows one to seewhich object frequencies are passed and which are not and thus gives strong insight intothe resolution possible. We have carried this analysis that indicates that spectral operationand delays between the two arms of the system have a greater impact in wide-field I5Mthan with 4-pi confocal microscopy. We have calculated the additional phase spacecoverage afforded by utilizing spectral interference and from the different phase spacecoverages at difference frequencies, the combined provides significant phase spaceenhancement and thus increased resolution.

There is currently great interest in the use of fluorescence microscopy for subsurfacebiological sensing. Data collection in three-dimensional fluorescence microscopyinvolves spatial scanning in either one dimension for widefield operation or threedimensions for confocal operation. We have developed a method that allows a significantreduction in the required spatial scanning rate for fluorescence microscopes that useinterferometric detection, such as the modern high-resolution 4Pi and I5M methods [30].The new system relies on two central innovations - detection at more than one emission

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wavelength, and the introduction of a path delay between the two detection arms. Thedelay between the two arms results in differing interference properties for each emissionwavelength collected. Mathematically, this results in significantly different transferfunctions for each emission wavelength. When the instrument is operated using spatialundersampling, aliasing may occur which means a degraded image will be collected ateach wavelength. However, since each image is formed using a different transferfunction, the aliasing effects differ in each image. Appropriate processing of theensemble of collected images allows a single unaliased image to be constructed [31].Thus a more complex hardware structure is used to collect a wavelength-dependent dataset and with the appropriate post-processing, this allows a reduction in the required rateof spatial scanning. The overall result is that image acquisition time, which is asignificant issue in fluorescence microscopy, is reduced.

2. Future Steps

We believe that at the current stage significant progress is being made in each task of thisprogram. Great results can be expected once the capabilities of the instruments have beenrefined and sufficient repeatability has been achieved. Therefore, in the coming monthswe will continue to push the independent developments of measurement modalities. Wewill continue to perfect different test samples and to interact with collaborators andindustrial partners to assess the metrology needs in industry and different scientific areas.For example, we have learned that nanoscale Raman microscopy/spectroscopy would bean invaluable tool for the pharmaceutical industry because it has the ability to chemicallyanalyze nanocomposite drugs that are increasingly being produced for reasons ofsolubility and drug uptake. The same technique holds also great promise forcharacterizing local stress in semiconductor nanostructures. In fact, one of the bighandicaps of the semiconductor industry is the characterization and control of stress. Asdevices become smaller and smaller local stress becomes a dominating factor for deviceperformance and reliability.

Parallel to the efforts represented by the four tasks of this project, we will continue ourdialogue of how to combine the different developments in a single measurementplatform. Our current strategy is to accommodate the different tasks in a commercialinstrument (WITec) for which a DURIP grant application is pending. WITec willorganize a short workshop with our team members during the fall MRS meeting and wewill develop a first strategy for a joint measurement platform design.

In spring 2005, we intend to organize a joint workshop to discuss research progress andto brainstorm about common goals and the development of a measurement platform. Weregularly receive positive feedback from outside research groups regarding our website(http://xray.optics.rochester.edu/muri03). This site is regularly updated and it helps us tobe informed about different activities and keeps our effort organized and structured.

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References:

[1] L. Novotny, E.J. Sanchez, and X.S. Xie, “Near-field optical imaging using metal tips illuminated by higher-orderHermite-Gaussian beams ", Ultramicroscopy 71, 21 (1998).

[2] L. Novotny, R.X. Bian, and X.S. Xie, “Theory of nanometric optical tweezers ", Phys. Rev. Lett. 79, 645 (1997).

[3] L. Novotny, M.R. Beversluis, K.S.Youngworth, and T.G. Brown, “Longitudinal field modes probed by singlemolecules ", Phys. Rev. Lett. 86, 5251 (2001).

[4] A. Hartschuh, E. J. Sanchez, X. S. Xie, and L. Novotny, “High-resolution near-field Raman microscopy of single-walled carbon nanotubes", Phys. Rev. Lett. 90, 95503 (2003).

[5] N. Anderson, A. Hartschuh, and L. Novotny, “Nanoscale vibrational analysis of single-walled carbon nanotubes",J. Am. Chem. Soc., in press (2004).

[6] U. C. Fischer and H. P. Zingsheim, “Submicroscopic pattern replication with visible light", J. Vac. Sci. Technol.19, 881 (1981).

[7] C. L. Haynes and R. P. Van Duyne, “Nanosphere Lithography: A Versatile Nanofabrication Tool for Studies ofSize-Dependent Nanoparticle Optics", J. Phys. Chem. B, 5599 (2001).

[8] G. Lucadamo and D. L. Medlin, “Geometric origin of hexagonal close packing at a grain boundary in gold",Science 300, 1272 (2003).

[9] U. Kreibig, G. Bour, A. Hilger, and M. Gartz, “Optical properties of cluster-matter: influences of interfaces",Phys. Stat. Sol. A 175, 351 (1999).

[10] A. T. Georges, “Calculation of surface electromagnetic fields in laser-metal surface interaction", Opt. Comm. 188,321 (2001).

[11] S. Mukamel, Principles of Nonlinear Optical Spectroscopy, Oxford University Press, New York (1995).

[12] R. Guckenberger and F. Keilmann, Max-Planck-Institute for Biochemistry, Martinsried, Germany, privatecommunication (2003).

[13] E. Betzig and R.J. Chichester, “Single molecules observed by near-field scanning optical microscopy", Science262, 1422 (1993).

[14] J.A. Veerman, M.F. Garcia Parajo, L.Kuipers, and N.F. van Hulst, “Single molecule mapping of the optical fielddistribution of probes for near-field microscopy ", J. Microsc. 194, 477 (1999).

[15] Y.C. Martin, H.F. Hamann, and H.K. Wickramasinghe, “Strength of the electric field in apertureless near-fieldoptical microscopy ", J. Appl. Phys. 89, 5774 (2001).

[16] H.G. Frey, F. Keilmann, A. Kriele, and R. Guckenberger, “Enhancing the resolution of scanning near-field opticalmicroscopy by a metal tip grown on an aperture probe ", Appl. Phys. Lett. 81, 5530 (2002).

[17] P. S. Carney, R. A. Frazin, S. I. Bozhevolnyi, V. S. Volkov, A. Boltasseva, and J. C. Schotland, “A computationallens for the near-field ", Phys. Rev. Lett. 92, 163903 (2004).

[18] P. S. Carney, J. C. Schotland, and E. Wolf, “A generalized optical theorem for reflection, transmission andextinction of power for scalar fields ", Phys. Rev. E 70, 036611 (2004).

[19] R A Frazin, D G Fischer, and P. S. Carney, “Information content of the near-field: two-dimensional samples ", J.Opt. Soc. Am. A 21, 1050 (2004).

[20] D G Fischer and P. S. Carney, “Total internal reflection tomography (TIRT) for three-dimensional sub-wavelength imaging”, in Tribute to Emil Wolf: Science and Engineering Legacy of Physical Optics, SPIE Press(2004).

[21] B. B. Goldberg, S. B. Ippolito, L. Novotny, Z. Liu, and M. S. Ünlü, "Immersion Lens Microscopy of PhotonicNanostructures and Quantum Dots," IEEE J. Selected Topics in Quantum Electron., vol. 8, no. 5, pp. 1051, 2002.(invited)

[22] S. B. Ippolito, S. A. Thorne, M. G. Eraslan, B. B. Goldberg, Y. Leblebici, and M. S. Ünlü, “High spatialresolution subsurface thermal emission microscopy,” IEEE/LEOS Annual Meeting, Tucson, AZ, October 2003.(invited)

[23] S. Thorne, S. B. Ippolito, M. Eraslan, B. Goldberg, M.S. Ünlü, and Y. Leblebici, “High Resolution BacksideThermography using a Numerical Aperture Increasing Lens,” Proceedings of 29th International Symposium forTesting and Failure Analysis, 2-6 November 2003, Santa Clara, CA

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[24] S. B. Ippolito, S. A. Thorne, M. G. Eraslan, B. B. Goldberg, M. S. Ünlü, and Y. Leblebici, "High spatialresolution subsurface thermal emission microscopy," Applied Physics Letters, Vol. 84, No. 22, 31 May 2004, pp.4529

[25] M. S. Ünlü and B. B. Goldberg, “Method for Fabrication of Solid Plano-Convex Lenses,” provisional patent filedin June 2004.

[26] T. Koyama, E. Yoshida, J. Komori, Y. Mashiko, T. Nakasuji, and H. Katoh, “High resolution backside faultisolation technique by directly forming Si substrate into solid immersion lens,” IEEE International ReliabilityPhysics Symposium, Dallas, Texas, March 30 – April 4, 2003.

[27] A.K. Swan, M. S. Ünlü, Y. Tong , B.B. Goldberg, L. Moiseev and C. Cantor, “Self-Interference FluorescentEmission Microscopy - 5nm Vertical Resolution” Proceedings of CLEO (2001); Anna K. Swan, Lev Moiseev,Yunjie Tong, S. H. Lipoff, W.C. Karl, B.B Goldberg, M.S. Ünlü, , "High resolution spectral self-interferencefluorescence microscopy", IEEE Photonics West/Bios 2002 Annual meeting, 2002

[28] A. K. Swan, L. Moiseev, C. R. Cantor, B. Davis, S. B. Ippolito, W. C. Karl, B. B. Goldberg, and M. S. Ünlü,"Towards nanoscale optical resolution in fluorescence microscopy," IEEE Journal of Selected Topics in QuantumElectronics, Vol. 9, No. 2, March/April 2003, pp. 294-300

[29] Lev Moiseev, Anna K. Swan, Selim M. Ünlü, Bennett B Goldberg, and Charles R. Cantor “DNA Conformationon Surfaces Measured by Fluorescence Self-Interference,” submitted to Langmuir.

[30] Brynmor J. Davis, W. Clem Karl, Bennett B. Goldberg, M. Selim Unlu, Anna K. Swan, “Relaxing ScanningRequirements by Using Multi-Wavelength Measurements in Interferometric Fluorescence Microscopy,” CenSSISworkshop on subsurface imaging, July, 2004.

[31] Brynmor J. Davis, W. Clem Karl, Bennett B. Goldberg, M. Selim Unlu, Anna K. Swan, “Sampling Below theNyquist Rate in Interferometric Fluorescence Microscopy with Multi-Wavelength Measurements to RemoveAliasing,” IEEE Digital Signal Processing Workshop, August, 2004. Presentation and publication in press.

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AFOSR sponsored publications (published and submitted 2004):

[1] M. A. Lieb, J. M. Zavislan, and L. Novotny, "Single-molecule orientations determined by direct emission patternimaging," J. Opt. Soc. Am. B 21, 1210 (2004).

[2] M. R. Beversluis, L. Novotny, and S. J. Stranick, “Programmable vector point-spread function engineering,” Opt.Lett., in print (2004).

[3] N. Anderson, A. Hartschuh, and L. Novotny, “Nanoscale vibrational analysis of single-walled carbon nanotubes",J. Am. Chem. Soc., in print (2004).

[4] A. Hartschuh, N. Anderson, and L. Novotny, “Near-field Raman spectroscopy of individual single-walled carbonnanotubes", Int. J. Nanosc. 3, 371 (2004).

[5] P. S. Carney, R. A. Frazin, S. I. Bozhevolnyi, V. S. Volkov, A. Boltasseva, and J. C. Schotland, “A computationallens for the near-field ", Phys. Rev. Lett. 92, 163903 (2004).

[6] P. S. Carney, J. C. Schotland, and E. Wolf, “A generalized optical theorem for reflection, transmission andextinction of power for scalar fields ", Phys. Rev. E 70, 036611 (2004).

[7] E. Charles H. Sykes, Luis C. Fernández-Torres, Sanjini U. Nanayakkara, Brent A. Mantooth, Ryan M. Nevin, andPaul S. Weiss, “Direct observation and manipulation of subsurface hydrogen in Pd{111} ", Nature, submitted(2004).

[8] D. Takhar, Z. Gu, J. L. Margrave, and K. F. Kelly, “STM of Fluorinated HiPco Nanotubes”, Langmuir, submitted(2004).

[9] S. B. Ippolito, S. A. Thorne, M. G. Eraslan, B. B. Goldberg, M. S. Ünlü, and Y. Leblebici, " High spatialresolution subsurface thermal emission microscopy," Appl. Phys. Lett. 84, 4529 (2004).

[10] Lev Moiseev, Anna K. Swan, Selim M. Ünlü, Bennett B Goldberg, and Charles R. Cantor “DNA Conformationon Surfaces Measured by Fluorescence Self-Interference,” Langmuir, submitted (2004).

[11] Brynmor J. Davis, W. Clem Karl, Bennett B. Goldberg, M. Selim Unlu, Anna K. Swan, “Sampling Below theNyquist Rate in Interferometric Fluorescence Microscopy with Multi-Wavelength Measurements to RemoveAliasing,” IEEE J. Signal Proc., in print (2004).

Presentations (Conferences/Workshops) with acknowledgment of AFOSR support:

[1] L. Novotny (invited), Frontiers of Optics (OSA Annual Meeting), Rochester NY, October (2004).

[2] L. Novotny (invited), Gordon Research Conference on Laser-Materials Interactions, Andover NH, August(2004).

[3] N. Anderson, A. Hartschuh, and L. Novotny, 8-th International Conference on Near-field Optics and RelatedTechniques (NFO-8), Seoul, South Korea, September (2004).

[4] L. Novotny (invited), Great Lakes Photonics Symposium, Cleveland OH, June (2004).

[5] L. Novotny (invited), American Chemical Society Meeting (Symposium on Microscopy beyond the DiffractionLimit), Anaheim CA, March (2004).

[6] N. Anderson, A. Hartschuh, and L. Novotny, American Physical Society Meeting, Montreal, Canada, March(2004).

[7] L. Novotny (plenary speaker), National Nanotechnology Initiative Interagency Workshop on Instrumentation andMetrology for Nanotechnology (Grand Challenge Workshop), National Institute of Standards and Technology(NIST), Gaithersburg MA, January (2004).

[8] L. Novotny (invited), XXI Brazilian Physical Society Meeting, Fortaleza CE, Brazil, November (2003).

[9] L. Novotny (invited), Stanford Photonics Research Center Annual Meeting, Stanford CA, USA, September(2003).

[10] L. Novotny (invited), Microscopy and Microanalysis 2003 Meeting, Symposium on Focus on Raman and InfraredMicroanalysis, San Antonio TX, August (2003).

[11] S. Stranick (invited), American Chemical Society Annual Meeting, New York NY, September (2004).

[12] S. Stranick (invited), FACSS National Meeting, Ft. Lauderdale FL, October (2003).

29

[13] S. Stranick (invited), American Chemical Society Meeting (Symposium on Microscopy beyond the DiffractionLimit), Anaheim CA, March (2004).

[14] S. Stranick (invited), American Chemical Society Annual Meeting, Philadelphia PA, August (2004).

[15] P. S. Carney (invited), Workshop on Optical Tomography (Rensselaer Polytechnic Institute), Troy NY, April(2004).

[16] P. S. Carney (invited), American Chemical Society Meeting (Symposium on Microscopy beyond the DiffractionLimit), Anaheim CA, March (2004).

[17] E. C. H. Sykes and P. S. Weiss, 47th Pittsburgh-Cleveland Catalysis Society Meeting, Pittsburgh PA, June (2004).

[18] L. C. Fernández-Torres and P. S. Weiss, 228th National Meeting of the American Chemical Society, PhiladelphiaPA, August (2004).

[19] B. A. Mantooth and P. S. Weiss, 226th National Meeting of the American Chemical Society, New York NY,September (2003).

[20] B. A. Mantooth and P. S. Weiss, Gordon Research Conference on Nanostructure Fabrication, Tilton School NH,July (2004).

[21] K. F. Kelly, American Vacuum Society Meeting, Baltimore MD, November (2003).

[22] D. Takhar and K. F. Kelly, Physical Electronics Conference, Davis CA, June (2004).

[23] P. S. Weiss (invited), American Chemical Society Meeting (Symposium on Microscopy beyond the DiffractionLimit), Anaheim CA, March (2004).

[24] M. S. Ünlü, M. G. Eraslan, A. N. Vamivakas, S. A. Thorne, S. B. Ippolito, and B. B. Goldberg (invited),American Chemical Society Meeting (Symposium on Microscopy beyond the Diffraction Limit), Anaheim CA,March (2004).

[25] S. B. Ippolito, S. A. Thorne, M. G. Eraslan, B. B. Goldberg, Y. Leblebici, and M. S. Ünlü, IEEE/LEOS AnnualMeeting, Tucson AZ, October (2003).

[26] B. B. Goldberg, Nanotech 2004, Boston MA, March (2004).

[27] B. B. Goldberg, Nanotech 2004, Boston MA, March (2004).

[28] B. B. Goldberg, A. K. Swan, L. Moiseev, M. Dogan, W. C. Karl, B. Davis, C. A. Cantor, M. B. Goldberg, and M.S. Ünlü (invited), American Chemical Society Meeting (Symposium on Microscopy beyond the Diffraction Limit),Anaheim CA, March (2004).

[29] B. B. Goldberg (invited), Great Lakes Photonics Symposium, Cleveland MA, June (2004).

[30] B. B. Goldberg (invited), CLEO / IQEC, Los Angeles CA, May (2004).

[31] B. J. Davis, W. C. Karl, B. B. Goldberg, M. S. Ünlü, A. K. Swan, IEEE Digital Signal Processing Workshop,August (2004).

[32] B. J. Davis, W. C. Karl, B. B. Goldberg, M. S. Ünlü, A. K. Swan, CenSSIS workshop on subsurface imaging, July(2004).

[33] B. J. Davis, W. C. Karl, A. K. Swan, B. B. Goldberg, M. S. Ünlü, M. B. Goldberg, SPIE Photonics West, San JoseCA, January (2004).

[34] L. Moiseev, C. R. Cantor, A. K. Swan, B. B Goldberg, and M. S. Ünlü, SPIE Photonics West, San Jose CA,January (2004).

[34] M. Dogan, I. Aksun, M. S. Ünlü, A. K. Swan, B. B. Goldberg, American Physical Society Meeting, Montreal,Canada, March (2004).

Workshops and Symposia organized by MURI team members:

[1] L. Novotny and R. Saykally, American Chemical Society Meeting (Symposium on Microscopy beyond theDiffraction Limit), Anaheim CA, March (2004).

[2] S. Unlu, CLEO / IQEC (Chair, Nano-Optics Subcommittee), Los Angeles CA, May (2004).

[3] S. Stranick, Third International Workshop on Nanoscale Spectroscopy and Nanotechnology (OrganizingCommittee), College Park MD, December (2004).