spring 2009 ee 710: nanoscience and engineering part 1: introduction i... · 2009-10-16 · spring...

Spring 2009 EE 710: Nanoscience and Engineering

Part 1: IntroductionCourse Texts:

Bhushan, Springer Handbook of Nanotechnology 2nd ed., Springer 2007H k t l I t d ti t N i CRC 2008Hornyak, et.al, Introduction to Nanoscience, CRC press, 2008

Goddard, et.al, Handbook of Nanoscience, Engineering, and Technology, CRC Press, 2004

Instructor: John D. Williams, Ph.D.Assistant Professor of Electrical and Computer EngineeringAssistant Professor of Electrical and Computer Engineering

Associate Director of the Nano and Micro Devices CenterUniversity of Alabama in Huntsville

406 Optics BuildingHuntsville, AL 35899Phone: (256) 824-2898

Fax: (256) 824-2898email: [email protected] 1

Molecule-Based DevicesMolecule Based Devices• Top down fabrication of molecular devices p

utilizes conventional patterning and etching techniques to define nanoscale regions that can then be chemically sensitized for devicethen be chemically sensitized for device applications.

• In nature tiny molecular building blocks areIn nature, tiny molecular building blocks are assembled with remarkable structural control in a variety of materials, shapes, and sizes. H h f thi b tt h tHowever, much of this bottom up approach to nano-engineering has yet to be mastered by human interventionu a te e t o

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JDW, UAHuntsville ECE, Spring 2009

Nucleic AcidsNucleic Acids• Some of the best examples of bottom up

nanoengineering are nucleic acids andnanoengineering are nucleic acids and proteins. Nucleic acids ensure the transmission and expression of genetic information.

• Nucleic acids are linear polymers with specific nucleotide repeating units thatspecific nucleotide repeating units that can contain enough information within a single molecule to describe all of the genetic structure of a living organism.

• DNA and RNA for example provide t i ll f th i f ti ( d )contain all of the information (commands)

required to produce or functionalize a living organism using only 4 nucleic bases in a approximately 100 repeating units. Thus, nature has systematically

i d h i t t 4100engineered a mechanism to generate 4100

or 1.6*1060 bits of information in a single molecule.

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ProteinsProteins• 20 different amino acids differing primarily in their side g p y

chains and all containing a similar backbone of carbon-carbon bonds are used by nature to generate every protein known currently known to man.p y

• This is achieved by covalent bonding of different amino acids into polypeptides that then bond with other amino acids and polypeptides to form proteins varying inacids and polypeptides to form proteins varying in complexity from a few amino acids to over 4000 individual building blocks.

• Thus nature has found a way to fabricate more than• Thus nature has found a way to fabricate more than 1*10100 different molecular devices, each containing a specific biological function through the manipulation of 20 simple molecules20 simple molecules.

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Organic and Inorganic ByproductsOrganic and Inorganic Byproducts• Nanotubes:

– Carbon nanotubes are known byproducts of high temperature reactions with organic material

• Ex. Soot contains multi-wall carbonEx. Soot contains multi wall carbon nanotubes

– Inorganic nanotubes and nanowires are known to form naturally under high pressures and temperatures (nearpressures and temperatures (near volcanic systems, especially those in water environments) or in areas where crystallization occursLiving organisms also generate– Living organisms also generate nanomaterials as byproducts. Spider silk, and several Group I and II crystallites are generated commonly by living organismsliving organisms

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Questions for Every NanoscientistQuestions for Every Nanoscientist

• The question we must ask ourselves, is this: q ,How can we use the simplicity of natural systems to engineer complex transducers capable of sensing storing and signaling suchcapable of sensing, storing, and signaling such large amounts of information and integrate them into our current designs for modern micro and gsemiconductor devices?

• Furthermore: How will we interface with future ti f th t d hgenerations of these transducers when we move

beyond the need for current semiconductor and top down machining applications?top do ac g app cat o s

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Modern Chemical SynthesisModern Chemical Synthesis• We have currently developed the technology required to join molecular

components with structural control at the picoliter levelcomponents with structural control at the picoliter level.• We know this through extensive use of chemical and spectroscopic testing

developed over the course of the last century.• Light, X-ray, electron, ion, and atomic spectroscopy techniques currently

provide us with the exact chemical and structural composition of manyprovide us with the exact chemical and structural composition of many simple molecular chemistries.

• However the chemical free energy present in very large molecules at room temperature prevents us from learning the exact structural shape of complex proteins and long chain polymers at any given timecomplex proteins and long chain polymers at any given time.

• Thus we rely on a combination of spectroscopy, molecular computing, and a solid understanding of various binding energies to predict the shape and functionality of very large organic molecules in order to interpret their true functionality.y

• With this information, we can currently construct very large organic molecules designed using nature’s template for the specific purpose of nanoscale transduction.

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From Structural Control to D i d F i liDesigned Functionality

• In a manner similar to that of nature supramolecular organic

No Visible Absorption

nature, supramolecular organic chemists currently engineer new molecules capable of passing current, other molecules or information formolecules, or information for next generation transducers.

563 nm Absorption band

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Easily Generated Chemically A i S M i lActive Sensor Materials

Pyrozaline Anthracene Derivative Anthracene

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Photochemical Optical Sensors d E d

No Visible Absorption

and Encoders

563 nm Absorption band

• While colorless 5 will not absorb in the optical, heat sensitized 7 retains a deep purple color reducing the amount of 563 nm visible light from propagatingamount of 563 nm visible light from propagating through to the detector.

• In fact if just one of the three ultraviolet (or chemically reacted) inputs is turned on then thechemically reacted) inputs is turned on then, the optical output drops by 3-5% of the input signal. If two or three inputs are turned on simultaneously, then the total output power is reduced to 0%.

Acetonitrile Solution10


Photochemically Active Sensors d O i l E dand Optical Encoders

Two communicating molecular switches in solution provide up to 4 possible combinations for a single state yielding much more information than a single

l l it h d b li htmolecule switch measured by light or electrochemical response alone

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Langmuir-Blodgett FilmsLangmuir Blodgett FilmsUsed to apply monolayers of a chemical onto an active surface.

Most common example is the application lipids to a glassapplication lipids to a glass, ceramic, or plastic substrate.

The ability to transfer l t ti l f felectroactive monolayers of from

the air water interface is often used to fabricate arrays of molecule based electronic devices.

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Self Assembled Monolayers (SAMS)(SAMS)

• Alternatively, certain compounds such as thiols absorb onto f i l lsurfaces as single monolayers

• Prepatterning of the surface to prevent adhesion in particular l ti id l t f bi di h i ll tilocations provides an excelent means of binding chemically active monolayers over large areas for device technologies.

• Nitride, oxide, certain metals, and in some cases even resist can be used as the barrier for adhesion of SAMsused as the barrier for adhesion of SAMs

• SAM layers are then used to:– Alter the surface tension of the substrate

Promote nanoparticle adhesion– Promote nanoparticle adhesion– Reduce friction and stiction– Promote adhesion of organic or inorganic media for sensing

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Combining Top Down and Bottom UpCombining Top Down and Bottom Up

• Combination of Top down patterning with bottom up chemistry

• Demonstrates that electroactive organic chemicals can be patterened uniformly over mesoscopic

f th t isurfaces that are micro patterned.

• The resulting surfaces can be d t l tused as catalyst or sensors

for either electrochemical, covalent, ionic, or photochemical detectionphotochemical detection

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Patterning Gold NanoparticlesPatterning Gold Nanoparticles

Uses Thiol chemistry to attach gold to surfaceAu nanoparticles provide single electron chemical sensitivity in solution near -0.2V 15


Solid State DevicesSolid State Devices

U d i bi ti ith Ti Al l t d ll f t k blUsed in combination with Ti or Al electrodes, allows for stackable junctions that provide significant changes in current below -0.7V

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Molecular TransistorsMolecular Transistors

30 nm oxide15 nm x 300 nm AuFormation of thiolate gold bonds between molecule and Au allowingbetween molecule and Au allowing the acceptance and donation of electrons to the Au leads via electromigration across a 20 nm gap. This nonlinear response produces a transistor like effect with an operational current of 0.05 nA around 20 mV20 mV

DNA transistors demonstrate 50nA when the gate voltage lowers from -1 0V t 1 3V1.0V to -1.3V

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Molecular Transistors (NOT gates)Molecular Transistors (NOT gates)

Off chip bias resistor connected to the train terminal of a single transistor while the source is

• Micro scale silicon gate with nanotube contact

transistor while the source is grounded

Micro scale silicon gate with nanotube contact• Application of -1.5V lowers the nanotube resistance (26 MOhm) below

that of the bias resistor (100 MOhm). As a result, the output bias drops to 0V.

• When no voltage is applied, the resistance of the nanotube increases leading to a -1.5V output 18


Molecular Transistors (NOR gates)Molecular Transistors (NOR gates)

Pair of off chip bias resistors connected to the train termainal of a single transistor while the source issingle transistor while the source is grounded

• When both nanotubes are in a nonconducting output state (no applied voltage) then the terminal output of the device is -1.5V

• Application of -1.5V to either or both nanotubes lowers the nanotube resistance (26 MOhm) below that of the bias resistor (100 MOhm). As a result, the output bias drops to 0V. 19


Probing the NanoscaleProbing the Nanoscale• Modern science and engineering uses

electrons photons ions and scannigelectrons, photons, ions, and scannig probes and thermodynamic analysis to probe the nanoscale.

– Optical• Confocal microscopy• Near field Scanning Optical Microscopy

– Particle• Mass spectrometry• Secondary ion mass specNear field Scanning Optical Microscopy

• Flouresence spectroscopy– Electron

• SEM, TEM, RHEED– Scanning Probe Techniques

(mechanical)

• Secondary ion mass spec• Rutherford Backscattering• Neutron scattering spectrometry• Particle induced X-ray emission

– Thermodynamic• Thermogravometric analysis(mechanical)

• Contact and non-contact AFM, STM, MFM, CFM

– Photon• Raman spectroscopy• Energy Dispersive Spectroscopy (EDS) EDAX

Thermogravometric analysis• Nanocalorimetry• Thermoluminescence

– Bulk engineering• Stiffness• Elasticity

• X-ray photoelectron Spectroscopy (XPS)• X-ray diffraction• Near IR• Surface Plasmon Resonance• Nuclear Magnetic Resonance (NMR)

EDAX y• Fluid response

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Manufacturing at the NanoscaleManufacturing at the Nanoscale• Patterning

E b lith h• Deposition

– E-beam lithography– Nano-imprint lithography– Focused Ion Beam lithography– X-ray Lithography

– Thin film Evaporation– Sputtering– MBE (single crystal)– PECVDay og ap y

• Patterning/positioning– SPM techniques– Electrostatic manipulators

M ti i l t

PECVD– LPCVD– Laser Assisted CVD– Atomic Layer Deposition

– Magnetic manipulators– Microtechnologies

• Etching– Reactive ion Etching

• Surface Chemistry– SAMs– Langmuir Blodget Films– Supramolecular chemicalsReactive ion Etching

– Chemical Etching– Electrochemical

deposition/etch/corrosion

Supramolecular chemicals

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Advances in Optical MicroscopyAdvances in Optical Microscopy• Conventional and conformal

microscopies that use conventionalmicroscopies that use conventional lenses to image multiple scattering orders of light reflected from a surface

• Thus the resolution limit of conventional optical microscopy is about 0 5 umabout 0.5 um

• Confocal microscopy that utilizes two image planes instead of one has a resolution of approximately 0.2 um with a much smaller depth of focus.

• Near field Scanning Optical Microscopy uses a sub wavelength aperture to image effervescent waves in very close proximity to a sample and can be used to resolve features smaller than 100 nm.

• Scanning NSOMS often use AFM type scanning systems to generate the proximity between the aperture and the sampleand the sample

http://www.optics.rochester.edu/workgroups/novotny/snom.html 22


Advances in Optical MicroscopyAdvances in Optical Microscopy• NSOMs generally use glass fiber tips that have been pulled

to diameters much smaller than the wavelength and coated with an aluminum film to prevent light from exiting the fiberwith an aluminum film to prevent light from exiting the fiber except at the end of the tip

• Light can be passed through the tip to illuminate a transparent surface, passed through the sample and collected in the tip, any combination of both. However signals passed through a tip in both directions significantly impact the background noise of the observationp g

• The transparent aperture is limited in size by the amount of optical power that can be transmitted through tip and distance placed above the surface

• Optical power squeezed into a very fine tip heats the aluminum film significantly causing local heating of the surface at very close proximities and thermal degradation of th fibthe fiber

• Thus NSOM tips are typically held to a diameter no less than 100 nm

http://www.physics.ncsu.edu/optics/nsom/NSOMintro.html



Advances in Optical MicroscopyAdvances in Optical Microscopy• The optical resolution lost by tip heating

can be overcome using localized electriccan be overcome using localized electric field enhancement.

• This technique uses reflected laser light focused on a tip as small as 10 nm to generate very large effervescent fields between the tip and the samplebetween the tip and the sample.

• The tip, and focal point are then scanned across the surface while constantly recording the potential generated in the tip during the scan.

• This produces highly accurate 10 nm optical images of surface being scanned.



Scanning Probe MicroscopesScanning Probe Microscopes• How exactly does one scan a surface with a

10 nm tip? Answer: Scanning Probe • The contact method is used to drag the tip 10 nm tip? Answer: Scanning Probe Microscopes

• SPMs use a wide variety of different sense technologies coupled with a very sharp tip, piezoelectric displacement stage, and an optical positioning sensor to measure

across the surface. This allows for nanolithography and positioning of atoms on the surface

• Noncontact uses a specific physical force measurement in the feedback loop as theoptical positioning sensor to measure

surfaces near the atomic scale.• SPM resolutions range from 5 – 10 nm

depending on the tip and the surface profile• SPM tips are generally silicon or Si3N4

b d b t b difi d b ti

measurement in the feedback loop as the sense technique

• Tapping mode relies on the spring constant of the tip to and its response to surface forces to provide information about the substrate

based but can be modified by magnetic coatings, electrically isolated leads, carbon nanotubes, etc.

• They are sometimes even constructed of tapered optical fibers to be used in conjuction

p

with an NSOM device. • SPMs operate in three types of modes:

– Contact - STM/AFM– Noncontact – AFM

T i M d AFM– Tapping Mode – AFM

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Scanning Tunneling MicroscopeScanning Tunneling Microscope• Original method (1981) for generating atomically

resolved structures using a mechanical systemresolved structures using a mechanical system• Tip is driven by a tube containing multiple

piezoelectric strips that direct the tube in x, z, and z directions.

• Original tips were generated by wet etching silicon crystals to a very sharp pointcrystals to a very sharp point.

• Measurements are made by measuring the tunneling voltage between the tip and the sample.

• Low temperature and UHV STMs became common in the early 90s for measuring pristine sample surfaces without thermal noise or oxidative effectssurfaces without thermal noise or oxidative effects.

• Two modes of operation:– Constant-height mode

• Tip travels across the plane above the sample and records changes in the tunneling current

• Faster but provides information only from smoothhttp://wills-nanotech.blogspot.com/2006_04_01_archive.html

Faster but provides information only from smooth surfaces

– Constant-current mode• Tip height is governed by a specified tunneling

current. Height is measured by the voltages recorded in the piezolelectric sensorsSl b t b d t i l• Slow but can be used to measure irregular surfaces with high precision

www.almaden.ibm.com/vis/stm/images/stm10.jpg 26


AFM TechnologiesAFM Technologies• Shortly after the STM was developed, IBM

researchers engineered a slightly different version that allowed the sample to be measured without direct contactdirect contact

• The Atomic Force Microscope (AFM) became a commercial tool within 4 years of its inception.

• The system differs by placing the PZT stage under the sample, and using a cantilevered beam to

l t th ib ti f th tiregulate the vibration of the tip.• An optical probe can then be used to measure the

vibration of the cantilever allowing for angstrom resolution of its deflection

• The cantilever can then be dragged across, tapped i l ib t b th f f thover, or simply vibrate above the surface of the

sample due to different electrostatic forces present at the surface of all materials

• However: AFM is unsuitable for UHV applications

Modern SPM

Dimension V SPM and 4nm probe tip from Veeco Instruments

http://wills-nanotech.blogspot.com/2006_04_01_archive.html

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AFM Sensing TechniquesAFM Sensing Techniques• Contact mode:

Tip makes soft physical contact with the sample– Tip makes soft physical contact with the sample– Van der Waals forces between the tip and the atoms on the surface prevent the tip from actually touching

the atoms on the surface– Measurement is made based on the strength of the Van der Waals repulsive force– Force exerted on the cantilever is like that of a compressed spring, which allows deflections to be readily

it d b ti l fl t tmonitored by optical reflectometry– Operating forces at the tip are approx. 10E-6 to 10E-7 N– Operation of contact AFM is very similar to that of an STM.

• Constant force• Constant height

• Non-contact mode:– Cantilever is vibrated near resonance (100-400 KHz) near the surface at an amplitude of 1-10 nm– Spacing is between 1 to 10s of Angstroms between tip and surface– Vibration of the cantilever is altered by the attractive force near the surface

Deflection force is lo and therefore more diffic lt to meas re than contact forces– Deflection force is low and therefore more difficult to measure than contact forces– This method is prefered for measuring soft samples that may be compressed by applications of a few

micronewtons such as liquids, biological samples, and soft polymers.• Tapping Mode

– Similar to NC mode, but the cantilever is actually brought into contact with the surface. Measurements are , y gthen made of the elastic response of continued tapping of the spring

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AFM TechnologiesAFM Technologies• Magnetic Force Microscopy

– Tips coated with ferromagnetic thin film (often NiFe)Vibrational response from NC mode operation provides nm scale resolution of magnetic domains as well as topographical properties of the– Vibrational response from NC mode operation provides nm scale resolution of magnetic domains as well as topographical properties of the sample

• Lateral Force Microscopy– Contact mode operation in which twisting of the cantilever arises from sliding friction forces on the substrate surface.– Soft cantilevers are used– Provides topography and surface tension or frictional information simultaneously

• Force Modulation MicroscopyProvides topographical and elastic material properties using NC and Tapping mode by observing the amplitude response change as the tip– Provides topographical and elastic material properties using NC and Tapping mode by observing the amplitude response change as the tip crosses the boundary from one material to another

• Phase Detection Microscopy– Uses NC and tapping mode to examine phase shifts in the frequency response due to changes in material properties such as elasticity,

adhesion, friction etc.• Electrostatic Force Microscopy

– Charged tips are used to measure different electrical responses in substrates. This can be used to map TFTs and provide nm resolution for identifying response and defects in circuit design

– NC Constant Voltage technique• Scanning Capacitance Microscopy

– NC Constant height– Measures change in capacitance across the sample and provides information on dielectric strength in circuit designs

• Electrochemical Force Microscopy– Liquid phase electrostatic and capacitance microscopy for examining cathodic potentials on the surface while mapping topography

• Near Field Scanning Optical Microscopy – previously coveredg p py p y• Nanolithography

– Becoming less important today due to the advent of nano-imprint – Uses contact AFM to alter the surface chemistry in a 5 x 5 um area allowing for further bottom up application – Uses contact AFM to alter the location of atoms at the surface to build nanodevices or quantum dot arrays

• Magnetic Resonance Force Microscopy– Single Spin Detection– High frequency RF coil used to oscillate the spin of local area magnetic momentsHigh frequency RF coil used to oscillate the spin of local area magnetic moments– NC magnetic AFM provides NMR elemental sensitivity with the topographical resolution of AFM.– Requires specific geometry and uniform applied magnetic fields to create spin sensitive magnetic circuits at the tip head to achieve detection

limits of 1E-18 N

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spring 2009 ee 710: nanoscience and engineering part 1: introduction i... · 2009-10-16 · spring...

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