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FMB O

xford Ltd

vacuum challenges and solutions

February 2008

Less than 10 kg !

The Smallest Scroll Pump on the Market

Introducing the IDP-3 scroll pump, aninnovative, compact, high performancedry pump that provides affordable oil freepumping, easy system integration, andthat is suitable for a wide variety ofapplications.The pump is a single stage scroll pumpthat delivers 60 l/m pumping speed, anda very low 250 milliTorr base pressure. These specifications make it the highestperforming dry pump in its class.

• The Varian IDP-3 scroll pump provides an oil free vacuum environment, withno hydrocarbon contamination in thevacuum system and no oil leaks into thework environment.

• The hermetic design with fully isolatedbearings and motor providescontainment for all pumped gases,allowing recovery of precious gases andpreventing leakage of toxic gases.

• With a footprint of only 14.09 x 5.50 x 7.13 in. (358 x 181 x 140 mm) it iseasy to integrate in OEM systems, andit weighs only 21 pounds (9.5 kg).

• The IDP-3 has a lower base pressure thandiaphragm pumps.

• It has low noise and vibration resulting ina quiet and pleasant work environment.

Varian, Inc.Vacuum Technologies

Canada and US Toll Free Number: 800.882.7426Europe Toll Free Number: 00.800.234.234.00

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Pag Varian PW_Robot IDP-3 11-06-2007 12:05 Page 1

From freeze-dried coffee to medical implants and from solar cells to com-puter chips, this special supplement to Physics World outlines why vacuum technology lies at the heart of 21st-century manufacturing. Vacuum depo-sition is key to many of these processes, and the supplement includes three articles outlining why vacuum is essential for the production of thin films (p7), explaining how the deposition of nanoparticles is helping to improve medical implants (p11) and examining the huge potential of polymers (p19). In other articles, thermodynamics is revealed as the way to improve freeze-drying (p5), while overcoming the problems of movement and manipulation under ultrahigh vacuum are also examined (p15). Cutting-edge equipment and techniques are worthless, however, if they are not used properly. The benefits of dedicated training in vacuum science are highlighted (p11), while education is also a main tenet of the work of the International Union for Vacuum Science, Technique and Applications, as new president Bill Rogers explains when he discusses what lies ahead for the organization in particular and vacuum science in general (p22). What is clear is that the future of manufacturing will see vacuum technology play a vital role.

Vacuum challenges and solutions

ContentsEmpirical data help freeze-drying 5From food to pharmaceuticals, freeze-drying is a key manufacturing tool. Richard Wood explains why thermodynamics is so important in these processes.

Thin-film deposition relies on vacuum 7Vacuum lies at the heart of coating technology. Rick Spencer describes how it can help to achieve the goal of purity in the production of thin films.

Could training improve your vacuum? 9A sound foundation in the basics of vacuum technology is essential for those working in academia or industry. Andy Willett extols the benefits of dedicated training.

Vacuum deposition improves medical devices 11New methods for the deposition of nanoparticles are enabling the creation of biocompatible coatings, as Alistair Kean and Lars Allers report.

Getting things moving in UHV 15Manipulating and moving samples under vacuum conditions can be a tricky business, but Carl Richardson is on hand with some innovative design solutions.

Versatile polymers offer big potential 19Solar cells are bringing polymers into the spotlight, but Charles Bishop reveals the range and diversity of the other applications for these materials.

New IUVSTA president looks forward 22Bill Rogers outlines his plans for the future of the International Union for Vacuum Science, Technique and Applications.

Project2 12/6/07 11:29 Page 1

©2008 IOP Publishing Ltd. All rights reserved.Dirac House, Temple Back, Bristol BS1 6BE, UK.

www.scanwel.co.uk

V a c u u m c h a l l e n g e s a n d s o l u t i o n s F e b r u a r y 2 0 0 8 �

Empirical data help freeze-drying

Freeze-drying (lyophilization) is the process of freezing a material under vacuum to remove water. It is used to preserve a range of substances (most famously coffee) and plays an important role in the manufacture of pharmaceutical, bio-logical and diagnostic healthcare products.

While commercial pharmaceutical freeze-drying has been commonplace for more than 60 years, controlling the process remains challenging and research continues into the method-ologies involved – often driven by industry regulators. Most freeze-dried products are made by processes developed through trial and error, rather than from empirical data.

A small number of companies, including Biopharma Technology (BTL), are working to change this by develop-ing analytical instruments to determine the temperatures at which materials go through key structural phase transitions. For BTL’s customers alone, this information has been cru-cial in controlling the quality of 470 different freeze-dried product formulations.

A freeze-dryer consists of a vacuum chamber where the product, often in vials, is placed on a special shelf, the temperature of which is controlled. Water vapour gener-ated during the drying process is removed via a connection to a second vessel called an ice trap, which condenses the vapour into ice. Both vessels are maintained at vacuum levels down to 10–3 mbar. The shelf-temperature range is typically –50 °C to 60 °C and the ice trap is at –75 °C.

The freeze-drying process involves three main phases: freezing; primary drying; and secondary drying. Each involves exposing the material to different thermodynamic conditions and success relies on understanding the behaviour of the water during each phase.

In the freezing phase, close attention must be paid to the behaviour of both the solvent (usually water) and the solute(s) in the starting material. The way in which a solution freezes defines the structure and porosity of the final product and must be controlled very carefully. Ice formation is a two-stage process. The first stage is nucleation, which involves water molecules arranging themselves in tiny crystals or gathering around impurities. The second is crystal growth, and in freeze-drying the size and networking of the crystals are of more interest than their shape.

The solutes will freeze into a crystalline, amorphous or multiphase structure depending on the type of material. There are three critical temperatures that affect the process. These correspond to the eutectic (Teu) phase transition for crystalline material, and the glass transition (Tg) and collapse transition (Tc) for amorphous material. These usually define the maximum allowable temperature that the sample can be held at until all of the ice has been removed.

Ice is removed by sublimation during primary drying. However, sublimation cools the material and so energy must

be put into the product to compensate for this. Energy is transmitted to the product mainly by gaseous convection and conduction, and transmission is controlled by adjusting the shelf temperature and chamber pressure. The pressure is con-trolled to within approximately ± 5 × 10–3 mbar, typically over a range of pressures between 2 × 10–2 and 50 × 10–2 mbar.

Only the top of the sample is exposed to the vacuum, so drying occurs from the top down. The sublimation interface, which moves down as drying proceeds, should be kept below the critical temperature of the product throughout primary drying to avoid processing defects. In crystalline systems, for example, the entire frozen mass should be maintained below Teu to avoid boiling, which can result in the product being splattered around the container.

Measuring the temperature of the sublimation interface is a significant challenge. Near-infrared thermal imaging has not been particularly successful, so instead the measured rise in vapour pressure can be used to calculate the temperature. Currently, however, the majority of commercial processes do not involve measuring the interface temperature.

Once sublimation is complete, the product will resemble a dried cake or powder, but it will often contain sufficient moisture to reduce shelf stability significantly. This mois-ture is referred to as “unfrozen water” and may be absorbed, associated or chemically bound to the product. It is removed by secondary drying, whereby higher shelf temperatures and lower chamber pressures are typically employed to encour-age desorption of the unfrozen water.

A freeze-drying process can take from a few hours to sev-eral days to complete, and the length of each phase can vary significantly, depending on factors such as the product and the type of containers used, and their depth of fill. Richard Wood is technical director at Biopharma Technology, Winchester, UK (www.biopharma.co.uk)

Richard Wood describes how the precise control and measurement of the thermodynamic properties of materials can improve freeze-drying processes.

BTL’s Lyostat 2 freeze-drying microscope system.

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V a c u u m c h a l l e n g e s a n d s o l u t i o n s F e b r u a r y 2 0 0 8 �

Being able to create thin layers of various materials is crucial for a range of applications. Thin films appear as optical coat-ings for astronomical telescopes, as barriers in food packag-ing, as transparent conductors in displays, as wear-resistant coatings on cutting tools and in semiconductor devices of many varieties. Each of these applications places different demands on the materials used, but what they all have in common is a need for the consistent and reliable production of thin films in a vacuum. The vacuum is essential for two main reasons: to keep impurities out of the film; and to pre-vent collisions with gas atoms and so avoid the deposition material being scattered.

In almost all vacuums the dominant species is water. This is because water bonds loosely with all surfaces at atmo-spheric pressure and can then subsequently “outgas” back into the vacuum long after all of the air has been removed. This means that if the film that is being grown is in any way reactive, then it is going to contain oxides, hydroxides and hydrides from water incident at the substrate. This contami-nation can cause variability and degrade performance in most thin-film growth processes, and it can severely affect sensi-tive materials like semiconductors and magnetic thin films.

Clearly we want to keep impurities to a minimum. To do this we need to consider the relative “arrival rates” at the sub-strate of the reactive impurities and of the film material. To keep the film pure, we need to ensure that it takes less time to grow a layer of the film material than to grow a layer of impurities. The arrival rate of the reactive impurities (usually water) is proportional to the vacuum pressure. A monolayer of water takes approximately 1 s to form at 10–6 mbar (and therefore 0.1 s at 10 –5mbar).

The arrival rate of the film atoms is proportional to the deposition rate. If we use an approximate atomic diameter of 0.2 nm and assume a typical deposition rate of 2 nm s–1, then the time required to form a monolayer of the coating material is 0.1 s. Comparing this with the time required to develop a monolayer of impurities, we can readily see that 10–5 mbar is the minimum vacuum that we should consider using (in which case the arrival rates of the film material and the impu-rities are equal) and that 10–6 mbar would be better (so that the film material arrives 10 times as fast as the impurities).

If we compare different coating applications, then we can see the need to balance the arrival rates of the coating mater-ial and the gaseous impurities. For example, the aluminium used in thin films for packaging would typically be evap-orated at about 300 nm s–1, so a vacuum of just 10–4 mbar would be sufficient. Meanwhile, for some research appli-cations the deposition rate required is particularly low at <0.1 nm s–1, so vacuums of 10–7 or 10–8 mbar are required to maintain pure film growth.

We can therefore see that the level of vacuum required is directly proportional to the deposition rate. A sometimes unexpected consequence of this is that we can improve the

film purity simply by increasing the deposition rate. This is often a more preferable route than improving the background vacuum because it also increases the production rate.

The average distance between collisions in a gas is the mean free path. This is roughly 1 m at 10–4 mbar and is inversely proportional to the pressure (i.e. it is 0.1 m at 10–3 mbar). Generally we need to make sure that this mean free path is the same as (or longer than) the distance over which we are trying to deliver the coating material. If we are not able to achieve this, then most of the film material will simply scat-ter off the gas atoms. This means that not much of the coat-ing material will reach the substrate and that the material that does make it will have so little energy that it will adhere badly and form poor-quality films.

For example, in a typical evaporative box coater the dis-tance between the evaporation source and the substrate is usually 0.5–1.0 m. A mean free path of 1 m requires a vacuum of 10–4 mbar, thus avoiding collisions. However, the depo-sition rate in a typical evaporative box is 10 nm s–1, which means that we need a vacuum of 10–5 mbar or better to be able to produce pure films.

When using vacuum for thin-film growth, we must there-fore bear in mind two important factors: the arrival rate of impurities from the vacuum; and the distance that an atom can travel between collisions in the vacuum. To obtain a pure film, the deposition material should arrive at the substrate faster than the impurities, and the distance between atom col-lisions should be the same as (or longer than) the distance between the source and the substrate. Rick Spencer runs Alacitas Consultancy Ltd, Leicestershire, UK (www.alacritas.net)

Thin-film deposition relies on vacuumRick Spencer explains how to attain both purity and consistency in film coating.

A vacuum coater that is used for making optical thin films.

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Project11 18/6/07 14:06 Page 1

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V a c u u m c h a l l e n g e s a n d s o l u t i o n s F e b r u a r y 2 0 0 8 �

Vacuum technology has a spectrum of applications, from freeze-drying phar-maceutical products to plate-glass manu-facture, as well as scientific applications that include semiconductor-device manufacture and analysing samples of Moon rock. This means that a huge variety of people – from machine opera-tors and maintenance technicians who may only be educated to GCSE level, to research scientists and engineers with PhDs – are required to work with the technology on a day-to-day basis. This situation makes it very difficult for employers to ensure that all of their employees who work with vacuum tech-nology receive the appropriate training.

Many people learn about their partic-ular area of vacuum technology on the job and never undergo any formal train-ing in vacuum engineering. Although on-the-job training has certain benefits, it often results in the inflexible “Well this is how it’s always done here” atti-tude. This is fine if the method being adhered to is an example of sound engin-eering; however, all too often it can offer vacuum newcomers an example of poor design and application.

A well structured vacuum training course can resolve these issues. All those who work with vacuum technol-ogy need a sound foundation of under-standing to provide them with a much better base from which to move for-ward, thus accelerating their learning curve. Over the past 10 years, I have taught hundreds of candidates, from all backgrounds, the basics of vacuum engineering via a three-day course that combines theoretical work with hands-on experimentation.

Even the most academic engineers have gaps in their knowledge, and indeed I have found that the more academic and specialized the engineer, the less time they have to widen their vacuum knowledge base. This results in them carrying on with existing working practices, unaware that there may be a much better way to operate and that their work could benefit greatly from some simple improvements to their understanding of the fundamentals and a broader under-standing of the subject.

There are several classic mistakes that I hear of when dis-cussing application issues during courses. In particular, meas-urement and gauge-reliability issues often stem from using the wrong type of gauge to measure the vacuum, while improper vacuum measurements can result from the way in which the

process gas is injected. Meanwhile, using the wrong type of valve, or incorrectly selecting the pumping lines and connec-tions, can lead to suboptimal vacuum performance. Poor design of the vacuum chamber makes fault finding and leak detection difficult, and leak-checking equipment is often incorrectly calibrated and its results wrongly interpreted.

On every course that I have ever delivered – even those where all of the attendees have PhDs – some candidates struggled to remember what direction to turn a valve to close it or what direc-tion to turn a regulator to increase gas pressure, while I see others overtight-ening needle valves to the extreme or having difficulty reading analogue vacuum gauges. I put this down to a lack of practical experience for some participants – many who come from an academic background have missed out on getting their hands dirty. A particu-lar advantage of training courses that include hands-on experiments is that these practical skills can be improved.

My three-day courses involve theor-etical work on the foundations of general vacuum technology, which is interspersed with practical experi-ments to illustrate or prove effects that are commonly encountered in vacuum systems. The foundation work is always well received because it provides an overview of what equipment is avail-able and how things are done in indus-try, and it sets out good general vacuum practice. Attendees also enjoy the prac-tical experiments, which provide breaks between the classroom “talk and chalk”

sessions and help to keep students interested when there is the possibility of information and theory overload.

Courses can be held at your premises or, if required, off-site at a conference centre or similar venue. Classes are lim-ited to 10 participants to give the opportunity to gain good access to the experiments, which use a range of cut-down vacuum components, pumps and gauges that enable those on the course to obtain a better feel for the technology.

Most participants will attend the course with existing knowledge and experience, but they will leave with many gaps filled in and a better, broad understanding, thus putting their own knowledge into context within the bigger picture.Andy Willett runs Willet Technical Services Ltd, which runs vacuum training courses throughout the UK (www.vacuumtraining.co.uk)

Could training improve your vacuum?Andy Willett outlines

how training can benefit the understanding and working practices of all of those who work with

vacuum technology.

From engineers to technicians, all can benefit from vacuum training.

Photolibrary

V a c u u m c h a l l e n g e s a n d s o l u t i o n s F e b r u a r y 2 0 0 8 11

Plasma-enhanced sputtering and nanoparticle deposition are among the new physical techniques that allow the generation and controlled deposition of materials such as silver, silicon carbide and tantalum. These materials are of great interest to medical-device scientists because they can be used to create biocompatible coatings for medical implants. Such coatings reduce the chance that an implanted device will be rejected by the patient’s immune system or cause infection, and they will surely play a leading role in the evolution of medical-device science in the near future.

Mantis Deposition has developed a novel technique that allows the generation and deposition of nanoparticles in vacuum via magnetron sputtering under relatively high pres-sures. Unlike normal thin-film vacuum-deposition tech-niques, such as electron-beam evaporation or sputtering, our nanoparticle method provides control over the density and porosity of the coating. In addition, no heat is generated at the substrate, so the most delicate of materials, including organic molecules, can be coated. Finally, almost all other techniques for producing nanoparticles create a powdered material that

has to be purified or refined further before being used for a coating, whereas our technique enables the direct genera-tion, characterization and energy-controlled deposition of the nanoparticles to form a nanostructured coating in a single

Novel techniques for the production and deposition of nanoparticles have some exciting medical applications, according to Alistair Kean and Lars Allers.

Deposition improves medical implants

The Mantis process can be used to coat materials such as stainless-steel braiding with silver nanoparticles.

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process. This has allowed us to produce revolutionary new materials and coatings.

The company is taking part in several European Union- and UK-funded research projects in the areas of antibacterial coatings, photocatalytic materials, fuel cells and biosensors. At the moment, for example, we are completing a project funded by the Department of Trade and Industry (now the Technology Strategy Board) that aims to develop a proto-type system for creating antibacterial coatings. In the first instance, this will be used for cleaning medical instruments. These are usually sterilized in an autoclave – a pressurized device designed to heat aqueous solutions above their boil-ing point – but it has recently been noted that certain prions (protein-based infectious particles) can withstand the auto-clave process. In contrast, our system first cleans the surface in vacuum using a radio-frequency plasma, which removes all contamination, and then applies a coating of silver nano-particles that have been accelerated electrostatically.

Silver is known to have antibacterial properties, so this generates an active antibacterial coating. The accelerated nanoparticles also form an extremely adherent coating with-out the need for any binders or additives. This technology could also be used to make nanoparticle markers for use in magnetic resonance imaging, to coat medical implants, to make biosensors and, indeed, any application where care-ful control of the surface structure and stoichiometry could improve the functionality of a product.

Vacuum-deposition technology must overcome several

challenges, however, if it is to be used to produce medi-cal devices. Health and safety are of utmost importance, and regulations influence the materials that can be used as well as how they are produced. Factors such as adhesion of the coating are critical where the device is to be implanted because any bits of coating that come off can be harmful to the patient. With our nanoparticle technology it is possible to control the adhesion of layers by applying electrostatic acceleration to the charged nanoparticles. It is also import-ant that coated surfaces are very clean, and in vacuum it is possible to employ any of several techniques for surface preparation, including plasma cleaning and heating. Finally, the successful technique must be both technically and eco-nomically scalable.

These advantages mean that vacuum-deposition tech-niques are finding unique roles to play in the production of medical devices, in many cases where chemical techniques have failed to produce materials and coatings of sufficient quality. The new physical nanoparticle techniques are pro-ducing materials that have demonstrated more than signifi-cant increases in the performance of certain medical devices during clinical tests. Mantis owns intellectual property that addresses the issues of process efficiency and scaling-up, and we envisage that this technology will be used in a commer-cial product within two years.Alistair Kean is technical director and Lars Allers is managing director of Mantis Deposition Ltd, Oxfordshire, UK (www.mantisdeposition.com)

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V a c u u m c h a l l e n g e s a n d s o l u t i o n s F e b r u a r y 2 0 0 8 1�

A fundamental challenge in designing many ultrahigh vac-uum (UHV) systems is ensuring that the equipment inside the vacuum chamber can be moved to the right place at the right time. This is not trivial for several reasons. For example, a UHV chamber is a cramped place that is sealed off from the outside world, making direct manipulation difficult; while opening the chamber to adjust equipment could contaminate the sample and will certainly cause a significant delay while UHV conditions are re-established.

There are a number of common factors that must be consid-ered when designing UHV motion systems. Parameters such as mass, speed, accuracy and repeatability must be defined; the space and geometrical constraints imposed by the UHV system must be accommodated; and the integration of the mechanical system with motion-control electronics must be considered. Any design will involve trade-offs such as speed versus positioning accuracy or stability versus resolution.

Many physicists use UHV in surface-science experiments, which need sophisticated motion systems. Often, several dif-ferent actions must be performed on a sample, requiring an “open” position to ensure that electron guns, lasers and other probes have access. This usually means that the sample must be rotated through a wide range.

Getting things moving in UHVThe latest manipulators and motion systems offer improved performance when deployed in ultrahigh-vacuum conditions, explains Carl Richardson.

An X-ray monochromator for use on a synchrotron beamline.

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16 V a c u u m c h a l l e n g e s a n d s o l u t i o n s F e b r u a r y 2 0 0 8

The most common motion system is the traditional bel-lows translator/manipulator. The sample stage is connected to the outside world through a bellows that expands and contracts to allow motion. These systems are popular because they occupy a small volume at the sample position while allowing up to three linear and three eucentric rotary motions in which the centre of the sample does not change position as it is rotated.

A typical bellows translator can achieve positioning accu-racies of ±5 µm linear and ±0.1º in rotation. The sample can be heated and cooled through a bellows translator. All elec-tric motors are mounted outside the chamber and well away from the sample position, which minimizes stray magnetic fields at the sample that could affect electron beams and other probes. The principal disadvantage of the bellows transla-tor is its inherent lack of stability, especially in devices that offer long distances of travel. It is also hard to determine the sample location to any great precision.

Bellows systems are not suitable for the X-ray mono-chromators used on synchrotron beamlines, for exam-ple, because long-term stability and repeatability are key requirements for experiments at such facilities. However, motion systems based on UHV-compatible in-vacuum motors and high-resolution position encoders have allowed sophisticated and highly accurate monochromators to be created. These UHV-compatible devices, when combined with precision linear and rotary stages, and clever flexure design, mean that complex monochromator mechanisms,

having 12 separate motion axes, can be housed inside the vacuum vessel. Most vacuum-compatible motors are based on stepper or piezo designs. Stepper motors can be fully UHV-bakeable (300 °C), while most piezo devices can only be heated to 150 °C.

Encoder development has also been rapid, with some manufacturers producing UHV versions of existing instru-ments and others providing radically new designs where the encoder scale and the read head are mounted separately, which gives great flexibility. Ring encoders can have accura-cies of ±0.5 arcseconds, with a repeatability of 0.01 arcsec-onds. Other alternatives include capacitance sensors that can measure linear displacements down to a few nanometres.

One area where vacuum scientists can look for inspiration is chip manufacture by electron-beam lithography. Although performed under less stringent vacuum conditions than UHV, the process is carried out using sample stages that can be positioned in an accurate and repeatable manner to distances of less than 1 nm – normally using laser interferometry. High-resolution stepper motors, or a combination of steppers and piezos, are used to drive the motion.

Vacuum engineers have access to an ever-growing range of devices to move and measure the position of equipment in a UHV environment. So whether your vacuum motion system needs millimetre or nanometre accuracy, there are design solutions available.Carl Richardson works for RTA Instruments Ltd, Suffolk, UK (www.rta-instruments.com)

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Versatile polymers offer big potential

The use of polymers in vacuum-deposition processing is cur-rently in the spotlight because of the rapid growth in popular-ity of solar power and the need to reduce the cost of solar-cell technology. One route to achieving this is to make solar cells based on flexible polymers rather than on the rigid glass or silicon of earlier designs.

Polymer solar cells are significantly cheaper because they can be manufactured using a technique called roll-to-roll (R2R) processing. Thin sheets of polymer are rolled up and processed by coating, patterning, embossing and so on as they are wound from one reel to another. A huge area of film can be coated in a very compact vacuum chamber, thus making it much cheaper than other methods. Indeed, thanks to R2R processing, vacuum-coated polymer films are now ubiquitous, with applications ranging from food packaging to banknotes.

The coatings are often simple reflective metals (as with the aluminium metallized polymer films that are used to make crisp packets) but, as they are often only a few tens

of nanometres thick, they can have holographic structures embossed on them. These coatings are often used as anti-forgery devices on banknotes.

There are several types of polymer film, each of which has properties that make it more suitable for certain applications than others. It is possible to make a thin web of a polymer either by extruding and stretching the material (tentering) to thin it out or by casting a thin film onto a belt and peel-ing it off when it has cured. Tentering orients the polymer chains, thus giving the material good tensile strength in the

Solar cells based on flexible polymers rather than rigid glass or silicon could ultimately reduce the cost of solar power.

Vacuum deposition of polymers is opening up a myriad of applications, as Charles Bishop reveals.

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20 V a c u u m c h a l l e n g e s a n d s o l u t i o n s F e b r u a r y 2 0 0 8

direction along which the chains are aligned. This is what gives magnetic recording tape such high tensile strength.

Polymers used in food packaging, for example, have to deliver tear and impact resistance, and offer tensile strength. They must also act as an oxygen and moisture barrier. They need to be able to withstand the vacuum-deposition process, during which the temperature can rise to more than 100 °C. Polymers typically used for this type of application include polypropyl-ene, polyester, polyethylene and polyamide (nylon).

R2R processing is also used to make flexible displays, which could one day replace paper, and the technical requirements for this application also pose significant challenges. Flexible displays contain organic, light-emitting materials, which can be degraded by moisture or oxygen, so the polymer substrate must be a good oxygen and moisture barrier. To put this into perspective, the barrier required for an organic display is approximately six orders of magnitude better than that typi-cally used in food packaging. These materials are known as “ultrabarriers” and are generally difficult to produce.

The problem is largely down to the surface quality of the polymer film. If the surface is too smooth, then the rolled-up polymer sticks to itself due to an adhesive effect known as “blocking”, which occurs when two smooth surfaces are in intimate contact. Blocking is usually prevented by the addition of talc, silica or limestone to the polymer, because these protrude from the surface and prevent such intimate contact. Another problem is that as polymers are wound and rewound during R2R processing, they pass over roll-

ers (metal or elastomer-sleeved metal) and the mismatch in materials means that the film can build up a tribo-electric charge, which attracts dust onto the surface.

The fillers and the dust make the polymer surface rough, which means that it is difficult to produce a perfect barrier coating via R2R processing. One solution is to deposit an extra layer of polymer – often an acrylate – onto the roll of substrate material inside the vacuum system before the inor-ganic coating is deposited. The extra polymer layer reduces the number and size of the surface defects on the substrate, thereby allowing a better inorganic layer.

These vacuum-deposited polymers can be fully cured (i.e. polymerized), as in the case of the acrylates mentioned above, or they can be partially polymerized, meaning that the coating can later be dissolved from the substrate reasonably easily. This enables thin inorganic coatings to be deposited onto the substrate but removed at a later stage, which is the process used to make the fine metal flakes in metallic inks and paints.

Polymers are hugely versatile but most of us never appreci-ate the range of options that they offer. If you have an applica-tion that requires coating a large surface area and that could benefit from using one of the variety of lightweight polymer substrates available, then R2R vacuum coating could be the ideal solution.Charles Bishop is a consultant on vacuum-deposition technology based in Leicestershire, UK, (www.cabuk1.co.uk)

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Meeting ActivitiesSymposia

ELECTRONICS, MAGNETICS, AND PHOTONICSA: Amorphous and Polycrystalline Thin-Film Silicon Science and TechnologyB: Materials and Devices for “Beyond CMOS” ScalingC: Advances in GaN, GaAs, SiC, and Related Alloys on Silicon SubstratesD: Silicon Carbide—Materials, Processing, and DevicesE: Doping Engineering for Front-End ProcessingF: Materials Science and Technology for Nonvolatile MemoriesG: Phase-Change Materials for Reconfigurable Electronics

and Memory ApplicationsH: Materials Science of High-k Dielectric Stacks—From

Fundamentals to TechnologyI: Synthesis and Metrology of Nanoscale Oxides and Thin FilmsJ: Passive and Electromechanical Materials and IntegrationK: Materials and Devices for Laser Remote Sensing and

Optical CommunicationL: Functional Plasmonics and NanophotonicsM: Materials and Technology for Flexible, Conformable, and

Stretchable Sensors and TransistorsN: Materials and Processes for Advanced Interconnects for Microelectronics

NANOMATERIALS, FUNDAMENTALS, AND CHARACTERIZATIONO: Semiconductor Nanowires—Growth, Physics, Devices, and ApplicationsP: Carbon Nanotubes and Related Low-Dimensional MaterialsQ: Ionic Liquids in Materials Synthesis and ApplicationR: Coupled Mechanical, Electrical, and Thermal Behaviors of NanomaterialsS: Weak Interaction Phenomena—Modeling and Simulation

from First PrinciplesT: Nanoscale Tribology—Impact for Materials and DevicesU: Mechanics of Nanoscale Materials

Symposium Tutorial ProgramAvailable only to meeting attendees, the symposiumtutorials will concentrate on new, rapidly breaking areas ofresearch and are designed to encourage the exchange ofinformation during the symposium.ExhibitA major exhibit encompassing the full spectrum ofequipment, instrumentation, products, software,publications, and services is scheduled for March 25-27 inMoscone West, convenient to the technical session rooms.Symposium Assistant OpportunitiesGraduate students who are interested in assisting in thesymposium rooms during the 2008 MRS Spring Meetingare encouraged to apply for a Symposium Assistantposition. By assisting in a minimum of four half-daysessions, students will receive a waiver of the studentmeeting registration fee, a one-year MRS studentmembership commencing July 1, 2008, and a stipend tohelp defray expenses. The application will be availableon our Web site by November 1.Career CenterA Career Center for MRS members and meeting attendeeswill be offered in Moscone West during the 2008 MRSSpring Meeting.Publications DeskA full display of over 950 books will be available at the MRSPublications Desk.Symposium Proceedings from both the2007 MRS Spring and Fall Meetings will be featured.Graduate Student AwardsThe Materials Research Society announces the availabilityof Gold and Silver Awards for graduate students conductingresearch on a topic to be addressed in the 2008 MRSSpring Meeting symposia.All finalists will receive a waiverof the meeting registration fee and a one-year MRS studentmembership commencing July 1, 2008.The award prizesconsist of $400 and a presentation plaque for the GoldAwards and $200 and a certificate for the Silver Awards.The application will be available on our Web site byOctober 1 and must be received at MRS headquarters byDecember 14, 2007.

Meeting Chairs

Jeffrey C. GelpeyMattson [email protected]

Robert J. HamersUniversity of [email protected]

Paul MuraltSwiss Federal Institute of Technology [email protected]

Christine A. OrmeLawrence Livermore National [email protected]

For Additional Information,visit the MRS Web site at www.mrs.org/meetings/or contact:

Member ServicesMaterials Research Society506 Keystone DriveWarrendale, PA 15086-7573Tel 724-779-3003Fax [email protected]

V: Crystal-Shape Control and Shape-Dependent Properties—Methods, Mechanism, Theory, and Simulation

W: Advances and Applications of Surface Electron MicroscopyY: Focused Ion Beams for Materials Characterization and MicromachiningZ: Materials Structures—The Nabarro Legacy

POLYMERS AND BIOMATERIALSAA: Conjugated Organic Materials—Synthesis, Structure,

Device, and ApplicationsBB: Signal Transduction Across the Biology-Technology InterfaceCC: Designer BiointerfacesDD: From Biological Materials to Biomimetic Material SynthesisEE: Responsive Biomaterials for Biomedical ApplicationsFF: Molecular Motors, Nanomachines, and Active NanostructuresGG: Mechanical Behavior of Biological Materials and Biomaterials

ENERGY AND ENVIRONMENTHH: The Hydrogen EconomyII: Heterostructures, Functionalization, and Nanoscale

Optimization in SuperconductivityJJ: Materials Research for Electrical Energy StorageKK: Light Management in Photovoltaic Devices— Theory and PracticeLL: Energy Harvesting—From Fundamentals to DevicesMM:Health and Environmental Impacts of Nanoscale

Materials—Safety by DesignNN: Actinides IV—Basic Science, Applications, and Technology

GENERAL INTERESTX: Frontiers of Materials ResearchOO:The Role of Lifelong Education in Nanoscience and

EngineeringPP:The Business of Nanotechnology

www.mrs.org/spring20082008 MRS SPRING MEETING

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The International Union for Vacuum Science, Technique and Applications (IUVSTA) is a federation of 30 national vacuum societies and it represents about 15 000 scientists, engineers and techni-cians worldwide who are active in basic and applied research, development, manufacturing, sales and education. Bill Rogers, who took over as president of the IUVSTA last year for a tenure of three years, trained as a surface scien-tist. Currently he is associate laboratory director for energy and environment science and technology at the Idaho National Laboratory in the US.

What is the IUVSTA’s role within the international vacuum community?The IUVSTA seeks to stimulate inter-national collaboration in the fields of vacuum science, techniques and appli-cations. It provides a strong programme of meetings, including the triennial International Vacuum Congress, an ongoing series of topi-cal workshops and schools, and a regular series of European Vacuum Conferences. It also has a growing awards and rec-ognition programme, and it has recently made great strides in expanding its educational efforts, which include a visual-aids series and a budding short-course programme. The IUVSTA also provides financial and organizational assistance to vari-ous international scientific groups and co-sponsorship for many of their activities.

How would you assess the current state of vacuum science and technology, both in academia and industry?In my opinion, the study of vacuum science and technology peaked in the 1970s. For example, the last truly new inno-vation in vacuum measurement was the development and deployment of the spinning-rotor gauge, which dates back to the mid-1980s. This is not to say that vacuum technology has stood still: turbomolecular pumps are much more robust than they were 20 years ago; materials and coatings for vacuum applications have proliferated at a rapid rate; and innovation and improvement in electronics design have revolutionized displays, interfaces, computer controls and many other areas. So, while revolutionary changes in vacuum technology have been absent in the last few decades, what has kept the industry afloat is the never-ending list of applications where controlled environments, and thus vacuum technology, are necessary to study new phenomena. A few examples include surface, thin-film and nano science; semiconductor physics; and new areas of materials science, such as low-dimensional materials and high-temperature superconductors. In many cases, advances in these fields have rapidly led to commercialization, such as the use of optoelectronics for flat-panel displays. This in

turn has been a boon for the vacuum-technology industry because most of the manufacturing techniques involved require some degree of vacuum. So the field continues to rejuvenate itself as new applications for vacuum emerge.

What do you see as the main challenges facing those involved in vacuum science and technology?From an academic perspective, the post-graduate educational process is becom-ing increasingly interdisciplinary. To my knowledge there is no major univer-sity where vacuum science and technol-ogy is offered as a degree, yet it is a field that must be mastered in order to study other phenomena of interest. Graduate students usually pick up these skills via self-study or from a practitioner in the field; rarely from a formal course. I see this as a major challenge for stu-dents and postdocs who need a work-

ing knowledge of vacuum science and technology to pursue their varied research interests. This offers an opportunity for the IUVSTA to enhance its educational programme, particu-larly with regard to topical schools and workshops in highly specialized areas. From an industrial prospective, very little fundamental research is done in industrial labs; they usually concentrate on applied research and development. Most new innovation occurs in academia and many new applications reach the market through small companies that are spun-out of universities, so being first to the market with a new prod-uct is the real challenge.

What are your predictions for the future of vacuum science and technology?I believe that field has a bright future because major advances in emerging and yet-to-be-discovered areas of interest will demand controlled environments. These environments are often created by the application of vacuum technology. Vacuum science and technology is an indispensable tool for cutting-edge science. A recent example is the comple-tion of the US Department of Energy’s $1.2 bn Spallation Neutron Source at the Oak Ridge National Laboratory in Tennessee. Vacuum science and technology is also a neces-sity for advanced-materials processing and manufacture, as can be seen at any state-of-the-art semiconductor-fabrication facility. The IUVSTA is in the final stages of developing a strategic plan that will be implemented in this triennium. The plan will help the organization to pursue new opportunities in vacuum science, technology and related fields. Being at the heart of science and manufacturing is a good place to be, now and in the future.Bill Rogers is president of the IUVSTA (www.iuvsta.com)

Bill Rogers explains how vacuum technology is at the heart of science

and manufacturing.

New IUVSTA president looks forward

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