Wednesday, May 26, 2010
Compared to silicon, semiconductors like gallium arsenide can be made into solar cells that convert more sunlight into electricity and transistors that are faster than their silicon counterparts. But devices made from these materials are expensive.
Now a new method for making large-area devices from gallium arsenide promises to bring down costs by eliminating manufacturing steps and wasting less materials. Researchers have used the method to make high-performance image sensors, transistors, and solar cells. Semprius, a Durham, NC, company, is using it to make solar modules that should be on the market by the end of the year.
Gallium arsenide solar cells convert twice as much of the energy in sunlight into electricity compared to silicon cells, says John Rogers, professor of materials science and engineering at the University of Illinois at Urbana-Champaign, who led the research. Gallium arsenide is also being eyed by microchip manufacturers such as Intel as a potential replacement for silicon.
The problem with gallium arsenide, however, is its price tag. To make a gallium arsenide solar panel today, manufacturers grow a semiconductor crystal on an expensive template in a high-vacuum, high-temperature chamber. The gallium arsenide is then diced into thin pieces, assembled, and bonded. This process destroys the underlying template, which is necessary to create a high-quality crystal. And making only a single layer of gallium arsenide at a time is inefficient--it takes more time to load and unload the vacuum chamber than it does to grow the crystal.
To address the problem, Rogers developed a method for growing multiple layers of devices at one time, and a way to release them from the substrate without destroying it. "Once the substrate is in the chamber at the right temperature, we grow a multilayer stack," explains Rogers. The stack alternates a device layer with a sacrificial layer. After all the layers are put down, the stack is etched in a chemical bath that eats away at the sacrificial layer, made of aluminum arsenide, releasing thin rectangular films of gallium arsenide. As the gallium arsenide films are released, they're picked up and placed on a substrate.
Sunday, January 17, 2010
The right side of a mirror has a polymer coating that fights fogging — making the camera visible — and helps wash away oil.
IMAGINE how great it would be if, after dinner, you could stack the greasy dishes, pots, pans and utensils in the sink and let plain old water rinse away the grime — with no help from detergents, and little or no scrubbing. Bye-bye, dishpan hands.
Plastic coatings under development may someday bring that moment to pass, rendering dinnerware, bathroom mirrors and even factory equipment sparkling clean with water alone.
The new materials may be appreciated not only by dish-washing family members, but also by environmentalists concerned about all of the soap that disappears down the drain. Detergents that end up in wastewater can cause algae to bloom, among other effects.
In experiments, Dr. Youngblood and his colleagues attached the coatings chemically to the surface of glass. But he is now working on polymer additives for liquids that can be poured into a spray bottle, for example, and then used to clean mirrors and even eyeglasses or goggles.
Scientists call the coatings self-cleaning because, once they are applied to a surface, they do much of the work of scrubbing away oily residue — like that from a greasy fingerprint. “The oil beads up and then the water moves under the oil, lifting it up so it floats away,” said Kirsten Genson, a postdoctoral researcher in Dr. Youngblood’s group.
Getting the coating to do this is ingenious, said Michael F. Rubner, a professor of polymer materials science and engineering, and director of the Center for Materials Science and Engineering at the Massachusetts Institute of Technology. “Jeff figured out a way to have molecules on the surface that can rearrange themselves so they can self-clean, rejecting grease,” he said.
at 3:39 PM
Thursday, April 2, 2009
By adjusting nine parameters in a single equation, a computer model can generate patterned shells (right example in each pair above) that closely resemble real mollusk shells. (Jump to original article in the link below for great animations.)
University of California, Berkeley, graduate student Alistair Boettiger has amassed a beautiful collection of seashells, but not by combing the beach. He created them in his computer.
A simple neural network model of seashell growth can generate realistic mollusk shells based on a simple principle discovered 140 years ago. He and George Oster, a UC Berkeley biophysicist, along with University of Pittsburgh mathematical neuroscientist Bard Ermentrout, have written a computer program that generates the complex patterns of seashells using simple principles developed to explain how the brain works and how memories are stored.
The "neural net" model explains how mollusks build their seashells based on the finding that the mollusk's tongue-like mantle, which overlaps the edge of the growing shell, senses or "tastes" the calcium carbonate layer laid down the day before in order to generate a new layer.
"The pattern on a seashell is the mollusk's memories," said Oster, a professor of environmental science, policy and management and of molecular and cell biology. "The shell is laid down in layers, so the mantle is sensing the history of the mollusk's 'thoughts' and extrapolating to the next layer, just like our brains project into the future."
The studies may help neuroscientists understand how neural networks work in the brain and throughout the body, where neural nets cover our skin and all internal organs.
The researchers' computer model can reproduce a wide variety of shell shapes, colors and patterns. The researchers' computer model, published this week in the early online edition of the journal Proceedings of the National Academy of Sciences, reproduces nearly all known shell shapes, ranging from scallops to whelks, and nearly all the shell patterns that make beachcombing so popular.
"The model gives us a remarkable ability to explain much of the dramatic diversity of both shape and pattern that we see in the natural world," Boettiger said.
Jump to the link for great animations.
at 3:13 PM
Wednesday, February 25, 2009
A garden of (very small) earthly delights. Carbon nanotube arrays could be the basis of high-density energy storage devices and efficient chip cooling systems. The performance of such devices, however, depends on the quality of the nanotubes and the precise structure of the array. So researchers including Anastasios John Hart, assistant professor of mechanical engineering at the University of Michigan, are honing techniques for growing carefully structured forests of high-quality carbon nanotubes. Hart made these images with a scanning electron microscope; all show vertically grown nanotubes. This is a composite of many images of carbon nanotubes grown on silicon wafers or in cavities etched in the wafers. Each stalklike structure is made up of thousands of nanotubes or more. The catalyst that starts off the nanotubes’ growth is visible under some of them as a dark, shadowlike spot. Structures that appear withered were dipped in liquid after they grew; as the liquid evaporated, the nanotubes shriveled.
at 8:26 PM
Friday, January 30, 2009
It is rare indeed that a justifiably "new" thin films deposition technique comes along. In my lifetime, I have not seen such a new technology, other than cathodic arc in the 1970s, that has the potential to significantly advance the field.
BERKELEY, CA – In the electronics industry, thin metal films are deposited on silicon wafers with a sputter gun, which uses ionized argon gas to knock the metal atoms off a target. Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have now developed a powerful new kind of sputter process that can deposit high-quality metal films in complex, three-dimensional nanoscale patterns at a rate that by one important measure is orders of magnitude greater than typical systems.
Called “self-sputtering far above the runaway threshold,” the new method “is an extraordinarily prolific generator of metal ions,” says Andre Anders, a senior scientist in Berkeley Lab’s Accelerator and Fusion Research Division, where he leads the Plasma Applications Group. Anders and his colleague Joakim Andersson, now at Uppsala University in Sweden, based their new "Self-Sputtering" method on the existing technique of High Power Impulse Magnetron Sputtering (HIPIMS). The new method uses much higher power in short pulses in order to keep the average power low enough to avoid overheating the sputtering target.
Self-sputtering occurs when target atoms that have themselves been ionized return to the target to knock out yet more target atoms. Some of the sputtered atoms remain neutral and may fly straight to the substrate; others are ionized and may return to the target, producing yet more ions and yet more free electrons (secondary electrons).
Once self-sputtering gets started, if enough new atoms get ionized and enough new ions return to the target, it becomes self-sustaining. The magnetic field lines near the target grow thick with spiraling electrons, the plasma is dominated by metal ions instead of gas, and the sheath becomes a potent source of a large flux of energetic electrons that produce still more “excess” plasma – the system runs away, until it finally reaches a new equilibrium at a much higher peak-power level than before.
Beyond the semiconductor industry Anders sees a wide range of applications for the efficient new process, some of which may sound exotic. Because a sustained, self-sputtering plasma can operate in pure vacuum, the new method could also be used for coating materials in space, or even for ion thrusters whose fuel consists of a low-cost, noncombustible metal target, making it unnecessary to carry bottled gases or liquids into space.
For now, Andersson and Anders’s demonstration of a 250-ampere current of copper ions to a substrate – far higher than any ever achieved in a magnetron system – stands as an achievement with the potential to revolutionize some of the semiconductor industry’s most important manufacturing processes.
at 11:13 AM
Thursday, July 17, 2008
Experiments performed at Penn State, the first study of diamond friction convincingly supported by spectroscopy, looked at two of the main hypotheses posited for years as to why diamonds demonstrate such low friction and wear properties. Using a highly specialized technique know as photoelectron emission microscopy, or PEEM, the study reveals that this slippery behavior comes from passivation of atomic bonds at the diamond surface that were broken during sliding and not from the diamond turning into its more stable form, graphite. The bonds are passivated by dissociative adsorption of water molecules from the surrounding environment. The researchers also found that friction increases dramatically if there is not enough water vapor in the environment.
Some previous explanations for the source of diamond’s super low friction and wear assumed that the friction between sliding diamond surfaces imparted energy to the material, converting diamond into graphite, itself a lubricating material. However, until this study no detailed spectroscopic tests had ever been performed to determine the legitimacy of this hypothesis. The PEEM instrument, part of the Advanced Light Source at Lawrence Berkeley National Laboratory, allowed the group to image and identify the chemical changes on the diamond surface that occurred during the sliding experiment.
The team tested a thin film form of diamond known as ultrananocrystalline diamond and found super low friction (a friction coefficient ~0.01, which is more slippery than typical ice) and low wear, even in extremely dry conditions, (relative humidity ~1.0%). Using a microtribometer, a precise friction tester, and x-ray photoelectron emission microscopy, a spatially resolved x-ray spectroscopy technique, they examined wear tracks produced by sliding ultrananocrystalline diamond surfaces together at different relative humidities and loads. They found no detectable formation of graphite and just a small amount of carbon re-bonded from diamond to amorphous carbon. However, oxygen was present on the worn part of the surface, indicating that bonds broken during sliding were eventually passivated by the water molecules in the environment.
The abstract of the study, “Origin of ultralow friction and wear in ultrananocrystalline diamond,” is available here http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000100000023235502000001&idtype=cvips&gifs=Yes
Friday, June 20, 2008
If you were looking for a new way to make semiconducting diamond, you might not have thought of starting with tequila. But the potent spirit turns out to be excellent raw material.
Diamond is normally an electrical insulator, but becomes a semiconductor when doped with the right impurities. Diamond film is tougher than silicon, so it could be useful for devices that must operate at high temperatures or under other harsh conditions.
However, diamond films are expensive and difficult to make. They are produced by vaporising organic material, and then controlling how the carbon atoms crystallise onto a surface. The process works best if the material contains carbon and oxygen in roughly equal parts, as well as some hydrogen.
Now a team of researchers led by Javier Morales of the University of Nueva Leon near Monterrey in Mexico have shown that ordinary tequila does the job nicely. They injected the heated vapour from 80-proof "tequila blanco" into a low-pressure chamber. Measurements confirmed that the carbon deposited on test surfaces had a diamond structure (www.arxiv.org/abs/0806.1485). "Some kinds of tequila seem naturally to have the right mix of atoms," says Morales. Other forms of alcohol have also worked, although it's not clear if this is faster or more reliable than using common precursors such as acetone.
"The result is certainly funny, but the process seems reasonable," says physicist Rudolf Pfeiffer of the University of Vienna in Austria. "I don't know of any previous attempts to make diamonds from drinks." http://technology.newscientist.com/article/mg19826615.700-tequila-is-surprise-raw-material-for-diamond--films.html
at 9:33 AM
Tuesday, June 17, 2008
Due to its excellent biocompatibility, diamond has been called the "Biomaterial of the 21st Century". There is a huge demand for medical implants for almost every body part you can think of. The market for medical implant devices in the U.S. alone is estimated to be $23 billion per year and it is expected to grow by about 10% annually for the next few years. Current medical implants, such as orthopedic implants and heart valves, are made of titanium and stainless steel alloys, primarily because they are biocompatible. Unfortunately, in many cases these metal alloys with a life span of 10-15 years may wear out within the lifetime of the patient. With recent advances in industrial synthesis of diamond and diamond-like carbon film bringing prices down significantly, researchers are increasingly experimenting with diamond coatings for medical implants. On the upside, the wear resistance of diamond is dramatically superior to titanium and stainless steel. On the downside, because it attracts coagulating proteins, its blood clotting response is slightly worse than these materials and the possibility has been raised that nanostructured surface features of diamond might abrade tissue. That's not something you necessarily want to have in your artificial knee or hip joints (although some of the currently used implant materials cause problems as well). Researchers have now run simulations (see video below) that show that thin layers of ice could persist on specially treated diamond coatings at temperatures well above body temperature. The soft and hydrophilic ice multilayers might enable diamond-coated medical devices that reduce abrasion and are highly resistant to protein absorption. http://www.nanowerk.com/spotlight/spotid=2617.php
at 1:02 PM
Tuesday, May 20, 2008
This inch-long beetle from Brazil accomplished a task that so far has stymied human researchers. University of Utah chemists determined the beetle glows iridescent green because it evolved a crystal structure in its scales that is like the crystal structure of diamonds. Such a structure is considered an ideal architecture for "photonic crystals" that will be needed to manipulate visible light in ultrafast optical computers of the future. http://www.physorg.com/news130481875.html
at 8:15 AM
Friday, April 25, 2008
Ford Research Centre Aachen (Germany) is developing a thermally sprayed nano-coating using a Plasma Transferred Wire Arc (PTWA) process that could replace the heavier cast iron liners that provide the necessary wear resistance of cylinder bores in aluminum block engines.
The thin, wear-resistant coating reduces weight and improves friction performance while delivering equal durability and reliability. Fuel consumption can be reduced by utilizing lightweight construction as well as by decreasing internal friction losses in the drive train.
Modern engine blocks are partly made of cast iron or aluminum material whereas for the later hypo-eutectic AlSi-alloys dominate. Due to the low hardness, surfaces made of these alloys cannot be used as a friction partner for the piston rings. Cast iron liners are often inserted into the engine block to provide a wear-resistant surface for the piston rings. This work describes how cast iron liners can be replaced by thin, nanocrystalline iron based coatings in order to decrease friction losses as well as reduce the engine weight. http://www.greencarcongress.com/2008/04/ford-developing.html#more
at 12:48 PM
Thursday, April 10, 2008
Carbon-based materials play a major role in today's science and technology. Carbon is a very versatile element that can crystallize in the form of diamond and graphite. In recent years, there have been continuous and important advances in the science of carbon such as chemical vapor deposition of diamond1 and the discovery of fullerenes2, carbon nanotubes3 and 4, and single-layer graphene5. There have also been major developments in the field of disordered carbons. In general, an amorphous carbon can have any mixture of sp3, sp2, and even sp1 sites, with the possible presence of hydrogen and nitrogen. The compositions of nitrogen-free carbon films are conveniently shown on a ternary phase diagram ( Fig. 1). An amorphous carbon with a high fraction of diamond-like (sp3) bonds is known as diamond-like carbon (DLC). Unlike diamond, DLC can be deposited at room temperature, which is an important practical advantage. DLCs possess an unique set of properties, which has lead to a large number of applications such as, for example, magnetic hard disk coatings; wear-protective and antireflective coatings for tribological tools, engine parts, razor blades, and sunglasses; biomedical coatings (such as hip implants or stents); and microelectromechanical systems6
Ultrathin DLC films also enable ultrahigh-density data storage in magnetic and optical disks and ultralong shelf life for beer canned in plastic bottles. In the first case, up to 1 Tbit/in2 can be reached using sub-2 nm, atomically smooth films that act as a corrosion barrier to the recording medium. In the second case, hydrogenated amorphous carbons in the 100 nm thickness range provide a gas permeation barrier and enable standard polyethylene terephthalate (PET) bottles to efficiently store beer and carbonated soft drinks for tens of weeks.http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6X1J-4MMXWMN-P&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=a491cd9c9cf3a58ae98a0b400fb1c646
Tuesday, March 25, 2008
Diamond thin films are making important contributions to our way of life; lowering wear in engines, rotary seals, cutting tools, improving efficiency (and reducing polution) in many economic domains. One of the best applications for DLC that I have run across is on the inside of pipes, providing wear, corrosion and friction benefits. These benefits applied just to the oil and gas industries, which use millions of miles of pipe, will be enormous. Sub-One Technology has a great solution for a significant need and has made DLC on the inside of pipes an industrial reality. Their results: A novel hollow cathode plasma immersion ion processing method is developed and used to deposit silicon containing DLC-Si inside a one foot long 1020CS pipe with 1.75 inch diameter. A layered coating structure was developed, including an improved adhesion layer with good mixing of substrate and coating constituents, to improve adhesion of the coating while a DLC top layer provided excellent wear and friction characteristics. Data showed that such a coating provides excellent corrosion protection to internal surfaces of pipes. Application of this coating technology is in industries such as oil and gas, tribological and corrosion performance improvement is expected for components such as pump barrels, downhole pipes, drilling fixtures, and drilling bores, etc. http://www.azom.com/Details.asp?ArticleID=4125
at 12:59 PM
Thursday, March 13, 2008
Image: A cross section of mother-of-pearl, or nacre, shows calcium carbonate platelets arranged in layers separated by a biopolymer (top). Researchers have mimicked nacre’s structure by dispersing aluminum oxide platelets in the biopolymer chitosan (bottom), which yields a nanocomposite that is strong, stretchy, and light.
In their efforts to create strong yet light materials, chemists and materials scientists have long tried to mimic nanostructures found in nature. Shells, bones, and tooth enamel all consist of stiff ceramic platelets arranged in a polymer matrix like bricks in mortar. These hybrid materials combine the strength of ceramics and the stretchability of polymers. Researchers at the Federal Institute of Technology Zurich have dispersed tiny platelets of aluminum oxide in a polymer to make a material that is tough, stretchy, and lightweight. A film of the composite is already as strong as aluminum foil, but if stretched, it can expand by up to 25 percent of its size; aluminum foil would break at 2 percent.
An added advantage of the hybrid material is that it's light, says Harvard materials scientist Andre Studart, who was involved in the work. The material is half to a quarter as heavy as steel of the same strength and it would make a good substitute for fiberglass, which is commonly used in car parts. Because the material's strength comes from the platelets diffused through it, it is strong in two directions, not just one direction, as is the case of fiber-reinforced material. Moreover, while the material is translucent now, its structure could be modified to render it transparent, making it suitable for dental material and transparent electronic circuits.
In designing the material, the researchers carefully studied the mechanical structure of nacre, the shiny layer on the inside of seashells, and tried to improve it. Nacre has platelets made of calcium carbonate arranged in layers inside a protein-based polymer. "There's something very special about the size of these platelets," Studart says. "Nacre uses specific platelet length and thickness to achieve the high strength and stretchability that you see in metals." The ratio between the length and thickness of the platelets has to be just right, Studart says. If it is too high, the platelets break when the material is stretched. If it is too low, the material is not very stiff. http://www.technologyreview.com/Nanotech/20333/page1/
at 12:03 PM
Tuesday, February 26, 2008
Important film properties including hardness, density and stoichiometry depend on the energy of the depositing species. Recent PVD advancements have involved increasing this energy through augmented process ionization. For example, unbalanced magnetron PVD increases the ionization of the sputtering gas through a special arrangement of the magnets - the source material isn't ionized, but the reactivity of the process is enhanced. If the the source material is fully ionized, the energy of virtually every particle impinging the growing film can be precisely controlled through substrate biasing to optimize film growth energetic conditions. This is especially important when depositing diamond like carbon films where high sp3 diamond is synthesized only in a narrow window of carbon ion energy around 100 eV. Cathodic arc PVD, offering high source material ionization, has long been where other PVD technologies strive to go, but suffers from macroparticles (MPs). Filtered cathodic arc (FCA) eliminates MPs and generates a fully ionized metal or carbon plasma (ionizing some of the process gas as well) but typically suffers from low rates, complexity, large size and high cost. FCA holds great promise as a versatile PVD source for producing the highest performing thin films, but these limitations must first be overcome.
A new kind of FCA has been developed by Fluxion (fluxion-inc.com). The Radial Arc source (shown above with a carbon plasma) may allow FCA technology to achieve on the coating center floor the success that it has so far achieved mainly in the laboratory. It accomplishes this by using a novel filter geometry that lends itself to uniform high rate deposition, compact size, simplicity and low cost (less than a magnetron, including power supplies). According to Fluxion's website, the geometry of the Radial Arc FCA can be visualized by imagining a ninety degree bent-tube filter rotated around one of its two ends where the axis of rotation is the large radius (the radius of the ninety degree bend), intersecting that end of the tube (see animation at http://fluxion-inc.com/index_OurTechnology.htm). The ions travel in a radial direction out from the cathode and are carried around curved trajectories through the large open area of the filter by strong magnetic and electric fields, then directed to the substrate in a uniform distribution. The much increased open area through the filter compared to a curvilinear filter, allows for greater ion throughput (and greater resulting deposition rate). The unique geometry of the Radial Arc also provides for strong magnetic fields in a compact design, also adding to ion transport efficiency. This visualization also indicates how MPs are filtered out by eliminating line-of-sight between the cathode and the substrate. In fact, the large and abrupt angle that MPs have to navigate to escape the filter further decreases the likelihood that MPs will reach the substrate.
Friday, February 15, 2008
Cathodic-arc evaporation is a relatively simple PVD technology that produces a large flux of highly ionized vapor, valuable for depositing hard, dense, and well adhered industrial coatings. Cathodic-arc evaporation also produces macroparticles (MPs) that create defects in the films, relegating this technology to applications that are mostly insensitive to these defects, such as cutting tool coatings. Many methods have been tried over the years to filter out MPs. Although more or less successful at reducing MPs, all of these filtered cathodic-arc (FCA) sources also reduce the coating rate and area to such an extent that they are mostly relegated to the laboratory or to applications needing only extremely thin films over small areas. FCA technology is also typically quite complicated, bulky and expensive.
The present convention in FCA, the curvilinear FCA, borrows from fusion research to bend the ions through a bent tube using a magnetic field. MPs, unlike the ions, are unaffected by the magnetic field and travel in straight lines, getting caught on the walls of the tube and are thereby prevented from reaching the part to be coated. The main problem, also present in fusion technology, is that the ions are imperfectly confined and mostly don’t make it out the filter, which explains the low deposition rates inherent to conventional FCA. Curvilinear filters are also complicated to operate and typically quite large, sticking some distance out of the side of the vacuum chamber. Low deposition rates over small areas (magnetic restoring can increase coating area, but adds even more complication), difficult operation, bulky size, and high cost have prevented wide-spread adoption of filtered-cathodic-arc (FCA) technology, despite the many advantages of ion deposition.
Thursday, February 7, 2008
Continuing our discussion of diamond thin films, we move on to PVD diamond-like-carbon (DLC) films. The main advantages of PVD DLC over CVD diamond are lower temperature deposition (room temperature versus 400C at best for CVD), lower cost typically and a benign environmental footprint. The best PVD DLC is deposited using cathodic arc and can be 3 times harder than sputtered DLC. Cathodic arc produces carbon ions which, with careful substrate bias control, allow the ideal energetic conditions for optimizing diamond, sp3 bonding in the growing film. High sp3 bond ratio correlates with high hardness, up to about 90 GPa, or about the same hardness as CVD diamond (http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=2574&DID=118953&action=detail). Some DLC films have been reported to be even harder than natural diamond; natural diamond nano-indentors can break during hardness measurements.
The main drawback of PVD versus CVD diamond is the difficulty in growing thick films due to compressive stress. CVD "diamond-sheet" films can be 50 microns thick, compared to about 2 microns maximum for the best PVD DLC films. Numerous process modifications have been developed for the relief of stress, including post deposition annealing and substrate high voltage pulsing, but no one has yet brought a high sp3 DLC film to market that is as easy to widely implement as other more standard PVD films, such as titanium-nitride.
Tuesday, February 5, 2008
Currently, three specific applications enabled by UNCD are under development. The first is wear-resistant, low friction coatings for mechanical components, including mechanical seals for fluid pumps. UNCD films as thin as 1 micron can change the performance of state-of-the-art silicon carbide seals and dramatically reduce the friction and wear at the seal face, increasing the lifetime of the pump for applications in chemical refineries, ethanol production, petroleum exploration and pharmaceutical processing. Since mechanical seals are found in most fluid pumps, it is estimated that reducing friction could save trillions of BTUs of energy annually. The same UNCD films can be used as a tribological coating in other industrial settings.
at 1:57 PM
Monday, February 4, 2008
Friday, January 11, 2008
Stylus profilometry is the conventional way to determine surface roughness. NIST researchers have found that 2-D profilometry, typically extrapolated to provide a 3-D roughness determination, may not be accurate.
NIST’s approach uses data from a scanning laser confocal microscope (SLCM), an instrument that builds a point-by-point image of a surface in three dimensions. The data from a single SLCM image are analyzed using mathematical techniques that treat every point in the image simultaneously to produce a roughness measure that effectively considers the entire 3-D surface rather than a collection of 2-D stripes.
One early finding is that the generally accepted linear relationship between surface roughness and material deformation is wrong. The more accurate data from the 3-D analysis shows that a more complicated relationship was masked by the large uncertainties of the linear profilometers. http://www.physorg.com/news119106592.html
at 1:11 PM
Monday, January 7, 2008
Hard coatings are a fascinating field of study where remarkable science is being done with extraordinary results. (see earlier posts: "Tribological Coatings..." and "PVD Hard Coatings...") The loss due to wear and corrosion in the US is estimated to be approximately $500 billion. A diamond coating can increase service lifetime for a coated article from 8 days to 85 years. The economic and environmental impact, then, can be enormous. I would be surprised if total market penetration was greater than 50%. Does anyone have specific market data? I find it remarkable, after years in the business, how difficult it can be to convince customers to use hard coatings, even though the lifetime savings can be so significant. Share your stories and ideas with us. Kudos to those of you doing the important and often overlooked work of hard coatings. The Surface Engineering Coating Association (SECA) is a valuable resource for information on hard coatings and providers. http://www.surfaceengineering.org/
Please email firstname.lastname@example.org if you would like your business to be added to our links.
at 2:01 PM
Friday, January 4, 2008
Winners from the Science as Art competition held at the 2007 Materials Research Society (MRS) Fall Meeting are beautiful and thought provoking.
Nano-Explosions: Color-enhanced scanning electron micrograph of an overflowed electrodeposited magnetic nanowire array (CoFeB), where the template has been subsequently completely etched. It’s a reminder that nanoscale research can have unpredicted consequences at a high level. (Image: Fanny Beron, École Polytechnique de Montréal, Montréal, Canada)
at 1:34 PM
Thursday, January 3, 2008
Thin Film solar superstar, Nanosolar, has shipped their first panels. Their 430 MW plant in California will be the largest in the world and allow them to sell at less than $1/Watt per panel, or about $2/Watt in a complete system. According to the Energy Department, building a new coal plant costs about $2.1 a watt, not including the costs of fuel and emissions. Is this a watershed for solar energy? It may be difficult for vacuum deposited thin film solar manufacturers to compete with Nanosolar, which uses nanoparticle ink jet printing in atmosphere on metal foil, roll to roll. Their plant reportedly is costing about 15 million dollars to build, compared to about 350 million for a vacuum deposited solar cell plant. Nanosolar is tight lipped about their efficiency, but Copper Indium Gallium Selenide (CIGS) cells have reached 19.5% in the laboratory.
at 2:43 PM
Thursday, December 20, 2007
Dr. Zhong Lin Wang, Regents' Professor, COE Distinguished Professor, and Director, Center for Nanostructure Characterization, at Georgia Tech, has examined the fine structure of the compound eyes of a household fly and precisely replicated its entire structure using a low-temperature atomic layer deposition technique. The results have been published in the December 6, 2007 online edition of Nanotechnology ("Bio-inspired fabrication of antireflection nanostructures by replicating fly eyes").
"Our contribution is the ability to replicate a biological structure and then measure its physical properties and find out why a particular structure exhibits unusual properties" Wang explains to Nanowerk. "By doing so, we are trying to find an effective fabrication path that follows the evolution of Nature for making extraordinary nanostructures."
"The surface of the fly eye is covered by highly packed protuberances, which potentially increases visual efficiency through increased photon capture for a given stimulus" Wang comments on his group's most recent bioinspired nano research. "We carefully examined the fine structure of the household fly compound eye and then completely replicated the entire configuration by alumina through a low-temperature atomic layer deposition process."
The Georgia Tech scientists' goal has been focused on the optical properties of the fly eye's nanostructure, aiming to understand the visible light, UV light and infrared light transmission through the structures.
"We achieved the alumina replica by removing the fly compound eye template at high temperature, and the alumina coating was crystallized simultaneously" Wang describes the experimental details. "The success of our replication was not only with the morphologies but also with the optical features – the unique antireflection property of the eye was also inherited by the alumina replica. By measuring the reflective spectra of the replica, we demonstrated that the alumina replica of a fly eye was an efficient antireflection structure of visible light at an incident angle up to 80°."
Wang says that the fly eye replica with antireflection structure exhibits great potential in the applications of optical coating, sensing or lens arrays. His group is now working on developing more sophisticated replication techniques for tuning the optical response of the structure in order to optimize the performance. http://www.nanowerk.com/spotlight/spotid=3744.php
at 1:57 PM
Monday, December 17, 2007
The National Institute of Standards and Technology (NIST) has developed an imaging system that quickly maps the mechanical properties of materials—how stiff or stretchy they are, for example—at scales on the order of billionths of a meter. The new tool can be a cost-effective way to design and characterize mixed nanoscale materials such as composites or thin-film structures.
The NIST nanomechanical mapper uses custom software and electronics to process data acquired by a conventional atomic force microscope (AFM), transforming the microscope’s normal topographical maps of surfaces into precise two-dimensional representations of mechanical properties near the surface. The images enable scientists to see variations in elasticity, adhesion or friction, which may vary in different materials even after they are mixed together. The NIST system can make an image in minutes whereas competing systems might take an entire day.
IMAGE: An atomic force microscope normally reveals the topography of a composite material (l.) NIST's new apparatus adds software and electronics to map nanomechanical properties (r.) The NIST system reveals that the glass fibers are stiffer than the surrounding polymer matrix but sometimes soften at their cores.
at 12:55 PM
World physical vapor deposition industry will be worth an estimated $9 bln in 2007 and $9.9 bln in 2008. It should reach $16.7 bln by 2013, a compound annual growth rate (CAGR) of 11% over the 5-year period, BCC Research says. The market is broken down into applications of PVD equipment, materials deposited and services. Of these segments, the PVD equipment will remain the largest market as shipments grow at CAGR of 9.6% to reach an estimated $7.1 bln in 2008 and then increase to $11.9 bln in 2013, at a CAGR of 10.9%. Materials deposited hold the second largest share of the market. Worth an estimated $1.3 bln in 2007, this segment is expected to be worth $1.5 bln in 2008 and $2.7 bln in 2013, a CAGR of 12.4% over the forecast period. The value of services will increase from $1.2 bln in 2007 to $1.3 bln in 2008, and will increase at a CAGR of 9.9% to reach $2.0 bln by 2013.
Thursday, December 13, 2007
Cymbet has announced commercial availability of its EnerChip thin-film battery products, the first commercial solid-state, highly rechargeable thin-film battery technology for the semiconductor industry. The solid-state battery can be integrated as an embedded device, or as a surface-mounted component.
Friday, December 7, 2007
A design of an implantable electronic device always takes into consideration the coating, as it is the only barrier that protects the gadget from fluids and from the natural immune responses of the body. Designing a protective coating for miniature electronics is an extremely difficult endevour. The silicon chip retinal implant is being developed by Second Sight, a company based in Sylmar, California, along with a consortium of university researchers. The device needs a hermetic case to prevent it from reacting with fluids in the eye. Researchers have developed an ultrananocrystalline diamond (UNCD) film that is guaranteed to be safe, long-lasting, electrically insulating and extremely tough. The coating can also be applied at low temperatures that do not melt the chip's microscopic circuits. The UNCD film is the first coating to meet all the necessary criteria for the implant, says Xingcheng Xiao, a materials scientist at Argonne National Laboratory, Illinois, who developed the film. The tiny diamond grains that make up the film are about 5 millionths of a millimetre across. They grow from a mixture of methane, argon and hydrogen passing over the surface of the five-millimetre-square chip at about 400 C. Xiao and his colleagues have already tested the implants in rabbits' eyes, and saw no adverse reaction after six months.
A new study reports that a laser can be used to switch a film of vanadium dioxide back and forth between reflective and transparent states without heating or cooling it. It is also among the most recent examples of “coherent control,” the use of coherent radiation like laser light to affect the behavior of atomic, molecular or electronic systems. The technique has been used to control photosynthesis and is being used in efforts to create quantum computers and other novel electronic and optical devices. The new discovery opens the possibility of a new generation of ultra-fast optical switches for communications. The study, which was published in the Sept. 18 issue of Physical Review Letters, was conducted by a team of physicists from Vanderbilt University and the University of Konstanz in Germany headed by Richard Haglund of Vanderbilt and Alfred Leitenstorfer from Konstanz.
Thursday, December 6, 2007
Martin Roscheisen, CEO of thin film solar company Nanosolar, founded the startup five years ago when solar was nowhere near the hot topic it is today. Sitting on a profoundly transformative new thin film solar technology and with great leadership, Nanosolar is the one to watch. Read the interview and be impressed. http://earth2tech.com/2007/07/30/10-questions-for-nanosolar-ceo-martin-roscheisen/
at 10:49 AM
Saturday, December 1, 2007
Diamond thin films are an extraordinary material with the potential to have enormous global economic impact. ThinFilmsBlog will be reporting on state-of-the-art diamond film technology and applications. It is significant that although the Diamondshield coating is relatively soft (2-3 GPa versus up to 75 GPa for non-hydrogenated, tetrahedral amorphous carbon: ta-C) this film none-the-less provides valuable benefit in this application. It shows how much room for improvement there still is for diamond film technology.
North American manufacturer of luxury mobile phones, Mobiado, is using a scratch-resistant coating on the front face of its exclusive Luminoso 3G phone. The new DiamondShield coating gives polycarbonate and acrylic screens a previously unattainable scratch-resistance that is comparable to glass, while maintaining the weight savings, impact resistance, formability and other benefits of plastic.
DIAMONEX produces Diamond-Like Carbon (DLC)and related coatings by both Ion Beam and RF Plasma CVD deposition processes operating under vacuum at substrate temperatures typically <150° C.
Thursday, November 29, 2007
Vacuum pumps can be broadly categorized according to three techniques:
Positive displacement pumps use a mechanism to repeatedly expand a cavity, allow gases to flow in from the chamber, seal off the cavity, and exhaust it to the atmosphere. Examples include: piston pump, diaphragm pump, liquid-ring pump, sliding vane rotary pump, miltiple-vane rotary pump, rotary piston pump, rotary plunger pump and roots pump.
Momentum transfer pumps, also called molecular pumps, use high speed jets of dense fluid or high speed rotating blades to knock gaseous molecules out of the chamber. Examples include: turbine pump, turbomolecular pump, liquid jet pump, vapor jet pump, diffusion pump and diffusion ejector pump.
Entrapment pumps capture gases in a solid or absorbed state. These include: absorption pump, sublimation pump, sputter-ion pump amd cryopump.
Positive displacement pumps are the most effective for low vacuums, but their high backstream flows through mechanical seals generally limit their usefulness in high vacuums. Momentum transfer pumps in series with positive displacement pumps are the most common configuration used to achieve high vacuums, but they stall at low vacuums. (Hence the need for a positive displacement pump in series.) Entrapment pumps can be added to reach ultrahigh vacuums, but they have a maximum operational time since they do not exhaust materials. They periodically saturate and require regeneration, which usually means bringing the system back up to higher pressures and temperatures. The available operational time is usually unacceptably short in low and high vacuums, thus limiting their use to ultrahigh vacuums. Pumps also differ in details like manufacturing tolerances, sealing material, pressure, flow, admission or no admission of oil vapor, service intervals, reliability, tolerance to dust, tolerance to chemicals, tolerance to liquids and vibration.
In most mechanical systems, friction or vibration are often considered to be negative attributes because they results in wear and unnecessary energy dissipation. Tribological issues such as friction, wear, and vibration have always plagued developers of small-scale mechanical devices. As devices get smaller and even reach the nanoscale, this problem becomes more acute due to the extreme surface-to-volume ratios these devices have. In nanomachines damage to even a single atom layer could mean disaster. Nanotechnology researchers basically have two ways to address this problem: they either could apply traditional tribological methods by trying to integrate dampers and low-friction materials with their nano- and microdevices - which becomes increasingly complex and costly at the nanoscale - or they could try and develop intrinsic damping materials that have hard, low-fiction surfaces to lower wear yet still maintain high compressibility and elastic properties to provide resistance to vibrations and shocks. Finding materials that address these problems individually is not difficult but fabricating a structure that combines all of them is nearly impossible because of the conflicting nature of these attributes. However, in what researchers have dubbed a 'nanomattress', a unique structure containing aligned carbon nanotubes (CNTs) covered with a hard layer of diamond-like carbon (DLC) results in a carbon-based composite material with outstanding mechanical properties.
The hybrid film was prepared by first growing a dense, vertically aligned, multi-walled CNT network (CNTs are ca. 7 µm long with 200 nm diameters) by thermal chemical vapor deposition (CVD) on a conductive silicon substrate. The prepared sample was then placed in a patented, off-plane, double-bend, filtered cathodic vacuum arc PVD system with substrate pulse biasing to deposit a 5 µm a-D film on the surface of the CNTs. In order to confine the coating to the top of the CNT film and prevent it from seeping through, a negative substrate pulse bias was used. Because of the negative voltage pulse on the CNT substrate, the high-energy positive carbon ions were attracted primarily to the tips of the CNTs, forming a-D nanospheres. As these spheres increase in size, they coagulate into a thick, solid a-D film on top of the CNTs. The top layer that formed in this manner adhered very well to the tips of the CNTs, as the carbon ions formed strong covalent C–C bonds to them. With a hard, solid top, the nanomattress is now capable of distributing the forces applied to it uniformly to the underlying CNTs, which act like the springs of a mattress.
This information was derived from: http://www.nanowerk.com/spotlight/spotid=3453.php
Monday, November 26, 2007
Tribology, the study of the friction and wear of materials, comes from the Greek word, tríbein, meaning to rub. The first tribological coating for controlling friction and wear was titanium carbide (TiC), introduced in 1969 on cemented carbide cutting tool inserts using chemical vapor deposition (CVD). The problem with the CVD process was that the substrate temperature during deposition was about 1000ºC so that CVD could not be used to coat high speed steel tooling, which is softened at those temperatures. To overcome this obstacle, workers began using physical vapor deposition (PVD) techniques that provide ion bombardment of the growing film, resulting in good film adhesion and densification of the film.
The first commercially successful PVD hard coating was titanium nitride (TiN). Balzers deposited it with their low voltage electron beam process, Ulvac with their hot hollow cathode process, and Multi-Arc with their cathodic arc process. Since the cost of the arc coating equipment was less than that of competing deposition processes, the cost of the arc coatings was lower, and the use of cathodic arc deposited hard coatings became widespread.
Initially, sputtering was not used for the commercial deposition of the tribological films because the quality of the films did not equal that of films produced by low voltage electron beam or cathodic arc methods. This situation was significantly improved with the introduction of closed-field unbalanced magnetron sputtering that provided for a higher degree of substrate ion bombardment during deposition.
One of the early themes in PVD tribological coatings was that high hardness was the most important property. It is true that a coating used for a machining application must be hard, but it is now understood that a coating should be both hard and ductile if it is going to perform well in a tribological application. Superlattice, multilayer, nanostructured, MAX phase, and carbon nitride (a form of diamond-like-carbon (DLC) film) coatings have succeeded in achieving a measure of success in providing both hardness and ductility.
Many DLC films are produced by PVD techniques including cathodic arc, filtered cathodic arc, sputtering, reactive sputtering, and low pressure CVD, and plasma assisted or plasma enhanced CVD processes. The hardness of DLC films covers the range from hard to superhard with hardness of 20-80 GPa. Whereas hard coatings such as titanium nitride, titanium aluminum nitride, and multilayer films have been used very successfully for tooling applications, the DLC films have been very successful where low friction and low wear are needed such as on gears and bearings.
There are two areas that will be very important for the future of tribological coatings. The first of these is nanolayered and nanocomposite coatings, which have already had a major impact on tribological coatings. Another area that should have a major impact on tribological coatings is the use of ionized PVD. Here the recent introduction of high power pulse magnetron sputtering (HPPMS) is used to provide a high degree of ionization of the sputtered material, improving the quality of the coatings and allowing the deposition of films that previously could not be done with conventional sputtering.
Most of this information was obtained from an article by William Sproul on page 46: http://online.qmags.com/SVC1007/
Thursday, November 22, 2007
Thin film photovoltaics, using inorganic or organic compounds as active layers, represent the most promising technology for significantly beating the cost of conventional solar amorphous or crystalline silicon electrical systems. These technologies have the potential to provide low cost, ac mains solar power by using non-silicon solar cells and low cost plastic substrates. Traditional silicon cell manufacturers have been constrained by the shortage of silicon, high prices of silicon, its weight and fragility and the difficulty of processing it.
See the table at right for more detail on the different types of thin film photovoltaic technologies including CIGS, DSSC and CdTe. These companies are doing extraordinary things with various thin films techniques, usually roll-to-roll (thin film vacuum coating or thin film ink-jet printing).
IDTechEx finds that the market for thin film photovoltaics beyond silicon will reach at least $1 billion in 2012 after a slow ramp up and grow rapidly after that to $6 billion in 2014. The global solar energy market is expected to reach $34 billion in 2010 and $100 billion in 2050 and most of that latter figure will be achieved by non-silicon photovoltaics. The market for printed batteries will reach $170 million in 2012 and $560 million in 2014. www.idtechex.com/power
Wednesday, November 21, 2007
The commercial acceptance of hard coatings for cutting tools is driven by demands on machining productivity, environmental mandates, and increased usage of new difficult-to-cut materials. Improved cutting performance is derived from synergies of machine tool system and cutting tool development. The latter strives for an optimized combination of tool material, hard coating and cutting edge geometry.
The integration of hard coatings in cutting tools has reached a mature stage after more than three decades of proven performance and productivity benefits in industrial metal cutting. Chemical vapor deposition (CVD) was the first technology used, which advanced from single layer to current multilayer types combining TiC, TiN, TiCN and Al2O3. Some 25 years later it is evident that novel physical vapor deposition (PVD) compositions have surpassed the limited set of available CVD coatings. The relative economics are debatable but it is accepted that total life cycle consideration and environmental friendliness favor PVD technology. Succeeding generations of PVD hard coatings have become commercially available, notably TiCN, TiAlN and AlCrN, with demonstrated success in expanding areas of application.
Intensive development of the superhard coatings diamond (diamond-like-carbon DLC) and cubic boron nitride (CBN) peaked in the 90’s. It seems that an insurmountable technical barrier – extremely high residual stress during deposition – has not been overcome and still prevents successful commercialization.
In mulitlayer coatings, particular properties suitable to the cutting wear conditions can be engineered by creative combinations of coating layers. For example, AlCrN-TiSiN performs well in high speed carbide drilling of 1045 steel. Although AlCrN has low thermal conductivity, it has been shown that the multilayer construction with TiSiN which has high thermal conductivity effectively raises the composite conductivity, minimizing the heat concentration at the critical drill outer corner. This apparently accounts for better performance of certain multilayer coatings with carbide drills. Another example is the TiAlN-WC/C coating designed for drills used for dry machining.
The figure: coating selection guide based on field performance and commercial acceptance.
An excellent historical overview of the development of PVD coatings leading up the latest innovations written by Dennis Quinto. Jump to page 17 for more... http://online.qmags.com/SVC1007/
Monday, November 19, 2007
Advances in thin films technologies are transforming traditional manufacturing processes and whetting the appetite of industry.Multiple new techniques in thin films technology are vying for supremacy in two rapidly growing sectors—microelectromechanical systems (MEMS) and highly-efficient photovoltaic systems.
Silicon wafer-based cells may soon give way to a new generation of thin film photovoltaics. According to The Information Network, a New Tripoli, Pa.,-based market research company for the semiconductor industry, manufacturing methods using cadmium telluride, CdTe, and copper indium gallium selenide, CIGS, will see a tremendous boost in research dollars for future equipment manufacture. A 275% increase in investment by 2010 is expected, which is a testament to their anticipated impact.CIGS and CdTe rely on the deposition of nanoparticles of the precursor materials on the substrate, followed by in-place sintering. The U.S. Dept. of Energy's National Renewable Energy Laboratory, Golden, Colo., says the best CIGS cell now matches the efficiency of the best polycrystalline-silicon cell, about 19.5% efficiency. Potential applications include newspaper-like roll-to-roll printing and CIGS-based inks.
Jump for more...