Thursday, July 17, 2008

Water, not Graphite, Makes Diamond Slippery

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

Friday, June 20, 2008

Diamond Films from Tequila!

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 ( "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."

Tuesday, June 17, 2008

Diamond films: The Biomaterial of the 21st Century

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.

Tuesday, May 20, 2008

The Photonic Beetle: Nature Builds Diamond-Like Crystals

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.

Friday, April 25, 2008

Nano-Coating Replaces Cylinder Liners for Advanced Engines

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.

Thursday, April 10, 2008

Diamond Like Carbon for Data and Beer Storage

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.

Tuesday, March 25, 2008

DLC on the Inside of Pipes: an Important Advance

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.

Thursday, March 13, 2008

Biomimic Nanocomposite Strong, Light, and Stretchy

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.

Tuesday, February 26, 2008

The Ultimate Deposition Source?

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 ( 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 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

Filtered Cathodic Arc PVD

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

PVD Diamond Like Carbon Thin Films

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 ( 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

Ultrananocrystalline Diamond Thin Films Applications

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.

The second important application area for UNCD is as a structural material in MEMS, including AFM probes, RF MEMS filters, oscillators and switches. These applications leverage the greatest number of diamond's superlative bulk and surface properties, since the performance and long-term stability of MEMS devices depend on the chemical stability of the exposed surface. For RF MEMS, such as resonators, UNCD acts like a tuning fork, vibrating at a set frequency that cannot vary with time, temperature or other environmental conditions. UNCD, like natural diamond, has a chemically inert, hydrophobic, low stiction surface that allows devices to function without the need for expensive die-level hermetic packaging.
By leveraging the high acoustic velocity and surface stability of UNCD, devices for X- and Ka-band (2-20 GHz) wireless communication systems can be developed that allow for smaller, more energy efficient and less expensive RF front-ends for radios in mobile phones, base stations and military applications. UNCD-based atomic force microscopy (AFM) probes,· which are simple forms of MEMS devices, entered the market in late 2007.
The third application area includes bio-implants and sensors, with the goal of creating functional devices that integrate both passive and active UNCD elements combining diamond's bio-inertness and bio-compatibility with the ability to covalently immobilize biomolecules on the surface (see Figure 5). Active electrochemical-based sensors using conductive UNCD thin films can enable implantable devices that conduct real-time monitoring of blood chemistry (e.g., glucose, alcohol, cholesterol). This advancement will enable a new generation of biosensors that work in real-time in devices that are both compact and light enough to wear as jewelry. Imagine the life-changing and potential life-saving impact of wearing a "watch" that automatically monitors and administers insulin continuously via a wireless link to an implanted UNCD-based biosensor. Such biomedical applications will take additional effort to overcome many fundamental technical challenges. However, diamond has finally come of age in a platform technology suitable for broad integration into numerous applications, and UNCD is being developed into commercially available products to turn the idea of diamond for use as an engineering material into a reality. See previous post for more on UNCD.

Monday, February 4, 2008

Ultrananocrystalline Diamond Thin Films Advance

Left: UNCD deposited onto a 200 mm silicon wafer shown on top of an uncoated wafer. Right: High-resolution transmission electron microscopy image of UNCD thin film showing nano-sized grains.

Thin film diamond chemical vapor deposition (CVD) technology was developed about 30 years ago. Despite advances over the years, CVD diamond has failed to meet lofty industry expectations based on the perfection of natural diamond. Instead of becoming the material of choice for demanding applications, thin film diamond has been commonly referred to as the material of last resort; engineers consider CVD diamond only if every other commercial material fails to do the job.
In addition to cost, a number of technological problems, such as poor reproducibility, lack of mature deposition technology, relatively small deposition areas and poor film properties, have restricted the application of thin film diamond to cutting tools, heat sinks and other niche markets. Over the past two decades, research at Argonne National Laboratory led to the discovery of ultrananocrystalline diamond (UNCD®), a new technology that overcomes previous limitations related to thin film diamond. Advanced Diamond Technologies (ADT) was formed in 2003 to commercialize the ultrananocrystalline diamond technology developed at Argonne National Laboratory.
The UNCD innovation is rooted in the chemistry used to synthesize the material. In the past, the growth chemistries used to synthesize pure CVD diamond resulted in rough films characterized by very large diamond grains (microns in size) and weak, low-angle grain boundaries. These large-grained, microcrystalline diamond (MCD) films were nearly impossible to integrate with other materials. Efforts to develop smoother films led to work on nanocrystalline diamond (NCD). Argonne researchers discovered that by adding argon gas, along with methane and hydrogen, to the vapor mixture, the radicals generated during growth changed and yielded diamond films consisting of approximately 5 nanometer grains without any graphitic phases (i.e., phase-pure, diamond-bonded carbon with high-energy, atomically abrupt grain boundaries).
Since 5 nm grain UNCD is phase-pure, diamond-bonded carbon, it retains the desirable characteristics of natural diamond, including hardness, modulus, refractive index, acoustic velocity and surface chemistry. UNCD's electronic, thermal and optical transport properties, however, are different from natural diamond. It also has a low thermal conductivity compared to single crystal diamond (10-20 vs. ~2200 W/m°K) and is not optically transparent. From an electronic structure point of view, UNCD has diamond's bandgap (5.5 eV), but the bonding states within the grain boundaries create a material that is more electrically conductive with lower electron mobility. UNCD features a number of unique properties, including low as-deposited film roughness, low stress, higher fracture toughness and higher strength compared to natural diamond. Unlike previous NCD technologies, UNCD films can be grown at lower temperatures (400°C compared to 600-900°C). All of these differences result in a thin film diamond that can be easily integrated with other materials, such as other thin film technologies that are the basis for microelectronics and microelectromechanical systems (MEMS). More on UNCD applications coming soon.

Friday, January 11, 2008

NIST's new approach to surface profiling

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.

Monday, January 7, 2008

Hard Thin Films are Important

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.
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Friday, January 4, 2008

Science as Art

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)

Red Planet: Combined 3-D representation of two images taken by scanning tunneling microscopy. The land is from an STM image of one monolayer of HATNA deposited on Au(111), and the sky is from an image of THAP/Au(111) exposed to a high background pressure of cobaltocene. (Image: Sieu Ha, Princeton University, Princeton, USA)
Beauty of Nature: SEM image of CuInSe2 film with Cu2Se (plates) and InSe (needles) crystals on the surface. (Image: Olga Volobujeva, Tallinn University of Technology, Tallinn, Estonia)

Thursday, January 3, 2008

Thin Film Solar Power - Cheaper than Coal?

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.