Two new research programs are supported by the US National Science Foundation
Lithiation and Sodiation
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This exciting new collaboration is with co-PIs Avinash Dongare (MSE, UConn) and Arthur Dobley of the Yardney Division of EaglePicher LLC. We are also collaborating with colleagues at LANL and Sandia NL, using the Titan ETEM for in-situ studies of reactions. Avinash is carrying out MD and DFT calculations. Arthur and his colleague Christine are advising on the challenges for energy storage. Matt Janish who started this project during his Ph.D. thesis is now a staff member at LANL. The program officially begins on July 1, 2018.
See: Janish MT, Carter CB (2015) Scripta Mater 107, 22–25 ‘In-Situ TEM Observations of the Lithiation of Molybdenum Disulfide’. and of course...... Carter, C.B. and Williams, P.M., 1972, Philos. Mag. 26(2), 393-398. 'An Electron Microscopy Study of Intercalation in Transition Metal Dichalcogenides.' |
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Phase-Change Materials
Our exciting new collaboration with Helena Silva (left) (ECE Department at UConn) and IBM (Yorktown Heights) on PCMs began on July 1, 2017 with support from NSF through the GOALI program. Research is currently underway in CINT through a CINT User Proposal. Dr. Shalini Tripathi (right) graduated from Prof. (Ravi) Ravishankar's group in IISc Bangalore and joined the project in December 2017.
Click the link to see more of Helena's activities . |
Defects in Ta and Related Metals
Another exciting collaboration, again with Avinash Dongare is being explored: the topic is the study of defects in bcc metals. This work will build on two recent papers:
Janish MT, Kotula PG, Boyce LB, Carter CB (2015) J Mater Sci 50, 3706-3715 ‘Observations of fcc and hcp tantalum’.
Janish MT, Mook WM, Carter CB, (2015) Scripta Mater 96, 21-24 ‘Nucleation of face-centered cubic Ta when heating thin films’.
and a long history of studying dislocations in many different materials.
Janish MT, Kotula PG, Boyce LB, Carter CB (2015) J Mater Sci 50, 3706-3715 ‘Observations of fcc and hcp tantalum’.
Janish MT, Mook WM, Carter CB, (2015) Scripta Mater 96, 21-24 ‘Nucleation of face-centered cubic Ta when heating thin films’.
and a long history of studying dislocations in many different materials.
A Brief Carter Research History
I began in 1971 at Imperial College with a study of intercalated layer materials - using the tape-pealing technique to make TEM specimens. These first observations were reported in Philos. Mag. with my MSc advisor Peter Williams in 1972. The main feature of my D.Phil. thesis at Oxford was the use of the weak-beam technique for studying defects in metals. Key papers from this time are those on the stacking-fault energies of copper alloys and Ni, those on in-situ observations of the climb and formation of jogs on dissociated dislocations, faulted dipoles (they are much more numerous than people knew before WB) and double ribbons (which tell us both the intrinsic and extrinsic stacking fault energies of a material. At Cornell my research emphasized the application of diffraction techniques to grain boundaries, solid-state reactions in oxides and defects in semiconductors. At Minnesota, the latter two topics were continued and nanoparticle research added. I now started to use in-situ studies to understand the behavior of nanoparticles and have continued this at UConn. At UConn I have collaborate with colleagues on energy materials, fibers, biomimetics for ceramics and more nanoparticles.
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Our groups Park XE-70 AFM was checked by Phani Kondapani after we moved to our second-floor lab and found to be exceeding specifications. Left are John Corsi, Kerry Davis and Aaron Gladstein preparing for some resolution tests on an alumina specimen.
This paper used our AFM: Bhowmick, S., Xue, Y., Winterstein, J. and Carter, C.B., 2011 Sol. St. Ionics 187, 68–77 'Influence of Alumina Impurities on Microstructure of LSM-CeO2 Composites'. The instrument was initially installed by our former student Dr. Nicole Munoz: Munoz, N.E., Gilliss, S.R. and Carter, C.B., 2004, Surface Sci. 573, 391-402, 'Remnant Grooves on Alumina Surfaces.' and Munoz, N.E., Gilliss, S.R. and Carter, C.B., 2004, Philos. Mag. Lett. 84(1) 21-26, 'The Monitoring of Grain-Boundary Grooves in Alumina.' |
John Corsi is now a Ph.D. student at UPenn, Kerry Davis work at Pratt and is a Ph.D. student at UConn, while Aaron Gladstein is a Ph.D. student at UMich
Projects that are always interesting
Defects in GaNs & Other III-Vs
GaN is arguably the most exciting development in electronic materials in the past 20 years. The material can be grown by several different methods but in all cases the GaN contains a large density of dislocations. Part of the reason for this high density of defects is the fact that, at present, there exists no ideal substrate for the epitactic growth of the III-V nitrides. Therefore, the material is generally grown on sapphire, SiC, GaAs, or Si substrates. The epitactic relationship between the various substrate orientations and the nitride films is well established. The best epitaxy for GaN on sapphire is obtained using the (0001) sapphire surface. However, neither the lattice parameters nor the coefficients of thermal expansion between the nitrides and their substrate materials match. Hence, most epitactic nitride films are strained and defects are invariably present.
GaN and related nitrides have been used successfully in spite of the high concentrations of defects present. If a cubic compound semiconductor contained a thousandth of this number of defects, the lifetime of any device made with such a material would make it valueless. However, the reason that such defects can be benign is not well understood and there is often disagreement on what the defects actually are. History shows us that it is best to understand such benign defects since we may (and already do) wish to use such materials in situations where their presence will be undesirable. Our research interests include the systematic study of dislocations and interfaces in in GaN.
GaN and related nitrides have been used successfully in spite of the high concentrations of defects present. If a cubic compound semiconductor contained a thousandth of this number of defects, the lifetime of any device made with such a material would make it valueless. However, the reason that such defects can be benign is not well understood and there is often disagreement on what the defects actually are. History shows us that it is best to understand such benign defects since we may (and already do) wish to use such materials in situations where their presence will be undesirable. Our research interests include the systematic study of dislocations and interfaces in in GaN.
Grain Boundaries and Interfaces
We have worked on interfaces in metals, ceramics and semiconductors using imaging and diffraction in the TEM. The common theme is understanding how the chemistry and structure influence the way interfaces move. When interfaces between grains of the same structure and composition move in a solid polycrystal (where 'poly' might just mean 'bi'), the materials will undergo grain growth and probably sintering. When the grains do not have the same structure or the same chemistry, then a phase transformation is taking place. The examples we have concentrated on are solid-state reactions. We have also studied situations where one of the 'grains' is amorphous or glassy. The two situations overlap when the grain boundary actually contains a layer of glass along the interface.
Interface Migration in Ceramics
This project concerns a detailed investigation of interactions between glass and oxide ceramics at high temperatures. The experimental approach uses controlled geometries and employs a combination of advanced microscopy techniques. Glass/oxide interactions play a critical role in the processing of ceramics by liquid-phase sintering. The alumina/anorthite system is chosen as representative of a system which is commonly present in commercial materials. At high temperatures the glass is liquid. Wetting of the ceramic by the liquid, mass transport in the presence of a liquid, and penetration/exudation of the liquid from a dense ceramic are therefore key basic issues that must be addressed. Bicrystals and tricrystals containing an intergranular glass layer are manufactured by hot-pressing glass-coated single crystals to clean single crystals and provide model geometries for grain boundaries and triple junctions in polycrystalline materials. The bicrystal/tricrystal assembly is annealed at temperatures where the intergranular glass forms a liquid. Conditions under which the intergranular liquid moves from the interior of the sample to the free surface have been established. The dependence on temperature of boundary-wetting parameters and the free-surface wetting parameters can be examined for different grain boundary geometries. Grain boundary migration only takes places when the bounding planes are crystallographically dissimilar.
Polishing Glass & Glass Ceramics
Polishing is a critical process in the manufacture of many products including lenses, substrates, screens, optical fibers and planarized devices. Polishing implies the smoothing of a surface. This is usually achieved by a combination of chemical and mechanical means and is thus known as chemical/mechanical polishing (CMP). In general, CMP is not well understood and special procedures are developed for each application which can make it difficult to extend the process to new materials.
The most promising polishing compounds are formulations based on ceria. Ceria is extensively used for polishing glass and can polish glass-ceramic precursors. Polishing compounds are rarely pure ceria, although there is disagreement in the literature as to the importance of the presence of other oxides to the effectiveness of the polishing compound. The program will use different formulations of ceria and related oxides which are available commercially or will be prepared in our lab.
Polishing is a critical process in the manufacture of many products including lenses, substrates, screens, optical fibers and planarized devices. Polishing implies the smoothing of a surface. This is usually achieved by a combination of chemical and mechanical means and is thus known as chemical/mechanical polishing (CMP). In general, CMP is not well understood and special procedures are developed for each application which can make it difficult to extend the process to new materials. It is proposed to study the CMP of glass-ceramics. This research will build on a small ongoing research program concerned with the CMP of glass.
One model for CMP of glass by ceria involves the formation of a new layer of silica which is actually deposited from the polishing slurry as other material is removed. A second model is that during polishing, the polishing compound actually bonds to the sample being polished and that subsequent polishing causes separation inside the glass rather than at the bonded interface. Clearly, these processes, if generally necessary and/or applicable, will depend not only on the slurry but also on the structure and chemistry of the material being polished. The polishing medium may be supplied as a slurry or as a fixed abrasive. We will use both approaches.
The most promising polishing compounds are formulations based on ceria. Ceria is extensively used for polishing glass and can polish glass-ceramic precursors. Polishing compounds are rarely pure ceria, although there is disagreement in the literature as to the importance of the presence of other oxides to the effectiveness of the polishing compound. The program will use different formulations of ceria and related oxides which are available commercially or will be prepared in our lab.
Polishing is a critical process in the manufacture of many products including lenses, substrates, screens, optical fibers and planarized devices. Polishing implies the smoothing of a surface. This is usually achieved by a combination of chemical and mechanical means and is thus known as chemical/mechanical polishing (CMP). In general, CMP is not well understood and special procedures are developed for each application which can make it difficult to extend the process to new materials. It is proposed to study the CMP of glass-ceramics. This research will build on a small ongoing research program concerned with the CMP of glass.
One model for CMP of glass by ceria involves the formation of a new layer of silica which is actually deposited from the polishing slurry as other material is removed. A second model is that during polishing, the polishing compound actually bonds to the sample being polished and that subsequent polishing causes separation inside the glass rather than at the bonded interface. Clearly, these processes, if generally necessary and/or applicable, will depend not only on the slurry but also on the structure and chemistry of the material being polished. The polishing medium may be supplied as a slurry or as a fixed abrasive. We will use both approaches.
Nanoparticles
As integrated circuits scale into the nanometer range, numerous problems arise including gate insulator and junction scaling, and power budgeting. Perhaps the most pervasive problem, however, is interconnect. The number of interconnections is increasing faster than the number of devices. IC manufacturers have gone to many layers of low k / Cu stacks, however, these approaches only delay the inevitable. The smaller the device, the more that performance, density, and yield are interconnect limited. Unless one is willing to impose draconian limits on circuit designers (such as nearest neighbor connections only), conventional FET performance will saturate at about the 30 nm node. Exotic device structures such as coulomb blockade and other single electron devices have significant disadvantages when it comes to charging device interconnect. So-called fat tree approaches espoused by some in the mole cular electronics community overcome a poor device yield only to exacerbate the interconnect problem. Furthermore, digital speeds have led to serious problems associated with propagating RF signals above the lossy silicon substrate. At a system level, the problem is that chips run internal clocks approaching 3 GHz (2.4 GHz will be released by Intel later this year) while board speeds are only a few hundred MHz. This faster chips provide little real advantage. We propose a radical new approach to the fabrication of electronic and optoelectronic systems: the use of single crystal nanoparticles. It is well known that one can create particles of silicon and other solid materials in the gas phase by homogeneous nucleation. By controlling the process conditions, one can create particles from a few nm up to several hundred nm in diameter (Figure 2). This is the range of sizes of single crystal islands that one would need to build nanodevices. A critical piece of technology for this work was developed at the University of Minnesota in the 1990's. Called an aerodynamic lens, the system allows one to focus particles in an aerosol into a narrow beam that can be sent through a small orifice. This separates the particles from their nucleation and growth ambient. By creating an aerosol of nanoparticles in an arbitrary ambient, one can anneal, dope, oxidize, and perform other high temperature processes with an unlimited thermal budget, then deposit them on a low temperature substrate. Using a nano DMA, which was also developed at the University, one can size select the particles to a standard deviation of about 1% of the mean particle diameter.
Our work with Alex Agrios and Radenka Maric on nanoparticles has now been published and may continue in the future.
Our work with Alex Agrios and Radenka Maric on nanoparticles has now been published and may continue in the future.
Solid State Reactions in Oxides
This research began with a close collaboration with Prof. Hermann Schmalzried author of 'the book'. Although it is a critical topic in much of ceramic processing, we are not continuing this work at this time.
Surfaces: Semiconductors and Metals, but mainly Ceramics
Our favorite materials are alumina, spinel and MgO. Several of the groups most highly cited papers are concerned with surfaces. The papers include not only the use of TEM and WFM to study surfaces but also, through collaborations with colleagues at Sandia, the use of STM and LEEM.
Ceramic Fibers
This is the topic where we have concentrated research in the past and continue at a lower level with Prof. Chris Cornelius at the U of Nebraska.