James F. Groves

Functionally graded materials synthesis via low vacuum directed vapor deposition

The spatially distributed microstructures needed to implement many functionally graded material (FGM) designs are difficult to realize affordably with todays materials synthesis/processing technologies. To address this need, a new directed vapor deposition (DVD) technique has been developed and explored as a potential FGM synthesis tool. The technique exploits supersonic helium jets in combination with electron beam/resistive evaporation under low vacuum (10−3-10 Torr) conditions to atomistically spray deposit a wide variety of monolithic and composite materials. Two of the most important processing parameters (the carrier gas velocity and the deposition chamber pressure) that control deposition are identified, and their effect upon deposition efficiency for flat and fiber substrates is explored systematically. Under certain conditions, the DVD approach is found to deposit vapor onto fibers with a significantly higher efficiency than traditional high vacuum line-of-sight vapor deposition techniques. It can even deposit material onto surfaces that are not in the line-of-sight of the source. A computational fluid dynamics model has been used to interpret the experimental observations and to identify the role of carrier gas dynamics in controlling deposition efficiency and spatial distribution.

Fiber fracture during the consolidation of metal matrix composites

Abstract A detailed study of conditions leading to fiber fracture during the consolidation of Ti14wt%Al21wt%Nb/SiC (SCS-6) composite monotapes has been conducted. For this continuous fiber reinforced composite system, the incidence of fracture increases with consolidation rate at higher process temperatures. Increasing consolidation temperature at a fixed pressure reduces the number of breaks per unit length of fiber. Examination of partially densified compacts has revealed the existence of significant fiber bending and ultimately fracture due to monotape surface roughness (asperities) which places the fibers in three point bending. A representative volume element has been defined for the consolidating lay-up and its response analyzed to predict the fiber deflection (and hence probability of failure) when the surface asperities deform either by plasticity or by steady state creep. The relationships between fiber fracture and process conditions predicted using the volume element are similar to those observed experimentally. The cell analysis suggests that fiber fracture is decreased by increases in fiber stiffness, strength, and diameter and by decreases in matrix yield and creep strength and monotape surface roughness.

Focused-ion-beam directed self-assembly of Cu2O islands on SrTiO3(100)

Nanoscale islands of Cu2O have been synthesized on single-crystal SrTiO3 (100) substrates using oxygen plasma-assisted molecular-beam epitaxy (MBE). Island growth location has been controlled by using an ex situ Ga+ focused ion beam (FIB) to modify the growth surface in discrete locations prior to island synthesis. The FIB modifications have generated surface topography with lateral dimensions of 150–200nm. Ex situ atomic force microscopy study after island growth reveals that certain FIB substrate modification and MBE growth condition combinations lead to directed self-assembly of metal oxide islands at the edges of the FIB modified zones.

Societal dimensions of nanotechnology

The United States Congress is currently refining the details of a Nanotechnology Research and Development Act. In contrast to the earlier investments, this new Act specifically calls for a focus on the societal and ethical implications of nanotechnology (SEIN). The Advocates of SEIN studies point to the difficult reception for genetically-modified organisms (GMOs), a technology that promised a new green revolution but encountered resistance in Europe, Canada, and other parts of the world.

Reactive vapor deposition of metal oxide coatings

The reactive deposition of metal oxide coatings has been achieved using an electron beam directed vapor deposition (DVD) approach. In this approach, a transonic helium carrier gas jet has been combined with electron beam evaporation to create and efficiently transport metal vapor to a substrate. Metal oxide coatings were then produced by adding oxygen to the carrier gas. The synthesis of multi-component oxide coatings could be achieved using either an alloy source or by simultaneous evaporation of metals from two or more sources. In the latter, the reactive carrier gas jet was used to facilitate vapor phase mixing of the evaporated fluxes. The preferred approach was found to be dependent on the vapor pressures of the individual source components. When large differences between the component vapor pressures exist, multi-source evaporation is preferred. Results are reported for the reactive deposition of zirconia from a single metal source and reactive deposition of yttria stabilized zirconia from two metal sources (Y and Zr). The phase and morphology are similar to those found in similar coating compositions created by the evaporation of a pre-compounded oxide. Very good compositional uniformity in the binary metal oxide films has been observed. Vapor transport modeling is used to explore the origin of the composition uniformity.

Formation of Cu2O quantum dots on SrTiO3 (100): Self-assembly and directed self-assembly

Cu2O quantum dots (QDs) have been synthesized on single crystal SrTiO3 (100) substrates with focused ion beam (FIB) modification using oxygen plasma-assisted molecular beam epitaxy. In a set of experiments, QD growth location has been controlled using FIB implants to modify the growth surface in discrete locations prior to dot synthesis. Atomic force microscopy has been used to characterize this directed self-assembly of oxide QDs. QDs have been observed to form first in the FIB generated surface features, filling those features before additional QDs have nucleated on neighboring, unmodified surface regions. The nature of the QDs on the modified surface is compared to those grown on unmodified substrate regions. While FIB modification provides lateral control over QDs, the QDs formed on the undamaged surfaces were more uniform in shape and size than those that nucleated in the FIB produced pits.

Reactor-scale models for rf diode sputtering of metal thin films

This article describes the development of an integrated physical model for the rf diode sputtering of metal thin films. The model consists of: (1) a computational fluid dynamic finite element model for the velocity and pressure distribution of the working gas Ar flow in the chamber, (2) a steady-state plasma model for the flux and energy of Ar ions striking the target and the substrate, (3) a molecular dynamics sputtering model for the energy distribution, angle distribution, and yield of the sputtered atoms (Cu) from the target, and (4) a direct simulation Monte Carlo (DSMC) model for the transport of Cu atoms through the low-pressure argon gas to the deposition substrate. The individual models for gas flow, plasma discharge, Cu sputtering, and DSMC-based Cu atom transport are then integrated to create a detailed, steady-state, input–output model capable of predicting thin-film deposition rate and uniformity as a function of the process input variables: power, pressure, gas temperature, and electrode spa...

A tablet-based paper exam grading system

We present the design and implementation of a system which allows a standard paper-based exam to be graded via tablet computers. The paper exam is given normally in a course, with a specialized footer that allows for automated recognition of each exam page. The exam pages are then scanned in via a high-speed scanner, graded by one or more people using tablet computers, and returned electronically to the students. The system provides many advantages over regular paper-based exam grading, and boasts a faster grading experience than traditional grading methods.

Multiscale Simulations of the RF Diode Sputtering of Copper

The morphology and microstructure of RF diode sputter deposited materials is a complicated function of many parameters of the reactor operating conditions. Using a combination of computational fluid dynamics (CFD), RF plasma, molecular dynamics (MD) sputter, and direct simulation Monte Carlo (DSMC) transport models, a multiscale approach has been used to analyze the RF diode sputtering of copper. The CFD model predicts the velocity and pressure distribution of the working gas flows in the deposition chamber. The plasma model uses these CFD results to compute ion energies and fluxes at the target and substrate. The MD model of sputtering is used to determine the initial energy distribution of sputtered atoms and reflected neutral working gas atoms and both of their angular distributions. A DSMC transport model then deduces the target atom deposition efficiency, the spatial distribution of the film thickness, the target and reflected neutral atoms energy and impact angle distributions given reactor operating input conditions such as background pressure, temperature, gas type, together with the reactor geometry. These results can then be used in atomistic growth models to begin a systematic evaluation of surface morphology, nanoscale structure, and defects dependences upon the reactor design and its operating conditions.

The Virginia partnership for nanotechnology education and workforce development

The University of Virginia (UVA) has partnered with universities in Virginia for the sharing of graduate nanotechnology courses by distance learning technology. With the other schools, UVA has developed a four semester sequence of shared courses. The program provides students at the schools and at companies with access to a broader set of nanotechnology course offerings than previously available. The program shares several types of courses. Some courses were previously available only to students at one institution because the only faculty expert was resident there. Some courses were previously common at all institutions but consuming significant faculty resources, with faculty teaching just a few students at their institution. Now, new courses are being developed, team-taught courses are being offered, and fully on-line courses are becoming available. While opening educational opportunities, this program has challenged the participants. Faculty are being asked to alternate teaching assignments with colleagues at other institutions. Departments are being asked to accept instruction from faculty at neighboring institutions. On-campus students are being asked to take classes offered over the commodity Internet. Working engineers are grappling with the challenge of taking graduate courses while working full time jobs. These challenges and some proposed solutions will be discussed.