Model for Dopant and Impurity Segregation During Vapor Phase Growth.

We propose a new kinetic model for surface segregation during vapor phase growth that takes into account multiple mechanisms for segregation, including mechanisms for inter-layer exchange and surface diffusion. The resulting behavior of the segregation length shows temperature and velocity dependence, both of which have been observed in experiments. We compare our analytic model to experimental measurements for segregation of Phosphorus in Si(001), and we find an excellent agreement using realistic energies and pre-exponential factors for kinetic rate constants.Engineering and Applied Science

Stoichiometry Issues in Pulsed Laser Deposition of Alloys Grown from Multicomponent Targets

We have examined the degree of congruent transfer in pulsed-laser deposition (PLD) of alloy thin films in phases that are stable over a wide range of compositions. SiGe films were deposited by PLD onto high-purity glassy carbon substrates. We analyzed the average composition of these films using Rutherford backscattering spectrometry (RBS), and results show that the deposited films have a higher relative concentration of Ge than the initial targets. We infer that the noncongruent transfer is due to differential scattering in the plume itself. Additionally, the local composition of the particulates was measured by the use of microprobe analysis, and observations of a sintered target of Si and Ge powders and a solidified target of melted Si and Ge were compared. We found that the sintered target produces particulates with a wide range of compositions, whereas the solidified target produces five times fewer particulates with a tighter distribution of compositions. In contrast with the average composition of the films, the average composition of the particulates is the same as that of the targets. These results are discussed in terms of the microstructure of the targets and the melting process at the surface. The implications of these observations for composition determination by laser ablation are discussed.Engineering and Applied SciencesPhysic

Kinetic Modeling of Dopant and Impurity Surface Segregation During Vapor Phase Growth: Multiple Mechanism Approach

We propose a new kinetic model for surface segregation during vapor phase growth that accounts for multiple segregation mechanisms, including mechanisms for terrace mediated exchange and step edge mediated exchange. The major result of the model is an analytic expression for the experimentally measured segregation length and profile broadening that can be readily calculated without the need for numerical simulations. We compare the model to experimental measurements for the temperature dependence of segregation of Sb in Si(001). The model is able to accurately describe both the anomalous segregation at low temperature and the transition between equilibrium and kinetically limited segregation at high temperature. An excellent agreement is obtained using realistic energies and pre-exponential factors for the kinetic rate constants. The model can be applied to other segregating systems in planar geometries, including metallic and III-V semiconducting thin films.Engineering and Applied Science

Unified Kinetic Model of Dopant Segregation During Vapor-Phase Growth

We develop a unified kinetic model for surface segregation during vapor phase growth that concisely and quantitatively describes the observed behavior in silicon-based systems. A simple analytic function for the segregation length is derived by treating terrace-mediated and step-edge-mediated mechanisms in parallel. The predicted behavior of this parameter is examined through its temperature, flux, and terrace length dependence. Six distinct temperature regimes are predicted for the segregation length that depend on the relative segregation energies and activation barriers of the two mechanisms. The model is compared to reported behavior of Sb and P in Si(001) and excellent agreement is obtained using realistic energies and preexponential factors. The model accounts for the experimentally observed anomalous low-temperature segregation of Sb as a consequence of the competition between step-edge-mediated segregation, dominant at low temperatures, and terrace-mediated segregation, dominant at higher temperatures. The generalized treatment of segregation mechanisms in the model makes it applicable to other segregating systems, including metals and III-V semiconductors.Engineering and Applied Science

Three-dimensional particle tracking via tunable color-encoded multiplexing.

We present a novel 3D tracking approach capable of locating single particles with nanometric precision over wide axial ranges. Our method uses a fast acousto-optic liquid lens implemented in a bright field microscope to multiplex light based on color into different and selectable focal planes. By separating the red, green, and blue channels from an image captured with a color camera, information from up to three focal planes can be retrieved. Multiplane information from the particle diffraction rings enables precisely locating and tracking individual objects up to an axial range about 5 times larger than conventional single-plane approaches. We apply our method to the 3D visualization of the well-known coffee-stain phenomenon in evaporating water droplets

Variable optical elements for fast focus control

In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great strides forward in recent years due to precise and rapid axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed, along with a discussion of the implications of the new developments in variable optical elements and their impact on technologically relevant applications

Parameter-Free Test of Alloy Dendrite Growth Theory

In rapid alloy solidification the dendrite-growth velocity depends sensitively on the deviations from local interfacial equilibrium manifested by kinetic effects such as solute trapping. The dendrite tip velocity undercooling function was measured in dilute Ni~Zr! over the range 1–25 m/s and 50–255 K using electromagnetic levitation techniques and compared to theoretical predictions of the model of Trivedi and colleagues for dendritic growth with deviations from local interfacial equilibrium. The input parameter to which the model predictions are most sensitive, the diffusive speed VD characterizing solute trapping, was not used as a free parameter but was measured independently by pulsed laser melting techniques, as was another input parameter, the liquid diffusivity DL. Best-fit values from the pulsed laser melting experiment are VD526 m/s and DL 52.731029 m2/s. Inserting these values into the dendrite growth model results in excellent agreement with experiment with no adjustable parameters.Engineering and Applied Science

The Interface between Intellectual Property Law and Competition Law in the North American Context

intellectual property and competition law in North Americ

The Interface between Intellectual Property Law and Competition Law in the North American Context

intellectual property and competition law in North Americ