Showing papers by "Robert S Averback published in 2001"
TL;DR: Irradiation causes significant smoothing of initially rough surfaces, and nearly atomically smooth films can be achieved, at high doses and long wavelengths.
Abstract: Surface roughening and smoothing reactions on vapor codeposited glassy Zr65Al7.5Cu27.5 films by 1.8 MeV Kr+ ion beam irradiation is investigated. Irradiation causes significant smoothing of initially rough surfaces, and nearly atomically smooth films can be achieved. Smooth surfaces roughen at high doses and long wavelengths. By a Fourier analysis, radiation-induced viscous flow is identified as the dominant surface relaxation mechanism. Two noise terms are identified, which operate on different length scales: One is due to sputtering and the other to thermal spikes. The irradiation-induced viscosity is compared with radiation-enhanced diffusion.
70 citations
TL;DR: In this paper, the dewetting and nanopattern formation of 3-10 nm Pt thin films upon ion irradiation using scanning electron microscopy (SEM) was studied.
Abstract: Dewetting and nanopattern formation of 3–10 nm Pt thin films upon ion irradiation is studied using scanning electron microscopy (SEM). Lateral feature size and the fraction of exposed surface area are extracted from SEM images and analyzed as functions of ion dose. The dewetting phenomenon has little temperature dependence for 3 nm Pt films irradiated by 800 keV Kr+ at temperatures ranging from 80 to 823 K. At 893 K, the films dewet without irradiation, and no pattern formation is observed even after irradiation. The thickness of the Pt films, in the range 3–10 nm, influences the pattern formation, with the lateral feature size increasing approximately linearly with film thickness. The effect of different ion species and energies on the dewetting process is also investigated using 800 keV Kr+ and Ar+ irradiation and 19.5 keV He+, Ar+, Kr+, and Xe+ irradiation. The lateral feature size and exposed surface fraction scale with energy deposition density (J/cm2) for all conditions except 19.5 keV Xe+ irradiation.
62 citations
TL;DR: In this article, a combination of ion range calculations and molecular dynamics computer simulations is used to predict the atomic-level damage structures produced by MeV ions, and the results show that the majority of damage produced in GaAs both by low energy self-recoils and 6 MeV He ions is in clusters, and that a clear majority of the isolated defects are interstitials.
Abstract: Defect formation in compound semiconductors such as GaAs under ion irradiation is not as well understood as in Si and Ge. We show how a combination of ion range calculations and molecular dynamics computer simulations can be used to predict the atomic-level damage structures produced by MeV ions. The results show that the majority of damage produced in GaAs both by low-energy self-recoils and 6 MeV He ions is in clusters, and that a clear majority of the isolated defects are interstitials. Implications of the results for suggested applications are also discussed.
56 citations
TL;DR: In this article, point-defect properties in ion-irradiated Si were investigated using in situ grazing incidence diffuse x-ray scattering, and the defect properties were characterized by close-pair configurations and by relaxation volumes of vacancies and interstitials that have nearly the same magnitude, but opposite sign.
Abstract: Point-defect properties in ion-irradiated Si were investigated using in situ grazing incidence diffuse x-ray scattering. Bombardment with 4.5-keV He at 100 K and 3-MeV electrons at 6 K led to the production of Frenkel pairs. These defects are characterized by close-pair configurations and by relaxation volumes of vacancies and interstitials that have nearly the same magnitude, but opposite sign. Thermally activated motion of interstitial atoms occurs above ’150 K, while that for vacancies occurs above ’175 K. The motion of interstitials below 150 K during electron irradiation is shown to be induced by electronic excitation, and it is negligible for ion irradiations. Similar results were observed for irradiation with 20-keV Ga and 1.0-MeV Ar, although the defects were already clustered upon bombardment at 100 K. Correlation distances between vacancies and interstitials in cascades are obtained.
42 citations
TL;DR: In this article, it is shown that for the simple case of symmetrical twist boundaries with low index planes, the structure and dynamics of the system are sensitive to finite size effects.
Abstract: Nanoscale Pt particles situated on a Pt surface are studied by molecular dynamics simulations. It is shown that for the simple case of symmetrical twist boundaries with low index planes, the structure and dynamics of the system are sensitive to finite size effects. Namely, below a specific nanoparticle size the particles will align themselves with the substrate, while for larger particles a stable array of grain boundary dislocations is created. It is shown that nanoparticle rotation is a direct result of athermal slip of the grain boundary dislocations that are created at the particle-substrate interface. The size effects are unique to nano-sized particles and thus have not yet been observed in past experiments. The simulations also show that the energy and structure of the boundaries are also affected by the system size.
25 citations
TL;DR: In this article, the effect of 10 keV primary knock-on atoms (PKA's) on a Ni-Ag interface, and a homogeneous random alloy was studied by molecular-dynamics simulation.
Abstract: By molecular-dynamics simulation, we study the effect of 10 keV primary knock-on atoms (PKA's) on a Ni-Ag interface, and a homogeneous random ${\mathrm{Ni}}_{0.5}{\mathrm{Ag}}_{0.5}$ alloy. The interface roughens; compact islands of 1 ML thickness are created. Only a few isolated impurity atoms are formed. Effects in the random alloy are stronger. It decomposes, creating Ag- and Ni-rich regions. Due to the different lattice constants of the elements, both the interface and in particular the random alloy amorphize. The thermal spike created by the PKA persists longer in the random alloy, due to heating by the large positive heat of mixing of the Ni-Ag system. Comparison with simulation of Cu-Ag demonstrates that the demixing in Ni-Ag derives from its immiscibility in the liquid phase.
25 citations
TL;DR: In this article, the authors investigated soft landings of Co nanoparticles on clean Cu(001) surfaces, where they were generated by dc magnetron sputtering in argon and transferred in the gas stream to an ultrahigh vacuum transmission electron microscope (TEM).
Abstract: We have investigated soft landings of Co nanoparticles on clean Cu(001) surfaces. The nanoparticles, {approx}10 nm in size, were generated by dc magnetron sputtering in argon and transferred in the gas stream to an ultrahigh vacuum transmission electron microscope (TEM), where they were deposited on the thin-film substrate. The surface morphology created in this fashion exhibits a unique smoothing mechanism. The nanoparticles do not remain on the surface at temperatures as low as 600 K, but rather reorient and burrow into the substrate. By analyzing the TEM data in combination with molecular dynamics simulations, we were able to study this process in detail and to develop a model to quantify the temperature and cluster size dependence of burrowing.
18 citations
08 Jun 2001
TL;DR: In this paper, the potential of thermoelectric and alpha-voltaic microdevices for system-on-a-chip (SOAC) architectures has been discussed, as well as the electrical and thermal performance of the first devices.
Abstract: Miniaturized solid-state devices for integrated thermal management packages and low power, high voltage, electrical power source systems are of interest for a variety of space and terrestrial applications. The National Aeronautics and Space Administration (NASA) and the Jet Propulsion Laboratory (JPL) have been planning the use of much smaller spacecraft that will incorporate a variety of micro/nanodevices, such as microdetectors and microsensors, into miniature autonomous vehicles, such as microprobes and microrovers. High performance solid-state microcoolers and microgenerators based on thermoelectric, alpha-voltaic and thermionic energy conversion offer attractive solutions to the accelerating trend towards miniaturization of electronic components and distributed "system-on-a-chip" (SOAC) architectures where the functions of sense, compute, actuate, control, communicate and power are integrated. Novel thermoelectric micro/nanodevices that will provide the ability to handle much higher heat fluxes (thus resulting in high cooling power or electrical power densities), possess much faster response time as well as the possibility of generating high voltages under very small temperature differentials are being fabricated. After discussing the potential of thermoelectric and alpha-voltaic microdevices for SOAC architectures, we will report on our progress in electrochemical deposition of thermoelectric micro/nanoelements, thermoelectric and alpha-voltaic device microfabrication techniques as well as the electrical and thermal performance of the first devices.
15 citations
3 citations
01 Jan 2001
TL;DR: In this article, the authors present the use of Radioisotope thermoelectric generators (RTGs) for a number of deep space missions RTGs have been successfully used for RTGs, but their energy conversion efficiency and specific power characteristics are quite low, and this technology has been limited to relatively large systems (more than 100 W).
Abstract: Deep space missions have a strong need for compact, high power density, reliable and long life electrical power generation and storage under extreme temperature conditions. Conventional power generating devices become inefficient at very low temperatures (temperatures lower than 200 K encountered during Mars missions for example) and rechargeable energy storage devices cannot be operated thereby limiting mission duration. At elevated temperatures (for example for planned solar probe or Venus lander missions), thin film interdiffusion destroys electronic devices used for generating and storing power. Solar power generation strongly depends upon the light intensity, which falls rapidly in deep interplanetary missions (beyond 5 AU), and in planetary missions in the sun shadow or in dusty environments (Mars, for example). Radioisotope thermoelectric generators (RTGs) have been successfully used for a number of deep space missions RTGs. However, their energy conversion efficiency and specific power characteristics are quite low, and this technology has been limited to relatively large systems (more than 100 W). The National Aeronautics and Space Administration (NASA) and the Jet Propulsion Laboratory (JPL) have been planning the use of much smaller spacecrafts that will incorporate a variety of microdevices and miniature vehicles such as microdetectors, microsensors, and microrovers. Except for electrochemical batteries and solar cells, there are currently no available miniaturized power sources. Novel technologies that will function reliably over a long duration mission (ten years and over), in harsh environments (temperature, pressure, and atmosphere) must be developed to enable the success of future space missions. It is also expected that such micropower sources could have a wide range of terrestrial applications, in particular when the limited lifetime and environmental limitations of batteries are key factors. Additional information is contained in the original extended abstract.
1 citations
TL;DR: The formation of epitaxial CoSi2 islands of nanoscopic dimensions is reported using the technique of reactive cluster deposition and observations were made using a JEOL 200CX transmission electron microscope modified for in situ sputtering and UHV conditions.
Abstract: The formation of epitaxial CoSi 2 islands of nanoscopic dimensions is reported using the technique of reactive cluster deposition. Co clusters in the size range 5-50 nm were synthesized by sputtering of a high purity Co target inside a ultra high vacuum (UHV) sputtering chamber, using the technique of inert gas condensation. The clusters were then deposited on the reconstructed Si (111) surface. Upon annealing, the particles reacted with the Si substrate to form epitaxial CoSi 2 , Our observations were made using a JEOL 200CX transmission electron microscope modified for in situ sputtering and UHV conditions.