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Top 20 Most Cited Articles
The 20 most cited articles over time based on CrossRef data.
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J. Vac. Sci. Technol. B 10, 1237 (1992); http://dx.doi.org/10.1116/1.585897 (30 pages) | Cited 749 times
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The status of research on both wurtzite and zinc‐blende GaN, AlN, and InN and their alloys is reviewed including exciting recent results. Attention is paid to the crystal growth techniques, structural, optical, and electrical properties of GaN, AlN, InN, and their alloys. The various theoretical results for each material are summarized. We also describe the performance of several device structures which have been demonstrated in these materials. Near‐term goals and critical areas in need of further research in the III–V nitride material system are identified. |
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Band offsets of wide-band-gap oxides and implications for future electronic devices J. Vac. Sci. Technol. B 18, 1785 (2000); http://dx.doi.org/10.1116/1.591472 (7 pages) | Cited 647 times
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Wide-band-gap oxides such as SrTiO3 are shown to be critical tests of theories of Schottky barrier heights based on metal-induced gap states and charge neutrality levels. This theory is reviewed and used to calculate the Schottky barrier heights and band offsets for many important high dielectric constant oxides on Pt and Si. Good agreement with experiment is found for barrier heights. The band offsets for electrons on Si are found to be small for many key oxides such as SrTiO3 and Ta2O5 which limit their utility as gate oxides in future silicon field effect transistors. The calculations are extended to screen other proposed oxides such as BaZrO3. ZrO2, HfO2, La2O3, Y2O3, HfSiO4, and ZrSiO4. Predictions are also given for barrier heights of the ferroelectric oxides Pb1−xZrxTiO3 and SrBi2Ta2O9 which are used in nonvolatile memories. © 2000 American Vacuum Society. |
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Sub-10 nm imprint lithography and applications J. Vac. Sci. Technol. B 15, 2897 (1997); http://dx.doi.org/10.1116/1.589752 (8 pages) | Cited 345 times
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New developments, further details, and applications of imprint lithography are presented. Arrays of 10 nm diameter and 40 nm period holes were imprinted not only in polymethylmethacrylate (PMMA) on silicon, but also in PMMA on gold substrates. The smallest hole diameter imprinted in PMMA is 6 nm. All the PMMA patterns were transferred to a metal using a liftoff. In addition, PMMA mesa’s of a size from 45 nm to 50 μm were obtained in a single imprint. Moreover, imprint lithography was used to fabricate the silicon quantum dot, wire, and ring transistors, which showed the same behavior as those fabricated using electron (e)-beam lithography. Finally, imprint lithography was used to fabricate nanocompact disks with 10 nm features and 400 Gbits/in.2 data density—near three orders of magnitude higher than current critical dimensions (CDs). A silicon scanning probe was used to read back the data successfully. The study of wear indicates that due to the ultrasmall force in tapping mode, both the nano-CD and the scanning probe will not show noticeable wear after a large number of scans. © 1997 American Vacuum Society. |
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Growth of silicon nanowires via gold/silane vapor–liquid–solid reaction J. Vac. Sci. Technol. B 15, 554 (1997); http://dx.doi.org/10.1116/1.589291 (4 pages) | Cited 272 times
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Silicon nanowires (whiskers) have been grown on Si(111) via the vapor–liquid–solid (VLS) reaction using silane as the Si source gas and Au as the mediating solvent. The silane partial pressure and temperature ranges were 0.01–1 Torr and 320–600 °C, respectively. Growth at high partial pressure and low temperature leads to the growth of Si nanowires as thin as 10 nm. These wires are single crystals but exhibit growth defects such as bending and kinking. Lowering the silane partial pressure leads to an increase in the wire width and a reduction in the tendency to form growth defects. At low pressure, 40–100 nm wide well-formed wires have been grown at 520 °C. The VLS reaction using silane allows the growth of Si wires, which are significantly thinner than those grown previously using SiCl4. © 1997 American Vacuum Society. |
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Recent advances in processing of ZnO J. Vac. Sci. Technol. B 22, 932 (2004); http://dx.doi.org/10.1116/1.1714985 (17 pages) | Cited 258 times Online Publication Date: 26 April 2004
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A review is given of recent results in developing improved fabrication processes for ZnO devices with the possible application to UV light emitters, spin functional devices, gas sensors, transparent electronics, and surface acoustic wave devices. There is also interest in integrating ZnO with other wide band-gap semiconductors, such as the AlInGaN system. In this article, we summarize recent progress in controlling n- and p-type doping, materials processing methods, such as ion implantation for doping or isolation, Ohmic and Schottky contact formation, plasma etching, the role of hydrogen in the background n-type conductivity of many ZnO films, and finally, the recent achievement of room-temperature ferromagnetism in transition-metal (Mn or Co)-doped ZnO. This may lead to another class of spintronic devices, in which the spin of the carriers is exploited rather than the charge as in more conventional structures. © 2004 American Vacuum Society. |
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J. Vac. Sci. Technol. B 14, 4129 (1996); http://dx.doi.org/10.1116/1.588605 (5 pages) | Cited 242 times
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Nanoimprint lithography, a high‐throughput, low‐cost, nonconventional lithographic method proposed and demonstrated recently, has been developed and investigated further. Nanoimprint lithography has demonstrated 25 nm feature size, 70 nm pitch, vertical and smooth sidewalls, and nearly 90° corners. Further experimental study indicates that the ultimate resolution of nanoimprint lithography could be sub‐10 nm, the imprint process is repeatable, and the mold is durable. In addition, uniformity over a 15 mm by 18 mm area was demonstrated and the uniformity area can be much larger if a better designed press is used. Nanoimprint lithography over a nonflat surface has also been achieved. Finally, nanoimprint lithography has been successfully used for fabricating nanoscale photodetectors, silicon quantum‐dot, quantum‐wire, and ring transistors. © 1996 American Vacuum Society |
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J. Vac. Sci. Technol. B 10, 1807 (1992); http://dx.doi.org/10.1116/1.586204 (13 pages) | Cited 178 times
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To obtain a large lattice constant on Si, we have grown compositionally graded GexSi1−x on Si. These buffer layers have been characterized with electron‐beam‐induced current, transmission electron microscopy, scanning electron microscopy, x‐ray diffraction, and photoluminescence to determine the extent of relaxation, the threading dislocation density, the surface morphology, and the optical properties. We have observed that it is possible to obtain completely relaxed GexSi1−x layers with 0.1<x<1, threading dislocation densities of 105–5 × 106 cm−2, and with bulk GexSi1−x optical properties. Calculations show that gradually graded layers grown at relatively high temperatures can remain in equilibrium throughout growth, thereby avoiding strain buildup and the introduction of more threading dislocations through dislocation nucleation. It is also shown that the degree of surface crosshatch is related to inhomogeneous strain fields in the epilayer and to the thickness at which dislocations are introduced. These relaxed buffers have been used for the fabrication of very high mobility two‐dimensional electron gases in Si and also as templates for lattice‐matched III–V growth. We have obtained electron gases in Si with mobilities as high as 170 000 cm2/V s and red‐emitting InGaP light emitting diodes on Si with less than 20 μA reverse current at −6 V bias. |
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Gas-assisted focused electron beam and ion beam processing and fabrication J. Vac. Sci. Technol. B 26, 1197 (2008); http://dx.doi.org/10.1116/1.2955728 (80 pages) | Cited 169 times Online Publication Date: 11 August 2008
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Beams of electrons and ions are now fairly routinely focused to dimensions in the nanometer range. Since the beams can be used to locally alter material at the point where they are incident on a surface, they represent direct nanofabrication tools. The authors will focus here on direct fabrication rather than lithography, which is indirect in that it uses the intermediary of resist. In the case of both ions and electrons, material addition or removal can be achieved using precursor gases. In addition ions can also alter material by sputtering (milling), by damage, or by implantation. Many material removal and deposition processes employing precursor gases have been developed for numerous practical applications, such as mask repair, circuit restructuring and repair, and sample sectioning. The authors will also discuss structures that are made for research purposes or for demonstration of the processing capabilities. In many cases the minimum dimensions at which these processes can be realized are considerably larger than the beam diameters. The atomic level mechanisms responsible for the precursor gas activation have not been studied in detail in many cases. The authors will review the state of the art and level of understanding of direct ion and electron beam fabrication and point out some of the unsolved problems.
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Microscopic uniformity in plasma etching J. Vac. Sci. Technol. B 10, 2133 (1992); http://dx.doi.org/10.1116/1.586180 (15 pages) | Cited 168 times
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As we enter the era of ultra‐large‐scale integrated circuit manufacture, plasma etching grows more important for fabricating structures with unprecedented dimensions. For feature sizes below 1 μm and aspect ratios (depth/width) much larger than one, etching rates have been observed to depend on aspect ratio and pattern density. Such dependencies tend to increase the cost of manufacturing because even small changes in device design rules, cell design, or wafer layout can result in time‐consuming, new plasma process development. In addition, microscopically nonuniform etching affects the trade‐off between chips lost from failure to clear and chips lost by damage from overetching. Although aspect ratio and pattern dependent etching have been observed for a large variety of material systems and processing conditions, the fundamental causes underlying these effects are poorly understood. Partly, this results from use of confusing and conflicting nomenclature and a lack of careful, quantitative comparisons between experiment and theory. In this article we review recent literature on microscopic uniformity in plasma etching and carefully define terminology to distinguish between aspect ratio dependent etching (ARDE) and the pattern dependent effect known as microloading. For ARDE, we use dimensional analysis to narrow the range of proposed mechanisms to four which involve ion transport, neutral transport, and surface charging. For microloading, we show that it is formally equivalent to the usual loading effect, where the reactant concentration is depeleted as a result of an excessive substrate load. |
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On the mechanism of the hydrogen-induced exfoliation of silicon J. Vac. Sci. Technol. B 15, 1065 (1997); http://dx.doi.org/10.1116/1.589416 (9 pages) | Cited 153 times
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We have investigated the fundamental mechanism underlying the hydrogen-induced exfoliation of silicon, using a combination of spectroscopic and microscopic techniques. We have studied the evolution of the internal defect structure as a function of implanted hydrogen concentration and annealing temperature and found that the mechanism consists of a number of essential components in which hydrogen plays a key role. Specifically, we show that the chemical action of hydrogen leads to the formation of (100) and (111) internal surfaces above 400 °C via agglomeration of the initial defect structure. In addition, molecular hydrogen is evolved between 200 and 400 °C and subsequently traps in the microvoids bounded by the internal surfaces, resulting in the build-up of internal pressure. This, in turn, leads to the observed “blistering” of unconstrained silicon samples, or complete layer transfer for silicon wafers joined to a supporting (handle) wafer which acts as a mechanical “stiffener.” © 1997 American Vacuum Society. |
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Field emission properties of carbon nanotubes J. Vac. Sci. Technol. B 18, 665 (2000); http://dx.doi.org/10.1116/1.591258 (14 pages) | Cited 153 times
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We have investigated the field emission properties of nanotube thin films deposited by a plasma enhanced chemical vapor deposition process from 2% CH4 in H2 atmosphere. Depending on the deposition of the metallic catalyst [Fe(NO3)3 in an ethanol solution or sputtered Ni] the nanotube films showed a nested or continuous dense distribution of tubes. The films consisted of multiwalled nanotubes (MWNTs) with diameters ranging from 40 down to 5 nm, with a large fraction of the tubes having open ends. The nanotube thin film emitters showed a turn-on field of less than 2 V μm−1 for an emission current of 1 nA. An emission site density of 10 000 emitters per cm−2 is achieved at fields around 4 V μm−1. The emission spots, observed on a phosphorous screen, show various irregular structures, which we attribute to open ended tubes. A combined measurement of the field emitted electron energy distribution (FEED) and the current-voltage characteristic allowed us to determine the work function at the field emission site. In the case of the MWNT thin films and arc discharge grown MWNTs we found work function values around 5 eV, which agree well with the global work function of 4.85 eV we determined by photoelectron spectroscopy. From the shape of the FEED peaks we can conclude that the field emission originates from continuum states at the Fermi energy, indicating the metallic character of the emission site. In the case of single-walled nanotubes we found significantly lower work function values of around 3.7 eV compared to those of MWNTs. We attribute this to a size dependent electrostatic effect of the image potential, which lowers the work function for small (<5 nm) structures. © 2000 American Vacuum Society. |
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Advanced techniques for glancing angle deposition J. Vac. Sci. Technol. B 16, 1115 (1998); http://dx.doi.org/10.1116/1.590019 (8 pages) | Cited 152 times
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When a thin film is deposited by physical vapor deposition, with the vapor flux arriving at an oblique angle from the substrate normal, and under conditions of sufficiently limited adatom mobility to create a columnar microstructure, the resulting structure is somewhat porous and grows at an angle inclined toward the vapor source. For a given material and set of deposition conditions, there is a fixed relationship between the angle of vapor flux incident on the substrate and the inclination angle at which the columnar thin film grows. As the porosity of the film is also dependent on the incident flux angle, column growth angle and porosity cannot be chosen independently. If a large columnar angle (more parallel to the substrate) is desired, the flux must be deposited at a large oblique angle resulting in a very porous film. Conversely, if a near vertical columnar film is desired, the flux must arrive more perpendicular to the substrate and the resulting film has a tightly packed, dense microstructure. We present a technique, based on glancing angle deposition, employing substrate motion during deposition, which allows the columnar growth inclination angle and film density to be controlled independently. With this method, microstructurally controlled materials can be fabricated with three dimensional control on a 10 nm scale for use in optical, chemical, biological, mechanical, magnetic, and electrical applications. © 1998 American Vacuum Society. |
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Three-dimensional nanostructure fabrication by focused-ion-beam chemical vapor deposition J. Vac. Sci. Technol. B 18, 3181 (2000); http://dx.doi.org/10.1116/1.1319689 (4 pages) | Cited 148 times
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Three-dimensional nanostructure fabrication has been demonstrated by 30 keV Ga+ focused ion beam assisted deposition using a aromatic hydrocarbon precursor. The characterization of deposited film on a silicon substrate was performed by a transmission microscope and Raman spectra. This result indicates that the deposition film is a diamondlike amorphous carbon. Production of three-dimensional nanostructure is discussed. Microcoil, drill, and bellows with 0.1 μm dimension were fabricated as parts of the microsystem. Furthermore, microstructure plastic arts is advocated as a new field using microbeam technology, presenting one example of a microwine glass with 2.75 μm external diameter and 12 μm height. © 2000 American Vacuum Society. |
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The advanced unified defect model for Schottky barrier formation J. Vac. Sci. Technol. B 6, 1245 (1988); http://dx.doi.org/10.1116/1.584244 (7 pages) | Cited 147 times
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The advanced unified defect model (AUDM) for GaAs proposed in this paper can be looked upon as a refinement of the unified defect model (UDM) proposed in 1979 to explain Fermi level pinning on 3–5 compounds due to metals or nonmetals. The refinement lies in identifying the defect producing pinning at 0.75 and 0.5 eV above the valence band maximum as the AsGa antisite. Since the AsGa antisite is a double donor, a minority compensating acceptor is necessary. This is tentatively identified as the GaAs antisite. The concentration of As excess or deficiency due to processing or reactions at interfaces is particularly emphasized in this model. A wide range of experimental data is discussed in terms of this model and found to be in agreement with it. This includes the original data on which the UDM was based as well as more recent data including Fermi level pinning on the free‐GaAs(100) molecular‐beam epitaxy surface, Schottky barrier height for thick (∼1000 Å) Ga films on GaAs, and the LaB6 Schottky barrier height on GaAs (including thermal annealing effects). Of particular importance is the ability of this model to explain the changes in Schottky barrier height for Al and Au on GaAs due to thermal annealing and to relate these changes to interfacial chemistry. |
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Critical Review: Adhesion in surface micromechanical structures J. Vac. Sci. Technol. B 15, 1 (1997); http://dx.doi.org/10.1116/1.589247 (20 pages) | Cited 138 times
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We present a review on the state of knowledge of surface phenomena behind adhesion in surface micromechanical structures. After introducing the problem of release-related and in-use adhesion, a theoretical framework for understanding the various surface forces that cause strong adhesion of micromechanical structures is presented. Various approaches are described for reducing the work of adhesion. These include surface roughening and chemical modification of polycrystalline silicon surfaces. The constraints that fabrication processes such as release, drying, assembly, and packaging place on surface treatments are described in general. Finally, we briefly outline some of the important scientific and technological issues in adhesion and friction phenomena in micromechanical structures that remain to be clarified. © 1997 American Vacuum Society. |
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Step and flash imprint lithography: Template surface treatment and defect analysis J. Vac. Sci. Technol. B 18, 3572 (2000); http://dx.doi.org/10.1116/1.1324618 (6 pages) | Cited 137 times
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We have finished the construction of an automated tool for step and flash imprint lithography. The tool was constructed to allow defect studies by making multiple imprints on a 200 mm wafer. The imprint templates for this study were treated with a low surface energy, self-assembled monolayer to ensure selective release at the template-etch barrier interface. This surface treatment is very durable and survives repeated imprints and multiple aggressive physical and chemical cleanings. The imprint and release forces were measured for a number of successive imprints, and did not change significantly. The process appears to be “self-cleaning.” Contamination on the template is entrained in the polymerizing liquid, and the number of defects is reduced with repeated imprints. © 2000 American Vacuum Society. |
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Single cell detection with micromechanical oscillators J. Vac. Sci. Technol. B 19, 2825 (2001); http://dx.doi.org/10.1116/1.1421572 (4 pages) | Cited 136 times
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The ability to detect small amounts of materials, especially pathogenic bacteria, is important for medical diagnostics and for monitoring the food supply. Engineered micro- and nanomechanical systems can serve as multifunctional, highly sensitive, immunospecific biological detectors. We present a resonant frequency-based mass sensor, comprised of low-stress silicon nitride cantilever beams for the detection of Escherichia coli (E. coli)-cell-antibody binding events with detection sensitivity down to a single cell. The binding events involved the interaction between anti-E. coli O157:H7 antibodies immobilized on a cantilever beam and the O157 antigen present on the surface of pathogenic E. coli O157:H7. Additional mass loading from the specific binding of the E. coli cells was detected by measuring a resonant frequency shift of the micromechanical oscillator. In air, where considerable damping occurs, our device mass sensitivities for a 15 μm and 25 μm long beam were 1.1 Hz/fg and 7.1 Hz/fg, respectively. In both cases, utilizing thermal and ambient noise as a driving mechanism, the sensor was highly effective in detecting immobilized anti-E. coli antibody monolayer assemblies, as well as single E. coli cells. Our results suggest that tailoring of oscillator dimensions is a feasible approach for sensitivity enhancement of resonant mass sensors. © 2001 American Vacuum Society. |
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J. Vac. Sci. Technol. B 21, 2231 (2003); http://dx.doi.org/10.1116/1.1622676 (31 pages) | Cited 131 times Online Publication Date: 3 November 2003
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Atomic layer deposition (ALD) has been studied for several decades now, but the interest in ALD of metal and nitride thin films has increased only recently, driven by the need for highly conformal nanoscale thin films in modern semiconductor device manufacturing technology. ALD is a very promising deposition technique with the ability to produce thin films with excellent conformality and compositional control with atomic scale dimensions. However, the applications of metals and nitrides ALD in semiconductor device processes require a deeper understanding about the underlying deposition process as well as the physical and electrical properties of the deposited films. This article reviews the current research efforts in ALD for metal and nitride films as well as their applications in modern semiconductor device fabrication. © 2003 American Vacuum Society. |
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Tunneling spectroscopy of the GaAs(110) surface J. Vac. Sci. Technol. B 5, 923 (1987); http://dx.doi.org/10.1116/1.583691 (7 pages) | Cited 131 times
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The scanning tunneling microscope is used to study the spectroscopy of p‐type, n‐type, and oxygen‐covered GaAs(110) surfaces. On the clean surface, three components of the current are identified—tunneling out of valence‐band states, tunneling into conduction‐band states, and tunneling through dopant‐induced states in the semiconductor. The results are compared with a theoretical computation of the tunneling current, including band bending in the semiconductor. Good agreement between theory and experiment is obtained only when tunneling through the space‐charge region of the semiconductor is included. On the oxygen‐covered surface, the spectroscopic results show evidence of band bending due to the oxygen adsorbates. |
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Structure shape and stability of nanometric sized particles J. Vac. Sci. Technol. B 19, 1091 (2001); http://dx.doi.org/10.1116/1.1387089 (13 pages) | Cited 127 times
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Nanoparticles are a state of matter that has properties different from either molecules or bulk solids. In the present work, we review the shape and structure of nanometer-sized particles; several shapes are discussed, such as the octahedron and truncated octahedron, the icosahedron, the Marks decahedron, the truncated “star-like” decahedron, the rounded decahedron and the regular decahedron. Experimental high-resolution transmission electron microscopy (TEM) images of each type of particle are presented together with the Fast Fourier Transform and a model of the particle. We consider only gold particles grown by vapor deposition or by colloidal methods. High-resolution TEM images of the particles in different orientations are shown. We discuss two basic types of particles uncapped and capped. Data for other metals and semiconductors are reviewed. We have also performed very extensive simulations obtaining the total energy and pair correlation functions for each cluster under study. Furthermore, distributions of single atom energy for every cluster are displayed in order to reveal the effect of surface on the stability of different types and sizes of clusters. We discuss the structure of the particles from ∼1 to ∼100 nm. The mechanisms for stress release as the particles grow larger are reviewed and a mechanism is suggested. Finally, we discuss the parameters that define the shape of a nanoparticle and the possible implications in technological applications. © 2001 American Vacuum Society. |
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