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Top 20 Most Cited Articles
The 20 most cited articles over time based on CrossRef data.
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The search for novel, superhard materials J. Vac. Sci. Technol. A 17, 2401 (1999); http://dx.doi.org/10.1116/1.581977 (20 pages) | Cited 414 times
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The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed. Two basic approaches are outlined including the intrinsic superhard materials, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure. The theoretically predicted high hardness of C3N4 has not been experimentally documented so far. Ceramics made of cubic boron nitride prepared at high pressure and temperature find many applications whereas thin films prepared by activated deposition from the gas phase are still in the stage of fundamental development. The greatest progress has been achieved in the field of nanostructured materials including superlattices and nanocomposites where superhardness of ⩾50 GPa was reported for several systems. More recently, nc-TiN/SiNx nanocomposites with hardness of 105 GPa were prepared, reaching the hardness of diamond. The principles of design for these materials are summarized and some unresolved questions outlined. © 1999 American Vacuum Society. |
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Structural analysis of Si(111)‐7×7 by UHV‐transmission electron diffraction and microscopy J. Vac. Sci. Technol. A 3, 1502 (1985); http://dx.doi.org/10.1116/1.573160 (5 pages) | Cited 257 times
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Structural analysis of the surface reconstructions investigated by ultrahigh vacuum (UHV) transmission electron microscopy (TEM) and diffraction (TED) is shown. By TED intensity analysis a new structural model of Si(111)‐7×7 is derived. The model basically consists of 12 adatoms arranged locally in the 2×2 structure, nine dimers on the sides of the triangular subunits of the 7×7 unit cell and a stacking fault layer. UHV–HREM of Si (111)‐7×7 surface is commented. |
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Theory of ripple topography induced by ion bombardment J. Vac. Sci. Technol. A 6, 2390 (1988); http://dx.doi.org/10.1116/1.575561 (6 pages) | Cited 253 times
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When an amorphous solid is etched by an off‐normal incidence ion beam, a ripple topography often results. A theory explaining the origin of these waves is presented. For incidence angles close to the normal, we find that the ripple wave vector is parallel to the surface component of the beam direction, provided that longitudinal straggling of the beam is not too large. The ripple orientation is rotated by 90° when the beam is close to grazing incidence. The wavelength given by the theory varies as λ∼( f T)−1/2 exp(−ΔE/2kBT) for high temperatures T and low fluxes f, where ΔE is the activation energy for surface self‐diffusion. The predicted magnitude of the wavelength is in reasonable accord with experiments in this regime. |
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Microstructural evolution during film growth J. Vac. Sci. Technol. A 21, S117 (2003); http://dx.doi.org/10.1116/1.1601610 (12 pages) | Cited 234 times Online Publication Date: 2 September 2003
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Atomic-scale control and manipulation of the microstructure of polycrystalline thin films during kinetically limited low-temperature deposition, crucial for a broad range of industrial applications, has been a leading goal of materials science during the past decades. Here, we review the present understanding of film growth processes—nucleation, coalescence, competitive grain growth, and recrystallization—and their role in microstructural evolution as a function of deposition variables including temperature, the presence of reactive species, and the use of low-energy ion irradiation during growth. © 2003 American Vacuum Society. |
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GexSi1−x/Si strained‐layer superlattice grown by molecular beam epitaxy J. Vac. Sci. Technol. A 2, 436 (1984); http://dx.doi.org/10.1116/1.572361 (5 pages) | Cited 201 times
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GexSi1−x films are grown on Si by molecular beam epitaxy and analyzed by Nomarski optical interference microscopy, Rutherford ion backscattering and channeling, x‐ray diffraction, and transmission electron microscopy. The full range of alloy compositions will grow smoothly on silicon. GexSi1−x films with x≤0.5 can be grown free of dislocations by means of strained‐layer epitaxy where lattice mismatch is accommodated by tetragonal strain. Critical thickness and composition values are tabulated for strained‐layer growth. Multiple strained layers are combined to form a GexSi1−x/Si strained‐layer superlattice. |
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In situ laser diagnostic studies of plasma‐generated particulate contamination J. Vac. Sci. Technol. A 7, 2758 (1989); http://dx.doi.org/10.1116/1.576175 (8 pages) | Cited 194 times
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Laser light scattering measurements show that certain silicon etching plasmas produce a significant amount of in situ, particulate contamination. The particles are suspended at the sheath boundaries. Simultaneous measurement of plasma negative ions by the use of two‐photon laser‐induced fluorescence technique suggests that the particles are negatively charged and so are electrostatically trapped at the sheath boundaries. The parametric conditions for particle formation and growth in the plasma are identified. A mechanism for nucleation and growth is suggested involving formation of plasma negative ions from etch products, ion clustering with plasma species, and cluster growth into particles with electrostatic suspension and trapping. The particles drop onto the wafer when the rf is turned off. Implications for dry process technology are discussed. |
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Nanosphere lithography: A materials general fabrication process for periodic particle array surfaces J. Vac. Sci. Technol. A 13, 1553 (1995); http://dx.doi.org/10.1116/1.579726 (6 pages) | Cited 190 times
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In this article nanosphere lithography (NSL) is demonstrated to be a materials general fabrication process for the production of periodic particle array (PPA) surfaces having nanometer scale features. A variety of PPA surfaces have been prepared using identical single‐layer (SL) and double‐layer (DL) NSL masks made by self‐assembly of polymer nanospheres with diameter, D=264 nm, and varying both the substrate material S and the particle material M. In the examples shown here, S was an insulator, semiconductor, or metal and M was a metal, inorganic ionic insulator, or an organic π‐electron semiconductor. PPA structural characterization and determination of nanoparticle metrics was accomplished with atomic force microscopy. This is the first demonstration of nanometer scale PPA surfaces formed from molecular materials. © 1995 American Vacuum Society |
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J. Vac. Sci. Technol. A 7, 2104 (1989); http://dx.doi.org/10.1116/1.575980 (6 pages) | Cited 186 times
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Multiple internal infrared reflection spectroscopy has been used to identify the chemical nature of chemically oxidized and subsequently HF stripped silicon surfaces. These very inert surfaces are found to be almost completely covered by atomic hydrogen. Results using polarized radiation on both flat and stepped Si(111) and Si(100) surfaces reveal the presence of many chemisorption sites (hydrides) that indicate that the surfaces are microscopically rough, although locally ordered. In particular, the HF‐prepared Si(100) surface appears to have little in common with the smooth H‐saturated Si(100) surface prepared in ultrahigh vacuum. |
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Application of reflectance difference spectroscopy to molecular‐beam epitaxy growth of GaAs and AlAs J. Vac. Sci. Technol. A 6, 1327 (1988); http://dx.doi.org/10.1116/1.575694 (6 pages) | Cited 179 times
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We perform an accuracy analysis of several possible reflectance–difference (RD) configurations that are compatible with standard molecular‐beam epitaxy (MBE) growth chambers, and describe in detail an optical‐bridge system that can determine relative changes in RD signals as small as 5×10−5 under standard growth conditions. Using this system, we determine the RD response of GaAs for changes in surface conditions at different wavelengths and correlate these to simultaneously measured reflection high‐energy electron diffraction (RHEED) intensities. Maximum anisotropies are found at 2.0–2.5 and 3.5 eV for Ga on GaAs and Al on AlAs, respectively, providing a way of spectrally distinguishing Ga–Ga and Al–Al dimers for surface‐chemical investigations, and suggesting that these photon energies are also optimal for modifying growth by light. At photon energies well removed from these anisotropy maxima, RD signals follow changes in surface structure, as RHEED. Our RD‐RHEED correlations provide insight concerning crystal growth by MBE and establish a common experimental link between MBE and non‐UHV methods of crystal growth where RHEED cannot be used. Finally, our results illustrate various possibilities of using reflectance difference spectroscopy to investigate surface structure, surface chemistry, and surface dynamics. |
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Infrared spectroscopic study of SiOx films produced by plasma enhanced chemical vapor deposition J. Vac. Sci. Technol. A 4, 689 (1986); http://dx.doi.org/10.1116/1.573833 (6 pages) | Cited 176 times
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We have studied the local atomic structure of silicon suboxide (SiOx, x<2) thin films using infrared (IR) spectroscopy. The films were prepared by plasma enhanced chemical vapor deposition (PECVD) of silane (SiH4) and nitrous oxide (N2O) mixtures, which were then diluted with He. The IR spectra were found to vary significantly with the degree of He dilution. Films grown with no He showed SiN, NH, and SiH bonding groups in addition to the three characteristic vibrations of the Si–O–Si linkage. The addition of He reduced the strength of the SiN, NH, and SiH absorption bands, and resulted in systematic increases in the frequency of the Si–O–Si asymmetric stretching vibration. The frequency of this Si–O–Si stretching vibration scales linearly with the oxygen concentration from approximately 940 cm−1 in oxygen doped amorphous silicon to 1075 cm−1 in stoichiometric noncrystalline SiO2. A deposition temperature of 350 °C and a He dilution of 50% gave a film composition close to SiO1.9. We propose a model for the deposition process that emphasizes the role of the He dilution. |
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J. Vac. Sci. Technol. A 19, 1800 (2001); http://dx.doi.org/10.1116/1.1380721 (6 pages) | Cited 173 times
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We have demonstrated large-scale production (10 g/day) of high-purity carbon single-walled nanotubes (SWNTs) using a gas-phase chemical-vapor-deposition process we call the HiPco process. SWNTs grow in high-pressure (30–50 atm), high-temperature (900–1100 °C) flowing CO on catalytic clusters of iron. The clusters are formed in situ: Fe is added to the gas flow in the form of Fe(CO)5. Upon heating, the Fe(CO)5 decomposes and the iron atoms condense into clusters. These clusters serve as catalytic particles upon which SWNT nucleate and grow (in the gas phase) via CO disproportionation: CO+CO⇒CO2+C(SWNT). SWNT material of up to 97 mol % purity has been produced at rates of up to 450 mg/h. The HiPco process has been studied and optimized with respect to a number of process parameters including temperature, pressure, and catalyst concentration. The behavior of the SWNT yield with respect to various parameters sheds light on the processes that currently limit SWNT production, and suggests ways that the production rate can be increased still further. © 2001 American Vacuum Society. |
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Sculptured thin films and glancing angle deposition: Growth mechanics and applications J. Vac. Sci. Technol. A 15, 1460 (1997); http://dx.doi.org/10.1116/1.580562 (6 pages) | Cited 166 times
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Sculptured thin films with three dimensional microstructure controlled on the 10 nm scale were fabricated with an evaporation technique. Glancing angle deposition (GLAD) and substrate motion were employed to “sculpt” columnar thin film microstructure into desired forms ranging from zigzag shaped to helical to four-sided “square” helical. Computer control of substrate motion was used to accurately position the substrate and to achieve the desired film structures. The growth mechanics of this novel thin film deposition technique are investigated with density measurements, scanning electron microscopy analysis, and measurements of effective refractive index. Adatom diffusion and atomic shadowing are the dominant growth mechanisms with glancing angle deposition conditions creating extreme shadowing. With controlled rotation of the substrate about two axes during deposition, a dense capping layer can be produced on top of the porous sculptured films. The success of the capping process was found to be strongly dependent on the technique used, with an exponential decrease(θ∝[1−A⋅eB⋅t]) with time of incident flux angle found to be the best to reduce filling of the porous film and fracturing of the capping film. The GLAD technique was found to have potentially promising application in optical, biological, and chemical devices and materials. © 1997 American Vacuum Society. |
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Microfabrication of cantilever styli for the atomic force microscope J. Vac. Sci. Technol. A 8, 3386 (1990); http://dx.doi.org/10.1116/1.576520 (11 pages) | Cited 163 times
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Atomic force microscopy (AFM) is a newly developed high resolution microscopy technique which is capable of mapping forces near surfaces or, by means of these forces, the topography of the surface itself. In one mode of operation, AFM can resolve individual atoms on both conducting and insulating surfaces. A crucial component for the AFM is a flexible force‐sensing cantilever stylus, whose properties should include, among other things: a sharp tip, a low force constant, and a high mechanical resonance frequency. These requirements can be met by reducing the size of the cantilever stylus through microfabrication techniques and employing novel methods to construct a sharp tip. Presented here are a number of microfabrication processes for constructing cantilever styli with properties ideal for the AFM. These fabrication processes include (1) a method for producing thin film SiO2 or Si3N4 cantilevers without tips, (2) a method for producing Si3N4 cantilevers with integrated pyramidal tips formed by using an etch pit on the (100) surface of Si as a mold, (3) a method for producing SiO2 cantilevers with conical tips formed by a combination of isotropic and anisotropic plasma etching of a small Si post, and (4) a method for producing SiO2 cantilevers with integrated tetrahedral tips formed by anisotropically etching a corner of a small Si post to a sharp point. Each of these processes uses a (100) Si wafer as a substrate and relies on conventional batch fabrication techniques. The quality (i.e., sharpness) of the tips produced by the above methods matches or exceeds that of conventional tips used in the AFM or scanning tunneling microscope (STM). Alternative methods for producing tips by evaporation of material through an orifice or by selective chemical vapor deposition of W metal into a pyramidal etch pit in Si have been demonstrated, but these methods have not yet been successfully used in cantilever assemblies. |
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Global model of Ar, O2, Cl2, and Ar/O2 high‐density plasma discharges J. Vac. Sci. Technol. A 13, 368 (1995); http://dx.doi.org/10.1116/1.579366 (13 pages) | Cited 161 times
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We develop a global (volume averaged) model of high‐density plasma discharges in molecular gases. For a specified discharge length and diameter, absorbed power, pressure, and feed gas composition, as well as the appropriate reaction rate coefficients and surface recombination constants, we solve the energy and particle balance equations to determine all species densities and the electron temperature. We use an expression for charged particle diffusive loss that is valid for low and high pressures and for electropositive and electronegative plasmas. We apply the model to Ar, O2, Cl2, and Ar/O2 discharges and compare with available experimental data. In Ar, we find that the ion density increases monotonically with increasing pressure, while for O2 and Cl2, the total positive ion density increases initially, then decreases as pressure is further increased. For a pure Cl2 discharge, we find that surface recombination processes are important in affecting the degree of dissociation and the negative‐ion density of the system. For mixtures of Ar and O2, we find that at a fixed ratio of Ar to O2 flowrates, the dominant ionic species changes from Ar+ to O+ as pressure is increased. When a small amount of Ar is added to a pure O2 discharge, the overall positive‐ion density increases, whereas the ratio of negative ion to electron density decreases. © 1995 American Vacuum Society |
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J. Vac. Sci. Technol. A 25, 1317 (2007); http://dx.doi.org/10.1116/1.2764082 (19 pages) | Cited 154 times Online Publication Date: 30 July 2007
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Physical vapor deposition under conditions of obliquely incident flux and limited adatom diffusion results in a film with a columnar microstructure. These columns will be oriented toward the vapor source and substrate rotation can be used to sculpt the columns into various morphologies. This is the basis for glancing angle deposition (GLAD), a technique for fabricating porous thin films with engineered structures. The origin of the columnar structure characteristic of GLAD films is discussed in terms of nucleation processes and structure zone models. As deposition continues, the columnar structures are influenced by atomic-scale ballistic shadowing and surface diffusion. Competitive growth is observed where the tallest columns grow at the expense of smaller features. The column shape evolves during growth, and power-law scaling behavior is observed as shown in both experimental results and theoretical simulations. Due to the porous nature of the films and the increased surface area, a variety of chemical applications and sensor device architectures are possible. Because the GLAD process provides precise nanoscale control over the film structure, characteristics such as the mechanical, magnetic, and optical properties of the deposited film may be engineered for various applications. Depositing onto prepatterned substrates forces the columns to adopt a planar ordering, an important requirement for photonic crystal applications.
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J. Vac. Sci. Technol. A 5, 3287 (1987); http://dx.doi.org/10.1116/1.574188 (26 pages) | Cited 151 times
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This paper reviews and analyzes the literature on thin carbon layers with emphasis on their use as protective overcoats for thin‐film magnetic media. We discuss carbon as a material, its preparation as a thin film, and review and evaluate various techniques for characterizing its thin‐film properties. |
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Metal–organic interface and charge injection in organic electronic devices J. Vac. Sci. Technol. A 21, 521 (2003); http://dx.doi.org/10.1116/1.1559919 (11 pages) | Cited 147 times Online Publication Date: 18 March 2003
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Charge injection at the interface between metallic electrodes and organic semiconductors plays a crucial role in the performance of organic (opto-)electronic devices. This article discusses the current understanding of the formation of the metal–organic contact and the parameters which control the injection current. Organic semiconductors differ significantly from their inorganic counterparts, primarily because they are amorphous van der Waals solids. As a result the electronic states are highly localized, and charge transport is by site-to-site hopping. Organics can also form clean interfaces with many metals, free of interface states in the gap. Nevertheless, there is generally found to be a significant vacuum level offset, the origins of which are not yet fully understood. Organic semiconductors are frequently free of donor and acceptor dopants, and as a result the depletion depth is larger than the organic layer thickness. Thus the Fermi level in the organic and the charge injection barriers depend most directly on the interface offset. The charge injection process is described as thermally assisted tunneling from the delocalized states of the metal into the localized states of the semiconductor, whose energy includes contributions from the mean barrier height, the image potential, the energetic disorder, and the applied electric field. There is no completely satisfactory analytic theory for the field and temperature dependence of the injection current, which, for well characterized interfaces, exhibits behavior relating to both thermionic emission and field-induced tunneling. © 2003 American Vacuum Society. |
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Electron cyclotron resonance microwave discharges for etching and thin‐film deposition J. Vac. Sci. Technol. A 7, 883 (1989); http://dx.doi.org/10.1116/1.575815 (11 pages) | Cited 146 times
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A recent, important development in low‐pressure and low‐temperature plasma processing is the microwave electron cyclotron resonance (ECR) discharge. Its lack of electrodes and its ability to create high densities of charged and excited species at low pressures (≲10−4 Torr) make it an attractive processing discharge in etching and thin‐film deposition applications. This article reviews the basic physics of ECR discharges and reviews the associated microwave system and applicator technologies. Waveguide and cavity ECR applicators are compared and are described in detail. Several ECR plasma processing reactors are also described. Methods of processing large surfaces are outlined, and typical experimentally measured ECR discharge characteristics are presented. |
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Raman scattering characterization of carbon bonding in diamond and diamondlike thin films J. Vac. Sci. Technol. A 6, 1783 (1988); http://dx.doi.org/10.1116/1.575297 (5 pages) | Cited 145 times
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The atomic bonding configurations of carbon bonding in diamond and diamondlike thin films are explored using Raman scattering. The general aspects of Raman scattering from composites are presented. Effects are discussed due to crystalline or amorphous structures, large versus microcrystalline domains, and strong optical absorption and transparent regions. The Raman scattering from diamondlike films shows several features which are attributed to microcrystalline graphitelike structures which all originate from the same region in the sample. In contrast, the spectra of diamond films show features attributed to different components of a composite film. Components identified are crystalline diamond, and disordered and microcrystalline graphitic structures. The presence of precursor microcrystalline or amorphous diamond structures is also suggested. |
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Plasma deposition of optical films and coatings: A review J. Vac. Sci. Technol. A 18, 2619 (2000); http://dx.doi.org/10.1116/1.1314395 (27 pages) | Cited 141 times
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Plasma enhanced chemical vapor deposition (PECVD) is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin film systems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties (refractive index, extinction coefficient, optical loss), these systems very frequently offer other desirable “functional” characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasma systems for the synthesis of thin film high and low index optical materials, and in the control of plasma–surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films (mainly physical vapor deposition), such as fabrication of graded index (inhomogeneous) layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others. © 2000 American Vacuum Society. |
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