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1 Oct 2000

Volume 88, Issue 7, pp. 3795-4457

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The properties of ion clouds in a Paul trap: A statistical model

Jidong Hou, Yiqiu Wang, and Donghai Yang

J. Appl. Phys. 88, 4334 (2000); http://dx.doi.org/10.1063/1.1286232 (6 pages) | Cited 1 time

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We present a statistical model to calculate the spatial and energy properties of an ion cloud in a Paul trap. In this model, we consider the collision between the ions and the molecules of background gases as the reason to cause the quasistable state of an ion cloud. The space-charge potential in an ion cloud is taken into account by a self-consistent method. From the real parameters of a Paul trap the properties of an ion cloud can be computed. The comparison between the calculated and experimental results shows good agreement. The influences of background gases and space charge on the properties of ion clouds are studied. Our calculation shows that laser cooling does not work when the number of confined ions is larger than 106. © 2000 American Institute of Physics.
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37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Theoretical study of the ground and excited states of silicon clusters: Si8Hx

Keizo Nakajima, Kazunari Yoshizawa, and Tokio Yamabe

J. Appl. Phys. 88, 4340 (2000); http://dx.doi.org/10.1063/1.1289048 (7 pages) | Cited 3 times

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The electronic structures of small silicon clusters in the ground and excited states have been studied based on ab initio configuration interaction by the single-substitutions approximation method. We consider Si8Hx clusters of chain, branch, ladder, and cubic types as model compounds, due to their variety of molecular structures. Calculated Stokes shifts and oscillator strengths successfully reproduce the experimental electronic spectrum. These phenomena are well explained by the detailed analysis of the orbital patterns and energy level changes related to the excitation. The optical properties of the cubic Si cluster are considerably different from those of the other Si8 clusters. It shows zero oscillator strength, i.e., “forbidden transition,” from the first to 20th excited states because of its high symmetry. © 2000 American Institute of Physics.
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36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
31.50.Df Potential energy surfaces for excited electronic states
71.10.Li Excited states and pairing interactions in model systems
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.A- Ab initio calculations
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.vj Electron correlation calculations for atoms and ions: excited states
71.15.-m Methods of electronic structure calculations

Suppression/reversal of natural convection by exploiting the temperature/composition dependence of magnetic susceptibility

C. D. Seybert, J. W. Evans, F. Leslie, and W. K. Jones

J. Appl. Phys. 88, 4347 (2000); http://dx.doi.org/10.1063/1.1289790 (5 pages) | Cited 11 times

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Natural convection, driven by temperature or concentration gradients or both, is an inherent phenomenon during solidification of materials on Earth. This convection has practical consequences (e.g., effecting macrosegregation) but also renders difficult the scientific examination of diffusive/conductive phenomena during solidification. It is possible to halt, or even reverse, natural convection by exploiting the variation (with temperature, for example) of the susceptibility of a material. If the material is placed in a vertical magnetic field gradient, a buoyancy force of magnetic origin arises and, at a critical field gradient, can balance the normal buoyancy forces to halt convection. At higher field gradients the convection can be reversed. The effect has been demonstrated in experiments at Marshall Space Flight Center where flow was measured by particle image velocimetry in MnCl2 solution in a superconducting magnet. In auxiliary experiments the field in the magnet and the properties of the solution were measured. Computations of the natural convection, its halting and reversal, using the commercial software FLUENT® were in good agreement with the measurements. © 2000 American Institute of Physics.
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44.25.+f Natural convection
47.27.T- Turbulent transport processes
64.70.D- Solid-liquid transitions
81.30.Fb Solidification
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Sg Magnetocaloric effect, magnetic cooling
81.30.Mh Solid-phase precipitation
64.75.-g Phase equilibria

Gas dynamics of laser ablation: Influence of ambient atmosphere

Andrey V. Gusarov, Alexey G. Gnedovets, and Igor Smurov

J. Appl. Phys. 88, 4352 (2000); http://dx.doi.org/10.1063/1.1286175 (13 pages) | Cited 44 times

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A two-stage two-dimensional (2D) gas-dynamic model of laser ablation in an ambient gas atmosphere is proposed. The initial one-dimensional stage of the process is related to the ablation plume formation under the action of a laser pulse (duration of the order of 10 ns; fluence about several J/cm2; laser spot diameter about 1 mm) and describes heating, melting, and evaporation of the target, the target–vapor interaction in the Knudsen layer, and the vapor dynamics. The final 2D stage is responsible for the formation of the energy and angular distributions of the ablated material. Considerable compression of the ambient gas around the expanding plume of the laser-evaporated material and a shock front propagating through the undisturbed ambient gas are found. The pressure of the compressed ambient gas behind the shock may be much higher than the ambient one. However, at the investigated ambient pressures below 100 Pa, it remains still much lower than the vapor pressure during laser evaporation. Therefore, the initial stage of laser ablation is essentially independent of the ambient atmosphere. Once the laser pulse is over, the vapor pressure eventually drops down to a value comparable to the compressed ambient gas pressure. From this time on, the gas considerably suppresses vapor expansion. There is a noticeable difference between the vapor distribution in vacuum and the one in the ambient atmosphere: the vapor fills the entire plume volume in vacuum while in the presence of ambient atmosphere it is accumulated near the plume boundary and tends to form a thin shell. The angular and energy distributions of the ablated material are especially sensitive to the nature and pressure of the ambient gas. Both the kinetic energy of the ablated atoms and the width of their angular distribution decrease with the ambient pressure. © 2000 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
79.20.Ds Laser-beam impact phenomena
47.11.-j Computational methods in fluid dynamics
47.40.Nm Shock wave interactions and shock effects
47.45.-n Rarefied gas dynamics

Composition and chemical bonding of pulsed laser deposited carbon nitride thin films

E. Riedo, F. Comin, J. Chevrier, and A. M. Bonnot

J. Appl. Phys. 88, 4365 (2000); http://dx.doi.org/10.1063/1.1309041 (6 pages) | Cited 26 times

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We studied composition, structure, and growth parameters of amorphous diamond-like carbon (DLC) and carbon nitride (CNx) films deposited by pulsed laser deposition in vacuum and in nitrogen atmosphere. The composition (0⩽N/C⩽0.4), the structural and the electronic properties of the deposited carbon and carbon nitride films were investigated for different laser fluences (1–12 J/cm2). Electron energy loss spectroscopy, x-ray photoelectron spectroscopy, and micro-Raman spectroscopy indicated an increase in sp3-bonded carbon sites in the DLC films and an increase in N-sp3 C bonded sites in the CNx films with increasing deposition laser fluence. Raman spectroscopy also showed the presence of a small amount of CN bonds in the CNx films. Furthermore, we observed that keeping the nitrogen pressure constant (P=100 mTorr) the increase in the deposition laser fluence is reflected by an increase in the nitrogen content in the films. All the results have been discussed in the framework of different theoretical models. © 2000 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
61.50.Lt Crystal binding; cohesive energy
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
73.61.Ng Insulators
79.60.Dp Adsorbed layers and thin films
78.66.Nk Insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Work function study of rhenium oxidation using an ultra high vacuum scanning Kelvin probe

I. D. Baikie, U. Petermann, A. Speakman, B. Lägel, K. M. Dirscherl, and P. J. Estrup

J. Appl. Phys. 88, 4371 (2000); http://dx.doi.org/10.1063/1.1289486 (5 pages) | Cited 8 times

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We have undertaken a study of high work function (ϕ) surfaces as part of an ongoing project searching for efficient target materials for use in hyperthermal surface ionization (HSI), a new mass spectroscopy ionization technique. HSI relies on high ϕ surfaces for the production of positive ions. Rhenium is particularly interesting in this respect as oxidation substantially increases ϕ to approximately 7 eV. Using a novel ultrahigh vacuum scanning Kelvin probe and Auger electron spectroscopy we have followed the oxidation kinetics of clean, polycrystalline rhenium at temperatures in the range (300–800) K and examined the effects of oxidation via high resolution ϕ topographies. Our results indicate a Δϕ increase of 1050 meV at 300 K rising to 1950 meV at 800 K. We observe two reaction stages in the 300 K data, with a transition at 150 L, characterized by different rates of oxide growth. Sputter-cleaned surfaces exhibit significant surface roughness even after annealing, which dramatically influences the second oxidation stage. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
73.30.+y Surface double layers, Schottky barriers, and work functions
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
79.20.Fv Electron impact: Auger emission
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Gh Other heat and thermomechanical treatments

Evolution of structure in thin microcrystalline silicon films grown by electron-cyclotron resonance chemical vapor deposition

M. Birkholz, B. Selle, E. Conrad, K. Lips, and W. Fuhs

J. Appl. Phys. 88, 4376 (2000); http://dx.doi.org/10.1063/1.1289783 (4 pages) | Cited 14 times

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The growth of microcrystalline silicon, μc-Si, films has been studied by infrared spectroscopy and x-ray diffraction. Thin films of various thickness have been prepared from SiH4–H2 mixtures by electron-cyclotron resonance chemical vapor deposition. Two structural transitions were observed during film growth. The first transition at a critical thickness of dac=9 nm manifested itself by a change from an initially amorphous growth to polycrystalline growth. The second structural transition was related to an increasing amount of silicon grains of preferred orientation with (110) lattice planes parallel to the substrate. The population of such (110)-oriented grains N110 was found to become dominant at about d110=310 nm, which may be considered as a second critical thickness above which the film exhibits a (110) fiber texture. The increase of N110 with increasing thickness follows a d1/6 dependence. The effect is understood in terms of an interplay between etching and deposition during growth. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Cy Elemental semiconductors
64.70.K- Solid-solid transitions
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators

Kinetics of the graphitization of dispersed diamonds at “low” temperatures

Yu. V. Butenko, V. L. Kuznetsov, A. L. Chuvilin, V. N. Kolomiichuk, S. V. Stankus, R. A. Khairulin, and B. Segall

J. Appl. Phys. 88, 4380 (2000); http://dx.doi.org/10.1063/1.1289791 (9 pages) | Cited 55 times

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The bulk density of graphitized ultradisperse diamond (UDD) was measured by a gamma-ray attenuation method at 1370–1870 K. These data combined with small angle x-ray scattering and true density measurements of the samples heated at various fixed temperatures were used to study the graphitization kinetics of the UDD. The reaction rate was modeled as a migration rate of the interface between the developing graphite-like carbon and the remaining diamond phase. A “reducing sphere” model was used to obtain the rates from the changes in densities. The estimated kinetic parameters in an Arrhenius expression, namely the activation energy, E=45±4 kcal/mol, and the pre-exponential factor, A=74±5 nm/s, allow quantitative calculations of the diamond graphitization rates in and around the indicated temperature range. The calculated graphitization rates agree well with the graphitization rates of diamonds with different dispersity estimated from high-resolution transmission electron microscopy data. The large difference between the rates and the kinetic parameters obtained in this study and those estimated by G. Davies and T. Evans [Proc. R. Soc. London 328, 413 (1972)] for the temperature range 2150–2300 K indicates that there are different graphitization mechanisms operating in the “low” and “high” temperatures regions. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
81.20.-n Methods of materials synthesis and materials processing
78.70.Ck X-ray scattering

Preparation and photoluminescence of nanocrystalline MSO4:xTb3+ (M=Ca, Sr, and Ba; x=0.001–0.005)

Xiong Gong, Lei Liu, and Wenju Chen

J. Appl. Phys. 88, 4389 (2000); http://dx.doi.org/10.1063/1.1289053 (5 pages) | Cited 5 times

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A series of nanocrystalline MSO4:xTb3+ (M=Ca, Sr, and Ba; x=0.001–0.005) samples have been prepared by the co-precipitation method following low-temperature treatment. The x-ray diffraction technique yielded an average grain size of approximately 24 nm. Based upon the experimental data and theoretical calculations, it is concluded that the photoluminescence quenching in nanocrystalline MSO4:xTb3+ results from the dipole–quadrupole interaction. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.55.Hx Other solid inorganic materials
61.66.Fn Inorganic compounds
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.46.-w Structure of nanoscale materials
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation

Surface acoustic wave depth profiling of elastically inhomogeneous materials

Christ Glorieux, Weimin Gao, Silvio Elton Kruger, Kris Van de Rostyne, Walter Lauriks, and Jan Thoen

J. Appl. Phys. 88, 4394 (2000); http://dx.doi.org/10.1063/1.1290457 (7 pages) | Cited 26 times

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The potential of Rayleigh wave spectroscopy for the in-depth reconstruction of elastic properties of multilayers for materials with a continuous profile of elastic properties is explored. Two models to calculate the surface acoustic wave (SAW) dispersion spectrum from the profile of the elastic parameters are elaborated and compared. It is found that the relevant elastic parameters for Rayleigh wave dispersion in multilayers are the “effective” Rayleigh velocities, i.e., the Rayleigh velocities calculated for virtually semi-infinite layers. For the solution of the inverse problem, a neural network and a singular value decomposition model are proposed and tested on simulated SAW spectra. The reconstruction techniques are applied to reconstruct the elastic depth profile of shot-peened steel samples from laser-generated and laser-detected SAW data. © 2000 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Elastic deformation of wafer surfaces in bonding

Weihua Han, Jinzhong Yu, and Qiming Wang

J. Appl. Phys. 88, 4401 (2000); http://dx.doi.org/10.1063/1.1289233 (3 pages) | Cited 3 times

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A model has been proposed for describing elastic deformation of wafer surfaces in bonding. The change of the surface shape is studied on the basis of the distribution of the periodic strain field. With the condition of diminishing periodic strain away from the interface, Airy stress function has been found that satisfies the elastic mechanical equilibrium. The result reveals that the wavy interface elastically deforms a spatial wavelength from the interface. © 2000 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
62.20.F- Deformation and plasticity
46.55.+d Tribology and mechanical contacts
46.25.-y Static elasticity

Modeling the dynamics of Si wafer bonding during annealing

Weihua Han, Jinzhong Yu, and Qiming Wang

J. Appl. Phys. 88, 4404 (2000); http://dx.doi.org/10.1063/1.1308069 (3 pages) | Cited 2 times

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The bonding behavior of silicon wafers depends on activation energy for the formation of siloxane bonds. In this article we developed a quantitative model on the dynamics of silicon wafer bonding during annealing. Based on this model, a significant difference in the bonding behaviors is compared quantitatively between the native oxide bonding interface and the thermal oxide bonding interface. The results indicate that the bonding strength of the native oxide interface increases with temperature much more rapidly than that of the thermal oxide interface. © 2000 American Institute of Physics.
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81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.90.+c Other topics in materials science (restricted to new topics in section 81)

Thermodynamic analysis of III–V semiconductor alloys grown by metalorganic vapor phase epitaxy

Toshihiro Asai and David S. Dandy

J. Appl. Phys. 88, 4407 (2000); http://dx.doi.org/10.1063/1.1290740 (10 pages) | Cited 1 time

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A thermodynamic analysis has been applied to systematically study III–V semiconductor alloy deposition, including nitrides grown by metalorganic vapor phase epitaxy. The predicted solid compositions of a number of ternary and quaternary alloys, including AlxGa1−xPyAs1−y, are compared with experimental data. For phosphorus-containing alloys, introduction of a parameter f representing incomplete PH3 pyrolysis yields good agreement with experimental data. It is shown that the input mole fraction of the group III metalorganic sources influences the incorporation of P into the solid for these alloys. Solid composition is also calculated for nitride alloys as a function of inlet gas concentration. To date, thermodynamic models have been applied solely to predict N solubility limits for nitride alloys where mixing occurs on the group V sublattice. The present model is used to predict N solid compositions in ternary and quaternary alloys, and it is demonstrated that these values are below the theoretical solubility limits for In-containing nitrides. The role of H2 in the carrier gas is investigated for III–N–V, III–III–N–V, and III–N–V–V systems. © 2000 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors

Two-dimensional simulation of an oxy-acetylene torch diamond reactor with a detailed gas-phase and surface mechanism

M. Okkerse, C. R. Kleijn, H. E. A. van den Akker, M. H. J. M. de Croon, and G. B. Marin

J. Appl. Phys. 88, 4417 (2000); http://dx.doi.org/10.1063/1.1309052 (12 pages) | Cited 9 times

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A two-dimensional model is presented for the hydrodynamics and chemistry of an oxy-acetylene torch reactor for chemical vapor deposition of diamond, and it is validated against spectroscopy and growth rate data from the literature. The model combines the laminar equations for flow, heat, and mass transfer with combustion and deposition chemistries, and includes multicomponent diffusion and thermodiffusion. A two-step solution approach is used. In the first step, a lumped chemistry model is used to calculate the flame shape, temperatures and hydrodynamics. In the second step, a detailed, 27 species / 119 elementary reactions gas phase chemistry model and a 41 species / 67 elementary reactions surface chemistry model are used to calculate radicals and intermediates concentrations in the gas phase and at the surface, as well as growth rates. Important experimental trends are predicted correctly, but there are some discrepancies. The main problem lies in the use of the Miller–Melius hydrocarbon combustion mechanism for rich oxy-acetylene flames. [J. A. Miller and C. F. Melius, Combustion and Flame 91, 21 (1992)]. Despite this problem, some aspects of the diamond growth process are clarified. It is demonstrated that gas-phase diffusion limitations play a minor role in the diamond growth process, which is determined by surface kinetics. Except for atomic hydrogen, gas phase diffusion is also of minor importance for the transport of species in and behind the flame front. Finally, it is shown that penetration of nitrogen from the ambient air into the flame cannot explain the observed changes at the center of the diamond films as reported in the literature. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.33.Vx Reactions in flames, combustion, and explosions
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
47.70.Fw Chemically reactive flows
81.15.Aa Theory and models of film growth
47.11.-j Computational methods in fluid dynamics
81.05.ub Fullerenes and related materials
82.20.Wt Computational modeling; simulation

Bi surfactant control of ordering and surface structure in GaInP grown by organometallic vapor phase epitaxy

S. W. Jun, R. T. Lee, C. M. Fetzer, J. K. Shurtleff, G. B. Stringfellow, C. J. Choi, and T.-Y. Seong

J. Appl. Phys. 88, 4429 (2000); http://dx.doi.org/10.1063/1.1289478 (5 pages) | Cited 6 times

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The surfactant Bi has been added during organometallic vapor phase epitaxial growth (OMVPE) of GaInP using the precursor trimethylbismuth. The addition of a small amount of Bi during growth results in disordered material using conditions that would otherwise produce highly ordered GaInP. Significant changes in the surface structure are observed to accompany the disordering. Atomic force microscopy measurements show that Bi causes an order of magnitude increase in step velocity, leading to the complete elimination of three-dimensional islands for growth on singular (001) GaAs substrates, and a significant reduction in surface roughness. Surface photoabsorption measurements indicate that Bi reduces the number of [1̄10] P dimers on the surface. Secondary ion mass spectroscopy measurements reveal that the Bi is rejected from the bulk, even though it changes the surface reconstruction. Clearly, Bi acts as a surfactant during OMVPE growth of GaInP. The difference in band gap energy caused by the reduction in order parameter during growth is measured using photoluminescence to be about 110 meV for layers grown on singular substrates. Disorder/order/disorder heterostructures were successfully produced in GaInP with a constant solid composition by modulating the TMBi flow rate during growth. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
78.40.Fy Semiconductors
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