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2 Feb 1998

Volume 72, Issue 5, pp. 513-622

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Visible-blind GaN Schottky barrier detectors grown on Si(111)

A. Osinsky, S. Gangopadhyay, J. W. Yang, R. Gaska, D. Kuksenkov, H. Temkin, I. K. Shmagin, Y. C. Chang, J. F. Muth, and R. M. Kolbas

Appl. Phys. Lett. 72, 551 (1998); http://dx.doi.org/10.1063/1.120755 (3 pages) | Cited 64 times

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We report novel GaN detectors grown by molecular beam epitaxy on Si(111) substrates. Wurtzite structure epitaxial GaN exhibits room-temperature photoluminescence with a band-edge-related emission width as narrow as 7 nm and intensities comparable to high quality layers grown on sapphire by metalorganic chemical vapor deposition. Spectral response of lateral geometry Schottky detectors shows a sharp cutoff at 365 nm with peak responsivities of ∼ 0.05 A/W at 0 V, and ∼ 0.1 A/W with a −4 V bias. The dark current is ∼ 60 nA at −2 V bias. The noise equivalent power is estimated to be 3.7×10−9 W over the response bandwidth of 2.2 MHz. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.05.Ea III-V semiconductors
07.60.-j Optical instruments and equipment
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
73.40.Ns Metal-nonmetal contacts

Hydrogen-related photoluminescence in CdTe

J. Hamann, D. Blass, C. Casimir, T. Filz, V. Ostheimer, C. Schmitz, H. Wolf, Th. Wichert, A. Burchard, M. Deicher, and R. Magerle

Appl. Phys. Lett. 72, 554 (1998); http://dx.doi.org/10.1063/1.120756 (3 pages) | Cited 3 times

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CdTe, nominally undoped, was exposed to a hydrogen plasma and to low energy H+ implantation. Under both conditions, seven typical photoluminescence lines are observed in the excitonic region. They are assigned to the presence of hydrogen in CdTe. © 1998 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
78.55.Et II-VI semiconductors

Measurement of phonon-exciton dephasing rate in GaN on sapphire by degenerate four-wave mixing

S. Pau, J. Kuhl, F. Scholz, V. Haerle, M. A. Khan, and C. J. Sun

Appl. Phys. Lett. 72, 557 (1998); http://dx.doi.org/10.1063/1.120757 (3 pages) | Cited 12 times

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The density and temperature dependence of the exciton dephasing time of two hexagonal GaN films on sapphire is measured using degenerate four-wave mixing (DFWM). The residual 4 ps dephasing time at low temperature and density is caused by exciton-impurity scattering. We present a theory of DFWM for various amount of inhomogeneous broadening. Good agreement of the temperature dependence of the dephasing time is found between theory and experiment. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
63.20.kk Phonon interactions with other quasiparticles
71.35.Gg Exciton-mediated interactions
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
73.50.-h Electronic transport phenomena in thin films

Smooth n-type GaN surfaces by photoenhanced wet etching

C. Youtsey, I. Adesida, L. T. Romano, and G. Bulman

Appl. Phys. Lett. 72, 560 (1998); http://dx.doi.org/10.1063/1.120758 (3 pages) | Cited 62 times

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A room-temperature photoelectrochemical wet etching process is described that produces smoothly etched GaN surfaces using KOH solution and Hg arc lamp illumination. Atomic force microscope measurements indicate a root-mean-square etched surface roughness of 1.5 nm, which compares favorably to the unetched surface roughness of approximately 0.3 nm. Etch rates of 50 nm/min were obtained using a KOH solution concentration of 0.02 M and an illumination intensity of 40 mW/cm2. It is shown that the smooth etching occurs under conditions of low KOH solution concentration and high light intensities, which result in a diffusion-limited etch process. © 1998 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
82.45.-h Electrochemistry and electrophoresis
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Ea III-V semiconductors

Interband transition studies on CdxZn1−xTe/ZnTe step quantum wells under applied electric fields

T. W. Kim, K. H. Lee, and H. L. Park

Appl. Phys. Lett. 72, 563 (1998); http://dx.doi.org/10.1063/1.120760 (3 pages) | Cited 10 times

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Photoluminescence (PL) measurements were carried out to investigate the interband transitions in CdxZn1−xTe/ZnTe asymmetric step quantum wells with and without an applied electric field. Transmission electron microscopy showed that the CdxZn1−xTe/ZnTe step quantum wells consisted of a shallow Cd0.1Zn0.9Te well and a deep Cd0.18Zn0.82Te well bound by two thick ZnTe barriers. The results for the PL data at 300 K for several applied electric fields showed that the excitonic transition from the first electronic state to the first heavy-hole state shifted to the larger energy side as the applied electric field increased. The electronic subband energies and the wave functions in the step quantum wells were calculated by an envelope-function approximation method, taking into account the strain effects, and the calculated values of the interband transitions were in qualitative agreement with those obtained from the PL measurements. The Stark shift of the step quantum well was much more sensitive to the applied electric field than that of the single quantum well. These results indicate that CdxZn1−xTe/ZnTe step quantum wells hold promise for potential applications such as new types of modulators and quantum-well infrared photodetectors in the blue–green region of the spectrum. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.20.Jq Electro-optical effects

Uniform multiatomic step arrays formed by atomic hydrogen assisted molecular beam epitaxy on GaAs (331) substrates

Hans-Peter Schönherr, Jörg Fricke, Zhichuan Niu, Klaus-Jürgen Friedland, Richard Nötzel, and Klaus H. Ploog

Appl. Phys. Lett. 72, 566 (1998); http://dx.doi.org/10.1063/1.120761 (3 pages) | Cited 19 times

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Coherently aligned multi-atomic step arrays are naturally formed during molecular beam epitaxy (MBE) of GaAs/(AlGa)As heterostructures on GaAs (331) substrates. The step height systematically increases with the substrate temperature while the lateral periodicity remains almost unchanged. With atomic hydrogen irradiation the step height is larger by more than a factor of 2 compared to that in conventional MBE which is attributed to a larger surface migration length of adatoms. The higher uniformity in atomic hydrogen assisted MBE allows the formation of step arrays, 12–13 nm high with a lateral periodicity around 250 nm, and straight step edges over 10 μm length. The step arrays reveal a strong influence on the electron transport of Si-modulation-doped GaAs/(AlGa)As heterostructures with the conductivity parallel to the step edges at cryogenic temperatures more than one order of magnitude larger than that perpendicular to the steps. © 1998 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors

Influence of barrier height on scanning tunneling spectroscopy experimental and theoretical aspects

D. Stiévenard, B. Grandidier, J. P. Nys, X. de la Broise, C. Delerue, and M. Lannoo

Appl. Phys. Lett. 72, 569 (1998); http://dx.doi.org/10.1063/1.120762 (3 pages) | Cited 4 times

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Scanning tunneling spectroscopy allows the determination of the density of states of the involved electrodes as well as the associated barrier height. We have measured the barrier height between tungsten tip and the GaAs (110) surface with a scanning tunneling microscope (STM) in ultrahigh vacuum. When the tunneling junction exhibited a low barrier height, we observed and explained an apparent widening of the GaAs gap which can mislead the real doping concentration of the sample. A theoretical model based on the self-consistent Keldysh–Green functions formalism is used to calculate the STM current. It shows a possible lowering of the barrier height according to the adsorption of As or Ga atoms on the apex of the tungsten tip. © 1998 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.20.At Surface states, band structure, electron density of states

Hall magnetometer in the ballistic regime

F. M. Peeters and X. Q. Li

Appl. Phys. Lett. 72, 572 (1998); http://dx.doi.org/10.1063/1.120759 (3 pages) | Cited 68 times

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A Monte Carlo simulation of the ballistic motion of electrons in a mesoscopic Hall bar containing a local inhomogeneous magnetic field profile is presented. We find that in the regime of low magnetic fields, the Hall resistance is determined by the average magnetic field in the cross junction and is independent of the shape and position of this profile in the junction. Information on the size of the local magnetic field profile can also be obtained from the Hall measurement. The bend resistance, on the other hand, is much more precise on the exact details of the local magnetic field in the cross junction. © 1998 American Institute of Physics.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
07.55.Ge Magnetometers for magnetic field measurements
72.20.Ht High-field and nonlinear effects

Lateral confinement in ZnSe/ZnCdSe quantum wells grown on patterned substrates

W. Heiß, D. Stifter, G. Prechtl, A. Bonanni, H. Sitter, J. Liu, L. Tóth, and Á. Barna

Appl. Phys. Lett. 72, 575 (1998); http://dx.doi.org/10.1063/1.120763 (3 pages) | Cited 2 times

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ZnSe/Zn0.75Cd0.25Se quantum wells have been grown on GaAs submicron gratings. In these quantum structures, we observe an optical anisotropy induced by lateral confinement. Photoluminescence (PL) energy-shifts and the PL temperature dependence indicate a moderate modulation of the two-dimensional electron gas in the quantum well. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors

Atomistic simulation of SiH interactions with silicon surfaces during deposition from silane containing plasmas

Shyam Ramalingam, Dimitrios Maroudas, and Eray S. Aydil

Appl. Phys. Lett. 72, 578 (1998); http://dx.doi.org/10.1063/1.120764 (3 pages) | Cited 12 times

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A systematic atomic-scale analysis is presented of the interactions of SiH radicals from a silane plasma with amorphous hydrogenated silicon (a-Si:H) film surfaces based on molecular dynamics and Monte Carlo simulations. The coordination of the silicon surface atoms and the hydrogen surface concentration determine the mechanisms by which the SiH radical interacts with the surface and attaches itself to the film, as well as the “sticking” probability of the radical. On a-Si:H surfaces with low hydrogen concentration, SiH radicals remain on the surface and attach to silicon dangling bonds. In contrast, on a-Si:H surfaces with high hydrogen concentration and lower density of dangling bonds, radicals penetrate into the bulk film and attach to subsurface silicon atoms. An average reaction probability of 95% is predicted, which is in excellent agreement with recent experimental data. © 1998 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Gc Amorphous semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

A universal damage induced technique for quantum well intermixing

O. P. Kowalski, C. J. Hamilton, S. D. McDougall, J. H. Marsh, A. C. Bryce, R. M. De La Rue, B. Vögele, C. R. Stanley, C. C. Button, and J. S. Roberts

Appl. Phys. Lett. 72, 581 (1998); http://dx.doi.org/10.1063/1.120765 (3 pages) | Cited 42 times

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We report a novel technique for quantum well intermixing which is simple, reliable and low cost, and appears universally applicable to a wide range of material systems. The technique involves the deposition of a thin layer of sputtered SiO2 and a subsequent high temperature anneal. The deposition process appears to generate point defects at the sample surface, leading to an enhanced intermixing rate and a commensurate reduction in the required anneal temperature. Using appropriate masking it is possible to completely suppress the intermixing process, enabling large differential band gap shifts (over 100 meV) to be obtained across a single wafer. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

High photoresponsivity of a p-channel InGaP/GaAs/InGaAs double heterojunction pseudomorphic modulation-doped field effect transistor

H. J. Kim, D. M. Kim, D. H. Woo, S.-I. Kim, S. H. Kim, J. I. Lee, K. N. Kang, and K. Cho

Appl. Phys. Lett. 72, 584 (1998); http://dx.doi.org/10.1063/1.120813 (3 pages) | Cited 5 times

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In this letter, we report the electrical and optical characteristics of p-channel In0.13Ga0.87As double heterojunction pseudomorphic modulation-doped field effect transistor (MODFET) structure grown by gas source molecular beam epitaxy. The Hall mobility and the density of 2-DHGs (two-dimensional hole gases) in the pseudomorphic In0.13Ga0.87As channel were measured to be 250 cm2/V s and 1.9×1012 cm−2 at 300 K, and 5800 cm2/V s and 1.5×1012 cm−2 at 23 K, respectively. The fabricated p-channel MODFET shows a good mobility property which is due to high valence band discontinuity of InGaP/GaAs/InGaAs double barriers. The peak energy in the photoluminescence spectrum from the p-channel pseudomorphic MODFET structure was found to be 1.4 eV (λ=881 nm). The photoresponsivity with this modified pseudomorphic MODFET structure shows outstandingly better than that of a pin photodiode, particularly at low incident optical power. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Effect of column III vacancy on arsenic precipitation in low-temperature grown III–V arsenides

M. N. Chang, J.-W. Pan, J.-I. Chyi, K. C. Hsieh, and T.-E. Nee

Appl. Phys. Lett. 72, 587 (1998); http://dx.doi.org/10.1063/1.120814 (3 pages) | Cited 9 times

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Separately grown p-type, intrinsic, and n-type GaAs at low temperatures as well as a combined p-i-n structure have been used to study the formation of As precipitates upon annealing at 800 °C. For the separate structures, least precipitates have been noticed in the n-type material. In contrast, the highest density of precipitates appears in the n region for the p-i-n structure. In addition, an obvious band depleted of precipitates, exists in the intrinsic region near the n-i interface. A general vacancy model, including Fermi level effect and crystal bonding strength (thermodynamic factor), has been developed to explain the current results as well as to predict As precipitation in various low temperature grown III–V heterostructures. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
64.75.-g Phase equilibria
61.72.J- Point defects and defect clusters
81.05.Ea III-V semiconductors
81.30.Mh Solid-phase precipitation
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Annealing effect on concentration of EL6-like deep-level state in low-temperature-grown molecular beam epitaxial GaAs

J. Darmo, F. Dubecký, P. Kordoš, and A. Förster

Appl. Phys. Lett. 72, 590 (1998); http://dx.doi.org/10.1063/1.120815 (3 pages) | Cited 2 times

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A deep-level donor state with signatures similar to the EL6 level observed in low-temperature-grown molecular beam epitaxial (MBE) GaAs grown at 250 °C and annealed in the temperature range 310–370 °C was studied. The annealing kinetics of this level suggest a confined pair recombination, likely VGa and Asi. A correlation between the deep level observed and recently published photoluminescence data of low-temperature-grown MBE GaAs is found. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.Cc Kinetics of defect formation and annealing
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Charge release of lanthanum-doped lead zirconate titanate stannate antiferroelectric thin films

Baomin Xu, Paul Moses, Neelesh G. Pai, and L. Eric Cross

Appl. Phys. Lett. 72, 593 (1998); http://dx.doi.org/10.1063/1.120817 (3 pages) | Cited 38 times

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The charge release speed and backward phase switching time of lanthanum-doped lead zirconate titanate stannate antiferroelectric thin films were investigated by directly measuring the switching current upon removal of the applied electric field. The backward switching time is about 6 ns. The maximum switching current density can reach 9400 A/cm2, and more than half of the stored charge can be released in 10 ns. These results show that the obtained antiferroelectric thin films are very promising for decoupling capacitor applications in high speed multichip modules. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.80.-e Ferroelectricity and antiferroelectricity

Solid-state metathesis reactions under pressure: A rapid route to crystalline gallium nitride

Charles H. Wallace, Sang-Ho Kim, Garry A. Rose, Lin Rao, James R. Heath, Malcolm Nicol, and Richard B. Kaner

Appl. Phys. Lett. 72, 596 (1998); http://dx.doi.org/10.1063/1.120818 (3 pages) | Cited 13 times

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High pressure chemistry has traditionally involved applying pressure and increasing temperature until conditions become thermodynamically favorable for phase transitions or reactions to occur. Here, high pressure alone is used as a starting point for carrying out rapid, self-propagating metathesis reactions. By initiating chemical reactions under pressure, crystalline phases, such as gallium nitride, can be synthesized which are inaccessible when initiated from ambient conditions. The single-phase gallium nitride made by metathesis reactions under pressure displays significant photoluminescence intensity in the blue/ultraviolet region. The absence of size or surface-state effects in the photoluminescence spectra show that the crystallites are of micron dimensions. The narrow lines of the x-ray diffraction patterns and scanning electron microscopy confirm this conclusion. Brightly luminescent thin films can be readily grown using pulsed laser deposition. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
62.50.-p High-pressure effects in solids and liquids

Damage-free separation of GaN thin films from sapphire substrates

W. S. Wong, T. Sands, and N. W. Cheung

Appl. Phys. Lett. 72, 599 (1998); http://dx.doi.org/10.1063/1.120816 (3 pages) | Cited 133 times

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Gallium nitride thin films grown on sapphire substrates were successfully separated and transferred onto Si substrates using single 38 ns KrF excimer laser pulses directed through the transparent substrate at fluences in the range of 400–600 mJ/cm2. The absorption of the 248 nm radiation by the GaN at the interface induces rapid thermal decomposition of the interfacial layer, yielding metallic Ga and N2 gas. The substrate is easily removed by heating above the Ga melting point of 30 °C. Scanning electron microscopy and x-ray diffraction of the GaN films before and after lift-off demonstrate that the structural quality of the GaN films is not altered by the separation and transfer process. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
79.20.Ds Laser-beam impact phenomena
85.40.Sz Deposition technology
81.65.-b Surface treatments
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.55.-a Thin film structure and morphology
68.35.Gy Mechanical properties; surface strains
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