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21 Feb 2013

Volume 113, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 073506 (2013); http://dx.doi.org/10.1063/1.4790173 (6 pages)

Uwe Kaiser, Sebastian Gies, Sebastian Geburt, Franziska Riedel, Carsten Ronning, and Wolfram Heimbrodt
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back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Interstitial oxygen behavior for thermal double donor formation in germanium: Infrared absorption studies

K. Inoue, T. Taishi, Y. Tokumoto, Y. Murao, K. Kutsukake, Y. Ohno, M. Suezawa, and I. Yonenaga

J. Appl. Phys. 113, 073501 (2013); http://dx.doi.org/10.1063/1.4792061 (5 pages)

Online Publication Date: 15 February 2013

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The kinetics of the reduction of interstitial oxygen (Oi) due to the formation of thermal double donors (TDDs) upon heat treatment in an oxygen-rich Ge crystal were investigated at various temperatures. Specimens were prepared from a Ge crystal with oxygen at a concentration of 4–5 × 1017 cm−3 grown by a new Czochralski method and were heat-treated in the temperature range 300–500 °C. Shrinkage of a dissolved oxygen absorption peak at 855 cm−1 and simultaneous development of a thermal double donor peak at 780 cm−1 were observed by infrared absorption spectroscopy at room temperature. The formation of TDDs was also detected electrically. Reduction of dissolved oxygen concentration upon the heat treatments was kinetically analyzed. The activation energy of the reduction of Oi concentration was evaluated to be 1.7 and 2.0 eV in the early and prolonged stages of the heat treatment, respectively, close to that of Oi diffusion. From the results, TDD development process was indicated to be the merge reaction of Oi-Oi to form oxygen dimers (Odimer) in the early stage of the heat treatment and further enlargement of Odimer to TDDs by absorbing Oi in the prolonged stage of the heat treatment in accordance with the On-2NN model.
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61.72.jj Interstitials
64.75.Bc Solubility
66.30.J- Diffusion of impurities
78.30.Am Elemental semiconductors and insulators
81.10.Fq Growth from melts; zone melting and refining
81.40.Gh Other heat and thermomechanical treatments

Optical characterization of free electron concentration in heteroepitaxial InN layers using Fourier transform infrared spectroscopy and a 2 × 2 transfer-matrix algebra

C. C. Katsidis, A. O. Ajagunna, and A. Georgakilas

J. Appl. Phys. 113, 073502 (2013); http://dx.doi.org/10.1063/1.4792259 (12 pages)

Online Publication Date: 15 February 2013

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Fourier Transform Infrared (FTIR) reflectance spectroscopy has been implemented as a non-destructive, non-invasive, tool for the optical characterization of a set of c-plane InN single heteroepitaxial layers spanning a wide range of thicknesses (30–2000 nm). The c-plane (0001) InN epilayers were grown by plasma-assisted molecular beam epitaxy (PAMBE) on GaN(0001) buffer layers which had been grown on Al2O3(0001) substrates. It is shown that for arbitrary multilayers with homogeneous anisotropic layers having their principal axes coincident with the laboratory coordinates, a 2 × 2 matrix algebra based on a general transfer-matrix method (GTMM) is adequate to interpret their optical response. Analysis of optical reflectance in the far and mid infrared spectral range has been found capable to discriminate between the bulk, the surface and interface contributions of free carriers in the InN epilayers revealing the existence of electron accumulation layers with carrier concentrations in mid 1019 cm−3 at both the InN surface and the InN/GaN interface. The spectra could be fitted with a three-layer model, determining the different electron concentration and mobility values of the bulk and of the surface and the interface electron accumulation layers in the InN films. The variation of these values with increasing InN thickness could be also sensitively detected by the optical measurements. The comparison between the optically determined drift mobility and the Hall mobility of the thickest sample reveals a value of rH = 1.49 for the Hall factor of InN at a carrier concentration of 1.11 × 1019 cm−3 at 300° Κ.
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78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
52.77.-j Plasma applications
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Vacuum ultraviolet dielectric function of ZnFe2O4 thin films

T. Böntgen, K. Brachwitz, R. Schmidt-Grund, M. Lorenz, and M. Grundmann

J. Appl. Phys. 113, 073503 (2013); http://dx.doi.org/10.1063/1.4790881 (4 pages) | Cited 1 time

Online Publication Date: 15 February 2013

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The dielectric function of ZnFe2O4 thin films has been studied in a wide spectral range from 0.5 eV to 9 eV. The observed optical transitions are identified as charge transfer and ligand field transitions. We propose a parametric model based on known model dielectric functions that fits well to the experimental data. The assignment of optical transitions is justified by a thorough comparison with optical data from other materials exhibiting similar transitions. The main contributions to the optical response are found to arise from charge transfer transitions from the O2p to the metal ion 4s and 3d bands. Furthermore weak crystal field transitions are observed. The evolution of the dielectric function as well as the crystal quality of the thin films with respect to growth temperature is further analyzed. A blue shift of the observed optical transitions is related to a relaxation of the lattice toward the bulk and an increase of the crystal quality with increasing growth temperature.
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78.66.Nk Insulators
68.55.at Other materials
71.70.-d Level splitting and interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Excitation intensity- and temperature-dependent photoluminescence in layered structured Tl2GaInSe2S2 crystals

N. M. Gasanly

J. Appl. Phys. 113, 073504 (2013); http://dx.doi.org/10.1063/1.4792499 (5 pages)

Online Publication Date: 15 February 2013

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Photoluminescence spectra of Tl2GaInSe2S2 layered crystals have been registered in the temperature range of 17–62 K and in the wavelength region of 525–690 nm. A broad visible photoluminescence band centered at 590 nm (2.10 eV) was observed at T = 17 K. Variation of emission band has been studied as a function of laser excitation intensity in the 0.1–55.7 mW cm−2 range. The analysis of the spectra reveals that the peak energy position changes with excitation intensity (blue shift). The radiative transitions from moderately deep donor level to shallow acceptor level were suggested to be responsible for the observed band. From X-ray powder diffraction study, the parameters of monoclinic unit cell of Tl2GaInSe2S2 were determined.
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78.55.Kz Solid organic materials
61.66.Fn Inorganic compounds
71.55.Ht Other nonmetals

Correlations between the morphology and emission properties of trench defects in InGaN/GaN quantum wells

F. C.-P. Massabuau, L. Trinh-Xuan, D. Lodié, E. J. Thrush, D. Zhu, F. Oehler, T. Zhu, M. J. Kappers, C. J. Humphreys, and R. A. Oliver

J. Appl. Phys. 113, 073505 (2013); http://dx.doi.org/10.1063/1.4792505 (7 pages)

Online Publication Date: 15 February 2013

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Atomic force microscopy (AFM) and scanning electron microscopy (SEM) with cathodoluminescence (CL) were performed on exactly the same defects in a blue-emitting InGaN/GaN multiple quantum well (QW) sample enabling the direct correlation of the morphology of an individual defect with its emission properties. The defects in question are observed in AFM and SEM as a trench partially or fully enclosing a region of the QW having altered emission properties. Their sub-surface structure has previously been shown to consist of a basal plane stacking fault (BSF) in the plane of the QW stack, and a stacking mismatch boundary (SMB) which opens up into a trench at the sample surface. In CL, the material enclosed by the trench may emit more or less intensely than the surrounding material, but always exhibits a redshift relative to the surrounding material. A strong correlation exists between the width of the trench and both the redshift and the intensity ratio, with the widest trenches surrounding regions which exhibit the brightest and most redshifted emission. Based on studies of the evolution of the trench width with the number of QWs from four additional MQW samples, we conclude that in order for a trench defect to emit intense, strongly redshifted light, the BSF must be formed in the early stages of the growth of the QW stack. The data suggest that the SMB may act as a non-radiative recombination center.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Nn Stacking faults and other planar or extended defects

Luminescence and energy transfer processes in ensembles and single Mn or Tb doped ZnS nanowires

Uwe Kaiser, Sebastian Gies, Sebastian Geburt, Franziska Riedel, Carsten Ronning, and Wolfram Heimbrodt

J. Appl. Phys. 113, 073506 (2013); http://dx.doi.org/10.1063/1.4790173 (6 pages)

Online Publication Date: 15 February 2013

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Zinc sulfide (ZnS) nanowires with a typical diameter of 100 to 300 nm have been doped with different concentrations of either Mn or Tb using ion implantation. Both systems show very efficient and long living intra-shell luminescence with strong non-exponential decay characteristics in the range of milliseconds. The time behavior of the corresponding luminescence is well described within a modified Förster model, taking into account the lower dimensionality of the nanowires in case of radiationless dipole-dipole energy transfer. The general applicability of this model for energy transfer processes in low dimensional systems will be shown as a function of concentration, temperature, excitation density as well as for measurements on the level of single nanowires.
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61.72.uj III-V and II-VI semiconductors
64.70.Nd Structural transitions in nanoscale materials
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
FREE

Ultrafast laser-induced premelting and structural transformation of gold nanorod

Yong Gan and Shan Jiang

J. Appl. Phys. 113, 073507 (2013); http://dx.doi.org/10.1063/1.4792659 (5 pages)

Online Publication Date: 19 February 2013

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Femtosecond laser irradiation of a gold nanorod has been simulated by a method that couples two-temperature model into molecular dynamics. Numerical results show that the surface premelting occurs prior to the initiation of planar defect and propagates from the surface layer into the inside of nanorod. Pressure relaxation leads to high-frequency temperature oscillation and two-way transformation between fcc and disordered atoms produced by the dynamic stresses. Partial dislocation cores are initiated on the crystal surfaces due to high stresses, and then noticeable planar defects including stacking faults and twin boundaries on {111} close-packed planes are developed. Finally, only parallel twin boundaries are present in the nanorod, showing favorable agreement with the experimental observation.
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64.70.kd Metals and alloys
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.dj Melting of specific substances

Oxygen diffusivity in silicon derived from dynamical X-ray diffraction

J. Will, A. Gröschel, D. Kot, M. A. Schubert, C. Bergmann, H.-G. Steinrück, G. Kissinger, and A. Magerl

J. Appl. Phys. 113, 073508 (2013); http://dx.doi.org/10.1063/1.4792747 (6 pages)

Online Publication Date: 20 February 2013

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Thickness dependent Pendellösung oscillations are highly sensitive to strain fields from defects in a host crystal. Based on this, we present a novel technique to measure the precipitation kinetics of oxygen in silicon already at its early stage of clustering at high temperatures. At 900 °C, precipitates with a radius smaller than 4 nm and with a density of 1 ± 0.5 × 1013 1/cm3 were observed. The technique was calibrated by complementary scanning transmission electron microscope and energy dispersive X-ray measurements in the range of normal diffusivity yielding a diffusion constant of 1.7 ± 0.1×10−12cm2/s, which is close to the literature value of 2.074×10−12cm2/s. The measurements have been made with the characteristic Kα1-line of a high voltage tungsten X-ray tube at 59.31 keV, which provides the opportunity to illuminate through complex sample environments like high temperature scattering furnaces.
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66.30.Lw Diffusion of other defects
66.30.Pa Diffusion in nanoscale solids
61.72.jd Vacancies
61.72.jj Interstitials
81.30.Mh Solid-phase precipitation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Computational investigation of the mechanical and tribological responses of amorphous carbon nanoparticles

Eric W. Bucholz and Susan B. Sinnott

J. Appl. Phys. 113, 073509 (2013); http://dx.doi.org/10.1063/1.4792753 (7 pages)

Online Publication Date: 20 February 2013

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Nanoparticles are a class of materials that have seen increasing use as friction and wear reducers in tribological applications. Amorphous carbon (a-C) films have been the subject of significant scientific and industrial interest for use as solid-state lubricants. Here, we present classical molecular dynamics simulations to investigate the mechanical and tribological responses of a-C nanoparticles that are subjected to external forces between hydrogen-terminated diamond surfaces. Over the range of a-C nanoparticle diameters (2–5 nm) and hydrogenation (0%–50%) considered, the simulations predict a consistent mechanical response where each nanoparticle is highly elastic. The simulations predict that the transition from elastic to plastic response is directly related to an increase in the percentage of carbon-carbon crosslinking within the individual nanoparticles. Contrarily, the simulations also predict that the tribological response is noticeably impacted by changes in diameter and hydrogenation. This is because during friction, hydrogen passivates the unsaturated carbon atoms near the nanoparticle's surface, which prevents interfacial bond formation and allows the nanoparticle to roll within the interface. From these findings, it is demonstrated that a-C nanoparticles are able to provide good tribological performance only when sufficient chemical passivation of the nanoparticles is maintained.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep

High-pressure study of the structural and elastic properties of defect-chalcopyrite HgGa2Se4

O. Gomis, R. Vilaplana, F. J. Manjón, D. Santamaría-Pérez, D. Errandonea, E. Pérez-González, J. López-Solano, P. Rodríguez-Hernández, A. Muñoz, I. M. Tiginyanu, and V. V. Ursaki

J. Appl. Phys. 113, 073510 (2013); http://dx.doi.org/10.1063/1.4792495 (10 pages) | Cited 2 times

Online Publication Date: 20 February 2013

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In this work, we focus on the study of the structural and elastic properties of mercury digallium selenide (HgGa2Se4) which belongs to the family of AB2X4 ordered-vacancy compounds with tetragonal defect chalcopyrite structure. We have carried out high-pressure x-ray diffraction measurements up to 13.2 GPa. Our measurements have been complemented and compared with total-energy ab initio calculations. The equation of state and the axial compressibilities for the low-pressure phase of HgGa2Se4 have been experimentally and theoretically determined and compared to other related ordered-vacancy compounds. The theoretical cation-anion and vacancy-anion distances in HgGa2Se4 have been determined. The internal distance compressibility in HgGa2Se4 has been compared with those that occur in binary HgSe and ε−GaSe compounds. It has been found that the Hg-Se and Ga-Se bonds behave in a similar way in the three compounds. It has also been found that bulk compressibility of the compounds decreases following the sequence “ε-GaSe > HgGa2Se4 > HgSe.” Finally, we have studied the pressure dependence of the theoretical elastic constants and elastic moduli of HgGa2Se4. Our calculations report that the low-pressure phase of HgGa2Se4 becomes mechanically unstable above 13.3 GPa.
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62.50.-p High-pressure effects in solids and liquids
64.30.Jk Equations of state of nonmetals
61.66.Fn Inorganic compounds
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
61.72.jd Vacancies

Strain induced intermixing of Ge atoms in Si epitaxial layer on Ge(111)

Aki Tosaka, Izumi Mochizuki, Ryota Negishi, and Yukichi Shigeta

J. Appl. Phys. 113, 073511 (2013); http://dx.doi.org/10.1063/1.4792503 (4 pages)

Online Publication Date: 20 February 2013

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The relationship between strain and effective mass of the √3 × √3-Ag structure surface metallic state, when formed on strained Si(111) layers on Ge(111), has been investigated by angle resolved photoelectron spectroscopy at various film thicknesses. Si layer lattice spacing expands and effective mass decreases at film thickness greater than 2 bilayers. This result is inconsistent with a previous study showing increasing effective mass with tensile strain for the √3 × √3-Ag structure. Ge-3d core level photoelectron spectra confirm that this disparity is caused by the intermixing of Ge atoms in the Si layer. The relationship between effective mass and strain is useful for gauging intermixing, and the effective mass of surface metallic states is useful for gauging nanoscale strain.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
68.35.bg Semiconductors
68.55.jd Thickness

Observation of the amorphous zinc oxide recrystalline process by molecular dynamics simulation

Ken-Huang Lin, Shih-Jye Sun, Shin-Pon Ju, Jen-Yu Tsai, Hsin-Tsung Chen, and Jin-Yuan Hsieh

J. Appl. Phys. 113, 073512 (2013); http://dx.doi.org/10.1063/1.4789956 (8 pages)

Online Publication Date: 21 February 2013

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The detailed structural variations of amorphous zinc oxide (ZnO) as well as wurtzite (B4) and zinc blende (B3) crystal structures during the temperature elevation process were observed by molecular dynamics simulation. The amorphous ZnO structure was first predicted through the simulated-annealing basin-hopping algorithm with the criterion to search for the least stable structure. The density and X-ray diffraction profiles of amorphous ZnO of the structure were in agreement with previous reports. The local structural transformation among different local structures and the recrystalline process of amorphous ZnO at higher temperatures are observed and can explain the structural transformation and recrystalline mechanism in a corresponding experiment [Bruncko et al., Thin Solid Films 520, 866-870 (2011)].
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64.70.kg Semiconductors
61.66.Fn Inorganic compounds
72.20.Ee Mobility edges; hopping transport
72.80.Ey III-V and II-VI semiconductors
72.80.Ng Disordered solids

Making use of x-ray optical effects in photoelectron-, Auger electron-, and x-ray emission spectroscopies: Total reflection, standing-wave excitation, and resonant effects

S.-H. Yang, A. X. Gray, A. M. Kaiser, B. S. Mun, B. C. Sell, J. B. Kortright, and C. S. Fadley

J. Appl. Phys. 113, 073513 (2013); http://dx.doi.org/10.1063/1.4790171 (25 pages)

Online Publication Date: 21 February 2013

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We present a general theoretical methodology and related open-access computer program for carrying out the calculation of photoelectron, Auger electron, and x-ray emission intensities in the presence of several x-ray optical effects, including total reflection at grazing incidence, excitation with standing-waves produced by reflection from synthetic multilayers and at core-level resonance conditions, and the use of variable polarization to produce magnetic circular dichroism. Calculations illustrating all of these effects are presented, including in some cases comparisons to experimental results. Sample types include both semi-infinite flat surfaces and arbitrary multilayer configurations, with interdiffusion/roughness at their interfaces. These x-ray optical effects can significantly alter observed photoelectron, Auger, and x-ray intensities, and in fact lead to several generally useful techniques for enhancing surface and buried-layer sensitivity, including layer-resolved densities of states and depth profiles of element-specific magnetization. The computer program used in this study should thus be useful for a broad range of studies in which x-ray optical effects are involved or are to be exploited in next-generation surface and interface studies of nanoscale systems.
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07.85.-m X- and γ-ray instruments

Diffusion of Mg dopant in metal-organic vapor-phase epitaxy grown GaN and AlxGa1−xN

K. Köhler, R. Gutt, J. Wiegert, and L. Kirste

J. Appl. Phys. 113, 073514 (2013); http://dx.doi.org/10.1063/1.4792662 (13 pages)

Online Publication Date: 21 February 2013

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Diffusion of the p-type dopant Mg in GaN and AlxGa1−xN which is accompanied by segregation and affected by transient effects in metal-organic vapor-phase epitaxy reactors is investigated. We have grown 110 nm thick Mg doped GaN and Al0.1Ga0.9N layers on top of undoped GaN and Al0.1Ga0.9N layers, respectively, in a temperature range between 925 °C and 1050 °C where we placed special emphasis on the lower temperature limit without diffusion to allow separation of Mg transients, diffusion, and segregation. Hereby, AlxGa1−xN layers enable monitoring of the resolution limit by secondary ion mass spectrometry analyses for the respective samples; therefore, thin AlxGa1−xN marker layers are incorporated in the thick GaN layers. We found an upper limit of 1.25 × 1019 cm−3 for diffusing Mg atoms in both sample types. Owing to the marked influence of Mg segregation in Al0.1Ga0.9N, diffusion is only seen by using a GaN cap on top of the Al0.1Ga0.9N layer sequence. Diffusion in Al0.1Ga0.9N is shown to be increased by about 25%−30% compared to GaN. Post growth annealing experiments under conditions equivalent to those used for growth of the Mg doped samples showed negligible diffusion. Comparing the results to well established findings on other doped III-V compounds, diffusion is explained by an interstitial-substitutional mechanism with a diffusion coefficient, which is concentration dependent. Analysis of the temperature dependent diffusivity revealed an activation energy of 5.0 eV for GaN:Mg and 5.2 eV for Al0.1Ga0.9N:Mg.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.sh Impurity distribution
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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