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15 Mar 2010

Volume 107, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 107, 061802 (2010); http://dx.doi.org/10.1063/1.3340518 (13 pages)

Vojtěch Minárik, Michal Beneš, and Jan Kratochvíl
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back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Microstructural properties and dislocation evolution on a GaN grown on patterned sapphire substrate: A transmission electron microscopy study

Y. H. Kim, H. Ruh, Y. K. Noh, M. D. Kim, and J. E. Oh

J. Appl. Phys. 107, 063501 (2010); http://dx.doi.org/10.1063/1.3327004 (4 pages) | Cited 5 times

Online Publication Date: 16 March 2010

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The microstructural properties of a GaN layer grown on a patterned sapphire substrate (PSS) were studied in detail using transmission electron microscope techniques to determine dislocation and growth behaviors. Regular and uniform recrystallized GaN islands were observed on the protruding pattern. On a flat sapphire surface, the crystallographic orientation relationship of 〈math2math0〉GaN on FS//〈1math00〉sapphire and {1math01}GaN on FS//{1math13}sapphire existed between the GaN and the substrate. On the other hand, the orientation relationship of 〈math2math0〉GaN layer//〈math2math0〉GaN island on IS//〈1math00〉sapphire and {1math01}GaN layer//{0002}GaN island on IS//{1math13}sapphire was confirmed among the GaN layer, the recrystallized GaN islands on an inclined sapphire surface and the PSS. The flat surface among the protruding patterns began to fill rapidly with GaN. Then, the GaN gradually overgrew the protruding pattern and coalesced near the summit as the growth time increased. The generation of threading dislocations was observed in the vicinity of the coalescence points near the top of the protruding patterns.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.J- Morphology of films
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

High precision thermal stress study on flip chips by synchrotron polychromatic x-ray microdiffraction

Kai Chen, N. Tamura, Wei Tang, M. Kunz, Yi-Chia Chou, K. N. Tu, and Yi-Shao Lai

J. Appl. Phys. 107, 063502 (2010); http://dx.doi.org/10.1063/1.3309750 (5 pages) | Cited 1 time

Online Publication Date: 16 March 2010

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The bending and residual stress of flip chips caused by the mismatch of thermal expansion between the chip and the substrate have been measured by polychromatic microfocused synchrotron x-ray beam. Precise orientation information as a function of position on the chip was obtained from Laue diffraction patterns, so that the bending angle with respect to a reference position at the center of the chip can be calculated at each position. This in turn allows deducing the local curvature of the entire flip chip. Local stress distribution was then mapped by applying a modified Stoney’s stress-strain equation to the measured curvature. Our study shows that thermal stress on the circuits and the solder joints in a flip chip strongly depend on temperature and the distance from the center of the chip, indicating that interconnects at the corner and edge of a flip chip are of reliability concerns.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

In situ x-ray diffraction studies on epitaxial VO2 films grown on c-Al2O3 during thermally induced insulator-metal transition

Kunio Okimura, Joe Sakai, and Shriram Ramanathan

J. Appl. Phys. 107, 063503 (2010); http://dx.doi.org/10.1063/1.3327422 (5 pages) | Cited 16 times

Online Publication Date: 16 March 2010

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The structural phase transition (SPT) of VO2 films epitaxially grown on c-Al2O3 substrates by pulsed laser deposition and reactive sputtering was investigated by in situ temperature-controlled x-ray diffraction (XRD) across metal-insulator transition (MIT). An intermediate insulator phase was observed between room temperature monoclinic phase and high temperature metallic tetragonal phase. Gaussian curve fittings for measured XRD patterns revealed a significant contribution of the intermediate phase covering wide temperature range across MIT. Polycrystalline VO2 films grown on Si substrates revealed pure rutile phase after MIT in contrast with the epitaxial films on c-Al2O3 substrates. Strained structure of the VO2 films grown on c-Al2O3 substrates could be a mechanism for the formation of such intermediate phase known as monoclinic M2 phase. Presence of the intermediate insulator phase in highly oriented VO2 films may be an important factor in understanding the relation between MIT and SPT.
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68.55.aj Insulators
71.30.+h Metal-insulator transitions and other electronic transitions
81.15.Cd Deposition by sputtering
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
64.70.K- Solid-solid transitions

Strain relaxation in high Ge content SiGe layers deposited on Si

G. Capellini, M. De Seta, Y. Busby, M. Pea, F. Evangelisti, G. Nicotra, C. Spinella, M. Nardone, and C. Ferrari

J. Appl. Phys. 107, 063504 (2010); http://dx.doi.org/10.1063/1.3327435 (8 pages) | Cited 11 times

Online Publication Date: 16 March 2010

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We have used Raman spectroscopy, transmission electron microscopy, x-ray diffraction, and x-ray photoemission spectroscopy to investigate strain relaxation mechanism of Si0.22Ge0.78 heteroepitaxial layer deposited on Si substrates in tensile, neutral, and compressive strain conditions. The three regimes have been obtained by interposing between the SiGe layer and the substrate a fully relaxed Ge layer, a partially relaxed Ge layer, or growing directly the alloy on Si. We found that the deposition of a Ge buffer layer prior to the growth of the SiGe is very promising in view of the realization of thin virtual substrates on silicon to be used for the deposition of strain-controlled high Ge content SiGe alloys. We demonstrate that this is mainly due to the strain relaxation mechanism in the Ge layer occurring via insertion of pure edge 90° misfit dislocations (MDs) and to the confinement of threading arms in to the Ge layer due to a second MD network formed at the SiGe/Ge heterointerface.
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68.60.Bs Mechanical and acoustical properties
68.55.ag Semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.30.-j Infrared and Raman spectra

Near-infrared quantum cutting via cooperative energy transfer in Gd2O3:Bi3+,Yb3+ phosphors

X. Y. Huang and Q. Y. Zhang

J. Appl. Phys. 107, 063505 (2010); http://dx.doi.org/10.1063/1.3354063 (4 pages) | Cited 13 times

Online Publication Date: 19 March 2010

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An efficient near-infrared (NIR) quantum-cutting (QC) by converting broadband ultraviolet (UV) into NIR via cooperative down-conversion (CD) has been demonstrated in Gd2O3:Bi3+,Yb3+ phosphors. Upon excitation of UV photon varying from 320–390 nm, NIR emissions has been obtained from transitions of the transition-metal Bi3+:3P1 level to the rare-earths Yb3+:2F5/2 level. The authors have analyzed the measured luminescence spectra and decay lifetimes and proposed a mechanism to rationalize the CD effect. Application of the broadband NIR-QC phosphors might greatly enhance response of silicon-based solar cells by means of down-conversion of UV part of the solar spectrum to NIR photons with a twofold increase in the photon number.
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88.40.H- Solar cells (photovoltaics)
78.40.Ha Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
84.60.Jt Photoelectric conversion
42.50.Ar Photon statistics and coherence theory

Lattice relaxation process and crystallographic tilt in GaP layers grown on misoriented Si(001) substrates by metalorganic vapor phase epitaxy

Yasufumi Takagi, Yuzo Furukawa, Akihiro Wakahara, and Hirofumi Kan

J. Appl. Phys. 107, 063506 (2010); http://dx.doi.org/10.1063/1.3310479 (8 pages) | Cited 13 times

Online Publication Date: 22 March 2010

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A lattice relaxation process and a crystallographic tilt in GaP layers grown on misoriented Si(001) substrates by metalorganic vapor phase epitaxy were investigated. Strained pseudomorphic GaP layers without defects on Si were successfully achieved by the optimization of growth conditions. Below critical thickness, the strained GaP layers were tilted in the misoriented direction of the Si substrates and triclinically distorted. Above critical thickness, the residual strain in the GaP layers was progressively relaxed with increased thickness of the GaP layers by forming 60° misfit dislocations propagating to the two orthogonal 〈110〉 directions at the heterointerface. X-ray diffuse scattering around the symmetrical GaP(004) diffraction was observed after introducing misfit dislocations. Diffuse scattering became dominant with an increase in the density of the misfit dislocations and resulted in a broadening of the full width at half maximum of the x-ray rocking curves. The GaP layers that were relaxed with highly dense misfit dislocations were tilted opposite of the misoriented direction due to the imbalance nucleation of the misfit dislocations on each {111} glide plane.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
78.70.Ck X-ray scattering
81.05.Ea III-V semiconductors

Phase stability of carbon clathrates at high pressure

Jian-Tao Wang, Changfeng Chen, Ding-Sheng Wang, H. Mizuseki, and Y. Kawazoe

J. Appl. Phys. 107, 063507 (2010); http://dx.doi.org/10.1063/1.3359682 (4 pages) | Cited 4 times

Online Publication Date: 22 March 2010

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Group-IV element clathrates have attracted considerable interest in recent years. Here, we report an ab initio study on the structural stability of carbon clathrates at high pressure and identify fcc-C136 clathrate as the third most stable carbon phase after cubic diamond and hexagonal graphite. A pressure-induced phase transition is predicted to occur around 17 GPa from hexagonal graphite to fcc-C136, which is more stable than other carbon clathrates such as hex-C40 and sc-C46, and the recently predicted metastable M-carbon up to 26 GPa. Phonon dispersion calculations confirm the dynamic stability of fcc-C136 as well as diamond.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.66.Bi Elemental solids
64.70.K- Solid-solid transitions
64.60.My Metastable phases
62.50.-p High-pressure effects in solids and liquids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

The basic polyhedral clusters, the optimum glass formers, and the composition-structure-property (glass-forming ability) correlation in Cu–Zr metallic glasses

Z. D. Sha, B. Xu, L. Shen, A. H. Zhang, Y. P. Feng, and Y. Li

J. Appl. Phys. 107, 063508 (2010); http://dx.doi.org/10.1063/1.3359683 (4 pages) | Cited 9 times

Online Publication Date: 22 March 2010

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Using the large-scale atomic/molecular massively parallel simulator, chemical short-range order of the Cu–Zr binary system over the three good glass-forming compositional ranges has been investigated. Based on a statistical analysis, a simple route has been developed for broad investigations of the basic polyhedral clusters, optimum glass formers, as well as the composition-structure-property (glass-forming ability) correlation. In addition, topological short-range orders of the basic polyhedral clusters in the three compositional ranges were characterized. Our findings have implications for understanding the nature, forming ability, and properties of metallic glasses.
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61.43.Fs Glasses
64.70.pe Metallic glasses

Stress-relaxation behavior in gels with ionic and covalent crosslinks

Xuanhe Zhao, Nathaniel Huebsch, David J. Mooney, and Zhigang Suo

J. Appl. Phys. 107, 063509 (2010); http://dx.doi.org/10.1063/1.3343265 (5 pages) | Cited 14 times

Online Publication Date: 23 March 2010

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Long-chained polymers in alginate hydrogels can form networks by either ionic or covalent crosslinks. This paper shows that the type of crosslinks can markedly affect the stress-relaxation behavior of the gels. In gels with only ionic crosslinks, stress relaxes mainly through breaking and subsequent reforming of the ionic crosslinks, and the time scale of the relaxation is independent of the size of the sample. By contrast, in gels with only covalent crosslinks, stress relaxes mainly through migration of water, and the relaxation slows down as the size of the sample increases. Implications of these observations are discussed.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
82.70.Gg Gels and sols
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.10.+s Mechanical properties of liquids

In situ laser-based resonant ultrasound measurements of microstructure mediated mechanical property evolution

D. H. Hurley, S. J. Reese, S. K. Park, Z. Utegulov, J. R. Kennedy, and K. L. Telschow

J. Appl. Phys. 107, 063510 (2010); http://dx.doi.org/10.1063/1.3327428 (5 pages) | Cited 3 times

Online Publication Date: 24 March 2010

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In situ laser-based resonant ultrasound spectroscopy is used to characterize the development of a recrystallized microstructure in a high purity copper sample. The modal shapes, used for mode identification, of several resonant modes are determined before and after annealing by raster scanning the laser interferometric probe. This information is used to isolate the motion of individual modes during high temperature annealing. The evolution of a particular mode during annealing is examined in detail. During recrystallization, the center frequency of this mode shifts by approximately 20% of the original value. Using electron backscatter data it is shown that the majority of this shift is due to changes in the polycrystal average elastic stiffness tensor, driven by changes in texture, and that changes in dislocation density and pinning length are secondary influences.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
79.20.Kz Other electron-impact emission phenomena
43.35.Yb Ultrasonic instrumentation and measurement techniques
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Colloidal gold nanosphere dispersions in smectic liquid crystals and thin nanoparticle-decorated smectic films

R. Pratibha, W. Park, and I. I. Smalyukh

J. Appl. Phys. 107, 063511 (2010); http://dx.doi.org/10.1063/1.3330678 (5 pages) | Cited 17 times

Online Publication Date: 24 March 2010

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We demonstrate that the layer structure and elasticity stabilize dispersions of colloidal nanoparticles in smectic liquid crystals. We use surface plasmon resonance spectra of gold nanospheres to probe their spatial distributions in the bulk of smectic lamellae. The average interparticle distances between the well-separated nanoinclusions in thin (<100 nm) smectic films are probed by atomic force microscopy. We show that limited motion of nanoparticles across layers due to the one-dimensional quasi-long-range solid-like structure and their elasticity-mediated interactions preclude irreversible aggregation and enhance the stability of the ensuing nanoscale dispersions in thermotropic smectic liquid crystals.
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61.30.-v Liquid crystals
64.75.St Phase separation and segregation in thin films
62.10.+s Mechanical properties of liquids
68.15.+e Liquid thin films
64.75.Xc Phase separation and segregation in colloidal systems
82.70.Dd Colloids

Homogeneous dislocation nucleation in cyclotrimethylene trinitramine under shock loading

M. J. Cawkwell, K. J. Ramos, D. E. Hooks, and Thomas D. Sewell

J. Appl. Phys. 107, 063512 (2010); http://dx.doi.org/10.1063/1.3305630 (11 pages) | Cited 13 times

Online Publication Date: 25 March 2010

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The propagation of shock waves normal to (111) in the energetic molecular crystal cyclotrimethylene trinitramine (RDX) has been studied using large-scale molecular dynamics simulations. Partial dislocation loops with Burgers vector 0.16[010] are nucleated homogeneously on (001) at Rankine–Hugoniot shock pressures greater than 1.3 GPa. Calculations of the [010] cross-section of the (001) generalized stacking fault energy surface as a function of applied pressure along [001] reveals that the stacking fault enclosed by the partial dislocation loops is rendered metastable by a stress-induced change in molecular conformation. Furthermore, large-scale molecular dynamics simulations performed on quasi-two-dimensional (111)-oriented single crystals show a two-wave elastic-plastic response with a “galloping” plastic wave. We propose that the onset of homogeneous dislocation nucleation accounts for the abrupt change in the elastic-plastic response of macroscopic (111)-oriented RDX single crystals observed in recent experiments by giving rise to an anomalous plastic hardening.
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62.50.Ef Shock wave effects in solids and liquids
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.72.Nn Stacking faults and other planar or extended defects
61.72.Bb Theories and models of crystal defects
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

1H and 7Li nuclear magnetic resonance study of the superionic crystals K4LiH3(SO4)4 and (NH4)4LiH3(SO4)4

Ae Ran Lim and Hongkee Shin

J. Appl. Phys. 107, 063513 (2010); http://dx.doi.org/10.1063/1.3331816 (6 pages) | Cited 3 times

Online Publication Date: 29 March 2010

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We have investigated the temperature dependences of the line shape, spin-lattice relaxation time, T1, and spin-spin relaxation time, T2, of the 1H and 7Li nuclei in K4LiH3(SO4)4 and (NH4)4LiH3(SO4)4 single crystals. We compared the nuclear magnetic resonance (NMR) results obtained for the two crystals. According to the NMR relaxation results, the influences of the H and Li atoms of K4LiH3(SO4)4 crystals on the superionic phase transition TS are not significant, whereas the influences of the H and Li atoms of (NH4)4LiH3(SO4)4 crystals on TS are significant. The increase in the relaxation time of the hydrogen-bond protons in (NH4)4LiH3(SO4)4 crystals above TS indicates that the breaking of O–H⋯O bonds and the formation of new H-bonds with HSO4− contribute significantly to their high temperature conductivity. The main contribution to this conductivity at high temperatures is the mobility of the hydrogen-bond protons.
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76.60.Es Relaxation effects
66.30.H- Self-diffusion and ionic conduction in nonmetals
64.70.K- Solid-solid transitions

Light-induced superlow electric field for domain reversal in near-stoichiometric magnesium-doped lithium niobate

Hao Zeng, Yongfa Kong, Hongde Liu, Shaolin Chen, Ziheng Huang, Xinyu Ge, and Jingjun Xu

J. Appl. Phys. 107, 063514 (2010); http://dx.doi.org/10.1063/1.3359721 (4 pages) | Cited 3 times

Online Publication Date: 29 March 2010

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Light-induced domain reversal of near-stoichiometric Mg-doped LiNbO3 crystal was investigated with a focused 532 nm continuous laser beam. The lowest electric field applied to accomplish domain nucleation is only 30 V/mm and 1/80 of the coercive field, which is safe and convenient for us to fabricate domain structures. Under this superlow applied field, the pinning effect of domain wall is so obvious that the inverted domain reveals a gear shape contrary to the hexagon in a higher applied field. Then two-dimensional domain patterns with the smallest domain size of 4 μm have been fabricated.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates

Growth, structure, and mechanical properties of hydrogenated amorphous carbon nitride films deposited by CH3CN dielectric barrier discharges

Jinhai Niu, Dongping Liu, Haibo Cai, Yang Liu, and Suolin Cui

J. Appl. Phys. 107, 063515 (2010); http://dx.doi.org/10.1063/1.3332115 (10 pages)

Online Publication Date: 29 March 2010

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Hydrogenated amorphous carbon nitride (a-C:N:H) films were synthesized with CH3CN dielectric barrier discharges (DBD) plasmas. The effects of varying the CH3CN pressure (p) and the frequency of the power supply (f) on the film growth and film properties were studied. The deposited films were characterized using Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy (AFM), and AFM-based nanoindentation. p and f were found to significantly influence the structures, compositions, deposition rates, surface roughness, and nanohardess of deposited a-C:N:H films. The experimental results indicate that dense a-C:N:H films with extremely low surface roughness (rms<1.0 nm) can be deposited with CH3CN DBD plasmas at f = 1 kHz and p = ∼ 100 Pa. The deposition systems were in situ characterized by means of optical emission spectroscopy. The emission intensities of major radicals, such as CN (B 2Σ→X 2Σ) and NH (A 3Π→X 3Σ) significantly increased with increasing f or decreasing p. N2 molecules were formed in the residual gas as a stable product, which leads to a decrease in the N/C ratio in deposited a-C:N:H films. The rotational and vibrational temperature of N2 C 3Π states in CH3CN and N2 DBD plasmas were examined and the N2 molecules produced in CH3CN DBD plasmas had the rotational temperature of ∼ 2000 K and vibrational temperature of ∼ 500 K. In the N2 DBD plasma, the rotational and vibrational temperature of the N2 molecules were 470±10 and 2850±50 K, respectively. The basic chemical reactions in the gas phase are presented and correlations between the film properties, the gas-phase plasma diagnostic data, and the film growth processes are discussed.
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68.55.at Other materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
78.66.Nk Insulators
79.60.Dp Adsorbed layers and thin films
68.60.Bs Mechanical and acoustical properties
78.30.Hv Other nonmetallic inorganics

Thermodynamic phase diagram for hydrogen on polar InP(111)B surfaces

Haibo Shu, Xiaoshuang Chen, Ruibin Dong, Xiaofang Wang, and Wei Lu

J. Appl. Phys. 107, 063516 (2010); http://dx.doi.org/10.1063/1.3331767 (5 pages) | Cited 2 times

Online Publication Date: 30 March 2010

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Thermodynamic stability of hydrogenated polar InP(111)B surfaces is systematically studied by performing first-principles density functional calculations. Employing a thermodynamic approach, the hydrogen chemical potential is considered as functions of temperature and pressure. The calculated Gibbs free energies demonstrate that the surface structures of InP(111)B strongly depend on growth condition and surface compositions. The (2×2) surfaces with 3PH2+PH3, 3H+PH3, 3H, and P trimer, and the (math×math) surface with In adatom are stable phases under different chemical potentials of P and H, respectively. Moreover, our calculations suggest that the ideal surface and most of (math×math) surfaces are just metastable due to their deviation from electron counting rule. The calculated surface phase diagrams as the functions of temperature and pressure of H2 reveal that the (2×2) surface with P trimer is stable under the experimental growth condition (550–800 K). Once the samples are cooled down in a H-rich ambient, the hydrogenated InP(111)B surfaces are more favorable.
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65.40.G- Other thermodynamical quantities
82.60.-s Chemical thermodynamics
73.20.At Surface states, band structure, electron density of states
68.35.Dv Composition, segregation; defects and impurities
68.43.Mn Adsorption kinetics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Carrier transfer from wetting layer to quantum dots studied by cw-resolved and time-resolved photoluminescence in CdSe/ZnSe quantum dot system

Tae Soo Kim, Byoung Woo Lee, Eunsoon Oh, Sanghoon Lee, and J. K. Furdyna

J. Appl. Phys. 107, 063517 (2010); http://dx.doi.org/10.1063/1.3354064 (3 pages)

Online Publication Date: 31 March 2010

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We have studied the cw-resolved and time-resolved photoluminescence (PL) spectra of the CdSe quantum dots (QDs), where PL peaks from the “wetting layer” and from the QDs are observed. The temporal behavior of the PL spectra after a short-pulse laser excitation provides evidence of carrier transfer from the wetting layer to the QDs for sufficiently low excitation power and sufficiently high temperature. The dependences of the cw-PL spectra and of PL lifetimes on excitation power are explained by the saturation of the carrier concentration in the QDs as the excitation power increases.
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78.55.Et II-VI semiconductors
78.47.jd Time resolved luminescence
68.08.Bc Wetting
78.67.Hc Quantum dots

Effects of nonframework metal cations and phonon scattering mechanisms on the thermal transport properties of polycrystalline zeolite LTA films

Abraham Greenstein, Yeny Hudiono, Samuel Graham, and Sankar Nair

J. Appl. Phys. 107, 063518 (2010); http://dx.doi.org/10.1063/1.3327419 (8 pages) | Cited 3 times

Online Publication Date: 31 March 2010

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We present a systematic study to investigate the effects of nonframework cations and the role of phonon scattering mechanisms on the thermal transport properties of zeolite LTA, via experiment and semiempirical lattice dynamics calculations. Our study is motivated by the increasing interest in accurate measurements and mechanistic understanding of the thermal transport properties of zeolite materials. The presence of a nanostructured pore network, extra-framework cations, and tunable framework structure and composition confer interesting thermophysical properties to these materials, making them a good model system to investigate thermal transport in complex materials. Continuous films of zeolite LTA with different nonframework cations (Na+, K+, and Ca+2) were synthesized and characterized. The thermal conductivity was measured using the three-omega method over a wide range of temperature (150–450 K). These are the first thermal conductivity measurements performed on bulk LTA, so they are more accurate than previous measurements, which involved the use of compacted zeolite powders. Our data showed significant dependence of the thermal conductivity on the extra-framework cations as well the temperature. The thermal conductivities of the zeolite LTA samples were modeled with the relaxation time approximation to the Boltzmann transport equation. The full phonon spectra for each type of LTA zeolite were calculated and used in conjunction with semiempirical relaxation time expressions to calculate the thermal conductivity. The results both validated, and suggested the limitations of, this modeling approach. Optical phonons dominated the thermal conductivity and boundarylike scattering was found to be the strongest phonon scattering mechanism, as also observed in MFI zeolite.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
82.75.-z Molecular sieves, zeolites, clathrates, and other complex solids
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Raman scattering of cadmium oxide epilayers grown by metal-organic vapor phase epitaxy

R. Cuscó, J. Ibáñez, N. Domenech-Amador, L. Artús, J. Zúñiga-Pérez, and V. Muñoz-Sanjosé

J. Appl. Phys. 107, 063519 (2010); http://dx.doi.org/10.1063/1.3357377 (4 pages) | Cited 4 times

Online Publication Date: 31 March 2010

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We present a lattice-dynamics study of rocksalt cadmium oxide (CdO). We use Raman scattering to investigate a series of high-quality CdO epilayers grown on sapphire substrates by means of metal-organic vapor phase epitaxy. Two main features are found to dominate the Raman spectra of CdO: a sharp peak at ∼ 265 cm−1 and a broad feature at ∼ 390 cm−1. To assign these and other weaker second-order features that appear in the Raman spectra, we have carried out an ab initio calculation of the phonon dispersion in CdO. From the calculated two-phonon density of states (PDOS) we tentatively assign the peak at 265 cm−1 to a 2TA(L) mode. The broadband centered at ∼ 390 cm−1 seems to reflect the high two-PDOS in the 300–450 cm−1 spectral region.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
71.15.-m Methods of electronic structure calculations
71.20.-b Electron density of states and band structure of crystalline solids
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