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18 Oct 2004

Volume 85, Issue 16, pp. 3343-3639

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3570 (2004); http://dx.doi.org/10.1063/1.1807953 (2 pages)

X. N. Zhang, C. R. Li, Z. Zhang, and Z. X. Cao
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Thermophotovoltaic generation with selective radiators based on tungsten surface gratings

Hitoshi Sai and Hiroo Yugami

Appl. Phys. Lett. 85, 3399 (2004); http://dx.doi.org/10.1063/1.1807031 (3 pages) | Cited 18 times

Online Publication Date: 22 October 2004

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Two-dimensional surface-relief gratings with a period of 1.0–0.2 μm composed of rectangular microcavities were fabricated on single crystalline W substrates to develop spectrally selective radiators for thermophotovoltaic generation. The radiators displayed strong emission in the near-infrared region where narrow-band-gap photovoltaic cells could convert photons into electricity. The enhancement of thermal emission was attributed to the microcavity effect. Power generation tests were carried out and the W gratings showed more than two times higher generation efficiency, compared to a SiC radiator. The results showed that the microstructured W radiators behave as good selective radiator, with both high efficiency and high power density.
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84.60.Jt Photoelectric conversion
85.60.Dw Photodiodes; phototransistors; photoresistors
42.79.Dj Gratings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Oxygen transport and incorporation mechanisms in the dry thermal oxidation of 6H-SiC

C. Radtke, I. J. R. Baumvol, B. C. Ferrera, and F. C. Stedile

Appl. Phys. Lett. 85, 3402 (2004); http://dx.doi.org/10.1063/1.1807033 (3 pages) | Cited 14 times

Online Publication Date: 22 October 2004

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Thermal oxidation of 6H-SiC was investigated by means of isotopic tracing and narrow nuclear resonant reaction profiling techniques. The mechanisms of oxygen transport and incorporation were accessed by sequential oxidations in dry O2 enriched or not in the 18O isotope and subsequent determinations of the 18O profiles. After sequential 16O2∕18O2 or 18O2∕16O2 oxidations of SiC, the 18O profiles were seen to be markedly different from those observed in Si oxidation, which led to the identification of different mechanisms of oxygen incorporation and transport. The gradual nature of the SiO2∕SiC interface was also evidenced by the 18O depth distributions in samples oxidized in a single step in 18O-enriched O2. A probable explanation for this gradual SiO2∕SiC interface is shown to be the formation of C clusters during oxidation.
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81.65.Mq Oxidation
82.80.-d Chemical analysis and related physical methods of analysis
68.35.Ct Interface structure and roughness
81.05.Hd Other semiconductors

Second-harmonic generation in transparent surface crystallized glasses in the BaO–B2O3–TeO2 system

G. Senthil Murugan, Takenobu Suzuki, Yasutake Ohishi, Yoshihiro Takahashi, Yasuhiko Benino, Takumi Fujiwara, and Takayuki Komatsu

Appl. Phys. Lett. 85, 3405 (2004); http://dx.doi.org/10.1063/1.1808873 (3 pages) | Cited 8 times

Online Publication Date: 22 October 2004

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A transparent glass–ceramic containing borate crystallites in tellurite glass is reported. Controlled heat treatment resulted in surface crystallization of BaB4O7 in the BaO–B2O3–TeO2 glass system. The second-order optical nonlinearities observed in these surface crystallized glasses were attributed to the distortion present in the BaB4O7 unit cell as evidenced by x-ray powder diffraction studies. A d33 value of 0.08 pm∕V was obtained from the Maker fringe analysis for a surface crystallized glass.
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81.05.Pj Glass-based composites, vitroceramics
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
81.40.Gh Other heat and thermomechanical treatments

Effect of nitride passivation on the visible photoluminescence from Si-nanocrystals

Moon-Seung Yang, Kwan-Sik Cho, Ji-Hong Jhe, Se-Young Seo, Jung H. Shin, Kyung Joong Kim, and Dae Won Moon

Appl. Phys. Lett. 85, 3408 (2004); http://dx.doi.org/10.1063/1.1787599 (3 pages) | Cited 27 times

Online Publication Date: 22 October 2004

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The effect of nitride passivation on the visible photoluminescence from nanocrystal Si (nc-Si) is investigated. Silicon-rich silicon nitride (SRSN) and silicon-rich silicon oxide (SRSO), which consist of nc-Si embedded in silicon nitride and silicon oxide, respectively, were prepared by reactive ultrahigh vacuum ion beam sputter deposition followed by a high temperature anneal. Both SRSN and SRSO display photoluminescence peaks after high temperature annealing, coincident with the formation of Si nanocrystals, and similar changes in the peak luminescence position with the excess Si content. However, the luminescence peak positions from SRSN are blueshifted by about 0.6 eV over that of comparable SRSO such that its luminescence peaks in the visible range. The results demonstrate that control of the surface passivation is critical in controlling the nc-Si luminescence, and indicate the possibility of using nitride-passivated nc-Si for visible luminescence applications including white luminescence.
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68.55.A- Nucleation and growth
81.65.Rv Passivation
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering
81.15.Jj Ion and electron beam-assisted deposition; ion plating
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Revealing all types of threading dislocations in GaN with improved contrast in a single plan view image

R. Datta, M. J. Kappers, J. S. Barnard, and C. J. Humphreys

Appl. Phys. Lett. 85, 3411 (2004); http://dx.doi.org/10.1063/1.1807962 (3 pages) | Cited 23 times

Online Publication Date: 22 October 2004

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In this letter, we demonstrate a transmission electron microscope based technique which reveals all types of threading dislocations (TDs) in GaN with high contrast over a relatively large area, even if the specimen is bent. This method uses a bright-field image with the crystal oriented at the 〈1–21–3〉 zone axis, taken using multi-beam diffraction conditions. Such an image reveals all screw, edge, and mixed types of threading dislocations. The multi-beam imaging technique described here for GaN is more generally applicable to counting the total dislocation density in a wide range of materials and structures.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)

Surface tension of superheated and undercooled liquid Co–Si alloy

H. P. Wang, W. J. Yao, C. D. Cao, and B. Wei

Appl. Phys. Lett. 85, 3414 (2004); http://dx.doi.org/10.1063/1.1808880 (3 pages) | Cited 6 times

Online Publication Date: 22 October 2004

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The surface tension of superheated and undercooled liquid Co 25 wt.% Si alloy was measured by an electromagnetic oscillating drop method. The experimental temperature regime was from 1384 to 2339 K and a maximum undercooling of 223 K (0.14 TL) was achieved. The surface tension of liquid Co 25 wt.% Si alloy is 1.604 Nm−1 at the liquidus temperature of 1607 K, and its temperature coefficient is −4.0×10−4 Nm−1K−1. On the basis of previous research results of pure Co and Si, an expression is developed to predict the surface tension of binary Co–Si alloy system. The other thermophysical properties, such as the viscosity, the solute diffusion coefficient, and the density of liquid Co 25 wt.% Si alloy are also derived by the relevant theoretical models.
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68.03.Cd Surface tension and related phenomena
66.20.-d Viscosity of liquids; diffusive momentum transport
66.10.C- Diffusion and thermal diffusion

Spatial variation of luminescence from AlGaN grown by facet controlled epitaxial lateral overgrowth

A. Bell, R. Liu, U. K. Parasuraman, F. A. Ponce, S. Kamiyama, H. Amano, and I. Akasaki

Appl. Phys. Lett. 85, 3417 (2004); http://dx.doi.org/10.1063/1.1807950 (3 pages) | Cited 6 times

Online Publication Date: 22 October 2004

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Interesting phenomena have been observed in the epitaxial lateral overgrowth of AlxGa1−xN alloys using facet control on serrated GaN templates. A complex microstructure is observed that involves misfit dislocation arrays that are closely related to regions with significantly large variations in composition. The dislocations are on inclined planar boundaries and result from basal-plane slip, which is allowed in this inclined facet geometry. The spatial variation of the aluminum composition in the overgrowth region is determined by cathodoluminescence spectroscopy and ranges from x=0.06 to 0.27, for constant growth conditions that after planarization result in a uniform composition at x=0.16. These results indicate that aluminum incorporation depends significantly on the growth direction with marked preference for facets parallel to the basal plane.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Photon tunneling via surface plasmon coupling

A. Passian, A. Wig, A. L. Lereu, F. Meriaudeau, T. Thundat, and T. L. Ferrell

Appl. Phys. Lett. 85, 3420 (2004); http://dx.doi.org/10.1063/1.1793351 (3 pages) | Cited 7 times

Online Publication Date: 22 October 2004

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The measurement of a photonic signal via plasmon-plasmon coupling in curved thin metal films is presented. In domains of subwavelength dimension, we calculate the resonant dispersion relations by modeling the curved thin film as a single sheeted hyperboloid of revolution. We show that several such surface modes are accessible optically at frequencies below the plasma frequency of the metal.
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68.55.-a Thin film structure and morphology
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Optical properties of single InAs quantum dots in close proximity to surfaces

C. F. Wang, A. Badolato, I. Wilson-Rae, P. M. Petroff, E. Hu, J. Urayama, and A. Imamoğlu

Appl. Phys. Lett. 85, 3423 (2004); http://dx.doi.org/10.1063/1.1806251 (3 pages) | Cited 33 times

Online Publication Date: 22 October 2004

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The optical properties of single InAs∕GaAs quantum dots (QDs) were studied as a function of their distance from the air∕GaAs interface. A short-period superlattice structure allows us to controllably shorten the distance between the QDs and the surface in 6-nm steps. The QD luminescence intensity and lifetime measurements show that quantum tunneling effect results in a sharp reduction in fluorescence efficiency and lifetime when the wetting-layer–surface distance is within 9 nm. For distances between 15 and 40 nm, broadening of the photoluminescence linewidths of single QDs was observed. Since exciton recombination time and efficiency are in this case unchanged with respect to bulk QDs, the observed line broadening is most likely due to dephasing or spectral diffusion processes.
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73.21.La Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Gk Tunneling
78.67.Hc Quantum dots
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Cr III-V semiconductors
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Epitaxial growth of Eu2O3 thin films on LaAlO3 substrates by polymer-assisted deposition

Y. Lin, H. Wang, M. E. Hawley, S. R. Foltyn, Q. X. Jia, G. E. Collis, A. K. Burrell, and T. M. McCleskey

Appl. Phys. Lett. 85, 3426 (2004); http://dx.doi.org/10.1063/1.1806265 (3 pages) | Cited 8 times

Online Publication Date: 22 October 2004

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Eu2O3 thin films were epitaxially grown on (001)LaAlO3 (LAO) substrates using a polymer-assisted deposition technique. Microstructural studies by x-ray diffraction and transmission electron microscopy show that the films are epitaxial with an orientational relationship of (001)Eu2O3‖(001)LAO and [1math0]Eu2O3‖[100]LAO. We have found a systematic change in the out-of-plane lattice parameter of Eu2O3 (a⊥) with the annealing temperature, which is believed to be from different strain effects.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.37.Lp Transmission electron microscopy (TEM)
81.40.Gh Other heat and thermomechanical treatments

Strong affinity of hydrogen for the GaN(000-1) surface: Implications for molecular beam epitaxy and metalorganic chemical vapor deposition

J. E. Northrup and J. Neugebauer

Appl. Phys. Lett. 85, 3429 (2004); http://dx.doi.org/10.1063/1.1808227 (3 pages) | Cited 18 times

Online Publication Date: 22 October 2004

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The stabilities of clean and hydrogen covered GaN(000-1) surfaces are determined using density functional theory together with a finite temperature thermodynamics approach. Hydrogen has an extremely high affinity for the N-face surface: Even under ultrahigh vacuum conditions as realized in molecular beam epitaxial growth, with a residual hydrogen pressure of 10−12 atm, the hydrogen terminated surface is, for very N-rich conditions, more stable than any clean surface. A transition to a surface covered by a Ga adlayer is predicted to occur as the Ga chemical potential increases. In typical metalorganic chemical vapor deposition conditions the (000-1) surface is predicted to be covered by 0.75 monolayers of hydrogen. The slower growth rate on the (000-1) surface in comparison to the (0001) surface is attributed to low adsorption of N on the H-covered (000-1) surface.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.47.Fg Semiconductor surfaces
68.35.Rh Phase transitions and critical phenomena
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Upconversion luminescence of Al2O3–SiO2:Ce3+ glass by femtosecond laser irradiation

Hongpeng You, Tomokatsu Hayakawa, and Masayuki Nogami

Appl. Phys. Lett. 85, 3432 (2004); http://dx.doi.org/10.1063/1.1808234 (3 pages) | Cited 13 times

Online Publication Date: 22 October 2004

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Near-infrared to visible upconversion luminescence was observed in a sol-gel processed Al2O3–SiO2 glass containing Ce3+ ions under femtosecond laser irradiation. The optical properties of the glasses reveal that the upconversion luminescence comes from the 5d→4f transition of the Ce3+ ions. The relationship between the intensity of the Ce3+ emission and the pump power reveals that a three-photon absorption predominates in the conversion process from the near-infrared into the blue luminescence. The analysis of the upconversion mechanism suggests that the upconversion luminescence may come from a three-photon simultaneous absorption that leads to a population of the 5d level in which the characteristic luminescence occurs.
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78.55.Qr Amorphous materials; glasses and other disordered solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Jg Amorphous semiconductors; glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Stretchability of thin metal films on elastomer substrates

Teng Li, Zhenyu Huang, Z. Suo, Stéphanie P. Lacour, and Sigurd Wagner

Appl. Phys. Lett. 85, 3435 (2004); http://dx.doi.org/10.1063/1.1806275 (3 pages) | Cited 71 times

Online Publication Date: 22 October 2004

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Many flexible electronic surfaces comprise inorganic films on organic substrates. Mechanical failure of such integrated structures of stiff and compliant materials poses a significant challenge. This letter studies the stretchability of metal films on elastomer substrates. Our experiment shows that, when stretched, elastomer-supported metal films rupture at strains larger than those reported for freestanding films. We use a finite element code to simulate the rupture process of metal films. A freestanding metal film ruptures by forming a single neck. By contrast, a metal film on an elastomer substrate may develop an array of necks before rupture. While the pre-rupture necks do not change the electrical conductance appreciably, they elongate the metal film, leading to a large overall rupture strain.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Textured nano-agglomerates embedded in the thin film of La0.8Sr0.2MnO3

Y. L. Zhu, B. Wu, X. L. Ma, D. X. Li, H. B. Lu, Z. H. Chen, and G. Z. Yang

Appl. Phys. Lett. 85, 3438 (2004); http://dx.doi.org/10.1063/1.1808236 (3 pages)

Online Publication Date: 22 October 2004

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We have observed nano-scale chemical composition separation in the thin film of La0.8Sr0.2MnO3 by means of high-angle-angular-dark-field imaging, elemental mapping, and composition line-scanning in a transmission electron microscope. It is found that highly dense and dimensionally uniform nano-agglomerates are embedded in the film. The ratio of Mn∕La in the nano-agglomerates is fluctuated and generally much higher than that in their surrounding medium. Such compositional inhomogeneities result in a textured microstructure, which is one of the most important parameters for tunning electronic properties in the colossal magnetoresistance oxides.
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61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
64.75.-g Phase equilibria
61.66.Bi Elemental solids
61.66.Dk Alloys

Evolution of stress in GaN heteroepitaxy on AlN∕Si(111): From hydrostatic compressive to biaxial tensile

A. Krost, A. Dadgar, J. Bläsing, A. Diez, T. Hempel, S. Petzold, J. Christen, and R. Clos

Appl. Phys. Lett. 85, 3441 (2004); http://dx.doi.org/10.1063/1.1808237 (3 pages) | Cited 16 times

Online Publication Date: 22 October 2004

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The initial steps of GaN growth on an AlN buffer layer on Si(111) substrates by metalorganic vapor phase epitaxy were investigated using field emission scanning electron microscopy, micro-photoluminescence, as well as by conventional and grazing incidence x-ray diffraction. A series of GaN layers was grown for various times ranging from 7.5 s to several minutes, doubling the growth time for each step. The AlN buffer layer is noncontinuous and consists of (0001)-oriented AlN islands with a mean diameter of about 50 nm. On top of these nucleation centers three-dimensional growth of GaN was observed. With increasing growth times up to 30 s these islands further expanded and their distribution became more homogeneous. At 60 s coalescence started with homogeneously distributed islands, and after 120 s the layer was fully coalesced. The layers grown for 7.5 and 15 s are under a high compressive hydrostatic pressure, which might be enhanced by the lattice mismatch between AlN and GaN. For longer growth times a biaxial tensile stress is observed. The occurrence of the biaxial tensile stress correlates with the onset of island coalescence. The x-ray results are in agreement with low-temperature optical measurements showing a consistent energy shift of the near band gap luminescence and longitudinal optical Raman modes with respect to relaxed GaN.
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68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Vj Field emission and field-ion microscopy
68.55.-a Thin film structure and morphology

Ultrafast optical switching at the telecommunication wavelength by single electron transfer between fluorene-containing redox polymer and its counter anion

Toshihiko Nagamura, Yasuyuki Nagai, Akihiro Furube, and Shigeo Murata

Appl. Phys. Lett. 85, 3444 (2004); http://dx.doi.org/10.1063/1.1808238 (3 pages) | Cited 5 times

Online Publication Date: 22 October 2004

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Ultrafast and large absorption change in the optical telecommunication wavelength region was achieved in solid films by making transitory expansion of a π-electronic system with photoinduced electron transfer and reverse reactions between redox-active ion pairs. Femtosecond dynamics of absorption changes at about 500–1550 nm due to single electron transfer was studied for a poly(tetramethyleneoxide) film containing 2,7-bis(4-pyridiniumyl)fluorene unit as part of the main chain. It showed ON response in less than 100 fs and fastest OFF response in 240 fs at the telecommunication wavelength. This polymer film may be applied to tetrahertz all optical information processing in the telecommunication system.
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42.70.Jk Polymers and organics
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
78.40.Me Organic compounds and polymers
78.30.Jw Organic compounds, polymers
73.50.Pz Photoconduction and photovoltaic effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

A hybrid epitaxy method for InAs on GaP

A. Chen, A. Yulius, J. M. Woodall, and C. C. Broadbridge

Appl. Phys. Lett. 85, 3447 (2004); http://dx.doi.org/10.1063/1.1808241 (3 pages) | Cited 3 times

Online Publication Date: 22 October 2004

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The interface formation mechanism during the molecular-beam epitaxy (MBE) of InAs∕GaP has been studied with the aid of the In–Ga–P phase diagram. It is discovered that an initial dissolution and crystallization process similar to liquid phase epitaxy (LPE) may happen at sufficiently high temperature, resulting in a graded composition at the interface. Consequently, “parasitic LPE∕MBE” is the name for this hybrid form of MBE. High-resolution TEM images confirm the existence of the interfacial layer in the sample grown at high temperature. The graded interface smears out the band offset and leads to a nonrectifying heterojunction. Low-temperature (LT) MBE growth can turn off the LPE component, enabling the growth of an abrupt interface. Based on this “LPE∕MBE” model, a LT MBE technique is developed to grow an abrupt InAs∕InGaP interface for heterojunction power Schottky rectifiers. The LT InAs∕InGaP heterojunction demonstrates nearly ideal Schottky rectifier characteristics, while the sample grown at high temperature shows resistive ohmic characteristics. The LT InAs∕InGaP Schottky diode also demonstrates good stability with respect to anneal temperature, similar to the InAs∕GaP heterojunctions.
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68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.37.Lp Transmission electron microscopy (TEM)
73.30.+y Surface double layers, Schottky barriers, and work functions
81.40.Gh Other heat and thermomechanical treatments
81.30.Dz Phase diagrams of other materials
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Highly flexible transparent electrodes for organic light-emitting diode-based displays

Jay Lewis, Sonia Grego, Babu Chalamala, Erik Vick, and Dorota Temple

Appl. Phys. Lett. 85, 3450 (2004); http://dx.doi.org/10.1063/1.1806559 (3 pages) | Cited 79 times

Online Publication Date: 22 October 2004

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Multilayer indium-tin-oxide (ITO)–Ag–ITO stacks were evaluated as transparent conductors for flexible organic light-emitting diode (OLED) displays. The ITO–metal–ITO (IMI) samples exhibited significantly reduced sheet resistance over ITO and greater than 80% optical transmission. The IMI films deposited on plastic substrates showed dramatically improved mechanical properties when subjected to bending both as a function of radius of curvature as well as number of cycles to a fixed radius. OLEDs were fabricated on both ITO and IMI anodes, and the devices with IMI anodes showed improved performance at current densities greater than 1 mA∕cm2 due to the improved conductivity of the anode.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems
73.40.Ns Metal-nonmetal contacts
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
78.60.Fi Electroluminescence
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Compressibility and pressure-induced phase transformation of Ti3GeC2

Zhongwu Wang, C. S. Zha, and M. W. Barsoum

Appl. Phys. Lett. 85, 3453 (2004); http://dx.doi.org/10.1063/1.1808491 (3 pages) | Cited 21 times

Online Publication Date: 22 October 2004

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In order to explore the large shear-strain-induced polymorph, α‐Ti3GeC2 polycrystals were investigated by using a synchrotron radiation source to 64 GPa under nonhydrostatic state. Upon compression to 26.6 GPa, α‐Ti3GeC2 starts to transform to β‐Ti3GeC2. As compared to α‐Ti3GeC2, the cell parameter a of β‐Ti3GeC2 is slightly shorter, and both c and c∕a larger. These two polymorphs exhibit similar compressibility. The bulk modulus is calculated to be 179 (±10) GPa at a fixed K′=4.0. This is lower than that of Ti3SiC2, and close to that of Ti3Si0.5Ge0.5C2. The compressibilities of these two Ti3GeC2 polymorphs do not display an apparent anisotropy, and differ from the large anisotropies observed from Ti3SiC2 and Ti3Si0.5Ge0.5C2.
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81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Simultaneous short-range smoothening and global roughening during growth of hydrogenated amorphous silicon films

Brent A. Sperling and John R. Abelson

Appl. Phys. Lett. 85, 3456 (2004); http://dx.doi.org/10.1063/1.1777414 (3 pages) | Cited 13 times

Online Publication Date: 22 October 2004

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We investigate the evolution of surface morphology during hot-wire chemical vapor deposition of amorphous silicon films onto rough substrates. Using in situ spectroscopic ellipsometry, we find that the surface smoothens as the film grows. However, postdeposition atomic force microscopy reveals that the roughness is actually increasing linearly. We resolve this discrepancy by examining the power spectrum densities of the atomic force images, which indicate that the growth surface experiences both short-range smoothening and global roughening. The ellipsometry data are consistent with the short-range atomic force microscopy data, but they exclude information about the long-range components of roughness. The slope of the power spectrum density indicates surface diffusion is the dominant smoothening mechanism; the linear increase in roughness is consistent with columnar growth caused by self-shadowing.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.47.Fg Semiconductor surfaces
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation

Mechanical aspects of epitaxial ferroelectric Pb(Zr0.5Ti0.5)O3 films investigated by nanoindentation methods and piezoresponse force microscopy

D. Liu and K. W. White

Appl. Phys. Lett. 85, 3459 (2004); http://dx.doi.org/10.1063/1.1806563 (3 pages) | Cited 4 times

Online Publication Date: 22 October 2004

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Mechanical behaviors of a lead zirconium titanate (PZT) thin film are investigated using a unique combination of nanoindentation methods and piezoresponse force microscopy (PFM) in various domain areas, following local domain pattern writing. The interaction between the ferroelectric domain character and the mechanical behavior is mapped using PFM for subsequent nanoindentation. Significant anisotropic behaviors between (100) and (001) domains are observed. An anomalous increase of indentation elastic modulus in the region near a domain wall is observed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity
62.20.M- Structural failure of materials
77.80.Dj Domain structure; hysteresis
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Suppressed surface morphology instabilities in amorphous hydrogenated silicon deposition

George T. Dalakos, Joel L. Plawsky, and Peter D. Persans

Appl. Phys. Lett. 85, 3462 (2004); http://dx.doi.org/10.1063/1.1808495 (3 pages) | Cited 7 times

Online Publication Date: 22 October 2004

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The surface chemistry associated with a‐Si:H growth by plasma-enhanced chemical vapor deposition is unique in that the hydrogen-passivated surface results in a low threshold energy for surface diffusion relative to the cohesive energies of the material. We show that helium ion bombardment enhances the hopping rate of loosely bound film precursors without substantially affecting the condensed a‐Si:H material. Our investigative approach consists of examination of the temporal evolution of the surface topography under different substrate bias conditions. Without biasing the substrate, the surface morphology becomes unstable, producing mounded-type structures, consistent with shadowing growth instability. Biasing the substrate suppresses these instabilities and allows an initially rough a‐Si:H surface to be smoothed during subsequent deposition.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Rv Passivation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Hydrogen site energetics in LaNi5Hn and LaCo5Hn: Toward predicting hydrides

J. F. Herbst and L. G. Hector

Appl. Phys. Lett. 85, 3465 (2004); http://dx.doi.org/10.1063/1.1808503 (3 pages) | Cited 2 times

Online Publication Date: 22 October 2004

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We have investigated the energetics of hydrogen site occupation in LaNi5Hn (hexagonal P63mc structure) and LaCo5Hn (orthorhombic Cmmm structure) via calculation of the site-dependent enthalpies of hydride formation ΔH. For each structure ΔH was determined for a broad variety of hydrogen configurations. In LaNi5Hn (LaCo5Hn) we find that the minimum ΔH occurs for hydrogen filling of the 2b6c16c2 (4e4h) sites, precisely those identified by neutron diffraction. Hydrogen-richer hydrides are predicted for both structures, in qualitative agreement with experiments performed at higher pressures.
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65.40.G- Other thermodynamical quantities
61.66.Fn Inorganic compounds

Thermal degradation of electrical properties and morphology of bulk single-crystal ZnO surfaces

Rohit Khanna, K. Ip, Y. W. Heo, D. P. Norton, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 85, 3468 (2004); http://dx.doi.org/10.1063/1.1801674 (3 pages) | Cited 17 times

Online Publication Date: 22 October 2004

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Bulk ZnO substrates were rapid thermal annealed in either air or N2 at temperatures up to 500°C. The root-mean-square roughness of the surface as measured by atomic force microscopy begins to increase even after 200°C anneals in N2 or 300°C in air. The Schottky barrier height, ΦB, obtained from Pt∕Au diodes fabricated on these surfaces shows a decrease in effective barrier height upon annealing from 0.35 eV in control samples to ∼0.30 eV in those annealed at 400°C and an increase in the saturation current density (from 4 A cm−2 in the control samples to 17–37 A cm−2 in the annealed samples). These results show that the ZnO surface is degraded by quite low annealing temperatures and care must be exercised in designing the thermal budget for processing of ZnO devices. At much higher annealing temperatures (1000°C), the surface completely decomposes to leave metallic Zn droplets.
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85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
64.75.-g Phase equilibria
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