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1 Oct 2005

Volume 98, Issue 7, Articles (07xxxx)

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Modeling and design of an optimized liquid-crystal optical phased array

Xinghua Wang, Bin Wang, Philip J. Bos, Paul F. McManamon, John J. Pouch, Felix A. Miranda, and James E. Anderson

J. Appl. Phys. 98, 073101 (2005); http://dx.doi.org/10.1063/1.2071450 (8 pages) | Cited 13 times

Online Publication Date: 10 October 2005

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In this paper, the physics that determines the performance limits of a diffractive optical element based on a liquid-crystal (LC) optical phased array (OPA) is investigated by numerical modeling. The influence of the fringing electric fields, the LC material properties, and the voltage optimization process is discussed. General design issues related to the LC OPA configuration, the diffraction angle, and the diffraction efficiency are discussed. A design for a wide-angle LC OPA is proposed for high-efficiency laser beam steering. This work provides fundamental understanding for a light beam deflected by a diffractive liquid-crystal device.
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42.79.Kr Display devices, liquid-crystal devices
42.15.Eq Optical system design

Analysis of the dynamics of a mechanical Q-switched CO2 laser: Six-temperature model

Tie-Jun Wang, Jin-Yue Gao, Qiong-Yi He, Tao Ma, Yun Jiang, and Zhi-Hui Kang

J. Appl. Phys. 98, 073102 (2005); http://dx.doi.org/10.1063/1.2084307 (5 pages) | Cited 6 times

Online Publication Date: 11 October 2005

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A six-temperature kinetic model for a CO2-N2-He system is used to describe the dynamic processes of a mechanical Q-switched CO2 laser that is set up using a fast chopper. We put special emphasis on the effect of dynamical parameters on the laser intensity. It takes into account the effects of electrical excitation, energy transfer processes, thermal energy transport, as well as the dissociation of CO2 molecules and rotational relaxation of rotational levels. The results calculated are in satisfactory agreement with experimental data.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
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Axial segregation in high intensity discharge lamps measured by laser absorption spectroscopy

A. J. Flikweert, T. Nimalasuriya, C. H. J. M. Groothuis, G. M. W. Kroesen, and W. W. Stoffels

J. Appl. Phys. 98, 073301 (2005); http://dx.doi.org/10.1063/1.2073970 (5 pages) | Cited 18 times

Online Publication Date: 3 October 2005

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High intensity discharge lamps have a high efficiency. These lamps contain rare-earth additives (in our case dysprosium iodide) which radiate very efficiently. A problem is color separation in the lamp because of axial segregation of the rare-earth additives, caused by diffusion and convection. Here two-dimensional atomic dysprosium density profiles are measured by means of laser absorption spectroscopy; the order of magnitude of the density is 1022 m−3. The radially resolved atomic density measurements show a hollow density profile. In the outer parts of the lamp molecules dominate, while the center is depleted of dysprosium atoms due to ionization. From the axial profiles the segregation parameter is determined. It is shown that the lamp operates on the right-hand side of the Fischer curve [ J. Appl. Phys. 47, 2954 (1976) ], i.e., a larger convection leads to less segregation.
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52.25.Fi Transport properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.80.-s Electric discharges

Growth precursors for a-C:H film deposition in pulsed inductively coupled methane plasmas

M. Bauer, T. Schwarz-Selinger, W. Jacob, and A. von Keudell

J. Appl. Phys. 98, 073302 (2005); http://dx.doi.org/10.1063/1.2061890 (11 pages) | Cited 19 times

Online Publication Date: 6 October 2005

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Film deposition in pulsed inductively coupled plasmas is investigated using methane as precursor gas. The densities of neutrals as well as ion and radical fluxes are quantified using mass spectrometry. Plasma composition is uniquely determined by the mean dissipated energy per source gas molecule in the plasma, Emean. Film growth rates are measured by in situ real-time ellipsometry. The contributions of individual precursors to film growth are discussed quantitatively by comparing absolute net growth fluxes of reactive species with deposited carbon atoms. It is shown that chemisorption of CH3 or implantation of energetic carbonaceous ions cannot explain the observed growth rates. Instead, film deposition occurs either by incorporation of CH radicals at small values of Emean(<10 eV) or by incorporation of unsaturated hydrocarbon radicals such as C2H3 or C2H at intermediate values of Emean(10<Emean<100 eV). Film growth depends strongly on incorporation of carbonaceous ions only at larger values of Emean(>100 eV).
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81.05.U- Carbon/carbon-based materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.A- Nucleation and growth
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.43.Dq Amorphous semiconductors, metals, and alloys

O2(math) production in flowing He/O2 plasmas. I. Axial transport and pulsed power formats

D. Shane Stafford and Mark J. Kushner

J. Appl. Phys. 98, 073303 (2005); http://dx.doi.org/10.1063/1.2076427 (12 pages) | Cited 9 times

Online Publication Date: 12 October 2005

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Chemical oxygen-iodine lasers (COILs) have promising applications due to their high efficiency and ease of scaling to multikilowatt powers. Recent research has focused on pumping the iodine with O2(math) produced by electric discharges. In a previous work, a global model was used to develop reaction mechanisms and determine the specific energy deposition (eV/O2) required to obtain high O2(math) yields for electric discharge COILs. Experiments have recently achieved positive laser gain and oscillation with these energy depositions and have highlighted the importance of axial expansion of the plasma in optimizing excitation of the O2(math). In this work, the consequences of axial transport on O2(math) yields have been computationally investigated in flowing He/O2 plasmas at a few Torrs using a one-dimensional plasma hydrodynamics and kinetics model. We show that the experimentally observed extension of the plasma glow upstream and downstream of the electrodes is due to electron diffusion and capacitive coupling of the radio-frequency power source. We also show that ≈ 50% higher O2(math) yields can be achieved with a pulsed discharge combined with continuous-wave discharge.
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52.25.Fi Transport properties
52.50.Dg Plasma sources
52.30.-q Plasma dynamics and flow
42.55.Ks Chemical lasers
52.80.Pi High-frequency and RF discharges
52.25.Dg Plasma kinetic equations
52.80.Hc Glow; corona
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

O2(math) production in flowing He/O2 plasmas. II. Two-dimensional modeling

Ramesh Arakoni, D. Shane Stafford, Natalia Y. Babaeva, and Mark J. Kushner

J. Appl. Phys. 98, 073304 (2005); http://dx.doi.org/10.1063/1.2076428 (7 pages) | Cited 9 times

Online Publication Date: 12 October 2005

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In conventional chemical oxygen-iodine lasers (COIL) the 1.315 μm transition in atomic iodine is pumped by a sequence of reactions of I2 and I with O2(math) which is generated using liquid chemistry. Ongoing studies are investigating means to produce the O2(math) precursor with an electric discharge (eCOIL) to enable a totally gas phase system. Due to the thermodynamic and power loading requirements, the plasma in eCOIL systems is sustained in a flow of a rare-gas diluent and the O2. In previous investigations, the scaling of production of O2(math) was investigated using global-kinetics and one-dimensional (1D) models. It was found that the production of O2(math) scaled linearly with energy deposition for moderate loadings (a few eV/O2 molecule). In this paper, these previous investigations are extended to two-dimensions using a plasma hydrodynamics model. The goal of this investigation is to determine if multidimensional considerations affect energy scalings for production of O2(math). We found that O2(math) production generally does scale linearly with energy loading, however, the saturation of O2(math) production occurs at lower-energy loadings than predicted with global and 1D models. This trend is a result of the more accurately depicted and more localized energy deposition afforded by the two-dimensional model, and emphasizes the need for volumetrically uniform power deposition to optimize O2(math) production.
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52.50.Dg Plasma sources
42.55.Ks Chemical lasers
52.80.-s Electric discharges
52.25.Kn Thermodynamics of plasmas
52.30.-q Plasma dynamics and flow
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
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Determination of the elastic moduli in LiAlO2

Fabian Jachmann, M. Pattabiraman, and Carsten Hucho

J. Appl. Phys. 98, 073501 (2005); http://dx.doi.org/10.1063/1.2061889 (4 pages) | Cited 1 time

Online Publication Date: 3 October 2005

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The precise determination of elastic constants of γ‐LiAlO2 has recently become important, as this material is being used as a substrate for intensely studied acousto-optical device structures and no values for the elastic moduli have been published to date. The precision of experimentally determined elastic constants hinges significantly on considering the influence of the acoustic transducer on the sound propagation in the system. Therefore, the influence of the transducer is discussed and an approach for corrections is presented. The compressional elastic constants C11 and C33 and the shear constants C12 and C13 of γ‐LiAlO2 are determined with an acoustic pulse-echo technique and with sampled-continuous-wave spectroscopy.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Origin of green luminescence in ZnO thin film grown by molecular-beam epitaxy

Y. W. Heo, D. P. Norton, and S. J. Pearton

J. Appl. Phys. 98, 073502 (2005); http://dx.doi.org/10.1063/1.2064308 (6 pages) | Cited 126 times

Online Publication Date: 3 October 2005

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The properties of ZnO films grown by molecular-beam epitaxy are reported. The primary focus was on understanding the origin of deep-level luminescence. A shift in deep-level emission from green to yellow is observed with reduced Zn pressure during the growth. Photoluminescence and Hall measurements were employed to study correlations between deep-level/near-band-edge emission and carrier density. With these results, we suggest that the green emission is related to donor-deep acceptor (Zn vacancy VZn−) and the yellow to donor-deep acceptor (oxygen vacancy, Oi−).
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
71.55.Gs II-VI semiconductors
61.72.J- Point defects and defect clusters
72.20.My Galvanomagnetic and other magnetotransport effects

On the role of oxygen in the catalysis of C54 titanium disilicide by Ti5Si3 phase

S. Ilango, G. Raghavan, S. Kalavathi, B. K. Panigrahi, and A. K. Tyagi

J. Appl. Phys. 98, 073503 (2005); http://dx.doi.org/10.1063/1.2067702 (5 pages) | Cited 5 times

Online Publication Date: 3 October 2005

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The influence of the native SiO2 in the phase formation sequence of Ti/Si system has been studied. Furnace annealing of Ti/Si couples has been investigated by secondary-ion-mass spectrometry, Rutherford backscattering, and glancing incidence x-ray diffraction. The influence of dilute concentration of oxygen at the interface in altering reaction kinetics was studied. These studies reveal that the highly metallic Ti5Si3 phase forms during the intermediate stages of heat treatment. This phase is found to catalyze the direct formation of the low-resistive C54 TiSi2 phase, completely bypassing its polymorphic C49 counterpart. X-ray-diffraction line profile analysis of Bragg peaks indicates that the formation of the C54 phase is accompanied by a reduction in the microstrain. Subsequent annealing results in the complete transformation to TiSi2 with an increase in the average grain size.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
64.70.K- Solid-solid transitions
82.20.-w Chemical kinetics and dynamics
81.40.Gh Other heat and thermomechanical treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Morphological evolution and strain relaxation of Ge islands grown on chemically oxidized Si(100) by molecular-beam epitaxy

Qiming Li, Belliappa Pattada, Steve R. J. Brueck, Stephen Hersee, and Sang M. Han

J. Appl. Phys. 98, 073504 (2005); http://dx.doi.org/10.1063/1.2067708 (8 pages) | Cited 9 times

Online Publication Date: 3 October 2005

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We have previously demonstrated that high-quality Ge can be grown on Si by the touchdown process, where chemically oxidized Si is exposed to a Ge molecular beam. The causes of strain relaxation in the Ge epilayer were also proposed and discussed. Herein, we present a detailed analysis on the morphological evolution and strain relaxation of nanoscale Ge islands on SiO2-covered Si in order to identify the mechanisms by which the high-quality epilayer forms. During the touchdown, the Ge seeds are anchored to the underlying Si. This immobility of Ge islands gives rise to a unique bimodal size distribution during coarsening. Three events are observed during coalescence: (1) merging of two small (<10 nm) islands largely driven by surface diffusion, (2) merging of a small island and a big island ( ∼ 50 nm), and (3) merging of two big islands. The coalescence of two small islands is characterized by the formation of twins or stacking faults at the two merging fronts. In contrast, no stacking fault or grain boundary results from the coalescence of large islands, indicating that their coalescence is favorable in achieving high-crystalline quality. For the Ge epilayer, the compressive strain exists mostly within 2 nm from the heterojunction, resulting in a fully relaxed Ge epilayer. We attribute the relaxation to three mechanisms: (1) the strain at the junction pad decays below the critical limit within 2 nm, a scale exactly comparable with the dimension of individual Ge–Si junction; (2) the remaining SiO2 serves as artificially introduced 60° dislocations; and (3) the intermixing between Ge and Si at the heterojunction reduces the effective lattice mismatch.
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68.47.Fg Semiconductor surfaces
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
68.35.Fx Diffusion; interface formation
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Biaxial modulus of fiber-textured cubic polycrystalline films with an arbitrary texture axis [hkl]

Feng Huang and Mark L. Weaver

J. Appl. Phys. 98, 073505 (2005); http://dx.doi.org/10.1063/1.2067688 (6 pages) | Cited 9 times

Online Publication Date: 3 October 2005

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A simple method to estimate the effective biaxial modulus of cubic polycrystalline films with an arbitrary [hkl] fiber texture is presented. Analytic expressions of the Voigt [ Lehrbuch der Kristallphysik (Teubner, Leipzig, 1910) ] and the Reuss [ Z. Angew. Math. Mech. 9, 49 (1929) ] averages of the biaxial modulus are given in terms of the axis orientation [hkl] and single-crystal elastic constants. We then explain why the two averages of the fiber-textured films are identical to the corresponding appropriate biaxial modulus of the constituent grain. Finally, we show that for fiber axes equivalent to [100] or [111], the Voigt and Reuss averages coincide and are identical to the true effective biaxial modulus of the fiber-textured film. For other fiber axes, we further show that the Voigt-Reuss-Hill average of the biaxial modulus is an excellent theoretical estimation.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Formation of SiCH6-mediated Ge quantum dots with strong field emission properties by ultrahigh vacuum chemical vapor deposition

S. W. Lee, Y. L. Chueh, L. J. Chen, L. J. Chou, P. S. Chen, M.-J. Tsai, and C. W. Liu

J. Appl. Phys. 98, 073506 (2005); http://dx.doi.org/10.1063/1.2060951 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2005

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Pretreatment of silicon surface with SiCH6 was used to modify the Stranski-Krastanow growth mode of Ge on Si(001) at 550 °C by ultrahigh vacuum chemical vapor deposition. With the appropriate SiCH6 mediation, the elongated Ge hut clusters can be transformed to highly uniform multifaceted domes with a high Ge composition at the core. These SiCH6-mediated Ge dots have an average diameter and height of 38 and 7 nm, respectively. The modified growth mode for the formation of SiCH6-mediated Ge dots can be attributed to (i) an almost hydrogen-passivated Si surface to limit the nucleation sites for dot formation and (ii) the incorporation of Ge atoms, repelled by the C-rich areas, into the existing Ge dots. The results also demonstrate that SiCH6-mediated dots exhibit the improved field emission characteristics compared to shallow Ge huts.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
68.65.Hb Quantum dots (patterned in quantum wells)

Model reconstructions for the Si(337) orientation

Feng-Chuan Chuang, Cristian V. Ciobanu, Cai-Zhuang Wang, and Kai-Ming Ho

J. Appl. Phys. 98, 073507 (2005); http://dx.doi.org/10.1063/1.2064309 (6 pages) | Cited 10 times

Online Publication Date: 4 October 2005

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Although unstable, the Si(337) orientation has been known to appear in diverse experimental situations such as the nanoscale faceting of Si(112), or in the case of miscutting a Si(113) surface. Various models for Si(337) have been proposed over time, which motivates a comprehensive study of the structure of this orientation. Such a study is undertaken in this article, where we report the results of a genetic algorithm optimization of the Si(337)-(2×1) surface. The algorithm is coupled with a highly optimized empirical potential for silicon, which is used as an efficient way to build a set of possible Si(337) models; these structures are subsequently relaxed at the level of ab initio density-functional methods. Using this procedure, we retrieve the (337) reconstructions proposed in previous works, as well as a number of different ones.
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68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Interdiffusion in InGaAsSb/AlGaAsSb quantum wells

Y. Wang, H. S. Djie, and B. S. Ooi

J. Appl. Phys. 98, 073508 (2005); http://dx.doi.org/10.1063/1.2061893 (7 pages) | Cited 7 times

Online Publication Date: 5 October 2005

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We modeled the effect of atomic interdiffusion in InGaAsSb/AlGaAsSb quantum well grown on GaSb substrate. The material modification after interdiffusion has been calculated using Fick’s second law of diffusion and the rationalized biquadratic quinary interpolation algorithm. Our results show that both the group-III and group-V atomic interdiffusions lead to blueshifts of ground-state transition energies. For identical diffusion lengths, the group-III interdiffusion produces a larger ground-state blueshift than the group-V interdiffusion. A wavelength blueshift as large as 772 nm is predicted from a 10-nm-wide interdiffused quantum well with an identical diffusion length of 5 nm for both the group-III and group-V sublattices. The large wavelength tuning range indicates that the interdiffusion method can be potentially used to trim the emission wavelengths of InGaAsSb/AlGaAsSb quantum-well structures for various mid-infrared-based photonics devices. Our results will also serve as useful references for a better process control of the epitaxial growth of Sb-based systems.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.Fg Quantum wells
78.67.De Quantum wells

Dynamic compaction of porous silica powder

John P. Borg, David J. Chapman, Kostas Tsembelis, William G. Proud, and John R. Cogar

J. Appl. Phys. 98, 073509 (2005); http://dx.doi.org/10.1063/1.2064315 (7 pages) | Cited 5 times

Online Publication Date: 5 October 2005

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The dynamic compaction characteristics of a porous silicon dioxide (SiO2) powder are reported. The initial specific volumes of the samples were either V00 = 1.30, 4.0, or 10.0 cm3/g whereas the silicon dioxide has a matrix specific volume of V0 = 0.455 cm3/g. The impact velocity ranges from 0.25 to 1.0 km/s and the shock incident pressure on the silica ranges from 0.77 to 2.25 GPa. The shock velocity–particle velocity exhibited a linear relationship within this range. Although these tests represent the low end of dynamic compaction, the dynamic tests compare favorably to extrapolated data available in the open literature. Theoretical pressure–particle velocity and shock velocity–particle velocity curves were generated using a P-α compaction curve. The P-α compaction curve accurately represented the pressure–particle velocity and shock velocity–particle velocity Hugoniot curves for the low specific volume powder, specifically V00 = 1.30 cm3/g. However, the P-α compaction curve did not accurately represent the pressure–particle velocity or the shock velocity–particle velocity Hugoniot curves for the high specific volume powder, specifically V00 = 4.0 or 10.0 cm3/g. For the high specific volume powders the wave dynamics appears to be more complicated than is predicted by a single linear wave over the impact velocity and specific volume range investigated.
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61.43.Gt Powders, porous materials
62.50.-p High-pressure effects in solids and liquids
64.30.-t Equations of state of specific substances

Selective self-assembly at room temperature of individual freestanding Ag2Ga alloy nanoneedles

Mehdi M. Yazdanpanah, Steven A. Harfenist, Abdelilah Safir, and Robert W. Cohn

J. Appl. Phys. 98, 073510 (2005); http://dx.doi.org/10.1063/1.2060930 (7 pages) | Cited 13 times

Online Publication Date: 5 October 2005

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Liquid gallium drops placed on thick Ag films at room temperature spontaneously form faceted nanoneedles of Ag2Ga alloy oriented nearly normal to the surface. This observation suggests that single nanoneedles can be selectively grown by drawing silver-coated microcantilevers from gallium. Needles from 25 nm to microns in diameter and up to 33 μm long were grown by this method. These metal-tipped cantilevers have been used to perform atomic force microscopy (AFM) and AFM voltage lithography.
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81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.16.Nd Micro- and nanolithography

Structural and photoluminescence properties of porous GaP formed by electrochemical etching

Katsuhiro Tomioka and Sadao Adachi

J. Appl. Phys. 98, 073511 (2005); http://dx.doi.org/10.1063/1.2076445 (7 pages) | Cited 13 times

Online Publication Date: 5 October 2005

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The structural and optical properties of porous GaP have been studied by scanning electron microscopy, spectroscopic ellipsometry, and photoluminescence (PL) spectroscopy. Porous GaP layers were fabricated by anodic etching in HF:H2O:C2H5OH = 1:1:2 electrolyte on n-type (100) and (111)A substrates. The morphology of the porous GaP layer is found to depend strongly on the surface orientation. Apart from the red emission band at ∼ 1.7 eV, a supra-band-gap (EgX) emission has been clearly observed on the porous GaP (111)A sample. The anodic porous layer on the (100) substrate, on the other hand, has shown only the red emission at 300 K and both red and green donor-acceptor pair emissions at low temperatures. The correlation between the PL properties and the porous morphology is discussed. An optical transition model is also proposed for the explanation of the PL emission properties of the porous GaP samples.
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78.55.Mb Porous materials
78.55.Cr III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
68.47.Fg Semiconductor surfaces
61.43.Gt Powders, porous materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Kinetics of the reaction between diamond and silicon at high pressure and temperature

C. Pantea, G. A. Voronin, and T. W. Zerda

J. Appl. Phys. 98, 073512 (2005); http://dx.doi.org/10.1063/1.2077845 (5 pages) | Cited 1 time

Online Publication Date: 5 October 2005

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Diamond-silicon carbide composites were sintered from diamond powder and liquid silicon at high pressure-high temperature (HPHT) conditions. Experiments were conducted in the diamond-stable region and then repeated in the graphite-stable region. X-ray diffractograms of the specimens sintered for different time periods provided information on the SiC formation rate and activation energy. Only the late stage of the reaction was investigated, and in the diamond-stable region it was shown that SiC growth was controlled by the diffusion rate of silicon and carbon atoms though the existing layer of SiC. This process is characterized by an activation energy of 264 kJ/mol. At 2 GPa, where graphite is the stable form of carbon, in addition to the direct reaction, diamond may first spontaneously transform into graphite, which next reacts with silicon. A combination of these two processes results in a higher activation energy of 410 kJ/mol.
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82.20.-w Chemical kinetics and dynamics
62.50.-p High-pressure effects in solids and liquids

Deformation of diesel soot aggregates as a function of pellet pressure: A study with ultra-small-angle x-ray scattering

Artur Braun, Jan Ilavsky, Sönke Seifert, and Pete R. Jemian

J. Appl. Phys. 98, 073513 (2005); http://dx.doi.org/10.1063/1.2071456 (5 pages)

Online Publication Date: 6 October 2005

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Diesel soot powder generated under idle and load engine conditions was pressed into pellets at pressures ranging up to approximately 8.5 GPa. Soot powder was also immersed in acetone in order to obtain soot aggregates without agglomeration. Small-angle x-ray scattering was carried out on the powder, the pellets, and on the acetone-immersed soot. Powder and pellets show characteristic aggregate structure at small scattering vectors. Scattering curves of the pellets show a shift of the aggregate size-related scattering feature towards larger scattering vectors for increasing pressure. For the highest pressures, this aggregate structure vanished, while the suspected primary particle scattering became visible as the asymptote of the aggregate scattering structure. Soot was immersed and ultrasonicated in acetone to prevent agglomeration of aggregates, which naturally occurs in powders. This can be considered as the simulation of asymptotic behavior for vanishing pressure. Aggregate size of powder was about 290 nm for the idle soot and 240 nm for the load soot. Primary particle sizes were 14.3 and 10.2 nm, respectively. The idle soot showed a higher compressibility (0.9 GPa/nm) than the load soot (12.0 GPa/nm). Pressing the soot into pellets eliminates scattering structures from aggregation of primary particles and provides a good route to reveal the otherwise inaccessible primary particle scattering. In addition, studying the aggregate structure as a function of pellet pressure allows us to derive compacticity data of the soot.
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61.43.Gt Powders, porous materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.70.Ck X-ray scattering
62.50.-p High-pressure effects in solids and liquids

Stress evolution during growth in direct-current-sputtered zinc oxide films at various oxygen flows

Robert J. Drese and Matthias Wuttig

J. Appl. Phys. 98, 073514 (2005); http://dx.doi.org/10.1063/1.2061888 (5 pages) | Cited 6 times

Online Publication Date: 7 October 2005

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The evolution of stress during the growth of zinc and zinc oxide films deposited from a metallic target using direct-current magnetron sputtering has been analyzed in situ. For this purpose a two-beam wafer curvature setup attached to the sputter chamber was employed. The oxygen flow during the deposition was varied over a wide range to obtain films with stoichiometries between metallic zinc and fully stoichiometric zinc oxide. In good agreement with results from Hinze and Ellmer [J. Appl. Phys. 88, 2443 (2000) ] on radio-frequency-sputtered zinc oxide from an oxidic target, the oxidic films analyzed in this work possess high levels of compressive stress. These stresses arise in the early stages of film growth and are constant above a certain film thickness. The level of stress in the films is highly dependent on the deposition pressure, which indicates that the stress originates from bombardment with energetic particles, namely, oxygen ions. In contrast to the oxidic films, metallic zinc films exhibit only very low levels of stress. The stress evolution is similar to that of evaporated high-mobility films and does not change upon variation of deposition pressure.
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81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
68.60.Bs Mechanical and acoustical properties

Residual stresses of diamond and diamondlike carbon films

E. Liu, L. Li, B. Blanpain, and J. P. Celis

J. Appl. Phys. 98, 073515 (2005); http://dx.doi.org/10.1063/1.2071451 (5 pages) | Cited 4 times

Online Publication Date: 10 October 2005

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This paper evaluated the internal stresses of different diamond and diamondlike carbon (DLC) coatings. For the diamond coatings, the stresses were determined using micro-Raman spectroscopy and x-ray diffraction (XRD), while the stresses of DLC films were determined with bent plate method. The internal stress was related to the structural properties of the coatings. Direct current plasma jet, combustion flame, and microwave chemical-vapor deposition processes were used to prepare the diamond coatings on the tungsten carbide or molybdenum substrates, while the DLC films were deposited on the silicon wafers with filtered cathodic vacuum arc process. From the Raman spectra of the diamond coatings, the compressive internal stresses were determined, which were related to the microstructure of the coatings. The results from XRD were comparable with those obtained from micro-Raman spectroscopy. Higher compressive residual stresses in the DLC films were noticed, which were also related to their chemical bonding nature as well as their microstructures.
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68.60.Bs Mechanical and acoustical properties
81.05.U- Carbon/carbon-based materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
78.30.Hv Other nonmetallic inorganics

Influence of rhodamine 6G doping on the optical properties of TiO2 sol-gel films

S. A. Tomás, S. Stolik, R. Palomino, R. Lozada, C. Persson, I. Pepe, and A. Ferreira da Silva

J. Appl. Phys. 98, 073516 (2005); http://dx.doi.org/10.1063/1.2073972 (4 pages) | Cited 5 times

Online Publication Date: 10 October 2005

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Amorphous titanium dioxide (TiO2) thin films doped with rhodamine 6G (R6G) were deposited on glass substrates by the sol-gel process. The optical properties of the films were characterized by photoacoustic, excitation, and fluorescence spectroscopies. The absorption spectra of the R6G-doped TiO2 films exhibited two well-defined absorption regions: an absorption band over 2.0 eV attributed to rhodamine 6G and a band above 3.0 eV corresponding to TiO2 absorption. While the onset of the R6G absorption band was shifted by 0.06 eV towards lower energies as the R6G doping concentration increased within the interval of 0.01–0.10 mol %, the onset to high absorption (TiO2 band) for the doped films decreased only by 0.01 eV within the same interval. In addition, the optical absorption of undoped rutile-phase bulk TiO2 was calculated and compared to the experimental results. The estimated theoretical value of rutile TiO2 sample was 3.0 eV. This theoretical result shows good agreement when compared with the experimental data of undoped TiO2 sol-gel films, as well as the undoped TiO2 film prepared by sputtering.
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81.05.Gc Amorphous semiconductors
61.72.S- Impurities in crystals
78.66.Jg Amorphous semiconductors; glasses
61.72.up Other materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.A- Nucleation and growth
68.55.Nq Composition and phase identification
62.65.+k Acoustical properties of solids
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
82.80.Kq Energy-conversion spectro-analytical methods (e.g., photoacoustic, photothermal, and optogalvanic spectroscopic methods)
78.55.Qr Amorphous materials; glasses and other disordered solids
78.55.Hx Other solid inorganic materials

Ge/Si islands in a three-dimensional island crystal studied by x-ray diffraction

J. Novák, V. Holý, J. Stangl, T. Fromherz, Zhenyang Zhong, Gang Chen, G. Bauer, and B. Struth

J. Appl. Phys. 98, 073517 (2005); http://dx.doi.org/10.1063/1.2073974 (9 pages) | Cited 4 times

Online Publication Date: 10 October 2005

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Coplanar high-resolution x-ray diffraction has been used for the characterization of size, chemical composition, and strain of Ge/Si (001) islands in a three-dimensional island crystal grown using self-assembly on a prepatterned (001) Si substrate. The measured diffusely scattered intensity is simulated using the kinematical approximation and the parameters of model islands are fitted. These simulations require calculations of the strain fields within the islands and the spacer layers. For this purpose, an analytical approach to solve the continuum elasticity equations has been extended to a full three-dimensional calculation. The Ge content in the islands is found to be on the average 40%, and the island shape does not change dramatically during capping.
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81.16.Dn Self-assembly
81.15.Aa Theory and models of film growth
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Indentation of rigid cones into conical holes molded in elastic blocks

Yong Yee Lim and M. Munawar Chaudhri

J. Appl. Phys. 98, 073518 (2005); http://dx.doi.org/10.1063/1.2060933 (9 pages) | Cited 3 times

Online Publication Date: 10 October 2005

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Results obtained from several series of experiments on the normal loading of rigid spherical and conical indenters onto elastic blocks are described. Different series of experiments conducted are (1) normal loading of a rigid sphere onto elastic blocks of polydimethylsiloxane of different elastic moduli, (2) normal loading of rigid cones of different included angles onto a flat of the elastic blocks, and (3) normal loading of rigid cones of different included angles into conical holes of various included angles molded in the two types of elastic block. It was found that the indenter load versus indenter displacement data corresponding to the normal loading of the sphere and cones of different included angles onto a flat surface of the elastic blocks were very well fitted by the theories of Hertz and Sneddon, respectively. It has also been found that when rigid cones were loaded into conical holes molded in the elastic blocks, the load versus indenter displacement data were not fitted by the Sneddon theory for a conical indenter loading onto an elastic half space. Neither were the experimental data fitted by a modified Sneddon equation in which the effective semi included angle β of the conical indenter was taken as β = [(π/2)−(α′−α)], with α′ and α being the semi-included angles of the conical hole and the indenter, respectively. These results cast some doubt on the validity of some of the current methods in use for analyzing the unloading curves obtained from nanoindentation experiments made using pointed pyramidal and conical indenters on elastic-plastic solids.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
61.41.+e Polymers, elastomers, and plastics
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.10.Fq Growth from melts; zone melting and refining

Dichroic reflection of InAs/GaAs quantum dots

E. W. Bogaart, J. E. M. Haverkort, T. J. Eijkemans, T. Mano, R. Nötzel, and J. H. Wolter

J. Appl. Phys. 98, 073519 (2005); http://dx.doi.org/10.1063/1.2073971 (5 pages) | Cited 3 times

Online Publication Date: 11 October 2005

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Polarization-resolved reflection measurements are performed on nearly circular InAs/GaAs quantum dots (QDs) by means of time-resolved differential reflection spectroscopy. We observe linear polarization anisotropy of the differential absorption, revealing the dichroic character of the QD reflection. The observed magnitude of the dichroism is math/Θ[110] = 1.07. The polarization has a preferential direction orientated along the [1math0] crystal axis, which is confirmed by polarization-resolved photoluminescence. We observe that the polarization anisotropy of the reflectivity is strongly dependent on the pump excitation density, decreasing from ρ = 0.14 at low excitation to ρ = 0.06 at high excitation. The pump power dependence is described by a binomial model taking into account the statistics of carrier capture into a limited number of QDs.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
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