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15 Sep 2002

Volume 92, Issue 6, pp. 2959-3416

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Magnetized foils as π flippers in neutron spin-echo spectrometry

M. Theo Rekveldt, Wim G. Bouwman, and Wicher H. Kraan

J. Appl. Phys. 92, 3354 (2002); http://dx.doi.org/10.1063/1.1499751 (9 pages) | Cited 7 times

Online Publication Date: 27 August 2002

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In neutron spin-echo spectrometry Larmor precession regions are used, in which the homogeneity of the field line integrals along the neutron paths play an essential role. In the application of this technique for small-angle scattering, the transmission angle encoding happens by strong precession gradients in a certain direction in a magnetic field. Here the use of magnetized foils as π flippers will be discussed. They appear to compensate very efficiently for field line inhomogeneities and moreover they create an effectively strong gradient in Larmor precession, needed for the small-angle scattering application. The π flippers consist of magnetized foils of the proper thickness, magnetized by the field of the precession devices itself. Application of such π flippers in a spin-echo small angle neutron scattering setup with fields perpendicular and parallel to the beam direction is discussed. It appears that such flippers avoid corrections for the inhomogeneity of the field line integrals for the main part in both options. © 2002 American Institute of Physics.
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61.05.fg Neutron scattering (including small-angle scattering)
41.85.-p Beam optics

Study of C3H5+ ion deposition on polystyrene and polyethylene surfaces using molecular dynamics simulations

Inkook Jang, Roshenda Phillips, and Susan B. Sinnott

J. Appl. Phys. 92, 3363 (2002); http://dx.doi.org/10.1063/1.1500788 (5 pages) | Cited 4 times

Online Publication Date: 27 August 2002

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Molecular dynamics simulations of ion deposition processes are used to study the deposition of C3H5+ ions on crystalline polystyrene (PS) and polyethylene (PE) surfaces at energies of 50 and 25 eV. For each system, 80 trajectories are carried out on pristine surfaces and the incident angle in every case is normal to the surface. The forces are determined using the reactive empirical bond order method developed by Tersoff and parametrized for hydrocarbons by Brenner, coupled to long-range Lennard–Jones potentials. The simulations predict that the ions deposited at 50 eV either dissociate and stick to the surface or remain on the surface intact in 98% of the trajectories on PS, and in 89% of the trajectories on PE. At 25 eV, the ions are deposited intact in 70% of the trajectories on PS and dissociate in only 3%. No dissociation of the incident ions is predicted to occur on PE at 25 eV. Rather, the ions scatter away in 90% of the trajectories. Consequently, ion deposition on PE at 25 eV is predicted to be very inefficient for thin-film growth. Many more ions or major ion fragments (such as C2Hn and CH2) remain near the surface on PS than PE at 50 eV. Thus, in general, polyatomic ion deposition for thin film growth is more efficient on PS than PE, and deposition at 50 eV is more efficient than deposition at 25 eV. © 2002 American Institute of Physics.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
02.70.Ns Molecular dynamics and particle methods

Mass sensitivity of acoustic wave devices from group and phase velocity measurements

G. McHale, F. Martin, and M. I. Newton

J. Appl. Phys. 92, 3368 (2002); http://dx.doi.org/10.1063/1.1499750 (6 pages) | Cited 6 times

Online Publication Date: 27 August 2002

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The effect of dispersion on acoustic wave sensors is considered. The discussion is focused upon layer guided surface acoustic waves (Love waves), which obtain their high mass sensitivity for the first Love wave mode by optimizing the guiding layer thickness, d, such that d∼λl/4; the wavelength in the layer is given by λl=f/vl where f is the operating frequency and vl is the shear acoustic speed of the guiding layer. We show that this optimization of guiding layer thickness corresponds to strong dispersion so that the phase and group velocities can be quite different. From the definition of the phase velocity mass sensitivity, we show that it can be determined from either the slope of the curve of phase velocity with normalized guiding layer thickness, z=d/λl, or from the phase and group velocities measured for a given guiding layer thickness. Experimental data for a poly(methylmethacrylate) polymer guiding layer on 36° XY Lithium Tantalate is presented. Measurements of phase velocity and group velocity determined by a network analyzer were obtained for systematically increasing guiding layer thicknesses; a pulse transit experiment was also used to provide independent confirmation of the group velocity data. Two independent estimates of the mass sensitivity are obtained for z=d/λl<0.22 from (i) the slope of the phase velocity curve and (ii) the measurements of the group and phase velocity. These two estimates are shown to be consistent and we, therefore, conclude that it is possible to determine the mass sensitivity for a Love wave device with a given guiding layer thickness from measurements of the phase and group velocities. Moreover, we argue that the formula using group velocity to determine phase velocity mass sensitivity can be extended to a wide range of other acoustic wave sensors. In addition, we suggest that variations in the group velocity due to deposited mass may be a more sensitive parameter than variations in the phase velocity. © 2002 American Institute of Physics.
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43.58.-e Acoustical measurements and instrumentation
43.35.Pt Surface waves in solids and liquids
06.30.Dr Mass and density
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.35.Yb Ultrasonic instrumentation and measurement techniques

Control of thermal runaway in microwave resonant cavities

X. Wu, J. R. Thomas, and W. A. Davis

J. Appl. Phys. 92, 3374 (2002); http://dx.doi.org/10.1063/1.1501744 (7 pages) | Cited 17 times

Online Publication Date: 27 August 2002

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This article reports direct experimental evidence of the so-called “S curve” of temperature versus electrical field strength when materials with positive temperature dependence of dielectric loss are heated in a microwave resonant cavity applicator. A complete discussion of how the experimental results were achieved is presented. From the experimental results, we believe the S curve theory provides an incomplete explanation of thermal runaway in microwave heating. To understand microwave heating in a resonant cavity, cavity effects must be considered. To explain the experimental results, a theoretical model based on single-mode waveguide theory is developed. Finally, a method to control thermal runaway is described.© 2002 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
07.20.Hy Furnaces; heaters

Titanium dioxide thin-film growth on silicon (111) by chemical vapor deposition of titanium(IV) isopropoxide

A. Sandell, M. P. Anderson, Y. Alfredsson, M. K.-J. Johansson, J. Schnadt, H. Rensmo, H. Siegbahn, and P. Uvdal

J. Appl. Phys. 92, 3381 (2002); http://dx.doi.org/10.1063/1.1501751 (7 pages) | Cited 24 times

Online Publication Date: 27 August 2002

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The initial stages of TiO2 growth on Si(111) under ultra-high vacuum conditions is studied using core level photoelectron spectroscopy, x-ray absorption spectroscopy, and scanning tunneling microscopy. The TiO2 film was formed by means of chemical vapor deposition of titanium(IV) isopropoxide at a sample temperature of 500 °C. The thickness and composition of the amorphous interface layer and its subsequent transition to crystalline anatase TiO2 are discussed. Three different stages are identified: In the initial stage (film thickness <10 Å), the oxygen atoms are coordinated mainly to Si atoms giving rise to Ti atoms with oxidation states lower than 4+. At this stage, a small amount of carbon (0.15 ML) is observed. The next stage (<25 Å) is best described as an amorphous TiSixOy compound in which the oxidation state of Ti is 4+ and the x and y values vary monotonically with the film thickness, from 2 to 0 and 4 to 2, respectively. Finally (>30 Å) a stoichiometric TiO2 layer starts to form. The TiO2 phase is anatase and the layer consists of particles ∼10 nm wide. © 2002 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
78.70.Dm X-ray absorption spectra
79.60.Dp Adsorbed layers and thin films
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Single crystal Si layers on glass formed by ion cutting

M. Cai, D. Qiao, L. S. Yu, S. S. Lau, C. P. Li, L. S. Hung, Tony E. Haynes, K. Henttinen, Ilkka Suni, V. M. C. Poon, T. Marek, and J. W. Mayer

J. Appl. Phys. 92, 3388 (2002); http://dx.doi.org/10.1063/1.1492017 (5 pages) | Cited 15 times

Online Publication Date: 27 August 2002

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The process of ion cutting was used to integrate single crystalline Si layers on glass for potential active matrix flat panel display and other applications. It was found that p-Si wafers implanted at 100–150 °C with H with a dose in the order of a few times 1016 cm−2 could be readily bonded to glass substrates when both of the surfaces were properly treated and activated. The as-implanted Si wafer surface was converted from p type to n type. Upon bonding at room temperature, annealing (300 °C) and exfoliation (450 °C), the transferred Si layer on glass and the as-exfoliated surface of the implanted Si wafer remained n type. A highly defective region was observed near the top of the Si layer on glass, however the crystalline quality was nearly defect free in the deeper region of the layer. Annealing at sequentially higher temperatures led to the recovery of p type conductivity at ∼600–650 °C. The type conversion and the subsequent annealing behavior observed on the samples were rationalized in terms of ion enhanced oxygen diffusion and the presence of H-related shallow donors in the Si. © 2002 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
66.30.J- Diffusion of impurities
71.55.Cn Elemental semiconductors

High quality chemical vapor deposition diamond growth on iron and stainless steel substrates

Eri Nakamura, Kenji K. Hirakuri, Manabu Ohyama, Gernot Friedbacher, and Nobuki Mutsukura

J. Appl. Phys. 92, 3393 (2002); http://dx.doi.org/10.1063/1.1502917 (4 pages) | Cited 10 times

Online Publication Date: 27 August 2002

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Due to the catalytic effect and the rapid diffusion coefficients of carbon species into iron-based materials such as iron and 18-8 stainless steel [18% chrome (Cr) and 8% nickel (Ni)], it is very difficult to produce diamond grains on such substrates. However, diamond growth on iron-based materials is extremely important for mechanical and electrical applications, since these materials are widely used in industrial field and fundamental science. In our previous study, diamond nucleation and subsequent growth have been precisely controlled by the residence time of the source gas, which is an essential parameter. Here, we have carried out diamond growth on iron-based materials using the hot-filament chemical vapor deposition technique with varying residence times. At low residence times, diamond grains with practically useful growth rate are grown. The growth rate of diamond grains on stainless steel substrates was a factor of about 10 greater than that on a regular silicon substrate at optimum conditions. At optimized conditions, diamond growths with high crystalline quality on stainless steel substrates were confirmed by Raman spectroscopy and scanning electron microscopy. The full width of half maximums of the Raman peaks for diamonds grown in this study are comparable to the ones of natural diamonds. © 2002 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.U- Carbon/carbon-based materials
68.55.A- Nucleation and growth
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
66.30.Ny Chemical interdiffusion; diffusion barriers
78.30.Hv Other nonmetallic inorganics
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.66.Nk Insulators

Crystal size and oxygen segregation for polycrystalline GaN

K. S. A. Butcher, H. Timmers, Afifuddin, Patrick P.-T. Chen, T. D. M. Weijers, E. M. Goldys, T. L. Tansley, R. G. Elliman, and J. A. Freitas

J. Appl. Phys. 92, 3397 (2002); http://dx.doi.org/10.1063/1.1499232 (7 pages) | Cited 13 times

Online Publication Date: 27 August 2002

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The grain size for polycrystalline GaN, grown in low-temperature gallium-rich conditions, is shown to be correlated to the oxygen content of the films. Films with lower oxygen content were observed to have larger crystals with an increased tendency to a single-preferred crystal orientation. Elastic recoil detection analysis with heavy ions (i.e., 200 MeV 197Au ions) was used to determine the composition of the GaN films grown for the study, including the hydrogen, carbon, gallium, nitrogen, and oxygen content. Atomic force microscopy and x-ray diffraction were used to study the sample morphology. From these measurements, the available surface area of the films was found to be sufficient for a significant proportion of the oxygen present in the films to segregate at the grain boundaries. This interpretation is consistent with earlier theoretical studies of the formation and segregation of the VGa-(ON)3 defect complex at dislocation sites in gallium-rich GaN. For this work, however, the defect complex is believed to segregate at the grain boundary of the polycrystalline GaN. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
64.75.-g Phase equilibria
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Quantitative electron microprobe analysis of aluminum, copper, and gold thin films on silicon substrates

Masaaki Yasuda, Shunji Yamauchi, Hiroaki Kawata, and Kenji Murata

J. Appl. Phys. 92, 3404 (2002); http://dx.doi.org/10.1063/1.1502923 (6 pages) | Cited 2 times

Online Publication Date: 27 August 2002

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The thicknesses of aluminum, copper, and gold thin films on silicon substrates have been measured with an electron probe microanalyzer. k ratio versus thickness calibration curves are obtained by a Monte Carlo simulation of electron scattering. The simulation results based on two energy loss models are compared. One is the continuous slowing down approximation model and another is the hybrid model for the discrete and the continuous energy loss processes. Inner shell ionizations and free electron excitations are selected out for the discrete process in the hybrid model. In both models the Mott cross section and the Gryzinski cross section are used for elastic collisions and ionizations, respectively. The exact film/substrate boundary condition is considered. The characteristic and continuum fluorescence corrections are also included in the simulation. The simulation results agree well with experimental ones measured with a quartz oscillator. Effects of the introduction of the discrete energy loss process and the fluorescence correction are discussed in comparison between simulation and experiment. © 2002 American Institute of Physics.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.Nq Composition and phase identification
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
81.05.Bx Metals, semimetals, and alloys
02.70.Uu Applications of Monte Carlo methods
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling
79.20.Uv Electron energy loss spectroscopy
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