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1 May 2001

Volume 89, Issue 9, pp. 4689-5231

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General thermodynamic framework for understanding temperature-entropy diagram of batchwise operating thermodynamic cooling cycles

H. T. Chua, K. C. Ng, A. Malek, and N. M. Oo

J. Appl. Phys. 89, 5151 (2001); http://dx.doi.org/10.1063/1.1360697 (8 pages) | Cited 4 times

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This article presents a general thermodynamic framework for the temperature-entropy (T-s) diagram of batchwise operating thermodynamic cooling cycles. Our approach is fully consistent with the rigor of classical thermodynamics and captures accurately characteristics of cyclic-steady-state performance of a batchwise operating cooling cycle. The Eulerian viewpoint is adopted to allow for a time invariant description of such a cycle on a T-s plane, and this results in the formation of close loops at all internal energy storage components and their connection(s). © 2001 American Institute of Physics.
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05.70.-a Thermodynamics
84.60.-h Direct energy conversion and storage
05.70.Ce Thermodynamic functions and equations of state

Influence of tip modulation on image formation in scanning near-field optical microscopy

J. N. Walford, J. A. Porto, R. Carminati, J.-J. Greffet, P. M. Adam, S. Hudlet, J.-L. Bijeon, A. Stashkevich, and P. Royer

J. Appl. Phys. 89, 5159 (2001); http://dx.doi.org/10.1063/1.1359153 (11 pages) | Cited 26 times

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Modulation of the probe height in a scanning near-field optical microscope (SNOM) is a technique that is commonly used for both distance control and separation of the near-field signal from a background. Detection of higher harmonic modulated signals has also been used to obtain an improvement in resolution, the elimination of background, or artifacts in the signal. This article presents a theoretical model for the effects induced in SNOM images by modulation of the probe. It is shown that probe modulation introduces a spatial filter into the image, generally suppressing propagating field components and enhancing the strength of evanescent field components. A simple example of detection of a single evanescent field above a prism is studied in some detail, and a complicated dependence on modulation parameters and waveform is shown. Some aspects of the application of this theory in a general experimental situation are discussed. Simulated images are displayed to explicitly show the effects of varying modulation amplitude with first and second harmonic detection. Finally, we discuss the suppression of background artifacts due to propagating fields through the use of higher harmonic detection. © 2001 American Institute of Physics.
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68.37.Uv Near-field scanning microscopy and spectroscopy
07.79.Fc Near-field scanning optical microscopes
42.30.Lr Modulation and optical transfer functions
42.30.Va Image forming and processing

Characterization of ultrathin silicon oxide films with mirror-enhanced polarized reflectance Fourier transform infrared spectroscopy

Zhenjiang Cui and Christos G. Takoudis

J. Appl. Phys. 89, 5170 (2001); http://dx.doi.org/10.1063/1.1334364 (7 pages) | Cited 5 times

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Ultrathin silicon oxide films thermally grown on Si (100) are characterized with mirror-enhanced polarized reflectance Fourier transform infrared spectroscopy (MEPR-FTIR). MEPR-FTIR is proposed to effectively probe properties of ultrathin films. Using a mirror and a polarizer, MEPR-FTIR overcomes the difficulty of weak IR intensities normally encountered in ultrathin gate dielectrics such as SiO2; the intensity of the silicon oxide longitudinal optical (LO) mode is found to increase by a factor of about 20. Therefore, FTIR spectrometers with sensitivity down to 0.01% may allow even submonolayer probing of silicon oxide on Si substrates. The relationship between film thickness and IR intensity of the LO mode at 1252 cm−1 is presented for silicon oxide films as thin as a few Å thick. Independent measurements with ellipsometry, cross-sectional transmission electron microscopy, and x-ray photoelectron spectroscopy as well as theoretical predictions using the general Fresnel function are utilized. Although nonlinear overall, the theoretically predicted relationship between the MEPR-FTIR intensity and film thickness is almost linear within the range 0–50 Å. Experimental data are shown to agree very well with the theoretical calculations for two different kinds of oxides: thermal oxides grown at 1050 °C and native oxides. Such results suggest that the MEPR-FTIR can be useful as an ex situ or in situ technique for thickness measurements and, in fact, for other properties of ultrathin gate dielectrics. © 2001 American Institute of Physics.
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78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Direct observation of the field-stimulated exoemission sites at tungsten surfaces using field ion microscopy

T. Shiota, M. Umeno, K. Dohkuni, M. Tagawa, and N. Ohmae

J. Appl. Phys. 89, 5177 (2001); http://dx.doi.org/10.1063/1.1359421 (6 pages)

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The spatial distribution of the field-stimulated exoemission (FSEE) from the W tip surface annealed at 800 K for 600 s and the atomic arrangement of the emitting surface were correlated using field ion microscopy (FIM) and field emission microscopy. The FSEE was observed at around the (111) plane of the annealed W tip surface. FIM observation of the annealed W tip revealed the existence of a pyramid-like protrusion at the W(111) surface. From these experimental results, a new emission model of the FSEE was proposed relating to the field-assisted surface structural change. This model deals with the buildup/collapse of the pyramid-like protrusion at the W(111) surface under the effect of negative high electric field. The temperature dependence of the FSEE reported previously [Shiota et al., J. Appl. Phys. 85, 6811 (1999)] was qualitatively explained by this emission model. © 2001 American Institute of Physics.
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79.75.+g Exoelectron emission
68.35.B- Structure of clean surfaces (and surface reconstruction)

Time-of-flight and emission spectroscopy study of femtosecond laser ablation of titanium

Mengqi Ye and Costas P. Grigoropoulos

J. Appl. Phys. 89, 5183 (2001); http://dx.doi.org/10.1063/1.1360696 (8 pages) | Cited 28 times

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Femtosecond laser ablation of titanium has been studied via time-of-flight (TOF) and emission spectroscopy measurement. Laser pulses of 80 fs full width at half maximum at λ=800 nm were delivered by a Ti:sapphire femtosecond laser system. A vacuum chamber with a base pressure of 10−7 Torr was built for ion TOF measurement. These ion TOF spectra were utilized to determine the velocity distribution of the ejected ions. While nanosecond laser ablation typically generates ions of tens of eV, femtosecond laser irradiation even at moderate energy densities were found to produce energetic ions with energies in the range of a few keV. Two ablation regimes, exhibiting different laser fluence dependence of the total ion yields, and the corresponding percentage of energetic ions and the crater depth, were identified and explained on the basis of the two-temperature model. Clean craters were observed by interferometric microscope measurements, indicating the advantages of and potential for applying femtosecond lasers to micromachining and advanced materials treatment. Emission spectroscopy and imaging have been carried out via a monochromator and an intensified CCD camera. Femtosecond laser-induced plumes were found to be much smaller and weaker in intensity than those induced by nanosecond laser pulses. © 2001 American Institute of Physics.
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52.38.Mf Laser ablation
61.82.Bg Metals and alloys
79.20.Ds Laser-beam impact phenomena
81.05.Bx Metals, semimetals, and alloys

Simulation of the initial transient of the Si+ and O+ signals from oxygen sputtered silicon by means of independent models on sputtering and secondary ionization

J. J. Serrano, H. De Witte, W. Vandervorst, B. Guzmán, and J. M. Blanco

J. Appl. Phys. 89, 5191 (2001); http://dx.doi.org/10.1063/1.1362370 (8 pages) | Cited 2 times

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The Si+ and O+ signals, as obtained in secondary ion mass spectrometry (SIMS) analysis of silicon when using oxygen as the primary species, pass through an initial transient region before reaching the stationary state. We simulate this transient zone to check a phenomenological model for the secondary ionization of sputtered atoms. The simulation is split into two parts: the sputtering of neutrals obtained from implantation, sputtering, relocation/replacement, and diffusion, simulations and their subsequent ionization. The ionization phenomena are also described by some ad hoc fitting functions with which the SIMS measurements are better approached than with the model. The fitting functions and the model outputs are verified with experimental secondary ionization data. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Properties of dc magnetron sputtered indium tin oxide films on polymeric substrates at room temperature

J. H. Shin, S. H. Shin, J. I. Park, and H. H. Kim

J. Appl. Phys. 89, 5199 (2001); http://dx.doi.org/10.1063/1.1357470 (5 pages) | Cited 33 times

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Indium tin oxide (ITO) thin films were deposited on polymeric substrates at room temperature by dc reactive magnetron sputtering from an In–Sn (90–10 wt%) alloy target. The electrical, optical, and mechanical properties of ITO films on various substrates such as polycarbonate, acrylic, polyethylene terephthalate, and glass are influenced sensitively by sputtering parameters. Therefore, the dependence of these properties on dc power, working pressure, and partial oxygen content has been systematically investigated. Low dc power was applied to avoid the deformation of polymeric substrates. The electrical resistivity of as-deposited ITO films decreases initially and then increases as oxygen partial pressure (PO2) increases. The optical transmittance at visible wavelength of 550 nm was as much as 85%. The friction force of as-deposited ITO films on various substrates is increased with an increase of dc power, and behaves similarly to the optimum curve of resistivity with increasing PO2. © 2001 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
81.15.Cd Deposition by sputtering
81.05.Hd Other semiconductors
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
78.40.Fy Semiconductors
68.60.Bs Mechanical and acoustical properties

Interface-controlled Au/GaAs Schottky contact with surface sulfidation and interfacial hydrogenation

Min-Gu Kang and Hyung-Ho Park

J. Appl. Phys. 89, 5204 (2001); http://dx.doi.org/10.1063/1.1360220 (5 pages) | Cited 2 times

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We report a GaAs passivation method using sulfidation and hydrogenation to achieve the Au/GaAs interface free of defective interfacial compounds, through which improves the electrical properties of the Schottky contact. A sulfur-passivated GaAs Schottky diode exhibited improved contact properties, for example an enhanced barrier height and the lower reverse leakage current compared to the diode with conventional HCl-cleaned GaAs. The combination of the H-plasma treatment and the predeposition of an ultrathin Au overlayer enable to control the defective interfacial state of metallization-induced excess As: the Au overlayer seems to effectively protect GaAs from plasma-induced damage and attenuate the energy of penetrating hydrogen then the hydrogenated interface became defect-free since interfacial excess As effectively sublimated as volatile As hydrides. The reverse leakage current was reduced by an order and photoluminescence efficiency was greatly enhanced while there was no change in the dopant profile of GaAs substrate and none of Si–H. We describe a mechanism of the evolution of interfacial bonds during the processes to correlate to the improved electrical properties, which are systematically characterized by the surface/interface analysis tools such as x-ray photoelectron spectroscopy and attenuated-total-reflection Fourier-transform infrared spectroscopy and particularly the role of excess As is discussed in detail. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Rv Passivation
68.35.Ct Interface structure and roughness
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Surface oxidation as a diffusion barrier for Al deposited on ferromagnetic metals

W. F. Egelhoff, P. J. Chen, R. D. McMichael, C. J. Powell, R. D. Deslattes, F. G. Serpa, and R. D. Gomez

J. Appl. Phys. 89, 5209 (2001); http://dx.doi.org/10.1063/1.1359151 (6 pages) | Cited 21 times

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Grazing incidence x-ray reflectometry has been used to study surface oxidation as a diffusion barrier for Al deposited on ferromagnetic metals (Co, Fe, Ni, and Ni80Fe20). Samples of the form SiO2\10 nm X\4 nm Al with X=(Co, Fe, Ni, and Ni80Fe20) were investigated for X\Al intermixing. Surface oxidation was achieved by exposing the ferromagnetic layer to O2 to oxidize the top two or three atomic layers before depositing the Al layer. Specular x-ray scans were used for the analysis. Samples of the form SiO2\10 nm X\4 nm Au were used to separate topographical roughness from intermixing. Surface oxidation was found to suppress the diffusion of Al into Co, Ni, and Ni80Fe20 but not into Fe. © 2001 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Bx Metals, semimetals, and alloys
68.35.Fx Diffusion; interface formation
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Growth and characterization of GaAs epitaxial layers on Si/porous Si/Si substrate by chemical beam epitaxy

S. Saravanan, Y. Hayashi, T. Soga, T. Jimbo, M. Umeno, N. Sato, and T. Yonehara

J. Appl. Phys. 89, 5215 (2001); http://dx.doi.org/10.1063/1.1362339 (4 pages) | Cited 4 times

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The initial growth of GaAs films on a Si/porous Si/Si (SPS) substrate has been investigated using reflection high-energy electron diffraction. The morphology and the thickness have been examined by a Nomarski optical microscope and scanning electron microscope, respectively. The results of the low temperature photoluminescence studies have shown that a significant reduction in the residual thermal tensile stress can be achieved with reduced growth temperature. The 77 K photoluminescence spectra for GaAs/Si show a strain-induced splitting between the heavy and light hole valence bands which corresponds to a biaxial tensile stress of 2.45 kbar acting on the GaAs layer where the same for GaAs/SPS grown at 450 °C is 1.69 kbar. The results have shown that a SPS substrate with the combination of low temperature growth is a promising candidate for obtaining GaAs films with low stress. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors

Modeling of the gas-phase chemistry in C–H–O gas mixtures for diamond chemical vapor deposition

James R. Petherbridge, Paul W. May, and Michael N. R. Ashfold

J. Appl. Phys. 89, 5219 (2001); http://dx.doi.org/10.1063/1.1360221 (5 pages) | Cited 5 times

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The boundaries of the diamond deposition region in the C–H–O (Bachmann) atomic phase composition diagram have been reproduced successfully for 38 different C, H, and O containing gas mixtures using the CHEMKIN computer package, together with just two criteria—a minimum mole fraction of methyl radicals [CH3] and a limiting value of the [H]/[C2H2] ratio. The diamond growth/no-growth boundary coincides with the line along which the input mole fractions of C and O are equal. For every gas mixture studied, no-growth regions are found to coincide with a negligible (<10−10) mole fraction of CH3 radicals, while for gas mixtures lying within the diamond growth region the CH3 mole fraction is ∼10−7. Each no-growth→diamond growth boundary is seen to be accompanied by a 2–3 order of magnitude step in CH3 mole fraction. The boundary between diamond and nondiamond growth is less clearly defined, but can be reproduced by assuming a critical, temperature dependent [H]/[C2H2] ratio (0.2, in the case that Tgas=2000 K) that reflects the crucial role of H atoms in the etching of nondiamond phases. The analysis allows prediction of the composition process window for good quality diamond growth for all stable input gas mixtures considered in this study. © 2001 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
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