bluuebunny/crossref_metadata_2025 huggingface dataset:
The interaction of atomic hydrogen with very thin amorphous hydrogenated silicon films analyzed using in situ real time infrared spectroscopy: Reaction rates and the formation of hydrogen platelets
Authors: von Keudell A. , Abelson J. R.
Published: July 2002

The interaction of thermal atomic hydrogen (H0) with very thin amorphous hydrogenated silicon (a-Si:H) films is investigated using real time in situ infrared spectroscopy. Hydrogen bonded in isolated and in clustered network configurations is identified from the analysis of the IR line positions and the kinetics of the hydrogen uptake in hydrogen-depleted, hydrogen-deficient and deuterated samples. The use of very thin films is important for this mode identification, since the penetration of atomic hydrogen is not diffusion limited and is therefore very uniform. The analysis yields an IR mode for the isolated SiH groups centered at ∼1985 cm−1, and a newly identified IR mode for platelet-like SiH groups at ∼2033 cm−1. On the basis of this mode identification, the relative reaction probabilities for H saturation of Si dangling bonds, the insertion into strained Si-Si bonds and the H abstraction reaction are determined to 1:0.44:0.26. The kinetic evolution of the two SiH bulk modes successfully describes the measured structural changes and etching of a-Si:H during exposure to H0.
Photoluminescence from nanometer Ge particle embedded Si oxide films
Authors: Ma S. Y. , Ma Z. C. , Zong W. H. , Han H. X. , Wang Z. P. , Li G. H. , Qin G. , Qin G. G.
Published: July 2002

Nanometer Ge particle (NGP) embedded Si oxide films were deposited on p-type Si substrates using the rf magnetron sputtering technique with a Ge–SiO2 composite target. The area ratio percentage of the Ge target to the composite target was 5%. These films were annealed in a N2 ambient at 300, 600, 800, or 900 °C for 30 min. By fitting Raman scattering spectra, the average diameters of the NGPs in the films were determined. They increased from 5.4 to 9.5 nm with increasing annealing temperatures from 600 to 900 °C. The photoluminescence (PL) peaks for all NGP embedded Si oxide films annealed at various temperatures are located at almost the same position around 580 nm (2.1 eV), although the average sizes of the NGPs in these films are very different from each other. After γ-ray irradiation, the PL peak intensity increases by a factor of 2.3, with the peak position unchanged. The PL peak position does not show any evident shift when the measurement temperature increases from 10 to 300 K. All experimental facts indicate that light emission originates mainly from the luminescence centers in the SiOx films covering the NGPs rather than from the NGPs. The role of NGPs in the PL process of the films is discussed.
Laser-assisted chemical vapor deposition of titanium nitride films
Authors: Ishihara Seiji , Hanabusa Mitsugu
Published: July 2002

We used a 193 nm ArF excimer laser to assist chemical vapor deposition of titanium nitride (TiN) films on Si (100) and SiO2. The source gases were tetrakis(dimethylamido)titanium (TDMAT) or tetrakis(diethylamido)titanium (TDEAT) mixed with ammonia. A correct stoichiometry was confirmed from Auger spectra. The laser helped to enhance TiN deposition rates at low temperatures (100 °C for TDMAT-NH3 and 200 °C for TDEAT-NH3). At higher temperatures the deposition rates decreased with an increasing laser energy density. Under irradiation the electrical resistivity of the TiN films was lowered. The laser-induced effect on electrical resistivity was particularly pronounced at low temperatures. A good conformality of the TiN films for contact holes with high aspect ratios was demonstrated.
Optoelectronic and structural properties of a-Ge1−xCx:H prepared by rf reactive cosputtering
Authors: Vilcarromero J. , Marques F. C. , Freire F. L.
Published: July 2002

Optoelectronic, structural, and mechanical properties of hydrogenated amorphous germanium carbon (a-Ge1−xCx:H) alloys are presented. The films were prepared by the rf cosputtering technique using graphite-germanium composite targets. Films with carbon contents in the 0<x<1 range were prepared under the same conditions used to obtain a-Ge:H films with good optoelectronic properties. The trends of the optical gap, infrared absorption, dark conductivity, and mechanical stress as a function of the carbon content suggest that the properties of films with low carbon concentration are mainly controlled by the incorporation of sp3 hybridized carbon. These films have good optoelectronic and structural properties. As the carbon content increases, the properties of the films are determined by the concentration of sp2 carbon sites.
Band gap and heterojunction discontinuities of pseudomorphic Si1−x−yGexCy alloy layers on Si(001)
Authors: Wu Liqing , Huang Meichun , Zhu Zizhong , Li Kaihang
Published: July 2002

We present a theoretical study of the minimum band gap of the pseudomorphic Si1−x−yGexCy ([C]⩽9%) alloy layers grown on Si(001). We also investigate the valence-band offset and conduction-band offset at the strained Si1−x−yGexCy/Si(001) heterointerfaces, in the framework of the average bond energy theory in conjunction with the deformation potential method. Self-consistent calculations are based on the local density functional theory, ab initio pseudopotentials and the virtual-crystal approximation. Our results show the correct tendency and order of magnitude compared with most of the theoretical and experimental data. It is encouraging to find that the tendencies of the minimum band gap and band offsets with the alloy composition and lattice mismatch are changed suddenly at the critical point due to the difference of the strain properties at the two sides of zero lattice mismatch. Our results also indicate that it is possible to obtain a larger conduction-band offset of the Si1−x−yGexCy/Si(001) heterostructure than that of the Si1−xGex/Si(001) heterostructure which offers a new prospect for the development of heterostructure devices compatible with Si integrated circuit technology.
Negative nonlinear absorption in Er3+-doped fluoroindate glass
Authors: Lozano B. W. , de Araújo Cid B. , Acioli L. H. , Messaddeq Y.
Published: July 2002

We report the observation of negative nonlinear absorption in fluoroindate glasses doped with erbium ions. The pumping wavelength is 800 nm which is doubly resonant with Er3+ ions transitions. A large nonlinear intensity dependence of the optical transmittance and strong upconverted fluorescence are obtained. The dependence of the upconverted fluorescence intensity with the laser power is described by a system of coupled-rate equations for the energy levels’ populations.
Neutron diffraction and Mössbauer spectral study of Nd2Fe16Ti and its nitride
Authors: Grandjean F. , Ezekwenna P. C. , Long Gary J. , Pringle O. A. , l’Héritier Ph. , Ellouze M. , Luo H. P. , Yelon W. B.
Published: July 2002

The 295 K powder neutron diffraction patterns and the temperature dependence of the Mössbauer spectra of Nd2Fe17−xTix and Nd2Fe17−xTixNy have been measured. A Rietveld refinement of the neutron diffraction patterns yields the Nd2Fe16.32Ti0.68 and Nd2Fe16.32Ti0.68N2.7 stoichiometries for the two compounds and indicates that titanium occupies only the 6c crystallographic site and nitrogen only the 9e site in the rhombohedral Th2Zn17 structure. The insertion of interstitial nitrogen into Nd2Fe16.32Ti0.68 produces a 6.8% increase in the unit cell volume. The relative areas of the Mössbauer spectral components indicate that iron–iron, iron–titanium, and titanium–titanium 6c–6c dumbbell pairs exist in both of these materials. The magnetic hyperfine fields observed for the iron on the 6c site in the iron–titanium dumbbell pair in both compounds is substantially reduced from that found in Nd2Fe17 and Nd2Fe17N2.6 because of the titanium dumbbell near neighbor. For all the remaining hyperfine parameters there is a good correlation with those observed in Nd2Fe17 and Nd2Fe17N2.6. A linear increase is observed for the weighted average isomer shift with increasing unit cell volume for Nd2Fe17, Nd2Fe17N2.6, Nd2Fe16.32Ti0.68, and Nd2Fe16.32Ti0.68N2.7, because of the decreasing s-electron density at the iron-57 nucleus.
Schottky barrier and interface formation of metal–GaTe(001) interfaces
Authors: Almeida J. , Berger H. , Margaritondo G.
Published: July 2002

We studied the deposition of Au, In, Ag, and Al overlayers onto clean-cleaved GaTe(001) surfaces at room temperature by x-ray photoelectron spectroscopy. Gold and In overlayers did not produce evidence of chemical reactions, and neither with cation nor anion outdiffusion. Gold overlayers exhibited no evidence of island formation and a layer-by-layer overlayer coverage. The deposition of In revealed the presence of clustering for a metal thickness higher than 6 Å. On the other hand, the deposition of Al lead to an exchange reaction with a metalliclike Ga phase separation. Core level analysis of the Ag–GaTe interface revealed no noticeable change of the shape of the peaks. The dependence of the peak intensities on overlayer thickness showed an initial layer-by-layer coverage until 1.8 Å, followed by a clustering growth mode. From about 3.7 Å Ag thickness, significant Te outdiffusion was observed.
Wavelength switching in multi-cavity laser diodes
Authors: Thiyagarajan S. M. K. , Kanjamala A. P. , Levi A. F. J.
Published: July 2002

We study experimentally and numerically electrical and optical methods to switch the lasing wavelength in a linear multi-cavity laser. The electrical method uses radio frequency modulation of the gain region to modify effective optical loss at a well-defined wavelength. The optical method uses injection of lasing light to modify effective photon lifetime at the injection wave-length. Short transient switching times corresponding to less than two photon-cavity round-trips are observed using both methods. However, this occurs for small spectral separation between lasing wavelengths, a less effective mode suppression ratio, and an asymmetry in switching time to and from a given lasing wavelength. The maximum wavelength switching speed is determined by the net optical gain and the initial number of photons in each cavity mode.
Temperature dependence of the photorefractive effect in Bi12GeO20
Authors: Bloom D. , McKeever S. W. S.
Published: July 2002

The temperature dependence of the photorefractive effect in undoped and Ga-doped Bi12GeO20 (BGO) crystals was measured over the temperature range from 40 to 300 K. From comparison of the decay curves of the laser-induced grating with thermally stimulated current and photoconductivity curves, we conclude that the major decay step between, ∼100 and ∼160 K, is due to the thermal release of trapped electrons from a distribution of traps centered near 0.3 eV, in both types of BGO sample. Additional thermal decay steps, between ∼200 and ∼300 K, correlate with other electron traps, in the energy range from ∼0.4 to ∼0.7 eV.
Comment on “Dispersion of birefringence in AgGaS2 and CuGaS2” [J. Appl. Phys. 82, 3100 (1997)]
Authors: Bhar G. C. , Kumbhakar P.
Published: July 2002

The importance of long wavelength natural birefringence in AgGaS2 is pointed out for nonlinear laser devices. Such an important aspect is absent in the model presented by Choi et al. [J. Appl. Phys. 82, 3100 (1997)]. Their model represents birefringence dispersion but locates the isotropic point at 0.52 μm instead of where actually found at 0.497 μm.
X-ray photoemission characterization of interface abruptness and band offset of Ga0.5In0.5P grown on GaAs
Authors: Dehaese O. , Wallart X. , Schuler O. , Mollot F.
Published: July 2002

We have studied by angle resolved x-ray photoemission spectroscopy (XPS) the interface between Ga0.5In0.5P and GaAs grown by gas source molecular beam epitaxy. For cations, we show that the interface is abrupt for a growth temperature of 400 °C and that indium segregation is effective at 500 °C but less than that in GaInAs at the same temperature. For anions, growth of the two layers in rapid succession results in the incorporation of an excess of arsenic in the GaInP epilayers and a diffuse interface. As soon as these predominant experimental effects are suppressed, the abruptness of the interface is limited by a weak arsenic surface segregation. For this quasi-abrupt interface, we report a valence band offset of ≈0.3 eV as determined by XPS.
Optical properties of ZnSe1−xSx epilayers grown on misoriented GaAs substrates
Authors: Chou W. C. , Yang C. S. , Chu A. H. M. , Yeh A. J. , Ro C. S. , Lan W. H. , Tu S. L. , Tu R. C. , Chou S. C. , Su Y. K. , Uen W. Y.
Published: July 2002

The strain induced heavy hole and light hole exciton splitting of ZnSe1−xSx (x<0.1) epilayers grown on misoriented GaAs (001) substrates has been studied by reflectance spectroscopy. The heavy hole and light hole exciton energies are determined by the composition of the layers. It was concluded that for both thin (largely unrelaxed strain) and thick epilayers (with largely relaxed strain) misorientation of the substrate results in increase of x, i.e., in increasing incorporation of sulphur. However, the additional strain expected due to the increasing incorporation of sulphur with misorientation was not observed due to partial strain relief of the epilayers grown on misoriented substrates. The optical quality of the epilayers is tilt angle dependent and is best for about 10° tilt from the (001) direction.
Real time spectroscopic ellipsometry characterization of structural and thermal equilibration of amorphous silicon–carbon alloy p layers in p-i-n solar cell fabrication
Authors: Fujiwara H. , Koh Joohyun , Lee Yeeheng , Wronski C. R. , Collins R. W.
Published: July 2002

Real time spectroscopic ellipsometry (RTSE) has been applied to investigate the near-surface optical changes that occur during p/i interface processing for hydrogenated amorphous silicon carbon alloy (a-Si1−xCx:H, x≈0.05) p layers prepared at ∼200 °C by plasma-enhanced chemical vapor deposition in the p-i-n solar cell configuration. Trimethylboron [B(CH3)3] was used as the p-type dopant source gas in order to avoid p-layer surface contamination that occurs when using diborane (B2H6). We have analyzed the changes in the RTSE data detected after extinguishing the plasma for a-Si1−xCx:H p-layer deposition while maintaining the p layer near its growth temperature. We have attributed these changes to: (i) structural equilibration characterized by the emission of bonded hydrogen (∼2 at. %) from the p layer into the vacuum, and (ii) thermal equilibration characterized by near-surface temperature variations (∼7 °C) due to gas composition and pressure variations within the reactor. From the RTSE data, the kinetics of H emission and the time evolution of the near-surface temperature have been determined separately. We have found that a significant fraction of the H emitted from the a-Si1−xCx:H p layer at ∼200 °C is lost within minutes of terminating the p-layer plasma. To restore the p-layer H content and improve the p/i interface characteristics in a-Si:H p-i-n solar cells, we applied a H2 plasma treatment to the p layer just prior to i-layer deposition at 200 °C. Such a treatment yielded a 0.05 V increase in the open circuit voltage of the cell.
Shear localization and chemical reaction in Ti–Si and Nb–Si powder mixtures: Thermochemical analysis
Authors: Chen H. C. , Nesterenko V. F. , Meyers M. A.
Published: July 2002

Chemical reactions in Ti–Si and Nb–Si powder mixtures were initiated in regions of high plastic strain induced by high-strain-rate deformation. These regions of high localized plastic strain had thicknesses of 10–25 μm and a characteristic spacing of 600–1000 μm. Scaling up of the experiments revealed a shear-band spacing that is constant and dictated by material and deformation parameters. The generation of heat due to plastic deformation and chemical reaction is treated in a one-dimensional calculation. The calculations are in qualitative agreement with experimental results: shear bands can serve as ignition regions for the propagation of the reaction throughout the entire specimen for Ti–Si, whereas in the Nb–Si system (that has a much lower enthalpy of reaction), the reaction is always localized in the shear bands. These results enable the estimation of a reaction time in the Ti–Si mixture (∼10 ms) and of a critical global strain required for the complete reaction to take place (εeff=0.38). This is a new regime of reaction, intermediate between combustion synthesis and shock compression synthesis.
Energy relaxation of hot electrons driven by intense terahertz fields in two-dimensional semiconductor systems
Authors: Lei X. L. , Chen Y. Q.
Published: July 2002

We examine the frequency dependence of the energy relaxation of hot electrons under the influence of an intense oscillating electric field of terahertz frequency. The calculated energy-loss rates in a GaAs/AlGaAs heterojunction and two GaAs-based quantum wells exhibit a frequency behavior quite different from that of the widely used Kogan formula. Their ratio shows an unexpected peak at around 0.5–0.6 THz, with a height about 3–10 times of its low-frequency value. This remarkable resonance is a unique indication of the role of the Doppler shift of the phonon frequency.
A model of interaction effects in granular magnetic solids
Authors: El-Hilo M. , Chantrell R. W. , O’Grady K.
Published: July 2002

The effects of interactions (dipolar and exchange) on the magnetic behavior of granular solid systems are examined using a Monte Carlo model capable of predicting the temperature and time dependence of the magnetic properties. Using this model the interaction effects on the magnetization and the magnetoresistance are studied. The results show that these properties depend critically on the strength and nature of the interactions. Magnetostatic interactions are found to decrease both remanence and coercivity and Hc is predicted to decrease linearly with concentration. It is shown that spatial disorder may be responsible for an increase of coercivity with exchange coupling which has been observed in some experimental studies. In systems with no hysteresis, magnetostatic interaction effects are found to increase the superparamagnetic transition temperature, in agreement with experimental data and previous analytical treatments. Calculations of the giant magnetoresistance (GMR) show that magnetostatic interaction effects give rise to a finite positive resistivity at zero field which increases with concentration. This causes the value of the maximum change in resistivity, which occurs near the coercivity, to be greater than the value at zero field. These calculations are in agreement with experimental observations of GMR in granular solids. It is predicted that the GMR is strongly dependent on the spin diffusion length via the local spin–spin correlation function.
Solar blind chemically vapor deposited diamond detectors for vacuum ultraviolet pulsed light-source characterization
Authors: Foulon F. , Bergonzo P. , Borel C. , Marshall R. D. , Jany C. , Besombes L. , Brambilla A. , Riedel D. , Museur L. , Castex M. C. , Gicquel A.
Published: July 2002

A major difficulty in characterizing vacuum ultraviolet (VUV) radiation produced by harmonic generation or four-wave sum frequency mixing arises in differentiating between the desired VUV signal and the remaining fundamental pump laser beam. To overcome this problem, visible and near UV blind VUV detectors, made from natural and synthetic diamond, have been developed. Such detectors have been used to characterize coherent VUV pulses (λ=125 nm, pulse duration at full width half maximum (FWHM) τFWHM∼7 ns) generated by resonance-enhanced four-wave sum mixing in mercury vapor. They allow full characterization of the intensity profile of the VUV pulses, without any significant parasitic signal from simultaneous stray light irradiation at λ=313 nm. Detectors were fabricated exhibiting response times of less than 70 ps at FWHM, corresponding to the lowest response time obtainable with a 7 GHz bandwidth single-shot oscilloscope.
In situ Raman monitoring of ultrathin Ge films
Authors: Kanakaraju S. , Sood A. K. , Mohan S.
Published: July 2002

We report the in situ interference enhanced Raman spectroscopy of ultrathin crystalline Ge films grown at 300 °C. The Raman spectra of the films show a peak at ∼290 cm−1 attributed to the confined optical phonon and a broadband on the low-frequency side at ∼254 cm−1 for 5 and 10 Å thick films. The latter is attributed to disordered surface with large number of dangling bonds. For thicker films, the low-frequency mode appears at 270 cm−1 assigned to surface optical phonons.
Electron spin resonance of Er–oxygen complexes in GaAs grown by metal organic chemical vapor deposition
Authors: Ishiyama T. , Katayama E. , Murakami K. , Takahei K. , Taguchi A.
Published: July 2002

We have performed electron spin resonance (ESR) measurements on Er-doped GaAs grown with oxygen codoping by metal organic chemical vapor deposition. An isotropic line (an effective g value, g=5.95) which had been already reported was observed in samples without oxygen codoping. On the other hand, for samples with oxygen codoping other strong anisotropic ESR lines originated from four kinds of Er3+(4f11) centers (A, B, C, and D) were newly observed in addition to the weaker isotropic line. The anisotropic g tensors obtained by analyzing the angular dependence of the ESR lines indicate that B and C centers are of orthorhombic C2v symmetry, A center has lower symmetry than orthorhombic symmetry, and D center is of trigonal C3i symmetry. The ESR intensities of A, B, and C centers were approximately two orders of magnitude higher than that of the isotropic line with g=5.95. The ESR intensity of D center was one order of magnitude lower than those of A, B, and C. The Er concentration dependence of the relative ESR intensities of these centers was investigated, which indicates (i) the ESR intensities of A and D increase with increasing Er concentration, and (ii) those of B and C are saturated above the Er concentration [Er]⩾1018 cm−3. The ESR measurement under light illumination, as well as the Er concentration dependence, suggests that the B center with C2v symmetry corresponds to the dominant Er luminescent center under host photoexcitation.
Inhomogeneity of anodic oxide films of Al and Al alloys characterized by scanning electron microscopy observation and analysis of frequency response behavior
Authors: Ozawa Kiyoshi , Majima Teiji
Published: July 2002

Inhomogeneity of anodic oxide films of pure Al, Al-0.42 at. % Ta, Al-1.1 at. % Ta, Al-0.5 at. % Ti, and Al-1.0 wt % Si formed in various electrolyte solutions has been investigated. Scanning electron microscopy observation of their cross sections revealed their structural inhomogeneity: they consist of an inner layer element with a smooth texture and an outer layer element distinguished by its textural properties such as roughness and macroscopic voids. An imaginary part of the impedance for those oxides revealed their electrical inhomogeneity: their impedance spectra were fitted by the summation of characteristic Debye functions, PC, PV1, and PV2, in the frequency regime where direct current conduction predominated. This indicates that three differing processes of charge transport coexist. Only PC which had the shortest conductivity relaxation time was manifested for the oxide, where a smooth texture was observed. PV1 which had the second shortest relaxation time was predominantly manifested for the oxide, where a rough texture indicating the existence of minute voids was observed. PV2 which had the longest relaxation time was predominantly manifested for the oxide, where macroscopic voids were observed. Based on the close correlation between the texture and the impedance spectra, PC, PV1, and PV2 were attributed to the traps induced at the microvoids, minute voids, and macroscopic voids. The temperature dependence of the conductivities, as derived from the Debye peaks, showed that oxides had a well-defined trap level 2.0±0.2 eV below the conduction band edge. The trap density was least for the oxide with a smooth texture and it was higher by more than an order of magnitude for the oxide with a rough texture. As regards the anodization behavior, it was shown that the oxidizing reactants migrating toward the matrix metal was OH− and that the reaction to produce H2 near the oxide–matrix metal interface was suppressed by the predominant reaction to form an Si–H bond in Al–Si.
Dynamics of photorefractive grating erasure in polymeric composites
Authors: Cui Yiping , Swedek Bogdan , Cheng Ning , Zieba Jaroslaw , Prasad Paras N.
Published: July 2002

Theoretical and experimental studies are presented of the dynamics of photorefractive grating erasure in polymeric photorefractive materials with hole traps. A bi-exponential decay for the rate of optical erasing of the space-charge field has been obtained by theoretical solution. The optically induced erasure rate for polymeric photorefractive materials is theoretically predicted to depend on optical intensity as a sublinear relation of Iα, in which α is dependent on the electric field. The characteristics of the traps in a photorefractive material play a key role in the dynamics of grating erasure. Experimentally studied was the dynamic process of erasing the photorefractive grating in a polymeric composite, poly-N-vinylcarbazole:fullerene:diethyl aminonitrostyrene:tricresyl phosphate. The theoretical analysis and experimental results reveal that shallow traps are dominant in this photorefractive material.
Thermal stability enhancement of Cu/WN/SiOF/Si multilayers by post-plasma treatment of fluorine-doped silicon dioxide
Authors: Lee Seoghyeong , Kim Dong Joon , Yang Sung-Hoon , Park Jeongwon , Sohn Seil , Oh Kyunghui , Kim Yong-Tae , Kim Jung-Yeul , Yeom Geun-Young , Park Jong-Wan
Published: July 2002

The effect of a post-plasma treatment on the dielectric property and reliability of fluorine doped silicon oxide (SiOF) film was studied. Also, the thermal stability of the Cu/WN interconnect system with SiOF interlayer dielectrics was examined by rapid thermal annealing. The surface roughness of SiOF films increased with increasing plasma treatment power due to ion bombardment effect during the plasma treatment. As the plasma treatment power increased, the dielectric constant increased from 3.16 to 3.43, while the change in the relative dielectric constant of the plasma treated films decreased in magnitude after treatment at 100 °C for 30 min in boiling water. Furthermore, the chemical properties of the plasma treated SiOF layers near the top surface tend to resemble those of thermal oxides after plasma treatment with sufficient plasma power, apparently due to the reduction in the Si–F bonding in the films. In the case of a Cu/WN/SiOF/Si multilayer structure, surface oxidation and densification due to the plasma treatment seemed to play an important role in suppressing the interdiffusion between SiOF and metal interconnects.
Anisotropic defect structure and transport properties of YBa2Cu3O7−δ films on vicinal SrTiO3(001)
Authors: Brötz J. , Fuess H. , Haage T. , Zegenhagen J. , Jooss Ch. , Forkl A. , Warthmann R.
Published: July 2002

The microstructure of YBa2Cu3O7−δ thin films grown on vicinal SrTiO3(001) has been studied as a function of the vicinal angle by x-ray diffraction using the two-dimensional q-scan technique. Our results reveal a strong correlation between the miscut of a SrTiO3(001) substrate and the anisotropic defect structure of the film. Furthermore, we observed an anisotropy of the corresponding critical current density up to 4.6 depending on the angle of miscut.
Noise-induced local heatings in beam irradiation
Authors: Plumereau G. , Aranda P. , Ailloud P. , Berger P. , Boutard D. , Ladieu F.
Published: July 2002

In every kind of beam irradiation, a part of the incident power is eventually dissipated within the irradiated sample, leading to a heating which has to be evaluated, in order to be sure that thermal effects (such as diffusion, phase transitions, etc.) are under control. Expanding on usual thermal estimations based upon the coherent part of the incident power, we focus on the thermal effects due to the noisy (i.e., incoherent) part of the power. Starting from the autocorrelation of the beam, we show analytically that white noise induces an extra heating whose relative influence increases as the distance to the center of the beam decreases. Relying on the physical results derived for white noise, a simple method is proposed to extract the main aspects of these extra heatings from experiments where the autocorrelation function of the beam is not known a priori. Experimental data from MeV light ion microbeam are briefly presented as an example.
Molecular orbital analysis of reaction processes of fluorine with H-terminated silicon (111) and (100) surfaces
Authors: Kanashima Takeshi , Okuyama Masanori
Published: July 2002

The atomic bonding of F2 molecules on Si(111) and Si(100) surfaces has been analyzed by the molecular orbital method. The stable geometry is obtained by minimizing the total energy of a system in which a F2 molecule approaches the Si surface, and the infrared absorption spectrum characteristic of its atomic bonds is analyzed. Si clusters consisting of 22 and 32 Si atoms for the Si(100) and Si(100) surfaces, respectively, with dangling bonds terminated by H atoms are treated. The F–F bond disappears and a Si–F bond is formed as the F2 molecule approaches the Si surface. The F2 molecule reacts with the Si(100) surface more easily than with the Si(111) surface. Moreover, etching of Si by F2 gas occurs in the case of Si(111), but not in the case of Si(100). The obtained infrared absorption spectra agree qualitatively with experimental data.
Enhanced electrical properties of rigid-rod polymer incorporated with electroactive triarylamino moieties
Authors: Bai S. J. , Srinivasan K. R. , Tan Loon-Seng , Spry R. J. , Price G. E.
Published: July 2002

Oxidatively stable and electrically insulating rigid-rod polymer poly(p-phenylenebenzobisthiazole) (PBT), was incorporated with electroactive triarylamino (TPA) moieties, (R)TPA-PBT with R=NMe2 and Me. Copolymers or homopolymers were synthesized with various TPA fractions changing the polymers to segmentally rigid configuration, and fabricated into films. On cast films, x-ray scattering revealed that the copolymers were random copolymers, microscopy showed “template effect” from the rigid segments. Iodine activation of the incorporated polymers led consistently to more than five order-of-magnitude increases in electrical conductivity. The activated conductivity also increased with TPA fraction. A conductivity value as high as 4.1×10−4 S/cm was realized for the activated (NMe2)TPA-PBT homopolymer. However, temporal stabilities were observed for the conductivity, which seemed to depend on the polymer composition and film morphology. Spectroscopic examination detected no new electronic state generated by iodine doping. Instead, optical absorbance was drastically increased for hν greater than 2 eV with a change in film color. Both enhanced conductivity and absorbance were not exhibited by the iodine-activated PBT polymer.
Quasiparticle losses at the surface of superconducting tunnel junction detectors
Authors: Panteleit F. , Schroeder T. , Martin J. , Huebener R. P. , Kiewiet F. B. , van den Berg M. L. , de Korte P. A. J.
Published: July 2002

Superconducting tunnel junctions (STJs) are promising as high energy resolution x-ray detectors. However, the theoretical limit of the energy resolution of STJs has not yet been reached for several reasons. In many cases quasiparticle losses limit the energy resolution. We have investigated STJs with different multilayer structures by means of low temperature scanning electron microscopy. By measuring the quasiparticle lifetime of Nb junctions with and without Ta passivation at the surface, we have identified quasiparticle losses at the surface of nonpassivated junctions as the dominant loss process. The temperature dependence of the quasiparticle lifetime gives information about the loss mechanism. The influence of quasiparticle traps on the effective quasiparticle lifetime is discussed.
Strain modification in thin Si1−x−yGexCy alloys on (100) Si for formation of high density and uniformly sized quantum dots
Authors: Shao Xiaoping , Jonczyk Ralf , Dashiell M. , Hits D. , Orner B. A. , Khan A.-S. , Roe K. , Kolodzey J. , Berger Paul R. , Kaba M. , Barteau M. A. , Unruh K. M.
Published: July 2002

The effects of alloying C with Ge and Si and varying the C/Ge ratio during the growth of very thin layers of the ternary alloy SiGeC grown on Si (100) substrates and the resulting strain modification on self-assembled and self-organized quantum dots are examined. During coherent islanded growth, where dislocations are not formed yet to relieve the strain, higher strain energy produced by greater lattice mismatch acts to reduce the island size, increase the density of islands, and significantly narrow the distribution of island sizes to nearly uniformly sized quantum dots. Strain energy can also control the critical thickness for dislocation generation within the three-dimensional islands, which then limits the maximum height which coherent islands can achieve. After the islands relax by misfit dislocations, the island sizes increase and the island size distribution becomes broader with the increase of misfit and strain. The optimal growth for a high density of uniform coherent islands occurred for the Si0.49Ge0.48C0.03 alloy composition grown on (100) Si, at a growth temperature of 600 °C, with an average thickness of 5 nm, resulting in a narrow size distribution (about 42 nm diameter) and high density (about 2×1010 dots/cm2) of quantum dots.
Effects of stacking faults on magnetic viscosity in thin film magnetic recording media
Authors: Dova P. , Laidler H. , O’Grady K. , Toney M. F. , Doerner M. F.
Published: July 2002

There is much interest in crystallographic defects in thin film magnetic recording media and their role in influencing recording performance such as media noise and thermal loss. In this article we report a correlation between the magnetic viscosity in CoPtCr thin film media, which is the origin of thermal loss effects, and the concentration of local fcc-like regions. The concentration of these defects (the type and density of stacking faults) was varied by growth on different underlayers (Cr and CrTa/Cr) and was measured with grazing incidence x-ray scattering using synchrotron radiation. We show that a substantial percentage of local fcc regions in an otherwise hcp cobalt alloy film leads to significant magnetic viscosity effects at quite modest magnetic fields. We find that the activation volume is reduced for a sample with a higher percentage of fcc-like regions and suggest that this can be understood in terms of the effect of weak links acting to stabilize local micromagnetic configurations.
Droplet formation during extended time pulsed laser deposition of La0.5Sr0.5CoO3 thin layers
Authors: Craciun V. , Craciun D. , Perriere J. , Boyd I. W.
Published: July 2002

The appearance of a strong splashing effect during extended time pulsed laser deposition of La0.5Sr0.5CoO3 (LSCO) films has been investigated. For this aim, films were grown in a base vacuum (4×10−7 Torr) from targets ablated for prolonged time duration or under an oxidizing atmosphere of 10−2 Torr of N2O from stoichiometric, as-prepared, fresh targets. The films grown under vacuum were found by Rutherford backscattering spectrometry to be oxygen deficient and transparent, while those grown under the oxidizing atmosphere were stoichiometric and opaque. The measured optical absorption coefficient (α) at the laser wavelength used for the ablation process (KrF, λ=248 nm) for these two series of films was found to be around 1–2×104 cm−1 and 2–3×105 cm−1, respectively. It is suggested here that, because of preferential oxygen evaporation from the surface layer of the LSCO target during prolonged laser ablation time, the value of α decreased, inducing a volume absorption of the laser radiation. This favored the formation on the target surface of a thick and hot layer of liquid which lasted a longer time than that formed on stoichiometric targets. Under these conditions, the occurrence of a subsurface, explosive volume boiling mechanism, which is the actual cause of the observed splashing effect, was very likely. Numerical estimations of the temperature depth profiles inside the irradiated targets, based on the one-dimensional heat diffusion equation, supported the appearance of an explosive boiling mechanism for the low α value targets.
Phase formation and thermal stability of mechanical alloyed iron–tantalum
Authors: Mertinat M. , Herr U. , Oelgeschläger D. , Samwer K.
Published: July 2002

Iron-rich iron–tantalum solid solutions were prepared by mechanical alloying of elemental powder mixtures. At low Ta concentrations the alloys form a crystalline solid solution with bcc structure. At higher contents additionally an amorphous phase appears. The phase fractions and their compositions were determined by x-ray diffraction and Mössbauer spectroscopy. The thermal stability of the supersaturated solid solutions was investigated by differential scanning calorimetry measurements. Upon annealing, the solid solutions are found to establish a metastable equilibrium by precipitation of the amorphous phase before transformation to the equilibrium phases sets in. The results are discussed on the basis of the phase stabilities of the participating stable and metastable phases. It is concluded that the phase formation in this system during milling can be described by a smeared-out polymorphous transition to the amorphous phase with increasing solute content rather than by a metastable phase equilibrium. The possibility of grain boundary wetting with the amorphous phase is discussed.
Interface characterization of nanocrystalline CdS/Au junction by current–voltage and capacitance–voltage studies
Authors: Patel B. K. , Nanda K. K. , Sahu S. N.
Published: July 2002

A Schottky junction in the configuration ITO/nano-CdS/Au has been fabricated and the current(I)–voltage(V) and capacitance(C)–voltage(V) characteristics studied. The I–V studies show series resistance effect resulting in two ideality factors: one in low and the other in high forward bias regime, suggesting the presence of surface/interface traps in nano-CdS. Frequency dependent capacitance has also been studied and different semiconductor parameters have been estimated from the I–V and C–V analysis.
Nanoscale desorption of H-passivated Si(100)–2×1 surfaces using an ultrahigh vacuum scanning tunneling microscope
Authors: Syrykh C. , Nys J. P. , Legrand B. , Stiévenard D.
Published: July 2002

Nanoscale desorption of the Si(100)–2×1 hydrogen terminated surface has been achieved using a scanning tunneling microscope (STM) in an ultrahigh vacuum chamber. We have studied the patterned linewidth as a function of the sample bias and the dose, either with the feedback servo loop on or off. We propose a simple analytical model to explain the variation of the linewidth versus the electron dose. Finally, we show that the best resolution is obtained for pulsed voltages with the STM feedback servo loop on.
2 MeV electron irradiation of silicon at elevated temperatures: Influence on platinum diffusion and creation of electrically active defects
Authors: Schmidt D. C. , Svensson B. G. , Lindström J. L. , Godey S. , Ntsoenzok E. , Barbot J. F. , Blanchard C.
Published: July 2002

Platinum has been diffused at 300–800 °C for 30 min into n-type epitaxial silicon samples during 2 MeV electron irradiation using a dose of 1×1017 e− cm−2. Thereafter the samples were characterized by capacitance–voltage measurements and deep level transient spectroscopy. The samples with irradiation temperatures of 500, 600, and 700 °C could be analyzed, while the compensation in the others was too high. Most of the observed deep levels were characterized using the Arrhenius method. Their possible identities are discussed. The deep level of substitutional platinum first appears in the sample irradiated at 600 °C and is the dominant defect level at even higher temperatures. We observe that at a chosen distance from the sample surface (17 μm), the concentration of electrically active platinum after an irradiation at 700 °C is a factor of 1000 higher than in an ordinarily diffused sample. Taking into account experiments where platinum was diffused into pre-irradiated samples, the observed behavior is attributed to a reduced correlated recombination of interstitials and vacancies.
Role of the substrate strain in the sheet resistance stability of NiSi deposited on Si(100)
Authors: Maillard-Schaller Eliane , Boyanov B. I. , English S. , Nemanich R. J.
Published: July 2002

In order to study the influence of strain on the formation and stability of NiSi, Ni has been deposited on strained and relaxed Si(100) n-type substrates. Strained Si substrates have been produced by depositing a pseudomorphic silicon film onto a 3000 Å thick relaxed Si0.8Ge0.2 film. Raman spectroscopy has established that the silicon film is strained. The presence of a characteristic cross-hatch pattern has been identified by atomic force microscopy. Measurements show that the sheet resistance (Rs) of the silicide formed on strained silicon remains stable up to 700 °C while the Rs of the silicide formed on bulk silicon (100) shows a significant increase at 600 °C . X-ray photoelectron spectroscopy shows that the NiSi–NiSi2 phase transition occurs at a higher temperature and is, therefore, not responsible for the Rs instability. Scanning electron microscopy measurements indicate that islanding occurs in the temperature region of the resistivity increase. Photoelectron emission microscopy has been employed to observe the surface morphology during annealing, and islanding is not observed until a higher annealing temperature for the NiSi on strained Si. The increase in Rs is apparently correlated to the islanding of NiSi which appears at lower temperature on the bulk silicon substrate than on the strained silicon substrate. The stability of the NiSi film on the strained Si substrate is related to the strain induced by thermal expansion and the increased lattice constant of the strained Si.
Dielectric properties of very thin low pressure chemically vapor deposited silicon films
Authors: Davazoglou D.
Published: July 2002

Very thin silicon films, with thicknesses approximately 10 nm, were low pressure chemically vapor deposited (LPCVD) on fused silica substrates at 0.23 Torr and temperatures of 550, 610, and 620 °C, from silane decomposition. Transmission and reflection spectra of these films were recorded within the energy range 6.2–0.5 eV, throughout which they were transparent. From these measurements the energy variation of the complex dielectric function ε(E)=ε1(E)+iε2(E) of the films was extracted. It was found that the overall shapes of ε1(E) and ε2(E) were similar to those for thicker LPCVD Si films. More precisely, structures attributed to the E0′, E1, E2, and E1′ transitions of crystalline silicon were shown on the ε1 and ε2 spectra of samples deposited at 610 and 620 °C at nearly the same energies as in crystalline Si. The above structures were not shown on the corresponding spectra for the sample at 550 °C. Absorption threshold and gap of the very thin samples coincided with those for thicker ones deposited under similar conditions. Analysis of the dielectric function of the films, with the aid of the effective medium approximation, has shown that samples deposited above 600 °C contained smaller fractions of crystalline material than thicker ones deposited at such temperatures. It was concluded that quantum effects, related to the confinement of electronic wave functions, do not cause significant changes to the electronic band structure of very thin LPCVD Si films relative to that of thicker films.
Glassy dynamics of the incommensurate–commensurate phase transition in Zr0.98Hf0.02TiO4 ceramics
Authors: Park Yung , Knowles Kevin M.
Published: July 2002

The complex dielectric constants of Zr0.98Hf0.02TiO4 ceramics are reported in the frequency range 10−3–1010 Hz for the temperature range 830 °C⩽T⩽860 °C, just above the commensurate-incommensurate phase transition temperature, Tc. The disappearance of x-ray satellite reflections at 825 °C was used to determine Tc experimentally. The dielectric measurements show that a relatively narrow distribution of relaxation times is present in the ceramics, which broadens as the temperature approaches Tc from above. By analyzing the temperature at which the dielectric constant is a maximum as a function of frequency using the Vogel-Fulcher relationship, an activation energy of 550±15 kb,where kb is the Boltzmann constant, and an effective freezing temperature, Tf, of 825 °C have been determined, confirming that, to within experimental error, Tf coincided with Tc. The experimental results for Zr0.98Hf0.02TiO4 are interpreted in terms of a possible dipole-glass-like phase that has been proposed for relaxor systems.
Study on recording beyond 10 Gbit/in.2 with Co–Cr based perpendicular recording media
Authors: Honda N. , Yanase S. , Ouchi K. , Iwasaki S.
Published: July 2002

Recording of beyond 10 Gbit/in.2 was studied with Co–Cr based perpendicular recording media and ring heads. A simple recording simulation based on an M–H loop sheared by the demagnetizing field in the film suggested that a steeper M–H loop slope in the medium results in a higher output and resolution. It was found that recording with a metal in gap head with a gap length of as small as 0.15 μm on a Co–Cr20–Nb4–Pt5 medium with an M–H loop slope of 1.5/4π emu/Oe cm3 exhibited a high output and a high resolution. The obtained high signal-to-noise ratio and resolution suggested a possibility of recording beyond 10 Gbit/in.2 for a track pitch of 0.4 μm.
Enhanced hydrogen desorption from Si sites during low-temperature Si1−xGex growth by disilane and solid-Ge molecular beam epitaxy
Authors: Liu J. P. , Huang D. D. , Li J. P. , Lin Y. X. , Sun D. Z. , Kong M. Y.
Published: July 2002

A phenomenological model is proposed to explain quantitatively the interesting compositional dependence on the Ge incorporation rate during low-temperature growth of Si1−xGex by disilane and solid-Ge molecular beam epitaxy, based on enhanced hydrogen desorption from Si sites due to the presence of Ge atoms. The hydrogen desorption rate constant for disilane on Si sites is fitted to an exponential function of Ge incorporation rate and a possible physical explanation is discussed. Simulated results are in excellent agreement with experimental data.
Investigation on phase jump in a differential interferometer
Authors: Zhou Weidong , Cai Lilong
Published: July 2002

This article presents a new phase jump phenomenon in a differential heterodyne interferometer. When the intensity of one arm of an interferometer changes from greater to less (or less to greater) than that of another, a phase jump of 180° will take place if the phase difference between two arms is prefixed at π. We call this phenomenon phase jump. To demonstrate phase jump, a modified differential heterodyne interferometer has been setup. The intensity of one arm is modulated as the arm is scanning across an edge. Both theoretical and experimental investigations are conducted in detail. The theoretical and experimental results indicate that the phase slope of the phase jump is infinite and the amplitude of output signal is zero when a phase jump occurs. Meanwhile the position of phase jump is very sensitive to the displacement. Therefore, both phase and amplitude signals of phase jump are suitable for precise position index and may find wide potential applications in the fields of edge detection, alignment, optical storage, and so on.