bluuebunny/crossref_metadata_2025 huggingface dataset:
Suppressed rf dissipation in Ag17+107 ion irradiated Bi2Sr2CaCu2O8 single crystals by enhanced flux line tilt modulus
Authors: Sudershan Y. S. , Rastogi Amit , Bhat S. V. , Grover A. K. , Yamaguchi Y. , Oka K. , Nishihara Y. , Senapati L. , Kanjilal D.
Published: July 2002

We have studied the isothermal, magnetic field (H‖c) dependent rf power P(H) dissipation (Hrf‖a) in the superconducting state of Bi2Sr2CaCu2O8 single crystals prior to and after irradiation with 250 MeV Ag17+107 ions. In the pristine state, P(H) shows an initial decrease with increase in field, reaches a minimum at HM(T) and increases monotonically for H>HM(T). This behavior arises when the electromagnetic coupling between the pancake vortices in adjacent CuO layers becomes dominant on increasing the field and minimizes the distortions of the flux lines by confining the 2D vortices. In the post irradiated state, such an initial decrease and the minimum in P(H) is not observed but only a much reduced rf dissipation that monotonically increases with field from H=0 onwards is seen. We attribute this difference to the strong enhancement of the tilt modulus C44 of the flux lines on irradiation when the pancake vortices in adjacent CuO bilayers are pinned along the track forming a well-stacked flux line in the field direction (‖c). We have also observed that the rf dissipation disappears at a certain temperature Tsf, at which the normal core of the flux line becomes commensurate with the columnar track diameter.
In situ observation and correction of resist patterns in atomic force microscope lithography
Authors: Shiokawa Takao , Aoyagi Yoshinobu , Shigeno Masatsugu , Namba Susumu
Published: July 2002

In atomic force microscope lithography using negative-type resist, the increase of the resist thickness of the exposed part before development is observed in the dose range from 8×10−13 to 10−16 cm−2. The increase is about 1 nm with a dose of 8×10−13 cm−2, which is less than one-tenth of the threshold dose for polymerization of resist. The phenomena of the increase of resist thickness is used for in situ observation of the exposed pattern before development. With this in situ observation, precise correction of the lithography pattern can be made before development.
Piezoelectric actuator generating torsional displacement from piezoelectric d15 shear response
Authors: Glazounov A. E. , Zhang Q. M. , Kim C.
Published: July 2002

A torsional actuator generating angular displacement from piezoelectric shear strain was developed. The actuator is a tube consisting of an even number of segments poled along the length, which are adhesively bonded together, and the joints act as electrodes to apply the driving voltage. The experimental data measured on the prototype actuator: (i) prove the proposed concept of the torsional actuator, (ii) show that the actuator functions well under the torque load, and (iii) demonstrate that it has superior characteristics compared to previously reported designs of torsional actuators.
Excitation of size selected nanocrystallites in porous silicon
Authors: Yamani Zain , Rigakis Nicholaos , Nayfeh Munir H.
Published: July 2002

We prepared silicon that exhibits green-to-red rainbow luminescence along the sample, reflecting gradients in the crystallite size. The excitation has a size-dependent feature, riding a smooth bulklike continuum. For the size-dependent contribution, we measured absorption band edges of 3.75 and 3.0–3.25 eV at the meniscus and opposite end. Excitation in the meniscus, monitored at the edge of the blue emission, isolates ultrasmall sizes, with “excitation coefficients” quadratic with energy, and emission encompassing much of the visible spectrum. Results are discussed in terms of quantum-confinement-induced restructuring of the diamondlike bonds to form radiative Si–Si surface states.
Impact of ultraviolet light during rapid thermal diffusion
Authors: Noël S. , Ventura L. , Slaoui A. , Muller J. C. , Groh B. , Schindler R. , Fröschle B. , Theiler T.
Published: July 2002

Rapid thermal processing for junction formation is emerging as a low cost technique for solar cell as well as for other semiconductor device production. Compared to conventional furnace processing, process differences are not only in very high heating and cooling rates, but also in the incoherent emitted radiation spectrum, which can act on dopant diffusion. The photons emitted from tungsten halogen lamps go from far ultraviolet, over visible to infrared light. In this work additional mercury ultraviolet lamps are used during rapid thermal annealing to analyze the influence of high energetic photons on diffusion mechanisms. The diffusion results are discussed in terms of radiation spectrum, involving analysis of diffusion profiles and sheet resistances.
Superconducting Nd1.85Ce0.15CuO4−y bicrystal grain boundary Josephson junctions
Authors: Kleefisch S. , Alff L. , Schoop U. , Marx A. , Gross R. , Naito M. , Sato H.
Published: July 2002

We have studied the electric transport properties of symmetrical [001] tilt Nd1.85Ce0.15CuO4−y (NCCO) bicrystal grain boundary Josephson junctions (GBJs) fabricated on SrTiO3 bicrystal substrates with misorientation angles of 24° and 36.8°. The superconducting properties of the NCCO GBJs are similar to those of GBJs fabricated from the hole doped high temperature superconductors (HTS). The critical current density Jc decreases strongly with increasing misorientation angle. The products of the critical current Ic and the normal resistance Rn (∼100 μV at 4.2 K) are small compared to the gap voltage and fit well to the universal scaling law IcRn∝Jc found for GBJs fabricated from the hole doped HTS. This suggests that the symmetry of the order parameter, which most likely is different for the electron and the hole doped HTS, has little influence on the characteristic properties of symmetrical [001] tilt GBJs.
Crystallization of amorphous (Ba, Sr)TiO3/MgO(001) thin films
Authors: Noh D. Y. , Lee H. H. , Kang T. S. , Je J. H.
Published: July 2002

The crystallization of amorphous BaxSr1−xTiO3 (BST) thin films was studied in a synchrotron x-ray scattering experiment. In a 550 Å thick film, the crystallization to perovskite phase was occurred at around 700 °C, while a 5500 Å thick film became crystalline at 500 °C. The thickness dependence of the crystallization was attributed to the observed intermediate phase nucleated near 600 °C at the interface. In thin films, high annealing temperature was required due to the energy barrier between the perovskite phase and the intermediate phase. In the thick film, the perovskite phase was nucleated directly from the amorphous phase in the bulk of the film concurrent to the nucleation of the intermediate phase at the interface.
Electrostrictive behavior observed in a low glass-transition temperature photorefractive polymeric composite during a two-beam coupling experiment
Authors: Wang Feng , Chen Zhijian , Wang Shufeng , Huang Zhiwen , Gong Qihuang , Zhang Zhijie , Chen Yiwang , Chen Huiying
Published: July 2002

A movement of refractive index grating was observed in two-beam coupling behavior with a low glass-transition temperature photorefractive polymeric film as the poling electric field was discharged. The photorefractive polymeric composite is poly(N-vinylcarbazole) doped with 2,5-dimethyl-4-(p-nitrophenylazo)anisole, N-ethylcarbazole and 2,4,7-trinitro-9-fluorenone in a weight ratio of 25:40:34:1. A theoretical explanation based on electrostrictive effect was given, and some evidential experiments, including degenerate four-wave mixing and Michelson interference measurement were also presented.
Kinetics of lossy grazing impact oscillators
Authors: Hunt Jeffery P. , Sarid Dror
Published: July 2002

The equation of motion of a grazing impact oscillator is generalized to include compliant boundaries and impact energy dissipation, yielding the phase diagram, indentation and force. Good agreement with experimental results using tapping-mode atomic force microscopy is demonstrated. The relationship between phase and set-point amplitude is discussed in terms of the dissipation, showing that for a parameter space for which the system is highly nonlinear a chaotic response is possible.
Comparison of some properties of nanosized silicon clusters in porous glasses
Authors: Savin D. P. , Gevelyuk S. A. , Roizin Ya. O. , Mugeński E. , Sokólska I.
Published: July 2002

The effects of pore size distribution in porous glasses on the photoluminescence of nanosized Si clusters and of the humidity on the sample dimensions have been investigated. Increase of the pore size brings about the blueshift of the emission peak. In the spectra, geminate and distant components of the emission have been resolved. The humidity influences the dimensions of the samples due to the competing of chemical bonding forces and capillary forces.
Stability of ultrasmooth surface morphology of (110) YBa2Cu3O7−δ homoepitaxial films and Nb/Au/(110) YBa2Cu3O7−δ junctions
Authors: Usagawa Toshiyuki , Wen Jianguo , Ishimaru Yoshihiro , Koyama Satoshi , Utagawa Tadashi , Enomoto Youichi
Published: July 2002

We report on ultrasmooth surface morphology and chemical activeness of (110)-oriented YBa2Cu3O7−δ (YBCO) films grown on (110) YBCO single-crystal substrates by scanning electron microscopy, reflection high-energy electron diffraction, and transmission electron microscopy observations. The stable (110) YBCO interface can be formed by in situ deposited thin Au film against the chemically active elements like Nb. The in situ formed Nb/Au/(110)YBCO junction shows clear two superconducting transitions Tc1=91.8 K and Tc2=8.20 K associated with YBCO and Nb films and large supercurrent (at least larger than 2.0×102 A/cm2) much more than expected phenomenological arguments of s wave and dx2−y2 wave.
Metalorganic molecular-beam-epitaxy-grown In0.77Ga0.23As/InGaAs multiple quantum well lasers emitting at 2.07 μm wavelength
Authors: Mitsuhara Manabu , Ogasawara Matsuyuki , Oishi Mamoru , Sugiura Hideo
Published: July 2002

We report the growth of a four-period multiple quantum well (MQW) structure with 115-Å-thick, +1.65% strained wells by metalorganic molecular beam epitaxy and its application to 2 μm wavelength lasers. Transmission electron microscopy and photoluminescence measurements reveal that the structural and optical properties of MQW are sensitive to the barrier strain: the values of barrier strain required for MQW with both flat barrier-well interfaces and strong photoluminescence fall within a small range from −0.17% to +0.14%. The double-crystal x-ray diffraction pattern of the MQW remains unchanged before and after annealing at 620 °C for 2.5 h. Buried heterostructure lasers fabricated using metalorganic vapor phase epitaxy regrowth have an emission wavelength of 2.07 μm under a continuous operation current of 120 mA at 55 °C.
Polymer-based highly multimode electro-optic waveguide modulator
Authors: Sun De-Gui , Chen Ray T.
Published: July 2002

A unidirectional electro-optic modulator based on an asymmetrical highly multimode waveguide coupler is proposed. To achieve high switching performance in a guided-wave coupler, a grating-based dumping wall is placed on the larger waveguide. This dumping effect makes the asymmetric highly multimode waveguide coupler possess a highly efficient unidirectional coupling process. A high modulation depth of 99% is experimentally achieved at 633 nm wavelength with an index modulation of 3.0×10−4. This device can be used for multimode optical interconnection systems such as data communications and fiber sensor networks.
Nonradiative recombination at GaAs homointerfaces fabricated using an As cap deposition/removal process
Authors: Passlack M. , Droopad R. , Yu Z. , Overgaard C. , Bowers B. , Abrokwah J.
Published: July 2002

GaAs homointerfaces have been grown by molecular beam epitaxy using the steps of GaAs growth, As cap deposition, wafer storage, thermal desorption of the As cap, and GaAs overgrowth. As cap layers with a thickness of up to 7.8 μm were deposited and the wafers were stored for 3–7 days in ultrahigh vacuum (UHV) or under atmospheric conditions. Nonradiative recombination originating from the GaAs homointerface of wafers stored in UHV could not be detected (interface recombination velocity S≪1000 cm/s), however, significant nonradiative recombination (S=104–105 cm/s) was found for all GaAs homointerfaces where wafer storage occurred under atmospheric conditions. This result demonstrates that the As cap deposition/removal process is inadequate for GaAs surface protection in a fabrication facility.
The effect of offset charge deposited directly onto single-electron devices
Authors: Graham M. R. , Ahmed H.
Published: July 2002

The effects of charge deposited directly in the vicinity of a multiple tunnel junction single-electron transistor have been investigated. Two regimes of offset effects have been observed with a continuous transition between them. The deposited charge causes the device current to oscillate in a manner analogous to sweeping the gate voltage, and an equivalence between the two phenomena has been demonstrated. In addition, ions landing very close to the device cause a discontinuous change in the device current such that the arrival of individual ions can be time resolved.
Laser plasma x-ray contact microscopy of living specimens using a chemically amplified epoxy resist
Authors: Cefalas A. C. , Argitis P. , Kollia Z. , Sarantopoulou E. , Ford T. W. , Stead A. D. , Marranca A. , Danson C. N. , Knott J. , Neely D.
Published: July 2002

We report on the use of an epoxy based chemically amplified resist, to produce x-ray images of living biological specimens, exposed with laser plasma generated soft x rays, in the water window (2.3–4.4 nm). The photoresist response was at least two orders of magnitude “faster” than polymethyl methacrylate, the standard resist used so far in soft x-ray contact microscopy. Atomic force and scanning electron microscopy of the biological specimen images, recorded in the resist, clearly showed the flagella of the motile green alga, chlamydomonas, suggesting a lateral resolution better than 150 nm. The resist was also capable of providing height features, as small as 20 nm, in atomic force microscope depth profiles and discriminating the flagella intersection areas.
All-optical mode mixer spatial switch based on cascading in lithium niobate
Authors: Baek Yongsoon , Schiek Roland , Stegeman George , Assanto Gaetano , Sohler W.
Published: July 2002

An all-optically induced spatial shift in the interference between the two lowest-order modes of a lithium niobate channel waveguide was demonstrated based on the power-dependent nonlinear phase shift induced via quadratic cascading.
Relaxation oscillations in single-frequency InAsSb narrow band-gap lasers
Authors: Popov Andrei , Sherstnev Victor , Yakovlev Yury , Werle Peter , Mücke Robert
Published: July 2002

Relaxation oscillations have been investigated in A3B5 narrow band-gap semiconductor lasers. Based on wideband intensity noise measurements, the relaxation oscillation frequency has been observed up to 2 GHz for a 2 mW cw single-frequency InAsSb laser at a 3.4 μm wavelength. Laser parameters that influence the bandwidth, including the photon lifetime τp, the differential gain A and the spontaneous recombination lifetime τs were calculated from experimental data obtained at 95 K. We found τp in the range 0.7–1.9 ps, A was estimated to be (4.7–7.3)×10−6 cm−3 s−1 and τs=2.5–6.9 ns. Relaxation oscillations occurred beyond the modulation bandwidth required for typical applications of antimonide lasers in spectroscopy.
Near-field scanning photoluminescence measurements using an uncoated fiber tip: A potential high resolution diagnostic technique for semiconductor devices
Authors: Song Ki-Bong , Bae Ji-Eun , Cho Kyuman , Yim Sang-Youp , Park Seung-Han
Published: July 2002

Near-field scanning optical microscopy, in which an uncoated fiber tip is used for delivering excitation light and picking up photoluminescence, is applied for diagnosing defects in semiconductor devices. Using this high resolution, potentially subdiffraction limited, and fast acquisition time scanning μ-photoluminescence (PL) technique, we are able to locate nonluminescing defects in a multiple quantum well grown by molecular beam epitaxy. Near-field characteristics of the measured spectral PL intensity are also discussed.
Surface-emitting, distributed-feedback diode lasers with uniform near-field intensity profile
Authors: Lopez James , Kasraian Masoud , Botez Dan
Published: July 2002

Theoretical analysis of second-order surface-emitting, complex-coupled distributed feedback diode lasers with first-order distributed Bragg reflectors (DBR) is presented. The DBR reflectors are shown to insure simultaneous operation in a virtually uniform near-field profile with high efficiency and adequate intermodal discrimination. Such devices display symmetric-mode (single-lobe) surface emission with relatively high external differential quantum efficiency (30%), low gain threshold (18 cm−1), and <8% near-field intensity profile variations (in the longitudinal direction). The devices have the potential to provide >100 mW of stable, single-mode cw power, significantly higher than it is possible with vertical-cavity surface-emitting lasers. It is also shown that the device studied here can be combined with a resonant optical waveguide array device to produce a 2D uniform near-field surface-emitting source capable of providing greater than 1 W cw power in a stable, single-lobed beam.
Wave form reconstruction of photoconductive switch using minimum phase retrieval algorithm
Authors: Kim Woopoung , Lee Jongjoo , Lee Jaehoon , Lee Heeseok , Kim Joungho
Published: July 2002

An ideal delta function or a Gaussian function has been assumed for the photoconductive switching response of a photoconductive sampling experiment. In this letter, an effective wave form reconstruction method, called minimum phase retrieval algorithm, is presented to find the correct response function of the photoconductive sampling gate. In addition, the method is applied to the retrieval of a picosecond guided pulse wave form obtained from an on-wafer photoconductive sampling experiment. The reconstruction method should be used for the terahertz wave form detection measurement, where the pulse width is comparable to the switching time of the sampling gate.
Wavelength shifting and amplification of optical pulses through cascaded second-order processes in periodically poled lithium niobate
Authors: Banfi G. P. , Datta P. K. , Degiorgio V. , Fortusini D.
Published: July 2002

We investigate the efficiency of wavelength shifting (generation of a pulse at the wavelength λp−Δλ from a signal at λp+Δλ under the action of a pump at λp) and parametric amplification through a cascaded second-order process in a periodically poled lithium niobate crystal. Our results show that, in a 19-mm-long sample, at λp=1.8 μm and Δλ as large as 60 nm, wavelength shifting with unit gain can be obtained with a pump intensity of 6 MW/cm2, while amplification by a factor 10 requires 18 MW/cm2.
Metalorganic vapor phase epitaxy growth and photoluminescence properties of cubic AlxGa1−xN
Authors: Wu J. , Yaguchi H. , Onabe K. , Shiraki Y.
Published: July 2002

We have grown cubic AlxGa1−xN (0<x<0.25) films on GaAs (100) substrates by metalorganic vapor phase epitaxy. A strong excitonic transition, as well as a donor–acceptor pair transition and a deep-level emission, was observed in the photoluminescence spectra at 5 K in all the samples. With increasing Al fraction, all the emission lines shift to higher energy, nevertheless, with different shift rates. The temperature-dependent photoluminescence spectra show that the behavior of the donor–acceptor pair transition varied with Al fraction; at higher Al concentrations, the donor–acceptor pair transition tends to transform to a free-electron to acceptor transition and survive even at room temperature. This can also explain the energy shift to higher energy with increasing temperature for this emission line.
Atomic ordering and the surface morphology of thin films
Authors: Léonard François , Desai Rashmi C.
Published: July 2002

The formation of ordered phases and associated surface instabilities during the growth of alloy films is studied using a nonequilibrium model. It is shown that considerations of the epitaxial thermodynamic energy as well as dynamical processes at the surface lead to a coupling between the order parameter, the composition and the surface morphology. It is demonstrated that the stability of the growing layer against atomic ordering depends on the growth rate and that even when the surface-selected ordered phase is thermodynamically unstable, the system can spontaneously order.
Refractive index and absorption of GaAs quantum wells across excitonic resonances
Authors: Marquezini M. V. , Tignon J. , Hasche T. , Chemla D. S.
Published: July 2002

We present simultaneous measurement of the refractive index and absorption coefficient in a AlGaAs/GaAs multiple quantum well structure near the band gap by Fourier transform spectral interferometry. Both quantities were measured across heavy- and light-hole excitons for temperatures ranging from liquid helium to room temperature. The experimental results are analyzed using an analytical expression for the complex dielectric function of Wannier excitons in fractional dimension.
Optical monitoring of InP monolayer growth rates
Authors: Parbrook P. J. , Ozanyan K. B. , Hopkinson M. , Whitehouse C. R. , Sobiesierski Z. , Westwood D. I.
Published: July 2002

Reflection anisotropy (RA) spectroscopy has been used to examine the in vacuo (001) surface of InP before and during growth by molecular beam epitaxy (MBE). The dominant effect on the RA signal occurring the initiation of growth is the change in the surface V/III ratio, caused by the exposure of the surface to the incident indium flux. During MBE growth of InP under commonly used conditions, RA oscillations are clearly observed. These oscillations have been confirmed to correspond to the growth of InP monolayers. The oscillations are tentatively ascribed to the variation in P coverage during the growth of each monolayer of material.
Resistivity anisotropy in ordered InxGa1−xP grown at 640 °C
Authors: Novák J. , Hasenöhrl S. , Kúdela R. , Kučera M. , Wüllner D. , Wehmann H.-H.
Published: July 2002

The anisotropy of electrical properties in ordered InxGa1−xP epitaxial layers was studied. These samples were prepared by a low-pressure metalorganic chemical vapor phase epitaxy technique at the growth temperature of 640 °C. Resistivity measurements using a four-point-probe method have shown that samples with a low misfit value (0–1.5×10−3) are electrically uniform. For samples with higher misfit the anisotropy of resistivity markedly increases up to a maximum of 950. Comparing the results obtained from x-ray diffraction, low temperature photoluminescence, and atomic force microscopy experiments, we have shown that lattice mismatch can support the evolution and extension of the ordering effect in the InxGa1−xP layers.
Nondestructive evaluation of carrier concentration in the channel layer of In0.5Ga0.5P/In0.2Ga0.8As/GaAs heterostructure field-effect transistors by Raman scattering
Authors: Araki Gako , Nittono Takumi , Furuta Tomofumi , Hyuga Fumiaki
Published: July 2002

Carrier concentration (N) in the channel layers of pseudomorphic In0.5Ga0.5P/In0.2Ga0.8As/GaAs heterostructure field-effect transistors (HFETs) is evaluated by Raman scattering measurements. The coupled mode between the InGaAs longitudinal optical phonons and electrons in the InGaAs channel shifts continuously to a low wave number with an increasing N in the InGaAs channel. Preliminary calculation indicates that N can be determined with an error of less than 0.35×1018/cm3 in the 1018/cm3 order range, which corresponds to a 100 mV HFET threshold voltage. Raman scattering measurement is nondestructive and has a high spatial resolution as small as 1 μm in diameter. Thus, this measurement is promising in HFET wafer selection.
Biomolecular recognition using submicron laser lithography
Authors: Shivashankar G. V. , Libchaber A.
Published: July 2002

Direct beam biomolecular patterning on gold-coated glass substrates, using diffraction limited near infrared laser spot, is used for DNA recognition and specific ligand-receptor interactions. Using a microscope objective lens, a near infrared laser beam is focused onto a glass slide coated with 50-Å gold film. Localized laser absorption results in partial melting and ablation of gold. Spatially moving the laser spot, a stable etched gold pattern is obtained at submicron resolution. During the process, submicron particles in suspension aggregate along the melted gold film. The submicron particles are themselves coated with specific biomolecules, like the protein avidin or single stranded DNA oligomers, for specific biomolecular recognition. This opens many possibilities for biomolecular networks, biochip microfabrication, and bioelectronic circuitry.
The electrorheological behavior of complex strontium titanate suspensions
Authors: Zhang Yuling , Ma Yong , Lan Yucheng , Lu Kunquan , Liu Wei
Published: July 2002

A type of water-free electrorheological (ER) material-complex strontium titanate (STO) was synthesized by means of modified sol–gel. The ER behavior of the suspensions of STO particles in silicone oil with a 37% volume fraction was investigated systematically under both dc and ac electric fields. It is found that this ER fluid has many advantages, such as long-term stability against sedimentation, strong ER effect at low electric field, and a wide operating temperature range. The frequency dependence of ER behavior was also studied and can be partly explained on the basis of dielectric measurement.
Noncontact excitation of high Q acoustic resonances in glass plates
Authors: Stevenson Adrian C. , Lowe Christopher R.
Published: July 2002

The applications of magnetic direct generation, a noncontact technique for generating acoustic waves, are limited by poor transduction efficiency. This letter describes an approach for substantially improving the transduction efficiency by application of a transduction format, enhanced direct magnetic generation, that utilizes continuous wave resonances and thin film generation. Glass plates coated with thin films of aluminium have been used as free-standing acoustic cavities to generate resonances with high transduction efficiencies and Q factors. These acoustic resonances have been excited without mechanical contact and their origin and characteristics are discussed with respect to resonances in 530 μm thick aluminized silica plates. The consequences of magnetic direct generation applied to thin metal films, as opposed to bulk metal, are also discussed, particularly with respect to high operating frequencies and acoustic Q factors. It is possible that novel sensors and time standards may be constructed by exploiting this approach.
Fracture phenomena in silicon imaged by infrared radiation from ejected small particles
Authors: Busch E. , Haneman D.
Published: July 2002

We have found that fracture of silicon wafer specimens without introduced flaws takes place with the ejection of many small particles that emit infrared radiation, which has been imaged with a sensitive CCD camera. The particles are of order micron dimensions, preventing surface-barrier separation of carriers excited by the bond breaking at cleavage. Furthermore, larger ejected particles can subsequently crack, allowing further ejection of small luminescent particles. The results show that a simple theory of spread of a pre-existing flaw can be a serious oversimplification of complex phenomena occurring at the onset of brittle cleavage.
Improved steady-state photocarrier grating in nanocrystalline thin films after surface-roughness reduction by mechanical polishing
Authors: Brüggemann R.
Published: July 2002

We detect elastic optical scattering resulting from the surface roughness of nanocrystalline silicon by a poor optical grating in the steady-state photocarrier grating experiment. The small variation of the experimental sampling function reduces the reliability of the ambipolar diffusion length measurements in this case. We demonstrate that the reduction in surface roughness of nanocrystalline silicon by polishing reduces optical scattering, improves the grating quality, and allows a reliable determination of the ambipolar diffusion length, making the experiment attractive for characterizing nanocrystalline silicon and other semiconductors which exhibit optical scattering.
Large periodic potential under lateral surface superlattices fabricated from heteroepitaxial stressor layers
Authors: Emeleus C. J. , Milton B. , Long A. R. , Davies J. H. , Petticrew D. E. , Holland M. C.
Published: July 2002

We have fabricated lateral surface superlattices by etching a strained layer of In0.2Ga0.8As near the surface of a heterostructure. This provides strong modulation of the electron gas while retaining a high electron mobility. The potential arises mainly from strain and the piezoelectric effect, which depends on orientation, and from the change in the surface profile. The fundamental components of these two contributions cancel in one orientation to leave a dominant second harmonic. This effectively halves the period of the superlattice from its lithographic value and provides a promising technique for creating potentials with a period comparable to the Fermi wavelength.
Time-domain analysis of frequency modulation laser oscillation
Authors: Longhi Stefano , Laporta Paolo
Published: July 2002

A simple analytical model of frequency-modulation (FM) laser operation is proposed in terms of a master equation time-domain description. The analysis is capable of capturing the main experimental features of FM oscillation, including the dependence of modulation depth on cavity parameters, distortion effects induced by finite cavity gain bandwidth, and transition to FM mode-locking operation. Experimental results for a FM erbium–ytterbium–glass laser show good agreement with the theoretical predictions.
Terahertz emission of population-inverted hot-holes in single-crystalline silicon
Authors: Bründermann E. , Haller E. E. , Muravjov A. V.
Published: July 2002

We report THz emission of hot-holes in p-type silicon doped with a boron acceptor concentration of NA=1.5×1015 cm−3. We apply crossed electric (E) and magnetic (B) fields to the crystal cooled to liquid helium temperature. Optical gain is found for field ratios E/B in the range 0.5–1 kV cm−1 T−1. We calculate optical gain spectra in Si and identify possible laser transitions.
Micromachinable ultrasonic leaky wave air transducers
Authors: Degertekin F. Levent , Atalar Abdullah , Khuri-Yakub Butrus T.
Published: July 2002

Ultrasonic air transducers using leaky waves on thin membranes are analyzed using perturbation and normal mode approaches. The transducers utilize the efficient coupling of ultrasonic energy to air through radiation of these leaky wave modes when their phase velocity is close to the sound speed in air. Theoretical results on optimum transducer dimensions and bandwidth estimation show that a minimum conversion loss of 8.7 dB with a 78% fractional bandwidth is possible. Common micromachining materials are shown to be suitable transducer materials and result in feasible devices. This is demonstrated by fabricating a 580 kHz transducer using a silicon membrane bonded to a ring of PZT-5H. With this configuration the transducer is self line focusing. Results of through transmission experiments on silicon and transmission images on paper are reported.
Field-dependent microsusceptometry on magnetic crystallites with integrated dc SQUIDs
Authors: Narasimhan L. R. , Patel C. K. N. , Ketchen M. B.
Published: July 2002

We report the use of unshielded planar low-Tc dc SQUIDs for temperature-dependent ac and dc magnetic susceptibility measurements on small particles in magnetic fields of up to 300 G. These measurements were made with integrated microsusceptometers which can operate in such fields when applied in the plane of the device. We show paramagnetic, antiferromagnetic, and superconducting behavior on various samples of order 20–50 μm from 0.3 to 4 K and discuss the effect of sample placement on the magnitude of the signal.
Cotton–Mouton effect measurement with the Fabry–Perot eigenstates
Authors: Chauvat Dominique , Le Floch Albert , Vallet Marc , Bretenaker Fabien
Published: July 2002

We show that, using the eigenstates of a high-finesse Fabry–Perot cavity, we can measure the small Cotton–Mouton birefringence of gases with a simple tabletop apparatus. It requires only modest magnetic fields (B<1 T) and uses an ultrastable Zerodur high-finesse optical cavity. The method is validated by the measurement of the Cotton–Mouton constant of air and a sensitivity of 2.5×10−9 rad is obtained for the single pass birefringence.
Characterization of dislocations in germanium substrates induced by mechanical stress
Authors: Gan S. , Li L. , Hicks R. F.
Published: July 2002

Dislocations are observed in germanium crystals (9° off axis toward the [011] direction) that have undergone plastic deformation. Optical microscopy reveals that the substrates exhibit a crosshatch pattern, consisting of ridges and trenches that extend in the [011] and [011̄] directions. Further characterization of these features with scanning tunneling microscopy shows that they consist of bands of steps. These bands are created when a group of dislocations emerge onto the crystal surface from the bulk. The dislocations are determined to be type (a/2)〈011〉.
Local Cu and Br environments and their relationship to superconductivity restoration in brominated YBa2Cu3Oy
Authors: Potrepka D. M. , Fenner D. B. , Balasubramanian M. , Hines W. A. , Budnick J. I.
Published: July 2002

Cu 63,65 nuclear quadrupole resonance (NQR) and Br k-edge x-ray absorption fine structure (XAFS) have been used to study the local structures in well-characterized samples of deoxygenated and brominated YBa2Cu3Oy(YBCO). NQR shows that after bromination of YBa2Cu3O6.1 at 260 °C, oxygen has repopulated the chain sites. From XAFS, it is concluded that Br does not enter the YBCO lattice, but rather precipitates out as small nanoscale particles of BaBr2. These results provide clear evidence of the role of Br in reoxygenating the YBCO structure and an explanation for the partial restoration of superconductivity in the YBCO system.
Intrinsic microcrystalline silicon by plasma-enhanced chemical vapor deposition from dichlorosilane
Authors: Platz R. , Wagner S.
Published: July 2002

Microcrystalline silicon (μc-Si:H) of truly intrinsic character can be deposited by plasma-enhanced chemical vapor deposition (PECVD) when dichlorosilane (SiH2Cl2) is added. A dark conductivity of 1.6×10−8 S/cm and an activation energy of 0.62 eV are obtained. No special gas purification or microdoping is required. SiH2Cl2 in small amounts has the additional effect of enhancing the crystallinity and reducing the oxygen incorporation by over a factor of 2. Sub-band-gap absorption spectroscopy indicates a low defect density.
Corrugated infrared hot-electron transistors
Authors: Chen C. J. , Choi K. K. , Chang W. H. , Tsui D. C.
Published: July 2002

The sensitivity of a focal plane array in terms of the noise equivalent temperature difference ultimately depends on the detector photocurrent to dark current ratio rI. In this work, we have integrated two approaches in the quantum well technology that can increase rI into a single detector structure. The new detector is referred to as the corrugated infrared hot-electron transistor (CI-HET). In this detector structure, an energy filter is grown next to a standard quantum well infrared photodetector (QWIP) for more selective collection of the photocurrent. At the same time, corrugated structures are physically fabricated into the detector pixel to increase light absorption in the QWIP. With this combined approach, rI is able to increase by more than a factor of five compared to a standard QWIP. In addition, the new structure reduces the total current of the detector to a level that is suitable for signal integration.
Optical modulation of bulk one-phonon state in diamond
Authors: Mita Y. , Kanehara H. , Adachi Y. , Nisida Y. , Okada M. , Kobayashi M.
Published: July 2002

Infrared absorption and electron spin resonance measurements have been performed in nitrogen-containing mixed-type diamonds under several illumination conditions. It has been observed that bulk one-phonon absorption spectra are modulated by illumination of higher than 2.0 eV in photon energy and the change recovers within a few hours after the excitation light is turned off. The results are explained by the change in the charge state of isolated nitrogen, and a characteristic absorption band created by the positive charge state of isolated nitrogen (N+) is proposed. This phenomenon is applicable in decomposing the infrared absorption spectra of diamonds into each component, which contain information about the type and concentration of nitrogen aggregate.
Time resolved photoluminescence investigations of polyacetylene derivatives
Authors: Wang Hui , Wong Kam Sam
Published: July 2002

Time resolved photoluminescence dynamics of poly(phenylacetylene)(PPA) and poly(1-phenyl-1-butyl)(PPB) were investigated by using femtosecond luminescence upconversion spectroscopy technique. An ultrafast initial luminescence decay (∼5 ps) was observed for PPA, but it was absent for PPB. The transient luminescence spectrum of PPA exhibits a much larger red-shift (∼140 meV) than that of PPB (∼60 meV). PPB shows a much higher luminescence efficiency than that of PPA. The influence of the substitution on the photoluminescence behaviors of PPA and PPB is discussed.
Behavior of negative ions and aggregation process of particle growth in silane plasma
Authors: Satake K. , Inoue Y. , Ukai O. , Takeuchi Y.
Published: July 2002

Particle formation processes in silane plasma have been studied by means of ab initio molecular orbital method and the Derjaguin–Landau–Verway–Overbeek (DLVO) theory. The results from a quantitative comparison between the Si–H bonding energy of negative species and that of neutral ones suggested the presence of the polymerization pathways via negative species. The DLVO theory has been applied to calculate the interaction potential energy between the charged particles. It was found that the heterogeneous aggregation accelerates the particle growth.
Lateral index guiding in ZnCdSe quantum well lasers by selective implantation-induced disordering
Authors: Kuttler M. , Strassburg M. , Pohl U. W. , Bimberg D. , Behringer M. , Hommel D.
Published: July 2002

Local implantation-induced disordering of ZnCdSe quantum wells is applied to generate lateral index guided II–VI lasers. Lateral selectivity of implanted nitrogen ions is achieved by metal stripes also used for contacts. Secondary ion mass spectroscopy and luminescence prove that quantum well intermixing can be generated without subsequent thermal treatment. Lateral index guiding in II–VI lasers after implantation is demonstrated by recording the near-field pattern, yielding a lateral index step of the order of 10−3. First full index-guided injection lasers with an implantation-induced lateral confinement are processed. Threshold current density is reduced by 40% and emission characteristics of these lasers are strongly improved.
Fabrication of sub-μm bipolar transistor structures by scanning probe microscopy
Authors: Richter Shachar , Cahen David , Cohen Sidney R. , Gartsman Konstantin , Lyakhovitskaya Vera , Manassen Yishay
Published: July 2002

We show how sub-μm sized transistor structures (down to 50 nm cross section) can be fabricated by thermally assisted electromigration of mobile dopants inside the semiconductor CuInSe2. Small device structures are fabricated by application of an electric field to the sample via the contact, defined by a conducting atomic force microscope tip. The structures are characterized by nm scale scanning spreading resistance and scanning capacitance measurements to reveal the inhomogeneous doping profiles created by the electric field.
Subterahertz signal crosstalk in transmission line interconnects
Authors: Currie Marc , Sobolewski Roman , Hsiang Thomas Y.
Published: July 2002

A low-temperature electro-optic sampling system was implemented to study the crosstalk of picosecond pulses between on-chip microstrip interconnects. With a submillivolt sensitivity and a subpicosecond temporal response, this system has allowed noninvasive, nodal testing of superconducting Nb integrated circuits. We have characterized pulse propagation and the crosstalk arising from two microstrip waveguides crossing perpendicular to each other, with one signal line crossing above the other. These results provided direct feedback for improving computer simulations of superconducting electronic circuits, but they are representative of any high-speed interconnect in today’s very large scale integrated circuit technology.
Microphotoluminescence of oval defects in a GaAs layer grown by molecular beam epitaxy
Authors: Kasai Jun-ichi , Kawata Masahiko
Published: July 2002

Using a low-temperature microphotoluminescence method, we have investigated the optical properties of oval defects in a GaAs layer grown by molecular beam epitaxy. The photoluminescence (PL) spectra of oval defects exhibited new distinct peaks, which had a narrow width (0.5 meV) and a strong intensity comparable to the exciton luminescence from a defect-free region of the epilayer. The excitation-power dependence and our PL image measurements suggest that the peaks are due to the recombination of excitons bound to the defects. The PL image of the free-exciton luminescence clearly revealed the features of a pair of asymmetric oval defects, each of which had a pyramidal structure consisting of stacking fault planes. The clear features indicate effective carrier confinement within the pyramid, where the stacking fault planes functioned as a potential barrier.
Self-starting passively mode-locked tunable Cr4+: yttrium–aluminum–garnet laser with a single prism for dispersion compensation
Authors: Chang Yongmao , Maciejko Roman , Leonelli Richard , Thorpe Anthony Spring
Published: July 2002

A self-starting passive mode-locked Cr4+:yttrium–aluminum–garnet laser that uses a saturable Bragg reflector with a single prism for dispersion compensation instead of the standard prism pair is demonstrated. We observed over 230 mW average output power with a pulse width of 400 fs at center wavelengths shorter than 1.5 μm. The tuning range for cw laser operation extends from 1345 to 1557 nm. The mode-locked pulses are self-starting and tunable from 1420 to 1510 nm by means of lossless prism tuning without aperture.
Observation of coherent hybrid reflection with synchrotron radiation
Authors: Morelhão S. L. , Avanci L. H. , Hayashi M. A. , Cardoso L. P. , Collins S. P.
Published: July 2002

High resolution synchrotron radiation has been used to investigate the occurrence of coherent hybrid reflections (CHR) in the In0.49Ga0.51P/GaAs(001) structure. Several φ scans at the 002 layer reflection were carried out. The scanned φ intervals are correlated by the [001] axis symmetry and should present the same pattern. A break in the symmetry is observed due to constructive/destructive interference of the hybrid amplitudes with the amplitude from the 002 layer reflection. The effects of substrate miscut and interface distance are taken into account to explain the observed patterns. The application of CHR as a high sensitive tool to analyze epitaxial growth is discussed.
Forced magnetostriction in FeZr-based amorphous alloys
Authors: Arcas J. , Hernando A. , Barandiarán J. M , Schwetz M. , Grössinger R.
Published: July 2002

The magnetostriction constant and forced volume expansion have been measured in amorphous melt–spun ribbons of composition Fe88Zr7B4Cu1, Fe87.2Zr7.4B4.3Cu1.1, Fe86Zr7B6Cu1, and Fe85Zr7B6Cu2. The values obtained show that the volume expansion plays the most important role at room temperature. The magnetic character of these samples was also estimated from the Arrott plots at room temperature and from the thermal dependence of the magnetization. As has been found, the volume contribution decreases with the Curie temperature, whereas the saturation magnetostriction contribution increases. The results measured are also related with the previously reported stress dependence of the Curie temperature.
Pinning and depinning of single vortices in niobium thin film dc superconducting quantum interference devices
Authors: Gail J. , Mück M. , Heiden C.
Published: July 2002

We have studied the influence of an rf magnetic field on pinning and depinning of single vortices in thin film dc superconducting quantum interference devices. We report on the measurements of two-level fluctuations caused by vortices hopping between two pinning sites. From the temperature-dependent time, for which a vortex remains in one of the pinning sites, it was possible to deduce the activation energy for hopping between the pinning sites. By the use of a high frequency demagnetization process, we could force the vortex to change the pinning site or to leave the superconductor.
Effects of KrF laser irradiation on Bi nanoclusters embedded in a-SiO2 by ion implantation
Authors: Park Seung Y. , Isobe Tetsuhiko , Senna Mamoru , Weeks Robert A. , Zuhr Raymond A.
Published: July 2002

Bismuth nanoclusters have been formed in optical grade silica glass (Corning 7940) by ion implantation which formed localized Bi:SiO2 composite in the near-surface region. Subsequent irradiation with 248 nm KrF excimer laser light modifies the distribution and chemical states of the implanted bismuth in the composite. Excimer laser irradiation causes not only photochemical reactions in the composite leaving a thin film of bismuth oxide on the surface, but also removal of the precipitated particles by both thermal and nonthermal desorption mechanisms from the surface.
Electrical properties of n-n ZnSe/In0.04Ga0.96As(001) heterojunctions
Authors: Cai C. , Nathan M. I. , Rubini S. , Sorba L. , Mueller B. , Pelucchi E. , Franciosi A.
Published: July 2002

Lattice-matched n-n ZnSe/In0.04Ga0.96As heterojunctions were studied by means of current density versus voltage (J–V) and capacitance versus voltage (C–V) measurements. The resulting characteristics indicate that the behavior of this n-n heterostructure can be explained by a back-to-back double Schottky diode model. The value of conduction band discontinuity (ΔEc) is found to be 0.10–0.12 eV.
Pulse compression using coupled-waveguide structures as highly dispersive elements
Authors: Lee Yong
Published: July 2002

Pulse compression is experimentally demonstrated by using a coupled-waveguide structure consisting of an InGaAsP/InP semiconductor as a highly dispersive element. In this structure, waveguide dispersion associated with supermodes is significantly enhanced. The maximum temporal compression factor was 4.3 (compression from 2.2 to 0.514 ps). This result indicates that the coupled-waveguide structure has the potential for use in a simple, compact, transmissive, and sign-free dispersion compensator.
Intrinsic Josephson effect in La2−xSrxCuO4 mesa junctions with niobium counter electrode
Authors: Uematsu Y. , Nakajima K. , Yamashita T. , Tanaka I. , Kojima H.
Published: July 2002

We reveal the intrinsic Josephson effect in a La2−xSrxCuO4 (LSCO) high-Tc superconductor. Nb counterelectrodes are deposited on top of mesas, which are formed on surfaces either parallel or perpendicular to the ab plane of LSCO single crystals. Nb/LSCO interfaces behave as SNS Josephson junctions. For the junctions parallel to the ab plane, we observe many branches in the current–voltage characteristics due to intrinsic Josephson effects. The voltage gaps between the branches are typically 0.1 mV, which is much smaller than the superconducting energy gap 2Δ≅11 mV expected for LSCO from Bardeen–Cooper–Schrieffer theory.