bluuebunny/crossref_metadata_2025 huggingface dataset:
VASCULITIC NEUROPATHY ‐ 8 YEARS FOLLOW‐UP STUDY ON PATIENTS ADMITTED TO HOSPITAL
Authors: Martini L. , Francia A. , Vitale A. , Finamore L. , Manfredi M.
Published: July 2002

International literature doesn't succeed in clarifing both clinical features and epidemiologic importance of isolated and nonisolated (associated with a systemic disease) vasculitic neuropathy.

During a three years period (1990–1993), 284 patients affected by peripheric nervous system disease were admitted, as Day Hospital patients or like ordinary hospitalization, into the III Clinic of Neurologic Science Department at “La Sapienza” University‐Rome. Seventy‐two patients in our group were affected by polineuropathy.

From an epidemiologic point of view, only 5–6% of population conformed with vasculitic polineuropathy diagnostic criteria; this percentage comprises equally systemic and isolated vasculopathy. After first admission, patients underwent clinical and instrumental checks through which modifications of nosographic classification were recordered.

At the end of the study period, in 1998, 13.8% of patients had a vasculitic neuropathy diagnosis expressed: 70% during systemic disease, 30% as isolated vasculopathy of peripheral nervous system. Simultaneously with the increase of vasculitic neuropathy, we noted a considerable decrease of cryptogenetic neuropathies, the incidence of which changed from 30% to 22%.

Diagnostic evaluations more suitable for nosographic change seem to be:

Clinical and Neurophysiological monitoring

Sierologic and cerebral spinal fluid monitoring

Histologic examination of the nerve

Evaluation of systemic involvment and of its peculiar features that, in our experience, is frequently difficult to frame.

Our results do not differ greatly from those found in international literature and confirm the need of a detailed follw up for a proper nosographic classification.
CLINICAL, MRI, AND SKIN BIOPSY FINDINGS IN SENSORY GANGLIONOPATHIES
Authors: Sghirlanzoni A. , Pareyson D. , Grisoli M. , Lombardi R. , Lauria G.
Published: July 2002

Unlike peripheral motor disorders, sensory disturbances are rarely diagnosed by the probable site of pathology. This approach is useful in the differential diagnosis between chronic sensory axonal neuropathies and ganglionopathies, in which routine clinical and neurophysiological evaluation alone often do not provide definite clues.

Methods: Thirty patients with peripheral sensory disturbances were investigated. MRI was performed at cervical level in all cases. Four patients also underwent thoracic and lumbar MRI. Seventeen patients underwent skin biopsy at the proximal thigh and the distal leg. In 4 of them, further skin biopsies were taken at C5 dermatome and at the hand. Density of intra‐epidermal nerve fibers (IENF) was quantified.

Results: In 22 patients, sensory ganglionopathy was suspected. Disease was idiopathic in 7 cases; paraneoplastic in 3 cases; and associated with Sjögren, AIDS, autoimmune chronic hepatitis, and cisplatin neurotoxicity in 4 cases. One patient had a hereditary sensory autonomic neuropathy. Four patients had vitamin E deficiency and 3 patients a spinocerebellar syndrome. In 8 patients, sensory axonal neuropathy related to diabetes, alcoholism, and AIDS on antiretroviral treatment, and monoclonal gammopathy of undetermined significance was diagnosed.

MRI findings: All ganglionopathy patients showed posterior columns hyperintensity on T2‐weighted MRI. Conversely, MRI was negative in all axonal sensory neuropathy patients.

Skin biopsy findings: In neuropathies, IENF density was significantly lower at the distal leg than at the proximal thigh, while ganglionopathies did not show any change with respect to the rostral:caudal orientation. A similar pattern of epidermal denervation was observed in the arm.

Discussion: The degeneration of both central and peripheral sensory pathway in a fashion that is not length‐dependent localizes the disease to T‐shaped sensory neurons Early ataxia and cutaneous sensory symptoms involving the proximal regions of the body reflect this pattern of denervation and should prompt the diagnosis of ganglionopathy. This can be confirmed by T2‐weighted hyperintensity in the posterior columns and a distinct pattern of IENF loss.
THE INCIDENCE OF THE GUILLAIN‐BARRE SYNDROME IN LOMBARDY, ITALY
Authors: Bogliun G. , Beghi E. , For The Guillain‐Barré Syndrome Registry Study Group. Citterio A.
Published: July 2002

The incidence of the Guillain‐Barré syndrome (GBS) tends to vary between 0.4 and 4 cases per 100,000 population per year, depending on the size of the target population, the diagnostic criteria, and the accuracy of case ascertainment. In this study, the incidence of GBS was estimated for the year 1996 by searching the affected individuals in a large geographic area (Lombardy, population 8,924,870), using standard diagnostic criteria, and investigating multiple data sources. A case was included if he/she was a resident of Lombardy at the time of the diagnosis and there was muscle weakness and/or tendon areflexia with/without typical CSF or EMG features. With reference to the Asbury criteria (Ann Neurol 1978; 3: 565), GBS was defined as typical or atypical. Excluded were patients with HIV infection, botulism, poliomyelitis, and dyphteria. The source of data included the hospital discharge diagnoses, a prospective GBS regional registry, and a concurrent case‐control study. A total of 136 cases met the inclusion criteria (regional registry, 87; hospital discharge diagnoses, 45; case‐control study, 4). The sample included 72 men and 64 women aged 2 to 91 years. The overall crude incidence rate was 1.52 per 100,000 per year (95% CI 1.31–1.73) and the standardized rate was 1.51 per 100,000 per year (95% CI 1.43–1.59). The rate was 1.71 in men and 1.35 in women, and tended to increase with age until 80 years (<40 yr, 0.87; 40–59 yr, 1.54; 60–79 yr, 3.06; 80+ yr, 2.52). There were 10 patients with atypical GBS (cranial polyneuritis, 6; muscle weakness or tendon areflexia, 4). After excluding these cases, the incidence rate fell to 1.41 (95% CI 1.20–1.61). Our study suggests that the incidence of GBS in Lombardy, Italy, is fairly similar to that reported in the most accurate surveys of the disease, and that multiple data sources must be investigated to provide an accurate case ascertainment.
MAY ELECTROPHYSIOLOGY DIFFERENTIATE CHRONIC INFLAMMATORY DEMYELINATING POLYNEUROPATHY (CIDP) AND POLINEUROPATHY WITH ANTI‐SGPG ANTIBODIES?
Authors: Capasso M. , Torrieri F. , Lugaresi A. , Uncini A.
Published: July 2002

Demyelinating polyneuropathy with anti‐MAG/SGPG ab is elecrophysiologically characterized by a disproportionate distal slowing of motor conductions. A terminal latency index TLI = 0.25 in at least two nerves has been proposed to differentiate polyneuropathy with anti‐MAG/SGPG ab from other chronic demyelinating disorders (Kaku et al. 1994).

We reviewed and compared the electrophysiogical studies of 18 patients with CIDP and 8 with polyneuropathy anti‐SGPG antibodies. The Anti‐SGPG group showed: (1) lower CMAP amplitudes and longer motor distal latencies; (2) lower TLI and longer F wave latencies; (3) higher percentages of nerves with TLI = 0.25; (4) much fewer conduction blocks; (5) more frequent absent SAPs.

CIDP and polyneuropathy with anti‐MAG/SGPG seems to be, as groups, electrophysiologically different. However, three patients with CIDP showed at least 2 nerves with TLI = 0.25 and one, although displaying all the additional electrophysiological features characteristic of anti‐MAG/SGPG polyneuropathy, was negative for ab search at diagnosis and one year later, and did not have immunoglobulin deposits in sural nerve. On the other hand, one patient with anti‐SGPG antibodies did not have distal disproportionate slowing of motor conduction velocities.

In conclusion, demyelination seems to be in anti‐MAG/SGPG polyneuropathy a length‐dependent process, whereas in CIDP it tends to be patchy and multifocal, which strengthens the view that these are two different pathophysiological entities. Electrophysiological findings can suggest an anti‐SGPG polyneuropathy and address the search of ab, but they are not pathognomonic in the individual patient.
Misfit stress dependence of dislocation density reduction in GaAs films on Si substrates grown by strained-layer superlattices
Authors: Yamaguchi Masafumi , Sugo Mitsuru , Itoh Yoshio
Published: July 2002

High quality GaAs films with dislocation densities of (1–2)×106 cm−2 on (100) Si substrates have been obtained for a combination of strained-layer superlattice (SLS) insertion such as InGaAs/GaAs, InGaAs/GaAsP, and AlGaAs/GaAs and thermal cycle annealing using the metalorganic chemical vapor deposition method. Remarkable reduction effects of dislocation density and dislocation generation in the GaAs layers due to SLS insertion on Si have been analyzed by a simple model, in which coalescence and generation of dislocations are assumed to be caused by dislocation motion under misfit stress of SLSs. Misfit stress dependence of dislocation density reduction in GaAs films on Si has been clarified using this model.
Carrier lifetimes in ion-damaged GaAs
Authors: Johnson M. B. , McGill T. C. , Paulter N. G.
Published: July 2002

Photoluminescence excitation correlation spectroscopy has been used to measure the dependence of carrier lifetime on the H+ ion implantation dose in GaAs. For doses greater than 1×1012 cm−2 the carrier lifetime is inversely proportional to the ion dose. The minimum lifetime measured was 0.6±0.2 ps for a dose of 1×1014 cm−2. Most important, there is no sign of saturation of carrier lifetime with ion dose down to this lifetime, thus still shorter lifetimes should be achievable with increased ion dose.
Is there a radar clutter attractor?
Authors: Leung Henry , Haykin Simon
Published: July 2002

Using experimental sea clutter data obtained with an instrument-quality radar research system, we show the existence of a chaotic attractor in the clutter. This new and exciting result is in sharp contrast with the conventional stochastic modeling of clutter as some kind of a random process with certain distribution.
Enhancement of lateral solid phase epitaxy over SiO2 using a densified and thinned amorphous Si layer
Authors: Kusukawa K. , Moniwa M. , Ohkura M. , Takeda E.
Published: July 2002

Formation of a thin-film silicon-on-insulator structure by lateral solid phase epitaxy of amorphous Si is described. Thinning of the amorphous Si layer after deposition and densification in an ultrahigh vacuum, prior to solid phase epitaxy, successfully enhances the lateral growth length. In addition, the crystallinity of thin silicon-on-insulator layers formed by this technique is found to be better than that achieved by the conventional method.
Bonding configuration and defects in amorphous SiNx:H films
Authors: Hasegawa S. , Matsuda M. , Kurata Y.
Published: July 2002

Amorphous SiNx:H films were prepared by rf glow discharge of SiH4-NH3 mixtures at 300 °C, and the optical properties and the density Ns of Si dangling bonds obtained from electron spin resonance were investigated as a function of the N content x. The slope E0 in the Urbach form of the absorption coefficient and Ns, respectively, have a maximum at x=1.2 and 0.7. The dependence of E0 on x was examined on the basis of the random-bonding model including H atoms, and the dependence of Ns was connected with the optical gap and E0, according to the weak-bond dangling-bond conversion model.
Image potentials and the dry etching of submicron trenches with low-energy ions
Authors: Davis Robert J.
Published: July 2002

The image potential between an ion and an etched sidewall is shown to be important in the dry etching of high-aspect ratio features. Low-energy ions are attracted to the walls of an etched trench, resulting in wall collisions which can lead to loss of etch directionality and slow vertical etch rates. Estimates are given for the depth at which one-half of the ion flux into an etched trench is lost to one of the etched walls, as a function of trench width and ion energy. The effect is particularly important in the etching of quarter-micron features and smaller using ion energies less than 200 eV.
Third harmonic generation from MOx-PbO-GaO1.5 ternary glasses
Authors: Miyaji Fumiaki , Tadanaga Kiyoharu , Sakka Sumio
Published: July 2002

Third harmonic generation from nonconventional MOx-PbO-GaO1.5 (M=Ti,Nb,W) glasses have been measured. The nonlinear susceptibility, χ(3), of these glasses at 0.635 μm are about 30 times higher than that of SiO2 glass at the same wavelength. It has been found that TiO2 is most effective in increasing refractive index and χ(3).
Dramatic enhancement of interlayer exchange coupling and giant magnetoresistance in Ni81Fe19/Cu multilayers by addition of thin Co interface layers
Authors: Parkin S. S. P.
Published: July 2002

The giant magnetoresistance (MR) of Ni81Fe19/Cu multilayers is dramatically enhanced by inserting thin Co layers at each Ni81Fe19/Cu interface, unambiguously demonstrating the predominant interfacial origin of the giant MR effect. Similarly the long-range oscillatory MR and interlayer exchange coupling only present in magnetron sputtered Ni81Fe19/Cu multilayers at low temperatures is restored at higher temperatures by the addition of thin Co interface layers. Multilayered structures comprised of Co/Ni81Fe19/Co/Cu exhibit MR of more than 17% for field changes of ±100 Oe at room temperature.
Frequency modulated mode locking of a diode laser pumped Nd:LiYF4 laser utilizing a KTiOPO4 phase modulator
Authors: Palese S. , Schilling L. , Wang X. D. , Miller R. J. Dwayne , Zhen Guo , Brown D.
Published: July 2002

A potassium titanyl phosphate phase modulator was used to mode lock a diode laser pumped Nd:LiYF4 laser at 270 MHz. The autocorrelation was 15 ps and the spectral bandwidth 73 GHz. The phase noise of the laser was found to be 70 fs for frequencies ≳100 Hz using a radio frequency spectrum analyzer technique. The high damage threshold and low absorption losses make this material well suited for the future development of high peak and average power laser systems. In addition, the low phase noise should be important for applications which require low timing jitter between a mode-locked laser source and an electronic reference signal.
High quality aluminum nitride epitaxial layers grown on sapphire substrates
Authors: Saxler A. , Kung P. , Sun C. J. , Bigan E. , Razeghi M.
Published: July 2002

In this letter we report the growth of high quality AlN epitaxial layers on sapphire substrates. The AlN grown on (00⋅1) sapphire exhibited a better crystalline quality than that grown on (01⋅2) sapphire. An x-ray rocking curve of AlN on (00⋅1) Al2O3 yielded a full width at half-maximum of 97.2 arcsec, which is the narrowest value reported to our knowledge. The AlN peak on (01⋅2) Al2O3 was about 30 times wider. The absorption edge measured by ultraviolet transmission spectroscopy for AlN grown on (00⋅1) Al2O3 was about 197 nm.
Preparation of aluminum nitride thin films by reactive sputtering and their applications to GHz-band surface acoustic wave devices
Authors: Okano Hiroshi , Tanaka Naoki , Takahashi Yusuke , Tanaka Toshiharu , Shibata Kenichi , Nakano Shoichi
Published: July 2002

Single crystal aluminum nitride (AlN) thin films were prepared by a low-temperature reactive sputtering on basal plane sapphire [(001)Al2O3] at a substrate temperature of less than 315 °C. Surface acoustic wave (SAW) characteristics with an interdigital transducer /(001)AlN/(001)Al2O3 structure were investigated. The phase velocity and temperature coefficient of delay time are 5750–5765 m/s and 55–63 ppm/°C at KH=1.2–1.6, respectively. Resonator-type 1-GHz-band SAW filters with its structure were fabricated. The insertion loss and suppression were 23 dB and more than 20 dB, respectively.
Pulsed-laser deposition of smooth high-T
c superconducting films using a synchronous velocity filter
Authors: Pechen E. V. , Varlashkin A. V. , Krasnosvobodtsev S. I. , Brunner B. , Renk K. F.
Published: July 2002

Pulsed-laser deposition of smooth high-Tc superconducting films almost free from droplets and precipitates with the use of velocity filtration of plasma particles is reported. We have removed droplets from laser-induced plasma by using a shutter technique; a reduction of the droplet density by a factor of 105 has been achieved. We have applied the technique to the preparation of high quality YBa2Cu3O7−δ films on (100)-oriented SrTiO3, MgO, Y2O3-stabilized ZrO2 (YSZ) substrates and, furthermore, on (11̄02)-oriented sapphire covered with (100) sublayers of Si and (100) YSZ buffer layers.
Kinetic model of element III segregation during molecular beam epitaxy of III-III′-V semiconductor compounds
Authors: Dehaese O. , Wallart X. , Mollot F.
Published: July 2002

Segregation of column III atoms during molecular beam epitaxy of III-III′-V semiconductor compounds causes nonabrupt interfaces and a surface composition different from the bulk one. To derive concentration profiles, a thermodynamical equilibrium model has been used for a long time. This model applies well to describe segregation processes at high growth temperatures, but fails in predicting concentration profile variations with substrate temperature. We have thus developed a kinetic model which correctly takes into account the evolution with the growth temperature. We apply this model to the case of indium segregation in the GaxIn1−xAs/GaAs system. The calculated indium concentration profiles are compared to those obtained with the thermodynamical equilibrium model. A kinetic limitation of segregation is shown to appear at low substrate temperatures and sufficiently high growth rates. This limitation is predicted to arise below 400 °C for a growth rate of 1 monolayer/s for In segregation in the GaxIn1−xAs/GaAs system.
Energy spread and ion current measurements of several ion sources
Authors: Gaus A. D. , Htwe W. T. , Brand J. A. , Gay T. J. , Schulz M.
Published: July 2002

Energy spread and extracted current measurements are presented for five different types of ion sources: hot cathode, cold cathode, magnetron, microwave, and electron cyclotron resonance (ECR). The measurements were performed with a 45° parallel-plate energy analyzer with a resolution of better than 0.5 eV at 500 eV incident energy. Energy spreads ranged from 0.5 to 4 eV, while total extracted beam currents ranged from 2 to 30 μA. Beam currents due specifically to protons, 3He++ ions, and H+2 ions are also presented. The ECR and magnetron sources gave the best overall performance. These, along with the energy analyzer, are currently being used in experiments to study ion-atom collision physics.
The influences of roughness on film thickness measurements by Mueller matrix ellipsometry
Authors: Ramsey David A. , Ludema Kenneth C.
Published: July 2002

The accuracy of measurement of the thickness of uniform thin films on solid substrates by null ellipsometry is severely limited when the substrate is rough. It is impossible to separate these two effects experimentally with the null ellipsometer, and there is no theoretical basis or generally used model available to separate these effects. Thus, a dual rotating-compensator Mueller matrix ellipsometer has been constructed to carry out film thickness measurements on rough substrates. Measurements were made on a set of specially prepared specimens of 8630 steel, roughened by grit blasting with aluminum oxide. Grit sizes and blasting pressures were varied to produce 11 different roughness values ranging from 0.01 to 1.295 μm Ra, as measured with a stylus tracer device. Upon each of the 11 roughness groups, films of magnesium fluoride were overlaid to thicknesses of 89, 180, 254, and 315 nm. One set of specimens was left uncoated. Experimental results for film thickness measurements on rough surfaces matched the ideal (for smooth surfaces) form well for roughnesses up to 0.13 μm Ra, at most angles of incidence. For rougher specimens, significant deviations in results were observed for all but the largest angles of incidence. The nonideal data were attributed to the cross-polarization effects of surface geometry, and apparent depolarization. The resolution of thickness measurements was 1 nm for polished specimens, and decreased continuously to 10 nm for the roughest specimens examined.
A method for measuring the dependence of internal friction on strain
Authors: Huang Yinglei , Saulson Peter R.
Published: July 2002

A new method for investigating possible increases of internal friction when a sample is subjected to a substantial constant strain is discussed here. A special beam oscillator was designed in which the orientation of the apparatus determines whether the gravitational torque will apply either a large constant strain or a negligible one. The method was applied to test the strain dependence of the internal friction of a steel flexure 2.0 cm in length and 0.5 mm in thickness. When bent through an angle of 14.5°, it exhibited an 18% increase in internal friction over its unstrained value.
Atomic force microscope with magnetic force modulation
Authors: Florin Ernst-Ludwig , Radmacher Manfred , Fleck Bernhard , Gaub Hermann E.
Published: July 2002

We have constructed a scanned stylus atomic force microscope (AFM) with direct force modulation and integrated microfluorescence optics. The instrument was designed to image the surface of massive samples under various ambient conditions. In force modulation microscopy the imaging force is modulated during the scanning process via an external magnetic field that acts directly on the magnetic AFM tip. Polymeric Langmuir–Blodgett films on silicon oxide were imaged to evaluate the application range of the instrument. We demonstrate that direct force modulation microscopy permits the quantitative recording of the local complex compliance both as a function of the location and as a function of the frequency. In a novel imaging mode referred to as sample resonance mode, the contrast of the image can be selectively enhanced based on local elasticity differences.
Novel InGaAs/GaAs quantum dot structures formed in tetrahedral-shaped recesses on (111)B GaAs substrate using metalorganic vapor phase epitaxy
Authors: Sugiyama Yoshihiro , Sakuma Yoshiki , Muto Shunichi , Yokoyama Naoki
Published: July 2002

We report a novel GaAs/InGaAs/GaAs quantum dot structure formed in a tetrahedral-shaped recess (TSR) patterned on a (111)B GaAs substrate with anisotropic chemical etching. The pseudomorphic heterostructure shows two clear photoluminescence peaks which are attributed to an In anisotropic incorporation on (111)B compared to (111)A. Cathodoluminescence at a lower energy peak with InGaAs of 2.5 nm shows a bright image at the bottom of TSRs which indicates the local minimum in potential energy at the bottom of TSR.
Artificial fabrication of an L10-type ordered FeAu alloy by alternate monatomic deposition
Authors: Takanashi K. , Mitani S. , Sano M. , Fujimori H. , Nakajima H. , Osawa A.
Published: July 2002

An FeAu ordered alloy has been fabricated artificially by depositing alternately monatomic layers of Fe and Au. Neither intermediate phase nor intermetallic compound is known for the Fe–Au system in the equilibrium state. Nevertheless, the x-ray diffraction for prepared FeAu films shows definite superlattice lines corresponding to the L10 ordered structure, and it is metastable at room temperature. The obtained FeAu ordered alloy is ferromagnetic, and it has the Fe moment of 2.5±0.3 μB, a considerably high Curie temperature over room temperature, and a large uniaxial magnetic anisotropy perpendicular to Fe and Au atomic planes.
Three dimensional single-particle tracking with nanometer resolution
Authors: Peters Inge M. , de Grooth Bart G. , Schins Juleon M. , Figdor Carl G. , Greve Jan
Published: July 2002

We have developed a method for three dimensional (3D) tracking of polystyrene spheres with nanometer resolution. The detection technique is based on measuring the displacement of a polystyrene sphere positioned in the center of a laser beam just behind the focus. A change in the lateral position of the sphere causes a deflection of the beam which can be measured using a position sensitive detector. A change in the axial position of the sphere causes a shift in the axial position of the focus behind another lens, which can be measured using an overfilled photodiode. A feedback system is used to keep the sphere in the center of the laser beam to avoid the influence of lateral displacements on the detection of the axial position. Spatial resolution for a 0.92 μm polystyrene sphere was better than 1 nm in three dimensions using a sampling rate of 1 kHz. This method was applied to track spheres bound to adhesion molecules LFA-1 expressed at the surface of living cells. It turned out to be a useful method to accurately measure the 3D trajectory of biological molecules on cells in real time.
Automated optical liquid film thickness measurement method
Authors: Shedd T. A. , Newell T. A.
Published: July 2002

A nonintrusive, automated, optical film thickness measurement technique has been developed to be used with a wide range of fluids and flow configurations. In this method, light is reflected from the surface of a liquid film flowing over a transparent wall. This reflected light generates an image on the outside of the wall which is captured and digitized using a charge coupled device camera and framegrabber card in a desktop computer. The image is processed to determine the positions of the reflected light rays, with which the film thickness is calculated. The entire process is automated, allowing for the collection of 600 data points in about 4 min using a personal computer with a 486 microprocessor. Film thicknesses on the order of 0.01 mm may be determined using inexpensive components, with the possibility of greater precision using more advanced imaging equipment. An automated calibration procedure allows for the determination of the necessary physical parameters, so the index of refraction of the test fluid or the test section wall need not be known a priori. Static liquid measurements agree to within 2.2% of measurements made using the needle-contact method. Film thickness data are presented for both round and square test sections operating under annular, two-phase flow conditions with air and water.
Precise rotary motor by inchworm motion using dual wrap belts
Authors: Kim Sang-Chae , Kim Soo Hyun
Published: July 2002

A new type of rotary motor by inchworm motion using two belts is developed. A rotor is wrapped by two opposite belts which are connected to piezoelectric actuators. A serial lever structure with flexure hinges is used to connect a belt and piezoelectric actuators. The lever structure amplifies micro displacement of a piezoelectric actuator. A rotational motion with the step size of 2.36 μrad is obtained through this work. An angular step size can be further reduced by increasing the rotor radius. We present a analysis model of the motor for a design of a similar precise motor.
Optical detection of ultrasound with a phase-modulated Michelson interferometer
Authors: Nakano Hidetoshi , Matsuda Youichi , Nagai Satoshi
Published: July 2002

A phase-modulated Michelson interferometer for optical detection for ultrasound is described. The operating point of the interferometer is kept to the minimum intensity of the interference pattern. This scheme allows the use of a high power laser to improve the sensitivity without a photodiode saturation. Ultrasonic displacement amplitudes as small as 10 pm can be detected when the maximum intensity on the photodiode is 100 mW. The detected root-mean-square noise is twice as much as the theoretical prediction of 3×10−16 m/Hz. The ultrasonic wave forms excited with a transducer and a pulsed laser in a Si sample are presented.
Ultrasmall volume refractive index detection using microinterferometry
Authors: Swinney Kelly , Markov Dmitry , Bornhop Darryl J.
Published: July 2002

A microinterferometric backscatter detector (MIBD) has been developed to perform subnanoliter volume refractive index measurements using a simple, folded optical train based on the interaction of a laser beam and a fused silica capillary tube. Positional changes of the interference pattern extrema (fringes) allow for the determination of Δn at the 10−7 level, corresponding to 5.3 pmole or 0.48 ng of solute, when thermal noise is controlled at 8×10−3 °C. MIBD is relatively path-length insensitive for capillaries ranging in inner diameter from 75 to 775 μm, allowing a large range of detection volumes, from 350 pL to 40 nL, to be produced. A theoretical model of the microinterferometric backscatter detector has also been developed and evaluated and has been found to be in agreement with experimental data. This model indicates increased sensitivity of the instrument as the wavelength of the probe beam and the wall thickness of the capillary tube are reduced.
High average power KTiOPO4 electro-optic Q-switch
Authors: Ebbers Christopher A. , Velsko Stephan P.
Published: July 2002

We have demonstrated a thermally compensated KTiOPO4 (KTP) Q-switch with a 10 mm × 6 mm clear aperture and high contrast ratio. This device showed excellent resistance to thermal depolarization at average power densities as high as 1 kW/cm2. Capacitive coupling allowed us to operate the Q-switch for greater than 109 shots with no sign of electrochromic damage.
Growth of device quality GaN at 550 °C by atomic layer epitaxy
Authors: Karam N. H. , Parodos T. , Colter P. , McNulty D. , Rowland W. , Schetzina J. , El-Masry N. , Bedair Salah M.
Published: July 2002

GaN single crystal films were grown by atomic layer epitaxy at 550 °C. The room temperature photoluminescence properties of these low-temperature-grown films are dominated by band edge emission with intensity comparable to those grown by metalorganic chemical vapor deposition at 1000 °C. The as-grown films have background-carrier concentrations that can be controlled to levels in the 1016/cm−3 range. Atomic layer epitaxy is therefore a good approach to the low temperature growth of nitride compounds.
Gas phase ultraviolet spectroscopy of high-temperature superconductor precursors for chemical vapor deposition processing
Authors: Rappoli Brian J. , DeSisto William J.
Published: July 2002

UV spectroscopy has been used as an in situ diagnostic to measure the gas phase concentration of 2,2,6,6-tetramethyl-3,5-heptanedionate (thd) complexes of Cu and Y in metalorganic chemical vapor deposition (MOCVD) bubbler effluent. These Cu and Y precursors for MOCVD synthesis of YBa2Cu3O7−δ (YBCO) show marked instability in gas phase concentration as a function of time during the initial bubbler purge. The precursors show ideal behavior as predicted by the Clausius–Clapeyron relation. The UV diagonstic technique has the potential of controlling precursor concentration for MOCVD fabrication of high-temperature superconducting thin films.
Discrete voltage states in one-dimensional parallel array of Josephson junctions
Authors: Braiman Y. , Family F. , Hentschel H. G. E.
Published: July 2002

We study low-voltage dynamics in highly discrete one-dimensional arrays of Josephson junctions. In particular, we focus on the resonant solutions emerging from the locking between the time period of the oscillations of the single junction with the spatial period of the wave propagating across the array. We find that the average voltage across the array scales as V∝(κ−κc)1/2, where κc is the critical value of the coupling. The connections to high voltage solutions are discussed.
Ultrafast carrier trapping in high energy ion implanted gallium arsenide
Authors: Jagadish C. , Tan H. H. , Krotkus A. , Marcinkevicius S. , Korona K. P. , Kaminska M.
Published: July 2002

Time resolved photoluminescence and electrical measurements were made on MeV As, Ga, Si, and O ion implanted GaAs to doses in the range of 1×1014–5×1016 cm−2 and subsequently annealed at 600 °C for 20 min under arsine ambient. Carrier trapping times were found to decrease with increase in implantation dose for all species studied and can be shorter than 1 ps. Sheet resistance values were found to be independent of implantation dose and were of the order of 108 Ω/⧠ for As, Ga, and O implantation and ∼2×102 Ω/⧠ for the Si case due to its electrical activation. Conductivity activation energies of 0.67–0.69 eV were observed for As, Ga, and O ion implanted and annealed GaAs, which are close to the reported activation energy for annealed low-temperature GaAs (0.65 eV).
Molecular beam epitaxial growth of InSb, GaSb, and AlSb nanometer-scale dots on GaAs
Authors: Bennett Brian R. , Magno R. , Shanabrook B. V.
Published: July 2002

Thin layers of InSb, GaSb, and AlSb were grown on GaAs substrates by molecular beam epitaxy. Atomic force microscopy was used to examine surface morphology as a function of growth temperature and monolayer coverage. For each material, conditions were found which resulted in Stranski–Krastanov growth with the strain-induced formation of nanometer-scale dots. Relatively uniform distributions of dots form in a temperature window near the congruent sublimation temperature for both InSb and GaSb. In the case of InSb, deposition of 2 monolayers at 430 °C produced a surface with 3×109/cm2 dots with heights of 58±5 Å and diameters of 600±50 Å.
Electromigration of aluminum cathodes in polymer-based electroluminescent devices
Authors: Cumpston B. H. , Jensen K. F.
Published: July 2002

Dark, nonemissive defects form on the metal cathode in most molecular organic and polymer-based light emitting devices and eventually lead to the failure of the device. These defects have been characterized in situ using optical microscopy and ex situ using atomic force microscopy and Auger electron spectroscopy. On the basis of these observations, an electromigration mechanism for the formation of dark spot defects is proposed. The high current density required to operate polymer-based light emitting devices leads to electron-induced diffusion of the Al cathode when a short circuit forms in the emissive polymer layer. This process results in a ‘‘pileup’’ of metal at the short circuit (anode) and a surrounding circular region where the Al is depleted, appearing as a dark spot on the cathode.
First order gain-coupled GaInAs/GaAs distributed feedback laser diodes patterned by focused ion beam implantation
Authors: Orth A. , Reithmaier J. P. , Zeh R. , Doleschel H. , Forchel A.
Published: July 2002

Electrically pumped gain-coupled distributed feedback lasers with first order gratings have been fabricated on a (Ga,In)As/(Al,Ga)As separate confinement heterostructure by focused ion beam implantation and epitaxial overgrowth. The lasers are operating at room temperature at wavelengths around 950 nm. All investigated devices show single longitudinal mode emission at all operating conditions.
Valence band discontinuity at a cubic GaN/GaAs heterojunction measured by synchrotron-radiation photoemission spectroscopy
Authors: Ding S. A. , Barman S. R. , Horn K. , Yang H. , Yang B. , Brandt O. , Ploog K.
Published: July 2002

The valence band discontinuity of the n-type cubic GaN/GaAs heterojunction is measured by means of angle-resolved photoemission spectroscopy using synchrotron radiation. High quality cubic GaN films are grown on GaAs(100) substrates by nitrogen plasma-assisted molecular beam epitaxy, and the valence band discontinuity is determined by a combination of core and valence level spectra. A value of ΔEV=(1.84±0.1) eV across the GaN/GaAs heterojunction is obtained, which means that the discontinuity in the conduction bands at this interface is very small, such that a vertical contact scheme may be realized for GaN/GaAs heterojunctions.
PbS quantum-dot doped glasses as saturable absorbers for mode locking of a Cr:forsterite laser
Authors: Guerreiro P. T. , Ten S. , Borrelli N. F. , Butty J. , Jabbour G. E. , Peyghambarian N.
Published: July 2002

Quantum confined nanocrystals of PbS in glass were used as intracavity saturable absorbers to obtain passive continuous-wave mode locking in a Cr:forsterite laser. We obtained near transformed-limited 4.6 ps laser pulses at 110 MHz repetition rate, and a wide tunability range of 1207–1307 nm. The absorption saturation intensity of the quantum-dot PbS doped glasses was measured to be 0.2 MW/cm2.
Confocal scanning optical microscopy of BaxSr1−xTiO3 thin films
Authors: Hubert Charles , Levy Jeremy , Carter Adrian C. , Chang Wontae , Kiechoefer Steven W. , Horwitz James S. , Chrisey Douglas B.
Published: July 2002

An optical technique based on confocal scanning optical microscopy (CSOM) is used to image the ferroelectric polarization of BaxSr1−xTiO3 (BST) thin films at room temperature with submicron spatial resolution. BST films were grown by pulsed laser deposition on (100) SrTiO3 and MgO substrates at 750 °C in 300 mTorr of oxygen and postdeposition annealed in flowing oxygen at temperatures ⩽1250 °C. Films of both paraelectric (x=0.5) and ferroelectric (x=0.8) compositions show a coexistence of both paraelectric and ferroelectric phases. The ferroelectric regions exhibit polarization switching and hysteresis at relatively low (1–2 kV/cm) applied fields. These results suggest that nonuniform stress is responsible for the strong inhomogeneous thermal broadening of the ferroelectric phase transition, and that dielectric loss in thin films may be dominated by a relatively small fraction of nanometer-sized regions.
Material characteristics of perovskite manganese oxide thin films for bolometric applications
Authors: Goyal A. , Rajeswari M. , Shreekala R. , Lofland S. E. , Bhagat S. M. , Boettcher T. , Kwon C. , Ramesh R. , Venkatesan T.
Published: July 2002

We are optimizing thin films of perovskite manganese oxides for bolometric applications. We have studied the relevant material characteristics of several members of this family namely, La0.7Ba0.3MnO3, La0.7Sr0.3MnO3, La0.7Ca0.3MnO3, and Nd0.7Sr0.3MnO3. Here, we discuss issues related to the choice of material, the influence of deposition parameters, and postdeposition heat treatments on the relevant characteristics such as the resistivity-peak temperature (Tp) and the temperature coefficient of resistance (TCR). For a given material, a higher peak temperature implies a larger temperature coefficient of resistance. In contrast, on comparing different material systems, the TCR tends to decrease as Tp increases.
Photothermal modulation for oscillating mode atomic force microscopy in solution
Authors: Ratcliff Glenn C. , Erie Dorothy A. , Superfine Richard
Published: July 2002

Solution imaging using resonant techniques for atomic force microscopy is greatly simplified by driving the cantilever directly. We have taken advantage of the temperature-sensitive bending properties of metal-coated silicon nitride cantilevers to induce vibrations in the lever using a modulated laser. We demonstrate that photothermal modulation with a nominal 2 mW laser in solution produces a single resonance, typically, of 8–20 nm amplitude, that can be used for imaging. We present high-quality images of DNA on a mica surface to show the capabilities of this technique for solution imaging.
Temperature dependence of impact ionization in AlGaN–GaN heterostructure field effect transistors
Authors: Dyakonova N. , Dickens A. , Shur M. S. , Gaska R. , Yang J. W.
Published: July 2002

We report on the studies of the impact ionization in AlGaN–GaN heterostructure field effect transistors in the temperature range 17–43 °C. The results show that the breakdown voltage and the characteristic electrical field Ei of the impact ionization have a positive temperature coefficient. The value of Ei at room temperature is estimated to be approximately 2.6 MV/cm, which agrees with recent theoretical prediction [J. Kolnik et al., J. Appl. Phys. 82, 726 (1997)].
Growth and field dependent dielectric properties of epitaxial Na0.5K0.5NbO3 thin films
Authors: Wang Xin , Helmersson Ulf , Olafsson Sveinn , Rudner Staffan , Wernlund Lars-David , Gevorgian Spartak
Published: July 2002

Na 0.5 K 0.5 NbO 3 thin films have been grown on LaAlO3(001) substrates using rf magnetron sputtering from a Na and K enriched target. X-ray diffraction showed that the films are epitaxial with mosaic broadening as narrow as 0.044°. Interdigital Au finger electrodes were photolithographically defined on the film surfaces. The dielectric properties of these interdigital capacitors were measured at 1 MHz from room temperature down to 50 K. The capacitor showed 35% tunability at room temperature and a loss tangent of 0.007 without dc bias applied. The loss decreased further with increasing dc bias. For lower temperatures, the capacitance exhibited a broad maximum at ∼200 K, which is possibly linked to a phase transformation of the Na0.5K0.5NbO3 film.
Room temperature operation of epitaxially grown Si/Si0.5Ge0.5/Si resonant interband tunneling diodes
Authors: Rommel Sean L. , Dillon Thomas E. , Dashiell M. W. , Feng H. , Kolodzey J. , Berger Paul R. , Thompson Phillip E. , Hobart Karl D. , Lake Roger , Seabaugh Alan C. , Klimeck Gerhard , Blanks Daniel K.
Published: July 2002

Resonant interband tunneling diodes on silicon substrates are demonstrated using a Si/Si0.5Ge0.5/Si heterostructure grown by low temperature molecular beam epitaxy which utilized both a central intrinsic spacer and δ-doped injectors. A low substrate temperature of 370 °C was used during growth to ensure a high level of dopant incorporation. A B δ-doping spike lowered the barrier for holes to populate the quantum well at the valence band discontinuity, and an Sb δ-doping reduces the doping requirement of the n-type bulk Si by producing a deep n+ well. Samples studied from the as-grown wafers showed no evidence of negative differential resistance (NDR). The effect of postgrowth rapid thermal annealing temperature was studied on tunnel diode properties. Samples which underwent heat treatment at 700 and 800 °C for 1 min, in contrast, exhibited NDR behavior. The peak-to-valley current ratio (PVCR) and peak current density of the tunnel diodes were found to depend strongly on δ-doping placement and on the annealing conditions. PVCRs ranging up to 1.54 were measured at a peak current density of 3.2 kA/cm2.
Determination of the concentration and temperature dependence of the fundamental energy gap in AlxIn1−xSb
Authors: Dai N. , Brown F. , Doezema R. E. , Chung S. J. , Goldammer K. J. , Santos M. B.
Published: July 2002

We use transmission spectroscopy to determine the energy gap for the AlxIn1−xSb alloy system in the Al concentration range from 0% to 25% from cryogenic to room temperature. The samples are epitaxial layers grown by molecular beam epitaxy on GaAs substrates. Our room temperature results are compared to those from two earlier studies. In our Al concentration range, we find a linear change of energy gap with alloy lattice constant.
Noncascaded intersubband injection lasers at λ≈7.7 μm
Authors: Gmachl Claire , Capasso Federico , Tredicucci Alessandro , Sivco Deborah L. , Hutchinson Albert L. , Chu S. N. George , Cho Alfred Y.
Published: July 2002

The realization of the first noncascaded intersubband injection lasers based on a single optical transition is reported. The unipolar lasers are based on an active region consisting of three InGaAs quantum wells closely coupled by thin AlInAs barriers. The lasers emit at λ≈7.7 μm wavelength and operate in pulsed mode up to 110 K. Peak power levels of 20 mW at 10 K and 4 mW at 110 K are obtained. The low-temperature threshold current density is 25.6 kA cm−2 in good agreement with calculations. Several advantages arise from this novel type of intersubband laser. First, only few layers are necessary to build the active region, simplifying sample preparation. Second, low operating voltages can be achieved, which is essential for many applications. Finally, the noncascaded intersubband laser allows studying fundamental properties of quantum cascade lasers without possible artifacts introduced by the sequential stacking of many active regions.
Nanometer-scale InGaN self-assembled quantum dots grown by metalorganic chemical vapor deposition
Authors: Tachibana K. , Someya T. , Arakawa Y.
Published: July 2002

We have successfully grown nanometer-scale InGaN self-assembled quantum dots (QDs) on a GaN surface without any surfactants, using atmospheric-pressure metalorganic chemical vapor deposition. Atomic force microscopy shows that the average diameter of InGaN QDs is as small as 8.4 nm. Next, we have investigated the dependence of the QDs properties on the growth conditions: the amount of InGaN deposited and the growth temperature. Moreover, we have investigated the optical property of InGaN QDs, so that the strong emission was seen at 2.86 eV at room temperature.
External quantum efficiency of single porous silicon nanoparticles
Authors: Credo G. M. , Mason M. D. , Buratto S. K.
Published: July 2002

We use a combination of single nanoparticle luminescence and scanning force microscopy to determine the quantum efficiency (QE) of single porous Si nanoparticles and to determine the ratio of luminescent nanoparticles deposited on a silica surface to the total nanoparticles. An estimate of the QE of bulk porous Si based on these data compares favorably to the QE measured experimentally. From this we conclude that the 1% QE of bulk porous Si measured experimentally results primarily from a statistical distribution of high QE quantum-confined Si chromophores.
Indium incorporation above 800 °C during metalorganic vapor phase epitaxy of InGaN
Authors: Schenk H. P. D. , de Mierry P. , Laügt M. , Omnès F. , Leroux M. , Beaumont B. , Gibart P.
Published: July 2002

We have studied the indium incorporation into InGaN ternary alloys during low-pressure metalorganic vapor-phase epitaxy as a function of the trimethylindium flow and the growth temperature in the 800–860 °C range. Partially relaxed InxGa1−xN bulk films with indium compositions 0.02≲x≲0.14 have been grown. In relation to the band-gap energy at room temperature, determined by photothermal deflection spectroscopy, we find a downward band-gap bowing of 2.65±0.15 eV. The required change of the trimethylindium flow as a function of the growth temperature, necessary to obtain isocomposition InGaN films, can be described by an Arrhenius law. We find an indium desorption energy of 0.8±0.3 eV.
AlGaInP light-emitting diodes with mirror substrates fabricated by wafer bonding
Authors: Horng R. H. , Wuu D. S. , Wei S. C. , Tseng C. Y. , Huang M. F. , Chang K. H. , Liu P. H. , Lin K. C.
Published: July 2002

An AlGaInP light-emitting diode (LED) with a Au/AuBe/SiO2/Si mirror substrate has been fabricated using wafer bonding. The bonded mirror-substrate LED is capable of emitting luminous intensity of 90 and 205 mcd under 20 and 50 mA injection, respectively. The emission wavelength was found to be independent of the injection current. This feature is attributed to the Si substrate providing a good heat sink.
High electron mobility in bathophenanthroline
Authors: Naka Shigeki , Okada Hiroyuki , Onnagawa Hiroyoshi , Tsutsui Tetsuo
Published: July 2002

We have measured electron mobility in vacuum-deposited films of 4,7-diphenyl-1,10phenanthroline (bathophenanthroline, or BPhen) using a time-of-flight technique. Electron transport was highly dispersive for BPhen with a dispersion parameter of a value 0.30. The electron mobility in excess of 10−4 cm2/V s has been observed at electric fields of the order of 105 V/cm with weakly dependent on the electric field. The characteristic energy of the distribution is obtained a value 0.09 eV. It is directly confirmed that the BPhen has superior electron-transport capability.
Stable avalanche-photodiode operation of ZnSe-based p+–n structure blue-ultraviolet photodetectors
Authors: Ishikura Hitoshi , Abe Tomoki , Fukuda Nariyuki , Kasada Hirofumi , Ando Koshi
Published: July 2002

A high-field operation of p+–n structure blue-ultraviolet photodetectors has been studied using ZnSe-based II–VI wide-band-gap compound semiconductors grown by molecular-beam epitaxy (MBE). With an improved crystal quality on macrodefects (dislocations and stacking faults) during an initial MBE growth as well as an optimized device structure including a complete superlattice ohmic-contact layer, a stable high electric-field operation up to 8×105 V/cm is established. It is demonstrated that the p+–n ZnSe photodiodes have shown a stable avalanche-photodiode operation with a large avalanche gain of G=60 in the blue-ultraviolet region at room temperature.