bluuebunny/crossref_metadata_2025 huggingface dataset:
The α1L‐adrenoceptor subtype in the lower urinary tract: a comparison of human urethra and prostate
Authors: Fukasawa  , Taniguchi  , Moriyama  , Ukai  , Yamazaki  , Ueki  , Kameyama  , Kimura  , Kawabe
Published: July 2002

Objective

 To identify the α1‐adrenoceptor subtypes present in the human urethra, by comparing the affinity of prazosin for α1‐adrenoceptors in the rabbit, dog and human prostatic urethra, and in the dog and human prostate.

Materials and methods

 The study comprised samples of human prostate and prostatic urethra, obtained by open prostatectomy of patients with benign prostatic hyperplasia, and of the proximal urethra and prostate from male Beagle dogs and rabbits. Specimens were homogenized, filtered and pelleted by centrifugation. Nonspecific binding was determined in the presence of 1 mmol/L prazosin when assessing [3H]YM‐617 (tamsulosin) binding, and 10 mmol/L phentolamine when assessing [3H]prazosin binding. Specific binding was defined as the difference between total binding and nonspecific binding.

Results

 The dissociation constant for [3H]prazosin in the human prostate (0.088 nmol/L) was less than that in the rabbit urethra (0.299 nmol/L), dog urethra (0.604 nmol/L), dog prostate (0.482 nmol/L) and human urethra (0.254 nmol/L). The affinity of prazosin was also investigated by determining the potency of the inhibition of [3H]YM‐617 binding. The affinity of prazosin for α1‐adrenoceptors in the human urethra (Ki, 2.5 nmol/L) was lower than its affinity for α1‐adrenoceptors in the human prostate (Ki, 0.25 nmol/L) and all of the cloned subtypes (Ki, 0.26–0.44 nmol/L).

Conclusion

 The α1L‐adrenoceptor subtype is more prominent in the human, rabbit and dog urethra and dog prostate than in the human prostate.
Gene expression of antioxidant enzymes in experimental diabetic neuropathy
Authors: Kishi Yutaka , Nickander Kim K. , Schmelzer James D. , Low Phillip A.
Published: July 2002

Abstract  Chronic hyperglycemia results in a large deficit in nerve blood flow. Both autoxidative‐ and ischemia‐induced lipid peroxidation occurs, with resultant peripheral sensory neuropathy in streptozotocin‐induced diabetes in the rat. Free radical defenses, especially involving antioxidant enzymes, have been suggested to be reduced, but scant information is available on chronic hyperglycemia. We evaluated the gene expression of glutathione peroxidase, catalase, and superoxide dismutase (cuprozinc and manganese separately) in L4,5 dorsal root ganglion (DRG) and superior cervical ganglion, as well as enzyme activity of glutathione peroxidase in DRG and sciatic nerve in experimental diabetic neuropathy of 3 months and 12 months durations. We also evaluated nerve electrophysiology of caudal, sciatic‐tibial, and digital nerves. A nerve conduction deficit was seen in all nerves in experimental diabetic neuropathy at both 3 and 12 months. Gene expression of glutathione peroxidase, catalase, cuprozinc superoxide dismutase, and manganese superoxide dismutase were not reduced in experimental diabetic neuropathy at either 3 or 12 months. Catalase mRNA was significantly increased in experimental diabetic neuropathy at 12 months. Glutathione peroxidase enzyme activity was normal in sciatic nerve. We conclude that gene expression is not reduced in peripheral nerve tissues in very chronic experimental diabetic neuropathy. Changes in enzyme activity may be related to duration of diabetes or due to post‐translational modifications.
NORMATIVE VALUES OF THE MOST COMMON ELECTRONEUROGRAPHIC PARAMETERS IN PEOPLE AGED FROM SEVENTY FIVE TO NINETY
Authors: Capo G. , Napoletano R. , Esposito A.
Published: July 2002

The average lifespan is 78 years for women and 74 years for men. By the year 2025, the average life expectancy for Italians is estimated to reach 82 years. Today people aged 70 years or more will no longer accept illnesses as in the past. In our lab, the number of older outpatients referred for a neurophysiological tests is increasing continously. Patients above 75 years represent 9% of the total number of our outpatients. Generally, the normative values of the majority of the most common electroneurographic parameters are available until a maximum age of 75–80 years. We examined 49 patients (28 women and 21 men). The examined parameters were motor nerve conduction (MNC) along median, ulnar, peroneal, posterior tibialis, axillary, and musculocutaneous nerves, and sensory nerve conductions (SNC) along median, ulnar, and superficial peroneal nerves.
ALTERED DOSAGE OF PERIPHERAL MYELIN PROTEIN 22 (PMP22) AFFECTS MYELIN PERIODICITY
Authors: Grandis M. , Nobbio L. , Abbruzzese M. , Gherardi G.F. , Bellone E. , Ansaldo G.L. , Mancardi G.L. , Schenone A.
Published: July 2002

PMP22 is a 22‐kD glycoprotein expressed by myelinating Schwann cells. PMP22 seems to play a dual role in regulating cell growth and in peripheral myelin compaction. Myelin formation and maintenance are the result of interactions between PMP22 and the peripheral myelin protein zero (P0), which form complexes at the myelin membrane and mutually contribute to stabilize the intraperiod lines and to held together the major dense lines. Both PMP22 and P0 mutations result in specific inherited demyelinating neuropathies, which are neuropathologically characterized by uncompaction of myelin lamellae and splitting of the major dense lines in some myelinated fibers (MF). However, the most common hereditary neuropathies, Charcot‐Marie‐Tooth 1A (CMT1A) and Hereditary Neuropathy with liability to Pressure Palsies (HNPP), are due to a duplication and a deletion respectively, of the PMP22 gene, leading to over‐ and underexpression of the protein. It is unknown how the altered PMP22 dosage impairs peripheral myelination. Using our imaging system for nerve morphometry directly connected to the electron microscope, we evaluated myelin lamellae periodicity in 150 MF from sural nerves of: 3 CMT 1A patients, 3 HNPP patients, and 3 normal controls. Furthermore, we measured myelin period in 50 MF obtained from a CMT1A culture model and in 50 MF from normal DRG cultures. Myelin periodicity was significantly increased in CMT1A patients (9.77 ± 0.9 nm) and in the CMT1A culture model (10.1 ± 0.1 nm) compared respectively to the normal sural nerves (9.1 ± 0.7 nm) and to the control cultures (9.6 ± 0.1 nm). Conversely, myelin periodicity was slightly reduced in HNPP patients (8.9 ± 0.7 nm).

In conclusion, PMP22 overexpression induces widening of myelin lamellae, which may be recorded with appropriate morphometric techniques. As this change has been also observed in DRG cultures from a CMT1A rat model, it may be the first stage of the demyelination process going on in this disease. The observation that altered dosage of PMP22 significantly affects myelin periodicity provides further clues in understanding the role of this protein in the process of myelin assembly and maintenance.
PLASMA EXCHANGE VERSUS IMMUNOGLOBULIN INFUSION THERAPY IN MYASTENIC CRISIS. REPORT OF SIX CASES
Authors: Inghilleri M. , Perinelli D. , Gozzer M. , Libertucci V. , Conte A. , Manfredi M.
Published: July 2002

The clinical effectiveness of plasma exchange (PE) and intravenous immunoglobulin infusion (IVIg) were compared in six patients during myastenic crisis. Five subjects had autoimmune myastenia and one myastenia‐like syndrome. Neurological examination showed low values of myastenic muscle score. The initial treatment was infusion of IVIg 0.4 gr/Kg/day for 5 days, but despite therapy, progressive dyspnea and worsening muscular weakness appeared. After a variable delay from the last IG infusion (from 2 to 12 days) patients underwent PE treatment (Dideco Vivacell 798DE System) for 8 days, receiving a daily, single‐volume exchange with 5% albumin replacement. After the fourth–fifth exchange, the patient weakness improved. Because PE started from 2 to 12 days after the last IVIg infusion, the therapeutic effect of PE did not depend on a delayed IVIg action. A spontaneous recovery also appears unlikely, because all the patients had severe, progressive neurological symptoms that proved insensitive to anticholinesterase drugs. A possible reason why IVIg proved ineffective is that the various immunoglobulin preparations differed in the proportion of specific antibody and therefore did not sufficiently counteract the patient's autoantibodies. In agreement with this hypothesis, others have recently described a remarkable post‐exchange response to IVIgs in a different dysimmune syndrome. PE was effective because it directly washed the autoantibodies off.

In conclusion, these findings lend support to the use of PE as first‐choice treatment in patients in myastenic crisis. Infusion of IgIV should be given only when PE is unavailable or contraindicated and supportive therapy alone proves inadequate.
MILD CARPAL TUNNEL SYNDROME: EARLY ELECTROPHYSIOLOGICAL DIAGNOSIS AND POST SURGICAL FOLLOW UP
Authors: Lanzillo B. , Nucciotti R. , Di Caprio G. , Crisci C. , Pappone N. , Saltalamacchia A.M. , Stancanelli A. , Caruso G.
Published: July 2002

We studied orthodromic sensory and motor conduction along median and ulnar nerves in 52 patients suspected for CTS (60 hands) and in 30 control subjects. Patients underwent electrophysiological examination before and up to 24 months after surgical decompression.

We evaluated the following electrophysiological tests:

1. sensory nerve conduction velocity (SNCV) from digit III and V to wrist (dSNCV) and from palm to wrist (pSNCV)

2. pSNCV/dSNCV ratio in median nerve

3. median/ulnar pSNCV ratio

4. Distal latency (DL)

5. SNAP and CMAP amplitudes.

In 3 patients, presurgical neurographic findings were normal. According to median dSNCV, the remaining 49 patients were classified into 3 groups: A = normal, B = mild slowing, C = marked slowing. In all B and C group patients, median pSNCV was significantly reduced. In group A, pSNCV was reduced in 16 patients (53%), pSNCV/dSNCV ratio was abnormal in 29 patients (97%), and median/ulnar pSNCV ratio in all subjects (100%). DL, SNAP, and CMAP amplitudes abnormalities were detected only in group B and C. Disease duration in the 3 goups was inversely correlated with SNCV and DL abnormalities.

After surgery, neurographic findings returned within the normal range earlier in group A, then in group B; group C showed an incomplete recovery of digit and palm SNCV at 24 months.

Median palm/digit SNCV and median/ulnar pSNCV ratios were the most sensitive tests, providing a reliable tool for the assessment of very early phase of CTS and for the subsequent surgery treatment.
CLINICAL AND IMMUNOLOGICAL FEATURES AND RESPONSE TO IVIg IN PATIENTS WITH CLINICALLY TYPICAL MULTIFOCAL MOTOR NEUROPATHY BUT NO OVERT CONDUCTION BLOCK
Authors: Nobile‐Orazio E. , Meucci N. , Terenghi F. , Bersano A. , Cappellari A. , Carpo M. , Barbieri S. , Scarlato G.
Published: July 2002

Multifocal motor neuropathy (MMN) is characterized by progressive asymmetric limb weakness usually predominant in the upper limbs associated with conduction block (CB) in motor but not sensory nerves. There are, however, occasional patients with clinically typical MMN in whom no CB can be detected. Whether these patients differ from patients with MMN and CB remains unclear. Since 1991, we have observed 24 patients with the typical clinical features of MMN. In 20 of them (14 men and 6 women), electrophysiological studies disclosed the presence of CB in at least one motor nerve. In four (all women), no evidence of CB could be detected in examined nerves even if three had some features of demyelination, including asymmetric reduction of motor conduction velocities (1 patient) or prolonged or absent F wave latencies (3 patients). Three of them had markedly reduced or absent proximal and distal CMAP amplitudes in some nerves. The mean age of onset of MMN was similar in patients with (41.5 years, range 21–70) and without CB (41.5 years, range 24–57). The mean duration of the disease at the time of our first visit was longer in patients without CB (18.5 years, range 13–25) than in those with CB (6.3 years, 3 months–25 years); only 3 patients with CB had a duration of the disease longer than 10 years. All patients without CB had a predominant or exclusive impairment of upper limbs compared with 18 (90%) of those with CB. The mean Rankin score before therapy was slightly worse in patients without (2.5) than with (2.2) CB. Anti‐ganglioside antibodies were found in 1 patient without CB (25%) and in 8 (40%) with CB. All but 2 patients with CB (90%) consistently improved with IVIg. All patients without CB also improved with IVIg, but only one did so consistently. In conclusion, patients with the typical clinical presentation of MMN but no overt CB are clinically and immunologically indistinguishable from those with MMN and CB. The longer duration of the disease and frequent axonal impairment in patients without CB may explain the lower efficacy of IVIg in these patients than in those with CB.
PARANEOPLASTIC PERIPHERAL NEUROPATHY
Authors: Quattrini A.
Published: July 2002

Paraneoplastic neurologic disorders are rare diseases that occur as a remote effect of cancer. Paraneoplastic syndrome may affect any portion of the nervous system, causing either diffuse or focal neurologic dysfunction. However, peripheral neuropathy is one of the most frequently encountered. Subacute sensory neuropathy, which usually occurs in patients with a previously undiscovered small‐cell lung carcinoma (SCLC), is believed to result from an immune reaction against a protein antigen(s) expressed jointly by neurons and tumor cells. Anti‐Hu antibodies are highly‐specific diagnostic markers for paraneoplastic sensory neuropathy/encephalomyelitis, which is nearly always associated with SCLC. Strong evidence suggests a pathogenic role for anti‐Hu antibodies.

Peripheral nerve disorders also occur with lymphoma and plasma cell dyscrasia. I shall briefly review the neuropathies observed in association with malignant dyscrasia, such as multiple myeloma, plasmacytoma, lymphoproliferative diseases, and amyloidosis.

Finally, peripheral neuropathy is an important and potentially dose‐limiting complication of the new chemotherapeutic agents, which are often used in treating solid tumors.
PURE MOTOR CIDP. A DISTINCT ENTITY?
Authors: Sabatelli M. , Madia F. , De Armas L. , Tonali P.
Published: July 2002

The spectrum of clinical, pathological, and electrophysiological features of CIDP is very heterogeneous. The onset may be acute or slowly progressive and clinical course monophasic or relapsing‐remitting. Motor‐sensory, ataxic sensory and pure motor variants have been described. The importance of the classification of CIDP is not an academic one, as each subtype might respond to specific treatments.

We describe clinical features and long term follow up of 4 patients affected by pure motor CIDP. 4 out of our 30 CIDP patients showed no clinical, electrophysiological, or (in three patients) sural nerve biopsy features of sensory fiber involvement. All four patients disclosed similar clinical, electrophysiological features: the age of onset was before 30 years, clinical course was relapsing‐remitting, and electrophysiological examination showed features of pure demyelinating neuropathy with normal distal CMAP amplitude and clear evidence of conduction blocks. None of them showed significant response to corticosteroids, while high‐dose intravenous immunoglobulins were very effective in all patients. Three patients showed marked improvement with interferon alpha therapy. Two patients showed marked myastenic‐like fluctuation of weakness

Our findings suggest that pure motor CIDP represents a distinct entity. Supported by Telethon Italy.
The emotional stroop task and chronic pain: what is threatening for chronic pain sufferers?
Authors: Crombez Geert , Hermans Dirk , Adriaensen Hugo
Published: July 2002

Using a computer version of the emotional stroop task, it was investigated whether chronic pain patients display an involuntary attentional shift towards pain‐related information (sensory, affective pain words and injury related words). Multiple regression analyses were used to investigate which pain and psychosocial variables (pain severity, pain‐related fear, pain catastrophizing and negative affect) were predictive of attentional bias. Results indicated: (1) that there was an attentional bias towards the sensory pain words; and (2) that current pain intensity was predictive of the effect. No other attentional effects were found. The results are discussed in terms of possible reasons for the difficulty of demonstrating attentional bias in chronic pain patients. Copyright 2000 European Federation of Chapters of the International Association for the Study of Pain
Structure and Development of the Axillary Complex and Extrafloral Nectaries in Capparis retusa Griseb.
Authors: Di Sapio O. A. , Gattuso M. A. , Prado D. E.
Published: July 2002

Abstract: The structure, organization and development of the axillary complex and extrafloral nectary in Capparis retusa Griseb. was analysed for the first time. The axillary complex presents three uniserial descending buds. Subordinated shoots originate from the distal and middle bud, while the proximal bud is usually quiescent. Close to the top of the axillary complex there is a subglobulous and umbilicated extrafloral nectary, normally visited by nectivore ants; a chronological coincidence between secretion, production and ant patrolling activities has been observed. The nectary structure differentiates at the second caulinar node, from an axillar meristem separated from the surrounding cells by a shell zone. On the fourth node a remarkably developed nectary primordium can be observed, inside which procambial strands develop acropetally. In the central region of the nectary primordium homogenous parenchyma differentiates progressively, later acquiring characteristics of nectariferous tissue. The mature nectary is vascularized by xylem and phloem, and the procambial differentiation is completed in a basipetal way. The first serial bud differentiates at the third node, from meristem cells near the base of its supporting leaf. The complex nodal structure with three buds completes its development at the eighth caulinar node. Ramular traces are observed as vascular semicylinders penetrating into the base of the buds to constitute a vascular system similar to that of the shoot. The scheme is repeated in the extrafloral nectary, giving rise to prolific branching in the periphery of the nectariferous tissue.
Semiconductor superlattice electron wave interference filters
Authors: Gaylord T. K. , Brennan K. F.
Published: July 2002

The quantitative analogies that have been established between electron wave propagation in semiconductors and optical wave propagation in dielectrics are used to demonstrate that high-resolution energy filters in semiconductors are possible. An example filter consisting of electron quarter-wavelength layers of GaAs and Ga0.55Al0.45As and a half-wavelength layer of GaAs is presented and theoretically analyzed. The pass electron energy is 0.139 eV and the passband is only 0.003 eV (2.2% of pass energy). Such a filter could be incorporated into semiconductor devices (e.g., as a hot-electron emitter in a ballistic transistor) or used to control free-space electron beams (e.g., in electron beam lithography).
Metalorganic chemical vapor deposition of PbTiO3 thin films
Authors: Kwak B. S. , Boyd E. P. , Erbil A.
Published: July 2002

PbTiO3 thin films have been grown successfully for the first time by using purely metalorganic precursors, namely, titanium isopropoxide and tetraethyllead. A scanning electron micrograph showed dense and noncolumnar growth with good surface morphology. Temperature-dependent x-ray diffraction studies provide evidences for a reversible tetragonal to cubic phase transition around 540 °C. At room temperature, the dielectric constant is about 180.
Long-lived InGaAs quantum well lasers
Authors: Fischer S. E. , Waters R. G. , Fekete D. , Ballantyne J. M. , Chen Y. C. , Soltz B. A.
Published: July 2002

Pseudomorphic InGaAs lasers with cw operating lifetimes exceeding 5000 h are reported for the first time. The device structure, grown by low-pressure metalorganic chemical vapor deposition, incorporates a single In0.37Ga0.63As strained-layer quantum well in a GaAs/AlGaAs graded-index separate confinement heterostructure. These devices are remarkable for their immunity to sudden failure and for their (gradual) degradation rates which are comparable to the best GaAs lasers.
Optical properties of SiC for crystalline/amorphous pattern fabrication
Authors: Derst G. , Wilbertz C. , Bhatia K. L. , Krätschmer W. , Kalbitzer S.
Published: July 2002

The optical contrast between crystalline and ion beam amorphized regions in SiC has been studied by transmission spectrometry for photon energies ranging up to the ultraviolet. The working range of such an optical device with crystalline/amorphous patterns, e.g., for use as a photolithographic mask, is extended to considerably higher photon energies than with Si as a recording material. Thus, SiC, in the form of thin crystalline layers on a transparent substrate, is a promising candidate for submicron structuring in various fields of application.
10 μm infrared hot-electron transistors
Authors: Choi K. K. , Dutta M. , Newman P. G. , Saunders M.-L. , Iafrate G. J.
Published: July 2002

A new hot-electron transistor for 10 μm infrared radiation detection is presented and discussed. The device utilizes an infrared sensitive GaAs/AlGaAs multiple quantum well structure as emitter, a wide quantum well as base, and a thick quantum barrier placed in front of the collector as an electron energy high pass filter. The energy filter selectively permits the higher energy photocurrent to pass to the collector; the lower energy dark current is rejected by the filter, and is drained through the base. The device detectivity, as noted by the collector photocurrent measurements, is much enhanced in comparison with companion infrared photoconductive devices.
Two-dimensional phase-locked arrays of vertical-cavity semiconductor lasers by mirror reflectivity modulation
Authors: Orenstein M. , Kapon E. , Stoffel N. G. , Harbison J. P. , Florez L. T. , Wullert J.
Published: July 2002

Coupling of two-dimensional (2D) vertical-cavity surface-emitting lasers (VCSELs) to give a coherent supermode is described. The top metal layer of a stained-layer InGaAs quantum well VCSEL structure was patterned laterally by depositing various metals with different optical reflectivities. This lateral reflectivity patterning defined a 2D laser array sharing the same ‘‘supercavity’’. It is shown that these 2D arrays oscillate in a stable single, coherent 2D supermode. This was achieved with a simple planar process and without significant deterioration of threshold current and efficiency relative to an equivalent broad-area VCSEL.
Feasibility of far-infrared lasers using multiple semiconductor quantum wells
Authors: Hu Qing , Feng Shechao
Published: July 2002

A feasibility study is performed for a new semiconductor multiple quantum well far-infrared (THz) laser device, based on selective injection of electrons into an upper subband, and selective removal from a lower subband of a quantum well, using quantum-well energy filters. Photon confinement is achieved between doped injector and collector semiconductor contacts which also serve as good photon reflectors. The lasing threshold current density is estimated to be in the range of Jth∼130 A/cm2 at 5 THz. Thus the feasibility of a far-infrared laser based on this design and operating at cryogenic temperatures (≤10 K) seems quite promising.
Polarization-dependent optical nonlinearities in fractional-layer superlattices
Authors: Chavez-Pirson A. , Yumoto J. , Ando H. , Fukui T. , Kanbe H.
Published: July 2002

We measure the room-temperature polarization-dependent nonlinear absorption and refractive-index spectra of a (Al0.5Ga0.5As)1/2(GaAs)1/2 fractional-layer superlattice (FLS) structure grown by metalorganic chemical vapor deposition. The anisotropic nonlinear effects between the directions parallel and perpendicular to the superlattice give rise to a nonlinear optical birefringence in the plane of the growth surface. From our measurements using a femtosecond optical pulse, we derive the magnitude and spectral shape of the nonlinear optical birefringence. We describe the basis of an all-optical polarization rotation switch using the FLS structure.
Replication of 50-nm-linewidth device patterns using proximity x-ray lithography at large gaps
Authors: Chu W. , Smith Henry I. , Schattenburg M. L.
Published: July 2002

We demonstrate the replication of device patterns consisting of interdigital lines ∼50 nm wide on 100 nm pitch using 1.32 nm x rays at a mask-to-substrate gap of 2.72 μm. The exposure latitude exceeds the factor 2.3 at this gap. From the expression that relates gap, G, linewidth, W, and wavelength λ (i.e., G=αW2/λ), we obtain α=1.44, which is well beyond the predictions of previous theoretical analyses based on the Kirchhoff boundary conditions. We attribute this disparity to the fact that an x-ray absorber is a lossy dielectric, hundreds of wavelengths thick, and hence the Kirchhoff boundary conditions are not applicable.
In situ definition of semiconductor structures by selective area growth and etching
Authors: Colas E. , Caneau C. , Frei M. , Clausen E. M. , Quinn W. E. , Kim M. S.
Published: July 2002

Selective area growth (etching) by low-pressure organometallic chemical vapor deposition (LP-OMCVD) is utilized to intentionally modulate the local growth (etch) rate by choosing the pattern of dielectric-masked areas, thereby defining III-V semiconductor structures in situ. This technique is applied to tune the emission wavelength of a GaAs/AlGaAs quantum well structure, and to obtain InP/InGaAs superlattice structures tapered in thickness with growth rate increases as high as 800%, suitable for integrated optics applications. In contrast, selective deposition by organometallic molecular beam epitaxy (OMMBE) does not produce growth rate enhancements, thereby preventing similar in situ definition schemes but allowing to integrate structures with optimized nominal thicknesses.
Transmission resonances and zeros in quantum waveguides with resonantly coupled cavities
Authors: Porod Wolfgang , Shao Zhi-an , Lent Craig S.
Published: July 2002

We report on the existence of transmission zeros in quantum waveguide structures with resonantly coupled cavities. Such zeros do not occur in the usual double-barrier resonant tunneling systems. For quantum waveguides, the transmission probability exhibits pairs of poles and zeros in the complex-energy plane. The observed sharp structure of the transmission resonances and zeros can be understood in terms of these zero-pole pairs.
Quantum wells with localized states at energies above the barrier height: A Fabry–Perot electron filter
Authors: Sirtori Carlo , Capasso Federico , Faist Jerome , Sivco Deborah L. , Chu Sung-Nee G. , Cho Alfred Y.
Published: July 2002

The observation of electronic states localized in a quantum well at energies greater than the barrier height is reported. In our GaInAs wells quantum confinement is achieved at an energy corresponding to a continuum transmission resonance using as barriers high reflectivity AlInAs/GaInAs quarter-wave stacks. The latter strongly narrow the resonance, thus forming a high finesse Fabry–Perot electron filter. Intersubband infrared absorption measurements at 300 K reveal a strong narrowing of the transition to a localized state above the well as the number of periods in the λ/4 stacks is increased. The narrowest absorption peaks exhibit widths equal to those of bound-to-bound state transitions in GaInAs wells with thick AlInAs barriers.
Condensed chlorine etching of GaAs induced by excimer laser radiation
Authors: Shih M. C. , Freiler M. B. , Haase G. , Scarmozzino R. , Osgood R. M.
Published: July 2002

We report excimer-laser-induced etching of GaAs surfaces covered with a layer of condensed Cl2. The experiments were performed at low temperatures (120–150 K) and in a chlorine ambient (P=1–40 mTorr). Spatially well-resolved, anisotropic etching has been demonstrated with an observed etch rate of 0.25 Å/pulse (0.1 μm/min for typical parameters). The etch rate is characterized as a function of the various system parameters (pressure, temperature, laser repetition rate, and fluence, etc.), and a model is proposed to describe the etching mechanism.
Low pressure metalorganic chemical vapor deposition of AIN over sapphire substrates
Authors: Asif Khan M. , Kuznia J. N. , Skogman R. A. , Olson D. T. , Mac Millan M. , Choyke W. J.
Published: July 2002

In this letter we report the deposition of high quality single-crystal films of AIN over basal plane sapphire substrates. A conventional low pressure metalorganic chemical vapor deposition (LPMOCVD) system was used for all the growths reported here. We present the results of conventional and switched atomic layer epitaxial (SALE) depositions. Conventional LPMOCVD yielded single-crystal AIN films at temperatures in excess of 750 °C. The ALE process in contrast produced extremely smooth single-crystal AIN layers at temperatures as low as 450 °C. To the best of our knowledge this is the lowest ever reported for chemical vapor deposition of single-crystal AIN. X-ray and optical characterization data are presented to compare the quality of the material resulting from the two deposition techniques.
Picosecond carrier lifetime in erbium-doped-GaAs
Authors: Gupta S. , Sethi S. , Bhattacharya P. K.
Published: July 2002

The dependence of free-carrier lifetime on erbium concentration has been measured in molecular-beam epitaxial GaAs epilayers doped with erbium. A gradual reduction in the lifetime is observed with increased dopant incorporation. For a high doping concentration in the range of 1019 cm−3 or greater, a carrier lifetime of ∼1 ps is obtained. Due to the high resistivity of these epilayers, they can also be used as a photoconductive switch, with good responsivity. This leads to new and novel applications for rare-earth doped III-V semiconductors.
Homoepitaxial growth of InP on (111)B substrates by gas-source molecular beam epitaxy
Authors: Hou H. Q. , Tu C. W.
Published: July 2002

InP has been homoepitaxially grown on both exactly (111)B oriented and misoriented substrates by gas-source molecular beam epitaxy. The optimal growth condition for obtaining a mirrorlike surface was found to be a substrate misorientation of 0.5°–1° toward 〈110〉, a substrate temperature of 470 °C, and a V/III incorporation ratio close to unity. The unity V/III ratio was established readily by monitoring the specular beam intensity of reflection high-energy electron diffraction when the phosphorus beam was modulated, similar to migration enhanced epitaxy. The InP epilayers with specular surfaces are of high quality as characterized by x-ray diffraction, Hall measurements, and low-temperature photoluminescence.
Electroabsorption in InGaAsP: electro-optical modulators and bistable optical switches
Authors: Knüpfer B. , Kiesel P. , Höfler A. , Riel P. , Döhler G. H. , Veuhoff E.
Published: July 2002

We report Franz–Keldysh absorption spectra of InGaAsP obtained from transmission and photoresponse measurements in InP/InGaAsP/InP p-i-n double heterostructures. The values of the absorption changes (Δαmax≊3000 cm−1) are comparable with those obtained from the quantum-confined Stark effect. Optical bistability is observed at very low light intensities (40 μW/cm−2), due to very low leakage currents and the strong absorption changes above the band gap.
Deposition of highly resistive, undoped, and p-type, magnesium-doped gallium nitride films by modified gas source molecular beam epitaxy
Authors: Wang Cheng , Davis Robert F.
Published: July 2002

Undoped, highly resistive (≳102 Ω cm) and Mg-doped, p-type (0.3 Ω cm) monocrystalline GaN films with a thickness of (4–5)×103 Å have been achieved via modified gas source molecular beam epitaxy on AIN buffer layers without the post-processing procedures of either electron beam irradiation or annealing necessary in chemical vapor deposition (CVD) derived films. The carrier concentrations and mobilities could not be accurately measured in the undoped films; values to 1018 cm−3 and 10 cm2/V s, respectively, have been achieved in the p-type films. These results indirectly support the hypothesis of Mg-H complexes as the cause of the difficulty in achieving highly conducting p-type materials using CVD techniques.
Cavity design for improved electrical injection in InAlGaP/AlGaAs visible (639–661 nm) vertical-cavity surface-emitting laser diodes
Authors: Schneider R. P. , Lott J. A.
Published: July 2002

A novel optical cavity design for improved electrical injection in visible vertical-cavity surface-emitting laser (VCSEL) diodes employing an InGaP/InAlGaP strained quantum-well active optical cavity and AlAs/Al0.5Ga0.5As distributed Bragg reflectors (DBRs) is described. The cavity design was determined by measuring the lasing threshold current density of visible edge-emitting laser diodes with AlAs/Al0.5Ga0.5As DBR cladding layers. By inserting InAlP spacer layers between the active region and the DBR cladding, significant improvement in the performance of the edge-emitting lasers was achieved. This approach was then applied to the design of visible VCSEL diodes, and resulted in the first demonstration of room-temperature electrically injected lasing, over the wavelength range 639–661 nm. The visible VCSELs, with a diameter of 20 μm, exhibit pulsed output power of 3.4 mW at 650 nm, and continue to lase at a duty cycle of 40%. The threshold current was 30 mA, with a low threshold voltage (2.7 V) and low series resistance (<15 Ω).
Selective encapsulation of the carbides of yttrium and titanium into carbon nanoclusters
Authors: Seraphin Supapan , Zhou Dan , Jiao Jun , Withers James C. , Loutfy Raouf
Published: July 2002

Characterization of the arc-discharge deposits at the cathode from anodes containing yttrium oxide and titanium by transmission electron microscopy and x-ray diffraction shows different results with respect to an encapsulation of the metal carbides into carbon clusters. Yttrium carbide is encapsulated into carbon nanoclusters in a crystalline phase. The formation of titanium carbide, on the other hand, preempts the formation of the carbon—carbon bonds necessary to form the carbon cages, so that only titanium carbide clusters are observed. Thermodynamic data support the interpretation of the results.
Bundles of carbon nanotubes generated by vapor-phase growth
Authors: Ge Maohui , Sattler Klaus
Published: July 2002

Bundles of nanotubes were produced by vapor-phase condensation of carbon on highly oriented pyrolytic graphite and analyzed by scanning tunneling microscopy. The bundles are found to have widths between 15 and 50 nm, and up to 200 nm long. They are composed of concentric tubules with 2–4 nm in diameter. Atomic resolution images reveal their graphitic surface structure.
Ballistic-electron emission microscopy study of the Au/Si(111)7×7 and Au/CaF2/Si(111)7×7 interfaces
Authors: Cuberes M. T. , Bauer A. , Wen H. J. , Prietsch M. , Kaindl G.
Published: July 2002

Ballistic-electron emission microscopy (BEEM) has been performed on Au/n-Si(111)7×7 and Au/CaF2/n-Si(111)7×7 in UHV. In both cases, the topography of the Au surface is characterized by ≊2.5 Å height terraces, stacked in several stages, with rounded shapes for Au/Si, and hexagonal shapes for Au/CaF2/Si. BEEM up to tip voltages of 8 V on Au/Si is not altering the ballistic transmissivity, in contrast to previous work on Au/Si interfaces which involved chemical preparations of the Si surfaces. The shape of the BEEM spectra on Au/CaF2/Si depends on spectral features of the density of states of the CaF2 thin film.
Growth-induced uniaxial in-plane magnetic anisotropy for ultrathin Fe deposited on MgO(001) by oblique-incidence molecular beam epitaxy
Authors: Park Yongsup , Fullerton Eric E. , Bader S. D.
Published: July 2002

In-plane uniaxial magnetic anisotropy is observed in the magnetic hysteresis loops of ultrathin Fe films grown on MgO(001) by means of oblique-incidence molecular beam epitaxy. The films are deposited from an angle of 45° from the surface normal in the (100) azimuth toward the [100]. The easy axis of magnetization is perpendicular to the incident Fe-beam direction. A strong structural asymmetry is observed in x-ray photoelectron diffraction and attributed to an oriented morphology that drives the growth-induced magnetic anisotropy.
Hot electron transport in SiO2 probed with a scanning tunnel microscope
Authors: Ludeke R. , Bauer A. , Cartier E.
Published: July 2002

Hot electrons injected with a scanning tunnel microscope (STM) tip into Pt/SiO2/Si(100) structures were detected as a collector current in the Si by using a STM configuration known as ballistic electron emission microscopy. The collector current, observed for STM tip potentials ≳4 V and for oxide biases ≥0 V, is direct evidence for electron transmission through the conduction band of the SiO2. Negative oxide biases delayed the onset of current to correspondingly higher tip potentials. A simple model was used to extract the energy and bias dependent transmission probabilities from the experimental data for a 62 Å SiO2 layer. The results are compared with Monte Carlo calculations.
Poly(p-phenylene vinylene)/tris(8-hydroxy) quinoline aluminum heterostructure light emitting diode
Authors: Wu C. C. , Chun J. K. M. , Burrows P. E. , Sturm J. C. , Thompson M. E. , Forrest S. R. , Register R. A.
Published: July 2002

Results are presented from polymer/molecular organic heterostructure light emitting diodes composed of a layer of the conjugated conducting polymer poly(p-phenylene vinylene) (PPV), and a layer of fluorescent molecular compound tris(8-hydroxy) quinoline aluminum (Alq). The external quantum efficiency of these heterostructure LEDs is ∼0.1%, which is over one order of magnitude higher than that of simple PPV LEDs. The electroluminescence (EL) spectra indicate that both materials in the device emit comparable amounts of light. The dependence of the EL spectra on the layer thicknesses and its independence on bias suggest that neutral excitons are formed in the Alq, far from the PPV/Alq interface, and subsequently diffuse into the PPV layer.
Improved scanning ion-conductance microscope using microfabricated probes
Authors: Prater C. B. , Hansma P. K. , Tortonese M. , Quate C. F.
Published: July 2002

The scanning ion-conductance microscope (SICM) is a member of the growing family of scanning probe microscopes, which includes the scanning tunneling microscope and the atomic force microscope. The SICM scans a small aperture over a sample immersed in electrolyte and measures the ionic current flowing through the aperture. This current serves as the feedback signal for standard scanning probe microscope electronics, which can then provide images of the topography of a sample surface, or the distribution of ionic current flow through the pores in a porous sample. The resolution of this microscope is essentially set by the size of the aperture. We have developed silicon microfabricated probes for the SICM that greatly improve its performance. Previous SICMs used fragile glass micropipettes as probes. The new microfabricated probes are end caps for a 1.5 mm glass capillary. A hollow tip is fabricated in the center of a silicon membrane. An aperture is formed at the tip apex using microfabrication techniques including photolithography and etching, giving typical minimum diameters of 250 nm. Unlike the glass micropipettes used previously, the new tips are compact and hence mechanically robust. The tips are mounted on a flexible membrane that allows the tip to deflect away from the surface in case of a collision with the sample surface. In addition, the microfabricated probes have been designed to have a high mechanical resonant frequency, allowing scan speeds up to 50 times faster than used with glass micropipette probes. With these new probes we have imaged the surface topography of a plastic diffraction grating, and the ion flow through porous polycarbonate membrane filters. Finally, the new microfabricated probe was designed as a general probe that may be adapted for use in other scanning probe microscopes.
Real-time sampling electronics for double modulation experiments with Fourier transform infrared spectrometers
Authors: Green Michael J. , Barner Barbara J. , Corn Robert M.
Published: July 2002

A novel synchronous real-time analog sampling method for obtaining the sum and difference interferograms in double modulation Fourier transform infrared absorption experiments is described, and the application of this sampling methodology to polarization-modulation FTIR measurements of thin films at metal surfaces is demonstrated. A quadratic approximation of the background signal is used to calculate the difference interferogram. The demodulation of a test waveform with the real-time sampling electronics reveals how the bandwidth limitations of previous double modulation experiments on FTIR interferometers that employed lock-in amplifiers have been eliminated.
Relationship between extraction of H− ions optimized by plasma grid potential and plasma parameters in a bucket source
Authors: Fukumasa Osamu , Hosoda Masayuki , Naitou Hiroshi
Published: July 2002

Although optimizing the magnetic filter position and the plasma grid potential is one of the most effective factors to enhance H− yield, details concerning their roles are not now clarified well. In this article, spatially resolved measurements of the electron energy distribution function, plasma fluctuations, and plasma parameters are presented. On the basis of these experimental results, we will discuss the roles of both the magnetic filter and the plasma grid biasing voltage Vb on enhancement of H− production and extraction of H− ions.
20 years of cesium catalysis for negative ion production in gas discharges (invited)
Authors: Dudnikov V. G.
Published: July 2002

Cesium catalysis, considerable acceleration of negative ion production in a gas discharge by injecting a small admixture of cesium or other substances with low ionization potential (for example, the first or the second group elements), is used now very widely in ion sources. The cesium injection turns on the catalysis of negative ion production on the electrodes surface, bombarded by particles from discharge plasma. The cesium adsorption significantly increases the probability of the electron capture from the electrode surface to the electron affinity levels of sputtered and reflected particles by decreasing the surface work function from 4–5 eV up to 1.5 eV. It increases considerably negative ion containment in particle flux from the surface. Ion sources using cesium catalysis have been named surface plasma sources (SPS), because for their operation a strong interaction of gas discharge plasma with a surface is very important. However, volume negative ion production depends on cesium admixture and surface processes also. Highly efficient cesium catalysis has been discovered in Novosibirsk Institute of Nuclear Physics on July 1, 1971. During 20 years in many laboratories around the world wide investigations of physics processes in surface-plasma sources have been executed. Various types of SPS, optimized for different applications in accelerators, in plasma physics and thermonuclear research, in technology, have been developed. The distinctive features of physical processes in SPS and technological development for high efficient SPS operation are reviewed in presented papers.
An observation chamber for light-microscopical studies of bacterial motility at high temperatures
Authors: Gluch M. F. , Gatz R. , Baumeister W.
Published: July 2002

The design of a temperature-controlled observation chamber is described, that allows light-microscopic studies of the motile behavior of thermophilic bacteria at temperatures up to 100 °C. The chamber is built for use on an inverted light microscope. Heating and cooling is performed by Peltier elements, with a maximum rate of temperature change of 2 °C/s. The temperature is controlled via a personal computer with an accuracy of ±0.25 °C.
Investigation of a large volume negative hydrogen ion source
Authors: Courteille C. , Bruneteau A. M. , Bacal M.
Published: July 2002

The electron and negative ion densities and temperatures are reported for a large volume hybrid multicusp negative ion source. Based on the scaling laws an analysis is made of the plasma formation and loss processes. It is shown that the positive ions are predominantly lost to the walls, although the observed scaling law is n+∝I0.57d. However, the total plasma loss scales linearly with the discharge current, in agreement with the theoretical model. The negative ion formation and loss is also discussed. It is shown that at low pressure (1 mTorr) the negative ion wall loss becomes a significant part of the total loss. The dependence of n−/ne versus the electron temperature is reported. When the negative ion wall loss is negligible, all the data on n−/ne versus the electron temperatures fit a single curve.
High resolution bolometry on the Alcator C-Mod tokamak (invited)
Authors: Boivin R. L. , Goetz J. A. , Marmar E. S. , Rice J. E. , Terry J. L.
Published: July 2002

Recent breakthroughs in silicon detector technology now permit measurement of radiated power over a wide range in photon energies. These detectors (also known as AXUV photodiodes) have a flat spectral power response from ultraviolet to x-ray energies, and with a slightly reduced efficiency all the way down to visible wavelengths. Since they can be made small, multichannel detectors allow high spatial resolution to be combined with an intrinsic high temporal resolution, which can reach the microsecond range, depending on the application. Additional features include ease of use and installation, and relatively low cost compared to other techniques. A combination of two multichannel toroidally viewing systems has been recently installed on the Alcator C-Mod tokamak. The first array, which is composed of 16 channels, sees tangentially the outer-half of the plasma at the midplane, and is used to measure the total power radiated. The second array, also located at the midplane, consists of 19 channels and views the edge of the plasma. This array has a 2 mm radial resolution, allowing, for example, the study of edge dynamics in high confinement (H mode) plasmas. Because these detectors are largely insensitive to neutral particles (at least at particle energies of interest), it is now possible to measure the radial distribution of neutral “radiated” power emissivity, by looking at the difference between these measurements and those obtained with standard bolometers. When neutrals are not important, we found a very good agreement between the AXUV detectors and standard bolometers. Examples of applications of these measurements to the study of edge H-mode dynamics, impurity injection, disruptions, and internal barrier formation, are described. Planned upgrades and new applications for Alcator C-Mod are also discussed.
Subresolution axial distance measurements in far-field fluorescence microscopy with precision of 1 nanometer
Authors: Schmidt Michael , Nagorni Matthias , Hell Stefan W.
Published: July 2002

Fluorescent objects closer than the diffraction resolution limit can be distinguished in far-field microscopy provided they feature different emission spectra. Utilizing the superior axial resolution of 4Pi-confocal microscopy of 100–150 nm, we investigate the precision with which fluorescence objects with subdiffraction axial distance can be measured in the far field. At a wavelength of 820 nm distances on the order of 60 nm between beads and a monomolecular Langmuir–Blodgett layer were determined with a precision of 1.2 nm within 3.2 s. The reduced spatial extent of the 4Pi-confocal point-spread-function improves the precision of colocalization measurements in double stained specimens and opens up the prospect on far-field fluorescence profilometry with (sub) nanometer height resolution.