Extremely high frequency Schottky diodes based on single GaN nanowires.

Gallium nitride (GaN) is one of the most promising materials for high-frequency devices owing to its prominent material properties. We report on the fabrication and study of a series of Schottky diodes in the ground-signal-ground topology based on individual GaN nanowires. The electrical characterization ofI-Vcurves demonstrated relatively high ideality factor value (about 6-9) in comparison to the planar Au/GaN diodes that can be attributed to the nanowire geometry. The effective barrier height in the studied structures was defined in the range of 0.25-0.4 eV. The small-signal frequency analysis was employed to study the dependency of the scattering parameters in the broad range from 0.1 to 40 GHz. The approximation fitting of the experimental data indicated the record high cutoff frequency of about 165.8 GHz.

Formation of wurtzite sections in self-catalyzed GaP nanowires by droplet consumption.

Wurtzite GaP nanowires are interesting for the direct bandgap engineering and can be used as templates for further growth of hexagonal Si shells. Most wurtzite GaP nanowires have previously been obtained with Au catalysts. Here, we show that long (∼500 nm) wurtzite sections are formed in the top parts of self-catalyzed GaP nanowires grown by molecular beam epitaxy on Si(111) substrates in the droplet consumption stage, which is achieved by abruptly increasing the atomic V/III flux ratio from 2 to 3. We investigate the temperature dependence of the length of wurtzite sections and show that the longest sections are obtained at 610 °C. A supporting model explains the observed trends using a phase diagram of GaP nanowires, where the wurtzite phase is formed within a certain range of the droplet contact angles. The optimal growth temperature for growing wurtzite nanowires corresponds to the largest diffusion length of Ga adatoms, which helps to maintain the required contact angle for the longest time.

Fabrication and electrical study of large area free-standing membrane with embedded GaP NWs for flexible devices.

Flexible optoelectronic structures are required in a wide range of applications. Large scale modified silicone-embedded n-GaP nanowire arrays of a record 6 µm thin membranes were studied. A homogeneous silicone encapsulation was enabled by G-coating using a heavy-load centrifuge. The synthesized graft-copolymers of polydimethylsiloxane (PDMS) and polystyrene demonstrated two times lower adhesion to Si compared to standard PDMS, allowing 3 square inch area high quality silicone/nanowire membrane mechanical release, preserving the growth Si substrate for a further re-use after chemical cleaning. The 90% transparent single-walled carbon nanotubes electrical contacts to the embedded n-GaP nanowires demonstrated mechanical and electrical stability. The presented methods can be used for the fabrication of large scale flexible inorganic optoelectronic devices.

Hydrogen passivation of the n-GaN nanowire/p-Si heterointerface.

The influence of hydrogen plasma treatment on the electrical and optical properties of vertical GaN nanowire (NW)/Si heterostructures synthesized via plasma assisted molecular beam epitaxy is studied. The effect of the treatment is thoroughly studied via variation of the passivation duration. Photoluminescence investigation demonstrates that the passivation affects the doping of the GaN NWs. The samples were processed as photodiodes with a top transparent electrode to obtain detailed information about the n-GaN NWs/p-Si heterointerface under illumination. The electron beam induced current measurements demonstrated the absence of potential barriers between the active parts of the diode and the contacts, indicating ohmic behavior of the latter. I-V characteristics obtained in the dark and under illumination show that hydrogen can effectively passivate the recombination centers at the GaN NWs/Si heterointerface. The optimum passivation duration, providing improved electrical properties, is found to be 10 min within the studied passivation regimes. It is demonstrated that longer treatment causes degradation of the electrical properties. The discovered phenomenon is discussed in detail.

Effects of the surface preparation and buffer layer on the morphology, electronic and optical properties of the GaN nanowires on Si.

The role of Si (111) substrate surface preparation and buffer layer composition in the growth, electronic and optical properties of the GaN nanowires (NWs) synthesized via plasma-assisted molecular beam epitaxy is studied. A comparison study of GaN NWs growth on the bare Si (111) substrate, silicon nitride interlayer, predeposited AlN and GaO x buffer layers, monolayer thick Ga wetting layer and GaN seeding layer prepared by the droplet epitaxy is performed. It is demonstrated that the homogeneity and the morphology of the NW arrays drastically depend on the chosen buffer layer and surface preparation technique. An effect of the buffer and seeding layers on the nucleation and desorption is also discussed. The lowest NWs surface density of 14 µm-2 is obtained on AlN buffer layer and the highest density exceeding the latter value by more than an order of magnitude corresponds to the growth on the 0.3 ML thick Ga wetting layer. It is shown, that the highest NWs mean elongation rate is obtained with AlN buffer layer, while the lowest elongation rate corresponds to the bare Si (111) surface and it is twice as lower as the first case. It is found, that use of AlN buffer layer corresponds to the most homogeneous NWs array with the smallest length dispersion while the least homogeneous array corresponds to the bare Si substrate. Vertically aligned GaN NWs array on the wide bandgap GaO x semiconductor buffer layer grown by plasma-enhanced chemical vapor deposition demonstrates its potential for electronic applications. Photoluminescence (PL) study of the synthesized samples is characterized by an intense optical response related to the excitons bound to neutral donors. The highest PL intensity is obtained in the sample with AlN buffer layer.

High power single-mode delivery of mid-infrared sources through chalcogenide fiber.

Mechanically robust and low loss single-mode arsenic sulfide fibers are used to deliver high power mid-infrared sources. Anti-reflection coatings were deposited on the fiber facets, enabling 90% transmission through 20 cm length fibers. 10.3 W was transmitted through an anti-reflection coated fiber at 2053 nm, and uncoated fibers sustained 12 MW/cm2 intensities on the facet without failure. A Cr:ZnSe laser transmitted >1 W at 2520 nm, and a Fe:ZnSe laser transmitted 0.5 W at 4102 nm. These results indicate that by improving the anti-reflection coatings and using a high beam quality mid-infrared source, chalcogenide fibers can reliably deliver ≥10 W in a single mode, potentially out to 6.5 µm.

[Endosurgery of benign diseases and injuries of esophagus].

AIM: To analyze the results of endoscopic interventions for benign diseases and injuries of the esophagus. MATERIAL AND METHODS: 159 patients with benign diseases and perforation of the esophagus were operated. There were 72 (45.3%) cases of achalasia, 56 (35.2%) with post-ambustial stenosis of esophagus, 14 (8.8%) with esophageal perforation, 13 (8.2%) with leuomyoma of esophagus and 4 (2.5%) with diverticulum of thoracic esophagus. RESULTS AND DISCUSSION: In long-term period 56 patients with achalasia were followed-up after laparoscopic Heller cardiomyotomy with Dor fundoplication. Good results were observed in all cases. Three patients died in early postoperative period after thoracoscopic extirpation of esophagus with esophagoplasty via laparotomy at the stage of development of the technique. There were no deaths after thoracoscopic extirpation of esophagus with simultaneous laparoscopic gastroplasty. Postoperative period was significantly less after thoracoscopic extirpation of esophagus with simultaneous laparoscopic esophagogastroplasty using whole stomach compared with esophagogastroplasty and esophagocoloplasty via laparotomy. In long-term postoperative period different complications occurred in 17 cases. Two patients with esophageal perforation died after video-assisted laparotranshiatal drainage of posterior mediastinum. Scarring of esophageal defect was observed in others. Seam failure after esophageal leuomyoma removal was diagnosed in 2 patients that required video-assisted laparotranshiatal drainage of posterior mediastinum and Maydl jejunostomy. Seam failure in thoracic esophagus after thoracoscopic removal of diverticulum was observed in 1 case. The complication was cured by video-assisted laparotranshiatal drainage of posterior mediastinum.

[Endoscopic surgery for benign diseases and injuries of the esophagus (with commentary)]. / Endokhirurgiya dobrokachestvennykh zabolevanii i povrezhdenii pishchevoda (s kommentariem).

AIM: To analyze the results of surgical treatment of patients with benign diseases and injuries of the esophagus. MATERIAL AND METHODS: We summarized the experience of different endoscopic interventions in 159 patients with various benign diseases and perforation of the esophagus. Patients with achalasia (72 cases) underwent videolaparoscopic Geller's esophagomyotomy with anterior hemiesophagofundoplication by Dor. Video-assisted thoracoscopic extirpation of the esophagus with simultaneous or delayed esophagocolo/gastroplasty was performed in 56 patients with post-ambustial cicatricial stenosis of the esophagus. Patients with esophageal perforation (14 cases) underwent videolaparoscopic transhiatal mediastinal drainage. Esophageal leiomyoma has been excised through thoracoscopic (9 cases) or laparoscopic access (4 cases). Removal of esophageal diverticulum was made via VATS-access in 4 patients. RESULTS: Satisfactory early and remote results were achieved in all patients with achalasia. Mortality rate was 5.4% (3 out of 56 patients) and 14.3% (2 out of 14 patients) in groups of cicatricial esophageal stenosis and esophageal perforation respectively. Sutures failure after removal of the diverticulum and leiomyoma occurred in 2 and 1 patient respectively and has been successfully cured. CONCLUSION: Endoscopic technologies allow to perform successfully complex reconstructive interventions for dysphagia in patients with cicatricial esophageal stenosis and achalasia even at late stages, to remove benign tumors and diverticula of thoracic esophagus and provide adequate drainage of posterior mediastinum in case of esophageal perforation.

Mid-IR photoluminescence of Fe(2+) and Cr(2+) ions in ZnSe crystal under excitation in charge transfer bands.

Spectroscopic characterization of Fe:ZnSe(Cr:ZnSe) crystals under visible excitation into the charge transfer bands of Transition Metal ions were studied. The excitation efficiencies of mid-IR photoluminescence between (5)T(2)((5)E) and (5)E((5)T(2)) states via direct relaxation to the upper laser levels and via metastable upper (3)T(1) were investigated. It was demonstrated that the latter route is the dominant process for Cr(2+) ions and could provide sufficient pump rate for mid-IR lasing. The pump efficiencies via direct relaxation to the upper laser levels were estimated to be <2% for both ions under 532 nm excitation wavelength.

Crystalline Cr²âº:ZnSe/chalcogenide glass composites as active mid-IR materials.

We propose new transition metal (TM)-doped ZnSe/As2S3:As2Se3 composite materials for mid-IR fiber lasers. The composites are the suspension of crystalline micro- and nanosized TM²âº:ZnSe or TM²âº:ZnS powders in chalcogenide glasses with the refraction index matching. Mid-IR room-temperature lasing of Cr²âº:ZnSe/As2S3:As2Se3 microcomposite material is demonstrated at the 2.4 µm wavelength.

Mid-IR laser oscillation in Cr2+:ZnSe planar waveguide.

We demonstrate 2.6 µm mid-infrared lasing at room temperature in a planar waveguide structure. Planar waveguides were fabricated using pulsed laser deposition (PLD) by depositing chromium doped zinc selenide thin films on sapphire substrate (Cr2+:ZnSe/sapphire). Highly doped Cr2+:ZnSe/Sapphire thin film sample was also used to demonstrate passive Q-switching of Er:YAG laser operating at 1.645 µm.

10-watt, pure continuous-wave, polycrystalline Cr2+:ZnS laser.

We demonstrate, for the first time, 10 W, Er-fiber laser pumped, pure CW, thermally diffusion doped, polycrystalline Cr(2+):ZnS laser operating at 2380 nm. We also show Littrow-grating, "single-knob", wavelength tuning of the laser spanning 1940-2780 nm spectral range with the maximum output power of 7.4 W near the central wavelength of 2400 nm and above 2 W over 1970-2760 nm wavelength range. The laser performs with 40% real optical- and 43% slope efficiency, and shows no output power roll-off up to the highest available incident pump power of 27 W.

[Maintaining of the morphological specificity and genetic introgression in populations of the great tit Parus major and the Japanese tit P. minor in the middle Amur region].

The ranges of the great tit Parus major and the Japanese tit P. minor overlap in the middle Amur region, where hybridization of these two species occur. These species have contacted for nearly a century on the western slope of the Malyi Khingan Ridge (the central part of the sympatry zone), but the great tit has colonized territories to the east of the ridge only in the last two decades. The percentage of the P. minor's allele of intron 2 of the mioglobin gene has significantly increased from 8.9% in the west to 27.8% in the east in phenotypically major's populations. Thus, the percentage of foreign mtDNA in P. major populations did not change significantly from west (6.2%, n = 120) to east (3.2%, n = 61). Simultaneous use of two genetic markers (one nuclear and the other mitochondrial) supports our conclusion on strong introgression in the populations of both species, which nevertheless maintain their morphological specificity in the contact zone.

Canine and human sinoatrial node: differences and similarities in the structure, function, molecular profiles, and arrhythmia.

The sinoatrial node (SAN) is the primary pacemaker in canine and human hearts. The SAN in both species has a unique three-dimensional heterogeneous structure characterized by small pacemaker myocytes enmeshed within fibrotic strands, which partially insulate the cells from aberrant atrial activation. The SAN pacemaker tissue expresses a unique signature of proteins and receptors that mediate SAN automaticity, ion channel currents, and cell-to-cell communication, which are predominantly similar in both species. Recent intramural optical mapping, integrated with structural and molecular studies, has revealed the existence of up to five specialized SAN conduction pathways that preferentially conduct electrical activation to atrial tissues. The intrinsic heart rate, intranodal leading pacemaker shifts, and changes in conduction in response to physiological and pathophysiological stimuli are similar. Structural and/or functional impairments due to cardiac diseases including heart failure cause SAN dysfunctions (SNDs) in both species. These dysfunctions are usually manifested as severe bradycardia, tachy-brady arrhythmias, and conduction abnormalities including exit block and SAN reentry, which could lead to atrial tachycardia and fibrillation, cardiac arrest, and heart failure. Pharmaceutical drugs and implantable pacemakers are only partially successful in managing SNDs, emphasizing a critical need to develop targeted mechanism-based therapies to treat SNDs. Because several structural and functional characteristics are similar between the canine and human SAN, research in these species may be mutually beneficial for developing novel treatment approaches. This review describes structural, functional, and molecular similarities and differences between the canine and human SAN, with special emphasis on arrhythmias and unique causal mechanisms of SND in diseased hearts.

Tunable, single-frequency, and multi-watt continuous-wave Cr2+:ZnSe lasers.

We demonstrate CW rapidly-tunable (4.5 microm/s), highpower (150 mW), single-longitudinal-mode (120 MHz) single-crystalline Cr(2+):ZnSe laser; CW widely-tunable (2.12-2.77 microm), multi-watt (2 W over 2.3-2.7 microm), polycrystalline Cr(2+):ZnSe laser; CW multi-watt (6 W, at 2.5 microm), highly efficient (48% real efficiency) polycrystalline Cr(2+):ZnSe laser; CW multi-watt (3 W, at 2.5 microm), highly efficient (41% real efficiency) ultra-compact polycrystalline Cr(2+):ZnSe laser; and CW hot-pressed ceramic Cr(2+):ZnSe laser.

Mid-infrared Cr2+:ZnSe random powder lasers.

We report simple methods of laser active Cr2+:ZnSe powder fabrication with average grain sizes of either approximately 10 or approximately 1 microm without crystal growth stage. Pure, uniformly mixed ZnSe and CrSe powders annealed at 1000 masculineC for 3 days in a sealed evacuated (approximately 10(-4) Torr) quartz ampoule exhibited middle-infrared laser action at room temperature under 1.56 microm excitation of D(2) Raman shifted radiation of Nd:YAG laser. The output-input characteristic clearly demonstrated the threshold-like behavior of the output signal with the threshold energy level of 0.5 and 3 mJ in 2.9 mm spot for 10 and 1 microm grain sizes, respectively.

Hot-pressed ceramic Cr(2+):ZnSe gain-switched laser.

The technology of hot-pressed Cr(2+):ZnSe ceramic preparation is reported. Comparative gain-switched lasing of hot-pressed ceramic and CVD grown Cr(2+):ZnSe samples with slope efficiencies up to 10% and output energies up to 2 mJ were demonstrated. This is a milestone in the development of future large scale mid-IR laser systems based on ceramic TM(2+):II-VI materials. This evolving technology has excellent potential as media for practical low cost, high power mid-IR laser applications.

[Ionic channels and currents in the cardiomyocytes.].

Review concerns modern views on ionic mechanism of action potential formation in cardiomyocytes. Main characteristics of cardiomyocyte ion current are described. Importance of ion current in formation of action potential phases in various regions of the heart is considered. Molecular structure and up-to-date classification of ion channels are presented. Number of genetic abnormalities which lead to appearance of arrhythmias are described.

3.9-4.8 microm gain-switched lasing of Fe:ZnSe at room temperature.

We report a room temperature Fe:ZnSe laser in gain-switched operation and tuning over the 3.9 - 4.8microm spectral range. Mid-IR emission of Fe2+:ZnSe was studied under three regimes of excitation: ordinary optical (2.92mum) excitation of 5T2 excited state of Fe2+; excitation via 5E level of Cr co-dopant (1.56mum); and excitation via photo-ionization transition of Fe2+ (0.532mum). The energy transfer from Cr2+ (5E level) to Fe2+ (5T2 level) under 1.56microm wavelength excitation was observed and resulted in simultaneous RT emission of Fe:Cr:ZnSe crystal over ultra-broadband spectral range of 2- 3 and 3.5-5mum. We also report the observation of mid-IR emission at 3.5- 5mum induced by 2+->3+->2+ ionization transitions of the iron ions in Fe:ZnSe.

[Pattern of excitation in isolated heart of hibernator ground squirrel Citellus undulatus].

Aim of our study was to measure conduction velocity and pattern of excitation during hypothermia in hearts of ground squirrels Citellus undulatus, known to be most resilient hibernators. We imaged electrical conduction in intact isolated hearts of summer active and winter hibernating ground squirrels at temperatures varying from +37 degrees C to +3 degrees C. Electrical activity was mapped using CCD camera (500 frames/sec) and voltage-sensitive dye di-4-ANEPPS during normal sinus rhythm and ventricular pacing. No spontaneous tachyarrhythmia was observed in all hearts at any temperature. Hearts were able to maintain spontaneous sinus rhythm and normal pattern of epicardial excitation throughout the whole range of studied temperatures. Despite responsiveness to pacing in all hearts ventricular conduction velocity was significantly reduced (about 10-fold) at low temperatures +3 degrees C. Our data provides the first direct demonstration that isolated heart of the summer active and winter hibernating ground squirrel Citellus undulatus is able to maintain normal excitation pattern in a range of temperatures from +37 degrees C to +3 degrees C.