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1.
Jan C. Schmidt Alvydas Lisauskas Hartmut G. Roskos Nataliya V. Demarina 《Superlattices and Microstructures》2012
Field-pinning layers are an approach to improve the homogeneity of the electric field in a biased semiconductor structure of length above the Kroemer criterion. Building a THz Bloch oscillator with such a structure requires superlattice regions. Nevertheless, GaAs layers are investigated here. We compare different periodic structures (alternating transit and field-pinning layers) via simulating the field distribution. It is shown that the development of propagating Gunn domains is suppressed when field-pinning layers are included, but the homogeneity of the field is still not satisfying for the purpose of building a Bloch gain THz source. Depending on the temperature, intra- and inter-period inhomogeneities occur. 相似文献
2.
We demonstrate the principle applicability of antenna-coupled complementary metal oxide semiconductor (CMOS) field-effect transistor arrays as cameras for real-time coherent imaging at 591.4 GHz. By scanning a few detectors across the image plane, we synthesize a focal-plane array of 100×100 pixels with an active area of 20×20 mm2, which is applied to imaging in transmission and reflection geometries. Individual detector pixels exhibit a voltage conversion loss of 24 dB and a noise figure of 41 dB for 16 μW of the local oscillator (LO) drive. For object illumination, we use a radio-frequency (RF) source with 432 μW at 590 GHz. Coherent detection is realized by quasioptical superposition of the image and the LO beam with 247 μW. At an effective frame rate of 17 Hz, we achieve a maximum dynamic range of 30 dB in the center of the image and more than 20 dB within a disk of 18 mm diameter. The system has been used for surface reconstruction resolving a height difference in the μm range. 相似文献
3.
A. Laurinavicius F. Anisimovas A. Deksnys V. Lisauskas B. Vengalis 《International Journal of Infrared and Millimeter Waves》1993,14(10):2261-2266
For the first time millimeter waves are used for non-destructive diagnostics of superconducting layers and their quality control. The quality of the whole layer depending on TC and TC is determined by local transmission of millimeter waves. 相似文献
4.
Sergej Orlov Rusnė Ivaškevičiūtė-Povilauskienė Karolis Mundrys Paulius Kizevičius Ernestas Nacius Domas Jokubauskis Kęstutis Ikamas Alvydas Lisauskas Linas Minkevičius Gintaras Valušis 《Laser \u0026amp; Photonics Reviews》2024,18(5):2301197
The art of light engineering unveils a world of possibilities through the meticulous manipulation of photonic properties such as intensity, phase, and polarization. Precision control over these properties finds application in a variety of fields spanning communications, light–matter interactions, laser direct writing, and imaging. Terahertz (THz) range, nestled between microwaves and infrared light, stands out for its remarkable ability to propagate with minimal losses in numerous dielectric materials and compounds, making THz imaging a powerful tool for noninvasive control and inspection. In this study, a rational framework for the design and optimal assembly of nonparaxial THz imaging systems is established. The research is centered on lensless photonic systems composed solely of high-resistivity silicon-based nonparaxial elements such as the Fresnel zone plate, the Fibonacci lens, the Bessel axicon, and the Airy zone plate, all fabricated using laser ablation technology. Through a comprehensive examination through illumination engineering and scattered light collection from raster-scanned samples in a single-pixel detector scheme, the imaging systems are evaluated via diverse metrics including contrast, resolution, depth of field, and focus. These findings chart an exciting course toward the development of compact and user-friendly THz imaging systems where sensors and optical elements seamlessly integrate into a single chip. 相似文献
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6.
A. Jukna L. Steponavičienė V. Plaušinaitienė A. Abrutis A. Maneikis K. Šliužienė V. Lisauskas Roman Sobolewski 《Applied physics. B, Lasers and optics》2013,113(3):327-332
We report our results of investigation of electric and magnetic properties of partially oxygen-depleted channels for easy vortex motion in YBa2Cu3O7?x (YBCO) superconducting, 50-μm-wide, and 100-μm-long microbridges at temperatures below the onset of the superconducting state critical temperature T c on . The channels were produced by means of a laser-writing technique. The writing was performed using a 0.1–0.3 W power, continuous-wave laser radiation focused down to a ~ 5 μm spot on the surface of a superconducting film in a nitrogen gas atmosphere, and resulted in perpendicular stripes (channels) with partial (x ~ 0.2) reduction of the oxygen content in the YBCO stripe. The oxygen-depleted channels exhibit a depressed T c and lower both the critical current density and the first critical magnetic field, as compared with the laser-untreated areas. The bias current applied to the bridge self-produced a magnetic flux that penetrated the channels in a form of Abrikosov magnetic vortices that, subsequently, moved coherently (a quasi-Josephson effect) along the channels in the narrow temperature range of 0.943 T c on –0.98 T c on and manifested themselves as steps on the current–voltage characteristics of our microbridges. Our results demonstrate that laser-induced formation of artificial channels of the flux flow can be used for a precise control of vortex nucleation and their coherent motion in pre-assigned regions of thin-film YBCO devices. 相似文献
7.
Chernyakova Katsiaryna Vrublevsky Igor Jagminas Arunas Klimas Vaclovas 《Journal of Solid State Electrochemistry》2021,25(4):1453-1460
Journal of Solid State Electrochemistry - The purpose of this work was to study and analyze the effect of electrolyte temperature and anodization voltage on cell morphology of thin films of... 相似文献
8.
Arūnas Jagminas K?stutis Ma?eikaNerijus Bernotas Vaclovas KlimasAlgirdas Selskis Dalis Baltrūnas 《Applied Surface Science》2011,257(9):3893-3897
We report on the composition and morphology of as-grown anodic oxide films onto the iron surface in an ethylene glycol solution containing some NH4F and H2O by anodizing under direct current bias. Decrease in the content of NH4F and the temperature of electrolyte allow us to form either nanochannel or nanotubular films over a larger potential window, ca. from 30 to 100 V. By this way, the films in thickness of up to10 μm have been formed. Mössbauer spectra recorded at room to cryogenic temperatures under conversion electron and transmission modes revealed the formation of lepidocrocite (γ-FeOOH) film containing some Fe(OH)2 and/or FeF2·4H2O. An increase in anodizing voltage results in fabrication of more porous and less Fe(II) compounds containing films. 相似文献
9.
Kazakeviciene B Valincius G Niaura G Talaikyte Z Kazemekaite M Razumas V Plausinaitis D Teiserskiene A Lisauskas V 《Langmuir : the ACS journal of surfaces and colloids》2007,23(9):4965-4971
The kinetics of electrocatalytic oxidation of ascorbate was studied on a series of redox self-assembled monolayers (SAMs) of the general formula Fc(CH2)4COO(CH2)nSH as electron-transfer mediators, where Fc is the ferrocenyl group and n = 3, 6, 9, and 11. We show that the rate of electron transfer from ascorbate to the surface-confined Fc+ decreases with increasing n. The rationale for the dependence of the rate of electrocatalytic activity and n, in the presence of ClO4, is obtained from Fourier-transform surface-enhanced Raman spectroscopy (FT-SERS), cyclic voltammetry, and electrochemical quartz crystal microbalance (EQCM) data. In particular, FT-SERS shows decreasing amounts of surface-bound ClO4- upon oxidation of the ferrocene with decreasing n, while EQCM data show the effective electrode mass increase was consistently higher on the shorter chain SAMs. This mass increase is likely due to increasing ferricinium cation hydration. As n decreases, the SAMs become less ordered (FT-SERS data), as is widely known from previous literature. Disorder favors water penetration into the SAM, which, in turn, increases the hydration of the Fc+ (EQCM data). Increased hydration of the Fc+ impedes the formation of Fc+-ClO4- ion pairs (EQCM and FT-SERS data), which, consequently, accelerates the electrocatalytic electron transfer from the solution-dissolved ascorbate. 相似文献
10.
Eimutis Juzeliūnas Konstantinas Leinartas Meilutė Samulevičienė Aloyzas Sudavičius Povilas Miečinskas Remigijus Juškėnas Vaclovas Lisauskas 《Journal of Solid State Electrochemistry》2002,6(5):302-310
A quartz crystal microbalance (QCM) has been used for in situ corrosion studies of magnetron-sputtered Co-Cr-Mo and Ni-Cr-Mo
alloys, which are of great importance in various technical and medical applications. The corrosion monitoring has been performed
in an oxygen-containing atmosphere and in NaCl solution. The alloys were deposited on quartz substrates by means of DC magnetron
sputtering. X-ray photoelectron spectroscopy analysis showed that the composition of the deposits was similar to that of the
magnetron-sputtering targets. X-ray diffraction revealed an amorphous structure of the sputtered deposits, while the casting
alloys had a crystalline structure. The polarization resistance of sputtered alloys in NaCl solution was higher than the activity
of conventional alloys, which implied a superior corrosion resistance of the sputtered deposits. Corrosion was initiated by
supplying oxygen gas into a wet argon atmosphere and the QCM detected corrosion with nanogram resolution as the increase in
mass. Corrosion currents were calculated from the mass versus time curves. The QCM appeared to be an effective tool for corrosive
characterization of sputtered alloys in gaseous environments. A corrosion current calculation in solution was complicated
by metal transfer to the liquid phase.
Electronic Publication 相似文献