- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2019
- polycrystalline ferrite-garnet
- magnetoplasmonic crystals
- magnetooptical effects
- deposition
- ion-beam methods
- sputtering
- plasmon resonance
- Physics
- Moscow Technological University
- Moscow State University
-
Geometric parameters effect of the atomic force microscopy smart piezoelectric cantilever on the different rough surface topography quality by considering the capillary force
摘要： Nowadays, the atomic force microscopy (AFM) is widely used in the nanotechnology as a powerful nano-robot. The surface topography in Nanoscale is by far one of the most important usages of the AFM device. Hence, in this article, the vibration motion of a piezoelectric rectangular cross-section micro-cantilever (MC) which oscillates in the moist environment has been examined based on the Timoshenko beam theory. After extracting the MC governing equations according to Hamilton's principle, the finite element method has been used to discretize the motion equations. The surface topography has been simulated for various roughness forms in the tapping and non-contact modes by considering the effects of the Van der Waals, capillary and contact forces. Also, the experimental results obtained from the glass surface topography have been simulated. The results illustrate that the time delay in higher natural frequencies in the tapping mode is shorter in comparison with the non-contact mode, especially, for the lower natural frequencies. The sensitivity analysis of the natural frequencies, topography depth and time delay have been simulated. Results indicate that the most effective parameter is the MC length. In the first mode, the first section length has the highest effect on the surface topography time delay, also, in the second vibration mode; the most effective parameter on the time delay is the MC tip length based on the simulation results.
关键词： AFM piezoelectric micro-cantilever,Timoshenko beam,sensitivity analysis,finite element method,topography depth
更新于2025-09-23 15:23:52
-
Do the representative beam data for TrueBeam <sup>?</sup> linear accelerators represent average data?
摘要： If the vendor's representative beam data (RBD) for TrueBeam linear accelerators are to be valid for use in clinical practice, the variations in the beam data used for beam modeling must be small. Although a few studies have reported the variation of the beam data of the TrueBeam machines, the numbers of machines analyzed in those studies were small. In this study, we investigated the variation in the beam data for 21 TrueBeam machines collected from 17 institutions with their agreement. In the exponential regions, the percent depth dose (PDD) values showed very small variation, <1% for all the photon energies analyzed. Similarly, the off‐center ratio (OCR) values also showed small variation for all energies. In the ?eld regions, the standard deviations of the values of dose difference (DD) between the data for each machine and the study average were <1% for ?eld sizes ≥100 × 100 mm2. The maximum distance‐to‐agreement from the average data was <0.5 mm in the penumbra regions. The output factor (OPF) values also showed very small variation (<1%) for all energies and ?eld sizes. Both the PDD and OCR of the average study data showed good agreement with the vendor's RBD for ?eld sizes ≥100 × 100 mm2. The OPF of the average study data also showed good agreement with the vendor's RBD for all ?eld sizes. However, although all the institutions used ionization chambers with similar cavity volumes, the 30 × 30 mm2 ?eld size showed large DD variations (≥2%) in OCR in the ?eld regions. We conclude that the intermachine variability of TrueBeam linear accelerators was very small except for small ?eld dosimetry, supporting the validity of the use of the RBD for clinical applications. The use of the vendor's RBD might greatly facilitate the quick installation of a new linear accelerator.
关键词： commissioning,linear accelerator,representative beam data
更新于2025-09-23 15:23:52
-
Optimization of X-ray image acquisition and reconstruction for a C-arm CBCT system with a flat-panel detector
摘要： A modern cone-beam computed tomography (CBCT) system with a C-arm gantry incorporating a large-area flat-panel detector is an important imaging tool widely used for diagnosis and image-guidance in spine surgery, orthopedic and interventional suite, and image-guided radiation therapy. In this study, the experimental prototype CBCT imaging platform consists of a benchtop system that is integrated with a cone-beam X-ray tube, a collimator, an anti-scatter grid, and a large-area TFT-based flat-panel detector. The different projection images in the C-arm CT system were usually acquired at short scanning angles with a constant interval for various exposure conditions. The performance of CT imaging quality was performed using the Feldkamp, Davis and Kress (FDK) reconstruction algorithm through acquired two-dimensional projection images at different scanning angles and projection numbers. Quantitative analysis of the image quality was performed by using the cone-beam CT phantom for spatial resolution, low-contrast resolution, noise, and two different phantoms, such as the head and pelvis.
关键词： Flat-panel X-ray detector,3D image reconstruction,Cone-beam CT system,C-arm CT system
更新于2025-09-23 15:23:52
-
Exploring the optical beam shifts in monolayers of transition metal dichalcogenides using Gaussian beams
摘要： We have extensively studied Goos-H?nchen (GH) and Imbert-Fedorov (IF) shifts for reflection of a fundamental Gaussian beam using transfer matrix method. By considering a dielectric slab coated with monolayer of transition metal dichalcogenides (TMDC), we theoretically investigate the potential role of four different TMDC monolayers (WS2, WSe2, MoS2, and MoSe2) on the spatial and angular GH and IF shifts for reflection of the light beam that has not been explored previously. We find the nature of GH and IF shifts to be explicitly dependent on the mode of polarization of light beam. In case of partial reflection of light, both GH and IF shifts acquire moderate magnitude. In contrary, giant negative spatial GH shifts are examined for total internal reflection. Our analysis revealed that the typical characteristics of GH and IF shifts are significantly affected by the complex surface conductivity of TMDC monolayers and consequently the shifts are found to differ for different TMDC monolayers. We also present a comparison of the beam shifts for the monolayer TMDC-coated surfaces with the corresponding bulk TMDCs. Finally, we address the most significant question of how the GH and IF shifts depend upon the wavelengths of incident light, in particular, establishing the role of optical conductivity in beam shifts.
关键词： Light matter interaction,Goos-H?nchen shift,Surface Optics,Gaussian beam,Transition metal dichalcogenides,Imbert-Fedorov shift
更新于2025-09-23 15:23:52
-
Separation of boron from silicon by steam-added electron beam melting
摘要： Removal of boron from silicon is a tough task by traditional directional solidification and vacuum refining techniques, due to its large and inappropriate segregation coefficient and low saturated vapor pressure. At high temperature boron react with oxygen to form volatile boron oxides which can be evaporated. So, the removal procedure of boron from silicon melt is investigated by incorporating a small amount of water vapor above the melted surface. The results show that boron is oxidized to mainly form BO and evaporated with 28% removal efficiency by average. It is considered that oxygen atoms experience a series of physical and chemical processes, such as a chemical reaction in the bulk of the melt, evaporation from the melt surface, transportation across the gas phase and ionization due the electron beam, which is conducive to the continuous removal of boron.
关键词： Electron beam melting,Photovoltaic,Boron removal,Oxygen self-circulating path,Solar-grade silicon
更新于2025-09-23 15:23:52
-
Effect of Electron Irradiation on the Transport and Field Emission Properties of Few-Layer MoS <sub/>2</sub> Field-Effect Transistors
摘要： Electrical characterization of few-layer MoS2 based field effect transistors with Ti/Au electrodes is performed in the vacuum chamber of a scanning electron microscope in order to study the effects of electron beam irradiation on the transport properties of the device. A negative threshold voltage shift and a carrier mobility enhancement is observed and explained in terms of positive charges trapped in the SiO2 gate oxide, during the irradiation. The transistor channel current is increased up to three order of magnitudes after the exposure to an irradiation dose of 100e-/nm2. Finally, a complete field emission characterization of the MoS2 flake, achieving emission stability for several hours and a minimum turn-on field of ≈ 20 V/μm with a field enhancement factor of about 500 at anode-cathode distance of ~1.5 μm, demonstrates the suitability of few-layer MoS2 as two-dimensional emitting surface for cold-cathode applications.
关键词： electron beam irradiation,2D materials,field emission,molybdenum disulfide,field effect transistors
更新于2025-09-23 15:23:52
-
Nanofluidic and monolithic environmental cells for cryogenic microscopy
摘要： We present a device capable of combining nanofluidics and cryogenic transmission electron microscopy (cryo-TEM) to allow inspection of water-soluble samples under near-native conditions. The devices can be produced in a multitude of designs, but as a general rule, they consist of channels or chambers enclosed between two electron-transparent silicon nitride windows. With the appropriate design, those devices can allow screening of multiple samples in parallel and remove the interaction between the sample and the environment (no air–water interface). We demonstrate channel sizes from 80 to 500 nm in height and widths from 100 to 2000 μm. The presented fabrication flow allows producing hollow devices on a single wafer eliminating the need of aligning or bonding two half-cavities from separate wafers, which provides additional resistance to thermal stress. Taking advantage of a single-step through-membrane exposure with a 100 keV electron beam, we introduced arrays of thin (10–15 nm) electron-transparent silicon nitride membrane windows aligned between top and bottom (200–250 nm) carrier membranes. Importantly, the final devices are compatible with standard TEM holders. Furthermore, they are compatible with rapid freezing of samples, which is crucial for the formation of vitreous water, hence avoiding the formation of crystalline ice, that is detrimental for TEM imaging. To demonstrate the potential of this technology, we tested those devices in imaging experiments verifying their applicability for cryo-TEM applications and proved that vitreous water could be prepared through conventional plunge freezing of the chips.
关键词： nanofabrication,TEM,environmental chamber,microfluidic cell,electron beam lithography,cryo-TEM
更新于2025-09-23 15:23:52
-
Characterization of beam splitters in the calibration of a six-channel Stokes polarimeter
摘要： Polarization distortion in a beam splitter is a phenomenon where the polarization state of output light deviates from the theoretical expectation, which is inevitable and will result in significant errors in the optical systems. A theoretical analysis method based on Mueller matrix ellipsometry is proposed for characterizing the beam splitters and the application in the calibration of a six-channel Stokes polarimeter (SP) is shown. In this study, polarization distortions in the beam splitters including depolarization, linear birefringence, circular birefringence, linear dichroism, and circular dichroism have been considered. With the proposed method, the beam splitters are characterized by the polarization distortions and the effective optical parameters extracted. In our experiment, the Mueller matrices of two different commonly used beam splitters measured by a commercial Mueller matrix ellipsometer (MME) are consistently fitted by the proposed method and the residual errors have shown improvement compared to the conventional methods. A practical application of the proposed method is exhibited by calibrating a SP system containing two non-polarization beam splitters and three polarization beam splitters. With the proposed method introduced, the general error of the measured Stokes vector can be reduced from 3% to 1%, and the errors of the thickness measurement of standard SiO2 thin film samples are within 1 nm compared with the results reported by a commercial MME.
关键词： beam splitter,characterization,calibration,Stokes polarimeter,polarization distortion
更新于2025-09-23 15:23:52
-
Molecular-beam resonance method with Zeeman-decelerated samples: Application to metastable helium molecules
摘要： We use a multistage Zeeman decelerator to generate slow beams (v ≈ 100 m/s) of translationally cold, spin-polarized metastable a 3Σ+u He2 molecules and perform a precision measurement of their spin-rotation fine structure. The spin polarization results from the elimination of the high-field-seeking J = N spin-rotational component of each rotational level (rotational quantum number N) by the Zeeman deceleration process. By repopulating the J = N component from the J = N ± 1 low-field-seeking components using radio-frequency radiation, we measured the spin-rotation fine structure of 13 rovibrational levels with v = 0, 1 and N = 1–21. The low beam velocity and the resulting long interaction times with the radio-frequency radiation were exploited to determine the transition frequencies with a precision of 300 Hz.
关键词： metastable helium molecules,precision spectroscopy,molecular-beam resonance,Zeeman deceleration,spin-rotation fine structure
更新于2025-09-23 15:23:52
-
Intrinsic method for the evaluation of beam shape coefficients in spheroidal coordinates for oblique illumination
摘要： When dealing with T-matrix scattering, e.g. in the framework of Generalized Lorenz-Mie Theory (GLMT) or of Extended Boundary Condition Method (EBCM), the incident electromagnetic fields are expanded over a set of vectorial wave functions, with expansion coefficients expressed in terms of beam shape coefficients (BSCs). In the case of structured beams, the evaluation of these BSCs may constitute a challenging issue, particularly in the case of spheroidal coordinates. BSCs in spheroidal coordinates have been originally evaluated using an extrinsic method, i.e. they have been expressed in terms of more conventional BSCs in spherical coordinates. Later on, it has been possible to provide expressions to evaluate spheroidal BSCs using an intrinsic approach, i.e. by working only inside the spheroidal coordinate system used to deal with the scattering problem. Fairly recently, the intrinsic method for the evaluation of BSCs in spheroidal coordinates for on-axis standard configuration has been released in the archival literature. The present paper extends the intrinsic method to the case of oblique illumination. It also serves as a review devoted to GLMTs in spheroidal coordinates.
关键词： Spheroidal coordinates,Intrinsic method,Generalized Lorenz-Mie theories,Beam shape coefficients
更新于2025-09-23 15:23:52