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Journal of Physics D: Applied Physics - latest papers
Latest articles for Journal of Physics D: Applied Physics
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Coherence effects in LIPSS formation on silicon wafers upon picosecond laser pulse irradiations
Using different laser irradiation patterns to modify the silicon surface, it has been demonstrated that, at rather small overlapping between irradiation spots, highly regular laser-induced periodic surface structures (LIPSS) can be produced already starting from the second laser pulse, provided that polarization direction coincides with the scanning direction. If the laser irradiation spot is shifted from the previous one perpendicular to light polarization, LIPSS are not formed even after many pulses. This coherence effect is explained by a three-wave interference, involving surface electromagnetic waves (SEWs) generated within the irradiated spot, SEWs scattered from the crater edge formed by the previous laser pulse, and the incoming laser pulse, that provides conditions for amplification of the periodic light-absorption pattern. To study possible consequences of SEW scattering from the laser-modified regions, where the refractive index can change due to material melting, amorphization, and the residual stress formed by previous laser pulses, hydrodynamic modelling and simulations have been performed within the melting regime. The simulations show that stress and vertical displacement could be amplified upon laser scanning. Both mechanisms, three-wave interference and stress accumulation, could enable an additional degree of controlling surface structuring.
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Investigation on capacitively coupled He discharges with a structured electrode and effective design of a high-density and uniform plasma
In this paper, a fluid model is performed to investigate the effect of a structured electrode on capacitively coupled helium discharges operated at 13.56 MHz with 100 V peak-to-peak voltage, and 200 Pa. Compared to discharges with conventional planar electrodes, it is found that the plasma density produced by the structured electrode is raised by 28.5%–161.2% from as the trench size (i.e. width and depth) in structured electrode varies. The results also indicate that the trench dimensions have a great effect on the plasma characteristics under the operating conditions in this study. With the increase of trench width, the plasma density below the trench region increases at trench widths lower than 22 mm, after which the opposite trend is observed. As the trench depth varies from 5 mm to 25 mm, the plasma density increases monotonously from to . Based on the results above, a modified ring-shaped structured electrode (MRSE) is proposed to successfully generate a large-area uniform and high-density plasma by adjusting the trench dimensions, position and number according to the discharge conditions. Compared to the flat electrode case, the plasma density and radial uniformity rise to 94.2% and from 92.2% and , respectively, with the adoption of MRSE. The simulation results also validate potential of the structured electrode as an effective tool in improvement of plasma processing.
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Critical comparison of interfacial boundary conditions in modelling plasma–liquid interaction
Several computational models have been developed over the past decade with the goal to investigate the various processes that occur during plasma–liquid interaction. However, many different boundary conditions to describe transfer of chemical species over the gas–liquid interface have been reported in these investigations. In this work, we employ a computational model to test these various boundary conditions, and compare the results to experimental data for H2O2, O3, ·NO and HNO2, in order to assess how well these boundary conditions can describe the dissolution of different species. We show that the validity of the different formulas depends on the solubility of the investigated chemical species; they appear valid for species with high solubility (H2O2), but not for species with low (O3 and ·NO) or intermediate (HNO2) solubility. Finally, we propose an approach to reach better agreement, based on film theory in combination with the mass accommodation coefficient.
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2D-phononic system with local phase transition and reconfigurable non-contact modulation
Contactless tuning of signals represents a promising avenue for advancing topological phononics and photonics devices, particularly in the frequency and spatial domains. For topological phase transitions, breaking the spatial inversion symmetry geometrically to obtain an open topological band gap is a typical way to introduce perturbations. This approach has great limitations in achieving reconfigurable topological protection routes. We present a thermally modulated two-dimensional elastic topological insulator made from a patterned substrate and a temperature-sensitive vanadium dioxide film, allowing elastic waves to propagate in the suspended region of the 2D material. The topological phase transition is activated by locally heating a portion of the unit cell. This heating induces a phase transition in the material by exploiting changes in mechanical properties, achieving symmetry breaking. The topological valley-locked states with strong localization at the interface are obtained by placing unit cells with different chirality adjacent to each other at the omnidirectional bulk band gap. Full-field simulations confirm both the reconfigurability of arbitrary paths and the robustness of the induced waves against defects. Eliminating the need for pre-etched topological protection paths on patterned substrates enhances flexibility in both manufacturing and application. This innovative scheme employs localized temperature control at the unit cell scale to achieve effects akin to approximately 10% geometric symmetry breaking, thereby significantly reducing precision manufacturing requirements. Moreover, localized thermal modulation holds considerable potential for improving modulation rates while minimizing energy loss.
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Temperature-dependent terahertz spectra and terahertz emission of GaTe
The terahertz spectra and terahertz emission characteristics of Gallium telluride (GaTe) as a function of temperature were studied by terahertz spectroscopy system, including terahertz time-domain spectroscopy, optical pump-terahertz probe spectroscopy and terahertz emission spectroscopy. The temperature range is 20 K–300 K. The temperature-dependence terahertz transmittance and dielectric properties, photocarrier recombination dynamics and terahertz radiation properties of GaTe are analyzed. As the temperature increases, thermal expansion and lattice vibration intensify, resulting in accelerated phonon scattering and reduced relaxation time. Meanwhile, due to the acceleration of the relaxation process, the carriers are rapidly recombined, which improves the terahertz transmittance of GaTe. Further, enhanced terahertz emission of GaTe was observed at low temperatures. This is because the excitation energy at low temperatures is more easily converted into transient photocurrents than energy dissipation. This work provides technical support for the fabrication of GaTe-based optoelectronic devices.