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The role of incidence angle in the morphology evolution of Ge surfaces irradiated by medium-energy Au ions
摘要： Germanium (Ge) surfaces have been irradiated with 26 keV gold (Au) ions at a constant fluence and at incidence angles varying from 0° to 85°. The evolution of the emerging nanostructures is studied by atomic force microscopy (AFM), scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy. The obtained results are compared with findings reported in the literature. Periodic rippled patterns with the wave vector parallel to the projection of the ion beam direction onto the Ge surface develop between 30° and 45°. From 75° the morphology changes from parallel-mode ripples to parallel-mode terraces, and by further increasing the incidence angle the terraces coarsen and show a progressive break-up of the front facing the ion beam. No perpendicular-mode ripples or terraces have been observed. The analysis of the AFM height profiles and slope distributions shows in the 45°–85° range an angular dependence of the temporal scale for the onset of nonlinear processes. For incidence angles below 45°, the surface develops a sponge-like structure, which persists at higher incidence angles on the top and partially on the face of the facets facing the ion beam. The XPS and the energy-dispersive x-ray spectroscopy evidence the presence of Au nano-aggregates of different sizes for the different incidence angles. This study points out the peculiar behavior of Ge surfaces irradiated with medium-energy Au ions and warns about the differences to be faced when trying to build a universal framework for the description of semiconductor pattern evolution under ion-beam irradiation.
关键词： ion beam irradiation,gold ions,terraces,germanium,binary system,sponge-like structures,ripples
更新于2025-09-23 15:23:52
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Klein collimation by rippled graphene superlattice
摘要： The hybridization of σ and π orbitals of carbon atoms in graphene depends on the surface curvature. Considering a single junction between flat and rippled graphene subsystems, it is found an accumulation of charge in the rippled subsystem due to Klein penetration phenomenon that gives rise to n–p junction. Using this fact, we show that the momentum distribution of electrons in ballisitically propagating beam can be selective without a waveguide, or external electric, and/or magnetic fields in graphene strip under experimentally feasible one-dimensional periodic potential. Such a potential is created with the aid of superlattice that consists of periodically repeated graphene pieces with different hybridizations of carbon orbits, produced by variation of the graphene surface curvature. The charge redistribution and selected transmission of electrons, caused by the superlattice, allows to control the electron focusing in the considered system by simply changing the element properties in the superlattice.
关键词： n–p junction,collimation,graphene,ripples
更新于2025-09-23 15:21:01
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Influence of defects on structural colours generated by laser-induced ripples
摘要： The colourisation of metallic surface which appears due to periodic surface patterns induced by ultrashort laser pulses is studied. Ripples due to the sub-micrometer size of their period act as a diffraction grating, generating structural colours. Carefully chosen strategy of the laser spot scanning allows us to mimic the nanostructures responsible for structural colours of some flowers on the metal substrate. We investigate the correlation between the colourising effects and the artificially-induced defects in the ripples structure and show that these defects can make the colours observable in a larger range of viewing angles. Further we address the influence of the processing parameters on the spectral profile of the reflected light.
关键词： structural colours,viewing angles,diffraction grating,defects,laser-induced ripples
更新于2025-09-23 15:19:57
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High Voltage Gain Three Coupled Winding DC-DC Interleaved Boost Converter with Arduino Microcontroller for the PV Panel Control
摘要： In many applications, high-step converters are widely used, including powered vehicles, Photovoltaic (PV) systems, continuous power supplies, Gas lighting and fuel cell systems. The most important requirements in the energy conversion process are reliability, quality, maintenance and size reduction. This paper presents an Interleaved Boost Converter (IBC) to raise voltage gain with three coupled winding. This converter consists of three pairs of coupled inductors to collect energy in parallel and release energy to the series load, which provides a much higher output load voltage than the traditional DC-DC boost converter. To validate the performance, an investigation was introduced by means of steady state analysis and operation. The operation modes and mathematical analysis are presented. Arduino UNO microcontroller was used to implement Pulse Width Modulation (PWM) gate drive based on Maximum Power Point Tracking (MPPT). The DC-DC IBC with High Voltage Gain (HVG) produces low voltage stress across switches, low input and output current ripple, and also improves the efficiency. These features made this converter suitable for applications where a high voltage gain is demanded. This converter was tested using Matlab/Simulink to validate the performance in terms of input and output ripples. The results supported the mathematical analysis. The cancelation of the ripple in input and output voltages has significantly detected. The ripple amplitude is reducing in DC-DC HVG IBC comparing with traditional DC-DC boost converter, and the ripple frequency is doubled. This tends to reduce the output filter losses, and size. Also improves the efficiency of the converter.
关键词： High voltage gain,Current and Voltage sensors,Arduino UNO Microcontroller,Low input and output ripples,Ferrite core,Maximum Power Point Tracking,Interleaved Boost Converter
更新于2025-09-23 15:19:57
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Antia??Counterfeiting Microstructures Induced by Ultrashort Laser Pulses
摘要： Ultrashort pulsed laser enables selective ablation of metal films on glass substrates, ripple formation on metal surface, and defect generation inside functional glass, etc. Correspondingly, direct writing of computer-generated holograms (CGHs), ripple rendered structure color, and defect featured photostimulated luminescence can be realized. Due to the feature of small size or invisibility, these induced microstructures can be used for anti-counterfeiting.
关键词： ultrashort laser pulses,computer-generated holograms,defects,anti-counterfeiting microstructures,ripples
更新于2025-09-23 15:19:57
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Picosecond Laser-Induced Hierarchical Periodic Near- and Deep-Subwavelength Ripples on Stainless-Steel Surfaces
摘要： Ultrafast laser-induced periodic surface subwavelength ripples, categorized based on the ripple period into near-subwavelength ripples (NSRs) and deep-subwavelength ripples (DSRs), are increasingly found in the variety of materials such as metals, semiconductors and dielectrics. The fabrication of hierarchical periodic NSRs and DSRs on the same laser-irradiated area is still a challenge since the connection between the two remains a puzzle. Here we present an experimental study of linearly polarized picosecond laser-induced hierarchical periodic NSRs and DSRs on stainless-steel surfaces. While experiencing peak power density higher than a threshold value of 91.9 GW/cm2, in the laser-scanned area appear the hierarchical periodic NSRs and DSRs (in particular, the DSRs are vertically located in the valley of parallel NSRs). A large area of the uniformly hierarchical periodic NSRs and DSRs, with the spatial periods 356 ± 17 nm and 58 ± 15 nm, respectively, is fabricated by a set of optimized laser-scanning parameters. A qualitative explanation based on the surface plasmon polariton (SPP) modulated periodic coulomb explosion is proposed for unified interpretation of the formation mechanism of hierarchical periodic NSRs and DSRs, which includes lattice orientation of grains as a factor at low peak power density, so that the initial DSRs formed have a clear conformance with the metallic grains.
关键词： stainless steel,surface plasmon polaritons,coulomb explosion,laser induced subwavelength ripples
更新于2025-09-19 17:13:59
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Self-organized fractal-like structures formation on the silicon wafer surface using the femtosecond laser pulses
摘要： In this paper interaction of a di?erent number of femtosecond laser pulses and various ?uences with silicon wafer has been studied. E?ects of the pulse number and the laser ?uence on self-organized structures created during femtosecond laser pulses processing are investigated. The scanning electron microscopy images of the sample show that by increasing the number of laser pulses, spike-like structures form on the surface, which gradually transform to hills and holes structure. The increment of the laser ?uence causes the microstructures to grow in diameter. However, the increase in diameter is limited by surface stability. When the micro-structures are at their maximum size and a stable geometrical shape, further ?uence increment can cause new self-organized nanos-tructures to be created over the microstructures’ surface. The hierarchical micro and nanostructures created after femtosecond laser pulse interaction have a similar shape. Thus fractal-like structures formed in the femtosecond pulse laser processing can be useful in the surface nano-structuring applications.
关键词： Femtosecond,Silicon,Spikes,Ripples,Fractal,Laser
更新于2025-09-16 10:30:52
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Concentric ripples of lubrication film in electrowetting
摘要： When a water drop approaches a solid surface in an ambient oil environment, a thin oil ?lm will be formed between the drop and the solid surface. The lubrication ?lm presents more complex behaviors when the external electrical ?eld varies discretely, and in this work, concentric ripples are found in the thin ?lm under a series of voltage steps, which is obviously different from the ?lm pro?le when the applied voltage is continuously increased. According to the time evolution of the thin ?lm, each voltage step adds a new concentric ripple outside the existing lubrication ?lm. The radial wavelength and the maximum height of each ripple are revealed to have a linear relationship with the amplitude of the corresponding voltage step. The ripples ?nally break into microscopic oil droplets, and the size and the number of the droplets can be predicted with the diameter and the radial wavelength of each ripple.
关键词： oil droplets,concentric ripples,voltage steps,electrowetting,lubrication film
更新于2025-09-16 10:30:52
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Modelling of Optical Damage in Nanorippled ZnO Produced by Ion Irradiation
摘要： Here, we report on the production of nanoripples on the surface of ZnO bulk substrates by ion beam erosion with 20 keV Ar+ ions at an oblique incidence (60°). The ripple patterns, analyzed by atomic force microscopy, follow a power law dependence for both the roughness and the wavelength. At high fluences these ripples show coarsening and asymmetric shapes, which become independent of the beam direction and evidence additional mechanisms for the pattern development. The shallow damaged layer is not fully amorphized by this process, as confirmed by medium energy ion scattering. A detailed study of the damage-induced changes on the optical properties was carried out by means of spectroscopic ellipsometry. Using a 3-layer model based on Tauc-Lorenz and critical point parameter band oscillators, the optical constants of the damaged layer were determined. The results showed a progressive reduction in the refractive index and enhanced absorption below the bandgap with the fluence.
关键词： ripples,ZnO,patterning,sputtering,damage,spectroscopic ellipsometry
更新于2025-09-11 14:15:04
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Universality of strain-induced anisotropic friction domains on 2D materials
摘要： Van der Waals two-dimensional (2D) materials have shown various physical characteristics depending on their growth methods and conditions. Among those characteristics, the surface structural properties are crucial for the application of 2D materials, as the surface structures readily affect their atomic arrangements and/or interaction with substrates due to their atomic-scale thicknesses. Here, we report on the anisotropic friction domains of MoS2 grown not only by chemical vapor deposition (CVD) under various sulfur pressure conditions but also by a mechanical exfoliation process. The 180° periodicity of each domain and the 60° shift between adjacent domains indicate the presence of linearly aligned structures along the armchair direction of MoS2, which is determined by the optical second-harmonic generation method. The anisotropic friction domains of CVD-grown MoS2 ?akes may be attributed to linearly aligned ripples caused by an inhomogeneous strain ?eld distribution, which is due, in turn, to randomly formed nucleation sites on the substrate. The universality of the anisotropic frictional behaviors of 2D materials, including graphene, hBN, and WS2 with honeycomb lattice stacking, which differ from ReSe2 with a distorted triclinic 1T’ structure, supports our assumption based on the linearly aligned ripples along the crystallographic axes, which result from an inhomogeneous strain ?eld.
关键词： strain-induced ripples,chemical vapor deposition,mechanical exfoliation,anisotropic friction domains,Van der Waals two-dimensional materials
更新于2025-09-04 15:30:14