Zhankun Weng

Fabrication of moth-eye structures on silicon by direct six-beam laser interference lithography

This paper presents a new method for the generation of cross-scale laser interference patterns and the fabrication of moth-eye structures on silicon. In the method, moth-eye structures were produced on a surface of silicon wafer using direct six-beam laser interference lithography to improve the antireflection performance of the material surface. The periodic dot arrays of the moth-eye structures were formed due to the ablation of the irradiance distribution of interference patterns on the wafer surface. The shape, size, and distribution of the moth-eye structures can be adjusted by controlling the wavelength, incidence angles, and exposure doses in a direct six-beam laser interference lithography setup. The theoretical and experimental results have shown that direct six-beam laser interference lithography can provide a way to fabricate cross-scale moth-eye structures for antireflection applications.

Bio-inspired hierarchical patterning of silicon by laser interference lithography.

This paper presents a facile approach for the rapid and maskless fabrication of hierarchical structures by multibeam laser interference. In the work, three- and four-beam laser interference lithographies were proposed to fabricate ordered multiscale surface structures instead of six or more beam interference with a complicated system setup. The pitch and shape of hierarchical structures can be controlled by adjusting the parameters of incident light. The experiment results have shown that the hierarchical anisotropy and isotropy surface structures can be fabricated by this method with the control of the parameters of each incident beam, which is in accordance with the theoretical analysis and computer simulations.

Sub-band transport mechanism and switching properties for resistive switching nonvolatile memories with structure of silver/aluminum oxide/p-type silicon

In this paper, we discuss a model of sub-band in resistive switching nonvolatile memories with a structure of silver/aluminum oxide/p-type silicon (Ag/AlxOy/p-Si), in which the sub-band is formed by overlapping of wave functions of electron-occupied oxygen vacancies in AlxOy layer deposited by atomic layer deposition technology. The switching processes exhibit the characteristics of the bipolarity, discreteness, and no need of forming process, all of which are discussed deeply based on the model of sub-band. The relationships between the SET voltages and distribution of trap levels are analyzed qualitatively. The semiconductor-like behaviors of ON-state resistance affirm the sub-band transport mechanism instead of the metal filament mechanism.

Fabrication and applications of two- and three-dimensional curved surfaces with robust underwater superoleophobic properties

In this work, a method for the fabrication of two- and three-dimensional curved surfaces with robust underwater superoleophobicity is reported for the first time on light alloys (including 5083 Al and TC4 Ti alloys) through the high speed wire electrical discharge machining (HS-WEDM). The surface morphology and compositions were characterized by scanning electron microscope and energy-dispersive X-ray spectrometer. The results showed that rough structures and a layer of oxidization were created on the light alloys by HS-WEDM cutting. The two- and three-dimensional structured curved surfaces after an ethanol immersion exhibited the extreme underwater superoleophobic property with the high oil contact angle and low oil sliding angle. More importantly, the underwater superoleophobic surfaces with the three-dimensional curved features could have many new applications. In order to use the potential functions, the durability of the fabricated samples was tested and the results showed that the samples still exhibited the underwater superoleophobic property after the underwater storage and physical mechanism tests. Additionally, this method is versatile, simple, environment-friendly, and cost-effective.

Fabrication of Pt nanowires with a diffraction-unlimited feature size by high-threshold lithography

Although the nanoscale world can already be observed at a diffraction-unlimited resolution using far-field optical microscopy, to make the step from microscopy to lithography still requires a suitable photoresist material system. In this letter, we consider the threshold to be a region with a width characterized by the extreme feature size obtained using a Gaussian beam spot. By narrowing such a region through improvement of the threshold sensitization to intensity in a high-threshold material system, the minimal feature size becomes smaller. By using platinum as the negative photoresist, we demonstrate that high-threshold lithography can be used to fabricate nanowire arrays with a scalable resolution along the axial direction of the linewidth from the micro- to the nanoscale using a nanosecond-pulsed laser source with a wavelength λ0 = 1064 nm. The minimal feature size is only several nanometers (sub λ0/100). Compared with conventional polymer resist lithography, the advantages of high-threshold lithogra...

Five-beam Interference Pattern Model for laser interference lithography

Laser interference lithography (LIL) is an established fabrication technology for micro and nano scale structuring of periodic and quasi-periodic surface patterns. This paper presents a Five-beam Interference Pattern Model for laser interference lithography. It can be programmed to obtain images of interference results showing interference intensity distributions. The majority of 2–5 beam interference patterns can be simulated by this model with every variable in an LIL system. In this work, different technologies for nano structuring are introduced, along with the principle of the five-beam interference pattern model. Several images of interference results obtained by the five-beam interference pattern model are shown and some of their possible applications are discussed. Three-beam interference patterns and five-beam interference patterns are formed using a laser beam that goes along the z axis which is not used commonly in other LIL models.

Nanosecond Laser-Induced Underwater Superoleophobic and Underoil Superhydrophobic Mesh for Oil/Water Separation

Materials with special wettability have drawn considerable attention especially in the practical application for the separation and recovery of the oily wastewater, whereas there still remain challenges of the high-cost materials, significant time, and complicated production equipment. Here, a simple method to fabricate the underwater superoleophobic and underoil superhydrophobic brass mesh via the nanosecond laser ablation is reported for the first time, which provided the micro-/nanoscale hierarchical structures. This mesh is superhydrophilic and superoleophilic in air but superoleophobic under water and superhydrophobic under oil. On the basis of the special wettability of the as-fabricated mesh, we demonstrate a proof of the light or heavy oil/water separation, and the excellent separation efficiencies (>96%) and the superior water/oil breakthrough pressure coupled with the high water/oil flux are achieved. Moreover, the nanosecond laser technique is simple and economical, and it is advisable for the large-area and mass fabrication of the underwater superoleophobic and underoil superhydrophobic mesh in the large-scale oil/water separation.

Effective intensity distributions used for direct laser interference exposure

This paper presents a method to obtain periodic structures with different feature shapes using direct laser interference lithography. In the method, the desired structures are produced by controlling the effective intensity distributions of interference patterns during the exposure process. The effective intensity distributions are adjusted by changing the exposure beam intensity based on the material modification thresholds. In the simulations and experiments, different exposure intensities were used to study the interactions between the effective intensity distributions and the materials, and direct four- and six-beam laser interference lithography systems were set up to pattern silicon wafers. The shapes and sizes of the fabricated surface structures changed with the effective intensities. The experimental results are in accordance with the theoretical models and simulations.

Phase-shift control in two-beam laser interference lithography

This paper presents a method of phase-shift control in two-beam laser interference lithography. In the method, a PZT actuator is used to push a mirror and introduce phase shifts in a He-Ne laser interference lithography simulation system. When different voltages are applied to the PZT actuator, fringe positions are changed accordingly, and the phase shifts are introduced. The phase shifts can be determined by fringe pattern correlation with subpixel accuracy. This method is useful in two-beam laser interference lithography for the control of phase shifts and fringe positions in interference patterns for multi-exposure patterning applications.

Oblique fringe measurement by pattern correlation

This paper introduces a method for the determination of the slope and period of oblique and equi-spaced fringes by pattern correlation. In the method, two pairs of image patches in two different regions of a fringe pattern are selected for pattern correlation calculations, and the phase shift between the two selected regions of the fringe pattern is obtained from the phase curves computed with the correlation function. The computer simulation and experiment have shown that this method is useful in interferometry and laser interference lithography for determining the slope and period of the oblique and equi-spaced fringe patterns with the advantage of high resistance to noise. It has potential applications for the measurement of the fringe pattern period, fringe angle, phase difference, displacement, and other relevant physical quantities. In practice, it can also be used for the orientation of interference patterns and alignment of laser interference lithography systems.