Subnanoscale Ion Beam Modification-Assisted Smoothing of Heterostructure Surfaces.

Glass ceramic (GC) is the most promising material for objective lenses for extreme ultraviolet lithography that must meet the subnanometer precision, which is characterized by low values of high spatial frequency surface roughness (HSFR). However, the HSFR of GC is typically degraded during ion beam figuring (IBF). Herein, a developed method for constructing molecular dynamics (MD) models of GC was presented, and the formation mechanisms of surface morphologies were investigated. The results indicated that the generation of the dot-like microstructure was the result of the difference in the erosion rate caused by the difference in the intrinsic properties between ceramic phases (CPs) and glass phases (GPs). Further, the difference in the microstructure of the IBF surface under different beam angles was mainly caused by the difference in the two types of sputtering. Quantum mechanical calculations showed that the presence of interstitial atoms would result in electron rearrangement and that the electron localization can lead to a reduction in CP stability. To obtain a homogeneous surface, the effects of beam parameters on the heterogeneous surface were systematically investigated based on the proposed MD model. Then, a novel ion beam modification (IBM) method was proposed and demonstrated by TEM and GIXRD. The range of ion beam smoothing parameters that could effectively converge the HSFR of the modified surface was determined through numerous experiments. Using the optimized beam parameters, an ultrathin homogeneous modified surface within 3 nm was obtained. The HSFR of GC smoothed by ion beam modification-assisted smoothing (IBMS) dropped from 0.348 to 0.090 nm, a 74% reduction. These research results offer a deeper understanding of the morphology formation mechanisms of the GC surfaces involved in ion beam processing and may point to a new approach for achieving ultrasmooth heterostructure surfaces down to the subnanometer scale.

Simulation and Experimental Study of Laser Processing NdFeB Microarray Structure.

NdFeB materials are widely used in the manufacturing of micro-linear motor sliders due to their excellent permanent magnetic properties. However, there are many challenges in processing the slider with micro-structures on the surface, such as complicated steps and low efficiency. Laser processing is expected to solve these problems, but few studies have been reported. Therefore, simulation and experiment studies in this area are of great significance. In this study, a two-dimensional simulation model of laser-processed NdFeB material was established. Based on the overall effects of surface tension, recoil pressure, and gravity, the temperature field distribution and morphological characteristics with laser processing were analyzed. The flow evolution in the melt pool was discussed, and the mechanism of microstructure formation was revealed. In addition, the effect of laser scanning speed and average power on machining morphology was investigated. The results show that at an average power of 8 W and a scanning speed of 100 mm/s, the simulated ablation depth is 43 µm, which is consistent with the experimental results. During the machining process, the molten material accumulated on the inner wall and the outlet of the crater after sputtering and refluxing, forming a V-shaped pit. The ablation depth decreases with the increment of the scanning speed, while the depth and length of the melt pool, along with the height of the recast layer, increase with the average power.

Surface hydroxylation process of YAG crystal in aqueous solution.

Surface hydroxylation is the basis for material removal in chemical mechanical polishing (CMP) of monocrystalline silicon, diamond, and YAG crystals. Existing studies use experimental observations to investigate surface hydroxylation, but lack in-depth understanding of the hydroxylation process. In this paper, for the first time to the best of our knowledge, we analyze the surface hydroxylation process of YAG crystals in an aqueous solution using first-principle calculations. The presence of surface hydroxylation was verified by X-ray photoelectron spectroscopy (XPS) and thermogravimetric mass spectrometry (TGA-MS) detections. This study complements the existing research on the material removal mechanism of the CMP process of YAG crystals and provides theoretical support for the future improvement of the CMP technology.

Internal stress and deformation analysis of ultra-thin plate-shaped optical parts in thinning process.

During the thinning process of plate-shaped optical parts (PSOP), the release of internal stress would cause the deformation of ultra-thin PSOP, which deteriorates the processed surface figure. The stress-release-induced deformation is hard to be predicted and controlled due to the difficulty in measuring the tiny internal stress in ultra-thin PSOP. In this paper, an analytical model is established to depict the variation of internal stress and deformation during the thinning process. It can be used to calculate the initial internal stress distribution along the thickness according to the deformation and the residual thickness of the sample. Meanwhile, the model can predict the residual stress distribution and deformation in the whole thinning process. The prediction results obtained from the proposed model agree well with the experimental results, and the prediction error is less than 13%. The presented model has great significance for the analysis of the tiny internal stress and then guide the process of making ultra-thin PSOP.

Modeling and Simulating of High Chromium Alloy Based on Molecular Dynamics.

High chromium alloy is a kind of metal material with high corrosion resistance and high hardness. It is used in the thrust bearing bush of nuclear main pump in a severe environment. Based on the content of elements in high chromium alloy and the manufacturing preparation process of the alloy, a method for constructing the molecular dynamics (MD) model was proposed to study the machinability of the alloy. The MD simulation model of high chromium alloy was established based on alloy structure with the atomic random permutation and two bubble algorithms. Then, according to the actual manufacturing process of the high chromium alloy, a quenching process was introduced to simulate the actual manufacturing process of the high chromium alloy, so the property of the high chromium alloy model was improved and it was more suitable for precision machining. The accuracy of the model was verified by the internal structure and by calculating the nanohardness and density of the high chromium alloy model after adequate relaxation to studying the nanomachining performance. The coordination number of the high chromium alloy is about 4.3 calculated by integrating the radial distribution function. And there is not a perfect crystal structure in the alloy model. The density of the alloy model is about 7.549 g/cm2, which agreed with the results of actual experimental measurement. A series of MD simulations were performed to investigate the nanomechanical property of the high chromium alloy by using the MD model. The maximum depth of 2 nm, 2.5 nm and 3 nm indentation simulations were carried out with 3 nm indenter. The results showed that the nanohardness is about 6.951 GPa-8.095 GPa, these properties are very close to the real measured results. The material and the deformation property of the high chromium alloy were stable during the indentation process.

Maskless Hydrophilic Patterning of the Superhydrophobic Aluminum Surface by an Atmospheric Pressure Microplasma Jet for Water Adhesion Controlling.

Superhydrophobic surfaces with hydrophilic patterns have great application potential in various fields, such as microfluidic systems and water harvesting. However, many reported preparation methods involve complicated devices and/or masks, making fabrication of these patterned surfaces time-consuming and inefficient. Here, we propose a highly efficient, simple, and maskless microplasma jet (MPJ) treatment method to prepare hydrophilic patterns such as dots, lines, and curves on superhydrophobic aluminum substrates. Contact angles, sliding angles, adhesive forces, and droplet impact behavior of the created patterns are investigated and analyzed. The prepared "dot" patterns exhibit great water adhesion, whereas the "line" patterns show anisotropic adhesion. Additionally, the MPJ treatment does not obviously change the surface structures, which makes it possible to achieve repeatable patterning on one substrate. The adhesion behavior of these patterns could be adjusted using MPJs with different diameters. MPJs with larger diameters are efficient for the creation of patterns with high water adhesion, which can be potentially used for open-channel lab-on-chip systems (e.g., continuous water transportation), whereas MPJs with smaller diameters are preferable in preparing patterns with low water adhesion for diverse applications in biomedical fields (e.g., lossless liquid droplet mixing and cell screening).

A Twice Electrochemical-Etching Method to Fabricate Superhydrophobic-Superhydrophilic Patterns for Biomimetic Fog Harvest.

Superhydrophobic-superhydrophilic patterned surfaces have attracted more and more attention due to their great potential applications in the fog harvest process. In this work, we developed a simple and universal electrochemical-etching method to fabricate the superhydrophobic-superhydrophilic patterned surface on metal superhydrophobic substrates. The anti-electrochemical corrosion property of superhydrophobic substrates and the dependence of electrochemical etching potential on the wettability of the fabricated dimples were investigated on Al samples. Results showed that high etching potential was beneficial for efficiently producing a uniform superhydrophilic dimple. Fabrication of long-term superhydrophilic dimples on the Al superhydrophobic substrate was achieved by combining the masked electrochemical etching and boiling-water immersion methods. A long-term wedge-shaped superhydrophilic dimple array was fabricated on a superhydrophobic surface. The fog harvest test showed that the surface with a wedge-shaped pattern array had high water collection efficiency. Condensing water on the pattern was easy to converge and depart due to the internal Laplace pressure gradient of the liquid and the contact angle hysteresis contrast on the surface. The Furmidge equation was applied to explain the droplet departing mechanism and to control the departing volume. The fabrication technique and research of the fog harvest process may guide the design of new water collection devices.

Fabrication of Long-Term Underwater Superoleophobic Al Surfaces and Application on Underwater Lossless Manipulation of Non-Polar Organic Liquids.

Underwater superoleophobic surfaces have different applications in fields from oil/water separation to underwater lossless manipulation. This kind of surfaces can be easily transformed from superhydrophilic surfaces in air, which means the stability of superhydrophilicity in air determines the stability of underwater superoleophobicity. However, superhydrophilic surfaces fabricated by some existing methods easily become hydrophobic or superhydrophobic in air with time. Here, a facile method combined with electrochemical etching and boiling water immersion is developed to fabricate long-term underwater superoleophobic surfaces. The surface morphologies and chemical compositions are investigated. The results show that the electrochemically etched and boiling-water immersed Al surfaces have excellent long-term superhydrophilicity in air for over 1 year and boehmite plays an important role in maintaining long-term stability of wettability. Based on the fabricated underwater superoleophobic surfaces, a special method and device were developed to realize the underwater lossless manipulation of immiscible organic liquid droplets with a large volume. The capture and release of liquid droplets were realized by controlling the resultant force of the applied driving pressure, gravity and buoyancy. The research has potential application in research-fields such as the transfer of valuable reagents, accurate control of miniature chemical reactions, droplet-based reactors, and eliminates contamination of manipulator components.