Silicon surface texturing with a combination of potassium hydroxide and tetra-methyl ammonium hydroxide etching

A two step silicon surface texturing, consisting of potassium hydroxide (KOH) etching followed by tetra-methyl ammonium hydroxide etching is presented. This combined texturing results in 13.8% reflectivity at 600 nm compared to 16.1% reflectivity for KOH etching due to the modification of microstructure of etched pyramids. This combined etching also results in significantly lower flat-band voltage (V-FB) (-0.19V compared to -1.3 V) and interface trap density (D-it) (2.13 x 10(12) cm(-2) eV(-1) compared to 3.2 x 10(12) cm(-2) eV(-1)). (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4776733]

Alternative methods for surface texturing

Surface texturing has a great potential to improve tribological performance. First, possible texturing methods were identified and classified according to their physical principles. In sequence, some alternative texturing methods are presented. Some of them are already currently used either in industry or in laboratory, and innovations or simplifications are described for them. Others are innovative techniques. Some were explored only tentatively, where basic ideas and simple experimental investigations were developed to check their validity. Others were explored in more detail, so that their practical applicability could be identified. The first texturing method was photochemical texturing using a simple and cheap apparatus. Masking with inkjet printing before chemical etching was also successful to texture metallic samples. A new method involving electrochemical texturing, without the need to previously mask the samples to be textured have been studied in terms of voltage, current, mechanical configuration of the apparatus and electrolyte flushing. Another method aims to generate randomly distributed circular pockets on steel surfaces and involves dispersion of small acid droplets in oil. The final method involves the selective formation of hard areas on a steel surface by locallised diffusion, which should then develop into a texture during wear.

Surface texturing through cylinder buckling

We consider the axial buckling of a thin-walled cylinder fitted onto a mandrel core with a prescribed annular gap. The buckling pattern develops fully and uniformly to yield a surface texture of regular diamond-shaped buckles, which we propose for novel morphing structures. We describe experiments that operate well into the postbuckling regime, where a classical analysis does not apply; we show that the size of buckles depends on the cylinder radius and the gap width, but not on its thickness, and we formulate simple relationships from kinematics alone for estimating the buckle proportions during loading. © 2014 by ASME.

Nanometer Scale Titanium Surface Texturing Are Detected by Signaling Pathways Involving Transient FAK and Src Activations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of a nanometer roughness scale resorbable media-processed surface: a study in dogs

Objectives: This study compared the biomechanical fixation and bone-to-implant contact (BIC) of implants with different surfaces treatment (experimental resorbable blasting media-processed nanometer roughness scale surface, and control dual acid-etched) in a dog model. Material and methods: Surface characterization was made in six implants by means of scanning electron microscopic imaging, atomic force microscopy to evaluate roughness parameters, and X-ray photoelectron spectroscopy (XPS) for chemical assessment. The animal model comprised the bilateral placement of control (n = 24) and experimental surface (n = 24) implants along the proximal tibiae of six mongrel dogs, which remained in place for 2 or 4 weeks. Half of the specimens were biomechanically tested (torque), and the other half was subjected to histomorphologic/ morphometric evaluation. BIC and resistance to failure measures were each evaluated as a function of time and surface treatment in a mixed model ANOVA. Results: Surface texturing was significantly higher for the experimental compared with the control surface. The survey XPS spectra detected O, C, Al, and Ti at the control group, and Ca (similar to 0.2-0.9%) and P (similar to 1.7-4.1%) besides O, C, Al, and Ti at experimental surfaces. While no statistical difference in BIC was found between experimental and control surfaces or between 2 and 4 weeks in vivo, both longer time and use of experimental surface significantly increased resistance to failure. Conclusions: The experimental surface resulted in enhanced biomechanical fixation but comparable BIC relative to control, suggesting higher bone mechanical properties around the experimental implants.

Fabrication of meso-porous sintered metal thin films by selective etching of silica based sacrificial template

 Meso-porous metal materials have enhanced surface energies offering unique surface properties with potential applications in chemical catalysis, molecular sensing and selective separation. In this paper, commercial 20 nm diameter metal nano-particles, including silver and copper were blended with 7 nm silica nano-particles by shear mixing. The resulted powders were cold-sintered to form dense, hybrid thin films. The sacrificial silica template was then removed by selective etching in 12 wt% hydrofluoric acid solutions for 15 min to reveal a purely metallic meso-porous thin film material. The impact of the initial silica nano-particle diameter (7–20 nm) as well as the sintering pressure (5–20 ton·m−2) and etching conditions on the morphology and properties of the final nano-porous thin films were investigated by porometry, pyknometery, gas and liquid permeation and electron microscopy. Furthermore, the morphology of the pores and particle aggregation during shear mixing were assessed through cross-sectioning by focus ion beam milling. It is demonstrated that meso-pores ranging between 50 and 320 nm in average diameter and porosities up to 47% can be successfully formed for the range of materials tested.

Growth evolution of self-textured ZnO films deposited by magnetron sputtering at low temperatures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

New strategies in laser processing of TCOs for light management improvement in thin-film silicon solar cells

Light confinement strategies play a crucial role in the performance of thin-film (TF) silicon solar cells. One way to reduce the optical losses is the texturing of the transparent conductive oxide (TCO) that acts as the front contact. Other losses arise from the mismatch between the incident light spectrum and the spectral properties of the absorbent material that imply that low energy photons (below the bandgap value) are not absorbed, and therefore can not generate photocurrent. Up-conversion techniques, in which two sub-bandgap photons are combined to give one photon with a better matching with the bandgap, were proposed to overcome this problem. In particular, this work studies two strategies to improve light management in thin film silicon solar cells using laser technology. The first one addresses the problem of TCO surface texturing using fully commercial fast and ultrafast solid state laser sources. Aluminum doped Zinc Oxide (AZO) samples were laser processed and the results were optically evaluated by measuring the haze factor of the treated samples. As a second strategy, laser annealing experiments of TCOs doped with rare earth ions are presented as a potential process to produce layers with up-conversion properties, opening the possibility of its potential use in high efficiency solar cells.

Influência do acabamento superficial no desempenho de lubrificantes de motor novos e usados em automóveis abastecidos com E22 e E100.

Superfícies anisotrópicas lisas e rugosas foram usadas para avaliar o efeito da rugosidade e da direção de acabamento na formação de MoS2 a partir de MoDTC em ensaios tribologicos lubrificados com óleos de motor completamente formulados. Igualmente foi avaliada a resposta de atrito de lubrificantes de motor usados em carros de passageiros e em testes de dinamômetro abastecidos com etanol (E100) e gasolina (E22). Encontrou-se que tanto a direção de acabamento quanto a rugosidade foram fundamentais na reação MoDTC - MoS2. A direção de acabamento influenciou na medida que carregamentos tangenciais geram respostas diferentes nos ensaios quando são realizados paralelos e perpendiculares às linhas de acabamento, dado que para os últimos apresenta-se maior deformação plástica das asperezas, o qual favorece a obtenção de superfícies livres de óxidos, que tem sido indicada como uma condição necessário para que aconteça a reação MoDTC - MoS2. Por esta razão os valores de coeficiente de atrito próprios da formação de MoS2 foram obtidos somente nas superfícies rugosas ensaiadas perpendiculares às marcas de acabamento. Para superfícies com valores de índice de plasticidade superiores a 1 e nos quais não são formados filmes com boas capacidades redutoras de atrito, como é o caso de ensaios realizados com óleos base (livres de aditivos), o coeficiente de atrito não depende da rugosidade e da direção de acabamento. Nos ensaios lubrificados com óleos usado, encontraram-se valores de coeficiente de atrito similares aos obtidos nas condições de lubrificação com óleo livres de aditivos, devido provavelmente à redução do MoDTC no lubrificante como tem sido identificado por diferentes autores. Quando foram comparados os óleos usados contaminados com etanol com os óleos usados contaminados com gasolina, encontrou-se maior oxidação nestes últimos. Mesmo que estas diferenças de oxidação dos óleos não significaram diferenças em termos de atrito, estas podem ser importantes na medida em que óleos mais oxidados podem favorecer o desgaste oxidativo.

Avaliação tribológica de novas modificações superficiais para cilindros de laminação a frio

The present work analyzed the tribological behavior of coatings/surface modifications traditionally used in cold rolling mill rolls and new coatings/surface modificationswith potential to replace the carcinogenic hard chrome. The study started with identification of wear mechanisms occurring in real coldrollingmill rolls. Due the high cost and dimensions of the rolls, thereplication technique was used. Replicas were obtained from 4 different rolling millBrazilian companies before and after a normal rolling campaign. Initial sliding tests were conducted using spherical and cylindrical counter bodies in order to verifywhichtribological conditions allowed to reproduce the wear mechanisms found in the replicas. These tests indicated the use of reciprocating sliding tests with cylindrical counter bodies (line contact), normal load of 100 N, and test times of and 1 h and 5 h. Different surface modifications were carried out on samples produced from a fragment of a rolling mill roll. The specimens were heat treated and ground on both sides. After, some specimens were surface textured by electrical discharge texturing (EDT). For both groups (ground and EDT), subsequent treatments of chromium plating, electroless NiP coating and plasma nitriding were carried out. The results of the reciprocating tests showed that specimens with electroless NiP coating presented the lowest friction coefficients, while plasma nitrided specimens showed the highest. In general, previous surface texturing before the coating/surface modification increased the wear of the counter bodies. Oneexceptionwas for EDT with subsequent electroless NiP coating, which presented the lowest counter bodies wear rate. The samples withelectroless NiP coating promoted a tribolayer consisting of Nickel, Phosphorus and Oxygen on both the specimens andthecounter bodies, which was apparently responsible for the reduction of friction coefficient and wear rate. The increase of the test time reduced the wear rate of the samples, apparently due the stability of the tribolayers formed, except for the nitrided samples. For the textured specimens, NiP coating showed the best performance in maintaining the surface topography of the specimens after the sliding tests.

Morphology-properties relationship of gas plasma treated hydrophobic meso-porous membranes and their improved performance for desalination by membrane distillation

The impact on performance of the surface energy and roughness of membrane materials used for direct contact membrane distillation are critical but yet poorly investigated parameters. The capacity to alter the wettability of highly hydrophobic materials such as poly(tetra-fluoro-ethylene) (PTFE) by gas plasma treatments is reported in this paper. An equally important contribution from this investigation arises from illustrating how vaporized material from the treated sample participates after a short while in the composition of the plasma and fundamentally changes the result of surface chemistry processes. The water contact angle across the hydrophobic membranes is generally controlled by varying the plasma gas conditions, such as the plasma power, chamber pressure and irradiation duration. Changes to surface porosity and roughness of the bulk material as well as the surface chemistry, through specific and partial de-fluorination of the surface were detected and systematically studied by Fourier transform infra-red analysis and scanning electron microscopy. It was found that the rupture of fibrils, formed during membrane processing by thermal-stretching, led to the formation of a denser surface composed of nodules similar to these naturally acting as bridging points across the membrane material between fibrils. This structural change has a profound and impart a permanent effect on the permeation across the modified membranes, which was found to be enhanced by up to 10% for long plasma exposures while the selectivity of the membranes was found to remain unaffected by the treatment at a level higher than 99.99%. This is the first time that an investigation demonstrates how the permeation characteristics of these membranes is directly related to data from spectral, morphological and surface charge analyses, which provide new insights on the impact of plasma treatments on both, the surface charge and roughness, of PTFE porous materials.

Surface modification of textured silicon and its wetting behaviour

Textured silicon (Si) substrate were prepared using various texturing methods both chemical and physical and their water contact angle, surface topography and Raman spectra were studied and investigated. The effect of plasma and chemical treatment on micro/nanostructure and roughness of the surface with and without deposition of Octadecyltrichlorosilane (ODTS, Cl3Si (CH3)(17)), self-assembled monolayer (SAM) is investigated for achieving higher water contact angle (theta(c)). The importance of synergism of texturing with deposition of ODTS SAM in preparing superhydrophobic silicon surfaces has been discussed. It is shown that superhydrophobic silicon surfaces can be achieved on silicon surfaces by coating with ODTS, irrespective of whether it is textured or not, polished or unpolished, provided a chemical treatment is given to the surface prior to the ODTS coating.

Investigation on Depth of Heat Affected Zone of Discharge Spot by High Repetitive Rate YAG Laser-Induced Discharge Texturing

It is known that the press formability and the elongation of laser textured sheet are improved, and the service life of textured roll is longer than that of the un-textured roll due to hardening of the treated surface. One of the goals to develop high repetitive rate YAG laser-induced discharge texturing (LIDT) is to get deeper hardening zone. By observing and measuring cross-section of LIDT spots in different discharge conditions, it is found that the single-crater, which is formed by the discharge conditions of anode, which is covered by an oil film and with rectangular current waveform, has the most depth of heat affected zone (HAZ) comparing with other crater shapes when discharge energy is the same. The depth of HAZ is mainly depends on pulse duration when the discharge spot is single-crater. The results are analyzed.

Seamless, Static Multi-Texturing of 3D Meshes

In the context of 3D reconstruction, we present a static multi-texturing system yielding a seamless texture atlas calculated by combining the colour information from several photos from the same subject covering most of its surface. These pictures can be provided by shooting just one camera several times when reconstructing a static object, or a set of synchronized cameras, when dealing with a human or any other moving object. We suppress the colour seams due to image misalignments and irregular lighting conditions that multi-texturing approaches typically suffer from, while minimizing the blurring effect introduced by colour blending techniques. Our system is robust enough to compensate for the almost inevitable inaccuracies of 3D meshes obtained with visual hull–based techniques: errors in silhouette segmentation, inherently bad handling of concavities, etc.