Papers by Keyword: Patterning

Abstract: Mesa- and trench-patterned surfaces of 4H-SiC(0001) 4°off wafers were structured in macrosteps using Si melting in a SiC-Si-SiC sandwich configuration. Si spreading difficulties were observed in the case of trench-patterned samples while the attempts on mesa-patterned ones were more successful. In the latter case, parallel macrosteps were formed on both the dry-etched and unetched areas though these macrosteps rarely cross the patterns edges. The proposed mechanism involved preferential etching at Si-C bilayer step edges and fast lateral propagation along the [1120] direction.

Abstract: Multiple-input multiple-output (MIMO) antenna technology owes its low weight and energy-saving electronic applications to the use of polymer substrates. Applying metallization to obtain conductive substrates involves spraying untreated molds with a gel to form a temporary protective coating. The coating is then partially removed with a laser to expose areas for metallization. After that, the exposed areas are modified with a palladium-tin (Pd-Sn) colloidal catalyst to enhance the adhesion between the insulating surface and copper deposition. It’s with these three steps that the modified areas become selective to metallization. It’s observed that copper deposited incessantly at a high speed of 5 μm/hr after above treatment, and formed a dense layer with a low resistivity. The conductive patterns plated on the 3D substrate render the MIMO antenna system applicable to wireless local area network (WLAN) with two switchable frequencies, as evidenced by the simulation tests in which the antennae had ECC values below 0.2, a VSWR of 3 to 1, and a radiation efficiency around 50% at 2.4 GHz and 37% at 5.8 GHz. The electroless plating technology used above adds to a duplicable MIMO-antenna manufacturing process of low temperature and cost.

Abstract: In this paper, we present the results of plasma nitriding treatments on austenitic stainless steel substrates previously coated with a patterned silicon oxide layer. For this purpose, masks were made by PECVD for the deposition of a silicon oxide layer on polished austenitic AISI 316L samples. For the final nitriding treatment, we used a multi-dipolar plasma providing independent substrate polarization. The interactions between expanded austenite and fixed silicon oxide mask in different shapes (circular and square dots) are observed by atomic force microscopy (AFM) on the same area before and after the nitriding treatment. After this thermochemical treatment, we obtain strong distortions of the dots, in particular at the edges of the larger size dots. The role of elastic deformation, due to the expanded austenitic phase formed by the diffusion of nitrogen under the mask is of primary importance.

Abstract: We report two possible routes of fabrication of large surfaces of ferromagnetic shape memory antidots with tunable pore size and center-to-center distances. By using the drop coating method, we have prepared a large area of 2D arrays (typically 1cm²) of polystyrene spheres (PS) (1.4±0.1μm diameter) on a Si substrate. We have used reactive ion etching with a gas mixture of O₂ (12sccm) and Ar (5sccm) to reduce the diameter of the PS spheres whereby controlling the size of pores. The film deposition was performed on a substrate heated at 500oC (route 1) and at room temperature with subsequent annealing in a furnace at 500oC for 4 hours (route 2). Route 1 proved to be promising but more work is needed to optimize it. The antidots of Ni-Mn-Ga obtained along route 2 are ferromagnetic with a Curie temperature ~100oC, and a spread martensitic transformation (between-100oC and-30oC).

Abstract: EHD (Electrohydrodynamic) patterning forming micro structures with UV light curable materials at room temperature is investigated in this paper. It is a process for fabricating patterns on polymer film by applying electrical field to the template and the substrate as an electrode pair. The maintaining time of EHD patterning is reduced from several hours to tens of minutes by using UV curable polymer with low viscosity. The flat template generates the periodic pillars with micro scale. The periodic pillars with different period are obtained by varying the applied voltage in the different phase of experiment. The micro scale replication with good fidelity is produced by using patterned template made of doped silicon wafer.

Abstract: Fouling of surfaces is a major challenge in design and operation of many industrial heat transfer equipment. Fouling causes significant energy, material and production losses, which increase the environmental impact and decrease economic profitability of processes. Even small improvements in prevention of fouling would lead to significant savings in a wide range of heat transfer applications. In this study, crystallization fouling of aqueous calcium carbonate solutions on a heated stainless steel surface is used to investigate the prevention of fouling in heat transfer equipment by physical surface modifications. Fouling behaviour of different surface patterns are studied experimentally in a laboratory scale fouling test apparatus. CFD modelling is used to study hydrodynamic and thermal conditions near surfaces with different patterns. In addition, the effect of surface pattern on the removal of particles is studied numerically. Surface patterning is found to affect the hydrodynamic and thermal conditions near the wall, and therefore to change the conditions for fouling layer build-up and removal, when compared to a flat heat transfer surface. The most promising surface pattern includes curved shapes, and it seems to create flow conditions in which improved convective heat transfer decreases the driving force for crystallization fouling. In addition, curved surfaces increase the shear forces at the wall, which prevents adhesion of the foulants to the surface and increases resuspension.

Abstract: This paper presents two crystal plasticity based computational constitutive models for the intrinsic formation of plastic microstructure during monotonic loading and its altered evolution under strain path changes in metal forming operations. The formation step is modeled via a non-convex strain gradient crystal plasticity framework which could simulate the intrinsic development of the plastic microstructures. The evolution under strain path changes is modeled via phenomenologically based constitutive equations incorporated into crystal plasticity framework. The latter is capable of simulating the transient anisotropy effects (e.g. cross hardening, Bauschinger effect) depending on the change in the strain path. The paper discusses the unification of such models for the continuous modeling of microstructure formation and evolution processes.

Abstract: Regular micro-apparatus which covered with periodic nano-hole, nano-ridge and ripple structures on silicon bulk were formed by laser micro-machining with tightly focused beam of the femtosecond laser with wavelength of 800 nm, repetition rate of 1 kHz and the pulse length of 130 fs in air. The periodic nano-hole structures which focus with a 20× focusing objective lens (NA = 0.4) is reported. Investigating the relationship between the width of structures and the speed of processing.

Abstract: Electronic, biology and chemical biology have pushed the scientists to develop new techniques to graft locally organic molecules on surfaces. The objective of the work was to develop a cheap and lithography-free technique by combining Scanning Electrochemical Microscopy (SECM) and electrografting processes in view of tuning locally chemical and physical surface properties on initially homogeneous substrates. The electrografting process was carried out with diazonium salts Plots, lines or more complex 2D-patterns have been “imprinted” on conducting substrates.

Abstract: Patterned octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) was fabricated on silicon substrates, utilizing short wave UV irradiation meter (λ=184.9nm) as the photolithograph apparatus under the cover of the photomask. The patterned BiFeO₃ were prepared on the functional OTS-SAMs by sol-gel method. The characterization of the samples patterns was carried out by various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and energy disperse spectroscopy (EDS). The results indicate that the pattern BiFeO₃ thin films were successfully prepared on the functional OTS-SAMs by sol-gel method and the thin films were BiFeO₃ thin films with hexagonal perovskite distorted structure which has clear boundaries and 200µm deposited lines width.