Combination Of Lithographic Techniques Research Articles

Preparation of Inverted Pyramids by Electrochemical and Chemical Etching of n-Type Silicon under Thermodynamic Equilibrium State

Inverted pyramids on silicon surfaces are usually produced by the combination of lithographic techniques and anisotropic wet etching. However, lithographic techniques are expensive and complicated. In this report, inverted pyramids were prepared successfully by electrochemical etching of moderately doped n-type Si in 8% HF ethanol solution at 15 mA cm−2 under back side illumination. The surface and interface morphologies of porous silicon (PSi) films and inverted pyramids were characterized by FE-SEM. The results show that inverted pyramids with thermodynamic stable {111} planes form at the PSi-Si interfaces and a thermodynamic equilibrium establishes between the dynamic-competitive electrochemical and chemical etching behaviors during the same etching process. They compete not only for the limited photocarriers in silicon but also for the limited reactive ions in HF solution. The anisotropic electrochemical etching in multiple <100> directions, the isotropic chemical etching in hemispheric-shaped directions and the local microenvironment facilitated by macroprores are also essential to the formation of inverted pyramids. Contrasted to lithographic techniques, this method in terms of electrochemical and chemical etching at thermodynamic equilibrium state is a simple, low-cost, but efficient method. We believe such a method will be beneficial to the crystalline silicon solar cells or MEMS in the future.

Microscale Patterning of Hydrophobic/Hydrophilic Surfaces by Spatially Controlled Galvanic Displacement Reactions

In this letter, we report the design and fabrication of different metal patterns for the realization of spatially controlled hydrophobic/hydrophilic regions with micrometer resolution. The fabrication procedure, based on a combination of lithographic techniques and wet-chemistry reactions (namely, spontaneous Galvanic displacement reactions) is reliable, undemanding, and highly versatile, allowing the achievement of precise spatial control along with the use of a wide variety of different materials.

Micro/Nanoscale Patterning of Nanostructured Metal Substrates for Plasmonic Applications

The ability to precisely control the pattern of different metals at the micro- and nanoscale, along with their topology, has been demonstrated to be essential for many applications, ranging from material science to biomedical devices, electronics, and photonics. In this work, we show a novel approach, based on a combination of lithographic techniques and galvanic displacement reactions, to fabricate micro- and nanoscale patterns of different metals, with highly controlled surface roughness, onto a number of suitable substrates. We demonstrate the possibility to exploit such metal films to achieve significant fluorescence enhancement of nearby fluorophores, while maintaining accurate spatial control of the process, from submicron resolution to centimeter-sized features. These patterns may be also exploited for a wide range of applications, including SERS, solar cells, DNA microarray technology, hydrophobic/hydrophilic substrates, and magnetic devices.

Synthesis of Nanostructured Tungsten Oxide Thin Films

A facile and inexpensive method to produce thin films of nanostructured tungsten oxide is described. A nanocrystalline tungstite (WO3·H2O) film is spontaneously formed when a tungsten substrate is immersed in nitric acid at elevated temperatures. The resulting thin film is composed of plate-like tungstite crystals with edges preferentially directed out from the substrate surface. The tungstite can easily be transformed into WO3 by annealing. Patterned WO3·H2O/W structures can be obtained by a combination of lithographic techniques and etching. In this study, the effect of exposure time, acid concentration, and temperature on the microstructure of the films has been investigated. The potential of this inexpensive synthesis method to produce large-area coatings of nanostructured tungsten oxide as well as patterned films makes it interesting for several different applications, such as batteries, gas sensors, and photocatalysts.