Low-energy-ion bombardment of semiconductors can lead to the development of complex and diverse nanostructures. Of particular interest in these structured surfaces is the formation of highly ordered patterns whose optical, electronic, and magnetic properties are different from those of bulk materials and might find technological uses. [1][2][3][4][5] Compared to the low efficiency of lithographic methods for mass production, this self-organized approach offers a new route for fabrication of ordered patterns over large areas in a short processing time on the nanometer scale, beyond the limits of lithography. [1,4] This technique is based on the morphological instability of a sputtered surface driven by a kinetic balance between roughening and smoothing. [6,7] Thus mechanisms that control the species concentration on the surface can make contributions to structure formation. [3,[7][8][9][10][11][12] It is now established that well-ordered quantum dots can be generated on the surface of semiconductors (Si, Ge, GaSb) under certain irradiation conditions. [1,13,14] For a long time it has been expected that the instability of a surface can also lead to well-ordered hole formation. However, to date experimental observation of such features has been lacking. In this Communication, we report that a hexagonally ordered, honeycomb-like structure of holes 35 nm across and 45 nm apart on the Ge surface can be formed under focused ion beam (FIB) bombardment at normal incidence. The structured Ge fabricated by FIB bombardment shows a high surface area and a considerably blue-shifted energy gap. We found that interplay between ion sputtering, redeposition, viscous flow, and surface diffusion is responsible for ordered pattern formation. Simulations of the evolution of the surface morphology on the basis of the damped Kuramoto-Sivashinsky (DKS) growth model have been performed to facilitate the interpretation of the experimental findings. [15][16][17][18][19] As an indirect energy-gap semiconductor, germanium is a poor light emitter, which makes it challenging to create efficient Ge-based light-emitting devices. Significant effort has been devoted to the development of the optical properties of Ge based on changing the surface morphology.[20] In the work reported here, we focused on the use of ion beam radiation to fabricate nanostructures on the Ge surface.The ion-induced nanostructures were fabricated on commercially available Ge with (100) orientation by FIB bombardment. Under normal bombardment with ion energy greater than 5 keV, worm-like structures were developed on Ge surface with large aspect ratio. When the energy was 5 keV, however, highly ordered hole arrays could be achieved. Figure 1 shows scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of a typical nanohole pattern induced on a Ge(100) surface by 5 keV (Ga þ ) FIB bombardment for 5 min. A perfect hexagonal arrangement of holes is observed within domains of ca. 500 nm. Like polycrystalline structure, there are ''grain boundaries'' separati...
An analytical formula is developed for the evolution of angular dependence of sputtering yields by extending the theory of sputtering yield proposed by Sigmund. We demonstrate that the peak of sputtering yield at oblique incidence can be attributed to a balance between the increased energy deposited on the surface by incident ion which enhances the sputtering yield and the decreased depth travelled by recoil atom which reduces the sputtering yield. The predicted dependence of sputtering yield on the incident angle is in good agreement with experimental observations.
Due to the outstanding electrical, magnetic and catalytic properties, nickel oxide (NiO) has been received considerable attention during the past decades. In this study, NiO nanoparticles were prepared by solgel method, which is one of the simplest and lowest-cost techniques. The synthesis was accomplished by using Poly(alkylene oxide) block copolymer as the surfactant, and Ni(NO 3 ) 2 ·6H 2 O as the inorganic precursor. The effect of experimental parameters, such as calcination temperatures and H 2 O concentration on the NiO nanoparticles formation were investigated. TGA, XRD, SEM, TEM and N 2 adsorptiondesorption isotherms were used to characterize the microstructure and specific surface area of the samples. TGA and FTIR analyses demonstrated that copolymers were expelled at 573 K. The formation of NiO nanoparticles and their structural features were greatly dependent on the calcination temperature. The sample calcined at 923 K was composed of pure NiO nanoparticles as shown by XRD. As H 2 O concentration was increased, the reoxidation process of metallic Ni to form NiO would reduce, but it would not affect the structural type of NiO nanoparticles. In general, the addition of water would weaken and inhibit oxidation effects. The temperature of stable metallic Ni was increased up to 823 K. The specific surface area evaluated from the N 2 adsorptiondesorption indicated that the samples consisting of non-porous NiO nanoparticles. Increasing H 2 O addition resulted in an increase of specific surface area of nanocrystalline NiO powder.
We study the variation of sputtering yields with surface morphologies under the assumption of a specially prescribed surface shape. Compared with a flat surface, we show that surface morphology can cause a decrease in the sputtering yield and an increase in the incident angle where sputtering yield is maximum. Based on Sigmund's theory, an analytical formula for the morphology dependent sputtering yield is developed by averaging the curvature dependent sputtering yield. The predicted dependence of sputtering yield on surface morphology is in good agreement with experimental observations.
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