Showing papers by "Rodney S. Ruoff published in 1997"

Silicon carbide formation by annealing C60 films on silicon

Abstract: Silicon carbide films were grown on (100) silicon substrates by deposition of 200-nm-thick C60 films, followed by annealing. The predeposited C60 is progressively destroyed by annealing, and carbon reacts with silicon to produce SiC. The reaction starts at the interface and continues by diffusion of silicon through the already formed SiC. At the lower temperatures (700 °C), the reaction is localized at the interface. Diffusion of silicon and formation of stoichiometric SiC requires annealing at 800 °C for t⩾100 min and at 900 °C for t⩾25 min. The stoichiometric films are uniform with a grain size of 20–40 nm. A diffusion coefficient of silicon in SiC of 4×10−15 cm2/s at 900 °C was determined. Because the diffusion of silicon is faster through preferential paths in the SiC film, such as grain boundaries and other crystalline defects, pits and voids are produced in the silicon substrate when the C60 predeposited film covers larger areas.

Designer particles of micron and submicron dimension

Abstract: Micron-sized particles are produced in quantity by one of various methods, including generally the steps of preparing a substrate surface through a lithographic process, the surface being characterized by defining a plurality of elements, depositing a layer of particle material on the substrate surface including the elements, processing the substrate surface to isolate the material deposited on the elements, and separating the particles from the elements. The size and shape of the elements predetermine the size and shape of the particles. The elements may comprise, inter alia, pillars of photoresist or spaces on the substrate surrounded and defined by photoresist.

The structure, slip systems, and microhardness of C60 crystals

Abstract: The structure and microplasticity of high-purity fullerite C60 have been investigated comprehensively. The crystalline structure, lattice parameters, and phase transitions have been studied by x-ray diffractometry in the temperature range 30–293 K. It is found that the temperature corresponding to the orientational order–disorder phase transition is Tc=260 K. A considerable number of regions with stacking faults discovered in the samples leads to blurring of the fcc→sc phase transition in the temperature interval Tc±3 K. The a(T) dependences of the lattice parameter display peculiarities at the following characteristic temperatures: Tc at which the lattice parameter jump Δa/a=3.3×10−3 is observed, and the temperatures T0≃155 K, and Tg≃95 K which are associated with the beginning and end of molecular orientation freezing. It is shown that the formation of orientational glass is accompanied by a considerable increase in the width of x-ray reflections. The slip geometry and the temperature dependence of micr...

Patterning silicon carbide on silicon by ion modification of C60 films

Abstract: Reaction of C60 with Si at temperatures above 800°C is known to give SiC. Furthermore, treatment of vapor-deposited C60 films with a beam of Ar+ transforms the surface layer of C60 into a nonvolatile carbon deposit. Based on these two findings, we have developed a method for patterning SiC structures on silicon. C60 is first vapor deposited onto a clean Si surface. By rastering the ion beam on selected parts of the sample, we write a chosen pattern on the C60 film. Upon increasing the temperature to around 300–350°C, the C60 film remains only in the areas that were subjected to irradiation, while it evaporates off the remaining surface. During the subsequent annealing at 900°C, the modified C60 layer confines the underlying C60 on the silicon surface, allowing the formation of SiC. At shorter times, traces of the capping layer are visible at the edges of the irradiated zone. These results demonstrate the principle of fabricating lithographically patterned SiC structures on silicon without masking and etching processes and with the high lateral resolution possible with ion beams.