Nanoparticles (NPs) of indium antimonide (InSb) were synthesized using a vapor phase synthesis technique known as inert gas condensation (IGC). NPs were directly deposited, at room temperature and under high vacuum, on glass cover slides, TEM grids and (111) p-type silicon wafers. TEM studies showed a bimodal distribution in the size of the NPs with average particle size of 13.70 nm and 33.20 nm. The Raman spectra of InSb NPs exhibited a peak centered at 184.27 cm−1, which corresponds to the longitudinal optical (LO) modes of phonon vibration in InSb. A 1:1 In-to-Sb composition ratio was confirmed by energy dispersive X-ray (EDX). X-ray diffractometer (XRD) and high-resolution transmission electron microscopy (HRTEM) studies revealed polycrystalline behavior of these NPs with lattice spacing around 0.37 and 0.23 nm corresponding to the growth directions of (111) and (220), respectively. The average crystallite size of the NPs obtained using XRD peak broadening results and the Debye-Scherrer formula was 25.62 nm, and the value of strain in NPs was found to be 0.0015. NP’s band gap obtained using spectroscopy and Fourier transform infrared (FTIR) spectroscopy was around 0.43–0.52 eV at 300 K, which is a blue shift of 0.26–0.35 eV. The effects of increased particle density resulting into aggregation of NPs are also discussed in this paper.
We describe techniques for performing photolithography and electron beam lithography in succession on the same resist-covered substrate. Larger openings are defined in the resist film through photolithography whereas smaller openings are defined through conventional electron beam lithography. The two processes are carried out one after the other and without an intermediate wet development step. At the conclusion of the two exposures, the resist film is developed once to reveal both large and small openings. Interestingly, these techniques are applicable to both positive and negative tone lithographies with both optical and electron beam exposure. Polymethyl methacrylate, by itself or mixed with a photocatalytic cross-linking agent, is used for this purpose. We demonstrate that such resists are sensitive to both ultraviolet and electron beam irradiation. All four possible combinations, consisting of optical and electron beam lithographies, carried out in positive and negative tone modes have been described. Demonstration grating structures have been shown and process conditions have been described for all four cases.
Acrylic resists are used for both electron beam lithography and for deep-ultraviolet (UV) lithography at 193 nm wavelength. Polymethyl methacrylate (PMMA) is the most widely used acrylic positive tone electron beam resist. While it offers superb resolution in this role, its dry etch resistance is quite poor. Here, the authors present a new technique for enhancing the dry etch resistance of PMMA. This involves adding Irgacure 651—a photo-cross-linking agent to PMMA. Irgacure-containing PMMA can be spin-coated onto substrates in exactly the same way as pure PMMA. Addition of Irgacure does not impair the chain scissioning properties of PMMA under electron beam irradiation. Electron beam lithography can be carried out with this resist in exactly the same manner as with pure PMMA, although at a higher dose. After electron beam exposure, the exposed sample can be developed in diluted methyl isobutyl ketone solvent, again just as with pure PMMA. A postlithography UV exposure step then cross-links the patterned resist; substantially enhancing its dry etch resistance. This technique enables the fabrication of deeper etched structures than is possible with PMMA alone.
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