Characterization of InSb Nanoparticles Synthesized Using Inert Gas Condensation
© Pandya and Kordesch. 2015
Received: 18 April 2015
Accepted: 1 June 2015
Published: 10 June 2015
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.
Indium antimonide (InSb) is a well-known III-IV semiconductor with one of the smallest band gaps (~0.17 eV at 300 K) and the highest room-temperature electron mobility (~78,000 cm2/(Vs)2). InSb has a very small effective mass for electrons and thus has a large Bohr radius of ~65 nm. All these properties make InSb a good candidate for infrared detectors, magnetic sensors, cooling devices, thermoelectric power generation, high-speed field-effect transistors, and low-power device applications [1–4]. Low-dimensional InSb structures show good quantum confinement and various studies have been published on synthesis and characterization of InSb thin films and nano-wires [5–11]. But on the other hand, InSb nanoparticles (NPs) have been rarely studied. The synthesis of low dimensional InSb structures has been challenging in general and problems like non-uniformity in size of NPs and aggregation of NPs have persisted. Here, we present a comparatively straightforward method for synthesis of InSb NPs with reasonable control over NP aggregation.
We have synthesized InSb NPs using a vapor phase technique known as inert gas condensation (IGC). The synthesis process will be described in detail in this paper. NPs were directly deposited on substrates at room temperature. The NPs were characterized using techniques like X-ray diffractometer (XRD), transmission electron microscopy (TEM)—regular and high-resolution mode, energy dispersive X-ray (EDX) spectroscopy, scanning optical Raman (SOR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy.
A diagram explaining the formation of NPs in the condensation chamber can be seen in Fig. 1b. A 99.99 % pure 1:1 InSb target, 38.1 mm in diameter and 3.175 mm in thickness, was sputtered in presence of 99.99 % pure Ar gas. The base pressure of the system was maintained at 10−7 Torr. The parameters used for synthesis were as follows: power =30–50 W, condensation chamber pressure =1 T, and deposition time =30–90 min. The ratio of pressure in the condensation chamber to that of deposition chamber was maintained at 1000. The aggregation length, defined as the distance between sputtering source and the nozzle, was 10 cm, and the distance between the substrate and the nozzle was 1 cm. Various substrates like glass cover slides, TEM grids, and (111) p-type silicon wafers were used to facilitate various types of NP characterization.
Structural characterization of NPs was carried out using a Rigaku MiniFlex-II X-Ray Diffractometer operated at 30 kV and 15 mA (with CuKα radiation at 0.154 nm) and a JEOL 1010 TEM operated at 100 kV and JEM 2100F high-resolution transmission electron microscopy (HRTEM) system. The composition of InSb NPs was obtained using a Noran Instruments EDX assembled with a S-2460N Hitachi thermionic emission SEM and operated at 25 kV accelerating voltage. The Raman spectrum was obtained using WITec R-SNOM-300s. A CW 532-nm wavelength YAG laser with adjustable power was used to excite the NPs. And the band gap of the NPs was obtained using a Perkin Elmer Spectrum Spotlight 300 FTIR microscope.
Results and discussions
Composition in InSb NPs using EDX
Weight % error
Atom % error
Here, D is the crystallite size, k is the shape factor (~1), λ is the wavelength of the CuΚα radiations (~0.154 nm), β is the integral broadening of XRD peaks in radians, and ε is the lattice strain. The β parameter was corrected for instrumental broadening.
The mean value of the grain size was found to be 25.62 nm, and the value of strain in NPs was found to be 0.0015 nm. The value of D is comparable to the average particle size of NPs seen under the TEM.
These NPs will be further characterized for photo detector applications, the results of which will be reported later.
To summarize, we have demonstrated a vapor phase technique to synthesize InSb NPs useful for various electronics applications. The TEM studies showed bimodal distribution with average particle sizes of 13.70 and 33.20 nm. Structural characterization using HRTEM indicated that the NPs are polycrystalline in nature with a cubic symmetry and are formed of smaller crystallites. X-ray diffraction result indicates that the sample has a crystalline zinc blende structure. 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. The crystallite size of the NPs calculated using Debye-Scherrer’s formula is in agreement with the NP size obtained using TEM. Raman spectra shows a peak at 184.27 cm−1 corresponding to the LO mode of InSb, and EDX study shows that the NPs have 1:1 In-to-Sb ratio. This confirms the formation of single phase InSb NPs. The band gap of the NPs as calculated using reflectance mode of FTIR was in the range of 0.43–0.52 eV. Thus, a blue shift of 0.26–0.35 eV was observed in the band gap of these NPs showing the effects of quantum confinement in nanostructures. Increased particle density shows reduction in the quantum confinement effects causing decrease in the band gap of the InSb NPs.
We would like to acknowledge CMSS and NQPI at Ohio University. We would also like to acknowledge the Center for Electrochemical Engineering Research (CEER) at Ohio University, and the National Science Foundation through the Major Research Instrumentation Grant # CBET-1126350 for the Transmission Electron Microscopy images and measurements. We would like to thank Mr. Gordon Renkes at the Analytical Spectroscopy Laboratory in the chemistry department at Ohio State University for his help with FTIR measurements. And we appreciate the help and support from Prof. Hugh Richardson, Prof. Arthur Smith, and Joseph Perry Corbett at Ohio University.
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