Chemical Vapor Deposition of TiSi Nanowires on C54 TiSi₂ Thin Film: An Amorphous Titanium Silicide Interlayer Assisted Nanowire Growth

Abstract

A C54-TiSi2 film was grown on a Si substrate at 1073 K by low pressure chemical vapor deposition (LPCVD) employing titanium subchlorides TiCl x(g), generated by reacting between TiCl4(g) and Ti(s) at 1173 K, as the Ti source. Growth of titanium silicide (TiSi) nanowires (NWs; diameter 30−80 nm, length several micrometers) on a C54-TiSi2 film was observed. Growth direction of the NWs was determined to be along the [010] axis. An amorphous titanium silicide interlayer was observed between the NWs and the C54-TiSi2 film. This interlayer, probably existing as a quasi-liquid thin film during the growth, appears to be the key factor to assist the NW development. Field emission properties, turn-on field E o and field enhancement factor β, of the vertically grown TiSi NWs were determined to be 5.25 V μm−1 and 876, respectively.

Metallic conduction and large electron-phonon-impurity interference effect in single TiSi nanowires

“…Our measured low residual resistivity ratios ρ (300 K)/ ρ 0 <2 strongly suggest the presence of large amounts of defects (e.g., point defects) in the NWs, where ρ 0 is the residual resistivity due to elastic electron scattering off defects. This observation is in sharp contrast to the conclusion drawn from HRTEM and XRD studies [5], where structure characterizations indicated good crystalline structures without noticeable lattice defects. Indeed, the electrical transport measurement is one of the most sensitive techniques for probing defects in single nanoscale structures [17-19].…”

“…Our TiSi NWs were synthesized via a low-pressure chemical vapor deposition process using TiCl 4 and titanium powder as precursors; no templates or catalysts were needed [5]. The growth mechanism and detailed structure and composition characterizations by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and other techniques have been reported by Lin et al in [5].…”

“…The growth mechanism and detailed structure and composition characterizations by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and other techniques have been reported by Lin et al in [5]. Since these NWs can be readily coated by a thick (approximately 10 nm) oxide layer over the surfaces [5,13], we choose the ‘invasive’ focused-ion-beam-induced deposition (FIBID) technique to fabricate the electrical contacts onto individual NWs. It should be stressed that the existence of the thick oxide layers prevented us from making good ohmic contacts when employing the electron-beam lithographic technique.…”

“…Among all the six phases of titanium silicides reported to date, titanium monosilicide (TiSi) [2] has the highest mechanical hardness which, combined with its low resistivity [3] (≈ 60 μΩ cm in bulk form at 300 K), can be of interest for the possible engineering of micro- and nano-electromechanical systems [4]. However, as compared to other titanium silicides, TiSi has not been much studied either in bulk form or at the nanoscale level due to the difficulties of either preparing quantities sufficient for bulk characterizations [3] or preparing single-phased nanostructures [5]. …”

“…Recently, some of us have successfully synthesized single-crystalline TiSi nanowires (NWs) [5]. The material belongs to one of the eight transition metal silicide NWs currently known [6].…”