C. P. Li

Silicon nanowires as chemical sensors

Chemical sensitivity of silicon nanowires bundles has been studied. Upon exposure to ammonia gas and water vapor, the electrical resistance of the HF-etched relative to non-etched silicon nanowires sample is found to dramatically decrease even at room temperature. This phenomenon serves as the basis for a new kind of sensor based on silicon nanowires. The sensor, made by a bundle of etched silicon nanowires, is simple and exhibits a fast response, high sensitivity and reversibility. The interactions between gas molecules and silicon nanowires, as well as the effect of silicon oxide sheath on the sensitivity and the mechanisms of gas sensing with silicon nanowires are discussed.

Ultrafine and uniform silicon nanowires grown with zeolites

Ultrafine and uniform silicon nanowires (SiNWs), with a Si crystalline core of 1–5 nm (average 3 nm) in diameter and a SiO2 outer layer of 10–20 nm thick, were synthesized by the oxide-assisted growth method via the disproportionation of thermally evaporated SiO using zeolite as a template/precursor. From transmission and secondary electron microscopic characterizations, we deduced that the zeolite acted to limit the lateral growth of the Si crystalline core and supply the excess oxide to form the thick oxide outer layer. The ultrafine SiNWs exhibited strong photoluminescence that peaked at 720 nm.

Single crystal Si layers on glass formed by ion cutting

The process of ion cutting was used to integrate single crystalline Si layers on glass for potential active matrix flat panel display and other applications. It was found that p-Si wafers implanted at 100–150 ° C with H with a dose in the order of a few times 10 16 cm −2 could be readily bonded to glass substrates when both of the surfaces were properly treated and activated. The as-implanted Si wafer surface was converted from p type to n type. Upon bonding at room temperature, annealing (300 ° C ) and exfoliation (450 ° C ), the transferred Si layer on glass and the as-exfoliated surface of the implanted Si wafer remained n type. A highly defective region was observed near the top of the Si layer on glass, however the crystalline quality was nearly defect free in the deeper region of the layer. Annealing at sequentially higher temperatures led to the recovery of p type conductivity at ∼600–650 ° C . The type conversion and the subsequent annealing behavior observed on the samples were rationalized in terms of ion enhanced oxygen diffusion and the presence of H-related shallow donors in the Si.

Gold nanowires from silicon nanowire templates

The work described in this letter is supported by two grants from the Research Grants Council of the Hong Kong SAR, China ~Project No. 8730016, e.g., CityU 3/01C; Project No. 9040633, e.g., CityU 1011/01P!, and by a grant from the Chinese Academy of Sciences, China.

Chainlike silicon nanowires: Morphology, electronic structure and luminescence studies

Research at the University of Western Ontario was supported by the Natural Science and Engineering Research Council (NSERC) of Canada. CSRF was supported by NSERC through a MFA grant and the National Research Council (NRC) of Canada. SRC was supported by the U.S. National Science Foundation under Grant No. DMR-00- 84402. N. B. W. acknowledges the support of a grant from the Research Grants Council of Hong Kong SAR [SiNWs RGC Grant 9040879 (CityU 1024/03)].

Effects of ambient pressure on silicon nanowire growth

Growth of silicon nanowires (SiNWs) by thermal evaporation of SiO in a closed system was studied. The yield of SiNWs obtained in the present closed system was much higher than that from the previous open systems. As the ambient pressure increased, the yield of SiNWs decreased and the diameter of the SiNWs increased, but the surface of the SiNWs was roughened. Transmission electron microscopic examination showed that the originally smooth surface of SiNWs was roughened by the formation of Si nano-particles. The implication of these results on the growth mechanism of the SiNWs is discussed.

Microstructure and field emission properties of coral-like carbon nanotubes

Coral-like carbon nanotubes (CNTs) have been synthesized by using chemical vapor deposition. Unlike conventional CNTs, the as-deposited CNT consisted of a high density of interlaced graphitic nanoflakes of about 5 nm in thickness. The CNTs had a bamboo-like internal structure with their outer walls consisting of many open graphite layers, and the nanoflakes stemming from the “bamboo knots.” The growth mechanism of CNTs was discussed. The field emission characteristics of CNT films showed a turn-on field as low as 4 V/μm. This special CNT might extend mechanical and electronic properties and applications of the CNTs.