Significant reduction of thermal conductivity in silicon nanowire arrays.

Vertically aligned single-crystal silicon nanowire arrays (SiNWs) with various lengths, surface roughnesses and porosities were fabricated with the metal-assisted chemical etching method. Using the laser flash technique and differential scanning calorimetry, we characterized the thermal conductivities of bulk SiNWs/Si/SiNWs sandwich-structured composites (SSCs) at room temperature (300 K). The results demonstrate that the thermal conductivities of SSCs notably decrease with increases in the length, surface roughness and porosity of SiNWs. Furthermore, based on the series thermal-resistance model, we calculated the thermal conductivity of porous SiNWs to be as low as 1.68 W m(-1) K(-1) at 300 K. Considering the remarkable phonon scattering from the diameter, surface roughness and porosity of SiNWs, leading to a significant reduction of the thermal conductivity, SSCs and SiNWs could be applied to high-performance thermoelectric devices.

Surface morphology-dependent photoelectrochemical properties of one-dimensional Si nanostructure arrays prepared by chemical etching.

Maximizing the optical absorption of one-dimensional Si nanostructure arrays (1DSiNSAs) is desirable for excellent performance of 1DSiNSA-based optoelectronic devices. However, a quite large surface-to-volume ratio and enhanced surface roughness are usually produced by modulation of the morphology of the 1DSiNSAs prepared in a top-down method to improve their optical absorption. Surface recombination is mainly determined by the surface characteristics and significantly affects the photogenerated carrier collection. In this paper, we systematically investigated the photoelectrochemical characteristics of 1DSiNSAs with various morphologies prepared by the metal-assisted chemical etching of Si wafers. Our results show that the saturation photocurrent density and photoresponsivity of 1DSiNSAs first increased and then gradually decreased with an increasing etching time, while the reflection spectrum was gradually suppressed to the measurable minimum. To identify the behaviors of the photoresponsivity and optical absorption of the various 1DSiNSAs, we analyzed the morphology, structure, and minority-carrier lifetime. Additionally, device physics simulations were used to confirm the significance of surface recombination. We proposed that future directions for the design of nanostructure-based optoelectronic devices should include not only strong optical absorption but also low surface carrier recombination. High-performance devices could be obtained only by balancing the requirements for light absorption and photogenerated carrier collection.

Structures and field emission properties of silicon nanowire arrays implanted with energetic carbon ion beam.

Structures and field emission properties of silicon nanowire arrays (SiNWAs), which were fabricated by using of electroless-chemical etching method and post-implanted by the energetic carbon ion beam with an average energy of 20 keV at various doses, have been investigated. Structural analysis of SEM and XPS shows that SiC compound had been formed at the top of SiNWAs, and Si-C/Si composite nanostructure had been obtained. Compared to as-grown SiNWAs, the C ion implanted SiNWAs have better field emission characteristics. The turn-on field and the applied field at 100 microA/cm2 are reduced from 5.01 V/microm and 5.93 V/microm for as-grown SiNWAs to 4.45 V/microm and 5.40 V/microm for SiNWAs implanted at the dose of 1 x 10(16) cm(-2), respectively. However, large implanting amounts made serious structural damages at the top of nanowires, and impaired the field emission characteristics. The influence of energetic C ion implantation on the structures and field emission properties of SiNWAs has been discussed.

Field emission enhancement of Au-Si nano-particle-decorated silicon nanowires.

Au-Si nano-particle-decorated silicon nanowire arrays have been fabricated by Au film deposition on silicon nanowire array substrates and then post-thermal annealing under hydrogen atmosphere. Field emission measurements illustrated that the turn-on fields of the non-annealed Au-coated SiNWs were 6.02 to 7.51 V/µm, higher than that of the as-grown silicon nanowires, which is about 5.01 V/µm. Meanwhile, after being annealed above 650°C, Au-Si nano-particles were synthesized on the top surface of the silicon nanowire arrays and the one-dimensional Au-Si nano-particle-decorated SiNWs had a much lower turn-on field, 1.95 V/µm. The results demonstrated that annealed composite silicon nanowire array-based electron field emitters may have great advantages over many other emitters.

Effects of CF(0) Proton Flow on the Distribution of Light Energy Between PSI and PSII.

The Influence of energy transfer inhibitors of ATP synthase on the chlorophyll fluorescence quenching of thylakoids was studied by the saturation pulse method. Triphenyltin chloride (TPT) treatment could result in an increase of q(Q) and a decrease of q(E) of the thylakoids, but DCCD could not. This increase could be abolished when the deltapH across the thylakoid membrane was dissipated by uncouplers (1O mM NH(4)Cl plus 1&mgr;M nigericin) or in higher salt medium which could relieve localized protons on the thylakoid membrane. In the electron transport system of H(2)O right curved arrow PD(0X) or H(2)O right curved arrow PBQ coupled with PSII. The stimulatory effect of TPT on q(Q) also diminished. By the methods of modulated fluorescence and low temperature fluorescence measurement we observed that TPT markedly increased the imbalance of the distribution of light energy between PSI and PSII in favor of PSII. These results suggest that the CF(0) proton flow could influence the light energy distribution between the two photosystems. This might be materialized by the regulation of the membrane-localized protons on the photochemical efficiency of photosystem II.