Tingting Wang

Scalable colloidal synthesis of uniform Bi2S3 nanorods as sensitive materials for visible-light photodetectors

A facile colloidal chemistry method is reported for synthesis of uniform Bi2S3 nanorods in a mixed solution of oleylamine with other organic amines including n-dodecylamine (C12), n-octylamine (C8), and n-hexylamine (C6). The nanorod length can be tuned through the carbon-chain length of these amines and importantly multigrams of Bi2S3 nanorods can be readily synthesized in a single scaled-up batch. Current–voltage (I–V) measurements showed that the Bi2S3 nanorods, obtained from both the small and large-scale batches or ones with different chain-length amines, exhibit fast light response characteristics (at the sub-second scale) with an obviously enhanced photocurrent (or photoconductivity) under broad-spectrum white light or monochromatic visible light of different wavelengths. The as-obtained nanorods, as determined by time-dependent current (I–t) curves, also exhibit excellent photoresponsive stability and reproducibility with the on–off switch of light. The photoconductivity enhancement in the Bi2S3 nanorods is assigned to the efficient electron–hole pair separation due to a hole-trapping mechanism. These results indicate the promising potential of Bi2S3 nanorods for optoelectronic device applications including photodetection (sensing), optical switch, photocatalysis, and photovoltaics within the visible spectrum range.

Wettability of Si and Al–12Si alloy on Pd-implanted 6H–SiC

SiC monocrystal substrates are implanted by Pd ions with different ion-beam energies and fluences, and the effects of Pd ion implantation on wettability of Si/SiC and Al–12Si/SiC systems are investigated by the sessile drop technique. The decreases of contact angles of the two systems are disclosed after the ion implantation, which can be attributed to the increase of surface energy (σSV) of SiC substrate derived from high concentration of defects induced by the ion-implantation and to the decrease of solid–liquid surface energy (σSL) resulting from the increasing interfacial interactions. This study can provide guidance in improving the wettability of metals on SiC and the electronic packaging process of SiC substrate.

Composition-Dependent Aspect Ratio and Photoconductivity of Ternary (BixSb1–x)2S3 Nanorods

The chemical composition, size and shape, and surface engineering play key roles in the performance of electronic, optoelectronic, and energy devices. V2VI3 (V = Sb, Bi; VI = S, Se) group materials are actively studied in these fields. In this paper, we introduce a colloidal method to synthesize uniform ternary (BixSb1-x)2S3 (0 < x < 1) nanorods. These nanorods show composition-dependent aspect ratios, enabling their composition, size, and shape control by varying Bi/Sb precursor ratios. It is found that the surface passivation by various thiols (L-SH) efficiently enhances the photoconductivity and optical responsive capability of (BixSb1-x)2S3 nanorods when used as active materials in indium tin oxide (ITO)/(BixSb1-x)2S3/ITO optoelectronic devices. Meanwhile, the increase of Sb content causes a gradual deterioration of photoconductivity of thiol-passivated nanorods. We propose that the thiol passivation is able to reduce the number of S vacancies, which act as the recombination centers (trapped states) for photogenerated electrons and holes, and thus boosts the carrier transport in (BixSb1-x)2S3 nanorods, and in particular that the composition-related conductivity deterioration is attributed to the increase of unpassivated S vacancies and surface oxidation due to the rise of Sb content.

Wetting and interfacial behavior of molten Al–Si alloys on SiC monocrystal substrates: effects of Cu or Zn addition and Pd ion implantation

C-terminated 6H-SiC (0001) single crystal substrates implanted with Pd ions with an energy of 20xa0keV and three fluences of 5u2009×u20091015, 5u2009×u20091016 and 5u2009×u20091017 ions/cm2 at room temperature. The wetting experiments of SiC by molten Al–10Si, Al–10Si–4Cu and Al–10Si–10Zn were performed by using the sessile drop method in a high vacuum at 1323xa0K to determine the effects of the third element (Cu and Zn) addition and Pd ion implantation on the wettability of Al–10Si/SiC system. The experimental results showed that the wettability of Al–10Si/SiC system can be improved significantly by adding the 4% Cu with the final contact angle decreasing from ~u200960° to ~u200940°. The final contact angle of Al–10Si/SiC system decreased sharply from ~u200960° to ~u200926° after the addition of 10% Zn, which can be mainly derived from the evaporation behavior of Zn at the interface. The spreading time for reaching the equilibrium or slow spreading stage of the three Al–10Si(–u20094Cu, –u200910Zn)/SiC systems was prolonged more or less with the increase of Pd implantation dose, which can be mainly attributed to the variation of interfacial interactions between drops and Pd-implanted SiC substrates. Moreover, the final contact angles of Al–10Si/SiC and Al–10Si–4Cu/SiC systems decreased while that of Al–10Si–10Zn/SiC system almost kept constant with increasing the Pd implantation dose.

Native point defects on hydrogen-passivated 4H–SiC (0001) surface and the effects on metal adsorptions

With the continued expansion of silicon carbides (SiC) applications, atomistic understanding on the native point defects of its surfaces, particularly on those of the hydrogen-passivated (HP) 4H-SiC (0001) surface, becomes imperative. Using first-principles calculations, the structures and formation energies of several typical native point defects (e.g., ISi, IC, VSi, VC, and SiC) on the (0001) HP-surface of 4H-SiC were systematically explored, including the effects of the unit cell size, environmental condition, charge state, and hydrogen incorporation. Furthermore, their adsorptions of Ag (Mo) atom on these defective sites were systematically investigated. The formation energies of these defects in the HP-surface, clean surface, and bulk SiC were concluded together with their thermodynamic concentrations in the HP-surface estimated. The influences of these defects to metal (Ag, Mo) adsorptions of HP-surfaces were concluded. Based on these conclusions, the wettability improvement between the metal liquid and ion (Ag or Mo) implanted SiC substrates in the previous studies can be well understood at the atomistic scale. This study provides a theoretical guideline to SiC surface modification for the production of metal-SiC composites, brazing of SiC with metals, fabrication of electronic devices, or the growth of two dimensional nanofilms.