Nanoscience & Nanotechnology-Asia - Volume 1, Issue 2, 2011

Seeding is critical for the hydrothermal synthesis of zinc oxide (ZnO) nanorod arrays on solid substrates. Herein, spray pyrolysis is proposed as a simple and efficient technique for the deposition of ZnO seeding film on glass. The method involves the in situ formation of ZnO nanocrystals by spraying aqueous solution of zinc acetate on hot substrate (°C) whereby ZnO nanocrystallites with narrow size distribution (4-8 nm) are formed. Majority of the crystals were found to have their polar (0001) facet oriented parallel perpendicular to the substrate surface. Upon hydrothermal growth of ZnO nanorods in an equimolar solution of zinc nitrate and hexamine, it was observed that seeding by spray pyrolysis led to the formation of dense ZnO nanorod arrays that were well aligned and strongly attached to the glass substrates.

Zinc oxide is an important II-VI semiconductor and ZnO nanowires have great potential in photovoltaic applications. In this article, we attempt to review the general synthetic strategies, doping and photovoltaic applications for ZnO nanowires. We first summarize various growth techniques of ZnO nanowires. Subsequently, we discuss mechanisms involved to generate ZnO nanowires from different synthetic schemes and conditions. Finally, we review the doping and photovoltaic applications of ZnO nanowires.

In this article we review the progress made in poly-Si nanowire (NW) transistor technology in recent years, with major attention paid on several device structures developed by our group. With these NW structures, superior device characteristics over the previous planar structures have been demonstrated. A common feature of fabricating these structures is that the formation of poly-Si NW can be accomplished with simple process techniques without involving advanced lithography tools and processes, such as e-beam or DUV. One important implication of this feature is that these NW structures can be readily integrated with modern poly-Si TFT-based electronics on the same panel or CMOS circuitry. This can increase the functionally of a panel and chip products. Several multi-gate (MG) configurations have been developed and characterized. Moreover, these MG structures can be designed with either common or independent gate configuration. The above NW devices have been applied to bio-logic sensor and memory applications. In the former regard, the testing is usually performed in an aqueous solution. In our experiments weve found an interesting water passivation effect. Specifically, the H-related species contained in the test solution would passivate the defects presenting at the grain boundaries of the poly-Si NW, greatly enhancing the device performance. This may further lift the concern associated with the granular structure of poly-Si NW. Finally, weve also employed the NW devices as the test vehicle and have successfully demonstrated its effectiveness in detecting the pH value of the solutions, as well as the dopamine and DNA. Weve also fabricated the NW SONOS devices and showed that the use of NW can help promote the programming/erasing (P/E) speed over the planar counterparts. Moreover, the independent double-gate (DG) configuration could further help improve the P/E efficiency and provide more flexibility for read operation. These promising results indicate the great potential of the poly-Si NW devices for future 3D high-density non-volatile memory (NVM) applications.

Significant developments have been made in III-nitride compound semiconductor nanowire heterostructures. This paper provides an overview on the recent progress of III-nitride nanowire heterostructures and their emerging device applications. The growth mechanisms of III-nitride nanowires are first described, followed by a review of the structural, electrical, and optical properties of In(Ga)N nanowires. The use of III-nitride nanowires to realize functional photonic devices, including light emitting diodes, lasers, solar cells, and sensors are also briefly described, with special attention paid to the emerging nanowire LEDs for applications in solid state lighting.

Long regarded as a matter of scientific curiosity, GaN has been continued as the most important and indispensable materials used among all other compound semiconductors and is also expected to play a critical role in future optoelectronic devices. We cover recent advances in growth and characterization of chemically synthesized quasi one dimensional GaN nanostructure in various forms, such as nanowires, nanorods, nanotubes, nanopipes, and nanotips and their complex heterostructures. We first briefly introduce the general scheme based on metal catalyzed vapour-liquid- solid growth mechanism for the synthesis of a broad range of nanostructures. The novelty of catalyst free growth of such nanostructures has also been highlighted. Complex structures, such as hierarchical and core-shell structures, are also touched upon. The electrical and optoelectronic properties depend on chemical composition, doping and other physical dimensions along with the type of growth technique being used. Size sensitive optical, electrical, thermal and mechanical properties of such nanostructure have strong influence on device properties. We intend to review these properties in case of GaN nanostructures. We will also explore the methods to assemble and integrate such nanostructures into large-scale functional devices for varied practical applications. Room-temperature high-performance electrical and optical devices will then be discussed at the single as well as assembly of nanowire. A section will be dedicated for detailed discussion on recent development of GaN nanostructures, including, light emitting diode, photovoltaic, photocatalysis, biosensor, gas and chemical sensor, and nanochannel. Technical challenges and scientific questions for the widespread use of GaN nanostructures, so relevant issues will also be briefly addressed.

CdS with a direct bandgap of 2.42 eV is considered to be an excellent material for various optoelectronic applications in the visible range of the electromagnetic spectrum, like nonlinear optical devices, LEDs and solar cells. CdS nanowires have drawn great attention owing to their novel properties. Here, we focus on recent strategies used to create CdS nanowires and the emergent properties of the one-dimensional CdS nanowires, and discuss their potential applicability in different fields. In particular, the mechanisms of various synthetic methods for the CdS nanowires are discussed detailedly.

The silicon nanowires (SiNWs) comprise a core-shell structure. Contrasted to conventional volume doping to modulate the transport properties of SiNWs, recent studies have revealed an economic and non-destructive approach to induce doping through surface engineering. In this review, extensive first principles theoretical investigations are presented which revealed the influence of surface passivation and ambience in modulating the conductivity of SiNWs. The theoretical findings rationalize several experimental results and provide useful pointers for tuning the electrical properties of nanomaterials.