An ultrahigh photocurrent gain has been found in the ultraviolet-absorbed GaN nanowires with m-directional long axis grown by chemical vapor deposition. The quantitative results have shown the gain values at 5.0×104–1.9×105 of the GaN nanowires with diameters from 40to135nm are near three orders of magnitude higher than the values of 5.2×101–1.6×102 estimated from the thin film counterparts. The intensity-dependent gain study has shown that the gain value is very sensitive to the excitation intensity following an inverse power law and no gain saturation observed in this investigated intensity range from 0.75to250W∕m2. This behavior has strongly suggested a surface-dominant rather than trap-dominant high gain mechanism in this one-dimensional nanostructure. The strong carrier localization effect induced by the surface electric field in the GaN nanowires is also discussed.

Iridium dioxide (IrO 2 ) nanorods with pointed tips have been grown on Si(100) and transition-metal-coated-Si(100) substrates, via metal-organic chemical vapor deposition (MOCVD), using (MeCp)Ir(COD) as the source reagent. The as-deposited nanorods were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). FESEM micrographs revealed that the majority of the nanorods are a wedge shape in cross section and converge at top; occasionally several of them pack into a column of a spiral tip. The vertical alignment and packing density are significantly improved by prior deposition of a thin layer of Ti on Si. TEM and XRD results indicate that the sputtered Ti thin layer erects the nanorods in the c-axis direction. XPS spectra show that iridium in IrO 2 nanorods also exist in a higher oxidation state.

In this study, we have successfully demonstrated that a GaN nanowire (GaNNW) based extended-gate field-effect-transistor (EGFET) biosensor is capable of specific DNA sequence identification under label-free in situ conditions. Our approach shows excellent integration of the wide bandgap semiconducting nature of GaN, surface-sensitivity of the NW-structure, and high transducing performance of the EGFET-design. The simple sensor-architecture, by direct assembly of as-synthesized GaNNWs with a commercial FET device, can achieve an ultrahigh detection limit below attomolar level concentrations: about 3 orders of magnitude higher in resolution than that of other FET-based DNA-sensors. Comparative in situ studies on mismatches ("hotspot" mutations related to human p53 tumor-suppressor gene) and complementary targets reveal excellent selectivity and specificity of the sensor, even in the presence of noncomplementary DNA strands, suggesting the potential pragmatic application in complex clinical samples. In comparison with GaN thin film, NW-based EGFET exhibits excellent performance with about 2 orders higher sensitivity, over a wide detection range, 10(-19)-10(-6) M, reaching about a 6-orders lower detection limit. Investigations illustrate the unique and distinguished feature of nanomaterials. Detailed studies indicate a positive effect of energy band alignment at the biomaterials-semiconductor hybrid interface influencing the effective capacitance and carrier-mobility of the system.

We review the results of the synthesis of IrO 2 nanocrystals (NCs) on different substrates via metal-organic chemical vapour deposition (MOCVD) using (MeCp)(COD)Ir as the source reagent. The surface morphology, structural and spectroscopic properties of the as-deposited NCs were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAD), x-ray diffractometry (XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The roles of different substrates for the formation of various textures of nanocrystalline IrO 2 are studied. Several one-dimensional (1D) nanostructures have evolved by decreasing the degree of interface instability. The morphological evolution occurs from triangular/wedged nanorods via incomplete/scrolled nanotubes to square nanotubes and square nanorods (NRs), with increasing morphological stability. The results show that the three-dimensional (3D) grains composing traditional film belong to the most stable form as compared to all the 1D NCs, and the sequential shape evolution has been found to be highly correlated to a morphological phase diagram based on the growth kinetics. In addition, area selective growth of IrO 2 NRs has been demonstrated on sapphire(012) and sapphire(100) substrates which consist of patterned SiO 2 as the nongrowth surface. The initial growth of IrO 2 nuclei is studied. Selectivity, rod orientation, and other morphological features of the nanorod forest can find their origins in the nucleation behaviour during initial growth. XPS analyses show the coexistence of higher oxidation states of iridium in the as-grown IrO 2 NCs. The usefulness of the experimental Raman scattering together with the modified spatial correlation (MSC) model analysis as a residual stress and structural characterization technique for 1D IrO 2 NCs has been demonstrated. The field emission properties of the vertically aligned IrO 2 NRs are studied and demonstrated as a high-performance and robust field emitter material owing to its low work function, low resistivity and excellent stability against oxygen.

We report on the preparation and field-emission properties of vertically aligned conductive IrO2 nanorods. The unique geometrical features of IrO2 nanorods, including nanosized structure and self-assembled sharp tip, exhibit a strong effect on field enhancement (β∼40 000), which result in a low threshold field (Eth∼0.7 V/μm) defined at the beginning of emission. A low turn-on field for driving a current of 10 μA/cm2 is about 5.6 V/μm, which is comparable with the carbon nanotube, diamond, and amorphous carbon. The potential of using IrO2 nanorods as an emitter material has been demonstrated.

was evaluated over a circular area measuring roughly 500 lm in diameter [13]. After deposition, each of the samples was inspected using an optical stereomicroscope and a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer. Growth of IrO 2 Films and Nanorods by Means of CVD: An Example of Compositional and Morphological Control of Nanostructures**By Reui-San Chen, Yi-Sin Chen, Ying-Sheng Huang,* Yao-Lun Chen, Yun Chi, Chao-Shiuan Liu, Kwong-Kau Tiong, and Arthur J. Carty Iridium dioxide, IrO 2 , belongs to the family of transition metal oxides that exhibit metallic conductivity at room temperature. It has been used in applications such as optical switching layers in electrochromic devices, [1] and durable electrode materials for chlorine or oxygen evolution.[2]Moreover, owing to its excellent resistance to the inter-diffusion of oxygen, as well as high thermal and chemical stability, [3] IrO 2 films serve as electrodes for high-density dynamic random access memory (DRAM), or nonvolatile ferroelectric random access memory (NVFRAM), devices.[4] Related investigations have indicated that polarization fatigue of PZT ferroelectric capacitors can be effectively suppressed by using IrO 2 thin film electrodes. [5] In recent reports, IrO 2 was also used to fabricate field-emission cathodes for microelectronic devices and field-emission displays.[6]As a result of these diverse applications, there is a growing need to develop easy and reliable methods for growing IrO 2 phases, either as thin films, or in other physical forms. Various methods such as reactive magnetron sputtering, [7] pulsed laser deposition, [8] and annealing of Ir films in an O 2 atmosphere, [9] have been employed for this purpose. However, CVD, a technique that possesses several advantages including better composition control, high deposition rate, excellent step coverage, and suitability for scale-up, [10] has not yet been successfully employed for IrO 2 even though Ir thin films are normally obtained using O 2 as the carrier gas to prevent carbon iridium metal impurities from being incorporated into the deposited film. [11] Recently, the influence of O 2 partial pressure on the formation of IrO 2 using (MeCp)Ir(COD)/O 2 as the reactive gas mixture, has been discussed by Maury and Senocq. [12] In this communication, we wish to report the successful deposition of IrO 2 thin films using the cold-wall CVD method. Moreover, by optimizing experimental parameters, the formation of distinct, rod-like, aligned IrO 2 nanocrystals can be observed, with good control of growth perpendicular to the substrate surfaces. The structural composition, surface morphology, and spectroscopic properties of the resulting IrO 2 materials are discussed.The reactive mixture (CpMe)Ir(COD)/O 2 was used in CVD experiments that were conducted under three different pressure settings, 1 torr, 10 torr, and 30 torr, while deposition temperatures were separated into six settings ranging from 250 C to 500 C. The combined X-ray diffraction (XRD) pattern...

RuO 2 nanometer-sized rods with pyramidal tips have been grown on Cu-coated Si͑100͒ substrates using metalorganic chemical vapor deposition. The geometry of these nanorods resembles an obelisk with an off-center tip. The aspect ratios of nanorod tips are between 0.55 and 0.73. The field emission properties of the RuO 2 nanorods are studied and the stability of its emission current is assessed. The field emission results demonstrate that RuO 2 nanorods material is an emitter of potential.Preparation of one-dimensional (1D) nano-scaled materials has attracted massive attention owing to their fundamental interests in science and promising applications in nanodevices. To understand the carrier confinement effects, many investigations have been focused on the preparation and characterization of nanorods and nanowires of semiconductors and their binary compounds, such as Si, 1,2 GaAs, 3,4 GaN 5,6 The interests in 1D nanowires, nanorods, and nanotubes have quickly spread into oxide materials. 7 The wideband-gap semiconductor of ZnO nanorod is brilliantly prepared and well characterized. 8,9 The electrically insulating oxides of nanostructured SiO 2 , 10 TiO 2 , 11,12 GeO 2 , 13 Ga 2 O 3 , 14 and VO x (Ref. 15) have also been synthesized and studied. Among the numerous oxides, the electrically conducting RuO 2 and IrO 2 belong to one family of unique properties, whose nanostructures are an uncultivated area worthwhile of extensive investigation. 7,16,17 The room-temperature conductive RuO 2 , possessing excellent chemical and thermal stability, is a legitimate candidate for fabricating durable field-emission arrays. Owing to its oxide nature, it could be an ideal material for durable field emitters. RuO 2 crystallizes in tetragonal rutile structure with space group P4 2 / mnm. RuO 2 has found applications in

The size effects on both the photoconductivity and dark conductivity have been observed in m-axial GaN nanowires grown by chemical vapor deposition (CVD). For these nanowires with diameters at 50–130 nm, the products of carrier lifetime (τ) and mobility (μ) derived from the photocurrent measurements are typically at (2–8)×10−1 cm2/V, which are over two orders of magnitude higher than the maximal reported values [τμ=(1–5)×10−4 cm2/V] for their thin film counterparts. A significant decrease of τμ value at diameter below the critical values (dcrt) at 30–40 nm is observed. Similar size dependence is also found from the dark conductivity study. The temperature-dependent measurements further indicate two different thermal activation mechanisms in GaN nanowires with sizes above and below the dcrt. These results suggest a surface-dominant transport property in GaN nanowires both in dark and under light illumination due to the presence of surface depletion and band bending. Probable reasons leading to the smaller dcrt of the CVD-grown m-axial GaN nanowires, compared to the c-axial ones grown by molecular beam epitaxy are discussed as well.