Papers by Keyword: ZnO Nanowires

Abstract: ZnO nanowires are recently used in optoelectronic devices such as sensors, solar cells, and light emitting diodes due to its unique optical and electrical properties. In such devices, a contact between the ZnO nanowires and a metal electrode exists. Hence understanding electrical characteristic between the ZnO nanowires and a metal electrode can facilitate optoelectronic device design. In this work, ZnO nanowires were grown on Indium Tin Oxide (ITO) substrates using a hydrothermal method. Simple devices using the nanowires sandwiched between the ITO and a metal contact (i.e. Au, Al) were fabricated and characterized by a current-voltage measurement. Moreover, studies on p-n junctions between the ZnO nanowires and p-type polymers, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) and poly(9,9-dioctylfluorene) (PFO), were also fabricated and characterized. The current-voltage measurement of devices clearly shows the rectifying behavior, which is an important characteristic of diodes.

Abstract: Piezoelectric properties of ZnO nanowires orientated along [0001] are investigated via density functional theory (DFT). A new method to calculate the volume of nanowires was proposed, which is crucial to the value of piezoelectric coefficients. Results show that the axial effective piezoelectric coefficients are 29.99 Cm^-2, 25.93 Cm^-2, 22.82 Cm^-2 for ZnO nanowires with diameters of about 0.6 nm, 1.2 nm, 1.8 nm, which are considerably larger than that of the bulk (20.19Cm^-2). It is found that the change in volume during the strain played a dominated role in size effects. This work helps to gain a deeper understanding of the piezoelectric size effects in ZnO nanowires.

Abstract: In this paper, we present a zigbee wireless ammonia sensor system which based on quartz crystal microbalance (QCM) coated with ZnO nanowires as sensing element. This system concludes two parts: one is the base station which is constructed with zigbee coordinator linked computer, the other is called the sensor transmitter module which is zigbee coordinator linked ZnO-nanowires-modified QCM sensor. We use star network of zigbee protocol to construct ammonia wireless sensing system. Experimental results indicate that the wireless sensing system has quite good stability and reproducibility. The interaction distance between the computer and RFD can be as far as 100 m in a buliding. The proposed system is potential to construct the low-cost, real-time online wireless gas sensor system, which can be used to monitor the pollutants in the family and the harsh environment.

Abstract: In this work, we demonstrate the functionalization of zinc oxide nanowires with carboxylic acid moieties and investigate their potential application as p-nitrophenol sensors. First, synthesis of high quality zinc oxide nanowires along with appropriate characterization results is discussed. Subsequently, oleic acid, as a model system, is used to examine functionalization behavior of nanowire surface. Vibrational spectroscopic techniques are employed to determine nature of bonding and orientation of oleic acid molecule at nanowire surface. Photoluminescence properties of modified- and unmodified ZnO nanowires with oleic acid were investigated. Based on these results, an appropriate receptor capable of sensitive optical detection of p-nitrophenol is proposed. In addition, results on sensing mechanism of the receptor based on fluorescence quenching are reported, which highlight the capability of selective and sensitive detection of p-nitrophenol analyte using the receptor.

Abstract: The effects of external stress field f on band gap E_g(D, f) of ZnO nanowires (NWs) in a diameter range of D = 0.6 - 2.0 nm are investigated using first-principles density-function theory for the future application as nanogenerators. It is shown that the E_g(D,0) values decreases with the increasing diameter of ZnO NWs without the stress field. Moreover, E_g(D, f) decreases with increasing of f due to the rapid drop of conduction band maximum of ZnO NWs when D is constant. These findings imply that E_g(D,f) functions of ZnO NWs can be modulated by manipulating D and f, which may be help for design of ZnO nanogenerators with a higher generation output voltage.

Abstract: Abstract. ZnO nanowires synthesis throught oxidative evaporation of pure zinc powder without catalyst is studied in detail to understand the nucleation and growth mechanisms involved with the so-called “self-catalysis” schemes. The structural features associated with different growth stages were monitored using scanning electron microscopy (SEM), describe the direct observation of the nucleation and growth process. X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) demonstrate that the as-obtained sample can be indexed to high crystallinity with wurtzite structure and only contain Zn and O without the presence of any impurities.

Abstract: Bulk heterojunction photovolataic devices based on blends of conjugated polymer poly (2- methoxyl-5- dodecoxyl p-phenyl vinylene) (PMODOPV) as electron donor and crystalline ZnO nanowires as electron acceptor have been studied. We show that photovoltaic devices using zinc oxide nanowires overlaid with conjugated polymers give improved performance compared with devices made only from polymer. The improvement is consistent with improved electron transport perpendicular to the plane of the film. Solar power conversion efficiency of 1.37% were achieved under AM1.5 illumination .

Abstract: A low cost and substrate-independent method has been established to synthesize vertically aligned ZnO nanowires (NWs) on iron oxide films coated silicon substrates via low pressure Chemical Vapor Deposition (CVD) method at 650oC. In this study, Si substrates were dipped into the iron (III) nitrate nonahydrate solution prior to the synthesis process. This oxidized iron film facilitated the growth of highly oriented (002) ZnO seed layer, which allowed subsequent vertically aligned ZnO NWs to be grown on top of it during the synthesis. This approach has provided a good alternative to grow vertically aligned ZnO NWs without the need of considering the epilayer relationship between the ZnO and the material to be used as substrate.

Abstract: A systematic study was carried out to study the effect of process parameters on the growth of Au-catalyzed ZnO nanowires (NWs). Growth of Au-catalyzed ZnO NWs could be mainly occurred at the tip or at the base of NWs. This study provided useful information in determining the process window for the tip-growth Au-catalyzed ZnO NWs. Besides, a generic growth mechanism, i.e. a combination of Vapor-Liquid-Solid and Vapor-Solid (VLS and VS) mechanism is proposed to explain the tip-growth and base-growth Au-catalyzed ZnO NWs.

Abstract: The p-n junction has been formed by using p-type boron doped silicon and n-type ZnO nanowires (NWs). It was prepared by using simple vapour-transport deposition method. Gas sensing property has been examined by measuring the resistance change of the junction sample towards 1 % of butane gas at room temperature. Significant improvement of sensing behaviour was observed from the fabricated junction sample when it was compared to sample of non-p-n junction ZnO NWs. The increase in the sensitivity of the p-n junction ZnO NWs and the ability to regain the sensing power by returning back to the initial state at room temperature are useful for future sensing device with minimum power consumption. Keywords: ZnO nanowires, Si-ZnO nanowires p-n junction, room temperature sensing and butane gas