Metal-oxide nanowires are showing a great interest in the domain of gas sensing due to their large response even at a low temperature, enabling low-power gas sensors. However their response is still not fully understood, and mainly restricted to the linear response regime, which limits the design of appropriate sensors for specific applications. Here we analyse the non-linear response of a sensor based on ZnO nanowires network, both as a function of the device geometry and as a response to oxygen exposure. Using an appropriate model, we disentangle the contribution of the nanowire resistance and of the junctions between nanowires in the network. The applied model shows a very good consistency with the experimental data, allowing us to demonstrate that the response to oxygen at room temperature is dominated by the barrier potential at low bias voltage, and that the nanowire resistance starts to play a role at higher bias voltage. This analysis allows us to find the appropriate device geometry and working point in order to optimize the sensitivity. Such analysis is important for providing design rules, not only for sensing devices, but also for applications in electronics and opto-electronics using nanostructures networks with different materials and geometries.
The effect of applying an external electric field on doping-induced spin-orbit splitting of the lowest conduction-band states in a bismuth-doped zinc oxide nanowire is studied by performing electronic structure calculations within the framework of density functional theory. It is demonstrated that spin splitting in Bi-doped ZnO nanowires could be tuned and enhanced electrically via control of the strength and direction of the applied electric field, thanks to the nonuniform and anisotropic response of the ZnO:Bi nanowire to external electric fields. The results reported here indicate that a si…
In this work, ZnO nanowire arrays decorated with titanium nitride (TiN) nanoparticles as surface enhanced Raman scattering (SERS) substrates is demonstrated. ZnO nanowires were grown by hydrothermal synthesis while ~100 nm TiN nanoparticles were obtained by grinding commercial powders for several hours. They were then decorated on the ZnO nanowire arrays using acetone as the medium. Scanning electron microscopy confirmed the presence of TiN nanoparticles on the ZnO nanowires. TiN nanoparticles exhibited localized surface plasmon resonances at 430, 520 and 600 nm. SERS experiments using Nile Bl…
We analyse the morphological, structural and luminescence properties of self-assembled ZnO nanowires grown by chemical vapour transport on Si(001). The examination of nanowire ensembles by scanning electron microscopy reveals that a non-negligible fraction of nanowires merge together forming coalesced aggregates during growth. We show that the coalescence degree can be unambiguously quantified by a statistical analysis of the cross-sectional shape of the nanowires. The examination of the structural properties by X-ray diffraction evidences that the nanowires crystallize in the wurtzite phase, …
In this work we have employed density-functional theory with hybrid functionals to investigate the atomic and electronic structure of bare and hydrogenated Mn doped ZnO nanowires with small diameter. We determine changes in magnetic and electronic structure of Mn-doped ZnO nanowires due to surface effects, such as hydrogen adsorption on the surface, presence of oxygen vacancies and dangling bonds. In the absence of passivation on the nanowire surface, the manganese atoms segregate to the surface, whereas under hydrogen adsorption the incorporation of Mn is energetically more favourable at inne…
Our predictions, based on density-functional calculations, reveal that surface doping of ZnO nanowires with Bi leads to a linear-in-$k$ splitting of the conduction-band states, through spin-orbit interaction, due to the lowering of the symmetry in the presence of the dopant. This finding implies that spin polarization of the conduction electrons in Bi-doped ZnO nanowires could be controlled with applied electric (as opposed to magnetic) fields, making them candidate materials for spin-orbitronic applications. Our findings also show that the degree of spin splitting could be tuned by adjusting …
An emerging branch of electronics, the optospintronics, would be highly boosted if the control of magnetic order by light is implemented in magnetic semiconductors nanostructures being compatible with the actual technology. Here we show that the ferromagnetic magnetization of low Fe-doped ZnO nanowires prepared by carbothermal process is enhanced under illumination up to temperatures slightly below room temperature. This enhancement is related to the existence of an oxygen vacancy V$_{\rm O}$ in the neighbouring of an antiferromagnetic superexchange Fe$^{3+}$-Fe$^{3+}$ pair. Under illumination…
Current voltage and Kelvin Probe Force Microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either ohmic or Schottky. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality ohmic contacts (linear I V behavior) or non-linear (diode like) Schottky contacts were obtained. Current voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to inv…
In this work we have employed density-functional theory with hybrid functionals to investigate the atomic and electronic structure of bare and hydrogenated Co doped ZnO nanowires. We find that in the absence of passivation on the nanowire surface, the cobalt atoms segregate to the surface. On the other hand, under hydrogen passivation, the incorporation of Co is more favorable at inner sites. This suggests that the incorporation of Co in nanostructures has a dependence on the environment and may be facilitated by external atoms and relaxation of the surface.
We fabricate and compare nanocomposite thin-film ZnO chemoresistive acetone sensors with gold or palladium nanoparticles on the surface, at low operating temperatures. The sensors are fabricated by pulsed laser deposition and operate in the temperature range 159-200oC. The ZnO films are polycrystalline, crystallizing mainly at the (002) and (101) orientations of the hexagonal phase. The nanocomposite ZnO:Au and ZnO:Pd sensors have a lower detection limit and show a response enhancement factor between 2-7, compared with pure ZnO sensors. The ZnO:Pd sensor performs better than the ZnO:Au sensor.…
The thin film configuration presents obvious practical advantages over the 1D implementation in energy harvesting systems such as easily manufacturing and processing and long lasting and stable devices. However, most of the ZnO-based piezoelectric nanogenerators (PENGs) reported so far relay in the exploitation of single-crystalline ZnO nanowires because their self-orientation in the c-axis and ability to accommodate long deformations resulting in a high piezoelectric performance. Herein, we show an innovative approach aiming to produce PENGs by combining polycrystalline ZnO layers fabricated …
We develop an InAs nanowire gate-all-around field-effect transistor using a transparent conductive zinc oxide (ZnO) gate electrode, which is in-situ atomic layer deposited after growth of gate insulator of Al2O3. We perform magneto-transport measurements and find a crossover from weak localization to weak antilocalization effect with increasing gate voltage, which demonstrates that the Rashba spin-orbit coupling is tuned by the gate electrode. The efficiency of the gate tuning of the spin-orbit interaction is higher than those obtained for two-dimensional electron gas, and as high as that for …
In this study, the effect of Sr- and Ni-doping on microstructural, morphological and sensing properties of ZnO nanorods has been investigated. Nanorods with different Sr and Ni loadings were prepared using a simple wet chemical method and characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis. XRD data confirmed that Sr- and Ni-doped samples maintainsthe wurtzite hexagonal structure of pure ZnO. However, unlikes Sr, Ni doping modifies the nanorod morphology, increases the surface area (SA) and decreases the ratio of IUV/Igreen …
This paper reports the application of zinc oxide (ZnO) in the pressure sensors that can be integrated with a microelectromechanical system (MEMS). ZnO is one of the materials that has received a great deal of attention due to its unique properties of being a semiconductor with wide bandgap and piezoelectric effects. The simpler crystal growth mechanisms of ZnO have resulted in a lower cost of ZnO-based sensors. Different types of pressure sensors based on ZnO sensing elements have also been explored. A thin circular ZnO film was simulated as a piezoelectric sensor employing the finite element …
The piezoelectric nanomaterial ZnO exhibits an excellent piezoelectric response that can transduce mechanical energy into electrical signals by applying pressure. The piezoelectric behavior of ZnO nanostructures (especially nanorods or microrods) is getting considerable attention in the fabrications of piezo tactile sensors, energy harvesting devices, and other self-powering implantable devices. Especially vertically aligned ZnO nanorods are of high interest due to their higher value of piezoelectric coefficient along the z-direction. In this report, various geometries and alignments of ZnO na…
Nanocomposite metal oxide thin films exhibit assuring qualities in the field of gas sensors because of the collective opportunities provided by the heterointerface formation. In this work, we present the synthesis of nitrogen doped mesoporous In$_2$O$_3$-ZnO nano-composite thin films by simple wet chemical method using urea as the nitrogen precursor. SEM investigation suggests formation of mesoporous nano-composite thin films, where the uniformity of surface pore distribution depends on the relative proportion of In$_2$O$_3$ and ZnO in the composites. HRTEM investigation suggest formation of s…
The exploration of new catalysts for the vapor-liquid-solid (VLS) synthesis of one-dimensional (1-D) materials promises to yield new morphologies and functionality. Here, we show, for the model ZnO system, that this possible using a semiconductor (Ge) catalyst. In particular, two unusual morphologies are described: twisted nanowires and twisted nanotubes, in addition to the usual straight nanowires. The twisted nanotubes show large hollow cores and surprisingly high twisting rates (up to 9o/μm), which cannot be easily explained through the Eshelby twist model. A combination of ex situ and in s…
Zinc oxide which is a n-type semiconducting metal oxide (SMO) has been a promising material for detecting ethanol vapor. However, pure ZnO based ethanol sensors often suffer from high working temperature, cross sensitivity towards methanol and poor stability against humidity. Doping ZnO with various metal ions has been widely explored as a proficient approach to improve its ethanol sensing properties, while anionic dopants have been rarely considered. Here in we demonstrate the effect of nitrogen doping on the ethanol sensing characteristics of ZnO thin films. Nitrogen doped ZnO (N-ZnO) thin f…
In this paper we show that the ionic conduction through surface chemisorbed ambient moisture leads to the remarkably high room temperature selective response towards hydrogen gas. The surface adsorbed moisture acts as surface states and shows ionic conduction, as a result of smaller size of ZnO nanoparticles of 20 +/- 5 nm. This response is enhanced remarkably i.e. from 10% to 190% for 1200 ppm H2 gas when p-type NiO quasi-nanowires (width ~50 nm) are mixed with these n-type ZnO nanoparticles to form a homogenous NiO/ZnO nano-bulk p-n heterostructure. The maximum response is obtained for about…
In this study, we evaluated the sensing performance of silver nanoprism/graphene oxide/silicon nanowires (AgNPr/GO/SiNWs) nanohybrid system for effective detection of organic dye and herbicide residues in freshwater via surface-enhanced Raman scattering (SERS). Homogenous and vertically aligned SiNWs have been successfully synthesized using metal-assisted chemical etching technique by varying the etching time from 10 to 30 min. AgNPr/GO/SiNW hybrids were assembled by spin-coating of GO followed by drop-casting deposition of AgNPr. The microstructures of AgNPr/GO/SiNWs are strongly affected by …
The miniaturization of diagnostic devices that exploit optical detection schemes requires the design of light-sources combining small size, high performance for effective excitation of chromophores, and mechanical flexibility for easy coupling to components with complex and non-planar shapes. Here, ZnO nanowire-in-fiber hybrids with internal architectural order are introduced, exhibiting a combination of polarized stimulated emission, low propagation losses of light modes, and structural flexibility. Ultrafast transient absorption experiments on the electrospun material show optical gain which…
We introduce herein the advanced application of low pressure plasma procedures for the development of piezo and triboelectric mode I hybrid nanogenerators. Thus, plasma assisted deposition and functionalization methods are presented as key enabling technologies for the nanoscale design of ZnO polycrystalline shells, the formation of conducting metallic cores in core@shell nanowires, and for the solventless surface modification of polymeric coatings and matrixes. We show how the perfluorinated chains grafting of PDMS provides a reliable approach to increase the hydrophobicity and surface charge…
Magnetic properties of quasi one-dimensional vanadium-benzene nanowires (VBNW) are investigated theoretically with the absorption of gas molecules-NO and NO2. With the increase adsorption of NO on VBNW, the phase transition from half metal to ferromagnetic metal and last to paramagnetic semiconductor can be observed. With the increase of NO2 on VBNW, half metallic property can be enhanced at first and decreased later. Thus, the electronic and magnetic properties of VBNW can be sensitive and selective to NO and NO2, revealing the potential applications in spintronic sensors of these two kinds o…
