Doped ZnO Nanowires Research Articles

The highly crystalline tellurium doped ZnO nanowires photodetector

In this paper, the stable and reproducible tellurium doped ZnO nanowires (Te-ZnO NWs) photodetector with intensive responsively is presented. The Te-ZnO NWs were fabricated by physical vapor deposition (PVD) growth mechanism. Field emission scanning electron microscope (FESEM) images showed that the fabricated nanowires were 50 nm in diameter and several microns in length. The high resolution transmission electron microscopy indicated that the synthesized nanowires were crystalline and their phase characterization was validated by the X-ray diffraction (XRD). The photoluminescence (PL) studies of these nanowires showed a strong photoluminescence (PL) emission peak in the green region. It was verified that the optical band gap of the NWs films increased as the Te concentration increased. The photo-conducting measurements were performed under field effect transistor principles. The tellurium doped ZnO nanowires photodetector showed the dynamic response of an on/off current contrast ratio of around 102. The carrier concentrations change in the fixed gate voltage was increased by 1.27 × 1018 cm−3 after 500 nm wavelength light illumination. The photocurrent studies of the samples showed that tellurium doped ZnO nanowires were the suitable photodetector.

Using Different Ions in the Hydrothermal Method to Enhance the Photoluminescence Properties of Synthesized ZnO-Based Nanowires

ZnO films with a thickness of ~200 nm were deposited on SiO2/Si substrates as the seed layer. Then Zn(NO3)2-6H2O and C6H12N4 containing different concentrations of Eu(NO3)2-6H2O or In(NO3)2-6H2O were used as precursors, and a hydrothermal process was used to synthesize pure ZnO as well as Eu-doped and In-doped ZnO nanowires at different synthesis temperatures. X-ray diffraction (XRD) was used to analyze the crystallization properties of the pure ZnO and the Eu-doped and In-doped ZnO nanowires, and field emission scanning electronic microscopy (FESEM) was used to analyze their surface morphologies. The important novelty in our approach is that the ZnO-based nanowires with different concentrations of Eu3+ and In3+ ions could be easily synthesized using a hydrothermal process. In addition, the effect of different concentrations of Eu3+ and In3+ ions on the physical and optical properties of ZnO-based nanowires was well investigated. FESEM observations found that the undoped ZnO nanowires could be grown at 100 °C. The third novelty is that we could synthesize the Eu-doped and In-doped ZnO nanowires at temperatures lower than 100 °C. The temperatures required to grow the Eu-doped and In-doped ZnO nanowires decreased with increasing concentrations of Eu3+ and In3+ ions. XRD patterns showed that with the addition of Eu3+ (In3+), the diffraction intensity of the (002) peak slightly increased with the concentration of Eu3+ (In3+) ions and reached a maximum at 3 (0.4) at%. We show that the concentrations of Eu3+ and In3+ ions have considerable effects on the synthesis temperatures and photoluminescence properties of Eu3+-doped and In3+-doped ZnO nanowires.

Polar surface dominated octagonal Sn doped ZnO nanowires and their room-temperature photoluminance properties

Polar surface dominated Sn doped ZnO nanowires (NWs) with an octagonal shaped cross section have been fabricated by chemical vapor deposition method. The NWs grew along [011¯0] direction, and were wrapped by non-polar surface (21¯1¯0) and polar surfaces (0001) and (101¯1). Planar defects in (0001) plane were formed in the middle of the doped NWs, and strain concentration occurred around the planar defects, which might lower the energy in the wurtzite lattice and thus maintain polar surface dominated configuration. X-ray photoelectron spectroscopy (XPS) and Raman tests reveal that the concentration of Oxygen vacancy (VO) was significantly lowered after doping, which led to the reduced deep level emission (DLE).

Electronic and optical properties of Mn impurities in ultra-thin ZnO nanowires: Insights from density-functional theory

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 inner sites. The presence of additional oxygen vacancies does not produce signficant changes in magnetic moments, although it produce significant changes in charge localization.

Exploring Surface Effects in Co Doped ZnO Nanowires With Hybrid‐Density Functional Theory

Exploring Surface Effects in Co Doped ZnO Nanowires With Hybrid‐Density Functional Theory

Magnetic and structural properties of Co doped ZnO nanowires prepared by heat treatment of electrospun PVA nanofibers containing Zn and Co acetates

We report the synthesis of inter-twined ZnO nanowires doped with Co by electrospinning polyvinyl alcohol along with metal oxide precursors followed by heat treatment in air at 550 °C for 90 min. This heat treatment removed PVA from the samples and ensured crystallization of 1-dimensional metal oxide nanostructure. X-ray diffraction (XRD) patterns also confirmed single phase wurtzite-type ZnO structure in samples with 3 wt% Co. Traces of Co3O4 could be observed in XRD patterns of samples with 5 wt% Co. However, micro-Raman spectra clearly indicate the presence of Co3O4 in samples with Co content more than 2 wt% which is also supported by electron paramagnetic resonance studies. UV–Vis absorption studies showed an increase in band gap energy with substitution of Co in ZnO structure. Field dependent magnetization curves recorded at room temperature revealed weak room temperature ferromagnetism with considerable paramagnetic component. The results are used to understand the origin of magnetism in this alloy and the extent of possible doping of Co in ZnO nanofibers.

Synthesis and properties of Pr3+-doped ZnO nanowires

Well-aligned Pr3+-doped ZnO nanowires (NWs) were obtained by chemical vapor deposition (CVD) method without catalysts on silicon substrates by vapor-solid process. The length and diameter of ZnO NWs were 1–2 μm and 50–100 nm, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) have been used to characterize the obtained Pr3+-doped ZnO nanowires. The concentration of dopant in the synthesized nanowires was 0.7 at %, according to EDX measurements. XPS was also used to characterize the samples and to confirm their composition. Pr3+-doped ZnO sensors were fabricated using a focused ion beam (FIB) with Au/Ti electrodes. A nanosensor is invented from an individual zinc oxide nanowire (80 nm in diameter). Response characteristics of the single nanowire towards dinitrogen monoxide (N2O), hydrogen (H2), ammonia (NH3) were examined at room temperature at different concentrations of gases.

High-speed photoresponse properties of ultraviolet (UV) photodiodes using vertically aligned Al:ZnO nanowires

Ultraviolet (UV) photodiodes with fast photoresponse properties were fabricated using vertically aligned aluminum doped ZnO nanowires. Stable p-type ZnO have been achieved by doping equimolar concentration of P-N (0.75 at.%) simultaneously in ZnO. The vertically aligned and electrically conducting n-type Al (3 at.%) doped ZnO nanowires were grown by a simple aqueous chemical growth process. The structural, morphological, optical, and electrical properties were investigated. For the fabrication of UV photodiodes, the optimum p-type ZnO layers and n-type ZnO nanowires were stacked upon ITO substrate. A 250 nm thin NiO was deposited as an electron blocking layer (EBL) in between the ZnO p–n junctions. The current density–voltage (J–V) characteristic of the fabricated UV photodiode was measured under dark and UV illumination conditions. Under a reverse bias of 3 V, the device exhibits a high photoresponsivity (R) value of 15.07 (A/W) upon illumination of UV light (λ = 365 nm). The fabricated photodiode exhibits a fast photoresponse switching characteristics with a response and recovery time calculated as 61 ± 11 and 455 ± 41 ms, respectively. The role of vertically aligned nanowires in the formation of oxygen interstitial (Oi) defects and its impact on improving the UV photoresponse properties were investigated.

Enhancement in red emission at room temperature from europium doped ZnO nanowires by 1,10 phenanthroline-europium interface induced resonant excitations

We show that europium doped ZnO nanowires after surface modification with organic ligand, 1,10 phenanthroline (phen) leads to strong red emission at 613 nm which is a characteristic emission from the atomic levels of Eu3+. Surface modification with phen leads to formation of phenanthroline-europium interface on the surface of the nanowires due to attachment of Eu3+ ions. After an optimized surface modification with phen, intensity of both the UV emission (band edge) and red emission improved by two orders of magnitude at room temperature. We observed multiple energy transfer pathways to the energy levels of Eu3+ ions through the phenanthroline-europium interface, which found to be very effective to the significant enhancement of emission from the dopant Eu3+. This study shows a new insight in to the energy transfer process from phen to the europium doped ZnO system.

Enhanced Visible Light Photocatalytic Activity of ZnO Nanowires Doped with Mn2+ and Co2+ Ions.

In this research, ZnO nanowires doped with Mn2+ and Co2+ ions were synthesized through a facile and inexpensive hydrothermal approach, in which Mn2+ and Co2+ ions successfully substituted Zn2+ in the ZnO crystal lattice without changing the morphology and crystalline structure of ZnO. The atomic percentages of Mn and Co were 6.29% and 1.68%, respectively, in the doped ZnO nanowires. The photocatalytic results showed that Mn-doped and Co-doped ZnO nanowires both exhibited higher photocatalytic activities than undoped ZnO nanowires. Among the doped ZnO nanowires, Co-doped ZnO, which owns a twice active visible-light photocatalytic performance compared to pure ZnO, is considered a more efficient photocatalyst material. The enhancement of its photocatalytic performance originates from the doped metal ions, which enhance the light absorption ability and inhibit the recombination of photo-generated electron-hole pairs as well. The effect of the doped ion types on the morphology, crystal lattice and other properties of ZnO was also investigated.

Transparent gas senor and photodetector based on Al doped ZnO nanowires synthesized on glass substrate

In this work high density, well-aligned Al doped ZnO (AZO) nanowires are hydrothermally synthesized on glass substrate at 99°C. The Al content is ~1.57at%. The PL spectrum shows that Al impurities caused an increase in the number of oxygen vacancies. The spectral response results show that the maximum responsivity and quantum efficiencies η of AZO NWs are 3.61A/W and 84.9%, at an incident light wavelength of 360nm. These AZO NWs have less humidity sensitivity, thus decreasing the effect of humidity effect on gas sensing. Low gas concentrations of 10ppm ethanol and 10ppm acetone can be detected with good responses of 24.5% and 21.2%, using the AZO NW sensor at 200°C and with 0.1V applied bias.

Ag Doped ZnO Nanowires as Highly Sensitive Ethanol Gas Sensor

Pristine ZnO micro-rods and Ag-doped ZnO nanowires were prepared by facile and cost effective co-precipitation route and were examined for their use as ethanol gas sensor. Characterization techniques such as X-Ray diffraction (XRD), Raman spectroscopy, X- Ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM) and Brunauer Emmet Teller (BET) technique were employed to obtain information regarding structural and morphological properties of pure and doped samples. For gas sensing measurements, thick films of pure and Ag doped ZnO powder were deposited on alumina substrate. It has been observed that dopant significantly enhanced the gas sensing performance towards ethanol vapours, and sensors were able to sense ethanol even at low concentration (∼10 ppm) as compared to pure ZnO. The high sensor response of Ag doped ZnO sensors towards ethanol may be attributed to catalytic effect of Ag and higher surface area of nanowires.

Manipulating the quantum interference effect and magnetotransport of ZnO nanowires through interfacial doping.

We carefully prepared interfacial Al-doped (IAD) and interfacial natively-doped (IND) ZnO nanowires (NWs) by introducing atomic-layer interfacial Δ-doping between the two steps of CVD growth. Variable-temperature electron transport as well as magnetotransport behaviours of these NWs were systematically investigated. By virtue of the unique architecture and the quality-guaranteed growth technique, a series of quantum interference effects were clearly observed in the IAD ZnO NWs, including weak localization, universal conductance fluctuation and Altshuler-Aronov-Spivak oscillations. The phase-coherence length (Lφ) of electrons exceeds 100 nm in the IAD ZnO NWs, much longer than those in the IND ones and most conventionally doped ZnO NWs. This ability to efficiently manipulate a variety of quantum interference effects in ZnO NWs is very desirable for applications in nano-optoelectronics, nano- & quantum-electronics and solid-state quantum computing.

Hybrid LEDs based on ZnO nanowire structures

This paper summarized the research, development, and state of the art of hybrid ZnO nanowire LEDs, in which electroluminescence is generated at the junction between n-type doped ZnO nanowire structures and specific p-type doped polymers (in particular PEDOT, PEDOT:PSS, or PFO). Different device architectures will be reviewed and discussed with a particular emphasis on the electronic transport through the hybrid structures and the microscopic processes of light emission. Finally, a gas-phase deposition technique for conductive polymers will be presented which might help improve the performance of hybrid ZnO nanowire LEDs in the future.

Self Assembled ZnO Nanowire Field Effect Transistors

Electrodeposition of ZnO from aqueous baths may be employed as a straightforward path in obtaining in a cheap way nanostructures with well tailored morphology. Nanowires are a particular type of nanostructure which can be obtained in this way with or without employing a template. Further these nanowires can be employed as channel in field effect transistors. However the fabrication of such electronic devices based on nanowires is a difficult and time consuming task due to the challenge in providing the nanostructures with electrical contacts. Usually techniques such as electron beam lithography or focused ion beam induced metallization are employed for this goal [1]. We present here an alternative to these approaches in which simple electrodeposition on interdigitated electrodes can lead to the formation of high quality field effect transistors with pure or doped ZnO nanowire channel. The applications of such nanostructure based devices are numerous most being related to sensing applications where one makes use of the high surface to volume ratio and a cheap and easily scalable method of fabrication represents an important advantage.

Effect of various synthesis protocols on doping profile of ZnO:Eu Nanowires

This paper emphasizes on developing protocols to improve the doping concentration in ZnO NWs. Eu doped ZnO Nanowires (ZnO:Eu NWs) were grown by the chemical bath deposition (CBD), ultra-sonication (US) and microwave (MW) assisted wet chemical methods. The effect of various synthesis methods on the doping profile along with the structural and morphological properties of ZnO:Eu NWs was investigated by X-ray diffraction (XRD), SEM and EDS. EDS results show that a maximum of 2.36 atomic percent Eu is doped via US assisted method, which was attributed to the violent vibrations of molecules set forth by ultrasonic waves, providing sufficient energy for doping. Photoconductivity (PC) properties have been investigated through an analysis of rise and decay curve of the photocurrent. Maximum gain (G) was obtained for MW assisted method, which shows conformal doping and better crystallinity of the ZnO NWs obtained by this method. The PC studies give an insight into the doping mechanism for ZnO. This study paves a way to the conformal doping of ZnO NWs, by modifying the existing methods.

Synthesis of Fe Doped ZnO Nanowire Arrays that Detect Formaldehyde Gas.

Owing to their chemical and thermal stability and doping effects on providing electrons to the conduction band, doped ZnO nanowires have generated interest for use in electronic devices. Here we report hydrothermally grown Fe-doped ZnO nanowires and their gas-sensing properties. The synthesized nanowires have a high crystallinity and are 60 nm in diameter and 1.7 μm in length. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are employed to understand the doping effects on the microstructures and gas sensing properties. When the Fe-doped ZnO nanowire arrays were evaluated for gas sensing, responses were recorded through changes in temperature and gas concentration. Gas sensors consisting of ZnO nanowires doped with 3-5 at.% Fe showed optimum formaldehyde (HCHO) sensing performance at each working temperature.

Co doped ZnO nanowires as visible light photocatalysts

High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV–visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10−3 min−1 in case of nanoparticles and 4.2·10−3 min−1 in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn0.95Co0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.

Luminescence dynamics of bound exciton of hydrogen doped ZnO nanowires

All-optical camera, converting X-rays into visible photons, is a promising strategy for high-performance X-ray imaging detector requiring high detection efficiency and ultrafast detector response time. Zinc oxide is a suitable material for all-optical camera due to its fast radiative recombination lifetime in sub-nanosecond regime and its radiation hardness. ZnO nanostructures have been considered as proper building blocks for ultrafast detectors with spatial resolution in sub-micrometer scale. To achieve remarkable enhancement of luminescence efficiency n-type doping in ZnO has been employed. However, luminescence dynamics of doped ZnO nanostructures have not been thoroughly investigated whereas undoped ZnO nanostructures have been employed to study their luminescence dynamics. Here we report a study of luminescence dynamics of hydrogen doped ZnO nanowires obtained by hydrogen plasma treatment. Hydrogen doping in ZnO nanowires gives rise to significant increase in the near-band-edge emission of ZnO and decrease in averaged photoluminescence lifetime from 300 to 140ps at 10K. The effects of hydrogen doping on the luminescent characteristics of ZnO nanowires were changed by hydrogen doping process variables.

Improvement in the Piezoelectric Performance of a ZnO Nanogenerator by a Combination of Chemical Doping and Interfacial Modification

In this work, we investigate the improvement in the piezoelectric performance of a ZnO nanowire film by a chemical doping and interfacial modification strategy. The Cl-doped ZnO nanowire films were synthesized by a modified hydrothermal approach and characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and I–V characterization. The effect of the Cl dopant with different doping concentrations has been demonstrated by an improvement of the piezoelectric output performance due to the induced lattice strain along the ZnO c-axis, which significantly facilitates the piezocharge separation under the applied stress. The experimental results indicate that the existence of lattice strain along the doped ZnO nanowire polar axis resulted from the different ionic sizes between Cl and O. More importantly, by preparing a Cl-doped ZnO nanowire film on a p-type CuO film, our...