Zinc Oxide Substrates Research Articles

Antibacterial Effects of Zinc Oxide Nanorod Surfaces

Antibacterial coating approaches are being investigated to modify implants to reduce bacterial adhesion and viability in order to reduce implant-associated infection. Nanostructured materials possess unique surface properties, and nanotopographic surfaces have been reported to modulate bacterial adhesion. Zinc oxide (ZnO) films presenting well-controlled nanorod surface structures have recently been developed. To assess the efficacy of ZnO nanorod surfaces as an anti-bacterial coating, we evaluated bacterial adhesion and viability, compared to sputtered ZnO substrates (a relatively flat control) and glass substrates (as a reference). Common implant-associated pathogens, Pseudomonas aeruginosa and Staphylococcus epidermidis were investigated. The number of adherent P. aeruginosa on ZnO nanorod surfaces was found to be reduced compared to glass and sputtered ZnO, while the adherent number of S. epidermidis on the ZnO nanorods was equivalent to glass. Regarding bacteria viability, the ZnO nanorod and sputtered ZnO surfaces demonstrated a modest, but significant bactericidal effect on adherent P. aeruginosa, killing 2.5-fold and 1.7-fold more over the number of dead P. aeruginosa on glass, respectively. A greater bactericidal effect of ZnO substrates on S. epidermidis was found, with sputtered ZnO and ZnO nanorod substrates killing -20-fold and 30-fold more over the number of dead S. epidermidis on glass, respectively. These data support the further investigation and optimization of ZnO nanorod coatings with potential for bacterial adhesion resistance and bactericidal properties.

Nanometer- and Micrometer-Scale Texturing for High-Efficiency Micromorph Thin-Film Silicon Solar Cells

Optimized transparent conductive oxide front electrodes are vital to further increase the efficiency of thin-film silicon solar devices. We report details on the fabrication of multiscale textured zinc oxide substrates and their implementation in amorphous silicon/microcrystalline silicon tandem (micromorph) devices. Such substrates allow separate optimization of light trapping in the top and bottom cells, and efficient decoupling of transparency and conduction. We show in particular the need for sharp, nanoscale texturing for antireflection and light trapping in the top cell. We also show that smooth, micrometer-scale texturing can efficiently improve large-wavelength light management without degrading the quality of the silicon material grown on the substrate. By combining the appropriate morphologies, high currents can be reached in both the top and bottom subcells, while conserving the optimal electrical properties of the solar cells.

SIMS analysis of zinc oxide LED structures: quantification and analysis issues

Zinc oxide (ZnO) is a wide band gap semiconductor that shows great promise for development of light emitting diode structures. Interest in this technology has increased significantly, but even though controlled n‐type doping can be readily achieved, p‐type doping has been difficult. Numerous potential p‐type dopants were investigated in this SIMS study using a CAMECA IMS‐6F. The dopants and other elements of interest were quantified by use of ion implantation into ZnO substrates. Relative sensitivity factor values were obtained for H, Li, N, F, Na, Mg, Al, Si, K, Ga, As, Se, Ag, Cd, Te. Sample charging was encountered for some specimens, and adjacent electron neutralization procedures were employed. ZnO structures were prepared and subsequently analyzed with both O2+ and Cs+ primary beams. Depth profiles exposed a number of analysis issues. Because of the large number of elements, especially those at low atomic number, that were present in the structures, many mass interferences were encountered. Ag in particular was very difficult to monitor. Matrix effects were also noted, especially when high Mg doping was used. The need to monitor Al, Na, and K in the near surface region required analysis without conductive Au coating to reduce contamination. With careful choice of secondary ion species, it was possible to monitor the elements of primary interest using O2+ primary beam. SIMS demonstrated the ability to characterize the layers in the ZnO structure, including quantum wells, and to determine dopant and contaminant levels. Copyright © 2012 John Wiley & Sons, Ltd.

Flexible Photovoltaic Solar Cells Based on AZO Anode

This paper presented an efficient flexible bulk-heterojunction [regioregular of poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C61 butyric acid methyl ester (PCBM)] solar cells with a highly transparent and electrical conductive NiO film as hole-transporting layer (HTL) on optimized Al doped zinc oxide (AZO) substrate. The strcture of this kind of devices is PET/AZO/NiO/P3HT: PCBM /Al. The highest power conversion efficiency (PCE) on glass substrate is 3.15%, and 1.66% on flexible substrate. The physical and electrical properties of AZO thin film were discussed, and the device photovoltaic characteristics were investigated in detail.

Pump-probe third harmonic generation kinetics of gold nanoparticle-attached aluminum-doped zinc oxide substrate

Size-aligned gold nanoparticles (AuNPs) of 5, 10, and 20nm were attached on aluminum-doped zinc oxide (Al–ZnO) substrates chemically using for the first time 3-aminopropyl-trimethoxysilane as a linker molecule. By using these substrates, we present the pump-probe studies of the AuNPs deposited on the Al–ZnO with the different particle sizes and inter-particle distances. The obtained results may be a consequence of interaction of surface Plasmon resonances with the intra-band contributions to the nonlinear optical susceptibilities and to the interactions with the phonons.

Functional one, two, and three-dimensional ZnO structures by solvothermal processing

Crystalline zinc oxide (ZnO) has been fabricated by solvothermal techniques under quite different temperature and pressure environment stretching from sub- to supercritical conditions. Among them, one-step processing of inorganic–inorganic hybrid ZnO structures based on ZnO substrate with attached ZnO nanocrystals has been challenged. Combination of doping ions was made to yield ZnO structures with luminescent properties of high potential for application in fast-decay devices. The room temperature decay of antimony, lithium (Sb, Li) codoped homoepitaxial films is reported.

In situ micro-Raman spectroscopic study of laser-induced crystallization of amorphous silicon thin films on aluminum-doped zinc oxide substrate

The effects of laser irradiation condition and deposition substrate on the laser crystallized 330 nm Si films structure were investigated using in situ micro-Raman spectroscopy. Results showed that crystallization of amorphous silicon (a-Si) films started at laser irradiation power density of 0.6 × 105 W/cm2 for 20 s. The crystalline volume fraction of Si films depended mostly on the laser power density but not on the laser irradiation time. The Si films on both smooth and textured aluminum-doped zinc oxide (AZO) substrates exhibited lower crystalline volume fraction and smaller average grain size than the Si films on glass did. The Si films on textured AZO revealed higher crystalline volume fraction and larger average grain size than the Si films on smooth AZO did. The stress in crystalline Si films was observed to be compressive on AZO and tensile on glass. The compressive stress in crystalline Si films on textured AZO was slightly less than that on smooth AZO. The present work indicated that the structure of crystalline Si films on textured AZO was improved than that on smooth AZO, which may be helpful to crystalline Si thin-film solar cell.

Atomic-level stress and induced growth of wurtzite zinc oxide using molecular dynamics simulation

Molecular dynamics is used to simulate the film growth process of zinc oxide (ZnO) deposited on a ZnO substrate. In the work, the Buckingham-type interatomic potential is modelled to describe the interaction of Zn–O atoms. The effects of incident energy and substrate temperature on the layer coverage function, radial distribution function and residual stress are investigated. Results show that the crystal growth of the deposition film is a symmetric wurtzite lattice along the [0 0 0 1] direction due to charge transformation. Epitaxial-like growth only occurs at very low incident energies, while the intermixing process could start from an incident energy of 3 eV. The average stress of the Zn layer is a compressive stress that is close to zero. However, the average mean biaxial stress and the normal stress of the O layer are −4.49 GPa and −3.07 GPa, respectively. The simulation results are compared with experimental results available in the literature.

Determination of secondary ion mass spectrometry relative sensitivity factors for polar and non-polar ZnO

Zinc oxide (ZnO) is regarded as a promising material for optoelectronic devices, due to its electronic properties. Solely, the difficulty in obtaining p-type ZnO impedes further progress. In this connection, the identification and quantification of impurities is a major demand. For quantitative information using secondary ion mass spectrometry (SIMS), so-called relative sensitivity factors (RSF) are mandatory. Such conversion factors did not yet exist for ZnO. In this work, we present the determined RSF values for ZnO using primary (ion implanted) as well as secondary (bulk doped) standards. These RSFs have been applied to commercially available ZnO substrates of different surface termination (a-plane, Zn-face, and O-face) to quantify the contained impurities. Although these ZnO substrates originate from the same single-crystal, we observe discrepancies in the impurity concentrations. These results cannot be attributed to surface termination dependent RSF values for ZnO.

Structural properties of RF-magnetron sputtered Cu2O thin films

Cuprous oxide thin films were produced on soda-lime glass substrates using reactive RF-magnetron sputtering. The influence of deposition parameters and temperature on composition and structural properties of the single layers was extensively studied using X-ray diffraction. The control over microstructure and residual stresses is possible by changing reactive gas pressure and deposition temperature. Fiber textured Cu2O films showing a [100] preferred orientation and a fraction of untextured domains can be obtained: suitable modeling taking this microstructure into account shows the presence of a strong compressive stress decreasing with the temperature. Highly reproducible films can be obtained, whose microstructure is preserved when sputtering on tungsten and zinc oxide substrates.

Fe 3O 4 on ZnO: A spectroscopic study of film and interface properties

Magnetite (Fe 3O 4) thin films have been grown epitaxially on zinc oxide (ZnO) substrates, using reactive molecular beam epitaxy. The film quality was found to be strongly dependent on the oxygen partial pressure during growth. For a uniform Fe 3O 4 film a certain pressure variation was needed during growth. Structural, electronic, and magnetic properties were analyzed utilizing low energy electron diffraction, Hard X-ray Photoelectron Spectroscopy (HAXPES), Magneto-Optical Kerr Effect (MOKE), and X-ray Magnetic Circular Dichroism (XMCD). Diffraction patterns show clear indication for growth of Fe 3O 4 in the [111] direction on ZnO(0001). Non-destructive depth profiling by HAXPES revealed uniform magnetite thin films. Both, MOKE and XMCD measurements show easy in-plane magnetization. The dichroic spectra clearly support the formation of Fe 3O 4.

The effect of ZnO surface conditions on the electronic structure of the ZnO/CuPc interface

The interfacial electronic structures of zinc oxide (ZnO)/copper-phthalocyanine (CuPc) were investigated by in situ x-ray and ultraviolet photoelectron spectroscopy (UPS) to determine the effects of air contamination on the ZnO substrate. UPS spectra showed that the 0.2 eV of the interface dipole is generated at the interface of the air exposed ZnO/CuPc while the interface of the annealed ZnO/CuPc generated −0.2 eV. In both cases, no band bending was observed. On the other hand, band bending at 0.3 eV and an interface dipole of 0.2 eV were observed at the interface of the sputter cleaned ZnO/CuPc. The energy offset between the conduction band maximum of ZnO and the highest occupied molecular orbital of CuPc was determined to be 0.6–0.7 eV for the contaminated ZnO interface while the offset was 1.0 eV for the cleaned ZnO interface. Contaminating moisture has little effect on the offset while the charge transfer was blocked and the offset was decreased in the presence of hydrocarbons.

INVESTIGATIONS ON THE ELECTRICAL PROPERTIES OF ZnO NANORODS AND COMPOSITES FOR PHOTOVOLTAIC AND ELECTROCHEMICAL APPLICATIONS

ZnO nanorods grown by hydrothermal technique on glass, Zinc, and Indium tin oxide (ITO) substrates exhibit both open and closed hexagonal structures. On the nanoscale, closed ZnO nanostructures exhibit two types of ion conduction regions as revealed by AC-impedance spectra collected through the tip of an atomic force microscope (AFM). One region has higher impedance values (apparent values of approximately 107 ohms) with two semicircles. Two semicircles are indicative of a ZnO structure composed of bulk and grain boundary conduction. Other regions were found to have impedance values that were two orders of magnitude lower (apparent values of 105 ohms). This indicates that these ZnO films have two conduction pathways. The polyethylene oxide ( PEO )– ZnO nanorod composite was made by spin-coating the ZnO rods growing from the ITO substrate with PEO. In the PEO – ZnO composite film, only the AC impedance values of 105 ohms were observed. This is higher than PEO electrolyte without ZnO nanorods. Since regions of higher impedance were not seen in the PEO – ZnO nanorod composites, the polymer electrolyte either dominated the conduction of the system or suppressed the first pathway of higher impedance in the ZnO rods.

Characterization of phosphonic acid binding to zinc oxide

Radio Frequency (RF) sputter-deposited zinc oxide (ZnO) films have been modified with alkylphosphonic acids in order to study both the binding of the phosphonic acid (PA) group to the ZnO surface and the packing of the alkyl chain. The characterization of these PA-modified ZnO substrates by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRRAS), atomic force microscopy (AFM) and contact angle measurements is presented herein. The surface modification procedure is straightforward and was adapted from earlier work. XPS analysis shows that oxygen plasma (OP) treatment creates reactive oxygen species on the surface of ZnO, allowing for a more robust binding of PAs to the ZnO surface. IRRAS analysis indicates that octadecylphosphonic acid binds to the ZnO surface in a predominantly tridentate fashion, forming dense, well-packed monolayers with alkyl chains in a fully anti-conformation. AFM and contact angle measurements indicate good surface coverage of the PAs with little to no multilayer formation.

Formation of ionic bonds between a fatty-acid Langmuir–Blodgett monolayer and a zinc oxide substrate

A fatty-acid Langmuir-Blodgett (LB) monolayer ionically adsorbed to the substrate has been prepared by adopting ZnO-based conductor and pure water respectively as the substrate and subphase. Ionization of the fatty-acid molecules has been detected by infrared reflection-absorption spectroscopy (IR-RAS), which is enabled by the condensed free electrons in the doped ZnO substrate. On the contrary, IR-RAS measurements have indicated that fatty-acid molecules transferred onto Au and indium-tin-oxide substrates from a pure-water surface are not ionized. In addition, it has been demonstrated that these ionically bonded fatty-acid monolayers protect the ZnO transparent electrode from chemical attack by NH(3) gas. Since the LB technique is a simple method applicable to a wide variety of materials, the present results may lead to a new way of obtaining functional organic-inorganic nanosystems.

Bulk heterojunction solar cells with NiO hole transporting layer based on AZO anode

We report efficient bulk-heterojunction [regioregular of poly(3-hexylthiophene) (P3HT):(6,6)-phenyl C 61 butyric acid methyl ester (PCBM)] solar cells with a highly transparent and electrical conductive NiO film as hole transporting layer (HTL) on optimized Al doped zinc oxide (AZO) substrate. The highest power conversion efficiency (PCE) of 3.15% of AZO/NiO/P3HT:PCBM/Al solar cells was achieved through NiO nano-layer sputtering O 2/Ar flow ratio, film thickness optimization and it was found that room temperature sputtered NiO at an O 2/Ar ratio of 3:7 and with a thickness of 10 nm shows the best photovoltaic properties.

Epitaxial growth of ZnO thin films on AlN substrates deposited at low temperature by magnetron sputtering

AbstractHexagonal aluminium nitride (AlN) and zinc oxide (ZnO) thin films have been deposited by DC and RF reactive magnetron sputtering at room temperature. For a first set of samples, sputtered AlN films were deposited on silicon ZnO substrate. For a second set, ZnO films were deposited on AlN substrate. X‐ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) analysis of the synthesized AlN film on ZnO buffer layer have shown some amorphous zones close to the interface followed by a nanocrystalline layer exhibiting (10−10) and (0002) orientations of the hexagonal AlN crystalline phase. At the top of the film, a relatively well‐crystallized layer with a single (0002) orientation has been observed. We have related the relatively bad interface to the presence of oxygen coming from ZnO substrate. This behaviour was different for the growth of ZnO film when AlN was used as substrate. In fact, we have observed thanks to HRTEM images and selected area electron diffraction patterns, that the ZnO film deposited on AlN substrate exhibits an epitaxial growth which is strongly dependent on the crystalline quality of AlN film.

Light-Emitting Diode Based on ZnO by Plasma-Enhanced Metal–Organic Chemical Vapor Deposition Employing Microwave Excited Plasma

In this paper we describe the growth of nitrogen doped zinc oxide (ZnO) films on single crystal ZnO substrates by plasma-enhanced metal–organic chemical vapor deposition (PE-MOCVD) employing microwave excited high-density plasma. We used Dimethylzinc (DMZ) as a Zinc precursor, and six different types of oxygen and nitrogen precursors: O2+N2, NO, N2O, O2+NH3, NO2, and O2. This paper considers the effects of nitrogen precursor material and utilizing the plasma on the structural properties and the nitrogen concentration by atomic force microscope and secondary ion mass spectrometry. It was only when using plasma and NO2 that the nitrogen (N) doped ZnO film with the steps and terraces surface structure of two-dimensional growth could be formed by our growth method. Furthermore, we fabricated a homostructural LED comprising the N-doped ZnO film and n-type ZnO substrate, and we achieved electroluminescence (EL) in forward bias at room-temperature (RT) and the current–voltage rectifying characteristics.

Reactivity of molten aluminium with polycrystalline ZnO substrate

The microstructure studies of the reaction product region (RPR) obtained due to the interaction between the liquid aluminium and polycrystalline zinc oxide substrate at 1273 K has been studied. The RPR extended over the oxide substrate and showed a typical C4 (co-continuous-ceramic-composites) structure composed of two interpenetrating phases. The scanning electron microscopy studies revealed that the large crystals of alumina were surrounded by an Al(Zn) metallic phase. Moreover, the transmission electron microscopy investigation showed the presence of a thin (~250 nm) layer next to the ZnO. The chemical analysis accompanied by the selected area electron diffraction patterns indicated in both cases the same stoichiometric aluminium oxide but of different crystallographic structure, i.e., large crystals had α-Al2O3 structure while the layer was identified as metastable δ-Al2O3. The results were compared to those reported for interaction between liquid aluminium and monocrystalline ZnO.

X-ray characterisation of zinc oxide (ZnO) single crystal substrates

Single crystal substrates of low defect density are paramount for fully realising the numerous applications of zinc oxide (ZnO) wide bandgap semiconductors. While ZnO substrates are commercially available from various vendors, very little information is available on the structural properties of these substrates. Therefore, an extensive evaluation of available substrates would serve as a basis for the development of ZnO based devices and technologies. In this study, bulk ZnO single crystal substrates grown by different growth techniques have been characterised using synchrotron white beam X-ray topography and high resolution X-ray diffraction. The substrates exhibit a wide range of dislocation densities from as high as 106 cm–2 down to less than 1000 cm–2 depending on the growth technique employed. The authors' evaluation reveals that ZnO crystals grown by the hydrothermal technique possess the best structural quality with dislocation densities of 800–1000 cm–2 and rocking curves with a full width half maximum of less than 12 arc seconds.