a perspective on materials, synthesis methods and applications

The oxides of copper (CuxO) are fascinating materials due to their remarkable optical, electrical, thermal and magnetic properties. Nanostructuring of CuxO can further enhance the performance of this important functional material and provide it with unique properties that do not exist in its bulk form. Three distinctly different phases of CuxO, mainly CuO, Cu2O and Cu4O3, can be prepared by numerous synthesis techniques including, vapour deposition and liquid phase chemical methods. In this article, we present a review of nanostructured CuxO focusing on their material properties, methods of synthesis and an overview of various applications that have been associated with nanostructured CuxO

Transparent metal electrodes from ordered nanosphere arrays

We show that perforated metal electrode arrays, fabricated using nanosphere lithography, provide a viable alternative to conductive metal oxides as transparent electrode materials. The inter-aperture spacing is tuned by varying etching times in an oxygen plasma, and the effect of inter-aperture “wire” thickness on the optical and electronic properties of perforated silver films is shown. Optical transmission is limited by reflection and surface plasmons, and for these results do not exceed 73%. Electrical sheet resistance is shown to be as low as 3 Ω ◻−1 for thermally evaporated silver films. The performance of organic photovoltaic devices comprised of a P3HT:PCBM bulk heterojunction deposited onto perforated metal arrays is shown to be limited by optical transmission, and a simple model is presented to overcome these limitations

Nanostructured copper oxide semiconductors : a perspective on materials, synthesis methods and applications

The oxides of copper (CuxO) are fascinating materials due to their remarkable optical, electrical, thermal and magnetic properties. Nanostructuring of CuxO can further enhance the performance of this important functional material and provide it with unique properties that do not exist in its bulk form. Three distinctly different phases of CuxO, mainly CuO, Cu2O and Cu4O3, can be prepared by numerous synthesis techniques including, vapour deposition and liquid phase chemical methods. In this article, we present a review of nanostructured CuxO focusing on their material properties, methods of synthesis and an overview of various applications that have been associated with nanostructured CuxO

Understanding Anisotropic Plasma Etching of Two-Dimensional Polystyrene Opals for Advanced Materials Fabrication

Anisotropic deformation of polystyrene particles in an oxygenated (O₂/Ar) plasma is observed for radio frequency (rf) plasma and inductively coupled plasma (ICP). A facile model based on a ratio of completely isotropic and completely anisotropic etching is presented to describe the anisotropy of the etching process and is implemented to determine the height of the spheroid-shaped polystyrene particles. In our systems, we find the plasma etching to be 54% isotropic in the rf plasma and 79% isotropic in the ICP. With this model, the maximum material deposition thickness for nanofabrication with plasma-etched nanosphere lithography or colloid lithography can be predicted. Moreover, the etching of polystyrene particles in an oxygenated plasma is investigated versus the etching time, gas flow, gas composition, temperature, substrate material, and particle size. The results of this study allow precise shape tuning during the fabrication of nanostructured surfaces with size-dependent properties for bionic, medical, and photonic applications

Enhancing the current density of electrodeposited ZnO-Cu 2O solar cells by engineering their heterointerfaces

Using ZnO seed layers, an efficient approach for enhancing the eterointerface quality of electrodeposited ZnO-Cu2O solar cells is devised. We introduce a sputtered ZnO seed layer followed by the sequential electrodeposition of ZnO and Cu2O films. The seed layer is employed to control the growth and crystallinity and to augment the surface area of the electrodeposited ZnO films, thereby tuning the quality of the ZnO-Cu2O heterointerface. Additionally, the seed layer also assists in forming high quality ZnO films, with no pin-holes, in a high pH electrolyte solution. X-ray electron diffraction patterns, scanning electron and atomic force microscopy images, as well as photovoltaic measurements, clearly demonstrate that the incorporation of certain seed layers results in the alteration of the heterointerface quality, a change in the heterojunction area and the crystallinity of the films near the junction, which influence the current density of photovoltaic devices

Time-of-flight studies of electron-collection kinetics in polymer : fullerene bulk-heterojunction solar cells

The charge-collection dynamics in poly(3-hexylthiophene:[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) bulk heterojunctions are studied in thick (>1 μm) devices using time-of-flight measurements and external quantum-efficiency measurements. The devices show Schottky-diode behavior with a large field-free region in the device. Consequently, electron transport occurs by diffusion in the bulk of the active layer. At high applied biases where the depletion region spans the entire active layer, normal time-of-flight transients are observed from which the electron mobility can be determined. Here, the electron mobility follows Poole–Frenkel behavior as a function of field. At lower applied biases, where the depletion region only spans a small portion of the active layer, due to a high density of dark holes, the recombination kinetics follow a first-order rate law with a rate constant about two orders of magnitude lower than that predicted by Langevin recombination. Erratum can be found in Advanced functional materials, vol. 21, issue 22, p. 4210 doi: 10.1002/adfm.2011900997 page(s

Effect of gold oxide in measurements of colloidal force

Atomic force microscopy, contact-angle, and spectroscopic ellipsometry measurements were employed to investigate the presence and properties of gold oxide on the surface of gold metal. It was found that, in agreement with available literature, unoxidized gold surfaces were hydrophobic, whereas oxidation rendered the surface highly hydrophilic. The oxide could be removed with ethanol or base but appeared to be stable over long periods in water or salt solutions between pH 3 and 7. After oxidation, the oxide layer thickness, determined using ellipsometry, was consistent with an approximate monolayer of Au-O bonds at the gold surface. The presence of gold oxide was found to alter significantly the electrical double-layer characteristics of the gold surface below pH 6 and may explain the apparent inconsistencies in observed force behavior where gold is employed as well as aiding in design of future microfluidic systems which incorporate gold as a coating

Defect-Mediated Energy Transfer between ZnO Nanocrystals and a Conjugated Dye

Energy transfer from the defect state of zinc oxide nanoparticles to the fluorescent dye AlexaFluor 594 (A594) cadaverine has been studied using both steady-state and time-resolved photoluminescence (PL) measurements. The addition of five stoichiometric equivalents of A594 cadaverine completely quenches the visible defect emission from zinc oxide nano crystals. We also find that the entire defect emission of ZnO is reduced without any change in the overall line shape of the emission, demonstrating that the defect emission is from a single electronic state coupled to the phonon modes of the crystal lattice. The energy transfer is modeled using the dynamic quenching model developed by Tachiya (Sadhu, S.; Tachiya, M. <i>J. Phys. Chem.</i> <b>2009</b>, <i>113</i>, 19488–19492). Remarkably, there is very efficient energy transfer when there is just one adsorbed dye molecule per nanocrystal, regardless of the orientation of the dipole moment of the cadaverine molecule and the distance to the defect state

Poly(lactic-<i>co</i>-glycolic acid) (PLGA) as Ion-Conducting Polymer for Biodegradable Light-Emitting Electrochemical Cells

The use of biocompatible and biodegradable materials in optoelectronics will enable the development of promising applications in the field of healthcare and environmental sensors as well as a more sustainable production of technology. Here, we present light-emitting electrochemical cells which utilize the biodegradable polymer poly­(lactic-<i>co</i>-glycolic acid) (PLGA) to promote ionic conductivity in the active layer of light-emitting electrochemical cells. The device performance was analyzed in terms of the volume fraction of PLGA in the active layer blend as well as with respect to three different lactic:glycolic monomer ratios (85:15, 75:25, 65:35). In all three cases, adding PLGA to the active layer leads to an improvement of the turn-on voltage of up to 2 V compared to reference devices without PLGA. This can be attributed to an increase in ionic conductivity, which was determined by impedance spectroscopy. Increasing the relative amount of PLGA in the active layer shows that the improvement is ultimately limited by poor intermixing with the polymeric emitter as observed by fluorescent microscopy. The best devices achieved turn-on voltages of 4.1 V and a maximum luminance of 3800 cd m^–2 at 7.1 V

Solution-Processed Bio-OLEDs with a Vitamin-Derived Riboflavin Tetrabutyrate Emission Layer

Solution processed biomaterials are required for the active component to develop printed biodegradable and biocompatible optoelectronic devices. Ideal film formation is crucial for the fabrication of multilayer thin film sandwich devices. We report on the characterization of thin films of the riboflavin-derived biomaterial riboflavin tetrabutyrate and its utilization in an organic light-emitting diode. We show that the nonsolution processable precursor can form homogeneous and smooth films with the addition of tailored side groups that change its solubility. We demonstrate by grazing incidence wide-angle X-ray scattering that this chemical derivative reduces the crystallinity and enhances emission, likely by suppressing π–π stacking interactions. Organic light-emitting diodes with a poly­(9-vinylcarbazole)–emissive riboflavin tetrabutyrate bilayer structure yield a maximum luminance of 10 cd/m² and external quantum efficiency of 0.02% with a 640 nm peak orange exciplex emission. External quantum efficiency measurements of a photodiode affirm the exciplex formation