This PDF file contains the front matter associated with SPIE Proceedings Volume 9364, including the Title Page, Copyright information, Table of Contents, Introduction, Authors, and Conference Committee listing.

Multilayer (ML) thin films, based on indium molybdenum oxide (IMO) and aluminum zinc oxide (AZO), having different stacking were deposited using RF sputtering at room temperature (RT). The total-layer thickness of the MLs ranges between 93 nm and 98 nm. The deposited films were characterized by their structural, electrical, microstructural, and optical properties. X-ray diffraction (XRD) peaks obtained at 2θ of around 30.6° and 34.27° are matched with cubic-In₂O₃ (222) and hexagonal-ZnO (002), respectively. The MLs have both nano-crystalline and polycrystalline structures depending on the layer properties. A conspicuous feature of XRD analysis is the absence of diffraction peak from 50 nm thick IMO layer when it is stacked below 50 nm thick AZO, whereas it appears significantly when the stacking is reversed to place IMO above AZO layer. Hall measurements confirmed that the deposited MLs are n- type conducting and the electrical properties are varied as a function of layer properties. The deposited MLs show high shortwavelength infrared transmittance (SWIRT) even at 3300 nm, which is ranging as high as 75 % - 90 %. Overall, the MLs show high transmittance in the entire Vis-SWIR region. The optical band gap (E_g) calculated using the absorption coefficient (α) and photon energy (hν) of the deposited MLs is ranging between 3.19 eV and 3.56 eV, depending on the layer properties. Selected as- deposited films were annealed in open air at 400 °C for 1 h; the transmittance of annealed films was improved but their electrical properties deteriorated. Atomic force microscopy (AFM) analysis shows that the root-mean-square (RMS) roughness of the MLs ranges between 0.8 nm and 1.5 nm.

We have developed a low-temperature, high-magnetic-field scanning tunneling microscope (STM) combined with pulsed laser deposition (PLD), and studied the electronic structures of homoepitaxial thin film surfaces of SrTiO₃(001). Thin film thicknesses were monitored during depositions using a reflection high-energy electron diffraction, and the samples were investigated by using the STM without exposing the sample surfaces to air. Scanning tunneling spectroscopy (STS) mapping reveals a number of defects that can be categorized into three feature-specific types. The development of this STM-PLD system opens up a way to investigate extraordinary and inhomogeneous electronic structures in complex oxide thin films, heterostructures and nanostructures.

Various zinc oxide (ZnO) nanocrystals are expected as new building blocks for optoelectronic devices. Among them, we have studied about fabricating ZnO nanowires using nanoparticle-assisted pulsed laser deposition (NAPLD). Recently, we achieved to fabricate the periodically-aligned ZnO nanowires with a period of from 4 to 5 μm using interfering four-beams of nanosecond ultraviolet (UV) laser processing. ZnO nanowires with diameters of several dozen nanometers were grown on the ZnO buffer layer prepared by pulsed laser deposition at the low-chamber pressure of 3 Pa. Additionally, crystallization of ZnO nanoparticles collected on a sapphire substrate was achieved by UV-laser annealing. In this method, ZnO nanoparticles were collected at room temperature, then they were laser-annealed with a KrF excimer laser. The particle size increased by instantaneous melting and aggregation of ZnO nanoparticles because of the high absorption efficiency of ZnO in the UV spectral region. It was found that the optical property was improved by UV-laser annealing process. Additionally, their x-ray diffraction peaks of wurtzite ZnO crystals had narrower full width half maximum than those before laser annealing.

Germanium telluride (GeTe) is a phase change material (PCM) that undergoes an exponential decrease in resistance from room temperature to its transition temperature at approximately 200 °C. Its resistivity decreases by as much as six orders of magnitude between amorphous and crystalline phases as it is heated. Chalcogenides such as GeTe have been utilized typically in nonvolatile optical memories such as CDs, DVDs, and Blu-ray discs, where the change in reflectivity between phases gives enough contrast for ON and OFF bits. Research over the past several years has begun to characterize the electronic control of PCM thin films for advanced electronic memory applications. By applying a voltage to control its resistance and crystallinity, GeTe has become a candidate for ultra-fast switching electronic memory, perhaps as an alternative to Flash memory. In this research, micro-scale PCM cells were fabricated using RF sputtering of a GeTe target and electron-beam evaporation on c-Si, SiO₂/Si, Si₃N₄/Si, and Al₂O₃. Characterizations of the crystallization process were completed with spectroscopic ellipsometry (SE), varied voltage, and varied temperature in order to draw a comparison of the switching mechanism between thermally and electronically induced transition. The results show an optical contrast of ∆n + i∆k = -0.858 + i1.056. Heat conduction experiments prove a growthdominated crystallization and fracturing of conductive crystallites when deposited on Al₂O₃. PCM cells exhibit memory-like I-V curves for smaller cell dimensions according to the trap-limited conduction model in chalcogenides. RF structures show the capability of being utilized as improved RF switches.

We present the vanadium dioxide (VO₂) thin films deposition using e-beam evaporation of a vanadium target under oxygen atmosphere on different substrates (sapphire, Si, SiO₂/Si…) and we focus on their electrical and optical properties variations as the material undergoes a metal-insulator transition under thermal and electrical stimuli. The phase transition induces extremely abrupt changes in the electronic and optical properties of the material: the electrical resistivity increases up to 5 orders of magnitude while the optical properties (transmission, reflection, refractive index) are drastically modified. We present the integration of these films in simple planar optical devices and we demonstrate electrical-activated optical modulators for visible-infrared signals with high discrimination between the two states. We will highlight a peculiar behavior of the VO₂ material in the infrared and far infrared regions (2- 20 μm), namely its anomalous emissivity change under thermal- end electrical activation (negative differential emittance phenomenon) with potential applications in active coatings for thermal regulation, optical limiting or camouflage coatings.

In this paper we report on the synthesis and development of vanadium oxide precursor flexographic ink for the printing of hole-transporting layers in organic solar cells. For the synthesis of vanadium oxide inks, a sol-gel methodology was utilized. By modifying the vanadium alkoxide precursor with a right type of coordinating ligands a stable and flexoprintable ink has been successfully developed. Flexo-printing afforded smooth and uniform vanadium oxide sol-gel films on top of PCDTBT:PC₇₀BM films. The conversion of the synthesized sol-gel film into a corresponding vanadium oxide layer was followed by DSC/TGA and XPS analyses. The inks were used for the fabrication of inverted organic solar cells by flexo-printing. Power conversion efficiencies ranging between 3.5 % and 4.5 % were achieved, which are slightly lower than the reference cells using vacuum-deposited MoO₃ as the hole-transporting layers.

LiCoO₂ thin films were epitaxially grown by pulsed laser deposition (PLD). PLD is widely used to form complex oxide thin films due to the relatively small deviation in cationic composition between the target and the film. The deviation highly depends on the ablation laser conditions, and it greatly affects the quality of the epitaxial LiCoO₂ thin films. Furthermore, relatively lower oxygen pressure was found to result in higher quality LiCoO₂ thin films with suppressed impurity phases, although much higher oxygen pressure had been often used to avoid the formation of a lower valence state Co₃O₄ as an impurity. In other words, gas pressure also affects the composition in the case of lithium compounds, because lithium is even lighter than oxygen. The results clearly indicate that the difference in the composition between the target and the film is controllable by adjusting these parameters. In this study, we demonstrated the high-rate epitaxial growth of stoichiometric LiCoO₂ films by using a lithium-enriched target through composition control.

In this study, we discuss the potential advantages of a new ZnO-based semiconductor, ZnInON (ZION), for application in multi quantum-well (MQW) photovoltaics. ZION is a pseudo-binary alloy of ZnO and InN, which has direct and tunable band gaps over the entire visible spectrum. It was found from simulation results that owing to the large piezoelectric constant, the spatial overlap of the electron and hole wave functions in the QWs is significantly small on the order of 10^-2, where the strong piezoelectric field enhances the separation of photo generated carriers. As a result, ZION QWs have low carrier recombination rate of 10¹⁴–10¹⁸ cm^-3s^-1, which is much lower than that in conventional QWs such as InGaAs/GaAs QW (10¹⁹ cm^-3s^-1) and InGaN/GaN QW (10¹⁸–10¹⁸ cm^-3s^-1). The long carrier life time in ZION QWs (∼1μs) should enable the extraction of photo-generated carriers from well layers before the recombination, and thus increase V_oc and J_sc. These simulation results are consistent with our experimental data showing that both V_oc and J_sc of a p-i-n solar cell with strained ZION MQWs and thus the efficiency were increased by the superimposition of laser light with lower photon energy than the band gap energy of the QWs. Since the laser light contributed not to carrier generation but to the carrier extraction from the QWs, and no increase in V_oc and J_sc was observed for relaxed ZION MQWs, the improvement in the efficiency was attributed to the long carrier lifetime in the strained ZION QWs.

ZnO is a highly efficient and promising semiconductor material because of its large bandgap (3.37 eV) and exciton binding energy (60 meV). MgO also has a very high bandgap (7.8 eV), and the incorporation of Mg into ZnO can result in an alloy with a bandgap of more than 4 eV . We used plasma immersion ion implantation to dope phosphorus into Zn_0.85Mg_0.15O for achieving p-type ZnMgO. RF sputtering was used to deposit ZnMgO on a Si substrate. Phosphorus doping was conducted from 10 s to 70 s. Rapid thermal annealing of the samples was performed to remove any implantation defects. A highly dominant acceptor-bound-exciton peak was observed at 3.36 eV by photoluminescence measurements, which continued to dominate from low temperature to room temperature. Donor-bound acceptor and free-electron acceptor peaks were also observed at 3.24 eV and 3.28 eV, respectively.

Epitaxial layers of ZnO have been grown on c-plane, (0001) sapphire substrates by plasma assisted molecular beam epitaxy. The oxygen:zinc flux ratio was found to be crucial in obtaining a film with a smooth surface and good crystallinity. When increasing film thickness from ~80 to 220 nm we observed an increase in the streakiness of RHEED images, and XRD revealed a reduction in crystal strain and increase in crystal alignment. A film with surface roughness of 0.5 nm and a XRD rocking curve FWHM of 0.1 for the main ZnO peak (0002) was achieved by depositing a low temperature ZnO buffer layer at 450 °C and then growing for 120 minutes at 700 °C with a Zn-cell temperature of 320 °C and an oxygen partial pressure of 7e^-7 Torr. We found novel structures on two samples grown outside of our ideal oxygen:zinc flux ratio. SEM images of a sample believed to have been grown in a Zn-rich environment showed flower like structures up to 150 um in diameter which appear to have formed during growth. Another sample believed to have been deposited in a Zn-deficient environment had rings approximately 1.5 um in diameter scattered on its surface.

The investigation of the differences between ordered and disordered materials (in the hundreds of nanometer lengthscale) is a crucial topic for a better understanding of light transport in photonic media. Here we study the light transmission properties of 1D photonic structures in which disorder is introduced in two different ways. In the first study, we have grouped the high refractive index layers in layer clusters, randomly distributed among layers of low refractive index. We have controlled the maximum size of such clusters and the ratio of the high-low refractive index layers (here called dilution). We studied the total transmission of the disordered structure within the photonic band gap of the ordered structure as a function of the maximum cluster size, and we have observed a valley in trend of the total transmission for a specific maximum cluster size. This value increases with increasing dilution. Furthermore, within one dilution we observe oscillations of the total transmission with increasing cluster size. In the second study, we have realized photonic structures with a random variation of the layer thickness. The structures were fabricated by radio-frequency (RF) sputtering technique. The transmission spectrum of the disordered structure was simulated by taking into account the refractive index dispersion of the materials, resulting in a good agreement between the experimental data and the simulations. We found that the transmission of the photonic structure in the range 300– 1200 nm is lower with respect the corresponding periodic photonic crystal. The studied disordered 1D photonic structures are very interesting for the modelization and realization of broad band filters and light harvesting devices.

Transparent glass-ceramics are nanocomposite materials which offer specific characteristics of capital importance in photonics. This kind of two-phase materials is constituted by nanocrystals embedded in a glass matrix and the respective composition and volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramic. Among these properties transparency is crucial, in particular when confined structures, such as dielectric optical waveguides and optical fibers, are considered, and the number of papers devoted to this topic is continuously increasing. Another important point is the role of the nanocrystals when activated by luminescent species, as rare earth ions, and their effect on the spectroscopic properties of the glass-ceramic. The presence of the crystalline environment around the rare earth ion allows high absorption and emission cross sections, reduction of the non-radiative relaxation thanks to the lower phonon cut-off energy, and tailoring of the ion-ion interaction by the control of the rare earth ion partition. This last point is crucial and still object of intense experimental and theoretical studies. The composition of the glass matrix also impacts the properties of the rare earth ions located in nanoparticles. Moreover, some kinds of nanocrystals can play as effective rare earth sensitizers. Fabrication, assessment and application of glass-ceramic photonic systems, especially waveguides, deserve an appropriate discussion which is the aim of this paper, focused on luminescent glass-ceramics. In this work, a brief historical review, consolidated results and recent advances in this important scientific and technological area will be presented, and some perspectives will be outlined.

In this paper we demonstrate the visibility of the low temperature chemical synthesis for developing device quality material grown on flexible and solid substrates. Both colorimetric sensors and UV photodetectors will be presented. The colorimetric sensors developed on paper were demonstrated for heavy metal detection, in particular for detecting copper ions in aqueous solutions. The demonstrated colorimetric copper ion sensors developed here are based on ZnO@ZnS core-shell nanoparticles (CSNPs). These sensors demonstrated an excellent low detection limit of less than 1 ppm of copper ions. Further the colorimetric sensors operate efficiently in a wide pH range between 4 and 11, and even in turbulent water. The CSNPs were additionally used as efficient photocatalytic degradation element and were found to be more efficient than pure ZnO nanoparticles (NPs). Also p-NiO/n-ZnO thin film/nanorods pn junctions were synthesized by a two-step synthesis process and were found to act as efficient UV photodetectors. Additionally we show the effect of the morphology of different CuO nanostructures on the efficiency of photo catalytic degradation of Congo red organic dye.

The modification of the surface reception properties of nanocrystalline structures is of great interest in environmental, catalysis and energy related applications. For instance, an oxide surface covered with a layer of another oxide opens the possibility of creating the nanosized counterparts of bulk catalytic systems. A relevant example is the TiO₂-WO₃, which is an active catalysts in a broad range of reactions. The chemical synthesis of the colloidal, nanocrystalline version of such system will first be exposed, by coupling suitable sol-gel chemistry with solvothermal processing. Then, the range of obtained structures will be discussed, ranging from WO_x-surface modified TiO₂ to TiO₂-WO₃ heterojunctions. The complex structural evolution of the materials will be discussed, depending on the W concentration. A summary of the acetone sensing properties of these systems will be shown. In particular, the surface activation of the otherwise almost inactive pure TiO₂ by surface deposition of WO₃-like layers will be highlighted. Addition of the smallest W concentration boosted the sensor response to values comparable to those of pure WO₃, ranging over 2-3 orders of magnitude of conductance variation in presence of ethanol or acetone gases. Simple analysis of the sensing data will evidence that the combination of such nanocrystalline oxides results in catalytic activation effects, with exactly opposite trend, with respect to pure TiO₂, of the activation energies and best responses.

In the last decades, considerable efforts have been carried out to develop new tools and knowledge in the domain of functionalized materials, for application ranging information, lighting, communication, energy, optical sources or detection. To couple an optical answer with another property is possible through the follow-up of the luminescence. The control of the structural symmetry, oxidation state or surface chemistry enables the chemists to precisely tune the emission. Illustrations will be provided on inorganic powder and crystal materials.

Nanocomposites of ZnO with p-type NiO and n-type SnO₂ in the equimolar ratio were prepared by microwave assisted method inorder to reduce the fast recombination rate of ZnO. XRD reveals the formation of nanocomposites of ZnO. The photocatalytic activity of nanocomposites against RhB is poor compared to control ZnO. The control ZnO nanocrystals exhibit 100% degradation efficiency and is mainly ascribed to the decrease in band gap and increase in surface defects. The decolorization of RhB follows the pseudo-first order kinetics and the mechanism is explained on the basis of charge trapping through defect sites.

We present a new generation of nanotracers with persistent luminescence properties in the red-near IR range for small animal imaging. Silicates, oxysulfides and calcium phosphates nanoparticles doped with transition metal and lanthanide ions were developed in this aim. We have focused our attention in this paper on the biocompatible TCP/HAp phosphate compounds doped with Eu, Mn, Dy and on the Gd₂O₂S:Eu, Mg, Ti materials in the form of nanoparticles. All the nanosensors were hydrothermally synthesized and if the phosphate has a very high interest due to its biocompatibility Gd₂O₂S:Eu, Mg, Ti was investigated as a multimodal agent for possible in vivo optical imaging and MRI imaging.

Titanium dioxide (TiO₂) is a wide bandgap (~3.4 eV) semiconductor material which is commonly used as a photocatalyst and antibacterial material. UV illumination with energy similar to the bandgap is often needed to make the material active. It would be favorable for practical applications, if its action can also be activated under ambient. Recently, robust antibacterial action was demonstrated on ZnO nanoparticles under ambient illumination. In this study, we demonstrated robust antibacterial activity of TiO₂ nanoparticles induced by annealing under ambient illumination. It was found that the antibacterial activity could be significantly changed by tuning the annealing temperatures and using different crucibles containing the nanoparticles. Bacterium Escherichia coli was used as the model organism in the test. It was observed that although no significant antibacterial activity was observed on the starting material (untreated commercial TiO₂ nanoparticles), the activity increases significantly if the nanoparticles were annealed above 650 °C with crucible lined with copper foil. The survival rate of E. coli bacteria approaches to zero if the nanoparticles annealing temperature reaches 850 °C. Under optimized conditions, three different titania nanoparticle samples exhibited antibacterial activity under ambient illumination. This work sheds light on the development of ambient-active antibacterial coating and in particular, on the modification of any TiO₂ material to become ambient-active with a suitable treatment.

In this work, we show that a 2D cleave layer (such as epitaxial graphene on SiC) can be used for precise release of GaNbased light emitting diodes (LEDs) from the LED-substrate interface. We demonstrate the thinnest GaN-based blue LED and report on the initial electrical and optical characteristics. Our LED device employs vertical architecture: promising excellent current spreading, improved heat dissipation, and high light extraction with respect to the lateral one. Compared to conventional LED layer release techniques used for forming vertical LEDs (such as laser-liftoff and chemical lift-off techniques), our process distinguishes itself with being wafer-scalable (large area devices are possible) and substrate reuse opportunity.

In respect of their adaptability and performance, electrochromic devices, ECDs, which are able to change their optical properties under an applied voltage, have received significant attention. Target applications are multifold both in the visible region (automotive sunroofs, smart windows, ophthalmic lenses, and domestic appliances (oven, fridge…)) and in the infrared region (Satellites Thermal Control, IR furtivity). In our group, focusing on oxide thin films grown preferentially at room temperature, optimization of ECDs performances have been achieved by tuning the microstructure, the stoichiometry and the cationic composition of the various layers. Herein, our approach for optimized ECDs is illustrated through the example of WO₃ electrochromic layer in the visible and in the IR domain as well as ZnO based transparent conducting oxide layer. Targeting the field of printed electronics, simplification of the device architecture for low power ECDs is also reported.

We review in this paper the application of ZnO/(Zn,Mg)O quantum wells to the photodetection of the polarization state of UV light. This photodetection is achieved by using the natural anisotropy that exists in non-polar ZnO/(Zn,Mg)O quantum wells, which separates the excitonic absorption from the three valence bands to the conduction band depending on the incident light polarization. The device structures covered here consist of Schottky photodiodes on a- and m-plane orientations, grown by molecular beam epitaxy on ZnO or sapphire substrates, and are analyzed as a function of the incident light polarization.

(-201) oriented β-Ga₂O₃ has the potential to be used as a transparent and conductive substrate for GaN-growth. The key advantages of Ga₂O₃ are its small lattice mismatches (4.7%), appropriate structural, thermal and electrical properties and a competitive price compared to other substrates. Optical characterization show that GaN layers grown on (-201) oriented β-Ga₂O₃ are dominated by intense bandedge emission with a high luminescence efficiency. Atomic force microscopy studies show a modest threading dislocation density of ~10⁸ cm^-2, while complementary Raman spectroscopy indicates that the GaN epilayer is of high quality with slight compressive strain. Room temperature time-findings suggest that the limitation of the photoluminescence lifetime (~500 ps) is due to nonradiative recombination arising from threading dislocation. Therefore, by optimizing the growth conditions, high quality material with significant optical efficiency can be obtained.

β-NaFeO₂ structure is an orthorhombic wurtzite-derived structure, of which the structural relationship with wurtzite structure is similar to that of the chalcopyrite sturcture with zincblende structure. β-LiGaO₂, β-AgGaO₂ and β-AgAlO₂ are known as materials possessing the β-NaFeO₂ structure; however, studies on the wurtzite-derived ternary oxide semiconductors are quite limited. Recently, we demonstrated the band gap engineering of zinc oxide by alloying with wurtzite-type β-AgGaO₂, and the band gap of ZnO was reduced to 2.55 eV by this alloying. Very recently, a new wurtzite-type ternary compound, β-CuGaO₂, was found out. Its energy band gap was 1.47 eV, and it exhibited p-type conduction. The first principle calculation indicated that β-CuGaO₂ is a direct semiconductor; therefore it is suitable to use in optoelectronic devices. Taking the 1.47 eV of the band gap and p-type electronic conduction into account, β- CuGaO₂ is a promising material for the thin film solar cell absorber. These new ternary oxide semiconductors possessing wurtzite-derived structure expanded the energy region that the oxide semiconductors cover into visible and near-infrared region.

The electronic, magnetic and optical properties of rutile Ti_1-xTM_xO₂ (where TM: Ni, Cu and x = 0.25) have been investigated by the density functional theory with the plane wave self consistent field method. For the calculation of exchange correlation potential, the local density approximation along with Hubbard correction (LDA +U) was used. Electronic, magnetic and optical properties were calculated using 12 atoms supercell of rutile TiO₂ with one Ti atom replaced by a dopant transition metal atom. The band structure of doped rutile phase indicates the reduction of band gap leading to improvement in the photocatalytic properties of TiO₂ as well as enhancement in its magnetic properties. The observed magnetism is explained on the basis of spin polarization of d states of Ti with dopants. Optical calculations by full potential, linear augmented plane wave plus local orbital (FP-LAPW+lo) method with ELK code established the presence of optical transitions in the visible light region. These theoretical calculations gave a meaningful information and excellent prediction to develop TiO₂ for spintronics applications and photocatalytic applications in the visible region.

NiO/ZnO heterostructures were fabricated on FTO/glass and bulk hydrothermal ZnO substrates by pulsed laser deposition. X-Ray diffraction and Room Temperature (RT) Raman studies were consistent with the formation of (0002) oriented wurtzite ZnO and (111) oriented fcc NiO. RT optical transmission studies revealed bandgap energy values of ~3.70 eV and ~3.30 eV for NiO and ZnO, respectively and more than 80% transmission for the whole ZnO/NiO/FTO/glass stack over the majority of the visible spectrum. Lateral p-n heterojunction mesas (~6mm x 6mm) were fabricated using a shadow mask during PLD growth. n-n and p-p measurements showed that Ti/Au contacting gave an Ohmic reponse for the NiO, ZnO and FTO. Both heterojunctions had rectifying I/V characteristics. The junction on FTO/glass gave forward bias currents (243mA at +10V) that were over 5 orders of magnitude higher than those for the junction formed on bulk ZnO. At ~ 10^-7 A (for 10V of reverse bias) the heterojunction leakage current was approximately two orders of magnitude lower on the bulk ZnO substrate than on FTO. Overall, the lateral p-NiO/n- ZnO/FTO/glass device proved far superior to that formed by growing p-NiO directly on the bulk n-ZnO substrate and gave a combination of electrical performance and visible wavelength transparency that could predispose it for use in various third generation transparent electronics applications.

The importance of a photon source that would be compatible with silicon circuitry is crucial for data communication networks. A photon source with energies ranging from UV to near infrared can be activated in Si as originationg from defects related to dislocations, vacancies, strain induced band edge transitions and quantum confinement effects. Using an etching method developed in this work, one can also enhance selectively the UV-VIS, band edge emission and emissions at telecom wavelengths, which are tunable depending on surface treatment. Deuterium D₂O etching favors near infrared emission with a characteristic single peak at 1320 nm at room temperature. The result offers an exciting solution to advanced microelectronics The method involves the treatment of Si surface by deuterium Deuterium containing acid vapor, resulting in a layer that emits at 1320 nm. Etching without deuterium, a strong band edge emission can be induced at 1150 nm or an emission at 1550 nm can be created depending on the engineered surface structure of silicon. Schottky diodes fabricated on treated surfaces exhibit a strong rectifying characteristics in both cases.

C-N-S tridoped TiO₂ nanoparticles were synthesized by sol-gel method using thiourea as a source compound for carbon (C), nitrogen (N) and sulphur (S). The crystalline phase and morphology of the doped and undoped TiO₂ nanoparticles are analyzed by XRD and FESEM. FTIR confirms the bonding interaction of C, N and S in TiO₂ lattice. Compared to the doped samples undoped sample annealed at 600°C shows more absorbance in the visible region due to the existence of rutile phase. Presence of oxygen vacancy is confirmed from the photoluminescence spectra. XPS indicates the existence of the carbon atom in the form of carbonaceous species on the surface of the TiO₂ and absorbs the visible light to enhance the photocatalytic activity. The photocatalytic activity of C-N-S tridoped TiO₂ nanoparticles were evaluated for the degradation of Rhodamine B organic dye under the visible light irradiation. Maximum of ~ 100% degradation exhibits for the C-N-S tridoped sample (D4) calcined at 600°C. This highly active photocatalytic performance is associated with the existence of oxygen vacancies, the acidic sites on the surface (SO₄ ^2-) and the mixed phases of anatase and rutile in TiO₂ lattices.

ZnO sphere made of aggregated nanoparticles with a mean diameter of 19 nm have been prepared by the forced thermohydrolysis in polyol medium technique which is a versatile synthesis method for the preparation of metal oxide particles with controlled properties. The sphere were polydisperse and sub-micrometric in size. Porous layers have been prepared using these building blocks. They showed a large specific surface area and were highly light scattering in the visible wavelength region. We have investigated the performances of D149-dyesensitized solar cells (DSSCs) based on these layers. The annealing temperature as well as the layer thickness has been optimized. Finally the best cells reached an overall conversion efficiency of about 4.7% for layers with a thickness ranging between 27 and 35 μm and annealed at 400°C.

Since the beginning of the era of third generation solar cells, researchers are motivated to explore various semiconductor-metal configurations for the efficient solar energy conversion. We first time report the use of non-stoichiometric PbO_x electrodes in the Schottky junction solar cell. This metal oxide makes an efficient Schottky junction with the high work function alloy of Au-Pd. It was found that thin films of anodized lead metal prepared via potential pulse technique result in the nanowall assemblies. When a few nanometer layer of Au-Pd was sputtered on these assemblies, we obtained a core-shell Schottky junction solar cells of PbO_x/Au-Pd. With these newly developed structures, we obtained highest J_sc of 2.04 mA/cm² with V_oc of 707 mV achieving an overall efficiency of 0.384%. The performance of solar cell was assessed by D.C. and A.C. techniques. An equivalent circuit model is also presented for understanding the charge transfer mechanisms in such solar cells.

Bisphenol A (BPA) and other organic pollutants from industrial wastewater have drawn increasing concern in the past decades regarding their environmental and biological risks, and hence developing strategies of effective degradation of BPA and other organic pollutants is imperative. Metal oxide nanostructures, in particular titanium oxide (TiO₂) and zinc oxide (ZnO), have been demonstrated to exhibit efficient photodegradation of various common organic dyes. ZnO tetrapods are of special interest due to their low density of native defects which consequently lead to lower recombination losses and higher photocatalytic efficiency. Tetrapods can be obtained by relatively simple and low-cost vapor phase deposition in large quantity; the micron-scale size would also be advantageous for catalyst recovery. In this study, the photodegradation of BPA with ZnO tetrapods and TiO₂ nanostructures under UV illumination were compared. The concentration of BPA dissolved in DI water was analyzed by high-performance liquid chromatography (HPLC) at specified time intervals. It was observed that the photocatalytic efficiency of ZnO tetrapods eventually surpassed Degussa P25 in free-standing form, and more than 80% of BPA was degraded after 60 min. Photodegradation of other organic dye pollutants by tetrapods and P25 were also examined. The superior photocatalytic efficiency of ZnO tetrapods for degradation of BPA and other organic dye pollutants and its correlation with the material properties were discussed.

The optical and structural characteristics of H⁻ ion-implanted ZnMgO were investigated by temperature-dependent photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD). Low-energy (40 keV and 50 keV) hydrogen implantation was performed on RF-sputter-deposited ZnMgO thin films by varying the fluences from 10¹³ ions/cm² to 5 × 10¹⁴ ions/cm² . Highly c-axis-oriented <002> ZnO films were observed for all samples, as confirmed by HRXRD. A gradual decrease in the acceptor concentration was observed with increasing fluence, as confirmed by low-temperature PL results. This suggests that hydrogen atoms act as a shallow donor.

Single layer and double layer thin ZnO films with Ag nano-clusters on top and between them are fabricated by magnetron sputtering with subsequent annealing procedures. Transmission spectra measurements of the Ag/ZnO nanocomposite shows that a disordering (yet controllable) annealing modification, leads to a high transmission in the near- to the mid-IR spectral regimes. The spectra also show oscillations in the visible wavelength regime due to the excitation of surface plasmons that propagate along the surface of the nano-cluster. The behavior reported here is of interest for future implementation of new sub-wavelength, nanoplasmonic devices.

Scintillation materials have been used widely in either military or civil areas, but most of them emit lights in the spectral range of ultraviolet or visible. There are few candidates with an emission in the spectral range of 650 to 1200nm. Here, we report a Bi²⁺ doped phosphor of Sr₂P₂O₇:Bi²⁺, which once exposed to X-ray can emit deep red peaking at ~700nm due to the typical ²P_3/2 to ²P_1/2 transition of Bi²⁺. Deep red radioluminescence manifests the potential application of the phosphor as implantable scintillator for instance or other sensor which can obtain real time dose information and reduce serious radiation accidents in the case of radiation therapy.

(In)GaN p-i-n structures were grown by MOVPE on both GaN- and ZnO-coated c-sapphire substrates. XRD studies of the as-grown layers revealed that a strongly c-axis oriented wurtzite crystal structure was obtained on both templates and that there was a slight compressive strain in the ZnO underlayer which increased after GaN overgrowth. The InGaN peak position gave an estimate of 13.6at% for the indium content in the active layer. SEM and AFM revealed that the top surface morphologies were similar for both substrates, with an RMS roughness (5 μm x 5 μm) of about 10 nm. Granularity appeared slightly coarser (40nm for the device grown on ZnO vs 30nm for the device grown on the GaN template) however. CL revealed a weaker GaN near band edge UV emission peak and a stronger broad defect-related visible emission band for the structure grown on the GaN template. Only a strong ZnO NBE UV emission was observed for the sample grown on the ZnO template. Quarter-wafer chemical lift-off (CLO) of the InGaN-based p-i-n structures from the sapphire substrate was achieved by temporary-bonding the GaN surface to rigid glass support with wax and then selectively dissolving the ZnO in 0.1M HCl. XRD studies revealed that the epitaxial nature and strong preferential c-axis orientation of the layers had been maintained after lift-off. This demonstration of CLO scale-up, without compromising the crystallographic integrity of the (In)GaN p-i-n structure opens up the perspective of transferring GaN based devices off of sapphire substrates industrially.

We present the cathodic electrochemical preparation of NiO porous films on transparent conducting oxide substrates from nickel nitrate precursor. Two approaches are developed. The first one consists in depositing a precursor by pulsed deposition using an aqueous medium. The precursor layer is shown to be a mixture of nickel oxide and hydroxide. It is subsequently transformed into NiO by thermal annealing. We have also developed the direct electrodeposition of NiO porous layers using dimethyl sulfoxide (DMSO) organic medium and higher deposition temperature. The films have been sensitized by the P1 dye and tested as the hole transport layers for p-type dye-sensitized solar cells.