An effective monitoring of the air quality in an urban environment requires the capability to measure polluting gas concentrations in the low-ppb range, a limit so far virtually neglected in most of the novel carbon nanotube (CNT)-based... more
An effective monitoring of the air quality in an urban environment requires the capability
to measure polluting gas concentrations in the low-ppb range, a limit so far virtually
neglected in most of the novel carbon nanotube (CNT)-based sensors, as they are usually
tested against pollutant concentrations in the ppm range. We present low-cost gas sensors
based on single-walled CNT (SWCNT) layers prepared on plastic substrates and operating
at room temperature, displaying a high sensitivity to [NH3]. Once combined with the low
noise, the high sensitivity allowed us to reach an ammonia detection limit of 13 ppb. This
matches the requirements for ammonia monitoring in the environment, disclosing the
possibility to access the ppt detection limit. Furthermore, a blend of SWCNT bundle layers
with indium-tin oxide (ITO) nanoparticles resulted in a threefold sensitivity increase with
respect to pristine CNT for concentrations above 200 ppb. Finally, the peculiar response of
the ITO-SWCNT blend to water vapor provides a way to tailor the sensor selectivity with
respect to the relevant interfering effects of humidity expected in outdoor environmental
monitoring.
Scientists have begun using self-replicating rapid prototyper (RepRap) 3-D printers to manufacture open source digital designs of scientific equipment. This approach is refined here to develop a novel instrument capable of performing... more
Scientists have begun using self-replicating rapid prototyper (RepRap) 3-D printers to manufacture open source digital designs of scientific equipment. This approach is refined here to develop a novel instrument capable of performing automated large-area four-point probe measurements. The designs for conversion of a RepRap 3-D printer to a 2-D open source four-point probe (OS4PP) measurement device are detailed for the mechanical and electrical systems. Free and open source software and firmware are developed to operate the tool. The OS4PP was validated against a wide range of discrete resistors and indium tin oxide (ITO) samples of different thicknesses both pre-and post-annealing. The OS4PP was then compared to two commercial proprietary systems. Results of resistors from 10 to 1 MΩ show errors of less than 1% for the OS4PP. The 3-D mapping of sheet resistance of ITO samples successfully demonstrated the automated capability to measure non-uniformities in large-area samples. The results indicate that all measured values are within the same order of magnitude when compared to two proprietary measurement systems. In conclusion, the OS4PP system, which costs less than 70% of manual proprietary systems, is comparable electrically while offering automated 100 micron positional accuracy for measuring sheet resistance over larger areas.
Indium and other geologically scarce metals are routinely integrated into green technologies and modern consumer electronics. The manufacture of solar cells and liquid crystal displays (LCDs) relies strongly on continued indium supply,... more
Indium and other geologically scarce metals are routinely integrated into green technologies and modern consumer electronics. The manufacture of solar cells and liquid crystal displays (LCDs) relies strongly on continued indium supply, yet very little research has been conducted to determine what total resources exist to meet future or even present needs. This paper provides an improved understanding of the nature of indium resources and the current and future production and supply of this critical metal through a summary of global trends in indium production and demand, and through a preliminary account of global code-based reporting of indium mineral resources. Authors also present an overview of the potential for indium extraction from mine wastes and recycled electronics using Canadian and Australian case studies. Our preliminary data suggest that considerable resources are likely to exist in a diversity of deposits globally, which have the potential to meet long-term demand for indium. However, it is clear that a secured future supply of this metal will require some shift of focus from conventional extraction practices. It will be necessary to revisit controls on the conversion of resources to reserves and to supply and the discovery of additional resources to replace those depleted by continuing production. The prospects for indium supply from mine wastes and recycled electronics are found to be substantial, and these sources warrant greater consideration given their probable environmental and social advantages over the discovery and development of new primary indium deposits.
This study investigates ultra-thin transparent conducting oxides (TCO) of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO) and zinc oxide (ZnO) to determine their viability as candidate materials for use in plasmonic-enhanced... more
This study investigates ultra-thin transparent conducting oxides (TCO) of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO) and zinc oxide (ZnO) to determine their viability as candidate materials for use in plasmonic-enhanced thin-film amorphous silicon solar photovoltaic (PV) devices. First a sensitivity analysis of the optical absorption for the intrinsic layer of a nano-disk patterned thin-film amorphous silicon-based solar cell as a function of TCO thickness (10–50 nm) was performed by simulation. These simulation results were then used to guide the design of the experimental work which investigated both optical and electrical properties of ultra-thin (10 nm on average) films simultaneously deposited on both glass and silicon substrates using conventional rf sputtering. The effects of deposition and post-processing parameters on material properties of ITO, AZO and ZnO ultra-thin TCOs were probed and the suitability of TCOs for integration into plasmonic-enhanced thin-film solar PV devices was assessed. The results show that ultra-thin TCOs present a number of challenges for use as thin top contacts on plasmonic-enhanced PV devices: (1) optical and electrical parameters differ greatly from those of thicker (bulk) films deposited under the same conditions, (2) the films are delicate due to their thickness, requiring very long annealing times to prevent cracking, and (3) reactive gases require careful monitoring to maintain stoichiometry. The results presented here found a trade-off between conductivity and transparency of the deposited films. Although the sub 50 nm TCO films investigated exhibited desirable optical properties (transmittance greater than 80 %), their resistivity was too high to be considered as materials for the top contact of conventional PV devices. Future work is necessary to improve thin TCO properties, or alternative materials, and geometries are needed in plasmonic-based amorphous silicon solar cells. The stability of ultra-thin TCO films also needs to be experimentally investigated under normal device operating conditions.
A new method of preparing highly conductive ultra-thin indium tin oxide for plasmonic-enhanced thin film solar photovoltaic devices. Abstract Recent numerical modeling of plasmonic metallic nanostructures have shown great potential as a... more
A new method of preparing highly conductive ultra-thin indium tin oxide for plasmonic-enhanced thin film solar photovoltaic devices. Abstract Recent numerical modeling of plasmonic metallic nanostructures have shown great potential as a method of light management in thin-film nanodisc-patterned hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells. A significant design challenge for such plasmonic-enhanced PV devices is the requirement for ultra-thin transparent conducting oxides (TCOs) with high transmittance (low loss) and low enough resistivity to be used as device top contacts/electrodes. Most work on TCOs is on relatively thick layers and the few reported cases of thin TCO showed a marked decrease in conductivity. Recent work on ultra-thin TCOs of aluminum-doped zinc oxide, indium-doped tin oxide and zinc oxide revealed an unavoidable trade-off between transmittance and resistivity when fabricated with conventional growth methods. Ultra-thin films showed a tendency to be either amorphous and continuous or form as isolated islands. This results in poor electrical properties, which cannot be improved with annealing as the delicate thin films nucleate to form grain clusters. In order to overcome this challenge, this study investigates a novel method of producing ultra-thin (<40 nm) high quality TCOs. First, ~80nm ITO films are sputtered in various argon-oxygen atmospheres and annealed to increase conductivity. The most promising materials were then reduced in thickness with a controlled low-cost room-temperature cyclic wet chemical etching process to reach the desired thickness. The degradation in the electrical conductivity was tracked as a function of thickness. The sheet resistance of 36nm thin films was observed to be of the same order compared to the much thicker commercial ITO films currently used as transparent electrodes in PV and other opto-electronic devices. Experimental optical properties of the shaved films were then used in an optimized model of nano-disc plasmonic a-Si:H solar cells. Simulations indicate that optical enhancement greater than 21% are possible in the 300 – 730 nm wavelength range, when compared to the reference cell. Using the novel chemical shaving method described here, high-quality ultra-thin ITO films capable of improving the efficiency of thin film a-Si:H solar cells have been demonstrated. The methods employed in the optimization process are well established and economically viable, which provide the technical potential for commercialization of plasmonic based solar cells. A new method of preparing highly conductive ultra-thin indium tin oxide for plasmonic-enhanced thin film solar photovoltaic devices.
The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low... more
The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low resistivity and high transmittances in the visible range of the electromagnetic spectrum. Fabricating ultra-thin indium tin oxide (ITO) films (sub-50 nm) using conventional methods has presented a number of challenges; however, a novel method involving chemical shaving of thicker (greater than 80 nm) RF sputter deposited high-quality ITO films has been demonstrated. This study investigates the effect of oxygen concentration on the etch rates of RF sputter deposited ITO films to provide a detailed understanding of the interaction of all critical experimental parameters to help create even thinner layers to allow for more finely tune plasmonic resonances. ITO films were deposited on silicon substrates with a 98-nm, thermally grown oxide using RF magnetron sputtering with oxygen concentrations of 0, 0.4 and 1.0 sccm and annealed at 300 °C air ambient. Then the films were etched using a combination of water and hydrochloric and nitric acids for 1, 3, 5 and 8 min at room temperature. In-between each etching process cycle, the films were characterized by X-ray diffraction, atomic force microscopy, Raman Spectroscopy, 4-point probe (electrical conductivity), and variable angle spectroscopic ellipsometry. All the films were polycrystalline in nature and highly oriented along the (222) reflection. Ultra-thin ITO films with record low resistivity values (as low as 5.83 × 10−4 Ω·cm) were obtained and high optical transparency is exhibited in the 300–1000 nm wavelength region for all the ITO films. The etch rate, preferred crystal lattice growth plane, d-spacing and lattice distortion were also observed to be highly dependent on the nature of growth environment for RF sputter deposited ITO films. The structural, electrical, and optical properties of the ITO films are discussed with respect to the oxygen ambient nature and etching time in detail to provide guidance for plasmonic enhanced a-Si:H solar PV cell fabrication.
The effects of adding silver and indium to lead-free solders was investigated through an experiment. The solder alloys used for this study included Sn-0.7Cu-1.01n-xAg, where x = 0, 0.1, 0.3, and 0.5. Thermal analysis of the solder alloys... more
The effects of adding silver and indium to lead-free solders was investigated through an experiment. The solder alloys used for this study included Sn-0.7Cu-1.01n-xAg, where x = 0, 0.1, 0.3, and 0.5. Thermal analysis of the solder alloys was performed using a DSC-50 differential scanning calorimetry. The heating rate was 5°C/min from room temperature to 350°C in 50mL/min argon gas flow. The wetting balance test was conducted using a SAT5100 Rhesca, and the parameters used for wetting balance test were 5 mm/s of dipping speed with a dipping depth of 10 mm. The Vickers hardness number of the solder alloy was determined by conducting a microhardness test. The curve obtained from DSC analysis shows the onset temperature of Sn-0.7Cu is 227.4°C. Indium was observed distributed in primary grain because of its similar atomic size. Higher Ag contents produced better wettability by lowering wetting time and increasing maximum wetting force.
The photosensitivity of aluminium (Al)/lead sulphide (PbS)/indium tin oxide (ITO) thin layered structure is investigated considering the photon wavelength dependent current-voltage and capacitance-voltage characteristics of the device.... more
The photosensitivity of aluminium (Al)/lead sulphide (PbS)/indium tin oxide (ITO) thin layered structure is investigated considering the photon wavelength dependent current-voltage and capacitance-voltage characteristics of the device. The current-voltage characteristics of the test structure are analyzed adopting the back-to-back Schottky barrier diode model. The diode possesses low dark current in contrast to the high value of photocurrents measured under different illumination wavelengths. The change in photocurrents with different illumination wavelengths clearly indicates the change in photo-sensitivity of the device. The capacitance-voltage characteristics of Al/PbS/ITO structure demonstrate a definite improvement of the device capacitance with the higher wavelength exposures. The matter is explained in terms of the additional capacitance owing to the excess carrier generation within the device under illumination. The photosensitivity modulation of the device can be exploited in photo-sensor or photo-detector applications in various electronic devices.
Thin films of Cadmium Indium Selenide (CdIn2Se4) have been deposited on indium doped tin oxide coated conducting glass (ITO) substrates using potentiostatic cathodic electrodeposition technique. Cyclic voltammetry has been carried out in... more
Thin films of Cadmium Indium Selenide (CdIn2Se4) have been deposited on indium doped tin oxide coated conducting glass (ITO) substrates using potentiostatic cathodic electrodeposition technique. Cyclic voltammetry has been carried out in order to fix the deposition potential in the range between −1500 and +600 mV versus SCE. X-ray diffraction pattern shows that the deposited films exhibit tetragonal structure with most prominent reflection along (200) plane. The dependency of microstructural parameters such as crystallite size, strain and dislocation density with deposition potential has been studied. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays, respectively. EDX analysis reveals that films with well defined stoichiometry has been obtained at a deposition potential −950 mV versus SCE. The optical band gap, refractive index and extinction coefficient are evaluated from optical absorption measurements. The experimental observations are discussed in detail.
Estimates of the world's mineral resources of numerous by-product metals remain highly uncertain at best, despite the high criticality of many of these elements to society. This stems from the limited reporting of the concentrations of... more
Estimates of the world's mineral resources of numerous by-product metals remain highly uncertain at best, despite the high criticality of many of these elements to society. This stems from the limited reporting of the concentrations of these elements within mineral deposits by the mining industry, meaning that we require methods to estimate the availability of these resources that overcome this limitation. Here, we present a method for quantifying poorly reported mineral resources of by-product metals that builds upon deposit-by-deposit approaches to global resource estimation, arguably the best-practice approach for well-reported commodities, but also adds the use of proxies for by-product grade estimation. This proxy method allows for deposits with known or inferred by-product metals to also be incorporated within global resource estimates and provides a greater basis for assessing future supply potential. We demonstrate the application and verification of this methodology with indium, a critical metal for which b 1% of identified zinc, tin, and copper deposits potentially hosting indium mineralisation report grades using CRIRSCO (or equivalent) mineral resource reporting codes. The use of the method outlined in this manuscript will allow the global resources of any metal commodity, especially the often under-reported by-and co-product metals that are becoming increasingly essential to modern life, to be quantified to a significantly greater level of accuracy and precision than is allowed by other approaches.
A novel and simple chemical method based on sol-gel processing was proposed to deposit metastable orthorhombic tin oxide (SnOx) thin films on glass substrates at room temperature. The resultant samples are labeled according to the... more
A novel and simple chemical method based on sol-gel processing was proposed to deposit metastable orthorhombic tin oxide (SnOx) thin films on glass substrates at room temperature. The resultant samples are labeled according to the solvents used: ethanol (SnO-EtOH), isopropanol (SnO-IPA) and methanol (SnO-MeOH). The variations in the structural, morphological and optical properties of the thin films deposited using different solvents were characterized by X-ray diffraction, atomic force microscopy, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy and photoluminescence (PL) analysis. The XRD patterns confirm that all the films, irrespective of the solvents used for preparation, were polycrystalline in nature and contained a mixed phases of tin (II) oxide and tin (IV) oxide in a metastable orthorhombic crystal structure. FTIR spectra confirmed the presence of Sn=O and Sn-O in all of the samples. PL spectra showed a violet emission band centered at 380 nm (3.25 eV) for all of the solvents. The UV-vis spectra indicated a maximum absorption band shown at 332 nm and the highest average transmittance around 97% was observed for the SnO-IPA and SnO-MeOH thin film samples. The AFM results show variations in the grain size with solvent. The structural and optical properties of the SnO thin films indicate that this method of fabricating tin oxide is promising and that future work is warranted to analyze the electrical properties of the films in order to determine the viability of these films for various transparent conducting oxide applications.
Poly[3-(2′,5′-dioctyloxyphenyl)thiophene] (PDOOPT), poly[3-(2′,5′-diheptyloxyphenyl)thiophene] (PDHOPT) and poly[3-(2′,5′-dibutyloxyphenyl)-thiophene] (PDBOPT) have been prepared electrochemically from their monomers within... more
Poly[3-(2′,5′-dioctyloxyphenyl)thiophene] (PDOOPT), poly[3-(2′,5′-diheptyloxyphenyl)thiophene] (PDHOPT) and poly[3-(2′,5′-dibutyloxyphenyl)-thiophene] (PDBOPT) have been prepared electrochemically from their monomers within nanocrystalline titanium dioxide (nc-TiO2) porous surface deposited on indium doped tin oxide coated glass (ITO-glass) for solar cell application. The redox properties of the polymers were characterized using cyclic voltammetry. The energy levels of the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) have been estimated from their cyclic voltammograms and UV–vis absorption spectra. The poly[3-(2′,5′-dialkoxyphenyl)thiophenes] studied sensitize nc-TiO2 in liquid-state photoelectrochemical cells. Devices that consist of PDBOPT/nc-TiO2 photoactive electrode showed improved performance over those that consist of PDHOPT/nc-TiO2 and PDOOPT/nc-TiO2. PDBOPT/nc-TiO2 based devices produced an open-circuit voltage of 0.56 V, a short-circuit current of 45 μA/cm2, and a fill factor of 0.52 when illuminated with white light intensity of 80 mW/cm2.
Novel aluminum and indium doped zinc oxide bilayer transparent conducting oxide thin films have been developed by simple sol gel spin coating and annealed at 500 C for an hour under nitrogen ambient towards solar cell applications. The... more
Novel aluminum and indium doped zinc oxide bilayer transparent conducting oxide thin films have been developed by simple sol gel spin coating and annealed at 500 C for an hour under nitrogen ambient towards solar cell applications. The structural, electrical and optical properties of both the as deposited and annealed bilayer thin films are characterized. X-ray diffraction studies showed a hexagonal wurtzite-type structure of ZnO with (002) orientation, which was enhanced with annealing. In atomic force microscopy studies minimum surface roughness is attained for the Al-doped ZnO/In-doped ZnO bilayer TCO films. The best Al-doped ZnO/In-doped ZnO films had sheet resistance of 0.057 M ohm/square and the films had an average transmittance in the visible region over 90%. Further results are discussed with single and bilayer structure.
Micromorphology analysis of sputtered indium tin oxide fabricated with variable ambient combinations. Abstract This study experimentally investigates the fractal nature of the 3-D surface morphology of sputtered indium tin oxide (ITO)... more
Micromorphology analysis of sputtered indium tin oxide fabricated with variable ambient combinations. Abstract This study experimentally investigates the fractal nature of the 3-D surface morphology of sputtered indium tin oxide (ITO) fabricated with five sets of ambient combinations. The samples were prepared on glass substrates by DC magnetron sputtering using argon, argon with oxygen, argon with oxygen and nitrogen, argon with oxygen and hydrogen and argon with oxygen, nitrogen and hydrogen ambient compositions at room temperature and the films were annealed at 450 °C in air. The characterization of the films surfaces was carried out by X-ray diffraction (XRD), and atomic force microscopy (AFM). The XRD results indicate that the cubic ITO films form with highly preferable (222) and (400) orientations. The AFM images were analyzed using the Areal Autocorrelation Function (AACF) and pseudo-topothesy K. This analysis revealed that these samples are well described as fractal structures at nanometer scale.
Indium tin oxide (ITO) is a semiconducting material combining high conductivity and high transparency in the visible range. It is the most widely used transparent conducting oxide in applications such as flat panel displays. In this work,... more
Indium tin oxide (ITO) is a semiconducting material combining high conductivity and high transparency in the visible range. It is the most widely used transparent conducting oxide in applications such as flat panel displays. In this work, ITO thin films were deposited by pulsed laser deposition (PLD) onto transparent glass substrates. The substrate temperature and oxygen pressure during deposition were controlled to generate a variety of microstructures and electro-optical properties. Similar film thicknesses were used to avoid any change of carrier concentration. The dielectric function and complex refractive index were derived using spectroscopic ellipsometry and electron energy loss spectroscopy.
In this paper, we report structural, microstructural and optical properties of nano-crystalline indium tin oxide (ITO) particle, which have been synthesized by sol-gel process using a simple starting hydro-alcoholic solution consisting of... more
In this paper, we report structural, microstructural and optical properties of nano-crystalline indium tin oxide (ITO) particle, which have been synthesized by sol-gel process using a simple starting hydro-alcoholic solution consisting of In(NO3)3,5H2O, SnCl4,5H2O, citric acid as complexing and ethylene glycol as polymerization agents.
The structural properties of indium tin oxide nano-powders annealed at different temperatures (T=350-650 °C), have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses.
The XRD patterns show In2O3-cubic phase in nano-powders without any indication of crystalline SnOx as an additional phase.
The TEM images show the nano-particles as nearly spherical shape with size in the range of 10–45 nm as size of grains increases by increasing the annealing temperatures.
The optical direct band gap of ITO nano-particles was calculated about 3.39-4.02 eV in the temperature range 350–650 °C by optical absorption measurements. The optical band gap shift to higher energy with increasing the annealing temperature is due to the improvement of the crystallinity and thereby, increasing the carrier concentration as determined from Burstein–Moss effect.
Giant unilamellar vesicles (GUVs) represent a versatile in vitro system widely used to study properties of lipid membranes and their interaction with biomacromolecules and colloids. Electroformation with indium tin oxide (ITO) coated... more
Giant unilamellar vesicles (GUVs) represent a versatile in vitro system widely used to study properties of lipid membranes and their interaction with biomacromolecules and colloids. Electroformation with indium tin oxide (ITO) coated coverslips as electrodes is a standard approach to GUV production. In case of cationic GUVs, however, application of this approach leads to notorious difficulties. We discover that this is related to aging of ITO-coated coverslips during their repeated use, which is reflected in their surface topography on the nanoscale. We find that mild annealing of the ITO-coated surface in air reverts the effects of aging and ensures efficient reproducible electroformation of super-giant (diameter >100 μm) unilamellar vesicles containing cationic lipids.
TCO (transparent conduction oxides) have been suitable materials for optoelectronics applications, Indium Tin Oxide is an n-type transparent conducting oxide semiconductor , which possess a combine property of transparency to visible... more
TCO (transparent conduction oxides) have been suitable materials for optoelectronics applications, Indium Tin Oxide is an n-type transparent conducting oxide semiconductor , which possess a combine property of transparency to visible light and electrical conductivity, its features have been studied in this paper using MATLAB computer programming. The features which consist optical and electrical properties were simulated using MATLAB programming, the drive ITO models were used within the range and limit of other researchers, whose have done the researches experimentally. The models were used to simulate optical transmittance, optical absorptions, and reflectance of ITO, which all depends on films thicknesses.
Polystyrene membranes were found to be an effective-assisted material in the growth of undoped and doped indium-tin-oxide (ITO) with different concentrations from 3 to 7 wt% of CuO nanoparticles. Nanocomposites were characterized by XRD,... more
Polystyrene membranes were found to be an effective-assisted material in the growth of undoped and doped indium-tin-oxide (ITO) with different concentrations from 3 to 7 wt% of CuO nanoparticles. Nanocomposites were characterized by XRD, FT-IR, HR-SEM/TEM, and dielectric measurements. Polystyrene-assisted ITO nanocomposites (ITO/PS) showed the high crystalline phase with lattice fringes, and well agreed on the cubic phase of ITO. As the concentration of CuO increases in ITO/PS nanocomposite, the conductivity decreases. Differential scanning calorimetry/thermogravimetric analysis showed a good thermal stability of the prepared nanocomposites. The increase of CuO wt% did not affect the major degeneration temperature and the thermal stability of undoped composite. The highest conductivity was obtained for ITO doped with 7 wt% of CuO. The formed Polystyrene-assisted ITO:Cu nanocomposites demonstrated a considerable antimicrobial activity against non-filamentous fungi (Candida albicans), Gram-positive bacteria (Bacillus mycoides), and Gram-negative bacteria (Escherichia coli) at all tested concentrations (3.0-7.0 wt% of CuO) with maximum activity at 7.0 wt% of CuO.
The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low... more
The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low resistivity and high transmittances in the visible range of the electromagnetic spectrum. Fabricating ultra-thin indium tin oxide (ITO) films (sub-50 nm) using conventional methods has presented a number of challenges; however, a novel method involving chemical shaving of thicker (greater than 80 nm) RF sputter deposited high-quality ITO films has been demonstrated. This study investigates the effect of oxygen concentration on the etch rates of RF sputter deposited ITO films to provide a detailed understanding of the interaction of all critical experimental parameters to help create even thinner layers to allow for more finely tune plasmonic resonances. ITO films were deposited on silicon substrates with a 98-nm, thermally grown oxide using RF magnetron sputtering with oxygen concentrations of 0, 0.4 and 1.0 sccm and annealed at 300 °C air ambient. Then the films were etched using a combination of water and hydrochloric and nitric acids for 1, 3, 5 and 8 min at room temperature. In-between each etching process cycle, the films were characterized by X-ray diffraction, atomic force microscopy, Raman Spectroscopy, 4-point probe (electrical conductivity), and variable angle spectroscopic ellipsometry. All the films were polycrystalline in nature and highly oriented along the (222) reflection. Ultra-thin ITO films with record low resistivity values (as low as 5.83 × 10−4 Ω·cm) were obtained and high optical transparency is exhibited in the 300–1000 nm wavelength region for all the ITO films. The etch rate, preferred crystal lattice growth plane, d-spacing and lattice distortion were also observed to be highly dependent on the nature of growth environment for RF sputter deposited ITO films. The structural, electrical, and optical properties of the ITO films are discussed with respect to the oxygen ambient nature and etching time in detail to provide guidance for plasmonic enhanced a-Si:H solar PV cell fabrication.
We proposed a facile film treatment with formic acid to enhance the conduct i v i t y of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by 4 orders of magnitude. The effect of formic acid concentration on... more
We proposed a facile film treatment with formic acid to enhance the conduct i v i t y of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by 4 orders of magnitude. The effect of formic acid concentration on conductivity was investigated; conductivity increased fast with increasing concentration up to 10
M and then increased slightly, the highest conductivity being 2050 S cm−1 using 26 M concentration. Formic acid treated PEDOT:PSS films also exhibited very high transmittances. The mechanism of conductivity enhancement was explored through SEM, AFM, and XPS. Formic acid with its high dielectric constant screens the charge between PEDOT and PSS bringing about phase separation between them. Increased carrier concentration, removal of PSS from the film, morphology, and conformation change with elongated and better connected PEDOT chains are the main mechanisms of conductivity enhancement. ITO-free polymer solar cells were also fabricated using PEDOT:PSS electrodes treated with different concentrations of formic acid and showed equal performance to that of ITO electrodes. The concentrated acid treatment did not impair the desirable film properties as well as stability and performance of the solar cells.
A new and effective method for the preparation of nanocrystalline TiO2 (anatase) thin films is presented. This method is based on the use of peroxo-titanium complex as a single precursor. Post-annealing treatment is necessary to convert... more
A new and effective method for the preparation of nanocrystalline TiO2 (anatase) thin films is presented. This method is based on the use of peroxo-titanium complex as a single precursor. Post-annealing treatment is necessary to convert the deposited amorphous film into TiO2 (anatase) phase. The films obtained are uniform, compact and free of pinholes. A wide range of techniques are used for characterization, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDAX) and UV-Vis-NIR spectrophotometer. Glass, indium-doped tin oxide (ITO) and quartz are used as substrates. TiO2 (anatase) phase with (101) preferred orientation is obtained for the films. Byproduct (collected powder) consists of the same crystal structure. The optical measurement reveals the indirect bandgap of 3.2eV.
We report on the synthesis of nanocrystalline titanium dioxide thin films and powders by chemical and electrochemical deposition methods. Both methods are simple, inexpensive and suitable for large-scale production. Air-annealing of the... more
We report on the synthesis of nanocrystalline titanium dioxide thin films and powders by chemical and electrochemical deposition methods. Both methods are simple, inexpensive and suitable for large-scale production. Air-annealing of the films and powders at T=500 °C leads to densely packed nanometer sized anatase TiO2 particles. The obtained layers are characterized by different methods such as: X-ray diffraction (XRD), transmission
A new method of preparing highly conductive ultra-thin indium tin oxide for plasmonic-enhanced thin film solar photovoltaic devices. Abstract Recent numerical modeling of plasmonic metallic nanostructures have shown great potential as a... more
A new method of preparing highly conductive ultra-thin indium tin oxide for plasmonic-enhanced thin film solar photovoltaic devices. Abstract Recent numerical modeling of plasmonic metallic nanostructures have shown great potential as a method of light management in thin-film nanodisc-patterned hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells. A significant design challenge for such plasmonic-enhanced PV devices is the requirement for ultra-thin transparent conducting oxides (TCOs) with high transmittance (low loss) and low enough resistivity to be used as device top contacts/electrodes. Most work on TCOs is on relatively thick layers and the few reported cases of thin TCO showed a marked decrease in conductivity. Recent work on ultra-thin TCOs of aluminum-doped zinc oxide, indium-doped tin oxide and zinc oxide revealed an unavoidable trade-off between transmittance and resistivity when fabricated with conventional growth methods. Ultra-thin films showed a tende...
