Electrochemical synthesis of calcium carbonate coatings on stainless steel substrates

Calcite CaCO₃ has been electrocrystallized on stainless steel substrates by the galvanostatic cathodic reduction of aqueous calcium bicarbonate solutions. The deposition is controlled by pH changes occurring close to the cathode due to electrogeneration of base. The deposit morphology varies from facetted rhombs observed at low (1-20 mA cm⁻²) current densities to corner-rounded particles observed at high (40 mA cm⁻²) current densities.     

Improving low pressure chemical vapor deposited zinc oxide contacts for thin film silicon solar cells by using rough glass substrates

Compared to zinc oxide grown (ZnO) on flat glass, rough etched glass substrates decrease the sheet resistance (R_sq) of zinc oxide layers grown on it. We explain this R_sq reduction from a higher thickness and an improved electron mobility for ZnO layers deposited on rough etched glass substrates. When using this etched glass substrate, we also obtain a large variety of surface texture by changing the thickness of the ZnO layer grown on it. This new combination of etched glass and ZnO layer shows improved light trapping potential compared to ZnO films grown on flat glass. With this new approach, Micromorph thin film silicon tandem solar cells with high total current densities (sum of the top and bottom cell current density) of up to 26.8 mA cm^− 2 were fabricated.     

Enhanced light to electricity conversion efficiency of CdS–ZnO composite nanorod based electrochemical solar cell

Cadmium sulfide–zinc oxide composite nanorods having at least 100 nm diameters were synthesized by a two-step chemical deposition technique. Polycrystalline nanorods of ZnO were grown on indium tin oxide coated quartz substrate by aqueous chemical growth technique. Cadmium sulfide was deposited on the surface of the ZnO nanorod thin film by chemical bath deposition. The X-ray diffraction results revealed the co-existence of polycrystalline CdS and ZnO, both having hexagonal structures. Neither any phase mixing nor any surface diffusion induced alloying was observed. Micro-Raman study detected a pair of optical phonons at 301 cm⁻¹ and 438 cm⁻¹ corresponding to hexagonal CdS and ZnO, respectively. An enhanced light to electricity conversion efficiency of 2.52% was recorded from CdS–ZnO photoanode based electrochemical solar cell under 0.5 sun illumination condition (50 mW cm⁻²). We observed a significant enhancement of short circuit current of the electrochemical solar cells due to addition of ionic salt solution to the electrolyte.     

Improving the conductance of ZnO thin film doping with Ti by using a cathodic vacuum arc deposition process

The Ti-doped ZnO films compared to un-doped ZnO films were deposited onto Corning XG glass substrates by using a cathodic vacuum arc deposition process in a mixture of oxygen and argon gases. The structural, electrical and optical properties of un-doped and Ti-doped ZnO films have been investigated. When the Ti target power is about 750 W, the incorporation of titanium atoms into zinc oxide films is obviously effective. Additionally, the resistivity of un-doped ZnO films is high and reduces to a value of 3.48 × 10⁻³ Ω-cm when Ti is incorporated. The Ti doped in the ZnO films gave rise to the improvement of the conductivity of the films obviously. The Ti-doped ZnO films have > 85% transmittance in a range of 400-700 nm.     

Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide

Highly doped indium-tin oxide films exhibit resistivities ρ as low as  1.2 × 10^− 4 Ω cm, while for ZnO films resistivities in the range of 2 to 4 × 10^− 4 Ω cm are reported. This difference is unexpected, if ionized impurity scattering would be dominant for carrier concentrations above 10²⁰ cm^− 3. By comparing the dependences of the effective Hall mobility on the carrier concentration of ZnO and ITO it is found that grain barriers limit the carrier mobility in ZnO for carrier concentrations as high as 2 × 10²⁰ cm^− 3, independently, if the films were grown on amorphous or single crystalline substrates. Depending on the deposition method, grain barrier trap densities between 10¹² and 3 × 10¹³ cm^− 2 were estimated for ZnO layers. Also, crystallographic defects seem to reduce the mobility for highly doped ZnO films. On the other hand, for ITO films such an influence of the grain barriers was not observed down to carrier concentrations of about 10¹⁸ cm^− 3. Thus the grain barrier trap densities of ZnO and ITO are significantly different, which seems to be connected with the defect chemistry of the two oxides and especially with the piezoelectricity of zinc oxide.     

Fabrication of ZnO films consisting of densely accumulated mesoporous nanosheets and their dye-sensitized solar cell performance

Nanocrystalline and mesoporous ZnO films approximately 4 μm in thickness were fabricated through a simple chemical deposition of Zn₄CO₃(OH)₆·H₂O in an aqueous solution of zinc nitrate and urea and subsequent pyrolysis at a low temperature of 300 °C. Microscopic observation of the films revealed that they were composed of mesoporous nanosheets accumulating with submicrometer-order spacing between them on conducting glass substrates. Adsorption of N-719 dye onto the ZnO surface, for application to dye-sensitized solar cells, led to dye-loading of 1.1 × 10^− 7 mol/cm² in spite of the relatively small thickness. The resultant ZnO/N-719 photoanode exhibited a short-circuit photocurrent density of 13.8 mA/cm², which is of the highest level ever reported for ZnO. An overall light-to-electricity conversion efficiency of 3.3% was achieved under 1 sun AM1.5 illumination without any optimization in view of the other cell components.     

Low-temperature deposition of ZnO thin films on PET and glass substrates by DC-sputtering technique

The structural, optical and electrical properties of ZnO thin films (260 - 490 nm thick) deposited by direct-current sputtering technique, at a relatively low-substrate temperature (363 K), onto polyethylene terephthalate and glass substrates have been investigated. X-ray diffraction patterns confirm the proper phase formation of the material. Optical transmittance data show high transparency (80% to more than 98%) of the films in the visible portion of solar radiation. Slight variation in the transparency of the films is observed with a variation in the deposition time. Electrical characterizations show the room-temperature conductivity of the films deposited onto polyethylene terephthalate substrates for 4 and 5 h around 0.05 and 0.25 S cm^− 1, respectively. On the other hand, for the films deposited on glass substrates, these values are 8.5 and 9.6 S cm^− 1 for similar variation in the deposition time. Room-temperature conductivity of the ZnO films deposited on glass substrates is at least two orders of magnitude higher than that of ZnO films deposited onto polyethylene terephthalate substrates under identical conditions. Hall-measurements show the maximum carrier concentration of the films on PET and glass substrate around 2.8 × 10¹⁶ and 3.1 × 10²⁰ cm^− 3, respectively. This report will provide newer applications of ZnO thin films in flexible display technology.     

Annealing effect on dielectric and leakage current characteristics of Mn-doped Ba0.6Sr0.4TiO3 thin films as gate insulators for low voltage ZnO thin film transistor

We report on the dielectric properties and leakage current characteristics of 3 mol% Mn-doped Ba_0.6Sr_0.4TiO₃ (BST) thin films post-annealed up to 600 °C following room temperature deposition. The suitability of 3 mol% Mn-doped BST films as gate insulators for low voltage ZnO thin film transistors (TFTs) is investigated. The dielectric constant of 3 mol% Mn-doped BST films increased from 24 at in-situ deposition up to 260 at an annealing temperature of 600 °C due to increased crystallinity and the formation of perovskite phase. The measured leakage current density of 3 mol% Mn-doped BST films remained on the order of 5 × 10^− 9 to 10^− 8 A/cm² without further reduction as the annealing temperature increased, thereby demonstrating significant improvement in the leakage current characteristics of in-situ grown Mn-doped BST films as compared to that (5 × 10^− 4 A/cm² at 5 V) of pure BST films. All room temperature processed ZnO-TFTs using a 3 mol% Mn-doped BST gate insulator exhibited a field effect mobility of 1.0 cm²/Vs and low voltage device performance of less than 7 V.     

One-minute microwave-assisted chemical bath deposition of nanostructured ZnO rod-arrays

Microwave-assisted chemical bath deposition (MACBD) is an emerging route for rapid synthesis of films and nanostructured particles. In this paper we report MACBD of ZnO rod-array films on bare glass substrates from an aqueous bath of tetra ammonium zinc complex. The deposition time is reduced to about 1 min as compared to around 60 min for conventional CBD. X-ray diffraction study shows that as-deposited films are uniaxially out-of-plane textured along the c-axis. Scanning Electron Microscopy reveals that the films consist of elongated elliptical tapered rods of diameters 250 to 350 nm. Atomic Force Microscopy shows that the films consist of about 350 nm grains. The RMS roughness is about 60 nm. The energy band gap is 3.27 eV as estimated from optical data. The films are n-type with electrical conductivity of 1 × 10^− 4 S/cm.     

Tin sulfide thin films and Mo/p-SnS/n-CdS/ZnO heterojunctions for photovoltaic applications

Tin sulfide (SnS) is one of the most promising materials for photovoltaics. Here we report on the preparation as well as chemical, structural and physical characterization of the Mo/p-SnS/n-CdS/ZnO heterojunctions. The SnS thin films were grown by hot wall deposition method on the Mo-coated glass substrates at 270-350 °C. The crystal structure and elemental composition were examined by X-ray diffraction and Auger electron spectroscopy methods. The CdS buffer layers were deposited onto the SnS films by chemical bath deposition. The ZnO window layers were deposited by a two step radio frequency magnetron sputtering, resulting in a ZnO bilayer structure: the first layer consists of undoped i-ZnO and the second of Al-doped n-ZnO. The best junctions have an open circuit voltage of 132 mV, a short circuit current density of 3.6 mA/cm², a fill-factor of 0.29 and efficiency up to 0.5%.     

Growth and characterization of LiNiVO4 thin film cathode by pulsed laser deposition

Crystallized LiNiVO₄ thin films have been prepared by pulsed laser deposition and their physical and electrochemical properties have been studied. With the increase of deposition temperatures and oxygen pressures, the crystallization became better, but accompanied with large sizes of grains. The initial discharge capacity of the film deposited at 873 K and 40 Pa of oxygen was just around 7.2 μA h/cm² μm when it was cycled between 3.0 and 4.8 V with a current density of 10 μA h/cm². Cyclic voltammetry at a sweep rate of 0.1 mV/s showed a main anodic peak at 4.20 V, a weak anodic peak at 4.59 V and a cathodic peak located at 3.73 V. Based on the linear relationship between the peak currents of cathodic peaks and the square roots of scan rates, the diffusion coefficient was estimated to be about 2.3 × 10^− 15 cm²/s. Electrochemical impedance spectra revealed high charge-transfer resistance of Li-ion, such as about 9000 Ω at 4.0 V. The extremely slow Li-ion diffusion and high charge-transfer resistance indicate that the electrochemical reaction in LiNiVO₄ thin films is sluggish.     

Doping induced structural and compositional changes in ZnO spray pyrolysed films and the effects on optical and electrical properties

Highly transparent, conductive ZnO films have been deposited by spray pyrolysis of a zinc acetate based solution. Quality films are yielded as our process is analogous to an aerosol assisted chemical vapour deposition rather than a droplet deposition spray pyrolysis technique. The properties of the films are governed by the additives to the base precursor solution. When aluminium acetylacetonate is added to the precursor solution, ZnO:Al films are grown with free charge carrier concentrations of more than 10²⁰ cm⁻³. The carrier density and mobility are measured by both Hall probe and near infrared spectroscopy. Film growth and grain size, morphology and orientation are altered using an increased percentage of ZnCl₂ in the precursor, which results in a 10 fold increase in charge carrier mobility. An investigation is presented correlating the composition of the precursor solution with the chemical, structural, electrical and optical properties of the grown films.     

High quality ZnO:Al transparent conducting oxide films synthesized by pulsed filtered cathodic arc deposition

Aluminum-doped zinc oxide, ZnO:Al or AZO, is a well-known n-type transparent conducting oxide with great potential in a number of applications currently dominated by indium tin oxide. In this study, the optical and electrical properties of AZO thin films deposited on glass and silicon by pulsed filtered cathodic arc deposition are systematically studied. In contrast to magnetron sputtering, this technique does not produce energetic negative ions, and therefore ion damage can be minimized. The quality of the AZO films strongly depends on growth temperature while only marginal improvements are obtained with post-deposition annealing. The best films, grown at a temperature of about 200 °C, have resistivities in the low to mid 10^− 4 Ω cm range with a transmittance better than 85% in the visible part of the spectrum. It is remarkable that relatively good films of small thickness (60 nm) can be fabricated using this method.     

Characterization of low mole fraction In-doped-ZnO/Si (111) heterostructure grown by pulsed laser deposition

In-doped ZnO films with low mole fraction (0.1, 0.3, 0.6 at.%) were prepared on p-Si (111) at 600 °C by the pulsed laser deposition (PLD). The effect of composition on structures, optical and electrical properties was studied by X-ray diffraction, atomic force microscopy, photoluminescence, and the Hall Effect measurement system. In-doped ZnO film has (101) preferred orientation and UV emissions of ZnO:In films were red shift with increasing In contents and there are no deep-level emissions. The lowest resistivity of 5.6 × 10^− 2 Ωcm and highest mobility of 33.1 cm²/Vs was observed at the In content of 0.3 at.%.     

A hybrid tandem solar cell based on hydrogenated amorphous silicon and dye-sensitized TiO2 film

Hydrogenated amorphous silicon film (a-Si:H) as top cell is introduced to dye-sensitized titanium dioxide nanocrystalline solar cell (DSSC) as bottom cell to assemble a hybrid tandem solar cell. The hybrid tandem solar cell fabricated with the thicknesses a-Si:H layer of 235 nm, ZnO/Pt interlayer of 100 nm and DSSC layer of 8.5 μm achieves a photo-to-electric energy conversion efficiency of 8.31%, a short circuit current density of 10.61 mA·cm^− 2 and an open-circuit voltage of 1.45 V under a simulated solar light irradiation of 100 mW·cm^− 2.     

A comparative study on the NO2 gas sensing properties of ZnO thin films, nanowires and nanorods

ZnO thin films were fabricated using the spin coating method, ZnO nanowires by cathodically induced sol-gel deposition by the means of an anodic aluminum oxide (AAO) template, and ZnO nanorods with the hydrothermal technique. For thin film preparation, a clear, homogeneous and stable ZnO solution was prepared by the sol-gel method using zinc acetate (ZnAc) precursor which was then coated on a glass substrate with a spin coater. Vertically aligned ZnO nanowires which were approximately 65 nm in diameter and 10 μm in length were grown in an AAO template by applying a cathodic voltage in aqueous zinc nitrate solution at room temperature. For fabrication of the ZnO nanorods, the sol-gel ZnO solution was coated on glass substrate by spin coating as a seed layer. Then ZnO nanorods were grown in zinc nitrate and hexamthylenetetramine aqueous solution. The ZnO nanorods are approximately 30 nm in diameter and 500 nm in length. The ZnO thin film, ZnO nanowires and nanorods were characterized by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). The NO₂ gas sensing properties of ZnO thin films, nanowires and nanorods were investigated in a dark chamber at 200 °C in the concentration range of 100 ppb-10 ppm. It was found that the response times of both ZnO thin films and ZnO nanorods were approximately 30 s, and the sensor response was depended on shape and size of ZnO nanostructures and electrode configurations.     

Influence of current density on crystalline structure and magnetic properties of electrodeposited Co-rich CoNiW alloys

The influence of current density, at the interval 5–100 mA cm⁻², on the structural and magnetic properties of electrodeposited (Co_100−xNi_x)_100−yW_y alloys (x = 23–33.5 at. % Ni, y = 1.7–7.3 at. % W) was studied from a glycine-containing bath. W-content decreases with the increase of the current density magnitude. X-ray data have shown stabilization of hexagonal close packed, face centered cubic or a mixture of these structures by modulating the applied cathodic current density, for values lower than 50 mA cm⁻². Two structural phase transitions were observed: one from hexagonal close packed to face centered cubic structural transition occurring for a current density of 20 mA cm⁻², and another one, from cubic crystalline phase to amorphous state, which happens for values higher than 50 mA cm⁻². These structural phase transitions seem to be associated with the W-content as well as average crystalline grain sizes that reduce with increasing the current density value. The grain size effect may explain the face centered cubic stabilization in Co-rich CoNiW alloys, which was initially assumed to be basically due to H-adsorption/incorporation. Magnetic properties of Co-rich CoNiW alloys are strongly modified by the current density value; as a result of the changes on the W-content and their structural properties.     

Improving the electrical and optical properties of DC-sputtered ZnO:Al by thermal post deposition treatments

Thermal post deposition treatments are applied to DC-sputtered aluminum-doped zinc oxide (ZnO:Al) films and lead to a significant improvement of the electrical properties. Protective layers of amorphous silicon are used to protect the films from degradation during the high temperature treatment. Annealing for 6 hours at 500 °C leads to a carrier mobility of 48 cm²/Vs at a carrier concentration of 5.5 · 10²⁰ cm^− 3. Furthermore, improvements in the optical as well as in the electrical properties are possible at the same time compared to the as-deposited film. This is achieved by carrying out two thermal treatments to the ZnO:Al film, one prior to the capping with the protective layer and one afterwards. A series of samples with different carrier concentrations allows us to draw conclusions on the specific electrical transport properties.     

Electrical and optical properties of amorphous indium zinc oxide films

Valence electron control and electron transport mechanisms on the amorphous indium zinc oxide (IZO) films were investigated. The amorphous IZO films were deposited by dc magnetron sputtering using an oxide ceramic IZO target (89.3 wt.% In₂O₃ and 10.7 wt.% ZnO). N-type impurity dopings, such as Sn, Al or F, could not lead to the increase in carrier density in the IZO. Whereas, H₂ introduction into the IZO deposition process was confirmed to be effective to increase carrier density. By 30% H₂ introduction into the deposition process, carrier density increased from 3.08 × 10²⁰ to 7.65 × 10²⁰ cm^− 3, which must be originated in generations of oxygen vacancies or interstitial Zn²⁺ ions. Decrease in the transmittance in the near infrared region and increase in the optical band gap were observed with the H₂ introduction, which corresponded to the increase in carrier density. The lowest resistivity of 3.39 × 10^− 4 Ω cm was obtained by 10% H₂ introduction without substrate heating during the deposition.     

Effects of growth variables on the properties of single crystalline ZnO thin film grown by inductively coupled plasma metal organic chemical vapor deposition

Single crystalline undoped and Ga-doped n-type zinc oxide (ZnO) films were grown on sapphire (Al₂O₃) substrates by inductively coupled plasma (ICP) metal organic chemical vapor deposition. Effects of growth variables on the structural, optical, and electrical properties of ZnO films have been studied in detail. Single crystal films with flat and smooth surfaces were reproducibly obtained, with application of sample bias and O₂ ICP. The best film properties were obtained at the growth condition of 650 °C, 400 W ICP power, − 94 V bias voltage, O/Zn (VI/II) ratio of 75. Single crystalline Ga doped n-ZnO films were also obtained, with free carrier concentration of about 1.5 × 10¹⁹/cm³ at 1 at.% Ga concentration.