Investigation of ZnO films on Si<111> substrate grown by low energy O+ assisted pulse laser deposited technology

Zinc oxide thin films (ZnO) with different thickness were prepared on Si (111) substrates using low energy O⁺ assisted pulse laser deposition (PLD). The structural and morphological properties of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements, respectively. The quality of ZnO films was also examined by using Rutherford backscattering spectroscopy/ion channeling (RBS/C) techniques. XRD showed that there was only one sharp diffraction peak at 2θ = 34.3° with the full width at the half maximum (FWHM) of around 0.34° for two ZnO samples, which also indicated that ZnO thin films had a good c-axis preferred orientation. Results of Rutherford backscattering and ion channeling clearly indicated that the Zn:O ratio in zinc oxide thin film approached to unity and the ZnO thin film grown by low energy O⁺ assisted pulse laser deposition had a polycrystalline structure. In the case of ZnO film fabricated by low energy O⁺ assisted pulse laser deposited under identical experimental conditions except growth time, AFM analysis has shown that the root mean square (RMS) roughness (2.37 nm) of thinner ZnO film (35 nm) was far below that (13.45 nm) of the thicker ZnO film (72 nm).     

Effects of substrate parameters on structure and optical properties of ZnO thin films fabricated by pulsed laser deposition

Highly oriented zinc oxide thin films have been grown on quartz, Si (1 1 1) and sapphire substrates by pulsed laser deposition (PLD). The effect of temperature and substrate parameter on structural and optical properties of ZnO thin films has been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission spectra and PL spectra. The experimental results show that the best crystalline thin films grown on different substrate with hexagonal wurtzite structure were achieved at growth temperature 400–500 °C. The growth temperature of ZnO thin film deposited on Si (1 1 1) substrate is lower than that of sapphire and quartz. The band gaps are increasing from 3.2 to 3.31 eV for ZnO thin film fabricated on quartz substrate at growth temperature from 100 to 600 °C. The crystalline quality and UV emission of ZnO thin film grown on sapphire substrate are significantly higher than those of other ZnO thin films grown on different substrates.     

Effect of substrate temperature on the properties of pyrolytically deposited nitrogen-doped zinc oxide thin films

The effect of substrate temperature (T_s) on the properties of pyrolytically deposited nitrogen (N) doped zinc oxide (ZnO) thin films was investigated. The T_s was varied from 300 °C to 500 °C, with a step of 50 °C. The positive sign of Hall coefficient confirmed the p-type conductivity in the films deposited at 450 °C and 500 °C. X-ray diffraction studies confirmed the ZnO structure with a dominant peak from (1 0 0) crystal plane, irrespective of the variation in T_s. The presence of N in the ZnO structure was evidenced through X-ray photoelectron spectroscopy (XPS) analysis. The obtained high N concentration reveals that the 450 °C is the optimal T_s. Atomic force microscope (AFM) analysis showed that the surface roughness was increased with the increasing T_s until 400 °C but then decreased. It is found that the transmittance of the deposited films is increased with the increasing T_s. The optical band gap calculated from the absorption edge showed that the films deposited with T_s of 300 °C and 350 °C possess higher values than those deposited at higher T_s.     

Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O₂ ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm⁻¹.     

Epitaxial growth of non-polar m-plane ZnO thin films by pulsed laser deposition

Non-polar ZnO thin films were deposited on m-plane sapphire substrates by pulsed laser deposition at various temperatures from 300 to 700 °C. The effects of growth temperature on surface morphology, structural, electrical, and optical properties of the films were investigated. All the films exhibited unique m-plane orientation indicated by X-ray diffraction and transmission electron microscopy. Based on the scanning electron microscopy and atomic force microscopy, the obtained films had smooth and highly anisotropic surface, and the root mean square roughness was less than 10 nm above 500 °C. The maximum electron mobility was ～18 cm²/V s, with resistivity of ～0.26 Ω cm for the film grown at 700 °C. Room temperature photoluminescence of the m-plane films was also investigated.     

Nano-structural characteristics of Ti/glass and Ti/Mo films as a function of deposition rate and angle of incidence

Titanium films of 90 nm thickness were deposited under UHV condition at different deposition rates, ranging from 0.3 to 10.2 Å s^− 1, at room temperature on glass and Mo substrates at two incidence angles of 8.5° and 45°. The samples were analyzed using XRD and AFM techniques. The grain sizes were obtained from AFM images, while the crystallite sizes and preferred orientation of the films were obtained from XRD profiles. Results show that Ti/glass films at 8.5° angle of incidence show (002) preferred orientation, while at 45° incidence angle, at lower deposition rates, films show an almost amorphous structure, which develops to a strong (002) preferred orientation for deposition rate of 1.6 Å s^− 1, and again at much higher deposition rate of 10.2 Å s^− 1 it changes to an amorphous structure. Ti/Mo films deposited at 45° incidence angle showed (101) preferred orientation.     

Microstructural and optical properties of nanocrystalline ZnO deposited onto vertically aligned carbon nanotubes by physical vapor deposition

Nanocrystalline ZnO films with thicknesses of 5 nm, 10 nm, 20 nm, and 50 nm were deposited via magnetron sputtering onto the surface of vertically aligned multi-walled carbon nanotubes (MWCNTs). The ZnO/CNTs heterostructures were characterized by scanning electron microscopy, high resolution transmission electron microscopy, and X-ray diffraction studies. No structural degradation of the CNTs was observed and photoluminescence (PL) measurements of the nanostructured ZnO layers show that the optical properties of these films are typical of ZnO deposited at low temperatures. The results indicate that magnetron sputtering is a viable technique for growing heterostructures and depositing functional layers onto CNTs.     

Preparation and characterization of copper nanoparticles/zinc oxide composite modified electrode and its application to glucose sensing

We report a new method for selective detection of d(+)-glucose using a copper nanoparticles (Cu-NPs) attached zinc oxide (ZnO) film coated electrode. The ZnO and Cu-NPs were electrochemically deposited onto indium tin oxide (ITO) coated glass electrode and glassy carbon electrode (GCE) by layer-by-layer. In result, Cu-NPs/ZnO composite film topography was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. SEM and AFM confirmed the presence of nanometer sized Cu-NPs/ZnO composite particles on the electrode surface. In addition, X-ray diffraction pattern revealed that Cu-NPs and ZnO films were attached onto the electrode surface. Indeed, the Cu-NPs/ZnO composite modified electrode showed excellent electrocatalytic activity for glucose oxidation in alkaline (0.1 M NaOH) solution. Further, we utilized the Cu-NPs/ZnO composite modified electrode as an electrochemical sensor for detection of glucose. This glucose sensor showed a linear relationship in the range from 1 × 10^? 6 M to 1.53 × 10^? 3 M and the detection limit (S/N = 3) was found to be 2 × 10^? 7 M. The Cu-NPs/ZnO composite as a non-enzymatic glucose sensor presents a number of attractive features such as high sensitivity, stability, reproducibility, selectivity and fast response. The applicability of the proposed method to the determination of glucose in human urine samples was demonstrated with satisfactory results.     

Growth and characterization of (Pb,La)TiO3 films with and without a special buffer layer prepared by RF magnetron sputtering

The (Pb, La)TiO₃ (PLT) ferroelectric thin films with and without a special buffer layer of PbO_x have been deposited on Pt/Ti/SiO₂/Si(100) substrates by RF magnetron sputtering technique at room temperature. The microstructure and the surface morphology of the films annealed at 600 °C for 1 h have been investigated by X-ray diffraction (XRD) and atomic force microscope (AFM). The surface roughness of the PLT thin film with a special buffer layer was 4.45 nm (5 μm × 5 μm) in comparison to that of 31.6 nm (5 μm × 5 μm) of the PLT thin film without a special buffer layer. Ferroelectric properties such as polarization hysteresis loop (P–V loop) and capacitance–voltage curve (C–V curve) of the films were investigated. The remanent polarization (P_r) and the coercive field (E_c) are 21 μC/cm² and 130 kV/cm respectively, and the pyroelectric coefficient is 2.75 × 10^− 8 C/cm² K for the PLT film with a special buffer layer. The results indicate that the (Pb, La)TiO₃ ferroelectric thin films with excellent ferroelectric properties can be deposited by RF magnetron sputtering with a special buffer layer.     

Preparation of nanocrystalline PbS thin films and effect of Sn doping and annealing on their structural and optical properties

Nanocrystalline PbS and Sn doped PbS thin films were successfully deposited on suitably cleaned glass substrate at constant room temperature, using the chemical bath deposition technique. Before, adding Sn doping content, the pure PbS thin films were deposited at room temperature for several dipping times to optimize the deposition time. After deposition, the films were also annealed at 400 °C for 1 h in air. The crystal structures of the films were determined by X-ray diffraction studies. The films were adherent to the substrate and well crystallized according to cubic structure with the preferential orientation (2 0 0). The crystallite size of the pure PbS thin films at optimized deposition time 30 min was found to be 40.4 nm, which increased with Sn content in pure PbS thin film. The surface roughness was measured by AFM studies. The band gaps of the films were determined by transmission spectra. Experiments showed that the growth parameters, doping and annealing, influenced the crystal structure, and optical properties of the films.     

Atomic layer deposition of BN thin films

Boron nitride has for the first time been deposited from gaseous BBr₃ and NH₃ by means of atomic layer deposition. The deposition temperatures were 400 and 750 °C, and the total pressure was 10 torr. The BN films, deposited on silica substrates, showed a turbostratic structure with a c-axis of 0.70 nm at a deposition temperature of 750 °C as determined by X-ray diffraction. The films deposited at 400 °C were significantly less ordered. The film density was obtained by means of X-ray reflectivity, and it was found to be 1.65–1.70 and 1.90–1.95 g cm⁻³ for the films deposited at 400 and 750 °C, respectively. Furthermore, the films were, regardless of deposition temperature, fully transparent and very smooth. The surface roughness was 0.3–0.5 nm as measured by optical interferometry.     

(Cu,Fe, Co,or Ni)-doped tin dioxide films deposited by spray pyrolysis: Doping influence on thermal stability of the film structure

The results of doping influence on thermal stability of the SnO₂ film morphology are presented in this article. The SnO₂ films doped by Fe, Cu, Ni, Co (16 at.%) were deposited by spray pyrolysis from 0.2 M SnCl₄–water solution at T_pyr 350–450 °C. The annealing at 850–1030 °C was carried out in the atmosphere of the air. The change of such parameters as film morphology, the grain size, texture and the intensity of X-ray diffraction (XRD) peaks have been controlled. For structural analysis of tested films we have been using X-ray diffraction, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) techniques. It was established that the doping does not improve thermal stability of both film morphology and the grain size. It was made a conclusion that the increased contents of the fine dispersion phase of tin oxide in the doped metal oxide films, and the coalescence of this phase during thermal treatment are the main factors, responsible for observed changes in the morphology of the doped SnO₂ films.     

Enhancement of photosensitivity by annealing in Bi2S3 thin films grown using SILAR method

Bi₂S₃ thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. The as prepared thin film were annealed at 250 °C in air for 30 min. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurement systems. The X-ray diffraction patterns reveal that Bi₂S₃ thin film have orthorhombic crystal structure. SEM images showed uniform deposition of the material over the entire glass substrate. The optical energy band gap observed to be decreased from 1.69 to 1.62 eV for as deposited and annealed films respectively. The I–V measurement under dark and illumination condition (100 W) show annealed Bi₂S₃ thin film gives good photoresponse as compared to as deposited thin film and Bi₂S₃ thin film exhibits photoconductivity phenomena suggesting its useful in sensors device. The thermo-emf measurements of Bi₂S₃ thin films revealed n-type electrical conductivity.     

Fabrication and characterization of tetrapod-like ZnO nanostructures prepared by catalyst-free thermal evaporation

Tetrapod-like ZnO nanostructures were fabricated on ZnO-coated sapphire (001) substrates by two steps: pulsed laser deposition (PLD) and catalyst-free thermal evaporation process. First, the ZnO films were pre-deposited on sapphire (001) substrates by PLD. Then the ZnO nanostructures grew on ZnO-coated sapphire (001) substrate by the simple thermal evaporation of the metallic zinc powder at 900 °C in the air without any catalysts. The pre-deposited ZnO films by PLD on the substrates can provide growing sites for the ZnO nanostructures. The as-synthesized ZnO nanostructures were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectrum (FTIR). The results show that the tetrapod-like ZnO nanostructures are highly crystalline with the wurtzite hexagonal structure. Photoluminescence (PL) spectrum of as-synthesized nanostructures exhibits a UV emission peak at ～ 389 nm and a broad green emission peak at ～ 513 nm. In addition, the growth mechanism of ZnO nanostructures is also briefly discussed.     

Bacterial adhesion studies on titanium,titanium nitride and modified hydroxyapatite thin films

A qualitative study on adhesion of the oral bacteria Porphyromonas gingivalis on titanium (Ti), titanium nitride (TiN), fluorine modified hydroxyapatite (FHA) and zinc modified FHA (Zn-FHA) thin films is investigated. Ti and TiN thin films were deposited by DC magnetron sputtering and hydroxyapatite-based films were prepared by solgel method. The crystalline structure, optical characteristics, chemical composition and surface topography of the films were studied by XRD, optical transmission, XPS, EDAX and AFM measurements. The predominant crystallite orientation in the Ti and TiN films was along (002) and (111) of hcp and cubic structures, respectively. The Ti : O : N composition ratio in the surface of the Ti and TiN films was found to be 7 : 21 : 1 and 3 : 8 : 2, respectively. The atomic concentration ratio (Zn + Ca) / P in Zn-FHA film was found to be 1.74 whereby the Zn replaced 3.2% of Ca. The rough surface feature in modified HA films was clearly observed in the SEM images and the surface roughness (rms) of Ti and TiN films was 2.49 and 3.5 nm, respectively, as observed using AFM. The film samples were sterilized, treated in the bacteria culture medium, processed and analyzed using SEM. Surface roughness of the films was found to have least influence on the bacterial adhesion. More bacteria were observed on the TiN film with oxide nitride surface layer and less number of adhered bacteria was noticed on the Ti film with native surface oxide layer and on Zn-FHA film.     

Structural,optical and electrical characterization of ZnO:Ga thin films for organic photovoltaic applications

Gallium-doped zinc oxide (ZnO:Ga) films were prepared on glass substrates by RF magnetron sputtering. The effect of growth temperature on microstructure, optical and electrical properties of the films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectrophotometer and four-point probe. The results show that all the films are polycrystalline and (002) oriented, and that the growth temperature significantly affects the microstructure and optoelectrical properties of the films. The film deposited at 670 K has the largest grain size of 71.9 nm, the lowest resistivity of 8.3 × 10^? 4 Ω?cm and the highest figure of merit of 2.1 × 10^? 2 Ω^? 1. Furthermore, the optical energy gaps and optical constants were determined by optical characterization methods. The dispersion behavior of the refractive index was also studied using the Sellmeir's dispersion model and the oscillator parameters of the films were obtained.     

Producing CuO and ZnO composite thin films using the spin coating method on microscope glasses

In this work, we have presented a new route to produce pure ZnO and composite ZnO-CuO thin films. In the process we have started with pure ZnO thin films and ended up with CuO by doping Cu in various percentages, ranging from 0% to 100%. We have managed to attain crystal phases in all doping concentrations. All the produced thin films have been crystallized at the annealing temperatures of 600 and 700 °C for 6 h. The X-ray diffraction (XRD) spectra have been performed to see the formation of crystal phases of all pure ZnO and composite ZnO-CuO thin films. These give insight that the two crystal phases related to ZnO and CuO stayed together within the thin film matrices, which were produced in different doping concentrations, i.e. nZnO + mCuO (0 ≤ n, m ≤ 100%). The scanning electron microscopy (SEM) micrographs and UV–vis absorption spectra have also been taken to elucidate the structure and composition of the all films.     

Preparation and thermomechanical properties of Ag-PVA nanocomposite films

Metal–polymer hybrid nanocomposites have been prepared from an aqueous solution of polyvinyl alcohol (PVA) and silver nitrate (AgNO₃). The silver nanoparticles were generated in PVA matrix by the reduction of silver ions with PVA molecule at 60–70 °C over magnetic stirrer. UV–vis analysis, X-ray diffraction studies, transmission electron microscopy, scanning electron microscopy and current–voltage analysis were used to characterize the nanocomposite films prepared. The X-ray diffraction analysis reveals that silver metal is present in face centered cubic (fcc) crystal structure. Average crystallite size of silver nanocrystal is 19 nm, which increases to 22 nm on annealing the film at 150 °C in air. This result is in good agreement with the result obtained from TEM. The UV–vis spectrum shows a single peak at 433 nm, arising from the surface plasmon absorption of silver nanocolloids. This result clearly indicates that silver nanoparticles are embedded in PVA. An improvement of mechanical properties (storage modulus) was also noticed due to a modification of PVA up to 0.5 wt% of silver content. The current–voltage (I–V) characteristic of nanocomposite films shows increase in current drawn with increasing Ag-content in the films.     

Influence of Ar/O2 ratio on the properties of transparent conductive ZnO:Ga films prepared by DC reactive magnetron sputtering

Ga-doped zinc oxide (ZnO:Ga) transparent conductive films with highly (002)-preferred orientation were deposited on glass substrates by DC reactive magnetron sputtering method in Ar + O₂ ambience with different Ar/O₂ ratios. The structural, electrical, and optical properties were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The resistivity and optical transmittance of the ZnO:Ga thin films are of the order of 10^− 4 Ω cm and over 85%, respectively. The lowest electrical resistivity of the film is found to be about 3.58 × 10^− 4 Ω cm. The influences of Ar/O₂ gas ratios on the resistivity, Hall mobility, and carrier concentration were analyzed.     

Influence of the molar concentration and substrate temperature on fluorine-doped zinc oxide thin films chemically sprayed

The effect of both the molar concentration of the starting solution and the substrate temperature on the electrical, morphological, structural and optical properties of chemically sprayed fluorine-doped zinc oxide (ZnO:F) thin films deposited on glass substrates is analyzed in this work. All the starting solutions employed were aged for 10 days before the deposition. The results show that as the molar concentration increases, a decrease in the electrical resistivity values is obtained, reaching the minimum resistivity in films ZnO:F deposited from a 0.4 M solution at 500 °C. A further increase in the molar concentration leads to a very slight increase in the resistivity. On the other hand, as the substrate temperature is increased, the resistivity decreases and a tendency towards to minimum value is evidenced; taking the molar concentration as parameter, minimum values are reached at 500 °C. The obtaining of ZnO:F thin films, with a resistivity as low as 7.8 × 10^− 3 Ω cm (sheet resistance of 130 Ω/□ and film thickness of 600 nm) measured in as-deposited films is reported here for the first time. The concurrent effect of the high molar concentration of the starting solution, the substrate temperature values used, and the ageing of the starting solution, which might cause polymerization of the zinc ions with the fluorine species, enhance the electrical properties. The structure of the films is polycrystalline, with a (002) preferential growth. Molar concentration rules the surface morphology as at low concentration an hexagonal and porous structure is developed changing to a uniform compact and small grain size surface in the films deposited with the high molar concentrations.