Effects of Ag interlayer on the optoelectrical properties of TiON films

A sandwich structure of TiON/Ag/TiON (TAgT) multilayer films was prepared onto glass substrates using RF and DC magnetron sputtering without intentional substrate heating. The thicknesses of each layer in the TAgT films were set at 50 nm, 5 nm and 45 nm. The optoelectrical properties of the TiON films were strongly influenced by the presence of an Ag interlayer. Although the optical transmittance of the film deteriorated when an Ag interlayer was added, the films had a low resistivity of 9.0 × 10⁻⁴ Ω cm due to increased carrier density. In addition, the TAgT films show work functions of 4.4 eV, which are suitable for organic light emitting diode (OLED) applications.The experimental results indicate that TiON film manufactured with a 5-nm thick Ag interlayer is an attractive candidate for use as a transparent electrode in large area electronic applications such as solar cells and displays.     

Ag diffusion in ZnS thin films prepared by spray pyrolysis

ZnS thin films were deposited by spray pyrolysis method on glass substrates. Diffusion of Ag in ZnS thin films was performed in the temperature range 80-400 °C under a nitrogen atmosphere. The diffusion of Ag is determined with XRF, and the obtained concentration profile allows to calculate the diffusion coefficient. The temperature dependence of Ag diffusion coefficient is determined by the equation D = 8 × 10^− 9 exp(− 0.10 eV / kT). It was found that the as-grown undoped high resistive n-type ZnS thin films were converted to the p-type upon Ag doping with a slight increase in resistivity only by rapid thermal annealing at 400 °C in N₂ atmosphere. In addition, the band gap of the p-type film was decreased as compared with the undoped sample annealed under the same conditions. The results were attributed to the migration of Ag atoms in polycrystalline ZnS films by means of both along intergrain surfaces and intragrain accompanied by interaction with native point defect.     

Effects of laser irradiation on the structure and optical properties of ZnO thin films

The effects of laser irradiation on the surface microstructure and optical properties of ZnO films deposited on glass substrates were investigated experimentally and compared with those of thermal annealing. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the irradiation treatment with an Ar⁺ laser of 514 nm for 5 min improves the crystalline quality of ZnO thin films through increasing the grain size and enhancing the c-axis orientation, with the effects similar to those of the thermal annealing at 500 °C for 1 h. Laser irradiation was found to be more effective both for the relaxation of the residual compressive stress in the as-grown films and for the modification of the surface morphology. A significant increase in the UV absorption and a widening in the optical band-gap of the films were also observed after laser irradiation.     

Influence of Ag thickness of aluminum-doped ZnO/Ag/aluminum-doped ZnO thin films

Highly conducting aluminum-doped ZnO (30 nm)/Ag (5-15 nm)/aluminum-doped ZnO (30 nm) multilayer thin films were deposited on glass substrate by rf magnetron sputtering (for top/bottom aluminum-doped ZnO films) and e-beam evaporation (for Ag film). The transmittance is more than 70% for wavelengths above 400 nm with the Ag layer thickness of 10 nm. The resistivity is 3.71 × 10^− 4 Ω-cm, which can be decreased to 3.8 × 10^− 5 Ω-cm with the increase of the Ag layer thickness to 15 nm. The Haacke figure of merit has been calculated for the films with the best value being 8 × 10^− 3 Ω^− 1. It was shown that the multilayer thin films have potential for applications in optoelectronics.     

Enhanced light absorption of Ag films deposited onto femtosecond laser microstructured silicon

Absorptive properties of silver (Ag) films with the thickness varied from 160 nm to 340 nm deposited onto the surface of femtosecond laser microstructured silicon by vacuum thermal evaporation were measured in a wavelength range of 0.3-16.7 μm. Greatly enhanced light absorption of Ag films has been observed in the whole measured wavelength range. For the same Ag film thickness (268 nm), the light absorption was strongly depended on the height and spacing of the spikes, especially in the region of 1-16.7 μm. The relation between light absorption and thickness of Ag films has also been investigated, it was shown that the light absorption decreases with the increasing thickness of Ag films. The strongly enhanced light absorption in such a wide wavelength range is mainly ascribed to the multiple reflection of light between spikes and surface plasmon excitation of noble metal nano-particles on the spikes surface.     

Enhancement of wettability and antibiotic loading/release of hydroxyapatite thin film modified by 100 MeV Ag ion irradiation

The effect of swift heavy 100 MeV Ag⁷⁺ ions irradiation was studied on hydroxyapatite (HAp) thin film prepared by pulsed laser deposition technique (PLD). The GIXRD analysis confirmed the absence of any phase in the HAp phase due to irradiation. In addition, there was a considerable decrease in crystallinity and crystallite size on irradiation. There was no significant variation in the stoichiometry of the irradiated films. Irradiation seemed to decrease the optical band gap energy of HAp thin films. The surface roughness, wettability and bioactivity were improved on irradiation of the samples. Amount of amoxicillin loading/release increased (10%) in ion beam irradiated (1 × 10¹² ions cm⁻²) sample. Irradiated sample showed fast rate of amoxicillin (AMX) release than the pristine. Bactericidal effect was found to increase on irradiation. Surface modified and antibiotics incorporated HAp coated titanium implants may be used to prevent post-surgical infections and to promote bone-bonding of orthopedic devices.     

Persistent conductivity in post-growth doped ZnO films following pulsed UV laser irradiation

Solution and rf sputter deposited doped ZnO films were subjected to cumulative 4-ns pulses of 355 nm light from a pulsed Nd:YAG laser at fluences between 5 and 150 mJ/cm². Film densification, change in refractive index, and an increase in conductivity were observed following room temperature irradiation in air, a carbon monoxide reducing environment, or under vacuum. At fluences between 20 and 80 mJ/cm², the films did not damage catastrophically under irradiation and high visible transparency persisted. The increase in conductivity is attributed to creation of oxygen vacancies and subsequent promotion of free carriers into the conduction band. Effects were most pronounced for films treated in vacuum. All treated films became insulating again upon equilibration in air at room temperature after several days. Films were characterized by means of UV-VIS-NIR transmission spectroscopy, Raman spectroscopy, and Hall measurements. Analysis of interference fringes in measured transmission spectra allowed evaluation of optical properties. Raman measurements showed an increase of LO mode intensity with respect to TO mode intensity as the films became more conducting in accord with previous work. Results of this study are not only important for continued development of transparent conducting oxides, but also provide compelling evidence for the role of free carriers as initiators of laser damage in wide bandgap metal oxide films.     

Ion beam studies of multi-quantum wells of III-nitrides

III-Nitrides have attracted much attention due to their versatile and wide range of applications, such as blue/UV light emitting diodes. Strained layer super lattices offer extra degree of freedom to alter the band gap of lattice-mismatched heterostructures. Swift heavy ion irradiation is a post-growth technique to alter the band gap of semiconductors, spatially. In the present study, strained AlGaN/GaN multi-quantum wells (MQWs) were grown on sapphire with insertion of AlN and GaN as buffer layers between substrate and epilayers. Such grown AlGaN/GaN MQWs, AlGaN/GaN heterostructures and GaN layers were irradiated with 200 MeV Au and 150 MeV Ag ions at a fluence of 5 × 10¹¹ ions/cm² and 5 × 10¹² ions/cm² respectively. As-grown and irradiated samples have been characterized by high resolution XRD, photoluminescence and RBS/channelling. Measured strain values show that strain increases upon irradiation and the luminescence properties are enhanced. RBS/channelling confirms the increase in strain values upon irradiation. In this paper we describe the effects of swift heavy ion irradiation on structural and optical properties.     

Influence of gamma irradiation on the refractive index of Fe-doped barium titanate thin films

Polycrystalline Fe-doped barium titanate (Fe-doped BaTiO₃) thin films were grown by thermal decomposition of the precursors deposited from a sol-gel system onto quartz substrates. The changes in the transmittance spectra induced by gamma irradiation on the Fe-doped BaTiO₃ thin films were quantified. The values for the optical energy band gap were in the range of 3.42-3.95 eV depending on the annealing time. The refractive index of the film, as measured in the 350-750 nm wavelength range was in the 2.17-1.88 range for the as prepared film, and this increased to 2.34-1.95 after gamma irradiation at 15 kGy. The extinction coefficient of the film was in the order of 10⁻² and increased after gamma irradiation. We obtained tuneable complex refractive index of the films by exposure to various gamma rays doses.     

Effect of a pulsed Nd:YAG laser irradiation on multi-walled carbon nanotubes film

Multi-walled carbon nanotubes (MWCNTs) film have been analyzed by Raman spectroscopy to clarify the effect of a pulsed Nd:YAG laser heating. The MWCNTs film surface was flashed with the fundamental harmonic (λ = 1064 nm) or the second harmonic (λ = 532 nm) of a single pulse of Nd:YAG laser in the air. The dynamics of pulsed nanosecond laser heating process was simulated by the solution of the one-dimensional heat conduction equation. At the laser fluence of 500 mJ/cm² with Nd:YAG laser (λ = 1064 nm), the surface reached the maximum temperature 1395 °C at 12 ns. Moreover, the Raman spectroscopy of MWCNTs films before and after irradiation were measured. The intensity of the two characteristic Raman shifts I_D (defect-mode) and I_G (graphite-mode) was measured by the Raman spectroscopy. The maximum surface temperature was calculated and compared with the I_G/I_D ratio of MWCNTs film. The graphitization occurred on the sample after irradiation.     

Tensile strain and water vapor transport testing of flexible, conductive and transparent indium-zinc-oxide/silver/indium-zinc-oxide thin films

Thin film laminates composed of sputtered indium zinc oxide and silver, optimized for conductance and transparency, were tested for water vapor permeation as well as mechanical durability in tension. The ~ 82 nm thick optimized indium-zinc-oxide/silver/indium-zinc-oxide (IZO/Ag/IZO) films were > 80% transparent in the visible range (400 nm-700 nm) with measured sheet resistances less than 5 Ω/sq. The water vapor permeation measurements using Ca test methods at several temperature/ humidity conditions indicated that the addition of the thin Ag layer provided little improvement relative to a single indium-zinc-oxide (IZO) layer of similar thickness. However, the critical strain in bending tests for IZO/Ag/IZO films was improved compared to IZO films. The modulus (E ~ 113 GPa), hardness (H ~ 7 GPa), fracture toughness (K_IC ~ 1.1 MPa⋅m^0.5), and interfacial shear (“adhesion”) (τ_c ~ 16 MPa) of/related to IZO, and measured by nanoindention are consistent with other brittle ceramic thin film materials.     

Ag and O ion irradiation induced improvement in dielectric properties of the Ba(Co1/3Nb2/3)O3 thin films

We present the preliminary results of temperature and frequency dependent dielectric measurements on Ba(Co_1/3Nb_2/3)O₃ (BCN) thin films. These films were prepared on indium tin oxide (ITO) coated glass substrates by the pulse laser deposition (PLD) technique. It exhibits single-phase hexagonal symmetry. These films were irradiated with Ag¹⁵⁺ (200 MeV) and O⁷⁺ (100 MeV) beams at the fluence 1 × 10¹¹, 1 × 10¹², and 1 × 10¹³ ions/cm². On irradiating these films, its dielectric constant (?′) and dielectric loss (tan δ) parameters improve compared to un-irradiated film. Compared to O⁷⁺ irradiation induced point/cluster defects Ag¹⁵⁺ induced columnar defects are more effective in reducing/pinning trapped charges within grains. The present paper highlights the role of swift heavy ion irradiation in engineering the dielectric properties of conductive samples to enable them to be useful for microwave device applications.     

Structure and tribological properties of Ag films deposited at low temperature

The effects of substrate temperature on the structure and tribological properties of Ag films deposited at low temperatures (LT, 130-217 K) by arc ion plating (AIP) have been studied. The structure and morphology of the Ag films were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM). The results showed that there exist (1 1 1) and (2 0 0) preferred orientation transitions for decreasing temperature at different bias voltages. The tribological properties were evaluated by a ball-on-disk tribometer and wear tracks were analyzed by means of scanning electron microscopy (SEM). The results show that substrate deposition temperature significantly affected the wear of LT Ag films. For each bias voltage studied, the film showing the highest wear rate was deposited at the lowest temperature and the film with the lowest wear rate, (significantly lower than room temperature (RT) deposited Ag films), was deposited at a temperature between the highest and the lowest temperatures examined. The wear mechanism was discussed in terms of lubrication effect of film material transferred to the counterpart and its dependence on the microstructure of the original deposited film.     

Optical response and surface morphology of crystalline Nd-doped fluoride films grown on monocrystalline LiYF4 substrates by pulsed laser deposition

The realization of crystalline films of Nd³⁺:YF₃ and Nd³⁺:LiYF₄ on a monocrystalline LiYF₄ substrate by pulsed laser deposition is reported. The films were obtained by laser ablation with 355 nm photons of a bulk LiYF₄ crystal doped with Nd³⁺ ions at 1.5% atomic concentration in the presence of different ablation/deposition parameters. The films optical characteristics, analyzed via laser induced polarized fluorescence spectroscopy upon IR excitation, are presented. Lifetime measurements of the fundamental Nd³⁺ ion transition in the film were also performed. All these results were compared with those obtained in the Nd³⁺:LiYF₄ bulk crystal. The surface morphology of the depositions was analyzed via a scanning electron microscope. When the production of the deposition took place in high vacuum (1 × 10^− 4 Pa) and the substrate temperature was 750 °C, the grown film was Nd³⁺:YF₃. A 1 Pa controlled atmosphere of He in the ablation chamber and a substrate temperature of 650 °C favoured the growth of a Nd³⁺:LiYF₄ film. In the latter case the film showed also a smoother surface.     

Preparation and characterization of polyoxometalate-Ag nanoparticles composite multilayer films

The multifunctional thin films (BW₁₂/Ag NPs)_n (BW₁₂ = BW₁₂O₄₀, NPs = nanoparticles) were prepared by layer-by-layer self-assembly method. The (BW₁₂/PEI-Ag⁺)_n (PEI = polyethylenimine) composite films were achieved through alternately depositing anionic BW₁₂ and cationic PEI-Ag⁺ complex. The deposition process of (BW₁₂/PEI-Ag⁺)₁₀ multilayer is linear layer-by-layer self-assembly. Under UV irradiation, Ag ions in (BW₁₂/PEI-Ag⁺)_n multilayer films were reduced photochemically into Ag NPs and (BW₁₂/Ag NPs)₁₀ films were obtained. Through UV-vis measurements, the presence of surface plasma absorption peak at 445 nm demonstrated the formation of silver NPs. The electrochemical and antibacterial activities of (BW₁₂/Ag NPs)_n films were investigated. The electrochemical results indicate that the glassy carbon electrode modified with (BW₁₂/Ag NP)_n film exhibits the electroreduction toward O₂. Moreover, the (BW₁₂/Ag NP)₁₀ multilayer films exhibit long-lasting antibacterial properties toward Escherichia coli (E. coli).     

Effects of annealing atmosphere on thermoelectric signals from ZnO films

Zinc oxide epilayer films were grown on vicinal cut sapphire substrates by pulsed laser deposition with in situ annealing oxygen pressures varied from 0 to 10 × 10³ Pa. The best crystalline quality was obtained for ZnO layer with annealing oxygen pressure of 6 × 10³ Pa. Laser induced thermoelectric voltage (LITV) were observed along the tilting angle orientation of the substrate when the pulsed KrF excimer laser of 248 nm were irradiated on the films. The largest LITV signal was measured for the film grown at 6 × 10³ Pa annealing oxygen pressure. According to the measured LITV signals, Seebeck anisotropy was evaluated and was found to range from 3 to 12 μV/K for ZnO films annealed at different oxygen pressures from 2 to 10 × 10³ Pa. It is suggested that oxygen ambient plays an important role in the electronic properties of the ZnO films.     

Analysis of thermal effect on transparent conductive oxide thin films ablated by UV laser

Transparent conductive oxide thin films are applied to many computer, communication and consumer electronics products including thin film transistor liquid crystal displays, organic light emitting diodes, solar cells, mobile phones, and digital cameras. The laser direct write patterning of the indium tin oxide (ITO) thin film processing technique produces a heat affected zone that has an enormous effect on the electro-optical efficiency of transparent conductive oxide films. This is because direct laser writing patterning in thermal machining process can create debris and micro-cracks in the substrate. Therefore, this study establishes the ultraviolet (UV) laser ablation of temperature model on the polycarbonate and soda-lime glass substrates using the finite element analysis software ANSYS, and measures the temperature field based on the laser micro-patterning process. The meshing model determines the structure of the pre-processors and parameters were set with ANSYS parameter design language. This study also simulates the Gaussian distribution laser irradiation on the pre-processor structure. A UV laser processing system made micro-patterning on ITO thin films to analyze which conditions damaged the substrates. Comparing the simulation and experiment results reveals the minimum laser ablation threshold of the ITO thin films with the melting and vaporization temperatures. Simulation results show that the temperature distribution on PC and soda-lime glass substrates after laser irradiation of 1.05 μs with a laser output power of 0.07 W produces temperatures of approximately 52 °C, 54 °C and 345°Cand 205 °C at the laser output power of 0.46 W. The experiment results show that the patterning region is similar to the simulation results, and the lower laser power does not damage the substrates.     

Photocatalytic properties of Cr-doped TiO2 films prepared by oxygen cluster ion beam assisted deposition

We prepared Cr-doped titanium dioxide (TiO₂) films by oxygen (O₂) cluster ion beam assisted deposition method, and investigated photocatalytic properties of the films as well as crystallographic property, optical property and surface morphology. The films prepared at a substrate temperature below 200 °C were found to be amorphous from the X-ray diffraction measurement. For the substrate temperatures such as 300 °C and 400 °C, the films exhibited rutile and/or anatase structures. The film surface measured by the atomic force microscope (AFM) was smooth at an atomic level. Furthermore, the optical band gap decreased with increase of Cr-composition, and it was approximately 3.3 eV for the non-doped films, 3.2 eV for the 1% Cr-doped films and 3.1 eV for the 10% Cr-doped films, respectively. With regard to the photocatalytic properties of the Cr-doped TiO₂ films, we measured the change of contact angle as well as the photocatalytic degradation of methylene blue by the UV light irradiation. Compared with the non-doped films, the 1% Cr-doped films prepared at a substrate temperature of 400 °C showed high degradation efficiency. In addition, the contact angle of the 1% Cr-doped films with an initial value of 60° decreased to 10° by the UV light irradiation for 20 min, and the films exhibited the predominant properties of photocatalytic hydrophilicity even for the UV light irradiation with longer wavelengths.     

Deposition of Al doped ZnO layers with various electrical types by atomic layer deposition

AlZnO thin films with various Al/Zn composition ratios were deposited by atomic layer deposition (ALD) at 200 °C. The effect of the composition of the AlZnO films on their electrical and optical characteristics was investigated. The AlZnO films with an Al content of up to 10 at.% showed high conductivity, while further increasing in the Al content resulted in the abrupt formation of an insulating oxide film. The lowest electrical resistivity of the ALD-deposited AlZnO film was 6.5 × 10^− 4 [Ω cm] at 5 at.% Al. The AlZnO films with up to 5 at.% Al exhibited crystalline phases and a near-band-edge emission. With increasing Al content, the optical band edge showed a blue shift, and a sudden shift associated with an insulating bandgap was observed in the AlZnO films containing 20 at.% Al.     

Influence of laser wavelength and beam profile on Nd:YAG laser assisted formation of polycrystalline-Si films

Influence of wavelengths and beam profiles of a pulsed Nd³⁺:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film is investigated. Two sets of samples of amorphous-Silicon (a-Si) thin films deposited on glass (a-Si/glass) and crystalline Si (a-Si/c-Si) substrates were treated with different laser-fluence values. After the laser treatment, the films were analyzed by a scanning electron microscope, the Raman spectroscopy technique and the resistance-measurement technique. In the case of the third harmonics (355 nm) of the Nd³⁺:YAG laser, poly-Si films were obtained with laser-fluence values ranging from 260 mJ/cm² to 560 mJ/cm², where as in the case of the second harmonics (532 nm), the process window for the formation of poly-Si films, in terms of the laser fluence, was ranging from 300 mJ/cm² to 480 mJ/cm². On the other hand, in the case of samples treated with the fundamental wavelength (1064 nm), a narrow process window with higher laser-fluence values around 1100 mJ/cm² was observed. Further, the substrate was also affected because of the higher laser-fluence value. It has also been observed that the crystallization characteristics of poly-Si films improved with the flat-top intensity distribution as compared to the Gaussian intensity distribution of the Nd³⁺:YAG laser beam. A theoretical simulation based on thermal modeling was performed to understand the mechanism of crystallization.