Growth and structural properties of Mg:C thin films prepared by magnetron sputtering

We investigate the growth and structure properties of Mg:C thin films. The films are prepared using a dc magnetron sputtering discharge where the electrical resistance over the films is monitored during growth in-situ with a four point probe setup. The structural properties of the films are investigated using X-ray diffraction measurements and the elemental composition and binding in the films is determined using elastic recoil detection analysis and X-ray photoelectron spectroscopy. The results show that during co-sputtering the carbon flux influences the initial stages of the film growth. The films are made of polycrystalline magnesium grains embedded in a carbon network, the size of which depends on the carbon content, but amorphous phases cannot be excluded. The XPS measurements show the presence of carbidic carbon whereas X-ray measurements find no Mg:C phases. The overall stability of the films is found to depend on the carbon content, where stable films capped with a 14 nm Pd layer cannot be obtained with carbon content above 18%.     

Optical properties of amorphous, erbium-doped yttrium alumino-borate thin films

In this paper, we report on the optical characterizations of erbium-doped yttrium alumino-borate glassy thin films prepared by the polymeric precursor and sol-gel routes and the spin-coating technique. High quality planar waveguides were produced by a multilayer processing of Y_1−xEr_xAl₃(BO₃)₄ compositions with x = 0.02, 0.05, 0.10, 0.30, and 0.50. Their optical properties were investigated using transmission, photoluminescence, and m-lines spectroscopy, whereas high resolution scanning electron microscopy (HR-SEM) was applied to check film thickness and surface homogeneity. The refractive indices determined from transmission and m-lines spectroscopy are in good agreement just like the film thickness measured by HR-SEM and transmission spectroscopy. We observed low propagation losses, together with efficient photoluminescence emission for polymeric precursor thin films, involving low cost and environment friendly reactants.     

Impedance spectroscopy and relaxation phenomena of (Na,K) excess Na0.5K0.5NbO3 thin films grown by chemical solution deposition

Na_0.5K_0.5NbO₃ (NKN) and 10 mol% (Na,K) excess Na_0.5K_0.5NbO₃ (NKN10) thin films on Pt/Ti/SiO₂/Si substrate were prepared by chemical solution deposition. Crystallization of NKN10 thin films was confirmed by X-ray diffraction. The (Na,K) excess Na_0.5K_0.5NbO₃ thin film shows a ferroelectric P-E hysteresis loop. Dielectric properties and impedance spectroscopy of thin films were investigated in the frequency range from 0.1 Hz to 100 kHz and the temperature range of 25 ~ 500 °C. By analyzing the complex impedance relaxation with Cole-Cole plots, we found impedance relaxations for the thin film. The contribution of electrical conduction is discussed in relation to grain, grain boundary, and interface effects.     

Investigation of adenine, uracil, and ribose phosphate thin films prepared by electrospray in vacuum deposition using photoemission spectroscopy

Previous results showed significant ionization energy differences between thin films of the four ribonucleic acid (RNA) polynucleotides. The experiments reported here aim at the investigation of the origin of these differences. Since the ribose phosphate backbone is common to all RNA nucleotides, the nucleobases are the most likely candidate defining the ionization energy of RNA. Consequently, experiments were performed to investigate the electronic structure and ionization energies of thin films of two nucleobases (adenine and uracil, representative for purines and pyrimidines), and ribose phosphate. These experiments were performed using x-ray and ultraviolet photoemission spectroscopy (XPS, UPS) in conjunction with an electrospray based in vacuum multi-step deposition technique. The presented results clearly demonstrate a significant ionization energy difference between the two nucleobases, qualitatively matching the previous results on the homopolymers of adenosine and uridine (poly rA, poly rU). As expected, the ionization energy of the prepared ribose phosphate thin films was much larger than those of the nucleobases.     

Optical,surface, and microstructural properties of Li4Ti5O12 thin films coated by RF magnetron sputtering

Li₄Ti₅O₁₂ thin films were deposited on glass substrates by the RF magnetron sputtering method in an argon gas atmosphere at different powers. Some properties of the coated Li₄Ti₅O₁₂ films were examined using some techniques. Structural characteristics of the produced Li₄Ti₅O₁₂ films were investigated by X-ray diffraction. The Li₄Ti₅O₁₂ phases were identified as (311) and (222). The surface morphology of the produced Li₄Ti₅O₁₂ films was investigated using an atomic force microscope. The transmittance and the absorbance were measured using a UV–vis spectrophotometer. The transmittance values were around 88% and 90%. The absorbance values were approximately 0.053 and 0.048. The film thickness values were 140 and 50?nm. The transparency values of the produced films were high. The optical band gap values of the produced LTO films were calculated as ～3.8?eV. The refractive index and the reflectance spectra values of samples were determined using interferometer measurements. The refractive index values were 1.51 and 1.44 at 550?nm, respectively.     

Semiconductor thin films directly from minerals—study of structural, optical, and transport characteristics of Cu2O thin films from malachite mineral and synthetic CuO

We demonstrate the proof-of-concept of using an abundantly occurring natural ore, malachite (Cu₂CO₃(OH)₂) to directly yield the semiconductor Cu₂O to be used as an active component of a functional thin film based device. Cu₂O is an archetype hole-conducting semiconductor that possesses several interesting characteristics particularly useful for solar cell applications, including low cost, non-toxicity, good hole mobility, large minority carrier diffusion length, and a direct energy gap ideal for efficient absorption. In this article, we compare the structural, optical, and electrical transport characteristics of Cu₂O thin films grown from the natural mineral malachite and synthetic CuO targets. Growth from either source material results in single-phase, fully epitaxial cuprous oxide thin films as determined by x-ray diffraction. The films grown from malachite have strong absorption coefficients ( 10⁴ cm^− 1), a direct allowed optical bandgap ( 2.4 eV), and majority carrier hole mobilities ( 35 cm² V^− 1 s^− 1at room temperature) that compare well with films grown from the synthetic target as well as with previously reported values. Our work demonstrates that minerals could be useful to directly yield the active components in functional devices and suggests a route for the exploration of low cost energy conversion and storage technologies.     

Properties of (K,Na)NbO3-based lead-free piezoelectric films prepared by pulsed laser deposition

To investigate the properties of (K,Na)NbO₃-based lead-free piezoelectric films at the morphotropic phase boundary composition, we fabricated epitaxial [(K_0.5Na_0.5)_0.97Li_0.03] (Nb_0.8Ta_0.2)O₃ films on (001), (110) and (111)-oriented single crystal SrTiO₃ substrates by pulsed laser deposition. The structure and electrical properties of the films were studied. Dielectric constants of 540, 390 and 300 and remnant polarizations of 4.00, 1.05, and 0.35 μC/cm² were observed for the (001), (110) and (111) oriented films, respectively.     

The properties of transparent semiconductor Zn1 − xTixO thin films prepared by the sol-gel method

Transparent semiconductor thin films of Zn_1 − xTi_xO (0 ≦ x ≦ 0.12) were deposited on alkali-free glass substrates by the sol-gel method. The effects of Ti addition on the crystallization, microstructure, optical properties and resistivity of ZnO thin films were investigated. The as-coated films were preheated at 300 °C, and then annealed at 500 °C in air ambiance. X-ray diffraction results showed all polycrystalline Zn_1 − xTi_xO thin films with preferred orientation along the (002) plane. Ti incorporated within the ZnO thin films not only decreased surface roughness but also increased optical transmittance and electrical resistivity. In the present study, the Zn_0.88Ti_0.12O film exhibited the best properties, namely an average transmittance of 91.0% (an increase of ~ 12% over the pure ZnO film) and an RMS roughness value of 1.04 nm.     

Phase composition of selenized Cu2ZnSnSe4 thin films determined by X-ray diffraction and Raman spectroscopy

Thin layers of Sn onto Cu-Zn alloy with different component ratios were processed at different temperatures. Scrupulous comparative analyses were performed by room temperature Raman spectroscopy and X-ray-diffractometry. An excess of tin on the surface results in isothermal selenization at 450 °C in the hexagonal residuals of unstable SnSe₂ in the well-crystallized Stannite — Cu₂ZnSnSe₄. In similar selenization conditions, copper-rich layers as precursors result in the Stannite phase with micro-immersions of CuSe. Low-temperature photoluminescence spectra of selenized films indicated to two Gaussian shaped bands at 0.81 and 1.16 eV.     

Dry etch properties of IZO thin films in a CF4/Ar adaptively coupled plasma system

In this study, we investigated to the etch characteristics of indium zinc oxide (IZO) thin films in a CF₄/Ar plasma, namely, etch rate and selectivity toward SiO₂. A maximum etch rate of 76.6 nm/min was obtained for IZO thin films at a gas mixture ratio of CF₄/Ar (25:75%). In addition, etch rates were measured as a function of etching parameters, including adaptively coupled plasma chamber pressure. X-ray photoelectron spectroscopy analysis showed efficient destruction of the oxide bonds by ion bombardment, as well as accumulation of low volatile reaction products on the surface of the etched IZO thin films. Field emission Auger electron spectroscopy analysis was used to examine the efficiency of ion-stimulated desorption of the reaction products.     

Structural and electrical characterisation of lanthanum nickelate reactively sputter-deposited thin films

La₂NiO₄ coatings were co-sputtered on rotating substrates from metallic La and Ni targets in the presence of a reactive argon-oxygen gas mixture. This material is a potential candidate as cathode material for Intermediate Temperature-Solid Oxide Fuel Cells. The structural and chemical features of these films have been determined by X-ray Diffraction and Scanning Electron Microscopy. Their electrical properties have been characterised using the four point probe method and by Complex Impedance Spectroscopy measurements.It is shown that the as-deposited coatings, initially amorphous, crystallise in the LaNiO₃ perovskite-type oxide or in the convenient K₂NiF₄ structure as a function of their composition. The electrical measurements show a clear relation between resistivity and structure of the coatings. Despite electrical resistivity values close to the theoretical ones, the activation energy of a coating presenting the convenient K₂NiF₄ structure is slightly higher than those given in the literature data.     

Structural properties of Cu(In,Ga)Se2 thin films prepared from chemically processed precursor layers

We have developed a chemical process for incorporating copper into indium gallium selenide layers with the goal of creating a precursor structure for the formation of copper indium gallium diselenide (CIGS) photovoltaic absorbers. Stylus profilometry, EDX, Raman spectroscopy, XRD and SIMS measurements show that when indium gallium selenide layers are immersed in a hot copper chloride solution, copper is incorporated as copper selenide with no increase in the thickness of the layers. Further measurements show that annealing this precursor structure in the presence of selenium results in the formation of CIGS and that the supply of selenium during the annealing process has a strong effect on the morphology and preferred orientation of these layers. When the supply of Se during annealing begins only once the substrate temperature reaches ≈ 400 °C, the resulting CIGS layers are smoother and have more pronounced preferred orientation than when Se is supplied throughout the entire annealing process.     

Characterization of MMoO4 (M = Ba, Sr and Ca) with different morphologies prepared using a cyclic microwave radiation

Scheelite molybdates (MMoO₄, M = Ba, Sr and Ca) were successfully prepared by the reactions of M(NO₃)₂·2H₂O and Na₂MoO₄·2H₂O in propylene glycol and NaOH using a microwave radiation. The phases were detected using XRD and SAED. TEM analysis revealed the presence of micro-sized bi-pyramids with a square base, nano-sized particles in clusters, and dispersed nano-sized particles for BaMoO₄, SrMoO₄ and CaMoO₄, respectively. Diffraction patterns of the bi-pyramids were simulated, and are in accord with the experimental results. Raman and FTIR spectra provide the evidence of scheelite structure with Mo-O stretching vibration in MoO₄²⁻ tetrahedrons at 742-901 cm^− 1.     

Synthesis, characterization and magnetoresistance properties study of magnetite thin films by electroless plating in aqueous solution

Polycrystalline half-metallic Fe₃O₄ films with 1 μm in thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90 °C without heat treatment. The films have single pure spinal phase structure and the well-crystallized columnar grains grow perpendicularly to the substrates, as revealed by XRD, XPS and SEM. At room temperature, the films exhibit negative magnetoresistance (MR) ratio of about −5.1%, which is ascribed to intergranular tunneling of spin polarized electrons of Fe₃O₄. The resistivity R of the films with 1 μm in thickness at room temperature is about 5.2 × 10⁻¹ Ω cm. The cation distribution and the arrangement of the magnetic moments of the plated Fe₃O₄ ferrite thin films are different from that of the bulk materials, which is likely to be one of the reasons for the modification of R and MR properties.     

Investigation and characterization of radio frequency sputtered Cr1.8Ti0.2O3−δ thin films derived by citrate, sol-gel and solid state routes

Cr_1.8Ti_0.2O_3−δ (CTO) powders were prepared by citrate, sol-gel and solid-state routes, respectively. The effect of preparation methods on the morphology of sputtered thin films was further investigated. X-ray diffraction patterns of the powders and films confirmed a single phase CTO. No impurity was observed even after sintering the powders at 1000 °C for 24 h. X-ray photoelectron spectroscopy analysis showed that Cr 2p (577.8 eV), and O 1 s (531.5 eV) core levels of the sputtered films have ∼1 eV variation in their binding energy positions compared to those of CTO powders. The atomic force microscopy analysis showed the grains of the films obtained by sputtering sol-gel powders had the smallest size in the range of 7-58 nm. The surface roughness of the thin films had the lowest value at 0.70 nm, whereas those obtained from solid state solution had the maximum value of 2.51 nm.     

Influence of oxygen/argon pressure ratio on the morphology, optical and electrical properties of ITO thin films deposited at room temperature

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO) thin films onto glass substrates are widely used as transparent and conductive electrodes for a variety of technological applications including flat panel displays, solar cells, smart windows, touch screens, etc.ITO films on glass and polycarbonate (PC) substrates were prepared at room temperature (RT) and at different PO₂. The films were characterized in terms of the surface roughness (δ), sheet resistance, the refractive index (n) and extinction coefficient (k). The free carrier density (n_c) and the carrier mobility (μ) of the ITO (In₂O₃:Sn) films were measured and studied. The n_c and μ values vary in different ratio of oxygen partial pressure (PO₂) of ITO deposition. The observed changes in the ITO film resistivity are due to the combined effect of different parameter values for n_c and μ. From AFM analysis and spectra calculations, the surface roughness values of the ITO films were studied and it was observed that the δ values were lower than 15 nm. The energy band gap E_g ranges from 3.26 eV to 3.66 eV as determined from the absorption spectrum. It was observed an increase on the energy band gap as the PO₂ decrease in the range of 20-2% PO₂. The Lorentz oscillator classical model has also been used to fit the ellipsometric spectra in order to obtain both refractive index n and extinction coefficient κ values.     

Preparation and conductive properties of neodymium-doped lanthanum nickelate thin films by chemical solution deposition method

Neodymium-doped lanthanum nickelate (La_1 − xNd_xNiO₃, LNNO) thin films have been prepared on Si substrates by chemical solution deposition method. The effects of annealing temperature and the neodymium concentration on the structural and electrical properties of the thin films have been investigated. X-ray diffraction analysis showed that the LNNO thin films exhibited perovskite structure with (100) preferential orientation. The (100) orientation degree of the thin films changed with neodymium content; however, the resistivity of the thin films was not related to the degree of orientation. Field emission scanning electron microscopy observations confirmed that the films had a smooth surface and uniform thickness. The resistivity of the thin films annealed at 700 °C increased from 1.97 mΩ·cm to 5.35 mΩ·cm, with increasing neodymium doping amount from LaNiO₃ to La_0.6Nd_0.4NiO₃.     

Electric response as a function of applied voltage of Nb-doped Bi4Ti3O12 thin films

We have investigated the electrical properties of sol-gel deposited Nb-doped Bi₄Ti₃O₁₂ (NBIT) ferroelectric thin films. The obtained values of remanent polarization (2P_r) and coercive voltage (V_c) were 7 μC/cm² and 2.5 V of NBIT thin film, respectively. From complex dielectric spectra, we observed the dielectric response consisting of two regions for measuring frequency; the low frequency region may be due to diffusion charge transport caused by impurities, while the dielectric relaxation mechanism of high frequency region seems to be the modified Debye type. A model was proposed to account for the observed phenomena, which fits very well to the dielectric dispersion relation: . The occurrence of an anomaly in n, σ, τ, and ε_S − ε_∞ parameters near V_c indicates a coupling between the charge carriers and ferroelectricity.     

Structural, electrical and optical properties of transparent Zn1 − xMgxO nanocomposite thin films

Zn_1 − xMg_xO thin films of various Mg compositions were deposited on quartz substrates using inexpensive ultrasonic spray pyrolysis technique. The influence of varying Mg composition and substrate temperature on structural, electrical and optical properties of Zn_1 − xMg_xO films were systematically investigated. The structural transition from hexagonal to cubic phase has been observed for Mg content greater than 70 mol%. AFM images of the Zn_1 − xMg_xO films (x = 0.3) deposited at optimized substrate temperature clearly reveals the formation of nanorods of hexagonal Zn_1 − xMg_xO. The variation of the cation-anion bond length to Mg content shows that the lattice constant of the hexagonal Zn_1 − xMg_xO decreases with corresponding increase in Mg content, which result in structure gradually deviating from wurtzite structure. The tuning of the band gap was obtained from 3.58 to 6.16 eV with corresponding increase in Mg content. The photoluminescence results also revealed the shift in ultraviolet peak position towards the higher energy side.     

Characterisation of K, Na, and Li birnessites prepared by oxidation with H2O2 in a basic medium. Ion exchange properties and study of the calcined products

Birnessites containing Na, K or Li in the interlayer have been prepared by oxidation of Mn(II) cations with H₂O₂ in a basic medium with different alkaline cation/Mn molar ratios. The solids prepared have been characterised by elemental chemical analysis, powder X-ray diffraction, thermal analyses (differential thermal analysis and thermogravimetric analysis), FT-IR spectroscopy and surface texture assessment by adsorption of N₂ at –196°C. Crystalline birnessites are obtained for A/Mn ratios (A = K, Li) larger than 3.4, but MnO(OH) has been also identificed when such a ratio is smaller than 3.4. Ion exchange is topotactic, but is not complete for exchanging Na, K, or Mg for pre-existing Li. The solids are stable up to 400°C, and formation of spinels and solids with tunnel structures is observed at this temperature. Li-containing birnessites are transformed to LiMn₂O₄ spinel at 400°C, and co-crystallization of bixbyte (Mn₂O₃) is observed at higher temperatures. Bixbyte and cryptomelane are formed at 500°C for the K-containing birnessites.