Liquid phase deposition of BiFeO3 thin film on self-assembly monolayers

BiFeO₃ (BFO) thin films were successfully deposited on self-assembled monolayers (SAMs) by the liquid phase deposition method. The measurement of contact angle and atomic force microscopy (AFM) showed that after immersion in an octadecyl trichlorosilane (OTS) solution for 30 min, the surface of the substrate was covered with a smooth, hydrophobic layer. After UV irradiation for 30 min, the smooth hydrophobic layer changed into a serrated hydrophilic layer. This indicated that the OTS-SAMs played an active role as chemical templates in controlling nucleation and growth of the BFO thin film. The phase and the surface topography of the BFO film were investigated respectively by X-ray diffraction, Field emission scanning electron microscopy (FE-SEM) and AFM. The results showed that the optimum annealing temperature and deposition temperature for preparing the BFO thin film were 600 and 70 °C respectively. The films were annealed at 600 °C for 2 h. As-prepared thin films were smooth, uniform, and dense with the height varying between 20 and 100 nm. Moreover, patterned BFO nanoarrays were prepared.     

Influence of temperature, voltage and hydrogen on the reversible transition of electrical conductivity in sol–gel grown nanocrystalline TiO2 thin film

Undoped nanocrystalline p-type TiO₂ thin film was deposited by sol–gel method on a thermally oxidized p-Si (2–5 Ω cm resistivity and $ \left\langle {100} \right\rangle $ orientation) substrate. The thin film was characterized by two-dimensional X-ray Diffraction (2D-XRD) and Field Emission Scanning Electron Microscopy (FESEM) to confirm the formation of stable nano crystalline anatase titania and to determine the grain size (~10 nm). Optical absorption spectroscopy was carried out to ascertain the band gap of the material. Two lateral Pd contacts were used as the metal electrodes to TiO₂ thin film to study the electrical conductivity. A clear p- to n-type transition was observed at 240 °C and a bias voltage of 0.83 V and the effect was enhanced on exposure to H₂ gas. The thin film showed fully n-type conductivity at 275 °C and 0.1 V. However, the reversal of the type of conductivity from n- to p-type was observed below 240 °C during lowering the temperature. The creation of oxygen vacancy and the diffusion of lattice oxygen to the surface of TiO₂ thin film might be the most possible mechanism of such transitions. Presence of hydrogen enhanced the process.     

Structural transition of ZnO thin films produced by RF magnetron sputtering at low temperatures

Zinc oxide (ZnO) thin films were prepared using reactive radio-frequency magnetron sputtering of a pure metallic zinc target onto glass substrates. The evolution of the surface morphology and the optical properties of the films were studied as a function of the substrate temperature, which was varied from 50 to 250 °C. The surface topography of the samples was examined using atomic force microscopy (AFM), and their optical properties were studied via transmittance measurements in the UV–Vis–NIR region. DRX and AFM analyses showed that the surface morphology undergoes a structural transition at substrate temperatures of around 150 °C. Actually, at 50 °C the formation of small grains was observed while at 250 °C the grains observed were larger and had more irregular shapes. The optical gap remained constant at ~3.3 eV for all films. In the visible region, the average optical transmittance was 80 %. From these results, one can conclude that the morphological properties of the ZnO thin films were more greatly affected by the substrate temperature, due to mis-orientation of polycrystalline grains, than were the optical properties.     

Characteristics of CeOx–VO2 composite thin films synthesized by sol–gel process

Pure vanadium dioxide (VO₂) and CeOx–VO₂ (1.5 < x < 2) composite thin films were grown on muscovite substrate by inorganic sol–gel process using vanadium pentaoxide and cerium(III) nitrate hexahydrate powder as precursor. The crystalline structure, morphology and phase transition properties of the thin films were systematically investigated by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, FE-SEM and optical transmission measurements. High quality of the VO₂ and CeOx–VO₂ composite films were obtained, in which the relative fractions of +4 valence state vanadium were above 70 % though the concentrations of cerium reached 9.77 at %. However, much of cerium compounds were formed at the edge of grains and the addition of cerium resulted in more clearly defined grain boundaries as shown in SEM images. Meanwhile, the composite films exhibited excellent phase transition properties and the infrared transmittance decreased from about 70 to 10 % at λ = 4 μm bellow and above the metal–insulator phase transition temperature. The metal–insulator phase transition temperatures were quite similar with about 66 °C of the pure VO₂ and CeOx–VO₂ composite thin films. But hysteresis widths increased with more addition of cerium, due to the limiting effect of grain boundaries on the propagation of the phase transition. Particularly, the CeOx–VO₂ composite film with an addition of 7.82 at % Ce showed a largest hysteresis width with about 20.6 °C. In addition, the thermochromic performance of visible transmittance did not change obviously with more addition of cerium.     

Role of annealing temperature on microstructural and electro-optical properties of ITO films produced by sputtering

This study probes the effect of annealing temperature on electrical, optical and microstructural properties of indium tin oxide (ITO) films deposited onto soda lime glass substrates by conventional direct current (DC) magnetron reactive sputtering technique at 100 watt using an ITO ceramic target (In₂O₃:SnO₂, 90:10 wt%) in argon atmosphere at room temperature. The films obtained are exposed to the calcination process at different temperature up to 700 °C. X–ray diffractometer (XRD), ultra violet-visible spectrometer (UV–vis) and atomic force microscopy (AFM) measurements are performed to characterize the samples. Moreover, phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. The results obtained show that all the properties depend strongly on the annealing temperature. XRD results indicate that all the samples produced contain the In₂O₃ phase only and exhibit the polycrystalline and cubic bixbite structure with more intensity of diffraction lines with increasing the annealing temperature until 400 °C; in fact the strongest intensity of (222) peak is obtained for the sample annealed at 400 °C, meaning that the sample has the greatest ratio I ₂₂₂/I ₄₀₀ and the maximum grain size (54 nm). As for the AFM results, the sample prepared at 400 °C has the best microstructure with the lower surface roughness. Additionally, the transmittance measurements illustrate that the amplitude of interference oscillation is in the range from 78 (for the film annealed at 400 °C) to 93 % (for the film annealed at 100 °C). The refractive index, packing density, porosity and optical band gap of the ITO thin films are also evaluated from the transmittance spectra. According to the results, the film annealed at 400 °C obtains the better optical properties due to the high refractive index while the film produced at 100 °C exhibits much better photoactivity than the other films as a result of the large optical energy band gap.     

Characterization of surface roughness of Pt Schottky contacts on quaternary n-Al0.08In0.08Ga0.84N thin film assessed by atomic force microscopy and fractal analysis

The purpose of this study was to analyze surface topography of Pt Schottky contacts on quaternary n-Al_0.08In_0.08Ga_0.84N thin film. To understand how the effect of temperature changes the layers surface, the surface topography was characterized through atomic force microscopy (AFM) and fractal analysis. Pt Schottky contacts grown on nanostructure Al_0.08In_0.08Ga_0.84N thin film grown by molecular beam epitaxy technique on sapphire substrate at annealing temperatures range of 300–500 °C were used. AFM analysis was performed in contact mode, on square areas of 10 × 10 μm², by using a Nanosurf Easyscan 2 AFM system. Detailed surface characterization of the surface topography was obtained using statistical parameters of 3D surface roughness, according with ISO 25178-2: 2012, provided by the AFM software. The results revealed that the high quality Schottky contact with the Schottky barrier heights and ideality factor of 0.76 and 1.03 respectively can be obtained under 30 min annealing at 400 °C in N₂ ambience. The surface roughness of Pt Schottky contacts on quaternary n-Al_0.08In_0.08Ga_0.84N thin film revealed a fractal structure at nanometer scale. Results obtained by fractal analysis confirm the relationship between the value of the fractal dimension and the statistical surface roughness parameters. AFM and fractal analysis are accurate tools that may assist manufacturers in developing Pt Schottky contacts on quaternary n-Al_0.08In_0.08Ga_0.84N thin film with optimal surface characteristics and provides different yet complementary information to that offered by traditional surface statistical parameters.     

Facile sol–gel preparation of nanocrystal embedded thin film material for memory device

A promising charge trapping film with crystal embedded material is proposed for future electronic devices. Instead of conventional high-vacuum and expensive tool, this technique adopts very cheaper process of sol–gel spin-coating for fabrication of thin film material in the charge trapping flash memory (CTFM). The crystal from spinodal phase separation is observed for sol–gel thin film at 900 °C annealing, and is strongly related to the thickness of the spin-coated thin film. The morphology of the crystal from the ethanol solvent system is in the isolated form, while from 2-propanol solvent is in the interconnected structure. The sol–gel-derived CTFM from ethanol exhibits the better memory performance of retention times for <5 and <10 % charge loss at applied temperature of 25 and 85 °C, respectively. The ethanol system CTFM demonstrates a large memory window (~10 V) and good reliability than 2-propanol (~3 V) due to the existence of several isolated crystals in silicon dioxide film.     

Magnetic properties and structure of cobalt-platinum thin films

The magnetic properties of RF sputtered Co-Pt alloy thin films were studied as a function of Pt content from 0 to 80 at%. At room temperature, ferromagnetic films were obtained in the range 0-32 and 40-80 at% Pt. For Pt contents between 32 and 40 at%, discontinuities in the magnetization, magnetostriction, and coercivity versus Pt content were observed; however no discontinuity was observed in the resistivity. The structure of films containing about 25 at% Pt is a mixture of hexagonal and face-centered cubic (FCC) phases. At this composition the magnetostriction is small, but coercivities are large-700 to 2000 Oe-and dependent upon film thickness. The coercivities of these films do not change with heat treatment up to temperatures of 600°C but decrease markedly at 700°C. The properties of equiatomic Co-Pt film s are similar to those of bulk alloys. In particular the large coercivity observed in films after heal treatment at 500° to 700°C is due to the formation of an ordered tetragonal phase within the face-centered cubic matrix. The structure of films of about 75 at% Pt is initially a disordered face-centered cubic phase and with heat treatment beginning at 500°C an ordered face-centered cubic phase forms. The coercivity of these films (∼200 Oe) does not change with annealing at 500°C. It decreases slightly upon further annealing at 600°C to 700°C. Electron microscope observations were used to correlate the magnetic properties with film structure.     

Effect of post annealing on structural and optical properties of ZnO thin films deposited by vacuum coating technique

We report the effect of annealing temperature on structural, electrical and optical properties of polycrystalline zinc oxide thin films grown on p-type silicon (100) and glass substrates by vacuum coating technique. The XRD and AFM measurements confirmed that the thin films grown by this technique have good crystalline hexagonal wurtzite structures and homogenous surfaces. The study also reveals that the rms value of thin film roughness increases from 6 to 16 nm, the optical band gap increases from 3.05 to 3.26 eV and resistivity from 0.3 to 5 Ωcm when the post-deposition annealing temperature is changed from 400 to 600 °C. It is observed that ZnO thin film annealed at 600 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Optical properties of nanostructured ruthenium dioxide thin films via sol–gel approach

High purity ruthenium dioxide (RuO₂) nanoparticles with the average size is about 9 nm in diameter are readily synthesized through a low cost sol–gel method. RuO₂ thin films have been deposited on SiO₂ substrates by sol–gel spin coating techniques at room temperature, followed by annealing at 500 °C for 2 h. The result of X-ray diffraction indicates that the RuO₂ nanoparticles are well crystallized with a rutile tetragonal structure. Morphological of RuO₂ films were characterized using atomic force microscopy (AFM), transmission electron microscopy and high resolution transmission electron microscopy. The AFM images confirmed a spherical-shape nanoparticles with diameter of 9 nm and surface roughness of 12 nm of the films. The optical absorption studies showed the presence of direct band transition with band gap equal to 1.87 eV. Refractive index and dielectric properties of the films were estimated from optical measurements. Room temperature photoluminescence of RuO₂ film showed an emission band at 432 nm.     

Microstructural and surface morphological studies on Co doped ZnS diluted magnetic semiconductor thin films

Microstructural and surface morphological studies of Co (2.5%) doped ZnS thin films deposited at different substrate temperatures (T_S) of 200, 400 and 600 °C by means of pulsed laser deposition are presented. The deposited films are in wurtzite-hexagonal crystal structure as confirmed by X-ray diffraction and Raman spectroscopy techniques. The films deposited at higher T_S show columnar morphology, as evidence by transmission electron microscopy measurements. Images of the surface topography have been taken by atomic force microscopy (AFM) for the film deposited at different T_S. The film deposited at T_S of 200 °C shows cone-like structures while deposited at T_S of 400 and 600 °C show columnar structures. A fractal analysis has been performed on AFM images to understand the microstructure and surface morphology of thin film at different T_S. Fractal analysis also reveals the morphological changes in the film with increasing T_S. The observed ferromagnetism is correlated with columnar growth of the film which can be used as diluted magnetic semiconductor for spintronic applications.     

Dependence of Magnetic Hysteresis on Evolving Single-Sample Sintering in Fine-Grained Yttrium Iron Garnet

Mono-dispersed yttrium iron garnet nanoparticles have been synthesized via mechanical alloying technique, and some attendant qualitative relationships between evolving microstructural parameters and magnetic properties have been clearly revealed. A rarely employed single-sample sintering scheme was adopted where only one sample was sintered repeatedly from 600 °C to 1400 °C prior to an analysis of evolution of microstructure-dependent magnetic properties after each sintering. A brief, yet detailed characterization of the sample was carried out using Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and B–H Hysteresis graph. A scrutiny of the B–H Hysteresis graph results showed a transition from disordered to ordered magnetism which belongs to three different magnetically dominant groups, namely weak ferro-, moderately strong ferro-, and strongly ferromagnetic groups. Three factors were found to strongly influence the ordered magnetism of the sample, namely the crystallinity degree of the crystalline phase, the number of grains with size larger than a critical diameter, and the number of large enough grains for magnetic order accommodation.     

Preparation of rare earth CeO<Subscript>2</Subscript> thin films using metal organic decomposition method for metal-oxide–semiconductor capacitors

Investigation of metal organic decomposed rare earth cerium oxide thin films deposited on Si substrate by sol–gel spin coating technique was carried out. The structural properties have been examined by using XRD, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XRD confirms the cubic phase of CeO₂ thin films with (111) plane observed at 28.54°. The FTIR and EDAX spectra confirm the formation of CeO₂ films with atomic percentage of 19.39 and 54.82% of Ce and O₂, respectively. Thickness of 60.11 nm of CeO₂ film measured by cross sectional FESEM image, the average roughness of ~0.6 nm of 400?°C annealed CeO₂ films were observed from AFM micrograph. The MOS capacitors were fabricated by using Ti/Au bilayer metal contact depositing by E-beam evaporator on CeO₂/Si thin film for electrical measurements. Capacitance and conductance voltage measurement was carried out to determine the effective oxide charges (Q_eff), interface trap density (D_it) and dielectric constant (k) and are 2.48?×?10¹² cm^?2, 1.26?×?10¹² eV^?1cm^?2 and ~39, respectively. The effective metal work function of 5.68 for Ti/Au bilayer is observed to be higher than the work function of Ti or Au metals in vacuum.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.     

Influence of ion-beam sputtering deposition parameters on highly photosensitive and transparent CdZnO thin films

CdZnO thin films with a nominal thickness of ~200 nm were grown on c-plane sapphire substrates by dual ion-beam sputtering deposition technique. The effect of substrate temperature (300–600 °C) and gas ambience on structural, morphological, compositional and opto-electronic properties was studied. X-ray diffraction patterns confirmed that all the films were polycrystalline in nature and were preferentially oriented along the c-axis. It was revealed that the films grown at Ar/O₂ ratio of 4:1 were structurally more ordered and the film quality was found to be the best at 500 °C. The compositional studies specify that approximately 11.8 at.% of cadmium were present in the film deposited at 300 °C in Ar–O₂ mixture. Investigations on optical properties by photoluminescence and absorption studies indicate band gap shrinkage with the increase in argon partial pressure and substrate temperature. It was found that photosensitivity of the deposited films was highly dependent on growth conditions. The photosensitivity was found to be 5000-fold higher for CdZnO film grown at 600 °C in Ar–O₂ ambience compared to the best reported result, and this was promising to realize high-performance opto-electronic devices on such CdZnO films.     

Bi2MoO6 dielectric thin films fabricated by thermal oxidation of Bi/Mo thin films at ultra-low temperature

Bi/Mo multilayer thin films are deposited on Si/SiO₂/Pt substrates by direct current magnetron sputtering. The effect of annealing temperature on the microstructure, dielectric and electrical properties of the as-sputtered films is characterized systematically. X-ray diffraction data indicate that the films annealed at 450–600 °C are a mixture of diphase with the main phase Bi₂MoO₆ and secondary phase Bi₂Mo₂O₉. Results of scanning electron microscope observation show that the films annealed at 500–550 °C are dense and uniform, in particular the films annealed at 500 °C exhibit optimal dielectric and electrical properties with dielectric constant as high as 37.5, dielectric loss 1.06 %, temperature coefficient of dielectric constant ?10.86 ppm °C^?1 at 1 kHz, and leakage current density of 1.46 × 10^?7 A mm^?2 at an electric field of 18.2 kV mm^?1. With the advantages of ultralow densification temperature (500 °C) and very high sputtering deposition rate (76 nm min^?1), it is anticipated that thermal oxidation method of the sputtered Bi/Mo thin films could be a promising technique for fabrication of Bi₂MoO₆ ceramic thin film embedded-capacitors.     

Growth and characterization of La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on different substrates

Colossal magnetoresistance La_5/8Sr_3/8MnO₃ (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was ?17.21 % for LSMO/MgO film followed by ?15.65 % for LSMO/Si and ?14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (T_P) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (T_C) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. T_C such as 363 and 352 K are the high T_C that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature.     

Dielectric and multiferroic properties of 0.75BiFeO3–0.25BaTiO3 solid solution

Solid solution 0.75BiFeO₃–0.25BaTiO₃ (BFO–25 % BT) was prepared by solid state reaction method. Powder X-ray diffraction showed the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases due to splitting in the line at 2θ = 39.7°. Scanning electron micrographs indicated that the ceramic has compact and uniform microstructure with average grain size <3 μm. The polarization vs applied electric field analysis showed an unsaturated hysteresis loop with the remnant polarization 12.95 μC/cm² at 22 kV/cm for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The calculations of diffuse parameter i.e. slope γ = 1.63 suggested a high degree of diffusion in BFO–BT lattice. The room temperature magnetic measurements confirmed the weak ferromagnetism of magnetization ~0.1 emu/gm at an applied magnetic field of H = 5 kOe for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The high temperature magnetic and dielectric analysis suggested a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition T_c ~ 310 °C, which was responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy and complex modulus analysis confirmed the conventional relaxor, NTCR (negative temperature coefficient of resistance), giant ferroelectricity and polydispersive non-Debye type dielectric relaxation behaviour for 0.75BiFeO₃–0.25BaTiO₃ ceramic at 170 °C on 1 kHz with activation energy 2.33 eV. The modulus analysis also confirmed the possibility of hopping mechanism for electrical transport process in material.     

Growth of Bi1.5MgNb1.5O7 thin films on Pt/Ti/SiO2/Si substrates by RF magnetron sputtering

In this letter, bismuth magnesium niobate (Bi_1.5MgNb_1.5O₇, BMN) thin films were deposited on Pt/Ti/SiO₂/Si substrates by using radio-frequency magnetron sputtering at various substrate temperatures. Based on the phase compositions and microstructures of these samples, we discussed the nucleation and growth of the BMN thin films and how the substrate temperature influenced these processes. The thin film begins to crystallize at 450 °C, and the annealed films were all composed of the cubic pyrochlore phase with a strong (222)-preferred orientation. The film deposited at 450 °C exhibited a large dielectric constant of 173, and a tunability of 26.6 % was obtained at a max dc bias field of 0.8 MV/cm.     

Ce-doped bismuth ferrite thin films with improved electrical and functional properties

Bi_1?xCe_xFeO₃ (BCFO) thin film capacitors (x = 0 to 0.2) are fabricated on indium tin oxide coated corning glass substrate by chemical solution deposition method. X-ray diffraction results show a partial phase transition from rhombohedral to tetragonal structure induced in BCFO thin film having preferred (110) orientation with increase in Ce dopant concentration. Current density–field (J–E) characteristics indicate that the leakage current density reduces by several orders of magnitude in Ce-doped BFO thin films resulting from smaller grain sizes and smoother surfaces. Space-charge-limited current and Fowler–Nordheim tunneling are identified as dominating leakage behavior in BCFO thin film capacitors at moderate and high field regions, respectively. Enhanced ferroelectric response with well-saturated (P–E) hysteresis loop is observed for Bi_0.88Ce_0.12FeO₃ thin film having high remnant polarization (P _r—127 µC/cm²) at an applied field of 1080 kV/cm. Bi_0.88Ce_0.12FeO₃ thin film exhibiting well-defined capacitance–field (C–E) butterfly loop with dielectric loss (tan δ—0.03) measured at 10 kHz suggested good ferroelectric properties with high tunability of about 88 %.