The effects of thermal annealing on the structure and the electrical transport properties of ultrathin gadolinia-doped ceria films grown by pulsed laser deposition

Ultrathin crystalline films of 10 mol% gadolinia-doped ceria (CGO10) are grown on MgO (100) substrates by pulsed laser deposition at a moderate temperature of 400°C. As-deposited CGO10 layers of approximately 4 nm, 14 nm, and 22 nm thickness consist of fine grains with dimensions ≤∼11 nm. The films show high density within the thickness probed in the X-ray reflectivity experiments. Thermally activated grain growth, density decrease, and film surface roughening, which may result in the formation of incoherent CGO10 islands by dewetting below a critical film thickness, are observed upon heat treatment at 400°C and 800°C. The effect of the grain coarsening on the electrical characteristics of the layers is investigated and discussed in the context of a variation of the number density of grain boundaries. The results are evaluated with regard to the use of ultrathin CGO10 films as seeding templates for the moderate temperature growth of thick solid electrolyte films with improved oxygen transport properties.     

A study on electrical and mechanical properties of hybrid-polymer thin films by a controlled TEOS bubbling ratio

Organic-inorganic hybrid-polymer thin films were deposited on silicon(1 0 0) substrates at room temperature by PECVD (plasma enhanced chemical vapor deposition). Ethylcyclohexane and TEOS (tetraethoxysilane) were utilized as organic and inorganic precursors with hydrogen gas for the ethylcyclohexane bubbler and argon gas for both the TEOS bubbler and as a carrier gas. To compare the electrical and the mechanical properties of the plasma polymerized thin films, we grew the hybrid-polymer thin films under conditions of various TEOS bubbling ratios. MTS nano-indenter was used to measure the hardness and Young's modulus and showed that these values increased as the TEOS bubbling ratio increased, with the highest hardness at 0.8 GPa in this experiment. An impedance analyzer was utilized for the measurements of I-V curves and capacitance, showing the lowest dielectric constant at approximately 1.83, with a leakage current density of 10⁻⁸ A/cm² at 1 MV/cm, respectively.     

Lead-free ferroelectric thin films obtained by pulsed laser deposition

Na_0.5Bi_0.5TiO₃-BaTiO₃ (NBT-BT) thin films grown by pulsed laser deposition have been investigated by X-ray diffraction, scanning electron microscopy, and dielectric spectroscopy in order to clarify the role of substrate temperature on crystalline structure, grain morphology, and dielectric properties. We have shown that the structural and dielectric properties of NBT-BT thin films with composition at morphotropic phase boundary (6% BT) critically depend on the substrate temperature: small variations of this parameter induce structural changes, shifting the morphotropic phase boundary toward tetragonal or rhombohedral side. Higher deposition temperature (1000 K) favor the formation of rhombohedral phase, films deposited at 923 K and 973 K have tetragonal symmetry at room temperature. Grains morphology depends also on the deposition temperature. Atomic force micrographs show grains with square or rectangular shape in a compact structure for films grown at lower temperatures, while grains with triangular shape in a porous structure are observed for films grown at 1000 K. Dielectric spectroscopy measurements evidenced the phase transition between ferroelectric and antiferroelectric phase at 370 K. Films grown at 1000 K shown low electrical resistivity due to their porous structure. High dielectric constant values (about 800 at room temperature and 2700 at 570 K) have been obtained for films grown at temperatures up to 973 K.     

Dielectric constant and current transport for HfO2 thin films on ITO

The dielectric constant and leakage current mechanisms for HfO₂ thin films deposited on indium–tin–oxide using reactive rf sputtering deposition were examined. Indium–tin–oxide was selected as the bottom metal as it is of interest as an electrode in transparent field-effect transistor development. The dielectric constant of HfO₂ films was approximately 20 and did not vary significantly with deposition conditions. Temperature-dependent leakage current measurements indicate that Schottky emission is the dominant transport mechanism in films deposited at low temperature and/or low oxygen pressure. The HfO₂/indium–tin–oxide barrier height was extracted to be 1.1±0.2 eV. Films deposited at high temperature and/or oxygen pressure deviate from the Schottky emission model, presumably due to the formation of polycrystalline material with grain boundary conduction. PACS  73.61.Ng; 73.50.Lw; 77.55.+f     

The size effect of Ba0.6Sr0.4TiO3 thin films on the ferroelectric properties

Barium strontium titanate (BST) thin films were prepared by RF magnetron sputtering. The dielectric constant-voltage curves and the hysteresis loops of BST thin films with different grain sizes and film thicknesses were investigated. When the grain size increases from 12 nm to 35 nm, remarkable increases in dielectric constant and tunability were observed. Above 12 nm, the BST films exhibited size effects, i.e. a decrease in maximal polarization (P_m) and an increase in coercive electric field (E_c) with reduction in grain size. In our investigation, the dielectric constant, tunability and maximal polarization increased as the film thickness increased. Furthermore, the size dependence of the dielectric constant and tunability of Ba_0.6Sr_0.4TiO₃ thin films is determined by that of the maximal polarization and the coercive electric field.     

Plasma resonance in granular silver films deposited on rough surfaces of NaCl and KCl single crystals

Granular silver films deposited on rough NaCl and KCl single-crystal surfaces exhibit, besides the low-frequency plasma-resonance band induced by the light-wave field and the field generated by the grain dipoles, a second, high-frequency plasma-resonance band, which is excited only by the light-wave field at the frequency ω₀ of the natural electron vibrations in the grains. The dielectric constant due to interband transitions was calculated from the known plasma frequency and the dielectric constant of the medium surrounding thegrains, the plasma frequency ω_p of the granular films, and the measured frequency of the maximum of surface plasmon vibrations in solid films. The results obtained agree with the data quoted by other authors.     

Effects of deposition temperature on the structural and morphological properties of thin ZnO films fabricated by pulsed laser deposition

ZnO thin films were grown on Si(1 0 0) substrates using pulsed laser deposition in O₂ gas ambient (10 Pa) and at different substrate temperatures (25, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using XRD, AFM and SEM. At substrate temperature of T=150 °C, a good quality ZnO film was fabricated that exhibits an average grain size of 15.1 nm with an average RMS roughness of 3.4 nm. The refractive index and the thickness of the thin films determined by the ellipsometry data are also presented and discussed.     

纳米晶Ti薄膜的结构研究

用高密度、高电离度的电子迴旋共振等离子体溅射方法在室温基片上沉积出纳米晶Ti薄膜,基体为玻璃、NaCl单晶、纯Al等。对Ti薄膜的结构、形貌和成分进行X射线衍射(XRD),透射电子显微镜(TEM)和X射线光电子能谱(XPS)分析,表明所沉积的Ti薄膜是平均粒径d<10nm,晶粒大小均匀且具有比较稳定的fcc反常结构的纳米晶粒膜。我们还较系统地研究了各工作参数对Ti薄膜的晶体结构、晶粒尺寸、成膜速率以及对基体粘附力的影响,分析了成膜机理。 关键词：     

Encapsulation and controlled release from core–shell nanoparticles fabricated by plasma polymerization

Core–shell nanostructures have been synthesized by plasma deposition in radio-frequency plasma reactor. Silica and KCl nanoparticles were encapsulated by deposition of isopropanol-based films of amorphous hydrogenated carbon. Through control of the deposition time, under constant deposition rate of 1 nm/min, particles are encapsulated in a layer of plasma polymer with thickness between 15 and 100 nm. Films are robust, chemically inert, thermally stable up to 250°C. The permeability of the shells is determined by depositing films of various thickness onto KCl nanoparticles and monitoring the dissolution of the core in aqueous solution. The dissolution profile is characterized by an initial rapid release, followed by a slow release that lasts up to 30 days for the thickest films. The profile is analyzed by Fickian diffusion through a spherical matrix. We find that this model captures very accurately the entire release profile except for the first 12 hours during which, the dissolution rate is higher than that predicted by the model. The overall diffusion coefficient for the dissolution of KCl is 3 × 10⁻²¹ m²/s.     

The morphology of tin cluster assembled films and the effect of nitrogen

Thin films produced by depositing tin clusters with sizes between 5 and 10 nm onto silicon nitride substrates were found to be highly coalesced resulting in grains with sizes ~30 nm. Exposing the clusters to nitrogen before they were deposited significantly reduced the coalescence between them and resulted in granular films where the clusters mostly retained their shape. This is due to a small amount of tin nitride forming in the clusters. The coalesced and granular films were used to fabricate tin oxide gas sensors. This was done by depositing the two types of films onto silicon nitride chips and then oxidising them by baking at 250 °C for 24 h. It was found that the sensors composed of uncoalesced clusters were much more sensitive to hydrogen. This was attributed to the smaller grain size and the larger surface area of the granular films.     

Pre- and post-breakdown electrical studies in ultrathin Al2O3 films by conductive atomic force microscopy

The loss of local dielectric integrity in ultrathin Al₂O₃ films grown by atomic layer deposition is investigated using conducting atomic force microscopy. I–V spectra acquired at different regions of the samples by constant and ramping voltage stress are analyzed for their pre- and post-breakdown signatures. Based on these observations, the thickness dependent dielectric reliability and failure mechanism are discussed. Our results show that remarkable enhancement in breakdown electric field as high as 130 MV/cm is observed for ultrathin films of thickness less than 1 nm.     

Effect of process parameters and post-deposition annealing on the microwave dielectric and optical properties of pulsed laser deposited Bi<Subscript>1.5</Subscript>Zn<Subscript>1.0</Subscript>Nb<Subscript>1.5</Subscript>O<Subscript>7</Subscript> thin films

Bismuth Zinc niobate (Bi_1.5Zn_1.0Nb_1.5O₇) thin films were deposited by pulsed laser deposition (PLD) method on fused silica substrates at different oxygen pressures. The structural, microwave dielectric and optical properties of these thin films were systematically studied for both the as-deposited and the annealed films at 600°C. The as-deposited films were all amorphous in nature but crystallized on annealing at 600°C in air. The surface morphology as studied by atomic force microscopy (AFM) reveals ultra-fine grains in the case of as-deposited thin films and cluster grain morphology on annealing. The as-deposited films exhibit refractive index in the range of 2.36–2.53 (at a wavelength of 750 nm) with an optical absorption edge value of 3.30–3.52 eV and a maximum dielectric constant of 11 at 12.15 GHz. On annealing the films at 600°C they crystallize to the cubic pyrochlore structure accompanied by an increase in band gap, refractive index and microwave dielectric constant.     

Dielectric behaviour of emeraldine base polymer–ZnO nanocomposite film in the low to medium frequency

Emeraldine base (EB) polymer–ZnO nanoparticles composite films has been synthesized by solution casting technique on ITO-coated glass substrate and characterized by XRD, FTIR and TEM for their structure and morphology. Dielectric behaviour of these composite films has been investigated in the very low frequency region to medium frequency region (1 kHz–1 MHz). The dielectric constant of the composite with 30% nanoparticles is almost one-tenth of the pure EB. The dielectric value becomes constant in the frequency region greater than 400 kHz. The change in dielectric behaviour of the composite is explained on the basis of multilayered interface formed between the ZnO nanoparticles and emeraldine chains. Nanoparticles have high energy surface which is responsible for the decrease of free volume for the orientation of polymer chains consequently decrease in dielectric constant of the composite. TEM images shows about 10 nm ZnO particles embedded in the emeraldine matrix. From the XRD data it has been observed that the lattice parameters of ZnO have been modified due to the alignment of polymer chains along the basal planes of the nanoparticles. The shift of N=Q=N and N–B–N vibration bands to higher wave number in IR indicates that interaction between emeraldine chain and nanoparticles which provides stability to emeraldine matrix.     

Fabrication and characterization of La-doped HfO2 gate dielectrics by metal-organic chemical vapor deposition

La-doped HfO₂ gate dielectric thin films have been deposited on Si substrates using La(acac)₃ and Hf(acac)₄ (acac = 2,4-pentanedionate) mixing sources by low-pressure metal-organic chemical vapor deposition (MOCVD). The structure, thermal stability, and electrical properties of La-doped HfO₂ films have been investigated. Inductive coupled plasma analyses confirm that the La content ranging from 1 to 5 mol% is involved in the films. The films show smaller roughness of ∼0.5 nm and improved thermal stability up to 750 °C. The La-doped HfO₂ films on Pt-coated Si and fused quartz substrates have an intrinsic dielectric constant of ∼28 at 1 MHz and a band gap of 5.6 eV, respectively. X-ray photoelectron spectroscopy analyses reveal that the interfacial layer is Hf-based silicate. The reliable value of equivalent oxide thickness (EOT) around 1.2 nm has been obtained, but with a large leakage current density of 3 A/cm² at V_g = 1V + V_fb. MOCVD-derived La-doped HfO₂ is demonstrated to be a potential high-k gate dielectric film for next generation metal oxide semiconductor field effect transistor applications.     

Growth and characterization of nanostructured anatase phase TiO<Subscript>2</Subscript> thin films prepared by DC reactive unbalanced magnetron sputtering

Titanium dioxide thin films were deposited on three different unheated substrates by unbalanced magnetron sputtering. The effects of the sputtering current and deposition time on the crystallization of TiO₂ thin films were studied. The TiO₂ thin films were deposited at three sputtering current values of 0.50, 0.75, and 1.00 A with different deposition times of 25, 35, and 45 min, respectively. The surface morphology of the films was investigated by atomic force microscopy (AFM). The structure was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The film thickness was determined by field emission scanning electron microscopy (FE-SEM), and the optical property was evaluated with spectroscopic ellipsometry. The results show that polycrystalline anatase films were obtained at a low sputtering current value. The crystallinity of the anatase phase increases as the sputtering current increases. Furthermore, nanostructured anatase phase TiO₂ thin films were obtained for all deposition conditions. The grain size of TiO₂ thin films was in the range 10–30 nm. In addition, the grain size increases as the sputtering current and deposition time increase.     

Dependence of film thickness on the structural and optical properties of ZnO thin films

ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10⁻⁴ Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.     

Evolution of structural and magnetic properties of FePt/C granular films with thermal annealing

We report the structural and magnetic properties of as-deposited and thermally annealed FePt/C granular multilayer films. The as-deposited system exhibits a disordered fcc FePt phase with an average grain size of 3 nm. Thermal annealing at 650 °C results in partial L1₀ ordering and an associated grain growth to 7 nm. Mössbauer measurements show that there is no non-magnetic component present, suggesting that carbon resides only in the grain boundary region. The ferromagnetic grains are magnetically decoupled.     

Influence of annealing temperature on optical properties of zinc oxide thin films analyzed by spectroscopic ellipsometry method

Zinc oxide (ZnO) thin films were sol–gel spin coated on glass substrates, annealed at various temperatures 300 °C, 400 °C and 500 °C and characterized by spectroscopic ellipsometry method. The optical properties of the films such as transmittance, refractive index, extinction coefficient, dielectric constant and optical band gap energy were determined from ellipsometric data recorded over the spectral range of 300–800 nm. The effect of annealing temperature in air on optical properties of the sol–gel derived ZnO thin films was studied. The transmission values of the annealed films were about 65% within the visible range. The optical band gap of the ZnO thin films were measured between 3.25 eV and 3.45 eV. Also the dispersion parameters such as single oscillator energy and dispersive energy were determined from the transmittance graph using the Wemple and DiDomenico model.     

Substrate effects on the microstructure of hydrogenated amorphous carbon films

In this work, plasma enhanced chemical vapour deposition was used to prepare hydrogenated amorphous carbon films (a-C:H) on different substrates over a wide range of thickness. In order to observe clear substrate effect the films were produced under identical growth conditions. Raman and near edge X-ray absorption fine structure (NEXAFS) spectroscopies were employed to probe the chemical bonding of the films. For the films deposited on silicon substrates, the Raman I_D/I_G ratio and G-peak positions were constant for most thickness. For metallic and polymeric substrates, these parameters increased with film thickness, suggesting a change from a sp³-bonded hydrogenated structure to a more sp² network, NEXAFS results also indicate a higher sp² content of a-C:H films grown on metals than silicon. The metals, which are poor carbide precursors, gave carbon films with low adhesion, easily delaminated from the substrate. The delamination can be decreased/eliminated by deposition of a thin (∼10 nm) silicon layer on stainless steel substrates prior to a-C:H coatings. Additionally we noted the electrical resistivity decreased with thickness and higher dielectric breakdown strength for a-C:H on silicon substrate.     

Randomly-grown high-dielectric-constant ZnO nanorods for?near-field enhanced Raman scattering

We investigate the dependence of the size parameter in the Mie scattering theory on the near-field enhanced Raman scattering properties for high dielectric constant ZnO nanorods grown randomly by PLD (pulsed laser deposition). High Raman signals of Rhodamine 6G (R6G) at 532 nm excitation wavelength were observed with nanorods of 400 nm average diameter. This experimental result was explained theoretically by the size parameter described in the Mie scattering theory, not by surface plasmon polaritons. This was also confirmed by the near-field distribution calculated by the FDTD (Finite-Difference Time Domain) method. The ZnO nanorods with 400 nm average diameter can detect as low as 1 μM of R6G. This near-field enhancement factor is equivalent to that with 10-nm-thick gold-coated ZnO nanorods (nanoshells) with an average core diameter of 100 nm. Controlling the diameter of bare ZnO nanorods is effective for obtaining large enhancement factors without an additional process of gold thin film coating on them.