Polycrystal Films Research Articles

Evaluation of Small Ultrasonic Probe using Lead Zirconate Titanate poly-crystal Film Deposited by Hydrothermal Method

Two types of transducers for small ultrasound probes were fabricated. Titanium or epoxy resin were used for the backing material of the transducers. The piezoelectric material was lead zirconate titanate (PZT) that was deposited by the hydrothermal method. These transducers were built into a small ultrasound probe and the characteristics were evaluated. As a result, we succeeded in the fabrication of a wideband ultrasound probe with a distance resolution of 16μm, a frequency bandwidth of 69MHz in the range of 39 to 98MHz, and a fractional bandwidth of 86% at the epoxy resin backing probe.

Polycrystal diamond growth in a microwave plasma torch

Diamond films of different structures were deposited on quartz, WC-Co, and molybdenum substrates in a microwave plasma torch discharge in an argon-hydrogen-methane gas mixture in a sealed chamber at pressures close to atmospheric by using the chemical vapor deposition technique. Images of diamond polycrystal films and separate crystals, as well as results of Raman spectroscopy, are presented. The spectra of optical plasma radiation recorded during film deposition demonstrate the presence of intense Hα hydrogen and C2 radical bands known as Swan bands.

Growth of diamond by DC Arcjet Plasma CVD: From nano-sized poly-crystal films to millimeter-sized single crystal grain

A 30 kW-powered DC Arcjet Plasma enhanced chemical-vapor deposition (CVD) system was applied to grow diamonds which included the nano-crystal free-standing film, the nano-/micro-crystal layered free-standing film, the gradient micro-crystal free-standing film and the millimeter-sized grain. The free-standing film quality, such as the roughness, the sp 2 content, the residual stress and the grain morphology, was studied by an atomic force microscope (AFM), Raman spectra, a scanning electron microscope (SEM) and a high resolution electron microscope (HREM). In large-sized grain deposition, as-grown deposit was obtained about 1 × 1 × 1 mm 3 in size under the condition of 10 μm/h of the substrate moving speed without Nitrogen enhancement. Characterized by Raman spectra and Laue back reflection X-ray diffraction, the deposit was proven to be single crystal diamond with small grains coving its surfaces. The growth rate was about 30 μm/h. Optical emission spectrum (OES) was utilized to characterize gas phases in the plasma for diamond deposition. The mean electron temperature (Te) in the plasma was calculated based on the value of the emission intensity ratio of I H γ / I H β . Te varied from 0.33 eV to 0.5 eV depending on the concentration of CH 4 in H 2 from 1.0% to 25%. C 2 radical was found to be the dominant carbon source compared with CH radical. The influence of the radical on the morphology of diamond was discussed. It was found that the nano-crystal could be grown when the ratio of the emission intensity, I C 2 / I CH, was larger than 8.

Molecular Dynamics Simulation of Grain Growth of Cu Film —Effects of Adhesion Strength between Substrate and Cu Atoms—

The growth process of Cu polycrystal films on Si, Ti, W and Ru substrate during isothermal annealing was studied by the molecular dynamics method. We focused on the influence of the adhesion strength between substrate and Cu on crystallinity and orientational order of the film. After structural relaxation at low temperature (50 K), the movements of individual Cu atoms were calculated for different annealing temperatures using the molecular dynamics method. The crystallinity and orientational order of the film were examined by 2D-Fourier transformation of the atomic structure. We found that the system with strong adhesion strength between substrate and Cu showed higher crystallinity and orientational order for (111) oriented Cu film.

Air-stable n-channel single-crystal transistors with negligible threshold gate voltage

Single-crystal transistors of highly electron-affine organic compounds were constructed on solid dielectrics to study intrinsic constraints for the n-channel field effect in ambient atmosphere. Tetracyanoquinodimethane field-effect devices reproducibly operate with a high mobility of 0.2–0.5 cm2/V s in the air. The threshold gate voltage is negligible unlike most other air-stable n-type organic transistors reported, including polycrystal film devices of the same compound. Together with the other example of less electron-affine semiconductor crystal showing air-stable field effect but with notable threshold voltage, the result suggests that crucial in air-stable n-channel field effect is sufficient electron-affinity of the organic semiconductors.

Tribological roles of nanometre thick Ag layers on Hertzian macroscopic contacts

Tribological performance of subnano to nanometre thick Ag layers deposited on Si(111) has been examined under ultra high vacuum conditions to understand effect of surface thin layers on the wear and friction characteristics. The slider was made of a diamond sphere 3 mm in radius. As a result, a minimum of the coefficient of friction 0·007 was observed over a film thickness range of 1·5–10 nm. The sliding planes were observed by Auger electron spectroscopy, reflection high energy electron diffraction (RHEED), synchrotron orbital radiated X-ray diffraction (SOR-XD) and scanning tunnelling microscopy (STM). No worn particles were found after 100 reciprocal sliding cycles, and the very low friction coefficient lasted for at least 1000 sliding cycles. Observations using STM on the sliding surfaces confirmed that the stacking Ag(111) planes slid. The SOR-XD and RHEED verified that a tribo-induced orientation of polycrystal film occurs as Ag(111) sliding planes are oriented parallel to the sliding direction on the track. The friction force of as deposited epitaxial Ag films as a function of the load was constant. On the other hand, in the 5 nm thick Ag films annealed to form complete single crystals, the friction coefficient showed a strong load dependency. At a load of 250 mN or more, the annealed films showed a low and static friction coefficient. These results suggested that the shearing resistance of nanometre thick Ag layers exhibits a strong anisotropic performance within the thickness range of nanometres, along with an orientation of Ag during sliding. Experimental results of sliding tests were discussed on the contribution of surface atoms to the friction, an extraordinarily low wear rate of the Ag layers, and the relationship between the nanoscopic structure and macroscopic tribological performance.

Behavior of 3 mol% yttria-stabilized tetragonal zirconia polycrystal film prepared by slurry spin coating

A dense and uniform 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3YSZ) electrolyte film of 6 μm in thickness was fabricated by slurry spin coating on a porous NiO/3YSZ anode substrate. Composite cathodes of La 0.7Sr 0.3MnO 3 impregnated with Sm 0.2Ce 0.8O 1.9 were fabricated on the 3YSZ films. A single cell produced in this way was tested at 700, 750 and 800 °C with hydrogen as fuel and stationary air as oxidant. Test results revealed an open-circuit voltage of 1.04 V at 800 °C, and maximum power density of 551, 895 and 1143 mW cm −2 at 700, 750 and 800 °C, respectively. Impedance spectra results demonstrated that the cell performance was determined by the polarization resistance of the cathode.

Effect of annealing temperatures on microstructure of (Zr 0.8Sn 0.2)TiO 4 thin films grown by a sol–gel process

The impact of annealing temperatures on microstructures of zirconium tin titanate (Zr 0.8Sn 0.2TiO 4, ZST) thin films grown by a sol–gel process is proposed. ZST thin films were deposited along the (1 0 0) orientation p-type Si substrate and were characterized by XRD, AFM, SIMS and TEM. Amorphous and polycrystal films were grown successfully on Si substrates with different annealing temperatures. The chemical compositions of the films were detected and showed a uniform concentration distribution for all species. Due to the interface layer formed during the annealing process, the dielectric constants of 81-nm-thick ZST films in the present study were ∼16.

Growth of Epitaxial ZnO Film on Y-Plane LiNbO3 Substrate

A <0001> oriented polycrystal ZnO film is deposited on many types of substrate. However, an epitaxial ZnO film is deposited on only specific substrates, because it depends greatly on the lattice constant of the substrate. An epitaxial ZnO film with the c-axis oriented horizontally on some types of substrate has been reported. In this study, a <1100> orientated epitaxial ZnO film has been deposited on a pre-heat-treated Y-plane (0110) LiNbO3 substrate for the first time. A <0001> oriented polycrystal ZnO film has also been deposited on this substrate without pre-heat-treatment. Thus, two orientation directions can be controlled by pre-heat-treatment for the first time. Moreover, their applications to shear bulk wave transducers and surface acoustic wave devices are discussed.

Thickness and optical constant determination of hydrogenated amorphous silicon thin film from transmittance spectra of ellipsometer

To cope with the problem that the thickness and optical constants of thin film can not be measured accurately when deposited on a transparent substrate due to the incoherent reflected-light from the back-side of the substrate, a method is presented to determine the thickness and optical constants of hydrogenated amorphous silicon (a-Si:H) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) from the transmittance spectra of ellipsometer only. The influence of the substrate temperature (Ts) and the gas temperature (Tg) before glow discharge on the thickness and optical constants of a-Si:H thin films is analysed. The results show that the thickness of a-Si:H thin films determined by transmittance spectra agrees well with that measured by scanning electron microscopy (SEM). The optical constants of the films deduced from the transmittance spectra accord with the results obtained by other researchers. This method can be applied in deposition of amorphous or polycrystal thin films on transparent substrates.

Influence of Ag Underlayer on the Microstructure and the Magnetic Properties of Fe Thin Films

Fe thin films were deposited directly and via Ag underlayer on glass and MgO(100) substrates by MBE. Polycrystal Fe films grew on the glass substrate while single crystal films grew on the MgO(100) substrate. Fe film growth followed the Volmer-Weber mode for both cases. The Fe film structure was influenced by the surface roughness of Ag underlayer at the early stage of film growth. The relationships between the Fe thin film morphology and the magnetic properties are discussed.

Structural and optoelectronic characterization of TiO2 films prepared using the sol–gel technique

TiO2 is a versatile material that makes for fascinating study in any of its several physical forms: monocrystal, polycrystal, powder or thin film. Its enhanced photosensitivity to UV radiation and excellent chemical stability in acidic and aqueous media point to its excellent potential for use in a variety of applications, such as solar cells, electronic devices, chemical sensors and photocatalysts. Of late, thin films of TiO2 have permitted the study of physical and chemical properties that are almost impossible to examine in powders. Using the sol–gel technique, it was possible to prepare TiO2 films, and to specifically modify their characteristic properties by means of annealing treatments. Optical measurements carried out on sol–gel derived films produced results similar to those found in films prepared using the sputtering technique. The use of TiO2 films facilitates the study of the behaviour of crystalline structure, grain size, photoresponse, electrical conductivity in both darkness and light and energy band gap (Eg) as a function of treatment temperature. For the first time, it has been demonstrated that the photoconductivity of TiO2 becomes apparent at a treatment temperature of 350 °C, which means that below this temperature the material is not photosensitive. The photosensitivity (S) of TiO2 films prepared by the sol–gel technique reaches values between 100 and 104, surpassing by more than two orders of magnitude the photosensitivity of TiO2 in powder form. In addition, it was possible to study the surface crystalline structure, where TEM studies clearly revealed both the polycrystalline order and the atomic arrangements of the TiO2 films. Our findings will afford us an opportunity to better study the nature of TiO2 and to enhance its performance with respect to the above-mentioned applications.

Comparative Analysis of VO2 Thin Films Prepared on Sapphire and SiO2/Si Substrates by the Sol–Gel Process

VO2 thin films were successfully grown on sapphire and SiO2/Si substrates by the sol–gel process. The VO2 phase was well formed during simplified low pressure annealing in oxygen. The films prepared on sapphire directly crystallized to the VO2 phase without passing through intermediate phases with increasing the annealing temperature, resulting in highly [010]-oriented films on Al2O3(1010) substrate. In contrast, the polycrystal films grown on SiO2/Si reached the final VO2 phase with passing through several phases. Mixed phases existed at the interface between the film and substrate. For the films on sapphire, the phases with low-valent vanadium appeared drastically at the interface region along the depth, whereas the phase of the polycrystal film slowly changed into a low valence state at the initial stage of the interface and then returned to a high value. And both films showed an abrupt change in resistivity at the different transition temperature. The property of the interface may affect the crystallization and the metal–insulator transition of the films.

Compound semiconductors grown on porous alumina substrate as a novel hydrogen permeation membrane

A highly p-type-doped InGaAs film was grown on a porous alumina substrate by metalorganic chemical vapor deposition (MOCVD). This structure was proposed as a novel hydrogen selective permeation membrane. In the p-type film, hydrogen atoms are converted to protons by giving their electrons to the dopant atoms. The protons easily diffuse in the film at elevated temperatures and are desorbed as hydrogen molecules from the surface of the film. When the hydrogen gas is supplied to both side of the film and there is difference in pressure, only hydrogen can penetrate into the film and move to the lower-pressure side. Preliminary experimental results are shown in this paper. Large amount of hydrogen was found in both the epitaxial InGaAs film (grown on InP) and the poly-crystal InGaAs films (grown on sapphire and porous alumina). Hydrogen was desorbed when the film was annealed in nitrogen gas. Hydrogen was absorbed into the film again by annealing in hydrogen gas. Scanning electron microscope (SEM) pictures suggest that a dense poly-crystal film without pin-holes was grown on the porous alumina substrate.

High negative temperature coefficient of resistance of heteroepitaxial (Ba, Sr) TiO 3 single crystal films prepared by pulsed laser deposition

Heteroepitaxial (Ba, Sr)TiO 3 (BST) films were grown on cleaved single crystal <100> MgO substrates by pulsed laser deposition. Highly <100> oriented BST films with atomic flat surfaces were obtained. By measuring Current–Voltage characteristics, a significant negative temperature coefficient of resistance (about − 4.95% at 300 K) was observed which is different from the positive temperature effect as reported for poly-crystal BST films. As has been suggested the positive temperature coefficient of resistance is attributed to the temperature-dependent barrier height and width at grain boundaries. In this paper, the negative temperature effect of resistance observed in our experiment is discussed and explained by the activation of electrons trapped by oxygen vacancies and absence of grain boundaries. Deep level spectroscopy measurement indicated that the activation energy is approximately 0.31 eV, which is consistent with the value deduced from the slope of ln ⁡ R ∼ 1 T curve.

The ICP etching technology of 3C-SiC films

The dry etching technology is one of the key process in the 3C-SiC MEMS fabrication. In this paper, the 3C-SiC ICP etching technology will be studied. The etching gas components we used include CHF3, SF6 and O2. The polycrystal 3C-SiC films deposited on SiO2 layer were etched in different condition. The effects of the key process parameters such as the etching gas component, the gas flow, the source power, the bias power and the etching pressure on the etch characteristics are studied detailedly. According to the results, the optimal process was obtained. Finally, we used the optimal ICP etching process to fabricate resonator successfully. The work is important and useful to fabricate the 3C-SiC MEMS devices.

Influence of Annealing on the 1.5 μm Light Emission of Er-doped ZnO Thin Films and its Crystal Quality

Intensity variation of 1.5 μm light emission at room temperature from Er-doped epitaxial and polycrystal ZnO films depending on annealing temperature (773–1373 K) was studied. As-grown Er-doped epitaxial ZnO film emitted 1.5 μm photoluminescence(PL) higher than as-grown Er-doped polycrystal ZnO. It was found that the annealing in air increases PL intensity and the maximum PL intensity was obtained by annealing at optimal temperature (1073 K). Spectrum shape and intensity of 1.5 μm PL of Er-doped epitaxial ZnO after annealing at 1073 K resembled those of Er-doped polycrystal ZnO after annealing at 1073 K. X-ray diffraction measurement demonstrated that annealing improves crystal quality of Er-doped ZnO film. We assumed that the process of 1.5 μm light emission is dependent on local area placement of Zn and O atoms around Er as well as crystal quality of ZnO.

An investigation of preferred orientation of doped ZnO films on the 36° YX-LiTaO 3 substrates and fabrications of Love-mode devices

Love-mode surface acoustic wave (SAW) devices are very promising for liquid and gas media sensing applications because of high sensitivity. In this paper, an experimental study of the structures based on zinc oxide (ZnO) guiding layer and 36° YX-lithium tantalate (LiTaO 3) substrate with different sputtering conditions to deposit ZnO films is presented. Poly-crystal ZnO films with c-axis (002) orientation have been successfully grown on the 36° YX-LiTaO 3 substrate by RF magnetron sputtering technique. The deposited films were characterized as a function of argon–oxygen gas flow ratio, RF power, deposition pressure, and annealing temperature. Crystalline structures, stress, and surface roughness characteristics of the films were investigated by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements. Highly orientated (002) films were obtained under a base pressure of 10 mTorr, containing 40% oxygen and 60% argon at RF power of 60 W and a substrate temperature around 120 °C. The films were then annealed at 600 °C. Love-mode devices based on this structure (ZnO/IDT/36° YX-LiTaO 3) are presented.

Sub-nanosecond time resolved XAFS of laser excited thin Ge films

A facility at PNC-CAT in the Advanced Photon Source measures with sub-nanosecond time resolution both XAFS and diffraction on femtosecond laser-excited samples. XAFS measures with relatively high efficiency the time for the laser excitation to couple to the lattice, the sample temperature after reaching thermal equilibrium, any ablation of the sample with time, and, in many cases can distinguish between the amorphous and crystalline states. Preliminary measurements on 200 nm thick polycrystal Ge films indicate that the time for transferring the laser excitation to thermal heating of the lattice is less than 2 nanoseconds when the initial temperature is 560 K.

Microstructure and bactericidal ability of photocatalytic TiO2 thin films prepared by rf helicon magnetron sputtering

The present study investigates the microstructure and bactericidal ability of polycrystalline and epitaxial TiO2 thin films with anatase and rutile structure. Phase formation and the distortion of the lattice of the film compared with bulk are proved by TEM observation. HRTEM images assure the good crystal quality and compact structure of the films prepared by rf helicon magnetron sputtering. This obtained larger band gap due to the lattice deformation could contribute to the better photocatalytic effect of the anatase film.Bactericidal abilities evaluated by the photokilling E. Coli using film stick method under UV irradiation show the following result: Both single and polycrystal anatase films exhibit obvious bactericidal abilities while no distinguishing difference for them. On the other hand, no bactericidal ability is observed for rutile films in this work. The band gap value of rutile film is lower than the energy potential required to O2/O2− reductions according to the principle proposed by Fujishima et al. This resulted in the observed poor photocatalyst effect of rutile film.