Use Of Thin Films Research Articles

Crystallization process and thermal stability of Ge1Cu2Te3 amorphous thin films for use as phase change materials

The crystallization kinetics of amorphous Ge1Cu2Te3 (GCT) films prepared by sputter deposition were investigated by differential scanning calorimetry under non-isothermal conditions. An exothermic peak due to crystallization was observed in the temperature range 230–270°C. It was found that the local activation energy for crystallization is almost constant when the crystallization fraction is less than about 0.15 and then monotonically decreases with increasing crystallization fraction, which indicates that the crystallization of amorphous GCT films is a multi-step mechanism. The local Avrami exponent decreased from more than 5 to 1.7 with increasing crystallization fraction. It was demonstrated by the Ozawa method that GCT amorphous films show a higher thermal stability than Ge2Sb2Te5 amorphous films, with an estimated failure time of over 70years at 125°C, which is well beyond the data retention requirements of the International Technology Roadmap for Semiconductors. In addition, the thickness change in GCT amorphous films accompanying crystallization was measured by atomic force microscopy. The GCT amorphous film was found to show a thickness increase of only 2.0% on crystallization, which is desirable to enhance the endurance of phase change random access memory devices.

Sputtering deposition of amorphous cadmium stannate as transparent conducting oxide

In this work we studied deposition conditions by RF sputtering of ternary oxides of Cd and Sn, starting from Cd2SnO4 target and varying substrate temperature, sputtering power and deposition gas (from inert Ar to oxidizing 50% Ar–50% O2 atmosphere). The aim of this study was to obtain thin films for use as Transparent Conducting Oxide (TCO). TCOs are oxides that couples low sheet resistance and high transparency that find application in many fields like solar cells, light emitting diodes and transparent thin film transistors.Thin films functional properties were characterised by means of sheet resistance and transmittance measurements in the visible region, and film composition and structure were investigated by total reflection X ray fluorescence and glancing incidence X ray diffraction. Morphology was studied by Atomic Force Microscopy and Scanning Electron Microscope and showed very smooth surface suitable for solar cells application. Composition and phase analysis allowed us to discuss possible correlation of film structure with functional properties. Deposition in inert atmosphere at 400°C substrate temperature was selected for its low sheet resistance and high transparency that are comparable to the ones of commercial TCOs like indium tin oxide or SnO2: F. The thin film obtained in these conditions was amorphous, and it crystallized into CdSnO3 ilmenite phase when annealed at 700°C; segregation of Sn3O4 was also observed. Since sheet resistance of thin films increases after annealing treatments, amorphous thin film was selected for future applications.

Investigations of As-S-Se thin films for use as inorganic photoresist for digital image-matrix holography

Abstract As-S-Se chalcogenide thin films are successfully employed in classical and dot-matrix holography as inorganic photoresists for obtaining a relief-phase hologram. However using these films for image-matrix hologram recording has not been studied due to some features of image-matrix technology. For the applied research of the optical properties of As-S-Se films an experimental device of digital image-matrix holographic recording based on 100 mW 405 nm semi-conductor laser and Spatial Light Modulator (SLM) has been created. The device has the following main parameters: 140 × 105 µm frame size; laser intensity during exposure 10 W/cm2. With the help of this device diffraction grating and security holograms were recorded on As-S-Se thin films. The work reported herein presents results of an experimental study of how diffraction efficiency (DE) of the received relief-phase holographic gratings depends on an exposure and period. Diffraction grating profiles and speed of etching corresponding to different exposure doses are shown. Hologram samples with DE = 65% have been received which allows for using chalcogenide film as alternative to organic photoresists in applied dot-matrix and image-matrix holography.

Synthesis and Characterization of Nanocrystalline TiO2 Thin Films for Use as Photoelectrodes in Dye Sensitized Solar Cell Application

In the event of escalating gasoline prices resulting from threatened oil reserves and nuclear meltdowns endangering the quality of life in near future it is expected that science would make priceless contributions to green technology and come up with environment friendly solutions. Third generation photovoltaic solar cells have attracted researchers in this respect. Dye-sensitized solar cell (DSSC) is a novel category of economical photovoltaic cell that belongs to the group of thin film solar cells. The ability of developing and modifying nanoparticles has given scope to produce dye sensitized solar cells with a principle similar to that of photosynthesis. Promising efficiencies of around 11% have given scope for investment and advancement of this sector to get cheaper renewable solar energy available in abundance. The underlying principle uses a network of nanocrystalline TiO2 on a glass plate coated with transparent conducting oxide. Sensitization of nanocrystalline TiO2 network with dye enhances the efficiency of the cell. Nanocrystalline TiO2 has been synthesized by modifying titanium isopropoxide with diacetyl acetone, diacetyloxime and also by peptization with HNO3. The mean size of the particles is around 10–20 nm. Dip and spin coated electrodes (ITO glass substrate) with different thicknesses by multi layer deposition has been annealed at different temperatures. The deposited thin films are characterized by FTIR, UV-Vis and XRD for structural conformation, transmittance and phase confirmation respectively. Photovoltaic characterization has been done under dark condition to establish the semiconductor diode properties of the synthesized and modified TiO2 pastes using source meter, and model parameters have been evaluated by considering equivalent diode model for the solar cell.

Drastic reduction of leakage current in ferroelectric Bi 3.15Nd 0.85Ti 3O 12 films by ionizing radiation

Bi 3.15Nd 0.85Ti 3O 12 (BNT) ferroelectric thin films were grown on Pt/Ti/SiO 2/Si substrates by a sol–gel method. The samples were exposed to different dosage of ionizing radiation. Distortions in the crystalline structure, changes in the surface roughness and decrease in the remnant polarization were observed after radiation. For films subjected to 100 Mrad radiation, decrease in the leakage current up to four orders of magnitude was also observed, which can be explained by the increased grain boundary barrier height. Our results suggest that ionizing radiation could be an effective tool in modifying the properties of ferroelectric thin film for use in non-volatile memory devices.

Vacuum vapour phase polymerised poly(3,4-ethyelendioxythiophene) thin films for use in large-scale electrochromic devices

Large-scale electrochromic devices were manufactured using vacuum vapour phase polymerised (VPP) poly(3,4-ethylenedioxythiophene) (PEDOT). Homogeneous 3,4-ethylenedioxythiophene (EDOT) and water vapour distribution within the large 115 L VPP chamber is paramount for the reproducible synthesis of high conductivity PEDOT thin films. Obtaining these conditions, however, was not trivial. The issue was resolved by synthesising PEDOT under vacuum, however, this altered the dynamics of the polymerisation process. As a result, surfactant addition, monomer and water vapour distribution, monomer and chamber temperature, and polymerisation times were all systematically investigated. Controlling these parameters has resulted in PEDOT with conductivity exceeding 1100 S · cm −1, with a best of 1485 S · cm −1, and electrochromic devices with an optical switch of Δ%Tx ≥ 50%. The resulting high conductivity and optical range are due to long undisrupted PEDOT polymer chains coupled with low levels of oligomers within the matrix.

Electro-optic characterization of epitaxial Ba 0.7Sr 0.3TiO 3 thin films using prism coupling technique

In this work, we present our study on evaluating electro-optic properties of Ba 0.7Sr 0.3TiO 3 thin films by prism coupling technique. Ferroelectric Ba 0.7Sr 0.3TiO 3 thin films were epitaxially deposited on LaNiO 3 electroded MgO (001) single-crystal substrates using pulsed laser deposition. Refractive indices and thickness of the Ba 0.7Sr 0.3TiO 3 thin film were determined with a rutile prism (Metricon 200-P-2) under zero electric field at a wavelength of 632.8 nm. The angular shift of guided mode was observed subsequently with a conductive prism (Metricon 200-P-4aC) when electric field was applied to the thin film sample. The ordinary refractive index n o changes 2.2% under a dc voltage of 4 V ( E ∼ 11 V/μm). The linear electro-optic coefficient tensor r 13 is thus calculated to be about 780 pm/V, showing the excellent potential of Ba 0.7Sr 0.3TiO 3 thin films for use in active optical devices.

Solid State Thermochromic Materials

Solid-state thermochromic materials undergo semiconductor to metal transitions at a 'critical temperature', Tc. This review begins by describing the phenomenon of thermochromism, whereby the optical properties of a material change reversibly as a result of a change in temperature. The various different types of thermochromism will be introduced with a focus on the thermochromism exhibited by solid-state materials. The fundamental chemical principles that describe the electronic structure and properties of solids, and the chronological developments in the theory behind the thermochromic transitions (such as, the effects of electron-electron interactions and structural phase changes due to lattice distortions) that led to the discovery of the semiconductor-to-metal transition, are presented. An extensive discussion of vanadium and titanium oxides is presented with a particular focus on vanadium (IV) oxide since its transition temperature is closest to room temperature. Observations and current understanding of the nature of the semiconductor-to-metal transition exhibited by these materials is detailed. The possibility of fine-tuning the transition temperature by introducing various dopants into the vanadium (IV) oxide lattice is examined and the effects of dopant charge and size is examined. Solid-state thermochromic materials may be exploited in areas such as microelectronics, data storage, or intelligent architectural glazing, thus are required to be synthesised as thin films for use in such applications. The numerous synthetic techniques (PVD, sol-gel method, PLD, CVD, APCVD and AACVD), for making metal oxide thermochromic thin films are described in reference to the production of vanadium (IV) oxide and compared. Finally rare earth nickelates exhibiting thermochromism are described. Copyright © 2010 VBRI press.

Electrical and optical properties of In–Zn–Sn–O thin film deposited on polymer substrates through facing targets co-sputtering system

The Indium Zinc Tin Oxide (IZTO) thin films for use as a transparent electrode in flexible display were deposited on polycarbonate (PC) and polyethersulfone (PES) and glass substrates at room temperature by facing targets sputtering (FTS). When two sheets of targets are installed on an FTS system, one of target is IZO and other is ITO. As a result, we could prepare the IZTO thin films with the resistivity of under 10 − 4 [Ω cm] and IZTO thin films deposited on PC, PES and glass substrate showed an average transmittance over 80% in visible range (400–800 nm) in all IZTO thin films except for IZTO thin film that was deposited in a filled chamber with pure Ar gas.

Persistence in photoconductivity and optical property of nanostructured copper (II) phthalocyanine thin films

The optical and photoconductive properties of nanostructured copper (II) phthalocyanine (CuPc) surface cells have been studied at room temperature (30 °C). The change in the conductivity of the surface type sample cells under illumination of light was studied as a function of duration and wavelength of photoexcitation. The photoconductivity spectrum of a film of CuPc surface cell does not agree with the absorption spectrum. Particularly for the photoexciting wavelengths in the region 400–500 nm, the photoconductivity shows an appreciable value (or comparatively higher value), although the absorbance in this region is minimum or very less. The change in current under illumination of light and after turning it off has indicated that photoinduced effects persist for a longer period of time even after turning off the illumination of light of various wavelengths and duration. An increase in persistence in photocurrent was noticed with the repeated exposure within a short interval of time. Such studies are important for searching new types of electrically conducting systems (semiconductors) in the form of nanostructured thin films for use as photoactive materials in optoelectronic and memory devices.

Fabrication of Organic Thin Films for Copper Diffusion Barrier Layers Using Molecular Layer Deposition

AbstractDevice scaling predicts that copper barrier layers of under 3 nm in thickness will soon be needed in back-end processing for integrated circuits, motivating the development of new barrier layer materials. In this work, nanoscale organic thin films for use as possible copper diffusion barrier layers are deposited by molecular layer deposition (MLD) utilizing a series of self-limiting reactions of organic molecules. MLD can be used to tailor film properties to optimize desirable barrier properties, including density, copper surface adhesion, thermal stability, and low copper diffusion. Three systems are examined as copper diffusion barriers, a polyurea film deposited by the reaction of 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED), a polyurea film with a sulfide-modified backbone, and a polythiourea films using a modified coupling chemistry. Following deposition of the MLD films, copper is sputter deposited. The copper diffusion barrier properties of the film are tested through adhesion and annealing tests, including 4-point bend testing and TEM imaging to examine the level of copper penetration. The promise and challenges of MLD-formed organic copper diffusion barriers will be discussed.

Comparative study of resistivity characteristics between transparent conducting AZO and GZO thin films for use at high temperatures

This paper compares in detail the resistivity behavior of transparent conducting Al-doped and Ga-doped ZnO (AZO and GZO) thin films for use in an air environment at high temperatures. AZO and GZO thin films with thicknesses in the range from approximately 30 to 100 nm were prepared on glass substrates at a temperature of 200 °C by rf superimposed dc or conventional dc magnetron sputtering deposition, pulsed laser deposition or vacuum arc plasma evaporation techniques. In heat-resistance tests, the resistivity was measured both before and after heat tests for 30 min in air at a temperature up to 400 °C. The resistivity stability of AZO thin films was found to be always lower than that of GZO thin films prepared with the same thickness under the same deposition conditions, regardless of the deposition technique. However, the resistivity of all AZO and GZO thin films prepared with a thickness above approximately 100 nm was stable when heat tested at a temperature up to approximately 250 °C. It was found that the resistivity stability in both GZO and AZO thin films is dominated by different mechanisms determined by whether the thickness is below or above approximately 50 nm. With thicknesses above approximately 100 nm, the increase in resistivity found in GZO and AZO films after heat testing at a temperature up to 400 °C exhibited different characteristics that resulted from a variation in the behavior of Hall mobility.

Latest innovations in large area web coating technology via plasma enhanced chemical vapor deposition source technology

In this article, the authors discuss the latest results of our development of large area plasma enhanced chemical vapor deposition (PECVD) source technologies for flexible substrates. A significant challenge is the economical application of thin films for use as vapor barriers, transparent conductive oxides, and optical interference thin films. Here at General Plasma the authors have developed two innovative PECVD source technologies that provide an economical alternative to low temperature sputtering technologies and enable some thin film materials not accessible by sputtering. The Penning Discharge Plasma (PDP™) source is designed for high rate direct PECVD deposition on insulating, temperature sensitive web [J. Modocks, Proceedings of the Society of Vacuum Coaters, 2003 (unpublished), p. 187]. This technology has been utilized to deposit SiO2 and SiC:H for barrier applications [V. Shamamian et al. Proceedings of the Flexible Displays and Manufacturing Conferrence, 2006 (unpublished)]. The Plasma Beam Source (PBS™) is a remote plasma source that is more versatile for deposition on not only insulating flexible substrates but also conductive or rigid substrates for deposition of thin films that are sensitive to the high ion bombardment flux inherent to the PDP™ technology. The authors have developed PBS thin film processes in our laboratory for deposition of SiO2, SiC:O, SiN:C, SiN:H, ZnO, FeOx, and Al2O3. [M. A. George, Conference Proceedings of the Association of Industrial Metallizers, Coaters, and Laminators (AIMCAL), 2007 (unpublished)]. The authors discuss the design of the patented sources, plasma physics, and chemistry of the deposited thin films.

A Novel Label-Free Optical Biosensor Using Synthetic Oligonucleotides from E. coli O157:H7: Elementary Sensitivity Tests

SiO2-TiO2 thin films for use as fiber optic guiding layers of optical DNA biosensors were fabricated by the sol-gel dip coating technique. The chemical structure and the surface morphology of the films were characterized before immobilization. Single probe DNA strands were immobilized on the surface and the porosity of the films before the hybridization process was measured. Refractive index values of the films were measured using a Metricon 2010 prism coupler. On the surface of each film, 12 different spots were taken for measurement and calculation of the mean refractive index values with their standard deviations. The increased refractive index values after the immobilization of single DNA strands indicated that immobilization was successfully achieved. A further refractive index increase after the hybridization with target single DNA strands showed the possibility of detection of the E. coli O157:H7 EDL933 species using strands of 20-mers (5′-TAATATCGGTTGCGGAGGTG -3′) sequence.

Optical and surface characterization of amorphous boron nitride thin films for use as blood compatible coatings

The aim of this work is the investigation of the haemocompatibility properties of homogeneous and amorphous boron nitride (a-BN) thin films, through the adsorption of two basic blood plasma proteins, human serum albumin (HSA) and fibrinogen (Fib). The a-BN thin films were grown onto c-Si(100) substrates under different values of substrate bias voltage, employing the radio frequency (RF) magnetron sputtering technique. For the consideration of the optical, compositional and structural properties of the films, Spectroscopic Ellipsometry (SE) in the Vis–UV spectral region was used, while for the study of surface topography and surface charge distribution as well as of the wetting properties of the a-BN thin films, Atomic Force Microscopy (AFM), Electric Force Microscopy (EFM) and Contact Angle measurements were additionally employed. The properties of the thin films were correlated with their haemocompatibility, through the estimation of the ratio of HSA/Fib surface concentration. The sp 3 content of the samples does not seem to correlate with the haemocompatibility of the a-BN thin films. However, the surface properties determine the thrombogenicity potential of the studied samples. More precisely, the a-BN films with a less negatively charged surface exhibit the smallest possibility of clot formation, possibly due to the interactions between the charged chains of the Fib molecules and the a-BN surface, while slight changes in the surface roughness do not affect their haemocompatibility properties. The wetting properties determine the thickness of the adsorbed Fib as well as the ratio of HSA/Fib surface concentration.

Hydrothermal preparation of octadecahedron Fe 3O 4 thin film for use in an electrochemical supercapacitor

A Fe 3O 4 film with regularly edge-affected cubic (octadecahedron) morphology was successfully prepared on stainless steel foil by a simple and benign hydrothermal process. The potential for the use of the film in a supercapacitor was tested by investigating the electrochemical behavior of the Fe 3O 4 film using cyclic voltammetry (CV) and galvanostatic charge/discharge tests. The Fe 3O 4 film showed a CV indicative of a typical pseudocapactive behavior in 1 mol L −1 Na 2SO 3 solution. Furthermore, this film exhibited a specific capacitance of 118.2 F g −1 at the current of 6 mA between −1 and 0.1 V with a capacity retention of 88.75% after 500 cycles.

Development of a liquid lithium thin film for use as a heavy ion beam stripper

A series of experiments was performed to investigate the feasibility of a liquid lithium thin film for a charge stripper in a high-power heavy ion linac. Various preliminary experiments using simulants were first conducted to determine the film formation scheme, to investigate the film stability, and to obtain the design parameters for a liquid lithium thin film system. Based on the results from these preliminary studies, a prototypical, high pressure liquid lithium system was constructed to demonstrate liquid lithium thin film formation. This system was capable of driving liquid lithium at ≲300 °C and up to 13.9 MPa (2000 psig) through a nozzle opening as large as 1 mm (40 mil) in diameter. This drive pressure corresponds to a Li velocity of >200 m/s. A thin lithium film of 9 mm in width at velocity of ∼58 m/s was produced. Its thickness was estimated to be roughly ≲13 μm. High vacuum was maintained in the area of the film. This type of liquid metal thin film may also be used in other high power beam applications such as for intense X-ray or neutron sources.

Deposition of silicon nitride thin films by hot-wire CVD at 100 °C and 250 °C

Silicon nitride thin films for use as passivation layers in solar cells and organic electronics or as gate dielectrics in thin-film transistors were deposited by the Hot-wire chemical vapor deposition technique at a high deposition rate (1–3 Ǻ/s) and at low substrate temperature. Films were deposited using NH 3/SiH 4 flow rate ratios between 1 and 70 and substrate temperatures of 100 °C and 250 °C. For NH 3/SiH 4 ratios between 40 and 70, highly transparent ( T ~ 90%), dense films (2.56–2.74 g/cm 3) with good dielectric properties and refractive index between 1.93 and 2.08 were deposited on glass substrates. Etch rates in BHF of 2.7 Ǻ/s and < 0.5 Ǻ/s were obtained for films deposited at 100 °C and 250 °C, respectively. Films deposited at both substrate temperatures showed electrical conductivity ~ 10 − 14 Ω − 1 cm − 1 and breakdown fields > 10 MV cm − 1 .

Atmospheric pressure chemical vapour deposition of thermochromic tungsten doped vanadium dioxide thin films for use in architectural glazing

Atmospheric pressure chemical vapour deposition of VCl 4, WCl 6 and water at 550 °C lead to the production of high quality tungsten doped vanadium dioxide thin films. Careful control of the gas phase precursors allowed for tungsten doping up to 8 at.%. The transition temperature of the thermochromic switch was tunable in the range 55 °C to − 23 °C. The films were analysed using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their optical properties were examined using variable-temperature transmission and reflectance spectroscopy. It was found that incorporation of tungsten into the films led to an improvement in the colour from yellow/brown to green/blue depending on the level of tungsten incorporation. The films were optimized for optical transmission, thermochromic switching temperature, magnitude of the switching behaviour and colour to produce films that are suitable for use as an energy saving environmental glass product.

Fabrication of amorphous silicon carbide films using VHF-PECVD for triple-junction thin-film solar cell applications

Preparation of intrinsic hydrogenated amorphous silicon carbide (i-a-SiC:H) thin films for use as a top cell of triple junction solar cells is presented. These films were deposited using very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique with monomethyl silane (MMS) gas as the carbon source. Deposition conditions were explored to obtain films with a wide gap and low defect density. It was confirmed that the hydrogen dilution ratio plays an important role in enhancing the film properties. Employing a-SiC:H film as an intrinsic layer of single junction cell, open-circuit voltage as high as 0.99 V has been achieved.