Crystallization of amorphous antimony films on silver films

The crystallization process in amorphous antimony films 70–330 Å thick evaporated onto silver films 10–150 Å thick which have previously been evaporated onto glass is directly observed through an optical microscope. The conditions under which the crystallization process in the amorphous antimony films is observed are found to be severely limited by the preparation conditions of the silver films. The crystallization can only be observed on silver films thinner than 30–40 Å which have previously been exposed to oxygen or nitrogen gas. The crystallization thickness of amorphous antimony films on these substrates is estimated to be 123-75 Å as the substrate temperature varies from 20 to 80 °C and the activation energy for crystallization to be 0.23-0.30 eV as the film thickness varies from infinity to 200 Å.     

Properties of indium tin oxide films prepared by ion-assisted deposition

Conducting transparent films of indium tin oxide were deposited by 100 eV oxygen-ion-assisted deposition. A refractive index of 2.13 at 550 nm was obtained for films deposited onto ambient temperature substrates. The refractive index decreased with increasing substrate temperature to a value of 2.0 at 400°C. The sheet resistance of films 135 nm thick decreased from 800 Ω/□ for layers deposited onto room temperature substrates to around 25 Ω/□ at 400°C. Structural studies revealed that ion-assisted deposition onto ambient temperature substrates produced amorphous films, and that at temperatures above 100°C the films exhibit In₂O₃ crystallinity. In addition, it was found that the number of voids in the ion-bombarded films was reduced relative to that in films produced by conventional reactive evaporation.     

Structural investigation of silicon films chemically vapour deposited onto amorphous SiO2 substrates

The influence of substrate temperature and the silane-to-nitrogen ratio on the structure of silicon films 0.5–0.6 μm thick deposited onto amorphous SiO₂ substrates was investigated by X-ray diffraction. The investigations were carried out for silicon films deposited at various temperatures in the range 500–750 °C and with various silane-to-nitrogen ratios in the range 3.04 × 10^-4-2.84 × 10^-3 by volume. The silicon films deposited at 500 °C were amorphous while the films deposited at 550 °C were randomly oriented polycrystalline. The films deposited in the temperature range 600–700 °C were polycrystalline with a preferred orientation that changed from 〈110〉 through 〈100〉 to 〈111〉. The structure of the films deposited at 750 °C was randomly oriented polycrystalline. Investigations of the influence of the silane-to-nitrogen ratio on the silicon film structure revealed that the structure of films deposited at a substrate temperature of 500 °C was independent of the silane-to-nitrogen ratio. The structure of the films deposited at 600 °C depended on the silane-to-nitrogen ratio and changed from polycrystalline with a 〈110〉 preferred orientation to randomly oriented polycrystalline when the ratio was increased. The structure of films deposited at 700 °C also depended on the silane-to-nitrogen ratio and changed from randomly oriented polycrystalline to polycrystalline with double preferred orientation (〈100〉 and 〈111〉) when the ratio was increased.     

Strain insensitive Ni-Co films over a wide composition range

The magnetic properties of vacuum deposited Ni-Co films have been studied as a function of film composition, film thickness, and substrate temperature. The experimental parameters ranged from 400-1000 Å for thickness 17-41-percent Ni for composition and room temperature to 300°C for the substrate temperature. It was found that the magnetoelastic strain coefficient approaches zero in the vicinity of 35-percent Ni in agreement with Tolman's result[1] and remains insensitive to film composition from 30-40- percent Ni. These results are in reasonably good agreement with calculations based on single crystal data and the expression of Callen and Goldberg [10]. The coercive force and anisotropy field are an order of magnitude larger than of nonmagnetostrictive Permalloy films. An unexpected result is an increased coercive field with increasing film thickness while the anisotropy field remains practically constant; the films become inverted at a critical thickness in the order of 750 Å For a wide variation of preparation parameters the crystallite size remained less than 100 Å     

Optical properties and solar selectivity of flash-evaporated copper sulphide films

The optical properties of copper sulphide films deposited onto glass and aluminium substrates using the flash evaporation technique were investigated. The films are stable and show good adhesive properties. A study of the optical properties of the films revealed that the films possess solar-selective properties. A film 7000 Å thick deposited onto aluminium showed a solar absorptance α_s of 0.92 with a thermal emittance ε_T (at temperature T = 100°C) of 0.20. The thermal emittance of the films increased linearly from 0.20 to 0.23 as the temperature was increased from 100 to 250°C. The films do not suffer from any UV degradation and can withstand temperatures as high as 150 °C for more than 250 h. Films coated on glass also show low values (about 0.20) of thermal emittance, thereby indicating the presence of intrinsic selective properties. The films on glass also possess excellent conducting properties and a film 2500 Å thick on glass has p-type conductivity with a sheet resistance of 25 Ω/□. X-ray and transmission electron microscopy studies revealed that the films were amorphous in nature. Auger electron spectroscopy studies carried out on the copper sulphide films indicated a slight excess of copper.     

Structure of vacuum-deposited thick films of NiCrAl

Vacuum-deposited thick films for resistors of low sheet resistance cannot be investigated by electron optical techniques because of their thickness. For the X-ray investigation of the structure of NiCrAl films it was necessary to produce very thick films by vapour deposition in a step-by-step manner. These films were deposited at a substrate temperature of 250 °C and subsequently tempered under a high vacuum for 30 min at 300, 400, 500 and 700 °C. It was found that these very thick as-deposited films are amorphous while reflections of the phases Ni₃Al, NiAl and chromium became visible with increasing annealing temperature.Thus the structure of these thick films corresponds to that found by electron optical techniques for thin films of the same composition.     

Stress Evolution With Temperature in Titanium‐Rich NiTi Shape Memory Alloy Films

Abstract: The effect of deposition temperature on residual stress evolution with temperature in Ti‐rich NiTi films deposited on silicon substrates was studied. Ti‐rich NiTi films were deposited on 3″ Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 °C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 °C and the lowest for the film deposited and annealed at 300 °C. All the three films were found to be amorphous in the as‐deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 °C) was similar for all three films although the spike in tensile stress, which occurs at ～330 °C, was significantly higher in the film deposited and annealed at 300 °C. All the films were also found to undergo partial crystallisation on heating up to 450 °C and this resulted in decrease in the stress values around 55–60 °C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 °C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.     

Epitaxial growth on MgO on (001) surfaces of silver single-crystal film substrates

The epitaxial growth of evaporated MgO films (<25–4000 Å) on smooth (001) surfaces of silver single-crystal film substrates at a temperature inthe range 25°–200°C has been studied by reflection high energy electron diffraction. At substrate temperatures below 150°C, MgO is oriented with its (111) plane parallel to the surface of the substrate. The (111) orientation is fibrous. At 150°C a major fraction of the deposit is oriented in parallel and at 200°C only the parallel orientation is observed. The deposit initially grows as oriented three-dimensional nuclei. As the film thickness increases to 500 Å, randomly oriented MgO is simultaneously formed at the surface. With further increase in thickness the degree of epitaxial orientation decreases and at 1000 Å a small amount of one- degree (111) orientation appears at the surface. At 4000 Å the surface orientation becomes one-degree (111); the (111) orientation is interpreted as a final growth orientation.     

The Effect of Substrate Temperature on the Optical Properties of MoO3 Nano-crystals Prepared Using Spray Pyrolysis

In this study, thin films of molybdenum oxide were prepared by spray pyrolysis technique on glass substrates. The influence of substrate temperature on their crystallographic structure, surface morphology, and optical properties was studied. The formation of a MoO₃ film on the substrate was confirmed through XRD analysis. Furthermore, the presence of the two phases α and β in each of the films was evident. The percentage of phase α varied from 55 % for the film deposited at 200 °C up to 97 % for the film deposited at 400 °C. According to SEM images, MoO₃ films have a sponge-type structure on the order of nanometers. Both the optical gap and the refraction index strongly depend on substrate temperature. The optical gap decreases from 3.63 eV for the film deposited at 150 °C up to 3.30 eV for the one prepared at 400 °C. On the contrary, the refraction index measured at 800 nm increases from 1.54 up to 1.61 for the films prepared at 150 °C and 400 °C, respectively.     

The ohmic stability and low temperature coefficient of resistance of Cu-Ni/Au-Ni multilayers obtained in ultrahigh vacuum by controlled co-evaporation

For compositions around 43 at.% Ni, thin films of CuNi alloys more than 1200 Å thick deposited in ultrahigh vacuum (UHV) onto a fused silica substrate by controlled co-evaporation from two separate copper and nickel sources show low negative temperature coefficients of resistance (TCRs) (-10^-4 to -10^-6 °C^-1) and a satisfactorily high stability in the temperature range 20–300 °C in UHV. In the atmosphere, however, the ohmic behaviour of the films shows hysteresis and appreciable instability due to oxidation.Thin Au-Ni films (38 at.% Ni) have a higher positive TCR (+2 × 10^-4 °C^-1) but they have the advantage of being less oxidized in atmospheric air up to 150 °C.In order to obtain unoxidizable multilayers with a low TCR we prepared CuNi films 1300 Å thick and stabilized them by annealing. AuNi films 200 Å thick were then deposited onto the CuNi films by controlled co-evaporation.After the annealing process the TCR was about -3 × 10^-6 °C^-1 from 20 to 150 °C. The ohmic stability tested from 20 to 150 °C in nitrogen and then in the atmosphere showed no appreciable zero balance drift or ohmic instability.     

High thermal stability,electrical and optical properties of amorphous IGZO film by coating ultrathin amorphous ITO film as barrier layer

As one kind of well known amorphous transparent conductive oxide films, In–Ga–Zn–O (IGZO) based films were broadly used as electric functional layer in optoelectronic devices. As IGZO film is sensitive to temperature and oxygen, and its electrical and optical properties may probably be deteriorated after subsequent high temperature and air atmosphere. In this work, amorphous indium tin oxide (ITO) layer with two adjustable type of thickness were employed to improve the thermal stability of IGZO films. The doubled ITO/IGZO films were deposited on glass by magnetron sputtering and annealed at high temperatures subsequently to investigate its thermal stability. Accordingly, the crystal structure, optical and electrical properties of ITO/IGZO films were further studied. The XRD results demonstrated that the annealed IGZO films could keep amorphous structure, and the ITO/IGZO films were consisted of uniform small particles which showed comparable dense structure and closely integration with the glass substrate. Furthermore, the sheet resistance results indicated that the increased thickness of top ITO film could suppress oxygen and improve thermal stability of electrical property. Moreover, the transmittance in the visible range was about 85%, and showed a little increase after annealing. The protective ITO layer was found to keep improved thermal stability, good electrical and optical properties at temperatures up to 550 °C.     

Crystallization control of the amorphous buffer layer in hydrogenated nanocrystalline silicon

Hydrogenated nanocrystalline silicon film have been deposited by RF sputtering in a pure hydrogen plasma at a substrate temperature of 150°C. The unintentionally grown amorphous buffer layer was almost completely crystallized at an annealing temperature as low as 150°C. By combining infrared absorption measurements and electron microscopy observations, the critical role of dihydride species, SiH₂, in the crystallization process have been clearly evidenced and discussed.     

Electron microscopy studies of sprayed thin tin dioxide films

Electron microscopy studies of thin tin dioxide films (about 80 nm thick) prepared by spraying from a mixture of SnCl₄ and ethyl acetate indicate that such films are amorphous at substrate temperatures of 340–350°C, partially crystallized at 360–410°C and polycrystalline at 420–500°C. Grains about 40 nm in size were found for all polycrystalline structures, independent of the substrate temperature. Only SnO₂, having values of the interplanar spacing d in agreement with the ASTM data, was clearly identified by electron diffraction. Scanning electron microscopy studies indicate smooth surfaces with pits of varying size and density depending on the preparation conditions.     

An economic CVD technique for pure SnO 2 thin films deposition: Temperature effects

A modified new method of CVD for formation of pure layers of tin oxide films was developed. This method is very simple and inexpensive and produces films with good electrical properties. The effect of substrate temperature on the sheet resistance, resistivity, mobility, carrier concentration and transparency of the films has been studied. The best sheet resistance obtained at substrate temperature of 500 °C was about 27 Ω/cm². X-ray diffraction showed that the structure of deposited films was polycrystalline with a grain size between 150–300 Å. The preferred orientation was (211) for films deposited at substrate temperature of about 500 °C. FESEM micrographs revealed that substrate temperature is an important factor for increasing grain size and modifies electrical parameters. UV-visible measurement showed reduction of transparency and bandgap of the layers with increasing substrate temperature.     

Contact reactions between amorphous silicon and single-crystal metallic films

Single-crystal palladium, chromium and gold films with (100) orientation were made by electron beam evaporation of the metal onto a rock-salt substrate maintained at about 400°C. Subsequently, an amorphous silicon film was deposited at room temperature onto the metal film in the same pump-down to form a reaction couple. Reactions between the amorphous silicon and the single-crystal metallic films were studied by transmission electron diffraction and microscopy. We found that metals such as palladium and chromium which form silicides react uniformly over the entire interface with the silicon, but gold which forms no stable silicides shows a non-uniform interfacial reaction. The nucleation and growth rate of silicon crystals in the Au-Si reaction was measured.     

Preparation of anatase TiO2 thin films for dye-sensitized solar cells by DC reactive magnetron sputtering technique

Anatase titanium dioxide (TiO₂) thin films are prepared by DC reactive magnetron sputtering using Ti target as the source material. In this work argon and oxygen are used as sputtering and reactive gas respectively. DC power is used at 100 W per 1 h. The distance between the target and substrate is fixed at 4 cm. The glass substrate temperature value varies from room temperature to 400 °C. The crystalline structure of the films is determined by X-ray diffraction analysis. All the films deposited at temperatures lower than 300 °C were amorphous, whereas films obtained at higher temperature grew in crystalline anatase phase. Phase transition from amorphous to anatase is observed at 400 °C annealing temperature. Transmittances of the TiO₂ thin films were measured using UV-visible NIR spectrophotometer. The direct and indirect optical band gap for room temperature and substrate temperature at 400 °C is found to be 3.50, 3.41 eV and 3.50, 3.54 eV respectively. The transmittance of TiO₂ thin films is noted higher than 75%. A comparison among all the films obtained at room temperature showed a transmittance value higher for films obtained at substrate temperature of 400 °C. The morphology of the films and the identification of the surface chemical stoichiometry of the deposited film at 400 °C were studied respectively, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface roughness and the grain size are measured using AFM.     

2.24 Structural and electrical properties of discontinuous gold films on glass

In the present work thin gold films are investigated in the thickness interval 10–160 Å. The films are deposited in UHV on to glass substrates at room temperature and with an electric field in the substrate plane. In the thickness interval 10–45 Å the film is discontinuous and the size distribution of the islands as determined from electron micrographs is described with a log-normal distribution function. The onset of the in situ electrical conduction at the average thickness 45 Å makes it possible to measure the film resistance as a function of the film thickness during the condensation. At the thickness 53 Å stable metallic continuous paths are formed and the film achieves metallic properties. The fraction of the surface covered with material and the island density are measured 20 h after the deposition. Both these entities change rapidly at the stage when the film grows to be metallic continuous.     

Optical and structural characteristics of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films synthesized from yttrium acetylacetonate

Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)₃). The decomposition of Y(acac)₃ was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)₃. The rest of the complex is then dissociated or degraded partially until Y₂O₃ is obtained in the final step with the presence of carbon related residues. Then the Y(acac)₃ was used to synthesize Y₂O₃ thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction. The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures (450–550 °C), resulted in polycrystalline with a cubic crystalline phase.     

Low temperature crystallization of amorphous silicon carbide thin films for p–n junction devices fabrication

Metal induced crystallization technique was used to crystallize hydrogenated amorphous silicon carbide (a-SiC:H) thin films at low temperatures. Two types of substrates, silicon and silicon carbide were considered and the substrate effects on the final crystallized film were studied. About 200 nm a-SiC:H films were deposited and crystallized successfully on n-type Si and n-type 6H SiC substrates at a temperature of 600 °C. Fourier Transform Infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) analysis confirmed the crystallization of a-SiC:H film. Current–voltage (I–V) and capacitance–voltage (C–V) measurement confirms the formation of p–n junction with rectification over five orders of magnitude from ?2 V to 2 V.     

Formation of a silicate layer between lead oxide and a silicon-wafer surface during heat treatment

PbO thin films were deposited on a silicon substrate by plasma-enhanced chemical vapour deposition (PECVD) using Pb(C₂H₅)₄ and oxygen at 250°C. The interdiffusion reaction phenomena between the PbO thin film and the silicon substrate during heat treatments were investigated in a horizontal furnace in the temperature range between 350 and 650°C under a nitrogen ambient for 1 h. The PECVD PbO film deposited on the silicon substrate at 250°C, was amorphous and contained carbon-related contaminants which could almost be removed by heat treatment at 350°C. The PbO on the silicon substrate initially participated in the interdiffusion reaction in the temperature range between 400 and 450°C. This produced a silicate layer containing lead components. The lead content in the film varied with the depth of film and heat-treatment temperature. Metallic lead was observed as a cluster in the specimen heated at 550°C. This cluster was produced by the agglomeration of metallic lead originating from PbO decomposition. The oxygen source for silicate formation was not ambient oxygen coming from the decomposition of Pb–O bonding. The metallic lead clusters dissolved as weakly bound metallic lead or as an unbound nanosized metal particle in the silicate layer at 650°C. This revised version was published online in November 2006 with corrections to the Cover Date.