As-evaporated Films Research Articles

Mixed phase formation of SnS-SnO2 on air-annealed thermally evaporated SnS thin films

The present study examined the influence of annealing temperature on structural, morphological, electrical, and optical properties of thermally evaporated tin sulfide (SnS) thin films. The annealing of the prepared thin films has been carried out in the ambient atmosphere at a temperature between 100 and 300 °C. Structural, Optical, and compositional investigation has been performed using various characterization techniques. The X-ray diffraction pattern exhibits the mixed phase of SnS-SnO2 for the annealed films, ascribed to the reaction of SnS with atmospheric oxygen. A band gap in the 1.7–1.94 eV range was estimated from the Tauc-plots for all the films under investigation. The stoichiometric composition ratio of Sn/S=1.0 was obtained for the as-evaporated films. However, it deviates from the air-annealed SnS thin films. The air-annealed SnS thin films exhibit resistivity, carrier concentration and mobility in the range of 5.03–17.7 Ω-cm, 1.48 × 1018 – 2.18 × 1018 cm−3, and 0.04–1.05 cm2/V-s, respectively. The acquired results from this study elucidate the phase conversion of SnS thin films annealed in an ambient atmosphere. The current study aims to find an optimal absorber layer to enhance photovoltaic device performance.

Nested potassium hydroxide etching and protective coatings for silicon-based microreactors

We have developed a multilayer, multichannel silicon-based microreactor that uses elemental fluorine as a reagent and generates hydrogen fluoride as a byproduct. Nested potassium hydroxide etching (using silicon nitride and silicon oxide as masking materials) was developed to create a large number of channels (60 reaction channels connected to individual gas and liquid distributors) of significantly different depths (50–650 µm) with sloped walls (54.7° with respect to the (1 0 0) wafer surface) and precise control over their geometry. The wetted areas were coated with thermally grown silicon oxide and electron-beam evaporated nickel films to protect them from the corrosive fluorination environment. Up to four Pyrex layers were anodically bonded to three silicon layers in a total of six bonding steps to cap the microchannels and stack the reaction layers. The average pinhole density in as-evaporated films was 3 holes cm−2. Heating during anodic bonding (up to 350 °C for 4 min) did not significantly alter the film composition. Upon fluorine exposure, nickel films (160 nm thick) deposited on an adhesion layer of Cr (10 nm) over an oxidized silicon substrate (up to 500 nm thick SiO2) led to the formation of a nickel fluoride passivation layer. This microreactor was used to investigate direct fluorinations at room temperature over several hours without visible signs of film erosion.

Sequential Evaporation of Bi-Te Thin Films with Controllable Composition and Their Thermoelectric Transport Properties

We report a simplified sequential evaporation route that can deposit compositionally controllable Bi-Te thermoelectric (TE) thin films without the need for a highly controlled facility. Te and Bi granules were used as starting materials, with their ratio being adjusted to obtain Bi-Te films with different compositions and thicknesses. The as-evaporated and annealed films were subjected to structural and morphological analysis, and their transport properties were measured. X-Ray diffraction data revealed multiple phases for most films. Energy-dispersive x-ray spectroscopy showed that the film composition was Te-enriched due to the large vapor pressure difference of Te and Bi. A Bi2Te3 single phase was obtained in the annealed films, having nominal composition of BiTe1.2. The existence of impurity phases, such as Bi4Te3 or elemental Te, was found in all the as-evaporated films and in the annealed films with other nominal Te/Bi ratios, which degraded the TE properties of the films by increasing their electrical conductivity and reducing their Seebeck coefficient. A pure Bi2Te3 film with nominal Te/Bi ratio of 1.2 exhibited a maximum power factor of 7.9 × 10−4 W m−1 K2 after annealing at 200°C. This work demonstrated a simple, undemanding, reliable method to deposit Bi-Te-based TE thin films that can be utilized to fabricate low-cost TE microgenerators.

Effect of microstructure on Au/sapphire interfacial thermal resistance

We deposit Au films on single crystal sapphire substrates by sputtering and evaporation methods. The microstructure characteristics such as crystal textures, grain sizes, and fraction of contacted area of the films are examined by x-ray diffraction and transmission electron microscopy. The sputtered films have an average grain size of about 200 nm and perfectly attach to the substrates; the as-evaporated films partially attach to the substrate; the grain size varies from 10 to 30 nm, and after annealing, increases to 50 nm. Au2Al phase is observed in the annealed samples. The interfacial thermal resistance is measured by a frequency domain thermoreflectance method. The thermal resistance of the sputtered Au/sapphire interfaces is 35.5×10−9 m2 K W−1, and those of the evaporated samples are up to three times as large as this value. The change in interfacial thermal resistance is explained by the effect of detachment using a parallel arranged thermal resistance model, the effect of grain size, and the influence of chemical bonding at the interfaces.

Structural and optical properties of In 35Sb 45Se 20− xTe x phase-change thin films

Physical properties of In 35Sb 45Se 20− x Te x thin films with different compositions ( x=2.5, 5, 7.5, 10, 12.5 and 15 at %) prepared by electron beam evaporation method are studied. X-ray diffraction results indicate that the as-evaporated films depend on the Te content and the crystallized compounds consist mainly of Sb 2Se 3 with small amount of Sb 2SeTe 2. Transmittance and reflectance of the films are found to be thickness dependent. Optical-absorption data indicate that the absorption mechanism is direct transition. Optical band gap values decrease with increase in Te content as well as with increase in film thickness.

On the atomic structure of thin amorphous Ge-Sb-Te films

The structure of thin films of Ge2Sb2Te5 was studied by high-resolution transmission electron microscopy (HRTEM) and by X-ray diffraction (XRD). The as-evaporated films prepared by flash evaporation were amorphous. Nearly, all the atoms were randomly distributed but even in as-evaporated films small areas with some ordering were noticeable. The number and size of the ordered areas increased with thermal treatment of films to temperatures ∼80 °C, i.e., ∼70 °C below the crystallization temperature of amorphous Ge2Sb2Te5. After thermal treatment, small embryos of nucleation centers (size <8 nm) were formed. According to XRD measurements the films as a whole were still fully amorphous. The crystallite model of the structure of amorphous solids is then partly valid, at least for Ge2Sb2Te5. We expect that it can be applied also for other Ge–Sb–Te-based films, as well as for the other amorphous chalcogenides. The possible impact of the formation of nucleation “embryos” on storage time of data in optical and electrical phase-change memory materials and devices is discussed.

Structural and optical properties of Ge-As-Te thin films

Chalcogenide glasses with Ge 10 As x Te 90− x ( x = 20, 25, 30, 35, 40, 45 and 55 at.%) were prepared by melt quenching technique. The glass transition temperature, the crystallization temperature, the melting temperature and the glass-forming tendency were determined from the differential scanning calorimetry measurements. The structural and optical properties of Ge 10 As x Te 90− x thin films prepared by electron beam evaporation were studied. X-ray diffraction showed that the as-evaporated films are amorphous and crystallize after annealing depending on the As content. The transmittance and reflectance of the films are found to be thickness dependent. The optical-absorption data indicate that the absorption mechanism is direct transition. The optical band gap values are increased with increasing As content while they decrease with increasing the film thickness. Upon annealing the transmittance and the optical band gap decrease whereas the reflectance and the refractive index increase.

Annealing behavior and solid-state reactions of Pd–Ge alloy thin films

Abstract Solid-state reactions and amorphous Ge crystallization for various ratios of thickness (or composition) in Pd–Ge alloy thin films after annealing have been investigated by transmission electron microscopy. Besides polycrystalline Pd (p-Pd) and amorphous Ge (a-Ge), polycrystalline Pd2Ge (p-Pd2Ge) phase is also formed in as-evaporated films. During annealing at 250 °C, polycrystalline Pd2Ge and PdGe are formed. The experimental results indicate that the formation of Pd2Ge and PdGe compounds may be dominant at low annealing temperatures, and also affect amorphous Ge crystallization. The reactions are sensitively dependent on the annealing temperatures and the thickness ratio of Pd and Ge films. The reactions and amorphous Ge crystallization are mutually competitive in Pd–Ge alloy thin films.

Structure of As–Se and As–P–Se glasses studied by Raman spectroscopy

The structure and the optical properties of bulk and thin films of the amorphous AsxSe100−x (x=0, 28.6, 33, 40, 50 and 57.1) and AsxP4−xSe3 (x=0, 1, 2, 3 and 4) chalcogenide systems have been studied in this work. Bulk samples were prepared from high purity elements, and thin films (d≈1000 nm) were deposited by the vacuum thermal evaporation. Both types of AsxSe100−x samples show long-term chemical stability. In the case of AsxP4−xSe3, especially the films, chemical stability of as-prepared samples generally decreases with increasing phosphorus content. Structure of bulk and film samples has been determined by Raman spectroscopy as a function of exposure to light. It was found that exposure to halogen lamp light causes structural changes in short range order mainly in phosphorus containing films such that their structure approaches the structure of bulk samples of the same composition. In addition, the medium and/or long range structures are also affected by light, which then further contribute to the photo-induced changes in the optical properties of as-evaporated films.

Photothermal deflection spectroscopy of chalcogenide glasses

Photothermal deflection spectroscopy has been applied to optical absorption measurements in As2S3, Se, and As–S glasses. The spectroscopic method is demonstrated to be suitable for evaluation of small absorption in thin samples, while its accuracy is affected by light scattering. For As2S3, as-evaporated films give higher residual absorption than those of the bulk. In the As–S system, As2S3 shows the most prominent weak absorption tail, and As17S83 exhibits a peculiar spectrum. The origins of these features are discussed.

Relaxation processes in film waveguides based on chalcogenide vitreous semiconductors

The investigation of relaxation changes of parameters of film waveguides based on as-evaporated As-S and As-Se films lias been carried out. The regularities which permit to connect the said regularities with the peculiarities of structural transformations in films in the after condensation period are determined. The nature and peculiarities of the structure-stipulated optical anisotropy in researched.

Photo-induced ring-to-chain conversion in as-evaporated films of amorphous selenium

Abstract Results of an in-situ extended X-ray absorption fine-structure study of photostructural changes in films of amorphous selenium are reported. It is shown that at first the average coordination number decreases by about 10%. As time elapses, the initial coordination number is restored. This change is attributed to breaking of ring-like structural fragments with subsequent formation of longer chains. This model is supported by a Raman scattering experiment demonstrating the disappearance upon photoexcitation of a peak at about 112cm−1 characteristic of rings.

Photo-induced ring-to-chain conversion in as-evaporated films of amorphous selenium

Photo-induced ring-to-chain conversion in as-evaporated films of amorphous selenium

Structural evaluation of epitaxially grown organic evaporated films by total reflection x-ray diffractometer

An in-plane-type total reflection x-ray diffractometer was newly constructed, and the epitaxial growth of paraffin molecules (n-C33H68) vacuum-evaporated onto a KCl (001) surface was investigated. The molecular chains in as-evaporated films were shown to arrange themselves parallel to the 〈110〉 direction of the KCl substrate. After the evaporation, moreover, some molecules were revealed to reorient and tend to deviate their c axis by about ±5° from the 〈110〉 direction of the KCl crystal, probably because of the lattice mismatchings between the paraffin and substrate crystals.

In-Situ X-Ray Observation of Molecular Structure in Organic Thin Films during Evaporation Process by Total Reflection In-Plane X-Ray Diffractometer

The in-plane X-ray diffractometer equipped with a vacuum evaporation apparatus was newly developed utilizing the total reflection phenomenon. The measuring system was applied to conduct an in-situ observation of the crystal growth and structural changes in the n-C33H68 molecules during an evaporation process. The results revealed that a certain amount of molecules in the as-evaporated films orient their (010) planes parallel to the surface of the SiO2 substrate. Moreover, the integrated intensity of the 110 reflection showed variation in the thickness dependence, suggesting that the molecular orientation altered as the interaction between the substrate and the adsored molecules became weaker.

Ion irradiation damage in nanocrystalline FeCo thin films

Abstract Thin films of the Fe60Co40 alloy produced by electron beam evaporation under ultra high vacuum are irradiated at 77 K with different ions: He, Ne, Ar, Xe. The as-evaporated films are polycrystalline with a very small grain size of about 8 nm and exhibit the structure of nanocrystalline materials formed of a crystalline component inside the grains and a second component in the grain boundaries with a random atomic arrangement. We have continuously measured the radiation damage as a function of the ion dose at 77 K using in situ electrical resistivity measurements. An important resistivity decrease is observed at high doses but only with heavy ions. This particular behaviour is discussed in relation with both the displacement cascade effects and the microstructural state of the films. It is suggested that nanocrystalline materials could be useful to study thermal spike behaviour and specific effects about displacement cascades.

Observation of molecular orientation in evaporated films of n-paraffins

Molecular orientation, its distribution and long periods of n-paraffin thin films evaporated on glass substrate were measured by an energy dispersive X-ray diffractometer. The number of crystallites whose c ∗ axes are normal to the glass substrate (normal orientation) increases with temperature up to the temperature at which a phase transition to a disordered state occurs in ordinary paraffin crystals. This orientational change was observed to be an irreversible process. The orientational distribution has a narrow peak with a full width at half-maximum of less than 0.1° around normal orientation even in as-evaporated films. Its population around normal orientation is increased by heating to be about three times as high as that of the as-evaporated films. This is the first report on accurate observations of the orientational distribution in evaporated thin films.

Doping of InSb thin films with elements of groups II and VI

The processes of incorporation of tellurium, selenium, sulphur, cadmium and zinc into flash-evaporated InSb thin films are investigated. The dopings are performed by the co-evaporation of the dopant materials and InSb from separate sources. Their effects are investigated using Hall effect measurements carried out at 77K both on the as-evaporated films and on the same films subjected to regrowth from the melt. The electrical properties of regrown films are close to those of bulk InSb with the same donor or acceptor concentration. The electrical and structural properties of as-evaporated films doped with tellurium, selenium and sulphur are consistently explained on the assumption that, on doping, thin layers of In 2Te 3, In 2Se 3 and In 2S 3 respectively are formed on the film grains. At a substrate temperature T s of 700K the sticking coefficients of tellurium, selenium and sulphur are close to unity and those of cadmium and zinc are several orders of magnitude lower. The main features of the process of incorporation of the dopants can be qualitatively explained within a thermodynamic framework describing the chemical equilibrium.

Ａｕ蒸着膜の擬圧縮破壊 ＩＩ

The compressive-type fracture of vacuum-evaporated gold films was observed directly in a scanning electron microscope and a transmission electron microscope by mounting the film on uniblock substrates. Gold films from 400 to 3400A in thickness used in this study were heated at different temperatures ranging from 300 to 800 °C. It was shown that as-evaporated films fractured in a smooth straight-line type while heated films exibited a graininterior type fracture. The predominant propagation for fracture of thicker films (>700A) occurred within the grain-interior by the formation of dislocation fissure. The total fracture strain of the film was usually of the order of 0.2 to 4.8% at fracture. The measurements showed that for thickness thicker than about 1000A there was an increase in the strain with increasing thickness.

Effects of Bi2O3 dissociation on the electrical properties of thermally evaporated films of bismuth oxide

Bismuth oxide films have been evaporated in an oil diffusion pump system at pressures of ∼0.50 mPa onto glass substrates held near room temperature. The films have been characterized by x-ray photoelectron spectroscopy (XPS), electron and x-ray diffraction, and measurements of the electrical properties. Whereas the as-evaporated films are found to contain a lower suboxide of bismuth and metallic bismuth, the oxidation of these films by heating in air results in bismuth (III) oxide. A capacitance density of ∼2.0 mF/m2 is observed for films as-evaporated. These films at room temperature show a thickness dependent dielectric constant and strong frequency and temperature dependence. In contrast, the oxidized films have a capacitance density of ∼1.0 mF/m2, a thickness independent dielectric constant, and show little dependence on frequency and temperature. In general, as-evaporated films compared to oxidized films have a high dielectric dissipation factor, temperature coefficient of capacitance, percentage variation in capacitance, and the defect density.