Quartz Crystal Thickness Monitor Research Articles

(Invited) Halide Perovskite Thin Films via Alternate Laser Deposition: Change in the Physical Properties with the Layered Structures

We have formed methylammonium lead iodide (MAPbI3) perovskite by alternating irradiation of PbI2 and CH3NH3I (MAI) with an infrared laser in an ultra-high vacuum to elucidate the growth mechanism and realize structural control of MAPbI3 [1]. In this study, we found that MAPbI3 contains both tetragonal and orthorhombic phases, and the ratio of these phases systematically changes depending on the thickness of alternating layers of PbI2 film.In the sample preparation, the PbI2 and MAI powder targets were alternately irradiated with an infrared laser (λ = 808 nm) to convert them into molecular beams, and then alternately deposited on a synthetic fused silica substrate at room temperature. The deposition rate of PbI2 was controlled to be about 0.1 nm/s using a quartz crystal microbalance thickness monitor. The deposition amount of MAI was adjusted by changing the deposition time while the evaporation pressure was fixed at 4×10-4 Pa. Four different multilayer samples consisting of [PbI2/MAI] × n (n = 1, 2, 5, 10) were prepared under the condition that the total thickness of PbI2 was 300 nm.By analyzing the crystal structures by X-ray diffraction measurements, the prepared samples were found to have the following two unique features: (1) In the samples with n = 1, unreacted PbI2 was present in addition to MAPbI3, while in the samples with n = 2, 5, and 10, only MAPbI3 was observed, indicating a complete solid-phase reaction. (2) The full width at half maximum and peak position of the diffraction peak for MAPbI3 at 2θ = 14.0° ~ 14.1° were different among the samples, and thus we performed the analysis by peak separation. As a result, it was determined that the tetragonal (002) and orthorhombic (020) diffraction peaks were included.Defining r tetra and r ortho as the ratio of the tetragonal and orthorhombic diffraction peak areas to the total peak area, it was found that r tetra : r ortho changes significantly with the thickness of the PbI2 layer. Specifically, r tetra : r ortho =[0.64 : 0.36], [0.39 : 0.61], [0.20 : 0.80], and [0.25 : 0.75] for n =1, 2, 5, and 10, respectively. It is noteworthy that the orthorhombic MAPbI3, which usually appears below 161 K due to the phase transition [2], is contained in the MAPbI3 film formed at room temperature, and that the mixing ratio of tetragonal and orthorhombic phases varies systematically with the thickness of the alternating deposited PbI2 films.[1] K. Kawashima et al., Sci. and Tech. of Adv. Mater. 18, 307 (2017).[2] N. Onoda-Yamamuro et al., J. Phys. Chem. Solids 51, 1383 (1990).

Fabrication and estimation of optical constants of hydrophobic Ta2O5 thin films

Present study investigates the optical properties and film thickness estimation of tantalum oxide (Ta2O5) thin films of various thicknesses, deposited by physical evaporation technique. The optical constants and thickness of deposited films were estimated by using envelope method. The thickness value obtained from this method has been compared with in-situ (quartz crystal thickness monitor) as well as Ex-situ (Coherence Correlation Interferometry) thickness estimation techniques. Refractive index calculated by envelope method was also validated using Reflectometer. These thickness values were used for the estimation of other optical constants such as refractive index, absorption and extinction coefficients. Contact angle measurement studies are also performed on uncoated as well as Ta2O5 coated glass substrates, which indicate the hydrophobic nature of these films.

Effect of Doping Concentration on the Optical Properties of Indium-Doped Gallium Arsenide Thin FILMS

Effects of indium doping (concentration 0.2, 0.3 and 0.4%) on the optical properties of GaAs thin films were studied. Thin films of 600 nm were grown onto chemically and ultrasonically cleaned glass substrate by thermal evaporation method in high vacuum (~10-4 Pa) at 50°C fixed substrate temperature. The samples were annealed for 15 minutes at a fixed temperature of 200°C. The thicknesses of films were being measured in situ by a quartz crystal thickness monitor during deposition. The transmittance and reflectance data were found using UV-VIS-NIR spectrophotometer in the photon wavelength range of 310 ~ 2500 nm. These data were utilized to compute the absorption coefficient, refractive index, extinction co-efficient and band gap energy of the studied films. Here transmittance was found 78 for 0.2% indium doping concentration. The band gap energy decreased with the increase of doping concentration.Journal of Bangladesh Academy of Sciences, Vol. 40, No. 2, 179-186, 2016

Effects of in-situ Heat-Treatment on Residual Stress Dependent Optical Properties of ZnI2 Thin Films

ZnI2, a hygroscopic chemical compound in thin film form has been investigated for residual stress dependent optical properties in in-situ heat-treated conditions up to 80oC. The tetragonal structured ZnI2 thin films were grown by thermal evaporation on glass substrates with deposition rate optimized at 1-2 nm/s and vacuum maintained at 10−6 Torr. Quartz crystal thickness monitor was used to monitor the film thickness and deposition rate during the film growth. Measurements like UV spectroscopy, X-ray diffraction and scanning electron microscopy were performed under low relativity humidity conditions (~40%). For in situ heat-treatment, films were heated inside the film growth glass chamber with inbuilt thermocouple to do temperature measurements. The in-situ heat-treatment of above-mentioned ZnI2 thin films shows a linear decrease in film thickness with increase of in-situ treatment temperature. The x-ray diffraction studies revealed a decrease in residual stress parameter with decreasing film thickness. Morphological studies support the internal stress behavior based on density effect or packing density of the films. The direct type-band gap for ZnI2 films found to increase almost linearly with increasing heat treatment temperature (and corresponding decreasing film thickness) from 3.25 eV to 4.06 eV. In-situ experiments estimate a much larger value of 8.39 eV of the band gap for a stress free perfect crystal of ZnI2 and give an indication of a large value of its deformation potential.

PECULIARITY OF FORMING TRANSPARENT CONDUCTING FILMS ON BASIS OF OXIDES INDIUM-TIN FOR CONTACTS ON GAN-BASED LIGHT EMITTING DIODES

ITO thin films were prepared by electron beam deposition method over a range of processing conditions. The target material used in this study was an ITO pellet with a composition: In2O3 90 wt% and SnO2 10 wt%. The evaporation conditions were: a vacuum of 5 × 10-4 or 4 × 10-2 Pa and the rate of evaporation were controlled within the range 0.075–0.4 nm/s. The thickness of thin film was controlled by using a quartz crystal thickness monitor, resulting in films having 200 nm. After the deposition, the samples were annealed in a thermal annealing furnace in air or nitrogen at 300-700 оC for 30 s. Experiments aimed at choosing the optimal atmosphere for annealing the films yielded the different results. Indium tin oxide coatings properties were researching as a function of the deposition atmosphere and conditions of a thermal annealing. The ITO films deposited and annealed under the optimized conditions work well as the transparent conducting electrode in the light emitting diodes based on GaN.

P15: Preparation of longitudinal sections of hair samples for analysis by multi-modal mass spectrometry imaging

Introduction Hair testing is a powerful tool routinely used for the detection of drugs of abuse in toxicology and forensic applications. The analysis of hair is highly advantageous as it can provide prolonged detectability versus that in biological fluids and chronological information about drug intake based on the average growth of hair. However, current methodology routinely involves complex and time-consuming sample preparation followed by gas or liquid chromatography coupled with mass spectrometry. Mass spectrometry imaging has been employed to monitor the distribution of cocaine throughout a single hair sample. Methods Longitudinal sections of hair samples were accomplished using an in-house built device before mounting onto a conductive glass slide. Prior to analysis samples were gold-coated using a Quorum Technologies SC7640 sputter coater (New Haven, USA) equipped with a FT7607 quartz crystal microbalance stage and FT690 film thickness monitor to deposit a 1 nm thick gold layer. Data was then acquired using a Physical Electronics TRIFT II TOF-SIMS (Physcial Electronics, USA) equipped with an Au liquid metal gun tuned for 22keV Au + primary ions. Data was analysed and visualized using WinCadence software version 4.4.0.17 (Physical Electronics). Results Scanning electron microscopy was performed to asses the quality of the longitudinal sections of hair samples. The images obtained from the sectioned hair sample showed the exposed medulla, cortex and a portion of the cuticle observed as a narrow layer surrounding the cortex. Metal assisted-secondary ion mass spectrometry (MetA-SIMS) images of longitudinally sectioned hair samples showed the distribution of endogenous elements such as sodium, potassium and calcium. Analysis of user hair samples showed the distribution of cocaine at m/z 304 and the major fragment at m/z 182 derived from the neutral loss of benzoic acid. Conclusion The work reported here presents a device for the preparation of longitudinal sections of hair samples without the use of an embedding medium for analysis by MetA-SIMS. By using high spatial resolution imaging a more precise time-line on drug intake can be obtained.

Effect of substrate temperature on the optical properties of thermally evaporated ZnS thin films

Zinc Sulfide (ZnS) thin films were formed onto cleaned glass substrates using the thermal evaporation method in vacuum. The substrate temperature was varied between as- deposited and 150 °C, keeping the film thickness and the rate of evaporation fixed at 200~nm and 0.3~nm \cdot s^{-1}, respectively. The film thickness was measured in situ by a quartz crystal thickness monitor. The structure of the films was ascertained by x-ray diffraction (XRD) method. The XRD spectra show that the films are polycrystalline in nature, which possess hexagonal structure. The optical properties of the films were ascertained by UV-VIS-NIR spectrophotometer (photon wavelength ranging between 300 and 2500~nm). The optical transmittance and reflectance were utilized to compute the absorption coefficient, band gap energy and refractive index of the films. Nature of the optical transition of the films has been observed in direct allowed with band gap energies between 3.37 and 3.46~eV depending on substrate temperatures. The refractive index was found to vary inversely with incident photon energy.

On-line characterisation of copper vapour evolution from linear vapour source generated using strip electron beam

In electron beam assisted physical vapour deposition (EB-PVD) technique, the online characterization of the evaporator is essential for process optimisation and control. In applications such as decorative and corrosion resistance coating, the knowledge of time average distribution of vapour is essential, whereas in some real time applications such as isotope purification, surface hardening and alloying etc., real time knowledge of vapour distribution and vapour propagation is important. The online characterization of various parameters related to the evaporator and associated processes using least expensive techniques is necessary to know the process throughput. Measurement of atom flux using quartz crystal thickness monitor can be one such techniques. The experimental studies were carried out to characterize the evaporator using thickness monitor by measuring copper vapour propagation and distribution over the two dimensional source. The experimental data measured at two heights corresponding to aspect ratio 2 and 3 are presented and the behaviour of expanding vapour is discussed. This technique can also be used to estimate the source temperature from the deposition rate data, which is discussed in the paper with its validation using measured temperature using two-colour pyrometer.

Investigation of an expanding copper plasma across a transverse magnetic field generated by strip-type electron-beam

The electron beam assisted thermal processes are well-established technique for various applications such melting, evaporation, isotope purification, ion-implantation etc. The processes are time average, wherein process is carried out over a larger duration so that real time dependent variations gets averaged out. During electron beam evaporation and atomic beam generation, ions also get generated inherently due to interaction of primary and back-scattered electrons with the atomic vapour along with other routes like Saha ionization, secondary electron ionization etc. The presence of ions has a bearing in the quality of deposited films and influence the ion implantation process. It also has strong effect on dilution factor in isotope purification. Thus the knowledge of ion content, its distribution and evolution in the freely expanding atomic beam in vacuum is important for any process optimisation in electron beam evaporation applications. The thermal ion content in atomic vapour for a given element as a function of aspect ratio (height/length) and source Knudsen number can be used as most inexpensive technique to characterized the evaporation on time average as well as teal time processes. With this intension, a series of experiments were carried out in a 100 kW strip beam evaporator with 130mm strip electron gun with copper as target material. A wedge shaped copper atomic beam is generated from a two dimensional evaporating source (120mm × 6mm) by impingement of the electron beam up to 90kW power. Disk type Langmuir probe is used for measuring I-V characteristic plots for deriving the thermal ion flux. The measurements are carried out as a function source Knudsen number (depends on incident electron beam power), and the probe distance from source that defines the aspect ratio. Along with probe data, the atom flux is also simultaneously measured using quartz crystal thickness monitor. The evolution of ions and atoms with distance from source is compared.

Hydrogen absorption mechanism in obliquely deposited [formula omitted] thin film

Hydrogen absorption mechanism in obliquely deposited MmNi 4.5 Al 0.5 thin films has been investigated in the present work. Thin films of 1150 Å thickness were prepared using the oblique deposition technique at different angles ( θ = 0 ∘ , 30 ∘ , 45 ∘ , 60 ∘ and 75 ∘ ) simultaneously at a pressure of 10 - 5 Torr and at room temperature. The thickness of the film was measured and controlled using a Quartz Crystal Thickness Monitor. Hydrogen charging of samples was carried out at 1 atm hydrogen pressure and discharging at 10 - 5 Torr pressure. This charging and discharging lead to saturation of thin films at 1 atm hydrogen pressure in the fourth cycle. The resistance of MmNi 4.5 Al 0.5 thin films increases on charging with 1 atm hydrogen and decreases on discharging at 10 - 5 Torr hydrogen pressure, which finally becomes constant in the fourth cycle indicating the saturation stage. Such types of thin films will find applications in the field of hydrogen energy where the amount of hydrogen required is limited to couple of grams only.

Activation energy of obliquely deposited [formula omitted] and [formula omitted] thin films

The effect of hydrogen absorption on the electrical resistance and activation energy of MmNi 4.5 Al 0.5 thin film was investigated. The samples were prepared by oblique deposition at different angles ( θ = 0 ∘ , 30 ∘ , 45 ∘ , 60 ∘ , and 75 ∘ ) simultaneously at a pressure of 10 - 5 Torr at room temperature and thickness of thin film were measured using quartz crystal thickness monitor. It was found that the resistance and activation energy of MmNi 4.5 Al 0.5 thin films increases with the angle of deposition. The activation energy of MmNi 4.5 Al 0.5 H x films is found to be higher than MmNi 4.5 Al 0.5 films for the same deposition angle and also increases with angle of deposition. The activation energy of hydrogenated samples in lower temperature range is found to increase with hydrogen charging cycle but in higher temperature range activation energy of hydrogenated samples is found to decrease due to discharge of hydrogen.

Control of porosity in fluoride thin films prepared by vapor deposition

We have measured the porosity in thin films of lithium fluoride (LiF), magnesium fluoride (MgF2), barium fluoride (BaF2), and calcium fluoride (CaF2) as a function of the substrate temperature for films deposited by thermal evaporation onto glass substrates. The amount of porosity in the thin films was measured using an atomic force microscope and a quartz crystal thickness monitor. The porosity was very sensitive to the substrate temperature and decreased as the substrate temperature increased. Consistent behavior was observed among all of the materials in this study.

Pulsed laser deposition of nanostructured Ag films

Abstract Ultra-thin (0.5–5 nm) films of Ag have been prepared by pulsed laser deposition in vacuum using a 26 ns KrF excimer laser at 1 J cm −2 . The deposition was controlled using a Langmuir ion probe and a quartz crystal thickness monitor. Transmission electron microscopy showed that the films are not continuous, but are structured on nanometer size scales. Optical absorption spectra showed the expected surface plasmon resonance feature, which shifted to longer wavelength and increased in strength as the equivalent film thickness was increased. It is shown that Maxwell Garnett effective medium theory can be used to calculate the main features of optical absorption spectra.

Size- and temperature-dependent thermoelectric and electrical properties of Bi 88Sb 12 alloy thin films

The thin films of Bi 88Sb 12 of different thicknesses have been vacuum deposited on glass and silicon substrates using the flash evaporation method. The structural characterization was carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The composition and thicknesses of as-grown and annealed films were measured by the quartz crystal thickness monitor and Rutherford back scattering spectroscopy (RBS). The thermoelectric power and electrical resistivity measurement have been carried out on the films in the temperature range 100–300 K. The thickness dependences of electrical resistivity and thermoelectric power of thin films have been analyzed using the effective mean-free path model. The thermoelectric power factors of films have been calculated and the nature of carrier scattering in these films has been reported.

Electrical resistivity of thermally evaporated bismuth telluride thin films

Semiconducting chalcogenide thin films have been receiving considerable attention in the recent years because of their wide applications in the various fields of science and technology. The studies of the electronic properties of semiconductors have been largely stimulated by attractive micro-electronic device applications. Among the various V–VI compounds, Bismuth Telluride (Bi2Te3) is an established low-temperature thermo electric material and is widely employed in thermoelectric generators and coolers. The present work deals with the structural and the electrical characterization of Bi2Te3 thin films vacuum deposited on well-cleaned glass substrates. A constant rate of deposition was maintained through out the process. To obtain uniform and homogeneous film thickness through out on all the substrates a rotary drive was employed. Quartz crystal thickness monitor was used to measure the thickness of the samples. From the X-ray diffractogram the Bi2Te3 films are found to be amorphous at lower thicknesses and posses hexagonal polycrystalline structure at higher thickness, having lattice parameters a=4.44 Å and c=29.40 Å. The grain size of the Bi2Te3 thin films before annealing and after annealing are found to be 100 and 160 Å, respectively. The micro-strain and the dislocation density are found to decrease after annealing. The thermogravimetry–differential thermal analysis (TG–DTA) studies revealed that the Bi2Te3 films are non-decomposable. Electrical resistivity, TCR measurements have been carried out as a function of varying temperatures in the range 303–453 K are found to show the size effect. Analyzing the size dependence of electrical resistivity it is found that the electrical resistivity is a linear function of the reciprocal of thickness of the film. The energy gap of Bi2Te3 thin film was calculated from the graph lnρ vs. 1/T and it is found that the energy gap decreases with increasing thickness. From the negative values of TCR, it is inferred that Bi2Te3 films exhibit semiconducting behavior.

Characterization of zinc phthalocyanine (ZnPc) for photovoltaic applications

Zinc phthalocyanine (ZnPc) is a promising candidate for solar-cell applications, because it is easily synthesized and is non-toxic to the environment. Recently, phthalocyanine (Pc) was considered by many researchers as the active part in all-organic solar cells, i.e. plastic solar cells. It is a self-assembling liquid crystal developed from a common deep-blue-green pigment. It exhibits a characteristic structural self-organization, which is reflected in an efficient energy migration in the form of extinction transport. In this paper we have report structural, surface morphological, optical and thermal properties of flash-evaporated zinc phthalocyanine thin films. The samples were prepared by using a vacuum coating unit on well-cleaned glass substrates under a pressure of 7×10-6 Torr. A constant rate of evaporation (1 A/s) was maintained throughout the evaporation of the ZnPc thin films. A rotary drive was employed to obtain uniform thickness during the evaporation. Thicknesses of the films were monitored by a quartz-crystal thickness monitor and were cross verified by the multiple-beam interferometry technique. The X-ray-diffraction pattern reveals the crystalline nature of the films deposited at higher substrate temperatures. Scanning electron microscope and scanning probe microscope nanoscope studies were carried out to determine the surface uniformity and homogeneity of the films for interfacing and application purposes. All the films were found to possess small crystallites less than 100 nm in size. The optical transmittance measurements were carried out using a spectrophotometer in the visible region (400–800 nm) and the films were found to be absorbing in nature. The band gap of the ZnPc thin films is 1.97 eV and the optical transition was found to be direct and allowed. The absorption coefficient, extinction coefficient and refractive index of the ZnPc films were evaluated and the results are discussed. Differential scanning calorimetry studies of ZnPc films were carried out and a phase transition from α to β was observed at 538 K.

Irradiation effect on microstructure and cmr of La(Sr)MnO3, the film grown by MBE

The role of disorder is of considerable importance in modulating the magneto transport properties of the doped perovskites as revealed by intensive experiments made on single crystal manganites of various compositions e.g, La1−x Srx MnO3 (x = Ca, Pr). The colossal magneto resistance (CMR) is most pronounced near the ferromagnetic (F) to paramagnetic transition temperature (associated with metal to insulator transition) can be improved by inserting suitable amounts of lattice defects. While such intrinsic CMR effect can be observed only under high magnetic field, in granular films MR can be observed under low field as well. Disorder has an important role to play in such a regimen, also. There have been a few studies carried out to investigate the influence of lattice disorder by ultra heavy ion irradiation on CMR effect. In this paper, we report our results on proton irradiation induced disorder on certain films with contrasting properties of La0.75Sr0.25MnO3 (LSMO) thin films deposited on Si (111) substrates. The results exhibit the grain-boundary effects on the magneto transport. The films were prepared in oil free Varian MBE -360 S. P. A. Lein # SII/745 PICOTORR 450 thin film deposition system. It has already been established that high quality epitaxial films of the manganites can be prepared by this technique [5]. Details and procedures used can be found in [6]. The 3.0 × 6.0 × 0.5 mm3 (111) oriented Si single crystals were used for growing consecutive layers of La0.75Sr0.25MnO3 with different thickness (75–1000 A). The detailed steps of the film deposition in the MBE set-up are as follows: Silicon substrate surface is thoroughly cleaned by a series of cleaning procedures: ultrasonic vibration in acetone medium followed by boiling in HNO3 medium which is followed by cleaning again by ultrasonic vibration in acetone medium. Finally it is boiled in HCl. Flowing dry nitrogen gas dries the surface. After thorough cleaning, the substrate is loaded in to the pre-preparation chamber. Before loading the sample the pre-preparation chamber is cleaned by flowing oxygen followed by nitrogen. The temperature of the chamber is raised in order to degas the chamber surface. After loading the substrate on the sample holder the chamber is evacuated by a set of turbo pumps and titanium sublimation ion pumps. The vacuum reaches down to ∼4.0 × 10−9 Torr. The actual film growth chamber is separately evacuated by a set of turbo pumps and ion pumps to reach a vacuum level ∼10−11 Torr. It requires approximately 75 h of evacuation to reach this level. The loaded substrate is transferred from the pre-preparation chamber to the actual growth chamber. The vacuum is maintained at ∼10−11 Torr. The oxygen and the magnetization of the films by virtue of ion irradiation. Monolayer at the surface of the substrate is removed by ion milling. It is important to remove this monolayer in order to improve the film adhesion and to enhance degree of epitaxy. The substrate temperature is raised to ∼800 ◦C which governs the rate of depositionnucleation and growth of the film. The deposition of the layers takes place through energization of the target ingots (La and Mn as the case may be) by high energy electron beam (727–850 eV) into vapors and subsequent condensation of the evaporated atoms (or molecules) at the surface of the substrate. The rate of deposition is governed by—apart from the rate of evaporation or evaporation flux (which is measured by the mass spectrometer and quartz crystal thickness monitor)—a complex process of surface adsorptiondesorption which, in turn, is governed by the substrate temperature. Nucleation of the seed layer is important which modulates the subsequent deposition process and the adhesion of the film. The deposition rate is found to be 0.1 A s−1 in this case and is measured by quartz crystal thickness monitor calibrated by ellipsometry and X-ray reflectivity. Several researchers [11–15] have studied the exact procedure of deposition. In our case, we have studied the reflection high-energy electron diffraction (RHEED) pattern and Auger electron spectra (AES) of the films to judge the quality of the films. The multilayer films, thus prepared, are irradiated with 28 MeV proton from a Pelletron. The fluence is varied over 4 × 10−12 to 4 × 10−16 ions/cm2 with a flux of 5 × 10−11 ions/cm2/s. The nature and the extent of the radiation damages have been studied by SEM and

On the electrical conductivity of thermally evaporated CdS thin films

Cadmium sulphide (CdS) plays an important role in the development of thin-film photovoltaic devices [1–5]. Hetrojunctions of CdS and other semiconductors such as CdTe, Cu2S, CuInSe2 and InP etc. have excited interest and made it possible to have efficient thin film solar cells. Low resistive CdS films are used in hetrojunctions in solar cells to lower the cell series resistance, whereas high resistive films are used for surface acoustic wave devices. The optimization of device characteristics requires a better understanding of the transport properties of these films. Electrical conductivity measurements are widely used in the characterization of transport properties of thin films [6–8]. It has been established that the boundaries between grains in the polycrystalline films play an important role in determining the conductivity of the films [9–11]. Many workers have grown CdS thin films using different deposition techniques such as thermal evaporation, spraying, chemical vapor deposition, sputtering etc. In this paper we report the electrical conductivity measurements of CdS thin films prepared by thermal evaporation. High purity (99.999%) cadmium and sulfur obtained from Johnson and Matthey (U.K.) were used in this investigation. An intimate mixture (8.01255 gm) of fresh powders of cadmium (150 μm) and sulfur (100 μm) in stoichiometric proportion corresponding to the composition CdS was placed in the graphite crucible. The crucible was kept in a transparent silica tube which after evacuation and insertion of argon (with oxygen impurity less than 2 ppm) was heated at a constant and reproducible rate of 3 K/min by a Thermal Program Controller (Make: ULVAC, Sinku Riku, Japan; Model: HPC-7000). The temperature of the sample was maintained constant at 900 K for 2 h and then heated again up to 1250 K at a rate of 5 K/min. It was held at 1250 K for 24 h and then furnace cooled to room temperature. The CdS sinter was taken out and ground into powder in a mortar and pestle. The formation of the compound was confirmed by X-ray powder diffraction patterns. Rectangular films (5 cm × 1.5 cm) of CdS varying in thickness from 1000 A to 5000 A were grown by the thermal evaporation technique in a vacuum ∼2 × 10−5 torr using a vacuum coating system (Make: HINDHIVAC; Model: 12A4DM). A molybdenum boat was used as the evaporation source and the substrates were cleaned glass plates held at room temperature, which were placed directly above the source at a distance of approximately 18 cm. The glass substrates were cleaned with freshly prepared chromic acid, detergent solution and distilled water, in that order and finally subjected to glow discharge cleaning. The growth rate and the thickness of the films were controlled in situ by a quartz crystal thickness monitor (Make: HINDHIVAC; Model: DTM 101). The deposition rate was kept at 1–2 A/s in all cases. Films of different thickness were prepared through different individual evaporations. For the electrical conductivity measurements, indium (In) contact films were used as they were found to make ohmic contact with the CdS film. The work function of In has been reported to be 4.12 eV and that of Cds to be >4.8 eV, which satisfy the condition for making ohmic contact [12]. The thick (∼2000 A) contact films were pre-deposited on both ends of the experimental film. Electrical resistance was measured using a Keithley Programmable Electrometer (Model: 617) while the temperature of the films was monitored using a copper-constantan thermocouple with the help of a Keithley DMM (Model: 196). Films were heated in vacuum ∼2 × 10−2 torr inside a tubular furnace. The rate of heating was kept at 3 K/min while hold time at the desired temperature was 10 min. After attaining the desired highest temperature, the films were subjected to furnace cooling.

Hydrogen in UHV deposited FeTi thin films

FeTi thin films of thickness 1550 A 0 were prepared in UHV at 10 −8 Torr pressure onto glass substrate. Thickness of the FeTi thin films and the content of hydrogen in films was measured by quartz crystal thickness monitor. In situ measurement shows that the resistance decreases with increase in thickness of the film. During hydrogen absorption in FeTi thin films, hydrogen pressure was varied between 10 −8 Torr to 1 atm . The resistance of film was found to increase due to hydrogen exposure and the value of H/M was found to vary between 0.03 and 1.05 and that of H at% 3–50, in the hydrogen pressure range between 10 −8 Torr to 1 atm . A relation was established between content of hydrogen in films and its resistance.

The Accurate Control of the Thickness of Evaporated Carbon Films

Abstract There are two approaches to determining the thickness of a carbon film evaporated onto a specimen. One approach is to do the evaporation first and to measure the result afterwards. There are several ways to do this. The second approach is to put down a determined amount of carbon in the first place. This clearly has advantages in many cases. The method described here is of this second kind. The thickness of the carbon coating is not measured, but by a predetermined recipe, the amount put on is controlled at the time of evaporation, In principle, the thickness could be measured during the evaporation with a quartz-crystal thickness monitor. However, we find that the monitor we have does not work well with carbon.