The surface morphology of the deposited Co1-xCdxS films was found to be inhomogeneous, and the film became homogeneous after annealing. The activation energy of Co1-xCdxS films increased between 0.25 to 0.50 eV with the increase of Cd in the solution.
Characterization of CoS and Co1-xCdxS thin films deposited by Spray Pyrolisis Technique Spray Pyrolisis Technique. A dissertation submitted to the Department of Physics, Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh, in partial fulfillment.
CANDIDATE’S DECLARATION
GENERAL INTRODUCTION
- INTRODUCTION
- REVIEW OF THE EARLIER WORK
- Chandramohan et al [14] studied structural, optical, vibrational and morphological properties of Co doped CdS thin films from 0.34 to 10.8 at % by ion
- Bacaksiz et al [16] investigated structural, optical and magnetic properties of CdS thin films with the addition of Co prepared by (i) Spray Pyrolysis deposition
- PHYSICAL PROPERTIES OF CoS
- CHARACTERISTICS OF THIN FILMS
- AIM OF THE PRESENT WORK
The study of the changes in thin film properties with temperature provides a lot of information about thin film properties. So a sufficiently low pressure is necessary for the deposition of the thin film on the substrate.
CHAPTR-II
THIN FILM DEPOSITION TECHNIQUES AND PROCESSES
DEPOSITION TECHNIQUES
- CHEMICAL VAPOR DEPOSITION (CVD)
- ELECTRODEPOSITION
- THERMAL OXIDATION
- PHYSICAL VAPOR DEPOSITION (PVD)
- CASTING
- SOL-GEL
- MOLECULAR BEAM EPITAXY ( MBE )
Some processes can even be used to perform selective depositions, depending on the surface of the substrate. Thus, the lattice of the grown film is the same as that of the substrate.
FORMATION STAGES OF THIN FILM
- CONDENSATION
- GROWTH
Chapter-II Thin Film Deposition Techniques and Processing the instantaneous dipole and quadruple moments of the surface atoms. The process of enlargement of the nuclei to finally form a coherent is called as growth. The tendency to form an island structure is increased by (1) at high substrate temperature, (2) at low boiling point film material, (3) at low deposition rate, (4) weak binding energy between film material and substrate, (5) ) a high surface energy of the film material and (6) a low surface energy of the substrate.
Eventually, most of the channels are eliminated and the film is continuous but contains many small irregular holes. Secondary nucleation occurs in the substrate within these holes, and growing nuclei are incorporated (in a fluid manner) into continuous depositional regions. Chapter-II Thin Film Deposition Techniques and Processes Significant changes in the orientation of the islands occur during film growth, particularly at the coalescence stage.
SURFACE MORPHOLOGY AND STRUCTURAL CHARACTERIZATION
- SCANNING ELECTRON MICROSCOPE
- ENERGY DISPERSIVE ANALYSIS OF X-RAY
- ENERGY DISPERSIVE X-RAY SPECTROSCOPY
- X-RAY DIFFRACTION
Chapter-III Theoretical principles of the thin layer Characterization by the interaction of the incident electron with the surface of the sample. The analysis represents the individual weight (%) of the element that is present in the thin films. The optical and electrical properties of thin films are very sensitively affected by the crystallographic and microstructural characteristics of the film.
The number and energy of X-rays emitted by a sample can be measured with an energy dispersive spectrometer. The wavelength of an X-ray is therefore of the same order of magnitude as the lattice constant of crystals. From the width of the diffraction line it is possible to estimate the average grain size in the film [54].
OPTICAL CHARACTERIZATION
- BEER-LAMBERT LAW
- ABSORPTION COEEFECIENT
- ELECTRONIC TRANSITIONS
- DIRECT AND INDIRECT OPTICAL TRANSITIONS
Thus, the intensity of the transmitted light can be expressed as I = I0 e-ad, where d is the path length through the sample and α is the absorption coefficient. The intensity of the transmitted light can be expressed as I = I0 e-αt, where t is the path length through the sample and α is the absorption coefficient. This is because the absorption peaks of these transitions fall in an experimentally convenient region of the spectrum (nm).
Band gap generally refers to the energy difference between the top of the valence band and the bottom of the conduction band. If the density of states of both band edges is parabolic, the photon energy dependence of the absorption becomes. One beam, the sample beam (colored magenta), passes through a small transparent container (curette) containing a solution of the compound being studied in a clear solvent.
MEASURMENT OF OPTICAL ABSORPTION OF THIN FILM
- ELECTRICAL PROPERTIES MEASURMENT
- RESISTIVITY AND ELECTRICAL CONDUCTIVITY OF THIN FILM
- RESISTIVITY MEASUREMENT TECHNIQUES
- DIRECT METHOD
- van-der Pauw’s Technique
- SHEET RESISTANCE
- ACTIVATION ENERGY
- ANNEALING
It can be measured either by in-situ monitoring of the deposition rate or after the film is removed from the deposition chamber. Multiple-Beam Interferometry technique was used to measure the thickness of the thin films. The thickness of the films deposited on glass substrates was measured using a multi-beam interferometric method.
The step generated on the surface of the slide was used to measure the film thickness. Resistivity is an intrinsic property of a material and depends only on the crystal structure of the material. Chapter-III Theoretical principles of thin film characterization binding energy of the charge to the island.
CHAPTER-IV
- EXPERIMENTAL EQUIPMENT
- PREPARATION OF MASKS
- HEATER
- THE DESIGN OF THE REACTOR
- THE FUME CHAMBER
- SPRAY HEAD / SPRAY NOZZLE
- TYPE OF SUBSTRATE AND SUBSTRATE CLEANING
- WORKING SOLUTION
- FILM DEPOSITION PARAMETERS
- SAMPLE DEPOSITION
- RATE OF DEPOSITION
- THICKNESS CONTROL
- OPTIMIZATION OF THE DEPOSITION PROCESS
The mask is placed in close proximity to the substrate, thus allowing evaporation to condense only on exposed areas of the substrate. There are openings on the side and top of the reactor for quick extraction of by-product gases. There is an exhaust fan located at the mouth of the chimney to remove unused gases from the room.
The cleaning of the substrate has a great influence on the properties of the thin film deposited on them. Fixing the distance ds and the substrate temperature Ts, a third set of films were deposited by varying the carrier gas pressure Pa. In this case, the concentration of solution C was changed to select the optimal concentration of the working solution.
CHAPTER-V
RESULTS AND DISCUSSION
INTRODUCTION
THICKNESS MEASUREMENT
Many small round precipitates were observed on the surface of the sample in the deposited state. The surface can be described as a conglomerate of random roughness, which is characteristic of an amorphous nature. Figure 5.1(b-e) describes various Cd inclusions in the CoS thin films and there are some opaque parts of clusters due to Cd and shows that the surface becomes homogeneous and quite smooth.
As a consequence of annealing, the atoms began to rearrange themselves periodically, and the surface of annealed samples shows that the surface is uniform and homogeneous. With the increase of the annealing temperature, the surface homogeneity, quality and crystallinity of the annealed films increase. With the increase in the annealing temperature, Cd diffuses well over the surface and becomes more homogeneous.
COMPOSITIONAL STUDIES
Chapter-V Results and Discussion annealed Co0.8Cd0.2S thin films are in good agreement reported by Zenrui Yu et al. Co0.8Cd0.2S film annealed at 673 K shows that the film is still amorphous, but the formation of the crystalline nature of the film is initiated at the 2θ peak of (130) preferential orientation. The grain size of the film has been determined from the stronger peaks on (130) from each XRD pattern using the Scherrer formula.
Average grain size of the film was determined in the range of 15 to 61 nm, indicating that the nanometric size of Co0.8Cd0.2S grains developed in the film. Lattice constants were calcd. using the dominant peaks for Co0.8Cd0.2S and the average value obtained, a ≅7.661. Å which is close to the standard value. a) X-ray diffraction patterns of as-deposited Co1-xCdx S thin films.
OPTICAL PROPERTIES
- ABSORBANCE AND TRANSMITTANCE
- ABSORPTION COEFFICIENT AND OPTICAL BAND GAP
- EXTINCTION COEFFICIENT
- REFRACTIVE INDEX
- DIELECTRIC CONSTANTS
- DIELECTRIC LOSS
5.4(c) it is seen that the 'α' of films deposited as Co1-xCdxSthin increases with increasing Cd in the solution. Chapter-V Results and discussion 'n' as a function of wavelength for different compositions is shown in Fig.5.6. The "N" of the deposited thin film decreases with increasing Cd in the system.
Chapter-V Results and Discussion The variation of εrandεi parts of the dielectric constant for different films. The εr and εi part of the dielectric constant increases in the UV region shown in Fig. From the optical data, it is observed that the εr and εi part of the dielectric constant follow the same pattern.
- REFRACTIVE INDEX
- DIELECTRIC CONSTANTS
- DIELECTRIC LOSS
The absorption spectra of the annealed thin films of Co0.8Cd0.2S, at different annealing temperatures, are presented in Fig. 5.10(b) shows the optical transmission spectra for annealed Co0.8Cd0.2S thin films at different annealing temperatures. The variation of 'n' of annealed Co0.8Cd0.2S films with wavelength for different annealing temperatures is shown in Fig.
The variation of the dielectric constant parts εr and εi with wavelength for annealed Co0.8Cd0.2S films is shown in the figure. Variation of the real part of the dielectric constants as a function of wavelength for Co0.8Cd0.2S films. The changes in the dielectric losses of the annealed Co0.8Cd0.2S films with hν are presented in Fig. 1b.
- VARIATION OF RESISTIVITY WITH TEMPERATURE
- VARIATION OF SHEET RESISTANCE WITH TEMPERATURE
- VARIATION OF TEMPERATURE COEFFICIENT OF RESISTANCE (T.C.R)
The variation of electrical resistance with temperature for the as-deposited thin films of Co1-xCdxS (0≤x≤1) is shown in Fig. Variation of electrical conductivity with temperature for as-deposited Co1-xCdxS thin films (0≤x≤1) is Sheet resistance variations with temperature for as-deposited Co1-xCdxS (0≤x≤1) thin film is shown in Fig.
This is due to the fact that the resistance of as-deposited Co1-xCdxS thin film decreases with temperature. Chapter-V Results and Discussion Table 1.4 Variation of activation energy with different compositions of Co1-xCdxS. Fig.5.21 shows the variation of temperature coefficient of resistance (T.C.R) with temperature for as-deposited Co1-xCdxS thin films.
CHAPTER-VI
CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK
CONCLUSIONS
The absorption spectra of the deposited Co1-xCdxS (0≤ x ≤1) thin films show that the absorption is low in the wavelength range of 500 -1100 nm and high in the ultraviolet region. The permeability of the prepared thin films decreases with increasing Cd incorporation into the solution. The direct band gap (Eg) of the films varies between 2.20 and 3.10 eV with the increase of Cd in the Co1-xCdxS system, indicating that the presence of Cd in the films strongly influences the optical band gap.
This is consistent with the observed increase in crystallite size as the annealing temperature increases, further consolidating the suggestion that annealing improves the crystallinity of the films. Chapter VI Conclusions and suggestions for future work The electrical resistance decreases and the conductivity of the deposited material decreases. The activation energy of deposited Co1-xCdxS films increases with increasing Cd in the solution.
SUGGESTIONS FOR FUTURE WORK
CHAPTER-I GENERAL INTRODUCTION
CHAPTER-II THIN FILM DEPOSITION TECHNIQUES AND PROCESSES
CHAPTER-III THEORETICAL PRINCIPLES OF FILM CHARACTERIZATION
CHAPTER-IV EXPERIMENTAL DETAILS
CHAPTER-V RESULTS AND DISCUSSION
CHAPTER-VI CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK
17] Bedir, M., Kayali, R., Oztas, M., "The effect of Zn concentration on the characteristic parameters of ZnxCd1-xS thin films developed by the spray pyrolysis method in a nitrogen atmosphere" Turk J. 22] Ortega- Borges, R. , Lincot, D., “Mechanism of chemical deposition of cadmium sulfide thin films in the ammonia-thiourea system” J., Electrochem., Soc. Electrical and Spectroscopic Properties of Amorphous Copper Sulfide Films Treated with Iodine, Lithium Iodide, and Sodium Iodide” Thin Solid Films, Vol-373, pp-01, 2000.
A., "Study of indium tin oxide (ITO) for new optoelectronic devices" PhD thesis, King's College London, University of London, Department of Electronic Engineering, 1998. D., "A Mössbauer effect and X-ray diffraction study of Fe - Ga- Al thin films prepared by combinatorial sputtering” J. Effect of Ru addition on the properties of Al-doped ZnO thin films prepared by radio frequency magnetron sputtering on polyethylene terephthalate substrate” J.
