Since the diamond like carbon features include high hardness and high wear resistance, low friction coefficient, chemical inertness, high resistance, low dielectric constant, the IR Transparency and field emission. The process of Diamond carbon film was usually by CVD or PVD techniques. However, high substrate temperature or low deposition rate and the can not make large area of films leads to limit the applications of diamond like film. Electrodeposition method is an innovative method to prepare DLC film and it meets these demands such as: equipment cheap, high deposition rate and larger area coatings. In this paper, ITO substrate was used for electrodeposition the diamond-like carbon films and to evaluate the possibility for the large area of DLC films.For the process of electrical deposition, the electrolyte consists of acetic acid and DI water mixed in different proportions. The deposition process were conditioned as: electrolyte concentration between 0.01% and 0.8%; voltage from 2.1V to 50V; growth temperature in the range of 300C ~ 850C. In addition, by using the control variables method, the deposition parameters including voltage, deposition temperature and solution concentration of electrolyte were varied to evaluate the characteristics and quality of diamond-like carbon films. The n & k film analyzer (n & k Analyze), X ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) were used to characterize the surface morphology, microstructure and compositional analysis. The reflectivity, transmittance, and refractive index of DLC Films were revealed by the n & k analyzer. Hence, the best conditions used for anti-reflective layer and projections Eopg can be achieved. For SEM analysis, the DLC film with uniformity surface structure can be found. Additionally, the current - time graph can be used to predict the properties of film varied with the applied voltage, percent of concentrations, growth temperature etc.. The microstructure of DLC film was investigated by the XPS measurement; the sp2 / sp3 ratio varies from the growth parameters changes. The hydrogen content of DLC films was obtained by FTIR measurements, the contents decrease as the operating voltage, electrolyte concentration and the substrate temperature increase. As for the DLC deposited on ITO glass as an anti-reflective layer, the experimental results showed that DLC film can reduce the reflectivity from 40% to 70%. Finally, the results obtained show a reasonable match for various measurements. T he characteristics of DLC films also shows that it very depends on the deposited parameters and the relationship beteen them was discussed in detailed. Some of the advance study will be investigated in future.

Recently, synthesis of Diamond-Like Carbon (DLC) films has received considerable interest. Owing to their similar characteristics of diamonds, such as extreme hardness, chemical stability, and high heat conductivity etc, DLC films are regarded as one of the most promising materials. But the practical applications have been limited due to their high internal stress and insufficient adhesion at the interface between DLC film and substrate. Several methods used to the deposition of Me-DLC films have been proposed. Studies have shown that the internal stress was released and the adhesion also improved by doping metallic element into DLC films. Conventionally, metal incorporation in DLC films were prepared by vapor deposition. The requirement of high vacuum equipment makes the process complicated. Besides, there are many merits in electrodeposition, such as low cost, simplicity of experimental set up, and availability for deposition on complex shapes substrate in large area. In this study, electrodepositing technique was used to synthesize the amorphous Cu-DLC films deposited on ITO substrate, in which the pH value of electrolyte varied, to study the characteristics and the composition of DLC films. According to the I-t curves of deposition, the end of current density was used for the impedance comparison of films. With the addition of Cu, the resistance of the electron transportation in Cu-DLC was reduced, and the awl-shaped surface morphology was observed by AFM measurement, which could enhance the electron field emission properties of thin films. For Raman analysis, the effect of Cu addition would promote the sp2 bonding¡F this result corresponds with the increasing ID/IG value. It indicates that film becomes graphitization due to the addition of Cu and leads the shift of G-peak position toward lower wavenumber. ESCA spectra of C1s and Cu2p indicate no obvious evidence of Cu-C formation. The sp2/(sp2+sp3) ratio increases with the pH value. In addition, we found that Cu-DLC in acidic environmental condition, or doping as [Cu(NH3)n]2+ complex is more conducive to the growth of copper metal in DLC films, and has the lowest optical band gap value deduced by n&k analyzer. Finally, we discussed the thin film growth mechanisms and the characteristic of electron field emission for the applications in the future.

Thin films of GeTe₂ were deposited on glass substrates using RF magnetron sputtering with various hydrogen flow rates in the growth chamber. Transmission data of deposited films were taken and used to determine optical constants: refractive index (n), extinction coefficient (κ), and absorption coefficient (α)) and the energies: E₀₄, E₀₃, Tauc band gap E[subscript]Tauc and Urbach energy E[subscript]U. An increase of these energies was observed with increasing hydrogen flow rate. This increase is interpreted on the basis of the density of state model proposed by Mott and Davis. An increase of network disorder due to the inclusion of hydrogen into the GeTe₂ thin films was determined from the B[superscript]1/2 parameter, Urbach energy and full width at half maximum of Raman vibrational modes. The crystallization process induced by thermal annealing on GeTe₂ was studied. X-ray diffraction measurements were performed and the results suggest that crystallization of GeTe₂ occurs via a phase separation into Te and GeTe crystalline phases. This observation is in agreement with a previous report. The crystallization temperature increases with the addition of hydrogen. This increase is explained in terms of dangling bonds. A large change (approximately 60 percent decrease) of the optical transmission occurs after the phase change from amorphous to crystalline. This decrease is interpreted as a result of the observed phase separation.

No description available.

Flash memories are solid-state non-volatile memories. They play a vital role especially in information storage in a wide range of consumer electronic devices and applications including smart phones, digital cameras, laptop computers, and satellite navigators. The demand for high density flash has surged as a result of the proliferation of these consumer electronic portable gadgets and the more features they offer – wireless internet, touch screen, video capabilities. The increase in the density of flash memory devices over the years has come as a result of continuous memory cell-size reduction. This size scaling is however approaching a dead end and it is widely agreed that further reduction beyond the 20 nm technological node is going to be very difficult, as it would result to challenges such as cross-talk or cell-to-cell interference, a high statistical variation in the number of stored electrons in the floating gate and high leakage currents due to thinner tunnel oxides. Because of these challenges a wide range of solutions in form of materials and device architectures are being investigated. Among them is three-dimensional (3-D) flash, which is widely acclaimed as the ideal solution, as they promise the integration of long-time retention and ultra-high density cells without compromising device reliability. However, current high temperature (>600 °C) growth techniques of the Polycrystalline silicon floating gate material are incompatible with 3-D flash memory; with vertically stacked memory layers, which require process temperatures to be ≤ 400 °C. There already exist some low temperature techniques for producing polycrystalline silicon such as laser annealing, solid-phase crystallization of amorphous silicon and metal-induced crystallization. However, these have some short-comings which make them not suitable for use in 3-D flash memory, e.g. the high furnace annealing temperatures (700 °C) in solid-phase crystallization of amorphous silicon which could potentially damage underlying memory layers in 3-D flash, and the metal contaminants in metal-induced crystallization which is a potential source of high leakage currents. There is therefore a need for alternative low temperature techniques that would be most suitable for flash memory purposes. With reference to the above, the main objective of this research was to develop a novel low temperature method for growing silicon structures at ≤ 400 °C. This thesis thus describes the development of a low-temperature method for polycrystalline silicon growth and the application of the technique in a capacitor-like flash memory device. It has been demonstrated that silicon structures with polycrystalline silicon-like properties can be grown at ≤ 400 °C in a 13.56 MHz radio frequency (RF) plasma-enhanced chemical vapour deposition (PECVD) reactor with the aid of Nickel Formate Dihydrate (NFD). It is also shown that the NFD coated on the substrates, thermally decomposes in-situ during the deposition process forming Ni particles that act as nucleation and growth sites of polycrystalline silicon. Silicon films grown by this technique and without annealing, have exhibited optical band gaps of ~ 1.2 eV compared to 1.78 eV for films grown under identical conditions but without the substrate being coated. These values were determined from UV-Vis spectroscopy and Tauc plots. These optical band gaps correspond to polycrystalline silicon and amorphous silicon respectively, meaning that the films grown on NFD-coated substrates are polycrystalline silicon while those grown on uncoated substrates remain amorphous. Moreover, this novel technique has been used to fabricate a capacitor-like flash memory that has exhibited hysteresis width corresponding to charge storage density in the order of 1012 cm-2 with a retention time well above 20 days for a device with silicon films grown at 300 °C. Films grown on uncoated films have not exhibit any significant hysteresis, and thus no flash memory-like behaviour. Given that all process temperatures throughout the fabrication of the devices are less than 400 °C and that no annealing of any sort was done on the material and devices, this growth method is thermal budget efficient and meets the crucial process temperature requirements of 3-D flash memory. Furthermore, the technique is glass compatible, which could prove a major step towards the acquisition of flash memory-integrated systems on glass, as well as other applications requiring low temperature polycrystalline silicon.

Un-doped, Er3+ doped (TiO2:Er3+) as well as Er3+/Yb3+ co-doped (TiO2:Er3+/Yb3+) nanocrystals with different concentrations of RE3+ (Er3+, Yb3+) were successfully synthesized using the sol-gel method. The powder X-ray diffraction (XRD) spectra revealed that all undoped and doped samples remained in anatase after annealing at 400°C. The presence of RE3+ ions in the TiO2 host lattice was confirmed by conducting elemental mapping on the samples using Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDX), which was in agreement with X-ray photoelectron spectroscopy (XPS) results. Transmission electron microscope (TEM) images approximated particle sizes of the samples to be between 1.5 – 3.5 nm in diameter and this compares well with XRD analyses. Phonon quantification in TiO2 was achieved using Fourier transform infrared (FT-IR) spectroscopy. Optical bandgap from Ultraviolet/Visible/Near-Infrared was extrapolated from Kubelka-Munk relation and the narrowing of the bandgap for the doped samples as compared to the undoped sample was observed. The photoluminescence PL study of the samples revealed two emission peaks attributed to direct band-gap and defect-related emissions. A laser beam with 980 nm wavelength was used to irradiate the samples, and the displayed emission lines of the TiO2: Er3+ in the visible region of the electromagnetic spectrum confirmed up-conversion luminescence. Enhancement of up-conversion luminescence intensity due to Yb3+ co-doping was observed, indicating an efficient energy transfer process from the sensitizer Yb3+ to the activator Er3+. / Physics / M. Sc. (Physics)

Chalcogenide glasses are a class of covalent amorphous semiconductors with interesting properties. The presence of short-range order and the pinned Fermi level are the two important properties that make them suitable for many applications. With flash memory technology reaching the scaling limit as per Moore’s law, alternate materials and techniques are being researched at for realizing next generation non-volatile memories. Two such possibilities that are being looked at are Phase Change Memory (PCM) and Programmable Metallization Cell (PMC) both of which make use of chalcogenide materials. This thesis starts with a survey of the work done so far in realizing PCMs in reality. For chalcogenides to be used as a main memory or as a replacement to FLASH technology, the electrical switching parameters like switching voltage, programming current, ON state and OFF state resistances, switching time and optical parameters like band gap are to be considered. A survey on the work done in this regard has revealed that various parameters such as chemical composition of the PC material, nature of additives used to enhance the performance of PCM, topological thresholds (Rigidity Percolation Threshold and Chemical Threshold), device geometry, thickness of the active volume, etc., influence the electrical switching parameters. This has motivated to further investigate the material and experimental parameters that affect switching and also to explore the possibility of multi level switching. In this thesis work, the feasibility of using two chalcogenide systems namely Si15Te85-xGex and Ge15Te85-xAgx in the form of amorphous thin films for PCM application is explored. In the process, electrical switching experiments have been carried out on thin films belonging to these systems and the results obtained are found to exhibit some interesting anomalies. Further experiments and analysis have been carried out to understand these anomalies. Finally, the dynamics of electrical switching has been investigated and presented for amorphous Si15Te85-xGex thin films. From these studies, it is also seen that multi state switching/multiple resistance levels of the material can be achieved by current controlled switching, the mechanisms of which have been further probed using XRD analysis and AFM studies. In addition, investigations have been carried out on the electrical switching behavior of amorphous Ge15Te85-xAgx thin film devices and optical band gap studies on amorphous Ge15Te85-xAgx thin films. Chapter one of the thesis, gives a brief introduction to the limitations in existing memory technology and the alternative memory technologies that are being researched, based on which it can be inferred that PCM is a promising candidate for the next generation non volatile memory. This chapter also discusses the principle of using PCM to store data, realization of PCM using chalcogenides, the material properties to be considered in designing PCM, the trade offs in the process of design and the current trends in PCM technology. Chapter two provides a brief review of the electrical switching phenomenon observed in various bulk chalcogenide glasses, as electrical switching is the underlying principle behind the working of a PCM. In the process of designing a memory, many parameters like read/write operation speed, data retentivity and life, etc., have to be optimized for which a thorough understanding on the dependence of electrical switching mechanism on various material parameters is essential. In this chapter, the dependence of electrical switching on parameters like network topological thresholds and electrical and thermal properties of the material is discussed. Doping is an efficient way of controlling the electrical parameters of chalcogenides. The nature of dopant also influences switching parameters and this also is briefly discussed. Chapter three provides a brief introduction to the different experimental techniques used for the thesis work such as bulk chalcogenide glass preparation, preparation of thin amorphous films, measurement of film thickness, confirmation of amorphous nature of the films using X-Ray Diffraction (XRD), electrical switching experiments using a custom made setup, crystallization study using XRD and Atomic Force Microscopy (AFM) and optical band gap studies using UV-Vis spectrometer. Vt is an important parameter in the design of a PCM. Chapter four discusses the dependence of Switching voltage, Vt, on input energy. It is already established that the Vt is influenced by the composition of the base glass, nature of dopants, thickness of films and by the ambient temperature. Based on the results of electrical switching experiments in Si15Te74Ge11 amorphous thin films a comprehensive analysis has been done to understand the kinetics of electrical switching. Chapter five discusses a current controlled crystallization technique that can be used to realize multi-bit storage with a single layer of chalcogenide material. In case of PCM, data is stored as structural information; the memory cell in the amorphous state is read as data ‘0’ and the memory cell in crystalline state is read as data ‘1’. This is accomplished through the process of electrical switching. In order to increase the memory density or storage density, multi-bit storage is being probed at by having multiple layers of chalcogenide material. However, with this technique, the problems of inter-diffusion between different layers cannot be ruled out. In this thesis work, a current controlled crystallization technique has been used to achieve multiple stable resistance states in Si15Te75Ge10 thin films. Chapter six discusses the mechanism behind multi state switching exhibited by certain compositions of Si15Te85-xGex thin films. Crystallization studies on certain Si15Te85-xGex films have been carried out using XRD and AFM to understand the phenomenon of multiple states. The results of these experiments and analysis are presented in this chapter. Chapter seven discusses the results of electrical switching experiments and optical band gap studies on amorphous Ge15Te85-xAgx thin films. Chapter eight gives the conclusion and scope for future work.