Rozprawy doktorskie na temat „Cobalt ferrite thin film”

When a permanent magnet is considered for an application, the quantity that quantifies the usability of that material is the magnetic energy product (BH)max. In today’s world, rare earth transition metal permanent magnets like Nd-Fe-B, Sm-Co possesses the maximum magnetic energy product. But still for the industrial application, the ferrite permanent magnets are the primary choice over these rare transition metal magnets. Thus, in the present context, the magnetic energy product of the low cost ferrite system makes it unsuitable for the high magnetic energy application. In this regard, exchange spring magnets which combine the magnetization of the soft phase and coercivity of the hard magnetic phases become important in enhancing the magnetic energy product of the system. In this thesis, the exchange spring behaviour is reported for the first time in hard/soft oxide nanocomposites by microstructural tailoring of hard Barium Ferrite and soft Nickel Zinc Ferrite particles. We have analyzed the magnetization reversal and its correlation with the coercivity mechanism in the Ni0.8Zn0.2Fe2O4/BaFe12O19 exchange spring systems. Using this exchange spring concept, we could enhance the magnetic energy product in Iron Oxide/ Barium Calcium Ferrite nanocomposites compared to the bare hard ferrite by ~13%. The presence of the exchange interaction in this nanocomposite is confirmed by the Henkel plot. Moreover, a detailed Reitveld study, magnetization loop and corresponding variation of the magnetic energy product, Henkel plot analysis and First Order Reversal Curve analysis are performed on nanocomposites of hard Strontium Ferrite and soft Cobalt Ferrite. We have proved the exchange spring behaviour in this composite. In addition, we could successfully tailor the magnetization behaviour of the soft Cobalt Ferrite- hard Strontium Ferrite nanocomposite from non exchange spring behaviour to exchange spring behaviour, by tuning the size of the soft Cobalt Ferrite in the Cobalt Ferrite/Strontium Ferrite nanocomposite. The relative strength of the interaction governing the magnetization process in the composites has been studied using Henkel plot and First Order Reversal Curve method. The FORC method has been utilized to understand the magnetization reversal behaviour as well as the extent of the irreversible magnetization present in both the nanocomposites, having smaller and larger particle size of the Cobalt Ferrite. It has been found that for the all the studied composites, the pinning is the dominant process for magnetization reversal. The detailed structural analysis using thin film XRD, angle dependent magnetic hysteresis and remanent coercivity measurement, coercivity mechanism by micromagnetic analysis and First Order Reversal Curve analysis are performed for thin films of Strontium Ferrite which are grown on c-plane alumina using Pulsed Laser Deposition (PLD) at two different oxygen partial pressures. The magnetic easy directions of both the films lie in the out of plane direction where as the in plane direction corresponds to the magnetic hard direction. Depending on the oxygen partial pressure during deposition, the magnetization reversal changes from S-W type reversal to Kondorsky kind of reversal. Thus, the growth parameter for the Strontium Ferrite single layer which will be used further as a hard layer for realizing oxide exchange spring in oxide multilayer, is optimized. The details of the magnetic and structural properties are analyzed for Nickel Zinc Ferrite thin film grown on (100) MgAl2O4. We have obtained an epitaxial growth of Nickel Zinc Ferrite by tuning the growth parameters of PLD deposition. The ferromagnetic resonance and the angle dependent hysteresis loop suggest that, the magnetic easy direction for the soft Nickel Zinc Ferrite lie in the film plane whereas the out of plane direction is the magnetic hard direction. Using the growth condition of respective Nickel Zinc Ferrite and Strontium Ferrite, we have realized the exchange spring behaviour for the first time in the trilayer structure of SrFe12O19 (20 nm)/Ni0.8Zn0.2Fe2O4(20 nm)/ SrFe12O19 (20 nm) grown on c-plane alumina (Al2O3) using PLD. The FORC distribution for this trilayer structure shows the single switching behaviour, corresponding to the exchange spring behaviour. The reversible ridge measurement shows that the reversible and the irreversible part of the magnetizations are not coupled with each other.

When a permanent magnet is considered for an application, the quantity that quantifies the usability of that material is the magnetic energy product (BH)max. In today’s world, rare earth transition metal permanent magnets like Nd-Fe-B, Sm-Co possesses the maximum magnetic energy product. But still for the industrial application, the ferrite permanent magnets are the primary choice over these rare transition metal magnets. Thus, in the present context, the magnetic energy product of the low cost ferrite system makes it unsuitable for the high magnetic energy application. In this regard, exchange spring magnets which combine the magnetization of the soft phase and coercivity of the hard magnetic phases become important in enhancing the magnetic energy product of the system. In this thesis, the exchange spring behaviour is reported for the first time in hard/soft oxide nanocomposites by microstructural tailoring of hard Barium Ferrite and soft Nickel Zinc Ferrite particles. We have analyzed the magnetization reversal and its correlation with the coercivity mechanism in the Ni0.8Zn0.2Fe2O4/BaFe12O19 exchange spring systems. Using this exchange spring concept, we could enhance the magnetic energy product in Iron Oxide/ Barium Calcium Ferrite nanocomposites compared to the bare hard ferrite by ~13%. The presence of the exchange interaction in this nanocomposite is confirmed by the Henkel plot. Moreover, a detailed Reitveld study, magnetization loop and corresponding variation of the magnetic energy product, Henkel plot analysis and First Order Reversal Curve analysis are performed on nanocomposites of hard Strontium Ferrite and soft Cobalt Ferrite. We have proved the exchange spring behaviour in this composite. In addition, we could successfully tailor the magnetization behaviour of the soft Cobalt Ferrite- hard Strontium Ferrite nanocomposite from non exchange spring behaviour to exchange spring behaviour, by tuning the size of the soft Cobalt Ferrite in the Cobalt Ferrite/Strontium Ferrite nanocomposite. The relative strength of the interaction governing the magnetization process in the composites has been studied using Henkel plot and First Order Reversal Curve method. The FORC method has been utilized to understand the magnetization reversal behaviour as well as the extent of the irreversible magnetization present in both the nanocomposites, having smaller and larger particle size of the Cobalt Ferrite. It has been found that for the all the studied composites, the pinning is the dominant process for magnetization reversal. The detailed structural analysis using thin film XRD, angle dependent magnetic hysteresis and remanent coercivity measurement, coercivity mechanism by micromagnetic analysis and First Order Reversal Curve analysis are performed for thin films of Strontium Ferrite which are grown on c-plane alumina using Pulsed Laser Deposition (PLD) at two different oxygen partial pressures. The magnetic easy directions of both the films lie in the out of plane direction where as the in plane direction corresponds to the magnetic hard direction. Depending on the oxygen partial pressure during deposition, the magnetization reversal changes from S-W type reversal to Kondorsky kind of reversal. Thus, the growth parameter for the Strontium Ferrite single layer which will be used further as a hard layer for realizing oxide exchange spring in oxide multilayer, is optimized. The details of the magnetic and structural properties are analyzed for Nickel Zinc Ferrite thin film grown on (100) MgAl2O4. We have obtained an epitaxial growth of Nickel Zinc Ferrite by tuning the growth parameters of PLD deposition. The ferromagnetic resonance and the angle dependent hysteresis loop suggest that, the magnetic easy direction for the soft Nickel Zinc Ferrite lie in the film plane whereas the out of plane direction is the magnetic hard direction. Using the growth condition of respective Nickel Zinc Ferrite and Strontium Ferrite, we have realized the exchange spring behaviour for the first time in the trilayer structure of SrFe12O19 (20 nm)/Ni0.8Zn0.2Fe2O4(20 nm)/ SrFe12O19 (20 nm) grown on c-plane alumina (Al2O3) using PLD. The FORC distribution for this trilayer structure shows the single switching behaviour, corresponding to the exchange spring behaviour. The reversible ridge measurement shows that the reversible and the irreversible part of the magnetizations are not coupled with each other.

碩士
國立臺灣大學
機械工程學研究所
107
In this thesis, we use radio frequency magnetron sputtering deposition technique to fabricate a multiferroic material, Bismuth ferrite(BFO), which possesses ferroelectric and anti-ferromagnetic property in the same time. We deposit BFO samples at the same temperature but anneal them at different temperature and in different atmosphere to find if there are some differences in crystal structure and electric properties. Then we choose the best of all to integrate with Barium titanate into a bilayer thin film. The combination of BTO and BFO is to learn the magneto-electric effect between ferroelectric and anti-ferromagnetic materials. In addition, we fabricate 5 different thickness ratio of the BTO/BFO bilayer to find out at which ratio will the best electric characteristic occur. According to results, the performance of Bismuth ferrite single layers is not good, the leakage current is about 10-1~10-2 ampere, the P-E loops look like a oval ball because of poor dielectric property, and worst of all, we cannot even measure the capacitance property. But everything changes in BTO/BFO bilayer structures due to the interlayer coupling effect. First, the leakage current plummets to 10-6~10-7 ampere. Second, the capacitance becomes measureable and the value is about 6x10-9 farad. Third, the maximum polarization is up to 4 μC/cm2. It’s a tremendous progress from BFO single layer to BTO/BFO bilayer. What disappoints us is that the magneto-electric measurements show that the applied magnetic field has no effect on our samples.

by Chiah Man Fat.
Thesis submitted in: September 1999.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references (leaves 94-97).
Abstracts in English and Chinese.
Acknowledgements --- p.2
Abstract --- p.3
Table of Contents --- p.5
List of Figures --- p.7
List of Tables --- p.13
Chapter Chapter 1 --- Introduction --- p.14
Chapter 1.1. --- Overview --- p.14
Chapter 1.2. --- Giant Magnetoresistance (GMR) --- p.15
Chapter 1.3. --- Application of GMR Materials --- p.20
Chapter 1.4. --- Preparation Methods --- p.22
Chapter 1.5. --- This Thesis --- p.23
Chapter Chapter 2 --- Sample Preparation and Experimental Methods --- p.24
Chapter 2.1. --- MEVVA Ion Source Implanter --- p.24
Chapter 2.2. --- The Pulsed Filtered Cathodic Arc Co-deposition System --- p.26
Chapter 2.3. --- Sample Preparation --- p.29
Chapter 2.3.1 --- Implantation Condition --- p.29
Chapter 2.3.2 --- Co-deposition Conditions --- p.31
Chapter 2.4. --- Characterization methods --- p.32
Chapter 2.4.1 --- Magnetoresistance Measurement --- p.32
Chapter 2.4.2 --- Atomic Force Microscopy and Magnetic Force Microscopy --- p.34
Chapter 2.4.3 --- Rutherford Backscattering Spectroscopy (RBS) --- p.37
Chapter 2.4.4 --- SQUID Magnetometer --- p.38
Chapter Chapter 3 --- Characterization of Implanted Samples --- p.39
Chapter 3.1. --- Introduction --- p.39
Chapter 3.2. --- Results and Discussion --- p.39
Chapter 3.2.1 --- Ag Film Thickness Dependence --- p.39
Chapter 3.2.2 --- Dose Dependence --- p.44
Chapter 3.2.3 --- Extraction Voltage Dependence --- p.46
Chapter 3.2.4 --- Annealing Temperature Dependence --- p.49
Chapter 3.2.5 --- Thicker Layer Formation --- p.56
Chapter 3.2.6 --- AFM and MFM Measurements --- p.58
Chapter 3.3. --- Summary --- p.64
Chapter Chapter 4 --- Characterization of Co-deposited Samples --- p.65
Chapter 4.1. --- Introduction --- p.65
Chapter 4.2. --- Results and discussion --- p.65
Chapter 4.2.1 --- RBS Measurement --- p.65
Chapter 4.2.2 --- Magnetoresistance Measurement --- p.66
Chapter 4.2.3 --- AFM Measurement --- p.69
Chapter 4.2.4 --- MFM Measurement --- p.76
Chapter 4.3. --- Summary --- p.84
Chapter Chapter 5 --- Conclusion --- p.85
Chapter 5.1. --- Main Results of This Work --- p.85
Chapter 5.2. --- Suggestions on Future Works --- p.87
Appendix --- p.89
Reference --- p.94
Publications --- p.97

碩士
國立中山大學
化學系研究所
104
It is necessary to develop clean and green energy because of the shortage of non-renewable energy. The hydrogen and oxygen generated by water splitting is one of the solution for clean energy. However, energy required for water splitting is usually greater than energy generated by water splitting. Oxygen evolution reaction (OER) is the main reason of excessive energy consumption in the splitting process, thus it is necessary to prepare a catalyst to promote the OER. In this research, by a simple redox method with heating, we successfully synthesized cobalt manganese oxide hydroxide (CMOH) catalyst. This method is fast and simple; efficiently deposit catalytic thin film on large area substrate even on complex surfaces. At first, we used cobalt sulfate as precursor to prepare catalytic films (CMOH-sulfate, CMOH-S) for electrochemical measurement. However, the films (CMOH-acetate, CMOH-A) prepared by cobalt acetate have superior optical properties to CMOH-S, so we chose cobalt acetate for subsequent experiments. To further understand the difference between CMOH-S and CMOH-A, We characterized these two thin film by a series of characterization. The results of UV-visible and AFM show that the thickness of CMOH-A is smaller than CMOH-S thus has higher transmittance. CMOH-A have transmittance of 87.15% with thickness of 60 nm versus CMOH-S having 60.39% transmittance and 120 nm thickness. We further confirmed the thickness of CMOH-A to be 5 to 10 nm by TEM (rather than 60 nm by AFM), and the composition is amorphous. Despite the difference on optical property, CMOH-S and CMOH-A exhibit almost the same on OER activity. To study the reason, we altered the length of CMOH-A films, knowing that the active sites actually lie at the interface of catalyst and FTO glass. Finally, after covering a layer of graphene on the catalytic thin films and go through 500ºC calcination under Ar, we tremendously raise the stability of OER catalyzing process, with only 7.6% decay of current after 3000 circles scanning and still remain at same over potential (0.47 V at 10 mA cm-2).

博士
國立臺灣海洋大學
材料工程研究所
98
To prevent the diffusion out of cobalt from cemented tungsten carbides at high working temperature, TaNx coatings were prepared as a diffusion barrier by direct current magnetron sputtering using a Ta target in an argon-nitrogen atmosphere. The nitrogen flow ratio, N2/(N2+Ar), in the sputtering process varied from 0.05 to 0.4. The deposition rate reduced as the nitrogen flow ratio increased. Silicon wafers and 6wt% cobalt cemented tungsten carbide were used as the substrates. Effects of nitrogen flow ratio on crystalline characteristics and mechanical properties of the TaNx coatings were examined by X-ray diffraction. The TaNx coatings were annealed at 500, 600, 700, and 800oC for 4 hours in air, respectively. The diffusion barrier performance was evaluated by Auger electron spectroscopy depth profiles and X-ray diffraction. Oxidation resistance of the TaNx coatings was also investigated. Orthorhombic Ta2O5 was observed after annealing above 600oC. If the 6wt% cobalt cemented tungsten carbide was used as the substrates, the WO3 oxide compound was found when the annealing temperature was over 600 oC in air. When the oxide appeared, the thin film surface become more rougher. The TaNx deposited on cemented tungsten carbides played the role of diffusion barrier for Co at 600oC for 4 hours in air. But the diffusion barrier was not effective under high temperature in air due to the oxidation problem, which was transferred from TaN to Ta2O5. If the diffusion barrier was used under low vacuum environment, such as, at 600 oC for 4 hours, the TaNx coating should be successful to play the role of diffusion barrier for Co diffusion.

碩士
國立臺灣海洋大學
材料工程研究所
99
To prevent the diffusion out of cobalt from cemented tungsten carbides at high working temperatures, CrTaN coating were prepared as a diffusion barrier by reactive direct current magnetron co-sputtering onto 6 wt.% cobalt cemented tungsten carbide substrates, using Ta and Cr targets in an argon-nitrogen atmosphere. The nitrogen flow ratio, N2/(Ar+N2), during the sputtering process was set at 0.4. The deposition rates of CrTaN coatings varied from 23 to 27 nm/min. The CrTaN coatings crystallized into a columnar structure, without heating the substrates during the sputtering process and exhibited surface hardness and Young's modulus values of 16–27 and 211–383 GPa, respectively. The annealing treatments were conducted at 500 and 600oC for 4 hours in air and 600oC for 4 hours in 50 ppm oxygen with balanced nitrogen gas. The diffusion barrier performance was evaluated by Auger electron spectroscopy depth profiles (AES), and X-ray diffraction (XRD). Oxidation resistance of the CrTaN coatings was also investigated. Orthorhombic L-Ta2O5 and rhombohedral Cr2O3 was observed after annealing at 500 and 600oC for 4 hours in air. When the oxide appeared, the thin film surface become more rough, the surface hardness and Young's modulus values decreased. Annealing in 600oC for 4 hours in a 50 ppm O2-N2 atmosphere, surface not oxide phase was observed. The hardness and Young's modulus values was increased. We also investigated oxidation resistance of the CrTaN coatings under a 50 ppm O2-N2 atmosphere, to assess the fabricated layers effectiveness as a protective coating for glass molding dies. Next carbon nitride films were deposited on the CrTaN films, to increase the surface wear property, because carbon nitride film has a batter wear resistance. The films were annealing in 50 ppm O2-N2 environment to simulate the glass molding environment, to observe the adhesion of CrTaN, surface roughness and hardness.

碩士
國立中山大學
化學系研究所
107
Electrolysis of water is an ideal way of clean, sustainable energy. However, the oxygen evolution reaction (OER), a half reaction in water electrolysis, has a high theoretical potential barrier (1.23 V) and multiple electron transfer steps causing poor kinetics, low efficiency. The conventional noble metal oxide for OER (IrO2, RuO¬2) are rare and too expensive for large scale application. It is necessary to have an OER catalyst with low-cost, high catalytic efficiency, and long-term stability to break through the bottleneck. In this work, we improved the catalytic efficiency of cobalt and manganese oxide hydroxide thin film (CMOH) by two different strategies. The first method is synthesis of other metal oxide systems apart from just cobalt and manganese. We choose iron and nickel as the resource of metal ions, and successfully synthesize the iron and manganese, and nickel and manganese oxide thin film. Iron can also play an excellent dopant into CMOH thin film, a Co, Fe, Mn trimetallic thin film has an overpotential (ƞ) 345 mV at current density 10 mA·cm-2, reducing ƞ of 163 mV compare to CMOH thin film. The second method is dividing the continuous CMOH thin film to many small pieces, producing more interfaces containing the catalyst, conductive substrate, and the electrolyte, increasing the active sites and the activity of CMOH thin film. We then built a series of CMOH thin films with different continuity. That one with the maximum discontinuity has only 1/188 coverage area, but reduce a ƞ of 326 mV (at 30 mA·cm-2) and show a 56 times TOF increasing compare to the continuous one. It can also generate a highly current density of 330 mA·cm-2 and maintain its stability for 720 hours.. The result reveals that a both strategies can improve the intrinsic activity of CMOH, reduce the energy consume, and give a higher atomic efficiency in oxygen evolution, realizing a low-cost, high efficiency, and sustainable water electrolysis.

碩士
逢甲大學
材料科學所
90
The Co-W-P alloy thin film with thickness of 55 nm exhibits good diffusion barrier between Cu and Si. After rapidly thermal annealing at 700℃ for 30 seconds, the barrier performance is not degenerated. The pretreatment of substrate for the deposition of Co-W-P thin film is very important to the barrier quality. Barrier layers with 6.5wt% W shows the best barrier result aqmong Co-W-P coatings. The post-treatment of Co-W-P thin film by heating under hydrogen atmosphere would lower the sheet resistance of thin film. Some impurities of Co-W-P film may be removed by hydrolysis in H2 atmosphere. The corrosion resistance of Co-W-P thin film was evaluated. The corrosion rate of copper can be slowed down if Co-W-P thin film is used as capping layer of Cu. The passivation region of Co-W-P can be enlarged as W content in thin film is increased.

碩士
國防大學理工學院
化學工程碩士班
100
In this study, the ferric components of microwave absorbers such as BaFe12O19 and Fe3O4 were prepared using aqueous combustion synthesis and chemical co-precipitation method, respectively. The composite of microwave absorbers were produced by carbon black, β-SiC and ferrites blending in TPR resin matrix. X-ray diffractomer, SEM, VSM were used to invegate the crystal structures, microstructures and magnetic properties of inorganic compoent in absorbers. The microwave properties and the reflection loss of absorbers had measured with HP8527B net work analyzer. For the fabrication of the thin film CIGS(Cu(In,Ga)Se2) solar cell, the absorption layer, CIGS, was sputtered Mo, Cu, Cu-Ga alloy and In metals sequencely on the surface of soda-lime glass by using RF energy source. The selenation was carried out with Se element at 525℃ in the final step. Buffer layer(CdS) was finished by precipitation method. ZnO and conducting ITO were deposited on the top of CdS layer by RF energy source too. The photoelectronic properties and the efficiency of CIGS solar cells were also measured and study in this research.

碩士
大同大學
化學工程學系(所)
104
In this study, the reduction mechanism of cobalt sulfide has been investigated by using cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The reduction equation is [CoTU]2+ + 2e- →CoS + 2CN- + 2NH4+ + TU .According to the results of role of thiourea(TU) by using a microfluidic device, we can find the current be lower when the concentration change to 1M. We can observe the equilibrium voltage become large when the concentration of TU raised by using Tafel analysis and it exhibit the large impedance when the concentration of TU go up by using Electrochemical impedance spectroscopy(EIS).according to the results,the role of TU in the electrolyte might serve as an inhibitor. We also successfully prepare Co9S8 on Nickel foam substrate by using pulse-reversal deposition. It is high capacitance and good rate capability at 750mM TU and 1M TU. The electroactive materials delivered remarkable specific capacity up to 159 mAhg-1 and 193mhAg-1 at 2Ag-1. The retained ratio of capacitance of both is 71% and 60% with 2Ag-1 to 32Ag-1. Finally in this study, we try to change the structure of Co9S8 by using additive (Cetyltrimethylammonium bromide,CTAB or Polyethylene glycol hexadecyl ether,brij58) to the electrolyte. According to the results, the additive CTAB has no effects. But brij58 made the flaky structure of Co9S8 be small. Therefore, we will still use the brij58 in our study.

碩士
國立成功大學
物理學系
102
ABSTRACT SUMMARY Based on previous study, we have already improve the luminous efficiency of light-emitting diodes (LEDs) by depositing zinc oxide related materials thin film between electrode layer and n-GaN layer. Although we get similar results by depositing cobalt doping zinc oxide on pulse laser deposition(PLD), the precise mechanisms that improve luminous efficiency have not confirm. In this research, we assume zinc oxide thin film will reduce the Efficiency droop effect. In order to solve PLD method can't deposit large size chip which is hard to apply by LEDs industry, we use sputter to reconfirm our result. In this research we focus on cobalt doping zinc oxide structure deposited by sputter and compare with PLD thin film. We use X-ray absorption spectrum including (XAS,XANES,EXAFS) and X-ray diffraction method to analyze our thin film. By changing different depositing parameters(Hydrogen, Temperature, Pressure, Percentage), we can observe the difference between each structure. In this research, we find out that Hydrogen can induce Hydrogen interstitial or oxygen vacancy. When the temperature raising, there are few cobalt interstitial will be observed and the amount of oxygen vacancy will also change. Pressure can also affect thin film structure. We use two target to modulate the percentage of cobalt doping in zinc oxide. At the end, we find out that under depositing parameters(temperature:400℃,pressure: 3.75E-3 mbar, Hydrogen mixed, power: 70w)can get the similar structure to previous result. Key word: Sputter, ZnO , XAS, Efficiency droop INTRODUCTION Light emitting diodes are one of the most important components in optoelectronic industry. Because of low power consumption, high lift time and fast reaction, LEDs research attracts increasing attention in the energy-price-up surging era. Some materials such as GaP, GaAs have been commonly used in yellow-blue LEDs. Facing strong global competition in full color LED industry, developing of high efficiency blue LEDs for illumination are ranged from 130-150 lm/W. Ideally, increasing the LED driving current enables the same lumen output to be achieved with less LED chips or using smaller LEDs. Unfortunately, this straightforward route to cost-per-lumen reduction is not readily available in actual GaN LEDs, One of the most significant challenges facing high-power and large size GaN-based LEDs is the efficiency droop effect which means the decrease in external quantum efficiency (EQE)of an LED with increasing injection current in quantum well. Peak internal quantum efficiency (IQE) occurs at relatively low-current densities , then rolls off as current density increases. Typical GaN-based LEDs have a peak in efficiency, typically at current densities less than 10 A/cm2, above which the efficiency gradually decreases. Despite having been the subject of extensive research efforts for a decade, the physical origin of droop has not been clarified. Several mechanism have been proposed to explain this LED droop effect, including electron leakage, poor hole injection, delocalization carriers, Auger recombination. In this research, we deposit cobalt doping zinc oxide thin film on n-GaN try to modulate mobility of n-GaN which can improve poor hole injection. Based on several reference, n-GaN mobility and carrier concentration will influence efficiency droop effect. Zinc oxide (ZnO), a wide bandgap (3.4 eV) II-VI compound semiconductor, has a stable wurtzite structure with lattice spacing a = 0.325 nm and c = 0.521 nm. It has attracted intensive research effort for its unique properties and versatile applications in transparent electronics. X-ray Absorption Spectroscopy (XAS) includes both Extended X-Ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES). X-ray absorption spectra also contain information about the valence state of elements in materials. If the element is present as a cation, the absorption edge is shifted to lower (higher) photon energy because of the lower (higher) ionization potential The “X-ray absorption near edge structure” (XANES) is due to transitions into unoccupied bound states below the edge of the continuum. The “Extended X-ray absorption fine structure” (EXAFS) above the edge is due to backscattering of the photoelectron to the emitting atom. In our research, we use XRD method to check that lattice distance change and secondary phase form when growth parameters change. But XRD can't precise observe whether cobalt substitute zinc place or not, and this method can just determine cobalt interstitials and vacancy formed roughly by lattice distance changed. So we use XAS to analyze thin film structure more precisely. MATERIALS AND METHODS We deposit cobalt doping zinc oxide by sputter. First, we compare two conditions, one is pure Ar gas, the other is 5％ H2 gas mixed. Second, we modulate different parameters, for example, temperature:(400-750℃),pressure(1E-2,3.75E-3,1E-3mbar), power:70w.Third,we use two targets(ZnO,CZO) with different power to modulate cobalt percentage in zinc oxide. Last, we compare with PLD thin film, which substrate temperature is 300℃,frequency is 2HZ, energy is 40mJ. X-ray Absorption(XAS,XANES, EXAFS) is measured in NSRRC 20A,07 beamline in Taiwan. Structural characterization was carried out by X-ray diffraction (XRD). Surface characterization was carried out by SEM, thickness of thin film was carried out by α-step, all were measuring in NCKU. RESULTS AND DISCUSSION First, we compare with the pure argon gas condition and five percentage hydrogen gas mixed condition. In XRD result, we can rule out secondary phase formed and we can observe a slightly move at 34 degree toward small angle when hydrogen gas mixed. It implies lattice distance increase that may cause by hydrogen interstitial. In XAS spectrum we can observe oxygen vacancy formed. In cobalt L-edge spectrum can find out that unoccupied states of cobalt are increasing when hydrogen mixed with argon and oxygen unoccupied states are decreasing. Because of oxygen vacancy formed, the amount of oxygen is decrease which hybridization with cobalt. This cause the peak and area in oxygen K-edge spectrum decrease. In XANES and EXAFS spectrum, we can rule out cobalt is metallic or cobalt oxide form in crystal, because of the shape of our spectrum is totally different to reference. So that we can confirm that cobalt substitute zinc. Second, we change different substrate temperature from 400-750℃. In XRD spectrum, we observe the lattice distance decrease when temperature raised. So we assume that hydrogen will escape from substrate when temperature raised. So the ability of forming oxygen vacancy decrease. In XAS spectrum, we can find out that the amount of oxygen vacancy decrease and unoccupied states increase in oxygen K-edge spectrum when temperature raised. At 750℃,the unoccupied states of oxygen are decrease. Based on reference, it may cause by cobalt interstitial. In XANES and EXAFS spectrum, we can confirm that cobalt substitute zinc whether temperature change or not. Because the cobalt interstitials amount are small, so it can't influence XRD and EXAFS spectrum. Third, we modulate pressure parameter (1E-2,3.75E-3,1E-3mbar),and we find out 3.75E-3 mbar is the better parameter of our sputter system. Obviously, the 3.75E-3 mbar condition FWHM of ZnO(002) peak is more narrow then the other. And photon energy of1E-2,1E-3mbar condition are shifting toward small angle that means the cobalt valence are more approaching to zero. Fourth, we can successfully use ZnO and CZO targets to deposit different cobalt percentage thin film by modulate different power of target, but sacrifice thin film quality. In XAS spectrum, different power of ZnO target can lead different cobalt behavior hybrid with oxygen. Last, we compare PLD with sputter result, we can observe at (temperature:400℃,pressure: 3.75E-3 mbar, Hydrogen mixed, power: 70w) this condition the structure that sputter is similar to PLD result whether in XRD or XAS spectrum. Although, the peak shape are slightly different, we approach our initial goal. CONCLUSION In Hydrogen condition, argon mix Hydrogen can produce oxygen vacancy but also formed some interstitial site. In Temperature condition, when the substrate temperature raise up, we can observe that may decrease hydrogen interstitial and little cobalt interstitials formed at 750.In Pressure condition,3.75E-3mbar is a better growth pressure in our system. In Co-sputter condition, we can modulate Co concentration by using CZO and ZNO target Co-sputter. But quality of thin film we be destroy slightly. we find out the growth condition at(temperature:400℃,pressure: 3.75E-3 mbar, Hydrogen mixed, power: 70w)can approach our previous PLD result. Because of the poor electrical properties of CZO film by sputter, we have to co-doping other materials( Al, Ga…) to improve its electrical properties. Then we can deposit on GaN substrate to check our result and apply on LED.

碩士
國立虎尾科技大學
材料科學與工程系材料科學與綠色能源工程碩士班
104
The effect of the additives on electrochemical-atomic-layer-deposited copper film on Co/SiO2/Si substrate was investigated. An underpotentially -deposited (UPD) Pb atomic layer was used as a sacrificial layer. The following Cu film was prepared using surface limiting redox reaction in copper solution with different additives. Additives significantly affect the replacement of UPD – Pb by Cu. The resistance of the film was measured by four points probe. Crystal structure was analyzed by x-ray diffraction. The surface morphology was analyzed by scanning electron microscope and atomic force microscope. Corrosive effect of the additives on cobalt film was analyzed by electrochemical analyzer. The results showed that lead residual exist in Cu film when adding sodium citrate because sodium citrate reduces the efficiency of copper displacement. On the other hand, sodium perchlorate increases crystallinity and electrical properties of the Cu film. However, the high content of Cu2+ ions in solution enhances the galvanic corrosive on the cobalt film, resulting in the poor adhesion of copper film. Ethylenediamine increases the replacement efficiency of copper film and reduces the corrosion of cobalt film. Thus, the Cu film can be stabilized. In the second part of the study, we investigated the thermal stability of the added ethylenediamine in copper solution to prepare copper film on CoP and CoWP substrates using EC-ALD. The results showed that the copper film can be successfully deposited on the electroless cobalt-based substrate by EC-ALD. The Cu on CoP substrate is thermally stable up to 550oC, and Cu on CoWP substrate is thermally stable at 500oC.

Iron-cobalt alloys have been extensively studied as potential hard disk drive write head materials due to their potentially high saturation flux densities (~2.4T), low coercivities and ease of deposition. Iron-cobalt plating solutions have, however, been shown to have stability issues, necessitating that they be used at low pH or that a stabilizing agent be added to the solution. The purpose of this thesis is to evaluate the stability of a dibasic ammonium citrate plating solution and to characterize the deposits which result from its use. The plating solutions are found to be less stable than previously claimed. The solutions are oxidized by dissolved oxygen, which leads to a valence change in the iron ions and eventually the formation of iron oxide/hydroxide precipitates. These effects are exacerbated by heating or the application of a voltage across the solution. Deposits plated from the solution are fine grained (<40nm) and compact through their thickness. While normally deposited as the equilibrium BCC phase, metastable phases are deposited at elevated temperatures, high pH or in the absence of a stabilizing agent. A metastable phase which is isomorphous to α-Mn is deposited at elevated temperatures. This phase transforms to the BCC phase when annealed at >174ºC and is highly textured. Its presence is detrimental to deposit coercivity.
Materials Engineering

碩士
國立臺灣科技大學
材料科學與工程系
105
In machining industries, dry machining will be considered as a necessity in the near future since it is economically and ecologically desirable. To meet the specific requirement for dry machining, the development of coatings on commonly used cutting tools has been built. These coatings must have abilities to withstand high temperature and reduce friction as “solid lubricants” at the same time. Thus, high-hardness coatings have been widely use for cutting tools to improve durability in dry machining. In recent decade, novel coatings with low coefficient of friction such as TFMGs have been developed. Unique properties of thin film metallic glasses (TFMGs) such as low coefficient of frictions, smooth surface, high strength and toughness, as well as corrosion and wear resistance, have been identified owing to amorphous structure. Thus, TFMGs are thought to be potential materials for machining tools. In this study, Zr-based TFMG (ZrCuAlNi) coated cobalt high-speed steel drill bits were prepared. A milling machine was used for drilling test at constant rotational speed and feed rate. The thrust forces and torques in drilling 7075 aluminum alloy blocks were measured by dynamometer. TFMG-coated drill bits reduced an average ~56% thrust force and had relatively low applied torque during drilling against aluminum alloy blocks, referring better chip removal ability. The lower force increment and applied torque further indicated better wear resistance since no wear or scratch were found in TFMG-coated drill bits by scanning electron microscopy (SEM), the durability then seemed to be better. Keywords: Dry machining; Drill bit; solid lubricant; Thin film metallic glass; Low COF; wear resistance

The development of radio frequency integrated circuits (RFICs), especially the dream of integrating analog, digital and radio frequency (RF) components on the same chip that is commonly known as System-on-a-Chip (SoC), is crucial to mobile communications of the future. Such SoC approach offers enhanced performance, greater reliability, and substantially less power consumption of integrated circuits while reducing overall physical size and thus manufacturing cost. However, the progress has been stalled by the lack of miniaturized inductor elements. Rise of unwanted parasitic effects limits down-scaling of the inductor structures and leaves the use of magnetic coating as a viable and attractive option to enhance the inductance and thus inductance density. It is also essential to shift from perm alloy and other amorphous alloys to ferrites and hex ferrites as the core material because of their very high electrical resistivity so as to keep losses in check, a criterion that cannot be compromised on in GHz frequency applications. This is viable, however, only if the integration of the magnetic core (film), particularly a ferrite film, is fully compatible with the CMOS fabrication process. Various approaches have been taken to meet this requirement, including investigations of employing layers of ferrite materials to envelop the inductor loop. However, the deposition of thin films of ferrites, whether by PVD or CVD, usually calls for the deposited ferrite layer to be annealed at an elevated temperature to crystallize the layer so that its magnetic characteristics are appropriate for the optimum performance of the circuit element. Such annealing is incompatible with CMOS process flow required for aggressive device geometries, as the inductor element is added after the active semiconductor circuit is processed, and any exposure of the processed circuit to elevated temperatures risks disturbing precise doping profiles employed and the integrity of the inter-layer dielectrics. What is called for is a low-temperature process for the deposition of a ferrite layer on top of the patterned inductor element – a layer of thickness such that most of the fringe field is encapsulated – while ensuring that the layer comprises crystallites of uniform size that leads to uniform magnetic behaviour. Recognizing the difficulty of meeting the various stringent requirements, it has recently been remarked that such a goal is a formidable challenge. In an attempt to address this challenge, in this work, we have adopted a counter-intuitive approach - the deposition of the desired ferrite composition on a processed die (that contains the inductor structures along with active semiconductor circuits) by immersing it into a chemical (reactant) solution, followed by a brief irradiation of microwave frequency. However, to identify the desired ferrite composition and the appropriate recipe to deposit them, a systematic effort had to be made first, to understand the inter-relationship between synthesis process, structure of resulting material, and its physical and chemical properties. Therefore, at the beginning, a general introduction in which key concepts related to the magnetic-core inductors, the microwave-irradiation-assisted synthesis of nanostructures, the ‗state of the art‘ in the field of integration of appropriate magnetic material to the RFICs, are all outlined. As a proof of concept, microwave-irradiation-assisted solution-based deposition of zinc ferrite thin films on the technologically important Si (100) substrate is demonstrated. The highlight of the process is the use of only non-toxic metal organic precursors and aqua-alcoholic solvents for the synthesis, which is complete in 10 minutes @< 100 °C, without any poisonous by-products. Effects of various process parameters such as solute concentrations, surfactant types, and their concentrations are investigated. A wide range of deposition rates (10 - 2000 nm/min) has been achieved by tweaking the process parameters. The simultaneous formation of zinc ferrite nanocrystallites (ZFNC) along with deposition of thin film is the hallmark of this synthesis technique. Unlike its bulk counterpart, both film and powder are found upon investigation to be rich in magnetic behavior– owing to plausible cationic distribution in the crystal lattice, induced by the inherently quick and far-from-equilibrium nature of the process. The accurate estimation of magnetic characteristics in film is, however, found to be difficult due to the high substrate-to-film mass ratio. The simultaneously prepared ZFNC is examined to arrive at the optimized process recipe that imparts the desired magnetic properties to the zinc ferrite system. The crystallographic cationic distribution in zinc ferrite powder is, however, difficult to study due to the nanoscale dimension of the as prepared material. To enable crystal growth, slow and rapid annealing in air at two different temperatures are employed. The effects of these annealing schemes on various attributes (magnetic properties in particular) are studied. Rapid annealing turns out to be an interesting pathway to promote rapid grain-growth without disturbing the crystallographic site occupancies. The presence of inversion, i.e., the amount of Fe3+ in the ‗A‘-sites in the spinel structure that ideally is zero in normal spinel structure of zinc ferrite, is evident in all annealed ZFNC, as determined by Riveted analysis. Such partially inverted ZFNC exhibits soft magnetic behavior with high saturation magnetization, which can easily be ―tuned‖ by choosing appropriate annealing conditions. However, a few unique strategic modifications to the same microwave-irradiation-assisted solution-based synthesis technique are tried for the formation of nanocrystalline powder with desired sizes and properties without the necessity of anneal. The approach eventually appears to pave a way for the formation of oriented structures of zinc ferrite. The effects of anneal, nevertheless, are studied with the help of neutron powder diffractometry and magnetic measurements. The magnetic ordering at various temperatures is analyzed and connected to the magnetic measurements. The study shows that long-range magnetic ordering, present even at room temperate, originates from the distribution of cations in the partially inverted spinel structures, induced by the rapid and kinetically driven microwave synthesis. Keeping the mild nature (<200 °C) of the processing in mind, a large degree of inversion (~0.5) is a surprise and results in a very high saturation magnetization, as much as 30 emu/g at room temperature (paramagnetic in bulk), in the ZFNC system. Based on the knowledge of process-structure-property interrelationship, a recipe for the deposition of ferrite thin films by the microwave-assisted deposition technique is optimized. Successful deposition of smooth and uniform zinc ferrite thin films on various substrates is, then, demonstrated. The mystery behind the strong adherence of the film to the substrate - an unexpected outcome of a low-temperature process - is probed by XPS and the formation of silicates at the interface is identified as the probable reason. The uniformity and consistency of film composition is also examined in this chapter. Another salient feature of the process is its capability to coat any complex geometry conformally, allowing the possibility of depositing the material in a way to ―wrap around‖ the three-dimensional inductor structures of RF-CMOS. Integration of nanostructure zinc ferrite thin films onto on-chip spiral inductor structures has been demonstrated successfully. The magnetic-core inductors so obtained exhibit the highest inductance density (700 nH/mm2) and the highest Q factor (~20), reported to date, operate at 5 GHz and above, by far the highest reported to date. An increase in inductance density of as much as 20% was achieved with the use of just 1 µm thick film of zinc ferrite covering only the ―top‖ of the spiral structure, i.e., up to 20% of chip real estate can potentially be freed to provide additional functionality. The microwave-assisted solution-based deposition process described in this thesis is meant for ‗post-CMOS‘ processing, wherein the film deposited on some specific electronic components can add desired functionality to or improve the performance of a component (circuit) underneath. However, the effect of such ‗post-CMOS‘ processing on the active MOS devices, interconnects, and even inter-layer-dielectrics fabricated prior to the deposition has to be mild enough to leave the performance of delicate MOS characteristics intact. Such CMOS-compatibility of the present deposition process has been tested with a satisfactorily positive result.

The development of radio frequency integrated circuits (RFICs), especially the dream of integrating analog, digital and radio frequency (RF) components on the same chip that is commonly known as System-on-a-Chip (SoC), is crucial to mobile communications of the future. Such SoC approach offers enhanced performance, greater reliability, and substantially less power consumption of integrated circuits while reducing overall physical size and thus manufacturing cost. However, the progress has been stalled by the lack of miniaturized inductor elements. Rise of unwanted parasitic effects limits down-scaling of the inductor structures and leaves the use of magnetic coating as a viable and attractive option to enhance the inductance and thus inductance density. It is also essential to shift from perm alloy and other amorphous alloys to ferrites and hex ferrites as the core material because of their very high electrical resistivity so as to keep losses in check, a criterion that cannot be compromised on in GHz frequency applications. This is viable, however, only if the integration of the magnetic core (film), particularly a ferrite film, is fully compatible with the CMOS fabrication process. Various approaches have been taken to meet this requirement, including investigations of employing layers of ferrite materials to envelop the inductor loop. However, the deposition of thin films of ferrites, whether by PVD or CVD, usually calls for the deposited ferrite layer to be annealed at an elevated temperature to crystallize the layer so that its magnetic characteristics are appropriate for the optimum performance of the circuit element. Such annealing is incompatible with CMOS process flow required for aggressive device geometries, as the inductor element is added after the active semiconductor circuit is processed, and any exposure of the processed circuit to elevated temperatures risks disturbing precise doping profiles employed and the integrity of the inter-layer dielectrics. What is called for is a low-temperature process for the deposition of a ferrite layer on top of the patterned inductor element – a layer of thickness such that most of the fringe field is encapsulated – while ensuring that the layer comprises crystallites of uniform size that leads to uniform magnetic behaviour. Recognizing the difficulty of meeting the various stringent requirements, it has recently been remarked that such a goal is a formidable challenge. In an attempt to address this challenge, in this work, we have adopted a counter-intuitive approach - the deposition of the desired ferrite composition on a processed die (that contains the inductor structures along with active semiconductor circuits) by immersing it into a chemical (reactant) solution, followed by a brief irradiation of microwave frequency. However, to identify the desired ferrite composition and the appropriate recipe to deposit them, a systematic effort had to be made first, to understand the inter-relationship between synthesis process, structure of resulting material, and its physical and chemical properties. Therefore, at the beginning, a general introduction in which key concepts related to the magnetic-core inductors, the microwave-irradiation-assisted synthesis of nanostructures, the ‗state of the art‘ in the field of integration of appropriate magnetic material to the RFICs, are all outlined. As a proof of concept, microwave-irradiation-assisted solution-based deposition of zinc ferrite thin films on the technologically important Si (100) substrate is demonstrated. The highlight of the process is the use of only non-toxic metal organic precursors and aqua-alcoholic solvents for the synthesis, which is complete in 10 minutes @< 100 °C, without any poisonous by-products. Effects of various process parameters such as solute concentrations, surfactant types, and their concentrations are investigated. A wide range of deposition rates (10 - 2000 nm/min) has been achieved by tweaking the process parameters. The simultaneous formation of zinc ferrite nanocrystallites (ZFNC) along with deposition of thin film is the hallmark of this synthesis technique. Unlike its bulk counterpart, both film and powder are found upon investigation to be rich in magnetic behavior– owing to plausible cationic distribution in the crystal lattice, induced by the inherently quick and far-from-equilibrium nature of the process. The accurate estimation of magnetic characteristics in film is, however, found to be difficult due to the high substrate-to-film mass ratio. The simultaneously prepared ZFNC is examined to arrive at the optimized process recipe that imparts the desired magnetic properties to the zinc ferrite system. The crystallographic cationic distribution in zinc ferrite powder is, however, difficult to study due to the nanoscale dimension of the as prepared material. To enable crystal growth, slow and rapid annealing in air at two different temperatures are employed. The effects of these annealing schemes on various attributes (magnetic properties in particular) are studied. Rapid annealing turns out to be an interesting pathway to promote rapid grain-growth without disturbing the crystallographic site occupancies. The presence of inversion, i.e., the amount of Fe3+ in the ‗A‘-sites in the spinel structure that ideally is zero in normal spinel structure of zinc ferrite, is evident in all annealed ZFNC, as determined by Riveted analysis. Such partially inverted ZFNC exhibits soft magnetic behavior with high saturation magnetization, which can easily be ―tuned‖ by choosing appropriate annealing conditions. However, a few unique strategic modifications to the same microwave-irradiation-assisted solution-based synthesis technique are tried for the formation of nanocrystalline powder with desired sizes and properties without the necessity of anneal. The approach eventually appears to pave a way for the formation of oriented structures of zinc ferrite. The effects of anneal, nevertheless, are studied with the help of neutron powder diffractometry and magnetic measurements. The magnetic ordering at various temperatures is analyzed and connected to the magnetic measurements. The study shows that long-range magnetic ordering, present even at room temperate, originates from the distribution of cations in the partially inverted spinel structures, induced by the rapid and kinetically driven microwave synthesis. Keeping the mild nature (<200 °C) of the processing in mind, a large degree of inversion (~0.5) is a surprise and results in a very high saturation magnetization, as much as 30 emu/g at room temperature (paramagnetic in bulk), in the ZFNC system. Based on the knowledge of process-structure-property interrelationship, a recipe for the deposition of ferrite thin films by the microwave-assisted deposition technique is optimized. Successful deposition of smooth and uniform zinc ferrite thin films on various substrates is, then, demonstrated. The mystery behind the strong adherence of the film to the substrate - an unexpected outcome of a low-temperature process - is probed by XPS and the formation of silicates at the interface is identified as the probable reason. The uniformity and consistency of film composition is also examined in this chapter. Another salient feature of the process is its capability to coat any complex geometry conformally, allowing the possibility of depositing the material in a way to ―wrap around‖ the three-dimensional inductor structures of RF-CMOS. Integration of nanostructure zinc ferrite thin films onto on-chip spiral inductor structures has been demonstrated successfully. The magnetic-core inductors so obtained exhibit the highest inductance density (700 nH/mm2) and the highest Q factor (~20), reported to date, operate at 5 GHz and above, by far the highest reported to date. An increase in inductance density of as much as 20% was achieved with the use of just 1 µm thick film of zinc ferrite covering only the ―top‖ of the spiral structure, i.e., up to 20% of chip real estate can potentially be freed to provide additional functionality. The microwave-assisted solution-based deposition process described in this thesis is meant for ‗post-CMOS‘ processing, wherein the film deposited on some specific electronic components can add desired functionality to or improve the performance of a component (circuit) underneath. However, the effect of such ‗post-CMOS‘ processing on the active MOS devices, interconnects, and even inter-layer-dielectrics fabricated prior to the deposition has to be mild enough to leave the performance of delicate MOS characteristics intact. Such CMOS-compatibility of the present deposition process has been tested with a satisfactorily positive result.

碩士
國立中興大學
材料科學與工程學系所
103
This study prepares p-type amorphous cobalt carbon (a-CoC) thin film alloys at different radio-frequency (RF) powers using reactive sputtering deposition, and investigates the microstructures, optical, and electrical properties of a-CoC thin film alloys. Moreover, the p-type a-CoC thin film alloys with identical thickness of 100 nm are deposited on n-type silicon substrates to fabricate a-CoC/n-Si device, and the properties of this device are also studied. Experimental results indicate that as the RF power increases from 50 to 250 W, the deposition rate rises; XPS results show that the cobalt/carbon ratio increases from 2.8 to 59.2%, and the sp2 carbon fraction of a-CoC thin film alloys increases from 24 to 60%; and Raman results indicate that ID/IG increases from 0.66 to 1.55. Additionally, as the RF power increases from 50 to 250 W, the optical band gap of a-CoC thin film alloys decreses from 2.16 to 0.17 eV and the resistivity decreases from 3.9×102 to 3.8×10-4 Ω·m. This is because the cobalt content in the a-CoC thin film alloys increases and their structure changes into metal. At the RF power of 100 W, the a-CoC/n-Si device has an optimal ideality factor of 1.6, and its built-in voltage is 0.51 V.

The research in permanent magnet thin films focuses on the search of new materials and methods to increase the prevalent data storage limit. In the recent past the work towards the application of these films to micro systems have also gained momentum. Materials like samarium cobalt with better magnetic properties and temperature stability are considered to be suitable in this regard. The essential requirement in miniaturization of these films is to deposit them on silicon substrates that can alleviate the micro fabrication process. In this work, an effort has been made to deposit SmCo films with better magnetic properties on silicon substrates. In the deposition of SmCo, the composition of the deposited films and the structural evolution are found to play an important role in determining the magnetic properties. Proper control over these parameters is essential in controlling the magnetic properties of the deposited films. SmCo being a two component material the composition of the films is dependent on the nature of the source and the transport of the material species from source to substrate. On the other hand, structural evolution is dependent on the energetical considerations between the SmCo lattice and substrate lattice. This most often is dominated by the lattice match between the condensing lattice and the substrate lattice. As such Si does not provide good lattice match to SmCo lattice. Hence suitable underlayers are essential in the deposition of these films. Materials like W, Cu, Mo and Cr were used as underlayers. Out of all these Cr is found to provide good lattice match and adhesion to SmCo lattice. Sputtering being the common deposition tool, SmCo could be sputtered either from the elemental targets of Sm and Co or from the compound target of SmCo5. Sputtering of elemental targets of Sm and Co provides the flexibility of varying the composition whereas sputtering from the SmCo alloy target provides to flexibility of controlling the structural evolution by different process parameters. In this work two different techniques namely Facing Target Sputtering (FTS) and Ion Beam Sputter Deposition (IBSD) were followed in depositing SmCo films. In FTS technique, SmCo films were directly deposited on silicon substrates by simultaneous sputtering of samarium and cobalt targets facing each other. This sputtering geometry enabled to achieve films with a wide composition range of 55 – 95 at. % of cobalt in single deposition. The resulting composition variation and material property variation were investigated in terms of process parameters like pressure, temperature, SubstrateTarget Distance (STD) and InterTarget Distance (ITD). The composition distribution of the films was found to be dependent on the thermalisation distances and the mean free path available during the transport. To explain the process and the composition variation, a simulation model based on Monte Carlo method has been employed. The simulated composition variation trends were in good agreement with that of the experimental observations. IBSD, known for its controlled deposition, was employed to deposit both Cr (as an underlayer) and SmCo films. Cr with close epitaxial match with SmCo induces structural evolution in deposited films. The initial growth conditions were found to play a dominant role in the structural evolution of these Cr films. Hence, initial growth conditions were modified by means of oblique incidence and preferential orientation of (200) plane was obtained. With three different angles of incidence, three different surface orientations of Cr films were achieved. These films were then used as structural templates in the deposition of SmCo films. The influence of parameters like composition, impurities, film thickness, beam energy, ion flux, annealing, angles of incidence and underlayer properties on the structural and magnetic properties of SmCo was studied. The structural evolution of SmCo has been found to depend on the structural orientation of Cr underlayers. This followed the structural relation of SmCo(100)||Cr(110)||Si(100) and SmCo(110)||Cr(100)||Si(100). A mixed surface plane orientation was observed in the case of mixed orientation Cr template. The magnetic coercivities were found to increase from 50 Oe to 5000 Oe with the change in the structure of the deposited films.

The research in permanent magnet thin films focuses on the search of new materials and methods to increase the prevalent data storage limit. In the recent past the work towards the application of these films to micro systems have also gained momentum. Materials like samarium cobalt with better magnetic properties and temperature stability are considered to be suitable in this regard. The essential requirement in miniaturization of these films is to deposit them on silicon substrates that can alleviate the micro fabrication process. In this work, an effort has been made to deposit SmCo films with better magnetic properties on silicon substrates. In the deposition of SmCo, the composition of the deposited films and the structural evolution are found to play an important role in determining the magnetic properties. Proper control over these parameters is essential in controlling the magnetic properties of the deposited films. SmCo being a two component material the composition of the films is dependent on the nature of the source and the transport of the material species from source to substrate. On the other hand, structural evolution is dependent on the energetical considerations between the SmCo lattice and substrate lattice. This most often is dominated by the lattice match between the condensing lattice and the substrate lattice. As such Si does not provide good lattice match to SmCo lattice. Hence suitable underlayers are essential in the deposition of these films. Materials like W, Cu, Mo and Cr were used as underlayers. Out of all these Cr is found to provide good lattice match and adhesion to SmCo lattice. Sputtering being the common deposition tool, SmCo could be sputtered either from the elemental targets of Sm and Co or from the compound target of SmCo5. Sputtering of elemental targets of Sm and Co provides the flexibility of varying the composition whereas sputtering from the SmCo alloy target provides to flexibility of controlling the structural evolution by different process parameters. In this work two different techniques namely Facing Target Sputtering (FTS) and Ion Beam Sputter Deposition (IBSD) were followed in depositing SmCo films. In FTS technique, SmCo films were directly deposited on silicon substrates by simultaneous sputtering of samarium and cobalt targets facing each other. This sputtering geometry enabled to achieve films with a wide composition range of 55 – 95 at. % of cobalt in single deposition. The resulting composition variation and material property variation were investigated in terms of process parameters like pressure, temperature, SubstrateTarget Distance (STD) and InterTarget Distance (ITD). The composition distribution of the films was found to be dependent on the thermalisation distances and the mean free path available during the transport. To explain the process and the composition variation, a simulation model based on Monte Carlo method has been employed. The simulated composition variation trends were in good agreement with that of the experimental observations. IBSD, known for its controlled deposition, was employed to deposit both Cr (as an underlayer) and SmCo films. Cr with close epitaxial match with SmCo induces structural evolution in deposited films. The initial growth conditions were found to play a dominant role in the structural evolution of these Cr films. Hence, initial growth conditions were modified by means of oblique incidence and preferential orientation of (200) plane was obtained. With three different angles of incidence, three different surface orientations of Cr films were achieved. These films were then used as structural templates in the deposition of SmCo films. The influence of parameters like composition, impurities, film thickness, beam energy, ion flux, annealing, angles of incidence and underlayer properties on the structural and magnetic properties of SmCo was studied. The structural evolution of SmCo has been found to depend on the structural orientation of Cr underlayers. This followed the structural relation of SmCo(100)||Cr(110)||Si(100) and SmCo(110)||Cr(100)||Si(100). A mixed surface plane orientation was observed in the case of mixed orientation Cr template. The magnetic coercivities were found to increase from 50 Oe to 5000 Oe with the change in the structure of the deposited films.