With increase in the number of three dimensional (3-D) nanometer-scale objects that are being either fabricated or studied, there is a need to accurately characterize their geometry. While the Atomic force microscope (AFM) is a versatile tool for performing nano-metrology, it suffers from issues of poor accessibility of 3-D features and inability to measure 3-D forces that limit its applicability in 3-D nano-metrology. This thesis investigates the design and development of a novel probing system based on AFM that improves accessibility and enables direct measurement of 3-D forces acting on the AFM tip. Two approaches are investigated to address the issue of poor accessibility. The first is to develop a novel system that enables in-situ replacement and reuse of specialized AFM tips that improve accessibility, and the second is to design a special AFM tip that can actively re-orient about two independent axes. In order to perform in-situ tip replacement, a liquid meniscus based micro-gripper is developed and integrated on to a conventional AFM probe. The stiffness of the gripper is analyzed and shown to be adequately high along all three axes for AFM imaging to be performed. Tip replacement and re-use are both experimentally demonstrated by employing a novel tip-exchange station. The replaced tips are employed to show artifact-free AFM imaging of a standard calibration grating in both tapping-mode and contact-mode. To actively re-orient a conventional tip, a novel magnetically-actuated micro-scale ball-and-socket joint is integrated onto an AFM probe. The quasi-static behavior of the joint is experimentally characterized, and the ability of the tip to independently re-orient about two axes is demonstrated. The achieved range is about +/- 90 degrees about both X- and Y-axes. In order to realize the potential of the proposed probes for 3-D nano-metrology, an AFM is developed in-house that possesses the capability to make direct measurement of 3-D forces. Optimization of the measurement system to achieve identical sensitivities and resolution along all three axes is studied. Subsequently, the necessary electronics for measurement, actuation and control are developed. All the subsystems are experimentally calibrated and integrated. The overall AFM is shown to have a resolution of about 0.2 nm when operated in tapping-mode. The developed AFM is employed to showcase the following applications: characterization of the coefficient of kinetic friction of Muscovite mica, force controlled nano-scribing on polymethyl methacrylate (PMMA) and tapping-mode imaging of a calibration grating with the developed re-orientable AFM probe. Finally, the unique ability of the re-orientable AFM probe to control its tip-orientation is employed to develop a nanometer-scale coordinate measurement machine (CMM). The developed nano-CMM is shown to access the vertical wall of a sample and obtain its topography.

Recently, efforts have been made for self-powering the batteries and portable electronic devices by piezoelectric nanogenerators. The piezoelectric nanogenerators can work as a power source for nano-systems and also as an active sensor. The piezoelectric nanogenerator is a device that converts random mechanical energy into electrical energy by utilizing the semiconducting and piezoelectric properties. Also, the mechanical energy is always available in and around us for powering these nano devices. The aim of the present thesis work is to explore 1D and 2D ZnO nanostructures (nanorods and nanosheets) on metal alloy substrates for the development of piezoelectric nanogenerators in energy harvesting and sensors applications. Hydrothermal synthesis method was adopted for the growth of ZnO nanostructures. The nanogenerators were fabricated by using the optimized synthesis parameters and subsequently studied their performance for power generation and as an active speed sensor. These 1D and 2D nanostructures based nanogenerators have opened up a new window for the energy harvesting applications and sensors development. The thesis is divided into following six chapters. Chapter 1: This chapter gives a general introduction about energy harvesting devices such as nanogenerators, available energy sources, mechanical energy harvesting, ZnO material and the details on hydrothermal synthesis process. A brief literature survey on different applications of piezoelectric nanogenerators is also included. Chapter 2: A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. Details on the synthesis of 1D ZnO nanorods on Phynox alloy substrate by hydrothermal method are presented. Further, the optimization of parameters such as growth temperature, seed layer annealing and substrate temperature effects on the synthesis of ZnO nanorods are discussed in detail. As-synthesized ZnO nanorods have been characterized using XRD, FE-SEM, TEM and XPS. Chapter 3: It reports on the fabrication of piezoelectric nanogenerator on Phynox alloy substrate as power generating device by harvesting the mechanical energy. Initially, the performance of the nanogenerator for power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the output voltage response of the nanogenerator was studied for its use as an active speed sensor. Chapter 4: Synthesis of Al doped 2D ZnO nanorsheets on Aluminum alloy (AA-6061) substrate by hydrothermal method is reported in this chapter. The optimized parameters such as growth temperature and growth time effects on the synthesis of ZnO nanosheets are discussed. As-synthesized ZnO nanosheets were characterized using XRD, FE-SEM, TEM and XPS. The Al doping in ZnO is confirmed by EDXS and XPS analysis. Chapter 5: Cost effective fabrication of Al doped 2D ZnO nanosheets based nanogenerator for direct current (DC) power generation is reported in this chapter. The performance of the nanogenerator for DC power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the DC output voltage response of the nanogenerator was studied for its use as an active speed sensor. Chapter 6: The first section summarizes the significant features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.

Vortex tube (VT) is a mechanical device with no moving parts. The fundamental principle of Vortex Tube is that it can split an incoming fluid flow of a constant pressure and constant temperature gas stream into two separate low pressure streams, one having higher enthalpy and the other having lower enthalpy than the inlet flow. So this device essentially works as a temperature separator. On separation from the device, a warmer flow exits through a terminal which is called the “hot end” and a low temperature stream comes out from another terminal known as the “cold end”. Just with a few bar pressure of compressed air at room temperature can produce a hot stream temperature of about 150°C and a cold stream temperature of about - 40°C. This temperature separation scheme allows us to get cooling and heating effect simultaneously using the same device which makes the Vortex tube one of the popular mechanical equipment and is used in many fields of engineering. The cooling or heating effect produced by this device is largely dependent on geometric parameters of the device itself. Since no exact theoretical correlation is there between the geometric parameters and the cooling (or heating) effect produced, VT design is solely based on empirical relations. There are quite a few geometric parameters which affect the cooling effect of this device and all the empirical correlation are needed to design the optimum VT for maximum cooling/heating effect. These relations can be derived in two ways, either by numerical methods or by experimental investigations. The first part of the thesis important geometric parameter of the VT namely the ratio of the “cold end” diameter (to the “tube diameter” , which has been numerically optimized in this work to achieve maximum temperature separation. In our efforts to design a VT based refrigeration system, optimization of the VT itself is not enough. A suitable heat exchanger (HX) which can extract the cold enthalpy from the VT also needs to be designed and cascaded with the VT to get the complete refrigeration system. The second part of the thesis is solely dedicated to the design of a suitable HX that can be used alongside a VT to produce refrigeration. The HXs design can be approached from two directions, dimensional aspect and material aspect. Rather than focusing on the dimensional aspect in this work we have concentrated of the material aspect of HX design. It is fairly obvious that the thermal conductivity (TC) of the HX material will play a crucial role on the cooling effect of the refrigeration system. Conventional metals with high TC can be used to design HXs but the downsides of using pure metals such as Copper, Iron are that they are heavy, quite expensive and highly reactive to corrosive fluids. Because of this, high TC ceramic material such as Aluminium Nitride (AlN) is quite often used to fabricate HXs and they are used for spot cooling in electronic systems. AlN has TC of 160 W/m-K which is high but not as high as of Copper or Iron. TC of AlN can be increased by mixing the right volume fraction of metal powder (such as pure Aluminium) with it to a great extent. So in a nutshell, instead of using pure AlN, if we use the particle reinforced binary composite [AlN + Al (powder)] to design a HX, we would achieve the benefits of having high TC as well as properties such as anti-corrosiveness, cost effectiveness and weight reduction. In the above context, prediction of TC of particle reinforced composite materials containing a base material of low TC and a filler material of high TC is of utmost importance. Till now a very few analytical heat transfer models are available in the literature that can accurately predict the TC value of such composites especially when high volume fraction of filler particles is added to the base material or if more than one type of filler particles are added. So in this thesis, three analytical heat transfer models have been developed that can predict the TC of binary as well as tertiary particle reinforced composites. The third and the final segment of the thesis deals with the performance study of a refrigeration system comprised of the optimized VT cascaded with a suitable HX made out of a particle reinforced composite material. The numerical results show how the HX effectiveness improves as the volume fraction of the filler particles in the composite increases. The key results of the works described in the thesis are as follows: • Through extensive numerical simulations it is shown that for = 0.5, the temperature separation in a VT is maximum. • The heat transfer models developed to predict the thermal conductivity of binary composites, shows the trend of how thermal conductivity varies with increasing volume fraction of filler. It has been shown that initially the thermal conductivity increases linearly with a small slope, then after a critical volume fraction an abrupt increment of slope is observed due to the formation of continuous heat conduction paths within the composite. Further increase in volume fraction shows linear increment of thermal conductivity with lesser slope as before. • The heat transfer model developed to predict the thermal conductivity of tertiary composites is suitable for low volume fraction (< 20 %). The model shows the addition of one component into the base matrix affects the distribution of the other component which is observed through the covariance. • The last part of the thesis shows that compared to a pure AlN heat exchanger, a heat exchanger made of AlN + 30 % volume fraction of pure Aluminium powder, has increased heat exchanger effectiveness by more than 50 %. Thesis outline is as follows: • Chapter 1 is a brief introduction to Vortex Tube. • Chapter 2 deals with the necessary literature review related to Vortex Tube as well as presently available heat transfer models that are equipped to handle composite materials to predict their TC. • Chapter 3 elaborates numerical modeling and optimization of a critical parameter ( to achieve maximum temperature separation in a VT. • Chapter 4 presents a stochastic heat transfer model to estimate the TC of Binary particle reinforced composites containing low volume fraction of filler particles. • Chapter 5 describes the development of a computational heat transfer model to predict the TC of Particle Reinforced Binary Composite materials containing high volume fraction of filler element. • Chapter 6 deals with a stochastic heat transfer model to calculate TC of Particle Reinforced Tertiary Composite materials containing low volume fractions of filler elements. • Chapter 7 consolidates all the necessary concepts and data from previous chapters to design the final cascaded VT based refrigeration system and presents a performance study. • The last chapter summarizes the entire work along with scope for future work.

Recently, efforts have been made for self-powering the batteries and portable electronic devices by piezoelectric nanogenerators. The piezoelectric nanogenerators can work as a power source for nano-systems and also as an active sensor. The piezoelectric nanogenerator is a device that converts random mechanical energy into electrical energy by utilizing the semiconducting and piezoelectric properties. Also, the mechanical energy is always available in and around us for powering these nano devices. The aim of the present thesis work is to explore 1D and 2D ZnO nanostructures (nanorods and nanosheets) on metal alloy substrates for the development of piezoelectric nanogenerators in energy harvesting and sensors applications. Hydrothermal synthesis method was adopted for the growth of ZnO nanostructures. The nanogenerators were fabricated by using the optimized synthesis parameters and subsequently studied their performance for power generation and as an active speed sensor. These 1D and 2D nanostructures based nanogenerators have opened up a new window for the energy harvesting applications and sensors development. The thesis is divided into following six chapters. Chapter 1: This chapter gives a general introduction about energy harvesting devices such as nanogenerators, available energy sources, mechanical energy harvesting, ZnO material and the details on hydrothermal synthesis process. A brief literature survey on different applications of piezoelectric nanogenerators is also included. Chapter 2: A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. Details on the synthesis of 1D ZnO nanorods on Phynox alloy substrate by hydrothermal method are presented. Further, the optimization of parameters such as growth temperature, seed layer annealing and substrate temperature effects on the synthesis of ZnO nanorods are discussed in detail. As-synthesized ZnO nanorods have been characterized using XRD, FE-SEM, TEM and XPS. Chapter 3: It reports on the fabrication of piezoelectric nanogenerator on Phynox alloy substrate as power generating device by harvesting the mechanical energy. Initially, the performance of the nanogenerator for power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the output voltage response of the nanogenerator was studied for its use as an active speed sensor. Chapter 4: Synthesis of Al doped 2D ZnO nanorsheets on Aluminum alloy (AA-6061) substrate by hydrothermal method is reported in this chapter. The optimized parameters such as growth temperature and growth time effects on the synthesis of ZnO nanosheets are discussed. As-synthesized ZnO nanosheets were characterized using XRD, FE-SEM, TEM and XPS. The Al doping in ZnO is confirmed by EDXS and XPS analysis. Chapter 5: Cost effective fabrication of Al doped 2D ZnO nanosheets based nanogenerator for direct current (DC) power generation is reported in this chapter. The performance of the nanogenerator for DC power generation due to finger tip impacts was studied and subsequently its switching polarity test was also carried out. Output voltage measurements were carried out using the in-house developed experimental setup. Stability test was also carried out to see the robustness of the nanogenerator. Finally, the DC output voltage response of the nanogenerator was studied for its use as an active speed sensor. Chapter 6: The first section summarizes the significant features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.

Carbon nanotubes (CNT) and graphene have been one of the noticeable research areas in science and technology. In recent years, the assembly of these carbon nanostructures is one of the most interesting topic to the scientific world due to its variety of applications from nano to macroscale. These bulk nanostructures to be applicable in shock absorbers, batteries, sensors, photodetectors, actuators, solar cells, fuel cells etc. The present work is motivated to study the detailed compressive behavior of three dimensional cellular assemblies of CNT and graphene. The CNT foams are synthesized by chemical vapor deposition method. It is interesting to study the compressive behavior of CNT foam in the presence external magnetic field applied perpendicular to CNT axis. The peak stress and energy absorption capability of CNT foam enhances by four and nearly two times in the presence of magnetic field as compared to the absence of the magnetic field. In the absence of magnetic field the deformation of CNT foam is obtained elastic, plateau and densification regions. Further CNT foam is loaded with iron oxide nanoparticles of diameter is ~ 40nm on the surface and detailed study of the compressive behavior of the foam by varying iron nanoparticles concentration. The peak stress and energy absorption capability of CNT foam initially decreases with increasing the intensity of the magnetic field, further increases the intensity of the magnetic field the maximum stress and energy absorption capability increases which is due to magnetic CNT and particles align in the direction of the magnetic field. CNT surfaces were further modified by fluid of different viscosities. The mechanical behavior of CNT foam filled with fluids of varying viscosities like 100%, 95% and 90% glycerol and silicone oil are 612, 237, 109 and 279 mPa-s respectively. The mechanical behavior of CNT foam depends on both the intensity of magnetic field and fluid viscosity. The non linear relation between peak stress of CNT and magnetic field intensity is σp(B, η) = σ0 ± α(B-B0) where σ0 is the peak stress at B = B0 , η is the fluid viscosity, parameter α depends on properties of the MR fluid and B0 is an optimum magnetic field for which peak stress is maximum or minimum depending on the fluid viscosity. Graphene is assembled into a three dimensional structure called graphene foam. The graphene foam is infiltrated with polymer and study the detailed compressive behavior of graphene foam and graphene foam/PDMS at different strains of 20, 40, 60 and 70%. The maximum stress and energy absorption capability of graphene foam/PDMS is six times higher than the graphene foam. Also the graphene foam/PDMS is highly stable and reversible for 100 cycles at strains of 30 and 50%. The mechanical behavior of CNT, graphene foam, CNT/PDMS and graphene foam/PDMS is compared. Among all the foams, graphene foam/PDMS has shown the highest elastic modulus as compared to other foams. This behavior can be attributed to the wrinkles formation during the growth of graphene and a coupling between PDMS and interfacial interactions of graphene foam. Therefore it suggests potential applications for dampers, cushions and electronic packaging. Furthermore, the interaction between nanoparticles and polymer in a novel architecture composed of PDMS and iron oxide nanoparticles is studied. The load bearing capacity of uniform composites enhanced by addition of nanoparticles, reaching to a maximum to 1.5 times of the PDMS upon addition of 5wt.% of nanoparticles, and then gradually decreased to 1/6th of PDMS upon addition of 20wt.% of nanoparticles. On the other hand, the load bearing capacity of architectured composites at high strains (≥40%) monotonically increased with addition of nanoparticles in the pillars.

Optically-transparent solids have a significant role in many emerging topics of fundamental and applied research, in areas related to Applied Optics and Photonics. In the functional devices based on them, the presence of ‘time-varying temperature fields’ critically limit their achievable performance, when used particularly for high power laser-related tasks such as light-generation, light-amplification, nonlinear-harmonic conversion etc. For optimization of these devices, accurate knowledge of the material thermal parameters is essential. Many optical and non-optical methods are currently in use, for the reliable estimation of the thermal parameters. The thermal diffusivity is a key parameter for dealing with ‘transient heat transport’ related problems. Although its importance in practical design for thermal management is well understood, its physical meaning however continues to be esoteric. The present effort concerns with a few investigations on the “Optical interrogation of ‘transient thermal conduction’ in dielectric solids”. In dielectric solids, the current understanding is that the conductive heat transport occurs only through phonons relevant to microscopic lattice vibrations. Introducing for the first time, a virtual linear translator motion as the basis for heat conduction in dielectric materials, the present investigation discusses an alternative physical mechanism and a new analytical model for the transient heat conduction in dielectric solids. The model brings into limelight a ‘new law of motion’ and a ‘new quantity’ which can be defined at every point in the material, through which time-varying heat flows resulting in time-varying temperature. Physically, this quantity is a measure for the linear translatory motion resulting from transient heat conduction. For step-temperature excitation it bears a simple algebraic relation to the thermal diffusivity of the material. This relationship helps to define the thermal diffusivity of a dielectric solid as the “translatory motion speed” measured at unit distance from the heat source. A novel two-beam interferometric technique is proposed and corroborated the proposed concept with significant advantages. Two new approaches are introduced to estimate thermal diffusivity of optically transparent dielectric solid; first of them involves measurement of the position dependent velocity of isothermal surface and second one depend on the measurement of position dependent instantaneous velocity of normalized moving intensity points. A ‘new mechanism’ is proposed and demonstrated to visualize, monitor and interrogate optically, the ‘linear translatory motion’ resulting from the transient heat flow due to step- temperature excitation. Two new approaches are introduced, first one is ‘mark’ and ‘track’ approach, it involves a new interaction between sample supporting unsteady heat flow with its ambient and produces optical mark. Thermal diffusivity is estimated by tracking the optical mark. Second one involves measurement of instantaneous velocity of optical mark for different step-temperature at a fixed location to estimate thermal diffusivity. A new inverse method is proposed to estimate thermal diffusivity and thermal conductivity from the volumetric specific heat capacity alone through thought experiment. A new method is proposed to predict volumetric specific heat capacity more accurately from thermal diffusivity.

Recently, high-κ materials have become the focus of research and been extensively utilized as the gate dielectric layer in aggressive scaled complementary metal-oxide-semiconductor (CMOS) technology. Hafnium dioxide (HfO2) is the most promising high-κ material because of its excellent chemical, thermal, mechanical and dielectric properties and also possesses good thermodynamic stability and better band offsets with silicon. Hence, HfO2 has already been used as gate dielectric in modern CMOS devices. For future technologies, it is very difficult to scale the silicon transistor gate length, so it is a necessary requirement of replacing the channel material from silicon to some high mobility material. Two-dimensional layered materials such as graphene and molybdenum disulfide (MoS2) are potential candidates to replace silicon. Due to its planar structure and atomically thin nature, they suit well with the conventional MOSFET technology and are very stable mechanically as well as chemically. HfO2 plays a vital role as a gate dielectric, not only in silicon CMOS technology but also in future nano-electronic devices such as graphene/MoS2 based devices, since high-κ media is expected to screen the charged impurities located in the vicinity of channel material, which results in enhancement of carrier mobility. So, for sustenance and enhancement of new technology, extensive study of the functional materials and its processing is required. In the present work, optimization of HfO2 thin films for gate dielectric applications in Nano-electronic devices using electron beam evaporation is discussed. HfO2 thin films have been optimized in two different thickness regimes, (i) about 35 nm physical thicknesses for back gate oxide graphene/MoS2 transistors and (ii) about 5 nm physical thickness to get Equivalent Oxide Thickness (EOT) less than 1 nm for top gate applications. Optical, chemical, compositional, structural and electrical characterizations of these films have been done using Ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford Back Scattering (RBS), X-ray Diffraction (XRD), Capacitance-Voltage and Current-Voltage characterization techniques. The amount of O2 flow rate, during evaporation is optimized for 35 nm thick HfO2 films, to achieve the best optical, chemical and electrical properties. It has been observed that with increasing oxygen flow rate, thickness of the films increased and refractive index decreased due to increase in porosity resulting from the scattering of the evaporant. The films deposited at low O2 flow rates (1 and 3 SCCM) show better optical and compositional properties. The effects of post deposition annealing (PDA) and post metallization annealing (PMA) in forming gas ambient (FGA) on the optical and electrical properties of the films have been analyzed. The film deposited at 3 SCCM O2 flow rate shows the best properties as measured on MOS capacitors. A high density film (ρ=8.2 gram/cm3, 85% of bulk density) with high dielectric constant of κ=19 and leakage current density of J=2.0×10-6 A/cm2 at -1 MV/cm has been achieved at optimized deposition conditions. Bilayer graphene on HfO2/Si substrate has been successfully identified and also transistor has been fabricated with HfO2 (35 nm) as a back gate. High transconductance compared to other back gated devices such as SiO2/Si and Al2O3/Si and high mobility have been achieved. The performance of back gated bilayer graphene transistors on HfO2 films deposited at two O2 flow rates of 3 SCCM and 20 SCCM has been evaluated. It is found that the device on the film deposited at 3 SCCM O2 flow rate shows better properties. This suggests that an optimum oxygen pressure is necessary to get good quality films for high performance devices. MoS2 layers on the optimized HfO2/Si substrate have been successfully identified and transistor has been fabricated with HfO2 (32 nm) as a back gate. The device is switching at lower voltages compared to SiO2 back gated devices with high ION/IOFF ratio (>106). The effect of film thickness on optical, structural, compositional and electrical properties for top gate applications has been studied. Also the effect of gate electrode material and its processing on electrical properties of MOS capacitors have been studied. EOT of 1.2 nm with leakage current density of 1×10-4 A/cm2 at -1V has been achieved.