Carbon nanotubes (CNTs) have gathered a lot of interest because of their extraordinary mechanical, electrical and thermal properties and have potential applications in a wide variety of areas such as material-reinforcement and nano-electronics. The properties of nanotubes are dependent on their diameter and methods for determining this using atomic force microscopy (AFM) in tapping mode assume that the measured height of the tubes represent the real diameter. Based on early, faulty calculations, the forces in tapping mode were assumed to be much lower than in contact mode, however it was later shown that forces in tapping mode can at point of impact rival the forces present in contact mode. This means that there is a potential risk of tube deformation during tapping mode measurements, resulting in incorrectly determined diameters. This work studies CNTs deposited on a silicon-substrate to analyze the effect of three common AFM settings (tapping frequency, free oscillation amplitude and setpoint) to determine their effect on measured CNT diameters and recommendations for choosing settings are given. / Kolnanorör har skapat mycket intresse på grund av sina extraordinära mekaniska, elektriska och termiska egenskaper och har lovande tillämpningar inom en mängd olika områden så som materialförstärkning och nanoelektronik. Kolnanorörens egenskaper påverkas kraftigt av deras diameter och de metoder som använder sig av atomkraftsmikroskopi(AFM) för att mäta diametern hos rören antar att den höjd-data man får fram är ett bra mått på den verkliga diametern hos rören. Baserat på tidiga, felaktiga beräkningar, antog man att kraften i ’tapping mode’ skulle vara mycket lägre än i ’contact mode’ vilket skulle leda till att man inte deformerar ytan man undersöker. Senare forskning visade att kraften mellan spets och prov kan vara lika stor eller rentutav större i tapping mode än i contact mode under det ögonblick då spetsen slår ner i provytan. Det medför att det finns en potentiell risk för att man deformerar kolnanorören när man mäter på dom vilket skulle resultera i att man får felaktiga värden på deras diametrar. Under det här projektet har kolnanorör som placerats på ett kisel-substrat undersökts för att analysera hur tre vanliga inställningar hos AFMet påverkar de erhållna värdena för diametern hos kolnanorören. De tre inställningarna som testats är svängnings-frekvensen, svängnings-amplituden i luft och börvärdet hos svängnings-amplituden.

Organic electrode materials represent an intriguing alternative to their inorganic counterparts due to their sustainable and environmental-friendly properties. Their plastic character allows for the realization of light-weight, versatile and disposable devices for energy storage. Conducting redox polymers (CRPs) are one type of the organic electrode materials involved, which consist of a π-conjugated polymer backbone and covalently attached redox units, the so-called pendant. The polymer backbone can provide conductivity while it is oxidized or reduced (i. e., p- or n-doped) and the concurrent redox chemistry of the pendant provides charge capacity. The combination of these two components enables CRPs to provide both high charge capacity and high power capability. This dyad polymeric framework provides a solution to the two main problems associated with organic electrode materials based on small molecules: the dissolution of the active material in the electrolyte, and the sluggish charge transport within the material. This thesis introduces a general synthetic strategy to obtain the monomeric CRPs building blocks, followed by electrochemical polymerization to afford the active CRPs material. The choice of pendant and of polymer backbone depends on the potential match between these two components, i.e. the redox reaction of the pendant and the doping of backbone occurring within the same potential region. In the thesis, terephthalate and polythiophene were selected as the pendant and polymer backbone respectively, to get access to low potential CRPs. It was found that the presence of a non-conjugated linker between polymer backbone and pendant is essential for the polymerizability of the monomers as well as for the preservation of individual redox activities. The resulting CRPs exhibited fast charge transport within the polymer film and low activation barriers for charge propagation. These low potential CRPs were designed as the anode materials for energy storage applications. The combination of redox active pendant as charge carrier and a conductive polymer backbone reveals new insights into the requirements of organic matter based electrical energy storage materials.

Different carbon nanostructures have different properties and different applications. It is needed to synthesize good quality and also on large scale. From the point of industrial applications, highly productive and low cost synthesis method is very essential. Research has been done extensively on the intrinsic and individual properties of both single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWC-NTs) in the range of nanometer to micrometer length scale. The important question is how the properties change beyond this length scale and if they are used in group in the form of an array instead of the individual carbon nanotubes (CNTs). Some applications require large current output, large energy production etc. For such kind of applications, it becomes essential to use CNTs in large number in the form of arrays or array, instead of using large numbers of CNTs in individual level. Future nanotechnology scope requires large scale application using the very rich intrinsic properties of the CNTs and nanomaterials. Keeping these problems and challenges in front, this thesis work is devoted to the research of the large scale synthesis of mm long MWCNTs, having different morphology and studies on various physical properties of MWCNTs in the form of arrays. Synthesis of mm long aligned and buckled MWCNTs have been reported for the first time. Generally buckled CNTs were obtained by compressing the straight CNTs. Apart from this, different morphologies like, aligned straight, helical or coiled CNTs are also synthesized. Resistance of the individual CNT increases with the increase in length. Resistance versus length of an array of CNT also shows similar behaviour. The thermal conductivity of CNT array is observed to decrease with the increase of array diameter (diameter �100 µm). There are few reports of the similar behaviour with the experiments done on small diameter CNT arrays (diameter �100 nm). From these observations, it seems that in the arrays of CNT, their intrinsic individual property is preserved though the magnitudes are different. The conductance measurements done on buckled CNT array by compressing it to apply uniaxial strain, shows the conductance oscillation. This conductance oscillation seems to be originating from the band gap change due to strain when the CNTs bend during compression. Recent research focuses on the arrays of CNT as they can carry large current of the order of several milliamperes that make the arrays suitable in nanoscale electronics and in controlling macroscopic devices such as light emitting diodes and electromotors. Regarding this aspect, a part of this thesis work is devoted on the application of CNT array to field effect transistor (FET) and study of thermoelectric power generation using CNT arrays. The entire thesis is based on the works discussed above. It has been organized as follows: Chapter 1 deals with introduction about the different carbon nanostructures and different synthesis methods. A brief introduction about the different current-voltage (IV) characteristics of SWCNTs and MWCNTs, length and diameter dependence and effect of the mode of contacts, are given. Some applications of the array of CNTs like buckling effect on compression, stretching of CNT into the form of rope, and conduction change on compression are discussed. Application of CNT as FET, as a thermometer, and thermoelectric effect of CNT are discussed. The electromechanical effect of CNT is also discussed briefly. Chapter 2 deals with experimental setup for synthesis of different morphologies of carbon nanostructures. The samples are characterized using common characterization techniques like, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. A brief introduction about Raman Spectroscopy of CNT is given. Chapter 3 reports the unusual IV characteristics and breakdown of long CNT arrays. The current carrying ability and the threshold voltage as a function of array diameter are reported. The effect of the ambient like temperature and pressure are discussed. Chapter 4 deals with theoretical models to analyze the IV characteristics reported in Chapter 3. It has been shown that a set of classical equations are applicable to quantum structures and the band gap can be evaluated. Chapter 5 describes with application of CNT arrays as temperature sensors. It has been shown that CNT arrays of suitable diameters are used as temperature sensors after calibration. Chapter 6 reports the high current FET application of CNT arrays. Effects of temperature and ambient pressure are discussed. The type of the majority charge carrier is determined. Chapter 7 deals with application of CNT arrays as thermoelectric power generator to get large thermoelectric current. Effects of different array diameter are discussed. Modulation of thermoemf with gate voltage is discussed. The type of the majority charge carrier is determined. Chapter 8 reports the effect of compressive strain on buckled MWCNT arrays. Conductance is measured during the compression of the array. Quantum electromechanical conductance oscillation is observed. The structural changes are observed with SEM. Raman spectroscopic study supports the explanation of the effect. Chapter 9 provides the conclusion and overall summary of the thesis.

As part of the EU SmartVista project to develop a multi-modal wearable sensor for health diagnostics, field-effect transistor (FET) based biosensors were explored, with glucose as the analyte, and carbon nanotubes (CNTs) or monolayer MoS2 as the semiconducting sensing layer.  Numerous arrays of CNT-FETs and MoS2-FETs were fabricated by photolithographic methods and packaged as integrated circuits.  Functionalization of the sensing layer using linkers and enzymes was performed, and the samples were characterized by atomic force microscopy, scanning electron microscopy, optical microscopy, and electrical measurements. ON/OFF ratios of 102 p-type and < 102 n-type were acheived, respectively, and the work helped survey the viability of realizing such sensors in a wearable device. / EU Horizon 2020 - SmartVista (825114)

Identifying the protein content in a cell in a fast and reliable manner has become a relevant goal in the field of proteomics. This thesis computationally explores the potential for silicon nitride nanopores to sense and distinguish single miniproteins, which are small domains that promise to facilitate the systematic study of larger proteins. Sensing and identification of these biomolecules using nanopores happens by studying modulations in ionic current during translocation. The approach taken in this work was to study two miniproteins of similar geometry, using a cylindrical-shaped pore. I employed molecular mechanics to compare occupied pore currents computed based on the trajectory of ions. I further used density functional theory along with relative surface accessibility values to compute changes in interaction energies for single amino acids and obtain relative dwell times. While the protein remained inside the nanopore, I found no noticeable differences in the occupied pore currents of the two miniproteins for systems subject to 0.5 and 1.0 V bias voltages. Dwell times were estimated based on the translocation time of a protein that exhibits no interaction with the pore walls. I found that both miniproteins feel an attractive force to the pore wall and estimated their relative dwell times to differ by one order of magnitude. This means even in cases where two miniproteins are indistinguishable by magnitude changes in the ionic current, the dwell time might still be used to identify them. This work was an initial investigation that can be further developed to increase the accuracy of the results and be expanded to assess other miniproteins with the goal to aid future experimental work.

Low dimensional semiconductor structures are modeled using techniques from the field of many-body atomic physics. B-splines are used to create a one-particle basis, used to solve the more complex many-body problems. Details on methods such as the Configuration Interaction (CI), Many-Body Perturbation Theory (MBPT) and Coupled Cluster (CC) are discussed. Results from the CC singles and doubles method are compared to other high-precision methods for the circular harmonic oscillator quantum dot. The results show a good agreement for the energy of many-body states of up to 12 electrons. Properties of elliptical quantum dots, circular quantum dots, quantum rings and concentric quantum rings are all reviewed. The effects of tilted external magnetic fields applied to the elliptical dot are discussed, and the energy splitting between the lowest singlet and triplet states is explored for varying geometrical properties. Results are compared to experimental energy splittings for the same system containing 2 electrons.

The studies in the present thesis explored the feasibility of using nanocellulose-based filters in virus removal filtration of plasma-derived proteins.   In Paper I, two-step nanofiltration of commercially available human serum albumin (HSA) product, which was diluted to 10 g L-1 by phosphate buffer saline (PBS) and adjusted pH to 7.4, was performed to remove soluble protein aggregates and reduce filter fouling. The two-step filtration of HSA employed nanocellulose-based filters of varying thickness, i.e. 11 μm and 22 μm filters.  The removal of HSA aggregates during filtration through 11 μm pre-filters dramatically improves the flow properties of the 22 μm filter, enabling high protein throughput and high virus clearance. A distribution of pore sizes between 50 nm and 80 nm, which is present in the 11 μm filter and is absent in the 22 μm filter, plays a crucial part in removing the HSA aggregates. With respect to virus filtration, 1 bar constant trans-membrane pressure filtration shows poor removal ability of ΦX174 bacteriophage (28 nm), i.e., log10 reduction value (LRV) ≤ 3.75, while that at 3 bar and 5 bar achieves LRV[MOU1] [LW2]  > 5 model virus clearance and overall rapid filtration. Removal of protein aggregates during bioprocessing of HSA products is key to improving the filtration flux, which makes it possible to apply virus removal filtration for HSA to ensure its virus safety.   In Paper II, nanofiltration of human plasma-derived intravenous immuno-globulin (IVIG) intermediate (11.26 g L-1, pH 4.9) was carried out to demonstrate high product recovery and high model virus clearance. Virus removal filtration of industrial-grade human IVIG was achieved using 33μm filters at both low (60 Lm-2) and high (288 Lm-2) volumetric load. No changes in IVIG structure were detected and high product recovery was recorded. High virus clearance (LRV ≥ 5-6) was achieved for the small-size model viruses (ΦX174 and MS2 bacteriophages) during the load volume of 60 Lm-2. Side-by-side comparisons with commercial virus removal filters suggest that the nanocellulose-based filter paper presents great potential for industrial bioprocessing of plasma-derived IVIG.   In Paper III, process analytical technology (PAT) approach was employed to identify the critical filter parameters, e.g. thickness, basis weight, pore size, and flux, affecting model virus removal efficiency using filters produced by different hot presses.  The quality parameters were analyzed with ANOVA and Shewhart charts. Compared with other studied parameters, the hydraulic flux appears as the most relevant final product quality attribute of the nanocellulose-based filter paper to reflect the virus removal efficiency. In particular, a 15% higher flux may be associated with a 0.5-1.0 log10 reduced virus clearance (p=0.007). The results are highlight the importance of continued systematic studies in quality assurance using statistical process control tools  [MOU1]Define LRV  [LW2]Defined in the line above

A novel scheme of optimizing the individual components of a phase locked loop (PLL) which is used for stable clock generation and synchronization of signals is considered in this work. Verilog-A is used for the high level system design of the main components of the PLL, followed by the individual component wise optimization. The design of experiments (DOE) approach to optimize the analog, 45nm voltage controlled oscillator (VCO) is presented. Also a mixed signal analysis using the analog and digital Verilog behavior of components is studied. Overall a high level system design of a PLL, a systematic optimization of each of its components, and an analog and mixed signal behavioral design approach have been implemented using cadence custom IC design tools.

In this study, the effect of AlN buffer layer structure and morphology on the GaN films deposited on Si (111) substrate by reactive DC magnetron sputtering have been studied. For structural and morphological characterization X-ray diffraction (XRD) and Scanning electron microscope (SEM) were used. It is found that AlN films without Al pre-deposition on Si have a poor crystalline quality due to the formation of an amorphous layer at Si/AlN interface. Various initial Al sputtering durations on Si substrate result in changing the AlN buffer layer’s quality and morphology and choosing proper deposition duration can improve AlN buffer layer and the subsequent GaN layer quality. It is found that more than 15 s Al pre deposition can suppress the amorphous layer formation and enhance the film quality. The Rocking curve FWHM for both in-plane and out-of-plane orientation decreased from 1.86 and 1.56   to 0.4   and 0.3  , respectively, by 4 minutes Al pre-deposition on Si, however, overlong Al deposition results in poor surface morphology. It is found that 15s Al deposition is sufficient to enhance the quality as well as keeping the surface relatively smooth. In addition, AlN films deposited at 1000   showed the best film quality. GaN films directly grown on Si showed a poor crystalline quality and surface morphology, improvement of quality and morphology was observed for GaN samples deposited on AlN buffer layer. Also, melt-back etching observed on the surface of GaN grown on Si without AlN buffer layer. It is found that duration of Al deposition has a significant effect on GaN surface morphology, Al layer deposition more than 15 s result in a rough surface for GaN films. With choosing the optimum duration of Al pre-deposition and proper growth temperature a good quality GaN with a smooth surface morphology can be produced.

Several sputtering depositions were done by direct current (DC) magnetron sputtering epitaxy (MSE) techniquefor the goal of improving the growth rate and crystalline quality of GaN thin film on Al2O3 substrate. Thegrowth rate was higher when substrate-to-target distance D = 7 cm compared with D = 9.3 cm with eitherfloating or positive bias on the substrate side. The crystalline quality was improved by raising up the growthtemperature from 700◦C to 900◦C, but the quality was declined from 900◦C to 1000◦C due to strong desorption.Gas composition in the metal mode gives better quality due to its sufficient Ga condition with less N2. Positivesubstrate bias boosted the plasma potential and therefore created higher actual sputtering power comparedwith the condition at floating substrate potential. In general, applying a higher power can elevate the growthrate and film quality. However, there has not been an evident difference of both growth rate and film qualitywhen the actual sputtering power is close for floating substrate potential and positive substrate bias.