Despite of their short history, conducting polymers such as polypyrrole (PPy) have emerged as a novel building block for label-free chemiresistive/FET chemical/biological sensors owing to a great environmental stability, active functional monomers for direct covalent immobilization of bioreceptors, remarkable optical, magnetic, and electrical properties like a semiconductor as well as mechanical property and ease of fabrication possessed by polymers. Tunable electrical conductivity can also be realized by several orders of magnitude via the process called `doping' where anions or dopants is chemically or electrochemically incorporated to oxidized CP backbones to attain the charge neutrality.

Confining conducting polymers to one-dimensional (1-D) nanoscale has ultimately increased the surface area to volume ratio and facilitated the electron transport through the bulk of 1-D nanomaterials. Therefore, a small perturbation by adsorbed charged chemical/biological molecules on their surfaces significantly affected the charge distribution within the bulk of 1-D nanomaterials, enhancing the sensitivity and detection limits. While this nano-electronic chemical/biological sensor showed a potential for advanced technology in detection and monitoring, device fabrication and assembly for 1-D conducting polymer nanostructures still appeared challenging to be scalable and reproducible in a cost effective manner.

Herein, this dissertation focused on fabrication and assembly of 1-D conducting polymer nanostructures based chemiresistive/FET chemical/biological sensors in a cost effective manner. First, lithographically patterned nanowire electrodeposition (LPNE) was used to batch-scale fabricate single PPy nanoribbon with controlled dimensions and defined location on various substrates for NH3 detection. Various bioreceptors were also surface functionalized on LPNE grown PPy nanoribbon to investigate sensing performance in terms of sensitivity, selectivity, dynamic range, and detection limits towards the specific virus and the target protein. Polyclonal antibodies (pAbs) that recognized cucumber mosaic virus (CMV) were anchored on PPy nanoribbons for the detection of CMV. Single chain fragment variables (scFvs) specific for mycobacterium tuberculosis antigen 85 complex protein (Ag85) were functionalized on PPy nanoribbons to accommodate the electrostatic screening effect caused by dissolved salt concentration in buffer solution and diluted human serum. On the other hand, template-directed electrodeposition was employed to synthesize PPy nanowires using various dopants and solvents in order to evaluate the structure dependent sensing performances for detection of Ag85B protein.

Science technologies have been in pursuit of smaller, faster and more efficient devices and enormous efforts made by myriad numbers of scientists have provided us with electronics in reduced volumes with improved performances. Miniaturization of electronic circuits down to micrometer scale has been well-developed as industrial processes and it is easy to witness electronic products containing integrated circuits consisted of microstructures in our everyday life. However, miniaturization of circuit components down to nanometer scale has revealed new challenges not only for difficult handling of diminutive structures but also for unusual physical properties of nanomaterials.

Countless numbers of conventional chemical and physical studies have been dedicated to exploit the benefit of the unique properties of nanostructures by developing efficient techniques for controlled synthesis and assembly of nanostructures. However, environmental concerns of using toxic solvent systems and high energy-consuming processes, and pursuit of highly selective molecular interactions for highly precise assemblies have averted the eyes of scientists to biological materials. Biorecognition properties of biological materials are attractive for achieving programmed self-assembly of nanostructures and biomolecules with metal-reducing ability are very inviting for developments of environmentally-acceptable synthesis processes.

In the light of above discussion, this thesis takes the advantages of biological approaches to assemble and synthesize inorganic nanostructures in a controlled manner. DNA was used for the assembly processes due to their facilities of sequence programming and chemical modifications. Spatially controlled assembly of multi-segmented Au/Pd/Au nanowires across gold electrodes has been demonstrated using thiolated DNA strands functionalized on the gold surface of nanowires and electrodes. Electron transport properties of DNA-assisted assembled nanowires were demonstrated showing negligible blocking effect by DNA layers hybridized between nanowires and electrodes. The assembled Au/Pd/Au nanowire was used for hydrogen sensing manifesting the applicability of DNA-assisted assembly to build functional nanodevices.

Amino acids are essential as building blocks for proteins and for metabolisms. Recently, amino acids have been given another important role as a reducing and capping agent for the synthesis of gold nanostructures. Amino acid-mediated synthesis of gold nanostructures has been demonstrated showing the capability of biological approaches to synthesize single crystalline gold nanostructures in 0-D, 1-D and 2-D dimensions by manipulating the reaction environment. Structural changes of gold nanostructures due to the speciation of gold complexes were systematically demonstrated by altering solvent conditions. The effect of the side chains of amino acids on the structural features of gold nanostructures was systematically demonstrated. Distinguished electron transport properties were observed for single crystalline nanoribbons showing resistivity lower by an order of magnitude than polycrystalline counterparts. Rapid reversible room temperature H2S gas sensor was fabricated using AC aligned gold nanoparticle ar

Electrospun nanofibers have gained great research interest for decades as attractive nanomaterial for various applications due to their ultra-high specific surface area, flexibility in materials, and ease of fabrication. Furthermore, fine tuning of electrospinning or post-electrospinning process conditions can allow for precise control of morphology, composition, physical, electrical, and electrochemical properties to tailor the nanofibers for a specific application. In this work, the effect of various electrospinning-related conditions on properties of polyacrylonitrile (PAN)-derived nanofibers was elucidated by series of systematic variation of parameters called design of experiment (DOE). Analyses on the DOE revealed solution viscosity, mainly controlled by polymer concentration, was the predominant factor for nanofiber morphology, while the addition of composite materials such as multi-walled carbon nanotubes and zinc acetate also strongly affected the nanofiber dimensions.

To study the suitability of the PAN nanofibers with controlled properties for applications in energy harvesting and generation, piezoelectric and electrochemical properties of PAN-derived as-spun and heat-treated nanofibers were characterized. For the first time, size-dependent piezoelectric properties for PAN nanofibers was carefully investigated, which showed the voltage generated perpendicular to the direction of the fiber (V33) increased as a function of decreasing fiber dimensions, similar to more commonly studied piezoelectric polymers. Electroanalytical methods such as cyclic voltammetry, linear polarization and electrochemical impedance spectroscopy were employed to investigate the feasibility of various carbonaceous nanofibers as electrode material.

Enzymatic fuel cell was chosen as the device of interest for energy generation application in this work. In an attempt to utilize the naturally abundant yet complex cellulose as fuel, a multienzyme cascade complex in nature called cellulosome was biomimetically fabricated by site-specific immobilization of 5 enzymes on customized DNA scaffold for sequential hydrolysis of cellulose followed by catalytic oxidation of glucose for electricity generation. With successful demonstration of the synergistic effect of enzyme immobilization on DNA scaffold, similar system was functionalized onto an electrode for preliminary electrochemical studies, which exhibited great promise as multienzyme cascade-based bioanode for cellulolytic fuel cell.

Metal Chalcogenide nanostructures have been extensively implemented for high-performance thermoelectric applications, which can directly convert waste-heat-energy into electricity, with the support of theoretical and empirical results. In fact, finding a novel and cost effective synthesis approach that facilitates the formation of stable and reproducible nanostructured thermoelectric materials determines the commercial applicability.

The overall objective of this work is to synthesize metal chalcogenide nanostructures with outstanding thermoelectric performance by an electrodeposition technique, which is one of the most versatile methods for low dimensional nanostructures in a cost effective and scalable manner. Precise control over dimension, chemical composition, crystallinity, crystal structure, grain size, preferred orientation, and the attainment of nanoinclusions and/or intermediate phases based on thermodynamically favored solid-state phase transition yields optimal electrical transport and thermoelectric properties of the metal chalcogenide nanostructures. In this dissertation, antimony telluride (SbxTey), silver doped antimony telluride, antimony telluride (AgxSb(2-x)Te(3-x)), bismuth antimony telluride (BixSb2-xTey) thin films were electrodeposited, followed by post annealing to create various nanocrystalline thin films. Additionally, antimony telluride nanowires were synthesized by a template-directed electrodeposition. The material, electrical, and thermoelectric properties of those metal chalcogenide nanostructures are systematically investigated to depend the effect of dimension, composition, crystallinity, crystallographic properties, and temperature for thermoelectric applications.

One-dimensional nanostructures, such as nanowires and nanotubes have attract intensive interest in various applications including gas sensors and thermoelectrics, due to their unique size-dependent electrical, thermal transport and mechanical properties. Miniature and portable gas sensors are of great importance in detecting gaseous molecules for environmental pollution analysis, homeland security, industrial emission control and outer space exploration. Thermoelectric energy converters, which generate electricity by harvesting waste thermal energy, can improve the efficiency of environmentally-friendly and renewable energy generation. The overall objective of this work is to engineer one-dimensional nanostructures using various techniques such as electrospinning and electrochemical routes for thermoelectric and gas sensor applications.

Electrospinning and galvanic displacement reaction were combining to synthesize ultra-long metal chalcogenide nanofibers with controlled dimensions, morphologies, and compositions. The structure, electrical and thermoelectric properties were systematically examined to understand relationships between nanofiber structures and their resulting thermoelectric performance.

In addition to thermoelectrics, high performance nano gas sensor were realized by either surface functionalizing CNTs with various Te morphologies or contacting the CNT with various electrodes for different types of electrical contacts (i.e. ohmic and Schottky contacts). An understanding of the underlying fundamental sensing mechanism was investigated to fabricate a high-performance gas sensor array.

Heat is the natural by-product of energy conversion processes. Of the 4.25 × 1020 J of energy the United States consumes every year, more than 60% is wasted in the form of heat. Therefore, waste heat recovery is a crucial step to improve the energy generation and utilization efficiency. Thermoelectric (TE) materials, which can directly convert rejected or waste heat into usable electric power, has been extensively developed for this issue. Thick-film-based devices have advantages over conventional TE module because of its compact size. By shrinking the size of thermoelectric devices, it not only allows the device to operate under smaller temperature gradients, but by so doing it expands its capability to handle a wider range of thermal and power management microelectronic systems. The combination of electrochemical deposition of compound semiconductors (metal tellurides) with standard integrated circuit technique makes fabrication of thermoelectric microdevices possible.

The overall objective of this work is to develop new baths to achieve high-rate electrodeposition of Te and PbTe thick films. The electrodeposition mechanisms of Te and PbTe were examined by electrochemical analysis method. Furthermore, the thermoelectric property of thick PbTe films were optimized by introducing energy barriers from crystal grain boundary and tellurium nanoinclusion, which was achieved by tailoring composition and crystal structures of the thick PbTe films. Additionally, control over the composition and crystal structures was realized by tuning the electrodeposition conditions, as well as post-annealing process.

The paramount issues of today such as the gathering energy crisis and rise in levels of pollution have largely resulted from our increasingly accelerated industrialization due to technology developments. Ironically, those issues demand the further advanced technology to answer. In addition, the overwhelming rate of data production due to the rapid development of computer technologies require even more improved technologies to overcome our current limits. Nanotechnology has been extensively developed to approach these issues, since engineered materials at the nano-scale level have demonstrated enhanced desirable properties due to their small dimensions. Chalcogenide nanostructures have shown potential for use in thermoelectric and phase change memory devices with potentially high performance.

The overall objective of this work is to engineer nanostructured chalcogenides using various techniques such as electrodeposition and wet-chemical synthesis as cost-effective and simple approaches. The dimension, size, composition and crystal structure of the chalcogenide materials are controlled to enhance their properties for thermoelectric and phase change memory applications. The specific research investigations in this work were the following:

1) Electrochemical analysis of SbxTe1-x electrodeposits was implemented. Linear sweep voltammetry and quartz crystal microbalance techniques were utilized to study the properties of SbxTe1-x depending on agitation and temperature. The mass transport, reduction behavior, surface morphology and crystal structure of SbxTe1-x electrodeposits were investigated.

2) SbxTe1-x nanocomposites were produced by the separation of the Sb2Te3 phase and the γ-SbTe phase in the annealed SbxTe1-x electrodeposits. The thermoelectric and phase transition properties of SbxTe1-x electrodeposits were characterized as a function of temperature and composition. The generated nanocomposites demonstrated a drastically enhanced Seebeck coefficient.

3) AgxTe1-x thin films were synthesized by a topochemical transformation reaction of thermally evaporated Te thin films. The thermoelectric properties of the transformed AgxTe1-x thin films with tailored compositions were analyzed. In addition, the composition-dependent Seebeck coefficients showed the transition of carrier transport behavior from p-type to n-type.

4) Ternary chalcogenide AgxSb1-xTey materials were synthesized by a cost-effective and simple cation exchange reaction of thermally evaporated SbxTey thin films. The composition of ternary AgxSb1-xTey was controlled by the reaction time. Temperature- and composition-dependent thermoelectric and phase transition properties of the synthesized films were investigated.

5) Single crystal PbTe nanowires were electrodeposited by a template-direct method. An electrical transport behavior of the electrodeposited PbTe nanowires with modulated electrical contacts was estimated. The improvement of the electrical contact was achieved by a galvanic displacement reaction of Au nanoparticles with PbTe exposed in the opened contact region.

6) Scalable Te nanoribbons with Au electrodes were fabricated by a lithographically patterned nanowire electrodeposition (LPNE) technique. A pulsed potential was applied to control the reduced width of nanoribbons. The dimensions of the nanoribbons were determined by a pattern design, the thickness of e-beam evaporated Ni layer and an electrodeposition time. Ultra-long Te nanoribbons with a length of several cm, a height of 100 nm and a ranged width from about 50 to 200 nm were demonstrated. Electrical properties of Te nanoribbons with different widths were studied. Moreover, the effect of the size of the nanoribbons and the electrical contact types on the NH3 sensing properties of Te nanoribbons on NH3 (g) was analyzed.

7) A combined technique of a LPNE and a galvanic displacement reaction was utilized to synthesize ultra-long BixTe1-x nanoribbons of which the dimensions were controlled in a length of several cm, a height of 100 nm and a ranged width from about 400 nm to 2.5 μm. Composition-dependent electrical resistivities and FET properties of the BixTe1-x nanoribbons were analyzed. Temperature-dependent thermoelectric properties of a Bi31Te69 nanoribbon were investigated.

In this dissertation, antimony telluride (SbxTe1-x), bismuth telluride (BixTe1-x), lead telluride (PbxTe1-x), tellurium (Te), silver telluride (AgxTe1-x), silver antimony telluride (AgxSb1-xTey) were synthesized by various techniques such as potentiostatic deposition, pulse plating, topochemical transformation reaction, cation exchange reaction and galvanic displacement reaction. The material properties and electrical/thermoelectric behaviors depending on their dimension, size, composition and crystal structure were investigated.

Nanostructured materials have attracted extensive attention due to their small dimension and enhanced properties compared to bulk materials, and their large range of potential applications in energy harvesting devices. Among these materials, nanostructured chalcogenides play an important role in thermoelectric and solar cell devices. Electrochemical techniques have drawn attention as an improved method for synthesizing nanostructured chalcogenide materials, since they provide a cost-effective, simple, and versatile method for depositing various kind of chalcogenides with tunable nanostructures and properties.

The overall objective of this dissertation work is to develop the following electrochemical techniques:

1) to synthesize nanostructured chalcogenide materials (e.g. Bi_xTe_y, Pb_xTe_y and Cd_xTe_y) with well-controlled dimensions, surface morphologies and compositions

2) to systematically investigate the effect of experimental parameters on their nanostructures

3) to characterize their tunable properties

4) and ultimately to establish a guidance of experimental design for further synthesis of other nanostructured chalcogenide materials.

In this dissertation, the viability of using electrochemical methods for synthesizing nanostructured three chalcogenide materials - Bismuth telluride (Bi_xTe_y) Lead telluride (Pb_xTe_y) and Cadmium telluride (Cd_xTe_y) was tested. An easy way to tune their size (nano to micro), surface morphology (from novel nanostructures to nanoparticles and core/shell hybrid nanostructure) and composition (excess either electropositive element or chalcogens) by tailoring the electrochemical parameters such as electrolyte composition, type and thickness of sacrificial materials, and reaction time of electrochemical techniques, including electrodeposition (ED) and galvanic displacement (GD), was demonstrated.

Chemical sensors have a deep influence in a wide variety of disciplines ranging from biomedical measurement, electrochemical analysis, detection of environmental toxins, pollution monitoring, and warfare threats, to industrial control. The pressure of legislation concerning environmental issues and increasing environmental regulations makes chemical sensing of pollutants extremely important.

The overarching goal of this proposed work is to develop cost effective routes to synthesize integrated 1-D materials onto prefabricated micro-electrodes for the detection of airborne toxins at ambient temperature as well as real-time and simultaneously measuring O3, CO, SO2, and NO2 to quantify Air Quality Index. The sensor arrays will be made out of novel conductometric/chemiresistive sensors based on functionalized single-walled carbon nanotubes (SWNTs). The array will employ sensors with varying sensing materials (organic/inorganic) and sensing mechanisms operated at optimum conditions which will enable more selective and accurate monitoring of AQI. Optimization of both the individual sensor and the sensor array will produce distinctive sensing response patterns for detecting the individual agents in the gas mixtures. Ink-jet printing will be utilized to deposit hybrid SWNTs inks to precise locations on a substrate, while electrodeposition techniques will be utilized to synthesize metal and metal oxide decorated SWNTs with controlled crystallinity, morphology, and electrical properties. The structure-property relationships of these materials, such as electrical transport, optical and gas sensing performance will be investigated, evaluated, and optimized.

One-dimensional (1-D) nanostructures, such as nanowires and nanotubes, are extremely attractive building blocks for electronics because of their small sizes, which provide for extremely high density devices, and their unique properties that emerge from increased surface to volume ratios. In addition their extremely high aspect ratios offer researchers the potential to build striped and coaxial structures with different components aligned along the cylindrical or radial axis of the wire, respectively. Composition modulation can be used to incorporate multiple functionalities from intrinsic properties of the material or through interfacial phenomena. However, spatial manipulation and the ability to assemble and position nanostructures in a controlled manner so they are registered to lithographically defined contacts is a critical step toward scalable integration in high-density nanodevices. In this dissertation a generalized template directed approach with ancillary assembly, contact, and displacement techniques were utilized to synthesize and characterize individual nanostructures from uniquely configured conducting polymer, magnetic, and semiconductor nanomaterials for sensor and spintronic applications.

Conducting polymers are particularly appealing because they exhibit tunable transport characteristics along with electronic, magnetic and optical properties of metals or semiconductors while retaining the attractive mechanical properties and processing advantages of polymers. In the first part of this work single component conducting polymer nanowires were electropolymerized, dielectrophoretically assembled, and contacted via maskless electrodeposition. Maskless electrodeposition was developed to selectively electrodeposit material on prefabricated microelectrode with no observable deposition on the conducting polymer nanowires, embedding the nanowire ends. Two different conducting polymers were investigated, polypyrrole (PPy) and polyethylendioxythiophene (PEDOT). Individual PPy nanowire devices demonstrated enhanced sensitivity to ammonia vapors, and PEDOT nanowire devices exhibited strong responses to volatile organic compounds. The gas sensing performances of these single nanowire devices were tuned by dopant type and synthesis conditions. Alternatively, single PEDOT nanowire devices were also completely coated in ferromagnetic material by implimenting non-selective electrodeposition. The magnetoresistance (MR) of these devices also displayed anomalous behavior, drastically deviating from typical anisotropic magnetoresistance responses. Additionally, multi-segmented noble/oxidizable nanowires were electrodeposited and subjected to galvanic displacement to create nanopeapod devices with Au peas and Te pods.