Nanoscale devices take many advantages, including low power consumption for energy sav- ing, highly miniaturized structures for portable equipment and tiny amount of materials needed for manufacturing purposes, particularly considering rare metals. Nano-devices have exhibited significant potentials for wide industrial applications, for example, chemical and biological sensing, nano-electronics, environment and health monitoring etc. In this disser- tation, two types of H2 sensors are discussed, they are based on single metal nanowires and metal nanoparticles-decorated carbon nanotube (CNT) ropes respectively.

Single nanowire H2 sensors are fabricated by applying the methods of lithographically patterned nanowire electrodepositon (LPNE). Single palladium (Pd) nanowires with the dimension of 40 nm (height) × 100 nm (width) × 50 μm (length) are electrodeposited within LPNE templates and electrically isolated by metal contacts. Then platinum (Pt) layers are electrodeposited onto single Pd nanowires (Pd@Pt nanowires) to catalytically enhance the H2 sensing performance. The Pt layer coverage thickness is altered as average 0.1 monolayer (ML), 1 ML and 10 ML. For each coverage, the Pd@Pt nanowire sensors are evaluated at five different working temperatures, Pd@Pt sensors exhibited lowest detection at 500 ppm H2 exposure. Both response and recovery behaviors of Pd@Pt sensors are accelerated at higher temperature, yet the drawback is deterioration of sensitivity and detection limit.

A type of more advanced H2 sensors based on semiconducting CNT ropes are developed, in order to enhance the H2 sensing performance for rapid response/ recovery and wider detec- tion range. CNT ropes deposition are achieved by applying processes of dielectrophoresis in aqueous solution containing suspended CNTs. Single CNT ropes are electrical isolated at the length of 50 μm, and employed as the electrode for electrodepositing Pd nanoparticles of four coulombic loadings. Bare CNT ropes show no response to H2/ air exposures, however the sensitivity to H2 is very strongly enhanced. Pd–CNT sensors are capable of detecting H2 mixture in a very wide range between 10 ppm to 4 vol% at room temperature. The influence of Pd nanoparticle diameter to H2 sensing is also evaluated.

Energy storage has been the biggest obstacle in the widespread adoption of renewable energy resources. The work presented in this thesis is aimed at developing and understanding the behavior of Niobium Pentoxide (Nb2O5) electrochemical energy storage devices. Nb2O5 is a Li+ intercalation metal oxide that is of current interest for lithium ion battery electrodes. In the first part of this thesis, electrophoretic deposition (ED) of Nb2O5 thin- films from aqueous NbOx colloidal solutions is described, which exhibits unusually high specific capacities for Li+ -based energy storage as a consequence of 70% porosity. The excellent energy storage metrics are attributed to augmentation of the faradaic capacity by high double-layer capacities enabled by the mesoporous structure of these films. In the second part of this thesis, the effect of Li+ intercalation on the conductivity of Nb2O5 has been explored. The electrical conductivity, σ, of battery and capacitor electrode materials is a factor determining the energy storage performance of these materials, but it is difficult to directly measure in-situ particularly for electrodeposited materials. Our approach exploits an array of nanoribbon of Nb2O5, fabricated using lithographically patterned nanoribbon electrodeposition (LPNE). σ of Nb2O5 nanoribbons is measured in-situ in a battery electrolyte as a function of the equilibrium potential and, separately, during repetitive lithiation/delithiation cycling. σ in the non-lithiated Nb2O5 is characteristic of semiconducting metal oxides, but it increases dramatically with lithiation. The last part of the thesis is aimed at uncovering the mechanism of capacity upon repetitive cycling for Nb2O5 based energy storage devices. Microscopy, spectroscopy and electrochemical characterization tools have been employed to gain insight into the electronic, structural, compositional and morphological evolution of Nb2O5 thin films as it undergoes thousands of cycles of charge-discharge. Overall, the work in this thesis elucidates a strategy towards fabrication of energy storage devices from materials that are difficult to electrodeposit using conventional redox reactions. Furthermore, it illustrates an approach to combine electrochemical and microscopy-based methods, to gain insights into the interactions between Li+ ions and the active material, during repetitive charge discharge cycling.

The preparation by electrodeposition of transverse nanowire electroluminescent junctions (tn-ELJs) is described and the electroluminescence (EL) properties of these devices are characterized. The lithographically patterned nanowire electrodeposition process (LPNE) is first used to prepare a long (mm's), linear, nanocrystalline CdSe nanowires on glass. The thickness of these nanowires along the emission axis is 60 nm and the width along the electrical axis is adjustable from 100 - 450 nm. Ten pairs of nickel-gold electrical contacts are then positioned along the axis of this nanowire using lithographically directed electrodeposition. The resulting linear array of nickel-CdSe-gold junctions produce electroluminescence (EL) with an external quantum efficiency, EQE, and threshold voltage that depends sensitively on the width of CdSe. EQE increases with increasing electric field and also with increasing width of CdSe, and threshold voltage also increases with the width of CdSe, and therefore the electrical resistance, of the tn-ELJs. Threshold voltage down to 1.8V (for the CdSe width around 100 nm) and EQE of 5.5*10^5 (for CdSe width around 450 nm) are obtained. tn-ELJs produce a broad EL emission envelope, spanning the wavelength range from 600 - 960 nm.

Electrodeposited nano-materials have huge potential to reduce the cost of nano and micro fabrications dramatically especially in light emitting diodes field. It is difficult to fabricate high performance devices and understand the working mechanisms due to the polycrystalline nature of most electrodeposited materials. In this dissertation, electrodeposited cadmium selenide was used to fabricated two different structures of light emitting devices. In the second chapter, the preparation by electrodeposition of transverse nanowire electroluminescent junctions (tn-ELJs) is described and the electroluminescence (EL) properties of these devices are characterized.The resulting linear array of nickel-CdSe-gold junctions produce electroluminescence (EL) with an external quantum efficiency, EQE, and threshold voltage, Vth, that depends sensitively on wCdSe. EQE increases with increasing electric field and also with increasing wCdSe, and Vth also increases with wCdSe, and therefore the electrical resistance, of the tn-ELJs. Vth down to 1.8(±0.2)V (for wCdSe ≈ 100 nm) and EL of 5.5(±0.5) 10^-5 (for wCdSe ≈ 450 nm) are obtained. tn-ELJs produce a broad EL emission envelope, spanning the wavelength range from 600 - 960 nm. In the third chapter, A wet chemical process involving two electrodeposition steps followed by a solution casting step, the EESC process, is described for the fabrication of electroluminescent, radial junction wires. EESC is demonstrated by assembling three well-studied nanocrystalline (or amorphous) materials: Au,CdSe, and PEDOT:PSS. The tri-layered device architecture produced by EESC minimizes the in influence of an electrically resistive CdSe emitter layer by using a highly conductive gold nanowire that serves both as a current collector and a negative electrode. Hole injection, at a high barrier CdSe-PEDOT:PSS interface (Φh ≈ 1.1 V), is facilitated by a contact area that is 1.9 - 4.7 fold larger than the complimentary gold-CdSe electron-injecting contact (Φe ≈ 0.6 V) contributing to low voltage thresholds (1.4 - 1.7 V) for EL emission. Au@CdSe@PEDOT:PSS wire EL emitters are 25 μm in length, but the EESC process is scalable to nanowires of any length, limited only by the length of the central gold nanowire that serves as a template for the fabrication process. Radial carrier transport within these multishell wires conforms to the back-to-back diode model.

Niobium pentoxide, Nb2O5, is a lithium-ion battery anode material that exhibits pseudocapacitance,particularly in the orthorhombic phase, from fast lithium intercalation kinetics. While the electrochemical characteristics of this material have been well studied, there is a gap in the knowledge of long-term cycle stability and degradation analysis of this material. Upon 10,000 lithiation/delithiation cycles, the main degradation pathways observed for electrophoretically deposited thin films of orthorhombic Nb2O5 were amorphization of the orthorhombic structure and delamination of the thin films from the current collector. Additionally, these films boasted exceptional capacities that exceeded the theoretical Faradaic capacity. This phenomenon can be attributed to high non-Faradaic surface capacitance arising from the observed 70% porosity of the films. Since pristine Nb2O5 is very insulating, these pores can only be accessed and contribute significantly to the capacitance if the conductivity of the films changes as a function of lithiation. In situ conductivity measurements of T-Nb2O5 nanoribbons illustrate a large ∼2000-fold increase in conductivity upon lithiation. Study of degradation and conductivity of electrophoretically deposited T- Nb2O5 is crucial in understanding why this material can perform beyond theoretical limits and how the electrochemical performance can be further improved.

Point of Care (PoC) diagnostics have made healthcare available for a large audience of non-specialists and patients with introduction of miniaturized, simple and user-friendly electronic devices. Electrochemical biosensors have emerged victorious candidates for PoC owing to the ease of transforming a biological interaction to simple electrical signal. This work is dedicated towards exploring a sensor architecture that connects the biological sensing element, virus, to an external circuitry at nanometer scale. Chapter 2 introduces the Virus-bioresistor in detail. It is demonstrated that M13 phage particles can be wired into an electrical circuit by embedding them in an electronically conductive polymer composed of poly(3,4-ethylenedioxythiophene) or PEDOT via electropolymerization. The signals transduced by impedance spectroscopy are recorded as an increased resistance of the virus-PEDOT material in the presence of the target protein and the amplitude of the resistance change allows its concentration in the contacting solution to be measured. This concept is demonstrated on a model system in which a dynamic range of 7.5 nM – 900 nM human serum albumin (HSA, 66kDa) is detected in phosphate buffer solution. The VBR overcomes the challenges of label-free, non-faradaic sensors pertaining to non-specific adsorption and lower sensitivity. Elemental problem of coupling of target binding from ionic conduction is solved as an equivalent circuit description for the data procured, establishes signal independence over solution conductivity. The next segment employs the VBR for detection of bladder cancer biomarker, DJ-1 (20 kDa), which is achieved by engineering the sensing layer that enables successful pico-molar detection of analyte without compromising on the speed and reproducibility of detection. A range of 10 pM – 300 nM DJ-1 protein is detected, which beautifully accommodates the established 100-1000 pM DJ-1 detected in bladder cancer patient’s urine. A possible signal transduction mechanism is uncovered with experiments based on quartz crystal microbalance (QCM) gravimetry. The last section exploits the potentiality of the VBR to be modified in a controlled fashion to enable large biomolecule (antibody) sensing. This is achieved by oxidizing the VBR channel using chronoamperometry. The morphological changes for VBRs have been tracked with microscopy techniques. Overall, this work establishes that VBRs can be associated with speed, specificity and reproducibility with coefficient of variation values <16%. The signal output can be tuned as per convenience to detect biomolecules with molecular weights that fall within an appreciable range of 20 kDa to 150 kDa.

Manganese oxide, MnO2, excels as a hybrid electrical energy storage material. The man- ganese centers in MnO2 are capable of undergoing a reduction from 4+ to 3+ balanced by the intercalation of lithium ions to form LixMnO2 while its conductive surfaces simultaneously store energy as an electrical double layer capacitor. Additionally, MnO2 nanowire structure for batteries and super-capacitors can produce superior power relative to films of the same materials. These advantages make MnO2 promising candidate for electrical energy storage material. But the Achilles Heel of nanowires is their susceptibility to degradation and failure. Typically such MnO2 nanowires are attached to a current collector at just one end and electrical conductivity of the nanowire therefore plays a very important role. In this work, the electrical conductance of δ-MnO2 nanowires is directly measured in-situ in 1M LiClO4, acetonitrile as a function of the equilibrium Li content for nanowires with varying lateral dimensions. As the equilibrium electrode potential is decreased from 0.60 V to -0.80 V and lithium is intercalated, the electrical conductivity of MnO2 nanowires increases by up to one order of magnitude. The measured change in conductivity is also dependent on the width of nanowires. After doping at -0.80 V vs. MSE, the conductivity increases by 30% for an 870 nm wide nanowire array and 880 % for a 275 nm wide array. Additionally, the combination of poly (methylmethacrylate)(PMMA) to the propylene carbonate (PC) electrolyte is discovered to eliminate the degradation processes in MnO2 nanowire capacitors. The nanowires investigated here have a Au@ δ-MnO2, core@shell, architecture in which a central gold nanowire current collector is surrounded by an electrodeposited layer of δ- MnO2. In the liquid PC electrolyte, the identical δ-MnO2 capacitors fractures, delaminates, and separates from the gold nanowire current collector. The addition of PMMA to the PC electrolyte prevents these deleterious processes and extends cycle stability to 100,000 cycles and beyond. This is shown through reversible cycle stability up to 200,000 cycles with 96 % average coulombic efficiency for symmetrical δ-MnO2 nanowire capacitors operating across 1.2V– 1.8 V voltage windows in a PMMA gel electrolyte.

Conductive polymers are often used in biosensing architectures of many kinds. Their biocompatibility, electrical conductivity, and ease of polymerization allows many routes to fabricate innovative, nanoscale biosensors for point-of-care diagnostic purposes. The focus of this dissertation will be on two different types of nanoscale, conductive polymer biosensors that were fabricated since 2018 in the Penner Lab by myself and my associates. The first device is the Virus BioResistor (VBR). This device employs poly(3,4-ethylenedioxythiophene) (PEDOT) which is electropolymerized in the presence of virus particles which have been genetically engineered to bind a specific protein. A baselayer of PEDOT:PSS is used as a target for this electrodeposition. This event produces an electrically conductive bioaffinity layer, through which impedance measurements can be taken. In Chapter 2, advances are made to this device by increasing the PEDOT:PSS baselayer are discussed. The increase in the baselayer resistance causes a ~4x signal enhancement, without sacrificing signal-to-noise or specificity. The resulting device can detect deglycase 1 (DJ-1), a bladder cancer biomarker, at 10 pM in ~30 s. Chapter 3 discusses further enhancements made to the VBR through over-oxidation. The process of over-oxidation allows for the detection of larger proteins and antibodies, up to 150 kDa. Without this process, the VBR is insensitive to proteins larger than 66.5 kDa. This process has been shown to enable detection of multiple antibodies. Following this work, an effort was made to engineer a conductive polymer sensor that is nanoscopic in 3 dimensions, compared to the VBR which is only nanoscopic in 1 dimension. This device is discussed in Chapter 4 and is called a Nanojunction pH sensor (NJ-pH). The NJ-pH sensor relies on lithographically patterned nanowire electrodeposition to fabricated single gold nanowires onto which electrical contacts are evaporated. A nanogap is formed in this nanowire through electromigration, and the gap is then bridged through electropolymerization of poly(aniline) (PANI) which has a resistance that is pH sensitive. This device is shown to have impedances that range 5 orders of magnitude between pH 1 – 9, and can give a reliable pH measurement within 30 s. This device is completely nanoscopic and offers a new avenue for monitoring local pH on the nanoscale.

Ultra-long (mm scale) polycrystalline gold nanowires were investigated for their ability to perform as thermophones, or thermoacoustic sound emitters. Arrays of ~4000 linear gold nanowires are fabricated at 5 um pitch on glass surfaces using lithographically patterned nanowire electrodeposition (LPNE). The properties of nanowire arrays for generating sound are evaluated as a function of frequency (from 5 - 120 kHz), angle from the plane of the nanowires, input power (from 0.30 - 2.5 W) and the width of the nanowires in the array (from 270 to 500 nm.) Classical theory for thermophones based upon metal films accurately predicts the measured properties of these gold nanowire arrays. Angular "nodes" for the off-axis sound pressure level (SPL) versus frequency data, predicted by the directivity factor, are faithfully reproduced by these nanowire arrays. The maximum efficiency of these arrays (~10^-10 at 25 kHz), the power dependence, and the frequency dependence is independent of the lateral dimensions of these wires over the range from 270 to 500 nm.

Lithographically patterned metal nanowires were utilized in two studies on sensing and transduction. First, ultra-long (mm scale) polycrystalline gold nanowires were investigated for their ability to perform as thermophones, or thermoacoustic sound emitters. Arrays of ~4000 linear nanowires were fabricated at 5 um pitch on glass surfaces. Sound generation by the nanowires was evaluated as a function of acoustic frequency (from 5 - 120 kHz), angle from the plane of the nanowires, input power (from 0.30 - 2.5 W) and the width of the nanowires in the array (from 270 to 500 nm.) Classical theory based upon metal films accurately predicts the measured properties of these gold nanowire arrays. Angular "nodes" for the off-axis sound pressure level (SPL) versus frequency data, predicted by the directivity factor, were faithfully reproduced by these nanowire arrays. The maximum efficiency of these arrays (~10^{-10} at 25 kHz), the power dependence, and the frequency dependence were independent of the lateral dimensions of these wires over the range from 270 to 500 nm. Second, a PEDOT-deferoxamine nanojunction chemiresistor was developed for the rapid detection of Fe(III) at sub-nanomolar concentrations. The backbone of the sensor is a single lithographically patterned metal nanowire in which a nanogap is formed by focused ion beam (FIB). The nanowire is then electrochemically reconnected by the ionophore-doped polymer PEDOT-deferoxamine, creating a chemically responsive junction selective for Fe(III). Fabrication challenges, centered on the adhesion between the metal nanowire core and the PEDOT-DFA transduction layer, led to three design iterations of the sensor. Two of these nanojunctions were able to detect 10^{-11}-10^{-4} M Fe(III), demonstrating a dynamic range that is on par with ion selective electrodes and a limit of detection that is three order of magnitude better. However, these junctions fail to decrease the detection time and show a significant response to the control ion Zn(II).