Nanostructured carbon materials, especially activated carbon, carbon nanotubes, and graphene, have been widely studied for supercapacitor applications. To maximize the efficacy of these materials for electrochemical energy storage, a detailed understanding of the relationship between the nanostructure of these materials and their performance as supercapacitors is required. A fundamental structural parameter obtained from the Raman spectra of these materials, the in-plane correlation length or nanocrystalline domain size, is found to correlate with the electrochemical capacitance, regardless of other morphological features. This correlation for a common nanostructural characteristic is believed to be the first result of its kind to span several distinct nanostructured carbon morphologies, including graphene–carbon nanotubes hybrid materials, and may allow more effective nanoscale engineering of supercapacitor electrode materials.

Graphene and carbon nanotubes (CNTs) are fascinating materials, both scientifically and technologically, due to their exceptional properties and potential use in applications ranging from high-frequency electronics to energy storage devices. This manuscript introduces a hybrid structure consisting of graphitic foliates grown along the length of aligned multiwalled CNTs. The foliate density and layer thickness vary as a function of deposition conditions, and a model is proposed for their nucleation and growth. The hybrid structures were studied using electron microscopy and Raman spectroscopy. The foliates consist of edges that approach the dimensions of graphene and provide enhanced charge storage capacity. Electrochemical impedance spectroscopy indicated that the weight-specific capacitance for the graphenated CNTs was 5.4× that of similar CNTs without the graphitic foliates. Pulsed charge injection measurements demonstrated a 7.3× increase in capacitance per unit area. These data suggest that this unique structure integrates the high surface charge density of the graphene edges with the high longitudinal conductivity of the CNTs and may have significant impact in charge storage and related applications.

Partially stabilized zirconia (PSZ) has been studied extensively, due to its high-temperature stability and stress-induced tetragonal (T)-to-monoclinic (M) martensitic phase transformation. This T ⇒ M phase transformation has been well-documented for bulk PSZ, but limited data exist for PSZ thin films. Data will be presented that support a stress-induced T ⇒ M transformation mechanism that occurs during sputter deposition in the presence of a substrate bias. Substrate bias (0–50 W) was originally applied to increase film density, modify microstructure, and vary film stress. The films were deposited using radio-frequency magnetron sputtering from a sintered yttria-stabilized zirconia target and were subsequently characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and wafer bow measurement (for stress analysis). With no substrate bias, the films exhibited a columnar grain structure that was consistent with sputter-deposited films, with a majority T phase as determined by XRD. Under higher substrate bias, wafer bow measurements indicated a steady increase in compressive stress as substrate bias increased (maximum, 310 MPa at 50-W bias), while XRD indicated a corresponding increase in the percentage of the M phase. Both SEM and TEM analyses revealed a shift from a defect-free columnar structure to one consisting of lateral intracolumnar or transgranular defects for films deposited under substrate-bias conditions. It is hypothesized that these defects form as a result of stress relief in the growing film via the T ⇒ M phase transformation due to bias-induced compressive stress.

Transmission electron microscopy (TEM) was used to investigate the structural properties of sputter-deposited yttria-stabilized zirconia (YSZ) thin films. YSZ films were deposited over a range of temperatures and background oxygen levels. Additionally, a multilayered structure was produced by cyclic application of a substrate bias. Plan-view TEM showed that temperature and oxygen levels did not have a significant effect on grain size but did alter the phases present in the thin films. Cross-sectional TEM showed the development of texture in the multilayer film, both within the individual layers and in the entire film.

Polycrystalline diamond films previously grown on silicon were polished to an RMS roughness of 15 nm and bonded to the silicon in a dedicated ultrahigh vacuum bonding chamber. Successful bonding under a uniaxial mechanical stress of 32 MPa was observed at temperatures as low as 950°C. Scanning acoustic microscopy indicated complete bonding at fusion temperatures above 1150°C. Cross-sectional transmission electron microscopy later revealed a 30 nm thick intermediate amorphous layer consisting of silicon, carbon and oxygen.

Carbon, silicon nitride and boron nitride nanostructures were synthesized using microwave plasma enhanced chemical vapor deposition. Both scanning and transmission electron microscopies and x-ray diffraction were used to observe the morphology and structures while energy dispersive x-ray was used to determine the composition of the nanostructured materials. Bamboo-like multiwalled carbon nanotube structures were observed while silicon nitride showed novel needle-like solid structures. All materials were deposited using a thin film iron catalyst seeded on either silicon with reactive plasma gases containing either a mixture of methane and ammonia or ammonia. A general discussion of the nucleation and growth mechanisms for the various materials will also be included.

Metal-oxide-semiconductor field-effect transistors (FETs) have been fabricated using B-doped diamond thin films deposited on polycrystalline, (100) highly-oriented, and single crystal diamond insulating substrates. Diamond films were grown using a microwave plasma chemical vapor deposition technique. Various electrical and materials characterization techniques were employed to confirm that the films exhibited properties suitable for FET fabrication. Devices with gate lengths and widths of 2 μm and 314 μm respectively, were processed using standard photolithography. Silicon dioxide was used as the gate dielectric. Current-voltage characteristics of these devices have been measured during variable temperature cycling in air. Devices fabricated on the randomly oriented polycrystalline diamond substrates have been operated to 285°C. Field-effect transistors fabricated using the highly-oriented diamond substrates have been characterized to 400°C. Single crystal diamond devices exhibited saturation and pinch-off of the channel current at temperatures up to 500°C. These devices have been biased in amplifier circuit configurations that have been characterized from 20 Hz to 1 MHz. Single crystal FETs exhibited voltage gain over an extended temperature range. Transconductances as large as 1.7 mS/mm have been observed. The electronic properties, fabrication technologies, and performance of devices fabricated on the three diamond substrate materials will be discussed and compared.

Electrical conductivity measurements were used to study the effects that sample distance from the plasma during growth has on the carrier transport properties of undoped CVD diamond. The films were grown by downstream microwave plasma chemical vapor deposition at distances from 0.5 to 2.0 cm from the edge of plasma glow. Electrical conductivity measurements were performed between room temperature and 1000 °C to gain a better understanding of the CVD growth process and the resulting electrical properties of the diamond film's. Room temperature electrical conductivity was found to vary by over 5 orders of magnitude with increasing growth distance from the plasma, and this is attributed to decreasing hydrogen incorporation efficiencies at further distances from the plasma.