Jimmy L. Davidson

A novel interdigitated capacitor based biosensor for detection of cardiovascular risk marker.

C-reactive protein (CRP) is a potential biomarker whose elevated levels in humans determine cardiovascular disease risk and inflammation. In this study, we have developed a novel capacitive biosensor for detection of CRP-antigen using capacitor with interdigitated gold (GID) electrodes on nanocrystalline diamond (NCD) surface. The NCD surface served as a dielectric layer between the gold electrodes. GID-surface was functionalized by antibodies and the immobilization was confirmed by Fourier transform spectroscopy (FT-IR) and contact angle measurements. The CRP-antigen detection was performed by capacitive/dielectric-constant measurements. The relaxation time and polarizability constants were estimated using Cole-Cole model. Our results showed that the relaxation time constant (tau) of only CRP-antibody was within 10(-16)-10(-13)s, which was increased to 10(-11)s after the incubation with CRP-antigen, suggesting that the CRP-antigen was captured by the antibodies on GID-surface. In addition, polarizability constant (m) of CRP was also increased upon incubation with increasing concentration of CRP-antigen. Our results showed that the response of GID-NCD-based capacitive biosensor for CRP-antigen was dependent on both concentration (25-800ng/ml) as well as frequency (50-350MHz). Furthermore, using optimized conditions, the GID-NCD based capacitive biosensor developed in this study can potentially be used for detection of elevated levels of protein risk markers in suspected subjects for early diagnosis of disease.

A new hydrogen sensor using a polycrystalline diamond-based Schottky diode

A new hydrogen sensor utilizing plasma-enhanced chemical vapor deposited diamond in conjunction with palladium (Pd) metal has been developed. The device is fabricated in a layered Pd/Undoped diamond/p-doped diamond Schottky diode configuration. Hydrogen sensing characteristics of the device have been examined in terms of sensitivity, linearity, response rate, and response time as a function of temperature and hydrogen partial pressure. Hydrogen adsorption activation energy is investigated in the temperature range from 27 to 85 C. Analysis of the steady-state reaction kinetics using the I-V method confirm that the hydrogen adsorption process is responsible for the barrier height change in the diamond Schottky diode. The ability to fabricate diamond-based hydrogen sensor on a variety of substrates makes the device very versatile for gas sensing.

Nanodiamond Lateral VFEM Technology for Harsh Environments

This paper reports the first total dose tests on a nanocrystalline diamond lateral vacuum field emission microelectronics (VFEM) technology. This technology operates efficiently at both low and high temperatures (200degC) and is inherently ldquohardrdquo to radiation. No measurable change in device response is observed after 15 Mrad(SiO2) total dose exposure, signifying an emerging electronics for extreme environment.

Thermal Conductivity of Nanoparticle Suspensions

* Graduate Research Assistant, Mechanical Engineering † Assistant Professor, Mechanical Engineering ‡ Professor, Electrical Engineering ABSTRACT This paper considers the thermal effects of different types and quantities of nanoparticles, such as diamond, aluminum oxide, and zinc oxide, suspended in transformer oil, soy-based transformer oil, and ethylene glycol. Thermal conductivity of the nanoparticle suspensions has measured by a steady-state parallel plate method. Experimental results consistently indicate a larger thermal conductivity increase than that predicted by theoretical models. Mechanisms possibly responsible the increase are discussed. Experiments on nanodiamond-soy-based-oil show 48% higher thermal conductivity than traditional transformer oil. These results can be applied in new transformers with smaller size and lower pumping power.

PECVD diamond-based high performance power diodes

In this study, we have designed, fabricated, characterized, and analyzed plasma-enhanced chemical vapor deposition (PECVD) diamond-based Schottky diodes for high power electronics applications. We have elaborated four critical issues in the synthetic-diamond semiconductor technology: 1) growth, 2) doping, 3) Schottky contact, and 4) different device structures in order to achieve better performance parameters. We have obtained 500 V of breakdown voltage on one device and 100 A/cm/sup 2/ of current density on another device, optimized for different applications. These values are among the highest reported with the polycrystalline diamond-based devices. We have utilized different fabrication techniques for the growth of PECVD-diamond, different metals as a Schottky contact on diamond film and also optimized structural parameters such as diamond film thickness and doping concentration in order to achieve a high-performance power diodes. Analysis of the current conduction mechanisms of these devices in this study revealed a space-charge-limited current conduction mechanism in the forward bias region while thermionic field emission controlled current conduction mechanism in the reverse bias region. Performance parameters such as forward voltage drop, barrier height, and current density were analyzed as a function of temperature and type of metal Schottky contacts.

Resonant tunneling and extreme brightness from diamond field emitters and carbon nanotubes

We report new results from field emission microscopy studies of multiwall carbon nanotubes and from energy spectrum measurements of beams from diamond field emitters. In both systems, we find that resonant tunneling through adsorbed species on the emitter surface is an important and sometimes dominant effect. For diamond emitters our observations include order-of-magnitude emission enhancement without spectral broadening, complex spectral structure, and sensitivity of that structure to the applied electric field. For carbon nanotubes we have observed electron beams from individual adsorbates which are estimated to approach the maximum beam brightness allowed by Pauli exclusion.

Influence of hydrogen on the thermionic electron emission from nitrogen-incorporated polycrystalline diamond films

Although hydrogen has been shown to enhance the thermionic emission properties of nitrogen-incorporated diamond cathodes, the effect diminishes when these cathodes are heated to temperatures in excess of 700u2009°C, possibly due to the hydrogen desorbing from the diamond. In order to further examine this behavior, this work examines the thermionic emission properties of a nitrogen-incorporated diamond film grown by chemical vapor deposition in a hydrogen-methane-nitrogen plasma. The film was tested for thermally stimulated electron emission at temperatures ranging from 500 to 900u2009°C in an as-grown state and after exposure to a hydrogen plasma treatment. Emission current increased, as described by the Richardson equation for thermal emission up tou2009∼u2009700u2009°C. Aboveu2009∼u2009800u2009°C the thermionic emission current was observed to diminish, an effect attributed to the loss of hydrogen from the diamond. Recovery of the hydrogen effect was explored by exposing the diamond film to a low-energy hydrogen plasma. The thermionic...

Diamond Vacuum Electronic Device Behavior After High Neutron Fluence Exposure

This paper reports the first neutron exposure on diamond electronic test structures for their possible application in very high fluence neutron conditions. The behavior of diamond lateral emission diodes after high neutron fluence of 4.4times1013 neutrons/cm2 is evaluated. No noticeable changes in the device structure and electrical behavior, specifically resistivity, dilation and emission characteristics were observed.

Advanced nanodiamond emitter with pyramidal tip-on-pole structure for emission self-regulation

In this paper, we report an innovative nanodiamond field emitter structure consisting of an individual pyramidal tip sitting on top of a ballast resistor “pole.” The tip-on-pole nanodiamond structures are fabricated by a new mold transfer process that is comprised of reactive-ion-etching of 3.5 μm-thick thermal oxide on Si substrate, anisotropic etching of Si, tip sharpening by thermal oxidation and chemical vapor deposition of nanodiamond. The fabricated tip-on-pole nitrogen-incorporated nanodiamond emitter exhibits a low turn-on electric field of 3.5 V/um and a very high emission current density of ∼1.7 A/cm2 at an electric field of ∼7.5 V/um. Analysis of the emission current based on Fowler–Nordheim theory indicates a current regulated regime due to the pole-structured ballast resistor with the resistance value of ∼140 kΩ. Thus, the diamond pole ballast resistor has proven to provide self-limiting of emission current that improves the total current density as well as the emission current stability of t...

Nanodiamond Vacuum Field Emission Integrated Differential Amplifier

The development of a novel vacuum differential amplifier (diff-amp) array employing vertically configured nanodiamond (ND) vacuum field emission transistors (ND-VFETs) on a single chip is presented. The diff-amp array is composed of a common ND emitter array integrated with partition gates and split anodes. An identical pair of ND-VFETs with well-matched field emission transistor characteristics was fabricated by using a dual-mask well-controlled microfabrication process, involving a mold-transfer self-aligned gate-emitter technique in conjunction with ND deposition into the micropatterned molds in the active layer of a silicon-on-insulator substrate followed by gate partitioning to form diff-amp array. The ND-VFETs show gate-controlled modulation of emission with distinct cutoff, linear, and saturation regions. Signal amplification characteristics of the ND-VFET diff-amp are presented. A large common-mode-rejection ratio (CMRR) of 54.6 dB was measured for the diff-amp. The variation of CMRR performance with transconductance was examined, and the results were found to agree with the equivalent circuit model analysis. The accomplishment of this basic circuit building block, consisting of an integrated diff-amp, demonstrates the feasibility of using vacuum integrated circuits for practical applications, including high-radiation and temperature-tolerant space electronics.