Weng P. Kang

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.

Morphology Effect of Vertical Graphene on the High Performance of Supercapacitor Electrode

Graphene and its composites are widely investigated as supercapacitor electrodes due to their large specific surface area. However, the severe aggregation and disordered alignment of graphene sheets hamper the maximum utilization of its surface area. Here we report an optimized structure for supercapacitor electrode, i.e., the vertical graphene sheets, which have a vertical structure and open architecture for ion transport pathway. The effect of morphology and orientation of vertical graphene on the performance of supercapacitor is examined using a combination of model calculation and experimental study. Both results consistently demonstrate that the vertical graphene electrode has a much superior performance than that of lateral graphene electrode. Typically, the areal capacitances of a vertical graphene electrode reach 8.4 mF/cm(2) at scan rate of 100 mV/s; this is about 38% higher than that of a lateral graphene electrode and about 6 times higher than that of graphite paper. To further improve its performance, a MnO2 nanoflake layer is coated on the surface of graphene to provide a high pseudocapacitive contribution to the overall areal capacitance which increases to 500 mF/cm(2) at scan rate of 5 mV/s. The reasons for these significant improvements are studied in detail and are attributed to the fast ion diffusion and enhanced charge storage capacity. The microscopic manipulation of graphene electrode configuration could greatly improve its specific capacitance, and furthermore, boost the energy density of supercapacitor. Our results demonstrate that the vertical graphene electrode is more efficient and practical for the high performance energy storage device with high power and energy densities.

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.

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.

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...

P2.14: Characterization of the thermionic electron emission properties of nitrogen-incorporated “ridged” nanodiamond for use in thermal energy conversion

The thermal electron emission of “ridged” type nanocrystalline diamond films has been characterized for use in thermal energy conversion via thermionic emission.

Nanodiamond vacuum field emission integrated devices

The superb material properties of nanocrystalline diamond (nanodiamond) materials coupled with practical chemical vapor deposition (CVD) processing of deposited nitrogen-incorporated nanodiamond on variety of substrates, have promoted further interest in the use of these diamond-derived materials as electron field emitters. Experimentally, nanodiamond emitters have been observed to emit electrons at relatively low electric fields and generate useful current densities. In this work, recent development in nanodiamond vacuum field emission integrated electronic devices, viz., the nanodiamond triodes, transistors and integrated differential amplifiers are examined. The material properties, device structure and fabrication process, and the electrical performance of these devices are presented.

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

We report new results from field emission microscopy studies of multi-wall 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 approach the maximum beam brightness allowed by Pauli exclusion.

Nanodiamond lateral field emission triode

Summary form only given. In this work, we report the fabrication and field emission characteristics of a nanodiamond lateral triode. The device fabrication involved a single-mask process, where a uniform layer of nanodiamond film of grain size 5-10 nm grown by CH4/H2/N2 MPECVD on a SOI substrate, was micropatterned using reactive ion etching in pure O2 plasma, with aluminum as the etch barrier for delineating the anode, cathode and the gate. On etching the silicon layer beneath the nanodiamond, the 1 mum-thick buried-oxide layer of the SOI serves to isolate the electrodes and achieve close inter-electrode spacing. The triode device structure (see figure 1) has a single finger nanodiamond cathode acting as the emitter, with 2 nanodiamond fingers in close proximity to the emitter on either side forming the gate, and a straight-edge geometry serving as the nanodiamond anode. A gate-cathode distance as small as 2 mum was achieved by photolithography and the subsequent etch processes. Fabricated anode-cathode distances per design were set to vary between 20 mum and 1 mm, so as to have a wide range to observe the modulation effect of the gate on the triode characteristics for field emission characterization of the device. A Ti/Au metal contact layer was applied on the nanodiamond to provide good electrical contact. A lateral triode with 2 mum gate-cathode and 20 mum anode-cathode spacing was characterized for field emission in a vacuum of 10-7 Torr. The triode achieved a very low gate turn-on voltage of ~9 V (threshold field: 4.5 V/mum) and displayed gate-controlled current modulation behavior whereby higher applied gate voltages gave rise to high emission current collected by the anode (see Figure 2). As a result, a large anode current of ~15 muA was achieved at Vg = 40 V and Va = 105 V. The device characteristics showed cut-off, linear and onset of saturation regions. The transistor parameters defining the performance of a triode amplifier were determined graphically from the DC characteristics curves. The transconductance gm of the triode was estimated to be ~ 0.83 muS at Va = 105 V, which will be improved by building a larger nanodiamond finger array for the electron emitter. At a constant Ia of 8 muA, the amplification factor mu was calculated to be ~ 10, indicating that this triode is an amplifier. The detailed dc characteristics of the nanodiamond lateral triode and further enhancements of the transistor performance will be investigated and presented. The nanodiamond lateral triode is a potential candidate for high frequency, high power amplification device applications