[Show abstract][Hide abstract] ABSTRACT: The desorption kinetics of deuterium from polycrystalline chemical vapor deposited diamond films were characterized by monitoring the isothermal thermionic emission current behavior. The reaction was observed to follow a first-order trend as evidenced by the decay rate of the thermionic emission current over time which is in agreement with previously reported studies. However, an Arrhenius plot of the reaction rates at each tested temperature did not exhibit the typical linear behavior which appears to contradict past observations of the hydrogen (or deuterium) desorption reaction from diamond. This observed deviation from linearity, specifically at lower temperatures, has been attributed to non-classical processes. Though no known previous studies reported similar deviations, a reanalysis of the data obtained in the present study was performed to account for tunneling which appeared to add merit to this hypothesis. Additional investigations were performed by reevaluating previously reported data involving the desorption of hydrogen (as opposed to deuterium) from diamond which further indicated this reaction to be dominated by tunneling at the temperatures tested in this study (<775 °C). An activation energy of 3.19 eV and a pre-exponential constant of 2.3 × 1012 s−1 were determined for the desorption reaction of deuterium from diamond which is in agreement with previously reported studies.
Journal of Applied Physics 01/2014; 115(23):234904-234904-6. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
IEEE Transactions on Electron Devices 01/2013; 60(1):487-493. · 2.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hydrogen influences many properties of diamond films, such as invoking negative electron affinity, inducing increased electron emission from diamond thermionic emitters. However, the thermionic emission diminishes at temperatures exceeding 750 °C. In this work, we observed the isothermal thermionic emission decrease followed first-order rate kinetics. Arrhenius examination indicated an activation energy consistent with values for the H-C bond at the surface derived from other works. Results obtained in this study establish a direct link between the presence of hydrogen and the degree of thermionic emission from diamond and is information relevant to the development of higher thermal emission from diamond.
[Show abstract][Hide abstract] ABSTRACT: Nitrogen-incorporated nanocrystalline diamond (ND) vacuum field emission transistor (VFET) with self-aligned gate is fabricated by mold transfer microfabrication technique in conjunction with chemical vapor deposition (CVD) of nanocrystalline diamond on emitter cavity patterned on silicon-on-insulator (SOI) substrate. The fabricated ND-VFET demonstrates gate-controlled emission current with good signal amplification characteristics. The dc characteristics of the ND-VFET show well-defined cutoff, linear, and saturation regions with low gate turn-on voltage, high anode current, negligible gate intercepted current, and large dc voltage gain. The ac performance of the ND-VFET is measured, and the experimental data are analyzed using a modified small signal circuit model. The experimental results obtained for the ac voltage gain are found to agree with the theoretical model. A higher ac voltage gain is attainable by using a better test setup to eliminate the associated parasitic capacitances. The paper reveals the amplifier characteristics of the ND-VFET for potential applications in vacuum microelectronics.
Journal of Applied Physics 06/2012; 111(11). · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This article reports successful fabrication and characterization of vacuum microelectronic OR gate logic using nanodiamond lateral diode structures. Two identical sets of four nanodiamond lateral diodes with different numbers of emitters, viz., 125, 325, 2340 and 9360, and with equal anode–cathode spacing of ~ 3.5-μm were fabricated on silicon-on-insulator (SOI) wafers. First the fabricated lateral emitters were characterized for emission current scaling to examine the scaling effect of different structures with respect to the forward emission current. Then, two identical diodes were connected in a circuit using diode–resister logic to realize the logic OR function with a square wave as an input signal. The current scaling behavior, demonstrating 1 μA current at 18, 15, 7 and 2.2 V for 125-, 325-, 2340- and 9360-fingered emitter structures respectively, directly affects the logic OR response. These nanodiamond vacuum logic gates are promising for application in harsh environments.
Diamond and Related Materials 03/2012; 23:120–124. · 1.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A vacuum field emission (VFE) transistor in vertical configuration with nitrogen-incorporated nanocrystalline-diamond emitters is presented. A novel self-aligned gate partition technique was utilized to construct the VFE device. The gate-controlled modulation of the emission current was demonstrated. A high emission current of 160 μA and a low gate turn-on voltage of 25 V were achieved. The device displayed high DC voltage gain of 1000 and negligible gate intercepted current, which are crucial features for microelectronic applications. Basic transistor characteristics with distinct cutoff, linear, and saturation regions were observed, revealing the practical application of the device for vacuum microelectronics and integrated circuits.
Diamond and Related Materials 02/2012; 22:142–146. · 1.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Biosensors for detecting/measuring/monitoring the concentration of neurotransmitters that vary at sub-second time-scale can be achieved by using an electrode with high temporal resolution and fast electron transfer kinetics. Neurotransmitters, such as dopamine, undergo rapid fluctuations in concentrations occurring at a sub-second time scale. Real-time monitoring and measurement of these concentrationn changes, in-vivo or in-vitro, requires the use of ultra-microelectrode array (UMEA). This work reports on the development of a reliable UMEA electrochemical biosensor which can be used to identify, quantify, and monitor essential bio-analytes such as dopamine (DA), ascorbic acid (AA) and uric acid (UA) by using CVD nitrogen-incorporated nanodiamond UMEA without the need of electrode surface functionalization or modifications, making real-time detection possible. The application of fast-scan voltammetry (FSCV) for detecting dopamine and interfering bio-chemicals, including ascorbic acid and uric acid in 0.1M PBS (pH 7.4) by the UMEA has been realized. The detailed experiential method for the sensor array fabrication, and the UMEA sensitivity, selectivity, and detection limit for the detection of bio-analytes will be discussed.
[Show abstract][Hide abstract] ABSTRACT: 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 700 °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 900 °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 to ∼ 700 °C. Above ∼ 800 °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 emission current at temperatures below ∼700 °C after this hydrogen plasma exposure was observed to increase by four orders of magnitude over the thermionic emission current observed in the initial (as-grown) test. Possible explanations for this emission current increase are discussed.
Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2012; 30(2):1202-. · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents the triode behavior of a gated nanodiamond vacuum field emitter array and its application in signal amplification. The triode feature is demonstrated with the observation of gate modulation on the emission current induced by the anode field. The emission characteristics are studied by considering the resultant electrical field on emitters, confirming the gate modulation effect. The voltage gain is examined, showing a reasonable value of 6.7 at the operating current of 50 μA. Higher gain is attainable at elevated operation currents.
[Show abstract][Hide abstract] ABSTRACT: Reported is a novel vacuum field emission transistor (VFET) differential amplifier (diff-amp) utilising nanocrystalline diamond emitters with self-aligned gate partitions. The integrated VFET diff-amp was fabricated by a dual-mask self-aligned mould transfer method in conjunction with chemical vapour deposited nanodiamond. Identical pairs of devices with well-matched field emission transistor characteristics were obtained, realising a negligible common-mode gain, high differential-mode gain, and large common-mode rejection ratio (CMRR) of 55 dB. The emission current was validated by a modified Fowler-Nordheim equation in transistor configuration, and the CMRR was modelled by an equivalent half-circuit with the calculated result found to agree well with the experimental value.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Successful fabrication and characterisation of a vacuum microelectronic half-wave rectifier and envelope detector using a 2000-fingered nanodiamond lateral field emitter diode with 4 μm inter-electrode spacing is reported. The electrical characterisation demonstrates low turn-on field (~1.4 V/ μm) and high emission current, verified by the Flower-Nordheim plot. The diode is then connected in appropriate circuits to realise half-wave rectification and envelope detection. This approach demonstrates a new way of developing temperature- and radiation-tolerant integrated microelectronics.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the electrical characteristics of lateral field emission vacuum microelectronic devices comprised of nanodiamond in two terminal (diode) and three terminal (transistor) cathode–gate–anode configuration and their resistance to failure in severe radiation conditions that would shut down conventional solid state electronics. This is the first published data on radiation tolerance of three terminal diamond vacuum lateral field emission devices. No changes in device structure or electrical behavior were observed after exposure to high levels of X-ray or neutron radiation.Graphical abstractHighlights► Electronic devices of diamond emitters demonstrate exceptional radiation hardness. ► Very high dosage of X-Ray and neutrons cause no changes in behavior of diodes or transistors. ► Vacuum electron transport not susceptible to carrier mobility degradation. ► Diamond devices can be fabricated and packaged as monolithic ‘chips’, treated as if silicon integrated circuits.
[Show abstract][Hide abstract] ABSTRACT: Reported are fabrication and characterisation of a novel vacuum logic OR gate using two identical nanodiamond lateral field emission diodes fabricated on silicon-on-insulator wafers. Each diode consists of 9000 finger-like emitters with 4 m interelectrode spacing. High and stable emission current with low turn-on field have been observed and verified by a Fowler-Nordheim plot for each structure. Diode-resistor logic is used to realise the logic OR function. This nanodiamond vacuum logic gate is very promising for application in harsh environments.
[Show abstract][Hide abstract] ABSTRACT: Researchers unveil a new way of developing temperature and radiation-tolerant logic circuits for integrated vacuum microelectronics interesting for Davidson from both a scientific and performance perspective is to shrink the gap between the cathode and the anode.
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Applied Physics 11/2010; 108(9). · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper reports the fabrication and characterization of miniaturized monolithic lateral field emission power cell (FEPC) comprising of carbon nanotube (CNT) emitters and an integrated metallic anode. Electron stimulation impact ionization on FEPC CNT cathode was activated by an integrated electron beam emitter. Field emission behavior with and without the activation of the electron beam was characterized in diode configuration. The emission current of the FEPC increased with the activation of the electron beam. At this operating condition, ten times current amplification and 1.4 μW of power was generated. Results demonstrate the feasibility of power generation using electron stimulated impact ionization.
[Show abstract][Hide abstract] ABSTRACT: Well established silicon microfabrication technology and PECVD nanodiamond growth process enabled us to fabricate an ultra-microelectrode array (UMEA) for biosensing applications. The UMEA consists of 2500 nanodiamond elements in a square array surrounded by a layer of thermally grown SiO2 on a highly doped silicon substrate. Fe(CN)63−/4− redox couple was used for electrochemical characterization of the UMEA using cyclic voltammetry and gave us a steady state response consistent with hemispherical diffusion limited mass transport mechanism. Using the nanodiamond UMEA, we were also able to detect different concentrations of Dopamine in phosphate buffered saline (pH 7.4) without any surface functionalization. The cyclic voltammograms show a steady state response and a linear relationship between the limiting current and Dopamine concentration.
Diamond and Related Materials 01/2010; 19:256-259. · 1.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this article, the authors report the fabrication and observation of electron-field emission from nanodiamond ridge structure array capped on micropatterned silicon pillars. The fabrication process began with a deposition of 1.5-μm-thick ridge-structured diamond on a highly conductive n-type silicon substrate using microwave-plasma-enhanced-chemical-vapor deposition followed by patterning and reactive-ion etching techniques to get the device structure, which is an array of 50×50 silicon pillars capped with ridge-structured nanodiamond. Scanning electron microscope image confirms the device structure. The electron-field emission, performed in vertical-diode configuration, demonstrated a low threshold turn-on field of 1.2 V/μm and a high emission current of 150 μA at the anode field of 5.5 V/μm. The emission behavior has been compared with that of planar film of identical nanodiamond morphology. A 6000 times increase in current density is observed and attributed to its better geometrical-enhancement factor.
Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2010; 28. · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This article reports the fabrication and characterization of a CNT field emission cell with a built-in electron beam source for electron excited amplified field emission. A monolithic lateral field emission cell (FEC) with integrated metallic anode was fabricated. Then the field emission behaviors with and without activation of the built-in electron beam were characterized in diode configuration. A high voltage of 1.8kV was applied to generate the bombarding electron beam on the FEC. The emission current of the FEC increases markedly with the activation of the electron beam source due to impact ionization and direct interaction with the FEC CNT cathode. The emission behaviors were confirmed by F–N plots. It was found that almost 10 times current amplification was achieved. These results demonstrate the feasibility of an electron beam amplified field emission using carbon nanotube emitters.
Diamond and Related Materials 01/2010; 19(2):247-251. · 1.71 Impact Factor