[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: A three-electrode nanodiamond vacuum field emission (VFE) device with gate modulated triode characteristics is developed by integrating nanodiamond emitter with self-aligned silicon gate and anode, employing a mold transfer technique in conjunction with chemical vapor deposition of nanodiamond. Triode behavior showing emission current modulation with high current density at low operating voltages is achieved. A systematic analysis based on modified Fowler-Nordheim theory is used to analyze gate modulated VFE characteristics, confirming the triode field emission mechanism and operating principle. The realization of an efficient VFE microtriode has achieved the fundamental step for further development of vacuum integrated microelectronics.
[Show abstract][Hide abstract] ABSTRACT: This article reports a vacuum multi-finger monolithic microtriode utilizing nanodiamond as the emitting material. The structure is comprised of 140-fingerlike nanodiamond emitters with built-in nanodiamond gate and Si anode. A mixed lithography patterning approach is used to fabricate the three-terminal device structure. Triode characteristics, demonstrating gate controlled emission current modulation at low operating gate and anode voltages, are obtained. The realization of the efficient monolithic microtriode allows further development of robust vacuum integrated circuit for application in high temperature and radiation harsh environments.
[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: A boron-doped polycrystalline diamond film was deposited on a molybdenum substrate and resistively heated in a high vacuum environment. The thermally excited emission current as a function of cathode temperature was measured. This phenomenon, known as thermionic emission, is characterized by electron emission arising from a surface at elevated temperatures and is described by the Richardson equation. The observed thermionic emission current from the diamond sample followed the Richardson equation from which a work function of 4.43 eV and a Richardson constant of ∼60 A/cm2K2 were observed. This indicates boron-doped polycrystalline diamond behaves as an interesting thermionic emitter for possible energy conversion and other electron emission applications.
physica status solidi (a) 10/2012; 209(10):1993-1995. · 1.21 Impact Factor
[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: Dye-sensitized solar cells (DSSCs), which were first reported in 1991 , have attracted much attention due to simple and low-cost fabrication processes and good energy conversion efficiency [2-3]. Typical DSSC consists of a nanocrystalline wide band-gap semiconductor film (e.g. titanium dioxide TiO 2) attached with a monolayer of dye molecules as the photoelectrode, a catalytic conductive layer as the counter electrode and a redox system of electrolyte in-between the electrodes. To enhance the energy conversion efficiency, various catalytic materials have been applied as the counter electrodes of DSSCs . Carbon nanotubes (CNTs) possess advantages of cost effectiveness, chemical inertness, large surface area and good electrochemical catalytic behavior. Besides, the vertical alignment of chemical vapor deposition (CVD) CNTs favors the diffusion of redox species. In this work, we used CVD multiwalled CNTs (MWCNTs) and manganese dioxide (MnO 2)-coated MWCNTs as the counter electrodes to enhance the catalytic performance. The photoelectrodes of DSSCs were prepared by an easy and reproducible spin coating method of TiO 2 colloidal paste onto FTO glass substrates, followed by sintering of TiO 2 at 450 °C and immersing them into the ruthenium (II) dye solution (N719). As for counter electrodes, MWCNTs were grown directly on silicon substrates by hot filament CVD with the gas mixture of H 2 /NH 3 /CH 4 . The MnO 2 films with different thickness were deposited onto MWCNTs substrates by electrochemical reduction of potassium permanganate solution. Scanning electron microscopy images of TiO 2 flims and MWCNTs are shown in figure 1. The sputtered Pt on a FTO glass substrate was used as a control counter electrode. The iodide-based electrolyte with composition of 0.5M LiI, 0.05M I 2 and 0.5M 4-tert-butylpyridine in acetonitrile was then filled in between the sensitized TiO 2 photoelectrodes and individual counter electrodes with 50 um spacers, followed by sealing the cells. An Oriel solar simulator with air mass 1.5 G filter installed was used for solar illumination and the combination of a voltage power supply and a digital multimeter was utilized for I-V measurements. The sampling delay time and measuring integration time were both 1 second and the voltage source step level was 10 mV . The MWCNTs-DSSC exhibited comparable photoexcitation behavior to that of Pt-DSSCs under 1-sun illumination, as shown in figure 2. The J sc , V oc and ff for Pt-DSSC are 13.3 mA/cm 2 , 0.635 V and 0.5, while those for MWCNTs-DSSC are 13.2 mA/cm 2 , 0.655 V and 0.48, respectively. The energy conversion efficiency for both cells is 4.25 % and 4.16 %, indicating that MWCNTs have well comparability with Pt for counter electrodes in DSSCs. Figure 2 also showed the photocurrent of DSSCs with two MnO 2 -coated MWCNTs counter electrodes under the same illumination. The enhancement of V oc from 0.655 V to 0.745 V and 0.715 V was observed from the MnO 2 -coated MWCNTs-DSSCs, respectively. This
[Show abstract][Hide abstract] ABSTRACT: Diamond cold-cathode devices have demonstrated significant potential as electron field emitters. Ultra-sharp diamond pyramidal tips (~ 5 nm tip radius) have been fabricated, and show improvement in emission when compared to conventional field emitters. However, the emission mechanisms in these complex diamond nanostructures are not well understood. Transmission electron microscopy performed in this study provides new insight into tip structure and composition with implications for field emission and diamond growth.
Microscopy and Microanalysis 07/2011; 17:1508-1509. · 2.50 Impact Factor
[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.