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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.

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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 the pyramidal nanodiamond emitters. Therefore, the proposed tip-on-pole nanodiamond emitters show great promise for high current and power applications.

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Harvesting solar energy using dye-sensitized solar cells (DSSCs) has been a promising option. Successful integration of a DSSC electrode with an energy storage electrode represents the next challenge for the researchers. In this paper, the fabrication and characterization of an integrated dye-sensitized photoanode and a supercapacitor cathode or a photocapacitor has been presented. This novel device employs N-719 dye-sensitized titanium dioxide on fluorine-doped tin oxide glass substrate as the photoanode. The supercapacitive counter electrode comprises MnO2 coated, vertically aligned, micro-array patterned carbon nanotubes (MA-CNTs). The CNTs were grown on n++ silicon (Si) substrates in a hot filament chemical vapor deposition system followed by in-situ electrochemical deposition of MnO2. Tetraethyl ammonium tetrafluoroborate electrolyte was used to investigate the photovoltaic and energy storage performances of the photocapacitors under 1-sun illumination and constant-current discharge tests. A high discharge capacitance of 13 mF/cm2 at 0.932 V was achieved by coating MnO2 onto the high surface area of MA-CNTs due to the pseudocapacitive behavior of MnO2, which led to a nearly 3-fold increase in the short circuit current density to 0.749 mA/cm2 and more than a 2-fold enhancement in the open circuit voltage to 0.46 V, as compared to the baseline CNT counter electrode. The corresponding increase in the fill factor and efficiency was also observed. Overall, we have demonstrated the viability of a compact, easy to fabricate, integrated photocapacitor with promising energy generation/storage performance.