Field emission enhancement in ultrananocrystalline diamond films by in situ heating during single or multienergy ion implantation processes

Abstract

The single or multienergy nitrogen ͑N͒ ion implantation ͑MENII͒ processes with a dose ͑4 ϫ 10 14 ions/ cm 2 ͒ just below the critical dose ͑1 ϫ 10 15 ions/ cm 2 ͒ for the structural transformation of ultrananocrystalline diamond ͑UNCD͒ films were observed to significantly improve the electron field emission ͑EFE͒ properties. The single energy N ion implantation at 300°C has shown better field emission properties with turn-on field ͑E 0 ͒ of 7.1 V / m, as compared to room temperature implanted sample at similar conditions ͑E 0 = 8.0 V / m͒ or the pristine UNCD film ͑E 0 = 13.9 V / m͒. On the other hand, the MENII with a specific sequence of implantation pronouncedly showed different effect on altering the EFE properties for UNCD films, and the implantation at 300°C further enhanced the EFE behavior. The best EFE characteristics achieved for the UNCD film treated with the implantation process are E 0 = 4.5 V / m and current density of ͑J e ͒ = 2.0 mA/ cm 2 ͑at 24.5 V / m͒. The prime factors for improving the EFE properties are presumed to be the grain boundary incorporation and activation of the implanted N and the healing of induced defects, which are explained based on surface charge transfer doping mechanism.

Crystallization Effects of Nanocrystalline GaN Films on Field Emission

“…The electrical properties of semiconductor materials are closely related to the microstructure of the emitters . In the case of diamond-like carbon (DLC), the grain size reduction in the transition from microcrystalline toward nanocrystalline improves the FE properties. , The content of sp 3 carbon atoms is one of the most important factors determining the FE properties of DLC films. − Therefore, electron emission can be enhanced by controlling crystallization during fabrication. Furthermore, GaN has favorable piezoelectric and spontaneous polarization properties due to the wurtzite crystal structure, which dramatically affects the electrical properties. ,− By fine-tuning crystallization and orientation, the FE properties of GaN can be dramatically improved, , but up to now, there has not been a systematic study on the influence of the microstructure on the FE properties of GaN films produced on Si.…”

On the role of graphite in ultrananocrystalline diamond films used for electron field emitter applications

“…In contrast to the observation that substitutional doping of MCD with nitrogen by the addition of N 2 ‐species in CVD plasma is extremely difficult, incorporation of nitrogen into NCD or UNCD has been consistently reported as beneficial to their EFE behaviour, regardless of the films being grown (at 800 °C) using CH 4 /N 2 plasma or CH 4 /Ar/N 2 plasma . Ion implantation of N‐ions at low dosage (10 14 –10 16 ions/cm 2 ) with low T S (<300 °C) also showed pronounced improvement of the EFE properties of UNCD films .…”

“…In another report Joseph et al show enhancement of EFE of UNCD films due to structural transformations after single or multi‐energy nitrogen ion implantation (S/MENII) processes. Initially a dosage of 4 × 10 14 ions/cm 2 , just below the critical dose of 1 × 10 15 ions/cm 2 , is used, wherein the structure remains intact.…”

“…Notably, in 50–100–150–200 keV MENII process the films were first ion implanted with 50 keV N‐ions, followed by 100, 150, and 200 keV N‐ion implantation sequentially. The prime factors for improving the EFE properties are presumed to be the GB incorporation of N, activation of the implanted N by the double annealing effect and the healing of induced defects, which are explained based on surface charge transfer doping mechanism .…”

Improvement in Tribological Properties by Modification of Grain Boundary and Microstructure of Ultrananocrystalline Diamond Films

“…The possibilities that this material presents for surface acoustic devices , and microelectromechanical devices are immense. , Among diamond films, ultrananocrystalline diamond (UNCD) films with distinctive microstructural features have received a lot of attention from researchers over the past decade. − The exceptional characteristics of UNCD are related to volume fraction of the grain boundary phase, which increases as grain size decreases, something that occurs to a greater extent in UNCD than in nano- and microcrystalline diamond films. The grains in the UNCD films are of ultrasmall sizes (up to 10 nm) leading to relatively smooth surface but still bring about an improvement in the electron field emission and electronic properties as well as mechanical properties such as hardness and elastic modulus which is almost similar to that of pure diamond. − The moderate hardness and elastic modulus of nanocrystalline diamond (NCD) films exhibit high wear resistance and low friction coefficient. , A significantly low friction coefficient is observed when the grain boundary volume fraction of NCD films, which consists of lubricant phases of amorphous carbon (a-C) and sp 2 bonded graphite, increases. , Chemical passivation of the surface is also required to obtain low friction. , Several unique properties of UNCD films may find potential applications as low friction, hard, and protective wear-resistant coating materials, robust conducting coating for electrochemical electrodes and biocompatible and biologically active substrates …”