1,721,091 research outputs found
Advances in n-Type Chemical Vapor Deposition Diamond Growth: Morphology and Dopant Control
No full textCONSPECTUS: Diamond, a wide bandgap semiconductor, has captivated researchers for decades due to its exceptional properties. While p-type doping has dominated the field, the advent of n-type diamond, doped by nitrogen or phosphorus, has unlocked novel prospects for diverse applications. Nonetheless, the chemical vapor deposition (CVD) of n-type diamond faces substantial hurdles, particularly concerning crystalline quality and dopant concentration control. In this Account, we summarize our progress in developing high quality CVD n-type diamond films. Our research initiates with nitrogen introduction into the CH 4 /H 2 CVD plasma for depositing polycrystalline diamond films. The addition of 4% N 2 gas induces the formation of ultra-nanosized diamond grains through CN species, but further increases in nitrogen content result in grain agglomeration into larger sizes. Fixing 3% of N 2 in the CVD plasma, we explore the influence of methane concentration on N-doped nanocrystalline diamond (NCD) films. At a low methane concentration of 1%, faceted diamond grains are formed, while increasing methane to 15% yields nanoneedles encased in nanographitic phases, featuring a low resistivity of 90 Ω·cm. We further investigate P-doped polycrystalline diamond films, where preliminary examinations of P-doped NCD reveal well-defined grain structures but also morphological imperfections and twin boundaries, with a phosphorus incorporation of ≈10 19 cm −3. Our investigations also cover P-doped (110)-textured polycrystalline CVD diamond films, finding that the phosphorus concentration varies with grain misorientation and that higher phosphine concentrations lead to a more uniform distribution. Additionally, we note that an increase in the [P]/[C] ratio in the CVD plasma of P-doped diamond growths leads to the transformation of NCD to ultra-NCD, reducing residual stress, and affecting film quality. In a complementary investigation, we explore the codoping of NCD films with nitrogen and phosphorus, observing a transition from micron-sized faceted diamond grains to nanosized grains with increasing nitrogen content at a fixed amount of phosphorus concentration in the CVD plasma. Exploring diamond's potential as a semiconductor, our research group investigated the captivating properties of P-doped single crystal diamond films, given a shallower donor energy level of 0.6 eV compared to nitrogen's deep donor level at 1.7 eV. Our findings indicate optically active defects with various electronic levels, using a doping range from 10 16 to 10 19 cm −3 in (111)-oriented P-doped diamond epilayers. However, challenges like formation of defects, persist for this orientation. In contrast, (100)-oriented diamond films are renowned for the p-type conductivity and high crystalline quality, though achieving n-type conductivity remains a challenge. Our research highlights the critical role of varying methane concentration during CVD in influencing both crystalline quality and phosphorus concentration. Elevated methane concentrations are found to induce surface degradation, affecting film quality and doping level. Surprisingly, (110)-oriented P-doped single crystal diamond growth demonstrates promising results with a 33 μm/h deposition rate using only 1% methane concentration. Furthermore, the off-angle from the (110) orientation can potentially impact film quality, indicated by cathodoluminescence spectroscopy, offering exciting prospects for future research. The insights provided in this Account will illuminate the CVD growth of n-type diamond films, contributing to the advancement of diamond-based devices.The authors would like to thank all the current and former members of the Wide Band Gap Material group for their valuable contribution to these remarkable findings on the CVD growth of n-type diamond. The authors acknowledge Prof. Dr. David Eon at Université Grenoble‑Alps, CNRS, Institut Néel, Grenoble, France, for his contribution to the cathodoluminescence spectroscopy measurements. Financial support provided by the Research Foundation Flanders (FWO) in the form of project G0D4920N, the Special Research Fund (BOF) via the Methusalem NANO network are gratefully acknowledged
Enhanced optoelectronic performances of vertically aligned hexagonal boron nitride nanowalls-nanocrystalline diamond heterostructures
No full textField electron emission (FEE) properties of vertically aligned hexagonal boron nitride nanowalls (hBNNWs) grown on Si have been markedly enhanced through the use of nitrogen doped nanocrystalline diamond (nNCD) films as an interlayer. The FEE properties of hBNNWs-nNCD heterostructures show a low turn-on field of 15.2 V/mu m, a high FEE current density of 1.48 mA/cm(2) and life-time up to a period of 248 min. These values are far superior to those for hBNNWs grown on Si substrates without the nNCD interlayer, which have a turn-on field of 46.6 V/mu m with 0.21 mA/cm(2) FEE current density and life-time of 27 min. Cross-sectional TEM investigation reveals that the utilization of the diamond interlayer circumvented the formation of amorphous boron nitride prior to the growth of hexagonal boron nitride. Moreover, incorporation of carbon in hBNNWs improves the conductivity of hBNNWs. Such a unique combination of materials results in efficient electron transport crossing nNCD-to-hBNNWs interface and inside the hBNNWs that results in enhanced field emission of electrons. The prospective application of these materials is manifested by plasma illumination measurements with lower threshold voltage (370 V) and longer life-time, authorizing the role of hBNNWs-nNCD heterostructures in the enhancement of electron emission.The authors like to thank the financial support of the Research Foundation Flanders (FWO) via Research Project G.0456.12, G0044.13N and the Methusalem "NANO" network. Kamatchi Jothiramalingam Sankaran, Stuart Turner, and Paulius Pobedinskas are Postdoctoral Fellows of the Research Foundations Flanders (FWO)
Diamond-gold nanohybrids – an enhanced cathode material for field electron emitter applications
No full textThis work aims to review the enhancement of electrical conductivity and field electron emission (FEE) properties of ultrananocrystalline diamond (UNCD) films as a function of gold ion implantation content. Au has been employed in UNCD films as an implanted species as well as an interlayer between diamond film and substrate. In the initial part of the review UNCD films are briefly introduced. The focus is on their FEE properties and multiple strategies employed for enhancing these properties using ion-implantation with the goal to obtain a better cathode material. A comparison of the characteristics of the UNCD films implanted with Au and other species after studying the modification of the microstructure and emission properties of the Au-implanted UNCD films is then provided. Subsequently, the use of a thin Au coating on silicon substrates covered by UNCD or hybrid granular structured diamond films is discussed. The Si diffusion through the Au-Si eutectic interface results in a SiC layer. This facilitates the nucleation of diamond clusters, thereby suppressing the development of the carbon layer which is amorphous and electrically resistive, resulting in improved FEE characteristics. Finally, in the third and final part, the combined effects of Au-ion implantation (including multi-energy Au ion implantation) and Au-interlayer is discussed. Based on the obtained results, the catalytic activity of gold for improving the electrical conductivity and the FEE properties of diamond films is highlighted.The authors would like to thank the Research Foundation Flanders (FWO) for the financial support via Research Grant 12I8416N and Research Projects 1519817N and G0D4920N, and the Methusalem ‘NANO’ network
Microplasma device architectures with various diamond nanostructures
No full textDiamond nanostructures (DNSs) were fabricated from three different morphological diamonds, microcrystalline diamond (MCD), nanocrystalline diamond (NCD), and ultrananocrystalline diamond (UNCD) films, using a reactive ion etching method. The plasma illumination ( PI) behavior of microplasma devices using the DNSs and the diamond films as cathode were investigated. The Paschen curve approach revealed that the secondary electron emission coefficient (gamma value) of diamond materials is similar irrespective of the microstructure (MCD, NCD, and UNCD) and geometry of the materials (DNSs and diamond films). The diamond materials show markedly larger gamma-coefficient than conventional metallic cathode materials such as Mo that resulted in markedly better PI behavior for the corresponding microplasma devices. Moreover, the PI behavior, i.e. the voltage dependence of plasma current density (J(pl)-V), plasma density (n(e)-V), and the robustness of the devices, varied markedly with the microstructure and geometry of the cathode materials that was closely correlated to the electron field emission (EFE) properties of the cathode materials. The UNCD nanopillars, possessing good EFE properties, resulted in superior PI behavior, whereas the MCD diamond films with insufficient EFE properties led to inferior PI behavior. Consequently, enhancement of plasma characteristics is the collective effects of EFE behavior and secondary electron emission characteristics of diamond-based cathode materials.The authors would like to thank the Ministry of Science and Technology, Republic of China, for the support of this research through the project No. MOST104-2112-M-032-003. Kamatchi Jothiramalingam Sankaran is a Postdoctoral Fellow of the Research Foundation-Flanders (FWO)
Enhancement of plasma illumination characteristics of few-layer graphenediamond nanorods hybrid
No full textFew-layer graphene (FLG) was catalytically formed on vertically aligned diamond nanorods (DNRs) by a high temperature annealing process. The presence of 4–5 layers of FLG on DNRs was confirmed by transmission electron microscopic studies. It enhances the field electron emission (FEE) behavior of the DNRs. The FLG-DNRs show excellent FEE characteristics with a low turn-on field of 4.21 V μm−1 and a large field enhancement factor of 3480. Moreover, using FLG-DNRs as cathode markedly enhances the plasma illumination behavior of a microplasma device, viz not only the plasma current density is increased, but also the robustness
of the devices is improved.The authors like to thank the financial support of the Research
Foundation Flanders (FWO) via Research Projects G.0456.12N and G.0905.12 N, and the Methusalem ‘NANO’ network. Kamatchi Jothiramalingam Sankaran and Paulius Pobedinskas are Postdoctoral Fellows of the Research FoundationFlanders (FWO). The Hercules Foundation Flanders is acknowledged for financial support of the Raman equipment
‐Plasma Chemical Vapor Deposition
No full textMicrostructural evolution as a function of film thickness of nitrogen incorporated ultrananocrystalline diamond (NUNCD) films, grown using bias-enhanced microwave plasma chemical vapor deposition with gas mixtures of N2/CH4, is systematically investigated. It is observed that by controlling the growth time, the morphology, the microstructure, and the electrical properties of NUNCD films can be manipulated. The growth of NUNCD films starts with the formation of amorphous carbon on Si surface prior to the nucleation of diamond. In the growth time of 10 min, the films retain rod-shaped diamond grains, whereas in the films grown for 30 min, needle-like diamond grains are formed, which comprises a diamond core encased in a sheath of sp2 -bonded graphite phase. On increasing the growth time to 60 min, the growth of acicular grains ceases and large proportion of graphite clusters or defective diamond clusters (n-diamond) is formed. The salient features of such materials with unique granular structure are that their electrical properties can be tuned in wide range such that they are especially useful in practical applications.The authors like to thank the financial support of Ministry of Science and Technology, Republic of China, through the project no. MOST 103-2112-M-032-002. Kamatchi Jothiramalingam Sankaran is a Postdoctoral Research Fellow of the Research Foundations-Flanders (FWO)
Triboenvironment Dependent Chemical Modification of Sliding Interfaces in Ultrananocrystalline Diamond Nanowall Film: Correlation with Friction and Wear
No full textTribological properties of ultrananocrystalline diamond nanowall (UNCD NW) films were investigated quantitatively in three different and controlled triboenvironmental conditions, proposing the passivation and graphitization mechanisms. However, these mechanisms are rather complicated and possibly can be understood in well-controlled tribological conditions. It was shown that the friction and wear of these films were high in high-vacuum and room temperature (HV-RT) tribo conditions where the passivation of carbon dangling bonds were restricted and frictional shear-induced transformation of sp(3) carbon into amorphous carbon (a-C) and tetrahedral amorphous carbon (t-aC) were noticed. However, the friction coefficients were reduced to the ultralow value in ambient atmospheric and room temperature (AA-RT) tribo conditions. Here, both passivation of dangling bonds through atmospheric water vapor and graphitization of the contact interfaces were energetically favorable mechanisms. Furthermore, the conversion of diamond sp(3) into hydrogenated-graphitized phase was the dominating mechanism for the observed superlow friction coefficient and ultrahigh wear resistance of films in high-vacuum and high temperature (HV-HT) tribo conditions. These mechanisms were comprehensively investigated by micro-Raman and X-ray photoelectron spectroscopy analyses of the sliding interfaces.Dr. Gomathi Natarajan (MSG/IGCAR, Kalpakkam) is acknowledged for helping in wear profile analysis with a contact stylus profilometer. Kamatchi Jothiramalingam Sankaran is a Postdoctoral Fellow of the Research Foundation Flanders (FWO). We thank the Department of Atomic Energy, India, for support. This work was also supported by the Polish National Science Centre (NCN) under Grant No. 2016/21/B/ST7/01430. The DS funds of faculty of Electronics; Telecommunications and informatics of the Gdansk University of Technology are also acknowledged
Probing the flat band potential and effective electronic carrier density in vertically aligned nitrogen doped diamond nanorods via electrochemical method
No full textOne-dimensional diamond nanorods (DNRs) were fabricated from nanocrystalline diamond films using a facile combination of microwave plasma enhanced chemical vapor deposition and reactive ion etching (RIE) techniques. Structural and electrochemical properties of undoped and nitrogen doped DNRs were thoroughly investigated. A cyclic voltammetry study revealed the increase in density of charge carriers when doped with nitrogen. Mott Schottky analysis was implemented for the quantitative determination of the flat band potential, effective density of charge carriers and energy band diagram, which revealed that the undoped sample exhibit p-type behavior, whereas the nitrogen doped sample showed n-type behavior. Defect related damage due to graphitization and hydrogen termination in the undoped DNRs (during RIE) was correlated with the p-type conductivity. Nitrogen doping induces n-type conductivity and enhances effective density of charge carriers. (C) 2017 Elsevier Ltd. All rights reserved.Gourav Bhattacharya, Shashi B. Srivastava and Sujit Deshmukh are indebted to Shiv Nadar University for providing scholarships. Kamatchi Jothiramalingam Sankaran and Paulius Pobedinskas are Postdoctoral Fellows of the Research Foundation-Flanders (FWO). The authors are also thankful for financial support from the Alexander von Humboldt Foundation for purchasing the contact angle measurement system and Mr. B. Ruttens, Ms. Hilde Pellaers and Prof. Jan D'Haen for technical and experimental assistance. The Hercules Foundation Flanders is acknowledged for financial support of the Raman equipment
Microwave cavity perturbation of nitrogen doped nano-crystalline diamond films
Full text linkNon-contact and non-destructive electrical conductivity measurements of nitrogen doped nano-crystalline diamond films have been demonstrated using a microwave cavity perturbation system. The conductivity of the films was controlled by simply varying the CH 4 gas concentration during microwave plasma assisted chemical vapour deposition, thereby promoting the formation of sp 2 carbon at the grain boundaries. The presence of sp 2 carbon is verified through Raman spectroscopy, x-ray photoelectron spectroscopy and electron energy loss spectroscopy, while scanning electron microscopy confirms an increasing surface area for sp 2 to form. The microwave cavity perturbation results show that the measured cavity quality factor varies with CH 4 concentration. The extraction of conductivity is achieved through a depolarisation model, which must be considered when the sample is smaller than the cavity and through both electric and magnetic field perturbations. The microwave measurements are comparable to contacting and damaging measurements when the film conductivity is greater than the substrate, thus demonstrating an invaluable method for determining conductivity without the need for depositing any electrodes on the film. © 2019 The Author11sciescopu
Direct nucleation of hexagonal boron nitride on diamond: Crystalline properties of hBN nanowalls
No full textHexagonal boron nitride (hBN) nanowalls were deposited by unbalanced radio frequency sputtering on (100)-oriented silicon, nanocrystalline diamond films, and amorphous silicon nitride (Si3N4) membranes. The hBN nanowall structures were found to grow vertically with respect to the surface of all of the substrates. To provide further insight into the nucleation phase and possible lattice distortion of the deposited films, the structural properties of the different interfaces were characterized by transmission electron microscopy. For Si and Si3N4 substrates, turbostratic and amorphous BN phases form a clear transition zone between the substrate and the actual hBN phase of the bulk nanowalls. However, surprisingly, the presence of these phases was suppressed at the interface with a nanocrystalline diamond film, leading to a direct coupling of hBN with the diamond surface, independent of the vertical orientation of the diamond grain. To explain these observations, a growth mechanism is proposed in which the hydrogen terminated surface of the nanocrystalline diamond film leads to a rapid formation of the hBN phase during the initial stages of growth, contrary to the case of Si and Si3N4 substrates. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.The Hercules Foundation Flanders is acknowledged for financial support of the Raman equipment
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