Self-organized multilayered graphene-boron doped diamond hybrid nanowalls for high performance electron emission devices
Carbon nanomaterials like nanotubes, nanoflakes/nanowalls and graphene have been used as electron sources due to their superior field electron emission (FEE) characteristics. Nevertheless, these materials show poor stability and a short lifetime, preventing them from being used in practical device applications. The intention of this study was to find an innovative nanomaterial, possessing both high robustness and reliable FEE behavior. A hybrid structure of self-organized multilayered graphene (MLG)boron doped diamond (BDD) nanowall materials with superior FEE characteristics are successfully synthesized using a microwave plasma enhanced chemical vapor deposition process. Transmission electron microscopy reveals that the carbon clusters thus prepared are of uniform, dense and sharp nanowall morphology with sp3 diamond cores encased by an sp2 MLG shell. Detailed nanoscale investigations by peak force-controlled tunneling atomic force microscopy show that each of the core-shell structured carbon clusters field emits electrons equally well. The MLG-BDD nanowall materials show a low turn-on field of 2.4 V/μm, a high emission current density of 4.2 mA/cm2 at an applied field of 4.0 V/μm, a large field enhancement factor of 4500 and prominently high lifetime stability lasting for 700 min, enlightening their superiority on comparison with other hybrid nanostructured materials. The potential in practical device applications for these MLG-BDD hybrid nanowall materials is further illustrated by the plasma illumination behavior of a microplasma device, which used these materials as cathode, where low threshold voltage of 330 V (low threshold field of 330 V/mm) and long plasma stability of 358 min are demonstrated. The fabrication of these hybrid nanowalls is straight forward and thereby opens up a pathway for the advancement in next generation cathode materials for high brightness electron emission and microplasma-based display devices.
Kamatchi J Sankaran,
The paper reports controlled deposition of optically transparent and electrically conductive ITO films prepared by a combination of rf (13.56 MHz) and High Power Impulse Magnetron Sputtering (HiPIMS) systems without any post deposition thermal treatment/annealing. It is shown that (i) reactive admixture of N2 gas to the process and (ii) pressure in the deposition chamber enable to optimize optical properties of ITO films. Furthermore, the changes of electrical resistivity were observed, too. The variation of these ITO properties are attributed to change of crystalline structure measured by XRD methods.
Tribo-Environment Dependent Chemical Modification of Sliding Interfaces in Ultrananocrystalline Diamond Nanowall Film: A Correlation with Friction and Wear
Tribological properties of ultrananocrystalline diamond nanowall (UNCD NW) films were investigated quantitatively in three different and controlled tribo-environmental 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 highPage 1 of 40 ACS Paragon Plus Environment The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 vacuum and room temperature (HV-RT) tribo-condition in which the passivation of carbon dangling bonds was restricted and frictional shear-induced transformation of sp3 carbon into amorphous carbon (a-C) and tetrahedral amorphous carbon (t-aC) was noticed. However, the friction coefficient was reduced to the ultralow value in ambient atmospheric and room temperature (AA-RT) tribo-condition. 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 sp3 into hydrogenated-graphitized phase was dominating mechanism for observed super-low friction coefficient and ultra-high wear resistance of films in high-vacuum and high-temperature (HV-HT) tribo-condition. These mechanisms were comprehensively investigated by micro-Raman and X-ray photoelectron spectroscopy analyses of the sliding interfaces.
Optical monitoring of electrochemical processes with ITO-based lossy-mode resonance optical fiber sensor applied as an electrode
In this work we discuss the application of optical fiber sensors based on lossy-mode resonance (LMR) phenomenon for real-time optical monitoring of electrochemical processes. The sensors were obtained by a reactive high power impulse magnetron sputtering of indium tin oxide (ITO) on a 2.5 cm-long core of polymer-clad silica fibers. The LMR effect made monitoring of changes in optical properties of both ITO and its surrounding medium possible. Moreover, since ITO is electrically conductive and electrochemically active, it was used as a working electrode in a 3-electrode cyclic voltammetry setup. The investigations have shown that the sensor's optical response strongly depends on the potential applied to the sensor, as well as on electrochemical modification of its surface. The obtained LMR effect can be applied in parallel to electrochemical measurements for real-time optical monitoring of the electrode conditions and properties of the surrounding medium.
Influence of reactive oxygen species during deposition of iron oxide films by high power impulse magnetron sputtering.
Iron oxide films were deposited using high power impulse magnetron sputtering (HiPIMS) of an iron cathode in an argon/oxygen gas mixture at different gas pressures (0.5~Pa, 1.5~Pa, and 5.0~Pa). The HiPIMS system was operated at a repetition frequency $f = 100$~Hz with a duty cycle of 1~\%. A main goal is a comparison of film growth during conventional and electron cyclotron wave resonance-assisted HiPIMS. The deposition plasma was investigated by means of optical emission spectroscopy and energy-resolved mass spectrometry. Active oxygen species were detected and their kinetic energy was found to depend on the gas pressure. Deposited films were characterized by means of spectroscopic ellipsometry and grazing incidence x-ray diffraction. Optical properties and crystallinity of as-deposited films were found to depend on the deposition conditions. Deposition of hematite iron oxide films with the HiPIMS-ECWR discharge is attributed to the enhanced production of reactive oxygen species.