Interaction of fcc-Palladium nano-crystals with Hydrogen during PECVD growth of Carbon nanotubes

Using plasma-enhanced chemical vapor deposition (PECVD) with Acetylene and Ammoniac on Pd-specimens Carbon nanotubes (CNT) could be produced successfully. Two different devices are compared and the conditions for best growth conditions are explained. The detailed analysis of electron diffraction pattern obtained by transmissions electron microscopy (TEM) of as-grown specimen showed an expansion of the Pd lattice, which can be explained by the formation of fcc-PdHx for x=0...1. For x=1..2 the first investigation of hexagonal -PdH2 is reported, which lattice spacing is independent on the hydrogen content. The amount of fcc-PdH and hcp-PdH2 increases when the specimens are treated subsequently with Hydrogen. A growth model is provided.Comment: 6 pages, 6 figure

Fundamentals of Chemical Vapor Deposited Graphene and Emerging Applications

Graphene, the atomically thin sheet of sp2 hybridized carbon atoms arranged in honeycomb structure, is becoming the forefront of material research. The chemical vapor deposition (CVD) process has been explored significantly to synthesis large size single crystals and uniform films of monolayer and bilayer graphene. In this prospect, the nucleation and growth mechanism of graphene on a catalytic substrate play the fundamental role on the control growth of layers and large domain. The transition metals and their alloys have been recognized as the active catalyst for growth of monolayer and bilayer graphene, where the surface composition of such catalysts also plays critical role on graphene growth. CVD-synthesized graphene has been integrated with bulk semiconductors such as Si and GaN for the fabrication of solar cells, photodetectors, and light-emitting diodes. Furthermore, CVD graphene has been integrated with hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDCs) for the fabrication of van der Waals heterostructure for nanoelectronic, optoelectronic, energy devices, and other emerging technologies. The fundamental of the graphene growth process by a CVD technique and various emerging applications in heterostructure devices is discussed in detail

Ab-initio calculations of the Optical band-gap of TiO2 thin films

Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band-gap of TiO2 plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO2 thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO3 substrates was correlated to the lattice constants estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of 3.20 eV for bulk-anatase increases to 3.51 on SrTiO3. In order to interpret the optical band gap expansion for both phases, ab-initio calculations were performed using the Vienna ab-initio software. The calculations for rutile as well anatase show an almost linear increase of the band gap width with decreasing volume or increasing lattice constant a. The calculated band gap fits well with the experimental values. The conclusion from these calculations is, in order to achieve a smaller band-gap for both, rutile or anatase, the lattice constants c has to be compressed, and a has to be expanded.Comment: 4 pages, 4 figures, 1 tabl

Field electron emission of double walled carbon nanotube film prepared by drop casting method

Thick films of double walled carbon nanotubes (DWCN) were deposited on indium-tin-oxide (ITO) coated glass substrates by drop casting method and were studied for their field electron emission property in a parallel plate configuration using bare ITO coated glass as counter electrode. They show excellent field electron emission property with low turn-on-field of about 0.8 V/lm and threshold field of about 1.8 V/lm. Field enhancement factor calculated from the non-saturated region of the FN plot is about 1715. Field electron emission current was observed to be stable up to 3000 min, indicating thereby that DWCNs are excellent electron emitters with appreciable stable performance

Boosting the local anodic oxidation of silicon through carbon nanofiber atomic force microscopy probes

Many nanofabrication methods based on scanning probe microscopy have been developed during the last decades. Local anodic oxidation (LAO) is one of such methods: Upon application of an electric field between tip and surface under ambient conditions, oxide patterning with nanometer-scale resolution can be performed with good control of dimensions and placement. LAO through the non-contact mode of atomic force microscopy (AFM) has proven to yield a better resolution and tip preservation than the contact mode and it can be effectively performed in the dynamic mode of AFM. The tip plays a crucial role for the LAO-AFM, because it regulates the minimum feature size and the electric field. For instance, the feasibility of carbon nanotube (CNT)-functionalized tips showed great promise for LAO-AFM, yet, the fabrication of CNT tips presents difficulties. Here, we explore the use of a carbon nanofiber (CNF) as the tip apex of AFM probes for the application of LAO on silicon substrates in the AFM amplitude modulation dynamic mode of operation. We show the good performance of CNF-AFM probes in terms of resolution and reproducibility, as well as demonstration that the CNF apex provides enhanced conditions in terms of field-induced, chemical process efficiency

Characteristics of Vertical Ga2O3 Schottky Junctions with the Interfacial Hexagonal Boron Nitride Film

We present the device properties of a nickel (Ni)- gallium oxide (Ga2O3) Schottky junction with an interfacial hexagonal boron nitride (hBN) layer. A vertical Schottky junction with the configuration Ni/hBN/Ga2O3/In was created using a chemical vapor-deposited hBN film on a Ga(2)O(3 )substrate. The current-voltage characteristics of the Schottky junction were investigated with and without the hBN interfacial layer. We observed that the turn-on voltage for the forward current of the Schottky junction was significantly enhanced with the hBN interfacial film. Furthermore, the Schottky junction was analyzed under the illumination of deep ultraviolet light (254 nm), obtaining a photoresponsivity of 95.11 mA/W under an applied bias voltage (-7.2 V). The hBN interfacial layer for the Ga2O3-based Schottky junction can serve as a barrier layer to control the turn-on voltage and optimize the device properties for deep-UV photosensor applications. Furthermore, the demonstrated vertical heterojunction with an hBN layer has the potential to be significant for temperature management at the junction interface to develop reliable Ga2O3-based Schottky junction devices

Structure of nitrogen-doped graphene synthesized by combination of imidazole and melamine solid precursors

Here, we demonstrate the synthesis of nitrogen-doped (N-doped) graphene using imidazole and melamine as two different nitrogen containing aromatic rings carbon precursors. Structure of N-doped graphene was investigated at different temperature (800–1020 °C) without changing the precursor quantity. It is observed that higher crystalline N-doped graphene can be obtained from the solid precursors at 1020 °C on Cu foil. X-ray photoelectron spectroscopy (XPS) analysis shows interesting features for the N-doped graphene synthesized from mixture of imidazole and melamine. Overall graphitic nitrogen content is enhanced in the graphene layers using the mixture of precursors, attributing better coordination of carbon and nitrogen atoms on Cu catalyst. Our finding shows that the graphitic and pyridinic nitrogen content in graphene lattice can be tuned by combination of two different nitrogen containing organic molecules

Carbon nanostructures grown from waste latex via chemical vapor deposition

In this work, CNS were successfully synthesized using waste latex from natural rubber gloves as carbon source via chemical vapor deposition. The synthesized process has been done at reaction temperature of 700˚C using iron oxide as catalyst. The CNS characterization were investigated by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS) and Raman spectrum techniques. It was found that the obtained carbon material existed in the form of nanotubes, fibers and nanocapsules with diameter of 5 - 20 nm. The IG/ID value was found to be approximately 0.84, indicating CNS in the samples were not well crystalline and contain defects. HRTEM images and EDS results reveal non-uniform of large catalyst size and impurities of carbon source might lead to less population of grown CNTs. This study demonstrates that waste latex can be an alternative and inexpensive carbon source for CNS production and promotes green technology