Surface Chemistry, Microstructure, and Tribological Properties of Cubic Boron Nitride Films

NASA Technical Reports Server (NTRS)

Watanabe, Shuichi; Wheeler, Donald R.; Abel, Phillip B.; Street, Kenneth W.; Miyoshi, Kazuhisa; Murakawa, Masao; Miyake, Shojiro

1998-01-01

This report deals with the surface chemistry, microstructure, bonding state, morphology, and friction and wear properties of cubic boron nitride (c-BN) films that were synthesized by magnetically enhanced plasma ion plating. Several analytical techniques - x-ray photoelectron spectroscopy, transmission electron microscopy and electron diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, and surface profilometry - were used to characterize the films. Sliding friction experiments using a ball-on-disk configuration were conducted for the c-BN films in sliding contact with 440C stainless-steel balls at room temperature in ultrahigh vacuum (pressure, 10(exp -6), in ambient air, and under water lubrication. Results indicate that the boron-to-nitrogen ratio on the surface of the as-deposited c-BN film is greater than 1 and that not all the boron is present as boron nitride but a small percentage is present as an oxide. Both in air and under water lubrication, the c-BN film in sliding contact with steel showed a low wear rate, whereas a high wear rate was observed in vacuum. In air and under water lubrication, c-BN exhibited wear resistance superior to that of amorphous boron nitride, titanium nitride, and titanium carbide.

The effect of surface nanocrystallization on plasma nitriding behaviour of AISI 4140 steel

NASA Astrophysics Data System (ADS)

Li, Yang; Wang, Liang; Zhang, Dandan; Shen, Lie

2010-11-01

A plastic deformation surface layer with nanocrystalline grains was produced on AISI 4140 steel by means of surface mechanical attrition treatment (SMAT). Plasma nitriding of SMAT and un-SMAT AISI 4140 steel was carried out by a low-frequency pulse excited plasma unit. A series of nitriding experiments has been conducted at temperatures ranging from 380 to 500 °C for 8 h in an NH 3 gas. The samples were characterized using X-ray diffraction, scanning electron microscopy, optical microscopy and Vickers microhardness tester. The results showed that a much thicker compound layer with higher hardness was obtained for the SMAT samples when compared with un-SMAT samples after nitriding at the low temperature. In particular, plasma nitriding SMAT AISI 4140 steel at 380 °C for 8 h can produced a compound layer of 2.5 μm thickness with very high hardness on the surface, which is similar to un-SMAT samples were plasma nitrided at approximately 430 °C within the same time.

Growth of gallium nitride and indium nitride nanowires on conductive and flexible carbon cloth substrates.

PubMed

Yang, Yi; Ling, Yichuan; Wang, Gongming; Lu, Xihong; Tong, Yexiang; Li, Yat

2013-03-07

We report a general strategy for synthesis of gallium nitride (GaN) and indium nitride (InN) nanowires on conductive and flexible carbon cloth substrates. GaN and InN nanowires were prepared via a nanocluster-mediated growth method using a home built chemical vapor deposition (CVD) system with Ga and In metals as group III precursors and ammonia as a group V precursor. Electron microscopy studies reveal that the group III-nitride nanowires are single crystalline wurtzite structures. The morphology, density and growth mechanism of these nanowires are determined by the growth temperature. Importantly, a photoelectrode fabricated by contacting the GaN nanowires through a carbon cloth substrate shows pronounced photoactivity for photoelectrochemical water oxidation. The ability to synthesize group III-nitride nanowires on conductive and flexible substrates should open up new opportunities for nanoscale photonic, electronic and electrochemical devices.

Characterization of two-dimensional hexagonal boron nitride using scanning electron and scanning helium ion microscopy

NASA Astrophysics Data System (ADS)

Guo, Hongxuan; Gao, Jianhua; Ishida, Nobuyuki; Xu, Mingsheng; Fujita, Daisuke

2014-01-01

Characterization of the structural and physical properties of two-dimensional (2D) materials, such as layer number and inelastic mean free path measurements, is very important to optimize their synthesis and application. In this study, we characterize the layer number and morphology of hexagonal boron nitride (h-BN) nanosheets on a metallic substrate using field emission scanning electron microscopy (FE-SEM) and scanning helium ion microscopy (HIM). Using scanning beams of various energies, we could analyze the dependence of the intensities of secondary electrons on the thickness of the h-BN nanosheets. Based on the interaction between the scanning particles (electrons and helium ions) and h-BN nanosheets, we deduced an exponential relationship between the intensities of secondary electrons and number of layers of h-BN. With the attenuation factor of the exponential formula, we calculate the inelastic mean free path of electrons and helium ions in the h-BN nanosheets. Our results show that HIM is more sensitive and consistent than FE-SEM for characterizing the number of layers and morphology of 2D materials.

Ultrasound exfoliation of inorganic analogues of graphene

PubMed Central

2014-01-01

High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C3N4)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented. PMID:24708572

Ultrasound exfoliation of inorganic analogues of graphene.

PubMed

Stengl, Václav; Henych, Jiří; Slušná, Michaela; Ecorchard, Petra

2014-04-05

High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C3N4)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.

TEM studies of plasma nitrided austenitic stainless steel.

PubMed

Stróz, D; Psoda, M

2010-03-01

Cross-sectional transmission electron microscopy and X-ray phase analysis were used to study the structure of a layer formed during nitriding the AISI 316L stainless steel at temperature 440 degrees C. It was found that the applied treatment led to the formation of 6-microm-thick layer of the S-phase. There is no evidence of CrN precipitation. The X-ray diffraction experiments proved that the occurred austenite lattice expansion - due to nitrogen atoms - depended on the crystallographic direction. The cross-sectional transmission electron microscopy studies showed that the layer consisted of a single cubic phase that contained a lot of defects such as dislocations, stacking faults, slip bands and twins. The high-resolution electron microscopy observations were applied to study the defect formation due to the nitriding process. It was shown that the presence of great number of stacking faults leads to formation of nanotwins. Weak, forbidden {100} reflections were still another characteristic feature of the S-phase. These were not detected in the X-ray spectra of the phase. Basing on the high-resolution electron microscopy studies it can be suggested that the short-range ordering of the nitrogen atoms in the octahedral sites inside the f.c.c. matrix lattice takes place and gives rise to appearance of these spots. It is suggested that the cubic lattice undergoes not only expansion but also slight rombohedral distortion that explains differences in the lattice expansion for different crystallographic directions.

Preparation of mesoporous carbon nitride structure by the dealloying of Ni/a-CN nanocomposite films

NASA Astrophysics Data System (ADS)

Zhou, Han; Shen, Yongqing; Huang, Jie; Liao, Bin; Wu, Xianying; Zhang, Xu

2018-05-01

The preparation of mesoporous carbon nitride (p-CN) structure by the selective dealloying process of Ni/a-CN nanocomposite films is investigated. The composition and structure of the Ni/a-CN nanocomposite films and porous carbon nitride (p-CN) films are determined by scan electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Phase separated structure including nickel carbide phase and the surrounding amorphous carbon nitride (a-CN) matrix are detected for the as-deposited films. Though the bulk diffusion is introduced in the film during the annealing process, the grain sizes for the post-annealed films are around 10 nm and change little comparing with the ones of the as-deposited films, which is associated with the thermostability of the CN surrounding in the film. The p-CN skeleton with its pore size around 12.5 nm is formed by etching the post-annealed films, indicative of the stability of the phase separated structure during the annealing process.

Reprint of: Atmospheric scanning electron microscope observes cells and tissues in open medium through silicon nitride film.

PubMed

Nishiyama, Hidetoshi; Suga, Mitsuo; Ogura, Toshihiko; Maruyama, Yuusuke; Koizumi, Mitsuru; Mio, Kazuhiro; Kitamura, Shinichi; Sato, Chikara

2010-11-01

Direct observation of subcellular structures and their characterization is essential for understanding their physiological functions. To observe them in open environment, we have developed an inverted scanning electron microscope with a detachable, open-culture dish, capable of 8 nm resolution, and combined with a fluorescence microscope quasi-simultaneously observing the same area from the top. For scanning electron microscopy from the bottom, a silicon nitride film window in the base of the dish maintains a vacuum between electron gun and open sample dish while allowing electrons to pass through. Electrons are backscattered from the sample and captured by a detector under the dish. Cells cultured on the open dish can be externally manipulated under optical microscopy, fixed, and observed using scanning electron microscopy. Once fine structures have been revealed by scanning electron microscopy, their component proteins may be identified by comparison with separately prepared fluorescence-labeled optical microscopic images of the candidate proteins, with their heavy-metal-labeled or stained ASEM images. Furthermore, cell nuclei in a tissue block stained with platinum-blue were successfully observed without thin-sectioning, which suggests the applicability of this inverted scanning electron microscope to cancer diagnosis. This microscope visualizes mesoscopic-scale structures, and is also applicable to non-bioscience fields including polymer chemistry. Copyright © 2010 Elsevier Inc. All rights reserved.

A simple method to synthesize polyhedral hexagonal boron nitride nanofibers

NASA Astrophysics Data System (ADS)

Lin, Liang-xu; Zheng, Ying; Li, Zhao-hui; shen, Xiao-nv; Wei, Ke-mei

2007-12-01

Hexagonal boron nitride (h-BN) fibers with polyhedral morphology were synthesized with a simple-operational, large-scale and low-cost method. The sample obtained was studied by X-ray photoelectron spectrometer (XPS), electron energy lose spectroscopy (EELS), X-ray powder diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), etc., which matched with h-BN. Environment scanning electron microscopy (ESEM) and transmission electron microscope (TEM) indicated that the BN fibers possess polyhedral morphology. The diameter of the BN fibers is mainly in the range of 100-500 nm.

Effect of zirconium nitride physical vapor deposition coating on preosteoblast cell adhesion and proliferation onto titanium screws.

PubMed

Rizzi, Manuela; Gatti, Giorgio; Migliario, Mario; Marchese, Leonardo; Rocchetti, Vincenzo; Renò, Filippo

2014-11-01

Titanium has long been used to produce dental implants. Problems related to its manufacturing, casting, welding, and ceramic application for dental prostheses still limit its use, which highlights the need for technologic improvements. The aim of this in vitro study was to evaluate the biologic performance of titanium dental implants coated with zirconium nitride in a murine preosteoblast cellular model. The purpose of this study was to evaluate the chemical and morphologic characteristics of titanium implants coated with zirconium nitride by means of physical vapor deposition. Chemical and morphologic characterizations were performed by scanning electron microscopy and energy dispersive x-ray spectroscopy, and the bioactivity of the implants was evaluated by cell-counting experiments. Scanning electron microscopy and energy dispersive x-ray spectroscopy analysis found that physical vapor deposition was effective in covering titanium surfaces with zirconium nitride. Murine MC-3T3 preosteoblasts were seeded onto titanium-coated and zirconium nitride-coated screws to evaluate their adhesion and proliferation. These experiments found a significantly higher number of cells adhering and spreading onto zirconium nitride-coated surfaces (P<.05) after 24 hours; after 7 days, both titanium and zirconium nitride surfaces were completely covered with MC-3T3 cells. Analysis of these data indicates that the proposed zirconium nitride coating of titanium implants could make the surface of the titanium more bioactive than uncoated titanium surfaces. Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Effect of low NH3 flux towards high quality semi-polar (11-22) GaN on m-plane sapphire via MOCVD

NASA Astrophysics Data System (ADS)

Omar, Al-Zuhairi; Shuhaimi Bin Abu Bakar, Ahmad; Makinudin, Abdullah Haaziq Ahmad; Khudus, Muhammad Imran Mustafa Abdul; Azman, Adreen; Kamarundzaman, Anas; Supangat, Azzuliani

2018-05-01

The effect of ammonia flux towards the quality of the semi-polar (11-22) gallium nitride thin film on m-plane (10-10) sapphire is presented. Semi-polar (11-22) gallium nitride epi-layers were obtained using a two-step growth method, consisting of high temperature aluminum nitride followed by gallium nitride via metal organic chemical vapor deposition. The surface morphology analysis via field emission scanning electron microscopy and atomic force microscopy of the semi-polar (11-22) gallium nitride has shown that low ammonia flux promotes two-dimensional growth with low surface roughness of 4.08 nm. A dominant diffraction peak of (11-22) gallium nitride was also observed via X-ray diffraction upon utilizing low ammonia flux. The on- and off-axis X-ray rocking curve measurements illustrate the enhancement of the crystal quality, which might result from the reduction of the basal stacking faults and perfect dislocation. The full width half maximum values were reduced by at least 15% for both on- and off-axis measurements.

Effect of substrate nitridation temperature on the persistent photoconductivity of unintentionally-doped GaN layer grown by PAMBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prakash, Nisha, E-mail: prakasnisha@gmail.com; Barvat, Arun; Anand, Kritika

2016-05-23

The surface roughness and defect density of GaN epitaxial layers grown on c-plane sapphire substrate are investigated and found to be dependent on nitridation temperature. GaN epitaxial layers grown after nitridation of sapphire at 200°C have a higher defect density and higher surface roughness compared to the GaN layers grown at 646°C nitridation as confirmed by atomic force microscopy (AFM). The persistent photoconductivity (PPC) was observed in both samples and it was found to be decreasing with decreasing temperature in the range 150-300°C due to long carrier lifetime and high electron mobility at low temperature. The photoresponse of the GaNmore » films grown in this study exhibit improved PPC due to their better surface morphology at 646°C nitrided sample. The point defects or extended microstructure defects limits the photocarrier lifetime and electron mobility at 200°C nitrided sample.« less

Synthesis of TiN/a-Si3N4 thin film by using a Mather type dense plasma focus system

NASA Astrophysics Data System (ADS)

Hussain, T.; R., Ahmad; Khalid, N.; A. Umar, Z.; Hussnain, A.

2013-05-01

A 2.3 kJ Mather type pulsed plasma focus device was used for the synthesis of a TiN/a-Si3N4 thin film at room temperature. The film was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The XRD pattern confirms the growth of polycrystalline TiN thin film. The XPS results indicate that the synthesized film is non-stoichiometric and contains titanium nitride, silicon nitride, and a phase of silicon oxy-nitride. The SEM and AFM results reveal that the surface of the synthesized film is quite smooth with 0.59 nm roughness (root-mean-square).

Single-Photon Emitters in Boron Nitride Nanococoons.

PubMed

Ziegler, Joshua; Blaikie, Andrew; Fathalizadeh, Aidin; Miller, David; Yasin, Fehmi S; Williams, Kerisha; Mohrhardt, Jordan; McMorran, Benjamin J; Zettl, Alex; Alemán, Benjamín

2018-04-11

Quantum emitters in two-dimensional hexagonal boron nitride (hBN) are attractive for a variety of quantum and photonic technologies because they combine ultra-bright, room-temperature single-photon emission with an atomically thin crystal. However, the emitter's prominence is hindered by large, strain-induced wavelength shifts. We report the discovery of a visible-wavelength, single-photon emitter (SPE) in a zero-dimensional boron nitride allotrope (the boron nitride nanococoon, BNNC) that retains the excellent optical characteristics of few-layer hBN while possessing an emission line variation that is lower by a factor of 5 than the hBN emitter. We determined the emission source to be the nanometer-size BNNC through the cross-correlation of optical confocal microscopy with high-resolution scanning and transmission electron microscopy. Altogether, this discovery enlivens color centers in BN materials and, because of the BN nanococoon's size, opens new and exciting opportunities in nanophotonics, quantum information, biological imaging, and nanoscale sensing.

Identification of light elements in silicon nitride by aberration-corrected scanning transmission electron microscopy.

PubMed

Idrobo, Juan C; Walkosz, Weronika; Klie, Robert F; Oğüt, Serdar

2012-12-01

In silicon nitride structural ceramics, the overall mechanical and thermal properties are controlled by the atomic and electronic structures at the interface between the ceramic grains and the amorphous intergranular films (IGFs) formed by various sintering additives. In the last ten years the atomic arrangements of heavy elements (rare-earths) at the Si(3)N(4)/IGF interfaces have been resolved. However, the atomic position of light elements, without which it is not possible to obtain a complete description of the interfaces, has been lacking. This review article details the authors' efforts to identify the atomic arrangement of light elements such as nitrogen and oxygen at the Si(3)N(4)/SiO(2) interface and in bulk Si(3)N(4) using aberration-corrected scanning transmission electron microscopy. Published by Elsevier B.V.

Exceptionally Slow Movement of Gold Nanoparticles at a Solid/Liquid Interface Investigated by Scanning Transmission Electron Microscopy.

PubMed

Verch, Andreas; Pfaff, Marina; de Jonge, Niels

2015-06-30

Gold nanoparticles were observed to move at a liquid/solid interface 3 orders of magnitude slower than expected for the movement in a bulk liquid by Brownian motion. The nanoscale movement was studied with scanning transmission electron microscopy (STEM) using a liquid enclosure consisting of microchips with silicon nitride windows. The experiments involved a variation of the electron dose, the coating of the nanoparticles, the surface charge of the enclosing membrane, the viscosity, and the liquid thickness. The observed slow movement was not a result of hydrodynamic hindrance near a wall but instead explained by the presence of a layer of ordered liquid exhibiting a viscosity 5 orders of magnitude larger than a bulk liquid. The increased viscosity presumably led to a dramatic slowdown of the movement. The layer was formed as a result of the surface charge of the silicon nitride windows. The exceptionally slow motion is a crucial aspect of electron microscopy of specimens in liquid, enabling a direct observation of the movement and agglomeration of nanoscale objects in liquid.

Continuous Growth of Hexagonal Graphene and Boron Nitride In-Plane Heterostructures by Atmospheric Pressure Chemical Vapor Deposition

PubMed Central

Han, Gang Hee; Rodríguez-Manzo, Julio A.; Lee, Chan-Woo; Kybert, Nicholas J.; Lerner, Mitchell B.; Qi, Zhengqing John; Dattoli, Eric N.; Rappe, Andrew M.; Drndic, Marija; Charlie Johnson, A. T.

2013-01-01

Graphene-boron nitride monolayer heterostructures contain adjacent electrically active and insulating regions in a continuous, single-atom thick layer. To date structures were grown at low pressure, resulting in irregular shapes and edge direction, so studies of the graphene-boron nitride interface were restricted to microscopy of nano-domains. Here we report templated growth of single crystalline hexagonal boron nitride directly from the oriented edge of hexagonal graphene flakes by atmospheric pressure chemical vapor deposition, and physical property measurements that inform the design of in-plane hybrid electronics. Ribbons of boron nitride monolayer were grown from the edge of a graphene template and inherited its crystallographic orientation. The relative sharpness of the interface was tuned through control of growth conditions. Frequent tearing at the graphene-boron nitride interface was observed, so density functional theory was used to determine that the nitrogen-terminated interface was prone to instability during cool down. The electronic functionality of monolayer heterostructures was demonstrated through fabrication of field effect transistors with boron nitride as an in-plane gate dielectric. PMID:24182310

Continuous growth of hexagonal graphene and boron nitride in-plane heterostructures by atmospheric pressure chemical vapor deposition.

PubMed

Han, Gang Hee; Rodríguez-Manzo, Julio A; Lee, Chan-Woo; Kybert, Nicholas J; Lerner, Mitchell B; Qi, Zhengqing John; Dattoli, Eric N; Rappe, Andrew M; Drndic, Marija; Johnson, A T Charlie

2013-11-26

Graphene-boron nitride monolayer heterostructures contain adjacent electrically active and insulating regions in a continuous, single-atom thick layer. To date structures were grown at low pressure, resulting in irregular shapes and edge direction, so studies of the graphene-boron nitride interface were restricted to the microscopy of nanodomains. Here we report templated growth of single crystalline hexagonal boron nitride directly from the oriented edge of hexagonal graphene flakes by atmospheric pressure chemical vapor deposition, and physical property measurements that inform the design of in-plane hybrid electronics. Ribbons of boron nitride monolayer were grown from the edge of a graphene template and inherited its crystallographic orientation. The relative sharpness of the interface was tuned through control of growth conditions. Frequent tearing at the graphene-boron nitride interface was observed, so density functional theory was used to determine that the nitrogen-terminated interface was prone to instability during cool down. The electronic functionality of monolayer heterostructures was demonstrated through fabrication of field effect transistors with boron nitride as an in-plane gate dielectric.

Microstructural Characteristics of Plasma Nitrided Layer on Hot-Rolled 304 Stainless Steel with a Small Amount of α-Ferrite

NASA Astrophysics Data System (ADS)

Xu, Xiaolei; Yu, Zhiwei; Cui, Liying; Niu, Xinjun; Cai, Tao

2016-02-01

The hot-rolled 304 stainless steel with γ-austenite and approximately 5 pct α-ferrite elongated along the rolling direction was plasma-nitrided at a low temperature of 693 K (420 °C). X-ray diffraction results revealed that the nitrided layer was mainly composed of the supersaturated solid solution of nitrogen in austenite ( γ N). Transmission electron microscopy (TEM) observations showed that the microstructure of the γ N phase exhibited "fracture factor contrast" reflective of the occurrence of fine pre-precipitations in γ N by the continuous precipitation. The occurrence of a diffuse scattering effect on the electron diffraction spots of γ N indicated that the pre-precipitation took place in γ N in the form of strongly bonded Cr-N clusters or pairs due to a strong attractive interaction of nitrogen with chromium. Scanning electron microscopy and TEM observations indicated that the discontinuous precipitation initiated from the γ/ α interfaces and grew from the austenite boundaries into austenite grains to form a lamellar structure consisting of CrN and ferrite. The orientation relationship between CrN and ferrite corresponded to a Baker-Nutting relationship: (100)CrN//(100) α ; [011]CrN//[001] α . A zigzag boundary line following the banded structure of alternating γ-austenite and elongated α-ferrite was presented between the nitrided layer and the substrate to form a continuous varying layer thickness, which resulted from the difference in diffusivities of nitrogen in α-ferrite and γ-austenite, along the γ/ α interfaces and through the lattice. Microstructural features similar to the γ N were also revealed in the ferrite of the nitrided layer by TEM. It was not excluded that a supersaturated solid solution of nitrogen in ferrite ( α N) formed in the nitrided layer.

Plasma Nitriding of AISI 304 Stainless Steel in Cathodic and Floating Electric Potential: Influence on Morphology, Chemical Characteristics and Tribological Behavior

NASA Astrophysics Data System (ADS)

Li, Yang; He, Yongyong; Wang, Wei; Mao, Junyuan; Zhang, Lei; Zhu, Yijie; Ye, Qianwen

2018-03-01

In direct current plasma nitriding (DCPN), the treated components are subjected to a high cathodic potential, which brings several inherent shortcomings, e.g., damage by arcing and the edging effect. In active screen plasma nitriding (ASPN) processes, the cathodic potential is applied to a metal screen that surrounds the workload, and the component to be treated is placed in a floating potential. Such an electrical configuration allows plasma to be formed on the metal screen surface rather than on the component surface; thus, the shortcomings of the DCPN are eliminated. In this work, the nitrided experiments were performed using a plasma nitriding unit. Two groups of samples were placed on the table in the cathodic and the floating potential, corresponding to the DCPN and ASPN, respectively. The floating samples and table were surrounded by a steel screen. The DCPN and ASPN of the AISI 304 stainless steels are investigated as a function of the electric potential. The samples were characterized using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy and transmission electron microscope. Dry sliding ball-on-disk wear tests were conducted on the untreated substrate, DCPN and ASPN samples. The results reveal that all nitrided samples successfully produced similar nitrogen-supersaturated S phase layers on their surfaces. This finding also shows the strong impact of the electric potential of the nitriding process on the morphology, chemical characteristics, hardness and tribological behavior of the DCPN and ASPN samples.

Microstructure of Haynes® 282® Superalloy after Vacuum Induction Melting and Investment Casting of Thin-Walled Components.

PubMed

Matysiak, Hubert; Zagorska, Malgorzata; Andersson, Joel; Balkowiec, Alicja; Cygan, Rafal; Rasinski, Marcin; Pisarek, Marcin; Andrzejczuk, Mariusz; Kubiak, Krzysztof; Kurzydlowski, Krzysztof J

2013-11-01

The aim of this work was to characterize the microstructure of the as-cast Haynes ® 282 ® alloy. Observations and analyses were carried out using techniques such as X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray spectroscopy (EDS), wave length dispersive X-ray spectroscopy (WDS), auger electron spectroscopy (AES) and electron energy-loss spectrometry (EELS). The phases identified in the as-cast alloy include: γ (gamma matrix), γ' (matrix strengthening phase), (TiMoCr)C (primary carbide), TiN (primary nitride), σ (sigma-TCP phase), (TiMo)₂SC (carbosulphide) and a lamellar constituent consisting of molybdenum and chromium rich secondary carbide phase together with γ phase. Within the dendrites the γ' appears mostly in the form of spherical, nanometric precipitates (74 nm), while coarser (113 nm) cubic γ' precipitates are present in the interdendritic areas. Volume fraction content of the γ' precipitates in the dendrites and interdendritic areas are 9.6% and 8.5%, respectively. Primary nitrides metallic nitrides (MN), are homogeneously dispersed in the as-cast microstructure, while primary carbides metallic carbides (MC), preferentially precipitate in interdendritic areas. Such preference is also observed in the case of globular σ phase. Lamellar constituents characterized as secondary carbides/γ phases were together with (TiMo)₂SC phase always observed adjacent to σ phase precipitates. Crystallographic relations were established in-between the MC, σ, secondary carbides and γ/γ' matrix.

Accurate calibration for the quantification of the Al content in AlGaN epitaxial layers by energy-dispersive X-ray spectroscopy in a Transmission Electron Microscope

NASA Astrophysics Data System (ADS)

Amari, H.; Lari, L.; Zhang, H. Y.; Geelhaar, L.; Chèze, C.; Kappers, M. J.; McAleese, C.; Humphreys, C. J.; Walther, T.

2011-11-01

Since the band structure of group III- nitrides presents a direct electronic transition with a band-gap energy covering the range from 3.4 eV for (GaN) to 6.2 eV (for AlN) at room temperature as well as a high thermal conductivity, aluminium gallium nitride (AlGaN) is a strong candidate for high-power and high-temperature electronic devices and short-wavelength (visible and ultraviolet) optoelectronic devices. We report here a study by energy-filtered transmission electron microscopy (EFTEM) and energy-dispersive X-ray spectroscopy (EDXS) of the micro structure and elemental distribution in different aluminium gallium nitride epitaxial layers grown by different research groups. A calibration procedure is out-lined that yields the Al content from EDXS to within ~1 at % precision.

Improvement of efficiency in graphene/gallium nitride nanowire on Silicon photoelectrode for overall water splitting

NASA Astrophysics Data System (ADS)

Bae, Hyojung; Rho, Hokyun; Min, Jung-Wook; Lee, Yong-Tak; Lee, Sang Hyun; Fujii, Katsushi; Lee, Hyo-Jong; Ha, Jun-Seok

2017-11-01

Gallium nitride (GaN) nanowires are one of the most promising photoelectrode materials due to their high stability in acidic and basic electrolytes, and tunable band edge potentials. In this study, GaN nanowire arrays (GaN NWs) were prepared by molecular beam epitaxy (MBE); their large surface area enhanced the solar to hydrogen conversion efficiency. More significantly, graphene was grown by chemical vapor deposition (CVD), which enhanced the electron transfer between NWs for water splitting and protected the GaN NW surface. Structural characterizations of the prepared composite were performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocurrent density of Gr/GaN NWs exhibited a two-fold increase over pristine GaN NWs and sustained water splitting up to 70 min. These improvements may accelerate possible applications for hydrogen generation with high solar to hydrogen conversion efficiency.

Microstructural characterization of Ti-6Al-4V alloy subjected to the duplex SMAT/plasma nitriding.

PubMed

Pi, Y; Faure, J; Agoda-Tandjawa, G; Andreazza, C; Potiron, S; Levesque, A; Demangel, C; Retraint, D; Benhayoune, H

2013-09-01

In this study, microstructural characterization of Ti-6Al-4V alloy, subjected to the duplex surface mechanical attrition treatment (SMAT)/nitriding treatment, leading to improve its mechanical properties, was carried out through novel and original samples preparation methods. Instead of acid etching which is limited for morphological characterization by scanning electron microscopy (SEM), an original ion polishing method was developed. Moreover, for structural characterization by transmission electron microscopy (TEM), an ion milling method based with the use of two ions guns was also carried out for cross-section preparation. To demonstrate the efficiency of the two developed methods, morphological investigations were done by traditional SEM and field emission gun SEM. This was followed by structural investigations through selected area electron diffraction (SAED) coupled with TEM and X-ray diffraction techniques. The results demonstrated that ionic polishing allowed to reveal a variation of the microstructure according to the surface treatment that could not be observed by acid etching preparation. TEM associated to SAED and X-ray diffraction provided information regarding the nanostructure compositional changes induced by the duplex SMAT/nitriding process. Copyright © 2013 Wiley Periodicals, Inc.

Structure and magnetic properties of FeSiAl-based soft magnetic composite with AlN and Al2O3 insulating layer prepared by selective nitridation and oxidation

NASA Astrophysics Data System (ADS)

Zhong, Xiaoxi; Liu, Ying; Li, Jun; Wang, Yiwei

2012-08-01

FeSiAl is widely used in switching power supply, filter inductors and pulse transformers. But when used under higher frequencies in some particular condition, it is required to reduce its high-frequency loss. Preparing a homogeneous insulating coating with good heat resistance and high resistivity, such as AlN and Al2O3, is supposed to be an effective way to reduce eddy current loss, which is less focused on. In this project, mixed AlN and Al2O3 insulating layers were prepared on the surface of FeSiAl powders after 30 min exposure at 1100 °C in high purity nitrogen atmosphere, by means of surface nitridation and oxidation. The results revealed that the insulating layers increase the electrical resistivity, and hence decrease the loss factor, improve the frequency stability and increase the quality factor, especially in the high-frequency range. The morphologies, microstructure and compositions of the oxidized and nitrided products on the surface were characterized by Scanning Electron Microscopy/Energy Disperse Spectroscopy, X-Ray Diffraction, Transmission Electron Microscopy, Selected Area Electron Diffraction and X-ray Photoelectron Spectroscopy.

Tubes of rhombohedral boron nitride

NASA Astrophysics Data System (ADS)

Bourgeois, L.; Bando, Y.; Sato, T.

2000-08-01

The structure of boron nitride bamboo-like tubular whiskers grown from boron nitride powder is investigated by high-resolution transmission electron microscopy. Despite the relatively small size of the tubes (20-200 nm in diameter), they all exhibit rhombohedral-like ordering in their layer stacking. The tubular sheets also tend to have their [10 bar 1 0] direction parallel to the fibre axis. Particles of iron alloys are commonly found encapsulated inside or at the end of the filaments. It is suggested that iron plays an active role in the growth of the fibres.

In vitro corrosion resistance of plasma source ion nitrided austenitic stainless steels.

PubMed

Le, M K; Zhu, X M

2001-04-01

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusing them into steel and alloy. In this work, a single high nitrogen face-centered-cubic (f.c.c.) phase (gammaN) formed on the 1Cr18Ni9Ti and AISI 316L austenitic stainless steels with a high nitrogen concentration of about 32 at % was characterized using Auger electron spectroscopy, electron probe microanalysis, glancing angle X-ray diffraction, and transmission electron microscopy. The corrosion resistance of the gammaN-phase layer was studied by the electrochemical cyclic polarization measurement in Ringer's solutions buffered to pH from 3.5 to 7.2 at a temperature of 37 degrees C. No pitting corrosion in the Ringer's solutions with pH = 7.2 and 5.5 was detected for the gammaN-phase layers on the two stainless steels. The high pitting potential for the gammaN-phase layers is higher, about 500 and 600 mV, above that of the two original stainless steels, respectively, in the Ringer's solution with pH = 3.5. The corroded surface morphologies of the gammaN-phase layers observed by scanning electron microscopy are consistent with the results of the electrochemical polarization measurement.

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride

NASA Astrophysics Data System (ADS)

Lee, Gwan-Hyoung; Yu, Young-Jun; Lee, Changgu; Dean, Cory; Shepard, Kenneth L.; Kim, Philip; Hone, James

2011-12-01

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using conductive atomic force microscopy. Low-bias direct tunneling was observed in mono-, bi-, and tri-layer h-BN. For all thicknesses, Fowler-Nordheim tunneling (FNT) occurred at high bias, showing an increase of breakdown voltage with thickness. Based on the FNT model, the barrier height for tunneling (3.07 eV) and dielectric strength (7.94 MV/cm) of h-BN are obtained; these values are comparable to those of SiO2.

Writing silica structures in liquid with scanning transmission electron microscopy.

PubMed

van de Put, Marcel W P; Carcouët, Camille C M C; Bomans, Paul H H; Friedrich, Heiner; de Jonge, Niels; Sommerdijk, Nico A J M

2015-02-04

Silica nanoparticles are imaged in solution with scanning transmission electron microscopy (STEM) using a liquid cell with silicon nitride (SiN) membrane windows. The STEM images reveal that silica structures are deposited in well-defined patches on the upper SiN membranes upon electron beam irradiation. The thickness of the deposits is linear with the applied electron dose. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrate that the deposited patches are a result of the merging of the original 20 nm-diameter nanoparticles, and that the related surface roughness depends on the electron dose rate used. Using this approach, sub-micrometer scale structures are written on the SiN in liquid by controlling the electron exposure as function of the lateral position. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron beam induced etching of carbon nanotubes enhanced by secondary electrons in oxygen.

PubMed

Yoshida, Hideto; Tomita, Yuto; Soma, Kentaro; Takeda, Seiji

2017-05-12

Multi-walled carbon nanotubes (CNTs) are subjected to electron-beam-induced etching (EBIE) in oxygen. The EBIE process is observed in situ by environmental transmission electron microscopy. The partial pressure of oxygen (10 and 100 Pa), energy of the primary electrons (80 and 200 keV), and environment of the CNTs (suspended or supported on a silicon nitride membrane) are investigated as factors affecting the etching rate. The EBIE rate of CNTs was markedly promoted by the effects of secondary electrons that were emitted from a silicon nitride membrane under irradiation by primary electrons. Membrane supported CNTs can be cut by EBIE with a spatial accuracy better than 3 nm, and a nanogap of 2 nm can be successfully achieved between the ends of two suspended CNTs.

Study of the Decomposition and Phase Transition of Uranium Nitride under UHV Conditions via TDS, XRD, SEM, and XPS.

PubMed

Wang, Xiaofang; Long, Zhong; Bin, Ren; Yang, Ruilong; Pan, Qifa; Li, Fangfang; Luo, Lizhu; Hu, Yin; Liu, Kezhao

2016-11-07

Uranium nitrides are among the most promising fuels for Generation IV nuclear reactors, but until now, very little has been known about their thermal stability properties under nonequilibrium conditions. In this work, thermal decomposition of nitrogen-rich uranium nitride (denoted as UN 2-x ) under ultrahigh-vacuum (UHV) conditions was investigated by thermal desorption spectroscopy (TDS). It has been shown that the nitrogen TDS spectrum consists of two peaks at about 723 and 1038 K. The X-ray diffraction, scanning electron microscopy, and X-ray photoelectron microscopy results indicate that UN 2-x (UN 2 phase) decomposed into the α-U 2 N 3 phase in the first step and the α-U 2 N 3 phase decomposed into the UN phase in the second step.

Ultrananocrystalline diamond-coated nanoporous membranes support SK-N-SH neuroblastoma endothelial cell attachment.

PubMed

Yang, Kai-Hung; Nguyen, Alexander K; Goering, Peter L; Sumant, Anirudha V; Narayan, Roger J

2018-06-06

Ultrananocrystalline diamond (UNCD) has been demonstrated to have attractive features for biomedical applications and can be combined with nanoporous membranes for applications in drug delivery systems, biosensing, immunoisolation and single molecule analysis. In this study, free-standing nanoporous UNCD membranes with pore sizes of 100 or 400 nm were fabricated by directly depositing ultrathin UNCD films on nanoporous silicon nitride membranes and then etching away silicon nitride using reactive ion etching. Successful deposition of UNCD on the substrate with a novel process was confirmed with Raman spectroscopy, X-ray photoelectron spectroscopy, cross-section scanning electron microscopy (SEM) and transmission electron microscopy. Both sample types exhibited uniform geometry and maintained a clear hexagonal pore arrangement. Cellular attachment of SK-N-SH neuroblastoma endothelial cells was examined using confocal microscopy and SEM. Attachment of SK-N-SH cells onto UNCD membranes on both porous regions and solid surfaces was shown, indicating the potential use of UNCD membranes in biomedical applications such as biosensors and tissue engineering scaffolds.

Nanoparticles of wurtzite aluminum nitride from the nut shells

NASA Astrophysics Data System (ADS)

Qadri, S. B.; Gorzkowski, E. P.; Rath, B. B.; Feng, C. R.; Amarasinghe, R.

2016-11-01

Nanoparticles of aluminum nitride were produced from a thermal treatment of a mixture of aluminum oxide (Al2O3) and shells of almond, cashew, coconuts, pistachio, and walnuts in a nitrogen atmosphere at temperatures in excess of 1450 °C. By selecting the appropriate ratios of each nut powder to Al2O3, it is shown that stoichiometric aluminum nitride can be produced by carbo-thermal reduction in nitrogen atmosphere. Using x-ray diffraction analysis, Raman scattering and Fourier Transform Infrared spectroscopy, it is demonstrated that aluminum nitride consists of pure wurtzite phase. Transmission electron microscopy showed the formation of nanoparticles and in some cases nanotubes of AlN.

Deformation-Induced Dissolution and Precipitation of Nitrides in Austenite and Ferrite of a High-Nitrogen Stainless Steel

NASA Astrophysics Data System (ADS)

Shabashov, V. A.; Makarov, A. V.; Kozlov, K. A.; Sagaradze, V. V.; Zamatovskii, A. E.; Volkova, E. G.; Luchko, S. N.

2018-02-01

Methods of Mössbauer spectroscopy and electron microscopy have been used to study the effect of the severe plastic deformation by high pressure torsion in Bridgman anvils on the dissolution and precipitation of chromium nitrides in the austenitic and ferritic structure of an Fe71.2Cr22.7Mn1.3N4.8 high-nitrogen steel. It has been found that an alternative process of dynamic aging with the formation of secondary nitrides affects the kinetics of the dissolution of chromium nitrides. The dynamic aging of ferrite is activated with an increase in the deformation temperature from 80 to 573 K.

Structural Analysis of a Carbon Nitride Film Prepared by Ion-Beam-Assisted Deposition

NASA Astrophysics Data System (ADS)

Hayashi, Toshiyuki; Matsumuro, Akihito; Muramatsu, Mutsuo; Kohzaki, Masao; Takahashi, Yutaka; Yamaguchi, Katsumi

1999-04-01

The microstructure of a carbon nitride (CNx) film formed by ion-beam-assisted deposition (IBAD) was investigated by transmission electron microscopy (TEM). This film was formed on the Si (100) substrate by IBAD with an N/C transport ratio of 1. Three different spacings (0.34 nm, 0.21 nm, 0.12 nm) were observed by transmission electron diffraction (TED) and the periodic structure corresponding to the spacing of 0.34 nm was aligned perpendicular to the substrate. The bending of this plane resembled a carbon nanotube; therefore, it seemed reasonable to suppose that the CNx film obtained consisted of numerous carbon-nanotube-like structural elements grown vertically, relative to the substrate, and it also seemed appropriate that these structural elements should be termed nanotube-like carbon nitride.

Application of scanning acoustic microscopy to advanced structural ceramics

NASA Technical Reports Server (NTRS)

Vary, Alex; Klima, Stanley J.

1987-01-01

A review is presentod of research investigations of several acoustic microscopy techniques for application to structural ceramics for advanced heat engines. Results obtained with scanning acoustic microscopy (SAM), scanning laser acoustic microscopy (SLAM), scanning electron acoustic microscopy (SEAM), and photoacoustic microscopy (PAM) are compared. The techniques were evaluated on research samples of green and sintered monolithic silicon nitrides and silicon carbides in the form of modulus-of-rupture bars containing deliberately introduced flaws. Strengths and limitations of the techniques are described with emphasis on statistics of detectability of flaws that constitute potential fracture origins.

Plasma induced sp 2 to sp 3 transition in boron nitride

NASA Astrophysics Data System (ADS)

Zhang, J.; Cui, Q.; Li, X.; He, Z.; Li, W.; Ma, Y.; Guan, Q.; Gao, W.; Zou, G.

2004-12-01

The transition from sp 2 to sp 3 hybridization in boron nitride has been induced in plasma. Nano-crystals of cubic boron nitride (cBN) have been synthesized by direct current arc discharge method using hexagonal boron nitride (hBN) as the starting material. The characterization of the as-grown powders is carried out by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. It has been shown that cBN and hBN grains with 20-60 nm in size co-exist in the powders. A reaction route of sublimation - re-hybridization - crystallization had been put forward to explain the mechanism of the hybridization transition and the growth of cBN by this method.

Osteoblastlike cell adhesion on titanium surfaces modified by plasma nitriding.

PubMed

da Silva, Jose Sandro Pereira; Amico, Sandro Campos; Rodrigues, Almir Olegario Neves; Barboza, Carlos Augusto Galvao; Alves, Clodomiro; Croci, Alberto Tesconi

2011-01-01

The aim of this study was to evaluate the characteristics of various titanium surfaces modified by cold plasma nitriding in terms of adhesion and proliferation of rat osteoblastlike cells. Samples of grade 2 titanium were subjected to three different surface modification processes: polishing, nitriding by plasma direct current, and nitriding by cathodic cage discharge. To evaluate the effect of the surface treatment on the cellular response, the adhesion and proliferation of osteoblastlike cells (MC3T3) were quantified and the results were analyzed by Kruskal-Wallis and Friedman statistical tests. Cellular morphology was observed by scanning electron microscopy. There was more MC3T3 cell attachment on the rougher surfaces produced by cathodic cage discharge compared with polished samples (P < .05). Plasma nitriding improves titanium surface roughness and wettability, leading to osteoblastlike cell adhesion.

Epitaxy of GaN in high aspect ratio nanoscale holes over silicon substrate

NASA Astrophysics Data System (ADS)

Wang, Kejia; Wang, Anqi; Ji, Qingbin; Hu, Xiaodong; Xie, Yahong; Sun, Ying; Cheng, Zhiyuan

2017-12-01

Dislocation filtering in gallium nitride (GaN) by epitaxial growth through patterned nanoscale holes is studied. GaN grown from extremely high aspect ratio holes by metalorganic chemical vapor deposition is examined by transmission electron microscopy and high-resolution transmission electron microscopy. This selective area epitaxial growth method with a reduced epitaxy area and an increased depth to width ratio of holes leads to effective filtering of dislocations within the hole and improves the quality of GaN significantly.

Structural-dependent thermal conductivity of aluminium nitride produced by reactive direct current magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belkerk, B. E.; Soussou, A.; Carette, M.

This Letter reports the thermal conductivity of aluminium nitride (AlN) thin-films deposited by reactive DC magnetron sputtering on single-crystal silicon substrates (100) with varying plasma and magnetic conditions achieving different crystalline qualities. The thermal conductivity of the films was measured at room temperature with the transient hot-strip technique for film thicknesses ranging from 100 nm to 4000 nm. The thermal conductivity was found to increase with the thickness depending on the synthesis conditions and film microstructure. The conductivity in the bulk region of the films, so-called intrinsic conductivity, and the boundary resistance were in the range [120-210] W m{sup -1}more » K{sup -1} and [2-30 Multiplication-Sign 10{sup -9}] K m{sup 2} W{sup -1}, respectively, in good agreement with microstructures analysed by x-ray diffraction, high-resolution-scanning-electron-microscopy, and transmission-electron-microscopy.« less

Growth of copper-benzene-1,3,5-tricarboxylate on boron nitride nanotubes and application of the composite in methane sensing

NASA Astrophysics Data System (ADS)

Xiang, Cuili; Chen, Ting; Zhang, Haitao; Zou, Yongjin; Chu, Hailiang; Zhang, Huanzhi; Xu, Fen; Sun, Lixian; Tang, Chengying

2017-12-01

A new composite material based on copper-benzene-1,3,5-tricarboxylate (Cu-BTC) deposited on boron nitride nanotubes (BNNTs) in a hydrothermal process were investigated for methane (CH4) sensing. The composite was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The Cu-BTC deposited on the BNNTs had an average grain size of 80 nm. The sensing performance of the as-grown product was studied for different concentrations of CH4 (20-200 ppm) at 150 °C. The results revealed that the Cu-BTC/BNNT composite exhibited high sensitivity and selectivity toward CH4. The good sensing performance of the composite was attributed to the high surface area and high affinity of Cu-BTC for CH4, which would allow the composite to act like a preconcentrator for CH4 gas sensing.

Validity of "sputtering and re-condensation" model in active screen cage plasma nitriding process

NASA Astrophysics Data System (ADS)

Saeed, A.; Khan, A. W.; Jan, F.; Abrar, M.; Khalid, M.; Zakaullah, M.

2013-05-01

The validity of "sputtering and re-condensation" model in active screen plasma nitriding for nitrogen mass transfer mechanism is investigated. The dominant species including NH, Fe-I, N2+, N-I and N2 along with Hα and Hβ lines are observed in the optical emission spectroscopy (OES) analysis. Active screen cage and dc plasma nitriding of AISI 316 stainless steel as function of treatment time is also investigated. The structure and phases composition of the nitrided layer is studied by X-ray diffraction (XRD). Surface morphology is studied by scanning electron microscopy (SEM) and hardness profile is obtained by Vicker's microhardness tester. Increasing trend in microhardness is observed in both cases but the increase in active screen plasma nitriding is about 3 times greater than that achieved by dc plasma nitriding. On the basis of metallurgical and OES observations the use of "sputtering and re-condensation" model in active screen plasma nitriding is tested.

Crystallization of the glassy phase of grain boundaries in silicon nitride

NASA Technical Reports Server (NTRS)

Jefferson, D. A.; Thomas, J. M.; Wen, S.

1984-01-01

Three types of hot-pressed silicon nitride specimens (containing 5wt% Y2O3 and 2wt% Al2O3 additives) which were subjected to different temperature heat treatments were studied by X-ray diffraction, X-ray microanalysis and high resolution electron microscopy. The results indicated that there were phase changes in the grain boundaries after heat treatment and the glassy phase at the grain boundaries was crystallized by heat treatment.

Dissolution and Characterization of Boron Nitride Nanotubes in Superacid.

PubMed

Kleinerman, Olga; Adnan, Mohammed; Marincel, Daniel M; Ma, Anson W K; Bengio, E Amram; Park, Cheol; Chu, Sang-Hyon; Pasquali, Matteo; Talmon, Yeshayahu

2017-12-19

Boron nitride nanotubes (BNNTs) are of interest for their unique combination of high tensile strength, high electrical resistivity, high neutron cross section, and low reactivity. The fastest route to employing these properties in composites and macroscopic articles is through solution processing. However, dispersing BNNTs without functionalization or use of a surfactant is challenging. We show here by cryogenic transmission electron microscopy that BNNTs spontaneously dissolve in chlorosulfonic acid as disentangled individual molecules. Electron energy loss spectroscopy of BNNTs dried from the solution confirms preservation of the sp 2 hybridization for boron and nitrogen, eliminating the possibility of BNNT functionalization or damage. The length and diameter of the BNNTs was statistically calculated to be ∼4.5 μm and ∼4 nm, respectively. Interestingly, bent or otherwise damaged BNNTs are filled by chlorosulfonic acid. Additionally, nanometer-sized synthesis byproducts, including boron nitride clusters, isolated single and multilayer hexagonal boron nitride, and boron particles, were identified. Dissolution in superacid provides a route for solution processing BNNTs without altering their chemical structure.

Nanoscale Visualization of Elastic Inhomogeneities at TiN Coatings Using Ultrasonic Force Microscopy

NASA Astrophysics Data System (ADS)

Hidalgo, J. A.; Montero-Ocampo, C.; Cuberes, M. T.

2009-12-01

Ultrasonic force microscopy has been applied to the characterization of titanium nitride coatings deposited by physical vapor deposition dc magnetron sputtering on stainless steel substrates. The titanium nitride layers exhibit a rich variety of elastic contrast in the ultrasonic force microscopy images. Nanoscale inhomogeneities in stiffness on the titanium nitride films have been attributed to softer substoichiometric titanium nitride species and/or trapped subsurface gas. The results show that increasing the sputtering power at the Ti cathode increases the elastic homogeneity of the titanium nitride layers on the nanometer scale. Ultrasonic force microscopy elastic mapping on titanium nitride layers demonstrates the capability of the technique to provide information of high value for the engineering of improved coatings.

Folate-grafted boron nitride nanotubes: possible exploitation in cancer therapy.

PubMed

Ferreira, Tiago H; Marino, Attilio; Rocca, Antonella; Liakos, Ioannis; Nitti, Simone; Athanassiou, Athanassia; Mattoli, Virgilio; Mazzolai, Barbara; de Sousa, Edesia M B; Ciofani, Gianni

2015-03-15

Boron nitride nanotubes (BNNTs) have generated considerable interest among the scientific community because of their unique physical and chemical properties. They present good chemical inertness, high thermal stability, and optimal resistance to oxidation, that make them ideal candidates for biomedical applications, in particular as nanovectors for drug, gene and protein delivery into the cells. In this study, BNNTs were prepared through a synthesis based on a chemical vapor deposition (CVD) method, and thereafter chemically functionalized with folic acid. The obtained nanostructures have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The characterization showed efficiently functionalized BNNTs of length of about 1 μm. Furthermore, confocal laser microscopy demonstrated that our nanotubes can be fluorescently-traced under appropriate excitation. Thanks to this property, it has been possible to investigate their internalization by HeLa cells through confocal microscopy, demonstrating that the BNNT up-take clearly increases after the functionalization with folate, a result confirmed by inductively coupled plasma (ICP) assessment of boron content inside the treated cell cultures. Copyright © 2015 Elsevier B.V. All rights reserved.

Boron nitride nanotubes as novel fillers for improving the properties of dental adhesives.

PubMed

Degrazia, Felipe Weidenbach; Leitune, Vicente Castelo Branco; Samuel, Susana Maria Werner; Collares, Fabrício Mezzomo

2017-07-01

This study aimed to evaluate the physical-chemical properties of experimental dental adhesives containing boron nitride nanotubes (BNNTs) as inorganic fillers. An experimental adhesive resin was prepared using HEMA-BisGMA, 66/33wt% (control). Inorganic BNNT fillers were first analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and then incorporated into the adhesive at different concentration (0.05, 0.075, 0.1, 0.15wt%). Degree of conversion (DC), ultimate strength, contact angle, surface free energy (SFE) microhardness, softening in solvent and bioactivity were assessed. Scanning and transmission electron microscopy (SEM and TEM) showed BNNTs with diameter ranging from 5 to 10nm with close end tips. No changes in DC were observed after incorporating BNNTs up to 0.15wt%. The contact angles of water and α-bromonaphthalene increased (p<0.05) and consequently the SFE decreased after incorporating BNNTs to the polymer matrix. Microhardness and solvent degradation strength increased after incorporation of 0.075, 0.1 and 0.15wt% BNNTs. Mineral deposition was found after 7days of immersion on adhesive specimens after incorporation of BNNT. The incorporation of BNNTs up to 0.15wt% improved the chemical and mechanical properties of dental adhesives and promoted mineral deposition. Incorporation of boron nitride nanotubes into adhesive resin materials improved physical-chemical properties and increased mineral deposition on its surface allowing enhanced properties of the resin-dentin interface. Thus, the novel adhesive material is promising as a dental adhesive and may contribute to the stability of the dentin-resin bonding. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tribological properties of epoxy composite coatings reinforced with functionalized C-BN and H-BN nanofillers

NASA Astrophysics Data System (ADS)

Yu, Jingjing; Zhao, Wenjie; Wu, Yinghao; Wang, Deliang; Feng, Ruotao

2018-03-01

A series of epoxy resin (EP) composite coatings reinforced with functionalized cubic boron nitride (FC-BN) and functionalized hexagonal boron nitride (FH-BN) were fabricated successfully on 316L stainless steel by hand lay-up technique. The structure properties were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The morphologies were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, UMT-3 tribometer and surface profiler were used to investigate tribological behaviors of as-prepared composite coatings under dry friction and seawater conditions respectively. The results demonstrated that the presence of FC-BN or FH-BN fillers could greatly decrease the friction coefficient (COF) and wear rate of epoxy, in addition, composite coatings possess better tribological properties under seawater condition which was attributed to the lubricating effect of seawater. Moreover, FC-BN endows the composite coatings the highest wear resistance, and FH-BN /EP composite coatings exhibited the best friction reduction performance which is attributed to the self-lubricating performance of lamella structure for FH-BN sheet.

Surface modification of boron nitride nanosheets by polyelectrolytes via atom transfer radical polymerization

NASA Astrophysics Data System (ADS)

Wu, Yuanpeng; Guo, Meiling; Liu, Guanfei; Xue, Shishan; Xia, Yuanmeng; Liu, Dan; Lei, Weiwei

2018-04-01

In this study, the surface modification of boron nitride nanosheets (BNNSs) with poly 2-acrylamido-2-methyl- propanesulfonate (PAMPS) brushes is achieved through electron transfer atom transfer radical polymerization (ARGET ATRP). BNNSs surface was first modified with α-bromoisobutyryl bromide (BIBB) via hydroxyl groups, then PAMPS brushes were grown on the surface through ARGET ATRP. Polyelectrolyte brushes modified BNNSs were further characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses (TGA), x-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The concentraction of water-dispersion of BNNSs have been enhanced significantly by PAMPS and the high water-dispersible functional BNNSs/PAMPS composites are expected to have potential applications in biomedical and thermal management in electronics.

Internal structure of multiphase zinc-blende wurtzite gallium nitride nanowires.

PubMed

Jacobs, B W; Ayres, V M; Crimp, M A; McElroy, K

2008-10-08

In this paper, the internal structure of novel multiphase gallium nitride nanowires in which multiple zinc-blende and wurtzite crystalline domains grow simultaneously along the entire length of the nanowire is investigated. Orientation relationships within the multiphase nanowires are identified using high-resolution transmission electron microscopy of nanowire cross-sections fabricated with a focused ion beam system. A coherent interface between the zinc-blende and wurtzite phases is identified. A mechanism for catalyst-free vapor-solid multiphase nanowire nucleation and growth is proposed.

Nanopipes in gallium nitride nanowires and rods.

PubMed

Jacobs, Benjamin W; Crimp, Martin A; McElroy, Kaylee; Ayres, Virginia M

2008-12-01

Gallium nitride nanowires and rods synthesized by a catalyst-free vapor-solid growth method were analyzed with cross section high-resolution transmission electron microscopy. The cross section studies revealed hollow core screw dislocations, or nanopipes, in the nanowires and rods. The hollow cores were located at or near the center of the nanowires and rods, along the axis of a screw dislocation. The formation of the hollow cores is consistent with effect of screw dislocations with giant Burgers vector predicted by Frank.

Laser sintered thin layer graphene and cubic boron nitride reinforced nickel matrix nanocomposites

NASA Astrophysics Data System (ADS)

Hu, Zengrong; Tong, Guoquan

2015-10-01

Laser sintered thin layer graphene (Gr)-cubic boron nitride (CBN)-Ni nanocomposites were fabricated on AISI 4140 plate substrate. The composites fabricating process, composites microstructure and mechanical properties were studied. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were employed to study the micro structures and composition of the composites. XRD and Raman tests proved that graphene and CBN were dispersed in the nanocomposites. Nanoindentation test results indicate the significant improvements were achieved in the composites mechanical properties.

Synthesis of nanowires and nanoparticles of cubic aluminium nitride

NASA Astrophysics Data System (ADS)

Balasubramanian, C.; Godbole, V. P.; Rohatgi, V. K.; Das, A. K.; Bhoraskar, S. V.

2004-03-01

Nanostructures of cubic aluminium nitride were synthesized by DC arc-plasma-induced melting of aluminium in a nitrogen-argon ambient. The material flux ejected from the molten aluminium surface was found to react with nitrogen under highly non-equilibrium conditions and subsequently condense on a water-cooled surface to yield a mixture of nanowires and nanoparticles of crystalline cubic aluminium nitride. Both x-ray diffraction and electron diffraction measurements revealed that the as-synthesized nitrides adopted the cubic phase. Fourier transform infrared spectroscopy was used to understand the bonding configuration. Microstructural features of the synthesized material were best studied by transmission electron microscopy. From these analyses cubic aluminium nitride was found to be the dominating phase for both nanowires and nanoparticles synthesized at low currents. The typical particle size distribution was found to range over 15-80 nm, whereas the wires varied from 30 to 100 nm in diameter and 500 to 700 nm in length, depending upon the process parameters such as arc current and the nitrogen pressure. The reaction products inside the plasma zone were also obtained theoretically by minimization of free energy and the favourable zone temperature necessary for the formation of aluminium nitride was found to be {\\sim } 6000 K. Results are discussed in view of the highly non-equilibrium conditions that prevail during the arc-plasma synthesis.

Molecular Beam Epitaxial Growth of Iron Nitrides on Zinc-Blende Gallium Nitride(001)

NASA Astrophysics Data System (ADS)

Pak, Jeongihm; Lin, Wenzhi; Chinchore, Abhijit; Wang, Kangkang; Smith, Arthur R.

2008-03-01

Iron nitrides are attractive materials for their high magnetic moments, corrosion, and oxidation resistance. We present the successful epitaxial growth of iron nitride on zinc-blende gallium nitride (c-GaN) in order to develop a novel magnetic transition metal nitride/semiconductor system. First, GaN is grown on magnesium oxide (MgO) substrates having (001) orientation using rf N2-plasma molecular beam epitaxy. Then we grow FeN at substrate temperature of ˜ 210 ^oC up to a thickness of ˜ 10.5 nm. In-situ reflection high-energy electron diffraction (RHEED) is used to monitor the surface during growth. Initial results suggest that the epitaxial relationship is FeN[001] || GaN[001] and FeN[100] || GaN[100]. Work in progress is to investigate the surface using in-situ scanning tunneling microscopy (STM) to reveal the surface structure at atomic scale, as well as to explore more Fe-rich magnetic phases.

Electronic and structural characteristics of zinc-blende wurtzite biphasic homostructure GaN nanowires

DOE PAGES

Jacobs, Benjamin W.; Ayres, Virginia M.; Petkov, Mihail P.; ...

2007-04-07

Here, we report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High-resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified.

Electronic and structural characteristics of zinc-blende wurtzite biphasic homostructure GaN nanowires.

PubMed

Jacobs, Benjamin W; Ayres, Virginia M; Petkov, Mihail P; Halpern, Joshua B; He, Maoqi; Baczewski, Andrew D; McElroy, Kaylee; Crimp, Martin A; Zhang, Jiaming; Shaw, Harry C

2007-05-01

We report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High-resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified.

Nitriding of AISI 4140 steel by a low energy broad ion source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ochoa, E. A.; Figueroa, C. A.; Alvarez, F.

2006-11-15

A comprehensive study of the thermochemical nitriding process of steel AISI 4140 by low energy ion implantation (Kaufmann cell) is reported. Different times of implantation were employed and the studied samples were characterized by x-ray diffraction, in situ photoemission electron spectroscopy, scanning electron microscopy, and hardness (nanoindentation) measurements. The linear relationship between nitrogen content and hardness was verified. The structure of the nitrided layer was characterized yielding that the compound layer is formed by coarse precipitates, around small grains, constituted principally by {epsilon}-Fe{sub 2-3}N and {gamma}-Fe{sub 4}N phases and the diffusion zone is formed by fine precipitates, around big grainsmore » of the original martensitic phase, constituted principally by {gamma}-Fe{sub 4}N phase. Finally, a diffusion model for multiphase systems was applied to determine effective diffusion coefficients of nitrogen in the different phases.« less

Atomic-scale structure and electronic properties of GaN/GaAs superlattices

NASA Astrophysics Data System (ADS)

Goldman, R. S.; Feenstra, R. M.; Briner, B. G.; O'Steen, M. L.; Hauenstein, R. J.

1996-12-01

We have investigated the atomic-scale structure and electronic properties of GaN/GaAs superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross-sectional scanning tunneling microscopy (STM) and spectroscopy, we show that the nitrided layers are laterally inhomogeneous, consisting of groups of atomic-scale defects and larger clusters. Analysis of x-ray diffraction data in terms of fractional area of clusters (determined by STM), reveals a cluster lattice constant similar to bulk GaN. In addition, tunneling spectroscopy on the defects indicates a conduction band state associated with an acceptor level of NAs in GaAs. Therefore, we identify the clusters and defects as nearly pure GaN and NAs, respectively. Together, the results reveal phase segregation in these arsenide/nitride structures, in agreement with the large miscibility gap predicted for GaAsN.

Syntheses, Characterization and Kinetics of Nickel-Tungsten Nitride Catalysts for Hydrotreating of Gas Oil

NASA Astrophysics Data System (ADS)

Botchwey, Christian

This thesis summarizes the methods and major findings of Ni-W(P)/gamma-Al 2O3 nitride catalyst synthesis, characterization, hydrotreating activity, kinetic analysis and correlation of the catalysts' activities to their synthesis parameters and properties. The range of parameters for catalyst synthesis were W (15-40 wt%), Ni (0-8 wt%), P (0-5 wt%) and nitriding temperature (TN) (500-900 °C). Characterization techniques used included: N2 sorption studies, chemisorption, elemental analysis, temperature programmed studies, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray, infrared spectroscopy, transmission electron microscopy and x-ray absorption near edge structure. Hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) were performed at: temperature (340-380 °C), pressure (6.2-9.0 MPa), liquid hourly space velocity (1-3 h-1) and hydrogen to oil ratio (600 ml/ml, STP). The predominant species on the catalyst surface were Ni3N, W2N and bimetallic Ni2W3N. The bimetallic Ni-W nitride species was more active than the individual activities of the Ni3N and W2N. P increased weak acid sites while nitriding temperature decreased amount of strong acid sites. Low nitriding temperature enhanced dispersion of metal particles. P interacted with Al 2O3 which increased the dispersion of metal nitrides on the catalyst surface. HDN activity increased with Ni and P loading but decreased with increase in nitriding temperature (optimum conversion; 60 wt%). HDS and HDA activities went through a maximum with increase in the synthesis parameters (optimum conversions; 88. wt% for HDS and 47 wt% for HDA). Increase in W loading led to increase in catalyst activity. The catalysts were stable to deactivation and had the nitride structure conserved during hydrotreating in the presence of hydrogen sulfide. The results showed good correlation between hydrotreating activities (HDS and HDN) and the catalyst nitrogen content, number of exposed active sites, catalyst particle size and BET surface area. HDS and HDN kinetic analyses, using Langmuir-Hinshelwood models, gave activation energies of 66 and 32 kJ/mol, respectively. There were no diffusion limitations in the reaction process. Two active sites were involved in HDS reaction while one site was used for HDN. HDS and HDN activities of the Ni-W(P)/gamma-Al 2O3 nitride catalysts were comparable to the corresponding sulfides.

Synthesis of rose-like boron nitride particles with a high specific surface area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Hongming; Huang, Xiaoxiao; Wen, Guangwu, E-mail: wgw@hitwh.edu.cn

2010-08-15

Novel rose-like BN nanostructures were synthesized on a large scale via a two-step procedure. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometer and nitrogen porosimetry. The results show that the obtained rose-like nanostructures are composed of a large amount of h-BN crystalline flakes and have a surface area of 90.31 m{sup 2}/g. A mechanism was proposed to explain the formation process of the rose-like BN nanostructures.

Probing low-energy hyperbolic polaritons in van der Waals crystals with an electron microscope.

PubMed

Govyadinov, Alexander A; Konečná, Andrea; Chuvilin, Andrey; Vélez, Saül; Dolado, Irene; Nikitin, Alexey Y; Lopatin, Sergei; Casanova, Fèlix; Hueso, Luis E; Aizpurua, Javier; Hillenbrand, Rainer

2017-07-21

Van der Waals materials exhibit intriguing structural, electronic, and photonic properties. Electron energy loss spectroscopy within scanning transmission electron microscopy allows for nanoscale mapping of such properties. However, its detection is typically limited to energy losses in the eV range-too large for probing low-energy excitations such as phonons or mid-infrared plasmons. Here, we adapt a conventional instrument to probe energy loss down to 100 meV, and map phononic states in hexagonal boron nitride, a representative van der Waals material. The boron nitride spectra depend on the flake thickness and on the distance of the electron beam to the flake edges. To explain these observations, we developed a classical response theory that describes the interaction of fast electrons with (anisotropic) van der Waals slabs, revealing that the electron energy loss is dominated by excitation of hyperbolic phonon polaritons, and not of bulk phonons as often reported. Thus, our work is of fundamental importance for interpreting future low-energy loss spectra of van der Waals materials.Here the authors adapt a STEM-EELS system to probe energy loss down to 100 meV, and apply it to map phononic states in hexagonal boron nitride, revealing that the electron loss is dominated by hyperbolic phonon polaritons.

Single step synthesis of nanostructured boron nitride for boron neutron capture therapy

NASA Astrophysics Data System (ADS)

Singh, Bikramjeet; Singh, Paviter; Kumar, Manjeet; Thakur, Anup; Kumar, Akshay

2015-05-01

Nanostructured Boron Nitride (BN) has been successfully synthesized by carbo-thermic reduction of Boric Acid (H3BO3). This method is a relatively low temperature synthesis route and it can be used for large scale production of nanostructured BN. The synthesized nanoparticles have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analyzer (DTA). XRD analysis confirmed the formation of single phase nanostructured Boron Nitride. SEM analysis showed that the particles are spherical in shape. DTA analysis showed that the phase is stable upto 900 °C and the material can be used for high temperature applications as well boron neutron capture therapy (BNCT).

Homoepitaxial n-core: p-shell gallium nitride nanowires: HVPE overgrowth on MBE nanowires.

PubMed

Sanders, Aric; Blanchard, Paul; Bertness, Kris; Brubaker, Matthew; Dodson, Christopher; Harvey, Todd; Herrero, Andrew; Rourke, Devin; Schlager, John; Sanford, Norman; Chiaramonti, Ann N; Davydov, Albert; Motayed, Abhishek; Tsvetkov, Denis

2011-11-18

We present the homoepitaxial growth of p-type, magnesium doped gallium nitride shells by use of halide vapor phase epitaxy (HVPE) on n-type gallium nitride nanowires grown by plasma-assisted molecular beam epitaxy (MBE). Scanning electron microscopy shows clear dopant contrast between the core and shell of the nanowire. The growth of magnesium doped nanowire shells shows little or no effect on the lattice parameters of the underlying nanowires, as measured by x-ray diffraction (XRD). Photoluminescence measurements of the nanowires show the appearance of sub-bandgap features in the blue and the ultraviolet, indicating the presence of acceptors. Finally, electrical measurements confirm the presence of electrically active holes in the nanowires.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korolev, D. S.; Mikhaylov, A. N.; Belov, A. I.

The composition and structure of silicon surface layers subjected to combined gallium and nitrogen ion implantation with subsequent annealing have been studied by the X-ray photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, Raman spectroscopy, and transmission electron microscopy techniques. A slight redistribution of the implanted atoms before annealing and their substantial migration towards the surface during annealing depending on the sequence of implantations are observed. It is found that about 2% of atoms of the implanted layer are replaced with gallium bonded to nitrogen; however, it is impossible to detect the gallium-nitride phase. At the same time, gallium-enriched inclusions containingmore » ∼25 at % of gallium are detected as candidates for the further synthesis of gallium-nitride inclusions.« less

Scanning Tunneling Spectroscopy of Potassium on Graphene

NASA Astrophysics Data System (ADS)

Cormode, Daniel; Leroy, Brian; Yankowitz, Matthew

2012-02-01

We investigate the effect of charged impurities on the electronic properties of large single crystal CVD grown graphene using scanning tunneling microscopy. Mono- and multilayer crystals were prepared by transferring graphene from copper onto exfoliated boron nitride flakes on 300 nm SiO2 substrates. The boron nitride provides an ultra flat surface for the graphene. Potassium atoms are controllably deposited on the graphene at low temperature by heating a nearby getter source. Scanning tunneling spectroscopy and transport measurements were performed in ultra high vacuum at 4.5 K. Transport measurements demonstrate the shifting of the Dirac point as the samples are doped, while STM measurements demonstrate the size, arrangement and local electronic influence of the potassium atoms.

Interface amorphization in hexagonal boron nitride films on sapphire substrate grown by metalorganic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Yang, Xu; Nitta, Shugo; Pristovsek, Markus; Liu, Yuhuai; Nagamatsu, Kentaro; Kushimoto, Maki; Honda, Yoshio; Amano, Hiroshi

2018-05-01

Hexagonal boron nitride (h-BN) films directly grown on c-plane sapphire substrates by pulsed-mode metalorganic vapor phase epitaxy exhibit an interlayer for growth temperatures above 1200 °C. Cross-sectional transmission electron microscopy shows that this interlayer is amorphous, while the crystalline h-BN layer above has a distinct orientational relationship with the sapphire substrate. Electron energy loss spectroscopy shows the energy-loss peaks of B and N in both the amorphous interlayer and the overlying crystalline h-BN layer, while Al and O signals are also seen in the amorphous interlayer. Thus, the interlayer forms during h-BN growth through the decomposition of the sapphire at elevated temperatures.

Deposition of magnesium nitride thin films on stainless steel-304 substrates by using a plasma focus device

NASA Astrophysics Data System (ADS)

Ramezani, Amir Hoshang; Habibi, Maryam; Ghoranneviss, Mahmood

2014-08-01

In this research, for the first time, we synthesize magnesium nitride thin films on 304-type stainless steel substrates using a Mather-type (2 kJ) plasma focus (PF) device. The films of magnesium nitride are coated with different number of focus shots (like 15, 25 and 35) at a distance of 8 cm from the anode tip and at 0° angular position with respect to the anode axis. For investigation of the structural properties and surface morphology of magnesium nitride films, we utilized the X-ray diffractometer (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis, respectively. Also, the elemental composition is characterized by energy-dispersive X-ray (EDX) analysis. Furthermore, Vicker's microhardness is used to study the mechanical properties of the deposited films. The results show that the degree of crystallinity of deposited thin films (from XRD), the average size of particles and surface roughness (from AFM), crystalline growth of structures (from SEM) and the hardness values of the films depend on the number of focus shots. The EDX analysis demonstrates the existence of the elemental composition of magnesium in the deposited samples.

Structure and Growth of Hexagonal Boron Nitride on Ir(111).

PubMed

Farwick Zum Hagen, Ferdinand H; Zimmermann, Domenik M; Silva, Caio C; Schlueter, Christoph; Atodiresei, Nicolae; Jolie, Wouter; Martínez-Galera, Antonio J; Dombrowski, Daniela; Schröder, Ulrike A; Will, Moritz; Lazić, Predrag; Caciuc, Vasile; Blügel, Stefan; Lee, Tien-Lin; Michely, Thomas; Busse, Carsten

2016-12-27

Using the X-ray standing wave method, scanning tunneling microscopy, low energy electron diffraction, and density functional theory, we precisely determine the lateral and vertical structure of hexagonal boron nitride on Ir(111). The moiré superstructure leads to a periodic arrangement of strongly chemisorbed valleys in an otherwise rather flat, weakly physisorbed plane. The best commensurate approximation of the moiré unit cell is (12 × 12) boron nitride cells resting on (11 × 11) substrate cells, which is at variance with several earlier studies. We uncover the existence of two fundamentally different mechanisms of layer formation for hexagonal boron nitride, namely, nucleation and growth as opposed to network formation without nucleation. The different pathways are linked to different distributions of rotational domains, and the latter enables selection of a single orientation only.

Nanoscale investigation of the piezoelectric properties of perovskite ferroelectrics and III-nitrides

NASA Astrophysics Data System (ADS)

Rodriguez, Brian Joseph

Nanoscale characterization of the piezoelectric and polarization related properties of III-Nitrides by piezoresponse force microscopy (PFM), electrostatic force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM) resulted in the measurement of piezoelectric constants, surface charge and surface potential. Photo-electron emission microscopy (PEEM) was used to determine the local electronic band structure of a GaN-based lateral polarity heterostructure (GaN-LPH). Nanoscale characterization of the imprint and switching behavior of ferroelectric thin films by PFM resulted in the observation of domain pinning, while nanoscale characterization of the spatial variations in the imprint and switching behavior of integrated (111)-oriented PZT-based ferroelectric random access memory (FRAM) capacitors by PFM have revealed a significant difference in imprint and switching behavior between the inner and outer parts of capacitors. The inner regions of the capacitors are typically negatively imprinted and consequently tend to switch back after being poled by a positive bias, while regions at the edge of the capacitors tend to exhibit more symmetric hysteresis behavior. Evidence was obtained indicating that mechanical stress conditions in the central regions of the capacitors can lead to incomplete switching. A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM, respectively) has been used to map the out-of-plane and in-plane polarization distribution, respectively, of integrated (111)-oriented PZT-based capacitors, which revealed poled capacitors are in a polydomain state.

The effect of SiO 2-doped boron nitride multiple coatings on mechanical properties of quartz fibers

NASA Astrophysics Data System (ADS)

Zheng, Yu; Wang, Shubin

2012-01-01

SiO2-doped boron nitride multiple coatings (SiO2/BN multiple coatings) were prepared on quartz fibers surface at 700 °C. Single fiber tensile test was employed to evaluate fiber tensile strength; Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were employed to evaluate morphology and structure of the fibers. Fiber tensile test results indicated that the strength of quartz fibers with SiO2/BN multiple coatings was about twice of the fibers with BN coatings and original fibers which were heated at 700 °C for 10 h. The SiO2/BN multiple coatings would provide compressive stress on quartz fibers, which would help to seal the defects on fiber surface. Furthermore, TEM images showed that the nano-SiO2 powders crystallized in advance of quartz fibers, which would suppress crystallization of quartz fibers and reduce damage from crystallization. Thus, nano-SiO2 powders would help to keep mechanical properties of quartz fibers.

Formation of conductive copper lines by femtosecond laser irradiation of copper nitride film on plastic substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Xiaodong; Yuan, Ningyi, E-mail: nyyuan@cczu.edu.cn; Center for Low-Dimensional Materials, Micro-Nano Devices and Systems, Changzhou University, Changzhou 213164, Jiangsu

2015-05-15

In this paper, we report a simple method to form conductive copper lines by scanning a single-beam femtosecond pulse laser on a plastic substrate covered with copper nitride (Cu{sub 3}N) film. The Cu{sub 3}N films were prepared by DC magnetron sputtering in the presence of an Ar + N{sub 2} atmosphere at 100 °C. The influence of the laser power and scanning speed on the formed copper line width, surface features, and morphology was analyzed by means of optical microscopy, X-ray diffraction, non-contact 3D profilometer, and scanning electron microscopy. The experimental results demonstrate that low laser power and low scanningmore » speed favor the formation of uniform and flat Cu lines. After process optimization, copper lines with a width less than 5 μm were obtained, which provides an attractive application prospect in the field of flexible electronic devices.« less

Effect of MoO3 on the synthesis of boron nitride nanotubes over Fe and Ni catalysts.

PubMed

Nithya, Jeghan Shrine Maria; Pandurangan, Arumugam

2012-05-01

Synthesis of boron nitride nanotubes at reduced temperature is important for industrial manufactures. In this study boron nitride nanotubes were synthesized by thermal evaporation method using B/Fe2O3/MoO3 and B/Ni2O3/MoO3 mixtures separately with ammonia as the nitrogen source. The growth of boron nitride nanotubes occurred at 1100 degrees C, which was relatively lower than other metal oxides assisted growth processes requiring higher than 1200 degrees C. MoO3 promoted formation of B2O2 and aided boron nitride nanotubes growth at a reduced temperature. The boron nitride nanotubes with bamboo shaped, nested cone structured and straight tubes like forms were evident from the high resolution transmission electron microscopy. Metallic Fe and Ni, formed during the process, were the catalysts for the growth of boron nitride nanotubes. Their formation was established by X-ray diffraction. FT Raman showed a peak due to B-N vibration of BNNTs close to 1370 cm(-1). Hence MoO3 assisted growth of boron nitride nanotubes is advantageous, as it significantly reduced the synthesis temperature.

Controlling Surface Morphology and Circumventing Secondary Phase Formation in Non-polar m-GaN by Tuning Nitrogen Activity

NASA Astrophysics Data System (ADS)

Chang, C. W.; Wadekar, P. V.; Guo, S. S.; Cheng, Y. J.; Chou, M.; Huang, H. C.; Hsieh, W. C.; Lai, W. C.; Chen, Q. Y.; Tu, L. W.

2018-01-01

For the development of non-polar nitrides based optoelectronic devices, high-quality films with smooth surfaces, free of defects or clusters, are critical. In this work, the mechanisms governing the topography and single phase epitaxy of non-polar m-plane gallium nitride ( m-GaN) thin films are studied. The samples were grown using plasma-assisted molecular beam epitaxy on m-plane sapphire substrates. Growth of pure m-GaN thin films, concomitant with smooth surfaces is possible at low radio frequency powers and high growth temperatures as judged by the high resolution x-ray diffraction, field emission scanning electron microscopy, and atomic force microscopy measurements. Defect types and densities are quantified using transmission electron microscopy, while Raman spectroscopy was used to analyze the in-plane stress in the thin films which matches the lattice mismatch analysis. Energy dispersive spectroscopy and cathodoluminescence support a congruent growth and a dominant near band edge emission. From the analysis, a narrow growth window is discovered wherein epitaxial growth of pure m-plane GaN samples free of secondary phases with narrow rocking curves and considerable smooth surfaces are successfully demonstrated.

Moessbauer spectroscopy study on the corrosion resistance of plasma nitrided ASTM F138 stainless steel in chloride solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Souza, S.D. de; Olzon-Dionysio, M., E-mail: dmod@df.ufscar.br; Basso, R.L.O.

2010-10-15

Plasma nitriding of ASTM F138 stainless steel samples has been carried out using dc glow discharge under 80% H{sub 2}-20% N{sub 2} gas mixture, at 673 K, and 2, 4, and 7 h time intervals, in order to investigate the influence of treatment time on the microstructure and the corrosion resistance properties. The samples were characterized by scanning electron microscopy, glancing angle X-ray diffraction and conversion electron Moessbauer spectroscopy, besides electrochemical tests in NaCl aerated solution. A modified layer of about 6 {mu}m was observed for all the nitrided samples, independent of nitriding time. The X-ray diffraction analysis shows broadmore » {gamma}{sub N} phase peaks, signifying a great degree of nitrogen supersaturation. Besides {gamma}{sub N,} the Moessbauer spectroscopy results indicated the occurrence of {gamma}' and {epsilon} phases, as well as some other less important phases. Corrosion measurements demonstrate that the plasma nitriding time affects the corrosion resistance and the best performance is reached at 4 h treatment. It seems that the {epsilon}/{gamma}' fraction ratio plays an important role on the resistance corrosion. Additionally, the Moessbauer spectroscopy was decisive in this study, since it was able to identify and quantify the iron phases that influence the corrosion resistance of plasma nitrided ASTM F138 samples.« less

Magnetization reversal of the domain structure in the anti-perovskite nitride Co{sub 3}FeN investigated by high-resolution X-ray microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hajiri, T., E-mail: t.hajiri@numse.nagoya-u.ac.jp; Kuroki, Y.; Ando, H.

2016-05-14

We performed X-ray magnetic circular dichroism (XMCD) photoemission electron microscopy imaging to reveal the magnetic domain structure of anti-perovskite nitride Co{sub 3}FeN exhibiting a negative spin polarization. In square and disc patterns, we systematically and quantitatively determined the statistics of the stable states as a function of geometry. By direct imaging during the application of a magnetic field, we revealed the magnetic reversal process in a spatially resolved manner. We compared the hysteresis on the continuous area and the square patterns from the magnetic field-dependent XMCD ratio, which can be explained as resulting from the effect of the shape anisotropy,more » present in nanostructured thin films.« less

Synthesis of atomically thin hexagonal boron nitride films on nickel foils by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Nakhaie, S.; Wofford, J. M.; Schumann, T.; Jahn, U.; Ramsteiner, M.; Hanke, M.; Lopes, J. M. J.; Riechert, H.

2015-05-01

Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as a dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence of crystalline h-BN over the entire substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used to examine the morphology and continuity of the synthesized films. A scanning electron microscopy study of films obtained using shorter depositions offers insight into the nucleation and growth behavior of h-BN on the Ni substrate. The morphology of h-BN was found to evolve from dendritic, star-shaped islands to larger, smooth triangular ones with increasing growth temperature.

Direct Measurement of Polarization-Induced Fields in GaN/AlN by Nano-Beam Electron Diffraction

NASA Astrophysics Data System (ADS)

Carvalho, Daniel; Müller-Caspary, Knut; Schowalter, Marco; Grieb, Tim; Mehrtens, Thorsten; Rosenauer, Andreas; Ben, Teresa; García, Rafael; Redondo-Cubero, Andrés; Lorenz, Katharina; Daudin, Bruno; Morales, Francisco M.

2016-06-01

The built-in piezoelectric fields in group III-nitrides can act as road blocks on the way to maximizing the efficiency of opto-electronic devices. In order to overcome this limitation, a proper characterization of these fields is necessary. In this work nano-beam electron diffraction in scanning transmission electron microscopy mode has been used to simultaneously measure the strain state and the induced piezoelectric fields in a GaN/AlN multiple quantum well system.

Tunable hole injection of solution-processed polymeric carbon nitride towards efficient organic light-emitting diode

NASA Astrophysics Data System (ADS)

Zhang, Xiaowen; Zheng, Qinghong; Tang, Zhenyu; Li, Wanshu; Zhang, Yan; Xu, Kai; Xue, Xiaogang; Xu, Jiwen; Wang, Hua; Wei, Bin

2018-02-01

Polymeric carbon nitride (CNxHy) has been facilely synthesized from dicyandiamide and functions as a solution-processed hole injection layer in organic light-emitting diodes (OLEDs). The measurements using X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and impedance spectroscopy elucidate that CNxHy exhibits superior film morphology and extra electric properties such as tailored work function and tunable hole injection. The luminous efficiency of CNxHy-based OLED is found to improve by 76.6% in comparison to the counterpart using favorite solution-processed poly(ethylene dioxythiophene):poly(styrene sulfonate) as the hole injection layer. Our results also pave a way for broadening carbon nitride applications in organic electronics using the solution process.

Single step synthesis of nanostructured boron nitride for boron neutron capture therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Bikramjeet; Singh, Paviter; Kumar, Akshay, E-mail: akshaykumar.tiet@gmail.com

2015-05-15

Nanostructured Boron Nitride (BN) has been successfully synthesized by carbo-thermic reduction of Boric Acid (H{sub 3}BO{sub 3}). This method is a relatively low temperature synthesis route and it can be used for large scale production of nanostructured BN. The synthesized nanoparticles have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analyzer (DTA). XRD analysis confirmed the formation of single phase nanostructured Boron Nitride. SEM analysis showed that the particles are spherical in shape. DTA analysis showed that the phase is stable upto 900 °C and the material can be used for high temperature applications asmore » well boron neutron capture therapy (BNCT)« less

Lattice distortion of square iron nitride monolayers induced by changing symmetry of substrate

NASA Astrophysics Data System (ADS)

Hattori, Takuma; Iimori, Takushi; Miyamachi, Toshio; Komori, Fumio

2018-04-01

Rectangular iron nitride monatomic layers are fabricated on the threefold symmetric Cu(111) substrate by taking advantage of the stability of the square nitride film. Two different ordered structures are observed on the Cu(111) substrate by scanning tunneling microscopy after annealing at 510 K and 580 K. Their chemical composition and lattice symmetry are investigated by x-ray photoelectron spectroscopy and low energy electron diffraction. The monolayer film prepared at 580 K is a distorted Fe2N monolayer analogous to a ferromagnetic square Fe2N monolayer with a clock reconstruction on the Cu(001) substrate. The lattice deformation of the square Fe2N monolayer is induced by using Cu(111) with threefold symmetry.

Nitride alloy layer formation of duplex stainless steel using nitriding process

NASA Astrophysics Data System (ADS)

Maleque, M. A.; Lailatul, P. H.; Fathaen, A. A.; Norinsan, K.; Haider, J.

2018-01-01

Duplex stainless steel (DSS) shows a good corrosion resistance as well as the mechanical properties. However, DSS performance decrease as it works under aggressive environment and at high temperature. At the mentioned environment, the DSS become susceptible to wear failure. Surface modification is the favourable technique to widen the application of duplex stainless steel and improve the wear resistance and its hardness properties. Therefore, the main aim of this work is to nitride alloy layer on the surface of duplex stainless steel by the nitriding process temperature of 400°C and 450°C at different time and ammonia composition using a horizontal tube furnace. The scanning electron microscopy and x-ray diffraction analyzer are used to analyse the morphology, composition and the nitrided alloy layer for treated DSS. The micro hardnesss Vickers tester was used to measure hardness on cross-sectional area of nitrided DSS. After nitriding, it was observed that the hardness performance increased until 1100 Hv0.5kgf compared to substrate material of 250 Hv0.5kgf. The thickness layer of nitride alloy also increased from 5μm until 100μm due to diffusion of nitrogen on the surface of DSS. The x-ray diffraction results showed that the nitride layer consists of iron nitride, expanded austenite and chromium nitride. It can be concluded that nitride alloy layer can be produced via nitriding process using tube furnace with significant improvement of microstructural and hardness properties.

Nitridation of silicon by nitrogen neutral beam

NASA Astrophysics Data System (ADS)

Hara, Yasuhiro; Shimizu, Tomohiro; Shingubara, Shoso

2016-02-01

Silicon nitridation was investigated at room temperature using a nitrogen neutral beam (NB) extracted at acceleration voltages of less than 100 V. X-ray photoelectron spectroscopy (XPS) analysis confirmed the formation of a Si3N4 layer on a Si (1 0 0) substrate when the acceleration voltage was higher than 20 V. The XPS depth profile indicated that nitrogen diffused to a depth of 36 nm for acceleration voltages of 60 V and higher. The thickness of the silicon nitrided layer increased with the acceleration voltages from 20 V to 60 V. Cross-sectional transmission electron microscopy (TEM) analysis indicated a Si3N4 layer thickness of 3.1 nm was obtained at an acceleration voltage of 100 V. Moreover, it was proved that the nitrided silicon layer formed by the nitrogen NB at room temperature was effective as the passivation film in the wet etching process.

Atmospheric pressure scanning transmission electron microscopy.

PubMed

de Jonge, Niels; Bigelow, Wilbur C; Veith, Gabriel M

2010-03-10

Scanning transmission electron microscope (STEM) images of gold nanoparticles at atmospheric pressure have been recorded through a 0.36 mm thick mixture of CO, O2, and He. This was accomplished using a reaction cell consisting of two electron-transparent silicon nitride membranes. Gold nanoparticles of a full width at half-maximum diameter of 1.0 nm were visible above the background noise, and the achieved edge resolution was 0.4 nm in accordance with calculations of the beam broadening.

Identification of sigma and chi phases in duplex stainless steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Llorca-Isern, Núria, E-mail: nullorca@ub.edu; López-Luque, Héctor, E-mail: hlopezlu7@alumnes.ub.edu; López-Jiménez, Isabel, E-mail: ilopezji9@alumnes.ub.edu

The aim of this work is to find out the most suitable method for detecting and analyzing accurately the formation conditions of secondary phases, particularly Sigma-phase (σ-phase) and Chi-phase (χ-phase) in duplex stainless steels (UNS S32205 and UNS S32750). The microstructure was characterized after a solution annealing at 1080 °C followed by an isothermal heating at 830 °C for different time ranges, ranging from 1 min to 9 h, in order to enlighten the controversial point concerning the mechanism of χ-phase nucleation in relation with the σ-phase. Etched samples were observed using optical microscopy (MO), and scanning electron microscopy (FESEM)more » with a backscattered electron detector (BSE) was used on unetched samples. Compositional microanalysis (EDS) was carried out for identifying the different phases present in the steels. Sigma phase was easily observed using different etching procedures, whereas χ-phase was only clearly detected with FESEM–BSE on unetched samples. The compositional analyses showed that the molybdenum content in χ-phase almost doubles the content of this element in σ-phase, and as a result the kinetics of nucleation and growth were also found to be remarkably faster when the alloy content in the steel is higher. In addition, chromium nitrides and carbides were also observed to precipitate as a result of the heat treatments and, in the case of the chromium nitrides, they act as a favorable site for the nucleation of σ-phase and χ-phase. - Highlights: • Microscopy was used on heat treated duplex steels for microstructure identification. • FESEM–BSE observation on unetched samples provided the best contrast between phases. • Analyses of carbides, nitrides, chi and sigma phases were possible by EDS and WDS. • Chromium nitrides act as favorable site for the nucleation of chi and sigma phases. • Secondary phases nucleation kinetics are faster in superduplex than in duplex steels.« less

Controlled Synthesis of Atomically Layered Hexagonal Boron Nitride via Chemical Vapor Deposition.

PubMed

Liu, Juanjuan; Kutty, R Govindan; Liu, Zheng

2016-11-29

Hexagonal boron nitrite (h-BN) is an attractive material for many applications including electronics as a complement to graphene, anti-oxidation coatings, light emitters, etc. However, the synthesis of high-quality h-BN is still a great challenge. In this work, via controlled chemical vapor deposition, we demonstrate the synthesis of h-BN films with a controlled thickness down to atomic layers. The quality of as-grown h-BN is confirmed by complementary characterizations including high-resolution transition electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray photo-electron spectroscopy. This work will pave the way for production of large-scale and high-quality h-BN and its applications as well.

Nano- and Macro-wear of Bio-carbo-nitrided AISI 8620 Steel Surfaces

NASA Astrophysics Data System (ADS)

Arthur, Emmanuel Kwesi; Ampaw, Edward; Zebaze Kana, M. G.; Adetunji, A. R.; Olusunle, S. O. O.; Adewoye, O. O.; Soboyejo, W. O.

2015-12-01

This paper presents the results of an experimental study of nano- and macro-scale wear in a carbo-nitrided AISI 8620 steel. Carbo-nitriding is carried out using a novel method that involves the use of dried, cyanide-containing cassava leaves, as sources of carbon and nitrogen. These are used in a pack cementation that is used to diffuse carbon and nitrogen into case layers at intermediate temperatures [673.15 K, 723.15 K, 773.15 K, and 823.15 K (400 °C, 450 °C, 500 °C, and 550 °C)]. Nano- and macro-scale wear properties are studied in the case-hardened surfaces, using a combination of nano-scratch and pin-on-disk experiments. The measured wear volumes (at both nano- and macro-length scales) are shown to increase with decreasing pack cyaniding temperature. The nano- and macro-wear resistances are also shown to be enhanced by the in situ diffusion of carbon and nitrogen from cyanide-containing bio-processed waste. The underlying wear mechanisms are also elucidated via atomic force microscopy and scanning electron microscopy observations of the wear tracks. The implications of the results are discussed for the design of hardened carbo-nitrided steel surfaces with improved wear resistance.

Characterization and Reliability of Vertical N-Type Gallium Nitride Schottky Contacts

DTIC Science & Technology

2016-09-01

barrier diode SEM scanning electron microscopy SiC silicon carbide SMU source measure unit xvi THIS PAGE INTENTIONALLY LEFT BLANK xvii...arguably the Schottky barrier diode (SBD). The SBD is a fundamental component in the majority of power electronic devices; specifically, those used in...Ishizuka, and Ueno demonstrated the long-term reliability of vertical metal-GaN Schottky barrier diodes through their analysis of the degradation

Structural and mechanical properties of CVD deposited titanium aluminium nitride (TiAlN) thin films

NASA Astrophysics Data System (ADS)

Das, Soham; Guha, Spandan; Ghadai, Ranjan; Kumar, Dhruva; Swain, Bibhu P.

2017-06-01

Titanium aluminium nitride (TiAlN) thin films were deposited by chemical vapour deposition using TiO2 powder, Al powder and N2 gas. The morphology and mechanical properties of the films were characterized by scanning electron microscopy and nanoindentation technique, respectively. The structural properties were characterized by Raman spectroscopy and X-ray diffraction. The XRD result shows TiAlN films are of NaCl-type metal nitride structure. Micro-Raman peaks of the TiAlN thin film were observed within 450 and 642 cm-1 for acoustic and optic range, respectively. A maximum hardness and Young modulus up to 22 and 272.15 GPa, respectively, were observed in the TiAlN film deposited at 1200 °C.

Shock-induced reaction synthesis of cubic boron nitride

NASA Astrophysics Data System (ADS)

Beason, M. T.; Pauls, J. M.; Gunduz, I. E.; Rouvimov, S.; Manukyan, K. V.; Matouš, K.; Son, S. F.; Mukasyan, A.

2018-04-01

Here, we report ultra-fast (0.1-5 μs) shock-induced reactions in the 3B-TiN system, leading to the direct synthesis of cubic boron nitride, which is extremely rare in nature and is the second hardest material known. Composite powders were produced through high-energy ball milling to provide intimate mixing and subsequently shocked using an explosive charge. High-resolution transmission electron microscopy and X-ray diffraction confirm the formation of nanocrystalline grains of c-BN produced during the metathetical reaction between boron and titanium nitride. Our results illustrate the possibility of rapid reactions enabled by high-energy ball milling possibly occurring in the solid state on incredibly short timescales. This process may provide a route for the discovery and fabrication of advanced compounds.

Improved memory characteristics by NH3-nitrided GdO as charge storage layer for nonvolatile memory applications

NASA Astrophysics Data System (ADS)

Liu, L.; Xu, J. P.; Ji, F.; Chen, J. X.; Lai, P. T.

2012-07-01

Charge-trapping memory capacitor with nitrided gadolinium oxide (GdO) as charge storage layer (CSL) is fabricated, and the influence of post-deposition annealing in NH3 on its memory characteristics is investigated. Transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction are used to analyze the cross-section and interface quality, composition, and crystallinity of the stack gate dielectric, respectively. It is found that nitrogen incorporation can improve the memory window and achieve a good trade-off among the memory properties due to NH3-annealing-induced reasonable distribution profile of a large quantity of deep-level bulk traps created in the nitrided GdO film and reduction of shallow traps near the CSL/SiO2 interface.

Fabrication of AlN/BN bishell hollow nanofibers by electrospinning and atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haider, Ali; Kayaci, Fatma; Uyar, Tamer

2014-09-01

Aluminum nitride (AlN)/boron nitride (BN) bishell hollow nanofibers (HNFs) have been fabricated by successive atomic layer deposition (ALD) of AlN and sequential chemical vapor deposition (CVD) of BN on electrospun polymeric nanofibrous template. A four-step fabrication process was utilized: (i) fabrication of polymeric (nylon 6,6) nanofibers via electrospinning, (ii) hollow cathode plasma-assisted ALD of AlN at 100 °C onto electrospun polymeric nanofibers, (iii) calcination at 500 °C for 2 h in order to remove the polymeric template, and (iv) sequential CVD growth of BN at 450 °C. AlN/BN HNFs have been characterized for their chemical composition, surface morphology, crystal structure, and internal nanostructuremore » using X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction. Measurements confirmed the presence of crystalline hexagonal BN and AlN within the three dimensional (3D) network of bishell HNFs with relatively low impurity content. In contrast to the smooth surface of the inner AlN layer, outer BN coating showed a highly rough 3D morphology in the form of BN nano-needle crystallites. It is shown that the combination of electrospinning and plasma-assisted low-temperature ALD/CVD can produce highly controlled multi-layered bishell nitride ceramic hollow nanostructures. While electrospinning enables easy fabrication of nanofibrous template, self-limiting reactions of plasma-assisted ALD and sequential CVD provide control over the wall thicknesses of AlN and BN layers with sub-nanometer accuracy.« less

Diffusion, convection, and solidification in cw-mode free electron laser nitrided titanium

NASA Astrophysics Data System (ADS)

Höche, Daniel; Shinn, Michelle; Müller, Sven; Schaaf, Peter

2009-04-01

Titanium sheets were irradiated by free electron laser radiation in cw mode in pure nitrogen. Due to the interaction, nitrogen diffusion occurs and titanium nitride was synthesized in the tracks. Overlapping tracks have been utilized to create coatings in order to improve the tribological properties of the sheets. Caused by the local heating and the spatial dimension of the melt pool, convection effects were observed and related to the track properties. Stress, hardness, and nitrogen content were investigated with x-ray diffraction, nanoindention, and resonant nuclear reaction analysis. The measured results were correlated with the scan parameters, especially to the lateral track shift. Cross section micrographs were prepared and investigated by means of scanning electron microscopy. They show the solidification behavior, phase formation, and the nitrogen distribution. The experiments give an insight into the possibilities of materials processing using such a unique heat source.

Phase stability tuning in the NbxZr1-xN thin-film system for large stacking fault density and enhanced mechanical strength

NASA Astrophysics Data System (ADS)

Joelsson, T.; Hultman, L.; Hugosson, H. W.; Molina-Aldareguia, J. M.

2005-03-01

The phase stability of hexagonal WC-structure and cubic NaCl-structure 4d transition metal nitrides was calculated using first-principles density functional theory. It is predicted that there is a multiphase or polytypic region for the 4d transition metal nitrides with a valence electron concentration around 9.5 to 9.7 per formula unit. For verification, epitaxial NbxZr1-xN (0⩽x⩽1) was grown by reactive magnetron sputter deposition on MgO(001) substrates and analyzed with transmission electron microscopy (TEM) and x-ray diffraction. The defects observed in the films were threading dislocations due to nucleation and growth on the lattice-mismatched substrate and planar defects (stacking faults) parallel to the substrate surface. The highest defect density was found at the x =0.5 composition. The nanoindentation hardness of the films varied between 21GPa for the binary nitrides, and 26GPa for Nb0.5Zr0.5N. Unlike the cubic binary nitrides, no slip on the preferred ⟨11¯0⟩{110} slip system was observed. The increase in hardness is attributed to the increase in defect density at x =0.5, as the defects act as obstacles for dislocation glide during deformation. The findings present routes for the design of wear-resistant nitride coatings by phase stability tuning.

One-step route to a hybrid TiO2/Ti x W1-x N nanocomposite by in situ selective carbothermal nitridation.

PubMed

Schnepp, Zoë; Hollamby, Martin J; Tanaka, Masahiko; Matsushita, Yoshitaka; Katsuya, Yoshio; Sakka, Yoshio

2012-06-01

Metal oxide/nitride nanocomposites have many existing and potential applications, e.g. in energy conversion or ammonia synthesis. Here, a hybrid oxide/nitride nanocomposite (anatase/Ti x W 1- x N) was synthesized by an ammonia-free sol-gel route. Synchrotron x-ray diffraction, complemented with electron microscopy and thermogravimetric analysis, was used to study the structure, composition and mechanism of formation of the nanocomposite. The nanocomposite contained nanoparticles (<5 nm diameter) of two highly intermixed phases. This was found to arise from controlled nucleation and growth of a single oxide intermediate from the gel precursor, followed by phase separation and in situ selective carbothermal nitridation. Depending on the preparation conditions, the composition varied from anatase/Ti x W 1- x N at low W content to an isostructural mixture of Ti-rich and W-rich Ti x W 1- x N at high W content. In situ selective carbothermal nitridation offers a facile route to the synthesis of nitride-oxide nanocomposites. This conceptually new approach is a significant advance from previous methods, which generally require ammonolysis of a pre-synthesized oxide.

Molybdenum Oxide Nitrides of the Mo2(O,N,□)5 Type: On the Way to Mo2O5.

PubMed

Weber, Dominik; Huber, Manop; Gorelik, Tatiana E; Abakumov, Artem M; Becker, Nils; Niehaus, Oliver; Schwickert, Christian; Culver, Sean P; Boysen, Hans; Senyshyn, Anatoliy; Pöttgen, Rainer; Dronskowski, Richard; Ressler, Thorsten; Kolb, Ute; Lerch, Martin

2017-08-07

Blue-colored molybdenum oxide nitrides of the Mo 2 (O,N,□) 5 type were synthesized by direct nitridation of commercially available molybdenum trioxide with a mixture of gaseous ammonia and oxygen. Chemical composition, crystal structure, and stability of the obtained and hitherto unknown compounds are studied extensively. The average oxidation state of +5 for molybdenum is proven by Mo K near-edge X-ray absorption spectroscopy; the magnetic behavior is in agreement with compounds exhibiting Mo V O 6 units. The new materials are stable up to ∼773 K in an inert gas atmosphere. At higher temperatures, decomposition is observed. X-ray and neutron powder diffraction, electron diffraction, and high-resolution transmission electron microscopy reveal the structure to be related to VNb 9 O 24.9 -type phases, however, with severe disorder hampering full structure determination. Still, the results demonstrate the possibility of a future synthesis of the potential binary oxide Mo 2 O 5 . On the basis of these findings, a tentative suggestion on the crystal structure of the potential compound Mo 2 O 5 , backed by electronic-structure and phonon calculations from first principles, is given.

Rolling Contact Fatigue Failure Mechanisms of Plasma-Nitrided Ductile Cast Iron

NASA Astrophysics Data System (ADS)

Wollmann, D.; Soares, G. P. P. P.; Grabarski, M. I.; Weigert, N. B.; Escobar, J. A.; Pintaude, G.; Neves, J. C. K.

2017-05-01

Rolling contact fatigue (RCF) of a nitrided ductile cast iron was investigated. Flat washers machined from a pearlitic ductile cast iron bar were quenched and tempered to maximum hardness, ground, polished and divided into four groups: (1) specimens tested as quenched and tempered; (2) specimens plasma-nitrided for 8 h at 400 °C; (3) specimens plasma-nitrided and submitted to a diffusion process for 16 h at 400 °C; and (4) specimens submitted to a second tempering for 24 h at 400 °C. Hardness profiles, phase analyses and residual stress measurements by x-ray diffraction, surface roughness and scanning electron microscopy were applied to characterize the surfaces at each step of this work. Ball-on-flat washer tests were conducted with a maximum contact pressure of 3.6 GPa, under flood lubrication with a SAE 90 API GL-5 oil at 50 °C. Test ending criterion was the occurrence of a spalling. Weibull analysis was used to characterize RCF's lifetime data. Plasma-nitrided specimens exhibited a shorter RCF lifetime than those just quenched and tempered. The effects of nitriding on the mechanical properties and microstructure of the ductile cast iron are discussed in order to explain the shorter endurance of nitrided samples.

Experimental and numerical study on plasma nitriding of AISI P20 mold steel

NASA Astrophysics Data System (ADS)

Nayebpashaee, N.; Vafaeenezhad, H.; Kheirandish, Sh.; Soltanieh, M.

2016-09-01

In this study, plasma nitriding was used to fabricate a hard protective layer on AISI P20 steel, at three process temperatures (450°C, 500°C, and 550°C) and over a range of time periods (2.5, 5, 7.5, and 10 h), and at a fixed gas N2:H2 ratio of 75vol%:25vol%. The morphology of samples was studied using optical microscopy and scanning electron microscopy, and the formed phase of each sample was determined by X-ray diffraction. The elemental depth profile was measured by energy dispersive X-ray spectroscopy, wavelength dispersive spectroscopy, and glow dispersive spectroscopy. The hardness profile of the samples was identified, and the microhardness profile from the surface to the sample center was recorded. The results show that ɛ-nitride is the dominant species after carrying out plasma nitriding in all strategies and that the plasma nitriding process improves the hardness up to more than three times. It is found that as the time and temperature of the process increase, the hardness and hardness depth of the diffusion zone considerably increase. Furthermore, artificial neural networks were used to predict the effects of operational parameters on the mechanical properties of plastic mold steel. The plasma temperature, running time of imposition, and target distance to the sample surface were all used as network inputs; Vickers hardness measurements were given as the output of the model. The model accurately reproduced the experimental outcomes under different operational conditions; therefore, it can be used in the effective simulation of the plasma nitriding process in AISI P20 steel.

Novel method for measurement of transistor gate length using energy-filtered transmission electron microscopy

NASA Astrophysics Data System (ADS)

Lee, Sungho; Kim, Tae-Hoon; Kang, Jonghyuk; Yang, Cheol-Woong

2016-12-01

As the feature size of devices continues to decrease, transmission electron microscopy (TEM) is becoming indispensable for measuring the critical dimension (CD) of structures. Semiconductors consist primarily of silicon-based materials such as silicon, silicon dioxide, and silicon nitride, and the electrons transmitted through a plan-view TEM sample provide diverse information about various overlapped silicon-based materials. This information is exceedingly complex, which makes it difficult to clarify the boundary to be measured. Therefore, we propose a simple measurement method using energy-filtered TEM (EF-TEM). A precise and effective measurement condition was obtained by determining the maximum value of the integrated area ratio of the electron energy loss spectrum at the boundary to be measured. This method employs an adjustable slit allowing only electrons with a certain energy range to pass. EF-TEM imaging showed a sharp transition at the boundary when the energy-filter’s passband centre was set at 90 eV, with a slit width of 40 eV. This was the optimum condition for the CD measurement of silicon-based materials involving silicon nitride. Electron energy loss spectroscopy (EELS) and EF-TEM images were used to verify this method, which makes it possible to measure the transistor gate length in a dynamic random access memory manufactured using 35 nm process technology. This method can be adapted to measure the CD of other non-silicon-based materials using the EELS area ratio of the boundary materials.

Thickness Influence on In Vitro Biocompatibility of Titanium Nitride Thin Films Synthesized by Pulsed Laser Deposition

PubMed Central

Duta, Liviu; Stan, George E.; Popa, Adrian C.; Husanu, Marius A.; Moga, Sorin; Socol, Marcela; Zgura, Irina; Miculescu, Florin; Urzica, Iuliana; Popescu, Andrei C.; Mihailescu, Ion N.

2016-01-01

We report a study on the biocompatibility vs. thickness in the case of titanium nitride (TiN) films synthesized on 410 medical grade stainless steel substrates by pulsed laser deposition. The films were grown in a nitrogen atmosphere, and their in vitro cytotoxicity was assessed according to ISO 10993-5 [1]. Extensive physical-chemical analyses have been carried out on the deposited structures with various thicknesses in order to explain the differences in biological behavior: profilometry, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and surface energy measurements. XPS revealed the presence of titanium oxynitride beside TiN in amounts that vary with the film thickness. The cytocompatibility of films seems to be influenced by their TiN surface content. The thinner films seem to be more suitable for medical applications, due to the combined high values of bonding strength and superior cytocompatibility. PMID:28787846

Precipitation and Phase Transformations in 2101 Lean Duplex Stainless Steel During Isothermal Aging

NASA Astrophysics Data System (ADS)

Maetz, Jean-Yves; Cazottes, Sophie; Verdu, Catherine; Kleber, Xavier

2016-01-01

The effect of isothermal aging at 963 K (690 °C) on the microstructure of a 2101 lean duplex stainless steel, with the composition Fe-21.5Cr-5Mn-1.6Ni-0.22N-0.3Mo, was investigated using a multi-technique and multi-scale approach. The kinetics of phase transformation and precipitation was followed from a few minutes to thousands of hours using thermoelectric power measurements; based on these results, certain aging states were selected for electron microscopy characterization. Scanning electron microscopy, electron back-scattered diffraction, and transmission electron microscopy were used to quantitatively describe the microstructural evolution through crystallographic analysis, chemical analysis, and volume fraction measurements from the macroscopic scale down to the nanometric scale. During aging, the precipitation of M23C6 carbides, Cr2N nitrides, and σ phase as well as the transformation of ferrite into austenite and austenite into martensite was observed. These complex microstructural changes are controlled by Cr volume diffusion. The precipitation and phase transformation mechanisms are described.

The Influence of Plasma-Based Nitriding and Oxidizing Treatments on the Mechanical and Corrosion Properties of CoCrMo Biomedical Alloy

NASA Astrophysics Data System (ADS)

Noli, Fotini; Pichon, Luc; Öztürk, Orhan

2018-04-01

Plasma-based nitriding and/or oxidizing treatments were applied to CoCrMo alloy to improve its surface mechanical properties and corrosion resistance for biomedical applications. Three treatments were performed. A set of CoCrMo samples has been subjected to nitriding at moderate temperatures ( 400 °C). A second set of CoCrMo samples was oxidized at 395 °C in pure O2. The last set of CoCrMo samples was nitrided and subsequently oxidized under the experimental conditions of previous sets (double treatment). The microstructure and morphology of the layers formed on the CoCrMo alloy were investigated by X-ray diffraction, Atomic Force Microscopy, and Scanning Electron Microscopy. In addition, nitrogen and oxygen profiles were determined by Glow Discharge Optical Emission Spectroscopy, Rutherford Backscattering Spectroscopy, Energy-Dispersive X-ray, and Nuclear Reaction Analysis. Significant improvement of the Vickers hardness of the CoCrMo samples after plasma nitriding was observed due to the supersaturated nitrogen solution and the formation of an expanded FCC γ N phase and CrN precipitates. In the case of the oxidized samples, Vickers hardness improvement was minimal. The corrosion behavior of the samples was investigated in simulated body fluid (0.9 pct NaCl solution at 37 °C) using electrochemical techniques (potentiodynamic polarization and cyclic voltammetry). The concentration of metal ions released from the CoCrMo surfaces was determined by Instrumental Neutron Activation Analysis. The experimental results clearly indicate that the CoCrMo surface subjected to the double surface treatment consisting in plasma nitriding and plasma oxidizing exhibited lower deterioration and better resistance to corrosion compared to the nitrided, oxidized, and untreated samples. This enhancement is believed to be due to the formation of a thicker and more stable layer.

Atomic bonding effects in annular dark field scanning transmission electron microscopy. II. Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Odlyzko, Michael L.; Held, Jacob T.; Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu

2016-07-15

Quantitatively calibrated annular dark field scanning transmission electron microscopy (ADF-STEM) imaging experiments were compared to frozen phonon multislice simulations adapted to include chemical bonding effects. Having carefully matched simulation parameters to experimental conditions, a depth-dependent bonding effect was observed for high-angle ADF-STEM imaging of aluminum nitride. This result is explained by computational predictions, systematically examined in the preceding portion of this study, showing the propagation of the converged STEM beam to be highly sensitive to net interatomic charge transfer. Thus, although uncertainties in experimental conditions and simulation accuracy remain, the computationally predicted experimental bonding effect withstands the experimental testing reportedmore » here.« less

Imaging TiO2 nanoparticles on GaN nanowires with electrostatic force microscopy

NASA Astrophysics Data System (ADS)

Xie, Ting; Wen, Baomei; Liu, Guannan; Guo, Shiqi; Motayed, Abhishek; Murphy, Thomas; Gomez, R. D.

Gallium nitride (GaN) nanowires that are functionalized with metal-oxides nanoparticles have been explored extensively for gas sensing applications in the past few years. These sensors have several advantages over conventional schemes, including miniature size, low-power consumption and fast response and recovery times. The morphology of the oxide functionalization layer is critical to achieve faster response and recovery times, with the optimal size distribution of nanoparticles being in the range of 10 to 30 nm. However, it is challenging to characterize these nanoparticles on GaN nanowires using common techniques such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Here, we demonstrate electrostatic force microscopy in combination with atomic force microscopy as a non-destructive technique for morphological characterization of the dispersed TiO2 nanoparticles on GaN nanowires. We also discuss the applicability of this method to other material systems with a proposed tip-surface capacitor model. This project was sponsored through N5 Sensors and the Maryland Industrial Partnerships (MIPS, #5418).

Nitride surface passivation of GaAs nanowires: impact on surface state density.

PubMed

Alekseev, Prokhor A; Dunaevskiy, Mikhail S; Ulin, Vladimir P; Lvova, Tatiana V; Filatov, Dmitriy O; Nezhdanov, Alexey V; Mashin, Aleksander I; Berkovits, Vladimir L

2015-01-14

Surface nitridation by hydrazine-sulfide solution, which is known to produce surface passivation of GaAs crystals, was applied to GaAs nanowires (NWs). We studied the effect of nitridation on conductivity and microphotoluminescence (μ-PL) of individual GaAs NWs using conductive atomic force microscopy (CAFM) and confocal luminescent microscopy (CLM), respectively. Nitridation is found to produce an essential increase in the NW conductivity and the μ-PL intensity as well evidence of surface passivation. Estimations show that the nitride passivation reduces the surface state density by a factor of 6, which is of the same order as that found for GaAs/AlGaAs nanowires. The effects of the nitride passivation are also stable under atmospheric ambient conditions for six months.

Boron Nitride Nanoribbons from Exfoliation of Boron Nitride Nanotubes

NASA Technical Reports Server (NTRS)

Hung, Ching-Cheh; Hurst, Janet; Santiago, Diana

2017-01-01

Two types of boron nitride nanotubes (BNNTs) were exfoliated into boron nitride nanoribbons (BNNR), which were identified using transmission electron microscopy: (1) commercial BNNTs with thin tube walls and small diameters. Tube unzipping was indicated by a large decrease of the sample's surface area and volume for pores less than 2 nm in diameter. (2) BNNTs with large diameters and thick walls synthesized at NASA Glenn Research Center. Here, tube unraveling was indicated by a large increase in external surface area and pore volume. For both, the exfoliation process was similar to the previous reported method to exfoliate commercial hexagonal boron nitride (hBN): Mixtures of BNNT, FeCl3, and NaF (or KF) were sequentially treated in 250 to 350 C nitrogen for intercalation, 500 to 750 C air for exfoliation, and finally HCl for purification. Property changes of the nanosized boron nitride throughout this process were also similar to the previously observed changes of commercial hBN during the exfoliation process: Both crystal structure (x-ray diffraction data) and chemical properties (Fourier-transform infrared spectroscopy data) of the original reactant changed after intercalation and exfoliation, but most (not all) of these changes revert back to those of the reactant once the final, purified products are obtained.

Liquid flow cells having graphene on nitride for microscopy

DOEpatents

Adiga, Vivekananda P.; Dunn, Gabriel; Zettl, Alexander K.; Alivisatos, A. Paul

2016-09-20

This disclosure provides systems, methods, and apparatus related to liquid flow cells for microscopy. In one aspect, a device includes a substrate having a first and a second oxide layer disposed on surfaces of the substrate. A first and a second nitride layer are disposed on the first and second oxide layers, respectively. A cavity is defined in the first oxide layer, the first nitride layer, and the substrate, with the cavity including a third nitride layer disposed on walls of the substrate and the second oxide layer that define the cavity. A channel is defined in the second oxide layer. An inlet port and an outlet port are defined in the second nitride layer and in fluid communication with the channel. A plurality of viewports is defined in the second nitride layer. A first graphene sheet is disposed on the second nitride layer covering the plurality of viewports.

Measuring Nanoscale Heat Transfer for Gold-(Gallium Oxide)-Gallium Nitride Interfaces as a Function

NASA Astrophysics Data System (ADS)

Szwejkowski, Chester; Sun, Kai; Constantin, Costel; Giri, Ashutosh; Saltonstall, Christopher; Hopkins, Patrick; NanoSynCh Team; Exsite Team

2014-03-01

Gallium nitride (GaN) is considered the most important semiconductor after the discovery of Silicon. Understanding the properties of GaN is imperative in determining the utility and applicability of this class of materials to devices. We present results of time domain thermoreflectance (TDTR) measurements as a function of surface root mean square (RMS) roughness. We used commercially available 5mm x 5mm, single-side polished GaN (3-7 μm)/Sapphire (430 μm) substrates that have a Wurtzite crystal structure and are slightly n-type doped. The GaN substrates were annealed in the open atmosphere for 10 minutes (900-1000 °C). This high-temperature treatment produced RMS values from 1-60 nm and growth of gallium oxide (GaO) as measured with an atomic force microscopy and transmission electron microscopy respectively. A gold film (80nm) was deposited on the GaN surface using electron beam physical vapor deposition which was verified using ellipsometry and profilometry. The TDTR measurements suggest that the thermal conductivity decays exponentially with RMS roughness and that there is a minimum value for thermal boundary conductance at a roughness of 15nm.

Introduction: A Symposium in Honor of Professor Sir John Meurig Thomas

NASA Astrophysics Data System (ADS)

Gai, P. L.; Saka, H.; Tomokiyo, Y.; Boyes, E. D.

2002-02-01

This issue is dedicated to Professor Sir John Meurig Thomas for his renowned contributions to electron microscopy in the chemical sciences. It is a collection of peer-reviewed leading articles in electron microscopy, based on the presentations at the Microscopy and Microanalysis (M&M) 2000 symposium, which was held to honor Professor Thomas's exceptional scientific leadership and wide-ranging fundamental contributions in the chemical applications of electron microscopy.The issue contains key papers by leading international researchers on the recent developments and applications of electron microscopy in the solid state and liquid state sciences. They include synthesis and characterization of silicon nitride nanorods, nanostructures of amorphous silica, electron microscopy studies of nanoscale structure and chemistry of Pt-Ru electrocatalysts of interest in direct methanol fuel cells, development of in situ wet-environmental transmission electron microscopy for the first nanoscale studies of dynamic liquid-catalyst reactions, strain analysis of silicon by finite element method and energy filtering convergent beam electron diffraction, applications of chemistry with electron microscopy, bismuth nanowires for applications in nanoelectronics technology, synthesis and characterization of quantum dots for superlattices and in situ electron microscopy at very high temperatures to study the motion of W5Si3 on [alpha][beta]-SiN3 substrates.We thank all the participants, including the invited speakers, contributors, and session chairs, who made the symposium successful. We also thank the authors and reviewers of the papers who worked assiduously towards the publication of this issue.We are very grateful to the Microscopy Society of America (MSA) for providing the opportunity to honor Professor Sir John Meurig Thomas. Organizational support from the MSA is also gratefully acknowledged.We thank Charles E. Lyman, editor in chief of Microscopy and Microanalysis for coordinating the publication of this issue and the entire journal staff for their efforts.

Nitrided SrTiO3 as charge-trapping layer for nonvolatile memory applications

NASA Astrophysics Data System (ADS)

Huang, X. D.; Lai, P. T.; Liu, L.; Xu, J. P.

2011-06-01

Charge-trapping characteristics of SrTiO3 with and without nitrogen incorporation were investigated based on Al/Al2O3/SrTiO3/SiO2/Si (MONOS) capacitors. A Ti-silicate interlayer at the SrTiO3/SiO2 interface was confirmed by x-ray photoelectron spectroscopy and transmission electron microscopy. Compared with the MONOS capacitor with SrTiO3 as charge-trapping layer (CTL), the one with nitrided SrTiO3 showed a larger memory window (8.4 V at ±10 V sweeping voltage), higher P/E speeds (1.8 V at 1 ms +8 V) and better retention properties (charge loss of 38% after 104 s), due to the nitrided SrTiO3 film exhibiting higher dielectric constant, higher deep-level traps induced by nitrogen incorporation, and suppressed formation of Ti silicate between the CTL and SiO2 by nitrogen passivation.

Caracterisation of Titanium Nitride Layers Deposited by Reactive Plasma Spraying

NASA Astrophysics Data System (ADS)

Roşu, Radu Alexandru; Şerban, Viorel-Aurel; Bucur, Alexandra Ioana; Popescu, Mihaela; Uţu, Dragoş

2011-01-01

Forming and cutting tools are subjected to the intense wear solicitations. Usually, they are either subject to superficial heat treatments or are covered with various materials with high mechanical properties. In recent years, thermal spraying is used increasingly in engineering area because of the large range of materials that can be used for the coatings. Titanium nitride is a ceramic material with high hardness which is used to cover the cutting tools increasing their lifetime. The paper presents the results obtained after deposition of titanium nitride layers by reactive plasma spraying (RPS). As deposition material was used titanium powder and as substratum was used titanium alloy (Ti6Al4V). Macroscopic and microscopic (scanning electron microscopy) images of the deposited layers and the X ray diffraction of the coatings are presented. Demonstration program with layers deposited with thickness between 68,5 and 81,4 μm has been achieved and presented.

Growth and characterizations of various GaN nanostructures on C-plane sapphire using laser MBE

NASA Astrophysics Data System (ADS)

Ch., Ramesh; Tyagi, P.; Maurya, K. K.; Kumar, M. Senthil; Kushvaha, S. S.

2017-05-01

We have grown various GaN nanostructures such as three-dimensional islands, nanowalls and nanocolumns on c-plane sapphire substrates using laser assisted molecular beam epitaxy (LMBE) system. The shape of the GaN nanostructures was controlled by using different nucleation surfaces such as bare and nitridated sapphire with GaN or AlN buffer layers. The structural and surface morphological properties of grown GaN nanostructures were characterized by ex-situ high resolution x-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy. The symmetric x-ray rocking curve along GaN (0002) plane shows that the GaN grown on pre-nitridated sapphire with GaN or AlN buffer layer possesses good crystalline quality compared to sapphire without nitridation. The Raman spectroscopy measurements revealed the wurtzite phase for all the GaN nanostructures grown on c-sapphire.

Failure Mechanisms of the Protective Coatings for the Hot Stamping Applications

NASA Astrophysics Data System (ADS)

Zhao, Chen

In the present study, four different nitriding techniques were carried on the ductile irons NAAMS-D6510 and cast steels NAAMS-S0050A, which are widely used stamping die materials; duplex treatments (PVD CrN coating+nitriding) were carried on H13 steels, which are common inserts for the hot stamping dies. Inclined impact-sliding wear tests were performed on the nitriding cases under simulated stamping conditions. Surface profilometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to investigate the wear and failure mechanisms of the protective coatings. It was found that the nitrided ductile iron samples performed better than the nitrided cast steel specimens. High temperature inclined impact-sliding wear tests were carried out on the CrN coatings. It was found that the coating performed better at elevated temperature. XPS analysis indicated the top surface layer (about 3-4nm) of the coating was oxidized at 400 °C and formed a Cr2O3 protective film. The in-situ formation of the thin Cr2O3 protective layer likely led to the change of wear mechanisms from severe adhesive failure to mild abrasive wear.

The Structure and Bonding State for Fullerene-Like Carbon Nitride Films with High Hardness Formed by Electron Cyclotron Resonance Plasma Sputtering

NASA Astrophysics Data System (ADS)

Kamata, Tomoyuki; Niwa, Osamu; Umemura, Shigeru; Hirono, Shigeru

2012-12-01

We studied pure carbon films and carbon nitride (CN) films by using electron cyclotron resonance (ECR) sputtering. The main feature of this method is high density ion irradiation during deposition, which enables the pure carbon films to have fullerene-like (FL) structures without nitrogen incorporation. Furthermore, without substrate heating, the ECR sputtered CN films exhibited an enhanced FL microstructure and hardness comparable to that of diamond at intermediate nitrogen concentration. This microstructure consisted of bent and cross-linked graphene sheets where layered areas remarkably decreased due to increased sp3 bonding. Under high nitrogen concentration conditions, the CN films demonstrated extremely low hardness because nitrile bonding not only decreased the covalent-bonded two-dimensional hexagonal network but also annihilated the bonding there. By evaluating lattice images obtained by transmission electron microscopy and the bonding state measured by X-ray photoelectron spectroscopy, we classified the ECR sputtered CN films and offered phase diagram and structure zone diagram.

Static tensile and tensile creep testing of four boron nitride coated ceramic fibers at elevated temperatures

NASA Technical Reports Server (NTRS)

Coguill, Scott L.; Adams, Donald F.; Zimmerman, Richard S.

1989-01-01

Six types of uncoated ceramic fibers were static tensile and tensile creep tested at various elevated temperatures. Three types of boron nitride coated fibers were also tested. Room temperature static tensile tests were initially performed on all fibers, at gage lengths of 1, 2, and 4 inches, to determine the magnitude of end effects from the gripping system used. Tests at one elevated temperature, at gage lengths of 8 and 10 inches, were also conducted, to determine end effects at elevated temperatures. Fiber cross sectional shapes and areas were determined using scanning electron microscopy. Creep testing was typically performed for 4 hours, in an air atmosphere.

Synthesis of galium nitride thin films using sol-gel dip coating method

NASA Astrophysics Data System (ADS)

Hamid, Maizatul Akmam Ab; Ng, Sha Shiong

2017-12-01

In this research, gallium nitride (GaN) thin film were grown on silicon (Si) substrate by a low-cost sol-gel dip coating deposition method. The GaN precursor solution was prepared using gallium (III) nitrate hydrate powder, ethanol and diethanolamine as a starting material, solvent and surfactant respectively. The structural, morphological and optical characteristics of the deposited GaN thin film were investigated. Field-emission scanning electron microscopy observations showed that crack free and dense grains GaN thin films were formed. Energy dispersive X-ray analysis confirmed that the oxygen content in the deposited films was low. X-ray diffraction results revealed that deposited GaN thin films have hexagonal wurtzite structure.

Corrosion resistance of zirconium oxynitride coatings deposited via DC unbalanced magnetron sputtering and spray pyrolysis-nitriding

NASA Astrophysics Data System (ADS)

Cubillos, G. I.; Bethencourt, M.; Olaya, J. J.

2015-02-01

ZrOxNy/ZrO2 thin films were deposited on stainless steel using two different methods: ultrasonic spray pyrolysis-nitriding (SPY-N) and the DC unbalanced magnetron sputtering technique (UBMS). Using the first method, ZrO2 was initially deposited and subsequently nitrided in an anhydrous ammonia atmosphere at 1023 K at atmospheric pressure. For UBMS, the film was deposited in an atmosphere of air/argon with a Φair/ΦAr flow ratio of 3.0. Structural analysis was carried out through X-ray diffraction (XRD), and morphological analysis was done through scanning electron microscopy (SEM) and atomic force microscopy (AFM). Chemical analysis was carried out using X-ray photoelectron spectroscopy (XPS). ZrOxNy rhombohedral polycrystalline film was produced with spray pyrolysis-nitriding, whereas using the UBMS technique, the oxynitride films grew with cubic Zr2ON2 crystalline structures preferentially oriented along the (2 2 2) plane. Upon chemical analysis of the surface, the coatings exhibited spectral lines of Zr3d, O1s, and N1s, characteristic of zirconium oxynitride/zirconia. SEM analysis showed the homogeneity of the films, and AFM showed morphological differences according to the deposition technique of the coatings. Zirconium oxynitride films enhanced the stainless steel's resistance to corrosion using both techniques. The protective efficacy was evaluated using electrochemical techniques based on linear polarization (LP). The results indicated that the layers provide good resistance to corrosion when exposed to chloride-containing media.

Structure analysis of aluminium silicon manganese nitride precipitates formed in grain-oriented electrical steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernier, Nicolas, E-mail: n.bernier@yahoo.fr; Xhoffer, Chris; Van De Putte, Tom, E-mail: tom.vandeputte@arcelormittal.com

We report a detailed structural and chemical characterisation of aluminium silicon manganese nitrides that act as grain growth inhibitors in industrially processed grain-oriented (GO) electrical steels. The compounds are characterised using energy dispersive X-ray spectrometry (EDX) and energy filtered transmission electron microscopy (EFTEM), while their crystal structures are analysed using X-ray diffraction (XRD) and TEM in electron diffraction (ED), dark-field, high-resolution and automated crystallographic orientation mapping (ACOM) modes. The chemical bonding character is determined using electron energy loss spectroscopy (EELS). Despite the wide variation in composition, all the precipitates exhibit a hexagonal close-packed (h.c.p.) crystal structure and lattice parameters ofmore » aluminium nitride. The EDX measurement of ∼ 900 stoichiometrically different precipitates indicates intermediate structures between pure aluminium nitride and pure silicon manganese nitride, with a constant Si/Mn atomic ratio of ∼ 4. It is demonstrated that aluminium and silicon are interchangeably precipitated with the same local arrangement, while both Mn{sup 2+} and Mn{sup 3+} are incorporated in the h.c.p. silicon nitride interstitial sites. The oxidation of the silicon manganese nitrides most likely originates from the incorporation of oxygen during the decarburisation annealing process, thus creating extended planar defects such as stacking faults and inversion domain boundaries. The chemical composition of the inhibitors may be written as (AlN){sub x}(SiMn{sub 0.25}N{sub y}O{sub z}){sub 1−x} with x ranging from 0 to 1. - Highlights: • We study the structure of (Al,Si,Mn)N inhibitors in grain oriented electrical steels. • Inhibitors have the hexagonal close-packed symmetry with lattice parameters of AlN. • Inhibitors are intermediate structures between pure AlN and (Si,Mn)N with Si/Mn ∼ 4. • Al and Si share the same local arrangement; Mn is incorporated in both Mn{sup 2+} and Mn{sup 3+}. • Oxygen incorporation is invoked to account for the thermal stability of (Al,Si,Mn)N.« less

Growth Structure and Properties of Gradient Nanocrystalline Coatings of the Ti-Al-Si-Cu-N System

NASA Astrophysics Data System (ADS)

Ovchinnikov, S. V.; Pinzhin, Yu. P.

2016-10-01

Methods of electron microprobe analysis, X-ray structure analysis and electron microscopy were used to study the element composition and features of the structure-phase, elastic stress state of nanocrystalline coatings of the Ti- Al- Si- Cu- N system with gradient of copper concentration across their thickness. The authors established the effects of element composition modification, non-monotonous behavior of the lattice constant of alloyed nitride and rise in the bending-torsion value of the crystalline lattice in individual nanocrystals to values of around 400 degrees/μm with increase in copper concentration, whereas the sizes of alloyed nitride crystals remained practically unchanged. Mechanical (hardness), adhesion and tribological properties of coatings were examined. Comparative analysis demonstrates higher values of adhesion characteristics in the case of gradient coatings of the Ti- Al- Si- Cu- N system than in the case of single-layer (with constant element concentration) analogues.

Study program to develop and evaluate die and container materials for the growth of silicon ribbons. [for development of low cost solar cells

NASA Technical Reports Server (NTRS)

Addington, L. A.; Ownby, P. D.; Yu, B. B.; Barsoum, M. W.; Romero, H. V.; Zealer, B. G.

1979-01-01

The development and evaluation of proprietary coatings of pure silicon carbide, silicon nitride, and aluminum nitride on less pure hot pressed substrates of the respective ceramic materials, is described. Silicon sessile drop experiments were performed on coated test specimens under controlled oxygen partial pressure. Prior to testing, X-ray diffraction and SEM characterization was performed. The reaction interfaces were characterized after testing with optical and scanning electron microscopy and Auger electron spectroscopy. Increasing the oxygen partial pressure was found to increase the molten silicon contact angle, apparently because adsorbed oxygen lowers the solid-vapor interfacial free energy. It was also found that adsorbed oxygen increased the degree of attack of molten silicon upon the chemical vapor deposited coatings. Cost projections show that reasonably priced, coated, molten silicon resistant refractory material shapes are obtainable.

Substrate nitridation induced modulations in transport properties of wurtzite GaN/p-Si (100) heterojunctions grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhat, Thirumaleshwara N.; Rajpalke, Mohana K.; Krupanidhi, S. B.

Phase pure wurtzite GaN films were grown on Si (100) substrates by introducing a silicon nitride layer followed by low temperature GaN growth as buffer layers. GaN films grown directly on Si (100) were found to be phase mixtured, containing both cubic ({beta}) and hexagonal ({alpha}) modifications. The x-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN films grown with silicon nitride buffer layer grown at 800 deg. C when compared to the samples grown in the absence of silicon nitridemore » buffer layer and with silicon nitride buffer layer grown at 600 deg. C. Core-level photoelectron spectroscopy of Si{sub x}N{sub y} layers reveals the sources for superior qualities of GaN epilayers grown with the high temperature substrate nitridation process. The discussion has been carried out on the typical inverted rectification behavior exhibited by n-GaN/p-Si heterojunctions. Considerable modulation in the transport mechanism was observed with the nitridation conditions. The heterojunction fabricated with the sample of substrate nitridation at high temperature exhibited superior rectifying nature with reduced trap concentrations. Lowest ideality factors ({approx}1.5) were observed in the heterojunctions grown with high temperature substrate nitridation which is attributed to the recombination tunneling at the space charge region transport mechanism at lower voltages and at higher voltages space charge limited current conduction is the dominating transport mechanism. Whereas, thermally generated carrier tunneling and recombination tunneling are the dominating transport mechanisms in the heterojunctions grown without substrate nitridation and low temperature substrate nitridation, respectively.« less

Defect-selective dry etching for quick and easy probing of hexagonal boron nitride domains.

PubMed

Wu, Qinke; Lee, Joohyun; Park, Sangwoo; Woo, Hwi Je; Lee, Sungjoo; Song, Young Jae

2018-03-23

In this study, we demonstrate a new method to selectively etch the point defects or the boundaries of as-grown hexagonal boron nitride (hBN) films and flakes in situ on copper substrates using hydrogen and argon gases. The initial quality of the chemical vapor deposition-grown hBN films and flakes was confirmed by UV-vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy. Different gas flow ratios of Ar/H 2 were then employed to etch the same quality of samples and it was found that etching with hydrogen starts from the point defects and grows epitaxially, which helps in confirming crystalline orientations. However, etching with argon is sensitive to line defects (boundaries) and helps in visualizing the domain size. Finally, based on this defect-selective dry etching technique, it could be visualized that the domains of a polycrystalline hBN monolayer merged together with many parts, even with those that grew from a single nucleation seed.

Defect-selective dry etching for quick and easy probing of hexagonal boron nitride domains

NASA Astrophysics Data System (ADS)

Wu, Qinke; Lee, Joohyun; Park, Sangwoo; Woo, Hwi Je; Lee, Sungjoo; Song, Young Jae

2018-03-01

In this study, we demonstrate a new method to selectively etch the point defects or the boundaries of as-grown hexagonal boron nitride (hBN) films and flakes in situ on copper substrates using hydrogen and argon gases. The initial quality of the chemical vapor deposition-grown hBN films and flakes was confirmed by UV-vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy. Different gas flow ratios of Ar/H2 were then employed to etch the same quality of samples and it was found that etching with hydrogen starts from the point defects and grows epitaxially, which helps in confirming crystalline orientations. However, etching with argon is sensitive to line defects (boundaries) and helps in visualizing the domain size. Finally, based on this defect-selective dry etching technique, it could be visualized that the domains of a polycrystalline hBN monolayer merged together with many parts, even with those that grew from a single nucleation seed.

Boron nitride nanotubes enhance properties of chitosan-based scaffolds.

PubMed

Emanet, Melis; Kazanç, Emine; Çobandede, Zehra; Çulha, Mustafa

2016-10-20

With their low toxicity, high mechanical strength and chemical stability, boron nitride nanotubes (BNNTs) are good candidates to enhance the properties of polymers, composites and scaffolds. Chitosan-based scaffolds are exhaustively investigated in tissue engineering because of their biocompatibility and antimicrobial activity. However, their spontaneous degradation prevents their use in a range of tissue engineering applications. In this study, hydroxylated BNNTs (BNNT-OH) were included into a chitosan scaffold and tested for their mechanical strength, swelling behavior and biodegradability. The results show that inclusion of BNNTs-OH into the chitosan scaffold increases the mechanical strength and pore size at values optimal for high cellular proliferation and adhesion. The chitosan/BNNT-OH scaffold was also found to be non-toxic to Human Dermal Fibroblast (HDF) cells due to its slow degradation rate. HDF cell proliferation and adhesion were increased as compared to the chitosan-only scaffold as observed by scanning electron microscopy (SEM) and fluorescent microscopy images. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dynamic determination of secondary electron emission using a calorimetric probe in a plasma immersion ion implantation experiment

NASA Astrophysics Data System (ADS)

Haase, Fabian; Manova, Darina; Hirsch, Dietmar; Mändl, Stephan; Kersten, Holger

2018-04-01

A passive thermal probe has been used to detect dynamic changes in the secondary electron emission (SEE). Oxidized and nitrided materials have been studied during argon ion sputtering in a plasma immersion ion implantation process. Identical measurements have been performed for the metallic state with high voltage pulses accelerating nitrogen ions towards the surface, supposedly forming a nitride layer. Energy flux data were combined with scanning electron microscopy images of the surface to obtain information about the actual surface composition as well as trends and changes during the process. Within the measurements, a direct comparison of the SEE within both employed ion species (argon and nitrogen) is possible while an absolute quantification is still open. Additionally, the nominal composition of the investigated oxide and nitride layers does not always correspond to stoichiometric compounds. Nevertheless, the oxides showed a remarkably higher SEE compared to the pure metals, while an indistinct behavior was observed for the nitrides: some higher, some lower than the clean metal surfaces. For the aluminum alloy AlMg3 a complex time dependent evolution was observed with consecutive oxidation/sputtering cycles leading to a very rough surface with a diminished oxide layer, leading to an almost black surface of the metal and non-reproducible changes in the SEE. The presented method is a versatile technique for measuring dynamic changes of the surface for materials commonly used in PVD processes with a time resolution of about 1 min, e.g. magnetron sputtering or HiPIMS, where changes in the target or electrode composition are occurring but cannot be measured directly.

Surface characterization of nickel titanium orthodontic arch wires

PubMed Central

Krishnan, Manu; Seema, Saraswathy; Tiwari, Brijesh; Sharma, Himanshu S.; Londhe, Sanjay; Arora, Vimal

2015-01-01

Background Surface roughness of nickel titanium orthodontic arch wires poses several clinical challenges. Surface modification with aesthetic/metallic/non metallic materials is therefore a recent innovation, with clinical efficacy yet to be comprehensively evaluated. Methods One conventional and five types of surface modified nickel titanium arch wires were surface characterized with scanning electron microscopy, energy dispersive analysis, Raman spectroscopy, Atomic force microscopy and 3D profilometry. Root mean square roughness values were analyzed by one way analysis of variance and post hoc Duncan's multiple range tests. Results Study groups demonstrated considerable reduction in roughness values from conventional in a material specific pattern: Group I; conventional (578.56 nm) > Group V; Teflon (365.33 nm) > Group III; nitride (301.51 nm) > Group VI (i); rhodium (290.64 nm) > Group VI (ii); silver (252.22 nm) > Group IV; titanium (229.51 nm) > Group II; resin (158.60 nm). It also showed the defects with aesthetic (resin/Teflon) and nitride surfaces and smooth topography achieved with metals; titanium/silver/rhodium. Conclusions Resin, Teflon, titanium, silver, rhodium and nitrides were effective in decreasing surface roughness of nickel titanium arch wires albeit; certain flaws. Findings have clinical implications, considering their potential in lessening biofilm adhesion, reducing friction, improving corrosion resistance and preventing nickel leach and allergic reactions. PMID:26843749

Formation of Different Si3N4 Nanostructures by Salt-Assisted Nitridation.

PubMed

Liu, Xiongzhang; Guo, Ran; Zhang, Sengjing; Li, Qingda; Saito, Genki; Yi, Xuemei; Nomura, Takahiro

2018-04-11

Silicon nitride (Si 3 N 4 ) products with different nanostructure morphologies and different phases for Si 3 N 4 ceramic with high thermal conductivity were synthesized by a direct nitriding method. NaCl and NH 4 Cl were added to raw Si powders, and the reaction was carried out under a nitrogen gas flow of 100 mL/min. The phase composition and morphologies of the products were systemically characterized by X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy. At 1450 °C, the NaCl content was 30 wt %, the NH 4 Cl content was 3 wt %, and the maximum α-Si 3 N 4 content was 96 wt %. The process of Si nitridation can be divided into three stages by analyzing the reaction schemes: in the first stage (25-900 °C), NH 4 Cl decomposition and the generation of stacked amorphous Si 3 N 4 occurs; in the second stage (900-1450 °C), NaCl melts and Si 3 N 4 generates; and in the third stage (>1450 °C), α-Si 3 N 4 → β-Si 3 N 4 phase change and the evaporation of NaCl occurs. The products are made of two layers: a thin upper layer of nanowires containing different nanostructures and a lower layer mainly comprising fluffy, blocky, and short needlelike products. The introduction of NaCl and NH 4 Cl facilitated the evaporation of Si powders and the decomposition of Al 2 O 3 from porcelain boat and furnace tube, which resulted in the mixing of N 2 , O 2 , Al 2 O, and Si vapors and generated Al x Si y O z nanowires with rough surfaces and lead to thin Si 3 N 4 nanowires, nanobranches by the vapor-solid (VS), vapor-liquid-solid (VLS), and the double-stage VLS base and VS tip growth mechanisms.

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy.

PubMed

Hermannsdörfer, Justus; de Jonge, Niels

2017-02-05

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

PubMed Central

Hermannsdörfer, Justus; de Jonge, Niels

2017-01-01

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline. PMID:28190028

Nanopore fabrication and characterization by helium ion microscopy

NASA Astrophysics Data System (ADS)

Emmrich, D.; Beyer, A.; Nadzeyka, A.; Bauerdick, S.; Meyer, J. C.; Kotakoski, J.; Gölzhäuser, A.

2016-04-01

The Helium Ion Microscope (HIM) has the capability to image small features with a resolution down to 0.35 nm due to its highly focused gas field ionization source and its small beam-sample interaction volume. In this work, the focused helium ion beam of a HIM is utilized to create nanopores with diameters down to 1.3 nm. It will be demonstrated that nanopores can be milled into silicon nitride, carbon nanomembranes, and graphene with well-defined aspect ratio. To image and characterize the produced nanopores, helium ion microscopy and high resolution scanning transmission electron microscopy were used. The analysis of the nanopores' growth behavior allows inferring on the profile of the helium ion beam.

Solid-state nanopores of controlled geometry fabricated in a transmission electron microscope

NASA Astrophysics Data System (ADS)

Qian, Hui; Egerton, Ray F.

2017-11-01

Energy-filtered transmission electron microscopy and electron tomography were applied to in situ studies of the formation, shape, and diameter of nanopores formed in a silicon nitride membrane in a transmission electron microscope. The nanopore geometry was observed in three dimensions by electron tomography. Drilling conditions, such as probe current, beam convergence angle, and probe position, affect the formation rate and the geometry of the pores. With a beam convergence semi-angle of α = 22 mrad, a conical shaped nanopore is formed but at α = 45 mrad, double-cone (hourglass-shaped) nanopores were produced. Nanopores with an effective diameter between 10 nm and 1.8 nm were fabricated by controlling the drilling time.

Laser Processing of Metals and Polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singaravelu, Senthilraja

2012-05-01

A laser offers a unique set of opportunities for precise delivery of high quality coherent energy. This energy can be tailored to alter the properties of material allowing a very flexible adjustment of the interaction that can lead to melting, vaporization, or just surface modification. Nowadays laser systems can be found in nearly all branches of research and industry for numerous applications. Sufficient evidence exists in the literature to suggest that further advancements in the field of laser material processing will rely significantly on the development of new process schemes. As a result they can be applied in various applicationsmore » starting from fundamental research on systems, materials and processes performed on a scientific and technical basis for the industrial needs. The interaction of intense laser radiation with solid surfaces has extensively been studied for many years, in part, for development of possible applications. In this thesis, I present several applications of laser processing of metals and polymers including polishing niobium surface, producing a superconducting phase niobium nitride and depositing thin films of niobium nitride and organic material (cyclic olefin copolymer). The treated materials were examined by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), atomic force microscopy (AFM), high resolution optical microscopy, surface profilometry, Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD). Power spectral density (PSD) spectra computed from AFM data gives further insight into the effect of laser melting on the topography of the treated niobium.« less

Evolution dependence of vanadium nitride nanoprecipitates on directionality of ion irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, L.; Kim, B. K.; Was, G. S.

The influence of the directionality of Fe 2+ ion irradiation on the evolution of vanadium nitride platelet–shaped nanoprecipitates at 500 °C was investigated in this paper in a ferritic alloy using transmission electron microscopy. When the ion-irradiation direction was approximately aligned with the initial particle length, particles grew longer and sectioned into shorter lengths at higher doses, resulting in increased particle densities. As ion-irradiation direction deviated from particle-length direction, some particles sectioned lengthwise and then dissolved, resulting in decreased particle densities. Surviving particles were transformed into parallelograms with a different orientation relationship with the matrix. Finally, nanoprecipitate evolution dependence onmore » beam-nanoprecipitate orientation is a process that may be different from reactor irradiation.« less

Evolution dependence of vanadium nitride nanoprecipitates on directionality of ion irradiation

DOE PAGES

Tan, L.; Kim, B. K.; Was, G. S.

2017-09-06

The influence of the directionality of Fe 2+ ion irradiation on the evolution of vanadium nitride platelet–shaped nanoprecipitates at 500 °C was investigated in this paper in a ferritic alloy using transmission electron microscopy. When the ion-irradiation direction was approximately aligned with the initial particle length, particles grew longer and sectioned into shorter lengths at higher doses, resulting in increased particle densities. As ion-irradiation direction deviated from particle-length direction, some particles sectioned lengthwise and then dissolved, resulting in decreased particle densities. Surviving particles were transformed into parallelograms with a different orientation relationship with the matrix. Finally, nanoprecipitate evolution dependence onmore » beam-nanoprecipitate orientation is a process that may be different from reactor irradiation.« less

Silicon nitride grids are compatible with correlative negative staining electron microscopy and tip-enhanced Raman spectroscopy for use in the detection of micro-organisms.

PubMed

Lausch, V; Hermann, P; Laue, M; Bannert, N

2014-06-01

Successive application of negative staining transmission electron microscopy (TEM) and tip-enhanced Raman spectroscopy (TERS) is a new correlative approach that could be used to rapidly and specifically detect and identify single pathogens including bioterrorism-relevant viruses in complex samples. Our objective is to evaluate the TERS-compatibility of commonly used electron microscopy (EM) grids (sample supports), chemicals and negative staining techniques and, if required, to devise appropriate alternatives. While phosphortungstic acid (PTA) is suitable as a heavy metal stain, uranyl acetate, paraformaldehyde in HEPES buffer and alcian blue are unsuitable due to their relatively high Raman scattering. Moreover, the low thermal stability of the carbon-coated pioloform film on copper grids (pioloform grids) negates their utilization. The silicon in the cantilever of the silver-coated atomic force microscope tip used to record TERS spectra suggested that Si-based grids might be employed as alternatives. From all evaluated Si-based TEM grids, the silicon nitride (SiN) grid was found to be best suited, with almost no background Raman signals in the relevant spectral range, a low surface roughness and good particle adhesion properties that could be further improved by glow discharge. Charged SiN grids have excellent particle adhesion properties. The use of these grids in combination with PTA for contrast in the TEM is suitable for subsequent analysis by TERS. The study reports fundamental modifications and optimizations of the negative staining EM method that allows a combination with near-field Raman spectroscopy to acquire a spectroscopic signature from nanoscale biological structures. This should facilitate a more precise diagnosis of single viral particles and other micro-organisms previously localized and visualized in the TEM. © 2014 The Society for Applied Microbiology.

Plasma enhanced ultrastable self-powered visible-blind deep ultraviolet photodetector based on atomically thin boron nitride sheets

NASA Astrophysics Data System (ADS)

Feng, Peter Xianping; Rivera, Manuel; Velazquez, Rafael; Aldalbahi, Ali

We extend our work on the use of digitally controlled plasma deposition technique to synthesize high quality boron nitride nanosheets (BNNSs). The nanoscale morphologies and layered growth characteristics of the BNNSs were characterized using scanning electron microscope, transmission electron microscopy, and atomic force microscopy. The experimental data indicated each sample consists of multiple atomically thin, highly transparent BNNSs that overlap one another with certain orientations. Purity and structural properties were characterized by Raman scattering, XRD, FTIR and XPS. Based on these characterizations, 2D BNNSs based self-powered, visible blind deep UV detectors were designed, fabricated, and tested. The bias, temperature, and humidity effects on the photocurrent strength were investigated. A significant increase of signal-to-noise ratio after plasma treatment was observed. The fabricated photodetectors presented exceptional properties: a very stable baseline and a high sensitivity to weak intensities of radiation in both UVC and UVB range while remaining visible-blind, a high signal-to-noise ratio, and excellent repeatability even when the operating temperature was up to 400 0C. The shift in cutoff wavelength was also observed. This work is supported by the Army Research Office/DoD Grant (62826-RT-REP) and the ISPP#0058 at King Saud University.

Electrophoretic deposition of hydroxyapatite-hexagonal boron nitride composite coatings on Ti substrate.

PubMed

Göncü, Yapıncak; Geçgin, Merve; Bakan, Feray; Ay, Nuran

2017-10-01

In this study, commercial pure titanium samples were coated with nano hydroxyapatite-nano hexagonal boron nitride (nano HA-nano hBN) composite by electrophoretic deposition (EPD). The effect of process parameters (applied voltage, deposition time and solid concentration) on the coating morphology, thickness and the adhesion behavior were studied systematically and crack free nano hBN-nano HA composite coating production was achieved for developing bioactive coatings on titanium substrates for orthopedic applications. For the examination of structural and morphological characteristics of the coating surfaces, various complementary analysis methods were performed. For the structural characterization, XRD and Raman Spectroscopy were used while, Scanning Electron Microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) and Transmission Electron Microscopy (TEM) techniques were carried out for revealing the morphological characterization. The results showed that nano HA-nano hBN were successfully deposited on Ti surface with uniform, crack-free coating by EPD. The amounts of hBN in suspension are considered to have no effect on coating thickness. By adding hBN into HA, the morphology of HA did not change and hBN has no significant effect on porous structure. These nanostructured surfaces are expected to be suitable for proliferation of cells and have high potential for bioactive materials. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of starting powder characteristics on density, microstructure and low temperature oxidation behavior of a Si3N48w/o Y2O3 ceramic

NASA Technical Reports Server (NTRS)

Schuon, S.; Dutta, S.

1980-01-01

The densification and oxidation behavior of Si3N4 - 8w/oY2O3 prepared from three commercial starting powders were studied. Bars of SN 402, SN 502, and CP 85/15 were sintered for 3 to 4.5 hours at 1750 C. A second set was hot pressed for 2 hours at 1750 C. The microstructures were studied by transmission electron microscopy and scanning electron microscopy, densities were determined, and the phase compositions were determined by X-ray diffraction. Densification and microstructure were greatly influenced by the starting powder morphology and impurity content. Although SN 402 exhibited the maximum weight lose, the highest sintered and hot pressed densities were obtained with this powder. All powders had both equiaxed and elongated grains. Sintered bars were composed of beta silicon nitride and n-melelite. In contrast, hot pressed bars contained beta silicon nitride, H-phase, and J-phase, but no melelite. Yttria distribution in sintered bars was related to the presence of cation impurities such as Ca, Fe, and Mg. A limited oxidation study at 750 C in air showed no instability in these Si3N4 - 8 w/oY2O3 specimens, regardless of startin powder.

Qualitative and quantitative interpretation of SEM image using digital image processing.

PubMed

Saladra, Dawid; Kopernik, Magdalena

2016-10-01

The aim of the this study is improvement of qualitative and quantitative analysis of scanning electron microscope micrographs by development of computer program, which enables automatic crack analysis of scanning electron microscopy (SEM) micrographs. Micromechanical tests of pneumatic ventricular assist devices result in a large number of micrographs. Therefore, the analysis must be automatic. Tests for athrombogenic titanium nitride/gold coatings deposited on polymeric substrates (Bionate II) are performed. These tests include microshear, microtension and fatigue analysis. Anisotropic surface defects observed in the SEM micrographs require support for qualitative and quantitative interpretation. Improvement of qualitative analysis of scanning electron microscope images was achieved by a set of computational tools that includes binarization, simplified expanding, expanding, simple image statistic thresholding, the filters Laplacian 1, and Laplacian 2, Otsu and reverse binarization. Several modifications of the known image processing techniques and combinations of the selected image processing techniques were applied. The introduced quantitative analysis of digital scanning electron microscope images enables computation of stereological parameters such as area, crack angle, crack length, and total crack length per unit area. This study also compares the functionality of the developed computer program of digital image processing with existing applications. The described pre- and postprocessing may be helpful in scanning electron microscopy and transmission electron microscopy surface investigations. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society.

The metalorganic chemical vapor deposition of III-V nitrides for optoelectronic device applications

NASA Astrophysics Data System (ADS)

Grudowski, Paul Alexander

Nitride-based light-emitting diodes (LEDs) and laser diodes are important for large-area LED displays, flat-panel displays, traffic signals, and optical data storage, due to their characteristic ultraviolet and visible light emission. However, much of the research and development addressing material related problems is recent. The room-temperature continuous wave (CW) operation of nitride-based laser diodes remains a major milestone because the material quality requirements for these devices are extremely high. This study investigates nitride material development by the metalorganic chemical vapor deposition (MOCVD) and characterization of GaN, AlGaN, and InGaN, and by qualifying these materials with fabricated devices. The ultimate goal was to develop a working laser diode. The nitride epitaxial films were characterized by 300K Hall effect, x-ray diffraction (XRD), photoluminescence (PL), cathodoluminescence (CL), secondary ion mass spectroscopy (SIMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). GaN grown heteroepitaxially on (0001) sapphire substrates was first optimized. A low-temperature GaN nucleation layer was developed that gave subsequent high-temperature GaN layers with low background carrier concentrations (n < 1×10sp{17}\\ cmsp{-3}). Intentional p-type hole concentrations up to 2× 10sp{18} cmsp{-3} and n-type electron concentrations up to 1× 10sp{19} cmsp{-3} were achieved at 300K with magnesium and silicon, respectively. The ternary alloy Insb{x}Gasb{1-x}N was grown with indium compositions up to x = 0.25. These films exhibited strong and narrow 300K PL bandedge peaks. Multiple-quantum-well structures with Insb{0.13}Gasb{0.87}N wells and Insb{0.03}Gasb{0.97}N barriers were grown and gave enhanced PL intensity compared to single InGaN layers. Modulation-doped MQW's produced enhanced PL intensity compared to uniformly-doped MQW's. 300K photopumping experiments produced stimulated emission from a five-period MQW. Light-emitting device structures comprised of InGaN MQW active regions and p-type and n-type GaN contact layers and AlGaN confinement layers were grown and fabricated. LED's showed bright emission at a wavelength of 400 nm. While optically pumped lasers were demonstrated, no injection lasing action was achieved in these devices. GaN grown by selective area lateral epitaxial overgrowth (SALEO) has reduced dislocation defect density and, therefore, may prove to be a promising substrate for nearly defect-free device structures. Plan-view and cross-sectional CL was used to compare spatial inhomogeneities in the bandedge luminescence.

Direct Growth of CuO Nanorods on Graphitic Carbon Nitride with Synergistic Effect on Thermal Decomposition of Ammonium Perchlorate.

PubMed

Tan, Linghua; Xu, Jianhua; Li, Shiying; Li, Dongnan; Dai, Yuming; Kou, Bo; Chen, Yu

2017-05-02

Novel graphitic carbon nitride/CuO (g-C₃N₄/CuO) nanocomposite was synthesized through a facile precipitation method. Due to the strong ion-dipole interaction between copper ions and nitrogen atoms of g-C₃N₄, CuO nanorods (length 200-300 nm, diameter 5-10 nm) were directly grown on g-C₃N₄, forming a g-C₃N₄/CuO nanocomposite, which was confirmed via X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). Finally, thermal decomposition of ammonium perchlorate (AP) in the absence and presence of the prepared g-C₃N₄/CuO nanocomposite was examined by differential thermal analysis (DTA), and thermal gravimetric analysis (TGA). The g-C₃N₄/CuO nanocomposite showed promising catalytic effects for the thermal decomposition of AP. Upon addition of 2 wt % nanocomposite with the best catalytic performance (g-C₃N₄/20 wt % CuO), the decomposition temperature of AP was decreased by up to 105.5 °C and only one decomposition step was found instead of the two steps commonly reported in other examples, demonstrating the synergistic catalytic activity of the as-synthesized nanocomposite. This study demonstrated a successful example regarding the direct growth of metal oxide on g-C₃N₄ by ion-dipole interaction between metallic ions, and the lone pair electrons on nitrogen atoms, which could provide a novel strategy for the preparation of g-C₃N₄-based nanocomposite.

Dynamic consolidation of cubic boron nitride and its admixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, H.; Ahrens, T.J.

1988-09-01

Cubic boron nitride (C-BN) powders admixed with graphite-structured boron nitride powder (g-BN), silicon carbide whisker (SCW), or silicon nitride whisker (SNW) were shock compacted to pressures up to 22 GPa. Unlike previous work with diamond and graphite (D. K. Potter and T. J. Ahrens, J. Appl. Phys. 63, 910 (1987)) it was found that the addition of g-BN inhibited dynamic consolidation. Good consolidation was achieved with a 4--8 ..mu..m particle size C-BN powder admixed with 15 wt.% SNW or 20 wt.% SCW. Whereas a 37--44 ..mu..m particle size C-BN mixture was only poorly consolidated. Scanning electron microscopy (SEM) analysis demonstratemore » that SCW and SNW in the mixtures were highly deformed and indicated melt textures. A skin heating model was used to describe the physics of consolidation. Model calculations are consistent with SEM analysis images that indicate plastic deformation of SCW and SNW. Micro-Vickers hardness values as high as 50 GPa were obtained for consolidated C-BN and SNW mixtures. This compares to 21 GPa for single-crystal Al/sub 2/O/sub 3/ and 120 GPa for diamond.« less

Deep eutectic solvent approach towards nickel/nickel nitride nanocomposites

DOE PAGES

Gage, Samuel H.; Ruddy, Daniel A.; Pylypenko, Svitlana; ...

2016-12-15

Nickel nitride is an attractive material for a broad range of applications including catalysis. However preparations and especially those targeting nanoscale particles remain a major challenge. Herein, we report a wet-chemical approach to produce nickel/nickel nitride nanocomposites using deep eutectic solvents. A choline chloride/urea deep eutectic solvent was used as a reaction medium to form gels containing nickel acetate tetrahydrate. Heat treatment of the gel in inert atmosphere forms nanoparticles embedded within a nitrogen-doped carbon matrix. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to understand the decomposition profile of the precursors and to select pyrolysis temperatures locatedmore » in regions of thermal stability. X-ray diffraction (XRD) confirmed the presence of metallic nickel, whereas X-ray photoelectron spectroscopy (XPS) suggested the existence of a nickel nitride surface layer. According to transmission electron microscopy (TEM) analysis these mixed phase, possibly core-shell type nanoparticles, have very defined facets. Furthermore, these materials represent a unique opportunity to tune catalytic properties of nickel-based catalysts through control of their composition, surface structure, and morphology; in addition to employing potential benefits of a nitrogen-doped carbon support.« less

Doped indium nitride thin film by sol-gel spin coating method

NASA Astrophysics Data System (ADS)

Lee, Hui San; Ng, Sha Shiong; Yam, Fong Kwong

2017-12-01

In this study, magnesium doped indium nitride (InN:Mg) thin films grown on silicon (100) substrate were prepared via sol-gel spin coating method followed by nitridation process. A custom-made tube furnace was used to perform the nitridation process. Through this method, the low dissociation temperature issue of InN:Mg thin films can be solved. The deposited InN:Mg thin films were investigated using various techniques. The X-rays diffraction results revealed that two intense diffraction peaks correspond to wurtzite structure InN (100), and InN (101) were observed at 29° and 33.1° respectively. Field emission scanning electron microscopy images showed that the surface of the films exhibits densely packed grains. The elemental composition of the deposited thin films was analyzed using energy dispersive X-rays spectroscopy. The detected atomic percentages for In, N, and Mg were 43.22 %, 3.28 %, and 0.61 % respectively. The Raman spectra showed two Raman- and infrared-active modes of E2 (High) and A1 (LO) of the wurtzite InN. The band gap obtained from the Tauc plot showed around 1.74 eV. Lastly, the average surface roughness measured by AFM was around 0.133 µm.

Non-carbon titanium cobalt nitride nanotubes supported platinum catalyst with high activity and durability for methanol oxidation reaction

NASA Astrophysics Data System (ADS)

Chen, Xiaoxiang; Li, Wuyi; Pan, Zhanchang; Xu, Yanbin; Liu, Gen; Hu, Guanghui; Wu, Shoukun; Li, Jinghong; Chen, Chun; Lin, Yingsheng

2018-05-01

Titanium cobalt nitride nanotubes (Ti0.95Co0.05N NTs) hybrid support, a novel robust non-carbon support material prepared by solvothermal and post-nitriding processes, is further decorated with Pt nanoparticles for the electrooxidation of methanol. The catalyst is characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The morphology, structure and composition of the synthesized Ti0.95Co0.05N NTs suggest that the nanotube wall is porous and consists of homogeneous cohesively attached nitrides nanocube particles. Notable, Ti0.95Co0.05N NTs supported Pt catalyst exhibits significantly improved catalytic activity and durability for methanol electrooxidation compared with the conventional JM Pt/C catalyst. The experimental data indicate that enhanced catalytic activity and stability of Pt/Ti0.95Co0.05N NTs towards methanol electrooxidation might be mainly attributed to the tubular nanostructures and synergistic effect introduced by the Co doping. Both of them are playing an important role in improving the activity and durability of the Ti0.95Co0.05N NTs catalyst.

Measurement of Minority Charge Carrier Diffusion Length in Gallium Nitride Nanowires Using Electron Beam Induced Current (EBIC)

DTIC Science & Technology

2009-12-01

MINORITY CHARGE CARRIER DIFFUSION LENGTH IN GALLIUM NITRIDE NANOWIRES USING ELECTRON BEAM INDUCED CURRENT (EBIC) by Chiou Perng Ong December... Gallium Nitride Nanowires Using Electron Beam Induced Current (EBIC) 6. AUTHOR(S) Ong, Chiou Perng 5. FUNDING NUMBERS DMR 0804527 7. PERFORMING...CARRIER DIFFUSION LENGTH IN GALLIUM NITRIDE NANOWIRES USING ELECTRON BEAM INDUCED CURRENT (EBIC) Chiou Perng Ong Major, Singapore Armed Forces B

Full-scale characterization of UVLED Al(x)Ga(1-x)N nanowires via advanced electron microscopy.

PubMed

Phillips, Patrick J; Carnevale, Santino D; Kumar, Rajan; Myers, Roberto C; Klie, Robert F

2013-06-25

III-Nitride semiconductor heterostructures continue to attract a great deal of attention due to the wide range of wavelengths at which they can emit light, and the subsequent desire to employ them in optoelectronic applications. Recently, a new type of pn-junction which relies on polarization-induced doping has shown promise for use as an ultraviolet light emitting diode (UVLED); nanowire growth of this device has been successfully demonstrated. However, as these devices are still in their infancy, in order to more fully understand their physical and electronic properties, they require a multitude of characterization techniques. Specifically, the present contribution will discuss the application of advanced scanning transmission electron microscopy (STEM) to AlxGa1-xN UVLED nanowires. In addition to structural data, chemical and electronic properties will also be probed through various spectroscopy techniques, with the focus remaining on practically applying the knowledge gained via STEM to the growth procedures in order to optimize device peformance.

Nondestructive evaluation of structural ceramics by photoacoustic microscopy

NASA Technical Reports Server (NTRS)

Khandelwal, Pramod K.

1987-01-01

A photoacoustic microscopy (PAM) digital imaging system was developed and utilized to characterize silicon nitride material at the various stages of the ceramic fabrication process. Correlation studies revealed that photoacoustic microscopy detected failure initiating defects in substantially more specimens than microradiography and ultrasonic techniques. Photoacoustic microscopy detected 10 to 100 micron size surface and subsurface pores and inclusions, respectively, up to 80 microns below the interrogating surface in machined sintered silicon nitride. Microradiography detected 50 micron diameter fracture controlling pores and inclusions. Subsurface holes were detected up to a depth of 570 microns and 1.00 mm in sintered silicon nitride and silicon carbide, respectively. Seeded voids of 20 to 30 micron diameters at the surface and 50 microns below the interrogating surface were detected by photoacoustic microscopy and microradiography with 1 percent X-ray thickness sensitivity. Tight surface cracks of 96 micron length x 48 micron depth were detected by photoacoustic microscopy. PAM volatilized and removed material in the green state which resulted in linear shallow microcracks after sintering. This significantly limits the use of PAM as an in-process NDE technique.

Low-energy Cathodoluminescence for (Oxy)Nitride Phosphors

PubMed Central

Cho, Yujin; Dierre, Benjamin; Sekiguchi, Takashi; Suehiro, Takayuki; Takahashi, Kohsei; Takeda, Takashi; Xie, Rong-Jun; Yamamoto, Yoshinobu; Hirosaki, Naoto

2016-01-01

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and flexibility of their emission properties can be achieved by controlling their composition and dopants. However, a lot of work is still required to improve their properties and to reduce the production cost. A possible approach is to correlate the luminescence properties of the Sialon particles with their local structural and chemical environment in order to optimize their growth parameters and find novel phosphors. For such a purpose, the low-voltage cathodoluminescence (CL) microscopy is a powerful technique. The use of electron as an excitation source allows detecting most of the luminescence centers, revealing their luminescence distribution spatially and in depth, directly comparing CL results with the other electron-based techniques, and investigating the stability of their luminescence properties under stress. Such advantages for phosphors characterization will be highlighted through examples of investigation on several Sialon phosphors by low-energy CL. PMID:27911365

Characterization of rhenium nitride films produced by reactive pulsed laser deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soto, G.; Rosas, A.; Farias, M.H.

2007-06-15

Rhenium nitride (ReN {sub x}) films were grown on (100)-Si substrates by the reactive pulsed laser deposition (PLD) method using a high purity Re rod in an environment of molecular nitrogen. The resulting films are characterized by several techniques, which include in situ Auger electron spectroscopy, X-ray photoelectron spectroscopy and ex situ X-ray diffraction, scanning electron and atomic force microscopy. Additionally, the four-probe method is used to determine the sheet resistance of deposited layers. Results show that films with N/Re ratios (x) lower than 1.3 are very good conductors. In fact, the resistivity of ReN films for 0.2 < xmore » < 1.3 is of the order of 5% of that of Re films, while at x = 1.3 there is an abrupt increment in resistivity, resulting in dielectric films for 1.3 < x < 1.35. These results differ from the prior understanding that in transition metals, resistivity should increase with nitrogen incorporation.« less

Characterization of stress corrosion cracks in Ni-based weld alloys 52, 52M and 152 grown in high-temperature water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Yi; Wu, Yaqiao; Burns, Jatuporn

Ni-based weld alloys 52, 52M and 152 are extensively used in repair and mitigation of primary water stress corrosion cracking (SCC) in nuclear power plants. In the present study, a series of microstructure and microchemistry at the SCC tips of these alloys were examined with scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM) and energy filtered transmission electron microscopy (EFTEM). The specimens have similar chemical compositions and testing conditions. Intergranular (IG) and transgranular (TG) SCC was observed in all of them. The cracks were filled with nickel-oxidesmore » and partial precipitations of chrome carbides (CrCs), niobium carbides (NbCs), titanium nitrides (TiNs) and silicon carbides (SiCs), while iron (Fe) was largely dissolved into the solution. However, the crack densities, lengths and distributions were different for all three specimens. - Highlights: • Microstructure and microchemistry at the SCC tips of Ni-based weld alloys 52, 52M and 152 were examined. • The crack densities, lengths and distributions were found to be different for different alloys. • IGSCC and TGSCC were observed on alloy 52, only TGSCC was observed on alloy 52M and 152. • The cracks were filled by Ni-oxides and precipitated CrCs, NbCs, TiNs and SiCs.« less

One-Step Synthesis of Fluorescent Boron Nitride Quantum Dots via a Hydrothermal Strategy Using Melamine as Nitrogen Source for the Detection of Ferric Ions.

PubMed

Huo, Bingbing; Liu, Bingping; Chen, Tao; Cui, Liang; Xu, Gengfang; Liu, Mengli; Liu, Jingquan

2017-10-10

A facile and effective approach for the preparation of functionalized born nitride quantum dots (BNQDs) with blue fluorescence was explored by the hydrothermal treatment of the mixture of boric acid and melamine at 200 °C for 15 h. The as-prepared BNQDs were characterized by transmission electron microscopy (TEM), high-resolution TEM, atomic force microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and fluorescence spectroscopy. The single layered BNQDs with the average size of 3 nm showed a blue light emission under the illumination of the UV light. The BNQDs could be easily dispersed in an aqueous medium and applied as fluorescent probes for selective detection of Fe 3+ with remarkable selectivity and sensitivity (the lowest detection limit was 0.3 μM). The fluorescence fiber imaging demonstrated that the as-prepared quantum dots could be used as a valuable fluorchrome. Therefore, the BNQDs could be envisioned for potential applications in many fields such as biocompatible staining, fluorescent probes, and biological labeling.

A novel passivation process of silicon nanowires by a low-cost PECVD technique for deposition of hydrogenated silicon nitride using SiH4 and N2 as precursor gases

NASA Astrophysics Data System (ADS)

Bouaziz, Lamia; Dridi, Donia; Karyaoui, Mokhtar; Angelova, Todora; Sanchez Plaza, Guillermo; Chtourou, Radhouane

2017-03-01

In this work, a different SiNx passivation process of silicon nanowires has been opted for the deposition of a hydrogenated silicon nitride (SiNx:H) by a low-cost plasma enhanced chemical vapor deposition (PECVD) using silane ( SiH4 and nitrogen ( N2 as reactive gases. This study is focused on the effect of the gas flow ratio on chemical composition, morphological, optical and optoelectronic properties of silicon nanowires. The existence of Si-N and Si-H bonds was proven by the Fourier transmission infrared (FTIR) spectrum. Morphological structures were shown by scanning electron microscopy (SEM), and the roughness was investigated by atomic force microscopy (AFM). A low reflectivity less than 6% in the wavelength range 250-1200nm has been shown by UV-visible spectroscopy. Furthermore, the thickness and the refractive index of the passivation layer is determined by ellipsometry measurements. As a result, an improvement in minority carrier lifetime has been obtained by reducing surface recombination of silicon nanowires.

A Microstructural Analysis of Orientation Variation in Epitaxial AlN on Si, Its Probable Origin, and Effect on Subsequent GaN Growth

NASA Technical Reports Server (NTRS)

Beye, R.; George, T.; Yang, J. W.; Khan, M. A.

1996-01-01

A structural examination of aluminum nitride growth on [111] silicon was carried out using transmission electron microscopy. Electron diffraction indicates that the basal planes of the wurtzitic overlayer mimic the orientation of the close-packed planes of the substrate. However, considerable, random rotation in the basal plane and random out-of-plane tilts were evident. This article examines these issues with a structural examination of AlN and GaN/AlN on silicon and compares the findings to those reported in the literature.

Oxidation of silicon nitride sintered with rare-earth oxide additions

NASA Technical Reports Server (NTRS)

Mieskowski, D. M.; Sanders, W. A.

1985-01-01

The effects of rare-earth oxide additions on the oxidation of sintered Si3N4 were examined. Insignificant oxidation occurred at 700 and 1000 C, with no evidence of phase instability. At 1370 C, the oxidation rate was lowest for Y2O3 and increased for additions of La2O3, Sm2O3, and CeO2, in that order. Data obtained from X-ray diffraction, electron microprobe analysis, and scanning electron microscopy indicate that oxidation occurs via diffusion of cationic species from Si3N4 grain boundaries.

Switching behaviors of graphene-boron nitride nanotube heterojunctions

DOE PAGES

Parashar, Vyom; Durand, Corentin P.; Hao, Boyi; ...

2015-07-20

High electron mobility of graphene has enabled their application in high-frequency analogue devices but their gapless nature has hindered their use in digital switches. In contrast, the structural analogous, h-BN sheets and BN nanotubes (BNNTs) are wide band gap insulators. Here we show that the growth of electrically insulating BNNTs on graphene can enable the use of graphene as effective digital switches. These graphene-BNNT heterojunctions were characterized at room temperature by four-probe scanning tunneling microscopy (4-probe STM) under real-time monitoring of scanning electron microscopy (SEM). A switching ratio as high as 105 at a turn-on voltage as low as 0.5more » V were recorded. Simulation by density functional theory (DFT) suggests that mismatch of the density of states (DOS) is responsible for these novel switching behaviors.« less

Experimental observation of boron nitride chains.

PubMed

Cretu, Ovidiu; Komsa, Hannu-Pekka; Lehtinen, Ossi; Algara-Siller, Gerardo; Kaiser, Ute; Suenaga, Kazu; Krasheninnikov, Arkady V

2014-12-23

We report the formation and characterization of boron nitride atomic chains. The chains were made from hexagonal boron nitride sheets using the electron beam inside a transmission electron microscope. We find that the stability and lifetime of the chains are significantly improved when they are supported by another boron nitride layer. With the help of first-principles calculations, we prove the heteroatomic structure of the chains and determine their mechanical and electronic properties. Our study completes the analogy between various boron nitride and carbon polymorphs, in accordance with earlier theoretical predictions.

Interface formation in monolayer graphene-boron nitride heterostructures.

PubMed

Sutter, P; Cortes, R; Lahiri, J; Sutter, E

2012-09-12

The ability to control the formation of interfaces between different materials has become one of the foundations of modern materials science. With the advent of two-dimensional (2D) crystals, low-dimensional equivalents of conventional interfaces can be envisioned: line boundaries separating different materials integrated in a single 2D sheet. Graphene and hexagonal boron nitride offer an attractive system from which to build such 2D heterostructures. They are isostructural, nearly lattice-matched, and isoelectronic, yet their different band structures promise interesting functional properties arising from their integration. Here, we use a combination of in situ microscopy techniques to study the growth and interface formation of monolayer graphene-boron nitride heterostructures on ruthenium. In a sequential chemical vapor deposition process, boron nitride grows preferentially at the edges of existing monolayer graphene domains, which can be exploited for synthesizing continuous 2D membranes of graphene embedded in boron nitride. High-temperature growth leads to intermixing near the interface, similar to interfacial alloying in conventional heterostructures. Using real-time microscopy, we identify processes that eliminate this intermixing and thus pave the way to graphene-boron nitride heterostructures with atomically sharp interfaces.

Investigation of features of plastic deformation and fracture of fine-crystalline V-4Ti-4Cr alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grinyaev, Konstantin V., E-mail: kvgrinyaev@inbox.ru; Tyumentsev, Alexander N., E-mail: tyuments@phys.tsu.ru; Siberian Physical-Technical Institute, Tomsk, 634050

2014-11-14

With the use of transmission electron microscopy the investigation of defect substructure was carried out in the V-4Ti-4Cr-(C, N, O) alloy with disperse strengthening (by nanoparticles of oxy-carbo-nitride phase) after deformation by active tension at temperatures of 20 and 800 °C. It has been shown that an important feature of plastic deformation is deformation localization with crystal lattice reorientation.

2D molybdenum and vanadium nitrides synthesized by ammoniation of 2D transition metal carbides (MXenes)

DOE PAGES

Urbankowski, Patrick; Anasori, Babak; Hantanasirisakul, Kanit; ...

2017-11-08

MXenes are a rapidly growing class of 2D transition metal carbides and nitrides, finding applications in fields ranging from energy storage to electromagnetic interference shielding and transparent conductive coatings. However, while more than 20 carbide MXenes have already been synthesized, Ti 4N 3 and Ti 2N are the only nitride MXenes reported so far. Here by ammoniation of Mo 2CT x and V 2CT x MXenes at 600 °C, we report on their transformation to 2D metal nitrides. Carbon atoms in the precursor MXenes are replaced with N atoms, resulting from the decomposition of ammonia molecules. The crystal structures ofmore » the resulting Mo 2N and V 2N were determined with transmission electron microscopy and X-ray pair distribution function analysis. Our results indicate that Mo 2N retains the MXene structure and V 2C transforms to a mixed layered structure of trigonal V 2N and cubic VN. Temperature-dependent resistivity measurements of the nitrides reveal that they exhibit metallic conductivity, as opposed to semiconductor-like behavior of their parent carbides. As important, room-temperature electrical conductivity values of Mo2N and V2N are three and one order of magnitude larger than those of the Mo 2CT x and V 2CT x precursors, respectively. In conclusion, this study shows how gas treatment synthesis such as ammoniation can transform carbide MXenes into 2D nitrides with higher electrical conductivities and metallic behavior, opening a new avenue in 2D materials synthesis.« less

Direct electrochemistry of cytochrome c immobilized on titanium nitride/multi-walled carbon nanotube composite for amperometric nitrite biosensor.

PubMed

Haldorai, Yuvaraj; Hwang, Seung-Kyu; Gopalan, Anantha-Iyengar; Huh, Yun Suk; Han, Young-Kyu; Voit, Walter; Sai-Anand, Gopalan; Lee, Kwang-Pill

2016-05-15

In this report, titanium nitride (TiN) nanoparticles decorated multi-walled carbon nanotube (MWCNTs) nanocomposite is fabricated via a two-step process. These two steps involve the decoration of titanium dioxide nanoparticles onto the MWCNTs surface and a subsequent thermal nitridation. Transmission electron microscopy shows that TiN nanoparticles with a mean diameter of ≤ 20 nm are homogeneously dispersed onto the MWCNTs surface. Direct electrochemistry and electrocatalysis of cytochrome c immobilized on the MWCNTs-TiN composite modified on a glassy carbon electrode for nitrite sensing are investigated. Under optimum conditions, the current response is linear to its concentration from 1 µM to 2000 µM with a sensitivity of 121.5 µA µM(-1)cm(-2) and a low detection limit of 0.0014 µM. The proposed electrode shows good reproducibility and long-term stability. The applicability of the as-prepared biosensor is validated by the successful detection of nitrite in tap and sea water samples. Copyright © 2015 Elsevier B.V. All rights reserved.

Near-infrared emitting In-rich InGaN layers grown directly on Si: Towards the whole composition range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aseev, Pavel, E-mail: pavel.aseev@upm.es; Rodriguez, Paul E. D. Soto; Gómez, Víctor J.

The authors report compact and chemically homogeneous In-rich InGaN layers directly grown on Si (111) by plasma-assisted molecular beam epitaxy. High structural and optical quality is evidenced by transmission electron microscopy, near-field scanning optical microscopy, and X-ray diffraction. Photoluminescence emission in the near-infrared is observed up to room temperature covering the important 1.3 and 1.55 μm telecom wavelength bands. The n-InGaN/p-Si interface is ohmic due to the absence of any insulating buffer layers. This qualitatively extends the application fields of III-nitrides and allows their integration with established Si technology.

Gallium nitride nanoneedles grown in extremely non-equilibrium nitrogen plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mangla, O., E-mail: onkarmangla@gmail.com; Physics Department, Hindu College, University of Delhi, Delhi, 110007; Roy, S.

2016-05-23

In the present work, gallium nitride (GaN) nanoneedles are grown on quartz substrates using the high fluence ions of GaN produced by hot, dense and extremely non-equlibrium nitrogen plasma in a modified dense plasma focus device. The formation of nanoneedles is obtained from the scanning electron microscopy with mean size of the head of nanoneedles ~ 70 nm. The nanoneedles are found to be poly-crystalline when studied structurally through the X-ray diffraction. The optical properties of nanoneedles studied using absorption spectra which show more absorption for nanoneedles depsoited one shot of ions irradiation. In addition, the band gap of nanoneedles ismore » found to be increased as compared to bulk GaN. The obtained nanoneedles with increased band gap have potential applications in detector systems.« less

Direct growth of graphene on in situ epitaxial hexagonal boron nitride flakes by plasma-assisted molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza

2015-11-23

Hexagonal boron nitride (h-BN) single-crystal domains were grown on cobalt (Co) substrates at a substrate temperature of 850–900 °C using plasma-assisted molecular beam epitaxy. Three-point star shape h-BN domains were observed by scanning electron microscopy, and confirmed by Raman and X-ray photoelectron spectroscopy. The h-BN on Co template was used for in situ growth of multilayer graphene, leading to an h-BN/graphene heterostructure. Carbon atoms preferentially nucleate on Co substrate and edges of h-BN and then grow laterally to form continuous graphene. Further introduction of carbon atoms results in layer-by-layer growth of graphene on graphene and lateral growth of graphene on h-BNmore » until it may cover entire h-BN flakes.« less

Tribological properties of CrN coatings deposited by nitro-chromizing treatment on AISI D2 steel

NASA Astrophysics Data System (ADS)

Durmaz, M.; Kilinc, B.; Abakay, E.; Sen, U.; Sen, S.

2015-03-01

In this work, the wear test of uncoated and chromium nitride coated AISI D2 cold work tool steel against alumina ball realized at 0.1 m/s sliding speeds and under the loads of 2.5N, 5N and 10N. Steel samples were nitrided at 575°C for 8 h in the first step of the coating process, and then chromium nitride coating was performed thermo-reactive deposition technique (TRD) in a powder mixture consisting of ferro-chromium, ammonium chloride and alumina at 1000°C for 2 h. Nitro-chromized samples were characterized by X-Ray diffraction analysis (XRD), scanning electron microscopy (SEM), micro-hardness and ball on disk wear tests. The coating layer formed on the AISI D2 steel was compact and homogeneous. X-ray studies showed that the phase formed in the coated layer is Cr2N. The depth of the layer was 8.15 µm. The average hardness of the layer was 2160±15 HV0.025. For uncoated and chromium nitride materials, wear rate increased with increasing load. The results of friction coefficient and wear rate of the tested materials showed that the CrN coating presents the lowest results.

Tribological properties of CrN coatings deposited by nitro-chromizing treatment on AISI D2 steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durmaz, M., E-mail: mdurmaz@sakarya.edu.tr; Abakay, E.; Sen, U.

2015-03-30

In this work, the wear test of uncoated and chromium nitride coated AISI D2 cold work tool steel against alumina ball realized at 0.1 m/s sliding speeds and under the loads of 2.5N, 5N and 10N. Steel samples were nitrided at 575°C for 8 h in the first step of the coating process, and then chromium nitride coating was performed thermo-reactive deposition technique (TRD) in a powder mixture consisting of ferro-chromium, ammonium chloride and alumina at 1000°C for 2 h. Nitro-chromized samples were characterized by X-Ray diffraction analysis (XRD), scanning electron microscopy (SEM), micro-hardness and ball on disk wear tests. The coating layermore » formed on the AISI D2 steel was compact and homogeneous. X-ray studies showed that the phase formed in the coated layer is Cr{sub 2}N. The depth of the layer was 8.15 µm. The average hardness of the layer was 2160±15 HV{sub 0.025}. For uncoated and chromium nitride materials, wear rate increased with increasing load. The results of friction coefficient and wear rate of the tested materials showed that the CrN coating presents the lowest results.« less

Influence of BN fiber coatings on the interfacial structure of sapphire fiber reinforced NiAl composites

NASA Astrophysics Data System (ADS)

Reichert, K.; Wen, K.; Cremer, R.; Hu, W.; Neuschütz, D.; Gottstein, G.

2001-07-01

A new concept for a tailored fiber-matrix interface for sapphire fiber reinforced NiAl matrix composites is proposed, consisting of an initial hexagonal boron nitride (hBN) fiber coating. For this, single crystal Al 2O 3 fibers were coated with hBN by chemical vapor deposition (CVD). Following a comprehensive characterization of the CVD coating as to composition and structure by means of X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray diffraction (GIXRD), the fiber reinforced NiAl matrix composites were fabricated by diffusion bonding at 1400°C. The interfaces NiAl/BN and BN/Al 2O 3 were analyzed by scanning electron microscopy (SEM), analytical transmission electron microscopy (TEM), and selected area diffraction (SAD). An interfacial reaction between NiAl and hBN to form AlN was revealed using these analytical techniques.

Excellent electrical conductivity of the exfoliated and fluorinated hexagonal boron nitride nanosheets.

PubMed

Xue, Yafang; Liu, Qian; He, Guanjie; Xu, Kaibing; Jiang, Lin; Hu, Xianghua; Hu, Junqing

2013-01-24

The insulator characteristic of hexagonal boron nitride limits its applications in microelectronics. In this paper, the fluorinated hexagonal boron nitride nanosheets were prepared by doping fluorine into the boron nitride nanosheets exfoliated from the bulk boron nitride in isopropanol via a facile chemical solution method with fluoboric acid; interestingly, these boron nitride nanosheets demonstrate a typical semiconductor characteristic which were studied on a new scanning tunneling microscope-transmission electron microscope holder. Since this property changes from an insulator to a semiconductor of the boron nitride, these nanosheets will be able to extend their applications in designing and fabricating electronic nanodevices.

Application of modern surface analytical tools in the investigation of surface deterioration processes

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1983-01-01

Surface profilometry and scanning electron microscopy were utilized to study changes in the surface of polymers when eroded. The X-ray photoelectron spectroscopy (XPS) and depth profile analysis indicate the corrosion of metal and ceramic surfaces and reveal the diffusion of certain species into the surface to produce a change in mechanical properties. Ion implantation, nitriding and plating and their effects on the surface are characterized. Auger spectroscopy analysis identified morphological properties of coatings applied to surfaces by sputter deposition.

Microwave Integrated Circuit Amplifier Designs Submitted to Qorvo for Fabrication with 0.09-micron High Electron Mobility Transistors (HEMTs) using 2-mil Gallium Nitride (GaN) on Silicon Carbide (SiC)

DTIC Science & Technology

2016-03-01

Fabrication with 0.09-µm High-Electron-Mobility Transistors (HEMTs) Using 2-mil Gallium Nitride (GaN) on Silicon Carbide (SiC) by John E Penn...for Fabrication with 0.09-µm High-Electron-Mobility Transistors (HEMTs) using 2-mil Gallium Nitride (GaN) on Silicon Carbide by John E Penn...µm High-Electron-Mobility Transistors (HEMTs) using 2-mil Gallium Nitride (GaN) on Silicon Carbide 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c

Electric field dynamics in nitride structures containing quaternary alloy (Al, In, Ga)N

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borysiuk, J., E-mail: jolanta.borysiuk@ifpan.edu.pl; Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw; Sakowski, K.

2016-07-07

Molecular beam epitaxy growth and basic physical properties of quaternary AlInGaN layers, sufficiently thick for construction of electron blocking layers (EBL), embedded in ternary InGaN layers are presented. Transmission electron microscopy (TEM) measurement revealed good crystallographic structure and compositional uniformity of the quaternary layers contained in other nitride layers, which are typical for construction of nitride based devices. The AlInGaN layer was epitaxially compatible to InGaN matrix, strained, and no strain related dislocation creation was observed. The strain penetrated for limited depth, below 3 nm, even for relatively high content of indium (7%). For lower indium content (0.6%), the strain wasmore » below the detection limit by TEM strain analysis. The structures containing quaternary AlInGaN layers were studied by time dependent photoluminescence (PL) at different temperatures and excitation powers. It was shown that PL spectra contain three peaks: high energy donor bound exciton peak from the bulk GaN (DX GaN) and the two peaks (A and B) from InGaN layers. No emission from quaternary AlInGaN layers was observed. An accumulation of electrons on the EBL interface in high-In sample and formation of 2D electron gas (2DEG) was detected. The dynamics of 2DEG was studied by time resolved luminescence revealing strong dependence of emission energy on the 2DEG concentration. Theoretical calculations as well as power-dependence and temperature-dependence analysis showed the importance of electric field inside the structure. At the interface, the field was screened by carriers and could be changed by illumination. From these measurements, the dynamics of electric field was described as the discharge of carriers accumulated on the EBL.« less

Growth and characterization of manganese doped gallium nitride nanowires.

PubMed

Kumar, V Suresh; Kesavamoorthy, R; Kumar, J

2008-08-01

Manganese doped GaN nanowires have been grown by chemical vapour transport method on sapphire (0001) substrates in the temperature range of 800-1050 degrees C. The surface features of nanowires have been investigated using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray analysis (EDAX), Raman scattering studies and Electron Paramagnetic Resonance (EPR). SEM images showed that the morphology of the one dimensional materials included straight nanorods and nanowires around 70-80 nm. Raman spectrum showed the GaMnN vibrational modes at 380, 432 and 445 cm(-1). EPR measurements were performed on Mn doped GaN nanowires in order to evaluate the magnetic behaviour.

Iron single crystal growth from a lithium-rich melt

NASA Astrophysics Data System (ADS)

Fix, M.; Schumann, H.; Jantz, S. G.; Breitner, F. A.; Leineweber, A.; Jesche, A.

2018-03-01

α -Fe single crystals of rhombic dodecahedral habit were grown from a Li84N12Fe∼3 melt. Crystals of several millimeter along a side form at temperatures around T ≈ 800 ° C. Upon further cooling the growth competes with the formation of Fe-doped Li3N. The b.c.c. structure and good sample quality of α -Fe single crystals were confirmed by X-ray and electron diffraction as well as magnetization measurements and chemical analysis. A nitrogen concentration of 90 ppm was detected by means of carrier gas hot extraction. Scanning electron microscopy did not reveal any sign of iron nitride precipitates.

Structural, electronic, mechanical and magnetic properties of rare earth nitrides REN (RE= Pm, Eu and Yb)

NASA Astrophysics Data System (ADS)

Murugan, A.; Rajeswarapalanichamy, R.; Santhosh, M.; Iyakutti, K.

2015-07-01

The structural, electronic and mechanical properties of rare earth nitrides REN (RE=Pm, Eu and Yb) are investigated in NaCl and CsCl, and zinc blende structures using first principles calculations based on density functional theory. The calculated lattice parameters are in good agreement with the available results. Among the considered structures, these nitrides are most stable in NaCl structure. A pressure induced structural phase transition from NaCl to CsCl phase is observed in all these nitrides. The electronic structure reveals that these rare earth nitrides are half metallic at normal pressure. These nitrides are found to be covalent and ionic in the stable phase. The computed elastic constants indicate that these nitrides are mechanically stable and elastically anisotropic. Our results confirm that these nitrides are ferromagnetic in nature. A ferromagnetic to non-magnetic phase transition is observed at the pressures of 21.5 GPa and 46.1 GPa in PmN and YbN respectively.

Thermionic field emission in gold nitride Schottky nanodiodes

NASA Astrophysics Data System (ADS)

Spyropoulos-Antonakakis, N.; Sarantopoulou, E.; Kollia, Z.; Samardžija, Z.; Kobe, S.; Cefalas, A. C.

2012-11-01

We report on the thermionic field emission and charge transport properties of gold nitride nanodomains grown by pulsed laser deposition with a molecular fluorine laser at 157 nm. The nanodomains are sandwiched between the metallic tip of a conductive atomic force microscope and a thin gold layer forming thus a metal-semiconductor-metal junction. Although the limited existing data in the literature indicate that gold nitride was synthesized previously with low efficiency, poor stability, and metallic character; in this work, it is shown that gold nitride nanodomains exhibit semiconducting behavior and the metal-semiconductor-metal contact can be modeled with the back-to-back Schottky barrier model. From the experimental I-V curves, the main charge carrier transport process is found to be thermionic field emission via electron tunneling. The rectifying, near symmetric and asymmetric current response of nanocontacts is related to the effective contact area of the gold nitride nanodomains with the metals. A lower limit for the majority charge carriers concentration at the boundaries of nanodomains is also established using the full depletion approximation, as nanodomains with thickness as low as 6 nm were found to be conductive. Current rectification and charge memory effects are also observed in "quite small" conductive nanodomains (6-10 nm) due to stored charges. Indeed, charges near the surface are identified as inversion domains in the phase shift mapping performed with electrostatic force microscopy and are attributed to charge trapping at the boundaries of the nanodomains.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Urbankowski, Patrick; Anasori, Babak; Hantanasirisakul, Kanit

MXenes are a rapidly growing class of 2D transition metal carbides and nitrides, finding applications in fields ranging from energy storage to electromagnetic interference shielding and transparent conductive coatings. However, while more than 20 carbide MXenes have already been synthesized, Ti 4N 3 and Ti 2N are the only nitride MXenes reported so far. Here by ammoniation of Mo 2CT x and V 2CT x MXenes at 600 °C, we report on their transformation to 2D metal nitrides. Carbon atoms in the precursor MXenes are replaced with N atoms, resulting from the decomposition of ammonia molecules. The crystal structures ofmore » the resulting Mo 2N and V 2N were determined with transmission electron microscopy and X-ray pair distribution function analysis. Our results indicate that Mo 2N retains the MXene structure and V 2C transforms to a mixed layered structure of trigonal V 2N and cubic VN. Temperature-dependent resistivity measurements of the nitrides reveal that they exhibit metallic conductivity, as opposed to semiconductor-like behavior of their parent carbides. As important, room-temperature electrical conductivity values of Mo2N and V2N are three and one order of magnitude larger than those of the Mo 2CT x and V 2CT x precursors, respectively. In conclusion, this study shows how gas treatment synthesis such as ammoniation can transform carbide MXenes into 2D nitrides with higher electrical conductivities and metallic behavior, opening a new avenue in 2D materials synthesis.« less

Structural modifications and corrosion behavior of martensitic stainless steel nitrided by plasma immersion ion implantation

NASA Astrophysics Data System (ADS)

Figueroa, C. A.; Alvarez, F.; Zhang, Z.; Collins, G. A.; Short, K. T.

2005-07-01

In this work we report a study of the structural modifications and corrosion behavior of martensitic stainless steels (MSS) nitrided by plasma immersion ion implantation (PI3). The samples were characterized by x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, photoemission electron spectroscopy, and potentiodynamic electrochemical measurements. Depending on the PI3 treatment temperature, three different material property trends are observed. At lower implantation temperatures (e.g., 360 °C), the material corrosion resistance is improved and a compact phase of ɛ-(Fe,Cr)3N, without changes in the crystal morphology, is obtained. At intermediate temperatures (e.g., 430 °C), CrN precipitates form principally at grain boundaries, leading to a degradation in the corrosion resistance compared to the original MSS material. At higher temperatures (e.g., 500 °C), the relatively great mobility of the nitrogen and chromium in the matrix induced random precipitates of CrN, transforming the original martensitic phase into α-Fe (ferrite), and causing a further degradation in the corrosion resistance.

Temperature-triggered chemical switching growth of in-plane and vertically stacked graphene-boron nitride heterostructures

PubMed Central

Gao, Teng; Song, Xiuju; Du, Huiwen; Nie, Yufeng; Chen, Yubin; Ji, Qingqing; Sun, Jingyu; Yang, Yanlian; Zhang, Yanfeng; Liu, Zhongfan

2015-01-01

In-plane and vertically stacked heterostructures of graphene and hexagonal boron nitride (h-BN-G and G/h-BN, respectively) are both recent focuses of graphene research. However, targeted synthesis of either heterostructure remains a challenge. Here, via chemical vapour deposition and using benzoic acid precursor, we have achieved the selective growth of h-BN-G and G/h-BN through a temperature-triggered switching reaction. The perfect in-plane h-BN-G is characterized by scanning tunnelling microscopy (STM), showing atomically patched graphene and h-BN with typical zigzag edges. In contrast, the vertical alignment of G/h-BN is confirmed by unique lattice-mismatch-induced moiré patterns in high-resolution STM images, and two sets of aligned selected area electron diffraction spots, both suggesting a van der Waals epitaxial mechanism. The present work demonstrates the chemical designability of growth process for controlled synthesis of graphene and h-BN heterostructures. With practical scalability, high uniformity and quality, our approach will promote the development of graphene-based electronics and optoelectronics. PMID:25869236

Comparative study of the interfaces of graphene and hexagonal boron nitride with silver

NASA Astrophysics Data System (ADS)

Garnica, Manuela; Schwarz, Martin; Ducke, Jacob; He, Yuanqin; Bischoff, Felix; Barth, Johannes V.; Auwärter, Willi; Stradi, Daniele

2016-10-01

Silver opens up interesting perspectives in the fabrication of complex systems based on heteroepitaxial layers after the growth of a silicene layer on its (111) face has been proposed. In this work we explore different synthesis methods of hexagonal boron nitride (h -BN) and graphene sheets on silver. The resulting layers have been examined by high-resolution scanning tunneling microscopy. A comparison of the interfacial electronic band structure upon growth of the distinct two-dimensional (2D) layers has been performed by scanning tunneling spectroscopy and complementary first-principle calculations. We demonstrate that the adsorption of the 2D layers has an effect on the binding energy of the Shockley state and the surface potential by lowering the local work function. These effects are larger in the case of graphene where the surface state of Ag(111) is depopulated due to charge transfer to the graphene. Furthermore, we show that the electronic properties of the h -BN/silver system can be tuned by employing different thicknesses of silver ranging from a few monolayers on Cu(111) to the single crystal Ag substrate.

Atomically Thin Graphene Windows That Enable High Contrast Electron Microscopy without a Specimen Vacuum Chamber.

PubMed

Han, Yimo; Nguyen, Kayla X; Ogawa, Yui; Park, Jiwoong; Muller, David A

2016-12-14

Scanning electron microscopes (SEMs) require a high vacuum environment to generate and shape an electron beam for imaging; however, the vacuum conditions greatly limit the nature of specimens that can be examined. From a purely scattering physics perspective, it is not necessary to place the specimen inside the vacuum chamber-the mean free paths (MFPs) for electron scattering in air at typical SEM beam voltages are 50-100 μm. This is the idea behind the airSEM, which removes the specimen vacuum chamber from the SEM and places the sample in air. The thickness of the gas layer is less than a MFP from an electron-transparent window to preserve the shape and resolution of the incident beam, resulting in comparable imaging quality to an all-vacuum SEM. Present silicon nitride windows scatter far more strongly than the air gap and are currently the contrast and resolution limiting factor in the airSEM. Graphene windows have been used previously to wrap or seal samples in vacuum for imaging. Here we demonstrate the use of a robust bilayer graphene window for sealing the electron optics from the room environment, providing an electron transparent window with only a 2% drop in contrast. There is a 5-fold-increase in signal/noise ratio for imaging compared to multi-MFP-thick silicon nitride windows, enabling high contrast in backscattered, transmission, and surface imaging modes for the new airSEM geometry.

Femtosecond laser-induced periodic surface structures on titanium nitride coatings for tribological applications

NASA Astrophysics Data System (ADS)

Bonse, J.; Kirner, S. V.; Koter, R.; Pentzien, S.; Spaltmann, D.; Krüger, J.

2017-10-01

Titanium nitride (TiN) was coated on different substrate materials, namely pure titanium (Ti), titanium alloy (Ti6Al4V) and steel (100Cr6), generating 2.5 μm thick TiN layers. Using femtosecond laser pulses (30 fs, 790 nm, 1 kHz pulse repetition rate), large surface areas (5 mm × 5 mm) of laser-induced periodic surface structures (LIPSS) with sub-wavelength periods ranging between 470 nm and 600 nm were generated and characterized by optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM). In tribological tests, coefficients of friction (COF) of the nanostructured surfaces were determined under reciprocating sliding conditions (1 Hz, 1.0 N normal load) against a 10-mm diameter ball of hardened 100Cr6 steel during 1000 cycles using two different lubricants, namely paraffin oil and engine oil. It turned out that the substrate material, the laser fluence and the lubricant are crucial for the tribological performance. However, friction and wear could not be significantly reduced by LIPSS on TiN layers in comparison to unstructured TiN surfaces. Finally, the resulting wear tracks on the nanostructured surfaces were investigated with respect to their morphology (OM, SEM), depth (WLIM) and chemical composition by energy dispersive X-ray spectroscopy (EDX) and, on one hand, compared with each other, on the other hand, with non-structured TiN surfaces.

Electronic structure and mechanical properties of plasma nitrided ferrous alloys

NASA Astrophysics Data System (ADS)

Portolan, E.; Baumvol, I. J. R.; Figueroa, C. A.

2009-04-01

The electronic structures of the near-surface regions of two different nitrided steels (AISI 316 and 4140) were investigated using X-ray photoelectron spectroscopy. Photoelectron groups from all main chemical elements involved were addressed for steel samples with implanted-N concentrations in the range 16-32 at.%. As the implanted-N concentrations were increased, rather contrasting behaviors were observed for the two kinds of steel. The N1s photoelectrons had spectral shifts toward lower (nitrided AISI 316) or higher (nitrided AISI 4140) binding energies, whereas the Fe2p 3/2 photoelectron spectrum remains at a constant binding energy (nitrided AISI 316) or shifts toward higher binding energies (AISI 4140). These trends are discussed in terms of the metallic nitride formation and the overlapping of atomic orbitals. For nitrided AISI 316, a semi-classical approach of charge transfer between Cr and N is used to explain the experimental facts (formation of CrN), while for nitrided AISI 4140 we propose that the interaction between orbitals 4s from Fe and 2p from N promotes electrons to the conduction band increasing the electrical attraction of the N1s and Fe2p electrons in core shells (formation of FeN x). The increase in hardness of the steel upon N implantation is attributed to the localization of electrons in specific bonds, which diminishes the metallic bond character.

The potentials and challenges of electron microscopy in the study of atomic chains

NASA Astrophysics Data System (ADS)

Banhart, Florian; Torre, Alessandro La; Romdhane, Ferdaous Ben; Cretu, Ovidiu

2017-04-01

The article is a brief review on the potential of transmission electron microscopy (TEM) in the investigation of atom chains which are the paradigm of a strictly one-dimensional material. After the progress of TEM in the study of new two-dimensional materials, microscopy of free-standing one-dimensional structures is a new challenge with its inherent potentials and difficulties. In-situ experiments in the TEM allowed, for the first time, to generate isolated atomic chains consisting of metals, carbon or boron nitride. Besides having delivered a solid proof for the existence of atomic chains, in-situ TEM studies also enabled us to measure the electrical properties of these fundamental linear structures. While ballistic quantum conductivity is observed in chains of metal atoms, electrical transport in chains of sp1-hybridized carbon is limited by resonant states and reflections at the contacts. Although substantial progress has been made in recent TEM studies of atom chains, fundamental questions have to be answered, concerning the structural stability of the chains, bonding states at the contacts, and the suitability for applications in nanotechnology. Contribution to the topical issue "The 16th European Microscopy Congress (EMC 2016)", edited by Richard Brydson and Pascale Bayle-Guillemaud

Radial direct bandgap p-i-n GaNP microwire solar cells with enhanced short circuit current

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sukrittanon, Supanee; Liu, Ren; Pan, Janet L.

2016-08-07

We report the demonstration of dilute nitride heterostructure core/shell microwire solar cells utilizing the combination of top-down reactive-ion etching to create the cores (GaP) and molecular beam epitaxy to create the shells (GaNP). Systematic studies of cell performance over a series of microwire lengths, array periods, and microwire sidewall morphologies examined by transmission electron microscopy were conducted to shed light on performance-limiting factors and to optimize the cell efficiency. We show by microscopy and correlated external quantum efficiency characterization that the open circuit voltage is degraded primarily due to the presence of defects at the GaP/GaNP interface and in themore » GaNP shells, and is not limited by surface recombination. Compared to thin film solar cells in the same growth run, the microwire solar cells exhibit greater short circuit current but poorer open circuit voltage due to greater light absorption and number of defects in the microwire structure, respectively. The comprehensive understanding presented in this work suggests that performance benefits of dilute nitride microwire solar cells can be achieved by further tuning of the epitaxial quality of the underlying materials.« less

Radial direct bandgap p-i-n GaNP microwire solar cells with enhanced short circuit current

NASA Astrophysics Data System (ADS)

Sukrittanon, Supanee; Liu, Ren; Breeden, Michael C.; Pan, Janet L.; Jungjohann, K. L.; Tu, Charles W.; Dayeh, Shadi A.

2016-08-01

We report the demonstration of dilute nitride heterostructure core/shell microwire solar cells utilizing the combination of top-down reactive-ion etching to create the cores (GaP) and molecular beam epitaxy to create the shells (GaNP). Systematic studies of cell performance over a series of microwire lengths, array periods, and microwire sidewall morphologies examined by transmission electron microscopy were conducted to shed light on performance-limiting factors and to optimize the cell efficiency. We show by microscopy and correlated external quantum efficiency characterization that the open circuit voltage is degraded primarily due to the presence of defects at the GaP/GaNP interface and in the GaNP shells, and is not limited by surface recombination. Compared to thin film solar cells in the same growth run, the microwire solar cells exhibit greater short circuit current but poorer open circuit voltage due to greater light absorption and number of defects in the microwire structure, respectively. The comprehensive understanding presented in this work suggests that performance benefits of dilute nitride microwire solar cells can be achieved by further tuning of the epitaxial quality of the underlying materials.

Radial direct bandgap p-i-n GaNP microwire solar cells with enhanced short circuit current

DOE PAGES

Sukrittanon, Supanee; Liu, Ren; Breeden, Michael C.; ...

2016-08-07

Here, we report the demonstration of dilute nitride heterostructure core/shell microwire solar cells utilizing the combination of top-down reactive-ion etching to create the cores (GaP) and molecular beam epitaxy to create the shells (GaNP). Systematic studies of cell performance over a series of microwire lengths, array periods, and microwire sidewall morphologies examined by transmission electron microscopy were conducted to shed light on performance-limiting factors and to optimize the cell efficiency. We also show by microscopy and correlated external quantum efficiency characterization that the open circuit voltage is degraded primarily due to the presence of defects at the GaP/GaNP interface andmore » in the GaNP shells, and is not limited by surface recombination. Compared to thin film solar cells in the same growth run, the microwire solar cells exhibit greater short circuit current but poorer open circuit voltage due to greater light absorption and number of defects in the microwire structure, respectively. Finally, we present performance benefits of dilute nitride microwire solar cells and show that it can be achieved by further tuning of the epitaxial quality of the underlying materials.« less

Pyrolytic boron nitride coatings on ceramic yarns and fabrication of insulations

NASA Technical Reports Server (NTRS)

Moore, Arthur W.

1992-01-01

Pyrolytic boron nitride (PBN) was deposited on Nicalon NL 202 silicon carbide yarns at 1000 to 1200 C with the goal of improving the resistance of the Nicalon to deterioration in an aerodynamic environment at temperatures up to 1000 C. For continuous coating, the yarns were fed through the deposition chamber of a pilot plant sized CVD furnace at a rate of about 2 feet per minute. PBN coatings were obtained by reacting boron trichloride and ammonia gases inside the deposition chamber. Most of the PBN coatings were made at around 1080 C to minimize thermal degradation of the Nicalon. Pressures were typically below 0.1 Torr. The coated yarns were characterized by weight per unit length, tensile strength and modulus, scanning electron microscopy, and scanning Auger microscopy. The PBN coated Nicalon was woven into cloth, but was not entirely satisfactory as a high temperature sizing. Several 13 in. square pieces of Nicalon cloth were coated with PBN in a batch process in a factory sized deposition furnace. Samples of cloth made from the PBN coated Nicalon were sewn into thermal insulation panels, whose performance is being compared with that of panels made using uncoated Nicalon.

An investigation of GaN thin films on AlN on sapphire substrate by sol-gel spin coating method

NASA Astrophysics Data System (ADS)

Amin, Nur Fahana Mohd; Ng, Sha Shiong

2017-12-01

In this research, the gallium nitride (GaN) thin films were deposited on aluminium nitride on sapphire (AlN/Al2O3) substrate by sol-gel spin coating method. Simple ethanol-based precursor with the addition of diethanolamine solution was used. The structural and morphology properties of synthesized GaN thin films were characterized by using X-ray Diffraction, Field-Emission Scanning Electron Microscopy and Atomic Force Microscopy. While the elemental compositions and the lattice vibrational properties of the films were investigated by means of the Energy Dispersive X-ray spectroscopy and Raman spectroscopy. All the results revealed that the wurtzite structure GaN thin films with GaN(002) preferred orientation and smooth surface morphology were successfully grown on AlN/Al2O3 substrate by using inexpensive and simplified sol-gel spin coating technique. The sol-gel spin coated GaN thin film with lowest oxygen content was also achieved.FESEM images show that GaN thin films with uniform and packed grains were formed. Based on the obtained results, it can be concluded that wurtzite structure GaN thin films were successfully deposited on AlN/Al2O3 substrate.

Silanization of boron nitride nanosheets (BNNSs) through microfluidization and their use for producing thermally conductive and electrically insulating polymer nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seyhan, A.Tuğrul, E-mail: atseyhan@anadolu.edu.tr; Composite Materials Manufacturing Science Laboratory; Göncü, Yapıncak

Chemical exfoliation of boron nitride nanosheets (BNNSs) from large flakes of specially synthesized micro-sized hexagonal boron nitride (h-BN) ceramics was carried out through microfluidization. The surface of BNNSs obtained was then functionalized with vinyl-trimethoxy silane (VTS) coupling agent through microfluidization once again in an effort to make them compatible with organic materials, especially those including polymers. The morphology of BNNSs with and without silane treatment was then systematically characterized by conducting various different analytical techniques, including Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Bright field Transmission Electron Microscopy (BF-TEM), Contact angle analyzer (CAA), Particle size analyzer (PSA)more » and Fourier Transmission Infrared (FTIR) spectroscopy attached with attenuated total reflectance (ATR) module. As a result, the silane treatment was determined to be properly and successfully carried out and to give rise to the irregularity of large flakes of the BNNSs by folding back their free edges upon themselves, which in turn assists in inducing further exfoliation of the few-layered nanosheets. To gain more insight into the effectiveness of the surface functionalization, thermal conductivity of polypropylene (PP) nanocomposites containing different amounts (1 wt% and 5 wt%) of BNNSs with and without silane treatment was experimentally investigated. Regardless of the weight content, PP nanocomposites containing silanized BNNSs were found to exhibit high thermal conductivity compared to PP nanocomposites containing BNNSs without silane treatment. It was concluded that microfluidization possesses the robustness to provide a reliable product quality, whether in small or large quantities, in a very time effective manner, when it comes to first exfoliating two-dimensional inorganic materials into few layered sheets, and functionalizing the surface of these sheets afterwards to make it possible to utilize them as promising filler constituent in manufacturing thermally conductive and electrically insulating polymer nanocomposites that could be considered as whole or a part of a heat-releasing device.« less

Silanization of boron nitride nanosheets (BNNSs) through microfluidization and their use for producing thermally conductive and electrically insulating polymer nanocomposites

NASA Astrophysics Data System (ADS)

Seyhan, A. Tuğrul; Göncü, Yapıncak; Durukan, Oya; Akay, Atakan; Ay, Nuran

2017-05-01

Chemical exfoliation of boron nitride nanosheets (BNNSs) from large flakes of specially synthesized micro-sized hexagonal boron nitride (h-BN) ceramics was carried out through microfluidization. The surface of BNNSs obtained was then functionalized with vinyl-trimethoxy silane (VTS) coupling agent through microfluidization once again in an effort to make them compatible with organic materials, especially those including polymers. The morphology of BNNSs with and without silane treatment was then systematically characterized by conducting various different analytical techniques, including Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Bright field Transmission Electron Microscopy (BF-TEM), Contact angle analyzer (CAA), Particle size analyzer (PSA) and Fourier Transmission Infrared (FTIR) spectroscopy attached with attenuated total reflectance (ATR) module. As a result, the silane treatment was determined to be properly and successfully carried out and to give rise to the irregularity of large flakes of the BNNSs by folding back their free edges upon themselves, which in turn assists in inducing further exfoliation of the few-layered nanosheets. To gain more insight into the effectiveness of the surface functionalization, thermal conductivity of polypropylene (PP) nanocomposites containing different amounts (1 wt% and 5 wt%) of BNNSs with and without silane treatment was experimentally investigated. Regardless of the weight content, PP nanocomposites containing silanized BNNSs were found to exhibit high thermal conductivity compared to PP nanocomposites containing BNNSs without silane treatment. It was concluded that microfluidization possesses the robustness to provide a reliable product quality, whether in small or large quantities, in a very time effective manner, when it comes to first exfoliating two-dimensional inorganic materials into few layered sheets, and functionalizing the surface of these sheets afterwards to make it possible to utilize them as promising filler constituent in manufacturing thermally conductive and electrically insulating polymer nanocomposites that could be considered as whole or a part of a heat-releasing device.

Half-metallicity and electronic structures for carbon-doped group III-nitrides: Calculated with a modified Becke-Johnson potential

NASA Astrophysics Data System (ADS)

Fan, Shuai-wei; Wang, Ri-gao; Xu, Pemg

2016-09-01

The electronic structures and magnetism for carbon-doped group III-nitrides are investigated by utilizing the first principle method with the modified Becke-Johnson potential. Calculations show that carbon substituting cations (anions) would induce the group III-nitrides to be paramagnetic metals (half-metallic ferromagnets). Single carbon substituting nitrogen could produce 1.00μB magnetic moment. Electronic structures indicate that the carriers-mediated double-exchange interaction plays a crucial role in forming the ferromagnetism. Based on the mean-field theory, the Curie temperature for carbon-doped group III-nitrides would be above the room temperature. Negative chemical pair interactions imply that carbon dopants tend to form clustering distribution in group III-nitrides. The nitrogen vacancy would make the carbon-doped group III-nitrides lose the half-metallic ferromagnetism.

The photocatalytic properties of hollow (GaN)1-x(ZnO)x composite nanofibers synthesized by electrospinning

NASA Astrophysics Data System (ADS)

Wang, Ding; Zhang, Minglu; Zhuang, Huaijuan; Chen, Xu; Wang, Xianying; Zheng, Xuejun; Yang, Junhe

2017-02-01

(GaN)1-x(ZnO)x composite nanofibers with hollow structure were prepared by initial electrospinning, and the subsequent calcination and nitridation. The structure and morphology characteristics of samples were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The characterization results showed the phase transition from ZnGa2O4 to (GaN)1-x(ZnO)x solid-solution under ammonia atmosphere. The preparation conditions were explored and the optimum nitridation temperature and holding time are 750 °C and 2 h, respectively. The photocatalytic properties of (GaN)1-x(ZnO)x with different Ga:Zn atomic ratios were investigated by degrading Rhodamine B under the visible light irradiation. The photocatalytic activity sequence is (GaN)1-x(ZnO)x (Ga:Zn = 1:2) > (GaN)1-x(ZnO)x (Ga:Zn = 1:3) > ZnO nanofibers > (GaN)1-x(ZnO)x (Ga:Zn = 1:4) > (GaN)1-x(ZnO)x (Ga:Zn = 1:1). The photocatalytic mechanism of the (GaN)1-x(ZnO)x hollow nanofibers was further studied by UV-vis diffuse reflectance spectra. The excellent photocatalytic performance of (GaN)1-x(ZnO)x hollow nanofibers was attributed to the narrow band gap and high surface area of porous nanofibers with hollow structure.

(abstract) Transmission Electron Microscopy of Al(sub x)Ga(sub 1-x)N/SiC Multilayer Structures Grown on Sapphire Substrates

NASA Technical Reports Server (NTRS)

Pike, W. T.; George, T.; Khan, M. A.; Kuznia, J. N.

1994-01-01

The potential of wide-band-gap III-V nitrides as ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wide-band-gap III-V nitrides: the growth of ultra-short period GaN/AlN superlattices; and the incorporation of SiC layers into Al(sub x)Ga(sub 1-x)N structures. By varying the relative periods in a GaN/AlN superlattice, the band gap of the composite can be tailored to lie between the elemental values of 365 nm for GaN and 200 nm for AlN. The group IV semiconductor, SiC, has a wide band-gap and has a close lattice match (less than 3 %) to Al(sub x)Ga(sub 1-x)N for growth on the basal plane. Demonstration of epitaxial growth for Al(sub x)Ga(sub 1-x)N/SiC multilayers would introduce a wide band-gap analog to the already existing family of III-V and Si(sub 1-x)Ge(sub x) heteroepitaxial growth systems. Although good quality growth of GaN on SiC substrates has been demonstrated, Al(sub x)Ga(sub 1-x)N/SiC multilayer structures have never been grown and the interfacial structure is unknown.

Large-area growth of multi-layer hexagonal boron nitride on polished cobalt foils by plasma-assisted molecular beam epitaxy

PubMed Central

Xu, Zhongguang; Tian, Hao; Khanaki, Alireza; Zheng, Renjing; Suja, Mohammad; Liu, Jianlin

2017-01-01

Two-dimensional (2D) hexagonal boron nitride (h-BN), which has a similar honeycomb lattice structure to graphene, is promising as a dielectric material for a wide variety of potential applications based on 2D materials. Synthesis of high-quality, large-size and single-crystalline h-BN domains is of vital importance for fundamental research as well as practical applications. In this work, we report the growth of h-BN films on mechanically polished cobalt (Co) foils using plasma-assisted molecular beam epitaxy. Under appropriate growth conditions, the coverage of h-BN layers can be readily controlled by growth time. A large-area, multi-layer h-BN film with a thickness of 5~6 nm is confirmed by Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. In addition, the size of h-BN single domains is 20~100 μm. Dielectric property of as-grown h-BN film is evaluated by characterization of Co(foil)/h-BN/Co(contact) capacitor devices. Breakdown electric field is in the range of 3.0~3.3 MV/cm, which indicates that the epitaxial h-BN film has good insulating characteristics. In addition, the effect of substrate morphology on h-BN growth is discussed regarding different domain density, lateral size, and thickness of the h-BN films grown on unpolished and polished Co foils. PMID:28230178

Layer speciation and electronic structure investigation of freestanding hexagonal boron nitride nanosheets

NASA Astrophysics Data System (ADS)

WangEqual Contribution To This Work., Jian; Wang, Zhiqiang; Cho, Hyunjin; Kim, Myung Jong; Sham, T. K.; Sun, Xuhui

2015-01-01

Chemical imaging, thickness mapping, layer speciation and polarization dependence have been performed on single and multilayered (up to three layers and trilayered nanosheets overlapping to form 6 and 9 layers) hexagonal boron nitride (hBN) nanosheets by scanning transmission X-ray microscopy. Spatially-resolved XANES directly from freestanding regions of different layers has been extracted and compared with sample normal and 30° tilted configurations. Notably a double feature σ* excitonic state and a stable high energy σ* state were observed at the boron site in addition to the intense π* excitonic state. The boron projected σ* DOS, especially the first σ* exciton, is sensitive to surface modification, particularly in the single layered hBN nanosheet which shows more significant detectable contaminants and defects such as tri-coordinated boron/nitrogen oxide. The nitrogen site has shown very weak or no excitonic character. The distinct excitonic effect on boron and nitrogen was interpreted to the partly ionic state of hBN. Bulk XANES of hBN nanosheets was also measured to confirm the spectro-microscopic STXM result. Finally, the unoccupied electronic structures of hBN and graphene were compared.Chemical imaging, thickness mapping, layer speciation and polarization dependence have been performed on single and multilayered (up to three layers and trilayered nanosheets overlapping to form 6 and 9 layers) hexagonal boron nitride (hBN) nanosheets by scanning transmission X-ray microscopy. Spatially-resolved XANES directly from freestanding regions of different layers has been extracted and compared with sample normal and 30° tilted configurations. Notably a double feature σ* excitonic state and a stable high energy σ* state were observed at the boron site in addition to the intense π* excitonic state. The boron projected σ* DOS, especially the first σ* exciton, is sensitive to surface modification, particularly in the single layered hBN nanosheet which shows more significant detectable contaminants and defects such as tri-coordinated boron/nitrogen oxide. The nitrogen site has shown very weak or no excitonic character. The distinct excitonic effect on boron and nitrogen was interpreted to the partly ionic state of hBN. Bulk XANES of hBN nanosheets was also measured to confirm the spectro-microscopic STXM result. Finally, the unoccupied electronic structures of hBN and graphene were compared. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr04445b

Nano-indentation used to study pyramidal slip in GaN single crystals

NASA Astrophysics Data System (ADS)

Krimsky, E.; Jones, K. A.; Tompkins, R. P.; Rotella, P.; Ligda, J.; Schuster, B. E.

2018-02-01

The nucleation and structure of dislocations created by the nano-indentation of GaN samples with dislocation densities ≈103, 106 or 109 ⊥/cm2 were studied in the interest of learning how dislocations can be created to relieve the mismatch strain in ternary nitride films grown on (0001) oriented binary nitride substrates. Using transmission electron microscopy and stress analyses to assist in interpreting the nano-indentation data, we determined that the pop-ins in the indenter load vs. penetration depth curves are created by an avalanche process at stresses well above the typical yield stress. The process begins by the homogeneous formation of a basal plane screw dislocation that triggers the formation of pyramidal and other basal plane dislocations that relieve the excess stored elastic energy. It appears that pyramidal slip can occur on either the {1122} or {0111} planes, as there is little resistance to the cross slip of screw dislocations.

Cathodic cage plasma deposition of TiN and TiO{sub 2} thin films on silicon substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sousa, Romulo R. M. de; Sato, Patricia S.; Nascente, Pedro A. P., E-mail: nascente@ufscar.br

2015-07-15

Cathodic cage plasma deposition (CCPD) was used for growing titanium nitride (TiN) and titanium dioxide (TiO{sub 2}) thin films on silicon substrates. The main advantages of the CCPD technique are the uniformity, tridimensionality, and high rate of the film deposition that occurs at higher pressures, lower temperatures, and lower treatment times than those used in conventional nitriding treatments. In this work, the influence of the temperature and gas atmosphere upon the characteristics of the deposited films was investigated. The TiN and TiO{sub 2} thin films were characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy to analyze their chemical,more » structural, and morphological characteristics, and the combination of these results indicates that the low-cost CCPD technique can be used to produce even and highly crystalline TiN and TiO{sub 2} films.« less

Utilizing boron nitride sheets as thin supports for high resolution imaging of nanocrystals.

PubMed

Wu, Yimin A; Kirkland, Angus I; Schäffel, Franziska; Porfyrakis, Kyriakos; Young, Neil P; Briggs, G Andrew D; Warner, Jamie H

2011-05-13

We demonstrate the use of thin BN sheets as supports for imaging nanocrystals using low voltage (80 kV) aberration-corrected high resolution transmission electron microscopy. This provides an alternative to the previously utilized 2D crystal supports of graphene and graphene oxide. A simple chemical exfoliation method is applied to get few layer boron nitride (BN) sheets with micrometer-sized dimensions. This generic approach of using BN sheets as supports is shown by depositing Mn doped ZnSe nanocrystals directly onto the BN sheets and resolving the atomic structure from both the ZnSe nanocrystals and the BN support. Phase contrast images reveal moiré patterns of interference between the beams diffracted by the nanocrystals and the BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes. Double diffraction is observed and has been analyzed.

Introducing Overlapping Grain Boundaries in Chemical Vapor Deposited Hexagonal Boron Nitride Monolayer Films

PubMed Central

2017-01-01

We demonstrate the growth of overlapping grain boundaries in continuous, polycrystalline hexagonal boron nitride (h-BN) monolayer films via scalable catalytic chemical vapor deposition. Unlike the commonly reported atomically stitched grain boundaries, these overlapping grain boundaries do not consist of defect lines within the monolayer films but are composed of self-sealing bilayer regions of limited width. We characterize this overlapping h-BN grain boundary structure in detail by complementary (scanning) transmission electron microscopy techniques and propose a catalytic growth mechanism linked to the subsurface/bulk of the process catalyst and its boron and nitrogen solubilities. Our data suggest that the overlapping grain boundaries are comparatively resilient against deleterious pinhole formation associated with grain boundary defect lines and thus may reduce detrimental breakdown effects when polycrystalline h-BN monolayer films are used as ultrathin dielectrics, barrier layers, or separation membranes. PMID:28410557

Adsorption Studies of Gadolinium ion on Graphitic Carbon Nitride

NASA Astrophysics Data System (ADS)

Kuila, S. K.; Kundu, T. K.

2018-03-01

Bulk graphitic carbon nitride (g-C3N4) is synthesized by thermal decomposition of urea and used as an adsorbent for gadolinium ion (Gd3+) from aqueous solution. Adsorption capacity of g-C3N4 is found to be influenced by initial Gd3+ concentration, solution pH and contact time. Adsorbed Gd3+is separated from g-C3N4 by ultracentrifuge. Initial and Gd ion accumulated g-C3N4 adsorbent are characterized by X-ray diffraction technique (XRD) for phase identification, UV-visible and Fourier transform infrared (FTIR) spectroscopy for adsorption characteristics and optical property, scanning electron microscopy (SEM) for morphological behaviour along with energy dispersive X-ray spectroscopy (EDS) for elemental study. HNO3(0.1M), NaOH (0.1M) and de-ionized water are used for desorption and around 97% quantitative recovery of Gd ion is observed.

Preparation of Si3N4 Form Diatomite via a Carbothermal Reduction-Nitridation Process

NASA Astrophysics Data System (ADS)

Ma, Bin; Huang, Zhaohui; Mei, Lefu; Fang, Minghao; Liu, Yangai; Wu, Xiaowen; Hu, Xiaozhi

2016-05-01

Si3N4 was produced using diatomite and sucrose as silicon and carbon sources, respectively. The effect of the C/SiO2 molar ratio, heating temperature and soaking time on the morphology and phase compositions of the final products was investigated by scanning electron microscopy, x-ray diffraction analysis and energy dispersive spectroscopy. The phase equilibrium relationships of the system at different heating temperatures were also investigated based on the thermodynamic analysis. The results indicate that the phase compositions depended on the C/SiO2 molar ratio, heating temperature and soaking time. Fabrication of Si3N4 from the precursor via carbothermal reduction nitridation was achieved at 1550°C for 1-8 h using a C/SiO2 molar ratio of 3.0. The as-prepared Si3N4 contained a low amount of Fe3Si (<1 wt.%).

Ga2O3 and GaN nanocrystalline film: reverse micelle assisted solvothermal synthesis and characterization.

PubMed

Sinha, Godhuli; Ganguli, Dibyendu; Chaudhuri, Subhadra

2008-03-01

Gallium oxide (beta-Ga2O3) nanoparticles were successfully deposited on quartz glass substrates using sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/n-hexane/ethylene glycol monomethyl ether (EGME) reverse micelle-mediated solvothermal process with different omega values. The mean diameter of Ga2O3 particles was approximately 2-3 nm and found to be approximately independent of omega values of the reverse micelles. However, when the Ga2O3 nanocrystalline films were nitrided at 900 degrees C under flowing NH3 atmosphere for 1 h, the mean diameter of the resulted gallium nitride (wurtzite-GaN) nanoparticles varied from 3-9 nm. Both nanocrystalline films of Ga2O3 and GaN were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy and photoluminescence in order to study their chemical and physical properties explicitly.

GaN nanophosphors for white-light applications

NASA Astrophysics Data System (ADS)

Kumar, Mirgender; Singh, V. P.; Dubey, Sarvesh; Suh, Youngsuk; Park, Si-Hyun

2018-01-01

GaN nanoparticles (NPs) were synthesized by carbothermal reduction combined with nitridation, using Ga2O3 powder and graphitic carbon nitride (g-C3N4) as precursors. Characterization of the NPs was performed by X-ray diffraction, scanning electron microscopy, and room-temperature photoluminescence measurements. X-ray photoelectron spectroscopy was also performed to detect the chemical states of the different species. A universal yellow luminescence (YL) band was observed from complexes of Ga vacancies with O anti-sites and of O anti-sites with C. Further increments in the C content were observed with continued growth and induced an additional blue luminescence (BL) band. Tuning of the YL and BL bands resulted in white-light emission under certain experimental conditions, thus offering a new way of employing GaN nanophosphors for solid-state white lighting. Calculations of the correlated color temperature and color-quality scale parameters confirmed the utility of the experimental process for different applications.

Dislocation-pipe diffusion in nitride superlattices observed in direct atomic resolution.

PubMed

Garbrecht, Magnus; Saha, Bivas; Schroeder, Jeremy L; Hultman, Lars; Sands, Timothy D

2017-04-06

Device failure from diffusion short circuits in microelectronic components occurs via thermally induced migration of atoms along high-diffusivity paths: dislocations, grain boundaries, and free surfaces. Even well-annealed single-grain metallic films contain dislocation densities of about 10 14  m -2 ; hence dislocation-pipe diffusion (DPD) becomes a major contribution at working temperatures. While its theoretical concept was established already in the 1950s and its contribution is commonly measured using indirect tracer, spectroscopy, or electrical methods, no direct observation of DPD at the atomic level has been reported. We present atomically-resolved electron microscopy images of the onset and progression of diffusion along threading dislocations in sequentially annealed nitride metal/semiconductor superlattices, and show that this type of diffusion can be independent of concentration gradients in the system but governed by the reduction of strain fields in the lattice.

Direct Growth of CuO Nanorods on Graphitic Carbon Nitride with Synergistic Effect on Thermal Decomposition of Ammonium Perchlorate

PubMed Central

Tan, Linghua; Xu, Jianhua; Li, Shiying; Li, Dongnan; Dai, Yuming; Kou, Bo; Chen, Yu

2017-01-01

Novel graphitic carbon nitride/CuO (g-C3N4/CuO) nanocomposite was synthesized through a facile precipitation method. Due to the strong ion-dipole interaction between copper ions and nitrogen atoms of g-C3N4, CuO nanorods (length 200–300 nm, diameter 5–10 nm) were directly grown on g-C3N4, forming a g-C3N4/CuO nanocomposite, which was confirmed via X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). Finally, thermal decomposition of ammonium perchlorate (AP) in the absence and presence of the prepared g-C3N4/CuO nanocomposite was examined by differential thermal analysis (DTA), and thermal gravimetric analysis (TGA). The g-C3N4/CuO nanocomposite showed promising catalytic effects for the thermal decomposition of AP. Upon addition of 2 wt % nanocomposite with the best catalytic performance (g-C3N4/20 wt % CuO), the decomposition temperature of AP was decreased by up to 105.5 °C and only one decomposition step was found instead of the two steps commonly reported in other examples, demonstrating the synergistic catalytic activity of the as-synthesized nanocomposite. This study demonstrated a successful example regarding the direct growth of metal oxide on g-C3N4 by ion-dipole interaction between metallic ions, and the lone pair electrons on nitrogen atoms, which could provide a novel strategy for the preparation of g-C3N4-based nanocomposite. PMID:28772844

Control of iron nitride layers growth kinetics in the binary Fe-N system

NASA Astrophysics Data System (ADS)

Torchane, L.; Bilger, P.; Dulcy, J.; Gantois, M.

1996-07-01

This study is within the framework of a research program dedicated to defining the optimal conditions for the nitriding of iron and steels at atmospheric pressure by using various mixtures, NH3-N2-H2 and NH3-Ar. After studying the mechanisms of phase formation and mass transfer at the gas-solid interface, a mathematical model is developed in order to predict the nitrogen transfer rate in the solid, the nitride layer growth rate, and the nitrogen concentration profiles. In order to validate the model and to show its possibilities, it is compared with thermogravimetric experiments, analyses, and metallurgical observations (X-ray diffraction, optical microscopy, and electron microprobe anal-ysis). The results obtained allow us to demonstrate the sound correlation between the experimental results and the theoretical predictions. By applying the model to the iron-nitrogen binary system, when the ɛ/γ/α configuration referred to the Fe-N phase diagram is formed, we have experimentally determined the effective diffusion coefficient of nitrogen in the ɛ phase. The latter is constant for a composition of the ɛ nitride between 8 and 9.5 wt pct nitrogen. All the results obtained show that it is possible, by means of dynamic gas flow regulation, to eliminate the incubation period and to control the thickness, composition, and structure of the compound layer at the beginning of the treatment.

Significant improvement in the electrical characteristics of Schottky barrier diodes on molecularly modified Gallium Nitride surfaces

NASA Astrophysics Data System (ADS)

Garg, Manjari; Naik, Tejas R.; Pathak, C. S.; Nagarajan, S.; Rao, V. Ramgopal; Singh, R.

2018-04-01

III-Nitride semiconductors face the issue of localized surface states, which causes fermi level pinning and large leakage current at the metal semiconductor interface, thereby degrading the device performance. In this work, we have demonstrated the use of a Self-Assembled Monolayer (SAM) of organic molecules to improve the electrical characteristics of Schottky barrier diodes (SBDs) on n-type Gallium Nitride (n-GaN) epitaxial films. The electrical characteristics of diodes were improved by adsorption of SAM of hydroxyl-phenyl metallated porphyrin organic molecules (Zn-TPPOH) onto the surface of n-GaN. SAM-semiconductor bonding via native oxide on the n-GaN surface was confirmed using X-ray photoelectron spectroscopy measurements. Surface morphology and surface electronic properties were characterized using atomic force microscopy and Kelvin probe force microscopy. Current-voltage characteristics of different metal (Cu, Ni) SBDs on bare n-GaN were compared with those of Cu/Zn-TPPOH/n-GaN and Ni/Zn-TPPOH/n-GaN SBDs. It was found that due to the molecular monolayer, the surface potential of n-GaN was decreased by ˜350 mV. This caused an increase in the Schottky barrier height of Cu and Ni SBDs from 1.13 eV to 1.38 eV and 1.07 eV to 1.22 eV, respectively. In addition to this, the reverse bias leakage current was reduced by 3-4 orders of magnitude for both Cu and Ni SBDs. Such a significant improvement in the electrical performance of the diodes can be very useful for better device functioning.

Protein adsorption on thin films of carbon and carbon nitride monitored with in situ ellipsometry.

PubMed

Berlind, T; Tengvall, P; Hultman, L; Arwin, H

2011-03-01

Thin films of amorphous carbon and amorphous, graphitic and fullerene-like carbon nitride were deposited by reactive magnetron sputtering and optically characterized with spectroscopic ellipsometry. Complementary studies using scanning electron microscopy and atomic force microscopy were performed. The films were exposed to human serum albumin (HSA) and the adsorption was monitored in situ using dynamic ellipsometry. From the ellipsometric data the adsorbed amount of proteins was quantified in terms of surface mass density using de Feijter's model. The results indicate larger adsorption of proteins onto the amorphous films compared to the films with a more textured structure. Complementary studies with 125I-labeled HSA showed an apparent protein adsorption up to six times larger compared to the ellipsometry measurement. In addition, the four types of films were incubated in blood plasma followed by exposure to anti-fibrinogen, anti-HMWK or anti-C3c, revealing the materials' response to complement and contact activation. The amorphous and graphitic carbon nitride exhibit rather high immune activity compared to a titanium reference, whereas the amorphous carbon and the fullerene-like CNx show less immune complement deposition. Compared to the reference, all films exhibit indications of a stronger ability to initiate the intrinsic pathway of coagulation. Finally, the surfaces' bone-bonding ability was investigated by examination of their ability to form calcium phosphate crystals in a simulated body fluid, with a-CNx depositing most calcium phosphate after 21 days of incubation. Copyright © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Synthesis and photocatalytic activity of N-doped TiO2 produced in a solid phase reaction

NASA Astrophysics Data System (ADS)

Xin, Gang; Pan, Hongfei; Chen, Dan; Zhang, Zhihua; Wen, Bin

2013-02-01

N-doped TiO2 was synthesized by calcining a mixture of titanic acid and graphitic carbon nitride (g-C3N4) at temperatures above 500 °C. The final samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and UV-vis diffuse reflectance spectra. The photocatalytic activity of N-doped TiO2 was studied by assessing the degradation of methylene blue in an aqueous solution, under visible light and UV light irradiation. It was found that the N-doped TiO2 displayed higher photocatalytic activity than pure TiO2, under both visible and UV light.

Thin-film preparation by back-surface irradiation pulsed laser deposition using metal powder targets

NASA Astrophysics Data System (ADS)

Kawasaki, Hiroharu; Ohshima, Tamiko; Yagyu, Yoshihito; Ihara, Takeshi; Yamauchi, Makiko; Suda, Yoshiaki

2017-01-01

Several kinds of functional thin films were deposited using a new thin-film preparation method named the back-surface irradiation pulsed laser deposition (BIPLD) method. In this BIPLD method, powder targets were used as the film source placed on a transparent target holder, and then a visible-wavelength pulsed laser was irradiated from the holder side to the substrate. Using this new method, titanium oxide and boron nitride thin films were deposited on the silicon substrate. Surface scanning electron microscopy (SEM) images suggest that all of the thin films were deposited on the substrate with some large droplets irrespective of the kind of target used. The deposition rate of the films prepared by using this method was calculated from film thickness and deposition time to be much lower than that of the films prepared by conventional PLD. X-ray diffraction (XRD) measurement results suggest that rutile and anatase TiO2 crystal peaks were formed for the films prepared using the TiO2 rutile powder target. Crystal peaks of hexagonal boron nitride were observed for the films prepared using the boron nitride powder target. The crystallinity of the prepared films was changed by annealing after deposition.

Corrosion, optical and magnetic properties of flexible iron nitride nano thin films deposited on polymer substrate

NASA Astrophysics Data System (ADS)

Khan, W. Q.; Wang, Qun; Jin, Xin; Yasin, G.

2017-11-01

Iron nitride thin films of different compositions and thicknesses were deposited on flexible polymer substrate in Ar/N2 atmosphere by reactive magnetron sputtering under varying nitrogen flow rates. The nano structured films were characterized by X-ray diffraction, UV-visible spectrophotometer, electrochemical impedance (EIS), atomic force (AFM) and transmission electron microscopies. The dependence of their functional properties on coating and growth conditions was studied in detail. It was found that the thin films show a uniform permeability in the frequency range of 200 MHz to 1 Ghz and can be used in this range without appreciable changes. Decrease of nitrogen flow rate resulted in the smoother surfaces which in turn increase transmittance quality and corrosion resistance. Functional properties are dependent of nature, relative concentration of the iron nitride phases and film thickness. Surface integrity is excellent for180 nm thick sample because the films appear to be very dense and free from open pores. By keeping sputtering power stable at 110 W, nitrogen flow rate of 10 sccm was ideal to develop the ferromagnetic γʹFe4N phase at room temperature.

Microstructures of BN/SiC coatings on nicalon fibers

NASA Technical Reports Server (NTRS)

Dickerson, R. M.; Singh, M.

1995-01-01

The microstructures of Nicalon silicon carbide (SiC) fibers and layered coatings of boron nitride (BN) followed by chemical vapor infiltrated silicon carbide (CVI-SiC) were characterized using optical and electron microscopy. Two different precursors and reactions were used to produce the BN layers while the deposition of CVI silicon carbide was nearly identical. Coated tows were examined in cross-section to characterize the chemistry and structures of the constituents and the interfaces. One BN precursor yielded three sublayers while the other gave a relatively homogeneous nanocrystalline layer.

Wafer-Scale and Wrinkle-Free Epitaxial Growth of Single-Orientated Multilayer Hexagonal Boron Nitride on Sapphire.

PubMed

Jang, A-Rang; Hong, Seokmo; Hyun, Chohee; Yoon, Seong In; Kim, Gwangwoo; Jeong, Hu Young; Shin, Tae Joo; Park, Sung O; Wong, Kester; Kwak, Sang Kyu; Park, Noejung; Yu, Kwangnam; Choi, Eunjip; Mishchenko, Artem; Withers, Freddie; Novoselov, Kostya S; Lim, Hyunseob; Shin, Hyeon Suk

2016-05-11

Large-scale growth of high-quality hexagonal boron nitride has been a challenge in two-dimensional-material-based electronics. Herein, we present wafer-scale and wrinkle-free epitaxial growth of multilayer hexagonal boron nitride on a sapphire substrate by using high-temperature and low-pressure chemical vapor deposition. Microscopic and spectroscopic investigations and theoretical calculations reveal that synthesized hexagonal boron nitride has a single rotational orientation with AA' stacking order. A facile method for transferring hexagonal boron nitride onto other target substrates was developed, which provides the opportunity for using hexagonal boron nitride as a substrate in practical electronic circuits. A graphene field effect transistor fabricated on our hexagonal boron nitride sheets shows clear quantum oscillation and highly improved carrier mobility because the ultraflatness of the hexagonal boron nitride surface can reduce the substrate-induced degradation of the carrier mobility of two-dimensional materials.

Effect of Pulse Detonation-Plasma Technology Treatment on T8 Steel Microstructures

NASA Astrophysics Data System (ADS)

Yu, Jiuming; Zhang, Linwei; Liu, Keming; Lu, Lei; Lu, Deping; Zhou, Haitao

2017-12-01

T8 steel surfaces were treated by pulse detonation-plasma technology (PDT) at capacitance values of 600, 800, and 1000 μF, and the effects of PDT were analyzed using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction, and micro-hardness tester and friction wear tester. The surface of T8 steel is first smoothed out, and then, craters are formed due to the inhomogeneity of the PDT energy and targeting during PDT treatment. The initial martensite in the T8 steel surface layer changes to austenite, and Fe3N is formed due to nitriding. The thickness of the modified layer, which is composed of columnar and fine grain structures, increases with the increasing capacity. Preferential orientation occurred in the {110} 〈 001 〉 direction in the modified layer, and the number of low-angle grain boundaries increased significantly after PDT treatment. The micro-hardness and wear resistance of the T8 steel was improved by PDT treatment, even doubled after the treatment with the capacitance of 1000 μF.

Microstructural Evolution of Secondary Phases in the Cast Duplex Stainless Steels CD3MN and CD3MWCuN

NASA Astrophysics Data System (ADS)

Kim, Yoon-Jun; Ugurlu, Ozan; Jiang, Chao; Gleeson, Brian; Chumbley, L. Scott

2007-02-01

The isothermal formation behavior of secondary phases in two types of duplex stainless steels (DSS), CD3MN and CD3MWCuN, was characterized. Samples were heat treated from 1 minute to 30 days at temperatures from 700°C to 900°C. Small carbide (M23C6) and nitride (Cr2N) precipitates, together with the intermetallic phases sigma and chi, were observed using scanning electron microscopy (SEM) and confirmed by transmission electron microscopy (TEM) analyses. Based on SEM analysis, time-temperature-transformation (TTT) curves for the sigma and chi phases were determined by measuring their volume fractions from backscattered electron micrographs of heat-treated and quenched sample cross sections. Resulting TTT curves showed that the maximum formation temperature for chi is lower than that for sigma, while the time to reach 1 vol pct formation is much less for sigma than it is for chi. The thermodynamic driving forces associated with the sigma and chi formation were assessed using Thermo-Calc.

Blueish green photoluminescence from nitrided GaAs(100) surfaces

NASA Astrophysics Data System (ADS)

Shimaoka, Goro; Udagawa, Takashi

1999-04-01

Optical and structural studies were made on the Si-doped (100)GaAs surfaces nitrided at a temperature between 650° and 750°C for 15 min in the flowing NH 3 gas. The wavelength of photoluminescence (PL) spectra were observed to be shortened from 820 nm of the GaAs nitrided at 650°C with increasing nitridation temperature. Blueish green PL with wavelengths of approx. 490 nm and 470 nm were emitted from the nitrided surfaces at 700° and 750°C, respectively. Results of AES and SIMS indicated that the surfaces are nitrided as GaAs 1- xN x, (0< x≤1) alloy layer, and the nitrided region also tended to increase as the temperature raised. High-resolution transmission electron microscopic (HRTEM), transmission electron diffraction (TED) and energy dispersive X-ray (EDX) results showed that films peeled off from the nitrided surfaces consisted mainly of hexagonal, wurtzite-type gallium nitride (GaN) with stacking faults and microtwins.

Dependence of mobility on the electron concentration upon scattering at polar optical phonons in A{sup III}–N nitrides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borisenko, S. I., E-mail: sib@tpu.ru

2016-04-15

The dependence of the effective relaxation time on the electron concentration in A{sup III}–N nitrides in the case of electron scattering at polar longitudinal optical phonons is calculated by the marching method. The method takes into account the inelasticity of electron scattering at polar optical phonons for nitrides in the zinc-blende approximation. The calculations show a substantial increase in mobility in samples with a degenerate electron gas, if screening of the long-range potential of polar longitudinal optical phonons is taken into account.

Phase controlled homodyne infrared near-field microscopy and spectroscopy reveal inhomogeneity within and among individual boron nitride nanotubes.

PubMed

Xu, Xiaoji G; Tanur, Adrienne E; Walker, Gilbert C

2013-04-25

We propose a practical method to obtain near-field infrared absorption spectra in apertureless near-field scanning optical microscopy (aNSOM) through homodyne detection with a specific choice of reference phase. The underlying mechanism of the method is illustrated by theoretical and numeric models to show its ability to obtain absorptive rather than dispersive profiles in near-field infrared vibrational microscopy. The proposed near-field nanospectroscopic method is applied to obtain infrared spectra from regions of individual multiwall boron nitride nanotubes (BNNTs) in spatial regions smaller than the diffraction limit of the light source. The spectra suggest variations in interwall spacing within the individual tubes probed.

Development of a Photoelectrochemical Etch Process to Enable Heterogeneous Substrate Integration of Epitaxial III-Nitride Semiconductors

DTIC Science & Technology

2017-12-01

Chung, Stephen Kelley, Kimberley Olver, Blair C. Connelly, Anand V. Sampath, and Meredith L. Reed Sensors and Electron Devices Directorate, ARL...nitride [GaN], indium nitride, and corresponding ternary alloys) provide a basis for a variety of electronic and photonic devices across several...and driven by an electron beam irradiation, which leads to high carrier densities. This necessitates the transfer/removal of the GaN substrate (or GaN

A Combination of Boron Nitride Nanotubes and Cellulose Nanofibers for the Preparation of a Nanocomposite with High Thermal Conductivity.

PubMed

Zeng, Xiaoliang; Sun, Jiajia; Yao, Yimin; Sun, Rong; Xu, Jian-Bin; Wong, Ching-Ping

2017-05-23

With the current development of modern electronics toward miniaturization, high-degree integration and multifunctionalization, considerable heat is accumulated, which results in the thermal failure or even explosion of modern electronics. The thermal conductivity of materials has thus attracted much attention in modern electronics. Although polymer composites with enhanced thermal conductivity are expected to address this issue, achieving higher thermal conductivity (above 10 W m -1 K -1 ) at filler loadings below 50.0 wt % remains challenging. Here, we report a nanocomposite consisting of boron nitride nanotubes and cellulose nanofibers that exhibits high thermal conductivity (21.39 W m -1 K -1 ) at 25.0 wt % boron nitride nanotubes. Such high thermal conductivity is attributed to the high intrinsic thermal conductivity of boron nitride nanotubes and cellulose nanofibers, the one-dimensional structure of boron nitride nanotubes, and the reduced interfacial thermal resistance due to the strong interaction between the boron nitride nanotubes and cellulose nanofibers. Using the as-prepared nanocomposite as a flexible printed circuit board, we demonstrate its potential usefulness in electronic device-cooling applications. This thermally conductive nanocomposite has promising applications in thermal interface materials, printed circuit boards or organic substrates in electronics and could supplement conventional polymer-based materials.

Growth of diamond by RF plasma-assisted chemical vapor deposition

NASA Technical Reports Server (NTRS)

Meyer, Duane E.; Ianno, Natale J.; Woollam, John A.; Swartzlander, A. B.; Nelson, A. J.

1988-01-01

A system has been designed and constructed to produce diamond particles by inductively coupled radio-frequency, plasma-assisted chemical vapor deposition. This is a low-pressure, low-temperature process used in an attempt to deposit diamond on substrates of glass, quartz, silicon, nickel, and boron nitride. Several deposition parameters have been varied including substrate temperature, gas concentration, gas pressure, total gas flow rate, RF input power, and deposition time. Analytical methods employed to determine composition and structure of the deposits include scanning electron microscopy, absorption spectroscopy, scanning Auger microprobe spectroscopy, and Raman spectroscopy. Analysis indicates that particles having a thin graphite surface, as well as diamond particles with no surface coatings, have been deposited. Deposits on quartz have exhibited optical bandgaps as high as 4.5 eV. Scanning electron microscopy analysis shows that particles are deposited on a pedestal which Auger spectroscopy indicates to be graphite. This is a phenomenon that has not been previously reported in the literature.

Detection of secondary phases in duplex stainless steel by magnetic force microscopy and scanning Kelvin probe force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramírez-Salgado, J.; Domínguez-Aguilar, M.A., E-mail: madoming@imp.mx; Castro-Domínguez, B.

2013-12-15

The secondary phase transformations in a commercial super duplex stainless steel were investigated by micro-chemical analyses and high resolution scanning probe microscopy. Energy dispersive X-ray and electron probe detected ferrite and austenite as well as secondary phases in unetched aged duplex stainless steel type 25Cr-7Ni-3Mo. Volta potential indicated that nitride and sigma appeared more active than ferrite, while secondary austenite and austenite presented a nobler potential. Reversal order in nobility is thought to be attributable to the potential ranking provided by oxide nature diversity as a result of secondary phase surface compositions on steel. After eutectoid transformation, secondary austenite wasmore » detected by electron probe microanalysis, whereas atomic force microscopy distinguished this phase from former austenite by image contrast. Magnetic force microscopy revealed a “ghosted” effect on the latter microstructure probably derived from metal memory reminiscence of mechanical polishing at passivity and long range magnetic forces of ferrite phase. - Highlights: • Nobility detection of secondary phases by SKPFM in DSS particles is not a straightforward procedure. • As Volta potential and contrast are not always consistent SKPFM surface oxides is thought played an important role in detection. • AFM distinguished secondary austenite from former austenite by image contrast though SEM required EPMA.« less

Intrinsic ferromagnetism in hexagonal boron nitride nanosheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Si, M. S.; Gao, Daqiang, E-mail: gaodq@lzu.edu.cn, E-mail: xueds@lzu.edu.cn; Yang, Dezheng

2014-05-28

Understanding the mechanism of ferromagnetism in hexagonal boron nitride nanosheets, which possess only s and p electrons in comparison with normal ferromagnets based on localized d or f electrons, is a current challenge. In this work, we report an experimental finding that the ferromagnetic coupling is an intrinsic property of hexagonal boron nitride nanosheets, which has never been reported before. Moreover, we further confirm it from ab initio calculations. We show that the measured ferromagnetism should be attributed to the localized π states at edges, where the electron-electron interaction plays the role in this ferromagnetic ordering. More importantly, we demonstratemore » such edge-induced ferromagnetism causes a high Curie temperature well above room temperature. Our systematical work, including experimental measurements and theoretical confirmation, proves that such unusual room temperature ferromagnetism in hexagonal boron nitride nanosheets is edge-dependent, similar to widely reported graphene-based materials. It is believed that this work will open new perspectives for hexagonal boron nitride spintronic devices.« less

Polarization-free integrated gallium-nitride photonics

PubMed Central

Bayram, C.; Liu, R.

2017-01-01

Gallium Nitride (GaN) materials are the backbone of emerging solid state lighting. To date, GaN research has been primarily focused on hexagonal phase devices due to the natural crystallization. This approach limits the output power and efficiency of LEDs, particularly in the green spectrum. However, GaN can also be engineered to be in cubic phase. Cubic GaN has a lower bandgap (~200 meV) than hexagonal GaN that enables green LEDs much easily. Besides, cubic GaN has more isotropic properties (smaller effective masses, higher carrier mobility, higher doping efficiency, and higher optical gain than hexagonal GaN), and cleavage planes. Due to phase instability, however, cubic phase materials and devices have remained mostly unexplored. Here we review a new method of cubic phase GaN generation: Hexagonal-to-cubic phase transition, based on novel nano-patterning. We report a new crystallographic modelling of this hexagonal-to-cubic phase transition and systematically study the effects of nano-patterning on the GaN phase transition via transmission electron microscopy and electron backscatter diffraction experiments. In summary, silicon-integrated cubic phase GaN light emitters offer a unique opportunity for exploration in next generation photonics. PMID:29307953

Low-loss and tunable near-zero-epsilon titanium nitride

NASA Astrophysics Data System (ADS)

Popović, M.; Novaković, M.; Schmidt, E.; Schöppe, P.; Bibić, N.; Ronning, C.; Rakočević, Z.

2017-10-01

Titanium nitride (TiN) has emerged as alternative plasmonic material in the visible and near-infrared spectral range due to its metallic properties. We studied the influence of silver ion implantation (fluence range from 0.5 × 1016-6 × 1016 ions/cm2) on the structural and optical properties of reactively sputtered 260 nm thick TiN films. The columnar structure was partially destroyed by the irradiation and up to 5 at.% of Ag was incorporated into the films within the projected ion range. The formation of cubic Ag nanoparticles with size of 1-2 nm was observed by high resolution transmission electron microscopy and subsequent fast Fourier transform analysis. This presence of Ag within the TiN matrix drastically changes both the real and imaginary component of the dielectric function and provides low optical losses. A Drude Lorentz dielectric analysis based on free electron and oscillator model are carried out to describe the silver influence on the optical behavior of TiN. With increasing ion fluence, the unscreened plasma frequency decreased and broadening increased. The energy, strength and broadening of the interband transitions were studied with respect to the silver ion fluence and correlated with the microstructural changes induced in TiN films.

Lattice dynamics and electron/phonon interactions in epitaxial transition-metal nitrides

NASA Astrophysics Data System (ADS)

Mei, Antonio Rodolph Bighetti

Transition metal (TM) nitrides, due to their unique combination of remarkable physical properties and simple NaCl structure, are presently utilized in a broad range of applications and as model systems in the investigation of complex phenomena. Group-IVB nitrides TiN, ZrN, and HfN have transport properties which include superconductivity and high electrical conductivity; consequentially, they have become technologically important as electrodes and contacts in the semiconducting and superconducting industries. The Group-VB nitride VN, which exhibits enhanced ductility, is a fundamental component in superhard and tough nanostructured hard coatings. In this thesis, I investigate the lattice dynamics responsible for controlling superconductivity and electrical conductivities in Group-IVB nitrides and elasticity and structural stability of the NaCl-structure Group-VB nitride VN. Our group has already synthesized high-quality epitaxial TiN, HfN, and CeN layers on MgO(001) substrates. By irradiating the growth surface with high ion fluxes at energies below the bulk lattice-atom displacement threshold, dense epitaxial single crystal TM nitride films with extremely smooth surfaces have been grown using ultra-high vacuum magnetically-unbalanced magnetron sputter deposition. Using this approach, I completed the Group-IVB nitride series by growing epitaxial ZrN/MgO(001) films and then grew Group-VB nitride VN films epitaxially on MgO(001), MgO(011), and MgO(111). The combination of high-resolution x-ray diffraction (XRD) reciprocal lattice maps (RLMs), high-resolution cross-sectional transmission electron microscopy (HR-XTEM), and selected-area electron diffraction (SAED) show that single-crystal stoichiometric ZrN films grown at 450 °C are epitaxially oriented cube-on-cube with respect to their MgO(001) substrates, (001) ZrN||(001)MgO and [100]ZrN||[100]MgO. The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm. X-ray reflectivity results reveal that the films are completely dense with smooth surfaces (roughness = 1.3 nm, consistent with atomic-force microscopy analyses). Based upon temperature-dependent electronic transport measurements, epitaxial ZrN/MgO(001) layers have a room-temperature resistivity rho 300K of 12.0 muO-cm, a temperature coefficient of resistivity between 100 and 300 K of 5.6x10-8 O-cm K -1, a residual resistivity rhoo below 30 K of 0.78 muO-cm (corresponding to a residual resistivity ratio rho300K/rho 15K = 15), and the layers exhibit a superconducting transition temperature Tc = 10.4 K. The relatively high residual resistivity ratio, combined with long in-plane and out-of-plane x-ray coherence lengths, xi|| = 18 nm and xi⊥ = 161 nm, indicates high crystalline quality with low mosaicity. The reflectance of ZrN(001), as determined by variable-angle spectroscopic ellipsometry, decreases slowly from 95% at 1 eV to 90% at 2 eV with a reflectance edge at 3.04 eV. Interband transitions dominate the dielectric response above 2 eV. The ZrN(001) nanoindentation hardness and modulus are 22.7+/-1.7 and 450+/-25 GPa. Transport electron/phonon coupling parameters and Eliashberg spectral functions alphatr2F(ho) are determined for Group-IV TM nitrides TiN, ZrN, and HfN, and the rare-earth (RE) nitride CeN using an inversion procedure based upon temperature-dependent (4 < T < 300 K) resistivity measurements. Transport electron/phonon coupling parameters lambdatr vary from 1.11 for ZrN to 0.82 for HfN, 0.73 for TiN, and 0.44 for CeN. The small variation in lambda tr among the TM nitrides and the weak coupling in CeN are consistent with measured Tc values: 10.4 (ZrN), 9.18 (HfN), 5.35 (TiN), and < 4 K for CeN. The Eliashberg spectral function describes the strength and energy spectrum of electron/phonon coupling in conventional superconductors. Spectral peaks in alpha2F(ho), corresponding to regions in energy-space for which electrons couple to acoustic hoac and optical ho op phonon modes, are centered at ho ac = 33 and hoop = 57 meV for TiN, 25 and 60 meV for ZrN, 18 and 64 meV for HfN, and 21 and 39 meV for CeN. The acoustic modes soften with increasing cation mass; optical mode energies remain approximately constant for the TM nitrides, but are significantly lower for the RE nitride due to a lower interatomic force constant. Optical/acoustic peak-intensity ratios are 1.15+/-0.1 for all four nitrides, indicating similar electron/phonon coupling strengths alphatr(h o) for both modes. Elastic constants are determined for single-crystal stoichiometric NaCl-structure VN(001), VN(011), and VN(111) epitaxial layers grown by magnetically-unbalanced reactive magnetron sputter deposition on 001-, 011-, and 111-oriented MgO substrates at 430 °C. The relaxed lattice parameter ao = 0.4134+/-0.0004 nm, obtained from high-resolution reciprocal space maps, and the mass density rho = 6.1 g/cm3, determined from the combination of Rutherford backscattering spectroscopy and film thickness measurements, of the VN layers are both in good agreement with reported values for bulk crystals. Sub-picosecond ultrasonic optical pump/probe techniques are used to generate and detect VN longitudinal sound waves with measured velocities v001 = 9.8+/-0.3, v011 = 9.1+/-0.3, and v111 = 9.1+/-0.3 km/s. The VN c11 elastic constant is determined from the sound wave velocity measurements as 585+/-30 GPa; the c44 elastic constant, 126+/-3 GPa, is obtained from surface acoustic wave measurements. From the combination of c11, c44, vhkl, and rho, the VN c 12 elastic constant is 178+/-33 GPa, the VN elastic anisotropy A = 0.62, the isotropic Poisson ratio nu = 0.29, and the anisotropic Poisson ratios nu001 = 0.23, nu011 = 0.30, and nu 111 = 0.29. The elastic stability criteria requires cubic crystals to resist [001] and [011] shears as well as isotropic compression or, equivalently, for G001 = (c11 -- c12)/2 > 0, G 011 = c44 > 0, and B = (c11 + 2c12)/3 > 0, in which G001 and G011 are directional shear moduli and B is the bulk modulus. Thus, NaCl-structure VN is elastically stable at room temperature. Structural phase transitions in epitaxial stoichiometric VN/MgO(011) thin films are investigated using temperature-dependent synchrotron XRD, SAED, resistivity measurements, HR-XTEM, and ab-initio molecular dynamics (AIMD). At room temperature, VN has the B1 NaCl structure. However, below Tc = 250 K, XRD and SAED results reveal forbidden (00 l) reflections of mixed parity associated with a non-centrosymmetric tetragonal structure. The intensities of the forbidden reflections increase with decreasing temperature following the scaling behavior I ∝ (T c - T)1/2. Resistivity measurements between 300 and 4 K consist of two linear regimes resulting from different electron/phonon coupling strengths in the cubic and tetragonal VN phases. The VN transport Eliashberg spectral function alpha2trF(ho), the product of the phonon density-of-states F(ho) and the transport electron/phonon coupling strength alpha2 tr(ho), is determined and used in combination with AIMD renormalized phonon dispersion relations to show that anharmonic vibrations stabilize the NaCl structure at T > Tc. Free-energy contributions due to vibrational entropy, often neglected in theoretical modeling, are essential for understanding the room-temperature stability of NaCl-structure VN, and of strongly anharmonic systems in general. (Abstract shortened by UMI.).

Joining and Integration of Silicon Nitride Ceramics for Aerospace and Energy Systems

NASA Technical Reports Server (NTRS)

Singh, M.; Asthana, R.

2009-01-01

Light-weight, creep-resistant silicon nitride ceramics possess excellent high-temperature strength and are projected to significantly raise engine efficiency and performance when used as turbine components in the next-generation turbo-shaft engines without the extensive cooling that is needed for metallic parts. One key aspect of Si3N4 utilization in such applications is its joining response to diverse materials. In an ongoing research program, the joining and integration of Si3N4 ceramics with metallic, ceramic, and composite materials using braze interlayers with the liquidus temperature in the range 750-1240C is being explored. In this paper, the self-joining behavior of Kyocera Si3N4 and St. Gobain Si3N4 using a ductile Cu-based active braze (Cu-ABA) containing Ti will be presented. Joint microstructure, composition, hardness, and strength as revealed by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Knoop microhardness test, and offset compression shear test will be presented. Additionally, microstructure, composition, and joint strength of Si3N4/Inconel 625 joints made using Cu-ABA, will be presented. The results will be discussed with reference to the role of chemical reactions, wetting behavior, and residual stresses in joints.

Pectin-coated boron nitride nanotubes: In vitro cyto-/immune-compatibility on RAW 264.7 macrophages.

PubMed

Rocca, Antonella; Marino, Attilio; Del Turco, Serena; Cappello, Valentina; Parlanti, Paola; Pellegrino, Mario; Golberg, Dmitri; Mattoli, Virgilio; Ciofani, Gianni

2016-04-01

Boron nitride nanotubes (BNNTs) represent a new opportunity for drug delivery and clinical therapy. The present work has the objective to investigate pectin-coated BNNTs (P-BNNTs) for their biocompatibility on macrophage cultures, since these cells are among the first components of the immune system to interact with administered nanoparticles. As first step, the potential toxicity of P-BNNTs is verified in terms of proliferation, oxidative stress induction and apoptosis/necrosis phenomena. Thereafter, the modulation of immune cell response following P-BNNT exposure is evaluated at gene and protein level, in particular focusing on cytokine release. Finally, P-BNNT internalization is assessed through transmission electron microscopy and confocal microscopy. The results proved that P-BNNTs are not toxic for macrophages up to 50 μg/ml after 24 h of incubation. The cytokine expression is not affected by P-BNNT administration both at gene and protein level. Moreover, P-BNNTs are internalized by macrophages without impairments of the cell structures. Collected data suggest that P-BNNTs cause neither adverse effects nor inflammation processes in macrophages. These findings represent the first and fundamental step in immune compatibility evaluation of BNNTs, mandatory before any further pre-clinical testing. Copyright © 2016 Elsevier B.V. All rights reserved.

A novel technique based on a plasma focus device for nano-porous gallium nitride formation on P-type silicon

NASA Astrophysics Data System (ADS)

Sharifi Malvajerdi, S.; Salar Elahi, A.; Habibi, M.

2017-04-01

A new deposition formation was observed with a Mather-type Plasma Focus Device (MPFD). MPFD was unitized to fabricate porous Gallium Nitride (GaN) on p-type Silicon (Si) substrate with a (100) crystal orientation for the first time in a deposition process. GaN was deposited on Si with 4 and 7 shots. The samples were subjected to a 3 phase annealing procedure. First, the semiconductors were annealed in the PFD with nitrogen plasma shots after their deposition. Second, a thermal chemical vapor deposition annealed the samples for 1 h at 1050 °C by nitrogen gas at a pressure of 1 Pa. Finally, an electric furnace annealed the samples for 1 h at 1150 °C with continuous flow of nitrogen. Porous GaN structures were observed by Field emission scanning electron microscopy and atomic force microscopy. Furthermore, X-Ray diffraction analysis was carried out to determine the crystallinity of GaN after the samples were annealed. Energy-Dispersive X-Ray Spectroscopy indicated the amount of gallium, nitrogen, and oxygen due to the self-oxidation of the samples. Photoluminescence spectroscopy revealed emissions at 2.94 eV and 3.39 eV, which shows that hexagonal wurtzite crystal structures were formed.

Wetting behaviour of carbon nitride nanostructures grown by plasma enhanced chemical vapour deposition technique

NASA Astrophysics Data System (ADS)

Ahmad Kamal, Shafarina Azlinda; Ritikos, Richard; Abdul Rahman, Saadah

2015-02-01

Tuning the wettability of various coating materials by simply controlling the deposition parameters is essential for various specific applications. In this work, carbon nitride (CNx) films were deposited on silicon (1 1 1) substrates using radio-frequency plasma enhanced chemical vapour deposition employing parallel plate electrode configuration. Effects of varying the electrode distance (DE) on the films' structure and bonding properties were investigated using Field emission scanning electron microscopy, Atomic force microscopy, Fourier transform infrared and X-ray photoemission spectroscopy. The wettability of the films was analyzed using water contact angle measurements. At high DE, the CNx films' surface was smooth and uniform. This changed into fibrous nanostructures when DE was decreased. Surface roughness of the films increased with this morphological transformation. Nitrogen incorporation increased with decrease in DE which manifested the increase in both relative intensities of Cdbnd N to Cdbnd C and Nsbnd H to Osbnd H bonds. sp2-C to sp3-C ratio increased as DE decreased due to greater deformation of sp2 bonded carbon at lower DE. The films' characteristics changed from hydrophilic to super-hydrophobic with the decrease in DE. Roughness ratio, surface porosity and surface energy calculated from contact angle measurements were strongly dependent on the morphology, surface roughness and bonding properties of the films.

Growth and characterization of GaN thin film on Si substrate by thermionic vacuum arc (TVA)

NASA Astrophysics Data System (ADS)

Kundakçı, Mutlu; Mantarcı, Asim; Erdoğan, Erman

2017-01-01

Gallium nitride (GaN) is an attractive material with a wide-direct band gap (3.4 eV) and is one of the significant III-nitride materials, with many advantageous device applications such as high electron mobility transistors, lasers, sensors, LEDs, detectors, and solar cells, and has found applications in optoelectronic devices. GaN could also be useful for industrial research in the future. Chemical vapor deposition (CVD), molecular beam epitaxy (MBE), sputter, and pulsed laser deposition (PLD) are some of the methods used to fabricate GaN thin film. In this research, a GaN thin film grown on a silicon substrate using the thermionic vacuum arc (TVA) technique has been extensively studied. Fast deposition, short production time, homogeneity, and uniform nanostructure with low roughness can be seen as some of the merits of this method. The growth of the GaN was conducted at an operating pressure of 1× {{10}-6} \\text{Torr} , a plasma current 0.6 \\text{A} and for a very short period of time of 40 s. For the characterization process, scanning electron microscopy (SEM) was conducted to determine the structure and surface morphology of the material. Energy dispersive x-ray spectroscopy (EDX) was used to comprehend the elemental analysis characterization of the film. X-ray diffraction (XRD) was used to analyze the structure of the film. Raman measurements were taken to investigate the phonon modes of the material. The morphological properties of the material were analyzed in detail by atomic force microscopy (AFM).

Structure, Microsegregation, and Precipitates of an Alloy 690 ESR Ingot in Industrial Scale

NASA Astrophysics Data System (ADS)

Wang, Min; Zha, Xiangdong; Gao, Ming; Ma, Yingche; Liu, Kui; Li, Yiyi

2015-11-01

The structure, interdendritic, and intergranular segregation, and precipitates of an Alloy 690 electro-slag remelting (ESR) ingot in commercial scale (3t) were investigated by the optical microscopy, electroprobe microanalysis, scanning electron microscopy, and transmission electron microscopy (TEM) techniques. The results indicate that the central longitudinal section of the ESR ingot comprised the ramp-up, steady-state, and hot-top regions, which could be easily distinguished from each other through the macrostructures of them. In the interdendritic area, Cr and Ti were enriched, while Ni and Fe were depleted, and the nominal segregation indexes ( ζ i = C 0 i / C interdendritic i ) of Ti, Cr, and Ni were 0.40, 0.91, and 1.04, respectively, in the hot-top region where suffered the severest segregation. Nitrides, principally precipitated between dendrites, were identified as TiN by TEM and EDS. The morphology, size distribution, and volume fraction of them were determined as well. In terms of the intergranular area, Cr and C coexisted, while Ni and Fe were depleted. And the dendrite-like carbides continuously distributed on the interface between grains, which were identified as M23C6 by the selected area diffraction pattern.

An investigation of nitride precipitates in archaeological iron artefacts from Poland.

PubMed

Kedzierski, Z; Stepiński, J; Zielińska-Lipiec, A

2010-03-01

The paper describes the investigations of nitride precipitates in a spearhead and a sword found in the territory of Poland, in cremation graveyards of the Przeworsk Culture, dated to the Roman Period. Three different techniques of the examination of nitride precipitates were employed: optical microscope, scanning electron microscope (scanning electron microscope with energy dispersive X-ray spectrometer) and transmission electron microscope. Two types of precipitates have been observed, and their plate-like shape was demonstrated. The large precipitate has been confirmed to be gamma'-Fe(4)N, whereas the small one has been identified as alpha''-Fe(16)N(2). The origin of nitride precipitates in archaeological iron artefacts from Poland is probably a result of the manufacturing process or cremation as part of burial rites. An examination of available iron artefacts indicates that nitride precipitates (have only limited effect on mechanical properties) influence the hardness of metal only to a very limited degree.

Growth of fullerene-like carbon nitride thin solid films consisting of cross-linked nano-onions

NASA Astrophysics Data System (ADS)

Czigány, Zs.; Brunell, I. F.; Neidhardt, J.; Hultman, L.; Suenaga, K.

2001-10-01

Fullerene-like CNx (x≈0.12) thin solid films were deposited by reactive magnetron sputtering of graphite in a nitrogen and argon discharge on cleaved NaCl and Si(001) substrates at 450 °C. As-deposited films consist of 5 nm diam CNx nano-onions with shell sizes corresponding to Goldberg polyhedra determined by high-resolution transmission electron microscopy. Electron energy loss spectroscopy revealed that N incorporation is higher in the core of the onions than at the perimeter. N incorporation promotes pentagon formation and provides reactive sites for interlinks between shells of the onions. A model is proposed for the formation of CNx nano-onions by continuous surface nucleation and growth of hemispherical shells.

Effect of pulsed duty cycle control on tribological and corrosion properties of AISI-316 in cathodic cage plasma nitriding

NASA Astrophysics Data System (ADS)

Naeem, M.; Raza, H. A.; Shafiq, M.; Zaka-ul-Islam, M.; Iqbal, Javed; Díaz-Guillén, J. C.; Zakaullah, M.

2017-11-01

Austenitic stainless steels are of prime importance in many industrial sectors because of their excellent corrosion resistance; however, their poor mechanical and tribological features lead to their reduced applicability. In this regard, low-temperature cathodic cage plasma nitriding (CCPN) can be used to improve surface properties of steels without scarifying the inherent corrosion resistance. In this study, AISI-316 samples are processed in CCPN reactor at a temperature of 400 °C, for the treatment time of 4 h, at a pressure of 150 Pa and variable pulsed duty cycle (15-75%). The microstructure and mechanical features are analyzed using x-ray diffraction, scanning electron microscopy, microhardness tester and ball-on-disc wear tester. The anodic polarization test in 3.5% NaCl is conducted to examine the corrosion properties. The results show that hardness is enhanced up to 1327 HV at low duty cycle, which is considerably higher than base material (278 HV). The wear rate is found to be reduced up to 90% over base material by processing at low duty cycle. The base material exhibits severe abrasive wear, and the nitrided sample has dominant adhesive wear. The corrosion rate is found to be reduced up to 95% over base material for the sample nitrided at low duty cycle. This study shows that wear and corrosion resistance in CCPN can be significantly boosted by reducing the pulsed duty cycle.

Nanostructured silicon nitride from wheat and rice husks

NASA Astrophysics Data System (ADS)

Qadri, S. B.; Rath, B. B.; Gorzkowski, E. P.; Wollmershauser, J. A.; Feng, C. R.

2016-04-01

Nanoparticles, submicron-diameter tubes, and rods of Si3N4 were synthesized from the thermal treatment of wheat and rice husks at temperatures at and above 1300 °C in a nitrogen atmosphere. The whole pattern Rietveld analysis of the observed diffraction data from treatments at 1300 °C showed the formation of only hexagonal α-phase of Si3N4 with an R-factor of 1%, whereas samples treated at 1400 °C and above showed both α- and β-phases with an R-factor of 2%. Transmission electron microscopy showed the presence of tubes, rods, and nanoparticles of Si3N4. In a two-step process, where pure SiC was produced first from rice or wheat husk in an argon atmosphere and subsequently treated in a nitrogen atmosphere at 1450 °C, a nanostructured composite material having α- and β-phases of Si3N4 combined with cubic phase of SiC was formed. The thermodynamics of the formation of silicon nitride is discussed in terms of the solid state reaction between organic matter (silica content), which is inherently present in the wheat and rice husks, with the nitrogen from the furnace atmosphere. Nanostructures of silicon nitride formed by a single direct reaction or their composites with SiC formed in a two-step process of agricultural byproducts provide an uncomplicated sustainable synthesis route for silicon nitride used in mechanical, biotechnology, and electro-optic nanotechnology applications.

Effect of laser power on the microstructure and mechanical properties of TiN/Ti3Al composite coatings on Ti6Al4V

NASA Astrophysics Data System (ADS)

Liu, Zhengdao; Zhang, Xiancheng; Xuan, Fuzhen; Wang, Zhengdong; Tu, Shandong

2013-07-01

Laser nitriding is one of the effective techniques to improve the surface properties of titanium alloys and has potential application in the life extension of last-stage steam turbine blades. However, cracking of surface coating is a common problem due to heat concentration in laser nitriding process. Conventionally, the cracks can be avoided through heat treatment, which may have an important influence on the mechanical properties of coating. Crack-free TiN/Ti3Al IMC coatings on Ti6Al4V are prepared by plasma spraying and laser nitriding. The microstructures, phase constitutes and compositions of the coating are observed and analyzed with scanning electron microscopy(SEM), X-ray diffraction(XRD) and X-ray energy-dispersive spectroscopy(EDS). Microhardness, elastic modulus, fracture toughness of the coating are measured. The results show that the crack- and pore-free IMC coatings can be made through the proposed method; with increasing laser power, the amount and density of TiN phase in the coating first increased and then decreased, leading to the similar trend of microhardness and elastic modulus and the reverse trend of fracture toughness of the coating. Both the average microhardness and elastic modulus of the coating increase three times higher than those of the substrate. The volume fraction of the TiN reinforced phase in composite can be controlled by varying the laser power and the cracking problem in laser nitriding process is successfully solved.

Comparison of the ultrafast hot electron dynamics of titanium nitride and gold for plasmonic applications

NASA Astrophysics Data System (ADS)

Doiron, Brock; Li, Yi; Mihai, Andrei P.; Cohen, Lesley F.; Petrov, Peter K.; Alford, Neil M.; Oulton, Rupert F.; Maier, Stefan A.

2017-08-01

With similar optical properties to gold and high thermal stability, titanium nitride continues to prove itself as a promising plasmonic material for high-temperature applications in the visible and near-infrared. In this work, we use transient pump probe differential reflection measurements to compare the electron energy decay channels in titanium nitride and gold thin films. Using an extended two temperature model to incorporate the photoexcited electrons, it is possible to separate the electron-electron and electron-phonon scattering contributions immediately following the arrival of the pump pulse. This model allows for incredibly accurate determination of the internal electronic properties using only optical measurements. As the electronic properties are key in hot electron applications, we show that titanium nitide has substantially longer electron thermalization and electron-phonon scattering times. With this, we were also able to resolve electron thermal conduction in the film using purely optical measurements.

Effect of Thickness on the Structure, Composition and Properties of Titanium Nitride Nano-Coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez, Gustavo; Shutthanandan, V.; Thevuthasan, Suntharampillai

2014-05-05

Titanium nitride (TiNx) coatings were grown by magnetron sputtering onto Si(1 0 0) substrates by varying time of deposition to produce coatings with variable thickness (dTiN) in the range of 20-120 nm. TiNx coatings were characterized by studying their structure, composition, and mechanical properties. Nuclear reaction analysis (NRA) combined with Rutherford backscattering spectrometry (RBS) analyses indicate that the grown coatings were stoichiometric TiN. Grazing incidence X-ray diffraction (GIXRD) measurements indicate that the texturing of TiN coatings changes as a function of dTiN. The (1 1 1) and (0 0 2) peaks appear initially; (1 1 1) becomes intense while (0more » 0 2) disappears with increasing dTiN. Dense, columnar grain structure was evident for all the coatings in electron microscopy analyses. The residual stress for TiN coatings with dTiN~120 nm was 1.07 GPa in compression while thinner samples exhibit higher values of stress.« less

Heteroepitaxial Growth of Single-Walled Carbon Nanotubes from Boron Nitride

PubMed Central

Tang, Dai-Ming; Zhang, Li-Li; Liu, Chang; Yin, Li-Chang; Hou, Peng-Xiang; Jiang, Hua; Zhu, Zhen; Li, Feng; Liu, Bilu; Kauppinen, Esko I.; Cheng, Hui-Ming

2012-01-01

The growth of single-walled carbon nanotubes (SWCNTs) with predefined structure is of great importance for both fundamental research and their practical applications. Traditionally, SWCNTs are grown from a metal catalyst with a vapor-liquid-solid mechanism, where the catalyst is in liquid state with fluctuating structures, and it is intrinsically unfavorable for the structure control of SWCNTs. Here we report the heteroepitaxial growth of SWCNTs from a platelet boron nitride nanofiber (BNNF), which is composed of stacked (002) planes and is stable at high temperatures. SWCNTs are found to grow epitaxially from the open (002) edges of the BNNFs, and the diameters of the SWCNTs are multiples of the BN (002) interplanar distance. In situ transmission electron microscopy observations coupled with first principles calculations reveal that the growth of SWCNTs from the BNNFs follows a vapor-solid-solid mechanism. Our work opens opportunities for the control over the structure of SWCNTs by hetero-crystallographic epitaxy. PMID:23240076

Texture and microstructure evolution in single-phase Ti{sub x}Ta{sub 1-x}N alloys of rocksalt structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koutsokeras, L. E.; Department of Materials Science and Engineering, University of Ioannina, GR-45100 Ioannina; Abadias, G.

2011-08-15

The mechanisms controlling the structural and morphological features (texture and microstructure) of ternary transition metal nitride thin films of the Ti{sub x}Ta{sub 1-x}N system, grown by various physical vapor deposition techniques, are reported. Films deposited by pulsed laser deposition, dual cathode magnetron sputtering, and dual ion beam sputtering have been investigated by means of x-ray diffraction in various geometries and scanning electron microscopy. We studied the effects of composition, energetic, and kinetics in the evolution of the microstructure and texture of the films. We obtain films with single and mixed texture as well as films with columnar ''zone-T'' and globularmore » type morphology. The results have shown that the texture evolution of ternary transition metal nitrides as well as the microstructural features of such films can be well understood in the framework of the kinetic mechanisms proposed for their binary counterparts, thus giving these mechanisms a global application.« less

Observation of phonon-polaritons in thin flakes of hexagonal boron nitride on gold

NASA Astrophysics Data System (ADS)

Ciano, C.; Giliberti, V.; Ortolani, M.; Baldassarre, L.

2018-04-01

Hexagonal Boron Nitride (hBN) is a layered van der Waals material able to sustain hyperbolic phonon-polaritons within its mid-infrared reststrahlen bands. We study the effect of a metallic substrate adjacent to hBN flakes on the polariton dispersion and on the standing wave patterns in nanostructures by means of mid-infrared nanospectroscopy and nanoimaging. We exploit the gold-coated tip apex for atomic force microscopy to launch polaritons in thin hBN flakes. The photo-thermal induced mechanical resonance is used to detect the amplitude profile of polariton standing waves with a lateral resolution of 30 nm. We observe the polariton excitation spectra on hBN flakes as thin as 4 nm, thanks to the infrared field enhancement in the nanogap between the gold-coated tip apex and an ultraflat gold substrate. The data indicate no major effect of remote screening of the free electrons in gold on the phonon-polariton excitation that appears robust also against geometrical imperfections.

Filtered pulsed cathodic arc deposition of fullerene-like carbon and carbon nitride films

NASA Astrophysics Data System (ADS)

Tucker, Mark D.; Czigány, Zsolt; Broitman, Esteban; Näslund, Lars-Åke; Hultman, Lars; Rosen, Johanna

2014-04-01

Carbon and carbon nitride films (CNx, 0 ≤ x ≤ 0.26) were deposited by filtered pulsed cathodic arc and were investigated using transmission electron microscopy and X-ray photoelectron spectroscopy. A "fullerene-like" (FL) structure of ordered graphitic planes, similar to that of magnetron sputtered FL-CNx films, was observed in films deposited at 175 °C and above, with N2 pressures of 0 and 0.5 mTorr. Higher substrate temperatures and significant nitrogen incorporation are required to produce similar FL structure by sputtering, which may, at least in part, be explained by the high ion charge states and ion energies characteristic of arc deposition. A gradual transition from majority sp3-hybridized films to sp2 films was observed with increasing substrate temperature. High elastic recovery, an attractive characteristic mechanical property of FL-CNx films, is evident in arc-deposited films both with and without nitrogen content, and both with and without FL structure.

Synthesis of zirconium oxynitride in air under DC electric fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morisaki, Nobuhiro; Tokunaga, Tomoharu; Sasaki, Katsuhiro

We synthesized zirconium oxynitride from yttria-stabilized zirconia (YSZ) in air by applying DC electric fields that produced a controlled electric current in the specimen. When YSZ was heated under an applied DC electric field, the electric current of the specimen steeply increased at a critical temperature, called a flash event, during flash sintering. By keeping the electric current of the specimen constant during the flash event and then holding the specimen at the critical temperature, YSZ was transformed into zirconium oxynitride under the optimal conditions of 50 V/cm, 500 mA, and 1000 °C. We confirmed that zirconium oxynitride formed using high-resolution transmission electronmore » microscopy, electron energy-loss spectroscopy, and energy-dispersive spectrometry. To convert oxides to nitrides, reducing conditions are necessary to form excess oxygen vacancies. Our technique produced the strong reducing conditions necessary to form nitrides from the oxides by delivering a controlled electric current to the specimen.« less

Hexagonal boron nitride cover on Pt(111): a new route to tune molecule-metal interaction and metal-catalyzed reactions.

PubMed

Zhang, Yanhong; Weng, Xuefei; Li, Huan; Li, Haobo; Wei, Mingming; Xiao, Jianping; Liu, Zhi; Chen, Mingshu; Fu, Qiang; Bao, Xinhe

2015-05-13

In heterogeneous catalysis molecule-metal interaction is often modulated through structural modifications at the surface or under the surface of the metal catalyst. Here, we suggest an alternative way toward this modulation by placing a two-dimensional (2D) cover on the metal surface. As an illustration, CO adsorption on Pt(111) surface has been studied under 2D hexagonal boron nitride (h-BN) overlayer. Dynamic imaging data from surface electron microscopy and in situ surface spectroscopic results under near ambient pressure conditions confirm that CO molecules readily intercalate monolayer h-BN sheets on Pt(111) in CO atmosphere but desorb from the h-BN/Pt(111) interface even around room temperature in ultrahigh vacuum. The interaction of CO with Pt has been strongly weakened due to the confinement effect of the h-BN cover, and consequently, CO oxidation at the h-BN/Pt(111) interface was enhanced thanks to the alleviated CO poisoning effect.

High performance SONOS flash memory with in-situ silicon nanocrystals embedded in silicon nitride charge trapping layer

NASA Astrophysics Data System (ADS)

Lim, Jae-Gab; Yang, Seung-Dong; Yun, Ho-Jin; Jung, Jun-Kyo; Park, Jung-Hyun; Lim, Chan; Cho, Gyu-seok; Park, Seong-gye; Huh, Chul; Lee, Hi-Deok; Lee, Ga-Won

2018-02-01

In this paper, SONOS-type flash memory device with highly improved charge-trapping efficiency is suggested by using silicon nanocrystals (Si-NCs) embedded in silicon nitride (SiNX) charge trapping layer. The Si-NCs were in-situ grown by PECVD without additional post annealing process. The fabricated device shows high program/erase speed and retention property which is suitable for multi-level cell (MLC) application. Excellent performance and reliability for MLC are demonstrated with large memory window of ∼8.5 V and superior retention characteristics of 7% charge loss for 10 years. High resolution transmission electron microscopy image confirms the Si-NC formation and the size is around 1-2 nm which can be verified again in X-ray photoelectron spectroscopy (XPS) where pure Si bonds increase. Besides, XPS analysis implies that more nitrogen atoms make stable bonds at the regular lattice point. Photoluminescence spectra results also illustrate that Si-NCs formation in SiNx is an effective method to form deep trap states.

High quality lamella preparation of gallium nitride compound semiconductor using Triple Beam™ system

NASA Astrophysics Data System (ADS)

Sato, T.; Nakano, K.; Matsumoto, H.; Torikawa, S.; Nakatani, I.; Kiyohara, M.; Isshiki, T.

2017-09-01

Gallium nitride (GaN) compound semiconductors have been known to be very sensitive to Ga focused ion beam (FIB) processing. Due to the nature of GaN based materials it is often difficult to produce damage-free lamellae, therefore applying the Triple Beam™ system which incorporates an enhanced method for amorphous removal is presented to make a high quality lamella. The damage or distortion layer thickness of GaN single crystal prepared with 30 kV Ga FIB and 1 kV Ga FIB were about 17 nm and 1.5 nm respectively. The crystallinity at the uppermost surface remained unaffected when the condition of 1 kV Ar ion milling with the Triple Beam™ system was used. The technique of combining traditional Ga FIB processing with an enhanced method for amorphous layer removal by low energy Ar ion milling allows us to analyse the InGaN/GaN interface using aberration corrected scanning transmission electron microscopy at atomic resolution levels.

M23C6 carbides and Cr2N nitrides in aged duplex stainless steel: A SEM, TEM and FIB tomography investigation.

PubMed

Maetz, J-Y; Douillard, T; Cazottes, S; Verdu, C; Kléber, X

2016-05-01

The precipitation evolution during ageing of a 2101 lean duplex stainless steel was investigated, revealing that the precipitate type and morphology depends on the nature of the grain boundary. Triangular M23C6 carbides precipitate only at γ/δ interfaces and rod-like Cr2N nitrides precipitate at both γ/δ and δ/δ interfaces. After 15min of ageing, the M23C6 size no longer evolves, whereas that of the Cr2N continues to evolve. For Cr2N, the morphology is maintained at γ/δ interfaces, whereas percolation occurs to form a continuous layer at δ/δ interfaces. By combining 2D and 3D characterisation at the nanoscale using transmission electron microscopy (TEM) and focused ion beam (FIB) tomography, a complete description of the precipitation evolution was obtained, including the composition, crystallographic structure, orientation relationship with the matrix phases, location, morphology, size and volume fraction. Copyright © 2016 Elsevier Ltd. All rights reserved.

Thin-walled boron nitride microtubes exhibiting intense band-edge UV emission at room temperature.

PubMed

Huang, Yang; Bando, Yoshio; Tang, Chengchun; Zhi, Chunyi; Terao, Takeshi; Dierre, Benjamin; Sekiguchi, Takashi; Golberg, Dmitri

2009-02-25

Boron nitride (BN) microtubes were synthesized in a vertical induction furnace using Li(2)CO(3) and B reactants. Their structures and morphologies were investigated using x-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The microtubes have diameters of 1-3 microm, lengths of up to hundreds of micrometers, and well-structured ultrathin walls only approximately 50 nm thick. A mechanism combining the vapor-liquid-solid (VLS) and template self-sacrificing processes is proposed to explain the formation of these novel one-dimensional microstructures, in which the Li(2)O-B(2)O(3) eutectic reaction plays an important role. Cathodoluminescence studies show that even at room temperature the thin-walled BN microtubes can possess an intense band-edge emission at approximately 216.5 nm, which is distinct compared with other BN nanostructures. The study suggests that the thin-walled BN microtubes should be promising for constructing compact deep UV devices and find potential applications in microreactors and microfluidic and drug delivery systems.

The Effect of Adjacent Materials on the Propagation of Phonon Polaritons in Hexagonal Boron Nitride.

PubMed

Kim, Kris S; Trajanoski, Daniel; Ho, Kevin; Gilburd, Leonid; Maiti, Aniket; van der Velden, Luuk; de Beer, Sissi; Walker, Gilbert C

2017-07-06

In order to apply the ability of hexagonal boron nitride (hBN) to confine energy in the form of hyperbolic phonon polariton (HPhP) modes in photonic-electronic devices, approaches to finely control and leverage the sensitivity of these propagating waves must be investigated. Here, we show that by surrounding hBN with materials of lower/higher dielectric responses, such as air and silicon, lower/higher surface momenta of HPhPs can be achieved. Furthermore, an alternative method for preparing thin hBN crystals with minimum contamination is presented, which provides opportunities to study the sensitivity of the damping mechanism of HPhPs on adsorbed materials. Infrared scanning near-field optical microscopy (IR-SNOM) results suggest that the reflections at the upper and lower hBN interfaces are primary causes of the damping of HPhPs, and that the damping coefficients of propagating waves are highly sensitive to adjacent layers, suggesting opportunities for sensor applications.

Compensation of native donor doping in ScN: Carrier concentration control and p-type ScN

NASA Astrophysics Data System (ADS)

Saha, Bivas; Garbrecht, Magnus; Perez-Taborda, Jaime A.; Fawey, Mohammed H.; Koh, Yee Rui; Shakouri, Ali; Martin-Gonzalez, Marisol; Hultman, Lars; Sands, Timothy D.

2017-06-01

Scandium nitride (ScN) is an emerging indirect bandgap rocksalt semiconductor that has attracted significant attention in recent years for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices and as a substrate material for high quality GaN growth. Due to the presence of oxygen impurities and native defects such as nitrogen vacancies, sputter-deposited ScN thin-films are highly degenerate n-type semiconductors with carrier concentrations in the (1-6) × 1020 cm-3 range. In this letter, we show that magnesium nitride (MgxNy) acts as an efficient hole dopant in ScN and reduces the n-type carrier concentration, turning ScN into a p-type semiconductor at high doping levels. Employing a combination of high-resolution X-ray diffraction, transmission electron microscopy, and room temperature optical and temperature dependent electrical measurements, we demonstrate that p-type Sc1-xMgxN thin-film alloys (a) are substitutional solid solutions without MgxNy precipitation, phase segregation, or secondary phase formation within the studied compositional region, (b) exhibit a maximum hole-concentration of 2.2 × 1020 cm-3 and a hole mobility of 21 cm2/Vs, (c) do not show any defect states inside the direct gap of ScN, thus retaining their basic electronic structure, and (d) exhibit alloy scattering dominating hole conduction at high temperatures. These results demonstrate MgxNy doped p-type ScN and compare well with our previous reports on p-type ScN with manganese nitride (MnxNy) doping.

Epitaxial growth of aligned AlGalnN nanowires by metal-organic chemical vapor deposition

DOEpatents

Han, Jung; Su, Jie

2008-08-05

Highly ordered and aligned epitaxy of III-Nitride nanowires is demonstrated in this work. <1010> M-axis is identified as a preferential nanowire growth direction through a detailed study of GaN/AlN trunk/branch nanostructures by transmission electron microscopy. Crystallographic selectivity can be used to achieve spatial and orientational control of nanowire growth. Vertically aligned (Al)GaN nanowires are prepared on M-plane AlN substrates. Horizontally ordered nanowires, extending from the M-plane sidewalls of GaN hexagonal mesas or islands demonstrate new opportunities for self-aligned nanowire devices, interconnects, and networks.

Targeting Endothelial Cells with Multifunctional GaN/Fe Nanoparticles

NASA Astrophysics Data System (ADS)

Braniste, Tudor; Tiginyanu, Ion; Horvath, Tibor; Raevschi, Simion; Andrée, Birgit; Cebotari, Serghei; Boyle, Erin C.; Haverich, Axel; Hilfiker, Andres

2017-08-01

In this paper, we report on the interaction of multifunctional nanoparticles with living endothelial cells. The nanoparticles were synthesized using direct growth of gallium nitride on zinc oxide nanoparticles alloyed with iron oxide followed by core decomposition in hydrogen flow at high temperature. Using transmission electron microscopy, we demonstrate that porcine aortic endothelial cells take up GaN-based nanoparticles suspended in the growth medium. The nanoparticles are deposited in vesicles and the endothelial cells show no sign of cellular damage. Intracellular inert nanoparticles are used as guiding elements for controlled transportation or designed spatial distribution of cells in external magnetic fields.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xiaoming; Ke, Changhong, E-mail: xqwang@uga.edu, E-mail: cke@binghamton.edu; Zhang, Liuyang

We investigate the mechanical strength of boron nitride nanotube (BNNT) polymer interfaces by using in situ electron microscopy nanomechanical single-tube pull-out techniques. The nanomechanical measurements show that the shear strengths of BNNT-epoxy and BNNT-poly(methyl methacrylate) interfaces reach 323 and 219 MPa, respectively. Molecular dynamics simulations reveal that the superior load transfer capacity of BNNT-polymer interfaces is ascribed to both the strong van der Waals interactions and Coulomb interactions on BNNT-polymer interfaces. The findings of the extraordinary mechanical strength of BNNT-polymer interfaces suggest that BNNTs are excellent reinforcing nanofiller materials for light-weight and high-strength polymer nanocomposites.

Structure, Mechanics and Synthesis of Nanoscale Carbon and Boron Nitride

NASA Astrophysics Data System (ADS)

Rinaldo, Steven G.

This thesis is divided into two parts. In Part I, we examine the properties of thin sheets of carbon and boron nitride. We begin with an introduction to the theory of elastic sheets, where the stretching and bending modes are considered in detail. The coupling between stretching and bending modes is thought to play a crucial role in the thermodynamic stability of atomically-thin 2D sheets such as graphene. In Chapter 2, we begin by looking at the fabrication of suspended, atomically thin sheets of graphene. We then study their mechanical resonances which are read via an optical transduction technique. The frequency of the resonators was found to depend on their temperature, as was their quality factor. We conclude by offering some interpretations of the data in terms of the stretching and bending modes of graphene. In Chapter 3, we look briefly at the fabrication of thin sheets of carbon and boron nitride nanotubes. We examine the structure of the sheets using transmission and scanning electron microscopy (TEM and SEM, respectively). We then show a technique by which one can make sheets suspended over a trench with adjustable supports. Finally, DC measurements of the resistivity of the sheets in the temperature range 600 -- 1400 C are presented. In Chapter 4, we study the folding of few-layer graphene oxide, graphene and boron nitride into 3D aerogel monoliths. The properties of graphene oxide are first considered, after which the structure of graphene and boron nitride aerogels is examined using TEM and SEM. Some models for their structure are proposed. In Part II, we look at synthesis techniques for boron nitride (BN). In Chapter 5, we study the conversion of carbon structures of boron nitride via the application of carbothermal reduction of boron oxide followed by nitridation. We apply the conversion to a wide variety of morphologies, including aerogels, carbon fibers and nanotubes, and highly oriented pyrolytic graphite. In the latter chapters, we look at the formation of boron nitride nanotubes (BNNTs). In Chapter 6, we look at various methods of producing BNNTs from boron droplets, and introduce a new method involving injection of boron powder into an induction furnace. In Chapter 7 we consider another useful process, where ammonia is reacted with boron vapor generated in situ, either through the reaction of boron with metal oxides or through the decomposition of metal borides.

Spatially Resolved One-Dimensional Boundary States in Graphene-Hexagonal Boron Nitride Planar Heterostructures

DOE PAGES

Li, An-Ping; Park, Jewook; Lee, Jaekwang; ...

2014-01-01

Two-dimensional (2D) interfaces between crystalline materials have been shown to generate unusual interfacial electronic states in complex oxides1-4. Recently, a onedimensional (1D) polar-on-nonpolar interface has been realized in hexagonal boron nitride (hBN) and graphene heterostructures 5-10, where a coherent 1D boundary is expected to possess peculiar electronic states dictated by edge states of graphene and the polarity of hBN 11-13. Here we present a combined scanning tunneling microscopy (STM) and firstprinciples theory study of the graphene-hBN boundary to provide a rare glimpse into the spatial and energetic distributions of the 1D boundary states in real-space. The interfaces studied here aremore » crystallographically coherent with sharp transitions from graphene zigzag edges to B (or N) terminated hBN atomic layers on a Cu foil substrate5. The revealed boundary states are about 0.6 eV below or above the Fermi energy depending on the termination of the hBN at the boundary, and are extended along but localized at the boundary with a lateral thickness of 2-3nm. These results suggest that unconventional physical effects similar to those observed at 2D interfaces can also exist in lower dimensions, opening a route for tuning of electronic properties at interfaces in 2D heterostructures.« less

Native gallium adatoms discovered on atomically-smooth gallium nitride surfaces at low temperature.

PubMed

Alam, Khan; Foley, Andrew; Smith, Arthur R

2015-03-11

In advanced compound semiconductor devices, such as in quantum dot and quantum well systems, detailed atomic configurations at the growth surfaces are vital in determining the structural and electronic properties. Therefore, it is important to investigate the surface reconstructions in order to make further technological advancements. Usually, conventional semiconductor surfaces (e.g., arsenides, phosphides, and antimonides) are highly reactive due to the existence of a high density of group V (anion) surface dangling bonds. However, in the case of nitrides, group III rich growth conditions in molecular beam epitaxy are usually preferred leading to group III (Ga)-rich surfaces. Here, we use low-temperature scanning tunneling microscopy to reveal a uniform distribution of native gallium adatoms with a density of 0.3%-0.5% of a monolayer on the clean, as-grown surface of nitrogen polar GaN(0001̅) having the centered 6 × 12 reconstruction. Unseen at room temperature, these Ga adatoms are strongly bound to the surface but move with an extremely low surface diffusion barrier and a high density saturation coverage in thermodynamic equilibrium with Ga droplets. Furthermore, the Ga adatoms reveal an intrinsic surface chirality and an asymmetric site occupation. These observations can have important impacts in the understanding of gallium nitride surfaces.

Direct spontaneous growth and interfacial structural properties of inclined GaN nanopillars on r-plane sapphire

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adikimenakis, A.; Aretouli, K. E.; Tsagaraki, K.

2015-06-28

The spontaneous growth of GaN nanopillars (NPs) by direct plasma-assisted molecular beam epitaxy on nitridated r-plane sapphire substrates has been studied. The emanation of metal-polarity NPs from inside an a-plane nonpolar GaN film was found to depend on both the substrate nitridation and the growth conditions. The density of NPs increased with increasing the duration of the nitridation process and the power applied on the radio-frequency plasma source, as well as the III/V flux ratio, while variation of the first two parameters enhanced the roughness of the substrate's surface. Transmission electron microscopy (TEM) techniques were employed to reveal the structuralmore » characteristics of the NPs and their nucleation mechanism from steps on the sapphire surface and/or interfacial semipolar GaN nanocrystals. Lattice strain measurements showed a possible Al enrichment of the first 5–6 monolayers of the NPs. By combining cross-sectional and plan-view TEM observations, the three-dimensional model of the NPs was constructed. The orientation relationship and interfacial accommodation between the NPs and the nonpolar a-plane GaN film were also elucidated. The NPs exhibited strong and narrow excitonic emission, suggesting an excellent structural quality.« less

Helium ion beam induced electron emission from insulating silicon nitride films under charging conditions

NASA Astrophysics Data System (ADS)

Petrov, Yu. V.; Anikeva, A. E.; Vyvenko, O. F.

2018-06-01

Secondary electron emission from thin silicon nitride films of different thicknesses on silicon excited by helium ions with energies from 15 to 35 keV was investigated in the helium ion microscope. Secondary electron yield measured with Everhart-Thornley detector decreased with the irradiation time because of the charging of insulating films tending to zero or reaching a non-zero value for relatively thick or thin films, respectively. The finiteness of secondary electron yield value, which was found to be proportional to electronic energy losses of the helium ion in silicon substrate, can be explained by the electron emission excited from the substrate by the helium ions. The method of measurement of secondary electron energy distribution from insulators was suggested, and secondary electron energy distribution from silicon nitride was obtained.

Predicting the structural and electronic properties of two-dimensional single layer boron nitride sheets

NASA Astrophysics Data System (ADS)

Li, Xiao-Dong; Cheng, Xin-Lu

2018-02-01

Three two-dimensional (2D) single layer boron nitride sheets have been predicted based on the first-principles calculations. These 2D boron nitride sheets are comprised of equivalent boron atoms and nitride atoms with sp2 and sp bond hybridization. The geometry optimization reflects that they all possess stable planar crystal structures with the space group P 6 bar 2 m (D3h3) symmetry. The charge density distribution manifests that the B-N bonds in these boron nitride sheets are covalent in nature but with ionic characteristics. The tunable band gaps indicate their potential applications in nanoscale electronic and optoelectronic devices by changing the length of sp-bonded Bsbnd N linkages.

Molecular Self-Assembly in a Poorly Screened Environment: F4TCNQ on Graphene/BN

PubMed Central

2015-01-01

We report a scanning tunneling microscopy and noncontact atomic force microscopy study of close-packed 2D islands of tetrafluorotetracyanoquinodimethane (F4TCNQ) molecules at the surface of a graphene layer supported by boron nitride. While F4TCNQ molecules are known to form cohesive 3D solids, the intermolecular interactions that are attractive for F4TCNQ in 3D are repulsive in 2D. Our experimental observation of cohesive molecular behavior for F4TCNQ on graphene is thus unexpected. This self-assembly behavior can be explained by a novel solid formation mechanism that occurs when charged molecules are placed in a poorly screened environment. As negatively charged molecules coalesce, the local work function increases, causing electrons to flow into the coalescing molecular island and increase its cohesive binding energy. PMID:26482218

Ultrafast Spectroscopy Reveals Electron-Transfer Cascade That Improves Hydrogen Evolution with Carbon Nitride Photocatalysts.

PubMed

Corp, Kathryn L; Schlenker, Cody W

2017-06-14

Solar hydrogen generation from water represents a compelling component of a future sustainable energy portfolio. Recently, chemically robust heptazine-based polymers known as graphitic carbon nitrides (g-C 3 N 4 ) have emerged as promising photocatalysts for hydrogen evolution using visible light while withstanding harsh chemical environments. However, since g-C 3 N 4 electron-transfer dynamics are poorly understood, rational design rules for improving activity remain unclear. Here, we use visible and near-infrared femtosecond transient absorption (TA) spectroscopy to reveal an electron-transfer cascade that correlates with a near-doubling in photocatalytic activity from 2050 to 3810 μmol h -1 g -1 when we infuse a suspension of bulk g-C 3 N 4 with 10% mass loading of chemically exfoliated carbon nitride. TA spectroscopy indicates that exfoliated carbon nitride quenches photogenerated electrons on g-C 3 N 4 at rates approaching the molecular diffusion limit. The TA signal for photogenerated electrons on g-C 3 N 4 decays with a time constant of 1/k e ' = 660 ps in the mixture versus 1/k e = 4.1 ns in g-C 3 N 4 alone. Our TA measurements suggest that the charge generation efficiency in g-C 3 N 4 is greater than 65%. Exfoliated carbon nitride, which liberates only trace hydrogen levels when photoexcited directly, does not appear to independently sustain appreciable long-lived charge generation. Thus, the activity enhancement in the two-component infusion evidently results from a cooperative effect in which charge is generated on g-C 3 N 4 , followed by electron transfer to exfoliated carbon nitride containing photocatalytic chain terminations. This correlation between electron transfer and photocatalytic activity provides new insight into structural modifications for controlling charge separation dynamics and activity of carbon-based photocatalysts.

Electronic Biosensors Based on III-Nitride Semiconductors.

PubMed

Kirste, Ronny; Rohrbaugh, Nathaniel; Bryan, Isaac; Bryan, Zachary; Collazo, Ramon; Ivanisevic, Albena

2015-01-01

We review recent advances of AlGaN/GaN high-electron-mobility transistor (HEMT)-based electronic biosensors. We discuss properties and fabrication of III-nitride-based biosensors. Because of their superior biocompatibility and aqueous stability, GaN-based devices are ready to be implemented as next-generation biosensors. We review surface properties, cleaning, and passivation as well as different pathways toward functionalization, and critically analyze III-nitride-based biosensors demonstrated in the literature, including those detecting DNA, bacteria, cancer antibodies, and toxins. We also discuss the high potential of these biosensors for monitoring living cardiac, fibroblast, and nerve cells. Finally, we report on current developments of covalent chemical functionalization of III-nitride devices. Our review concludes with a short outlook on future challenges and projected implementation directions of GaN-based HEMT biosensors.

Proton Irradiation-Induced Metal Voids in Gallium Nitride High Electron Mobility Transistors

DTIC Science & Technology

2015-09-01

13. ABSTRACT (maximum 200 words) Gallium nitride/aluminum gallium nitride high electron mobility transistors with nickel/ gold (Ni/Au) and...platinum/ gold (Pt/Au) gating are irradiated with 2 MeV protons. Destructive physical analysis revealed material voids underneath the gate finger of the...nickel/ gold (Ni/Au) and platinum/ gold (Pt/Au) gating are irradiated with 2 MeV protons. Destructive physical analysis revealed material voids underneath

Through a Window, Brightly: A Review of Selected Nanofabricated Thin-Film Platforms for Spectroscopy, Imaging, and Detection.

PubMed

Dwyer, Jason R; Harb, Maher

2017-09-01

We present a review of the use of selected nanofabricated thin films to deliver a host of capabilities and insights spanning bioanalytical and biophysical chemistry, materials science, and fundamental molecular-level research. We discuss approaches where thin films have been vital, enabling experimental studies using a variety of optical spectroscopies across the visible and infrared spectral range, electron microscopies, and related techniques such as electron energy loss spectroscopy, X-ray photoelectron spectroscopy, and single molecule sensing. We anchor this broad discussion by highlighting two particularly exciting exemplars: a thin-walled nanofluidic sample cell concept that has advanced the discovery horizons of ultrafast spectroscopy and of electron microscopy investigations of in-liquid samples; and a unique class of thin-film-based nanofluidic devices, designed around a nanopore, with expansive prospects for single molecule sensing. Free-standing, low-stress silicon nitride membranes are a canonical structural element for these applications, and we elucidate the fabrication and resulting features-including mechanical stability, optical properties, X-ray and electron scattering properties, and chemical nature-of this material in this format. We also outline design and performance principles and include a discussion of underlying material preparations and properties suitable for understanding the use of alternative thin-film materials such as graphene.

Atmospheric scanning electron microscope for correlative microscopy.

PubMed

Morrison, Ian E G; Dennison, Clare L; Nishiyama, Hidetoshi; Suga, Mitsuo; Sato, Chikara; Yarwood, Andrew; O'Toole, Peter J

2012-01-01

The JEOL ClairScope is the first truly correlative scanning electron and optical microscope. An inverted scanning electron microscope (SEM) column allows electron images of wet samples to be obtained in ambient conditions in a biological culture dish, via a silicon nitride film window in the base. A standard inverted optical microscope positioned above the dish holder can be used to take reflected light and epifluorescence images of the same sample, under atmospheric conditions that permit biochemical modifications. For SEM, the open dish allows successive staining operations to be performed without moving the holder. The standard optical color camera used for fluorescence imaging can be exchanged for a high-sensitivity monochrome camera to detect low-intensity fluorescence signals, and also cathodoluminescence emission from nanophosphor particles. If these particles are applied to the sample at a suitable density, they can greatly assist the task of perfecting the correlation between the optical and electron images. Copyright © 2012 Elsevier Inc. All rights reserved.

Tensile Strength and Microstructural Characterization of Uncoated and Coated HPZ Ceramic Fibers

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Wheeler, Donald R.; Dickerson, Robert M.

1996-01-01

Tensile strengths of as-received HPZ fiber and those surface coated with BN, BN/SiC, and BN/Si3N4 have been determined at room temperature using a two-parameter Weibull distribution. Nominally approx. 0.4 micron BN and 0.2 micron SiC or Si3N4 coatings were deposited on the fibers by chemical vapor deposition using a continuous reactor. The average tensile strength of uncoated HPZ fiber was 2.0 +/- 0.56 GPa (290 +/- 81 ksi) with a Weibull modulus of 4.1. For the BN coated fibers, the average strength and the Weibull modulus increased to 2.39 +/- 0.44 GPa (346 +/- 64 ksi) and 6.5, respectively. The HPZ/BN/SiC fibers showed an average strength of 2.0 +/- 0.32 GPa (290 +/- 47 ksi) and Weibull modulus of 7.3. Average strength of the fibers having a dual BN/Si3N4 surface coating degraded to 1.15 +/- 0.26 GPa (166 +/- 38 ksi) with a Weibull modulus of 5.3. The chemical composition and thickness of the fiber coatings were determined using scanning Auger analysis. Microstructural analysis of the fibers and the coatings was carried out by scanning electron microscopy and transmission electron microscopy. A microporous silica-rich layer approx. 200 nm thick is present on the as-received HPZ fiber surface. The BN coatings on the fibers are amorphous to partly turbostratic and contaminated with carbon and oxygen. Silicon carbide coating was crystalline whereas the silicon nitride coating was amorphous. The silicon carbide and silicon nitride coatings are non-stoichiometric, non-uniform, and granular. Within a fiber tow, the fibers on the outside had thicker and more granular coatings than those on the inside.

Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

PubMed

Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

2014-04-01

Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without breaking vacuum, and convenient visual access to the sample and tip inside a superconducting magnet cryostat. A sample/tip handling system is optimized for both the molecular beam epitaxy growth system and the scanning tunneling microscope system. The sample/tip handing system enables in situ STM studies on epitaxially grown samples, and tip exchange in the superconducting magnet cryostat. The hybrid molecular beam epitaxy and low temperature scanning tunneling microscopy system is capable of growing semiconductor-based hetero-structures with controlled accuracy down to a single atomic-layer and imaging them down to atomic resolution.

Silicon nitride films deposited with an electron beam created plasma

NASA Technical Reports Server (NTRS)

Bishop, D. C.; Emery, K. A.; Rocca, J. J.; Thompson, L. R.; Zamani, H.; Collins, G. J.

1984-01-01

The electron beam assisted chemical vapor deposition (EBCVD) of silicon nitride films using NH3, N2, and SiH4 as the reactant gases is reported. The films have been deposited on aluminum, SiO2, and polysilicon film substrates as well as on crystalline silicon substrates. The range of experimental conditions under which silicon nitrides have been deposited includes substrate temperatures from 50 to 400 C, electron beam currents of 2-40 mA, electron beam energies of 1-5 keV, total ambient pressures of 0.1-0.4 Torr, and NH3/SiH4 mass flow ratios of 1-80. The physical, electrical, and chemical properties of the EBCVD films are discussed.

Defect sensitive etching of hexagonal boron nitride single crystals

NASA Astrophysics Data System (ADS)

Edgar, J. H.; Liu, S.; Hoffman, T.; Zhang, Yichao; Twigg, M. E.; Bassim, Nabil D.; Liang, Shenglong; Khan, Neelam

2017-12-01

Defect sensitive etching (DSE) was developed to estimate the density of non-basal plane dislocations in hexagonal boron nitride (hBN) single crystals. The crystals employed in this study were precipitated by slowly cooling (2-4 °C/h) a nickel-chromium flux saturated with hBN from 1500 °C under 1 bar of flowing nitrogen. On the (0001) planes, hexagonal-shaped etch pits were formed by etching the crystals in a eutectic mixture of NaOH and KOH between 450 °C and 525 °C for 1-2 min. There were three types of pits: pointed bottom, flat bottom, and mixed shape pits. Cross-sectional transmission electron microscopy revealed that the pointed bottom etch pits examined were associated with threading dislocations. All of these dislocations had an a-type burgers vector (i.e., they were edge dislocations, since the line direction is perpendicular to the [ 2 11 ¯ 0 ]-type direction). The pit widths were much wider than the pit depths as measured by atomic force microscopy, indicating the lateral etch rate was much faster than the vertical etch rate. From an Arrhenius plot of the log of the etch rate versus the inverse temperature, the activation energy was approximately 60 kJ/mol. This work demonstrates that DSE is an effective method for locating threading dislocations in hBN and estimating their densities.

Direct growth of nanocrystalline hexagonal boron nitride films on dielectric substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tay, Roland Yingjie; Temasek Laboratories@NTU, 50 Nanyang Avenue, Singapore, Singapore 639798; Tsang, Siu Hon

Atomically thin hexagonal-boron nitride (h-BN) films are primarily synthesized through chemical vapor deposition (CVD) on various catalytic transition metal substrates. In this work, a single-step metal-catalyst-free approach to obtain few- to multi-layer nanocrystalline h-BN (NCBN) directly on amorphous SiO{sub 2}/Si and quartz substrates is demonstrated. The as-grown thin films are continuous and smooth with no observable pinholes or wrinkles across the entire deposited substrate as inspected using optical and atomic force microscopy. The starting layers of NCBN orient itself parallel to the substrate, initiating the growth of the textured thin film. Formation of NCBN is due to the random andmore » uncontrolled nucleation of h-BN on the dielectric substrate surface with no epitaxial relation, unlike on metal surfaces. The crystallite size is ∼25 nm as determined by Raman spectroscopy. Transmission electron microscopy shows that the NCBN formed sheets of multi-stacked layers with controllable thickness from ∼2 to 25 nm. The absence of transfer process in this technique avoids any additional degradation, such as wrinkles, tears or folding and residues on the film which are detrimental to device performance. This work provides a wider perspective of CVD-grown h-BN and presents a viable route towards large-scale manufacturing of h-BN substrates and for coating applications.« less

Characterization of Plasma Synthesized Vertical Carbon Nanofibers for Nanoelectronics Applications

NASA Technical Reports Server (NTRS)

Lee, Jaesung; Feng, Philip X.-L.; Kaul, Anupama B.

2013-01-01

We report on the material characterization of carbon nanofibers (CNFs) which are assembled into a three-dimensional (3D) configuration for making new nanoelectromechanical systems (NEMS). High-resolution scanning electron microscopy (SEM) and x-ray electron dispersive spectroscopy (XEDS) are employed to decipher the morphology and chemical compositions of the CNFs at various locations along individual CNFs grown on silicon (Si) and refractory nitride (NbTiN) substrates, respectively. The measured characteristics suggest interesting properties of the CNF bodies and their capping catalyst nanoparticles, and growth mechanisms on the two substrates. Laser irradiation on the CNFs seems to cause thermal oxidation and melting of catalyst nanoparticles. The structural morphology and chemical compositions of the CNFs revealed in this study should aid in the applications of the CNFs to nanoelectronics and NEMS.

Evolution of Moiré Profiles from van der Waals Superstructures of Boron Nitride Nanosheets

PubMed Central

Liao, Yunlong; Cao, Wei; Connell, John W.; Chen, Zhongfang; Lin, Yi

2016-01-01

Two-dimensional (2D) van der Waals (vdW) superstructures, or vdW solids, are formed by the precise restacking of 2D nanosheet lattices, which can lead to unique physical and electronic properties that are not available in the parent nanosheets. Moiré patterns formed by the crystalline mismatch between adjacent nanosheets are the most direct features for vdW superstructures under microscopic imaging. In this article, transmission electron microscopy (TEM) observation of hexagonal Moiré patterns with unusually large micrometer-sized lateral areas (up to ~1 μm2) and periodicities (up to ~50 nm) from restacking of liquid exfoliated hexagonal boron nitride nanosheets (BNNSs) is reported. This observation was attributed to the long range crystallinity and the contaminant-free surfaces of these chemically inert nanosheets. Parallel-line-like Moiré fringes with similarly large periodicities were also observed. The simulations and experiments unambiguously revealed that the hexagonal patterns and the parallel fringes originated from the same rotationally mismatched vdW stacking of BNNSs and can be inter-converted by simply tilting the TEM specimen following designated directions. This finding may pave the way for further structural decoding of other 2D vdW superstructure systems with more complex Moiré images. PMID:27188697

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge.

PubMed

Yeh, Yao-Wen; Raitses, Yevgeny; Koel, Bruce E; Yao, Nan

2017-06-08

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm 2 , is above the boron melting point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. Stable and reliable arc operation and arc synthesis were achieved with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. The results also show evidence of root-growth of BNNTs produced in the arc discharge.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge

DOE PAGES

Yeh, Yao-Wen; Raitses, Yevgeny; Koel, Bruce E.; ...

2017-06-08

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. In order to sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of similar to 100 A/cm 2, is above the boron meltingmore » point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. We achieved a stable and reliable arc operation and arc synthesis with the boronrich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. Our results also show evidence of root-growth of BNNTs produced in the arc discharge.« less

Nanoscale Electronic Conditioning for Improvement of Nanowire Light-Emitting-Diode Efficiency.

PubMed

May, Brelon J; Belz, Matthew R; Ahamed, Arshad; Sarwar, A T M G; Selcu, Camelia M; Myers, Roberto C

2018-04-24

Commercial III-Nitride LEDs and lasers spanning visible and ultraviolet wavelengths are based on epitaxial films. Alternatively, nanowire-based III-Nitride optoelectronics offer the advantage of strain compliance and high crystalline quality growth on a variety of inexpensive substrates. However, nanowire LEDs exhibit an inherent property distribution, resulting in uneven current spreading through macroscopic devices that consist of millions of individual nanowire diodes connected in parallel. Despite being electrically connected, only a small fraction of nanowires, sometimes <1%, contribute to the electroluminescence (EL). Here, we show that a population of electrical shorts exists in the devices, consisting of a subset of low-resistance nanowires that pass a large portion of the total current in the ensemble devices. Burn-in electronic conditioning is performed by applying a short-term overload voltage; the nanoshorts experience very high current density, sufficient to render them open circuits, thereby forcing a new current path through more nanowire LEDs in an ensemble device. Current-voltage measurements of individual nanowires are acquired using conductive atomic force microscopy to observe the removal of nanoshorts using burn-in. In macroscopic devices, this results in a 33× increase in peak EL and reduced leakage current. Burn-in conditioning of nanowire ensembles therefore provides a straightforward method to mitigate nonuniformities inherent to nanowire devices.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeh, Yao-Wen; Raitses, Yevgeny; Koel, Bruce E.

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. In order to sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of similar to 100 A/cm 2, is above the boron meltingmore » point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. We achieved a stable and reliable arc operation and arc synthesis with the boronrich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. Our results also show evidence of root-growth of BNNTs produced in the arc discharge.« less

Sliding Seal Materials for Adiabatic Engines, Phase 2

NASA Technical Reports Server (NTRS)

Lankford, J.; Wei, W.

1986-01-01

An essential task in the development of the heavy-duty adiabatic diesel engine is identification and improvements of reliable, low-friction piston seal materials. In the present study, the sliding friction coefficients and wear rates of promising carbide, oxide, and nitride materials were measured under temperature, environmental, velocity, and loading conditions that are representative of the adiabatic engine environment. In addition, silicon nitride and partially stabilized zirconia disks were ion implanted with TiNi, Ni, Co, and Cr, and subsequently run against carbide pins, with the objective of producing reduced friction via solid lubrication at elevated temperature. In order to provide guidance needed to improve materials for this application, the program stressed fundamental understanding of the mechanisms involved in friction and wear. Electron microscopy was used to elucidate the micromechanisms of wear following wear testing, and Auger electron spectroscopy was used to evaluate interface/environment interactions which seemed to be important in the friction and wear process. Unmodified ceramic sliding couples were characterized at all temperatures by friction coefficients of 0.24 and above. The coefficient at 800 C in an oxidizing environment was reduced to below 0.1, for certain material combinations, by the ion implanation of TiNi or Co. This beneficial effect was found to derive from lubricious Ti, Ni, and Co oxides.

Computational simulation of subatomic-resolution AFM and STM images for graphene/hexagonal boron nitride heterostructures with intercalated defects

NASA Astrophysics Data System (ADS)

Lee, Junsu; Kim, Minjung; Chelikowsky, James R.; Kim, Gunn

2016-07-01

Using ab initio density functional calculations, we predict subatomic-resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM) images of vertical heterostructures of graphene/hexagonal boron nitride (h-BN) with an intercalated metal atom (Li, K, Cr, Mn, Co, or Cu), and study the effects of the extrinsic metal defect on the interfacial coupling. We find that the structural deformation of the graphene/h-BN layer caused by the metal defect strongly affects the AFM images, whereas orbital hybridization between the metal defect and the graphene/h-BN layer characterizes the STM images.

Covalent coupling via dehalogenation on Ni(111) supported boron nitride and graphene.

PubMed

Morchutt, Claudius; Björk, Jonas; Krotzky, Sören; Gutzler, Rico; Kern, Klaus

2015-02-11

Polymerization of 1,3,5-tris(4-bromophenyl)benzene via dehalogenation on graphene and hexagonal boron nitride is investigated by scanning tunneling microscopy experiments and density functional theory calculations. This work reveals how the interactions between molecules and graphene or h-BN grown on Ni(111) govern the surface-confined synthesis of polymers through C-C coupling.

Growth of hierarchical GaN nanowires for optoelectronic device applications

NASA Astrophysics Data System (ADS)

Raj, Rishabh; Vignesh, Veeramuthu; Ra, Yong-Ho; Nirmala, Rajkumar; Lee, Cheul-Ro; Navamathavan, Rangaswamy

2017-01-01

Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers, and nanofluidic biochemical sensors. We report on the growth of hierarchical GaN nanowires (NWs) by dynamically adjusting the growth parameters using the pulsed flow metal-organic chemical vapor deposition technique. We carried out two step growth processes to grow hierarchical GaN NWs. In the first step, the GaN NWs were grown at 950°C, and in the second, we suitably decreased the growth temperature to 630°C and 710°C to grow the hierarchical structures. The surface morphology and optical characterization of the grown GaN NWs were studied by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and cathodoluminescence measurements. These kinds of hierarchical GaN NWs are promising for allowing flat band quantum structures that are shown to improve the efficiency of LEDs.

Optimized Deconvolution for Maximum Axial Resolution in Three-Dimensional Aberration-Corrected Scanning Transmission Electron Microscopy

PubMed Central

Ramachandra, Ranjan; de Jonge, Niels

2012-01-01

Three-dimensional (3D) data sets were recorded of gold nanoparticles placed on both sides of silicon nitride membranes using focal series aberration-corrected scanning transmission electron microscopy (STEM). The deconvolution of the 3D datasets was optimized to obtain the highest possible axial resolution. The deconvolution involved two different point spread function (PSF)s, each calculated iteratively via blind deconvolution.. Supporting membranes of different thicknesses were tested to study the effect of beam broadening on the deconvolution. It was found that several iterations of deconvolution was efficient in reducing the imaging noise. With an increasing number of iterations, the axial resolution was increased, and most of the structural information was preserved. Additional iterations improved the axial resolution by maximal a factor of 4 to 6, depending on the particular dataset, and up to 8 nm maximal, but at the cost of a reduction of the lateral size of the nanoparticles in the image. Thus, the deconvolution procedure optimized for highest axial resolution is best suited for applications where one is interested in the 3D locations of nanoparticles only. PMID:22152090

Chlorination Kinetics of Titanium Nitride for Production of Titanium Tetrachloride from Nitrided Ilmenite

NASA Astrophysics Data System (ADS)

Ahmadi, Eltefat; Rezan, Sheikh Abdul; Baharun, Norlia; Ramakrishnan, Sivakumar; Fauzi, Ahmad; Zhang, Guangqing

2017-10-01

The kinetics of chlorination of titanium nitride (TiN) was investigated in the temperature range of 523 K to 673 K (250 °C to 400 °C). The results showed that the extent of chlorination slightly increased with increasing temperature and decreasing particle size of titanium nitride at constant flow rate of N2-Cl2 gas mixture. At 523 K (250 °C), the extent of chlorination was 85.6 pct in 60 minutes whereas at 673 K (400 °C), it was 97.7 pct investigated by weight loss measurement and confirmed by ICP analyses. The experimental results indicated that a shrinking unreacted core model with mixed-control mechanism governed the chlorination rate. It was observed that the surface chemical reaction of chlorine gas on the surface of TiN particles was rate controlling in the initial stage and, during later stage, internal (pore) diffusion through the intermediate product layer was rate controlling step. Overall the process follows the mixed-control model incorporating both chemical reaction and internal diffusion control. The activation energy for the chlorination of TiN was found to be about 10.97 kJ mol-1. In processing TiCl4 from TiN and TiO0.02C0.13N0.85, the solids involved in the chlorination process were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy-dispersive X-ray spectrometer (EDX). The SEM/EDX results demonstrated the consumption of TiN particles with extent of chlorination that showed shrinking core behavior.

Spatially-resolved studies on the role of defects and boundaries in electronic behavior of 2D materials

NASA Astrophysics Data System (ADS)

Hus, Saban M.; Li, An-Ping

2017-08-01

Two-dimensional (2D) materials are intrinsically heterogeneous. Both localized defects, such as vacancies and dopants, and mesoscopic boundaries, such as surfaces and interfaces, give rise to compositional or structural heterogeneities. The presence of defects and boundaries can break lattice symmetry, modify the energy landscape, and create quantum confinement, leading to fascinating electronic properties different from the ;ideal; 2D sheets. This review summarizes recent progress in understanding the roles of defects and boundaries in electronic, magnetic, thermoelectric, and transport properties of 2D layered materials. The focus is on the understanding of correlation of atomic-scale structural information with electronic functions by interrogating heterogeneities individually. The materials concerned are graphene, transition metal dichalcogenides (TMDs), hexagonal boron nitride (hBN), and topological insulators (TIs). The experimental investigations benefit from new methodologies and techniques in scanning tunneling microscopy (STM), including spin-polarized STM, scanning tunneling potentiometry (STP), scanning tunneling thermopower microscopy, and multi-probe STM. The experimental effort is complemented by the computational and theoretical approaches, capable of discriminating between closely competing states and achieving the length scales necessary to bridge across features such as local defects and complex heterostructures. The goal is to provide a general view of current understanding and challenges in studying the heterogeneities in 2D materials and to evaluate the potential of controlling and exploiting these heterogeneities for novel functionalities and electron devices.

Reduction of Defects on Microstructure Aluminium Nitride Using High Temperature Annealing Heat Treatment

NASA Astrophysics Data System (ADS)

Tanasta, Z.; Muhamad, P.; Kuwano, N.; Norfazrina, H. M. Y.; Unuh, M. H.

2018-03-01

Aluminium Nitride (AlN) is a ceramic 111-nitride material that is used widely as components in functional devices. Besides good thermal conductivity, it also has a high band gap in emitting light which is 6 eV. AlN thin film is grown on the sapphire substrate (0001). However, lattice mismatch between both materials has caused defects to exist along the microstructure of AlN thin films. The defects have affected the properties of Aluminium Nitride. Annealing heat treatment has been proved by the previous researcher to be the best method to improve the microstructure of Aluminium Nitride thin films. Hence, this method is applied at four different temperatures for two hour. The changes of Aluminium Nitride microstructures before and after annealing is observed using Transmission Electron Microscope. It is observed that inversion domains start to occur at temperature of 1500 °C. Convergent Beam Electron Diffraction pattern simulation has confirmed the defects as inversion domain. Therefore, this paper is about to extract the matters occurred during the process of producing high quality Aluminium Nitride thin films and the ways to overcome this problem.

Effect of Variation of Silicon Nitride Passivation Layer on Electron Irradiated Aluminum Gallium Nitride/Gallium Nitride HEMT Structures

DTIC Science & Technology

2014-06-19

the AlGaN is unintentionally doped . Figure 2.3. AlGaN/GaN band diagram showing polarization charges. The band diagram in Figure 2.3 shows...intentionally doped as are MESFETS, and the channel gets its electrons from the unintentional doping . There is less Coulomb scattering in the...temperature measurements are often used to provide spatial PL maps of doping and trap densities. Laser excitation (quasi-monochromatic) is

Early stages of plasma induced nitridation of Si (111) surface and study of interfacial band alignment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shetty, Satish; Shivaprasad, S. M., E-mail: smsprasad@jncasr.ac.in

2016-02-07

We report here a systematic study of the nitridation of the Si (111) surface by nitrogen plasma exposure. The surface and interface chemical composition and surface morphology are investigated by using RHEED, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). At the initial stage of nitridation two superstructures—“8 × 8” and “8/3 × 8/3”—form, and further nitridation leads to 1 × 1 stoichiometric silicon nitride. The interface is seen to have the Si{sup 1+} and Si{sup 3+} states of silicon bonding with nitrogen, which suggests an atomically abrupt and defect-free interface. The initial single crystalline silicon nitride layers are seen to become amorphous at higher thicknesses.more » The AFM image shows that the nitride nucleates at interfacial dislocations that are connected by sub-stoichiometric 2D-nitride layers, which agglomerate to form thick overlayers. The electrical properties of the interface yield a valence band offset that saturates at 1.9 eV and conduction band offset at 2.3 eV due to the evolution of the sub-stoichiometric interface and band bending.« less

N-Doped Hybrid Graphene and Boron Nitride Armchair Nanoribbons As Nonmagnetic Semiconductors with Widely Tunable Electronic Properties

NASA Astrophysics Data System (ADS)

Habibpour, Razieh; Kashi, Eslam; Vazirib, Raheleh

2018-03-01

The electronic and chemical properties of N-doped hybrid graphene and boron nitride armchair nanoribbons (N-doped a-GBNNRs) in comparison with graphene armchair nanoribbon (pristine a-GNR) and hybrid graphene and boron nitride armchair nanoribbon (C-3BN) are investigated using the density functional theory method. The results show that all the mentioned nanoribbons are nonmagnetic direct semiconductors and all the graphitic N-doped a-GBNNRs are n-type semiconductors while the rest are p-type semiconductors. The N-doped graphitic 2 and N-doped graphitic 3 structures have the lowest work function and the highest number of valence electrons (Lowdin charges) which confirms that they are effective for use in electronic device applications.

Application of low-temperature plasma for the synthesis of hydrogenated graphene (graphane)

NASA Astrophysics Data System (ADS)

Shavelkina, M. B.; Amirov, R. H.; Katarzhis, V. A.; Kiselev, V. I.

2017-12-01

The possibility of a direct synthesis of hydrogenated graphene in decomposition of methane by means of low-temperature plasma was investigated. A DC plasma torch with an expanding channel-anode, a vortex gas supply and a self-setting arc length was used as a generator of low-temperature plasma. Argon was used as the plasma-forming gas. The temperatures of argon plasma and with methane addition to it were determined on the basis of spectral measurements. The synthesis products were characterized by electron microscopy and thermogravimetry. The effect of hydrogenated graphene as a nanomodifier on the properties of the cubic boron nitride based functional ceramics was investigated.

Functional carbon nitride materials — design strategies for electrochemical devices

NASA Astrophysics Data System (ADS)

Kessler, Fabian K.; Zheng, Yun; Schwarz, Dana; Merschjann, Christoph; Schnick, Wolfgang; Wang, Xinchen; Bojdys, Michael J.

2017-06-01

In the past decade, research in the field of artificial photosynthesis has shifted from simple, inorganic semiconductors to more abundant, polymeric materials. For example, polymeric carbon nitrides have emerged as promising materials for metal-free semiconductors and metal-free photocatalysts. Polymeric carbon nitride (melon) and related carbon nitride materials are desirable alternatives to industrially used catalysts because they are easily synthesized from abundant and inexpensive starting materials. Furthermore, these materials are chemically benign because they do not contain heavy metal ions, thereby facilitating handling and disposal. In this Review, we discuss the building blocks of carbon nitride materials and examine how strategies in synthesis, templating and post-processing translate from the molecular level to macroscopic properties, such as optical and electronic bandgap. Applications of carbon nitride materials in bulk heterojunctions, laser-patterned memory devices and energy storage devices indicate that photocatalytic overall water splitting on an industrial scale may be realized in the near future and reveal a new avenue of 'post-silicon electronics'.

Synthesis, Properties, and Applications Of Boron Nitride

NASA Technical Reports Server (NTRS)

Pouch, John J.; Alterovitz, Samuel A.

1993-01-01

Report describes synthesis, properties, and applications of boron nitride. Especially in thin-film form. Boron nitride films useful as masks in x-ray lithography; as layers for passivation of high-speed microelectronic circuits; insulating films; hard, wear-resistant, protective films for optical components; lubricants; and radiation detectors. Present status of single-crystal growth of boron nitride indicates promising candidate for use in high-temperature semiconductor electronics.

Characterization of Pb-Doped GaN Thin Films Grown by Thermionic Vacuum Arc

NASA Astrophysics Data System (ADS)

Özen, Soner; Pat, Suat; Korkmaz, Şadan

2018-03-01

Undoped and lead (Pb)-doped gallium nitride (GaN) thin films have been deposited by a thermionic vacuum arc (TVA) method. Glass and polyethylene terephthalate were selected as optically transparent substrates. The structural, optical, morphological, and electrical properties of the deposited thin films were investigated. These physical properties were interpreted by comparison with related analysis methods. The crystalline structure of the deposited GaN thin films was hexagonal wurtzite. The optical bandgap energy of the GaN and Pb-doped GaN thin films was found to be 3.45 eV and 3.47 eV, respectively. The surface properties of the deposited thin films were imaged using atomic force microscopy and field-emission scanning electron microscopy, revealing a nanostructured, homogeneous, and granular surface structure. These results confirm that the TVA method is an alternative layer deposition system for Pb-doped GaN thin films.

Molecular Self-Assembly in a Poorly Screened Environment: F 4TCNQ on Graphene/BN

DOE PAGES

Tsai, Hsin-Zon; Omrani, Arash A.; Coh, Sinisa; ...

2015-10-20

Here we report a scanning tunneling microscopy and noncontact atomic force microscopy study of close-packed 2D islands of tetrafluoro-tetracyanoquinodimethane (F 4TCNQ) molecules at the surface of a graphene layer supported by boron nitride. While F 4TCNQ molecules are known to form cohesive 3D solids, the intermolecular interactions that are attractive for F 4TCNQ in 3D are repulsive in 2D. Our experimental observation of cohesive molecular behavior for F 4TCNQ on graphene is thus unexpected. This self-assembly behavior can be explained by a novel solid formation mechanism that occurs when charged molecules are placed in a poorly screened environment. As negativelymore » charged molecules coalesce, the local work function increases, causing electrons to flow into the coalescing molecular island and increase its cohesive binding energy.« less

Remote Joule heating by a carbon nanotube.

PubMed

Baloch, Kamal H; Voskanian, Norvik; Bronsgeest, Merijntje; Cumings, John

2012-04-08

Minimizing Joule heating remains an important goal in the design of electronic devices. The prevailing model of Joule heating relies on a simple semiclassical picture in which electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density, and this model has been supported by most experiments. Recently, however, it has been predicted that electric currents in graphene and carbon nanotubes can couple to the vibrational modes of a neighbouring material, heating it remotely. Here, we use in situ electron thermal microscopy to detect the remote Joule heating of a silicon nitride substrate by a single multiwalled carbon nanotube. At least 84% of the electrical power supplied to the nanotube is dissipated directly into the substrate, rather than in the nanotube itself. Although it has different physical origins, this phenomenon is reminiscent of induction heating or microwave dielectric heating. Such an ability to dissipate waste energy remotely could lead to improved thermal management in electronic devices.

Remote Joule heating by a carbon nanotube

NASA Astrophysics Data System (ADS)

Baloch, Kamal H.; Voskanian, Norvik; Bronsgeest, Merijntje; Cumings, John

2012-05-01

Minimizing Joule heating remains an important goal in the design of electronic devices. The prevailing model of Joule heating relies on a simple semiclassical picture in which electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density, and this model has been supported by most experiments. Recently, however, it has been predicted that electric currents in graphene and carbon nanotubes can couple to the vibrational modes of a neighbouring material, heating it remotely. Here, we use in situ electron thermal microscopy to detect the remote Joule heating of a silicon nitride substrate by a single multiwalled carbon nanotube. At least 84% of the electrical power supplied to the nanotube is dissipated directly into the substrate, rather than in the nanotube itself. Although it has different physical origins, this phenomenon is reminiscent of induction heating or microwave dielectric heating. Such an ability to dissipate waste energy remotely could lead to improved thermal management in electronic devices.

Electronic properties of III-nitride semiconductors: A first-principles investigation using the Tran-Blaha modified Becke-Johnson potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Araujo, Rafael B., E-mail: rafaelbna@gmail.com; Almeida, J. S. de, E-mail: jailton-almeida@hotmail.com; Ferreira da Silva, A.

In this work, we use density functional theory to investigate the influence of semilocal exchange and correlation effects on the electronic properties of III-nitride semiconductors considering zinc-blende and wurtzite crystal structures. We find that the inclusion of such effects through the use of the Tran-Blaha modified Becke-Johnson potential yields an excellent description of the electronic structures of these materials giving energy band gaps which are systematically larger than the ones obtained with standard functionals such as the generalized gradient approximation. The discrepancy between the experimental and theoretical band gaps is then significantly reduced with semilocal exchange and correlation effects. However,more » the effective masses are overestimated in the zinc-blende nitrides, but no systematic trend is found in the wurtzite compounds. New results for energy band gaps and effective masses of zinc-blende and wurtzite indium nitrides are presented.« less

Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy.

PubMed

Jobst, Johannes; van der Torren, Alexander J H; Krasovskii, Eugene E; Balgley, Jesse; Dean, Cory R; Tromp, Rudolf M; van der Molen, Sense Jan

2016-11-29

High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the 'chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of.

Manufacturing of composite titanium-titanium nitride coatings by reactive very low pressure plasma spraying (R-VLPPS)

NASA Astrophysics Data System (ADS)

Vautherin, B.; Planche, M.-P.; Quet, A.; Bianchi, L.; Montavon, G.

2014-11-01

Very Low Pressure Plasma Spraying (VLPPS) is an emerging spray process nowadays intensively studied by many research centers in the World. To date, studies are mostly focused on the manufacturing of ceramic or metallic coatings. None refers to composite coatings manufacturing by reactive plasma spraying under very low pressure (i.e., ~150 Pa). This paper aims at presenting the carried-out developments and some results concerning the manufacturing of composite coatings by reactive spraying. Titanium was selected as metallic material in order to deposit titanium-nitride titanium coatings (Ti-TiN). Nitrogen was used as plasma gas and was injected along an Ar-H2-N2 plasma jet via a secondary injector in order to reach the nitrogen content on the substrate surface. Thus, different kind of reactive mechanisms were highlighted. Resulting coatings were characterized by Scanning Electron Microscopy (SEM) observations. Porous microstructures are clearly identified and the deposits exhibit condensed vapours and molten particles. Glow Discharge Optical Emission Spectroscopy (GDOES) analysis evidenced nitrogen inside the deposits and X-Ray Diffraction (XRD) analysis confirmed the formation of titanium nitride phases, such as TiN and Ti2N, depending upon the location of the nitrogen injection. Microhardness values as high as 800 VHN were measured on manufactured samples (to be compared to 220 VHN for pure titanium VLPPS-manufactured coatings).

Epitaxial hexagonal boron nitride on Ir(111): A work function template

NASA Astrophysics Data System (ADS)

Schulz, Fabian; Drost, Robert; Hämäläinen, Sampsa K.; Demonchaux, Thomas; Seitsonen, Ari P.; Liljeroth, Peter

2014-06-01

Hexagonal boron nitride (h-BN) is a prominent member in the growing family of two-dimensional materials with potential applications ranging from being an atomically smooth support for other two-dimensional materials to templating growth of molecular layers. We have studied the structure of monolayer h-BN grown by chemical vapor deposition on Ir(111) by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments and state-of-the-art density functional theory (DFT) calculations. The lattice mismatch between the h-BN and Ir(111) surface results in the formation of a moiré superstructure with a periodicity of ˜29 Å and a corrugation of ˜0.4 Å. By measuring the field emission resonances above the h-BN layer, we find a modulation of the work function within the moiré unit cell of ˜0.5 eV. DFT simulations for a 13-on-12 h-BN/Ir(111) unit cell confirm our experimental findings and allow us to relate the change in the work function to the subtle changes in the interaction between boron and nitrogen atoms and the underlying substrate atoms within the moiré unit cell. Hexagonal boron nitride on Ir(111) combines weak topographic corrugation with a strong work function modulation over the moiré unit cell. This makes h-BN/Ir(111) a potential substrate for electronically modulated thin film and heterosandwich structures.

Anticorrosive performance of waterborne epoxy coatings containing water-dispersible hexagonal boron nitride (h-BN) nanosheets

NASA Astrophysics Data System (ADS)

Cui, Mingjun; Ren, Siming; Chen, Jia; Liu, Shuan; Zhang, Guangan; Zhao, Haichao; Wang, Liping; Xue, Qunji

2017-03-01

Homogenous dispersion of hexagonal boron nitride (h-BN) nanosheets in solvents or in the polymer matrix is crucial to initiate their many applications. Here, homogeneous dispersion of hexagonal boron nitride (h-BN) in epoxy matrix was achieved with a water-soluble carboxylated aniline trimer derivative (CAT-) as a dispersant, which was attributed to the strong π-π interaction between h-BN and CAT-, as proved by Raman and UV-vis spectra. Transmission electron microscopy (TEM) analysis confirmed a random dispersion of h-BN nanosheets in the waterborne epoxy coatings. The deterioration process of water-borne epoxy coating with and without h-BN nanosheets during the long-term immersion in 3.5 wt% NaCl solution was investigated by electrochemical measurements and water absorption test. Results implied that the introduction of well dispersed h-BN nanosheets into waterborne epoxy system remarkably improved the corrosion protection performance to substrate. Moreover, 1 wt% BN/EP composite coated substrate exhibited higher impedance modulus (1.3 × 106 Ω cm2) and lower water absorption (4%) than those of pure waterborne epoxy coating coated electrode after long-term immersion in 3.5 wt% NaCl solution, demonstrating its superior anticorrosive performance. This enhanced anticorrosive performance was mainly ascribed to the improved water barrier property of epoxy coating via incorporating homogeneously dispersed h-BN nanosheets.

Taming interfacial electronic properties of platinum nanoparticles on vacancy-abundant boron nitride nanosheets for enhanced catalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Wenshuai; Wu, Zili; Foo, Guo Shiou

Taming interfacial electronic effects on Pt nanoparticles modulated by their concomitants has emerged as an intriguing approach to optimize Pt catalytic performance. Here, we report Pt nanoparticles assembled on vacancy-abundant hexagonal boron nitride nanosheets and their use as a model catalyst to embrace an interfacial electronic effect on Pt induced by the nanosheets with N-vacancies and B-vacancies for superior CO oxidation catalysis. Experimental results indicate that strong interaction exists between Pt and the vacancies. Bader charge analysis shows that with Pt on B-vacancies, the nanosheets serve as a Lewis acid to accept electrons from Pt, and on the contrary, whenmore » Pt sits on N-vacancies, the nanosheets act as a Lewis base for donating electrons to Pt. The overall-electronic effect demonstrates an electron-rich feature of Pt after assembling on hexagonal boron nitride nanosheets. Such an interfacial electronic effect makes Pt favour the adsorption of O 2, alleviating CO poisoning and promoting the catalysis.« less

Taming interfacial electronic properties of platinum nanoparticles on vacancy-abundant boron nitride nanosheets for enhanced catalysis

DOE PAGES

Zhu, Wenshuai; Wu, Zili; Foo, Guo Shiou; ...

2017-06-09

Taming interfacial electronic effects on Pt nanoparticles modulated by their concomitants has emerged as an intriguing approach to optimize Pt catalytic performance. Here, we report Pt nanoparticles assembled on vacancy-abundant hexagonal boron nitride nanosheets and their use as a model catalyst to embrace an interfacial electronic effect on Pt induced by the nanosheets with N-vacancies and B-vacancies for superior CO oxidation catalysis. Experimental results indicate that strong interaction exists between Pt and the vacancies. Bader charge analysis shows that with Pt on B-vacancies, the nanosheets serve as a Lewis acid to accept electrons from Pt, and on the contrary, whenmore » Pt sits on N-vacancies, the nanosheets act as a Lewis base for donating electrons to Pt. The overall-electronic effect demonstrates an electron-rich feature of Pt after assembling on hexagonal boron nitride nanosheets. Such an interfacial electronic effect makes Pt favour the adsorption of O 2, alleviating CO poisoning and promoting the catalysis.« less

Gradient microstructure and microhardness in a nitrided 18CrNiMo7-6 gear steel

NASA Astrophysics Data System (ADS)

Yang, R.; Wu, G. L.; Zhang, X.; Fu, W. T.; Huang, X.

2017-07-01

A commercial gear steel (18CrNiMo7-6) containing a tempered martensite structure was nitrided using a pressurized gas nitriding process under a pressure of 5 atm at 530 °C for 5 hours. The mechanical properties and microstructure of the nitrided sample were characterized by Vickers hardness measurements, X-ray diffraction, and backscatter electron imaging in a scanning electron microscope. A micro-hardness gradient was identified over a distance of 500 μm with hardness values of 900 HV at the top surface and 300 HV in the core. This micro-hardness gradient corresponds to a gradient in the microstructure that changes from a nitride compound layer at the top surface (∼ 20 μm thick) to a diffusion zone with a decreasing nitrogen concentration and precipitate density with distance from the surface, finally reaching the core matrix layer with a recovered martensite structure.

Structural stability and electronic properties of an octagonal allotrope of two dimensional boron nitride.

PubMed

Takahashi, Lauren; Takahashi, Keisuke

2017-03-27

An octagonal allotrope of two dimensional boron nitride is explored through first principles calculations. Calculations show that two dimensional octagonal boron nitride can be formed with a binding energy comparable to two dimensional hexagonal boron nitride. In addition, two dimensional octagonal boron nitride is found to have a band gap smaller than two dimensional hexagonal boron nitride, suggesting the possibility of semiconductive attributes. Two dimensional octagonal boron nitride also has the ability to layer through physisorption. Defects present within two dimensional octagonal boron nitride also lead toward the introduction of a magnetic moment through the absence of boron atoms. The presence of defects is also found to render both hexagonal and octagonal boron nitrides reactive against hydrogen, where greater reactivity is seen in the presence of nitrogen. Thus, two dimensional octagonal boron nitride is confirmed with potential to tailor properties and reactivity through lattice shape and purposeful introduction of defects.

Helical Growth of Aluminum Nitride: New Insights into Its Growth Habit from Nanostructures to Single Crystals

PubMed Central

Zhang, Xing-Hong; Shao, Rui-Wen; Jin, Lei; Wang, Jian-Yu; Zheng, Kun; Zhao, Chao-Liang; Han, Jie-Cai; Chen, Bin; Sekiguchi, Takashi; Zhang, Zhi; Zou, Jin; Song, Bo

2015-01-01

By understanding the growth mechanism of nanomaterials, the morphological features of nanostructures can be rationally controlled, thereby achieving the desired physical properties for specific applications. Herein, the growth habits of aluminum nitride (AlN) nanostructures and single crystals synthesized by an ultrahigh-temperature, catalyst-free, physical vapor transport process were investigated by transmission electron microscopy. The detailed structural characterizations strongly suggested that the growth of AlN nanostructures including AlN nanowires and nanohelixes follow a sequential and periodic rotation in the growth direction, which is independent of the size and shape of the material. Based on these experimental observations, an helical growth mechanism that may originate from the coeffect of the polar-surface and dislocation-driven growth is proposed, which offers a new insight into the related growth kinetics of low-dimensional AlN structures and will enable the rational design and synthesis of novel AlN nanostructures. Further, with the increase of temperature, the growth process of AlN grains followed the helical growth model. PMID:25976071

Microstructural Evolution of Thor™ 115 Creep-Strength Enhanced Ferritic Steel

NASA Astrophysics Data System (ADS)

Ortolani, Matteo; D'Incau, Mirco; Ciancio, Regina; Scardi, Paolo

2017-12-01

A new ferritic steel branded as Thor™ 115 has been developed to enhance high-temperature resistance. The steel design combines an improved oxidation resistance with long-term microstructural stability. The new alloy, cast to different product forms such as plates and tubes, was extensively tested to assess the high-temperature time-dependent mechanical behavior (creep). The main strengthening mechanism is precipitation hardening by finely dispersed carbide and nitride phases. Information on the evolution of secondary phases and time-temperature-precipitation behavior of the alloy, essential to ensure long-term property stability, was obtained by scanning transmission electron microscopy with energy dispersive spectroscopy, and by X-ray Powder Diffraction on specimens aged up to 50,000 hours. A thermodynamic modeling supports presentation and evaluation of the experimental results. The evolution of precipitates in the new alloy confirms the retention of the strengthening by secondary phases, even after long-term exposure at high temperature. The deleterious conversion of nitrides into Z phase is shown to be in line with, or even slower than that of the comparable ASME grade 91 steel.

Large Reduction of Hot Spot Temperature in Graphene Electronic Devices with Heat-Spreading Hexagonal Boron Nitride.

PubMed

Choi, David; Poudel, Nirakar; Park, Saungeun; Akinwande, Deji; Cronin, Stephen B; Watanabe, Kenji; Taniguchi, Takashi; Yao, Zhen; Shi, Li

2018-04-04

Scanning thermal microscopy measurements reveal a significant thermal benefit of including a high thermal conductivity hexagonal boron nitride (h-BN) heat-spreading layer between graphene and either a SiO 2 /Si substrate or a 100 μm thick Corning flexible Willow glass (WG) substrate. At the same power density, an 80 nm thick h-BN layer on the silicon substrate can yield a factor of 2.2 reduction of the hot spot temperature, whereas a 35 nm thick h-BN layer on the WG substrate is sufficient to obtain a factor of 4.1 reduction. The larger effect of the h-BN heat spreader on WG than on SiO 2 /Si is attributed to a smaller effective heat transfer coefficient per unit area for three-dimensional heat conduction into the thick, low-thermal conductivity WG substrate than for one-dimensional heat conduction through the thin oxide layer on silicon. Consequently, the h-BN lateral heat-spreading length is much larger on WG than on SiO 2 /Si, resulting in a larger degree of temperature reduction.

Aluminum nanoparticles burning - still a puzzle?

NASA Astrophysics Data System (ADS)

Gromov, A. A.; Popenko, E. M.

2009-09-01

The experimental data on the aluminum nanopowders (nAl) combustion in oxidizing media (air, propellants AP∗/HTPB†/Al/HMX‡, and energetic compositions) assuming the phenomenon of nitrides formation with the high yield is generalized. In the present work, the nAl produced by electrical explosion of wires was studied. The temperature, burning rate, and radiation were measured at combustion and the actual burning process was recorded by a videocamera. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analysis were performed on the both initial powders and final condensed products. It was experimentally proved that the combustion process of aluminum nanoparticles was two staged independently of burning conditions in nitrogen-containing media. The formation of nitrides in presence of molecular nitrogen is the determining stage in the particles combustion. A qualitative discussion is given on the kinetic limitation for AlN (AlON) oxidation due to rapid condensation and encapsulation of solid AlN (AlON).

Determination of Cd2+ and Pb2+ Based on Mesoporous Carbon Nitride/Self-Doped Polyaniline Nanofibers and Square Wave Anodic Stripping Voltammetry

PubMed Central

Zhang, Chang; Zhou, Yaoyu; Tang, Lin; Zeng, Guangming; Zhang, Jiachao; Peng, Bo; Xie, Xia; Lai, Cui; Long, Beiqing; Zhu, Jingjing

2016-01-01

The fabrication and evaluation of a glassy carbon electrode (GCE) modified with self-doped polyaniline nanofibers (SPAN)/mesoporous carbon nitride (MCN) and bismuth for simultaneous determination of trace Cd2+ and Pb2+ by square wave anodic stripping voltammetry (SWASV) are presented here. The morphology properties of SPAN and MCN were characterized by transmission electron microscopy (TEM), and the electrochemical properties of the fabricated electrode were characterized by cyclic voltammetry (CV). Experimental parameters, such as deposition time, pulse potential, step potential, bismuth concentration and NaCl concentration, were optimized. Under the optimum conditions, the fabricated electrode exhibited linear calibration curves ranging from 5 to 80 nM for Cd2+ and Pb2+. The limits of detection (LOD) were 0.7 nM for Cd2+ and 0.2 nM for Pb2+ (S/N = 3). Additionally, the repeatability, reproducibility, anti-interference ability and application were also investigated, and the proposed electrode exhibited excellent performance. The proposed method could be extended for other heavy metal determination. PMID:28344264

Filtered pulsed cathodic arc deposition of fullerene-like carbon and carbon nitride films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tucker, Mark D., E-mail: martu@ifm.liu.se; Broitman, Esteban; Näslund, Lars-Åke

Carbon and carbon nitride films (CN{sub x}, 0 ≤ x ≤ 0.26) were deposited by filtered pulsed cathodic arc and were investigated using transmission electron microscopy and X-ray photoelectron spectroscopy. A “fullerene-like” (FL) structure of ordered graphitic planes, similar to that of magnetron sputtered FL-CN{sub x} films, was observed in films deposited at 175 °C and above, with N{sub 2} pressures of 0 and 0.5 mTorr. Higher substrate temperatures and significant nitrogen incorporation are required to produce similar FL structure by sputtering, which may, at least in part, be explained by the high ion charge states and ion energies characteristic of arc deposition. A gradualmore » transition from majority sp{sup 3}-hybridized films to sp{sup 2} films was observed with increasing substrate temperature. High elastic recovery, an attractive characteristic mechanical property of FL-CN{sub x} films, is evident in arc-deposited films both with and without nitrogen content, and both with and without FL structure.« less

Facile preparation of a TiO2 quantum dot/graphitic carbon nitride heterojunction with highly efficient photocatalytic activity

NASA Astrophysics Data System (ADS)

Wang, Xing; Jiang, Subin; Huo, Xuejian; Xia, Rui; Muhire, Elisée; Gao, Meizhen

2018-05-01

In this article, mechanical grinding, an effortless and super-effective synthetic strategy, is used to successfully synthesize a TiO2 quantum dot (TiO2QD)/graphitic carbon nitride (g-C3N4) heterostructure. X-ray photoelectron spectroscopy results together with transmission electron microscopy reveal the formation of the TiO2QD/g-C3N4 heterostructure with strong interfacial interaction. Because of the advantages of this characteristic, the prepared heterostructure exhibits excellent properties for photocatalytic wastewater treatment. Notably, the optimum photocatalytic activity of the TiO2QD/g-C3N4 heterostructure is nearly 3.4 times higher than that of the g-C3N4 nanosheets used for the photodegradation of rhodamine B pollutant. In addition, the stability and possible degradation mechanism of the TiO2QD/g-C3N4 heterojunction are studied in detail. This method may stimulate an effective approach to synthesizing QD-sensitized semiconductor materials and facilitate their application in environmental protection.

Bone response to a titanium aluminium nitride coating on metallic implants.

PubMed

Freeman, C O; Brook, I M

2006-05-01

The design, surface characteristics and strength of metallic implants are dependant on their intended use and clinical application. Surface modifications of materials may enable reduction of the time taken for osseointegration and improve the biological response of bio-mechanically favourable metals and alloys. The influence of a titanium aluminium nitride (TAN) coating on the response of bone to commercially pure titanium and austenitic 18/8 stainless steel wire is reported. TAN coated and plain rods of stainless steel and commercially pure titanium were implanted into the mid-shaft of the femur of Wistar rats. The femurs were harvested at four weeks and processed for scanning electron and light microscopy. All implants exhibited a favourable response in bone with no evidence of fibrous encapsulation. There was no significant difference in the amount of new bone formed around the different rods (osseoconduction), however, there was a greater degree of shrinkage separation of bone from the coated rods than from the plain rods (p = 0.017 stainless steel and p = 0.0085 titanium). TAN coating may result in reduced osseointegration between bone and implant.

Template growth of Au, Ni and Ni–Au nanoclusters on hexagonal boron nitride/Rh(111): a combined STM, TPD and AES study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Fanglue; Huang, Dali; Yue, Yuan

In this study, the template growth of Au, Ni, and Ni–Au bimetallic nanoclusters on hexagonal boron nitride/Rh(111), i.e. h-BN/Rh(111), was investigated via scanning tunneling microscopy (STM), temperature programmed-desorption (TPD), and Auger electron spectroscopy (AES). STM study shows that template growth of Au clusters on h-BN/Rh(111) forms mainly well-dispersed monolayer clusters. In contrast, Ni forms large multilayer clusters showing a relatively high diffusivity on h-BN/Rh(111) substrate. Ni–Au bimetallic clusters are effectively formed first by Au deposition followed by Ni deposition, with the Au clusters functioning as nucleation sites for the subsequently deposited Ni. Further structural analysis was carried out via TPDmore » and AES. The resulting TPD and AES data show the surface composition and charge transfer between Au and Ni of the bimetallic clusters. These results suggest that the h-BN/Rh(111) substrate represents a unique candidate for supporting Ni–Au bimetallic clusters in further catalytic reactions.« less

Template growth of Au, Ni and Ni–Au nanoclusters on hexagonal boron nitride/Rh(111): a combined STM, TPD and AES study

DOE PAGES

Wu, Fanglue; Huang, Dali; Yue, Yuan; ...

2017-09-12

In this study, the template growth of Au, Ni, and Ni–Au bimetallic nanoclusters on hexagonal boron nitride/Rh(111), i.e. h-BN/Rh(111), was investigated via scanning tunneling microscopy (STM), temperature programmed-desorption (TPD), and Auger electron spectroscopy (AES). STM study shows that template growth of Au clusters on h-BN/Rh(111) forms mainly well-dispersed monolayer clusters. In contrast, Ni forms large multilayer clusters showing a relatively high diffusivity on h-BN/Rh(111) substrate. Ni–Au bimetallic clusters are effectively formed first by Au deposition followed by Ni deposition, with the Au clusters functioning as nucleation sites for the subsequently deposited Ni. Further structural analysis was carried out via TPDmore » and AES. The resulting TPD and AES data show the surface composition and charge transfer between Au and Ni of the bimetallic clusters. These results suggest that the h-BN/Rh(111) substrate represents a unique candidate for supporting Ni–Au bimetallic clusters in further catalytic reactions.« less

Observation of rare-earth segregation in silicon nitride ceramics at subnanometre dimensions.

PubMed

Shibata, Naoya; Pennycook, Stephen J; Gosnell, Tim R; Painter, Gayle S; Shelton, William A; Becher, Paul F

2004-04-15

Silicon nitride (Si3N4) ceramics are used in numerous applications because of their superior mechanical properties. Their intrinsically brittle nature is a critical issue, but can be overcome by introducing whisker-like microstructural features. However, the formation of such anisotropic grains is very sensitive to the type of cations used as the sintering additives. Understanding the origin of dopant effects, central to the design of high-performance Si3N4 ceramics, has been sought for many years. Here we show direct images of dopant atoms (La) within the nanometre-scale intergranular amorphous films typically found at grain boundaries, using aberration corrected Z-contrast scanning transmission electron microscopy. It is clearly shown that the La atoms preferentially segregate to the amorphous/crystal interfaces. First-principles calculations confirm the strong preference of La for the crystalline surfaces, which is essential for forming elongated grains and a toughened microstructure. Whereas principles of micrometre-scale structural design are currently used to improve the mechanical properties of ceramics, this work represents a step towards the atomic-level structural engineering required for the next generation of ceramics.

On the luminescence of freshly introduced a-screw dislocations in low-resistance GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Medvedev, O. S., E-mail: o.s.medvedev@spbu.ru; Vyvenko, O. F.; Bondarenko, A. S.

2015-09-15

Using scanning electron microscopy in the cathodoluminescence mode, it is shown that straight segments of a-screw dislocations introduced by plastic deformation at room temperature into unintentionally doped low-resistance gallium nitride luminesce in the spectral range 3.1–3.2 eV at 70 K. The spectral composition of dislocation luminescence shows a fine doublet structure with a component width of ∼15 meV and splitting of ∼30 meV, accompanied by LO-phonon replicas. Luminescent screw dislocations move upon exposure to an electron beam and at low temperatures, but retain immobility for a long time without external excitation. Optical transitions involving the quantum-well states of a stackingmore » fault in a split-dislocation core are considered to be the most probable mechanism of the observed phenomenon.« less

Two-dimensional dopant profiling of gallium nitride p-n junctions by scanning capacitance microscopy

NASA Astrophysics Data System (ADS)

Lamhamdi, M.; Cayrel, F.; Frayssinet, E.; Bazin, A. E.; Yvon, A.; Collard, E.; Cordier, Y.; Alquier, D.

2016-04-01

Two-dimensional imaging of dopant profiles for n and p-type regions are relevant for the development of new power semiconductors, especially for gallium nitride (GaN) for which classical profiling techniques are not adapted. This is a challenging task since it needs a technique with simultaneously good sensitivity, high spatial resolution and high dopant gradient resolution. To face these challenges, scanning capacitance microscopy combined with Atomic Force Microscopy is a good candidate, presenting reproducible results, as demonstrated in literature. In this work, we attempt to distinguish reliably and qualitatively the various doping concentrations and type at p-n and unipolar junctions. For both p-n and unipolar junctions three kinds of samples were prepared and measured separately. The space-charge region of the p-n metallurgical junction, giving rise to different contrasts under SCM imaging, is clearly observed, enlightening the interest of the SCM technique.

Nanoprobe studies: Electrical transport in carbon nanotubes and crystal structure of aluminum nitride surfaces

NASA Astrophysics Data System (ADS)

Biswas, Sujit Kumar

Nanoprobes are an extraordinary set of experimental tools that allow fabrication, manipulation, and measurement in nano-scale systems. The primary use of a nanoprobe for imaging tiny objects is supplemented by powerful electrical techniques, namely scanning surface potential microscopy and current sensing atomic force microscopy. They allow us to measure potential, and current in carbon nanotube circuits. Nanoprobes are superior to conventional two- or four-probe measurements because they can provide spatial information of local electronic properties. This makes them highly attractive in studying junctions and contacts with carbon nanotubes. We have studied single-walled carbon nanotube circuits, forming junctions to other nanotubes. The experimental results indicate that these junctions act like potential barriers of about 50 meV that can confine electrons with an effective mass of 0.003 me , within nanotube channels of length 0.5 mum lying in-between two such potential barriers. This leads to quantization of the channel, forming a resonant tunneling structure. We have also found that single-walled nanotubes have phase coherence lengths of the order of 1 mum. This leads to situations where the electron interference effects at scattering centers need to be considered. We have seen direct evidence of this, in the non-linear resistance increase within nanotubes with few defects. Ambipolar transistor behavior was measured in a p-type single-walled nanotube circuit that showed electron injection across the Schottky junction at high positive bias. We have also studied multi-walled carbon nanotube circuits using scanning potential microscopy, and found that a back gate potential can vary the resistance of the channel. Vertical nanotube arrays, suitable for interconnects, were also measured. These hollow multi-walled nanotube channels were about 45 nm in diameter, and 50 mum in length, fabricated in an anodized alumina template. We found that these structures could sustain current densities greater than 105 A/cm2. Conventional use of nanoprobes in imaging aluminum nitride surfaces displayed curious step bunching structures. We have used an innovative analysis technique with which the bulk lattice constant of the crystal was measured to an accuracy of about 4% of X-ray crystallography value of 0.497 nm. In addition, this technique showed that there were regions on the surface that had a larger lattice parameter of 0.64 nm, which we interpreted to be due to a variation in the chemical composition of the surface such as oxide formation. We believe that this technique may prove useful as a study of chemical-composition variations on a surface as well as relaxation of the surface layer.

Nanoporous Boron Nitride as Exceptionally Thermally Stable Adsorbent: Role in Efficient Separation of Light Hydrocarbons.

PubMed

Saha, Dipendu; Orkoulas, Gerassimos; Yohannan, Samuel; Ho, Hoi Chun; Cakmak, Ercan; Chen, Jihua; Ozcan, Soydan

2017-04-26

In this work, nanoporous boron nitride sample was synthesized with a Brunauer-Emmett-Teller (BET) surface area of 1360 m 2 /g and particle size 5-7 μm. The boron nitride was characterized with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electron microscopy (TEM and SEM). Thermogravimetric analysis (TGA) under nitrogen and air and subsequent analysis with XPS and XRD suggested that its structure is stable in air up to 800 °C and in nitrogen up to 1050 °C, which is higher than most of the common adsorbents reported so far. Nitrogen and hydrocarbon adsorption at 298 K and pressure up to 1 bar suggested that all hydrocarbon adsorption amounts were higher than that of nitrogen and the adsorbed amount of hydrocarbon increases with an increase in its molecular weight. The kinetics of adsorption data suggested that adsorption becomes slower with the increase in molecular weight of hydrocarbons. The equilibrium data suggested that that boron nitride is selective to paraffins in a paraffin-olefin mixture and hence may act as an "olefin generator". The ideal adsorbed solution theory (IAST)-based selectivity for CH 4 /N 2 , C 2 H 6 /CH 4 , and C 3 H 8 /C 3 H 6 was very high and probably higher than the majority of adsorbents reported in the literature. IAST-based calculations were also employed to simulate the binary mixture adsorption data for the gas pairs of CH 4 /N 2 , C 2 H 6 /CH 4 , C 2 H 6 /C 2 H 4 , and C 3 H 8 /C 3 H 6 . Finally, a simple mathematical model was employed to simulate the breakthrough behavior of the above-mentioned four gas pairs in a dynamic column experiment. The overall results suggest that nanoporous boron nitride can be used as a potential adsorbent for light hydrocarbon separation.

Selective-area growth of GaN nanowires on SiO{sub 2}-masked Si (111) substrates by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruse, J. E.; Doundoulakis, G.; Institute of Electronic Structure and Laser, Foundation for Research and Technology–Hellas, N. Plastira 100, 70013 Heraklion

2016-06-14

We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single molecular beam epitaxy MBE growth process, i.e., the SiO{sub 2} mask is formed on silicon instead of on a previously grown GaN or AlN buffer layer. We present a systematic and analytical study involving various mask patterns, characterization by scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy, as well asmore » numerical simulations, to evaluate how the dimensions (window diameter and spacing) of the mask affect the distribution of the nanowires, their morphology, and alignment, as well as their photonic properties. Capabilities and limitations for this method of selective-area growth of nanowires have been identified. A window diameter less than 50 nm and a window spacing larger than 500 nm can provide single nanowire nucleation in nearly all mask windows. The results are consistent with a Ga diffusion length on the silicon dioxide surface in the order of approximately 1 μm.« less

Charge Modulation in Graphitic Carbon Nitride as a Switchable Approach to High-Capacity Hydrogen Storage.

PubMed

Tan, Xin; Kou, Liangzhi; Tahini, Hassan A; Smith, Sean C

2015-11-01

Electrical charging of graphitic carbon nitride nanosheets (g-C4 N3 and g-C3 N4 ) is proposed as a strategy for high-capacity and electrocatalytically switchable hydrogen storage. Using first-principle calculations, we found that the adsorption energy of H2 molecules on graphitic carbon nitride nanosheets is dramatically enhanced by injecting extra electrons into the adsorbent. At full hydrogen coverage, the negatively charged graphitic carbon nitride achieves storage capacities up to 6-7 wt %. In contrast to other hydrogen storage approaches, the storage/release occurs spontaneously once extra electrons are introduced or removed, and these processes can be simply controlled by switching on/off the charging voltage. Therefore, this approach promises both facile reversibility and tunable kinetics without the need of specific catalysts. Importantly, g-C4 N3 has good electrical conductivity and high electron mobility, which can be a very good candidate for electron injection/release. These predictions may prove to be instrumental in searching for a new class of high-capacity hydrogen storage materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Processing of Silver-Implanted Aluminum Nitride for Energy Harvesting Devices

NASA Astrophysics Data System (ADS)

Alleyne, Fatima Sierre

One of the more attractive sources of green energy has roots in the popular recycling theme of other green technologies, now known by the term "energy scavenging." In its most promising conformation, energy scavenging converts cyclic mechanical vibrations in the environment or random mechanical pressure pulses, caused by sources ranging from operating machinery to human footfalls, into electrical energy via piezoelectric transducers. While commercial piezoelectrics have evolved to favor lead zirconate titanate (PZT) for its combination of superior properties, the presence of lead in these ceramic compounds raises resistance to their application in anything "green" due to potential health implications during their manufacturing, recycling, or in-service application, if leaching occurs. Therefore in this study we have pursued the application of aluminum nitride (AlN) as a non-toxic alternative to PZT, seeking processing pathways to augment the modest piezoelectric performance of AlN and exploit its compatibility with complementary-metal-oxide semiconductor (CMOS) manufacturing. Such piezoelectric transducers have been categorized as microelectromechanical systems (MEMS), which despite more than a decade of research in this field, is plagued by delamination at the electrode/piezoelectric interface. Consequently the electric field essential to generate and sustain the piezoelectric response of these devices is lost, resulting in device failure. Working on the hypothesis that buried conducting layers can both mitigate the delamination problem and generate sufficient electric field to engage the operation of resonator devices, we have undertaken a study of silver ion implantation to experimentally assess its feasibility. As with most ion implantation procedures employed in semiconductor fabrication, the implanted sample is subjected to a thermal treatment, encouraging diffusion-assisted precipitation of the implanted species at high enough concentrations. The objective of this study is to understand the resulting phase transformation behavior during Ag precipitation with the intent to ultimately control the electrical operation of AlN piezoelectric resonators in energy scavenging applications. In this work, multiple source reactive ion sputtering was employed to deposit a thin film of AlN on a 525 microns thick Si substrate, followed by ion implantation (Ag cathode) into the aluminum nitride, and subsequent thermal annealing. Computer simulations were conducted to elucidate the projected range of the silver in the AlN epilayer as a result of the ion implantation process. A myriad of characterization methods including Rutherford Backscattering Spectrometry (RBS), x-ray diffraction (XRD), rocking curve, electron microscopy was employed to quantify the concentration of silver, morphology of silver precipitates, as well as the composition, crystallinity and degree of damage in the ion-implanted AlN samples with respect to thermal annealing conditions. The presence, or lack of precipitates in the samples was utilized to draw conclusions about the feasibility of developing a buried conductive layer in a ceramic matrix via ion implantation. Computer simulations results obtained via TRIM and TRIDYN confirmed that the maximum concentration of silver lied within 30 -- 47 nm from the surface. The RBS data verified the presence of Si, Al, N, Ag, and O2 , whose concentration varied with temperature. X-ray diffraction and electron microscopy corroborated the crystallinity of the AlN epilayer. Electron diffraction confirmed both the epitaxy of the AlN film on the (001) Si substrate and the crystalline quality of the epilayer prior to and after the thermal annealing treatment. Electron microscopy revealed that the sputtered AlN film grew epitaxially in a columnar morphology and silver precipitates did form in some of the aluminum nitride samples implanted but only in those implanted with a higher concentration of Ag under high-energy implantation conditions. It is concluded that the Ag implanted region does indeed have potential as a buried contact layer for piezoelectric activation and sensing if the critical concentration and appropriate thermal conditions can be attained.

Nitrogen doping, optical characterization, and electron emission study of diamond

NASA Astrophysics Data System (ADS)

Park, Minseo

Nitrogen-doped chemical vapor deposited (CVD) diamond films were synthesized with N2 (nitrogen) and C3H6N6 (melamine) as doping sources. More effective substitutional nitrogen doping was achieved with C3H6N6 than with N 2. Since a melamine molecule has an existing cyclic C-N bonded ring, it is expected that the incorporation of nitrogen on substitution diamond lattice should be facilitated. The diamond film doped with N2 contained a significant amount of non-diamond carbon phases. The samples were analyzed by scanning electron microscopy, Raman scattering, photoluminescence spectroscopy, and field emission measurements. The sample produced using N 2 exhibited a lower field emission turn-on field than the sample produced using C3H6N6. It is believed that the presence of the graphitic phases (or amorphous sp2 carbon) at the grain boundaries of the diamond and/or the nanocrystallinity (or microcrystallinity) of the diamond play a significant role in lowering the turn-on field of the film produced using N2. The nature of the nitrogen-related 1190 cm-1 Raman peak was investigated. Nitrogen is incorporated predominantly to the crystalline or amorphous sp2 phases when nitrogen is added to the growing diamond. Field emission characteristics from metallic field emitter coated with type Ia and Ib diamond powders were also investigated. No significant difference in electron emission characteristics were found in these samples. Voltage-dependent field emission energy distribution (V-FEED) measurement was performed to analyze the energy distribution of the emitted electrons. It is believed that substitutional nitrogen doping plays only a minor role in changing field emission characteristics in diamond. Discontinuous diamond films were deposited on silicon using a microwave plasma chemical vapor deposition (MPCVD) system. The diamond deposits were sharpened by argon ion beam etching. Raman spectroscopy was carried out to study the structural change of the diamond after ion beam bombardment. Field emission measurements were performed in-situ with an electron beam induced current (EBIC) probe inside the chamber of the scanning electron microscope. It was found that amorphous sp2 carbon is produced as the diamond is sputtered by the Ar ion beam. The field emission turn-on field was also significantly lowered after sharpening, which, it is speculated, is caused by field enhancement due to a change in geometry and/or structural changes (such as amorphization of crystalline diamond into graphitic or amorphous sp2 carbon) by Ar ion irradiation. Secondary electron emission patterning of single crystal diamond surfaces with hydrogen and oxygen plasma treatments was demonstrated. Hydrogen plasma treated regions were much brighter than the oxygen terminated regions. Results of atomic force microscopy confirmed that the observed contrast is not topographical. Several other possible negative electron affinity (or low positive electron affinity) materials such as chemical vapor deposited (CVD) diamond, aluminum nitride and tetrahedrally bonded amorphous carbon [tx a-C 1-x] were also investigated. Faint image contrast (patterning) was also observed from polycrystalline CVD diamond, single crystal aluminum nitride films, and polycrystalline aluminum nitride films; however, no contrast at all was obtained from tetrahedrally bonded amorphous carbon [tx a-C1-x] films.

Analysis of Proton Radiation Effects on Gallium Nitride High Electron Mobility Transistors

DTIC Science & Technology

2017-03-01

energy levels on a GaN-on-silicon high electron mobility transistor was created. Based on physical results of 2.0-MeV protons irradiation to fluence...and the physical device at 2.0-MeV proton irradiation , predictions were made for 5.0, 10.0, 20.0 and 40.0-MeV proton irradiation . The model generally...nitride, high electron mobility transistor, electronics, 2 MeV proton irradiation , radiation effects 15. NUMBER OF PAGES 87 16. PRICE CODE 17. SECURITY

Seebeck Coefficient Measurements on Micron-Size Single-Crystal Zinc Germanium Nitride Rods

NASA Astrophysics Data System (ADS)

Dyck, J. S.; Colvin, J. R.; Quayle, P. C.; Peshek, T. J.; Kash, K.

2016-06-01

II-IV-nitride compounds are tetrahedrally bonded, heterovalent ternary semiconductors that have recently garnered attention for their potential technological applications. These materials are derived from the parent III-nitride compounds; ZnGeN2 is the II-IV-nitride analogue to the III-nitride GaN. Very little is known about the transport properties of ZnGeN2. In this work, we present Seebeck coefficient ( S) data on 3-micron-diameter, 70-micron-long, single-crystal ZnGeN2 rods, employing a novel measurement approach. The measurements of S show that the majority free carriers are electrons, and imply that the carrier gas is degenerate. Within a single-band model for the conduction band, a carrier concentration of order 1019 cm-3 was estimated for a measured S = -90 μV/K. Together with electrical transport measurements, a lower limit for the electron mobility is estimated to be ˜20 cm2/V-s. A discussion of this material as a thermoelectric is presented. The background level of free electrons in this unintentionally doped ZnGeN2 is very near the predicted optimum value for maximum thermoelectric performance.

Optical waveguiding properties into porous gallium nitride structures investigated by prism coupling technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alshehri, Bandar; Dogheche, Elhadj, E-mail: elhadj.dogheche@univ-valenciennes.fr; Lee, Seung-Min

2014-08-04

In order to modulate the refractive index and the birefringence of Gallium Nitride (GaN), we have developed a chemical etching method to perform porous structures. The aim of this research is to demonstrate that optical properties of GaN can be tuned by controlling the pores density. GaN films are prepared on sapphire by metal organic chemical vapor deposition and the microstructure is characterized by transmission electron microscopy, and scanning electron microscope analysis. Optical waveguide experiment is demonstrated here to determine the key properties as the ordinary (n{sub 0}) and extraordinary (n{sub e}) refractive indices of etched structures. We report heremore » the dispersion of refractive index for porous GaN and compare it to the bulk material. We observe that the refractive index decreases when the porous density p is increased: results obtained at 0.975 μm have shown that the ordinary index n{sub 0} is 2.293 for a bulk layer and n{sub 0} is 2.285 for a pores density of 20%. This value corresponds to GaN layer with a pore size of 30 nm and inter-distance of 100 nm. The control of the refractive index into GaN is therefore fundamental for the design of active and passive optical devices.« less

Pulsed laser deposition of single layer, hexagonal boron nitride (white graphene, h-BN) on fiber-oriented Ag(111)/SrTiO3(001)

NASA Astrophysics Data System (ADS)

Velázquez, Daniel; Seibert, Rachel; Man, Hamdi; Spentzouris, Linda; Terry, Jeff

2016-03-01

We report on the growth of 1-10 ML films of hexagonal boron nitride (h-BN), also known as white graphene, on fiber-oriented Ag buffer films on SrTiO3(001) by pulsed laser deposition. The Ag buffer films of 40 nm thickness were used as substitutes for expensive single crystal metallic substrates. In-situ, reflection high-energy electron diffraction was used to monitor the surface structure of the Ag films and to observe the formation of the characteristic h-BN diffraction pattern. Further evidence of the growth of h-BN was provided by attenuated total reflectance spectroscopy, which showed the characteristic h-BN peaks at ˜780 cm-1 and 1367.4 cm-1. Ex-situ photoelectron spectroscopy showed that the surface of the h-BN films is stoichiometric. The physical structure of the films was confirmed by scanning electron microscopy. The h-BN films grew as large, sub-millimeter sheets with nano- and micro-sheets scattered on the surface. The h-BN sheets can be exfoliated by the micromechanical adhesive tape method. Spectral analysis was performed by energy dispersive spectroscopy in order to identify the h-BN sheets after exfoliation. The use of thin film Ag allows for reduced use of Ag and makes it possible to adjust the surface morphology of the thin film prior to h-BN growth.

Preparation and characterization of boron nitride coatings on carbon fibers from borazine by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Li, Jun-Sheng; Zhang, Chang-Rui; Li, Bin

2011-06-01

Boron nitride (BN) coatings were deposited on carbon fibers by chemical vapor deposition (CVD) using borazine as single source precursor. The deposited coatings were characterized by scanning electron microscopy (SEM), Auger electron spectroscopy (AES), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The effect of temperatures on growth kinetics, morphology, composition and structure of the coatings was investigated. In the low temperature range of 900 °C-1000 °C, the growth rate increased with increasing temperature complying with Arrhenius law, and an apparent active energy of 72 kJ/mol was calculated. The coating surface was smooth and compact, and the coatings uniformly deposited on individual fibers of carbon fiber bundles. The growth was controlled by surface reaction. At 1000 °C, the deposition rate reached a maximum (2.5 μm/h). At the same time, the limiting step of the growth translated to be mass-transportation. Above 1100 °C, the growth rate decreased drastically due to the occurrence of gas-phase nucleation. Moreover, the coating surface became loose and rough. Composition and structure examinations revealed that stoichiometric BN coatings with turbostratic structure were obtained below 1000 °C, while hexagonal BN coatings were deposited above 1100 °C. A penetration of carbon element from the fibers to the coatings was observed.

Ab initio calculations of the concentration dependent band gap reduction in dilute nitrides

NASA Astrophysics Data System (ADS)

Rosenow, Phil; Bannow, Lars C.; Fischer, Eric W.; Stolz, Wolfgang; Volz, Kerstin; Koch, Stephan W.; Tonner, Ralf

2018-02-01

While being of persistent interest for the integration of lattice-matched laser devices with silicon circuits, the electronic structure of dilute nitride III/V-semiconductors has presented a challenge to ab initio computational approaches. The origin of the computational problems is the strong distortion exerted by the N atoms on most host materials. Here, these issues are resolved by combining density functional theory calculations based on the meta-GGA functional presented by Tran and Blaha (TB09) with a supercell approach for the dilute nitride Ga(NAs). Exploring the requirements posed to supercells, it is shown that the distortion field of a single N atom must be allowed to decrease so far that it does not overlap with its periodic images. This also prevents spurious electronic interactions between translational symmetric atoms, allowing us to compute band gaps in very good agreement with experimentally derived reference values. In addition to existing approaches, these results offer a promising ab initio avenue to the electronic structure of dilute nitride semiconductor compounds.

High efficiency III-nitride light-emitting diodes

DOEpatents

Crawford, Mary; Koleske, Daniel; Cho, Jaehee; Zhu, Di; Noemaun, Ahmed; Schubert, Martin F; Schubert, E. Fred

2013-05-28

Tailored doping of barrier layers enables balancing of the radiative recombination among the multiple-quantum-wells in III-Nitride light-emitting diodes. This tailored doping enables more symmetric carrier transport and uniform carrier distribution which help to reduce electron leakage and thus reduce the efficiency droop in high-power III-Nitride LEDs. Mitigation of the efficiency droop in III-Nitride LEDs may enable the pervasive market penetration of solid-state-lighting technologies in high-power lighting and illumination.

Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy

PubMed Central

Jobst, Johannes; van der Torren, Alexander J. H.; Krasovskii, Eugene E.; Balgley, Jesse; Dean, Cory R.; Tromp, Rudolf M.; van der Molen, Sense Jan

2016-01-01

High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the ‘chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of. PMID:27897180

Near Field Scanning Optical Microscopy (NSOM) of Nano Devices

DTIC Science & Technology

2008-12-01

FEATURES OF GaN NANOWIRES Gallium Nitride (GaN) nanowires are semiconductor wires of great interest lately for its some of its unique properties. These...via chemical vapour deposition (CVD) [19] or even with gas source molecular beam epitaxy (MBE) [20] The GaN nanowires growth techniques will not be...Denlinger, and Peidong Yang, Crystallographic alignment of high-density gallium nitride nanowire arrays, Nature Materials, Issue 3 Vol 8, pg 524

The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

NASA Technical Reports Server (NTRS)

Todd, J. A.; Xu, Zhi-Yue

1988-01-01

The creep properties of silicon nitride containing 6 wt percent yttria and 2 wt percent alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation epsilon dot varies as sigma sup n, was determined to be 2.00 + or - 0.15 and the true activation energy was found to be 692 + or - 25 kJ/mol. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.

3-D Observation of dopant distribution at NAND flash memory floating gate using Atom probe tomography

NASA Astrophysics Data System (ADS)

Lee, Ji-hyun; Chae, Byeong-Kyu; Kim, Joong-Jeong; Lee, Sun Young; Park, Chan Gyung

2015-01-01

Dopant control becomes more difficult and critical as silicon devices become smaller. We observed the dopant distribution in a thermally annealed polysilicon gate using Transmission Electron Microscopy (TEM) and Atom probe tomography (APT). Phosphorus was doped at the silicon-nitride-diffusion-barrier-layer-covered polycrystalline silicon gate. Carbon also incorporated at the gate for the enhancement of operation uniformity. The impurity distribution was observed using atom probe tomography. The carbon atoms had segregated at grain boundaries and suppressed silicon grain growth. Phosphorus atoms, on the other hand, tended to pile-up at the interface. A 1-nm-thick diffusion barrier effectively blocked P atom out-diffusion. [Figure not available: see fulltext.

STM/STS study of graphene directly grown on h-BN films on Cu foils

NASA Astrophysics Data System (ADS)

Jang, Won-Jun; Wang, Min; Jang, Seong-Gyu; Kim, Minwoo; Park, Seong-Yong; Kim, Sang-Woo; Kahng, Se-Jong; Choi, Jae-Young; Song, Young; Lee, Sungjoo; Sanit Collaboration; Department Of Physics, Korea University Collaboration; Graphene Research Center, Samsung Advanced Institute Of Technology Collaboration

2013-03-01

Graphene-based devices on standard SiO2 substrate commonly exhibit inferior characteristics relative to the expected intrinsic properties of graphene, due to the disorder existing at graphene-SiO2 interface. Recently, it has been shown that exfoliated and chemical vapor deposition (CVD) graphene transferred onto hexagonal boron nitride (h-BN) possesses significantly reduced charge inhomogeneity, and yields improved device performance. Here we report the scanning tunneling microscopy (STM) and spectroscopy (STS) results obtained from a graphene layer directly grown on h-BN insulating films on Cu foils. STS measurements illustrate that graphene/h-BN film is charge neutral without electronic perturbation from h-BN/Cu substrate. Corresponding Author

Atomic Resolution in Situ Imaging of a Double-Bilayer Multistep Growth Mode in Gallium Nitride Nanowires

DOE PAGES

Gamalski, A. D.; Tersoff, J.; Stach, E. A.

2016-04-13

We study the growth of GaN nanowires from liquid Au–Ga catalysts using environmental transmission electron microscopy. GaN wires grow in either (11¯20) or (11¯00) directions, by the addition of {11¯00} double bilayers via step flow with multiple steps. Step-train growth is not typically seen with liquid catalysts, and we suggest that it results from low step mobility related to the unusual double-height step structure. Finally, the results here illustrate the surprising dynamics of catalytic GaN wire growth at the nanoscale and highlight striking differences between the growth of GaN and other III–V semiconductor nanowires.

Electron transport and electron energy distributions within the wurtzite and zinc-blende phases of indium nitride: Response to the application of a constant and uniform electric field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siddiqua, Poppy; Hadi, Walid A.; Salhotra, Amith K.

2015-03-28

Within the framework of an ensemble semi-classical three-valley Monte Carlo electron transport simulation approach, we critically contrast the nature of the electron transport that occurs within the wurtzite and zinc-blende phases of indium nitride in response to the application of a constant and uniform electric field. We use the electron energy distribution and its relationship with the electron transport characteristics in order to pursue this analysis. For the case of zinc-blende indium nitride, only a peak corresponding to the electrons within the lowest energy conduction band valley is observed, this peak being seen to broaden and shift to higher energiesmore » in response to increases in the applied electric field strength, negligible amounts of upper energy conduction band valley occupancy being observed. In contrast, for the case of wurtzite indium nitride, in addition to the aforementioned lowest energy conduction band valley peak in the electron energy distribution, and its broadening and shifting to higher energies in response to increases in the applied electric field strength, beyond a certain critical electric field strength, 30 kV/cm for the case of this particular material, upper energy conduction band valley occupancy is observed, this occupancy being further enhanced in response to further increases in the applied electric field strength. Reasons for these results are provided. The potential for device consequences is then commented upon.« less

Effect of Annealing Time of YAG:Ce3+ Phosphor on White Light Chromaticity Values

NASA Astrophysics Data System (ADS)

Abd, Husnen R.; Hassan, Z.; Ahmed, Naser M.; Almessiere, Munirah Abdullah; Omar, A. F.; Alsultany, Forat H.; Sabah, Fayroz A.; Osman, Ummu Shuhada

2018-02-01

Yttrium and aluminium nitrate phosphors doped with cerium nitrate and mixed with urea (fuel) are prepared by using microwave-induced combustion synthesis according to the formula Y(3-0.06)Al5O12:0.06Ce3+ (YAG:Ce3+) to produce white light emitting diodes by conversion from blue indium gallium nitride-light emitting diode chips. The sintering time with fixed temperature (1050°C) for phosphor powder was optimized and found to be 5 h. The crystallinity, structure, chemical composition, luminescent properties with varying currents densities and chromaticity were characterized by x-ray diffraction, field emission-scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, photoluminescence emission, electroluminescence and standard CIE 1931 chromaticity diagram, respectively. The energy levels of Ce3+ in YAG were discussed based on its absorption and excitation spectra. The results show that the obtained YAG:Ce3+ phosphor sintered for 5 h has good crystallinity with pure phase, low agglomerate with spherical shaped particles and strong yellow emission, offering cool-white LED with tuneable correlated color temperature and a good color rendering index compared to those prepared by sintering for 2 h and as-prepared phosphor powders.

Reduction of Defects in AlGaN Grown on Nanoscale-Patterned Sapphire Substrates by Hydride Vapor Phase Epitaxy

PubMed Central

Tasi, Chi-Tsung; Wang, Wei-Kai; Tsai, Tsung-Yen; Huang, Shih-Yung; Horng, Ray-Hua; Wuu, Dong-Sing

2017-01-01

In this study, a 3-μm-thick AlGaN film with an Al mole fraction of 10% was grown on a nanoscale-patterned sapphire substrate (NPSS) using hydride vapor phase epitaxy (HVPE). The growth mechanism, crystallization, and surface morphology of the epilayers were examined using X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy at various times in the growth process. The screw threading dislocation (TD) density of AlGaN-on-NPSS can improve to 1–2 × 109 cm−2, which is significantly lower than that of the sample grown on a conventional planar sapphire substrate (7 × 109 cm−2). TEM analysis indicated that these TDs do not subsequently propagate to the surface of the overgrown AlGaN layer, but bend or change directions in the region above the voids within the side faces of the patterned substrates, possibly because of the internal stress-relaxed morphologies of the AlGaN film. Hence, the laterally overgrown AlGaN films were obtained by HVPE, which can serve as a template for the growth of ultraviolet III-nitride optoelectronic devices. PMID:28772961

Reduction of Defects in AlGaN Grown on Nanoscale-Patterned Sapphire Substrates by Hydride Vapor Phase Epitaxy.

PubMed

Tasi, Chi-Tsung; Wang, Wei-Kai; Tsai, Tsung-Yen; Huang, Shih-Yung; Horng, Ray-Hua; Wuu, Dong-Sing

2017-05-31

In this study, a 3-μm-thick AlGaN film with an Al mole fraction of 10% was grown on a nanoscale-patterned sapphire substrate (NPSS) using hydride vapor phase epitaxy (HVPE). The growth mechanism, crystallization, and surface morphology of the epilayers were examined using X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy at various times in the growth process. The screw threading dislocation (TD) density of AlGaN-on-NPSS can improve to 1-2 × 10⁸ cm -2 , which is significantly lower than that of the sample grown on a conventional planar sapphire substrate (7 × 10⁸ cm -2 ). TEM analysis indicated that these TDs do not subsequently propagate to the surface of the overgrown AlGaN layer, but bend or change directions in the region above the voids within the side faces of the patterned substrates, possibly because of the internal stress-relaxed morphologies of the AlGaN film. Hence, the laterally overgrown AlGaN films were obtained by HVPE, which can serve as a template for the growth of ultraviolet III-nitride optoelectronic devices.

III-Nitride Digital Alloy: Electronics and Optoelectronics Properties of the InN/GaN Ultra-Short Period Superlattice Nanostructures.

PubMed

Sun, Wei; Tan, Chee-Keong; Tansu, Nelson

2017-07-27

The III-Nitride digital alloy (DA) is comprehensively studied as a short-period superlattice nanostructure consisting of ultra-thin III-Nitride epitaxial layers. By stacking the ultra-thin III-Nitride epitaxial layers periodically, these nanostructures are expected to have comparable optoelectronic properties as the conventional III-Nitride alloys. Here we carried out numerical studies on the InGaN DA showing the tunable optoelectronic properties of the III-Nitride DA. Our study shows that the energy gap of the InGaN DA can be tuned from ~0.63 eV up to ~2.4 eV, where the thicknesses and the thickness ratio of each GaN and InN ultra-thin binary layers within the DA structure are the key factors for tuning bandgap. Correspondingly, the absorption spectra of the InGaN DA yield broad wavelength tunability which is comparable to that of bulk InGaN ternary alloy. In addition, our investigation also reveals that the electron-hole wavefunction overlaps are remarkably large in the InGaN DA structure despite the existence of strain effect and build-in polarization field. Our findings point out the potential of III-Nitride DA as an artificially engineered nanostructure for optoelectronic device applications.

Boron Nitride Nanotubes for Engineering Applications

NASA Technical Reports Server (NTRS)

Hurst, Janet; Hull, David; Gorican, Daniel

2005-01-01

Boron nitride nanotubes (BNNT) are of significant interest to the scientific and technical communities for many of the same reasons that carbon nanotubes (CNT) have attracted wide attention. Both materials have potentially unique and important properties for structural and electronic applications. However of even more consequence than their similarities may be the complementary differences between carbon and boron nitride nanotubes While BNNT possess a very high modulus similar to CNT, they also possess superior chemical and thermal stability. Additionally, BNNT have more uniform electronic properties, with a uniform band gap of 5.5 eV while CNT vary from semi-conductive to highly conductive behavior. Boron nitride nanotubes have been synthesized both in the literature and at NASA Glenn Research Center, by a variety of methods such as chemical vapor deposition, arc discharge and reactive milling. Consistent large scale production of a reliable product has proven difficult. Progress in the reproducible synthesis of 1-2 gram sized batches of boron nitride nanotubes will be discussed as well as potential uses for this unique material.

Synthesis of Boron Nitride Nanotubes for Engineering Applications

NASA Technical Reports Server (NTRS)

Hurst, Janet; Hull, David; Gorican, Dan

2005-01-01

Boron Nitride nanotubes (BNNT) are of interest to the scientific and technical communities for many of the same reasons that carbon nanotubes (CNT) have attracted large amounts of attention. Both materials have potentially unique and significant properties which may have important structural and electronic applications in the future. However of even more interest than their similarities may be the differences between carbon and boron nanotubes. Whilt boron nitride nanotubes possess a very high modulus similaar to CNT, they are also more chemically and thermally inert. Additionally BNNT possess more uniform electronic properties, having a uniform band gap of approximately 5.5 eV while CNT vary from semi-conductin to conductor behavior. Boron Nitride nanotubes have been synthesized by a variety of methods such as chemical vapor deposition, arc discharge and reactive milling. Consistently producing a reliable product has proven difficult. Progress in synthesis of 1-2 gram sized batches of Boron Nitride nanotubes will be discussed as well as potential uses for this unique material.

Photodetectors using III-V nitrides

DOEpatents

Moustakas, T.D.; Misra, M.

1997-10-14

A photodetector using a III-V nitride and having predetermined electrical properties is disclosed. The photodetector includes a substrate with interdigitated electrodes formed on its surface. The substrate has a sapphire base layer, a buffer layer formed from a III-V nitride and a single crystal III-V nitride film. The three layers are formed by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy (ECR-assisted MBE). Use of the ECR-assisted MBE process allows control and predetermination of the electrical properties of the photodetector. 24 figs.

Photodetectors using III-V nitrides

DOEpatents

Moustakas, Theodore D.; Misra, Mira

1997-01-01

A photodetector using a III-V nitride and having predetermined electrical properties is disclosed. The photodetector includes a substrate with interdigitated electrodes formed on its surface. The substrate has a sapphire base layer, a buffer layer formed from a III-V nitride and a single crystal III-V nitride film. The three layers are formed by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy (ECR-assisted MBE). Use of the ECR-assisted MBE process allows control and predetermination of the electrical properties of the photodetector.

Structure refinement for tantalum nitrides nanocrystals with various morphologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lianyun; School of Science, Beijing Jiaotong University, 3 Shang Yuan Cun, Haidian District, Beijing 100044; Huang, Kai

2012-07-15

Graphical abstract: Tantalum nitrides nanocrystals with various phases and morphologies for the first time have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. Highlights: ► The spherical TaN, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. ► The crystal structures of different tantalum nitrides were determined by Rietveld refinement on the X-ray diffraction data and the examinations of electron microcopies. ► The specific surface area of the tantalum nitrides powders was around 10 m{supmore » 2} g{sup −1}. ► Tantalum nitrides powders could be suitable for capacitor with high specific capacitance. -- Abstract: Tantalum nitrides (TaN{sub x}) nanocrystals with different phase and morphology have been synthesized through homogenous sodium reduction under low temperature with the subsequent annealing process under high vacuum. The crystal structures of tantalum nitrides were determined by Rietveld refinement based on the X-ray diffraction data. The morphologies of various tantalum nitrides nanocrystals in high quality were analyzed through the electron microcopies examinations. The spherical TaN nanoparticles, cuboidal TaN{sub 0.83} and TaN{sub 0.5} nanocrystals have been selectively prepared at different annealing temperatures. In addition, the specific surface areas of the tantalum nitrides nanocrystals measured by BET method were around 9.87–11.64 m{sup 2} g{sup −1}, indicating that such nano-sized tantalum nitrides could be suitable for capacitor with high specific capacitance.« less

GaN@ZIF-8: selective formation of gallium nitride quantum dots inside a zinc methylimidazolate framework.

PubMed

Esken, Daniel; Turner, Stuart; Wiktor, Christian; Kalidindi, Suresh Babu; Van Tendeloo, Gustaaf; Fischer, Roland A

2011-10-19

The microporous zeolitic imidazolate framework [Zn(MeIM)(2); ZIF-8; MeIM = imidazolate-2-methyl] was quantitatively loaded with trimethylamine gallane [(CH(3))(3)NGaH(3)]. The obtained inclusion compound [(CH(3))(3)NGaH(3)]@ZIF-8 reveals three precursor molecules per host cavity. Treatment with ammonia selectively yields the caged cyclotrigallazane intermediate (H(2)GaNH(2))(3)@ZIF-8, and further annealing gives GaN@ZIF-8. This new composite material was characterized with FT-IR spectroscopy, solid-state NMR spectroscopy, powder X-ray diffraction, elemental analysis, (scanning) transmission electron microscopy combined with electron energy-loss spectroscopy, photoluminescence (PL) spectroscopy, and N(2) sorption measurements. The data give evidence for the presence of GaN nanoparticles (1-3 nm) embedded in the cavities of ZIF-8, including a blue-shift of the PL emission band caused by the quantum size effect.

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors.

PubMed

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L; Banyai, Douglas; Savaikar, Madhusudan A; Jaszczak, John A; Yap, Yoke Khin

2016-02-05

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

The microstructural characterization of an in situ grown Si{sub 3}N{sub 4} whisker-reinforced BAS glass-ceramic matrix composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Feng; Ortiz-Longo, C.R.; White, K.W.

The microstructure of barium aluminum silicate (BAS)/silicon nitride in situ whisker reinforced ceramic matrix composite was examined by X-ray diffraction, transmission electron microscopy, electron diffraction and energy-dispersive X-ray microanalysis. Although the authors can not conclusively exclude the presence of orthorhombic BAS, hexagonal BAS and both {alpha}-Si{sub 3}N{sub 4} and {beta}-Si{sub 3}N{sub 4} were identified in this material. The {beta}-Si{sub 3}N{sub 4} whiskers nucleate and grow in random directions in the nearly continuous matrix of metastable hexacelsian. The crystallization process of the glass phase can be taken almost to completion but a small proportion of residual glass phase is present atmore » the interface and grains-junction. Both whisker-like and equiaxed {beta}-Si{sub 3}N{sub 4} exist in this material.« less

Ab initio study of boron nitride lines on graphene

NASA Astrophysics Data System (ADS)

Mata-Carrizal, Berenice; Sanginés-Mendoza, Raúl; Martinez, Edgar

2013-03-01

Graphene has unusual electronic properties which make it a promising material for electronic devices. Neverthless, the absence of a band gap sets limitations on its practical applications. Thus, it is crucial to find methods to create and tune the band gap of systems based on graphene. In this way, we explore the modulation of the electronic properties of graphene through doping with boron nitride lines. In particular, we studied the electronic structure of graphene sheets doped with boron nitride lines armchair and zigzag type. The calculations were performed using the pseudopotential LCAO method with a Generalized Gradient Approximation (GGA) for the exchange-correlation energy functional. We found that both doping lines type induce a bandgap and that the energy gap increases as the length of doping lines increases. Accordingly to our DFT calculations, we found that the energy gap on graphene doped with armchair and zigzag lines is due to a two different mechanisms to drain charge from pi- to sigma- orbitals. Thus, we found that doping graphene with boron nitride lines is a useful way to induce and modulate the bandgap on graphene. This research was supported by Consejo Nacional de Ciencia y Tecnología (Conacyt) under Grant No. 133022.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qadri, S. B.; Rath, B. B.; Gorzkowski, E. P.

Nanoparticles, submicron-diameter tubes, and rods of Si{sub 3}N{sub 4} were synthesized from the thermal treatment of wheat and rice husks at temperatures at and above 1300 °C in a nitrogen atmosphere. The whole pattern Rietveld analysis of the observed diffraction data from treatments at 1300 °C showed the formation of only hexagonal α-phase of Si{sub 3}N{sub 4} with an R-factor of 1%, whereas samples treated at 1400 °C and above showed both α- and β-phases with an R-factor of 2%. Transmission electron microscopy showed the presence of tubes, rods, and nanoparticles of Si{sub 3}N{sub 4}. In a two-step process, where pure SiC wasmore » produced first from rice or wheat husk in an argon atmosphere and subsequently treated in a nitrogen atmosphere at 1450 °C, a nanostructured composite material having α- and β-phases of Si{sub 3}N{sub 4} combined with cubic phase of SiC was formed. The thermodynamics of the formation of silicon nitride is discussed in terms of the solid state reaction between organic matter (silica content), which is inherently present in the wheat and rice husks, with the nitrogen from the furnace atmosphere. Nanostructures of silicon nitride formed by a single direct reaction or their composites with SiC formed in a two-step process of agricultural byproducts provide an uncomplicated sustainable synthesis route for silicon nitride used in mechanical, biotechnology, and electro-optic nanotechnology applications.« less

Synthesis of titanium oxycarbonitride by carbothermal reduction and nitridation of ilmenite with recycling of polyethylene terephthalate (PET)

NASA Astrophysics Data System (ADS)

Ahmadi, Eltefat; Fauzi, Ahmad; Hussin, Hashim; Baharun, Norlia; Ariffin, Kamar Shah; Rezan, Sheikh Abdul

2017-04-01

An innovative and sustainable carbothermal reduction and nitridation (CTRN) process of ilmenite (FeTiO3) using a mixture of polyethylene terephthalate (PET) and coal as the primary reductant under an H2-N2 atmosphere was proposed. The use of PET as an alternative source of carbon not only enhances the porosity of the pellets but also results in the separation of Fe from titanium oxycarbonitride (TiO x C y N z ) particles because of the differences in surface tension. The experiments were carried out at 1250°C for 3 h using four different PET contents ranging from 25wt% to 100wt% in the reductant. X-ray diffraction (XRD), scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDX), and LECO elemental analysis were used to study the phases and microstructures of the reduced samples. In the case of 75wt% PET, iron distinctly separated from the synthesized TiO x C y N z phase. With increasing PET content in the sample, the reduction and nitridation rates substantially increased. The synthesis of an oxycarbonitride with stoichiometry of TiO0.02C0.13N0.85 with minimal intermediate titanium sub-oxides was achieved. The results also showed that the iron particles formed from CTRN of FeTiO3 exhibited a spherical morphology, which is conducive for Fe removal via the Becher process.

A novel anti-frictional multiphase layer produced by plasma nitriding of PVD titanium coated ZL205A aluminum alloy

NASA Astrophysics Data System (ADS)

Lu, C.; Yao, J. W.; Wang, Y. X.; Zhu, Y. D.; Guo, J. H.; Wang, Y.; Fu, H. Y.; Chen, Z. B.; Yan, M. F.

2018-02-01

The heat treatment (consisting of solid solution and aging), is integrated with the nitriding process of titanium coated ZL205A aluminum alloy to improve the surface and matrix mechanical properties simultaneously. Two-step duplex treatment is adopted to prepare the gradient multiphase layer on a magnesium-free ZL205A aluminum-copper based alloy. Firstly, pure titanium film is deposited on the aluminum alloy substrate using magnetron sputtering. Secondly, the Ti-coated specimen is nitrided at the solid solution temperature of the substrate alloying elements in a gas mixture of N2 and H2 and aged at 175 °C. The microstructure evolution, microhardness as well as the wear resistance of obtained multiphase layers are investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS), microhardness tester and pin-on-disc tribometer. The multiphase layer, dominated by TiN0.3 or Al3Ti, is prepared with significantly increased layer depth after duplex treatment. The surface hardness of multiphase layer is remarkably improved from 23.7HV to 457HV. The core matrix hardness is also increased to 65HV after aging. The wear rate of the multiphase layer decreases about 55.22% and 49.28% in comparison with the aged and Ti coated specimens, respectively. The predominant wear mechanism for the multiphase layer is abrasive and oxidation, but severe adhesive wear for the aged and Ti coated specimens.

In situ fabrication of the Bi2O3-V2O5 hybrid embedded with graphitic carbon nitride nanosheets: Oxygen vacancies mediated enhanced visible-light-driven photocatalytic degradation of organic pollutants and hydrogen evolution

NASA Astrophysics Data System (ADS)

Vattikuti, S. V. Prabhakar; Police, Anil Kumar Reddy; Shim, Jaesool; Byon, Chan

2018-07-01

Novel mesoporous ternary hybrids comprising Bi2O3/V2O5 photocatalysts anchored on graphitic carbon nitride (g-C3N4) nanosheets were synthesized via an in situ co-pyrolysis approach and characterized by a series of techniques, including X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, thermogravimetric-differential thermal analysis, Fourier transform infrared spectroscopy, ultraviolet-visible spectrometry, photoluminescence and electron paramagnetic resonance (EPR). The hybrids were subsequently tested as photocatalysts for the degradation of the phenol red (PR) pollutant under visible light irradiation. The well-designed ternary hybrids showed pure and randomly distributed Bi2O3/V2O5 (denoted as BiV) nanoparticles on monodispersed g-C3N4 nanosheets. The as-prepared ternary Bi2O3/V2O5@g-C3N4 (i.e., BiV@g-C3N4) hybrids demonstrated high specific surface areas with remarkable mesoporous characteristics. The photodegradation efficiencies of the ternary hybrids for PR were 1.2 and 1.8 times higher than those of binary BiV and pristine Bi2O3, respectively, at 50 min irradiation time under simulated solar light irradiation. At the end of the phototreatment, the amount of PR pollutant was reduced to 98.1% in 50 min by using the BiV@g-C3N4 nanocomposites under simulated solar light irradiation and more efficient for photocatalytic H2 production. Based on an electrochemical analysis, we propose a photocatalytic degradation pathway for PR under visible light irradiation. In addition, the BiV@g-C3N4 nanocomposite photocatalysts exhibited both long-term stability and photocatalytic efficiency for the degradation of the PR dye. The excellent photoelectrochemical performance of the BiV@g-C3N4 photocatalysts can be ascribed to their highly dispersed V2O5 and Bi2O3 nanoparticles, mesoporous structure, and high specific surface area (83.75 m2 g-1).

Fabrication of Ta2O5/GeNx gate insulator stack for Ge metal-insulator-semiconductor structures by electron-cyclotron-resonance plasma nitridation and sputtering deposition techniques

NASA Astrophysics Data System (ADS)

Otani, Yohei; Itayama, Yasuhiro; Tanaka, Takuo; Fukuda, Yukio; Toyota, Hiroshi; Ono, Toshiro; Mitsui, Minoru; Nakagawa, Kiyokazu

2007-04-01

The authors have fabricated germanium (Ge) metal-insulator-semiconductor (MIS) structures with a 7-nm-thick tantalum pentaoxide (Ta2O5)/2-nm-thick germanium nitride (GeNx) gate insulator stack by electron-cyclotron-resonance plasma nitridation and sputtering deposition. They found that pure GeNx ultrathin layers can be formed by the direct plasma nitridation of the Ge surface without substrate heating. X-ray photoelectron spectroscopy revealed no oxidation of the GeNx layer after the Ta2O5 sputtering deposition. The fabricated MIS capacitor with a capacitance equivalent thickness of 4.3nm showed excellent leakage current characteristics. The interface trap density obtained by the modified conductance method was 4×1011cm-2eV-1 at the midgap.

Origin of band gaps in graphene on hexagonal boron nitride

PubMed Central

Jung, Jeil; DaSilva, Ashley M.; MacDonald, Allan H.; Adam, Shaffique

2015-01-01

Recent progress in preparing well-controlled two-dimensional van der Waals heterojunctions has opened up a new frontier in materials physics. Here we address the intriguing energy gaps that are sometimes observed when a graphene sheet is placed on a hexagonal boron nitride substrate, demonstrating that they are produced by an interesting interplay between structural and electronic properties, including electronic many-body exchange interactions. Our theory is able to explain the observed gap behaviour by accounting first for the structural relaxation of graphene’s carbon atoms when placed on a boron nitride substrate, and then for the influence of the substrate on low-energy π-electrons located at relaxed carbon atom sites. The methods we employ can be applied to many other van der Waals heterojunctions. PMID:25695638

GaN/NbN epitaxial semiconductor/superconductor heterostructures

NASA Astrophysics Data System (ADS)

Yan, Rusen; Khalsa, Guru; Vishwanath, Suresh; Han, Yimo; Wright, John; Rouvimov, Sergei; Katzer, D. Scott; Nepal, Neeraj; Downey, Brian P.; Muller, David A.; Xing, Huili G.; Meyer, David J.; Jena, Debdeep

2018-03-01

Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductors—silicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistor—an electronic gain element—to be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistance—a feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family.

GaN/NbN epitaxial semiconductor/superconductor heterostructures.

PubMed

Yan, Rusen; Khalsa, Guru; Vishwanath, Suresh; Han, Yimo; Wright, John; Rouvimov, Sergei; Katzer, D Scott; Nepal, Neeraj; Downey, Brian P; Muller, David A; Xing, Huili G; Meyer, David J; Jena, Debdeep

2018-03-07

Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductors-silicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistor-an electronic gain element-to be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistance-a feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family.

Gallium nitride optoelectronic devices

NASA Technical Reports Server (NTRS)

Chu, T. L.; Chu, S. S.

1972-01-01

The growth of bulk gallium nitride crystals was achieved by the ammonolysis of gallium monochloride. Gallium nitride single crystals up to 2.5 x 0.5 cm in size were produced. The crystals are suitable as substrates for the epitaxial growth of gallium nitride. The epitaxial growth of gallium nitride on sapphire substrates with main faces of (0001) and (1T02) orientations was achieved by the ammonolysis of gallium monochloride in a gas flow system. The grown layers had electron concentrations in the range of 1 to 3 x 10 to the 19th power/cu cm and Hall mobilities in the range of 50 to 100 sq cm/v/sec at room temperature.

Electron energy loss spectroscopy on semiconductor heterostructures for optoelectronics and photonics applications.

PubMed

Eljarrat, A; López-Conesa, L; Estradé, S; Peiró, F

2016-05-01

In this work, we present characterization methods for the analysis of nanometer-sized devices, based on silicon and III-V nitride semiconductor materials. These methods are devised in order to take advantage of the aberration corrected scanning transmission electron microscope, equipped with a monochromator. This set-up ensures the necessary high spatial and energy resolution for the characterization of the smallest structures. As with these experiments, we aim to obtain chemical and structural information, we use electron energy loss spectroscopy (EELS). The low-loss region of EELS is exploited, which features fundamental electronic properties of semiconductor materials and facilitates a high data throughput. We show how the detailed analysis of these spectra, using theoretical models and computational tools, can enhance the analytical power of EELS. In this sense, initially, results from the model-based fit of the plasmon peak are presented. Moreover, the application of multivariate analysis algorithms to low-loss EELS is explored. Finally, some physical limitations of the technique, such as spatial delocalization, are mentioned. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Electronic structure and STM images simulation of defects on hBN/ black-phosphorene heterostructures: A theoretical study

NASA Astrophysics Data System (ADS)

Ospina, D. A.; Cisternas, E.; Duque, C. A.; Correa, J. D.

2018-03-01

By first principles calculations which include van der Waals interactions, we studied the electronic structure of hexagonal boron-nitride/black-phosphorene heterostructures (hBN/BP). In particular the role of several kind of defects on the electronic properties of black-phosphorene monolayer and hBN/BP heterostructure was analyzed. The defects under consideration were single and double vacancies, as well Stone-Wale type defects, all of them present in the phosphorene layer. In this way, we found that the electronic structure of the hBN/BP is modified according the type of defect that is introduced. As a remarkable feature, our results show occupied states at the Fermi Level introduced by a single vacancy in the energy gap of the hBN/BP heterostructure. Additionally, we performed simulations of scanning tunneling microscopy images. These simulations show that is possible to discriminate the kind of defect even when the black-phosphorene monolayer is part of the heterostructure hBN/BP. Our results may help to discriminate among several kind of defects during experimental characterization of these novel materials.

Conversion electron Mössbauer spectroscopy of plasma immersion ion implanted H13 tool steel

NASA Astrophysics Data System (ADS)

Terwagne, G.; Collins, G. A.; Hutchings, R.

1994-12-01

Conversion electron Mössbauer spectroscopy (CEMS) has been used to investigate nitride formation in AISI-H13 tool steel after treatment by plasma immersion ion implantation (PI3) at 350 °C. With only slight variation in the plasma conditions, it is possible to influence the kinetics of nitride precipitation so as to obtain nitrogen concentrations that range from those associated with ɛ-Fe2N through ɛ-Fe3N to γ'-Fe4N. The CEMS results enable a more definite identification of the nitrides than that obtained by glancing-angle X-ray diffraction and nuclear reaction analysis alone.

Metal Immiscibility Route to Synthesis of Ultrathin Carbides, Borides, and Nitrides.

PubMed

Wang, Zixing; Kochat, Vidya; Pandey, Prafull; Kashyap, Sanjay; Chattopadhyay, Soham; Samanta, Atanu; Sarkar, Suman; Manimunda, Praveena; Zhang, Xiang; Asif, Syed; Singh, Abhisek K; Chattopadhyay, Kamanio; Tiwary, Chandra Sekhar; Ajayan, Pulickel M

2017-08-01

Ultrathin ceramic coatings are of high interest as protective coatings from aviation to biomedical applications. Here, a generic approach of making scalable ultrathin transition metal-carbide/boride/nitride using immiscibility of two metals is demonstrated. Ultrathin tantalum carbide, nitride, and boride are grown using chemical vapor deposition by heating a tantalum-copper bilayer with corresponding precursor (C 2 H 2 , B powder, and NH 3 ). The ultrathin crystals are found on the copper surface (opposite of the metal-metal junction). A detailed microscopy analysis followed by density functional theory based calculation demonstrates the migration mechanism, where Ta atoms prefer to stay in clusters in the Cu matrix. These ultrathin materials have good interface attachment with Cu, improving the scratch resistance and oxidation resistance of Cu. This metal-metal immiscibility system can be extended to other metals to synthesize metal carbide, boride, and nitride coatings. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tribological and corrosion properties of plasma nitrided and nitrocarburized 42CrMo4 steel

NASA Astrophysics Data System (ADS)

Kusmic, D.; Van Thanh, D.

2017-02-01

This article deals with tribological and corrosion resistance comparison of plasma nitrided and nitrocarburized 42CrMo4 steel used for breech mechanism in the armament production. Increasing of materials demands (like wear resistance, surface hardness, running-in properties and corrosion resistance) used for armament production and in other industrial application leads in the field of surface treatment. Experimental steel samples were plasma nitrided under different nitriding gas ratio at 500 °C for 15h and nitrocarburized for 45 min at temperature 590°C and consequently post-oxidized for 10 min at 430°C. Individual 42CrMo4 steel samples were subsequently metallographically evaluated and characterized by hardness and microhardness measuring. The wear test “ball on disc” was realized for measuring of adhesive wear and coefficient of friction during unlubricated sliding. NSS corrosion tests were realized for corrosion resistance evaluation and expressed by corroded area and calculated corrosion rate. The corrosion resistance evaluation is by the surface corrosion-free surfaces evaluation supplemented using the laser confocal microscopy. Due to different surface treatment and plasma nitriding conditions, there are wear resistance and corrosion resistance differences evident between the plasma nitrided steel samples as well.

Scattering-type scanning near-field optical microscopy with reconstruction of vertical interaction

PubMed Central

Wang, Le; Xu, Xiaoji G.

2015-01-01

Scattering-type scanning near-field optical microscopy provides access to super-resolution spectroscopic imaging of the surfaces of a variety of materials and nanostructures. In addition to chemical identification, it enables observations of nano-optical phenomena, such as mid-infrared plasmons in graphene and phonon polaritons in boron nitride. Despite the high lateral spatial resolution, scattering-type near-field optical microscopy is not able to provide characteristics of near-field responses in the vertical dimension, normal to the sample surface. Here, we present an accurate and fast reconstruction method to obtain vertical characteristics of near-field interactions. For its first application, we investigated the bound electromagnetic field component of surface phonon polaritons on the surface of boron nitride nanotubes and found that it decays within 20 nm with a considerable phase change in the near-field signal. The method is expected to provide characterization of the vertical field distribution of a wide range of nano-optical materials and structures. PMID:26592949

STIR: Novel Electronic States by Gating Strongly Correlated Materials

DTIC Science & Technology

2016-03-01

plan built on my group’s recent demonstration of electrolyte gating in Strontium Titanate, using an atomically thin hexagonal Boron Nitride barrier to...demonstration of electrolyte gating in Strontium Titanate, using an atomically thin hexagonal Boron Nitride barrier to prevent disorder and chemical...techniques and learned to apply thin hexagonal Boron Nitride to single crystals of materials expected to show some of the most exciting correlated

Calcination Method Synthesis of SnO2/g-C3N4 Composites for a High-Performance Ethanol Gas Sensing Application

PubMed Central

Cao, Jianliang; Qin, Cong; Wang, Yan; Zhang, Bo; Gong, Yuxiao; Zhang, Huoli; Sun, Guang; Bala, Hari; Zhang, Zhanying

2017-01-01

The SnO2/g-C3N4 composites were synthesized via a facile calcination method by using SnCl4·5H2O and urea as the precursor. The structure and morphology of the as-synthesized composites were characterized by the techniques of X-ray diffraction (XRD), the field-emission scanning electron microscopy and transmission electron microscopy (SEM and TEM), energy dispersive spectrometry (EDS), thermal gravity and differential thermal analysis (TG-DTA), and N2-sorption. The analysis results indicated that the as-synthesized samples possess the two dimensional structure. Additionally, the SnO2 nanoparticles were highly dispersed on the surface of the g-C3N4nanosheets. The gas-sensing performance of the as-synthesized composites for different gases was tested. Moreover, the composite with 7 wt % g-C3N4 content (SnO2/g-C3N4-7) SnO2/g-C3N4-7 exhibits an admirable gas-sensing property to ethanol, which possesses a higher response and better selectivity than that of the pure SnO2-based sensor. The high surface area of the SnO2/g-C3N4 composite and the good electronic characteristics of the two dimensional graphitic carbon nitride are in favor of the elevated gas-sensing property. PMID:28468245

PHYSICAL PROPERTIES OF ZIRCONIUM NITRIDE IN THE HOMOGENEITY REGION (in Ukrainian)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samsonov, G.V.; Verkhoglyadova, T.S.

1962-01-01

The x-ray method was used to determine the homogeneity region of zirconium nitride as 40 to 50 at.% (9.5 to 13.3% by weight) of nitrogen. It is also shown that part of the ionic bond in the zirconium nitride lattice increases with a decrease in the nitrogen content in this region, this increase being higher than in the homogeneity region of titunium nitride due to the smaller degree of unfilling of the electron d-shell of the zirconium atom in comparison with that of the titanium atom. (auth)

Electron transport in zinc-blende wurtzite biphasic gallium nitride nanowires and GaNFETs

DOE PAGES

Jacobs, Benjamin W.; Ayres, Virginia M.; Stallcup, Richard E.; ...

2007-10-19

Two-point and four-point probe electrical measurements of a biphasic gallium nitride nanowire and current–voltage characteristics of a gallium nitride nanowire based field effect transistor are reported. The biphasic gallium nitride nanowires have a crystalline homostructure consisting of wurtzite and zinc-blende phases that grow simultaneously in the longitudinal direction. There is a sharp transition of one to a few atomic layers between each phase. Here, all measurements showed high current densities. Evidence of single-phase current transport in the biphasic nanowire structure is discussed.

Friction and wear of some ferrous-base metallic glasses

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1983-01-01

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminum oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

Nanostructured Boron Nitride With High Water Dispersibility For Boron Neutron Capture Therapy

PubMed Central

Singh, Bikramjeet; Kaur, Gurpreet; Singh, Paviter; Singh, Kulwinder; Kumar, Baban; Vij, Ankush; Kumar, Manjeet; Bala, Rajni; Meena, Ramovatar; Singh, Ajay; Thakur, Anup; Kumar, Akshay

2016-01-01

Highly water dispersible boron based compounds are innovative and advanced materials which can be used in Boron Neutron Capture Therapy for cancer treatment (BNCT). Present study deals with the synthesis of highly water dispersible nanostructured Boron Nitride (BN). Unique and relatively low temperature synthesis route is the soul of present study. The morphological examinations (Scanning/transmission electron microscopy) of synthesized nanostructures showed that they are in transient phase from two dimensional hexagonal sheets to nanotubes. It is also supported by dual energy band gap of these materials calculated from UV- visible spectrum of the material. The theoretically calculated band gap also supports the same (calculated by virtual nano lab Software). X-ray diffraction (XRD) analysis shows that the synthesized material has deformed structure which is further supported by Raman spectroscopy. The structural aspect of high water disperse ability of BN is also studied. The ultra-high disperse ability which is a result of structural deformation make these nanostructures very useful in BNCT. Cytotoxicity studies on various cell lines (Hela(cervical cancer), human embryonic kidney (HEK-293) and human breast adenocarcinoma (MCF-7)) show that the synthesized nanostructures can be used for BNCT. PMID:27759052

Effects of nano-sized boron nitride (BN) reinforcement in expandable graphite based in-tumescent fire retardant coating

NASA Astrophysics Data System (ADS)

Zulkurnain, E. S.; Ahmad, F.; Gillani, Q. F.

2016-08-01

The purpose of in-tumescent fire retardant coating (IFRC) is to protect substrate from fire attack by limiting heat transfer. A range of coating formulations have been prepared using Bisphenol A epoxy resin BE-188 and polyamide solidifier H-2310 as two-part binder, ammonium polyphosphate (APP) as acid source, melamine (MEL) as the blowing agent, expandable graphite (EG) as carbon source and nano-boron nitride (BN) as inorganic nano filler. The filler was used to improve the performances of the APP-EG-MEL coating. The effects of nano-BN on the char morphology and thermal degradation were investigated by fire test, thermo gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X- ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). The results showed that by substituting or reinforcing of 4% weight percentage of nano-BN, residual weight of the char increases by 23.82% compared to APP-EG-MEL coating without filler. Higher carbon content was obtained in the char and a more compact char was produced. The results indicated that nano-BN could be used as a filler to improve thermal stability of the APP-EG-MEL coating.

Nanostructured Boron Nitride With High Water Dispersibility For Boron Neutron Capture Therapy

NASA Astrophysics Data System (ADS)

Singh, Bikramjeet; Kaur, Gurpreet; Singh, Paviter; Singh, Kulwinder; Kumar, Baban; Vij, Ankush; Kumar, Manjeet; Bala, Rajni; Meena, Ramovatar; Singh, Ajay; Thakur, Anup; Kumar, Akshay

2016-10-01

Highly water dispersible boron based compounds are innovative and advanced materials which can be used in Boron Neutron Capture Therapy for cancer treatment (BNCT). Present study deals with the synthesis of highly water dispersible nanostructured Boron Nitride (BN). Unique and relatively low temperature synthesis route is the soul of present study. The morphological examinations (Scanning/transmission electron microscopy) of synthesized nanostructures showed that they are in transient phase from two dimensional hexagonal sheets to nanotubes. It is also supported by dual energy band gap of these materials calculated from UV- visible spectrum of the material. The theoretically calculated band gap also supports the same (calculated by virtual nano lab Software). X-ray diffraction (XRD) analysis shows that the synthesized material has deformed structure which is further supported by Raman spectroscopy. The structural aspect of high water disperse ability of BN is also studied. The ultra-high disperse ability which is a result of structural deformation make these nanostructures very useful in BNCT. Cytotoxicity studies on various cell lines (Hela(cervical cancer), human embryonic kidney (HEK-293) and human breast adenocarcinoma (MCF-7)) show that the synthesized nanostructures can be used for BNCT.

Friction and wear of some ferrous-base metallic glasses

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1984-01-01

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminium oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

Selective formation of GaN-based nanorod heterostructures on soda-lime glass substrates by a local heating method.

PubMed

Hong, Young Joon; Kim, Yong-Jin; Jeon, Jong-Myeong; Kim, Miyoung; Choi, Jun Hee; Baik, Chan Wook; Kim, Sun Il; Park, Sung Soo; Kim, Jong Min; Yi, Gyu-Chul

2011-05-20

We report on the fabrication of high-quality GaN on soda-lime glass substrates, heretofore precluded by both the intolerance of soda-lime glass to the high temperatures required for III-nitride growth and the lack of an epitaxial relationship with amorphous glass. The difficulties were circumvented by heteroepitaxial coating of GaN on ZnO nanorods via a local microheating method. Metal-organic chemical vapor deposition of ZnO nanorods and GaN layers using the microheater arrays produced high-quality GaN/ZnO coaxial nanorod heterostructures at only the desired regions on the soda-lime glass substrates. High-resolution transmission electron microscopy examination of the coaxial nanorod heterostructures indicated the formation of an abrupt, semicoherent interface. Photoluminescence and cathodoluminescence spectroscopy was also applied to confirm the high optical quality of the coaxial nanorod heterostructures. Mg-doped GaN/ZnO coaxial nanorod heterostructure arrays, whose GaN shell layers were grown with various different magnesocene flow rates, were further investigated by using photoluminescence spectroscopy for the p-type doping characteristics. The suggested method for fabrication of III-nitrides on glass substrates signifies potentials for low-cost and large-size optoelectronic device applications.

Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

NASA Astrophysics Data System (ADS)

Wan, Yimao; Bullock, James; Cuevas, Andres

2015-05-01

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta2O5) underneath plasma enhanced chemical vapour deposited silicon nitride (SiNx). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta2O5 and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Ω.cm and n-type 1.0 Ω.cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm2 and 68 fA/cm2 are measured on 150 Ω/sq boron-diffused p+ and 120 Ω/sq phosphorus-diffused n+ c-Si, respectively. Capacitance-voltage measurements reveal a negative fixed insulator charge density of -1.8 × 1012 cm-2 for the Ta2O5 film and -1.0 × 1012 cm-2 for the Ta2O5/SiNx stack. The Ta2O5/SiNx stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.

Boron nitride nanotubes radiolabeled with ⁹⁹mTc: preparation, physicochemical characterization, biodistribution study, and scintigraphic imaging in Swiss mice.

PubMed

Soares, Daniel Crístian Ferreira; Ferreira, Tiago Hilário; Ferreira, Carolina de Aguiar; Cardoso, Valbert Nascimento; de Sousa, Edésia Martins Barros

2012-02-28

In the present study, boron nitride nanotubes (BNNTs) were synthesized from an innovative process and functionalized with a glycol chitosan polymer in CDTN (Centro de Desenvolvimento da Tecnologia Nuclear) laboratories. As a means of studying their in vivo biodistribution behavior, these nanotubes were radiolabeled with (99m)Tc and injected in mice. Their size, distribution, and homogeneity were determined by photon correlation spectroscopy (PCS), while their zeta potential was determined by laser Doppler anemometry. The morphology and structural organization were evaluated by scanning electron microscopy (SEM). The functionalization in the nanotubes was evaluated by thermogravimetry analysis (TGA) and Fourier transformer infrared spectroscopy. The results showed that BNNTs were obtained and functionalized successfully, reaching a mean size and dispersity deemed adequate for in vivo studies. The BNNTs were also evaluated by ex vivo biodistribution studies and scintigraphic imaging in healthy mice. The results showed that nanostructures, after 24h, having accumulated in the liver, spleen and gut, and eliminated via renal excretion. The findings from this study reveal a potential application of functionalized BNNTs as new potential drugs or radioisotope nanocarriers to be applied in therapeutic procedures. Copyright © 2011 Elsevier B.V. All rights reserved.

Structure and luminescence of nanocrystalline gallium nitride synthesized by a novel polymer pyrolysis route

NASA Astrophysics Data System (ADS)

Garcia, Rafael; Hirata, Gustavo A.; Thomas, Alan C.; Ponce, Fernando A.

2006-10-01

Thermal decomposition in a horizontal quartz tube reactor of a polymer [-(CH 6N 4O) 3Ga(NO 3) 3-] in a nitrogen atmosphere, yield directly nano-structured gallium nitride (GaN) powder. The polymer was obtained by the reaction between high purity gallium nitrate (Ga(NO 3) 3) dissolved in toluene and carbohydrazide as an azotic ligand. The powder synthesized by this method showed a yellow color and elemental analysis suggested that the color is due to some carbon and oxygen impurities in the as-synthesized powder. Electron microscopy showed that the as-synthesized powders consist of a mixture of various porous particles containing nanowires and nano-sized platelets. The size of the crystallites can be controlled by annealing processes under ammonia. Photoluminescence analysis at 10 K on as-synthesized powders showed a broad red luminescence around 668 nm under UV laser excitation (He-Cd laser, 325 nm). However after annealing process the red luminescence disappears and the typical band edge emission of GaN around 357 nm (3.47 eV) and the UV band were the dominant emissions in the PL spectra.

One-pot synthesis of h-BN fullerenes usinsg a graphene oxide template

NASA Astrophysics Data System (ADS)

Kim, Sang Sub; Khai, Tran Van; Kwon, Yong Jung; Katoch, Akash; Wu, Ping; Kim, Hyoun Woo

2015-09-01

Hexagonal-boron nitride ( h-BN) fullerenes were synthesized from a graphene oxide (GO) template by simultaneously heating the GO and B2O3 in the presence of NH3 gas. Transmission electron microscopy (TEM) observations revealed that a considerable amount of product had a fullerene-like nanostructure. Typical BN fullerenes have a polyhedral shape, being hollow nanocages. Lattice-resolved TEM and X-ray diffraction consistently demonstrated the formation of h-BN fullerenes. The FTIR spectrum exhibited absorption bands at approximately 800 and 1378 cm-1, which were related to the h-BN structure. The Raman spectra exhibited peaks at 1368 and 1399 cm-1, which can be related to BN sheets and BN fullerenes, respectively. The photoluminescence spectrum of the h-BN fullerenes taken at 8 K exhibited intense white-light emission. To reveal the origin of the broad emission band, which could be a superimposition of several peaks, we used a deconvolution procedure based on Gaussian functions. We proposed a growth mechanism of the h-BN fullerenes and verified it with a thermodynamic calculation. This work provides a cost-effective approach to synthesize fullerene-type boron nitride on a production scale.

Surface improvement and biocompatibility of TiAl 24Nb 10 intermetallic alloy using rf plasma nitriding

NASA Astrophysics Data System (ADS)

Abd El-Rahman, A. M.; Maitz, M. F.; Kassem, M. A.; El-Hossary, F. M.; Prokert, F.; Reuther, H.; Pham, M. T.; Richter, E.

2007-09-01

The present work describes the surface improvement and biocompatibility of TiAl 24Nb 10 intermetallic alloy using rf plasma nitriding. The nitriding process was carried out at different plasma power from 400 W to 650 W where the other plasma conditions were fixed. Grazing incidence X-ray diffractometry (GIXRD), Auger electron spectroscopy (AES), tribometer and a nanohardness tester were employed to characterize the nitrided layer. Further potentiodynamic polarization method was used to describe the corrosion behavior of the un-nitrided and nitrided alloy. It has been found that the Vickers hardness (HV) and corrosion resistance values of the nitrided layers increase with increasing plasma power while the wear rates of the nitrided layers reduce by two orders of magnitude as compared to those of the un-nitrided layer. This improvement in surface properties of the intermetallic alloy is due to formation of a thin modified layer which is composed of titanium nitride in the alloy surface. Moreover, all modified layers were tested for their sustainability as a biocompatible material. Concerning the application area of biocompatibility, the present treated alloy show good surface properties especially for the nitrided alloy at low plasma power of 400 W.

Novel band gap-tunable K-Na co-doped graphitic carbon nitride prepared by molten salt method

NASA Astrophysics Data System (ADS)

Zhao, Jiannan; Ma, Lin; Wang, Haoying; Zhao, Yanfeng; Zhang, Jian; Hu, Shaozheng

2015-03-01

Novel band gap-tunable K-Na co-doped graphitic carbon nitride was prepared by molten salt method using melamine, KCl, and NaCl as precursor. X-ray diffraction (XRD), N2 adsorption, Scanning electron microscope (SEM), UV-vis spectroscopy, Photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The CB and VB potentials of graphitic carbon nitride could be tuned from -1.09 and +1.55 eV to -0.29 and +2.25 eV by controlling the weight ratio of eutectic salts to melamine. Besides, ions doping inhibited the crystal growth of graphitic carbon nitride, enhanced the surface area, and increased the separation rate of photogenerated electrons and holes. The visible-light-driven Rhodamine B (RhB) photodegradation and mineralization performances were significantly improved after K-Na co-doping.

Controlled Expansion of a Strong-Field Iron Nitride Cluster: Multi-Site Ligand Substitution as a Strategy for Activating Interstitial Nitride Nucleophilicity.

PubMed

Drance, Myles J; Mokhtarzadeh, Charles C; Melaimi, Mohand; Agnew, Douglas W; Moore, Curtis E; Rheingold, Arnold L; Figueroa, Joshua S

2018-05-02

Multimetallic clusters have long been investigated as molecular surrogates for reactive sites on metal surfaces. In the case of the μ 4 -nitrido cluster [Fe 4 (μ 4 -N)(CO) 12 ] - , this analogy is limited owing to the electron-withdrawing effect of carbonyl ligands on the iron nitride core. Described here is the synthesis and reactivity of [Fe 4 (μ 4 -N)(CO) 8 (CNAr Mes2 ) 4 ] - , an electron-rich analogue of [Fe 4 (μ 4 -N)(CO) 12 ] - , where the interstitial nitride displays significant nucleophilicity. This characteristic enables rational expansion with main-group and transition-metal centers to yield unsaturated sites. The resulting clusters display surface-like reactivity through coordination-sphere-dependent atom rearrangement and metal-metal cooperativity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

III-nitride integration on ferroelectric materials of lithium niobate by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Namkoong, Gon; Lee, Kyoung-Keun; Madison, Shannon M.; Henderson, Walter; Ralph, Stephen E.; Doolittle, W. Alan

2005-10-01

Integration of III-nitride electrical devices on the ferroelectric material lithium niobate (LiNbO3) has been demonstrated. As a ferroelectric material, lithium niobate has a polarization which may provide excellent control of the polarity of III-nitrides. However, while high temperature, 1000°C, thermal treatments produce atomically smooth surfaces, improving adhesion of GaN epitaxial layers on lithium niobate, repolarization of the substrate in local domains occurs. These effects result in multi domains of mixed polarization in LiNbO3, producing inversion domains in subsequent GaN epilayers. However, it is found that AlN buffer layers suppress inversion domains of III-nitrides. Therefore, two-dimensional electron gases in AlGaN /GaN heterojunction structures are obtained. Herein, the demonstration of the monolithic integration of high power devices with ferroelectric materials presents possibilities to control LiNbO3 modulators on compact optoelectronic/electronic chips.

The effect of plasma surface treatment on the bioactivity of titanium implant materials (in vitro)

PubMed Central

Abdelrahim, Ramy A.; Badr, Nadia A.; Baroudi, Kusai

2016-01-01

Background: The surface of an implantable biomaterial plays a very important role in determining the biocompatibility, osteoinduction, and osteointegration of implants because it is in intimate contact with the host bone and soft tissues. Objective: This study was aimed to assess the effect of plasma surface treatment on the bioactivity of titanium alloy (Ti–6Al–4V). Materials and Methods: Fifteen titanium alloy samples were used in this study. The samples were divided into three groups (with five samples in each group). Five samples were kept untreated and served as control (group A). Another five plasma samples were sprayed for nitrogen ion implantation on their surfaces (group B) and the last five samples were pre-etched with acid before plasma treatment (group C). All the investigated samples were immersed for 7 days in Hank's balanced salt solution (HBSS) which was used as a simulating body fluid (SBF) at pH 7.4 and 37°C. HBSS was renewed every 3 days. The different surfaces were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDXA), and Fourier Transformation Infrared Spectroscopy (FTIR). Results: Nitriding of Ti-alloy samples via plasma nitrogen ion implantation increased the bioactivity of titanium. Moreover, the surface topography affected the chemical structure of the formed apatite. Increasing the surface roughness enhanced the bioactivity of the implant material. Conclusions: Nitridation can be exploited as an effective way to promote the formation of bone-like material on the implant surface. PMID:27011927

The steady-state and transient electron transport within bulk zinc-blende indium nitride: The impact of crystal temperature and doping concentration variations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siddiqua, Poppy; O'Leary, Stephen K., E-mail: stephen.oleary@ubc.ca

2016-03-07

Within the framework of a semi-classical three-valley Monte Carlo electron transport simulation approach, we analyze the steady-state and transient aspects of the electron transport within bulk zinc-blende indium nitride, with a focus on the response to variations in the crystal temperature and the doping concentration. We find that while the electron transport associated with zinc-blende InN is highly sensitive to the crystal temperature, it is not very sensitive to the doping concentration selection. The device consequences of these results are then explored.

Method of fabricating boron containing coatings

DOEpatents

Makowiecki, Daniel M.; Jankowski, Alan F.

1999-01-01

Hard coatings are fabricated from boron nitride, cubic boron nitride, and multilayer boron/cubic boron nitride, and the fabrication thereof involves magnetron sputtering in a selected atmosphere. These hard coatings may be applied to tools and engine and other parts, as well to reduce wear on tribological surfaces and electronic devices. These boron coatings contain no morphological growth features. For example, the boron is formed in an inert (e.g. argon) atmosphere, while the cubic boron nitride is formed in a reactive (e.g. nitrogen) atmosphere. The multilayer boron/cubic boron nitride, is produced by depositing alternate layers of boron and cubic boron nitride, with the alternate layers having a thickness of 1 nanometer to 1 micrometer, and at least the interfaces of the layers may be discrete or of a blended or graded composition.

Method of fabricating boron containing coatings

DOEpatents

Makowiecki, D.M.; Jankowski, A.F.

1999-04-27

Hard coatings are fabricated from boron nitride, cubic boron nitride, and multilayer boron/cubic boron nitride, and the fabrication thereof involves magnetron sputtering in a selected atmosphere. These hard coatings may be applied to tools and engine and other parts, as well to reduce wear on tribological surfaces and electronic devices. These boron coatings contain no morphological growth features. For example, the boron is formed in an inert (e.g. argon) atmosphere, while the cubic boron nitride is formed in a reactive (e.g. nitrogen) atmosphere. The multilayer boron/cubic boron nitride, is produced by depositing alternate layers of boron and cubic boron nitride, with the alternate layers having a thickness of 1 nanometer to 1 micrometer, and at least the interfaces of the layers may be discrete or of a blended or graded composition. 3 figs.

Amorphous Carbon-Boron Nitride Nanotube Hybrids

NASA Technical Reports Server (NTRS)

Kim, Jae Woo (Inventor); Siochi, Emilie J. (Inventor); Wise, Kristopher E. (Inventor); Lin, Yi (Inventor); Connell, John (Inventor)

2016-01-01

A method for joining or repairing boron nitride nanotubes (BNNTs). In joining BNNTs, the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures. In repairing BNNTs, the damaged site of the nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation to form well bonded hybrid a-C/BNNT structures at the damage site.

Phonon-Assisted Resonant Tunneling of Electrons in Graphene-Boron Nitride Transistors.

PubMed

Vdovin, E E; Mishchenko, A; Greenaway, M T; Zhu, M J; Ghazaryan, D; Misra, A; Cao, Y; Morozov, S V; Makarovsky, O; Fromhold, T M; Patanè, A; Slotman, G J; Katsnelson, M I; Geim, A K; Novoselov, K S; Eaves, L

2016-05-06

We observe a series of sharp resonant features in the differential conductance of graphene-hexagonal boron nitride-graphene tunnel transistors over a wide range of bias voltages between 10 and 200 mV. We attribute them to electron tunneling assisted by the emission of phonons of well-defined energy. The bias voltages at which they occur are insensitive to the applied gate voltage and hence independent of the carrier densities in the graphene electrodes, so plasmonic effects can be ruled out. The phonon energies corresponding to the resonances are compared with the lattice dispersion curves of graphene-boron nitride heterostructures and are close to peaks in the single phonon density of states.

Dynamics-Enabled Nanoelectromechanical Systems (NEMS) Oscillators

DTIC Science & Technology

2014-06-01

it becomes strongly nonlinear, and thus constitutes an archetypal candidate for nonlinear engineering • its fundamental resonant frequency...width of spectral peaks of atomic force microscopy (AFM) resonators as they are brought close to a surface. 39 Approved for public release...alternating current AD Allan Deviation AFM atomic force microscopy AFRL Air Force Research Laboratory AlN aluminum nitride APN Anomalous Phase

Interlayer interaction and mechanical properties in multi-layer graphene, Boron-Nitride, Aluminum-Nitride and Gallium-Nitride graphene-like structure: A quantum-mechanical DFT study

NASA Astrophysics Data System (ADS)

Ghorbanzadeh Ahangari, Morteza; Fereidoon, A.; Hamed Mashhadzadeh, Amin

2017-12-01

In present study, we investigated mechanical, electronic and interlayer properties of mono, bi and 3layer of Boron-Nitride (B-N), Aluminum-Nitride (Al-N) and Gallium-Nitride (Ga-N) graphene sheets and compared these results with results obtained from carbonic graphenes (C-graphenes). For reaching this purpose, first we optimized the geometrical parameters of these graphenes by using density functional theory (DFT) method. Then we calculated Young's modulus of graphene sheet by compressing and then elongating these sheets in small increment. Our results indicates that Young's modulus of graphenes didn't changed obviously by increasing the number of layer sheet. We also found that carbonic graphene has greatest Young's modulus among another mentioned sheets because of smallest equilibrium distance between its elements. Next we modeled the van der Waals interfacial interaction exist between two sheets with classical spring model by using general form of Lennard-Jones (L-J) potential for all of mentioned graphenes. For calculating L-J parameters (ε and σ), the potential energy between layers of mentioned graphene as a function of the separation distance was plotted. Moreover, the density of states (DOS) are calculated to understand the electronic properties of these systems better.

A Screened Hybrid DFT Study of Actinide Oxides, Nitrides, and Carbides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wen, Xiaodong; Martin, Richard L.; Scuseria, Gustavo E.

2013-06-27

A systematic study of the structural, electronic, and magnetic properties of actinide oxides, nitrides, and carbides (AnX1–2 with X = C, N, O) is performed using the Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Our computed results show that the screened hybrid HSE functional gives a good description of the electronic and structural properties of actinide dioxides (strongly correlated insulators) when compared with available experimental data. However, there are still some problems reproducing the electronic properties of actinide nitrides and carbides (strongly correlated metals). In addition, in order to compare with the results by HSE, the structures, electronic, and magnetic properties of thesemore » actinide compounds are also investigated in the PBE and PBE+U approximation. Interestingly, the density of states of UN obtained with PBE compares well with the experimental photoemission spectra, in contrast to the hybrid approximation. This is presumably related to the need of additional screening in the Hartree–Fock exchange term of the metallic phases.« less

Scanning transmission electron microscopy analysis of Ge(O)/(graphitic carbon nitride) nanocomposite powder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawasaki, Masahiro; Sompetch, Kanganit; Sarakonsri, Thapanee, E-mail: tsarakonsri@gmail.com

2015-12-15

Analytical electron microscopy has revealed the structure of particles that were synthesized by chemical reaction of GeO{sub 2} with NaBH{sub 4} in the basic solution including graphitic carbon nitride (g-C{sub 3}N{sub 4}) powders. The g-C{sub 3}N{sub 4} was arranged by recrystallization of melamine at 600 °C under N{sub 2} gas atmosphere. The samples were dried at 60 °C or 180 °C for 4 h. The g-C{sub 3}N{sub 4} was observed as lamellae of several ten nm or less in size and had an amorphous-like structure with a distorted lattice in an area as small as a few hundred pm inmore » size. The reaction product was Ge(O) particles as fine as several nm in size and composed of Ge and O atoms. Most of the particles must be of GeO{sub 2−x} with the amorphous-like structure that has also a distorted lattice in an area of a few hundred pm in size. In the sample dried at 60 °C, the particles were found to be dispersed in a wide area on the g-C{sub 3}N{sub 4} lamella. It is hard to recognize those particles in TEM images. The particles in the sample dried at 180 °C became larger and were easily observed as isolated lumps. Hence, these powders can be regarded as GeO{sub 2}/g-C{sub 3}N{sub 4} or Ge/GeO{sub 2}/g-C{sub 3}N{sub 4} nanocomposites, and expected to be applicable to anode materials for high energy Li-ion batteries due to Ge catalysis effect, accordingly. - Graphical abstract: STEM analysis of Ge(O)/(graphitic carbon nitride) nanocomposite powder. - Highlights: • Graphitic (g)-C{sub 3}N{sub 4} powder was prepared at 600 °C by recrystallization of melamine. • Ge(O) was prepared by chemical reaction in a solution including the g-C{sub 3}N{sub 4} powders. • The products can be regarded as GeO{sub 2}/g-C{sub 3}N{sub 4} or Ge/GeO{sub 2}/g-C{sub 3}N{sub 4} nanocomposites. • GeO{sub 2} was amorphous several-nm particles and g-C{sub 3}N{sub 4} was amorphous lamella of several 10 nm in size. • We expect them to be applicable for high energy Li-ion battery anode materials.« less

Characteristics of an Electron Cyclotron Resonance Plasma Source for the Production of Active Nitrogen Species in III-V Nitride Epitaxy

NASA Technical Reports Server (NTRS)

Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

1997-01-01

A simple analysis is provided to determine the characteristics of an electron cyclotron resonance (ECR) plasma source for the generation of active nitrogen species in the molecular beam epitaxy of III-V nitrides. The effects of reactor geometry, pressure, power, and flow rate on the dissociation efficiency and ion flux are presented. Pulsing the input power is proposed to reduce the ion flux.

Gate-dependent Pseudospin Mixing in Graphene/boron Nitride Moire Superlattices

DTIC Science & Technology

2014-08-31

LETTERS PUBLISHED ONLINE: 31 AUGUST 2014 | DOI : 10.1038/NPHYS3075 Gate-dependent pseudospin mixing in graphene/boron nitride moiré superlattices... Dirac –Weyl spinors with a two-component pseudospin1–12. The unique pseudospin structure of Dirac electrons leads to emerging phenomena such as the...massless Dirac cone2, anomalous quantum Hall eect2,3, and Klein tunnelling4,5 in graphene. The capability to manipulate electron pseudospin is highly

Ultra-thin alumina and silicon nitride MEMS fabricated membranes for the electron multiplication

NASA Astrophysics Data System (ADS)

Prodanović, V.; Chan, H. W.; Graaf, H. V. D.; Sarro, P. M.

2018-04-01

In this paper we demonstrate the fabrication of large arrays of ultrathin freestanding membranes (tynodes) for application in a timed photon counter (TiPC), a novel photomultiplier for single electron detection. Low pressure chemical vapour deposited silicon nitride (Si x N y ) and atomic layer deposited alumina (Al2O3) with thicknesses down to only 5 nm are employed for the membrane fabrication. Detailed characterization of structural, mechanical and chemical properties of the utilized films is carried out for different process conditions and thicknesses. Furthermore, the performance of the tynodes is investigated in terms of secondary electron emission, a fundamental attribute that determines their applicability in TiPC. Studied features and presented fabrication methods may be of interest for other MEMS application of alumina and silicon nitride as well, in particular where strong ultra-thin membranes are required.

Two-dimensional X-ray diffraction and transmission electron microscopy study on the effect of magnetron sputtering atmosphere on GaN/SiC interface and gallium nitride thin film crystal structure

NASA Astrophysics Data System (ADS)

Shen, Huaxiang; Zhu, Guo-Zhen; Botton, Gianluigi A.; Kitai, Adrian

2015-03-01

The growth mechanisms of high quality GaN thin films on 6H-SiC by sputtering were investigated by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The XRD θ-2θ scans show that high quality ( 0002 ) oriented GaN was deposited on 6H-SiC by reactive magnetron sputtering. Pole figures obtained by 2D-XRD clarify that GaN thin films are dominated by ( 0002 ) oriented wurtzite GaN and { 111 } oriented zinc-blende GaN. A thin amorphous silicon oxide layer on SiC surfaces observed by STEM plays a critical role in terms of the orientation information transfer from the substrate to the GaN epilayer. The addition of H2 into Ar and/or N2 during sputtering can reduce the thickness of the amorphous layer. Moreover, adding 5% H2 into Ar can facilitate a phase transformation from amorphous to crystalline in the silicon oxide layer and eliminate the unwanted { 3 3 ¯ 02 } orientation in the GaN thin film. Fiber texture GaN thin films can be grown by adding 10% H2 into N2 due to the complex reaction between H2 and N2.

Synthesis of GaN:ZnO solid solution by solution combustion method and characterization for photocatalytic application

NASA Astrophysics Data System (ADS)

Menon, Sumithra Sivadas; Anitha, R.; Gupta, Bhavana; Baskar, K.; Singh, Shubra

2016-05-01

GaN-ZnO solid solution has emerged as a successful and reproducible photocatalyst for overall water splitting by one-step photoexcitation, with a bandgap in visible region. When the solid solution is formed, some of the Zn and O ions are replaced by Ga and N ions respectively and there is a narrowing of bandgap which is hypothesized as due to Zn3d-N2p repulsion. The traditional method of synthesis of GaN-ZnO solid solution is by nitridation of the starting oxides under constant ammonia flow. Here we report a solution combustion technique for the synthesis of the solid solution at a temperature about 500 ° C in a muffle furnace with metal nitrates as precursors and urea as the fuel. The as prepared samples showed change in color with the increased concentration of ZnO in the solution. The structural, microstructural, morphological and optical properties of the samples were realized by Powder X ray diffraction, Scanning electron microscopy, Energy dispersive X ray analysis, Transmission electron microscopy and Photoluminescence. Finally the hydrogen production efficiency of the GaN-ZnO nanopowders by water splitting was found, using methanol as a scavenger. The apparent quantum yield (AQY) of 0.048% is obtained for GaN-ZnO solid solution.

Tailoring the structural and optical properties of TiN thin films by Ag ion implantation

NASA Astrophysics Data System (ADS)

Popović, M.; Novaković, M.; Rakočević, Z.; Bibić, N.

2016-12-01

Titanium nitride (TiN) thin films thickness of ∼260 nm prepared by dc reactive sputtering were irradiated with 200 keV silver (Ag) ions to the fluences ranging from 5 × 1015 ions/cm2 to 20 × 1015 ions/cm2. After implantation TiN layers were annealed 2 h at 700 °C in a vacuum. Ion irradiation-induced microstructural changes were examined by using Rutherford backscattering spectrometry, X-ray diffraction and transmission electron microscopy, while the surface topography was observed using atomic force microscopy. Spectroscopic ellipsometry was employed to get insights on the optical and electronic properties of TiN films with respect to their microstructure. The results showed that the irradiations lead to deformation of the lattice, increasing disorder and formation of new Ag phase. The optical results demonstrate the contribution of surface plasmon resonace (SPR) of Ag particles. SPR position shifted in the range of 354.3-476.9 nm when Ag ion fluence varied from 5 × 1015 ions/cm2 to 20 × 1015 ions/cm2. Shift in peak wavelength shows dependence on Ag particles concentration, suggesting that interaction between Ag particles dominate the surface plasmon resonance effect. Presence of Ag as second metal in the layer leads to overall decrease of optical resistivity of TiN.

The effect of incorporated self-lubricated BN(h) particles on the tribological properties of Ni-P/BN(h) composite coatings

NASA Astrophysics Data System (ADS)

Hsu, Chih-I.; Hou, Kung-Hsu; Ger, Ming-Der; Wang, Gao-Liang

2015-12-01

Ni-P/BN(h) composite coatings are prepared by means of the conventional electroless plating from the bath containing up to 10.0 g/l of hexagonal boron nitride particles with size 0.5 μm. The Ni-P coating is also prepared as a comparison. Cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to stabilize the electrolyte, and the optimum CTAB concentration resulting in a nonagglomerated dispersion of particles is obtained using a dispersion stability analyzer. Morphology of the coatings and the effect of incorporated particles on coating structure and composition are investigated via scanning electron microscopy, field emission electron probe micro-analyzer and X-ray diffraction analysis. Hardness, roughness, friction coefficient and wear resistance of the coatings are also evaluated using Vickers microhardness tester, atomic force microscopy and ball-on disk machine. The presence of CTAB in the depositing bath has a positive effect on the surface roughness and performance of Ni-P/BN(h) composite coatings. The friction and wear tests results show that incorporation of 14.5 vol% BN(h) particles into the Ni-P coating lowers the coating friction coefficient by about 75% and the wear resistance of the Ni-P composites is approximately 10 times higher than Ni-P coating.

Mapping Strain Gradients in the FIB-Structured InGaN/GaN Multilayered Films with 3D X-ray Microbeam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barabash, Rozaliya; Gao, Yanfei; Ice, Gene E

2010-01-01

This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence ({mu}-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation ofmore » complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent.« less

Mapping strain gradients in the FIB-structured InGaN/GaN multilayered films with 3D x-ray microbeam.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barabash, R. I.; Gao, Y. F.; Ice, G. E.

2010-11-25

This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence ({mu}-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation ofmore » complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent.« less

Neutron powder diffraction study on the iron-based nitride superconductor ThFeAsN

NASA Astrophysics Data System (ADS)

Mao, Huican; Wang, Cao; Maynard-Casely, Helen E.; Huang, Qingzhen; Wang, Zhicheng; Cao, Guanghan; Li, Shiliang; Luo, Huiqian

2017-03-01

We report neutron diffraction and transport results on the newly discovered superconducting nitride ThFeAsN with T_c= 30 \\text{K} . No magnetic transition, but a weak structural distortion around 160 K, is observed by cooling from 300 K to 6 K. Analysis on the resistivity, Hall transport and crystal structure suggests that this material behaves as an electron optimally doped pnictide superconductor due to extra electrons from nitrogen deficiency or oxygen occupancy at the nitrogen site, which, together with the low arsenic height, may enhance the electron itinerancy and reduce the electron correlations, thus suppressing the static magnetic order.

Boron nitride nanowires synthesis via a simple chemical vapor deposition at 1200 °C

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmad, Pervaiz; Khandaker, Mayeen Uddin; Amin, Yusoff Mohd

2015-04-24

A very simple chemical vapor deposition technique is used to synthesize high quality boron nitride nanowires at 1200 °C within a short growth duration of 30 min. FESEM micrograph shows that the as-synthesized boron nitride nanowires have a clear wire like morphology with diameter in the range of ∼20 to 150 nm. HR-TEM confirmed the wire-like structure of boron nitride nanowires, whereas XPS and Raman spectroscopy are used to find out the elemental composition and phase of the synthesized material. The synthesized boron nitride nanowires have potential applications as a sensing element in solid state neutron detector, neutron capture therapy and microelectronicmore » devices with uniform electronic properties.« less

Near-Field Infrared Pump-Probe Imaging of Surface Phonon Coupling in Boron Nitride Nanotubes.

PubMed

Gilburd, Leonid; Xu, Xiaoji G; Bando, Yoshio; Golberg, Dmitri; Walker, Gilbert C

2016-01-21

Surface phonon modes are lattice vibrational modes of a solid surface. Two common surface modes, called longitudinal and transverse optical modes, exhibit lattice vibration along or perpendicular to the direction of the wave. We report a two-color, infrared pump-infrared probe technique based on scattering type near-field optical microscopy (s-SNOM) to spatially resolve coupling between surface phonon modes. Spatially varying couplings between the longitudinal optical and surface phonon polariton modes of boron nitride nanotubes are observed, and a simple model is proposed.

Auger electron spectroscopy analysis for growth interface of cubic boron nitride single crystals synthesized under high pressure and high temperature

NASA Astrophysics Data System (ADS)

Lv, Meizhe; Xu, Bin; Cai, Lichao; Guo, Xiaofei; Yuan, Xingdong

2018-05-01

After rapid cooling, cubic boron nitride (c-BN) single crystals synthesized under high pressure and high temperature (HPHT) are wrapped in the white film powders which are defined as growth interface. In order to make clear that the transition mechanism of c-BN single crystals, the variation of B and N atomic hybrid states in the growth interface is analyzed with the help of auger electron spectroscopy in the Li-based system. It is found that the sp2 fractions of B and N atoms decreases, and their sp3 fractions increases from the outer to the inner in the growth interface. In addition, Lithium nitride (Li3N) are not found in the growth interface by X-ray diffraction (XRD) experiment. It is suggested that lithium boron nitride (Li3BN2) is produced by the reaction of hexagonal boron nitride (h-BN) and Li3N at the first step, and then B and N atoms transform from sp2 into sp3 state with the catalysis of Li3BN2 in c-BN single crystals synthesis process.

Shear-Assisted Production of Few-Layer Boron Nitride Nanosheets by Supercritical CO2 Exfoliation and Its Use for Thermally Conductive Epoxy Composites.

PubMed

Tian, Xiaojuan; Li, Yun; Chen, Zhuo; Li, Qi; Hou, Liqiang; Wu, Jiaye; Tang, Yushu; Li, Yongfeng

2017-12-19

Boron nitride nanosheets (BNNS) hold the similar two-dimensional structure as graphene and unique properties complementary to graphene, which makes it attractive in application ranging from electronics to energy storage. The exfoliation of boron nitride (BN) still remains challenge and hinders the applications of BNNS. In this work, the preparation of BNNS has been realized by a shear-assisted supercritical CO 2 exfoliation process, during which supercritical CO 2 intercalates and diffuses between boron nitride layers, and then the exfoliation of BN layers is obtained in the rapid depressurization process by overcoming the van der Waals forces. Our results indicate that the bulk boron nitride has been successfully exfoliated into thin nanosheets with an average 6 layers. It is found that the produced BNNS is well-dispersed in isopropyl alcohol (IPA) with a higher extinction coefficient compared with the bulk BN. Moreover, the BNNS/epoxy composite used as thermal interface materials has been prepared. The introduction of BNNS results in a 313% enhancement in thermal conductivity. Our results demonstrate that BNNS produced by supercritical CO 2 exfoliation show great potential applications for heat dissipation of high efficiency electronics.

Structural stability and electronic structure of transition metal compound: HfN

NASA Astrophysics Data System (ADS)

Sarwan, Madhu; Shukoor, V. Abdul; Singh, Sadhna

2018-05-01

The structural stability of transition metal nitride (HfN) has been investigated using density functional theory (DFT) with the help of Quantum-espresso codes. Our calculations confirm that the hafnium nitride (HfN) is stable in zinc-blende (B3) and rock-salt (B1) type structure. We have also reported the structural and electronic properties of HfN compound. These structural properties have been compared with experimental and theoretical data available on this compound.

Synthesis of metal free ultrathin graphitic carbon nitride sheet for photocatalytic dye degradation of Rhodamine B under visible light irradiation

NASA Astrophysics Data System (ADS)

Rahman, Shakeelur; Momin, Bilal; Higgins M., W.; Annapure, Uday S.; Jha, Neetu

2018-04-01

In recent times, low cost and metal free photocatalyts driven under visible light have attracted a lot of interest. One such photo catalyst researched extensively is bulk graphitic carbon nitride sheets. But the low surface area and weak mobility of photo generated electrons limits its photocatalytic performance in the visible light spectrum. Here we present the facile synthesis of ultrathin graphitic carbon nitride using a cost effective melamine precursor and its application in highly efficient photocatalytic dye degradation of Rhodamine B molecules. Compared to bulk graphitic carbon nitride, the synthesized ultrathin graphitic carbon nitride shows an increase in surface area, a a decrease in optical band gap and effective photogenerated charge separation which facilitates the harvest of visible light irradiation. Due to these optimal properties of ultrathin graphitic carbon nitride, it shows excellent photocatalytic activity with photocatalytic degradation of about 95% rhodamine B molecules in 1 hour.

Cubic nitride templates

DOEpatents

Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Mueller, Alexander H; Luo, Hongmei

2013-04-30

A polymer-assisted deposition process for deposition of epitaxial cubic metal nitride films and the like is presented. The process includes solutions of one or more metal precursor and soluble polymers having binding properties for the one or more metal precursor. After a coating operation, the resultant coating is heated at high temperatures under a suitable atmosphere to yield metal nitride films and the like. Such films can be used as templates for the development of high quality cubic GaN based electronic devices.

The Atmospheric Scanning Electron Microscope with open sample space observes dynamic phenomena in liquid or gas.

PubMed

Suga, Mitsuo; Nishiyama, Hidetoshi; Konyuba, Yuji; Iwamatsu, Shinnosuke; Watanabe, Yoshiyuki; Yoshiura, Chie; Ueda, Takumi; Sato, Chikara

2011-12-01

Although conventional electron microscopy (EM) requires samples to be in vacuum, most chemical and physical reactions occur in liquid or gas. The Atmospheric Scanning Electron Microscope (ASEM) can observe dynamic phenomena in liquid or gas under atmospheric pressure in real time. An electron-permeable window made of pressure-resistant 100 nm-thick silicon nitride (SiN) film, set into the bottom of the open ASEM sample dish, allows an electron beam to be projected from underneath the sample. A detector positioned below captures backscattered electrons. Using the ASEM, we observed the radiation-induced self-organization process of particles, as well as phenomena accompanying volume change, including evaporation-induced crystallization. Using the electrochemical ASEM dish, we observed tree-like electrochemical depositions on the cathode. In silver nitrate solution, we observed silver depositions near the cathode forming incidental internal voids. The heated ASEM dish allowed observation of patterns of contrast in melting and solidifying solder. Finally, to demonstrate its applicability for monitoring and control of industrial processes, silver paste and solder paste were examined at high throughput. High resolution, imaging speed, flexibility, adaptability, and ease of use facilitate the observation of previously difficult-to-image phenomena, and make the ASEM applicable to various fields. Copyright © 2011 Elsevier B.V. All rights reserved.

Convergent beam electron-diffraction investigation of lattice mismatch and static disorder in GaAs/GaAs1-xNx intercalated GaAs/GaAs1-xNx:H heterostructures

NASA Astrophysics Data System (ADS)

Frabboni, S.; Grillo, V.; Gazzadi, G. C.; Balboni, R.; Trotta, R.; Polimeni, A.; Capizzi, M.; Martelli, F.; Rubini, S.; Guzzinati, G.; Glas, F.

2012-09-01

Hydrogen incorporation in diluted nitride semiconductors dramatically modifies the electronic and structural properties of the crystal through the creation of nitrogen-hydrogen complexes. We report a convergent beam electron-diffraction characterization of diluted nitride semiconductor-heterostructures patterned at a sub-micron scale and selectively exposed to hydrogen. We present a method to determine separately perpendicular mismatch and static disorder in pristine and hydrogenated heterostructures. The roles of chemical composition and strain on static disorder have been separately assessed.

Preparation of boron nitride fiber by organic precursor method

NASA Astrophysics Data System (ADS)

Zhou, Yingying; Sun, Runjun; Zhang, Zhaohuan; Fan, Wei; Zhou, Dan; Sheng, Cuihong

In this paper, boron nitride polymer precursor was made by boric acid, melamine, twelve sodium alkyl sulfate as raw materials and pure water as medium which is heated to 70 °C. Boron nitride precursor polymer was soluble in formic acid solution. The boron nitride precursor can be electrostatically spun at the voltage in 23 kV and the distance between the positive and negative poles is 15 cm. The formed fiber is very uniform. The properties of the precursors were analyzed through electron microscope, infrared spectrum, X-ray and ultraviolet spectrum. The aim of the job is to got the precursor of BN and spun it.

Mesoporous coaxial titanium nitride-vanadium nitride fibers of core-shell structures for high-performance supercapacitors.

PubMed

Zhou, Xinhong; Shang, Chaoqun; Gu, Lin; Dong, Shanmu; Chen, Xiao; Han, Pengxian; Li, Lanfeng; Yao, Jianhua; Liu, Zhihong; Xu, Hongxia; Zhu, Yuwei; Cui, Guanglei

2011-08-01

In this study, titanium nitride-vanadium nitride fibers of core-shell structures were prepared by the coaxial electrospinning, and subsequently annealed in the ammonia for supercapacitor applications. These core-shell (TiN-VN) fibers incorporated mesoporous structure into high electronic conducting transition nitride hybrids, which combined higher specific capacitance of VN and better rate capability of TiN. These hybrids exhibited higher specific capacitance (2 mV s(-1), 247.5 F g(-1)) and better rate capability (50 mV s(-1), 160.8 F g(-1)), which promise a good candidate for high-performance supercapacitors. It was also revealed by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) characterization that the minor capacitance fade originated from the surface oxidation of VN and TiN.

Engineering and Localization of Quantum Emitters in Large Hexagonal Boron Nitride Layers.

PubMed

Choi, Sumin; Tran, Toan Trong; Elbadawi, Christopher; Lobo, Charlene; Wang, Xuewen; Juodkazis, Saulius; Seniutinas, Gediminas; Toth, Milos; Aharonovich, Igor

2016-11-02

Hexagonal boron nitride is a wide-band-gap van der Waals material that has recently emerged as a promising platform for quantum photonics experiments. In this work, we study the formation and localization of narrowband quantum emitters in large flakes (up to tens of micrometers wide) of hexagonal boron nitride. The emitters can be activated in as-grown hexagonal boron nitride by electron irradiation or high-temperature annealing, and the emitter formation probability can be increased by ion implantation or focused laser irradiation of the as-grown material. Interestingly, we show that the emitters are always localized at the edges of the flakes, unlike most luminescent point defects in three-dimensional materials. Our results constitute an important step on the roadmap of deploying hexagonal boron nitride in nanophotonics applications.

Algan/Gan Hemt By Magnetron Sputtering System

NASA Astrophysics Data System (ADS)

Garcia Perez, Roman

In this thesis, the growth of the semiconductor materials AlGaN and GaN is achieved by magnetron sputtering for the fabrication of High Electron Mobility Transistors (HEMTs). The study of the deposited nitrides is conducted by spectroscopy, diffraction, and submicron scale microscope methods. The preparation of the materials is performed using different parameters in terms of power, pressure, temperature, gas, and time. Silicon (Si) and Sapphire (Al2O3) wafers are used as substrates. The chemical composition and surface topography of the samples are analyzed to calculate the materials atomic percentages and to observe the devices surface. The instruments used for the semiconductors characterization are X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscope (AFM). The project focused its attention on the reduction of impurities during the deposition, the controlled thicknesses of the thin-films, the atomic configuration of the alloy AlxGa1-xN, and the uniformity of the surfaces.

Morphological, structural and thermal studies of gallium nitride ferrite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Indrakanti, Rajani; Rao, V. Brahmaji; Kiran, C. Udaya

2016-05-06

We report the synthesis and Characterization of III-V doped Nano ferrite Ga{sub (2x+2)}N Fe{sub 2(49-x)}O{sub 3} for x=1 and x=5 by Sol-Gel method. The Morphological, structural and Thermal characterisation studies are done by using Transmission Electron Microscopy, Energy Dispersive X-ray Analysis, Selected Area Electron Diffraction, Thermo-Gravimetric Analysis and Differential Thermal Analysis. Using the Sci-Finder software we could not trace any reports related to GaNFe{sub 2}O{sub 3} in the literature. It has been observed from our studies that the particles are in the Cylindrical and the Globular structure. The particle diameter values from the Histograms are in good agreement with themore » XRD values that were communicated by us earlier. The SAED and the EDAX studies reveal the confirmation of the composition and also that the synthesized Ferrite exhibits crystalline nature. The TG-DTA results show that the compound indicates constant sample weight.« less

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

PubMed Central

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L.; Banyai, Douglas; Savaikar, Madhusudan A.; Jaszczak, John A.; Yap, Yoke Khin

2016-01-01

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending. PMID:26846587

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

DOE PAGES

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; ...

2016-02-05

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under variousmore » bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). Ultimately, as suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.« less

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under variousmore » bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). Ultimately, as suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.« less

Droplet heteroepitaxy of zinc-blende vs. wurtzite GaN quantum dots

NASA Astrophysics Data System (ADS)

Reese, C.; Jeon, S.; Hill, T.; Jones, C.; Shusterman, S.; Yacoby, Y.; Clarke, R.; Deng, H.; Goldman, Rs

We have developed a GaN droplet heteroepitaxy process based upon plasma-assisted molecular-beam epitaxy. Using various surface treatments and Ga deposition parameters, we have demonstrated polycrystalline, zinc-blende (ZB), and wurtzite (WZ) GaN quantum dots (QDs) on Si(001), r-Al2O3, Si(111), and c-GaN substrates. For the polar substrates (i.e. Si(111) and c-GaN), high-resolution transmission electron microscopy and coherent Bragg rod analysis reveals the formation of coherent WZ GaN QDs with nitridation-temperature-dependent sizes and densities. For the non-polar substrates (i.e. Si(001) and r-Al2O3) , QDs with strong near-band photoluminescence emission are observed and ZB GaN QD growth on Si(001) is demonstrated for the first time.

Microtribological Mechanisms of Tungsten and Aluminum Nitride Films

NASA Astrophysics Data System (ADS)

Zhao, Hongjian; Mu, Chunyan; Ye, Fuxing

2016-04-01

Microtribology experiments were carried out on the W1- x Al x N films, deposited by radio frequency magnetron reactive sputtering on 304 stainless steel substrates and Si(100). Film wear mechanisms were investigated from the evolution of the friction coefficient and scanning electron microscopy observations. The results show that the WAlN films consist of a mixture of face-centered cubic W(Al)N and hexagonal wurtzite structure AlN phases and the preferred orientation changes from (111) to (200). The film damage after sliding test is mainly attributed to the composition and microstructure of the films. The amount of debris generated by friction is linked to the crack resistance. The better tribological properties for W1- x Al x N films ( x < 0.4) are mainly determined by the higher toughness.

Large scale 2D/3D hybrids based on gallium nitride and transition metal dichalcogenides.

PubMed

Zhang, Kehao; Jariwala, Bhakti; Li, Jun; Briggs, Natalie C; Wang, Baoming; Ruzmetov, Dmitry; Burke, Robert A; Lerach, Jordan O; Ivanov, Tony G; Haque, Md; Feenstra, Randall M; Robinson, Joshua A

2017-12-21

Two and three-dimensional (2D/3D) hybrid materials have the potential to advance communication and sensing technologies by enabling new or improved device functionality. To date, most 2D/3D hybrid devices utilize mechanical exfoliation or post-synthesis transfer, which can be fundamentally different from directly synthesized layers that are compatible with large scale industrial needs. Therefore, understanding the process/property relationship of synthetic heterostructures is priority for industrially relevant material architectures. Here we demonstrate the scalable synthesis of molybdenum disulfide (MoS 2 ) and tungsten diselenide (WSe 2 ) via metal organic chemical vapor deposition (MOCVD) on gallium nitride (GaN), and elucidate the structure, chemistry, and vertical transport properties of the 2D/3D hybrid. We find that the 2D layer thickness and transition metal dichalcogenide (TMD) choice plays an important role in the transport properties of the hybrid structure, where monolayer TMDs exhibit direct tunneling through the layer, while transport in few layer TMDs on GaN is dominated by p-n diode behavior and varies with the 2D/3D hybrid structure. Kelvin probe force microscopy (KPFM), low energy electron microscopy (LEEM) and X-ray photoelectron spectroscopy (XPS) reveal a strong intrinsic dipole and charge transfer between n-MoS 2 and p-GaN, leading to a degraded interface and high p-type leakage current. Finally, we demonstrate integration of heterogeneous 2D layer stacks of MoS 2 /WSe 2 on GaN with atomically sharp interface. Monolayer MoS 2 /WSe 2 /n-GaN stacks lead to near Ohmic transport due to the tunneling and non-degenerated doping, while few layer stacking is Schottky barrier dominated.

Effect of applied bias voltage on corrosion-resistance for TiC 1- xN x and Ti 1- xNb xC 1- yN y coatings

NASA Astrophysics Data System (ADS)

Caicedo, J. C.; Amaya, C.; Yate, L.; Aperador, W.; Zambrano, G.; Gómez, M. E.; Alvarado-Rivera, J.; Muñoz-Saldaña, J.; Prieto, P.

2010-02-01

Corrosion-resistance behavior of titanium carbon nitride (Ti-C-N) and titanium niobium carbon nitride (Ti-Nb-C-N) coatings deposited onto Si(1 0 0) and AISI 4140 steel substrates via r.f. magnetron sputtering process was analyzed. The coatings in contact with a solution of sodium chloride at 3.5% were studied by Tafel polarization curves and impedance spectroscopy methods (EIS). Variations of the bias voltage were carried out for each series of deposition to observe the influence of this parameter upon the electrochemical properties of the coatings. The introduction of Nb in the ternary Ti-C-N film was evaluated via X-ray diffraction (XRD) analysis. The structure was characterized by using Raman spectroscopy to identify ternary and quaternary compounds. Surface corrosion processes were characterized using optical microscopy and scanning electron microscopy (SEM). XRD results show conformation of the quaternary phase, change in the strain of the film, and lattice parameter as the effect of the Nb inclusion. The main Raman bands were assigned to interstitial phases and "impurities" of the coatings. Changes in Raman intensities were attributed to the incorporation of niobium in the Ti-C-N structure and possibly to resonance enhancement. Finally, the corrosion data obtained for Ti-C-N were compared with the results of corrosion tests of Ti-Nb-C-N coating. The results obtained showed that the incorporation of niobium to Ti-C-N coatings led to an increase in the corrosion-resistance. On another hand, an increase in the bias voltage led to a decrease in the corrosion-resistance for both Ti-C-N and Ti-Nb-C-N coatings.

Silicon technology-based micro-systems for atomic force microscopy/photon scanning tunnelling microscopy.

PubMed

Gall-Borrut, P; Belier, B; Falgayrettes, P; Castagne, M; Bergaud, C; Temple-Boyer, P

2001-04-01

We developed silicon nitride cantilevers integrating a probe tip and a wave guide that is prolonged on the silicon holder with one or two guides. A micro-system is bonded to a photodetector. The resulting hybrid system enables us to obtain simultaneously topographic and optical near-field images. Examples of images obtained on a longitudinal cross-section of an optical fibre are shown.

The Effects of Thermal Cycling on Gallium Nitride and Silicon Carbide Semiconductor Devices for Aerospace Use

NASA Technical Reports Server (NTRS)

Patterson, Richard L.; Hammoud, Ahmad

2012-01-01

Electronics designed for use in NASA space missions are required to work efficiently and reliably under harsh environment conditions. These Include radiation, extreme temperatures, thermal cycling, to name a few. Preliminary data obtained on new Gallium Nitride and Silicon Carbide power devices under exposure to radiation followed by long term thermal cycling are presented. This work was done in collaboration with GSFC and JPL in support of the NASA Electronic Parts and Packaging (NEPP) Program

Process for growing epitaxial gallium nitride and composite wafers

DOEpatents

Weber, Eicke R.; Subramanya, Sudhir G.; Kim, Yihwan; Kruger, Joachim

2003-05-13

A novel growth procedure to grow epitaxial Group III metal nitride thin films on lattice-mismatched substrates is proposed. Demonstrated are the quality improvement of epitaxial GaN layers using a pure metallic Ga buffer layer on c-plane sapphire substrate. X-ray rocking curve results indicate that the layers had excellent structural properties. The electron Hall mobility increases to an outstandingly high value of .mu.>400 cm.sup.2 /Vs for an electron background concentration of 4.times.10.sup.17 cm.sup.-3.

Surface passivation of p-type Ge substrate with high-quality GeNx layer formed by electron-cyclotron-resonance plasma nitridation at low temperature

NASA Astrophysics Data System (ADS)

Fukuda, Yukio; Okamoto, Hiroshi; Iwasaki, Takuro; Otani, Yohei; Ono, Toshiro

2011-09-01

We have investigated the effects of the formation temperature and postmetallization annealing (PMA) on the interface properties of GeNx/p-Ge fabricated by the plasma nitridation of Ge substrates using an electron-cyclotron-resonance-generated nitrogen plasma. The nitridation temperature is found to be a critical parameter in improving the finally obtained GeNx/Ge interface properties. The GeNx/Ge formed at room temperature and treated by PMA at 400 °C exhibits the best interface properties with an interface trap density of 1 × 1011 cm-2 eV-1. The GeNx/Ge interface is unpinned and the Fermi level at the Ge surface can move from the valence band edge to the conduction band edge.

Growth of Gallium Nitride Nanowires: A Study Using In Situ Transmission Electron Microscopy

NASA Astrophysics Data System (ADS)

Diaz Rivas, Rosa Estela

Owing to their special characteristics, group III-Nitride semiconductors have attracted special attention for their application in a wide range of optoelectronic devices. Of particular interest are their direct and wide band gaps that span from ultraviolet to the infrared wavelengths. In addition, their stronger bonds relative to the other compound semiconductors makes them thermally more stable, which provides devices with longer life time. However, the lattice mismatch between these semiconductors and their substrates cause the as-grown films to have high dislocation densities, reducing the life time of devices that contain these materials. One possible solution for this problem is to substitute single crystal semiconductor nanowires for epitaxial films. Due to their dimensionality, semiconductor nanowires typically have stress-free surfaces and better physical properties. In order to employ semiconductor nanowires as building blocks for nanoscale devices, a precise control of the nanowires' crystallinity, morphology, and chemistry is necessary. This control can be achieved by first developing a deeper understanding of the processes involved in the synthesis of nanowires, and then by determining the effects of temperature and pressure on their growth. This dissertation focuses on understanding of the growth processes involved in the formation of GaN nanowires. Nucleation and growth events were observed in situ and controlled in real-time using an environmental transmission electron microscope. These observations provide a satisfactory elucidation of the underlying growth mechanism during the formation of GaN nanowires. Nucleation of these nanowires appears to follow the vapor-liquid-solid mechanism. However, nanowire growth is found to follow both the vapor-liquid-solid and vapor-solid-solid mechanisms. Direct evidence of the effects of III/V ratio on nanowire growth is also reported, which provides important information for tailoring the synthesis of GaN nanowires. These findings suggest in situ electron microscopy is a powerful tool to understand the growth of GaN nanowires and also that these experimental approach can be extended to study other binary semiconductor compound such as GaP, GaAs, and InP, or even ternary compounds such as InGaN. However, further experimental work is required to fully elucidate the kinetic effects on the growth process. A better control of the growth parameters is also recommended.

Preparation and Characterization of Ni Spines Grown on the Surface of Cubic Boron Nitride Grains by Electroplating Method

PubMed Central

Gui, Yanghai; Zhao, Jianbo; Chen, Jingbo; Jiang, Yuanli

2016-01-01

Cubic boron nitride (cBN) is widely applied in cutting and grinding tools. cBN grains plated by pure Ni and Ni/SiC composite were produced under the same conditions from an additive-free nickel Watts type bath. The processed electroplating products were characterized by the techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermoanalysis (TG-DTA). Due to the presence of SiC particles, there are some additional nodules on the surface of Ni/SiC plated cBN compared with the pure Ni plated cBN. The unique morphology of Ni/SiC plated cBN should attain greater retention force in resin bond. Moreover, the coating weight of cBN grains could be controlled by regulating the plating time. cBN grains with 60% coating weight possess the optimum grinding performance due to their roughest and spiniest surface. In addition, Ni spines plated cBN grains show good thermal stability when temperature is lower than 464 °C. Therefore, the plated cBN grains are more stable and suitable for making resin bond abrasive tools below 225 °C. Finally, the formation mechanism of electroplating products is also discussed. PMID:28773283

Growth of defect-free GaAsSbN axial nanowires via self-catalyzed molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Sharma, Manish; Deshmukh, Prithviraj; Kasanaboina, Pavan; Reynolds, C. Lewis, Jr.; Liu, Yang; Iyer, Shanthi

2017-12-01

Bandgap reduction of 10% by incorporation of a dilute amount of N is reported for the first time, in axial GaAsSb nanowires (NWs) grown on Si (111) via Ga-assisted molecular beam epitaxy. Impact of N incorporation on the surface morphology, NW growth kinetics, and their structural and optical properties were examined. Dilute nitride NWs with Sb composition of 7 at% did not exhibit any noticeable planar defects, as revealed by the absence of satellite twin peaks in the selected-area diffraction pattern and high-resolution transmission electron microscopy imaging. Point defects were also minimal in as-grown dilute nitride NWs, as ascertained from the comparison of low-temperature photoluminescence spectra as well as the shape and shift of Raman modes, with in situ annealed NWs in different ambients. Evidence of enhanced incorporation of N was found in the NWs in situ annealed in N ambient, but with deteriorated optical quality due to simultaneous creation of N-induced defects. The lack of any noticeable defects in the as-grown GaAsSbN NWs demonstrates the advantage of the vapor-liquid-solid mechanism responsible for growth of axial configuration over the vapor-solid growth mechanism for core-shell NWs as well as their thin film counterpart, which commonly exhibit N-induced point defects.

Deuterium permeation behaviors in tungsten implanted with nitrogen

NASA Astrophysics Data System (ADS)

Liang, Chuan-hui; Wang, Dongping; Jin, Wei; Lou, Yuanfu; Wang, Wei; Ye, Xiaoqiu; Chen, Chang-an; Liu, Kezhao; Xu, Haiyan; Wang, Xiaoying; Kleyn, Aart W.

2018-07-01

Surface modification of tungsten due to the cooling species nitrogen seeded in the divertor region, i.e., by nitrogen ion implantation or re-deposition, is considered to affect the permeation behavior of H isotopes. This work focuses on the effect of nitrogen ion implantation into tungsten (W-N) on the deuterium gas-driven permeation behavior. For comparison, both permeation in tungsten implanted with W ion (W-W) and without implantation (pristine W) are studied. These three samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photo-electron spectroscopy (XPS). The SEM results revealed that the W-W sample has various voids on the surface, and the W-N sample has a rough surface with pretty fine microstructures. These are different from the pristine W sample with a smooth and compact surface. The XRD patterns show the disappearance of crystallinity on both W-W and W-N sample surfaces. It indicates that the ion implantation process results in an almost complete conversion from crystalline to amorphous in the sample surfaces. The sputter-depth profiling XPS spectra show that the implanted nitrogen prefers to form a 140 nm thick tungsten nitride layer. In permeation experiments, it was found that the D permeability is temperature dependent. Interestingly, the W-N sample presented a lower D permeability than the W-W sample, but higher than the pristine W sample. Such behavior implies that tungsten nitride acts as a permeation barrier, while defects created by ions implantation can promote permeability. The possible permeation mechanism correlated with sample surface composition and microstructure is consequently discussed in this work.

Towards efficient solar hydrogen production by intercalated carbon nitride photocatalyst.

PubMed

Gao, Honglin; Yan, Shicheng; Wang, Jiajia; Huang, Yu An; Wang, Peng; Li, Zhaosheng; Zou, Zhigang

2013-11-07

The development of efficient photocatalytic material for converting solar energy to hydrogen energy as viable alternatives to fossil-fuel technologies is expected to revolutionize energy shortage and environment issues. However, to date, the low quantum yield for solar hydrogen production over photocatalysts has hindered advances in the practical applications of photocatalysis. Here, we show that a carbon nitride intercalation compound (CNIC) synthesized by a simple molten salt route is an efficient polymer photocatalyst with a high quantum yield. We found that coordinating the alkali metals into the C-N plane of carbon nitride will induce the un-uniform spatial charge distribution. The electrons are confined in the intercalated region while the holes are in the far intercalated region, which promoted efficient separation of photogenerated carriers. The donor-type alkali metal ions coordinating into the nitrogen pots of carbon nitrides increase the free carrier concentration and lead to the formation of novel nonradiative paths. This should favor improved transport of the photogenerated electron and hole and decrease the electron-hole recombination rate. As a result, the CNIC exhibits a quantum yield as high as 21.2% under 420 nm light irradiation for solar hydrogen production. Such high quantum yield opens up new opportunities for using cheap semiconducting polymers as energy transducers.

Group-III Nitride Field Emitters

NASA Technical Reports Server (NTRS)

Bensaoula, Abdelhak; Berishev, Igor

2008-01-01

Field-emission devices (cold cathodes) having low electron affinities can be fabricated through lattice-mismatched epitaxial growth of nitrides of elements from group III of the periodic table. Field emission of electrons from solid surfaces is typically utilized in vacuum microelectronic devices, including some display devices. The present field-emission devices and the method of fabricating them were developed to satisfy needs to reduce the cost of fabricating field emitters, make them compatible with established techniques for deposition of and on silicon, and enable monolithic integration of field emitters with silicon-based driving circuitry. In fabricating a device of this type, one deposits a nitride of one or more group-III elements on a substrate of (111) silicon or other suitable material. One example of a suitable deposition process is chemical vapor deposition in a reactor that contains plasma generated by use of electron cyclotron resonance. Under properly chosen growth conditions, the large mismatch between the crystal lattices of the substrate and the nitride causes strains to accumulate in the growing nitride film, such that the associated stresses cause the film to crack. The cracks lie in planes parallel to the direction of growth, so that the growing nitride film becomes divided into microscopic growing single-crystal columns. The outer ends of the fully-grown columns can serve as field-emission tips. By virtue of their chemical compositions and crystalline structures, the columns have low work functions and high electrical conductivities, both of which are desirable for field emission of electrons. From examination of transmission electron micrographs of a prototype device, the average column width was determined to be about 100 nm and the sharpness of the tips was determined to be characterized by a dimension somewhat less than 100 nm. The areal density of the columns was found to about 5 x 10(exp 9)/sq cm . about 4 to 5 orders of magnitude greater than the areal density of tips in prior field-emission devices. The electric field necessary to turn on the emission current and the current per tip in this device are both lower than in prior field-emission devices, such that it becomes possible to achieve longer operational lifetime. Moreover, notwithstanding the lower current per tip, because of the greater areal density of tips, it becomes possible to achieve greater current density averaged over the cathode area. The thickness of the grown nitride film (equivalently, the length of the columns) could lie between about 0.5 microns and a few microns; in any event, a thickness of about 1 micron is sufficient and costs less than do greater thicknesses. It may be possible to grow nitride emitter columns on glass or other substrate materials that cost less than silicon does. What is important in the choice of substrate material is the difference between the substrate and nitride crystalline structures. Inasmuch as the deposition process is nondestructive, an ability to grow emitter columns on a variety of materials would be advantageous in that it would facilitate the integration of field-emitter structures onto previously processed integrated circuits.

Thermodynamic Routes to Novel Metastable Nitrogen-Rich Nitrides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Wenhao; Holder, Aaron; Orvañanos, Bernardo

Compared to oxides, the nitrides are relatively unexplored, making them a promising chemical space for novel materials discovery. Of particular interest are nitrogen-rich nitrides, which often possess useful semiconducting properties for electronic and optoelectronic applications. However, such nitrogen-rich compounds are generally metastable, and the lack of a guiding theory for their synthesis has limited their exploration. Here, we review the remarkable metastability of observed nitrides, and examine the thermodynamics of how reactive nitrogen precursors can stabilize metastable nitrogen-rich compositions during materials synthesis. We map these thermodynamic strategies onto a predictive computational search, training a data-mined ionic substitution algorithm specifically formore » nitride discovery, which we combine with grand-canonical DFT-SCAN phase stability calculations to compute stabilizing nitrogen chemical potentials. We identify several new nitrogen-rich binary nitrides for experimental investigation, notably the transition metal nitrides Mn3N4, Cr3N4, V3N4, and Nb3N5, the main group nitride SbN, and the pernitrides FeN2, CrN2, and Cu2N2. By formulating rational thermodynamic routes to metastable compounds, we expand the search space for functional technological materials beyond equilibrium phases and compositions.« less

Thermodynamic Routes to Novel Metastable Nitrogen-Rich Nitrides

DOE PAGES

Sun, Wenhao; Holder, Aaron; Orvañanos, Bernardo; ...

2017-07-17

Compared to oxides, the nitrides are relatively unexplored, making them a promising chemical space for novel materials discovery. Of particular interest are nitrogen-rich nitrides, which often possess useful semiconducting properties for electronic and optoelectronic applications. However, such nitrogen-rich compounds are generally metastable, and the lack of a guiding theory for their synthesis has limited their exploration. Here, we review the remarkable metastability of observed nitrides, and examine the thermodynamics of how reactive nitrogen precursors can stabilize metastable nitrogen-rich compositions during materials synthesis. We map these thermodynamic strategies onto a predictive computational search, training a data-mined ionic substitution algorithm specifically formore » nitride discovery, which we combine with grand-canonical DFT-SCAN phase stability calculations to compute stabilizing nitrogen chemical potentials. We identify several new nitrogen-rich binary nitrides for experimental investigation, notably the transition metal nitrides Mn3N4, Cr3N4, V3N4, and Nb3N5, the main group nitride SbN, and the pernitrides FeN2, CrN2, and Cu2N2. By formulating rational thermodynamic routes to metastable compounds, we expand the search space for functional technological materials beyond equilibrium phases and compositions.« less

Enhanced optoelectronic performances of vertically aligned hexagonal boron nitride nanowalls-nanocrystalline diamond heterostructures

NASA Astrophysics Data System (ADS)

Sankaran, Kamatchi Jothiramalingam; Hoang, Duc Quang; Kunuku, Srinivasu; Korneychuk, Svetlana; Turner, Stuart; Pobedinskas, Paulius; Drijkoningen, Sien; van Bael, Marlies K.; D' Haen, Jan; Verbeeck, Johan; Leou, Keh-Chyang; Lin, I.-Nan; Haenen, Ken

2016-07-01

Field 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/μm, a high FEE current density of 1.48 mA/cm2 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/μm with 0.21 mA/cm2 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.

Electron transport in polycyclic aromatic hydrocarbons/boron nitride hybrid structures: density functional theory combined with the nonequilibrium Green's function.

PubMed

Panahi, S F K S; Namiranian, Afshin; Soleimani, Maryam; Jamaati, Maryam

2018-02-07

We investigate the electronic transport properties of two types of junction based on single polyaromatic hydrocarbons (PAHs) and PAHs embedded in boron nitride (h-BN) nanoribbons, using nonequilibrium Green's functions (NEGF) and density functional theory (DFT). In the PAH junctions, a Fano resonance line shape at the Fermi energy in the transport feature can be clearly seen. In hybrid junctions, structural asymmetries enable interactions between the electronic states, leading to observation of interface-based transport. Our findings reveal that the interface of PAH/h-BN strongly affects the transport properties of the structures.

Tribological and structural properties of titanium nitride and titanium aluminum nitride coatings deposited with modulated pulsed power magnetron sputtering

NASA Astrophysics Data System (ADS)

Ward, Logan

The demand for economical high-performance materials has brought attention to the development of advanced coatings. Recent advances in high power magnetron sputtering (HPPMS) have shown to improve tribological properties of coatings. These coatings offer increased wear and oxidation resistance, which may facilitate the use of more economical materials in harsh applications. This study demonstrates the use of novel forms of HPPMS, namely modulated pulsed-power magnetron sputtering (MPPMS) and deep oscillation magnetron sputtering (DOMS), for depositing TiN and Ti1-xAlxN tribological coatings on commonly used alloys, such as Ti-6Al-4V and Inconel 718. Both technologies have been shown to offer unique plasma characteristics in the physical vapor deposition (PVD) process. High power pulses lead to a high degree of ionization compared to traditional direct-current magnetron sputtering (DCMS) and pulsed magnetron sputtering (PMS). Such a high degree of ionization was previously only achievable by cathodic arc deposition (CAD); however, CAD can lead to increased macroparticles that are unfavorable in high friction and corrosive environments. MPPMS, DOMS, and other HPPMS techniques offer unique plasma characteristics and have been shown to produce coatings with refined grain structure, improved density, hardness, adhesion, and wear resistance. Using DOMS and MPPMS, TiN and Ti1-xAlxN coatings were deposited using PMS to compare microstructures and tribological performance. For Ti1-xAlxN, two sputtering target compositions, Ti 0.5Al0.5 and Ti0.3Al0.7, were used to evaluate the effects of MPPMS on the coating's composition and tribological properties. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize microstructure and crystallographic texture. Several tribological properties were evaluated including: wear rate, coefficient of friction, adhesion, and nanohardness. Results show that substrate material can have a significant effect on adhesion and the mechanical response between the coating and substrate. Depending on deposition parameters and the selected material MPPMS and DOMS are promising alternatives to DCMS, PMS, and CAD.

Sustainable carbothermal reduction and nitridation of Malaysian ilmenite by polyethylene terephthalate and coal

NASA Astrophysics Data System (ADS)

Ahmadi, Eltefat; Hamid, Sheikh Abdul Rezan Sheikh Abdul; Hussin, Hashim; Baharun, Norlia; Ariffin, Kamar Shah; Ramakrishnan, Sivakumar; Fauzi, M. N. Ahmad; Ismail, Hanafi

2017-07-01

In this paper, the carbothermal reduction and nitridation (CTRN) of Malaysian ilmenite has been studied as a part of crucial steps involved in reduction and subsequent chlorination processes for synthesizing titanium tetrachloride (TiCl4) from nitrided Malaysian ilmenite concentrates. In CTRN, waste plastics such as polyethylene terephthalate (PET) could be utilized as an alternative source of carbon reductant. In this study, titanium oxycarbonitride (TiOxCyNz) separated from iron (Fe) phase was synthesized by non-isothermal CTRN of Malaysian ilmenite under H2-N2 atmosphere by utilizing a mixture of Sarawak Mukah-Balingan coal and PET as reducing agents in a horizontal tube furnace. Experiments have been carried out in the temperature range of 1150-1250°C for 3 hours with various ratios of PET to coal (25 wt.% PET, 50 wt.% PET, and 75 wt.% PET). X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) methods of analysis were conducted to assess the microstructures and chemical compositions of the unreduced and reduced samples. The results indicated that utilizing PET had a significant effect on iron separation from titanium oxycarbonitride (TiO0.02C0.13N0.85) at 1250°C with a mixture of 75 wt.% PET. Furthermore, XRD and SEM studies demonstrated that with increasing PET weight ratio in the mixtures, the rate of conversion increased and a low-carbon TiOxCyNz with minimal intermediate titanium sub-oxides was synthesized. The method of applying PET as potential reductant for CTRN of ilmenite has beneficial side effects in sustainable recycling of waste PET.

Electronic transport in graphene-based heterostructures

NASA Astrophysics Data System (ADS)

Tan, J. Y.; Avsar, A.; Balakrishnan, J.; Koon, G. K. W.; Taychatanapat, T.; O'Farrell, E. C. T.; Watanabe, K.; Taniguchi, T.; Eda, G.; Castro Neto, A. H.; Özyilmaz, B.

2014-05-01

While boron nitride (BN) substrates have been utilized to achieve high electronic mobilities in graphene field effect transistors, it is unclear how other layered two dimensional (2D) crystals influence the electronic performance of graphene. In this Letter, we study the surface morphology of 2D BN, gallium selenide (GaSe), and transition metal dichalcogenides (tungsten disulfide (WS2) and molybdenum disulfide (MoS2)) crystals and their influence on graphene's electronic quality. Atomic force microscopy analysis shows that these crystals have improved surface roughness (root mean square value of only ˜0.1 nm) compared to conventional SiO2 substrate. While our results confirm that graphene devices exhibit very high electronic mobility (μ) on BN substrates, graphene devices on WS2 substrates (G/WS2) are equally promising for high quality electronic transport (μ ˜ 38 000 cm2/V s at room temperature), followed by G/MoS2 (μ ˜ 10 000 cm2/V s) and G/GaSe (μ ˜ 2200 cm2/V s). However, we observe a significant asymmetry in electron and hole conduction in G/WS2 and G/MoS2 heterostructures, most likely due to the presence of sulphur vacancies in the substrate crystals. GaSe crystals are observed to degrade over time even under ambient conditions, leading to a large hysteresis in graphene transport making it a less suitable substrate.

Is hexagonal boron nitride always good as a substrate for carbon nanotube-based devices?

PubMed

Kang, Seoung-Hun; Kim, Gunn; Kwon, Young-Kyun

2015-02-21

Hexagonal boron nitride sheets have been noted especially for their enhanced properties as substrates for sp(2) carbon-based nanodevices. To evaluate whether such enhanced properties would be retained under various realistic conditions, we investigate the structural and electronic properties of semiconducting carbon nanotubes on perfect and defective hexagonal boron nitride sheets under an external electric field as well as with a metal impurity, using density functional theory. We verify that the use of a perfect hexagonal boron nitride sheet as a substrate indeed improves the device performances of carbon nanotubes, compared with the use of conventional substrates such as SiO2. We further show that even the hexagonal boron nitride with some defects can show better performance as a substrate. Our calculations, on the other hand, also suggest that some defective boron nitride layers with a monovacancy and a nickel impurity could bring about poor device behavior since the imperfections impair electrical conductivity due to residual scattering under an applied electric field.

Oriented graphene nanoribbons embedded in hexagonal boron nitride trenches

PubMed Central

Chen, Lingxiu; He, Li; Wang, Hui Shan; Wang, Haomin; Tang, Shujie; Cong, Chunxiao; Xie, Hong; Li, Lei; Xia, Hui; Li, Tianxin; Wu, Tianru; Zhang, Daoli; Deng, Lianwen; Yu, Ting; Xie, Xiaoming; Jiang, Mianheng

2017-01-01

Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the potential to be used in high-performance graphene-based semiconductor electronics. However, controlled growth of GNRs on dielectric substrates remains a challenge. Here, we report the successful growth of GNRs directly on hexagonal boron nitride substrates with smooth edges and controllable widths using chemical vapour deposition. The approach is based on a type of template growth that allows for the in-plane epitaxy of mono-layered GNRs in nano-trenches on hexagonal boron nitride with edges following a zigzag direction. The embedded GNR channels show excellent electronic properties, even at room temperature. Such in-plane hetero-integration of GNRs, which is compatible with integrated circuit processing, creates a gapped channel with a width of a few benzene rings, enabling the development of digital integrated circuitry based on GNRs. PMID:28276532

Charge retention in scaled SONOS nonvolatile semiconductor memory devices—Modeling and characterization

NASA Astrophysics Data System (ADS)

Hu, Yin; White, Marvin H.

1993-10-01

A new analytical model is developed to investigate the influence of the charge loss processes in the retention mode of the SONOS NVSM device. The model considers charge loss by the following processes: (1) electron back-tunneling from the nitride traps to the Si conduction band, (2) electron back-tunneling from the nitride traps to the Si/SiO 2 interface traps and (3) hole injection from the Si valence band to the nitride traps. An amphoteric trap charge distribution is used in this model. The new charge retention model predicts that process (1) determines the short term retention, while processes (2) and (3) determine the long term retention. Good agreement has been reached between the results of analytical calculations and the experimental retention data on both surface channel and buried channel SONOS devices.

Interface Engineering of Monolayer MoS2/GaN Hybrid Heterostructure: Modified Band Alignment for Photocatalytic Water Splitting Application by Nitridation Treatment.

PubMed

Zhang, Zhaofu; Qian, Qingkai; Li, Baikui; Chen, Kevin J

2018-05-23

Interface engineering is a key strategy to deal with the two-dimensional (2D)/three-dimensional (3D) hybrid heterostructure, since the properties of this atomic-layer-thick 2D material can easily be impacted by the substrate environment. In this work, the structural, electronic, and optical properties of the 2D/3D heterostructure of monolayer MoS 2 on wurtzite GaN surface without and with nitridation interfacial layer are systematically investigated by first-principles calculation and experimental analysis. The nitridation interfacial layer can be introduced into the 2D/3D heterostructure by remote N 2 plasma treatment to GaN sample surface prior to stacking monolayer MoS 2 on top. The calculation results reveal that the 2D/3D integrated heterostructure is energetically favorable with a negative formation energy. Both interfaces demonstrate indirect band gap, which is a benefit for longer lifetime of the photoexcited carriers. Meanwhile, the conduction band edge and valence band edge of the MoS 2 side increases after nitridation treatment. The modification to band alignment is then verified by X-ray photoelectron spectroscopy measurement on MoS 2 /GaN heterostructures constructed by a modified wet-transfer technique, which indicates that the MoS 2 /GaN heterostructure without nitridation shows a type-II alignment with a conduction band offset (CBO) of only 0.07 eV. However, by the deployment of interface nitridation, the band edges of MoS 2 move upward for ∼0.5 eV as a result of the nitridized substrate property. The significantly increased CBO could lead to better electron accumulation capability at the GaN side. The nitridized 2D/3D heterostructure with effective interface treatment exhibits a clean band gap and substantial optical absorption ability and could be potentially used as practical photocatalyst for hydrogen generation by water splitting using solar energy.

The Influence of Hot-Rolled Temperature on Plasma Nitriding Behavior of Iron-Based Alloys

NASA Astrophysics Data System (ADS)

El-Hossary, F. M.; Khalil, S. M.; Lotfy, Kh.; Kassem, M. A.

2009-07-01

Experiments were performed with an aim of studying the effect of hot-rolled temperature (600 and 900°C) on radio frequency (rf) plasma nitriding of Fe93Ni4Zr3 alloy. Nitriding was carried out for 10 min in a nitrogen atmosphere at a base pressure of 10-2 mbarr. Different continuous plasma processing powers of 300-550 W in steps 50 W or less were applied. Nitrided hot-rolled specimens were characterized by optical microscopy (OM), X-ray diffraction (XRD) and microhardness measurements. The results reveal that the surface of hot-rolled rf plasma nitrided specimens at 600°C is characterized with a fine microstructure as a result of the high nitrogen solubility and diffusivity. Moreover, the hot-rolled treated samples at 600°C exhibit higher microhardness value than the associated values of hot-rolled treated samples at 900°C. The enhancement of microhardness is due to precipitation and predominance of new phases ( γ and ɛ phases). Mainly, this conclusion has been attributed to the high defect densities and small grain sizes of the samples hot-rolled at 600°C. Generally, the refinement of grain size plays a dramatic role in improvement of mechanical properties of tested samples.

Effects of 200 keV Ar-ions irradiation on the structural and optical properties of reactively sputtered CrN films

NASA Astrophysics Data System (ADS)

Novaković, M.; Popović, M.; Zhang, K.; Rakočević, Z.; Bibić, N.

2016-12-01

Modification in structural and optical properties of chromium-nitride (CrN) films induced by argon ion irradiation and thermal annealings were investigated using various experimental techniques. CrN films deposited by d. c. reactive sputtering on Si substrate were implanted with 200 keV argon ions, at fluences of 5-20 × 1015 ions/cm2. As-implanted samples were then annealed in vacuum, for 2 h at 700 °C. Rutherford backscattering spectrometry, X-ray diffraction, cross-sectional (high-resolution) transmission electron microscopy and spectroscopic ellipsometry (SE) measurements were carried out in order to study structural and optical properties of the layers. After irradiation with 200 keV Ar ions a damaged surface layer of nanocrystalline structure was generated, which extended beyond the implantation profile, but left an undamaged bottom zone. Partial loss of columnar structure observed in implanted samples was recovered after annealing at 700 °C and CrN started to decompose to Cr2N. This layer geometry determined from transmission electron microscopy was inferred in the analysis of SE data using the combined Drude and Tauc-Lorentz model, and the variation of the optical bandgap was deduced. The results are discussed on the basis of the changes induced in the microstructure. It was found that the optical properties of the layers are strongly dependent on the defects' concentration of CrN.

Bone Response to Surface-Modified Titanium Implants: Studies on the Early Tissue Response to Implants with Different Surface Characteristics

PubMed Central

Larsson Wexell, C.; Thomsen, P.; Aronsson, B.-O.; Tengvall, P.; Rodahl, M.; Lausmaa, J.; Kasemo, B.; Ericson, L. E.

2013-01-01

In a series of experimental studies, the bone formation around systematically modified titanium implants is analyzed. In the present study, three different surface modifications were prepared and evaluated. Glow-discharge cleaning and oxidizing resulted in a highly stoichiometric TiO2 surface, while a glow-discharge treatment in nitrogen gas resulted in implants with essentially a surface of titanium nitride, covered with a very thin titanium oxide. Finally, hydrogen peroxide treatment of implants resulted in an almost stoichiometric TiO2, rich in hydroxyl groups on the surface. Machined commercially pure titanium implants served as controls. Scanning Auger Electron Spectroscopy, Scanning Electron Microscopy, and Atomic Force Microscopy revealed no significant differences in oxide thickness or surface roughness parameters, but differences in the surface chemical composition and apparent topography were observed. After surface preparation, the implants were inserted in cortical bone of rabbits and evaluated after 1, 3, and 6 weeks. Light microscopic evaluation of the tissue response showed that all implants were in contact with bone and had a large proportion of newly formed bone within the threads after 6 weeks. There were no morphological differences between the four groups. Our study shows that a high degree of bone contact and bone formation can be achieved with titanium implants of different surface composition and topography. PMID:24174936

Indium droplet formation in InGaN thin films with single and double heterojunctions prepared by MOCVD

PubMed Central

2014-01-01

Indium gallium nitride (InGaN) samples with single heterojunction (SH) and double heterojunction (DH) were prepared using metal-organic chemical vapor deposition. SH has a layer of InGaN thin film (thicknesses, 25, 50, 100, and 200 nm) grown on an uGaN film (thickness, 2 μm). The DH samples are distinguished by DH uGaN film (thickness, 120 nm) grown on the InGaN layer. Reciprocal space mapping measurements reveal that the DH samples are fully strained with different thicknesses, whereas the strain in the SH samples are significantly relaxed with the increasing thickness of the InGaN film. Scanning electron microscopy results show that the surface roughness of the sample increases when the sample is relaxed. High-resolution transmission electron microscopy images of the structure of indium droplets in the DH sample indicate that the thickness of the InGaN layer decreases with the density of indium droplets. The formation of these droplets is attributed to the insufficient kinetic energy of indium atom to react with the elements of group V, resulting to aggregation. The gallium atoms in the GaN thin film will not be uniformly replaced by indium atoms; the InGaN thin film has an uneven distribution of indium atoms and the quality of the epitaxial layer is degraded. PMID:25024692

Synthesis of GaN:ZnO solid solution by solution combustion method and characterization for photocatalytic application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menon, Sumithra Sivadas; Anitha, R.; Baskar, K.

2016-05-23

GaN-ZnO solid solution has emerged as a successful and reproducible photocatalyst for overall water splitting by one-step photoexcitation, with a bandgap in visible region. When the solid solution is formed, some of the Zn and O ions are replaced by Ga and N ions respectively and there is a narrowing of bandgap which is hypothesized as due to Zn3d-N2p repulsion. The traditional method of synthesis of GaN-ZnO solid solution is by nitridation of the starting oxides under constant ammonia flow. Here we report a solution combustion technique for the synthesis of the solid solution at a temperature about 500 °more » C in a muffle furnace with metal nitrates as precursors and urea as the fuel. The as prepared samples showed change in color with the increased concentration of ZnO in the solution. The structural, microstructural, morphological and optical properties of the samples were realized by Powder X ray diffraction, Scanning electron microscopy, Energy dispersive X ray analysis, Transmission electron microscopy and Photoluminescence. Finally the hydrogen production efficiency of the GaN-ZnO nanopowders by water splitting was found, using methanol as a scavenger. The apparent quantum yield (AQY) of 0.048% is obtained for GaN-ZnO solid solution.« less

Synergic Effect between Adsorption and Photocatalysis of Metal-Free g-C3N4 Derived from Different Precursors

PubMed Central

Xu, Huan-Yan; Wu, Li-Cheng; Zhao, Hang; Jin, Li-Guo; Qi, Shu-Yan

2015-01-01

Graphitic carbon nitride (g-C3N4) used in this work was obtained by heating dicyandiamide and melamine, respectively, at different temperatures. The differences of g-C3N4 derived from different precursors in phase composition, functional group, surface morphology, microstructure, surface property, band gap and specific surface area were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-visible diffuse reflection spectroscopy and BET surface area analyzer, respectively. The photocatalytic discoloration of an active cationic dye, Methylene Blue (MB) under visible-light irradiation indicated that g-C3N4 derived from melamine at 500°C (CN-M500) had higher adsorption capacity and better photocatalytic activity than that from dicyandiamide at 500°C (CN-D500), which was attributed to the larger surface area of CN-M500. MB discoloration ratio over CN-M500 was affected by initial MB concentration and photocatalyst dosage. After 120 min reaction time, the blue color of MB solution disappeared completely. Subsequently, based on the measurement of the surface Zeta potentials of CN-M500 at different pHs, an active anionic dye, Methyl Orange (MO) was selected as the contrastive target pollutant with MB to reveal the synergic effect between adsorption and photocatalysis. Finally, the photocatalytic mechanism was discussed. PMID:26565712

Effects of Radiation and Long-Term Thermal Cycling on EPC 1001 Gallium Nitride Transistors

NASA Technical Reports Server (NTRS)

Patterson, Richard L.; Scheick, Leif; Lauenstein, Jean-Marie; Casey, Megan; Hammoud, Ahmad

2012-01-01

Electronics designed for use in NASA space missions are required to work efficiently and reliably under harsh environment conditions. These include radiation, extreme temperatures, and thermal cycling, to name a few. Data obtained on long-term thermal cycling of new un-irradiated and irradiated samples of EPC1001 gallium nitride enhancement-mode transistors are presented. This work was done by a collaborative effort including GRC, GSFC, and support the NASA www.nasa.gov 1 JPL in of Electronic Parts and Packaging (NEPP) Program

P-type gallium nitride

DOEpatents

Rubin, M.; Newman, N.; Fu, T.; Ross, J.; Chan, J.

1997-08-12

Several methods have been found to make p-type gallium nitride. P-type gallium nitride has long been sought for electronic devices. N-type gallium nitride is readily available. Discovery of p-type gallium nitride and the methods for making it will enable its use in ultraviolet and blue light-emitting diodes and lasers. pGaN will further enable blue photocathode elements to be made. Molecular beam epitaxy on substrates held at the proper temperatures, assisted by a nitrogen beam of the proper energy produced several types of p-type GaN with hole concentrations of about 5{times}10{sup 11} /cm{sup 3} and hole mobilities of about 500 cm{sup 2} /V-sec, measured at 250 K. P-type GaN can be formed of unintentionally-doped material or can be doped with magnesium by diffusion, ion implantation, or co-evaporation. When applicable, the nitrogen can be substituted with other group III elements such as Al. 9 figs.

P-type gallium nitride

DOEpatents

Rubin, Michael; Newman, Nathan; Fu, Tracy; Ross, Jennifer; Chan, James

1997-01-01

Several methods have been found to make p-type gallium nitride. P-type gallium nitride has long been sought for electronic devices. N-type gallium nitride is readily available. Discovery of p-type gallium nitride and the methods for making it will enable its use in ultraviolet and blue light-emitting diodes and lasers. pGaN will further enable blue photocathode elements to be made. Molecular beam epitaxy on substrates held at the proper temperatures, assisted by a nitrogen beam of the proper energy produced several types of p-type GaN with hole concentrations of about 5.times.10.sup.11 /cm.sup.3 and hole mobilities of about 500 cm.sup.2 /V-sec, measured at 250.degree. K. P-type GaN can be formed of unintentionally-doped material or can be doped with magnesium by diffusion, ion implantation, or co-evaporation. When applicable, the nitrogen can be substituted with other group III elements such as Al.

Transition-Metal Nitride Core@Noble-Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

DOE PAGES

Garg, Aaron; Milina, Maria; Ball, Madelyn; ...

2017-05-25

Core–shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. In conclusion, the ability to control shell coveragemore » and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.« less

Plasmonic spectral tunability of conductive ternary nitrides

NASA Astrophysics Data System (ADS)

Kassavetis, S.; Bellas, D. V.; Abadias, G.; Lidorikis, E.; Patsalas, P.

2016-06-01

Conductive binary transition metal nitrides, such as TiN and ZrN, have emerged as a category of promising alternative plasmonic materials. In this work, we show that ternary transition metal nitrides such as TixTa1-xN, TixZr1-xN, TixAl1-xN, and ZrxTa1-xN share the important plasmonic features with their binary counterparts, while having the additional asset of the exceptional spectral tunability in the entire visible (400-700 nm) and UVA (315-400 nm) spectral ranges depending on their net valence electrons. In particular, we demonstrate that such ternary nitrides can exhibit maximum field enhancement factors comparable with gold in the aforementioned broadband range. We also critically evaluate the structural features that affect the quality factor of the plasmon resonance and we provide rules of thumb for the selection and growth of materials for nitride plasmonics.

Boron containing multilayer coatings and method of fabrication

DOEpatents

Makowiecki, D.M.; Jankowski, A.F.

1997-09-23

Hard coatings are fabricated from multilayer boron/boron carbide, boron carbide/cubic boron nitride, and boron/boron nitride/boron carbide, and the fabrication thereof involves magnetron sputtering in a selected atmosphere. These hard coatings may be applied to tools and engine and other parts, as well to reduce wear on tribological surfaces and electronic devices. These boron coatings contain no morphological growth features. For example, the boron and boron carbide used in forming the multilayers are formed in an inert (e.g. argon) atmosphere, while the cubic boron nitride is formed in a reactive (e.g. nitrogen) atmosphere. The multilayer boron/boron carbide, and boron carbide/cubic boron nitride is produced by depositing alternate layers of boron, cubic boron nitride or boron carbide, with the alternate layers having a thickness of 1 nanometer to 1 micrometer, and at least the interfaces of the layers may be of a discrete or a blended or graded composition. 6 figs.

Boron containing multilayer coatings and method of fabrication

DOEpatents

Makowiecki, Daniel M.; Jankowski, Alan F.

1997-01-01

Hard coatings are fabricated from multilayer boron/boron carbide, boron carbide/cubic boron nitride, and boron/boron nitride/boron carbide, and the fabrication thereof involves magnetron sputtering in a selected atmosphere. These hard coatings may be applied to tools and engine and other parts, as well to reduce wear on tribological surfaces and electronic devices. These boron coatings contain no morphological growth features. For example, the boron and boron carbide used in forming the multilayers are formed in an inert (e.g. argon) atmosphere, while the cubic boron nitride is formed in a reactive (e.g. nitrogen) atmosphere. The multilayer boron/boron carbide, and boron carbide/cubic boron nitride is produced by depositing alternate layers of boron, cubic boron nitride or boron carbide, with the alternate layers having a thickness of 1 nanometer to 1 micrometer, and at least the interfaces of the layers may be of a discrete or a blended or graded composition.

Transition-Metal Nitride Core@Noble-Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garg, Aaron; Milina, Maria; Ball, Madelyn

Core–shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. In conclusion, the ability to control shell coveragemore » and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.« less

Surface wet-ability modification of thin PECVD silicon nitride layers by 40 keV argon ion treatments

NASA Astrophysics Data System (ADS)

Caridi, F.; Picciotto, A.; Vanzetti, L.; Iacob, E.; Scolaro, C.

2015-10-01

Measurements of wet-ability of liquid drops have been performed on a 30 nm silicon nitride (Si3N4) film deposited by a PECVD reactor on a silicon wafer and implanted by 40 keV argon ions at different doses. Surface treatments by using Ar ion beams have been employed to modify the wet-ability. The chemical composition of the first Si3N4 monolayer was investigated by means of X-ray Photoelectron Spectroscopy (XPS). The surface morphology was tested by Atomic Force Microscopy (AFM). Results put in evidence the best implantation conditions for silicon nitride to increase or to reduce the wet-ability of the biological liquid. This permits to improve the biocompatibility and functionality of Si3N4. In particular experimental results show that argon ion bombardment increases the contact angle, enhances the oxygen content and increases the surface roughness.

Tungsten nitride coatings obtained by HiPIMS as plasma facing materials for fusion applications

NASA Astrophysics Data System (ADS)

Tiron, Vasile; Velicu, Ioana-Laura; Porosnicu, Corneliu; Burducea, Ion; Dinca, Paul; Malinský, Petr

2017-09-01

In this work, tungsten nitride coatings with nitrogen content in the range of 19-50 at% were prepared by reactive multi-pulse high power impulse magnetron sputtering as a function of the argon and nitrogen mixture and further exposed to a deuterium plasma jet. The elemental composition, morphological properties and physical structure of the samples were investigated by Rutherford backscattering spectrometry, atomic force microscopy and X-ray diffraction. Deuterium implantation was performed using a deuterium plasma jet and its retention in nitrogen containing tungsten films was investigated using thermal desorption spectrometry. Deuterium retention and release behaviour strongly depend on the nitrogen content in the coatings and the films microstructure. All nitride coatings have a polycrystalline structure and retain a lower deuterium level than the pure tungsten sample. Nitrogen content in the films acts as a diffusion barrier for deuterium and leads to a higher desorption temperature, therefore to a higher binding energy.

EDITORIAL: Micro-pixellated LEDs for science and instrumentation

NASA Astrophysics Data System (ADS)

Dawson, Martin D.; Neil, Mark A. A.

2008-05-01

This Cluster Issue of Journal of Physics D: Applied Physics highlights micro-pixellated gallium nitride light-emitting diodes or `micro-LEDs', an emerging technology offering considerable attractions for a broad range of scientific and instrumentation applications. It showcases the results of a Research Councils UK (RCUK) Basic Technology Research programme (http://bt-onethousand.photonics.ac.uk), running from 2004-2008, which has drawn together a multi-disciplinary and multi-institutional research partnership to develop these devices and explore their potential. Images of LEDs Examples of GaN micro-pixel LEDs in operation. Images supplied courtesy of the Guest Editors. The partnership, of physicists, engineers and chemists drawn from the University of Strathclyde, Heriot-Watt University, the University of Sheffield and Imperial College London, has sought to move beyond the established mass-market uses of gallium nitride LEDs in illumination and lighting. Instead, it focuses on specialised solid-state micro-projection devices the size of a match-head, containing up to several thousand individually-addressable micro-pixel elements emitting light in the ultraviolet or visible regions of the spectrum. Such sources are pattern-programmable under computer control and can project into materials fixed or high-frame rate optical images or spatially-controllable patterns of nanosecond excitation pulses. These materials can be as diverse as biological cells and tissues, biopolymers, photoresists and organic semiconductors, leading to new developments in optical microscopy, bio-sensing and chemical sensing, mask-free lithography and direct writing, and organic electronics. Particular areas of interest are multi-modal microscopy, integrated forms of organic semiconductor lasers, lab-on-a-chip, GaN/Si optoelectronics and hybrid inorganic/organic semiconductor structures. This Cluster Issue contains four invited papers and ten contributed papers. The invited papers serve to set the work in an international context. Fan et al, who introduced the original forms of these devices in 2000, give a historical perspective as well as illustrating some recent trends in their work. Xu et al, another of the main international groups in this area, concentrate on biological imaging and detection applications. One of the most exciting prospects for this technology is its compatibility with CMOS, and Charbon reviews recent results with single-photon detection arrays which facilitate integrated optical lab-on-chip devices in conjunction with the micro-LEDs. Belton et al, from within the project partnership, overview the hybrid inorganic/organic semiconductor structures achieved by combining gallium nitride optoelectronics with organic semiconductor materials. The contributed papers cover many other aspects related to the devices themselves, their integration with polymers and CMOS, and also cover several associated developments such as UV-emitting nitride materials, new polymers, and the broader use of LEDs in microscopy. Images of LED fibres Emission patterns generated at the end of a multicore image fibre 600 μm in diameter, from article 094013 by H Xu et al of Brown University. We would like to thank Paul French for suggesting this special issue, the staff of IOP Publishing for their help and support, Dr Caroline Vance for her administration of the programme, and EPSRC (particularly Dr Lindsey Weston) for organizational and financial support.

Selective heteroepitaxy on deeply grooved substrate: A route to low cost semipolar GaN platforms of bulk quality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tendille, Florian, E-mail: florian.tendille@crhea.cnrs.fr; Vennéguès, Philippe; De Mierry, Philippe

2016-08-22

Semipolar GaN crystal stripes larger than 100 μm with dislocation densities below 5 × 10{sup 6} cm{sup −2} are achieved using a low cost fabrication process. An original sapphire patterning procedure is proposed, enabling selective growth of semipolar oriented GaN stripes while confining the defects to specific areas. Radiative and non-radiative crystalline defects are investigated by cathodoluminescence and can be correlated to the development of crystal microstructure during the growth process. A dislocation reduction mechanism, supported by transmission electron microscopy, is proposed. This method represents a step forward toward low-cost quasi-bulk semipolar GaN epitaxial platforms with an excellent structural quality which will allowmore » for even more efficient III-nitride based devices.« less

Controlled Growth of Ordered III-Nitride Core-Shell Nanostructure Arrays for Visible Optoelectronic Devices

DOE PAGES

Rishinaramangalam, Ashwin K.; Mishkat Ul Masabih, Saadat; Fairchild, Michael N.; ...

2014-10-21

In our paper, we demonstrate the growth of ordered arrays of nonpolar {101 ¯ 0} core–shell nanowalls and semipolar {101 ¯ 1} core–shell pyramidal nanostripes on c-plane (0001) sapphire substrates using selective-area epitaxy and metal organic chemical vapor deposition. The nanostructure arrays are controllably patterned into LED mesa regions, demonstrating a technique to impart secondary lithography features into the arrays. Moreover, we study the dependence of the nanostructure cores on the epitaxial growth conditions and show that the geometry and morphology are strongly influenced by growth temperature, V/III ratio, and pulse interruption time. We also demonstrate the growth of InGaNmore » quantum well shells on the nanostructures and characterize the structures by using micro-photoluminescence and cross-section scanning tunneling electron microscopy.« less

ZnO/p-GaN heterostructure for solar cells and the effect of ZnGa2O4 interlayer on their performance.

PubMed

Nam, Seung Yong; Choi, Yong Seok; Lee, Ju Ho; Park, Seong Ju; Lee, Jeong Yong; Lee, Dong Seon

2013-01-01

We report the usage of ZnO material as an alternative for n-GaN for realizing III-nitride based solar cell. The fabricated solar cell shows large turn-on voltage of around 8 volts and a rapid decrease of photocurrent at low bias voltage under darkness and 1-sun illumination conditions, respectively. This phenomenon can be attributed to the formation of high-resistive ultra-thin layers at the ZnO/ p-GaN junction interface during high temperature deposition. Transmission electron microscopy (TEM) studies carried out on the grown samples reveals that the ultra-thin layer consists of ZnGa2O4. It is found that the presence of insulating ZnGa2O4 film is detrimental in the performance of proposed heterostructure for solar cells.

Evolution of secondary-phase precipitates during annealing of the 12Kh18N9T steel irradiated with neutrons to a dose of 5 DPA

NASA Astrophysics Data System (ADS)

Tsai, K. V.; Maksimkin, O. P.; Turubarova, L. G.

2007-03-01

The formation and evolution of thermally-induced secondary precipitates in an austenitic stainless steel 12Kh18N9T irradiated in the core of a laboratory reactor VVR-K to a dose of 5 dpa and subjected to post-radiation isochronous annealings for 1 h in a temperature range from 450 to 1050°C have been studied using transmission electron microscopy (TEM) and microhardness measurements. It has been shown that the formation of stitch (secondary) titanium carbides and M 23C6 carbides at grain and twin boundaries after annealing at 1050°C is preceded by a complex evolution of fineparticles of secondary phases (titanium carbides and nitrides) precipitated at dislocation loops and dislocations during annealing at temperatures above 750°C.

Laser nitriding for niobium superconducting radio-frequency accelerator cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senthilraja Singaravelu, John Klopf, Gwyn Williams, Michael Kelley

2010-10-01

Particle accelerators are a key tool for scientific research ranging from fundamental studies of matter to analytical studies at light sources. Cost-forperformance is critical, both in terms of initial capital outlay and ongoing operating expense, especially for electricity. It depends on the niobium superconducting radiofrequency (SRF) accelerator cavities at the heart of most of these machines. Presently Nb SRF cavities operate near 1.9 K, well (and expensively) below the 4.2 K atmospheric boiling point of liquid He. Transforming the 40 nm thick active interior surface layer from Nb to delta NbN (Tc = 17 K instead of 9.2 K) appearsmore » to be a promising approach. Traditional furnace nitriding appears to have not been successful for this. Further, exposing a complete SRF cavity to the time-temperature history required for nitriding risks mechanical distortion. Gas laser nitriding instead has been applied successfully to other metals [P.Schaaf, Prog. Mat. Sci. 47 (2002) 1]. The beam dimensions and thermal diffusion length permit modeling in one dimension to predict the time course of the surface temperature for a range of per-pulse energy densities. As with the earlier work, we chose conditions just sufficient for boiling as a reference point. We used a Spectra Physics HIPPO nanosecond laser (l = 1064 nm, Emax= 0.392 mJ, beam spot@ 34 microns, PRF =15 – 30 kHz) to obtain an incident fluence of 1.73 - 2.15 J/cm2 for each laser pulse at the target. The target was a 50 mm diameter SRF-grade Nb disk maintained in a nitrogen atmosphere at a pressure of 550 – 625 torr and rotated at a constant speed of 9 rpm. The materials were examined by scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and x-ray diffraction (XRD). The SEM images show a sharp transition with fluence from a smooth, undulating topography to significant roughening, interpreted here as the onset of ablation. EPMA measurements of N/Nb atom ratio as a function of depth found a constant value to depths greater than the SRF active layer thickness. Certain irradiation conditions resulted in values consistent with formation of delta NbN. Under certain irradiation conditions, XRD data were consistent only with delta NbN on top of Nb metal. Funding: authored by Jefferson Science Associates LLC under US DOE Contract De-AC05-06OR23177. We are indebted to Prof. P. Schaaf (Goettingen) for the simulation code and helpful discussions.« less

Silver Nanoparticle-Deposited Boron Nitride Nanosheets as Fillers for Polymeric Composites with High Thermal Conductivity.

PubMed

Wang, Fangfang; Zeng, Xiaoliang; Yao, Yimin; Sun, Rong; Xu, Jianbin; Wong, Ching-Ping

2016-01-19

Polymer composites with high thermal conductivity have recently attracted much attention, along with the rapid development of the electronic devices toward higher speed and performance. However, a common method to enhance polymer thermal conductivity through an addition of high thermally conductive fillers usually cannot provide an expected value, especially for composites requiring electrical insulation. Here, we show that polymeric composites with silver nanoparticle-deposited boron nitride nanosheets as fillers could effectively enhance the thermal conductivity of polymer, thanks to the bridging connections of silver nanoparticles among boron nitride nanosheets. The thermal conductivity of the composite is significantly increased from 1.63 W/m-K for the composite filled with the silver nanoparticle-deposited boron nitride nanosheets to 3.06 W/m-K at the boron nitride nanosheets loading of 25.1 vol %. In addition, the electrically insulating properties of the composite are well preserved. Fitting the measured thermal conductivity of epoxy composite with one physical model indicates that the composite with silver nanoparticle-deposited boron nitride nanosheets outperforms the one with boron nitride nanosheets, owning to the lower thermal contact resistance among boron nitride nanosheets' interfaces. The finding sheds new light on enhancement of thermal conductivity of the polymeric composites which concurrently require the electrical insulation.

Silver Nanoparticle-Deposited Boron Nitride Nanosheets as Fillers for Polymeric Composites with High Thermal Conductivity

PubMed Central

Wang, Fangfang; Zeng, Xiaoliang; Yao, Yimin; Sun, Rong; Xu, Jianbin; Wong, Ching-Ping

2016-01-01

Polymer composites with high thermal conductivity have recently attracted much attention, along with the rapid development of the electronic devices toward higher speed and performance. However, a common method to enhance polymer thermal conductivity through an addition of high thermally conductive fillers usually cannot provide an expected value, especially for composites requiring electrical insulation. Here, we show that polymeric composites with silver nanoparticle-deposited boron nitride nanosheets as fillers could effectively enhance the thermal conductivity of polymer, thanks to the bridging connections of silver nanoparticles among boron nitride nanosheets. The thermal conductivity of the composite is significantly increased from 1.63 W/m-K for the composite filled with the silver nanoparticle-deposited boron nitride nanosheets to 3.06 W/m-K at the boron nitride nanosheets loading of 25.1 vol %. In addition, the electrically insulating properties of the composite are well preserved. Fitting the measured thermal conductivity of epoxy composite with one physical model indicates that the composite with silver nanoparticle-deposited boron nitride nanosheets outperforms the one with boron nitride nanosheets, owning to the lower thermal contact resistance among boron nitride nanosheets’ interfaces. The finding sheds new light on enhancement of thermal conductivity of the polymeric composites which concurrently require the electrical insulation. PMID:26783258

Electronic and optical properties of GaSb:N from first principles

NASA Astrophysics Data System (ADS)

Jadaun, Priyamvada; Nair, Hari; Lordi, Vincenzo; Bank, Seth; Banerjee, Sanjay

2014-03-01

We present an ab-initio study of dilute nitride III-Vs, focusing on dilute nitride GaSb (GaSb:N). GaSb:N displays promise towards realization of optoelectronic devices accessing the mid-infrared wavelength regime. Theoretical and experimental results on its electronic and optical properties are however few. To address this, we present a first principles, density functional theory study using the hybrid HSE06 exchange-correlation functional of GaSb doped with 1.6% nitrogen. We conduct a comparative study on GaAs:N, also with 1.6% nitrogen mole fraction, and find that GaSb:N has a smaller band gap and displays more band gap bowing than GaAs:N. In addition we examine the orbital character of the bands, finding the lowest conduction band to be quasi-delocalized, with a large N-3s contribution. At high concentrations, the N atoms interact via the host matrix, forming a dispersive band of their own which governs optoelectronic properties and dominates band gap bowing. While this band drives the optical and electronic properties of GaSb:N, its physics is not captured by traditional models for dilute-nitrides. We thus propose that a complete theory of dilute-nitrides should incorporate orbital character examination, especially at high N concentrations. Texas Advanced Computing Center (TACC), U.S. Department of Energy, Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

The sensitivity of the electron transport within bulk zinc-blende gallium nitride to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siddiqua, Poppy; O'Leary, Stephen K., E-mail: stephen.oleary@ubc.ca

2016-09-07

Within the framework of a semi-classical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport that occurs within bulk zinc-blende gallium nitride. In particular, we examine how the steady-state and transient electron transport that occurs within this material changes in response to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley. These results are then contrasted with those corresponding to a number of other compound semiconductors of interest.

Study of electronic and magnetic properties of h-BN on Ni surfaces: A DFT approach

NASA Astrophysics Data System (ADS)

Sahoo, M. R.; Sahu, S.; Kushwaha, A. K.; Nayak, S.

2018-04-01

Hexagonal boron nitride (h-BN) is a promising material for implementation in spintronics due to large band gap, low spin-orbit coupling, and a small lattice mismatch to graphene and close-packedsurfaces of fcc-Ni(111). Electronic and magnetic properties of single layer hexagonal Boron Nitride (h-BN) on Ni (111) surface have been studied with density functional calculation. Since lattice constants of nickel surfaces are very close to that of h-BN, nickel acts as a good substrate. We found that the interaction between 2Pz - 3dz2 orbitals leads to change in electronic band structure as well as density of states which results spin polarization in h-BN.

Modification of silicon nitride surfaces with GOPES and APTES for antibody immobilization: computational and experimental studies

NASA Astrophysics Data System (ADS)

Dien To, Thien; Nguyen, Anh Tuan; Nhat Thanh Phan, Khoa; Thu Thi Truong, An; Doan, Tin Chanh Duc; Mau Dang, Chien

2015-12-01

Chemical modification of silicon nitride (SiN) surfaces by silanization has been widely studied especially with 3-(aminopropyl)triethoxysilane (APTES) and 3-(glycidyloxypropyl) dimethylethoxysilane (GOPES). However few reports performed the experimental and computational studies together. In this study, surface modification of SiN surfaces with GOPES and APTES covalently bound with glutaraldehyde (GTA) was investigated for antibody immobilization. The monoclonal anti-cytokeratin-FITC (MACF) antibody was immobilized on the modified SiN surfaces. The modified surfaces were characterized by water contact angle measurements, atomic force microscopy and fluorescence microscopy. The FITC-fluorescent label indicated the existence of MACF antibody on the SiN surfaces and the efficiency of the silanization reaction. Absorption of APTES and GOPES on the oxidized SiN surfaces was computationally modeled and calculated by Materials Studio software. The computational and experimental results showed that modification of the SiN surfaces with APTES and GTA was more effective than the modification with GOPES.

A convenient method for X-ray analysis in TEM that measures mass thickness and composition

NASA Astrophysics Data System (ADS)

Statham, P.; Sagar, J.; Holland, J.; Pinard, P.; Lozano-Perez, S.

2018-01-01

We consider a new approach for quantitative analysis in transmission electron microscopy (TEM) that offers the same convenience as single-standard quantitative analysis in scanning electron microscopy (SEM). Instead of a bulk standard, a thin film with known mass thickness is used as a reference. The procedure involves recording an X-ray spectrum from the reference film for each session of acquisitions on real specimens. There is no need to measure the beam current; the current only needs to be stable for the duration of the session. A new reference standard with a large (1 mm x 1 mm) area of uniform thickness of 100 nm silicon nitride is used to reveal regions of X-ray detector occlusion that would give misleading results for any X-ray method that measures thickness. Unlike previous methods, the new X-ray method does not require an accurate beam current monitor but delivers equivalent accuracy in mass thickness measurement. Quantitative compositional results are also automatically corrected for specimen self-absorption. The new method is tested using a wedge specimen of Inconel 600 that is used to calibrate the high angle angular dark field (HAADF) signal to provide a thickness reference and results are compared with electron energy-loss spectrometry (EELS) measurements. For the new X-ray method, element composition results are consistent with the expected composition for the alloy and the mass thickness measurement is shown to provide an accurate alternative to EELS for thickness determination in TEM without the uncertainty associated with mean free path estimates.

Structural and electronic properties of double-walled boron nitride nanocones

NASA Astrophysics Data System (ADS)

Brito, E.; Silva, T. S.; Guerra, T.; Leite, L.; Azevedo, S.; Freitas, A.; Kaschny, J. R.

2018-01-01

First principles calculations were applied to study the structural and electronic properties of different configurations of double-walled boron nitride nanocones with a disclination angle of 60°. The analysis includes different rotation angles, distance between apexes, as well as distinct types of antiphase boundaries. The calculations indicate that the non-rotated configuration of double-walled nanocone with a defective line composed by C and N atoms, forming C-N bonds, is the most stable configuration. It was found that the yam angle, apexes distance and defective line composition present significant influence on the electronic properties of such structures. Moreover, analyzing the spin charge density, for the electronic states near the Fermi level, it was also found that the configuration with a defective line containing C atoms presents a net magnetic moment.

Large spin accumulation and crystallographic dependence of spin transport in single crystal gallium nitride nanowires

PubMed Central

Park, Tae-Eon; Park, Youn Ho; Lee, Jong-Min; Kim, Sung Wook; Park, Hee Gyum; Min, Byoung-Chul; Kim, Hyung-jun; Koo, Hyun Cheol; Choi, Heon-Jin; Han, Suk Hee; Johnson, Mark; Chang, Joonyeon

2017-01-01

Semiconductor spintronics is an alternative to conventional electronics that offers devices with high performance, low power and multiple functionality. Although a large number of devices with mesoscopic dimensions have been successfully demonstrated at low temperatures for decades, room-temperature operation still needs to go further. Here we study spin injection in single-crystal gallium nitride nanowires and report robust spin accumulation at room temperature with enhanced spin injection polarization of 9%. A large Overhauser coupling between the electron spin accumulation and the lattice nuclei is observed. Finally, our single-crystal gallium nitride samples have a trigonal cross-section defined by the (001), () and () planes. Using the Hanle effect, we show that the spin accumulation is significantly different for injection across the (001) and () (or ()) planes. This provides a technique for increasing room temperature spin injection in mesoscopic systems. PMID:28569767

UV absorption in metal decorated boron nitride flakes: a theoretical analysis of excited states

NASA Astrophysics Data System (ADS)

Chopra, Siddheshwar; Plasser, Felix

2017-10-01

The excited states of single metal atom (X = Co, Al and Cu) doped boron nitride flake (MBNF) B15N14H14-X and pristine boron nitride (B15N15H14) are studied by time-dependent density functional theory. The immediate effect of metal doping is a red shift of the onset of absorption from about 220 nm for pristine BNF to above 300 nm for all metal-doped variants with the biggest effect for MBNF-Co, which shows appreciable intensity even above 400 nm. These energy shifts are analysed by detailed wavefunction analysis protocols using visualisation methods, such as the natural transition orbital analysis and electron-hole correlation plots, as well as quantitative analysis of the exciton size and electron-hole populations. The analysis shows that the Co and Cu atoms provide strong contributions to the relevant states whereas the aluminium atom is only involved to a lesser extent.

Surface passivation of p-type Ge substrate with high-quality GeN{sub x} layer formed by electron-cyclotron-resonance plasma nitridation at low temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukuda, Yukio; Otani, Yohei; Okamoto, Hiroshi

2011-09-26

We have investigated the effects of the formation temperature and postmetallization annealing (PMA) on the interface properties of GeN{sub x}/p-Ge fabricated by the plasma nitridation of Ge substrates using an electron-cyclotron-resonance-generated nitrogen plasma. The nitridation temperature is found to be a critical parameter in improving the finally obtained GeN{sub x}/Ge interface properties. The GeN{sub x}/Ge formed at room temperature and treated by PMA at 400 deg. C exhibits the best interface properties with an interface trap density of 1 x 10{sup 11 }cm{sup -2 }eV{sup -1}. The GeN{sub x}/Ge interface is unpinned and the Fermi level at the Ge surfacemore » can move from the valence band edge to the conduction band edge.« less

Growth features and spectroscopic structure investigations of nanoprofiled AlN films formed on misoriented GaAs substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V., E-mail: paul@phys.vsu.ru; Goloshchapov, D. L.; Lenshin, A. S.

Nanostructured aluminum-nitride films are formed by reactive ion-plasma sputtering onto GaAs substrates with different orientations. The properties of the films are studied via structural analysis, atomic force microscopy, and infrared and visible–ultraviolet spectroscopy. The aluminum-nitride films can have a refractive index in the range of 1.6–4.0 at a wavelength of ~250 nm and an optical band gap of ~5 eV. It is shown that the morphology, surface composition, and optical characteristics of AlN/GaAs heterophase systems can be controlled using misoriented GaAs substrates.

Nitriding of titanium and titanium: 8 percent aluminum, 1 percent molybdenum, 1 percent vanadium alloy with an ion-beam source

NASA Technical Reports Server (NTRS)

Gill, A.

1983-01-01

Titanium and Ti-8Al-1Mo-1V alloy were nitrided with an ion-beam source of nitrogen or argon and nitrogen at a total pressure of 2 x 10 to the minus 4th power to 10 x 10 to the minus 4th power torr. The treated surface was characterized by surface profilometry, X-ray diffractometry, Auger electron spectroscopy and microhardness measurements. The tetragonal Ti2N phase formed in pure titanium and Ti-8Al-1Mo-1V alloy with traces of AlN in the alloy. Two opposite processes competed during the ion-beam-nitriding process: (1) formation of nitrides in the surface layer and (2) sputtering of the nitrided layers by the ion beam. The highest surface hardnesses, about 500 kg/sq mm in titanium and 800 kg/sq mm in Ti-8Al-1Mo-1V, were obtained by ion nitriding with an ion beam of pure nitrogen at 4.2 x 10 to the minus 4th power torr at a beam voltage of 1000 V.