Effects of chemical states of carbon on deuterium retention in carbon-containing materials

NASA Astrophysics Data System (ADS)

Oyaidzu, Makoto; Kimura, Hiromi; Nakahata, Toshihiko; Nishikawa, Yusuke; Tokitani, Masayuki; Oya, Yasuhisa; Iwakiri, Hirotomo; Yoshida, Naoaki; Okuno, Kenji

2007-08-01

Deuterium retention behavior in highly oriented pyrolytic graphite (HOPG), poly-crystalline diamond, poly-crystalline SiC, sintered WC, and converted B 4C were investigated to reveal tritium behavior in re-deposition and co-deposition layers. Such layers would contain carbon, when the first wall and/or divertor were made of graphite or carbon-containing materials. Furthermore, the employment of other materials such as tungsten, and first wall conditioning such as boronization would complicate the layers. No different deuterium trapping sites due to carbon from those in HOPG were found in all the samples, where two deuterium trapping processes were observed: hot atom chemical trapping of energetic deuterium by a dangling bond of carbon and thermochemical trapping of thermalized deuterium in a constituent atom vacancy surrounded by carbons. Additionally, the latter reaction could be easily counteracted by or competed with the other deuterium trapping reactions by constituent atoms.

Formation of Micro- and Nanostructures on the Nanotitanium Surface by Chemical Etching and Deposition of Titania Films by Atomic Layer Deposition (ALD)

PubMed Central

Nazarov, Denis V.; Zemtsova, Elena G.; Valiev, Ruslan Z.; Smirnov, Vladimir M.

2015-01-01

In this study, an integrated approach was used for the preparation of a nanotitanium-based bioactive material. The integrated approach included three methods: severe plastic deformation (SPD), chemical etching and atomic layer deposition (ALD). For the first time, it was experimentally shown that the nature of the etching medium (acidic or basic Piranha solutions) and the etching time have a significant qualitative impact on the nanotitanium surface structure both at the nano- and microscale. The etched samples were coated with crystalline biocompatible TiO2 films with a thickness of 20 nm by Atomic Layer Deposition (ALD). Comparative study of the adhesive and spreading properties of human osteoblasts MG-63 has demonstrated that presence of nano- and microscale structures and crystalline titanium oxide on the surface of nanotitanium improve bioactive properties of the material. PMID:28793716

Atomic layer deposition of a high-k dielectric on MoS2 using trimethylaluminum and ozone.

PubMed

Cheng, Lanxia; Qin, Xiaoye; Lucero, Antonio T; Azcatl, Angelica; Huang, Jie; Wallace, Robert M; Cho, Kyeongjae; Kim, Jiyoung

2014-08-13

We present an Al2O3 dielectric layer on molybdenum disulfide (MoS2), deposited using atomic layer deposition (ALD) with ozone/trimethylaluminum (TMA) and water/TMA as precursors. The results of atomic force microscopy and low-energy ion scattering spectroscopy show that using TMA and ozone as precursors leads to the formation of uniform Al2O3 layers, in contrast to the incomplete coverage we observe when using TMA/H2O as precursors. Our Raman and X-ray photoelectron spectroscopy measurements indicate minimal variations in the MoS2 structure after ozone treatment at 200 °C, suggesting its excellent chemical resistance to ozone.

Resolving the Chemically Discrete Structure of Synthetic Borophene Polymorphs.

PubMed

Campbell, Gavin P; Mannix, Andrew J; Emery, Jonathan D; Lee, Tien-Lin; Guisinger, Nathan P; Hersam, Mark C; Bedzyk, Michael J

2018-05-09

Atomically thin two-dimensional (2D) materials exhibit superlative properties dictated by their intralayer atomic structure, which is typically derived from a limited number of thermodynamically stable bulk layered crystals (e.g., graphene from graphite). The growth of entirely synthetic 2D crystals, those with no corresponding bulk allotrope, would circumvent this dependence upon bulk thermodynamics and substantially expand the phase space available for structure-property engineering of 2D materials. However, it remains unclear if synthetic 2D materials can exist as structurally and chemically distinct layers anchored by van der Waals (vdW) forces, as opposed to strongly bound adlayers. Here, we show that atomically thin sheets of boron (i.e., borophene) grown on the Ag(111) surface exhibit a vdW-like structure without a corresponding bulk allotrope. Using X-ray standing wave-excited X-ray photoelectron spectroscopy, the positions of boron in multiple chemical states are resolved with sub-angström spatial resolution, revealing that the borophene forms a single planar layer that is 2.4 Å above the unreconstructed Ag surface. Moreover, our results reveal that multiple borophene phases exhibit these characteristics, denoting a unique form of polymorphism consistent with recent predictions. This observation of synthetic borophene as chemically discrete from the growth substrate suggests that it is possible to engineer a much wider variety of 2D materials than those accessible through bulk layered crystal structures.

Normal incidence x-ray mirror for chemical microanalysis

DOEpatents

Carr, M.J.; Romig, A.D. Jr.

1987-08-05

An x-ray mirror for both electron column instruments and micro x-ray fluorescence instruments for making chemical, microanalysis comprises a non-planar mirror having, for example, a spherical reflecting surface for x-rays comprised of a predetermined number of alternating layers of high atomic number material and low atomic number material contiguously formed on a substrate and whose layers have a thickness which is a multiple of the wavelength being reflected. For electron column instruments, the wavelengths of interest lie above 1.5nm, while for x-ray fluorescence instruments, the range of interest is below 0.2nm. 4 figs.

Atomic-Level Co3O4 Layer Stabilized by Metallic Cobalt Nanoparticles: A Highly Active and Stable Electrocatalyst for Oxygen Reduction.

PubMed

Liu, Min; Liu, Jingjun; Li, Zhilin; Wang, Feng

2018-02-28

Developing atomic-level transition oxides may be one of the most promising ways for providing ultrahigh electrocatalytic performance for oxygen reduction reaction (ORR), compared with their bulk counterparts. In this article, we developed a set of atomically thick Co 3 O 4 layers covered on Co nanoparticles through partial reduction of Co 3 O 4 nanoparticles using melamine as a reductive additive at an elevated temperature. Compared with the original Co 3 O 4 nanoparticles, the synthesized Co 3 O 4 with a thickness of 1.1 nm exhibits remarkably enhanced ORR activity and durability, which are even higher than those obtained by a commercial Pt/C in an alkaline environment. The superior activity can be attributed to the unique physical and chemical structures of the atomic-level oxide featuring the narrowed band gap and decreased work function, caused by the escaped lattice oxygen and the enriched coordination-unsaturated Co 2+ in this atomic layer. Besides, the outstanding durability of the catalyst can result from the chemically epitaxial deposition of the Co 3 O 4 on the cobalt surface. Therefore, the proposed synthetic strategy may offer a smart way to develop other atomic-level transition metals with high electrocatalytic activity and stability for energy conversion and storage devices.

Atomistics of Ge deposition on Si(100) by atomic layer epitaxy.

PubMed

Lin, D S; Wu, J L; Pan, S Y; Chiang, T C

2003-01-31

Chlorine termination of mixed Ge/Si(100) surfaces substantially enhances the contrast between Ge and Si sites in scanning tunneling microscopy observations. This finding enables a detailed investigation of the spatial distribution of Ge atoms deposited on Si(100) by atomic layer epitaxy. The results are corroborated by photoemission measurements aided by an unusually large chemical shift between Cl adsorbed on Si and Ge. Adsorbate-substrate atomic exchange during growth is shown to be important. The resulting interface is thus graded, but characterized by a very short length scale of about one monolayer.

A Microstructural Comparison of the Initial Growth of AIN and GaN Layers on Basal Plane Sapphire and SiC Substrates by Low Pressure Metalorganic Chemical Vapor Depositon

NASA Technical Reports Server (NTRS)

George, T.; Pike, W. T.; Khan, M. A.; Kuznia, J. N.; Chang-Chien, P.

1994-01-01

The initial growth by low pressure metalorganic chemical vapor deposition and subsequent thermal annealing of AIN and GaN epitaxial layers on SiC and sapphire substrates is examined using high resolution transmission electron microscopy and atomic force microscopy.

Breakthrough to Non-Vacuum Deposition of Single-Crystal, Ultra-Thin, Homogeneous Nanoparticle Layers: A Better Alternative to Chemical Bath Deposition and Atomic Layer Deposition

PubMed Central

Liao, Yu-Kuang; Liu, Yung-Tsung; Hsieh, Dan-Hua; Shen, Tien-Lin; Hsieh, Ming-Yang; Tzou, An-Jye; Chen, Shih-Chen; Tsai, Yu-Lin; Lin, Wei-Sheng; Chan, Sheng-Wen; Shen, Yen-Ping; Cheng, Shun-Jen; Chen, Chyong-Hua; Wu, Kaung-Hsiung; Chen, Hao-Ming; Kuo, Shou-Yi; Charlton, Martin D. B.; Hsieh, Tung-Po; Kuo, Hao-Chung

2017-01-01

Most thin-film techniques require a multiple vacuum process, and cannot produce high-coverage continuous thin films with the thickness of a few nanometers on rough surfaces. We present a new ”paradigm shift” non-vacuum process to deposit high-quality, ultra-thin, single-crystal layers of coalesced sulfide nanoparticles (NPs) with controllable thickness down to a few nanometers, based on thermal decomposition. This provides high-coverage, homogeneous thickness, and large-area deposition over a rough surface, with little material loss or liquid chemical waste, and deposition rates of 10 nm/min. This technique can potentially replace conventional thin-film deposition methods, such as atomic layer deposition (ALD) and chemical bath deposition (CBD) as used by the Cu(In,Ga)Se2 (CIGS) thin-film solar cell industry for decades. We demonstrate 32% improvement of CIGS thin-film solar cell efficiency in comparison to reference devices prepared by conventional CBD deposition method by depositing the ZnS NPs buffer layer using the new process. The new ZnS NPs layer allows reduction of an intrinsic ZnO layer, which can lead to severe shunt leakage in case of a CBD buffer layer. This leads to a 65% relative efficiency increase. PMID:28383488

Structural building principles of complex face-centered cubic intermetallics.

PubMed

Dshemuchadse, Julia; Jung, Daniel Y; Steurer, Walter

2011-08-01

Fundamental structural building principles are discussed for all 56 known intermetallic phases with approximately 400 or more atoms per unit cell and space-group symmetry F43m, Fd3m, Fd3, Fm3m or Fm3c. Despite fundamental differences in chemical composition, bonding and electronic band structure, their complex crystal structures show striking similarities indicating common building principles. We demonstrate that the structure-determining elements are flat and puckered atomic {110} layers stacked with periodicities 2p. The atoms on this set of layers, which intersect each other, form pentagon face-sharing endohedral fullerene-like clusters arranged in a face-centered cubic packing (f.c.c.). Due to their topological layer structure, all these crystal structures can be described as (p × p × p) = p(3)-fold superstructures of a common basic structure of the double-diamond type. The parameter p, with p = 3, 4, 7 or 11, is determined by the number of layers per repeat unit and the type of cluster packing, which in turn are controlled by chemical composition.

Patterned growth of p-type MoS 2 atomic layers using sol-gel as precursor

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

Zheng, Wei; Lin, Junhao; Feng, Wei

2D layered MoS 2 has drawn intense attention for its applications in flexible electronic, optoelectronic, and spintronic devices. Most of the MoS 2 atomic layers grown by conventional chemical vapor deposition techniques are n-type due to the abundant sulfur vacancies. Facile production of MoS 2 atomic layers with p-type behavior, however, remains challenging. Here, a novel one-step growth has been developed to attain p-type MoS 2 layers in large scale by using Mo-containing sol–gel, including 1% tungsten (W). Atomic-resolution electron microscopy characterization reveals that small tungsten oxide clusters are commonly present on the as-grown MoS 2 film due to themore » incomplete reduction of W precursor at the reaction temperature. These omnipresent small tungsten oxide clusters contribute to the p-type behavior, as verified by density functional theory calculations, while preserving the crystallinity of the MoS 2 atomic layers. The Mo containing sol–gel precursor is compatible with the soft-lithography techniques, which enables patterned growth of p-type MoS 2 atomic layers into regular arrays with different shapes, holding great promise for highly integrated device applications. Lastly, an atomically thin p–n junction is fabricated by the as-prepared MoS 2, which shows strong rectifying behavior.« less

Patterned growth of p-type MoS 2 atomic layers using sol-gel as precursor

DOE PAGES

Zheng, Wei; Lin, Junhao; Feng, Wei; ...

2016-07-19

2D layered MoS 2 has drawn intense attention for its applications in flexible electronic, optoelectronic, and spintronic devices. Most of the MoS 2 atomic layers grown by conventional chemical vapor deposition techniques are n-type due to the abundant sulfur vacancies. Facile production of MoS 2 atomic layers with p-type behavior, however, remains challenging. Here, a novel one-step growth has been developed to attain p-type MoS 2 layers in large scale by using Mo-containing sol–gel, including 1% tungsten (W). Atomic-resolution electron microscopy characterization reveals that small tungsten oxide clusters are commonly present on the as-grown MoS 2 film due to themore » incomplete reduction of W precursor at the reaction temperature. These omnipresent small tungsten oxide clusters contribute to the p-type behavior, as verified by density functional theory calculations, while preserving the crystallinity of the MoS 2 atomic layers. The Mo containing sol–gel precursor is compatible with the soft-lithography techniques, which enables patterned growth of p-type MoS 2 atomic layers into regular arrays with different shapes, holding great promise for highly integrated device applications. Lastly, an atomically thin p–n junction is fabricated by the as-prepared MoS 2, which shows strong rectifying behavior.« less

The initial stages of ZnO atomic layer deposition on atomically flat In0.53Ga0.47As substrates.

PubMed

Skopin, Evgeniy V; Rapenne, Laetitia; Roussel, Hervé; Deschanvres, Jean-Luc; Blanquet, Elisabeth; Ciatto, Gianluca; Fong, Dillon D; Richard, Marie-Ingrid; Renevier, Hubert

2018-06-21

InGaAs is one of the III-V active semiconductors used in modern high-electron-mobility transistors or high-speed electronics. ZnO is a good candidate material to be inserted as a tunneling insulator layer at the metal-semiconductor junction. A key consideration in many modern devices is the atomic structure of the hetero-interface, which often ultimately governs the electronic or chemical process of interest. Here, a complementary suite of in situ synchrotron X-ray techniques (fluorescence, reflectivity and absorption) as well as modeling is used to investigate both structural and chemical evolution during the initial growth of ZnO by atomic layer deposition (ALD) on In0.53Ga0.47As substrates. Prior to steady-state growth behavior, we discover a transient regime characterized by two stages. First, substrate-inhibited ZnO growth takes place on InGaAs terraces. This leads eventually to the formation of a 1 nm-thick, two-dimensional (2D) amorphous layer. Second, the growth behavior and its modeling suggest the occurrence of dense island formation, with an aspect ratio and surface roughness that depends sensitively on the growth condition. Finally, ZnO ALD on In0.53Ga0.47As is characterized by 2D steady-state growth with a linear growth rate of 0.21 nm cy-1, as expected for layer-by-layer ZnO ALD.

Atomic to Nanoscale Investigation of Functionalities of an Al2O3 Coating Layer on a Cathode for Enhanced Battery Performance

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

Yan, Pengfei; Zheng, Jianming; Zhang, Xiaofeng

2016-02-09

Surface coating has been identified as an effective approach for enhancing the capacity retention of layered structure cathode. However, the underlying operating mechanism of such a thin coating layer, in terms of surface chemical functionality and capacity retention, remains unclear. In this work, we use aberration-corrected scanning transmission electron microscopy and high-efficiency spectroscopy to probe the delicate functioning mechanism of an Al2O3 coating layer on a Li1.2Ni0.2Mn0.6O2 cathode. We discovered that in terms of surface chemical function, the Al2O3 coating suppresses the side reaction between the cathode and the electrolyte during battery cycling. At the same time, the Al2O3 coatingmore » layer also eliminates the chemical reduction of Mn from the cathode particle surface, therefore preventing the dissolution of the reduced Mn into the electrolyte. In terms of structural stability, we found that the Al2O3 coating layer can mitigate the layer to spinel phase transformation, which otherwise will be initiated from the particle surface and propagate toward the interior of the particle with the progression of battery cycling. The atomic to nanoscale effects of the coating layer observed here provide insight into the optimized design of a coating layer on a cathode to enhance the battery properties.« less

Atomic to Nanoscale Investigation of Functionalities of Al2O3 Coating Layer on Cathode for Enhanced Battery Performance

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

Yan, Pengfei; Zheng, Jianming; Zhang, Xiaofeng

2016-01-06

Surface coating of cathode has been identified as an effective approach for enhancing the capacity retention of layered structure cathode. However, the underlying operating mechanism of such a thin layer of coating, in terms of surface chemical functionality and capacity retention, remains unclear. In this work, we use aberration corrected scanning transmission electron microscopy and high efficient spectroscopy to probe the delicate functioning mechanism of Al2O3 coating layer on Li1.2Ni0.2Mn0.6O2 cathode. We discovered that in terms of surface chemical function, the Al2O3 coating suppresses the side reaction between cathode and the electrolyte upon the battery cycling. At the same time,more » the Al2O3 coating layer also eliminates the chemical reduction of Mn from the cathode particle surface, therefore avoiding the dissolution of the reduced Mn into the electrolyte. In terms of structural stability, we found that the Al2O3 coating layer can mitigate the layer to spinel phase transformation, which otherwise will initiate from the particle surface and propagate towards the interior of the particle with the progression of the battery cycling. The atomic to nanoscale effects of the coating layer observed here provide insight for optimized design of coating layer on cathode to enhance the battery properties.« less

Atomic Layer Deposition of Chemical Passivation Layers and High Performance Anti-Reflection Coatings on Back-Illuminated Detectors

NASA Technical Reports Server (NTRS)

Hoenk, Michael E. (Inventor); Greer, Frank (Inventor); Nikzad, Shouleh (Inventor)

2014-01-01

A back-illuminated silicon photodetector has a layer of Al2O3 deposited on a silicon oxide surface that receives electromagnetic radiation to be detected. The Al2O3 layer has an antireflection coating deposited thereon. The Al2O3 layer provides a chemically resistant separation layer between the silicon oxide surface and the antireflection coating. The Al2O3 layer is thin enough that it is optically innocuous. Under deep ultraviolet radiation, the silicon oxide layer and the antireflection coating do not interact chemically. In one embodiment, the silicon photodetector has a delta-doped layer near (within a few nanometers of) the silicon oxide surface. The Al2O3 layer is expected to provide similar protection for doped layers fabricated using other methods, such as MBE, ion implantation and CVD deposition.

Interfacial chemical and electronic structure of cobalt deposition on 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT)

NASA Astrophysics Data System (ADS)

Zhu, Menglong; Lyu, Lu; Niu, Dongmei; Zhang, Hong; Zhang, Yuhe; Liu, Peng; Gao, Yongli

2017-04-01

Interfacial chemical and electronic structure of Co deposition on 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene(C8-BTBT) was investigated by ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS). Chemical reaction of cobalt with C8-BTBT at the interface is confirmed by a new component of S 2s peak which is electron-rich compared to the original one of C8-BTBT molecules. Intensity evolution of the core level in XPS indicates that the adsorption of Co atoms is mainly at the surface without deeper diffusion into C8-BTBT layer. Initial deposition of Co atoms downward shifts the core levels of C8-BTBT by electron transfer from isolated Co atoms or clusters to the C8-BTBT. Further deposition of Co upward shifts the core levels of C8-BTBT because of the neutralization of the thicker metal Co film. Our investigation suggests an inert buffer layer inserted to protect organic layer from reaction or decomposition and to lower the carrier barriers for both the electron and hole to improve the performance of Co/C8-BTBT-based OFETs.

Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

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

Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.

We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

A role for ion implantation in quantum computing

NASA Astrophysics Data System (ADS)

Jamieson, David N.; Prawer, Steven; Andrienko, Igor; Brett, David A.; Millar, Victoria

2001-04-01

We propose to create arrays of phosphorus atoms in silicon for quantum computing using ion implantation. Since the implantation of the ions is essentially random, the yield of usefully spaced atoms is low and therefore some method of registering the passage of a single ion is required. This can be accomplished by implantation of the ions through a thin surface layer consisting of resist. Changes to the chemical and/or electrical properties of the resist will be used to mark the site of the buried ion. For chemical changes, the latent damage will be developed and the atomic force microscope (AFM) used to image the changes in topography. Alternatively, changes in electrical properties (which obviate the need for post-irradiation chemical etching) will be used to register the passage of the ion using scanning tunneling microscopy (STM), the surface current imaging mode of the AFM. We address the central issue of the contrast created by the passage of a single ion through resist layers of PMMA and C 60.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-05-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

PubMed Central

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-01-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Atomic composition and electrical characteristics of epitaxial CVD diamond layers doped with boron

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

Surovegina, E. A., E-mail: suroveginaka@ipmras.ru; Demidov, E. V.; Drozdov, M. N.

2016-12-15

The results of analysis of the atomic composition, doping level, and hole mobility in epitaxial diamond layers when doped with boron are reported. The layers are produced by chemical-vapor deposition. The possibilities of uniform doping with boron to a level in the range 5 × 10{sup 17} to ~10{sup 20} at cm{sup –3} and of δ doping to the surface concentration (0.3–5) × 10{sup 13} at cm{sup –3} are shown. The conditions for precision ion etching of the structures are determined, and barrier and ohmic contacts to the layers are formed.

Internal and external atomic steps in graphite exhibit dramatically different physical and chemical properties.

PubMed

Lee, Hyunsoo; Lee, Han-Bo-Ram; Kwon, Sangku; Salmeron, Miquel; Park, Jeong Young

2015-04-28

We report on the physical and chemical properties of atomic steps on the surface of highly oriented pyrolytic graphite (HOPG) investigated using atomic force microscopy. Two types of step edges are identified: internal (formed during crystal growth) and external (formed by mechanical cleavage of bulk HOPG). The external steps exhibit higher friction than the internal steps due to the broken bonds of the exposed edge C atoms, while carbon atoms in the internal steps are not exposed. The reactivity of the atomic steps is manifested in a variety of ways, including the preferential attachment of Pt nanoparticles deposited on HOPG when using atomic layer deposition and KOH clusters formed during drop casting from aqueous solutions. These phenomena imply that only external atomic steps can be used for selective electrodeposition for nanoscale electronic devices.

Enhanced magnetic anisotropies of single transition-metal adatoms on a defective MoS2 monolayer.

PubMed

Cong, W T; Tang, Z; Zhao, X G; Chu, J H

2015-03-23

Single magnetic atoms absorbed on an atomically thin layer represent the ultimate limit of bit miniaturization for data storage. To approach the limit, a critical step is to find an appropriate material system with high chemical stability and large magnetic anisotropic energy. Here, on the basis of first-principles calculations and the spin-orbit coupling theory, it is elucidated that the transition-metal Mn and Fe atoms absorbed on disulfur vacancies of MoS2 monolayers are very promising candidates. It is analysed that these absorption systems are of not only high chemical stabilities but also much enhanced magnetic anisotropies and particularly the easy magnetization axis is changed from the in-plane one for Mn to the out-of-plane one for Fe by a symmetry-lowering Jahn-Teller distortion. The results point out a promising direction to achieve the ultimate goal of single adatomic magnets with utilizing the defective atomically thin layers.

Local Chemical Ordering and Negative Thermal Expansion in PtNi Alloy Nanoparticles.

PubMed

Li, Qiang; Zhu, He; Zheng, Lirong; Fan, Longlong; Wang, Na; Rong, Yangchun; Ren, Yang; Chen, Jun; Deng, Jinxia; Xing, Xianran

2017-12-13

An atomic insight into the local chemical ordering and lattice strain is particular interesting to recent emerging bimetallic nanocatalysts such as PtNi alloys. Here, we reported the atomic distribution, chemical environment, and lattice thermal evolution in full-scale structural description of PtNi alloy nanoparticles (NPs). The different segregation of elements in the well-faceted PtNi nanoparticles is convinced by extended X-ray absorption fine structure (EXAFS). Atomic pair distribution function (PDF) study evidences the coexistence of the face-centered cubic and tetragonal ordering parts in the local environment of PtNi nanoparticles. Further reverse Monte Carlo (RMC) simulation with PDF data obviously exposed the segregation as Ni and Pt in the centers of {111} and {001} facets, respectively. Layer-by-layer statistical analysis up to 6 nm for the local atomic pairs revealed the distribution of local tetragonal ordering on the surface. This local coordination environment facilitates the distribution of heteroatomic Pt-Ni pairs, which plays an important role in the negative thermal expansion of Pt 41 Ni 59 NPs. The present study on PtNi alloy NPs from local short-range coordination to long-range average lattice provides a new perspective on tailoring physical properties in nanomaterials.

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

PubMed Central

Xie, Jin; Liao, Lei; Gong, Yongji; Li, Yanbin; Shi, Feifei; Pei, Allen; Sun, Jie; Zhang, Rufan; Kong, Biao; Subbaraman, Ram; Christensen, Jake; Cui, Yi

2017-01-01

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formation during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. The protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte. PMID:29202031

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

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

Xie, Jin; Liao, Lei; Gong, Yongji

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formationmore » during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. In conclusion, the protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte.« less

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

DOE PAGES

Xie, Jin; Liao, Lei; Gong, Yongji; ...

2017-11-29

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formationmore » during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. In conclusion, the protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte.« less

Origins of Moiré Patterns in CVD-grown MoS2 Bilayer Structures at the Atomic Scales.

PubMed

Wang, Jin; Namburu, Raju; Dubey, Madan; Dongare, Avinash M

2018-06-21

The chemical vapor deposition (CVD)-grown two-dimensional molybdenum disulfide (MoS 2 ) structures comprise of flakes of few layers with different dimensions. The top layers are relatively smaller in size than the bottom layers, resulting in the formation of edges/steps across adjacent layers. The strain response of such few-layer terraced structures is therefore likely to be different from exfoliated few-layered structures with similar dimensions without any terraces. In this study, the strain response of CVD-grown few-layered MoS 2 terraced structures is investigated at the atomic scales using classic molecular dynamics (MD) simulations. MD simulations suggest that the strain relaxation of CVD-grown triangular terraced structures is observed in the vertical displacement of the atoms across the layers that results in the formation of Moiré patterns. The Moiré islands are observed to nucleate at the corners or edges of the few-layered structure and propagate inwards under both tensile and compressive strains. The nucleation of these islands is observed to happen at tensile strains of ~ 2% and at compressive strains of ~2.5%. The vertical displacements of the atoms and the dimensions of the Moiré islands predicted using the MD simulation are in excellent agreement with that observed experimentally.

Solid state synthesis of Mn{sub 5}Ge{sub 3} in Ge/Ag/Mn trilayers: Structural and magnetic studies

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

Myagkov, V.G.; Bykova, L.E.; Matsynin, A.A.

The thin-film solid-state reaction between elemental Ge and Mn across chemically inert Ag layers with thicknesses of (0, 0.3, 1 and 2.2 µm) in Ge/Ag/Mn trilayers was studied for the first time. The initial samples were annealed at temperatures between 50 and 500 °C at 50 °C intervals for 1 h. The initiation temperature of the reaction for Ge/Mn (without a Ag barrier layer) was ~ 120 °C and increased slightly up to ~ 250 °C when the Ag barrier layer thickness increased up to 2.2 µm. In spite of the Ag layer, only the ferromagnetic Mn{sub 5}Ge{sub 3} compoundmore » and the Nowotny phase were observed in the initial stage of the reaction after annealing at 500 °C. The cross-sectional studies show that during Mn{sub 5}Ge{sub 3} formation the Ge is the sole diffusing species. The magnetic and cross-sectional transmission electron microscopy (TEM) studies show an almost complete transfer of Ge atoms from the Ge film, via a 2.2 µm Ag barrier layer, into the Mn layer. We attribute the driving force of the long-range transfer to the long-range chemical interactions between reacting Mn and Ge atoms. - Graphical abstract: The direct visualization of the solid state reaction between Mn and Ge across a Ag buffer layer at 500 °C. - Highlights: • The migration of Ge, via an inert 2.2 µm Ag barrier, into a Mn layer. • The first Mn{sub 5}Ge{sub 3} phase was observed in reactions with different Ag layers. • The Ge is the sole diffusing species during Mn{sub 5}Ge{sub 3} formation • The long-range chemical interactions control the Ge atomic transfer.« less

Characterization of atomic-layer MoS2 synthesized using a hot filament chemical vapor deposition method

NASA Astrophysics Data System (ADS)

Ying-Zi, Peng; Yang, Song; Xiao-Qiang, Xie; Yuan, Li; Zheng-Hong, Qian; Ru, Bai

2016-05-01

Atomic-layer MoS2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy (AFM), x-ray diffraction (XRD), high-resolution transition electron microscopy (HRTEM), photoluminescence (PL), and x-ray photoelectron spectroscopy (XPS) characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation (002). The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasi-honeycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS2. The stoichiometric mole ratio of S/Mo is about 2.0-2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS2 under our experimental conditions. Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant Nos. LY16F040003 and LY16A040007) and the National Natural Science Foundation of China (Grant Nos. 51401069 and 11574067).

Nanoparticle layer deposition for highly controlled multilayer formation based on high- coverage monolayers of nanoparticles

PubMed Central

Liu, Yue; Williams, Mackenzie G.; Miller, Timothy J.; Teplyakov, Andrew V.

2015-01-01

This paper establishes a strategy for chemical deposition of functionalized nanoparticles onto solid substrates in a layer-by-layer process based on self-limiting surface chemical reactions leading to complete monolayer formation within the multilayer system without any additional intermediate layers – nanoparticle layer deposition (NPLD). This approach is fundamentally different from previously established traditional layer-by-layer deposition techniques and is conceptually more similar to well-known atomic and molecular – layer deposition processes. The NPLD approach uses efficient chemical functionalization of the solid substrate material and complementary functionalization of nanoparticles to produce a nearly 100% coverage of these nanoparticles with the use of “click chemistry”. Following this initial deposition, a second complete monolayer of nanoparticles is deposited using a copper-catalyzed “click reaction” with the azide-terminated silica nanoparticles of a different size. This layer-by-layer growth is demonstrated to produce stable covalently-bound multilayers of nearly perfect structure over macroscopic solid substrates. The formation of stable covalent bonds is confirmed spectroscopically and the stability of the multilayers produced is tested by sonication in a variety of common solvents. The 1-, 2- and 3-layer structures are interrogated by electron microscopy and atomic force microscopy and the thickness of the multilayers formed is fully consistent with that expected for highly efficient monolayer formation with each cycle of growth. This approach can be extended to include a variety of materials deposited in a predesigned sequence on different substrates with a highly conformal filling. PMID:26726273

Atomic-Resolution X-ray Energy-Dispersive Spectroscopy Chemical Mapping of Substitutional Dy Atoms in a High-Coercivity Neodymium Magnet

NASA Astrophysics Data System (ADS)

Itakura, Masaru; Watanabe, Natsuki; Nishida, Minoru; Daio, Takeshi; Matsumura, Syo

2013-05-01

We have investigated local element distributions in a Dy-doped Nd2Fe14B hot-deformed magnet by atomic-column resolution chemical mapping using an X-ray energy-dispersive spectrometer (XEDS) attached to an aberration-corrected scanning transmission electron microscope (Cs-corrected STEM). The positions of the Nd and Dy atomic columns were visualized in the XEDS maps. The substitution of Dy was limited to a surface layer 2-3 unit cells thick in the Nd2Fe14B grains, and the Dy atoms preferentially occupied the 4f-Nd sites of Nd2Fe14B. These results provide further insights into the principal mechanism governing the coercivity enhancement due to Dy doping.

Studies of Atomic Free Radicals Stored in a Cryogenic Environment

NASA Technical Reports Server (NTRS)

Lee, David M.; Hubbard, Dorthy (Technical Monitor); Alexander, Glen (Technical Monitor)

2003-01-01

Impurity-Helium Solids are porous gel-like solids consisting of impurity atoms and molecules surrounded by thin layers of solid helium. They provide an ideal medium for matrix isolation of free radicals to prevent recombination and store chemical energy. In this work electron spin resonance, nuclear magnetic resonance, X-ray diffraction, and ultrasound techniques have all been employed to study the properties of these substances. Detailed studies via electron spin resonance of exchange tunneling chemical reactions involving hydrogen and deuterium molecular and atomic impurities in these solids have been performed and compared with theory. Concentrations of hydrogen approaching the quantum solid criterion have been produced. Structured studies involving X ray diffraction, ultrasound, and electron spin resonance have shown that the impurities in impurity helium solids are predominantly contained in impurity clusters, with each cluster being surrounded by thin layers of solid helium.

Synthesis of Large-area Crystalline MoTe2 Atomic layer from Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Zhou, Lin; Zubair, Ahmad; Xu, Kai; Kong, Jing; Dresselhaus, Mildred

The controlled synthesis of highly crystalline large-area molybdenum ditelluride MoTe2 atomic layers is crucial for the practical applications of this emerging material. Here we develop a novel approach for the growth of large-area, uniform and highly crystalline few-layer MoTe2 film via chemical vapour deposition (CVD). Large-area atomically thin MoTe2 film has been successfully synthesized by tellurization of a MoO3 film. The as-grown MoTe2 film is uniform, stoichiometric, and highly crystalline. As a result of the high crystallinity, the electronic properties of MoTe2 film are comparable with that of mechanically exfoliated MoTe2 flakes. Moreover, we found that two different phases of MoTe2 (2H and 1T') can be grown depending on the choice of Mo precursor. Since the MoTe2 film is highly homogenous, and the size of the film is only limited by the substrate and CVD system size, our growth method paves the way for large-scale application of MoTe2 in high performance nanoelectronics and optoelectronics.

Atom-scale depth localization of biologically important chemical elements in molecular layers.

PubMed

Schneck, Emanuel; Scoppola, Ernesto; Drnec, Jakub; Mocuta, Cristian; Felici, Roberto; Novikov, Dmitri; Fragneto, Giovanna; Daillant, Jean

2016-08-23

In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.

Solute segregation and deviation from bulk thermodynamics at nanoscale crystalline defects.

PubMed

Titus, Michael S; Rhein, Robert K; Wells, Peter B; Dodge, Philip C; Viswanathan, Gopal Babu; Mills, Michael J; Van der Ven, Anton; Pollock, Tresa M

2016-12-01

It has long been known that solute segregation at crystalline defects can have profound effects on material properties. Nevertheless, quantifying the extent of solute segregation at nanoscale defects has proven challenging due to experimental limitations. A combined experimental and first-principles approach has been used to study solute segregation at extended intermetallic phases ranging from 4 to 35 atomic layers in thickness. Chemical mapping by both atom probe tomography and high-resolution scanning transmission electron microscopy demonstrates a markedly different composition for the 4-atomic-layer-thick phase, where segregation has occurred, compared to the approximately 35-atomic-layer-thick bulk phase of the same crystal structure. First-principles predictions of bulk free energies in conjunction with direct atomistic simulations of the intermetallic structure and chemistry demonstrate the breakdown of bulk thermodynamics at nanometer dimensions and highlight the importance of symmetry breaking due to the proximity of interfaces in determining equilibrium properties.

Impacts of Thermal Atomic Layer-Deposited AlN Passivation Layer on GaN-on-Si High Electron Mobility Transistors.

PubMed

Zhao, Sheng-Xun; Liu, Xiao-Yong; Zhang, Lin-Qing; Huang, Hong-Fan; Shi, Jin-Shan; Wang, Peng-Fei

2016-12-01

Thermal atomic layer deposition (ALD)-grown AlN passivation layer is applied on AlGaN/GaN-on-Si HEMT, and the impacts on drive current and leakage current are investigated. The thermal ALD-grown 30-nm amorphous AlN results in a suppressed off-state leakage; however, its drive current is unchanged. It was also observed by nano-beam diffraction method that thermal ALD-amorphous AlN layer barely enhanced the polarization. On the other hand, the plasma-enhanced chemical vapor deposition (PECVD)-deposited SiN layer enhanced the polarization and resulted in an improved drive current. The capacitance-voltage (C-V) measurement also indicates that thermal ALD passivation results in a better interface quality compared with the SiN passivation.

Corrosion resistance of monolayer hexagonal boron nitride on copper

PubMed Central

Mahvash, F.; Eissa, S.; Bordjiba, T.; Tavares, A. C.; Szkopek, T.; Siaj, M.

2017-01-01

Hexagonal boron nitride (hBN) is a layered material with high thermal and chemical stability ideal for ultrathin corrosion resistant coatings. Here, we report the corrosion resistance of Cu with hBN grown by chemical vapor deposition (CVD). Cyclic voltammetry measurements reveal that hBN layers inhibit Cu corrosion and oxygen reduction. We find that CVD grown hBN reduces the Cu corrosion rate by one order of magnitude compared to bare Cu, suggesting that this ultrathin layer can be employed as an atomically thin corrosion-inhibition coating. PMID:28191822

Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: opportunities and challenges.

PubMed

Duan, Xidong; Wang, Chen; Pan, Anlian; Yu, Ruqin; Duan, Xiangfeng

2015-12-21

The discovery of graphene has ignited intensive interest in two-dimensional layered materials (2DLMs). These 2DLMs represent a new class of nearly ideal 2D material systems for exploring fundamental chemistry and physics at the limit of single-atom thickness, and have the potential to open up totally new technological opportunities beyond the reach of existing materials. In general, there are a wide range of 2DLMs in which the atomic layers are weakly bonded together by van der Waals interactions and can be isolated into single or few-layer nanosheets. The van der Waals interactions between neighboring atomic layers could allow much more flexible integration of distinct materials to nearly arbitrarily combine and control different properties at the atomic scale. The transition metal dichalcogenides (TMDs) (e.g., MoS2, WSe2) represent a large family of layered materials, many of which exhibit tunable band gaps that can undergo a transition from an indirect band gap in bulk crystals to a direct band gap in monolayer nanosheets. These 2D-TMDs have thus emerged as an exciting class of atomically thin semiconductors for a new generation of electronic and optoelectronic devices. Recent studies have shown exciting potential of these atomically thin semiconductors, including the demonstration of atomically thin transistors, a new design of vertical transistors, as well as new types of optoelectronic devices such as tunable photovoltaic devices and light emitting devices. In parallel, there have also been considerable efforts in developing diverse synthetic approaches for the rational growth of various forms of 2D materials with precisely controlled chemical composition, physical dimension, and heterostructure interface. Here we review the recent efforts, progress, opportunities and challenges in exploring the layered TMDs as a new class of atomically thin semiconductors.

Chemical Composition of Surfaces of Polycrystalline Silver Held in Water Vapor

NASA Astrophysics Data System (ADS)

Ashkhotov, O. G.; Khubezhov, S. A.; Aleroev, M. A.; Grigorkina, G. S.; Ashkhotova, I. B.; Magkoev, T. T.; Bliev, A. P.; Ramonova, A. G.; Kibizov, D. D.

2018-01-01

The chemical composition of surfaces and near-surface layers of massive polycrystalline silver held in water vapor for 2 h at 1073 K is studied via Auger and X-ray photoelectron spectroscopy. It is shown that the oxygen on a surface is in the molecular state. In near-surface layers at depths of up to 8 nm, it is predominantly in the atomic state typical of chemisorbed Ag2O.

Rich interfacial chemistry and properties of carbon-doped hexagonal boron nitride nanosheets revealed by electronic structure calculations

NASA Astrophysics Data System (ADS)

Xie, Wei; Tamura, Takahiro; Yanase, Takashi; Nagahama, Taro; Shimada, Toshihiro

2018-04-01

The effect of C doping to hexagonal boron nitride (h-BN) to its electronic structure is examined by first principles calculations using the association from π-electron systems of organic molecules embedded in a two-dimensional insulator. In a monolayered carbon-doped structure, odd-number doping with carbon atoms confers metallic properties with different work functions. Various electronic interactions occur between two layers with odd-number carbon substitution. A direct sp3 covalent chemical bond is formed when C replaces adjacent B and N in different layers. A charge transfer complex between layers is found when C replaces B and N in the next-neighboring region, which results in narrower band gaps (e.g., 0.37 eV). Direct bonding between C and B atoms is found when two C atoms in different layers are at a certain distance.

FAST TRACK COMMUNICATION: Electronic structure of a graphene/hexagonal-BN heterostructure grown on Ru(0001) by chemical vapor deposition and atomic layer deposition: extrinsically doped graphene

NASA Astrophysics Data System (ADS)

Bjelkevig, Cameron; Mi, Zhou; Xiao, Jie; Dowben, P. A.; Wang, Lu; Mei, Wai-Ning; Kelber, Jeffry A.

2010-08-01

A significant BN-to-graphene charge donation is evident in the electronic structure of a graphene/h-BN(0001) heterojunction grown by chemical vapor deposition and atomic layer deposition directly on Ru(0001), consistent with density functional theory. This filling of the lowest unoccupied state near the Brillouin zone center has been characterized by combined photoemission/k vector resolved inverse photoemission spectroscopies, and Raman and scanning tunneling microscopy/spectroscopy. The unoccupied σ*(Γ1 +) band dispersion yields an effective mass of 0.05 me for graphene in the graphene/h-BN(0001) heterostructure, in spite of strong perturbations to the graphene conduction band edge placement.

Chemistry in protoplanetary disks

NASA Astrophysics Data System (ADS)

Semenov, D. A.

2012-01-01

In this lecture I discuss recent progress in the understanding of the chemical evolution of protoplanetary disks that resemble our Solar system during the first ten million years. At the verge of planet formation, strong variations of temperature, density, and radiation intensities in these disks lead to a layered chemical structure. In hot, dilute and heavily irradiated atmosphere only simple radicals, atoms, and atomic ions can survive, formed and destroyed by gas-phase processes. Beneath the atmosphere a partly UV-shielded, warm molecular layer is located, where high-energy radiation drives rich chemistry, both in the gas phase and on dust surfaces. In a cold, dense, dark disk midplane many molecules are frozen out, forming thick icy mantles where surface chemistry is active and where complex (organic) species are synthesized.

Chemically sensitive free-volume study of amorphization of Cu60Zr40 induced by cold rolling and folding

NASA Astrophysics Data System (ADS)

Puff, Werner; Rabitsch, Herbert; Wilde, Gerhard; Dinda, Guru P.; Würschum, Roland

2007-06-01

With the aim to contribute to a microscopical understanding of the processes of solid-state amorphization, the chemically sensitive technique of background—reduced Doppler broadening of positron-electron annihilation radiation in combination with positron lifetime spectroscopy and microstructural characterization is applied to a free volume study of the amorphization of Cu60Zr40 induced by consecutive folding and rolling. Starting from the constituent pure metal foils, a nanosale multilayer structure of elemental layers and amorphous interlayers develops in an intermediate state of folding and rolling, where free volumes with a Zr-rich environment occur presumably located in the hetero-interfaces between the various layers or in grain boundaries of the Cu layers. After complete intermixing and amorphization, the local chemical environment of the free volumes reflects the average chemical alloy composition. In contrast to other processes of amorphization, free volumes of the size of few missing atoms occur in the rolling-induced amorphous state. Self-consistent results from three different methods for analyzing the Doppler broadening spectra, i.e., S-W-parameter correlation, multicomponent fit, and the shape of ratio curves, demonstrate the potential of the background-reduced Doppler technique for chemically sensitive characterization of structurally complex materials on an atomic scale.

Reducing interface recombination for Cu(In,Ga)Se{sub 2} by atomic layer deposited buffer layers

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

Hultqvist, Adam; Bent, Stacey F.; Li, Jian V.

2015-07-20

Partial CuInGaSe{sub 2} (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnO{sub x} buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystallinemore » II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Reducing interface recombination for Cu(In,Ga)Se 2 by atomic layer deposited buffer layers

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

Hultqvist, Adam; Li, Jian V.; Kuciauskas, Darius

2015-07-20

Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II-VImore » systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Reducing interface recombination for Cu(In,Ga)Se 2 by atomic layer deposited buffer layers

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

Hultqvist, Adam; Li, Jian V.; Kuciauskas, Darius

2015-07-20

Partial CuInGaSe2 (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnOx buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VImore » systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.« less

Atomic scale imaging of competing polar states in a Ruddlesden-Popper layered oxide.

PubMed

Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J; Schlom, Darrell G; Alem, Nasim; Gopalan, Venkatraman

2016-08-31

Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.

Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

PubMed Central

Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J.; Schlom, Darrell G.; Alem, Nasim; Gopalan, Venkatraman

2016-01-01

Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden–Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure. PMID:27578622

Atomic scale imaging of competing polar states in a Ruddlesden-Popper layered oxide

NASA Astrophysics Data System (ADS)

Stone, Greg; Ophus, Colin; Birol, Turan; Ciston, Jim; Lee, Che-Hui; Wang, Ke; Fennie, Craig J.; Schlom, Darrell G.; Alem, Nasim; Gopalan, Venkatraman

2016-08-01

Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), An+1BnO3n+1, thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Srn+1TinO3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases. We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.

Low-frequency Raman fingerprints of two-dimensional metal dichalcogenide layer stacking configurations

DOE PAGES

Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan; ...

2015-05-12

In this study, stacked monolayers of two-dimensional (2D) materials present a new class of hybrid materials with tunable optoelectronic properties determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks, however fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe 2 and WSe 2 crystals synthesized by chemical vapor deposition we show that the generally unexplored low frequency (LF) Raman modes (< 50more » cm -1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.« less

Low-Temperature Process for Atomic Layer Chemical Vapor Deposition of an Al2O3 Passivation Layer for Organic Photovoltaic Cells.

PubMed

Kim, Hoonbae; Lee, Jihye; Sohn, Sunyoung; Jung, Donggeun

2016-05-01

Flexible organic photovoltaic (OPV) cells have drawn extensive attention due to their light weight, cost efficiency, portability, and so on. However, OPV cells degrade quickly due to organic damage by water vapor or oxygen penetration when the devices are driven in the atmosphere without a passivation layer. In order to prevent damage due to water vapor or oxygen permeation into the devices, passivation layers have been introduced through methods such as sputtering, plasma enhanced chemical vapor deposition, and atomic layer chemical vapor deposition (ALCVD). In this work, the structural and chemical properties of Al2O3 films, deposited via ALCVD at relatively low temperatures of 109 degrees C, 200 degrees C, and 300 degrees C, are analyzed. In our experiment, trimethylaluminum (TMA) and H2O were used as precursors for Al2O3 film deposition via ALCVD. All of the Al2O3 films showed very smooth, featureless surfaces without notable defects. However, we found that the plastic flexible substrate of an OPV device passivated with 300 degrees C deposition temperature was partially bended and melted, indicating that passivation layers for OPV cells on plastic flexible substrates need to be formed at temperatures lower than 300 degrees C. The OPV cells on plastic flexible substrates were passivated by the Al2O3 film deposited at the temperature of 109 degrees C. Thereafter, the photovoltaic properties of passivated OPV cells were investigated as a function of exposure time under the atmosphere.

Remote catalyzation for direct formation of graphene layers on oxides.

PubMed

Teng, Po-Yuan; Lu, Chun-Chieh; Akiyama-Hasegawa, Kotone; Lin, Yung-Chang; Yeh, Chao-Hui; Suenaga, Kazu; Chiu, Po-Wen

2012-03-14

Direct deposition of high-quality graphene layers on insulating substrates such as SiO(2) paves the way toward the development of graphene-based high-speed electronics. Here, we describe a novel growth technique that enables the direct deposition of graphene layers on SiO(2) with crystalline quality potentially comparable to graphene grown on Cu foils using chemical vapor deposition (CVD). Rather than using Cu foils as substrates, our approach uses them to provide subliming Cu atoms in the CVD process. The prime feature of the proposed technique is remote catalyzation using floating Cu and H atoms for the decomposition of hydrocarbons. This allows for the direct graphitization of carbon radicals on oxide surfaces, forming isolated low-defect graphene layers without the need for postgrowth etching or evaporation of the metal catalyst. The defect density of the resulting graphene layers can be significantly reduced by tuning growth parameters such as the gas ratios, Cu surface areas, and substrate-to-Cu distance. Under optimized conditions, graphene layers with nondiscernible Raman D peaks can be obtained when predeposited graphite flakes are used as seeds for extended growth. © 2012 American Chemical Society

Atom-scale depth localization of biologically important chemical elements in molecular layers

PubMed Central

Schneck, Emanuel; Scoppola, Ernesto; Drnec, Jakub; Mocuta, Cristian; Felici, Roberto; Novikov, Dmitri; Fragneto, Giovanna; Daillant, Jean

2016-01-01

In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers’ global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces. PMID:27503887

Atomically Thin Hexagonal Boron Nitride Nanofilm for Cu Protection: The Importance of Film Perfection.

PubMed

Khan, Majharul Haque; Jamali, Sina S; Lyalin, Andrey; Molino, Paul J; Jiang, Lei; Liu, Hua Kun; Taketsugu, Tetsuya; Huang, Zhenguo

2017-01-01

Outstanding protection of Cu by high-quality boron nitride nanofilm (BNNF) 1-2 atomic layers thick in salt water is observed, while defective BNNF accelerates the reaction of Cu toward water. The chemical stability, insulating nature, and impermeability of ions through the BN hexagons render BNNF a great choice for atomic-scale protection. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fabricating Large-Area Sheets of Single-Layer Graphene by CVD

NASA Technical Reports Server (NTRS)

Bronikowski, Michael; Manohara, Harish

2008-01-01

This innovation consists of a set of methodologies for preparing large area (greater than 1 cm(exp 2)) domains of single-atomic-layer graphite, also called graphene, in single (two-dimensional) crystal form. To fabricate a single graphene layer using chemical vapor deposition (CVD), the process begins with an atomically flat surface of an appropriate substrate and an appropriate precursor molecule containing carbon atoms attached to substituent atoms or groups. These molecules will be brought into contact with the substrate surface by being flowed over, or sprayed onto, the substrate, under CVD conditions of low pressure and elevated temperature. Upon contact with the surface, the precursor molecules will decompose. The substituent groups detach from the carbon atoms and form gas-phase species, leaving the unfunctionalized carbon atoms attached to the substrate surface. These carbon atoms will diffuse upon this surface and encounter and bond to other carbon atoms. If conditions are chosen carefully, the surface carbon atoms will arrange to form the lowest energy single-layer structure available, which is the graphene lattice that is sought. Another method for creating the graphene lattice includes metal-catalyzed CVD, in which the decomposition of the precursor molecules is initiated by the catalytic action of a catalytic metal upon the substrate surface. Another type of metal-catalyzed CVD has the entire substrate composed of catalytic metal, or other material, either as a bulk crystal or as a think layer of catalyst deposited upon another surface. In this case, the precursor molecules decompose directly upon contact with the substrate, releasing their atoms and forming the graphene sheet. Atomic layer deposition (ALD) can also be used. In this method, a substrate surface at low temperature is covered with exactly one monolayer of precursor molecules (which may be of more than one type). This is heated up so that the precursor molecules decompose and form one monolayer of the target material.

Characterization of Ultrathin Ta-oxide Films Formed on Ge(100) by ALD and Layer-by-Layer Methods

NASA Astrophysics Data System (ADS)

Mishima, K.; Murakami, H.; Ohta, A.; Sahari, S. K.; Fujioka, T.; Higashi, S.; Miyazaki, S.

2013-03-01

Atomic layer deposition (ALD) and Layer-by-Layer deposition of Ta-oxide films on Ge(100) with using tris (tert-butoxy) (tert-butylimido) tantalum have been studied systematically. From the analysis of the chemical bonding features of the interface between TaOx and Ge(100) using x-ray photoelectron spectroscopy (XPS), Ge atom diffusion into the Ta oxide layer and resultant TaGexOy formation during deposition at temperatures higher than 200°C were confirmed. Also, we have demonstrated that nanometer-thick deposition of Tantalum oxide as an interfacial layer effectively suppresses the formation of GeOx in the HfO2 ALD on Ge. By the combination of TaOx pre-deposition on Ge(100) and subsequent ALD of HfO2, a capacitance equivalent thickness (CET) of 1.35 nm and relative dielectric constant of 23 were achieved.

Nanostructure templating using low temperature atomic layer deposition

DOEpatents

Grubbs, Robert K [Albuquerque, NM; Bogart, Gregory R [Corrales, NM; Rogers, John A [Champaign, IL

2011-12-20

Methods are described for making nanostructures that are mechanically, chemically and thermally stable at desired elevated temperatures, from nanostructure templates having a stability temperature that is less than the desired elevated temperature. The methods comprise depositing by atomic layer deposition (ALD) structural layers that are stable at the desired elevated temperatures, onto a template employing a graded temperature deposition scheme. At least one structural layer is deposited at an initial temperature that is less than or equal to the stability temperature of the template, and subsequent depositions made at incrementally increased deposition temperatures until the desired elevated temperature stability is achieved. Nanostructure templates include three dimensional (3D) polymeric templates having features on the order of 100 nm fabricated by proximity field nanopatterning (PnP) methods.

Perspective: Maintaining surface-phase purity is key to efficient open air fabricated cuprous oxide solar cells

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

Hoye, Robert L. Z., E-mail: rlzh2@cam.ac.uk, E-mail: jld35@cam.ac.uk; Ievskaya, Yulia; MacManus-Driscoll, Judith L., E-mail: rlzh2@cam.ac.uk, E-mail: jld35@cam.ac.uk

2015-02-01

Electrochemically deposited Cu{sub 2}O solar cells are receiving growing attention owing to a recent doubling in efficiency. This was enabled by the controlled chemical environment used in depositing doped ZnO layers by atomic layer deposition, which is not well suited to large-scale industrial production. While open air fabrication with atmospheric pressure spatial atomic layer deposition overcomes this limitation, we find that this approach is limited by an inability to remove the detrimental CuO layer that forms on the Cu{sub 2}O surface. Herein, we propose strategies for achieving efficiencies in atmospherically processed cells that are equivalent to the high values achievedmore » in vacuum processed cells.« less

Parametric Investigation of the Isothermal Kinetics of Growth of Graphene on a Nickel Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

NASA Astrophysics Data System (ADS)

Futko, S. I.; Shulitskii, B. G.; Labunov, V. A.; Ermolaeva, E. M.

2016-11-01

A kinetic model of isothermal synthesis of multilayer graphene on the surface of a nickel foil in the process of chemical vapor deposition, on it, of hydrocarbons supplied in the pulsed regime is considered. The dependences of the number of graphene layers formed and the time of their growth on the temperature of the process, the concentration of acetylene, and the thickness of the nickel foil were calculated. The regime parameters of the process of chemical vapor deposition, at which single-layer graphene and bi-layer graphene are formed, were determined. The dynamics of growth of graphene domains at chemical-vapor-deposition parameters changing in wide ranges was investigated. It is shown that the time dependences of the rates of growth of single-layer graphene and bi-layer graphene are nonlinear in character and that they are determined by the kinetics of nucleation and growth of graphene and the diffusion flow of carbon atoms in the nickel foil.

Formation of atomically smooth epitaxial metal films on a chemically reactive interface: Mg on Si(111)

NASA Astrophysics Data System (ADS)

Özer, Mustafa M.; Weitering, Hanno H.

2013-07-01

Deposition of Mg on Si(111)7 × 7 produces an epitaxial magnesium silicide layer. Under identical annealing conditions, the thickness of this Mg2Si(111) layer increases with deposition amount, reaching a maximum of 4 monolayer (ML) and decreasing to ˜3 ML at higher Mg coverage. Excess Mg coalesces into atomically flat, crystalline Mg(0001) films. This surprising growth mode can be attributed to the accidental commensurability of the Mg(0001), Si(111), and Mg2Si(111) interlayer spacing and the concurrent minimization of in-plane Si mass transfer and domain-wall energies. The commensurability of the interlayer spacing defines a highly unique solid-phase epitaxial growth process capable of producing trilayer structures with atomically abrupt interfaces and atomically smooth surface morphologies.

The remarkable chemical uniformity of Apollo 16 layered deep drill core section 60002

NASA Technical Reports Server (NTRS)

Nava, D. F.; Philpotts, J. A.; Lindstrom, M. M.; Schuhmann, P. J.; Lindstrom, D. J.

1976-01-01

Atomic absorption and colorimetric spectrophotometers were used to determine major- and minor-element abundances in 12 samples from layered section 60002 of the Apollo 16 deep drill core. It is suggested that gardening of a relatively thick local unit produced the layering in this section in such a manner that the proportions of materials of different compositions remained virtually unchanged.

Surface characterization of Nb samples electropolished together with real superconducting rf accelerator cavities

DOE PAGES

Xin Zhao; Geng, Rong -Li; Tyagi, P. V.; ...

2010-12-30

Here, we report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris and the beam-pipe. Auger electron spectroscopy (AES) was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive X-ray for elemental analysis (SEM/EDX) was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples non-uniformly. Niobium oxide granulesmore » with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.« less

Atomic-scale and pit-free flattening of GaN by combination of plasma pretreatment and time-controlled chemical mechanical polishing

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

Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya, E-mail: yamamura@upst.eng.osaka-u.ac.jp

2015-08-03

Chemical mechanical polishing (CMP) combined with atmospheric-pressure plasma pretreatment was applied to a GaN (0001) substrate. The irradiation of a CF{sub 4}-containing plasma was proven to be very useful for modifying the surface of GaN. When CMP was conducted on a plasma-irradiated surface, a modified layer of GaF{sub 3} acted as a protective layer on GaN by preventing the formation of etch pits. Within a short duration (8 min) of CMP using a commercially available CeO{sub 2} slurry, an atomically flat surface with a root mean square (rms) roughness of 0.11 nm was obtained. Moreover, etch pits, which are inevitably introduced inmore » conventional CMP, could not be observed at the dislocation sites on the polished GaN surface. It was revealed that CMP combined with the plasma pretreatment was very effective for obtaining a pit-free and atomically flat GaN surface.« less

Direct observation of interfacial Au atoms on TiO₂ in three dimensions.

PubMed

Gao, Wenpei; Sivaramakrishnan, Shankar; Wen, Jianguo; Zuo, Jian-Min

2015-04-08

Interfacial atoms, which result from interactions between the metal nanoparticles and support, have a large impact on the physical and chemical properties of nanoparticles. However, they are difficult to observe; the lack of knowledge has been a major obstacle toward unraveling their role in chemical transformations. Here we report conclusive evidence of interfacial Au atoms formed on the rutile (TiO2) (110) surfaces by activation using high-temperature (∼500 °C) annealing in air. Three-dimensional imaging was performed using depth-sectioning enabled by aberration-corrected scanning transmission electron microscopy. Results show that the interface between Au nanocrystals and TiO2 (110) surfaces consists of a single atomic layer with Au atoms embedded inside Ti-O. The number of interfacial Au atoms is estimated from ∼1-8 in an interfacial atomic column. Direct impact of interfacial Au atoms is observed on an enhanced Au-TiO2 interaction and the reduction of surface TiO2; both are critical to Au catalysis.

Low-temperature ({<=}200 Degree-Sign C) plasma enhanced atomic layer deposition of dense titanium nitride thin films

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

Samal, Nigamananda; Du Hui; Luberoff, Russell

Titanium nitride (TiN) has been widely used in the semiconductor industry for its diffusion barrier and seed layer properties. However, it has seen limited adoption in other industries in which low temperature (<200 Degree-Sign C) deposition is a requirement. Examples of applications which require low temperature deposition are seed layers for magnetic materials in the data storage (DS) industry and seed and diffusion barrier layers for through-silicon-vias (TSV) in the MEMS industry. This paper describes a low temperature TiN process with appropriate electrical, chemical, and structural properties based on plasma enhanced atomic layer deposition method that is suitable for themore » DS and MEMS industries. It uses tetrakis-(dimethylamino)-titanium as an organometallic precursor and hydrogen (H{sub 2}) as co-reactant. This process was developed in a Veeco NEXUS Trade-Mark-Sign chemical vapor deposition tool. The tool uses a substrate rf-biased configuration with a grounded gas shower head. In this paper, the complimentary and self-limiting character of this process is demonstrated. The effects of key processing parameters including temperature, pulse time, and plasma power are investigated in terms of growth rate, stress, crystal morphology, chemical, electrical, and optical properties. Stoichiometric thin films with growth rates of 0.4-0.5 A/cycle were achieved. Low electrical resistivity (<300 {mu}{Omega} cm), high mass density (>4 g/cm{sup 3}), low stress (<250 MPa), and >85% step coverage for aspect ratio of 10:1 were realized. Wet chemical etch data show robust chemical stability of the film. The properties of the film have been optimized to satisfy industrial viability as a Ruthenium (Ru) preseed liner in potential data storage and TSV applications.« less

Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

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

Choudhary, B. S.; Rajasthan Technical University, Rawatbhata Road, Kota 324010; Singh, A.

We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surfacemore » with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.« less

CVD synthesis of large-area, highly crystalline MoSe2 atomic layers on diverse substrates and application to photodetectors.

PubMed

Xia, Jing; Huang, Xing; Liu, Ling-Zhi; Wang, Meng; Wang, Lei; Huang, Ben; Zhu, Dan-Dan; Li, Jun-Jie; Gu, Chang-Zhi; Meng, Xiang-Min

2014-08-07

Synthesis of large-area, atomically thin transition metal dichalcogenides (TMDs) on diverse substrates is of central importance for the large-scale fabrication of flexible devices and heterojunction-based devices. In this work, we successfully synthesized a large area of highly-crystalline MoSe2 atomic layers on SiO2/Si, mica and Si substrates using a simple chemical vapour deposition (CVD) method at atmospheric pressure. Atomic force microscopy (AFM) and Raman spectroscopy reveal that the as-grown ultrathin MoSe2 layers change from a single layer to a few layers. Photoluminescence (PL) spectroscopy demonstrates that while the multi-layer MoSe2 shows weak emission peaks, the monolayer has a much stronger emission peak at ∼ 1.56 eV, indicating the transition from an indirect to a direct bandgap. Transmission electron microscopy (TEM) analysis confirms the single-crystallinity of MoSe2 layers with a hexagonal structure. In addition, the photoresponse performance of photodetectors based on MoSe2 monolayer was studied for the first time. The devices exhibit a rapid response of ∼ 60 ms and a good photoresponsivity of ∼ 13 mA/W (using a 532 nm laser at an intensity of 1 mW mm(-2) and a bias of 10 V), suggesting that MoSe2 monolayer is a promising material for photodetection applications.

Enhancement of the emission efficiency of InGaN films by suppressing the incorporation of unintentional gallium atoms

NASA Astrophysics Data System (ADS)

Yang, J.; Liu, S. T.; Wang, X. W.; Zhao, D. G.; Jiang, D. S.; Chen, P.; Zhu, J. J.; Liu, Z. S.; Liang, F.; Liu, W.; Zhang, L. Q.; Yang, H.; Wang, W. J.; Li, M.

2018-01-01

InGaN samples are grown using metalorganic chemical vapor deposition (MOCVD) and the dependences of structural and luminescence properties of InGaN layers on growth temperature are studied. It is found that the luminescence properties of InGaN layer are improved by increasing growth temperature properly. However, when the growth temperature of InGaN layer is too higher (740 °C in our work), a large amount of unintentionally incorporated gallium atoms enter into InGaN, and a spiral growth mode dominates in this case. It results in an inferior crystalline and interface quality, and ultimately degrades the luminescence of InGaN.

Interpenetration of a 3D Icosahedral M@Ni12 (M=Al, Ga) Framework with Porphyrin-Reminiscent Boron Layers in MNi9 B8.

PubMed

Zheng, Qiang; Wagner, Frank R; Ormeci, Alim; Prots, Yurii; Burkhardt, Ulrich; Schmidt, Marcus; Schnelle, Walter; Grin, Yuri; Leithe-Jasper, Andreas

2015-11-09

Two ternary borides MNi9 B8 (M=Al, Ga) were synthesized by thermal treatment of mixtures of the elements. Single-crystal X-ray diffraction data reveal AlNi9 B8 and GaNi9 B8 crystallizing in a new type of structure within the space group Cmcm and the lattice parameters a=7.0896(3) Å, b=8.1181(3) Å, c=10.6497(4) Å and a=7.0897(5) Å, b=8.1579(4) Å, c=10.6648(7) Å, respectively. The boron atoms build up two-dimensional layers, which consist of puckered [B16 ] rings with two tailing B atoms, whereas the M atoms reside in distorted vertices-condensed [Ni12 ] icosahedra, which form a three-dimensional framework interpenetrated by boron porphyrin-reminiscent layers. An unusual local arrangement resembling a giant metallo-porphyrin entity is formed by the [B16 ] rings, which, due to their large annular size of approximately 8 Å, chelate four of the twelve icosahedral Ni atoms. An analysis of the chemical bonding by means of the electron localizability approach reveals strong covalent B-B interactions and weak Ni-Ni interactions. Multi-center dative B-Ni interaction occurs between the Al-Ni framework and the boron layers. In agreement with the chemical bonding analysis and band structure calculations, AlNi9 B8 is a Pauli-paramagnetic metal. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron-stimulated reactions in layered CO/H2O films: Hydrogen atom diffusion and the sequential hydrogenation of CO to methanol

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

Petrik, Nikolay G.; Monckton, Rhiannon J.; Koehler, Sven

Low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices are investigated. For CO trapped within approximately 50 ML of the vacuum interface in the amorphous solid water (ASW) films, both oxidation and reduction reactions are observed. However for CO buried more deeply in the film, only the reduction of CO to methanol is observed. Experiments with layered films of H2O and D2O show that the hydrogen atoms participating in the reduction of the buried CO originate in region from ~10 – 40 ML below the surface of the ASW films and subsequently diffuse through the film. For deeply buried COmore » layers, the CO reduction reactions quickly increase with temperature above ~60 K. We present a simple chemical kinetic model that treats the diffusion of hydrogen atoms in the ASW and sequential hydrogenation of the CO to methanol that accounts for the observations.« less

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

Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan

In this study, stacked monolayers of two-dimensional (2D) materials present a new class of hybrid materials with tunable optoelectronic properties determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks, however fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe 2 and WSe 2 crystals synthesized by chemical vapor deposition we show that the generally unexplored low frequency (LF) Raman modes (< 50more » cm -1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.« less

Few-layer graphene growth from polystyrene as solid carbon source utilizing simple APCVD method

NASA Astrophysics Data System (ADS)

Ahmadi, Shahrokh; Afzalzadeh, Reza

2016-07-01

This research article presents development of an economical, simple, immune and environment friendly process to grow few-layer graphene by controlling evaporation rate of polystyrene on copper foil as catalyst and substrate utilizing atmospheric pressure chemical vapor deposition (APCVD) method. Evaporation rate of polystyrene depends on molecular structure, amount of used material and temperature. We have found controlling rate of evaporation of polystyrene by controlling the source temperature is easier than controlling the material weight. Atomic force microscopy (AFM) as well as Raman Spectroscopy has been used for characterization of the layers. The frequency of G‧ to G band ratio intensity in some samples varied between 0.8 and 1.6 corresponding to few-layer graphene. Topography characterization by atomic force microscopy confirmed Raman results.

SERS Taper-Fiber Nanoprobe Modified by Gold Nanoparticles Wrapped with Ultrathin Alumina Film by Atomic Layer Deposition

PubMed Central

Xu, Wenjie; Chen, Zhenyi; Chen, Na; Zhang, Heng; Liu, Shupeng; Hu, Xinmao; Wen, Jianxiang; Wang, Tingyun

2017-01-01

A taper-fiber SERS nanoprobe modified by gold nanoparticles (Au-NPs) with ultrathin alumina layers was fabricated and its ability to perform remote Raman detection was demonstrated. The taper-fiber nanoprobe (TFNP) with a nanoscale tip size under 80 nm was made by heated pulling combined with the chemical etching method. The Au-NPs were deposited on the TFNP surface with the electrostatic self-assembly technology, and then the TFNP was wrapped with ultrathin alumina layers by the atomic layer deposition (ALD) technique. The results told us that with the increasing thickness of the alumina film, the Raman signals decreased. With approximately 1 nm alumina film, the remote detection limit for R6G aqueous solution reached 10−6 mol/L. PMID:28245618

The study of metal sulphide nanomaterials obtained by chemical bath deposition and hot-injection technique

NASA Astrophysics Data System (ADS)

Maraeva, E. V.; Alexandrova, O. A.; Forostyanaya, N. A.; Levitskiy, V. S.; Mazing, D. S.; Maskaeva, L. N.; Markov, V. Ph; Moshnikov, V. A.; Shupta, A. A.; Spivak, Yu M.; Tulenin, S. S.

2015-11-01

In this study lead sulphide - cadmium sulphide based layers were obtained through chemical deposition of water solutions and cadmium sulphide quantum dots were formed through hot-injection technique. The article discusses the results of surface investigations with the use of atomic force microscopy, Raman spectroscopy and photoluminescence measurements.

Atomic layer deposited oxide films as protective interface layers for integrated graphene transfer

NASA Astrophysics Data System (ADS)

Cabrero-Vilatela, A.; Alexander-Webber, J. A.; Sagade, A. A.; Aria, A. I.; Braeuninger-Weimer, P.; Martin, M.-B.; Weatherup, R. S.; Hofmann, S.

2017-12-01

The transfer of chemical vapour deposited graphene from its parent growth catalyst has become a bottleneck for many of its emerging applications. The sacrificial polymer layers that are typically deposited onto graphene for mechanical support during transfer are challenging to remove completely and hence leave graphene and subsequent device interfaces contaminated. Here, we report on the use of atomic layer deposited (ALD) oxide films as protective interface and support layers during graphene transfer. The method avoids any direct contact of the graphene with polymers and through the use of thicker ALD layers (≥100 nm), polymers can be eliminated from the transfer-process altogether. The ALD film can be kept as a functional device layer, facilitating integrated device manufacturing. We demonstrate back-gated field effect devices based on single-layer graphene transferred with a protective Al2O3 film onto SiO2 that show significantly reduced charge trap and residual carrier densities. We critically discuss the advantages and challenges of processing graphene/ALD bilayer structures.

Atomic scale imaging of competing polar states in a Ruddlesden–Popper layered oxide

DOE PAGES

Stone, Greg; Ophus, Colin; Birol, Turan; ...

2016-08-31

Layered complex oxides offer an unusually rich materials platform for emergent phenomena through many built-in design knobs such as varied topologies, chemical ordering schemes and geometric tuning of the structure. A multitude of polar phases are predicted to compete in Ruddlesden-Popper (RP), A n+1 B n O 3n+1 , thin films by tuning layer dimension (n) and strain; however, direct atomic-scale evidence for such competing states is currently absent. Using aberration-corrected scanning transmission electron microscopy with sub-Ångstrom resolution in Sr n+1 Ti n O 3n+1 thin films, we demonstrate the coexistence of antiferroelectric, ferroelectric and new ordered and low-symmetry phases.more » We also directly image the atomic rumpling of the rock salt layer, a critical feature in RP structures that is responsible for the competing phases; exceptional quantitative agreement between electron microscopy and density functional theory is demonstrated. The study shows that layered topologies can enable multifunctionality through highly competitive phases exhibiting diverse phenomena in a single structure.« less

Environmental sensing with optical fiber sensors processed with focused ion beam and atomic layer deposition

NASA Astrophysics Data System (ADS)

Flores, Raquel; Janeiro, Ricardo; Dahlem, Marcus; Viegas, Jaime

2015-03-01

We report an optical fiber chemical sensor based on a focused ion beam processed optical fiber. The demonstrated sensor is based on a cavity formed onto a standard 1550 nm single-mode fiber by either chemical etching, focused ion beam milling (FIB) or femtosecond laser ablation, on which side channels are drilled by either ion beam milling or femtosecond laser irradiation. The encapsulation of the cavity is achieved by optimized fusion splicing onto a standard single or multimode fiber. The empty cavity can be used as semi-curved Fabry-Pérot resonator for gas or liquid sensing. Increased reflectivity of the formed cavity mirrors can be achieved with atomic layer deposition (ALD) of alternating metal oxides. For chemical selective optical sensors, we demonstrate the same FIB-formed cavity concept, but filled with different materials, such as polydimethylsiloxane (PDMS), poly(methyl methacrylate) (PMMA) which show selective swelling when immersed in different solvents. Finally, a reducing agent sensor based on a FIB formed cavity partially sealed by fusion splicing and coated with a thin ZnO layer by ALD is presented and the results discussed. Sensor interrogation is achieved with spectral or multi-channel intensity measurements.

Large scale atomistic simulation of single-layer graphene growth on Ni(111) surface: molecular dynamics simulation based on a new generation of carbon-metal potential

NASA Astrophysics Data System (ADS)

Xu, Ziwei; Yan, Tianying; Liu, Guiwu; Qiao, Guanjun; Ding, Feng

2015-12-01

To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results.To explore the mechanism of graphene chemical vapor deposition (CVD) growth on a catalyst surface, a molecular dynamics (MD) simulation of carbon atom self-assembly on a Ni(111) surface based on a well-designed empirical reactive bond order potential was performed. We simulated single layer graphene with recorded size (up to 300 atoms per super-cell) and reasonably good quality by MD trajectories up to 15 ns. Detailed processes of graphene CVD growth, such as carbon atom dissolution and precipitation, formation of carbon chains of various lengths, polygons and small graphene domains were observed during the initial process of the MD simulation. The atomistic processes of typical defect healing, such as the transformation from a pentagon into a hexagon and from a pentagon-heptagon pair (5|7) to two adjacent hexagons (6|6), were revealed as well. The study also showed that higher temperature and longer annealing time are essential to form high quality graphene layers, which is in agreement with experimental reports and previous theoretical results. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06016h

2D Heterostructure coatings of hBN-MoS2 layers for corrosion resistance

NASA Astrophysics Data System (ADS)

Vandana, Sajith; Kochat, Vidya; Lee, Jonghoon; Varshney, Vikas; Yazdi, Sadegh; Shen, Jianfeng; Kosolwattana, Suppanat; Vinod, Soumya; Vajtai, Robert; Roy, Ajit K.; Sekhar Tiwary, Chandra; Ajayan, P. M.

2017-02-01

Heterostructures of atomically thin 2D materials could have improved physical, mechanical and chemical properties as compared to its individual components. Here we report, the effect of heterostructure coatings of hBN and MoS2 on the corrosion behavior as compared to coatings employing the individual 2D layer compositions. The poor corrosion resistance of MoS2 (widely used as wear resistant coating) can be improved by incorporating hBN sheets. Depending on the atomic stacking of the 2D sheets, we can further engineer the corrosion resistance properties of these coatings. A detailed spectroscopy and microscopy analysis has been used to characterize the different combinations of layered coatings. Detailed DFT based calculation reveals that the effect on the electrical properties due to atomic stacking is one of the major reasons for the improvement seen in corrosion resistance.

Comparison of precursor infiltration into polymer thin films via atomic layer deposition and sequential vapor infiltration using in-situ quartz crystal microgravimetry

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

Padbury, Richard P.; Jur, Jesse S., E-mail: jsjur@ncsu.edu

Previous research exploring inorganic materials nucleation behavior on polymers via atomic layer deposition indicates the formation of hybrid organic–inorganic materials that form within the subsurface of the polymer. This has inspired adaptations to the process, such as sequential vapor infiltration, which enhances the diffusion of organometallic precursors into the subsurface of the polymer to promote the formation of a hybrid organic–inorganic coating. This work highlights the fundamental difference in mass uptake behavior between atomic layer deposition and sequential vapor infiltration using in-situ methods. In particular, in-situ quartz crystal microgravimetry is used to compare the mass uptake behavior of trimethyl aluminummore » in poly(butylene terephthalate) and polyamide-6 polymer thin films. The importance of trimethyl aluminum diffusion into the polymer subsurface and the subsequent chemical reactions with polymer functional groups are discussed.« less

A Hybrid Density Functional Study of Atomic Hydrogen and Oxygen Adsorptions on the (0001) Surface of Non-Magnetic DHCP Americium

NASA Astrophysics Data System (ADS)

Amdani-Moten, Shafaq; Atta-Fynn, Raymond; Ray, Asok

2010-03-01

As our group have recently shown^+, hybrid density functional theory (HDFT) which replaces a fraction (40%) of approximate DFT exchange with exact Hartree-Fock exchange yield structural, magnetic, and electronic properties for Americium-I that are in excellent agreement with experimental data. As a natural progression, ab initio calculations for atomic adsorptions on the (0001) surface of non-magnetic americium have been performed using HDFT. The americium surface is modeled by a seven-layer slab using inversion symmetry consisting of one atom per layer and non-magnetic ABAC stacking arrangement of these layers. Top, bridge, hcp and fcc chemisorption sites have been investigated with energies optimized with respect to the adatom distance from the surface. Details of the chemisorptions processes as well as comparisons of different sites will be presented. ^+ R. Atta-Fynn and A. K. Ray, Chemical Physics Letters, 482, 223-227 (2009).

Ultra-Shallow Depth Profiling of Arsenic Implants in Silicon by Hydride Generation-Inductively Coupled Plasma Atomic Emission Spectrometry

NASA Astrophysics Data System (ADS)

Matsubara, Atsuko; Kojima, Hisao; Itoga, Toshihiko; Kanehori, Keiichi

1995-08-01

High resolution depth profiling of arsenic (As) implanted into silicon wafers by a chemical technique is described. Silicon wafers are precisely etched through repeated oxidation by hydrogen peroxide solution and dissolution of the oxide by hydrofluoric acid solution. The etched silicon thickness is determined by inductively-coupled plasma atomic emission spectrometry (ICP-AES). Arsenic concentration is determined by hydride generation ICP-AES (HG-ICP-AES) with prereduction using potassium iodide. The detection limit of As in a 4-inch silicon wafer is 2.4×1018 atoms/cm3. The etched silicon thickness is controlled to less than 4±2 atomic layers. Depth profiling of an ultra-shallow As diffusion layer with the proposed method shows good agreement with profiling using the four-probe method or secondary ion mass spectrometry.

Electronic transport properties of graphene doped by gallium.

PubMed

Mach, J; Procházka, P; Bartošík, M; Nezval, D; Piastek, J; Hulva, J; Švarc, V; Konečný, M; Kormoš, L; Šikola, T

2017-10-13

In this work we present the effect of low dose gallium (Ga) deposition (<4 ML) performed in UHV (10 -7 Pa) on the electronic doping and charge carrier scattering in graphene grown by chemical vapor deposition. In situ graphene transport measurements performed with a graphene field-effect transistor structure show that at low Ga coverages a graphene layer tends to be strongly n-doped with an efficiency of 0.64 electrons per one Ga atom, while the further deposition and Ga cluster formation results in removing electrons from graphene (less n-doping). The experimental results are supported by the density functional theory calculations and explained as a consequence of distinct interaction between graphene and Ga atoms in case of individual atoms, layers, or clusters.

Electronic transport properties of graphene doped by gallium

NASA Astrophysics Data System (ADS)

Mach, J.; Procházka, P.; Bartošík, M.; Nezval, D.; Piastek, J.; Hulva, J.; Švarc, V.; Konečný, M.; Kormoš, L.; Šikola, T.

2017-10-01

In this work we present the effect of low dose gallium (Ga) deposition (<4 ML) performed in UHV (10-7 Pa) on the electronic doping and charge carrier scattering in graphene grown by chemical vapor deposition. In situ graphene transport measurements performed with a graphene field-effect transistor structure show that at low Ga coverages a graphene layer tends to be strongly n-doped with an efficiency of 0.64 electrons per one Ga atom, while the further deposition and Ga cluster formation results in removing electrons from graphene (less n-doping). The experimental results are supported by the density functional theory calculations and explained as a consequence of distinct interaction between graphene and Ga atoms in case of individual atoms, layers, or clusters.

Thermal functionalization of GaN surfaces with 1-alkenes.

PubMed

Schwarz, Stefan U; Cimalla, Volker; Eichapfel, Georg; Himmerlich, Marcel; Krischok, Stefan; Ambacher, Oliver

2013-05-28

A thermally induced functionalization process for gallium nitride surfaces with 1-alkenes is introduced. The resulting functionalization layers are characterized with atomic force microscopy and X-ray photoelectron spectroscopy and compared to reference samples without and with a photochemically generated functionalization layer. The resulting layers show very promising characteristics as functionalization for GaN based biosensors. On the basis of the experimental results, important characteristics of the functionalization layers are estimated and a possible chemical reaction scheme is proposed.

Growth mechanism of Al2O3 film on an organic layer in plasma-enhanced atomic layer deposition

NASA Astrophysics Data System (ADS)

Lee, J. Y.; Kim, D. W.; Kang, W. S.; Lee, J. O.; Hur, M.; Han, S. H.

2018-01-01

Differences in the physical and chemical properties of Al2O3 films on a Si wafer and a C x H y layer were investigated in the case of plasma-enhanced atomic layer deposition. The Al2O3 film on the Si had a sharper interface and lower thickness than the Al2O3 film on the C x H y . The amount of carbon-impurity near the interface was larger for Al2O3 on the C x H y than for Al2O3 on the Si. In order to understand these differences, the concentrations of Al, O, C, and Si atoms through the Al2O3 films were evaluated by using x-ray photoelectron spectroscopy (XPS) depth profiling. The emission intensities of CO molecule were analyzed for different numbers of deposition cycles, by using time-resolved optical emission spectroscopy (OES). Finally, a growth mechanism for Al2O3 on an organic layer was proposed, based on the XPS and OES results for the Si wafer and the C x H y layer.

Effect of processing parameters on microstructure of MoS{sub 2} ultra-thin films synthesized by chemical vapor deposition method

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

Song, Yang; You, Suping; Sun, Kewei

2015-06-15

MoS{sub 2} ultra-thin layers are synthesized using a chemical vapor deposition method based on the sulfurization of molybdenum trioxide (MoO{sub 3}). The ultra-thin layers are characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy and atomic force microscope (AFM). Based on our experimental results, all the processing parameters, such as the tilt angle of substrate, applied voltage, heating time and the weight of source materials have effect on the microstructures of the layers. In this paper, the effects of such processing parameters on the crystal structures and morphologies of the as-grown layers are studied. It is found that the film obtainedmore » with the tilt angle of 0.06° is more uniform. A larger applied voltage is preferred to the growth of MoS{sub 2} thin films at a certain heating time. In order to obtain the ultra-thin layers of MoS{sub 2}, the weight of 0.003 g of source materials is preferred. Under our optimal experimental conditions, the surface of the film is smooth and composed of many uniformly distributed and aggregated particles, and the ultra-thin MoS{sub 2} atomic layers (1∼10 layers) covers an area of more than 2 mm×2 mm.« less

Chemically Layered Porous Solids

NASA Technical Reports Server (NTRS)

Koontz, Steve

1991-01-01

Aerogels and other porous solids in which surfaces of pores have chemical properties varying with depth below macroscopic surfaces prepared by sequences of chemical treatments. Porous glass or silica bead treated to make two depth zones having different chemical properties. Beads dropped along tube filled with flowing gas containing atomic oxygen, generated in microwave discharge. General class of materials treatable include oxides of aluminum, silicon, zirconium, tin, titanium, and nickel, and mixtures of these oxides. Potential uses of treated materials include chromatographic separations, membrane separations, controlled releases of chemicals, and catalysis.

Temperature dependence of the crystalline quality of AlN layer grown on sapphire substrates by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Li, Xiao-Hang; Wei, Yong O.; Wang, Shuo; Xie, Hongen; Kao, Tsung-Ting; Satter, Md. Mahbub; Shen, Shyh-Chiang; Douglas Yoder, P.; Detchprohm, Theeradetch; Dupuis, Russell D.; Fischer, Alec M.; Ponce, Fernando A.

2015-03-01

We studied temperature dependence of crystalline quality of AlN layers at 1050-1250 °C with a fine increment step of around 18 °C. The AlN layers were grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD) and characterized by X-ray diffraction (XRD) ω-scans and atomic force microscopy (AFM). At 1050-1068 °C, the templates exhibited poor quality with surface pits and higher XRD (002) and (102) full-width at half-maximum (FWHM) because of insufficient Al atom mobility. At 1086 °C, the surface became smooth suggesting sufficient Al atom mobility. Above 1086 °C, the (102) FWHM and thus edge dislocation density increased with temperatures which may be attributed to the shorter growth mode transition from three-dimension (3D) to two-dimension (2D). Above 1212 °C, surface macro-steps were formed due to the longer diffusion length of Al atoms than the expected step terrace width. The edge dislocation density increased rapidly above 1212 °C, indicating this temperature may be a threshold above which the impact of the transition from 3D to 2D is more significant. The (002) FWHM and thus screw dislocation density were insensitive to the temperature change. This study suggests that high-quality AlN/sapphire templates may be potentially achieved at temperatures as low as 1086 °C which is accessible by most of the III-nitride MOCVD systems.

Hydrodynamical instabilities induced by atomic diffusion in F and A stars : Impact on the opacity profile and asteroseimic age determination

NASA Astrophysics Data System (ADS)

Deal, M.; Richard, O.; Vauclair, S.

2017-12-01

Atomic diffusion, including the effect of radiative accelerations on individual elements, leads to important variations of the chemical composition inside the stars. The accumulation in specific layers of the elements, which are the main contributors of the local opacity, leads to hydrodynamical instabilities that modify the internal stellar structure and surface abundances. The modification of the initial chemical composition has important effects on the internal stellar mixing and leads to different surface and internal abundances of the elements. These processes also modify the age determination by asteroseismology.

Large-Area WS2 Film with Big Single Domains Grown by Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Liu, Pengyu; Luo, Tao; Xing, Jie; Xu, Hong; Hao, Huiying; Liu, Hao; Dong, Jingjing

2017-10-01

High-quality WS2 film with the single domain size up to 400 μm was grown on Si/SiO2 wafer by atmospheric pressure chemical vapor deposition. The effects of some important fabrication parameters on the controlled growth of WS2 film have been investigated in detail, including the choice of precursors, tube pressure, growing temperature, holding time, the amount of sulfur powder, and gas flow rate. By optimizing the growth conditions at one atmospheric pressure, we obtained tungsten disulfide single domains with an average size over 100 μm. Raman spectra, atomic force microscopy, and transmission electron microscopy provided direct evidence that the WS2 film had an atomic layer thickness and a single-domain hexagonal structure with a high crystal quality. And the photoluminescence spectra indicated that the tungsten disulfide films showed an evident layer-number-dependent fluorescence efficiency, depending on their energy band structure. Our study provides an important experimental basis for large-area, controllable preparation of atom-thick tungsten disulfide thin film and can also expedite the development of scalable high-performance optoelectronic devices based on WS2 film.

Optimization of ion-atomic beam source for deposition of GaN ultrathin films.

PubMed

Mach, Jindřich; Šamořil, Tomáš; Kolíbal, Miroslav; Zlámal, Jakub; Voborny, Stanislav; Bartošík, Miroslav; Šikola, Tomáš

2014-08-01

We describe the optimization and application of an ion-atomic beam source for ion-beam-assisted deposition of ultrathin films in ultrahigh vacuum. The device combines an effusion cell and electron-impact ion beam source to produce ultra-low energy (20-200 eV) ion beams and thermal atomic beams simultaneously. The source was equipped with a focusing system of electrostatic electrodes increasing the maximum nitrogen ion current density in the beam of a diameter of ≈15 mm by one order of magnitude (j ≈ 1000 nA/cm(2)). Hence, a successful growth of GaN ultrathin films on Si(111) 7 × 7 substrate surfaces at reasonable times and temperatures significantly lower (RT, 300 °C) than in conventional metalorganic chemical vapor deposition technologies (≈1000 °C) was achieved. The chemical composition of these films was characterized in situ by X-ray Photoelectron Spectroscopy and morphology ex situ using Scanning Electron Microscopy. It has been shown that the morphology of GaN layers strongly depends on the relative Ga-N bond concentration in the layers.

Magnesium effects on CdSe self-assembled quantum dot formation on Zn xCd yMg 1-x-ySe layers

NASA Astrophysics Data System (ADS)

Noemi Perez-Paz, M.; Lu, Hong; Shen, Aidong; Jean Mary, F.; Akins, Daniel; Tamargo, Maria C.

2006-09-01

Optical and morphological studies are used to investigate the effects of chemical composition and, in particular, the magnesium content of the Zn xCd yMg 1-x-ySe barrier layers on the size, density and uniformity of CdSe self-assembled quantum dots (QDs). A reduction of the uncapped QD size, as well as a blue shift of the capped QD photoluminescence peak position by increasing Mg concentration in the Zn xCd yMg 1-x-ySe barrier has been demonstrated by changing the Mg cell temperature during growth. In addition, a more uniform and more densely packed QD layer has been observed with an increase of the MgSe fraction in the Zn xCd yMg 1-x-ySe barrier layer using three-dimensional topographic atomic force microscopy images of the surface of uncapped QDs. Results point to Mg as a chemical factor that induces QD formation, either by increasing the density of atomic steps or/and by changing the energy of the Zn xCd yMg 1-x-ySe surface.

Oxidation of atomically thin MoS2 on SiO2

NASA Astrophysics Data System (ADS)

Yamamoto, Mahito; Cullen, William; Einstein, Theodore; Fuhrer, Michael

2013-03-01

Surface oxidation of MoS2 markedly affects its electronic, optical, and tribological properties. However, oxidative reactivity of atomically thin MoS2 has yet to be addressed. Here, we investigate oxidation of atomic layers of MoS2 using atomic force microscopy and Raman spectroscopy. MoS2 is mechanically exfoliated onto SiO2 and oxidized in Ar/O2 or Ar/O3 (ozone) at 100-450 °C. MoS2 is much more reactive to O2 than an analogous atomic membrane of graphene and monolayer MoS2 is completely etched very rapidly upon O2 treatment above 300 °C. Thicker MoS2 (> 15 nm) transforms into MoO3 after oxidation at 400 °C, which is confirmed by a Raman peak at 820 cm-1. However, few-layer MoS2 oxidized below 400 °C exhibits no MoO3 Raman mode but etch pits are formed, similar to graphene. We find atomic layers of MoS2 shows larger reactivity to O3 than to O2 and monolayer MoS2 transforms chemically upon O3 treatment even below 100 °C. Work supported by the U. of Maryland NSF-MRSEC under Grant No. DMR 05-20741.

Atomic Resolution Structural and Chemical Imaging Revealing the Sequential Migration of Ni, Co, and Mn upon the Battery Cycling of Layered Cathode

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

Yan, Pengfei; Zheng, Jianming; Zhang, Ji-Guang

Layered lithium transition metal oxides (LTMO) are promising candidate cathode materials for next generation high energy density lithium ion battery. The challenge for using this category of cathode is the capacity and voltage fading, which is believed to be associated with the layered structure disordering, a process that is initiated from the surface or solid-electrolyte interface and facilitated by transition metal (TM) reduction and oxygen vacancy formation. However, the atomic level dynamic mechanism of such a layered structure disordering is still not fully clear. In this work, utilizing atomic resolution electron energy loss spectroscopy (EELS), we map, for the firstmore » time at atomic scale, the spatial evolution of Ni, Co and Mn in a cycled LiNi1/3M1/3Co1/3O2 layered cathode. In combination with atomic level structural imaging, we discovered the direct correlation of TM ions migration behavior with lattice disordering, featuring the residing of TM ions in the tetrahedral site and a sequential migration of Ni, Co, and Mn upon the increased lattice disordering of the layered structure. This work highlights that Ni ions, though acting as the dominant redox species in many LTMO, are labile to migrate to cause lattice disordering upon battery cycling; while the Mn ions are more stable as compared with Ni and Co and can act as pillar to stabilize layered structure. Direct visualization of the behavior of TM ions during the battery cycling provides insight for designing of cathode with structural stability and correspondingly a superior performance.« less

Metalorganic chemical vapor deposition growth of InAs/GaSb type II superlattices with controllable AsxSb1-x interfaces

PubMed Central

2012-01-01

InAs/GaSb type II superlattices were grown on (100) GaSb substrates by metalorganic chemical vapor deposition (MOCVD). A plane of mixed As and Sb atoms connecting the InAs and GaSb layers was introduced to compensate the tensile strain created by the InAs layer in the SL. Characterizations of the samples by atomic force microscopy and high-resolution X-ray diffraction demonstrate flat surface morphology and good crystalline quality. The lattice mismatch of approximately 0.18% between the SL and GaSb substrate is small compared to the MOCVD-grown supperlattice samples reported to date in the literature. Considerable optical absorption in 2- to 8-μm infrared region has been realized. PACS: 78.67.Pt; 81.15.Gh; 63.22.Np; 81.05.Ea PMID:22373387

Nitride passivation reduces interfacial traps in atomic-layer-deposited Al2O3/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Aoki, T.; Fukuhara, N.; Osada, T.; Sazawa, H.; Hata, M.; Inoue, T.

2014-07-01

Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al2O3. This AlN passivation incorporated nitrogen at the Al2O3/GaAs interface, improving the capacitance-voltage (C-V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C-V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (Dit). The Dit was reduced over the entire GaAs band gap. In particular, these devices exhibited Dit around the midgap of less than 4 × 1012 cm-2eV-1, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.

The optical properties of transferred graphene and the dielectrics grown on it obtained by ellipsometry

NASA Astrophysics Data System (ADS)

Kasikov, Aarne; Kahro, Tauno; Matisen, Leonard; Kodu, Margus; Tarre, Aivar; Seemen, Helina; Alles, Harry

2018-04-01

Graphene layers grown by chemical vapour deposition (CVD) method and transferred from Cu-foils to the oxidized Si-substrates were investigated by spectroscopic ellipsometry (SE), Raman and X-Ray Photoelectron Spectroscopy (XPS) methods. The optical properties of transferred CVD graphene layers do not always correspond to the ones of the exfoliated graphene due to the contamination from the chemicals used in the transfer process. However, the real thickness and the mean properties of the transferred CVD graphene layers can be found using ellipsometry if a real thickness of the SiO2 layer is taken into account. The pulsed laser deposition (PLD) and atomic layer deposition (ALD) methods were used to grow dielectric layers on the transferred graphene and the obtained structures were characterized using optical methods. The approach demonstrated in this work could be useful for the characterization of various materials grown on graphene.

Evaluation of atomic layer deposited alumina as a protective layer for domestic silver articles: Anti-corrosion test in artificial sweat

NASA Astrophysics Data System (ADS)

Park, Suk Won; Han, Gwon Deok; Choi, Hyung Jong; Prinz, Fritz B.; Shim, Joon Hyung

2018-05-01

This study evaluated the effectiveness of alumina fabricated by atomic layer deposition (ALD) as a protective coating for silver articles against the corrosion caused by body contact. An artificial sweat solution was used to simulate body contact. ALD alumina layers of varying thicknesses ranging from 20 to 80 nm were deposited on sputtered silver samples. The stability of the protective layer was evaluated by immersing the coated samples in the artificial sweat solution at 25 and 35 °C for 24 h. We confirmed that a sufficiently thick layer of ALD alumina is effective in protecting the shape and light reflectance of the underlying silver, whereas the uncoated bare silver is severely degraded by the artificial sweat solution. Inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy were used for in-depth analyses of the chemical stability of the ALD-coated silver samples after immersion in the sweat solution.

Work function variation of MoS{sub 2} atomic layers grown with chemical vapor deposition: The effects of thickness and the adsorption of water/oxygen molecules

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

Kim, Jong Hun; Kim, Jae Hyeon; Park, Jeong Young, E-mail: peterlee@skku.edu, E-mail: jeongypark@kaist.ac.kr

2015-06-22

The electrical properties of two-dimensional atomic sheets exhibit remarkable dependences on layer thickness and surface chemistry. Here, we investigated the variation of the work function properties of MoS{sub 2} films prepared with chemical vapor deposition (CVD) on SiO{sub 2} substrates with the number of film layers. Wafer-scale CVD MoS{sub 2} films with 2, 4, and 12 layers were fabricated on SiO{sub 2}, and their properties were evaluated by using Raman and photoluminescence spectroscopies. In accordance with our X-ray photoelectron spectroscopy results, our Kelvin probe force microscopy investigation found that the surface potential of the MoS{sub 2} films increases by ∼0.15 eVmore » when the number of layers is increased from 2 to 12. Photoemission spectroscopy (PES) with in-situ annealing under ultra high vacuum conditions was used to directly demonstrate that this work function shift is associated with the screening effects of oxygen or water molecules adsorbed on the film surface. After annealing, it was found with PES that the surface potential decreases by ∼0.2 eV upon the removal of the adsorbed layers, which confirms that adsorbed species have a role in the variation in the work function.« less

Epitaxial growth of HfS2 on sapphire by chemical vapor deposition and application for photodetectors

NASA Astrophysics Data System (ADS)

Wang, Denggui; Zhang, Xingwang; Liu, Heng; Meng, Junhua; Xia, Jing; Yin, Zhigang; Wang, Ye; You, Jingbi; Meng, Xiang-Min

2017-09-01

Group IVB transition metal (Zr and Hf) dichalcogenides (TMDs) have been attracting intensive attention as promising candidates in the modern electronic and/or optoelectronic fields. However, the controllable growth of HfS2 monolayers or few layers still remains a great challenge, thus hindering their further applications so far. Here, for the first time we demonstrate the epitaxial growth of high-quality HfS2 with a controlled number of layers on c-plane sapphire substrates by chemical vapor deposition (CVD). The HfS2 layers exhibit an atomically sharp interface with the sapphire substrate, followed by flat, 2D layers with octahedral coordination. The epitaxial relationship between HfS2 and substrate was determined by x-ray diffraction and transmission electron microscopy measurements to be: HfS2 (0 0 0 1) [10-10]||sapphire (0 0 0 1)[1-100]. Moreover, a high-performance photodetector with a high on/off ratio of more than 103 and an ultrafast response rate of 130 µs for the rise and 155 µs for the decay times were fabricated based on the CVD-grown HfS2 layers on sapphire substrates. This simple and controllable approach opens up a new way to produce highly crystalline HfS2 atomic layers, which are promising materials for nanoelectronics.

Imaging and three-dimensional reconstruction of chemical groups inside a protein complex using atomic force microscopy

NASA Astrophysics Data System (ADS)

Kim, Duckhoe; Sahin, Ozgur

2015-03-01

Scanning probe microscopes can be used to image and chemically characterize surfaces down to the atomic scale. However, the localized tip-sample interactions in scanning probe microscopes limit high-resolution images to the topmost atomic layer of surfaces, and characterizing the inner structures of materials and biomolecules is a challenge for such instruments. Here, we show that an atomic force microscope can be used to image and three-dimensionally reconstruct chemical groups inside a protein complex. We use short single-stranded DNAs as imaging labels that are linked to target regions inside a protein complex, and T-shaped atomic force microscope cantilevers functionalized with complementary probe DNAs allow the labels to be located with sequence specificity and subnanometre resolution. After measuring pairwise distances between labels, we reconstruct the three-dimensional structure formed by the target chemical groups within the protein complex using simple geometric calculations. Experiments with the biotin-streptavidin complex show that the predicted three-dimensional loci of the carboxylic acid groups of biotins are within 2 Å of their respective loci in the corresponding crystal structure, suggesting that scanning probe microscopes could complement existing structural biological techniques in solving structures that are difficult to study due to their size and complexity.

Observation of hidden atomic order at the interface between Fe and topological insulator Bi2Te3.

PubMed

Sánchez-Barriga, Jaime; Ogorodnikov, Ilya I; Kuznetsov, Mikhail V; Volykhov, Andrey A; Matsui, Fumihiko; Callaert, Carolien; Hadermann, Joke; Verbitskiy, Nikolay I; Koch, Roland J; Varykhalov, Andrei; Rader, Oliver; Yashina, Lada V

2017-11-22

To realize spintronic devices based on topological insulators (TIs), well-defined interfaces between magnetic metals and TIs are required. Here, we characterize atomically precisely the interface between the 3d transition metal Fe and the TI Bi 2 Te 3 at different stages of its formation. Using photoelectron diffraction and holography, we show that after deposition of up to 3 monolayers Fe on Bi 2 Te 3 at room temperature, the Fe atoms are ordered at the interface despite the surface disorder revealed by our scanning-tunneling microscopy images. We find that Fe occupies two different sites: a hollow adatom deeply relaxed into the Bi 2 Te 3 quintuple layers and an interstitial atom between the third (Te) and fourth (Bi) atomic layers. For both sites, our core-level photoemission spectra and density-functional theory calculations demonstrate simultaneous chemical bonding of Fe to both Te and Bi atoms. We further show that upon deposition of Fe up to a thickness of 20 nm, the Fe atoms penetrate deeper into the bulk forming a 2-5 nm interface layer containing FeTe. In addition, excessive Bi is pushed down into the bulk of Bi 2 Te 3 leading to the formation of septuple layers of Bi 3 Te 4 within a distance of ∼25 nm from the interface. Controlling the magnetic properties of the complex interface structures revealed by our work will be of critical importance when optimizing the efficiency of spin injection in TI-based devices.

Preface: Special Topic on Atomic and Molecular Layer Processing: Deposition, Patterning, and Etching

NASA Astrophysics Data System (ADS)

Engstrom, James R.; Kummel, Andrew C.

2017-02-01

Thin film processing technologies that promise atomic and molecular scale control have received increasing interest in the past several years, as traditional methods for fabrication begin to reach their fundamental limits. Many of these technologies involve at their heart phenomena occurring at or near surfaces, including adsorption, gas-surface reactions, diffusion, desorption, and re-organization of near-surface layers. Moreover many of these phenomena involve not just reactions occurring under conditions of local thermodynamic equilibrium but also the action of energetic species including electrons, ions, and hyperthermal neutrals. There is a rich landscape of atomic and molecular scale interactions occurring in these systems that is still not well understood. In this Special Topic Issue of The Journal of Chemical Physics, we have collected recent representative examples of work that is directed at unraveling the mechanistic details concerning atomic and molecular layer processing, which will provide an important framework from which these fields can continue to develop. These studies range from the application of theory and computation to these systems to the use of powerful experimental probes, such as X-ray synchrotron radiation, probe microscopies, and photoelectron and infrared spectroscopies. The work presented here helps in identifying some of the major challenges and direct future activities in this exciting area of research involving atomic and molecular layer manipulation and fabrication.

Preface: Special Topic on Atomic and Molecular Layer Processing: Deposition, Patterning, and Etching.

PubMed

Engstrom, James R; Kummel, Andrew C

2017-02-07

Thin film processing technologies that promise atomic and molecular scale control have received increasing interest in the past several years, as traditional methods for fabrication begin to reach their fundamental limits. Many of these technologies involve at their heart phenomena occurring at or near surfaces, including adsorption, gas-surface reactions, diffusion, desorption, and re-organization of near-surface layers. Moreover many of these phenomena involve not just reactions occurring under conditions of local thermodynamic equilibrium but also the action of energetic species including electrons, ions, and hyperthermal neutrals. There is a rich landscape of atomic and molecular scale interactions occurring in these systems that is still not well understood. In this Special Topic Issue of The Journal of Chemical Physics, we have collected recent representative examples of work that is directed at unraveling the mechanistic details concerning atomic and molecular layer processing, which will provide an important framework from which these fields can continue to develop. These studies range from the application of theory and computation to these systems to the use of powerful experimental probes, such as X-ray synchrotron radiation, probe microscopies, and photoelectron and infrared spectroscopies. The work presented here helps in identifying some of the major challenges and direct future activities in this exciting area of research involving atomic and molecular layer manipulation and fabrication.

Optimization of chemical structure of Schottky-type selection diode for crossbar resistive memory.

PubMed

Kim, Gun Hwan; Lee, Jong Ho; Jeon, Woojin; Song, Seul Ji; Seok, Jun Yeong; Yoon, Jung Ho; Yoon, Kyung Jean; Park, Tae Joo; Hwang, Cheol Seong

2012-10-24

The electrical performances of Pt/TiO(2)/Ti/Pt stacked Schottky-type diode (SD) was systematically examined, and this performance is dependent on the chemical structures of the each layer and their interfaces. The Ti layers containing a tolerable amount of oxygen showed metallic electrical conduction characteristics, which was confirmed by sheet resistance measurement with elevating the temperature, transmission line measurement (TLM), and Auger electron spectroscopy (AES) analysis. However, the chemical structure of SD stack and resulting electrical properties were crucially affected by the dissolved oxygen concentration in the Ti layers. The lower oxidation potential of the Ti layer with initially higher oxygen concentration suppressed the oxygen deficiency of the overlying TiO(2) layer induced by consumption of the oxygen from TiO(2) layer. This structure results in the lower reverse current of SDs without significant degradation of forward-state current. Conductive atomic force microscopy (CAFM) analysis showed the current conduction through the local conduction paths in the presented SDs, which guarantees a sufficient forward-current density as a selection device for highly integrated crossbar array resistive memory.

Molecular processes in a high temperature shock layer

NASA Technical Reports Server (NTRS)

Guberman, S. L.

1984-01-01

Models of the shock layer encountered by an Aeroassisted Orbital Transfer Vehicle require as input accurate cross sections and rate constants for the atomic and molecular processes that characterize the shock radiation. From the estimated atomic and molecular densities in the shock layer and the expected residence time of 1 m/s, it can be expected that electron-ion collision processes will be important in the shock model. Electron capture by molecular ions followed by dissociation, e.g., O2(+) + e(-) yields 0 + 0, can be expected to be of major importance since these processes are known to have high rates (e.g., 10 to the -7th power cu/cm/sec) at room temperature. However, there have been no experimental measurements of dissociative recombination (DR) at temperatures ( 12000K) that are expected to characterize the shock layer. Indeed, even at room temperature, it is often difficult to perform experiments that determine the dependence of the translational energy and quantum yields of the product atoms on the electronic and vibrational state of the reactant molecular ions. Presented are ab initio quantum chemical studies of DR for molecular ions that are likely to be important in the atmospheric shock layer.

Polar Cation Ordering: A Route to Introducing >10% Bond Strain Into Layered Oxide Films

DOE PAGES

Nelson-Cheeseman, Brittany B.; Zhou, Hua; Balachandran, Prasanna V.; ...

2014-09-05

The 3d transition metal (M) perovskite oxides exhibit a remarkable array of properties, including novel forms of superconductivity, magnetism and multiferroicity. Strain can have a profound effect on many of these properties. This is due to the localized nature of the M 3d orbitals, where even small changes in the M–O bond lengths and M–O–M bond angles produced by strain can be used to tune the 3d– O 2p hybridization, creating large changes in electronic structure. We present a new route to strain the M–O bonds in epitaxial two-dimensional perovskite films by tailoring local electrostatic dipolar interactions within every formulamore » unit via atomic layer-by-layer synthesis. The response of the O anions to the resulting dipole electric fields distorts the M–O bonds by more than 10%, without changing substrate strain or chemical composition. We found that this distortion is largest for the apical oxygen atoms (O ap), and alters the transition metal valence state via self-doping without chemical substitution.« less

Evidence of a reduction reaction of oxidized iron/cobalt by boron atoms diffused toward naturally oxidized surface of CoFeB layer during annealing

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

Sato, Soshi, E-mail: sato.soshi@cies.tohoku.ac.jp; Honjo, Hiroaki; Niwa, Masaaki

2015-04-06

We have investigated the redox reaction on the surface of Ta/CoFeB/MgO/CoFeB magnetic tunnel junction stack samples after annealing at 300, 350, and 400 °C for 1 h using angle-resolved X-ray photoelectron spectroscopy for precise analysis of the chemical bonding states. At a capping tantalum layer thickness of 1 nm, both the capping tantalum layer and the surface of the underneath CoFeB layer in the as-deposited stack sample were naturally oxidized. By comparison of the Co 2p and Fe 2p spectra among the as-deposited and annealed samples, reduction of the naturally oxidized cobalt and iron atoms occurred on the surface of the CoFeB layer.more » The reduction reaction was more significant at higher annealing temperature. Oxidized cobalt and iron were reduced by boron atoms that diffused toward the surface of the top CoFeB layer. A single CoFeB layer was prepared on SiO{sub 2}, and a confirmatory evidence of the redox reaction with boron diffusion was obtained by angle-resolved X-ray photoelectron spectroscopy analysis of the naturally oxidized surface of the CoFeB single layer after annealing. The redox reaction is theoretically reasonable based on the Ellingham diagram.« less

Evolution of crystal structure during the initial stages of ZnO atomic layer deposition

DOE PAGES

Boichot, R.; Tian, L.; Richard, M. -I.; ...

2016-01-05

In this study, a complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al 2O 3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films depend strongly on the nature of the interfacial bonds.

FT-IR characterization of the acidic and basic sites on a nanostructured aluminum nitride surface

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

Baraton, M.I.; Chen, X.; Gonsalves, K.E.

1997-12-31

A nanostructured aluminum nitride powder prepared by sol-gel type chemical synthesis is analyzed by Fourier transform infrared spectrometry. The surface acidic and basic sites are probed out by adsorption of several organic molecules. Resulting from the unavoidable presence of oxygen, the aluminum nitride surface is an oxinitride layer in fact, and its surface chemistry should present some analogies with alumina. Therefore, a thorough comparison between the acido-basicity of aluminum nitride and aluminum oxide is discussed. The remaining nitrogen atoms in the first atomic layer modify the acidity-basicity relative balance and reveals the specificity of the aluminum nitride surface.

Atomic layer epitaxy of hematite on indium tin oxide for application in solar energy conversion

DOEpatents

Martinson, Alex B.; Riha, Shannon; Guo, Peijun; Emery, Jonathan D.

2016-07-12

A method to provide an article of manufacture of iron oxide on indium tin oxide for solar energy conversion. An atomic layer epitaxy method is used to deposit an uncommon bixbytite-phase iron (III) oxide (.beta.-Fe.sub.2O.sub.3) which is deposited at low temperatures to provide 99% phase pure .beta.-Fe.sub.2O.sub.3 thin films on indium tin oxide. Subsequent annealing produces pure .alpha.-Fe.sub.2O.sub.3 with well-defined epitaxy via a topotactic transition. These highly crystalline films in the ultra thin film limit enable high efficiency photoelectrochemical chemical water splitting.

Atomic layer deposition of nanoporous biomaterials.

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

Narayan, R. J.; Adiga, S. P.; Pellin, M. J.

2010-03-01

Due to its chemical stability, uniform pore size, and high pore density, nanoporous alumina is being investigated for use in biosensing, drug delivery, hemodialysis, and other medical applications. In recent work, we have examined the use of atomic layer deposition for coating the surfaces of nanoporous alumina membranes. Zinc oxide coatings were deposited on nanoporous alumina membranes using atomic layer deposition. The zinc oxide-coated nanoporous alumina membranes demonstrated antimicrobial activity against Escherichia coli and Staphylococcus aureus bacteria. These results suggest that atomic layer deposition is an attractive technique for modifying the surfaces of nanoporous alumina membranes and other nanostructured biomaterials.more » Nanoporous alumina, also known as anodic aluminum oxide (AAO), is a nanomaterial that exhibits several unusual properties, including high pore densities, straight pores, small pore sizes, and uniform pore sizes. In 1953, Keller et al. showed that anodizing aluminum in acid electrolytes results in a thick layer of nearly cylindrical pores, which are arranged in a close-packed hexagonal cell structure. More recently, Matsuda & Fukuda demonstrated preparation of highly ordered platinum and gold nanohole arrays using a replication process. In this study, a negative structure of nanoporous alumina was initially fabricated and a positive structure of a nanoporous metal was subsequently fabricated. Over the past fifteen years, nanoporous alumina membranes have been used as templates for growth of a variety of nanostructured materials, including nanotubes, nanowires, nanorods, and nanoporous membranes.« less

Effect of gradual ordering of Ge/Sb atoms on chemical bonding: A proposed mechanism for the formation of crystalline Ge2Sb2Te5

NASA Astrophysics Data System (ADS)

Singh, Janpreet; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

2018-04-01

Using first principle calculations, we study the atomic arrangement and bonding mechanism in the crystalline phase of Ge2Sb2Te5 (GST). It is found that the stability of GST depends on the gradual ordering of Ge/Sb atoms. The configurations with different concentration of Ge/Sb in layers have been analyzed by the partial density of state, electron localization function and Bader charge distribution. The s and p-states of Ge atom alter with different stacking configurations but there is no change in Sb and Te atom states. Our findings show that the bonding between Ge-Te is not only responsible for the stability of GST alloy but can also predict which composition can show generic features of phase change material. As the number of Ge atoms near to vacancy layer decreases, Ge donates more charge. A growth model has been proposed for the formation of crystalline phase which justifies the structure models proposed in the literature.

Modeling the processing of interstellar ices by energetic particles

NASA Astrophysics Data System (ADS)

Kalvāns, J.; Shmeld, I.

2013-06-01

Context. Interstellar ice is the main form of metal species in dark molecular clouds. Experiments and observations have shown that the ice is significantly processed after the freeze-out of molecules onto grains. The processing is caused by cosmic-ray particles and cosmic-ray-induced UV photons. These transformations are included in current astrochemical models only to a very limited degree. Aims: We aim to establish a model of the "cold" chemistry in interstellar ices and to evaluate its general impact on the composition of interstellar ices. Methods: The ice was treated as consisting of two layers - the surface and the mantle (or subsurface) layer. Subsurface chemical processes are described with photodissociation of ice species and binary reactions on the surfaces of cavities inside the mantle. Hydrogen atoms and molecules can diffuse between the layers. We also included deuterium chemistry. Results: The modeling results show that the content of chemically bound H is reduced in subsurface molecules by about 30% on average. This promotes the formation of more hydrogen-poor species in the ice. The enrichment of ice molecules with deuterium is significantly reduced by the subsurface processes. On average, it follows the gas-phase atomic D/H abundance ratio, with a delay. The delay produced by the model is on the order of several Myr. Conclusions: The processing of ice may place new constraints on the production of deuterated species on grains. In a mantle with a two-layer structure the upper layer (CO) should be processed substantially more intensively than the lower layer (H2O). Chemical explosions in interstellar ice might not be an important process. They destroy the structure of the mantle, which forms over long timescales. Besides, ices may lack the high radical content needed for the explosions.

Method of making dense, conformal, ultra-thin cap layers for nanoporous low-k ILD by plasma assisted atomic layer deposition

DOEpatents

Jiang, Ying-Bing [Albuquerque, NM; Cecchi, Joseph L [Albuquerque, NM; Brinker, C Jeffrey [Albuquerque, NM

2011-05-24

Barrier layers and methods for forming barrier layers on a porous layer are provided. The methods can include chemically adsorbing a plurality of first molecules on a surface of the porous layer in a chamber and forming a first layer of the first molecules on the surface of the porous layer. A plasma can then be used to react a plurality of second molecules with the first layer of first molecules to form a first layer of a barrier layer. The barrier layers can seal the pores of the porous material, function as a diffusion barrier, be conformal, and/or have a negligible impact on the overall ILD k value of the porous material.

The possibility of multi-layer nanofabrication via atomic force microscope-based pulse electrochemical nanopatterning

NASA Astrophysics Data System (ADS)

Kim, Uk Su; Morita, Noboru; Lee, Deug Woo; Jun, Martin; Park, Jeong Woo

2017-05-01

Pulse electrochemical nanopatterning, a non-contact scanning probe lithography process using ultrashort voltage pulses, is based primarily on an electrochemical machining process using localized electrochemical oxidation between a sharp tool tip and the sample surface. In this study, nanoscale oxide patterns were formed on silicon Si (100) wafer surfaces via electrochemical surface nanopatterning, by supplying external pulsed currents through non-contact atomic force microscopy. Nanoscale oxide width and height were controlled by modulating the applied pulse duration. Additionally, protruding nanoscale oxides were removed completely by simple chemical etching, showing a depressed pattern on the sample substrate surface. Nanoscale two-dimensional oxides, prepared by a localized electrochemical reaction, can be defined easily by controlling physical and electrical variables, before proceeding further to a layer-by-layer nanofabrication process.

Room-Temperature Atomic Layer Deposition of Al2 O3 : Impact on Efficiency, Stability and Surface Properties in Perovskite Solar Cells.

PubMed

Kot, Malgorzata; Das, Chittaranjan; Wang, Zhiping; Henkel, Karsten; Rouissi, Zied; Wojciechowski, Konrad; Snaith, Henry J; Schmeisser, Dieter

2016-12-20

In this work, solar cells with a freshly made CH 3 NH 3 PbI 3 perovskite film showed a power conversion efficiency (PCE) of 15.4 % whereas the one with 50 days aged perovskite film only 6.1 %. However, when the aged perovskite was covered with a layer of Al 2 O 3 deposited by atomic layer deposition (ALD) at room temperature (RT), the PCE value was clearly enhanced. X-ray photoelectron spectroscopy study showed that the ALD precursors are chemically active only at the perovskite surface and passivate it. Moreover, the RT-ALD-Al 2 O 3 -covered perovskite films showed enhanced ambient air stability. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Conductive atomic force microscopy studies on the transformation of GeSi quantum dots to quantum rings.

PubMed

Zhang, S L; Xue, F; Wu, R; Cui, J; Jiang, Z M; Yang, X J

2009-04-01

Conductive atomic force microscopy has been employed to study the topography and conductance distribution of individual GeSi quantum dots (QDs) and quantum rings (QRs) during the transformation from QDs to QRs by depositing an Si capping layer on QDs. The current distribution changes significantly with the topographic transformation during the Si capping process. Without the capping layer, the QDs are dome-shaped and the conductance is higher at the ring region between the center and boundary than that at the center. After capping with 0.32 nm Si, the shape of the QDs changes to pyramidal and the current is higher at both the center and the arris. When the Si capping layer increases to 2 nm, QRs are formed and the current of individual QRs is higher at the rim than that at the central hole. By comparing the composition distributions obtained by scanning Auger microscopy and atomic force microscopy combined with selective chemical etching, the origin of the current distribution change is discussed.

Atomic layer deposited high-k dielectric on graphene by functionalization through atmospheric plasma treatment

NASA Astrophysics Data System (ADS)

Shin, Jeong Woo; Kang, Myung Hoon; Oh, Seongkook; Yang, Byung Chan; Seong, Kwonil; Ahn, Hyo-Sok; Lee, Tae Hoon; An, Jihwan

2018-05-01

Atomic layer-deposited (ALD) dielectric films on graphene usually show noncontinuous and rough morphology owing to the inert surface of graphene. Here, we demonstrate the deposition of thin and uniform ALD ZrO2 films with no seed layer on chemical vapor-deposited graphene functionalized by atmospheric oxygen plasma treatment. Transmission electron microscopy showed that the ALD ZrO2 films were highly crystalline, despite a low ALD temperature of 150 °C. The ALD ZrO2 film served as an effective passivation layer for graphene, which was shown by negative shifts in the Dirac voltage and the enhanced air stability of graphene field-effect transistors after ALD of ZrO2. The ALD ZrO2 film on the functionalized graphene may find use in flexible graphene electronics and biosensors owing to its low process temperature and its capacity to improve device performance and stability.

Biomimetic whisker-shaped apatite coating of titanium powder.

PubMed

Sim, Young Uk; Kim, Jong Hee; Yang, Tae Young; Yoon, Seog Young; Park, Hong Chae

2010-05-01

Biomimetic apatite coatings on chemically modified titanium powder have been processed and the resulting coating layers evaluated in terms of morphology, composition and structure, using TF-XRD, XPS, SEM, TEM and FTIR analysis. After 7 days immersion in a simulated body fluid (SBF), nanometer-sized fine precipitates with an amorphous whisker-like phase and a Ca/P atomic ratio of 1.94 were obtained on the external surface of the titanium particles. When the immersion time in SBF was extended to 16 days, the coating layer consisted of the whisker-like nanostructured crystals of carbonated hydroxyapatite with a atomic ratio of 3; in such a case, a double coating layer was developed. The double layer could be divided into two regions and could be clearly distinguished: an inner dense region (approximately 200 nm in thickness) which may include hard agglomerated crystals and an outer less dense region (> 500 nm in thickness) in which crystals are loosely distributed.

Atomic layer deposited high-k dielectric on graphene by functionalization through atmospheric plasma treatment.

PubMed

Shin, Jeong Woo; Kang, Myung Hoon; Oh, Seongkook; Yang, Byung Chan; Seong, Kwonil; Ahn, Hyo-Sok; Lee, Tae Hoon; An, Jihwan

2018-05-11

Atomic layer-deposited (ALD) dielectric films on graphene usually show noncontinuous and rough morphology owing to the inert surface of graphene. Here, we demonstrate the deposition of thin and uniform ALD ZrO 2 films with no seed layer on chemical vapor-deposited graphene functionalized by atmospheric oxygen plasma treatment. Transmission electron microscopy showed that the ALD ZrO 2 films were highly crystalline, despite a low ALD temperature of 150 °C. The ALD ZrO 2 film served as an effective passivation layer for graphene, which was shown by negative shifts in the Dirac voltage and the enhanced air stability of graphene field-effect transistors after ALD of ZrO 2 . The ALD ZrO 2 film on the functionalized graphene may find use in flexible graphene electronics and biosensors owing to its low process temperature and its capacity to improve device performance and stability.

The vertical growth of MoS2 layers at the initial stage of CVD from first-principles

NASA Astrophysics Data System (ADS)

Xue, Xiong-Xiong; Feng, Yexin; Chen, Keqiu; Zhang, Lixin

2018-04-01

Chemical vapor deposition (CVD) is the highly preferred method for mass production of transition metal dichalcogenide (TMD) layers, yet the atomic-scale knowledge is still lacking about the nucleation and growth. In this study, by using first-principles calculations, we show that, on Au(111) surface, one-dimensional (1D) MoxSy chains are first formed by coalescing of smaller feeding species and are energetically favored at the early stage of nucleation. Two-dimensional (2D) layers can be stabilized only after the number of Mo atoms exceeds ˜12. A vertical growth mode is revealed which accomplishes the structural transformation from the 1D chains to the 2D layers for the clusters while growing. The competition between intralayer and interlayer interactions is the key. These findings serve as new insights for better understanding the atomistic mechanism of the nucleation and growth of TMDs on the surface.

Comparison of tungsten films grown by CVD and hot-wire assisted atomic layer deposition in a cold-wall reactor

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

Yang, Mengdi, E-mail: M.Yang@utwente.nl; Aarnink, Antonius A. I.; Kovalgin, Alexey Y.

2016-01-15

In this work, the authors developed hot-wire assisted atomic layer deposition (HWALD) to deposit tungsten (W) with a tungsten filament heated up to 1700–2000 °C. Atomic hydrogen (at-H) was generated by dissociation of molecular hydrogen (H{sub 2}), which reacted with WF{sub 6} at the substrate to deposit W. The growth behavior was monitored in real time by an in situ spectroscopic ellipsometer. In this work, the authors compare samples with tungsten grown by either HWALD or chemical vapor deposition (CVD) in terms of growth kinetics and properties. For CVD, the samples were made in a mixture of WF{sub 6} and molecularmore » or atomic hydrogen. Resistivity of the WF{sub 6}-H{sub 2} CVD layers was 20 μΩ·cm, whereas for the WF{sub 6}-at-H-CVD layers, it was 28 μΩ·cm. Interestingly, the resistivity was as high as 100 μΩ·cm for the HWALD films, although the tungsten films were 99% pure according to x-ray photoelectron spectroscopy. X-ray diffraction reveals that the HWALD W was crystallized as β-W, whereas both CVD films were in the α-W phase.« less

Strain and Structure Heterogeneity in MoS2 Atomic Layers Grown by Chemical Vapour Deposition

DTIC Science & Technology

2014-11-18

substrate and material. To better explain the experimental results and estimate the strain transferred to MoS2 layer under such tensile tests, a 3D... ACS Nano 7, 7126 7131 (2013). 29. He, K., Poole, C., Mak, K. F. & Shan, J. Experimental demonstration of continuous electronic structure tuning via...transition as it is thinned down from multi layer to monolayer, producing a significant enhancement of photoluminescence (PL) quantum yield as a result of the

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

Stair, Peter C.

The research took advantage of our capabilities to perform in-situ and operando Raman spectroscopy on complex systems along with our developing expertise in the synthesis of uniform, supported metal oxide materials to investigate relationships between the catalytically active oxide composition, atomic structure, and support and the corresponding chemical and catalytic properties. The project was organized into two efforts: 1) Synthesis of novel catalyst materials by atomic layer deposition (ALD). 2) Spectroscopic and chemical investigations of coke formation and catalyst deactivation. ALD synthesis was combined with conventional physical characterization, Raman spectroscopy, and probe molecule chemisorption to study the effect of supportedmore » metal oxide composition and atomic structure on acid-base and catalytic properties. Operando Raman spectroscopy studies of olefin polymerization leading to coke formation and catalyst deactivation clarified the mechanism of coke formation by acid catalysts.« less

Quantum Chemical Insight into the LiF Interlayer Effects in Organic Electronics: Reactions between Al Atom and LiF Clusters.

PubMed

Wu, Shui-Xing; Kan, Yu-He; Li, Hai-Bin; Zhao, Liang; Wu, Yong; Su, Zhong-Min

2015-08-06

It is well known that the aluminum cathode performs dramatically better when a thin lithium fluoride (LiF) layer inserted in organic electronic devices. The doping effect induced by the librated Li atom via the chemical reactions producing AlF3 as byproduct was previously proposed as one of possible mechanisms. However, the underlying mechanism discussion is quite complicated and not fully understood so far, although the LiF interlayer is widely used. In this paper, we perform theoretical calculations to consider the reactions between an aluminum atom and distinct LiF clusters. The reaction pathways of the Al-(LiF)n (n = 2, 4, 16) systems were discovered and the energetics were theoretically evaluated. The release of Li atom and the formation of AlF3 were found in two different chemical reaction routes. The undissociated Al-(LiF)n systems have chances to change to some structures with loosely bound electrons. Our findings about the interacted Al-(LiF)n systems reveal new insights into the LiF interlayer effects in organic electronics applications.

Surface functionalization of two-dimensional metal chalcogenides by Lewis acid-base chemistry

NASA Astrophysics Data System (ADS)

Lei, Sidong; Wang, Xifan; Li, Bo; Kang, Jiahao; He, Yongmin; George, Antony; Ge, Liehui; Gong, Yongji; Dong, Pei; Jin, Zehua; Brunetto, Gustavo; Chen, Weibing; Lin, Zuan-Tao; Baines, Robert; Galvão, Douglas S.; Lou, Jun; Barrera, Enrique; Banerjee, Kaustav; Vajtai, Robert; Ajayan, Pulickel

2016-05-01

Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid-base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti4+ to form planar p-type [Ti4+n(InSe)] coordination complexes. Using this strategy, we fabricate planar p-n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B3+, Al3+ and Sn4+) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid-base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.

Deposition of dopant impurities and pulsed energy drive-in

DOEpatents

Wickboldt, Paul; Carey, Paul G.; Smith, Patrick M.; Ellingboe, Albert R.

2008-01-01

A semiconductor doping process which enhances the dopant incorporation achievable using the Gas Immersion Laser Doping (GILD) technique. The enhanced doping is achieved by first depositing a thin layer of dopant atoms on a semiconductor surface followed by exposure to one or more pulses from either a laser or an ion-beam which melt a portion of the semiconductor to a desired depth, thus causing the dopant atoms to be incorporated into the molten region. After the molten region recrystallizes the dopant atoms are electrically active. The dopant atoms are deposited by plasma enhanced chemical vapor deposition (PECVD) or other known deposition techniques.

Deposition of dopant impurities and pulsed energy drive-in

DOEpatents

Wickboldt, Paul; Carey, Paul G.; Smith, Patrick M.; Ellingboe, Albert R.

1999-01-01

A semiconductor doping process which enhances the dopant incorporation achievable using the Gas Immersion Laser Doping (GILD) technique. The enhanced doping is achieved by first depositing a thin layer of dopant atoms on a semiconductor surface followed by exposure to one or more pulses from either a laser or an ion-beam which melt a portion of the semiconductor to a desired depth, thus causing the dopant atoms to be incorporated into the molten region. After the molten region recrystallizes the dopant atoms are electrically active. The dopant atoms are deposited by plasma enhanced chemical vapor deposition (PECVD) or other known deposition techniques.

Deposition of dopant impurities and pulsed energy drive-in

DOEpatents

Wickboldt, P.; Carey, P.G.; Smith, P.M.; Ellingboe, A.R.

1999-06-29

A semiconductor doping process which enhances the dopant incorporation achievable using the Gas Immersion Laser Doping (GILD) technique is disclosed. The enhanced doping is achieved by first depositing a thin layer of dopant atoms on a semiconductor surface followed by exposure to one or more pulses from either a laser or an ion-beam which melt a portion of the semiconductor to a desired depth, thus causing the dopant atoms to be incorporated into the molten region. After the molten region recrystallizes the dopant atoms are electrically active. The dopant atoms are deposited by plasma enhanced chemical vapor deposition (PECVD) or other known deposition techniques. 2 figs.

Modeling and in Situ Probing of Surface Reactions in Atomic Layer Deposition.

PubMed

Zheng, Yuanxia; Hong, Sungwook; Psofogiannakis, George; Rayner, G Bruce; Datta, Suman; van Duin, Adri C T; Engel-Herbert, Roman

2017-05-10

Atomic layer deposition (ALD) has matured into a preeminent thin film deposition technique by offering a highly scalable and economic route to integrate chemically dissimilar materials with excellent thickness control down to the subnanometer regime. Contrary to its extensive applications, a quantitative and comprehensive understanding of the reaction processes seems intangible. Complex and manifold reaction pathways are possible, which are strongly affected by the surface chemical state. Here, we report a combined modeling and experimental approach utilizing ReaxFF reactive force field simulation and in situ real-time spectroscopic ellipsometry to gain insights into the ALD process of Al 2 O 3 from trimethylaluminum and water on hydrogenated and oxidized Ge(100) surfaces. We deciphered the origin for the different peculiarities during initial ALD cycles for the deposition on both surfaces. While the simulations predicted a nucleation delay for hydrogenated Ge(100), a self-cleaning effect was discovered on oxidized Ge(100) surfaces and resulted in an intermixed Al 2 O 3 /GeO x layer that effectively suppressed oxygen diffusion into Ge. In situ spectroscopic ellipsometry in combination with ex situ atomic force microscopy and X-ray photoelectron spectroscopy confirmed these simulation results. Electrical impedance characterizations evidenced the critical role of the intermixed Al 2 O 3 /GeO x layer to achieve electrically well-behaved dielectric/Ge interfaces with low interface trap density. The combined approach can be generalized to comprehend the deposition and reaction kinetics of other ALD precursors and surface chemistry, which offers a path toward a theory-aided rational design of ALD processes at a molecular level.

Photoelectrochemical Water Oxidation by GaAs Nanowire Arrays Protected with Atomic Layer Deposited NiO x Electrocatalysts

NASA Astrophysics Data System (ADS)

Zeng, Joy; Xu, Xiaoqing; Parameshwaran, Vijay; Baker, Jon; Bent, Stacey; Wong, H.-S. Philip; Clemens, Bruce

2018-02-01

Photoelectrochemical (PEC) hydrogen production makes possible the direct conversion of solar energy into chemical fuel. In this work, PEC photoanodes consisting of GaAs nanowire (NW) arrays were fabricated, characterized, and then demonstrated for the oxygen evolution reaction (OER). Uniform and periodic GaAs nanowire arrays were grown on a heavily n-doped GaAs substrates by metal-organic chemical vapor deposition selective area growth. The nanowire arrays were characterized using cyclic voltammetry and impedance spectroscopy in a non-aqueous electrochemical system using ferrocene/ferrocenium (Fc/Fc+) as a redox couple, and a maximum oxidation photocurrent of 11.1 mA/cm2 was measured. GaAs NW arrays with a 36 nm layer of nickel oxide (NiO x ) synthesized by atomic layer deposition were then used as photoanodes to drive the OER. In addition to acting as an electrocatalyst, the NiO x layer served to protect the GaAs NWs from oxidative corrosion. Using this strategy, GaAs NW photoanodes were successfully used for the oxygen evolution reaction. This is the first demonstration of GaAs NW arrays for effective OER, and the fabrication and protection strategy developed in this work can be extended to study any other nanostructured semiconductor materials systems for electrochemical solar energy conversion.

Mn induced 1 × 2 reconstruction in the τ-MnAl(0 0 1) surface

NASA Astrophysics Data System (ADS)

Guerrero-Sánchez, J.; Takeuchi, Noboru

2018-05-01

We report on first principles total energy calculations to describe the structural, electronic and magnetic properties of MnAl(0 0 1) surfaces. We have concentrated in structural models having 1 × 1 and 1 × 2 periodicities, since recent experiments of the similar MnGa(0 0 1) surface have found 1 × 1 and 1 × 2 reconstructions. Our calculations show the existence of two stable structures for different ranges of chemical potential. A 1 × 1 surface is stable for Al-rich conditions, whereas a Mn-induced 1 × 2 reconstruction appears after increasing the Mn chemical potential up to Mn-rich conditions. It is important to notice that experimentally, Mn rich conditions are important for improved magnetic properties. The Mn layers in both structures have ferromagnetic arrangements, but they are aligned antiferromagnetically with the almost no magnetic Al atoms. Moreover, the on top Mn atoms, which produce the 1 × 2 reconstruction, align antiferromagnetically with the second layer Mn atoms. These findings are similar to those obtained experimentally in MnGa thin films grown by molecular beam epitaxy. Therefore, this method could also be used to grow the proposed MnAl films.

Crystal Structure and Crystal Chemistry of Some Common REE Minerals and Nanpingite

NASA Astrophysics Data System (ADS)

Ni, Yunxiang

1995-01-01

Part I. Crystal structure and crystal chemistry of fluorocarbonate minerals. The crystal structure of bastnasite-(Ce) have been solved in P-62c and refined to R = 0.018. The structure is composed of (001) (CeF) layers interspersed with (CO_3) layers in a 1:1 ratio. The Ce atom is coordinated in rm CeO_6F_3 polyhedra. The atomic arrangement of synchysite-(Ce) has been solved and refined to R = 0.036 with a monoclinic space group C2/c. It possesses a (001) layer structure, with layers of (Ca) and (CeF) separated by layers of carbonate groups. The layers stack in a manner analogous to C2/c muscovite. Polytypism similar to the micas may exist in synchysite. The crystal structures of cordylite-(Ce) have been solved in P6 _3/mmc and refined to R = 0.023. The structure and chemical formula are different from those deduced by Oftedal. The formula is rm MBaCe_2(CO _3)_4F, where M is rm Na^+, Ca^{2+}_{1/2 }+ O_{1/2}, or any solution. The presence of (NaF) layer in the structure is the key difference from the Oftedal's structure. This redefinition of the chemical formula and crystal structure of cordylite will be proposed to IMA-CNMMN. Part II. Crystal structure and crystal chemistry of monazite-xenotime series. Monazite is monoclinic, P2 _1/n, and xenotime is isostructural with zircon (I4_1/amd). Both atomic arrangements are based on (001) chains of intervening phosphate tetrahedra and RE polyhedra, with a REO_8 polyhedron in xenotime that accommodates HRE (Tb - Lu) and a REO_9 polyhedron in monazite that preferentially incorporates LRE (La - Gd). As the structure "transforms" from xenotime to monazite, the crystallographic properties are comparable along the (001) chains, with structural adjustments of 2.2 A along (010) to accommodate the different size RE atoms. Part III. Crystal structure of nanpingite-2M _2, the Cs end-member of muscovite. The crystal structure of nanpingite has been refined to R = 0.058. Compared to K^+ in muscovite, the largest interlayer Cs^+ in nanpingite increases (001) separation between adjacent 2:1 layers, but has little effect on the dimensions in (001). The existence of rare 2M_2 polytype in nanpingite is attributed to this large layer separation, which minimizes the repulsion of the superimposed (along (001)) basal oxygens in neighboring tetrahedral layers.

Improved mobility in InAlN/AlGaN two-dimensional electron gas heterostructures with an atomically smooth heterointerface

NASA Astrophysics Data System (ADS)

Hosomi, Daiki; Miyachi, Yuta; Egawa, Takashi; Miyoshi, Makoto

2018-04-01

We attempted to improve the mobility of InAlN/AlGaN two-dimensional electron gas (2DEG) heterostructures by achieving an atomically smooth heterointerface in metalorganic chemical vapor deposition processes. In the result, it was confirmed that the high-growth-rate AlGaN layer was very effective to improve the surface morphology. The atomically smooth surface morphology with a root-mean-square roughness of 0.26 nm was achieved for an Al0.15Ga0.85N layer under the growth rate of approximately 6 µm/h. Furthermore, nearly lattice-matched In0.17Al0.83N/Al0.15Ga0.85N 2DEG heterostructures with the atomically smooth heterointerface exhibited a 2DEG mobility of 242 cm2 V-1 s-1 with a 2DEG density of 2.6 × 1013/cm2, which was approximately 1.5 times larger than the mobility in a sample grown under original conditions.

Electrochemical Control of Copper Intercalation into Nanoscale Bi 2Se 3

DOE PAGES

Zhang, Jinsong; Sun, Jie; Li, Yanbin; ...

2017-02-20

Intercalation of exotic atoms or molecules into the layered materials remains an extensively investigated subject in current physics and chemistry. However, traditionally melt-growth and chemical interaction strategies are either limited by insufficiency of intercalant concentrations or destitute of accurate controllability. Here, we have developed a general electrochemical intercalation method to efficaciously regulate the concentration of zerovalent copper atoms into layered Bi 2Se 3, followed by comprehensive experimental characterization and analyses. Up to 57% copper atoms (Cu 6.7Bi 2Se 3) can be intercalated with no disruption to the host lattice. Meanwhile the unconventional resistance dip accompanied by a hysteresis loop belowmore » 40 K, as well as the emergence of new Raman peak in Cu xBi 2Se 3, is a distinct manifestation of the interplay between intercalated Cu atoms with Bi 2Se 3 host. Furthermore, our work demonstrates a new methodology to study fundamentally new and unexpected physical behaviors in intercalated metastable materials.« less

Strain-engineered diffusive atomic switching in two-dimensional crystals

PubMed Central

Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.

2016-01-01

Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3–GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways. PMID:27329563

Selective etching of InGaAs/GaAs(100) multilayers of quantum-dot chains

NASA Astrophysics Data System (ADS)

Wang, Zh. M.; Zhang, L.; Holmes, K.; Salamo, G. J.

2005-04-01

We report selective chemical etching as a promising procedure to study the buried quantum dots in multiple InGaAs/GaAs layers. The dot layer-by-dot layer etching is demonstrated using a mixed solution of NH4OH:H2O2:H2O. Regular plan-view atomic force microscopy reveals that all of the exposed InGaAs layers have a chain-like lateral ordering despite the potential of significant In-Ga intermixing during capping. The vertical self-correlation of quantum dots in the chains is observed.

Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide

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

Kerr, A. J.; Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093; Chagarov, E.

2014-09-14

A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al{sub 2}O{sub 3} gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge.more » These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001)« less

Atomic layer deposition of sub-10 nm high-K gate dielectrics on top-gated MoS2 transistors without surface functionalization

NASA Astrophysics Data System (ADS)

Lin, Yu-Shu; Cheng, Po-Hsien; Huang, Kuei-Wen; Lin, Hsin-Chih; Chen, Miin-Jang

2018-06-01

Sub-10 nm high-K gate dielectrics are of critical importance in two-dimensional transition metal dichalcogenides (TMDs) transistors. However, the chemical inertness of TMDs gives rise to a lot of pinholes in gate dielectrics, resulting in large gate leakage current. In this study, sub-10 nm, uniform and pinhole-free Al2O3 high-K gate dielectrics on MoS2 were achieved by atomic layer deposition without surface functionalization, in which an ultrathin Al2O3 layer prepared with a short purge time at a low temperature of 80 °C offers the nucleation cites for the deposition of the overlaying oxide at a higher temperature. Conductive atomic force microscopy reveals the significant suppression of gate leakage current in the sub-10 nm Al2O3 gate dielectrics with the low-temperature nucleation layer. Raman and X-ray photoelectron spectroscopies indicate that no oxidation occurred during the deposition of the low-temperature Al2O3 nucleation layer on MoS2. With the high-quality sub-10 nm Al2O3 high-K gate dielectrics, low hysteresis and subthreshold swing were demonstrated on the normally-off top-gated MoS2 transistors.

Probing the initiation of voltage decay in Li-rich layered cathode materials at the atomic scale

DOE PAGES

Wu, Yan; Ma, Cheng; Yang, Jihui; ...

2015-01-21

Li-rich layered oxides hold great promise for improving the energy density of present-day Li-ion batteries. However, their application is limited by the voltage decay upon cycling, and the origin of such a phenomenon is poorly understood. A major issue is determining the voltage range over which detrimental reactions originate. In the present study, a unique yet effective approach was employed to probe this issue. Instead of studying the materials during the first cycle, electrochemical behavior and evolution of the atomic structures were compared in extensively cycled specimens under varied charge/discharge voltages. With the upper cutoff voltage lowered from 4.8 tomore » 4.4 V, the voltage decay ceased to occur even after 60 cycles. In the meantime, the material maintained its layered structure without any spinel phase emerging at the surface, which is unambiguously shown by the atomic-resolution Z-contrast imaging and electron energy loss spectroscopy. These results have conclusively demonstrated that structural/chemical changes responsible for the voltage decay began between 4.4 and 4.8 V, where the layered-to-spinel transition was the most dramatic structural change observed. Thus, this discovery lays important groundwork for the mechanistic understanding of the voltage decay in Li-rich layered cathode materials.« less

Ultrathin and Atomically Flat Transition-Metal Oxide: Promising Building Blocks for Metal-Insulator Electronics.

PubMed

Cui, Qingsong; Sakhdari, Maryam; Chamlagain, Bhim; Chuang, Hsun-Jen; Liu, Yi; Cheng, Mark Ming-Cheng; Zhou, Zhixian; Chen, Pai-Yen

2016-12-21

We present a new and viable template-assisted thermal synthesis method for preparing amorphous ultrathin transition-metal oxides (TMOs) such as TiO 2 and Ta 2 O 5 , which are converted from crystalline two-dimensional (2D) transition-metal dichalcogenides (TMDs) down to a few atomic layers. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the chemical composition and bonding, surface morphology, and atomic structure of these ultrathin amorphous materials to validate the effectiveness of our synthesis approach. Furthermore, we have fabricated metal-insulator-metal (MIM) diodes using the TiO 2 and Ta 2 O 5 as ultrathin insulating layers with low potential barrier heights. Our MIM diodes show a clear transition from direct tunneling to Fowler-Nordheim tunneling, which was not observed in previously reported MIM diodes with TiO 2 or Ta 2 O 5 as the insulating layer. We attribute the improved performance of our MIM diodes to the excellent flatness and low pinhole/defect densities in our TMO insulting layers converted from 2D TMDs, which enable the low-threshold and controllable electron tunneling transport. We envision that it is possible to use the ultrathin TMOs converted from 2D TMDs as the insulating layer of a wide variety of metal-insulator and field-effect electronic devices for various applications ranging from microwave mixing, parametric conversion, infrared photodetection, emissive energy harvesting, to ultrafast electronic switching.

The nanostructure and microstructure of SiC surface layers deposited by MWCVD and ECRCVD

NASA Astrophysics Data System (ADS)

Dul, K.; Jonas, S.; Handke, B.

2017-12-01

Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to investigate ex-situ the surface topography of SiC layers deposited on Si(100) by Microwave Chemical Vapour Deposition (MWCVD) -S1,S2 layers and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) - layers S3,S4, using silane, methane, and hydrogen. The effects of sample temperature and gas flow on the nanostructure and microstructure have been investigated. The nanostructure was described by three-dimensional surface roughness analysis based on digital image processing, which gives a tool to quantify different aspects of surface features. A total of 13 different numerical parameters used to describe the surface topography were used. The scanning electron image (SEM) of the microstructure of layers S1, S2, and S4 was similar, however, layer S3 was completely different; appearing like grains. Nonetheless, it can be seen that no grain boundary structure is present in the AFM images.

Theoretical aspects of studies of oxide and semiconductor surfaces using low energy positrons

NASA Astrophysics Data System (ADS)

Fazleev, N. G.; Maddox, W. B.; Weiss, A. H.

2011-01-01

This paper presents the results of a theoretical study of positron surface and bulk states and annihilation characteristics of surface trapped positrons at the oxidized Cu(100) single crystal and at both As- and Ga-rich reconstructed GaAs(100) surfaces. The variations in atomic structure and chemical composition of the topmost layers of the surfaces associated with oxidation and reconstructions and the charge redistribution at the surfaces are found to affect localization and spatial extent of the positron surface-state wave functions. The computed positron binding energy, work function, and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the surfaces. Theoretical positron annihilation probabilities with relevant core electrons computed for the oxidized Cu(100) surface and the As- and Ga-rich reconstructed GaAs(100) surfaces are compared with experimental ones estimated from the positron annihilation induced Auger peak intensities measured from these surfaces.

Soft chemical synthesis of silicon nanosheets and their applications

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

Nakano, Hideyuki; Ikuno, Takashi

2016-12-15

Two-dimensional silicon nanomaterials are expected to show different properties from those of bulk silicon materials by virtue of surface functionalization and quantum size effects. Since facile fabrication processes of large area silicon nanosheets (SiNSs) are required for practical applications, a development of soft chemical synthesis route without using conventional vacuum processes is a challenging issue. We have recently succeeded to prepare SiNSs with sub-nanometer thicknesses by exfoliating layered silicon compounds, and they are found to be composed of crystalline single-atom-thick silicon layers. In this review, we present the synthesis and modification methods of SiNSs. These SiNSs have atomically flat andmore » smooth surfaces due to dense coverage of organic moieties, and they are easily self-assembled in a concentrated state to form a regularly stacked structure. We have also characterized the electron transport properties and the electronic structures of SiNSs. Finally, the potential applications of these SiNSs and organic modified SiNSs are also reviewed.« less

The synthesis of graphene from palm oil at different annealing time of nickel substrate via thermal chemical vapor deposition

NASA Astrophysics Data System (ADS)

Salifairus, M. J.; Soga, T.; Alrokayan, Salman A. H.; Khan, Haseeb A.; Rusop, M.

2018-05-01

Graphene has shown a plethora potential of applications with its extraordinary electronic and mechanical properties. It is a 2D carbon allotrope which carbon atoms are arrayed in a hexagonal honeycomb lattice. Graphene was synthesized on the polycrystalline nickel substrate with a dimension of 0.10 mm × 10 mm × 10 mm via thermal chemical vapor deposition (TCVD). The carbon precursor was obtained from a commercial palm oil as a natural carbon source. The D, G, and 2D bands described the vibration of graphitic layer and overtone of the D band at 1357, 1595 and 2703 cm-1 respectively. The lowest G band full width at half maximum (FWHM) was 42.95 cm-1 at 15 minutes annealing time. Raman spectroscopy, UV-vis spectrophotometry, atomic force microscopy, XRD and field emission scanning microscopy characterized the synthesized graphene. Multi-layer graphene was successfully synthesized from the palm oil via TCVD.

Low-frequency Raman modes as fingerprints of layer stacking configurations of transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Liang, Liangbo; Puretzky, Alexander; Sumpter, Bobby; Meunier, Vincent; Geohegan, David; David B. Geohegan Team; Vincent Meunier Team

The tunable optoelectronic properties of stacked two-dimensional (2D) crystal monolayers are determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) can be used to determine the exact atomic registration between different layers in few-layer 2D stacks; however, fast and relatively inexpensive optical characterization techniques are essential for rapid development of the field. Using two- and three-layer MoSe2 and WSe2 crystals synthesized by chemical vapor deposition, we show that the generally unexplored low-frequency (LF) Raman modes (<50 cm-1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations [Puretzky and Liang et al, ACS Nano 2015, 9, 6333]. First-principles Raman calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries. Our combined experimental/theoretical work demonstrates the LF Raman modes potentially more effective than HF Raman modes to probe the layer stacking and interlayer interaction for 2D materials. The authors acknowledge support from Eugene P. Wigner Fellowship at the Oak Ridge National Laboratory and the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility.

Confocal absorption spectral imaging of MoS2: optical transitions depending on the atomic thickness of intrinsic and chemically doped MoS2.

PubMed

Dhakal, Krishna P; Duong, Dinh Loc; Lee, Jubok; Nam, Honggi; Kim, Minsu; Kan, Min; Lee, Young Hee; Kim, Jeongyong

2014-11-07

We performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra (over the range 1.5-3.2 eV) within regions having different numbers of layers and studied the variation of optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to the bulk MoS2 and this shift was attributed to the reduction of the gap energy in the Brillouin zone at the K-point as the atomic thickness increased. We also performed n-type chemical doping of MoS2 films using reduced benzyl viologen (BV) and the confocal absorption spectra modified by the doping showed a strong dependence on the atomic thickness: A and B exciton peaks were greatly quenched in the monolayer MoS2 while much less effect was shown in larger thickness and the BG peak either showed very small quenching for 1 L MoS2 or remained constant for larger thicknesses. Our results indicate that confocal absorption spectral imaging can provide comprehensive information on optical transitions of microscopic size intrinsic and doped two-dimensional layered materials.

UiO-66-NH2 Metal-Organic Framework (MOF) Nucleation on TiO2, ZnO, and Al2O3 Atomic Layer Deposition-Treated Polymer Fibers: Role of Metal Oxide on MOF Growth and Catalytic Hydrolysis of Chemical Warfare Agent Simulants.

PubMed

Lee, Dennis T; Zhao, Junjie; Oldham, Christopher J; Peterson, Gregory W; Parsons, Gregory N

2017-12-27

Metal-organic frameworks (MOFs) chemically bound to polymeric microfibrous textiles show promising performance for many future applications. In particular, Zr-based UiO-66-family MOF-textiles have been shown to catalytically degrade highly toxic chemical warfare agents (CWAs), where favorable MOF/polymer bonding and adhesion are attained by placing a nanoscale metal-oxide layer on the polymer fiber preceding MOF growth. To date, however, the nucleation mechanism of Zr-based MOFs on different metal oxides and how product performance is affected are not well understood. Herein, we provide new insight into how different inorganic nucleation films (i.e., Al 2 O 3 , ZnO, or TiO 2 ) conformally coated on polypropylene (PP) nonwoven textiles via atomic layer deposition (ALD) influence the quality, overall surface area, and the fractional yield of UiO-66-NH 2 MOF crystals solvothermally grown on fiber substrates. Of the materials explored, we find that TiO 2 ALD layers lead to the most effective overall MOF/fiber adhesion, uniformity, and a rapid catalytic degradation rate for a CWA simulant, dimethyl p-nitrophenyl phosphate (DMNP) with t 1/2 = 15 min, 580-fold faster than the catalytic performance of untreated PP textiles. Interestingly, compared to ALD TiO 2 and Al 2 O 3 , ALD ZnO induces a larger MOF yield in solution and mass loading on PP fibrous mats. However, this larger MOF yield is ascribed to chemical instability of the ZnO layer under MOF formation condition, leading to Zn 2+ ions that promote further homogeneous MOF growth. Insights presented here improve understanding of compatibility between active MOF materials and substrate surfaces, which we believe will help advanced MOF composite materials for a variety of useful functions.

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

Atomically Precise Interfaces from Non-stoichiometric Deposition

NASA Astrophysics Data System (ADS)

Nie, Yuefeng; Zhu, Ye; Lee, Che-Hui; Kourkoutis, Lena; Mundy, Julia; Junquera, Javier; Ghosez, Philippe; Baek, David; Sung, Suk Hyun; Xi, Xiaoxing; Shen, Kyle; Muller, David; Schlom, Darrell

2015-03-01

Complex oxide heterostructures display some of the most chemically abrupt, atomically precise interfaces, which is advantageous when constructing new interface phases with emergent properties by juxtaposing incompatible ground states. One might assume that atomically precise interfaces result from stoichiometric growth. Here we show that the most precise control is, however, obtained by using deliberate and specific non-stoichiometric growth conditions. For the precise growth of Srn+1TinO3n+1 Ruddlesden-Popper (RP) phases, stoichiometric deposition leads to the loss of the first RP rock-salt double layer, but growing with a strontium-rich surface layer restores the bulk stoichiometry and ordering of the subsurface RP structure. Our results dramatically expand the materials that can be prepared in epitaxial heterostructures with precise interface control--from just the n = 1 end members (perovskites) to the entire RP homologous series--enabling the exploration of novel quantum phenomena at a richer variety of oxide interfaces.

Atomically precise interfaces from non-stoichiometric deposition

NASA Astrophysics Data System (ADS)

Nie, Y. F.; Zhu, Y.; Lee, C.-H.; Kourkoutis, L. F.; Mundy, J. A.; Junquera, J.; Ghosez, Ph.; Baek, D. J.; Sung, S.; Xi, X. X.; Shen, K. M.; Muller, D. A.; Schlom, D. G.

2014-08-01

Complex oxide heterostructures display some of the most chemically abrupt, atomically precise interfaces, which is advantageous when constructing new interface phases with emergent properties by juxtaposing incompatible ground states. One might assume that atomically precise interfaces result from stoichiometric growth. Here we show that the most precise control is, however, obtained by using deliberate and specific non-stoichiometric growth conditions. For the precise growth of Srn+1TinOn+1 Ruddlesden-Popper (RP) phases, stoichiometric deposition leads to the loss of the first RP rock-salt double layer, but growing with a strontium-rich surface layer restores the bulk stoichiometry and ordering of the subsurface RP structure. Our results dramatically expand the materials that can be prepared in epitaxial heterostructures with precise interface control—from just the n=∞ end members (perovskites) to the entire RP homologous series—enabling the exploration of novel quantum phenomena at a richer variety of oxide interfaces.

Non-destructive spatial characterization of buried interfaces in multilayer stacks via two color picosecond acoustics

NASA Astrophysics Data System (ADS)

Faria, Jorge C. D.; Garnier, Philippe; Devos, Arnaud

2017-12-01

We demonstrate the ability to construct wide-area spatial mappings of buried interfaces in thin film stacks in a non-destructive manner using two color picosecond acoustics. Along with the extraction of layer thicknesses and sound velocities from acoustic signals, the morphological information presented is a powerful demonstration of phonon imaging as a metrological tool. For a series of heterogeneous (polymer, metal, and semiconductor) thin film stacks that have been treated with a chemical procedure known to alter layer properties, the spatial mappings reveal changes to interior thicknesses and chemically modified surface features without the need to remove uppermost layers. These results compare well to atomic force microscopy scans showing that the technique provides a significant advantage to current characterization methods for industrially important device stacks.

Selenium-assisted controlled growth of graphene-Bi2Se3 nanoplates hybrid Dirac materials by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Sun, Zhencui; Man, Baoyuan; Yang, Cheng; Liu, Mei; Jiang, Shouzhen; Zhang, Chao; Zhang, Jiaxin; Liu, Fuyan; Xu, Yuanyuan

2016-03-01

Se seed layers were used to synthesize the high-quality graphene-Bi2Se3 nanoplates hybrid Dirac materials via chemical vapor deposition (CVD) method. The morphology, crystallization and structural properties of the hybrid Dirac materials were characterized by SEM, EDS, Raman, XRD, AFM and HRTEM. The measurement results verify that the Se seed layer on the graphene surface can effectively saturate the surface dangling bonds of the graphene, which not only impel the uniform Bi2Se3 nanoplates growing along the horizontal direction but also can supply enough Se atoms to fill the Se vacancies. We also demonstrate the Se seed layer can effectively avoid the interaction of Bi2Se3 and the graphene. Further experiments testify the different Se seed layer on the graphene surface can be used to control the density of the Bi2Se3 nanoplates.

Revealing the planar chemistry of two-dimensional heterostructures at the atomic level.

PubMed

Chou, Harry; Ismach, Ariel; Ghosh, Rudresh; Ruoff, Rodney S; Dolocan, Andrei

2015-06-23

Two-dimensional (2D) atomic crystals and their heterostructures are an intense area of study owing to their unique properties that result from structural planar confinement. Intrinsically, the performance of a planar vertical device is linked to the quality of its 2D components and their interfaces, therefore requiring characterization tools that can reveal both its planar chemistry and morphology. Here, we propose a characterization methodology combining (micro-) Raman spectroscopy, atomic force microscopy and time-of-flight secondary ion mass spectrometry to provide structural information, morphology and planar chemical composition at virtually the atomic level, aimed specifically at studying 2D vertical heterostructures. As an example system, a graphene-on-h-BN heterostructure is analysed to reveal, with an unprecedented level of detail, the subtle chemistry and interactions within its layer structure that can be assigned to specific fabrication steps. Such detailed chemical information is of crucial importance for the complete integration of 2D heterostructures into functional devices.

Facile Phase Control of Multivalent Vanadium Oxide Thin Films (V2O5 and VO2) by Atomic Layer Deposition and Postdeposition Annealing.

PubMed

Song, Gwang Yeom; Oh, Chadol; Sinha, Soumyadeep; Son, Junwoo; Heo, Jaeyeong

2017-07-19

Atomic layer deposition was adopted to deposit VO x thin films using vanadyl tri-isopropoxide {VO[O(C 3 H 7 )] 3 , VTIP} and water (H 2 O) at 135 °C. The self-limiting and purge-time-dependent growth behaviors were studied by ex situ ellipsometry to determine the saturated growth conditions for atomic-layer-deposited VO x . The as-deposited films were found to be amorphous. The structural, chemical, and optical properties of the crystalline thin films with controlled phase formation were investigated after postdeposition annealing at various atmospheres and temperatures. Reducing and oxidizing atmospheres enabled the formation of pure VO 2 and V 2 O 5 phases, respectively. The possible band structures of the crystalline VO 2 and V 2 O 5 thin films were established. Furthermore, an electrochemical response and a voltage-induced insulator-to-metal transition in the vertical metal-vanadium oxide-metal device structure were observed for V 2 O 5 and VO 2 films, respectively.

Interaction of epitaxial silicene with overlayers formed by exposure to Al atoms and O2 molecules.

PubMed

Friedlein, R; Van Bui, H; Wiggers, F B; Yamada-Takamura, Y; Kovalgin, A Y; de Jong, M P

2014-05-28

As silicene is not chemically inert, the study and exploitation of its electronic properties outside of ultrahigh vacuum environments require the use of insulating capping layers. In order to understand if aluminum oxide might be a suitable encapsulation material, we used high-resolution synchrotron photoelectron spectroscopy to study the interactions of Al atoms and O2 molecules, as well as the combination of both, with epitaxial silicene on thin ZrB2(0001) films grown on Si(111). The deposition of Al atoms onto silicene, up to the coverage of about 0.4 Al per Si atoms, has little effect on the chemical state of the Si atoms. The silicene-terminated surface is also hardly affected by exposure to O2 gas, up to a dose of 4500 L. In contrast, when Al-covered silicene is exposed to the same dose, a large fraction of the Si atoms becomes oxidized. This is attributed to dissociative chemisorption of O2 molecules by Al atoms at the surface, producing reactive atomic oxygen species that cause the oxidation. It is concluded that aluminum oxide overlayers prepared in this fashion are not suitable for encapsulation since they do not prevent but actually enhance the degradation of silicene.

Chemical Evolution of a Protoplanetary Disk

NASA Astrophysics Data System (ADS)

Semenov, Dmitry A.

2011-12-01

In this paper we review recent progress in our understanding of the chemical evolution of protoplanetary disks. Current observational constraints and theoretical modeling on the chemical composition of gas and dust in these systems are presented. Strong variations of temperature, density, high-energy radiation intensities in these disks, both radially and vertically, result in a peculiar disk chemical structure, where a variety of processes are active. In hot, dilute and heavily irradiated atmosphere only the most photostable simple radicals and atoms and atomic ions exist, formed by gas-phase processes. Beneath the atmosphere a partly UV-shielded, warm molecular layer is located, where high-energy radiation drives rich ion-molecule and radical-radical chemistry, both in the gas phase and on dust surfaces. In a cold, dense, dark disk midplane many molecules are frozen out, forming thick icy mantles where surface chemistry is active and where complex polyatomic (organic) species are synthesized. Dynamical processes affect disk chemical composition by enriching it in abundances of complex species produced via slow surface processes, which will become detectable with ALMA.

Effect of dual-dielectric hydrogen-diffusion barrier layers on the performance of low-temperature processed transparent InGaZnO thin-film transistors

NASA Astrophysics Data System (ADS)

Tari, Alireza; Wong, William S.

2018-02-01

Dual-dielectric SiOx/SiNx thin-film layers were used as back-channel and gate-dielectric barrier layers for bottom-gate InGaZnO (IGZO) thin-film transistors (TFTs). The concentration profiles of hydrogen, indium, gallium, and zinc oxide were analyzed using secondary-ion mass spectroscopy characterization. By implementing an effective H-diffusion barrier, the hydrogen concentration and the creation of H-induced oxygen deficiency (H-Vo complex) defects during the processing of passivated flexible IGZO TFTs were minimized. A bilayer back-channel passivation layer, consisting of electron-beam deposited SiOx on plasma-enhanced chemical vapor-deposition (PECVD) SiNx films, effectively protected the TFT active region from plasma damage and minimized changes in the chemical composition of the semiconductor layer. A dual-dielectric PECVD SiOx/PECVD SiNx gate-dielectric, using SiOx as a barrier layer, also effectively prevented out-diffusion of hydrogen atoms from the PECVD SiNx-gate dielectric to the IGZO channel layer during the device fabrication.

Molecular dynamics simulation studies of ionic liquid electrolytes for electric double layer capacitors

NASA Astrophysics Data System (ADS)

Hu, Zongzhi

Molecular Dynamics (MD) simulation has been performed on various Electric Double Layer Capacitors (EDLCs) systems with different Room Temperature Ionic Liquids (RTILs) as well as different structures and materials of electrodes using a computationally efficient, low cost, united atom (UA)/explicit atom (EA) force filed. MD simulation studies on two 1-butyl-3-methylimidazolium (BMIM) based RTILs, i.e., [BMIM][BF4] and [BMIM][PF6], have been conducted on both atomic flat and corrugated graphite as well as (001) and (011) gold electrode surfaces to understand the correlations between the Electric Double Layer (EDL) structure and their corresponding differential capacitance (DC). Our MD simulations have strong agreement with some experimental data. The structures of electrodes also have a strong effect on the capacitance of EDLCs. MD simulations have been conducted on RTILs of N-methyl-N- propylpyrrolidinium [pyr13] and bis(fluorosulfonyl)imide (FSI) as well as [BMIM][PF6] on both curvature electrodes (fullerenes, nanotube, nanowire) and atomic flat electrode surfaces. It turns out that the nanowire electrode systems have the largest capacitance, following by fullerene systems. Nanotube electrode systems have the smallest capacitance, but they are still larger than that of atomically flat electrode system. Also, RTILs with slightly different chemical structure such as [Cnmim], n = 2, 4, 6, and 8, FSI and bis(trifluoromethylsulfonyl)imide (TFSI), have been examined by MD simulation on both flat and nonflat graphite electrode surfaces to study the effect of cation and anion's chemical structures on EDL structure and DC. With prismatic (nonflat) graphite electrodes, a transition from a bell-shape to a camel-shape DC dependence on electrode potential was observed with increase of the cation alkyl tail length for FSI systems. In contrast, the [Cnmim][TFSI] ionic liquids generated only a camel-shape DC on the rough surface regardless of the length of alkyl tail.

Cryo-mediated exfoliation and fracturing of layered materials into 2D quantum dots

PubMed Central

Wang, Yan; Liu, Yang; Zhang, Jianfang; Wu, Jingjie; Xu, Hui; Wen, Xiewen; Zhang, Xiang; Tiwary, Chandra Sekhar; Yang, Wei; Vajtai, Robert; Zhang, Yong; Chopra, Nitin; Odeh, Ihab Nizar; Wu, Yucheng; Ajayan, Pulickel M.

2017-01-01

Atomically thin quantum dots from layered materials promise new science and applications, but their scalable synthesis and separation have been challenging. We demonstrate a universal approach for the preparation of quantum dots from a series of materials, such as graphite, MoS2, WS2, h-BN, TiS2, NbS2, Bi2Se3, MoTe2, Sb2Te3, etc., using a cryo-mediated liquid-phase exfoliation and fracturing process. The method relies on liquid nitrogen pretreatment of bulk layered materials before exfoliation and breakdown into atomically thin two-dimensional quantum dots of few-nanometer lateral dimensions, exhibiting size-confined optical properties. This process is efficient for a variety of common solvents with a wide range of surface tension parameters and eliminates the use of surfactants, resulting in pristine quantum dots without surfactant covering or chemical modification. PMID:29250597

Low-Temperature Atomic Layer Deposition of MoS2 Films.

PubMed

Jurca, Titel; Moody, Michael J; Henning, Alex; Emery, Jonathan D; Wang, Binghao; Tan, Jeffrey M; Lohr, Tracy L; Lauhon, Lincoln J; Marks, Tobin J

2017-04-24

Wet chemical screening reveals the very high reactivity of Mo(NMe 2 ) 4 with H 2 S for the low-temperature synthesis of MoS 2 . This observation motivated an investigation of Mo(NMe 2 ) 4 as a volatile precursor for the atomic layer deposition (ALD) of MoS 2 thin films. Herein we report that Mo(NMe 2 ) 4 enables MoS 2 film growth at record low temperatures-as low as 60 °C. The as-deposited films are amorphous but can be readily crystallized by annealing. Importantly, the low ALD growth temperature is compatible with photolithographic and lift-off patterning for the straightforward fabrication of diverse device structures. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

NASA Astrophysics Data System (ADS)

Zhou, Yangen; Zhang, Yongfan; Lin, Mousheng; Long, Jinlin; Zhang, Zizhong; Lin, Huaxiang; Wu, Jeffrey C.-S.; Wang, Xuxu

2015-09-01

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+-[WO4]2--[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

PubMed Central

Zhou, Yangen; Zhang, Yongfan; Lin, Mousheng; Long, Jinlin; Zhang, Zizhong; Lin, Huaxiang; Wu, Jeffrey C.-S.; Wang, Xuxu

2015-01-01

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+–[WO4]2−–[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface. PMID:26359212

Synthesis of millimeter-scale transition metal dichalcogenides single crystals

DOE PAGES

Gong, Yongji; Ye, Gonglan; Lei, Sidong; ...

2016-02-10

The emergence of semiconducting transition metal dichalcogenide (TMD) atomic layers has opened up unprecedented opportunities in atomically thin electronics. Yet the scalable growth of TMD layers with large grain sizes and uniformity has remained very challenging. Here is reported a simple, scalable chemical vapor deposition approach for the growth of MoSe2 layers is reported, in which the nucleation density can be reduced from 105 to 25 nuclei cm -2, leading to millimeter-scale MoSe 2 single crystals as well as continuous macrocrystalline films with millimeter size grains. The selective growth of monolayers and multilayered MoSe2 films with well-defined stacking orientation canmore » also be controlled via tuning the growth temperature. In addition, periodic defects, such as nanoscale triangular holes, can be engineered into these layers by controlling the growth conditions. The low density of grain boundaries in the films results in high average mobilities, around ≈42 cm 2 V -1 s -1, for back-gated MoSe 2 transistors. This generic synthesis approach is also demonstrated for other TMD layers such as millimeter-scale WSe 2 single crystals.« less

Efficient Planar Perovskite Solar Cells Using Passivated Tin Oxide as an Electron Transport Layer.

PubMed

Lee, Yonghui; Lee, Seunghwan; Seo, Gabseok; Paek, Sanghyun; Cho, Kyung Taek; Huckaba, Aron J; Calizzi, Marco; Choi, Dong-Won; Park, Jin-Seong; Lee, Dongwook; Lee, Hyo Joong; Asiri, Abdullah M; Nazeeruddin, Mohammad Khaja

2018-06-01

Planar perovskite solar cells using low-temperature atomic layer deposition (ALD) of the SnO 2 electron transporting layer (ETL), with excellent electron extraction and hole-blocking ability, offer significant advantages compared with high-temperature deposition methods. The optical, chemical, and electrical properties of the ALD SnO 2 layer and its influence on the device performance are investigated. It is found that surface passivation of SnO 2 is essential to reduce charge recombination at the perovskite and ETL interface and show that the fabricated planar perovskite solar cells exhibit high reproducibility, stability, and power conversion efficiency of 20%.

Staff Directory | Argonne National Laboratory

Science.gov Websites

Engineer essam@anl.gov Jeff Elam Elam, Jeffrey Senior Chemist/Group Leader - Atomic Layer Deposition jelam of Greg Krumdick Krumdick, Greg Manager, Materials Engineering and Research Facility (MERF), Group Postdoctoral Appointee qi.li@anl.gov Photo of Yupo Lin Lin, YuPo Group Leader, Chemical and Biological

Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

NASA Astrophysics Data System (ADS)

Metzler, Dominik; Li, Chen; Engelmann, Sebastian; Bruce, Robert L.; Joseph, Eric A.; Oehrlein, Gottlieb S.

2017-02-01

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.

Matrix Synthesis of Graphene on a Diamond Surface and Its Simulation

NASA Astrophysics Data System (ADS)

Alekseev, N. I.

2018-07-01

A quantum-chemical simulation is performed for the transformation of the upper sublayer of carbon atoms in the lattice of single-crystal diamond into a flat graphene lattice under the influence of the atoms of a molten copper film on the diamond surface. It is established that the stable system configuration corresponds to the thermally activated motion of carbon atoms in the lower sublayer of the interface diamond layer to the position of graphene, i.e., at the same level as the atoms of the upper sublayer. The energy gain in comparison to the noninteracting subsystems of the copper and diamond atoms is approximately 0.7 eV per atom of the lower sublayer. The maximum size of the resulting graphene film is estimated and a possible mechanism for its rupture is considered.

Overcoming nanoscale friction barriers in transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Cammarata, Antonio; Polcar, Tomas

2017-08-01

We study the atomic contributions to the nanoscale friction in layered M X2 (M =Mo , W; X =S , Se, Te) transition metal dichalcogenides by combining ab initio techniques with group-theoretical analysis. Starting from stable atomic configurations, we propose a computational method, named normal-modes transition approximation (NMTA), to individuate possible sliding paths from only the analysis of the phonon modes of the stable geometry. The method provides a way to decompose the atomic displacements realizing the layer sliding in terms of phonon modes of the stable structure, so as to guide the selection and tuning of specific atomic motions promoting M X2 sheets gliding, and to adjust the corresponding energy barrier. The present results show that main contributions to the nanoscale friction are due to few low frequency phonon modes, corresponding to rigid shifts of M X2 layers. We also provide further evidences that a previously reported Ti-doped MoS2 phase is a promising candidate as new material with enhanced tribologic properties. The NMTA approach can be exploited to tune the energetic and the structural features of specific phonon modes, and, thanks to its general formulation, can also be applied to any solid state system, irrespective of the chemical composition and structural topology.

Topography and nanostructural evaluation of chemically and thermally modified titanium substrates.

PubMed

Salemi, Hoda; Behnamghader, Aliasghar; Afshar, Abdollah

2016-10-01

In this research, the effects of chemical and thermal treatment on the morphological and compositional aspects of titanium substrates and so, potentially, on development of biomimetic bone like layers formation during simulated body fluid (SBF) soaking was investigated. The HF, HF/HNO3 and NaOH solutions were used for chemical treatment and some of alkali-treated samples followed a heat treatment at 600°C. The treated samples before and after soaking were subjected to material characterization tests using scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). White light interferometry (WLI) was used to determine the roughness parameters such as Ra, Rq, RKu and Rsk. The significance of the obtained data was assessed using ANOVA variance analysis between all samples. It was observed that the reaction at grain boundaries and sodium titanate intermediate layers play a great role in the nucleation of calcium phosphate layers. Based on the obtained results in this work, the calcium phosphate microstructure deposited on titanium substrates was more affected by chemical modification than surface topography.

Structure determination of the ordered (2 × 1) phase of NiSi surface alloy on Ni(111) using low-energy electron diffraction

NASA Astrophysics Data System (ADS)

Sazzadur Rahman, Md.; Amirul Islam, Md.; Saha, Bidyut Baran; Nakagawa, Takeshi; Mizuno, Seigi

2015-12-01

The (2 × 1) structure of the two-dimensional nickel silicide surface alloy on Ni(111) was investigated using quantitative low-energy electron diffraction analysis. The unit cell of the determined silicide structure contains one Si and one Ni atom, corresponding to a chemical formula of NiSi. The Si atoms adopt substitutional face-centered cubic hollow sites on the Ni(111) substrate. The Ni-Si bond lengths were determined to be 2.37 and 2.34 Å. Both the alloy surface and the underlying first layers of Ni atoms exhibit slight corrugation. The Ni-Si interlayer distance is smaller than the Ni-Ni interlayer distance, which indicates that Si atoms and underlying Ni atoms strongly interact.

Arizona porphyry copper/hydrothermal deposits II: Crystal structure of ajoite, (K + Na)3Cu20Al3Si29O76(OH)16⋅∼8H2O

PubMed Central

Pluth, Joseph J.; Smith, Joseph V.

2002-01-01

A crystal from the type locality Ajo, AZ, yielded just enough intensity from streaked diffractions using synchrotron x-rays at the Advanced Photon Source to solve the crystal structure with composition (K + Na)3Cu20Al3Si29O76(OH)16⋅∼8H2O; triclinic, P1̄, a = 13.634(5) Å, b = 13.687(7), c = 14.522(7), α = 110.83(1)°, β = 107.21(1), γ = 105.68(1); refined to a final R = 12.5%. Electron microprobe analysis yielded a similar chemical composition that is slightly different from the combined chemical and electron microprobe analyses in the literature. The ajoite structure can be described as a zeolitic octahedral-tetrahedral framework that combines the alternate stacking of edge-sharing octahedral CuO6 layers and curved aluminosilicate layers and strings. Channels bounded by elliptical 12-rings and circular 8-rings of tetrahedra contain (K and Na) ions and water. The Al atoms occupy some of the Si tetrahedral sites. Each Cu atom has near-planar bonds to four oxygen atoms plus two longer distances that generate a distorted octahedron. Valence bond estimates indicate that 8 oxygen atoms of 46 are hydroxyl. Only one alkali atom was located in distorted octahedral coordination, and electron microprobe analyses indicate K and Na as major substituents. The water from chemical analysis presumably occurs as disordered molecules of zeolitic type not giving electron density from diffraction. The high R factor results from structural disorder and many weak intensities close to detection level. The crystal chemistry is compared with shattuckite, Cu5(SiO3)4(OH)2, and planchéite, Cu8Si8O22(OH)4⋅H2O, both found in oxidized copper deposits of Arizona but only the former directly with ajoite. PMID:12177404

Arizona porphyry copper/hydrothermal deposits II: crystal structure of ajoite, (K + Na)3Cu20Al3Si29O76(OH)16*~8H2O.

PubMed

Pluth, Joseph J; Smith, Joseph V

2002-08-20

A crystal from the type locality Ajo, AZ, yielded just enough intensity from streaked diffractions using synchrotron x-rays at the Advanced Photon Source to solve the crystal structure with composition (K + Na)3Cu20Al3Si29O76(OH)16* approximately 8H2O; triclinic, P1, a = 13.634(5) A, b = 13.687(7), c = 14.522(7), alpha = 110.83(1) degrees, beta = 107.21(1), gamma = 105.68(1); refined to a final R = 12.5%. Electron microprobe analysis yielded a similar chemical composition that is slightly different from the combined chemical and electron microprobe analyses in the literature. The ajoite structure can be described as a zeolitic octahedral-tetrahedral framework that combines the alternate stacking of edge-sharing octahedral CuO6 layers and curved aluminosilicate layers and strings. Channels bounded by elliptical 12-rings and circular 8-rings of tetrahedra contain (K and Na) ions and water. The Al atoms occupy some of the Si tetrahedral sites. Each Cu atom has near-planar bonds to four oxygen atoms plus two longer distances that generate a distorted octahedron. Valence bond estimates indicate that 8 oxygen atoms of 46 are hydroxyl. Only one alkali atom was located in distorted octahedral coordination, and electron microprobe analyses indicate K and Na as major substituents. The water from chemical analysis presumably occurs as disordered molecules of zeolitic type not giving electron density from diffraction. The high R factor results from structural disorder and many weak intensities close to detection level. The crystal chemistry is compared with shattuckite, Cu5(SiO3)4(OH)2, and planchéite, Cu8Si8O22(OH)4.H2O, both found in oxidized copper deposits of Arizona but only the former directly with ajoite.

Positron Annihilation Induced Auger and Gamma Spectroscopy of Catalytically Important Surfaces

NASA Astrophysics Data System (ADS)

Weiss, A. H.; Nadesalingam, M. P.; Sundaramoorthy, R.; Mukherjee, S.; Fazleev, N. G.

2006-10-01

The annihilation of positrons with core electrons results in unique signatures in the spectra of Auger-electron and annihilation-gamma rays that can be used to make clear chemical identification of atoms at the surface. Because positrons implanted at low energies are trapped with high efficiency in the image-correlation well where they are localized just outside the surface it is possible to use annihilation induced Auger and Gamma signals to probe the surfaces of solids with single atomic layer depth resolution. In this talk we will report recent applications of Positron Annihilation Induced Auger Electron Spectroscopy (PAES) and Auger-Gamma Coincidence Spectroscopy (AGCS) to the study of surface structure and surface chemistry. Our research has demonstrated that PAES spectra can provide new information regarding the composition of the top-most atomic layer. Applications of PAES to the study of catalytically important surfaces of oxides and wide band-gap semiconductors including TiO2, SiO2,Cu2O, and SiC will be presented. We conclude with a discussion of the use of Auger-Gamma and Gamma-Gamma coincidence spectroscopy for the study of surfaces at pressures closer to those found in practical chemical reactors. Research supported by the Welch Foundation Grant Number Y-1100.

Comparison of some effects of modification of a polylactide surface layer by chemical, plasma, and laser methods

NASA Astrophysics Data System (ADS)

Moraczewski, Krzysztof; Rytlewski, Piotr; Malinowski, Rafał; Żenkiewicz, Marian

2015-08-01

The article presents the results of studies and comparison of selected properties of the modified PLA surface layer. The modification was carried out with three methods. In the chemical method, a 0.25 M solution of sodium hydroxide in water and ethanol was utilized. In the plasma method, a 50 W generator was used, which produced plasma in the air atmosphere under reduced pressure. In the laser method, a pulsed ArF excimer laser with fluency of 60 mJ/cm2 was applied. Polylactide samples were examined by using the following techniques: scanning electron microscopy (SEM), atomic force microscopy (AFM), goniometry and X-ray photoelectron spectroscopy (XPS). Images of surfaces of the modified samples were recorded, contact angles were measured, and surface free energy was calculated. Qualitative and quantitative analyses of chemical composition of the PLA surface layer were performed as well. Based on the survey it was found that the best modification results are obtained using the plasma method.

Direct synthesis of large area graphene on insulating substrate by gallium vapor-assisted chemical vapor deposition

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

Murakami, Katsuhisa, E-mail: k.murakami@bk.tsukuba.ac.jp; Hiyama, Takaki; Kuwajima, Tomoya

2015-03-02

A single layer of graphene with dimensions of 20 mm × 20 mm was grown directly on an insulating substrate by chemical vapor deposition using Ga vapor catalysts. The graphene layer showed highly homogeneous crystal quality over a large area on the insulating substrate. The crystal quality of the graphene was measured by Raman spectroscopy and was found to improve with increasing Ga vapor density on the reaction area. High-resolution transmission electron microscopy observations showed that the synthesized graphene had a perfect atomic-scale crystal structure within its grains, which ranged in size from 50 nm to 200 nm.

Effects of combined irradiation of 500 keV protons and atomic oxygen on polyimide films

NASA Astrophysics Data System (ADS)

Novikov, Lev; Chernik, Vladimir; Zhilyakov, Lev; Voronina, Ekaterina; Chirskaia, Natalia

2016-07-01

Polyimide films are widely used on the spacecraft surface as thermal control coating, films in different constuctions, etc. However, the space ionizing radiation of different types can alter the mechanical, optical and electrical properties of polyimide films. For example, it is well known that 20-100 keV proton irradiation causes breaking of chemical bonds and destruction of the surface layer in polyimide, deterioration of its optical properties, etc. In low-Earth orbits serious danger for polymeric materials is atomic oxygen of the upper atmosphere of the Earth, which is the main component in the range of heights of 200-800 km. Due to the orbital spacecraft velocity, the collision energy of oxygen atoms with the surface ( 5 eV) enhances their reactivity and opens additional pathways of their reaction with near-surface layers of materials. Hyperthermal oxygen atom flow causes erosion of the polyimide surface by breaking chemical bonds and forming of volatiles products (primarily, CO and CO _{2}), which leads to mass losses and degradation of material properties. Combined effect of protons and oxygen plasma is expected to give rise to synergistic effects enhancing the destruction of polyimide surface layers. This paper describes experimental investigation of polyimide films sequential irradiation with protons and oxygen plasma. The samples were irradiated by 500 keV protons at fluences of 10 ^{14}-10 ^{16} cm ^{-2} produced with SINP cascade generator KG-500 and 5-20 eV neutral oxygen atoms at fluence of 10 ^{20} cm ^{-2} generated by SINP magnetoplasmodynamics accelerator. The proton bombardment causes the decrease in optical transmission coefficient of samples, but their transmittance recovers partially after the exposure to oxygen plasma. The results of the comparative analysis of polyimide optical transmission spectra, Raman and XPS spectra obtained at different stages of the irradiation of samples, data on mass loss of samples due to erosion of the surface are given. The report also presents the results of computer simulation of protons and oxygen atoms interaction with polyimide, and a comparison of the experimental and calculated data.

Superhydrophobic alumina surface based on stearic acid modification

NASA Astrophysics Data System (ADS)

Feng, Libang; Zhang, Hongxia; Mao, Pengzhi; Wang, Yanping; Ge, Yang

2011-02-01

A novel superhydrophobic alumina surface is fabricated by grafting stearic acid layer onto the porous and roughened aluminum film. The chemical and phase structure, morphology, and the chemical state of the atoms at the superhydrophobic surface were investigated by techniques as FTIR, XRD, FE-SEM, and XPS, respectively. Results show that a super water-repellent surface with a contact angle of 154.2° is generated. The superhydrophobic alumina surface takes on an uneven flowerlike structure with many nanometer-scale hollows distribute in the nipple-shaped protrusions, and which is composed of boehmite crystal and γ-Al2O3. Furthermore, the roughened and porous alumina surface is coated with a layer of hydrophobic alkyl chains which come from stearic acid molecules. Therefore, both the roughened structure and the hydrophobic layer endue the alumina surface with the superhydrophobic behavior.

Electrical properties of solution processed highly transparent ZnO TFT with organic gate dielectric

NASA Astrophysics Data System (ADS)

Pandya, Nirav C.; Joshi, Nikhil G.; Trivedi, U. N.; Joshi, U. S.

2013-02-01

All oxide thin film transistors (TFT) with zinc oxide active layer were fabricated by chemical solution deposition (CSD) using aqueous solutions on glass substrate. Thin film transistors (TFTs) with amorphous zinc oxide as channel layers and poly-vinyl alcohol as dielectric layers were fabricated at low temperatures by chemical solution deposition (CSD). Atomic force microscopy (AFM) confirmed nano grain size with fairly smooth surface topography. Very small leakage currents were achieved in the transfer curves, while soft saturation was observed in the output current voltage (I-V) characteristics of the device. Optical transmission of better than 87% in the visible region was estimated, which is better than the organic gate insulator based ZnO TFTs reported so far. Our results offer lot of promise to TFT based display and optoelectronics.

Chemical mixing at “Al on Fe” and “Fe on Al” interfaces

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

Süle, P.; Horváth, Z. E.; Kaptás, D.

2015-10-07

The chemical mixing at the “Al on Fe” and “Fe on Al” interfaces was studied by molecular dynamics simulations of the layer growth and by {sup 57}Fe Mössbauer spectroscopy. The concentration distribution along the layer growth direction was calculated for different crystallographic orientations, and atomically sharp “Al on Fe” interfaces were found when Al grows over (001) and (110) oriented Fe layers. The Al/Fe(111) interface is also narrow as compared to the intermixing found at the “Fe on Al” interfaces for any orientation. Conversion electron Mössbauer measurements of trilayers—Al/{sup 57}Fe/Al and Al/{sup 57}Fe/Ag grown simultaneously over Si(111) substrate by vacuummore » evaporation—support the results of the molecular dynamics calculations.« less

Laser-assisted atom probe tomography of four paired poly-Si/SiO2 multiple-stacks with each thickness of 10 nm

NASA Astrophysics Data System (ADS)

Kwak, C.-M.; Seol, J.-B.; Kim, Y.-T.; Park, C.-G.

2017-02-01

For the past 10 years, laser-assisted atom probe tomography (APT) analysis has been performed to quantify the near-atomic scale distribution of elements and their local chemical compositions within interfaces that determine the design, processing, and properties of virtually all materials. However, the nature of the occurring laser-induced emission at the surface of needle-shaped sample is highly complex and it has been an ongoing challenge to understand the surface-related interactions between laser-sources and tips containing non-conductive oxides for a robust and reliable analysis of multiple-stacked devices. Here, we find that the APT analysis of four paired poly-Si/SiO2 (conductive/non-conductive) multiple stacks with each thickness of 10 nm is governed by experimentally monitoring three experimental conditions, such as laser-beam energies ranged from 30 to 200 nJ, analysis temperatures varying with 30-100 K, and the inclination of aligned interfaces within a given tip toward analysis direction. Varying with laser-energy and analysis temperature, a drastic compositional ratio of doubly charged Si ions to single charged Si ions within conductive poly-Si layers is modified, as compared with ones detected in the non-conductive layers. Severe distorted APT images of multiple stacks are also inevitable, especially at the conductive layers, and leading to a lowering of the successful analysis yields. This lower throughput has been overcome though changing the inclination of interfaces within a given tip to analysis direction (planar interfaces parallel to the tip axis), but significant deviations in chemical compositions of a conductive layer counted from those of tips containing planar interfaces perpendicular to the tip axis are unavoidable owing to the Si2, SiH2O, and Si2O ions detected, for the first time, within poly-Si layers.

Phonon shift in chemically exfoliated WS2 nanosheet

NASA Astrophysics Data System (ADS)

Sarkar, Abdus Salam; Pal, Suman Kalyan

2018-04-01

We have synthesized few layer WS2 nanosheets in a low boiling point solvent. Few layer of WS2 sheets are characterized by various techniques such as UV-visible and Raman spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). UV-Vis absorption spectra confirm the well dispersed in isopropyl alcohol. SEM and TEM images indicate the sheet like morphology of WS2. Atomic force microscopy image and room temperature Raman spectroscopy confirm the exfoliation of few layer (4-5 layer) of WS2. Further, Raman spectroscopy was used as a meteorology tool to determine the temperature co-efficient. We have systematically investigated the temperature dependent Raman spectroscopic behavior of few layer WS2. Our results depict the softening of the Raman modes E12g in plane vibration and A1g out of plane vibration with increasing the temperature from 77 K to 300 K. Softening of the Raman modes could be explained in terms of the double resonance which is active in the layered materials. The observed temperature coefficients for two Raman peaks E12g and A1g, are - 0.022 cm-1 and -0.009 cm-1, respectively.

Structure and Formation Mechanism of Black TiO 2 Nanoparticles

DOE PAGES

Tian, Mengkun; Mahjouri-Samani, Masoud; Eres, Gyula; ...

2015-10-27

The remarkable properties of black TiO 2 are due to its disordered surface shell surrounding a crystalline core. However, the chemical composition and the atomic and electronic structure of the disordered shell and its relationship to the core remain poorly understood. Using advanced transmission electron microscopy methods, we show that the outermost layer of black TiO 2 nanoparticles consists of a disordered Ti 2O 3 shell. The measurements show a transition region that connects the disordered Ti 2O 3 shell to the perfect rutile core consisting first of four to five monolayers of defective rutile, containing clearly visible Ti interstitialmore » atoms, followed by an ordered reconstruction layer of Ti interstitial atoms. Our data suggest that this reconstructed layer presents a template on which the disordered Ti 2O 3 layers form by interstitial diffusion of Ti ions. In contrast to recent reports that attribute TiO 2 band-gap narrowing to the synergistic action of oxygen vacancies and surface disorder of nonspecific origin, our results point to Ti 2O 3, which is a narrow-band-gap semiconductor. In conclusion, as a stoichiometric compound of the lower oxidation state Ti 3+ it is expected to be a more robust atomic structure than oxygen-deficient TiO 2 for preserving and stabilizing Ti 3+ surface species that are the key to the enhanced photocatalytic activity of black TiO 2.« less

Catalyst design with atomic layer deposition

DOE PAGES

O'Neill, Brandon J.; Jackson, David H. K.; Lee, Jechan; ...

2015-02-06

Atomic layer deposition (ALD) has emerged as an interesting tool for the atomically precise design and synthesis of catalytic materials. Herein, we discuss examples in which the atomic precision has been used to elucidate reaction mechanisms and catalyst structure-property relationships by creating materials with a controlled distribution of size, composition, and active site. We highlight ways ALD has been utilized to design catalysts with improved activity, selectivity, and stability under a variety of conditions (e.g., high temperature, gas and liquid phase, and corrosive environments). In addition, due to the flexibility and control of structure and composition, ALD can create myriadmore » catalytic structures (e.g., high surface area oxides, metal nanoparticles, bimetallic nanoparticles, bifunctional catalysts, controlled microenvironments, etc.) that consequently possess applicability for a wide range of chemical reactions (e.g., CO 2 conversion, electrocatalysis, photocatalytic and thermal water splitting, methane conversion, ethane and propane dehydrogenation, and biomass conversion). Lastly, the outlook for ALD-derived catalytic materials is discussed, with emphasis on the pending challenges as well as areas of significant potential for building scientific insight and achieving practical impacts.« less

Catalyst design with atomic layer deposition

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

O'Neill, Brandon J.; Jackson, David H. K.; Lee, Jechan

Atomic layer deposition (ALD) has emerged as an interesting tool for the atomically precise design and synthesis of catalytic materials. Herein, we discuss examples in which the atomic precision has been used to elucidate reaction mechanisms and catalyst structure-property relationships by creating materials with a controlled distribution of size, composition, and active site. We highlight ways ALD has been utilized to design catalysts with improved activity, selectivity, and stability under a variety of conditions (e.g., high temperature, gas and liquid phase, and corrosive environments). In addition, due to the flexibility and control of structure and composition, ALD can create myriadmore » catalytic structures (e.g., high surface area oxides, metal nanoparticles, bimetallic nanoparticles, bifunctional catalysts, controlled microenvironments, etc.) that consequently possess applicability for a wide range of chemical reactions (e.g., CO 2 conversion, electrocatalysis, photocatalytic and thermal water splitting, methane conversion, ethane and propane dehydrogenation, and biomass conversion). Lastly, the outlook for ALD-derived catalytic materials is discussed, with emphasis on the pending challenges as well as areas of significant potential for building scientific insight and achieving practical impacts.« less

Structural and elastoplastic properties of β -Ga2O3 films grown on hybrid SiC/Si substrates

NASA Astrophysics Data System (ADS)

Osipov, A. V.; Grashchenko, A. S.; Kukushkin, S. A.; Nikolaev, V. I.; Osipova, E. V.; Pechnikov, A. I.; Soshnikov, I. P.

2018-04-01

Structural and mechanical properties of gallium oxide films grown on (001), (011) and (111) silicon substrates with a buffer layer of silicon carbide are studied. The buffer layer was fabricated by the atom substitution method, i.e., one silicon atom per unit cell in the substrate was substituted by a carbon atom by chemical reaction with carbon monoxide. The surface and bulk structure properties of gallium oxide films have been studied by atomic-force microscopy and scanning electron microscopy. The nanoindentation method was used to investigate the elastoplastic characteristics of gallium oxide, and also to determine the elastic recovery parameter of the films under study. The ultimate tensile strength, hardness, elastic stiffness constants, elastic compliance constants, Young's modulus, linear compressibility, shear modulus, Poisson's ratio and other characteristics of gallium oxide have been calculated by quantum chemistry methods based on the PBESOL functional. It is shown that all these properties of gallium oxide are essentially anisotropic. The calculated values are compared with experimental data. We conclude that a change in the silicon orientation leads to a significant reorientation of gallium oxide.

Chemical Patterning by Mechanical Removal of Aqueous Polymers

NASA Astrophysics Data System (ADS)

Barnett, Katherine; Knoebel, Jodi; Davis, Robert C.

2006-10-01

We are developing a new method for micro and nanoscale patterning of lipids and proteins on solid surfaces. A layer of polyethylene glycol (PEG) teminated polyallyl amine (PAA) was initially applied to a mica surface. The PEG surface is a low adhesion surface for proteins. Following polymer deposition an Atomic Force Microscope (AFM) tip was used to remove the polymer layer in desired regions. AFM imaging of the surface after mechanical polymer removal shows squares of exposed MICA surrounded by the PEG surface. The clean mica regions are now available for specific adsorption of lipid or protein layers.

Single-crystalline monolayer and multilayer graphene nano switches

NASA Astrophysics Data System (ADS)

Li, Peng; Jing, Gaoshan; Zhang, Bo; Sando, Shota; Cui, Tianhong

2014-03-01

Growth of monolayer, bi-layer, and tri-layer single-crystalline graphene (SCG) using chemical vapor deposition method is reported. SCG's mechanical properties and single-crystalline nature were characterized and verified by atomic force microscope and Raman spectroscopy. Electro-mechanical switches based on mono- and bi-layer SCG were fabricated, and the superb properties of SCG enable the switches to operate at pull-in voltage as low as 1 V, and high switching speed about 100 ns. These devices exhibit lifetime without a breakdown of over 5000 cycles, far more durable than any other graphene nanoelectromechanical system switches reported.

Single-crystalline monolayer and multilayer graphene nano switches

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

Li, Peng; Cui, Tianhong, E-mail: tcui@me.umn.edu; Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455

2014-03-17

Growth of monolayer, bi-layer, and tri-layer single-crystalline graphene (SCG) using chemical vapor deposition method is reported. SCG's mechanical properties and single-crystalline nature were characterized and verified by atomic force microscope and Raman spectroscopy. Electro-mechanical switches based on mono- and bi-layer SCG were fabricated, and the superb properties of SCG enable the switches to operate at pull-in voltage as low as 1 V, and high switching speed about 100 ns. These devices exhibit lifetime without a breakdown of over 5000 cycles, far more durable than any other graphene nanoelectromechanical system switches reported.

Structural and electrical characterization of microcrystalline silicon films prepared by a layer-by-layer technique with a plasma-enhanced chemical-vapor deposition system

NASA Astrophysics Data System (ADS)

Hong, J. P.; Kim, C. O.; Nahm, T. U.; Kim, C. M.

2000-02-01

Microcrystalline silicon films have been prepared on indium-coated glass utilizing a layer-by-layer technique with a plasma-enhanced chemical-vapor deposition system. The microcrystalline films were fabricated by varying the number of cycles from 10 to 60 under a fixed H2 time (t2) of 120 s, where the corresponding deposition time (t1) of amorphous silicon thin film was 60 s. Structural properties, such as the crystalline volume fraction (Xc) and grain sizes were analyzed by using Raman spectroscopy and a scanning electron microscopy. The carrier transport was characterized by the temperature dependence of dark conductivity, giving rise to the calculation of activation energy (Ea). Optical energy gaps (Eg) were also investigated using an ultraviolet spectrophotometer. In addition, the process under different hydrogen plasma time (t2) at a fixed number of 20 cycles was extensively carried out to study the dominant role of hydrogen atoms in layer-by-layer deposition. Finally, the correlation between structural and electrical properties has been discussed on the basis of experimental results.

Al2O3 Passivation Effect in HfO2·Al2O3 Laminate Structures Grown on InP Substrates.

PubMed

Kang, Hang-Kyu; Kang, Yu-Seon; Kim, Dae-Kyoung; Baik, Min; Song, Jin-Dong; An, Youngseo; Kim, Hyoungsub; Cho, Mann-Ho

2017-05-24

The passivation effect of an Al 2 O 3 layer on the electrical properties was investigated in HfO 2 -Al 2 O 3 laminate structures grown on indium phosphide (InP) substrate by atomic-layer deposition. The chemical state obtained using high-resolution X-ray photoelectron spectroscopy showed that interfacial reactions were dependent on the presence of the Al 2 O 3 passivation layer and its sequence in the HfO 2 -Al 2 O 3 laminate structures. Because of the interfacial reaction, the Al 2 O 3 /HfO 2 /Al 2 O 3 structure showed the best electrical characteristics. The top Al 2 O 3 layer suppressed the interdiffusion of oxidizing species into the HfO 2 films, whereas the bottom Al 2 O 3 layer blocked the outdiffusion of In and P atoms. As a result, the formation of In-O bonds was more effectively suppressed in the Al 2 O 3 /HfO 2 /Al 2 O 3 /InP structure than that in the HfO 2 -on-InP system. Moreover, conductance data revealed that the Al 2 O 3 layer on InP reduces the midgap traps to 2.6 × 10 12 eV -1 cm -2 (compared to that of HfO 2 /InP, that is, 5.4 × 10 12 eV -1 cm -2 ). The suppression of gap states caused by the outdiffusion of In atoms significantly controls the degradation of capacitors caused by leakage current through the stacked oxide layers.

Purification of silicon powder by the formation of thin porous layer followed byphoto-thermal annealing.

PubMed

Khalifa, Marouan; Hajji, Messaoud; Ezzaouia, Hatem

2012-08-08

Porous silicon has been prepared using a vapor-etching based technique on a commercial silicon powder. Strong visible emission was observed in all samples. Obtained silicon powder with a thin porous layer at the surface was subjected to a photo-thermal annealing at different temperatures under oxygen atmosphere followed by a chemical treatment. Inductively coupled plasma atomic emission spectrometry results indicate that silicon purity is improved from 99.1% to 99.994% after annealing at 900°C.

Purification of silicon powder by the formation of thin porous layer followed byphoto-thermal annealing

PubMed Central

2012-01-01

Porous silicon has been prepared using a vapor-etching based technique on a commercial silicon powder. Strong visible emission was observed in all samples. Obtained silicon powder with a thin porous layer at the surface was subjected to a photo-thermal annealing at different temperatures under oxygen atmosphere followed by a chemical treatment. Inductively coupled plasma atomic emission spectrometry results indicate that silicon purity is improved from 99.1% to 99.994% after annealing at 900°C. PMID:22873706

Adhesion-dependent negative friction coefficient on chemically modified graphite at the nanoscale

NASA Astrophysics Data System (ADS)

Deng, Zhao; Smolyanitsky, Alex; Li, Qunyang; Feng, Xi-Qiao; Cannara, Rachel J.

2012-12-01

From the early tribological studies of Leonardo da Vinci to Amontons’ law, friction has been shown to increase with increasing normal load. This trend continues to hold at the nanoscale, where friction can vary nonlinearly with normal load. Here we present nanoscale friction force microscopy (FFM) experiments for a nanoscale probe tip sliding on a chemically modified graphite surface in an atomic force microscope (AFM). Our results demonstrate that, when adhesion between the AFM tip and surface is enhanced relative to the exfoliation energy of graphite, friction can increase as the load decreases under tip retraction. This leads to the emergence of an effectively negative coefficient of friction in the low-load regime. We show that the magnitude of this coefficient depends on the ratio of tip-sample adhesion to the exfoliation energy of graphite. Through both atomistic- and continuum-based simulations, we attribute this unusual phenomenon to a reversible partial delamination of the topmost atomic layers, which then mimic few- to single-layer graphene. Lifting of these layers with the AFM tip leads to greater deformability of the surface with decreasing applied load. This discovery suggests that the lamellar nature of graphite yields nanoscale tribological properties outside the predictive capacity of existing continuum mechanical models.

Reactions of Azine Anions with Nitrogen and Oxygen Atoms: Implications for Titan's Upper Atmosphere and Interstellar Chemistry.

PubMed

Wang, Zhe-Chen; Cole, Callie A; Demarais, Nicholas J; Snow, Theodore P; Bierbaum, Veronica M

2015-08-26

Azines are important in many extraterrestrial environments, from the atmosphere of Titan to the interstellar medium. They have been implicated as possible carriers of the diffuse interstellar bands in astronomy, indicating their persistence in interstellar space. Most importantly, they constitute the basic building blocks of DNA and RNA, so their chemical reactivity in these environments has significant astrobiological implications. In addition, N and O atoms are widely observed in the ISM and in the ionospheres of planets and moons. However, the chemical reactions of molecular anions with abundant interstellar and atmospheric atomic species are largely unexplored. In this paper, gas-phase reactions of deprotonated anions of benzene, pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine with N and O atoms are studied both experimentally and computationally. In all cases, the major reaction channel is associative electron detachment; these reactions are particularly important since they control the balance between negative ions and free electron densities. The reactions of the azine anions with N atoms exhibit larger rate constants than reactions of corresponding chain anions. The reactions of azine anions with O atoms are even more rapid, with complex product patterns for different reactants. The mechanisms are studied theoretically by employing density functional theory; spin conversion is found to be important in determining some product distributions. The rich gas-phase chemistry observed in this work provides a better understanding of ion-atom reactions and their contributions to ionospheric chemistry as well as the chemical processing that occurs in the boundary layers between diffuse and dense interstellar clouds.

Formation of the low-resistivity compound Cu{sub 3}Ge by low-temperature treatment in an atomic hydrogen flux

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

Erofeev, E. V., E-mail: erofeev@micran.ru; Kazimirov, A. I.; Fedin, I. V.

The systematic features of the formation of the low-resistivity compound Cu{sub 3}Ge by low-temperature treatment of a Cu/Ge two-layer system in an atomic hydrogen flux are studied. The Cu/Ge two-layer system is deposited onto an i-GaAs substrate. Treatment of the Cu/Ge/i-GaAs system, in which the layer thicknesses are, correspondingly, 122 and 78 nm, in atomic hydrogen with a flux density of 10{sup 15} at cm{sup 2} s{sup –1} for 2.5–10 min at room temperature induces the interdiffusion of Cu and Ge, with the formation of a polycrystalline film containing the stoichiometric Cu{sub 3}Ge phase. The film consists of vertically orientedmore » grains 100–150 nm in size and exhibits a minimum resistivity of 4.5 µΩ cm. Variations in the time of treatment of the Cu/Ge/i-GaAs samples in atomic hydrogen affect the Cu and Ge depth distribution, the phase composition of the films, and their resistivity. Experimental observation of the synthesis of the Cu{sub 3}Ge compound at room temperature suggests that treatment in atomic hydrogen has a stimulating effect on both the diffusion of Cu and Ge and the chemical reaction of Cu{sub 3}Ge-compound formation. These processes can be activated by the energy released upon the recombination of hydrogen atoms adsorbed at the surface of the Cu/Ge/i-GaAs sample.« less

Laser peening for reducing hydrogen embrittlement

DOEpatents

Hackel, Lloyd A.; Zaleski, Tania M.; Chen, Hao-Lin; Hill, Michael R.; Liu, Kevin K.

2010-05-25

A laser peening process for the densification of metal surfaces and sub-layers and for changing surface chemical activities provides retardation of the up-take and penetration of atoms and molecules, particularly Hydrogen, which improves the lifetime of such laser peened metals. Penetration of hydrogen into metals initiates an embrittlement that leaves the material susceptible to cracking.

Nitride passivation reduces interfacial traps in atomic-layer-deposited Al{sub 2}O{sub 3}/GaAs (001) metal-oxide-semiconductor capacitors using atmospheric metal-organic chemical vapor deposition

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

Aoki, T., E-mail: aokit@sc.sumitomo-chem.co.jp; Fukuhara, N.; Osada, T.

2014-07-21

Using an atmospheric metal-organic chemical vapor deposition system, we passivated GaAs with AlN prior to atomic layer deposition of Al{sub 2}O{sub 3}. This AlN passivation incorporated nitrogen at the Al{sub 2}O{sub 3}/GaAs interface, improving the capacitance-voltage (C–V) characteristics of the resultant metal-oxide-semiconductor capacitors (MOSCAPs). The C–V curves of these devices showed a remarkable reduction in the frequency dispersion of the accumulation capacitance. Using the conductance method at various temperatures, we extracted the interfacial density of states (D{sub it}). The D{sub it} was reduced over the entire GaAs band gap. In particular, these devices exhibited D{sub it} around the midgap ofmore » less than 4 × 10{sup 12} cm{sup −2}eV{sup −1}, showing that AlN passivation effectively reduced interfacial traps in the MOS structure.« less

DFT studies on the Al, B, and P doping of silicene

NASA Astrophysics Data System (ADS)

Hernández Cocoletzi, H.; Castellanos Águila, J. E.

2018-02-01

The search for efficient adsorbents of atoms and molecules has motivated the study of systems in the presence of defects. For this reason, we have investigated theoretically the creation of mono- and di-vacancies on single layer silicene, as well as the Al, B, and P doping of silicene. Using the first-principles method with the generalized gradient approximation in the parameterization of Perdew-Burke-Ernzerhof, we have found that Al, B, and P interact strongly with Si atoms. Besides, when the vacancies are generated, the dangling bonds are saturated in pairs to form new bonds. Optimal geometries, binding energies, density of states (DOS) and charge density are reported. The results suggest that new chemical modifications can be used to modify the electronic properties of single-layer silicene.

Iron-Terephthalate Coordination Network Thin Films Through In-Situ Atomic/Molecular Layer Deposition.

PubMed

Tanskanen, A; Karppinen, M

2018-06-12

Iron terephthalate coordination network thin films can be fabricated using the state-of-the-art gas-phase atomic/molecular layer deposition (ALD/MLD) technique in a highly controlled manner. Iron is an Earth-abundant and nonhazardous transition metal, and with its rich variety of potential applications an interesting metal constituent for the inorganic-organic coordination network films. Our work underlines the role of the metal precursor used when aiming at in-situ ALD/MLD growth of crystalline inorganic-organic thin films. We obtain crystalline iron terephthalate films when FeCl 3 is employed as the iron source whereas depositions based on the bulkier Fe(acac) 3 precursor yield amorphous films. The chemical composition and structure of the films are investigated with GIXRD, XRR, FTIR and XPS.

Monolayer atomic crystal molecular superlattices.

PubMed

Wang, Chen; He, Qiyuan; Halim, Udayabagya; Liu, Yuanyue; Zhu, Enbo; Lin, Zhaoyang; Xiao, Hai; Duan, Xidong; Feng, Ziying; Cheng, Rui; Weiss, Nathan O; Ye, Guojun; Huang, Yun-Chiao; Wu, Hao; Cheng, Hung-Chieh; Shakir, Imran; Liao, Lei; Chen, Xianhui; Goddard, William A; Huang, Yu; Duan, Xiangfeng

2018-03-07

Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 10 7 , along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.

Monolayer atomic crystal molecular superlattices

NASA Astrophysics Data System (ADS)

Wang, Chen; He, Qiyuan; Halim, Udayabagya; Liu, Yuanyue; Zhu, Enbo; Lin, Zhaoyang; Xiao, Hai; Duan, Xidong; Feng, Ziying; Cheng, Rui; Weiss, Nathan O.; Ye, Guojun; Huang, Yun-Chiao; Wu, Hao; Cheng, Hung-Chieh; Shakir, Imran; Liao, Lei; Chen, Xianhui; Goddard, William A., III; Huang, Yu; Duan, Xiangfeng

2018-03-01

Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 107, along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.

Multilayer moisture barrier

DOEpatents

Pankow, Joel W; Jorgensen, Gary J; Terwilliger, Kent M; Glick, Stephen H; Isomaki, Nora; Harkonen, Kari; Turkulainen, Tommy

2015-04-21

A moisture barrier, device or product having a moisture barrier or a method of fabricating a moisture barrier having at least a polymer layer, and interfacial layer, and a barrier layer. The polymer layer may be fabricated from any suitable polymer including, but not limited to, fluoropolymers such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), or ethylene-tetrafluoroethylene (ETFE). The interfacial layer may be formed by atomic layer deposition (ALD). In embodiments featuring an ALD interfacial layer, the deposited interfacial substance may be, but is not limited to, Al.sub.2O.sub.3, AlSiO.sub.x, TiO.sub.2, and an Al.sub.2O.sub.3/TiO.sub.2 laminate. The barrier layer associated with the interfacial layer may be deposited by plasma enhanced chemical vapor deposition (PECVD). The barrier layer may be a SiO.sub.xN.sub.y film.

Properties of nanostructured undoped ZrO{sub 2} thin film electrolytes by plasma enhanced atomic layer deposition for thin film solid oxide fuel cells

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

Cho, Gu Young; Noh, Seungtak; Lee, Yoon Ho

2016-01-15

Nanostructured ZrO{sub 2} thin films were prepared by thermal atomic layer deposition (ALD) and by plasma-enhanced atomic layer deposition (PEALD). The effects of the deposition conditions of temperature, reactant, plasma power, and duration upon the physical and chemical properties of ZrO{sub 2} films were investigated. The ZrO{sub 2} films by PEALD were polycrystalline and had low contamination, rough surfaces, and relatively large grains. Increasing the plasma power and duration led to a clear polycrystalline structure with relatively large grains due to the additional energy imparted by the plasma. After characterization, the films were incorporated as electrolytes in thin film solidmore » oxide fuel cells, and the performance was measured at 500 °C. Despite similar structure and cathode morphology of the cells studied, the thin film solid oxide fuel cell with the ZrO{sub 2} thin film electrolyte by the thermal ALD at 250 °C exhibited the highest power density (38 mW/cm{sup 2}) because of the lowest average grain size at cathode/electrolyte interface.« less

Thermal stability of atomic layer deposited WCxNy electrodes for metal oxide semiconductor devices

NASA Astrophysics Data System (ADS)

Zonensain, Oren; Fadida, Sivan; Fisher, Ilanit; Gao, Juwen; Danek, Michal; Eizenberg, Moshe

2018-01-01

This study is a thorough investigation of the chemical, structural, and electrical stability of W based organo-metallic films, grown by atomic layer deposition, for future use as gate electrodes in advanced metal oxide semiconductor structures. In an earlier work, we have shown that high effective work-function (4.7 eV) was produced by nitrogen enriched films (WCxNy) dominated by W-N chemical bonding, and low effective work-function (4.2 eV) was produced by hydrogen plasma resulting in WCx films dominated by W-C chemical bonding. In the current work, we observe, using x-ray diffraction analysis, phase transformation of the tungsten carbide and tungsten nitride phases after 900 °C annealing to the cubic tungsten phase. Nitrogen diffusion is also observed and is analyzed with time-of-flight secondary ion mass spectroscopy. After this 900 °C anneal, WCxNy effective work function tunability is lost and effective work-function values of 4.7-4.8 eV are measured, similar to stable effective work function values measured for PVD TiN up to 900 °C anneal. All the observed changes after annealing are discussed and correlated to the observed change in the effective work function.

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

Protecting nickel with graphene spin-filtering membranes: A single layer is enough

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

Martin, M.-B.; Dlubak, B.; Piquemal-Banci, M.

2015-07-06

We report on the demonstration of ferromagnetic spin injectors for spintronics which are protected against oxidation through passivation by a single layer of graphene. The graphene monolayer is directly grown by catalytic chemical vapor deposition on pre-patterned nickel electrodes. X-ray photoelectron spectroscopy reveals that even with its monoatomic thickness, monolayer graphene still efficiently protects spin sources against oxidation in ambient air. The resulting single layer passivated electrodes are integrated into spin valves and demonstrated to act as spin polarizers. Strikingly, the atom-thick graphene layer is shown to be sufficient to induce a characteristic spin filtering effect evidenced through the signmore » reversal of the measured magnetoresistance.« less

Efficiency Enhancement of Nanotextured Black Silicon Solar Cells Using Al2O3/TiO2 Dual-Layer Passivation Stack Prepared by Atomic Layer Deposition.

PubMed

Wang, Wei-Cheng; Tsai, Meng-Chen; Yang, Jason; Hsu, Chuck; Chen, Miin-Jang

2015-05-20

In this study, efficient nanotextured black silicon (NBSi) solar cells composed of silicon nanowire arrays and an Al2O3/TiO2 dual-layer passivation stack on the n(+) emitter were fabricated. The highly conformal Al2O3 and TiO2 surface passivation layers were deposited on the high-aspect-ratio surface of the NBSi wafers using atomic layer deposition. Instead of the single Al2O3 passivation layer with a negative oxide charge density, the Al2O3/TiO2 dual-layer passivation stack treated with forming gas annealing provides a high positive oxide charge density and a low interfacial state density, which are essential for the effective field-effect and chemical passivation of the n(+) emitter. In addition, the Al2O3/TiO2 dual-layer passivation stack suppresses the total reflectance over a broad range of wavelengths (400-1000 nm). Therefore, with the Al2O3/TiO2 dual-layer passivation stack, the short-circuit current density and efficiency of the NBSi solar cell were increased by 11% and 20%, respectively. In conclusion, a high efficiency of 18.5% was achieved with the NBSi solar cells by using the n(+)-emitter/p-base structure passivated with the Al2O3/TiO2 stack.

Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns

DOE PAGES

Chang, Tzu-Hsuan; Xiong, Shisheng; Jacobberger, Robert M.; ...

2016-08-16

Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyreneblock-poly(methyl methacrylate). Faster assembly kinetics aremore » observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. Lastly, the rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces.« less

Toward the growth of an aligned single-layer MoS2 film.

PubMed

Kim, Daeho; Sun, Dezheng; Lu, Wenhao; Cheng, Zhihai; Zhu, Yeming; Le, Duy; Rahman, Talat S; Bartels, Ludwig

2011-09-20

Molybdenum disulfide (molybdenite) monolayer islands and flakes have been grown on a copper surface at comparatively low temperature and mild conditions through sulfur loading of the substrate using thiophenol (benzenethiol) followed by the evaporation of Mo atoms and annealing. The MoS(2) islands show a regular Moiré pattern in scanning tunneling microscopy, attesting to their atomic ordering and high quality. They are all aligned with the substrate high-symmetry directions providing for rotational-domain-free monolayer growth. © 2011 American Chemical Society

Robust forests of vertically aligned carbon nanotubes chemically assembled on carbon substrates.

PubMed

Garrett, David J; Flavel, Benjamin S; Shapter, Joseph G; Baronian, Keith H R; Downard, Alison J

2010-02-02

Forests of vertically aligned carbon nanotubes (VACNTs) have been chemically assembled on carbon surfaces. The structures show excellent stability over a wide potential range and are resistant to degradation from sonication in acid, base, and organic solvent. Acid-treated single-walled carbon nanotubes (SWCNTs) were assembled on amine-terminated tether layers covalently attached to pyrolyzed photoresist films. Tether layers were electrografted to the carbon substrate by reduction of the p-aminobenzenediazonium cation and oxidation of ethylenediamine. The amine-modified surfaces were incubated with cut SWCNTs in the presence of N,N'-dicyclohexylcarbodiimide (DCC), giving forests of vertically aligned carbon nanotubes (VACNTs). The SWCNT assemblies were characterized by scanning electron microscopy, atomic force microscopy, and electrochemistry. Under conditions where the tether layers slow electron transfer between solution-based redox probes and the underlying electrode, the assembly of VACNTs on the tether layer dramatically increases the electron-transfer rate at the surface. The grafting procedure, and hence the preparation of VACNTs, is applicable to a wide range of materials including metals and semiconductors.

Chemical Substitution and High Pressure Effects on Superconductors in the LnOBiS$$_2$$ (Ln = La-Nd) System

DOE PAGES

Fang, Yuankan; Wolowiec, Christian T.; Yazici, Duygu; ...

2015-12-14

A large number of compounds which contain BiSmore » $$_2$$ layers exhibit enhanced superconductivity upon electron doping. Much interest and research effort has been focused on BiS$$_2$$-based compounds which provide new opportunities for exploring the nature of superconductivity. Important to the study of BiS2-based superconductors is the relation between structure and superconductivity. By modifying either the superconducting BiS$$_2$$ layers or the blocking layers in these layered compounds, one can effectively tune the lattice parameters, local atomic environment, electronic structure, and other physical properties of these materials. In this article, we will review some of the recent progress on research of the effects of chemical substitution in BiS$$_2$$-based compounds, with special attention given to the compounds in the LnOBiSS$$_2$$ (Ln = La-Nd) system. Strategies which are reported to be essential in optimizing superconductivity of these materials will also be discussed.« less

Compositional depth profile of a native oxide LPCVD MNOS structure using X-ray photoelectron spectroscopy and chemical etching

NASA Technical Reports Server (NTRS)

Wurzbach, J. A.; Grunthaner, F. J.

1983-01-01

It is pointed out that there is no report of an unambiguous analysis of the composition and interfacial structure of MNOS (metal-nitride oxide semiconductor) systems, despite the technological importance of these systems. The present investigation is concerned with a study of an MNOS structure on the basis of a technique involving the use of X-ray photoelectron spectroscopy (XPS) with a controlled stopped-flow chemical-etching procedure. XPS is sensitive to the structure of surface layers, while stopped-flow etching permits the controlled removal of overlying material on a scale of atomic layers, to expose new surface layers as a function of thickness. Therefore, with careful analysis of observed intensities at measured depths, this combination of techniques provides depth resolution between 5 and 10 A. According to the obtained data there is intact SiO2 at the substrate interface. There appears to be a thin layer containing excess bonds to silicon on top of the SiO2.

Topographic, optical and chemical properties of zinc particle coatings deposited by means of atmospheric pressure plasma

NASA Astrophysics Data System (ADS)

Wallenhorst, L. M.; Loewenthal, L.; Avramidis, G.; Gerhard, C.; Militz, H.; Ohms, G.; Viöl, W.

2017-07-01

In this research, topographic, optical and chemical properties of zinc oxide layers deposited by a cold plasma-spray process were measured. Here, zinc micro particles were fed to the afterglow of a plasma spark discharge whereas the substrates were placed in a quite cold zone of the effluent plasma jet. In this vein, almost closed layers were realised on different samples. As ascertained by laser scanning and atomic force microscopic measurements the particle size of the basic layer is in the nanometre scale. Additionally, larger particles and agglomerates were found on its top. The results indicate a partial plasma-induced diminishment of the initial particles, most probably due to melting or vaporisation. It is further shown that the plasma gives rise to an increased oxidation of such particles as confirmed by X-ray photoelectron spectroscopy. Quantitative analysis of the resulting mixed layer was performed. It is shown that the deposited layers consist of zinc oxide and elemental zinc in approximately equal shares. In addition, the layer's band gap energy was determined by spectroscopic analysis. Here, considerable UV blocking properties of the deposited layers were observed. Possible underlying effects as well as potential applications are presented.

Advances in single-molecule magnet surface patterning through microcontact printing.

PubMed

Mannini, Matteo; Bonacchi, Daniele; Zobbi, Laura; Piras, Federica M; Speets, Emiel A; Caneschi, Andrea; Cornia, Andrea; Magnani, Agnese; Ravoo, Bart Jan; Reinhoudt, David N; Sessoli, Roberta; Gatteschi, Dante

2005-07-01

We present an implementation of strategies to deposit single-molecule magnets (SMMs) using microcontact printing microCP). We describe different approaches of microCP to print stripes of a sulfur-functionalized dodecamanganese (III, IV) cluster on gold surfaces. Comparison by atomic force microscopy profile analysis of the patterned structures confirms the formation of a chemically stable single layer of SMMs. Images based on chemical contrast, obtained by time-of-flight secondary ion mass spectrometry, confirm the patterned structure.

Adsorbed Layers of Ferritin at Solid and Fluid Interfaces Studied by Atomic Force Microscopy.

PubMed

Johnson; Yuan; Lenhoff

2000-03-15

The adsorption of the iron storage protein ferritin was studied by liquid tapping mode atomic force microscopy in order to obtain molecular resolution in the adsorbed layer within the aqueous environment in which the adsorption was carried out. The surface coverage and the structure of the adsorbed layer were investigated as functions of ionic strength and pH on two different charged surfaces, namely chemically modified glass slides and mixed surfactant films at the air-water interface, which were transferred to graphite substrates after adsorption. Surface coverage trends with both ionic strength and pH indicate the dominance of electrostatic effects, with the balance shifting between intermolecular repulsion and protein-surface attraction. The resulting behavior is more complex than that seen for larger colloidal particles, which appear to follow a modified random sequential adsorption model monotonically. The structure of the adsorbed layers at the solid surfaces is random, but some indication of long-range order is apparent at fluid interfaces, presumably due to the higher protein mobility at the fluid interface. Copyright 2000 Academic Press.

Atomic layer deposition of ZrO2 on W for metal-insulator-metal capacitor application

NASA Astrophysics Data System (ADS)

Lee, Sang-Yun; Kim, Hyoungsub; McIntyre, Paul C.; Saraswat, Krishna C.; Byun, Jeong-Soo

2003-04-01

A metal-insulator-metal (MIM) capacitor using ZrO2 on tungsten (W) metal bottom electrode was demonstrated and characterized in this letter. Both ZrO2 and W metal were synthesized by an atomic layer deposition (ALD) method. High-quality 110˜115 Å ZrO2 films were grown uniformly on ALD W using ZrCl4 and H2O precursors at 300 °C, and polycrystalline ZrO2 in the ALD regime could be obtained. A 13˜14-Å-thick interfacial layer between ZrO2 and W was observed after fabrication, and it was identified as WOx through angle-resolved x-ray photoelectron spectroscopy analysis with wet chemical etching. The apparent equivalent oxide thickness was 20˜21 Å. An effective dielectric constant of 22˜25 including an interfacial WOx layer was obtained by measuring capacitance and thickness of MIM capacitors with Pt top electrodes. High capacitance per area (16˜17 fF/μm2) and low leakage current (10-7 A/cm2 at ±1 V) were achieved.

Infrared spectroscopy of wafer-scale graphene.

PubMed

Yan, Hugen; Xia, Fengnian; Zhu, Wenjuan; Freitag, Marcus; Dimitrakopoulos, Christos; Bol, Ageeth A; Tulevski, George; Avouris, Phaedon

2011-12-27

We report spectroscopy results from the mid- to far-infrared on wafer-scale graphene, grown either epitaxially on silicon carbide or by chemical vapor deposition. The free carrier absorption (Drude peak) is simultaneously obtained with the universal optical conductivity (due to interband transitions) and the wavelength at which Pauli blocking occurs due to band filling. From these, the graphene layer number, doping level, sheet resistivity, carrier mobility, and scattering rate can be inferred. The mid-IR absorption of epitaxial two-layer graphene shows a less pronounced peak at 0.37 ± 0.02 eV compared to that in exfoliated bilayer graphene. In heavily chemically doped single-layer graphene, a record high transmission reduction due to free carriers approaching 40% at 250 μm (40 cm(-1)) is measured in this atomically thin material, supporting the great potential of graphene in far-infrared and terahertz optoelectronics.

Direct Growth of Graphene on Silicon by Metal-Free Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Tai, Lixuan; Zhu, Daming; Liu, Xing; Yang, Tieying; Wang, Lei; Wang, Rui; Jiang, Sheng; Chen, Zhenhua; Xu, Zhongmin; Li, Xiaolong

2018-06-01

The metal-free synthesis of graphene on single-crystal silicon substrates, the most common commercial semiconductor, is of paramount significance for many technological applications. In this work, we report the growth of graphene directly on an upside-down placed, single-crystal silicon substrate using metal-free, ambient-pressure chemical vapor deposition. By controlling the growth temperature, in-plane propagation, edge-propagation, and core-propagation, the process of graphene growth on silicon can be identified. This process produces atomically flat monolayer or bilayer graphene domains, concave bilayer graphene domains, and bulging few-layer graphene domains. This work would be a significant step toward the synthesis of large-area and layer-controlled, high-quality graphene on single-crystal silicon substrates. [Figure not available: see fulltext.

Evidence for Chemical and Electronic Nonuniformities in the Formation of the Interface of RbF-Treated Cu(In,Ga)Se2 with CdS.

PubMed

Nicoara, Nicoleta; Kunze, Thomas; Jackson, Philip; Hariskos, Dimitrios; Duarte, Roberto Félix; Wilks, Regan G; Witte, Wolfram; Bär, Marcus; Sadewasser, Sascha

2017-12-20

We report on the initial stages of CdS buffer layer formation on Cu(In,Ga)Se 2 (CIGSe) thin-film solar cell absorbers subjected to rubidium fluoride (RbF) postdeposition treatment (PDT). A detailed characterization of the CIGSe/CdS interface for different chemical bath deposition (CBD) times of the CdS layer is obtained from spatially resolved atomic and Kelvin probe force microscopy and laterally integrating X-ray spectroscopies. The observed spatial inhomogeneity in the interface's structural, chemical, and electronic properties of samples undergoing up to 3 min of CBD treatments is indicative of a complex interface formation including an incomplete coverage and/or nonuniform composition of the buffer layer. It is expected that this result impacts solar cell performance, in particular when reducing the CdS layer thickness (e.g., in an attempt to increase the collection in the ultraviolet wavelength region). Our work provides important findings on the absorber/buffer interface formation and reveals the underlying mechanism for limitations in the reduction of the CdS thickness, even when an alkali PDT is applied to the CIGSe absorber.

The stability boundary of group-III transition metal diboride ScB 2 (0 0 0 1) surfaces

NASA Astrophysics Data System (ADS)

Zhao, Hui; Qin, Na

2012-01-01

Experimental observations and theoretical investigations exhibit that a group-IV(V) transition metal diboride (0 0 0 1) surface is terminated with a 1 × 1 TM(B) layer. As to a group-III transition metal diboride, we have investigated the stability boundary of ScB2 (0 0 0 1) surfaces using first principles total energy plane-wave pseudopotential method based on density functional theory. The Mulliken charge population analysis shows that Sc atoms in the second layer cannot provide B atoms in the first layer with sufficient electrons to form a complete graphene-like boron layer. We also found that the charge transfer between the first and the second layer for the B-terminated surface is more than that for Sc-terminated surface. It elucidates the reason that the outermost interlayer spacing contract more strongly in the B-terminated surface than in the Sc-terminated surface. The surface energies of both terminated ScB2 (0 0 0 1) surfaces as a function of the chemical potential of B are also calculated to check the relative stability of the two surface structures.

Dielectric discontinuity at interfaces in the atomic-scale limit: permittivity of ultrathin oxide films on silicon.

PubMed

Giustino, Feliciano; Umari, Paolo; Pasquarello, Alfredo

2003-12-31

Using a density-functional approach, we study the dielectric permittivity across interfaces at the atomic scale. Focusing on the static and high-frequency permittivities of SiO2 films on silicon, for oxide thicknesses from 12 A down to the atomic scale, we find a departure from bulk values in accord with experiment. A classical three-layer model accounts for the calculated permittivities and is supported by the microscopic polarization profile across the interface. The local screening varies on length scales corresponding to first-neighbor distances, indicating that the dielectric transition is governed by the chemical grading. Silicon-induced gap states are shown to play a minor role.

The Influence of Atomic Diffusion on Stellar Ages and Chemical Tagging

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

Dotter, Aaron; Conroy, Charlie; Cargile, Phillip

2017-05-10

In the era of large stellar spectroscopic surveys, there is an emphasis on deriving not only stellar abundances but also the ages for millions of stars. In the context of Galactic archeology, stellar ages provide a direct probe of the formation history of the Galaxy. We use the stellar evolution code MESA to compute models with atomic diffusion—with and without radiative acceleration—and extra mixing in the surface layers. The extra mixing consists of both density-dependent turbulent mixing and envelope overshoot mixing. Based on these models we argue that it is important to distinguish between initial, bulk abundances (parameters) and current,more » surface abundances (variables) in the analysis of individual stellar ages. In stars that maintain radiative regions on evolutionary timescales, atomic diffusion modifies the surface abundances. We show that when initial, bulk metallicity is equated with current, surface metallicity in isochrone age analysis, the resulting stellar ages can be systematically overestimated by up to 20%. The change of surface abundances with evolutionary phase also complicates chemical tagging, which is the concept that dispersed star clusters can be identified through unique, high-dimensional chemical signatures. Stars from the same cluster, but in different evolutionary phases, will show different surface abundances. We speculate that calibration of stellar models may allow us to estimate not only stellar ages but also initial abundances for individual stars. In the meantime, analyzing the chemical properties of stars in similar evolutionary phases is essential to minimize the effects of atomic diffusion in the context of chemical tagging.« less

All-Diamond Microelectrodes as Solid State Probes for Localized Electrochemical Sensing.

PubMed

Silva, Eduardo L; Gouvêa, Cristol P; Quevedo, Marcela C; Neto, Miguel A; Archanjo, Braulio S; Fernandes, António J S; Achete, Carlos A; Silva, Rui F; Zheludkevich, Mikhail L; Oliveira, Filipe J

2015-07-07

The fabrication of an all-diamond microprobe is demonstrated for the first time. This ME (microelectrode) assembly consists of an inner boron doped diamond (BDD) layer and an outer undoped diamond layer. Both layers were grown on a sharp tungsten tip by chemical vapor deposition (CVD) in a stepwise manner within a single deposition run. BDD is a material with proven potential as an electrochemical sensor. Undoped CVD diamond is an insulating material with superior chemical stability in comparison to conventional insulators. Focused ion beam (FIB) cutting of the apex of the ME was used to expose an electroactive BDD disk. By cyclic voltammetry, the redox reaction of ferrocenemethanol was shown to take place at the BDD microdisk surface. In order to ensure that the outer layer was nonelectrically conductive, a diffusion barrier for boron atoms was established seeking the formation of boron-hydrogen complexes at the interface between the doped and the undoped diamond layers. The applicability of the microelectrodes in localized corrosion was demonstrated by scanning amperometric measurements of oxygen distribution above an Al-Cu-CFRP (Carbon Fiber Reinforced Polymer) galvanic corrosion cell.

Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices

NASA Astrophysics Data System (ADS)

Giri, Ashutosh; Niemelä, Janne-Petteri; Tynell, Tommi; Gaskins, John T.; Donovan, Brian F.; Karppinen, Maarit; Hopkins, Patrick E.

2016-03-01

Nanomaterial interfaces and concomitant thermal resistances are generally considered as atomic-scale planes that scatter the fundamental energy carriers. Given that the nanoscale structural and chemical properties of solid interfaces can strongly influence this thermal boundary conductance, the ballistic and diffusive nature of phonon transport along with the corresponding phonon wavelengths can affect how energy is scattered and transmitted across an interfacial region between two materials. In hybrid composites composed of atomic layer building blocks of inorganic and organic constituents, the varying interaction between the phononic spectrum in the inorganic crystals and vibronic modes in the molecular films can provide a new avenue to manipulate the energy exchange between the fundamental vibrational energy carriers across interfaces. Here, we systematically study the heat transfer mechanisms in hybrid superlattices of atomic- and molecular-layer-grown zinc oxide and hydroquinone with varying thicknesses of the inorganic and organic layers in the superlattices. We demonstrate ballistic energy transfer of phonons in the zinc oxide that is limited by scattering at the zinc oxide/hydroquinone interface for superlattices with a single monolayer of hydroquinone separating the thicker inorganic layers. The concomitant thermal boundary conductance across the zinc oxide interfacial region approaches the maximal thermal boundary conductance of a zinc oxide phonon flux, indicative of the contribution of long wavelength vibrations across the aromatic molecular monolayers in transmitting energy across the interface. This transmission of energy across the molecular interface decreases considerably as the thickness of the organic layers are increased.

Quantum Chemical Study of Water Adsorption on the Surfaces of SrTiO3 Nanotubes.

PubMed

Bandura, Andrei V; Kuruch, Dmitry D; Evarestov, Robert A

2015-07-20

We have studied the adsorption of water molecules on the inner and outer surfaces of nanotubes generated by rolling (001) layers of SrTiO3 cubic crystals. The stability and the atomic and electronic structures of the adsorbed layers are determined by using hybrid density functional theory. The absorption energy and the preferred adsorbate structure are essentially governed by the nature of the surface of the nanotube. Dissociative adsorption prevails on the outer nanotube surfaces. The stability of the adsorbed layers on the inner surfaces is related to the possibility of the formation of hydrogen bonds between water molecules and surface oxygen atoms, and depends on the surface curvature. The presence of water molecules on the inner surface of the nanotubes leads to an increase of the electronic band gap. Externally TiO2 -terminated nanotubes could be used for the photocatalytic decomposition of water by ultraviolet radiation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study of Strength Characteristics of Steel Specimens after Selective Laser Melting of Powder Materials 17-4PH, 316L, 321

NASA Astrophysics Data System (ADS)

Zhukov, Anton; Barakhtin, Boris; Kuznetsov, Pavel

By the method of selective laser melting of powder materials nanostructured stainless steels 17-4PH, 316L, 321 were obtained. In all experiments the recorded hardness increase depending on the construction parameters. Obtained relationship of hardness increase with the carbon ratio, which explained by the chemical composition of the metal in the melting zone. It is suggested that the effect of hardness increase is associated with structural changes as to the formation and dissolution of hardening nanophases. Methods of metallography were performed in structural studies. Traces of interlayer segregation were detected inside the grains as turbulent eddies in the bands of different saturation tone caused by the migration of convective (mass transfer) metal atoms. It was visible signs of crystallization through the grain places the image (dendrite crystals). These facts revealed structural features suggest that the adhesion layers of melted powder was initiated by the colder layers and going mechanism epitaxy by coherently oriented groups of atoms from layers of melting.

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

NASA Astrophysics Data System (ADS)

Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

2007-06-01

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)- p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

Nano-fabricated superconducting radio-frequency composites, method for producing nano-fabricated superconducting rf composites

DOEpatents

Norem, James H.; Pellin, Michael J.

2013-06-11

Superconducting rf is limited by a wide range of failure mechanisms inherent in the typical manufacture methods. This invention provides a method for fabricating superconducting rf structures comprising coating the structures with single atomic-layer thick films of alternating chemical composition. Also provided is a cavity defining the invented laminate structure.

Surface functionalization of cyclic olefin copolymer with aryldiazonium salts: A covalent grafting method

NASA Astrophysics Data System (ADS)

Brisset, Florian; Vieillard, Julien; Berton, Benjamin; Morin-Grognet, Sandrine; Duclairoir-Poc, Cécile; Le Derf, Franck

2015-02-01

Covalent immobilization of biomolecules on the surface of cyclic olefin copolymer (COC) is still a tough challenge. We developed a robust method for COC surface grafting through reaction with aryldiazonium. Chemical diazonium reduction generated an aryl radical and the formation of a grafted film layer on the organic surface. We also demonstrated that the chemical reduction of diazonium salt was not sufficient to form a film on the COC surface. UV illumination had to be combined with chemical reduction to graft an aryl layer onto the COC surface. We optimized organic film deposition by using different chemical reducers, different reaction times and reagent proportions. We characterized surface modifications by fluorescence microscopy and contact angle measurements, infrared spectroscopy, X-ray photoemission spectroscopy and Raman spectroscopy, and assessed the topography of the aryl film by atomic force microscopy. This original strategy allowed us to evidence various organic functions to graft biomolecules onto COC surfaces with a fast and efficient technique.

Surface passivation of n-type doped black silicon by atomic-layer-deposited SiO2/Al2O3 stacks

NASA Astrophysics Data System (ADS)

van de Loo, B. W. H.; Ingenito, A.; Verheijen, M. A.; Isabella, O.; Zeman, M.; Kessels, W. M. M.

2017-06-01

Black silicon (b-Si) nanotextures can significantly enhance the light absorption of crystalline silicon solar cells. Nevertheless, for a successful application of b-Si textures in industrially relevant solar cell architectures, it is imperative that charge-carrier recombination at particularly highly n-type doped black Si surfaces is further suppressed. In this work, this issue is addressed through systematically studying lowly and highly doped b-Si surfaces, which are passivated by atomic-layer-deposited Al2O3 films or SiO2/Al2O3 stacks. In lowly doped b-Si textures, a very low surface recombination prefactor of 16 fA/cm2 was found after surface passivation by Al2O3. The excellent passivation was achieved after a dedicated wet-chemical treatment prior to surface passivation, which removed structural defects which resided below the b-Si surface. On highly n-type doped b-Si, the SiO2/Al2O3 stacks result in a considerable improvement in surface passivation compared to the Al2O3 single layers. The atomic-layer-deposited SiO2/Al2O3 stacks therefore provide a low-temperature, industrially viable passivation method, enabling the application of highly n- type doped b-Si nanotextures in industrial silicon solar cells.

Atomic-Scale Variations of the Mechanical Response of 2D Materials Detected by Noncontact Atomic Force Microscopy.

PubMed

de la Torre, B; Ellner, M; Pou, P; Nicoara, N; Pérez, Rubén; Gómez-Rodríguez, J M

2016-06-17

We show that noncontact atomic force microscopy (AFM) is sensitive to the local stiffness in the atomic-scale limit on weakly coupled 2D materials, as graphene on metals. Our large amplitude AFM topography and dissipation images under ultrahigh vacuum and low temperature resolve the atomic and moiré patterns in graphene on Pt(111), despite its extremely low geometric corrugation. The imaging mechanisms are identified with a multiscale model based on density-functional theory calculations, where the energy cost of global and local deformations of graphene competes with short-range chemical and long-range van der Waals interactions. Atomic contrast is related with short-range tip-sample interactions, while the dissipation can be understood in terms of global deformations in the weakly coupled graphene layer. Remarkably, the observed moiré modulation is linked with the subtle variations of the local interplanar graphene-substrate interaction, opening a new route to explore the local mechanical properties of 2D materials at the atomic scale.

Atom-Dependent Edge-Enhanced Second-Harmonic Generation on MoS2 Monolayers.

PubMed

Lin, Kuang-I; Ho, Yen-Hung; Liu, Shu-Bai; Ciou, Jian-Jhih; Huang, Bo-Ting; Chen, Christopher; Chang, Han-Ching; Tu, Chien-Liang; Chen, Chang-Hsiao

2018-02-14

Edge morphology and lattice orientation of single-crystal molybdenum disulfide (MoS 2 ) monolayers, a transition metal dichalcogenide (TMD), possessing a triangular shape with different edges grown by chemical vapor deposition are characterized by atomic force microscopy and transmission electron microscopy. Multiphoton laser scanning microscopy is utilized to study one-dimensional atomic edges of MoS 2 monolayers with localized midgap electronic states, which result in greatly enhanced optical second-harmonic generation (SHG). Microscopic S-zigzag edge and S-Mo Klein edge (bare Mo atoms protruding from a S-zigzag edge) terminations and the edge-atom dependent resonance energies can therefore be deduced based on SHG images. Theoretical calculations based on density functional theory clearly explain the lower energy of the S-zigzag edge states compared to the corresponding S-Mo Klein edge states. Characterization of the atomic-scale variation of edge-enhanced SHG is a step forward in this full-optical and high-yield technique of atomic-layer TMDs.

Characterizing Fluorocarbon Assisted Atomic Layer Etching of Si Using Cyclic Ar/C 4F 8 and Ar/CHF 3 Plasma

DOE PAGES

Metzler, Dominik; Li, Chen; Engelmann, Sebastian; ...

2016-09-08

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO 2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C 4F 8 and CHF 3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32,more » 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO 2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF 3 has a lower FC deposition yield for both SiO 2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F 8. The thickness of deposited FC layers using CHF 3 is found to be greater for Si than for SiO 2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.« less

Effect of intermediate layers on atomic layer deposition-aluminum oxide protected silver mirrors

NASA Astrophysics Data System (ADS)

Fryauf, David M.; Diaz Leon, Juan J.; Phillips, Andrew C.; Kobayashi, Nobuhiko P.

2017-07-01

This work investigates intermediate materials deposited between silver (Ag) thin-film mirrors and an aluminum oxide (AlOx) barrier overlayer and compares the effects on mirror durability to environmental stresses. Physical vapor deposition of various fluorides, oxides, and nitrides in combination with AlOx by atomic layer deposition (ALD) is used to develop several coating recipes. Ag-AlOx samples with different intermediate materials undergo aggressive high-temperature (80°C), high-humidity (80%) (HTHH) testing for 10 days. Reflectivity of mirror samples is measured before and after HTHH testing, and image processing techniques are used to analyze the specular surface of the samples after HTHH testing. Among the seven intermediate materials used in this work, TiN, MgAl2O4, NiO, and Al2O3 intermediate layers offer more robust protection against chemical corrosion and moisture when compared with samples with no intermediate layer. In addition, results show that the performance of the ALD-AlOx barrier overlayer depends significantly on the ALD-growth process temperature. Because higher durability is observed in samples with less transparent TiN and NiO layers, we propose a figure of merit based on post-HTHH testing reflectivity change and specular reflective mirror surface area remaining after HTHH testing to judge overall barrier performance.

CMUTs with high-K atomic layer deposition dielectric material insulation layer.

PubMed

Xu, Toby; Tekes, Coskun; Degertekin, F

2014-12-01

Use of high-κ dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especially as the vacuum gap thickness is reduced. In particular, ALD hafnium oxide (HfO2) is evaluated and used as an improvement over plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (Six)Ny)) for CMUTs fabricated by a low-temperature, complementary metal oxide semiconductor transistor-compatible, sacrificial release method. Relevant properties of ALD HfO2) such as dielectric constant and breakdown strength are characterized to further guide CMUT design. Experiments are performed on parallel fabricated test CMUTs with 50-nm gap and 16.5-MHz center frequency to measure and compare pressure output and receive sensitivity for 200-nm PECVD Six)Ny) and 100-nm HfO2) insulation layers. Results for this particular design show a 6-dB improvement in receiver output with the collapse voltage reduced by one-half; while in transmit mode, half the input voltage is needed to achieve the same maximum output pressure.

Lateral gas phase diffusion length of boron atoms over Si/B surfaces during CVD of pure boron layers

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

Mohammadi, V., E-mail: V.Mohammadi@tudelft.nl; Nihtianov, S.

The lateral gas phase diffusion length of boron atoms, L{sub B}, along silicon and boron surfaces during chemical vapor deposition (CVD) using diborane (B{sub 2}H{sub 6}) is reported. The value of L{sub B} is critical for reliable and uniform boron layer coverage. The presented information was obtained experimentally and confirmed analytically in the boron deposition temperature range from 700 °C down to 400 °C. For this temperature range the local loading effect of the boron deposition is investigated on the micro scale. A L{sub B} = 2.2 mm was determined for boron deposition at 700 °C, while a L{sub B}more » of less than 1 mm was observed at temperatures lower than 500 °C.« less

Freestanding palladium nanosheets with plasmonic and catalytic properties

NASA Astrophysics Data System (ADS)

Huang, Xiaoqing; Tang, Shaoheng; Mu, Xiaoliang; Dai, Yan; Chen, Guangxu; Zhou, Zhiyou; Ruan, Fangxiong; Yang, Zhilin; Zheng, Nanfeng

2011-01-01

Ultrathin metal films can exhibit quantum size and surface effects that give rise to unique physical and chemical properties. Metal films containing just a few layers of atoms can be fabricated on substrates using deposition techniques, but the production of freestanding ultrathin structures remains a significant challenge. Here we report the facile synthesis of freestanding hexagonal palladium nanosheets that are less than 10 atomic layers thick, using carbon monoxide as a surface confining agent. The as-prepared nanosheets are blue in colour and exhibit a well-defined but tunable surface plasmon resonance peak in the near-infrared region. The combination of photothermal stability and biocompatibility makes palladium nanosheets promising candidates for photothermal therapy. The nanosheets also exhibit electrocatalytic activity for the oxidation of formic acid that is 2.5 times greater than that of commercial palladium black catalyst.

Theoretical study of the structures and chemical ordering of CoPd nanoalloys supported on MgO(001)

NASA Astrophysics Data System (ADS)

Taran, Songul; Garip, Ali Kemal; Arslan, Haydar

2016-06-01

Metal nanoalloys on oxide surface are a widely studied topic in surface science and technology. In this study, the structures of CoPd nanoalloys adsorbed on MgO(001) have been searched by basin-hopping global optimization method within an atomistic model. Two different sizes (34 and 38 atom) have been considered for all compositions of CoPd/MgO(001) nanoalloys. Co and Pd atoms, for all the compositions, have cube-on-cube (001) epitaxy with substrate at interface. For both sizes, we have found that Pd rich composition nanoalloys have three layers, Co rich composition nanoalloys have four layers in morphology. Excess energy and second difference in energy analyzes have been performed to investigate the relative stability of nanoalloys with respect to their size and composition.

The Atmospheric Tomography Mission (ATom): Comparing the Chemical Climatology of Reactive Species and Air Parcels from Measurements and Global Models

NASA Astrophysics Data System (ADS)

Prather, M. J.; Flynn, C.; Wennberg, P. O.; Kim, M. J.; Ryerson, T. B.; Hanisco, T. F.; Diskin, G. S.; Daube, B. C.; Commane, R.; McKain, K.; Apel, E. C.; Blake, N. J.; Blake, D. R.; Elkins, J. W.; Hall, S.; Steenrod, S.; Strahan, S. E.; Lamarque, J. F.; Fiore, A. M.; Horowitz, L. W.; Murray, L. T.; Mao, J.; Shindell, D. T.; Wofsy, S. C.

2017-12-01

The NASA Atmospheric Tomography Mission (ATom) is building a photochemical climatology of the remote troposphere based on objective sampling and profiling transects over the Pacific and Atlantic Oceans. These statistics provide direct tests of chemistry-climate models. The choice of species focuses on those controlling primary reactivity (a.k.a. oxidative state) of the troposphere, specifically chemical tendencies of O3 and CH4. These key species include, inter alia, O3, CH4, CO, C2H6, other alkanes, alkenes, aromatics, NOx, HNO3, HO2NO2, PAN, other organic nitrates, H2O, HCHO, H2O2, CH3OOH. Three of the four ATom deployments are now complete, and data from the first two (ATom-1 & -2) have been released as of this talk (see espoarchive.nasa.gov/archive/browse/atom). The statistical distributions of key species are presented as 1D and 2D probability densities (PDs) and we focus here on the tropical and mid-latitude regions of the Pacific during ATom-1 (Aug) and -2 (Feb). PDs are computed from ATom observations and 6 global chemistry models over the tropospheric depth (0-12 km) and longitudinal extent of the observations. All data are weighted to achieve equal mass-weighting by latitude regimes to account for spatial sampling biases. The models are used to calculate the reactivity in each ATom air parcel. Reweighting parcels with loss of CH4 or production of O3, for example, allows us to identify which air parcels are most influential, including assessment of the importance of fine pollution layers in the most remote troposphere. Another photochemical climatology developed from ATom, and used to test models, includes the effect of clouds on photolysis rates. The PDs and reactivity-weighted PDs reveal important seasonal differences and similarities between the two campaigns and also show which species may be most important in controlling reactivities. They clearly identify some very specific failings in the modeled climatologies and help us evaluate the chemical importance of fine-scale laminae with distinct chemical composition that are beyond model simulations.

Monoatomic layer removal mechanism in chemical mechanical polishing process: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Si, Lina; Guo, Dan; Luo, Jianbin; Lu, Xinchun

2010-03-01

Molecular dynamics simulations of nanoscratching processes were used to study the atomic-scale removal mechanism of single crystalline silicon in chemical mechanical polishing (CMP) process and particular attention was paid to the effect of scratching depth. The simulation results under a scratching depth of 1 nm showed that a thick layer of silicon material was removed by chip formation and an amorphous layer was formed on the silicon surface after nanoscratching. By contrast, the simulation results with a depth of 0.1 nm indicated that just one monoatomic layer of workpiece was removed and a well ordered crystalline surface was obtained, which is quite consistent with previous CMP experimental results. Therefore, monoatomic layer removal mechanism was presented, by which it is considered that during CMP process the material was removed by one monoatomic layer after another, and the mechanism could provide a reasonable understanding on how the high precision surface was obtained. Also, the effects of the silica particle size and scratching velocity on the removal mechanism were investigated; the wear regimes and interatomic forces between silica particle and workpiece were studied to account for the different removal mechanisms with indentation depths of 0.1 and 1 nm.

Effect of Si, Mg, and Mg Zn doping on structural properties of a GaN layer grown by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Cho, H. K.; Lee, J. Y.; Kim, K. S.; Yang, G. M.

2001-12-01

We have studied the structural properties of undoped, Si-doped, Mg-doped, and Mg-Zn codoped GaN using high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy. When compared with undoped GaN, the dislocation density at the surface of the GaN layer decreases with Si doping and increases with Mg doping. In addition, we observed a reduction of dislocation density by codoping with Zn atoms in the Mg-doped GaN layer. The full width at half maximum of HRXRD shows that Si doping and Mg-Zn codoping improve the structural quality of the GaN layer as compared with undoped and Mg-doped GaN, respectively.

Comparative Study of Zn(O,S) Buffer Layers and CIGS Solar Cells Fabricated by CBD, ALD, and Sputtering: Preprint

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

Ramanathan, K.; Mann, J.; Glynn, S.

2012-06-01

Zn(O,S) thin films were deposited by chemical bath deposition (CBD), atomic layer deposition, and sputtering. Composition of the films and band gap were measured and found to follow the trends described in the literature. CBD Zn(O,S) parameters were optimized and resulted in an 18.5% efficiency cell that did not require post annealing, light soaking, or an undoped ZnO layer. Promising results were obtained with sputtering. A 13% efficiency cell was obtained for a Zn(O,S) emitter layer deposited with 0.5%O2. With further optimization of process parameters and an analysis of the loss mechanisms, it should be possible to increase the efficiency.

Aqueous chemical growth of free standing vertical ZnO nanoprisms, nanorods and nanodiskettes with improved texture co-efficient and tunable size uniformity

NASA Astrophysics Data System (ADS)

Ram, S. D. Gopal; Ravi, G.; Athimoolam, A.; Mahalingam, T.; Kulandainathan, M. Anbu

2011-12-01

Tuning the morphology, size and aspect ratio of free standing ZnO nanostructured arrays by a simple hydrothermal method is reported. Pre-coated ZnO seed layers of two different thicknesses (≈350 nm or 550 nm) were used as substrates to grow ZnO nanostructures for the study. Various parameters such as chemical ambience, pH of the solution, strength of the Zn2+ atoms and thickness of seed bed are varied to analyze their effects on the resultant ZnO nanostructures. Vertically oriented hexagonal nanorods, multi-angular nanorods, hexagonal diskette and popcorn-like nanostructures are obtained by altering the experimental parameters. All the produced nanostructures were analysed by X-ray powder diffraction analysis and found to be grown in the (002) orientation of wurtzite ZnO. The texture co-efficient of ZnO layer was improved by combining a thick seed layer with higher cationic strength. Surface morphological studies reveal various nanostructures such as nanorods, diskettes and popcorn-like structures based on various preparation conditions. The optical property of the closest packed nanorods array was recorded by UV-VIS spectrometry, and the band gap value simulated from the results reflect the near characteristic band gap of ZnO. The surface roughness profile taken from the Atomic Force Microscopy reveals a roughness of less than 320 nm.

The low coherence Fabry-Pérot interferometer with diamond and ZnO layers

NASA Astrophysics Data System (ADS)

Majchrowicz, D.; Den, W.; Hirsch, M.

2016-09-01

The authors present a fiber-optic Fabry-Pérot interferometer built with the application of diamond and zinc oxide (ZnO) thin layers. Thin ZnO films were deposited on the tip of a standard telecommunication single-mode optical fiber (SMF- 28) while the diamond layer was grown on the plate of silicon substrate. Investigated ZnO layers were fabricated by atomic layer deposition (ALD) and the diamond films were deposited using Microwave Plasma Enhanced Chemical Vapor Deposition (μPE CVD) system. Different thickness of layers was examined. The measurements were performed for the fiber-optic Fabry-Pérot interferometer working in the reflective mode. Spectra were registered for various thicknesses of ZnO layer and various length of the air cavity. As a light source, two superluminescent diodes (SLD) with central wavelength of 1300 nm and 1550 nm were used in measurement set-up.

Understanding the mechanisms of interfacial reactions during TiO{sub 2} layer growth on RuO{sub 2} by atomic layer deposition with O{sub 2} plasma or H{sub 2}O as oxygen source

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

Chaker, A.; Szkutnik, P. D.; Pointet, J.

2016-08-28

In this paper, TiO{sub 2} layers grown on RuO{sub 2} by atomic layer deposition (ALD) using tetrakis (dimethyla-mino) titanium (TDMAT) and either oxygen plasma or H{sub 2}O as oxygen source were analyzed using X-ray diffraction (XRD), Raman spectroscopy, and depth-resolved X-ray Photoelectron spectroscopy (XPS). The main objective is to investigate the surface chemical reactions mechanisms and their influence on the TiO{sub 2} film properties. The experimental results using XRD show that ALD deposition using H{sub 2}O leads to anatase TiO{sub 2} whereas a rutile TiO{sub 2} is obtained when oxygen-plasma is used as oxygen source. Depth-resolved XPS analysis allows tomore » determine the reaction mechanisms at the RuO{sub 2} substrate surface after growth of thin TiO{sub 2} layers. Indeed, the XPS analysis shows that when H{sub 2}O assisted ALD process is used, intermediate Ti{sub 2}O{sub 3} layer is obtained and RuO{sub 2} is reduced into Ru as evidenced by high resolution transmission electron microscopy. In this case, there is no possibility to re-oxidize the Ru surface into RuO{sub 2} due to the weak oxidation character of H{sub 2}O and an anatase TiO{sub 2} layer is therefore grown on Ti{sub 2}O{sub 3}. In contrast, when oxygen plasma is used in the ALD process, its strong oxidation character leads to the re-oxidation of the partially reduced RuO{sub 2} following the first Ti deposition step. Consequently, the RuO{sub 2} surface is regenerated, allowing the growth of rutile TiO{sub 2}. A surface chemical reaction scheme is proposed that well accounts for the observed experimental results.« less

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

Rajkumar, K.; Rajavel, K.; Cameron, D. C.

This paper reports the electrowetting properties of liquid droplet on superhydrophobic silicon nanowires with Atomic layer deposited (ALD) Al{sub 2}O{sub 3} as dielectric layer. Silicon wafer were etched by metal assisted wet chemical etching with silver as catalyst. ALD Al{sub 2}O{sub 3} films of 10nm thickness were conformally deposited over silicon nanowires. Al{sub 2}O{sub 3} dielectric film coated silicon nanowires was chemically modified with Trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane to make it superhydrophobic(SHP). The contact angle was measured and all the samples exhibited superhydrophobic nature with maximum contact angles of 163° and a minimum contact angle hysteresis of 6°.more » Electrowetting induced a maximum reversible decrease of the contact angle of 20°at 150V in air.« less

Controlling the surface termination of NdGaO3 (110): the role of the gas atmosphere.

PubMed

Cavallaro, Andrea; Harrington, George F; Skinner, Stephen J; Kilner, John A

2014-07-07

In this work the effect of gas atmosphere on the surface termination reconstruction of single crystal NdGaO3 (110) (NGO) during thermal annealing was analyzed. Using Low Energy Ion Scattering (LEIS) it has been possible to study the chemical composition of the first atomic layer of treated NGO single crystal samples. NGO has been analyzed both as-received and after a specific thermal treatment at 1000 °C under different gas fluxes (argon, nitrogen, static air, synthetic air, nitrogen plus 5% hydrogen and wet synthetic air respectively). Thermal annealing of perovskite single crystals, as already reported in the literature, is used to obtain a fully A-cation surface termination. Nevertheless the effect of the gas-atmosphere on this process has not been previously reported. By the use of sequential low energy Ar(+) sputtering combined with the primary ion LEIS analysis, the reconstruction of the outermost atomic layers has allowed the clarification of the mechanism of NGO neodymium surface enrichment. It is proposed that the gallium at the surface is submitted to a reduction/evaporation mechanism caused by low oxygen partial pressure and/or high water pressure in the vector gas. Below the first surface atomic layers of an as-received NGO single-crystal a gallium-rich phase has also been observed.

Unique coordination of pyrazine in T[Ni(CN){sub 4}].2pyz with T=Mn, Zn, Cd

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

Lemus-Santana, A.A.; Rodriguez-Hernandez, J.; Castillo, L.F. del, E-mail: lfelipe@servidor.unam.m

2009-04-15

The materials under study, T[Ni(CN){sub 4}].2pyz with T=Mn, Zn, Cd, were prepared by separation of T[Ni(CN){sub 4}] layers in citrate aqueous solution to allow the intercalation of the pyrazine molecules. The obtained solids were characterized from chemical analyses, X-ray diffraction, infrared, Raman, thermogravimetry, UV-Vis, magnetic and adsorption data. Their crystal structure was solved from ab initio using direct methods and then refined by the Rietveld method. A unique coordination for pyrazine to metal centers at neighboring layers was observed. The pyrazine molecule is found forming a bridge between Ni and T atoms, quite different from the proposed structures for T=Fe,more » Ni where it remains coordinated to two T atoms to form a vertical pillar between neighboring layers. The coordination of pyrazine to both Ni and T atoms minimizes the material free volume and leads to form a hydrophobic framework. On heating the solids remain stable up to 140 deg. C. No CO{sub 2} and H{sub 2} adsorption was observed in the small free spaces of their frameworks. - Graphical abstract: Framework for T[Ni(CN){sub 4}].2pyz with T=Mn, Zn, Cd.« less

Crystalline TiO 2 grafted with poly(2-methacryloyloxyethyl phosphorylcholine) via surface-initiated atom-transfer radical polymerization

NASA Astrophysics Data System (ADS)

Zhao, Yuancong; Tu, Qiufen; Wang, Jin; Huang, Qiongjian; Huang, Nan

2010-12-01

Crystalline TiO 2 films were prepared by unbalanced magnetron sputtering and the structure was confirmed by XRD. An organic layer of 11-hydroxyundecylphosphonic acid (HUPA) was prepared on the TiO 2 films by self-assembling, and the HUPA on TiO 2 films was confirmed by FTIR analysis. Simultaneously, hydroxyl groups were introduced in the phosphonic acid molecules to provide a functionality for further chemical modification. 2-Methacryloyloxyethyl phosphorylcholine (MPC), a biomimetic monomer, was chemically grafted on the HUPA surfaces at room temperature by surface-initiated atom-transfer radical polymerization. The surface characters of TiO 2 films modified by poly-MPC were confirmed by FTIR, XPS and SEM analysis. Platelet adhesion experiment revealed that poly-MPC modified surface was effective to inhibit platelet adhesion in vitro.

Defining Tropospheric Chemistry As A Heterogeneous Ensemble Of Reactive Air Parcels

NASA Astrophysics Data System (ADS)

Prather, M. J.; Zhu, X.; Flynn, C.; Mao, J.; Strode, S. A.; Steenrod, S. D.; Strahan, S. E.; Lamarque, J. F.; Fiore, A. M.; Horowitz, L. W.; Shindell, D. T.; Murray, L. T.

2016-12-01

Two major challenges in model-measurement comparisons have been: Which measurements are the most important to match? At what level do models need to simulate the variegated fine structures observed in trace gases and aerosols? This talk presents a novel approach for evaluating high-resolution global chemistry models (1/2 to 1 deg) that is integral to NASA's Atmospheric Tomography (ATom) mission. The approach seeks to develop a chemical climatology for tropospheric regions rather than just event-based testing of specific observations. It enables chemistry-climate models to be readily compared and more severely tested with observations. It uses the reactivity of air parcels (e.g., loss of methane, production and loss of ozone) to weight each parcel in terms of its importance in controlling the two most important chemically reactive greenhouse gases. It looks at the entire statistical distribution of air parcels in terms of a chemical phase space for those species that control the reactivity (e.g., O3, H2O, CH4, CO, NOx, HNO3, HNO4, PAN, CH3NO3, HCHO, HOOH, CH3OOH, C2H6, C3H6O, and other VOCs when present in sufficiently large abundances). It builds statistics of chemically extreme air parcels such as pollution layers to determine if a model failure to match such cases affects the overall reactivity of the region. This approach was designed for the ATom in situ measurements using the DC-8 to slice through the middle of the Pacific and Atlantic Ocean basins each season. The ATom payload will measure the above key trace gases and many other gases and aerosols in every designated air parcel (i.e., 10-sec averages). The first ATom measurements will not be available until mid-2017 and this presentation shows how this climatology looks when sampled with different models. Six global chemistry models have simulated one day in August (no particular year), and we sample all six showing how the 2D probability density plots highlight different regions when weighted by chemical reactivity. These models pre-simulation of ATom provide a target for the ATom measurements. The models also enable us to estimate the representativeness of ATom's single tomographic slice down the ocean basins, and therefore just how well we can observationally determine this chemical climatology of the reactivity of the troposphere.

Magnetic Nanostructures Patterned by Self-Organized Materials

DTIC Science & Technology

2016-01-05

solvent composition on the structural and magnetic properties of MnZn ferrite nanoparticles obtained by hydrothermal synthesis Microfluid...techniques such as chemical synthesis , self-organized methods, sputtering, lithography and atomic layer deposition (ALD). We also performed micromagnetic...range of temperatures (1.8 to 300 K) and at high fields (up to 5 T). The low temperature measurements of magnetic nanoparticles allowed us to

Understanding the Mechanism of SiC Plasma-Enhanced Chemical Vapor Deposition (PECVD) and Developing Routes toward SiC Atomic Layer Deposition (ALD) with Density Functional Theory.

PubMed

Filatova, Ekaterina A; Hausmann, Dennis; Elliott, Simon D

2018-05-02

Understanding the mechanism of SiC chemical vapor deposition (CVD) is an important step in investigating the routes toward future atomic layer deposition (ALD) of SiC. The energetics of various silicon and carbon precursors reacting with bare and H-terminated 3C-SiC (011) are analyzed using ab initio density functional theory (DFT). Bare SiC is found to be reactive to silicon and carbon precursors, while H-terminated SiC is found to be not reactive with these precursors at 0 K. Furthermore, the reaction pathways of silane plasma fragments SiH 3 and SiH 2 are calculated along with the energetics for the methane plasma fragments CH 3 and CH 2 . SiH 3 and SiH 2 fragments follow different mechanisms toward Si growth, of which the SiH 3 mechanism is found to be more thermodynamically favorable. Moreover, both of the fragments were found to show selectivity toward the Si-H bond and not C-H bond of the surface. On the basis of this, a selective Si deposition process is suggested for silicon versus carbon-doped silicon oxide surfaces.

Influence of Different Defects in Vertically Aligned Carbon Nanotubes on TiO2 Nanoparticle Formation through Atomic Layer Deposition.

PubMed

Acauan, Luiz; Dias, Anna C; Pereira, Marcelo B; Horowitz, Flavio; Bergmann, Carlos P

2016-06-29

The chemical inertness of carbon nanotubes (CNT) requires some degree of "defect engineering" for controlled deposition of metal oxides through atomic layer deposition (ALD). The type, quantity, and distribution of such defects rules the deposition rate and defines the growth behavior. In this work, we employed ALD to grow titanium oxide (TiO2) on vertically aligned carbon nanotubes (VACNT). The effects of nitrogen doping and oxygen plasma pretreatment of the CNT on the morphology and total amount of TiO2 were systematically studied using transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. The induced chemical changes for each functionalization route were identified by X-ray photoelectron and Raman spectroscopies. The TiO2 mass fraction deposited with the same number of cycles for the pristine CNT, nitrogen-doped CNT, and plasma-treated CNT were 8, 47, and 80%, respectively. We demonstrate that TiO2 nucleation is dependent mainly on surface incorporation of heteroatoms and their distribution rather than structural defects that govern the growth behavior. Therefore, selecting the best way to functionalize CNT will allow us to tailor TiO2 distribution and hence fabricate complex heterostructures.

MicroED Structure of Au146(p-MBA)57 at Subatomic Resolution Reveals a Twinned FCC Cluster.

PubMed

Vergara, Sandra; Lukes, Dylan A; Martynowycz, Michael W; Santiago, Ulises; Plascencia-Villa, Germán; Weiss, Simon C; de la Cruz, M Jason; Black, David M; Alvarez, Marcos M; López-Lozano, Xochitl; Barnes, Christopher O; Lin, Guowu; Weissker, Hans-Christian; Whetten, Robert L; Gonen, Tamir; Yacaman, Miguel Jose; Calero, Guillermo

2017-11-16

Solving the atomic structure of metallic clusters is fundamental to understanding their optical, electronic, and chemical properties. Herein we present the structure of the largest aqueous gold cluster, Au 146 (p-MBA) 57 (p-MBA: para-mercaptobenzoic acid), solved by electron micro-diffraction (MicroED) to subatomic resolution (0.85 Å) and by X-ray diffraction at atomic resolution (1.3 Å). The 146 gold atoms may be decomposed into two constituent sets consisting of 119 core and 27 peripheral atoms. The core atoms are organized in a twinned FCC structure, whereas the surface gold atoms follow a C 2 rotational symmetry about an axis bisecting the twinning plane. The protective layer of 57 p-MBAs fully encloses the cluster and comprises bridging, monomeric, and dimeric staple motifs. Au 146 (p-MBA) 57 is the largest cluster observed exhibiting a bulk-like FCC structure as well as the smallest gold particle exhibiting a stacking fault.

MicroED structure of Au146(p-MBA)57 at subatomic resolution reveals a twinned FCC cluster

PubMed Central

Vergara, Sandra; Lukes, Dylan A.; Martynowycz, Michael W.; Santiago, Ulises; Plascencia-Villa, German; Weiss, Simon C.; de la Cruz, M. Jason; Black, David M.; Alvarez, Marcos M.; Lopez-Lozano, Xochitl; Barnes, Christopher O.; Lin, Guowu; Weissker, Hans-Christian; Whetten, Robert L.; Gonen, Tamir; Jose-Yacaman, Miguel; Calero, Guillermo

2018-01-01

Solving the atomic structure of metallic clusters is fundamental to understanding their optical, electronic, and chemical properties. Herein we present the structure of the largest aqueous gold cluster, Au146(p-MBA)57 (p-MBA: para-mercaptobenzoic acid), solved by electron diffraction (MicroED) to subatomic resolution (0.85 Å) and by X-ray diffraction at atomic resolution (1.3 Å). The 146 gold atoms may be decomposed into two constituent sets consisting of 119 core and 27 peripheral atoms. The core atoms are organized in a twinned FCC structure whereas the surface gold atoms follow a C2 rotational symmetry about an axis bisecting the twinning plane. The protective layer of 57 p-MBAs fully encloses the cluster and comprises bridging, monomeric, and dimeric staple motifs. Au146(p-MBA)57 is the largest cluster observed exhibiting a bulk-like FCC structure as well as the smallest gold particle exhibiting a stacking fault. PMID:29072840

Disentangling atomic-layer-specific x-ray absorption spectra by Auger electron diffraction spectroscopy

NASA Astrophysics Data System (ADS)

Matsui, Fumihiko; Matsushita, Tomohiro; Kato, Yukako; Hashimoto, Mie; Daimon, Hiroshi

2009-11-01

In order to investigate the electronic and magnetic structures of each atomic layer at subsurface, we have proposed a new method, Auger electron diffraction spectroscopy, which is the combination of x-ray absorption spectroscopy (XAS) and Auger electron diffraction (AED) techniques. We have measured a series of Ni LMM AED patterns of the Ni film grown on Cu(001) surface for various thicknesses. Then we deduced a set of atomic-layer-specific AED patterns in a numerical way. Furthermore, we developed an algorithm to disentangle XANES spectra from different atomic layers using these atomic-layer-specific AED patterns. Surface and subsurface core level shift were determined for each atomic layer.

Characteristics of the surface layer of barium strontium titanate thin films deposited by laser ablation

NASA Astrophysics Data System (ADS)

Craciun, V.; Singh, R. K.

2000-04-01

Ba0.5Sr0.5TiO3 (BST) thin films grown on Si by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique exhibited significantly higher dielectric constant and refractive index values and lower leakage current densities than films grown by conventional PLD under similar conditions. X-ray photoelectron spectroscopy (XPS) investigations have shown that the surface layer of the grown films contained, besides the usual BST perovskite phase, an additional phase with Ba atoms in a different chemical state. PLD grown films always exhibited larger amounts of this phase, which was homogeneously mixed with the BST phase up to several nm depth, while UVPLD grown films exhibited a much thinner (˜1 nm) and continuous layer. The relative fraction of this phase was not correlated with the amount of C atoms present on the surface. Fourier transform infrared spectroscopy did not find any BaCO3 contamination layer, which was believed to be related to this new phase. X-ray diffraction measurement showed that although PLD grown films contained less oxygen atoms, the lattice parameter was closer to the bulk value than that of UVPLD grown films. After 4 keV Ar ion sputtering for 6 min, XPS analysis revealed a small suboxide Ba peak for the PLD grown films. This finding indicates that the average Ba-O bonds are weaker in these films, likely due to the presence of oxygen vacancies. It is suggested here that this new Ba phase corresponds to a relaxed BST surface layer.

Chemical precursor impact on the properties of Cu{sub 2}ZnSnS{sub 4} absorber layer

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

Vashistha, Indu B., E-mail: indu-139@yahoo.com; Sharma, S. K.; Sharma, Mahesh C.

2016-04-13

In present work impact of different chemical precursor on the deposition of solar absorber layer Cu{sub 2}ZnSnS{sub 4} (CZTS) were studied by Chemical Bath Deposition (CBD) method without using expensive vacuum facilities and followed by annealing. As compared to the other deposition methods, CBD method is interesting one because it is simple, reproducible, non-hazardous, cost effective and well suited for producing large-area thin films at low temperatures, although effect of precursors and concentration plays a vital role in the deposition. So, the central theme of this work is optimizing and controlling of chemical reactions for different chemical precursors. Further Effectmore » of different chemical precursors i.e. sulphate and chloride is analyzed by structural, morphological, optical and electrical properties. The X-ray diffraction (XRD) of annealed CZTS thin film revealed that films were polycrystalline in nature with kestarite tetragonal crystal structure. The Atomic Force micrographs (AFM) images indicated total coverage compact film and as well as growth of crystals. The band gap of annealed CZTS films was found in the range of optimal band gap by absorption spectroscopy.« less

Large-scale Growth and Simultaneous Doping of Molybdenum Disulfide Nanosheets

PubMed Central

Kim, Seong Jun; Kang, Min-A; Kim, Sung Ho; Lee, Youngbum; Song, Wooseok; Myung, Sung; Lee, Sun Sook; Lim, Jongsun; An, Ki-Seok

2016-01-01

A facile method that uses chemical vapor deposition (CVD) for the simultaneous growth and doping of large-scale molybdenum disulfide (MoS2) nanosheets was developed. We employed metalloporphyrin as a seeding promoter layer for the uniform growth of MoS2 nanosheets. Here, a hybrid deposition system that combines thermal evaporation and atomic layer deposition (ALD) was utilized to prepare the promoter. The doping effect of the promoter was verified by X-ray photoelectron spectroscopy and Raman spectroscopy. In addition, the carrier density of the MoS2 nanosheets was manipulated by adjusting the thickness of the metalloporphyrin promoter layers, which allowed the electrical conductivity in MoS2 to be manipulated. PMID:27044862

Recent Development of Advanced Electrode Materials by Atomic Layer Deposition for Electrochemical Energy Storage.

PubMed

Guan, Cao; Wang, John

2016-10-01

Electrode materials play a decisive role in almost all electrochemical energy storage devices, determining their overall performance. Proper selection, design and fabrication of electrode materials have thus been regarded as one of the most critical steps in achieving high electrochemical energy storage performance. As an advanced nanotechnology for thin films and surfaces with conformal interfacial features and well controllable deposition thickness, atomic layer deposition (ALD) has been successfully developed for deposition and surface modification of electrode materials, where there are considerable issues of interfacial and surface chemistry at atomic and nanometer scale. In addition, ALD has shown great potential in construction of novel nanostructured active materials that otherwise can be hardly obtained by other processing techniques, such as those solution-based processing and chemical vapor deposition (CVD) techniques. This review focuses on the recent development of ALD for the design and delivery of advanced electrode materials in electrochemical energy storage devices, where typical examples will be highlighted and analyzed, and the merits and challenges of ALD for applications in energy storage will also be discussed.

Recent Development of Advanced Electrode Materials by Atomic Layer Deposition for Electrochemical Energy Storage

PubMed Central

2016-01-01

Electrode materials play a decisive role in almost all electrochemical energy storage devices, determining their overall performance. Proper selection, design and fabrication of electrode materials have thus been regarded as one of the most critical steps in achieving high electrochemical energy storage performance. As an advanced nanotechnology for thin films and surfaces with conformal interfacial features and well controllable deposition thickness, atomic layer deposition (ALD) has been successfully developed for deposition and surface modification of electrode materials, where there are considerable issues of interfacial and surface chemistry at atomic and nanometer scale. In addition, ALD has shown great potential in construction of novel nanostructured active materials that otherwise can be hardly obtained by other processing techniques, such as those solution‐based processing and chemical vapor deposition (CVD) techniques. This review focuses on the recent development of ALD for the design and delivery of advanced electrode materials in electrochemical energy storage devices, where typical examples will be highlighted and analyzed, and the merits and challenges of ALD for applications in energy storage will also be discussed. PMID:27840793

Patterning of supported gold monolayers via chemical lift-off lithography

PubMed Central

Slaughter, Liane S; Cheung, Kevin M; Kaappa, Sami; Cao, Huan H; Yang, Qing; Young, Thomas D; Serino, Andrew C; Malola, Sami; Olson, Jana M; Link, Stephan

2017-01-01

The supported monolayer of Au that accompanies alkanethiolate molecules removed by polymer stamps during chemical lift-off lithography is a scarcely studied hybrid material. We show that these Au–alkanethiolate layers on poly(dimethylsiloxane) (PDMS) are transparent, functional, hybrid interfaces that can be patterned over nanometer, micrometer, and millimeter length scales. Unlike other ultrathin Au films and nanoparticles, lifted-off Au–alkanethiolate thin films lack a measurable optical signature. We therefore devised fabrication, characterization, and simulation strategies by which to interrogate the nanoscale structure, chemical functionality, stoichiometry, and spectral signature of the supported Au–thiolate layers. The patterning of these layers laterally encodes their functionality, as demonstrated by a fluorescence-based approach that relies on dye-labeled complementary DNA hybridization. Supported thin Au films can be patterned via features on PDMS stamps (controlled contact), using patterned Au substrates prior to lift-off (e.g., selective wet etching), or by patterning alkanethiols on Au substrates to be reactive in selected regions but not others (controlled reactivity). In all cases, the regions containing Au–alkanethiolate layers have a sub-nanometer apparent height, which was found to be consistent with molecular dynamics simulations that predicted the removal of no more than 1.5 Au atoms per thiol, thus presenting a monolayer-like structure. PMID:29259879

Chemical Intercalation of Topological Insulator Grid Nanostructures for High-Performance Transparent Electrodes.

PubMed

Guo, Yunfan; Zhou, Jinyuan; Liu, Yujing; Zhou, Xu; Yao, Fengrui; Tan, Congwei; Wu, Jinxiong; Lin, Li; Liu, Kaihui; Liu, Zhongfan; Peng, Hailin

2017-11-01

2D layered nanomaterials with strong covalent bonding within layers and weak van der Waals' interactions between layers have attracted tremendous interest in recent years. Layered Bi 2 Se 3 is a representative topological insulator material in this family, which holds promise for exploration of the fundamental physics and practical applications such as transparent electrode. Here, a simultaneous enhancement of optical transmittancy and electrical conductivity in Bi 2 Se 3 grid electrodes by copper-atom intercalation is presented. These Cu-intercalated 2D Bi 2 Se 3 electrodes exhibit high uniformity over large area and excellent stabilities to environmental perturbations, such as UV light, thermal fluctuation, and mechanical distortion. Remarkably, by intercalating a high density of copper atoms, the electrical and optical performance of Bi 2 Se 3 grid electrodes is greatly improved from 900 Ω sq -1 , 68% to 300 Ω sq -1 , 82% in the visible range; with better performance of 300 Ω sq -1 , 91% achieved in the near-infrared region. These unique properties of Cu-intercalated topological insulator grid nanostructures may boost their potential applications in high-performance optoelectronics, especially for infrared optoelectronic devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of nonequilibrium radiation and shape change on aerothermal environment of a Jovian entry body

NASA Technical Reports Server (NTRS)

Tiwari, S. N.; Subramanian, S. V.

1981-01-01

The influence of nonequilibrium radiative energy transfer and the effect of probe configuration changes on the flow phenomena around a Jovian entry body are investigated. The radiating shock layer flow is assumed to be axisymmetric, viscous, laminar and in chemical equilibrium. The radiative transfer equations are derived under nonequilibrium conditions which include multilevel energy transitions. The equilibrium radiative transfer analysis is performed with an existing nongray radiation model which accounts for molecular band, atomic line, and continuum transitions. The nonequilibrium results are obtained with and without ablation injection in the shock layer. The nonequilibrium results are found to be greatly influenced by the temperature distribution in the shock layer. In the absence of ablative products, the convective and radiative heating to the entry body are reduced under nonequilibrium conditions. The influence of nonequilibrium is found to be greater at higher entry altitudes. With coupled ablation and carbon phenolic injection, 16 chemical species are used in the ablation layer for radiation absorption. Equilibrium and nonequilibrium results are compared under peak heating conditions.

Effect of sulfur passivation on the InP surface prior to plasma-enhanced chemical vapor deposition of SiNx

NASA Astrophysics Data System (ADS)

Tang, Hengjing; Wu, Xiaoli; Xu, Qinfei; Liu, Hongyang; Zhang, Kefeng; Wang, Yang; He, Xiangrong; Li, Xue; Gong, Hai Mei

2008-03-01

The fabrication of Au/SiNx/InP metal-insulator-semiconductor (MIS) diodes has been achieved by depositing a layer of SiNx on the (NH4)2Sx-treated n-InP. The SiNx layer was deposited at 200 °C using plasma-enhanced chemical vapor deposition (PECVD). The effect of passivation on the InP surface before and after annealing was evaluated by current-voltage (I-V) and capacitance-voltage (C-V) measurements, and Auger electron spectroscopy (AES) analysis was used to investigate the depth profiles of several atoms. The results indicate that the SiNx passivation layer exhibits good insulative characteristics. The annealing process causes distinct inter-diffusion in the SiNx/InP interface and contributes to the decrease of the fixed charge density and minimum interface state density, which are 1.96 × 1012 cm-2 and 7.41 × 1011 cm-2 eV-1, respectively. A 256 × 1 InP/InGaAs/InP heterojunction photodiode, fabricated with sulfidation and SiNx passivation layer, has good response uniformity.

Improved passivation effect in multicrystalline black silicon by chemical solution pre-treatment

NASA Astrophysics Data System (ADS)

Jiang, Ye; Shen, Honglie; Pu, Tian; Zheng, Chaofan

2018-04-01

Though black silicon has excellent anti-reflectance property, its passivation is one of the main technical bottlenecks due to its large specific surface area. In this paper, multicrystalline black silicon is fabricated by metal assisted chemical etching, and is rebuilt in low concentration alkali solution. Different solution pre-treatment is followed to make surface modification on black silicon before Al2O3 passivation by atomic layer deposition. HNO3 and H2SO4 + H2O2 solution pre-treatment makes the silicon surface become hydrophilic, with contact angle decrease from 117.28° to about 30°. It is demonstrated that when the pre-treatment solution is nitric acid, formed ultrathin SiO x layer between Al2O3 layer and black silicon is found to increase effective carrier lifetime to 72.64 µs, which is obviously higher than that of the unpassivated black silicon. The passivation stacks of SiO x /Al2O3 are proved to be effective double layers for nanoscaled multicrystalline silicon surface.

Coating and functionalization of high density ion track structures by atomic layer deposition

NASA Astrophysics Data System (ADS)

Mättö, Laura; Szilágyi, Imre M.; Laitinen, Mikko; Ritala, Mikko; Leskelä, Markku; Sajavaara, Timo

2016-10-01

In this study flexible TiO2 coated porous Kapton membranes are presented having electron multiplication properties. 800 nm crossing pores were fabricated into 50 μm thick Kapton membranes using ion track technology and chemical etching. Consecutively, 50 nm TiO2 films were deposited into the pores of the Kapton membranes by atomic layer deposition using Ti(iOPr)4 and water as precursors at 250 °C. The TiO2 films and coated membranes were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray reflectometry (XRR). Au metal electrode fabrication onto both sides of the coated foils was achieved by electron beam evaporation. The electron multipliers were obtained by joining two coated membranes separated by a conductive spacer. The results show that electron multiplication can be achieved using ALD-coated flexible ion track polymer foils.

Atomic Layer Deposition of the Solid Electrolyte LiPON

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

Kozen, Alexander C.; Pearse, Alexander J.; Lin, Chuan -Fu

We demonstrate an atomic layer deposition (ALD) process for the solid electrolyte lithium phosphorousoxynitride (LiPON) using lithium tert-butoxide (LiO tBu), H 2O, trimethylphosphate (TMP), and plasma N 2 ( PN 2) as precursors. We use in-situ spectroscopic ellipsometry to determine growth rates for process optimization to design a rational, quaternary precursor ALD process where only certain substrate–precursor chemical reactions are favorable. We demonstrate via in-situ XPS tunable nitrogen incorporation into the films by variation of the PN 2 dose and find that ALD films over approximately 4.5% nitrogen are amorphous, whereas LiPON ALD films with less than 4.5% nitrogen aremore » polycrystalline. Lastly, we characterize the ionic conductivity of the ALD films as a function of nitrogen content and demonstrate their functionality on a model battery electrode—a Si anode on a Cu current collector.« less

First-principles calculations of the thermodynamic properties of transuranium elements in a molten salt medium

NASA Astrophysics Data System (ADS)

Noh, Seunghyo; Kwak, Dohyun; Lee, Juseung; Kang, Joonhee; Han, Byungchan

2014-03-01

We utilized first-principles density-functional-theory (DFT) calculations to evaluate the thermodynamic feasibility of a pyroprocessing methodology for reducing the volume of high-level radioactive materials and recycling spent nuclear fuels. The thermodynamic properties of transuranium elements (Pu, Np and Cm) were obtained in electrochemical equilibrium with a LiCl-KCl molten salt as ionic phases and as adsorbates on a W(110) surface. To accomplish the goal, we rigorously calculated the double layer interface structures on an atomic resolution, on the thermodynamically most stable configurations on W(110) surfaces and the chemical activities of the transuranium elements for various coverages of those elements. Our results indicated that the electrodeposition process was very sensitive to the atomic level structures of Cl ions at the double-layer interface. Our studies are easily expandable to general electrochemical applications involving strong redox reactions of transition metals in non-aqueous solutions.

Atomic Layer Deposition of the Solid Electrolyte LiPON

DOE PAGES

Kozen, Alexander C.; Pearse, Alexander J.; Lin, Chuan -Fu; ...

2015-07-09

We demonstrate an atomic layer deposition (ALD) process for the solid electrolyte lithium phosphorousoxynitride (LiPON) using lithium tert-butoxide (LiO tBu), H 2O, trimethylphosphate (TMP), and plasma N 2 ( PN 2) as precursors. We use in-situ spectroscopic ellipsometry to determine growth rates for process optimization to design a rational, quaternary precursor ALD process where only certain substrate–precursor chemical reactions are favorable. We demonstrate via in-situ XPS tunable nitrogen incorporation into the films by variation of the PN 2 dose and find that ALD films over approximately 4.5% nitrogen are amorphous, whereas LiPON ALD films with less than 4.5% nitrogen aremore » polycrystalline. Lastly, we characterize the ionic conductivity of the ALD films as a function of nitrogen content and demonstrate their functionality on a model battery electrode—a Si anode on a Cu current collector.« less

Gas-phase measurements of combustion interaction with materials for radiation-cooled chambers

NASA Technical Reports Server (NTRS)

Barlow, R. S.; Lucht, R. P.; Jassowski, D. M.; Rosenberg, S. D.

1991-01-01

Foil samples of Ir and Pt are exposed to combustion products in a controlled premixed environment at atmospheric pressure. Electrical heating of the foil samples is used to control the surface temperature and to elevate it above the radiative equilibrium temperature within the test apparatus. Profiles of temperature and OH concentration in the boundary layer adjacent to the specimen surface are measured by laser-induced fluorescence. Measured OH concentrations are significantly higher than equilibrium concentrations calculated for the known mixture ratio and the measured temperature profiles. This result indicates that superequilibrium concentrations of H-atoms and O-atoms are also present in the boundary layer, due to partial equilibrium of the rapid binary reactions of the H2/O2 chemical kinetic system. These experiments are conducted as part of a research program to investigate fundamental aspects of the interaction of combustion gases with advanced high-temperature materials for radiation-cooled thrusters.

High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

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

Mu, Haichuan; Zhang, Zhiqiang; Wang, Keke

2014-07-21

Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36 s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductivemore » graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.« less

Substrate temperature influence on the properties of GaN thin films grown by hollow-cathode plasma-assisted atomic layer deposition

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

Alevli, Mustafa, E-mail: mustafaalevli@marmara.edu.tr; Gungor, Neşe; Haider, Ali

2016-01-15

Gallium nitride films were grown by hollow cathode plasma-assisted atomic layer deposition using triethylgallium and N{sub 2}/H{sub 2} plasma. An optimized recipe for GaN film was developed, and the effect of substrate temperature was studied in both self-limiting growth window and thermal decomposition-limited growth region. With increased substrate temperature, film crystallinity improved, and the optical band edge decreased from 3.60 to 3.52 eV. The refractive index and reflectivity in Reststrahlen band increased with the substrate temperature. Compressive strain is observed for both samples, and the surface roughness is observed to increase with the substrate temperature. Despite these temperature dependent material properties,more » the chemical composition, E{sub 1}(TO), phonon position, and crystalline phases present in the GaN film were relatively independent from growth temperature.« less

Analysis of Surface and Bulk Behavior in Ni-Pd Alloys

NASA Technical Reports Server (NTRS)

Bozzolo, Guillermo; Noebe, Rondald D.

2003-01-01

The most salient features of the surface structure and bulk behavior of Ni-Pd alloys have been studied using the BFS method for alloys. Large-scale atomistic simulations were performed to investigate surface segregation profiles as a function of temperature, crystal face, and composition. Pd enrichment of the first layer was observed in (111) and (100) surfaces, and enrichment of the top two layers occurred for (110) surfaces. In all cases, the segregation profile shows alternate planes enriched and depleted in Pd. In addition, the phase structure of bulk Ni-Pd alloys as a function of temperature and composition was studied. A weak ordering tendency was observed at low temperatures, which helps explain the compositional oscillations in the segregation profiles. Finally, based on atom-by-atom static energy calculations, a comprehensive explanation for the observed surface and bulk features will be presented in terms of competing chemical and strain energy effects.

Laser-induced atomic assembling of periodic layered nanostructures of silver nanoparticles in fluoro-polymer film matrix

NASA Astrophysics Data System (ADS)

Bagratashvili, V. N.; Rybaltovsky, A. O.; Minaev, N. V.; Timashev, P. S.; Firsov, V. V.; Yusupov, V. I.

2010-05-01

Fluorinated acrylic polymer (FAP) films have been impregnated with silver precursor (Ag(hfac)COD) by supercritical fluid technique and next irradiated with laser (λ = 532 nm). Laser-chemically reduced Ag atoms have been assembled into massifs of Ag nanoparticles (3 - 8 nm) in FAP/Ag(hfac)COD films matrix in the form of periodic layered nanostructures (horizontal to film surface) with unexpectedly short period (90 - 180 nm). The wavelet analysis of TEM images reveals the existence of even shorter-period structures in such films. Photolysis with non-coherent light or pyrolysis of FAP/Ag(hfac)COD film results in formation of Ag nanoparticles massifs but free of any periodic nanoparticle assemblies. Our interpretation of the observed effect of laser formation of short-period nano-sized Ag nanoparticle assemblies is based on self-enhanced interference process in the course of modification of optical properties of film.

Effective passivation of silicon surfaces by ultrathin atomic-layer deposited niobium oxide

NASA Astrophysics Data System (ADS)

Macco, B.; Bivour, M.; Deijkers, J. H.; Basuvalingam, S. B.; Black, L. E.; Melskens, J.; van de Loo, B. W. H.; Berghuis, W. J. H.; Hermle, M.; Kessels, W. M. M. Erwin

2018-06-01

This letter reports on effective surface passivation of n-type crystalline silicon by ultrathin niobium oxide (Nb2O5) films prepared by atomic layer deposition (ALD) and subjected to a forming gas anneal at 300 °C. A champion recombination parameter J0 of 20 fA/cm2 and a surface recombination velocity Seff of 4.8 cm/s have been achieved for ultrathin films of 1 nm. The surface pretreatment was found to have a strong impact on the passivation. Good passivation can be achieved on both HF-treated c-Si surfaces and c-Si surfaces with a wet-chemically grown interfacial silicon oxide layer. On HF-treated surfaces, a minimum film thickness of 3 nm is required to achieve a high level of surface passivation, whereas the use of a wet chemically-grown interfacial oxide enables excellent passivation even for Nb2O5 films of only 1 nm. This discrepancy in passivation between both surface types is attributed to differences in the formation and stoichiometry of interfacial silicon oxide, resulting in different levels of chemical passivation. On both surface types, the high level of passivation of ALD Nb2O5 is aided by field-effect passivation originating from a high fixed negative charge density of 1-2 × 1012 cm-3. Furthermore, it is demonstrated that the passivation level provided by 1 nm of Nb2O5 can be further enhanced through light-soaking. Finally, initial explorations show that a low contact resistivity can be obtained using Nb2O5-based contacts. Together, these properties make ALD Nb2O5 a highly interesting building block for high-efficiency c-Si solar cells.

Atomic layer deposition on polymer fibers and fabrics for multifunctional and electronic textiles

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

Brozena, Alexandra H.; Oldham, Christopher J.; Parsons, Gregory N., E-mail: gnp@ncsu.edu

Textile materials, including woven cotton, polymer knit fabrics, and synthetic nonwoven fiber mats, are being explored as low-cost, flexible, and light-weight platforms for wearable electronic sensing, communication, energy generation, and storage. The natural porosity and high surface area in textiles is also useful for new applications in environmental protection, chemical decontamination, pharmaceutical and chemical manufacturing, catalytic support, tissue regeneration, and others. These applications raise opportunities for new chemistries, chemical processes, biological coupling, and nanodevice systems that can readily combine with textile manufacturing to create new “multifunctional” fabrics. Atomic layer deposition (ALD) has a unique ability to form highly uniform andmore » conformal thin films at low processing temperature on nonuniform high aspect ratio surfaces. Recent research shows how ALD can coat, modify, and otherwise improve polymer fibers and textiles by incorporating new materials for viable electronic and other multifunctional capabilities. This article provides a current overview of the understanding of ALD coating and modification of textiles, including current capabilities and outstanding problems, with the goal of providing a starting point for further research and advances in this field. After a brief introduction to textile materials and current textile treatment methods, the authors discuss unique properties of ALD-coated textiles, followed by a review of recent electronic and multifunctional textiles that use ALD coatings either as direct functional components or as critical nucleation layers for active materials integration. The article concludes with possible future directions for ALD on textiles, including the challenges in materials, manufacturing, and manufacturing integration that must be overcome for ALD to reach its full potential in electronic and other emerging multifunctional textile systems.« less

Surface and Interface Engineering of Organometallic and Two Dimensional Semiconductor

NASA Astrophysics Data System (ADS)

Park, Jun Hong

For over half a century, inorganic Si and III-V materials have led the modern semiconductor industry, expanding to logic transistor and optoelectronic applications. However, these inorganic materials have faced two different fundamental limitations, flexibility for wearable applications and scaling limitation as logic transistors. As a result, the organic and two dimensional have been studied intentionally for various fields. In the present dissertation, three different studies will be presented with followed order; (1) the chemical response of organic semiconductor in NO2 exposure. (2) The surface and stability of WSe2 in ambient air. (3) Deposition of dielectric on two dimensional materials using organometallic seeding layer. The organic molecules rely on the van der Waals interaction during growth of thin films, contrast to covalent bond inorganic semiconductors. Therefore, the morphology and electronic property at surface of organic semiconductor in micro scale is more sensitive to change in gaseous conditions. In addition, metal phthalocyanine, which is one of organic semiconductor materials, change their electronic property as reaction with gaseous analytes, suggesting as potential chemical sensing platforms. In the present part, the growth behavior of metal phthalocyanine and surface response to gaseous condition will be elucidated using scanning tunneling microscopy (STM). In second part, the surface of layered transition metal dichalcogenides and their chemical response to exposure ambient air will be investigated, using STM. Layered transition metal dichalcogenides (TMDs) have attracted widespread attention in the scientific community for electronic device applications because improved electrostatic gate control and suppression of short channel leakage resulted from their atomic thin body. To fabricate the transistor based on TMDs, TMDs should be exposed to ambient conditions, while the effect of air exposure has not been understood fully. In this part, the effect of ambient air on TMDs will be investigated and partial oxidation of TMDs. In the last part, uniform deposition of dielectric layers on 2D materials will be presented, employing organic seedling layer. Although 2D materials have been expected as next generation semiconductor platform, direct deposition of dielectric is still challenging and induces leakage current commonly, because inertness of their surface resulted from absent of dangling bond. Here, metal phthalocyanine monolayer (ML) is employed as seedling layers and the growth of atomic layer deposition (ALD) dielectric is investigated in each step using STM.

Effect of Group-III precursors on unintentional gallium incorporation during epitaxial growth of InAlN layers by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Kim, Jeomoh; Ji, Mi-Hee; Detchprohm, Theeradetch; Dupuis, Russell D.; Fischer, Alec M.; Ponce, Fernando A.; Ryou, Jae-Hyun

2015-09-01

Unintentional incorporation of gallium (Ga) in InAlN layers grown with different molar flow rates of Group-III precursors by metalorganic chemical vapor deposition has been experimentally investigated. The Ga mole fraction in the InAl(Ga)N layer was increased significantly with the trimethylindium (TMIn) flow rate, while the trimethylaluminum flow rate controls the Al mole fraction. The evaporation of metallic Ga from the liquid phase eutectic system between the pyrolized In from injected TMIn and pre-deposited metallic Ga was responsible for the Ga auto-incorporation into the InAl(Ga)N layer. The theoretical calculation on the equilibrium vapor pressure of liquid phase Ga and the effective partial pressure of Group-III precursors based on growth parameters used in this study confirms the influence of Group-III precursors on Ga auto-incorporation. More Ga atoms can be evaporated from the liquid phase Ga on the surrounding surfaces in the growth chamber and then significant Ga auto-incorporation can occur due to the high equilibrium vapor pressure of Ga comparable to effective partial pressure of input Group-III precursors during the growth of InAl(Ga)N layer.

Deep-level traps in lightly Si-doped n-GaN on free-standing m-oriented GaN substrates

NASA Astrophysics Data System (ADS)

Yamada, H.; Chonan, H.; Takahashi, T.; Yamada, T.; Shimizu, M.

2018-04-01

In this study, we investigated the deep-level traps in Si-doped GaN epitaxial layers by metal-organic chemical vapor deposition on c-oriented and m-oriented free-standing GaN substrates. The c-oriented and m-oriented epitaxial layers, grown at a temperature of 1000 °C and V/III ratio of 1000, contained carbon atomic concentrations of 1.7×1016 and 4.0×1015 cm-3, respectively. A hole trap was observed at about 0.89 eV above the valence band maximum by minority carrier transient spectroscopy. The trap concentrations in the c-oriented and m-oriented GaN epitaxial layers were consistent with the carbon atomic concentrations from secondary ion mass spectroscopy and the yellow luminescence intensity at 2.21 eV from photoluminescence. The trap concentrations in the m-oriented GaN epitaxial layers were lower than those in the c-oriented GaN. Two electron traps, 0.24 and 0.61 eV below the conduction band (EC) minimum, were observed in the c-oriented GaN epitaxial layer. In contrast, the m-oriented GaN epitaxial layer was free from the electron trap at EC - 0.24 eV, and the trap concentration at EC - 0.61 eV in the m-oriented GaN epitaxial layer was lower than that in the c-oriented GaN epitaxial layer. The m-oriented GaN epitaxial layer exhibited fewer hole and electron traps compared to the c-oriented GaN epitaxial layers.

Ultrathin epitaxial barrier layer to avoid thermally induced phase transformation in oxide heterostructures

DOE PAGES

Baek, David J.; Lu, Di; Hikita, Yasuyuki; ...

2016-12-22

Incorporating oxides with radically different physical and chemical properties into heterostructures offers tantalizing possibilities to derive new functions and structures. Recently, we have fabricated freestanding 2D oxide membranes using the water-soluble perovskite Sr 3Al 2O 6 as a sacrificial buffer layer. Here, with atomic-resolution spectroscopic imaging, we observe that direct growth of oxide thin films on Sr 3Al 2O 6 can cause complete phase transformation of the buffer layer, rendering it water-insoluble. More importantly, we demonstrate that an ultrathin SrTiO 3 layer can be employed as an effective barrier to preserve Sr 3Al 2O 6 during subsequent growth, thus allowingmore » its integration in a wider range of oxide heterostructures.« less

Highly air stable passivation of graphene based field effect devices.

PubMed

Sagade, Abhay A; Neumaier, Daniel; Schall, Daniel; Otto, Martin; Pesquera, Amaia; Centeno, Alba; Elorza, Amaia Zurutuza; Kurz, Heinrich

2015-02-28

The sensitivity of graphene based devices to surface adsorbates and charge traps at the graphene/dielectric interface requires proper device passivation in order to operate them reproducibly under ambient conditions. Here we report on the use of atomic layer deposited aluminum oxide as passivation layer on graphene field effect devices (GFETs). We show that successful passivation produce hysteresis free DC characteristics, low doping level GFETs stable over weeks though operated and stored in ambient atmosphere. This is achieved by selecting proper seed layer prior to deposition of encapsulation layer. The passivated devices are also demonstrated to be robust towards the exposure to chemicals and heat treatments, typically used during device fabrication. Additionally, the passivation of high stability and reproducible characteristics is also shown for functional devices like integrated graphene based inverters.

On-stack two-dimensional conversion of MoS2 into MoO3

NASA Astrophysics Data System (ADS)

Yeoung Ko, Taeg; Jeong, Areum; Kim, Wontaek; Lee, Jinhwan; Kim, Youngchan; Lee, Jung Eun; Ryu, Gyeong Hee; Park, Kwanghee; Kim, Dogyeong; Lee, Zonghoon; Lee, Min Hyung; Lee, Changgu; Ryu, Sunmin

2017-03-01

Chemical transformation of existing two-dimensional (2D) materials can be crucial in further expanding the 2D crystal palette required to realize various functional heterostructures. In this work, we demonstrate a 2D ‘on-stack’ chemical conversion of single-layer crystalline MoS2 into MoO3 with a precise layer control that enables truly 2D MoO3 and MoO3/MoS2 heterostructures. To minimize perturbation of the 2D morphology, a nonthermal oxidation using O2 plasma was employed. The early stage of the reaction was characterized by a defect-induced Raman peak, drastic quenching of photoluminescence (PL) signals and sub-nm protrusions in atomic force microscopy images. As the reaction proceeded from the uppermost layer to the buried layers, PL and optical second harmonic generation signals showed characteristic modulations revealing a layer-by-layer conversion. The plasma-generated 2D oxides, confirmed as MoO3 by x-ray photoelectron spectroscopy, were found to be amorphous but extremely flat with a surface roughness of 0.18 nm, comparable to that of 1L MoS2. The rate of oxidation quantified by Raman spectroscopy decreased very rapidly for buried sulfide layers due to protection by the surface 2D oxides, exhibiting a pseudo-self-limiting behavior. As exemplified in this work, various on-stack chemical transformations can be applied to other 2D materials in forming otherwise unobtainable materials and complex heterostructures, thus expanding the palette of 2D material building blocks.

CMUTs with High-K Atomic Layer Deposition Dielectric Material Insulation Layer

PubMed Central

Xu, Toby; Tekes, Coskun; Degertekin, F. Levent

2014-01-01

Use of high-κ dielectric, atomic layer deposition (ALD) materials as an insulation layer material for capacitive micromachined ultrasonic transducers (CMUTs) is investigated. The effect of insulation layer material and thickness on CMUT performance is evaluated using a simple parallel plate model. The model shows that both high dielectric constant and the electrical breakdown strength are important for the dielectric material, and significant performance improvement can be achieved, especially as the vacuum gap thickness is reduced. In particular, ALD hafnium oxide (HfO2) is evaluated and used as an improvement over plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SixNy) for CMUTs fabricated by a low-temperature, complementary metal oxide semiconductor transistor-compatible, sacrificial release method. Relevant properties of ALD HfO2 such as dielectric constant and breakdown strength are characterized to further guide CMUT design. Experiments are performed on parallel fabricated test CMUTs with 50-nm gap and 16.5-MHz center frequency to measure and compare pressure output and receive sensitivity for 200-nm PECVD SixNy and 100-nm HfO2 insulation layers. Results for this particular design show a 6-dB improvement in receiver output with the collapse voltage reduced by one-half; while in transmit mode, half the input voltage is needed to achieve the same maximum output pressure. PMID:25474786

Modifying the morphology and properties of aligned CNT foams through secondary CNT growth.

PubMed

Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S; Bradford, Philip D

2018-07-20

In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam's extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

Modifying the morphology and properties of aligned CNT foams through secondary CNT growth

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh; Stano, Kelly; Akyildiz, Halil; Yildiz, Ozkan; Jur, Jesse S.; Bradford, Philip D.

2018-07-01

In this work, we report for the first time, growth of secondary carbon nanotubes (CNTs) throughout a three-dimensional assembly of CNTs. The assembly of nanotubes was in the form of aligned CNT/carbon (ACNT/C) foams. These low-density CNT foams were conformally coated with an alumina buffer layer using atomic layer deposition. Chemical vapor deposition was further used to grow new CNTs. The CNT foam’s extremely high porosity allowed for growth of secondary CNTs inside the bulk of the foams. Due to the heavy growth of new nanotubes, density of the foams increased more than 2.5 times. Secondary nanotubes had the same graphitic quality as the primary CNTs. Microscopy and chemical analysis revealed that the thickness of the buffer layer affected the diameter, nucleation density as well as growth uniformity across the thickness of the foams. The effects of secondary nanotubes on the compressive mechanical properties of the foams was also investigated.

Metallorganic chemical vapor deposition and atomic layer deposition approaches for the growth of hafnium-based thin films from dialkylamide precursors for advanced CMOS gate stack applications

NASA Astrophysics Data System (ADS)

Consiglio, Steven P.

To continue the rapid progress of the semiconductor industry as described by Moore's Law, the feasibility of new material systems for front end of the line (FEOL) process technologies needs to be investigated, since the currently employed polysilicon/SiO2-based transistor system is reaching its fundamental scaling limits. Revolutionary breakthroughs in complementary-metal-oxide-semiconductor (CMOS) technology were recently announced by Intel Corporation and International Business Machines Corporation (IBM), with both organizations revealing significant progress in the implementation of hafnium-based high-k dielectrics along with metal gates. This announcement was heralded by Gordon Moore as "...the biggest change in transistor technology since the introduction of polysilicon gate MOS transistors in the late 1960s." Accordingly, the study described herein focuses on the growth of Hf-based dielectrics and Hf-based metal gates using chemical vapor-based deposition methods, specifically metallorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD). A family of Hf source complexes that has received much attention recently due to their desirable properties for implementation in wafer scale manufacturing is the Hf dialkylamide precursors. These precursors are room temperature liquids and possess sufficient volatility and desirable decomposition characteristics for both MOCVD and ALD processing. Another benefit of using these sources is the existence of chemically compatible Si dialkylamide sources as co-precursors for use in Hf silicate growth. The first part of this study investigates properties of MOCVD-deposited HfO2 and HfSixOy using dimethylamido Hf and Si precursor sources using a customized MOCVD reactor. The second part of this study involves a study of wet and dry surface pre-treatments for ALD growth of HfO2 using tetrakis(ethylmethylamido)hafnium in a wafer scale manufacturing environment. The third part of this study is an investigation of the properties of conductive HfN grown via plasma-assisted atomic layer deposition (PA-ALD) using tetrakis(ethylmethylamido)hafnium on a modified commercially available wafer processing tool. Key properties of these materials for use as gate stack replacement materials are addressed and future directions for further characterization and novel material investigations are proposed.

Rubidium distribution at atomic scale in high efficient Cu(In,Ga)Se2 thin-film solar cells

NASA Astrophysics Data System (ADS)

Vilalta-Clemente, Arantxa; Raghuwanshi, Mohit; Duguay, Sébastien; Castro, Celia; Cadel, Emmanuel; Pareige, Philippe; Jackson, Philip; Wuerz, Roland; Hariskos, Dimitrios; Witte, Wolfram

2018-03-01

The introduction of a rubidium fluoride post deposition treatment (RbF-PDT) for Cu(In,Ga)Se2 (CIGS) absorber layers has led to a record efficiency up to 22.6% for thin-film solar cell technology. In the present work, high efficiency CIGS samples with RbF-PDT have been investigated by atom probe tomography (APT) to reveal the atomic distribution of all alkali elements present in CIGS layers and compared with non-treated samples. A Scanning Electron Microscopy Dual beam station (Focused Ion Beam-Gas Injection System) as well as Transmission Kikuchi diffraction is used for atom probe sample preparation and localization of the grain boundaries (GBs) in the area of interest. The analysis of the 3D atomic scale APT reconstructions of CIGS samples with RbF-PDT shows that inside grains, Rb is under the detection limit, but the Na concentration is enhanced as compared to the reference sample without Rb. At the GBs, a high concentration of Rb reaching 1.5 at. % was found, and Na and K (diffusing from the glass substrate) are also segregated at GBs but at lower concentrations as compared to Rb. The intentional introduction of Rb leads to significant changes in the chemical composition of CIGS matrix and at GBs, which might contribute to improve device efficiency.

Isolated Pt Atoms Stabilized by Amorphous Tungstenic Acid for Metal-Support Synergistic Oxygen Activation.

PubMed

Zhang, Qian; Qin, Xixi; Duanmu, Fanpeng; Ji, Huiming; Shen, Zhurui; Han, Xiaopeng; Hu, Wenbin

2018-06-05

Oxygen activation plays a crucial role in many important chemical reactions such as organics oxidation and oxygen reduction. For developing highly active materials for oxygen activation, herein, we report an atomically dispersed Pt on WO3 nanoplates stabilized by in-situ formed amorphous H2WO4 out-layer and the mechanism for activating molecular oxygen. Experimental and theoretical studies demonstrate that the isolated Pt atoms coordinated with oxygen atoms from [WO6] and water of H2WO4, consequently leading to optimized surface electronic configuration and strong metal support interaction (SMSI). In exemplified reactions of butanone oxidation sensing and oxygen reduction, the atomic Pt/WO3 hybrid exhibits superior activity than those of Pt nanoclusters/WO3 and bare WO3 as well as enhanced long-term durability. This work will provide insight on the origin of activity and stability for atomically dispersed materials, thus promoting the development of highly efficient and durable single atom-based catalysts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical reaction of atomic oxygen with evaporated films of copper, part 4

NASA Technical Reports Server (NTRS)

Fromhold, A. T.; Williams, J. R.

1990-01-01

Evaporated copper films were exposed to an atomic oxygen flux of 1.4 x 10(exp 17) atoms/sq cm per sec at temperatures in the range 285 to 375 F (140 to 191 C) for time intervals between 2 and 50 minutes. Rutherford backscattering spectroscopy (RBS) was used to determine the thickness of the oxide layers formed and the ratio of the number of copper to oxygen atoms in the layers. Oxide film thicknesses ranged from 50 to 3000 A (0.005 to 0.3 microns, or equivalently, 5 x 10(exp -9) to 3 x 10(exp -7); it was determined that the primary oxide phase was Cu2O. The growth law was found to be parabolic (L(t) varies as t(exp 1/2)), in which the oxide thickness L(t) increases as the square root of the exposure time t. The analysis of the data is consistent with either of the two parabolic growth laws. (The thin-film parabolic growth law is based on the assumption that the process is diffusion controlled, with the space charge within the growing oxide layer being negligible. The thick-film parabolic growth law is also based on a diffusion controlled process, but space-charge neutrality prevails locally within very thick oxides.) In the absence of a voltage measurement across the growing oxide, a distinction between the two mechanisms cannot be made, nor can growth by the diffusion of neutral atomic oxygen be entirely ruled out. The activation energy for the reaction is on the order of 1.1 eV (1.76 x 10(exp -19) joule, or equivalently, 25.3 kcal/mole).

Etching-free patterning method for electrical characterization of atomically thin MoSe2 films grown by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Utama, M. Iqbal Bakti; Lu, Xin; Zhan, Da; Ha, Son Tung; Yuan, Yanwen; Shen, Zexiang; Xiong, Qihua

2014-10-01

Patterning two-dimensional materials into specific spatial arrangements and geometries is essential for both fundamental studies of materials and practical applications in electronics. However, the currently available patterning methods generally require etching steps that rely on complicated and expensive procedures. We report here a facile patterning method for atomically thin MoSe2 films using stripping with an SU-8 negative resist layer exposed to electron beam lithography. Additional steps of chemical and physical etching were not necessary in this SU-8 patterning method. The SU-8 patterning was used to define a ribbon channel from a field effect transistor of MoSe2 film, which was grown by chemical vapor deposition. The narrowing of the conduction channel area with SU-8 patterning was crucial in suppressing the leakage current within the device, thereby allowing a more accurate interpretation of the electrical characterization results from the sample. An electrical transport study, enabled by the SU-8 patterning, showed a variable range hopping behavior at high temperatures.Patterning two-dimensional materials into specific spatial arrangements and geometries is essential for both fundamental studies of materials and practical applications in electronics. However, the currently available patterning methods generally require etching steps that rely on complicated and expensive procedures. We report here a facile patterning method for atomically thin MoSe2 films using stripping with an SU-8 negative resist layer exposed to electron beam lithography. Additional steps of chemical and physical etching were not necessary in this SU-8 patterning method. The SU-8 patterning was used to define a ribbon channel from a field effect transistor of MoSe2 film, which was grown by chemical vapor deposition. The narrowing of the conduction channel area with SU-8 patterning was crucial in suppressing the leakage current within the device, thereby allowing a more accurate interpretation of the electrical characterization results from the sample. An electrical transport study, enabled by the SU-8 patterning, showed a variable range hopping behavior at high temperatures. Electronic supplementary information (ESI) available: Further experiments on patterning and additional electrical characterizations data. See DOI: 10.1039/c4nr03817g

Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo2O5.5+δ thin films

NASA Astrophysics Data System (ADS)

Bao, Shanyong; Xu, Xing; Enriquez, Erik; Mace, Brennan E.; Chen, Garry; Kelliher, Sean P.; Chen, Chonglin; Zhang, Yamei; Whangbo, Myung-Hwan; Dong, Chuang; Zhang, Qinyu

2015-12-01

Single-crystalline epitaxial thin films of PrBaCo2O5.5+δ (PrBCO) were prepared, and their resistance R(t) under a switching flow of oxidizing and reducing gases were measured as a function of the gas flow time t in the temperature range of 200-800 °C. During the oxidation cycle under O2, the PrBCO films exhibit fast oscillations in their dR(t)/dt vs. t plots, which reflect the oxidation processes, Co2+/Co3+ → Co3+ and Co3+ → Co3+/Co4+, that the Co atoms of PrBCO undergo. Each oscillation consists of two peaks, with larger and smaller peaks representing the oxygen/hydrogen diffusion through the (BaO)(CoO2)(PrO)(CoO2) layers of PrBCO via the oxygen-vacancy-exchange mechanism. This finding paves a significant avenue for cathode materials operating in low-temperature solid-oxide-fuel-cell devices and for chemical sensors with wide range of operating temperature.

Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

PubMed Central

Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; Unocic, Raymond R.; Guo, Daqiang; Okatan, M. Baris; Dai, Sheng; Cummings, Peter T.; Kalinin, Sergei V.; Feng, Guang; Balke, Nina

2016-01-01

Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained. PMID:27587276

Composition and structure of surfaces by time-of-flight scattering and recoiling spectrometry (TOF-SARS)

NASA Astrophysics Data System (ADS)

Ahn, Jeongheon

1997-10-01

Time-of-flight scattering and recoiling spectrometry (TOF-SARS) was applied to characterize surface structures in order to understand the chemical and physical phenomena on various surfaces. The combination of TOF-SARS, LEED, and classical ion trajectory simulations has allowed characterization of the elemental composition in the outermost atomic layers, surface symmetry, and possible reconstruction or relaxation. The composition and structure of the CdS\\{0001\\}-(1 x 1) and CdS\\{000bar1\\}-(1 x 1) surfaces were investigated. The termination layer of each surface was determined by grazing incidence TOF-SARS. Both (1 x 1) surfaces are bulk-terminated without any reconstruction or relaxation detected by TOF-SARS. Each surface has two domains which are rotated by 60sp° from each other and there exist steps on both surfaces. The CdS\\{0001\\}-(1 x 1) surface is stabilized by O and H covering half a monolayer which are structurally ordered on the surface, while the O and H on the CdS\\{000bar1\\}-(1 x 1) stabilize the surface without ordering. The study of GaN\\{000bar1\\}-(1 x 1) shows the bulk-termination of the surface with no detectable reconstruction or relaxation. The surface is terminated in a N layer with Ga in the 2sp{nd}-layer. H atoms are bound to the outermost N atoms with a coverage of ˜3/4 monolayer and protrude outward from the surface. The surface termination, composition and structure of the Alsb2Osb3 (sapphire) were examined. The surface relaxation was studied quantitatively using classical ion trajectory simulations along with TOF-SARS. The surface undergoes 1sp{st}{-}2sp{nd}-layer relaxation as large as 0.5 A from the bulk value resulting in near coplanarity of Al and O atoms. The reconstruction of the Ni\\{100\\}-(2 x 2)-C surface was studied by TOF-SARS. The surface contained 80% of the (2 x 2)p4g phase and 20% of the unreconstructed (2 x 2) phase. The displacement of Ni atoms was determined by comparing the experimental and simulated results.

Isolation and characterization of nanosheets containing few layers of the Aurivillius family of oxides and metal-organic compounds

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

Sreedhara, M.B.; Prasad, B.E.; Moirangthem, Monali

2015-04-15

Nanosheets containing few-layers of ferroelectric Aurivillius family of oxides, Bi{sub 2}A{sub n−1}B{sub n}O{sub 3n+3} (where A=Bi{sup 3+}, Ba{sup 2+} etc. and B=Ti{sup 4+}, Fe{sup 3+} etc.) with n=3, 4, 5, 6 and 7 have been prepared by reaction with n-butyllithium, followed by exfoliation in water. The few-layer samples have been characterized by Tyndall cones, atomic force microscopy, optical spectroscopy and other techniques. The few-layer species have a thickness corresponding to a fraction of the c-parameter along which axis the perovskite layers are stacked. Magnetization measurements have been carried out on the few-layer samples containing iron. Few-layer species of a fewmore » layered metal-organic compounds have been obtained by ultrasonication and characterized by Tyndall cones, atomic force microscopy, optical spectroscopy and magnetic measurements. Significant changes in the optical spectra and magnetic properties are found in the few-layer species compared to the bulk samples. Few-layer species of the Aurivillius family of oxides may find uses as thin layer dielectrics in photovoltaics and other applications. - Graphical abstract: Exfoliation of the layered Aurivillius oxides into few-layer nanosheets by chemical Li intercalation using n-BuLi followed by reaction in water. Exfoliation of the layered metal-organic compounds into few-layer nanosheets by ultrasonication. - Highlights: • Few-layer nanosheets of Aurivillius family of oxides with perovskite layers have been generated by lithium intercalation. • Few-layer nanosheets of few layered metal-organic compounds have been generated by ultrasonication. • Few-layer nanosheets of the Aurivillius oxides have been characterized by AFM, TEM and optical spectroscopy. • Aurivillius oxides containing Fe show layer dependent magnetic properties. • Exfoliated few-layer metal-organic compounds show changes in spectroscopic and magnetic properties compared with bulk materials.« less

Freestanding films of crosslinked gold nanoparticles prepared via layer-by-layer spin-coating.

PubMed

Schlicke, Hendrik; Schröder, Jan H; Trebbin, Martin; Petrov, Alexey; Ijeh, Michael; Weller, Horst; Vossmeyer, Tobias

2011-07-29

A new, extremely efficient method for the fabrication of films comprised of gold nanoparticles (GNPs) crosslinked by organic dithiols is presented in this paper. The method is based on layer-by-layer spin-coating of both components, GNPs and crosslinker, and enables the deposition of films several tens of nanometers in thickness within a few minutes. X-ray diffraction and conductance measurements reveal the proper adjustment concentration of the crosslinker solution of the critical is in order to prevent the destabilization and coalescence of particles. UV/vis spectroscopy, atomic force microscopy, and conductivity measurements indicate that films prepared via layer-by-layer spin-coating are of comparable quality to coatings prepared via laborious layer-by-layer self-assembly using immersion baths. Because spin-coated films are not bound chemically to the substrate, they can be lifted-off by alkaline underetching and transferred onto 3d-electrodes to produce electrically addressable, freely suspended films. Comparative measurements of the sheet resistances indicate that the transfer process does not compromise the film quality.

Freestanding films of crosslinked gold nanoparticles prepared via layer-by-layer spin-coating

NASA Astrophysics Data System (ADS)

Schlicke, Hendrik; Schröder, Jan H.; Trebbin, Martin; Petrov, Alexey; Ijeh, Michael; Weller, Horst; Vossmeyer, Tobias

2011-07-01

A new, extremely efficient method for the fabrication of films comprised of gold nanoparticles (GNPs) crosslinked by organic dithiols is presented in this paper. The method is based on layer-by-layer spin-coating of both components, GNPs and crosslinker, and enables the deposition of films several tens of nanometers in thickness within a few minutes. X-ray diffraction and conductance measurements reveal the proper adjustment concentration of the crosslinker solution of the critical is in order to prevent the destabilization and coalescence of particles. UV/vis spectroscopy, atomic force microscopy, and conductivity measurements indicate that films prepared via layer-by-layer spin-coating are of comparable quality to coatings prepared via laborious layer-by-layer self-assembly using immersion baths. Because spin-coated films are not bound chemically to the substrate, they can be lifted-off by alkaline underetching and transferred onto 3d-electrodes to produce electrically addressable, freely suspended films. Comparative measurements of the sheet resistances indicate that the transfer process does not compromise the film quality.

Solute segregation and deviation from bulk thermodynamics at nanoscale crystalline defects

PubMed Central

Titus, Michael S.; Rhein, Robert K.; Wells, Peter B.; Dodge, Philip C.; Viswanathan, Gopal Babu; Mills, Michael J.; Van der Ven, Anton; Pollock, Tresa M.

2016-01-01

It has long been known that solute segregation at crystalline defects can have profound effects on material properties. Nevertheless, quantifying the extent of solute segregation at nanoscale defects has proven challenging due to experimental limitations. A combined experimental and first-principles approach has been used to study solute segregation at extended intermetallic phases ranging from 4 to 35 atomic layers in thickness. Chemical mapping by both atom probe tomography and high-resolution scanning transmission electron microscopy demonstrates a markedly different composition for the 4–atomic-layer–thick phase, where segregation has occurred, compared to the approximately 35–atomic-layer–thick bulk phase of the same crystal structure. First-principles predictions of bulk free energies in conjunction with direct atomistic simulations of the intermetallic structure and chemistry demonstrate the breakdown of bulk thermodynamics at nanometer dimensions and highlight the importance of symmetry breaking due to the proximity of interfaces in determining equilibrium properties. PMID:28028543

Atomic level characterization of cadmium selenide nanocrystal systems using atomic number contrast scanning transmission electron microscopy and Rutherford backscattering spectroscopy

NASA Astrophysics Data System (ADS)

McBride, James R.

This project involved the characterization of CdSe nanocrystals. Through the use of Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-STEM) and Rutherford Backscattering Spectroscopy (RBS), atomic level structure and chemical information was obtained. Specifically, CdSe nanocrystals produced using a mixture of hexadecylamine (HDA) and trioctylphosphine oxide (TOPO) were determined to be spherical compared to nanocrystals produced in TOPO only, which had elongated (101) facets. Additionally, the first Z-STEM images of CdSe/ZnS core/shell nanocrystals were obtained. From these images, the growth mechanism of the ZnS shell was determined and the existence of non-fluorescent ZnS particles was confirmed. Through collaboration with Quantum Dot Corp., core/shell nanocrystals with near unity quantum yield were developed. These core/shell nanocrystals included a US intermediate layer to improve shell coverage.

Insight into the Near-Conduction Band States at the Crystallized Interface between GaN and SiN x Grown by Low-Pressure Chemical Vapor Deposition.

PubMed

Liu, Xinyu; Wang, Xinhua; Zhang, Yange; Wei, Ke; Zheng, Yingkui; Kang, Xuanwu; Jiang, Haojie; Li, Junfeng; Wang, Wenwu; Wu, Xuebang; Wang, Xianping; Huang, Sen

2018-06-12

Constant-capacitance deep-level transient Fourier spectroscopy is utilized to characterize the interface between a GaN epitaxial layer and a SiN x passivation layer grown by low-pressure chemical vapor deposition (LPCVD). A near-conduction band (NCB) state E LP ( E C - E T = 60 meV) featuring a very small capture cross section of 1.5 × 10 -20 cm -2 was detected at 70 K at the LPCVD-SiN x /GaN interface. A partially crystallized Si 2 N 2 O thin layer was detected at the interface by high-resolution transmission electron microscopy. Based on first-principles calculations of crystallized Si 2 N 2 O/GaN slabs, it was confirmed that the NCB state E LP mainly originates from the strong interactions between the dangling bonds of gallium and its vicinal atoms near the interface. The partially crystallized Si 2 N 2 O interfacial layer might also give rise to the very small capture cross section of the E LP owing to the smaller lattice mismatch between the Si 2 N 2 O and GaN epitaxial layer and a larger mean free path of the electron in the crystallized portion compared with an amorphous interfacial layer.

Fluorinion transfer in silver-assisted chemical etching for silicon nanowires arrays

NASA Astrophysics Data System (ADS)

Feng, Tianyu; Xu, Youlong; Zhang, Zhengwei; Mao, Shengchun

2015-08-01

Uniform silicon nanowires arrays (SiNWAs) were fabricated on unpolished rough silicon wafers through KOH pretreatment followed by silver-assisted chemical etching (SACE). Density functional theory (DFT) calculations were used to investigate the function of silver (Ag) at atomic scale in the etching process. Among three adsorption sites of Ag atom on Si(1 0 0) surface, Ag(T4) above the fourth-layer surface Si atoms could transfer fluorinion (F-) to adjacent Si successfully due to its stronger electrostatic attraction force between Ag(T4) and F-, smaller azimuth angle of Fsbnd Ag(T4)sbnd Si, shorter bond length of Fsbnd Si compared with Fsbnd Ag. As F- was transferred to adjacent Si by Ag(T4) one by one, the Si got away from the wafer in the form of SiF4 when it bonded with enough F- while Ag(T4) was still attached onto the Si wafer ready for next transfer. Cyclic voltammetry tests confirmed that Ag can improve the etching rate by transferring F- to Si.

Atomic-Scale Fingerprint of Mn Dopant at the Surface of Sr3(Ru1−xMnx)2O7

PubMed Central

Li, Guorong; Li, Qing; Pan, Minghu; Hu, Biao; Chen, Chen; Teng, Jing; Diao, Zhenyu; Zhang, Jiandi; Jin, Rongying; Plummer, E. W.

2013-01-01

Chemical doping in materials is known to give rise to emergent phenomena. These phenomena are extremely difficult to predict a priori, because electron-electron interactions are entangled with local environment of assembled atoms. Scanning tunneling microscopy and low energy electron diffraction are combined to investigate how the local electronic structure is correlated with lattice distortion on the surface of Sr3(Ru1−xMnx)2O7, which has double-layer building blocks formed by (Ru/Mn)O6 octahedra with rotational distortion. The presence of doping-dependent tilt distortion of (Ru/Mn)O6 octahedra at the surface results in a C2v broken symmetry in contrast with the bulk C4v counterpart. It also enables us to observe two Mn sites associated with the octahedral rotation in the bulk through the “chirality” of local electronic density of states surrounding Mn, which is randomly distributed. These results serve as fingerprint of chemical doping on the atomic scale. PMID:24108411

Technologies for deposition of transition metal oxide thin films: application as functional layers in “Smart windows” and photocatalytic systems

NASA Astrophysics Data System (ADS)

Gesheva, K.; Ivanova, T.; Bodurov, G.; Szilágyi, I. M.; Justh, N.; Kéri, O.; Boyadjiev, S.; Nagy, D.; Aleksandrova, M.

2016-02-01

“Smart windows” are envisaged for future low-energy, high-efficient architectural buildings, as well as for the car industry. By switching from coloured to fully bleached state, these windows regulate the energy of solar flux entering the interior. Functional layers in these devices are the transition metals oxides. The materials (transitional metal oxides) used in smart windows can be also applied as photoelectrodes in water splitting photocells for hydrogen production or as photocatalytic materials for self-cleaning surfaces, waste water treatment and pollution removal. Solar energy utilization is recently in the main scope of numerous world research laboratories and energy organizations, working on protection against conventional fuel exhaustion. The paper presents results from research on transition metal oxide thin films, fabricated by different methods - atomic layer deposition, atmospheric pressure chemical vapour deposition, physical vapour deposition, and wet chemical methods, suitable for flowthrough production process. The lower price of the chemical deposition processes is especially important when the method is related to large-scale glazing applications. Conclusions are derived about which processes are recently considered as most prospective, related to electrochromic materials and devices manufacturing.

Space Survivability of Main-Chain and Side-Chain POSS-Kapton Polyimides

NASA Astrophysics Data System (ADS)

Tomczak, Sandra J.; Wright, Michael E.; Guenthner, Andrew J.; Pettys, Brian J.; Brunsvold, Amy L.; Knight, Casey; Minton, Timothy K.; Vij, Vandana; McGrath, Laura M.; Mabry, Joseph M.

2009-01-01

Kapton® polyimde (PI) is extensively used in solar arrays, spacecraft thermal blankets, and space inflatable structures. Upon exposure to atomic oxygen (AO) in low Earth orbit (LEO), Kapton® is severely degraded. An effective approach to prevent this erosion is chemically bonding polyhedral oligomeric silsesquioxane (POSS) into the polyimide matrix by copolymerization of POSS-diamine with the polyimide monomers. POSS is a silicon and oxygen cage-like structure surrounded by organic groups and can be polymerizable. The copolymerization of POSS provides Si and O in the polymer matrix on the nano level. During POSS polyimide exposure to atomic oxygen, organic material is degraded and a silica passivation layer is formed. This silica layer protects the underlying polymer from further degradation. Ground-based studies and MISSE-1 and MISSE-5 flight results have shown that POSS polyimides are resistant to atomic-oxygen attack in LEO. In fact, 3.5 wt% Si8O11 main-chain POSS polyimide eroded about 2 μm during the 3.9 year flight in LEO, whereas 32 μm of 0 wt% POSS polyimide would have eroded within 4 mos. The atomic-oxygen exposure of main-chain POSS polyimides and new side-chain POSS polyimides has shown that copolymerized POSS imparts similar AO resistance to polyimide materials regardless of POSS monomer structure.

Atomic structures of Ruddlesden-Popper faults in LaCoO3/SrRuO3 multilayer thin films induced by epitaxial strain

NASA Astrophysics Data System (ADS)

Wang, Wei; Zhang, Hui; Shen, Xi; Guan, Xiangxiang; Yao, Yuan; Wang, Yanguo; Sun, Jirong; Yu, Richeng

2018-05-01

In this paper, scanning transmission electron microscopy is used to study the microstructures of the defects in LaCoO3/SrRuO3 multilayer films grown on the SrTiO3 substrates, and these films have different thickness of SrRuO3 (SRO) layers. Several types of Ruddlesden-Popper (R.P.) faults at an atomic level are found, and these chemical composition fluctuations in the growth process are induced by strain fields originating from the film-film and film-substrate lattice mismatches. Furthermore, we propose four types of structural models based on the atomic arrangements of the R.P. planar faults, which severely affect the functional properties of the films.

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework.

PubMed

Kim, In Soo; Li, Zhanyong; Zheng, Jian; Platero-Prats, Ana E; Mavrandonakis, Andreas; Pellizzeri, Steven; Ferrandon, Magali; Vjunov, Aleksei; Gallington, Leighanne C; Webber, Thomas E; Vermeulen, Nicolaas A; Penn, R Lee; Getman, Rachel B; Cramer, Christopher J; Chapman, Karena W; Camaioni, Donald M; Fulton, John L; Lercher, Johannes A; Farha, Omar K; Hupp, Joseph T; Martinson, Alex B F

2018-01-22

Single atoms and few-atom clusters of platinum are uniformly installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 °C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and X-ray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomic Oxygen Treatment as a Method of Recovering Smoke Damaged Paintings

NASA Technical Reports Server (NTRS)

Rutledge, Sharon K.; Banks, Bruce A.; Forkapa, Mark; Stueber, Thomas; Sechkar, Edward; Malinowski, Kevin

1998-01-01

Smoke damage, as a result of a fire, can be difficult to remove from some types of painting media without causing swelling, leaching or pigment movement or removal. A non-contact technique has been developed which can remove soot from the surface of a painting by use of a gently flowing gas containing atomic oxygen. The atomic oxygen chemically reacts with the soot on the surface creating gasses such as carbon monoxide and carbon dioxide which can be removed through the use of an exhaust system. The reaction is limited to the surface so that the process can be timed to stop when the paint layer is reached. Atomic oxygen is a primary component of the low Earth orbital environment, but can be generated on Earth through various methods. This paper will discuss the results of atomic oxygen treatment of soot exposed acrylic gesso, ink on paper, and a varnished oil painting. Reflectance measurements were used to characterize the surfaces before and after treatment.

Atomic-scale epitaxial aluminum film on GaAs substrate

NASA Astrophysics Data System (ADS)

Fan, Yen-Ting; Lo, Ming-Cheng; Wu, Chu-Chun; Chen, Peng-Yu; Wu, Jenq-Shinn; Liang, Chi-Te; Lin, Sheng-Di

2017-07-01

Atomic-scale metal films exhibit intriguing size-dependent film stability, electrical conductivity, superconductivity, and chemical reactivity. With advancing methods for preparing ultra-thin and atomically smooth metal films, clear evidences of the quantum size effect have been experimentally collected in the past two decades. However, with the problems of small-area fabrication, film oxidation in air, and highly-sensitive interfaces between the metal, substrate, and capping layer, the uses of the quantized metallic films for further ex-situ investigations and applications have been seriously limited. To this end, we develop a large-area fabrication method for continuous atomic-scale aluminum film. The self-limited oxidation of aluminum protects and quantizes the metallic film and enables ex-situ characterizations and device processing in air. Structure analysis and electrical measurements on the prepared films imply the quantum size effect in the atomic-scale aluminum film. Our work opens the way for further physics studies and device applications using the quantized electronic states in metals.

Graphene Chemical Sensor for Heliophysics Applications

NASA Technical Reports Server (NTRS)

Sultana, Mahmooda; Herrero, Fred; Khazanov, George

2013-01-01

Graphene is a single layer of carbon atoms that offer a unique set of advantages as a chemical sensor due to a number of its inherent properties. Graphene has been explored as a gas sensor for a variety of gases, and molecular sensitivity has been demonstrated by measuring the change in electrical properties due to the adsorption of target species. In this paper, we discuss the development of an array of chemical sensors based on graphene and its relevance to plasma physics due to its sensitivity to radical species such as oxonium, hydron and the corresponding neutrals. We briefly discuss the great impact such sensors will have on a number of heliophysics applications such as ground-based manifestations of space weather.

Local Structure Analysis and Interface Layer Effect of Phase-Change Recording Material Using Actual Media

NASA Astrophysics Data System (ADS)

Nakai, Tsukasa; Yoshiki, Masahiko; Satoh, Yasuhiro; Ashida, Sumio

2008-07-01

The influences of the interface layer on crystal structure, the local atomic arrangement, and the electronic and chemical structure of a GeBiTe (GBT) phase-change recording material have been investigated using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), and hard X-ray photoelectron spectroscopy (HX-PES) methods using actual rewritable high-speed HD DVD media without special sample processing. XRD results showed that the crystal structure of laser-crystallized GBT alloy in the actual HD DVD media is the same as that of GeSbTe (GST) alloy, which has a NaCl-type structure. No differences between samples with and without interface layers were found. The lattice constant of GBT is larger than that of GST. Bi increases the lattice constant of GST with respect to the Bi substitution ratio of Sb. According to HX-PES, the DOS of in the recording film amorphous state with an interface layer is closer to that of the crystalline state than the recording film without an interface layer. From XAFS results, clear differences between amorphous (Amo.) and crystalline states (Cry.) were observed. The interatomic distance of amorphous recording material is independent of the existence of an interface layer. On the other hand, the coordination number varied slightly due to the presence of the interface layer. Therefore, the electronic state of the recording layer changes because of the interface layer, although the local structure changes only slightly except for the coordination number. Combining these results, we conclude that the interface layer changes the electronic state of the recording layer and promotes crystallization, but only affects the local structure of the atomic arrangement slightly.

Self-limited growth of Si on B atomic-layer formed Ge(1 0 0) by ultraclean low-pressure CVD system

NASA Astrophysics Data System (ADS)

Yokogawa, Takashi; Ishibashi, Kiyohisa; Sakuraba, Masao; Murota, Junichi; Inokuchi, Yasuhiro; Kunii, Yasuo; Kurokawa, Harushige

2008-07-01

Utilizing BCl 3 reaction on Ge(1 0 0) and subsequent Si epitaxial growth by SiH 4 reaction at 300 °C, B atomic-layer doping in Si/Ge(1 0 0) heterostructure was investigated. Cl atoms on the B atomic-layer formed Ge(1 0 0) scarcely affect upon the SiH 4 reaction. It is also found that Si atom amount deposited by SiH 4 reaction on Ge(1 0 0) is effectively enhanced by the existence of B atomic layer and the deposition rate tends to decrease at around 2-3 atomic layers which is three times larger than that in the case without B. The results of angle-resolved X-ray photoelectron spectroscopy show that most B atoms are incorporated at the heterointerface between the Si and Ge.

Epitaxial Growth of Rhenium with Sputtering

DTIC Science & Technology

2016-05-06

corresponds to two atomic Re layers , considering that the c-axis lattice constant of the tri- atomic layered hcp Re unit cell is ~4.5 Å. Frequently, two...Å) corresponds to two Re atomic layers since the c-axis lattice constant of hcp Re, which is composed of three Re atomic layers , is ~4.5 Å...The growth starts in a three dimensional mode but transforms into two dimensional mode as the film gets thicker. With a thin (~2 nm) seed layer

Titanium modified with layer-by-layer sol-gel tantalum oxide and an organodiphosphonic acid: a coating for hydroxyapatite growth.

PubMed

Arnould, C; Volcke, C; Lamarque, C; Thiry, P A; Delhalle, J; Mekhalif, Z

2009-08-15

Titanium and its alloys are widely used in surgical implants due to their appropriate properties like corrosion resistance, biocompatibility, and load bearing. Unfortunately when metals are used for orthopedic and dental implants there is the possibility of loosening over a long period of time. Surface modification is a good way to counter this problem. A thin tantalum oxide layer obtained by layer-by-layer (LBL) sol-gel deposition on top of a titanium surface is expected to improve biocorrosion resistance in the body fluid, biocompatibility, and radio-opacity. This elaboration step is followed by a modification of the tantalum oxide surface with an organodiphosphonic acid self-assembled monolayer, capable of chemically binding to the oxide surface, and also improving hydroxyapatite growth. The different steps of this proposed process are characterized by surfaces techniques like contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM).

Oxygen octahedral distortions in LaMO 3/SrTiO 3 superlattices

DOE PAGES

Sanchez-Santolino, Gabriel; Cabero, Mariona; Varela, Maria; ...

2014-04-24

Here we study the interfaces between the Mott insulator LaMnO 3 (LMO) and the band insulator SrTiO 3 (STO) in epitaxially grown superlattices with different thickness ratios and different transport and magnetic behaviors. Using atomic resolution electron energy-loss spectrum imaging, we analyze simultaneously the structural and chemical properties of these interfaces. We find changes in the oxygen octahedral tilts within the LaMnO 3 layers when the thickness ratio between the manganite and the titanate layers is varied. Superlattices with thick LMO and ultrathin STO layers present unexpected octahedral tilts in the STO, along with a small amount of oxygen vacancies.more » On the other hand, thick STO layers exhibit undistorted octahedra while the LMO layers present reduced O octahedral distortions near the interfaces. In conclusion, these findings will be discussed in view of the transport and magnetic differences found in previous studies.« less

Ultrahard carbon film from epitaxial two-layer graphene

NASA Astrophysics Data System (ADS)

Gao, Yang; Cao, Tengfei; Cellini, Filippo; Berger, Claire; de Heer, Walter A.; Tosatti, Erio; Riedo, Elisa; Bongiorno, Angelo

2018-02-01

Atomically thin graphene exhibits fascinating mechanical properties, although its hardness and transverse stiffness are inferior to those of diamond. So far, there has been no practical demonstration of the transformation of multilayer graphene into diamond-like ultrahard structures. Here we show that at room temperature and after nano-indentation, two-layer graphene on SiC(0001) exhibits a transverse stiffness and hardness comparable to diamond, is resistant to perforation with a diamond indenter and shows a reversible drop in electrical conductivity upon indentation. Density functional theory calculations suggest that, upon compression, the two-layer graphene film transforms into a diamond-like film, producing both elastic deformations and sp2 to sp3 chemical changes. Experiments and calculations show that this reversible phase change is not observed for a single buffer layer on SiC or graphene films thicker than three to five layers. Indeed, calculations show that whereas in two-layer graphene layer-stacking configuration controls the conformation of the diamond-like film, in a multilayer film it hinders the phase transformation.

Synthesis of reduced carbon nitride at the reduction by hydroquinone of water-soluble carbon nitride oxide (g-C{sub 3}N{sub 4})O

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

Kharlamov, Alexey; Bondarenko, Marina, E-mail: mebondarenko@ukr.net; Kharlamova, Ganna

For the first time at the reduction by hydroquinone of water-soluble carbon nitride oxide (g-C{sub 3}N{sub 4})O reduced carbon nitride (or reduced multi-layer azagraphene) is obtained. It is differed from usually synthesized carbon nitride by a significantly large (on 0.09 nm) interplanar distance is. At the same time, the chemical bonds between atoms in a heteroatomic plane of reduced carbon nitride correspond to the bonds in a synthesized g-C{sub 3}N{sub 4}. The samples of water-soluble carbon nitride oxide were synthesized under the special reactionary conditions of a pyrolysis of melamine and urea. We believe that reduced carbon nitride consists ofmore » weakly connected carbon-nitrogen monosheets (azagraphene sheets) as well as reduced (from graphene oxide) graphene contains weakly connected graphene sheets. - Graphical abstract: XRD pattern and schematic atomic model of one layer of reduced carbon nitride, carbon nitride oxide and synthesized carbon nitride. For the first time at the reduction by hydroquinone of the water-soluble carbon nitride oxide (g-C{sub 3}N{sub 4})O is obtained the reduced carbon nitride (or reduced multi-layer azagraphene). Display Omitted - Highlights: • First the reduced carbon nitride (RCN) at the reduction of the carbon nitride oxide was obtained. • Water-soluble carbon nitride oxide was reduced by hydroquinone. • The chemical bonds in a heteroatomic plane of RCN correspond to the bonds in a synthesized g-C{sub 3}N{sub 4}. • Reduced carbon nitride consists of poorly connected heteroatomic azagraphene layers.« less

Normal incidence X-ray mirror for chemical microanalysis

DOEpatents

Carr, Martin J.; Romig, Jr., Alton D.

1990-01-01

A non-planar, focusing mirror, to be utilized in both electron column instruments and micro-x-ray fluorescence instruments for performing chemical microanalysis on a sample, comprises a concave, generally spherical base substrate and a predetermined number of alternating layers of high atomic number material and low atomic number material contiguously formed on the base substrate. The thickness of each layer is an integral multiple of the wavelength being reflected and may vary non-uniformly according to a predetermined design. The chemical analytical instruments in which the mirror is used also include a predetermined energy source for directing energy onto the sample and a detector for receiving and detecting the x-rays emitted from the sample; the non-planar mirror is located between the sample and detector and collects the x-rays emitted from the sample at a large solid angle and focuses the collected x-rays to the sample. For electron column instruments, the wavelengths of interest lie above 1.5 nm, while for x-ray fluorescence instruments, the range of interest is below 0.2 nm. Also, x-ray fluorescence instruments include an additional non-planar focusing mirror, formed in the same manner as the previously described m The invention described herein was made in the performance of work under contract with the Department of Energy, Contract No. DE-AC04-76DP00789, and the United States Government has rights in the invention pursuant to this contract.

Maximizing the electromagnetic and chemical resonances of surface-enhanced Raman scattering for nucleic acids.

PubMed

Freeman, Lindsay M; Pang, Lin; Fainman, Yeshaiahu

2014-08-26

Although surface-enhanced Raman spectroscopy (SERS) has previously been performed with nucleic acids, the measured intensities for each nucleic acid have varied significantly depending on the SERS substrate and excitation wavelength. We have demonstrated that the charge-transfer (CT) mechanism, also known as the chemical enhancement of SERS, is responsible for the discrepancies previously reported in literature. The electronic states of cytosine and guanine attached to silver atoms are computationally calculated and experimentally measured to be in the visible range, which leads to a resonance Raman effect at the corresponding maximum wavelengths. The resulting SERS measurements are in good agreement with the simulated values, in which cytosine-silver shows stronger enhancement at 532 nm and guanine-silver shows stronger enhancement at 785 nm. An atomic layer of aluminum oxide is deposited on substrates to prevent charge-transfer, and corresponding measurements show weaker Raman signals caused by the suppression of the chemical resonance. These findings suggest the optimal SERS signal can be achieved by tuning the excitation wavelength to match both the electromagnetic and chemical resonances, paving the way for future single molecule detection of nucleic acids other than adenine.

A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

NASA Astrophysics Data System (ADS)

Toyota, K.; Kanaya, Y.; Takahashi, M.; Akimoto, H.

2003-09-01

A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit treatment of oxidative degradation of up to C3-hydrocarbons CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in the formation of halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. On the other hand, the reaction between Br atoms and C2H2 is unimportant for determining the degree of bromine activation in the remote MBL. It is suggested that peroxyacetic acid formed via CH3CHO oxidation is one of the important chemical agents for triggering autocatalytic halogen release from sea-salt aerosols. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

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

McNeill, Jason Douglas

Electronic states of a thin layer of material on a surface possess unique physical and chemical properties. Some of these properties arise from the reduced dimensionality of the thin layer with respect to the bulk or the properties of the electric field where two materials of differing dielectric constants meet at an interface. Other properties are related to the nature of the surface chemical bond. Here, the properties of excess electrons in thin layers of Xenon, Krypton, and alkali metals are investigated, and the bound state energies and effective masses of the excess electrons are determined using two-photon photoemission. Formore » Xenon, the dependence of bound state energy, effective mass, and lifetime on layer thickness from one to nine layers is examined. Not all quantities were measured at each coverage. The two photon photoemission spectra of thin layers of Xenon on a Ag(111) substrate exhibit a number of sharp, well-defined peaks. The binding energy of the excess electronic states of Xenon layers exhibited a pronounced dependence on coverage. A discrete energy shift was observed for each additional atomic layer. At low coverage, a series of states resembling a Rydberg series is observed. This series is similar to the image state series observed on clean metal surfaces. Deviations from image state energies can be described in terms of the dielectric constant of the overlayer material and its effect on the image potential. For thicker layers of Xe (beyond the first few atomic layers), the coverage dependence of the features begins to resemble that of quantum well states. Quantum well states are related to bulk band states. However, the finite thickness of the layer restricts the perpendicular wavevector to a discrete set of values. Therefore, the spectrum of quantum well states contains a series of peaks which correspond to the various allowed values of the perpendicular wavevector. Analysis of the quantum well spectrum yields electronic band structure information. In this case, the quantum well states examined are derived from the Xenon conduction band. Measurements of the energies as a function of coverage yield the dispersion along the axis perpendicular to the surface while angle-resolved two-photon photoemission measurements yield information about dispersion along the surface parallel. The relative importance of the image potential and the overlayer band structure also depends on the quantum number and energy of the state. Some members of the image series may have an energy which is in an energy gap of the layer material, therefore such states may tend to remain physically outside the layer and retain much of their image character even at higher coverages. This is the case for the n = 1 image state of the Xe/Ag(111) system. The energies of image states which are excluded from the layer have a complex dependence on the thickness of the layer and its dielectric constant. The population decay kinetics of excited electronic states of the layer were also determined. Lifetimes are reported for the first three excited states for 1-6 atomic layers of Xe on Ag(111). As the image states evolve into quantum well states with increasing coverage, the lifetimes undergo an oscillation which marks a change in the spatial extent of the state. For example, the n = 2 quantum well state decreases substantially at 3-5 layers as the electron probability density in the layer increases. The lifetime data are modeled by extending the two-band nearly-free-electron approximation to account for the insulating Xe layer.« less

Towards lightweight and flexible high performance nanocrystalline silicon solar cells through light trapping and transport layers

NASA Astrophysics Data System (ADS)

Gray, Zachary R.

This thesis investigates ways to enhance the efficiency of thin film solar cells through the application of both novel nano-element array light trapping architectures and nickel oxide hole transport/electron blocking layers. Experimental results independently demonstrate a 22% enhancement in short circuit current density (JSC) resulting from a nano-element array light trapping architecture and a ˜23% enhancement in fill factor (FF) and ˜16% enhancement in open circuit voltage (VOC) resulting from a nickel oxide transport layer. In each case, the overall efficiency of the device employing the light trapping or transport layer was superior to that of the corresponding control device. Since the efficiency of a solar cell scales with the product of JSC, FF, and VOC, it follows that the results of this thesis suggest high performance thin film solar cells can be realized in the event light trapping architectures and transport layers can be simultaneously optimized. The realizations of these performance enhancements stem from extensive process optimization for numerous light trapping and transport layer fabrication approaches. These approaches were guided by numerical modeling techniques which will also be discussed. Key developments in this thesis include (1) the fabrication of nano-element topographies conducive to light trapping using various fabrication approaches, (2) the deposition of defect free nc-Si:H onto structured topographies by switching from SiH4 to SiF 4 PECVD gas chemistry, and (3) the development of the atomic layer deposition (ALD) growth conditions for NiO. Keywords: light trapping, nano-element array, hole transport layer, electron blocking layer, nickel oxide, nanocrystalline silicon, aluminum doped zinc oxide, atomic layer deposition, plasma enhanced chemical vapor deposition, electron beam lithography, ANSYS HFSS.

Fixed-Gap Tunnel Junction for Reading DNA Nucleotides

PubMed Central

2015-01-01

Previous measurements of the electronic conductance of DNA nucleotides or amino acids have used tunnel junctions in which the gap is mechanically adjusted, such as scanning tunneling microscopes or mechanically controllable break junctions. Fixed-junction devices have, at best, detected the passage of whole DNA molecules without yielding chemical information. Here, we report on a layered tunnel junction in which the tunnel gap is defined by a dielectric layer, deposited by atomic layer deposition. Reactive ion etching is used to drill a hole through the layers so that the tunnel junction can be exposed to molecules in solution. When the metal electrodes are functionalized with recognition molecules that capture DNA nucleotides via hydrogen bonds, the identities of the individual nucleotides are revealed by characteristic features of the fluctuating tunnel current associated with single-molecule binding events. PMID:25380505

Liquid-phase-deposited siloxane-based capping layers for silicon solar cells

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

Veith-Wolf, Boris; Wang, Jianhui; Hannu-Kuure, Milja

2015-02-02

We apply non-vacuum processing to deposit dielectric capping layers on top of ultrathin atomic-layer-deposited aluminum oxide (AlO{sub x}) films, used for the rear surface passivation of high-efficiency crystalline silicon solar cells. We examine various siloxane-based liquid-phase-deposited (LPD) materials. Our optimized AlO{sub x}/LPD stacks show an excellent thermal and chemical stability against aluminum metal paste, as demonstrated by measured surface recombination velocities below 10 cm/s on 1.3 Ωcm p-type silicon wafers after firing in a belt-line furnace with screen-printed aluminum paste on top. Implementation of the optimized LPD layers into an industrial-type screen-printing solar cell process results in energy conversion efficiencies ofmore » up to 19.8% on p-type Czochralski silicon.« less

Covalent functionalization and passivation of exfoliated black phosphorus via aryl diazonium chemistry.

PubMed

Ryder, Christopher R; Wood, Joshua D; Wells, Spencer A; Yang, Yang; Jariwala, Deep; Marks, Tobin J; Schatz, George C; Hersam, Mark C

2016-06-01

Functionalization of atomically thin nanomaterials enables the tailoring of their chemical, optical and electronic properties. Exfoliated black phosphorus (BP)-a layered two-dimensional semiconductor-exhibits favourable charge-carrier mobility, tunable bandgap and highly anisotropic properties, but it is chemically reactive and degrades rapidly in ambient conditions. Here we show that covalent aryl diazonium functionalization suppresses the chemical degradation of exfoliated BP even after three weeks of ambient exposure. This chemical modification scheme spontaneously forms phosphorus-carbon bonds, has a reaction rate sensitive to the aryl diazonium substituent and alters the electronic properties of exfoliated BP, ultimately yielding a strong, tunable p-type doping that simultaneously improves the field-effect transistor mobility and on/off current ratio. This chemical functionalization pathway controllably modifies the properties of exfoliated BP, and thus improves its prospects for nanoelectronic applications.

Covalent functionalization and passivation of exfoliated black phosphorus via aryl diazonium chemistry

NASA Astrophysics Data System (ADS)

Ryder, Christopher R.; Wood, Joshua D.; Wells, Spencer A.; Yang, Yang; Jariwala, Deep; Marks, Tobin J.; Schatz, George C.; Hersam, Mark C.

2016-06-01

Functionalization of atomically thin nanomaterials enables the tailoring of their chemical, optical and electronic properties. Exfoliated black phosphorus (BP)—a layered two-dimensional semiconductor—exhibits favourable charge-carrier mobility, tunable bandgap and highly anisotropic properties, but it is chemically reactive and degrades rapidly in ambient conditions. Here we show that covalent aryl diazonium functionalization suppresses the chemical degradation of exfoliated BP even after three weeks of ambient exposure. This chemical modification scheme spontaneously forms phosphorus-carbon bonds, has a reaction rate sensitive to the aryl diazonium substituent and alters the electronic properties of exfoliated BP, ultimately yielding a strong, tunable p-type doping that simultaneously improves the field-effect transistor mobility and on/off current ratio. This chemical functionalization pathway controllably modifies the properties of exfoliated BP, and thus improves its prospects for nanoelectronic applications.

Coatings Would Protect Polymers Against Atomic Oxygen

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Rutledge, Sharon K.

1995-01-01

Proposed interposition of layers of silver oxide tens to hundreds of angstroms thick between polymeric substrates and overlying films helps protect substrates against chemical attack by monatomic oxygen. In original application, polymer substrate would be, sheet of polyimide supporting array of solar photovoltaic cells on spacecraft in low orbit around Earth. Concept also applicable to protection of equipment in terrestrial laboratory and industrial vacuum and plasma chambers in which monatomic oxygen present.

Passivation mechanism of thermal atomic layer-deposited Al2O3 films on silicon at different annealing temperatures.

PubMed

Zhao, Yan; Zhou, Chunlan; Zhang, Xiang; Zhang, Peng; Dou, Yanan; Wang, Wenjing; Cao, Xingzhong; Wang, Baoyi; Tang, Yehua; Zhou, Su

2013-03-02

Thermal atomic layer-deposited (ALD) aluminum oxide (Al2O3) acquires high negative fixed charge density (Qf) and sufficiently low interface trap density after annealing, which enables excellent surface passivation for crystalline silicon. Qf can be controlled by varying the annealing temperatures. In this study, the effect of the annealing temperature of thermal ALD Al2O3 films on p-type Czochralski silicon wafers was investigated. Corona charging measurements revealed that the Qf obtained at 300°C did not significantly affect passivation. The interface-trapping density markedly increased at high annealing temperature (>600°C) and degraded the surface passivation even at a high Qf. Negatively charged or neutral vacancies were found in the samples annealed at 300°C, 500°C, and 750°C using positron annihilation techniques. The Al defect density in the bulk film and the vacancy density near the SiOx/Si interface region decreased with increased temperature. Measurement results of Qf proved that the Al vacancy of the bulk film may not be related to Qf. The defect density in the SiOx region affected the chemical passivation, but other factors may dominantly influence chemical passivation at 750°C.

Passivation mechanism of thermal atomic layer-deposited Al2O3 films on silicon at different annealing temperatures

PubMed Central

2013-01-01

Thermal atomic layer-deposited (ALD) aluminum oxide (Al2O3) acquires high negative fixed charge density (Qf) and sufficiently low interface trap density after annealing, which enables excellent surface passivation for crystalline silicon. Qf can be controlled by varying the annealing temperatures. In this study, the effect of the annealing temperature of thermal ALD Al2O3 films on p-type Czochralski silicon wafers was investigated. Corona charging measurements revealed that the Qf obtained at 300°C did not significantly affect passivation. The interface-trapping density markedly increased at high annealing temperature (>600°C) and degraded the surface passivation even at a high Qf. Negatively charged or neutral vacancies were found in the samples annealed at 300°C, 500°C, and 750°C using positron annihilation techniques. The Al defect density in the bulk film and the vacancy density near the SiOx/Si interface region decreased with increased temperature. Measurement results of Qf proved that the Al vacancy of the bulk film may not be related to Qf. The defect density in the SiOx region affected the chemical passivation, but other factors may dominantly influence chemical passivation at 750°C. PMID:23452508

Direct observation of nanowire growth and decomposition.

PubMed

Rackauskas, Simas; Shandakov, Sergey D; Jiang, Hua; Wagner, Jakob B; Nasibulin, Albert G

2017-09-26

Fundamental concepts of the crystal formation suggest that the growth and decomposition are determined by simultaneous embedding and removal of the atoms. Apparently, by changing the crystal formation conditions one can switch the regimes from the growth to decomposition. To the best of our knowledge, so far this has been only postulated, but never observed at the atomic level. By means of in situ environmental transmission electron microscopy we monitored and examined the atomic layer transformation at the conditions of the crystal growth and its decomposition using CuO nanowires selected as a model object. The atomic layer growth/decomposition was studied by varying an O 2 partial pressure. Three distinct regimes of the atomic layer evolution were experimentally observed: growth, transition and decomposition. The transition regime, at which atomic layer growth/decomposition switch takes place, is characterised by random nucleation of the atomic layers on the growing {111} surface. The decomposition starts on the side of the nanowire by removing the atomic layers without altering the overall crystal structure, which besides the fundamental importance offers new possibilities for the nanowire manipulation. Understanding of the crystal growth kinetics and nucleation at the atomic level is essential for the precise control of 1D crystal formation.

Low-temperature remote plasma enhanced atomic layer deposition of ZrO2/zircone nanolaminate film for efficient encapsulation of flexible organic light-emitting diodes.

PubMed

Chen, Zheng; Wang, Haoran; Wang, Xiao; Chen, Ping; Liu, Yunfei; Zhao, Hongyu; Zhao, Yi; Duan, Yu

2017-01-06

Encapsulation is essential to protect the air-sensitive components of organic light-emitting diodes (OLEDs) such as active layers and cathode electrodes. In this study, hybrid zirconium inorganic/organic nanolaminates were fabricated using remote plasma enhanced atomic layer deposition (PEALD) and molecular layer deposition at a low temperature. The nanolaminate serves as a thin-film encapsulation layer for OLEDs. The reaction mechanism of PEALD process was investigated using an in-situ quartz crystal microbalance (QCM) and in-situ quadrupole mass spectrometer (QMS). The bonds present in the films were determined by Fourier transform infrared spectroscopy. The primary reaction byproducts in PEALD, such as CO, CO 2 , NO, H 2 O, as well as the related fragments during the O 2 plasma process were characterized using the QMS, indicating a combustion-like reaction process. The self-limiting nature and growth mechanisms of the ZrO 2 during the complex surface chemical reaction of the ligand and O 2 plasma were monitored using the QCM. The remote PEALD ZrO 2 /zircone nanolaminate structure prolonged the transmission path of water vapor and smooth surface morphology. Consequently, the water barrier properties were significantly improved (reaching 3.078 × 10 -5  g/m 2 /day). This study also shows that flexible OLEDs can be successfully encapsulated to achieve a significantly longer lifetime.

Low-temperature remote plasma enhanced atomic layer deposition of ZrO2/zircone nanolaminate film for efficient encapsulation of flexible organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Chen, Zheng; Wang, Haoran; Wang, Xiao; Chen, Ping; Liu, Yunfei; Zhao, Hongyu; Zhao, Yi; Duan, Yu

2017-01-01

Encapsulation is essential to protect the air-sensitive components of organic light-emitting diodes (OLEDs) such as active layers and cathode electrodes. In this study, hybrid zirconium inorganic/organic nanolaminates were fabricated using remote plasma enhanced atomic layer deposition (PEALD) and molecular layer deposition at a low temperature. The nanolaminate serves as a thin-film encapsulation layer for OLEDs. The reaction mechanism of PEALD process was investigated using an in-situ quartz crystal microbalance (QCM) and in-situ quadrupole mass spectrometer (QMS). The bonds present in the films were determined by Fourier transform infrared spectroscopy. The primary reaction byproducts in PEALD, such as CO, CO2, NO, H2O, as well as the related fragments during the O2 plasma process were characterized using the QMS, indicating a combustion-like reaction process. The self-limiting nature and growth mechanisms of the ZrO2 during the complex surface chemical reaction of the ligand and O2 plasma were monitored using the QCM. The remote PEALD ZrO2/zircone nanolaminate structure prolonged the transmission path of water vapor and smooth surface morphology. Consequently, the water barrier properties were significantly improved (reaching 3.078 × 10-5 g/m2/day). This study also shows that flexible OLEDs can be successfully encapsulated to achieve a significantly longer lifetime.

A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

NASA Astrophysics Data System (ADS)

Toyota, K.; Kanaya, Y.; Takahashi, M.; Akimoto, H.

2004-09-01

A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit description of oxidative degradation of up to C3-hydrocarbons (CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in forming halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from a reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. The reaction between Br atoms and C2H2 is shown to be unimportant for determining the degree of bromine activation in the remote MBL. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

Etching-free patterning method for electrical characterization of atomically thin MoSe2 films grown by chemical vapor deposition.

PubMed

Utama, M Iqbal Bakti; Lu, Xin; Zhan, Da; Ha, Son Tung; Yuan, Yanwen; Shen, Zexiang; Xiong, Qihua

2014-11-07

Patterning two-dimensional materials into specific spatial arrangements and geometries is essential for both fundamental studies of materials and practical applications in electronics. However, the currently available patterning methods generally require etching steps that rely on complicated and expensive procedures. We report here a facile patterning method for atomically thin MoSe2 films using stripping with an SU-8 negative resist layer exposed to electron beam lithography. Additional steps of chemical and physical etching were not necessary in this SU-8 patterning method. The SU-8 patterning was used to define a ribbon channel from a field effect transistor of MoSe2 film, which was grown by chemical vapor deposition. The narrowing of the conduction channel area with SU-8 patterning was crucial in suppressing the leakage current within the device, thereby allowing a more accurate interpretation of the electrical characterization results from the sample. An electrical transport study, enabled by the SU-8 patterning, showed a variable range hopping behavior at high temperatures.

Effect of Elastic Strain Fluctuation on Atomic Layer Growth of Epitaxial Silicide in Si Nanowires by Point Contact Reactions.

PubMed

Chou, Yi-Chia; Tang, Wei; Chiou, Chien-Jyun; Chen, Kai; Minor, Andrew M; Tu, K N

2015-06-10

Effects of strain impact a range of applications involving mobility change in field-effect-transistors. We report the effect of strain fluctuation on epitaxial growth of NiSi2 in a Si nanowire via point contact and atomic layer reactions, and we discuss the thermodynamic, kinetic, and mechanical implications. The generation and relaxation of strain shown by in situ TEM is periodic and in synchronization with the atomic layer reaction. The Si lattice at the epitaxial interface is under tensile strain, which enables a high solubility of supersaturated interstitial Ni atoms for homogeneous nucleation of an epitaxial atomic layer of the disilicide phase. The tensile strain is reduced locally during the incubation period of nucleation by the dissolution of supersaturated Ni atoms in the Si lattice but the strained-Si state returns once the atomic layer epitaxial growth of NiSi2 occurs by consuming the supersaturated Ni.

HfO2 Gate Dielectric on (NH4)2S Passivated (100) GaAs Grown by Atomic Layer Deposition

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

Chen, P.T.; /Stanford U., Materials Sci. Dept.; Sun, Y.

2007-09-28

The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH{sub 4}){sub 2}S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As{sub 2}O{sub 3} formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out-diffusion into the hafnia film were observed after a 450 C post-deposition anneal, and may be the origins for the electrically active defects. Transmission electron microscopymore » cross section images showed thicker HfO{sub 2} films for a given precursor exposure on S-treated GaAs versus the non-treated sample. In addition, the valence-band and the conduction-band offsets at the HfO{sub 2}/GaAs interface were deduced to be 3.18 eV and a range of 0.87-0.97 eV, respectively. It appears that HCl+(NH{sub 4})2{sub S} treatments provide a superior chemical passivation for GaAs and initial surface for ALD deposition.« less

Phase inversion and frequency doubling of reflection high-energy electron diffraction intensity oscillations in the layer-by-layer growth of complex oxides

NASA Astrophysics Data System (ADS)

Mao, Zhangwen; Guo, Wei; Ji, Dianxiang; Zhang, Tianwei; Gu, Chenyi; Tang, Chao; Gu, Zhengbin; Nie*, Yuefeng; Pan, Xiaoqing

In situ reflection high-energy electron diffraction (RHEED) and its intensity oscillations are extremely important for the growth of epitaxial thin films with atomic precision. The RHEED intensity oscillations of complex oxides are, however, rather complicated and a general model is still lacking. Here, we report the unusual phase inversion and frequency doubling of RHEED intensity oscillations observed in the layer-by-layer growth of SrTiO3 using oxide molecular beam epitaxy. In contacts to the common understanding that the maximum(minimum) intensity occurs at SrO(TiO2) termination, respectively, we found that both maximum or minimum intensities can occur at SrO, TiO2, or even incomplete terminations depending on the incident angle of the electron beam, which raises a fundamental question if one can rely on the RHEED intensity oscillations to precisely control the growth of thin films. A general model including surface roughness and termination dependent mean inner potential qualitatively explains the observed phenomena, and provides the answer to the question how to prepare atomically and chemically precise surface/interfaces using RHEED oscillations for complex oxides. We thank National Basic Research Program of China (No. 11574135, 2015CB654901) and the National Thousand-Young-Talents Program.

Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS2

PubMed Central

Trainer, Daniel J.; Putilov, Aleksei V.; Di Giorgio, Cinzia; Saari, Timo; Wang, Baokai; Wolak, Mattheus; Chandrasena, Ravini U.; Lane, Christopher; Chang, Tay-Rong; Jeng, Horng-Tay; Lin, Hsin; Kronast, Florian; Gray, Alexander X.; Xi, Xiaoxing X.; Nieminen, Jouko; Bansil, Arun; Iavarone, Maria

2017-01-01

Recent progress in the synthesis of monolayer MoS2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS2 as a function of the number of layers at the nanoscale and show in-depth how the band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS2. PMID:28084465

Inter-layer coupling induced valence band edge shift in mono- to few-layer MoS 2

DOE PAGES

Trainer, Daniel J.; Putilov, Aleksei V.; Di Giorgio, Cinzia; ...

2017-01-13

In this study, recent progress in the synthesis of monolayer MoS 2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here,we report a study of highly crystalline islands of MoS 2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS 2 as a function of the number of layers at the nanoscale and show in-depth how themore » band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS 2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS 2.« less

Intricate Short-Range Ordering and Strongly Anisotropic Transport Properties of Li 1–x Sn 2+x As 2

DOE PAGES

Lee, Kathleen; Kaseman, Derrick; Sen, Sabyasachi; ...

2015-02-22

A new ternary compound, Li 1-xSn 2+xAs 2, 0.2 < x < 0.4, was synthesized via solid-state reaction of elements. The compound crystallizes in a layered structure in the Rmore » $$\\overline{3}m$$ space group (No. 166) with Sn-As layers separated by layers of jointly occupied Li/Sn. The Sn-As layers are comprised of Sn 3As 3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As 6 octahedron. Thorough investigations by synchrotron x-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, local Sn/Li ordering was revealed by synergistic investigations via solid-state 6,7Li NMR spectroscopy, HR-TEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions creating substantial inhomogeneity on the nanoscale. Inhomogeneous local structure has high impact on the physical properties of the synthesized compounds: local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li 1-xSn 2+xAs 2.« less

Atomic-Layer-Deposited Transparent Electrodes for Silicon Heterojunction Solar Cells

DOE PAGES

Demaurex, Benedicte; Seif, Johannes P.; Smit, Sjoerd; ...

2014-11-01

We examine damage-free transparent-electrode deposition to fabricate high-efficiency amorphous silicon/crystalline silicon heterojunction solar cells. Such solar cells usually feature sputtered transparent electrodes, the deposition of which may damage the layers underneath. Using atomic layer deposition, we insert thin protective films between the amorphous silicon layers and sputtered contacts and investigate their effect on device operation. We find that a 20-nm-thick protective layer suffices to preserve, unchanged, the amorphous silicon layers beneath. Insertion of such protective atomic-layer-deposited layers yields slightly higher internal voltages at low carrier injection levels. However, we identify the presence of a silicon oxide layer, formed during processing,more » between the amorphous silicon and the atomic-layer-deposited transparent electrode that acts as a barrier, impeding hole and electron collection.« less

Ab initio molecular dynamics study of thermite reaction at Al and CuO nano-interfaces at different temperatures

NASA Astrophysics Data System (ADS)

Tang, Cui-Ming; Chen, Xiao-Xu; Cheng, Xin-Lu; Zhang, Chao-Yang; Lu, Zhi-Peng

2018-05-01

The thermite reaction at Al/CuO nano-interfaces is investigated with ab initio molecular dynamics calculations in canonical ensemble at 500 K, 800 K, 1200 K and 1500 K, respectively. The reaction process and reaction products are analyzed in terms of chemical bonds, average charge, time constants and total potential energy. The activity of the reactants enhances with increasing temperature, which induces a faster thermite reaction. The alloy reaction obviously expands outward at Cu-rich interface of Al/CuO system, and the reaction between Al and O atoms obviously expands outward at O-rich interface as temperature increases. Different reaction products are found at the outermost layer of different interfaces in the Al/CuO system. In generally, the average charge of the outer layer aluminum atoms (i.e., Al1, Al2, Al5 and Al6) increases with temperature. The potential energy of Al/CuO system decreases significantly, which indicates that drastic exothermic reaction occurs at the Al/CuO system. This research enhances fundamental understanding in temperature effect on the thermite reaction at atomic level, which can potentially open new possibilities for its industrial application.

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

Vissers, Daniel R.; Isheim, Dieter; Zhan, Chun

Lithium-ion batteries utilizing 5 V spinel material, LixMn1.5Ni0.5O4 have received considerable interest in recent years for their ability to deliver high energy and power densities. In this paper, we report an atomic scale analysis of the surface layer of a core–shell 5 V spinel structure where a small amount of the manganese lattice sites have been substituted with cobalt in the shell to reach a stoichiometry of LixMn1.18Ni0.55Co0.27O4. Our analyses include electrochemical analysis, atom probe tomography (APT) analysis, kinetic analysis of the interfacial reactions, and high resolution scanning transmission electron microscopy (HR-TEM) analysis. The APT analysis is performed on themore » material before and after long-term cycling at room temperature to provide insights into the atomic scale phenomena within the surface layer of the electrode material. Our APT data reveals a 25–30 nano-meter (nm) region which forms after cycling. From our analyses, we believe that the outer few nanometers of this region stabilizes the 5 V spinel within the chemical environment of the lithium-ion cell such that its structure is not compromised and thereby enables this material to cycle without significant capacity fading.« less

Engineered ZnO nanowire arrays using different nanopatterning techniques

NASA Astrophysics Data System (ADS)

Volk, János; Szabó, Zoltán; Erdélyi, Róbert; Khánh, Nguyen Q.

2012-02-01

The impact of various masking patterns and template layers on the wet chemically grown vertical ZnO nanowire arrays was investigated. The nanowires/nanorods were seeded at nucleation windows which were patterned in a mask layer using various techniques such as electron beam lithography, nanosphere photolithography, and atomic force microscope type nanolithography. The compared ZnO templates included single crystals, epitaxial layer, and textured polycrystalline films. Scanning electron microscopy revealed that the alignment and crystal orientation of the nanowires were dictated by the underlying seed layer, while their geometry can be tuned by the parameters of the certain nanopatterning technique and of the wet chemical process. The comparison of the alternative nanolithography techniques showed that using direct writing methods the diameter of the ordered ZnO nanowires can be as low as 30-40 nm at a density of 100- 1000 NW/μm2 in a very limited area (10 μm2-1 mm2). Nanosphere photolithography assisted growth, on the other hand, favors thicker nanopillars (~400 nm) and enables large-area, low-cost patterning (1-100 cm2). These alternative lowtemperature fabrication routes can be used for different novel optoelectronic devices, such as nanorod based ultraviolet photodiode, light emitting device, and waveguide laser.

Effect of the Chemical State of the Surface on the Relaxation of the Surface Shell Atoms in SiC and GaN Nanocrystals

NASA Technical Reports Server (NTRS)

Palosz, B.; Grzanka, E.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H. P.; Janik, J. F.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

2002-01-01

The effect of the chemical state of the surface of nanoparticles on the relaxation in the near-surface layer was examined using the concept of the apparent lattice parameter (alp) determined for different diffraction vectors Q. The apparent lattice parameter is a lattice parameter determined either from an individual Bragg reflection, or from a selected region of the diffraction pattern. At low diffraction vectors the Bragg peak positions are affected mainly by the structure of the near-surface layer, while at high Q-values only the interior of the nano-grain contributes to the diffraction pattern. Following the measurements on raw (as prepared) powders we investigated powders cleaned by annealing at 400C under vacuum, and the same powders wetted with water. Theoretical alp-Q plots showed that the structure of the surface layer depends on the sample treatment. Semi-quantitative analysis based on the comparison of the experimental and theoretical alp-Q plots was performed. Theoretical alp-Q relations were obtained from the diffraction patterns calculated for models of nanocrystals with a strained surface layer using the Debye functions.

Oxygen-implanted induced formation of oxide layer enhances blood compatibility on titanium for biomedical applications.

PubMed

Hung, Wei-Chiang; Chang, Fang-Mo; Yang, Tzu-Sen; Ou, Keng-Liang; Lin, Che-Tong; Peng, Pei-Wen

2016-11-01

Titanium dioxide (TiO2) layers were prepared on a Ti substrate by using oxygen plasma immersion ion implantation (oxygen PIII). The surface chemical states, structure, and morphology of the layers were studied using X-ray photoelectron spectroscopy, X-ray diffraction, Raman microscopy, atomic force microscopy and scanning electron microscope. The mechanical properties, such as the Young's modulus and hardness, of the layers were investigated using nanoindentation testing. The Ti(4+) chemical state was determined to be present on oxygen-PIII-treated surfaces, which consisted of nanocrystalline TiO2 with a rutile structure. Compared with Ti substrates, the oxygen-PIII-treated surfaces exhibited decreased Young's moduli and hardness. Parameters indicating the blood compatibility of the oxygen-PIII-treated surfaces, including the clotting time and platelet adhesion and activation, were studied in vitro. Clotting time assays indicated that the clotting time of oxygen-PIII-treated surfaces was longer than that of the Ti substrate, which was associated with decreased fibrinogen adsorption. In conclusion, the surface characteristics and the blood compatibility of Ti implants can be modified and improved using oxygen PIII. Copyright © 2016 Elsevier B.V. All rights reserved.

Thickness scaling of atomic-layer-deposited HfO2 films and their application to wafer-scale graphene tunnelling transistors

PubMed Central

Jeong, Seong-Jun; Gu, Yeahyun; Heo, Jinseong; Yang, Jaehyun; Lee, Chang-Seok; Lee, Min-Hyun; Lee, Yunseong; Kim, Hyoungsub; Park, Seongjun; Hwang, Sungwoo

2016-01-01

The downscaling of the capacitance equivalent oxide thickness (CET) of a gate dielectric film with a high dielectric constant, such as atomic layer deposited (ALD) HfO2, is a fundamental challenge in achieving high-performance graphene-based transistors with a low gate leakage current. Here, we assess the application of various surface modification methods on monolayer graphene sheets grown by chemical vapour deposition to obtain a uniform and pinhole-free ALD HfO2 film with a substantially small CET at a wafer scale. The effects of various surface modifications, such as N-methyl-2-pyrrolidone treatment and introduction of sputtered ZnO and e-beam-evaporated Hf seed layers on monolayer graphene, and the subsequent HfO2 film formation under identical ALD process parameters were systematically evaluated. The nucleation layer provided by the Hf seed layer (which transforms to the HfO2 layer during ALD) resulted in the uniform and conformal deposition of the HfO2 film without damaging the graphene, which is suitable for downscaling the CET. After verifying the feasibility of scaling down the HfO2 thickness to achieve a CET of ~1.5 nm from an array of top-gated metal-oxide-graphene field-effect transistors, we fabricated graphene heterojunction tunnelling transistors with a record-low subthreshold swing value of <60 mV/dec on an 8″ glass wafer. PMID:26861833

Low-Temperature Plasma-Assisted Atomic Layer Deposition of Silicon Nitride Moisture Permeation Barrier Layers.

PubMed

Andringa, Anne-Marije; Perrotta, Alberto; de Peuter, Koen; Knoops, Harm C M; Kessels, Wilhelmus M M; Creatore, Mariadriana

2015-10-14

Encapsulation of organic (opto-)electronic devices, such as organic light-emitting diodes (OLEDs), photovoltaic cells, and field-effect transistors, is required to minimize device degradation induced by moisture and oxygen ingress. SiNx moisture permeation barriers have been fabricated using a very recently developed low-temperature plasma-assisted atomic layer deposition (ALD) approach, consisting of half-reactions of the substrate with the precursor SiH2(NH(t)Bu)2 and with N2-fed plasma. The deposited films have been characterized in terms of their refractive index and chemical composition by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). The SiNx thin-film refractive index ranges from 1.80 to 1.90 for films deposited at 80 °C up to 200 °C, respectively, and the C, O, and H impurity levels decrease when the deposition temperature increases. The relative open porosity content of the layers has been studied by means of multisolvent ellipsometric porosimetry (EP), adopting three solvents with different kinetic diameters: water (∼0.3 nm), ethanol (∼0.4 nm), and toluene (∼0.6 nm). Irrespective of the deposition temperature, and hence the impurity content in the SiNx films, no uptake of any adsorptive has been observed, pointing to the absence of open pores larger than 0.3 nm in diameter. Instead, multilayer development has been observed, leading to type II isotherms that, according to the IUPAC classification, are characteristic of nonporous layers. The calcium test has been performed in a climate chamber at 20 °C and 50% relative humidity to determine the intrinsic water vapor transmission rate (WVTR) of SiNx barriers deposited at 120 °C. Intrinsic WVTR values in the range of 10(-6) g/m2/day indicate excellent barrier properties for ALD SiNx layers as thin as 10 nm, competing with that of state-of-the-art plasma-enhanced chemical vapor-deposited SiNx layers of a few hundred nanometers in thickness.

Mitigating leaks in membranes

DOEpatents

Karnik, Rohit N.; Bose, Suman; Boutilier, Michael S.H.; Hadjiconstantinou, Nicolas G.; Jain, Tarun Kumar; O'Hern, Sean C.; Laoui, Tahar; Atieh, Muataz A.; Jang, Doojoon

2018-02-27

Two-dimensional material based filters, their method of manufacture, and their use are disclosed. In one embodiment, a membrane may include an active layer including a plurality of defects and a deposited material associated with the plurality of defects may reduce flow therethrough. Additionally, a majority of the active layer may be free from the material. In another embodiment, a membrane may include a porous substrate and an atomic layer deposited material disposed on a surface of the porous substrate. The atomic layer deposited material may be less hydrophilic than the porous substrate and an atomically thin active layer may be disposed on the atomic layer deposited material.

Direct synthesis of graphene on silicon oxide by low temperature plasma enhanced chemical vapor deposition.

PubMed

Muñoz, Roberto; Martínez, Lidia; López-Elvira, Elena; Munuera, Carmen; Huttel, Yves; García-Hernández, Mar

2018-06-27

Direct graphene growth on silicon with a native oxide using plasma enhanced chemical vapour deposition at low temperatures [550 °C-650 °C] is demonstrated for the first time. It is shown that the fine-tuning of a two-step synthesis with gas mixtures C2H2/H2 yields monolayer and few layer graphene films with a controllable domain size from 50 nm to more than 300 nm and the sheet resistance ranging from 8 kΩ sq-1 to less than 1.8 kΩ sq-1. Differences are understood in terms of the interaction of the plasma species - chiefly atomic H - with the deposited graphene and the native oxide layer. The proposed low temperature direct synthesis on an insulating substrate does not require any transfer processes and improves the compatibility with the current industrial processes.

Structural and optical properties of PbS thin films grown by chemical bath deposition

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

Seghaier, S.; Kamoun, N.; Guasch, C.

2007-09-19

Lead sulphide thin films are grown on glass substrates at various deposition times tD, in the range of 40-60 min per step of 2 min, using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the film structure. The surface composition is analysed by Auger electron spectroscopy. It appears that the as-prepared thin films are polycrystalline with cubic structure. Nanometric scale crystallites are uniformly distributed on the surface. They exhibit almost a stoechiometric composition with a [Pb]/[S] ratio equal to 1.10. Optical properties are studied in the range of 300-3300 nm by spectrophotometric measurements.more » Analysis of the optical absorption data of lead sulphide thin layers reveals a narrow optical direct band gap equal to 0.46 eV for the layer corresponding to a deposition time equal to 60 min.« less

Effect of Group-III precursors on unintentional gallium incorporation during epitaxial growth of InAlN layers by metalorganic chemical vapor deposition

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

Kim, Jeomoh, E-mail: jkim610@gatech.edu; Ji, Mi-Hee; Detchprohm, Theeradetch

2015-09-28

Unintentional incorporation of gallium (Ga) in InAlN layers grown with different molar flow rates of Group-III precursors by metalorganic chemical vapor deposition has been experimentally investigated. The Ga mole fraction in the InAl(Ga)N layer was increased significantly with the trimethylindium (TMIn) flow rate, while the trimethylaluminum flow rate controls the Al mole fraction. The evaporation of metallic Ga from the liquid phase eutectic system between the pyrolized In from injected TMIn and pre-deposited metallic Ga was responsible for the Ga auto-incorporation into the InAl(Ga)N layer. The theoretical calculation on the equilibrium vapor pressure of liquid phase Ga and the effectivemore » partial pressure of Group-III precursors based on growth parameters used in this study confirms the influence of Group-III precursors on Ga auto-incorporation. More Ga atoms can be evaporated from the liquid phase Ga on the surrounding surfaces in the growth chamber and then significant Ga auto-incorporation can occur due to the high equilibrium vapor pressure of Ga comparable to effective partial pressure of input Group-III precursors during the growth of InAl(Ga)N layer.« less

Transport mechanisms through PE-CVD coatings: influence of temperature, coating properties and defects on permeation of water vapour

NASA Astrophysics Data System (ADS)

Kirchheim, Dennis; Jaritz, Montgomery; Mitschker, Felix; Gebhard, Maximilian; Brochhagen, Markus; Hopmann, Christian; Böke, Marc; Devi, Anjana; Awakowicz, Peter; Dahlmann, Rainer

2017-03-01

Gas transport mechanisms through plastics are usually described by the temperature-dependent Arrhenius-model and compositions of several plastic layers are represented by the CLT. When it comes to thin films such as plasma-enhanced chemical vapour deposition (PE-CVD) or plasma-enhanced atomic layer deposition (PE-ALD) coatings on substrates of polymeric material, a universal model is lacking. While existing models describe diffusion through defects, these models presume that permeation does not occur by other means of transport mechanisms. This paper correlates the existing transport models with data from water vapour transmission experiments.

Strengthened PAN-based carbon fibers obtained by slow heating rate carbonization.

PubMed

Kim, Min-A; Jang, Dawon; Tejima, Syogo; Cruz-Silva, Rodolfo; Joh, Han-Ik; Kim, Hwan Chul; Lee, Sungho; Endo, Morinobu

2016-03-23

Large efforts have been made over the last 40 years to increase the mechanical strength of polyacrylonitrile (PAN)-based carbon fibers (CFs) using a variety of chemical or physical protocols. In this paper, we report a new method to increase CFs mechanical strength using a slow heating rate during the carbonization process. This new approach increases both the carbon sp(3) bonding and the number of nitrogen atoms with quaternary bonding in the hexagonal carbon network. Theoretical calculations support a crosslinking model promoted by the interstitial carbon atoms located in the graphitic interlayer spaces. The improvement in mechanical performance by a controlled crosslinking between the carbon hexagonal layers of the PAN based CFs is a new concept that can contribute further in the tailoring of CFs performance based on the understanding of their microstructure down to the atomic scale.

Atomic-Scale Observations of (010) LiFePO4 Surfaces Before and After Chemical Delithiation.

PubMed

Kobayashi, Shunsuke; Fisher, Craig A J; Kato, Takeharu; Ukyo, Yoshio; Hirayama, Tsukasa; Ikuhara, Yuichi

2016-09-14

The ability to view directly the surface structures of battery materials with atomic resolution promises to dramatically improve our understanding of lithium (de)intercalation and related processes. Here we report the use of state-of-the-art scanning transmission electron microscopy techniques to probe the (010) surface of commercially important material LiFePO4 and compare the results with theoretical models. The surface structure is noticeably different depending on whether Li ions are present in the topmost surface layer or not. Li ions are also found to migrate back to surface regions from within the crystal relatively quickly after partial delithiation, demonstrating the facile nature of Li transport in the [010] direction. The results are consistent with phase transformation models involving metastable phase formation and relaxation, providing atomic-level insights into these fundamental processes.

Science and Emerging Technology of 2D Atomic Layered Materials and Devices

DTIC Science & Technology

2017-09-09

AFRL-AFOSR-JP-TR-2017-0067 Science & Emerging Technology of 2D Atomic Layered Materials and Devices Angel Rubio UNIVERSIDAD DEL PAIS VASCO - EUSKAL...Emerging Technology of 2D Atomic Layered Materials and Devices 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA2386-15-1-0006 5c.  PROGRAM ELEMENT NUMBER...reporting documents for AOARD project 144088, “2D Materials and Devices Beyond Graphene Science & Emerging Technology of 2D Atomic Layered Materials and

Orientation dependences of atomic structures in chemically heterogeneous Cu{sub 50}Ta{sub 50}/Ta glass-crystal interfaces

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

Yang, Guiqin; Gao, Xiaoze; Li, Jinfu

2015-01-07

Molecular dynamics simulations based on an angular-dependent potential were performed to examine the structural properties of chemically heterogeneous interfaces between amorphous Cu{sub 50}Ta{sub 50} and crystalline Ta. Several phenomena, namely, layering, crystallization, intermixing, and composition segregation, were observed in the Cu{sub 50}Ta{sub 50} region adjacent to the Ta layers. These interfacial behaviors are found to depend on the orientation of the underlying Ta substrate: Layering induced by Ta(110) extends the farthest into Cu{sub 50}Ta{sub 50}, crystallization in the Cu{sub 50}Ta{sub 50} region is most significant for interface against Ta(100), while inter-diffusion is most pronounced for Ta(111). It turns out thatmore » the induced layering behavior is dominated by the interlayer distances of the underlying Ta layers, while the degree of inter-diffusion is governed by the openness of the Ta crystalline layers. In addition, composition segregations are observed in all interface models, corresponding to the immiscible nature of the Cu-Ta system. Furthermore, Voronoi polyhedra 〈0,5,2,6〉 and 〈0,4,4,6〉 are found to be abundant in the vicinity of the interfaces for all models, whose presence is believed to facilitate the structural transition between amorphous and body centered cubic.« less

Centimeter Scale Patterned Growth of Vertically Stacked Few Layer Only 2D MoS2/WS2 van der Waals Heterostructure.

PubMed

Choudhary, Nitin; Park, Juhong; Hwang, Jun Yeon; Chung, Hee-Suk; Dumas, Kenneth H; Khondaker, Saiful I; Choi, Wonbong; Jung, Yeonwoong

2016-05-05

Two-dimensional (2D) van der Waal (vdW) heterostructures composed of vertically-stacked multiple transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are envisioned to present unprecedented materials properties unobtainable from any other material systems. Conventional fabrications of these hybrid materials have relied on the low-yield manual exfoliation and stacking of individual 2D TMD layers, which remain impractical for scaled-up applications. Attempts to chemically synthesize these materials have been recently pursued, which are presently limited to randomly and scarcely grown 2D layers with uncontrolled layer numbers on very small areas. Here, we report the chemical vapor deposition (CVD) growth of large-area (>2 cm(2)) patterned 2D vdW heterostructures composed of few layer, vertically-stacked MoS2 and WS2. Detailed structural characterizations by Raman spectroscopy and high-resolution/scanning transmission electron microscopy (HRTEM/STEM) directly evidence the structural integrity of two distinct 2D TMD layers with atomically sharp vdW heterointerfaces. Electrical transport measurements of these materials reveal diode-like behavior with clear current rectification, further confirming the formation of high-quality heterointerfaces. The intrinsic scalability and controllability of the CVD method presented in this study opens up a wide range of opportunities for emerging applications based on the unconventional functionalities of these uniquely structured materials.

A new solution chemical method to make low dimensional thermoelectric materials

NASA Astrophysics Data System (ADS)

Ding, Zhongfen

2001-11-01

Bismuth telluride and its alloys are currently the best thermoelectric materials known at room temperature and are therefore used for portable solid-state refrigeration. If the thermal electric figure of merit ZT could be improved by a factor of about 3, quiet and rugged solid-state devices could eventually replace conventional compressor based cooling systems. In order to test a theory that improved one-dimensional or two-dimensional materials could enhance ZT due to lower thermal conductivity, we are developing solution processing methods to make low dimensional materials. Bismuth telluride and its p-type and n-type alloys have layered structures consisting of 5 atom thick Te-Bi-Te-Bi-Te sheets, each sheet about 10 A thick. Lithium ions are intercalated into the layered materials using liquid ammonia. The lithium-intercalated materials are then exfoliated in water to form colloidal suspensions with narrow particle size distributions and are stable for more than 24 hours. The layers are then deposited on substrates, which after annealing at low temperatures, form highly c-axis oriented thin films. The exfoliated layers can potentially be restacked with other ions or layered materials in between the sheets to form novel structures. The restacked layers when treated with nitric acid and sonication form high yield nanorod structured materials. This new intercalation and exfoliation followed by sonication method could potentially be used for many other layered materials to make nanorod structured materials. The low dimensional materials are characterized by powder X-ray diffraction, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma (ICP) and dynamic light scattering.

Partially Oxidized SnS2 Atomic Layers Achieving Efficient Visible-Light-Driven CO2 Reduction.

PubMed

Jiao, Xingchen; Li, Xiaodong; Jin, Xiuyu; Sun, Yongfu; Xu, Jiaqi; Liang, Liang; Ju, Huanxin; Zhu, Junfa; Pan, Yang; Yan, Wensheng; Lin, Yue; Xie, Yi

2017-12-13

Unraveling the role of surface oxide on affecting its native metal disulfide's CO 2 photoreduction remains a grand challenge. Herein, we initially construct metal disulfide atomic layers and hence deliberately create oxidized domains on their surfaces. As an example, SnS 2 atomic layers with different oxidation degrees are successfully synthesized. In situ Fourier transform infrared spectroscopy spectra disclose the COOH* radical is the main intermediate, whereas density-functional-theory calculations reveal the COOH* formation is the rate-limiting step. The locally oxidized domains could serve as the highly catalytically active sites, which not only benefit for charge-carrier separation kinetics, verified by surface photovoltage spectra, but also result in electron localization on Sn atoms near the O atoms, thus lowering the activation energy barrier through stabilizing the COOH* intermediates. As a result, the mildly oxidized SnS 2 atomic layers exhibit the carbon monoxide formation rate of 12.28 μmol g -1 h -1 , roughly 2.3 and 2.6 times higher than those of the poorly oxidized SnS 2 atomic layers and the SnS 2 atomic layers under visible-light illumination. This work uncovers atomic-level insights into the correlation between oxidized sulfides and CO 2 reduction property, paving a new way for obtaining high-efficiency CO 2 photoreduction performances.

Atomic Layer Deposition in Bio-Nanotechnology: A Brief Overview.

PubMed

Bishal, Arghya K; Butt, Arman; Selvaraj, Sathees K; Joshi, Bela; Patel, Sweetu B; Huang, Su; Yang, Bin; Shukohfar, Tolou; Sukotjo, Cortino; Takoudis, Christos G

2015-01-01

Atomic layer deposition (ALD) is a technique increasingly used in nanotechnology and ultrathin film deposition; it is ideal for films in the nanometer and Angstrom length scales. ALD can effectively be used to modify the surface chemistry and functionalization of engineering-related and biologically important surfaces. It can also be used to alter the mechanical, electrical, chemical, and other properties of materials that are increasingly used in biomedical engineering and biological sciences. ALD is a relatively new technique for optimizing materials for use in bio-nanotechnology. Here, after a brief review of the more widely used modes of ALD and a few of its applications in biotechnology, selected results that show the potential of ALD in bio-nanotechnology are presented. ALD seems to be a promising means for tuning the hydrophilicity/hydrophobicity characteristics of biomedical surfaces, forming conformal ultrathin coatings with desirable properties on biomedical substrates with a high aspect ratio, tuning the antibacterial properties of substrate surfaces of interest, and yielding multifunctional biomaterials for medical implants and other devices.

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

Hong, Seung Sae; Yu, Jung Ho; Lu, Di

Long-range order and phase transitions in two-dimensional (2D) systems—such as magnetism, superconductivity, and crystallinity—have been important research topics for decades. The issue of 2D crystalline order has reemerged recently, with the development of exfoliated atomic crystals. Understanding the dimensional limit of crystalline phases, with different types of bonding and synthetic techniques, is at the foundation of low-dimensional materials design. We study ultrathin membranes of SrTiO 3, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released after synthesis by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO 3 membrane lattice collapsesmore » below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length is analogous to the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) transition. Finally, the transition is likely driven by chemical bond breaking at the 2D layer-3D bulk interface, defining an effective dimensional phase boundary for coherent crystalline lattices.« less

Tuning oxidation level, electrical conductance and band gap structure on graphene sheets by cyclic atomic layer reduction technique

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

Gu, Si-Yong; Hsieh, Chien-Te; Lin, Tzu-Wei

The present work develops an atomic layer reduction (ALR) method to accurately tune oxidation level, electrical conductance, band-gap structure, and photoluminescence (PL) response of graphene oxide (GO) sheets. The ALR route is carried out at 200 °C within ALR cycle number of 10–100. The ALR treatment is capable of striping surface functionalities (e.g., hydroxyl, carbonyl, and carboxylic groups), producing thermally-reduced GO sheets. The ALR cycle number serves as a controlling factor in adjusting the crystalline, surface chemistry, electrical, optical properties of GO sheets. With increasing the ALR cycle number, ALR-GO sheets display a high crystallinity, a low oxidation level, anmore » improved electrical conductivity, a narrow band gap, and a tunable PL response. Finally, on the basis of the results, the ALR technique offers a great potential for accurately tune electrical and optical properties of carbon materials through the cyclic removal of oxygen functionalities, without any complicated thermal and chemical desorption processes.« less

Electrical and thermal conduction in atomic layer deposition nanobridges down to 7 nm thickness.

PubMed

Yoneoka, Shingo; Lee, Jaeho; Liger, Matthieu; Yama, Gary; Kodama, Takashi; Gunji, Marika; Provine, J; Howe, Roger T; Goodson, Kenneth E; Kenny, Thomas W

2012-02-08

While the literature is rich with data for the electrical behavior of nanotransistors based on semiconductor nanowires and carbon nanotubes, few data are available for ultrascaled metal interconnects that will be demanded by these devices. Atomic layer deposition (ALD), which uses a sequence of self-limiting surface reactions to achieve high-quality nanolayers, provides an unique opportunity to study the limits of electrical and thermal conduction in metal interconnects. This work measures and interprets the electrical and thermal conductivities of free-standing platinum films of thickness 7.3, 9.8, and 12.1 nm in the temperature range from 50 to 320 K. Conductivity data for the 7.3 nm bridge are reduced by 77.8% (electrical) and 66.3% (thermal) compared to bulk values due to electron scattering at material and grain boundaries. The measurement results indicate that the contribution of phonon conduction is significant in the total thermal conductivity of the ALD films. © 2012 American Chemical Society

Tuning oxidation level, electrical conductance and band gap structure on graphene sheets by cyclic atomic layer reduction technique

DOE PAGES

Gu, Si-Yong; Hsieh, Chien-Te; Lin, Tzu-Wei; ...

2018-05-12

The present work develops an atomic layer reduction (ALR) method to accurately tune oxidation level, electrical conductance, band-gap structure, and photoluminescence (PL) response of graphene oxide (GO) sheets. The ALR route is carried out at 200 °C within ALR cycle number of 10–100. The ALR treatment is capable of striping surface functionalities (e.g., hydroxyl, carbonyl, and carboxylic groups), producing thermally-reduced GO sheets. The ALR cycle number serves as a controlling factor in adjusting the crystalline, surface chemistry, electrical, optical properties of GO sheets. With increasing the ALR cycle number, ALR-GO sheets display a high crystallinity, a low oxidation level, anmore » improved electrical conductivity, a narrow band gap, and a tunable PL response. Finally, on the basis of the results, the ALR technique offers a great potential for accurately tune electrical and optical properties of carbon materials through the cyclic removal of oxygen functionalities, without any complicated thermal and chemical desorption processes.« less

Resonant tunnelling and negative differential conductance in graphene transistors

PubMed Central

Britnell, L.; Gorbachev, R. V.; Geim, A. K.; Ponomarenko, L. A.; Mishchenko, A.; Greenaway, M. T.; Fromhold, T. M.; Novoselov, K. S.; Eaves, L.

2013-01-01

The chemical stability of graphene and other free-standing two-dimensional crystals means that they can be stacked in different combinations to produce a new class of functional materials, designed for specific device applications. Here we report resonant tunnelling of Dirac fermions through a boron nitride barrier, a few atomic layers thick, sandwiched between two graphene electrodes. The resonance occurs when the electronic spectra of the two electrodes are aligned. The resulting negative differential conductance in the device characteristics persists up to room temperature and is gate voltage-tuneable due to graphene’s unique Dirac-like spectrum. Although conventional resonant tunnelling devices comprising a quantum well sandwiched between two tunnel barriers are tens of nanometres thick, the tunnelling carriers in our devices cross only a few atomic layers, offering the prospect of ultra-fast transit times. This feature, combined with the multi-valued form of the device characteristics, has potential for applications in high-frequency and logic devices. PMID:23653206

Atomic Layer Deposition of Pd Nanoparticles on TiO₂ Nanotubes for Ethanol Electrooxidation: Synthesis and Electrochemical Properties.

PubMed

Assaud, Loïc; Brazeau, Nicolas; Barr, Maïssa K S; Hanbücken, Margrit; Ntais, Spyridon; Baranova, Elena A; Santinacci, Lionel

2015-11-11

Palladium nanoparticles are grown on TiO2 nanotubes by atomic layer deposition (ALD), and the resulting three-dimensional nanostructured catalysts are studied for ethanol electrooxidation in alkaline media. The morphology, the crystal structure, and the chemical composition of the Pd particles are fully characterized using scanning and transmission electron microscopies, X-ray diffraction, and X-ray photoelectron spectroscopy. The characterization revealed that the deposition proceeds onto the entire surface of the TiO2 nanotubes leading to the formation of well-defined and highly dispersed Pd nanoparticles. The electrooxidation of ethanol on Pd clusters deposited on TiO2 nanotubes shows not only a direct correlation between the catalytic activity and the particle size but also a steep increase of the response due to the enhancement of the metal-support interaction when the crystal structure of the TiO2 nanotubes is modified by annealing at 450 °C in air.

All-gas-phase synthesis of UiO-66 through modulated atomic layer deposition

NASA Astrophysics Data System (ADS)

Lausund, Kristian Blindheim; Nilsen, Ola

2016-11-01

Thin films of stable metal-organic frameworks (MOFs) such as UiO-66 have enormous application potential, for instance in microelectronics. However, all-gas-phase deposition techniques are currently not available for such MOFs. We here report on thin-film deposition of the thermally and chemically stable UiO-66 in an all-gas-phase process by the aid of atomic layer deposition (ALD). Sequential reactions of ZrCl4 and 1,4-benzenedicarboxylic acid produce amorphous organic-inorganic hybrid films that are subsequently crystallized to the UiO-66 structure by treatment in acetic acid vapour. We also introduce a new approach to control the stoichiometry between metal clusters and organic linkers by modulation of the ALD growth with additional acetic acid pulses. An all-gas-phase synthesis technique for UiO-66 could enable implementations in microelectronics that are not compatible with solvothermal synthesis. Since this technique is ALD-based, it could also give enhanced thickness control and the possibility to coat irregular substrates with high aspect ratios.

Structure and optical properties of TiO2 thin films deposited by ALD method

NASA Astrophysics Data System (ADS)

Szindler, Marek; Szindler, Magdalena M.; Boryło, Paulina; Jung, Tymoteusz

2017-12-01

This paper presents the results of study on titanium dioxide thin films prepared by atomic layer deposition method on a silicon substrate. The changes of surface morphology have been observed in topographic images performed with the atomic force microscope (AFM) and scanning electron microscope (SEM). Obtained roughness parameters have been calculated with XEI Park Systems software. Qualitative studies of chemical composition were also performed using the energy dispersive spectrometer (EDS). The structure of titanium dioxide was investigated by X-ray crystallography. A variety of crystalline TiO2 was also confirmed by using the Raman spectrometer. The optical reflection spectra have been measured with UV-Vis spectrophotometry.

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

Metzler, Dominik; Li, Chen; Engelmann, Sebastian

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO 2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C 4F 8 and CHF 3), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32,more » 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO 2 and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF 3 has a lower FC deposition yield for both SiO 2 and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F 8. The thickness of deposited FC layers using CHF 3 is found to be greater for Si than for SiO 2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.« less

Low Ozone in the Marine Boundary Layer of the Tropical Pacific Ocean

NASA Technical Reports Server (NTRS)

Singh, Hanwant B.; Gregory, G. L.; Andesrson, B.; Browell, E.; Sachse, G. W.; Davis, D. D.; Crawford, J.; Bradshaw, J. D.; Talbot, R.; Blake, D. R.;

Effects of nitrogen incorporation in HfO(2) grown on InP by atomic layer deposition: an evolution in structural, chemical, and electrical characteristics.

PubMed

Kang, Yu-Seon; Kim, Dae-Kyoung; Kang, Hang-Kyu; Jeong, Kwang-Sik; Cho, Mann-Ho; Ko, Dae-Hong; Kim, Hyoungsub; Seo, Jung-Hye; Kim, Dong-Chan

2014-03-26

We investigated the effects of postnitridation on the structural characteristics and interfacial reactions of HfO2 thin films grown on InP by atomic layer deposition (ALD) as a function of film thickness. By postdeposition annealing under NH3 vapor (PDN) at 600 °C, an InN layer formed at the HfO2/InP interface, and ionized NHx was incorporated in the HfO2 film. We demonstrate that structural changes resulting from nitridation of HfO2/InP depend on the film thickness (i.e., a single-crystal interfacial layer of h-InN formed at thin (2 nm) HfO2/InP interfaces, whereas an amorphous InN layer formed at thick (>6 nm) HfO2/InP interfaces). Consequently, the tetragonal structure of HfO2 transformed into a mixture structure of tetragonal and monoclinic because the interfacial InN layer relieved interfacial strain between HfO2 and InP. During postdeposition annealing (PDA) in HfO2/InP at 600 °C, large numbers of oxidation states were generated as a result of interfacial reactions between interdiffused oxygen impurities and out-diffused InP substrate elements. However, in the case of the PDN of HfO2/InP structures at 600 °C, nitrogen incorporation in the HfO2 film effectively blocked the out-diffusion of atomic In and P, thus suppressing the formation of oxidation states. Accordingly, the number of interfacial defect states (Dit) within the band gap of InP was significantly reduced, which was also supported by DFT calculations. Interfacial InN in HfO2/InP increased the electron-barrier height to ∼0.6 eV, which led to low-leakage-current density in the gate voltage region over 2 V.

Atomic and electronic structures of Si(1 1 1)-(√3 x √3)R30°-Au and (6 × 6)-Au surfaces.

PubMed

Patterson, C H

2015-12-02

Si(1 1 1)-Au surfaces with around one monolayer of Au exhibit many ordered structures and structures containing disordered domain walls. Hybrid density functional theory (DFT) calculations presented here reveal the origin of these complex structures and tendency to form domain walls. The conjugate honeycomb chain trimer (CHCT) structure of the [Formula: see text]-Au phase contains Si atoms with non-bonding surface states which can bind Au atoms in pairs in interstices of the CHCT structure and make this surface metallic. Si adatoms adsorbed on the [Formula: see text]-Au surface induce a gapped surface through interaction with the non-bonding states. Adsorption of extra Au atoms in interstitial sites of the [Formula: see text]-Au surface is stabilized by interaction with the non-bonding orbitals and leads to higher coverage ordered structures including the [Formula: see text]-Au phase. Extra Au atoms bound in interstitial sites of the [Formula: see text]-Au surface result in top layer Si atoms with an SiAu4 butterfly wing configuration. The structure of a [Formula: see text]-Au phase, whose in-plane top atomic layer positions were previously determined by an electron holography technique (Grozea et al 1998 Surf. Sci. 418 32), is calculated using total energy minimization. The Patterson function for this structure is calculated and is in good agreement with data from an in-plane x-ray diffraction study (Dornisch et al 1991 Phys. Rev. B 44 11221). Filled and empty state scanning tunneling microscopy (STM) images are calculated for domain walls and the [Formula: see text]-Au structure. The [Formula: see text]-Au phase is 2D chiral and this is evident in computed and actual STM images. [Formula: see text]-Au and domain wall structures contain the SiAu4 motif with a butterfly wing shape. Chemical bonding within the Si-Au top layers of the [Formula: see text]-Au and [Formula: see text]-Au surfaces is analyzed and an explanation for the SiAu4 motif structure is given.

Surface modification of paper on a continuous atmospheric-pressure-plasma system

NASA Astrophysics Data System (ADS)

Cruz-Barba, Luis Emilio

Plasma technologies for the continuous modification of materials in atmospheric-pressure-plasma conditions were used to evaluate the surface modification of paper under different plasma conditions. The generation of hydrophobic layers was used to characterize the efficiency of the originally designed system for future application in the paper industry. Generation of hydrophobic layers was carried out by deposition of thin layers from fluorine containing gases, as well as cross-linking of pre-deposited thin layers of hydrophobic materials, such as fluoropolymers and silicones, in a continuous system plasma reactor (CSPR). Physical and chemical characterization of these layers was carried out by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), contact angle goniometry, and water absorption evaluations. Pure gaseous CF4 and a CF4/CH4 mixture were used to deposit fluorinated layers, rendering paper surfaces with low to moderate relative surface atomic contents of fluorine (2.5 to 16.3%). Morphological characterization revealed that the deposition consists of small clusters of fluorinated species scattered on the surface. Contact angle evaluations (50°--70°) indicated a reduction in the water affinity of the paper. Thin layers of fluoropolymer pre-deposited on paper surfaces were cross-linked in the presence of CF4, CF4/CH4, and NH 3 plasmas. All of the gases proved to be effective for the cross-linking under different conditions. These cross-linked layers were determined to maintain the original polymer structure, consisting mainly of CF2-CF 2 and small quantities of CFx. Surface characterization by AFM indicated lower roughness values compared to the untreated additive-free paper (45.1 vs 67.1 nm). Paper samples treated by this approach showed a highly hydrophobic character with up to 160° contact angles, and water absorption was reduced by as much as 61.6%. Silicone layers were cross-linked in the presence of argon and oxygen plasmas. Characterization of the silicone-coated paper indicated, as in the case of fluoropolymers, the retention of the original chemical structure. Surface roughness values (AFM) were in the range of 11.8 to 18.2 nm, evidence of a very smooth surface. High hydrophobicity levels were reached, as shown by contact angles of up to 126°, and water absorption showed a maximum reduction of 76.8%.

Theoretical study for heterojunction surface of NEA GaN photocathode dispensed with Cs activation

NASA Astrophysics Data System (ADS)

Xia, Sihao; Liu, Lei; Wang, Honggang; Wang, Meishan; Kong, Yike

2016-09-01

For the disadvantages of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, new-type NEA GaN photocathodes with heterojunction surface dispensed with Cs activation are investigated based on first-principle study with density functional theory. Through the growth of an ultrathin n-type GaN cap layer on p-type GaN emission layer, a p-n heterojunction is formed on the surface. According to the calculation results, it is found that Si atoms tend to replace Ga atoms to result in an n-type doped cap layer which contributes to the decreasing of work function. After the growth of n-type GaN cap layer, the atom structure near the p-type emission layer is changed while that away from the surface has no obvious variations. By analyzing the E-Mulliken charge distribution of emission surface with and without cap layer, it is found that the positive charge of Ga and Mg atoms in the emission layer decrease caused by the cap layer, while the negative charge of N atom increases. The conduction band moves downwards after the growth of cap layer. Si atom produces donor levels around the valence band maximum. The absorption coefficient of GaN emission layer decreases and the reflectivity increases caused by n-type GaN cap layer.

Compositional modulated atomic layer stacking and uniaxial magnetocrystalline anisotropy of CoPt alloy sputtered films with close-packed plane orientation

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

Saito, Shin, E-mail: ssaito@ecei.tohoku.ac.jp; Nozawa, Naoki; Hinata, Shintaro

An atomic layer stacking structure in hexagonal close packed (hcp) Co{sub 100−x}Pt{sub x} alloy films with c-plane sheet texture was directly observed by a high-angle annular dark-field imaging scanning transmission electron microscopy. The analysis of sequential and/or compositional atomic layer stacking structure and uniaxial magnetocrystalline anisotropy (K{sub u} = K{sub u1} + K{sub u2}) revealed that (1) integrated intensity of the superlattice diffraction takes the maximum at x = 20 at. % and shows broadening feature against x for the film fabricated under the substrate temperature (T{sub sub}) of 400 °C. (2) Compositional separation structure in atomic layers is formed for the films fabricated under T{sub sub} = 400 °C.more » A sequential alternative stacking of atomic layers with different compositions is hardly formed in the film with x = 50 at. %, whereas easily formed in the film with x = 20 at. %. This peculiar atomic layer stacking structure consists of in-plane-disordered Pt-rich and Pt-poor layers, which is completely different from the so-called atomic site ordered structure. (3) A face centered cubic atomic layer stacking as faults appeared in the host hcp atomic layer stacking exists in accompanies with irregularities for the periodicity of the compositional modulation atomic layers. (4) K{sub u1} takes the maximum of 1.4 × 10{sup 7 }erg/cm{sup 3} at around x = 20 at. %, whereas K{sub u2} takes the maximum of 0.7 × 10{sup 7 }erg/cm{sup 3} at around x = 40 at. %, which results in the maximum of 1.8 × 10{sup 7 }erg/cm{sup 3} of K{sub u} at x = 30 at. % and a shoulder in compositional dependence of K{sub u} in the range of x = 30–60 at. %. Not only compositional separation of atomic layers but also sequential alternative stacking of different compositional layers is quite important to improve essential uniaxial magnetocrystalline anisotropy.« less

Segregation and Migration of the Oxygen Vacancies in the 3 (111) Tilt Grain Boundaries of Ceria

DOE PAGES

Yuan, Fenglin; Liu, Bin; Zhang, Yanwen; ...

2016-03-01

In nanocrystalline materials, defect-grain boundary (GB) interaction plays a key role in determining the structure stability, as well as size-dependent ionic, electronic, magnetic and chemical properties. In this study, we systematically investigated using density functional theory segregation and migration of oxygen vacancies at the Σ3 [110] / (111) grain boundary of ceria. Three oxygen layers near the GB are predicted to be segregation sites for oxygen vacancies. Moreover, the presence of oxygen vacancies stabilizes this tilt GB at a low Fermi level and/or oxygen poor conditions. An atomic strain model was proposed to rationalize layer dependency of the relaxation energymore » for +2 charged oxygen vacancy. The structural origin of large relaxation energies at layers 1 and 2 was determined to be free-volume space that induces ion relaxation towards the GB. Our results not only pave the way for improving the oxygen transport near GBs of ceria, but also provide important insights into engineering the GB structure for better ionic, magnetic and chemical properties of nanocrystalline ceria.« less

Synthesis of layer-tunable graphene: A combined kinetic implantation and thermal ejection approach

DOE PAGES

Wang, Gang; Zhang, Miao; Liu, Su; ...

2015-05-04

Layer-tunable graphene has attracted broad interest for its potentials in nanoelectronics applications. However, synthesis of layer-tunable graphene by using traditional chemical vapor deposition (CVD) method still remains a great challenge due to the complex experimental parameters and the carbon precipitation process. Herein, by performing ion implantation into a Ni/Cu bilayer substrate, the number of graphene layers, especially single or double layer, can be controlled precisely by adjusting the carbon ion implant fluence. The growth mechanism of the layer-tunable graphene is revealed by monitoring the growth process is observed that the entire implanted carbon atoms can be expelled towards the substratemore » surface and thus graphene with designed layer number can be obtained. Such a growth mechanism is further confirmed by theoretical calculations. The proposed approach for the synthesis of layer-tunable graphene offers more flexibility in the experimental conditions. Being a core technology in microelectronics processing, ion implantation can be readily implemented in production lines and is expected to expedite the application of graphene to nanoelectronics.« less

Method for producing high energy electroluminescent devices

DOEpatents

Meyerson, Bernard S.; Scott, Bruce A.; Wolford, Jr., Donald J.

1992-09-29

A method is described for fabricating electroluminescent devices exhibiting visible electroluminescence at room temperature, where the devices include at least one doped layer of amorphous hydrogenated silicon (a-Si:H). The a-Si:H layer is deposited on a substrate by homogeneous chemical vapor deposition (H-CVD) in which the substrate is held at a temperature lower than about 200.degree. C. and the a-Si:H layer is doped in-situ during deposition, the amount of hydrogen incorporated in the deposited layer being 12-50 atomic percent. The bandgap of the a-Si:H layer is between 1.6 and 2.6 eV, and in preferrable embodiments is between 2.0 and 2.6 eV. The conductivity of the a-Si:H layer is chosen in accordance with device requirements, and can be 10.sup.16 -10.sup.19 carriers/cm.sup.2. The bandgap of the a-Si:H layer depends at least in part on the temperature of the substrate on which the layer is deposited, and can be "tuned" by changing the substrate temperature.

Metal ferrite spinel energy storage devices and methods for making and using same

DOEpatents

Weimer, Alan W [Niwot, CO; Perkins, Christopher [Boulder, CO; Scheffe, Jonathan [Westminster, CO; George, Steven M [Boulder, CO; Lichty, Paul [Westminster, CO

2012-05-29

1-100 nm metal ferrite spinel coatings are provided on substrates, preferably by using an atomic layer deposition process. The coatings are able to store energy such as solar energy, and to release that stored energy, via a redox reaction. The coating is first thermally or chemically reduced. The reduced coating is then oxidized in a second step to release energy and/or hydrogen, carbon monoxide or other reduced species.

Metal ferrite spinel energy storage devices and methods for making and using same

DOEpatents

Weimer, Alan W.; Perkins, Christopher; Scheffe, Jonathan; George, Steven M.; Lichty, Paul

2013-03-19

1-100 nm metal ferrite spinel coatings are provided on substrates, preferably by using an atomic layer deposition process. The coatings are able to store energy such as solar energy, and to release that stored energy, via a redox reaction. The coating is first thermally or chemically reduced. The reduced coating is then oxidized in a second step to release energy and/or hydrogen, carbon monoxide or other reduced species.

Formation of atomically ordered and chemically selective Si-O-Ti monolayer on Si0.5Ge0.5(110) for a MIS structure via H2O2(g) functionalization.

PubMed

Park, Sang Wook; Choi, Jong Youn; Siddiqui, Shariq; Sahu, Bhagawan; Galatage, Rohit; Yoshida, Naomi; Kachian, Jessica; Kummel, Andrew C

2017-02-07

Si 0.5 Ge 0.5 (110) surfaces were passivated and functionalized using atomic H, hydrogen peroxide (H 2 O 2 ), and either tetrakis(dimethylamino)titanium (TDMAT) or titanium tetrachloride (TiCl 4 ) and studied in situ with multiple spectroscopic techniques. To passivate the dangling bonds, atomic H and H 2 O 2 (g) were utilized and scanning tunneling spectroscopy (STS) demonstrated unpinning of the surface Fermi level. The H 2 O 2 (g) could also be used to functionalize the surface for metal atomic layer deposition. After subsequent TDMAT or TiCl 4 dosing followed by a post-deposition annealing, scanning tunneling microscopy demonstrated that a thermally stable and well-ordered monolayer of TiO x was deposited on Si 0.5 Ge 0.5 (110), and X-ray photoelectron spectroscopy verified that the interfaces only contained Si-O-Ti bonds and a complete absence of GeO x . STS measurements confirmed a TiO x monolayer without mid-gap and conduction band edge states, which should be an ideal ultrathin insulating layer in a metal-insulator-semiconductor structure. Regardless of the Ti precursors, the final Ti density and electronic structure were identical since the Ti bonding is limited by the high coordination of Ti to O.

Hybrid quantum and molecular mechanics embedded cluster models for chemistry on silicon and silicon carbide surfaces

NASA Astrophysics Data System (ADS)

Shoemaker, James Richard

Fabrication of silicon carbide (SiC) semiconductor devices are of interest for aerospace applications because of their high-temperature tolerance. Growth of an insulating SiO2 layer on SiC by oxidation is a poorly understood process, and sometimes produces interface defects that degrade device performance. Accurate theoretical models of surface chemistry, using quantum mechanics (QM), do not exist because of the huge computational cost of solving Schrodinger's equation for a molecular cluster large enough to represent a surface. Molecular mechanics (MM), which describes a molecule as a collection of atoms interacting through classical potentials, is a fast computational method, good at predicting molecular structure, but cannot accurately model chemical reactions. A new hybrid QM/MM computational method for surface chemistry was developed and applied to silicon and SiC surfaces. The addition of MM steric constraints was shown to have a large effect on the energetics of O atom adsorption on SiC. Adsorption of O atoms on Si-terminated SiC(111) favors above surface sites, in contrast to Si(111), but favors subsurface adsorption sites on C- terminated SiC(111). This difference, and the energetics of C atom etching via CO2 desorption, can explain the observed poor performance of SiC devices in which insulating layers were grown on C-terminated surfaces.

Atomic oxygen in the lower thermosphere

NASA Technical Reports Server (NTRS)

Lin, Florence J.; Chance, Kelly V.; Traub, Wesley A.

1987-01-01

The 63-micron line due to thermospheric atomic oxygen O(P-3), using a far-infrared spectrometer on a balloon platform at 37 km altitude over Palestine, TX, on June 20, 1983. From measurements of the equivalent width of this line at two elevation angles, a weak angular dependence is found: the equivalent width increases by a factor of 1.5 + or - 0.3 as the angle decreases from +30 deg to +1 deg. Since the optical depth of the O(P-3) line is large, the measured line intensity cannot be directly converted to a column abundance. Instead, the measurements are interpreted in terms of radiative transfer through a 16-layer atmosphere extending to 200 km. A model atmosphere for summer at 30 deg N, with an exospheric temperature of 1300 K, including an assumed daytime atomic oxygen abundance profile constructed from recent chemical and dynamical models and a water vapor abundance profile constructed from recent experimental and model results is used. For this assumed O(P-3) vertical profile shape a multiplicative scaling factor of 0.8, with an altitude-dependent uncertainty is determined. In the best-determined layer the uncertainty in the multiplier is + or - 0.2 at 119 km. The model-dependent peak atomic oxygen density is 3.6 (+ or - 1.9) x 10 to the 11th/cu cm at an altitude of about 101 km.

Engineering Particle Surface Chemistry and Electrochemistry with Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Jackson, David Hyman Kentaro

Atomic layer deposition (ALD) is a vapor phase thin film coating technique that relies on sequential pulsing of precursors that undergo self-limited surface reactions. The self- limiting reactions and gas phase diffusion of the precursors together enable the conformal coating of microstructured particles with a high degree of thickness and compositional control. ALD may be used to deposit thin films that introduce new functionalities to a particle surface. Examples of new functionalities include: chemical reactivity, a mechanically strong protective coating, and an electrically resistive layer. The coatings properties are often dependent on the bulk properties and microstructure of the particle substrate, though they usually do not affect its bulk properties or microstructure. Particle ALD finds utility in the ability to synthesize well controlled, model systems, though it is expensive due to the need for costly metal precursors that are dangerous and require special handling. Enhanced properties due to ALD coating of particles in various applications are frequently described empirically, while the details of their enhancement mechanisms often remain the focus of ongoing research in the field. This study covers the various types of particle ALD and attempts to describe them from the unifying perspective of surface science.

Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

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

Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei

In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements aremore » sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.« less

Mg/Ti multilayers: Structural and hydrogen absorption properties

NASA Astrophysics Data System (ADS)

Baldi, A.; Pálsson, G. K.; Gonzalez-Silveira, M.; Schreuders, H.; Slaman, M.; Rector, J. H.; Krishnan, G.; Kooi, B. J.; Walker, G. S.; Fay, M. W.; Hjörvarsson, B.; Wijngaarden, R. J.; Dam, B.; Griessen, R.

2010-06-01

Mg-Ti alloys have uncommon optical and hydrogen absorbing properties, originating from a “spinodal-like” microstructure with a small degree of chemical short-range order in the atomic distribution. In the present study we artificially engineer short-range order by depositing Pd-capped Mg/Ti multilayers with different periodicities. Notwithstanding the large lattice mismatch between Mg and Ti, the as-deposited metallic multilayers show good structural coherence. On exposure to H2 gas a two-step hydrogenation process occurs with the Ti layers forming the hydride before Mg. From in situ measurements of the bilayer thickness Λ at different hydrogen pressures, we observe large out-of-plane expansions of Mg and Ti layers on hydrogenation, indicating strong plastic deformations in the films and a consequent shortening of the coherence length. On unloading at room temperature in air, hydrogen atoms remain trapped in the Ti layers due to kinetic constraints. Such loading/unloading sequence can be explained in terms of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by diffusion calculations on a model multilayered systems. Absorption isotherms measured by hydrogenography can be interpreted as a result of the elastic clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces.

Electrodeposited Ni-Based Magnetic Mesoporous Films as Smart Surfaces for Atomic Layer Deposition: An "All-Chemical" Deposition Approach toward 3D Nanoengineered Composite Layers.

PubMed

Zhang, Jin; Quintana, Alberto; Menéndez, Enric; Coll, Mariona; Pellicer, Eva; Sort, Jordi

2018-05-02

Mesoporous Ni and Cu-Ni (Cu 20 Ni 80 and Cu 45 Ni 55 in at. %) films, showing a three-dimensional (3D) porous structure and tunable magnetic properties, are prepared by electrodeposition from aqueous surfactant solutions using micelles of P-123 triblock copolymer as structure-directing entities. Pores between 5 and 30 nm and dissimilar space arrangements (continuous interconnected networks, circular pores, corrugated mesophases) are obtained depending on the synthetic conditions. X-ray diffraction studies reveal that the Cu-Ni films have crystallized in the face-centered cubic structure, are textured, and exhibit certain degree of phase separation, particularly those with a higher Cu content. Atomic layer deposition (ALD) is used to conformally coat the mesopores of Cu 20 Ni 80 film with amorphous Al 2 O 3 , rendering multiphase "nano-in-meso" metal-ceramic composites without compromising the ferromagnetic response of the metallic scaffold. From a technological viewpoint, these 3D nanoengineered composite films could be appealing for applications like magnetically actuated micro/nanoelectromechanical systems (MEMS/NEMS), voltage-driven magneto-electric devices, capacitors, or as protective coatings with superior strength and tribological performance.

Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

DOE PAGES

Black, Jennifer M.; Zhu, Mengyang; Zhang, Pengfei; ...

2016-09-02

In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements aremore » sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.« less

Difference in charge transport properties of Ni-Nb thin films with native and artificial oxide

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

Trifonov, A. S., E-mail: trifonov.artem@phys.msu.ru; Physics Faculty, Lomonosov Moscow State University, Moscow 119991; Lubenchenko, A. V.

2015-03-28

Here, we report on the properties of native and artificial oxide amorphous thin film on a surface of an amorphous Ni-Nb sample. Careful measurements of local current-voltage characteristics of the system Ni-Nb / NiNb oxide/Pt, were carried out in contact mode of an atomic force microscope. Native oxide showed n-type conductivity, while in the artificial one exhibited p-type one. The shape of current-voltage characteristic curves is unique in both cases and no analogical behavior is found in the literature. X-ray photoelectron spectroscopy (XPS) measurements were used to detect chemical composition of the oxide films and the oxidation state of themore » alloy components. Detailed analysis of the XPS data revealed that the structure of natural Ni-Nb oxide film consists of Ni-NbO{sub x} top layer and nickel enriched bottom layer which provides n-type conductivity. In contrast, in the artificial oxide film Nb is oxidized completely to Nb{sub 2}O{sub 5}, Ni atoms migrate into bulk Ni-Nb matrix. Electron depletion layer is formed at the Ni-Nb/Nb{sub 2}O{sub 5} interface providing p-type conductivity.« less

Atomic layer deposition of dielectrics on graphene using reversibly physisorbed ozone.

PubMed

Jandhyala, Srikar; Mordi, Greg; Lee, Bongki; Lee, Geunsik; Floresca, Carlo; Cha, Pil-Ryung; Ahn, Jinho; Wallace, Robert M; Chabal, Yves J; Kim, Moon J; Colombo, Luigi; Cho, Kyeongjae; Kim, Jiyoung

2012-03-27

Integration of graphene field-effect transistors (GFETs) requires the ability to grow or deposit high-quality, ultrathin dielectric insulators on graphene to modulate the channel potential. Here, we study a novel and facile approach based on atomic layer deposition through ozone functionalization to deposit high-κ dielectrics (such as Al(2)O(3)) without breaking vacuum. The underlying mechanisms of functionalization have been studied theoretically using ab initio calculations and experimentally using in situ monitoring of transport properties. It is found that ozone molecules are physisorbed on the surface of graphene, which act as nucleation sites for dielectric deposition. The physisorbed ozone molecules eventually react with the metal precursor, trimethylaluminum to form Al(2)O(3). Additionally, we successfully demonstrate the performance of dual-gated GFETs with Al(2)O(3) of sub-5 nm physical thickness as a gate dielectric. Back-gated GFETs with mobilities of ~19,000 cm(2)/(V·s) are also achieved after Al(2)O(3) deposition. These results indicate that ozone functionalization is a promising pathway to achieve scaled gate dielectrics on graphene without leaving a residual nucleation layer. © 2012 American Chemical Society

Large-Area Atomic Layers of the Charge-Density-Wave Conductor TiSe2.

PubMed

Wang, Hong; Chen, Yu; Duchamp, Martial; Zeng, Qingsheng; Wang, Xuewen; Tsang, Siu Hon; Li, Hongling; Jing, Lin; Yu, Ting; Teo, Edwin Hang Tong; Liu, Zheng

2018-02-01

Layered transition metal (Ti, Ta, Nb, etc.) dichalcogenides are important prototypes for the study of the collective charge density wave (CDW). Reducing the system dimensionality is expected to lead to novel properties, as exemplified by the discovery of enhanced CDW order in ultrathin TiSe 2 . However, the syntheses of monolayer and large-area 2D CDW conductors can currently only be achieved by molecular beam epitaxy under ultrahigh vacuum. This study reports the growth of monolayer crystals and up to 5 × 10 5 µm 2 large films of the typical 2D CDW conductor-TiSe 2 -by ambient-pressure chemical vapor deposition. Atomic resolution scanning transmission electron microscopy indicates the as-grown samples are highly crystalline 1T-phase TiSe 2 . Variable-temperature Raman spectroscopy shows a CDW phase transition temperature of 212.5 K in few layer TiSe 2 , indicative of high crystal quality. This work not only allows the exploration of many-body state of TiSe 2 in 2D limit but also offers the possibility of utilizing large-area TiSe 2 in ultrathin electronic devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of carbon nanofibers by CVD as a catalyst support material using atomically ordered Ni3C nanoparticles

NASA Astrophysics Data System (ADS)

Li, Meifeng; Li, Na; Shao, Wei; Zhou, Chungen

2016-12-01

Atomically ordered nickel carbide (Ni3C) nanoparticles in polygonal shapes were prepared through the reduction of nickelocene. A novel type of carbon nanofiber (CNF) with twisted conformation was synthesized successfully by catalytic chemical vapor deposition (CCVD) using the obtained Ni3C nanoparticles at a relatively low temperature of 350 °C, which is below the lower limit temperature of 400 °C for the growth of CNFs using metal catalysts. The growth mechanism of the twisted CNFs from Ni3C was freshly derived based on the detailed characterizations. Compared with the growth of CNFs from Ni, graphene layers nucleate at monoatomic step edges and grow in a layer-by-layer manner, while the rotation of the polygonal Ni3C nanoparticles fabricates the twisted conformation during the CNF growth. The electrochemical activity and performance of the twisted CNFs loaded with Pt as electrode catalysts for a polymer electrolyte membrane fuel cell (PEMFC) were measured to be better than those of straight CNFs grown from Ni nanoparticles at 500 °C, since the specific surface conformation helps to make the loaded Pt more homogeneous.

Synthesis of carbon nanofibers by CVD as a catalyst support material using atomically ordered Ni3C nanoparticles.

PubMed

Li, Meifeng; Li, Na; Shao, Wei; Zhou, Chungen

2016-11-22

Atomically ordered nickel carbide (Ni 3 C) nanoparticles in polygonal shapes were prepared through the reduction of nickelocene. A novel type of carbon nanofiber (CNF) with twisted conformation was synthesized successfully by catalytic chemical vapor deposition (CCVD) using the obtained Ni 3 C nanoparticles at a relatively low temperature of 350 °C, which is below the lower limit temperature of 400 °C for the growth of CNFs using metal catalysts. The growth mechanism of the twisted CNFs from Ni 3 C was freshly derived based on the detailed characterizations. Compared with the growth of CNFs from Ni, graphene layers nucleate at monoatomic step edges and grow in a layer-by-layer manner, while the rotation of the polygonal Ni 3 C nanoparticles fabricates the twisted conformation during the CNF growth. The electrochemical activity and performance of the twisted CNFs loaded with Pt as electrode catalysts for a polymer electrolyte membrane fuel cell (PEMFC) were measured to be better than those of straight CNFs grown from Ni nanoparticles at 500 °C, since the specific surface conformation helps to make the loaded Pt more homogeneous.

Water Desalination Using Nanoporous Single-Layer Graphene with Tunable Pore Size

DOE PAGES

Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; ...

2015-03-23

Graphene has great potential to serve as a separation membrane due to its unique properties such as chemical and mechanical stability, flexibility and most importantly its one-atom thickness. In this study, we demonstrate first experimental evidence of the use of single-layer porous graphene as a desalination membrane. Nanometer-sized pores are introduced into single layer graphene using a convenient oxygen plasma etching process that permits tuning of the pore size. The resulting porous graphene membrane exhibited high rejection of salt ions and rapid water transport, thus functioning as an efficient water desalination membrane. Salt rejection selectivity of nearly 100% and exceptionallymore » high water fluxes exceeding 105 g m-2 s-1 at 40 C were measured using saturated water vapor as a driving force.« less

Interface Trap Density Reduction for Al2O3/GaN (0001) Interfaces by Oxidizing Surface Preparation prior to Atomic Layer Deposition.

PubMed

Zhernokletov, Dmitry M; Negara, Muhammad A; Long, Rathnait D; Aloni, Shaul; Nordlund, Dennis; McIntyre, Paul C

2015-06-17

We correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface in metal-oxide-semiconductor (MOS) structures using synchrotron photoelectron emission spectroscopy (PES), cathodoluminescence and high-temperature capacitance-voltage measurements. The influence of the wet chemical pretreatments involving (1) HCl+HF etching or (2) NH4OH(aq) exposure prior to atomic layer deposition (ALD) of Al2O3 were investigated on n-type GaN (0001) substrates. Prior to ALD, PES analysis of the NH4OH(aq) treated surface shows a greater Ga2O3 component compared to either HCl+HF treated or as-received surfaces. The lowest surface concentration of oxygen species is detected on the acid etched surface, whereas the NH4OH treated sample reveals the lowest carbon surface concentration. Both surface pretreatments improve electrical characteristics of MOS capacitors compared to untreated samples by reducing the Al2O3/GaN interface state density. The lowest interfacial trap density at energies in the upper band gap is detected for samples pretreated with NH4OH. These results are consistent with cathodoluminescence data indicating that the NH4OH treated samples show the strongest band edge emission compared to as-received and acid etched samples. PES results indicate that the combination of reduced carbon contamination while maintaining a Ga2O3 interfacial layer by NH4OH(aq) exposure prior to ALD results in fewer interface traps after Al2O3 deposition on the GaN substrate.

Synthesis of graphene oxide and reduced graphene oxide by needle platy natural vein graphite

NASA Astrophysics Data System (ADS)

Rathnayake, R. M. N. M.; Wijayasinghe, H. W. M. A. C.; Pitawala, H. M. T. G. A.; Yoshimura, Masamichi; Huang, Hsin-Hui

2017-01-01

Among natural graphite varieties, needle platy vein graphite (NPG) has very high purity. Therefore, it is readily used to prepare graphene oxide (GO) and reduced graphene oxide (rGO). In this study, GO and rGO were prepared using chemical oxidation and reduction process, respectively. The synthesized materials were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. XRD studies confirmed the increase of the interlayer spacing of GO and rGO in between 3.35 to 8.66 A°. AFM studies showed the layer height of rGO to be 1.05 nm after the reduction process. TEM micrographs clearly illustrated that the prepared GO has more than 25 layers, while the rGO has only less than 15 layers. Furthermore, the effect of chemical oxidation and reduction processes on surface morphology of graphite were clearly observed in FESEM micrographs. The calculated RO/C of GO and rGO using XPS analysis are 5.37% and 1.77%, respectively. The present study revealed the successful and cost effective nature of the chemical oxidation, and the reduction processes for the production of GO and rGO out of natural vein graphite.

Electronic structure of layered quaternary chalcogenide materials for band-gap engineering: The example of Cs2MIIM3IVQ8

NASA Astrophysics Data System (ADS)

Besse, Rafael; Sabino, Fernando P.; Da Silva, Juarez L. F.

2016-04-01

Quaternary chalcogenide materials offer a wide variety of chemical and physical properties, and hence, those compounds have been widely studied for several technological applications. Recently, experimental studies have found that the chalcogenide Cs2MIIM3IVQ8 family (MII = Mg , Zn , Cd , Hg , MIV = Ge , Sn and Q = S , Se , Te ), which includes 24 compounds, yields a wide range of band gaps, namely, from 1.07 to 3.4 eV, and hence, they have attracted great interest. To obtain an improved atomistic understanding of the role of the cations and anions on the physical properties, we performed a first-principles investigation of the 24 Cs2MIIM3IVQ8 compounds employing density functional theory within semilocal and hybrid exchange-correlation energy functionals and the addition of van der Waals corrections to improve the description of the weakly interacting layers. Our lattice parameters are in good agreement with the available experimental data (i.e., 11 compounds), and the equilibrium volume increases linearly by increasing the atomic number of the chalcogen, which can be explained by the increased atomic radius of the chalcogen atoms from S to Te . We found that van der Waals corrections play a crucial role in the lattice parameter in the stacking direction of the Cs2MIIM3IVQ8 layers, while the binding energy per unit area has similar magnitude as obtained for different layered materials. We obtained that the band gaps follow a linear relation as a function of the unit cell volume, which can be explained by the atomic size of the chalcogen atom and the relative position of the Q p states within the band structure. The fundamental and optical band gaps differ by less than 0.1 eV. The band gaps obtained with the hybrid functional are in good agreement with the available experimental data. Furthermore, we found from the Bader analysis, that the Coulomb interations among the cations and anions play a crucial role on the energetic properties.

A nitride-based epitaxial surface layer formed by ammonia treatment of silicene-terminated ZrB{sub 2}

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

Wiggers, F. B., E-mail: F.B.Wiggers@utwente.nl; Van Bui, H.; Schmitz, J.

We present a method for the formation of an epitaxial  surface layer involving B, N, and Si atoms on a ZrB{sub 2}(0001) thin film on Si(111). It has the potential to be an insulating growth template for 2D semiconductors. The chemical reaction of NH{sub 3} molecules with the silicene-terminated ZrB{sub 2}  surface was characterized by synchrotron-based, high-resolution core-level photoelectron spectroscopy and low-energy electron diffraction. In particular, the dissociative chemisorption of NH{sub 3} at 400 °C leads to surface  nitridation, and subsequent annealing up to 830 °C results in a solid phase reaction with the ZrB{sub 2} subsurface layers. In this way, amore » new nitride-based epitaxial  surface layer is formed with hexagonal symmetry and a single in-plane crystal orientation.« less

Effect of dopent on the structural and optical properties of ZnS thin film as a buffer layer in solar cell application

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

Vashistha, Indu B., E-mail: indu-139@yahoo.com; Sharma, S. K.; Sharma, Mahesh C.

2015-08-28

In order to find the suitable alternative of toxic CdS buffer layer, deposition of pure ZnS and doped with Al by chemical bath deposition method have been reported. Further as grown pure and doped thin films have been annealed at 150°C. The structural and surface morphological properties have been characterized by X-Ray diffraction (XRD) and Atomic Force Microscope (AFM).The XRD analysis shows that annealed thin film has been polycrystalline in nature with sphalerite cubic crystal structure and AFM images indicate increment in grain size as well as growth of crystals after annealing. Optical measurement data give band gap of 3.5more » eV which is ideal band gap for buffer layer for solar cell suggesting that the obtained ZnS buffer layer is suitable in a low-cost solar cell.« less

Simulations of carbon sputtering in fusion reactor divertor plates

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

Marian, J; Zepeda-Ruiz, L A; Gilmer, G H

2005-10-03

The interaction of edge plasma with material surfaces raises key issues for the viability of the International Thermonuclear Reactor (ITER) and future fusion reactors, including heat-flux limits, net material erosion, and impurity production. After exposure of the graphite divertor plate to the plasma in a fusion device, an amorphous C/H layer forms. This layer contains 20-30 atomic percent D/T bonded to C. Subsequent D/T impingement on this layer produces a variety of hydrocarbons that are sputtered back into the sheath region. We present molecular dynamics (MD) simulations of D/T impacts on amorphous carbon layer as a function of ion energymore » and orientation, using the AIREBO potential. In particular, energies are varied between 10 and 150 eV to transition from chemical to physical sputtering. These results are used to quantify yield, hydrocarbon composition and eventual plasma contamination.« less

Electrochemistry at Edge of Single Graphene Layer in a Nanopore

PubMed Central

Banerjee, Shouvik; Shim, Jiwook; Rivera, Jose; Jin, Xiaozhong; Estrada, David; Solovyeva, Vita; You, Xiuque; Pak, James; Pop, Eric; Aluru, Narayana; Bashir, Rashid

2013-01-01

We study the electrochemistry of single layer graphene edges using a nanopore-based structure consisting of stacked graphene and Al2O3 dielectric layers. Nanopores, with diameters ranging from 5 to 20 nm, are formed by an electron beam sculpting process on the stacked layers. This leads to unique edge structure which, along with the atomically thin nature of the embedded graphene electrode, demonstrates electrochemical current densities as high as 1.2 × 104 A/cm2. The graphene edge embedded structure offers a unique capability to study the electrochemical exchange at an individual graphene edge, isolated from the basal plane electrochemical activity. We also report ionic current modulation in the nanopore by biasing the embedded graphene terminal with respect to the electrodes in the fluid. The high electrochemical specific current density for a graphene nanopore-based device can have many applications in sensitive chemical and biological sensing, and energy storage devices. PMID:23249127

High-Quality Crystal Growth and Characteristics of AlGaN-Based Solar-Blind Distributed Bragg Reflectors with a Tri-layer Period Structure

PubMed Central

Chang, Jianjun; Chen, Dunjun; Yang, Lianhong; Liu, Yanli; Dong, Kexiu; Lu, Hai; Zhang, Rong; Zheng, Youdou

2016-01-01

To realize AlGaN-based solar-blind ultraviolet distributed Bragg reflectors (DBRs), a novel tri-layer AlGaN/AlInN/AlInGaN periodical structure that differs from the traditional periodically alternating layers of high- and low-refractive-index materials was proposed and grown on an Al0.5Ga0.5N template via metal-organic chemical vapour deposition. Because of the intentional design of the AlInGaN strain transition layer, a state-of-the-art DBR structure with atomic-level-flatness interfaces was achieved using an AlGaN template. The fabricated DBR exhibits a peak reflectivity of 86% at the centre wavelength of 274 nm and a stopband with a full-width at half-maximum of 16 nm. PMID:27381651

Titanium bone implants with superimposed micro/nano-scale porosity and antibacterial capability

NASA Astrophysics Data System (ADS)

Necula, B. S.; Apachitei, I.; Fratila-Apachitei, L. E.; van Langelaan, E. J.; Duszczyk, J.

2013-05-01

This study aimed at producing a multifunctional layer with micro/nano-interconnected porosity and antibacterial capability on a rough macro-porous plasma sprayed titanium surface using the plasma electrolytic oxidation process. The layers were electrochemically formed in electrolytes based on calcium acetate and calcium glycerophosphate salts bearing dispersed Ag nanoparticles. They were characterized with respect to surface morphology and chemical composition using a scanning electron microscope equipped with the energy dispersive spectroscopy and back scattering detectors. Scanning electron microscopy images showed the formation of a micro/nano-scale porous layer, comprised of TiO2 bearing Ca and P species and Ag nanoparticles, following accurately the surface topography of the plasma sprayed titanium coating. The Ca/P atomic ratio was found to be close to that of bone apatite. Ag nanoparticles were incorporated on both on top and inside the porous structure of the TiO2 layer.

Comparison and characterization of different tunnel layers, suitable for passivated contact formation

NASA Astrophysics Data System (ADS)

Ling, Zhi Peng; Xin, Zheng; Ke, Cangming; Jammaal Buatis, Kitz; Duttagupta, Shubham; Lee, Jae Sung; Lai, Archon; Hsu, Adam; Rostan, Johannes; Stangl, Rolf

2017-08-01

Passivated contacts for solar cells can be realized using a variety of differently formed ultra-thin tunnel oxide layers. Assessing their interface properties is important for optimization purposes. In this work, we demonstrate the ability to measure the interface defect density distribution D it(E) and the fixed interface charge density Q f for ultra-thin passivation layers operating within the tunnel regime (<2 nm). Various promising tunnel layer candidates [i.e., wet chemically formed SiO x , UV photo-oxidized SiO x , and atomic layer deposited (ALD) AlO x ] are investigated for their potential application forming electron or hole selective tunnel layer passivated contacts. In particular, ALD AlO x is identified as a promising tunnel layer candidate for hole-extracting passivated contact formation, stemming from its high (negative) fixed interface charge density in the order of -6 × 1012 cm-2. This is an order of magnitude higher compared to wet chemically or UV photo-oxidized formed silicon oxide tunnel layers, while keeping the density of interface defect states D it at a similar level (in the order of ˜2 × 1012 cm-2 eV-1). This leads to additional field effect passivation and therefore to significantly higher measured effective carrier lifetimes (˜2 orders of magnitude). A surface recombination velocity of ˜40 cm/s has been achieved for a 1.5 nm thin ALD AlO x tunnel layer prior to capping by an additional hole transport material, like p-doped poly-Si or PEDOT:PSS.

Sharp chemical interface in epitaxial Fe{sub 3}O{sub 4} thin films

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

Gálvez, S.; Rubio-Zuazo, J., E-mail: rubio@esrf.fr; Salas-Colera, E.

Chemically sharp interface was obtained on single phase single oriented Fe{sub 3}O{sub 4} (001) thin film (7 nm) grown on NiO (001) substrate using oxygen assisted molecular beam epitaxy. Refinement of the atomic structure, stoichiometry, and oxygen vacancies were determined by soft and hard x-ray photoelectron spectroscopy, low energy electron diffraction and synchrotron based X-ray reflectivity, and X-ray diffraction. Our results demonstrate an epitaxial growth of the magnetite layer, perfect iron stoichiometry, absence of oxygen vacancies, and the existence of an intermixing free interface. Consistent magnetic and electrical characterizations are also shown.

Self-ordering of a Ge island single layer induced by Si overgrowth.

PubMed

Capellini, G; De Seta, M; Evangelisti, F; Zinovyev, V A; Vastola, G; Montalenti, F; Miglio, Leo

2006-03-17

We provide a direct experimental proof and the related modeling of the role played by Si overgrowth in promoting the lateral ordering of Ge islands grown by chemical vapor deposition on Si(001). The deposition of silicon induces a shape transformation, from domes to truncated pyramids with a larger base, generating an array of closely spaced interacting islands. By modeling, we show that the resulting gradient in the chemical potential across the island should be the driving force for a selective flow of both Ge and Si atoms at the surface and, in turn, to a real motion of the dots, favoring the lateral order.

Computational study on the functionalization of BNNC with pyrrole molecule

NASA Astrophysics Data System (ADS)

Payvand, Akram; Tavangar, Zahra

2018-05-01

The functionalization of the boron nitride nanocone (BNNC) by pyrrole molecule was studied using B3LYP/6-311+G(d) level of theory. The reaction was studied in three methods in different layers of the nanocone: Diels-Alder cycloaddition, quartet cycloaddition and the reaction of the nitrogen atom of the pyrrole molecule with the boron or nitrogen atom of the BNNC. Thermodynamic quantities, Chemical hardness and potential and electrophilicity index of the functionalized BNNC were studied. The results show that the tip of nanocone has a higher tendency for participation in the reaction and the most favorable product of the reaction between BNNC and pyrrole molecule is produced from the reaction of N atom of pyrrole with the B atom of BNNC. The reaction decreases the energy gap value which leads to increasing the reactivity and conductivity of functionalized nanocone. The calculated NICS values confirm the aromaticity in the pristine nanocone as well as in the functionalized nanocone.

Double-walled silicon nanotubes: an ab initio investigation

NASA Astrophysics Data System (ADS)

Lima, Matheus P.

2018-02-01

The synthesis of silicon nanotubes realized in the last decade demonstrates multi-walled tubular structures consisting of Si atoms in {{sp}}2 and the {{sp}}3 hybridizations. However, most of the theoretical models were elaborated taking as the starting point {{sp}}2 structures analogous to carbon nanotubes. These structures are unfavorable due to the natural tendency of the Si atoms to undergo {{sp}}3. In this work, through ab initio simulations based on density functional theory, we investigated double-walled silicon nanotubes proposing layered tubes possessing most of the Si atoms in an {{sp}}3 hybridization, and with few {{sp}}2 atoms localized at the outer wall. The lowest-energy structures have metallic behavior. Furthermore, the possibility to tune the band structure with the application of a strain was demonstrated, inducing a metal-semiconductor transition. Thus, the behavior of silicon nanotubes differs significantly from carbon nanotubes, and the main source of the differences is the distortions in the lattice associated with the tendency of Si to make four chemical bonds.

Few-layer nanoplates of Bi 2 Se 3 and Bi 2 Te 3 with highly tunable chemical potential.

PubMed

Kong, Desheng; Dang, Wenhui; Cha, Judy J; Li, Hui; Meister, Stefan; Peng, Hailin; Liu, Zhongfan; Cui, Yi

2010-06-09

A topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk band gap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that group V-VI materials Bi(2)Se(3), Bi(2)Te(3), and Sb(2)Te(3) are TIs with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi(2)Te(3) and Bi(2)Se(3) nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor-solid (VS) growth mechanism. Optical images reveal thickness-dependent color and contrast for nanoplates grown on oxidized silicon (300 nm SiO(2)/Si). As a new member of TI nanomaterials, ultrathin TI nanoplates have an extremely large surface-to-volume ratio and can be electrically gated more effectively than the bulk form, potentially enhancing surface state effects in transport measurements. Low-temperature transport measurements of a single nanoplate device, with a high-k dielectric top gate, show decrease in carrier concentration by several times and large tuning of chemical potential.

Synthesis and structure of cesium complexes of nitrilotris(methylenephosphonic) acid [Cs-μ6-NH(CH2PO3)3H4] and [Cs2-μ10-NH(CH2PO3H)3] · H2O

NASA Astrophysics Data System (ADS)

Somov, N. V.; Chausov, F. F.; Zakirov, R. M.

2017-07-01

3D coordination polymers cesium nitrilotris(methylenephosphonate) and dicesium nitrilotris( methylenephosphonate) are synthesized and their crystal structure is determined. In the crystal of [Cs-μ6-NH(CH2PO3)3H4] (space group P, Z = 2), cesium atoms occupy two crystallographically inequivalent positions with c.n. = 10 and c.n. = 14. The phosphonate ligand plays the bridging function; its denticity is nine. The crystal packing consists of alternating layers of Cs atoms in different environments with layers of ligand molecules between them. A ligand is bound to three Cs atoms of one layer and three Cs atoms of another layer. In the crystal of [Cs2-μ10-NH(CH2PO3H)3] · H2O (space group P, Z = 2), the complex has a dimeric structure: the bridging phosphonate ligand coordinates Cs to form a three-dimensional Cs4O6 cluster. The denticity of the ligand is equal to nine; the coordination numbers of cesium atoms are seven and nine. Two-dimensional corrugated layers of Cs4O6 clusters lie in the (002) plane, and layers of ligand molecules are located between them. Each ligand molecule coordinates eight Cs atoms of one layer and two Cs atoms of the neighboring layer.

The effects of the initial stages of native-oxide formation on the surface properties of GaSb (001)

NASA Astrophysics Data System (ADS)

Bermudez, V. M.

2013-07-01

Atomically clean surfaces of n-type GaSb (001) have been prepared by a combination of ex-situ wet-chemical treatment in HCl and in-situ annealing in a flux of H atoms in ultra-high vacuum (UHV). The surfaces are exposed to "excited" O2 and studied using primarily x-ray photoelectron spectroscopy. Low O2 exposures, up to ˜3 × 103 Langmuirs (L), result in a partial passivation of electrically active defects as shown by a decrease in upward band bending. Adsorption of O2 in this exposure range appears to form mainly Ga+1 sites, with little or no indication of Ga+3, and saturates at an O coverage of ˜0.2-0.3 monolayers. For exposures of ˜104 L or higher, oxidation occurs through insertion into Ga-Sb bonds as indicated by the onset of Ga+3 as well as of Sb+4 and/or Sb+5 together with the appearance of an O 1s feature. Defects resulting from this process cause a reversal of the band-bending change seen for smaller exposures. Data obtained for the composition of a native oxide formed in situ in UHV are compared with those for a "practical" surface produced by processing under ambient conditions. These results suggest an optimum procedure for forming a Ga2O3 layer prior to the growth by atomic layer deposition of an Al2O3 layer.

Imaging Cell Wall Architecture in Single Zinnia elegans Tracheary Elements1[OA

PubMed Central

Lacayo, Catherine I.; Malkin, Alexander J.; Holman, Hoi-Ying N.; Chen, Liang; Ding, Shi-You; Hwang, Mona S.; Thelen, Michael P.

2010-01-01

The chemical and structural organization of the plant cell wall was examined in Zinnia elegans tracheary elements (TEs), which specialize by developing prominent secondary wall thickenings underlying the primary wall during xylogenesis in vitro. Three imaging platforms were used in conjunction with chemical extraction of wall components to investigate the composition and structure of single Zinnia TEs. Using fluorescence microscopy with a green fluorescent protein-tagged Clostridium thermocellum family 3 carbohydrate-binding module specific for crystalline cellulose, we found that cellulose accessibility and binding in TEs increased significantly following an acidified chlorite treatment. Examination of chemical composition by synchrotron radiation-based Fourier-transform infrared spectromicroscopy indicated a loss of lignin and a modest loss of other polysaccharides in treated TEs. Atomic force microscopy was used to extensively characterize the topography of cell wall surfaces in TEs, revealing an outer granular matrix covering the underlying meshwork of cellulose fibrils. The internal organization of TEs was determined using secondary wall fragments generated by sonication. Atomic force microscopy revealed that the resulting rings, spirals, and reticulate structures were composed of fibrils arranged in parallel. Based on these combined results, we generated an architectural model of Zinnia TEs composed of three layers: an outermost granular layer, a middle primary wall composed of a meshwork of cellulose fibrils, and inner secondary wall thickenings containing parallel cellulose fibrils. In addition to insights in plant biology, studies using Zinnia TEs could prove especially productive in assessing cell wall responses to enzymatic and microbial degradation, thus aiding current efforts in lignocellulosic biofuel production. PMID:20592039

Do Chemistry-Climate Models Project the Same Greenhouse Gas Chemistry if Initialized with Observations of the Trace Gases: A Pre-ATom Test

NASA Astrophysics Data System (ADS)

Flynn, C. M.; Prather, M. J.; Zhu, X.; Strode, S. A.; Steenrod, S. D.; Strahan, S. E.; Lamarque, J. F.; Fiore, A. M.; Horowitz, L. W.; Mao, J.; Murray, L. T.; Shindell, D. T.

2016-12-01

Experience with climate and chemistry model intercomparison projects (MIPs) has demonstrated a diversity in model projections for the chemical greenhouse gases CH4 and O3, even when forced by the same emissions. In general, the MIPs show that models diverge in the distribution of the many key trace species that control the reactivity of the troposphere (defined here as the loss of CH4 and the production and loss of O3). Two possible sources of model differences are the chemistry-transport coupling that creates the pattern of the essential precursor species, and the calculation of reactivity. Suppose that observations, such as those planned by NASA's Atmospheric Tomography (ATom) mission, provide us with enough of a chemical climatology to constrain the modeled distribution of the essential chemical species for the current epoch. Would the models calculate the same reactivity? ATom uses the DC-8 to make in situ measurements slicing through the middle of the Pacific and Atlantic Ocean basins each season and measuring the essential trace species. Unfortunately, ATom measurements will not be available until mid-2017. Here we take the baseline chemistry from one model version (as pseudo-observations) and use it to initialize 6 other global chemistry models. In this pre-ATom MIP, we take the full chemical composition for meridional slices centered on the Dateline (UC Irvine Chemistry-Transport Model, 0.6 deg resolution, 30 layers in the troposphere). We use grid cells between 0.5 and 12 km from 60 S to 60 N to initialize grid cells in the other six models (GEOS-Chem, GFDL-AM3, GISS ModelE2, GSFC GMI, NCAR, UCI CTM). The models are then integrated for 1 day and the key chemical rates (CH4, O3) are saved. These simulations assume that the initialized parcels remain unmixed over the 24 hours, and, hence, model-to-model variations will be due to differences in photochemistry, including clouds. In addition, we assess the relative importance of the precursor species by running sensitivity tests in which each of the major precursors (e.g., NOx, HOOH, HCHO, CO) is perturbed by 10%. Such sensitivity tests can help determine the causes of model differences. Overall, this new approach allows us to characterize each model's chemistry package for a wide range of designated chemical composition. The real test will be with ATom data next year.

Growth energetics of germanium quantum dots by atomistic simulation

NASA Astrophysics Data System (ADS)

Wagner, Richard Joseph

Strained epitaxial growth of Ge on Si(001) produces self-assembled, nanometer scale islands, or quantum dots. We study this growth by atomistic simulation, computing the energy of island structures to determine when and how islanding occurs. We also describe experimental methods of island growth and characterization in order to understand the relevant physical processes and to interpret experimental observations for comparison with simulation. We show that pyramidal Ge islands with rebonded step {105} facets are energetically favorable compared to growth of planar Ge (2 x 8) on Si(001). We determine how the chemical potential of these islands varies with size, lateral spacing, and wetting layer thickness. We also illustrate the atomic-level structure of these islands with favorable formation energy. Intermixing can occur between the growing Ge film and the Si substrate. We show that although Ge prefers to wet the surface, entropy drives some fraction into the underlying layers. We present a simple model of intermixing by equilibration of the top crystal layers. The equilibration is performed with a flexible lattice Monte Carlo simulation. Ultimately, intermixing produces a temperature-dependent graded Ge concentration. The resulting chemical potential leads to the onset of islanding after 3-4 monolayers of deposition, consistent with experimental observations. The distribution of island sizes on a surface is determined by the relation of island energy to size. We find that there exists a minimum-energy island size due to the interaction of surface energy and bulk relaxation. Applying the calculated chemical potential to the Boltzmann-Gibbs distribution, we predict size distributions as functions of coverage and temperature. The distributions, with peak populations around 86 000 atoms, compare favorably with experiment. This work explores the driving force in growth of Ge on Si(001). The knowledge derived here explains why islanding occurs and provides guidance for the control of island self-assembly to construct useful microelectronic devices from quantum dots.

Defect Characterization in SiGe/SOI Epitaxial Semiconductors by Positron Annihilation

PubMed Central

2010-01-01

The potential of positron annihilation spectroscopy (PAS) for defect characterization at the atomic scale in semiconductors has been demonstrated in thin multilayer structures of SiGe (50 nm) grown on UTB (ultra-thin body) SOI (silicon-on-insulator). A slow positron beam was used to probe the defect profile. The SiO2/Si interface in the UTB-SOI was well characterized, and a good estimation of its depth has been obtained. The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers. In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum. After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film. Chemical analysis of the SiGe layers suggests a prevalent trapping site surrounded by germanium atoms, presumably Si vacancies associated with misfit dislocations and threading dislocations in the SiGe films. PMID:21170391

Investigation of Corrosion Protection in Oil Mineral Reservoirs by Nanocomposites Used as Coating Layers

NASA Astrophysics Data System (ADS)

Al-Sarraf, Abdulhameed R.; Al-Saaidi, Samer A.

2018-05-01

In this study, a number of nanocomposites were prepared by adding magnesium oxide (MgO) with weight percentages (1, 2 & 3)% to cellulose nitrate and sodium silicate as an intermediate layer and other nanocomposites by adding MgO, coal coke and hybrid (MgO & coal coke with ratio 1:1) with weight percentages (1, 2 & 3)% to epoxy resin as final layer. The identity of the used metal is determined by spectrometer OE thermo. The nature and topography of the surface layers were examined by optical microscope and atomic force microscope (AFM). Mechanical properties are indicated by hardness, wear rate, impact strength and adhesion strength. The efficiency of the layers prepared to inhibit corrosion in the oil mineral reservoirs of the oil products distribution company was studied by electrochemical corrosion test in addition to the chemical corrosion test. The used metal is (St-37) according to (ASTM). It was found that the best intermediate layer (cellulose nitrate+3%MgO) and the final layer is the epoxy resin reinforced by 2% hybrid.

Formation of a Crack-Free, Hybrid Skin Layer with Tunable Surface Topography and Improved Gas Permeation Selectivity on Elastomers Using Gel–Liquid Infiltration Polymerization

DOE PAGES

Wang, Mengyuan; Gorham, Justin M.; Killgore, Jason P.; ...

2017-07-31

Surface modifications of elastomers and gels are crucial for emerging applications such as soft robotics and flexible electronics, in large part because they provide a platform to control wettability, adhesion, and permeability. Current surface modification methods via ultraviolet-ozone (UVO) and/or O2 plasma, atomic layer deposition (ALD), plasmas deposition, and chemical treatment impart a dense polymer or inorganic layer on the surface that is brittle and easy to fracture at low strain levels. This paper presents a new method, based on gel–liquid infiltration polymerization, to form hybrid skin layers atop elastomers. The method is unique in that it allows for controlmore » of the skin layer topography, with tunable feature sizes and aspect ratios as high as 1.8 without fracture. Unlike previous techniques, the skin layer formed here dramatically improves the barrier properties of the elastomer, while preserving skin layer flexibility. Furthermore, the method is versatile and likely applicable to most interfacial polymerization systems and network polymers on flat and patterned surfaces.« less

Formation of a Crack-Free, Hybrid Skin Layer with Tunable Surface Topography and Improved Gas Permeation Selectivity on Elastomers Using Gel–Liquid Infiltration Polymerization

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

Wang, Mengyuan; Gorham, Justin M.; Killgore, Jason P.

Surface modifications of elastomers and gels are crucial for emerging applications such as soft robotics and flexible electronics, in large part because they provide a platform to control wettability, adhesion, and permeability. Current surface modification methods via ultraviolet-ozone (UVO) and/or O2 plasma, atomic layer deposition (ALD), plasmas deposition, and chemical treatment impart a dense polymer or inorganic layer on the surface that is brittle and easy to fracture at low strain levels. This paper presents a new method, based on gel–liquid infiltration polymerization, to form hybrid skin layers atop elastomers. The method is unique in that it allows for controlmore » of the skin layer topography, with tunable feature sizes and aspect ratios as high as 1.8 without fracture. Unlike previous techniques, the skin layer formed here dramatically improves the barrier properties of the elastomer, while preserving skin layer flexibility. Furthermore, the method is versatile and likely applicable to most interfacial polymerization systems and network polymers on flat and patterned surfaces.« less

Stability Enhancement of Silver Nanowire Networks with Conformal ZnO Coatings Deposited by Atmospheric Pressure Spatial Atomic Layer Deposition.

PubMed

Khan, Afzal; Nguyen, Viet Huong; Muñoz-Rojas, David; Aghazadehchors, Sara; Jiménez, Carmen; Nguyen, Ngoc Duy; Bellet, Daniel

2018-06-06

Silver nanowire (AgNW) networks offer excellent electrical and optical properties and have emerged as one of the most attractive alternatives to transparent conductive oxides to be used in flexible optoelectronic applications. However, AgNW networks still suffer from chemical, thermal, and electrical instabilities, which in some cases can hinder their efficient integration as transparent electrodes in devices such as solar cells, transparent heaters, touch screens, and organic light emitting diodes. We have used atmospheric pressure spatial atomic layer deposition (AP-SALD) to fabricate hybrid transparent electrode materials in which the AgNW network is protected by a conformal thin layer of zinc oxide. The choice of AP-SALD allows us to maintain the low-cost and scalable processing of AgNW-based transparent electrodes. The effects of the ZnO coating thickness on the physical properties of AgNW networks are presented. The composite electrodes show a drastic enhancement of both thermal and electrical stabilities. We found that bare AgNWs were stable only up to 300 °C when subjected to thermal ramps, whereas the ZnO coating improved the stability up to 500 °C. Similarly, ZnO-coated AgNWs exhibited an increase of 100% in electrical stability with respect to bare networks, withstanding up to 18 V. A simple physical model shows that the origin of the stability improvement is the result of hindered silver atomic diffusion thanks to the presence of the thin oxide layer and the quality of the interfaces of hybrid electrodes. The effects of ZnO coating on both the network adhesion and optical transparency are also discussed. Finally, we show that the AP-SALD ZnO-coated AgNW networks can be effectively used as very stable transparent heaters.

Incorporation of dopant impurities into a silicon oxynitride matrix containing silicon nanocrystals

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

Ehrhardt, Fabien; Muller, Dominique; Slaoui, Abdelilah, E-mail: abdelilah.slaoui@unistra.fr

2016-05-07

Dopant impurities, such as gallium (Ga), indium (In), and phosphorus (P), were incorporated into silicon-rich silicon oxynitride (SRSON) thin films by the ion implantation technique. To form silicon nanoparticles, the implanted layers were thermally annealed at temperatures up to 1100 °C for 60 min. This thermal treatment generates a phase separation of the silicon nanoparticles from the SRSON matrix in the presence of the dopant atoms. We report on the position of the dopant species within the host matrix and relative to the silicon nanoparticles, as well as on the effect of the dopants on the crystalline structure and the size ofmore » the Si nanoparticles. The energy-filtered transmission electron microscopy technique is thoroughly used to identify the chemical species. The distribution of the dopant elements within the SRSON compound is determined using Rutherford backscattering spectroscopy. Energy dispersive X-ray mapping coupled with spectral imaging of silicon plasmons was performed to spatially localize at the nanoscale the dopant impurities and the silicon nanoparticles in the SRSON films. Three different behaviors were observed according to the implanted dopant type (Ga, In, or P). The In-doped SRSON layers clearly showed separated nanoparticles based on indium, InOx, or silicon. In contrast, in the P-doped SRSON layers, Si and P are completely miscible. A high concentration of P atoms was found within the Si nanoparticles. Lastly, in Ga-doped SRSON the Ga atoms formed large nanoparticles close to the SRSON surface, while the Si nanoparticles were localized in the bulk of the SRSON layer. In this work, we shed light on the mechanisms responsible for these three different behaviors.« less

Method of making maximally dispersed heterogeneous catalysts

DOEpatents

Jennison, Dwight R [Albuquerque, NM

2005-11-15

A method of making a catalyst with monolayer or sub-monolayer metal by controlling the wetting characteristics on the support surface and increasing the adhesion between the catalytic metal and an oxide layer. There are two methods that have been demonstrated by experiment and supported by theory. In the first method, which is useful for noble metals as well as others, a negatively-charged species is introduced to the surface of a support in sub-ML coverage. The layer-by-layer growth of metal deposited onto the oxide surface is promoted because the adhesion strength of the metal-oxide interface is increased. This method can also be used to achieve nanoislands of metal upon sub-ML deposition. The negatively-charged species can either be deposited onto the oxide surface or a compound can be deposited that dissociates on, or reacts with, the surface to form the negatively-charged species. The deposited metal adatoms can thereby bond laterally to the negatively-charged species as well as vertically to the oxide surface. Thus the negatively-charged species serve as anchors for the metal. In the second method, a chemical reaction that occurs when most metals are deposited on a fully hydroxylated oxide surface is used to create cationic metal species that bind strongly both to the substrate and to metallic metal atoms. These are incorporated into the top layer of the substrate and bind strongly both to the substrate and to metallic metal atoms. In this case, these oxidized metal atoms serve as the anchors. Here, as in the previous method, nanoislands of catalytic metal can be achieved to increase catalytic activity, or monolayers or bilayers of reactive metal can also be made.

Oxidation precursor dependence of atomic layer deposited Al2O3 films in a-Si:H(i)/Al2O3 surface passivation stacks.

PubMed

Xiang, Yuren; Zhou, Chunlan; Jia, Endong; Wang, Wenjing

2015-01-01

In order to obtain a good passivation of a silicon surface, more and more stack passivation schemes have been used in high-efficiency silicon solar cell fabrication. In this work, we prepared a-Si:H(i)/Al2O3 stacks on KOH solution-polished n-type solar grade mono-silicon(100) wafers. For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used. Interface trap density spectra were obtained for Si passivation with a-Si films and a-Si:H(i)/Al2O3 stacks by a non-contact corona C-V technique. After the fabrication of a-Si:H(i)/Al2O3 stacks, the minimum interface trap density was reduced from original 3 × 10(12) to 1 × 10(12) cm(-2) eV(-1), the surface total charge density increased by nearly one order of magnitude for PE-ALD samples and about 0.4 × 10(12) cm(-2) for a T-ALD sample, and the carrier lifetimes increased by a factor of three (from about 10 μs to about 30 μs). Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives. In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

On the surface trapping parameters of polytetrafluoroethylene block

NASA Astrophysics Data System (ADS)

Zhang, Guan-Jun; Yang, Kai; Zhao, Wen-Bin; Yan, Zhang

2006-12-01

Surface flashover phenomena under high electric field are closely related to the surface characteristics of a solid insulating material between energized electrodes. Based on measuring the surface potential decaying curve of polytetrafluoroethylene (PTFE) block charged by a needle-plane corona discharge, its surface trapping parameters are calculated with the isothermal current theory, and the correlative curve between the surface trap density and its energy level is obtained. The maximum density of electron traps and hole traps in the surface layer of PTFE presents a similar value of ∼2.7 × 1017 eV-1 m-3, and the energy level of its electron and hole traps is of about 0.85-1.0 eV and 0.80-0.90 eV, respectively. Via the X-ray photoelectron spectroscopy (XPS) technique, the F, C, K and O elements are detected on the surface of PTFE samples, and F shows a remarkable atom proportion of ∼73.3%, quite different from the intrinsic distribution corresponding to its chemical formula. The electron traps are attributed to quantities of F atoms existing on the surface of PTFE due to its molecular chain with C atoms surrounded by F atoms spirally. It is considered that the distortions of chemical and electronic structure on solid surface are responsible for the flashover phenomena occurring at a low applied voltage.

High temperature growth of Pt on the Rh(111) surface

NASA Astrophysics Data System (ADS)

Duisberg, M.; Dräger, M.; Wandelt, K.; Gruber, E. L. D.; Schmid, M.; Varga, P.

1999-08-01

The epitaxial growth of Pt on the Rh(111) surface at 700 K was studied with AES, UPS, ISS and STM. From AES and ISS measurements a 2D growth mode is concluded at this substrate temperature. The morphology of the surface is studied by photoemission spectra of adsorbed Xe (PAX) and STM. A disperse distribution of the Pt atoms is suggested by PAX and is consistent with an incorporation of these atoms into the first substrate layer. Atomically and chemically resolved STM measurements confirm these conclusions. The interaction of CO with the surface alloy is investigated by UPS. The CO-induced features in UP spectra show significant differences in the peak positions and shape between the clean substrate and the surface precovered with different amounts of Pt. The CO induced emissions are, thus, used for a quantitative titration of Pt on the Rh surface.

Strengthened PAN-based carbon fibers obtained by slow heating rate carbonization

PubMed Central

Kim, Min-A; Jang, Dawon; Tejima, Syogo; Cruz-Silva, Rodolfo; Joh, Han-Ik; Kim, Hwan Chul; Lee, Sungho; Endo, Morinobu

2016-01-01

Large efforts have been made over the last 40 years to increase the mechanical strength of polyacrylonitrile (PAN)-based carbon fibers (CFs) using a variety of chemical or physical protocols. In this paper, we report a new method to increase CFs mechanical strength using a slow heating rate during the carbonization process. This new approach increases both the carbon sp3 bonding and the number of nitrogen atoms with quaternary bonding in the hexagonal carbon network. Theoretical calculations support a crosslinking model promoted by the interstitial carbon atoms located in the graphitic interlayer spaces. The improvement in mechanical performance by a controlled crosslinking between the carbon hexagonal layers of the PAN based CFs is a new concept that can contribute further in the tailoring of CFs performance based on the understanding of their microstructure down to the atomic scale. PMID:27004752

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework

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

Kim, In Soo; Li, Zhanyong; Zheng, Jian

Installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 degrees C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and Xray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novelmore » catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support.« less

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

Susarla, Sandhya; Kochat, Vidya; Kutana, Alex

Transition metal dichalcogenide (TMD) alloys form a broad class of two-dimensional (2D) layered materials with tunable bandgaps leading to interesting optoelectronic applications. In the bottom-up approach of building these atomically thin materials, atomic doping plays a crucial role. Here we demonstrate a single step CVD (chemical vapor deposition) growth procedure for obtaining binary alloys and heterostructures by tuning atomic composition. We show that a minute doping of tin during the growth phase of the Mo 1–xW xS 2 alloy system leads to formation of lateral and vertical heterostructure growth. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imagingmore » and density functional theory (DFT) calculations also support the modified stacking and growth mechanism due to the nonisomorphous Sn substitution. Our experiments demonstrate the possibility of growing heterostructures of TMD alloys whose spectral responses can be desirably tuned for various optoelectronic applications.« less

Low-temperature remote plasma enhanced atomic layer deposition of ZrO2/zircone nanolaminate film for efficient encapsulation of flexible organic light-emitting diodes

PubMed Central

Chen, Zheng; Wang, Haoran; Wang, Xiao; Chen, Ping; Liu, Yunfei; Zhao, Hongyu; Zhao, Yi; Duan, Yu

2017-01-01

Encapsulation is essential to protect the air-sensitive components of organic light-emitting diodes (OLEDs) such as active layers and cathode electrodes. In this study, hybrid zirconium inorganic/organic nanolaminates were fabricated using remote plasma enhanced atomic layer deposition (PEALD) and molecular layer deposition at a low temperature. The nanolaminate serves as a thin-film encapsulation layer for OLEDs. The reaction mechanism of PEALD process was investigated using an in-situ quartz crystal microbalance (QCM) and in-situ quadrupole mass spectrometer (QMS). The bonds present in the films were determined by Fourier transform infrared spectroscopy. The primary reaction byproducts in PEALD, such as CO, CO2, NO, H2O, as well as the related fragments during the O2 plasma process were characterized using the QMS, indicating a combustion-like reaction process. The self-limiting nature and growth mechanisms of the ZrO2 during the complex surface chemical reaction of the ligand and O2 plasma were monitored using the QCM. The remote PEALD ZrO2/zircone nanolaminate structure prolonged the transmission path of water vapor and smooth surface morphology. Consequently, the water barrier properties were significantly improved (reaching 3.078 × 10−5 g/m2/day). This study also shows that flexible OLEDs can be successfully encapsulated to achieve a significantly longer lifetime. PMID:28059160

Initial and steady-state Ru growth by atomic layer deposition studied by in situ Angle Resolved X-ray Photoelectron Spectroscopy

NASA Astrophysics Data System (ADS)

Egorov, Konstantin V.; Lebedinskii, Yury Yu.; Soloviev, Anatoly A.; Chouprik, Anastasia A.; Azarov, Alexander Yu.; Markeev, Andrey M.

2017-10-01

The clear substrate-dependent growth and delayed film continuity are essential challenges of Ru atomic layer deposition (ALD) demanding adequate and versatile approaches for their study. Here, we report on the application of in situ Angle Resolved X-ray Phototelectron Spectroscopy (ARXPS) for investigation of initial and steady-state ALD growth of Ru using Ru(EtCp)2 and O2 as precursors. Using ARXPS surface analysis technique we determine such parameters of Ru ALD initial growth as incubation period, fractional coverage and the thickness of islands/film depending on the substrate chemical state, governed by the presence/absence of NH3/Ar plasma pretreatment. It was demonstrated that NH3/Ar plasma pretreatment allows to obtain the lowest incubation period (∼7 ALD cycles) resulting in a continuous ultrathin (∼20 Å) and smooth Ru films after 70 ALD cycles. In situ XPS at UHV was used at steady state Ru growth for analysis of half-cycle reactions that revealed formation of RuOx (x ≈ 2) layer with thickness of ∼8 Å after O2 pulse (first half-cycle). It was also shown that oxygen of RuOx layer combusts Ru(EtCp)2 ligands in the second half-cycle reaction and the observed Ru growth of ∼0.34 Å per cycle is in a good agreement with the amount of oxygen in the RuOx layer.

Zn or O? An Atomic Level Comparison on Antibacterial Activities of Zinc Oxides.

PubMed

Yu, Fen; Fang, Xuan; Jia, Huimin; Liu, Miaoxing; Shi, Xiaotong; Xue, Chaowen; Chen, Tingtao; Wei, Zhipeng; Fang, Fang; Zhu, Hui; Xin, Hongbo; Feng, Jing; Wang, Xiaolei

2016-06-06

For the first time, the influence of different types of atoms (Zn and O) on the antibacterial activities of nanosized ZnO was quantitatively evaluated with the aid of a 3D-printing-manufactured evaluation system. Two different outermost atomic layers were manufactured separately by using an ALD (atomic layer deposition) method. Interestingly, we found that each outermost atomic layer exhibited certain differences against gram-positive or gram-negative bacterial species. Zinc atoms as outermost layer (ZnO-Zn) showed a more pronounced antibacterial effect towards gram-negative E. coli (Escherichia coli), whereas oxygen atoms (ZnO-O) showed a stronger antibacterial activity against gram-positive S. aureus (Staphylococcus aureus). A possible antibacterial mechanism has been comprehensively discussed from different perspectives, including Zn(2+) concentrations, oxygen vacancies, photocatalytic activities and the DNA structural characteristics of different bacterial species. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Silicon solar cell performance deposited by diamond like carbon thin film ;Atomic oxygen effects;

NASA Astrophysics Data System (ADS)

Aghaei, Abbas Ail; Eshaghi, Akbar; Karami, Esmaeil

2017-09-01

In this research, a diamond-like carbon thin film was deposited on p-type polycrystalline silicon solar cell via plasma-enhanced chemical vapor deposition method by using methane and hydrogen gases. The effect of atomic oxygen on the functioning of silicon coated DLC thin film and silicon was investigated. Raman spectroscopy, field emission scanning electron microscopy, atomic force microscopy and attenuated total reflection-Fourier transform infrared spectroscopy were used to characterize the structure and morphology of the DLC thin film. Photocurrent-voltage characteristics of the silicon solar cell were carried out using a solar simulator. The results showed that atomic oxygen exposure induced the including oxidation, structural changes, cross-linking reactions and bond breaking of the DLC film; thus reducing the optical properties. The photocurrent-voltage characteristics showed that although the properties of the fabricated thin film were decreased after being exposed to destructive rays, when compared with solar cell without any coating, it could protect it in atomic oxygen condition enhancing solar cell efficiency up to 12%. Thus, it can be said that diamond-like carbon thin layer protect the solar cell against atomic oxygen exposure.

Novel insights into pericarp, protein body globoids of aleurone layer, starchy granules of three cereals gained using atomic force microscopy and environmental scanning electronic microscopy

PubMed Central

Antonini, Elena; Zara, Carolina; Valentini, Laura; Gobbi, Pietro; Menotta, Michele

2018-01-01

In this study, we applied Environmental Scanning Electron Microscopy-Energy Dispersive Spectroscopy (ESEM-EDS) and Atomic Force Microscopy (AFM) analysis to three different cereal caryopses: barley, oat and einkorn wheat. The morphological structures, chemical elemental composition and surface characteristics of the three cereals were described. Regarding the morphology, barley showed the thickest pericarp, providing a strong barrier to digestion and absorption of nutrients. The aleurone layer of each cereal type contained protein body globoids within its cells. Large type-A and small type-B starchy granules were revealed in the endosperm of barley and einkorn wheat, whereas irregular starchy granules were found in oats. The starchy granule elemental composition, detected by ESEM-EDS, was rather homogenous in the three cereals, whereas the pericarp and protein body globoids showed heterogeneity. In the protein body globoids, oats showed higher P and K concentrations than barley and einkorn wheat. Regarding the topographic profiles, detected by AFM, einkorn wheat starchy granules showed a surface profile that differed significantly from that of oats and barley, which were quite similar to one another. The present work provides insights into the morphological and chemical makeup of the three grains shedding light on the higher bio-accessibility of einkorn wheat nutrients compared to barley and oats, providing important suggestions for human nutrition and technological standpoints. PMID:29569870

Novel insights into pericarp, protein body globoids of aleurone layer, starchy granules of three cereals gained using atomic force microscopy and environmental scanning electronic microscopy.

PubMed

Antonini, Elena; Zara, Carolina; Valentini, Laura; Gobbi, Pietro; Ninfali, Paolino; Menotta, Michele

2018-02-05

In this study, we applied Environmental Scanning Electron Microscopy-Energy Dispersive Spectroscopy (ESEM-EDS) and Atomic Force Microscopy (AFM) analysis to three different cereal caryopses: barley, oat and einkorn wheat. The morphological structures, chemical elemental composition and surface characteristics of the three cereals were described. Regarding the morphology, barley showed the thickest pericarp, providing a strong barrier digestion and absorption of nutrients. The aleurone layer of each cereal type contained protein body globoids within its cells. Large type-A and small type-B starchy granules were revealed in the endosperm of barley and einkorn wheat, whereas irregular starchy granules were found in oats. The starchy granule elemental composition, detected by ESEM-EDS, was rather homogenous in the three cereals, whereas the pericarp and protein body globoids showed heterogeneity. In the protein body globoids, oats showed higher P and K concentrations than barley and einkorn wheat. Regarding the topographic profiles, detected by AFM, einkorn wheat starchy granules showed a surface profile that differed significantly from that of oats and barley, which were quite similar to one another. The present work provides insights into the morphological and chemical makeup of the three grains shedding light on the higher bio-accessibility of einkorn wheat nutrients compared to barley and oats, providing important suggestions for human nutrition and technological standpoints.

Quantum chemical investigation on the role of Li adsorbed on anatase (101) surface nano-materials on the storage of molecular hydrogen.

PubMed

Srinivasadesikan, V; Raghunath, P; Lin, M C

2015-06-01

Lithiation of TiO2 has been shown to enhance the storage of hydrogen up to 5.6 wt% (Hu et al. J Am Chem Soc 128:11740-11741, 2006). The mechanism for the process is still unknown. In this work we have carried out a study on the adsorption and diffusion of Li atoms on the surface and migration into subsurface layers of anatase (101) by periodic density functional theory calculations implementing on-site Coulomb interactions (DFT+U). The model consists of 24 [TiO2] units with 11.097 × 7.655 Å(2) surface area. Adsorption energies have been calculated for different Li atoms (1-14) on the surface. A maximum of 13 Li atoms can be accommodated on the surface at two bridged O, Ti-O, and Ti atom adsorption sites, with 83 kcal mol(-1) adsorption energy for a single Li atom adsorbed between two bridged O atoms from where it can migrate into the subsurface layer with 27 kcal mol(-1) energy barrier. The predicted adsorption energies for H2 on the lithiated TiO2 (101) surface with 1-10 Li atoms revealed that the highest adsorption energies occurred on 1-Li, 5-Li, and 9-Li surfaces with 3.5, 4.4, and 7.6 kcal mol(-1), respectively. The values decrease rapidly with additional H2 co-adsorbed on the lithiated surfaces; the maximum H2 adsorption on the 9Li-TiO2(a) surface was estimated to be only 0.32 wt% under 100 atm H2 pressure at 77 K. The result of Bader charge analysis indicated that the reduction of Ti occurred depending on the Li atoms covered on the TiO2 surface.

Copper Benzenetricarboxylate Metal-Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition.

PubMed

Lemaire, Paul C; Zhao, Junjie; Williams, Philip S; Walls, Howard J; Shepherd, Sarah D; Losego, Mark D; Peterson, Gregory W; Parsons, Gregory N

2016-04-13

Chemically functional microporous metal-organic framework (MOF) crystals are attractive for filtration and gas storage applications, and recent results show that they can be immobilized on high surface area substrates, such as fiber mats. However, fundamental knowledge is still lacking regarding initial key reaction steps in thin film MOF nucleation and growth. We find that thin inorganic nucleation layers formed by atomic layer deposition (ALD) can promote solvothermal growth of copper benzenetricarboxylate MOF (Cu-BTC) on various substrate surfaces. The nature of the ALD material affects the MOF nucleation time, crystal size and morphology, and the resulting MOF surface area per unit mass. To understand MOF nucleation mechanisms, we investigate detailed Cu-BTC MOF nucleation behavior on metal oxide powders and Al2O3, ZnO, and TiO2 layers formed by ALD on polypropylene substrates. Studying both combined and sequential MOF reactant exposure conditions, we find that during solvothermal synthesis ALD metal oxides can react with the MOF metal precursor to form double hydroxy salts that can further convert to Cu-BTC MOF. The acidic organic linker can also etch or react with the surface to form MOF from an oxide metal source, which can also function as a nucleation agent for Cu-BTC in the mixed solvothermal solution. We discuss the implications of these results for better controlled thin film MOF nucleation and growth.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing.

PubMed

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-03

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future.

Low-temperature atomic layer epitaxy of AlN ultrathin films by layer-by-layer, in-situ atomic layer annealing

PubMed Central

Shih, Huan-Yu; Lee, Wei-Hao; Kao, Wei-Chung; Chuang, Yung-Chuan; Lin, Ray-Ming; Lin, Hsin-Chih; Shiojiri, Makoto; Chen, Miin-Jang

2017-01-01

Low-temperature epitaxial growth of AlN ultrathin films was realized by atomic layer deposition (ALD) together with the layer-by-layer, in-situ atomic layer annealing (ALA), instead of a high growth temperature which is needed in conventional epitaxial growth techniques. By applying the ALA with the Ar plasma treatment in each ALD cycle, the AlN thin film was converted dramatically from the amorphous phase to a single-crystalline epitaxial layer, at a low deposition temperature of 300 °C. The energy transferred from plasma not only provides the crystallization energy but also enhances the migration of adatoms and the removal of ligands, which significantly improve the crystallinity of the epitaxial layer. The X-ray diffraction reveals that the full width at half-maximum of the AlN (0002) rocking curve is only 144 arcsec in the AlN ultrathin epilayer with a thickness of only a few tens of nm. The high-resolution transmission electron microscopy also indicates the high-quality single-crystal hexagonal phase of the AlN epitaxial layer on the sapphire substrate. The result opens a window for further extension of the ALD applications from amorphous thin films to the high-quality low-temperature atomic layer epitaxy, which can be exploited in a variety of fields and applications in the near future. PMID:28045075

Effect of Sn Composition in Ge1- x Sn x Layers Grown by Using Rapid Thermal Chemical Vapor Deposition

NASA Astrophysics Data System (ADS)

Kil, Yeon-Ho; Kang, Sukill; Jeong, Tae Soo; Shim, Kyu-Hwan; Kim, Dae-Jung; Choi, Yong-Dae; Kim, Mi Joung; Kim, Taek Sung

2018-05-01

The Ge1- x Sn x layers were grown by using rapid thermal chemical-vapor deposition (RTCVD) on boron-doped p-type Si (100) substrates with Sn compositions up to x = 0.83%. In order to obtain effect of the Sn composition on the structural and the optical characteristics, we utilized highresolution X-ray diffraction (HR-XRD), etch pit density (EPD), atomic force microscopy (AFM), Raman spectroscopy, and photocurrent (PC) spectra. The Sn compositions in the Ge1- x Sn x layers were found to be of x = 0.00%, 0.51%, 0.65%, and 0.83%. The root-mean-square (RMS) of the surface roughness of the Ge1- x Sn x layer increased from 2.02 nm to 3.40 nm as the Sn composition was increased from 0.51% to 0.83%, and EPD was on the order of 108 cm-2. The Raman spectra consist of only one strong peak near 300 cm-1, which is assigned to the Ge-Ge LO peaks and the Raman peaks shift to the wave number with increasing Sn composition. Photocurrent spectra show near energy band gap peaks and their peak energies decrease with increasing Sn composition due to band-gap bowing in the Ge1- x Sn x layer. An increase in the band gap bowing parameter was observed with increasing Sn composition.

Atomically Thin-Layered Molybdenum Disulfide (MoS2) for Bulk-Heterojunction Solar Cells.

PubMed

Singh, Eric; Kim, Ki Seok; Yeom, Geun Young; Nalwa, Hari Singh

2017-02-01

Transition metal dichalcogenides (TMDs) are becoming significant because of their interesting semiconducting and photonic properties. In particular, TMDs such as molybdenum disulfide (MoS 2 ), molybdenum diselenide (MoSe 2 ), tungsten disulfide (WS 2 ), tungsten diselenide (WSe 2 ), titanium disulfide (TiS 2 ), tantalum sulfide (TaS 2 ), and niobium selenide (NbSe 2 ) are increasingly attracting attention for their applications in solar cell devices. In this review, we give a brief introduction to TMDs with a focus on MoS 2 ; and thereafter, emphasize the role of atomically thin MoS 2 layers in fabricating solar cell devices, including bulk-heterojunction, organic, and perovskites-based solar cells. Layered MoS 2 has been used as the hole-transport layer (HTL), electron-transport layer (ETL), interfacial layer, and protective layer in fabricating heterojunction solar cells. The trilayer graphene/MoS 2 /n-Si solar cell devices exhibit a power-conversion efficiency of 11.1%. The effects of plasma and chemical doping on the photovoltaic performance of MoS 2 solar cells have been analyzed. After doping and electrical gating, a power-conversion efficiency (PCE) of 9.03% has been observed for the MoS 2 /h-BN/GaAs heterostructure solar cells. The MoS 2 -containing perovskites-based solar cells show a PCE as high as 13.3%. The PCE of MoS 2 -based organic solar cells exceeds 8.40%. The stability of MoS 2 solar cells measured under ambient conditions and light illumination has been discussed. The MoS 2 -based materials show a great potential for solar cell devices along with high PCE; however, in this connection, their long-term environmental stability is also of equal importance for commercial applications.

Atomic force microscopy based nanoindentation study of onion abaxial epidermis walls in aqueous environment

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

Xi, Xiaoning; Tittmann, Bernhard; Kim, Seong H.

An atomic force microscopy based nanoindentation method was employed to study how the structure of cellulose microfibril packing and matrix polymers affect elastic modulus of fully hydrated primary plant cell walls. The isolated, single-layered abaxial epidermis cell wall of an onion bulb was used as a test system since the cellulose microfibril packing in this cell wall is known to vary systematically from inside to outside scales and the most abundant matrix polymer, pectin, can easily be altered through simple chemical treatments such as ethylenediaminetetraacetic acid and calcium ions. Experimental results showed that the pectin network variation has significant impactsmore » on the cell wall modulus, and not the cellulose microfibril packing.« less

Atomic scale morphology, growth behaviour and electronic properties of semipolar {101[overline]3} GaN surfaces.

PubMed

Kioseoglou, J; Kalesaki, E; Lymperakis, L; Karakostas, Th; Komninou, Ph

2013-01-30

First-principles calculations relating to the atomic structure and electronic properties of {101[overline]3} GaN surfaces reveal significant differentiations between the two polarity orientations. The (101[overline]3) surface exhibits a remarkable morphological stability, stabilizing a metallic structure (Ga adlayer) over the entire range of the Ga chemical potential. In contrast, the semiconducting, cleaved surface is favoured on (101[overline]3[overline]) under extremely and moderately N-rich conditions, a Ga bilayer is stabilized under corresponding Ga-rich conditions and various transitions between metallic reconstructions take place in intermediate growth stoichiometries. Efficient growth schemes for smooth, two-dimensional GaN layers and the isolation of {101[overline]3} material from parasitic orientations are identified.

PEALD grown high-k ZrO{sub 2} thin films on SiC group IV compound semiconductor

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

Khairnar, A. G., E-mail: agkhairnar@gmail.com; Patil, V. S.; Agrawal, K. S.

The study of ZrO{sub 2} thin films on SiC group IV compound semiconductor has been studied as a high mobility substrates. The ZrO{sub 2} thin films were deposited using the Plasma Enhanced Atomic Layer Deposition System. The thickness of the thin films were measured using ellipsometer and found to be 5.47 nm. The deposited ZrO{sub 2} thin films were post deposition annealed in rapid thermal annealing chamber at temperature of 400°Ð¡. The atomic force microscopy and X-гау photoelectron spectroscopy has been carried out to study the surface topography, roughness and chemical composition of thin film, respectively.

Graphenes in the absence of metals as carbocatalysts for selective acetylene hydrogenation and alkene hydrogenation

NASA Astrophysics Data System (ADS)

Primo, Ana; Neatu, Florentina; Florea, Mihaela; Parvulescu, Vasile; Garcia, Hermenegildo

2014-10-01

Catalysis makes possible a chemical reaction by increasing the transformation rate. Hydrogenation of carbon-carbon multiple bonds is one of the most important examples of catalytic reactions. Currently, this type of reaction is carried out in petrochemistry at very large scale, using noble metals such as platinum and palladium or first row transition metals such as nickel. Catalysis is dominated by metals and in many cases by precious ones. Here we report that graphene (a single layer of one-atom-thick carbon atoms) can replace metals for hydrogenation of carbon-carbon multiple bonds. Besides alkene hydrogenation, we have shown that graphenes also exhibit high selectivity for the hydrogenation of acetylene in the presence of a large excess of ethylene.

Atomic layer epitaxy of Ruddlesden-Popper SrO(SrTiO{sub 3}){sub n} films by means of metalorganic aerosol deposition

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

Jungbauer, M.; Hühn, S.; Moshnyaga, V.

2014-12-22

We report an atomic layer epitaxial growth of Ruddlesden-Popper (RP) thin films of SrO(SrTiO{sub 3}){sub n} (n = ∞, 2, 3, 4) by means of metalorganic aerosol deposition (MAD). The films are grown on SrTiO{sub 3}(001) substrates by means of a sequential deposition of Sr-O/Ti-O{sub 2} atomic monolayers, monitored in-situ by optical ellipsometry. X-ray diffraction and transmission electron microscopy (TEM) reveal the RP structure with n = 2–4 in accordance with the growth recipe. RP defects, observed by TEM in a good correlation with the in-situ ellipsometry, mainly result from the excess of SrO. Being maximal at the film/substrate interface, the SrO excess rapidlymore » decreases and saturates after 5–6 repetitions of the SrO(SrTiO{sub 3}){sub 4} block at the level of 2.4%. This identifies the SrTiO{sub 3} substrate surface as a source of RP defects under oxidizing conditions within MAD. Advantages and limitations of MAD as a solution-based and vacuum-free chemical deposition route were discussed in comparison with molecular beam epitaxy.« less

Li intercalation in graphite: A van der Waals density-functional study

NASA Astrophysics Data System (ADS)

Hazrati, E.; de Wijs, G. A.; Brocks, G.

2014-10-01

Modeling layered intercalation compounds from first principles poses a problem, as many of their properties are determined by a subtle balance between van der Waals interactions and chemical or Madelung terms, and a good description of van der Waals interactions is often lacking. Using van der Waals density functionals we study the structures, phonons and energetics of the archetype layered intercalation compound Li-graphite. Intercalation of Li in graphite leads to stable systems with calculated intercalation energies of -0.2 to -0.3 eV/Li atom, (referred to bulk graphite and Li metal). The fully loaded stage 1 and stage 2 compounds LiC6 and Li1 /2C6 are stable, corresponding to two-dimensional √{3 }×√{3 } lattices of Li atoms intercalated between two graphene planes. Stage N >2 structures are unstable compared to dilute stage 2 compounds with the same concentration. At elevated temperatures dilute stage 2 compounds easily become disordered, but the structure of Li3 /16C6 is relatively stable, corresponding to a √{7 }×√{7 } in-plane packing of Li atoms. First-principles calculations, along with a Bethe-Peierls model of finite temperature effects, allow for a microscopic description of the observed voltage profiles.

Extracting elastic properties of an atomically thin interfacial layer by time-domain analysis of femtosecond acoustics

NASA Astrophysics Data System (ADS)

Chen, H.-Y.; Huang, Y.-R.; Shih, H.-Y.; Chen, M.-J.; Sheu, J.-K.; Sun, C.-K.

2017-11-01

Modern devices adopting denser designs and complex 3D structures have created much more interfaces than before, where atomically thin interfacial layers could form. However, fundamental information such as the elastic property of the interfacial layers is hard to measure. The elastic property of the interfacial layer is of great importance in both thermal management and nano-engineering of modern devices. Appropriate techniques to probe the elastic properties of interfacial layers as thin as only several atoms are thus critically needed. In this work, we demonstrated the feasibility of utilizing the time-resolved femtosecond acoustics technique to extract the elastic properties and mass density of a 1.85-nm-thick interfacial layer, with the aid of transmission electron microscopy. We believe that this femtosecond acoustics approach will provide a strategy to measure the absolute elastic properties of atomically thin interfacial layers.

Triangular lattice atomic layer of Sn(1 × 1) at graphene/SiC(0001) interface

NASA Astrophysics Data System (ADS)

Hayashi, Shingo; Visikovskiy, Anton; Kajiwara, Takashi; Iimori, Takushi; Shirasawa, Tetsuroh; Nakastuji, Kan; Miyamachi, Toshio; Nakashima, Shuhei; Yaji, Koichiro; Mase, Kazuhiko; Komori, Fumio; Tanaka, Satoru

2018-01-01

Sn atomic layers attract considerable interest owing to their spin-related physical properties caused by their strong spin-orbit interactions. We performed Sn intercalation into the graphene/SiC(0001) interface and found a new type of Sn atomic layer. Sn atoms occupy on-top sites of Si-terminated SiC(0001) with in-plane Sn-Sn bondings, resulting in a triangular lattice. Angle-resolved photoemission spectroscopy revealed characteristic dispersions at \\bar{\\text{K}} and \\bar{\\text{M}} points, which agreed well with density functional theory calculations. The Sn triangular lattice atomic layer at the interface showed no oxidation upon exposure to air, which is useful for characterization and device fabrication ex situ.

Coated armor system and process for making the same

DOEpatents

Chu, Henry S.; Lillo, Thomas M.; McHugh, Kevin M.

2010-11-23

An armor system and method involves providing a core material and a stream of atomized coating material that comprises a liquid fraction and a solid fraction. An initial layer is deposited on the core material by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is less than the liquid fraction of the stream of atomized coating material on a weight basis. An outer layer is then deposited on the initial layer by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is greater than the liquid fraction of the stream of atomized coating material on a weight basis.

Armor systems including coated core materials

DOEpatents

Chu, Henry S [Idaho Falls, ID; Lillo, Thomas M [Idaho Falls, ID; McHugh, Kevin M [Idaho Falls, ID

2012-07-31

An armor system and method involves providing a core material and a stream of atomized coating material that comprises a liquid fraction and a solid fraction. An initial layer is deposited on the core material by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is less than the liquid fraction of the stream of atomized coating material on a weight basis. An outer layer is then deposited on the initial layer by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is greater than the liquid fraction of the stream of atomized coating material on a weight basis.

Armor systems including coated core materials

DOEpatents

Chu, Henry S; Lillo, Thomas M; McHugh, Kevin M

2013-10-08

An armor system and method involves providing a core material and a stream of atomized coating material that comprises a liquid fraction and a solid fraction. An initial layer is deposited on the core material by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is less than the liquid fraction of the stream of atomized coating material on a weight basis. An outer layer is then deposited on the initial layer by positioning the core material in the stream of atomized coating material wherein the solid fraction of the stream of atomized coating material is greater than the liquid fraction of the stream of atomized coating material on a weight basis.

In situ monitoring of atomic layer epitaxy via optical ellipsometry

NASA Astrophysics Data System (ADS)

Lyzwa, F.; Marsik, P.; Roddatis, V.; Bernhard, C.; Jungbauer, M.; Moshnyaga, V.

2018-03-01

We report on the use of time-resolved optical ellipsometry to monitor the deposition of single atomic layers with subatomic sensitivity. Ruddlesden-Popper thin films of SrO(SrTiO3) n=4 were grown by means of metalorganic aerosol deposition in the atomic layer epitaxy mode on SrTiO3(1 0 0), LSAT(1 0 0) and DyScO3(1 1 0) substrates. The measured time dependences of ellipsometric angles, Δ(t) and Ψ(t), were described by using a simple optical model, considering the sequence of atomic layers SrO and TiO2 with corresponding bulk refractive indices. As a result, valuable online information on the atomic layer epitaxy process was obtained. Ex situ characterization techniques, i.e. transmission electron microscopy, x-ray diffraction and x-ray reflectometry verify the crystal structure and confirm the predictions of optical ellipsometry.

Atom Probe Tomography Analysis of Ag Doping in 2D Layered Material (PbSe) 5(Bi 2Se 3) 3

DOE PAGES

Ren, Xiaochen; Singh, Arunima K.; Fang, Lei; ...

2016-09-07

Impurity doping in two-dimensional (2D) materials can provide a route to tuning electronic properties, so it is important to be able to determine the distribution of dopant atoms within and between layers. Here we report the totnographic mapping of dopants in layered 2D materials with atomic sensitivity and subnanometer spatial resolution using atom, probe tomography (APT). Also, APT analysis shows that Ag dopes both Bi 2Se 3 and PbSe layers in (PbSe) 5(Bi 2Se 3) 3, and correlations :in the position of Ag atoms suggest a pairing across neighboring Bi 2Se 3 and PbSe layers. Finally, density functional theory (DFT)more » calculations confirm the favorability of substitutional-doping for both Pb and Bi and provide insights into the,observed spatial correlations in dopant locations.« less

Atomic Oxygen Durability of Second Surface Silver Microsheet Glass Concentrators

NASA Technical Reports Server (NTRS)

deGroh, Kim K.; Jaworske, Donald A.; Smith, Daniela C.; Mroz, Thaddeus S.

1996-01-01

Second surface silver microsheet glass concentrators are being developed for potential use in future solar dynamic space power systems. Traditional concentrators are aluminum honeycomb sandwich composites with either aluminum or graphite epoxy face sheets, where a reflective aluminum layer is deposited onto an organic leveling layer on the face sheet. To protect the underlying layers, a SiO2 layer is applied on top of the aluminum reflective layer. These concentrators may be vulnerable to atomic oxygen degradation due to possible atomic oxygen attack of the organic layers at defect sites in the protective and reflective coatings. A second surface microsheet glass concentrator would be inherently more atomic oxygen durable than these first surface concentrators. In addition, a second surface microsheet glass concentrator design provides a smooth optical surface and allows for silver to be used as a reflective layer, which would improve the reflectivity of the concentrator and the performance of the system. A potential threat to the performance of second surface microsheet glass concentrators is atomic oxygen attack of the underlying silver at seams and edges or at micrometeoroid and debris (MMD) impacts sites. Second surface silver microsheet glass concentrator samples were fabricated and tested for atomic oxygen durability. The samples were iteratively exposed to an atomic oxygen environment in a plasma asher. Samples were evaluated for potential degradation at fabrication seams, simulated MMD impact sites, and edges. Optical microscopy was used to evaluate atomic oxygen degradation. Reflectance was obtained for an impacted sample prior to and after atomic oxygen exposure. After an initial atomic oxygen exposure to an effective fluence of approx. 1 x 10(exp 21) atoms/cm(exp 2), oxidation of the silver at defect sites and edges was observed. Exposure to an additional approx. 1 x 10(exp 21) atoms/cm(exp 2) caused no observed increase in oxidation. Oxidation at an impact site caused negligible changes in reflectance. In all cases oxidation was found to be confined to the vicinity of the seams, impact sites, edges or defect sites. Asher to in-space atomic oxygen correlation issues will be addressed.

Surface passivation investigation on ultra-thin atomic layer deposited aluminum oxide layers for their potential application to form tunnel layer passivated contacts

NASA Astrophysics Data System (ADS)

Xin, Zheng; Ling, Zhi Peng; Nandakumar, Naomi; Kaur, Gurleen; Ke, Cangming; Liao, Baochen; Aberle, Armin G.; Stangl, Rolf

2017-08-01

The surface passivation performance of atomic layer deposited ultra-thin aluminium oxide layers with different thickness in the tunnel layer regime, i.e., ranging from one atomic cycle (∼0.13 nm) to 11 atomic cycles (∼1.5 nm) on n-type silicon wafers is studied. The effect of thickness and thermal activation on passivation performance is investigated with corona-voltage metrology to measure the interface defect density D it(E) and the total interface charge Q tot. Furthermore, the bonding configuration variation of the AlO x films under various post-deposition thermal activation conditions is analyzed by Fourier transform infrared spectroscopy. Additionally, poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) is used as capping layer on ultra-thin AlO x tunneling layers to further reduce the surface recombination current density to values as low as 42 fA/cm2. This work is a useful reference for using ultra-thin ALD AlO x layers as tunnel layers in order to form hole selective passivated contacts for silicon solar cells.

Additives to reduce susceptibility of thermosets and thermoplastics to erosion from atomic oxygen

NASA Technical Reports Server (NTRS)

Orwoll, Robert A.

1990-01-01

Polymeric materials have many attractive features such as light weight, high strength, and broad applicability in the form of films, fibers, and molded objects. In low earth orbit (LEO), these materials, when exposed on the exterior of the spacecraft, have the serious disadvantage of being susceptible to erosion by atomic oxygen (AO). AO is the most common chemical species at LEO altitudes. AO can be an extremely efficient oxidizing agent as was apparent from the extensive erosion of organic films exposed in STS missions. The mechanism for erosion involves the reaction of oxygen atoms at the surface of the substrate to form small molecular species. The susceptibility of polymeric materials varies with their chemical composition. Films with silicon atoms incorporated in the molecular structures have large coefficients of thermal expansion. This limits their utility. In an alternative approach additives were sought that mix physically and form a protective oxide layer when the film is exposed to AO. A large number of organic compounds containing silicon, germanium, or tin atoms were screened. Most were found to have very limited solubility in the polyetherimide (Ultem) films that were being protected from AO. However, one, bis(triphenyl tin) oxide, (BTO), is miscible in Ultem up to about 25 percent. Films of Ultem polyimide containing up to 25 wt percent BTO were prepared by evaporation of solvent from a solution of Ultem and BTO. The effects of AO on these films were simulated in the oxygen atmosphere of a radio frequency glow-discharge chamber. In the second part of this study, atoms were incorporated in epoxy resins. Experiments are in progress to measure the resistance of films of the cured epoxy to AO in the discharge chamber.

Imprint control of BaTiO 3 thin films via chemically induced surface polarization pinning

DOE PAGES

Lee, Hyungwoo; Kim, Tae Heon; Patzner, Jacob J.; ...

2016-02-22

Surface-adsorbed polar molecules can significantly alter the ferroelectric properties of oxide thin films. Thus, fundamental understanding and controlling the effect of surface adsorbates are crucial for the implementation of ferroelectric thin film devices, such as ferroelectric tunnel junctions. Herein, we report an imprint control of BaTiO 3 (BTO) thin films by chemically induced surface polarization pinning in the top few atomic layers of the water-exposed BTO films. Our studies based on synchrotron X-ray scattering and coherent Bragg rod analysis demonstrate that the chemically induced surface polarization is not switchable but reduces the polarization imprint and improves the bistability of ferroelectricmore » phase in BTO tunnel junctions. Here, we conclude that the chemical treatment of ferroelectric thin films with polar molecules may serve as a simple yet powerful strategy to enhance functional properties of ferroelectric tunnel junctions for their practical applications.« less

High enthalpy hypersonic boundary layer flow

NASA Technical Reports Server (NTRS)

Yanow, G.

1972-01-01

A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.

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

Thi, Trinh Cham, E-mail: s1240009@jaist.ac.jp; Koyama, Koichi; Ohdaira, Keisuke

We improve the passivation property of n-type crystalline silicon (c-Si) surface passivated with a catalytic chemical vapor deposited (Cat-CVD) Si nitride (SiN{sub x}) film by inserting a phosphorous (P)-doped layer formed by exposing c-Si surface to P radicals generated by the catalytic cracking of PH{sub 3} molecules (Cat-doping). An extremely low surface recombination velocity (SRV) of 2 cm/s can be achieved for 2.5 Ω cm n-type (100) floating-zone Si wafers passivated with SiN{sub x}/P Cat-doped layers, both prepared in Cat-CVD systems. Compared with the case of only SiN{sub x} passivated layers, SRV decreases from 5 cm/s to 2 cm/s. The decrease in SRVmore » is the result of field effect created by activated P atoms (donors) in a shallow P Cat-doped layer. Annealing process plays an important role in improving the passivation quality of SiN{sub x} films. The outstanding results obtained imply that SiN{sub x}/P Cat-doped layers can be used as promising passivation layers in high-efficiency n-type c-Si solar cells.« less

High Ms Fe16N2 thin film with Ag under layer on GaAs substrate

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

Allard Jr, Lawrence Frederick

2016-01-01

(001) textured Fe16N2 thin film with Ag under layer is successfully grown on GaAs substrate using a facing target sputtering (FTS) system. After post annealing, chemically ordered Fe16N2 phase is formed and detected by X-ray diffraction (XRD). High saturation magnetization (Ms) is measured by a vibrating sample magnetometer (VSM). In comparison with Fe16N2 with Ag under layer on MgO substrate and Fe16N2 with Fe under layer on GaAs substrate, the current layer structure shows a higher Ms value, with a magnetically softer feature in contrast to the above cases. In addition, X-ray photoelectron spectroscopy (XPS) is performed to characterize themore » binding energy of N atoms. To verify the role of strain that the FeN layer experiences in the above three structures, Grazing Incidence X-ray Diffraction (GIXRD) is conducted to reveal a large in-plane lattice constant due to the in-plane biaxial tensile strain. INTRODUCTION« less

Surface cleaning for negative electron affinity GaN photocathode

NASA Astrophysics Data System (ADS)

Qiao, Jianliang; Yin, Yingpeng; Gao, Youtang; Niu, Jun; Qian, Yunsheng; Chang, Benkang

2012-10-01

In the preparation process for negative electron affinity (NEA) GaN photocathode, the surface cleanness is very important to activation, it influences the sensitivity and stability of NEA GaN photocathode. The traditional corrosion methods based on oxidizing and dissolving can't remove oxygen (O) and carbon (C) on GaN surface effectively. How to get an ideal atom clean surface is still an important question at present. The cleaning techniques for GaN photocathode was studied by using NEA photocathode activation system and XPS surface analysis system. The experiment sample is p-type GaN doped with Mg, doped concentration is 1.37×1017 cm-3, the transfer rate is 3.08 cm2/V-S, and the thickness of activation layer is 0.51 μm, the substrate is 300 μm thick sapphire. The sample was dealed with chemical cleaning depuration at first. And to get the atom clean surface, the vacuum heat cleaning process was needed. The methods of chemical cleaning and the vacuum heating cleaning were given in detail. According to the X-ray photoelectron spectroscopy of GaN surface after chemical cleaning and the vacuum degree curve of the activation chamber during the heat cleaning, the cleaning effect and the cleaning mechanism were discussed. After the effective chemical cleaning and the heating of 700 Centigrade degree about 20 minutes in ultrahigh vacuum system, the oxides and carbon contaminants on cathode surface can be removed effectively, and the ideal atom clean surface can be obtained. The purpose of heating depuration process is that not only to get the atom clean GaN surface, but also to guarantee the contents of Ga, N on GaN surface stabilize and to keep the system ultra-high vacuum degree. Because of the volatilization of oxide and carbon impurity on the cathode surface, the vacuum degree curve drops with the rising of temperature on the whole.

Atomic hydrogen storage method and apparatus

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1978-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid helium temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Atomic hydrogen storage method and apparatus

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1980-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compounds maintained at liquid helium temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Atomic hydrogen storage. [cryotrapping and magnetic field strength

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1980-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Using Meteoric Ablation to Constrain Vertical Transport in the Upper Mesosphere

NASA Astrophysics Data System (ADS)

Plane, J. M. C.; Carrillo-Sánchez, J. D.; Nesvorny, D.; Pokorný, P.; Janches, D.

2016-12-01

Meteoric ablation injects a variety of metals into the upper mesosphere and lower thermosphere, giving rise to layers of metal atoms centered around 90 km. The Na, Fe, K and Ca atom densities are measured accurately using resonance lidars. Since the reaction kinetics of many of the chemical reactions which produce these layers have now been studied in the laboratory, chemistry modules for each of the metals have been developed with a reasonable degree of confidence. When these modules are put into a global high-top model such as NCAR's Whole Atmosphere Community Climate Model (WACCM), a major problem emerges: the injection flux of each of the metals, termed the Meteoric Input Function (MIF), has to be reduced substantially in order to model the observed metal atom densities. For instance, the Na and Fe MIFs need to be reduced by factors of 8 and 14, respectively, compared with the MIFs determined from the lidar-measured vertical fluxes of Na and Fe atoms. The accumulation of meteoric smoke particles in polar ice cores also indicates that the meteoric ablation flux is significantly larger that can be handled in models where vertical transport is solely due to eddy diffusional mixing. Here we derive new Na and Fe MIFs by determining the relative contributions of the known dust sources in the near-Earth environment: Jupiter Family Comets (JFCs), the main asteroid belt, Halley Type comets, and Oort Cloud comets. The mass/velocity/radiant distributions of these cosmic dust populations are Monte Carlo sampled and the elemental ablation rates calculated with the Leeds Chemical Ablation Model. The contribution of each dust source in the Earth's atmosphere is then determined by fitting the measured cosmic spherule accretion rate at the South Pole, and the measured vertical Na and Fe fluxes above 86 km. We conclude that JFCs contribute either 85% or 93% to the total incoming mass, depending on whether infra-red observations of the Zodiacal Dust Cloud by the IRAS or Planck satellites, respectively, are used. The global ablated meteoric mass is then 6 tonnes per day, of which 0.2 tonnes is Na and 2.1 tonnes is Fe. We show that these large fluxes can be accommodated by including wave-driven chemical transport along with eddy diffusion in a 1-D model.

Studies of carbon incorporation on the diamond [100] surface during chemical vapor deposition using density functional theory.

PubMed

Cheesman, Andrew; Harvey, Jeremy N; Ashfold, Michael N R

2008-11-13

Accurate potential energy surface calculations are presented for many of the key steps involved in diamond chemical vapor deposition on the [100] surface (in its 2 x 1 reconstructed and hydrogenated form). The growing diamond surface was described by using a large (approximately 1500 atoms) cluster model, with the key atoms involved in chemical steps being described by using a quantum mechanical (QM, density functional theory, DFT) method and the bulk of the atoms being described by molecular mechanics (MM). The resulting hybrid QM/MM calculations are more systematic and/or at a higher level of theory than previous work on this growth process. The dominant process for carbon addition, in the form of methyl radicals, is predicted to be addition to a surface radical site, opening of the adjacent C-C dimer bond, insertion, and ultimate ring closure. Other steps such as insertion across the trough between rows of dimer bonds or addition to a neighboring dimer leading to formation of a reconstruction on the next layer may also contribute. Etching of carbon can also occur; the most likely mechanism involves loss of a two-carbon moiety in the form of ethene. The present higher-level calculations confirm that migration of inserted carbon along both dimer rows and chains should be relatively facile, with barriers of approximately 150 kJ mol (-1) when starting from suitable diradical species, and that this step should play an important role in establishing growth of smooth surfaces.

Superconducting and Magnetic Properties of Vanadium/iron Superlattices.

NASA Astrophysics Data System (ADS)

Wong, Hong-Kuen

A novel ultrahigh vacuum evaporator was constructed for the preparation of superlattice samples. The thickness control was much better than an atomic plane. With this evaporator we prepared V/Fe superlattice samples on (0001) sapphire substrates with different thicknesses. All samples showed a good bcc(110) structure. Mossbauer experiments showed that the interface mixing extended a distance of about one atomic plane indicating an almost rectangular composition profile. Because of this we were able to prepare samples with layer thickness approaching one atomic plane. Even with ultrathin Fe layers, the samples are ferromagnetic, at least at lower temperatures. Superparamagnetism and spin glass states were not seen. In the absence of an external field, the magnetic moments lie close to the film plane. In addition to this shape anisotropy, there is some uniaxial anisotropy. No magnetic dead layers have been observed. The magnetic moments within the Fe layers vary little with the distance from the interfaces. At the interfaces the Fe moment is reduced and an antiparallel moment is induced on the vanadium atoms. It is observed that ultrathin Fe layers behave in a 2D fashion when isolated by sufficiently thick vanadium layers; however, on thinning the vanadium layers, a magnetic coupling between the Fe layers has been observed. We also studied the superconducting properties of V/Fe sandwiches and superlattices. In both cases, the Fe layer, a strong pair-breaker, suppresses the superconducting transition temperature consistent with the current knowledge of the magnetic proximity effect. For the sandwiches with thin (thick) vanadium layers, the temperature dependence of the upper critical fields is consistent with the simple theory for a 2D (3D) superconductor. For the superlattices, when the vanadium layer is on the order of the BCS coherence length and the Fe layer is only a few atomic planes thick, a 2D-3D crossover has been observed in the temperature dependence of the parallel upper critical field. This implies the coexistence of superconductivity and ferromagnetism. We observe three dimensional behavior for thinner Fe layers ((TURN)1 atomic plane) and two dimensional behavior for thicker Fe layers (greater than 10 atomic planes).

X-ray absorption spectra: Graphene, h-BN, and their alloy

NASA Astrophysics Data System (ADS)

Bhowmick, Somnath; Rusz, Jan; Eriksson, Olle

2013-04-01

Using first-principles density functional theory calculations, in conjunction with the Mahan-Nozières-de Dominicis theory, we calculate the x-ray absorption spectra of the alloys of graphene and monolayer hexagonal boron nitride on a Ni (111) substrate. The chemical neighborhood of the constituent atoms (B, C, and N) inside the alloy differs from that of the parent phases. In a systematic way, we capture the change in the K-edge spectral shape, depending on the chemical neighborhood of B, C, and N. Our work also reiterates the importance of the dynamical core-hole screening for a proper description of the x-ray absorption process in sp2-bonded layered materials.

Growth of single-layer graphene on Ge (1 0 0) by chemical vapor deposition

NASA Astrophysics Data System (ADS)

Mendoza, C. D.; Caldas, P. G.; Freire, F. L.; Maia da Costa, M. E. H.

2018-07-01

The integration of graphene into nanoelectronic devices is dependent on the availability of direct deposition processes, which can provide uniform, large-area and high-quality graphene on semiconductor substrates such as Ge or Si. In this work, we synthesised graphene directly on p-type Ge (1 0 0) substrates by chemical vapour deposition. The influence of the CH4:H2 flow ratio on the graphene growth was investigated. Raman Spectroscopy, Raman mapping, Scanning Electron Microscopy, Atomic Force Microscopy and Scanning Tunnelling Microscopy/Scanning Tunnelling Spectroscopy results showed that good quality and homogeneous monolayer graphene over a large area can be achieved on Ge substrates directly with optimal growth conditions.

Heteroepitaxial growth of Cd(1-x)Mn(x)Te on GaAs by metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Nouhi, Akbar; Stirn, Richard J.

1987-01-01

In this letter, preliminary results are reported of heteroepitaxial growth of the dilute magnetic semiconductor alloy Cd(1-x)Mn(x)Te on GaAs by metalorganic chemical vapor deposition. Dimethylcadmium (DMCd), diethyltellurium (DETe), and tricarbonyl (methylcyclopentadienyl) manganese (TCPMn) were used as source materials. The TCPMn had to be heated to as high as 140 C to provide the required vapor pressure. Films with Mn atomic fractions up to 30 percent have been grown over the temperature range 410-450 C. Results of optical absorption/transmission, photoluminescence, and X-ray diffraction measurements are presented along with a scanning electron micrograph showing good surface morphology of the grown layers.

Effects of argon sputtering and UV-ozone radiation on the physico-chemical surface properties of ITO

NASA Astrophysics Data System (ADS)

Che, Hui; El Bouanani, M.

2018-01-01

X-ray photoelectron spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS) were used to evaluate and determine the effects of 1 KeV Ar+ irradiation (sputtering) on the surface chemical composition and work function of Indium Thin Oxide (ITO). While Ar+ sputtering removes carbon-based surface contaminants, it also modifies the Sn-rich surface of ITO and leads to a reduction of the oxidation state of Sn from Sn4+ to Sn2+. The decrease in the work function of ITO is directly correlated to the decrease of Sn atomic concentration in the Sn-rich top surface layer and the reduction of the oxidation state of surface Sn.

Crystalline boron nitride aerogels

DOEpatents

Zettl, Alexander K.; Rousseas, Michael; Goldstein, Anna P.; Mickelson, William; Worsley, Marcus A.; Woo, Leta

2017-04-04

This disclosure provides methods and materials related to boron nitride aerogels. In one aspect, a material comprises an aerogel comprising boron nitride. The boron nitride has an ordered crystalline structure. The ordered crystalline structure may include atomic layers of hexagonal boron nitride lying on top of one another, with atoms contained in a first layer being superimposed on atoms contained in a second layer.

Multimillion atom simulations of dynamics of oxidation of an aluminum nanoparticle and nanoindentation on ceramics.

PubMed

Vashishta, Priya; Kalia, Rajiv K; Nakano, Aiichiro

2006-03-02

We have developed a first-principles-based hierarchical simulation framework, which seamlessly integrates (1) a quantum mechanical description based on the density functional theory (DFT), (2) multilevel molecular dynamics (MD) simulations based on a reactive force field (ReaxFF) that describes chemical reactions and polarization, a nonreactive force field that employs dynamic atomic charges, and an effective force field (EFF), and (3) an atomistically informed continuum model to reach macroscopic length scales. For scalable hierarchical simulations, we have developed parallel linear-scaling algorithms for (1) DFT calculation based on a divide-and-conquer algorithm on adaptive multigrids, (2) chemically reactive MD based on a fast ReaxFF (F-ReaxFF) algorithm, and (3) EFF-MD based on a space-time multiresolution MD (MRMD) algorithm. On 1920 Intel Itanium2 processors, we have demonstrated 1.4 million atom (0.12 trillion grid points) DFT, 0.56 billion atom F-ReaxFF, and 18.9 billion atom MRMD calculations, with parallel efficiency as high as 0.953. Through the use of these algorithms, multimillion atom MD simulations have been performed to study the oxidation of an aluminum nanoparticle. Structural and dynamic correlations in the oxide region are calculated as well as the evolution of charges, surface oxide thickness, diffusivities of atoms, and local stresses. In the microcanonical ensemble, the oxidizing reaction becomes explosive in both molecular and atomic oxygen environments, due to the enormous energy release associated with Al-O bonding. In the canonical ensemble, an amorphous oxide layer of a thickness of approximately 40 angstroms is formed after 466 ps, in good agreement with experiments. Simulations have been performed to study nanoindentation on crystalline, amorphous, and nanocrystalline silicon nitride and silicon carbide. Simulation on nanocrystalline silicon carbide reveals unusual deformation mechanisms in brittle nanophase materials, due to coexistence of brittle grains and soft amorphous-like grain boundary phases. Simulations predict a crossover from intergranular continuous deformation to intragrain discrete deformation at a critical indentation depth.

Laser polishing for topography management of accelerator cavity surfaces

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

Zhao, Liang; Klopf, J. Mike; Reece, Charles E.

2015-07-20

Improved energy efficiency and reduced cost are greatly desired for advanced particle accelerators. Progress toward both can be made by atomically-smoothing the interior surface of the niobium superconducting radiofrequency accelerator cavities at the machine's heart. Laser polishing offers a green alternative to the present aggressive chemical processes. We found parameters suitable for polishing niobium in all surface states expected for cavity production. As a result, careful measurement of the resulting surface chemistry revealed a modest thinning of the surface oxide layer, but no contamination.

Simulation of the Dynamics of Isothermal Growth of Single-Layer Graphene on a Copper Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

NASA Astrophysics Data System (ADS)

Futko, S. I.; Shulitskii, B. G.; Labunov, V. A.; Ermolaeva, E. M.

2018-01-01

A new kinetic model of isothermal growth of single-layer graphene on a copper catalyst as a result of the chemical vapor deposition of hydrocarbons on it at a low pressure has been developed on the basis of in situ measurements of the growth of graphene in the process of its synthesis. This model defines the synthesis of graphene with regard for the chemisorption and catalytic decomposition of ethylene on the surface of a copper catalyst, the diffusion of carbon atoms in the radial direction to the nucleation centers within the thin melted near-surface copper layer, and the nucleation and autocatalytic growth of graphene domains. It is shown that the time dependence of the rate of growth of a graphene domain has a characteristic asymmetrical bell-like shape. The dependences of the surface area and size of a graphene domain and the rate of its growth on the time at different synthesis temperatures and ethylene concentrations have been obtained. Time characteristics of the growth of graphene domains depending on the parameters of their synthesis were calculated. The results obtained can be used for determining optimum regimes of synthesis of graphene in the process of chemical vapor deposition of hydrocarbons on different catalysts with a low solubility of carbon.

Optimization Methods on Synthesis of Atomically Thin Layered Materials and Heterostructures

NASA Astrophysics Data System (ADS)

Temiz, Selcuk

Two dimensional (2D) materials have emerged as a new class of materials that only a few atoms thick. Owing to their low dimensionality, 2D materials bear rather unusual properties that do not exist in traditional three dimensional (3D) materials. Graphene, a single layer of carbon atoms arrange in a 2D hexagonal lattice, has started the revolutionary progress in materials science and condensed matter physics, and motivated intense research in other 2D materials such as h-BN, and layered metal dichalcogenides. Chemical vapor deposition (CVD) is the most studied bottom-up graphene production method for building the prototypes of next-generation electronic devices due to its scalability; however, there is still not an ultimate consensus of growth mechanisms on control the size and morphology of synthesized-crystals. In order to have better understanding the growth mechanisms, the role of oxygen exposure in the graphene growth has been comprehensively studied. The oxygen gas is introduced into the CVD reactor before and during the growth, and its effects on the morphology, crystallinity, and nucleation density of graphene are systematically studied. It is found that introducing oxygen during growth significantly improves the graphene crystallinity while pre-dosing oxygen before growth reduces the graphene nucleation density. The stacking of graphene and other layered materials in the lateral or vertical geometries can offer extended functionality by exploiting interfacial phenomena, quantum confinement and tunneling, which requires the interface between the layered materials be free of contaminates. The vertical heterostructures of CVD-grown graphene and h-BN single crystals are deeply investigated by analytical scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). It is shown that graphene contamination, undetectable using optical microscopy, is prevalent at the nanoscale, and the interfacial contamination between the layers reduces the interlayer coupling and ultimately undermines the graphene/h-BN heterostructures. Raman spectroscopy is a versatile and non-destructive technique for the identification of structural properties and phonon features of atomically thin layered materials. Especially, the second order resonant Raman spectroscopy, which can be applied to the resonance conditions in energy of the incoming photon and interband transitions of an electron in a crystal lattice, reveals additional phonon modes to typical Raman active modes in a spectra. Various 2D materials, including SnSe2, WSe2, SnS2, and MoTe2, and their heterostructures are fabricated by dry transfer method as a top-down approach. The vibrational characteristics of these 2D materials systems are unambiguously established by using second order Resonant Raman spectroscopy.