Diffusion of One-Dimensional Crystals in Channels of Single-Walled Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Zhigalina, V. G.; Kumskov, A. S.; Falaleev, N. S.; Vasiliev, A. L.; Kiselev, N. A.

2018-05-01

The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10-21 m2/s, which corresponds to an activation-barrier height of 1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene.

Optical coupling between atomically thin black phosphorus and a two dimensional photonic crystal nanocavity

NASA Astrophysics Data System (ADS)

Ota, Yasutomo; Moriya, Rai; Yabuki, Naoto; Arai, Miho; Kakuda, Masahiro; Iwamoto, Satoshi; Machida, Tomoki; Arakawa, Yasuhiko

2017-05-01

Atomically thin black phosphorus (BP) is an emerging two dimensional (2D) material exhibiting bright photoluminescence in the near infrared region. Coupling its radiation to photonic nanostructures will be an important step toward the realization of 2D material based nanophotonic devices that operate efficiently in the near infrared region, which includes the technologically important optical telecommunication wavelength bands. In this letter, we demonstrate the optical coupling between atomically thin BP and a 2D photonic crystal nanocavity. We employed a home-build dry transfer apparatus for placing a thin BP flake on the surface of the nanocavity. Their optical coupling was analyzed through measuring cavity mode emission under optical carrier injection at room temperature.

Manufacturing method of photonic crystal

DOEpatents

Park, In Sung; Lee, Tae Ho; Ahn, Jin Ho; Biswas, Rana; Constant, Kristen P.; Ho, Kai-Ming; Lee, Jae-Hwang

2013-01-29

A manufacturing method of a photonic crystal is provided. In the method, a high-refractive-index material is conformally deposited on an exposed portion of a periodic template composed of a low-refractive-index material by an atomic layer deposition process so that a difference in refractive indices or dielectric constants between the template and adjacent air becomes greater, which makes it possible to form a three-dimensional photonic crystal having a superior photonic bandgap. Herein, the three-dimensional structure may be prepared by a layer-by-layer method.

Crystal structure of the co-crystal fac-tri-aqua-tris(thio-cyanato-κN)iron(III)-2,3-di-methyl-pyrazine (1/3).

PubMed

Kucheriv, Olesia I; Shylin, Sergii I; Ilina, Tetiana A; Dechert, Sebastian; Gural'skiy, Il'ya A

2015-04-01

In the crystal of the title compound, [Fe(NCS)3(H2O)3]·3C6H8N2, the Fe(III) cation is located on a threefold rotation axis and is coordinated by three N atoms of the thiocyanate anions and three water mol-ecules in a fac arrangement, forming a slightly distorted N3O3 octa-hedron. Stabilization within the crystal structure is provided by O-H⋯N hydrogen bonds; the H atoms from coordinating water mol-ecules act as donors to the N atoms of guest 2,3-di-methyl-pyrazine mol-ecules, leading to a three-dimensional supra-molecular framework.

Three-dimensional structure of porcine pancreatic carboxypeptidase B with an acetate ion and two zinc atoms in the active site

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

Akparov, V. Kh., E-mail: valery@akparov.ru; Timofeev, V. I., E-mail: tostars@mail.ru; Maghsoudi, N. N., E-mail: maghsudi@yahoo.com

2017-03-15

Crystals of porcine pancreatic carboxypeptidase B (CPB) were grown by the capillary counter-diffusion method in the presence of polyethylene glycol and zinc acetate. The three-dimensional structure of CPB was determined at 1.40 Å resolution using the X-ray diffraction data set collected from the crystals of the enzyme at the SPring 8 synchrotron facility and was refined to R{sub fact} = 17.19%, R{sub free} = 19.78%. The structure contains five zinc atoms, two of which are present in the active site of the enzyme, and an acetate ion. The arrangement of an additional zinc atom in the active site and themore » acetate ion is different from that reported by Yoshimoto et al.« less

Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction

PubMed Central

2014-01-01

Semiconductor heterostructures form the cornerstone of many electronic and optoelectronic devices and are traditionally fabricated using epitaxial growth techniques. More recently, heterostructures have also been obtained by vertical stacking of two-dimensional crystals, such as graphene and related two-dimensional materials. These layered designer materials are held together by van der Waals forces and contain atomically sharp interfaces. Here, we report on a type-II van der Waals heterojunction made of molybdenum disulfide and tungsten diselenide monolayers. The junction is electrically tunable, and under appropriate gate bias an atomically thin diode is realized. Upon optical illumination, charge transfer occurs across the planar interface and the device exhibits a photovoltaic effect. Advances in large-scale production of two-dimensional crystals could thus lead to a new photovoltaic solar technology. PMID:25057817

Spin-orbit interaction of light on the surface of atomically thin crystals

NASA Astrophysics Data System (ADS)

Zhou, Junxiao; Chen, Shizhen; Zhang, Wenshuai; Luo, Hailu; Wen, Shuangchun

2017-09-01

Two-dimensional (2D) atomic crystals have extraordinary electronic and photonic properties and hold great promise in the applications of photonic and optoelectronics. Here, we review some of our works about the spin-orbit interaction of light on the surface of 2D atomic crystals. First, we propose a general model to describe the spin-orbit interaction of light of the 2D free standing atomic crystal, and find that it is not necessary to involve the effective refractive index to describe the spin-orbit interaction. By developing the quantum weak measurements, we detect the spin-orbit interaction of light in 2D atomic crystals, which can act as a simple method for defining the layer numbers of graphene. Moreover, we find the transverse spin-dependent splitting in the photonic spin Hall effect exhibits a quantized behavior. Furthermore, the spin-orbit interaction of light for the case of air-topological insulator interface can be routed by adjusting the strength of the axion coupling. These basic finding may enhance the comprehension of the spin-orbit interaction, and find the important application in optoelectronic.

Resolution extension by image summing in serial femtosecond crystallography of two-dimensional membrane-protein crystals

DOE PAGES

Casadei, Cecilia M.; Tsai, Ching-Ju; Barty, Anton; ...

2018-01-01

Previous proof-of-concept measurements on single-layer two-dimensional membrane-protein crystals performed at X-ray free-electron lasers (FELs) have demonstrated that the collection of meaningful diffraction patterns, which is not possible at synchrotrons because of radiation-damage issues, is feasible. Here, the results obtained from the analysis of a thousand single-shot, room-temperature X-ray FEL diffraction images from two-dimensional crystals of a bacteriorhodopsin mutant are reported in detail. The high redundancy in the measurements boosts the intensity signal-to-noise ratio, so that the values of the diffracted intensities can be reliably determined down to the detector-edge resolution of 4 Å. The results show that two-dimensional serial crystallography atmore » X-ray FELs is a suitable method to study membrane proteins to near-atomic length scales at ambient temperature. The method presented here can be extended to pump–probe studies of optically triggered structural changes on submillisecond timescales in two-dimensional crystals, which allow functionally relevant large-scale motions that may be quenched in three-dimensional crystals.« less

Resolution extension by image summing in serial femtosecond crystallography of two-dimensional membrane-protein crystals

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

Casadei, Cecilia M.; Tsai, Ching-Ju; Barty, Anton

Previous proof-of-concept measurements on single-layer two-dimensional membrane-protein crystals performed at X-ray free-electron lasers (FELs) have demonstrated that the collection of meaningful diffraction patterns, which is not possible at synchrotrons because of radiation-damage issues, is feasible. Here, the results obtained from the analysis of a thousand single-shot, room-temperature X-ray FEL diffraction images from two-dimensional crystals of a bacteriorhodopsin mutant are reported in detail. The high redundancy in the measurements boosts the intensity signal-to-noise ratio, so that the values of the diffracted intensities can be reliably determined down to the detector-edge resolution of 4 Å. The results show that two-dimensional serial crystallography atmore » X-ray FELs is a suitable method to study membrane proteins to near-atomic length scales at ambient temperature. The method presented here can be extended to pump–probe studies of optically triggered structural changes on submillisecond timescales in two-dimensional crystals, which allow functionally relevant large-scale motions that may be quenched in three-dimensional crystals.« less

Overview of electron crystallography of membrane proteins: crystallization and screening strategies using negative stain electron microscopy.

PubMed

Nannenga, Brent L; Iadanza, Matthew G; Vollmar, Breanna S; Gonen, Tamir

2013-01-01

Electron cryomicroscopy, or cryoEM, is an emerging technique for studying the three-dimensional structures of proteins and large macromolecular machines. Electron crystallography is a branch of cryoEM in which structures of proteins can be studied at resolutions that rival those achieved by X-ray crystallography. Electron crystallography employs two-dimensional crystals of a membrane protein embedded within a lipid bilayer. The key to a successful electron crystallographic experiment is the crystallization, or reconstitution, of the protein of interest. This unit describes ways in which protein can be expressed, purified, and reconstituted into well-ordered two-dimensional crystals. A protocol is also provided for negative stain electron microscopy as a tool for screening crystallization trials. When large and well-ordered crystals are obtained, the structures of both protein and its surrounding membrane can be determined to atomic resolution.

Coplanar semiconductor-metal circuitry defined on few-layer MoTe2 via polymorphic heteroepitaxy

NASA Astrophysics Data System (ADS)

Sung, Ji Ho; Heo, Hoseok; Si, Saerom; Kim, Yong Hyeon; Noh, Hyeong Rae; Song, Kyung; Kim, Juho; Lee, Chang-Soo; Seo, Seung-Young; Kim, Dong-Hwi; Kim, Hyoung Kug; Yeom, Han Woong; Kim, Tae-Hwan; Choi, Si-Young; Kim, Jun Sung; Jo, Moon-Ho

2017-11-01

Crystal polymorphism selectively stabilizes the electronic phase of atomically thin transition-metal dichalcogenides (TMDCs) as metallic or semiconducting, suggesting the potential to integrate these polymorphs as circuit components in two-dimensional electronic circuitry. Developing a selective and sequential growth strategy for such two-dimensional polymorphs in the vapour phase is a critical step in this endeavour. Here, we report on the polymorphic integration of distinct metallic (1T‧) and semiconducting (2H) MoTe2 crystals within the same atomic planes by heteroepitaxy. The realized polymorphic coplanar contact is atomically coherent, and its barrier potential is spatially tight-confined over a length of only a few nanometres, with a lowest contact barrier height of ∼25 meV. We also demonstrate the generality of our synthetic integration approach for other TMDC polymorph films with large areas.

1D cyanide complexes with 2-pyridinemethanol: Synthesis, crystal structures and spectroscopic properties

NASA Astrophysics Data System (ADS)

Sayın, Elvan; Kürkçüoğlu, Güneş Süheyla; Yeşilel, Okan Zafer; Hökelek, Tuncer

2015-12-01

Two new one-dimensional coordination polymers, [Cu(hmpH)2Pd(μ-CN)2(CN)2]n (1) and [Cu(hmpH)2Pt(μ-CN)2(CN)2]n (2), (hmpH = 2-pyridinemethanol), have been synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal and elemental analyses techniques. Single crystal X-ray diffraction analysis indicates that complexes 1 and 2 are isomorphous and isostructural, and crystallize in the triclinic system and P-1 space group. The Pd(II) or Pt(II) ions are four coordinated with four cyanide-carbon atoms in a square planar geometry. Cu(II) ion displays a distorted octahedral coordination by two N-atoms and two O-atoms of hmpH ligands, two bridging cyanide groups. In one dimensional structure of the complexes, [M(CN)4]2- (M = Pd(II) or Pt(II)) anions and [Cu(hmpH)2]2+ cations are linked via bridging cyanide ligands. In the complexes, the presence of intramolecular C-H⋯M (M = Pd(II) or Pt(II)) interactions with distance values of 3.00-2.95 Å are established, respectively.

Magnetic interactions in a quasi-one-dimensional antiferromagnet Cu(H{sub 2}O){sub 2}(en)SO{sub 4}

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

Sýkora, Rudolf, E-mail: rudolf.sykora@vsb.cz; Legut, Dominik

A theoretical ab-initio investigation of exchange interaction between Cu atoms in an insulating antiferromagnet Cu(H{sub 2}O){sub 2}(en)SO{sub 4}, en = C{sub 2}H{sub 8}N{sub 2}, is reported. While the previous experimental studies described the system's magnetism to be quasi-two-dimensional, our results, based on a mapping of the system onto an effective Heisenberg model, rather support a quasi-one-dimensional character with the exchange coupling between the Cu atoms being propagated mainly along a zigzag line lying in the crystal's bc plane and connecting the Cu atoms through the N atoms. Further, the direction of magnetic moments on the Cu atoms is suggested to be nearlymore » along the crystal's a axis. A check of the change in the exchange constants induced either by external pressure or by various values of U in the GGA + U approximation is made. Finally, based on experimental values of positions of broad maxima in magnetic-susceptibility and specific-heat curves and using theoretical expressions available in the literature a relevant value of the U parameter and related expected value of the electronic gap are estimated to be about 5 eV and 2 eV, respectively.« less

Immunoactive two-dimensional self-assembly of monoclonal antibodies in aqueous solution revealed by atomic force microscopy

NASA Astrophysics Data System (ADS)

Ido, Shinichiro; Kimiya, Hirokazu; Kobayashi, Kei; Kominami, Hiroaki; Matsushige, Kazumi; Yamada, Hirofumi

2014-03-01

The conformational flexibility of antibodies in solution directly affects their immune function. Namely, the flexible hinge regions of immunoglobulin G (IgG) antibodies are essential in epitope-specific antigen recognition and biological effector function. The antibody structure, which is strongly related to its functions, has been partially revealed by electron microscopy and X-ray crystallography, but only under non-physiological conditions. Here we observed monoclonal IgG antibodies in aqueous solution by high-resolution frequency modulation atomic force microscopy (FM-AFM). We found that monoclonal antibodies self-assemble into hexamers, which form two-dimensional crystals in aqueous solution. Furthermore, by directly observing antibody-antigen interactions using FM-AFM, we revealed that IgG molecules in the crystal retain immunoactivity. As the self-assembled monolayer crystal of antibodies retains immunoactivity at a neutral pH and is functionally stable at a wide range of pH and temperature, the antibody crystal is applicable to new biotechnological platforms for biosensors or bioassays.

X-ray fluorescence holography studies for a Cu3Au crystal

NASA Astrophysics Data System (ADS)

Dąbrowski, K. M.; Dul, D. T.; Jaworska-Gołąb, T.; Rysz, J.; Korecki, P.

2015-12-01

In this work we show that performing a numerical correction for beam attenuation and indirect excitation allows one to fully restore element sensitivity in the three-dimensional reconstruction of the atomic structure. This is exemplified by a comparison of atomic images reconstructed from holograms measured for ordered and disordered phases of a Cu3Au crystal that clearly show sensitivity to changes in occupancy of the atomic sites. Moreover, the numerical correction, which is based on quantitative methods of X-ray fluorescence spectroscopy, was extended to take into account the influence of a disturbed overlayer in the sample.

Method for construction of a biased potential for hyperdynamic simulation of atomic systems

NASA Astrophysics Data System (ADS)

Duda, E. V.; Kornich, G. V.

2017-10-01

An approach to constructing a biased potential for hyperdynamic simulation of atomic systems is considered. Using this approach, the diffusion of an atom adsorbed on the surface of a two-dimensional crystal and a vacancy in the bulk of the crystal are simulated. The influence of the variation in the potential barriers due to thermal vibrations of atoms on the results of calculations is discussed. It is shown that the bias of the potential in the hyperdynamic simulation makes it possible to obtain statistical samples of transitions of atomic systems between states, similar to those given by classical molecular dynamics. However, hyperdynamics significantly accelerates computations in comparison with molecular dynamics in the case of temperature-activated transitions and the associated processes in atomic systems.

Crystal structure of 1,2,3,5-di-O-methyl­ene-α-d-xylo­furan­ose

PubMed Central

Tiritiris, Ioannis; Tussetschläger, Stefan; Kantlehner, Willi

2015-01-01

The title compound, C7H10O5, was synthesized by reaction of d-xylose with paraformaldehyde. In the crystal, the central part of the mol­ecule consists of a five-membered C4O ring with an envelope conformation, with the methine C atom adjacent to the O atom being the flap. The protected O atoms of both cyclic acetal groups are oriented so that the four chiral C atoms of the furan­ose part show an R configuration. C—H⋯O hydrogen bonds are present between adjacent mol­ecules, generating a three-dimensional network. PMID:26594582

Crystal structure of poly[{μ-N,N′-bis[(pyridin-4-yl)meth­yl]oxalamide}-μ-oxalato-cobalt(II)

PubMed Central

Zou, Hengye; Qi, Yanjuan

2014-01-01

In the polymeric title compound, [Co(C2O4)(C14H14N4O2)]n, the CoII atom is six-coordinated by two N atoms from symmetry-related bis­[(pyridin-4-yl)meth­yl]oxalamide (BPMO) ligands and four O atoms from two centrosymmetric oxalate anions in a distorted octa­hedral coordination geometry. The CoII atoms are linked by the oxalate anions into a chain running parallel to [100]. The chains are linked by the BPMO ligands into a three-dimensional architecture. In addition, N—H⋯O hydrogen bonds stabilize the crystal packing. PMID:25309173

Fabrication of crystals from single metal atoms

PubMed Central

Barry, Nicolas P. E.; Pitto-Barry, Anaïs; Sanchez, Ana M.; Dove, Andrew P.; Procter, Richard J.; Soldevila-Barreda, Joan J.; Kirby, Nigel; Hands-Portman, Ian; Smith, Corinne J.; O’Reilly, Rachel K.; Beanland, Richard; Sadler, Peter J.

2014-01-01

Metal nanocrystals offer new concepts for the design of nanodevices with a range of potential applications. Currently the formation of metal nanocrystals cannot be controlled at the level of individual atoms. Here we describe a new general method for the fabrication of multi-heteroatom-doped graphitic matrices decorated with very small, ångström-sized, three-dimensional (3D)-metal crystals of defined size. We irradiate boron-rich precious-metal-encapsulated self-spreading polymer micelles with electrons and produce, in real time, a doped graphitic support on which individual osmium atoms hop and migrate to form 3D-nanocrystals, as small as 15 Å in diameter, within 1 h. Crystal growth can be observed, quantified and controlled in real time. We also synthesize the first examples of mixed ruthenium–osmium 3D-nanocrystals. This technology not only allows the production of ångström-sized homo- and hetero-crystals, but also provides new experimental insight into the dynamics of nanocrystals and pathways for their assembly from single atoms. PMID:24861089

Black phosphorus-based one-dimensional photonic crystals and microcavities.

PubMed

Kriegel, Ilka; Toffanin, Stefano; Scotognella, Francesco

2016-11-10

The latest achievements in the fabrication of thin layers of black phosphorus (BP), toward the technological breakthrough of a phosphorene atomically thin layer, are paving the way for their use in electronics, optics, and optoelectronics. In this work, we have simulated the optical properties of one-dimensional photonic structures, i.e., photonic crystals and microcavities, in which few-layer BP is one of the components. The insertion of the 5-nm black phosphorous layers leads to a photonic band gap in the photonic crystals and a cavity mode in the microcavity that is interesting for light manipulation and emission enhancement.

Atomically thin two-dimensional organic-inorganic hybrid perovskites

NASA Astrophysics Data System (ADS)

Dou, Letian; Wong, Andrew B.; Yu, Yi; Lai, Minliang; Kornienko, Nikolay; Eaton, Samuel W.; Fu, Anthony; Bischak, Connor G.; Ma, Jie; Ding, Tina; Ginsberg, Naomi S.; Wang, Lin-Wang; Alivisatos, A. Paul; Yang, Peidong

2015-09-01

Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.

Tailoring Vacancies Far Beyond Intrinsic Levels Changes the Carrier Type and Optical Response in Monolayer MoSe 2-x Crystals

DOE PAGES

Mahjouri-Samani, Masoud; Liang, Liangbo; Oyedele, Akinola; ...

2016-01-01

Defect engineering has been a critical step in controlling the transport characteristics of electronic devices, and the ability to create, tune, and annihilate defects is essential to enable the range of next-generation devices. Whereas defect formation has been well-demonstrated in three-dimensional semiconductors, similar exploration of the heterogeneity in atomically thin two-dimensional semiconductors and the link between their atomic structures, defects, and properties has not yet been extensively studied. In this paper, we demonstrate the growth of MoSe 2–x single crystals with selenium (Se) vacancies far beyond intrinsic levels, up to ~20%, that exhibit a remarkable transition in electrical transport propertiesmore » from n- to p-type character with increasing Se vacancy concentration. A new defect-activated phonon band at ~250 cm -1 appears, and the A 1g Raman characteristic mode at 240 cm -1 softens toward ~230 cm -1 which serves as a fingerprint of vacancy concentration in the crystals. We show that post-selenization using pulsed laser evaporated Se atoms can repair Se-vacant sites to nearly recover the properties of the pristine crystals. Finally, first-principles calculations reveal the underlying mechanisms for the corresponding vacancy-induced electrical and optical transitions.« less

Revealing the preferred interlayer orientations and stackings of two-dimensional bilayer gallium selenide crystals

DOE PAGES

Li, Xufan; Basile Carrasco, Leonardo A.; Yoon, Mina; ...

2015-01-21

Characterizing and controlling the interlayer orientations and stacking order of bilayer two-dimensional (2D) crystals and van der Waals (vdW) heterostructure is crucial to optimize their electrical and optoelectronic properties. The four polymorphs of layered gallium selenide (GaSe) that result from different layer stacking provide an ideal platform to study the stacking configurations in bilayer 2D crystals. Here, through a controllable vapor-phase deposition method we selectively grow bilayer GaSe crystals and investigate their two preferred 0° or 60° interlayer rotations. The commensurate stacking configurations (AA' and AB-stacking) in as-grown 2D bilayer GaSe crystals are clearly observed at the atomic scale andmore » the Ga-terminated edge structure are identified for the first time by using atomic-resolution scanning transmission electron microscopy (STEM). Theoretical analysis of the interlayer coupling energetics vs. interlayer rotation angle reveals that the experimentally-observed orientations are energetically preferred among the bilayer GaSe crystal polytypes. Here, the combined experimental and theoretical characterization of the GaSe bilayers afforded by these growth studies provide a pathway to reveal the atomistic relationships in interlayer orientations responsible for the electronic and optical properties of bilayer 2D crystals and vdW heterostructures.« less

Ground Based Program for the Physical Analysis of Macromolecular Crystal Growth

NASA Technical Reports Server (NTRS)

Malkin, Alexander J.

1998-01-01

During the past year we have focused on application of in situ Atomic Force Microscopy (AFM) for studies of the growth mechanisms and kinetics of crystallization for different macromolecular systems. Mechanisms of macrostep formation and their decay, which are important in understanding of defect formation, were studied on the surfaces of thaumatin, catalase, canavalin and lysozyme crystals. Experiments revealed that step bunching on crystalline surfaces occurred either due to two- or three-dimensional nucleation on the terraces of vicinal slopes or as a result of uneven step generation by complex dislocation sources. No step bunching arising from interaction of individual steps in the course of the experiment was observed. The molecular structure of the growth steps for thaumatin and lipase crystals were deduced. It was further shown that growth step advance occurs by incorporation of single protein molecules. In singular directions growth steps move by one-dimensional nucleation on step edges followed by lateral growth. One-dimensional nuclei have different sizes, less then a single unit cell, varying for different directions of step movement. There is no roughness due to thermal fluctuations, and each protein molecule which incorporated into the step remained. Growth kinetics for catalase crystals was investigated over wide supersaturation ranges. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was seen. The influence of impurities on growth kinetics and cessation of macromolecular crystals was studied. Thus, for catalase, in addition to pronounced impurity effects on the kinetics of crystallization, we were also able to directly observe adsorption of some impurities. At low supersaturation we repeatedly observed filaments which formed from impurity molecules sedimenting on the surfaces. Similar filaments were observed on the surfaces of thaumatin, canavalin and STMV crystals as well, but the frequency was low compared with catalase crystallization. Cessation of growth of xylanase and lysozyme crystals was also observed and appeared to be a consequence of the formation of dense impurity adsorption layers. Attachment: "An in situ AFM investigation of catalase crystallization", "Atomic force microscopy studies of living cells: visualization of motility, division, aggregation, transformation, and apoptosis", AFM studies on mechanisms of nucleation and growth of macromolecular crystals", and "In situ atomic force microscopy studies of surface morphology, growth kinetics, defect structure and dissolution in macromolecular crystallization".

Topology-Scaling Identification of Layered Solids and Stable Exfoliated 2D Materials.

PubMed

Ashton, Michael; Paul, Joshua; Sinnott, Susan B; Hennig, Richard G

2017-03-10

The Materials Project crystal structure database has been searched for materials possessing layered motifs in their crystal structures using a topology-scaling algorithm. The algorithm identifies and measures the sizes of bonded atomic clusters in a structure's unit cell, and determines their scaling with cell size. The search yielded 826 stable layered materials that are considered as candidates for the formation of two-dimensional monolayers via exfoliation. Density-functional theory was used to calculate the exfoliation energy of each material and 680 monolayers emerge with exfoliation energies below those of already-existent two-dimensional materials. The crystal structures of these two-dimensional materials provide templates for future theoretical searches of stable two-dimensional materials. The optimized structures and other calculated data for all 826 monolayers are provided at our database (https://materialsweb.org).

Investigation on nanoscale processes on the BaF{sub 2}(111) surface in various solutions by frequency modulation atomic force microscopy

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

Kobayashi, Naritaka, E-mail: naritaka@mail.saitama-u.ac.jp; Kawamura, Ryuzo; Yoshikawa, Hiroshi Y.

2016-06-07

In this study, we have directly observed nanoscale processes that occur on BaF{sub 2}(111) surfaces in various solutions using liquid-environment frequency modulation atomic force microscopy (FM-AFM) with a true atomic resolution. In addition, to investigate atomic-scale mechanisms of crystal growth process of BaF{sub 2}, we determined a suitable solution for atomic-resolution FM-AFM imaging of the BaF{sub 2}(111) surface. For undersaturated solutions, the surface is roughened by barium hydroxo complexes in the case of high pH, whereas by dissolution and proton or water molecule adsorption throughout the surface in the case of low pH. On the other hand, for supersaturated solutions,more » the surface shows two-dimensional nucleation and growth (σ = 0.1) and three-dimensional crystal growth with tetrahedral structures (σ = 1), where σ is the degree of supersaturation. The atomic-resolution imaging of the BaF{sub 2}(111) surface has been demonstrated in potassium fluoride (KF) and the supersaturated (σ = 0.1 and 1) solutions, wherein atomically flat terraces are shown at least for about 30 min.« less

Phonon interference control of atomic-scale metamirrors, meta-absorbers, and heat transfer through crystal interfaces

NASA Astrophysics Data System (ADS)

Kosevich, Yu. A.; Potyomina, L. G.; Darinskii, A. N.; Strelnikov, I. A.

2018-03-01

The paper theoretically studies the possibility of using the effects of phonon interference between paths through different interatomic bonds for the control of phonon heat transfer through internal crystal interfaces and for the design of phonon metamirrors and meta-absorbers. These metamirrors and meta-absorbers are considered to be defect nanolayers of atomic-scale thicknesses embedded in a crystal. Several analytically solvable three-dimensional lattice-dynamics models of the phonon metamirrors and meta-absorbers at the internal crystal planes are described. It is shown that due to destructive interference in the two or more phonon paths, the internal crystal planes, fully or partially filled with weakly bound or heavy-isotope defect atoms, can completely reflect or completely absorb phonons at the transmission antiresonances, whose wavelengths are larger than the effective thickness of the metamirror or meta-absorber. Due to cooperative superradiant effect, the spectral widths of the two-path interference antiresonances for the plane waves are given by the square of partial filling fraction in the defect crystal plane. Our analysis reveals that the presence of two or more phonon paths plays the dominant role in the emergence of the transmission antiresonances in phonon scattering at the defect crystal planes and in reduction of the thermal interface conductance in comparison with the Fano-resonance concept. We study analytically phonon transmission through internal crystal plane in a model cubic lattice of Si-like atoms, partially filled with Ge-like defect atoms. Such a plane can serve as interference phonon metamirror with the transmission antiresonances in the vicinities of eigenmode frequencies of Ge-like defect atoms in the terahertz frequency range. We predict the extraordinary phonon transmission induced by the two-path constructive interference of the lattice waves in resonance with the vibrations of rare host atoms, periodically distributed in the crystal plane almost completely filled with heavy-isotope defects. We show that the phonon-interference-induced transparency can be produced by the defect nanolayer with the non-nearest-neighbor interactions, filled with two types of isotopes with relatively small difference in masses or binding force constants. In this case, relatively broad transmission antiresonance is accompanied by the narrow transmission peak close to the antiresonance frequency. We describe the softening of the flexural surface acoustic wave, localized at the embedded defect nanolayer, caused by negative surface stress in the layer. The surface wave softening results in spatially periodic static bending deformation of the embedded nanolayer with the definite wave number. The latter effect is estimated for graphene monolayer embedded in a strained matrix of polyethylene. We analyze the effect of nonlinearity in the dynamics of defect atoms on the one- and two-path phonon interference and show that the interference transmission resonances and antiresonances are shifted in frequencies but not completely suppressed by rather strong anharmonicity of interatomic bonds. The reduction of the Kapitza thermal interface conductance caused by the destructive phonon interference in a defect monolayer is described. We show that the additional relatively weak non-nearest-neighbor interactions through the defect crystal plane filled with heavy isotopes substantially reduces the interface thermal conductance, and this effect is stronger in the three-dimensional system than in the quasi-one-dimensional systems studied previously.

Crystallization and preliminary X-ray diffraction study of the protealysin precursor belonging to the peptidase family M4

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

Gromova, T. Yu., E-mail: duk@img.ras.ru; Demidyuk, I. V.; Kostrov, S. V.

2008-09-15

A protealysin precursor (the enzyme of the peptidase family M4) was crystallized for the first time. The crystal-growth conditions were found, and single crystals of the protein with dimensions of 0.3-0.5 mm were grown. The preliminary X-ray diffraction study of the enzyme was performed. The protealysin precursor was shown to crystallize in two crystal modifications suitable for the X-ray diffraction study of the three-dimensional structure of the protein molecule at atomic resolution.

One dimensional coordination polymers: Synthesis, crystal structures and spectroscopic properties

NASA Astrophysics Data System (ADS)

Karaağaç, Dursun; Kürkçüoğlu, Güneş Süheyla; Şenyel, Mustafa; Şahin, Onur

2016-11-01

Two new one dimensional (1D) cyanide complexes, namely [M(4-aepy)2(H2O)2][Pt(CN)4], (4-aepy = 4-(2-aminoethyl)pyridine M = Cu(II) (1) or Zn(II) (2)), have been synthesized and characterized by vibrational (FT-IR and Raman) spectroscopy, single crystal X-ray diffraction, thermal and elemental analyses techniques. The crystallographic analyses reveal that 1 and 2 are isomorphous and isostructural, and crystallize in the monoclinic system and C2 space group. The Pt(II) ions are coordinated by four cyanide-carbon atoms in the square-planar geometry and the [Pt(CN)4]2- ions act as a counter ion. The M(II) ions display an N4O2 coordination sphere with a distorted octahedral geometry, the nitrogen donors belonging to four molecules of the organic 4-aepy that act as unidentate ligands and two oxygen atoms from aqua ligands. The crystal structures of 1 and 2 are similar each other and linked via intermolecular hydrogen bonding, Pt⋯π interactions to form 3D supramolecular network. Vibration assignments of all the observed bands are given and the spectral features also supported to the crystal structures of the complexes.

Atomically thin two-dimensional organic-inorganic hybrid perovskites.

PubMed

Dou, Letian; Wong, Andrew B; Yu, Yi; Lai, Minliang; Kornienko, Nikolay; Eaton, Samuel W; Fu, Anthony; Bischak, Connor G; Ma, Jie; Ding, Tina; Ginsberg, Naomi S; Wang, Lin-Wang; Alivisatos, A Paul; Yang, Peidong

2015-09-25

Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials. Copyright © 2015, American Association for the Advancement of Science.

Phase time delay and Hartman effect in a one-dimensional photonic crystal with four-level atomic defect layer

NASA Astrophysics Data System (ADS)

Jamil, Rabia; Ali, Abu Bakar; Abbas, Muqaddar; Badshah, Fazal; Qamar, Sajid

2017-08-01

The Hartman effect is revisited using a Gaussian beam incident on a one-dimensional photonic crystal (1DPC) having a defect layer doped with four-level atoms. It is considered that each atom of the defect layer interacts with three driving fields, whereas a Gaussian beam of width w is used as a probe light to study Hartman effect. The atom-field interaction inside the defect layer exhibits electromagnetically induced transparency (EIT). The 1DPC acts as positive index material (PIM) and negative index material (NIM) corresponding to the normal and anomalous dispersion of the defect layer, respectively, via control of the phase associated with the driving fields and probe detuning. The positive and negative Hartman effects are noticed for PIM and NIM, respectively, via control of the relative phase corresponding to the driving fields and probe detuning. The advantage of using four-level EIT system is that a much smaller absorption of the transmitted beam occurs as compared to three-level EIT system corresponding to the anomalous dispersion, leading to negative Hartman effect.

Two-dimensional crystals: managing light for optoelectronics.

PubMed

Eda, Goki; Maier, Stefan A

2013-07-23

Semiconducting two-dimensional (2D) crystals such as MoS2 and WSe2 exhibit unusual optical properties that can be exploited for novel optoelectronics ranging from flexible photovoltaic cells to harmonic generation and electro-optical modulation devices. Rapid progress of the field, particularly in the growth area, is beginning to enable ways to implement 2D crystals into devices with tailored functionalities. For practical device performance, a key challenge is to maximize light-matter interactions in the material, which is inherently weak due to its atomically thin nature. Light management around the 2D layers with the use of plasmonic nanostructures can provide a compelling solution.

Deciphering chemical order/disorder and material properties at the single-atom level.

PubMed

Yang, Yongsoo; Chen, Chien-Chun; Scott, M C; Ophus, Colin; Xu, Rui; Pryor, Alan; Wu, Li; Sun, Fan; Theis, Wolfgang; Zhou, Jihan; Eisenbach, Markus; Kent, Paul R C; Sabirianov, Renat F; Zeng, Hao; Ercius, Peter; Miao, Jianwei

2017-02-01

Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling 'real' materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily on average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. This work combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure-property relationships at the fundamental level.

Three-Dimensional Localized-Delocalized Anderson Transition in the Time Domain

NASA Astrophysics Data System (ADS)

Delande, Dominique; Morales-Molina, Luis; Sacha, Krzysztof

2017-12-01

Systems which can spontaneously reveal periodic evolution are dubbed time crystals. This is in analogy with space crystals that display periodic behavior in configuration space. While space crystals are modeled with the help of space periodic potentials, crystalline phenomena in time can be modeled by periodically driven systems. Disorder in the periodic driving can lead to Anderson localization in time: the probability for detecting a system at a fixed point of configuration space becomes exponentially localized around a certain moment in time. We here show that a three-dimensional system exposed to a properly disordered pseudoperiodic driving may display a localized-delocalized Anderson transition in the time domain, in strong analogy with the usual three-dimensional Anderson transition in disordered systems. Such a transition could be experimentally observed with ultracold atomic gases.

BiSr3(YO)3(BO3)4: a new gaudefroyite-type rare-earth borate with moderate SHG response.

PubMed

Gao, Jianhua; Li, Shuai

2012-01-02

The synthesis, crystal structure, crystal growth, and characterization of a new noncentrosymmetric rare-earth borate BiSr(3)(YO)(3)(BO(3))(4) are reported. BiSr(3)(YO)(3)(BO(3))(4) belongs to gaudefroyite type of structure and crystallizes in the polar hexagonal space group P6(3) (no. 173) with a = 10.6975(16) Å and c = 6.7222(12) Å. In the structure, the YO(7) polyhedra share edges to form an one-dimensional chain along the [001] direction. These chains are interconnected by the BO(3) group to construct a three-dimensional framework, leaving two kinds of channels for Bi atoms and Sr atoms together with BO(3) groups, respectively. On the basis of the powder second-harmonic generation (SHG) measurement, BiSr(3)(YO)(3)(BO(3))(4) belongs to the phase-matchable class with a SHG response of about 3 × KDP.

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

Universal two-dimensional characteristics in perovskite-type oxyhydrides ATiO2H (A = Li, Na, K, Rb, Cs)

NASA Astrophysics Data System (ADS)

Sato, Nobuya; Akashi, Ryosuke; Tsuneyuki, Shinji

2017-07-01

A series of unsynthesized perovskite-type oxyhydrides ATiO2H (A = Li, Na, K, Rb, Cs) are investigated by the density functional calculations. These oxyhydrides are stable in the sense of the formation energies for some possible synthesis reactions. They are crystallized into quite similar crystal structures with the long c-axis, and the corner-sharing TiO4H2 octahedra of the ideal perovskite-type structure are deformed into the 5-fold coordinated titanium atoms with the OH plane and the apical oxygen atoms. All of these oxyhydrides exhibit two-dimensional electronic states at the valence band maximum characterized by the in-plane oxygen 2p and the hydrogen 1s orbitals. While the c-axis becomes short as the ionic radius of the A atom becomes small and the two-dimensional characteristics are weakened, the electronic state at the valence band maximum is still characterized as the O-H in-plane state. Additionally, the Born effective charge tensors, spontaneous electric polarizations, dielectric tensors, and piezoelectric tensors are evaluated. It is found that the spontaneous electric polarizations of these oxyhydrides are much larger than that of tetragonal BaTiO3.

Atomic electron tomography: 3D structures without crystals

DOE PAGES

Miao, Jianwei; Ercius, Peter; Billinge, S. J. L.

2016-09-23

Crystallography has been fundamental to the development of many fields of science over the last century. However, much of our modern science and technology relies on materials with defects and disorders, and their three-dimensional (3D) atomic structures are not accessible to crystallography. One method capable of addressing this major challenge is atomic electron tomography. By combining advanced electron microscopes and detectors with powerful data analysis and tomographic reconstruction algorithms, it is now possible to determine the 3D atomic structure of crystal defects such as grain boundaries, stacking faults, dislocations, and point defects, as well as to precisely localize the 3Dmore » coordinates of individual atoms in materials without assuming crystallinity. In this work, we review the recent advances and the interdisciplinary science enabled by this methodology. We also outline further research needed for atomic electron tomography to address long-standing unresolved problems in the physical sciences.« less

Synthesis of two-dimensional TlxBi1−x compounds and Archimedean encoding of their atomic structure

PubMed Central

Gruznev, Dimitry V.; Bondarenko, Leonid V.; Matetskiy, Andrey V.; Mihalyuk, Alexey N.; Tupchaya, Alexandra Y.; Utas, Oleg A.; Eremeev, Sergey V.; Hsing, Cheng-Rong; Chou, Jyh-Pin; Wei, Ching-Ming; Zotov, Andrey V.; Saranin, Alexander A.

2016-01-01

Crystalline atomic layers on solid surfaces are composed of a single building block, unit cell, that is copied and stacked together to form the entire two-dimensional crystal structure. However, it appears that this is not an unique possibility. We report here on synthesis and characterization of the one-atomic-layer-thick TlxBi1−x compounds which display quite a different arrangement. It represents a quasi-periodic tiling structures that are built by a set of tiling elements as building blocks. Though the layer is lacking strict periodicity, it shows up as an ideally-packed tiling of basic elements without any skips or halting. The two-dimensional TlxBi1−x compounds were formed by depositing Bi onto the Tl-covered Si(111) surface where Bi atoms substitute appropriate amount of Tl atoms. Atomic structure of each tiling element as well as arrangement of TlxBi1−x compounds were established in a detail. Electronic properties and spin texture of the selected compounds having periodic structures were characterized. The shown example demonstrates possibility for the formation of the exotic low-dimensional materials via unusual growth mechanisms. PMID:26781340

Atomic and electronic structure of exfoliated black phosphorus

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

Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok

2015-11-15

Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolutionmore » view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO{sub 3} or H{sub 3}PO{sub 3} during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.« less

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

Yang, Yongsoo; Chen, Chien-Chun; Scott, M. C.

Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling ‘real’ materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily onmore » average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. The work presented here combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure–property relationships at the fundamental level.« less

Nitrilotris(methylenephosphonato)potassium K[μ{sup 6}-NH(CH{sub 2}PO{sub 3}){sub 3}H{sub 4}]: Synthesis, structure, and the nature of the K–O chemical bond

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

Somov, N. V., E-mail: somov@phys.unn.ru; Chausov, F. F., E-mail: xps@ftiudm.ru; Zakirova, R. M., E-mail: ftt@udsu.ru

2016-07-15

The crystal structure of nitrilotris(methylenephosphonato)potassium K[μ{sup 6}-NH(CH{sub 2}PO{sub 3}){sub 3}H{sub 4}]—a three-dimensional coordination polymer—was determined. The potassium atom is coordinated by seven oxygen atoms belonging to the six nearest ligand molecules, resulting in distorted monocapped octahedral coordination geometry. The complex contains the four-membered chelate ring K–O–P–O. The K–O chemical bond is predominantly ionic. Meanwhile, the bonds of the potassium atom with some oxygen atoms have a noticeable covalent component. In addition to coordination bonds, the molecules in the crystal packing are linked by hydrogen bonds.

Microgravity

NASA Image and Video Library

2004-04-15

A semiconductor's usefulness is determined by how atoms are ordered within the crystal's underlying three-dimensional structure. While this mercury telluride and cadmium telluride alloy sample mixes completely in Earth -based laboratories, convective flows prevent them from mixing uniformly.

Preliminary crystallographic studies of four crystal forms of serum albumin

NASA Technical Reports Server (NTRS)

Carter, D. C.; Chang, B.; Ho, J. X.; Keeling, K.; Krishnasami, Z.

1994-01-01

Several crystal forms of serum albumin suitable for three-dimensional structure determination have been grown. These forms include crystals of recombinant and wild-type human serum albumin, baboon serum albumin, and canine serum albumin. The intrinsic limits of X-ray diffraction for these crystals are in the range 0.28-0.22 nm. Two of the crystal forms produced from human and canine albumin include incorporated long-chain fatty acids. Molecular replacement experiments have been successfully conducted on each crystal form using the previously determined atomic coordinates of human serum albumin illustrating the conserved tertiary structure.

DNA-mediated nanoparticle crystallization into Wulff polyhedra

NASA Astrophysics Data System (ADS)

Auyeung, Evelyn; Li, Ting I. N. G.; Senesi, Andrew J.; Schmucker, Abrin L.; Pals, Bridget C.; de La Cruz, Monica Olvera; Mirkin, Chad A.

2014-01-01

Crystallization is a fundamental and ubiquitous process much studied over the centuries. But although the crystallization of atoms is fairly well understood, it remains challenging to predict reliably the outcome of molecular crystallization processes that are complicated by various molecular interactions and solvent involvement. This difficulty also applies to nanoparticles: high-quality three-dimensional crystals are mostly produced using drying and sedimentation techniques that are often impossible to rationalize and control to give a desired crystal symmetry, lattice spacing and habit (crystal shape). In principle, DNA-mediated assembly of nanoparticles offers an ideal opportunity for studying nanoparticle crystallization: a well-defined set of rules have been developed to target desired lattice symmetries and lattice constants, and the occurrence of features such as grain boundaries and twinning in DNA superlattices and traditional crystals comprised of molecular or atomic building blocks suggests that similar principles govern their crystallization. But the presence of charged biomolecules, interparticle spacings of tens of nanometres, and the realization so far of only polycrystalline DNA-interconnected nanoparticle superlattices, all suggest that DNA-guided crystallization may differ from traditional crystal growth. Here we show that very slow cooling, over several days, of solutions of complementary-DNA-modified nanoparticles through the melting temperature of the system gives the thermodynamic product with a specific and uniform crystal habit. We find that our nanoparticle assemblies have the Wulff equilibrium crystal structure that is predicted from theoretical considerations and molecular dynamics simulations, thus establishing that DNA hybridization can direct nanoparticle assembly along a pathway that mimics atomic crystallization.

Alloy-assisted deposition of three-dimensional arrays of atomic gold catalyst for crystal growth studies

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

Fang, Yin; Jiang, Yuanwen; Cherukara, Mathew J.

Large-scale assembly of individual atoms over smooth surfaces is difficult to achieve. A configuration of an atom reservoir, in which individual atoms can be readily extracted, may successfully address this challenge. In this work, we demonstrate that a liquid gold-silicon alloy established in classical vapor-liquid-solid growth can deposit ordered and three-dimensional rings of isolated gold atoms over silicon nanowire sidewalls. Here, we perform ab initio molecular dynamics simulation and unveil a surprising single atomic gold-catalyzed chemical etching of silicon. Experimental verification of this catalytic process in silicon nanowires yields dopant-dependent, massive and ordered 3D grooves with spacing down to similarmore » to 5 nm. Finally, we use these grooves as self-labeled and ex situ markers to resolve several complex silicon growths, including the formation of nodes, kinks, scale-like interfaces, and curved backbones.« less

Alloy-assisted deposition of three-dimensional arrays of atomic gold catalyst for crystal growth studies

DOE PAGES

Fang, Yin; Jiang, Yuanwen; Cherukara, Mathew J.; ...

2017-12-08

Large-scale assembly of individual atoms over smooth surfaces is difficult to achieve. A configuration of an atom reservoir, in which individual atoms can be readily extracted, may successfully address this challenge. In this work, we demonstrate that a liquid gold-silicon alloy established in classical vapor-liquid-solid growth can deposit ordered and three-dimensional rings of isolated gold atoms over silicon nanowire sidewalls. Here, we perform ab initio molecular dynamics simulation and unveil a surprising single atomic gold-catalyzed chemical etching of silicon. Experimental verification of this catalytic process in silicon nanowires yields dopant-dependent, massive and ordered 3D grooves with spacing down to similarmore » to 5 nm. Finally, we use these grooves as self-labeled and ex situ markers to resolve several complex silicon growths, including the formation of nodes, kinks, scale-like interfaces, and curved backbones.« less

Deciphering chemical order/disorder and material properties at the single-atom level

DOE PAGES

Yang, Yongsoo; Chen, Chien-Chun; Scott, M. C.; ...

2017-02-01

Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling ‘real’ materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily onmore » average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. The work presented here combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure–property relationships at the fundamental level.« less

Combining X-ray and neutron crystallography with spectroscopy.

PubMed

Kwon, Hanna; Smith, Oliver; Raven, Emma Lloyd; Moody, Peter C E

2017-02-01

X-ray protein crystallography has, through the determination of the three-dimensional structures of enzymes and their complexes, been essential to the understanding of biological chemistry. However, as X-rays are scattered by electrons, the technique has difficulty locating the presence and position of H atoms (and cannot locate H + ions), knowledge of which is often crucially important for the understanding of enzyme mechanism. Furthermore, X-ray irradiation, through photoelectronic effects, will perturb the redox state in the crystal. By using single-crystal spectrophotometry, reactions taking place in the crystal can be monitored, either to trap intermediates or follow photoreduction during X-ray data collection. By using neutron crystallography, the positions of H atoms can be located, as it is the nuclei rather than the electrons that scatter neutrons, and the scattering length is not determined by the atomic number. Combining the two techniques allows much greater insight into both reaction mechanism and X-ray-induced photoreduction.

Effects of molecular geometry on the properties of compressed diamondoid crystals

DOE PAGES

Yang, Fan; Lin, Yu; Baldini, Maria; ...

2016-11-01

Diamondoids are an intriguing group of carbon-based nanomaterials, which combine desired properties of inorganic nanomaterials and small hydrocarbon molecules with atomic-level uniformity. In this Letter, we report the first comparative study on the effect of pressure on a series of diamondoid crystals with systematically varying molecular geometries and shapes, including zero-dimensional (0D) adamantane; one-dimensional (1D) diamantane, [121]tetramantane, [123]tetramantane, and [1212]pentamantane; two-dimensional (2D) [12312]hexamantane; and three-dimensional (3D) triamantane and [1(2,3)4]pentamantane. We find the bulk moduli of these diamondoid crystals are strongly dependent on the diamondoids’ molecular geometry with 3D [1(2,3)4]pentamantane being the least compressible and 0D adamantane being the most compressible.more » These diamondoid crystals possess excellent structural rigidity and are able to sustain large volume deformation without structural failure even after repetitive pressure loading cycles. These properties are desirable for constructing cushioning devices. Furthermore, we also demonstrate that lower diamondoids outperform the conventional cushioning materials in both the working pressure range and energy absorption density.« less

Three-dimensional coordinates of individual atoms in materials revealed by electron tomography

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

Xu, Rui; Chen, Chien-Chun; Wu, Li

Crystallography, the primary method for determining the 3D atomic positions in crystals, has been fundamental to the development of many fields of science. However, the atomic positions obtained from crystallography represent a global average of many unit cells in a crystal. In this paper, we report, for the first time, the determination of the 3D coordinates of thousands of individual atoms and a point defect in a material by electron tomography with a precision of ~19 pm, where the crystallinity of the material is not assumed. From the coordinates of these individual atoms, we measure the atomic displacement field andmore » the full strain tensor with a 3D resolution of ~1 nm 3 and a precision of ~10 -3, which are further verified by density functional theory calculations and molecular dynamics simulations. Finally, the ability to precisely localize the 3D coordinates of individual atoms in materials without assuming crystallinity is expected to find important applications in materials science, nanoscience, physics, chemistry and biology.« less

Three-dimensional coordinates of individual atoms in materials revealed by electron tomography

DOE PAGES

Xu, Rui; Chen, Chien-Chun; Wu, Li; ...

2015-09-21

Crystallography, the primary method for determining the 3D atomic positions in crystals, has been fundamental to the development of many fields of science. However, the atomic positions obtained from crystallography represent a global average of many unit cells in a crystal. In this paper, we report, for the first time, the determination of the 3D coordinates of thousands of individual atoms and a point defect in a material by electron tomography with a precision of ~19 pm, where the crystallinity of the material is not assumed. From the coordinates of these individual atoms, we measure the atomic displacement field andmore » the full strain tensor with a 3D resolution of ~1 nm 3 and a precision of ~10 -3, which are further verified by density functional theory calculations and molecular dynamics simulations. Finally, the ability to precisely localize the 3D coordinates of individual atoms in materials without assuming crystallinity is expected to find important applications in materials science, nanoscience, physics, chemistry and biology.« less

Unexpected Huge Dimerization Ratio in One-Dimensional Carbon Atomic Chains.

PubMed

Lin, Yung-Chang; Morishita, Shigeyuki; Koshino, Masanori; Yeh, Chao-Hui; Teng, Po-Yuan; Chiu, Po-Wen; Sawada, Hidetaka; Suenaga, Kazutomo

2017-01-11

Peierls theory predicted atomic distortion in one-dimensional (1D) crystal due to its intrinsic instability in 1930. Free-standing carbon atomic chains created in situ in transmission electron microscope (TEM)1-3 are an ideal example to experimentally observe the dimerization behavior of carbon atomic chain within a finite length. We report here a surprisingly huge distortion found in the free-standing carbon atomic chains at 773 K, which is 10 times larger than the value expected in the system. Such an abnormally distorted phase only dominates at the elevated temperatures, while two distinct phases, distorted and undistorted, coexist at lower or ambient temperatures. Atom-by-atom spectroscopy indeed shows considerable variations in the carbon 1s spectra at each atomic site but commonly observes a slightly downshifted π* peak, which proves its sp 1 bonding feature. These results suggest that the simple model, relaxed and straight, is not fully adequate to describe the realistic 1D structure, which is extremely sensitive to perturbations such as external force or boundary conditions.

Protein nanocrystallography: growth mechanism and atomic structure of crystals induced by nanotemplates.

PubMed

Pechkova, E; Vasile, F; Spera, R; Fiordoro, S; Nicolini, C

2005-11-01

Protein nanocrystallography, a new technology for crystal growth based on protein nanotemplates, has recently been shown to produce diffracting, stable and radiation-resistant lysozyme crystals. This article, by computing these lysozyme crystals' atomic structures, obtained by the diffraction patterns of microfocused synchrotron radiation, provides a possible mechanism for this increased stability, namely a significant decrease in water content accompanied by a minor but significant alpha-helix increase. These data are shown to be compatible with the circular dichroism and two-dimensional Fourier transform spectra of high-resolution H NMR of proteins dissolved from the same nanotemplate-based crystal versus those from a classical crystal. Finally, evidence for protein direct transfer from the nanotemplate to the drop and the participation of the template proteins in crystal nucleation and growth is provided by high-resolution NMR spectrometry and mass spectrometry. Furthermore, the lysozyme nanotemplate appears stable up to 523 K, as confirmed by a thermal denaturation study using spectropolarimetry. The overall data suggest that heat-proof lysozyme presence in the crystal provides a possible explanation of the crystal's resistance to synchrotron radiation.

Revealing the preferred interlayer orientations and stackings of two-dimensional bilayer gallium selenide crystals.

PubMed

Li, Xufan; Basile, Leonardo; Yoon, Mina; Ma, Cheng; Puretzky, Alexander A; Lee, Jaekwang; Idrobo, Juan C; Chi, Miaofang; Rouleau, Christopher M; Geohegan, David B; Xiao, Kai

2015-02-23

Characterizing and controlling the interlayer orientations and stacking orders of two-dimensional (2D) bilayer crystals and van der Waals (vdW) heterostructures is crucial to optimize their electrical and optoelectronic properties. The four polymorphs of layered gallium selenide (GaSe) crystals that result from different layer stackings provide an ideal platform to study the stacking configurations in 2D bilayer crystals. Through a controllable vapor-phase deposition method, bilayer GaSe crystals were selectively grown and their two preferred 0° or 60° interlayer rotations were investigated. The commensurate stacking configurations (AA' and AB stacking) in as-grown bilayer GaSe crystals are clearly observed at the atomic scale, and the Ga-terminated edge structure was identified using scanning transmission electron microscopy. Theoretical analysis reveals that the energies of the interlayer coupling are responsible for the preferred orientations among the bilayer GaSe crystals. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanisms of heterogeneous crystal growth in atomic systems: insights from computer simulations.

PubMed

Gulam Razul, M S; Hendry, J G; Kusalik, P G

2005-11-22

In this paper we analyze the atomic-level structure of solid/liquid interfaces of Lennard-Jones fcc systems. The 001, 011, and 111 faces are examined during steady-state growth and melting of these crystals. The mechanisms of crystallization and melting are explored using averaged configurations generated during these steady-state runs, where subsequent tagging and labeling of particles at the interface provide many insights into the detailed atomic behavior at the freezing and melting interfaces. The interfaces are generally found to be rough and we observe the structure of freezing and melting interfaces to be very similar. Large structural fluctuations with solidlike and liquidlike characteristics are apparent in both the freezing and melting interfaces. The behavior at the interface observed under either growth or melting conditions reflects a competition between ordering and disordering processes. In addition, we observe atom hopping that imparts liquidlike characteristics to the solid side of the interfaces for all three crystal faces. Solid order is observed to extend as rough, three-dimensional protuberances through the interface, particularly for the 001 and 011 faces. We are also able to reconcile our different measures for the interfacial width and address the onset of asymmetry in the growth rates at high rates of crystal growth/melting.

Crystal structure and Hirshfeld surface analysis of aqua-bis-(nicotinamide-κN)bis-(4-sulfamoylbenzoato-κO1)copper(II).

PubMed

Hökelek, Tuncer; Yavuz, Vijdan; Dal, Hakan; Necefoğlu, Hacali

2018-01-01

In the crystal of the title complex, [Cu(C 7 H 6 NO 4 S) 2 (C 6 H 6 N 2 O) 2 (H 2 O)], the Cu II cation and the O atom of the coordinated water mol-ecule reside on a twofold rotation axis. The Cu II ion is coordinated by two carboxyl-ate O atoms of the two symmetry-related 4-sulfamoylbenzoate (SB) anions and by two N atoms of the two symmetry-related nicotinamide (NA) mol-ecules at distances of 1.978 (2) and 2.025 (3) Å, respectively, forming a slightly distorted square-planar arrangement. The distorted square-pyramidal coordination environment is completed by the water O atom in the axial position at a distance of 2.147 (4) Å. In the crystal, the mol-ecules are linked via O-H⋯O and N-H⋯O hydrogen bonds with R 2 2 (8) and R 2 2 (18) ring motifs, forming a three-dimensional architecture. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯O/O⋯H (42.2%), H⋯H (25.7%) and H⋯C/C⋯H (20.0%) inter-actions.

A new series of two-dimensional silicon crystals with versatile electronic properties

NASA Astrophysics Data System (ADS)

Chae, Kisung; Kim, Duck Young; Son, Young-Woo

2018-04-01

Silicon (Si) is one of the most extensively studied materials owing to its significance to semiconductor science and technology. While efforts to find a new three-dimensional (3D) Si crystal with unusual properties have made some progress, its two-dimensional (2D) phases have not yet been explored as much. Here, based on a newly developed systematic ab initio materials searching strategy, we report a series of novel 2D Si crystals with unprecedented structural and electronic properties. The new structures exhibit perfectly planar outermost surface layers of a distorted hexagonal network with their thicknesses varying with the atomic arrangement inside. Dramatic changes in electronic properties ranging from semimetal to semiconducting with indirect energy gaps and even to one with direct energy gaps are realized by varying thickness as well as by surface oxidation. Our predicted 2D Si crystals with flat surfaces and tunable electronic properties will shed light on the development of silicon-based 2D electronics technology.

Crystal structure of fac-aquatricarbonyl[(S)-valin-ato-κ(2) N,O]-rhenium(I).

PubMed

Piletska, Kseniia O; Domasevitch, Kostiantyn V; Shtemenko, Alexander V

2016-04-01

In the mol-ecule of the title compound, [Re(C5H10NO2)(CO)3(H2O)], the Re(I) atom adopts a distorted octa-hedral coordination sphere defined by one aqua and three carbonyl ligands as well as one amino N and one carboxyl-ate O atom of the chelating valinate anion. The carbonyl ligands are arranged in a fac-configuration around the Re(I) ion. In the crystal, an intricate hydrogen-bonding system under participation of two O-H, two N-H and one C-H donor groups and the carboxyl-ate and carbonyl O atoms as acceptor groups contribute to the formation of a three-dimensional supra-molecular network.

Crystal structure of tri­hydrogen bis­{[1,1,1-tris­(2-oxido­ethyl­amino­meth­yl)ethane]­cobalt(III)} trinitrate

PubMed Central

Sethi, Waqas; Johannesen, Heini V.; Morsing, Thorbjørn J.; Piligkos, Stergios; Weihe, Høgni

2015-01-01

The title compound, [Co2(L)2]3+·3NO3 − [where L = CH3C(CH2NHCH2CH2OH1/2)3], has been synthesized from the ligand 1,1,1-tris­(2-hy­droxy­ethyl­amino­meth­yl)ethane. The cobalt(III) dimer has an inter­esting and uncommon O—H⋯O hydrogen-bonding motif with the three bridging hy­droxy H atoms each being equally disordered over two positions. In the dimeric trication, the octa­hedrally coordinated CoIII atoms and the capping C atoms lie on a threefold rotation axis. The N atoms of two crystallographically independent nitrate anions also lie on threefold rotation axes. N—H⋯O hydrogen bonding between the complex cations and nitrate anions leads to the formation of a three-dimensional network structure. The compound is a racemic conglomerate of crystals containing either d or l mol­ecules. The crystal used for this study is a d crystal. PMID:26870462

Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors

PubMed Central

Mahjouri-Samani, Masoud; Lin, Ming-Wei; Wang, Kai; Lupini, Andrew R.; Lee, Jaekwang; Basile, Leonardo; Boulesbaa, Abdelaziz; Rouleau, Christopher M.; Puretzky, Alexander A.; Ivanov, Ilia N.; Xiao, Kai; Yoon, Mina; Geohegan, David B.

2015-01-01

The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional crystalline semiconductors as building blocks in next-generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate an approach for the formation of lithographically patterned arrays of lateral semiconducting heterojunctions within a single two-dimensional crystal. Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns. The junctions and conversion process are studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy and device characterization. This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices. PMID:26198727

Excitation of Bloch surface wave on tapered fiber coated with one-dimensional photonic crystal for refractive index sensing.

PubMed

Tu, Tianyu; Pang, Fufei; Zhu, Shan; Cheng, Jiajing; Liu, Huanhuan; Wen, Jianxiang; Wang, Tingyun

2017-04-17

We have theoretically and experimentally demonstrated a novel approach to excite Bloch surface wave (BSW) on tapered optical fibers, which are coated with one-dimensional photonic crystal (1DPC) consisting of periodic TiO₂ and Al₂O₃ by atomic layer deposition technology. Two resonant dips are found in transmission spectra that are originated from the excitation of BSW for p-polarized light and s-polarized light, respectively. For the first time, we have demonstrated the developed device for refractive index (RI) sensing.

Dynamics of vacancies in two-dimensional Lennard-Jones crystals

NASA Astrophysics Data System (ADS)

Yao, Zhenwei; Olvera de La Cruz, Monica

2015-03-01

Vacancies represent an important class of crystallographic defects, and their behaviors can be strongly coupled with relevant material properties. We report the rich dynamics of vacancies in two-dimensional Lennard-Jones crystals in several thermodynamic states. Specifically, we numerically observe significantly faster diffusion of the 2-point vacancy with two missing particles in comparison with other types of vacancies; it opens the possibility of doping 2-point vacancies into atomic materials to enhance atomic migration. In addition, the resulting dislocations in the healing of a long vacancy suggest the intimate connection between vacancies and topological defects that may provide an extra dimension in the engineering of defects in extensive crystalline materials for desired properties. We thank the financial support from the U.S. Department of Commerce, National Institute of Standards and Technology, the Office of the Director of Defense Research and Engineering (DDR&E) and the Air Force Office of Scientific Research.

Synthesis and Structural Studies of Calcium and Magnesium Phosphinate and Phosphonate Compounds

NASA Astrophysics Data System (ADS)

Bampoh, Victoria Naa Kwale

The work presented herein describes synthetic methodologies leading to the design of a wide array of magnesium and calcium based phosphinate and phosphonates with possible applications as bone scaffolding materials or additives to bone cements. The challenge to the chemistry of the alkaline earth phosphonate target compounds includes poor solubility of compounds, and poorly understood details on the control of the metal's coordination environment. Hence, less is known on phosphonate based alkaline earth metal organic frameworks as compared to transition metal phosphonates. Factors governing the challenges in obtaining crystalline, well-defined magnesium and calcium solids lie in the large metal diameters, the absence of energetically available d-orbitals to direct metal geometry, as well as the overall weakness of the metal-ligand bonds. A significant part of this project was concerned with the development of suitable reaction conditions to obtain X-ray quality crystals of the reaction products to allow for structural elucidation of the novel compounds. Various methodologies to aid in crystal growth including hydrothermal methods and gel crystallization were employed. We have used phosphinate and phosphonate ligands with different number of phosphorus oxygen atoms as well as diphosphonates with different linker lengths to determine their effects on the overall structural features. An interesting correlation is observed between the dimensionality of products and the increasing number of donor oxygen atoms in the ligands as we progress from phosphinic acid to the phosphorous acids. As an example, monophosphinate ligand only yielded one-dimensional compounds, whereas the phosphonates crystallize as one and two-dimensional compounds, and the di- and triphosphonate based compounds display two or three-dimensional geometries. This thesis provides a selection of calcium and magnesium compounds with one-dimensional geometry, as represented in a calcium phosphinate to novel two-dimensional sheets of magnesium and pillared calcium phosphonates. The preparation of these novel compounds has led to the establishment of synthetic protocols that allow for the direct preparation of compounds with defined structural features.

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

Chumakov, Yu. M.; Tsapkov, V. I., E-mail: vtsapkov@gmail.com; Antosyak, B. Ya.

Nitrato-4-bromo-2-[(2-hydroxyethylimino)methyl]phenolatoimidazolecopper and nitrato-4-chloro-2-[(2-hydroxyethylimino)methyl]phenolatoimidazolecopper were synthesized and studied by X-ray diffraction. The crystals are isostructural. The coordination polyhedron of the copper atom can be described as a distorted square pyramid whose basal plane is formed by the phenolic and alcoholic oxygen atoms and the nitrogen atom of the monodeprotonated tridentate azomethine molecule and the imidazole nitrogen atom. The apex of the copper polyhedron is occupied by the oxygen atom of the nitrato group. The complexes are linked together by hydrogen bonds with the participation of the nitrato groups to form a three-dimensional framework.

Generalized Kubo formulas for the transport properties of incommensurate 2D atomic heterostructures

NASA Astrophysics Data System (ADS)

Cancès, Eric; Cazeaux, Paul; Luskin, Mitchell

2017-06-01

We give an exact formulation for the transport coefficients of incommensurate two-dimensional atomic multilayer systems in the tight-binding approximation. This formulation is based upon the C* algebra framework introduced by Bellissard and collaborators [Coherent and Dissipative Transport in Aperiodic Solids, Lecture Notes in Physics (Springer, 2003), Vol. 597, pp. 413-486 and J. Math. Phys. 35(10), 5373-5451 (1994)] to study aperiodic solids (disordered crystals, quasicrystals, and amorphous materials), notably in the presence of magnetic fields (quantum Hall effect). We also present numerical approximations and test our methods on a one-dimensional incommensurate bilayer system.

An Example of Body-Centered Cubic Crystal Structure: The Atomium in Brussels as an Educative Tool for Introductory Materials Chemistry

ERIC Educational Resources Information Center

Pinto, Gabriel

2012-01-01

When students are introduced to the ways in which atoms are arranged in crystal structures, transposing the textbook illustrations into three-dimensional structures is difficult for some of them. To facilitate this transition, this article describes an approach to the study of the structure of solids through a well-known monument, the Atomium in…

A new Pb{sup II}(ethylenediaminetetraacetate) coordination polymer with a two-dimensional layer structure

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

Zhao, D., E-mail: iamzd@hpu.edu.cn; Zhang, R. H.; Li, F. F.

2016-12-15

A new Pb{sup II}−edta{sup 4–} coordination polymer, Pb{sub 2}(edta)(H{sub 2}O){sub 0.76} (edta{sup 4–} = ethylenediaminetetraacetate) was synthesized under hydrothermal condition. Single crystal X-ray analysis reveals that it represents a novel two-dimensional (2D) Pb{sup 2+}–edta{sup 4–} layer structure with a (4,8{sup 2})-topology. Each edta{sup 4–} ligand employs its four carboxylate O and two N atoms to chelate one Pb{sup II} atom (hexa-coordinated) and connects five Pb{sup II} atoms (ennea-coordinated) via its four carboxylate groups to form 2D layer framework. Adjacent layers are packed into the overall structure through vander Waals interactions.

Clean Floquet Time Crystals: Models and Realizations in Cold Atoms

NASA Astrophysics Data System (ADS)

Huang, Biao; Wu, Ying-Hai; Liu, W. Vincent

2018-03-01

Time crystals, a phase showing spontaneous breaking of time-translation symmetry, has been an intriguing subject for systems far away from equilibrium. Recent experiments found such a phase in both the presence and the absence of localization, while in theories localization by disorder is usually assumed a priori. In this work, we point out that time crystals can generally exist in systems without disorder. A series of clean quasi-one-dimensional models under Floquet driving are proposed to demonstrate this unexpected result in principle. Robust time crystalline orders are found in the strongly interacting regime along with the emergent integrals of motion in the dynamical system, which can be characterized by level statistics and the out-of-time-ordered correlators. We propose two cold atom experimental schemes to realize the clean Floquet time crystals, one by making use of dipolar gases and another by synthetic dimensions.

The ground state of two-dimensional silicon

NASA Astrophysics Data System (ADS)

Borlido, Pedro; Rödl, Claudia; Marques, Miguel A. L.; Botti, Silvana

2018-07-01

We perform ab initio structure-prediction calculations of the low-energy crystal structures of two-dimensional silicon. Besides the well-known silicene and a few other allotropes proposed earlier in the literature, we discover a wealth of new phases with interesting properties. In particular, we find that the ground state of two-dimensional silicon is an unreported structure formed by a honeycomb lattice with dumbbell atoms arranged in a zigzag pattern. This material, that we call zigzag dumbbell silicene, is 218 meV/atom more stable than silicene and displays a quasi-direct band gap of around 1.11 eV, with a very dispersive electron band. These properties should make it easier to synthesize than silicene and interesting for a wealth of opto-electronic applications.

Atomic force microscopy study on crystal growth of Cu 2+-doped L-arginine phosphate monohydrate crystals

NASA Astrophysics Data System (ADS)

Geng, Y. L.; Xu, D.; Wang, Y. L.; Du, W.; Liu, H. Y.; Zhang, G. H.; Wang, X. Q.; Sun, D. L.

2005-01-01

Sub-steps and defects of the {1 0 0} planes of Cu 2+-doped L-arginine phosphate monohydrate (LAP) crystals are observed by atomic force microscopy. Formation of sub-steps is not due to the stacking faults but a result of single LAP: Cu 2+ molecule acting as growth unit. Two-dimensional (2D) nuclei with the same height as sub-steps occur on the step-edges. Impurities of Cu 2+ ions cause steps bunch and macrosteps formation. Liquid inclusions in the form of long channels form when the macrosteps lose their stability. Numerous small 3D growth hillocks are found in the channels. The extra stress induced by the 3D islands can result in dislocations and steps mismatches.

Which strategy for a protein crystallization project?

NASA Technical Reports Server (NTRS)

Kundrot, C. E.

2004-01-01

The three-dimensional, atomic-resolution protein structures produced by X-ray crystallography over the past 50+ years have led to tremendous chemical understanding of fundamental biochemical processes. The pace of discovery in protein crystallography has increased greatly with advances in molecular biology, crystallization techniques, cryocrystallography, area detectors, synchrotrons and computing. While the methods used to produce single, well-ordered crystals have also evolved over the years in response to increased understanding and advancing technology, crystallization strategies continue to be rooted in trial-and-error approaches. This review summarizes the current approaches in protein crystallization and surveys the first results to emerge from the structural genomics efforts.

Which Strategy for a Protein Crystallization Project?

NASA Technical Reports Server (NTRS)

Kundrot, Craig E.

2003-01-01

The three-dimensional, atomic-resolution protein structures produced by X-ray crystallography over the past 50+ years have led to tremendous chemical understanding of fundamental biochemical processes. The pace of discovery in protein crystallography has increased greatly with advances in molecular biology, crystallization techniques, cryo-crystallography, area detectors, synchrotrons and computing. While the methods used to produce single, well-ordered crystals have also evolved over the years in response to increased understanding and advancing technology, crystallization strategies continue to be rooted in trial-and-error approaches. This review summarizes the current approaches in protein crystallization and surveys the first results to emerge from the structural genomics efforts.

Crystal structure of N′′-benzyl-N′′-[3-(benzyl­dimethyl­aza­nium­yl)prop­yl]-N,N,N′,N′-tetra­methyl­guanidinium bis­(tetra­phenyl­borate)

PubMed Central

Tiritiris, Ioannis; Kantlehner, Willi

2015-01-01

In the crystal structure of the title salt, C24H38N4 2+·2C24H20B−, the C—N bond lengths in the central CN3 unit of the guanidinium ion are 1.3364 (13), 1.3407 (13) and 1.3539 (13) Å, indicating partial double-bond character. The central C atom is bonded to the three N atoms in a nearly ideal trigonal–planar geometry and the positive charge is delocalized in the CN3 plane. The bonds between the N atoms and the terminal methyl groups of the guanidinium moiety and the four C—N bonds to the central N atom of the (benzyl­dimethyl­aza­nium­yl)propyl group have single-bond character. In the crystal, C—H⋯π inter­actions between the guanidin­ium H atoms and the phenyl C atoms of the tetra­phenyl­borate ions are present, leading to the formation of a two-dimensional supra­molecular pattern parallel to the ac plane. PMID:26870511

Crystal structure and Hirshfeld surface analysis of aqua­bis­(nicotinamide-κN)bis­(4-sulfamoylbenzoato-κO 1)copper(II)

PubMed Central

Hökelek, Tuncer; Yavuz, Vijdan; Dal, Hakan; Necefoğlu, Hacali

2018-01-01

In the crystal of the title complex, [Cu(C7H6NO4S)2(C6H6N2O)2(H2O)], the CuII cation and the O atom of the coordinated water mol­ecule reside on a twofold rotation axis. The CuII ion is coordinated by two carboxyl­ate O atoms of the two symmetry-related 4-sulfamoylbenzoate (SB) anions and by two N atoms of the two symmetry-related nicotinamide (NA) mol­ecules at distances of 1.978 (2) and 2.025 (3) Å, respectively, forming a slightly distorted square-planar arrangement. The distorted square-pyramidal coordination environment is completed by the water O atom in the axial position at a distance of 2.147 (4) Å. In the crystal, the mol­ecules are linked via O—H⋯O and N—H⋯O hydrogen bonds with R 2 2(8) and R 2 2(18) ring motifs, forming a three-dimensional architecture. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯O/O⋯H (42.2%), H⋯H (25.7%) and H⋯C/C⋯H (20.0%) inter­actions. PMID:29416889

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.

Trapped Atoms in One-Dimensional Photonic Crystals

DTIC Science & Technology

2013-08-09

a single silicon -nitride nanobeam (refractive index n = 2) with a 1D array of filleted rectangular holes along the propagation direction; atoms are...trapped in the centers of the holes (figure 1( a )). The second waveguide consists of two parallel silicon nitride nanobeams, each with a periodic array...the refractive index of silicon nitride is approximately constant across the optical domain, we adopt the approximation based on a frequency

Transport properties of high quality heterostructures from unstable 2D crystals prepared in inert atmosphere

NASA Astrophysics Data System (ADS)

Yu, Geliang; Yang, Cao; Khestanova, Ekaterina; Mishchenko, Artem; Kretinin, Andy; Gorbachev, Roman; Novoselov, Konstantin; Andre, Geim; Manchester Group Team

Many layered materials can be cleaved down to individual atomic planes, similar to graphene, but only a small minority of them are stable under ambient conditions. The rest reacts and decomposes in air, which has severely hindered their investigation and possible uses. Here we introduce a remedial approach based on cleavage, transfer, alignment and encapsulation of airsensitive crystals, all inside a controlled inert atmosphere. To illustrate the technology, we choose two archetypal two-dimensional crystals unstable in air: black phosphorus and niobium diselenide. Our field-effect devices made from their monolayers are conductive and fully stable under ambient conditions, in contrast to the counterparts processed in air. NbSe2 remains superconducting down to the monolayer thickness. Starting with a trilayer, phosphorene devices reach sufficiently high mobilities to exhibit Landau quantization. The approach offers a venue to significantly expand the range of experimentally accessible two-dimensional crystals and their heterostructures.

Integration of neutron time-of-flight single-crystal Bragg peaks in reciprocal space

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

Schultz, Arthur J; Joergensen, Mads; Wang, Xiaoping

2014-01-01

The intensity of single crystal Bragg peaks obtained by mapping neutron time-of-flight event data into reciprocal space and integrating in various ways are compared. These include spherical integration with a fixed radius, ellipsoid fitting and integrating of the peak intensity and one-dimensional peak profile fitting. In comparison to intensities obtained by integrating in real detector histogram space, the data integrated in reciprocal space results in better agreement factors and more accurate atomic parameters. Furthermore, structure refinement using integrated intensities from one-dimensional profile fitting is demonstrated to be more accurate than simple peak-minus-background integration.

Inversion layer on the Ge(001) surface from the four-probe conductance measurements

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

Wojtaszek, Mateusz; Lis, Jakub, E-mail: j.lis@uj.edu.pl; Zuzak, Rafal

2014-07-28

We report four-probe conductance measurements with sub-micron resolution on atomically clean Ge(001) surfaces. A qualitative difference between n-type and p-type crystals is observed. The scaling behavior of the resistance on n-type samples indicates two-dimensional current flow, while for the p-type crystal a three-dimensional description is appropriate. We interpret this in terms of the formation of an inversion layer at the surface. This result points to the surface states, i.e., dangling bonds, as the driving force behind band bending in germanium. It also explains the intrinsic character of band bending in germanium.

Large Area 2D and 3D Colloidal Photonic Crystals Fabricated by a Roll-to-Roll Langmuir-Blodgett Method.

PubMed

Parchine, Mikhail; McGrath, Joe; Bardosova, Maria; Pemble, Martyn E

2016-06-14

We present our results on the fabrication of large area colloidal photonic crystals on flexible poly(ethylene terephthalate) (PET) film using a roll-to-roll Langmuir-Blodgett technique. Two-dimensional (2D) and three-dimensional (3D) colloidal photonic crystals from silica nanospheres (250 and 550 nm diameter) with a total area of up to 340 cm(2) have been fabricated in a continuous manner compatible with high volume manufacturing. In addition, the antireflective properties and structural integrity of the films have been enhanced via the use of a second roll-to-roll process, employing a slot-die coating of an optical adhesive over the photonic crystal films. Scanning electron microscopy images, atomic force microscopy images, and UV-vis optical transmission and reflection spectra of the fabricated photonic crystals are analyzed. This analysis confirms the high quality of the 2D and 3D photonic crystals fabricated by the roll-to-roll LB technique. Potential device applications of the large area 2D and 3D colloidal photonic crystals on flexible PET film are briefly reviewed.

"Building" 3D visualization skills in mineralogy

NASA Astrophysics Data System (ADS)

Gaudio, S. J.; Ajoku, C. N.; McCarthy, B. S.; Lambart, S.

2016-12-01

Studying mineralogy is fundamental for understanding the composition and physical behavior of natural materials in terrestrial and extraterrestrial environments. However, some students struggle and ultimately get discouraged with mineralogy course material because they lack well-developed spatial visualization skills that are needed to deal with three-dimensional (3D) objects, such as crystal forms or atomic-scale structures, typically represented in two-dimensional (2D) space. Fortunately, spatial visualization can improve with practice. Our presentation demonstrates a set of experiential learning activities designed to support the development and improvement of spatial visualization skills in mineralogy using commercially available magnetic building tiles, rods, and spheres. These instructional support activities guide students in the creation of 3D models that replicate macroscopic crystal forms and atomic-scale structures in a low-pressure learning environment and at low cost. Students physically manipulate square and triangularly shaped magnetic tiles to build 3D open and closed crystal forms (platonic solids, prisms, pyramids and pinacoids). Prismatic shapes with different closing forms are used to demonstrate the relationship between crystal faces and Miller Indices. Silica tetrahedra and octahedra are constructed out of magnetic rods (bonds) and spheres (oxygen atoms) to illustrate polymerization, connectivity, and the consequences for mineral formulae. In another activity, students practice the identification of symmetry elements and plane lattice types by laying magnetic rods and spheres over wallpaper patterns. The spatial visualization skills developed and improved through our experiential learning activities are critical to the study of mineralogy and many other geology sub-disciplines. We will also present pre- and post- activity assessments that are aligned with explicit learning outcomes.

Crystal structure of (eth­oxy­ethyl­idene)di­methyl­aza­nium ethyl sulfate

PubMed Central

Tiritiris, Ioannis; Saur, Stefan; Kantlehner, Willi

2015-01-01

In the title salt, C6H14NO+·C2H5SO4 −, the C—N bond lengths in the cation are 1.2981 (14), 1.4658 (14) and 1.4707 (15) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.3157 (13) Å shows double-bond character, indicating charge delocalization within the NCO plane of the iminium ion. In the crystal, C—H⋯O hydrogen bonds between H atoms of the cations and O atoms of neighbouring ethyl sulfate anions are present, generating a three-dimensional network. PMID:26870525

Microgravity

NASA Image and Video Library

2004-04-15

A semiconductor's usefulness is determined by how atoms are ordered within the crystal's underlying three-dimensional structure. While this mercury telluride and cadmium telluride alloy sample mixes completely in Earth -based laboratories, convective flows prevent them from mixing uniformly. In space, the ingredients mix more homogenously, resulting in a superior product.

Electron-phonon interaction in efficient perovskite blue emitters

NASA Astrophysics Data System (ADS)

Gong, Xiwen; Voznyy, Oleksandr; Jain, Ankit; Liu, Wenjia; Sabatini, Randy; Piontkowski, Zachary; Walters, Grant; Bappi, Golam; Nokhrin, Sergiy; Bushuyev, Oleksandr; Yuan, Mingjian; Comin, Riccardo; McCamant, David; Kelley, Shana O.; Sargent, Edward H.

2018-06-01

Low-dimensional perovskites have—in view of their high radiative recombination rates—shown great promise in achieving high luminescence brightness and colour saturation. Here we investigate the effect of electron-phonon interactions on the luminescence of single crystals of two-dimensional perovskites, showing that reducing these interactions can lead to bright blue emission in two-dimensional perovskites. Resonance Raman spectra and deformation potential analysis show that strong electron-phonon interactions result in fast non-radiative decay, and that this lowers the photoluminescence quantum yield (PLQY). Neutron scattering, solid-state NMR measurements of spin-lattice relaxation, density functional theory simulations and experimental atomic displacement measurements reveal that molecular motion is slowest, and rigidity greatest, in the brightest emitter. By varying the molecular configuration of the ligands, we show that a PLQY up to 79% and linewidth of 20 nm can be reached by controlling crystal rigidity and electron-phonon interactions. Designing crystal structures with electron-phonon interactions in mind offers a previously underexplored avenue to improve optoelectronic materials' performance.

Highly anisotropic solar-blind UV photodetector based on large-size two-dimensional α-MoO3 atomic crystals

NASA Astrophysics Data System (ADS)

Zhong, Mianzeng; Zhou, Ke; Wei, Zhongming; Li, Yan; Li, Tao; Dong, Huanli; Jiang, Lang; Li, Jingbo; Hu, Wenping

2018-07-01

Orthorhombic MoO3 (α-MoO3) is a typical layered n-type semiconductor with optical band gap over 2.7 eV, which have been widely studied in catalysis, gas sensing, lithium-ion batteries, field-emission, photoelectrical, photochromic and electrochromic devices, supercapacitors and organic solar cells. However, the bottleneck of generation large size atomic thin two-dimensional (2D) α-MoO3 crystals remain challenging this field (normally several micrometers size). Herein, we developed a facile vapor–solid (VS) process for controllable growth of large-size 2D α-MoO3 single crystals with a few nanometers thick and over 300 μm in lateral size. High-performance solar-blind photodetectors were fabricated based on individual 2D α-MoO3 single crystal. The detectors demonstrate outstanding optoelectronic properties under solar-blind UV light (254 nm), with a photoresponsivity of 67.9 A W‑1, external quantum efficiency of 3.3  ×  104%. More important, the devices showed strong in-plane anisotropy in optoelectronic response and transport properties, e.g. the photocurrent along b-axis was found to be 5 times higher than the values along c-axis under 254 nm UV light, and current ON/OFF ratio and mobility anisotropy is about 2 times high. Our work suggests an optimized synthesis routine for 2D crystals, and the great potential of 2D oxides in functional optoelectronics.

Ethyl 2-(4-meth-oxy-phen-yl)-6-oxa-3-aza-bicyclo[3.1.0]hexane-3-carboxyl-ate: crystal structure and Hirshfeld analysis.

PubMed

Zukerman-Schpector, Julio; Sugiyama, Fabricia H; Garcia, Ariel L L; Correia, Carlos Roque D; Jotani, Mukesh M; Tiekink, Edward R T

2017-07-01

The title compound, C 14 H 17 NO 4 , features an epoxide-O atom fused to a pyrrolidyl ring, the latter having an envelope conformation with the N atom being the flap. The 4-meth-oxy-phenyl group is orthogonal to [dihedral angle = 85.02 (6)°] and lies to the opposite side of the five-membered ring to the epoxide O atom, while the N-bound ethyl ester group (r.m.s. deviation of the five fitted atoms = 0.0187 Å) is twisted with respect to the ring [dihedral angle = 17.23 (9)°]. The most prominent inter-actions in the crystal are of the type methine-C-H⋯O(carbon-yl) and these lead to the formation of linear supra-molecular chains along the c axis; weak benzene-C-H⋯O(epoxide) and methine-C-H⋯O(meth-oxy) inter-actions connect these into a three-dimensional architecture. The analysis of the Hirshfeld surface confirms the presence of C-H⋯O inter-actions in the crystal, but also the dominance of H⋯H dispersion contacts.

Generalization of soft phonon modes

NASA Astrophysics Data System (ADS)

Rudin, Sven P.

2018-04-01

Soft phonon modes describe a collective movement of atoms that transform a higher-symmetry crystal structure into a lower-symmetry crystal structure. Such structural transformations occur at finite temperatures, where the phonons (i.e., the low-temperature vibrational modes) and the static perfect crystal structures provide an incomplete picture of the dynamics. Here, principal vibrational modes (PVMs) are introduced as descriptors of the dynamics of a material system with N atoms. The PVMs represent the independent collective movements of the atoms at a given temperature. Molecular dynamics (MD) simulations, here in the form of quantum MD using density functional theory calculations, provide both the data describing the atomic motion and the data used to construct the PVMs. The leading mode, PVM0, represents the 3 N -dimensional direction in which the system moves with greatest amplitude. For structural phase transitions, PVM0 serves as a generalization of soft phonon modes. At low temperatures, PVM0 reproduces the soft phonon mode in systems where one phonon dominates the phase transformation. In general, multiple phonon modes combine to describe a transformation, in which case PVM0 culls these phonon modes. Moreover, while soft phonon modes arise in the higher-symmetry crystal structure, PVM0 can be equally well calculated on either side of the structural phase transition. Two applications demonstrate these properties: first, transitions into and out of bcc titanium, and, second, the two crystal structures proposed for the β phase of uranium, the higher-symmetry structure of which stabilizes with temperature.

Self-organization of atoms coupled to a chiral reservoir

NASA Astrophysics Data System (ADS)

Eldredge, Zachary; Jarzynski, Christopher; Chang, Darrick; Gorshkov, Alexey

2016-05-01

Tightly confined modes of light, as in optical nanofibers or photonics crystal waveguides, can lead to large optical coupling in atomic systems, which mediates long-range interactions between atoms. These one-dimensional systems can naturally possess couplings which are asymmetric between modes in different directions. In this poster, we examine the self-organizing behavior of atoms in one dimension coupled to a chiral reservoir. We determine the behavior of the self-organized solution to the equations of motion in different parameter regimes, relative to both the detuning of the pump laser and the degree of reservoir chirality. In addition to the spatial configuration of self-organized atoms, we calculate possible experimental signatures.

Molecular transport through capillaries made with atomic-scale precision

NASA Astrophysics Data System (ADS)

Radha, B.; Esfandiar, A.; Wang, F. C.; Rooney, A. P.; Gopinadhan, K.; Keerthi, A.; Mishchenko, A.; Janardanan, A.; Blake, P.; Fumagalli, L.; Lozada-Hidalgo, M.; Garaj, S.; Haigh, S. J.; Grigorieva, I. V.; Wu, H. A.; Geim, A. K.

2016-10-01

Nanometre-scale pores and capillaries have long been studied because of their importance in many natural phenomena and their use in numerous applications. A more recent development is the ability to fabricate artificial capillaries with nanometre dimensions, which has enabled new research on molecular transport and led to the emergence of nanofluidics. But surface roughness in particular makes it challenging to produce capillaries with precisely controlled dimensions at this spatial scale. Here we report the fabrication of narrow and smooth capillaries through van der Waals assembly, with atomically flat sheets at the top and bottom separated by spacers made of two-dimensional crystals with a precisely controlled number of layers. We use graphene and its multilayers as archetypal two-dimensional materials to demonstrate this technology, which produces structures that can be viewed as if individual atomic planes had been removed from a bulk crystal to leave behind flat voids of a height chosen with atomic-scale precision. Water transport through the channels, ranging in height from one to several dozen atomic planes, is characterized by unexpectedly fast flow (up to 1 metre per second) that we attribute to high capillary pressures (about 1,000 bar) and large slip lengths. For channels that accommodate only a few layers of water, the flow exhibits a marked enhancement that we associate with an increased structural order in nanoconfined water. Our work opens up an avenue to making capillaries and cavities with sizes tunable to ångström precision, and with permeation properties further controlled through a wide choice of atomically flat materials available for channel walls.

Exploring the atomic structure and conformational flexibility of a 320 Å long engineered viral fiber using X-ray crystallography.

PubMed

Bhardwaj, Anshul; Casjens, Sherwood R; Cingolani, Gino

2014-02-01

Protein fibers are widespread in nature, but only a limited number of high-resolution structures have been determined experimentally. Unlike globular proteins, fibers are usually recalcitrant to form three-dimensional crystals, preventing single-crystal X-ray diffraction analysis. In the absence of three-dimensional crystals, X-ray fiber diffraction is a powerful tool to determine the internal symmetry of a fiber, but it rarely yields atomic resolution structural information on complex protein fibers. An 85-residue-long minimal coiled-coil repeat unit (MiCRU) was previously identified in the trimeric helical core of tail needle gp26, a fibrous protein emanating from the tail apparatus of the bacteriophage P22 virion. Here, evidence is provided that an MiCRU can be inserted in frame inside the gp26 helical core to generate a rationally extended fiber (gp26-2M) which, like gp26, retains a trimeric quaternary structure in solution. The 2.7 Å resolution crystal structure of this engineered fiber, which measures ∼320 Å in length and is only 20-35 Å wide, was determined. This structure, the longest for a trimeric protein fiber to be determined to such a high resolution, reveals the architecture of 22 consecutive trimerization heptads and provides a framework to decipher the structural determinants for protein fiber assembly, stability and flexibility.

Semiconductor Characterization: from Growth to Manufacturing

NASA Astrophysics Data System (ADS)

Colombo, Luigi

The successful growth and/or deposition of materials for any application require basic understanding of the materials physics for a given device. At the beginning, the first and most obvious characterization tool is visual observation; this is particularly true for single crystal growth. The characterization tools are usually prioritized in order of ease of measurement, and have become especially sophisticated as we have moved from the characterization of macroscopic crystals and films to atomically thin materials and nanostructures. While a lot attention is devoted to characterization and understanding of materials physics at the nano level, the characterization of single crystals as substrates or active components is still critically important. In this presentation, I will review and discuss the basic materials characterization techniques used to get to the materials physics to bring crystals and thin films from research to manufacturing in the fields of infrared detection, non-volatile memories, and transistors. Finally I will present and discuss metrology techniques used to understand the physics and chemistry of atomically thin two-dimensional materials for future device applications.

Simulation of Phonon Spectra in Three-Component Two-Dimensional Crystals of Refractory-Metal Dichalcogenides

NASA Astrophysics Data System (ADS)

Alexeev, A. Yu.; Krivosheeva, A. V.; Shaposhnikov, V. L.; Borisenko, V. E.

2017-09-01

A model for ab initio calculation of the phonon properties of three-component solid solutions of refractory-metal dichalcogenides was developed based on the assumption that displacements of the same type of chalcogen atoms and decoupled displacements of the metal atoms were identical. The calculated phonon frequencies at the Γ-point for monomolecular layers of MoS2-xSex and MoS2-xTex agreed with existing experimental Raman spectra.

Coherent and radiative couplings through two-dimensional structured environments

NASA Astrophysics Data System (ADS)

Galve, F.; Zambrini, R.

2018-03-01

We study coherent and radiative interactions induced among two or more quantum units by coupling them to two-dimensional (2D) lattices acting as structured environments. This model can be representative of atoms trapped near photonic crystal slabs, trapped ions in Coulomb crystals, or to surface acoustic waves on piezoelectric materials, cold atoms on state-dependent optical lattices, or even circuit QED architectures, to name a few. We compare coherent and radiative contributions for the isotropic and directional regimes of emission into the lattice, for infinite and finite lattices, highlighting their differences and existing pitfalls, e.g., related to long-time or large-lattice limits. We relate the phenomenon of directionality of emission with linear-shaped isofrequency manifolds in the dispersion relation, showing a simple way to disrupt it. For finite lattices, we study further details such as the scaling of resonant number of lattice modes for the isotropic and directional regimes, and relate this behavior with known van Hove singularities in the infinite lattice limit. Furthermore, we export the understanding of emission dynamics with the decay of entanglement for two quantum, atomic or bosonic, units coupled to the 2D lattice. We analyze in some detail completely subradiant configurations of more than two atoms, which can occur in the finite lattice scenario, in contrast with the infinite lattice case. Finally, we demonstrate that induced coherent interactions for dark states are zero for the finite lattice.

The 2DX robot: a membrane protein 2D crystallization Swiss Army knife.

PubMed

Iacovache, Ioan; Biasini, Marco; Kowal, Julia; Kukulski, Wanda; Chami, Mohamed; van der Goot, F Gisou; Engel, Andreas; Rémigy, Hervé-W

2010-03-01

Among the state-of-the-art techniques that provide experimental information at atomic scale for membrane proteins, electron crystallography, atomic force microscopy and solid state NMR make use of two-dimensional crystals. We present a cyclodextrin-driven method for detergent removal implemented in a fully automated robot. The kinetics of the reconstitution processes is precisely controlled, because the detergent complexation by cyclodextrin is of stoichiometric nature. The method requires smaller volumes and lower protein concentrations than established 2D crystallization methods, making it possible to explore more conditions with the same amount of protein. The method yielded highly ordered 2D crystals diffracting to high resolution from the pore-forming toxin Aeromonas hydrophila aerolysin (2.9A), the plant aquaporin SoPIP2;1 (3.1A) and the human aquaporin-8 (hAQP8; 3.3A). This new method outperforms traditional 2D crystallization approaches in terms of accuracy, flexibility, throughput, and allows the usage of detergents having low critical micelle concentration (CMC), which stabilize the structure of membrane proteins in solution. (c) 2009 Elsevier Inc. All rights reserved.

Large Area Atomically Flat Surfaces via Exfoliation of Bulk Bi 2Se 3 Single Crystals

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

Melamed, Celeste L.; Ortiz, Brenden R.; Gorai, Prashun

In this paper, we present an exfoliation method that produces cm 2-area atomically flat surfaces from bulk layered single crystals, with broad applications such as for the formation of lateral heterostructures and for use as substrates for van der Waals epitaxy. Single crystals of Bi 2Se 3 were grown using the Bridgman method and examined with X-ray reciprocal space maps, Auger spectroscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. An indium-bonding exfoliation technique was developed that produces multiple ~100 um thick atomically flat, macroscopic (>1 cm 2) slabs from each Bi 2Se 3 source crystal. Two-dimensional X-ray diffraction and reciprocalmore » space maps confirm the high crystalline quality of the exfoliated surfaces. Atomic force microscopy reveals that the exfoliated surfaces have an average root-mean-square (RMS) roughness of ~0.04 nm across 400 μm 2 scans and an average terrace width of 70 um between step edges. First-principles calculations reveal exfoliation energies of Bi 2Se 3 and a number of other layered compounds, which demonstrate relevance of our method across the field of 2D materials. While many potential applications exist, excellent lattice matching with the III-V alloy space suggests immediate potential for the use of these exfoliated layered materials as epitaxial substrates for photovoltaic development.« less

Large Area Atomically Flat Surfaces via Exfoliation of Bulk Bi 2Se 3 Single Crystals

DOE PAGES

Melamed, Celeste L.; Ortiz, Brenden R.; Gorai, Prashun; ...

2017-09-12

In this paper, we present an exfoliation method that produces cm 2-area atomically flat surfaces from bulk layered single crystals, with broad applications such as for the formation of lateral heterostructures and for use as substrates for van der Waals epitaxy. Single crystals of Bi 2Se 3 were grown using the Bridgman method and examined with X-ray reciprocal space maps, Auger spectroscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. An indium-bonding exfoliation technique was developed that produces multiple ~100 um thick atomically flat, macroscopic (>1 cm 2) slabs from each Bi 2Se 3 source crystal. Two-dimensional X-ray diffraction and reciprocalmore » space maps confirm the high crystalline quality of the exfoliated surfaces. Atomic force microscopy reveals that the exfoliated surfaces have an average root-mean-square (RMS) roughness of ~0.04 nm across 400 μm 2 scans and an average terrace width of 70 um between step edges. First-principles calculations reveal exfoliation energies of Bi 2Se 3 and a number of other layered compounds, which demonstrate relevance of our method across the field of 2D materials. While many potential applications exist, excellent lattice matching with the III-V alloy space suggests immediate potential for the use of these exfoliated layered materials as epitaxial substrates for photovoltaic development.« less

Probing interlayer interactions in WS2 -graphene van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Chung, Ting Fung; Yuan, Long; Huang, Libai; Chen, Yong P.

Two-dimensional crystals based van der Waals coupled heterostructures are of interest owing to their potential applications for flexible and transparent electronics and optoelectronics. The interaction between the 2D layered crystals at the interfaces of these heterostructures is crucial in determining the overall performance and is strongly affected by contamination and interfacial strain. We have fabricated heterostructures consisting of atomically thin exfoliated WS2 and chemical-vapor-deposited (CVD) graphene, and studied the interaction and coupling between the WS2 and graphene using atomic force microscopy (AFM), Raman spectroscopy and femtosecond transient absorption measurement (TAM). Information from Raman-active phonon modes allows us to estimate charge doping in graphene and interfacial strain on the crystals. Spatial imaging probed by TAM can be correlated to the heterostructure surface morphology measured by AFM and Raman maps of graphene and WS2, showing how the interlayer coupling alters exciton decay dynamics quantitatively.

Synthesis and Crystal Structure of a New Ruthenium Silicophosphate: RuP 3SiO 11

NASA Astrophysics Data System (ADS)

Fukuoka, Hiroshi; Imoto, Hideo; Saito, Taro

1996-01-01

A new ruthenium silicophosphate RuP3SiO11was obtained and the structure was determined by single-crystal X-ray diffraction. It crystallizes in the trigonal space groupR3cwitha= 8.253(3)Å,c= 39.317(4)Å,V= 2319(2)Å3,Z= 12,R= 0.029, andRW= 0.026. The structure is composed of RuO6, Si2O7, and P2O7units. The Si2O7unit shares the six oxygen atoms with six P2O7units, while the P2O7unit shares the six oxygen atoms with two Si2O7units and four RuO6octahedra. The anionic part forms an infinite three-dimensional network of silicophosphate. RuP3SiO11is isotypic with MoP3SiO11.

Fabrication of Al2O3 coated 2D TiO2 nanoparticle photonic crystal layers by reverse nano-imprint lithography and plasma enhanced atomic layer deposition.

PubMed

Kim, Ki-Kang; Ko, Ki-Young; Ahn, Jinho

2013-10-01

This paper reports simple process to enhance the extraction efficiency of photoluminescence (PL) from Eu-doped yttrium oxide (Y2O3:Eu3+) thin-film phosphor (TFP). Two-dimensional (2D) photonic crystal layer (PCL) was fabricated on Y2O3:Eu3+ phosphor films by reverse nano-imprint method using TiO2 nanoparticle solution as a nano-imprint resin and a 2D hole-patterned PDMS stamp. Atomic scale controlled Al2O3 deposition was performed onto this 2D nanoparticle PCL for the optimization of the photonic crystal pattern size and stabilization of TiO2 nanoparticle column structure. As a result, the light extraction efficiency of the Y2O3:Eu3+ phosphor film was improved by 2.0 times compared to the conventional Y2O3:Eu3+ phosphor film.

2-(4,5-Dihydro-1H-imidazol-2-yl)­pyridine

PubMed Central

Kia, Reza; Fun, Hoong-Kun; Kargar, Hadi

2009-01-01

In the mol­ecule of the title compound, C8H9N3, a new imidazoline derivative, the six- and five-membered rings are slightly twisted away from each other, forming a dihedral angle of 7.96 (15)°. In the crystal structure, neighbouring mol­ecules are linked together by inter­molecular N—H⋯N hydrogen bonds into extended one-dimensional chains along the a axis. The pyridine N atom is in close proximity to a carbon-bound H atom of the imidazoline ring, with an H⋯N distance of 2.70 Å, which is slightly shorter than the sum of the van der Waals radii of these atoms (2.75 Å). The crystal structure is further stabilized by inter­molecular C—H⋯π and π–π inter­actions (centroid-to-centroid distance 3.853 Å). PMID:21582505

A new type of two-dimensional carbon crystal prepared from 1,3,5-trihydroxybenzene

NASA Astrophysics Data System (ADS)

Du, Qi-Shi; Tang, Pei-Duo; Huang, Hua-Lin; Du, Fang-Li; Huang, Kai; Xie, Neng-Zhong; Long, Si-Yu; Li, Yan-Ming; Qiu, Jie-Shan; Huang, Ri-Bo

2017-01-01

A new two-dimensional (2D) carbon crystal, different from graphene, has been prepared from 1,3,5-trihydroxybenzene, consisting of 4-carbon and 6-carbon rings in 1:1 ratio, named 4-6 carbophene by authors, in which all carbon atoms possess sp2 hybrid orbitals with some distortion, forming an extensive conjugated π-bonding planar structure. The angles between the three σ-bonds of the carbon sp2 orbitals are roughly 120°, 90°, and 150°. Each of the three non-adjacent sides of a 6C-ring is shared with a 4C-ring; and each of the two opposite sides of a 4C-ring is shared with a 6C-ring. Dodecagonal holes with a diameter of approximate 5.8 Å are regularly located throughout the 2D carbon crystal. Even though the bond energies in 4-6 carbophene are weaker than those in the graphene, the new planar crystal is quite stable in ambient conditions. The 4-6 carbophene can be synthetized from 1,3,5-trihydroxybenzene or other benzene derivatives through dehydration and polymerization reactions, and may possess several possible patterns that form a family of 2D carbon crystals. A possible side reaction involving 1,3,5-trihydroxybenzene is also discussed, which may produce a carbon-oxygen two dimensional crystal.

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

Kalsi, Deepti; Rayaprol, S.; Siruguri, V.

We report the crystallographic properties of RE{sub 2}NiGe{sub 3} (RE=La, Ce) synthesized by arc melting. Rietveld refinement on the powder neutron diffraction (ND) data suggest both compounds are isostructural and crystallize in the non-centrosymmetric Er{sub 2}RhSi{sub 3} type structure having hexagonal space group P6{sup ¯}2c. In the crystal structure of RE{sub 2}NiGe{sub 3}, two dimensional arrangements of nickel and germanium atoms lead to the formation of hexagonal layers with rare earth atoms sandwiched between them. Magnetic susceptibility measurements performed in low fields exhibit antiferromagnetic ordering in cerium compound around (T{sub o}=) 3.2 K. Neutron diffraction measurements at 2.8 K (i.e.,more » at T« less

Crystal structure of ethyl (E)-2-cyano-3-(thio-phen-2-yl)acrylate: two conformers forming a discrete disorder.

PubMed

Castro Agudelo, Brian; Cárdenas, Juan C; Macías, Mario A; Ochoa-Puentes, Cristian; Sierra, Cesar A

2017-09-01

In the title compound, C 10 H 9 NO 2 S, all the non-H atoms, except for the ethyl fragment, lie nearly in the same plane. Despite the mol-ecular planarity, the ethyl fragment presents more than one conformation, giving rise to a discrete disorder, which was modelled with two different crystallographic sites for the eth-oxy O and eth-oxy α-C atoms, with occupancy values of 0.5. In the crystal, the three-dimensional array is mainly directed by C-H⋯(O,N) inter-actions, giving rise to inversion dimers with R 2 2 (10) and R 2 2 (14) motifs and infinite chains running along the [100] direction.

Deducing 2D crystal structure at the liquid/solid interface with atomic resolution: a combined STM and SFG study.

PubMed

McClelland, Arthur A; Ahn, Seokhoon; Matzger, Adam J; Chen, Zhan

2009-11-17

Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional (2D) crystals formed by an isophthalic acid diester on the surface of highly oriented pyrolytic graphite, providing complementary measurements to scanning tunneling microscopy (STM) and computational modeling. SFG results indicate that both aromatic and C=O groups in the 2D crystal tilt from the surface. This study demonstrates that a combination of SFG and STM techniques can be used to gain a more complete picture of 2D crystal structure, and it is necessary to consider solvent-2D crystal interactions and dynamics in the computer models to achieve an accurate representation of interfacial structure.

Hydrothermal synthesis of zinc(II)-phosphonate coordination polymers with different dimensionality (0D, 2D, 3D) and dimensionality change in the solid phase (0D→3D) induced by temperature

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

Fernández-Zapico, Eva; Montejo-Bernardo, Jose; Fernández-González, Alfonso

2015-05-15

Three new zinc(II) coordination polymers, [Zn(HO{sub 3}PCH{sub 2}CH{sub 2}COO)(C{sub 12}H{sub 8}N{sub 2})(H{sub 2}O)] (1), [Zn{sub 3}(O{sub 3}PCH{sub 2}CH{sub 2}COO){sub 2}(C{sub 12}H{sub 8}N{sub 2})](H{sub 2}O){sub 3.40} (2) and [Zn{sub 5}(HO{sub 3}PCH{sub 2}CH{sub 2}COO){sub 2}(O{sub 3}PCH{sub 2}CH{sub 2}COO){sub 2}(C{sub 12}H{sub 8}N{sub 2}){sub 4}](H{sub 2}O){sub 0.32} (3), with different structural dimensionality (0D, 2D and 3D, respectively) have been prepared by hydrothermal synthesis, and their structures were determined by single-crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic system (P2{sub 1}/c) forming discrete dimeric units bonded through H-bonds, while compounds 2 and 3 crystallize in the triclinic (P−1) and the monoclinic (C2/c) systems, respectively.more » Compound 3, showing three different coordination numbers (4, 5 and 6) for the zinc atoms, has also been obtained by thermal treatment of 1 (probed by high-temperature XRPD experiments). The crystalline features of these compounds, related to the coordination environments for the zinc atoms in each structure, provoke the increase of the relative fluorescence for 2 and 3, compared to the free phenanthroline. Thermal analysis (TG and DSC) and XPS studies have been also carried out for all compounds. - Graphical abstract: Three new coordination compounds of zinc with 2-carboxyethylphosphonic acid (H{sub 2}PPA) and phenanthroline have been obtained by hydrothermal synthesis. The crystalline structure depends on the different coordination environments of the zinc atoms (see two comparative Zn{sub 6}-moieties). The influence of the different coordination modes of H{sub 2}PPA with the central atom in all structures have been studied, being found new coordination modes for this ligand. Several compounds show a significant increase in relative fluorescence with respect to the free phenanthroline. - Highlights: • Compounds have been obtained modifying the reaction time and the rate of reagents. • Dimensionality and crystalline structure is a function of the zinc environments. • New coordination modes for 2-carboxyethylphosphonic acid are reported. • 3D-compound presents three different coordination environments for the zinc atoms. • Fluorescence properties are related to the structural dimensionality.« less

Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit.

PubMed

Huang, Bevin; Clark, Genevieve; Navarro-Moratalla, Efrén; Klein, Dahlia R; Cheng, Ran; Seyler, Kyle L; Zhong, Ding; Schmidgall, Emma; McGuire, Michael A; Cobden, David H; Yao, Wang; Xiao, Di; Jarillo-Herrero, Pablo; Xu, Xiaodong

2017-06-07

Since the discovery of graphene, the family of two-dimensional materials has grown, displaying a broad range of electronic properties. Recent additions include semiconductors with spin-valley coupling, Ising superconductors that can be tuned into a quantum metal, possible Mott insulators with tunable charge-density waves, and topological semimetals with edge transport. However, no two-dimensional crystal with intrinsic magnetism has yet been discovered; such a crystal would be useful in many technologies from sensing to data storage. Theoretically, magnetic order is prohibited in the two-dimensional isotropic Heisenberg model at finite temperatures by the Mermin-Wagner theorem. Magnetic anisotropy removes this restriction, however, and enables, for instance, the occurrence of two-dimensional Ising ferromagnetism. Here we use magneto-optical Kerr effect microscopy to demonstrate that monolayer chromium triiodide (CrI 3 ) is an Ising ferromagnet with out-of-plane spin orientation. Its Curie temperature of 45 kelvin is only slightly lower than that of the bulk crystal, 61 kelvin, which is consistent with a weak interlayer coupling. Moreover, our studies suggest a layer-dependent magnetic phase, highlighting thickness-dependent physical properties typical of van der Waals crystals. Remarkably, bilayer CrI 3 displays suppressed magnetization with a metamagnetic effect, whereas in trilayer CrI 3 the interlayer ferromagnetism observed in the bulk crystal is restored. This work creates opportunities for studying magnetism by harnessing the unusual features of atomically thin materials, such as electrical control for realizing magnetoelectronics, and van der Waals engineering to produce interface phenomena.

Synthesis, spectral characterization and X-ray crystal structure studies of 3-(benzo[d][1,3]dioxol-5-yl)-5-(3-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazole-1-carboxamide: Hirshfeld surface, DFT and thermal analysis

NASA Astrophysics Data System (ADS)

Kumara, Karthik; Dileep Kumar, A.; Naveen, S.; Ajay Kumar, K.; Lokanath, N. K.

2018-06-01

A novel pyrazole derivative, 3-(benzo[d][1,3]dioxol-5-yl)-5-(3-methylthiophen-2-yl)-4,5-dihydro-1H-pyrazole-1-carboxamide was synthesized and characterized by elemental analysis, FT-IR, NMR (1H and 13C), MS, UV-visible spectra and finally the structure was confirmed by the single crystal X-ray diffraction studies. The title compound (C16H15N3O3S) crystallized in the triclinic crystal system, with the space group Pī. A dihedral angle of 65.84(1)° between the pyrazole and the thiophene rings confirms the twisted conformation between them. The X-ray structure revealed that the pyrazole ring adopts an E-form and an envelope conformation on C7 atom. The crystal and molecular structure of the title compound is stabilized by inter molecular hydrogen bonds. The compound possesses three dimensional supramolecular self-assembly, in which Csbnd H⋯O and Nsbnd H⋯O chains build up two dimensional arrays, which are extended to 3D network through Csbnd H···Cg and Csbnd O···Cg interactions. The structure also exhibits intramolecular hydrogen bonds of the type Nsbnd H⋯N and π···π stacking interactions, which contributes to the crystal packing. Further, Hirshfeld surface analysis was carried out for the graphical visualization of several short intermolecular interactions on the molecular surface while the 2D finger-print plot provides percentage contribution of each individual atom-to-atom interactions. The thermal decomposition of the compound has been studied by thermogravimetric analysis. The molecular geometries and electronic structures of the compounds were fully optimized, calculated with ab-initio methods by HF, DFT/B3LYP functional in combination of different basis set with different solvent environment and the structural parameters were compared with the experimental data. The Mulliken atomic charges and molecular electrostatic potential on molecular van der Waals (vdW) surface were calculated to know the electrophilic and nucleophilic regions of the molecular surface. Nonlinear optical properties of the title compound were also discussed based on the polarizability and hyperpolarizability values.

Two- and three-dimensional networks of gadolinium(III) with dicarboxylate ligands: synthesis, crystal structure, and magnetic properties.

PubMed

Cañadillas-Delgado, Laura; Pasan, Jorge; Fabelo, Oscar; Hernandez-Molina, María; Lloret, Francesc; Julve, Miguel; Ruiz-Pérez, Catalina

2006-12-25

Four gadolinium(III) complexes with dicarboxylate ligands of formulas [Gd2(mal)3(H2O)5]n.2nH2O (1), [Gd2(mal)3(H2O)6]n (2), [NaGd(mal)(ox)(H2O)3]n (3), and [Gd2(ox)3(H2O)6]n.2.5nH2O (4) (mal = malonate; ox = oxalate) have been prepared, and their magnetic properties have been investigated as a function of the temperature. The structures of 1-3 have been determined by X-ray diffraction methods. The crystal structure of 4 was already known, and it is made of hexagonal layers of Gd atoms that are bridged by bis-bidentate oxalate. Compound 1 is isostructural with the europium(III) malonate complex [Eu2(mal)3(H2O)5]n.2nH2O,1 whose structure was reported elsewhere. The Gd atoms in 1 define a two-dimensional network where a terminal bidentate and bridging bidentate/bis-monodentate and tris-bidentate coordination modes of malonate occur. Compound 2 has a three-dimensional structure with a structural phase transition at 226 K, which involves a change of the space group from I2/a to Ia. Although its structure at room temperature was already known, that below 226 K was not. Pairs of Gd atoms with a double oxo-carboxylate bridge occur in both phases, and the main differences between both structures deal with the Gd environment and the H-bond pattern. 3 is also a three-dimensional compound, and it was obtained by reacting Gd(III) ions with malonic acid in a silica gel medium. Oxalic acid results as an oxidized product of the malonic acid, and single crystals of the heteroleptic complex were produced. The Gd atoms in 3 are connected through bis-bidentate oxalate and carboxylate-malonate bridges in the anti-anti and anti-syn coordination modes. Compounds 1 and 2 exhibit weak but significant ferromagnetic couplings between the Gd(III) ions through the single (1) and double (2) oxo-carboxylate bridges, whereas antiferromagnetic interactions across the bis-bidentate oxalate account for the overall antiferromagnetic behavior observed in 3 and 4.

In-plane heterostructures of graphene and hexagonal boron nitride with controlled domain sizes

NASA Astrophysics Data System (ADS)

Liu, Zheng; Ma, Lulu; Shi, Gang; Zhou, Wu; Gong, Yongji; Lei, Sidong; Yang, Xuebei; Zhang, Jiangnan; Yu, Jingjiang; Hackenberg, Ken P.; Babakhani, Aydin; Idrobo, Juan-Carlos; Vajtai, Robert; Lou, Jun; Ajayan, Pulickel M.

2013-02-01

Graphene and hexagonal boron nitride (h-BN) have similar crystal structures with a lattice constant difference of only 2%. However, graphene is a zero-bandgap semiconductor with remarkably high carrier mobility at room temperature, whereas an atomically thin layer of h-BN is a dielectric with a wide bandgap of ~5.9 eV. Accordingly, if precise two-dimensional domains of graphene and h-BN can be seamlessly stitched together, hybrid atomic layers with interesting electronic applications could be created. Here, we show that planar graphene/h-BN heterostructures can be formed by growing graphene in lithographically patterned h-BN atomic layers. Our approach can create periodic arrangements of domains with size ranging from tens of nanometres to millimetres. The resulting graphene/h-BN atomic layers can be peeled off the growth substrate and transferred to various platforms including flexible substrates. We also show that the technique can be used to fabricate two-dimensional devices, such as a split closed-loop resonator that works as a bandpass filter.

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.

7-Chloro-4-[(7-chloro­quinolin-4-yl)sulfan­yl]quinoline dihydrate

PubMed Central

Wardell, James L.; Tiekink, Edward R. T.

2012-01-01

In the title thio­ether dihydrate, C18H10Cl2N2S·2H2O, the S-bound quinolinyl residues are almost orthogonal, forming a dihedral angle of 72.36 (4)°. In the crystal, the four water mol­ecules are connected via an eight-membered {⋯OH}4 synthon with each of the four pendent water H atoms hydrogen bonded to a pyridine N atom to stabilize a three-dimensional architecture. PMID:22589973

A novel artificial condensed matter lattice and a new platform for one-dimensional topological phases

DOE PAGES

Belopolski, Ilya; Xu, Su -Yang; Koirala, Nikesh; ...

2017-03-24

Engineered lattices in condensed matter physics, such as cold-atom optical lattices or photonic crystals, can have properties that are fundamentally different from those of naturally occurring electronic crystals. We report a novel type of artificial quantum matter lattice. Our lattice is a multilayer heterostructure built from alternating thin films of topological and trivial insulators. Each interface within the heterostructure hosts a set of topologically protected interface states, and by making the layers sufficiently thin, we demonstrate for the first time a hybridization of interface states across layers. In this way, our heterostructure forms an emergent atomic chain, where the interfacesmore » act as lattice sites and the interface states act as atomic orbitals, as seen from our measurements by angle-resolved photoemission spectroscopy. By changing the composition of the heterostructure, we can directly control hopping between lattice sites. We realize a topological and a trivial phase in our superlattice band structure. We argue that the superlattice may be characterized in a significant way by a one-dimensional topological invariant, closely related to the invariant of the Su-Schrieffer-Heeger model. Our topological insulator heterostructure demonstrates a novel experimental platform where we can engineer band structures by directly controlling how electrons hop between lattice sites.« less

A novel artificial condensed matter lattice and a new platform for one-dimensional topological phases

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

Belopolski, Ilya; Xu, Su -Yang; Koirala, Nikesh

Engineered lattices in condensed matter physics, such as cold-atom optical lattices or photonic crystals, can have properties that are fundamentally different from those of naturally occurring electronic crystals. We report a novel type of artificial quantum matter lattice. Our lattice is a multilayer heterostructure built from alternating thin films of topological and trivial insulators. Each interface within the heterostructure hosts a set of topologically protected interface states, and by making the layers sufficiently thin, we demonstrate for the first time a hybridization of interface states across layers. In this way, our heterostructure forms an emergent atomic chain, where the interfacesmore » act as lattice sites and the interface states act as atomic orbitals, as seen from our measurements by angle-resolved photoemission spectroscopy. By changing the composition of the heterostructure, we can directly control hopping between lattice sites. We realize a topological and a trivial phase in our superlattice band structure. We argue that the superlattice may be characterized in a significant way by a one-dimensional topological invariant, closely related to the invariant of the Su-Schrieffer-Heeger model. Our topological insulator heterostructure demonstrates a novel experimental platform where we can engineer band structures by directly controlling how electrons hop between lattice sites.« less

Exploring the atomic structure and conformational flexibility of a 320 Å long engineered viral fiber using X-ray crystallography

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

Bhardwaj, Anshul; Casjens, Sherwood R.; Cingolani, Gino, E-mail: gino.cingolani@jefferson.edu

2014-02-01

This study presents the crystal structure of a ∼320 Å long protein fiber generated by in-frame extension of its repeated helical coiled-coil core. Protein fibers are widespread in nature, but only a limited number of high-resolution structures have been determined experimentally. Unlike globular proteins, fibers are usually recalcitrant to form three-dimensional crystals, preventing single-crystal X-ray diffraction analysis. In the absence of three-dimensional crystals, X-ray fiber diffraction is a powerful tool to determine the internal symmetry of a fiber, but it rarely yields atomic resolution structural information on complex protein fibers. An 85-residue-long minimal coiled-coil repeat unit (MiCRU) was previously identifiedmore » in the trimeric helical core of tail needle gp26, a fibrous protein emanating from the tail apparatus of the bacteriophage P22 virion. Here, evidence is provided that an MiCRU can be inserted in frame inside the gp26 helical core to generate a rationally extended fiber (gp26-2M) which, like gp26, retains a trimeric quaternary structure in solution. The 2.7 Å resolution crystal structure of this engineered fiber, which measures ∼320 Å in length and is only 20–35 Å wide, was determined. This structure, the longest for a trimeric protein fiber to be determined to such a high resolution, reveals the architecture of 22 consecutive trimerization heptads and provides a framework to decipher the structural determinants for protein fiber assembly, stability and flexibility.« less

Generalization of soft phonon modes

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

Rudin, Sven P.

Soft phonon modes describe a collective movement of atoms that transform a higher-symmetry crystal structure into a lower-symmetry crystal structure. Such structural transformations occur at finite temperatures, where the phonons (i.e., the low-temperature vibrational modes) and the static perfect crystal structures provide an incomplete picture of the dynamics. In this paper, principal vibrational modes (PVMs) are introduced as descriptors of the dynamics of a material system withmore » $N$ atoms. The PVMs represent the independent collective movements of the atoms at a given temperature. Molecular dynamics (MD) simulations, here in the form of quantum MD using density functional theory calculations, provide both the data describing the atomic motion and the data used to construct the PVMs. The leading mode, $${\\mathrm{PVM}}_{0}$$, represents the $3N$-dimensional direction in which the system moves with greatest amplitude. For structural phase transitions, $${\\mathrm{PVM}}_{0}$$ serves as a generalization of soft phonon modes. At low temperatures, $${\\mathrm{PVM}}_{0}$$ reproduces the soft phonon mode in systems where one phonon dominates the phase transformation. In general, multiple phonon modes combine to describe a transformation, in which case $${\\mathrm{PVM}}_{0}$$ culls these phonon modes. Moreover, while soft phonon modes arise in the higher-symmetry crystal structure, $${\\mathrm{PVM}}_{0}$$ can be equally well calculated on either side of the structural phase transition. Finally, two applications demonstrate these properties: first, transitions into and out of bcc titanium, and, second, the two crystal structures proposed for the $${\\beta}$$ phase of uranium, the higher-symmetry structure of which stabilizes with temperature.« less

Generalization of soft phonon modes

DOE PAGES

Rudin, Sven P.

2018-04-27

Soft phonon modes describe a collective movement of atoms that transform a higher-symmetry crystal structure into a lower-symmetry crystal structure. Such structural transformations occur at finite temperatures, where the phonons (i.e., the low-temperature vibrational modes) and the static perfect crystal structures provide an incomplete picture of the dynamics. In this paper, principal vibrational modes (PVMs) are introduced as descriptors of the dynamics of a material system withmore » $N$ atoms. The PVMs represent the independent collective movements of the atoms at a given temperature. Molecular dynamics (MD) simulations, here in the form of quantum MD using density functional theory calculations, provide both the data describing the atomic motion and the data used to construct the PVMs. The leading mode, $${\\mathrm{PVM}}_{0}$$, represents the $3N$-dimensional direction in which the system moves with greatest amplitude. For structural phase transitions, $${\\mathrm{PVM}}_{0}$$ serves as a generalization of soft phonon modes. At low temperatures, $${\\mathrm{PVM}}_{0}$$ reproduces the soft phonon mode in systems where one phonon dominates the phase transformation. In general, multiple phonon modes combine to describe a transformation, in which case $${\\mathrm{PVM}}_{0}$$ culls these phonon modes. Moreover, while soft phonon modes arise in the higher-symmetry crystal structure, $${\\mathrm{PVM}}_{0}$$ can be equally well calculated on either side of the structural phase transition. Finally, two applications demonstrate these properties: first, transitions into and out of bcc titanium, and, second, the two crystal structures proposed for the $${\\beta}$$ phase of uranium, the higher-symmetry structure of which stabilizes with temperature.« less

Electronic distributions within protein phenylalanine aromatic rings are reflected by the three-dimensional oxygen atom environments.

PubMed Central

Thomas, K A; Smith, G M; Thomas, T B; Feldmann, R J

1982-01-01

The atomic environments of 170 phenylalanine-residue aromatic rings from 28 protein crystal structures are transformed into a common orientation and combined to calculate an average three-dimensional environment. The spatial distribution of atom types in this environment reveals a preferred interaction between oxygen atoms and the edge of the planar aromatic rings. From the difference in frequency of interaction of oxygen atoms with the edge and the top of the ring, an apparent net free energy difference of interaction favoring the edge of the ring is estimated to be about -1 kcal/mol (1 cal = 4.184 J). Ab initio quantum mechanical calculations, performed on a model consisting of benzene and formamide, indicate that the observed geometry is stabilized by a favorable enthalpic interaction. Although benzene rings are considered to be nonpolar, the electron distribution is a complex multipole with no net dipole moment. The observed interaction orientation frequencies demonstrate that these multipolar electron distributions, when occurring at the short distances encountered in densely packed protein molecules, are significant determinants of internal packing geometries. PMID:6956896

Optical Kerr effect in graphene: Theoretical analysis of the optical heterodyne detection technique

NASA Astrophysics Data System (ADS)

Savostianova, N. A.; Mikhailov, S. A.

2018-04-01

Graphene is an atomically thin two-dimensional material demonstrating strong optical nonlinearities, including harmonics generation, four-wave mixing, Kerr, and other nonlinear effects. In this paper we theoretically analyze the optical heterodyne detection (OHD) technique of measuring the optical Kerr effect (OKE) in two-dimensional crystals and show how to relate the quantities measured in such experiments with components of the third-order conductivity tensor σαβ γ δ (3 )(ω1,ω2,ω3) of the two-dimensional crystal. Using results of a recently developed quantum theory of the third-order nonlinear electrodynamic response of graphene, we analyze the frequency, charge carrier density, temperature, and other dependencies of the OHD-OKE response of this material. We compare our results with a recent OHD-OKE experiment in graphene and find good agreement between the theory and experiment.

Structural, electronic and magnetic properties of layered REB{sub 2}C compounds (RE=Dy, Tm, Lu)

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

Babizhetskyy, Volodymyr, E-mail: v.babizhetskyy@googlemail.com; Department of Inorganic Chemistry, Ivan Franko National University of L'viv, Kyryla and Mefodiya Str. 6, UA-79005 Lviv; Simon, Arndt

2012-07-15

The crystal structure of LuB{sub 2}C has been determined from single crystal and powder X-ray diffraction data. It crystallizes in the orthorhombic space group Pbam (a=6.7429(1) A, b=6.7341(1) A, c=3.5890(1) A, Z=4, R1=0.024 (wR2=0.059) for 436 reflections with I{sub o}>2{sigma}(I{sub o})). The compounds REB{sub 2}C (RE=Y, Tb-Lu) are isotypic. The boron and carbon atoms form infinite, planar two-dimensional nets which alternate with sheets of rare-earth metal atoms. Inside the nonmetal atom nets, a coloring with fused B{sub 2}C{sub 2} rhombuses and B{sub 5}C{sub 2} heptagons is proposed, supported by NMR experiments and density functional theory calculations. The calculated density ofmore » states of LuB{sub 2}C indicates this compound to be metallic. The magnetic properties of the isotypic compound TmB{sub 2}C, has been measured in the temperature range 2 K3 T a metamagnetic transition is encountered. The temperature dependence of the electrical resistivity proves the metallic character of the TmB{sub 2}C compound as well as the AFM ordering. - Graphical abstract: The crystal structure of LuB{sub 2}C has been determined from single crystal and powder X-ray diffraction data. It crystallizes in the orthorhombic space group Pbam. The compounds REB{sub 2}C (RE=Y, Tb-Lu) are isotypic. The boron and carbon atoms form infinite, planar two-dimensional nets which alternate with sheets of rare-earth metal atoms. Inside the nonmetal atom nets, a coloring with fused B{sub 2}C{sub 2} rhombuses and B{sub 5}C{sub 2} heptagons is proposed, supported by NMR experiments and density functional theory calculations. The magnetic properties of the isotypic compound TmB{sub 2}C, has been measured in the temperature range 2 K3 T a metamagnetic transition is encountered. The temperature dependence of the electrical resistivity proves the metallic character of the TmB{sub 2}C compound as well as the AFM ordering. Highlights: Black-Right-Pointing-Pointer LuB{sub 2}C compound crystallizes in orthorhombic symmetry. Black-Right-Pointing-Pointer In the structure the B{sub 2}C layers are stacked directly on top of each other. Black-Right-Pointing-Pointer A coloring with fused B{sub 2}C{sub 2} rhombuses and B{sub 5}C{sub 2} heptagons is proposed. Black-Right-Pointing-Pointer The coloring is supported by NMR experiments and theoretical calculations. Black-Right-Pointing-Pointer TmB{sub 2}C undergoes an antiferromagnetic transition at T{sub N}=12 K at elevated fields.« less

Synthesis, crystal structure and characterization of chiral, three-dimensional anhydrous potassium tris(oxalato)ferrate(III)

NASA Astrophysics Data System (ADS)

Saritha, A.; Raju, B.; Ramachary, M.; Raghavaiah, P.; Hussain, K. A.

2012-11-01

The synthesis, crystal structure and physical properties of chiral, three-dimensional anhydrous potassium tris(oxalato)ferrate(III) [K3Fe(C2O4)3] are described. X-ray analysis reveals that the compound crystallized in the chiral space group P4132 of cubic system with a=b=c=13.5970(2), Z=4. The structure of the complex consists of infinite anionic [Fe(C2O4)3]3- units with distorted octahedral environment of iron surrounded by six oxygen atoms of three oxalato groups. The anionic units are interlinked through K+ ions of three different coordination environments of distorted octahedral, bicapped trigonal prismatic and trigonal prismatic yielding a three-dimensional motif. The two broad absorption bands at 644 and 924 nm from UV-vis-NIR transmittance spectra were ascribed to a ligand-to-metal charge transfer. The room temperature crystalline EPR spectra indicate the high-spin (S=5/2) of Fe(III) ion. The vibrating sample magnetometer measurement shows the paramagnetic nature at room temperature. Thermal studies of the compound confirm the absence of water molecule.

Synthesis, Crystal Structure, and Topology-Symmetry Analysis of a New Modification of NaIn[IO3]4

NASA Astrophysics Data System (ADS)

Belokoneva, E. L.; Karamysheva, A. S.; Dimitrova, O. V.; Volkov, A. S.

2018-01-01

Crystals of new iodate NaIn[IO3]4 were prepared by the hydrothermal synthesis. The unit cell parameters are a = 7.2672(2) Å, b = 15.2572(6) Å, c = 15.0208(6) Å, β = 101.517(3)°, sp. gr. P21/ c. The formula was determined during the structure determination and refinement of a twinned crystal based on a set of reflections from the atomic planes of the major individual. The refinement with anisotropic displacement parameters was performed for both twin components to the final R factor of 0.050. The In and Na atoms are in octahedral coordination formed by oxygen atoms. The oxygen octahedra are arranged into columns by sharing edges, and the columns are connected by isolated umbrella-like [IO3]- groups to form layers. The new structure is most similar to the isoformular iodate NaIn[IO3]4, which crystallizes in the same sp. gr. P21/ c and is structurally similar, but has a twice smaller unit cell and is characterized by another direction of the monoclinic axis. The structural similarity and difference between the two phases were studied by topologysymmetry analysis. The formation of these phases is related to different combinations of identical one-dimensional infinite chains of octahedra.

Viral capsomere structure, surface processes and growth kinetics in the crystallization of macromolecular crystals visualized by in situ atomic force microscopy

NASA Astrophysics Data System (ADS)

Malkin, A. J.; Kuznetsov, Yu. G.; McPherson, A.

2001-11-01

In situ atomic force microscopy (AFM) was used to investigate surface evolution during the growth of single crystals of turnip yellow mosaic virus (TYMV), cucumber mosaic virus (CMV) and glucose isomerase. Growth of these crystals proceeded by two-dimensional (2D) nucleation. For glucose isomerase, from supersaturation dependencies of tangential step rates and critical step length, the kinetic coefficients of the steps and the surface free energy of the step edge were calculated for different crystallographic directions. The molecular structure of the step edges, the adsorption of individual virus particles and their aggregates, and the initial stages of formation of 2D nuclei on the surfaces of TYMV and CMV crystals were recorded. The surfaces of individual TYMV virions within crystals were visualized, and hexameric and pentameric capsomers of the T=3 capsids were clearly resolved. This, so far as we are aware, is the first direct visualization of the capsomere structure of a virus by AFM. In the course of recording the in situ development of the TYMV crystals, a profound restructuring of the surface arrangement was observed. This transformation was highly cooperative in nature, but the transitions were unambiguous and readily explicable in terms of an organized loss of classes of virus particles from specific lattice positions.

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

NASA Astrophysics Data System (ADS)

Li, Xiao-Dong; Cheng, Xin-Lu

2018-02-01

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

New Display-type Analyzer for Three-dimensional Fermi Surface Mapping and Atomic Orbital Analysis

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

Takahashi, Nobuaki; Matsuda, Hiroyuki; Shigenai, Shin

2007-01-19

We have developed and installed a new Display-type ANAlyzer (DIANA) at Ritsumeikan SR center BL-7. We measured the angle-integrated energy distribution curve of poly-crystal gold and the photoelectron intensity angular distribution (PIAD) of HOPG to estimate the total energy resolution and to check the condition of the analyzer. The total energy resolution ({delta}E/E) is up to 0.78%, which is much higher than the old type. The PIAD of HOPG we obtained was the ring pattern as expected. Therefore, a detailed three-dimensional Fermi surface mapping and an analysis of the atomic orbitals constituting the electron energy bands are possible by combiningmore » them with a linearly polarized synchrotron radiation.« less

Crystallization of PTP Domains.

PubMed

Levy, Colin; Adams, James; Tabernero, Lydia

2016-01-01

Protein crystallography is the most powerful method to obtain atomic resolution information on the three-dimensional structure of proteins. An essential step towards determining the crystallographic structure of a protein is to produce good quality crystals from a concentrated sample of purified protein. These crystals are then used to obtain X-ray diffraction data necessary to determine the 3D structure by direct phasing or molecular replacement if the model of a homologous protein is available. Here, we describe the main approaches and techniques to obtain suitable crystals for X-ray diffraction. We include tools and guidance on how to evaluate and design the protein construct, how to prepare Se-methionine derivatized protein, how to assess the stability and quality of the sample, and how to crystallize and prepare crystals for diffraction experiments. While general strategies for protein crystallization are summarized, specific examples of the application of these strategies to the crystallization of PTP domains are discussed.

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

[Crystal structure of SMU.2055 protein from Streptococcus mutans and its small molecule inhibitors design and selection].

PubMed

Xiaodan, Chen; Xiurong, Zhan; Xinyu, Wu; Chunyan, Zhao; Wanghong, Zhao

2015-04-01

The aim of this study is to analyze the three-dimensional crystal structure of SMU.2055 protein, a putative acetyltransferase from the major caries pathogen Streptococcus mutans (S. mutans). The design and selection of the structure-based small molecule inhibitors are also studied. The three-dimensional crystal structure of SMU.2055 protein was obtained by structural genomics research methods of gene cloning and expression, protein purification with Ni²⁺-chelating affinity chromatography, crystal screening, and X-ray diffraction data collection. An inhibitor virtual model matching with its target protein structure was set up using computer-aided drug design methods, virtual screening and fine docking, and Libdock and Autodock procedures. The crystal of SMU.2055 protein was obtained, and its three-dimensional crystal structure was analyzed. This crystal was diffracted to a resolution of 0.23 nm. It belongs to orthorhombic space group C222(1), with unit cell parameters of a = 9.20 nm, b = 9.46 nm, and c = 19.39 nm. The asymmetric unit contained four molecules, with a solvent content of 56.7%. Moreover, five small molecule compounds, whose structure matched with that of the target protein in high degree, were designed and selected. Protein crystallography research of S. mutans SMU.2055 helps to understand the structures and functions of proteins from S. mutans at the atomic level. These five compounds may be considered as effective inhibitors to SMU.2055. The virtual model of small molecule inhibitors we built will lay a foundation to the anticaries research based on the crystal structure of proteins.

DNA-nanoparticle superlattices formed from anisotropic building blocks

NASA Astrophysics Data System (ADS)

Jones, Matthew R.; Macfarlane, Robert J.; Lee, Byeongdu; Zhang, Jian; Young, Kaylie L.; Senesi, Andrew J.; Mirkin, Chad A.

2010-11-01

Directional bonding interactions in solid-state atomic lattices dictate the unique symmetries of atomic crystals, resulting in a diverse and complex assortment of three-dimensional structures that exhibit a wide variety of material properties. Methods to create analogous nanoparticle superlattices are beginning to be realized, but the concept of anisotropy is still largely underdeveloped in most particle assembly schemes. Some examples provide interesting methods to take advantage of anisotropic effects, but most are able to make only small clusters or lattices that are limited in crystallinity and especially in lattice parameter programmability. Anisotropic nanoparticles can be used to impart directional bonding interactions on the nanoscale, both through face-selective functionalization of the particle with recognition elements to introduce the concept of valency, and through anisotropic interactions resulting from particle shape. In this work, we examine the concept of inherent shape-directed crystallization in the context of DNA-mediated nanoparticle assembly. Importantly, we show how the anisotropy of these particles can be used to synthesize one-, two- and three-dimensional structures that cannot be made through the assembly of spherical particles.

Self-organization of atoms coupled to a chiral reservoir

NASA Astrophysics Data System (ADS)

Eldredge, Zachary; Solano, Pablo; Chang, Darrick; Gorshkov, Alexey V.

2016-11-01

Tightly confined modes of light, as in optical nanofibers or photonic crystal waveguides, can lead to large optical coupling in atomic systems, which mediates long-range interactions between atoms. These one-dimensional systems can naturally possess couplings that are asymmetric between modes propagating in different directions. Strong long-range interaction among atoms via these modes can drive them to a self-organized periodic distribution. In this paper, we examine the self-organizing behavior of atoms in one dimension coupled to a chiral reservoir. We determine the solution to the equations of motion in different parameter regimes, relative to both the detuning of the pump laser that initializes the atomic dipole-dipole interactions and the degree of reservoir chirality. In addition, we calculate possible experimental signatures such as reflectivity from self-organized atoms and motional sidebands.

An Essential Protein Repair Enzyme: Investigation of the Molecular Recognition Mechanism of Methionine Sulfoxide Reductase A

DTIC Science & Technology

2008-05-01

4 ). The three-dimensional spatial orientation of the atoms for these resolved solution structures (Protein Data Bank accession codes: 2gt3...Crystal structure of the Escherichia coli peptide methionine sulphoxide reductase at 1.9 Å resolution . Struct. Fold. Des. 8: 1167 – 1178. 2 . Brot...sources (8). There is a 67% sequence identity between the E.coli and human MsrA ( 2 ). N-terminus C-terminus Figure 2 . Three-dimensional structure

Crystal structure of hydrocortisone acetate, C23H32O6

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

Kaduk, James A.; Gindhart, Amy M.; Blanton, Thomas N.

The crystal structure of hydrocortisone acetate has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Hydrocortisone acetate crystallizes in space groupP2 1(#4) witha= 8.85173(3) Å,b= 13.53859(3) Å,c= 8.86980(4) Å,β= 101.5438(3)°,V= 1041.455(6) Å 3, andZ= 2. Both hydroxyl groups form hydrogen bonds to the ketone oxygen atom on the steroid ring system, resulting in a three-dimensional hydrogen bond network. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™.

Unified structure theory of icosahedral quasicrystals: Evidence from neutron powder diffraction patterns that AlCrFeMnSi, AlCuLiMg, and TiNiFeSi icosahedral quasicrystals are twins of cubic crystals containing about 820 or 1012 atoms in a primitive unit cube

PubMed Central

Pauling, Linus

1988-01-01

A unified structure theory of icosahedral quasicrystals, combining the twinned-cubic-crystal theory and the Penrose-tiling-six-dimensional-projection theory, is described. Values of the primitive-cubic lattice constant for several quasicrystals are evaluated from x-ray and neutron diffraction data. The fact that the low-angle diffraction maxima can be indexed with cubic unit cells provides additional support for the twinned-cubic-crystal theory of icosahedral quasicrystals. PMID:16593990

Purification, crystallization, and preliminary X-ray diffraction study of purine nucleoside phosphorylase from E. coli

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

Abramchik, Yu. A., E-mail: inna@ns.crys.ras.ru; Timofeev, V. I., E-mail: espiov@ibch.ru; Zhukhlistova, N. E., E-mail: tostars@mail.ru

2015-07-15

Crystals of E. coli purine nucleoside phosphorylase were grown in microgravity by the capillary counter-diffusion method through a gel layer. The X-ray diffraction data set suitable for the determination of the three-dimensional structure at atomic resolution was collected from one crystal at the Spring-8 synchrotron facility to 0.99 Å resolution. The crystals belong to sp. gr. P2{sub 1} and have the following unit-cell parameters: a = 74.1 Å, b = 110.2 Å, c = 88.2 Å, α = γ = 90°, β = 111.08°. The crystal contains six subunits of the enzyme comprising a hexamer per asymmetric unit. The hexamermore » is the biological active form of E. coli. purine nucleoside phosphorylase.« less

Two-dimensional limit of crystalline order in perovskite membrane films

PubMed Central

Hong, Seung Sae; Yu, Jung Ho; Lu, Di; Marshall, Ann F.; Hikita, Yasuyuki; Cui, Yi; Hwang, Harold Y.

2017-01-01

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 SrTiO3, 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 SrTiO3 membrane lattice collapses 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. 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. PMID:29167822

Two-dimensional limit of crystalline order in perovskite membrane films

DOE PAGES

Hong, Seung Sae; Yu, Jung Ho; Lu, Di; ...

2017-11-17

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

Crystal structure of ammonium/potassium trans-bis­(N-methyl­iminodi­acetato-κ3 O,N,O′)chromate(III) from synchrotron data

PubMed Central

Moon, Dohyun; Choi, Jong-Ha

2016-01-01

The structure of the title compound, [(NH4)0.8K0.2][Cr(C5H7NO4)2] (C5H7NO4 is methyl­iminodi­acetate; mida), has been determined from synchrotron data. The CrIII atom is located on a centre of symmetry and is coordinated by two N atoms and four O atoms of two facially arranged tridentate mida ligands, displaying a slightly distorted octa­hedral coordination environment. The Cr—N and mean Cr—O bond lengths are 2.0792 (14) and 1.958 (14) Å, respectively. The cation site is located on a twofold rotation axis and shows occupational disorder, being occupied by ammonium and potassium cations in a 0.8:0.2 ratio. In the crystal, inter­molecular hydrogen bonds involving the N—H groups of the ammonium cation as donor and the two non-coordinating O atoms of the carboxyl­ate group as acceptor groups consolidate the three-dimensional packing. PMID:27536411

Redetermination of (+)-methamphetamine hydro­chloride at 90 K

PubMed Central

Hakey, Patrick; Ouellette, Wayne; Zubieta, Jon; Korter, Timothy

2008-01-01

The title crystal structure (systematic name: N-methyl-1-phenyl­propan-2-aminium chloride), C10H16N+·Cl−, was orginally determined by Simon, Bocskei & Torok [Acta Pharm. Hung. (1992). 62, 225–230] and Yao, Kan & Wang [Huaxue Shijie (1999). 40, 568–570] at room temperature but no atomic coordinates are available for these determinations. The mol­ecule has inter­est with respect to biological activity. In the crystal structure, inter­molecular N—H⋯Cl hydrogen bonds form one-dimensional chains. PMID:21202421

Recombination activity of nickel, copper, and oxygen atoms segregating at grain boundaries in mono-like silicon crystals

NASA Astrophysics Data System (ADS)

Ohno, Yutaka; Kutsukake, Kentaro; Deura, Momoko; Yonenaga, Ichiro; Shimizu, Yasuo; Ebisawa, Naoki; Inoue, Koji; Nagai, Yasuyoshi; Yoshida, Hideto; Takeda, Seiji

2016-10-01

Three-dimensional distribution of impurity atoms was determined at functional Σ5{013} and small-angle grain boundaries (GBs) in as-grown mono-like silicon crystals by atom probe tomography combined with transmission electron microscopy, and it was correlated with the recombination activity of those GBs, CGB, revealed by photoluminescence imaging. Nickel (Ni), copper (Cu), and oxygen atoms preferentially segregated at the GBs on which arrays of dislocations existed, while those atoms scarcely segregated at Σ5{013} GBs free from dislocations. Silicides containing Ni and Cu about 5 nm in size and oxides about 1 nm in size were formed along the dislocation arrays on those GBs. The number of segregating impurity atoms per unit GB area for Ni and that for Cu, NNi and NCu, were in a trade-off correlation with that for oxygen, NO, as a function of CGB, while the sum of those numbers was almost constant irrespective of the GB character, CGB, and the dislocation density on GBs. CGB would be explained as a linear combination of those numbers: CGB (in %) ˜400(0.38NO + NNi + NCu) (in atoms/nm2). The GB segregation of oxygen atoms would be better for solar cells, rather than that of metal impurities, from a viewpoint of the conversion efficiency of solar cells.

Phasing and structure of bestrophin-1: a case study in the use of heavy-atom cluster compounds with multi-subunit transmembrane proteins

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

Kane Dickson, Veronica

The purification and three-dimensional crystallization of membrane proteins are commonly affected by a cumulation of pathologies that are less prevalent in their soluble counterparts. This may include severe anisotropy, poor spot shape, poor to moderate-resolution diffraction, crystal twinning, translational pseudo-symmetry and poor uptake of heavy atoms for derivatization. Such challenges must be circumvented by adaptations in the approach to crystallization and/or phasing. Here, an example of a protein that exhibited all of the above-mentioned complications is presented. Bestrophin-1 is a eukaryotic calcium-activated chloride channel, the structure of which was recently determined in complex with monoclonal antibody fragments using SAD phasingmore » with tantalum bromide clusters (Ta 6Br 12·Br 2). Some of the obstacles to obtaining improved diffraction and phasing for this particular channel are discussed, as well as the approach and adaptations that were key to determining the structure.« less

In situ single-atom array synthesis using dynamic holographic optical tweezers

PubMed Central

Kim, Hyosub; Lee, Woojun; Lee, Han-gyeol; Jo, Hanlae; Song, Yunheung; Ahn, Jaewook

2016-01-01

Establishing a reliable method to form scalable neutral-atom platforms is an essential cornerstone for quantum computation, quantum simulation and quantum many-body physics. Here we demonstrate a real-time transport of single atoms using holographic microtraps controlled by a liquid-crystal spatial light modulator. For this, an analytical design approach to flicker-free microtrap movement is devised and cold rubidium atoms are simultaneously rearranged with 2N motional degrees of freedom, representing unprecedented space controllability. We also accomplish an in situ feedback control for single-atom rearrangements with the high success rate of 99% for up to 10 μm translation. We hope this proof-of-principle demonstration of high-fidelity atom-array preparations will be useful for deterministic loading of N single atoms, especially on arbitrary lattice locations, and also for real-time qubit shuttling in high-dimensional quantum computing architectures. PMID:27796372

Analysis of Crystallographic Structure of a Japanese Sword by the Pulsed Neutron Transmission Method

NASA Astrophysics Data System (ADS)

Kino, K.; Ayukawa, N.; Kiyanagi, Y.; Uchida, T.; Uno, S.; Grazzi, F.; Scherillo, A.

We measured two-dimensional transmission spectra of pulsed neutron beams for a Japanese sword sample. Atom density, crystalline size, and preferred orientation of crystals were obtained using the RITS code. The position dependence of the atomic density is consistent with the shape of the sample. The crystalline size is very small and shows position dependence, which is understood by the unique structure of Japanese swords. The preferred orientation has strong position dependence. Our study shows the usefulness of the pulsed neutron transmission method for cultural metal artifacts.

Three-dimensional imaging of dislocation propagation during crystal growth and dissolution

PubMed Central

Schenk, Anna S.; Kim, Yi-Yeoun; Kulak, Alexander N.; Campbell, James M.; Nisbet, Gareth; Meldrum, Fiona C.; Robinson, Ian K.

2015-01-01

Atomic level defects such as dislocations play key roles in determining the macroscopic properties of crystalline materials 1,2. Their effects range from increased chemical reactivity 3,4 to enhanced mechanical properties 5,6. Dislocations have been widely studied using traditional techniques such as X-ray diffraction and optical imaging. Recent advances have enabled atomic force microscopy to study single dislocations 7 in two-dimensions (2D), while transmission electron microscopy (TEM) can now visualise strain fields in three-dimensions (3D) with near atomic resolution 8–10. However, these techniques cannot offer 3D imaging of the formation or movement of dislocations during dynamic processes. Here, we describe how Bragg Coherent Diffraction Imaging (BCDI) 11,12 can be used to visualize in 3D, the entire network of dislocations present within an individual calcite crystal during repeated growth and dissolution cycles. These investigations demonstrate the potential of BCDI for studying the mechanisms underlying the response of crystalline materials to external stimuli. PMID:26030304

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

X-ray Scintillation in Lead Halide Perovskite Crystals

PubMed Central

Birowosuto, M. D.; Cortecchia, D.; Drozdowski, W.; Brylew, K.; Lachmanski, W.; Bruno, A.; Soci, C.

2016-01-01

Current technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI3 and MAPbBr3 and two-dimensional (2D) (EDBE)PbCl4 hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl4 significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications. PMID:27849019

Metal Flux Growth, Structural Relations, and Physical Properties of EuCu2Ge2 and Eu3T2In9 (T = Cu and Ag).

PubMed

Subbarao, Udumula; Roy, Soumyabrata; Sarma, Saurav Ch; Sarkar, Sumanta; Mishra, Vidyanshu; Khulbe, Yatish; Peter, Sebastian C

2016-10-17

Single crystals (SCs) of the compounds Eu 3 Ag 2 In 9 and EuCu 2 Ge 2 were synthesized through the reactions run in liquid indium. Eu 3 Ag 2 In 9 crystallizes in the La 3 Al 11 structure type [orthorhombic space group (SG) Immm] with the lattice parameters: a = 4.8370(1) Å, b = 10.6078(3) Å, and c = 13.9195(4) Å. EuCu 2 Ge 2 crystallizes in the tetragonal ThCr 2 Si 2 structure type (SG I4/mmm) with the lattice parameters: a = b = 4.2218(1) Å, and c = 10.3394(5) Å. The crystal structure of Eu 3 Ag 2 In 9 is comprised of edge-shared hexagonal rings consisting of indium. The one-dimensional chains of In 6 rings are shared through the edges, which are further interconnected with other six-membered rings forming a three-dimensional (3D) stable crystal structure along the bc plane. The crystal structure of EuCu 2 Ge 2 can be explained as the complex [CuGe] (2+δ)- polyanionic network embedded with Eu ions. These polyanionic networks present in the crystal structure of EuCu 2 Ge 2 are shared through the edges of the 011 plane containing Cu and Ge atoms, resulting in a 3D network. The structural relationship between Eu 3 T 2 In 9 and EuCu 2 Ge 2 has been discussed in detail, and we conclude that Eu 3 T 2 In 9 is the metal deficient variant of EuCu 2 Ge 2 . The magnetic susceptibilities of Eu 3 T 2 In 9 (T = Cu and Ag) and EuCu 2 Ge 2 were measured between 2 and 300 K. In all cases, magnetic susceptibility data followed Curie-Weiss law above 150 K. Magnetic moment values obtained from the measurements indicate the probable mixed/intermediate valent behavior of the europium atoms, which was further confirmed by X-ray absorption studies and bond distances around the Eu atoms. Electrical resistivity measurements suggest that Eu 3 T 2 In 9 and EuCu 2 Ge 2 are metallic in nature.

Crystal structure of bis-(μ-3-nitro-benzoato)-κ3O,O':O;κ3O:O,O'-bis-[bis-(3-cyano-pyridine-κN1)(3-nitro-benzoato-κ2O,O')cadmium].

PubMed

Hökelek, Tuncer; Akduran, Nurcan; Özen, Azer; Uğurlu, Güventürk; Necefoğlu, Hacali

2017-03-01

The asymmetric unit of the title compound, [Cd 2 (C 7 H 4 NO 4 ) 4 (C 6 H 4 N 2 ) 4 ], contains one Cd II atom, two 3-nitro-benzoate (NB) anions and two 3-cyano-pyridine (CPy) ligands. The two CPy ligands act as monodentate N(pyridine)-bonding ligands, while the two NB anions act as bidentate ligands through the carboxyl-ate O atoms. The centrosymmetric dinuclear complex is generated by application of inversion symmetry, whereby the Cd II atoms are bridged by the carboxyl-ate O atoms of two symmetry-related NB anions, thus completing the distorted N 2 O 5 penta-gonal-bipyramidal coordination sphere of each Cd II atom. The benzene and pyridine rings are oriented at dihedral angles of 10.02 (7) and 5.76 (9)°, respectively. In the crystal, C-H⋯N hydrogen bonds link the mol-ecules, enclosing R 2 2 (26) ring motifs, in which they are further linked via C-H⋯O hydrogen bonds, resulting in a three-dimensional network. In addition, π-π stacking inter-actions between parallel benzene rings and between parallel pyridine rings of adjacent mol-ecules [shortest centroid-to-centroid distances = 3.885 (1) and 3.712 (1) Å, respectively], as well as a weak C-H⋯π inter-action, may further stabilize the crystal structure.

Three-Particle Complexes in Two-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Ganchev, Bogdan; Drummond, Neil; Aleiner, Igor; Fal'ko, Vladimir

2015-03-01

We evaluate binding energies of trions X±, excitons bound by a donor or acceptor charge XD (A ) , and overcharged acceptors or donors in two-dimensional atomic crystals by mapping the three-body problem in two dimensions onto one particle in a three-dimensional potential treatable by a purposely developed boundary-matching-matrix method. We find that in monolayers of transition metal dichalcogenides the dissociation energy of X± is typically much larger than that of localized exciton complexes, so that trions are more resilient to heating, despite the fact that their recombination line in optics is less redshifted from the exciton line than the line of XD (A ) .

An Overview of Biological Macromolecule Crystallization

PubMed Central

Krauss, Irene Russo; Merlino, Antonello; Vergara, Alessandro; Sica, Filomena

2013-01-01

The elucidation of the three dimensional structure of biological macromolecules has provided an important contribution to our current understanding of many basic mechanisms involved in life processes. This enormous impact largely results from the ability of X-ray crystallography to provide accurate structural details at atomic resolution that are a prerequisite for a deeper insight on the way in which bio-macromolecules interact with each other to build up supramolecular nano-machines capable of performing specialized biological functions. With the advent of high-energy synchrotron sources and the development of sophisticated software to solve X-ray and neutron crystal structures of large molecules, the crystallization step has become even more the bottleneck of a successful structure determination. This review introduces the general aspects of protein crystallization, summarizes conventional and innovative crystallization methods and focuses on the new strategies utilized to improve the success rate of experiments and increase crystal diffraction quality. PMID:23727935

Crystallization and preliminary X-ray diffraction study of phosphopantetheine adenylyltransferase from M. tuberculosis crystallizing in space group P3{sub 2}

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

Timofeev, V. I., E-mail: tostars@mail.ru; Chupova, L. A.; Esipov, R. S.

Crystals of M. tuberculosis phosphopantetheine adenylyltransferase were grown in microgravity by the capillary counter-diffusion method through a gel layer. The X-ray diffraction data set suitable for the determination of the three-dimensional structure at atomic resolution was collected from one crystal at the Spring-8 synchrotron facility to 2.00-Å resolution. The crystals belong to sp. gr. P3{sub 2} and have the following unit-cell parameters: a = b = 106.47 Å, c = 71.32 Å, α = γ = 90°, β = 120°. The structure was solved by the molecular-replacement method. There are six subunits of the enzyme comprising a hexamer per asymmetricmore » unit. The hexamer is a biologically active form of phosphopantetheine adenylyltransferase from M. tuberculosis.« less

Atomic level characterization in corrosion studies

NASA Astrophysics Data System (ADS)

Marcus, Philippe; Maurice, Vincent

2017-06-01

Atomic level characterization brings fundamental insight into the mechanisms of self-protection against corrosion of metals and alloys by oxide passive films and into how localized corrosion is initiated on passivated metal surfaces. This is illustrated in this overview with selected data obtained at the subnanometre, i.e. atomic or molecular, scale and also at the nanometre scale on single-crystal copper, nickel, chromium and stainless steel surfaces passivated in well-controlled conditions and analysed in situ and/or ex situ by scanning tunnelling microscopy/spectroscopy and atomic force microscopy. A selected example of corrosion modelling by ab initio density functional theory is also presented. The discussed aspects include the surface reconstruction induced by hydroxide adsorption and formation of two-dimensional (hydr)oxide precursors, the atomic structure, orientation and surface hydroxylation of three-dimensional ultrathin oxide passive films, the effect of grain boundaries in polycrystalline passive films acting as preferential sites of passivity breakdown, the differences in local electronic properties measured at grain boundaries of passive films and the role of step edges at the exposed surface of oxide grains on the dissolution of the passive film. This article is part of the themed issue 'The challenges of hydrogen and metals'.

Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors

DOE PAGES

Mahjouri-Samani, Masoud; Lin, Ming-Wei; Wang, Kai; ...

2015-07-22

The formation of semiconductor heterojunctions and their high density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional (2D) crystalline semiconductors as building blocks in next generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate a process strategy for the formation of lithographically-patterned lateral semiconducting heterojunctions within a single 2D crystal. E-beam lithography is used to pattern MoSe 2 monolayer crystals with SiO 2, and the exposed locations are selectively and totally converted to MoS 2 using pulsed laser deposition (PLD) of sulfur in order to form MoSe 2/MoS 2 heterojunctions in predefinedmore » patterns. The junctions and conversion process are characterized by atomically resolved scanning transmission electron microscopy, photoluminescence, and Raman spectroscopy. This demonstration of lateral semiconductor heterojunction arrays within a single 2D crystal is an essential step for the lateral integration of 2D semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin circuitry.« less

Two novel mixed-ligand complexes containing organosulfonate ligands.

PubMed

Li, Mingtian; Huang, Jun; Zhou, Xuan; Fang, Hua; Ding, Liyun

2008-07-01

The structures reported herein, viz. bis(4-aminonaphthalene-1-sulfonato-kappaO)bis(4,5-diazafluoren-9-one-kappa(2)N,N')copper(II), [Cu(C(10)H(8)NO(3)S)(2)(C(11)H(6)N(2)O)(2)], (I), and poly[[[diaquacadmium(II)]-bis(mu-4-aminonaphthalene-1-sulfonato)-kappa(2)O:N;kappa(2)N:O] dihydrate], {[Cd(C(10)H(8)NO(3)S)(2)(H(2)O)(2)].2H(2)O}(n), (II), are rare examples of sulfonate-containing complexes where the anion does not fulfill a passive charge-balancing role, but takes an active part in coordination as a monodentate and/or bridging ligand. Monomeric complex (I) possesses a crystallographic inversion center at the Cu(II) atom, and the asymmetric unit contains one-half of a Cu atom, one complete 4-aminonaphthalene-1-sulfonate (ans) ligand and one 4,5-diazafluoren-9-one (DAFO) ligand. The Cu(II) atom has an elongated distorted octahedral coordination geometry formed by two O atoms from two monodentate ans ligands and by four N atoms from two DAFO molecules. Complex (II) is polymeric and its crystal structure is built up by one-dimensional chains and solvent water molecules. Here also the cation (a Cd(II) atom) lies on a crystallographic inversion center and adopts a slightly distorted octahedral geometry. Each ans anion serves as a bridging ligand linking two Cd(II) atoms into one-dimensional infinite chains along the [010] direction, with each Cd(II) center coordinated by four ans ligands via O and N atoms and by two aqua ligands. In both structures, there are significant pi-pi stacking interactions between adjacent ligands and hydrogen bonds contribute to the formation of two- and three-dimensional networks.

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.

Poly[tetra­aqua-μ3-benzene-1,2-di­carboxyl­ato-μ3-bromido-penta-μ2-bromido-octa-μ3-isonicotinato-hepta­copper(I)trilanthanum(III)

PubMed Central

Wang, Guo-Ming; Li, Zeng-Xin; Xue, Shu-Yun; Liu, Hui-Luan

2009-01-01

A new lanthanum(III)–copper(I) heterometallic coordination polymer, [Cu7La3Br6(C6H4NO2)8(C8H4O4)(H2O)4]n, has been prepared by a hydro­thermal method. Of the three La atoms in the asymmetric unit, two are eight-coordinate with bicapped trigonal–prismatic configurations; the third is nine-coordinated and has a tricapped trigonal–prismatic coordination geometry. Of the seven Cu atoms, two are two-coordinate with CuBrN and CuN2 ligand sets, three have trigonal configurations, viz. CuBrN2, CuBr2N and CuBr3, while the remaining two adopt distorted tetra­hedral CuBr3N geometries. In the crystal structure, adjacent La centers are linked by isonicotinate (IN−) and benzene-1,2-dicarboxyl­ate ligands to form a two-dimensional La–carboxyl­ate layer in the ab plane. These layers are further inter­connected with each other by bridging [Cu(IN)2] motifs, leading to an unusual three-dimensional heterometallic Cu–halide–lanthanide–organic framework, with the inorganic [Cu6Br6]n chains located in the resulting channels. Two Cu atoms are disordered over two positions, both with site occupancy factors of 0.80 and 0.20. O—H⋯O hydrogen bonding between water molecules and carboxylate O atoms helps to consolidate the crystal packing. PMID:21583784

The origin of the superstructure in Bi2Sr2CaCu2O(8+delta) as revealed by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Kirk, M. D.; Nogami, J.; Baski, A. A.; Mitzi, D. B.; Kapitulnik, A.

1988-12-01

Real-space images with atomic resolution of the BiO plane of Bi2Sr2CaCu2O(8+delta) were obtained with a scanning tunneling microscope. Single-crystal samples were cleaved and imaged under ultrahigh vacuum conditions at room temperature. The images clearly show the one-dimensional incommensurate superstructure along the b-axis that is common to this phase. High-resolution images show the position of the Bi atoms, revelaing the structural nature of the superlattice. A missing row of Bi atoms occurs either every nine or ten atomic sites in both 110-line directions, accounting for the measured incommensurate periodicity of the superstructure. A model is proposed that includes missing rows of atoms, as well as displacements of the atomic positions along both the a- and c-axis directions.

The Origin of the Superstructure in Bi2Sr2CaCu2O8+dgr as Revealed by Scanning Tunneling Microscopy.

PubMed

Kirk, M D; Nogami, J; Baski, A A; Mitzi, D B; Kapitulnik, A; Geballe, T H; Quate, C F

1988-12-23

Real-space images with atomic resolution of the BiO plane of Bi(2)Sr(2)CaCu(2)O(8+delta) were obtained with a scanning tunneling microscope. Single-crystal samples were cleaved and imaged under ultrahigh vacuum conditions at room temperature. The images clearly show the one-dimensional incommensurate superstructure along the b-axis that is common to this phase. High-resolution images show the position of the Bi atoms, revealing the structural nature of the superlattice. A missing row of Bi atoms occurs either every nine or ten atomic sites in both (110) directions, accounting for the measured incommensurate periodicity of the superstructure. A model is proposed that includes missing rows of atoms, as well as displacements of the atomic positions along both the a- and c-axis directions.

Ferromagnetic Coupling of Mononuclear Fe Centers in a Self-Assembled Metal-Organic Network on Au(111)

NASA Astrophysics Data System (ADS)

Umbach, T. R.; Bernien, M.; Hermanns, C. F.; Krüger, A.; Sessi, V.; Fernandez-Torrente, I.; Stoll, P.; Pascual, J. I.; Franke, K. J.; Kuch, W.

2012-12-01

The magnetic state and magnetic coupling of individual atoms in nanoscale structures relies on a delicate balance between different interactions with the atomic-scale surroundings. Using scanning tunneling microscopy, we resolve the self-assembled formation of highly ordered bilayer structures of Fe atoms and organic linker molecules (T4PT) when deposited on a Au(111) surface. The Fe atoms are encaged in a three-dimensional coordination motif by three T4PT molecules in the surface plane and an additional T4PT unit on top. Within this crystal field, the Fe atoms retain a magnetic ground state with easy-axis anisotropy, as evidenced by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The magnetization curves reveal the existence of ferromagnetic coupling between the Fe centers.

Formation of Gd coordination polymer with 1D chains mediated by Bronsted acidic ionic liquids

NASA Astrophysics Data System (ADS)

Luo, Qianqian; Han, Ying; Lin, Hechun; Zhang, Yuanyuan; Duan, Chungang; Peng, Hui

2017-03-01

One dimensional coordination polymer Gd[(SO4)(NO3)(C2H6SO)2] (1) is prepared through the mediation of Bronsted acid ionic liquid, which crystallized in the monoclinic space of C2/c. In this polymer, adjacent Gd atoms are linked by two SO42- ions to generate a 1-D chain, and all oxygen atoms in SO42- groups are connected to three nearest Gd atoms in μ3:η1:η1:η2 fashion. Gd, S and N from SO42- and NO3- are precisely coplanar. The planar is coordinated by a pair of DMSO molecules, which is parallel and linked by hydrogen bonding to form a three-dimensional supramolecular network. Magnetic susceptibility measurement of 1 reveals weak antiferromagnetic interactions between the Gd (III) ions. It exhibits relatively large magneto-caloric effect with -ΔSm=28.8 J Kg-1 K-1 for ΔH=7 T.

2-and 1-D coordination polymers of Dy(III) and Ho(III) with near infrared and visible luminescence by efficient charge-transfer antenna ligand

NASA Astrophysics Data System (ADS)

Oylumluoglu, Gorkem; Coban, Mustafa Burak; Kocak, Cagdas; Aygun, Muhittin; Kara, Hulya

2017-10-01

Two new lanthanide-based coordination complexes, [Dy(2-stp).2(H2O)]n (1) and {[Ho(2-stp).3(H2O)]·(H2O)}n (2) [2-stp = 2-sulfoterephthalic acid] were synthesized by hydrothermal reaction and characterized by elemental analysis, UV, IR, single crystal X-ray diffraction and solid state photoluminescence. DyIII and HoIII atoms are eight-coordinated and adopt a distorted square-antiprismatic geometry in complexes 1 and 2, respectively. In compound 1, Dy atoms are coordinated by four bridging 2-stp ligands forming two-dimensional (2D) layer, while Ho atoms by three bridging 2-stp ligands creating one dimensional (1D) double chains in 2. In addition, complexes 1 and 2 display in the solid state and at room temperature an intense yellow emission, respectively; this photoluminescence is achieved by an indirect process (antenna effect). The excellent luminescent performances make these complexes very good candidates for potential luminescence materials.

Poly[[diaqua­hemi-μ4-oxalato-μ2-oxalato-praseodymium(III)] monohydrate

PubMed Central

Yang, Ting-Hai; Chen, Qiang; Zhuang, Wei; Wang, Zhe; Yue, Bang-Yi

2009-01-01

In the title complex, {[Pr(C2O4)1.5(H2O)2]·H2O}n, the PrIII ion, which lies on a crystallographic inversion centre, is coordinated by seven O atoms from four oxalate ligands and two O atoms from two water ligands; further Pr—O coordination from tetra­dentate oxalate ligands forms a three-dimensional structure. The compound crystallized as a monohydrate, the water mol­ecule occupying space in small voids and being secured by O—H⋯O hydrogen bonding as an acceptor from ligand water H atoms and as a donor to oxalate O-acceptor sites. PMID:21577485

Calculation of the Energy-Band Structure of the Kronig-Penney Model Using the Nearly-Free and Tightly-Bound-Electron Approximations

ERIC Educational Resources Information Center

Wetsel, Grover C., Jr.

1978-01-01

Calculates the energy-band structure of noninteracting electrons in a one-dimensional crystal using exact and approximate methods for a rectangular-well atomic potential. A comparison of the two solutions as a function of potential-well depth and ratio of lattice spacing to well width is presented. (Author/GA)

Enhanced absorption in two-dimensional materials via Fano-resonant photonic crystals

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

Wang, Wenyi; Klots, Andrey; Bolotin, Kirill I.

2015-05-04

The use of two-dimensional (2D) materials in optoelectronics has attracted much attention due to their fascinating optical and electrical properties. However, the low optical absorption of 2D materials arising from their atomic thickness limits the maximum attainable external quantum efficiency. For example, in the visible and near-infrared regimes monolayer MoS{sub 2} and graphene absorb only ∼10% and 2.3% of incoming light, respectively. Here, we experimentally demonstrate the use of Fano-resonant photonic crystals to significantly boost absorption in atomically thin materials. Using graphene as a test bed, we demonstrate that absorption in the monolayer thick material can be enhanced to 77%more » within the telecommunications band, the highest value reported to date. We also show that the absorption in the Fano-resonant structure is non-local, with light propagating up to 16 μm within the structure. This property is particularly beneficial in harvesting light from large areas in field-effect-transistor based graphene photodetectors in which separation of photo-generated carriers only occurs ∼0.2 μm adjacent to the graphene/electrode interface.« less

Synthesis, structure and electrochemical behavior of a 3D crystalline copper(II) metal-organic framework

NASA Astrophysics Data System (ADS)

Bai, Hong-Ye; Fan, Wei-Qiang; Liu, Chun-Bo; Shi, Wei-Dong; Yan, Yong-Sheng

2014-05-01

Using an flexible amide-type tripodal ligand N,N‧,N″-tris(3-pyridyl)-1,3,5-benzenetricarboxamide (L) and 1,4-benzenedicarboxylic acid (H2bdc), a three-dimensional copper(II) metal-organic framework (MOF) formulated as [Cu(bdc)(L)]n has been hydrothermally synthesized and structurally characterized by IR, elemental, X-ray single-crystal diffraction and thermal analysis. The complex crystallizes in the triclinic, space group P - 1, a = 8.891(2) Å, b = 11.760(2) Å, c = 15.348(3) Å, α = 96.73(3)°, β = 105.96(3)°, γ = 106.47(3)°, V = 1446.2(5) Å3, Mr = 666.10, Dc = 1.530 g/cm3, Z = 2, F(000) = 682, GOOF = 1.0560, μ(MoKα) = 0.817 mm-1, R = 0.0366 and wR = 0.0885. The structural analyses reveal that the title compound consists of one Cu(II) atom, two halves of bdc, and one L ligand. Each Cu(II) atom is linked by two bdc ligands and three L ligands to form a three-dimensional network. In addition, the electrochemical behavior of title compound has been studied. CCDC No. 990526.

Two sodium and lanthanide(III) MOFs based on oxalate and V-shaped 4,4‧-oxybis(benzoate) ligands: Hydrothermal synthesis, crystal structure, and luminescence properties

NASA Astrophysics Data System (ADS)

Wang, Chongchen; Guo, Guangliang; Wang, Peng

2013-01-01

Two lanthanide based metal-organic frameworks, [NaLn(oba)(ox)(H2O)] (Lndbnd6 Eu(1) and Sm(2)) were obtained from 4,4'-oxybisbenzoic acid, sodium oxalate and corresponding lanthanide salts by hydrothermal synthesis. They were characterized by single-crystal X-ray diffraction, IR spectra, and photoluminescent spectra. The crystallographic data reveals that complexes 1 and 2 are isomorphous and isostructural, composed of three-dimensional framework built up of distorted tricapped trigonal EuO9 units, distorted octahedron NaO6 units, 4,4'-oxybis(benzoate) and oxalate. The carboxylate oxygen atoms of the 4,4'-oxybis(benzoate) and oxalate ligand are coordinated to lanthanide ions and sodium ions, resulting into two-dimensional inorganic sheets, which are further linked into three-dimensional network by organic ligands. Thermogravimetric analyses of 1-2 display a considerable thermal stability. Photoluminescent measurements indicated that europium complex 1 displayed strong red emission.

Solvothermal synthesis and structural characterization of a three-dimensional metal organic polymer [NaZn(1,2,4-BTC)] (1,2,4-BTC=1,2,4-benzenetricarboxylate)

NASA Astrophysics Data System (ADS)

Wang, Lei; Shi, Zhan; Li, Guanghua; Fan, Yong; Fu, Wensheng; Feng, Shouhua

2004-01-01

A new three-dimensional metal-organic polymer, [NaZn(1,2,4-BTC)] (where 1,2,4-BTC=1,2,4-benzenetricarboxylate), has been prepared under solvothermal conditions and characterized by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2 1/ c, with cell parameters: a=9.7706(4) Å, b=12.3549(5) Å, c=6.8897(3) Å, β=91.640(2)°, V=831.35(6) Å 3 and Z=4. In the three-dimensional structure of the compound, each Zn atom is five-coordinated in distorted trigonal bipyramidal geometry, while the sixfold coordination of Na corresponds to a slightly distorted triangular prism. The organic ligand, 1,2,4-BTC, shows a novel and unprecedented coordination mode: 11 bonds to 10 metals with each carboxylate function exhibiting different linkages. It remains stable when desolvated and when heated up to 410 °C.

Large structural modulations in the relaxor ferroelectric and intermediate state of strontium rich members (x>0.6) of the Sr{sub x}Ba{sub 1−x}Nb{sub 2}O{sub 6} (sbn) solid solution series

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

Graetsch, H.A., E-mail: heribert.graetsch@rub.de

The amplitudes of the positional, occupational and adp modulations of sbn mixed crystals are strongly enhanced for high strontium contents. The increase of structural modulations is accompanied by reduced spontaneous electric polarization largely due to smaller off-center shifts of the niobium atoms. Beyond the room temperature ferroelectric – intermediate transition near x=0.77, anomal large U{sub 33} atomic displacement parameters of the niobium atoms indicate static disorder caused by loss of orientational coupling between residual shifts of Nb atoms in neighboring NbO{sub 6} octahedra. Change of satellite intensities show a reduction from two-dimensional to one-dimensional modulation which is not consistent withmore » tetragonal symmetry. The pseudo-tetragonally twinned crystal structure of sbn82 was refined in the orthorhombic super-space group A2mm(½0γ)000. The apparent tetragonal symmetry of the other investigated sbn samples also seems to be due to pseudo tetragonal twinning with equal twin volumes. The modulations mainly consist of cooperatively tilted NbO{sub 6} octahedra and wave-like ordered incomplete occupation of the largest cation sites (Me2a and b) by Ba{sup 2+} and Sr{sup 2+}. Furthermore, the atomic displacement parameters of the Me2 sites are strongly modulated. - Graphical abstract: Satellite reflections and modulation coefficients in the solid solution series Sr{sub x}Ba{sub 1−x}Nb{sub 2}O{sub 6}. - Highlights: • The modulationed structures are refined for the whole composition range of sbn32–sbn82 in tetragonal and orthorhombic setting. • The amplitudes of positional, occupational and adp modulations increase strongly with the strontium content. • Evidence is presented that the sbn crystals are pseudo tetragonally twinned. • The ferroelectric–intermediate paraelectric transition is not accompanied by a change of symmetry. • Anomal adp of intermediate (non-ferroelectric) sbn82 indicate loss of coupling between off-center shifts of neighboring niobium.« less

One dimensional metallic edges in atomically thin WSe2 induced by air exposure

NASA Astrophysics Data System (ADS)

Addou, Rafik; Smyth, Christopher M.; Noh, Ji-Young; Lin, Yu-Chuan; Pan, Yi; Eichfeld, Sarah M.; Fölsch, Stefan; Robinson, Joshua A.; Cho, Kyeongjae; Feenstra, Randall M.; Wallace, Robert M.

2018-04-01

Transition metal dichalcogenides are a unique class of layered two-dimensional (2D) crystals with extensive promising applications. Tuning the electronic properties of low-dimensional materials is vital for engineering new functionalities. Surface oxidation is of particular interest because it is a relatively simple method of functionalization. By means of scanning probe microscopy and x-ray photoelectron spectroscopy, we report the observation of metallic edges in atomically thin WSe2 monolayers grown by chemical vapor deposition on epitaxial graphene. Scanning tunneling microscopy shows structural details of WSe2 edges and scanning tunneling spectroscopy reveals the metallic nature of the oxidized edges. Photoemission demonstrates that the formation of metallic sub-stoichiometric tungsten oxide (WO2.7) is responsible for the high conductivity measured along the edges. Ab initio calculations validate the susceptibility of WSe2 nanoribbon edges to oxidation. The zigzag terminated edge exhibits metallic behavior prior the air-exposure and remains metallic after oxidation. Comprehending and exploiting this property opens a new opportunity for application in advanced electronic devices.

Synthesis and description of intermolecular interactions in new sulfonamide derivatives of tranexamic acid

NASA Astrophysics Data System (ADS)

Ashfaq, Muhammad; Arshad, Muhammad Nadeem; Danish, Muhammad; Asiri, Abdullah M.; Khatoon, Sadia; Mustafa, Ghulam; Zolotarev, Pavel N.; Butt, Rabia Ayub; Şahin, Onur

2016-01-01

Tranexamic acid (4-aminomethyl-cyclohexanecarboxylic acid) was reacted with sulfonyl chlorides to produce structurally related four sulfonamide derivatives using simple and environmental friendly method to check out their three-dimensional behavior and van der Walls interactions. The molecules were crystallized in different possibilities, as it is/after alkylation at its O and N atoms/along with a co-molecule. All molecules were crystallized in monoclinic crystal system with space group P21/n, P21/c and P21/a. X-ray studies reveal that the molecules stabilized themselves by different kinds of hydrogen bonding interactions. The molecules are getting connected through O-H⋯O hydrogen bonds to form inversion dimers which are further connected through N-H⋯O interactions. The molecules in which N and O atoms were alkylated showed non-classical interaction and generated centro-symmetric R22(24) ring motif. The co-crystallized host and guest molecules are connected to each other via O-H⋯O interactions to generate different ring motifs. By means of the ToposPro software an analysis of the topologies of underlying nets that correspond to molecular packings and hydrogen-bonded networks in structures under consideration was carried out.

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS.

PubMed

Suturin, S M; Fedorov, V V; Korovin, A M; Valkovskiy, G A; Konnikov, S G; Tabuchi, M; Sokolov, N S

2013-08-01

In this work epitaxial growth of cobalt on CaF 2 (111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF 2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS

PubMed Central

Suturin, S. M.; Fedorov, V. V.; Korovin, A. M.; Valkovskiy, G. A.; Konnikov, S. G.; Tabuchi, M.; Sokolov, N. S.

2013-01-01

In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles. PMID:24046491

Crystal structure of poly[di­aqua­bis­(μ5-benzene-1,3-di­carboxyl­ato)(N,N-di­methyl­formamide)­cadmium(II)disodium(I)

PubMed Central

Sangsawang, Matimon; Chainok, Kittipong; Wannarit, Nanthawat

2017-01-01

The title compound, [CdNa2(C8H4O4)2(C3H7NO)(H2O)2]n or [CdNa2(1,3-bdc)2(DMF)(H2O)2]n, is a new CdII–NaI heterobimetallic coordination polymer. The asymmetric unit consists of one CdII atom, two NaI atoms, two 1,3-bdc ligands, two coordinated water mol­ecules and one coordinated DMF mol­ecule. The CdII atom exhibits a seven-coordinate geometry, while the NaI atoms can be considered to be penta­coordinate. The metal ions and their symmetry-related equivalents are connected via chelating–bridging carboxyl­ate groups of the 1,3-bdc ligands to generate a three-dimensional framework. In the crystal, there are classical O—H⋯O hydrogen bonds involving the coordinated water mol­ecules and the 1,3-bdc carboxyl­ate groups and π–π stacking between the benzene rings of the 1,3-bdc ligands present within the frameworks. PMID:29152332

Colloidal crystals with diamond symmetry at optical lengthscales

NASA Astrophysics Data System (ADS)

Wang, Yifan; Jenkins, Ian C.; McGinley, James T.; Sinno, Talid; Crocker, John C.

2017-02-01

Future optical materials promise to do for photonics what semiconductors did for electronics, but the challenge has long been in creating the structure they require--a regular, three-dimensional array of transparent microspheres arranged like the atoms in a diamond crystal. Here we demonstrate a simple approach for spontaneously growing double-diamond (or B32) crystals that contain a suitable diamond structure, using DNA to direct the self-assembly process. While diamond symmetry crystals have been grown from much smaller nanoparticles, none of those previous methods suffice for the larger particles needed for photonic applications, whose size must be comparable to the wavelength of visible light. Intriguingly, the crystals we observe do not readily form in previously validated simulations; nor have they been predicted theoretically. This finding suggests that other unexpected microstructures may be accessible using this approach and bodes well for future efforts to inexpensively mass-produce metamaterials for an array of photonic applications.

Liquid Crystal Colloids

NASA Astrophysics Data System (ADS)

Smalyukh, Ivan I.

2018-03-01

Colloids are abundant in nature, science, and technology, with examples ranging from milk to quantum dots and the colloidal atom paradigm. Similarly, liquid crystal ordering is important in contexts ranging from biological membranes to laboratory models of cosmic strings and liquid crystal displays in consumer devices. Some of the most exciting recent developments in both of these soft matter fields emerge at their interface, in the fast-growing research arena of liquid crystal colloids. Mesoscale self-assembly in such systems may lead to artificial materials and to structures with emergent physical behavior arising from patterning of molecular order and nano- or microparticles into precisely controlled configurations. Liquid crystal colloids show exceptional promise for new discovery that may impinge on composite material fabrication, low-dimensional topology, photonics, and so on. Starting from physical underpinnings, I review the state of the art in this fast-growing field, with a focus on its scientific and technological potential.

Analysis about diamond tool wear in nano-metric cutting of single crystal silicon using molecular dynamics method

NASA Astrophysics Data System (ADS)

Wang, Zhiguo; Liang, Yingchun; Chen, Mingjun; Tong, Zhen; Chen, Jiaxuan

2010-10-01

Tool wear not only changes its geometry accuracy and integrity, but also decrease machining precision and surface integrity of workpiece that affect using performance and service life of workpiece in ultra-precision machining. Scholars made a lot of experimental researches and stimulant analyses, but there is a great difference on the wear mechanism, especially on the nano-scale wear mechanism. In this paper, the three-dimensional simulation model is built to simulate nano-metric cutting of a single crystal silicon with a non-rigid right-angle diamond tool with 0 rake angle and 0 clearance angle by the molecular dynamics (MD) simulation approach, which is used to investigate the diamond tool wear during the nano-metric cutting process. A Tersoff potential is employed for the interaction between carbon-carbon atoms, silicon-silicon atoms and carbon-silicon atoms. The tool gets the high alternating shear stress, the tool wear firstly presents at the cutting edge where intension is low. At the corner the tool is splitted along the {1 1 1} crystal plane, which forms the tipping. The wear at the flank face is the structure transformation of diamond that the diamond structure transforms into the sheet graphite structure. Owing to the tool wear the cutting force increases.

Atom based grain extraction and measurement of geometric properties

NASA Astrophysics Data System (ADS)

Martine La Boissonière, Gabriel; Choksi, Rustum

2018-04-01

We introduce an accurate, self-contained and automatic atom based numerical algorithm to characterize grain distributions in two dimensional Phase Field Crystal (PFC) simulations. We compare the method with hand segmented and known test grain distributions to show that the algorithm is able to extract grains and measure their area, perimeter and other geometric properties with high accuracy. Four input parameters must be set by the user and their influence on the results is described. The method is currently tuned to extract data from PFC simulations in the hexagonal lattice regime but the framework may be extended to more general problems.

Al(0.5)Nb(1.5)(PO(4))(3).

PubMed

Zhao, Dan; Liang, Peng; Su, Ling; Chang, Huan; Yan, Shi

2011-02-12

Single crystals of the title compound, aluminium niobium triphosphate, Al(0.5)Nb(1.5)(PO(4))(3), have been synthesized by a high-temperature reaction in a platinium crucible. The Al(III) and Nb(V) atoms occupy the same site on the axis, with disorder in the ratio of 1:3. The fundamental building units of the title structure are isolated Al/NbO(6) octa-hedra and PO(4) tetra-hedra (. 2 symmetry), which are further inter-locked by corner-sharing O atoms, leading to a three-dimensional framework structure with infinite channels along the a axis.

Bis(2,4-dibromo-6-formyl­phenolato-κ2 O,O′)copper(II)

PubMed Central

Li, Guang Zhao; Zhang, Shu Hua; Liu, Zheng

2008-01-01

In the title compound, [Cu(C7H3Br2O2)2], the CuII atom, which lies on an inversion centre, is coordinated by four O atoms from two chelating bidentate 2,4-dibromo-6-formyl­phenolate ligands in a slightly distorted square-planar coordination geometry. In the crystal structure, short inter­molecular Br⋯Br [3.516 (4) and 3.653 (4) Å] and Cu⋯Br [3.255 (1) Å] contacts together with C—H⋯O hydrogen bonds generate a three-dimensional network. PMID:21200624

2-Amino-4,6-dimethyl­pyrimidin-1-ium chloride

PubMed Central

Hu, Hui-Ling; Yeh, Chun-Wei

2012-01-01

In the title compound, C6H10N3 +·Cl−, the cation is essentially planar with an r.m.s. deviations of the fitted atoms of 0.008 Å. In the crystal, adjacent ions are linked by weak N—H⋯Cl hydrogen bonds involving the pyrimidine and amine N atoms, forming a three-dimensional network. C—H⋯π inter­actions between the methyl and pyrimidine groups and π–π stacking [centroid–centroid distance = 3.474 (1) Å] between parallel pyrimidine ring systems are also observed. PMID:23476204

A general approach to DNA-programmable atom equivalents.

PubMed

Zhang, Chuan; Macfarlane, Robert J; Young, Kaylie L; Choi, Chung Hang J; Hao, Liangliang; Auyeung, Evelyn; Liu, Guoliang; Zhou, Xiaozhu; Mirkin, Chad A

2013-08-01

Nanoparticles can be combined with nucleic acids to programme the formation of three-dimensional colloidal crystals where the particles' size, shape, composition and position can be independently controlled. However, the diversity of the types of material that can be used is limited by the lack of a general method for preparing the basic DNA-functionalized building blocks needed to bond nanoparticles of different chemical compositions into lattices in a controllable manner. Here we show that by coating nanoparticles protected with aliphatic ligands with an azide-bearing amphiphilic polymer, followed by the coupling of DNA to the polymer using strain-promoted azide-alkyne cycloaddition (also known as copper-free azide-alkyne click chemistry), nanoparticles bearing a high-density shell of nucleic acids can be created regardless of nanoparticle composition. This method provides a route to a virtually endless class of programmable atom equivalents for DNA-based colloidal crystallization.

Crystal structure of (S)-sec-butyl­ammonium l-tartrate monohydrate

PubMed Central

Publicover, Ernlie A.; Kolwich, Jennifer; Stack, Darcie L.; Doué, Alyssa J.; Ylijoki, Kai E. O.

2017-01-01

The title hydrated mol­ecular salt, C4H12N+·C4H5O6 −·H2O, was prepared by deprotonation of enanti­opure l-tartaric acid with racemic sec-butyl­amine in water. Only one enanti­omer was observed crystallographically, resulting from the combination of (S)-sec-butyl­amine with l-tartaric acid. The sec-butyl­ammonium moiety is disordered over two conformations related by rotation around the CH–CH2 bond; the refined occupancy ratio is 0.68 (1):0.32 (1). In the crystal, mol­ecules are linked through a network of O—H⋯O and N—H⋯O hydrogen-bonding inter­actions, between the ammonium H atoms, the tartrate hy­droxy H atoms, and the inter­stitial water, forming a three-dimensional supra­molecular structure. PMID:28529783

Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

DOE PAGES

Li, Xufan; Basile, Leonardo; Huang, Bing; ...

2015-07-22

Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigationsmore » of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E 2 1g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.« less

Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

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

Li, Xufan; Basile, Leonardo; Huang, Bing

Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigationsmore » of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E 2 1g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.« less

A neodymium(III)-ammonium complex involving oxalate and carbonate ligands: (NH4)2[Nd2(C2O4)3(CO3)(H2O)].H2O.

PubMed

Trombe, Jean-Christian; Galy, Jean; Enjalbert, Renée

2002-10-01

The title compound, diammonium aqua-mu-carbonato-tri-mu-oxalato-dineodymium(III) hydrate, (NH(4))(2)[Nd(2)(CO(3))(C(2)O(4))(3)(H(2)O)].H(2)O, involving the two ligands oxalate and carbonate, has been prepared hydrothermally as single crystals. The Nd atoms form a tetranuclear unit across the inversion centre at (1/2, 1/2, 1/2). Starting from this tetranuclear unit, the oxalate ligands serve to develop a three-dimensional network. The carbonate group acts as a bis-chelating ligand to two Nd atoms, and is monodentate to a third Nd atom. The oxalate groups are all bis-chelating. The two independent Nd atoms are ninefold coordinated and the coordination polyhedron of these atoms is a distorted monocapped antiprism.

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

Miao, Jianwei; Ercius, Peter; Billinge, S. J. L.

Crystallography has been fundamental to the development of many fields of science over the last century. However, much of our modern science and technology relies on materials with defects and disorders, and their three-dimensional (3D) atomic structures are not accessible to crystallography. One method capable of addressing this major challenge is atomic electron tomography. By combining advanced electron microscopes and detectors with powerful data analysis and tomographic reconstruction algorithms, it is now possible to determine the 3D atomic structure of crystal defects such as grain boundaries, stacking faults, dislocations, and point defects, as well as to precisely localize the 3Dmore » coordinates of individual atoms in materials without assuming crystallinity. In this work, we review the recent advances and the interdisciplinary science enabled by this methodology. We also outline further research needed for atomic electron tomography to address long-standing unresolved problems in the physical sciences.« less

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.

Enhancement of Raman scattering from monolayer graphene by photonic crystal nanocavities

NASA Astrophysics Data System (ADS)

Kimura, Issei; Yoshida, Masahiro; Sota, Masaki; Inoue, Taiki; Chiashi, Shohei; Maruyama, Shigeo; Kato, Yuichiro K.

Monolayer graphene is an atomically thin two-dimensional material that shows strong Raman scattering, while photonic crystal nanocavities with small mode volumes allow for efficient optical coupling at the nanoscale. Here we demonstrate resonant enhancement of graphene Raman G' band by coupling to photonic crystal cavity modes. Hexagonal-lattice photonic crystal L3 cavities are fabricated from silicon-on-insulator substrates. and monolayer graphene sheets grown by chemical vapor deposition are transferred onto the nanocavities. Excitation wavelength dependence of Raman spectra show that the Raman intensity is enhanced when the G' peak is in resonance with the cavity mode. By performing imaging measurements, we confirm that such an enhancement is only observed at the cavity position. Work supported by JSPS KAKENHI Grant Numbers JP16K13613, JP25107002 and MEXT (Photon Frontier Network Program, Nanotechnology Platform).

Study on formation of step bunching on 6H-SiC (0001) surface by kinetic Monte Carlo method

NASA Astrophysics Data System (ADS)

Li, Yuan; Chen, Xuejiang; Su, Juan

2016-05-01

The formation and evolution of step bunching during step-flow growth of 6H-SiC (0001) surfaces were studied by three-dimensional kinetic Monte Carlo (KMC) method and compared with the analytic model based on the theory of Burton-Cabera-Frank (BCF). In the KMC model the crystal lattice was represented by a structured mesh which fixed the position of atoms and interatomic bonding. The events considered in the model were adatoms adsorption and diffusion on the terrace, and adatoms attachment, detachment and interlayer transport at the step edges. In addition, effects of Ehrlich-Schwoebel (ES) barriers at downward step edges and incorporation barriers at upwards step edges were also considered. In order to obtain more elaborate information for the behavior of atoms in the crystal surface, silicon and carbon atoms were treated as the minimal diffusing species. KMC simulation results showed that multiple-height steps were formed on the vicinal surface oriented toward [ 1 1 bar 00 ] or [ 11 2 bar 0 ] directions. And then the formation mechanism of the step bunching was analyzed. Finally, to further analyze the formation processes of step bunching, a one-dimensional BCF analytic model with ES and incorporation barriers was used, and then it was solved numerically. In the BCF model, the periodic boundary conditions (PBC) were applied, and the parameters were corresponded to those used in the KMC model. The evolution character of step bunching was consistent with the results obtained by KMC simulation.

A Hirshfeld surface analysis, supramolecular structure and magnetic properties of a new Cu(II) complex with the 4-amino-6-methoxypyrimidine ligand

NASA Astrophysics Data System (ADS)

Nbili, W.; Kaabi, K.; Ferenc, W.; Cristovão, B.; Lefebvre, F.; Jelsch, Christian; Ben Nasr, Cherif

2017-02-01

A new Cu(II) complex with the bridge bidentate ligand 4-amino-6-methoxypyrimidine, [Cu(C5H7N3O)(H2O)(NO3)2], has been prepared at room temperature and characterized by single crystal X-ray diffraction and IR spectroscopy. The compound crystallizes in the monoclinic space group C2/c with lattice parameters a = 17.783 (4), b = 11.131 (3), c = 12.594 (3) Å, β = 117.616 (3)°, V = 2209.0 (9) Å3 and Z = 8. The Cu(II) cation is hexa-coordinated, in distorted octahedral fashion, by two nitrogen atoms of two 4-amino-6-methoxypyrimidine ligands, one water oxygen atom and three oxygen atoms of two nitrate anions. In the atomic arrangement, the organic ligands and the 6-connected Cu centers are linked with each other to give a 1-D corrugated chain running along the b-axis direction. The chains are interconnected via Osbnd H⋯O, Csbnd H⋯O, Nsbnd H⋯O hydrogen bonds to form a three dimensional network. The analysis of contacts on the Hirshfeld surface shows that the crystal packing is driven mainly by the electrostatic interactions: the coordination of Cu(II) by O and N as well as strong hydrogen bonds. The vibrational absorption bands were identified by infrared spectroscopy. Magnetic properties were also studied to characterize the complex.

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

Zhu, Bo; Zhao, Hongwei, E-mail: hwzhao@jlu.edu.cn, E-mail: khl69@163.com; Zhao, Dan

It has always been a critical issue to understand the material removal behavior of Vibration-Assisted Machining (VAM), especially on atomic level. To find out the effects of vibration frequency on material removal response, a three-dimensional molecular dynamics (MD) model has been established in this research to investigate the effects of scratched groove, crystal defects on the surface quality, comparing with the Von Mises shear strain and tangential force in simulations during nano-scratching process. Comparisons are made among the results of simulations from different vibration frequency with the same scratching feed, depth, amplitude and crystal orientation. Copper potential in this simulationmore » is Embedded-Atom Method (EAM) potential. Interaction between copper and carbon atoms is Morse potential. Simulational results show that higher frequency can make groove smoother. Simulation with high frequency creates more dislocations to improve the machinability of copper specimen. The changing frequency does not have evident effects on Von Mises shear strain. Higher frequency can decrease the tangential force to reduce the consumption of cutting energy and tool wear. In conclusion, higher vibration frequency in VAM on mono-crystalline copper has positive effects on surface finish, machinablility and tool wear reduction.« less

Band structure engineering of 2D materials using patterned dielectric superlattices.

PubMed

Forsythe, Carlos; Zhou, Xiaodong; Watanabe, Kenji; Taniguchi, Takashi; Pasupathy, Abhay; Moon, Pilkyung; Koshino, Mikito; Kim, Philip; Dean, Cory R

2018-05-07

The ability to manipulate electrons in two-dimensional materials with external electric fields provides a route to synthetic band engineering. By imposing artificially designed and spatially periodic superlattice potentials, electronic properties can be further altered beyond the constraints of naturally occurring atomic crystals 1-5 . Here, we report a new approach to fabricate high-mobility superlattice devices by integrating surface dielectric patterning with atomically thin van der Waals materials. By separating the device assembly and superlattice fabrication processes, we address the intractable trade-off between device processing and mobility degradation that constrains superlattice engineering in conventional systems. The improved electrostatics of atomically thin materials allows smaller wavelength superlattice patterns relative to previous demonstrations. Moreover, we observe the formation of replica Dirac cones in ballistic graphene devices with sub-40 nm wavelength superlattices and report fractal Hofstadter spectra 6-8 under large magnetic fields from superlattices with designed lattice symmetries that differ from that of the host crystal. Our results establish a robust and versatile technique for band structure engineering of graphene and related van der Waals materials with dynamic tunability.

Avalanche atomic switching in strain engineered Sb2Te3-GeTe interfacial phase-change memory cells

NASA Astrophysics Data System (ADS)

Zhou, Xilin; Behera, Jitendra K.; Lv, Shilong; Wu, Liangcai; Song, Zhitang; Simpson, Robert E.

2017-09-01

By confining phase transitions to the nanoscale interface between two different crystals, interfacial phase change memory heterostructures represent the state of the art for energy efficient data storage. We present the effect of strain engineering on the electrical switching performance of the {{Sb}}2{{Te}}3-GeTe superlattice van der Waals devices. Multiple Ge atoms switching through a two-dimensional Te layer reduces the activation barrier for further atoms to switch; an effect that can be enhanced by biaxial strain. The out-of-plane phonon mode of the GeTe crystal remains active in the superlattice heterostructures. The large in-plane biaxial strain imposed by the {{Sb}}2{{Te}}3 layers on the GeTe layers substantially improves the switching speed, reset energy, and cyclability of the superlattice memory devices. Moreover, carefully controlling residual stress in the layers of {{Sb}}2{{Te}}3-GeTe interfacial phase change memories provides a new degree of freedom to design the properties of functional superlattice structures for memory and photonics applications.

Causes of High-temperature Superconductivity in the Hydrogen Sulfide Electron-phonon System

NASA Astrophysics Data System (ADS)

Degtyarenko, N. N.; Mazur, E. A.

The electron and phonon spectra, as well as the density of electron and phonon states of the stable orthorhombic structure of hydrogen sulfide (SH2) at pressures 100-180 GPa have been calculated. It is found that the set of parallel planes of hydrogen atoms is formed at pressure ∼175 GPa as a result of structural changes in the unit cell of the crystal under pressure. There should be complete concentration of hydrogen atoms in these planes. As a result the electron properties of the system acquire a quasi-two-dimensional character. The features of in phase and antiphase oscillations of hydrogen atoms in these planes leading to two narrow high-energy peaks in the phonon density of states are investigated.

Persistent mobility edges and anomalous quantum diffusion in order-disorder separated quantum films

NASA Astrophysics Data System (ADS)

Zhong, Jianxin; Stocks, G. Malcolm

2007-01-01

A concept of order-disorder separated quantum films is proposed for the design of ultrathin quantum films of a few atomic layers thick with unconventional transport properties. The concept is demonstrated through studying an atomic bilayer comprised of an ordered layer and a disordered layer. Without the disordered layer or the ordered layer, the system is a conducting two-dimensional (2D) crystal or an insulating disordered 2D electron system. Without the order-disorder phase separation, a disordered bilayer is insulating under large disorder. In an order-disorder separated atomic bilayer, however, we show that the system behaves remarkably different from conventional ordered or disordered electron systems, exhibiting metal-insulator transitions with persistent mobility edges and superdiffusive anomalous quantum diffusion.

Shear-induced partial translational ordering of a colloidal solid

NASA Astrophysics Data System (ADS)

Ackerson, B. J.; Clark, N. A.

1984-08-01

Highly charged submicrometer plastic spheres suspended in water at low ionic strength will order spontaneously into bcc crystals or polycrystals. A simple linear shear orients and disorders these crystals by forcing (110) planes to stack normal to the shear gradient and to slide relative to each other with a <111> direction parallel to the solvent flow. In this paper we analyze in detail the disordering and flow processes occurring beyond the intrinsic elastic limit of the bcc crystal. We are led to a model in which the flow of a colloidal crystal is interpreted as a fundamentally different process from that found in atomic crystals. In the colloidal crystal the coupling of particle motion to the background fluid forces a homogeneous flow, where every layer is in motion relative to its neighboring layers. In contrast, the plastic flow in an atomic solid is defect mediated flow. At the lowest applied stress, the local bcc order in the colloidal crystal exhibits shear strains both parallel and perpendicular to the direction of the applied stress. The magnitude of these deformations is estimated using the configurational energy for bcc and distorted bcc crystals, assuming a screened Coulomb pair interaction between colloidal particles. As the applied stress is increased, the intrinsic elastic limit of the crystal is exceeded and the crystal begins to flow with adjacent layers executing an oscillatory path governed by the balance of viscous and screened Coulomb forces. The path takes the structure from the bcc1 and bcc2 twins observed at zero shear to a distorted two-dimensional hcp structure at moderate shear rates, with a loss of interlayer registration as the shear is increased. This theoretical model is consistent with other experimental observations, as well.

Ferromagnetism in CVT grown tungsten diselenide single crystals with nickel doping

NASA Astrophysics Data System (ADS)

Habib, Muhammad; Muhammad, Zahir; Khan, Rashid; Wu, Chuanqiang; Rehman, Zia ur; Zhou, Yu; Liu, Hengjie; Song, Li

2018-03-01

Two dimensional (2D) single crystal layered transition materials have had extensive consideration owing to their interesting magnetic properties, originating from their lattices and strong spin-orbit coupling, which make them of vital importance for spintronic applications. Herein, we present synthesis of a highly crystalline tungsten diselenide layered single crystal grown by chemical vapor transport technique and doped with nickel (Ni) to tailor its magnetic properties. The pristine WSe2 single crystal and Ni-doped crystal were characterized and analyzed for magnetic properties using both experimental and computational aspects. It was found that the magnetic behavior of the 2D layered WSe2 crystal changed from diamagnetic to ferromagnetic after Ni-doping at all tested temperatures. Moreover, first principle density functional theory (DFT) calculations further confirmed the origin of room temperature ferromagnetism of Ni-doped WSe2, where the d-orbitals of the doped Ni atom promoted the spin moment and thus largely contributed to the magnetism change in the 2D layered material.

Aqua­{6,6′-dimeth­oxy-2,2′-[ethane-1,2-diylbis(nitrilo­methyl­idyne)]diphenolato}nickel(II)

PubMed Central

Guo, Zhenghua; Li, Lianzhi; Xu, Tao; Li, Jinghong; Wang, Daqi

2009-01-01

The title complex, [Ni(C18H18N2O4)(H2O)], lies on a mirror plane with the NiII ion coordinated by two N and two O atoms of a tetra­dentate Schiff base ligand and one water O atom in a distorted square-pyramidal enviroment. The –CH2–CH2– group of the ligand is disordered equally over two sites about the mirror plane. The dihedral angle between the mean planes of the two symmetry-related chelate rings is 37.16 (6)°. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link complex mol­ecules into one-dimensional chains along [100] and these chains are linked, in turn, by very weak inter­molecular C—H⋯O hydrogen bonds into a two-dimensional network. PMID:21577698

Imaging quasiperiodic electronic states in a synthetic Penrose tiling

NASA Astrophysics Data System (ADS)

Collins, Laura C.; Witte, Thomas G.; Silverman, Rochelle; Green, David B.; Gomes, Kenjiro K.

2017-06-01

Quasicrystals possess long-range order but lack the translational symmetry of crystalline solids. In solid state physics, periodicity is one of the fundamental properties that prescribes the electronic band structure in crystals. In the absence of periodicity and the presence of quasicrystalline order, the ways that electronic states change remain a mystery. Scanning tunnelling microscopy and atomic manipulation can be used to assemble a two-dimensional quasicrystalline structure mapped upon the Penrose tiling. Here, carbon monoxide molecules are arranged on the surface of Cu(111) one at a time to form the potential landscape that mimics the ionic potential of atoms in natural materials by constraining the electrons in the two-dimensional surface state of Cu(111). The real-space images reveal the presence of the quasiperiodic order in the electronic wave functions and the Fourier analysis of our results links the energy of the resonant states to the local vertex structure of the quasicrystal.

Imaging quasiperiodic electronic states in a synthetic Penrose tiling.

PubMed

Collins, Laura C; Witte, Thomas G; Silverman, Rochelle; Green, David B; Gomes, Kenjiro K

2017-06-22

Quasicrystals possess long-range order but lack the translational symmetry of crystalline solids. In solid state physics, periodicity is one of the fundamental properties that prescribes the electronic band structure in crystals. In the absence of periodicity and the presence of quasicrystalline order, the ways that electronic states change remain a mystery. Scanning tunnelling microscopy and atomic manipulation can be used to assemble a two-dimensional quasicrystalline structure mapped upon the Penrose tiling. Here, carbon monoxide molecules are arranged on the surface of Cu(111) one at a time to form the potential landscape that mimics the ionic potential of atoms in natural materials by constraining the electrons in the two-dimensional surface state of Cu(111). The real-space images reveal the presence of the quasiperiodic order in the electronic wave functions and the Fourier analysis of our results links the energy of the resonant states to the local vertex structure of the quasicrystal.

Resonant tunneling through discrete quantum states in stacked atomic-layered MoS2.

PubMed

Nguyen, Linh-Nam; Lan, Yann-Wen; Chen, Jyun-Hong; Chang, Tay-Rong; Zhong, Yuan-Liang; Jeng, Horng-Tay; Li, Lain-Jong; Chen, Chii-Dong

2014-05-14

Two-dimensional crystals can be assembled into three-dimensional stacks with atomic layer precision, which have already shown plenty of fascinating physical phenomena and been used for prototype vertical-field-effect-transistors.1,2 In this work, interlayer electron tunneling in stacked high-quality crystalline MoS2 films were investigated. A trilayered MoS2 film was sandwiched between top and bottom electrodes with an adjacent bottom gate, and the discrete energy levels in each layer could be tuned by bias and gate voltages. When the discrete energy levels aligned, a resonant tunneling peak appeared in the current-voltage characteristics. The peak position shifts linearly with perpendicular magnetic field, indicating formation of Landau levels. From this linear dependence, the effective mass and Fermi velocity are determined and are confirmed by electronic structure calculations. These fundamental parameters are useful for exploitation of its unique properties.

Spontaneous resolution of binary copper(II) complexes with racemic dipeptides: crystal structures of glycyl-L-alpha-amino-n-butyrato copper(II) monohydrate, glycyl-D-valinato copper(II) hemihydrate, and glycyl-L-valinato copper(II) hemihydrate.

PubMed

Inomata, Yoshie; Yamaguchi, Takeshi; Tomita, Airi; Yamada, Dai; Howell, F Scott

2005-08-01

Copper(II) complexes with glycyl-DL-alpha-amino-n-butyric acid (H2gly-DL-but), glycyl-DL-valine (H2gly-DL-val), glycyl-DL-norleucine (H2gly-DL-norleu), glycyl-DL-threonine (H2gly-DL-thr), glycyl-DL-serine (H2gly-DL-ser), glycyl-DL-phenylalanine (H2gly-DL-phe), and glycyl-L-valine (H2gly-L-val), have been prepared and characterized by IR, powder diffuse reflection, CD and ORD spectra, and magnetic susceptibility measurements, and by single-crystal X-ray diffraction. The crystal structures of the copper complex with H2gly-DL-but, the copper complex with H2gly-DL-val, and [Cu(gly-L-val)]n.0.5nH2O have been determined by a single-crystal X-ray diffraction method. As for the structure of the copper complex with H2gly-DL-but, the configuration around the asymmetric carbon atom is similar to that of [Cu(gly-L-val)]n.0.5nH2O. Therefore it is concluded that the copper complex with H2gly-DL-but is [Cu(gly-L-but)]n.nH2O. On the contrary, as for the structure of the copper complex with H2gly-DL-val, the configuration around the asymmetric carbon atom is different from that of [Cu(gly-L-val)]n.0.5nH2O. Therefore it is concluded that the copper complex with H2gly-dl-val is [Cu(gly-D-val)]n.0.5nH2O. So during the crystallization of the copper(II) complexes with H2gly-DL-but and H2gly-DL-val, spontaneous resolution has been observed; the four complexes have separated as [Cu(gly-D-but)]n.nH2O, [Cu(gly-L-but)]n.nH2O, [Cu(gly-D-val)]n.0.5nH2O, and [Cu(gly-L-val)]n.0.5nH2O, respectively. [Cu(gly-L-but)]n.nH2O is orthorhombic with the space group P2(1)2(1)2(1). [Cu(gly-D-val)]n.0.5nH2O and [Cu(gly-L-val)]n.0.5nH2O are monoclinic with the space group C2. In these complexes, the copper atom is in a square-pyramidal geometry, ligated by a peptide nitrogen atom, an amino nitrogen atom, a carboxyl oxygen atom, and a carboxyl oxygen atom and a peptide oxygen atom from neighboring molecules. So these complexes consist of a two-dimensional polymer chain bridged by a carboxyl oxygen atom and a peptide oxygen atom from neighboring molecules. The axial oxygen atom is located above the basal plane and the side chain of an amino acid is located below it. These polymer chains consist of only one or the other type of optical isomers; no racemic dipeptides are found. Therefore, spontaneous resolution has been observed in the crystallization of copper(II) complexes with H2gly-DL-but and H2gly-DL-val. The crystal structure of [Cu(gly-D-val)]n.0.5nH2O agrees almost completely with that of [Cu(gly-L-val)]n.0.5nH2O, except for the configuration around the asymmetric carbon atom.

Topological mosaics in moiré superlattices of van der Waals heterobilayers

NASA Astrophysics Data System (ADS)

Tong, Qingjun; Yu, Hongyi; Zhu, Qizhong; Wang, Yong; Xu, Xiaodong; Yao, Wang

2017-04-01

Van der Waals (vdW) heterostructures formed by two-dimensional atomic crystals provide a powerful approach towards designer condensed matter systems. Incommensurate heterobilayers with small twisting and/or lattice mismatch lead to the interesting concept of moiré superlattices, where the atomic registry is locally indistinguishable from commensurate bilayers but has local-to-local variation over long range. Here we show that such moiré superlattices can lead to periodic modulation of local topological order in vdW heterobilayers formed by two massive Dirac materials. By tuning the vdW heterojunction from normal to the inverted type-II regime via an interlayer bias, the commensurate heterobilayer can become a topological insulator (TI), depending on the interlayer hybridization controlled by the atomic registry between the vdW layers. This results in a mosaic pattern of TI regions and normal insulator (NI) regions in moiré superlattices, where topologically protected helical modes exist at the TI/NI phase boundaries. By using symmetry-based k .p and tight-binding models, we predict that this topological phenomenon can be present in inverted transition metal dichalcogenides heterobilayers. Our work points to a new means of realizing programmable and electrically switchable topological superstructures from two-dimensional arrays of TI nano-dots to one-dimensional arrays of TI nano-stripes.

Three Dimensional Positron Annihilation Momentum Spectroscopy of Lithium Tetraborate Crystals

DTIC Science & Technology

2013-03-21

Technique Applied to Measure Oxygen-Atom Defects in 6H Silicon Carbide ." AFIT PhD Dissertation. AFIT/DS/ENP/10-M02, (Mar 2010) [4] Charlton, M., and...of Experimental Observables of Positron-Vacancy Complexes in Silicon Carbide .” Ph.D. dissertation, Air Force Institute of Technology, 2005. [18...Resonances ............................ 19 2.1.2 3D Positron Annihilation Momentum Measurements (3DPAMMs) of 6H SiC

Characterization technique for detection of atom-size crystalline defects and strains using two-dimensional fast-Fourier-transform sampling Moiré method

NASA Astrophysics Data System (ADS)

Kodera, Masako; Wang, Qinghua; Ri, Shien; Tsuda, Hiroshi; Yoshioka, Akira; Sugiyama, Toru; Hamamoto, Takeshi; Miyashita, Naoto

2018-04-01

Recently, we have developed a two-dimensional (2D) fast-Fourier-transform (FFT) sampling Moiré technique to visually and quantitatively determine the locations of minute defects in a transmission electron microscopy (TEM) image. We applied this technique for defect detection with GaN high electron mobility transistor (HEMT) devices, and successfully and clearly visualized atom-size defects in AlGaN/GaN crystalline structures. The defect density obtained in the AlGaN/GaN structures is ∼1013 counts/cm2. In addition, we have successfully confirmed that the distribution and number of defects closely depend on the process conditions. Thus, this technique is quite useful for a device development. Moreover, the strain fields in an AlGaN/GaN crystal were effectively calculated with nm-scale resolution using this method. We also demonstrated that this sampling Moiré technique is applicable to silicon devices, which have principal directions different from those of AlGaN/GaN crystals. As a result, we believe that the 2D FFT sampling Moiré method has great potential applications to the discovery of new as yet unknown phenomena occurring between the characteristics of a crystalline material and device performance.

Colloquium: Excitons in atomically thin transition metal dichalcogenides

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

Wang, Gang; Chernikov, Alexey; Glazov, Mikhail M.

Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weakmore » dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. In this article, recent progress in understanding of the excitonic properties in monolayer TMDs is reviewed and future challenges are laid out. Discussed are the consequences of the strong direct and exchange Coulomb interaction, exciton light-matter coupling, and influence of finite carrier and electron-hole pair densities on the exciton properties in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.« less

Colloquium: Excitons in atomically thin transition metal dichalcogenides

DOE PAGES

Wang, Gang; Chernikov, Alexey; Glazov, Mikhail M.; ...

2018-04-04

Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weakmore » dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. In this article, recent progress in understanding of the excitonic properties in monolayer TMDs is reviewed and future challenges are laid out. Discussed are the consequences of the strong direct and exchange Coulomb interaction, exciton light-matter coupling, and influence of finite carrier and electron-hole pair densities on the exciton properties in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.« less

Colloquium: Excitons in atomically thin transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Wang, Gang; Chernikov, Alexey; Glazov, Mikhail M.; Heinz, Tony F.; Marie, Xavier; Amand, Thierry; Urbaszek, Bernhard

2018-04-01

Atomically thin materials such as graphene and monolayer transition metal dichalcogenides (TMDs) exhibit remarkable physical properties resulting from their reduced dimensionality and crystal symmetry. The family of semiconducting transition metal dichalcogenides is an especially promising platform for fundamental studies of two-dimensional (2D) systems, with potential applications in optoelectronics and valleytronics due to their direct band gap in the monolayer limit and highly efficient light-matter coupling. A crystal lattice with broken inversion symmetry combined with strong spin-orbit interactions leads to a unique combination of the spin and valley degrees of freedom. In addition, the 2D character of the monolayers and weak dielectric screening from the environment yield a significant enhancement of the Coulomb interaction. The resulting formation of bound electron-hole pairs, or excitons, dominates the optical and spin properties of the material. Here recent progress in understanding of the excitonic properties in monolayer TMDs is reviewed and future challenges are laid out. Discussed are the consequences of the strong direct and exchange Coulomb interaction, exciton light-matter coupling, and influence of finite carrier and electron-hole pair densities on the exciton properties in TMDs. Finally, the impact on valley polarization is described and the tuning of the energies and polarization observed in applied electric and magnetic fields is summarized.

Crystal structure of langbeinite-related Rb0.743K0.845Co0.293Ti1.707(PO4)3.

PubMed

Strutynska, Nataliia Yu; Bondarenko, Marina A; Ogorodnyk, Ivan V; Baumer, Vyacheslav N; Slobodyanik, Nikolay S

2015-03-01

Potassium rubidium cobalt(II)/titanium(IV) tris-(orthophosphate), Rb0.743K0.845Co0.293Ti1.707(PO4)3, has been obtained using a high-temperature crystallization method. The obtained compound has a langbeinite-type structure. The three-dimensional framework is built up from mixed-occupied (Co/Ti(IV))O6 octa-hedra (point group symmetry .3.) and PO4 tetra-hedra. The K(+) and Rb(+) cations are statistically distributed over two distinct sites (both with site symmetry .3.) in the large cavities of the framework. They are surrounded by 12 O atoms.

Poly[[di-μ-aqua-(μ-4-formyl-2-meth­oxy­phenol­ato)disodium] 4-formyl-2-meth­oxy­phenolate

PubMed Central

Asghar, Muhammad Nadeem; Şahin, Onur; Arshad, Muhammad Nadeem; Mazhar, Uzma; Khan, Islam Ullah; Büyükgüngör, Orhan

2010-01-01

In the title coordination polymer, {[Na2(C8H7O3)(H2O)4](C8H7O3)}n, all the non-H atoms except the water O atoms lie on a crystallographic mirror plane. One sodium cation is bonded to four water O atoms and one vanillinate O atom in a distorted square-based pyramidal arrangement; the other Na+ ion is six-coordinated by four water O atoms and two vanillinate O atoms in an irregular geometry. One of the vanillinate anions is directly bonded to two sodium ions, whilst the other only inter­acts with the polymeric network by way of hydrogen bonds. In the crystal, a two-dimensional polymeric array is formed; this is reinforced by O—H⋯O hydrogen bonds, which generate R 2 1(6) and R 2 2(20) loops. PMID:21579628

A two-dimensional Zn coordination polymer with a three-dimensional supra-molecular architecture.

PubMed

Liu, Fuhong; Ding, Yan; Li, Qiuyu; Zhang, Liping

2017-10-01

The title compound, poly[bis-{μ 2 -4,4'-bis-[(1,2,4-triazol-1-yl)meth-yl]biphenyl-κ 2 N 4 : N 4' }bis-(nitrato-κ O )zinc(II)], [Zn(NO 3 ) 2 (C 18 H 16 N 6 ) 2 ] n , is a two-dimensional zinc coordination polymer constructed from 4,4'-bis-[(1 H -1,2,4-triazol-1-yl)meth-yl]-1,1'-biphenyl units. It was synthesized and characterized by elemental analysis and single-crystal X-ray diffraction. The Zn II cation is located on an inversion centre and is coordinated by two O atoms from two symmetry-related nitrate groups and four N atoms from four symmetry-related 4,4'-bis-[(1 H -1,2,4-triazol-1-yl)meth-yl]-1,1'-biphenyl ligands, forming a distorted octa-hedral {ZnN 4 O 2 } coordination geometry. The linear 4,4'-bis-[(1 H -1,2,4-triazol-1-yl)meth-yl]-1,1'-biphenyl ligand links two Zn II cations, generating two-dimensional layers parallel to the crystallographic (132) plane. The parallel layers are connected by C-H⋯O, C-H⋯N, C-H⋯π and π-π stacking inter-actions, resulting in a three-dimensional supra-molecular architecture.

Two-dimensionally grown single-crystal silicon nanosheets with tunable visible-light emissions.

PubMed

Kim, Sung Wook; Lee, Jaejun; Sung, Ji Ho; Seo, Dong-jae; Kim, Ilsoo; Jo, Moon-Ho; Kwon, Byoung Wook; Choi, Won Kook; Choi, Heon-Jin

2014-07-22

Since the discovery of graphene, growth of two-dimensional (2D) nanomaterials has greatly attracted attention. However, spontaneous growth of atomic two-dimensional (2D) materials is limitedly permitted for several layered-structure crystals, such as graphene, MoS2, and h-BN, and otherwise it is notoriously difficult. Here we report the gas-phase 2D growth of silicon (Si), that is cubic in symmetry, via dendritic growth and an interdendritic filling mechanism and to form Si nanosheets (SiNSs) of 1 to 13 nm in thickness. Thin SiNSs show strong thickness-dependent photoluminescence in visible range including red, green, and blue (RGB) emissions with the associated band gap energies ranging from 1.6 to 3.2 eV; these emission energies were greater than those from Si quantum dots (SiQDs) of the similar sizes. We also demonstrated that electrically driven white, as well as blue, emission in a conventional organic light-emitting diode (OLED) geometry with the SiNS assembly as the active emitting layers. Tunable light emissions in visible range in our observations suggest practical implications for novel 2D Si nanophotonics.

4-{[4-(Hy­droxy­meth­yl)piperidin-1-yl]meth­yl}phenol

PubMed Central

Simões, M. C. R.; Landre, I. M. R.; Moreira, M. S.; Viegas Jr, C.; Doriguetto, A. C.

2012-01-01

In the title compound, C13H19NO2, the piperidine ring has a chair conformation with the exocyclic N—C bond in an equatorial position. In the crystal, mol­ecules are linked head-to-tail by phenol O—H⋯O hydrogen bonds to hy­droxy­methyl­ene O-atom acceptors, forming chains which extend along [100]. These chains form two-dimensional networks lying parallel to (101) through cyclic hydrogen-bonding associations [graph set R 4 4(30)], involving hy­droxy O—H donors and piperidine N-atom acceptors. PMID:22798921

1-Do-decyl-indoline-2,3-dione.

PubMed

Qachchachi, Fatima-Zahrae; Ouazzani Chahdi, Fouad; Misbahi, Houria; Bodensteiner, Michael; El Ammari, Lahcen

2014-02-01

The structure of the title compound, C20H29NO2, is isotypic to that of its homologue 1-octylindoline-2,3-dione. The indoline ring and the two carbonyl-group O atoms are approximately coplanar, the largest deviation from the mean plane being 0.0760 (10) Å. The mean plane through the fused-ring system is nearly perpendicular to the mean plane passing through the 1-dodecyl chain [dihedral angle = 77.69 (5)°]. All C atoms of the dodecyl group are in an anti-periplanar arrangement. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds, forming a three-dimensional network.

X-ray diffraction studies of enkephalins. Crystal structure of [(4'-bromo) Phe4,Leu5]enkephalin.

PubMed Central

Ishida, T; Kenmotsu, M; Mino, Y; Inoue, M; Fujiwara, T; Tomita, K; Kimura, T; Sakakibara, S

1984-01-01

In order to investigate the structure-activity relationship of [Leu5]- and [Met5]enkephalins, [(4'-bromo)Phe4, Leu5]-, [(4'-bromo)Phe4, Met5]- and [Met5] enkephalins were synthesized and crystallized. The crystal structure of [(4'-bromo) Phe4, Leu5]- enkephalin was determined by X-ray diffraction method using the heavy atom method and refined to R = 0.092 by the least-squares method. The molecule in this crystal took essentially the same type I' beta-turn conformation found in [Leu5]enkephalin [Smith & Griffin (1978) Science 199, 1214-1216). On the other hand, the preliminary three-dimensional Patterson analyses showed that the most probable conformations of [(4'-bromo)Phe4,Met5]- and [Met5]enkephalins are both the dimeric extended forms. Based on these insights, the biologically active conformation of enkephalin was discussed in relation to the mu- and delta-receptors. PMID:6721829

Self-organization processes and topological defects in nanolayers in a nematic liquid crystal

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

Chuvyrov, A. N.; Girfanova, F. M.; Mal'tsev, I. S.

Atomic force microscopy is used to study the self-organization processes that occur during the formation of topological defects in nanomolecular layers in a nematic liquid crystal with the homeotropic orientation of its molecules with respect to the substrate. In this case, a smectic monolayer with a thickness of one molecule length (about 2.2 nm) forms on the substrate, and a nanomolecular layer of a nematic liquid crystal forms above this monolayer. In such virtually two-dimensional layers, numerous different nanoclusters, namely, hut structures, pyramids, raft structures with symmetry C{sub nm} (where n = 2, 4, 5, 6, 7, ?, {infinity}), cones,more » and nanopools, form [1]. They have a regular shape close to the geometry of solid crystals. Modulated linear structures and topological point defects appear spontaneously in the nanopools and raft structures.« less

Multiple period s-p hybridization in nano-strip embedded photonic crystal.

PubMed

Han, Seunghoon; Lee, Il-Min; Kim, Hwi; Lee, Byoungho

2005-04-04

We report and analyze hybridization of s-state and p-state modes in photonic crystal one-dimensional defect cavity array. When embedding a nano-strip into a dielectric rod photonic crystal, an effective cavity array is made, where each cavity possesses two cavity modes: s-state and p-state. The two modes are laterally even versus the nano-strip direction, and interact with each other, producing defect bands, of which the group velocity becomes zero within the first Brillouin zone. We could model and describe the phenomena by using the tight-binding method, well agreeing with the plane-wave expansion method analysis. We note that the reported s- and p-state mode interaction corresponds to the hybridization of atomic orbital in solid-state physics. The concept of multiple period s-p hybridization and the proposed model can be useful for analyzing and developing novel photonic crystal waveguides and devices.

Tautomeric and ionisation forms of dopamine and tyramine in the solid state

NASA Astrophysics Data System (ADS)

Cruickshank, Laura; Kennedy, Alan R.; Shankland, Norman

2013-11-01

Crystallisation of the phenylethylamine neurotransmitter dopamine from basic aqueous solution yielded the 3-phenoxide Zwitterionic tautomer, despite this being a minority form in the solution state. In the crystal structure, dopamine has a dimeric [OCCOH]2 hydrogen bonded catechol motif that expands through Nsbnd H⋯O interactions to give a 2-dimensional sheet of classical hydrogen bonds. These sheets are further interconnected by Nsbnd H⋯π interactions. The structurally related base tyramine crystallises under similar conditions as a hemihydrate with all four possible species of tyramine present (cationic, anionic, Zwitterionic and neutral) in the crystal structure. Single crystal X-ray diffraction studies at 121 and 293 K showed dynamic hydrogen atom disorder for the phenol/phenoxide group, suggesting that the tyramine speciation observed arises from a solid-state process.

Exciton Rydberg series in mono- and few-layer WS2

NASA Astrophysics Data System (ADS)

Chernikov, Alexey; Berkelbach, Timothy C.; Hill, Heather M.; Rigosi, Albert; Li, Yilei; Aslan, Özgur B.; Hybertsen, Mark S.; Reichman, David R.; Heinz, Tony F.

2014-03-01

Considered a long-awaited semiconducting analogue to graphene, the family of atomically thin transition metal dichalcogenides (TMDs) attracted intense interest in the scientific community due to their remarkable physical properties resulting from the reduced dimensionality. A fundamental manifestation of the two-dimensional nature is a strong increase in the Coulomb interaction. The resulting formation of tightly bound excitons plays a crucial role for a majority of optical and transport phenomena. In our work, we investigate the excitons in atomically thin TMDs by optical micro-spectroscopy and apply a microscopic, ab-initio theoretical approach. We observe a full sequence of excited exciton states, i.e., the Rydberg series, in the monolayer WS2, identifying tightly bound excitons with energies exceeding 0.3 eV - almost an order of magnitude higher than in the corresponding, three-dimensional crystal. We also find significant deviations of the excitonic properties from the conventional hydrogenic physics - a direct evidence of a non-uniform dielectric environment. Finally, an excellent quantitative agreement is obtained between the experimental findings and the developed theoretical approach.

Tunable two-dimensional interfacial coupling in molecular heterostructures

DOE PAGES

Xu, Beibei; Chakraborty, Himanshu; Yadav, Vivek K.; ...

2017-08-22

Two-dimensional van der Waals heterostructures are of considerable interest for the next generation nanoelectronics because of their unique interlayer coupling and optoelectronic properties. Here, we report a modified Langmuir–Blodgett method to organize twodimensional molecular charge transfer crystals into arbitrarily and vertically stacked heterostructures, consisting of bis(ethylenedithio)tetrathiafulvalene (BEDT–TTF)/C 60 and poly (3-dodecylthiophene-2,5-diyl) (P3DDT)/C 60 nanosheets. A strong and anisotropic interfacial coupling between the charge transfer pairs is demonstrated. The van der Waals heterostructures exhibit pressure dependent sensitivity with a high piezoresistance coefficient of -4.4 × 10 -6 Pa -1, and conductance and capacitance tunable by external stimuli (ferroelectric field and magneticmore » field). Density functional theory calculations confirm charge transfer between the n-orbitals of the S atoms in BEDT–TTF of the BEDT–TTF/C 60 layer and the π* orbitals of C atoms in C 60 of the P3DDT/C 60 layer contribute to the inter-complex CT. Thus, the two-dimensional molecular van der Waals heterostructures with tunable optical–electronic–magnetic coupling properties are promising for flexible electronic applications.« less

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.

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.

Crystal structure of tetra­aqua­[2-(pyridin-2-yl)-1H-imidazole-κ2 N 2,N 3]iron(II) sulfate

PubMed Central

Setifi, Zouaoui; Setifi, Fatima; Francuski, Bojana M.; Novaković, Sladjana B.; Merazig, Hocine

2015-01-01

In the title compound, [Fe(C8H7N3)(H2O)4]SO4, the central FeII ion is octa­hedrally coordinated by two N atoms from the bidentate 2-(pyridin-2-yl)-1H-imidazole ligand and by four O atoms of the aqua ligands. The largest deviation from the ideal octa­hedral geometry is reflected by the small N—Fe—N bite angle of 76.0 (1)°. The Fe—N coordination bonds have markedly different lengths [2.1361 (17) and 2.243 (2) Å], with the shorter one to the pyrimidine N atom. The four Fe—O coordination bond lengths vary from 2.1191 (18) to 2.1340 (17) Å. In the crystal, the cations and anions are arranged by means of medium-strength O—H⋯O hydrogen bonds into layers parallel to the ab plane. Neighbouring layers further inter­connect by N—H⋯O hydrogen bonds involving the imidazole fragment as donor group to one sulfate O atom as an acceptor. The resulting three-dimensional network is consolidated by C—H⋯O, C—H⋯π and π–π inter­actions. PMID:26029386

Singular Atom Optics with Spinor BECs

NASA Astrophysics Data System (ADS)

Schultz, Justin T.; Hansen, Azure; Bigelow, Nicholas P.

2015-05-01

We create and study singular spin textures in pseudo-spin-1/2 BECs. A series of two-photon Raman interactions allows us to not only engineer the spinor wavefunction but also perform the equivalent of atomic polarimetry on the BEC. Adapting techniques from optical polarimetry, we can image two-dimensional maps of the atomic Stokes parameters, thereby fully reconstructing the atomic wavefunction. In a spin-1/2 system, we can represent the local spin superposition with ellipses in a Cartesian basis. The patterns that emerge from the major axes of the ellipses provide fingerprints of the singularities that enable us to classify them as lemons, stars, saddles, or spirals similar to classification schemes for singularities in singular optics, condensed matter, and liquid crystals. These techniques may facilitate the study of geometric Gouy phases in matter waves as well as provide an avenue for utilizing topological structures as quantum gates.

Molecular dynamics simulation of melting of 2D glassy monatomic system

NASA Astrophysics Data System (ADS)

Nhu Tranh, Duong Thi; Van Hoang, Vo; Thu Hanh, Tran Thi

2018-01-01

The melting of two-dimensional (2D) glassy monatomic systems is studied using the molecular dynamics simulation with Lennard-Jones-Gauss interaction potential. The temperature dependence of various structural and dynamical properties of the systems during heating is analyzed and discussed via the radial distribution functions, the coordination number distributions, the ring statistics, the mobility of atoms and their clustering. Atomic mechanism of melting is also analyzed via tendency to increase mobility and breaking clusters of atoms upon heating. We found that melting of a 2D glass does not follow any theory of the melting of 2D crystals proposed in the past. The melting exhibits a homogeneous nature, i.e. liquid-like atoms occur homogeneously throughout the system and melting proceeds further leading to the formation of an entire liquid phase. In addition, we found a defined transition temperature region in which structural and dynamical properties of systems strongly change with increasing temperature.

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.

Two Keggin-type heteropolytungstates with transition metal as a central atom: Crystal structure and magnetic study with 2D-IR correlation spectroscopy

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

Chai, Feng; Chen, YiPing, E-mail: ypchen007@sina.com; State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002

2013-06-01

Two Keggin-type heteropolytungstates, [Co(phen)₃]₃[CoW₁₂O₄₀]·9H₂O 1 (phen=1,10-phenanthroline) and [Fe(phen)₃]₂[FeW₁₂O₄₀]·H₃O·H₂O 2, have been synthesized via the hydrothermal technique and characterized by single crystal X-ray diffraction analyses, IR, XPS, TG analysis, UV–DRS, XRD, thermal-dependent and magnetic-dependent 2D-COS IR (two-dimensional infrared correlation spectroscopy). Crystal structure analysis reveals that the polyanions in compound 1 are linked into 3D supramolecule through hydrogen bonding interactions between lattice water molecules and terminal oxygen atoms of polyanion units, and [Co(phen)₃]²⁺ cations distributed in the polyanion framework with many hydrogen bonding interactions. The XPS spectra indicate that all the Co atoms in 1 are +2 oxidation state, the Fe atomsmore » in 2 existing with +2 and +3 mixed oxidation states. - Graphical abstract: The magnetic-dependent synchronous 2D correlation IR spectra of 1 (a), 2 (b) over 0–50 mT in the range of 600–1000 cm⁻¹, the obvious response indicate two Keggin polyanions skeleton susceptible to applied magnetic field. Highlights: • Two Keggin-type heteropolytungstates with transition metal as a central atom has been obtained. • Compound 1 forms into 3D supramolecular architecture through hydrogen bonding between water molecules and polyanions. • Magnetic-dependent 2D-IR correlation spectroscopy was introduced to discuss the magnetism of polyoxometalate.« less

Data Mining for New Two- and One-Dimensional Weakly Bonded Solids and Lattice-Commensurate Heterostructures.

PubMed

Cheon, Gowoon; Duerloo, Karel-Alexander N; Sendek, Austin D; Porter, Chase; Chen, Yuan; Reed, Evan J

2017-03-08

Layered materials held together by weak interactions including van der Waals forces, such as graphite, have attracted interest for both technological applications and fundamental physics in their layered form and as an isolated single-layer. Only a few dozen single-layer van der Waals solids have been subject to considerable research focus, although there are likely to be many more that could have superior properties. To identify a broad spectrum of layered materials, we present a novel data mining algorithm that determines the dimensionality of weakly bonded subcomponents based on the atomic positions of bulk, three-dimensional crystal structures. By applying this algorithm to the Materials Project database of over 50,000 inorganic crystals, we identify 1173 two-dimensional layered materials and 487 materials that consist of weakly bonded one-dimensional molecular chains. This is an order of magnitude increase in the number of identified materials with most materials not known as two- or one-dimensional materials. Moreover, we discover 98 weakly bonded heterostructures of two-dimensional and one-dimensional subcomponents that are found within bulk materials, opening new possibilities for much-studied assembly of van der Waals heterostructures. Chemical families of materials, band gaps, and point groups for the materials identified in this work are presented. Point group and piezoelectricity in layered materials are also evaluated in single-layer forms. Three hundred and twenty-five of these materials are expected to have piezoelectric monolayers with a variety of forms of the piezoelectric tensor. This work significantly extends the scope of potential low-dimensional weakly bonded solids to be investigated.

Synthesis, crystal structure, and magnetic properties of two-dimensional divalent metal glutarate/dipyridylamine coordination polymers, with a single crystal-to-single crystal transformation in the copper derivative

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

Montney, Matthew R.; Supkowski, Ronald M.; Staples, Richard J.

Hydrothermal reaction of divalent metal chlorides with glutaric acid and 4,4'-dipyridylamine (dpa) has afforded an isostructural family of coordination polymers with formulation [M(glu)(dpa)]{sub n} (M=Co (1), Ni (2), Cu (3); glu=glutarate). Square pyramidal coordination is seen in 1-3, with semi-ligation of a sixth donor to produce a '5+1' extended coordination sphere. Neighboring metal atoms are linked into 1D [M(glu)]{sub n} neutral chains through chelating/monodentate bridging glutarate moieties with a syn-anti binding mode, and semi-chelation of the pendant carboxylate oxygen. These chains further connect into 2D layers through dipodal dpa ligands. Neighboring layers stack into the pseudo 3D crystal structure ofmore » 1-3 through supramolecular hydrogen bonding between dpa amine units and the semi-chelated glutarate oxygen atoms. The variable temperature magnetic behavior of 1-3 was explored and modeled as infinite 1D Heisenberg chains. Notably, complex 3 undergoes a thermally induced single crystal-to-single crystal transformation between centric and acentric space groups, with a conformationally disordered unilayer structure at 293 K and an ordered bilayer structure at 173 K. All materials were further characterized via infrared spectroscopy and elemental and thermogravimetric analyses. - Graphical abstract: The coordination polymers [M(glu)(dpa)]{sub n} (M=Co (1), Ni (2), Cu (3); glu=glutarate, dpa=4,4'-dipyridylamine) exhibit 2D layer structures based on 1D [M(glu)]{sub n} chains linked through dpa tethers. Antiferromagnetic coupling is observed for 2 and 3, while ferromagnetism is predominant in 1. Compound 3 undergoes a thermally induced single crystal-to-single crystal transformation from an acentric to a centrosymmetric space group.« less

CRITIC2: A program for real-space analysis of quantum chemical interactions in solids

NASA Astrophysics Data System (ADS)

Otero-de-la-Roza, A.; Johnson, Erin R.; Luaña, Víctor

2014-03-01

We present CRITIC2, a program for the analysis of quantum-mechanical atomic and molecular interactions in periodic solids. This code, a greatly improved version of the previous CRITIC program (Otero-de-la Roza et al., 2009), can: (i) find critical points of the electron density and related scalar fields such as the electron localization function (ELF), Laplacian, … (ii) integrate atomic properties in the framework of Bader’s Atoms-in-Molecules theory (QTAIM), (iii) visualize non-covalent interactions in crystals using the non-covalent interactions (NCI) index, (iv) generate relevant graphical representations including lines, planes, gradient paths, contour plots, atomic basins, … and (v) perform transformations between file formats describing scalar fields and crystal structures. CRITIC2 can interface with the output produced by a variety of electronic structure programs including WIEN2k, elk, PI, abinit, Quantum ESPRESSO, VASP, Gaussian, and, in general, any other code capable of writing the scalar field under study to a three-dimensional grid. CRITIC2 is parallelized, completely documented (including illustrative test cases) and publicly available under the GNU General Public License. Catalogue identifier: AECB_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECB_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: yes No. of lines in distributed program, including test data, etc.: 11686949 No. of bytes in distributed program, including test data, etc.: 337020731 Distribution format: tar.gz Programming language: Fortran 77 and 90. Computer: Workstations. Operating system: Unix, GNU/Linux. Has the code been vectorized or parallelized?: Shared-memory parallelization can be used for most tasks. Classification: 7.3. Catalogue identifier of previous version: AECB_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 157 Nature of problem: Analysis of quantum-chemical interactions in periodic solids by means of atoms-in-molecules and related formalisms. Solution method: Critical point search using Newton’s algorithm, atomic basin integration using bisection, qtree and grid-based algorithms, diverse graphical representations and computation of the non-covalent interactions index on a three-dimensional grid. Additional comments: !!!!! The distribution file for this program is over 330 Mbytes and therefore is not delivered directly when download or Email is requested. Instead a html file giving details of how the program can be obtained is sent. !!!!! Running time: Variable, depending on the crystal and the source of the underlying scalar field.

Edge-Controlled Growth and Etching of Two-Dimensional GaSe Monolayers

DOE PAGES

Li, Xufan; Dong, Jichen; Idrobo, Juan C.; ...

2016-12-07

Understanding the atomistic mechanisms governing the growth of two-dimensional (2D) materials is of great importance in guiding the synthesis of wafer-sized, single-crystalline, high-quality 2D crystals and heterostructures. Etching, in many cases regarded as the reverse process of material growth, has been used to study the growth kinetics of graphene. In this paper, we explore a growth–etching–regrowth process of monolayer GaSe crystals, including single-crystalline triangles and irregularly shaped domains formed by merged triangles. We show that the etching begins at a slow rate, creating triangular, truncated triangular, or hexagonally shaped holes that eventually evolve to exclusively triangles that are rotated 60°more » with respect to the crystalline orientation of the monolayer triangular crystals. The regrowth occurs much faster than etching, reversibly filling the etched holes and then enlarging the size of the monolayer crystals. A theoretical model developed based on kinetic Wulff construction (KWC) theory and density functional theory (DFT) calculations accurately describe the observed morphology evolution of the monolayer GaSe crystals and etched holes during the growth and etching processes, showing that they are governed by the probability of atom attachment/detachment to/from different types of edges with different formation energies of nucleus/dents mediated by chemical potential difference Δμ between Ga and Se. Finally, our growth–etching–regrowth study provides not only guidance to understand the growth mechanisms of 2D binary crystals but also a potential method for the synthesis of large, shape-controllable, high-quality single-crystalline 2D crystals and their lateral heterostructures.« less

From atoms to steps: The microscopic origins of crystal evolution

NASA Astrophysics Data System (ADS)

Patrone, Paul N.; Einstein, T. L.; Margetis, Dionisios

2014-07-01

The Burton-Cabrera-Frank (BCF) theory of crystal growth has been successful in describing a wide range of phenomena in surface physics. Typical crystal surfaces are slightly misoriented with respect to a facet plane; thus, the BCF theory views such systems as composed of staircase-like structures of steps separating terraces. Adsorbed atoms (adatoms), which are represented by a continuous density, diffuse on terraces, and steps move by absorbing or emitting these adatoms. Here we shed light on the microscopic origins of the BCF theory by deriving a simple, one-dimensional (1D) version of the theory from an atomistic, kinetic restricted solid-on-solid (KRSOS) model without external material deposition. We define the time-dependent adatom density and step position as appropriate ensemble averages in the KRSOS model, thereby exposing the non-equilibrium statistical mechanics origins of the BCF theory. Our analysis reveals that the BCF theory is valid in a low adatom-density regime, much in the same way that an ideal gas approximation applies to dilute gasses. We find conditions under which the surface remains in a low-density regime and discuss the microscopic origin of corrections to the BCF model.

Crystal structure of bis-(benzyl-amine-κN)[5,10,15,20-tetra-kis-(4-chloro-phen-yl)porphyrinato-κ(4) N]iron(II) n-hexane monosolvate.

PubMed

Dhifaoui, Selma; Harhouri, Wafa; Bujacz, Anna; Nasri, Habib

2016-01-01

In the title compound, [Fe(II)(C44H24Cl4N4)(C6H5CH2NH2)2]·C6H14 or [Fe(II)(TPP-Cl)(BzNH2)2]·n-hexane [where TPP-Cl and BzNH2 are 5,10,15,20-tetra-kis-(4-chloro-phen-yl)porphyrinate and benzyl-amine ligands, respectively], the Fe(II) cation lies on an inversion centre and is octa-hedrally coordinated by the four pyrrole N atoms of the porphyrin ligand in the equatorial plane and by two amine N atoms of the benzyl-amine ligand in the axial sites. The crystal structure also contains one inversion-symmetric n-hexane solvent mol-ecule per complex mol-ecule. The average Fe-Npyrrole bond length [1.994 (3) Å] indicates a low-spin complex. The crystal packing is sustained by N-H⋯Cl and C-H⋯Cl hydrogen-bonding inter-actions and by C-H⋯π inter-molecular inter-actions, leading to a three-dimensional network structure.

First Principles Predictions of the Structure and Function of G-Protein-Coupled Receptors: Validation for Bovine Rhodopsin

PubMed Central

Trabanino, Rene J.; Hall, Spencer E.; Vaidehi, Nagarajan; Floriano, Wely B.; Kam, Victor W. T.; Goddard, William A.

2004-01-01

G-protein-coupled receptors (GPCRs) are involved in cell communication processes and with mediating such senses as vision, smell, taste, and pain. They constitute a prominent superfamily of drug targets, but an atomic-level structure is available for only one GPCR, bovine rhodopsin, making it difficult to use structure-based methods to design receptor-specific drugs. We have developed the MembStruk first principles computational method for predicting the three-dimensional structure of GPCRs. In this article we validate the MembStruk procedure by comparing its predictions with the high-resolution crystal structure of bovine rhodopsin. The crystal structure of bovine rhodopsin has the second extracellular (EC-II) loop closed over the transmembrane regions by making a disulfide linkage between Cys-110 and Cys-187, but we speculate that opening this loop may play a role in the activation process of the receptor through the cysteine linkage with helix 3. Consequently we predicted two structures for bovine rhodopsin from the primary sequence (with no input from the crystal structure)—one with the EC-II loop closed as in the crystal structure, and the other with the EC-II loop open. The MembStruk-predicted structure of bovine rhodopsin with the closed EC-II loop deviates from the crystal by 2.84 Å coordinate root mean-square (CRMS) in the transmembrane region main-chain atoms. The predicted three-dimensional structures for other GPCRs can be validated only by predicting binding sites and energies for various ligands. For such predictions we developed the HierDock first principles computational method. We validate HierDock by predicting the binding site of 11-cis-retinal in the crystal structure of bovine rhodopsin. Scanning the whole protein without using any prior knowledge of the binding site, we find that the best scoring conformation in rhodopsin is 1.1 Å CRMS from the crystal structure for the ligand atoms. This predicted conformation has the carbonyl O only 2.82 Å from the N of Lys-296. Making this Schiff base bond and minimizing leads to a final conformation only 0.62 Å CRMS from the crystal structure. We also used HierDock to predict the binding site of 11-cis-retinal in the MembStruk-predicted structure of bovine rhodopsin (closed loop). Scanning the whole protein structure leads to a structure in which the carbonyl O is only 2.85 Å from the N of Lys-296. Making this Schiff base bond and minimizing leads to a final conformation only 2.92 Å CRMS from the crystal structure. The good agreement of the ab initio-predicted protein structures and ligand binding site with experiment validates the use of the MembStruk and HierDock first principles' methods. Since these methods are generic and applicable to any GPCR, they should be useful in predicting the structures of other GPCRs and the binding site of ligands to these proteins. PMID:15041637

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.

Crystal structure of bis­(μ-N-hy­droxy­picolin­amid­ato)bis­[bis­(N-hy­droxy­picolinamide)­sodium

PubMed Central

Safyanova, Inna S.; Ohui, Kateryna A.; Omelchenko, Irina V.

2017-01-01

The title compound, [Na2(C6H5N2O2)2(C6H6N2O2)4], is a centrosymmetric coordination dimer based on the sodium(I) salt of N-hy­droxy­picolinamide. The mol­ecule has an {Na2O6(μ-O)2} core with two bridging carbonyl O atoms and two hydroxamate O atoms of two mono-deprotonated residues of N-hy­droxy­picolinamide, while two neutral N-hy­droxy­picolinamide mol­ecules are coordinated in a monodentate manner to each sodium ion via the carbonyl O atoms [the Na—O distances range from 2.3044 (2) to 2.3716 (2) Å]. The penta­coordinated sodium ion exhibits a distorted trigonal–pyramidal coordination polyhedron. In the crystal, the coordination dimers are linked into chains along the c axis via N—H⋯O and N—H⋯N hydrogen bonds; the chains are linked into a two-dimensional framework parallel to (100) via weak C—H⋯O and π–π stacking inter­actions. PMID:28083127

Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound S r 14 C u 24 O 41

DOE PAGES

Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; ...

2016-10-21

Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr 14Cu 24O 41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7–1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements alsomore » reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr 14Cu 24O 41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. Furthermore, these findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.« less

Charge transport through one-dimensional Moiré crystals

PubMed Central

Bonnet, Roméo; Lherbier, Aurélien; Barraud, Clément; Rocca, Maria Luisa Della; Lafarge, Philippe; Charlier, Jean-Christophe

2016-01-01

Moiré superlattices were generated in two-dimensional (2D) van der Waals heterostructures and have revealed intriguing electronic structures. The appearance of mini-Dirac cones within the conduction and valence bands of graphene is one of the most striking among the new quantum features. A Moiré superstructure emerges when at least two periodic sub-structures superimpose. 2D Moiré patterns have been particularly investigated in stacked hexagonal 2D atomic lattices like twisted graphene layers and graphene deposited on hexagonal boron-nitride. In this letter, we report both experimentally and theoretically evidence of superlattices physics in transport properties of one-dimensional (1D) Moiré crystals. Rolling-up few layers of graphene to form a multiwall carbon nanotube adds boundaries conditions that can be translated into interference fringes-like Moiré patterns along the circumference of the cylinder. Such a 1D Moiré crystal exhibits a complex 1D multiple bands structure with clear and robust interband quantum transitions due to the presence of mini-Dirac points and pseudo-gaps. Our devices consist in a very large diameter (>80 nm) multiwall carbon nanotubes of high quality, electrically connected by metallic electrodes acting as charge reservoirs. Conductance measurements reveal the presence of van Hove singularities assigned to 1D Moiré superlattice effect and illustrated by electronic structure calculations. PMID:26786067

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.

Crystal structures of two mixed-valence copper cyanide complexes with N-methyl­ethylenedi­amine

PubMed Central

Sabatino, Alexander

2017-01-01

The crystal structures of two mixed-valence copper cyanide compounds involving N-methyl­ethylenedi­amine (meen), are described. In compound (I), poly[bis(μ3-cyanido-κ3 C:C:N)tris(μ2-cyanido-κ2 C:N)bis(N-methylethane-1,2-di­amine-κ2 N,N′)tricopper(I)copper(II)], [Cu4(CN)5(C3H10N2)2] or Cu4(CN)5meen2, cyanide groups link CuI atoms into a three-dimensional network containing open channels parallel to the b axis. In the network, two tetra­hedrally bound CuI atoms are bonded by the C atoms of two end-on bridging CN groups to form Cu2(CN)6 moieties with the Cu atoms in close contact at 2.560 (1) Å. Other trigonally bound CuI atoms link these units together to form the network. The CuII atoms, coordinated by two meen units, are covalently linked to the network via a cyanide bridge, and project into the open network channels. In the mol­ecular compound (II), [(N-methylethylenediamine-κ2 N,N′)copper(II)]-μ2-cyanido-κ2 C:N-[bis(cyanido-κC)copper(I)] monohydrate, [Cu2(CN)3(C3H10N2)2]·H2O or Cu2(CN)3meen2·H2O, a CN group connects a CuII atom coordinated by two meen groups with a trigonal–planar CuI atom coordinated by CN groups. The mol­ecules are linked into centrosymmetric dimers via hydrogen bonds to two water mol­ecules. In both compounds, the bridging cyanide between the CuII and CuI atoms has the N atom bonded to CuII and the C atom bonded to CuI, and the CuII atoms are in a square-pyramidal coordination. PMID:28217329

Syntheses and crystal structures of two new hydrated borates, Zn{sub 8}[(BO{sub 3}){sub 3}O{sub 2}(OH){sub 3}] and Pb[B{sub 5}O{sub 8}(OH)].1.5H{sub 2}O

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

Chen Xuean; Zhao Yinghua; Chang Xinan

Two new hydrated borates, Zn{sub 8}[(BO{sub 3}){sub 3}O{sub 2}(OH){sub 3}] and Pb[B{sub 5}O{sub 8}(OH)].1.5H{sub 2}O, have been prepared by hydrothermal reactions at 170 {sup o}C. Single-crystal X-ray structural analyses showed that Zn{sub 8}[(BO{sub 3}){sub 3}O{sub 2}(OH){sub 3}] crystallizes in a non-centrosymmetric space group R32 with a=8.006(2) A, c=17.751(2) A, Z=3 and Pb[B{sub 5}O{sub 8}(OH)].1.5H{sub 2}O in a triclinic space group P1-bar with a=6.656(2) A, b=6.714(2) A, c=10.701(2) A, {alpha}=99.07(2){sup o}, {beta}=93.67(2){sup o}, {gamma}=118.87(1){sup o}, Z=2. Zn{sub 8}[(BO{sub 3}){sub 3}O{sub 2}(OH){sub 3}] represents a new structure type in which Zn-centered tetrahedra are connected via common vertices leading to helical ribbons {submore » {infinity}} {sup 1}[Zn{sub 8}O{sub 15}(OH){sub 3}]{sup 17-} that pack side by side and are further condensed through sharing oxygen atoms to form a three-dimensional {sub {infinity}} {sup 3}[Zn{sub 8}O{sub 11}(OH){sub 3}]{sup 9-} framework. The boron atoms are incorporated into the channels in the framework to complete the final structure. Pb[B{sub 5}O{sub 8}(OH)].1.5H{sub 2}O is a layered compound containing double ring [B{sub 5}O{sub 8}(OH)]{sup 2-} building units that share exocyclic oxygen atoms to form a two-dimensional layer. Symmetry-center-related layers are stacked along the c-axis and held together by interlayer Pb{sup 2+} ions and water molecules via electrostatic and hydrogen bonding interactions. The IR spectra further confirmed the existence of both triangular BO{sub 3} and OH groups in Zn{sub 8}[(BO{sub 3}){sub 3}O{sub 2}(OH){sub 3}], and BO{sub 3}, BO{sub 4}, OH groups as well as guest water molecules in Pb[B{sub 5}O{sub 8}(OH)].1.5H{sub 2}O. -- Zn{sub 8}[(BO{sub 3}){sub 3}O{sub 2}(OH){sub 3}] represents a new structure type in which Zn-centered tetrahedra are connected via common vertices to form a three-dimensional framework. The boron atoms are incorporated into the channels in the framework to strengen the structure via B-O bonds. Pb[B{sub 5}O{sub 8}(OH)].1.5H{sub 2}O is a new layered material containing double ring [B{sub 5}O{sub 8}(OH)]{sup 2-} building units that share exocyclic oxygen atoms to form a two-dimensional layer.« less

Recent progress in boron nanomaterials

PubMed Central

Kondo, Takahiro

2017-01-01

Abstract Various types of zero, one, and two-dimensional boron nanomaterials such as nanoclusters, nanowires, nanotubes, nanobelts, nanoribbons, nanosheets, and monolayer crystalline sheets named borophene have been experimentally synthesized and identified in the last 20 years. Owing to their low dimensionality, boron nanomaterials have different bonding configurations from those of three-dimensional bulk boron crystals composed of icosahedra or icosahedral fragments. The resulting intriguing physical and chemical properties of boron nanomaterials are fascinating from the viewpoint of material science. Moreover, the wide variety of boron nanomaterials themselves could be the building blocks for combining with other existing nanomaterials, molecules, atoms, and/or ions to design and create materials with new functionalities and properties. Here, the progress of the boron nanomaterials is reviewed and perspectives and future directions are described. PMID:29152014

Crystal structure of 1,2,3,4-di-O-methyl­ene-α-d-galacto­pyran­ose

PubMed Central

Tiritiris, Ioannis; Tussetschläger, Stefan; Kantlehner, Willi

2015-01-01

The title compound, C8H12O6, was synthesized by de­acetyl­ation of 6-acetyl-1,2,3,4-di-O-methyl­ene-α-d-galactose with sodium methoxide. The central part of the mol­ecule consists of a six-membered C5O pyran­ose ring with a twist-boat conformation. Both fused dioxolane rings adopt an envelope conformation with C and O atoms as the flap. In the crystal, O—H⋯O and C—H⋯O hydrogen bonds are present between adjacent mol­ecules, generating a three-dimensional network. PMID:26870551

Crystal structure of 2-benzoyl­amino-N′-(4-hy­droxy­benzyl­idene)-3-(thio­phen-2-yl)prop-2-eno­hydrazide

PubMed Central

Subbulakshmi, Karanth N.; Narayana, Badiadka; Yathirajan, Hemmige S.; Jasinski, Jerry P.; Rathore, Ravindranath S.; Glidewell, Christopher

2016-01-01

In the title compound, C21H17N3O3S, the non-H atoms, apart from those in the benzoyl group, are almost coplanar (r.m.s. deviation = 0.049 Å) and the benzoyl group is almost orthogonal to the plane of the rest of the mol­ecule [dihedral angle = 80.34 (6)°]. In the crystal, a combination of N—H⋯O and asymmetric bifurcated O—H⋯(N,O) hydrogen bonds link the mol­ecules into a three-dimensional network. Weak C—H⋯O inter­actions are also observed. PMID:27536390

Crystal structure of langbeinite-related Rb0.743K0.845Co0.293Ti1.707(PO4)3

PubMed Central

Strutynska, Nataliia Yu.; Bondarenko, Marina A.; Ogorodnyk, Ivan V.; Baumer, Vyacheslav N.; Slobodyanik, Nikolay S.

2015-01-01

Potassium rubidium cobalt(II)/titanium(IV) tris­(orthophosphate), Rb0.743K0.845Co0.293Ti1.707(PO4)3, has been obtained using a high-temperature crystallization method. The obtained compound has a langbeinite-type structure. The three-dimensional framework is built up from mixed-occupied (Co/TiIV)O6 octa­hedra (point group symmetry .3.) and PO4 tetra­hedra. The K+ and Rb+ cations are statistically distributed over two distinct sites (both with site symmetry .3.) in the large cavities of the framework. They are surrounded by 12 O atoms. PMID:25844179

Incoherent Diffractive Imaging via Intensity Correlations of Hard X Rays

NASA Astrophysics Data System (ADS)

Classen, Anton; Ayyer, Kartik; Chapman, Henry N.; Röhlsberger, Ralf; von Zanthier, Joachim

2017-08-01

Established x-ray diffraction methods allow for high-resolution structure determination of crystals, crystallized protein structures, or even single molecules. While these techniques rely on coherent scattering, incoherent processes like fluorescence emission—often the predominant scattering mechanism—are generally considered detrimental for imaging applications. Here, we show that intensity correlations of incoherently scattered x-ray radiation can be used to image the full 3D arrangement of the scattering atoms with significantly higher resolution compared to conventional coherent diffraction imaging and crystallography, including additional three-dimensional information in Fourier space for a single sample orientation. We present a number of properties of incoherent diffractive imaging that are conceptually superior to those of coherent methods.

Extraordinary wavelength reduction in terahertz graphene-cladded photonic crystal slabs

PubMed Central

Williamson, Ian A. D.; Mousavi, S. Hossein; Wang, Zheng

2016-01-01

Photonic crystal slabs have been widely used in nanophotonics for light confinement, dispersion engineering, nonlinearity enhancement, and other unusual effects arising from their structural periodicity. Sub-micron device sizes and mode volumes are routine for silicon-based photonic crystal slabs, however spectrally they are limited to operate in the near infrared. Here, we show that two single-layer graphene sheets allow silicon photonic crystal slabs with submicron periodicity to operate in the terahertz regime, with an extreme 100× wavelength reduction from graphene’s large kinetic inductance. The atomically thin graphene further leads to excellent out-of-plane confinement, and consequently photonic-crystal-slab band structures that closely resemble those of ideal two-dimensional photonic crystals, with broad band gaps even when the slab thickness approaches zero. The overall photonic band structure not only scales with the graphene Fermi level, but more importantly scales to lower frequencies with reduced slab thickness. Just like ideal 2D photonic crystals, graphene-cladded photonic crystal slabs confine light along line defects, forming waveguides with the propagation lengths on the order of tens of lattice constants. The proposed structure opens up the possibility to dramatically reduce the size of terahertz photonic systems by orders of magnitude. PMID:27143314

Life in the fast lane for protein crystallization and X-ray crystallography

NASA Technical Reports Server (NTRS)

Pusey, Marc L.; Liu, Zhi-Jie; Tempel, Wolfram; Praissman, Jeremy; Lin, Dawei; Wang, Bi-Cheng; Gavira, Jose A.; Ng, Joseph D.

2005-01-01

The common goal for structural genomic centers and consortiums is to decipher as quickly as possible the three-dimensional structures for a multitude of recombinant proteins derived from known genomic sequences. Since X-ray crystallography is the foremost method to acquire atomic resolution for macromolecules, the limiting step is obtaining protein crystals that can be useful of structure determination. High-throughput methods have been developed in recent years to clone, express, purify, crystallize and determine the three-dimensional structure of a protein gene product rapidly using automated devices, commercialized kits and consolidated protocols. However, the average number of protein structures obtained for most structural genomic groups has been very low compared to the total number of proteins purified. As more entire genomic sequences are obtained for different organisms from the three kingdoms of life, only the proteins that can be crystallized and whose structures can be obtained easily are studied. Consequently, an astonishing number of genomic proteins remain unexamined. In the era of high-throughput processes, traditional methods in molecular biology, protein chemistry and crystallization are eclipsed by automation and pipeline practices. The necessity for high-rate production of protein crystals and structures has prevented the usage of more intellectual strategies and creative approaches in experimental executions. Fundamental principles and personal experiences in protein chemistry and crystallization are minimally exploited only to obtain "low-hanging fruit" protein structures. We review the practical aspects of today's high-throughput manipulations and discuss the challenges in fast pace protein crystallization and tools for crystallography. Structural genomic pipelines can be improved with information gained from low-throughput tactics that may help us reach the higher-bearing fruits. Examples of recent developments in this area are reported from the efforts of the Southeast Collaboratory for Structural Genomics (SECSG).

Life in the Fast Lane for Protein Crystallization and X-Ray Crystallography

NASA Technical Reports Server (NTRS)

Pusey, Marc L.; Liu, Zhi-Jie; Tempel, Wolfram; Praissman, Jeremy; Lin, Dawei; Wang, Bi-Cheng; Gavira, Jose A.; Ng, Joseph D.

2004-01-01

The common goal for structural genomic centers and consortiums is to decipher as quickly as possible the three-dimensional structures for a multitude of recombinant proteins derived from known genomic sequences. Since X-ray crystallography is the foremost method to acquire atomic resolution for macromolecules, the limiting step is obtaining protein crystals that can be useful of structure determination. High-throughput methods have been developed in recent years to clone, express, purify, crystallize and determine the three-dimensional structure of a protein gene product rapidly using automated devices, commercialized kits and consolidated protocols. However, the average number of protein structures obtained for most structural genomic groups has been very low compared to the total number of proteins purified. As more entire genomic sequences are obtained for different organisms from the three kingdoms of life, only the proteins that can be crystallized and whose structures can be obtained easily are studied. Consequently, an astonishing number of genomic proteins remain unexamined. In the era of high-throughput processes, traditional methods in molecular biology, protein chemistry and crystallization are eclipsed by automation and pipeline practices. The necessity for high rate production of protein crystals and structures has prevented the usage of more intellectual strategies and creative approaches in experimental executions. Fundamental principles and personal experiences in protein chemistry and crystallization are minimally exploited only to obtain "low-hanging fruit" protein structures. We review the practical aspects of today s high-throughput manipulations and discuss the challenges in fast pace protein crystallization and tools for crystallography. Structural genomic pipelines can be improved with information gained from low-throughput tactics that may help us reach the higher-bearing fruits. Examples of recent developments in this area are reported from the efforts of the Southeast Collaboratory for Structural Genomics (SECSG).

Simulation and understanding of atomic and molecular quantum crystals

NASA Astrophysics Data System (ADS)

Cazorla, Claudio; Boronat, Jordi

2017-07-01

Quantum crystals abound in the whole range of solid-state species. Below a certain threshold temperature the physical behavior of rare gases (He 4 and Ne), molecular solids (H2 and CH4 ), and some ionic (LiH), covalent (graphite), and metallic (Li) crystals can be explained only in terms of quantum nuclear effects (QNE). A detailed comprehension of the nature of quantum solids is critical for achieving progress in a number of fundamental and applied scientific fields such as planetary sciences, hydrogen storage, nuclear energy, quantum computing, and nanoelectronics. This review describes the current physical understanding of quantum crystals formed by atoms and small molecules, as well as the wide palette of simulation techniques that are used to investigate them. Relevant aspects in these materials such as phase transformations, structural properties, elasticity, crystalline defects, and the effects of reduced dimensionality are discussed thoroughly. An introduction to quantum Monte Carlo techniques, which in the present context are the simulation methods of choice, and other quantum simulation approaches (e.g., path-integral molecular dynamics and quantum thermal baths) is provided. The overarching objective of this article is twofold: first, to clarify in which crystals and physical situations the disregard of QNE may incur in important bias and erroneous interpretations. And second, to promote the study and appreciation of QNE, a topic that traditionally has been treated in the context of condensed matter physics, within the broad and interdisciplinary areas of materials science.

Abnormal growth kinetics of h-BN epitaxial monolayer on Ru(0001) enhanced by subsurface Ar species

NASA Astrophysics Data System (ADS)

Wei, Wei; Meng, Jie; Meng, Caixia; Ning, Yanxiao; Li, Qunxiang; Fu, Qiang; Bao, Xinhe

2018-04-01

Growth kinetics of epitaxial films often follows the diffusion-limited aggregation mechanism, which shows a "fractal-to-compact" morphological transition with increasing growth temperature or decreasing deposition flux. Here, we observe an abnormal "compact-to-fractal" morphological transition with increasing growth temperature for hexagonal boron nitride growth on the Ru(0001) surface. The unusual growth process can be explained by a reaction-limited aggregation (RLA) mechanism. Moreover, introduction of the subsurface Ar atoms has enhanced this RLA growth behavior by decreasing both reaction and diffusion barriers. Our work may shed light on the epitaxial growth of two-dimensional atomic crystals and help to control their morphology.

1-Do­decyl­indoline-2,3-dione

PubMed Central

Qachchachi, Fatima-Zahrae; Ouazzani Chahdi, Fouad; Misbahi, Houria; Bodensteiner, Michael; El Ammari, Lahcen

2014-01-01

The structure of the title compound, C20H29NO2, is isotypic to that of its homologue 1-octylindoline-2,3-dione. The indoline ring and the two carbonyl-group O atoms are approximately coplanar, the largest deviation from the mean plane being 0.0760 (10) Å. The mean plane through the fused-ring system is nearly perpendicular to the mean plane passing through the 1-dodecyl chain [dihedral angle = 77.69 (5)°]. All C atoms of the dodecyl group are in an anti­periplanar arrangement. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, forming a three-dimensional network. PMID:24764928

Dependence of Interfacial Excess on the Threshold Value of the Isoconcentration Surface

NASA Technical Reports Server (NTRS)

Yoon, Kevin E.; Noebe, Ronald D.; Hellman, Olof C.; Seidman, David N.

2004-01-01

The proximity histogram (or proxigram for short) is used for analyzing data collected by a three-dimensional atom probe microscope. The interfacial excess of Re (2.41 +/- 0.68 atoms/sq nm) is calculated by employing a proxigram in a completely geometrically independent way for gamma/gamma' interfaces in Rene N6, a third-generation single-crystal Ni-based superalloy. A possible dependence of interfacial excess on the variation of the threshold value of an isoconcentration surface is investigated using the data collected for Rene N6 alloy. It is demonstrated that the dependence of the interfacial excess value on the threshold value of the isoconcentration surface is weak.

Layer-dependent quantum cooperation of electron and hole states in the anomalous semimetal WTe 2

DOE PAGES

Das, Pranab Kumar; Di Sante, D.; Vobornik, I.; ...

2016-02-29

The behaviour of electrons and holes in a crystal lattice is a fundamental quantum phenomenon, accounting for a rich variety of material properties. Boosted by the remarkable electronic and physical properties of two-dimensional materials such as graphene and topological insulators, transition metal dichalcogenides have recently received renewed attention. In this context, the anomalous bulk properties of semimetallic WTe 2 have attracted considerable interest. We report angle- and spin-resolved photoemission spectroscopy of WTe 2 single crystals, through which we disentangle the role of W and Te atoms in the formation of the band structure and identify the interplay of charge, spinmore » and orbital degrees of freedom. Supported by first-principles calculations and high-resolution surface topography, we also reveal the existence of a layer-dependent behaviour. The balance of electron and hole states is found only when considering at least three Te–W–Te layers, showing that the behaviour of WTe 2 is not strictly two dimensional.« less

Dichlorido[N′-(3,5-dichloro-2-hydroxy­benzyl­idene)pyridine-4-carbohydrazide-κN](1,10-phenanthroline-κ2 N,N′)cobalt(II) methanol monosolvate

PubMed Central

Wang, Yuan; Liu, Zheng; Liu, Baoyu

2009-01-01

In the title compound, [CoCl2(C13H9Cl2N3O2)2(C12H8N2)]·CH3OH, the CoII atom is octahedrally coordinated by two N atoms from the pyridyl rings of the tridentate N′-(3,5-dichloro-2-hydroxy­benzyl­idene)pyridine-4-carbohydrazide (H2 L) ligand, two N atoms from the 1,10-phenanthroline ligand and two chloride ions. The acyl­hydrazone groups are not involved into the coordination of the metal ion. In the crystal packing an extended three-dimensional network formed by N—H⋯Cl, N—H⋯O, O—H⋯N, O—H⋯N and O—H⋯Cl hydrogen bonds is observed. PMID:21578623

Energy Trapping, Release, and Transport in Three Dimensional Energetic Solids and Molecular Crystals.

DTIC Science & Technology

1986-06-30

excited state and the correlation primitives. These additions had little effect on the tTi ground-state energy. Also included in this table is an...an additional s and p primitive was placed on the C atom and both optimised-with little effect. These were then removed. Finally, the calculation was...the excited vibrational and rotational states of nitromethane have been studied, little work has been done on its low-lying excited electronic states

Intrinsically low thermal conductivity from a quasi-one-dimensional crystal structure and enhanced electrical conductivity network via Pb doping in SbCrSe 3

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

Yang, Dingfeng; Yao, Wei; Yan, Yanci

The development of new routes for the production of thermoelectric materials with low-cost and high-performance characteristics has been one of the long-term strategies for saving and harvesting thermal energy. We report a new approach for improving thermoelectric properties by employing the intrinsically low thermal conductivity of a quasi-one-dimensional (quasi-1D) crystal structure and optimizing the power factor with aliovalent ion doping. As an example, we demonstrated that SbCrSe 3, in which two parallel chains of CrSe 6 octahedra are linked by antimony atoms, possesses a quasi-1D property that resulted in an ultra-low thermal conductivity of 0.56 W m -1 K -1more » at 900 K. After maximizing the power factor by Pb doping, the peak ZT value of the optimized Pb-doped sample reached 0.46 at 900 K, which is an enhancement of 24 times that of the parent SbCrSe 3 structure. The mechanisms that lead to low thermal conductivity derive from anharmonic phonons with the presence of the lone-pair electrons of Sb atoms and weak bonds between the CrSe 6 double chains. Our results shed new light on the design of new and high-performance thermoelectric materials.« less

Intrinsically low thermal conductivity from a quasi-one-dimensional crystal structure and enhanced electrical conductivity network via Pb doping in SbCrSe 3

DOE PAGES

Yang, Dingfeng; Yao, Wei; Yan, Yanci; ...

2017-06-09

The development of new routes for the production of thermoelectric materials with low-cost and high-performance characteristics has been one of the long-term strategies for saving and harvesting thermal energy. We report a new approach for improving thermoelectric properties by employing the intrinsically low thermal conductivity of a quasi-one-dimensional (quasi-1D) crystal structure and optimizing the power factor with aliovalent ion doping. As an example, we demonstrated that SbCrSe 3, in which two parallel chains of CrSe 6 octahedra are linked by antimony atoms, possesses a quasi-1D property that resulted in an ultra-low thermal conductivity of 0.56 W m -1 K -1more » at 900 K. After maximizing the power factor by Pb doping, the peak ZT value of the optimized Pb-doped sample reached 0.46 at 900 K, which is an enhancement of 24 times that of the parent SbCrSe 3 structure. The mechanisms that lead to low thermal conductivity derive from anharmonic phonons with the presence of the lone-pair electrons of Sb atoms and weak bonds between the CrSe 6 double chains. Our results shed new light on the design of new and high-performance thermoelectric materials.« less

Homology modeling, molecular docking and MD simulation studies to investigate role of cysteine protease from Xanthomonas campestris in degradation of Aβ peptide.

PubMed

Dhanavade, Maruti J; Jalkute, Chidambar B; Barage, Sagar H; Sonawane, Kailas D

2013-12-01

Cysteine protease is known to degrade amyloid beta peptide which is a causative agent of Alzheimer's disease. This cleavage mechanism has not been studied in detail at the atomic level. Hence, a three-dimensional structure of cysteine protease from Xanthomonas campestris was constructed by homology modeling using Geno3D, SWISS-MODEL, and MODELLER 9v7. All the predicted models were analyzed by PROCHECK and PROSA. Three-dimensional model of cysteine protease built by MODELLER 9v7 shows similarity with human cathepsin B crystal structure. This model was then used further for docking and simulation studies. The molecular docking study revealed that Cys17, His87, and Gln88 residues of cysteine protease form an active site pocket similar to human cathepsin B. Then the docked complex was refined by molecular dynamic simulation to confirm its stable behavior over the entire simulation period. The molecular docking and MD simulation studies showed that the sulfhydryl hydrogen atom of Cys17 of cysteine protease interacts with carboxylic oxygen of Lys16 of Aβ peptide indicating the cleavage site. Thus, the cysteine protease model from X. campestris having similarity with human cathepsin B crystal structure may be used as an alternate approach to cleave Aβ peptide a causative agent of Alzheimer's disease. © 2013 Elsevier Ltd. All rights reserved.

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.

Synthesis, crystal structure, and electrical and magnetic properties of BaMo{sub 6}Te{sub 6}: A novel reduced molybdenum telluride containing infinite chains of trans-face shared Mo{sub 6} octahedra

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

Gall, Philippe; Guizouarn, Thierry; Potel, Michel

Powder samples and single crystals of the new ternary compound BaMo{sub 6}Te{sub 6} were obtained by solid state reaction. The structure was determined by single-crystal X-ray diffraction. BaMo{sub 6}Te{sub 6} crystallizes in the hexagonal space group P6{sub 3}/m (No. 176) with unit-cell parameters a=9.3941(2) Å, c=4.5848(1) Å and Z=1. Full-matrix least-squares refinement on F{sup 2} using 452 independent reflections for 17 refinable parameters resulted in R1=0.0208 and wR2=0.0539. The structure consists of one-dimensional infinite chains of trans-face shared Mo{sub 6} octahedra capped by Se atoms. These chains that are running along the c axis are separated from each other bymore » nine-coordinate Ba atoms. Resistivity measurements on a single crystal indicated that the BaMo{sub 6}Te{sub 6} compound is metallic down to 160 K and semiconductor below. Magnetic susceptibility measurements showed that BaMo{sub 6}Te{sub 6} is weakly diamagnetic with no anomaly at the metal–semiconductor transition. - Graphical abstract: We present here the synthesis, the crystal structure, and the electrical and magnetic properties of the new compound BaMo{sub 6}Te{sub 6} containing infinite chains of trans-face shared Mo{sub 6} octahedra. - Highlights: • BaMo{sub 6}Te{sub 6} contains infinite chains of trans-face-sharing Mo{sub 6} octahedra |Mo{sub 6/2}|{sub ∞}{sup 1}. • Synthesis by solid state reaction. • Single-crystal X-ray study. • Continuous metal–nonmetal transition. • Anderson localization.« less

Quantum incommensurate skyrmion crystals and commensurate to in-commensurate transitions in cold atoms and materials with spin-orbit couplings in a Zeeman field

NASA Astrophysics Data System (ADS)

Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming

2017-08-01

In this work, we study strongly interacting spinor atoms in a lattice subject to a two dimensional (2d) anisotropic Rashba type of spin orbital coupling (SOC) and an Zeeman field. We find the interplay between the Zeeman field and the SOC provides a new platform to host rich and novel classes of quantum commensurate and in-commensurate phases, excitations and phase transitions. These commensurate phases include two collinear states at low and high Zeeman field, two co-planar canted states at mirror reflected SOC parameters respectively. Most importantly, there are non-coplanar incommensurate Skyrmion (IC-SkX) crystal phases surrounded by the four commensurate phases. New excitation spectra above all the five phases, especially on the IC-SKX phase are computed. Three different classes of quantum commensurate to in-commensurate transitions from the IC-SKX to its four neighboring commensurate phases are identified. Finite temperature behaviors and transitions are discussed. The critical temperatures of all the phases can be raised above that reachable by current cold atom cooling techniques simply by tuning the number of atoms N per site. In view of recent impressive experimental advances in generating 2d SOC for cold atoms in optical lattices, these new many-body phenomena can be explored in the current and near future cold atom experiments. Applications to various materials such as MnSi, {Fe}}0.5 {Co}}0.5Si, especially the complex incommensurate magnetic ordering in Li2IrO3 are given.

Effect of local structures on crystallization in deeply undercooled metallic glass-forming liquids

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

Jiang, S. Q.; Li, M. Z., E-mail: maozhili@ruc.edu.cn; Wu, Z. W.

2016-04-21

The crystallization mechanism in deeply undercooled ZrCu metallic glass-forming liquids was investigated via molecular dynamics simulations. It was found that the crystallization process is mainly controlled by the growth of crystal nuclei formed by the BCC-like atomic clusters, consistent with experimental speculations. The crystallization rate is found to relate to the number of growing crystal nuclei in the crystallization process. The crystallization rate in systems with more crystal nuclei is significantly hindered by the larger surface fractions of crystal nuclei and their different crystalline orientations. It is further revealed that in the crystallization in deeply undercooled regions, the BCC-like crystalmore » nuclei are formed from the inside of the precursors formed by the FCC-like atomic clusters, and growing at the expense of the precursors. Meanwhile, the precursors are expanding at the expense of the outside atomic clusters. This process is consistent with the so-called Ostwald step rule. The atomic structures of metallic glasses are found to have significant impact on the subsequent crystallization process. In the Zr{sub 85}Cu{sub 15} system, the stronger spatial correlation of Cu atoms could hinder the crystallization processes in deeply undercooled regions.« less

Visualization and manipulation of magnetic domains in the quasi-two-dimensional material F e3GeT e2

NASA Astrophysics Data System (ADS)

Nguyen, Giang D.; Lee, Jinhwan; Berlijn, Tom; Zou, Qiang; Hus, Saban M.; Park, Jewook; Gai, Zheng; Lee, Changgu; Li, An-Ping

2018-01-01

The magnetic domains in two-dimensional layered material F e3GeT e2 are studied by using a variable-temperature scanning tunneling microscope with a magnetic tip after in situ cleaving of single crystals. A stripy domain structure is revealed in a zero-field-cooled sample below the ferromagnetic transition temperature of 205 K, which is replaced by separate double-walled domains and bubble domains when cooling the sample under a magnetic field of a ferromagnetic Ni tip. The Ni tip can further convert the double-walled domain to a bubble domain pattern as well as move the Neel-type chiral bubble in submicrometer distance. The temperature-dependent evolutions of both zero-field-cooled and field-cooled domain structures correlate well with the bulk magnetization from magnetometry measurements. Atomic resolution scanning tunneling images and spectroscopy are acquired to understand the atomic and electronic structures of the material, which are further corroborated by first-principles calculations.

Three-Dimensional Mapping of Microenvironmental Control of Methyl Rotational Barriers

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

Hembree, William I; Baudry, Jerome Y

2011-01-01

Sterical (van der Waals-induced) rotational barriers of methyl groups are investigated theoretically, using ab initio and empirical force field calculations, for various three-dimensional microenvironmental conditions around the methyl group rotator of a model neopentane molecule. The destabilization (reducing methyl rotational barriers) or stabilization (increasing methyl rotational barriers) of the staggered conformation of the methyl rotator depends on a combination of microenvironmental contributions from (i) the number of atoms around the rotator, (ii) the distance between the rotator and the microenvironmental atoms, and (iii) the dihedral angle between the stator, rotator, and molecular environment around the rotator. These geometrical criteria combinemore » their respective effects in a linearly additive fashion, with no apparent cooperative effects, and their combination in space around a rotator may increase, decrease, or leave the rotator s rotational barrier unmodified. This is exemplified in a geometrical analysis of the alanine dipeptide crystal where microenvironmental effects on methyl rotators barrier of rotation fit the geometrical mapping described in the neopentane model.« less

First-principles simulations of Graphene/Transition-metal-Dichalcogenides/Graphene Field-Effect Transistor

NASA Astrophysics Data System (ADS)

Li, Xiangguo; Wang, Yun-Peng; Zhang, X.-G.; Cheng, Hai-Ping

A prototype field-effect transistor (FET) with fascinating properties can be made by assembling graphene and two-dimensional insulating crystals into three-dimensional stacks with atomic layer precision. Transition metal dichalcogenides (TMDCs) such as WS2, MoS2 are good candidates for the atomically thin barrier between two layers of graphene in the vertical FET due to their sizable bandgaps. We investigate the electronic properties of the Graphene/TMDCs/Graphene sandwich structure using first-principles method. We find that the effective tunnel barrier height of the TMDC layers in contact with the graphene electrodes has a layer dependence and can be modulated by a gate voltage. Consequently a very high ON/OFF ratio can be achieved with appropriate number of TMDC layers and a suitable range of the gate voltage. The spin-orbit coupling in TMDC layers is also layer dependent but unaffected by the gate voltage. These properties can be important in future nanoelectronic device designs. DOE/BES-DE-FG02-02ER45995; NERSC.

Berezinskii-Kosterlitz-Thouless crossover in a trapped atomic gas.

PubMed

Hadzibabic, Zoran; Krüger, Peter; Cheneau, Marc; Battelier, Baptiste; Dalibard, Jean

2006-06-29

Any state of matter is classified according to its order, and the type of order that a physical system can possess is profoundly affected by its dimensionality. Conventional long-range order, as in a ferromagnet or a crystal, is common in three-dimensional systems at low temperature. However, in two-dimensional systems with a continuous symmetry, true long-range order is destroyed by thermal fluctuations at any finite temperature. Consequently, for the case of identical bosons, a uniform two-dimensional fluid cannot undergo Bose-Einstein condensation, in contrast to the three-dimensional case. However, the two-dimensional system can form a 'quasi-condensate' and become superfluid below a finite critical temperature. The Berezinskii-Kosterlitz-Thouless (BKT) theory associates this phase transition with the emergence of a topological order, resulting from the pairing of vortices with opposite circulation. Above the critical temperature, proliferation of unbound vortices is expected. Here we report the observation of a BKT-type crossover in a trapped quantum degenerate gas of rubidium atoms. Using a matter wave heterodyning technique, we observe both the long-wavelength fluctuations of the quasi-condensate phase and the free vortices. At low temperatures, the gas is quasi-coherent on the length scale set by the system size. As the temperature is increased, the loss of long-range coherence coincides with the onset of proliferation of free vortices. Our results provide direct experimental evidence for the microscopic mechanism underlying the BKT theory, and raise new questions regarding coherence and superfluidity in mesoscopic systems.

Di­aqua­[5,10,15,20-tetra­kis­(4-chloro­phen­yl)porphyrinato-κ4 N]iron(III) tri­fluoro­methane­sulfonate–4-hy­droxy-3-meth­oxy­benzaldehyde–water (1/1/2)

PubMed Central

Ben Haj Hassen, Leila; Ezzayani, Khaireddine; Rousselin, Yoann; Nasri, Habib

2014-01-01

In the title compound, [Fe(C44H24Cl4N4)(H2O)2](SO3CF3)·C8H8O3·2H2O, the FeIII cation is chelated by the four N atoms of the deprotonated tetra­kis­(4-chloro­tetra­phen­yl)porphyrin (TClPP) and further coordinated by two water mol­ecules in a distorted octa­hedral geometry. In the crystal, the cations, anions, 4-hy­droxy-3-meth­oxy­benzaldehyde and water mol­ecules of crystallization are linked by classical O—H⋯O hydrogen bonds and weak C—H⋯O and C—H⋯Cl hydrogen bonds into a three-dimensional supra­molecular architecture. The crystal packing is further stabilized by weak C—H⋯π inter­actions involving pyrrole and benzene rings. π–π stacking between parallel benzene rings of adjacent 4-hy­droxy-3-meth­oxy­benzaldehyde mol­ecules is also observed, the centroid–centroid distance being 3.8003 (13) Å. The three F atoms of the anion are disordered over two sets of sites, with a refined occupancy ratio 0.527 (12):0.473 (12). The O atom of one water mol­ecule of crystallization is also disordered over two positions in an occupancy ratio of 0.68 (5):0.32 (5). PMID:25249880

Miscut dependent surface evolution in the process of N-polar GaN(000 1 bar) growth under N-rich condition

NASA Astrophysics Data System (ADS)

Krzyżewski, Filip; Załuska-Kotur, Magdalena A.; Turski, Henryk; Sawicka, Marta; Skierbiszewski, Czesław

2017-01-01

The evolution of surface morphology during the growth of N-polar (000 1 bar) GaN under N-rich conditions is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2° and 4°. The results are compared with experimentally observed surface morphologies of (000 1 bar) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(000 1 bar) surface where both types of atoms, nitrogen and gallium, attach to the surface and diffuse independently shows that at relatively high rates of the step flow (miscut angle < 2 °) the low mobility of gallium adatoms causes surface instabilities and leads to experimentally observed roughening while for low rates of the step flow (miscut 4°), smooth surface can be obtained. In the presence of almost immobile nitrogen atoms under N-rich conditions crystal growth is realized by the process of two-dimensional island nucleation and coalescence. Larger crystal miscut, lower growth rate or higher temperature results in similar effect of the surface smoothening. We show that the surface also smoothens for the growth conditions with very high N-excess. In the presence of large number of nitrogen atoms the mobility of gallium atoms changes locally thus providing easier coalescence of separated island.

Pauli structures arising from confined particles interacting via a statistical potential

NASA Astrophysics Data System (ADS)

Batle, Josep; Ciftja, Orion; Farouk, Ahmed; Alkhambashi, Majid; Abdalla, Soliman

2017-09-01

There have been suggestions that the Pauli exclusion principle alone can lead a non-interacting (free) system of identical fermions to form crystalline structures dubbed Pauli crystals. Single-shot imaging experiments for the case of ultra-cold systems of free spin-polarized fermionic atoms in a two-dimensional harmonic trap appear to show geometric arrangements that cannot be characterized as Wigner crystals. This work explores this idea and considers a well-known approach that enables one to treat a quantum system of free fermions as a system of classical particles interacting with a statistical interaction potential. The model under consideration, though classical in nature, incorporates the quantum statistics by endowing the classical particles with an effective interaction potential. The reasonable expectation is that possible Pauli crystal features seen in experiments may manifest in this model that captures the correct quantum statistics as a first order correction. We use the Monte Carlo simulated annealing method to obtain the most stable configurations of finite two-dimensional systems of confined particles that interact with an appropriate statistical repulsion potential. We consider both an isotropic harmonic and a hard-wall confinement potential. Despite minor differences, the most stable configurations observed in our model correspond to the reported Pauli crystals in single-shot imaging experiments of free spin-polarized fermions in a harmonic trap. The crystalline configurations observed appear to be different from the expected classical Wigner crystal structures that would emerge should the confined classical particles had interacted with a pair-wise Coulomb repulsion.

Five-coordinate Co(II) complexes with nitrilotriacetic acid: Crystal structures of Ca[Co(Nta)X] . nH{sub 2}O (X{sup -} = Cl, Br, or NCS)

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

Polyakova, I. N.; Poznyak, A. L.; Sergienko, V. S.

2006-07-15

The synthesis and X-ray diffraction study of three Ca[Co(Nta)X] . nH{sub 2}O complexes [X{sup -} = Cl, n = 2.3 (I); X{sup -} = Br, n = 2 (II); and X{sup -} = NCS, n = 2 (III)] are performed. The main structural units of crystals I-III are the [CoX(Nta)]{sup 2-} anionic complexes and hydrated Ca{sup 2+} cations. The anionic complexes have similar structures. The coordination of the Co{sup 2+} atom in the shape of a trigonal bipyramid is formed by N + 3O atoms of the Nta{sup 3-} ligand and the X{sup -} anion in the trans position withmore » respect to N. In structures I-III, the Co-O and Co-N bond lengths lie in the ranges 1.998-2.032 and 2.186-2.201 A, respectively. The Co-X bond lengths are 2.294 (I), 2.436 and 2.445 (II), and 1.982 A (III). The environments of the Ca{sup 2+} cations include oxygen atoms of one or two water molecules and six or seven O(Nta) atoms with the coordination number of 9 in I or 8 in II and III. The Ca-O(Nta) bonds form a three-dimensional framework in I or layers in II and III. Water molecules are involved in the hydrogen bonds O(w)-H...O(Nta), O(w)-H...X, and O(w)-H...O(w). Structural data for crystals I-III are deposited with the Cambridge Structural Database (CCDC nos. 287 814-287 816)« less

Diamond Lattice Colloidal Crystals from Binary DNA-grafted Microspheres

NASA Astrophysics Data System (ADS)

Crocker, John; Wang, Yifan; Jenkins, Ian; McGinley, James; Sinno, Talid

Future optical materials promise to do for photonics what semiconductors did for electronics, but the challenge has long been in creating the structure they require regular, three-dimensional array of transparent microspheres arranged like the atoms in a diamond crystal. Here we demonstrate a simple approach for spontaneously growing double-diamond (or B32) crystals from a binary suspension of sub-micron polymer microspheres with synthetic DNA grafted to their surfaces. While diamond symmetry crystals have previously been grown from much smaller nanoparticles, none of those methods appear workable for the larger particles needed for photonic applications, whose size must be comparable to the wavelength of visible light. Intriguingly, matched simulations fail to nucleate or grow B32 crystals from suspension; nor have they been predicted on the basis of theoretical arguments. We conjecture that the B32 crystals may form via transformation from a precursor with a different lattice structure in the bulk or on its surface. The feasibility of converting our self-assembled crystals into diamond-symmetry photonic templates will be discussed. This finding suggests that still other unexpected microstructures may be accessible using this approach. US National Science Foundation, CBET- 1403237.

Integrated digital inverters based on two-dimensional anisotropic ReS₂ field-effect transistors

DOE PAGES

Liu, Erfu; Fu, Yajun; Wang, Yaojia; ...

2015-05-07

Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS₂) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS₂ field-effect transistors, which exhibit competitive performance with large current on/off ratios (~10⁷) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconductingmore » materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS₂ anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications.« less

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.

Crystallization, structure and dynamics of the proton-translocating P-type ATPase.

PubMed

Scarborough, G A

2000-01-01

Large single three-dimensional crystals of the dodecylmaltoside complex of the Neurospora crassa plasma membrane H(+)-ATPase (H(+) P-ATPase) can be grown in polyethylene-glycol-containing solutions optimized for moderate supersaturation of both the protein surfaces and detergent micellar region. Large two-dimensional H(+) P-ATPase crystals also grow on the surface of such mixtures and on carbon films located at such surfaces. Electron crystallographic analysis of the two-dimensional crystals grown on carbon films has recently elucidated the structure of the H(+) P-ATPase at a resolution of 0.8 nm in the membrane plane. The two-dimensional crystals comprise two offset layers of ring-shaped ATPase hexamers with their exocytoplasmic surfaces face to face. Side-to-side interactions between the cytoplasmic regions of the hexamers in each layer can be seen, and an interaction between identical exocytoplasmic loops in opposing hexamer layers holds the two layers together. Detergent rings around the membrane-embedded region of the hexamers are clearly visible, and detergent-detergent interactions between the rings are also apparent. The crystal packing forces thus comprise both protein-protein and detergent-detergent interactions, supporting the validity of the original crystallization strategy. Ten transmembrane helices in each ATPase monomer are well-defined in the structure map. They are all relatively straight, closely packed, moderately tilted at various angles with respect to a plane normal to the membrane surface and average approximately 3.5 nm in length. The transmembrane helix region is connected in at least three places to the larger cytoplasmic region, which comprises several discrete domains separated by relatively wide, deep clefts. Previous work has shown that the H(+) P-ATPase undergoes substantial conformational changes during its catalytic cycle that are not changes in secondary structure. Importantly, the results of hydrogen/deuterium exchange experiments indicate that these conformational changes are probably rigid-body interdomain movements that lead to cleft closure. When interpreted within the framework of established principles of enzyme catalysis, this information on the structure and dynamics of the H(+) P-ATPase molecule provides the basis of a rational model for the sequence of events that occurs as the ATPase proceeds through its transport cycle. The forces that drive the sequence can also be clearly stipulated. However, an understanding of the molecular mechanism of ion transport catalyzed by the H(+) P-ATPase awaits an atomic resolution structure.

Study of intermolecular contacts in proteins and oligomer interfaces and preliminary investigations into the design and production of nanomaterials from proteins

NASA Astrophysics Data System (ADS)

Iyer, Ganesh Hariharan

The first part of this research involved a study of the nature and extent of nonbonded interactions at crystal and oligomer interfaces. A survey was compiled of several characteristics of intersubunit contacts in 58 different oligomeric proteins, and of the intermolecular contacts in 223 protein crystal structures. Routines written in "S" language were utilized for the generation of the observed and expected contacts. The information in the Protein Data Bank (PDB) was extracted using the database management system, Protein Knowledge Base (PKB). Potentials of mean force for atom-atom contacts and residue-residue contacts were derived by comparison of the number of observed interactions with the number expected by mass action. Preference association matrices and log-linear analyses were applied to determine the different factors that could contribute to the overall interactions at the interfaces of oligomers and crystals. Surface patches at oligomer and crystal interfaces were also studied to further investigate the origin of the differences in their stabilities. Total number of atoms in contact and the secondary structure elements involved are similar in the two types of interfaces. Crystal contacts result from more numerous interactions by polar residues, compared with a tendency toward nonpolar amino acid prominent in oligomer interfaces. Contact potentials indicate that hydrophobic interactions at oligomer interfaces favor aromatic amino acids and methionine over aliphatic amino acids; and that crystal contacts form in such a way as to avoid inclusion of hydrophobic interactions. The second part involved the development of a new class of biomaterials from two-dimensional arrays of ordered proteins. Point mutations were planned to introduce cysteine residues at appropriate locations to enable cross-linking at the molecular interface within given crystallographic planes. Crystallization and subsequent cross-linking of the modified protein would lead to the formation of arrays on subsequent dissociation of the crystal. Novel protein architectures can be generated from these cross-linked nanostructures. Experiments with model protein, maltose-binding protein (MBP) were performed to develop purification, cross-linking and crystallization techniques. The long-term goal of this project is to apply the experience gained with MBP to the fabrication of nanomaterials from other, application-specific proteins for ultrafiltration and microelectronic devices.

Hydrothermal synthesis, crystal structure and properties of 2-D and 3-D lanthanide sulfates

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

Xu Yan; Ding Shaohua; Zheng Xuefang

2007-07-15

Two new lanthanum sulfates DySO{sub 4}(OH) 1 and Eu{sub 2}(SO{sub 4}){sub 3}(H{sub 2}O){sub 8} 2 have been hydrothermally synthesized. The colorless crystals were characterized by IR, TGA, ICP and XRD. The structure was determined by single-crystal X-ray diffraction. 1 crystallizes with monoclinic symmetry, space group P2(1)/n [a=7.995(4) A, b=10.945(5) A, c=8.164(4) A, {alpha}=90{sup o}, {beta}=93.619(6){sup o}, {gamma}=90{sup o}, V=713.0(5) A{sup 3}, Z=8]. It displays a three-dimensional framework, based on the novel Dy-O chains connected by the sulfate groups through helical chains. 2 crystallizes with monoclinic symmetry, space group C2/c, [a=13.5605(17) A, b=6.7676(8) A, c=18.318(2) A, {alpha}=90{sup o}, {beta}=102.265(2){sup o}, {gamma}=90{supmore » o}, V=1642.7 (4) A{sup 3}, Z=4]. Its layered framework is attained by the europium atoms connected by the sulfate groups arranged in a helical manner. - Graphical abstract: Two new lanthanum sulfates DySO{sub 4}(OH) 1 and Eu{sub 2} (SO{sub 4}){sub 3} (H{sub 2}O){sub 8} 2 have been hydrothermally synthesized. The colorless crystals were characterized by IR, TGA, ICP and XRD. The structure was determined by single-crystal X-ray diffraction. It displays a three dimensional framework, based on the novel Dy-O chains connected by the sulfate groups through helical chains.« less

Crystal Structure and Characterization of Ba 2V 3O 9: A Vanadyl(IV) Vanadate Containing Rutile-like Chains of VO 6Octahedra

NASA Astrophysics Data System (ADS)

Dhaussy, Anne-Claire; Abraham, Francis; Mentre, Olivier; Steinfink, Hugo

1996-11-01

The crystal structure of Ba2V3O9has been determined and refined to finalRandRwvalues of 0.025 and 0.028 from 1562 independent single crystal reflections. It crystallizes in the space groupP21/mwitha= 9.302(1) Å,b= 5.969(1) Å,c= 8.118(1) Å, and β = 113.96 (1)°. The structure consists of one-dimensional rutile-type chains of edge-sharing VO6octahedra parallel to thebaxis. The VO4tetrahedra share corners with VO6octahedra of a single rutile-type chain to form one-dimensional [V3O9]4-∞columns which are held together by Ba2+ions. In this mixed valence compound V4+and V5+ions are distributed in an ordered way in octahedra and tetrahedra, respectively. In the almost perfect O6octahedron the vanadium atom is off-center so that it forms a short vanadyl V_dbO bond of 1.686(3) Å, typical of a V4+ion. This compound is a barium vanadyl vanadate Ba2(VO)(VO4)2. It is the first example of isolated rutile-type chains found with V4+ions. Magnetic susceptibility measurements show that this phase is an antiferromagnet withTN≅ 58 K. At about 20 K magnetic anisotropy causes a canted spin arrangement.

Dependence of the shape of graphene nanobubbles on trapped substance

NASA Astrophysics Data System (ADS)

Ghorbanfekr-Kalashami, H.; Vasu, K. S.; Nair, R. R.; Peeters, François M.; Neek-Amal, M.

2017-06-01

Van der Waals (vdW) interaction between two-dimensional crystals (2D) can trap substances in high pressurized (of order 1 GPa) on nanobubbles. Increasing the adhesion between the 2D crystals further enhances the pressure and can lead to a phase transition of the trapped material. We found that the shape of the nanobubble can depend critically on the properties of the trapped substance. In the absence of any residual strain in the top 2D crystal, flat nanobubbles can be formed by trapped long hydrocarbons (that is, hexadecane). For large nanobubbles with radius 130 nm, our atomic force microscopy measurements show nanobubbles filled with hydrocarbons (water) have a cylindrical symmetry (asymmetric) shape which is in good agreement with our molecular dynamics simulations. This study provides insights into the effects of the specific material and the vdW pressure on the microscopic details of graphene bubbles.

Dependence of the shape of graphene nanobubbles on trapped substance.

PubMed

Ghorbanfekr-Kalashami, H; Vasu, K S; Nair, R R; Peeters, François M; Neek-Amal, M

2017-06-16

Van der Waals (vdW) interaction between two-dimensional crystals (2D) can trap substances in high pressurized (of order 1 GPa) on nanobubbles. Increasing the adhesion between the 2D crystals further enhances the pressure and can lead to a phase transition of the trapped material. We found that the shape of the nanobubble can depend critically on the properties of the trapped substance. In the absence of any residual strain in the top 2D crystal, flat nanobubbles can be formed by trapped long hydrocarbons (that is, hexadecane). For large nanobubbles with radius 130 nm, our atomic force microscopy measurements show nanobubbles filled with hydrocarbons (water) have a cylindrical symmetry (asymmetric) shape which is in good agreement with our molecular dynamics simulations. This study provides insights into the effects of the specific material and the vdW pressure on the microscopic details of graphene bubbles.

Dependence of the shape of graphene nanobubbles on trapped substance

PubMed Central

Ghorbanfekr-Kalashami, H.; Vasu, K. S.; Nair, R. R.; Peeters, François M.; Neek-Amal, M.

2017-01-01

Van der Waals (vdW) interaction between two-dimensional crystals (2D) can trap substances in high pressurized (of order 1 GPa) on nanobubbles. Increasing the adhesion between the 2D crystals further enhances the pressure and can lead to a phase transition of the trapped material. We found that the shape of the nanobubble can depend critically on the properties of the trapped substance. In the absence of any residual strain in the top 2D crystal, flat nanobubbles can be formed by trapped long hydrocarbons (that is, hexadecane). For large nanobubbles with radius 130 nm, our atomic force microscopy measurements show nanobubbles filled with hydrocarbons (water) have a cylindrical symmetry (asymmetric) shape which is in good agreement with our molecular dynamics simulations. This study provides insights into the effects of the specific material and the vdW pressure on the microscopic details of graphene bubbles. PMID:28621311

Crystallization in supercooled liquid Cu: Homogeneous nucleation and growth

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

E, J. C.; Key Laboratory of Advanced Technologies of Materials, Ministry of Education, Southwest Jiaotong University, Chengdu, Sichuan 610031; Wang, L.

2015-02-14

Homogeneous nucleation and growth during crystallization of supercooled liquid Cu are investigated with molecular dynamics simulations, and the microstructure is characterized with one- and two-dimensional x-ray diffraction. The resulting solids are single-crystal or nanocrystalline, containing various defects such as stacking faults, twins, fivefold twins, and grain boundaries; the microstructure is subject to thermal fluctuations and extent of supercooling. Fivefold twins form via sequential twinning from the solid-liquid interfaces. Critical nucleus size and nucleation rate at 31% supercooling are obtained from statistical runs with the mean first-passage time and survival probability methods, and are about 14 atoms and 10{sup 32} m{supmore » −3}s{sup −1}, respectively. The bulk growth dynamics are analyzed with the Johnson-Mehl-Avrami law and manifest three stages; the Avrami exponent varies in the range of 1–19, which also depends on thermal fluctuations and supercooling.« less

Molecular association via halogen bonding and other weak interactions in the crystal structures of 11-bromo-12-oxo-5β-cholan derivatives

NASA Astrophysics Data System (ADS)

Salunke, Deepak B.; Hazra, Braja G.; Gonnade, Rajesh G.; Pore, Vandana S.; Bhadbhade, Mohan M.

2008-12-01

Methyl 3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate 2, methyl 11α-bromo-3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate 3, methyl 11β-bromo-3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate 4 and methyl 11,11-dibromo-3α,7α-diacetoxy-12-oxo-5β-cholan-24-oate 5 were synthesized. The crystal structures of these molecules were resolved to study the effect of bulky bromine atom in the steroid skeleton of cholic acid with different stereo-chemical orientations at C-11 on the two-dimensional arrangement of molecules and solid-state properties. All the molecules associate only via weak intermolecular interactions in their crystal structures, notable one being the Halogen Bonded assembly (C-Br…O) in 5.

Room temperature ferromagnetism in Fe-doped semiconductor ZrS2 single crystals

NASA Astrophysics Data System (ADS)

Muhammad, Zahir; Lv, Haifeng; Wu, Chuanqiang; Habib, Muhammad; Rehman, Zia ur; Khan, Rashid; Chen, Shuangming; Wu, Xiaojun; Song, Li

2018-04-01

Two dimensional (2D) layered magnetic materials have obtained much attention due to their intriguing properties with a potential application in the field of spintronics. Herein, room-temperature ferromagnetism with 0.2 emu g‑1 magnetic moment is realized in Fe-doped ZrS2 single crystals of millimeter size, in comparison with diamagnetic behaviour in ZrS2. The electron paramagnetic resonance spectroscopy reveals that 5.2wt% Fe-doping ZrS2 crystal exhibit high spin value of g-factor about 3.57 at room temperature also confirmed this evidence, due to the unpaired electrons created by doped Fe atoms. First principle static electronic and magnetic calculations further confirm the increased stability of long range ferromagnetic ordering and enhanced magnetic moment in Fe-doped ZrS2, originating from the Fe spin polarized electron near the Fermi level.

Bromidotetra-kis-(2-ethyl-1H-imidazole-κN (3))copper(II) bromide.

PubMed

Godlewska, Sylwia; Kelm, Harald; Krüger, Hans-Jörg; Dołęga, Anna

2012-12-01

The Cu(II) ion in the title mol-ecular salt, [CuBr(C5H8N2)4]Br, is coordinated in a square-pyramidal geometry by four N atoms of imidazole ligands and one bromide anion in the apical position. In the crystal, the ions are linked by N-H⋯Br hydrogen bonds involving both the coordinating and the free bromide species as acceptors. A C-H⋯Br inter-action is also observed. Overall, a three-dimensional network results.

Microstructurally Based Cross-slip Mechanisms and Their Effects on Dislocation Microstructure Evolution in fcc Crystals

DTIC Science & Technology

2015-01-01

still necessary. One such model that could bridge this gap is discrete dis- location dynamics ( DDD ) simulations, in which both the time- and length-scale...limitations from atomic simulations are greatly reduced. Over the past two decades, two-dimen- sional (2D) and three-dimensional (3D) DDD methods have...dislocation ensem- bles according to physics-based rules [27–34]. The physics that can be incorporated in DDD simulations can range http://dx.doi.org

Electronic structure studies of La2CuO4

NASA Astrophysics Data System (ADS)

Wachs, A. L.; Turchi, P. E. A.; Jean, Y. C.; Wetzler, K. H.; Howell, R. H.; Fluss, M. J.; Harshman, D. R.; Remeika, J. P.; Cooper, A. S.; Fleming, R. M.

1988-07-01

We report results of positron-electron momentum-distribution measurements of single-crystal La2CuO4 using two-dimensional angular correlation of positron-annihilation-radiation techniques. The data contain two components: a large (~85%), isotropic corelike electron contribution and a remaining, anisotropic valence-electron contribution modeled using a linear combination of atomic orbitals-molecular orbital method and a localized ion scheme, within the independent-particle model approximation. This work suggests a ligand-field Hamiltonian to be justified for describing the electronic properties of perovskite materials.

Au 2PbP 2, Au 2TlP 2, and Au 2HgP 2: Ternary Gold Polyphosphides with Lead, Thallium, and Mercury in the Oxidation State Zero

NASA Astrophysics Data System (ADS)

Eschen, Marcus; Jeitschko, Wolfgang

2002-05-01

The polyphosphide Au2PbP2 was prepared by reaction of the elemental components using liquid lead as a reaction medium. Well-developed crystals were obtained after dissolving the matrix in hydrochloric acid. Their crystal structure was determined from four-circle X-ray diffractometer data: Cmcm, a=323.6(1) pm, b=1137.1(2) pm, c=1121.8(1) pm, Z=4, R=0.023 for 478 structure factors and 20 variable parameters. The structure contains zigzag chains of phosphorus atoms with a typical single-bond distance of 219.4(2) pm. The two different kinds of gold atoms are both in linear phosphorus coordination with typical single-bond distances of 232.6(2) and 234.2(2) pm, and the lead atoms have only metal neighbors (7 Au and 2 Pb). Accordingly, chemical bonding of the compound may be expressed by the formula (Au+1)2Pb±0(P-1)2. The corresponding thallium and mercury polyphosphides Au2TlP2 (a=324.1(1) pm, b=1136.1(1) pm, c=1122.1(1) pm) and Au2HgP2 (a=322.1(1) pm, b=1131.4(2) pm, c=1122.6(1) pm) were found to be almost isotypic with Au2PbP2. Their crystal structures were refined from single-crystal X-ray data to R=0.036 (682 F values, 25 variables) and R=0.026 (539 F values, 35 variables), respectively. The structure of these compounds may also be described as consisting of a three-dimensional network of condensed 8- and 10-membered Au2P6 and Au4P6 rings forming parallel channels, which are filled by the lead, thallium, and mercury atoms. The lead atoms are well localized in these channels, while the thallium and even more the mercury atoms occupy additional positions within these channels. Freshly prepared samples of Au2HgP2 show reproducibly slightly different axial ratios and larger cell volumes (ΔV=0.5%) than those after exposure of the samples to air for several days.

Features in simulation of crystal growth using the hyperbolic PFC equation and the dependence of the numerical solution on the parameters of the computational grid

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

Starodumov, Ilya; Kropotin, Nikolai

2016-08-10

We investigate the three-dimensional mathematical model of crystal growth called PFC (Phase Field Crystal) in a hyperbolic modification. This model is also called the modified model PFC (originally PFC model is formulated in parabolic form) and allows to describe both slow and rapid crystallization processes on atomic length scales and on diffusive time scales. Modified PFC model is described by the differential equation in partial derivatives of the sixth order in space and second order in time. The solution of this equation is possible only by numerical methods. Previously, authors created the software package for the solution of the Phasemore » Field Crystal problem, based on the method of isogeometric analysis (IGA) and PetIGA program library. During further investigation it was found that the quality of the solution can strongly depends on the discretization parameters of a numerical method. In this report, we show the features that should be taken into account during constructing the computational grid for the numerical simulation.« less

Crystal structure, vibrational and DFT simulation studies of melaminium dihydrogen phosphite monohydrate

NASA Astrophysics Data System (ADS)

Arjunan, V.; Kalaivani, M.; Marchewka, M. K.; Mohan, S.

2013-08-01

The crystal structure investigations of melamine with phosphorous acid, namely melaminium dihydrogenphosphite monohydrate (C3N6H7·H2PO3·H2O) have been investigated by means of single crystal X-ray diffraction method. The title compound crystallizes in monoclinic crystal system, and the space group is P21/c with a = 10.069 Å, b = 21.592 Å, c = 12.409 Å and Z = 12. The vibrational assignments and analysis of melaminium dihydrogen phosphite monohydrate have also been performed by FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical simulations were performed with DFT (B3LYP) method using 6-31G**, cc-pVTZ, and 6-311++G** basis sets to determine the energy, structural, thermodynamic parameters and vibrational frequencies of melaminium dihydrogen phosphite monohydrate. The hydrogen atom from phosphorous acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak Osbnd H···O and Nsbnd H···O hydrogen bonds shows notable vibrational effects.

Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

DOE PAGES

Perea, Daniel E.; Arslan, Ilke; Liu, Jia; ...

2015-07-02

Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Ultimately, using a nearest-neighbour statisticalmore » analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al–Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.« less

Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography

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

Perea, Daniel E.; Arslan, Ilke; Liu, Jia

Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Ultimately, using a nearest-neighbour statisticalmore » analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al–Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.« less

5-Chloro-5''-[4-(di-methyl-amino)-benzyl-idene]-4'-[4-(di-methyl-amino)-phen-yl]-1',1''-di-methyl-dispiro-[indoline-3,2'-pyrrolidine-3',3''-piperidine]-2,4''-dione.

PubMed

Farag, I S Ahmed; Girgis, Adel S; Ramadan, A A; Moustafa, A M; Tiekink, Edward R T

2014-01-01

The title compound, C34H38ClN5O2, has spiro links connecting the pyrrolidine ring and indole residue, as well as the piperidine and pyrrolidine rings. A half-chair conformation is found for the piperidine ring with the C atom connected to the spiro-C atom lying 0.738 (4) Å out of the plane of the remaining five atoms (r.m.s. deviation = 0.0407 Å). The methyl-ene C atom is the flap in the envelope conformation for the pyrrolidine ring. In the crystal, supra-molecular chains are sustained by alternating eight-membered {⋯HNCO}2 and 14-membered {⋯HC5O}2 synthons. Chains are connected into a three-dimensional network by (pyrrolidine-bound phenyl-meth-yl)C-H⋯π(pyrrolidine-bound phen-yl) edge-to-face inter-actions.

Atomically thin gallium layers from solid-melt exfoliation

PubMed Central

Kochat, Vidya; Samanta, Atanu; Zhang, Yuan; Bhowmick, Sanjit; Manimunda, Praveena; Asif, Syed Asif S.; Stender, Anthony S.; Vajtai, Robert; Singh, Abhishek K.; Tiwary, Chandra S.; Ajayan, Pulickel M.

2018-01-01

Among the large number of promising two-dimensional (2D) atomic layer crystals, true metallic layers are rare. Using combined theoretical and experimental approaches, we report on the stability and successful exfoliation of atomically thin “gallenene” sheets on a silicon substrate, which has two distinct atomic arrangements along crystallographic twin directions of the parent α-gallium. With a weak interface between solid and molten phases of gallium, a solid-melt interface exfoliation technique is developed to extract these layers. Phonon dispersion calculations show that gallenene can be stabilized with bulk gallium lattice parameters. The electronic band structure of gallenene shows a combination of partially filled Dirac cone and the nonlinear dispersive band near the Fermi level, suggesting that gallenene should behave as a metallic layer. Furthermore, it is observed that the strong interaction of gallenene with other 2D semiconductors induces semiconducting to metallic phase transitions in the latter, paving the way for using gallenene as promising metallic contacts in 2D devices. PMID:29536039

Octa-akis(4-amino-pyridine)-1κN,2κN-aqua-2κO-μ-carbonato-1:2κO,O':O''-dinickel(II) dichloride penta-hydrate.

PubMed

Fun, Hoong-Kun; Sinthiya, A; Jebas, Samuel Robinson; Ravindran Durai Nayagam, B; Alfred Cecil Raj, S

2008-10-18

In the title compound, [Ni(2)(CO(3))(C(5)H(6)N(2))(8)(H(2)O)]Cl(2)·5H(2)O, one of the the Ni(II) ions is six-coordinated in a distorted octa-hedral geometry, with the equatorial plane defined by four pyridine N atoms from four amino-pyridine ligands, the axial positions being occupied by one water O and a carbonate O atom. The other Ni(II) ion is also six-coordinated, by four other pyridine N atoms from four other amino-pyridine ligands and two carbonate O atoms to complete a distorted octa-hedral geometry. In the crystal structure, mol-ecules are linked into an infinite three-dimensional network by O-H⋯O, N-H⋯Cl, N-H⋯O, O-H⋯N, C-H⋯O, C-H⋯N and C/N-H⋯π inter-actions involving the pyridine rings.

Crystal structure of fac-tri-chlorido-[tris-(pyridin-2-yl-N)amine]-chromium(III).

PubMed

Yamaguchi-Terasaki, Yukiko; Fujihara, Takashi; Nagasawa, Akira; Kaizaki, Sumio

2015-01-01

In the neutral complex mol-ecule of the title compound, fac-[CrCl3(tpa)] [tpa is tris-(pyridin-2-yl)amine; C15H12N4], the Cr(III) ion is bonded to three N atoms that are constrained to a facial arrangement by the tpa ligand and by three chloride ligands, leading to a distorted octa-hedral coordination sphere. The average Cr-N and Cr-Cl bond lengths are 2.086 (5) and 2.296 (4) Å, respectively. The complex mol-ecule is located on a mirror plane. In the crystal, a combination of C-H⋯N and C-H⋯Cl hydrogen-bonding inter-actions connect the mol-ecules into a three-dimensional network.

Crystal structure of tetra-kis-(μ3-2-{[1,1-bis-(hy-droxy-meth-yl)-2-oxidoeth-yl]imino-meth-yl}-6-meth-oxy-phenolato)tetra-kis-[aqua-copper(II)]: a redetermination at 200 K.

PubMed

Buvaylo, Elena A; Vassilyeva, Olga Yu; Skelton, Brian W

2015-10-01

The crystal structure of the tetra-nuclear title compound, [Cu4(C12H15NO5)4(H2O)4], has been previously reported by Back, Oliveira, Canabarro & Iglesias [Z. Anorg. Allg. Chem. (2015), 641, 941-947], based on room-temperature data. In the previously published structure, no standard uncertainties are recorded for the deprotonated hy-droxy-methyl group and water mol-ecule O atoms coordinating to the metal atom indicating that they were not refined; furthermore, the H atoms of some OH groups and water mol-ecules have not been positioned accurately. Since the current structure was determined at a lower temperature, all atoms, including the H atoms of these hy-droxy groups and the water mol-ecule, have been determined more accurately resulting in improved standard uncertainties in the bond lengths and angles. Diffraction data were collected at 200 K, rather than the more usual 100 K, due to apparent disordering at lower temperatures. In addition, it is now possible to report intra- and inter-molecular O-H⋯O inter-actions. In the title complex molecule, which has crystallographic -4 symmetry, the Cu(II) ions are coordinated by the tridentate Schiff base ligands and water mol-ecules, forming a tetra-nuclear Cu4O4 cubane-like core. The Cu(II) ion adopts a CuNO5 elongated octa-hedral environment. The coordination environment of Cu(II) at 200 K displays a small contraction of the Cu-N/O bonds, compared with the room-temperature structure. In the crystal lattice, the neutral clusters are linked by inter-molecular O-H⋯O hydrogen bonds into a one-dimensional hydrogen-bonding network propagating along the b axis.

Poly[[(μ2-acetato-κ3 O,O′:O′)aqua­bis­(μ3-isonicotinato-κ3 O:O′:N)samarium(III)silver(I)] perchlorate

PubMed Central

Zhu, Li-Cai; Zhu, Si-Ming

2011-01-01

The title compound, {[AgSm(C6H4NO2)2(CH3CO2)(H2O)]ClO4}n, is a three-dimensional heterobimetallic complex constructed from a repeating dimeric unit. Only half of the dimeric moiety is found in the asymmetric unit; the unit cell is completed by crystallographic inversion symmetry. The SmIII ion is eight-coordinated by four O atoms of four different isonicotinate ligands, three O atoms of two different acetate ligands, and one O atom of a water mol­ecule. The two-coordinate AgI ion is bonded to two N atoms of two different isonicotinate anions, thereby connecting the disamarium units. In addition, the isonicotinate ligands also act as bridging ligands, generating a three-dimensional network. The coordinated water mol­ecules link the carboxyl­ate group and acetate ligands by O—H⋯O hydrogen bonding. Another O—H⋯O hydrogen bond is observed in the crystal structure. The perchlorate ion is disordered over two sites with site-occupancy factors of 0.560 (11) and 0.440 (11), whereas the methyl group of the acetate ligand is disordered over two sites with site-occupancy factors of 0.53 (5) and 0.47 (5). PMID:22090841

Geometrically unrestricted, topologically constrained control of liquid crystal defects using simultaneous holonomic magnetic and holographic optical manipulation.

PubMed

Varney, Michael C M; Jenness, Nathan J; Smalyukh, Ivan I

2014-02-01

Despite the recent progress in physical control and manipulation of various condensed matter, atomic, and particle systems, including individual atoms and photons, our ability to control topological defects remains limited. Recently, controlled generation, spatial translation, and stretching of topological point and line defects have been achieved using laser tweezers and liquid crystals as model defect-hosting systems. However, many modes of manipulation remain hindered by limitations inherent to optical trapping. To overcome some of these limitations, we integrate holographic optical tweezers with a magnetic manipulation system, which enables fully holonomic manipulation of defects by means of optically and magnetically controllable colloids used as "handles" to transfer forces and torques to various liquid crystal defects. These colloidal handles are magnetically rotated around determined axes and are optically translated along three-dimensional pathways while mechanically attached to defects, which, combined with inducing spatially localized nematic-isotropic phase transitions, allow for geometrically unrestricted control of defects, including previously unrealized modes of noncontact manipulation, such as the twisting of disclination clusters. These manipulation capabilities may allow for probing topological constraints and the nature of defects in unprecedented ways, providing the foundation for a tabletop laboratory to expand our understanding of the role defects play in fields ranging from subatomic particle physics to early-universe cosmology.

Formation of fivefold axes in the FCC-metal nanoclusters

NASA Astrophysics Data System (ADS)

Myasnichenko, Vladimir S.; Starostenkov, Mikhail D.

2012-11-01

Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu-Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000 K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu-Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

Cd4As2Br3

PubMed Central

Kars, Mohammed; Roisnel, Thierry; Dorcet, Vincent; Rebbah, Allaoua; Otero-Diáz, L. Carlos

2014-01-01

Single crystals of Cd4As2Br3 (tetra­cadmium biarsenide tri­bromide) were grown by a chemical transport reaction. The structure is isotypic with the members of the cadmium and mercury pnictidohalides family with general formula M 4 A 2 X 3 (M = Cd, Hg; A = P, As, Sb; X = Cl, Br, I) and contains two independent As atoms on special positions with site symmetry -3 and two independent Cd atoms, of which one is on a special position with site symmetry -3. The Cd4As2Br3 structure consists of AsCd4 tetra­hedra sharing vertices with isolated As2Cd6 octa­hedra that contain As–As dumbbells in the centre of the octahedron. The Br atoms are located in the voids of this three-dimensional arrangement and bridge the different polyhedra through Cd⋯Br contacts. PMID:24764933

Metallic atomically-thin layered silicon epitaxially grown on silicene/ZrB 2

DOE PAGES

Gill, Tobias G.; Fleurence, Antoine; Warner, Ben; ...

2017-02-17

We observe a new two-dimensional (2D) silicon crystal, using low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) and it's formed by depositing additional Si atoms onto spontaneously-formed epitaxial silicene on a ZrB 2 thin film. From scanning tunnelling spectroscopy (STS) studies, we find that this atomically-thin layered silicon has distinctly different electronic properties. Angle resolved photoelectron spectroscopy (ARPES) reveals that, in sharp contrast to epitaxial silicene, the layered silicon exhibits significantly enhanced density of states at the Fermi level resulting from newly formed metallic bands. Furthermore, the 2D growth of this material could allow for direct contacting tomore » the silicene surface and demonstrates the dramatic changes in electronic structure that can occur by the addition of even a single monolayer amount of material in 2D systems.« less

Intrinsic cavity QED and emergent quasinormal modes for a single photon

NASA Astrophysics Data System (ADS)

Dong, H.; Gong, Z. R.; Ian, H.; Zhou, Lan; Sun, C. P.

2009-06-01

We propose a special cavity design that is constructed by terminating a one-dimensional waveguide with a perfect mirror at one end and doping a two-level atom at the other. We show that this atom plays the intrinsic role of a semitransparent mirror for single-photon transports such that quasinormal modes emerge spontaneously in the cavity system. This atomic mirror has its reflection coefficient tunable through its level spacing and its coupling to the cavity field, for which the cavity system can be regarded as a two-end resonator with a continuously tunable leakage. The overall investigation predicts the existence of quasibound states in the waveguide continuum. Solid-state implementations based on a dc-superconducting quantum interference device circuit and a defected line resonator embedded in a photonic crystal are illustrated to show the experimental accessibility of the generic model.

Trisodium citrate, Na 3 (C 6 H 5 O 7 )

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

Rammohan, Alagappa; Kaduk, James A.

2016-05-10

The crystal structure of anhydrous trisodium citrate, Na 3(C 6H 5O 7), has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory (DFT). There are two independent five-coordinate Na +and one six-coordinate Na +cations in the asymmetric unit. The [NaO 5] and [NaO 6] polyhedra share edges and corners to form a three-dimensional framework. There are channels parallel to theaandbaxes in which the remainder of the citrate anions reside. The only hydrogen bonds are an intramolecular one between the hydroxy group and one of the terminal carboxylate O atoms and an intermolecular onemore » between a methylene group and the hydroxyl O atom.« less

5-Bromo-N-methyl­pyrimidin-2-amine

PubMed Central

Yang, Qi; Xu, Ning; Zhu, Kai; Lv, Xiaoping; Han, Ping-fang

2012-01-01

In the title mol­ecule, C5H6BrN3, the pyrimidine ring is essentially planar, with an r.m.s. deviation of 0.007 Å. The Br and N atoms substituted to the pyrimidine ring are coplanar with the ring [displacements = 0.032 (1) and 0.009 (5) Å, respectively], while the methyl C atom lies 0.100 (15) Å from this plane with a dihedral angle between the pyrimidine ring and the methyl­amine group of 4.5 (3)°. In the crystal, C—H⋯N, C—H⋯Br and N—H⋯N hydrogen bonds link the mol­ecules into a two-dimensional network in the (011) plane. PMID:22259398

Bromidotetra-kis-(1H-2-ethyl-5-methyl-imidazole-κN)copper(II) bromide.

PubMed

Godlewska, Sylwia; Baranowska, Katarzyna; Socha, Joanna; Dołęga, Anna

2011-12-01

The Cu(II) ion in the title compound, [CuBr(C(6)H(10)N(2))(4)]Br, is coordinated in a square-based-pyramidal geometry by the N atoms of four imidazole ligands and a bromide anion in the apical site. Both the Cu(II) and Br(-) atoms lie on a crystallographic fourfold axis. In the crystal, the [CuBr(C(6)H(10)N(2))(4)](+) complex cations are linked to the uncoordinated Br(-) anions (site symmetry [Formula: see text]) by N-H⋯Br hydrogen bonds, generating a three-dimensional network. The ethyl group of the imidazole ligand was modelled as disordered over two orientations with occupancies of 0.620 (8) and 0.380 (8).

Li15Al3Si6 (Li14.6Al3.4Si6), a compound displaying a heterographite-like anionic framework.

PubMed

Spina, Laurent; Tillard, Monique; Belin, Claude

2003-02-01

The title compound, lithium aluminium silicide (15/3/6), crystallizes in the hexagonal centrosymmetric space group P6(3)/m. The three-dimensional structure of this ternary compound may be depicted as two interpenetrating lattices, namely a graphite-like Li(3)Al(3)Si(6) layer and a distorted diamond-like lithium lattice. As is commonly found for LiAl alloys, the Li and Al atoms are found to share some crystallographic sites. The diamond-like lattice is built up of Li cations, and the graphite-like anionic layer is composed of Si, Al and Li atoms in which Si and Al are covalently bonded [Si-Al = 2.4672 (4) A].

The complex metal-rich boride Ti1+xRh2-x+yIr3-yB3 (x=0.68, y=1.06) with a new structure type containing B4 zigzag fragments: Synthesis, crystal chemistry and theoretical calculations

NASA Astrophysics Data System (ADS)

Goerens, Christian; Fokwa, Boniface P. T.

2012-08-01

Polycrystalline samples and single crystals of the new complex boride Ti1+xRh2-x+yIr3-yB3 (x=0.68; y=1.06) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-Ray diffraction as well as EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase, which represents a new structure type containing trans zigzag B4 fragments as well as isolated boron atoms crystallizes in the orthorhombic space group Pbam (Nr. 55) with the lattice parameters a=8.620(1) Å, b=14.995(2) Å and c=3.234(1) Å. First-principles density functional theory calculations using the Vienna ab-initio simulation package (VASP) were performed on an appropriate structural model (using a supercell approach) and the experimental crystallographic data could be reproduced accurately. Based on this model, the density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron-boron interactions are observed in the trans zigzag B4 fragment, which induce a clear differentiation of two types of metal-boron contacts with different strength. The observed three-dimensional metal-metal interaction is in good agreement with the predicted metallic behavior.

Crystal structures of the three closely related compounds: bis-[(1H-tetra-zol-5-yl)meth-yl]nitramide, tri-amino-guanidinium 5-({[(1H-tetra-zol-5-yl)meth-yl](nitro)-amino}-meth-yl)tetra-zol-1-ide, and di-ammonium bis-[(tetra-zol-1-id-5-yl)meth-yl]nitramide monohydrate.

PubMed

Mitchell, Lauren A; Imler, Gregory H; Parrish, Damon A; Deschamps, Jeffrey R; Leonard, Philip W; Chavez, David E

2017-07-01

In the mol-ecule of neutral bis-[(1 H -tetra-zol-5-yl)meth-yl]nitramide, (I), C 4 H 6 N 10 O 2 , there are two intra-molecular N-H⋯O hydrogen bonds. In the crystal, N-H⋯N hydrogen bonds link mol-ecules, forming a two-dimensional network parallel to (-201) and weak C-H⋯O, C-H⋯N hydrogen bonds, and inter-molecular π-π stacking completes the three-dimensional network. The anion in the molecular salt, tri-amino-guanidinium 5-({[(1 H -tetra-zol-5-yl)meth-yl](nitro)-amino}-meth-yl)tetra-zol-1-ide, (II), CH 9 N 6 + ·C 4 H 5 N 10 O 2 - , displays intra-molecular π-π stacking and in the crystal, N-H⋯N and N-H⋯O hydrogen bonds link the components of the structure, forming a three-dimensional network. In the crystal of di-ammonium bis-[(tetra-zol-1-id-5-yl)meth-yl]nitramide monohydrate, (III), 2NH 4 + ·C 4 H 4 N 10 O 2 2- ·H 2 O, O-H⋯N, N-H⋯N, and N-H⋯O hydrogen bonds link the components of the structure into a three-dimensional network. In addition, there is inter-molecular π-π stacking. In all three structures, the central N atom of the nitramide is mainly sp 2 -hybridized. Bond lengths indicate delocalization of charges on the tetra-zole rings for all three compounds. Compound (II) was found to be a non-merohedral twin and was solved and refined in the major component.

Two novel magnesium(II) meso-tetraphenylporphyrin-based coordination complexes: Syntheses, combined experimental and theoretical structures elucidation, spectroscopy, photophysical properties and antibacterial activity

NASA Astrophysics Data System (ADS)

Amiri, Nesrine; Hajji, Melek; Taheur, Fadia Ben; Chevreux, Sylviane; Roisnel, Thierry; Lemercier, Gilles; Nasri, Habib

2018-02-01

Two novel magnesium(II) tetraphenylporphyrin-based six-coordinate complexes; bis(hexamethylenetetramine)(5,10,15,2O tetrakis[4(benzoyloxy)phenyl]porphinato) magnesuim(II) (1) and bis(1,4-diazabicyclo(2.2.2)octane) (5,10,15,2O-tetrakis[4- (benzoyloxy)phenyl]porphinato)magnesium(II) (2) have been synthesised and confirmed by proton nuclear magnetic resonance, mass spectrometry, elemental analysis and IR spectroscopy. Both crystal structures were determined and described by single crystal X-ray diffraction analysis and Hirshfeld surfaces computational method. All Mg(II) atoms are surrounded by four porphyrin nitrogen atoms and two axial ligands coordinated to the metal ion through one nitrogen atom, forming a regular octahedron. In both complexes, molecular structures and three-dimensional framework are stabilised by inter-and intramolecular C-H ⋯O and C-H ⋯N hydrogen bonds, and by weak C-H ⋯Cg π interactions. UV-visible and Fluorescence investigations, respectively, show that studied complexes have a strong absorption in red part and exhibit an emission in the blue region. The HOMO-LUMO energy gap values, modelled using the DFT approach, indicates that both studied compounds can be classified as semiconductors. The role of these complexes as novel antibacterial agents was also performed.

Crystal structure and chemical bonding of the high-temperature phase of AgN3.

PubMed

Schmidt, Carsten L; Dinnebier, Robert; Wedig, Ulrich; Jansen, Martin

2007-02-05

The crystal structure of silver azide (AgN3) in its high-temperature (HT) modification was determined from X-ray powder diffraction data, recorded at T = 170 degrees C and was further refined by the Rietveld method. The structure is monoclinic (P21/c (No. 14), a = 6.0756(2) A, b = 6.1663(2) A, c = 6.5729(2) A, beta = 114.19(0) degrees, V = 224.62(14) A3, Z = 4) and consists of two-dimensional Ag and N containing layers in which the silver atoms are coordinated by four nitrogen atoms exhibiting a distorted square coordination environment. These sheets are linked together by weaker perpendicular Ag-N contacts, thus forming a 4 + 2 coordination geometry around the silver atoms. The phase transition has been characterized by DTA, DSC, and measurement of the density, as well as of the ionic conductivity. Both, the room-temperature and the HT phase are electrically insulating. This fact is getting support by DFT band structure calculations within the generalized gradient approximation, using the PBE functional. On the basis of the DFT band structure, the bonding characteristics of both phases are essentially the same. Finally, the implication of the existence of a low-symmetry HT-phase in a crystalline explosive concerning decomposition mechanisms is discussed.

Twenty years of molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Cho, A. Y.

1995-05-01

The term "molecular beam epitaxy" (MBE) was first used in one of our crystal growth papers in 1970, after having conducted extensive surface physics studies in the late 1960's of the interaction of atomic and molecular beams with solid surfaces. The unique feature of MBE is the ability to prepare single crystal layers with atomic dimensional precision. MBE sets the standard for epitaxial growth and has made possible semiconductor structures that could not be fabricated with either naturally existing materials or by other crystal growth techniques. MBE led the crystal growth technologies when it prepared the first semiconductor quantum well and superlattice structures that gave unexpected and exciting electrical and optical properties. For example, the discovery of the fractional quantized Hall effect. It brought experimental quantum physics to the classroom, and practically all major universities throughout the world are now equipped with MBE systems. The fundamental principles demonstrated by the MBE growth of III-V compound semiconductors have also been applied to the growth of group IV, II-VI, metal, and insulating materials. For manufacturing, the most important criteria are uniformity, precise control of the device structure, and reproducibility. MBE has produced more lasers (3 to 5 million per month for compact disc application) than any other crystal growth technique in the world. New directions for MBE are to incorporate in-situ, real-time monitoring capabilities so that complex structures can be precisely "engineered". In the future, as environmental concerns increase, the use of toxic arsine and phosphine may be limited. Successful use of valved cracker cells for solid arsenic and phosphorus has already produced InP based injection lasers.

Efficient evaluation of atom tunneling combined with electronic structure calculations.

PubMed

Ásgeirsson, Vilhjálmur; Arnaldsson, Andri; Jónsson, Hannes

2018-03-14

Methodology for finding optimal tunneling paths and evaluating tunneling rates for atomic rearrangements is described. First, an optimal JWKB tunneling path for a system with fixed energy is obtained using a line integral extension of the nudged elastic band method. Then, a calculation of the dynamics along the path is used to determine the temperature at which it corresponds to an optimal Feynman path for thermally activated tunneling (instanton) and a harmonic approximation is used to estimate the transition rate. The method is illustrated with calculations for a modified two-dimensional Müller-Brown surface but is efficient enough to be used in combination with electronic structure calculations of the energy and atomic forces in systems containing many atoms. An example is presented where tunneling is the dominant mechanism well above room temperature as an H 3 BNH 3 molecule dissociates to form H 2 . Also, a solid-state example is presented where density functional theory calculations of H atom tunneling in a Ta crystal give close agreement with experimental measurements on hydrogen diffusion over a wide range in temperature.

Sulfide bonded atomic radii

NASA Astrophysics Data System (ADS)

Gibbs, G. V.; Ross, N. L.; Cox, D. F.

2017-09-01

The bonded radius, r b(S), of the S atom, calculated for first- and second-row non-transition metal sulfide crystals and third-row transition metal sulfide molecules and crystals indicates that the radius of the sulfur atom is not fixed as traditionally assumed, but that it decreases systematically along the bond paths of the bonded atoms with decreasing bond length as observed in an earlier study of the bonded radius of the oxygen atom. When bonded to non-transition metal atoms, r b(S) decreases systematically with decreasing bond length from 1.68 Å when the S atom is bonded to the electropositive VINa atom to 1.25 Å when bonded to the more electronegative IVP atom. In the case of transition metal atoms, rb(S) likewise decreases with decreasing bond length from 1.82 Å when bonded to Cu and to 1.12 Å when bonded to Fe. As r b(S) is not fixed at a given value but varies substantially depending on the bond length and the field strength of the bonded atoms, it is apparent that sets of crystal and atomic sulfide atomic radii based on an assumed fixed radius for the sulfur atom are satisfactory in that they reproduce bond lengths, on the one hand, whereas on the other, they are unsatisfactory in that they fail to define the actual sizes of the bonded atoms determined in terms of the minima in the electron density between the atoms. As such, we urge that the crystal chemistry and the properties of sulfides be studied in terms of the bond lengths determined by adding the radii of either the atomic and crystal radii of the atoms but not in terms of existing sets of crystal and atomic radii. After all, the bond lengths were used to determine the radii that were experimentally determined, whereas the individual radii were determined on the basis of an assumed radius for the sulfur atom.

I Situ Surface X-Ray Diffraction Studies of Electrochemically Deposited Monolayers

NASA Astrophysics Data System (ADS)

Yee, Dennis

1995-01-01

In situ x-ray diffraction has been used to determine the detailed atomic structure of electrochemically deposited lead, thallium, and bismuth monolayers on the silver (111) electrode surface. A review of our previously published lead and thallium monolayer results and the first in situ surface x-ray crystallographic study of the bismuth monolayer structure is presented. The crystallographic analysis of the bismuth Bragg rod intensities and the interference between the bismuth Bragg rod and silver crystal truncation rod scattering were used to determine the detailed atomic structure of the bismuth on silver (111) system at the liquid-solid interface. Our previous in situ x-ray diffraction studies showed that the bismuth monolayer lattice is rectangular and uniaxially incommensurate with the underlying hexagonal silver surface. A crystallographic analysis of the measured structure factor magnitudes reveals that the monolayer forms chains of atoms on the silver surface, similar to the bulk Bi(110)_{rh} plane, with a near neighbor distance of 3.12 +/- 0.01 A and a bond angle of 93 +/- 1^circ, consistent with the bulk Bi(110) _{rh} plane values. The crystallographic refinement also shows that the bismuth monolayer atoms are anisotropically disordered with a rms disorder of 0.25 +/- 0.03 A in the incommensurate direction and 0.09 +/- 0.03 A rms in the commnensurate direction. The interference between the Bi(20) Bragg rod and the Ag(10L)_ {h} crystal truncation rod scattering reveals that one set of bismuth atoms is registered near the bridge sites of the silver (111) surface while another set is registered near the 3-fold hollow sites. In addition, the Bi-Ag d-spacing (3.1 +/- 0.1 A) is found to be consistent with the bulk bismuth near neighbor distance. The bismuth z-direction rms disorder (1.01 +/- 0.08 A) is found to be dominated by the roughness of the underlying silver (sigma_{Ag} = 0.9 +/- 0.1 A rms). Using the estimated bismuth-bismuth spring constant of 1.41 +/- 0.07 eV/A^2 from our measured bismuth two-dimensional compressibility, two simple models are used to try and understand the origin of the anisotropic disorder. A simple two-dimensional isotropic thermal fluctuation model shows that thermal fluctuations are not large enough to account for all of the measured excess disorder in the incommensurate direction. A simple one-dimensional Frenkel-Kontorova model shows that the substrate-induced disorder can account for the anisotropic disorder, assuming a substrate sinusoidal potential strength of 0.35 +/- 0.02 eV.

Crystal Engineering; How molecules build solids

NASA Astrophysics Data System (ADS)

Williams, Jeffrey H.

2017-09-01

There are more than 20 million chemicals in the literature, with new materials being synthesized each week. Most of these molecules are stable, and the 3-dimensional arrangement of the atoms in the molecules, in the various solids may be determined by routine x-ray crystallography. When this is done, it is found that this vast range of molecules, with varying sizes and shapes can be accommodated by only a handful of solid structures. This limited number of architectures for the packing of molecules of all shapes and sizes, to maximize attractive intermolecular forces and minimizing repulsive intermolecular forces, allows us to develop simple models of what holds the molecules together in the solid. In this volume we look at the origin of the molecular architecture of crystals; a topic that is becoming increasingly important and is often termed, crystal engineering. Such studies are a means of predicting crystal structures, and of designing crystals with particular properties by manipulating the structure and interaction of large molecules. That is, creating new crystal architectures with desired physical characteristics in which the molecules pack together in particular architectures; a subject of particular interest to the pharmaceutical industry.

Crystal structure of catena-poly[[aquadi-n-propyl­tin(IV)]-μ-oxalato

PubMed Central

Reichelt, Martin; Reuter, Hans

2014-01-01

The title compound, [Sn(C3H7)2(H2O)(C2O4)]n, represents the first diorganotin(IV) oxalate hydrate to be structurally characterized. The tin(IV) atom of the one-dimensional coordination polymer is located on a twofold rotation axis and is coordinated by two chelating oxalate ligands with two slightly different Sn—O bond lengths of 2.290 (2) and 2.365 (2) Å, two symmetry-related n-propyl groups with a Sn—C bond lengths of 2.127 (3) Å, and a water mol­ecule with a Sn—O bond length of 2.262 (2) Å. The coordination polyhedron around the SnIV atom is a slightly distorted penta­gonal bipyramid with a nearly linear axis between the trans-oriented n-propyl groups [C—Sn—C = 176.8 (1)°]. The bond angles between the oxygen atoms of the equatorial plane range from 70.48 (6)° to 76.12 (8)°. A one-dimensional coordination polymer results from the less asymmetric bilateral coordination of the centrosymmetric oxalate anion, inter­nally reflected by two slightly different C—O bond lengths of 1.248 (3) and 1.254 (3) Å. The chains of the polymer propagate parallel to [001] and are held together by hydrogen bonds between water mol­ecules and oxalate anions of neighboring chains, leading to a two-dimensional network parallel to (100). PMID:25249862

William Barlow and the Determination of Atomic Arrangement in Crystals.

PubMed

Mauskopf, Seymour H

2015-04-01

William Barlow (1845-1934) was an important if unconventional scientist, known for having developed the 'closest-packing' atomic models of crystal structure. He resumed an early nineteenth-century tradition of utilizing crystallographical and chemical data to determine atomic arrangements in crystals. This essay recounts Barlow's career and scientific activity in three parts: (a) His place in the tradition of determining atomic arrangement in context of this earlier tradition and of contemporaneous developments of crystallography and chemistry, (b) his unconventional career, and (c) the 'success' of his program to determine atomic arrangements in crystals and its influence on the work of William Lawrence Bragg.

Reactions of atomic oxygen with the chlorate ion and the perchlorate ion

NASA Astrophysics Data System (ADS)

Anan'ev, Vladimir; Miklin, Mikhail; Kriger, Ludmila

2014-06-01

The reactions of the chlorate ion with atomic oxygen formed under photolysis of the nitrate ion introduced to potassium chlorate crystal by co-crystallization were studied by optical and infrared absorption spectroscopy. The perchlorate ion was found to form in solids as product of addition reaction of singlet atomic oxygen, formed under dissociation of the peroxynitrite ion - the product of isomerization of the excited nitrate ion. Triplet atomic oxygen does not react with the chlorate ion. The atomic oxygen formed under photolysis of the nitrate ion introduced to potassium perchlorate crystal by co-crystallization does not react with the perchlorate ion.

Atomic-Scale Design, Synthesis and Characterization of Two-Dimensional Material Interfaces

NASA Astrophysics Data System (ADS)

Kiraly, Brian Thomas

The reduction of material dimensions to near atomic-scales leads to changes in the properties of these materials. The most recent development in reduced dimensionality is the isolation of atomically thin materials with 2 "bulk" or large-scale dimensions. The isolation of a single plane of carbon atoms has thus paved the way for the study of material properties when one of three dimensions is confined. Early studies revealed a wealth of exotic physical phenomena in these two-dimensional (2D) layers due to the valence and crystalline symmetry of the materials, focusing primarily on understanding the intrinsic properties of the system. Recent studies have begun to investigate the influence that the surroundings have on the 2D material properties and how those effects may be used to tune the composite system properties. In this thesis, I will examine the synthesis and characterization of these 2D interfaces to understand how the constituents impact the overall observations and discuss how these interfaces might be used to deliberately manipulate 2D materials. I will begin by demonstrating how ultra-high vacuum (UHV) conditions enable the preparation and synthesis of 2D materials on air-unstable surfaces by utilizing a characteristic example of crystalline silver. The lack of catalytic activity of silver toward carbon-containing precursors is overcome by using atomic carbon to grow the graphene on the surface. The resulting system provides unique insight into graphene-metal interactions as it marks the lower boundary for graphene-metal interaction strength. I will then show how new 2D materials can be grown utilizing this growth motif, demonstrating the methodology with elemental silicon. The atomically thin 2D silicon grown on the silver surfaces clearly demonstrates a diamond-cubic crystal structure, including an electronic bandgap of 1eV. This work marks the realization of both a new 2D semiconductor and the direct scaling limit for bulk sp3 silicon. The common growth technique is extended to integrate the two 2D materials onto the same silver surface under vacuum conditions; these new interfaces reveal characteristics of van der Waals interactions and electronic decoupling from the metallic substrate. The heterogeneous 2D system provides key insight into the competition between physical and chemical interactions in this novel material system. Finally, a larger scale graphene-semiconductor interface is examined between graphene and crystalline germanium. The covalent-bonding of the germanium crystal provides strong anisotropy at the surface, leading to symmetry-dependent growth and behavior. These systems show unique tunability afforded by strain at the interface, leading to the potential for wafer-scale manipulation. These results clearly call for the treatment of 2D material interfaces as composite material systems, with effective properties derived from each constituent material.

Electronic dispersion from long-range atomic ordering and periodic potentials in two overlapping graphene sheets

NASA Astrophysics Data System (ADS)

Ohta, Taisuke; Robinson, Jeremy; Feibelman, Peter; Beechem, Thomas; Diaconescu, Bogdan; Bostwick, Aaron; Rotenberg, Eli; Kellogg, Gary

2013-03-01

A worldwide effort is underway to learn how to build devices that take advantage of the remarkable electronic properties of graphene and other two-dimensional crystals. An outstanding question is how stacking two or a few such crystals affects their joint electronic behavior. Our talk concerns ``twisted bilayer graphene (TBG),'' that is, two graphene layers azimuthally misoriented. Applying angle-resolved photoemission spectroscopy and density functional theory, we have found van Hove singularities (vHs) and associated mini-gaps in the TBG electronic spectrum, which represent unambiguous proof that the layers interact. Of particular interest is that the measured and calculated electronic dispersion manifests the periodicity of the moiré superlattice formed by the twist. Thus, there are vHs not just where the Dirac cones of the two layers overlap, but also at the boundaries of the moiré superlattice Brillouin zone. Moirés, ubiquitous in hybrid solids based on two-dimensional crystals, accordingly present themselves as tools for manipulating the electronic behavior. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Surface and interior views on origins of two types of banded spherulites in poly(nonamethylene terephthalate).

PubMed

Woo, Eamor M; Nurkhamidah, Siti; Chen, Yu-Fan

2011-10-21

Top-surface and three-dimensional views of Type-1 and Type-2 of ring-banded spherulites in poly(nonamethylene terephthalate) (PNT) in thicker bulk crystallized on a nucleating potassium bromide (KBr) substrate were examined using various microscopy techniques: scanning electron microscopy (SEM), polarized-optical microscopy (POM), and atomic-force microscopy (AFM). In PNT crystallized at higher crystallization temperature (T(c)) with heterogeneous nucleating substrate, typically two types of ring-banded spherulites are present that differ significantly in patterns and ring spacings: Type-1 Type-2 (single- and double-ring-banded spherulites). Three-dimensional view on fractured spherulites in bulk PNT samples reveals that the single-ring-banded spherulite (Type-1) tends to be well-rounded spheres as they are nucleated homogeneously from bulk; the double-ring-banded spherulite (Type-2) is concentric hemisphere or truncated sphere shells owing to be nucleated from bottom. With confined thickness of films, the 3-D hemispheres in PNT may become truncated into multi-shell annular cones or arcs when thickness or growth is restricted. Based on the top-surface vs. interior views of banded lamellar assembly, origins and inner structures of dual types of ring bands in PNT were examined in greater details. This journal is © the Owner Societies 2011

8-Hy­droxy­quinolin-1-ium hydrogen sulfate monohydrate

PubMed Central

Damous, Maamar; Dénès, George; Bouacida, Sofiane; Hamlaoui, Meriem; Merazig, Hocine; Daran, Jean-Claude

2013-01-01

In the crystal structure of the title salt hydrate, C9H8NO+·HSO4 −·H2O, the quinoline N—H atoms are hydrogen bonded to the bis­ulfate anions. The bis­ulfate anions and water mol­ecules are linked together by O—H⋯O hydrogen-bonding inter­actions. The cations and anions form separate layers alternating along the c axis, which are linked by N—H⋯O and O—H⋯O hydrogen bonds into a two-dimensional network parallel to (100). Further O—H⋯O contacts connect these layers, forming a three-dimensional network, in which two R 4 4(12) rings and C 2 2(13) infinite chains can be identified. PMID:24427083

Coulomb engineering of the bandgap and excitons in two-dimensional materials

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

Raja, Archana; Chaves, Andrey; Yu, Jaeeun

Here, the ability to control the size of the electronic bandgap is an integral part of solid-state technology. Atomically thin two-dimensional crystals offer a new approach for tuning the energies of the electronic states based on the unusual strength of the Coulomb interaction in these materials and its environmental sensitivity. Here, we show that by engineering the surrounding dielectric environment, one can tune the electronic bandgap and the exciton binding energy in monolayers of WS 2 and WSe 2 by hundreds of meV. We exploit this behaviour to present an in-plane dielectric heterostructure with a spatially dependent bandgap, as anmore » initial step towards the creation of diverse lateral junctions with nanoscale resolution.« less

Coulomb engineering of the bandgap and excitons in two-dimensional materials

DOE PAGES

Raja, Archana; Chaves, Andrey; Yu, Jaeeun; ...

2017-05-04

Here, the ability to control the size of the electronic bandgap is an integral part of solid-state technology. Atomically thin two-dimensional crystals offer a new approach for tuning the energies of the electronic states based on the unusual strength of the Coulomb interaction in these materials and its environmental sensitivity. Here, we show that by engineering the surrounding dielectric environment, one can tune the electronic bandgap and the exciton binding energy in monolayers of WS 2 and WSe 2 by hundreds of meV. We exploit this behaviour to present an in-plane dielectric heterostructure with a spatially dependent bandgap, as anmore » initial step towards the creation of diverse lateral junctions with nanoscale resolution.« less

Coulomb engineering of the bandgap and excitons in two-dimensional materials

PubMed Central

Raja, Archana; Chaves, Andrey; Yu, Jaeeun; Arefe, Ghidewon; Hill, Heather M.; Rigosi, Albert F.; Berkelbach, Timothy C.; Nagler, Philipp; Schüller, Christian; Korn, Tobias; Nuckolls, Colin; Hone, James; Brus, Louis E.; Heinz, Tony F.; Reichman, David R.; Chernikov, Alexey

2017-01-01

The ability to control the size of the electronic bandgap is an integral part of solid-state technology. Atomically thin two-dimensional crystals offer a new approach for tuning the energies of the electronic states based on the unusual strength of the Coulomb interaction in these materials and its environmental sensitivity. Here, we show that by engineering the surrounding dielectric environment, one can tune the electronic bandgap and the exciton binding energy in monolayers of WS2 and WSe2 by hundreds of meV. We exploit this behaviour to present an in-plane dielectric heterostructure with a spatially dependent bandgap, as an initial step towards the creation of diverse lateral junctions with nanoscale resolution. PMID:28469178

Accessibility of selenomethionine proteins by total chemical synthesis: structural studies of human herpesvirus-8 MIP-II.

PubMed

Shao, W; Fernandez, E; Wilken, J; Thompson, D A; Siani, M A; West, J; Lolis, E; Schweitzer, B I

1998-12-11

The determination of high resolution three-dimensional structures by X-ray crystallography or nuclear magnetic resonance (NMR) is a time-consuming process. Here we describe an approach to circumvent the cloning and expression of a recombinant protein as well as screening for heavy atom derivatives. The selenomethionine-modified chemokine macrophage inflammatory protein-II (MIP-II) from human herpesvirus-8 has been produced by total chemical synthesis, crystallized, and characterized by NMR. The protein has a secondary structure typical of other chemokines and forms a monomer in solution. These results indicate that total chemical synthesis can be used to accelerate the determination of three-dimensional structures of new proteins identified in genome programs.

Synthesis, structure characterization and optical properties of a new tripotassium cadmium pentaborate, K{sub 3}CdB{sub 5}O{sub 10}

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

Yu Hongwei; Graduate school of Chinese Academy of Sciences, Beijing 100049; Pan Shilie, E-mail: slpan@ms.xjb.ac.cn

A new ternary borate oxide, K{sub 3}CdB{sub 5}O{sub 10}, has been synthesized by solid-state reaction at 580 deg. C. The compound crystallizes in the monoclinic space group P2{sub 1}/n with a=7.6707 (7) A, b=19.1765 (17) A, c=7.8784 (6) A, {beta}=115.6083 (49){sup o}, and Z=4. The crystal structure consists of a two-dimensional infinite [CdB{sub 5}O{sub 10}] layer, which forms by connecting isolated double ring [B{sub 5}O{sub 10}] groups and CdO{sub 4} tetrahedra. K atoms filling in the interlayer and intralayer link the layers together and balance charge. The IR spectrum has been studied and confirmed the presence of both BO{sub 3}more » and BO{sub 4} groups, and the UV-vis-IR diffuse reflectance spectrum exhibits a band gap of about 3.4 eV. The DSC analysis proves that K{sub 3}CdB{sub 5}O{sub 10} is a congruent melting compound. - Graphical abstract: A new phase, K{sub 3}CdB{sub 5}O{sub 10}, has been discovered in the ternary K{sub 2}O-CdO-B{sub 2}O{sub 3} system. The crystal structure consists of a two-dimensional infinite [CdB{sub 5}O{sub 10}] layer. Highlights: > The compound, K{sub 3}CdB{sub 5}O{sub 10}, was synthesized and characterized for the first time. {yields}K{sub 3}CdB{sub 5}O{sub 10} is a congruent melting compound, which means the large single crystals could be grown from the melt using the Czochralski pulling method. {yields}The crystal structure consists of a two-dimensional infinite [CdB{sub 5}O{sub 10}].« less

Crystal structure of poly[N,N-diethyl-2-hy-droxy-ethan-1-aminium [μ3-cyanido-κ(3) C:C:N-di-μ-cyanido-κ(4) C:N-dicuprate(I)

PubMed

Corfield, Peter W R; Cleary, Emma; Michalski, Joseph F

2016-07-01

In the title compound, {(C6H16NO)[Cu2(CN)3]} n , the cyanide groups link the Cu(I) atoms into an open three-dimensional anionic network, with the mol-ecular formula Cu2(CN)3 (-). One Cu(I) atom is tetra-hedrally bound to four CN groups, and the other Cu(I) atom is bonded to three CN groups in an approximate trigonal-planar coordination. The tetra-hedrally coordinated Cu(I) atoms are linked into centrosymmetric dimers by the C atoms of two end-on bridging CN groups which bring the Cu(I) atoms into close contact at 2.5171 (7) Å. Two of the cyanide groups bonded to the Cu(I) atoms with trigonal-planar surrounding link the dimeric units into columns along the a axis, and the third links the columns together to form the network. The N,N-di-ethyl-ethano-lamine mol-ecules used in the synthesis have become protonated at the N atoms and are situated in cavities in the network, providing charge neutrality, with no covalent inter-actions between the cations and the anionic network.

Atomic-scale analysis of cation ordering in reduced calcium titanate.

PubMed

Li, Luying; Hu, Xiaokang; Jiang, Fan; Jing, Wenkui; Guo, Cong; Jia, Shuangfeng; Gao, Yihua; Wang, Jianbo

2017-11-03

The phenomenon of cation ordering is closely related to certain physical properties of complex oxides, which necessitates the search of underlying structure-property relationship at atomic resolution. Here we study the superlattices within reduced calcium titanate single crystal micro-pillars, which are unexpected from the originally proposed atomic model. Bright and dark contrasts at alternating Ti double layers perpendicular to b axis are clearly observed, but show no signs in corresponding image simulations based on the proposed atomic model. The multi-dimensional chemical analyses at atomic resolution reveal periodic lower Ti concentrations at alternating Ti double layers perpendicular to b axis. The following in-situ heating experiment shows no phase transition at the reported T c and temperature independence of the superlattices. The dimerization of the Ti-Ti bonds at neighboring double rutile-type chains within Ti puckered sheets are directly observed, which is found to be not disturbed by the cation ordering at alternating Ti double layers. The characterization of cation ordering of complex oxides from chemical and structural point of view at atomic resolution, and its reaction to temperature variations are important for further understanding their basic physical properties and exploiting potential applications.

Poly[tetra­aqua­(μ6-9,10-dioxo-9,10-dihydro­anthracene-1,4,5,8-tetra­carboxyl­ato)dimanganese(II)

PubMed Central

Xu, Rui; Liu, Jian-Lan

2012-01-01

The title complex, [Mn2(C18H4O10)(H2O)4]n, was synthesized from manganese(II) chloride tetra­hydrate and 9,10-dioxo-9,10-dihydro­anthracene-1,4,5,8-tetra­carb­oxy­lic acid (H4AQTC) in water. The anthraquinone unit is located about a crystallographic center of inversion. Each asymmetric unit therefore contains one MnII atom, two water ligands and one half AQTC4− anion. The MnII atom is coordinated in a distorted octa­hedral geometry by four O atoms from three AQTC4− ligands and two water O atoms. Two of the carboxyl­ate groups coordinate one MnII atom in a chelating mode, whereas the others each coordinate two MnII atoms. Each AQTC4− tetra-anion therefore coordinates six different MnII ions and, as a result, a three-dimensional coordination polymer is formed. O—H⋯O hydrogen bonds, some of them bifurcated, between water ligands and neighboring water or anthraquinone ligands are observed in the crystal structure. PMID:22807779

First-principles study of hydrogen-bonded molecular conductor κ -H3(Cat-EDT-TTF/ST)2

NASA Astrophysics Data System (ADS)

Tsumuraya, Takao; Seo, Hitoshi; Kato, Reizo; Miyazaki, Tsuyoshi

2015-07-01

We theoretically study hydrogen-bonded molecular conductors synthesized recently, κ -H3(Cat-EDT-TTF) 2 and its diselena analog, κ -H3(Cat-EDT-ST) 2, by first-principles density functional theory calculations. In these crystals, two H(Cat-EDT-TTF/ST) units share a hydrogen atom with a short O-H-O hydrogen bond. The calculated band structure near the Fermi level shows a quasi-two-dimensional character with a rather large interlayer dispersion due to the absence of insulating layers, in contrast with conventional molecular conductors. We discuss effective low-energy models based on H(Cat-EDT-TTF/ST) units and its dimers, respectively, where the microscopic character of the orbitals composing them are analyzed. Furthermore, we find a stable structure which is different from the experimentally determined structure, where the shared hydrogen atom becomes localized to one of the oxygen atoms, in which charge disproportionation between the two types of H(Cat-EDT-TTF) units is associated. The calculated potential energy surface for the H atom is very shallow near the minimum points; therefore the probability of the H atom can be delocalized between the two O atoms.

Crystal structure of tetra-aqua-bis(3,5-di-amino-4H-1,2,4-triazol-1-ium)cobalt(II) bis-[bis-(pyridine-2,6-di-carboxyl-ato)cobaltate(II)] dihydrate.

PubMed

Johnson, Atim; Mbonu, Justina; Hussain, Zahid; Loh, Wan-Sin; Fun, Hoong-Kun

2015-06-01

The asymmetric unit of the title compound, [Co(C2H6N5)2(H2O)4][Co(C7H3NO4)2]2·2H2O, features 1.5 Co(II) ions (one anionic complex and one half cationic complex) and one water mol-ecule. In the cationic complex, the Co(II) atom is located on an inversion centre and is coordinated by two triazolium cations and four water mol-ecules, adopting an octa-hedral geometry where the N atoms of the two triazolium cations occupy the axial positions and the O atoms of the four water mol-ecules the equatorial positions. The two triazole ligands are parallel offset (with a distance of 1.38 Å between their planes). In the anionic complex, the Co(II) ion is six-coordinated by two N and four O atoms of the two pyridine-2,6-di-carboxyl-ate anions, exhibiting a slightly distorted octa-hedral coordination geometry in which the mean plane of the two pyridine-2,6-di-carboxyl-ate anions are almost perpendicular to each other, making a dihedral angle of 85.87 (2)°. In the crystal, mol-ecules are linked into a three-dimensional network via C-H⋯O, C-H⋯N, O-H⋯O and N-H⋯O hydrogen bonds.

Molarity (Aromic Density) of the Elements as Pure Crystals.

ERIC Educational Resources Information Center

Pauling, Linus; Herman, Zelek S.

1985-01-01

Provides background information for teachers on the atomic density of the elements as pure crystals. Atomic density is defined as the reciprocal of the atomic volume. Includes atomic-density diagrams which were prepared using the atomic-volume values given by Singman, supplemented by additional values for some allotropes. (JN)

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

NASA Astrophysics Data System (ADS)

Carey, Benjamin J.; Ou, Jian Zhen; Clark, Rhiannon M.; Berean, Kyle J.; Zavabeti, Ali; Chesman, Anthony S. R.; Russo, Salvy P.; Lau, Desmond W. M.; Xu, Zai-Quan; Bao, Qiaoliang; Kevehei, Omid; Gibson, Brant C.; Dickey, Michael D.; Kaner, Richard B.; Daeneke, Torben; Kalantar-Zadeh, Kourosh

2017-02-01

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (~1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals.

PubMed

Carey, Benjamin J; Ou, Jian Zhen; Clark, Rhiannon M; Berean, Kyle J; Zavabeti, Ali; Chesman, Anthony S R; Russo, Salvy P; Lau, Desmond W M; Xu, Zai-Quan; Bao, Qiaoliang; Kevehei, Omid; Gibson, Brant C; Dickey, Michael D; Kaner, Richard B; Daeneke, Torben; Kalantar-Zadeh, Kourosh

2017-02-17

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

PubMed Central

Carey, Benjamin J.; Ou, Jian Zhen; Clark, Rhiannon M.; Berean, Kyle J.; Zavabeti, Ali; Chesman, Anthony S. R.; Russo, Salvy P.; Lau, Desmond W. M.; Xu, Zai-Quan; Bao, Qiaoliang; Kavehei, Omid; Gibson, Brant C.; Dickey, Michael D.; Kaner, Richard B.; Daeneke, Torben; Kalantar-Zadeh, Kourosh

2017-01-01

A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes. PMID:28211538

A disorder-enhanced quasi-one-dimensional superconductor

PubMed Central

Petrović, A. P.; Ansermet, D.; Chernyshov, D.; Hoesch, M.; Salloum, D.; Gougeon, P.; Potel, M.; Boeri, L.; Panagopoulos, C.

2016-01-01

A powerful approach to analysing quantum systems with dimensionality d>1 involves adding a weak coupling to an array of one-dimensional (1D) chains. The resultant quasi-1D (q1D) systems can exhibit long-range order at low temperature, but are heavily influenced by interactions and disorder due to their large anisotropies. Real q1D materials are therefore ideal candidates not only to provoke, test and refine theories of strongly correlated matter, but also to search for unusual emergent electronic phases. Here we report the unprecedented enhancement of a superconducting instability by disorder in single crystals of Na2−δMo6Se6, a q1D superconductor comprising MoSe chains weakly coupled by Na atoms. We argue that disorder-enhanced Coulomb pair-breaking (which usually destroys superconductivity) may be averted due to a screened long-range Coulomb repulsion intrinsic to disordered q1D materials. Our results illustrate the capability of disorder to tune and induce new correlated electron physics in low-dimensional materials. PMID:27448209

A disorder-enhanced quasi-one-dimensional superconductor.

PubMed

Petrović, A P; Ansermet, D; Chernyshov, D; Hoesch, M; Salloum, D; Gougeon, P; Potel, M; Boeri, L; Panagopoulos, C

2016-07-22

A powerful approach to analysing quantum systems with dimensionality d>1 involves adding a weak coupling to an array of one-dimensional (1D) chains. The resultant quasi-1D (q1D) systems can exhibit long-range order at low temperature, but are heavily influenced by interactions and disorder due to their large anisotropies. Real q1D materials are therefore ideal candidates not only to provoke, test and refine theories of strongly correlated matter, but also to search for unusual emergent electronic phases. Here we report the unprecedented enhancement of a superconducting instability by disorder in single crystals of Na2-δMo6Se6, a q1D superconductor comprising MoSe chains weakly coupled by Na atoms. We argue that disorder-enhanced Coulomb pair-breaking (which usually destroys superconductivity) may be averted due to a screened long-range Coulomb repulsion intrinsic to disordered q1D materials. Our results illustrate the capability of disorder to tune and induce new correlated electron physics in low-dimensional materials.

Ferromagnetic coupling in the three-dimensional malonato-bridged gadoliniumIII complex [Gd2(mal)3(H2O)6] (H2mal = malonic acid).

PubMed

Hernández-Molina, María; Ruiz-Pérez, Catalina; López, Trinidad; Lloret, Francesc; Julve, Miguel

2003-09-08

The novel gadolinium(III) complex of formula [Gd(2)(mal)(3)(H(2)O)(6)] (1) (H(2)mal = 1,3-propanedioic acid) has been prepared and characterized by X-ray diffraction analysis. Crystal data for 1: monoclinic, space group I2/a, a = 11.1064(10) A, b = 12.2524(10) A, c =13.6098(2) A, beta = 92.925(10) degrees, U = 1849.5(3) A(3), Z = 4. Compound 1 is a three-dimensional network made up of malonate-bridged gadolinium(III) ions where the malonate exhibits two bridging modes, eta(5)-bidentate + unidentate and eta(3):eta(3) + bis(unidentate). The gadolinium atom is nine-coordinate with three water molecules and six malonate oxygen atoms from three malonate ligands forming a distorted monocapped square antiprism. The shortest metal-metal separations are 4.2763(3) A [through the oxo-carboxylate bridge] and 6.541(3) A [through the carboxylate in the anti-syn coordination mode]. The value of the angle at the oxo-carboxylate atom is 116.8(2) degrees. Variable-temperature magnetic susceptibility measurements reveal the occurrence of a significant ferromagnetic interaction through the oxo-carboxylate pathway (J = +0.048(1) cm(-1), H = -JS(Gd(1)) x S(Gd(1a))).

Dynamics of metal-induced crystallization of ultrathin Ge films by rapid thermal annealing

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

Liao, Yuanxun; Huang, Shujuan; Shrestha, Santosh

2015-12-07

Though Ge crystallization has been widely studied, few works investigate metal-induced crystallization of ultrathin Ge films. For 2 nm Ge films in oxide matrix, crystallization becomes challenging due to easy oxidation and low mobility of Ge atoms. Introducing metal atoms may alleviate these problems, but the functions and the behaviours of metal atoms need to be clarified. This paper investigates the crystallization dynamics of a multilayer structure 1.9 nm Ge/0.5 nm Al/1.5 nm Al{sub 2}O{sub 3} under rapid thermal annealing (RTA). The functions of metal atoms, like effective anti-oxidation, downshifting Raman peaks, and incapability to decrease crystallization temperature, are found and explained. The metalmore » behaviours, such as inter-diffusion and defect generation, are supported with direct evidences, Al-Ge nanobicrystals, and Al cluster in Ge atoms. With these understandings, a two-step RTA process achieves high-quality 2 nm nanocrystal Ge films with Raman peak at 298 cm{sup −1} of FWHM 10.3 cm{sup −1} and atomic smooth interfaces.« less

Hydrothermal synthesis and characterization of a two-dimensional piperazinium cobalt–zinc phosphate via a metastable one-dimensional phase

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

Torre-Fernández, Laura; Khainakova, Olena A.; Espina, Aránzazu

2015-05-15

A two-dimensional piperazinium cobalt–zinc phosphate, formulated as (C{sub 4}N{sub 2}H{sub 12}){sub 1.5}(Co{sub 0.6}Zn{sub 0.4}){sub 2}(HPO{sub 4}){sub 2}(PO{sub 4})·H{sub 2}O (2D), was synthesized under hydrothermal conditions. The crystal structure was determined using single-crystal X-ray diffraction data (monoclinic P2{sub 1}/c, a=8.1165(3) Å, b=26.2301(10) Å, c=8.3595(4) Å, and β=110.930(5)°) and the hydrogen atom positions were optimized by DFT calculations. A single-crystal corresponding to one-dimensional metastable phase, (C{sub 4}N{sub 2}H{sub 12})Co{sub 0.3}Zn{sub 0.7}(HPO{sub 4}){sub 2}·H{sub 2}O (1D), was also isolated and the crystal structure was determined (monoclinic P2{sub 1}/c, a=8.9120(6) Å, b=14.0290(1) Å, c=12.2494(5) Å, and β=130.884(6)°). The bulk was characterized by chemical (C–H–N)more » analysis, powder X-ray diffraction (PXRD), powder X-ray thermodiffractometry (HT-XRD), transmission electron microscopy (STEM(DF)-EDX and EFTEM), and thermal analysis (TG/SDTA-MS), including activation energy data of its thermal decomposition. The magnetic susceptibility and magnetization measurements show no magnetic ordering down to 4 K. - Graphical abstract: Hydrothermal synthesis and structural characterization of a two-dimensional piperazinium cobalt–zinc phosphate, (C{sub 4}N{sub 2}H{sub 12}){sub 1.5}(Co{sub 0.6}Zn{sub 0.4}){sub 2}(HPO{sub 4}){sub 2}(PO{sub 4})·H{sub 2}O (2D), have been reported. The crystal structure of a one-dimensional piperazinium cobalt–zinc phosphate, (C{sub 4}N{sub 2}H{sub 12})Co{sub 0.3}Zn{sub 0.7}(HPO{sub 4}){sub 2}·H{sub 2}O (1D) a metastable phase during the hydrothermal synthesis, was also determined. The thermal behavior of 2D compound is strongly dependent on the selected heating rate and the magnetic susceptibility and magnetization measurements show no magnetic ordering down to 4 K. - Highlights: • A 2D piperazinium cobalt–zinc phosphate has been synthesized and characterized. • Crystal structure of 1D metastable phase was also determined. • Thermal behavior of 2D compound is strongly dependent on the selected heating rate. • Magnetic measurements show no magnetic ordering down to 4 K.« less

Reflection spectra and their angular dependences of one-dimensional photonic crystals based on aluminium oxide

NASA Astrophysics Data System (ADS)

Gorelik, V. S.; Yashin, M. M.; Pudovkin, A. V.; Vodchits, A. I.

2017-11-01

The article considers optical properties (transmission and reflection) of one-dimensional photonic crystals based on mesoporous anodic aluminum oxide, with periods of crystal lattices 188 and 194 nm. A comparison of the experimentally measured reflection spectrum in the spectral region of the first stop-zone with the theoretical dependence obtained from the dispersion relation for one-dimensional photonic crystal is carried out. The angular dependence of the first stop-zone spectral positions of one-dimensional photonic crystal is established. The authors analyze the possibility of applications of mesoporous one-dimensional photonic crystals based on aluminum oxide as the selective narrowband filters and mirrors.

Description of the atomic disorder (local order) in crystals by the mixed-symmetry method

NASA Astrophysics Data System (ADS)

Dudka, A. P.; Novikova, N. E.

2017-11-01

An approach to the description of local atomic disorder (short-range order) in single crystals by the mixed-symmetry method based on Bragg scattering data is proposed, and the corresponding software is developed. In defect-containing crystals, each atom in the unit cell can be described by its own symmetry space group. The expression for the calculated structural factor includes summation over different sets of symmetry operations for different atoms. To facilitate the search for new symmetry elements, an "atomic disorder expert" was developed, which estimates the significance of tested models. It is shown that the symmetry lowering for some atoms correlates with the existence of phase transitions (in langasite family crystals) and the anisotropy of physical properties (in rare-earth dodecaborides RB12).

Highly robust crystalsome via directed polymer crystallization at curved liquid/liquid interface

PubMed Central

Wang, Wenda; Qi, Hao; Zhou, Tian; Mei, Shan; Han, Lin; Higuchi, Takeshi; Jinnai, Hiroshi; Li, Christopher Y.

2016-01-01

Lipids and amphiphilic block copolymers spontaneously self-assemble in water to form a plethora of micelles and vesicles. They are typically fluidic in nature and often mechanically weak for applications such as drug delivery and gene therapeutics. Mechanical properties of polymeric materials could be improved by forming crystalline structures. However, most of the self-assembled micelles and vesicles have curved surfaces and precisely tuning crystallization within a nanoscale curved space is challenging, as the curved geometry is incommensurate with crystals having three-dimensional translational symmetry. Herein, we report using a miniemulsion crystallization method to grow nanosized, polymer single-crystal-like capsules. We coin the name crystalsome to describe this unique structure, because they are formed by polymer lamellar crystals and their structure mimics liposomes and polymersomes. Using poly(L-lactic acid) (PLLA) as the model polymer, we show that curved water/p-xylene interface formed by the miniemulsion process can guide the growth of PLLA single crystals. Crystalsomes with the size ranging from ∼148 nm to over 1 μm have been formed. Atomic force microscopy measurement demonstrate a two to three orders of magnitude increase in bending modulus compared with conventional polymersomes. We envisage that this novel structure could shed light on investigating spherical crystallography and drug delivery. PMID:26837260

Direct k-space imaging of Mahan cones at clean and Bi-covered Cu(111) surfaces

NASA Astrophysics Data System (ADS)

Winkelmann, Aimo; Akin Ünal, A.; Tusche, Christian; Ellguth, Martin; Chiang, Cheng-Tien; Kirschner, Jürgen

2012-08-01

Using a specifically tailored experimental approach, we revisit the exemplary effect of photoemission from quasi-free electronic states in crystals. Applying a momentum microscope, we measure photoelectron momentum patterns emitted into the complete half-space above the sample after excitation from a linearly polarized laser light source. By the application of a fully three-dimensional (3D) geometrical model of direct optical transitions, we explain the characteristic intensity distributions that are formed by the photoelectrons in k-space under the combination of energy conservation and crystal momentum conservation in the 3D bulk as well as at the two-dimensional (2D) surface. For bismuth surface alloys on Cu(111), the energy-resolved photoelectron momentum patterns allow us to identify specific emission processes in which bulk excited electrons are subsequently diffracted by an atomic 2D surface grating. The polarization dependence of the observed intensity features in momentum space is explained based on the different relative orientations of characteristic reciprocal space directions with respect to the electric field vector of the incident light.

DHS Internship Summary-Crystal Assembly at Different Length Scales

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

Mishchenko, L

2009-08-06

I was part of a project in which in situ atomic force microscopy (AFM) was used to monitor growth and dissolution of atomic and colloidal crystals. At both length scales, the chemical environment of the system greatly altered crystal growth and dissolution. Calcium phosphate was used as a model system for atomic crystals. A dissolution-reprecipitation reaction was observed in this first system, involving the conversion of brushite (DCPD) to octacalcium phosphate (OCP). In the second system, polymeric colloidal crystals were dissolved in an ionic solvent, revealing the underlying structure of the crystal. The dissolved crystal was then regrown through anmore » evaporative step method. Recently, we have also found that colloids can be reversibly deposited in situ onto an ITO (indium tin oxide) substrate via an electrochemistry setup. The overall goal of this project was to develop an understanding of the mechanisms that control crystallization and order, so that these might be controlled during material synthesis. Controlled assembly of materials over a range of length scales from molecules to nanoparticles to colloids is critical for designing new materials. In particular, developing materials for sensor applications with tailorable properties and long range order is important. In this work, we examine two of these length scales: small molecule crystallization of calcium phosphate (whose crystal phases include DCPD, OCP, and HAP) and colloidal crystallization of Poly(methyl methacrylate) beads. Atomic Force Microscopy is ideal for this line of work because it allows for the possibility of observing non-conducting samples in fluid during growth with high resolution ({approx} 10 nm). In fact, during atomic crystal growth one can observe changes in atomic steps, and with colloidal crystals, one can monitor the individual building blocks of the crystal. Colloids and atoms crystallize under the influence of different forces acting at different length scales as seen in Table 1. In particular, molecular crystals, which are typically dominated by ionic and covalent bonding, are an order of magnitude more strongly bonded than colloidal crystals. In molecular crystals, ordering is driven by the interaction potentials between molecules. By contrast, colloidal assembly is a competition between the repulsive electrostatic forces that prevent aggregation in solution (due to surface charge), and short-range van der Waals and entropic forces that leads to ordering. Understanding atomic crystallization is fundamentally important for fabrication of tailorable crystalline materials, for example for biological or chemical sensors. The transformation of brushite to OCP not only serves as a model system for atomic crystal growth (applicable to many other crystal growth processes), but is also important in bone cements. Colloidal crystals have unique optical properties which respond to chemical and mechanical stimuli, making them very important for sensing applications. The mechanism of colloidal crystal assembly is thus fundamentally important. Our in situ dissolution and regrowth experiments are one good method of analyzing how these crystals pack under different conditions and how defect sites are formed and filled. In these experiments, a silica additive was used to strengthen the colloidal crystal during initial assembly (ex situ) and to increase domain size and long range order. Reversible electrodeposition of colloids onto a conductive substrate (ITO in our case) is another system which can further our knowledge of colloidal assembly. This experiment holds promise of allowing in situ observation of colloidal crystal growth and the influence of certain additives on crystal order. The ultimate goal would be to achieve long range order in these crystals by changing the surface charge or the growth environment.« less

Signatures of exciton condensation in a transition metal dichalcogenide

NASA Astrophysics Data System (ADS)

Kogar, Anshul; Rak, Melinda S.; Vig, Sean; Husain, Ali A.; Flicker, Felix; Joe, Young Il; Venema, Luc; MacDougall, Greg J.; Chiang, Tai C.; Fradkin, Eduardo; van Wezel, Jasper; Abbamonte, Peter

2017-12-01

Bose condensation has shaped our understanding of macroscopic quantum phenomena, having been realized in superconductors, atomic gases, and liquid helium. Excitons are bosons that have been predicted to condense into either a superfluid or an insulating electronic crystal. Using the recently developed technique of momentum-resolved electron energy-loss spectroscopy (M-EELS), we studied electronic collective modes in the transition metal dichalcogenide semimetal 1T-TiSe2. Near the phase-transition temperature (190 kelvin), the energy of the electronic mode fell to zero at nonzero momentum, indicating dynamical slowing of plasma fluctuations and crystallization of the valence electrons into an exciton condensate. Our study provides compelling evidence for exciton condensation in a three-dimensional solid and establishes M-EELS as a versatile technique sensitive to valence band excitations in quantum materials.

Hidden topological constellations and polyvalent charges in chiral nematic droplets

NASA Astrophysics Data System (ADS)

Posnjak, Gregor; Čopar, Simon; Muševič, Igor

2017-02-01

Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=-2, -3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules.

Hidden topological constellations and polyvalent charges in chiral nematic droplets

PubMed Central

Posnjak, Gregor; Čopar, Simon; Muševič, Igor

2017-01-01

Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=−2, −3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules. PMID:28220770

Crystal structure of (±)-1-({[4-(all­yloxy)phen­yl]sulfan­yl}meth­yl)-2-(di­phenyl­thio­phosphor­yl)ferrocene

PubMed Central

Michelot, Audric; Sarda, Stéphanie; Daran, Jean-Claude; Deydier, Eric; Manoury, Eric

2015-01-01

The title compound, [Fe(C5H5)(C27H24OPS2)], is built up from a ferrocene moiety substituted in the 1- and 2-positions by {[4-(all­yloxy)phen­yl]sulfan­yl}methyl and di­phenyl­thio­phosphoryl groups, respectively. The two S atoms lie on opposite sides of the cyclo­penta­dienyl ring plane to which they are attached. In the crystal, C—H⋯S hydrogen bonds link the mol­ecules into a ribbon running parallel to the (-110) plane. C—H⋯π inter­actions link the ribbons to form a three-dimensional network. PMID:26396768

The young person's guide to the PDB.

PubMed

Minor, Wladek; Dauter, Zbigniew; Jaskolski, Mariusz

The Protein Data Bank (PDB), created in 1971 when merely seven protein crystal structures were known, today holds over 120, 000 experimentally-determined three-dimensional models of macromolecules, including gigantic structures comprised of hundreds of thousands of atoms, such as ribosomes and viruses. Most of the deposits come from X-ray crystallography experiments, with important contributions also made by NMR spectroscopy and, recently, by the fast growing Cryo-Electron Microscopy. Although the determination of a macromolecular crystal structure is now facilitated by advanced experimental tools and by sophisticated software, it is still a highly complicated research process requiring specialized training, skill, experience and a bit of luck. Understanding the plethora of structural information provided by the PDB requires that its users (consumers) have at least a rudimentary initiation. This is the purpose of this educational overview.

Multiscale Microstructures and Microstructural Effects on the Reliability of Microbumps in Three-Dimensional Integration

PubMed Central

Huang, Zhiheng; Xiong, Hua; Wu, Zhiyong; Conway, Paul; Altmann, Frank

2013-01-01

The dimensions of microbumps in three-dimensional integration reach microscopic scales and thus necessitate a study of the multiscale microstructures in microbumps. Here, we present simulated mesoscale and atomic-scale microstructures of microbumps using phase field and phase field crystal models. Coupled microstructure, mechanical stress, and electromigration modeling was performed to highlight the microstructural effects on the reliability of microbumps. The results suggest that the size and geometry of microbumps can influence both the mesoscale and atomic-scale microstructural formation during solidification. An external stress imposed on the microbump can cause ordered phase growth along the boundaries of the microbump. Mesoscale microstructures formed in the microbumps from solidification, solid state phase separation, and coarsening processes suggest that the microstructures in smaller microbumps are more heterogeneous. Due to the differences in microstructures, the von Mises stress distributions in microbumps of different sizes and geometries vary. In addition, a combined effect resulting from the connectivity of the phase morphology and the amount of interface present in the mesoscale microstructure can influence the electromigration reliability of microbumps. PMID:28788356

Growth of nano hexagon-like flake arrays cerium carbonate created with PAH as the substrate

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

Li, M., E-mail: limei@imust.cn; School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Department of Inorganic and Metalloid Materials, Key Laboratory of New Technologies of Modern Metallurgy and Application of Rare Materials, Baotou 014010; Hu, Y.H., E-mail: bthyh@163.com

Petals-like Ce{sub 2}(CO{sub 3}){sub 3} on Ce{sub 2}(CO{sub 3}){sub 3} nano hexagon-like flake arrays have been precipitatingly fabricated using PAH substrates. By changing the way of feeding, PAH concentration and aging time, petals-like Ce{sub 2}(CO{sub 3}){sub 3} was created best when adding PAH into the Ce(NO{sub 3}){sub 3} solution, joined (NH{sub 4}){sub 2}CO{sub 3} solution along with mixing, PAH concentration is 0.9 g/L, aging time is 4 h. A growth mechanism was proposed to account for the growth of the petals-like Ce{sub 2}(CO{sub 3}){sub 3} with PAH as the substrate. Poly allylamine hydrochloride (PAH) is as template agent which formsmore » π-allyl complex with Ce{sup 3+} and controls the morphology of Ce{sub 2}(CO{sub 3}){sub 3} particle. PAH and Ce{sup 3+} form π-allyl complex, and then induce the formation of Ce{sub 2}(CO{sub 3}){sub 3} crystal nucleus. And infrared spectrum analysis verified. XRD show that after adding PAH which is adsorbed on the crystal plane, the growth of Ce{sub 2}(CO{sub 3}){sub 3} crystal is inhibited on (2 4 2), the growth is promoted on (2 0 2) which is differentiated into the new (1 5 1), (2 2 2) is unchanged, Ce{sub 2}(CO{sub 3}){sub 3} crystal is accumulated petals shape by hexagon-like flake. UV absorption spectra show that CeO{sub 2} as prepared precursor Ce{sub 2}(CO{sub 3}){sub 3} after calcinations in air at high temperatures, the petal-like CeO{sub 2} has strong UV absorption and reflection effects, and absorption interval changed significantly by the move to UVA from UVB. - Graphical abstract: Each Ce-atom connects three Cl-atoms and three allyls in three dimensional spaces. To take the plane as a reference plane which is arrayed with three Ce-atom as equilateral triangle. The triangular each vertex is Ce-atom, the triangular center place is Cl-atom, the equilateral triangle which is mutually perpendicular with Ce-triangle surface and the inclined angle is 60° is made up with three Cl-atoms. - Highlights: • Petals-like Ce{sub 2}(CO{sub 3}){sub 3} were synthesized with PAH. • PAH and Ce{sup 3+} form π-allyl complex. • The growth crystal is inhibited on (2 4 2) and promoted on (2 0 2). • CeO{sub 2} absorption interval changed by the move to UVA from UVB.« less

Aberrated surface soliton formation in a nonlinear 1D and 2D photonic crystal

PubMed Central

Lysak, Tatiana M.; Trykin, Evgenii M.

2018-01-01

We discuss a novel type of surface soliton—aberrated surface soliton—appearance in a nonlinear one dimensional photonic crystal and a possibility of this surface soliton formation in two dimensional photonic crystal. An aberrated surface soliton possesses a nonlinear distribution of the wavefront. We show that, in one dimensional photonic crystal, the surface soliton is formed at the photonic crystal boundary with the ambient medium. Essentially, that it occupies several layers at the photonic crystal boundary and penetrates into the ambient medium at a distance also equal to several layers, so that one can infer about light energy localization at the lateral surface of the photonic crystal. In the one dimensional case, the surface soliton is formed from an earlier formed soliton that falls along the photonic crystal layers at an angle which differs slightly from the normal to the photonic crystal face. In the two dimensional case, the soliton can appear if an incident Gaussian beam falls on the photonic crystal face. The influence of laser radiation parameters, optical properties of photonic crystal layers and ambient medium on the one dimensional surface soliton formation is investigated. We also discuss the influence of two dimensional photonic crystal configuration on light energy localization near the photonic crystal surface. It is important that aberrated surface solitons can be created at relatively low laser pulse intensity and for close values of alternating layers dielectric permittivity which allows their experimental observation. PMID:29558497

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

Gill, Tobias G.; Fleurence, Antoine; Warner, Ben

We observe a new two-dimensional (2D) silicon crystal, using low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) and it's formed by depositing additional Si atoms onto spontaneously-formed epitaxial silicene on a ZrB 2 thin film. From scanning tunnelling spectroscopy (STS) studies, we find that this atomically-thin layered silicon has distinctly different electronic properties. Angle resolved photoelectron spectroscopy (ARPES) reveals that, in sharp contrast to epitaxial silicene, the layered silicon exhibits significantly enhanced density of states at the Fermi level resulting from newly formed metallic bands. Furthermore, the 2D growth of this material could allow for direct contacting tomore » the silicene surface and demonstrates the dramatic changes in electronic structure that can occur by the addition of even a single monolayer amount of material in 2D systems.« less

Bromidotetra­kis­(1H-2-ethyl-5-methyl­imidazole-κN 3)copper(II) bromide

PubMed Central

Godlewska, Sylwia; Baranowska, Katarzyna; Socha, Joanna; Dołęga, Anna

2011-01-01

The CuII ion in the title compound, [CuBr(C6H10N2)4]Br, is coordinated in a square-based-pyramidal geometry by the N atoms of four imidazole ligands and a bromide anion in the apical site. Both the CuII and Br− atoms lie on a crystallographic fourfold axis. In the crystal, the [CuBr(C6H10N2)4]+ complex cations are linked to the uncoordinated Br− anions (site symmetry ) by N—H⋯Br hydrogen bonds, generating a three-dimensional network. The ethyl group of the imidazole ligand was modelled as disordered over two orientations with occupancies of 0.620 (8) and 0.380 (8). PMID:22199662

1-(Prop-2-yn-yl)indoline-2,3-dione.

PubMed

Qachchachi, Fatima-Zahrae; Ouazzani Chahdi, Fouad; Misbahi, Houria; Bodensteiner, Michael; El Ammari, Lahcen

2014-03-01

The structure of the title compound, C11H7NO2, is isotypic to that of its homologue, 1-octylindoline-2,3-dione [Qachchachi et al. (2013 ▶). Acta Cryst. E69, o1801]. The indoline ring and the two carbonyl O atoms are approximately coplanar, the largest deviation from the mean plane being 0.021 (1) Å for one of the O atoms. The mean plane through the fused ring system is nearly perpendicular to the propynyl group, as indicated by the N-C-C-C torsion angle of 77.9 (1)°. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds and π-π inter-actions between benzene rings [inter-centroid distance = 3.5630 (10) Å], forming a three-dimensional structure.

Integrated digital inverters based on two-dimensional anisotropic ReS2 field-effect transistors

PubMed Central

Liu, Erfu; Fu, Yajun; Wang, Yaojia; Feng, Yanqing; Liu, Huimei; Wan, Xiangang; Zhou, Wei; Wang, Baigeng; Shao, Lubin; Ho, Ching-Hwa; Huang, Ying-Sheng; Cao, Zhengyi; Wang, Laiguo; Li, Aidong; Zeng, Junwen; Song, Fengqi; Wang, Xinran; Shi, Yi; Yuan, Hongtao; Hwang, Harold Y.; Cui, Yi; Miao, Feng; Xing, Dingyu

2015-01-01

Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS2) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS2 field-effect transistors, which exhibit competitive performance with large current on/off ratios (∼107) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconducting materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS2 anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications. PMID:25947630

Potassium deca­borate monohydrate

PubMed Central

Gao, Yi-Hong

2011-01-01

In the crystal structure of the title compound, K2[B10O14(OH)4]·H2O, the polyborate [B10O14(OH)4]2− anions are linked together through their common O atoms, forming a helical chain-like structure. Adjacent chains are further connected into a three-dimensional structure by O—H⋯O hydrogen bonds. The water mol­ecules and potassium cations are located between these chains. Further O—H⋯O hydrogen bonds occur between the anions and the water mol­ecules PMID:22058681

catena-Poly[[triphenyl-tin(IV)]-μ-phenyl-phosphinato-κO:O'].

PubMed

Diop, Tidiane; Diop, Libasse; Kociok-Köhn, Gabriele; Molloy, Kieran C; Stoeckli-Evans, Helen

2011-12-01

In the structure of the title coordination polymer, [Sn(C(6)H(5))(3)(C(6)H(6)O(2)P)](n) or [PhP(H)O(2)Sn(IV)(Ph)(3)](n), the Sn(IV) atom is five-coordinate, with the SnC(3)O(2) framework in a trans trigonal-bipyramidal arrangement having the PhP(H)O(2) (-) anions in apical positions. In the crystal, neighbouring polymer chains are linked via C-H⋯π inter-actions, forming a two-dimensional network lying parallel to (001).

2-Ferrocenyl-6-methyl­pyridin-3-ol

PubMed Central

Wang, Zhi-Qiang; Xu, Chen; Cen, Fei-Fei; Li, Ying-Fei; Ji, Bao-Ming

2008-01-01

In the title compound, [Fe(C5H5)(C11H10NO)], the dihedral angle between the pyridyl and substituted cyclo­penta­dienyl rings is 20.4 (3)°. The H atoms of the methyl group are disordered over two positions; their site-occupation factors were fixed at 0.5. The crystal structure is stabilized by well defined inter­molecular O—H⋯N and C—H⋯O hydrogen bonds, leading to the formation of a two-dimensional network parallel to (101). PMID:21581222

Bromidotetra­kis­(2-ethyl-1H-imidazole-κN 3)copper(II) bromide

PubMed Central

Godlewska, Sylwia; Kelm, Harald; Krüger, Hans-Jörg; Dołęga, Anna

2012-01-01

The CuII ion in the title mol­ecular salt, [CuBr(C5H8N2)4]Br, is coordinated in a square-pyramidal geometry by four N atoms of imidazole ligands and one bromide anion in the apical position. In the crystal, the ions are linked by N—H⋯Br hydrogen bonds involving both the coordinating and the free bromide species as acceptors. A C—H⋯Br inter­action is also observed. Overall, a three-dimensional network results. PMID:23468738

Synthesis, crystal structure and optical properties of a novel sodium lead pentaborate, NaPbB{sub 5}O{sub 9}

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

Zhang, Min; Graduate University of Chinese Academy of Sciences, Beijing 100049; Pan, Shilie, E-mail: slpan@ms.xjb.ac.c

A novel sodium lead pentaborate, NaPbB{sub 5}O{sub 9}, has been successfully synthesized by standard solid-state reaction. The single-crystal X-ray structural analysis showed that NaPbB{sub 5}O{sub 9} crystallizes in the monoclinic space group P2{sub 1}/c with a=6.5324(10) A, b=13.0234(2) A, c=8.5838(10) A, {beta}=104.971(10){sup o}, and Z=4. The crystal structure is composed of double ring [B{sub 5}O{sub 9}]{sup 3-} units, [PbO{sub 7}] and [NaO{sub 7}] polyhedra. [B{sub 5}O{sub 9}]{sup 3-} groups connect with each other forming two-dimensional infinite {sub {infinity}}[B{sub 5}O{sub 9}]{sup 3-} layers, while [PbO{sub 7}] and [NaO{sub 7}] polyhedra are located between the layers. [PbO{sub 7}] polyhedra linked together viamore » corner-sharing O atom forming novel infinite {sub {infinity}}[PbO{sub 6}] chains along the c axis. The thermal behavior, IR spectrum and the optical diffuse reflectance spectrum of NaPbB{sub 5}O{sub 9} were reported. -- Graphical abstract: A new phase, NaPbB{sub 5}O{sub 9}, has been discovered in the ternary M{sub 2}O-PbO-B{sub 2}O{sub 3} (M=alkali-metal) system. The crystal structure consists of a novel infinite {sub {infinity}}[PbO{sub 6}] chains. Display Omitted Research highlights: NaPbB{sub 5}O{sub 9} is the first borate discovered in the ternary M{sub 2}O-PbO-B{sub 2}O{sub 3} (M=alkali-metal) system. NaPbB{sub 5}O{sub 9} crystal structure includes a two-dimensional infinite {sub {infinity}}[B{sub 5}O{sub 9}]{sup 3-} layers and a novel one-dimensional infinite {sub {infinity}}[PbO{sub 6}] chains. [PbO{sub 7}] polyhedron has a highly asymmetric bonding configuration.« less

Superoxide reductase from the syphilis spirochete Treponema pallidum: crystallization and structure determination using soft X-rays

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

Santos-Silva, Teresa; Trincão, José; Carvalho, Ana L.

2005-11-01

Superoxide reductase is a non-haem iron-containing protein involved in resistance to oxidative stress. The oxidized form of the protein has been crystallized and its three-dimensional structure solved. A highly redundant X-ray diffraction data set was collected on a rotating-anode generator using Cu Kα X-ray radiation. Four Fe atoms were located in the asymmetric unit corresponding to four protein molecules arranged as a dimer of homodimers. Superoxide reductase is a 14 kDa metalloprotein containing a catalytic non-haem iron centre [Fe(His){sub 4}Cys]. It is involved in defence mechanisms against oxygen toxicity, scavenging superoxide radicals from the cell. The oxidized form of Treponemamore » pallidum superoxide reductase was crystallized in the presence of polyethylene glycol and magnesium chloride. Two crystal forms were obtained depending on the oxidizing agents used after purification: crystals grown in the presence of K{sub 3}Fe(CN){sub 6} belonged to space group P2{sub 1} (unit-cell parameters a = 60.3, b = 59.9, c = 64.8 Å, β = 106.9°) and diffracted beyond 1.60 Å resolution, while crystals grown in the presence of Na{sub 2}IrCl{sub 6} belonged to space group C2 (a = 119.4, b = 60.1, c = 65.6 Å, β = 104.9°) and diffracted beyond 1.55 Å. A highly redundant X-ray diffraction data set from the C2 crystal form collected on a copper rotating-anode generator (λ = 1.542 Å) clearly defined the positions of the four Fe atoms present in the asymmetric unit by SAD methods. A MAD experiment at the iron absorption edge confirmed the positions of the previously determined iron sites and provided better phases for model building and refinement. Molecular replacement using the P2{sub 1} data set was successful using a preliminary trace as a search model. A similar arrangement of the four protein molecules could be observed.« less

Atomic modeling of cryo-electron microscopy reconstructions--joint refinement of model and imaging parameters.

PubMed

Chapman, Michael S; Trzynka, Andrew; Chapman, Brynmor K

2013-04-01

When refining the fit of component atomic structures into electron microscopic reconstructions, use of a resolution-dependent atomic density function makes it possible to jointly optimize the atomic model and imaging parameters of the microscope. Atomic density is calculated by one-dimensional Fourier transform of atomic form factors convoluted with a microscope envelope correction and a low-pass filter, allowing refinement of imaging parameters such as resolution, by optimizing the agreement of calculated and experimental maps. A similar approach allows refinement of atomic displacement parameters, providing indications of molecular flexibility even at low resolution. A modest improvement in atomic coordinates is possible following optimization of these additional parameters. Methods have been implemented in a Python program that can be used in stand-alone mode for rigid-group refinement, or embedded in other optimizers for flexible refinement with stereochemical restraints. The approach is demonstrated with refinements of virus and chaperonin structures at resolutions of 9 through 4.5 Å, representing regimes where rigid-group and fully flexible parameterizations are appropriate. Through comparisons to known crystal structures, flexible fitting by RSRef is shown to be an improvement relative to other methods and to generate models with all-atom rms accuracies of 1.5-2.5 Å at resolutions of 4.5-6 Å. Copyright © 2013 Elsevier Inc. All rights reserved.

Cutting Materials in Half: A Graph Theory Approach for Generating Crystal Surfaces and Its Prediction of 2D Zeolites

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

Witman, Matthew; Ling, Sanliang; Boyd, Peter

Scientific interest in two-dimensional (2D) materials, ranging from graphene and other single layer materials to atomically thin crystals, is quickly increasing for a large variety of technological applications. While in silico design approaches have made a large impact in the study of 3D crystals, algorithms designed to discover atomically thin 2D materials from their parent 3D materials are by comparison more sparse. Here, we hypothesize that determining how to cut a 3D material in half (i.e., which Miller surface is formed) by severing a minimal number of bonds or a minimal amount of total bond energy per unit area canmore » yield insight into preferred crystal faces. We answer this question by implementing a graph theory technique to mathematically formalize the enumeration of minimum cut surfaces of crystals. While the algorithm is generally applicable to different classes of materials, we focus on zeolitic materials due to their diverse structural topology and because 2D zeolites have promising catalytic and separation performance compared to their 3D counterparts. We report here a simple descriptor based only on structural information that predicts whether a zeolite is likely to be synthesizable in the 2D form and correctly identifies the expressed surface in known layered 2D zeolites. The discovery of this descriptor allows us to highlight other zeolites that may also be synthesized in the 2D form that have not been experimentally realized yet. Finally, our method is general since the mathematical formalism can be applied to find the minimum cut surfaces of other crystallographic materials such as metal-organic frameworks, covalent-organic frameworks, zeolitic-imidazolate frameworks, metal oxides, etc.« less

Origin and effective reduction of inversion domains in aluminum nitride grown by a sublimation method

NASA Astrophysics Data System (ADS)

Shigetoh, Keisuke; Horibuchi, Kayo; Nakamura, Daisuke

2017-11-01

Owing to the large differences in the chemical properties between Al and N polarities in aluminum nitride (AlN), the choice of the polar direction for crystal growth strongly affects not only the quality but also the shape (facet formation) of the grown crystal. In particular, N-polar (0 0 0 -1) has been considered to be a more preferable direction than Al-polar (0 0 0 1) for sublimation growth because compared to Al-polar (0 0 0 1), N-polar (0 0 0 -1) exhibits better stability at high growth rate (high supersaturation) conditions and enables easier lateral enlargement of the crystal. However, some critical growth conditions induce polarity inversion and hinder stable N-polar growth. Furthermore, the origin of the polarity inversion in AlN growth by the sublimation method is still unclear. To ensure stable N-polar growth without polarity inversion, the formation mechanism of the inversion domain during AlN sublimation growth must be elucidated. Therefore, herein, we demonstrate homoepitaxial growth on an N-polar seed and carefully investigate the obtained crystal that shows polarity inversion. Annular bright-field scanning transmission electron microscopy reveals that polarity is completely converted to the Al polarity via the formation of a 30 nm thick mixed polar layer (MPL) just above the seed. Moreover, three-dimensional atom probe tomography shows the segregation of the oxygen impurities in the MPL with a high concentration of about 3 atom%. Finally, by avoiding the incorporation of oxygen impurity into the crystal at the initial stage of the growth, we demonstrate an effective reduction (seven orders of magnitude) of the inversion domain boundary formation.

Crystal structure, spectral and thermal properties of 1,2-bis[2-(4,4,4-trifluoro-1-hydroxy-3-oxobut-1-enyl)phenoxy]-ethane and luminescent properties of its complexes with Al(III) and Eu(III)

NASA Astrophysics Data System (ADS)

Khamidullina, Liliya A.; Obydennov, Konstantin L.; Slepukhin, Pavel A.; Puzyrev, Igor S.

2016-12-01

Describing the crystal structure, packing, FT-IR, UV-Vis and NMR spectra and thermal properties of new polydentate O-ligand based on aryl-β-diketone moieties connected by ethylene glycol spacer is the subject of this article. The results of IR, UV-Vis and 1H NMR spectroscopy as well X-ray crystallography of 1,2-bis[2-(4,4,4-trifluoro-1-hydroxy-3-oxobut-1-enyl)phenoxy]-ethane (BTFPE) indicate that the compound exists in solution and in solid as enol. The crystal structure analysis shows that BTFPE has C2/c group of the monoclinic system. Typical S(6) intramolecular hydrogen bond occurs in each 1,3-diketo moiety. This bond is asymmetric and the H atom is closest to the O atom adjacent to the phenyl ring. The packing of the crystal is sustained by numerous Csbnd H⋯O, Osbnd H⋯F, Csbnd H⋯F interactions. In the crystal, supramolecular zig-zag chains are formed along the c-axis. Short contacts interconnect the molecules into a two-dimensional layered structure wherein each molecule is node between chains. According to the thermal investigation this compound is stable up to 200 °C in air atmosphere, above this temperature it decomposes. Photoluminescent properties of aluminum(III) and europium(III) complexes of BTFPE were evaluated in chloroform solution and in the solid state. Aluminum complex of BTFPE shows blue luminescence with maximum at 445 nm. Europium complex exhibits intense red color luminescence at 613 nm from central Eu(III) ion through the excitation of the ligand.

Cutting Materials in Half: A Graph Theory Approach for Generating Crystal Surfaces and Its Prediction of 2D Zeolites.

PubMed

Witman, Matthew; Ling, Sanliang; Boyd, Peter; Barthel, Senja; Haranczyk, Maciej; Slater, Ben; Smit, Berend

2018-02-28

Scientific interest in two-dimensional (2D) materials, ranging from graphene and other single layer materials to atomically thin crystals, is quickly increasing for a large variety of technological applications. While in silico design approaches have made a large impact in the study of 3D crystals, algorithms designed to discover atomically thin 2D materials from their parent 3D materials are by comparison more sparse. We hypothesize that determining how to cut a 3D material in half (i.e., which Miller surface is formed) by severing a minimal number of bonds or a minimal amount of total bond energy per unit area can yield insight into preferred crystal faces. We answer this question by implementing a graph theory technique to mathematically formalize the enumeration of minimum cut surfaces of crystals. While the algorithm is generally applicable to different classes of materials, we focus on zeolitic materials due to their diverse structural topology and because 2D zeolites have promising catalytic and separation performance compared to their 3D counterparts. We report here a simple descriptor based only on structural information that predicts whether a zeolite is likely to be synthesizable in the 2D form and correctly identifies the expressed surface in known layered 2D zeolites. The discovery of this descriptor allows us to highlight other zeolites that may also be synthesized in the 2D form that have not been experimentally realized yet. Finally, our method is general since the mathematical formalism can be applied to find the minimum cut surfaces of other crystallographic materials such as metal-organic frameworks, covalent-organic frameworks, zeolitic-imidazolate frameworks, metal oxides, etc.

Cutting Materials in Half: A Graph Theory Approach for Generating Crystal Surfaces and Its Prediction of 2D Zeolites

PubMed Central

2018-01-01

Scientific interest in two-dimensional (2D) materials, ranging from graphene and other single layer materials to atomically thin crystals, is quickly increasing for a large variety of technological applications. While in silico design approaches have made a large impact in the study of 3D crystals, algorithms designed to discover atomically thin 2D materials from their parent 3D materials are by comparison more sparse. We hypothesize that determining how to cut a 3D material in half (i.e., which Miller surface is formed) by severing a minimal number of bonds or a minimal amount of total bond energy per unit area can yield insight into preferred crystal faces. We answer this question by implementing a graph theory technique to mathematically formalize the enumeration of minimum cut surfaces of crystals. While the algorithm is generally applicable to different classes of materials, we focus on zeolitic materials due to their diverse structural topology and because 2D zeolites have promising catalytic and separation performance compared to their 3D counterparts. We report here a simple descriptor based only on structural information that predicts whether a zeolite is likely to be synthesizable in the 2D form and correctly identifies the expressed surface in known layered 2D zeolites. The discovery of this descriptor allows us to highlight other zeolites that may also be synthesized in the 2D form that have not been experimentally realized yet. Finally, our method is general since the mathematical formalism can be applied to find the minimum cut surfaces of other crystallographic materials such as metal–organic frameworks, covalent-organic frameworks, zeolitic-imidazolate frameworks, metal oxides, etc. PMID:29532024

Cutting Materials in Half: A Graph Theory Approach for Generating Crystal Surfaces and Its Prediction of 2D Zeolites

DOE PAGES

Witman, Matthew; Ling, Sanliang; Boyd, Peter; ...

2018-02-06

Scientific interest in two-dimensional (2D) materials, ranging from graphene and other single layer materials to atomically thin crystals, is quickly increasing for a large variety of technological applications. While in silico design approaches have made a large impact in the study of 3D crystals, algorithms designed to discover atomically thin 2D materials from their parent 3D materials are by comparison more sparse. Here, we hypothesize that determining how to cut a 3D material in half (i.e., which Miller surface is formed) by severing a minimal number of bonds or a minimal amount of total bond energy per unit area canmore » yield insight into preferred crystal faces. We answer this question by implementing a graph theory technique to mathematically formalize the enumeration of minimum cut surfaces of crystals. While the algorithm is generally applicable to different classes of materials, we focus on zeolitic materials due to their diverse structural topology and because 2D zeolites have promising catalytic and separation performance compared to their 3D counterparts. We report here a simple descriptor based only on structural information that predicts whether a zeolite is likely to be synthesizable in the 2D form and correctly identifies the expressed surface in known layered 2D zeolites. The discovery of this descriptor allows us to highlight other zeolites that may also be synthesized in the 2D form that have not been experimentally realized yet. Finally, our method is general since the mathematical formalism can be applied to find the minimum cut surfaces of other crystallographic materials such as metal-organic frameworks, covalent-organic frameworks, zeolitic-imidazolate frameworks, metal oxides, etc.« less

Lamb-Dicke spectroscopy of atoms in a hollow-core photonic crystal fibre

PubMed Central

Okaba, Shoichi; Takano, Tetsushi; Benabid, Fetah; Bradley, Tom; Vincetti, Luca; Maizelis, Zakhar; Yampol'skii, Valery; Nori, Franco; Katori, Hidetoshi

2014-01-01

Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom–atom and atom–wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturization. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kagome-lattice hollow-core photonic crystal fibre are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom–atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the 1S0−3P1(m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibres improve the optical depth while preserving atomic coherence time. PMID:24934478

Resonance fluorescence based two- and three-dimensional atom localization

NASA Astrophysics Data System (ADS)

Wahab, Abdul; Rahmatullah; Qamar, Sajid

2016-06-01

Two- and three-dimensional atom localization in a two-level atom-field system via resonance fluorescence is suggested. For the two-dimensional localization, the atom interacts with two orthogonal standing-wave fields, whereas for the three-dimensional atom localization, the atom interacts with three orthogonal standing-wave fields. The effect of the detuning and phase shifts associated with the corresponding standing-wave fields is investigated. A precision enhancement in position measurement of the single atom can be noticed via the control of the detuning and phase shifts.

Influence of precipitating agents on thermodynamic parameters of protein crystallization solutions.

PubMed

Stavros, Philemon; Saridakis, Emmanuel; Nounesis, George

2016-09-01

X-ray crystallography is the most powerful method for determining three-dimensional structures of proteins to (near-)atomic resolution, but protein crystallization is a poorly explained and often intractable phenomenon. Differential Scanning Calorimetry was used to measure the thermodynamic parameters (ΔG, ΔH, ΔS) of temperature-driven unfolding of two globular proteins, lysozyme, and ribonuclease A, in various salt solutions. The mixtures were categorized into those that were conducive to crystallization of the protein and those that were not. It was found that even fairly low salt concentrations had very large effects on thermodynamic parameters. High concentrations of salts conducive to crystallization stabilized the native folded forms of proteins, whereas high concentrations of salts that did not crystallize them tended to destabilize them. Considering the ΔH and TΔS contributions to the ΔG of unfolding separately, high concentrations of crystallizing salts were found to enthalpically stabilize and entropically destabilize the protein, and vice-versa for the noncrystallizing salts. These observations suggest an explanation, in terms of protein stability and entropy of hydration, of why some salts are good crystallization agents for a given protein and others are not. This in turn provides theoretical insight into the process of protein crystallization, suggesting ways of predicting and controlling it. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 642-652, 2016. © 2016 Wiley Periodicals, Inc.

Large three-dimensional photonic crystals based on monocrystalline liquid crystal blue phases.

PubMed

Chen, Chun-Wei; Hou, Chien-Tsung; Li, Cheng-Chang; Jau, Hung-Chang; Wang, Chun-Ta; Hong, Ching-Lang; Guo, Duan-Yi; Wang, Cheng-Yu; Chiang, Sheng-Ping; Bunning, Timothy J; Khoo, Iam-Choon; Lin, Tsung-Hsien

2017-09-28

Although there have been intense efforts to fabricate large three-dimensional photonic crystals in order to realize their full potential, the technologies developed so far are still beset with various material processing and cost issues. Conventional top-down fabrications are costly and time-consuming, whereas natural self-assembly and bottom-up fabrications often result in high defect density and limited dimensions. Here we report the fabrication of extraordinarily large monocrystalline photonic crystals by controlling the self-assembly processes which occur in unique phases of liquid crystals that exhibit three-dimensional photonic-crystalline properties called liquid-crystal blue phases. In particular, we have developed a gradient-temperature technique that enables three-dimensional photonic crystals to grow to lateral dimensions of ~1 cm (~30,000 of unit cells) and thickness of ~100 μm (~ 300 unit cells). These giant single crystals exhibit extraordinarily sharp photonic bandgaps with high reflectivity, long-range periodicity in all dimensions and well-defined lattice orientation.Conventional fabrication approaches for large-size three-dimensional photonic crystals are problematic. By properly controlling the self-assembly processes, the authors report the fabrication of monocrystalline blue phase liquid crystals that exhibit three-dimensional photonic-crystalline properties.

Synthesis, structure, and characterization of two Zn(II) complex containing two-dimensional bilayer structure

NASA Astrophysics Data System (ADS)

Zhang, Meili; Ren, Yixia; Chen, Xiaoli

2014-10-01

Two new Zn(II) complexes, [Zn2(L)(H2O)3]ṡH2O (1) and [Zn3(HL)2(bpp)2(Hbpp)2]ṡ10H2Oṡ2ClO4 (2) (H4L = cis,cis,cis,cis-1,2,3,4-cyclopentanetracarboxylic acid, bpp = 1,3-bis(4-pyridyl)propane), have been synthesized and characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction techniques. The structure indicates that the complex 1 crystallizes in triclinic, space group Pī, in which, the four carboxylate groups of L ligand adopt μ2-η1:η0, μ2-η1:η1, μ1-η1:η1 coordination modes, respectively, bridging Zn(II) atoms to generate a (4,6)-connected 2D bilayer network. The structure indicates that the complex 2 crystallizes in monoclinic, space group C2/c, in which, three deprotonated carboxylate groups of L ligand adopt uniform μ1-η1:η0 coordination mode linking Zn(II) atoms to form a 1D polymeric ribbon, the bpp ligands further extend such ribbon giving rised to a (3,4)-connected 2D bilayer network. The most striking feature of 1 and 2 is that both of bilayer networks contain 1D solvent channel, where water molecules are located. In additional, luminescent properties of two complexes have also been studied.

Synthesis, characterization, crystal structure and antimicrobial studies of a novel Cu(II) complex based on itaconic acid and nicotinamide

NASA Astrophysics Data System (ADS)

Tella, Adedibu C.; Owalude, Samson O.; Ajibade, Peter A.; Simon, Nzikahyel; Olatunji, Sunday J.; Abdelbaky, Mohammed S. M.; Garcia-Granda, Santiago

2016-12-01

A novel complex was synthesized from Cu(II), nicotinamide and itaconic acid and is formulated as [Cu(C5H4O4)2(C6H6N2O)2(H2O)2·2(H2O)] (1). The compound was characterized by elemental analysis, FTIR spectroscopy, UV-Vis and single crystal X-ray diffraction. The complex crystallizes in the triclinic P-1 space group, with a = 7.5111(2) Å, b = 9.8529(3) Å, c = 10.5118(4) Å, α = 116.244(3)°, β = 90.291(3)°, γ = 103.335(3)°, V = 673.81(4) Å3, Z = 1.The octahedral geometry around the copper(II) ion is of the form CuN2O4 consisting of two molecules of nicotinamide acting as monodentate ligand through the nitrogen atoms, two molecules itaconate ligand and two coordinated water molecules each coordinating through the oxygen atoms. The structure of 1 showed infinite chains build up linking the molecules together via strong Osbnd H⋯O and Nsbnd H⋯O intermolecular hydrogen bonds generating a two dimensional network sheet along c axis. The antimicrobial study of the synthesized complex 1 was investigated and showed higher antibacterial activity against all the organisms comparing with Copper(II) nicotinamide 2 and Copper(II) itaconate 3.

One-dimensional, two-dimensional, and three-dimensional photonic crystals fabricated with interferometric techniques on ultrafine-grain silver halide emulsions

NASA Astrophysics Data System (ADS)

Ulibarrena, Manuel; Carretero, Luis; Acebal, Pablo; Madrigal, Roque; Blaya, Salvador; Fimia, Antonio

2004-09-01

Holographic techniques have been used for manufacturing multiple band one-dimensional, two-dimensional, and three-dimensional photonic crystals with different configurations, by multiplexing reflection and transmission setups on a single layer of holographic material. The recording material used for storage is an ultra fine grain silver halide emulsion, with an average grain size around 20 nm. The results are a set of photonic crystals with the one-dimensional, two-dimensional, and three-dimensional index modulation structure consisting of silver halide particles embedded in the gelatin layer of the emulsion. The characterisation of the fabricated photonic crystals by measuring their transmission band structures has been done and compared with theoretical calculations.

Crystal structures and hydrogen bonding in the anhydrous tryptaminium salts of the isomeric (2,4-di­chloro­phen­oxy)acetic and (3,5-di­chloro­phen­oxy)acetic acids

PubMed Central

Smith, Graham; Lynch, Daniel E.

2015-01-01

The anhydrous salts of 2-(1H-indol-3-yl)ethanamine (tryptamine) with isomeric (2,4-di­chloro­phen­oxy)acetic acid (2,4-D) and (3,5-di­chloro­phen­oxy)acetic (3,5-D), both C10H13N2 +·C8H5Cl2O3 − [(I) and (II), respectively], have been determined and their one-dimensional hydrogen-bonded polymeric structures are described. In the crystal of (I), the aminium H atoms are involved in three separate inter-species N—H⋯O hydrogen-bonding inter­actions, two with carboxyl­ate O-atom acceptors and the third in an asymmetric three-centre bidentate carboxyl­ate O,O′ chelate [graph set R 1 2(4)]. The indole H atom forms an N—H⋯Ocarboxyl­ate hydrogen bond, extending the chain structure along the b-axis direction. In (II), two of the three aminium H atoms are also involved in N—H⋯Ocarboxyl­ate hydrogen bonds similar to (I) but with the third, a three-centre asymmetric inter­action with carboxyl­ate and phen­oxy O atoms is found [graph set R 1 2(5)]. The chain polymeric extension is also along b. There are no π–π ring inter­actions in either of the structures. The aminium side-chain conformations differ significantly between the two structures, reflecting the conformational ambivalence of the tryptaminium cation, as found also in the benzoate salts. PMID:26090147

Octa­akis(4-amino­pyridine)-1κ4 N 1,2κ4 N 1-aqua-2κO-μ-carbonato-1:2κ3 O,O′:O′′-dinickel(II) dichloride penta­hydrate

PubMed Central

Fun, Hoong-Kun; Sinthiya, A; Jebas, Samuel Robinson; Ravindran Durai Nayagam, B.; Alfred Cecil Raj, S.

2008-01-01

In the title compound, [Ni2(CO3)(C5H6N2)8(H2O)]Cl2·5H2O, one of the the NiII ions is six-coordinated in a distorted octa­hedral geometry, with the equatorial plane defined by four pyridine N atoms from four amino­pyridine ligands, the axial positions being occupied by one water O and a carbonate O atom. The other NiII ion is also six-coordinated, by four other pyridine N atoms from four other amino­pyridine ligands and two carbonate O atoms to complete a distorted octa­hedral geometry. In the crystal structure, mol­ecules are linked into an infinite three-dimensional network by O—H⋯O, N—H⋯Cl, N—H⋯O, O—H⋯N, C—H⋯O, C—H⋯N and C/N—H⋯π inter­actions involving the pyridine rings. PMID:21580879

A three-dimensional coordination polymer based on 1,2,3-triazole-4,5-dicarboxylic acid (H{sub 3}tda): ([Cd{sub 12}(tda){sub 8}(H{sub 2}O){sub 11}] · (H{sub 2}O)6.25){sub n}

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

Zhou, Xin-Hui, E-mail: iamxhzhou@njupt.edu.cn; Chen, Qiang

The title coordination polymer ([Cd{sub 12}(tda){sub 8}(H{sub 2}O){sub 11}] · (H{sub 2}O){sub 6.25}){sub n} (H{sub 3}tda = 1,2,3-triazole-4,5-dicarboxylic acid), has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complex crystallizes in orthorhombic sp. gr. Pmn2{sub 1} with Z = 4. The Cd{sub 2} unit doublebridged by one carboxylate oxygen atom and two neighboring nitrogen atoms from the tda{sup 3–} ligands are linked by the tda{sup 3–}ligands to lead to the 2D (4,4) network in the ac plane. The almost coplanar Cd{sub 2}(μ{sub 5}-tda){sub 2} unit comprised of two Cd ions double-bridged by two tda{sup 3–} ligands through themore » neighboring nitrogen atoms is connected with the other four Cd{sub 2}(μ{sub 5}-tda){sub 2} units form the undulating 2D network in the ac plane. The (4,4) networks and undulating 2D networks are alternatively connected along the b axis by the tda{sup 3–} ligands coordinating to the Cd ions to form the 3D framework.« less

2-[(4-Chloro­phen­yl)selan­yl]-3,4-di­hydro-2H-benzo[h]chromene-5,6-dione: crystal structure and Hirshfeld analysis

PubMed Central

Prado, Karinne E.; Name, Luccas L.; Jotani, Mukesh M.

2017-01-01

The title organoselenium compound, C19H13ClO3Se {systematic name: 2-[(4-chloro­phen­yl)selan­yl]-2H,3H,4H,5H,6H-naphtho­[1,2-b]pyran-5,6-dione}, has the substituted 2-pyranyl ring in a half-chair conformation with the methyl­ene-C atom bound to the methine-C atom being the flap atom. The dihedral angle between the two aromatic regions of the mol­ecule is 9.96 (9)° and indicates a step-like conformation. An intra­molecular Se⋯O inter­action of 2.8122 (13) Å is noted. In the crystal, π–π contacts between naphthyl rings [inter-centroid distance = 3.7213 (12) Å] and between naphthyl and chloro­benzene rings [inter-centroid distance = 3.7715 (13) Å], along with C—Cl⋯π(chloro­benzene) contacts, lead to supra­molecular layers parallel to the ab plane, which are connected into a three-dimensional architecture via methyl­ene-C—H⋯O(carbon­yl) inter­actions. The contributions of these and other weak contacts to the Hirshfeld surface is described. PMID:28638659

A one-dimensional zinc(II) coordination polymer with a three-dimensional supramolecular architecture incorporating 1-[(1H-benzimidazol-2-yl)methyl]-1H-tetrazole and adipate.

PubMed

Liu, Chun Li; Huang, Qiu Ying; Meng, Xiang Ru

2016-12-01

The synthesis of coordination polymers or metal-organic frameworks (MOFs) has attracted considerable interest owing to the interesting structures and potential applications of these compounds. It is still a challenge to predict the exact structures and compositions of the final products. A new one-dimensional coordination polymer, catena-poly[[[bis{1-[(1H-benzimidazol-2-yl)methyl]-1H-tetrazole-κN 3 }zinc(II)]-μ-hexane-1,6-dicarboxylato-κ 4 O 1 ,O 1' :O 6 ,O 6' ] monohydrate], {[Zn(C 6 H 8 O 4 )(C 9 H 8 N 6 ) 2 ]·H 2 O} n , has been synthesized by the reaction of Zn(Ac) 2 (Ac is acetate) with 1-[(1H-benzimidazol-2-yl)methyl]-1H-tetrazole (bimt) and adipic acid (H 2 adi) at room temperature. In the polymer, each Zn II ion exhibits an irregular octahedral ZnN 2 O 4 coordination geometry and is coordinated by two N atoms from two symmetry-related bimt ligands and four O atoms from two symmetry-related dianionic adipate ligands. Zn II ions are connected by adipate ligands into a one-dimensional chain which runs parallel to the c axis. The bimt ligands coordinate to the Zn II ions in a monodentate mode on both sides of the main chain. In the crystal, the one-dimensional chains are further connected through N-H...O hydrogen bonds, leading to a three-dimensional supramolecular architecture. In addition, the title polymer exhibits fluorescence, with emissions at 334 and 350 nm in the solid state at room temperature.

Electron Doping of Ultrathin Black Phosphorus with Cu Adatoms.

PubMed

Koenig, Steven P; Doganov, Rostislav A; Seixas, Leandro; Carvalho, Alexandra; Tan, Jun You; Watanabe, Kenji; Taniguchi, Takashi; Yakovlev, Nikolai; Castro Neto, Antonio H; Özyilmaz, Barbaros

2016-04-13

Few-layer black phosphorus is a monatomic two-dimensional crystal with a direct band gap that has high carrier mobility for both holes and electrons. Similarly to other layered atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is sensitive to surface impurities, adsorbates, and adatoms. Here we study the effect of Cu adatoms onto few-layer black phosphorus by characterizing few-layer black phosphorus field effect devices and by performing first-principles calculations. We find that the addition of Cu adatoms can be used to controllably n-dope few layer black phosphorus, thereby lowering the threshold voltage for n-type conduction without degrading the transport properties. We demonstrate a scalable 2D material-based complementary inverter which utilizes a boron nitride gate dielectric, a graphite gate, and a single bP crystal for both the p- and n-channels. The inverter operates at matched input and output voltages, exhibits a gain of 46, and does not require different contact metals or local electrostatic gating.

Atomic density functional and diagram of structures in the phase field crystal model

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

Ankudinov, V. E., E-mail: vladimir@ankudinov.org; Galenko, P. K.; Kropotin, N. V.

2016-02-15

The phase field crystal model provides a continual description of the atomic density over the diffusion time of reactions. We consider a homogeneous structure (liquid) and a perfect periodic crystal, which are constructed from the one-mode approximation of the phase field crystal model. A diagram of 2D structures is constructed from the analytic solutions of the model using atomic density functionals. The diagram predicts equilibrium atomic configurations for transitions from the metastable state and includes the domains of existence of homogeneous, triangular, and striped structures corresponding to a liquid, a body-centered cubic crystal, and a longitudinal cross section of cylindricalmore » tubes. The method developed here is employed for constructing the diagram for the homogeneous liquid phase and the body-centered iron lattice. The expression for the free energy is derived analytically from density functional theory. The specific features of approximating the phase field crystal model are compared with the approximations and conclusions of the weak crystallization and 2D melting theories.« less

High-dimensional atom localization via spontaneously generated coherence in a microwave-driven atomic system.

PubMed

Wang, Zhiping; Chen, Jinyu; Yu, Benli

2017-02-20

We investigate the two-dimensional (2D) and three-dimensional (3D) atom localization behaviors via spontaneously generated coherence in a microwave-driven four-level atomic system. Owing to the space-dependent atom-field interaction, it is found that the detecting probability and precision of 2D and 3D atom localization behaviors can be significantly improved via adjusting the system parameters, the phase, amplitude, and initial population distribution. Interestingly, the atom can be localized in volumes that are substantially smaller than a cubic optical wavelength. Our scheme opens a promising way to achieve high-precision and high-efficiency atom localization, which provides some potential applications in high-dimensional atom nanolithography.

Enzymatically Controlled Vacancies in Nanoparticle Crystals

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

Barnaby, Stacey N.; Ross, Michael B.; Thaner, Ryan V.

In atomic systems, the mixing of metals results in distinct phase behavior that depends on the identity and bonding characteristics of the atoms. In nanoscale systems, the use of oligonucleotides as programmable “bonds” that link nanoparticle “atoms” into superlattices allows for the decoupling of atom identity and bonding. While much research in atomic systems is dedicated to understanding different phase behavior of mixed metals, it is not well understood on the nanoscale how changes in the nanoscale “bond” affect the phase behavior of nanoparticle crystals. In this work, the identity of the atom is kept the same but the chemicalmore » nature of the bond is altered, which is not possible in atomic systems, through the use of DNA and RNA bonding elements. These building blocks assemble into single crystal nanoparticle superlattices with mixed DNA and RNA bonding elements throughout. The nanoparticle crystals can be dynamically changed through the selective and enzymatic hydrolysis of the RNA bonding elements, resulting in superlattices that retain their crystalline structure and habit, while incorporating up to 35% random vacancies generated from the nanoparticles removed. Therefore, the bonding elements of nanoparticle crystals can be enzymatically and selectively addressed without affecting the nature of the atom.« less

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

Kumada, Nobuhiro, E-mail: kumada@yamanashi.ac.jp; Nakamura, Ayumi; Miura, Akira

A new lithium copper bismuth oxide, LiCuBiO{sub 4} was prepared by hydrothermal reaction using NaBiO{sub 3}0.1*4H{sub 2}O. The crystal structural model of this compound was refined by using synchrotron X-ray powder diffraction data. This bismuthate has the LiCuSbO{sub 4} related structure with the orthorhombic cell (Space group: Pnma) of a=10.9096(9), b=5.8113(5) and c=5.0073(4) Å, and the final R-factors were R{sub wp}=4.84 and R{sub p}=3.58%. This compound is the first example of a lithium copper bismuthate containing Bi{sup 5+}. An antiferromagnetic ordering of Cu{sup 2+} moment was observed at 6 K. - Graphical abstract: In the crystal structure of LiCuBiO{sub 4}more » all metal atoms are coordinated octahedrally by six O atoms and LiO{sub 6} and CuO{sub 6} octahedra form the one-dimensional chains by edge-sharing along the b-axis. The LiO{sub 6} and CuO{sub 6} chains form the layer by face-sharing in the bc plane. The Bi atoms are placed in that interlayer and BiO{sub 6} octahedra are edge-sharing with LiO{sub 6} and CuO{sub 6} octahedra. - Highlights: • A new lithium copper bismuth oxide, LiCuBiO{sub 4} is prepared by hydrothermal reaction. • The crystal structure of LiCuBiO{sub 4} is closely related with that of LiCuSbO{sub 4}. • This new compound exhibits an antiferromagnetic ordering of Cu{sup 2+} moment at 6 K.« less

A rational approach to heavy-atom derivative screening

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

Joyce, M. Gordon; Radaev, Sergei; Sun, Peter D., E-mail: psun@nih.gov

2010-04-01

In order to overcome the difficulties associated with the ‘classical’ heavy-atom derivatization procedure, an attempt has been made to develop a rational crystal-free heavy-atom-derivative screening method and a quick-soak derivatization procedure which allows heavy-atom compound identification. Despite the development in recent times of a range of techniques for phasing macromolecules, the conventional heavy-atom derivatization method still plays a significant role in protein structure determination. However, this method has become less popular in modern high-throughput oriented crystallography, mostly owing to its trial-and-error nature, which often results in lengthy empirical searches requiring large numbers of well diffracting crystals. In addition, the phasingmore » power of heavy-atom derivatives is often compromised by lack of isomorphism or even loss of diffraction. In order to overcome the difficulties associated with the ‘classical’ heavy-atom derivatization procedure, an attempt has been made to develop a rational crystal-free heavy-atom derivative-screening method and a quick-soak derivatization procedure which allows heavy-atom compound identification. The method includes three basic steps: (i) the selection of likely reactive compounds for a given protein and specific crystallization conditions based on pre-defined heavy-atom compound reactivity profiles, (ii) screening of the chosen heavy-atom compounds for their ability to form protein adducts using mass spectrometry and (iii) derivatization of crystals with selected heavy-metal compounds using the quick-soak method to maximize diffraction quality and minimize non-isomorphism. Overall, this system streamlines the process of heavy-atom compound identification and minimizes the problem of non-isomorphism in phasing.« less

A 2:1 co-crystal of p-nitro-benzoic acid and N,N'-bis-(pyridin-3-ylmeth-yl)ethanedi-amide: crystal structure and Hirshfeld surface analysis.

PubMed

Syed, Sabrina; Halim, Siti Nadiah Abdul; Jotani, Mukesh M; Tiekink, Edward R T

2016-01-01

The title 2:1 co-crystal, 2C7H5NO4·C14H14N4O2, in which the complete di-amide mol-ecule is generated by crystallographic inversion symmetry, features a three-mol-ecule aggregate sustained by hydroxyl-O-H⋯N(pyrid-yl) hydrogen bonds. The p-nitro-benzoic acid mol-ecule is non-planar, exhibiting twists of both the carb-oxy-lic acid and nitro groups, which form dihedral angles of 10.16 (9) and 4.24 (4)°, respectively, with the benzene ring. The di-amide mol-ecule has a conformation approximating to a Z shape, with the pyridyl rings lying to either side of the central, almost planar di-amide residue (r.m.s. deviation of the eight atoms being 0.025 Å), and forming dihedral angles of 77.22 (6)° with it. In the crystal, three-mol-ecule aggregates are linked into a linear supra-molecular ladder sustained by amide-N-H⋯O(nitro) hydrogen bonds and orientated along [10-4]. The ladders are connected into a double layer via pyridyl- and benzene-C-H⋯O(amide) inter-actions, which, in turn, are connected into a three-dimensional architecture via π-π stacking inter-actions between pyridyl and benzene rings [inter-centroid distance = 3.6947 (8) Å]. An evaluation of the Hirshfeld surfaces confirm the importance of inter-molecular inter-actions involving oxygen atoms as well as the π-π inter-actions.

Ce{sub 11}Ge{sub 3.73(2)}In{sub 6.27}: Solid-state synthesis, crystal structure and site-preference

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

Jeon, Beom-Yong; Nam, Gnu; Lee, Dong Woo

A novel intermetallic compound of Ce{sub 11}Ge{sub 3.73(2)}In{sub 6.27} has been synthesized through the high-temperature solid-state reaction using Nb-ampoules. A batch of well grown block-/short bar-shaped single-crystals has been obtained, and the crystal structure of the title compound has been characterized by single-crystal X-ray diffraction analyses. Ce{sub 11}Ge{sub 3.73(2)}In{sub 6.27} adopts the Ho{sub 11}Ge{sub 10}-type structure belonging to the tetragonal space group I4/mmm (Z=4, Pearson symbol tI84) with nine crystallographically unique atomic positions in the asymmetric unit. The lattice parameters are a=12.0163(1) Å and c=16.5396(2) Å. The overall crystal structure can simply be depicted as an assembly of three differentmore » types of co-facial cationic polyhedra centered by anions, which is further enclosed by the three-dimensional (3-D) cage-like anionic framework. The extra amount of In is observed in one of three isolated anionic sites resulting in introducing the Ge/In-mixed site at the Wyckoff 4e site. This unique site-preference of In substitution for Ge at the 4e site has been enlightened via the atomic size-aspect which was fully supported and rationalized by the site- and bond-energies analyses using tight-binding linear muffin-tin orbital (TB-LMTO) calculations. Energy-dispersive X-ray spectroscopy (EDS), density of states (DOS), crystal orbital Hamilton population (COHP), and electron localization function (ELF) analyses for the title compound are also presented. Magnetic susceptibility measurement proves that an antiferromagnetic ordering of Ce atoms at a low temperature with a paramagnetic Curie temperature of −23.2 K. - Graphical abstract: Reported is experimental and theoretical investigations for Ce{sub 11}Ge{sub 3.73(2)}In{sub 6.27}, which is the first reported example having the extra amounts of In substitution for Ge at one of three “isolated” anionic sites in the Ho{sub 11}Ge{sub 10}-type phase. The observed In site-preference toward the particular anionic site was rationalized via the atomic size-aspect supported by comprehensive analyses for the site-energies including the Wyckoff 4e and 8j sites. - Highlights: • Block or short-bar shaped single-crystals of Ce{sub 11}Ge{sub 3.73(2)}In{sub 6.27} were synthesized. • The first example of having the In/Ge mixture at the “isolated” anionic site. • The site-preference of In was rationalized by the site- and bond-energies.« less

Study of crystallization mechanisms of Fe nanoparticle

NASA Astrophysics Data System (ADS)

Kien, P. H.; Trang, G. T. T.; Hung, P. K.

2017-06-01

In this paper, the nanoparticle (NP) Fe was investigated by means of molecular dynamics simulation. The crystallization mechanism was studied through the time evolution of crystal cluster and potential energies of different atom types. The simulation shows that the NP was crystallized into bcc crystal structure when it was annealed at 900 K for long times. At early stage of the annealing, small nuclei form in different places of NP and dissolve for short times. After long times some nuclei form and gather nearby which create the stable clusters in the core of NP. After that the crystal clusters grow in the direction to cover the core and then to spread into the surface of NP. Analyzing the energies of different type atoms, we found that the crystal growth is originated from specific atomic arrangement in the boundary region of crystal clusters.

Diaqua­bis­(5-carb­oxy-2-propyl-1H-imidazole-4-carboxyl­ato-κ2 N 3,O 4)cadmium N,N-dimethyl­formamide disolvate

PubMed Central

Tong, Shao-Wei; Li, Shi-Jie; Song, Wen-Dong; Miao, Dong-Liang; An, Jing-Bo

2011-01-01

In the title complex, [Cd(C8H9N2O4)2(H2O)2]·2C3H7NO, the six-coordinate CdII ion is in a slightly distorted octa­hedral environment, defined by two O atoms from two coordinated water mol­ecules and two carboxyl­ate O atoms and two N atoms from two N,O-bidentate 5-carb­oxy-2-propyl-1H-imidazole-4-carboxyl­ate ligands. In the crystal, complex mol­ecules and dimethyl­formamide solvent mol­ecules are linked by O—H⋯O and N—H⋯O hydrogen bonds into a two-dimensional supra­molecular structure. The propyl groups of the ligands are disordered over two conformations with refined occupancies of 0.680 (7) and 0.320 (7). PMID:22199635

MoS2 monolayers on nanocavities: enhancement in light-matter interaction

NASA Astrophysics Data System (ADS)

Janisch, Corey; Song, Haomin; Zhou, Chanjing; Lin, Zhong; Elías, Ana Laura; Ji, Dengxin; Terrones, Mauricio; Gan, Qiaoqiang; Liu, Zhiwen

2016-06-01

Two-dimensional (2D) atomic crystals and van der Waals heterostructures constitute an emerging platform for developing new functional ultra-thin electronic and optoelectronic materials for novel energy-efficient devices. However, in most thin-film optical applications, there is a long-existing trade-off between the effectiveness of light-matter interactions and the thickness of semiconductor materials, especially when the materials are scaled down to atom thick dimensions. Consequently, enhancement strategies can introduce significant advances to these atomically thick materials and devices. Here we demonstrate enhanced absorption and photoluminescence generation from MoS2 monolayers coupled with a planar nanocavity. This nanocavity consists of an alumina nanolayer spacer sandwiched between monolayer MoS2 and an aluminum reflector, and can strongly enhance the light-matter interaction within the MoS2, increasing the exclusive absorption of monolayer MoS2 to nearly 70% at a wavelength of 450 nm. The nanocavity also modifies the spontaneous emission rate, providing an additional design freedom to control the interaction between light and 2D materials.

Structure of Se-Te glasses studied using neutron, X-ray diffraction and reverse Monte Carlo modelling

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

Itoh, Keiji, E-mail: itoh@okayama-u.ac.jp; Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494

Pulsed neutron diffraction and synchrotron X-ray diffraction measurements were performed on Se{sub 100-x}Te{sub x} bulk glasses with x=10, 20, 30 and 40. The coordination numbers obtained from the diffraction results demonstrate that Se and Te atoms are twofold coordinated and the glass structure is formed by the chain network. The three-dimensional structure model for Se{sub 60}Te{sub 40} glass obtained by using reverse Monte Carlo modelling shows that the alternating arrangements of Se and Te atoms compose the major part of the chain clusters but several other fragments such as Se{sub n} chains and Te-Te dimers are also present in largemore » numbers. The chain clusters have geometrically disordered forms and the interchain atomic order is different from those in the crystal structures of trigonal Se and trigonal Te. - Graphical abstract: Coordination environment in Se{sub 60}Te{sub 40} glass.« less

Stacking of 2D electron gases in Ge probed at the atomic level and its correlation to low-temperature magnetotransport.

PubMed

Scappucci, G; Klesse, W M; Hamilton, A R; Capellini, G; Jaeger, D L; Bischof, M R; Reidy, R F; Gorman, B P; Simmons, M Y

2012-09-12

Stacking of two-dimensional electron gases (2DEGs) obtained by δ-doping of Ge and patterned by scanning probe lithography is a promising approach to realize ultrascaled 3D epitaxial circuits, where multiple layers of active electronic components are integrated both vertically and horizontally. We use atom probe tomography and magnetotransport to correlate the real space 3D atomic distribution of dopants in the crystal with the quantum correction to the conductivity observed at low temperatures, probing if closely stacked δ-layers in Ge behave as independent 2DEGs. We find that at a separation of 9 nm the stacked-2DEGs, while interacting, still maintain their individuality in terms of electron transport and show long phase coherence lengths (∼220 nm). Strong vertical electron confinement is crucial to this finding, resulting in an interlayer scattering time much longer (∼1000 × ) than the scattering time within the dopant plane.

Unified Description of the Optical Phonon Modes inN-Layer MoTe2

NASA Astrophysics Data System (ADS)

Froehlicher, Guillaume; Lorchat, Etienne; Fernique, François; Joshi, Chaitanya; Molina-Sánchez, Alejandro; Wirtz, Ludger; Berciaud, Stéphane

2015-10-01

$N$-layer transition metal dichalcogenides provide a unique platform to investigate the evolution of the physical properties between the bulk (three dimensional) and monolayer (quasi two-dimensional) limits. Here, using high-resolution micro-Raman spectroscopy, we report a unified experimental description of the $\\Gamma$-point optical phonons in $N$-layer $2H$-molybdenum ditelluride (MoTe$_2$). We observe a series of $N$-dependent low-frequency interlayer shear and breathing modes (below $40~\\rm cm^{-1}$, denoted LSM and LBM) and well-defined Davydov splittings of the mid-frequency modes (in the range $100-200~\\rm cm^{-1}$, denoted iX and oX), which solely involve displacements of the chalcogen atoms. In contrast, the high-frequency modes (in the range $200-300~\\rm cm^{-1}$, denoted iMX and oMX), arising from displacements of both the metal and chalcogen atoms, exhibit considerably reduced splittings. The manifold of phonon modes associated with the in-plane and out-of-plane displacements are quantitatively described by a force constant model, including interactions up to the second nearest neighbor and surface effects as fitting parameters. The splittings for the iX and oX modes observed in $N$-layer crystals are directly correlated to the corresponding bulk Davydov splittings between the $E_{2u}/E_{1g}$ and $B_{1u}/A_{1g}$ modes, respectively, and provide a measurement of the frequencies of the bulk silent $E_{2u}$ and $B_{1u}$ optical phonon modes. Our analysis could readily be generalized to other layered crystals.

Protein crystal growth

NASA Technical Reports Server (NTRS)

Bugg, Charles E.

1993-01-01

Proteins account for 50% or more of the dry weight of most living systems and play a crucial role in virtually all biological processes. Since the specific functions of essentially all biological molecules are determined by their three-dimensional structures, it is obvious that a detailed understanding of the structural makeup of a protein is essential to any systematic research pertaining to it. At the present time, protein crystallography has no substitute, it is the only technique available for elucidating the atomic arrangements within complicated biological molecules. Most macromolecules are extremely difficult to crystallize, and many otherwise exciting and promising projects have terminated at the crystal growth stage. There is a pressing need to better understand protein crystal growth, and to develop new techniques that can be used to enhance the size and quality of protein crystals. There are several aspects of microgravity that might be exploited to enhance protein crystal growth. The major factor that might be expected to alter crystal growth processes in space is the elimination of density-driven convective flow. Another factor that can be readily controlled in the absence of gravity is the sedimentation of growing crystal in a gravitational field. Another potential advantage of microgravity for protein crystal growth is the option of doing containerless crystal growth. One can readily understand why the microgravity environment established by Earth-orbiting vehicles is perceived to offer unique opportunities for the protein crystallographer. The near term objectives of the Protein Crystal Growth in a Microgravity Environment (PCG/ME) project is to continue to improve the techniques, procedures, and hardware systems used to grow protein crystals in Earth orbit.

An overview of heavy-atom derivatization of protein crystals

PubMed Central

Pike, Ashley C. W.; Garman, Elspeth F.; Krojer, Tobias; von Delft, Frank; Carpenter, Elisabeth P.

2016-01-01

Heavy-atom derivatization is one of the oldest techniques for obtaining phase information for protein crystals and, although it is no longer the first choice, it remains a useful technique for obtaining phases for unknown structures and for low-resolution data sets. It is also valuable for confirming the chain trace in low-resolution electron-density maps. This overview provides a summary of the technique and is aimed at first-time users of the method. It includes guidelines on when to use it, which heavy atoms are most likely to work, how to prepare heavy-atom solutions, how to derivatize crystals and how to determine whether a crystal is in fact a derivative. PMID:26960118

Synthesis and crystal structure of a novel pentaborate, Na{sub 3}ZnB{sub 5}O{sub 10}

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

Chen Xuean; Li Ming; Chang Xinan

A novel ternary borate, trisodium zinc pentaborate, Na{sub 3}ZnB{sub 5}O{sub 10}, has been prepared by solid-state reaction at temperature below 750deg. C. The single-crystal X-ray structural analysis showed that Na{sub 3}ZnB{sub 5}O{sub 10} crystallizes in the monoclinic space group P2{sub 1}/n with a=6.6725(7)A, b=18.1730(10)A, c=7.8656(9)A, {beta}=114.604(6){sup o}, Z=4. It represents a new structure type in which double ring [B{sub 5}O{sub 10}]{sup 5-} building units are bridged by ZnO{sub 4} tetrahedra through common O atoms to form a two-dimensional {sub {approx}}{sup 2}[ZnB{sub 5}O{sub 10}]{sup 3-}-layer that affords one-dimensional channels running parallel to the [101] direction. Symmetry-center related {sub {approx}}{sup 2}[ZnB{sub 5}O{submore » 10}]{sup 3-} layers are stacked along the b-axis, with the interlayer void spaces and intralayer open channels filled by Na{sup +} cations to balance charge. The IR spectrum further confirms the presence of both BO{sub 3} and BO{sub 4} groups and UV-vis diffuse reflectance spectrum shows a band gap of about 3.2eV.« less

Three-Dimensional Self-Assembled Photonic Crystal Waveguide

NASA Astrophysics Data System (ADS)

Baek, Kang-Hyun

Photonic crystals (PCs), two- or three-dimensionally periodic, artificial, and dielectric structures, have a specific forbidden band for electromagnetic waves, referred to as photonic bandgap (PBG). The PBG is analogous to the electronic bandgap in natural crystal structures with periodic atomic arrangement. A well-defined and embedded planar, line, or point defect within the PCs causes a break in its structural periodicity, and introduces a state in the PBG for light localization. It offers various applications in integrated optics and photonics including optical filters, sharp bending light guides and very low threshold lasers. Using nanofabrication processes, PCs of the 2-D slab-type and 3-D layer-by-layer structures have been investigated widely. Alternatively, simple and low-cost self-assembled PCs with full 3-D PBG, inverse opals, have been suggested. A template with face centered cubic closed packed structure, opal, may initially be built by self-assembly of colloidal spheres, and is selectively removed after infiltrating high refractive index materials into the interstitials of spheres. In this dissertation, the optical waveguides utilizing the 3-D self-assembled PCs are discussed. The waveguides were fabricated by microfabrication technology. For high-quality colloidal silica spheres and PCs, reliable synthesis, self-assembly, and characterization techniques were developed. Its theoretical and experimental demonstrations are provided and correlated. They suggest that the self-assembled PCs with PBG are feasible for the applications in integrated optics and photonics.

Neutron Diffraction Structure of Melampodin: Its Role in the Reclassification of the Germacranolides

PubMed Central

Watkins, Steven F.; Fischer, Nikolaus H.; Bernal, Ivan

1973-01-01

The precise crystal and molecular structure of melampodin, C21H24O9, was determined from three-dimensional neutron diffraction data collected by counter techniques and phases by direct statistical methods. Crystals are orthorhombic, P212121, a = 8,990(9), b = 14.352(14), c = 16.294(16) Å, V = 2102 Å3, d(calc.) = 1.328 g·cm-3, Z = 4 molecules per unit cell. The structural model was refined by full matrix least-squares of 2303 observed independent reflections, with all 54 atoms treated anisotropically, to R(F) = 5.0%. Hydrogen bonds link melampodin molecules together in the solid state. The conformation of the cyclodeca-1,5-diene ring is such that one intraannular hydrogen atom interacts strongly with one double bond, but there is little or no transannular interaction between double bonds. Strain in the ten-membered ring and in the trans-fused lactone ring is discussed, as are chemical implications of the unsymmetric epoxide in the epoxyangelic acid side chain. The previously suggested reclassification of germacranolide sesquiterpene lactones into four subgroups is supported, and a new convention for configurational representations of the four subgroups is proposed. PMID:16592106

Crystal structure of poly[[μ-4-(hy-droxy-meth-yl)pyridine-κ(2) N:O][4-(hy-droxy-meth-yl)pyridine-κN](μ-thio-cyanato-κ(2) N:S)(thio-cyanato-κN)cadmium].

PubMed

Werner, Julia; Jess, Inke; Näther, Christian

2015-06-01

The crystal structure of the title compound, [Cd(NCS)2(C6H7NO)2] n is made up of Cd(2+) cations that are coordinated by three thio-cyanate ligands and three 4-(hy-droxy-meth-yl)pyridine ligands within distorted N4OS octa-hedra. The asymmetric unit consists of one Cd(2+) cation, two thio-cyanate anions and two 4-(hy-droxy-meth-yl)pyridine ligands in general positions. Two Cd(2+) cations are linked by two μ-1,3 N- and S-bonding thio-ycanate anions into dimers which are further linked into branched chains along [100] by two μ-1,6 N- and O-bonding 4-(hy-droxy-meth-yl)pyridine ligands. One additional N-bonded 4-(hy-droxy-meth-yl)pyridine ligand and one additional N-bonded thio-cyanate anion are only terminally bonded to the metal cation. Inter-chain O-H⋯S hydrogen bonds between the hy-droxy H atoms and one of the thio-cyanate S atoms connect the chains into a three-dimensional network.

Surface morphology and structure of Ge layer on Si(111) after solid phase epitaxy

NASA Astrophysics Data System (ADS)

Yoshida, Ryoma; Tosaka, Aki; Shigeta, Yukichi

2018-05-01

The surface morphology change of a Ge layer on a Si(111) surface formed by solid phase epitaxy has been investigated with a scanning tunneling microscope (STM). The Ge film was deposited at room temperature and annealed at 400 °C or 600 °C. The STM images of the sample surface after annealing at 400 °C show a flat wetting layer (WL) with small three-dimensional islands on the WL. After annealing at 600 °C, the STM images show a surface roughening with large islands. From the relation between the average height of the roughness and the deposited layer thickness, it is confirmed that the diffusion of Ge atoms becomes very active at 600 °C. The Si crystal at the interface is reconstructed and the intermixing occurs over 600 °C. However, the intermixing is fairly restricted in the solid phase epitaxy growth at 400 °C. The surface morphology changes with the crystallization at 400 °C are discussed by the shape of the islands formed on the WL surface. It is shown that the diffusion of the Ge atoms in the amorphous phase is active even at 400 °C.

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.

Epitaxy: Programmable Atom Equivalents Versus Atoms

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

Wang, Mary X.; Seo, Soyoung E.; Gabrys, Paul A.

The programmability of DNA makes it an attractive structure-directing ligand for the assembly of nanoparticle superlattices in a manner that mimics many aspects of atomic crystallization. However, the synthesis of multilayer single crystals of defined size remains a challenge. Though previous studies considered lattice mismatch as the major limiting factor for multilayer assembly, thin film growth depends on many interlinked variables. Here, a more comprehensive approach is taken to study fundamental elements, such as the growth temperature and the thermodynamics of interfacial energetics, to achieve epitaxial growth of nanoparticle thin films. Under optimized equilibrium conditions, single crystal, multilayer thin filmsmore » can be synthesized over 500 × 500 μm2 areas on lithographically patterned templates. Importantly, these superlattices follow the same patterns of crystal growth demonstrated in thin film atomic deposition, allowing for these processes to be understood in the context of well-studied atomic epitaxy, and potentially enabling a nanoscale model to study fundamental crystallization processes.« less

Possible quantum liquid crystal phases of helium monolayers

NASA Astrophysics Data System (ADS)

Nakamura, S.; Matsui, K.; Matsui, T.; Fukuyama, Hiroshi

2016-11-01

The second-layer phase diagrams of 4He and 3He adsorbed on graphite are investigated. Intrinsically rounded specific-heat anomalies are observed at 1.4 and 0.9 K, respectively, over extended density regions in between the liquid and incommensurate solid phases. They are identified to anomalies associated with the Kosterlitz-Thouless-Halperin-Nelson-Young type two-dimensional melting. The prospected low temperature phase (C2 phase) is a commensurate phase or a quantum hexatic phase with quasi-bond-orientational order, both containing zero-point defectons. In either case, this would be the first atomic realization of the quantum liquid crystal, a new state of matter. From the large enhancement of the melting temperature over 3He, we propose to assign the observed anomaly of 4He-C 2 phase at 1.4 K to the hypothetical supersolid or superhexatic transition.

Multiplexed image storage by electromagnetically induced transparency in a solid

NASA Astrophysics Data System (ADS)

Heinze, G.; Rentzsch, N.; Halfmann, T.

2012-11-01

We report on frequency- and angle-multiplexed image storage by electromagnetically induced transparency (EIT) in a Pr3+:Y2SiO5 crystal. Frequency multiplexing by EIT relies on simultaneous storage of light pulses in atomic coherences, driven in different frequency ensembles of the inhomogeneously broadened solid medium. Angular multiplexing by EIT relies on phase matching of the driving laser beams, which permits simultaneous storage of light pulses propagating under different angles into the crystal. We apply the multiplexing techniques to increase the storage capacity of the EIT-driven optical memory, in particular to implement multiplexed storage of larger two-dimensional amounts of data (images). We demonstrate selective storage and readout of images by frequency-multiplexed EIT and angular-multiplexed EIT, as well as the potential to combine both multiplexing approaches towards further enhanced storage capacities.

Structure of catalase determined by MicroED

PubMed Central

Nannenga, Brent L; Shi, Dan; Hattne, Johan; Reyes, Francis E; Gonen, Tamir

2014-01-01

MicroED is a recently developed method that uses electron diffraction for structure determination from very small three-dimensional crystals of biological material. Previously we used a series of still diffraction patterns to determine the structure of lysozyme at 2.9 Å resolution with MicroED (Shi et al., 2013). Here we present the structure of bovine liver catalase determined from a single crystal at 3.2 Å resolution by MicroED. The data were collected by continuous rotation of the sample under constant exposure and were processed and refined using standard programs for X-ray crystallography. The ability of MicroED to determine the structure of bovine liver catalase, a protein that has long resisted atomic analysis by traditional electron crystallography, demonstrates the potential of this method for structure determination. DOI: http://dx.doi.org/10.7554/eLife.03600.001 PMID:25303172

Crystal structure of fac-tri­chlorido­[tris­(pyridin-2-yl-N)amine]­chromium(III)

PubMed Central

Yamaguchi-Terasaki, Yukiko; Fujihara, Takashi; Nagasawa, Akira; Kaizaki, Sumio

2015-01-01

In the neutral complex mol­ecule of the title compound, fac-[CrCl3(tpa)] [tpa is tris­(pyridin-2-yl)amine; C15H12N4], the CrIII ion is bonded to three N atoms that are constrained to a facial arrangement by the tpa ligand and by three chloride ligands, leading to a distorted octa­hedral coordination sphere. The average Cr—N and Cr—Cl bond lengths are 2.086 (5) and 2.296 (4) Å, respectively. The complex mol­ecule is located on a mirror plane. In the crystal, a combination of C—H⋯N and C—H⋯Cl hydrogen-bonding inter­actions connect the mol­ecules into a three-dimensional network. PMID:25705455

The young person’s guide to the PDB*

PubMed Central

Minor, Wladek; Dauter, Zbigniew; Jaskolski, Mariusz

2017-01-01

The Protein Data Bank (PDB), created in 1971 when merely seven protein crystal structures were known, today holds over 120,000 experimentally-determined three-dimensional models of macromolecules, including gigantic structures comprised of hundreds of thousands of atoms, such as ribosomes and viruses. Most of the deposits come from X-ray crystallography experiments, with important contributions also made by NMR spectroscopy and, recently, by the fast growing Cryo-Electron Microscopy. Although the determination of a macromolecular crystal structure is now facilitated by advanced experimental tools and by sophisticated software, it is still a highly complicated research process requiring specialized training, skill, experience and a bit of luck. Understanding the plethora of structural information provided by the PDB requires that its users (consumers) have at least a rudimentary initiation. This is the purpose of this educational overview. PMID:28132477

Environmentally sensitive theory of electronic and optical transitions in atomically thin semiconductors

NASA Astrophysics Data System (ADS)

Cho, Yeongsu; Berkelbach, Timothy C.

2018-01-01

We present an electrostatic theory of band-gap renormalization in atomically thin semiconductors that captures the strong sensitivity to the surrounding dielectric environment. In particular, our theory aims to correct known band gaps, such as that of the three-dimensional bulk crystal. Combining our quasiparticle band gaps with an effective-mass theory of excitons yields environmentally sensitive optical gaps as would be observed in absorption or photoluminescence. For an isolated monolayer of MoS2, the presented theory is in good agreement with ab initio results based on the G W approximation and the Bethe-Salpeter equation. We find that changes in the electronic band gap are almost exactly offset by changes in the exciton binding energy such that the energy of the first optical transition is nearly independent of the electrostatic environment, rationalizing experimental observations.

Macroscopic self-reorientation of interacting two-dimensional crystals

PubMed Central

Woods, C. R.; Withers, F.; Zhu, M. J.; Cao, Y.; Yu, G.; Kozikov, A.; Ben Shalom, M.; Morozov, S. V.; van Wijk, M. M.; Fasolino, A.; Katsnelson, M. I.; Watanabe, K.; Taniguchi, T.; Geim, A. K.; Mishchenko, A.; Novoselov, K. S.

2016-01-01

Microelectromechanical systems, which can be moved or rotated with nanometre precision, already find applications in such fields as radio-frequency electronics, micro-attenuators, sensors and many others. Especially interesting are those which allow fine control over the motion on the atomic scale because of self-alignment mechanisms and forces acting on the atomic level. Such machines can produce well-controlled movements as a reaction to small changes of the external parameters. Here we demonstrate that, for the system of graphene on hexagonal boron nitride, the interplay between the van der Waals and elastic energies results in graphene mechanically self-rotating towards the hexagonal boron nitride crystallographic directions. Such rotation is macroscopic (for graphene flakes of tens of micrometres the tangential movement can be on hundreds of nanometres) and can be used for reproducible manufacturing of aligned van der Waals heterostructures. PMID:26960435

1-(Prop-2-yn­yl)indoline-2,3-dione

PubMed Central

Qachchachi, Fatima-Zahrae; Ouazzani Chahdi, Fouad; Misbahi, Houria; Bodensteiner, Michael; El Ammari, Lahcen

2014-01-01

The structure of the title compound, C11H7NO2, is isotypic to that of its homologue, 1-octylindoline-2,3-dione [Qachchachi et al. (2013 ▶). Acta Cryst. E69, o1801]. The indoline ring and the two carbonyl O atoms are approximately coplanar, the largest deviation from the mean plane being 0.021 (1) Å for one of the O atoms. The mean plane through the fused ring system is nearly perpendicular to the propynyl group, as indicated by the N—C—C—C torsion angle of 77.9 (1)°. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds and π–π inter­actions between benzene rings [inter­centroid distance = 3.5630 (10) Å], forming a three-dimensional structure. PMID:24765046

Band engineering in twisted molybdenum disulfide bilayers

NASA Astrophysics Data System (ADS)

Zhao, Yipeng; Liao, Chengwei; Ouyang, Gang

2018-05-01

In order to explore the theoretical relationship between interlayer spacing, interaction and band offset at the atomic level in vertically stacked two-dimensional (2D) van der Waals (vdW) structures, we propose an analytical model to address the evolution of interlayer vdW coupling with random stacking configurations in MoS2 bilayers based on the atomic-bond-relaxation correlation mechanism. We found that interlayer spacing changes substantially with respect to the orientations, and the bandgap increases from 1.53 eV (AB stacking) to 1.68 eV (AA stacking). Our results reveal that the evolution of interlayer vdW coupling originates from the interlayer interaction, leading to interlayer separations and electronic properties changing with stacking configurations. Our predictions constitute a demonstration of twist engineering the band shift in the emergent class of 2D crystals, transition-metal dichalcogenides.

Experimental and theoretical study of hydrogen thiocarbonate for heterogeneous reaction of carbonyl sulfide on magnesium oxide.

PubMed

Liu, Yongchun; He, Hong

2009-04-09

In situ diffuse reflectance infrared Fourier transform spectroscopy combined with derivative spectroscopy analysis, two-dimensional correlation spectroscopy analysis, and quantum chemical calculations were used to investigate the infrared absorbance assignment and the molecular structure of hydrogen thiocarbonate on magnesium oxide. The bands at 1283 and 1257 cm(-1), which had the typical characteristic of intermediate, were observed in experiments for the heterogeneous reaction of COS on MgO. On the basis of two-dimensional correlation spectroscopy analysis and quantum chemical calculations, the band at 1283 cm(-1) was assigned to the v(s) band of bridged thiocarbonate which formed on the two neighboring Mg atoms in the (100) face of MgO crystal, and the band at 1257 cm(-1) was the v(s) band of monodentate thiocarbonate on MgO. The v(as)(OCO) band of thiocarbonates was invisible in the experiment due to their weak absorbance and the interruption of surface carbonate. The formation mechanism of thiocarbonates is proposed, which occurred through a nucleophilic attack of preadsorbed COS by surface -OH groups followed by hydrogen atom transfer from the -OH group to the sulfur atom of preadsorbed COS. The activation energy for the intramolecular proton-transfer reaction of bridged thiocarbonate was calculated to be 18.52 kcal x mol(-1) at the B3LYP/6-31+G(d,p) level of theory.

trans-Bis[4-amino-3,5-bis­(2-pyrid­yl)-4H-1,2,4-triazole-κN 3]diaqua­cobalt(II) bis­(3-carb­oxy-5-nitro­benzoate)

PubMed Central

Wang, Xi; Shao, Chun-Fu; Li, Cheng-Peng

2011-01-01

The title complex, [Co(C12H10N6)2(H2O)2](C8H4NO6)2, is composed of a mononuclear cobalt(II) cation and two 3-carb­oxy-5-nitro­benzoate anions for charge balance. In the cation, the CoII atom is six-coordinated in a distorted octa­hedral geometry. It bonds to two O atoms of two water mol­ecules, and two pairs of N atoms from two 4-amino-3,5-bis­(2-pyrid­yl)-4H-1,2,4-triazole mol­ecules, which behave as bidentate chelating ligands. There are intra­molecular N—H⋯N hydrogen bonds in the cation. In the crystal, there are a number of inter­molecular N—H⋯O and O—H⋯O hydrogen bonds, as well as inter­molecular π–π stacking inter­actions [centroid–centroid distances = 3.657 (2) and 3.847 (2) Å], that link the mol­ecules into two-dimensional networks lying parallel to the ab plane. The presence of C—H⋯O inter­actions leads to the formation of a three-dimensional network. PMID:22058688

Crystal structure of the ternary silicide Gd2Re3Si5.

PubMed

Fedyna, Vitaliia; Kozak, Roksolana; Gladyshevskii, Roman

2014-12-01

A single crystal of the title compound, the ternary silicide digadolinium trirhenium penta-silicide, Gd2Re3Si5, was isolated from an alloy of nominal composition Gd20Re30Si50 synthesized by arc melting and investigated by X-ray single-crystal diffraction. Its crystal structure belongs to the U2Mn3Si5 structure type. All atoms in the asymmetric lie on special positions. The Gd site has site symmetry m..; the two Mn atoms have site symmetries m.. and 2.22; the three Si atoms have site symmetries m.., ..2 and 4.. . The coordination polyhedra of the Gd atoms have 21 vertices, while those of the Re atoms are cubo-octa-hedra and 13-vertex polyhedra. The Si atoms are arranged as tricapped trigonal prisms, bicapped square anti-prisms, or 11-vertex polyhedra. The crystal structure of the title compound is also related to the structure types CaBe2Ge2 and W5Si3. It can be represented as a stacking of Gd-centred polyhedra of composition [GdSi9]. The Re atoms form infinite chains with an Re-Re distance of 2.78163 (5) Å and isolated squares with an Re-Re distance of 2.9683 (6) Å.

Crystal structure of the ternary silicide Gd2Re3Si5

PubMed Central

Fedyna, Vitaliia; Kozak, Roksolana; Gladyshevskii, Roman

2014-01-01

A single crystal of the title compound, the ternary silicide digadolinium trirhenium penta­silicide, Gd2Re3Si5, was isolated from an alloy of nominal composition Gd20Re30Si50 synthesized by arc melting and investigated by X-ray single-crystal diffraction. Its crystal structure belongs to the U2Mn3Si5 structure type. All atoms in the asymmetric lie on special positions. The Gd site has site symmetry m..; the two Mn atoms have site symmetries m.. and 2.22; the three Si atoms have site symmetries m.., ..2 and 4.. . The coordination polyhedra of the Gd atoms have 21 vertices, while those of the Re atoms are cubo­octa­hedra and 13-vertex polyhedra. The Si atoms are arranged as tricapped trigonal prisms, bicapped square anti­prisms, or 11-vertex polyhedra. The crystal structure of the title compound is also related to the structure types CaBe2Ge2 and W5Si3. It can be represented as a stacking of Gd-centred polyhedra of composition [GdSi9]. The Re atoms form infinite chains with an Re—Re distance of 2.78163 (5) Å and isolated squares with an Re—Re distance of 2.9683 (6) Å. PMID:25552967

‘Pd20Sn13’ revisited: crystal structure of Pd6.69Sn4.31

PubMed Central

Klein, Wilhelm; Jin, Hanpeng; Hlukhyy, Viktor; Fässler, Thomas F.

2015-01-01

The crystal structure of the title compound was previously reported with composition ‘Pd20Sn13’ [Sarah et al. (1981 ▸). Z. Metallkd, 72, 517–520]. For the original structure model, as determined from powder X-ray data, atomic coordinates from the isostructural compound Ni13Ga3Ge6 were transferred. The present structure determination, resulting in a composition Pd6.69Sn4.31, is based on single crystal X-ray data and includes anisotropic displacement parameters for all atoms as well as standard uncertainties for the atomic coordinates, leading to higher precision and accuracy for the structure model. Single crystals of the title compound were obtained via a solid-state reaction route, starting from the elements. The crystal structure can be derived from the AlB2 type of structure after removing one eighth of the atoms at the boron positions and shifting adjacent atoms in the same layer in the direction of the voids. One atomic site is partially occupied by both elements with a Pd:Sn ratio of 0.38 (3):0.62 (3). One Sn and three Pd atoms are located on special positions with site symmetry 2. (Wyckoff letter 3a and 3b). PMID:26279872

Crystal structure and spectroscopic behavior of synthetic novgorodovaite Ca2(C2O4)Cl2·2H2O and its twinned triclinic heptahydrate analog

NASA Astrophysics Data System (ADS)

Piro, Oscar E.; Echeverría, Gustavo A.; González-Baró, Ana C.; Baran, Enrique J.

2018-02-01

Synthetic novgorodovaite analog Ca2(C2O4)Cl2·2H2O is identical to its natural counterpart. It crystallizes in the monoclinic I2/ m space group with a = 6.9352(3), b = 7.3800(4), c = 7.4426(3) Å, β = 94.303(4)°, V = 379.85(3) Å3 and Z = 2. The heptahydrate analog, Ca2(C2O4)Cl2·7H2O, crystallizes as triclinic twins in the P \\overline{1} space group with a = 7.3928(8), b = 8.9925(4), c = 10.484(2) Å, α = 84.070(7), β = 70.95(1), γ = 88.545(7)°, V = 655.3(1) Å3 and Z = 2. The crystal packing of both calcium oxalate-chloride double salts favors the directional bonding of oxalate, C2O4 2-, ligands to calcium ions as do other related calcium oxalate minerals. The π-bonding between C and O atoms of the C2O4 2- oxalate group leaves sp 2-hydridised orbitals of the oxygen atoms available for bonding to Ca. Thus, the Ca-O bonds in both calcium oxalate-chloride double salts are directed so as to lie in the plane of the oxalate group. This behavior is reinforced by the short O···O distances between the oxygens attached to a given carbon atom, which favors them bonding to a shared Ca atom in bidentate fashion. Strong bonding in the plane of the oxalate anion and wide spacing perpendicular to that plane due to repulsion between oxalate π-electron clouds gives rise to a polymerized structural units which are common to both hydrates, explaining the nearly equal cell constants 7.4 Å which are defined by the periodicity of Ca-oxalate chains in the framework (monoclinic b ≈ triclinic a). When compared with novgorodovaite, the higher water content of Ca2(C2O4)Cl2·7H2O leads to some major differences in their structures and ensuing physical properties. While novgorodovaite has a three-dimensional framework structure, in the higher hydrate, the highly polar water molecules displace chloride ions from the calcium coordination sphere and surround them through OwH···Cl hydrogen bonds. As a result, polymerization in Ca2(C2O4)Cl2·7H2O solid is limited to the formation of two-dimensional Ca2(C2O4)(H2O)5 slabs parallel to (001), inter-layered with hydrated chloride anions. This layered structure accounts for (001) being both a perfect cleavage and a twin interface plane. The infrared and Raman spectra of both salts are also briefly discussed.

Phenomenological model of spin crossover in molecular crystals as derived from atom-atom potentials.

PubMed

Sinitskiy, Anton V; Tchougréeff, Andrei L; Dronskowski, Richard

2011-08-07

The method of atom-atom potentials, previously applied to the analysis of pure molecular crystals formed by either low-spin (LS) or high-spin (HS) forms (spin isomers) of Fe(II) coordination compounds (Sinitskiy et al., Phys. Chem. Chem. Phys., 2009, 11, 10983), is used to estimate the lattice enthalpies of mixed crystals containing different fractions of the spin isomers. The crystals under study were formed by LS and HS isomers of Fe(phen)(2)(NCS)(2) (phen = 1,10-phenanthroline), Fe(btz)(2)(NCS)(2) (btz = 5,5',6,6'-tetrahydro-4H,4'H-2,2'-bi-1,3-thiazine), and Fe(bpz)(2)(bipy) (bpz = dihydrobis(1-pyrazolil)borate, and bipy = 2,2'-bipyridine). For the first time the phenomenological parameters Γ pertinent to the Slichter-Drickamer model (SDM) of several materials were independently derived from the microscopic model of the crystals with use of atom-atom potentials of intermolecular interaction. The accuracy of the SDM was checked against the numerical data on the enthalpies of mixed crystals. Fair semiquantitative agreement with the experimental dependence of the HS fraction on temperature was achieved with use of these values. Prediction of trends in Γ values as a function of chemical composition and geometry of the crystals is possible with the proposed approach, which opens a way to rational design of spin crossover materials with desired properties. This journal is © the Owner Societies 2011

Probing periodic potential of crystals via strong-field re-scattering

NASA Astrophysics Data System (ADS)

You, Yong Sing; Cunningham, Eric; Reis, David A.; Ghimire, Shambhu

2018-06-01

Strong-field ionization and re-scattering phenomena have been used to image angstrom-scale structures of isolated molecules in the gas phase. These methods typically make use of the anisotropic response of the participating molecular orbital. Recently, an anisotropic strong-field response has also been observed in high-order harmonic generation (HHG) from bulk crystals (2016 Nat. Phys. 13 345). In a (100) cut magnesium oxide crystal, extreme ultraviolet high-harmonics are found to depend strongly on the crystal structure and inter-atomic bonding. Here, we extend these measurements to other two important crystal orientations: (111) and (110). We find that HHG from these orientations is also strongly anisotropic. The underlying dynamics is understood using a real-space picture, where high-harmonics are produced via coherent collision of strong-field driven electrons from the atomic sites, including from the nearest neighbor atoms. We find that harmonic efficiency is enhanced when semi-classical electron trajectories connect to the concentrated valence charge distribution regions around the atomic cores. Similarly, the efficiency is suppressed when the trajectories miss the atomic cores. These results further support the real-space picture of HHG with implications for retrieving the periodic potential of the crystal, if not the wavefunctions in three-dimensions.

Analysis of the physical atomic forces between noble gas atoms, alkali ions and halogen ions

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Heinbockel, J. H.; Outlaw, R. A.

1986-01-01

The physical forces between atoms and molecules are important in a number of processes of practical importance, including line broadening in radiative processes, gas and crystal properties, adhesion, and thin films. The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base for the dispersion forces is developed from the literature based on evaluations with the harmonic oscillator dispersion model for higher order coefficients. The Zener model of the repulsive core is used in the context of the recent asymptotic wave functions of Handler and Smith; and an effective ionization potential within the Handler and Smith wave functions is defined to analyze the two body potential data of Waldman and Gordon, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

In Situ Three-Dimensional Reciprocal-Space Mapping of Diffuse Scattering Intensity Distribution and Data Analysis for Precursor Phenomenon in Shape-Memory Alloy

NASA Astrophysics Data System (ADS)

Cheng, Tian-Le; Ma, Fengde D.; Zhou, Jie E.; Jennings, Guy; Ren, Yang; Jin, Yongmei M.; Wang, Yu U.

2012-01-01

Diffuse scattering contains rich information on various structural disorders, thus providing a useful means to study the nanoscale structural deviations from the average crystal structures determined by Bragg peak analysis. Extraction of maximal information from diffuse scattering requires concerted efforts in high-quality three-dimensional (3D) data measurement, quantitative data analysis and visualization, theoretical interpretation, and computer simulations. Such an endeavor is undertaken to study the correlated dynamic atomic position fluctuations caused by thermal vibrations (phonons) in precursor state of shape-memory alloys. High-quality 3D diffuse scattering intensity data around representative Bragg peaks are collected by using in situ high-energy synchrotron x-ray diffraction and two-dimensional digital x-ray detector (image plate). Computational algorithms and codes are developed to construct the 3D reciprocal-space map of diffuse scattering intensity distribution from the measured data, which are further visualized and quantitatively analyzed to reveal in situ physical behaviors. Diffuse scattering intensity distribution is explicitly formulated in terms of atomic position fluctuations to interpret the experimental observations and identify the most relevant physical mechanisms, which help set up reduced structural models with minimal parameters to be efficiently determined by computer simulations. Such combined procedures are demonstrated by a study of phonon softening phenomenon in precursor state and premartensitic transformation of Ni-Mn-Ga shape-memory alloy.

Polymorphism in 'L' shaped lipids: structure of N-, O-diacylethanolamines with mixed acyl chains.

PubMed

Tarafdar, Pradip K; Swamy, Musti J

2009-11-01

Although solid state polymorphism in lipids has been established by spectroscopic and calorimetric studies long ago, only in a few cases crystal structures of different polymorphs of the same compound have been reported, possibly due to difficulties in obtaining high quality single crystals of individual polymorphs. Recent studies show that N-, O-diacylethanolamines (DAEs) can be derived by the O-acylation of the stress-related lipids, the N-acylethanolamines under physiological conditions. In this study, two DAEs with mixed acyl chains, namely N-palmitoyl, O-octanoylethanolamine and N-palmitoyl, O-decanoylethanolamine have been synthesized and their three-dimensional structures were determined. Both the compounds were found to adopt 'L' shaped structures and exist in two polymorphic forms, alpha and beta. In the alpha form a mixed-type chain packing has been observed whereas in the beta form the chain packing is symmetric. Similar polymorphic forms are likely to exist in other 'L' shaped lipids such as 1,3-diacylglycerols and ceramides, where polymorphism has been detected earlier, but three-dimensional structures - which can give precise information about the packing at atomic resolution - have not been reported.

Rapid, all-optical crystal orientation imaging of two-dimensional transition metal dichalcogenide monolayers

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

David, Sabrina N.; Zhai, Yao; van der Zande, Arend M.

Two-dimensional (2D) atomic materials such as graphene and transition metal dichalcogenides (TMDCs) have attracted significant research and industrial interest for their electronic, optical, mechanical, and thermal properties. While large-area crystal growth techniques such as chemical vapor deposition have been demonstrated, the presence of grain boundaries and orientation of grains arising in such growths substantially affect the physical properties of the materials. There is currently no scalable characterization method for determining these boundaries and orientations over a large sample area. We here present a second-harmonic generation based microscopy technique for rapidly mapping grain orientations and boundaries of 2D TMDCs. We experimentallymore » demonstrate the capability to map large samples to an angular resolution of ±1° with minimal sample preparation and without involved analysis. A direct comparison of the all-optical grain orientation maps against results obtained by diffraction-filtered dark-field transmission electron microscopy plus selected-area electron diffraction on identical TMDC samples is provided. This rapid and accurate tool should enable large-area characterization of TMDC samples for expedited studies of grain boundary effects and the efficient characterization of industrial-scale production techniques.« less

Network dimensionality and ligand flexibility in lanthanide terephthalate hydrates

NASA Astrophysics Data System (ADS)

Zehnder, Ralph A.; Renn, Robert A.; Pippin, Ethan; Zeller, Matthias; Wheeler, Kraig A.; Carr, Jason A.; Fontaine, Nick; McMullen, Nathan C.

2011-01-01

Various lanthanide open framework materials incorporating the terephthalate (TP) entity were prepared using hydrothermal synthesis methods at a moderate temperature of 170 °C. The compounds Nd 2(TP) 3(H 2O) 4( 1), Er 2(TP) 3(H 2O) 4( 2), Yb 2(TP) 3(H 2O) 2( 3), Yb 2(TP) 3(H 2O) 6( 4), and Yb 2(TP) 3(H 2O) 8·2H 2O ( 5), were characterized by single crystal structural analysis and FT-IR spectroscopy. While compounds 1 and 2 have been reported before on the basis of powder X-ray diffraction, the structural characterization of any ytterbium terephthalate species is unprecedented. Compounds 1- 5 crystallize in triclinic settings with space group P-1. The compounds are compared with their previously reported Er and Tb-counterparts and the reduction of the dimensionality of the resulting networks from 3D over 2D to 1D with increasing level of hydration is discussed. Compounds 1, 2, and 3 with the lowest water content assemble in three-dimensional network lattices. Compounds 4 and 5, however, form 2D layered systems and 1D rod like chains, respectively, which are held together by hydrogen bonds originating from coordinating H 2O. The crystal lattices of the 3D networks experience higher levels of tension as can be seen by increasing out-of-plane torsion with regard to the terephthalate carboxylate groups. Moreover, there seems to be a correlation between the level of strain on the aromatic ligands and the reduction of the number of carboxylate oxygen atoms that are part of the coordination polyhedra.

Theoretical investigation of microstructure evolution and deformation of zirconium under neutron irradiation

DOE PAGES

Barashev, A. V.; Golubov, S. I.; Stoller, R. E.

2015-06-01

We studied the radiation growth of zirconium using a reaction–diffusion model which takes into account intra-cascade clustering of self-interstitial atoms and one-dimensional diffusion of interstitial clusters. The observed dose dependence of strain rates is accounted for by accumulation of sessile dislocation loops during irradiation. Moreover, the computational model developed and fitted to available experimental data is applied to study deformation of Zr single crystals under irradiation up to hundred dpa. Finally, the effect of cold work and the reasons for negative prismatic strains and co-existence of vacancy and interstitial loops are elucidated.

Magnetic transport property of NiFe/WSe2/NiFe spin valve structure

NASA Astrophysics Data System (ADS)

Zhao, Kangkang; Xing, Yanhui; Han, Jun; Feng, Jiafeng; Shi, Wenhua; Zhang, Baoshun; Zeng, Zhongming

2017-06-01

Two-dimensional (2D) materials have been proposed as promising candidate for spintronic applications due to their atomic crystal structure and physical properties. Here, we introduce exfoliated few-layer tungsten diselenide (WSe2) as spacer in a Py/WSe2/Py vertical spin valve. In this junction, the WSe2 spacer exhibits metallic behavior. We observed negative magnetoresistance (MR) with a ratio of -1.1% at 4 K and -0.21% at 300 K. A general phenomenological analysis of the negative MR property is discussed. Our result is anticipated to be beneficial for future spintronic applications.

1,3-Bis[(5-amino-furan-2-yl)meth-yl]-3,4,5,6-tetra-hydro-pyrimidin-1-ium hexa-fluoro-phosphate.

PubMed

Akkurt, Mehmet; Akkoç, Senem; Gök, Yetkin; Tahir, Muhammad Nawaz

2013-01-01

The asymmetric unit of the title salt, C16H21N2O2 (+)·PF6 (-), contains half of the whole ion pair, which has crystallographic mirror symmetry. Two F atoms related by the mirror plane are disordered over two sites of equal occupancy. The dihedral angle between the central ring and the furan ring is 59.3 ()°. In the crystal, the anions and cations are linked through C-H⋯F inter-actions, forming a three-dimensional network.

2-(2-Thien­yl)-4,5-dihydro-1H-imidazole

PubMed Central

Kia, Reza; Fun, Hoong-Kun; Kargar, Hadi

2009-01-01

In title compound, C7H8N2S, the five-membered rings are twisted by a dihedral angle of 5.17 (10)°. Two inter­molecular N—H⋯N and C—H⋯N hydrogen bonds to the same acceptor N atom form seven-membered rings, producing R 2 1(7) ring motifs. These inter­actions link neighbouring mol­ecules into one-dimensional chains extended along the c axis. The crystal structure is further stabilized by weak inter­molecular C—H⋯π inter­actions. PMID:21581910

Universal description of III-V/Si epitaxial growth processes

NASA Astrophysics Data System (ADS)

Lucci, I.; Charbonnier, S.; Pedesseau, L.; Vallet, M.; Cerutti, L.; Rodriguez, J.-B.; Tournié, E.; Bernard, R.; Létoublon, A.; Bertru, N.; Le Corre, A.; Rennesson, S.; Semond, F.; Patriarche, G.; Largeau, L.; Turban, P.; Ponchet, A.; Cornet, C.

2018-06-01

Here, we experimentally and theoretically clarify III-V/Si crystal growth processes. Atomically resolved microscopy shows that monodomain three-dimensional islands are observed at the early stages of AlSb, AlN, and GaP epitaxy on Si, independently of misfit. It is also shown that complete III-V/Si wetting cannot be achieved in most III-V/Si systems. Surface/interface contributions to the free-energy variations are found to be prominent over strain relief processes. We finally propose a general and unified description of III-V/Si growth processes, including a description of the formation of antiphase boundaries.

Unusual Features of Crystal Structures of Some Simple Copper Compounds

ERIC Educational Resources Information Center

Douglas, Bodie

2009-01-01

Some simple copper compounds have unusual crystal structures. Cu[subscript 3]N is cubic with N atoms at centers of octahedra formed by 6 Cu atoms. Cu[subscript 2]O (cuprite) is also cubic; O atoms are in tetrahedra formed by 4 Cu atoms. These tetrahedra are linked by sharing vertices forming two independent networks without linkages between them.…

Quasi-One-Dimensional Ultracold Fermi Gases

NASA Astrophysics Data System (ADS)

Revelle, Melissa C.

Ultracold atoms have become an essential tool in studying condensed matter phenomena. The advantage of atomic physics experiments is that they provide an easily tunable system. This experiment uses the lowest two ground state hyperfine levels of fermionic lithium. Having two different states creates a pseudo-spin- 1/2 system and allows us to emulate electronic systems, such as superconductors and crystal lattices. In our experiment, we can control the ratio between these two states resulting in either a spin-balanced or a spin-imbalanced gas. Imposing an imbalance is analogous to applying a magnetic field to a superconductor which causes the electrons in the material to align to the field (thus breaking the electron pairs which cause superconductivity). This motivates us to understand the phases created when a spin-imbalance is created and the effect of changing the atomic interactions. In a 3D system, we find where superfluidity is suppressed throughout the BEC to BCS crossover. Using phase separation as a guide, we probe the dimensional crossover between 1D and 3D. The phase separation in 1D is inverted from that in 3D, which provides a unique characteristic to distinguish between the dimensions. By varying the tunneling between tubes and the atomic interactions in a 2D optical lattice, we control whether the system is 1D, 3D, or in between. Using the properties of a 3D gas as a guide, we directly observe when the gas has crossed over from being dominated by 1D-like behavior to 3D. In this way, we have found a universal value for the dimensional crossover. The 1D-3D crossover paves the way to search for the exotic FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) superconductor. While most superconductors do not coexist with magnetism, the FFLO phase requires large magnetic fields to support its pairing mechanism. Additionally, this phase is more likely to be found in lower dimensional systems. However, at low dimensions, the effect of temperature fluctuations on the phase is destabilizing, but these temperature effects are reduced with higher dimensionality. Thus, the quasi-1D regime is the optimal region of parameter space to find this phase. The search for direct evidence of FFLO continues in this regime.

Isomorphous rare-earth bis[bis(2,6-diisopropylphenyl)phosphate] complexes and their self-assembly into two-dimensional frameworks by intramolecular hydrogen bonds.

PubMed

Minyaev, Mikhail E; Nifant'ev, Ilya E; Tavtorkin, Alexander N; Korchagina, Sof'ya A; Zeynalova, Shadana Sh; Ananyev, Ivan V; Churakov, Andrei V

2017-10-01

The crystal structures of rare-earth diaryl- or dialkylphosphate derivatives are poorly explored. Crystals of bis[bis(2,6-diisopropylphenyl)phosphato-κO]chloridotetrakis(methanol-κO)neodymium methanol disolvate, [Nd(C 24 H 34 O 4 P)Cl(CH 4 O) 4 ]·2CH 3 OH, (1), and of the lutetium, [Lu(C 24 H 34 O 4 P)Cl(CH 4 O) 4 ]·2CH 3 OH, (2), and yttrium, [Y(C 24 H 34 O 4 P)Cl(CH 4 O) 4 ]·2CH 3 OH, (3), analogues have been obtained by reactions between lithium bis(2,6-diisopropylphenyl)phosphate and LnCl 3 (H 2 O) 6 (in a 2:1 ratio) in methanol. Compounds (1)-(3) crystallize in the C2/c space group. Their crystal structures are isomorphous. The molecule possesses C 2 symmetry with a twofold crystallographic axis passing through the Ln and Cl atoms. The bis(2,6-diisopropylphenyl)phosphate ligands all display a κ 1 O-monodentate coordination mode. The coordination polyhedron for the metal atom [coordination number (CN) = 7] is a distorted pentagonal bipyramid. Each [Ln{O 2 P(O-2,6- i Pr 2 C 6 H 3 ) 2 } 2 Cl(CH 3 OH) 4 ] molecular unit exhibits two intramolecular O-H...O hydrogen bonds, forming six-membered rings, and two intramolecular O-H...Cl interactions, forming four-membered rings. Intermolecular O-H...O hydrogen bonds connect each unit via four noncoordinating methanol molecules with four other units, forming a two-dimensional hydrogen-bond network. Crystals of bis[bis(2,6-diisopropylphenyl)phosphato-κO]tetrakis(methanol-κO)(nitrato-κ 2 O,O')neodymium methanol disolvate, [Nd(C 24 H 34 O 4 P)(NO 3 )(CH 4 O) 4 ]·2CH 3 OH, (4), have been obtained in an analogous manner from NdCl 3 (H 2 O) 6 . Compound (4) also crystalizes in the C2/c space group. Its crystal structure is similar to those of (1)-(3). The κ 2 O,O'-bidentate nitrate anion is disordered over a twofold axis, being located nearly on it. Half of the molecule is crystallographically unique (CN Nd = 8). Unlike (1)-(3), complex (4) exhibits disorder of all three methanol molecules, one isopropyl group of the phosphate ligand and the NO 3 - ligand. The structure of (4) displays intra- and intermolecular O-H...O hydrogen bonds similar to those in (1)-(3). Compounds (1)-(4) represent the first reported mononuclear bis[bis(diaryl/dialkyl)phosphate] rare-earth complexes.

Strong photon antibunching in weakly nonlinear two-dimensional exciton-polaritons

NASA Astrophysics Data System (ADS)

Ryou, Albert; Rosser, David; Saxena, Abhi; Fryett, Taylor; Majumdar, Arka

2018-06-01

A deterministic and scalable array of single photon nonlinearities in the solid state holds great potential for both fundamental physics and technological applications, but its realization has proved extremely challenging. Despite significant advances, leading candidates such as quantum dots and group III-V quantum wells have yet to overcome their respective bottlenecks in random positioning and weak nonlinearity. Here we consider a hybrid light-matter platform, marrying an atomically thin two-dimensional material to a photonic crystal cavity, and analyze its second-order coherence function. We identify several mechanisms for photon antibunching under different system parameters, including one characterized by large dissipation and weak nonlinearity. Finally, we show that by patterning the two-dimensional material into different sizes, we can drive our system dynamics from a coherent state into a regime of strong antibunching with second-order coherence function g(2 )(0 ) ˜10-3 , opening a possible route to scalable, on-chip quantum simulations with correlated photons.

Syntheses, structures and properties of three new two-dimensional Cu(I)-Ln(III) heterometallic coordination polymers based on 2,2'-dipyridyl-5,5'-dicarboxylate ligands.

PubMed

Zhao, Junwei; Cheng, Yamin; Shang, Sensen; Zhang, Fang; Chen, Li; Chen, Lijuan

2013-12-01

Three new two-dimensional Cu(I)-Ln(III) heterometallic coordination polymers [Ln(III)Cu2(I)(Hbpdc)4] · Cl · xH2O [Ln(III) = La(III), x = 8 (1); Ln(III) = Pr(III), x=9 (2); Ln(III) = Eu(III), x = 8 (3)] (H2bpdc = 2,2'-bipyridyl-5,5'-dicarboxylic acid) have been prepared under hydrothermal conditions and structurally characterized by elemental analyses, inductively coupled plasma atomic emission spectrometry (ICP-AES) analyses, IR spectra, X-ray photoelectron spectroscopy (XPS) and single-crystal X-ray diffraction. X-ray diffraction indicates that the isomorphic 1-3 display the two-dimensional sheet structure constructed from [Cu(I)(Hbpdc)2](-) fragments through Ln(3+) connectors. Moreover, the solid-state photoluminescence measurements of 3 indicate that the Eu(III) ions, Hbpdc(-) ligands and Cu(I) cations make contributions to its luminescent properties simultaneously. Copyright © 2013 Elsevier B.V. All rights reserved.

Artificial two-dimensional polar metal at room temperature.

PubMed

Cao, Yanwei; Wang, Zhen; Park, Se Young; Yuan, Yakun; Liu, Xiaoran; Nikitin, Sergey M; Akamatsu, Hirofumi; Kareev, M; Middey, S; Meyers, D; Thompson, P; Ryan, P J; Shafer, Padraic; N'Diaye, A; Arenholz, E; Gopalan, Venkatraman; Zhu, Yimei; Rabe, Karin M; Chakhalian, J

2018-04-18

Polar metals, commonly defined by the coexistence of polar crystal structure and metallicity, are thought to be scarce because the long-range electrostatic fields favoring the polar structure are expected to be fully screened by the conduction electrons of a metal. Moreover, reducing from three to two dimensions, it remains an open question whether a polar metal can exist. Here we report on the realization of a room temperature two-dimensional polar metal of the B-site type in tri-color (tri-layer) superlattices BaTiO 3 /SrTiO 3 /LaTiO 3 . A combination of atomic resolution scanning transmission electron microscopy with electron energy-loss spectroscopy, optical second harmonic generation, electrical transport, and first-principles calculations have revealed the microscopic mechanisms of periodic electric polarization, charge distribution, and orbital symmetry. Our results provide a route to creating all-oxide artificial non-centrosymmetric quasi-two-dimensional metals with exotic quantum states including coexisting ferroelectric, ferromagnetic, and superconducting phases.

Growing three-dimensional biomorphic graphene powders using naturally abundant diatomite templates towards high solution processability.

PubMed

Chen, Ke; Li, Cong; Shi, Liurong; Gao, Teng; Song, Xiuju; Bachmatiuk, Alicja; Zou, Zhiyu; Deng, Bing; Ji, Qingqing; Ma, Donglin; Peng, Hailin; Du, Zuliang; Rümmeli, Mark Hermann; Zhang, Yanfeng; Liu, Zhongfan

2016-11-07

Mass production of high-quality graphene with low cost is the footstone for its widespread practical applications. We present herein a self-limited growth approach for producing graphene powders by a small-methane-flow chemical vapour deposition process on naturally abundant and industrially widely used diatomite (biosilica) substrates. Distinct from the chemically exfoliated graphene, thus-produced biomorphic graphene is highly crystallized with atomic layer-thickness controllability, structural designability and less noncarbon impurities. In particular, the individual graphene microarchitectures preserve a three-dimensional naturally curved surface morphology of original diatom frustules, effectively overcoming the interlayer stacking and hence giving excellent dispersion performance in fabricating solution-processible electrodes. The graphene films derived from as-made graphene powders, compatible with either rod-coating, or inkjet and roll-to-roll printing techniques, exhibit much higher electrical conductivity (∼110,700 S m -1 at 80% transmittance) than previously reported solution-based counterparts. This work thus puts forward a practical route for low-cost mass production of various powdery two-dimensional materials.

Growing three-dimensional biomorphic graphene powders using naturally abundant diatomite templates towards high solution processability

NASA Astrophysics Data System (ADS)

Chen, Ke; Li, Cong; Shi, Liurong; Gao, Teng; Song, Xiuju; Bachmatiuk, Alicja; Zou, Zhiyu; Deng, Bing; Ji, Qingqing; Ma, Donglin; Peng, Hailin; Du, Zuliang; Rümmeli, Mark Hermann; Zhang, Yanfeng; Liu, Zhongfan

2016-11-01

Mass production of high-quality graphene with low cost is the footstone for its widespread practical applications. We present herein a self-limited growth approach for producing graphene powders by a small-methane-flow chemical vapour deposition process on naturally abundant and industrially widely used diatomite (biosilica) substrates. Distinct from the chemically exfoliated graphene, thus-produced biomorphic graphene is highly crystallized with atomic layer-thickness controllability, structural designability and less noncarbon impurities. In particular, the individual graphene microarchitectures preserve a three-dimensional naturally curved surface morphology of original diatom frustules, effectively overcoming the interlayer stacking and hence giving excellent dispersion performance in fabricating solution-processible electrodes. The graphene films derived from as-made graphene powders, compatible with either rod-coating, or inkjet and roll-to-roll printing techniques, exhibit much higher electrical conductivity (~110,700 S m-1 at 80% transmittance) than previously reported solution-based counterparts. This work thus puts forward a practical route for low-cost mass production of various powdery two-dimensional materials.

Artificial two-dimensional polar metal at room temperature

DOE PAGES

Cao, Yanwei; Wang, Zhen; Park, Se Young; ...

2018-04-18

Polar metals, commonly defined by the coexistence of polar crystal structure and metallicity, are thought to be scarce because the long-range electrostatic fields favoring the polar structure are expected to be fully screened by the conduction electrons of a metal. Moreover, reducing from three to two dimensions, it remains an open question whether a polar metal can exist. Here we report on the realization of a room temperature two-dimensional polar metal of the B-site type in tri-color (tri-layer) superlattices BaTiO 3/SrTiO 3/LaTiO 3. A combination of atomic resolution scanning transmission electron microscopy with electron energy-loss spectroscopy, optical second harmonic generation,more » electrical transport, and first-principles calculations have revealed the microscopic mechanisms of periodic electric polarization, charge distribution, and orbital symmetry. Lastly, our results provide a route to creating all-oxide artificial non-centrosymmetric quasi-two-dimensional metals with exotic quantum states including coexisting ferroelectric, ferromagnetic, and superconducting phases.« less

Artificial two-dimensional polar metal at room temperature

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

Cao, Yanwei; Wang, Zhen; Park, Se Young

Polar metals, commonly defined by the coexistence of polar crystal structure and metallicity, are thought to be scarce because the long-range electrostatic fields favoring the polar structure are expected to be fully screened by the conduction electrons of a metal. Moreover, reducing from three to two dimensions, it remains an open question whether a polar metal can exist. Here we report on the realization of a room temperature two-dimensional polar metal of the B-site type in tri-color (tri-layer) superlattices BaTiO 3/SrTiO 3/LaTiO 3. A combination of atomic resolution scanning transmission electron microscopy with electron energy-loss spectroscopy, optical second harmonic generation,more » electrical transport, and first-principles calculations have revealed the microscopic mechanisms of periodic electric polarization, charge distribution, and orbital symmetry. Lastly, our results provide a route to creating all-oxide artificial non-centrosymmetric quasi-two-dimensional metals with exotic quantum states including coexisting ferroelectric, ferromagnetic, and superconducting phases.« less

Characterization of iron ferromagnetism by the local atomic volume: from three-dimensional structures to isolated atoms.

PubMed

Zhang, Lei; Sob, M; Wu, Zhe; Zhang, Ying; Lu, Guang-Hong

2014-02-26

We present a comprehensive study of the relationship between the ferromagnetism and the structural properties of Fe systems from three-dimensional ones to isolated atoms based on the spin-density functional theory. We have found a relation between the magnetic moment and the volume of the Voronoi polyhedron, determining, in most cases, the value of the total magnetic moment as a function of this volume with an average accuracy of ±0.28 μ(B) and of the 3d magnetic moment with an average accuracy of ±0.07 μ(B) when the atomic volume is larger than 22 ų. It is demonstrated that this approach is applicable for many three-dimensional systems, including high-symmetry structures of perfect body-centered cubic (bcc), face-centered cubic (fcc), hexagonal close-packed (hcp), double hexagonal close-packed (dhcp), and simple cubic (sc) crystals, as well as for lower-symmetry ones, for example atoms near a grain boundary (GB) or a surface, around a vacancy or in a linear chain (for low-dimensional cases, we provide a generalized definition of the Voronoi polyhedron). Also, we extend the validity of the Stoner model to low-dimensional structures, such as atomic chains, free-standing monolayers and surfaces, determining the Stoner parameter for these systems. The ratio of the 3d-exchange splitting to the magnetic moment, corresponding to the Stoner parameter, is found to be I(3d) = (0.998 ± 0.006) eV /μ(B) for magnetic moments up to 3.0 μ(B). Further, the 3d exchange splitting changes nearly linearly in the region of higher magnetic moments (3.0-4.0 μ(B)) and the corresponding Stoner exchange parameter equals I(h)(3d) = (0.272 ± 0.006) eV /μ(B). The existence of these two regions reflects the fact that, with increasing Voronoi volume, the 3d bands separate first and, consequently, the 3d magnetic moment increases. When the Voronoi volume is sufficiently large (≥22 ų), the separation of the 3d bands is complete and the magnetic moment reaches a value of 3.0 μ(B). Then, when the volume further increases, the 4s bands start to separate, increasing thus the 4s magnetic moment. Surprisingly, in the region of higher magnetic moments (≥3.0 μ(B)), there is also a linear relationship between the 4s exchange splitting and the total magnetic moment with a slope of I(h)(4s) = (1.053 ± 0.016) eV /μ(B), which is nearly identical to I(3d) for magnetic moments up to 3.0 μB. These linear relations can be considered as an extension of the Stoner model for low-dimensional systems.

Crystal structure of 2-diazo-imidazole-4,5-dicarbo-nitrile.

PubMed

Parrish, Damon A; Kramer, Stephanie; Windler, G Kenneth; Chavez, David E; Leonard, Philip W

2015-07-01

In the title compound, C5N6, all the atoms are approximately coplanar. In the crystal, mol-ecules are packed with short contact distances of 2.885 (2) (between the diazo N atom connected to the ring and a cyano N atom on a neighboring mol-ecule) and 3.012 (2) Å (between the terminal diazo N atom and an N atom of a neighboring imidazole ring).

Observation of extraordinary transmission in deep UV region from aluminum film coated two dimensional photonic crystals

NASA Astrophysics Data System (ADS)

Venkatesh, A.; Piragash Kumar, R. M.; Moorthy, V. H. S.

2018-05-01

We report the first observation of extraordinary transmission of deep-UV light (λ = 289nm) through 20nm aluminum film coated two-dimensional photonic crystals. The two-dimensional photonic crystals are made of self-assembled hexagonally arranged monolayer of 200 nm polystyrene spheres fabricated using drop casting method. The high quality photonic crystal exhibits a well-defined photonic band gap of 4.59 eV (λ = 270nm) and the aluminum coated two-dimensional photonic crystal displays extraordinary transmission in the deep-UV region at λ = 289 nm. The fabricated aluminum nanostructure produces a sensitivity of 42nm/RIU and 57nm/RIU when the refractive index of the surrounding medium is changed from 1 (= air) to 1.36 (= ethanol) and 1.49 (=toluene), respectively. Therefore, the aluminum film coated two-dimensional photonic crystals could be utilized to fabricate cost-effective and ultrasensitive chemical sensors.

Absence of Dirac states in BaZnBi 2 induced by spin-orbit coupling

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

Ren, Weijun; Wang, Aifeng; Graf, D.

We report magnetotransport properties of BaZnBi 2 single crystals. Whereas electronic structure features Dirac states, such states are removed from the Fermi level by spin-orbit coupling (SOC) and consequently electronic transport is dominated by the small hole and electron pockets. Our results are consistent with not only three-dimensional, but also with quasi-two-dimensional portions of the Fermi surface. The SOC-induced gap in Dirac states is much larger when compared to isostructural SrMnBi 2. This suggests that not only long-range magnetic order, but also mass of the alkaline-earth atoms A in ABX 2 ( A = alkaline-earth, B = transition-metal, and Xmore » = Bi/Sb) are important for the presence of low-energy states obeying the relativistic Dirac equation at the Fermi surface.« less

In situ three-dimensional reciprocal-space mapping during mechanical deformation.

PubMed

Cornelius, T W; Davydok, A; Jacques, V L R; Grifone, R; Schülli, T; Richard, M I; Beutier, G; Verdier, M; Metzger, T H; Pietsch, U; Thomas, O

2012-09-01

Mechanical deformation of a SiGe island epitaxically grown on Si(001) was studied by a specially adapted atomic force microscope and nanofocused X-ray diffraction. The deformation was monitored during in situ mechanical loading by recording three-dimensional reciprocal-space maps around a selected Bragg peak. Scanning the energy of the incident beam instead of rocking the sample allowed the safe and reliable measurement of the reciprocal-space maps without removal of the mechanical load. The crystal truncation rods originating from the island side facets rotate to steeper angles with increasing mechanical load. Simulations of the displacement field and the intensity distribution, based on the finite-element method, reveal that the change in orientation of the side facets of about 25° corresponds to an applied pressure of 2-3 GPa on the island top plane.

Absence of Dirac states in BaZnBi 2 induced by spin-orbit coupling

DOE PAGES

Ren, Weijun; Wang, Aifeng; Graf, D.; ...

2018-01-22

We report magnetotransport properties of BaZnBi 2 single crystals. Whereas electronic structure features Dirac states, such states are removed from the Fermi level by spin-orbit coupling (SOC) and consequently electronic transport is dominated by the small hole and electron pockets. Our results are consistent with not only three-dimensional, but also with quasi-two-dimensional portions of the Fermi surface. The SOC-induced gap in Dirac states is much larger when compared to isostructural SrMnBi 2. This suggests that not only long-range magnetic order, but also mass of the alkaline-earth atoms A in ABX 2 ( A = alkaline-earth, B = transition-metal, and Xmore » = Bi/Sb) are important for the presence of low-energy states obeying the relativistic Dirac equation at the Fermi surface.« less

Synthesis and structural characterization of dinuclear Cd2+, Hg2+ and Fe2+ complexes with neutral bi and tetradentate flexible pyrazole-based ligands

NASA Astrophysics Data System (ADS)

Beheshti, Azizolla; Lalegani, Arash; Behvandi, Fatemeh; Safaeiyan, Forough; Sarkarzadeh, Afsoon; Bruno, Giuseppe; Amiri Rudbari, Hadi

2015-02-01

Four new complexes of [Hg2Cl4(bpp)]n (1), [Hg2Cl4(tdmpp)] (2), [Cd2I4(tdmpp)] (3) and [Fe2Cl4(tdmpp)] (4) were prepared by using the neutral N-donor ligands 1,3-bis(3,5-dimethyl-1-pyrazolyl)propane (bpp) and 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazolyl)propane (tdmpp) with different flexibility and appropriate metal salts of Cd(II), Hg(II) and Fe(II) ions. These compounds were characterized by the infrared spectroscopy, elemental analysis and X-ray crystallography. Flexible ligands and non-covalent Csbnd H⋯Cl hydrogen bonds play a major role in the crystal packing of compounds 1, 2 and 4. In the two-dimensional non-covalent structure of 1, there are two distinctly different coordination modes for the mercury atoms. One mercury atom has pseudo-trigonal bipyramidal geometry and the other adopts a distorted tetrahedral environment. In the dinuclear structures of 2 and 4 the neutral molecules are linked together by the Csbnd H⋯Cl hydrogen bonds, forming an infinite one-dimensional zigzag chain structure. Compounds 2-4 are isostructural with each other.

Two-dimensional antimonene single crystals grown by van der Waals epitaxy.

PubMed

Ji, Jianping; Song, Xiufeng; Liu, Jizi; Yan, Zhong; Huo, Chengxue; Zhang, Shengli; Su, Meng; Liao, Lei; Wang, Wenhui; Ni, Zhenhua; Hao, Yufeng; Zeng, Haibo

2016-11-15

Unlike the unstable black phosphorous, another two-dimensional group-VA material, antimonene, was recently predicted to exhibit good stability and remarkable physical properties. However, the synthesis of high-quality monolayer or few-layer antimonenes, sparsely reported, has greatly hindered the development of this new field. Here, we report the van der Waals epitaxy growth of few-layer antimonene monocrystalline polygons, their atomical microstructure and stability in ambient condition. The high-quality, few-layer antimonene monocrystalline polygons can be synthesized on various substrates, including flexible ones, via van der Waals epitaxy growth. Raman spectroscopy and transmission electron microscopy reveal that the obtained antimonene polygons have buckled rhombohedral atomic structure, consistent with the theoretically predicted most stable β-phase allotrope. The very high stability of antimonenes was observed after aging in air for 30 days. First-principle and molecular dynamics simulation results confirmed that compared with phosphorene, antimonene is less likely to be oxidized and possesses higher thermodynamic stability in oxygen atmosphere at room temperature. Moreover, antimonene polygons show high electrical conductivity up to 10 4  S m -1 and good optical transparency in the visible light range, promising in transparent conductive electrode applications.

Two-dimensional antimonene single crystals grown by van der Waals epitaxy

PubMed Central

Ji, Jianping; Song, Xiufeng; Liu, Jizi; Yan, Zhong; Huo, Chengxue; Zhang, Shengli; Su, Meng; Liao, Lei; Wang, Wenhui; Ni, Zhenhua; Hao, Yufeng; Zeng, Haibo

2016-01-01

Unlike the unstable black phosphorous, another two-dimensional group-VA material, antimonene, was recently predicted to exhibit good stability and remarkable physical properties. However, the synthesis of high-quality monolayer or few-layer antimonenes, sparsely reported, has greatly hindered the development of this new field. Here, we report the van der Waals epitaxy growth of few-layer antimonene monocrystalline polygons, their atomical microstructure and stability in ambient condition. The high-quality, few-layer antimonene monocrystalline polygons can be synthesized on various substrates, including flexible ones, via van der Waals epitaxy growth. Raman spectroscopy and transmission electron microscopy reveal that the obtained antimonene polygons have buckled rhombohedral atomic structure, consistent with the theoretically predicted most stable β-phase allotrope. The very high stability of antimonenes was observed after aging in air for 30 days. First-principle and molecular dynamics simulation results confirmed that compared with phosphorene, antimonene is less likely to be oxidized and possesses higher thermodynamic stability in oxygen atmosphere at room temperature. Moreover, antimonene polygons show high electrical conductivity up to 104 S m−1 and good optical transparency in the visible light range, promising in transparent conductive electrode applications. PMID:27845327

Structural Analysis of MoS2 and other 2D layered materials using LEEM/LEED-I(V) and STM

NASA Astrophysics Data System (ADS)

Grady, Maxwell; Dai, Zhongwei; Jin, Wencan; Dadap, Jerry; Osgood, Richard; Sadowski, Jerzy; Pohl, Karsten

Layered two-dimensional materials, such as molybdenum disulfide, MoS2, are of interest for the development of many types of novel electronic devices. To fully understand the interfaces between these new materials, the atomic reconstructions at their surfaces must be understood. Low Energy Electron Microscopy and Diffraction, LEEM/ μLEED, present a unique method for rapid material characterization in real space and reciprocal space with high resolution. Here we present a study of the surface structure of 2H-MoS2 using μLEED intensity-voltage analysis. To aid this analysis, software is under development to automate the procedure of extracting I(V) curves from LEEM and LEED data. When matched with computational modeling, this data provides information with angstrom level resolution concerning the three dimensional atomic positions. We demonstrate that the surface structure of bulk MoS2 is distinct from the bulk crystal structure and exhibits a smaller surface relaxation at 320K compared to previous results at 95K. Furthermore, suspended monolayer samples exhibit large interlayer relaxations compared to the bulk surface termination. Further techniques for refining layer thickness determination are under development.

The Nature of Bonding in Bulk Tellurium Composed of One-Dimensional Helical Chains.

PubMed

Yi, Seho; Zhu, Zhili; Cai, Xiaolin; Jia, Yu; Cho, Jun-Hyung

2018-05-07

Bulk tellurium (Te) is composed of one-dimensional (1D) helical chains which have been considered to be coupled by van der Waals (vdW) interactions. However, on the basis of first-principles density functional theory calculations, we here propose a different bonding nature between neighboring chains: i.e., helical chains made of normal covalent bonds are connected together by coordinate covalent bonds. It is revealed that the lone pairs of electrons of Te atoms participate in forming coordinate covalent bonds between neighboring chains, where each Te atom behaves as both an electron donor to neighboring chains and an electron acceptor from neighboring chains. This ligand-metal-like bonding nature in bulk Te results in the same order of bulk moduli along the directions parallel and perpendicular to the chains, contrasting with the large anisotropy of bulk moduli in vdW crystals. We further find that the electron effective masses parallel and perpendicular to the chains are almost the same as each other, consistent with the observed nearly isotropic electrical resistivity. It is thus demonstrated that the normal/coordinate covalent bonds parallel/perpendicular to the chains in bulk Te lead to a minor anisotropy in structural and transport properties.

Three-dimensional imaging of individual point defects using selective detection angles in annular dark field scanning transmission electron microscopy.

PubMed

Johnson, Jared M; Im, Soohyun; Windl, Wolfgang; Hwang, Jinwoo

2017-01-01

We propose a new scanning transmission electron microscopy (STEM) technique that can realize the three-dimensional (3D) characterization of vacancies, lighter and heavier dopants with high precision. Using multislice STEM imaging and diffraction simulations of β-Ga 2 O 3 and SrTiO 3 , we show that selecting a small range of low scattering angles can make the contrast of the defect-containing atomic columns substantially more depth-dependent. The origin of the depth-dependence is the de-channeling of electrons due to the existence of a point defect in the atomic column, which creates extra "ripples" at low scattering angles. The highest contrast of the point defect can be achieved when the de-channeling signal is captured using the 20-40mrad detection angle range. The effect of sample thickness, crystal orientation, local strain, probe convergence angle, and experimental uncertainty to the depth-dependent contrast of the point defect will also be discussed. The proposed technique therefore opens new possibilities for highly precise 3D structural characterization of individual point defects in functional materials. Copyright © 2016 Elsevier B.V. All rights reserved.

High-harmonic generation from an atomically thin semiconductor [Observation of high harmonics from an atomically thin semiconductor

DOE PAGES

Liu, Hanzhe; Li, Yilei; You, Yong Sing; ...

2016-11-14

High-harmonic generation (HHG) in bulk solids permits the exploration of materials in a new regime of strong fields and attosecond timescales. The generation process has been discussed in the context of strongly driven electron dynamics in single-particle bands. Two-dimensional materials exhibit distinctive electronic properties compared to the bulk that could significantly modify the HHG process, including different symmetries, access to individual valleys and enhanced many-body interactions. Here we demonstrate non-perturbative HHG from a monolayer MoS 2 crystal, with even and odd harmonics extending to the 13th order. The even orders are predominantly polarized perpendicular to the pump and are compatiblemore » with the anomalous transverse intraband current arising from the material’s Berry curvature, while the weak parallel component suggests the importance of interband transitions. The odd harmonics exhibit a significant enhancement in efficiency per layer compared to the bulk, which is attributed to correlation effects. In conclusion, the combination of strong many-body Coulomb interactions and widely tunable electronic properties in two-dimensional materials offers a new platform for attosecond physics.« less

Commensurate Superstructure of the {Cu(NO3)(H2O)}(HTae)(Bpy) Coordination Polymer: An Example of 2D Hydrogen-Bonding Networks as Magnetic Exchange Pathway.

PubMed

Fernández de Luis, Roberto; Larrea, Edurne S; Orive, Joseba; Lezama, Luis; Arriortua, María I

2016-11-21

The average and commensurate superstructures of the one-dimensional coordination polymer {Cu(NO 3 )(H 2 O)}(HTae)(Bpy) (H 2 Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4'-bipyridine) were determined by single-crystal X-ray diffraction, and the possible symmetry relations between the space group of the average structure and the superstructure were checked. The crystal structure consists in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal-organic chains stacked along the [100] crystallographic direction. The origin of the fivefold c axis in the commensurate superstructure is ascribed to a commensurate modulation of the coordination environment of the copper atoms. The commensurately ordered nitrate groups and coordinated water molecules establish a two-dimensional hydrogen-bonding network. Moreover, the crystal structure shows a commensurate to incommensurate transition at room temperature. The release of the coordination water molecules destabilizes the crystal framework, and the compound shows an irreversible structure transformation above 100 °C. Despite the loss of crystallinity, the spectroscopic studies indicate that the main building blocks of the crystal framework are retained after the transformation. The hydrogen-bonding network not only plays a crucial role stabilizing the crystal structure but also is an important pathway for magnetic exchange transmission. In fact, the magnetic susceptibility curves indicate that after the loss of coordinated water molecules, and hence the collapse of the hydrogen-bonding network, the weak anti-ferromagnetic coupling observed in the initial compound is broken. The electron paramagnetic resonance spectra are the consequence of the average signals from Cu(II) with different orientations, indicating that the magnetic coupling is effective between them. In fact, X- and Q-band data are reflecting different situations; the X-band spectra show the characteristics of an exchange g-tensor, while the Q-band signals are coming from both the exchange and the molecular g-tensors.

Crystallized N-terminal domain of influenza virus matrix protein M1 and method of determining and using same

NASA Technical Reports Server (NTRS)

Luo, Ming (Inventor); Sha, Bingdong (Inventor)

2000-01-01

The matrix protein, M1, of influenza virus strain A/PR/8/34 has been purified from virions and crystallized. The crystals consist of a stable fragment (18 Kd) of the M1 protein. X-ray diffraction studies indicated that the crystals have a space group of P3.sub.t 21 or P3.sub.2 21. Vm calculations showed that there are two monomers in an asymmetric unit. A crystallized N-terminal domain of M1, wherein the N-terminal domain of M1 is crystallized such that the three dimensional structure of the crystallized N-terminal domain of M1 can be determined to a resolution of about 2.1 .ANG. or better, and wherein the three dimensional structure of the uncrystallized N-terminal domain of M1 cannot be determined to a resolution of about 2.1 .ANG. or better. A method of purifying M1 and a method of crystallizing M1. A method of using the three-dimensional crystal structure of M1 to screen for antiviral, influenza virus treating or preventing compounds. A method of using the three-dimensional crystal structure of M1 to screen for improved binding to or inhibition of influenza virus M1. The use of the three-dimensional crystal structure of the M1 protein of influenza virus in the manufacture of an inhibitor of influenza virus M1. The use of the three-dimensional crystal structure of the M1 protein of influenza virus in the screening of candidates for inhibition of influenza virus M1.

Synthesis, crystal structure, characterizations and magnetic study of a novel two-dimensional iron fluoride

NASA Astrophysics Data System (ADS)

Bouketaya, Sabrine; Smida, Mouna; Abdelbaky, Mohammed S. M.; Dammak, Mohamed; García-Granda, Santiago

2018-06-01

A new hybrid compound formulated as [Fe3F8(H2O)2](Am2TAZ)2 (Am2TAZ= 3,5-diamino-1,2,4-triazole) was prepared under hydrothermal conditions. The crystal structure was solved by single-crystal X-ray diffraction and the bulk was characterized by thermal analyses (TG-MS), vibrational spectroscopy (FTIR, Raman), Ultraviolet-visible spectroscopy (UV-Vis), and scanning electron microscopy (SEM-EDX). It crystallizes in the triclinic system space group P 1 ̅ with unit cell parameters a= 7.100(2) Å, b= 7.658(2) Å, c= 8.321(2) Å, α = 107.330(20)°, β = 111.842(18)°, γ = 93.049(17)°, Z = 1 and V= 394.01(17) Å3. The studied X-ray crystal structure shows the two oxidation states for iron atoms (Fe2+, Fe3+) and generates a 2D inorganic network, built up of inorganic layers constructed from infinite inorganic chains running along a axis. In fact, these chains are connected via (Fe3+(3)F6) octahedral. OW-H…F and N-H…F hydrogen bonds, making up the whole 3D network, are strongly linked in the layers. Magnetization measurements were performed, exhibiting the paramagnetic feature of the studied compound above 150 K.

High Surface Area Dendrite Nanoelectrodes for Electrochemistry

NASA Astrophysics Data System (ADS)

Nesbitt, Nathan; Glover, Jennifer; Goyal, Saurabh; Simidjiysky, Svetoslav; Naughton, Michael

2014-03-01

Solution-based electrodeposition of metal using a low ion concentration, surface passivation agents, and/or electrochemical crystal conditioning has allowed for the formation of high surface area metal electrodes, useful for Raman spectroscopy and electrochemical sensors. Additionally, high frequency electrical oscillations have been used to electrically connect co-planar electrodes, a process called directed electrochemical nanowire assembly (DENA). These approaches aim to control the crystal face that metal atoms in solution will nucleate onto, thus causing anisotropic growth of metal crystals. However, DENA has not been used to create high surface area electrodes, and no study has been conducted on the effect of micron-scale surface topography on the initial nucleation of metal crystals on the electrode surface. When DENA is used to create a high surface area electrode, such a texture has a strong impact on the subsequent topography of the three dimensional dendritic structures by limiting the areal density of crystals on the electrode surface. Such structures both demonstrate unique physics concerning the nucleation of metal dendrites, and offer a unique and highly facile fabrication method of high surface area electrodes, useful for chemical and biological sensing. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. (DGE-1258923).

Reduced-temperature crystallization of thin amorphous Fe80B20 films studied via empirical modeling of extended x-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Harris, V. G.; Oliver, S. A.; Ayers, J. D.; Das, B. N.; Koon, N. C.

1996-04-01

The evolution of the local atomic environment around Fe atoms in very thin (15 nm), amorphous, partially crystallized and fully crystallized films of Fe80B20 was studied using extended x-ray absorption fine structure (EXAFS) measurements. The relative atomic fraction of each crystalline phase present in the annealed samples was extracted from the Fe EXAFS data by a least-squares fitting procedure, using data collected from t-Fe3B, t-Fe2B, and α-Fe standards. The type and relative fraction of the crystallization products follows the trends previously measured in Fe80B20 melt-spun ribbons, except for the fact that crystallization temperatures are ≊200 K lower than those measured in bulk equivalents. This greatly reduced crystallization temperature may arise from the dominant role of surface nucleation sites in the crystallization of very thin amorphous films.

Topological defects and shapes of triatic liquid crystal vesicles

NASA Astrophysics Data System (ADS)

Serafin, Francesco; Manyuhina, Oksana; Bowick, Mark

Is shape the manifestation of function, or does shape determine function? Since the time of Aristotle, the study of shape has proven to be a fruitful way to understand the behavior of physical systems, from atomic to biological systems scales. Two dimensional soft membranes are a perfect setting to understand the emergence of shape. An interesting possibility is to control and design new self-assemblable supramolecular shapes by coating the surface of soft closed vesicles with liquid crystals (LC) of various symmetries. The microscopic geometry of the liquid crystal molecules, in particular the structure of topological defects, when combined with the topology of the vesicle's surface, ultimately determines the vesicle's shape. Recent work has shown that the minimal energy shapes of smectic and nematic vesicles are faceted polyhedra. A very soft smectic vesicle develops sharp creases and forms a faceted tetrahedron. When the coating LC has the symmetries of the square, the vesicle forms a cube. In this work we extend these results to a 3-fold symmetric LC, proving that the vesicle's ground state is an octahedron. This gives a systematic way of predicting vesicle's shapes as we change the liquid crystal's symmetry. Soft Matter Program of Syracuse University.

Fabrication of poly(methyl methacrylate)-MoS{sub 2}/graphene heterostructure for memory device application

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

Shinde, Sachin M.; Tanemura, Masaki; Kalita, Golap, E-mail: kalita.golap@nitech.ac.jp

2014-12-07

Combination of two dimensional graphene and semi-conducting molybdenum disulfide (MoS{sub 2}) is of great interest for various electronic device applications. Here, we demonstrate fabrication of a hybridized structure with the chemical vapor deposited graphene and MoS{sub 2} crystals to configure a memory device. Elongated hexagonal and rhombus shaped MoS{sub 2} crystals are synthesized by sulfurization of thermally evaporated molybdenum oxide (MoO{sub 3}) thin film. Scanning transmission electron microscope studies reveal atomic level structure of the synthesized high quality MoS{sub 2} crystals. In the prospect of a memory device fabrication, poly(methyl methacrylate) (PMMA) is used as an insulating dielectric material asmore » well as a supporting layer to transfer the MoS{sub 2} crystals. In the fabricated device, PMMA-MoS{sub 2} and graphene layers act as the functional and electrode materials, respectively. Distinctive bistable electrical switching and nonvolatile rewritable memory effect is observed in the fabricated PMMA-MoS{sub 2}/graphene heterostructure. The developed material system and demonstrated memory device fabrication can be significant for next generation data storage applications.« less

Syntheses, crystal structures and spectroscopic properties of copper(II)-tetracyanometallate(II) complexes with nicotinamide and isonicotinamide ligands

NASA Astrophysics Data System (ADS)

Sayın, Elvan; Kürkçüoğlu, Güneş Süheyla; Yeşilel, Okan Zafer; Hökelek, Tuncer

2015-09-01

Four new one dimensional (1D) cyanide complexes, namely {[Cu(NH3)4(μ-na)][M‧(CN)4]}n and {[Cu(NH3)2(ina)2M‧(μ-CN)2(CN)2]}n (M‧(II) = Pd (1 and 3) or Pt (2 and 4), na:nicotinamide and ina:isonicotinamide) have been synthesized and characterized by elemental, spectral (FT-IR and Raman), and thermal (TG, DTG and DTA) analyses. The crystal structures of complexes 1-3 have been determined by single crystal X-ray diffraction technique. In complexes 1 and 2, na ligand is coordinated to the adjacent Cu(II) ions as a bridging ligand, giving rise to 1D linear cationic chain and the [M‧(CN)4]2- anionic complex acts as a counter ion. Complexes 3 and 4 are also 1D linear chain in which two cyanide ligands bridged neighboring M‧(II) and Cu(II) ions, while ina ligand is coordinated Cu(II) ion through nitrogen atom of pyridine ring. In the complexes, the Cu(II) ions adopt distorted octahedral geometries, while M‧(II) ions are four coordinated with four carbon atoms from cyanide ligands in square-planar geometries. The adjacent chains are further stacked through intermolecular hydrogen bond, Nsbnd Hṡṡṡπ, Csbnd H⋯M‧ and M‧⋯π interactions to form 3D supramolecular networks. Vibration assignments are given for all the observed bands. In addition, thermal stabilities of the compounds are also discussed.

Supra-molecular architecture in a co-crystal of the N(7)-H tautomeric form of N (6)-benzoyl-adenine with adipic acid (1/0.5).

PubMed

Swinton Darious, Robert; Thomas Muthiah, Packianathan; Perdih, Franc

2016-06-01

The asymmetric unit of the title co-crystal, C12H9N5O·0.5C6H10O4, consists of one mol-ecule of N (6)-benzoyl-adenine (BA) and one half-mol-ecule of adipic acid (AA), the other half being generated by inversion symmetry. The dihedral angle between the adenine and phenyl ring planes is 26.71 (7)°. The N (6)-benzoyl-adenine mol-ecule crystallizes in the N(7)-H tautomeric form with three non-protonated N atoms. This tautomeric form is stabilized by intra-molecular N-H⋯O hydrogen bonding between the carbonyl (C=O) group and the N(7)-H hydrogen atom on the Hoogsteen face of the purine ring, forming an S(7) ring motif. The two carboxyl groups of adipic acid inter-act with the Watson-Crick face of the BA mol-ecules through O-H⋯N and N-H⋯O hydrogen bonds, generating an R 2 (2)(8) ring motif. The latter units are linked by N-H⋯N hydrogen bonds, forming layers parallel to (10-5). A weak C-H⋯O hydrogen bond is also present, linking adipic acid mol-ecules in neighbouring layers, enclosing R (2) 2(10) ring motifs and forming a three-dimensional structure. C=O⋯π and C-H⋯π inter-actions are also present in the structure.

Application of discrete solvent reaction field model with self-consistent atomic charges and atomic polarizabilities to calculate the χ(1) and χ(2) of organic molecular crystals

NASA Astrophysics Data System (ADS)

Lu, Shih-I.

2018-01-01

We use the discrete solvent reaction field model to evaluate the linear and second-order nonlinear optical susceptibilities of 3-methyl-4-nitropyridine-1-oxyde crystal. In this approach, crystal environment is created by supercell architecture. A self-consistent procedure is used to obtain charges and polarizabilities for environmental atoms. Impact of atomic polarizabilities on the properties of interest is highlighted. This approach is shown to give the second-order nonlinear optical susceptibilities within error bar of experiment as well as the linear optical susceptibilities in the same order as experiment. Similar quality of calculations are also applied to both 4-N,N-dimethylamino-3-acetamidonitrobenzene and 2-methyl-4-nitroaniline crystals.

Synthesis and Transfer of Large-Area Monolayer WS2 Crystals: Moving Toward the Recyclable Use of Sapphire Substrates.

PubMed

Xu, Zai-Quan; Zhang, Yupeng; Lin, Shenghuang; Zheng, Changxi; Zhong, Yu Lin; Xia, Xue; Li, Zhipeng; Sophia, Ponraj Joice; Fuhrer, Michael S; Cheng, Yi-Bing; Bao, Qiaoliang

2015-06-23

Two-dimensional layered transition metal dichalcogenides (TMDs) show intriguing potential for optoelectronic devices due to their exotic electronic and optical properties. Only a few efforts have been dedicated to large-area growth of TMDs. Practical applications will require improving the efficiency and reducing the cost of production, through (1) new growth methods to produce large size TMD monolayer with less-stringent conditions, and (2) nondestructive transfer techniques that enable multiple reuse of growth substrate. In this work, we report to employ atmospheric pressure chemical vapor deposition (APCVD) for the synthesis of large size (>100 μm) single crystals of atomically thin tungsten disulfide (WS2), a member of TMD family, on sapphire substrate. More importantly, we demonstrate a polystyrene (PS) mediated delamination process via capillary force in water which reduces the etching time in base solution and imposes only minor damage to the sapphire substrate. The transferred WS2 flakes are of excellent continuity and exhibit comparable electron mobility after several growth cycles on the reused sapphire substrate. Interestingly, the photoluminescence emission from WS2 grown on the recycled sapphire is much higher than that on fresh sapphire, possibly due to p-type doping of monolayer WS2 flakes by a thin layer of water intercalated at the atomic steps of the recycled sapphire substrate. The growth and transfer techniques described here are expected to be applicable to other atomically thin TMD materials.

Crystal structure of tris­(trans-1,2-cyclo­hexa­ne­diamine-κ2 N,N′)chromium(III) tetra­chlorido­zincate chloride trihydrate from synchrotron data

PubMed Central

Moon, Dohyun; Choi, Jong-Ha

2016-01-01

The structure of the title double salt, [Cr(rac-chxn)3][ZnCl4]Cl·3H2O (chxn is trans-1,2-cyclo­hexa­nedi­amine; C6H14N2), has been determined from synchrotron data. The CrIII ion is coordinated by six N atoms of three chelating chxn ligands, displaying a slightly distorted octa­hedral coordination environment. The distorted tetra­hedral [ZnCl4]2− anion, the isolated Cl− anion and three lattice water mol­ecules remain outside the coordination sphere. The Cr—N(chxn) bond lengths are in a narrow range between 2.0737 (12) and 2.0928 (12) Å; the mean N—Cr—N bite angle is 82.1 (4)°. The crystal packing is stabilized by hydrogen-bonding inter­actions between the amino groups of the chxn ligands and the water mol­ecules as donor groups, and O atoms of the water mol­ecules, chloride anions and Cl atoms of the [ZnCl4]2− anions as acceptor groups, leading to the formation of a three-dimensional network. The [ZnCl4]2− anion is disordered over two sets of sites with an occupancy ratio of 0.94:0.06. PMID:27308016

Crystal structure of poly[di­aqua­(μ2-benzene-1,4-di­carboxyl­ato-κ2 O 1:O 4)(μ2-benzene-1,4-di­carboxyl­ato-κ4 O 1,O 1′:O 4,O 4′)bis­(μ2-3,3′,5,5′-tetra­methyl-4,4′-bi­pyrazole-κ2 N:N′)dinickel(II)

PubMed Central

Wu, Chao; Cao, Peng

2015-01-01

The asymmetric unit of the polymeric title compound, [Ni(C8H4O4)(C10H14N4)(H2O)]n, contains one Ni2+ cation, one coordinating water mol­ecule, one 3,3′,5,5′-tetra­methyl-4,4′-bi­pyrazole ligand and half each of two benzene-1,4-di­carboxyl­ate anions, the other halves being generated by inversion symmetry. The Ni2+ cation exhibits an octa­hedral N2O4 coordination sphere defined by the O atoms of the water mol­ecule and two different anions and the N atoms of two symmetry-related N-heterocycles. The N-heterocycles and both anions bridge adjacent Ni2+ cations into a three-dimensional network structure, with one of the anions in a bis-bidentate and the other in a bis-monodentate bridging mode. N—H⋯O and O—H⋯O hydrogen bonds between the N-heterocycles and water mol­ecules as donor groups and the carboxyl­ate O atoms as acceptor groups consolidate the crystal packing. PMID:26090165

[Structure of crambin in solution, crystal and in the trajectories of molecular dynamics simulations].

PubMed

Abaturov, L V; Nosova, N G

2013-01-01

The mechanisms of the three-dimensional crambin structure alterations in the crystalline environments and in the trajectories of the molecular dynamics simulations in the vacuum and crystal surroundings have been analyzed. In the crystalline state and in the solution the partial regrouping of remote intramolecular packing contacts, involved in the formation and stabilization of the tertiary structure of the crambin molecule, occurs in NMR structures. In the crystalline state it is initiated by the formation of the intermolecular contacts, the conformational influence of its appearance is distributed over the structure. The changes of the conformations and positions of the residues of the loop segments, where the intermolecular contacts of the crystal surroundings are preferably concentrated, are most observable. Under the influence of these contacts the principal change of the regular secondary structure of crambin is taking place: extension of the two-strand beta structure to the three-strand structure with the participation of the single last residue N46 of the C-terminal loop. In comparison with the C-terminal loop the more profound changes are observed in the conformation and the atomic positions of the backbone atoms and in the solvent accessibility of the residues of the interhelical loop. In the solution of the ensemble of the 8 NMR structures relative accessibility to the solvent differs more noticeably also in the region of the loop segments and rather markedly in the interhelical loop. In the crambin cryogenic crystal structures the positions of the atoms of the backbone and/or side chain of 14-18 of 46 residues are discretely disordered. The disorganizations of at least 8 of 14 residues occur directly in the regions of the intermolecular contacts and another 5 residues are disordered indirectly through the intramolecular contacts with the residues of the intermolecular contacts. Upon the molecular dynamics simulation in the vacuum surrounding as in the solution of the crystalline structure of crambin the essential changes of the backbone conformation are caused by the intermolecular contacts absence, but partly masked by the structure changes owing to the nonpolar H atoms absence on the simulated structure. The intermolecular contact absence is partly manifested upon the molecular dynamics simulation of the crambin crystal with one protein molecule. Compared to the crystal structure the lengths of the interpeptide hydrogen bonds and other interresidue contacts in an average solution NMR structure are somewhat shorter and accordingly the energy of the interpeptide hydrogen bonds is better. This length shortening can occur at the stage of the refinement of the NMR structures of the crambin and other proteins by its energy minimizations in the vacuum surroundings and not exist in the solution protein structures.

New structure type in the mixed-valent compound YbCu4Ga8.

PubMed

Subbarao, Udumula; Gutmann, Matthias J; Peter, Sebastian C

2013-02-18

The new compound YbCu(4)Ga(8) was obtained as large single crystals in high yield from reactions run in liquid gallium. Preliminary investigations suggest that YbCu(4)Ga(8) crystallizes in the CeMn(4)Al(8) structure type, tetragonal space group I4/mmm, and lattice constants are a = b = 8.6529(4) Å and c = 5.3976(11) Å. However, a detailed single-crystal XRD revealed a tripling of the c axis and crystallizing in a new structure type with lattice constants of a = b = 8.6529(4) Å and c = 15.465(1) Å. The structural model was further confirmed by neutron diffraction measurements on high-quality single crystal. The crystal structure of YbCu(4)Ga(8) is composed of pseudo-Frank-Kasper cages occupying one ytterbium atom in each ring which are shared through the corner along the ab plane, resulting in a three-dimensional network. The magnetic susceptibility of YbCu(4)Ga(8) investigated in the temperature range 2-300 K showed Curie-Weiss law behavior above 100 K, and the experimentally measured magnetic moment indicates mixed-valent ytterbium. Electrical resistivity measurements show the metallic nature of the compound. At low temperatures, variation of ρ as a function of T indicates a possible Fermi-liquid state at low temperatures.

Structural, crystal structure, Hirshfeld surface analysis and physicochemical studies of a new chlorocadmate template by 1-(2-hydroxyethyl)piperazine

NASA Astrophysics Data System (ADS)

Soudani, S.; Jeanneau, E.; Jelsch, C.; Lefebvre, F.; Ben Nasr, C.

2016-11-01

The synthesis, crystal structure and spectroscopic characterization of a new chlorocadmate template by the 1-(2-hydroxyethyl)piperazine ligand are reported. In the atomic arrangement, the CdCl5O entities are deployed in corrugated rows along the a-axis at y = 1/4 and y = 3/4 to form layers parallel to the (a,b) plane. In these crystals, piperazinediium cations are in a chair conformation and are inserted between these layers through Nsbnd H⋯Cl, Csbnd H⋯Cl, Osbnd H⋯Cl and Nsbnd H⋯O hydrogen bonds to form infinite three-dimensional network. Investigation of intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that H⋯Cl and Csbnd H⋯Hsbnd C intermolecular interactions are the most abundant contacts of the organic cation in the crystal packing. The crystal contacts enrichments reveals that, the Cd++ … Cl- salt bridges, the Cd⋯O complexation and Osbnd H⋯Cl- and Nsbnd H⋯Cl-strong H-bonds are the driving forces in the packing formation. The presence of twelve independent chloride anions and four organic cation in the asymmetric unit allowed comparing their contact propensities. The 13C and 15N CP-MAS NMR spectra are in agreement with the X-ray structure. Additional characterization of this compound has also been performed by IR spectroscopy.

Solvent selection for explaining the morphology of nitroguanidine crystal by molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Song, Liang; Chen, Lizhen; Cao, Duanlin; Wang, Jianlong

2018-02-01

In this article, a method was performed to predict the morphology of needle-shaped crystals by analyzing the growth mechanisms for the various crystal faces. As an example, the crystal morphology of a nitroguanidine (NQ) was investigated via molecular dynamics simulations. The modified attachment energy (MEA) model was constructed by introducing surface chemistry terms and the relevant morphology of the habit crystal faces. The results indicate that the growth morphology of NQ in vacuum is dominated by {2 2 0}, {0 4 0}, {1 1 1}, {1 3 1} and {3 1 1} faces. The {2 2 0} and {0 4 0} faces are parallel to the elongation direction of the crystal, while the other faces are at the needle tips direction. The atoms or atomic groups exposed in crystal surface were used to analyze the relationship between structure and morphology. Compared to the surrounding faces, the needle tip faces have a large number of polar atoms or atomic groups. The needle tip faces have a high electronegativity on N, O atoms via molecular electrostatic potential (ESP) analysis. Furthermore, the protic solvent was used to reduce the attachment energy of the tip surfaces for achieving the purpose of inhibiting the growth of needle tips. Gamma-butyrolactone as the selected solvent inhibited effectively the growth of the needle tip faces. The predicted result is serviceable for the formation design.

Patterning two-dimensional chalcogenide crystals of Bi2Se3 and In2Se3 and efficient photodetectors

PubMed Central

Zheng, Wenshan; Xie, Tian; Zhou, Yu; Chen, Y.L.; Jiang, Wei; Zhao, Shuli; Wu, Jinxiong; Jing, Yumei; Wu, Yue; Chen, Guanchu; Guo, Yunfan; Yin, Jianbo; Huang, Shaoyun; Xu, H.Q.; Liu, Zhongfan; Peng, Hailin

2015-01-01

Patterning of high-quality two-dimensional chalcogenide crystals with unique planar structures and various fascinating electronic properties offers great potential for batch fabrication and integration of electronic and optoelectronic devices. However, it remains a challenge that requires accurate control of the crystallization, thickness, position, orientation and layout. Here we develop a method that combines microintaglio printing with van der Waals epitaxy to efficiently pattern various single-crystal two-dimensional chalcogenides onto transparent insulating mica substrates. Using this approach, we have patterned large-area arrays of two-dimensional single-crystal Bi2Se3 topological insulator with a record high Hall mobility of ∼1,750 cm2 V−1 s−1 at room temperature. Furthermore, our patterned two-dimensional In2Se3 crystal arrays have been integrated and packaged to flexible photodetectors, yielding an ultrahigh external photoresponsivity of ∼1,650 A W−1 at 633 nm. The facile patterning, integration and packaging of high-quality two-dimensional chalcogenide crystals hold promise for innovations of next-generation photodetector arrays, wearable electronics and integrated optoelectronic circuits. PMID:25898022

Synthesis, crystal structure and magnetic properties of diaquabis(2,6-diamino-7H-purin-1-ium-κN9)bis(4,4'-oxydibenzoato-κO)cobalt(II) dihydrate.

PubMed

Atria, Ana María; Parada, José; Moreno, Yanko; Suárez, Sebastián; Baggio, Ricardo; Peña, Octavio

2018-01-01

The title mononuclear Co II complex, [Co(C 5 H 7 N 6 ) 2 (C 14 H 8 O 5 ) 2 (H 2 O) 2 ]·2H 2 O, has been synthesized and its crystal structure determined by X-ray diffraction. The complex crystallizes in the triclinic space group P-1, with one formula unit per cell (Z = 1 and Z' = 1/2). It consists of a mononuclear unit with the Co II ion on an inversion centre coordinated by two 2,6-diamino-7H-purin-1-ium cations, two 4,4'-oxydibenzoate anions (in a nonbridging κO-monodentate coordination mode, which is less common for the anion in its Co II complexes) and two water molecules, defining an octahedral environment around the metal atom. There is a rich assortment of nonbonding interactions, among which a strong N + -H...O - bridge, with a short N...O distance of 2.5272 (18) Å, stands out, with the H atom ostensibly displaced away from its expected position at the donor side, towards the acceptor. The complex molecules assemble into a three-dimensional hydrogen-bonded network. A variable-temperature magnetic study between 2 and 300 K reveals an orbital contribution to the magnetic moment and a weak antiferromagnetic interaction between Co II centres as the temperature decreases. The model leads to the following values: A (crystal field strength) = 1.81, λ (spin-orbit coupling) = -59.9 cm -1 , g (Landé factor) = 2.58 and zJ (exchange coupling) = -0.5 cm -1 .

Solid State Chemistry of Clathrate Phases: Crystal Structure, Chemical Bonding and Preparation Routes

NASA Astrophysics Data System (ADS)

Baitinger, Michael; Böhme, Bodo; Ormeci, Alim; Grin, Yuri

Clathrates represent a family of inorganic materials called cage compounds. The key feature of their crystal structures is a three-dimensional (host) framework bearing large cavities (cages) with 20-28 vertices. These polyhedral cages bear—as a rule—guest species. Depending on the formal charge of the framework, clathrates are grouped in anionic, cationic and neutral. While the bonding in the framework is of (polar) covalent nature, the guest-host interaction can be ionic, covalent or even van-der Waals, depending on the chemical composition of the clathrates. The chemical composition and structural features of the cationic clathrates can be described by the enhanced Zintl concept, whereas the composition of the anionic clathrates deviates often from the Zintl counts, indicating additional atomic interactions in comparison with the ionic-covalent Zintl model. These interactions can be visualized and studied by applying modern quantum chemical approaches such as electron localizability.

Eco-friendly p-type Cu2SnS3 thermoelectric material: crystal structure and transport properties

PubMed Central

Shen, Yawei; Li, Chao; Huang, Rong; Tian, Ruoming; Ye, Yang; Pan, Lin; Koumoto, Kunihito; Zhang, Ruizhi; Wan, Chunlei; Wang, Yifeng

2016-01-01

As a new eco-friendly thermoelectric material, copper tin sulfide (Cu2SnS3) ceramics were experimentally studied by Zn-doping. Excellent electrical transport properties were obtained by virtue of 3-dimensionally conductive network for holes, which are less affected by the coexistence of cubic and tetragonal phases that formed upon Zn subsitition for Sn; a highest power factors ~0.84 mW m−1 K−2 at 723 K was achieved in the 20% doped sample. Moreover, an ultralow lattice thermal conductivity close to theoretical minimum was observed in these samples, which could be related to the disordering of atoms in the coexisting cubic and tetragonal phases and the interfaces. Thanks to the phonon-glass-electron-crystal features, a maximum ZT ~ 0.58 was obtained at 723 K, which stands among the tops for sulfide thermoelectrics at the same temperature. PMID:27666524

Structural and functional characterization of a calcium-activated cation channel from Tsukamurella paurometabola

NASA Astrophysics Data System (ADS)

Dhakshnamoorthy, Balasundaresan; Rohaim, Ahmed; Rui, Huan; Blachowicz, Lydia; Roux, Benoît

2016-09-01

The selectivity filter is an essential functional element of K+ channels that is highly conserved both in terms of its primary sequence and its three-dimensional structure. Here, we investigate the properties of an ion channel from the Gram-positive bacterium Tsukamurella paurometabola with a selectivity filter formed by an uncommon proline-rich sequence. Electrophysiological recordings show that it is a non-selective cation channel and that its activity depends on Ca2+ concentration. In the crystal structure, the selectivity filter adopts a novel conformation with Ca2+ ions bound within the filter near the pore helix where they are coordinated by backbone oxygen atoms, a recurrent motif found in multiple proteins. The binding of Ca2+ ion in the selectivity filter controls the widening of the pore as shown in crystal structures and in molecular dynamics simulations. The structural, functional and computational data provide a characterization of this calcium-gated cationic channel.

Electron crystallography and aquaporins.

PubMed

Schenk, Andreas D; Hite, Richard K; Engel, Andreas; Fujiyoshi, Yoshinori; Walz, Thomas

2010-01-01

Electron crystallography of two-dimensional (2D) crystals can provide information on the structure of membrane proteins at near-atomic resolution. Originally developed and used to determine the structure of bacteriorhodopsin (bR), electron crystallography has recently been applied to elucidate the structure of aquaporins (AQPs), a family of membrane proteins that form pores mostly for water but also other solutes. While electron crystallography has made major contributions to our understanding of the structure and function of AQPs, structural studies on AQPs, in turn, have fostered a number of technical developments in electron crystallography. In this contribution, we summarize the insights electron crystallography has provided into the biology of AQPs, and describe technical advancements in electron crystallography that were driven by structural studies on AQP 2D crystals. In addition, we discuss some of the lessons that were learned from electron crystallographic work on AQPs. Copyright © 2010 Elsevier Inc. All rights reserved.

Three-dimensional textures and defects of soft material layering revealed by thermal sublimation.

PubMed

Yoon, Dong Ki; Kim, Yun Ho; Kim, Dae Seok; Oh, Seong Dae; Smalyukh, Ivan I; Clark, Noel A; Jung, Hee-Tae

2013-11-26

Layering is found and exploited in a variety of soft material systems, ranging from complex macromolecular self-assemblies to block copolymer and small-molecule liquid crystals. Because the control of layer structure is required for applications and characterization, and because defects reveal key features of the symmetries of layered phases, a variety of techniques have been developed for the study of soft-layer structure and defects, including X-ray diffraction and visualization using optical transmission and fluorescence confocal polarizing microscopy, atomic force microscopy, and SEM and transmission electron microscopy, including freeze-fracture transmission electron microscopy. Here, it is shown that thermal sublimation can be usefully combined with such techniques to enable visualization of the 3D structure of soft materials. Sequential sublimation removes material in a stepwise fashion, leaving a remnant layer structure largely unchanged and viewable using SEM, as demonstrated here using a lamellar smectic liquid crystal.