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Sample records for commensurate monolayer films

  1. Commensurate-incommensurate transition of monolayer krypton on graphite by helium-atom scattering

    NASA Astrophysics Data System (ADS)

    Chung, S.; Kara, A.; Larese, J. Z.; Leung, W. Y.; Frankl, And D.

    1987-04-01

    The commensurate-incommensurate transition of monolayer krypton films on a graphite single-crystal substrate is observed by helium-atom diffraction for transition temperatures in the range 50-60 K. The change in lattice spacing appears continuous, with an upper limit of 0.3% on a possible jump, with no detectable hysteresis. The slightly incommensurate phase is disordered but apparently well correlated. The spatial correlation length changes in a possibly discontinuous manner. A decrease of specular and diffracted intensities while the film is still commensurate is observed. This may be due to incoherent elastic scattering from isolated defects, or possibly to increased inelastic scattering.

  2. Faceting and commensurability in crystal structures of colloidal thin films.

    PubMed

    Ramiro-Manzano, F; Meseguer, F; Bonet, E; Rodriguez, I

    2006-07-14

    This Letter investigates the influence of finite size effects on the particle arrangement of thin film colloidal crystals. A rich variety of crystallographic faceting with large single domain microcrystallites is shown. Optical reflectance experiments together with scanning electron microscopy permit the identification of the crystal symmetry and the facet orientation, as well as the exact number of monolayers. When the cell thickness is not commensurable with a high symmetry layering, particles arrange themselves in a periodic distribution of (111)- and (100)-orientated face centered cubic (fcc) microcrystallites separated by planar defects. These structures can be described as a fcc ordering orientated along a vicinal surface, modified by a periodic distribution of fcc (111) stacking faults. PMID:16907485

  3. Effective and accurate approach for modeling of commensurate-incommensurate transition in krypton monolayer on graphite.

    PubMed

    Ustinov, E A

    2014-10-01

    Commensurate-incommensurate (C-IC) transition of krypton molecular layer on graphite received much attention in recent decades in theoretical and experimental researches. However, there still exists a possibility of generalization of the phenomenon from thermodynamic viewpoint on the basis of accurate molecular simulation. Recently, a new technique was developed for analysis of two-dimensional (2D) phase transitions in systems involving a crystalline phase, which is based on accounting for the effect of temperature and the chemical potential on the lattice constant of the 2D layer using the Gibbs-Duhem equation [E. A. Ustinov, J. Chem. Phys. 140, 074706 (2014)]. The technique has allowed for determination of phase diagrams of 2D argon layers on the uniform surface and in slit pores. This paper extends the developed methodology on systems accounting for the periodic modulation of the substrate potential. The main advantage of the developed approach is that it provides highly accurate evaluation of the chemical potential of crystalline layers, which allows reliable determination of temperature and other parameters of various 2D phase transitions. Applicability of the methodology is demonstrated on the krypton-graphite system. Analysis of phase diagram of the krypton molecular layer, thermodynamic functions of coexisting phases, and a method of prediction of adsorption isotherms is considered accounting for a compression of the graphite due to the krypton-carbon interaction. The temperature and heat of C-IC transition has been reliably determined for the gas-solid and solid-solid system. PMID:25296827

  4. Zone-center phonons of bulk, few-layer, and monolayer 1 T -TaS2 : Detection of commensurate charge density wave phase through Raman scattering

    NASA Astrophysics Data System (ADS)

    Albertini, Oliver R.; Zhao, Rui; McCann, Rebecca L.; Feng, Simin; Terrones, Mauricio; Freericks, James K.; Robinson, Joshua A.; Liu, Amy Y.

    2016-06-01

    We present first-principles calculations of the vibrational properties of the transition-metal dichalcogenide 1 T -TaS2 for various thicknesses in the high-temperature (undistorted) phase and the low-temperature commensurate charge density wave (CDW) phase. We also present measurements of the Raman spectra for bulk, few-layer, and monolayer samples at temperatures well below that of the bulk transition to the commensurate phase. Through our calculations, we identify the low-frequency folded-back acoustic modes as a convenient signature of the commensurate CDW structure in vibrational spectra. In our measured Raman spectra, this signature is clearly evident in all of the samples, indicating that the commensurate phase remains the ground state as the material is thinned, even down to a single layer. This is in contrast to some previous studies, which suggest a suppression of the commensurate CDW transition in thin flakes. We also use polarized Raman spectroscopy to probe c -axis orbital texture in the low-T phase, which has recently been suggested to play a role in the metal-insulator transition that accompanies the structural transition to the commensurate CDW phase.

  5. Commensurability condition and hierarchy of fillings for FQHE in higher Landau levels in conventional 2DEG systems and in graphene—monolayer and bilayer

    NASA Astrophysics Data System (ADS)

    Jacak, Janusz; Jacak, Lucjan

    2016-01-01

    The structure of the filling rate hierarchy referred to as the fractional quantum Hall effect is studied in higher Landau levels using the commensurability condition. The hierarchy of fillings that are derived in this manner is consistent with the experimental observations of the first three Landau levels in conventional semiconductor Hall systems. The relative poverty of the fractional structure in higher Landau levels compared with the lowest Landau level is explained using commensurability topological arguments. The commensurability criterion for correlated states for higher Landau levels (with n≥slant 1) including the paired states at half fillings of the spin-subbands of these levels is formulated. The commensurability condition is applied to determine the hierarchy of the fractional fillings of Landau levels in the monolayer and bilayer graphene. Good agreement with current experimental observations of fractional quantum Hall effect in the graphene monolayer and bilayer is achieved. The presence of even denominator rates in the hierarchy for fractional quantum Hall effect in the bilayer graphene is also explained.

  6. Equilibrating nanoparticle monolayers using wetting films.

    PubMed

    Pontoni, Diego; Alvine, Kyle J; Checco, Antonio; Gang, Oleg; Ocko, Benjamin M; Pershan, Peter S

    2009-01-01

    Monolayers of bimodal gold nanoparticles on silicon are investigated by a combination of microscopy (dry monolayers) and x-ray diffraction (dry and wet monolayers). In the presence of an excess of small particles, the nanoscale packing structure closely resembles the small-particle-rich scenario of the structural crossover transition that has been predicted and also observed with micron-scale hard-sphere colloids. Structural morphology is monitored in situ during monolayer dissolution and reassembly within the thin liquid wetting film. This approach allows investigation of size and solvent effects on nanoparticles in quasi-two-dimensional confinement. PMID:19257214

  7. Sub-monolayer film growth of a volatile lanthanide complex on metallic surfaces

    PubMed Central

    Chen, Jinjie; Edelmann, Kevin; Wulfhekel, Wulf

    2015-01-01

    Summary We deposited a volatile lanthanide complex, tris(2,2,6,6-tetramethyl-3,5-heptanedionato)terbium(III), onto metal surfaces of Cu(111), Ag(111) and Au(111) in vacuum and observed well-ordered sub-monolayer films with low temperature (5 K) scanning tunneling microscopy. The films show a distorted three-fold symmetry with a commensurate structure. Scanning tunneling spectroscopy reveals molecular orbitals delocalized on the ligands of the molecule. Our results imply that this complex can be transferred onto the metal substrates without molecular decomposition or contamination of the surface. This new rare-earth-based class of molecules broadens the choice of molecular magnets to study with scanning tunneling microscopy. PMID:26733215

  8. The influence of the surface composition of mixed monolayer films on the evaporation coefficient of water.

    PubMed

    Miles, Rachael E H; Davies, James F; Reid, Jonathan P

    2016-07-20

    We explore the dependence of the evaporation coefficient of water from aqueous droplets on the composition of a surface film, considering in particular the influence of monolayer mixed component films on the evaporative mass flux. Measurements with binary component films formed from long chain alcohols, specifically tridecanol (C13H27OH) and pentadecanol (C15H31OH), and tetradecanol (C14H29OH) and hexadecanol (C16H33OH), show that the evaporation coefficient is dependent on the mole fractions of the two components forming the monolayer film. Immediately at the point of film formation and commensurate reduction in droplet evaporation rate, the evaporation coefficient is equal to a mole fraction weighted average of the evaporation coefficients through the equivalent single component films. As a droplet continues to diminish in surface area with continued loss of water, the more-soluble, shorter alkyl chain component preferentially partitions into the droplet bulk with the evaporation coefficient tending towards that through a single component film formed simply from the less-soluble, longer chain alcohol. We also show that the addition of a long chain alcohol to an aqueous-sucrose droplet can facilitate control over the degree of dehydration achieved during evaporation. After undergoing rapid gas-phase diffusion limited water evaporation, binary aqueous-sucrose droplets show a continued slow evaporative flux that is limited by slow diffusional mass transport within the particle bulk due to the rapidly increasing particle viscosity and strong concentration gradients that are established. The addition of a long chain alcohol to the droplet is shown to slow the initial rate of water loss, leading to a droplet composition that remains more homogeneous for a longer period of time. When the sucrose concentration has achieved a sufficiently high value, and the diffusion constant of water has decreased accordingly so that bulk phase diffusion arrest occurs in the monolayer

  9. Commensurate registry and chemisorption at a hetero-organic interface.

    PubMed

    Stadtmüller, Benjamin; Sueyoshi, Tomoki; Kichin, Georgy; Kröger, Ingo; Soubatch, Sergey; Temirov, Ruslan; Tautz, F Stefan; Kumpf, Christian

    2012-03-01

    We present evidence for a partly chemisorptive bonding between single monolayers of copper-II-phthalocyanine (CuPc) and 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) that are stacked on Ag(111). A commensurate registry between the two molecular layers and the substrate, i.e., a common crystallographic lattice for CuPc and PTCDA films as well as for the Ag(111) surface, indicates that the growth of the upper layer is dominated by the structure of the lower. Photoemission spectroscopy clearly reveals a gradual filling of the lowest unoccupied molecular orbital of PTCDA due to CuPc adsorption, which proves the chemisorptive character. PMID:22463427

  10. Commensurate Registry and Chemisorption at a Hetero-organic Interface

    NASA Astrophysics Data System (ADS)

    Stadtmüller, Benjamin; Sueyoshi, Tomoki; Kichin, Georgy; Kröger, Ingo; Soubatch, Sergey; Temirov, Ruslan; Tautz, F. Stefan; Kumpf, Christian

    2012-03-01

    We present evidence for a partly chemisorptive bonding between single monolayers of copper-II-phthalocyanine (CuPc) and 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) that are stacked on Ag(111). A commensurate registry between the two molecular layers and the substrate, i.e., a common crystallographic lattice for CuPc and PTCDA films as well as for the Ag(111) surface, indicates that the growth of the upper layer is dominated by the structure of the lower. Photoemission spectroscopy clearly reveals a gradual filling of the lowest unoccupied molecular orbital of PTCDA due to CuPc adsorption, which proves the chemisorptive character.

  11. Heat Capacity of Dilute 3He-4He Monolayer Films

    NASA Astrophysics Data System (ADS)

    Morishita, Masashi

    2016-05-01

    The heat capacities of a small amount of 3He dissolved in monolayer 4He films are measured to clarify natures of monolayer 4He films. With increasing areal density, the measured heat capacities gradually increase and subsequently gradually decrease. With further increase in areal density, the measured heat capacity rapidly decreases to zero over a very narrow areal density range near that of the sqrt{3} × sqrt{3} phase. These slightly complex areal-density variations and dependence on 3He concentration are discussed from the viewpoint of the known properties of 4He films. The behaviors can be explained. However, the expected two-dimensional gas-liquid or gas-solid coexistence is not observed in this study.

  12. Monolayer graphene growth on sputtered thin film platinum

    SciTech Connect

    Kang, Byung Jin; Mun, Jeong Hun; Cho, Byung Jin; Hwang, Chan Yong

    2009-11-15

    It is demonstrated that sputtered thin film platinum (Pt) can be used as a catalytic metal for graphene growth on metal. During the crystallization annealing, the sputtered Pt is crystallized mostly into Pt (111) orientation, maintaining excellent surface roughness with no sign of agglomeration. The relatively lower carbon solubility in Pt and the good surface roughness of the thin film Pt enable us to form a uniform monolayer graphene on Pt over the entire region of the thin film Pt/SiO{sub 2}/Si substrate by carbon dissolution and segregation method processed in a methane ambient. The monolayer graphene grown on Pt has been successfully transferred to SiO{sub 2}/Si substrate by simple wet etching of Pt. The results of Raman spectroscopic and scanning tunneling microscopic measurements of the synthesized graphene layer are presented.

  13. Monolayer-Mediated Patterning of Electroceramic Thin Films

    SciTech Connect

    Clem, P.G.; Payne, D.A.

    1998-10-11

    Integrated electroceramic thin film devices on semiconductor and insulator substrates feature a variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electronic and optical properties. The ability to pattern such ceramic materials atop semiconductor substrates, thus, is a critical technology. Patterned oxide thin film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment. We review here the development of an ambient atmosphere technique which allows selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayer to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective fictionalization is achieved through microcontact printing (v-CP) of self-assembled monolayer of the chemical octadecyltrichlorosilane on substrates of technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron- scale dielectric oxide devices have been fabricated using this process, with lateral resolution as fine as 0.5Lm. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)03 [PZT], LiNb03, and Ta205. An applied device example is also presented in combination with selective MOCVD deposition of metal electrodes: integrated, fully monolayer-patterned Pt//PZT//PSi(Si(100) ferroelectric memory cells.

  14. Synthesis, Assembly, and Characterization of Monolayer Protected Gold Nanoparticle Films for Protein Monolayer Electrochemistry

    PubMed Central

    Doan, Tran T.; Freeman, Michael H.; Schmidt, Adrienne R.; Nguyen, Natalie D. T.; Leopold, Michael C.

    2011-01-01

    Colloidal gold nanoparticles protected with alkanethiolate ligands called monolayer protected gold clusters (MPCs) are synthesized and subsequently incorporated into film assemblies that serve as adsorption platforms for protein monolayer electrochemistry (PME). PME is utilized as the model system for studying electrochemical properties of redox proteins by confining them to an adsorption platform at a modified electrode, which also serves as a redox partner for electron transfer (ET) reactions. Studies have shown that gold nanoparticle film assemblies of this nature provide for a more homogeneous protein adsorption environment and promote ET without distance dependence compared to the more traditional systems modified with alkanethiol self-assembled monolayers (SAM).1-3 In this paper, MPCs functionalized with hexanethiolate ligands are synthesized using a modified Brust reaction4 and characterized with ultraviolet visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and proton (1H) nuclear magnetic resonance (NMR). MPC films are assembled on SAM modified gold electrode interfaces by using a "dip cycle" method of alternating MPC layers and dithiol linking molecules. Film growth at gold electrode is tracked electrochemically by measuring changes to the double layer charging current of the system. Analogous films assembled on silane modified glass slides allow for optical monitoring of film growth and cross-sectional TEM analysis provides an estimated film thickness. During film assembly, manipulation of the MPC ligand protection as well as the interparticle linkage mechanism allow for networked films, that are readily adaptable, to interface with redox protein having different adsorption mechanism. For example, Pseudomonas aeruginosa azurin (AZ) can be adsorbed hydrophobically to dithiol-linked films of hexanethiolate MPCs and cytochrome c (cyt c) can be immobilized electrostatically at a carboxylic acid modified MPC interfacial layer. In this

  15. Controlled electrodeposition of Au monolayer film on ionic liquid

    NASA Astrophysics Data System (ADS)

    Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei; Liu, Shengzhong Frank

    2016-05-01

    Gold (Au) nanoparticles have been attractive for centuries for their vibrant appearance enhanced by their interaction with sunlight. Nowadays, there have been tremendous research efforts to develop them for high-tech applications including therapeutic agents, sensors, organic photovoltaics, medical applications, electronics and catalysis. However, there remains to be a challenge to fabricate a monolayer Au coating with complete coverage in controlled fashion. Here we present a facile method to deposit a uniform Au monolayer (ML) film on the [BMIM][PF6] ionic liquid substrate using an electrochemical deposition process. It demonstrates that it is feasible to prepare a solid phase coating on the liquid-based substrate. Moreover, the thickness of the monolayer coating can be controlled to a layer-by-layer accuracy.

  16. Articles including thin film monolayers and multilayers

    SciTech Connect

    Li, DeQuan; Swanson, B.I.

    1992-12-31

    This invention pertains to thin film assemblies or devices useful as sensors, nonlinear optical materials, and trace material scavengers. It claims a base substrate having an oxide surface layer, and a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate. A metal species may be provided attached to the ligand, and a multifunctional organic ligand may be provided attached to the metal species. A second metal species may be provided attached to the multifunctional ligand.

  17. Controlling the adhesion of conducting polymer films with patterned self-assembled monolayers

    SciTech Connect

    Rozsnyai, L.F.; Wrighton, M.S.

    1996-02-01

    A photosensitive self-assembled monolayer (SAM) is selectively irradiated to fabricate a pattern on an Au electrode, and a thin film of aniline or 3-methylthiophene is deposited on it by electopolymerization. Adhesion of the polymer films can be controlled by the monolayer terminal group. Applying tape to the sample and peeling it away selectively removes the conducting polymer film to the tape in a near-micron resolution pattern. 14 refs., 1 fig.

  18. Preparation of porous monolayer film by immersing the stearic acid Langmuir-Blodgett monolayer on mica in salt solution

    NASA Astrophysics Data System (ADS)

    Wang, S.; Li, Y. L.; Zhao, H. L.; Liang, H.; Liu, B.; Pan, S.

    2012-11-01

    Porous materials have drawn attention from scientists in many fields such as life sciences, catalysis and photonics since they can be used to induce some materials growth as expected. Especially, porous Langmuir-Blodgett (LB) film is an ideal material with controlled thickness and flat surface. In this paper, stearic acid (SA), which has been extensively explored in LB film technique, is chosen as the template material with known parameters to prepare the LB film, and then the porous SA monolayer film is obtained by means of etching in salt solution. The main etching mechanism is suggested that the cations in the solution block the electrostatic interaction between the polar carboxyl group of SA and the electronegative mica surface. The influencing factors (such as concentration of salt solution, valence of cation and surface pressure) of the porous SA film are systematically studied in this work. The novel method proposed in this paper makes it convenient to prepare porous monolayer film for designed material growth or cell culture.

  19. Assembly of oriented zeolite monolayers and thin films on polymeric surfaces via hydrogen bonding.

    PubMed

    Zhou, Ming; Liu, Xiufeng; Zhang, Baoquan; Zhu, Huiming

    2008-10-21

    The b-oriented monolayers of microsized silicalite-1 crystals have been manually assembled on glass plate supported poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA), chitosan, and poly(methyl methacrylate) (PMMA) thin films via hydrogen bonding with much enhanced binding strength and satisfactory degrees of coverage and close packing. The exerted pressure and rubbing time in the manual assembly do not affect the binding strength of the silicalite-1 monolayer on the glass plate supported polymeric film. This manual assembly has been further applied to fabricate zeolite monolayers on commercially available Plexiglas surfaces and b-oriented multilayered films of silicalite-1 crystals on glass plates. The assembly method established in this study provides a feasible way to produce zeolite monolayers on polymer-modified solid substrates and Plexiglas and to fabricate zeolite-polymer composite membranes by means of the layer-by-layer technique. PMID:18785711

  20. Morphology and Composition of Structured, Phase-Separated Behenic Acid-Perfluorotetradecanoic Acid Monolayer Films.

    PubMed

    Rehman, Jeveria; Araghi, Hessamaddin Younesi; He, Anqiang; Paige, Matthew F

    2016-05-31

    The phase separation of immiscible surfactants in mixed monolayer films provides an approach to physically manipulate important properties of thin films, including surface morphology, microscale composition, and mechanical properties. In this work, we predict, based upon existing miscibility studies and their thermodynamic underpinnings described in the literature, the miscibility and film morphology of mixed monolayers comprised of behenic acid (C21H43COOH) and perfluorotetradecanoic acid (C13F27COOH) in various molar ratios. Predictions are tested using a combination of experimental surface characterization methods for probing miscibility and film morphology at the solid/air and air/water interfaces. Film components were immiscible and phase-separated into chemically well-defined domains under a variety of experimental conditions, with monolayer morphology consistent with initial predictions. The extensibility of these basic predictions to other systems is discussed in the context of using these works for different perfluorinated surfactant molecules. PMID:27163482

  1. Wrinkle to fold transitions: Stress relaxation in lipid monolayers and other elastic thin films

    NASA Astrophysics Data System (ADS)

    Lee, Ka Yee C.

    2009-03-01

    Surfactants at air/water interfaces are often subjected to mechanical stresses as the interfaces they occupy are reduced in area. The most well characterized forms of stress relaxation in these systems are first order phase transitions. However, once chemical phase transitions have been exhausted, the monolayer undergoes global mechanical relaxations termed collapse. We have previously demonstrated that for lung surfactants, a mixture of lipids and proteins that coats the alveoli to reduce the work of breathing, collapse manifests itself as protrusions of folds into the subphase. These folds remain attached to the monolayer and reversibly reincorporated upon expansion. By studying different types of monolayers, we have shown that this folding transition in monolayers is not limited to lung surfactant films, but rather represents a much more general type of stress relaxation mechanism. Our study indicates that collapse modes are found most closely linked to in-plane rigidity. We characterize the rigidity of the monolayer by analyzing in-plane morphology on numerous length scales. More rigid monolayers collapse out-of-plane via a hard elastic mode similar to an elastic membrane, with the folded state being the final collapse state, while softer monolayers relax in-plane by shearing. For the hard elastic mode of collapse, we have further demonstrated experimentally and theoretically that the folded state is preceded by a wrinkled state, and similar wrinkle to fold transitions has been observed in elastic thin films ranging from 2 nm to 10 μm in thickness of completely different chemical nature (lung surfactant lipid monolayers, gold nanoparticle trilayers, and polyester sheets).

  2. Preparation and Characterization of Large Area Monolayer Films of Pt Nanoparticles

    NASA Astrophysics Data System (ADS)

    Kelly, Brian; Cichocki, Ronald; Ren, Jie; Schmidt, Robert; Theopold, Klaus; Unruh, Karl

    Highly uniform monolayer thick coatings of Pt nanoparticles with areas as large as 20 cm2 have been prepared by first self-assembling the desired Pt film at the interface between two immiscible liquids and then transferring the film to a glass substrate. The controlled addition of ethyl alcohol to a phase separated mixture of an aqueous colloidal solution of Pt nanoparticles and hexane allowed both monolayer and multilayer films to be prepared. Optical microscopy and UV-vis spectrophotometry measurements have been used to verify the large scale uniformity of the coatings while transmission electron and atomic force microscopy measurements confirmed that single and multilayer films can be prepared. This material is based upon work supported by the National Science Foundation under Grant No. 1410076.

  3. Second-harmonic generation in resonant waveguide gratings incorporating ionic self-assembled monolayer polymer films.

    PubMed

    Purvinis, Georgeanne; Priambodo, Purnomo S; Pomerantz, Martin; Zhou, Ming; Maldonado, Theresa A; Magnusson, Robert

    2004-05-15

    Experimental results on resonantly excited second-harmonic generation (SHG) in a periodic ionically self-assembled monolayer (ISAM) film are reported. A double-layer guided-mode resonance filter (GMRF) structure is coated with 40 bilayers of pyrlium-based chi(2) ISAM thin film and excited with the fundamental of a Nd:YAG laser. Enhanced second-harmonic conversion in the ISAM film is achieved because of the local field enhancement associated with the fundamental resonating leaky mode. This method of SHG is particularly promising, as the ISAM films under investigation exhibit anomalous dispersion that may be applied for phase matching to improve nonlinear conversion efficiency. PMID:15182001

  4. Second-harmonic generation in resonant waveguide gratings incorporating ionic self-assembled monolayer polymer films

    NASA Astrophysics Data System (ADS)

    Purvinis, Georgeanne; Priambodo, Purnomo S.; Pomerantz, Martin; Zhou, Ming; Maldonado, Theresa A.; Magnusson, Robert

    2004-05-01

    Experimental results on resonantly excited second-harmonic generation (SHG) in a periodic ionically self-assembled monolayer (ISAM) film are reported. A double-layer guided-mode resonance filter (GMRF) structure is coated with 40 bilayers of pyrlium-based chi^(2) ISAM thin film and excited with the fundamental of a Nd:YAG laser. Enhanced second-harmonic conversion in the ISAM film is achieved because of the local field enhancement associated with the fundamental resonating leaky mode. This method of SHG is particularly promising, as the ISAM films under investigation exhibit anomalous dispersion that may be applied for phase matching to improve nonlinear conversion efficiency.

  5. Rapid permeation measurement system for the production control of monolayer and multilayer films

    NASA Astrophysics Data System (ADS)

    Botos, J.; Müller, K.; Heidemeyer, P.; Kretschmer, K.; Bastian, M.; Hochrein, T.

    2014-05-01

    Plastics have been used for packaging films for a long time. Until now the development of new formulations for film applications, including process optimization, has been a time-consuming and cost-intensive process for gases like oxygen (O2) or carbon dioxide (CO2). By using helium (He) the permeation measurement can be accelerated from hours or days to a few minutes. Therefore a manometric measuring system for tests according to ISO 15105-1 is coupled with a mass spectrometer to determine the helium flow rate and to calculate the helium permeation rate. Due to the accelerated determination the permeation quality of monolayer and multilayer films can be measured atline. Such a system can be used to predict for example the helium permeation rate of filled polymer films. Defined quality limits for the permeation rate can be specified as well as the prompt correction of process parameters if the results do not meet the specification. This method for process control was tested on a pilot line with a corotating twin-screw extruder for monolayer films. Selected process parameters were varied iteratively without changing the material formulation to obtain the best process parameter set and thus the lowest permeation rate. Beyond that the influence of different parameters on the helium permeation rate was examined on monolayer films. The results were evaluated conventional as well as with artificial neuronal networks in order to determine the non-linear correlation between all process parameters.

  6. Wafer-Scale Monolayer Films of Semiconducting Metal Dichalcogenides for High-Performance Electronics

    NASA Astrophysics Data System (ADS)

    Xie, Saien; Kang, Kibum; Huang, Lujie; Han, Yimo; Huang, Pinshane; Mak, Kin Fai; Kim, Cheol-Joo; Muller, David; Park, Jiwoong

    2015-03-01

    Two-dimensional semiconducting transition metal dichalcogenides (TMDs) have shown their potential in electronics, optoelectronic and valleytronis. However, large-scale growth methods reported to date have only produced materials with limited structural and electrical uniformity, hindering further technological applications. Here we present a 4-inch scale growth of continuous monolayer molybdenum disulfide (MoS2) and tungsten disulfide (WS2) films that show excellent structural and electrical uniformity over the entire wafer using metal-organic chemical vapor deposition. The resulting monolayer films show high mobility of 30 cm2/Vs at room temperature, as well as the phonon-limited transport for MoS2, regardless of the channel length and device location. They allow for the batch fabrication of monolayer MoS2 field effect transistors with a 99% yield, which display spatially-uniform n-type transistor operation with a high on/off ratio. We further demonstrate the multi-level growth and fabrication of vertically-stacked monolayer MoS2 films and devices, which could enable the development of novel three-dimensional circuitry and device integration.

  7. Manipulating the Assembly of Spray-Deposited Nanocolloids: In Situ Study and Monolayer Film Preparation.

    PubMed

    Zhang, Peng; Santoro, Gonzalo; Yu, Shun; Vayalil, Sarathlal K; Bommel, Sebastian; Roth, Stephan V

    2016-05-01

    Fabrication of nanoparticle arrays on a substrate is one of the most concerned aspects for manipulating assembly of nanoparticles and preparing functional nanocomposites. Here, we studied in situ the assembly kinetics of polystyrene nanocolloids by using grazing incidence small-angle X-ray scattering. The structure formation of the nanoparticle film is monitored during air-brush spraying, which provides a rapid and scalable preparation. By optimizing the substrate temperature, the dispersion of the nanocolloids can be tailored to prepare monolayer film. The success of the monolayer preparations is attributed to the fast solvent evaporation which inhibits the aggregation of the nanocolloids. The present study may open a new avenue for the manufacture-friendly preparation of well-dispersed nanoparticle thin films. PMID:27070283

  8. Cantilever measurements of surface stress, surface reconstruction, film stress and magnetoelastic stress of monolayers

    PubMed Central

    Sander, Dirk; Tian, Zhen; Kirschner, Jürgen

    2008-01-01

    We review the application of cantilever-based stress measurements in surface science and magnetism. The application of thin (thickness appr. 0.1 mm) single crystalline substrates as cantilevers has been used successfully to measure adsorbate-induced surface stress changes, lattice misfit induced film stress, and magneto-elastic stress of ferromagnetic monolayers. Surface stress changes as small as 0.01 N/m can be readily measured, and this translates into a sensitivity for adsorbate-coverage well below 0.01 of one layer. Stress as large as several GPa, beyond the elasticity limits of high strength materials, is measured, and it is ascribed to the lattice misfit between film and substrate. Our results point at the intimate relation between surface stress and surface reconstruction, stress-induced structural changes in epitaxially strained films, and strain-induced modifications of the magneto-elastic coupling in ferromagnetic monolayers.

  9. Sputtering and secondary ion emission properties of alkali metal films and adsorbed monolayers

    SciTech Connect

    Krauss, A R; Gruen, D M

    1980-01-01

    The secondary ion emission of alkali metal adsorbed monlayer and multilayer films has been studied. Profiling with sub-monolayer resolution has been performed by Auger, x-ray photoemission and secondary ion mass spectroscopy. Characteristic differences in the sputtering yields, and ion fraction have been observed which are associated with both the surface bonding properties and the mechanism leading to the formation of secondary ions. By sputtering with a negative bias applied to the sample, positive secondary ions are returned to the surface, resulting in a reduced sputter-induced erosion rate. Comparison with the results obtained with K and Li overlayers sputtered without sample bias provides an experimental value of both the total and secondary ion sputtering yields. The first and second monolayers can be readily identified and the first monolayer exhibits a lower sputtering yield and higher secondary ion fraction. This result is related to adsorption theory and measured values are compared with those obtained by thermal desorption measurements.

  10. Efficient Lateral Electron Transport inside a Monolayer of Aromatic Amines Anchored on Nanocrystalline Metal Oxide Films.

    PubMed

    Bonhôte, P; Gogniat, E; Tingry, S; Barbé, C; Vlachopoulos, N; Lenzmann, F; Comte, P; Grätzel, M

    1998-02-26

    A monolayer of a phosphonated triarylamine adsorbed on nanocrystalline TiO2, ZrO2, or Al2O3 film deposited on conducting glass displays reversible electrochemical and electrochromic behavior although the redox potential of the electroactive molecules (0.80 V vs NHE) lies in the forbidden band of the semiconducting or insulating oxides. The mechanism of charge transport was found to involve hole injection from the conducting support followed by lateral electron hopping within the monolayer. The apparent diffusion coefficient ranged from 2.8 × 10(-12) m(2) s(-1) in the neat 1-ethyl-2-methylimidazolium bis(trifluoromethylsulfonyl)imide (EtMeIm(+)Tf2N(-)) to 1.1 × 10(-11) m(2) s(-1) in acetonitrile + 2 M EtMeIm(+)Tf2N(-). A percolation threshold for electronic conductivity was found at a surface coverage corresponding to 50% of a full monolayer. PMID:27577008

  11. Growth of polypyrrole ultrathin films on MoS₂ monolayers as high-performance supercapacitor electrodes.

    PubMed

    Tang, Hongjie; Wang, Jiangyan; Yin, Huajie; Zhao, Huijun; Wang, Dan; Tang, Zhiyong

    2015-02-01

    A scalable solution-based approach is developed to controllably grow PPy ultrathin films on 2D MoS2 monolayers. When these sandwiched nanocomposites are utilized as supercapacitor electrodes, a record high specific capacitance, remarkable rate capability, and improved cycling stability are achieved, offering a feasible solution to create the next generation of energy-storage device with superior power density and energy density. PMID:25529000

  12. Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains

    PubMed Central

    Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

    2015-01-01

    A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability. PMID:26537788

  13. Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains

    NASA Astrophysics Data System (ADS)

    Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

    2015-11-01

    A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.

  14. Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains.

    PubMed

    Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

    2015-01-01

    A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability. PMID:26537788

  15. Biotinylated polyalkylthiophene thin films and monolayers that specifically incorporate phycobiliproteins: toward smart materials

    NASA Astrophysics Data System (ADS)

    Ayyagari, Madhu S. R.; Pande, Rajiv; Lim, Jeong O.; Kamath, Manohar; Beladakere, Nagendra; Gao, Harry H.; Marx, Kenneth A.; Tripathy, Sukant K.; Kumar, Jayant; Samuelson, Lynne A.; Akkara, Joseph A.; Kaplan, David L.

    1994-05-01

    We are investigating thin film and monolayer systems that involve conjugated conducting polymers and specific biological macromolecules. One class of conducting polymers, polyalkylthiophenes, are derivatized with biotin. These biotinylated polymers form the basis for a generic cassette system of attachment for any biological molecule through biotinylation or interaction with streptavidin. The high affinity of the biotin-streptavidin system, used in sequential steps, forms the basis of the cassette method. We have formed both monolayers and thin films (a few nanometers) of the cassette assembly in which phycobiliproteins are incorporated. We are investigating the optical signal transduction properties of specific phycobiliproteins (phycoerythrin, phycocyanin and allophycocyanain) using the cassette system on the inner surface of glass capillaries and on optical fiber surfaces. Phycobiliprotein photocurrent signals in conducting polymer matrices on microelectrodes are also being investigated. Our aim is to integrate the signal transduction mechanisms of the phycobiliproteins within monolayers or thin films of the conducting polymers to create biosensors and related smart materials for applications in biomedicine and biotechnology.

  16. Catalystlike behavior of Si adatoms in the growth of monolayer Al film on Si(111).

    PubMed

    Teng, Jing; Zhang, Lixin; Jiang, Ying; Guo, Jiandong; Guo, Qinlin; Wang, Enge; Ebert, Philipp; Sakurai, T; Wu, Kehui

    2010-07-01

    The formation mechanism of monolayer Al(111)1x1 film on the Si(111) radical3x radical3-Al substrate was studied by scanning tunneling microscopy and first-principles calculations. We found that the Si adatoms on the radical3x radical3-Al substrate play important roles in the growth process. The growth of Al-1x1 islands is mediated by the formation and decomposition of SiAl(2) clusters. Based on experiments and theoretical simulations we propose a model where free Si atoms exhibit a catalystlike behavior by capturing and releasing Al atoms during the Al film growth. PMID:20614981

  17. Conformation-triggered flow instability in monolayer thick polymer films

    NASA Astrophysics Data System (ADS)

    Sheiko, Sergei; Beers, Kathryn; Matyjaszewski, Krzysztof; Rubinstein, Michael; Dobrynin, Andrey

    2005-03-01

    Here we have report on a new type of flow instability triggered by conformational changes of brush-like macromolecules as they spread on a solid substrate. By tracing the movement of individual molecules by atomic force microscopy, we were able to follow the evolution of the instability pattern on the molecular level enabling a microscopic understanding of the underlying physical mechanism. The instability is an analog of the Saffman-Taylor instability in thin films. However, the instability is driven by a variation in flow velocity controlled by molecular conformation instead of a viscosity gradient.

  18. Chemical Vapor Deposition of Fluoroalkylsilane Monolayer Films for Adhesion Control in Microelectromechanical Systems

    SciTech Connect

    MAYER,THOMAS M.; DE BOER,MAARTEN P.; SHINN,NEAL D.; CLEWS,PEGGY J.; MICHALSKE,TERRY A.

    2000-01-26

    We have developed a new process for applying a hydrophobic, low adhesion energy coating to microelectromechanical (MEMS) devices. Monolayer films are synthesized from tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS) and water vapor in a low-pressure chemical vapor deposition process at room temperature. Film thickness is self-limiting by virtue of the inability of precursors to stick to the fluorocarbon surface of the film once it has formed. We have measured film densities of {approx}3 molecules nm{sup 2} and film thickness of {approx}1 nm. Films are hydrophobic, with a water contact angle >110{sup o}. We have also incorporated an in-situ downstream microwave plasma cleaning process, which provides a clean, reproducible oxide surface prior to film deposition. Adhesion tests on coated and uncoated MEMS test structures demonstrate superior performance of the FOTS coatings. Cleaned, uncoated cantilever beam structures exhibit high adhesion energies in a high humidity environment. An adhesion energy of 100 mJ m{sup -2} is observed after exposure to >90% relative humidity. Fluoroalkylsilane coated beams exhibit negligible adhesion at low humidity and {<=} 20 {micro}J m{sup -2} adhesion energy at >90% relative humidity. No obvious film degradation was observed for films exposed to >90% relative humidity at room temperature for >24 hr.

  19. Evolution of pentacene films on Ag(1 1 1): Growth beyond the first monolayer

    NASA Astrophysics Data System (ADS)

    Käfer, Daniel; Witte, Gregor

    2007-07-01

    The formation and structure of pentacene films upon molecular beam deposition at room temperature onto a Ag(1 1 1) surface have been studied by means of SEM, XRD, TDS and NEXAFS. It is shown that multilayer films actually consist of separate crystalline islands revealing a bulk structure reported before by Siegrist et al. [T. Siegrist, C. Kloc, J.H. Schon, B. Batlogg, R.C. Haddon, S. Berg, G.A. Thomas, Angew. Chem. Int. Ed. 40 (2001) 1732]. Distinctly different π ∗-resonances were observed in the C1s NEXAFS spectra of pentacene for the first monolayer and the crystalline films reflecting differences in the electronic coupling and the molecular orientation. Moreover, such characteristic π ∗-signatures were used to monitor in situ the film evolution upon deposition indicating an immediate formation of crystalline islands on top of a chemisorbed wetting layer.

  20. Multilayer structures in lipid monolayer films containing surfactant protein C: effects of cholesterol and POPE.

    PubMed

    Malcharek, Stefan; Hinz, Andreas; Hilterhaus, Lutz; Galla, Hans-Joachim

    2005-04-01

    The influence of cholesterol and POPE on lung surfactant model systems consisting of DPPC/DPPG (80:20) and DPPC/DPPG/surfactant protein C (80:20:0.4) has been investigated. Cholesterol leads to a condensation of the monolayers, whereas the isotherms of model lung surfactant films containing POPE exhibit a slight expansion combined with an increased compressibility at medium surface pressure (10-30 mN/m). An increasing amount of liquid-expanded domains can be visualized by means of fluorescence light microscopy in lung surfactant monolayers after addition of either cholesterol or POPE. At surface pressures of 50 mN/m, protrusions are formed which differ in size and shape as a function of the content of cholesterol or POPE, but only if SP-C is present. Low amounts of cholesterol (10 mol %) lead to an increasing number of protrusions, which also grow in size. This is interpreted as a stabilizing effect of cholesterol on bilayers formed underneath the monolayer. Extreme amounts of cholesterol (30 mol %), however, cause an increased monolayer rigidity, thus preventing reversible multilayer formation. In contrast, POPE, as a nonbilayer lipid thought to stabilize the edges of protrusions, leads to more narrow protrusions. The lateral extension of the protrusions is thereby more influenced than their height. PMID:15653721

  1. Physical and monolayer film properties of potential fatty ester biolubricants

    SciTech Connect

    Yao, Linxing; Hammond, Earl G; Wang, Tong; Bu, Wei; Vaknin, David

    2014-04-03

    The desire to replace petroleum-based lubricants with alternatives that are environmentally friendly and made from sustainable sources has encouraged the development of biolubricants based on vegetable oils. To be good lubricants, the materials should have low melting points, appropriate viscosity and oxidative stability. In this paper, we report the melting point and viscosity of oleate esters of ethylene glycol, 1,2-propanediol, 2,3-butanediol, and pentaerythritol as well as the decanoate esters of 2,3-butanediol and the 12-methyltetradecanoate esters of 1,2-propanediol. Polyol esters that have a free hydroxy group had lower melting points than the completely esterified polyols, but the completely esterified polyol esters exhibited less change in viscosity with temperature than those having a free hydroxy group. 2, 3-Butanediol monooleate, which melted at -48.6°C shows promise as a biolubricant, but its viscosity index was estimated to be 100. Pentaerythritol oleate esters, with melting points below -10°C and viscosity indices in the range of 170–197, may be suitable candidates as biolubricants. The behavior of esters spread as a monomolecular film at air/water interface may provide insight into the way they behave when spread on metal or polar surfaces, so the pressure-area isotherms of 2,3-butanediol monoleate and selected esters are also reported.

  2. Structural transitions in different monolayers of cobalt phthalocyanine film grown on Bi(1 1 1)

    NASA Astrophysics Data System (ADS)

    Tao, Min-Long; Tu, Yu-Bing; Sun, Kai; Zhang, Yao; Zhang, Xin; Li, Zhao-Bing; Hao, Shao-Jie; Xiao, Hua-Fang; Ye, Juan; Wang, Jun-Zhong

    2016-01-01

    The structural evolution of cobalt phthalocyanine (CoPc) thin films grown on a Bi(1 1 1) surface from the sub-monolayer to the third layer has been investigated with low-temperature scanning tunneling microscopy (STM). Two crucial transitions have been identified during the film epitaxial growth: one is the structural transition from zigzag chains to linear dimerized chains in the monolayer regime; the other is the molecular orientational transition from a flat-lying to a standing-up configuration in the multilayer regime. These results are helpful in understanding the growth mechanism of transition-metal phthalocyanine films on semi-metallic surfaces.

  3. Characterization of Monolayer Formation on Aluminum-Doped Zinc Oxide Thin Films

    SciTech Connect

    Rhodes,C.; Lappi, S.; Fischer, D.; Sambasivan, S.; Genzer, J.; Franzen, S.

    2008-01-01

    The optical and electronic properties of aluminum-doped zinc oxide (AZO) thin films on a glass substrate are investigated experimentally and theoretically. Optical studies with coupling in the Kretschmann configuration reveal an angle-dependent plasma frequency in the mid-IR for p-polarized radiation, suggestive of the detection of a Drude plasma frequency. These studies are complemented by oxygen depletion density functional theory studies for the calculation of the charge carrier concentration and plasma frequency for bulk AZO. In addition, we report on the optical and physical properties of thin film adlayers of n-hexadecanethiol (HDT) and n-octadecanethiol (ODT) self-assembled monolayers (SAMs) on AZO surfaces using reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our characterization of the SAM deposition onto the AZO thin film reveals a range of possible applications for this conducting metal oxide.

  4. Smooth cubic commensurate oxides on gallium nitride

    SciTech Connect

    Paisley, Elizabeth A.; Gaddy, Benjamin E.; LeBeau, James M.; Shelton, Christopher T.; Losego, Mark D.; Mita, Seiji; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.; Maria, Jon-Paul; Biegalski, Michael D.; Christen, Hans M.

    2014-02-14

    Smooth, commensurate alloys of 〈111〉-oriented Mg{sub 0.52}Ca{sub 0.48}O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

  5. Morphology of Monolayer MgO Films on Ag(100): Switching from Corrugated Islands to Extended Flat Terraces

    NASA Astrophysics Data System (ADS)

    Pal, Jagriti; Smerieri, Marco; Celasco, Edvige; Savio, Letizia; Vattuone, Luca; Rocca, Mario

    2014-03-01

    The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps.

  6. Morphology of monolayer MgO films on Ag(100): switching from corrugated islands to extended flat terraces.

    PubMed

    Pal, Jagriti; Smerieri, Marco; Celasco, Edvige; Savio, Letizia; Vattuone, Luca; Rocca, Mario

    2014-03-28

    The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps. PMID:24724662

  7. Probing Thin Films and Monolayers on Gold with Large Amplitude Temperature Jumps

    NASA Astrophysics Data System (ADS)

    Sun, Yuxiao; Berg, Christopher M.; Dlott, Dana

    2014-06-01

    A methodology to probe localized vibrational transitions of self-assembled monolayers (SAMs) adsorbed on gold films using vibrational sum-frequency generation (SFG) is described. The gold film is subjected to heating from a 400nm pump laser, exposing the adsorbed molecules to a temperature jump in the 30-175° K range, calibrated using ultrafast reflectance measurements of the gold compared to steady state oven heating . SAMs of alkyl thiols as well as nitro functionalized aryl thiols were deposited and temperature jumped while be observed with SFG, monitoring the symmetric and asymmetric methyl vibrations as well as nitro vibrations. The amplitude, center, and width of the transitions were measured and provide information about delay and orientation of the molecules, as well as providing an indicator of the overall monolayer state. All transitions probed exhibited overshoot decay plateau patterns, attributed to a fast hot electron process directly exciting the probed transitions, followed by a slower bulk heating process causing monolayer disordering. This leads to a shift in the average angle of the terminal methyl, manifesting itself as a change in the amplitude of the vibration. These techniques will be applied to thin films of energetic materials to study reactions to temperature jumps. HMX is known to have a peak in sensitivity as δ-HMX transitions to β-HMX at high temperatures, but fairly little information about the reason for this is known. This technique should be able to probe that process and provide data that can be used with computational models to gain some understanding of the process.

  8. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers.

    PubMed

    Badali, D S; Gengler, R Y N; Miller, R J D

    2016-05-01

    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the "medium" energy regime (1-10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples. PMID:27226978

  9. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    PubMed Central

    Badali, D. S.; Gengler, R. Y. N.; Miller, R. J. D.

    2016-01-01

    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the “medium” energy regime (1–10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples. PMID:27226978

  10. Comparative Study of Electroless Copper Film on Different Self-Assembled Monolayers Modified ABS Substrate

    PubMed Central

    Xu, Jiushuai; Fan, Ruibin; Wang, Jiaolong; Jia, Mengke; Xiong, Xuanrui; Wang, Fang

    2014-01-01

    Copper films were grown on (3-Mercaptopropyl)trimethoxysilane (MPTMS), (3-Aminopropyl)triethoxysilane (APTES) and 6-(3-(triethoxysilyl)propylamino)-1,3,5- triazine-2,4-dithiol monosodium (TES) self-assembled monolayers (SAMs) modified acrylonitrile-butadiene-styrene (ABS) substrate via electroless copper plating. The copper films were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their individual deposition rate and contact angle were also investigated to compare the properties of SAMs and electroless copper films. The results indicated that the formation of copper nuclei on the TES-SAMs modified ABS substrate was faster than those on the MPTMS-SAMs and APTES-SAMs modified ABS substrate. SEM images revealed that the copper film on TES-SAM modified ABS substrate was smooth and uniform, and the density of copper nuclei was much higher. Compared with that of TES-SAMs modified resin, the coverage of copper nuclei on MPTMS and APTES modified ABS substrate was very limited and the copper particle size was too big. The adhesion property test demonstrated that all the SAMs enhanced the interfacial interaction between copper plating and ABS substrate. XRD analysis showed that the copper film deposited on SAM-modified ABS substrate had a structure with Cu(111) preferred orientation, and the copper film deposited on TES-SAMs modified ABS substrate is better than that deposited on MPTMS-SAMs or APTES-SAMs modified ABS resins in electromigrtion resistance. PMID:24739812

  11. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer

    PubMed Central

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi

    2014-01-01

    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications. PMID:24619247

  12. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer

    NASA Astrophysics Data System (ADS)

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; di, Zengfeng; Liu, Xuanyong; Wang, Xi

    2014-03-01

    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications.

  13. Angle-resolved XPS analysis and characterization of monolayer and multilayer silane films for DNA coupling to silica.

    PubMed

    Shircliff, Rebecca A; Stradins, Paul; Moutinho, Helio; Fennell, John; Ghirardi, Maria L; Cowley, Scott W; Branz, Howard M; Martin, Ina T

    2013-03-26

    We measure silane density and Sulfo-EMCS cross-linker coupling efficiency on aminosilane films by high-resolution X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. We then characterize DNA immobilization and hybridization on these films by (32)P-radiometry. We find that the silane film structure controls the efficiency of the subsequent steps toward DNA hybridization. A self-limited silane monolayer produced from 3-aminopropyldimethylethoxysilane (APDMES) provides a silane surface density of ~3 nm(-2). Thin (1 h deposition) and thick (19 h deposition) multilayer films are generated from 3-aminopropyltriethoxysilane (APTES), resulting in surfaces with increased roughness compared to the APDMES monolayer. Increased silane surface density is estimated for the 19 h APTES film, due to a ∼32% increase in surface area compared to the APDMES monolayer. High cross-linker coupling efficiencies are measured for all three silane films. DNA immobilization densities are similar for the APDMES monolayer and 1 h APTES. However, the DNA immobilization density is double for the 19 h APTES, suggesting that increased surface area allows for a higher probe attachment. The APDMES monolayer has the lowest DNA target density and hybridization efficiency. This is attributed to the steric hindrance as the random packing limit is approached for DNA double helices (dsDNA, diameter ≥ 2 nm) on a plane. The heterogeneity and roughness of the APTES films reduce this steric hindrance and allow for tighter packing of DNA double helices, resulting in higher hybridization densities and efficiencies. The low steric hindrance of the thin, one to two layer APTES film provides the highest hybridization efficiency of nearly 88%, with 0.21 dsDNA/nm(2). The XPS data also reveal water on the cross-linker-treated surface that is implicated in device aging. PMID:23445373

  14. Evanescent wave absorption sensor based on tapered multimode fiber coated with monolayer graphene film

    NASA Astrophysics Data System (ADS)

    Qiu, Hengwei; Gao, Saisai; Chen, Peixi; Li, Zhen; Liu, Xiaoyun; Zhang, Chao; Xu, Yuanyuan; Jiang, Shouzhen; Yang, Cheng; Huo, Yanyan; Yue, Weiwei

    2016-05-01

    An evanescent wave absorption (EWA) sensor based on tapered multimode fiber (TMMF) coated with monolayer graphene film for the detection of double-stranded DNA (DS-DNA) is investigated in this work. The TMMF is a silica multimode fiber (nominally at 62.5 μm), which was tapered to symmetric taper with waist diameters of ~30 μm and total length of ~3 mm. Monolayer graphene film was grown on a copper foil via chemical vapor deposition (CVD) technology and transferred onto skinless tapered fiber core via dry transfer technology. All the components of the sensor are coupled together by fusion splicer in order to eliminate the external disturbance. DS-DNA is created by the assembly of two relatively complemented oligonucleotides. The measurements are obtained by using a spectrometer in the optical wavelength range of 400-900 nm. With the increase of DS-DNA concentration, the output light intensity (OPLI) arisen an obvious attenuation. Importantly, the absorbance (A) and the DS-DNA concentrations shown a reasonable linear variation in a wide range of 5-400 μM. Through a series of comparison, the accuracy of TMMF sensor with graphene (G-TMMF) is much better than that without graphene (TMMF), which can be attributed to the molecular enrichment of graphene by π-π stacking.

  15. Chemical vapor deposition and etching of high-quality monolayer hexagonal boron nitride films.

    PubMed

    Sutter, Peter; Lahiri, Jayeeta; Albrecht, Peter; Sutter, Eli

    2011-09-27

    The growth of large-area hexagonal boron nitride (h-BN) monolayers on catalytic metal substrates is a topic of scientific and technological interest. We have used real-time microscopy during the growth process to study h-BN chemical vapor deposition (CVD) from borazine on Ru(0001) single crystals and thin films. At low borazine pressures, individual h-BN domains nucleate sparsely, grow to macroscopic dimensions, and coalescence to form a closed monolayer film. A quantitative analysis shows borazine adsorption and dissociation predominantly on Ru, with the h-BN covered areas being at least 100 times less reactive. We establish strong effects of hydrogen added to the CVD precursor gas in controlling the in-plane expansion and morphology of the growing h-BN domains. High-temperature exposure of h-BN/Ru to pure hydrogen causes the controlled edge detachment of B and N and can be used as a clean etching process for h-BN on metals. PMID:21793550

  16. Tribological and cutting behavior of silicon nitride tools coated with monolayer- and multilayer-microcrystalline HFCVD diamond films

    NASA Astrophysics Data System (ADS)

    Chen, Naichao; Shen, Bin; Yang, Guodong; Sun, Fanghong

    2013-01-01

    Monolayer-micrometric (MN-MCD), monolayer-submicrometric (MN-SMCD) and multilayer-micrometric (MT-MCD) diamond films are grown on silicon nitride substrates by hot filament chemical vapor deposition (HFCVD) technique. The as-deposited diamond films are characterized with scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectrometer (EDS), Raman spectrum and 3D surface topography. Tribological properties are assessed by the sliding tests using a reciprocal motion ball-on-flat (BOF) configuration. The friction coefficients are measured as 0.126 for the MN-MCD films, 0.076 for the MN-SMCD films and 0.071 for the MT-MCD films during dry sliding against silicon nitride counterface. The different carbon content of the films may result in the visible diminution of friction coefficient for the MT-MCD films relative to the MN-MCD films. The results show that the MN-MCD and MT-MCD films present the much higher wear resistance than the MN-SMCD films. Meanwhile, the cutting performances of as-deposited diamond films are evaluated by machining aluminum-silicon alloy material. The experimental results show that the MT-MCD insert presents the best behavior regarding the tool wear.

  17. Realization of Large-Area Wrinkle-Free Monolayer Graphene Films Transferred to Functional Substrates

    PubMed Central

    Park, Byeong-Ju; Choi, Jin-Seok; Kim, Hyun-Suk; Kim, Hyun-You; Jeong, Jong-Ryul; Choi, Hyung-Jin; Jung, Hyun-June; Jung, Min-Wook; An, Ki-Seok; Yoon, Soon-Gil

    2015-01-01

    Structural inhomogeneities, such as the wrinkles and ripples within a graphene film after transferring the free-standing graphene layer to a functional substrate, degrade the physical and electrical properties of the corresponding electronic devices. Here, we introduced titanium as a superior adhesion layer for fabricating wrinkle-free graphene films that is highly applicable to flexible and transparent electronic devices. The Ti layer does not influence the electronic performance of the functional substrates. Experimental and theoretical investigations confirm that the strong chemical interactions between Ti and any oxygen atoms unintentionally introduced on/within the graphene are responsible for forming the clean, defect-free graphene layer. Our results accelerate the practical application of graphene-related electronic devices with enhanced functionality. The large-area monolayer graphenes were prepared by a simple attachment of the Ti layer with the multi-layer wrinkle-free graphene films. For the first time, the graphene films were addressed for applications of superior bottom electrode for flexible capacitors instead of the novel metals. PMID:26043868

  18. An atomic force microcopy study of the mechanical and electricalproperties of monolayer films of molecules with aromatic end groups

    SciTech Connect

    Fang, Liang; Park, J.Y.; Ma, H.; Jen, A.K.-Y.; Salmeron, M.

    2007-09-06

    The effect of intermolecular {pi}-{pi} stacking on the electrical and mechanical properties of monolayer films molecules containing aromatic groups was studied using atomic force microscopy. Two types of aromatic molecules, (4-mercaptophenyl) anthrylacetylene (MPAA) and (4-mercaptophenyl)-phenylacetylene (MPPA) were used as model systems with different {pi}-{pi} stacking strength. Monolayer films of these molecules on Au(111) surfaces exhibited conductivities differing by more than one order of magnitude, MPAA being the most conductive and MPPA the least conductive. The response to compressive loads by the AFM tip was also found to be very different for both molecules. In MPAA films distinct molecular conductivity changes are observed upon mechanical perturbation. This effect however was not observed on the MPPA film, where intermolecular {pi}-{pi} interactions are likely weaker.

  19. Spreading of a surfactant monolayer on a thin liquid film: Onset and evolution of digitated structures

    NASA Astrophysics Data System (ADS)

    Matar, Omar K.; Troian, Sandra M.

    1999-03-01

    We describe the response of an insoluble surfactant monolayer spreading on the surface of a thin liquid film to small disturbances in the film thickness and surfactant concentration. The surface shear stress, which derives from variations in surfactant concentration at the air-liquid interface, rapidly drives liquid and surfactant from the source toward the distal region of higher surface tension. A previous linear stability analysis of a quasi-steady state solution describing the spreading of a finite strip of surfactant on a thin Newtonian film has predicted only stable modes. [Dynamics in Small Confining Systems III, Materials Research Society Symposium Proceedings, edited by J. M. Drake, J. Klafter, and E. R. Kopelman (Materials Research Society, Boston, 1996), Vol. 464, p. 237; Phys. Fluids A 9, 3645 (1997); O. K. Matar Ph.D. thesis, Princeton University, Princeton, NJ, 1998]. A perturbation analysis of the transient behavior, however, has revealed the possibility of significant amplification of disturbances in the film thickness within an order one shear time after the onset of flow [Phys. Fluids A 10, 1234 (1998); "Transient response of a surfactant monolayer spreading on a thin liquid film: Mechanism for amplification of disturbances," submitted to Phys. Fluids]. In this paper we describe the linearized transient behavior and interpret which physical parameters most strongly affect the disturbance amplification ratio. We show how the disturbances localize behind the moving front and how the inclusion of van der Waals forces further enhances their growth and lifetime. We also present numerical solutions to the fully nonlinear 2D governing equations. As time evolves, the nonlinear system sustains disturbances of longer and longer wavelength, consistent with the quasi-steady state and transient linearized descriptions. In addition, for the parameter set investigated, disturbances consisting of several harmonics of a fundamental wavenumber do not couple

  20. Spreading of a surfactant monolayer on a thin liquid film: Onset and evolution of digitated structures.

    PubMed

    Matar, Omar K.; Troian, Sandra M.

    1999-03-01

    We describe the response of an insoluble surfactant monolayer spreading on the surface of a thin liquid film to small disturbances in the film thickness and surfactant concentration. The surface shear stress, which derives from variations in surfactant concentration at the air-liquid interface, rapidly drives liquid and surfactant from the source toward the distal region of higher surface tension. A previous linear stability analysis of a quasi-steady state solution describing the spreading of a finite strip of surfactant on a thin Newtonian film has predicted only stable modes. [Dynamics in Small Confining Systems III, Materials Research Society Symposium Proceedings, edited by J. M. Drake, J. Klafter, and E. R. Kopelman (Materials Research Society, Boston, 1996), Vol. 464, p. 237; Phys. Fluids A 9, 3645 (1997); O. K. Matar Ph.D. thesis, Princeton University, Princeton, NJ, 1998]. A perturbation analysis of the transient behavior, however, has revealed the possibility of significant amplification of disturbances in the film thickness within an order one shear time after the onset of flow [Phys. Fluids A 10, 1234 (1998); "Transient response of a surfactant monolayer spreading on a thin liquid film: Mechanism for amplification of disturbances," submitted to Phys. Fluids]. In this paper we describe the linearized transient behavior and interpret which physical parameters most strongly affect the disturbance amplification ratio. We show how the disturbances localize behind the moving front and how the inclusion of van der Waals forces further enhances their growth and lifetime. We also present numerical solutions to the fully nonlinear 2D governing equations. As time evolves, the nonlinear system sustains disturbances of longer and longer wavelength, consistent with the quasi-steady state and transient linearized descriptions. In addition, for the parameter set investigated, disturbances consisting of several harmonics of a fundamental wavenumber do not couple

  1. Commensurism at electronically weakly interacting phthalocyanine/PTCDA heterointerfaces

    NASA Astrophysics Data System (ADS)

    Gruenewald, Marco; Sauer, Christoph; Peuker, Julia; Meissner, Matthias; Sojka, Falko; Schöll, Achim; Reinert, Friedrich; Forker, Roman; Fritz, Torsten

    2015-04-01

    Interfaces in multilayered electronic devices are of paramount importance, especially for layer thicknesses in the nanometer range. Among the interfacial processes are charge injection or extraction and excitonic dissociation, the latter being particularly relevant if molecular components are involved. Highly ordered superstructures are preferable to prevent undesired losses of charge carriers and/or excitons. Epitaxial organic-inorganic systems have already received eminent attention, but only few studies have dealt with organic-organic heterointerfaces so far. Here, we focus on the adsorption of metal-phthalocyanines (MePc, Me = Sn or Cu) on 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) in the form of stacked monolayers (ML) on Ag(111). Using scanning tunneling microscopy and low-energy electron diffraction we reveal an initial nonordered growth for dilute SnPc submonolayers and consecutively three condensed phases at coverages ranging up to 1 ML —each possessing a distinct commensurate registry with the underlying PTCDA. By applying in situ optical differential reflectance spectroscopy and photoelectron spectroscopy we find that neither the SnPc nor the CuPc phases exhibit significant electronic or optical coupling with the PTCDA interlayer. Therefore, our results demonstrate that commensurism does not necessarily imply chemisorption, as stated previously in the literature, but that physisorption may be accompanied by commensurate superstructures.

  2. AFM Observation of Self-Assembled Monolayer Films on GaAs (110)

    NASA Astrophysics Data System (ADS)

    Ohno, Hirotaka; Motomatsu, Makoto; Mizutani, Wataru; Tokumoto, Hiroshi

    1995-02-01

    We have confirmed that a self-assembled monolayer (SAM) film of octadecanethiol (ODT), CH3(CH2)17SH, can be formed on a cleaved GaAs (110) surface, by using an atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). Circular depressions were observed on the surface after film formation. The area of the circular depressions increased with immersion time, indicating that the solution oxidized the interface between ODT molecules and the GaAs surface, resulting in removal of ODT molecules. The oxidation was considerably faster in pure ethanol solution than that in ODT solution, demonstrating that the SAM film protects the GaAs surface from oxidation. High-resolution lateral force microscope (LFM) images revealed a periodic structure that had two types of lines: periodic lines 0.57 nm apart and lines rotated 55° with respect to them. A structural model of the SAM successfully explained both the features in high-resolution LFM images and the depression depth observed in AFM images.

  3. Thickness-dependent nanofriction of a rare gas monolayer sliding on Pb(111) ultrathin films

    NASA Astrophysics Data System (ADS)

    Cai, X. L.; Wang, J. J.; Fu, X. N.; Bai, S. Y.; Niu, C. Y.; Jia, Y.

    2016-02-01

    The friction can be affected dramatically by quantum size effects (QSEs) and edge effects at nanoscale. The modulations of QSEs on nanofriction of a rare gas (RG) monolayer sliding on Pb(111) ultrathin films were investigated by using the first-principles approach within density functional theory (DFT) with van der Waals (vdW) interaction correction. Our findings revealed that there exist even-odd oscillations in the friction with the thickness of Pb(111) substrate and the friction can be tuned up to 30% by the different thicknesses of Pb(111) films. Moreover, such modulation is more obvious for the RG adatoms with larger radius. The underlying physics is that the oscillations of the electronic density of states at Fermi level induce different interactions and energy barriers between RG and Pb(111) films with different thicknesses. Overall, we here propose an approach to tune friction and a way to identify the electronic contribution to friction via the different thicknesses of substrates at nanoscale.

  4. Si adatoms as catalyst for the growth of monolayer Al film on Si(111)

    NASA Astrophysics Data System (ADS)

    Teng, Jing; Zhang, Lixin; Wu, Kehui; Jiang, Ying; Guo, Jiandong; Guo, Qinlin; Ebert, Philipp; Sakurai, Toshio; Wang, Enge

    2010-03-01

    Recently, we reported the growth of atomically smooth Al(111) films on Si(111) with continuously controllable thickness down to the extreme level of 1 ML. Here, we study the underlying unexpected Si adatom-mediated clustering-melting mechanism by scanning tunneling microscopy and by the first-principles calculations. The Si adatoms in the initial Si(111)3x3-Al surface act as seeds to form SiAl2 clusters. The clusters are then transformed into Al(111)1x1 by incorporating further incoming Al atoms and spontaneously releasing the Si atoms, which then participate in the next cycle of the process. As a result, a two-dimensional growth of monolayer Al(111) is achieved.

  5. Ordered 1,6-bis(2-hydroxyphenyl) pyridine boron complex films grown on Ag(110): From submonolayer to multilayer

    SciTech Connect

    Zhong, D.Y.; Lin, F.; Fuchs, H.; Chi, L.F.; Wang, Y.

    2005-03-15

    Ordered molecular films of a blue-light-emitting material, 1,6-bis(2-hydroxyphenyl) pyridine boron complex [(dppy)BF], grown on the Ag(110) surface by means of organic molecular beam epitaxy, were investigated by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) under an ultrahigh vacuum. Two commensurate structures exist in the monolayer film grown at 300 K, as found by STM. In the monolayer film, two types of hydrogen bonds are formed between the molecules, which, in addition to the molecule-substrate interaction, essentially determine the monolayer structures. The structural evolution of the (dppy)BF films from submonolayer to three monolayers was monitored by LEED in situ and in real time. The results indicate that the growth of the first two monolayers is affected by the periodic potential on the substrate surface, while such a template effect is weakened beyond the second monolayer.

  6. Interface Shape and Speed of a Surfactant Monolayer Spreading on a Thin Liquid Film: Comparison Between Theory and Experiment

    NASA Astrophysics Data System (ADS)

    Troian, Sandra M.; Dussaud, Anne D.; Matar, Omar K.

    1998-11-01

    Marangoni convection of a surfactant monolayer at a free surface produces significant deformation in thin films. Numerical solutions of the film thickness predict significant thinning near the surfactant source and an elevated rim at the monolayer leading edge. While previous experimental studies have sought the relation governing the speed of the surfactant film, we focus instead on the evolution of the film thickness, whose interface shape provides an even more stringent test of the model equations. Using refracted image Moiré topography, we obtain the time variant shape and speed of an insoluble surfactant monolayer spreading on a thin viscous liquid. Good agreement between theory and experiment is obtained when the surfactant reservoir is modelled as a finite source (despite an excess of surfactant at the origin) and when a small level of pre-existing surface contamination is introduced (Troian, Dussaud and Matar, submitted to Phys. Fluids (1998)). Our studies reveal that perhaps more than any other features, the degree of film thinning (which determines the efflux of material from the source) and the presence of pre-existing surface contamination ultimately determine the optimal conditions for rapid and efficient transport of surfactant.

  7. Tribological properties of self-assembled monolayers of catecholic imidazolium and the spin-coated films of ionic liquids.

    PubMed

    Liu, Jianxi; Li, Jinlong; Yu, Bo; Ma, Baodong; Zhu, Yangwen; Song, Xinwang; Cao, Xulong; Yang, Wu; Zhou, Feng

    2011-09-20

    A novel compound of an imidazolium type of ionic liquid (IL) containing a biomimetic catecholic functional group normally seen in mussel adhesive proteins was synthesized. The IL can be immobilized on a silicon surface and a variety of other engineering material surfaces via the catecholic anchor, allowing the tribological protection of these substrates for engineering applications. The surface wetting and adhesive properties and the tribological property of the synthesized self-assembled monolayers (SAMs) are successfully modulated by altering the counteranions. The chemical composition and wettability of the IL SAMs were characterized by means of X-ray photoelectron spectroscopy (XPS) and contact angle (CA) measurements. The adhesive and friction forces were measured with an atomic force microscope (AFM) on the nanometer scale. IL composite films were prepared by spin coating thin IL films on top of the SAMs. The macrotribological properties of these IL composite films were investigated with a pin-on-disk tribometer. The results indicate that the presence of IL SAMs on a surface can improve the wettability of spin-coated ionic liquids and thus the film quality and the tribological properties. These films registered a reduced friction coefficient and a significantly enhanced durability and load-carrying capacity. The tribological properties of the composite films are better than those of pure IL films because the presence of the monolayers improves the adhesion and compatibility of spin-coated IL films with substrates. PMID:21834561

  8. In situ synthesis of a large area boron nitride/graphene monolayer/boron nitride film by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Wu, Qinke; Jang, Sung Kyu; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Lee, Young Hee; Lee, Sungjoo; Song, Young Jae

    2015-04-01

    We describe the successful in situ chemical vapor deposition synthesis of a graphene-based heterostructure in which a graphene monolayer is protected by top and bottom boron nitride films. The boron nitride film/graphene monolayer/boron nitride film (BGB) was found to be a mechanically robust and chemically inert heterostructure, from which the deleterious effects of mechanical transfer processes and unwanted chemical doping under air exposure were eliminated. The chemical compositions of each film layer were monitored ex situ using UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy, and the crystalline structures were confirmed using transmission electron microscopy and selected-area electron diffraction measurements. The performance of the devices fabricated using the BGB film was monitored over six months and did not display large changes in the mobility or the Dirac point, unlike the conventional graphene devices prepared on a SiO2 substrate. The in situ-grown BGB film properties suggest a novel approach to the fabrication of commercial-grade graphene-based electronic devices.We describe the successful in situ chemical vapor deposition synthesis of a graphene-based heterostructure in which a graphene monolayer is protected by top and bottom boron nitride films. The boron nitride film/graphene monolayer/boron nitride film (BGB) was found to be a mechanically robust and chemically inert heterostructure, from which the deleterious effects of mechanical transfer processes and unwanted chemical doping under air exposure were eliminated. The chemical compositions of each film layer were monitored ex situ using UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy, and the crystalline structures were confirmed using transmission electron microscopy and selected-area electron diffraction measurements. The performance of the devices fabricated using the BGB film was monitored over six months and did not display large changes in the

  9. In situ growth of monolayer porous gold nanoparticles film as high-performance SERS substrates

    NASA Astrophysics Data System (ADS)

    Song, Chunyuan; Wei, Yuhan; Da, Bingtao; Zhang, Haiting; Cong, Xing; Yang, Boyue; Yang, Yanjun; Wang, Lianhui

    2016-07-01

    Surface-enhanced Raman scattering (SERS) has recently received considerable attention as an ultrasensitive analytic technique. However, its wide application is limited by lack of excellent SERS-active substrates. In this work a SERS substrate with arrayed monolayer films of porous gold nanoparticles is prepared on a solid substrate by a facile, in situ and one-step growth approach. Specifically, the solid substrate was coated with a layer of dense positive charges first by layer-by-layer assembly, followed by patterned a PDMS film with arrayed wells on the substrate. Then the growth solution including chlorauric acid, cetyltrimethylammonium chloride, and ascorbic acid in a certain proportion was transferred into the wells for in situ and one-step growth of porous gold nanoparticles on the substrate. The growth time, feed ratio of the reagents, and repeat times of the in situ growth were studied systematically to obtain optimal parameters for preparing an optimal SERS substrate. The as-prepared optimal SERS substrate not only has good SERS performance with the enhancement factor up to ∼1.10 × 106, but also shows good uniformity and stability. The SERS substrate was further utilized to be ultrasensitive SERS-based chemical sensors for ppb-level detection of highly toxic dyfonate. The preliminary result indicates that the as-prepared SERS substrate has good SERS performance and shows a number of great potential applications in SERS-based sensors.

  10. Epitaxial Templating of C60 with a Molecular Monolayer.

    PubMed

    Rochford, L A; Jones, T S; Nielsen, C B

    2016-09-01

    Commensurate epitaxial monolayers of truxenone on Cu (111) were employed to template the growth of monolayer and bilayer C60. Through the combination of STM imaging and LEED analysis we have demonstrated that C60 forms a commensurate 8 × 8 overlayer on truxenone/Cu (111). Bilayers of C60 retain the 8 × 8 periodicity of templated monolayers and although Kagome lattice arrangements are observed these are explained with combinations of 8 × 8 symmetry. PMID:27540868

  11. 7 CFR 1400.503 - Commensurate reduction.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ..., general partnership, or joint venture will be reduced by an amount commensurate with the direct and indirect ownership interest in the legal entity, general partnership, or joint venture of each person...

  12. 7 CFR 1400.503 - Commensurate reduction.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ..., general partnership, or joint venture will be reduced by an amount commensurate with the direct and indirect ownership interest in the legal entity, general partnership, or joint venture of each person...

  13. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solids

    SciTech Connect

    Greene, J. E.

    2015-03-15

    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (∼1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ∼78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese “floating-ink” art (suminagashi) developed ∼1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO{sub 2} and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including

  14. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solidsa)

    NASA Astrophysics Data System (ADS)

    Greene, J. E.

    2015-03-01

    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (˜1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ˜78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese "floating-ink" art (suminagashi) developed ˜1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO2 and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including controlled wetting

  15. Controlling dynamic SERS hot spots on a monolayer film of Fe3O4@Au nanoparticles by a magnetic field

    NASA Astrophysics Data System (ADS)

    Guo, Qing-Hua; Zhang, Chen-Jie; Wei, Chao; Xu, Min-Min; Yuan, Ya-Xian; Gu, Ren-Ao; Yao, Jian-Lin

    2016-01-01

    A large surface-enhanced Raman scattering (SERS) effect is critically dependent on the gap distance of adjacent nanostructures, i.e., "hot spots". However, the fabrication of dynamically controllable hot spots still remains a remarkable challenge. In the present study, we employed an external magnetic field to dynamically control the interparticle spacing of a two-dimensional monolayer film of Fe3O4@Au nanoparticles at a hexane/water interface. SERS measurements were performed to monitor the expansion and shrinkage of the nanoparticles gaps, which produced an obvious effect on SERS activities. The balance between the electrostatic repulsive force, surface tension, and magnetic attractive force allowed observation of the magnetic-field-responsive SERS effect. Upon introduction of an external magnetic field, a very weak SERS signal appeared initially, indicating weak enhancement due to a monolayer film with large interparticle spacing. The SERS intensity reached maximum after 5 s and thereafter remained almost unchanged. The results indicated that the observed variations in SERS intensities were fully reversible after removal of the external magnetic field. The reduction of interparticle spacing in response to a magnetic field resulted in about one order of magnitude of SERS enhancement. The combined use of the monolayer film and external magnetic field could be developed as a strategy to construct hot spots both for practical application of SERS and theoretical simulation of enhancement mechanisms.

  16. Inorganic-organic composite nanoengineered films using self-assembled monolayers for directed zeolite film growth

    SciTech Connect

    Dye, R.C.; Hermes, R.E.; Martinez, M.G.; Peachey, N.M.

    1997-10-01

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Zeolites, or molecular sieves, are aluminosilicate cage structures that are typically grown from a heterogeneous mixture of organic template molecules, inorganic salts of alumina and silica, and water. These zeolites are used in industry for catalytic cracking of hydrocarbons (gasoline manufacture from oil), and contaminant removal from chemical production processes. Within one year, we developed a viable method for the deposition of a quaternary ammonium salt amphiphile onto silicon wafer substrates. Using a biomimetic growth process, we were also able to demonstrate the first thin-film formation of a zeolite structure from such an organic template. Additionally, we synthesized the precursor to another amphiphile which was to be for further studies.

  17. Copper phthalocyanine thin films on Cu(111): Sub-monolayer to multi-layer

    NASA Astrophysics Data System (ADS)

    Stock, T. J. Z.; Nogami, J.

    2015-07-01

    Scanning tunneling microscopy (STM) has been used to observe the growth mode and crystal structure of sub-monolayer (ML) to multilayer thin films of copper phthalocyanine (CuPc) molecules on the Cu(111) surface at room temperature (RT). At sub-ML coverage the molecules are mobile on the surface. At approximately one ML coverage the molecules become sterically confined and lying flat on the Cu substrate form an ordered, multi-domained, 2D oblique lattice. As coverage is increased beyond 1 ML the molecule-substrate interaction diminishes in strength while the intermolecular interaction begins to dominate, causing the layer separation to increase, and the crystal domain size and lattice constants to shrink as the crystal structure begins to more closely resemble the bulk α-phase CuPc molecular solid. This trend continues for the layer-by-layer growth of 3 complete ML, eventually giving way to the emergence of large 3D islands at a coverage equivalent to 4 ML.

  18. Vapor-phase-processed fluorinated self-assembled monolayer for organic thin-film transistors

    NASA Astrophysics Data System (ADS)

    Roh, Jeongkyun; Lee, Changhee; Kwak, Jeonghun; Jung, Byung Jun; Kim, Hyeok

    2015-09-01

    A vapor-phase-processed fluorinated silazane self-assembled monolayer (SAM), 1,3-bis(trifluoropropyl)-1,1,3,3-tetramethyldisilazane (FPDS), was introduced as a surface modifier for pentacene-based organic thin-film transistors (OTFTs). A remarkable improvement in the field effect mobility from 0.25 cm2/Vs (without SAM-treatment) to 0.42 cm2/Vs (with FPDS-treatment) was observed, which was attributed to the better pentacene growth on a hydrophobic surface. A significant reduction in the contact resistance was also observed by FPDS treatment due to the improved bulk conductivity and diminished charge trapping at the gate dielectric surface by the SAM treatment. In addition, FPDS treatment efficiently improved the bias stability of the OTFTs; the drain-to-source current degradation by the bias stress was greatly reduced from 80% to 50% by FPDS treatment, and the characteristic time for charge trapping of the FPDS treated OTFTs was approximately one order of magnitude larger than that of the OTFTs without SAM treatment.

  19. Vortex phase transitions in monolayer FeSe film on SrTiO3

    NASA Astrophysics Data System (ADS)

    Zhao, Weiwei; Chang, Cui-Zu; Xi, Xiaoxiang; Mak, Kin Fai; Moodera, Jagadeesh S.

    2016-06-01

    The voltage–current (V–I) characteristics in superconducting monolayer FeSe film on SrTiO3 (100) under different magnetic fields are investigated. The zero-field V–I result exhibits signatures of a Berezinski–Kosterlitz–Thouless transition, a characteristic of two-dimensional (2D) superconductors. Under an applied magnetic field, with current density lower than the critical current density, the sheet resistance versus current density (R sq–J) dependence changes from ohmic (R sq independent of J) to non-ohmic (a nonlinear dependence of R sq on J) as the temperature decreases, indicative of a vortex phase transition/crossover. We interpret the high-temperature phase as the vortex liquid phase and the low-temperature phase as the vortex slush phase, which has short-ranged vortex lattice correlation, while long-range correlation (i.e. true superconductivity) is absent. No transition into a vortex glass phase is seen, illustrating the importance of thermal fluctuations in a perfect 2D superconductor under a magnetic field.

  20. Self-Assembly of Tetraphenyldibenzoperiflanthene (DBP) Films on Ag(111) in the Monolayer Regime.

    PubMed

    Kirchhuebel, Tino; Gruenewald, Marco; Sojka, Falko; Kera, Satoshi; Bussolotti, Fabio; Ueba, Takahiro; Ueno, Nobuo; Rouillé, Gaël; Forker, Roman; Fritz, Torsten

    2016-03-01

    Tetraphenyldibenzoperiflanthene (DBP) is a promising candidate as a component of highly efficient organic photovoltaic cells and organic light-emitting diodes. The structural properties of thin films of this particular lander-type molecule on Ag(111) were investigated by complementary techniques. Highly ordered structures were obtained, and their mutual alignment was characterized by means of low-energy electron diffraction (LEED). Scanning tunneling microscopy (STM) images reveal two slightly different arrangements within the first monolayer (ML), both describable as specific herringbone patterns with two molecules per unit cell whose dibenzoperiflanthene framework is parallel to the surface. In contrast, single DBP molecules in the second ML were imaged with much higher intramolecular resolution, resembling the shape of the frontier orbitals in the gas phase as calculated by means of density functional theory (DFT). Further deposition leads to the growth of highly ordered bilayer islands on top of the first ML with identical unit cell dimensions and orientation but slightly inclined molecules. This suggests that the first ML acts as a template for the epitaxial growth of further layers. Simultaneously, a significant number of second-layer molecules mainly located at step edges or scattered over narrow terraces do not form highly ordered aggregates. PMID:26844381

  1. Intercalated samarium as an agent enabling the intercalation of oxygen under a monolayer graphene film on iridium

    NASA Astrophysics Data System (ADS)

    Afanas'eva, E. Yu.; Rut'kov, E. V.; Gall', N. R.

    2016-06-01

    Using thermal desorption time-of-flight mass spectrometry and thermionic methods, it is shown that oxygen does not intercalate under a graphene monolayer grown correctly on iridium, at least at temperatures of T = 300-400 K and exposures below 12000 L. However, if the graphene film on iridium is preliminary intercalated with samarium atoms (up to coverage of θSm = 0.2-0.45), the penetration of oxygen atoms under the graphene film is observed. The oxygen atoms in the intercalated state are chemically bonded to samarium atoms and remain under graphene up to high temperatures (~2150 K).

  2. Effects of different self-assembled monolayers on thin-film morphology: a combined DFT/MD simulation protocol.

    PubMed

    Alberga, Domenico; Mangiatordi, Giuseppe Felice; Motta, Alessandro; Nicolotti, Orazio; Lattanzi, Gianluca

    2015-10-01

    Organic thin film transistors (OTFTs) are multilayer field-effect transistors that employ an organic conjugated material as semiconductor. Several experimental groups have recently demonstrated that the insertion of an organic self-assembled monolayer (SAM) between the dielectric and the semiconductive layer is responsible for a sensible improvement of the OTFT performances in terms of an increased charge carrier mobility caused by a higher degree of order in the organic semiconductor layer. Here, we describe a combined periodic density functional theory (DFT) and classical molecular dynamics (MD) protocol applied to four different SAMs and a pentacene monolayer deposited onto their surfaces. In particular, we investigate the morphology and the surface of the four SAMs and the translational, orientational, and nematic order of the monolayer through the calculation of several distribution functions and order parameters pointing out the differences among the systems and relating them to known experimental results. Our calculations also suggest that small differences in the SAM molecular design will produce remarkable differences in the SAM surface and monolayer order. In particular, our simulations explain how a SAM with a bulky terminal group results in an irregular and rough surface that determines the deposition of a disordered semiconductive monolayer. On the contrary, SAMs with a small terminal group generate smooth surfaces with uninterrupted periodicity, thus favoring the formation of an ordered pentacene monolayer that increases the mobility of charge carriers and improves the overall performances of the OTFT devices. Our results clearly point out that the in silico procedure presented here might be of help in tuning the design of SAMs in order to improve the quality of OTFT devices. PMID:26367250

  3. Monolayers and Langmuir-Blodgett films of luminescent 1,3,5-triazine derivatives containing naphthalene or anthracene chromophores

    NASA Astrophysics Data System (ADS)

    Cai, Ya-Qi; Wu, Wei; Wang, Hua; Miyake, Jun; Qian, Dong-Jin

    2011-02-01

    Monolayer behaviors and Langmuir-Blodgett (LB) films of three luminescent aryl triazines, 2,4,6-tri(naphthalen-1-yl)-1,3,5-triazine (TN 1Ta), 2,4,6-tri(naphthalen-2-yl)-1,3,5-triazine (TN 2Ta), and 2,4,6-tri(anthracen-9-yl)-1,3,5-triazine (TATa) have been investigated. Surface pressure-area isotherms indicated that pure aryl triazines were difficult to form stable monolayers, while their mixtures with arachidic acid (AA) could be stabilized at the air-water interface. The mixed LB films of triazine-AA were deposited on substrate surfaces and analyzed by using UV-vis and infrared absorption spectra, X-ray photoelectron spectra, as well as scanning electron microscopy. Morphologies of the LB films and molecular aggregates were closely dependent on the structure of triazines and the surface pressures of deposition. Under UV radiation, TN 1Ta and TN 2Ta emitted at 410-460 nm while TATa emitted at 500-510 nm, with the emission lifetime falling into the range of 0.29 to 10.8 ns. Compared with those in solutions, the emissions of aryl triazines were red shifted in the LB films, especially for the TN 1Ta-AA and TN 2Ta-AA, which was attributed to the closely packed arrangement for the molecules in the LB films.

  4. Support-Free Transfer of Ultrasmooth Graphene Films Facilitated by Self-Assembled Monolayers for Electronic Devices and Patterns.

    PubMed

    Wang, Bin; Huang, Ming; Tao, Li; Lee, Sun Hwa; Jang, A-Rang; Li, Bao-Wen; Shin, Hyeon Suk; Akinwande, Deji; Ruoff, Rodney S

    2016-01-26

    We explored a support-free method for transferring large area graphene films grown by chemical vapor deposition to various fluoric self-assembled monolayer (F-SAM) modified substrates including SiO2/Si wafers, polyethylene terephthalate films, and glass. This method yields clean, ultrasmooth, and high-quality graphene films for promising applications such as transparent, conductive, and flexible films due to the absence of residues and limited structural defects such as cracks. The F-SAM introduced in the transfer process can also lead to graphene transistors with enhanced field-effect mobility (up to 10,663 cm(2)/Vs) and resistance modulation (up to 12×) on a standard silicon dioxide dielectric. Clean graphene patterns can be realized by transfer of graphene onto only the F-SAM modified surfaces. PMID:26701198

  5. Controlled scalable synthesis of uniform, high-quality monolayer and few-layer MoS2 films.

    PubMed

    Yu, Yifei; Li, Chun; Liu, Yi; Su, Liqin; Zhang, Yong; Cao, Linyou

    2013-01-01

    Two dimensional (2D) materials with a monolayer of atoms represent an ultimate control of material dimension in the vertical direction. Molybdenum sulfide (MoS2) monolayers, with a direct bandgap of 1.8 eV, offer an unprecedented prospect of miniaturizing semiconductor science and technology down to a truly atomic scale. Recent studies have indeed demonstrated the promise of 2D MoS2 in fields including field effect transistors, low power switches, optoelectronics, and spintronics. However, device development with 2D MoS2 has been delayed by the lack of capabilities to produce large-area, uniform, and high-quality MoS2 monolayers. Here we present a self-limiting approach that can grow high quality monolayer and few-layer MoS2 films over an area of centimeters with unprecedented uniformity and controllability. This approach is compatible with the standard fabrication process in semiconductor industry. It paves the way for the development of practical devices with 2D MoS2 and opens up new avenues for fundamental research. PMID:23689610

  6. Commensurabilities between ETNOs: a Monte Carlo survey

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, C.; de la Fuente Marcos, R.

    2016-04-01

    Many asteroids in the main and trans-Neptunian belts are trapped in mean motion resonances with Jupiter and Neptune, respectively. As a side effect, they experience accidental commensurabilities among themselves. These commensurabilities define characteristic patterns that can be used to trace the source of the observed resonant behaviour. Here, we explore systematically the existence of commensurabilities between the known ETNOs using their heliocentric and barycentric semimajor axes, their uncertainties, and Monte Carlo techniques. We find that the commensurability patterns present in the known ETNO population resemble those found in the main and trans-Neptunian belts. Although based on small number statistics, such patterns can only be properly explained if most, if not all, of the known ETNOs are subjected to the resonant gravitational perturbations of yet undetected trans-Plutonian planets. We show explicitly that some of the statistically significant commensurabilities are compatible with the Planet Nine hypothesis; in particular, a number of objects may be trapped in the 5:3 and 3:1 mean motion resonances with a putative Planet Nine with semimajor axis ˜700 au.

  7. Commensurabilities between ETNOs: a Monte Carlo survey

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, C.; de la Fuente Marcos, R.

    2016-07-01

    Many asteroids in the main and trans-Neptunian belts are trapped in mean motion resonances with Jupiter and Neptune, respectively. As a side effect, they experience accidental commensurabilities among themselves. These commensurabilities define characteristic patterns that can be used to trace the source of the observed resonant behaviour. Here, we explore systematically the existence of commensurabilities between the known ETNOs using their heliocentric and barycentric semimajor axes, their uncertainties, and Monte Carlo techniques. We find that the commensurability patterns present in the known ETNO population resemble those found in the main and trans-Neptunian belts. Although based on small number statistics, such patterns can only be properly explained if most, if not all, of the known ETNOs are subjected to the resonant gravitational perturbations of yet undetected trans-Plutonian planets. We show explicitly that some of the statistically significant commensurabilities are compatible with the Planet Nine hypothesis; in particular, a number of objects may be trapped in the 5:3 and 3:1 mean motion resonances with a putative Planet Nine with semimajor axis ˜700 au.

  8. Solution and displacement in monolayer and multilayer binary films of SF6 and CF4 on graphite.

    PubMed

    Thomas, Petros; Grogan, Michael D W; Hess, George B

    2015-09-21

    Infrared reflection absorption spectroscopy is used to study the evolution of binary physisorbed films on graphite. A predeposited monolayer of SF6 is exposed to slowly increasing pressure of CF4 at constant temperature between 80 and 113 K. Shifts in the frequencies of the dominant vibrational mode of each species due to resonant dipole-dipole coupling serve as proxies for the areal density of each species in the monolayer. If the initial SF6 film is far below saturation (coexistence with bulk solid), the SF6 can be largely displaced by continuous solution of CF4. However, if the initial SF6 layer is at or near saturation, a layer of CF4 condenses on top at a well defined CF4 pressure after only 2%-3% dilution of the SF6 layer. Simultaneously, most of the dissolved CF4 is withdrawn from the SF6 layer. With further increase in CF4 pressure, the CF4 layer is compressed and additional layers condense, while the SF6 layer is again diluted. Still, the SF6 layer retains about 90% concentration until the CF4 pressure is very close to saturation, at which point the SF6 is rapidly displaced, apparently going into dilute solution in the rapidly growing CF4 multilayer. Monte Carlo simulations are used to quantitatively relate measured frequency shifts to concentrations in the binary monolayer. PMID:26395723

  9. CO Oxidation Prefers the Eley-Rideal or Langmuir-Hinshelwood Pathway: Monolayer vs Thin Film of SiC.

    PubMed

    Sinthika, S; Vala, Surya Teja; Kawazoe, Y; Thapa, Ranjit

    2016-03-01

    Using the first-principles approach, we investigated the electronic and chemical properties of wurtzite silicon carbide (2H-SiC) monolayer and thin film structures and substantiated their catalytic activity toward CO oxidation. 2H-SiC monolayer, being planar, is quite stable and has moderate binding with O2, while CO interacts physically; thus, the Eley-Rideal (ER) mechanism prevails over the Langmuir-Hinshelwood (LH) mechanism with an easily cleared activation barrier. Contrarily, 2H-SiC thin film, which exhibits a nonplanar structure, allows moderate binding of both CO and O2 on its surface, thus favoring the LH mechanism over the ER one. Comprehending these results leads to a better understanding of the reaction mechanisms involving structural contrast. Weak overlapping between the 2p(z)(C) and 3p(z)(Si) orbitals of the SiC monolayer system has been found to be the primary reason to revert the active site toward sp(3) hybridization, during interaction with the molecules. In addition, the influences of graphite and Ag(111) substrates on the CO oxidation mechanism were also studied, and it is observed that the ER mechanism is preserved on SiC/G system, while CO oxidation on the SiC/Ag(111) system follows the LH mechanism. The calculated Sabatier activities of the SiC catalysts show that the catalysts are very efficient in catalyzing CO oxidation. PMID:26866799

  10. Charge Dynamics and Electronic Structures of Monolayer MoS2 Films Grown by Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Shen, Chih-Chiang; Hsu, Yu-Te; Li, Lain-Jong; Liu, Hsiang-Lin

    2013-12-01

    THz absorption and spectroscopic ellipsometry were used to investigate the charge dynamics and electronic structures of chemical-vapor-deposited monolayer MoS2 films. THz conductivity displays a coherent response of itinerant charge carriers at zero frequency. Drude plasma frequency (˜7 THz) decreases with decreasing temperature while carrier relaxation time (˜26 fs) is almost temperature independent. The absorption spectrum of monolayer MoS2 shows a direct 1.95 eV band gap and charge transfer excitations that are ˜0.2 eV higher than those of the bulk counterpart. The ground-state exciton binding energy is found to be about 0.48 eV.

  11. Phase Determination of Second-Order Surface Susceptibility Tensor of Liquid Crystal Monolayer Using Ultra-Thin Film Local Oscillator

    NASA Astrophysics Data System (ADS)

    Sei, Masaki; Nagayama, Kohei; Kajikawa, Kotaro; Ishii, Hisao; Seki, Kazuhiko; Kondo, Katsumi; Matsumoto, Yoshiyasu; Ouchi, Yukio

    1998-04-01

    We demonstrated full determination of second-order nonlinear susceptibility of a 4‧-n-octyl-4-cyanobiphenyl (8CB) liquid crystal (LC) monolayer adsorbed on a second-harmonic (SH) active polyimide (PI) substrate. In order to separate the SH signal of the LC film from that of the PI film, we adopted an interferometry technique of second-harmonic generation (SHG) using an ultra-thin film local oscillator. We have found a variety of phases in the components of susceptibility: those of χzii and χizi are almost the same but the phase of χzzz differs by 80° from the other two. The phases of the components of the surface susceptibility tensor are not always identical. This fact indicates that the surface SH response is more complicated than what we expected.

  12. An epitaxial organic film. The self-assembled monolayer of docosanoic acid on silver(111)

    SciTech Connect

    Samant, M.G.; Brown, C.A.; Gordon, J.G. II )

    1993-04-01

    Docosanoic acid in solution spontaneously forms an ordered self-assembled (SA) monolayer on the silver(111) surface, exposing methyl groups to the atmosphere. The contact wetting angles for water and hexadecane are 116[degrees] and 55[degrees], respectively. Surface X-ray diffraction shows that the in-plane structure of the SA monolayer is p(2 [times] 2). The SA monolayer is present in domains of about 215 A with a mosaic spread of 0.85[degrees]C. The chains within the monolayer are titled at 27 [+-] 1[degrees] from the surface normal toward the near neighbors. We conclude that the carboxylate group is bound nearly normal to specific sites on the Ag surface and that this determines the interchain spacing. The tilt angle is a consequence of this interchain spacing. 17 refs., 6 figs., 1 tab.

  13. Difference in Surface Properties between Insoluble Monolayer and Adsorbed Film from Kinetics of Water Evaporation and BAM Image.

    PubMed

    Moroi, Yoshikiyo; Rusdi, Muhammad; Kubo, Izumi

    2004-05-20

    The evaporation rate of water molecules across three kinds of interfaces (air/water interface (1), air/surfactant solution interface (2), and air/water interface covered by insoluble monolayer (3)) was examined using a remodeled thermogravimetric balance. There was no difference in both the evaporation rate and the activation energy for the first two interfaces for three types of surfactant solutions below and above the critical micelle concentration (cmc). This means that the molecular surface area from the Gibbs surface excess has nothing to do with the evaporation rate. In the third case, the insoluble monolayer of 1-heptadecanol decreased the evaporation rate and increased the activation energy, indicating a clear difference between an insoluble monolayer and an adsorbed film of soluble surfactant. This difference was substantiated by BAM images, too. The images of three surfactant solution interfaces were similar to that of just the water surface, while distinct structures of molecular assemblies were observed for the insoluble monolayer. The concentration profile of water molecules in an air/liquid interfacial region was derived by Fix's second law. The profile indicates that a definite layer just beneath the air/liquid interface of the surfactant solution is made mostly of water molecules and that the layer thickness is a few times the root-mean-square displacement %@mt;sys@%%@rl;;@%2%@ital@%Dt%@rsf@%%@rlx@%%@mx@% of the water molecules. The thickness was found to be more than a few nanometers, as estimated from several relaxation times derived from the other kinetics than evaporation of amphiphilic molecules in aqueous systems and a maximum evaporation rate of purified water. PMID:18950121

  14. Growth mechanism of largescale MoS2 monolayer by sulfurization of MoO3 film

    NASA Astrophysics Data System (ADS)

    Taheri, Payam; Wang, Jieqiong; Xing, Hui; Destino, Joel F.; Murat Arik, Mumtaz; Zhao, Chuan; Kang, Kaifei; Blizzard, Brett; Zhang, Lijie; Zhao, Puqin; Huang, Shaoming; Yang, Sen; Bright, Frank V.; Cerne, John; Zeng, Hao

    2016-07-01

    Monolayer two-dimensional transition metal dichalcogenides (TMDCs) such as MoS2 with broken inversion symmetry possesses two degenerate yet inequivalent valleys that can be selectively excited by circularly polarized light. This unique property renders interesting valley physics. The ability to manipulate valley degrees of freedom with light or external field makes them attractive for optoelectronic and spintronic applications. There is great demand for large area monolayer (ML) TMDCs for certain measurements and device applications. Recent reports on large area ML TDMCs focus on chemical vapor deposition growth. In this work, we report a facile approach to grow largescale continuous ML MoS2 nearly free of overgrowth and voids, by sulfurizing evaporated molybdenum trioxide ultrathin films. Photo conductivity scales with device sizes up to 4.5 mm, suggesting excellent film uniformity. The growth mechanism is found to be vaporization, diffusion, sulfurization and lateral growth, all at local micrometer scale. Our approach provides a new pathway for large-area ML TMDC growth and lithography-free device fabrication.

  15. Site-selective electroless metallization on porous organosilica films by multisurface modification of alkyl monolayer and vacuum plasma.

    PubMed

    Chen, Giin-Shan; Chen, Sung-Te; Chen, Yenying W; Hsu, Yen-Che

    2013-01-15

    Taking plasma-enhanced chemical vapor deposited porous SiOCH (p-SiOCH) and octadecyltrichlorosilane (OTS) as model cases, this study elucidates the chemical reaction pathways for alkyl-based self-assembled monolayers (SAMs) on porous carbon-doped organosilica films under N(2)-H(2) vacuum plasma illumination. In contrast to previous findings that carboxylic groups are found in alkyl-based SAMs only by exposure to oxygen-based plasma, this study discovers that, upon exposure to reductive nitrogen-based vacuum plasma, surface carboxylic functional groups can be instantly formed on OTS-coated p-SiOCH films. Particular attention is given to developing a multisurface modification process, starting with the modification of p-SiOCH films by N(2)-H(2) plasma and continuing with SAM deposition and plasma patterning; this ultimately leads to site-selective seeding for the spatially controlled fabrication of Cu-wire metallization by electroless deposition. Plasma diagnosis and X-ray near-edge absorption and Fourier transform infrared spectroscopies show that, by adequately controlling the plasma parameters, the bulk of the p-SiOCH films are free from plasma damage (in terms of degradation in bonding structures and electrical properties); the formation of the seed-trapping carboxylic functional groups on the surface, the key factor for the validity of this new seeding process, is due to a water-mediated chemical oxygenation route. PMID:23205708

  16. Characteristic Fragmentation of Polysiloxane Monolayer Films by Bombardment with Monatomic and Polyatomic Primary Ions in TOF-SIMS

    NASA Astrophysics Data System (ADS)

    Moon, Hye Kyoung; Wells, David D.; Gardella, Joseph A.

    2012-01-01

    This study reports the characteristic fragmentation patterns from two polysiloxane polymers that form ordered overlayer on silver substrates. Results are compared for the bombardment of various monatomic and polyatomic projectiles of Cs+, C{60/+} (10 keV), Bi{1/+}, and Bi{3/+} (25 keV) in the high mass range time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra. Results are reported from sub-monolayer (solution cast) coverages of poly(dimethylsiloxane)s with the number average molecular weights (Mn) of 2200 and 6140 Da, respectively, and Langmuir-Blodgett monolayers of poly(methylphenylsiloxane) with molecular weights (MW) from 600 and 1000 Da. For each film, Bi projectiles resulted in the emission of positive silver cluster ions from the substrate under the polymer overlayer and peaks corresponding to silver cluster ions with larger mass were observed by impact of polyatomic 25 keV Bi{3/+} projectiles. In addition, depending on the change of energy of Bi{3/+}, a different pattern of fragments was observed. With Cs+ and C{60/+} impact, however, the emission of silver cluster ions was not detected. In the case of C{60/+} impact for PDMS-6140, peaks corresponding to silver-cationized intact oligomers were not observed. In this paper, these results are explained by the possible bombardment mechanism for each projectile, based on its mass, energy, and split trajectories of the component atoms under the polyatomic impact.

  17. Mapping for 5/2 asteroidal commensurability

    NASA Astrophysics Data System (ADS)

    Sidlichovsky, M.; Melendo, B.

    1986-03-01

    The method of Wisdom (1982) is applied to the 5/2 commensurability Kirkwood gap. The secular and resonant Hamiltonian is analyzed, and the algebraic mapping for the planar problem is addressed. For this case, the calculations strongly support the collisional hypothesis for the origin of the Kirkwood gaps. The values of the mapping constants are determined, and the mapping is used to recalculate Scholl's and Froeschle's (1975) results for much longer time intervals. A suggestion is made for improving the order of eccentricity. The complete three-dimensional mapping is given.

  18. Langmuir monolayers and thin films of amphifilic thiacalix[4]arenes. Properties and matrix for the immobilization of cytochrome c.

    PubMed

    Solovieva, Svetlana E; Safiullin, Roman A; Kochetkov, Evgeni N; Melnikova, Nina B; Kadirov, Marsil K; Popova, Elena V; Antipin, Igor S; Konovalov, Alexander I

    2014-12-23

    Formation and properties of Langmuir films of thiacalix[4]arene (TCA) derivatives containing N-donor groups on the lower rim (Y═O(CH2)3CN; OCH2CN; NH2; OCH2ArCN-p) in 1,3-alternate conformation on aqueous subphase and solid substrates have been studied. Only tetra-cyanopropoxy-p-tert-butylthiacalix[4]arene 1 forms a typical monomolecular layer with perpendicular orientation of the macrocycle relative to the water-air interface that is able to immobilize cytochrome c in the entire range of the surface pressure. Obtained monolayers were transferred by Langmuir-Schaefer technique onto quartz, indium-tin oxide (ITO), and silicon. It was demonstrated that protein activity is retained after immobilization on the substrate. PMID:25435075

  19. Molecular mobility in the monolayers of foam films stabilized by porcine lung surfactant.

    PubMed Central

    Lalchev, Z I; Todorov, R K; Christova, Y T; Wilde, P J; Mackie, A R; Clark, D C

    1996-01-01

    Certain physical properties of a range of foam film types that are believed to exist in vivo in the lung have been investigated. The contribution of different lung surfactant components found in porcine lung surfactant to molecular surface diffusion in the plane of foam films has been investigated for the first time. The influence of the type and thickness of black foam films, temperature, electrolyte concentration, and extract composition on surface diffusion has been studied using the fluorescence recovery after photobleaching technique. Fluorescent phospholipid probe molecules in foam films stabilized by porcine lung surfactant samples or their hydrophobic extracts consisting of surfactant lipids and hydrophobic lung surfactant proteins, SP-B and SP-C, exhibited more rapid diffusion than observed in films of its principal lipid component alone, L-alpha-phosphatidylcholine dipalmitoyl. This effect appears to be due to contributions from minor lipid components present in the total surfactant lipid extracts. The minor lipid components influence the surface diffusion in foam films both by their negative charge and by lowering the phase transition temperature of lung surfactant samples. In contrast, the presence of high concentrations of the hydrophillic surfactant protein A (SP-A) and non-lung-surfactant proteins in the sample reduced the diffusion coefficient (D) of the lipid analog in the adsorbed layer of the films. Hysteresis behavior of D was observed during temperature cycling, with the cooling curve lying above the heating curve. However, in cases where some surface molecular aggregation and surface heterogeneity were observed during cooling, the films became more rigid and molecules at the interfaces became immobilized. The thickness, size, capillary pressure, configuration, and composition of foam films of lung surfactant prepared in vitro support their investigation as realistic structural analogs of the surface films that exist in vivo in the lung

  20. Improved Endothelial Function of Endothelial Cell Monolayer on the Soft Polyelectrolyte Multilayer Film with Matrix-Bound Vascular Endothelial Growth Factor.

    PubMed

    Chang, Hao; Hu, Mi; Zhang, He; Ren, Ke-Feng; Li, Bo-Chao; Li, Huan; Wang, Li-Mei; Lei, Wen-Xi; Ji, Jian

    2016-06-15

    Endothelialization on the vascular implants is of great importance for prevention of undesired postimplantation symptoms. However, endothelial dysfunction of regenerated endothelial cell (EC) monolayer has been frequently observed, leading to severe complications, such as neointimal hyperplasia, late thrombosis, and neoatherosclerosis. It has significantly impeded long-term success of the therapy. So far, very little attention has been paid on endothelial function of EC monolayer. Bioinspired by the microenvironment of the endothelium in a blood vessel, this study described a soft polyelectrolyte multilayer film (PEM) through layer-by-layer assembly of poly(l-lysine) (PLL) and hyaluronan (HA). The (PLL/HA) PEM was chemically cross-linked and further incorporated with vascular endothelial growth factor. It demonstrated that this approach could promote EC adhesion and proliferation, further inducing formation of EC monolayer. Further, improved endothelial function of the EC monolayer was achieved as shown with the tighter integrity, higher production of nitric oxide, and expression level of endothelial function related genes, compared to EC monolayers on traditional substrates with high stiffness (e.g., glass, tissue culture polystyrene, and stainless steel). Our findings highlighted the influence of substrate stiffness on endothelial function of EC monolayer, giving a new strategy in the surface design of vascular implants. PMID:27223460

  1. Fabricating chiral polydiacetylene film by monolayer compression and circularly polarized ultra-violet light

    NASA Astrophysics Data System (ADS)

    Zou, Gang; Kohn, Hideki; Ohshima, Yuki; Manaka, Takaaki; Iwamoto, Mitsumasa

    2007-07-01

    We study polydiacetylene films that are pertinent to the problems of mirror symmetry breaking induced by the effects of compression and circularly polarized ultra-violet (UV) light. The subphase is only pure water. After polymerization, polymerized 10,12-tricosadiynoic acid (PTDA) LB films that deposited at the surface pressure of 20 mN m -1 showed obviously chiral properties, however, no obvious Cotton effect was obtained for PTDA LB films that deposited at the surface pressure of 10 mN m -1. In addition, TDA LB films could be polymerized to a designed chirality by using chiral circular polarized ultra-violet light (CPUL).

  2. Effects of electrolyte gating on photoluminescence spectra of large-area WSe2 monolayer films

    NASA Astrophysics Data System (ADS)

    Matsuki, Keiichiro; Pu, Jiang; Kozawa, Daichi; Matsuda, Kazunari; Li, Lain-Jong; Takenobu, Taishi

    2016-06-01

    We fabricated electric double-layer transistors comprising large-area WSe2 monolayers and investigated the effects of electrolyte gating on their photoluminescence (PL) spectra. Using the efficient gating effects of electric double layers, we succeeded in the application of a large electric field (∼107 V cm‑1) and the accumulation of high carrier density (>1013 cm‑2). As a result, we observed PL spectra based on both positively and negatively charged excitons and their gate-voltage-dependent redshifts, suggesting the effects of both an electric field and charge accumulation.

  3. The structure of deuterated benzene films adsorbed on the graphite (0001) basal plane: what happens below and above the monolayer coverage?

    PubMed

    Bahn, Emanuel; Hedgeland, Holly; Jardine, Andrew P; Henry, Paul F; Hansen, Thomas C; Fouquet, Peter

    2014-10-28

    An exact description of the interactions in aromatic carbon systems is a key condition for the design of carbon based nanomaterials. In this paper we investigate the binding and adsorbate structure of the simplest prototype system in this class - the single aromatic ring molecule benzene on graphite. We have collected neutron diffraction data of the ordered phase of deuterated benzene, C6D6, adsorbed on the graphite (0001) basal plane surface. We examined relative coverages from 0.15 up to 1.3 monolayers (ML) in a temperature range of 80 to 250 K. The results confirm the flat lying commensurate (√7 × √7)R19.1° monolayer with lattice constants a = b = 6.5 Å at coverages of less than 1 ML. For this structure we observe a progressive melting well below the desorption temperature. At higher coverages we do neither observe an ordered second layer nor a densification of the structure by upright tilting of first layer molecules, as generally assumed up to now. Instead, we see the formation of clusters with a bulk crystalline structure for coverages only weakly exceeding 1 ML. PMID:25209023

  4. Direct Observation of Degenerate Two-Photon Absorption and Its Saturation in WS2 and MoS2 Monolayer and Few-Layer Films.

    PubMed

    Zhang, Saifeng; Dong, Ningning; McEvoy, Niall; O'Brien, Maria; Winters, Sinéad; Berner, Nina C; Yim, Chanyoung; Li, Yuanxin; Zhang, Xiaoyan; Chen, Zhanghai; Zhang, Long; Duesberg, Georg S; Wang, Jun

    2015-07-28

    The optical nonlinearity of WS2 and MoS2 monolayer and few-layer films was investigated using the Z-scan technique with femtosecond pulses from the visible to the near-infrared range. The nonlinear absorption of few- and multilayer WS2 and MoS2 films and their dependences on excitation wavelength were studied. WS2 films with 1-3 layers exhibited a giant two-photon absorption (TPA) coefficient as high as (1.0 ± 0.8) × 10(4) cm/GW. TPA saturation was observed for the WS2 film with 1-3 layers and for the MoS2 film with 25-27 layers. The giant nonlinearity of WS2 and MoS2 films is attributed to a two-dimensional confinement, a giant exciton effect, and the band edge resonance of TPA. PMID:26135798

  5. Improved microstructure and performance of PbS thin films via in-situ thermal decomposition of lead xanthate precursors using self-assembling monolayer

    NASA Astrophysics Data System (ADS)

    Wang, Jingni; Yao, Kai; Jia, Zhenrong; Wang, Xiaofeng; Li, Fan

    2016-09-01

    Microstructure control is critical to achieve thin film-based devices with high performance. The surface properties of the substrates on which thin films grow are expected to greatly influence the morphology and the resulting performance. Generally, homogeneous, dense and highly crystalline films are required. However, "island" like structures are usually obtained mainly due to the non-uniform nucleation. In this article, the self-assembling monolayer (SAM) strategy was applied to efficiently realize the uniform nucleation and modulate the microstructure of lead sulfide (PbS) thin films, which were fabricated on the modified ZnO-coated substrates with 3-mercaptopropionic acid (MPA) SAM via in-situ thermal decomposition of lead xanthate precursors. The results showed that PbS thin films with reduced pin-holes and uniform crystalline grains were fabricated with the incorporation of MPA SAM. More importantly, PbS thin films modulated by MPA showed better photoelectric response.

  6. Structure and spectroscopic analysis of the graphene monolayer film directly grown on the quartz substrate via the HF-CVD technique

    NASA Astrophysics Data System (ADS)

    Mahmoud, Waleed E.; Al-Hazmi, Farag S.; Al-Ghamdi, A. A.; Shokr, F. S.; Beall, Gary W.; Bronstein, Lyudmila M.

    2016-08-01

    Direct growth of a monolayer graphene film on a quartz substrate by a hot filament chemical vapor deposition technique is reported. The monolayer graphene film prepared was characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED), and atomic force microscopy (AFM). The optical properties were studied by spectroscopic elliposmetry. The experimental data were fitted by the Forouhi-Bloomer model to estimate the extinction coefficient and the refractive index of the monolayer graphene film. The refractive index spectrum in the visible region was studied based on the harmonic oscillator model. The lattice dielectric constant, real and imaginary dielectric constants and the ratio of the charge carrier number to the effective mass were determined. The surface and volume energy loss parameters were also found and showed that the value of the surface energy loss is greater than the volume energy loss. The determination of these optical constants will open new avenue for novel applications of graphene films in the field of wave plates, light modulators, ultrahigh-frequency signal processing and LCDs.

  7. Cognition and order in Langmuir-Blodgett films of a 3-hexadecyl pyrrole and ferrocene-derivatized pyrrole mixed monolayer system

    NASA Astrophysics Data System (ADS)

    Samuelson, L.; Rahman, A. K. M.; Puglia, G. P.; Clough, S.; Tripathy, S.; Inagaki, T.; Yang, X. Q.; Skotheim, T. A.; Okamoto, Y.

    Novel, self-assembled materials were designed and produced from first principle to possess unique structural hierarchy and electronic and optical properties. The Langmuir-Blodgett technique was used to study the molecular organization of a mixed 3-hexadecyl pyrrole (3HDP) and ferrocene-derivatized pyrrole (Fc-Py) surfactant system. The pyrrole moiety was chosen for its' well established electronic and optical properties when polymerized, while ferrocene, it is theorized, if properly oriented into a Langmuir-Blodgett monolayer film may show a layered array of transition metals which would be extremely valuable as a model for 2-D magnets. The ferrocene group may also provide the possibility of charge coupling between neutral ferrocene and oxidized ferricenium which could be controlled electrochemically or photochemically. It has been determined that stable monolayer films of the mixed system could be formed at the air-water interface. The growth and assembly process led to polypyrrole 2-D lattices with heretofore unsurpassed order. In fact, the process of template polymerization leads to a new crystal phase for the polypyrrole component of the thin film structure. Various monolayer and multilayer films were prepared on platinum coated substrates for surface spectroscopic characterization using synchrotron radiation. Near Edge X-Ray Absorption Fine Structure studies revealed that highly ordered multilayer structures are being formed.

  8. Cognition and order in Langmuir-Blodgett films of a 3-hexadecyl pyrrole and ferrocene-derivatized pyrrole mixed monolayer system

    SciTech Connect

    Samuelson, L.; Rahman, A.K.M.; Puglia, G.P.; Clough, S.; Tripathy, S.; Inagaki, T.; Yang, X.Q.; Skotheim, T.A.; Okamoto, Y.

    1989-01-01

    Novel, self-assembled materials have been designed and produced from first principle to possess unique structural hierarchy and electronic and optical properties. The Langmuir-Blodgett technique was used to study the molecular organization of a mixed 3-hexadecyl pyrrole (3HDP) and ferrocene-derivatized pyrrole (Fc-Py) surfactant system. The pyrrole moiety was chosen for its' well established electronic and optical properties when polymerized, while ferrocene, it is theorized, if properly oriented into a Langmuir-Blodgett monolayer film may show a layered array of transition metals which would be extremely valuable as a model for two-dimensional magnets. The ferrocene group may also provide the possibility of charge coupling between neutral ferrocene and oxidized ferricenium which could be controlled electrochemically or photochemically. It has been determined that stable monolayer films of the mixed system could be formed at the air-water interface. The growth and assembly process led to polypyrrole 2-D lattices with heretofore unsurpassed order. In fact, the process of template polymerization leads to a new crystal phase for the polypyrrole component of the thin film structure. Various monolayer and multilayer films were prepared on platinum coated substrates for surface spectroscopic characterization using synchrotron radiation. Near Edge X-Ray Absorption Fine Structure studies revealed that highly ordered multilayer structures are being formed. 8 refs., 4 figs., 1 tab.

  9. Calcium ion interactions with insoluble phospholipid monolayer films at the A/W interface. External reflection-absorption IR studies.

    PubMed Central

    Flach, C R; Brauner, J W; Mendelsohn, R

    1993-01-01

    External reflection Fourier transform infrared (FT-IR) experiments are reported for insoluble monomolecular films of an equimolar mixture of 1,2-dipalmitoylphosphatidylcholine (DPPC) and 1,2-dipalmitoylphosphatidylserine (DPPS) at the A/W interface as a function of surface pressure and Ca2+ ion presence. The separate components showed a surface pressure-induced conformational ordering of the acyl chains. The conformational ordering occurred more cooperatively for the DPPS. Acyl chain perdeuteration of the DPPC permitted the observation of the response of the individual components in the binary mixture to changes in surface tension and to the presence of Ca2+. Plots of surface pressure versus CH2 or CD2 stretching frequencies were analyzed with a two-state model. At each surface pressure within the two-state region, the fraction of disordered form was the same for each lipid component, suggesting that they are well mixed on the surface. Calcium ion (5 mM in the subphase) produces almost no effect on the pressure-induced acyl chain ordering of the DPPC in a single component film, whereas the same levels of Ca2+ induce acyl chain ordering at all surface pressures in both components of the binary mixture. Thus, unlike the bulk phase mixture of DPPC/DPPS, the binary lipids in this mixed monolayer film appear to retain their miscibility in the presence of Ca2+. Finally, Ca(2+)-induced dehydration of the phosphate group was observed through characteristic frequency shifts in the asymmetric PO2- stretching mode. PMID:8298029

  10. Chemical stability of nonwetting, low adhesion self-assembled monolayer films formed by perfluoroalkylsilanization of copper

    SciTech Connect

    Hoque, E.; DeRose, J. A.; Hoffmann, P.; Bhushan, B.; Mathieu, H. J.

    2007-03-21

    A self-assembled monolayer (SAM) has been produced by reaction of 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (PFMS) with an oxidized copper (Cu) substrate and investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), friction force microscopy (FFM), a derivative of AFM, and contact angle measurement. FFM showed a significant reduction in the adhesive force and friction coefficient of PFMS modified Cu (PFMS/Cu) compared to unmodified Cu. The perfluoroalkyl SAM on Cu is found to be extremely hydrophobic, yielding sessile drop static contact angles of more than 130 degree sign for pure water and a 'surface energy' (which is proportional to the Zisman critical surface tension for a Cu surface with 0 rms roughness) of 14.5 mJ/m{sup 2}(nM/m). Treatment by exposure to harsh conditions showed that PFMS/Cu SAM can withstand boiling nitric acid (pH=1.8), boiling water, and warm sodium hydroxide (pH=12, 60 degree sign C) solutions for at least 30 min. Furthermore, no SAM degradation was observed when PFMS/Cu was exposed to warm nitric acid solution for up to 70 min at 60 degree sign C or 50 min at 80 degree sign C. Extremely hydrophobic (low surface energy) and stable PFMS/Cu SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for antiwetting, low adhesion surfaces or dropwise condensation on heat exchange surfaces.

  11. Chemical stability of nonwetting, low adhesion self-assembled monolayer films formed by perfluoroalkylsilanization of copper

    NASA Astrophysics Data System (ADS)

    Hoque, E.; DeRose, J. A.; Hoffmann, P.; Bhushan, B.; Mathieu, H. J.

    2007-03-01

    A self-assembled monolayer (SAM) has been produced by reaction of 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (PFMS) with an oxidized copper (Cu) substrate and investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), friction force microscopy (FFM), a derivative of AFM, and contact angle measurement. FFM showed a significant reduction in the adhesive force and friction coefficient of PFMS modified Cu (PFMS/Cu) compared to unmodified Cu. The perfluoroalkyl SAM on Cu is found to be extremely hydrophobic, yielding sessile drop static contact angles of more than 130° for pure water and a "surface energy" (which is proportional to the Zisman critical surface tension for a Cu surface with 0rms roughness) of 14.5mJ/m2(nM/m). Treatment by exposure to harsh conditions showed that PFMS/Cu SAM can withstand boiling nitric acid (pH=1.8), boiling water, and warm sodium hydroxide (pH =12, 60°C) solutions for at least 30min. Furthermore, no SAM degradation was observed when PFMS/Cu was exposed to warm nitric acid solution for up to 70min at 60°C or 50min at 80°C. Extremely hydrophobic (low surface energy) and stable PFMS/Cu SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for antiwetting, low adhesion surfaces or dropwise condensation on heat exchange surfaces.

  12. Bimetallic PdAg nanoparticle arrays from monolayer films of diblock copolymer micelles

    NASA Astrophysics Data System (ADS)

    Ehret, E.; Beyou, E.; Mamontov, G. V.; Bugrova, T. A.; Prakash, S.; Aouine, M.; Domenichini, B.; Cadete Santos Aires, F. J.

    2015-07-01

    The self-assembly technique provides a highly efficient route to generate well-ordered structures on a nanometer scale. In this paper, well-ordered arrays of PdAg alloy nanoparticles on flat substrates with narrow distributions of particle size (6-7 nm) and interparticle spacing (about 60 nm) were synthesized by the block copolymer micelle approach. A home-made PS-b-P4VP diblock copolymer was prepared to obtain a micellar structure in toluene. Pd and Ag salts were then successfully loaded in the micellar core of the PS-b-P4VP copolymer. A self-assembled monolayer of the loaded micelles was obtained by dipping the flat substrate in the solution. At this stage, the core of the micelles was still loaded with the metal precursor rather than with a metal. Physical and chemical reducing methods were used to reduce the metal salts embedded in the P4VP core into PdAg nanoparticles. HRTEM and EDX indicated that Pd-rich PdAg alloy nanoparticles were synthesized by chemical or physical reduction; UV-visible spectroscopy observations confirmed that metallic PdAg nanoparticles were quickly formed after chemical reduction; XPS measurements revealed that the PdAg alloy nanoparticles were in a metallic state after a short time of exposure to O2 plasma and after hydrazine reduction.

  13. Improving the Performance of Organic Thin-Film Transistors by Ion Doping of Ethylene-Glycol-Based Self-Assembled Monolayer Hybrid Dielectrics.

    PubMed

    Dietrich, Hanno; Scheiner, Simon; Portilla, Luis; Zahn, Dirk; Halik, Marcus

    2015-12-22

    Tuning the electrostatics of ethylene-glycol-based self-assembled monolayers (SAMs) by doping with ions is shown. Molecular dynamics simulations unravel binding mechanisms and predict dipole strengths of the doped layers. Additionally, by applying such layers as dielectrics in organic thin-film transistors, the incorporated ions are proven to enhance device performance by lowering the threshold voltage and increasing conductivity. PMID:26524344

  14. Commensurability Effects in Viscosity of Nanoconfined Water.

    PubMed

    Neek-Amal, Mehdi; Peeters, Francois M; Grigorieva, Irina V; Geim, Andre K

    2016-03-22

    The rate of water flow through hydrophobic nanocapillaries is greatly enhanced as compared to that expected from macroscopic hydrodynamics. This phenomenon is usually described in terms of a relatively large slip length, which is in turn defined by such microscopic properties as the friction between water and capillary surfaces and the viscosity of water. We show that the viscosity of water and, therefore, its flow rate are profoundly affected by the layered structure of confined water if the capillary size becomes less than 2 nm. To this end, we study the structure and dynamics of water confined between two parallel graphene layers using equilibrium molecular dynamics simulations. We find that the shear viscosity is not only greatly enhanced for subnanometer capillaries, but also exhibits large oscillations that originate from commensurability between the capillary size and the size of water molecules. Such oscillating behavior of viscosity and, consequently, the slip length should be taken into account in designing and studying graphene-based and similar membranes for desalination and filtration. PMID:26882095

  15. Commensurability and stability in nonperiodic systems

    PubMed Central

    Fasano, Y.; De Seta, M.; Menghini, M.; Pastoriza, H.; de la Cruz, F.

    2005-01-01

    We have investigated the response of 3D Bi2Sr2CaCu2O8 vortex structures to a weak perturbation induced by 2D Fe pinning structures acting on one extremity of vortex lines. The pinning patterns were nano-engineered at the sample surface by means of either a Bitter decoration of the vortex lattice or electron-beam lithography. The commensurability conditions between 2D rigid pinning potentials and 3D elastic structures with short-range positional and long-range orientational correlation have been experimentally determined. When the 2D potential is a replica of the nonperiodic vortex structure an amplification of its interaction with the vortex structure takes place. This effect is detected only for the first matching field, becoming negligible for other matching fields. On the other hand, a periodic 2D perturbation is shown to transform the nonperiodic Bragg glass-like structure into an Abrikosov crystal with an effective Debye–Waller factor. PMID:16576763

  16. Location of the heme-Fe atoms within the profile structure of a monolayer of cytochrome c bound to the surface of an ultrathin lipid multilayer film.

    PubMed Central

    Pachence, J M; Fischetti, R F; Blasie, J K

    1989-01-01

    We have recently developed x-ray diffraction methods to derive the profile structure of ultrathin lipid multilayer films having one to five bilayers (e.g., Skita, V., W. Richardson, M. Filipkowski, A.F. Garito, and J.K. Blasie. 1987. J. Physique. 47:1849-1855). Furthermore, we have employed these techniques to determine the location of a monolayer of cytochrome c bound to the carboxyl group surface of various ultrathin lipid multilayer substrates via nonresonance x-ray diffraction (Pachence, J.M., and J.K. Blasie. 1987. Biophys. J. 52:735-747). Here an intense tunable source of x-rays (beam line X9-A at the National Synchrotron Light Source at the Brookhaven National Laboratory) was utilized to measure the resonance x-ray diffraction effect from the heme-Fe atoms within the cytochrome c molecular monolayer located on the carboxyl surface of a five monolayer arachidic acid film. Lamellar x-ray diffraction was recorded for energies above, below, and at the Fe K-absorption edge (E = 7,112 eV). An analysis of the resonance x-ray diffraction effect is presented, whereby the location of the heme-Fe atoms within the electron density profile of the cytochrome c/arachidic acid ultrathin multilayer film is indicated to +/- 3 A accuracy. PMID:2550089

  17. Detection of saccharides with a fluorescent sensing device based on a gold film modified with 4-mercaptophenylboronic acid monolayer

    NASA Astrophysics Data System (ADS)

    Chen, Shu-Jen; Chang, Jui-Feng; Cheng, Nai-Jen; Yih, Jeng-Nan; Chiu, Kuo-Chi

    2013-09-01

    An extremely sensitive fluorescent sensor based on a phenylboronic acid monolayer was developed for detecting saccharide molecules. The fluorescent sensor was prepared by assembling a monolayer of 4-mercaptophenylboronic acid (4-MPBA) onto a gold-coated compact disk. The change in the fluorescence of the 4-MPBA monolayer was extremely obvious in basic methanolic buffer containing monosaccharides down to the picomolar level. The fluorescence spectra demonstrated that the 4-MPBA monolayer was sensitive to monosaccharides and disaccharides, and the affinity of the monolayer toward saccharides was in the order of glucose < fructose < mannose < galactose < maltose > lactose > sucrose. Additionally, the fluorescence intensity of 4-MPBA monolayer was restorable after cleaning with weak acid, indicating that the reported fluorescent sensor with the detection limit of glucose down to the picomolar level is reusable for sensing saccharides.

  18. Fabrication of SnO2-Reduced Graphite Oxide Monolayer-Ordered Porous Film Gas Sensor with Tunable Sensitivity through Ultra-Violet Light Irradiation

    PubMed Central

    Xu, Shipu; Sun, Fengqiang; Yang, Shumin; Pan, Zizhao; Long, Jinfeng; Gu, Fenglong

    2015-01-01

    A new graphene-based composite structure, monolayer-ordered macroporous film composed of a layer of orderly arranged macropores, was reported. As an example, SnO2-reduced graphite oxide monolayer-ordered macroporous film was fabricated on a ceramic tube substrate under the irradiation of ultra-violet light (UV), by taking the latex microsphere two-dimensional colloid crystal as a template. Graphite oxide sheets dispersed in SnSO4 aqueous solution exhibited excellent affinity with template microspheres and were in situ incorporated into the pore walls during UV-induced growth of SnO2. The growing and the as-formed SnO2, just like other photocatalytic semiconductor, could be excited to produce electrons and holes under UV irradiation. Electrons reduced GO and holes adsorbed corresponding negative ions, which changed the properties of the composite film. This film was directly used as gas-sensor and was able to display high sensitivity in detecting ethanol gas. More interestingly, on the basis of SnO2-induced photochemical behaviours, this sensor demonstrated tunable sensitivity when UV irradiation time was controlled during the fabrication process and post in water, respectively. This study provides efficient ways of conducting the in situ fabrication of a semiconductor-reduced graphite oxide film device with uniform surface structure and controllable properties. PMID:25758292

  19. Impedance analysis of different cell monolayers grown on gold-film electrodes.

    PubMed

    Reiss, Bjoern; Wegener, Joachim

    2015-08-01

    Impedance analysis of mammalian cells grown on planar film electrodes provides a label-free, non-invasive and unbiased observation of cell-based assays addressing the biological response to drugs, toxins or stressors in general. Whereas the time course of the measured impedance at one particular frequency has been used a lot for quantitative monitoring, in-depth analysis of the frequency-dependent impedance spectra is rarely performed. This study summarizes and validates the existing model for spectral analysis by applying it to eight different cell types from different mammalian tissues. Model parameters correctly predict the functional and/or structural properties of the individual cells under study. PMID:26737923

  20. Effect of alkanethiol self-assembled monolayers on the plastic and elastic deformation of gold(111) films

    NASA Astrophysics Data System (ADS)

    Aponte, Milca I.

    Surface chemistry is known to affect the elastic deformation of nanocontacts, but its role in plastic deformation is less clear. Alkanethiol self-assembled monolayers (SAMs) were used to modify the surface energy and surface stress of Au(111) films. The chemical effect of this nanometer scale film on elastic and plastic deformation was investigated using nanoindentation combined with atomic force microscopy (AFM) imaging of indents. A range of maximum indentation displacements and SAM chain lengths were used. Comparisons were made between the mechanical response of the gold substrate alone and the gold modified with the different SAMs. The nanoindentation load-displacement curves and the mechanical properties were found to be dependent on the presence of the SAM. A decrease in the reduced elastic modulus was observed when indenting the SAM systems. The work of indentation and the hardness showed a similar effect with the SAM layer lowering hardness in both cases. Remarkably, the SAM was found to affect hardness, and hence plasticity, at indentation depths over 100 times the SAM thickness. Comparisons were made between the projected contact areas approximated using the Oliver and Pharr method with the actual areas directly measured by AFM analysis. This accounts for underestimation of the contact area due to pile-up of gold around the indent. AFM characterization of the residual nanoindentation impressions showed substantial differences between the indent shape and pile-up when comparing the gold to the gold plus SAM surfaces. The differences are more pronounced for the longer chain length SAM and as the indents become deeper. The SAM reduces the adhesion force between the indenter tip and surface which may affect the observed mechanical properties for shallow indents. For the deeper indentations the exothermic reaction of the alkanethiol molecules chemisorbed on the gold surface reduces the surface free energy of the gold substrate which favors the creation of new

  1. Observation of dopant-profile independent electron transport in sub-monolayer TiOx stacked ZnO thin films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Saha, D.; Misra, P.; Das, Gangadhar; Joshi, M. P.; Kukreja, L. M.

    2016-01-01

    Dopant-profile independent electron transport has been observed through a combined study of temperature dependent electrical resistivity and magnetoresistance measurements on a series of Ti incorporated ZnO thin films with varying degree of static-disorder. These films were grown by atomic layer deposition through in-situ vertical stacking of multiple sub-monolayers of TiOx in ZnO. Upon decreasing ZnO spacer layer thickness, electron transport smoothly evolved from a good metallic to an incipient non-metallic regime due to the intricate interplay of screening of spatial potential fluctuations and strength of static-disorder in the films. Temperature dependent phase-coherence length as extracted from the magnetotransport measurement revealed insignificant role of inter sub-monolayer scattering as an additional channel for electron dephasing, indicating that films were homogeneously disordered three-dimensional electronic systems irrespective of their dopant-profiles. Results of this study are worthy enough for both fundamental physics perspective and efficient applications of multi-stacked ZnO/TiOx structures in the emerging field of transparent oxide electronics.

  2. Raman spectroscopic investigation of the single-monolayer Langmuir-Blodgett film of C16NaphOH and C10AzoNaphC4N-SDS.

    PubMed

    Wu, Yuqing; Zhao, Bing; Xu, Weiqing; Li, Guowen; Li, Bofu

    2003-04-01

    Raman spectra were measured for Langmuir-Blodgett (LB) films of C(16)NaphOH and C(10)AzoNaphC(4)N-SDS on Calcium Fluorite substrate for the first time. In order to find out favorable excitation condition, Raman spectra of the single and multi-monolayer LB films excited at different lines at 244, 514, 633 and 778 nm are recorded and compared in the present study. Raman spectrum of the monolayer LB film of C(16)NaphOH excited by 244 nm demonstrate that excellent signal to noise is achieved even for one monolayer LB film with an extremely short integrating time as 60 s because of being resonantly enhanced, while no meaningful spectra were recorded under the same condition for the monolayer LB film of C(10)AzoNaphC(4)N-SDS because of burning. Using a HeNe 633 nm excitation the problem with strong substrate fluorescence was partially solved, since under these conditions this fluorescence is mainly outside the fingerprint region of the LB film molecules (1000-2000 cm(-1)). Therefore by using the HeNe laser excitation, Raman spectra with high signal to noise ratio of LB films of C(16)NaphOH were collected and shown in this paper. These findings stress again the necessity to define an appropriate Raman system for this special application of LB film diagnosis. PMID:12659885

  3. Iso-oriented monolayer α-MoO3(010) films epitaxially grown on SrTiO3(001)

    NASA Astrophysics Data System (ADS)

    Du, Yingge; Li, Guoqiang; Peterson, Erik W.; Zhou, Jing; Zhang, Xin; Mu, Rentao; Dohnálek, Zdenek; Bowden, Mark; Lyubinetsky, Igor; Chambers, Scott A.

    2016-01-01

    The ability to synthesize well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented α-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) substrates by molecular beam epitaxy ((010)MoO3||(001)STO, [100]MoO3||[100]STO or [010]STO) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (aMoO3 = 3.96 Å, aSTO = 3.905 Å), the lattice mismatch along other direction is large (~5%, cMoO3 = 3.70 Å), which leads to relaxation as clearly observed from the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. A narrow range in the growth temperature is found to be optimal for the growth of monolayer α-MoO3 films. Increasing deposition time will not lead to further increase in thickness, which is explained by a balance between deposition and thermal desorption due to the weak van der Waals force between α-MoO3 layers. Lowering growth temperature after the initial iso-oriented α-MoO3 monolayer leads to thicker α-MoO3(010) films with excellent crystallinity.The ability to synthesize well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented α-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) substrates by molecular beam epitaxy ((010)MoO3||(001)STO, [100]MoO3||[100]STO or [010]STO) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (aMoO3 = 3.96 Å, aSTO = 3.905 Å), the lattice mismatch along other direction is large (~5%, cMoO3 = 3

  4. Surface-energy-assisted perfect transfer of centimeter-scale monolayer and few-layer MoS₂ films onto arbitrary substrates.

    PubMed

    Gurarslan, Alper; Yu, Yifei; Su, Liqin; Yu, Yiling; Suarez, Francisco; Yao, Shanshan; Zhu, Yong; Ozturk, Mehmet; Zhang, Yong; Cao, Linyou

    2014-11-25

    The transfer of synthesized 2D MoS2 films is important for fundamental and applied research. However, it is problematic to translate the well-established transfer processes for graphene to MoS2 due to different growth mechanisms and surface properties. Here we demonstrate a surface-energy-assisted process that can perfectly transfer centimeter-scale monolayer and few-layer MoS2 films from original growth substrates onto arbitrary substrates with no observable wrinkles, cracks, and polymer residues. The unique strategies used in this process include leveraging the penetration of water between hydrophobic MoS2 films and hydrophilic growth substrates to lift off the films and dry transferring the film after the lift off. This is in stark contrast with the previous transfer process for synthesized MoS2 films, which explores the etching of the growth substrate by hot base solutions to lift off the films. Our transfer process can effectively eliminate the mechanical force caused by bubble generations, the attacks from chemical etchants, and the capillary force induced when transferring the film outside solutions as in the previous transfer process, which consists of the major causes for the previous unsatisfactory transfer. Our transfer process also benefits from using polystyrene (PS), instead of poly(methyl methacrylate) (PMMA) that was widely used previously, as the carrier polymer. PS can form more intimate interaction with MoS2 films than PMMA and is important for maintaining the integrity of the film during the transfer process. This surface-energy-assisted approach can be generally applied to the transfer of other 2D materials, such as WS2. PMID:25347296

  5. Iso-oriented monolayer α-MoO3(010) films epitaxially grown on SrTiO3(001).

    PubMed

    Du, Yingge; Li, Guoqiang; Peterson, Erik W; Zhou, Jing; Zhang, Xin; Mu, Rentao; Dohnálek, Zdenek; Bowden, Mark; Lyubinetsky, Igor; Chambers, Scott A

    2016-02-01

    The ability to synthesize well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented α-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) substrates by molecular beam epitaxy ((010)(MoO3)‖(001)(STO), [100](MoO3)‖[100](STO) or [010](STO)) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (a(MoO3) = 3.96 Å, a(STO) = 3.905 Å), the lattice mismatch along other direction is large (∼5%, c(MoO3) = 3.70 Å), which leads to relaxation as clearly observed from the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. A narrow range in the growth temperature is found to be optimal for the growth of monolayer α-MoO3 films. Increasing deposition time will not lead to further increase in thickness, which is explained by a balance between deposition and thermal desorption due to the weak van der Waals force between α-MoO3 layers. Lowering growth temperature after the initial iso-oriented α-MoO3 monolayer leads to thicker α-MoO3(010) films with excellent crystallinity. PMID:26788784

  6. Synthesis and Evaluation of Self-Assembled Azido Monolayer as a Novel Dielectric Layer for Fabricating Pentacene-Based Organic Thin Film Transistors.

    PubMed

    Yeh, Je-Yuan; Tsai, Tzung-Da; Kuo, An Tsung; Chou, Ying-Shiun; Liou, Ying-Shian; Chang, Zhao-You; Tsiang, Raymond Chien-Chao; Guo, Tzung-Fang; Chang, Chien-Hsiang

    2015-05-01

    Self-assembled 3-azidopropyltriethoxysilane monolayer (SAM) is used as a dielectric layer to modify the interface between the silicon dioxide wafer and the pentacene semiconductor layer in an organic thin film transistor (OTFT), Au/pentacene/3-azidopropyltriethoxysilane/SiO2/Si. Compared to the commonly used alkyl siliane C18 dielectric, 3-azidopropyltriethoxysilane which possesses stable formal charges is far more effective in increasing the ON/OFF ratio of OTFT device with an improvement of nearly three orders of magnitude. Analysis and measurements reported in this paper have illustrated for the first time the improvement of OTFT performance by a SAM compound with stable formal charges. PMID:26504992

  7. Assembly of polymer-gold nanostructures with high reproducibility into a monolayer film SERS substrate with 5 nm gaps for pesticide trace detection.

    PubMed

    Zhou, Xia; Zhou, Fei; Liu, Honglin; Yang, Liangbao; Liu, Jinhuai

    2013-10-01

    A very simple and versatile polymer assembly approach was developed. We use methoxy-mercapto-poly(ethylene glycol) (mPEG-SH) to conjugate multiple Au shapes to form dense Au monolayer films (MLFs) with 5 nm gaps and generate gigantic enhancement. The results of the discrete dipole approximation (DDA) method to calculate the local electric field distribution of the nanoparticle dimer are in agreement with the experimental data of sensitivity of multiple Au MLFs. 3D Raman spectra, relative standard deviation (RSD) calculation and Raman mapping were used to study the high-reproducibility of the assembled substrate, which is sufficient for trace pesticide residue detection. PMID:23912071

  8. Self-assembled monolayers of cyclohexyl-terminated phosphonic acids as a general dielectric surface for high-performance organic thin-film transistors.

    PubMed

    Liu, Danqing; He, Zikai; Su, Yaorong; Diao, Ying; Mannsfeld, Stefan C B; Bao, Zhenan; Xu, Jianbin; Miao, Qian

    2014-11-12

    A novel self-assembled monolayer (SAM) on AlOy /TiOx is terminated with cyclohexyl groups, an unprecedented terminal group for all kinds of SAMs. The SAM-modified AlOy /TiOx functions as a general dielectric, enabling organic thin-film transistors with a field-effect mobility higher than 5 cm(2) V(-1) s(-1) for both holes and electrons, good air stability with low operating voltage, and general applicability to solution-processed and vacuum-deposited n-type and p-type organic semiconductors. PMID:25205623

  9. Rotation dynamics of C{sub 60} molecules in a monolayer fullerene film on the WO{sub 2}/W(110) surface near the rotational phase transition

    SciTech Connect

    Bozhko, S. I.; Levchenko, E. A.; Semenov, V. N.; Bulatov, M. F.; Shvets, I. V.

    2015-05-15

    The rotation dynamics of C{sub 60} molecules in monolayer fullerene films grown on the WO{sub 2}/W(110) surface is studied by scanning tunneling microscopy. The formation of molecule clusters, which have a high libron vibration amplitude, is detected near the rotational phase transition temperature. The energy parameters that determine a change in the molecule orientation, namely, the energy difference between the nearest minima of the C{sub 60} molecule energy (30 meV) as a function of the molecule orientation and the potential barrier between them (610 meV), are determined. The results are discussed in terms of the mean-field approximation.

  10. Self-assembled monolayers and chemical derivatization of Ba 0.5Sr 0.5TiO 3 thin films: Applications in phase shifter devices

    NASA Astrophysics Data System (ADS)

    Morales-Cruz, Angel L.; Keuls, Fred W. Van; Miranda, Félix A.; Cabrera, Carlos R.

    2005-11-01

    Thin films of barium strontium titanate (Ba 1- xSr x TiO 3 (BSTO)) have been used in coupled microstrip phase shifters (CMPS) for possible insertion in satellite and wireless communication platforms primarily because of their high dielectric constant, low loss, large tunability, and good structural stability. In an attempt to improve the figure of merit K (phase shift °/dB of loss) of phase shifters, modification of the metal/BSTO interface of these devices has been done through surface modification of the BSTO layer using a self-assembled monolayer approach. The impact of this nanotechnology promises to reduce RF losses by improving the quality of the metal/BSTO interface. In this study, compounds such as 3-mercaptopropyltrimethoxysilane (MPS), 16-mercaptohexadecanois acid (MHDA) and 3-mercaptopropionic acid (MPA) were used to form the self-assembled monolayers on the BSTO surface. As a result of the previous modification, chemical derivatization of the self-assembled monolayers was done in order to increase the chain length. Chemical derivatization was done using 3-aminopropyltrimethoxysilane (APS) and 16-mercaptohexadecanoic acid. Surface chemical analysis was done to reveal the composition of the derivatization via X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared (FT-IR). Low and high frequencies measurements of phase shifters were done in order measure the performance of these devices for insertion in antennas. X-ray photoelectron spectroscopy characterization of modified BSTO thin films with MPS showed a binding energy peak at 162.9 eV, indicative of a possible S sbnd O interaction: sulfur of the mercapto compound, MPS, used to modify the surface with the oxygen site of the BSTO thin film. This interaction is at higher binding energies compared with the thiolate interaction. This behavior is observed with the other mercapto compounds such as: MHDA and MPA. An FT-IR analysis present a band at 780 cm -1, which is characteristic of an O

  11. Rotationally Commensurate Growth of MoS2 on Epitaxial Graphene.

    PubMed

    Liu, Xiaolong; Balla, Itamar; Bergeron, Hadallia; Campbell, Gavin P; Bedzyk, Michael J; Hersam, Mark C

    2016-01-26

    Atomically thin MoS2/graphene heterostructures are promising candidates for nanoelectronic and optoelectronic technologies. Among different graphene substrates, epitaxial graphene (EG) on SiC provides several potential advantages for such heterostructures, including high electronic quality, tunable substrate coupling, wafer-scale processability, and crystalline ordering that can template commensurate growth. Exploiting these attributes, we demonstrate here the thickness-controlled van der Waals epitaxial growth of MoS2 on EG via chemical vapor deposition, giving rise to transfer-free synthesis of a two-dimensional heterostructure with registry between its constituent materials. The rotational commensurability observed between the MoS2 and EG is driven by the energetically favorable alignment of their respective lattices and results in nearly strain-free MoS2, as evidenced by synchrotron X-ray scattering and atomic-resolution scanning tunneling microscopy (STM). The electronic nature of the MoS2/EG heterostructure is elucidated with STM and scanning tunneling spectroscopy, which reveals bias-dependent apparent thickness, band bending, and a reduced band gap of ∼0.4 eV at the monolayer MoS2 edges. PMID:26565112

  12. Effect of Self-Assembled Monolayer Modification on Indium-Tin Oxide Surface for Surface-Initiated Vapor Deposition Polymerization of Carbazole Thin Films

    NASA Astrophysics Data System (ADS)

    Yuya Umemoto,; Seong-Ho Kim,; Rigoberto C. Advincula,; Kuniaki Tanaka,; Hiroaki Usui,

    2010-04-01

    With the aim of controlling the interface between an inorganic electrode and an organic layer, a surface-initiated vapor deposition polymerization method was employed to prepare carbazole polymer thin films that are chemically bound to an indium-tin oxide (ITO) surface. A self-assembled monolayer (SAM) that has an azo initiator as a terminal group was prepared on an ITO surface, on which carbazole acrylate monomers were evaporated under ultraviolet (UV) irradiation. The surface morphological characteristics of the films prepared with/without UV irradiation and with/without the SAM were compared. It was found that the UV irradiation leads to the polymerization of carbazole monomers irrespective of the type of substrate used. On the other hand, the surface morphological characteristics were largely dependent on the existence of the SAM. Uniform and smooth polymer thin films were obtained only when the monomers were evaporated on the SAM-modified surface under UV irradiation. A comparison of film growth characteristics on a UV-ozone-treated ITO surface suggested that the formation of uniform films was made possible not by the modification of surface energy but by the growth of the polymers chemically bound to the substrate surface.

  13. Experimental investigation and molecular dynamics simulations of impact-mode wear mechanisms in silicon micromachines with alkylsilane self-assembled monolayer films

    NASA Astrophysics Data System (ADS)

    Douglas, C. M.; Rouse, W. A.; Driscoll, J. A.; Timpe, S. J.

    2015-10-01

    In the current work, polycrystalline silicon microdevices are treated with a 1H,1H,2H,2H-Perfluorodecyltrichlorosilane (FDTS) self-assembled monolayer (SAM) film. Using a microelectromechanical systems-based tribometer, the adhesion characteristics of the FDTS-treated surfaces are compared to those of untreated surfaces over a range of approximately 10 × 106 impact cycles. FDTS-treated surfaces showed a lower zero-hour adhesion force compared to untreated surfaces under identical environmental conditions. The presence of the monolayer did not have a discernible effect on the number of cycles to initiate the surface degradation that was manifested as an increase in the adhesion force. Based on trends in degradation, it is concluded that similar chemical and physical wear mechanisms dominate the evolution of adhesion in both treated and untreated devices. The qualitative results of the experiment are reinforced by molecular dynamics (MD) simulations of a single nanoasperity contact coated with an octadecyltrichlorosilane (ODTS) SAM. MD simulations show cleavage of bonds along the aliphatic chains of ODTS resulting in adhesion fluctuations. In agreement with experimental observations, the MD simulation shows a logarithmic increase in adhesion force with increasing number of cycles. MD simulations also predict a logarithmic decrease in adhesion energy with increasing cycles. These results provide insight into the physicohemical changes occurring during repetitive impact of surfaces coated with low surface energy films.

  14. Self-assembled monolayer exchange reactions as a tool for channel interface engineering in low-voltage organic thin-film transistors.

    PubMed

    Lenz, Thomas; Schmaltz, Thomas; Novak, Michael; Halik, Marcus

    2012-10-01

    In this work, we compared the kinetics of monolayer self-assembly long-chained carboxylic acids and phosphonic acids on thin aluminum oxide surfaces and investigated their dielectric properties in capacitors and low-voltage organic thin-film transistors. Phosphonic acid anchor groups tend to substitute carboxylic acid molecules on aluminum oxide surfaces and thus allow the formation of mixed or fully exchanged monolayers. With different alkyl chain substituents (n-alkyl or fluorinated alkyl chains), the exchange reaction can be monitored as a function of time by static contact angle measurements. The threshold voltage in α,α'-dihexyl-sexithiophene thin-film transistors composed of such mixed layer dielectrics correlates with the exchange progress and can be tuned from negative to positive values or vice versa depending on the dipole moment of the alkyl chain substituents. The change in the dipole moment with increasing exchange time also shifts the capacitance of these devices. The rate constants for exchange reactions determined by the time-dependent shift of static contact angle, threshold voltage, and capacitance exhibit virtually the same value thus proving the exchange kinetics to be highly controllable. In general, the exchange approach is a powerful tool in interface engineering, displaying a great potential for tailoring of device characteristics. PMID:22963322

  15. Electric bistability induced by incorporating self-assembled monolayers/aggregated clusters of azobenzene derivatives in pentacene-based thin-film transistors.

    PubMed

    Tseng, Chiao-Wei; Huang, Ding-Chi; Tao, Yu-Tai

    2012-10-24

    Composite films of pentacene and a series of azobenzene derivatives are prepared and used as the active channel material in top-contact, bottom-gate field-effect transistors. The transistors exhibit high field-effect mobility as well as large I-V hysteresis as a function of the gate bias history. The azobenzene moieties, incorporated either in the form of self-assembled monolayer or discrete multilayer clusters at the dielectric surface, result in electric bistability of the pentacene-based transistor either by photoexcitation or gate biasing. The direction of threshold voltage shifts, size of hysteresis, response time, and retention characteristics all strongly depend on the substituent on the benzene ring. The results show that introducing a monolayer of azobenzene moieties results in formation of charge carrier traps responsible for slower switching between the bistable states and longer retention time. With clusters of azobenzene moieties as the trap sites, the switching is faster but the retention is shorter. Detailed film structure analyses and correlation with the transistor/memory properties of these devices are provided. PMID:22974132

  16. Characterization of heterojunctions via x-ray and uv photoemission spectroscopy: energy level implications for single and mixed monolayer SAMs, cadmium selenide nanoparticle films, and organic semiconductor depositions

    NASA Astrophysics Data System (ADS)

    Graham, Amy L.

    This work has centered on the interface dipoles arising at heterojunctions between metals, semiconductor nanoparticles, self-assembled monolayers, and organic semiconductor materials. Alkanethiol self-assembled monolayers, CdSe nanocrystals, and the organic semiconductors zinc phthalocyanine (ZnPc) and Buckminster fullerene (C60) were the basis of these investigations. UV photoemission spectroscopy has proven to be an invaluable tool to observe the vacuum level shifts for these analyses while using XPS to corroborate surface structure. With a full evaluation of these surfaces, the shifts in the vacuum level, valence ionizations, and core ionizations, the impact of these interfaces, as well as their influence on the subsequent deposition of organic semiconductor layers is established. Alkanethiols possessing varying dipole moments were examined on gold and silver substrates. The viability of these alkanethiols was demonstrated to predictively adjust the work function of these metals as a function of their intrinsic dipole moments projected to surface normal, and established differences between Ag---S and Au---S bonds. The capability of the SAMs to modify the work function of gold provided an opportunity for mixed monolayers of the alkanethiols to produce a precise range of work functions by minimal adjustments of solution concentration, which were examined with a simple point dipole model. Photoemission spectroscopy offers a thorough analysis of CdSe nanoparticle films. Despite a plethora of research on these nanocrystals, there still is controversy on the magnitude of the shift in the valence band with diameter. In our research we found the majority of the valence band shift could be attributed to the interface dipole, ignored previously. Meanwhile, the valence band tethered films was obscured by the sulfur of the thiol tether. Finally, organic semiconductor layers deposited on SAMs on gold exhibited various interface dipole effects at these heterojunctions. Charge

  17. Effect of fluorocarbon self-assembled monolayer films on sidewall adhesion and friction of surface micromachines with impacting and sliding contact interfaces

    SciTech Connect

    Xiang, H.; Komvopoulos, K.

    2013-06-14

    A self-assembled monolayer film consisting of fluoro-octyltrichlorosilane (FOTS) was vapor-phase deposited on Si(100) substrates and polycrystalline silicon (polysilicon) surface micromachines. The hydrophobic behavior and structural composition of the FOTS film deposited on Si(100) were investigated by goniometry and X-ray photoelectron spectroscopy, respectively. The effects of contact pressure, relative humidity, temperature, and impact/sliding cycles on the adhesive and friction behavior of uncoated and FOTS-coated polysilicon micromachines (referred to as the Si and FOTS/Si micromachines, respectively) were investigated under controlled loading and environmental conditions. FOTS/Si micromachines demonstrated much lower and stable adhesion than Si micromachines due to the highly hydrophobic and conformal FOTS film. Contrary to Si micromachines, sidewall adhesion of FOTS/Si micromachines demonstrated a weak dependence on relative humidity, temperature, and impact cycles. In addition, FOTS/Si micromachines showed low and stable adhesion and low static friction for significantly more sliding cycles than Si micromachines. The adhesive and static friction characteristics of Si and FOTS/Si micromachines are interpreted in the context of physicochemical surface changes, resulting in the increase of the real area of contact and a hydrophobic-to-hydrophilic transition of the surface chemical characteristics caused by nanoscale surface smoothening and the removal of the organic residue (Si micromachines) or the FOTS film (FOTS/Si micromachines) during repetitive impact and oscillatory sliding of the sidewall surfaces.

  18. Commensurate Phases of Kr Adsorbed on Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Mbaye, Mamadou T.; Maiga, Sidi M.; Gatica, Silvina M.

    2016-02-01

    In this paper, we show that Krypton atoms form a commensurate solid (CS) phase with a fractional coverage of one krypton atom per every four carbons on zigzag carbon nanotubes. This is a unique phase, different from the √{3} × √{3} R30° CS monolayer formed on graphite, which has a lower coverage of one krypton atom per every six carbons. Our prediction disagrees with experiments that observe in nanotubes the same solid structure found on graphite. In order to address this discrepancy, we simulated adsorption of Kr on zigzag and armchair single-walled carbon nanotubes with radii ranging from 4.7 to 28.83 Å. Our simulations confirm that the CS of coverage 1/4 forms on medium-sized zigzag nanotubes. We also found the 1/6-coverage solid on graphene, which represents the infinite-radius limit of a nanotube. Our findings are key to experiments of adsorption on nanotubes where the interpretation and justification of the results are based on the monolayer coverage, such as mass or conductance isotherms measurements.

  19. [60]-fullerene and single-walled carbon nanotube-based ultrathin films stepwise grafted onto a self-assembled monolayer on ITO.

    PubMed

    Wang, Qiguan; Moriyama, Hiroshi

    2009-09-15

    A step-by-step method was used to prepare homogeneous ultrathin films composed of [60]-fullerene (C60) and single-walled carbon nanotubes (SWNTs), grafted onto the functional surface of an alkylsilane self-assembled monolayer (SAM) on an ITO substrate with an ITO-C60-SWNT sequence using amine addition across a double bond in C60 followed by amidation coupling with acid-functionalized SWNTs. Atomic force microscope and scanning electron microscope images of the resulting composite film showed two-component ball-tube microstructures with high-density coverage, where C60 was homogeneously distributed in the SWNT forest. The attachment of SWNTs to the residual amine units in the SAM on the ITO substrate (SAM-ITO) as well as on the C60 sphere results in the C60 molecules in the aggregated clusters being more separately dispersed, which forms a densely packed composite film as a result of the pi-pi interaction between the C60 buckyballs and the SWNT walls. It was found using ferrocene as an internal redox probe that the oxidative and reductive processes at the film-solution surface were effectively retarded because of obstruction from the densely packed film and the electronic effect of SWNT and C60. In addition, the electrochemical properties of C60 on SAM-ITO plates observed by cyclic voltammetry were significantly modified by chemical anchorage using SWNTs. X-ray photoelectron spectroscopy (XPS) analysis also indicated the successful grafting of C60 and SWNT. The XPS chemical shift of the binding energy showed the presence of electronic interactions between C60, SWNT, and ITO components. Such a uniformly distributed C60-SWNT film may be useful for future research in electrochemical and photoactive nanodevices. PMID:19639982

  20. 7 CFR 1400.7 - Commensurate contributions and risk.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 10 2010-01-01 2010-01-01 false Commensurate contributions and risk. 1400.7 Section... contributions and risk. (a) In order to be considered eligible to receive payments under the programs specified...'s contribution(s) to the operation; (2) Contribution(s) to the farming operation that are at...

  1. Study of Fused Thiophene Based Organic Semiconductors and Interfacial Self-Assembled Monolayer (SAM) for Thin-Film Transistor (TFT) Application

    NASA Astrophysics Data System (ADS)

    Youn, Jangdae

    In this thesis, the molecular packing motifs of our newly designed fused thiophenes, benzo[d,d]thieno[3,2-b;4,5-b]dithiophene (BTDT) derivatives, were studied by utilizing grazing incidence wide angle X-ray scattering (GIWAXS). Considering the potential of fused thiophene molecules as an environmentally stable, high performance semiconductor building block, it must be an important groundwork to investigate their thin film structures in relation to molecular structures, single crystal structures, and organic thin-film transistors (OTFT) performances. OTFT device performance is not only determined by semiconductor materials, but also influenced by the interfacial properties. Since there are three major components in TFT structures---electrodes, semiconductors, and dielectrics, two types of major interfaces exist. One is the semiconductor-electrode interface, and the other is the semiconductor-dielectric interface. Both of these interfaces have critical roles for TFT operation. For example, the semiconductor-electrode interface determines the charge injection barrier. Before charge carriers go through the electrode (source)-semiconductor-electrode (drain) pathways, the energy gaps between the work function of the electrodes and the HOMO energy of the semiconductor materials must be overcome for hole injection, or the energy gap between the metal work function of the electrodes and the LUMO energy of the semiconductor materials must be overcome for electron injection. These charge injection barriers are largely determined by the energetic structure of the semiconductor material and work function of the electrode. However, the size of energy gap can be modified by introducing an organic self-assembled monolayer (SAM) on the surface of metal electrode. In addition, the structure of semiconductor films, especially within several monolayers right above the electrode, is greatly influenced by the SAM, and it changes charge injection property of OTFT devices. In this thesis

  2. Temperature effect on thin lipid film elasticity and phase separation: insights from Langmuir monolayer and fluorescence microscopy techniques

    NASA Astrophysics Data System (ADS)

    Khattari, Z.; Maghrabi, M.; Al-Abdullah, T.

    2015-07-01

    Langmuir monolayer pressure isotherms and compressibility modulus measurements of phospholipid mixtures in several Langmuir monolayer systems at the air/water interface were investigated in this study. The ultimate aim was to carry out a comparison of the elasticity modulus for monolayers with different mixtures of l,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), l,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and chicken egg yolk sphingomyelin (eSM), in the presence/absence of cholesterol (Chol). In particular, we were able to propose that the leading force beyond the phase separation into liquid expanded (LE-) and liquid condensed (LC-) phases emerges from the increasing barrier to incorporate DOPC molecules into a highly ordered LC-phase. In addition, our findings suggest that DOPC lipid molecules have a priority to incorporate in a disordered LE-phase, while DPPC and eSM prefer the ordered one. Also, Chol seems to split almost equally into both phases, indicating that Chol has no priority for either phase and there are no particular interactions between Chol and saturated lipid molecules.

  3. Frictional transition from superlubric islands to pinned monolayers.

    PubMed

    Pierno, Matteo; Bruschi, Lorenzo; Mistura, Giampaolo; Paolicelli, Guido; di Bona, Alessandro; Valeri, Sergio; Guerra, Roberto; Vanossi, Andrea; Tosatti, Erio

    2015-08-01

    The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu(111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena will be essential in future applications of friction at crystal/adsorbate interfaces. PMID:26006001

  4. Research of the relations between monolayer SiNx optical thin film processing techniques and laser-induced damage properties prepared by PECVD technology

    NASA Astrophysics Data System (ADS)

    Li, Peng; Hang, Lingxia; Li, Linjun; Huang, Fabin

    2015-02-01

    The monolayer SiNx optical thin films were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) technology on the BK7 glass substrate, the laser-induced damage threshold was measured by laser damage testing equipment, and we also investigated the relations between processing techniques and laser-induced damage properties. The study and analysis to orthogonal experiment results show that PECVD processing techniques have an effect on the laser-induced damage properties. Among them,radio frequency has the biggest effection, temperature is the main factor, working pressure is the unimportant factor, and we also achieve the optimal processing parameters (Temperature is 350°; RF power is 250W; Working pressure is 60Pa).

  5. Phase behavior of mixed submonolayer films of krypton and xenon on graphite.

    PubMed

    Patrykiejew, A; Sokołowski, S

    2012-04-14

    Using the results of extensive Monte Carlo simulations in the canonical and grand canonical ensembles, we discuss the phase behavior of mixed submonolayer films of krypton and xenon adsorbed on the graphite basal plane. The calculations have been performed using two- and three-dimensional models of the systems studied. It has been demonstrated that out-of-plane motion does not affect the properties of the films as long as the total density is well below the monolayer completion and at moderate temperatures. For the total densities close to the monolayer completion, the promotion of particles to the second layer considerably affects the film properties. Our results are in a reasonable agreement with the available experimental data. The melting point of submonolayer films has been shown to exhibit non-monotonous changes with the film composition, and reaches minimum for the xenon concentration of about 50%. At the temperatures below the melting point, the structure of solid phases depends upon the film composition and the temperature; one can also distinguish commensurate and incommensurate phases. Two-dimensional calculations have demonstrated that for the xenon concentration between about 15% and 65% the adsorbed film exhibits the formation of a superstructure, in which each Xe atom is surrounded by six Kr atoms. This superstructure is stable only at very low temperatures and transforms into the mixed commensurate (√3×√3)R30° phase upon the increase of temperature. Such a superstructure does not appear when a three-dimensional model is used. Grand canonical ensemble calculations allowed us to show that for the xenon concentration of about 3% the phase diagram topology of monolayer films changes from the krypton-like (with incipient triple point) to the xenon-like (with ordinary triple point). PMID:22502538

  6. Orthogonally Spin-Coated Bilayer Films for Photochemical Immobilization and Patterning of Sub-10-Nanometer Polymer Monolayers.

    PubMed

    Janes, Dustin W; Kim, Chae Bin; Maher, Michael J; Ellison, Christopher J

    2016-07-12

    Versatile and spatiotemporally controlled methods for decorating surfaces with monolayers of attached polymers are broadly impactful to many technological applications. However, current materials are usually designed for very specific polymer/surface chemistries and, as a consequence, are not very broadly applicable and/or do not rapidly respond to high-resolution stimuli such as light. We describe here the use of a polymeric adhesion layer, poly(styrene sulfonyl azide-alt-maleic anhydride) (PSSMA), which is capable of immobilizing a 1-7 nm thick monolayer of preformed, inert polymers via photochemical grafting reactions. Solubility of PSSMA in very polar solvents enables processing alongside hydrophobic polymers or solutions and by extension orthogonal spin-coating deposition strategies. Therefore, these materials and processes are fully compatible with photolithographic tools and can take advantage of the immense manufacturing scalability they afford. For example, the thicknesses of covalently grafted poly(styrene) obtained after seconds of exposure are quantitatively equivalent to those obtained by physical adsorption after hours of thermal equilibration. Sequential polymer grafting steps using photomasks were used to pattern different regions of surface energy on the same substrate. These patterns spatially controlled the self-assembled domain orientation of a block copolymer possessing 21 nm half-periodicity, demonstrating hierarchical synergy with leading-edge nanopatterning approaches. PMID:27351974

  7. Synthesis of KCa₂Nb₃O₁₀ Crystals with Varying Grain Sizes and Their Nanosheet Monolayer Films As Seed Layers for PiezoMEMS Applications.

    PubMed

    Yuan, Huiyu; Nguyen, Minh; Hammer, Tom; Koster, Gertjan; Rijnders, Guus; ten Elshof, Johan E

    2015-12-16

    The layered perovskite-type niobate KCa2Nb3O10 and its derivatives show advantages in several fields, such as templated film growth and (photo)catalysis. Conventional synthesis routes generally yield crystal size smaller than 2 μm. We report a flux synthesis method to obtain KCa2Nb3O10 crystals with significantly larger sizes. By using different flux materials (K2SO4 and K2MoO4), crystals with average sizes of 8 and 20 μm, respectively, were obtained. The KCa2Nb3O10 crystals from K2SO4 and K2MoO4 assisted synthesis were protonated and exfoliated into monolayer nanosheets, and the optimal exfoliation conditions were determined. Using pulsed laser deposition, highly (001)-oriented piezoelectric stacks (SrRuO3/PbZr0.52Ti0.48O3/SrRuO3, SRO/PZT/SRO) were deposited onto Langmuir-Blodgett films of Ca2Nb3O10(-) (CNO) nanosheets with varying lateral nanosheet sizes on Si substrates. The resulting PZT thin films showed high crystallinity irrespective of nanosheet size. The small sized nanosheets yielded a high longitudinal piezoelectric coefficient d33 of 100 pm/V, while the larger sized sheets had a d33 of 72 pm/V. An enhanced transverse piezoelectric coefficient d31 of -107 pm/V, an important input parameter for the actuation of active structures in microelectromechanical systems (MEMS) devices, was obtained for PZT films grown on CNO nanosheets with large lateral size, while the corresponding value on small sized sheets was -96 pm/V. PMID:26583282

  8. Low-lying lattice modes of highly uniform pentacene monolayers

    NASA Astrophysics Data System (ADS)

    He, Rui; Tassi, Nancy G.; Blanchet, Graciela B.; Pinczuk, Aron

    2009-06-01

    The authors report that monolayers of pentacene grown on a functionalized polymeric substrate display high uniformity that enable observations of Raman spectra of low-lying optical vibrations. The evolution of the frequencies and widths of the modes has been studied in films reaching the single monolayer level. Raman spectra of low-lying lattice modes display major changes when the film thickness changes from 1 to 2 monolayers, revealing that a phase akin to a thin film phase of pentacene already emerges in films of only 2 monolayers.

  9. Persistent monolayer-scale chemical ordering in Si1-xGex heteroepitaxial films during surface roughening and strain relaxation

    NASA Astrophysics Data System (ADS)

    Amatya, J. M.; Floro, J. A.

    2015-12-01

    Chemical ordering in semiconductor alloys could modify thermal and electronic transport, with potential benefits to thermoelectric properties. Here, metastable ordering that occurs during heteroepitaxial growth of Si1-xGex thin film alloys on Si(001) and Ge(001) substrates is investigated. A parametric study was performed to study how strain, surface roughness, and growth parameters affect the order parameter during the alloy growth. The order parameter for the alloy films was carefully quantified using x-ray diffraction, taking into account an often-overlooked issue associated with the presence of multiple spatial variants associated with ordering along equivalent <111> directions. Optimal ordering was observed in the films having the smoothest surfaces. Extended strain relaxation is suggested to reduce the apparent order through creation of anti-phase boundaries. Ordering surprisingly persists even when the film surface extensively roughens to form {105} facets. Growth on deliberately miscut Si(001) surfaces does not affect the volume-averaged order parameter but does impact the relative volume fractions of the equivalent ordered variants in a manner consistent with geometrically necessary changes in step populations. These results provide somewhat self-contradictory implications for the role of step edges in controlling the ordering process, indicating that our understanding is still incomplete.

  10. Tuning friction with an external magnetic field: A Quartz Crystal Microbalance study of physisorbed oxygen monolayers and multilayers sliding on nickel substrates

    NASA Astrophysics Data System (ADS)

    Fredricks, Z. B.; Stevens, K. M.; Acharya, B.; Krim, J.

    The sliding friction levels of oxygen monolayer and multilayer films adsorbed on nickel close to the oxygen monolayer solid-liquid melting transition temperature have been monitored by means of a Quartz Crystal Microbalance (QCM) technique in the presence and absence of a weak external magnetic field. Friction levels for the monolayers in the presence of the field were observed to be half of those observed in the absence of a field. For thick films, the reduction was proportionately less, indicating an interfacial effect as the source of the magnetic sensitivity. While the presence of the field is expected to increase the normal force between the paramagnetic oxygen overlayer and the ferromagnetic substrate, the impact of this mechanism on friction appears to be minimal, or possibly masked by more dominant mechanisms. These include magnetically induced structural reorientation (magnetostriction), and/or realignment of adlayer spins in response to the applied field, both of which would reduce the physical or magnetic interfacial commensurability, thus lowering friction levels. Work supported by NSF DMR1310456.

  11. Nanosecond imaging of microboiling behavior on pulsed-heated au films modified with hydrophilic and hydrophobic self-assembled monolayers.

    PubMed

    Balss, Karin M; Avedisian, C Thomas; Cavicchi, Richard E; Tarlov, Michael J

    2005-11-01

    Fast transient microboiling has been characterized on modified gold microheaters using a novel laser strobe microscopy technique. Microheater surfaces of different hydrophobicity were prepared using self-assembled monolayers of hexadecane thiol (hydrophobic) and 16-mercaptohexadecanol (hydrophilic) as well as the naturally hydrophilic bare gold surface. The microheater was immersed in a pool of water, and a 5-micros voltage pulse to the heater was applied, causing superheating of the water and nucleation of a vapor bubble on the heater surface. Light from a pulsed Nd:Yag laser was configured to illuminate and image the sample through a microscope assembly. The timing of the short duration (7.5 ns) laser flash was varied with respect to the voltage pulse applied to the heater to create a series of images illuminated by the flash of the laser. These images were correlated with the transient resistance change of the heater both during and after the voltage pulse. It was found that hydrophobic surfaces produced a bubble that nucleated at an earlier time, grew more slowly to a smaller maximum size, and collapsed more rapidly than bubbles formed on hydrophilic surfaces. PMID:16262306

  12. Facile fabrication of rutile monolayer films consisting of well crystalline nanorods by following an IL-assisted hydrothermal route

    SciTech Connect

    Peng Peng; Liu Xiaodi; Sun, Chuansheng; Ma Jianmin; Zheng Wenjun

    2009-05-15

    In this study, rutile films consisting of rectangular nanorods were facilely deposited on glass substrates from strongly acid solution of TiCl{sub 4}. The highly ordered array of nanorods was realized in presence of ionic liquid (IL) of [Bmim]Br by following a hydrothermal process. In this process, Degussa P25 nanoparticles served as seeds that were pre-deposited on the substrates to facilitate the array of rutile nanorods. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectrum were used to characterize the obtained nanorod films. The measurements showed that the nanorods were rectangular with width of 100-200 nm and length of more than 1 {mu}m, and grew up typically along c-axis to form the arrays against the substrate. The presence of IL was found vital for the formation of rutile nanorods, and the suitable molar ratio of [Bmim]Br to TiCl{sub 4} ranged from 500:1 to 1500:1. The excessive [Bmim]Br may hinder the precipitation of rutile particles. - Graphical abstract: The rutile film consisting of rectangular nanorods is successfully deposited on glass substrate in presence of ionic liquid (IL) of [Bmim]Br. The nanorods were rectangular with width of 100-200 nm and length of more than 1 {mu}m, which grew up typically along c-axis to form the arrays against the substrate.

  13. Direct monitoring of opto-mechanical switching of self-assembled monolayer films containing the azobenzene group

    PubMed Central

    Tirosh, Einat; Benassi, Enrico; Pipolo, Silvio; Mayor, Marcel; Valášek, Michal; Frydman, Veronica

    2011-01-01

    Summary The potential for manipulation and control inherent in molecule-based motors holds great scientific and technological promise. Molecules containing the azobenzene group have been heavily studied in this context. While the effects of the cis–trans isomerization of the azo group in such molecules have been examined macroscopically by a number of techniques, modulations of the elastic modulus upon isomerization in self-assembled films were not yet measured directly. Here, we examine the mechanical response upon optical switching of bis[(1,1'-biphenyl)-4-yl]diazene organized in a self-assembled film on Au islands, using atomic force microscopy. Analysis of higher harmonics by means of a torsional harmonic cantilever allowed real-time extraction of mechanical data. Quantitative analysis of elastic modulus maps obtained simultaneously with topographic images show that the modulus of the cis-form is approximately twice that of the trans-isomer. Quantum mechanical and molecular dynamics studies show good agreement with this experimental result, and indicate that the stiffer response in the cis-form comprises contributions both from the individual molecular bonds and from intermolecular interactions in the film. These results demonstrate the power and insights gained from cutting-edge AFM technologies, and advanced computational methods. PMID:22259768

  14. The breakdown of superlubricity by driving-induced commensurate dislocations

    PubMed Central

    Benassi, A.; Ma, Ming; Urbakh, M.; Vanossi, A.

    2015-01-01

    In the framework of a Frenkel-Kontorova-like model, we address the robustness of the superlubricity phenomenon in an edge-driven system at large scales, highlighting the dynamical mechanisms leading to its failure due to the slider elasticity. The results of the numerical simulations perfectly match the length critical size derived from a parameter-free analytical model. By considering different driving and commensurability interface configurations, we explore the distinctive nature of the transition from superlubric to high-friction sliding states which occurs above the critical size, discovering the occurrence of previously undetected multiple dissipative jumps in the friction force as a function of the slider length. These driving-induced commensurate dislocations in the slider are then characterized in relation to their spatial localization and width, depending on the system parameters. Setting the ground to scale superlubricity up, this investigation provides a novel perspective on friction and nanomanipulation experiments and can serve as a theoretical basis for designing high-tech devices with specific superlow frictional features. PMID:26553308

  15. Multiferroicity Broken by Commensurate Magnetic Ordering in Terbium Orthomanganite.

    PubMed

    Zhang, Hao; Flacau, Roxana; Du, Xin; Manuel, Pascal; Cong, Junzhuang; Sun, Young; Sun, Junliang; Yang, Sihai; Li, Guobao; Liao, Fuhui; Lin, Jianhua

    2016-04-18

    TbMnO3 is an important multiferroic material with strong coupling between magnetic and ferroelectric orderings. Incommensurate magnetic ordering is suggested to be vital for this coupling in TbMnO3 , which can be modified by doping at the site of Tb and/or Mn. Our study shows that a self-doped solid solution Tb1-x Mny MnO3 (y≤x) can be formed with Mn doped into the site of Tb of TbMnO3 . When y is small Tb1-x Mny MnO3 shows both ferroelectric and incommensurate magnetic orders at low temperature, which is similar to TbMnO3 . However, if y is large enough, a commensurate antiferromagnetic ordering appears along with the incommensurate magnetic ordering to prevent the appearance of multiferroicity in Tb1-x Mny MnO3 . That is to say, the magnetoeletric coupling can be broken by the co-existence of a commensurate antiferromagnetic ordering. This finding may be useful to the study of TbMnO3 . PMID:26833883

  16. Phase Transitions in Dipalmitoylphosphatidylcholine Monolayers.

    PubMed

    Zuo, Yi Y; Chen, Rimei; Wang, Xianju; Yang, Jinlong; Policova, Zdenka; Neumann, A Wilhelm

    2016-08-23

    A self-assembled phospholipid monolayer at an air-water interface is a well-defined model system for studying surface thermodynamics, membrane biophysics, thin-film materials, and colloidal soft matter. Here we report a study of two-dimensional phase transitions in the dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface using a newly developed methodology called constrained drop surfactometry (CDS). CDS is superior to the classical Langmuir balance in its capacity for rigorous temperature control and leak-proof environments, thus making it an ideal alternative to the Langmuir balance for studying lipid polymorphism. In addition, we have developed a novel Langmuir-Blodgett (LB) transfer technique that allows the direct transfer of lipid monolayers from the droplet surface under well-controlled conditions. This LB transfer technique permits the direct visualization of phase coexistence in the DPPC monolayer. With these technological advances, we found that the two-dimensional phase behavior of the DPPC monolayer is analogous to the three-dimensional phase transition of a pure substance. This study has implications in the fundamental understanding of surface thermodynamics as well as applications such as self-assembled monolayers and pulmonary surfactant biophysics. PMID:27479299

  17. Interface effects and deposition process of ionically self-assembled monolayer films: In situ and ex situ second harmonic generation measurements

    NASA Astrophysics Data System (ADS)

    Brands, Charles

    2003-07-01

    In this thesis, detailed studies are presented into self-assembled, noncentrosymmetric, optically active films. Second harmonic generation (SHG) is used to measure the second order nonlinear optical susceptibility (chi(2)) of ionically self-assembled monolayer (ISAM) thin films. Conventional ISAM films are fabricated by alternately immersing a substrate into oppositely-charged polyelectrolyte solutions. The polyelectrolytes bind electrostatically to the oppositely-charged substrate, and thus reverse the charge of the substrate. The charge reversal limits the amount of adsorbed material and primes the substrate for the next layer. During the deposition of the nonlinear optical (NLO) active layer, the chromophores are attracted to the oppositely-charged surface, which results in net orientation of the chromophores. Some of the net orientation is lost during the deposition of the next NLO-inactive layer as this layer orients some of the chromophores away from the substrate. A disadvantage of the polymer ISAM deposition method is that although there is a net orientation toward the substrate, a large number of chromophores are randomly or oppositely oriented. This reduces the nonlinear optical response. To overcome this problem, two alternative methods with a better net orientation are discussed: hybrid covalent/ionic deposition and multivalent monomer deposition. In both deposition methods, the NLO-active material is a monomer instead of a polymer. In hybrid covalent/ionic deposition, the NLO-inactive polymer is deposited using electrostatic attraction while the NLO-active monomer is deposited covalently. This forces alignment of the chromophores. The multivalent method uses chromophores with multiple charges on one side of the molecule and one charge (same sign) on the other. The difference in electrostatic attraction causes a preferential orientation of the chromophores during deposition. Attempts have been made to further improve the net orientation by complexation

  18. On the relationship between the structure of self-assembled carboxylic acid monolayers on alumina and the organization and electrical properties of a pentacene thin film

    NASA Astrophysics Data System (ADS)

    Lang, Philippe; Mottaghi, Daniel; Lacaze, Pierre-Camille

    2016-03-01

    The modification of insulating surfaces by self-assembled monolayers (SAMs) is an elegant way of tailoring the gate dielectric of organic field effect transistors (OFET) to pentacene and is commonly used to improve electrical performance. A SAM based on an alkylcarboxylic acid deposited on a thin layer of alumina, serving as the gate dielectric is considered. The relationship between carrier mobility and (i) the length of the carboxylic acid (CH3(CH2)nCOOH; n = 9, 14, 18), (ii) substrate preparation and (iii) the SAM and pentacene thin film structures is considered. The size and boundaries of pentacene grains are not limiting factors for carrier mobility, and the most relevant parameter, which depends on whether there is a SAM or not, is the organization of the first pentacene layers in contact with the gate dielectric. The variation of the interplanar distance d(0 0 1) of the pentacene layers close to the alumina surface is much greater without SAM than with, and this could explain the lower carrier mobility observed in the case of a bare alumina dielectric. The relationship between the disorder associated with this variation and mobility is discussed.

  19. Hierarchy of fillings for the FQHE in monolayer graphene

    NASA Astrophysics Data System (ADS)

    Łydżba, Patrycja; Jacak, Lucjan; Jacak, Janusz

    2015-09-01

    In this paper, the commensurability conditions, which originated from the unique topology of two-dimensional systems, are applied to determine the quantum Hall effect hierarchy in the case of a monolayer graphene. The fundamental difference in a definition of a typical semiconductor and a monolayer graphene filling factor is pointed out. The calculations are undertaken for all spin-valley branches of two lowest Landau levels, since only they are currently experimentally accessible. The obtained filling factors are compared with the experimental data and a very good agreement is achieved. The work also introduces a concept of the single-loop fractional quantum Hall effect.

  20. Hierarchy of fillings for the FQHE in monolayer graphene

    PubMed Central

    Łydżba, Patrycja; Jacak, Lucjan; Jacak, Janusz

    2015-01-01

    In this paper, the commensurability conditions, which originated from the unique topology of two-dimensional systems, are applied to determine the quantum Hall effect hierarchy in the case of a monolayer graphene. The fundamental difference in a definition of a typical semiconductor and a monolayer graphene filling factor is pointed out. The calculations are undertaken for all spin-valley branches of two lowest Landau levels, since only they are currently experimentally accessible. The obtained filling factors are compared with the experimental data and a very good agreement is achieved. The work also introduces a concept of the single-loop fractional quantum Hall effect. PMID:26392385

  1. Morphological transitions in polymer monolayers under compression.

    PubMed

    Srivastava, S; Basu, J K; Sprung, M; Wang, J

    2009-05-01

    We present a systematic investigation of morphological transitions in poly vinylacetate Langmuir monolayers. On compression, the polymer monolayer is converted to a continuous membrane with a thickness of approximately 2-3 nm. Above a certain surface concentration the monolayer, on water, undergoes a morphological transition-buckling, leading to formation of striped patterns of period of lambda(b) approximately 160 nm, as determined from in situ grazing incidence small angle x-ray scattering measurements. The obtained value is much smaller than what has been typically observed for Langmuir monolayers on water or thin films on soft substrates. Using existing theories for buckling of fluidlike films on fluid substrates, we obtain very low values of bending rigidity and Young's modulus of the polymer monolayer compared to that observed earlier for lipid or polymeric monolayers. Since buckling in these monolayers occurs only above a certain surface concentration, we have looked at the possibility that the buckling in these films occurs due to changes in their mechanical properties under compression. Using the model of Huang and Suo of buckling of solidlike films on viscoelastic substrates, we find values of the mechanical properties, which are much closer to the bulk values but still significantly lower. Although the reduction could be along the lines of what has been observed earlier for ultrathin polymer film or surface layers of polymers, the possibility of micromechanical effects also determining the buckling in such polymer monolayers cannot be ruled out. We have provided possible explanation of the buckling of the poly vinylacetate monolayers in terms of the change in isothermal compression modulus with surface concentration. PMID:19425809

  2. Thermodynamic study of argon films adsorbed on boron nitride

    SciTech Connect

    Migone, A.D.; Alkhafaji, M.T. ); Vidali, G. ); Karimi, M. )

    1993-03-15

    We have performed a detailed adsorption isotherm study of Ar on BN for temperatures between 65 and 80 K. The isothermal compressibility of the films was obtained from adsorption data. At monolayer coverages, a small isotherm substep is present at melting. We found two isothermal compressibility peaks in the first layer: a sharp peak, corresponding to the melting substep, and a smaller, broader peak that occurs at lower pressures. At multilayer coverages we found reentrant layering occurring in the third and fourth layers of the film. We compare our layering results with predictions for the preroughening transition. We also found a series of small steps in the isotherms between the second and third layers and between the third and fourth layers of the film. These small steps are evidence of individual layer melting for the second and third layers. Our results at monolayer and at multilayer coverages are extensively compared to those found for Ar on graphite. We have also performed calculations of the rare-gas--BN interaction potentials. Our calculations indicate the substrate corrugation is smaller for the rare-gas--BN systems than it is for the same rare gases on graphite. The implications of this result for the possible existence of monolayer-commensurate solids on BN are discussed.

  3. Monolayer graphene from a green solid precursor

    NASA Astrophysics Data System (ADS)

    Kalita, Golap; Wakita, Koichi; Umeno, Masayoshi

    2011-06-01

    Monolayer and bilayer graphene sheets are synthesized by simple control pyrolysis of solid botanical derivative camphor (C 10H 16O), a green and renewable carbon source. Raman studies show much intense 2D peak than that of G peak, signifying presence of monolayer graphene. Transmission electron microscopic study shows predominately monolayer or bilayer graphene sheets, while trilayer graphene sheet were also observed. Synthesized graphene film on copper foil is transferred to poly(ethylene terephthalate) substrate to fabricate transparent electrode. Electrical and optical measurement shows a sheet resistance of 860 Ω/sq with a transmittance of 91% at 550 nm wavelength of the graphene film. The technique to fabricate monolayer or bilayer graphene based film from camphor is both viable and scalable for potential large area electronic applications.

  4. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-12-01

    Goal of this research program is to create ultrathin organic membranes that possess uniform and adjustable pores ( < 7[angstrom] diameter). Such membranes are expected to possess high permeation selectivity (permselectivity) and high permeability, and to provide the basis for energy-efficient methods of molecular separation. Work carried out has demonstrated feasibility of using perforated monolayer''-based composites as molecular sieve membranes. Specifically, composite membranes derived from Langmuir-Blodgett multilayers of the calix[6]arene-based surfactant shown below plus poly[l-(trimethylsilyl)-l-propyne] (PTMSP) were found to exhibit sieving behavior towards He, N[sub 2] and SF[sub 6]. Results of derivative studies that have also been completed are also described in this report.

  5. Simultaneous Modification of Bottom-Contact Electrode and Dielectric Surfaces for Organic Thin-Film Transistors Through Single-Component Spin-Cast Monolayers

    SciTech Connect

    O Acton; M Dubey; t Weidner; K OMalley; T Kim; G Ting; D Hutchins; J Baio; T Lovejoy; et al.

    2011-12-31

    An efficient process is developed by spin-coating a single-component, self-assembled monolayer (SAM) to simultaneously modify the bottom-contact electrode and dielectric surfaces of organic thin-film transistors (OTFTs). This efficient interface modification is achieved using n-alkyl phosphonic acid based SAMs to prime silver bottom-contacts and hafnium oxide (HfO{sub 2}) dielectrics in low-voltage OTFTs. Surface characterization using near edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well-defined phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n-channel (C60) and p-channel (pentacene) based OTFTs. Specifically, SAMs of n-octylphos-phonic acid (OPA) provide both low-contact resistance at the bottom-contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO{sub 2} dielectric bottom-contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm-cm), low subthreshold swing (as low as 75 mV dec{sup -1}), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm{sup 2} V{sup -1} s{sup -1}, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom-contact OTFTs.

  6. Structure and Phase Transitions of Monolayers of Intermediate-length n-alkanes on Graphite Studied by Neutron Diffraction and Molecular Dynamics Simulation

    SciTech Connect

    Taub, H.; Hansen, F.Y.; Diama, Amand; Matthies, Blake; Criswell, Leah; Mo, Haiding; Bai, M; Herwig, Kenneth W

    2009-01-01

    We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C(24)H(50) denoted as C24) and dotriacontane (n-C(32)H(66) denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 A=sqrt[3a(g)], where a(g)=2.46 A is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a 'smectic' phase in which the inter-row spacing within a lamella expands by approximately 10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously.

  7. Molecular orientation of copper phthalocyanine thin films on different monolayers of fullerene on SiO{sub 2} or highly oriented pyrolytic graphite

    SciTech Connect

    Wang, Chenggong; Wang, Congcong; Liu, Xiaoliang; Xu, Xumei; Li, Youzhen; Xie, Fangyan; Gao, Yongli

    2015-03-23

    The interface electronic structures of copper phthalocyanine (CuPc) have been studied using ultraviolet photoemission spectroscopy as different monolayers of C{sub 60} were inserted between CuPc and a SiO{sub 2} or highly ordered pyrolytic graphite (HOPG) substrate. The results show that CuPc has standing up configuration with one monolayer of C{sub 60} insertion on SiO{sub 2} while lying down on HOPG, indicating that the insertion layer propagates the CuPc-substrate interaction. Meanwhile, CuPc on more than one monolayers of C{sub 60} on different substrates show that the substrate orientation effect quickly vanished. Our study elucidates intriguing molecular interactions that manipulate molecular orientation and donor-acceptor energy level alignment.

  8. A conformation and orientation model of the carboxylic group of fatty acids dependent on chain length in a Langmuir monolayer film studied by polarization-modulation infrared reflection absorption spectroscopy.

    PubMed

    Muro, Maiko; Itoh, Yuki; Hasegawa, Takeshi

    2010-09-01

    The conformation of the carboxylic group of fatty acids in a Langmuir (L) monolayer film on water is described in relation to the aggregation property of the hydrocarbon chain. Polarization-modulation infrared reflection absorption spectra (PM-IRRAS) of L films of heptadecanoic acid (C(17)), octadecanoic acid (C(18)), and nonadecanoic acid (C(19)) exhibit systematic spectral changes in both the C-H and C=O stretching vibration regions. Through a stabilization analysis of the L films at a high surface pressure, the C(19) L film has been found outstandingly stable exhibiting no film shrink, while the other two compounds exhibit a large shrink at high surface pressure. By taking into account the uniquely high aggregation property of the hydrocarbon chains of C(19), the three major bands arising from the C=O stretching vibration mode propose three types of molecular conformations about the carboxylic group, which are elucidated by a balance of the hydration of the carboxylic group, the chain length of the hydrocarbon chain, and the surface pressure. PMID:20718412

  9. Monolayer hexagonal boron nitride films with large domain size and clean interface for enhancing the mobility of graphene-based field-effect transistors.

    PubMed

    Wang, Lifeng; Wu, Bin; Chen, Jisi; Liu, Hongtao; Hu, Pingan; Liu, Yunqi

    2014-03-12

    Viable and general techniques that allow effective size control of triangular-shaped, single-crystal, monolayer h-BN domains grown by the CVD method, direct optical visualization of h-BN domains, and the cleaning of the h-BN surface to achieve reliable graphene device quality are reported for the first time. This study points to a critical role of the interfacial properties between the graphene and the monolayer h-BN in determining reliable, enhanced graphene-device performance. PMID:24343959

  10. Investigation of a Langmuir Film Using a Current-Measuring Technique: Influence of the Behavior of Monolayers at the Edge of the LB Trough

    NASA Astrophysics Data System (ADS)

    Iwamoto, Mitsumasa; Majima, Yutaka

    1989-10-01

    Using a current-measuring technique, we investigated the abrupt change of a current observed at the liquid-to-solid phase transition in a current-area (I-A) isotherm of a fatty acid monolayer at the air/water interface. The change occurred when an electrode suspended in air was not electrically shielded. It was found both experimentally and theoretically that the behavior of the monolayer at the edge of the trough plays a very important role in the abrupt change described above.

  11. Commensurability condition and fractional quantum Hall effect hierarchy in higher Landau levels

    NASA Astrophysics Data System (ADS)

    Jacak, J.; Jacak, L.

    2015-07-01

    The odd structure of the fractional filling hierarchy, which is referred to as the fractional quantum Hall effect, is studied in higher Landau levels using the commensurability condition. The hierarchy of fillings that are derived in this manner is consistent with the experimental observations in the first three Landau levels. The relative poverty of the fractional structure in higher Landau levels compared with the lowest Landau level is explained using commensurability topological arguments. The commensurability criterion for correlated states specific for higher Landau levels (with n ≥ 1), including also the paired states at half fillings of the spinsubbands of these levels, is formulated.

  12. Molecular self-assembly guided by surface reconstruction: CH 3SH monolayer on the Au(1 1 1) surface

    NASA Astrophysics Data System (ADS)

    Maksymovych, Peter; Dougherty, Daniel B.

    2008-06-01

    Self-assembly of methanethiol (CH 3SH) on Au(1 1 1) was studied using scanning tunneling microscopy at T < 150 K when the S-H bond is intact. The CH 3SH monolayer assumes a commensurate structure with a

  13. Characterization of organosulfur monolayer formation at gold electrodes

    SciTech Connect

    Tani Woods, N.

    1996-08-01

    Among the many types of organic films, covalently-attached organosulfur monolayers have attracted a great deal of attention. The authors have focused their interest on the fundamental characterization of spontaneously adsorbed organosulfur monolayers. An introductory chapter presents general aspects of monolayer preparation and characterization, followed by a few examples that illustrate the range of applications of these films. This thesis contains two papers. In the first paper, three analogous monolayer precursors are studied to determine their similarities and differences in the monolayer structure. A GC-MS analysis of products form the chemisorption process and open circuit potential measurements are used to derive possible mechanisms behind monolayer formation. The second paper focuses on monolayers formed from thioctic acid, including its characterization and application to cytochrome c electrochemistry. Although thiols and disulfides have been extensively studied as monolayer precursors, thioctic acid is particularly interesting because the disulfide functionality of this asymmetric molecule is contained in a strained five-membered ring. Given the ring strain, steric bulk and asymmetry of the molecule, the study of these monolayers lend insight into the factors important for the formation of organosulfur monolayers. This thesis concludes with a general summary and directions for future studies. 40 refs.

  14. Optical spectroscopy of organic semiconductor monolayers

    NASA Astrophysics Data System (ADS)

    He, Rui; Tassi, Nancy G.; Blanchet, Graciela B.; Pinczuk, Aron

    2011-02-01

    Growing interest in organic molecular semiconductors is stimulated by their promising applications in flexible devices. Pentacene is a benchmark organic semiconductor material because of its potential applications in high mobility thin film transistors and optoelectronic devices. Highly uniform monolayers of pentacene grown on polymeric substrate of poly alpha-methylstyrene exhibit sharp and intense free exciton (FE) luminescence at low temperatures. The FE emission displays characteristic intensity that grows quadratically with the number of layers. Large enhancements of Raman scattering intensities at the FE resonance enable the first observations of low-lying lattice vibrational modes in films reaching the single monolayer level. The low-lying modes exhibit characteristic changes when going from a single monolayer to two layers, revealing that a phase akin to a thin film phase of pentacene already emerges in structures of only two monolayers. A simple analysis of mode splittings offers estimates of the strength of inter-layer interactions. The results demonstrate novel venues for ultra-thin film characterization and studies of interface effects in organic molecular semiconductor structures.

  15. Optical spectroscopy of organic semiconductor monolayers

    NASA Astrophysics Data System (ADS)

    He, Rui; Tassi, Nancy G.; Blanchet, Graciela B.; Pinczuk, Aron

    2010-10-01

    Growing interest in organic molecular semiconductors is stimulated by their promising applications in flexible devices. Pentacene is a benchmark organic semiconductor material because of its potential applications in high mobility thin film transistors and optoelectronic devices. Highly uniform monolayers of pentacene grown on polymeric substrate of poly alpha-methylstyrene exhibit sharp and intense free exciton (FE) luminescence at low temperatures. The FE emission displays characteristic intensity that grows quadratically with the number of layers. Large enhancements of Raman scattering intensities at the FE resonance enable the first observations of low-lying lattice vibrational modes in films reaching the single monolayer level. The low-lying modes exhibit characteristic changes when going from a single monolayer to two layers, revealing that a phase akin to a thin film phase of pentacene already emerges in structures of only two monolayers. A simple analysis of mode splittings offers estimates of the strength of inter-layer interactions. The results demonstrate novel venues for ultra-thin film characterization and studies of interface effects in organic molecular semiconductor structures.

  16. Structural Development of Mercaptophenol Self-Assembled Monolayers And the Overlying Mineral Phase During Templated CaCo(3) Crystallization From a Transient Amorphous Film

    SciTech Connect

    Lee, J.R.I.; Han, T.Y.-J.; Willey, T.M.; Wang, D.; Meulenberg, R.W.; Nilsson, J.; Dove, P.M.; Terminello, L.J.; Buuren, T.van; Yoreo, J.J.De

    2009-06-01

    Formation of biomineral structures is increasingly attributed to directed growth of a mineral phase from an amorphous precursor on an organic matrix. While many in vitro studies have used calcite formation on organothiol self-assembled monolayers (SAMs) as a model system to investigate this process, they have generally focused on the stability of amorphous calcium carbonate (ACC) or maximizing control over the order of the final mineral phase. Little is known about the early stages of mineral formation, particularly the structural evolution of the SAM and mineral. Here we use near-edge X-ray absorption spectroscopy (NEXAFS), photoemission spectroscopy (PES), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to address this gap in knowledge by examining the changes in order and bonding of mercaptophenol (MP) SAMs on Au(111) during the initial stages of mineral formation as well as the mechanism of ACC to calcite transformation during template-directed crystallization. We demonstrate that formation of ACC on the MP SAMs brings about a profound change in the morphology of the monolayers: although the as-prepared MP SAMs are composed of monomers with well-defined orientations, precipitation of the amorphous mineral phase results in substantial structural disorder within the monolayers. Significantly, a preferential face of nucleation is observed for crystallization of calcite from ACC on the SAM surfaces despite this static disorder.

  17. Electrosorbed carbon monoxide monolayers on Pt(111).

    SciTech Connect

    Chang, K.-C.; Menzel, A.; Komanicky, V.; You, H.; Materials Science Division; Paul Scherrer Inst.; Slovakia Sci. Acad. Sci.

    2007-05-10

    We review structures of high-density CO monolayers on Pt(1 1 1) surfaces in CO-saturated electrolytes or in gaseous CO at near atmospheric pressure, using surface X-ray scattering (SXS) and scanning tunneling microscopy (STM). In electrolytes, we confirmed the well-known (2 x 2)-3CO and ({radical}19 x {radical}19)-13CO structures and were able to study the transition between them. For gas-phase studies, we were able to stabilize extremely well-ordered CO monolayers by emersion transfer from an electrochemical cell. We found that the hexagonal close-packed (2 x 2)-3CO structure is the equilibrium phase at room temperature in {approx}1 atm CO gas pressure. This commensurate (C) phase transforms continuously to an incommensurate (IC) phase at elevated temperature (a second-order phase transition). We also confirm that the ({radical}19 x {radical}19)-13CO structure is stable at lower CO partial pressure. This C phase transforms discontinuously to an IC phase (a first-order phase transition). A tentative phase diagram and a brief review of structure details of the (2 x 2)-3CO and ({radical}19 x {radical}19)-13CO phases will be presented.

  18. Atomic scattering from an adsorbed monolayer solid with a helium beam that penetrates to the substrate

    SciTech Connect

    Hansen, F. Y.; Bruch, L. W.; Dammann, B.

    2013-03-14

    Diffraction and one-phonon inelastic scattering of a thermal energy helium atomic beam are evaluated in the situation that the target monolayer lattice is so dilated that the atomic beam penetrates to the interlayer region between the monolayer and the substrate. The scattering is simulated by propagating a wavepacket and including the effect of a feedback of the inelastic wave onto the diffracted wave, which represents a coherent re-absorption of the created phonons. Parameters are chosen to be representative of an observed p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/NaCl(001) and a conjectured p(1 Multiplication-Sign 1) commensurate monolayer solid of H{sub 2}/KCl(001). For the latter, there are cases where part of the incident beam is trapped in the interlayer region for times exceeding 50 ps, depending on the spacing between the monolayer and the substrate and on the angle of incidence. The feedback effect is large for cases of strong transient trapping.

  19. Optical emission and vibrational modes of uniform pentacene monolayers (*)

    NASA Astrophysics Data System (ADS)

    He, Rui; Tassi, Nancy; Blanchet, Graciela; Pinczuk, Aron

    2006-03-01

    Pentacene monolayers are probed by photoluminescence and resonant Raman spectroscopies below 10K. Monolayers grown on polymeric substrate of poly-alpha-methyl-styrene (PAMS) exhibit high uniformity within micron size clusters. These films show sharp exciton luminescence bands, and the energy of the exciton optical emission displays a red-shift as the average film thickness increases. The large resonance enhancements of Raman scattering intensities enable the measurements of low-lying (40- 200cm-1) optical lattice vibrations from these monolayers. These experiments demonstrate that luminescence and resonant Raman scattering from single pentacene monolayers are venues for probing 2D properties, studies of interface effects, and thin film characterization. (*) Supported primarily by the Nanoscale Science and Engineering Initiative of the National Science Foundation under NSF Award No. CHE-0117752 and by the New York State Office of Science, Technology, and Academic Research (NYSTAR), and by a research grant of the W. M. Keck Foundation.

  20. Electromagnetic interference shielding effectiveness of monolayer graphene.

    PubMed

    Hong, Seul Ki; Kim, Ki Yeong; Kim, Taek Yong; Kim, Jong Hoon; Park, Seong Wook; Kim, Joung Ho; Cho, Byung Jin

    2012-11-16

    We report the first experimental results on the electromagnetic interference (EMI) shielding effectiveness (SE) of monolayer graphene. The monolayer CVD graphene has an average SE value of 2.27 dB, corresponding to ~40% shielding of incident waves. CVD graphene shows more than seven times (in terms of dB) greater SE than gold film. The dominant mechanism is absorption rather than reflection, and the portion of absorption decreases with an increase in the number of graphene layers. Our modeling work shows that plane-wave theory for metal shielding is also applicable to graphene. The model predicts that ideal monolayer graphene can shield as much as 97.8% of EMI. This suggests the feasibility of manufacturing an ultrathin, transparent, and flexible EMI shield by single or few-layer graphene. PMID:23085718

  1. Light-Modulation of the Charge Injection in a Polymer Thin-Film Transistor by Functionalizing the Electrodes with Bistable Photochromic Self-Assembled Monolayers.

    PubMed

    Mosciatti, Thomas; Del Rosso, Maria G; Herder, Martin; Frisch, Johannes; Koch, Norbert; Hecht, Stefan; Orgiu, Emanuele; Samorì, Paolo

    2016-08-01

    High fatigue resistance, bistability, and drastic property changes among isomers allow efficient modulation of the current output of organic thin-film transistors (OTFTs) to be obtained by a photogating of the charge-injection mechanism. PMID:27184349

  2. Methods of making monolayers

    DOEpatents

    Alford, Kentin L.; Simmons, Kevin L.; Samuels, William D.; Zemanian, Thomas S.; Liu, Jun; Shin, Yongsoon; Fryxell, Glen E.

    2009-09-15

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  3. Methods of making monolayers

    DOEpatents

    Alford, Kentin L.; Simmons, Kevin L.; Samuels, William D.; Zemanian, Thomas S.; Liu, Jun; Shin, Yongsoon; Fryxell, Glen E.

    2009-12-08

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  4. Psychometric Approaches for Developing Commensurate Measures across Independent Studies: Traditional and New Models

    ERIC Educational Resources Information Center

    Bauer, Daniel J.; Hussong, Andrea M.

    2009-01-01

    When conducting an integrative analysis of data obtained from multiple independent studies, a fundamental problem is to establish commensurate measures for the constructs of interest. Fortunately, procedures for evaluating and establishing measurement equivalence across samples are well developed for the linear factor model and commonly used item…

  5. Reduction of interfacial friction in commensurate graphene/h-BN heterostructures by surface functionalization.

    PubMed

    Guo, Yufeng; Qiu, Jiapeng; Guo, Wanlin

    2016-01-01

    The reduction of interfacial friction in commensurately stacked two-dimensional layered materials is important for their application in nanoelectromechanical systems. Our first-principles calculations on the sliding energy corrugation and friction at the interfaces of commensurate fluorinated-graphene/h-BN and oxidized-graphene/h-BN heterostructures show that the sliding energy barriers and shear strengths for these heterostructures are approximately decreased to 50% of those of commensurate graphene/h-BN. The adsorbed F and O atoms significantly suppress the interlayer electrostatic and van der Waals energy corrugations by modifying the geometry and charge redistribution of the graphene layers. Our empirical registry index models further reveal the difference between the roles of the F and O atoms in affecting the sliding energy landscapes, and are also utilized to predict the interlayer superlubricity in a large-scale oxidized-graphene/h-BN system. Surface functionalization is a valid way to control and reduce the interlayer friction in commensurate graphene/h-BN heterostructures. PMID:26645099

  6. Commensurate and incommensurate spin-density waves in heavy electron systems

    NASA Astrophysics Data System (ADS)

    Schlottmann, P.

    2016-05-01

    The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point (QCP) is obtained as the Néel temperature tends to zero. The transfer of pairs of electrons between the pockets can lead to a superconducting dome above the QCP (if Q is commensurate with the lattice, i.e. equal to G/2). If the vector Q is not commensurate with the lattice there are eight possible phases: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with modulated order parameter of the FFLO type. The renormalization group equations are studied and numerically integrated. A re-entrant SDW phase (either commensurate or incommensurate) is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of |Q - G/2|.

  7. Epitaxial two dimensional aluminum films on silicon (111) by ultra-fast thermal deposition

    SciTech Connect

    Levine, Igal; Li Wenjie; Vilan, Ayelet; Yoffe, Alexander; Feldman, Yishay; Salomon, Adi

    2012-06-15

    Aluminum thin films are known for their extremely rough surface, which is detrimental for applications such as molecular electronics and photonics, where protrusions cause electrical shorts or strong scattering. We achieved atomically flat Al films using a highly non-equilibrium approach. Ultra-fast thermal deposition (UFTD), at rates >10 nm/s, yields RMS roughness of 0.4 to 0.8 nm for 30-50 nm thick Al films on variety of substrates. For UFTD on Si(111) substrates, the top surface follows closely the substrate topography (etch pits), indicating a 2D, layer-by-layer growth. The Al film is a mixture of (100) and (111) grains, where the latter are commensurate with the in-plane orientation of the underlying Si (epitaxy). We show the use of these ultra-smooth Al films for highly reproducible charge-transport measurements across a monolayer of alkyl phosphonic acid as well as for plasmonics applications by directly patterning them by focused ion beam to form a long-range ordered array of holes. UFTD is a one-step process, with no need for annealing, peeling, or primer layers. It is conceptually opposite to high quality deposition methods, such as MBE or ALD, which are slow and near-equilibrium processes. For Al, though, we find that limited diffusion length (and good wetting) is critical for achieving ultra-smooth thin films.

  8. Optical modeling of the plasmon band of monolayer-protected nanometal clusters in pure and in polymer matrix thin films as a function of heat treatment

    NASA Astrophysics Data System (ADS)

    Sivaramakrishnan, Sankaran; Anto, Bibin T.; Ho, Peter K.-H.

    2009-03-01

    The plasmon band shape of thin films of gold nanoparticles and their composites can be quantitatively modeled in a surprisingly simple way by taking into account (i) quantum-size effect of the Au core on its permittivity, (ii) nanostructure effect of the core shell and matrix on the effective medium, and (iii) optical properties of thin films in a transfer-matrix formalism. From the excellent agreement achieved with the optical spectra of these films, neat and when dispersed in poly(3,4-ethylenedioxythiophene) matrices, details of the nanocrystal relaxation, desorption of the ligand shell, and ultimate surface melting and core-core coalescence to give percolating conductive paths during heat treatment were extracted.

  9. Modern approaches to investigation of thin films and monolayers: X-ray reflectivity, grazing-incidence X-ray scattering and X-ray standing waves

    NASA Astrophysics Data System (ADS)

    Shcherbina, M. A.; Chvalun, S. N.; Ponomarenko, S. A.; Kovalchuk, M. V.

    2014-12-01

    The review concerns modern experimental methods of structure determination of thin films of different nature. The methods are based on total reflection of X-rays from the surface and include X-ray reflectivity, grazing-incidence X-ray scattering and X-ray standing waves. Their potential is exemplified by the investigations of various organic macromolecular systems that exhibit the properties of semiconductors and are thought to be promising as thin-film transistors, light-emitting diodes and photovoltaic cells. It is shown that combination of the title methods enable high-precision investigations of the structure of thin-film materials and structure formation in them, i.e., it is possible to obtain information necessary for improvement of the operating efficiency of elements of organic electronic devices. The bibliography includes 92 references.

  10. Metastability of a Supercompressed Fluid Monolayer

    PubMed Central

    Smith, Ethan C.; Crane, Jonathan M.; Laderas, Ted G.; Hall, Stephen B.

    2003-01-01

    Previous studies showed that monomolecular films of extracted calf surfactant collapse at the equilibrium spreading pressure during quasi-static compressions but become metastable at much higher surface pressures when compressed faster than a threshold rate. To determine the mechanism by which the films become metastable, we studied single-component films of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC). Initial experiments confirmed similar metastability of POPC if compressed above a threshold rate. Measurements at different surface pressures then showed that rates of collapse, although initially increasing above the equilibrium spreading pressure, reached a sharply defined maximum and then slowed considerably. When heated, rapidly compressed films recovered their ability to collapse with no discontinuous change in area, arguing that the metastability does not reflect transition of the POPC film to a new phase. These observations indicate that in several respects, the supercompression of POPC monolayers resembles the supercooling of three-dimensional liquids toward a glass transition. PMID:14581205

  11. Monolayer Tungsten Disulfide Laser

    NASA Astrophysics Data System (ADS)

    Ye, Yu; Wong, Zi Jing; Lu, Xiufang; Ni, Xingjie; Zhu, Hanyu; Chen, Xianhui; Wang, Yuan; Zhang, Xiang

    Two-dimensional van der Waals materials have opened a new paradigm for fundamental physics exploration and device applications because of their emerging physical properties. Unlike gapless graphene, monolayer transition-metal dichalcogenides are two-dimensional semiconductors that undergo an indirect-to-direct band gap transition, creating new optical functionalities for next-generation ultra-compact photonics and optoelectronics. Here, we report the realization of a two-dimensional excitonic laser by embedding monolayer tungsten disulfide in a microdisk resonator.

  12. Ionization of covalent immobilized poly(4-vinylphenol) monolayers measured by ellipsometry, QCM and SPR

    PubMed Central

    Uppalapati, Suji; Kong, Na; Norberg, Oscar; Ramström, Olof; Yan, Mingdi

    2015-01-01

    Covalently immobilized poly(4-vinylphenol) (PVP) monolayer films were fabricated by spin coating PVP on perfluorophenyl azide (PFPA)-functionalized surface followed by UV irradiation. The pH-responsive behavior of these PVP ultrathin films was evaluated by ellipsometry, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). By monitoring the responses of these films to pH in situ, the ionization constant of the monolayer thin films was obtained. The apparent pKa value of these covalently immobilized PVP monolayers, 13.4 by SPR, was 3 units higher than that of the free polymer in aqueous solution. PMID:26097271

  13. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2012-04-10

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  14. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2013-10-29

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  15. Young's modulus of a solid two-dimensional Langmuir monolayer

    NASA Astrophysics Data System (ADS)

    Bercegol, H.; Meunier, J.

    1992-03-01

    LANGMUIR monolayers-films of amphiphilic molecules at the surface of water-exhibit many phases1,2. Some of these behave like two-dimensional solids on experimental timescales, but previous measurements of the shear modulus of these 'solid' monolayers3-5 have yielded a value too small to be compatible with a two-dimensional crystal. The interpretation of these is complicated, however, by the likelihood of inhomogeneities in the films, which are probably assemblies of microscopic crystalline domains. Here we describe measurements of the Young's modulus of an isolated "solid' domain of NBD-stearic acid monolayers. We obtain a value large enough to be compatible with the modulus of a two-dimensional crystal6-8. This suggests that Langmuir monolayers should provide model systems for studies of melting in two dimensions6-8.

  16. Persistent monolayer-scale chemical ordering in Si{sub 1−x}Ge{sub x} heteroepitaxial films during surface roughening and strain relaxation

    SciTech Connect

    Amatya, J. M.; Floro, J. A.

    2015-12-28

    Chemical ordering in semiconductor alloys could modify thermal and electronic transport, with potential benefits to thermoelectric properties. Here, metastable ordering that occurs during heteroepitaxial growth of Si{sub 1−x}Ge{sub x} thin film alloys on Si(001) and Ge(001) substrates is investigated. A parametric study was performed to study how strain, surface roughness, and growth parameters affect the order parameter during the alloy growth. The order parameter for the alloy films was carefully quantified using x-ray diffraction, taking into account an often-overlooked issue associated with the presence of multiple spatial variants associated with ordering along equivalent <111> directions. Optimal ordering was observed in the films having the smoothest surfaces. Extended strain relaxation is suggested to reduce the apparent order through creation of anti-phase boundaries. Ordering surprisingly persists even when the film surface extensively roughens to form (105) facets. Growth on deliberately miscut Si(001) surfaces does not affect the volume-averaged order parameter but does impact the relative volume fractions of the equivalent ordered variants in a manner consistent with geometrically necessary changes in step populations. These results provide somewhat self-contradictory implications for the role of step edges in controlling the ordering process, indicating that our understanding is still incomplete.

  17. External reflection FTIR of peptide monolayer films in situ at the air/water interface: experimental design, spectra-structure correlations, and effects of hydrogen-deuterium exchange.

    PubMed Central

    Flach, C R; Brauner, J W; Taylor, J W; Baldwin, R C; Mendelsohn, R

    1994-01-01

    A Fourier transform infrared spectrometer has been interfaced with a surface balance and a new external reflection infrared sampling accessory, which permits the acquisition of spectra from protein monolayers in situ at the air/water interface. The accessory, a sample shuttle that permits the collection of spectra in alternating fashion from sample and background troughs, reduces interference from water vapor rotation-vibration bands in the amide I and amide II regions of protein spectra (1520-1690 cm-1) by nearly an order of magnitude. Residual interference from water vapor absorbance ranges from 50 to 200 microabsorbance units. The performance of the device is demonstrated through spectra of synthetic peptides designed to adopt alpha-helical, antiparallel beta-sheet, mixed beta-sheet/beta-turn, and unordered conformations at the air/water interface. The extent of exchange on the surface can be monitored from the relative intensities of the amide II and amide I modes. Hydrogen-deuterium exchange may lower the amide I frequency by as much as 11-12 cm-1 for helical secondary structures. This shifts the vibrational mode into a region normally associated with unordered structures and leads to uncertainties in the application of algorithms commonly used for determination of secondary structure from amide I contours of proteins in D2O solution. PMID:7919013

  18. Multifunctional self-assembled monolayers

    SciTech Connect

    Zawodzinski, T.; Bar, G.; Rubin, S.; Uribe, F.; Ferrais, J.

    1996-06-01

    This is the final report of at three year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The specific goals of this research project were threefold: to develop multifunctional self-assembled monolayers, to understand the role of monolayer structure on the functioning of such systems, and to apply this knowledge to the development of electrochemical enzyme sensors. An array of molecules that can be used to attach electrochemically active biomolecules to gold surfaces has been synthesized. Several members of a class of electroactive compounds have been characterized and the factors controlling surface modification are beginning to be characterized. Enzymes have been attached to self-assembled molecules arranged on the gold surface, a critical step toward the ultimate goal of this project. Several alternative enzyme attachment strategies to achieve robust enzyme- modified surfaces have been explored. Several means of juxtaposing enzymes and mediators, electroactive compounds through which the enzyme can exchange electrons with the electrode surface, have also been investigated. Finally, the development of sensitive biosensors based on films loaded with nanoscale-supported gold particles that have surface modified with the self-assembled enzyme and mediator have been explored.

  19. Low-energy electron transmission through organic monolayers: An estimation of the effective monolayer potential by an excess electron interference

    NASA Astrophysics Data System (ADS)

    Yamane, Hiroyuki; Ito, Kazuyuki; Kera, Satoshi; Okudaira, Koji K.; Ueno, Nobuo

    2002-11-01

    In low-energy-electron transmission spectra of monolayer films of various organic-semiconductor molecules deposited on MoS2 and graphite surfaces, we found that the energy positions of spectral minima are proportional to (n+1/2)2, where n is positive integer and 0, independent of molecules and substrates. Despite the complex structure of each molecule, the (n+1/2)2 rule can be simply explained by the interference of an excess electron passing through the potential of the monolayer on the substrate. Using these results, we estimated the effective potential, the potential width and depth, of the monolayer felt by the injected excess electron.

  20. Ionically self-assembled monolayers (ISAMs)

    NASA Astrophysics Data System (ADS)

    Janik, John

    2001-04-01

    Ionically self-assembled monolayers (ISAMs), fabricated by alternate adsorption of cationic and anionic components, yield exceptionally homogeneous thin films with sub-nanometer control of the thickness and relative special location of the component materials. Using organic electrochromic materials such as polyaniline, we report studies of electrochromic responses in ISAM films. Reversible changes in the absorption spectrum are observed with the application of voltages on the order of 1.0 V. Measurements are made using both liquid electrolytes and in all-solid state devices incorporating solid polyelectrolytes such as poly(2-acylamido 2-methyl propane sulfonic acid) (PAMPS).

  1. Secular resonances in mean motion commensurabilities - The 2/1 and 3/2 cases

    NASA Astrophysics Data System (ADS)

    Morbidelli, A.; Moons, M.

    1993-04-01

    The role of secular resonances inside the 2/1 and 3/2 mean motion commensurabilities is examined. The interaction between nu5 and nu6 gives rise to a wide chaotic layer at large eccentricity. Conversely, the nu16 resonance, which pumps up the asteroids's inclination, is present at moderate eccentricity in the 2/1 and at large eccentricity in the 3/2. Thus, the distribution of the asteroids in the Hilda group (3/2 commensurability) is bounded by this secular resonance, which would cross a fictitious family in the 2.1. This provides new clues for a possible expansion of the existence of the Hecuba gap and the Hilda group.

  2. Dislocations in stacking and commensurate-incommensurate phase transition in bilayer graphene and hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Lebedeva, Irina V.; Lebedev, Alexander V.; Popov, Andrey M.; Knizhnik, Andrey A.

    2016-06-01

    Dislocations corresponding to a change of stacking in two-dimensional hexagonal bilayers, graphene and boron nitride, and associated with boundaries between commensurate domains are investigated using the two-chain Frenkel-Kontorova model on top of ab initio calculations. Structural transformations of bilayers in which the bottom layer is stretched and the upper one is left to relax freely are considered for gradually increased elongation of the bottom layer. Formation energies of dislocations, dislocation width, and orientation of the boundary between commensurate domains are analyzed depending on the magnitude and direction of elongation. The second-order phase transition from the commensurate phase to the incommensurate one with multiple dislocations is predicted to take place at some critical elongation. The order parameter for this transition corresponds to the density of dislocations, which grows continuously upon increasing the elongation of the bottom layer above the critical value. In graphene and metastable boron nitride with the layers aligned in the same direction, where elementary dislocations are partial, this transition, however, is preceded by formation of the first dislocation at the elongation smaller than the critical one. The phase diagrams including this intermediate state are plotted in coordinates of the magnitude and direction of elongation of the bottom layer.

  3. Hydrolytic kinetics of biodegradable polyester monolayers

    SciTech Connect

    Lee, W.K.; Gardella, J.A. Jr.

    2000-04-04

    The rate of hydrolysis of Langmuir monolayer films of a series of biodegradable polyesters was investigated at the air/water interface. The present study investigated parameters such as degradation medium, pH, and time. The hydrolysis of polyester monolayers strongly depended on both the degradation medium used to control subphase pH and the concentration of active ions. Under the conditions studied here, polymer monolayers showed faster hydrolysis when they were exposed to a basic subphase rather than that of acidic or neutral subphase. The basic (pH = 10) hydrolysis of [poly(l-lactide)/polycaprolactone](l-PLA/PCL 1/1 by mole) blend was faster than that of each homopolymer at the initial stage. This result is explained by increasing numbers of base attack sites per unit area owing to the very slow hydrolysis of PCL, a dilution effect on the concentration of l-PLA monolayers. Conversely the hydrolytic behavior of l-lactide-co-caprolactone (1/1 by mole) was similar to that of PCL even though the chemical compositions of the blend and the copolymer are very similar to each other. The resistance of the copolymer to hydrolysis might be attributed to the hydrophobicity and the steric hindrance of caprolactone unit in the copolymer.

  4. Adsorption of Ions at Uncharged Insoluble Monolayers.

    PubMed

    Peshkova, Tatyana V; Minkov, Ivan L; Tsekov, Roumen; Slavchov, Radomir I

    2016-09-01

    A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state). We applied the method to alcohols spread at the surface of concentrated halide solutions. The measured salt adsorption is positive and has nonmonotonic dependence on the area per surfactant molecule. For the liquid expanded film, depending on the concentration, there is one couple of ions adsorbed per each 3-30 surfactant molecules. We analyzed which ion, the positive or the negative, stands closer to the surface, by measuring the effect of NaCl on the Volta potential of the monolayer. The potentiometric data suggest that Na(+) is specifically adsorbed, while Cl(-) remains in the diffuse layer, i.e., the surface is positively charged. The observed reverse Hofmeister series of the adsorptions of NaF, NaCl, and NaBr suggests the same conclusion holds for all these salts. The force that causes the adsorption of Na(+) seems to be the interaction of the ion with the dipole moment of the monolayer. PMID:27529571

  5. Nanoglassified, Optically-Active Monolayer Films of Gold Nanoparticles for in Situ Orthogonal Detection by Localized Surface Plasmon Resonance and Surface-Assisted Laser Desorption/Ionization-MS

    PubMed Central

    2015-01-01

    Localized surface plasmon resonance (LSPR) represents a sensitive and versatile method for detection of biomolecules in a label-free fashion, but identification of bound analytes can be challenging with LSPR alone, especially for samples in a complex medium. We report the fabrication of an optically active, plasmonic film of gold nanoparticles by using a self-assembly and calcination process, which offers orthogonal measurements enabling multifaceted characterization on the same surface with LSPR and surface-assisted laser desorption/ionization mass spectrometry. This proof-of-concept study involves plasmonic characterization of the fabricated nanofilm, real-time monitoring of vesicle–surface interactions toward formation of fluid lipid bilayer, and mass spectrometric analysis of peptides and cytochrome c digest. This multifunction-enabling surface material can yield complementary analytical information, providing new tools for comprehensive analysis of biomolecular samples. PMID:25417963

  6. Nanoglassified, optically-active monolayer films of gold nanoparticles for in situ orthogonal detection by localized surface plasmon resonance and surface-assisted laser desorption/ionization-MS.

    PubMed

    Chen, Chih-Yuan; Hinman, Samuel S; Duan, Jicheng; Cheng, Quan

    2014-12-16

    Localized surface plasmon resonance (LSPR) represents a sensitive and versatile method for detection of biomolecules in a label-free fashion, but identification of bound analytes can be challenging with LSPR alone, especially for samples in a complex medium. We report the fabrication of an optically active, plasmonic film of gold nanoparticles by using a self-assembly and calcination process, which offers orthogonal measurements enabling multifaceted characterization on the same surface with LSPR and surface-assisted laser desorption/ionization mass spectrometry. This proof-of-concept study involves plasmonic characterization of the fabricated nanofilm, real-time monitoring of vesicle-surface interactions toward formation of fluid lipid bilayer, and mass spectrometric analysis of peptides and cytochrome c digest. This multifunction-enabling surface material can yield complementary analytical information, providing new tools for comprehensive analysis of biomolecular samples. PMID:25417963

  7. Monolayer excitonic laser

    NASA Astrophysics Data System (ADS)

    Ye, Yu; Wong, Zi Jing; Lu, Xiufang; Ni, Xingjie; Zhu, Hanyu; Chen, Xianhui; Wang, Yuan; Zhang, Xiang

    2015-11-01

    Two-dimensional van der Waals materials have opened a new paradigm for fundamental physics exploration and device applications because of their emerging physical properties. Unlike gapless graphene, monolayer transition-metal dichalcogenides (TMDCs) are two-dimensional semiconductors that undergo an indirect-to-direct bandgap transition, creating new optical functionalities for next-generation ultra-compact photonics and optoelectronics. Although the enhancement of spontaneous emission has been reported on TMDC monolayers integrated with photonic crystals and distributed Bragg reflector microcavities, coherent light emission from a TMDC monolayer has not been demonstrated. Here, we report the realization of a two-dimensional excitonic laser by embedding monolayer WS2 in a microdisk resonator. Using a whispering gallery mode with a high quality factor and optical confinement, we observe bright excitonic lasing at visible wavelengths. This demonstration of a two-dimensional excitonic laser marks a major step towards two-dimensional on-chip optoelectronics for high-performance optical communication and computing applications.

  8. Transfer of CVD-grown monolayer graphene onto arbitrary substrates.

    PubMed

    Suk, Ji Won; Kitt, Alexander; Magnuson, Carl W; Hao, Yufeng; Ahmed, Samir; An, Jinho; Swan, Anna K; Goldberg, Bennett B; Ruoff, Rodney S

    2011-09-27

    Reproducible dry and wet transfer techniques were developed to improve the transfer of large-area monolayer graphene grown on copper foils by chemical vapor deposition (CVD). The techniques reported here allow transfer onto three different classes of substrates: substrates covered with shallow depressions, perforated substrates, and flat substrates. A novel dry transfer technique was used to make graphene-sealed microchambers without trapping liquid inside. The dry transfer technique utilizes a polydimethylsiloxane frame that attaches to the poly(methyl methacrylate) spun over the graphene film, and the monolayer graphene was transferred onto shallow depressions with 300 nm depth. The improved wet transfer onto perforated substrates with 2.7 μm diameter holes yields 98% coverage of holes covered with continuous films, allowing the ready use of Raman spectroscopy and transmission electron microscopy to study the intrinsic properties of CVD-grown monolayer graphene. Additionally, monolayer graphene transferred onto flat substrates has fewer cracks and tears, as well as lower sheet resistance than previous transfer techniques. Monolayer graphene films transferred onto glass had a sheet resistance of ∼980 Ω/sq and a transmittance of 97.6%. These transfer techniques open up possibilities for the fabrication of various graphene devices with unique configurations and enhanced performance. PMID:21894965

  9. Transition from superlubrically sliding islands to pinned monolayer, demonstrated in Xe/Cu(111)

    NASA Astrophysics Data System (ADS)

    Guerra, Roberto; Vanossi, Andrea; Tosatti, Erio; Trieste Nanofriction Team

    A molecular dynamics simulation case study of Xe on Cu(111) reveals unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity which is argued to emerge in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized sqrt()x sqrt()commensurate (and pinned, and therefore immobile) monolayer. These results match with recent quartz crystal microbalance data which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena should be essential in future applications of friction at crystal/adsorbate interfaces. Matching experimental work by M. Pierno, L. Bruschi, G. Mistura, G. Paolicelli, A. di Bona, S. Valeri. Supported by ERC Advanced Grant N. 320796 - MODPHYSFRICT.

  10. Dynamics of xenon, krypton, and methane monolayers in registry with graphite

    SciTech Connect

    Hakim, T.M.; Glyde, H.R.; Chui, S.T.

    1988-01-15

    The self-consistent phonon (SCP) theory is used to study the dynamics of monolayers of xenon, krypton, and methane adsorbed on graphite. Only the ..sqrt..3 x ..sqrt..3 solid phase is considered. It is shown that the phonon energies of the Xe monolayers are very similar to those of their floating counterparts, while the interaction of the Kr and CH/sub 4/ monolayers with the graphite significantly affects the phonon dispersion curves. The gap in the phonon dispersion curves at the center of the Brillouin zone is computed as a function of temperature. At a critical temperature, the gap goes spontaneously to zero and a transition from a locked-in commensurate phase to a floating phase takes place. This transition appears to describe the commensurate to floating transition in CH/sub 4/ well. A simple model of the floating transition is compared to the full SCP calculations. The one-phonon dynamic form factor, including the cubic anharmonic term, and phonon lifetimes are also evaluated for Kr and CH/sub 4/.

  11. Superfluid--Insulator Transition in Commensurate One-Dimensional Bosonic System with Off-Diagonal Disorder

    NASA Astrophysics Data System (ADS)

    Balabanyan, Karén; Prokof'ev, Nikolay; Svistunov, Boris

    2005-03-01

    We analyze the superfluid--insulator transition in a system of one-dimensional (1D) lattice bosons with off-diagonal disorder in the limit of large commensurate filling. We argue---in contrast to the recent prediction (E. Altman, Y. Kafri, A. Polkovnikov, and G. Refael, cond-mat/0402177) of strong- randomness fixed point for this system---that at any strength of disorder the universality class of the transition on the superfluid side coincides with that of the superfluid--Mott- insulator transition in a pure system. We present results of Monte Carlo simulations for two strongly disordered models that are in excellent agreement with the advocated scenario.

  12. Chemoresponsive Monolayer Transistors

    SciTech Connect

    Guo,X.; Myers, M.; Xiao, S.; Lefenfeld, M.; Steiner, R.; Tulevski, G.; Tang, J.; Baumert, J.; Leibfarth, F.; et al.

    2006-01-01

    This work details a method to make efficacious field-effect transistors from monolayers of polycyclic aromatic hydrocarbons that are able to sense and respond to their chemical environment. The molecules used in this study are functionalized so that they assemble laterally into columns and attach themselves to the silicon oxide surface of a silicon wafer. To measure the electrical properties of these monolayers, we use ultrasmall point contacts that are separated by only a few nanometers as the source and drain electrodes. These contacts are formed through an oxidative cutting of an individual metallic single-walled carbon nanotube that is held between macroscopic metal leads. The molecules assemble in the gap and form transistors with large current modulation and high gate efficiency. Because these devices are formed from an individual stack of molecules, their electrical properties change significantly when exposed to electron-deficient molecules such as tetracyanoquinodimethane (TCNQ), forming the basis for new types of environmental and molecular sensors.

  13. Patterning Self-Assembled Monolayers on Gold: Green Materials Chemistry in the Teaching Laboratory

    ERIC Educational Resources Information Center

    McFarland, Adam D.; Huffman, Lauren M.; Parent, Kathryn, E.; Hutchison, James E.; Thompson, John E.

    2004-01-01

    An experiment demonstrating self-assembled monolayer (SAM) chemistry, organic thin-film patterning and the use of molecular functionality to control macroscopic properties is described. Several important green chemistry principles are introduced.

  14. Neutron Reflectivity Measurement for Polymer Dynamics near Graphene Oxide Monolayers

    NASA Astrophysics Data System (ADS)

    Koo, Jaseung

    We investigated the diffusion dynamics of polymer chains confined between graphene oxide layers using neutron reflectivity (NR). The bilayers of polymethylmetacrylate (PMMA)/ deuterated PMMA (d-PMMA) films and polystyrene (PS)/d-PS films with various film thickness sandwiched between Langmuir-Blodgett (LB) monolayers of graphene oxide (GO) were prepared. From the NR results, we found that PMMA diffusion dynamics was reduced near the GO surface while the PS diffusion was not significantly changed. This is due to the different strength of GO-polymer interaction. In this talk, these diffusion results will be compared with dewetting dynamics of polymer thin films on the GO monolayers. This has given us the basis for development of graphene-based nanoelectronics with high efficiency, such as heterojunction devices for polymer photovoltaic (OPV) applications.

  15. Femtosecond transient absorption dynamics of close-packed gold nanocrystal monolayer arrays.

    SciTech Connect

    Eah, S.-K.; Jaeger, H. M.; Scherer, N. F.; Lin, X.-M.; Weiderrecht, G. P.; Univ. of Chicago

    2004-03-11

    Femtosecond transient absorption spectroscopy is used to investigate hot electron dynamics of close-packed 6 nm gold nanocrystal monolayers. Morphology changes of the monolayer caused by the laser pump pulse are monitored by transmission electron microscopy. At low pump power, the monolayer maintains its structural integrity. Hot electrons induced by the pump pulse decay through electron-phonon (e-ph) coupling inside the nanocrystals with a decay constant that is similar to the value for bulk films. At high pump power, irreversible particle aggregation and sintering occur in the nanocrystal monolayer, which cause damping and peak shifting of the transient bleach signal.

  16. Magneto-optical investigations of molecular nanomagnet monolayers.

    PubMed

    Rozbořil, J; Rechkemmer, Y; Bloos, D; Münz, F; Wang, C N; Neugebauer, P; Čechal, J; Novák, J; van Slageren, J

    2016-05-01

    We report field-dependent magnetization measurements on monolayers of [Dy(Pc)2] on quartz, prepared by the Langmuir-Blodgett technique. The films are thoroughly characterized by means of X-ray reflectivity and atomic force microscopy. The magnetisation of the sample is measured through the magnetic circular dichroism of a ligand-based electronic transition. PMID:27080152

  17. Proximity Driven Commensurate Pinning in YBa2Cu3O7 through All-Oxide Magnetic Nanostructures.

    PubMed

    Rocci, M; Azpeitia, J; Trastoy, J; Perez-Muñoz, A; Cabero, M; Luccas, R F; Munuera, C; Mompean, F J; Garcia-Hernandez, M; Bouzehouane, K; Sefrioui, Z; Leon, C; Rivera-Calzada, A; Villegas, J E; Santamaria, J

    2015-11-11

    The design of artificial vortex pinning landscapes is a major goal toward large scale applications of cuprate superconductors. Although disordered nanometric inclusions have shown to modify their vortex phase diagram and to produce enhancements of the critical current ( MacManus-Driscoll , J. L. ; Foltyn , S. R. ; Jia , Q. X. ; Wang , H. ; Serquis , A. ; Civale , L. ; Maiorov , B. ; Hawley , M. E. ; Maley , M. P. ; Peterson , D. E. Nat. Mater. 2004 , 3 , 439 - 443 and Yamada , Y. ; Takahashi , K. ; Kobayashi , H. ; Konishi , M. ; Watanabe , T. ; Ibi , A. ; Muroga , T. ; Miyata , S. ; Kato , T. ; Hirayama , T. ; Shiohara , Y. Appl. Phys. Lett. 2005 , 87 , 1 - 3 ), the effect of ordered oxide nanostructures remains essentially unexplored. This is due to the very small nanostructure size imposed by the short coherence length, and to the technological difficulties in the nanofabrication process. Yet, the novel phenomena occurring at oxide interfaces open a wide spectrum of technological opportunities to interplay with the superconductivity in cuprates. Here, we show that the unusual long-range suppression of the superconductivity occurring at the interface between manganites and cuprates affects vortex nucleation and provides a novel vortex pinning mechanism. In particular, we show evidence of commensurate pinning in YBCO films with ordered arrays of LCMO ferromagnetic nanodots. Vortex pinning results from the proximity induced reduction of the condensation energy at the vicinity of the magnetic nanodots, and yields an enhanced friction between the nanodot array and the moving vortex lattice in the liquid phase. This result shows that all-oxide ordered nanostructures constitute a powerful, new route for the artificial manipulation of vortex matter in cuprates. PMID:26441137

  18. Universality of commensurate 4 a-period charge density modulations throughout the cuprate pseudogap regime

    NASA Astrophysics Data System (ADS)

    Mesaros, Andrej; Fujita, Kazuhiro; Hamidian, Mohammad; Eisaki, Hiroshi; Uchida, Shin-Ichi; Davis, J. C.; Lawler, Michael J.; Kim, Eun-Ah

    Theories for the hole-doped Mott insulator, representing underdoped cuprates, are based upon the strong real space (r-space) interactions, and have long predicted a modulation of charge that is commensurate with the underlying lattice. Such a charge density modulation (CDM) state is unrelated to any momentum space (k-space) features such as the nesting of regions on a Fermi surface. Experimentally, with increasing hole density, the reported wavevector Q of the CDM diminishes continuously with increasing hole-density as if driven by k-space phenomena. Using a novel technique based upon phase-sensitive electronic structure visualization, we demonstrate that the cuprate CDM actually exhibits a commensurate 4 a-period throughout the entire underdoped region of the Bi2 Sr2 CaCu2O8 phase diagram. Our technique is designed for extracting Q from inhomogeneous, short-ranged CDM, as the ones observed in experiments. Thus, a strong-interaction r-space perspective appears to be relevant to achieving a predictive theory for the cuprate pseudogap regime.

  19. Incommensurate-commensurate transitions in the monoaxial chiral helimagnet driven by the magnetic field

    NASA Astrophysics Data System (ADS)

    Laliena, Victor; Campo, Javier; Kishine, Jun-Ichiro; Ovchinnikov, Alexander S.; Togawa, Yoshihiko; Kousaka, Yusuke; Inoue, Katsuya

    2016-04-01

    The zero-temperature phase diagram of the monoaxial chiral helimagnet in the magnetic-field plane formed by the components parallel and perpendicular to the helical axis is thoroughly analyzed. The nature of the transition to the commensurate state depends on the angle between the field and the helical axis. For field directions close to the directions parallel or perpendicular to the helical axis the transition is continuous, while for intermediate angles the transition is discontinuous and the incommensurate and commensurate states coexist on the transition line. The continuous and discontinuous transition lines are separated by two tricritical points with specific singular behavior. The location of the continuous and discontinuous lines and of the tricritical points depend strongly on the easy-plane anisotropy, the effect of which is analyzed. For high anisotropy the conical approximation locates the transition line very accurately, although it does not predict the continuous transitions and the tricritical behavior. It is shown that for high anisotropy, as in CrNb3S6 , the form of the transition line is universal, that is, independent of the sample, and obeys a simple equation. The position of the tricritical points, which is not universal, is theoretically estimated for a sample of CrNb3S6 .

  20. Stellar rotation-planetary orbit period commensurability in the HAT-P-11 system

    SciTech Connect

    Béky, Bence; Holman, Matthew J.; Noyes, Robert W.; Kipping, David M.

    2014-06-10

    A number of planet host stars have been observed to rotate with a period equal to an integer multiple of the orbital period of their close planet. We expand this list by analyzing Kepler data of HAT-P-11 and finding a period ratio of 6:1. In particular, we present evidence for a long-lived spot on the stellar surface that is eclipsed by the planet in the same position four times, every sixth transit. We also identify minima in the out-of-transit light curve and confirm that their phase with respect to the stellar rotation is mostly stationary for the 48 month time frame of the observations, confirming the proposed rotation period. For comparison, we apply our methods to Kepler-17 and confirm the findings of Bonomo and Lanza that the period ratio is not exactly 8:1 in that system. Finally, we provide a hypothesis on how interactions between a star and its planet could possibly result in an observed commensurability for systems where the stellar differential rotation profile happens to include a period at some latitude that is commensurable to the planetary orbit.

  1. Synthesis of boron-doped graphene monolayers using the sole solid feedstock by chemical vapor deposition.

    PubMed

    Wang, Huan; Zhou, Yu; Wu, Di; Liao, Lei; Zhao, Shuli; Peng, Hailin; Liu, Zhongfan

    2013-04-22

    Substitutionally boron-doped monolayer graphene film is grown on a large scale by using a sole phenylboronic acid as the source in a low-pressure chemical vapor deposition system. The B-doped graphene film is a homogeneous monolayer with high crystalline quality, which exhibits a stable p-type doping behavior with a considerably high room-temperature carrier mobility of about 800 cm(2) V(-1) s(-1) . PMID:23463717

  2. Collapse of Langmuir monolayer at lower surface pressure: Effect of hydrophobic chain length

    NASA Astrophysics Data System (ADS)

    Das, Kaushik; Kundu, Sarathi

    2016-05-01

    Long chain fatty acid molecules (e.g., stearic and behenic acids) form a monolayer on water surface in the presence of Ba2+ ions at low subphase pH (≈ 5.5) and remain as a monolayer before collapse generally occurs at higher surface pressure (πc > 50 mN/m). Monolayer formation is verified from the surface pressure vs. area per molecule (π-A) isotherms and also from the atomic force microscopy (AFM) analysis of the films deposited by single upstroke of hydrophilic Si (001) substrate through the monolayer covered water surface. At high subphase pH (≈ 9.5), barium stearate molecules form multilayer structure at lower surface pressure which is verified from the π-A isotherms and AFM analysis of the film deposited at 25 mN/m. Such monolayer to multilayer structure formation or monolayer collapse at lower surface pressure is unusual as at this surface pressure generally fatty acid salt molecules form a monolayer on the water surface. Formation of bidentate chelate coordination in the metal containing headgroups is the reason for such monolayer to multilayer transition. However, for longer chain barium behenate molecules only monolayer structure is maintained at that high subphase pH (≈ 9.5) due to the presence of relatively more tail-tail hydrophobic interaction.

  3. Oxidation of oleic acid monolayers at air/liquid interfaces

    NASA Astrophysics Data System (ADS)

    Voss, L. F.; Bazerbashi, M. F.; Beekman, C. P.; Hadad, C. M.; Allen, H. C.

    2006-12-01

    Field studies of marine and continental aerosols find that fatty acid films form on aqueous tropospheric aerosols. Oxidation of the acyl chains is thought to be key to aerosol growth. Oxidation of oleic acid monolayers by ozone was studied to understand the fate of fat-coated aerosols from both fresh and salt water sources. Using vibrational sum frequency generation spectroscopy and reflection absorption infrared spectroscopy, we present a molecular-level investigation of fatty acid monolayers at the air-water and air- sodium chloride solution interface and explore reactions with atmospheric oxidants by these model systems. Using sum frequency generation spectroscopy coupled with a Langmuir trough, concurrent spectroscopic and thermodynamic data were collected to obtain a molecular picture of the monolayers. No substantial difference was observed between oxidation of monolayers spread on water and on 0.6 molar sodium chloride solutions. Results indicate that depending on the size of the aerosol and the extent of oxidation, the subsequent oxidation products may not remain at the surface of these films, but instead be dissolved in the aqueous sub-phase of the aerosol particle. Results also indicate that oxidation of oleic acid could produce monolayers containing species that have no oxidized acyl chains.

  4. Oxidation of oleic acid monolayers at air/liquid interfaces

    NASA Astrophysics Data System (ADS)

    Voss, Laura

    2008-03-01

    Field studies of marine and continental aerosols find that fatty acid films form on aqueous tropospheric aerosols. Oxidation of oleic acid monolayers by ozone was studied to understand the fate of fat-coated aerosols from both fresh and salt water sources. Using vibrational sum frequency generation spectroscopy and reflection absorption infrared spectroscopy, we present a molecular-level investigation of fatty acid monolayers at the air-water and air-sodium chloride solution interface and explore reactions with atmospheric oxidants by these model systems. Coupling sum frequency generation spectroscopy with a Langmuir trough, concurrent spectroscopic and thermodynamic data were collected to obtain a molecular picture of the monolayers. No substantial difference was observed between oxidation of monolayers spread on water and on 0.6 molar sodium chloride solutions. Results indicate that depending on the size of the aerosol and the extent of oxidation, the subsequent oxidation products may not remain at the surface of these films, but instead be dissolved in the aqueous sub-phase of the aerosol particle. Results also indicate that oxidation of oleic acid could produce monolayers containing species that have no oxidized acyl chains.

  5. Frictional dynamics of stiff monolayers: from nucleation dynamics to thermal sliding

    NASA Astrophysics Data System (ADS)

    Hasnain, Jaffar; Jungblut, Swetlana; Tröster, Andreas; Dellago, Christoph

    2014-08-01

    The inherently nonlinear dynamics of two surfaces as they are driven past each other, a phenomenon known as dry friction, has yet to be fully understood on an atomistic level. New experiments on colloidal monolayers forced over laser-generated substrates now offer the opportunity to investigate friction with single-particle resolution. Here, we use analytical theory and computer simulations to study the effect of thermal fluctuations on the stick-slip mechanism characteristic for the frictional response of a stiff colloidal monolayer on a commensurate substrate. By performing a harmonic expansion of the energy and employing elementary statistical mechanics, we map the motion of the monolayer onto a simple differential equation. Analytical expressions derived from our approach predict a transition from nucleation dynamics, where the monolayer moves in a sequence of activated hops over energy barriers, to ``thermal sliding'', in which the effective substrate barrier opposing the motion of the monolayer disappears due to thermal fluctuations, leading to continuous, uninterrupted sliding motion. Furthermore, we find that the average velocity of the monolayer for large driving forces obeys a simple scaling behavior that is consistent with the existence of a static friction. For small forces, however, nucleation provides a mode of motion that leads to a small but non-vanishing mobility of the monolayer. Data obtained from simulations confirm this picture and agree quantitatively with our analytical formulae. The theory developed here holds under general conditions for sufficiently strong inter-particle repulsions and it yields specific predictions that can be tested in experiments.The inherently nonlinear dynamics of two surfaces as they are driven past each other, a phenomenon known as dry friction, has yet to be fully understood on an atomistic level. New experiments on colloidal monolayers forced over laser-generated substrates now offer the opportunity to investigate

  6. Thermodynamic aspects of cholesterol effect on properties of phospholipid monolayers: Langmuir and Langmuir-Blodgett monolayer study.

    PubMed

    Jurak, Małgorzata

    2013-04-01

    Cholesterol is an important component of lipid rafts in mammalian cell membranes. Studies of phospholipid monolayers containing cholesterol provide insight into the role of cholesterol in regulating the properties of animal cells, raft stability, and organization. In this contribution, a study of the characteristics of binary Langmuir monolayers consisting of phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC), 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DPPG), and cholesterol (Chol), was conducted on the basis of the surface pressure-area per molecule (π-A) isotherms. Analysis of the results obtained provided information on the mean molecular area, the excess Gibbs energy of mixing, and condensation in the monolayer. The mixed monolayers were also deposited onto the mica plates and investigated by the contact angle measurements of water, formamide, and diiodomethane. The contact angles allowed calculating surface free energy of the films from the van Oss et al. approach. It was found that cholesterol determines the molecular packing and ordering of the monolayers closely connected with the kind of phospholipid. This is reflected in the values of surface free energy of the model membranes. From the thermodynamic analysis of phospholipid/cholesterol/liquid interactions, one may draw conclusions about the most favorable composition (stoichiometry) of the binary film which is especially important in view of the lipid rafts formation. PMID:23470025

  7. Subharmonic Shapiro steps of sliding colloidal monolayers in optical lattices.

    PubMed

    Paronuzzi Ticco, Stella V; Fornasier, Gabriele; Manini, Nicola; Santoro, Giuseppe E; Tosatti, Erio; Vanossi, Andrea

    2016-04-01

    We investigate theoretically the possibility to observe dynamical mode locking, in the form of Shapiro steps, when a time-periodic potential or force modulation is applied to a two-dimensional (2D) lattice of colloidal particles that are dragged by an external force over an optically generated periodic potential. Here we present realistic molecular dynamics simulations of a 2D experimental setup, where the colloid sliding is realized through the motion of soliton lines between locally commensurate patches or domains, and where the Shapiro steps are predicted and analyzed. Interestingly, the jump between one step and the next is seen to correspond to a fixed number of colloids jumping from one patch to the next, across the soliton line boundary, during each ac cycle. In addition to ordinary 'integer' steps, coinciding here with the synchronous rigid advancement of the whole colloid monolayer, our main prediction is the existence of additional smaller 'subharmonic' steps due to localized solitonic regions of incommensurate layers executing synchronized slips, while the majority of the colloids remains pinned to a potential minimum. The current availability and wide parameter tunability of colloid monolayers makes these predictions potentially easy to access in an experimentally rich 2D geometrical configuration. PMID:26933976

  8. Subharmonic Shapiro steps of sliding colloidal monolayers in optical lattices

    NASA Astrophysics Data System (ADS)

    Paronuzzi Ticco, Stella V.; Fornasier, Gabriele; Manini, Nicola; Santoro, Giuseppe E.; Tosatti, Erio; Vanossi, Andrea

    2016-04-01

    We investigate theoretically the possibility to observe dynamical mode locking, in the form of Shapiro steps, when a time-periodic potential or force modulation is applied to a two-dimensional (2D) lattice of colloidal particles that are dragged by an external force over an optically generated periodic potential. Here we present realistic molecular dynamics simulations of a 2D experimental setup, where the colloid sliding is realized through the motion of soliton lines between locally commensurate patches or domains, and where the Shapiro steps are predicted and analyzed. Interestingly, the jump between one step and the next is seen to correspond to a fixed number of colloids jumping from one patch to the next, across the soliton line boundary, during each ac cycle. In addition to ordinary ‘integer’ steps, coinciding here with the synchronous rigid advancement of the whole colloid monolayer, our main prediction is the existence of additional smaller ‘subharmonic’ steps due to localized solitonic regions of incommensurate layers executing synchronized slips, while the majority of the colloids remains pinned to a potential minimum. The current availability and wide parameter tunability of colloid monolayers makes these predictions potentially easy to access in an experimentally rich 2D geometrical configuration.

  9. Electrodeposited bismuth monolayers on Au(111) electrodes. Comparison of surface X-ray scattering, scanning tunneling microscopy, and atomic force microscopy lattice structures

    SciTech Connect

    Chen, C.H.; Kepler, K.D.; Gewirth, A.A. ); Ocko, B.M.; Wang, J. )

    1993-07-15

    Surface X-ray scattering (SXS) and scanning tunneling microscope (STM) studies have been carried out to determine the structure of electrochemically deposited Bi monolayers on a Au(111) electrode. Between 10 and 190 mV (relative to bulk deposition), a uniaxially commensurate rectangular phase is formed in which the Bi coverage decreases from 0.646 to 0.616 relative to a gold monolayer. A 25% coverage (2 [times] 2) phase is stable between 200 and 280 mV. The structures determined by SXS and STM are in agreement with those determined previously by AFM. 15 refs., 5 figs.

  10. Internal resonance with commensurability induced by an auxiliary oscillator for broadband energy harvesting

    NASA Astrophysics Data System (ADS)

    Xiong, Liuyang; Tang, Lihua; Mace, Brian R.

    2016-05-01

    An internal resonance based broadband vibration energy harvester is proposed by introducing an auxiliary oscillator to the main nonlinear harvesting oscillator. Compared to conventional nonlinear energy harvesters, the natural frequencies of this two-degree-of-freedom nonlinear system can be easily adjusted to be commensurable which will result in more resonant peaks and better wideband performance. Experimental measurements and equivalent circuit simulations demonstrate that this design outperforms its linear counterpart. In addition to the open-circuit voltage, the optimal resistance to obtain the maximum power is determined. Nearly 130% increase in the bandwidth is achieved compared to the linear counterpart at an excitation level of 2 m/s2. The findings provide insight for the design of a broadband energy harvester when there is nonlinearity and internal resonance.

  11. Correlation versus commensurability effects for finite bosonic systems in one-dimensional lattices

    SciTech Connect

    Brouzos, Ioannis; Schmelcher, Peter; Zoellner, Sascha

    2010-05-15

    We investigate few-boson systems in finite one-dimensional multiwell traps covering the full interaction crossover from uncorrelated to fermionized particles. Our treatment of the ground-state properties is based on the numerically exact multiconfigurational time-dependent Hartree method. For commensurate filling, we trace the fingerprints of localization as the interaction strength increases, in several observables like reduced-density matrices, fluctuations, and momentum distribution. For a filling factor larger than 1 we observe on-site repulsion effects in the densities and fragmentation of particles beyond the validity of the Bose-Hubbard model upon approaching the Tonks-Girardeau limit. The presence of an incommensurate fraction of particles induces incomplete localization and spatial modulations of the density profiles, taking into account the finite size of the system.

  12. Probing high quality pentacene monolayers by optical methods

    NASA Astrophysics Data System (ADS)

    He, Rui; Tassi, Nancy G.; Blanchet, Graciela B.; Pinczuk, Aron

    2006-05-01

    We report optical studies of pentacene monolayers grown on poly-alpha-methyl-styrene (PAMS) substrates of high uniformity that reaches into the micron length-scale in the lateral dimension. Raman scattering intensities from a two-monolayer pentacene film exhibit large resonance enhancements when incoming and outgoing photon energies overlap the free exciton measured in optical emission. The incoming and outgoing resonance enhancements are of about the same strength. The free exciton optical emission band is sharp and intense, and it blue-shifts by about 85 meV from that of the pentacene single crystal.

  13. Chemoresponsive monolayer transistors

    PubMed Central

    Guo, Xuefeng; Myers, Matthew; Xiao, Shengxiong; Lefenfeld, Michael; Steiner, Rachel; Tulevski, George S.; Tang, Jinyao; Baumert, Julian; Leibfarth, Frank; Yardley, James T.; Steigerwald, Michael L.; Kim, Philip; Nuckolls, Colin

    2006-01-01

    This work details a method to make efficacious field-effect transistors from monolayers of polycyclic aromatic hydrocarbons that are able to sense and respond to their chemical environment. The molecules used in this study are functionalized so that they assemble laterally into columns and attach themselves to the silicon oxide surface of a silicon wafer. To measure the electrical properties of these monolayers, we use ultrasmall point contacts that are separated by only a few nanometers as the source and drain electrodes. These contacts are formed through an oxidative cutting of an individual metallic single-walled carbon nanotube that is held between macroscopic metal leads. The molecules assemble in the gap and form transistors with large current modulation and high gate efficiency. Because these devices are formed from an individual stack of molecules, their electrical properties change significantly when exposed to electron-deficient molecules such as tetracyanoquinodimethane (TCNQ), forming the basis for new types of environmental and molecular sensors. PMID:16855049

  14. Articles including thin film monolayers and multilayers

    SciTech Connect

    Li, DeQuan; Swanson, Basil I.

    1995-01-01

    Articles of manufacture including: (a) a base substrate having an oxide surface layer, and a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, (b) a base substrate having an oxide surface layer, a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, and a metal species attached to the multidentate ligand, (c) a base substrate having an oxide surface layer, a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, a metal species attached to the multidentate ligand, and a multifunctional organic ligand attached to the metal species, and (d) a base substrate having an oxide surface layer, a multidentate ligand, capable of binding a metal ion, attached to the oxide surface layer of the base substrate, a metal species attached to the multidentate ligand, a multifunctional organic ligand attached to the metal species, and a second metal species attached to the multifunctional organic ligand, are provided, such articles useful in detecting the presence of a selected target species, as nonliear optical materials, or as scavengers for selected target species.

  15. Organic semiconductor interfaces: low-lying lattice modes of pentacene monolayers

    NASA Astrophysics Data System (ADS)

    He, Rui; Blanchet, Graciela; Pinczuk, Aron

    2010-03-01

    Highly uniform monolayers of pentacene that are grown on polymeric substrate of poly alpha-methylstyrene exhibit sharp and intense free exciton luminescence. Large enhancements of Raman scattering intensities at the free exciton resonance enable the first observations of low-lying lattice vibration modes in films reaching the single monolayer level.footnotetextRui He, et al. Appl. Phys. Lett. 94, 223310 (2009). The low- lying modes display characteristic changes when going from a single monolayer to two layers, revealing that a phase akin to a thin film phase of pentacene already emerges in structures of only two monolayers. A simple analysis of mode splittings offers estimates of the strength of inter-layer interactions. The results demonstrate novel venues for ultra-thin film characterization and studies of interface effects in organic molecular semiconductor structures.

  16. Free exciton emission and vibrations in pentacene monolayers

    NASA Astrophysics Data System (ADS)

    He, Rui

    2011-03-01

    Pentacene is a benchmark organic semiconductor material because of its potential applications in electronic and optoelectronic devices. Recently we demonstrated that optical and vibrational characterizations of pentacene films can be carried out down to the sub-monolayer limit. These milestones were achieved in highly uniform pentacene films that were grown on a compliant polymeric substrate. Films with thickness ranging from sub- monolayer to tens of monolayers were studied at low temperatures. The intensity of the free exciton (FE) luminescence band increases quadratically with the number of layers N when N is small. This quadratic dependence is explained as arising from the linear dependence of the intensity of absorption and the probability of emission on the number of layers N. Large enhancements of Raman scattering intensities at the FE resonance enable the first observations of low-lying lattice modes in the monolayers. The measured low- lying modes (in the 20 to 100 cm-1 range) display characteristic changes when going from a single monolayer to two layers. The Raman intensities by high frequency intra-molecular vibrations display resonance enhancement double-peaks when incident or scattered photon energies overlap the FE optical emission. The double resonances are about the same strength which suggests that Franck-Condon overlap integrals for the respective vibronic transitions have the same magnitude. The interference between scattering amplitudes in the Raman resonance reveals quantum coherence of the symmetry-split states (Davydov doublet) of the lowest intrinsic singlet exciton. These results demonstrate novel venues for ultra-thin film characterization and studies of fundamental physics in organic semiconductor structures. In collaboration with Nancy G. Tassi (Dupont), Graciela B. Blanchet (Nanoterra, Cambridge, MA), and Aron Pinczuk (Columbia University).

  17. Effect of lipid composition and packing on the adsorption of apolipoproteins to lipid monolayers

    SciTech Connect

    Ibdah, J.A.; Lund-Katz, S.; Phillips, M.C.

    1987-05-01

    The monolayer system has been used to study the effects of lipoprotein surface lipid composition and packing on the affinities of apolipoproteins for the surfaces of lipoprotein particles. The adsorption of apolipoproteins injected beneath lipid monolayers prepared with pure lipids or lipoprotein surface lipids is evaluated by monitoring the surface pressure of the film and the surface concentration (Gamma) of /sup 14/C-labelled apolipoprotein. At a given initial film pressure (..pi../sub i/) there is a higher adsorption of human apo A-I to unsaturated phosphatidylcholine (PC) monolayers compared to saturated PC monolayers (e.g., at ..pi../sub i/ = 10 mN/m, Gamma = 0.35 and 0.06 mg/m/sup 2/ for egg PC and distearoyl PC, respectively, with 3 x 10/sup -4/ mg/ml apo A-I in the subphase). In addition, adsorption of apo A-I is less to an egg sphingomyelin monolayer than to an egg PC monolayer. The adsorption of apo A-I to PC monolayers is decreased by addition of cholesterol. Generally, apo A-I adsorption diminishes as the lipid molecular area decreases. Apo A-I adsorbs more to monolayers prepared with HDL/sub 3/ surface lipids than with LDL surface lipids. These studies suggest that lipoprotein surface lipid composition and packing are crucial factors influencing the transfer and exchange of apolipoproteins among various lipoprotein classes during metabolism of lipoprotein particles.

  18. a Heat Capacity Study of Para-Hydrogen Monolayers on Graphite.

    NASA Astrophysics Data System (ADS)

    Motteler, Frederick Clark

    The heat capacity of monolayer p-H(,2) adsorbed on graphite foam has been measured over the 0.0631(ANGSTROM)(' -2) to 0.0891(ANGSTROM)('-2) density range and the 2 to 25(DEGREES)K temperature range. Specific heat peaks are observed over almost the entire density range and are similar to those observed for ('4)He and ('3)He monolayers on graphite for similar densities. Low density data (0.0631(ANGSTROM)('-2) to 0.0727(ANGSTROM)(' -2)) contains a heat capacity peak attributed to the commensurate order-disorder transition. At commensurate density. 0.0637(ANGSTROM)(' -2), the peak attains a maximum height of C/Nk(,b) = 11.7 at 21.4(DEGREES)K and may be characterized by the critical exponent (alpha) = 0.33. For temperatures below the order -disorder transition, the commensurate monolayer heat capacity is characterized by Einstein like behavior with (theta)(,E) = 53.4(DEGREES)K. High density data (0.0787(ANGSTROM)('-2) to 0.0815(ANGSTROM)(' -2)) contains a heat capacity peak attributed to the disordering of a close packed triangular incommensurate solid. The incommensurate solid is characterized by its Debye like heat capacity behavior. The density region between the commensurate structure and incommensurate solid (0.0707(ANGSTROM)('-2) to 0.772(ANGSTROM)(' -2)) contains two heat capacity peaks. At about 20(DEGREES)K there is broad rounded remnant of the order-disorder peak. At lower temperatures (6 to 9(DEGREES)K) there is a small, but very sharp heat capacity peak. The peak attains a maximum height of C/Nk(,b) = 0.89 at a density of 0.0727(ANGSTROM)(' -2) and a temperature of 9.54(DEGREES)K. The remnant of the order-disorder transition seen in p-H(,2) data, together with re-examination of ('4)He data indicates that a shoulder-like remnant intersects the melting line. The melting peak of ('4)He undergoes significant change at the intersection point. The low temperature intermediate density region is consistent with a striped phase of domain walls. The sharp low

  19. Self assembled monolayers of octadecyltrichlorosilane for dielectric materials

    NASA Astrophysics Data System (ADS)

    Kumar, Vijay; Puri, Paridhi; Nain, Shivani; Bhat, K. N.; Sharma, N. N.

    2016-04-01

    Treatment of surfaces to change the interaction of fluids with them is a critical step in constructing useful microfluidics devices, especially those used in biological applications. Selective modification of inorganic materials such as Si, SiO2 and Si3N4 is of great interest in research and technology. We evaluated the chemical formation of OTS self-assembled monolayers on silicon substrates with different dielectric materials. Our investigations were focused on surface modification of formerly used common dielectric materials SiO2, Si3N4 and a-poly. The improvement of wetting behaviour and quality of monolayer films were characterized using Atomic force microscope, Scanning electron microscope, Contact angle goniometer, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) monolayer deposited oxide surface.

  20. Quantitative Characterization of Mechanical Property of Annealed Monolayer Colloidal Crystal.

    PubMed

    Zhang, Lijing; Wang, Weiqi; Zheng, Lu; Wang, Xiuyu; Yan, Qingfeng

    2016-01-19

    Quantitative characterization of the mechanical properties of a polystyrene (PS) monolayer colloidal crystal (MCC) annealed with solvent vapor has been performed for the first time by means of atomic force microscopy nanoindentation. The results showed that both the compressive and bending elastic modulus of PS MCC increased with the prolongation of annealing time from initial to 13 min. When the annealing time reached 15 min or even more, the PS MCC almost deformed to a planar film, and the elastic modulus of the PS MCC presented a drastic increase. These results provide a basis for tailoring the mechanical properties of a polymer colloidal monolayer via solvent vapor annealing. Such self-supported and high-mechanical-strength colloidal monolayers can be transferred to other surfaces for potential and promising applications in the bottom-up fabrication of highly ordered nanostructured materials such as nano dot arrays, photonic crystals, and many others. PMID:26700374

  1. Assembly of designed protein scaffolds into monolayers for nanoparticle patterning.

    PubMed

    Mejias, Sara H; Couleaud, Pierre; Casado, Santiago; Granados, Daniel; Garcia, Miguel Angel; Abad, Jose M; Cortajarena, Aitziber L

    2016-05-01

    The controlled assembly of building blocks to achieve new nanostructured materials with defined properties at different length scales through rational design is the basis and future of bottom-up nanofabrication. This work describes the assembly of the idealized protein building block, the consensus tetratricopeptide repeat (CTPR), into monolayers by oriented immobilization of the blocks. The selectivity of thiol-gold interaction for an oriented immobilization has been verified by comparing a non-thiolated protein building block. The physical properties of the CTPR protein thin biomolecular films including topography, thickness, and viscoelasticity, are characterized. Finally, the ability of these scaffolds to act as templates for inorganic nanostructures has been demonstrated by the formation of well-packed gold nanoparticles (GNPs) monolayer patterned by the CTPR monolayer. PMID:26844645

  2. Prediction of stable C7 /12 and metastable C4 /7 commensurate solid phases for 4He on graphite

    NASA Astrophysics Data System (ADS)

    Ahn, Jeonghwan; Lee, Hoonkyung; Kwon, Yongkyung

    2016-02-01

    Using a substrate potential described by a pairwise sum of empirical 4He-C interatomic potentials, we have performed path-integral Monte Carlo calculations for 4He adatoms on graphite. It is found that a second-layer commensurate structure is not stable above an incommensurate first-layer triangular solid. This is consistent with the conclusion of the previous theoretical study of Corboz et al. [Phys. Rev. B 78, 245414 (2008), 10.1103/PhysRevB.78.245414] that was based on a laterally averaged one-dimensional potential. On the other hand, we observe a new stable C7 /12 commensurate solid in the first 4He layer at the areal density of 0.111 Å-2, which is close to the second-layer promotion density. This high-density commensurate solid exhibits a √{12 }×√{12 } structure registered to the graphite surface that is not disrupted by the development of the second 4He layer. Furthermore, a second-layer 4/7 commensurate structure relative to the first-layer C7 /12 solid is found to be at least metastable, opening the possibility of two-dimensional supersolidity.

  3. Structure and Function Evolution of Thiolate Monolayers on Gold

    SciTech Connect

    Grant Alvin Edwards

    2006-05-01

    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  4. Shear-induced molecular precession in a hexatic Langmuir monolayer.

    PubMed

    Ignés-Mullol, J; Schwartz, D K

    2001-03-15

    Liquid crystalline behaviour is generally limited to a select group of specially designed bulk substances. By contrast, it is a common feature of simple molecular monolayers and other quasi-two-dimensional systems, which often possess a type of in-plane ordering that results from unbinding of dislocations-a 'hexatic' liquid crystalline phase. The flow of monolayers is closely related to molecular transport in biological membranes, affects foam and emulsion stability and is relevant to microfluidics research. For liquid crystalline phases, it is important to understand the coupling of the molecular orientation to the flow. Orientationally ordered (nematic) phases in bulk liquid crystals exhibit 'shear aligning' or 'tumbling' behaviour under shear, and are described quantitatively by Leslie-Ericksen theory. For hexatic monolayers, the effects of flow have been inferred from textures of Langmuir-Blodgett films and directly observed at the macroscopic level. However, there is no accepted model of hexatic flow at the molecular level. Here we report observations of a hexatic Langmuir monolayer that reveal continuous, shear-induced molecular precession, interrupted by occasional jump discontinuities. Although superficially similar to tumbling in a bulk nematic phase, the kinematic details are quite different and provide a possible mechanism for domain coarsening and eventual molecular alignment in monolayers. We explain the precession and jumps within a quantitative framework that involves coupling of molecular orientation to the local molecular hexatic 'lattice', which is continuously deformed by shear. PMID:11268206

  5. Monolayer Graphene as Ultimate Chemical Passivation Layer for Arbitrarily Shaped Metal Surfaces

    SciTech Connect

    Sutter E.; Albrecht, P.; Camino, F.E.; Sutter, P.

    2010-12-01

    Monolayer graphene was grown on polycrystalline Ru thin films on patterned fused silica. The Ru films grow with columnar structure with strongly aligned grains exposing flat (0 0 0 1) surface facets within the 3D geometric patterns and on the adjacent planar silica surface. The monolayer graphene was found to completely and uniformly cover the Ru films on the complex engineered substrates. In addition, we demonstrate that the single atomic layer graphene protects the underlying metal surface against reaction with ambient gases of particular importance for applications such as concave focusing mirrors, non-planar microelectrode arrays, etc.

  6. Assembled monolayers of hydrophilic particles on water surfaces.

    PubMed

    Moon, Geon Dae; Lee, Tae Il; Kim, Bongsoo; Chae, GeeSung; Kim, Jinook; Kim, SungHee; Myoung, Jae-Min; Jeong, Unyong

    2011-11-22

    A facile and quick approach to prepare self-assembled monolayers of water-dispersible particles on the water surface is presented. Particle suspensions in alcohols were dropped on a water reservoir to form long-range ordered monolayers of various particles, including spherical solid particles, soft hydrogel particles, metal nanoparticles, quantum dots, nanowires, single-wall carbon nanotubes (SWCNTs), nanoplates, and nanosheets. A systematic study was conducted on the variables affecting the monolayer assembly: the solubility parameter of spreading solvents, particle concentration, zeta potential of the particles in the suspension, surface tension of the water phase, hardness of the particles, and addition of a salt in the suspension. This method requires no hydrophobic surface treatment of the particles, which is useful to exploit these monolayer films without changing the native properties of the particles. The study highlights a quick 2D colloidal assembly without cracks in the wafer scale as well as transparent conductive thin films made of SWCNTs and graphenes. PMID:21962177

  7. Incommensurate-commensurate magnetic phase transition in SmRu2Al10

    NASA Astrophysics Data System (ADS)

    Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi

    2015-11-01

    Magnetic properties of single crystalline SmRu2Al10 have been investigated by electrical resistivity, magnetic susceptibility, and specific heat. We have confirmed the successive magnetic phase transitions at TN=12.3 K and TM=5.6 K. Resonant x-ray diffraction has also been performed to study the magnetic structures. Below TN, the Sm3 + moments order in an incommensurate structure with q1=(0 ,0.759 ,0 ) . The magnetic moments are oriented along the orthorhombic b axis, which coincides with the magnetization easy axis in the paramagnetic phase. A very weak third harmonic peak is also observed at q3=(0 ,0.278 ,0 ) . The transition at TM is a lock-in transition to the commensurate structure described by q1=(0 ,0.75 ,0 ) . A well-developed third harmonic peak is observed at q3=(0 ,0.25 ,0 ) . From the discussion of the magnetic structure, we propose that the long-range RKKY interaction plays an important role, in addition to the strong nearest-neighbor antiferromagnetic interaction.

  8. Probing a Wigner Crystal via Composite Fermion Commensurability Oscillations in an Adjacent Layer

    NASA Astrophysics Data System (ADS)

    Deng, Hao; Jo, Insun; Liu, Yang; Shayegan, Mansour; Pfeiffer, Loren N.; West, Ken W.; Baldwin, Kirk W.

    At high magnetic fields and low temperatures, two-dimensional electrons form a composite fermion (CF) Fermi sea with a well-defined Fermi wave vector when the Landau level fillings factor (ν) is near 1/2. In contrast, when ν << 1 , the Wigner crystal (WC) is the favored ground state. We report measurements of the magneto-resistance in a bilayer electron system with unequal layer densities at high magnetic fields. One layer has a very low density and is in the WC regime (ν << 1), while the other (``probe'') layer is near ν = 1 / 2 and hosts a CF sea. As the magnetic field is swept away from ν = 1 / 2 of the CF layer, the CFs feel the periodic electric potential of the WC in the other layer and exhibit magneto-resistance maxima whenever their cyclotron orbit encircles certain integer number of the WC lattice points. Via measuring the temperature dependence of strength of these commensurability features, we probe the melting of the WC.

  9. Commensurability Oscillations of Composite Fermions Induced by the Periodic Potential of a Wigner Crystal.

    PubMed

    Deng, H; Liu, Y; Jo, I; Pfeiffer, L N; West, K W; Baldwin, K W; Shayegan, M

    2016-08-26

    When the kinetic energy of a collection of interacting two-dimensional (2D) electrons is quenched at very high magnetic fields so that the Coulomb repulsion dominates, the electrons are expected to condense into an ordered array, forming a quantum Wigner crystal (WC). Although this exotic state has long been suspected in high-mobility 2D electron systems at very low Landau level fillings (ν≪1), its direct observation has been elusive. Here we present a new technique and experimental results directly probing the magnetic-field-induced WC. We measure the magnetoresistance of a bilayer electron system where one layer has a very low density and is in the WC regime (ν≪1), while the other ("probe") layer is near ν=1/2 and hosts a sea of composite fermions (CFs). The data exhibit commensurability oscillations in the magnetoresistance of the CF layer, induced by the periodic potential of WC electrons in the other layer, and provide a unique, direct glimpse at the symmetry of the WC, its lattice constant, and melting. They also demonstrate a striking example of how one can probe an exotic many-body state of 2D electrons using equally exotic quasiparticles of another many-body state. PMID:27610870

  10. Paying for particulars in people-to-be: commercialisation, commodification and commensurability in human reproduction.

    PubMed

    Fox, D

    2008-03-01

    The push of biomedical profits and pull of consumer desire for greater happiness and superior performance heralds a robust market in offspring enhancement. There are two reasons we might worry about the reach of commerce into the realm of selective reproduction. The first concern is that for-profit genetic enhancement, under conditions of economic necessity, would exploit the poor, by coercing them, in effect, to part with reproductive material they would prefer not to sell for money, if not for their desperate situation. The second concern is that the market valuation and exchange of sperm, eggs, and embryos would distort the meaning, and degrade the worth, of those procreative goods. I argue that the concern about exploitation does not give reason to resist a market in pre-natal enhancement, but that the concern about degradation does. This degradation concern gives rise to two specific worries: one about altruism and another about commensurability. I conclude by sketching several policy recommendations to regulate the transfer of money in exchange for sperm and eggs with specified characteristics. PMID:18316456