Figure 6 STM images of CuPc molecules adsorbed on the TiO2(011) surface, panels a) and b) show sample before annealing, two distinct phases are observed, panels c) and d) illustrate sample after 2 hour annealing at 150°C, only phase II is visible, the amount of molecule dislocations, vacancies and defects is decreased after annealing, panels e) and f) show sample after two-hour annealing at 200°C, when completely new phase III is formed with up-right molecules, bias voltage +3.0V, tunnelling current 2pA. High resolution STM maps, shown in Figure 6, give more insight into the molecular structure of the islands in the 2nd layer. Phase II is composed of flat-lying molecules forming a brick-wall structure. The separation between neighboring molecules in the direction equals 1.8nm, that is a double of the surface unit cell dimension. The longitudinal separation between neighboring molecular rows also matches the double of the surface cell dimension (approximately 1.15nm). In a consequence, a c(44) superstructure is formed, that is significantly different from previously observed flat-lying molecular structures on different templates (i. e. on graphite [14, T. G. Gopakumar et al., J. Phys. Chem. B 108, 7839 (2004).], VOPc on Au(111) [15, K. W. Hipps, D. E. Barlow, U. Mazur, J. Phys. Chem. B 104, 2444 (2000).], CuPc on graphite and alkane adlayer [16, A. Yin et al., J. Phys. Chem. B 106, 9044 (2002).], on Cu(111) [17, H. Karacuban, M. Lange, J. Schaffert, O. Weingart, Th. Wagner, R. Möller, Surf. Sci. Lett. 603 (2009) L39], on Au(111) [18-20, M. Takada, H. Tada, Chem. Phys. Lett. 392, 265 (2004). J. Y. Grand et al., Surf. Sci. 366, 403 (1996). K. W. Hipps et al., J. Phys. Chem. 100, 11207 (1996).]). At this point, it is worth to noti... ... middle of paper ... ...f phase III ordered layer (one domain). Presumably, the layer is stabilized by the π-π interaction between neighboring molecules and by the interaction of their hydrogen atoms with the π-plane of the first molecular layer [H. Huang et al., Appl. Phys. Lett. 94, 163304 (2009)., S. Tsuzuki et al., J. Am. Chem. Soc. 122, 3746 (2000).]. With regards to possible future applications of the presented system in solar power converting devices or optoelectronics, it is worth to point out here that 200°C annealing not only leads to a reorientation of molecules into the up-right configuration, but also provides large, stable and well-ordered domains with much lower density of defects, molecule dislocations and vacancies when compared to phases I and II. Formation of such large, well-ordered domains is of great importance to increase the efficiency of any optoelectronic device.
Kim, Taewoo, Trey L Arnold, Kyle A Leland, Aimee M Morey, Department of Chemistry, USAF Academy, CO 80840
David and John Free. (26 Nov 2006). MadSci Network: Chemistry. Retrieved on March 6, 2011, from http://www.madsci.org/posts/archives/2007-02/1171045656.Ch.r.html
Schlesinger, Mordechay. "Electrochemistry Encyclopedia." Electroplating. Department of Physics, University of Windsor, Sept. 2002. Web. 17 Nov. 2013.
Acknowledgements. Special thanks go to the Department of Chemistry and Chemical Biology at IUPUI, Dr. Ryan E. Denton, Professor and Dan Preston, TA.
In basic research, special model systems are needed for quantitative investigations of the relevant and fundamental processes in thin film materials science. In particular, these model systems enable the investigation of i.e. nucleation and growth processes, solid state reactions, the thermal and mechanical stability of thin film systems and phase boundaries. Results of combined experimental and theoretical investigations are a prerequisite for the development of new thin film systems and tailoring of their microstructure and performance.
The molecular shape of a molecule has a lot to do with how a molecule functions and how it can be used. Molecular shape is the three-dimensional grouping of atoms that make up a molecule.1 It determines several properties of a substance. These include the molecule’s color, reactivity, biological activity, polarity, magnetism, and phase of matter. To decide the shape of a molecule, the Lewis electron dot structure must be drawn. To be clear though, the Lewis dot drawing does not determine the shape of a molecule. It is just the first part in determining the shape of a molecule. The Lewis dot drawing helps to identify the lone pairs and bond pairs of a molecule. Then, with the Lewis dot drawing, the valence-shell electron-pair repulsion (VSPER) theory can be used to determine the molecular geometry and the electron-group geometry of a molecule.2 It is important to know how to draw the Lewis structure of a molecule because that is what everything else that will be stated is based on. The Lewis dot structure can not give any exact answers, but it is an essential guide to determine a ...
In the last 30 years, data obtained from spectrometric measurements, Xray and electron diffraction studies, and other experiments have yielded precise information about bond distances, angles, and energies. In many cases, the data confirmed conclusions reached earlier. In other cases, valuable new insights were acquired. Structure theory has advanced far beyond the simple electron dot representations and now rests securely on the foundations of quantum and wave mechanics. Although problems involving only simple molecules can now be solved with mathematical rigor, approximations such as the valence bond theory and the molecular orbital theory are very successful in giving results that agree with experimental measurements.
[18] R.C. Weast, (Ed.-in-Cheif) CRC Handbook of Chemistry and Physics, 90th ed. CRC Press, Boca Raton, 1977-2009.
Arti bandgar et.al. in 2012 used aqueous peroxo titanate complex (PTC) precursor to obtain pure titanium dioxide[81] .Several characterization were done such as DSC–TGA, XRD, UV–Vis, SEM and TEM. In the study reflux time of PTC has increase and crystalline size too. The surface morphology of TiO2 changed to rice like shape and furtherin ellipsoid rods like shape from hexagonal shape.
Crystal Structures are divided into seven systems called lattices. A lattice is the arrangement of points of the atoms, ions, or molecules composing a crystal are centered at. The seven systems crystals are divided into consist of Cubic, Tetragonal, Orthorhombic, Hexagonal, Trigonal, Triclinic, and Monoclinic. The Cubic system is fairly basic. It consists of one lattice point on each corner of the cube, which each lattice point shared equally between eight adjacent cubes. The Tetragonal system is similar to the cubic crystals, but it is longer along one axis. Tetragonal crystal lattices form when stretching has occurred along one lattice vector. As a result, the cube is turned into a rectangular prism with a square base. The Orthorhombic system is like the Tetragonal crystals, but it does not have a square in the cross section. This lattice is formed when stretching has occurred along two lattice vectors, which fo...
Inorganic nanowires often exhibit unique property that is useful for future applications. As the sizes of materials are decreasing down to the nanoscale level, the physical structure and chemical properties of nanomaterials are also diverging away from its bulk form [N&N]. Nanowires display the quantum confinement effect which describes the energy level of electrons as discrete unit [N&N]. For example, the transfer of electrons from the valence band to the conducting band requires a specific amount of energy [N&N]. Additionally, the surface area to volume ratio increases as the particles gets smaller [N&N]. This property supports many of the future application of TiO2 nanowires that requires a large surface a...
[5] M. Uchida, Y. Fukuoka, Y. Sugawara, N. Eda, A. Ohta, J. Electrochem. Soc. 143 (1996) 2245−2252.
Raman and IR spectral studies is an important area in the field of lattice dynamics as it contains rich and valuable information. It gives the information about the structure and chemical composition of the compound. Raman and infrared spectra is used in the identification of the molecule. This data is also helpful in determining the site symmetry occupied by the atom and its exact position within a crystal. Many inorganic complex structured compounds change their structural phase at particular physical conditions. These transitions in the compound from one phase to the other can be determined through the Raman and infrared spectral data. Using this, vibrational frequencies of the compounds can also be identified and assigned on the basis of normal coordinate analysis.
Plontke, R. (2003, March 13). Chemnitz UT. TU Chemnitz: - Technische Universität Chemnitz. Retrieved April 1, 2014, from http://www.tu-chemnitz.de/en/
Ionic compounds, when in the solid state, can be described as ionic lattices whose shapes are dictated by the need to place oppositely charged ions close to each other and similarly charged ions as far apart as possible. Though there is some structural diversity in ionic compounds, covalent compounds present us with a world of structural possibilities. From simple linear molecules like H2 to complex chains of atoms like butane (CH3CH2CH2CH3), covalent molecules can take on many shapes. To help decide which shape a polyatomic molecule might prefer we will use Valence Shell Electron Pair Repulsion theory (VSEPR). VSEPR states that electrons like to stay as far away from one another as possible to provide the lowest energy (i.e. most stable) structure for any bonding arrangement. In this way, VSEPR is a powerful tool for predicting the geometries of covalent molecules.