X-ray diffraction on chlorine adsorbed on graphite

Cl₂ layers adsorbed on Grafoil have been investigated by X-ray diffraction between 78 and 285 K. Mono- and submonolayers crystallize in a parallelogram lauttce, incommensurate with the (001) graphite surfaces, the molecules oriented almost perpendicular to the surface. The structure is closely related to that of the (001) planes of three-dimensional solid chlorine. For coverages above the monolayer completion bulk crystalization sets in.     

STM investigations of PTCDA and PTCDI on graphite and MoS2. A systematic study of epitaxy and STM image contrast

Monolayers of the organic molecules perylene-3,4,9,10-tetra-carboxylic-dianhydride (PTCDA) and diimide (PTCDI) on graphite and MoS₂ have been imaged with scanning tunneling microscopy. The epitaxial growth of the two molecules is determined by the intermolecular interaction but nearly independent of the substrate. On both substrates the STM image contrast in the submolecularly resolved images is dominated by the aromatic perylene system whereas the polar oxygen and nitrogen groups are invisible. The correlation of the observed inner structure of the molecules to their molecular structure allows us to compare our results with theoretical considerations.     

A LEED study of adsorbed neon on graphite

Neon monolayers on graphite have been investigated by high resolution LEED in the range 14.5 < T < 7.5 K and 10^?8 < p < 10^?4 Torr. The fluid-solid transition line has the form ln$\text{(}\text{p}\text{Torr}\text{)= ?}\text{A}\text{T + B}\text{,}\text{with}\text{A = 740 ± 45}\text{K and}\text{B = 31.0 ± 2.8}$. The solid is an incommensurate rotated phase whose lattice parameter decreases and rotation angle increases away from the transition line. Comparison is made with other thermodynamic and diffraction studies, and a preliminary phase diagram is constructed. Extrapolation of these data to higher temperatures and pressure suggests that this rotated solid monolayer is stable up to 23–25 K (P = 3?10 Torr) at coverage x = 1, and is stable over the range 0.88 < x < 1.0 at T = 16 K (2 × 10^?7 < p 1.5 × 10^?2 Torr). Extrapolation to lower temperatures gives the 2D triple point pressure in the range p = (0.3?3) × 10^?10 Torr. The steep slope of the fluid-solid transition line is consistent with the fluid phase having a high density (x?0.80) in the temperature range studied.     

Tetracene film morphology: Comparative atomic force microscopy, X-ray diffraction and ellipsometry investigations

X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry were used to study tetracene thin films as a function of deposition rate. A comparative analysis of the thickness and roughness values allows for detailed modelling of the film morphology. An interdigitated growth mode is established for the coexisting thin film and bulk phases. By comparison with the respective quinone-derivative of tetracene, we were additionally able to identify reaction products by their optical response.     

X-ray diffraction study of the structure of xenon multilayers on single crystal graphite

The structures of xenon multilayers (1 to 44 layers) physisorbed onto a graphite single crystal surface have been studied using x-ray scattering techniques. Both the intra-planar and inter-planar structures could be examined by measurements of the (1 0l) diffraction rods. The (0 0l) diffraction provides direct information about the thickness of the multilayer. We find two principal and surprising results. First, the xenon does not form an infinite number of layers at low temperatures. This disagrees with a number of previous reports which suggest complete wetting of xenon on graphite. Second, the structures of the adsorbed layers turn out to be rather elaborate. Instead of uniform, defect free layers, the xenon multilayers exhibit stacking disorder and a commensurate-incommensurate transition in the first layer.     

Raman scattering and X-ray diffraction investigations about the polyamorphism in triphenyl phosphite

The polyamorphism of triphenyl phosphite has been investigated from low-frequency Raman scattering and X-ray diffraction investigations. From a dynamic point of view, the use of the usual low-frequency criteria to characterize the fragility of the glacial state has revealed that glacial TPP was not truly amorphous. Furthermore, X-ray investigations allow us to describe the glacial state in terms of nanocrystallized domains characterized by a large unit cell that appears as a clear picture of the long-range order developing in the crystalline phase.     

LEED and Auger investigations of Cu (111) surface

After ultrahigh vacuum bake-out, electropolished Cu (111) surfaces were shown by Auger analysis to be contaminated by C, N, O, S and Cl. Other than C and S, which were contained in the bulk, the impurities were introduced by surface preparation; but all were easily removed by light Ar ion bombardment. Heating to ≈ 750°C caused diffusion of C and S from the bulk to the extent that a clear diffraction pattern corresponding to a √7 × √7 structure was produced by S on the surface. At ≈ b 900°C evaporation of Cu occurred to an observable degree, and S and C could no longer be detected on the surface. Auger analysis of clean Cu surfaces showed many details of the LMM and MMM types of transitions. Kinetic energies of all observed Auger electrons were in excellent agreement with calculated values. Also, the ≈ 62 eV MMM peak was resolved into two components related to the small differences in the M₂ and M₃ energy levels. The LMM transitions were classified according to their intensities, which could be rationalized on the basis of Coster-Kronig transitions and transition probabilities, as L₃MM > L₂MM > L₁MM.     

Orientational order in CO and N2 monolayers on graphite studied by X-ray diffraction

X-ray diffraction has been used to study the structure and orientational phase transitions of CO and N₂ adsorbed on graphite (Papyex). Both form orientationally ordered 2√3 × 2√3 R30° commensurate phases on graphite at low temperatures (10 K). The in-plane herringbone structure of N₂ has been confirmed but CO has more orientational disorder than N₂, which may be associated either with tilting, random static or systematic, of the molecules away from the surface and/or with orientational order of shorter range than the centre of mass order. In the first case the average tilt would have to be about 26° and in the second case the orientational correlation length would have to be 200 Å compared with 450 Å for the translational order. The orientational phase transition is sharp for N₂, occurring over the range 27–30 K, in agreement with previous work. For CO the transition is broad and starts at lower temperatures. This and the structural data indicate that a point quadrupolar interaction is not a suitable model for comparing the properties of N₂ and CO layers. The orientational phase transition in the incommensurate phase of N₂ is found to be broad and occurs below 20 K. For CO it is sharper than for the commensurate phase and occurs at a higher temperature. The lattice parameter changes by 0.75% across the orientational phase transition. For both N₂ and CO there is evidence of translational disorder in the commensurate phases but it cannot be interpreted quantitatively.     

LEED investigations on pure and metal treated vicinal silicon(111)

The structure of vicinal Si(111) surfaces as a function of misorientation (16°-[ ] 16°-[ ]) was studied by LEED measurements. We find significant differences in morphology dependent on the step orientation. In part drastical changes of the structure have been observed after evaporation of small amounts of Ni or Pd, and after additional high temperature heat treatment. For Ag/Si(111) no changes were observed.     

Adsorption of krypton on the basal plane of graphite: LEED and Auger measurements

The adsorption of krypton on (0001) graphite has been studied by LEED and Auger. Stepwise isotherms are observed and thermodynamic quantities such as the latent heat of two dimensional adsorption and the binding energy of a krypton atom are determined. The mean free path of electrons in krypton is measured. The LEED pattern of the krypton layer shows a √3 × √3 superstructure. Some vibrational properties are examined by LEED and possible implications of the experimental findings are discussed. The potentials and limitations of the techniques used in the present work are critically examined with respect to other techniques.     

X-ray diffraction on denatured ferritin

Denatured ferritin, in contrast to other denatured corpuscular proteins, gives several diffractions, even in the regiond>15 Å. These diffractions correspond to the mutual arrangement of the micelles and proteinic component of ferritin. Diffractions in the regiond<15 Å correspond both to the internal structure of the denatured proteinic component — apoferritin — and to the internal structure of ferric micelles of ferritin. Regions containing only the denatured proteinic component with polypeptide chains in-configuration, occur in the structure of denatured ferritin in addition to the crystallites or crystalline regions with regular arrangement of micelles and the proteinic component.

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, , d>15 Å. . d<15 Å — , — . , gb-.

     

Intermediate range order in concentrated aqueous solutions of copper nitrate. X-ray diffraction and Raman investigations

Concentrated aqueous solutions of copper nitrate of different concentrations (0.66 mol dm⁻³ up to 4.84 mol dm⁻³) have been investigated by X-ray diffraction at room temperature. In these solutions a maximum of intensity (prepeak) is observed at low values of Q (approx. 0.6 to 1 Å⁻¹) suggesting the existence of an intermediate range order in their structure, in agreement with previous investigations on different electrolytes. In order to get information on the solvation shell of the copper cation, Raman spectroscopy experiments have been performed for the more concentrated solution. Polarization observations, isotopic substitution of the solvent and the comparison with a Raman spectrum of a concentrated aqueous solution of aluminum nitrate were performed in order to improve the interpretation of the obtained results with these convergent observations.     

A LEED study of methane films adsorbed on graphite in the monolayer range

The submonolayer structural properties of methane on graphite have been studied by means of low energy electron diffraction in the range 30–67 K, allowing the determination of the orientational epitaxy of the CH₄ monolayer adsorbed on graphite single crystals. Thermodynamic adsorption properties have also been measured, and are compared with earlier volumetric measurements recorded in the temperature range 77–84 K.     

X-ray diffraction investigations of the crystallographic parameters and thermal expansion of β-BaB2O4 crystals

The lattice parameters a and c of β-BaB₂O₄ crystals have been measured in the temperature range 80–300 K by the x-ray diffraction method. The thermal expansion coefficients α are calculated from the measured values of the parameters. A substantial anisotropy of the thermal expansion is found. It is shown that the thermal expansion coefficient α _c along the c axis is an order of magnitude greater than the thermal expansion coefficient α _a in a plane perpendicular to this axis. It is established that α _a becomes negative in the temperature range 80–190 K. Fiz. Tverd. Tela (St. Petersburg) 39, 1038–1040 (June 1997)     

Observation of an ordered surface structure on the edge surface of graphite by LEED

We report the first observation of an ordered LEED pattern from the edge or prism surface of graphite. The surface structure was developed after in-situ gasification and is not equivalent to that resulting from any termination of the low index crystal planes of graphite. The pattern is indexed c(2 × $\text{2}\text{3}$) relative to termination parallel to {101&#x0304;0} and its occurrence can be rationalized.     

德拜对多晶X射线衍射的研究

简述了德拜的生平,回顾了他在多晶X射线衍射研究过程中所作的工作,并分析了他取得成功的因素,展现了他独特的人格魅力.     

X-ray diffraction from rough, relaxed and reconstructed surfaces

A general formalism is presented for computing the scattered X-ray intensity from surfaces showing disorder in the form of atomic-scale roughness or in the form of reconstructed domains of finite size. Special attention is paid to the interference between bulk and surface contributions, since this is important in the determination of relaxation parameters or of the registry of a surface unit cell.