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Relaxed Langmuir monolayers of methyl eicosanoate were studied using Brewster angle microscopy (BAM) and grazing incidence x-ray diffraction (GIXD). The structure of the various phases in this system was determined and compared to previous isotherm and microscopy measurements. At low pressure and low temperature, a crystalline phase with tilt toward nearest neighbor, I(L2″), is observed. At a temperature of ∼14 °C and low pressure there is a transition to a phase with tilt toward next-nearest neighbor, F(L2′). Finally, as the temperature continues to be raised at low pressure, there is a transition to a phase where the two F(L2′) peaks have the same values of Qxy, here called the τ phase, with a Rotator IV-like structure. At high pressure and low temperature, an untilted, orthorhombic phase, U′(CS), is observed. As the temperature is increased, a second untilted, orthorhombic phase, U(S), is observed, beginning at ∼12 °C. Above 21 °C and at high pressure, a Rotator-II-like phase is seen, with an undistorted, untilted structure. Finally, results from BAM measurements are used to monitor the texture of the film in the different phases. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied Langmuir monolayers composed of mixtures of heneicosanoic acid and heneicosanol using π-A isotherms and x-ray diffraction. We find that the two materials are miscible in monolayer form. We have determined how the phase diagram of the acid evolves to that of the alcohol as the composition varies. X-ray diffraction data along isotherms and isobars show that the head–head interactions, like the tail–tail interactions, are anisotropic. The ‘‘swiveling transition’’ between phases with different tilt directions is accompanied by a rotation of the molecules about their long axes. [ABSTRACT FROM AUTHOR]

We have studied Langmuir monolayers of CH3(CH2)20OH (heneicosanol) using x-ray diffraction. Over the temperature range 7–55 °C, the monolayer isotherms show only one discontinuity, which may be either a ‘‘flat section’’ or a ‘‘kink;’’ we find that these are transitions between tilted and untilted phases. There are several untilted phases, with hexagonal and distorted-hexagonal structures, as in monolayers of the corresponding (heneicosanoic) acid. However, in contrast to the acid, when the pressure is lowered the molecules tilt only towards a next-nearest neighbor. The dependence of the lattice spacings on pressure and temperature indicate that the monolayer does not form a ‘‘tilted hexagonal’’ phase, even at temperatures where the untilted phase is hexagonal (rotator-II). [ABSTRACT FROM AUTHOR]

We have studied the effect of pressure and pH on Langmuir monolayers of heneicosanoic acid in the presence of calcium ions in the subphase. At very low pH the monolayer is unaffected by calcium ions; as the pH is increased, the head groups are pulled closer together and the chain tilt at zero pressure decreases. As a result, the phase transitions seen along the isotherms occur at lower pressures. When the isotherms become featureless, the chains are untilted at all pressures. At very high pH, a new untilted structure is observed. [ABSTRACT FROM AUTHOR]

X-ray diffraction data from water-supported monolayers of fatty acids with chain lengths from 19 to 22 is presented. The structures of the tilted mesophases L2’, L2, and Ov are characterized in detail. The contributions to the unit cell distortion from the tilt and the ordering of the backbone planes of the molecules are separated. It is shown that at the swiveling transition L2’–L2, not only the tilt azimuth but also the packing of the backbone planes change discontinuously. We demonstrate that the tilting transition LS–L2 is accompanied by the ordering of the backbone planes and may be discontinuous. Evidence is presented for a herringbone ordering transition within the L2 region. The distortions are related to symmetry of the phases and described by the order parameters responsible for tilt and herringbone ordering of the backbone planes of the molecules. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Deals with a study which examined in situ x-ray diffraction studies of the growth of thin films using a synchrotron light source. Information on an off-axis faced magnetron sputtering chamber; Methodology of the study; Results and discussion.

Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors. Van der Waals crystals are expected to have an inert surface because of the absence of dangling bonds. However, here we show that the surface of high-quality synthesized molybdenum disulfide (MoS2) is a major n-doping source. The surface electron concentration of MoS2 is nearly four orders of magnitude higher than that of its inner bulk. Substantial thickness-dependent conductivity in MoS2 nanoflakes was observed. The transfer length method suggested the current transport in MoS2 following a two-dimensional behavior rather than the conventional threedimensional mode. Scanning tunneling microscopy and angle-resolved photoemission spectroscopy measurements confirmed the presence of surface electron accumulation in this layered material. Notably, the in situ-cleaved surface exhibited a nearly intrinsic state without electron accumulation. [ABSTRACT FROM AUTHOR]