Stripe phase

A very different model of tubules with tilt variations was developed by Selinger et al.132,186 Instead of thermal fluctuations, these authors consider the possibility of systematic modulations in the molecular tilt direction. The concept of systematic modulations in tubules is motivated by modulated structures in chiral liquid crystals. Bulk chiral liquid crystals form cholesteric phases, with a helical twist in the molecular director, and thin films of chiral smectic-C liquid crystals form striped phases, with periodic arrays of defect lines.176 To determine whether tubules can form analogous structures, these authors generalize the free-energy of Eq. (5) to consider the expression... 

A > 0, i.e. repulsive walls. The number of walls tends to be as small as possible, i.e. a striped network of parallel walls (SI) will be formed in the incommensurate region. The C-SI transition should be continuous. The striped phase is expected to be stable only close to the C-I transition. At larger misfits the hexagonal symmetry should be recovered in a first-order SI-HI transition. 

The analysis in the last paragraph has shown that the incommensurate Xe layer on Pt(lll) at misfits of about 6% is a striped phase with fully relaxed domain walls, i.e. a uniaxially compressed layer. For only partially relaxed domain walls and depending on the extent of the wall relaxation and on the nature of the walls (light, heavy or superheavy) additional statellites in the (n, n) diffraction patterns should appear. Indeed, closer to the beginning of the C-I transition, i.e. in the case of a weakly incommensurate layer (misfits below 4%) we observe an additional on-axis peak at Qcimm + e/2 in the (2,2) diffraction pattern. In order to determine the nature of the domain walls we have calculated the structure factor for the different domain wall types as a function of the domain wall relaxation following the analysis of Stephens et al. The observed additional on-axis satellite is consistent with the occurrence of superheavy striped domain wails the observed peak intensities indicate a domain wall width of A=i3-5Xe inter-row distances. With... 

Proposed structure for the low coverage striped phase of MMB (Reprinted with permission from [4] F. Schreiber Prog. Suif. Sci. 

Figure 8.6 Stripe period as a function of temperature for various thickness PbTiOs films, showing transition between Fa and h p stripe phases.

Figure 8.8 Phase diagram for epitaxial PbTiOa thin films on SrTiOs. Circles no satellites, paraelectric phase P. Triangles ferroelectric stripe phase Diamonds ferroelectric stripe phase Fp. Squares ferroelectric monodomain phase If.

Ultrathin films of hexagonal symmetry under compressive strains (e.g. Ag/Pt(lll) with a misfit of +4.3%) relax the strain in a similar way by forming striped-phases. The domain walls are now regions of locally lower atomic density and are imaged dark in STM [73]. The stable configuration, however, consists of a trigonal network of crossed domain walls. 

McConnell, H.M. Theory of hexagonal and stripe phase in monolayers. Proc. Natl. Acad. Sci. USA 1989, 86, 3452. 

Charge stripes have also been found in a few other transition metal oxides and were first reported in the isostructural hole-doped nickelates, La2xSrxNi04 and La2Ni04+, which contain modulated Ni02 sheets.1291 But there is a striking difference between the nickelates and the cuprates in that the stripe phase in the former is insulating, much less superconducting, unlike in... 

Figure 8 Schematic illustration for the formation of SAMs of alkanethiolates on gold [73], (A) Alkanethiols adopt the highly mobile lattice-gas phase (B) above a critical value of coverage, striped-phase islands are formed (C) surface reaches saturation coverage of striped phase (D) surface undergoes lateral-pressure-induced solid phase transition high-density islands nucleate and grow at domain boundaries (E) high-density islands grow at the expense of the striped phase until the surface reaches saturation...

Figure 9.17 Density of Ne at T= 12K and log P (atm) = —19, —16, and —9, from top to bottom. The middle curve superimposes results for nearly degenerate seven-stripe and eight-stripe phases of the monolayer. (Adapted from Ref. [84].)...

Figure 9-19 Phonon dispersion relation (angular frequency vs. relative wave vector) for the three-stripe phase of CH4 on the external surface of a bundle. LI, L2, and L3 are longitudinal branches, i.e., molecular motion parallel to the groove. The dotted curve is the result for a ID adsorbate at the same density. The remaining curves correspond to the dispersion relation of transverse modes. (Adapted from Ref. [89].)...

Figure 11.5 Structure models of (a) the saturated petylene monolayer and (b) the (5 X 5) stripe phase formed on the reconstructed Cu(l 10) substrate.

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