Pulak Dutta

Tilted phases of fatty acid monolayers

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.

Self-Propagating Assembly of a Molecular-Based Multilayer

Accelerated growth of a molecular-based material that is an active participant in its continuing self-propagated assembly has been demonstrated. This nonlinear growth process involves diffusion of palladium into a network consisting of metal-based chromophores linked via palladium.

Selective monitoring of parts per million levels of CO by covalently immobilized metal complexes on glass

Optical detection of parts-per-million (ppm) levels of CO by a structurally well-defined monolayer consisting of bimetallic rhodium complexes on glass substrates has been demonstrated.

Stepwise Assembly of Coordination-Based Metal−Organic Networks

Metal-organic networks (MONs) were created by a stepwise solution deposition approach from vinylpyridine-based building blocks and PdCl(2). The combined experimental and computational study demonstrates the formation of saturated, structurally organized systems on solid supports. The rigid nature and geometry of the components are well-suited to form honeycomb and parallelogram structures, as predicted by a computational study. Detailed structural information of the new MONs was obtained by optical (UV/vis) spectroscopy, ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and synchrotron X-ray reflectivity (XRR). Notably, the XPS elemental composition indicates the formation of a palladium coordination-based network.

Molecular Assembly of a 3D-Ordered Multilayer

Combining strong metal-ligand coordination and pi-pi interactions affords a 3D-ordered molecular-based multilayer. The organization of the assembly is apparent from the optical properties and X-ray reflectivity.

X‐ray diffraction study of heneicosanol monolayers on the surface of water

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).

X-ray diffraction study of the in-plane structure of an organic multilayer (“langmuir—blodgett”) film

Abstract Using X-ray diffraction at glancing angles, we find that in Langmuir—Blodgett films of lead stearate the lead atoms form plane arrays identical to one set of planes in a bulk crystal, but with little correlation between the planes. The resulting system of two-dimensional layers is similar in its static structure to an ideal smectic-B liquid crystal

Effect of oxygen partial pressure on the in situ growth of Y‐Ba‐Cu‐O thin films on SrTiO3

The evolution of YBCO film growth with thickness at various oxygen pressures was observed by in situ synchrotron x‐ray diffraction in real time. When the films were deposited at 2 A/s and 730 °C under higher oxygen partial pressures (in an Ar/O2 mixture of 90 mTorr), the nucleation was observed to have c‐axis orientation. After the films reached a critical thickness, the growth of the YBCO film changed from c axis to a axis and then propagated epitaxially. This provides evidence that a‐axis epitaxial growth nucleates on a c‐axis base. The critical thickness reflects the competition between the growth of the c and a axes, which is determined by the oxygen partial pressure in the process of thin‐film formation. The a‐axis oriented films showed a very sharp rocking curve (less than 0.1°) which indicates a very high structural quality. For very low oxygen partial pressures, the in situ growth process was very similar, but the initial nuclei involve a second phase mixed with a small amount of c‐axis ‘‘123’’ ph...

The effect of interface roughness on the intensity profiles of Bragg peaks from superlattices

We have derived an expression for the structure factor of a superlattice with ‘‘rough’’ interfaces, i.e., with random variations in the thicknesses of the layers. Our expression allows the determination of x‐ray diffraction profiles in both radial (θ‐2θ) and rocking scans. We have shown that the rocking curve of the central peak is essentially unaffected by this kind of disorder; and we have calculated the rocking curve widths of the satellites as a function of roughness. The implications of our model for the use of satellite/central peak intensity ratios as a measure of superlattice perfection are discussed.

Triarylamine siloxane anode functionalization/hole injection layers in high efficiency/high luminance small-molecule green- and blue-emitting organic light-emitting diodes

High efficiency/high luminance small-molecule organic light-emitting diodes (OLEDs) are fabricated by combining thin, covalently bound triarylamine hole injection/adhesion interlayers with hole- and exciton-blocking/electron transport interlayers in tris(8-hydroxyquinolato)aluminum(III) (Alq) and tetrakis(2-methyl-8-hydroxyquinolinato)borate (BQ4−)-based OLEDs. Green-emitting OLEDs with maximum luminance ∼85000cd∕m2, power and forward external quantum efficiencies as high as 15.2lm∕W and 4.4±0.5%, respectively, and turn-on voltages ∼4.5V are achieved in devices of the structure, ITO∕N,N′-diphenyl-N,N′-bis(p-trichlorosilylpropylphenyl)(1,1′-biphenyl)-4,4′-diamine (TPD-Si2)/1,4-bis(1-naphthylphenylamino)biphenyl (NPB)/Alq doped with N,N′-di(3-heptyl)quinacridone (DIQA)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)∕Li∕AgMg. Also, bright and efficient blue-emitting OLEDs with turn-on voltages ∼5.0V, maximum luminance ∼30000cd∕m2, and ∼5.0lm∕W and 1.6±0.2% power and external forward quantum efficiencies,...