Fluorenone derivatives (F−OC n ) with various lengths of peripheral alkyl chains (with carbon numbers of n = 12−18) were synthesized, and their self-assembled adlayers were investigated in solvents with different polarities and functionalities by scanning tunneling microscopy (STM) on a highly oriented pyrolytic graphite (HOPG) surface. The chain-length effect on the self-assembly of F− OC even was observed in 1-phenyloctane. With the shortening of the side chain, the self-assembled pattern changed from a dense-and loose-packed structure to a pliers-like structure. Self-assembly of F− OC odd showed a uniform lamellar pattern. An even−odd effect was observed resulting from the direction of the end methyl group in the alkyl chain unit. Furthermore, when the samples using dichloromethane as solvent were observed within 3 h, a less ordered lamellar structure appeared in most cases. The pliers-like pattern was observed for self-assembly of F−OC 16 and F−OC 14 . However, F− OC 17 formed a zigzag structure. Observation of the odd−even and chain-length effects on the self-assembled adlayers might provide an analytical method for examining the structural and chemical homogeneities.

Heat transfer across metal-semiconductor interfaces involves multiple fundamental transport mechanisms such as elastic and inelastic phonon scattering, and electron-phonon coupling within the metal and across the interface. The relative contributions of these different transport mechanisms to interface conductance remains unclear in the current literature. In this work, we use a combination of first-principles calculations under the density functional theory framework and heat transport simulations using the atomistic Green's function (AGF) method to quantitatively predict the contribution of the different scattering mechanisms to the thermal interface conductance of epitaxial CoSi 2 -Si interfaces. An important development in the present work is the direct computation of interfacial bonding from density functional perturbation theory (DFPT) and hence the avoidance of commonly used 'mixing rules' to obtain the cross-interface force constants from bulk material force constants. Another important algorithmic development is the integration of the recursive Green's function (RGF) method with Büttiker probe scattering that enables computationally efficient simulations of inelastic phonon scattering and its contribution to the thermal interface conductance. First-principles calculations of electron-phonon coupling reveal that crossinterface energy transfer between metal electrons and atomic vibrations in the semiconductor is mediated by delocalized acoustic phonon modes that extend on both sides of the interface, and phonon modes that are localized inside the semiconductor region of the interface exhibit negligible coupling with electrons in the metal. We also provide a direct comparison between simulation predictions and experimental measurements of thermal interface conductance of epitaxial CoSi 2 -Si interfaces using the time-domain thermoreflectance technique. Importantly, the experimental results, performed across a wide temperature range, only agree well with predictions that include all transport processes: elastic and inelastic phonon scattering, electron-phonon coupling in the metal, and electron-phonon coupling across the interface.2

The self-assembled behaviors of two fluorenone derivatives, 2,7-bis­((11-hydroxyundecyl)­oxy)-9-fluorenone (BHUF) and 2,7-bis­((10-carboxydecyl)­oxy)-9-fluorenone (BCDF), were investigated at the liquid–solid interface by scanning tunneling microscopy. Two solvents, 1-octanoic acid and 1-phenyloctane, were employed in consideration of their distinct polarity and solubility. It is observed that the BHUF molecules self-assemble into seven different polymorphs upon adsorption, while only two different polymorphs are observed in the BCDF monolayer. The theoretical calculation is performed to reveal the underlying mechanism. As compared to that of CO···HO hydrogen bonds, the enhanced binding energy of intermolecular CO···HOOC hydrogen bonds in the BCDF monolayer would dominate the intermolecular van der Waals (vdWs) interactions and the molecule–solvent interactions, thereby resulting in a limitation of expression of structural polymorphism. In addition, the concentration-dependent polymorphism as well as the relative phase transition is discussed in terms of the stability and packing density of different polymorphs. Furthermore, the different self-assembled behaviors of BHUF molecules in these two solvents at lower concentrations are associated with the different energy gain upon solvent coadsorption. The investigation provides a simple and alternative strategy to construct the structural polymorphs by utilizing multiple hydrogen bonds at the liquid–solid interface.

Two-dimensional supramolecular assemblies of a series of 2,7-bis(10-n-alkoxycarbonyl-decyloxy)-9-fluorenone derivatives (BAF-Cn, n = 1, 3-6) consisting of polar fluorenone moieties and ester alkoxy chains were investigated by scanning tunneling microscopy on highly oriented pyrolytic graphite surfaces. The chain-length effect was observed in the self-assembly of BAF-Cn. Self-assembly of BAF-C1 was composed of a linear I pattern, where the side chains adopted a fully interdigitated arrangement. As the length of side chains increased, the coexistence of a linear I pattern and a cyclic pattern for the self-assembly of BAF-C3 was observed. Upon increasing the length of the alkoxy chain even further (n = 4-6), another linear II structure was observed in the BAF-Cn monolayer, in which the side chains in adjacent rows were arranged in a tail-to-tail configuration. It is reasonable to conclude that not only the van der Waals forces but also the dipole-dipole interactions from both the fluorenone cores and the ester alkoxy chains play critical roles in the self-assemblies of BAF-Cn. Our work provides detailed insights into the effect of intermolecular dipole-dipole and van der Waals interactions on the monolayer morphology of fluorenone derivatives.

Herein, the photophysical properties of two π-conjugated thienophenanthrene derivatives (6,9- and 5,10-DBTD) are reported. Their self-assembled monolayers in aliphatic hydrocarbon solvents under different concentrations were investigated by scanning tunneling microscopy on a graphite surface. The STM results revealed that the self-assembled structures of the two geometrical isomers exhibited absolutely different behaviors. At the aliphatic solvent/graphite interface, 6,9-DBTD produced almost a single stable coassembled linear structure, except for that with n-tridecane as the solvent. However, the self-assembly of 5,10-DBTD showed structural diversity, and it presented a gradient variety through increasing the chain length of the aliphatic solvents as well as the solution concentration. All ordered self-assembled adlayers critically depend on not only the interchain van der Waals (vdW) interactions, but also on multiple intermolecular interactions, including BrO[double bond, length as m-dash]C and BrS hetero-halogen bonds, homo-BrBr interactions, and HBr and HO hydrogen bonds. We proposed that the cooperation and competition of the intermolecular interactions involving a Br atom and interchain vdW forces induce this structural variety. Density functional theory calculations support to unravel the different elementary structural units based on halogen bonds and hydrogen bonds and were useful tools to dissect and explain the formation mechanism.