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Self-assembly and molecular recognition are critical processes both in life and material sciences. They usually depend on strong, directional non-covalent interactions to gain specificity and to make long-range organization possible. Most supramolecular constructs are also at least partially governed by topography, whose role is hard to disentangle. This makes it nearly impossible to discern the potential of shape and motion in the creation of complexity. Here, we demonstrate that long-range order in supramolecular constructs can be assisted by the topography of the individual units even in the absence of highly directional interactions. Molecular units of remarkable simplicity self-assemble in solution to give single-molecule thin two-dimensional supramolecular polymers of defined boundaries. This dramatic example spotlights the critical function that topography can have in molecular assembly and paves the path to rationally designed systems of increasing sophistication.

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A thermodynamic analysis was made of the pseudobinary phase diagrams of the III-V semiconductor alloys, InSb-GaSb, InAs-GaAs, and InP-GaP. The excess free energy of mixing is expressed as Bxlx2, where B is a parameter characteristic of each system and xl and x2 are the mole fractions of the end components. This homologous series of alloys showed consistent behavior in that all of the B/RT vs. composition plots were linear for both the liquids and solids. The greater part of the excess free energy of mixing of the solids appears to be in the excess entropy rather than in the enthalpy, indicating that these materials freeze with local ordering or structure rather than as homogeneous random solids. The magnitude of the departure from ideality in the solids increases from the antimonide to the arsenide and to the phosphide, which is also the order of increasing lattice mismatch between the pairs of pure components. Implications of these results in the use of the alloys in semiconductor devices are discussed.It has been recognized for many years that the III-V alloy semiconductors might be useful for fabrication of new electronic and optical devices because of the possibility of adjusting the width of the forbidden energy gap by varying the composition of the alloys (1-3). In principle, by selecting the proper combinations of III-V compounds and adjusting the composition of the mixtures, semiconductors with band gaps ranging more or less continuously from 0.18 eV (InSb) to about 2.4 eV (ALP) could be prepared. * Electrochemical Society Active Member.Whether these mixtures will be useful semiconductors will depend not only on solving such obvious problems as the growth of suitably doped single crystals, but also on whether such alloys are indeed homogeneous mixtures with properties that are smooth blends of the properties of the individual components. Thermodynamic analysis of the phase diagrams of these pseudobinary systems can give an insight into the nature of the solid alloys. This information comes from the magnitude of the departure of the systems from ideal behavior and how this depends on temperature and composition.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.122.253.228 Downloaded on 2014-10-19 to IP

BaTiO3 positive temperature coefficient of resistance (PTCR) specimens were made from commercial BaTiO3 which was mixed with 0.35 mol. % of Ho2O3 to make it semiconducting and 0.07 mol. % of MnCO3. After sintering at 1320 °C the samples were annealed in batches at 1220 °C for various periods between 0 and 5 h. The effect of Mn was studied by making direct comparison with previous results obtained from Mn free but otherwise identical specimens. Room-temperature dielectric measurements in the audio and radio frequency ranges revealed that Mn had a negligible effect on the grain bulk resistance. Mn was found to result in an increase in the minimum and maximum values of the resistivity, the temperature at which the resistivity is a maximum and the slope of the resistivity-temperature characteristic in the transition region, all of which were attributed to an enhancement of the potential barrier at the grain boundaries. The acceptor state energy of the Mn-doped samples was found to be ∼1.4 eV, while a lower value was obtained for Mn-free material (∼1.12 eV). The effective concentration of Mn acceptors was observed to increase with the annealing time. To explain this behavior a thin Mn-rich boundary layer was assumed to exist, within which there was partial compensation of the Mn ions due to the formation of ionized oxygen vacancies. During annealing in air at 1220 °C, oxidation takes place and more of these vacancies are filled resulting in an increase in the effective Mn concentration. This model is also capable of explaining other phenomena such as the disappearance of the PTCR effect in reduced samples and the effects of cooling rate and quenching on the PTCR behavior.