Adjustable Thermal Expansion Properties in Zr2MoP2O12/ZrO2 Ceramic Composites

Polymorphism and Building-Block-Resolved STM Imaging of Self-Assembled Monolayers of 4-Fluorobenzenemethanethiol on Au(111)

Self-assembled monolayers (SAMs) of 4-fluorobenzenemethanethiol (p-FBMT) on Au(111), prepared by immersion procedure (1 mM ethanolic solution; 60 °C; 18 h), were characterized by scanning tunneling microscopy (STM). The data suggest the formation of highly ordered monolayer with a commensurate structure, described by the 2 3 × 13 R 13 ∘ unit cell. The STM appearance of this cell occurs, however, in two different forms, with either well-localized individual spots or splitting of these spots in two components. These components are assigned to the tunneling through the entire molecule or sulfur docking group only. The respective spots correspond then to the terminal fluorine atom and sulfur docking group, manifesting, thus, building-block-resolving STM imaging. The accessibility of the docking group for direct tunneling is most likely related to a specific molecular organization for one of the two possible internal structures of the unit cell. The above results represent a showcase for potential of STM for imaging of upright-arranged and densely packed molecular assemblies, such as SAMs.

ZrW2O8/ZrO2 Composites with Low/Near-Zero Coefficients of Thermal Expansion Fabricated at Ultralow Temperature: An Integration of Hydrothermal Assembly and a Cold Sintering Process

ZrW₂O₈/ZrO₂ composites with tunable low/near-zero coefficients of thermal expansion (CTE) are promising candidates in several fields including aerospace, precision manufacturing and measurement, electronic circuit, etc., for counteracting the thermal expansion effect. However, bottleneck issues (such as the unstable decomposition of ZrW₂O₈ phase, manufacturing size limitation, etc.) caused by conventional high-temperature sintering impede the development and application of ZrW₂O₈/ZrO₂. To solve these scientific issues, a methodology integrating hydrothermal assembly with a cold sintering process (CSP) is exploited. The ZrW₂O₈/ZrO₂ composite powders with a mace-like structure, in which the spherical ZrO₂ nanoparticles peripherally embed on the rod-like ZrW₂O₈ matrix particles, are hydrothermally assembled. Then, the relatively dense ZrW₂O₈/ZrO₂ composites with excellent low or even near-zero CTE are successfully achieved by CSP (as low as 190 °C) with a postannealing treatment (550 °C). The evolution of sintering densification, phase composition, and microstructure followed by the fundamental mechanism regarding the hydrothermal assembly of the mace-like structure and densification of CSP are investigated in detail. This research not only effectively overcomes the bottleneck issues of ZrW₂O₈/ZrO₂ via integrating the hydrothermal assembly with the sintering technology at ultralow temperature but also develops a promising prospect for the fabrication of a broader range of metastable functional materials.

Graphene Origami with Highly Tunable Coefficient of Thermal Expansion

The coefficient of thermal expansion, which measures the change in length, area, or volume of a material upon heating, is a fundamental parameter with great relevance for many applications. Although there are various routes to design materials with targeted coefficient of thermal expansion at the macroscale, no approaches exist to achieve a wide range of values in graphene-based structures. Here, we use molecular dynamics simulations to show that graphene origami structures obtained through pattern-based surface functionalization provide tunable coefficients of thermal expansion from large negative to large positive. We show that the mechanisms giving rise to this property are exclusive to graphene origami structures, emerging from a combination of surface functionalization, large out-of-plane thermal fluctuations, and the three-dimensional geometry of origami structures.