Engineering Of Functional Materials Research Articles

Crystal engineering of functional materials via halogen bonding

Crystal engineering of functional materials <i>via</i> halogen bonding

ChemInform Abstract: Recent Approaches for Bridging the Pressure Gap in Photoelectron Microspectroscopy

AbstractReview: 103 refs.

Recent approaches for bridging the pressure gap in photoelectron microspectroscopy.

Ambient-pressure photoelectron spectroscopy (APPES) and microscopy are at the frontier of modern chemical analysis at liquid-gas, solid-liquid and solid-gas interfaces, bridging science and engineering of functional materials. Complementing the current state-of-the art of the instruments, we survey in this short review several alternative APPES approaches, developed recently in the scanning photoelectron microscope (SPEM) at the Elettra laboratory. In particular, we report on experimental setups for dynamic near-ambient pressure environment, using pulsed-gas injection in the vicinity of samples or reaction cells with very small apertures, allowing for experiments without introducing additional differential pumping stages. The major part of the review is dedicated to the construction and performance of novel environmental cells using ultrathin electron-transparent but molecularly impermeable membranes to isolate the gas or liquid ambient from the electron detector operating in ultra-high vacuum (UHV). We demonstrate that two dimensional materials, such as graphene and derivatives, are mechanically robust to withstand atmospheric - UHV pressure differences and are sufficiently transparent for the photoelectrons emitted from samples immersed in the liquid or gaseous media. There are many unique opportunities for APPES using X-rays over a wide energy range. We show representative results that illustrate the potential of these 'ambient-pressure' approaches. Combined with the ca 100 nm lateral resolution of SPEM, they can overcome the pressure gap challenges and address the evolution of chemical composition and electronic structure at surface and interfaces under realistic operation conditions with unprecedented lateral and spectral resolution.

Molecular Mobility and Interfacial Dynamics in Organic Nano-electromechanical Systems (NEMS)

The underpinnings of material properties in nanoscopic polymer systems are reviewed in light of the relaxation modes available for molecular motion. When motion is altered due to the presence of constraints, a rich variety of material and transport behaviors become apparent. On the one hand, external constraints imposed by interfaces and system boundaries generate structural and dynamical anisotropies that can propagate over device-relevant length scales. On the other hand, the ability to cater relaxation behavior through molecularly-engineered internal constraints offers a path to optimize material properties in nanoscopic systems. These two aspects are highlighted throughout the review, and their technological implications are discussed for MEMS/NEMS operations, including frictional and mechanical loading of polymer thin films. In this regard, material performance attributes and feedback for molecular designs are drawn from perturbation techniques that provide access to the energetic signatures and characteristic scales of molecular relaxation. In particular, the importance of the operating time scale in nanoscopic devices is emphasized with examples of both quasi-static and dynamic operations. Material responses have been found to change significantly when the drive velocity or loading rate was either comparable to or in excess of the characteristic molecular frequencies. Correspondingly, intrinsic molecular modes were found to either couple with the external mechanical disturbance, thus establishing channels for energy transport, or to remain passive, leading to apparent material stiffening. Findings such as these suggest that comprehensive investigations of the spatial distribution of molecular relaxation spectra in confined systems are necessary in order to match (or mismatch) molecular response times with system operating times. Along this line, this review provides examples for cognitive engineering of functional materials, with molecular structures that are tailored to system constraints and employed in nanoscale device technologies.

RESEARCH INITIATIVES: What Lies Ahead for Nanotechnology?

RESEARCH INITIATIVES: What Lies Ahead for Nanotechnology?

Biologically inspired polyoxometalate–surfactant composite materials. Investigations on the structures of discrete, surfactant-encapsulated clusters, monolayers, and Langmuir–Blodgett films of (DODA)40(NH4)2[(H2O)n ⊂ Mo132O372(CH3CO2)30(H2O)72] †

A detailed analysis of the supramolecular architecture of the nanoporous surfactant-encapsulated cluster (SEC) with the empirical formula (DODA)40(NH4)2[(H2O)n ⊂ Mo132O372(CH3CO2)30(H2O)72] 1 (n ≈ 50) is presented. The open framework architecture of the Keplerate cluster is investigated by means of small angle neutron scattering (SANS) in CDCl3 solutions containing discrete SECs. A simplifying core–shell model of 1 is developed, which describes the SEC as a solvent-filled nanocavity, surrounded by two concentric shells (a first polyoxometalate shell of 2.96 nm outer diameter, and a consecutive surfactant shell of 6.18 nm outer diameter, respectively). The model is successfully applied to probe the content of H2O/D2O guest molecules in the Keplerate host. Different surface analytical techniques are applied to characterize the hierarchical structures of monolayers and thin films of 1. Monolayers at the air–water interface are investigated by means of optical ellipsometry and Brewster angle microscopy. Electron density profiles of the monolayers of 1 are gained from synchrotron X-ray reflectance (XRR) measurements that provide further evidence for the supramolecular core-shell architecture of the SEC. Within the spatial resolution limits of these analytical methods, the current data support a monolayer model consisting of hexagonal close-packed arrays of discrete SECs, floating at the air–water interface. Langmuir–Blodgett (LB) transfer of compressed monolayers on to a solid substrate leads to homogeneous multilayers. In the XRR spectra of LB multilayers of 1 multiple Bragg reflections appear, thus indicating an intrinsic tendency of the SECs to adapt a 3-dimensional, highly ordered solid state structure. Considering the huge variety of structurally different polyoxometalates and the possibility to tailor the surfactant shell by means of classic organic synthesis, the self-organization of hierarchically structured thin films and solids based on SECs bears promising perspectives towards the engineering of functional materials.