Silica-based glass is a household name, providing insulation for windows to microelectronics. The debate over the types of motions thought to occur in or on SiO2 glass well below the glass transition temperature continues. Here, we form glassy silica films by oxidizing the Si(100) surface (from 0.5 to 1.5 nm thick, to allow tunneling). We then employ scanning tunneling microscopy in situ to image and classify these motions at room temperature on a millisecond to hour time scale and 50-pm to 5-nm length scale. We observe two phenomena on different time scales. Within minutes, compact clusters with an average diameter of several SiO2 glass-forming units (GFUs) hop between a few (mostly two) configurations, hop cooperatively (facilitation), and merge into larger clusters (aging) or split into smaller clusters (rejuvenation). Within seconds, Si–O–Si bridges connect two GFUs within a single cluster flip, providing a vibrational fine structure to the energy landscape. We assign the vibrational fine structure using electronic structure calculations. Calculations also show that our measured barrier height for whole cluster hopping at the glass surface (configurational dynamics) is consistent with the configurational entropy predicted by thermodynamic models of the glass transition and that the vibrational entropy for GFU flipping and configurational entropy for cluster hopping are comparable (on a per GFU basis).

At the intersection of spectroscopy and microscopy lie techniques that are capable of providing subnanometer imaging of excited states of individual molecules or nanoparticles. Such approaches are particularly important for imaging macromolecules or nanoparticles large enough to have a high probability of containing a defect. These inevitable defects often control properties and function despite an otherwise ideal structure. We discuss real-space imaging techniques such as using scanning tunneling microscopy tips to enhance optical measurements and electron energy-loss spectroscopy in a scanning transmission electron microscope, which is based on focused electron beams to obtain high-resolution spatial information on excited states. The outlook for these methods is bright, as they will provide critical information for the characterization and improvement of energy-switching, electron-switching, and energy-harvesting materials.

Periodic surface structures at the nanometer or micrometer scale have been achieved by various methods, while atomic-scale surface structures over large areas are unavailable. Herein, we report the formation of highly coherent atomic-scale ripple patterns on bulk metallic glass (MG) surfaces by low-energy ion irradiation. The pattern arises through three consecutive stages: emergence of initial random dots, subsequent transition to ripples, and ordering of the ripple pattern through annihilation reactions of mobile defects, while the wavelength and amplitude remain invariant throughout the patterning. No pattern is generated for the crystalline counterpart at the same irradiation condition. These observations suggest a distinct ripple forming process typical of MGs associated with their enhanced surface mobility, which enables a controllable self-organization approach for large-area surface structuring with atomic-scale precision.

A Brewster Angle Microscope (BAM) built from a LEGO Mindstorms kit, additional LEGO bricks, and several standard optics components, is described. The BAM was built as part of an undergraduate senior project and was designed, calibrated, and used to image phospholipid, cholesterol, soap, and oil films on the surface of water. A BAM uses p-polarized laser light reflected off a surface at the Brewster angle, which ideally yields zero reflectivity. When a film of different refractive index is added to the surface a small amount of light is reflected, which can be imaged in a microscope camera. Films of only one molecule (approximately 1 nm) thick, a monolayer, can be observed easily in the BAM. The BAM was used in a junior-level Physical Chemistry class to observe phase transitions of a monolayer and the collapse of a monolayer deposited on the water surface in a Langmuir trough. Using a photometric calculation, students observed a change in thickness of a monolayer during a phase transition of 7 Å, which was accurate to within 1 Å of the value determined by more advanced methods. As supplementary material, we provide a detailed manual on how to build the BAM, software to control the BAM and camera, and image processing software.

Efficient heat dissipation and large gate capacitance have made carbon nanotube field-effect transistors (CNT FETs) devices of interest for over 20 years. The mechanism of CNT FETs involves localization of the electronic structure due to a transverse electric field, yet little is known about the localization effect, nor has the electronic polarization been visualized directly. Here, we co-deposit PbS quantum dots (QDs) with CNTs and optically excite the QD so its excited-state dipolar field biases the local environment of a CNT. Using single-molecule absorption scanning tunneling microscopy, we show that the electronic states of the CNT become transversely localized. By nudging QDs to different distances from the CNT, the magnitude of the localization can be controlled. Different bias voltages probe the degree of localization in different CNT excited states. A simple tight-binding model for the CNT in an electrostatic field provides a semiquantitative model for the observed behavior.