Direct atomically resolved observation of dynamics deep in the glassy regime has proved elusive for atomic and molecular glasses. Studies below the glass transition temperature T g are especially rare due to long waiting times required to observe dynamics. Here we directly visualize surface glass dynamics deep in the glassy regime. We analyze scanning tunneling microscopy movies of the surface of metallic glasses with time resolution as fast as 1 minute and extending up to 1,000 minutes. Rearrangements of surface cluster occur almost exclusively by two-state hopping (P 3-state ≈ 0.06). All clusters are compact structures with a width of 2-8 atomic spacings along the surface plane. The two-state dynamics is both spatially and temporally heterogeneous. We estimate an average activation free energy of 14 k B T for surface clusters.TOC Figure:

Protein stability is measured by denaturation: When solvent conditions are changed (e.g., temperature, denaturant concentration, or pH) the protein population switches between thermodynamic states. The resulting denaturation curves have baselines. If the baselines are steep, nonlinear, or incomplete, it becomes difficult to characterize protein denaturation. Baselines arise because the chromophore probing denaturation is sensitive to solvent conditions, or because the thermodynamic states evolve structurally when solvent conditions are changed, or because the barriers are very low (downhill folding). Kinetics can largely eliminate such baselines: Relaxation of chromophores, or within thermodynamic states, is much faster than the transition over activation barriers separating states. This separation of time scales disentangles population switching between states (desired signal) from chromophore or population relaxation within states (baselines). We derive simple formulas to extract unfolding thermodynamics from kinetics. The formulas are tested with model data and with a difficult experimental test case: the apparent two-state folder PI3K SH3 domain. Its melting temperature T(m) can be extracted reliably by our "thermodynamics from kinetics approach," even when conventional fitting is unreliable.

An underlying goal in most chemistry curricula is to enable students to think like chemists, yet there is much evidence to suggest that students can learn to solve problems without thinking conceptually like a chemist. There are few tools, however, that assess whether students are learning to think like Ph.D. faculty, putative experts in the field. Here, we present a card-sorting task that probes how individuals organize information about problems in chemistry. Chemistry faculty tend to organize around "deep" features centered on fundamental ideas in chemistry while novices tend to organize around "surface" features such as problem presentation or specific vocabulary. We used established statistical techniques from card-sorting tasks in other fields and introduce a new quantitative measure that compares individual performance on the sorting task to faculty and novices that is hypothesis-independent. Initial results indicate that the card-sorting task is effective at distinguishing between populations of faculty and novices in chemistry and can be used to track progress toward more expert-like thinking over time through a chemistry education program.

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Chiral junctions of carbon nanotubes have the potential of serving as optically or electrically controllable switches. To investigate optoelectronic tuning of a chiral junction, we stamp carbon nanotubes onto a transparent gold surface and locate a tube with a semiconducting-metallic junction. We image topography, laser absorption at 532 nm, and measure I-V curves of the junction with nanometer spatial resolution. The bandgaps on both sides of the junction depend on the applied tip field (Stark effect), so the semiconducting-metallic nature of the junction can be tuned by varying the electric field from the STM tip. Although absolute field values can only be estimated because of the unknown tip geometry, the bandgap shifts are larger than expected from the tip field alone, so optical rectification of the laser and carrier generation by the laser must also affect the bandgap switching of the chiral junction.