Single-crystal, Si nanotubes, and their mechanical resonant properties.

Single-crystalline Si nanotubes (NTs) were fabricated using vapor-liquid-solid grown, Ge nanowires (NWs) as a template upon which a Si shell was deposited to first grow Ge-core, Si-shell NWs. The tips of these NWs were removed, enabling exposure of the Ge core to H(2)SO(4) and H(2)O(2). After removing the Ge core, single-crystalline Si NTs remained. In addition to growing these Ge-core, Si-shell NWs from a Si (111) substrate, these NWs were also grown horizontally from a vertical Si surface to enable the fabrication of horizontal NTs after focused ion-beam cutting and etching steps. The resonant properties of the Ge-core, Si-shell NW, and the Si NT after the cutting and etching steps were measured and found to have a quality factor, Q, of approximately 1800.

Diverse metastable structures formed by small oligomers of α-synuclein probed by force spectroscopy.

Oligomeric aggregates are widely suspected as toxic agents in diseases caused by protein aggregation, yet they remain poorly characterized, partly because they are challenging to isolate from a heterogeneous mixture of species. We developed an assay for characterizing structure, stability, and kinetics of individual oligomers at high resolution and sensitivity using single-molecule force spectroscopy, and applied it to observe the formation of transient structured aggregates within single oligomers of α-synuclein, an intrinsically-disordered protein linked to Parkinson's disease. Measurements of the molecular extension as the proteins unfolded under tension in optical tweezers revealed that even small oligomers could form numerous metastable structures, with a surprisingly broad range of sizes. Comparing the structures formed in monomers, dimers and tetramers, we found that the average mechanical stability increased with oligomer size. Most structures formed within a minute, with size-dependent rates. These results provide a new window onto the complex α-synuclein aggregation landscape, characterizing the microscopic structural heterogeneity and kinetics of different pathways.

A simple cell for the analysis of nanoelectromechanical systems under gas pressure.

A simple yet versatile apparatus for optical microscopy investigations of solid-state devices under high gas pressures is presented. Interchangeable high-grade sapphire windows with different thicknesses allow variable choice of trade-off between the maximum operating pressure and maximum spatial resolution. The capabilities of this compact chamber were tested by performing stroboscopic optical interferometry on nanoelectromechanical systems (NEMSs) under capacitive excitation. With a 1.7 mm thick sapphire window, the cell is safe to operate at pressures ranging from vacuum to 5 MPa. Minimal optical wavefront distortion allows NEMSs with linear dimensions of 0.1x1.6 microm(2) to be explored. For a sapphire window with a maximum thickness of 6 mm, the safe operating pressure increases up to an estimated 60 MPa; however, the increasing distortions inhibit signal from NEMSs smaller than approximately 0.5x1 microm(2). The cell can be used for confocal microscopy, microphotoluminescence and electroluminescence, light scattering spectroscopy, and reflectivity. The light weight and compact design of the chamber allow mounting on a precision piezomotion control stage or inside a volume tight apparatus such as cryostats.