The mechanical and electrical properties of CdTe tetrapod-shaped nanocrystals have been studied with atomic force microscopy. Tapping mode images of tetrapods deposited on silicon wafers revealed that they contact the surface with the ends of three arms. The length of these arms was found to be 130 ± 10 nm. A large fraction of the tetrapods had a shortened vertical arm as a result of fracture during sample preparation. Fracture also occurs when the applied load is a few nanonewtons. Compression experiments with the AFM tip indicate that tetrapods with the shortened vertical arm deform elastically when the applied force was less than 50 nN. Above 90 nN additional fracture events occurred that further shorted the vertical arm. Loads above 130 nN produced irreversible damage to the other arms as well. Current-voltage characteristics of tetrapods deposited on gold indicated semiconducting behavior with a current gap of ~2 eV at low loads (<50 nN) and a narrowing to about 1 eV at loads between 60 and 110 nN. Atomic calculation of the deformation suggests that the ends of the tetrapod arms are stuck during compression so that the deformations are due to bending modes. The reduction of the current gap is due to electrostatic effects, rather than strain deformation effects inside the tetrapod.
A covalently connected rGO–TpPa-1-COF hybrid material synthesized by one-pot reaction for enhanced photocatalytic hydrogen evolution under visible light irradiation.
The direct assembly of polymer blends on chemically functionalized surfaces is shown to produce a variety of nonuniform complex patterns. This method provides a powerful tool for easily producing nonuniform patterns in a rapid (30 s), one‐step process with high specificity and selectivity for a variety of applications, such as nanolithography, polymeric optoelectronic devices, integrated circuits, and biosensors.
Polymeric microdevices bearing features
like nonspherical shapes
or spatially segregated surface properties are of increasing importance
in biological and medical analysis, drug delivery, and bioimaging
or microfluidic systems as well as in micromechanics, sensors, information
storage, or data carrier devices. Here, a method to fabricate programmable
microcuboids with shape-memory capability and the quantification of
their recovery at different levels is reported. The method uses the
soft lithographic technique to create microcuboids with well-defined
sizes and surface properties. Microcuboids having an edge length of
25 μm and a height of 10 μm were prepared from cross-linked
poly[ethylene-co-(vinyl acetate)] (cPEVA) with different
vinyl acetate contents and were programmed by compression with various
deformation degrees at elevated temperatures. The microlevel shape-recovery
of the cuboidal geometry during heating was monitored by optical microscopy
(OM) and atomic force microscopy (AFM) studying the related changes
in the projected area (PA) or height, while the nanolevel changes
of the nanosurface roughness were investigated by in situ AFM. The shape-memory effect at the microlevel was quantified by
the recovery ratio of cuboids (R
r,micro), while at the nanolevel, the recovery ratio of the nanoroughness
(R
r,nano) was measured. The values of R
r,micro could be tailored in a range from 42
± 1% to 102 ± 1% and R
r,nano from 89 ± 6% to 136 ± 21% depending on the applied compression
ratio and the amount of vinyl acetate content in the cPEVA microcuboids.
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