Scanning Electrochemical Microscopy of One-Dimensional Nanostructure: Effects of Nanostructure Dimensions on the Tip Feedback Current under Unbiased Conditions

Visualizing the Spatial Heterogeneity of Electron Transfer on a Metallic Nanoplate Prism

The involvement between electron transfer (ET) and catalytic reaction at the electrocatalyst surface makes the electrochemical process challenging to understand and control. Even ET process, a primary step, is still ambiguous because it is unclear how the ET process is related to the nanostructured electrocatalyst. Herein, locally enhanced ET current dominated by mass transport effect at corner and edge sites bounded by {111} facets on single Au triangular nanoplates was clearly imaged. After decoupling mass transport effect, the ET rate constant of corner sites was measured to be about 2-fold that of basal {111} plane. Further, we demonstrated that spatial heterogeneity of local inner potential differences of Au nanoplates/solution interfaces plays a key role in the ET process, supported by the linear correlation between the logarithm of rate constants and the potential differences of different sites. These results provide direct images for heterogeneous ET, which helps to understand and control the nanoscopic electrochemical process and electrode design.

Ballistic transport simulation of acceptor-donor C3N/C3B double-wall hetero-nanotube field effect transistors

The one-dimensional (1D) acceptor-donor (A-D) hetero-nanotube (HNT) has attracted much attention as a potential candidate for a channel structure of next-generation field effect transistors (FETs). Herein, we designed A-D C₃N/C₃B double-wall (dw) HNTs by coaxially wrapping C₃N and C₃B nanotubes together. By using density functional theory (DFT) combined with the nonequilibrium Green's function (NEGF) formalism, we studied the electronic properties and ballistic transport behavior of C₃N/C₃B dwHNTs in comparison with the ones in vertical stacking contact. The remarkable charge transfer between C₃N and C₃B nanotubes and band hybridization in C₃N/C₃B dwHNTs originate from the strong intertubular π-π stacking interaction. In the simulated all-around-gated FET devices, (12,0) C₃N/(6,0) C₃B dwHNT with 2 repeated wrapping units possesses the optimal performance, including rectifying ratio and subthreshold swing (SS), by enhancing the A-D asymmetry. Our work suggests that coaxial wrapping is a method superior to vertical stacking in constructing A-D HNTs for high-performance electronic and optoelectronic devices based on 1D materials.

Recent advances in high resolution scanning electrochemical microscopy of living cells--a review

This review discusses advances in the field of high resolution scanning electrochemical microscopy (HR-SECM) and scanning ion conductance microscopy (SICM) to study living cells. Relevant references from the advent of this technique in the late 1980s to most recent contributions in 2012 are presented with special discussion on high resolution images. A clear progress especially within the last 5 years can be seen in the field of HR-SECM. Furthermore, we also concentrate on the intrinsic properties of SECM imaging techniques e.g. different modes of image acquisition, their advantages and disadvantages in imaging living cells and strategies for further enhancement of image resolution, etc. Some of the recent advances of SECM in nanoimaging have also been discussed which may have potential applications in high resolution imaging of cellular processes.

Scanning electrochemical microscopy of individual single-walled carbon nanotubes

Here we report on the novel application of scanning electrochemical microscopy (SECM) to enable spatially resolved electrochemical characterization of individual single-walled carbon nanotubes (SWNTs). The feedback imaging mode of SECM was employed to detect a pristine SWNT (approximately 1.6 nm in diameter and approximately 2 mm in length) grown horizontally on a SiO(2) surface by chemical vapor deposition. The resulting image demonstrates that the individual nanotube under an unbiased condition is highly active for the redox reaction of ferrocenylmethyltrimethylammonium used as a mediator. Micrometer-scale resolution of the image is determined by the diameter of a disk-shaped SECM probe rather than by the nanotube diameter as assessed using 1.5 and 10 microm diameter probes. Interestingly, the long SWNT is readily detectable using the larger probe although the active SWNT covers only approximately 0.05% of the insulating surface just under the tip. This high sensitivity of the SECM feedback method is ascribed to efficient mass transport and facile electron transfer at the individual SWNT.

Spatially resolved detection of a nanometer-scale gap by scanning electrochemical microscopy

Nanowires with nanometer-scale gaps are an emerging class of nanomaterials with potential applications in electronics and optics. Here, we demonstrate that the feedback mode of scanning electrochemical microscopy (SECM) allows for spatially resolved detection of a nanogap on the basis of its electrical conductivity. A gapped nanoband is used as a model system to describe a mechanism of a unique feedback effect from a nanogap. Interestingly, both experiments and numerical simulations confirm that a peak current response is obtained when an SECM tip is laterally scanned above an insulating nanogap formed in an unbiased nanoband. On the other hand, no peak current response is expected for a highly conductive nanogap, which must be extremely narrow or filled with highly conductive molecules for efficient electron transport.