Scanning tunneling spectroscopy STS

Scanning tunneling spectroscopy (STS) can, in principle, probe the electronic density of states of a singlewall nanotube, or the outermost cylinder of a multi-wall tubule, or of a bundle of tubules. With this technique, it is further possible to carry out both STS and scanning tunneling microscopy (STM) measurements at the same location on the same tubule and, therefore, to measure the tubule diameter concurrently with the STS spectrum. No reports have yet been made of a determination of the chiral angle of a tubule with the STM technique. Several groups have, thus far, attempted STS studies of individual tubules. 

The next smaller ligand-protected nanocluster that was investigated by scanning tunneling spectroscopy (STS) was the four-shell cluster Pt309phen 36O20 [20,21]. The diameter of the Pt core is 1.8 nm, about a tenth of the former example. However, even here a Coulomb blockade could only be observed at 4.2 K, i.e. at room temperature the particle still has metallic behaviour. Since... 

The ESTM experiment provides actually five measurable quantities tunnelling current, / at the applied voltage, U, and three dimensions, x, y, z. The standard STM can therefore easily be modified by recording the local l-Uy U-zy or /-z characteristics (z is vertical distance of the tip from the electrode surface). Plot of dl/dU or d//dz versus x and y brings additional information on the electronic and chemical surface properties (local work functions, density-of-states effects, etc.), since these manifest themselves primarily as l-U dependences. The mentioned plots are basis of the scanning tunnelling spectroscopy (STS). 

Yu et al. prepared 48, bound to an Au(lll) surface by a thiol on the biphenyl end, then deprotected on the bipyrimidine end to expose a thiol to bind an Au nanoparticle. Rectification was measured by scanning tunneling spectroscopy (STS), and it could be reversed by the addition of acid, which protonated the pyrimidine rings, converting them from donor to acceptor [121]. Yu s group has also inverted the attachment of a rectifier, as shown with 49 and 50, and confirmed that the rectification direction reversed [122]. This was recently verified by STM-BJ measurements [123]. 

Fig. 21. Current-voltage I v.r. V traces taken with scanning tunneling spectroscopy (STS) on individual nanotubes of various outer diameters (1) dt = 8.7 nm, (2) dt = 4.0 nm, and (3) dt = 1.7 nm. The top inset shows the conductance v.r. voltage plot for data taken on the 1.7 nm nanotube. The bottom inset shows an I-V trace taken on a gold surface under the same conditions [182]. 

It is possible to obtain chemical information from STM when it is used in the spectroscopic mode, for example by measuring at a fixed distance the tunneling current / as a function of the voltage over the gap (I/V spectroscopy). This method of measurement is called scanning tunneling spectroscopy (STS) [49],... 

There have been a few reports on the electronic properties ofjunction nanotubes [1,6-10]. Rao and coworkers [1] carried out scanning tunneling spectroscopy (STS) measurements on Y-junction carbon nanotubes (CNTs)... 

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