Large Anisotropic Conductance and Band Gap Fluctuations in Nearly Round-Shape Bismuth Nanoparticles

Abstract

Unlike their bulk counterpart, nanoparticles often show spontaneous fluctuations in their crystal structure at constant temperature [Iijima, S.; Ichihashi T. Phys. Rev. Lett.1985, 56, 616; Ajayan, P. M.; Marks L. D. Phys. Rev. Lett.1988, 60, 585; Ben-David, T.; Lereah, Y.; Deutscher, G.; Penisson, J. M.; Bourret, A.; Korman, R.; Cheyssac, P. Phys. Rev. Lett.1997, 78, 2585]. This phenomenon takes place whenever the net gain in the surface energy of the particles outweighs the energy cost of internal strain. The configurational space is then densely populated due to shallow free-energy barriers between structural local minima. Here we report that in the case of bismuth (Bi) nanoparticles (BiNPs), given the high anisotropy of the mass tensor of their charge carriers, structural fluctuations result in substantial dynamic changes in their electronic and conductance properties. Transmission electron microscopy is used to probe the stochastic dynamic structural fluctuations of selected BiNPs. The related fluctuations in the electronic band structure and conductance properties are studied by scanning tunneling spectroscopy and are shown to be temperature dependent. Continuous probing of the conductance of individual BiNPs reveals corresponding dynamic fluctuations (as high as 1 eV) in their apparent band gap. At 80 K, upon freezing of structural fluctuations, conductance anisotropy in BiNPs is detected as band gap variations as a function of tip position above individual particles. BiNPs offer a unique system to explore anisotropy in zero-dimension conductors as well as the dynamic nature of nanoparticles.

Size-controllable synthesis and bandgap modulation of single-layered RF-sputtered bismuth nanoparticles

“…The bandgap decreases as the diameter of BiNPs increases. The results are reasonable compared with the data acquired by Selzer's group [32], in which the bandgap of 3-nm BiNPs was measured by other methods to be approximately 2 eV.…”

Highly efficient photocatalytic reduction of Cr(VI) by bismuth hollow nanospheres

“…However, few literatures have reported the band gap energy of metallic bismuth. The recently published work reported both indirect and direct band gap values of bismuth ranging from 0.8 to 2.7 eV [25,26]. In this study, two different relations of (αhν) 1/2 (n = 4) and (αhν) 2 (n = 1) versus the photon energy (hν) are plotted and illustrated in Fig.…”

Rashba Band Splitting in CH3NH3PbI3: An Insight from Spin-Polarized Scanning Tunneling Spectroscopy

“…Such a nature of conductivity in MAPbI 3 , when formed with stoichiometric content of CH 3 NH 3 I and PbI 2 , is in fact known to appear due to iodine-vacancies present in the perovskite; the vacancies can be passivated when the perovskite is formed with PbI 2 -rich precursors. − The histograms show a symmetric distribution of nearly equal full width at half-maximum (fwhm). It may be stated that band-energies of a semiconductor obtained from d I /d V spectra as such exhibit a distribution; , in MAPbI 3 , the histogram of CB and VB-edges may have originated due to presence of grains and grain-boundaries in the solution-cast film (inset of Figure a) as well as CH 3 NH 3 I-rich and PbI 2 -rich regions in the ultrathin layer. In the STM topography, we did not achieve an atomic resolution which is observed if a single crystal after an in situ cleaving or films grown through vacuum codeposition method are imaged. , …”