Indirect L to T point optical transition in bismuth nanowires

Abstract

An indirect electronic transition from the L point valence band to the T point valence band has been previously observed in Bi nanowires oriented along the ͓0112͔ crystalline direction ͑used by Black et al. and by Reppert et al.͒ but not in ͓1120͔-oriented nanowires ͑used by Cornelius et al.͒ or in bulk bismuth. Here we measure the Bi nanowire samples from each of these prior experimental studies on the same Fourier transform infrared apparatus, confirming that the differences are indeed physical and are not associated with the experimental setup. We develop an analytical model for the threshold energy of the indirect L to T point valence-band transition that takes as parameters the nanowire diameter and crystalline orientation. Our model shows good agreement with experimental results, and demonstrates that the nonparabolic nature of the L point bands is essential for calculating the energy of this transition. Finally, we propose a mechanism based on symmetry lowering to explain why this indirect transition is observed for ͓0112͔-oriented but not for ͓1120͔-oriented nanowires.

Reinventing solid state electronics: Harnessing quantum confinement in bismuth thin films

“…As a result, quantum confinement in lowdimensional (2D, 1D) semimetal materials leads to a semimetal-to-semiconductor transition as the physical size of a nanostructure becomes comparable to the Fermi wavelengths of electrons and holes (6). Bulk bismuth has a rhombohedral crystal structure, which can be expressed in terms of a hexagonal unit cell, and is a semimetal with band overlap between the valence and conduction band of 38 meV and 98 meV at 2 K and 300 K, respectively (7)(8)(9)(10). Here, the quantum confinement effect is used to demonstrate that for (111) Bi thin films of thickness less than 6 nm, a 'positive' band gap > 100 meV emerges allowing for the formation of a metal-semiconductor junction between a thick (semimetallic) and thin (semiconducting) region in a single film.…”

Thermal transport in individual thermoelectric nanowires: a review

“…Therefore, Bi and Bi x Sb 12x nanowires have been researched for the potential to observe the quantum confinement effect. 10,[13][14][15][16][17][18][19][20][21][22][23][24] A qualitative explanation of the quantum confinement effect has been well documented by Chen and Shakouri. 13 According to the Boltzmann transport equation, the Seebeck and electric conductivity can be expressed as follows…”

Preparation and photocatalytic performance of Bi nanoparticles by microwave-assisted method using ascorbic acid as reducing agent

“…Where α is the absorbance and here it can be regarded as the Kubelka-Munk absorbance, h is the Plank constant, ν is the frequency of the incident photon, n is a constant which characterizes the nature of the band transition and n is 2 for Bi since it is considered as an indirect material [22,23]. The result is displayed in Fig.…”