Linear strain-gradient effect on the energy bandgap in bent CdS nanowires

Abstract

Although possible non-homogeneous strain effects in semiconductors have been investigated for over a half century and the strain-gradient can be over 1% per micrometer in flexible nanostructures, we still lack an understanding of their influence on energy bands. Here we conduct a systematic cathodoluminescence spectroscopy study of the strain-gradient induced exciton energy shift in elastically curved CdS nanowires at low temperature, and find that the red-shift of the exciton energy in the curved nanowires is proportional to the strain-gradient, an index of lattice distortion. Density functional calculations show the same trend of band gap reduction in curved nanostructures and reveal the underlying mechanism. The significant linear straingradient effect on the band gap of semiconductors should shed new light on ways to tune optical-electronic properties in nanoelectronics.

Highly-sensitive detection of the lattice distortion in single bent ZnO nanowires by second-harmonic generation microscopy

“…It can be seen clearly that the lattice spacing in the tensile region (c=0.267 nm) is larger than that in the compressive region (c=0.258 nm). Thus, the variation of the bending distortion of lattice spacing in the single ZnO NW is estimated to be 4%, which is in good agreement with the previous works [16][17][18] (Supplementary Table 1 respectively. The black dots indicate the experimental data, and the red solid curves present the theoretical fits (see Method Section for the detailed procedure).…”

“…However, HRTEM technique provides a limited sensitivity for distinguishing the tiny variation in lattice spacing (<0.01 nm) [16][17][18] . Also, it is challenging to study thick samples (>300 nm) 19 and requires high vacuum conditions.…”

Strain-Induced Large Exciton Energy Shifts in Buckled CdS Nanowires

“…It would be interesting to study the effect of large strains on the optical and electronic properties of CdS NWs in order to further understand its properties under extreme conditions, which is likely to experience large strains for flexible electronics/photonics applications. Recently, by using a glass tip to manipulate the straight nanowires to a curved geometry, strain-induced redshift of cathdoluminescence peaks in CdS NW was reported [39]; however, the bandgap tuning range of CdS NW was quite small with 32 meV shift under a strain gradient of 0.7 cm -1 . Furthermore, since the techniques for manipulating nanowires for optical measurements was limited by the amount of strain, the effect of strain on the properties of different types of excitons (A, B and C in CdS) could not be studied.…”

Polar-surface-driven growth of ZnS microsprings with novel optoelectronic properties

“…3 For example, in the photoluminescence spectra of bending wurtzite micro/nanowires, a red shift of the near-band energy induced by deformation has been shown to have a linear relation between the peak shift and the strain gradient. 4 Because the peaks of the photoluminescence spectra are near the band gap of these materials, such a linear correlation between the band gap and strain gradient could provide an alternative method in optoelectronics, such as enhanced photodetectors. 5 Conversely, from both scientific and practical viewpoints, one-dimensional structures are ideal materials to measure the optical gains of miniaturized lasers and light amplification due to their strong ability to confine electrons, holes and photons.…”