On the origins of anomalous elastic moduli and failure strains of GaP nanowires

Abstract

Previous reports suggest that Raman peaks in uniaxially loaded nanowires with diamond cubic and zinc blende crystal structures shift at rates that are significantly different from bulk specimens. We have investigated the first order Raman scattering from individual, free-standing, [111] oriented GaP nanowires ranging from 75 to 180 nm in diameter at uniaxial tensile stresses up to 5 GPa. All of the phonon modes were shifted to frequencies lower than previously reported for bulk GaP, and significant splitting of the degenerate transverse optical mode was observed. A general analysis method using single and double Lorentzian fits of the Raman peaks is presented and used to report more accurate values of the phonon deformation potentials (PDPs) that relate uniaxial strains to Raman peak shifts in GaP. A new set of PDPs determined from the nanowires revealed that the they have elastic moduli and failure strains that are consistent with bulk GaP. The analysis method eliminated the anomalous, inconsistent deformation behavior commonly reported in Raman-based strain measurements of nanowires, and can be extended to other materials systems with degenerate phonons.

Deep-Subwavelength Raman Imaging of the Strained GaP Nanowires

“…Using above-mentioned formulas, we find that PDP r /ω 0 2 and γ = ( p + 2 q )/6ω 0 2 are −0.44 ± 0.04 and 2.08 ± 0.13, respectively. In the previous work on GaP NWs, these parameters were found to be −1.27 ± 0.46 and 2.99 ± 0.63 . In bulk GaP, they are −0.58 and 0.9 .…”

“…When strain is applied, the observed change in the Raman spectrum can be described as the spectral shift of the combined mode LA + TA, which does not require taking into account the shift rates of the acoustic modes separately. We considered splitting of TO mode, and TO 1 and TO 2 amplitudes were set equal according to previous study . LA + TA amplitude in the NW center and in tensed regions was set four times lower than TO, according to the fitting of the spectrum of the straight NW (presented in Figure ) and previous studies .…”

“…NWs are known for their mechanical strength. In particular, theoretical failure strain in tensed 100 nm thick GaP NW exceeds 15% with an estimated fracture stress of 17.8 GPa . A bending strength of 100 nm thick Si NWs is estimated to be as high as 12 GPa while the fracture toughness of bulk Si and GaP single crystals is only 0.6–0.8 GPa. , …”

“…In particular, theoretical failure strain in tensed 100 nm thick GaP NW exceeds 15% with an estimated fracture stress of 17.8 GPa. 24 A bending strength of 100 nm thick Si NWs is estimated to be as high as 12 GPa 25 while the fracture toughness of bulk Si and GaP single crystals is only 0.6−0.8 GPa. 26,27 Strain affects the semiconductor band structure through change in the lattice symmetry.…”

Photocurrent Engineering of Silicon Nanowire Field‐Effect Transistors by Ultrathin Poly(3‐hexylthiophene)

“…Photoresponse across semiconductor interfaces is an important subject in understanding the light‐induced device performance. In particular, silicon nanowires (SiNWs) employing organic–inorganic interfaces have attracted great research attention, particularly due to the straightforward device integration with nanoscale devices exhibiting a high surface‐to‐volume ratio . Furthermore, the on/off ratio of the field‐effect transistors (FETs) containing SiNWs can be significantly improved by the reduction of the off‐current originated from the leakage carriers of the main body under the depletion region .…”