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Improvement of Terahertz Wave Radiation for InAs Nanowires by Simple Dipping Into Tap Water

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Improvement of Terahertz Wave Radiation for InAs Nanowires by Simple Dipping Into Tap Water

Dong Woo Park et al. Sci Rep.

Abstract

We report improvement of terahertz (THz) wave radiation for Si-based catalyst-free InAs nanowires (NWs) by simple dipping into tap water (DTW). In addition, the possibility of using InAs NWs as a cost-effective method for biomedical applications is discussed by comparison to bulk InAs. The peak-to-peak current signals (PPCSs) of InAs NWs measured from THz time-domain spectroscopy increased with increasing NW height. For example, the PPCS of 10 μm-long InAs NWs was 2.86 times stronger than that of 2.1 μm-long NWs. The THz spectra of the InAs NWs obtained by applying a fast Fourier transformation to the current signals showed a main frequency of 0.5 THz, which can be applied to a variety of medical imaging systems. After the DTW process, structural variation was not observed for 2.1 μm-long InAs NWs. However, the top region of several InAs NWs with heights of 4.6 and 5.8 μm merged into a conical structure. InAs NWs with a height of 10 μm resulted in a bundle feature forming above the conical shape, where the length of bundle region was 4 μm. After the DTW process, the PPCS for 10 μm-long InAs NWs increased by 15 percent compared to that of the as-grown case.

Figures

Figure 1
Figure 1
FE-SEM images of as-grown InAs NWs in the (a) NW1, (b) NW2, (c) NW3, and (d) NW4 samples, where each right-hand side shows a plan-view image (upper image, scale bar: 2 μm) and height distribution (bottom graph) of InAs NWs, (f) THz spectra obtained by applying FFT to the current signals of InAs NWs, and (g) schematic illustration of the carrier dynamics.
Figure 2
Figure 2
HR-TEM images of the (a) region exhibiting ZB and SF (bottom of an InAs NW), (b) region exhibiting SF only (center), and (c) region exhibiting WZ only (top).
Figure 3
Figure 3
FE-SEM images of InAs NWs in the (a) NW1, (b) NW2, (c) NW3, and (d) NW4 samples after the DTW process. The inset in each FE-SEM image shows an expanded image, where the scale bar is 2 μm. The right-hand side is a schematic of the formation of InAs conical and bundle structures.
Figure 4
Figure 4
(a) TDs current signals, (b) THz spectra of InAs NW samples, and (c) comparison of the current signals of the NW4 sample before and after the DTW process. (d) Summary of the PPCS of the NW samples before and after the DTW process, and (e) schematic illustration of the improvement of THz wave radiation for the bundle structure of the InAs NWs. The band structure of InAs NWs consisting of bundle structure was schematically shown, where the bending of EC and EV bands surely occurs.

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