Pictorial representation of sample A, B, and C NW structures. The NWs are not drawn to scale. White and light gray segments represent As-rich and P-rich GaAsP layers, respectively. The dark gray segment of the sample B NW signifies the GaP layer. Dotted boxes, labeled 1, 2, and 3, correspond to the regions of interest on the ultramicrotomed lamellae presented in Figs. 4 and 5. The striped segments at the NW tips represent the Au seed nanoparticles.
Cross-sectional SEM images of as-grown NW samples (a) A, (b) B, and (c) C. The highlighted region and inset in (b) further illustrates the reverse tapering phenomenon, due to shadowing effects. All scale bars represent a length.
FWHL NW diameters of samples A, B, and C, fit to a Gaussian distribution. The profiles represent sample sets of 100 single NWs.
HAADF image showing the cross-section of a single sample B NW near its base (corresponding to box 1 in Fig. 1). EDXS linescans, representative of elemental Ga (green), As (blue), and P (red), are superimposed. The decrease in the As profile and increase in P profile observed near the center corresponds to the region of dark contrast, and demonstrates the presence of a P-rich region near the NW center. The scale bar represents a 20 nm length.
Cross-sectional HAADF image and superimposed EDXS linescans showing elemental counts of Ga (green), As (blue), and P (red), obtained from the axial midsection of a single sample B NW (corresponding to box 2 in Fig. 1). A passivating GaP shell is seen as an outer disk of dark contrast. A central spot of dark contrast shows the location of a small P-rich region near the NW center, which is unresolved by the EDXS linescan. The scale bar represents a 20 nm length.
Raman spectra of the samples A, B, and C measured at . The spectra have been shifted vertically for clarity.
PL spectra of the samples A, B, and C measured at . Insets show the comparisons between the PL measured close to the peak positions without the magnetic field (black lines) and in the magnetic field (red lines). The dashed lines show two contributions to the PL emission in sample B.
Sketch of the radial distribution of the electron gap in the core-shell GaAsP/GaP (a) and in the single segment GaAsP (b) NWs. The electron transitions active in the PL are shown by the vertical arrows.
Description and dimensions of NW samples A–C.
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