Figure 1

PLE spectra for CdSe QRs are shown in the left frame (a) $31\times 1.9$ (length times radius) nm, $E_{\mathrm{d}\mathrm{e}\mathrm{t}}=2.25\mathrm{e}\mathrm{V}$; (b) $11\times 1.6\mathrm{n}\mathrm{m}$, $E_{\mathrm{d}\mathrm{e}\mathrm{t}}=2.25\mathrm{e}\mathrm{V}$; (c) $60\times 3.3\mathrm{n}\mathrm{m}$, $E_{\mathrm{d}\mathrm{e}\mathrm{t}}=2.00\mathrm{e}\mathrm{V}$; (d) $11\times 2.9\mathrm{n}\mathrm{m}$, $E_{\mathrm{d}\mathrm{e}\mathrm{t}}=2.03\mathrm{e}\mathrm{V}$, with the zero energy representing the position of the detection window, $E_{\mathrm{d}\mathrm{e}\mathrm{t}}$. Relevant optical transitions are marked. The structure above 0.7 eV is overlapping peaks of the excitation lamp that could not be completely normalized out. TEM images of two QR samples, $31\times 1.9\mathrm{n}\mathrm{m}$ (top), and $30\times 3.2\mathrm{n}\mathrm{m}$ (bottom), are shown to the right. Scale bar is 50 nm.Reuse & Permissions

Figure 2

(a) STM topographic image of a QR 25 nm long and 2 nm in radius (the apparent height is $\sim 4.5\mathrm{n}\mathrm{m}$). (b) Schematic of the DBTJ configuration used for acquiring the tunneling spectra. (c) $dI/dV-V$ tunneling spectra for QRs of various lengths and radii, marked above each curve in nm. For clarity, the spectra were shifted horizontally to align the CB1 peaks. The vertical dashed lines are guides to the eye. The tunneling set values were in the range $V_s=1.5–2\mathrm{V}$ and $I_s=50–80\mathrm{p}\mathrm{A}$.Reuse & Permissions

Figure 3

Calculated energy levels of CdSe QRs. (a) First three CB states versus nanorod radius, for a 30 nm long QR. The quantum numbers $(n,L_z,m)$ are denoted. (b) The VB energy levels versus QR radius calculated for a 30 nm long rod. The quantum numbers $(n,F_z)$ are denoted $(m=1)$. Group VB3 consists of states with $F_z=1/2$, $3/2$, $5/2$, and $7/2$. Insets: Length dependence for the respective energy levels for a rod 2 nm in radius. The upper inset shows also the dependence on the $m$ quantum number. The energies are given with respect to the bulk VB edge. Effective masses for electrons and holes and the bulk energy gap were taken from Ref. 17.Reuse & Permissions

Figure 4

(a) Energy gap versus QR radius. The tunneling data (empty circles, size digitized due to uncertainty) and the theory (solid line) represent the energy separations VB1-CB1. The optical data (solid circles) were determined from the first absorption peak and corrected for the electron-hole Coulomb interaction; see text. The inset illustrates the band-gap optical transition from VB1 to CB1. (b) Excited energy states versus energy gap. The calculated energy level separations, as denoted, are depicted by the solid and dashed lines. The respective separations between the tunneling peaks are denoted by open symbols. Spacing between PLE transitions I and II and the optical energy gap are presented by solid stars and squares, respectively. For the optical data, the energy gap was taken as the detection window corrected for the Coulomb interaction. The STM data represent 15 (out of 20) QRs whose spectra showed clear charging-free peak structure.Reuse & Permissions