Structure and Composition of Cu-Doped CdSe Nanocrystals Using Soft X-ray Absorption Spectroscopy

Abstract

The local structure and composition of Cu ions dispersed in CdSe nanocrystals is examined using soft x-ray absorption near edge spectroscopy (XANES). Using Cu L-edge XANES and X-ray photoelectron measurements (XPS), we find that the Cu ions exist in the Cu(I) oxidation state. We also find that the observed Cu L-edge XANES signal is directly proportional to the molar percent of Cu present in our final material. Se L-edge XANES indicates changes in the Se density of states with Cu doping, due to a chemical bonding effect, and supports a statistical doping mechanism. Photoluminescence (PL) measurements indicate the Cu ions may act as deep electron traps. We show that XANES, XPS, and PL are a powerful combination of methods to study the electronic and chemical structure of dopants in nanostructured materials.

Effects of dopants on the band structure of quantum dots: A theoretical and experimental study

“…Both we 15 and others 19 have argued for Cu(I) doping, leading to a d 10 dopant that is magnetically silent while other groups have found evidence for Cu(II) doping 17,18,21 . As Cu(II) is d 9 , we expect this paramagnetic (s = 1 2 ) center to be magnetically active, and therefore either electron spin resonance or magnetometry should be employed to confirm this oxidation state 18 .…”

“…The zinc blende (ZB) structure limits the equation to 4 nearest neighbors and 12 next nearest neighbors. Dopants shall be considered as the reference atom as reports 15 indicate that a dopant substitutionally replaces Cd atoms in the lattice, thus resulting in the maintaining the original geometry. Cations and anions are topologically identical in the ZB system allowing for simplification via symmetry.…”

“…The Cu doped CdSe QDs are synthesized using a previously established method 15 . To achieve consistent particle sizes for both doped and undoped materials, a parallel plate methodology was employed in which samples vials were heated simultaneously on a stainless steel block.…”

“…Here we use the Cu L 3 -edge as we have shown that this edge provides a spectroscopic signature for the oxidation state of Cu dopants in QDs 15 . As shown in Figure 5, the appearance of the feature at ∼933 eV, with a minimal peak at ∼930 eV, suggests the Cu(I) oxidation state.…”

Experimental Observation of Quantum Confinement in the Conduction Band of CdSe Quantum Dots

“…[3] Hence, CdSe represents an archetypal system for numerous QD applications (including uses in biomedical imaging and laser diodes) and an ideal model for the study of quantum confinement effects. Although extensive research has been devoted to characterization of the electronic structure in CdSe QDs, [4][5][6][7][8][9] the sizedependent evolution of the valence band (VB) and CB-DOS remain unresolved from one another via experimental study. It has been demonstrated that theoretical calculations provide a means for the deconvolution and isolated study of the VB and CB.…”