CdTe Nanowires studied by Transient Absorption Microscopy

Abstract

Abstract. Transient absorption measurements were performed on single CdTe nanowires. The traces show fast decays that were assigned to charge carrier trapping at surface states. The observed power dependence suggests the existence of a trap-filling mechanism. Acoustic phonon modes were also observed, which were assigned to breathing modes of the nanowires. Both the fundamental breathing mode and the first overtone were observed, and the dephasing times provide information about how the nanowires interact with their environment.

Long-Lived 1D Excitons in Bright CdTe Quantum Wires

“…The second conclusion drawn from the PL lifetime experiments is that the lifetimes measured for CdTe QWs with high Φ PL , >200 ns, exceed the radiative lifetime of CdTe QDs, τ rad ∼ 25 ns, − which is estimated to be the radiative lifetime for CdTe QWs. These lifetimes are significantly longer than those reported for other colloidal QW samples, <1 ns, which typically have low Φ PL . − ,, Following the absorption of a photon with energy well above the band gap energy of a semiconductor QW, the photogenerated electron and hole quickly relax to the lowest-energy quantum-confinement states in the conduction and valence bands, 1Σ e and 1Σ 3/2h . The efficiencies of these relaxation processes are not perfect, however, and the densities of the electron and hole quantum-confinement states, the surface passivation, and local environments of the QWs all have roles in dictating the fraction of the charge carriers that reach the ground states. ,, It is important to emphasize that changes in the PL lifetimes result from dynamics of the charge carriers at the band edge and have little or no dependence on the dynamics incurred while relaxing to the ground state.…”

“…These lifetimes are significantly longer than those reported for other colloidal QW samples, <1 ns, which typically have low Φ PL . [27][28][29][30][31]33,34 Following the absorption of a photon with energy well above the band gap energy of a semiconductor QW, the photogenerated electron and hole quickly relax to the lowest-energy quantumconfinement states in the conduction and valence bands, 1Σ e and 1Σ 3/2h . The efficiencies of these relaxation processes are not perfect, however, and the densities of the electron and hole quantum-confinement states, the surface passivation, and local environments of the QWs all have roles in dictating the fraction of the charge carriers that reach the ground states.…”

“…In general, QWs with higher irregularities in surface passivation, crystal structure, and diameter will have more nonradiative relaxation pathways and lower Φ PL values than QWs that are nearly ideal. Due to the long lengths of the QWs, the surface areas sampled by photogenerated electron–hole pairs in QWs are significantly larger than in QDs, and the dynamics of 1D excitons within QWs tend to be dominated by nonradiative relaxation pathways that arise from the large number of surface trap sites. − Consequently, the Φ PL values of QWs − are typically <0.1%, orders of magnitude lower than those of QDs. Likely due to the less-than-ideal quality of QW samples, attempts at incorporating semiconductor QWs in PV devices have been limited.…”

Intraband Relaxation Dynamics of Charge Carriers within CdTe Quantum Wires

“…The relaxation dynamics that occur within semiconductor NPs are commonly characterized using transient absorption (TA) spectroscopy to photoexcite the carriers and probe the changes in the absorption spectrum induced by the carriers. ,,,,− These TA data are often complicated and difficult to analyze due to overlapping transient signals. In ref , we demonstrated that some of the overlapping induced-absorption (ΔAbs > 0) and bleach (ΔAbs < 0) signals within the TA data are associated with changes in the electron density distribution induced by photoexcitation; these effects are termed quantum-state renormalization (QSR) .…”

Transient absorption microscopy: advances in chemical imaging of photoinduced dynamics

“…It should be stressed that the potential of TAM is not limited to studies on the specific material systems and nanostructures highlighted here. This limited review aims at introducing representative results in some detail, but also likes acknowledge existing work on the detection and photophysics of gold and silver nanoparticles and hybrid nanoparticle structures , silver nanocubes , gold nanorods and surface plasmon polariton propagation in gold nanowires , the exciton dynamics in CdTe and CdSe nanowires or ZnO nanorods .…”