Spatial Localization of Defects in Halide Perovskites Using Photothermal Deflection Spectroscopy

Photothermal deflection spectroscopy (PDS) emerges as a highly sensitive noncontact technique for measuring absorption spectra and serves for studying defect states within semiconductor thin films. In our study, we applied PDS to methyl­ammonium lead bromide single crystals. By analyzing the frequency dependence of the PDS spectra and the phase difference of the signal, we can differentiate between surface and bulk deep defect absorption states. This methodology allowed us to investigate the effects of bismuth doping and light-induced degradation. The identified absorption states are attributed to MA+ vibrational states and structural defects, and their influence on the nonradiative recombination probability is discussed. This distinction significantly enhances our capability to characterize and analyze perovskite materials at a deeper level

Spatial Localization of Defects in Halide Perovskites Using Photothermal Deflection Spectroscopy

Photothermal deflection spectroscopy (PDS) emerges as a highly sensitive noncontact technique for measuring absorption spectra and serves for studying defect states within semiconductor thin films. In our study, we applied PDS to methyl­ammonium lead bromide single crystals. By analyzing the frequency dependence of the PDS spectra and the phase difference of the signal, we can differentiate between surface and bulk deep defect absorption states. This methodology allowed us to investigate the effects of bismuth doping and light-induced degradation. The identified absorption states are attributed to MA+ vibrational states and structural defects, and their influence on the nonradiative recombination probability is discussed. This distinction significantly enhances our capability to characterize and analyze perovskite materials at a deeper level

Size and Purity Control of HPHT Nanodiamonds down to 1 nm

High-pressure high-temperature (HPHT) nanodiamonds originate from grinding of diamond microcrystals obtained by HPHT synthesis. Here we report on a simple two-step approach to obtain as small as 1.1 nm HPHT nanodiamonds of excellent purity and crystallinity, which are among the smallest artificially prepared nanodiamonds ever shown and characterized. Moreover we provide experimental evidence of diamond stability down to 1 nm. Controlled annealing at 450 °C in air leads to efficient purification from the nondiamond carbon (shells and dots), as evidenced by X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and scanning transmission electron microscopy. Annealing at 500 °C promotes, besides of purification, also size reduction of nanodiamonds down to ∼1 nm. Comparably short (1 h) centrifugation of the nanodiamonds aqueous colloidal solution ensures separation of the sub-10 nm fraction. Calculations show that an asymmetry of Raman diamond peak of sub-10 nm HPHT nanodiamonds can be well explained by modified phonon confinement model when the actual particle size distribution is taken into account. In contrast, larger Raman peak asymmetry commonly observed in Raman spectra of detonation nanodiamonds is mainly attributed to defects rather than to the phonon confinement. Thus, the obtained characteristics reflect high material quality including nanoscale effects in sub-10 nm HPHT nanodiamonds prepared by the presented method