Raman spectroscopy determination of the Debye temperature and atomic cohesive energy of CdS, CdSe, Bi2Se3, and Sb2Te3 nanostructures

Abstract

We have formulated the size and temperature dependence of the phonon relaxation dynamics for CdS, CdSe, Bi 2 Se 3 , and Sb 2 Te 3 nanostructures based on the framework of bond order-lengthstrength correlation, core-shell configuration, and local bond averaging approach. The Raman shifts are correlated directly to the identities (nature, order, length, and energy) of the representative bond of the specimen without needing involvement of the Gr€ uneisen mode parameters or considering the processes of phonon decay or multi-phonon resonant scattering. Quantitative information of the Debye temperature, the atomic cohesive energy, the reference frequencies from which the Raman shifts proceed, and the effective coordination numbers of the randomly sized particles, as well as the length and energy of the representative bond, has been obtained. It is clarified that the size-induced phonon softening arises intrinsically from the cohesive weakening of the undercoordinated atoms in the skin up to three atomic layers and the thermally derived phonon softening results from the thermally lengthening and weakening of bonds. Developed approach empowers the Raman technique in deriving quantitative and direct information regarding bond stiffness relaxation with applied stimuli such as coordination, mechanical, thermal, and chemical environment, which are crucial to practical applications.

Laser‐Induced Formation of CdS Crystallites in Cd‐Doped Amorphous Arsenic Sulfide Thin Films

“…Another factor which can contribute to the observed downward shift of the CdS crystallite Raman features with increasing P exc is the sample temperature increase due to the laser irradiation‐induced heating. It is known that the LO phonon frequency in CdS (both bulk and nanoscale) decreases with temperature at a rate 0.015 cm −1 K −1 . Hence, the maximal LO phonon frequency downshift from 305 to 297 cm −1 would correspond to the temperature at the laser spot of about 700 K. Local heating of the sample up to such temperature within less than a minute seems rather unrealistic; moreover, this temperature noticeably exceeds the As 2 S 3 melting point of 585 K .…”

Laser heating effect on Raman spectra of Si nanocrystals embedded into SiOx matrix

“…5) with increasing the relative intensity (as compared to TO peak) with the excitation power (see inset in Fig. 5) could be an evidence of significant excitation of the phonon system as well as effective decay of optical phonons into low-frequency acoustical phonons at temperatures higher than the Debye one (the latter for nanocrystals is expected to be lower than that for bulk crystals [27]). In systems excited in such a manner, anharmonicity of phonon vibrations may additionally influence the scattering process.…”

Electrodeposition and characterization of composition-graded CdS x Se (1–x) multilayer thin film structures

“…[58][59] Experimental Raman spectra of CdSe nanocrsytals whose size is below 10 nm, exhibit a dominant peak between 208 and 203 cm -1 . [60] The CdSe Raman band at 200 cm -1 has been attributed to the first-order longitudinal optical (LO), which is red shifted of the expected CdSe bulk.…”

“…[53, 63] Furthermore, proper background subtraction has always been used before fitting (Figure S5, SI). As in the case of CdS, the Raman phonons also undergo a red shift when the crystal size is reduced or when the sample is heated [59]. The bands around 400 and 600 cm -1 are mixed Raman LO band overtones of both materials.…”