scholarly journals Lattice Vibrations and Time-Dependent Evolution of Local Phonon Modes during Exciton Formation in Conjugated Polymeric Molecules

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1724
Author(s):  
Yusong Zhang ◽  
Huayan Shi ◽  
Junteng Luo ◽  
Jianguo Shen ◽  
Sheng Li ◽  
...  

Based on nonadiabatic molecular dynamics that integrate electronic transitions with the time-dependent phonon spectrum, this article provides a panoramic landscape of the dynamical process during the formation of photoinduced excitons in conjugated polymers. When external optical beam/pulses with intensities of 10 µJ/cm2 and 20 µJ/cm2 are utilized to excite a conjugated polymer, it is found that the electronic transition firstly triggers local lattice vibrations, which not only locally distort alternating bonds but change the phonon spectrum as well. Within the first 60 fs, the occurrence of local distortion of alternating bonds accompanies the localization of the excited-state’s electron. Up to 100 fs, both alternating bonds and the excited electronic state are well localized in the middle of the polymer chain. In the first ~200 fs, the strong lattice vibration makes a local phonon mode at 1097.7 cm−1 appear in the phonon spectrum. The change of electron states then induces the self-trapping effect to act on the following photoexcitation process of 1.2 ps. During the following relaxation of 1.0 ps, new local infrared phonon modes begin to occur. All of this, incorporated with the occurrence of local infrared phonon modes and localized electronic states at the end of the relaxation, results in completed exciton formation.

Nanomaterials ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 1047 ◽  
Author(s):  
Marie Krečmarová ◽  
Daniel Andres-Penares ◽  
Ladislav Fekete ◽  
Petr Ashcheulov ◽  
Alejandro Molina-Sánchez ◽  
...  

The successful integration of few-layer thick hexagonal boron nitride (hBN) into devices based on two-dimensional materials requires fast and non-destructive techniques to quantify their thickness. Optical contrast methods and Raman spectroscopy have been widely used to estimate the thickness of two-dimensional semiconductors and semi-metals. However, they have so far not been applied to two-dimensional insulators. In this work, we demonstrate the ability of optical contrast techniques to estimate the thickness of few-layer hBN on SiO2/Si substrates, which was also measured by atomic force microscopy. Optical contrast of hBN on SiO2/Si substrates exhibits a linear trend with the number of hBN monolayers in the few-layer thickness range. We also used bandpass filters (500–650 nm) to improve the effectiveness of the optical contrast methods for thickness estimations. We also investigated the thickness dependence of the high frequency in-plane E2g phonon mode of atomically thin hBN on SiO2/Si substrates by micro-Raman spectroscopy, which exhibits a weak thickness-dependence attributable to the in-plane vibration character of this mode. Ab initio calculations of the Raman active phonon modes of atomically thin free-standing crystals support these results, even if the substrate can reduce the frequency shift of the E2g phonon mode by reducing the hBN thickness. Therefore, the optical contrast method arises as the most suitable and fast technique to estimate the thickness of hBN nanosheets.


1997 ◽  
Vol 482 ◽  
Author(s):  
T. F. Forbang ◽  
C. R. McIntyre

AbstractWe have studied the effects on the phonon spectrum and on the electron-longitudinal optical phonon scattering in GaN/AlN and GaAs/AlAs quantum wells. Phonon modes and potentials have been calculated for both systems. Results for emission due to electroninterface phonons interactions are presented. We will discuss the implications for relaxation times and electron mobility due to modified LO-phonon scattering in both systems.


1988 ◽  
Vol 01 (09n10) ◽  
pp. 353-361 ◽  
Author(s):  
S. TAJIMA ◽  
S. UCHIDA ◽  
H. ISHII ◽  
H. TAKAGI ◽  
S. TANAKA ◽  
...  

The optical reflectivity spectra were measured for single crystalline La2CuO4 and La1.8Sr0.2CuO4 over a wide energy range from 12meV to 3eV. Comparing the phonon spectrum of single crystal with that of polycrystal, the observed four phonon modes can be classified into the two—the vibrations parallel and perpendicular to the c-axis. The infrared spectrum of La1.8Sr0.2CuO4 shows the normal Drude-type behavior without any extra excitation.


2015 ◽  
Vol 29 (35n36) ◽  
pp. 1550247
Author(s):  
Xiao-Meng Liang ◽  
Guo-Qiao Zha

In this paper, based on the time-dependent Ginzburg–Landau theory, we study the dynamics of vortex–antivortex (V–Av) pairs in a mesoscopic superconducting square with a small hole under applied bias currents. For the sample with a centered hole, a V–Av pair can nucleate at the hole edges and moves in opposite directions perpendicular to applied constant DC drive. The influence of the external magnetic field on the (anti)vortex velocity and the lifetime of V–Av pairs is mainly investigated. Different modes in the dynamical process of the V–Av collision and annihilation are identified. Moreover, in the case when the hole is displaced from the center of the square, the V–Av dynamics behaves quite differently from the symmetric case due to the shift of the V–Av creation point.


2007 ◽  
Vol 21 (08n09) ◽  
pp. 1568-1573
Author(s):  
LI-CHUN TUNG ◽  
YONG-JIE WANG ◽  
GRZEGORZ KARCZEWSKI

The CdMnTe/CdMgTe quantum wells have been a focus of interests for its novel magnetic and transport properties and applications in spintronics. We have carried out a systematic study over a series of CdMnTe quantum wells with a range of Mn concentration (0%–3.9%) and modulation doping. Far-infrared transmission spectra have revealed several new infrared-active modes which are both magnetic-field and Mn -concentration dependent. The absorption mode near 125cm-1 (B1) is possibly resulted from the magnetic-order-dependent phonon mode due to an ion-position dependent spin Hamiltonian, while the other two (M1 & M2) may be related to the CdTe optical phonon modes.


2005 ◽  
Vol 2005 (8) ◽  
pp. 863-887
Author(s):  
Fouzi Zaouch

The time-dependent Ginzburg-Landau equations of superconductivity with a time-dependent magnetic fieldHare discussed. We prove existence and uniqueness of weak and strong solutions withH1-initial data. The result is obtained under the “φ=−ω(∇⋅A)” gauge withω>0. These solutions generate a dynamical process and are uniformly bounded in time.


2021 ◽  
Vol 2015 (1) ◽  
pp. 012076
Author(s):  
N.N. Kurus ◽  
A.G. Milekhin ◽  
R.B. Vasiliev ◽  
B.M. Saidzhonov ◽  
K.V. Anikin ◽  
...  

Abstract We report the phonon spectra of core/shell CdSe/CdS nanoplatelets with different shell thicknesses studied using Raman scattering. The nanoplatelets are rectangular colloidal nanocrystals, with thicknesses of core and shell layers of a few nanometers. The Raman spectra show features corresponding to the dominating longitudinal optical (LO) and surface optical (SO) phonon modes of the CdSe core in CdS shell located in the frequency regions of 200-210 and 250-290 cm-1, respectively. As the shell thickness increases, the phonon modes reveal a frequency shift and a change in intensity. The frequency shift associated with a change in the stress state in the core and shell, as well as with confinement effects is discussed. The phonon mode intensities are determined by the thickness of the shell and the proximity to resonant Raman scattering conditions.


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