Vibrational modes, semiconductor

Organic semiconductors such as K-TCNQ and TEA(TCNQ)2 have anomalous infrared (IR) absorption lines at frequencies corresponding the totally symmetric (ag) vibration modes of the TCNQ molecule. Normally, these modes would not be IR active, but because they modulate the electron overlap integrals, they induce charge oscillations along the (nonuniform) TCNQ stacks [108]. This is perhaps the clearest experimental evidence for... 

Local vibrational modes between 2800 and 3150 cm (see Fig. 1) have been observed in a number of semiconductors such as amorphous silicon carbide, GaAs, ° and GaN. In these materials the vibrational modes are assigned to symmetric and antisymmetric stretching modes of CHx complexes with x = 1, 2, 3. Therefore, the vibrational modes located at 2854 cm-i, 2890 cm-i, 2918 cm-i, 2948 cm-i, and 2988 cm-i should be due to the... 

Table II. Localized Vibrational Modes of Isolated Impurities in Semiconductors...

In the past five decades, a number of donors, acceptors, and their complexes with excitons in semiconductors have been discovered and delineated. Isoelectronic impurities and their localized vibrational modes have also been extensively studied in infrared absorption and Raman and luminescence spectroscopies. 

While the electronic and optical properties of semiconductor NCs are well luiderstood, the vibrational properties (phonons confined in spherical quantum dots of several nanometers in size) of NCs received much less attention until the last few years [1-4]. An accurate description of the vibrational modes of a NC is of fundamental interest and is required to understand the coupling of vibrational modes to electronic charge. Recently, it has been shown theoretically that geometrical confinement becomes important both for infrared and Raman-active phonons in the limit of a small size of QDs [5]. In this paper, we report the observation of coupled phonon modes in ZnSe spherical quantum dots. 

IRS Infrared Spectroscopy Thin crystal, glass, liquid I.R. light (W-filament, globar, Hg-arc) I.R. spectrum Electronic transitions (mainly in semiconductors and superconductors) vibrational modes (in crystals and molecules) 12,13,14... 

Any species showing infrared active vibrational modes adsorbed on a reflecting surface can be studied with infrared spectroscopy. The beam of light will interact absorptively with the species when passing through the adsorbate layer before and after the point of reflection. This enables studies of all kinds of adsorbates on many surfaces. Of particular interest in electrochemistry are surfaces of metals and semiconductors employed as electrodes. Thus the following text deals only with reflection at these surfaces other surface and interfaces are not treated. Attempts to record infrared spectra of emersed electrodes (i.e. ex situ measurements) have been reported infrequently in studies of adsorption of hydroquinone and benzoquinone on a polycrystalline platinum electrode [174-177]. Further development of this approach has... 

Together with the Banin group, the authors of Refs [10-12] carried out optical spectroscopy investigations on some of the cluster molecules obtained ] 14-16]. These materials were treated as the molecular limit of the bulk semiconductor CdSe, and issues such as oscillator strength, steady-state and time-resolved photoluminescence and photoluminescence excitation were addressed. In addition, emission-mediating vibrational modes were detected, and photobleaching effects observed. 

Nevertheless, even for polyacetylene, the electronic structure is not that of a simple metal in which the bond-alternation and the tc-tc gap have gone to zero there are infrared active vibrational modes (IRAV) and a pseudo-gap. This is indicated by the spectra in Figure 2 which demonstrate the remarkable similarity between the doping-induced absorption found with heavily doped trans-(CH)x, and the photoinduced absorption spectrum observed in the pristine semiconductor containing a very few photoexcitations. Not only are the same IRAV mode spectral features observed, they have almost identical frequencies. 

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