Single crystal CdTe films are desirable for optoelectronic device applications. An important strategy of creating films with high crystallinity is through epitaxial growth on a proper single crystal substrate. We report the metalorganic chemical vapor deposition of epitaxial CdTe films on the CdS/mica substrate. The epitaxial CdS film was grown on a mica surface by thermal evaporation. Due to the weak van der Waals forces, epitaxy is achieved despite the very large interface lattice mismatch between CdS and mica (~21-55%). The surface morphology of mica, CdS and CdTe were quantified by atomic force microscopy. The near surface structures, orientations and texture of CdTe and CdS films were characterized by the unique reflection highenergy electron diffraction surface pole figure technique. The interfaces of CdTe and CdS films and mica were characterized by X-ray pole figure technique and transmission electron microscopy. The out-of-plane and in-plane epitaxy of the heteroepitaxial films stack are determined to be CdTe(111)//CdS(0001)//mica(001) and [1 � 21 � ] CdTe //[1100] CdS //[010] mica , respectively. The measured photoluminescence (PL), time resolved PL, photoresponse, and Hall mobility of the CdTe/CdS/mica indicate quality films. The use of van der Waals surface to grow epitaxial CdTe/CdS films offers an alternative strategy towards infrared imaging and solar cell applications.
With VO , a classic strongly correlated oxide material, a model semiconductor CdS is stretched and its electron-lattice interaction in a nonlinear manner is modulated. Optical spectroscopy is applied to probe the electronic band structure-associated parameters which is explained by the theoretical prediction based on k·p method and microscopy study. The research provides a new avenue on dynamic straining engineering.
Wurtzite (W) and zinc-blende (ZB) polytypism has long been observed in epitaxial CdS thin films. The present work, based on van der Waals epitaxial CdS thin films, is an attempt to explain which crystal modification, W or ZB, is favored under different growth conditions. In this van der Waals epitaxy system where the substrate influence is considered weak, it is found that the substrate temperature plays a crucial role in determining the crystal modification of CdS, that is, W and ZB CdS are more stable at low and high ends of substrate temperature, respectively. We attribute this temperature effect to the entropy difference (SW < SZB), a conclusion well supported by the thermodynamic hard sphere model formulation of the entropy difference between hexagonal close-packed and face-centered cubic structures. By summarizing other works, we find that the entropy difference model can also be applied to large mismatched (≳3%) CdS-substrate chemical epitaxy systems but not for small mismatched (≲3%) ones. In the latter case, the energy benefit in terms of high density of bonding contributed by the substrate-film interface is believed to be too overwhelming for the intrinsic entropy difference to overcome. Furthermore, the deposition rate is found to affect the crystalline quality and strain level in CdS films but not the crystal modification of the CdS films. Last, Raman and photoluminescence spectroscopies reveal the strain behaviors in the films. The phase change from W to ZB CdS is well-correlated with the observed peak shifts in Raman and photoluminescence spectroscopies.
Unlike most other wind instruments, in reed organ pipes it is not the length of the resonator tube that primarily determines the pitch, but the length of the vibrating reed. The reed, its fluid-structure interaction with the airflow, and feedback from the resonator form a very complicated dynamical system. By utilizing a Polytec PSV-400 scanning laser Doppler vibrometer, it is possible to monitor the operating deflection shapes of a vibrating reed, while using a microphone to monitor the sound production. In the current study, an experienced organ builder made adjustments to the reed/resonator/airflow parameters, both within a musically appropriate range, and for ranges outside of the norm. Results will be presented of the acoustical and vibrational spectral envelope, and the corresponding deflection shapes for each harmonic, for a range of different adjustments to the system. The vibrational results for the reed will be compared to measurements where the non-contact ultrasound radiation force is used to excite the natural resonance frequencies and deflection shapes of the reed in the absence of airflow. In addition to steady-state deflection shapes, results will be presented for the transient dynamics of the system as the airflow into the pipe is initiated.
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