Browsing by Subject "Quantum-wells"

Now showing 1 - 4 of 4

Open Access
Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2
(Wiley, 2020-09) Ebrahimi, Elnaz; İrfan, Muhammad; Shabani, Farzan; Koçak, Yusuf; Karakurt, Bartu; Erdem, E.; Demir, Hilmi Volkan; Özensoy, Emrah
Functionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.
Open Access
Core-crown quantum-well nanoplatelet functionalized TIO2 for photocatalytic NOx abatement
(2020-07) Ebrahimi, Elnaz
Oleic acid capped core/crown CdSe/CdSeTe quantum-well nanoplatelets (NPL) were used in the surface functionalization of TiO2. Structural characterization of the synthesized photocatalytic architecture was carried out to shed light on its surface chemistry, electronic, and crystallographic structure. NPL/TiO2 composites were tested in NO photo-oxidation under ultraviolet-A (UVA) and visible (VIS) light, showing a remarkable activity in NOx abatement and high selectivity for nitrate storage as compared to standard benchmark TiO2 photocatalyst (i.e. P25). Improved photocatalytic behavior can be attributed to the decrease in the bandgap and enhanced photogenerated electron-hole pair separation as a result of the incorporation of CdSe/CdSeTe NPL onto TiO2. Stability of composites was also investigated in durability tests. Even though some decrease in photocatalytic activity and selectivity of NPL/TiO2 composites was observed, performance of the NPL/TiO2 composites was found to be significantly better than pure TiO2.
Open Access
The Influence of the Rashba spin orbit coupling on the two dimensional magnetoexcitons
(IOP Publishing, 2011) Hakioglu, T.; Liberman, M. A.; Moskalenko, S. A.; Podlesny, I. V.
The influence of the Rashba spin-orbit coupling (RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba (1960 Fiz. Tverd. Tela 2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field.
Open Access
On the origin of the redshift in the emission wavelength of InGaN/GaN blue light emitting diodes grown with a higher temperature interlayer
(AIP Publishing, 2012-03-20) Ju, Z. G.; Tan S.T.; Zhang Z.-H.; Ji Y.; Kyaw, Z. B.; Dikme, Y.; Sun, X. W.; Demir, Hilmi Volkan
A redshift of the peak emission wavelength was observed in the blue light emitting diodes of InGaN/GaN grown with a higher temperature interlayer that was sandwiched between the low-temperature buffer layer and high-temperature unintentionally doped GaN layer. The effect of interlayer growth temperature on the emission wavelength was probed and studied by optical, structural, and electrical properties. Numerical studies on the effect of indium composition and quantum confinement Stark effect were also carried out to verify the experimental data. The results suggest that the redshift of the peak emission wavelength is originated from the enhanced indium incorporation, which results from the reduced strain during the growth of quantum wells.