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Publication Metadata only A profound analysis of Rb-2[PH] and Cs-2[PH] and the role of [PH](2-) ions during temperature-induced solid-solid phase transitions(Elsevier, 2014) Hochrein, Oliver; Zahn, Dirk; Department of Chemistry; Department of Chemistry; Somer, Mehmet Suat; Schnering, H. G. Von; Faculty Member; Other; Department of Chemistry; College of Sciences; College of Sciences; 178882; N/AThe temperature-induced solid-solid transformation of Rb-2[PH] and Cs-2[PH] is characterized from both experiment and theory. Neutron diffraction, IR-spectroscopy and ab-initio molecular dynamics simulations reveal an asymmetric shift of the lattice constants at 80 K. The molecular mechanism of the structural transformation as identified from IR-spectroscopy and ab-initio molecular dynamics simulations is closely connected to the orientation of the [PH](2-) moieties which undergo a partial order-disorder phase transition.Publication Metadata only Analysis of the knight shift data on Li and Zn substituted YBa2Cu3O6+x(Elsevier, 2001) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; N/AThe Knight shift data on Li and Zn substituted YBa2Cu3O6+x are analyzed using an itinerant model with short-range antiferromagnetic correlations. The model parameters, which are determined by fitting the experimental data on the transverse nuclear relaxation rate T-2(-1) of pure YBa2Cu3O6+x, are used to calculate the Knight shifts for various nuclei around a nonmagnetic impurity located in the CuO2 planes. The calculations are carried out for Li and Zn impurities substituted into optimally doped and underdoped YBa2Cu3O6+x. The results are compared with the Li-7 and Y-89 Knight shift measurements on these materials. (C) 2001 Elsevier Science B.V. All rights reserved.Publication Metadata only Defect structure in aliovalently-doped and isovalently-substituted PbTiO3 nano-powders(Institute of Physics (IOP) Publishing, 2010) Erdem, Emre; Jakes, Peter; Parashar, S. K. S.; Ruediger, Andreas; Eichel, Ruediger-A; N/A; Department of Chemistry; Kiraz, Kamil; Somer, Mehmet Suat; Researcher; Faculty Member; Department of Chemistry; N/A; College of Sciences; N/A; 178882The defect structure of Fe3+-, Cu2+-, Mn4+- and Gd3+-doped PbTiO3 nano-powders has been studied by electron paramagnetic resonance (EPR) spectroscopy. Analogous to the situation for 'bulk' ferroelectrics, Fe3+ and Cu2+ act as acceptor-type functional centers that form defect complexes with charge-compensating oxygen vacancies. The corresponding defect dipoles are aligned along the direction of spontaneous polarization, PS, and possess an additional defect polarization, P-D. Upon the transition to the nano-regime, the defect structure is modified such that orientations perpendicular to P-S, (Fe-Ti'-V-O(center dot center dot))(perpendicular to)(center dot) and (Cu-Ti ''-V-O(center dot center dot))(perpendicular to)(x) also become realized. Moreover, the binding energy for the defect complexes is lowered such that instead 'free' Fe-Ti' and V-O(center dot center dot)-centers are formed. As a consequence, the concentration of mobile V-O(center dot center dot) that enhances the ionic conductivity through drift diffusion is increased for the nano-powders. Finally, in the nano-regime the ferroelectric 'hardening' is expected to be considerably decreased as compared to the 'bulk' compounds. In contrast to the acceptor-type dopants, the donor-type Gd3+ dopant is incorporated as an 'isolated' functional center, where charge compensation by means of lead vacancies is performed in distant coordination spheres.Publication Metadata only Effects of dilute nonmagnetic impurities on the Q = (π,π) spin-fluctuation spectrum in YBa2Cu3O7(Elsevier, 2001) Department of Physics; Bulut, Nejat; Faculty Member; Department of Physics; College of Sciences; N/AThe effects of nonmagnetic impurities on the Q = (pi, pi) spin-fluctuation spectral weight Im chi (Q, omega) are studied within the framework of the two-dimensional Hubbard model using the random phase approximation. In the first part of the paper, the effects of the nonmagnetic impurities on the magnetic susceptibility of the noninteracting (U = 0) system, chi (0)(q, omega), are calculated with the self-energy and the vertex corrections using various forms of the effective electron-impurity interaction. Here, the range and the strength of the impurity potential are varied as well as the concentration of the impurities. It Is shown that the main effect of dilute impurities on X,(Q, w) is to cause a weak smearing. In the second part, Im chi (Q, omega) is calculated for the interacting system. Here, the calculations are concentrated on the processes which involve the impurity scattering of the spin fluctuations with finite momentum transfers. Results are given for various values of the model parameters, and comparisons are made with the neutron scattering data on Zn substituted YBa2Cu3O7. (C) 2001 Elsevier Science B.V. All rights reserved.Publication Metadata only Modifying hydrogen binding strength of graphene(Elsevier Science Bv, 2019) N/A; N/A; N/A; Department of Chemistry; Panahi, Mohammad; Solati, Navid; Kaya, Sarp; PhD Student; PhD Student; Faculty Member; Department of Chemistry; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 116541The effect of the substrate on the binding strength of hydrogen on single layer graphene grown on Pt(111) surfaces has been investigated via determining its desorption activation energy. We showed that subsurface alloys on Pt(111) can dramatical modify the C-H bond strength in hydrogenated graphene. Various 3d metals, vanadium, iron, cobalt, and nickel were deposited in the subsurface layer to modify the chemical and electronical properties of the substrate. Analysis of the temperature programmed desorption data shows that subsurface alloys reduce the hydrogen desorption activation energy by weakening C-H bond energy in graphene, down to 57 kJ/mol in the case of Pt/Co/Pt(111) as compared to similar to 111 kJ/mol obtained from hydrogenated graphene grown on a bare Pt(111).Publication Metadata only Nanoparticle based induction heating at low magnitudes of magnetic field strengths for breast cancer therapy(Elsevier, 2019) Zuvin, Merve; Koçak, Muhammed; Akkoç, Yunus; Kutlu, Özlem; Gözüaçık, Devrim; Koşar, Ali; N/A; Department of Chemistry; Ünal, Özlem; Acar, Havva Funda Yağcı; PhD Student; Faculty Member; Department of Chemistry; Graduate School of Sciences and Engineering; College of Sciences; N/A; 178902Magnetic hyperthermia has received much attention during the last decade due to its implementation in cancer treatment. Recently, functionalized superparamagnetic iron oxide nanoparticles (SPION) emerged as a strong alternative adjuvant treatment approach, which complements conventional methods such as chemotherapy. In this study, we demonstrate the anticancer effect of Poly(acrylic acid)-coated, anti-HER2-tagged SPIONs on breast cancer cells using a low magnetic field strength of 0.8 kAm(-1), which is significantly lower compared to the literature, with a frequency of 400 kHz. Specificity was achieved via anti-HER2 antibody attachment to nanoparticles. HER2-positive SKBR3 and MDA-MB-453 cell lines internalized the nanoparticles successfully. These nanoparticles, which were not toxic to these cell lines, led to a prominent decrease in cell proliferation and survival in MDA-MB-453 cells when subjected to hyperthermia. Therefore, the hyperthermia-targeted SPION approach could be developed as a potential cancer treatment approach against breast cancer and possible other cancer types.Publication Metadata only Silicon microspheres for near-IR communication applications(IOP Publishing Ltd, 2008) Demir, Abdullah; Department of Physics; Serpengüzel, Ali; Faculty Member; Department of Physics; College of Sciences; 27855We have performed transverse electric and transverse magnetic polarized elastic light scattering calculations at 90 degrees and 0 degrees in the o-band at 1.3 mu m for a 15 mu m radius silicon microsphere with a refractive index of 3.5. The quality factors are on the order of 10(7) and the mode/channel spacing is 7 nm, which correlate well with the refractive index and the optical size of the microsphere. The 90 degrees elastic light scattering can be used to monitor a dropped channel (drop port), whereas the 0 degrees elastic scattering can be used to monitor the transmission channel (through port). The optical resonances of the silicon microspheres provide the necessary narrow linewidths that are needed for high-resolution optical communication applications. Potential telecommunication applications include filters, modulators, switches, wavelength converters, detectors, amplifiers and light sources. Silicon microspheres show promise as potential building blocks for silicon-based electrophotonic integration.Publication Metadata only Spectroscopic analysis of Tm3+:LuAG(IOP Publishing Ltd, 2007) Özen, Gönül; N/A; Department of Physics; Department of Physics; Kalaycıoğlu, Hamit; Sennaroğlu, Alphan; Kurt, Adnan; PhD Student; Faculty Member; Teaching Faculty; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; 23851; 194455We studied the spectroscopic properties of two thulium-doped Lu3Al5O12 (Tm:LuAG) samples with Tm3+ concentrations of 0.5 and 5 at.%. Judd– Ofelt theory was used to analyse the absorption spectra and to determine the radiative transition rates. Fluorescence measurements were further performed to determine the luminescence quantum efficiencies. The average radiative lifetimes of the 3H4 and 3F4 levels were calculated to be 1041 ± 143 μs and 17.7 ± 3.4 ms, respectively. We observed a sharp increase in the strength of cross relaxation for the 5% Tm:LuAG sample evidenced by the much shorter fluorescence lifetime of 42.3 μs for the 3H4 level, in comparison with 851 μs for the 0.5% Tm:LuAG sample. This was further supported by the relative emission measurements at 1470 and 1800 nm. The measured fluorescence lifetime of the 3F4 level showed a smaller decrease from 11.2 ms (0.5% doping) to 7.1 ms (5% doping). By using the Judd–Ofelt theory, the stimulated emission cross section was further calculated to be 1.2 ± 0.2 × 10−21 cm2 at 2023 nm, corresponding to the free running wavelength of Tm:LuAG lasers. Finally, the critical distance parameter R0 for cross relaxation was determined to be 10.2 ± 0.8 A from the ˚ fluorescence decay data.Publication Metadata only Weakly bound finite systems: (4He)N–Rb2(3Σu), clustering structures from a quantum Monte Carlo approach(Iop Publishing Ltd, 2012) Lopez-Duran, D.; Rodriguez-Cantano, R.; Gonzalez-Lezana, T.; Delgado-Barrio, G.; Villarreal, P.; Gianturco, F. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129We report here (He-4)(N)-Rb-2((3)Sigma(u)) complexes, 2 <= N <= 20, analysed through a quantum diffusion Monte Carlo stochastic approach. The calculations show that the spin stretched dimer molecule is bound outside the pure He sub-complex, due to the stronger He-He potential as compared with the He-Rb-2 interaction, while the rare gas atom moiety presents, in turn, a shell-like structure with ten He adatoms completing the first shell. Our results agree with previous findings on this and similarly weakly interacting systems.