Polarization Raman study of protein ordering by controllable RBC deformation

Polarized Raman spectroscopy is used to provide evidence of hemoglobin protein ordering as the red blood cell (RBC) is stretched with optical tweezers. The stretching of the cell is intended to mimic the deformation that it experiences as it travels through vessels and capillaries. The depolarization ratios for a number of heme Raman bands change as the cell is stretched, confirming the semi‐ordered nature of the hemoglobin ensemble in the cytoplasm. Furthermore, trends observed in the ratio shifts point to increased packing and ordering of the Hb after cell stretching. This evidence should shed more light on to the role of deformation in the RBC function. Copyright © 2009 John Wiley & Sons, Ltd.     

GaMnAs合金中等离子体激元-LO声子耦合模的拉曼光谱研究

理论分析了两种阻尼条件下重掺杂GaAs中的等离子体激元-LO声子耦合模,证实在小阻尼条件下耦合模的拉曼谱分为两支,而在大阻尼条件下只有一个耦合模可以被观测到。推导得到了只出现一个耦合模所需的最小阻尼的解析表达式。测量了Mn组分从2.6%到9%的GaMnAs合金的拉曼光谱。利用等离子体激元-LO声子耦合模理论进行了谱形拟合,得到了所测的GaMnAs合金中的空穴浓度。     

A Mössbauer effect study of structural ordering in rapidly quenched Fe–Ga alloys

Samples of Fe_100−xGa_x (x=8.3, 17.9, 20.5 and 23.3) were prepared by rapid solidification from the melt using a single Cu roller. X-ray diffraction studies of all samples showed them to be single phase with the disordered BCC structure. No evidence of superlattice reflections from D0₃ ordering was observed for any of the samples. Room-temperature ⁵⁷Fe Mössbauer effect spectra indicated that all samples were ferromagnetically ordered. Spectra were fit to distributions of hyperfine fields. The x=8.3 sample showed a hyperfine field distribution that was single peaked and indicated a reasonably random distribution of local Fe environments. The x=17.9 and 20.5 samples showed hyperfine field distributions that were bimodal and indicated two distinct local Fe environments. The x=23.3 sample showed three distinct field components. It is suggested that the x=8.3, 17.9 and 20.5 alloys are primarily a disordered BCC phase. The x=8.3 alloy shows a small amount of short-range Ga–Ga pairing, while this short-range pairing is significantly greater in the x=17.9 and 20.5 alloys. The three field components in the x=23.3 alloy correspond well to the two sites associated with the D0₃ phase and a third component corresponding to a remaining L1₂ phase suggesting the presence of at least short-range D0₃ clustering in this alloy.     

Resonant Raman studies of surface composition and structural ordering in laser-irradiated Hg1-xCdxTe

1-x Cd_xTe for x=0.165 and x=0.18. The annealing was performed in air with a Nd:YAG laser tuned to the first harmonic. A pulse duration of 72 ns and irradiation energy densities of 270 and 400 mJ/cm² were used. Information on both the structural ordering and the alloy composition in irradiated Hg_1-xCd_xTe was obtained by resonance Raman spectroscopy with laser photon energies of between 2.41 and 2.54 eV. The presented Raman spectra from annealed samples indicate structural disorder and a decrease in the degree of alloying as a result of Hg outdiffusion and segregation caused by laser-induced nonequilibrium melting and solidification. Moreover, a shift of the maximum resonant enhancement for the TO₂, LO₂, A, and LO₁&TO₁ modes in the case of a Hg_0.82Cd_0.18Te sample, annealed by 400 mJ/cm² laser pulse, to higher photon energy points to an increase in the composition from x=0.18 to x?0.3. Received: 14 July 1997/Accepted: 10 October 1997     

Magnetoelectric effect and toroidal ordering in Ga2−x FexO3

The field dependence of the magnetoelectric effect and longitudinal magnetostriction of Ga_2−x Fe_xO₃ single crystals is studied in magnetic fields up to 200 kOe in the temperature range from 4.2 to 300 K. It is shown that the magnetoelectric effect in these materials is determined mainly by the toroidal moment T and is not related to magnetostriction, as was previously theorized. A new method for determining the toroidal moment by measuring the electric polarization in a strong magnetic field is proposed. The value of the toroidal moment of the unit cell in Ga_1.15Fe_0.85O₃ is calculated: T=(T _a ,0,0), where T _a =24.155μ _B Å per unit cell. Experimental data are analyzed using a theory of toroidal spin ordering, which gives good agreement with experiment. Zh. éksp. Teor. Fiz. 114, 263–272 (July 1998) Deceased.     

Orbital ordering in LaMnO3 investigated by resonance Raman spectroscopy

Orbital ordering leads to an unconventional excitation spectrum that we investigate by resonance Raman scattering using incident photon energies between 1.7 and 5.0 eV. We use spectral ellipsometry to determine the corresponding dielectric function. Our results show resonant behavior of the phonon Raman cross section when the laser frequency is close to the orbiton-excitation energy of 2 eV in LaMnO3. We show an excellent agreement between theoretical calculations based on the Franck-Condon mechanism activating multiphonon Raman scattering in first order of the electron-phonon coupling and the experimental data of phonons with different symmetries.     

Effect of electron-phonon interactions on Raman line at ferromagnetic ordering

The theory of Raman scattering in half-metals by optical phonons interacting with conduction electrons is developed. We evaluate the effect of electron-phonon interactions at ferromagnetic ordering in terms of the Boltzmann equation for carriers. The chemical potential is found to decrease as the temperature decreases. Both the linewidth and frequency shift exhibit a dependence on temperature.     

MBE生长的In_(1-x-y)Ga_xAl_yAs/InP四元混晶的拉曼散射

ＭＢＥ生长的Ｉｎ１－ｘ－ｙＧａｘＡｌｙＡｓ／ＩｎＰ四元混晶的拉曼散射韩和相汪兆平李国华徐士杰刘南竹朱作明（中国科学院半导体研究所半导体超晶格国家重点实验室北京１０００８３）ＯｐｔｉｃａｌＰｈｏｎｏｎＲａｍａｎＳｃａｔｅｒｉｎｇｆｒｏｍＩｎ１－ｘ－ｙＧ...     

Scaled nano-and microrelief of ordering regions in Al x Ga1 − x As/GaAs(100) epitaxial heterostructures

The Al _x Ga_{1 ? x} As/GaAs(100) heterostructures grown by MOS hydride epitaxy were studied using atomic force and scanning electron microscopy. Regions with an ordered nanorelief with a period of approximately 115 nm were discovered on the surface of the sample with x ～ 0.50. An AlGaAs₂ superstructural phase appears in these regions.     

Carrier-induced magnetic ordering control in a digital (Ga,Mn)as structure

With the full potential linearized augmented plane method, we theoretically investigated the carrier-induced magnetization reversal in digital (Ga,Mn)As heterostructures with varying distance between the two Mn layers along with the distribution and concentration of external carriers. The presence of external holes induces switching from the antiferromagnetic to ferromagnetic state when d(Mn-Mn)=16.96 A, whereas the addition of electrons produces no significant effect. We demonstrate a possibility to separately control T(c) and magnetic reversal in digital (Ga,MN)As alloys.     

Raman scattering from GaAs-Al0.5Ga0.5As-AlAs polytype superlattices

We report the first Raman study of GaAs-Al_0.5Ga_0.5As-AlAs polytype superlattices grown by molecular-beam epitaxy. Folded longitudinal acoustic phonon modes were observed for all the samples. The frequencies agree well with those calculated using an elastic continuum model. The intensities of the folded modes have novel properties, compared with double-constituent superlattices like GaAs-(AlGa)As.     

Raman scattering studies of the magnetic ordering in hexagonal HoMnO3 thin films

We present the results of the temperature dependence of the Raman spectra of hexagonal HoMnO₃ thin films in the 13–300 K temperature range. The films were grown on Pt(111)//Al₂O₃ (0001) substrates using the laser ablation method. In the HoMnO₃ thin films, we initially observedseveral broad Raman peaks at ∼510, 760, 955, 1120, and 1410 cm⁻¹. These broad Raman peaks display an anomalous behavior near the magnetic transition temperature, and the intensity difference of the Raman spectra at different temperatures shows several pairs of negative and positive peaks as the temperature is lowered below the Néel temperature. Our analyses indicate that all the broad peaks are correlated with magnetic ordering, and we have assigned the origin of all the broad peaks. Purely on the basis of the Raman analysis, we have deduced the Néel temperature and the spin exchange integrals of HoMnO₃ thin films. We also investigated the effects of the growth condition on the strongest broad peak at ∼760 cm⁻¹, which is related with pure magnetic ordering. This result indicates that the oxygen defect in the HoMnO₃ sample has negligible effect on magnetic ordering. Copyright © 2009 John Wiley & Sons, Ltd.