Morphology-dependent frequency shifts of the infrared parallel bands of poly(tetrafluoroethylene) (PTFE) were investigated using a PTFE sample having a whisker-like crystal morphology and lamellar crystals of linear oligomers of PTFE (perfluoro-re-eicosane (C20F42) and perfluoro-n-tetracosane (C24F50)). The vibrational assignments of the infrared-active zone-center fundamentals were established through polarization measurements on well-oriented thin films of PTFE and thin layers of C20F42 deposited on a metal surface. Based on the assignments thus decided, it has been demonstrated that the A2 bands with the transition dipoles parallel to the chain axis are blue-shifted as the crystal morphology of the sample goes from the extended-chain crystal to the lamellar crystal, whereas the Ej perpendicular bands as well as the infrared-inactive Raman bands (the Ai and E2 bands) remain unshifted. The magnitudes of the frequency shifts of the A2 bands were interpreted quantitatively in terms of the transition dipolar coupling theory. The role of the in-phase oscillation of the parallel transition dipoles in this spectral phenomenon was investigated by the analysis of the frequency shifts of the parallel progression bands of the oligomers in their lamellar type mixed crystals of various compositions.
In order to make vibrational assignments of the metastable orthorhombic modification of polyoxymethylene (o-POM), polarized Raman and infrared spectra of a single crystal of deca(oxymethy1ene) diacetate, CH3COO(CH,0),,COCH3 (POMAclO), a linear oligomer of POM, were measured and compared with previous results obtained using a micron-sized single crystal of o-POM. On the basis of the orientation of the o-POM sublattice in the POMAclO crystal, assignments of the zone-centre modes of o-POM was established and the unit cell orientation in the micron-sized o-POM single crystal was decided. The morphology-dependent frequency shifts of the parallel infrared bands (B, modes) in the POMAclO crystal, which has a specific morphological structure different from the lamellar crystal of high-molecular-weight o-POM, were investigated on the basis of the transition dipolar coupling theory.
We investigated the effects of c/a anisotropy and local crystal structure on superconductivity (SC) in As/P solid solution systems, AFe 2 (As 1−x P x ) 2 (A122P) with various A ions. With decreasing A site atomic size from A=Ba to Eu, the structural anisotropy decreases, and the rate of decreasing with x also increases. The rapid narrowing of the region of antiferromagnetic composition (x) can be considered to be a result of this anisotropy change due mainly to the change in the Fermi surface (FS) nesting condition. By contrast, although the structural anisotropy systematically changes, the maximum T c values are almost the same in all A122P systems except for Eu122P. These results indicate that the modification of the FS topology via the structural anisotropy does not affect SC. However local structural parameters, such as pnictogen height, are crucial for T c .The discovery of iron based superconductors in 2008 has stimulated much discussion. 1) Their rich phase diagrams have suggested various bosonic fluctuations, such as spin, orbital and charge, possibly acting as a glue between electrons. Many theories have been proposed to explain the superconducting mechanism in terms of these fluctuations. However, which fluctuation plays the most important role in superconductivity (SC) remains in dispute.In some theories, Fermi surface (FS) nesting plays a crucial role. For example, spin fluctuation is enhanced when the condition of nesting between the hole and electron FSs is good, J. Phys. Soc. Jpn. which induces unconventional SC. [2][3][4] In the case of BaFe 2 (As 1−x P x ) 2 (Ba122P), the experimental results of inelastic neutron scattering and nuclear magnetic resonance (NMR) studies revealed that spin fluctuation was clearly enhanced in the optimally doped x-region. 5, 6) Furthermore, the study of angle-resolved photoemission spectroscopy (ARPES) 7) demonstrated that the observed FSs fulfill the nesting condition between the electron and hole FSs, which was consistent with the spin fluctuation theory in Ba122P. 8,9) From the crystallographic viewpoint, the appearance of SC would be ascribed to the optimization of the pnictogen (Pn) height from the Fe layer (h Pn ) 10) or the Pn-Fe-Pn bond angle (α), 11) which was also explained by nesting-based theories. 9,12) On the other hand, according to the nesting scenario, the distance between neighboring Fe layers, which must be correlated with interlayer hybridization and thus with anisotropy, should have a distinct influence on antiferromagnetism (AFM) and SC. Nevertheless, both Néel temperature (T N ) and superconducting transition temperature (T c ) are not higher in Ba122P than in Sr122P, although the ratio of a-and c-axes lattice constants, c/a, which is an index of structural anisotropy, is larger in Ba122P than in Sr122P. These behaviors are inconsistent with the nesting-based model. 13,14) The change in the FS with structural anisotropy has been confirmed in a recent ARPES study. 15) According to that study, the d z 2 FS at the Brillouin zone center was war...
We clarified the impact of the fifth material incorporation into HfSiON technology for V th control on the reliability of high-k/metal gate stacks CMOSFETs. HfMgSiON is remarkably effective for suppressing electron traps, giving rise to a dramatic PBTI lifetime improvement for nMOSFETs. With pMOSFETs, Al incorporation is effective for the thermal deactivation of hole traps, resulting in NBTI lifetime improvement. We have established the guidelines of material selection to be incorporated into HfSiON for reliability improvement for nMOS and pMOS individually.Introduction A high-k/metal gate stack is required for scaled CMOSFETs, but one of its most serious problems is in V th control. There have been many reports of the incorporation of some material into the Hf-based high-k gate dielectrics to modulate V th [1][2][3][4]. However there have been only a few reports on the impact of these incorporations on the reliability [1]. In this paper, we clarified the effect of material incorporation to control V th on the high-k gate dielectrics reliability and its improvement mechanism. Experimental Fig. 1 shows the schematic of the dual high-k CMOSFET. Dual high-k were fabricated to control V th . HfSiON was used as the starting material for high-k gate dielectrics. Mg [2] and La [3] incorporations were used for nMOSFETs, whilst Al [4] and Ta were used for pMOSFETs. Each material was incorporated into HfSiON with 1000 o C annealing following a capping deposition. All T inv were between 1.6 and 1.8 nm. For the assessment of the reliability, PBTI and NBTI measurements, charge pumping, and 1/f noise measurements were carried out.Results and Discussion Fig. 2 shows the I d -V g characteristics (V d =50 mV) of nMOSFETs. As an effect of Mg and La incorporation, V th were lowered by 350 mV for La, 500 mV for Mg respectively. Although both materials were effective for V th control, their impact on the reliability was very different. Fig. 3 shows the time evolution of ∆V th in PBTI. This clearly shows that Mg was effective for aggressively suppressing the PBTI degradation. On the other hand, La incorporation accelerated the V th shift. Fig. 4 shows the PBTI lifetime (∆V th =50 mV) as a function of overdrive stress voltage (V g -V th ). Using the Mg, PBTI lifetime was dramatically improved over four orders of magnitude. Mg was better than La from the point of reliability. Fig. 5 shows the charge pumping current (I cp ) as a function of base bias. With La incorporation, N it was reduced, whilst N it was increased with Mg. These results can not explain the PBTI phenomena. Thus, we can say that electron traps causing V th shift in PBTI exist in the bulk high-k not in the interface. Mg incorporation gave rise to the dramatic reduction in electron traps, but not so with La. This electron trap suppressions affect on the 1/f noise also. Fig. 6 shows the input-referred spectral noise density (S vg ) as a function of frequency for nMOSFETs. Since it has been reported that origin of the S vg of HfSiON nMOSFET is the mobility fluctuation (pr...
We report comprehensive temperature and doping-dependences of the Raman scattering spectra for BaFe 2 (As 1−x P x ) 2 (x = 0, 0.07, 0.24, 0.32, and 0.38), focusing on the nematic fluctuation and the superconducting responses. With increasing x, the bare nematic transition temperature estimated from the Raman spectra reaches T = 0 K at the optimal doping, which indicates a quantum critical point (QCP) at this composition. In the superconducting compositions, in addition to the pair breaking peaks observed in the A 1g and B 1g spectra, another strong B 1g peak appears below the superconducting transition temperature which is ascribed to the nematic resonance peak. The observation of this peak indicates significant nematic correlations in the superconducting state near the QCP in this compound.
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