The Influence of Ultraviolet Light on Luminescence (700–1000 nm) of LiF and LiF:OH Crystals Irradiated in a Nuclear Reactor

Optics and Spectroscopy - The emission (700–1000 nm) and absorption (200–800 nm) spectra of LiF and LiF:ОН crystals irradiated in a reactor and by UV light, as well as...     

The Influence of Relative Content of a Metal Component in a Dielectric Matrix on the Formation and Dimensions of Cobalt Nanocrystallites in Cox(MgF2)100 – x Film Composites

Physics of the Solid State - The influence of relative content of a metal component on the phase composition and substructure of Cox(MgF2)100 – x in a wide range of x =...     

Field-dependent resistive transitions in YBa_2Cu_3O_(7-δ) thin films:Influence of the pseudogap on vortex dynamics

The nature of resistive transition of high-quality crystalline thin films of YBa2Cu3O7-δhas been studied under magnetic fields(H)applied along the c direction over a wide range of doped holes,p,in the Cu O2planes.The field-and temperature-dependent in-plane resistivity,ρab(T,H),has been analyzed within the thermally assisted flux-flow(TAFF)formalism.The flux activation energy,U(T,H),has been extracted from this analysis.The low-T part of theρab(T,H)data can be described by an activation energy having the functional form of U(T,H)=(1-t)m(H-0/H)β,where t=T/Tc(reduced temperature),and H0is a field scale that primarily determines the magnitude of U(T,H).The temperature exponent,m,shows a systematic variation with p,whereas the field exponent,β,is insensitive to the p values and is close to unity.The H0,on the other hand,changes rapidly as p is varied.U(T,H)is linked to the pinning potential and consequently on the superconducting condensation energy.Since the normal state pseudogap directly affects superconducting condensation energy,a clear correspondence between H0and the PG energy scale,εg,is found.Possible implications of these results are discussed.     

Relative reactivities of amino and ethenyl groups in allylamine on Si(100)2 × 1: Temperature-dependent X-ray photoemission and thermal desorption studies of a common linker molecule

The room-temperature adsorption and thermal evolution of allylamine on Si(100)2 × 1 have been investigated by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS). The presence of a broad N 1 s feature at 398.9 eV, attributed to a N―Si bond, indicates N―H dissociative adsorption. On the other hand, the presence of C 1 s features at 284.6 eV and 286.2 eV, corresponding to C═C and C―N, respectively, and the absence of the Si―C feature expected at 283.2 eV shows that [2 + 2] C═C cycloaddition does not occur at room temperature. These XPS data are consistent with the unidentate staggered and eclipsed allylamine conformer adstructures arising from N―H dissociation and not [2 + 2] C═C cycloaddition. The apparent conversion of the N 1 s feature for Si―N(H)―C

at 398.9 eV to that for Si―N(H) at 397.7 eV and the total depletion of C 1 s feature for C―N at 286.2 eV near 740 K indicates cleavage of the C―N bond, leaving behind a Si―N(H) radical. Furthermore, the C═C C 1 s feature at 284.6 eV undergoes steep intensity reduction between 740 K and 825 K, above which a new C 1 s feature at 283.2 eV corresponding to SiC is found to emerge. These spectral changes suggest total dissociation of the ethenyl fragment and the formation of SiC. Moreover, while the total N 1 s intensity undergoes a minor reduction (24%) upon annealing up to 1090 K, a considerable reduction (43%) is found in the overall C 1 s intensity. This observation is consistent with our TDS data, which shows the desorption of C-containing molecules including propene and ethylene at 580 K and of acetylene at 700 K. The lack of N-containing desorbates suggests that the dissociated N species are likely bonded to multiple surface Si atoms or diffused into the bulk. Interestingly, both the staggered and eclipsed N―H dissociative adstructures are found to have a less negative adsorption energy than the [N, C, C] tridentate or the [2 + 2] C═C cycloaddition adstructures by our DFT calculations, which suggests that the observed formation of N―H dissociative adstructures is kinetically favored on the Si(100)2 × 1 surface.     

Influence of thermal treatment in oxidizing and reducing atmospheres on the composition and properties of solid solutions based on bismuth vanadate: (Bi,La)4(V,Me)2O11?y (Me = Ga, Zr, Cu)

Ceramic solid solutions (Bi_{1 − y} La _y )₄(V_{1 − x} Me _x )₂O_{11 − z} (x, y < 0.2: Me = Zr, Ga, Fe, Cu) were prepared by solid-state reaction. It was shown that the annealing (973 K, reducing atmosphere H₂/Ar (20/80)) of the samples whose compositions belong to the stability domains of α, β, and γ′ polymorphs increases their electronic conductivity by six orders of magnitude. The samples with low concentrations of dopant cations exhibited good compositional stability and a reversible change in their structure parameters. At the same time, the solid solutions with a high concentration of lanthanum cations and/or copper cations (y, x ∼ 0.1) underwent partial decomposition.