[en] The purpose of this paper is to report some experiments with HfO₂ film, which was deposited onto silicon substrates at different growth rates by electron beam evaporation. The chemical states were measured by X-ray photoelectron spectroscopy (XPS). The rms roughness as low as 0.85 nm was measured by atomic force microscope (AFM). Scanning electron microscopy (SEM) was also used to determine cross-section morphology. Spectroscopic ellipsometry (SE) was applied to measure the refractive index, extinction coefficient and the thickness of the films. The results of SE presented the refractive indices varied in the range of 1.81-1.95 around 1550 nm by altering deposition rates. The transmittance and reflectance spectrum were measured to determine the effectiveness of HfO₂ thin film as a single layer anti-reflection coating on Si substrates. The results suggested that the Fresnel losses below 0.05 dB/chip are achieved by depositing HfO₂ film onto SOI rib waveguide endface

[en] The geometric structure, electronic structure and formation energy of CaCu₃Ti₄O₁₂ (CCTO) with interstitial copper atom have been studied using the density-functional method within the GGA approximation. Result of structural optimization shows that the interstitial Cu-atom (Cu₇) prefers to occupy a special location which is symmetrical with an intrinsic copper atom (Cu₁₃) deviated from the normal site. The mulliken analysis indicates the loss of electrons from interstitial atom (Cu₇) and Cu₁₃ are only half more of the losing in other copper atom, which reveals a characteristics of covalent bonding between Cu₇/Cu₁₃ and surrounding oxygen atoms respectively. Meanwhile, it is found from electron density difference (EDD) and orbital analysis that the introduction of interstitial Cu atom causes prominent structural reconstruction of a new “CuO₄” quadrilateral. Moreover, the new “CuO₄” planar leads to a corresponding electronic reconstruction in the hybridization between Cu₇/Cu₁₃ 3d and O 2p at the vicinity of fermi surface, for which a new conductive filament channel comes into being. Besides, the formation energies of the interstitial defects in various charge states are corrected with the value of 2.18, −4.17 and −9.46 eV for charge of 0, 1+ and 2+, respectively.

[en] A novel spirobifluorene derivative SPF-TMS, which containing dithioacetal groups and triphenylamine units, was synthesized. The probing behaviors toward various metal ions were investigated via UV/Vis absorption spectra as well as one-photon fluorescence changes. The results indicated that SPF-TMS exhibits high sensitivity and selectivity for mercury ions. The detection limit was at least 8.6 × 10"−"8M, which is excellent comparing with other optical sensors for Hg"2"+. When measured by two-photon excited fluorescence technique in THF at 800 nm, the two-photon cross-section of SPF-TMS is 272 GM. Especially, upon reaction with mercury species, SPF-TMS yielded another two-photon dye SPF-DA. Both SPF-TMS and SPF-DA emit strong two-photon induced fluorescence and can be applied in cell imaging by two-photon microscopy. - Highlights: • We report a spirobifluorene-based molecule as two-photon fluorescent probe with large two-photon cross-section. • The molecule has exclusive selectivity and sensitivity for mercury species. • The molecule has large two-photon emission changes before and after addition of Hg"2"+. • Both the probe and the mercury ion-promoted reaction product can be applied in cell imaging by two-photon microscopy.

[en] Boron-doped hydrogenated silicon films with different gaseous doping ratios (B₂H₆/SiH₄) were deposited in a plasma-enhanced chemical vapor deposition (PECVD) system. The microstructure of the films was investigated by atomic force microscopy (AFM) and Raman scattering spectroscopy. The electrical properties of the films were characterized by their room temperature electrical conductivity (σ) and the activation energy (E_a). The results show that with an increasing gaseous doping ratio, the silicon films transfer from a microcrystalline to an amorphous phase, and corresponding changes in the electrical properties were observed. The thin boron-doped silicon layers were fabricated as recombination layers in tunnel junctions. The measurements of the I-V characteristics and the transparency spectra of the junctions indicate that the best gaseous doping ratio of the recombination layer is 0.04, and the film deposited under that condition is amorphous silicon with a small amount of crystallites embedded in it. The junction with such a recombination layer has a small resistance, a nearly ohmic contact, and a negligible optical absorption.

[en] Highlights: • Fe-doped Ni44Mn45-xSn11Fex (x = 0, 1, 2 and 3) Heusler alloys were fabricated. • Structural and magnetic properties of Ni44Mn45-xSn11Fex were investigated. • Considerable magnetocaloric performances in Ni44Mn44Sn11Fe were realized. The structural, magnetic, and magnetocaloric properties of Ni₄₄Mn_45-xSn₁₁Fe_x (x = 0, 1, 2 and 3) Heusler alloys have been studied detailly by means of X-ray diffraction, differential scanning calorimetry, and magnetization measurements. The martensitic transition temperature (T_M) and austenite Curie temperature (T^A_C) increase gradually with increasing Fe content. Large differences in magnetization between the ferromagnetic austenite and weakly magnetic martensite phases and obvious thermal hysteresis have also been observed during the martensite transformation. With the magnetic field change up to 0–7 T, the maximum value of magnetic entropy changes reaches 26.7 and 23 J kg⁻¹K⁻¹ for x = 1 and 2, respectively, which are much larger than the undoped sample (9.8 J kg⁻¹K⁻¹). Whereas, the effective refrigerant capacity RC_eff reduced due to Fe doping increased the hysteresis loss. The alloy for x = 1 has highest RC value of 172 (255) J kg⁻¹ for a magnetic field change of 0–5 T (0–7 T), furthermore, a large magnetic entropy change and moderate RC_eff has been obtained around room temperature.

[en] The effect of hydrogen plasma treatment (HPT) during the initial stage of microcrystalline silicon (μc-Si) growth on the defect density of μc-Si has been investigated. Lower absorption coefficient in the 0.8–1.0 eV indicated less defect density compared to its counterpart without HPT. The infrared spectroscopy of μc-Si with HPT shows an increase in 2040 cm"−"1, which reveals more Si—H in the amorphous/crystalline interfaces. We ascribe the decrease of defect density to hydrogen passivation of the dangling bonds. Improved performance of μc-Si solar cell with HPT is due to the reduced defect density. (semiconductor materials)

[en] Highlights: • We predict an occurrence of pressure induced metallic FIM to half-metallic FM transition in cubic phase of Mn₂PtGa with pressure up to 43 GPa. • With the pressure up to 100 GPa, the spin-down gap of Mn₂PtGa starts to close and the half metallicity begins to disappear. • The energy difference between the austenitic and martensitic phases implies a variation trend of martensitic phase transition temperature. • Curie temperatures in both austenitic and martensitic phases are estimated under pressure by using the standard mean-field approximation. - Abstract: First-principles calculations are performed to investigate pressure effects on structure, magnetism, martensitic phase transition and Curie temperatures of Mn₂PtGa Heusler alloy in framework of the density functional theory. It is shown that Mn₂PtGa prefer to crystallize in the inverse Heusler type structure. Besides, we predict an extraordinary occurrence of pressure induced metallic ferrimagnetism to half-metallic ferromagnetism transition in cubic phase of Mn₂PtGa alloy under hydrostatic pressure up to 43 GPa and the half-metallic ferromagnetism is found to be robust even the lattice further compression to 90 GPa. However, with the pressure up to 100 GPa, the spin-down gap starts to close and the half metallicity begin to disappear, while with the pressure increasing from 100 GPa to 300 GPa, the alloy returns to metallic characteristic. In addition, the energy difference between the austenitic and martensitic phases is found to increase with increasing pressure followed by a decrease when pressure reaches to 43 GPa, which implies a variation trend of martensitic phase transition temperature. Furthermore, Curie temperatures in both austenitic and martensitic phases are estimated under pressure by using the standard mean-field approximation which agrees well with the theoretical results in literature. The robustness of the half metallicity, magnetic transition and the high Curie temperature under pressure make Mn₂PtGa alloy a promising candidate for applications in spintronic devices.

[en] Highlights: • BiFeO₃/P(VDF-TrFE) composite films of different mass ratios were fabricated. • Polycrystalline phases of BiFeO₃ and P(VDF-TrFE) were confirmed separately. • Space charge limited conduction mechanism contributed to its leakage behaviors. -- Abstract: BiFeO₃ (BFO) nanopowders (NPs) were synthesized using sol-gel method. BFO/P(VDF-TrFE) (poly(vinylidene fluoride-trifluoroethylene)) composite films were then fabricated on fluorine-doped tin oxide conductive glass substrates by solution spin-coating method. Polycrystalline phases of BFO and P(VDF-TrFE) were identified by X-ray diffraction. Field emission scanning electron microscopy showed that BFO NPs were uniformly dispersed in the P(VDF-TrFE) matrix. The conduction mechanism of BFO/P(VDF-TrFE) composite films was analyzed on account of various conduction mechanisms by analyzing the current-voltage (I-V) curves. As a result, the space charge limited conduction mechanism should be reasonable for the special I-V characteristics of the composite films. Furthermore, the space charge region of the curve mainly came from traps/defects that may be originated from imperfect crystallization of the copolymer matrix and high conductivity BFO NPs as well.

[en] Composites consisting of hydrogenated amorphous silicon (a-Si: H, inorganic) and zinc phthalocyanine (ZnPc, organic) were prepared by vacuum evaporation of ZnPc and sequential deposition amorphous silicon via plasma enhanced chemical vapor deposition (PECVD). The optical and electrical properties of the composite film have been investigated. The results demonstrate that ZnPc can endure the temperature and bombardment of the PECVD plasma and photoconductivity of the composite film was improved by 89.9% compared to pure a-Si: H film. Electron mobility-lifetime products μτ of the composite film were increased by nearly one order of magnitude from 6.96 x 10^-7 to 5.08 x 10^-6 cm²/V. Combined with photoconductivity spectra of the composites and pure a-Si: H, we tentatively elucidate the improvement in photoconductivity of the composite film. (semiconductor materials)

[en] Two dipolar compounds with dipicolinate as electron acceptor group named trans-dimethyl-4-[4’-(N,N-dimethylamino)-styry1]-pyridin-2,6-dicarboxylate (M-1), trans-dimethyl-4-[4'-(N,N-diphenylamino)-styry1]-pyridin-2,6-dicarboxylate (P-1) as well as a P-1 based multi-branched octupolar compound {4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl) vinyl]}-N,N-bis{4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl)vinylphenyl]} aniline (P-3) with intense two-photon fluorescence emission properties are systematically investigated by using steady-state absorption and fluorescence spectroscopy, Z-scan, and two-photon excited fluorescence (TPF) method. The two-photon absorption cross section of octupolar compound P-3 in THF solution is determined to be 376 GM, which is approximately 12 times greater than that of dipolar counterpart P-1 (32 GM). Transient absorption spectroscopy is employed to investigate the excited state dynamics of the dipolar and octupolar compounds. The formation and relaxation lifetimes of the intra-molecular charge transfer (ICT) state are determined to be in the ranges of several picoseconds and several-hundreds of picoseconds, respectively, for all the three compounds in THF solutions. An extended π-conjugated system and increased intra-molecular cooperative effect are responsible for the observed large two-photon absorption character. - Highlights: • Octupolar compound gain 12-fold enhancement of two photon absorption. • Dynamic properties of intra-molecular charge transfer state are determined. • Cooperative effect is responsible for great increase of two photon character.