GeV能量的Fe离子在C60薄膜中的辐照效应研究

利用傅立叶转换红外光谱和Raman谱仪分析了0.98 GeV的Fe离子在电子能损Se为3.5 keV/nm时， 不同辐照剂量（5×1010 —8×1013 ions/cm2)下， 在C60薄膜中引起的辐照损伤效应。 分析表明， Fe离子辐照引起了C60分子的聚合与损伤。 在辐照剂量达到一中间值1×1012 ions/cm2， C60分子的损伤得到部分恢复， 归因于电子激发引起的退火效应。 通过对Raman数据的拟合分析， 演绎出Fe离子辐照在C60材料中形成的潜径迹截面或引起损伤的截面约为1.32×10-14 cm2。     

Coplanar Phase Shifters Based on Ferroelectric Thin Films

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, short for BST) thin films were prepared by RF-magnetron sputtering. The dielectric tunability, loss tangent, remanent polarization (2Pr) and coercive electric field (Ec) of the BST films are respectively 29.5%, 0.013, 2.29 μC/cm² and 22.27 kV/cm at 1 kHz and 20 V. The designed coplanar waveguide (CPW) phase shifter consists of 56 same sections. It is shown that the fabricated lines of electrodes are smooth and the widths at the tip of bottom electrodes are about 5 μm. At the central frequency of 28 GHz and a bias voltage of 20 V, the figure of merit is approximately 13°/dB.     

Emission properties of thin films of electroactive doped polymers

We have studied the effect of the intensity of the exciting radiation and the temperature on the emission properties of two kinds of thin-film samples based on blends of two types of organic electroactive materials: polyfluorene + iridium triphenylpyridinate and polyepoxypropylcarbazole + zero-th order PAMAM dendrimer with eosin. We have shown that an increase in the excitation intensity leads to an increase in the intensity of the luminescence of the polymer matrices and the iridium complex up to a power density of 300 kW/cm², and the emission of the dendrimer is rapidly saturated and does not return to the initial value when the excitation level decreases. Heating up to 170°C followed by cooling causes an increase in the intensity for all the components except the dendrimer. The data obtained show that annealing is an important method for improving the emission efficiency of the proposed thin-film structures, due to a change in the packing of the activator molecules in the polymer matrix leading to more efficient transfer of the excitation energy. Molecules of the studied dendrimer are not stable when exposed to optical radiation and temperature. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 820–825, November–December, 2007.     

Silver oligomer and single fullerene electronic properties revealed by a scanning tunnelling microscope

Clusters on surfaces have been investigated with low-temperature scanning tunnelling microscopy and spectroscopy. Constant current spectra acquired on Ag oligomers and one-dimensional chains on a Ag(111) reveal a single resonance peak whose energy shifts towards the Fermi level with increasing cluster size. Next, controlled and reproducible contact between a STM tip and a C₆₀ molecule adsorbed on Cu(100) is reported. The transition from tunnelling to contact is discussed in terms of local heating of the tip-molecule junction.     

Temperature dependent magnetic spin and orbital moments of mass-filtered cobalt clusters on Au(111)

Mass-filtered cobalt clusters with a size of 8 nm have been deposited in-situ under soft-landing conditions onto Au(111). The spin and orbital moments of the Co nanoparticles on a Au (111) single crystal have been investigated as a function of the temperature using the element-specific method of X-ray magnetic circular dichroism in photoabsorption. The results hint at an temperature-dependent spin-reorientation transition which is discussed with respect to different contribution to the magnetic anisotropy. Furthermore, by means of an in-situ oxidation experiment, the influence of an exposure to oxygen on the properties of the cobalt clusters has been investigated.     

The role of oxygen and hydrogen partial pressures on structural and optical properties of ITO films deposited by reactive rf-magnetron sputtering

Sn doped In₂O₃ films are deposited by rf-magnetron sputtering at 300 °C under Ar, Ar + O₂ and Ar + H₂ gas ambients. For the film prepared under argon ambient, electrical resistivity 6.5 × 10⁻⁴ Ω cm and 95% optical transmission in the visible region have been achieved optimizing the power and chamber pressure during the film deposition. X-ray diffraction spectra of the ITO film reveal (2 2 2) and (4 0 0) crystallographic planes of In₂O₃. With the introduction of 1.33% oxygen in argon, (2 2 2) peak of In₂O₃ decreases and resistivity increases for the deposited film. With further increase of oxygen in the sputtering gas mixture crystallinity in the film deteriorates and both the peaks disappeared. On the other hand, when 1.33% hydrogen is mixed with argon, the resistivity of the deposited film decreases to 5.5 × 10⁻⁴ Ω cm and the crystallinity remains almost unchanged. In case of reactive sputtering, the deposition rate is lower compared to that in case of non-reactive sputtering. HRTEM and first Fourier patterns show the highly crystalline structure of the samples deposited under Ar and Ar + H₂ ambients. Crystallinity of the film becomes lower with the introduction of oxygen in argon but refractive index increases from 1.86 to 1.9. The surface morphology of the ITO films have been studied by high resolution scanning electron microscopy.     

Effect of film thickness on interface and electric properties of BiFeO3 thin films

Bismuth ferrite (BFO) thin films were fabricated by RF-magnetron sputtering deposition method on Pt/Ti/SiO₂/Si(1 0 0) substrate. The effect of the thickness of BFO films varying from 85 to 280 nm on electrical properties was investigated. Saturated coercive fields were found to increase with the BFO film thickness. The dielectric constant of BFO thin films measured at 1 kHz decreased with decreasing thickness from 98 to 86, while tangent losses increased from 0.013 to 0.021. The presence of bismuth oxide at the interface between BFO films and Pt bottom electrodes was responsible for the high leakage currents in thin BFO thin films as was demonstrated by X-ray diffraction, grazing-incident X-ray diffraction, and secondary ion mass spectroscopy analysis.     

Growth of cubic MgxZn1−xO alloy films by electron beam evaporation

We report the growth of cubic Mg_xZn_1−xO alloy thin films on quartz by electron beam evaporation. It can be found that all the samples have sharp absorption edges by the absorption measurements. X-ray diffraction measurements indicate the Mg_xZn_1−xO films are cubic phase with preferred orientation along the (1 1 1) direction. Energy dispersive spectrometry (EDS) demonstrates that the Mg concentration in Mg_xZn_1−xO films is much higher than the ceramic target used, and the composition can be tuned in a small scope by varying the substrate temperature and the beam electric current. The reasons of this phenomenon are also discussed.     

Stress dependence of growth mode change of epitaxial layered cobaltite γ-Na0.7CoO2

We report stress dependence of growth characteristics of epitaxial γ-Na_0.7CoO₂ films on various substrates deposited by pulsed laser deposition method. On the sapphire substrate, the γ-Na_0.7CoO₂ thin film exhibits spiral surface growth with multi-terraces and highly crystallized texture. For the γ-Na_0.7CoO₂ thin film grown on the (1 1 1) SrTiO₃ substrate, the nano-islands of ∼30 nm diameter on the hexagonal grains are observed. These islands indicate that the growth mode changes from step-flow growth mode to Stranski-Krastanow (SK) growth mode. On the (1 1 1) MgO substrate, the large grains formed by excess adatoms covering an aperture between hexagonal grains are observed. These experimental demonstrations and controllability could provide opportunities of strain effects of Na_xCoO₂, physical properties of thin films, and growth dynamics of heterogeneous epitaxial thin films.     

Nd:YAG laser synthesis of nanostructural V2O5 from vanadium oxide sols: Morphological and structural characterizations

Vanadium oxide thin films were prepared by sol-gel method, then subjected to Nd:YAG laser (CW, 1064 nm) radiation. The characteristics of the films were changed by varying the intensity of the laser radiation. The nanocrystalline films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD revealed that above 102 W/cm² the original xerogel structure disappears and above 129 W/cm² the films become totally polycrystalline with an orthorhombic structure. From TEM observations, we can see that due to laser radiation, the originally fibrillar-like particles disappear and irregular shaped, layer structured V₂O₅ particles are created. From XPS spectra we can conclude that due to laser radiation the O/V ratio increased with higher intensities.