Structure and composition of secondary phase particles in cobalt-doped TiO2 films

The microstructural properties of secondary phase particles formed in epitaxial Co_xTi_1−xO₂ anatase thin films grown on (0 0 1)LaAlO₃ by a reactive RF magnetron co-sputter deposition are examined. These films exhibit ferromagnetic behavior in magnetization measurements, showing a M–H loop at room temperature with a saturation magnetization on the order of 0.7 μ_B /Co. X-ray photoemission spectrometry indicates that the Co cations are in the Co²⁺ valence state. Cross-section electron microscopy reveals that a significant fraction of the cobalt segregates into Co–Ti–O secondary phase particles. Selected area electron diffraction shows that the secondary phase particles are cobalt-rich anatase. While the cobalt is concentrated in the segregated particles, local energy dispersive spectrometry indicates some Co throughout the film.     

Structural and optical properties of nitrogen-incorporated HfO2 gate dielectrics deposited by reactive sputtering

High-k HfO_xN_y thin films with different nitrogen-incorporation content have been fabricated on Si (1 0 0) substrate by means of radio-frequency reactive sputtering method. Analyses from X-ray diffraction (XRD) and atomic force microscopic have indicated that the increase of the crystallization temperature of HfO₂ thin films and the decrease of the roughness root-mean-square value of HfO₂ thin films due to the incorporation of nitrogen. Based on a parameterized Tauc-Lorentz (TL) dispersion model, the optical properties of the HfO_xN_y thin films related to different nitrogen-incorporation content are systematically investigated by spectroscopic ellipsometer. Increase in the refractive index and the extinction coefficient and reduction in band gap with increase of nitrogen-incorporation content are discussed in detail.     

Adsorption of 7-ethynyl-2,4,9-trithia-tricyclo[3.3.1.1]decane on ultra-thin CdS films

The adsorption mechanism for the new compound, 7-ethynyl-2,4,9-trithia-tricyclo[3.3.1.1^3,7]decane (7ETTD), on ultra-thin films (∼3 nm) of CdS is investigated. Multiple reflection absorption IR spectroscopy, in conjunction with inelastic electron tunneling spectroscopy, indicates that this compound forms a self-assembled monolayer adsorbed on the CdS surface via each molecule’s trithia-adamantane anchor. Conductance-voltage data are recorded for tunnel junctions of the type Al/CdS/7ETTD/Pb over a temperature range of 4 K to room temperature and they indicate that the presence of the 7ETTD layer on the CdS dramatically modifies the conductance-voltage behavior of the junctions. These measurements show that different conduction mechanisms, including tunneling and possibly hopping, are responsible for charge transfer through the junctions depending on current, temperature, and voltage. WKB fits to the data are used to determine barrier parameters (height and width) for Al/CdS/Pb junctions with and without adsorbed 7ETTD layers on the CdS. Analysis of the fits shows that tunneling occurs at low bias (less than ∼0.2 V) but, at higher bias voltages, modification of the barrier parameters alone is insufficient to account for the observed conductance changes. A frontier orbital model is invoked which does offer a plausible explanation for these conductance changes. The model assumes bias-dependent coupling between HOMO and LUMO states of the adsorbed 7ETTD and the surface states on the CdS. The present work suggests that, because of the marked effect on the conductance of CdS ultra-thin films, 7ETTD and other similar compounds may be candidates for use in molecular electronic device fabrication.     

Angle dependent laser nanopatterning of poly(ethylene terephthalate) surfaces

Interference effects can lead to the formation of ripple structures at laser-irradiated poly(ethylene terephthalate) surfaces. Poly(ethylene terephthalate) surface was irradiated with linearly polarized light of a pulsed 157 nm laser. In a certain range of irradiation parameters, the irradiation resulted in the formation of coherent ripples patterns. The dimension of the pattern depends on the angle of the laser beam incidence. The surface morphology of the nano-patterned poly(ethylene terephthalate) was analyzed by atomic force microscopy and focused ion beam-scanning electron microscopy. Oxygen concentration in the modified polymer surface was studied by angular resolved X-ray induced photo-electron spectroscopy. Gold nano-layers were consecutively sputtered onto the laser irradiated poly(ethylene terephthalate) surfaces. The morphology of the sputtered gold nano-layers was investigated with atomic force microscopy too. We found that the morphology of the gold nano-layers changes and depends on the surface pattern of the laser irradiated poly(ethylene terephthalate). Formation of gold “nano-hills” is observed at the ridges of the ripple structures. The amount of oxygen together with the morphology of prepared polymer pattern may be the dominant factors controlling the gold layer growth. The present results are compared with those obtained earlier on PET irradiated with krypton fluoride laser.     

Chemical effects during ripple formation with isobaric ion beams

The formation of nanostructures on SiGe surfaces by erosion using mixed beams of isobaric species (Cs/Xe) is shown to depend on the Cs/Xe ratio. The nanostructures exhibit different wavelengths (longer wavelengths for higher Cs concentrations) contrary to the present theoretical understanding. Moreover, experiments with pure Cs and Xe beams also demonstrate that such differences are enhanced at lower bombarding energies. Such effects are primarily due to the fact that the retentivity and mobility of cesium at the sample surface gets enhanced at lower bombarding energies. The phenomenon could be explained theoretically by including an additional diffusion term in the growth equation describing the mobility of the primary ions on the irradiated surface. Semi-empirical calculations done in this direction also confirm this phenomenon.     

Synthesis of hexagonal boron nitride thin film on Pt substrates for resistive switching memory applications

Hexagonal boron nitride (hBN), due to its high reliability as a two-dimensional (2D) dielectric material, has attracted much attention for its potential applications in nanoelectronic devices. Here, the use of radio frequency (RF) magnetron sputtering-grown hBN films to construct hBN-based resistive switching (RS) memory device is reported, and the RS mechanism is deduced. The hBN-based RS memory shows low operating voltage, reproducible write cycles, and long retention time. First-principles simulations further confirm the resistive switching. This work provides an important case to facilitate the future applications of 2D materials in the RS memory.     

The equivalence between Forward and Backward Boltzmann Equations in multi-component medium

The author generalized the propagator function theory introduced first by Sigmund, and gave an explicitly proof of an equivalence between Forward and Backward Boltzmann Equations in a multi-component medium by using the generalized propagator function theory.     

Effect of ionizing radiations on the crystalline structure and electric resistivity of cadmium sulphide thin films

The effect of ionizing radiations on semiconductor thin films has been less investigated.^1.2 In Ref. 1 the authors studied the effect of electron irradiation on the resistivity of thin epitaxial silicon films. The effects of electron irradiation at energies varying between 11 keV and 100 keV confirmed those obtained with monocrystals.³ The variation of electrical conductivity and of the distribution of carriers in the silicon epitaxial thin films due to the simultaneous action of silicon ion implantation and evaporation in vacuum was studied in Ref. 4.     

Mass dependence of nitride sputtering

A molecular dynamics simulation was performed to study the sputtering yield Y for BN, AlN and GaN polycrystals of wurtzite structure as a function of the masses m ₁ of bombarding ions with energies from 200 to 2000 eV. A nonmonotonic behavior of the Y(m ₁) curve was obtained for the irradiation by low-energy ions, the curve having a maximum with a position being dependent on m₂/m₁ (m₂ is the average mass of atoms in a compound). For AlN and GaN the maximum was observed at m₂/m₁ = 2, and for BN at m₂/m₁ = 1. The effect of the mass of bombarding ions on the mean energies and energy spectra of sputtered particles, the depth of sputtering origin, and the generation of emitted atoms for nitrides was also investigated and discussed.     

射频超导腔加速性能的改进

 为提高超导加速腔的加速梯度和Q值，改进了薄膜型超导腔的加速性能。研究证明，对于铜铌溅射腔，在无氧铜衬底和铌膜之间加入NbN 层可以提高铌膜的超导转变温度，改善晶格结构；对纯铌超导腔提出了改进方法，在传统的纯铌超导腔表面制备多层的超导-绝缘-超导复合膜可以屏蔽Nb腔表面的界面场，提高超导腔的临界磁场，从而提高了铌腔的加速梯度。