A Thin Liquid Film and Its Effects in an Atomic Force Microscopy Measurement

Recently, it has been observed that a liquid film spreading on a sample surface will significantly distort atomic force microscopy （AFM） measurements. In order to elaborate on the effect, we establish an equation governing the deformation of liquid film under its interaction with the AFM tip and substrate. A key issue is the critical liquid bump height yoc, at which the liquid film jumps to contact the AFM tip. It is found that there are three distinct regimes in the variation of yoc with film thickness H, depending on Hamaker constants of tip, sample and liquid. Noticeably, there is a characteristic thickness H^＊ physically defining what a thin film is; namely, once the film thickness H is the same order as H^＊, the effect of film thickness should be taken into account. The value of H^＊ is dependent on Hamaker constants and liquid surface tension as well as tip radius.     

Electronic Structure and Elastic Properties of Ti3AlC from First-Principles Calculations

We perform a first-principles study on the electronic structure and elastic properties of TiaA1C with an antiperovskite structure. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of this compound. The elastic constants of Ti3AlC are derived yielding c11 = 356 GPa, c12 = 55 GPa, c44 = 157 GPa. The bulk modulus B, shear modulus G and Young＇s modulus E are determined to be 156, 151 and 342 GPa, respectively. These properties are compared with those of Ti3AlC2 and Ti2AlC with a layered structure in the Ti-Al-C system and FeaAlC with the same antiperovskite structure.     

Effect of Ca and Sr alkaline earth ions on luminescence properties of BaAl12O19:Eu nanophosphor

Nanosized barium aluminate materials was doped by divalent cations (Ca²⁺, Sr²⁺) and Eu²⁺ having nominal compositions Ba_1−xMxAl₁₂O₁₉:Eu (M=Ca and Sr) (x=0.1-0.5), were synthesized by the combustion method. These phosphors were characterized by XRD, scanning electron microscopy-energy-dispersive spectrometry (SEM-EDS) and photoluminescence measurement. The photoluminescence characterization showed the presence of Eu ion in divalent form which gave emission bands peaking at 444 nm for the 320 nm excitation (solid-state lighting excitation), while for 254 nm it gave the same emission wavelength of low intensity (1.5 times) compared to 320 nm excitation. It was also observed that alkaline earth metal (Ca²⁺ and Sr²⁺) dopants increase the intensity of Eu²⁺ ion in BaAl₁₂O₁₉ lattice, thus this phosphor may be useful for solid-state lighting.     

Fast and efficient VUV/UV emissions from (Ba,La)F2:Er crystals

We report observation of fast and efficient VUV/UV luminescence from the mixed (Ba,La)F₂:Er crystals. The broad bands, peaking at 162.5, 181.9, 194.2, 202.8, 216.1, 233.5 and 281.5 nm and decaying, at 10 and 293 K, with time constants of 46 and 35 ns respectively, are due to spin-allowed transitions from the low-spin (LS) state of the 4f¹⁰5d configuration.We also observed a weak and slow broad band emission peaking at 170 nm due to the spin-forbidden transition from the high-spin (HS) state of the 4f¹⁰5d configuration.While at room temperature the excitation into any of the three identified LS bands (J=8, 7 and 6) dominating the excitation spectrum yields fast VUV and UV emissions, at 10 K the excitation into higher lying J=7 and 6 bands generates slow and sharp line emissions. The positions of these lines fit energies of transitions originating from the ²G_7/2 multiplet at 66140 cm⁻¹. The emission from the ²G_7/2 multiplet has been never, to the best of our knowledge, observed before.The efficient and fast VUV and UV emissions from the higher (LS, J=8) with almost no contribution from the lower (HS, J=8) level of the 4f¹⁰5d configuration are possible because the modified crystal field in (Ba,La)F₂ shifts the level of the (LS, J=8) state below the ²F_5/2 multiplet which, therefore, does not contribute to nonradiative relaxation between the LS and HS levels.We conclude that the ²G_7/2 and ²F_5/2 levels have major impact on VUV and UV emissions from the Er³⁺ ion in (Ba,La)F₂ contributing to complex emission pattern described in this report Their key role, elucidated by the VUV and UV luminescence spectroscopy, is consistent with predictions from a simple configuration coordinate model based on experimental results and calculations of the 4f¹¹ energy levels.     

Surface chemical modification of fullerene by mechanochemical treatment

In this study different encapsulating agents have been used for chemical modification of fullerenes. Fullerenes have reacted with tetrahydrofuran, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and ethylene vinyl acetate-ethylene vinyl versatate at room temperature under mechanical milling. The obtained powder has been dispersed in water by ultrasonication. The fullerene based colloids have been characterized by UV-vis, FTIR, Raman spectroscopy and atomic force microscopy. FTIR and Raman analysis have shown the presence of C₆₀ after surface functionalization.     

Insulator–semiconductor–metallic state transition induced by electric fields in Mn‐doped NaNbO3

The electro‐forming procedure was applied to NaNbO₃:Mn and NaNbO₃ insulator crystals. The electric current flow induced a transition to the metallic‐type temperature dependence of the resistance. The Mn dopant shortened the time needed for the transition. The LC‐AFM measurement showed a non‐homogeneous distribution in local resistance resulting from the electric field via the AFM tip. We ascribe this effect to percolation in the network of the highly conducting filaments, whose formation is facilitated by the Mn ions. We conclude that the insulator–metal transition is induced within a subsystem of extended defects already existing in the NaNbO₃:Mn crystal lattice host. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication and thermal evolution of nanoparticles in SiO2 by Zn ion implantation

SiO₂ samples were implanted with 45 keV Zn ions at doses ranging from 5×10¹⁵ to 1.0×10¹⁷ ions/cm², and were then subjected to furnace annealing at different temperatures. Several techniques, such as ultra-violet–visible spectroscopy (UV–vis), grazing incidence X-ray diffraction spectroscopy (GXRD) and atomic force microscopy (AFM), have been used to investigate formation of nanoparticles and their thermal evolution. Our results clearly show that Zn nanoparticles could be effectively formed in SiO₂ at doses higher than 5×10¹⁶ ions/cm². The subsequent thermal annealing at oxygen ambient could induce the growth of Zn nanoparticles at intermediate annealing temperature range. While at temperature above 600 °C, Zn nanoparticles could be transformed into ZnO, or even Zn₂SiO₄ nanoparticles. The results have been tentatively discussed in combination with Zn diffusion and migration obtained by Rutherford backscattering spectroscopy (RBS) measurements.     

Irradiation-assisted photoelastic domain wall formation in X- and Y-cut lithium niobate

Irradiation-assisted photoelastic domain wall formation in single-crystalline X- and Y-cut lithium niobate (LNO) is studied at low displacement doses, namely, up to a maximum of 2.5×10⁻² dpa and annealed at 270 °C. The formation of surface ridges (or striations) is observed and quantified using atomic force and optical microscopy. In spite of the different crystallographic orientation of the two single-crystals a correlation between the density of surface defects and the displacement dose is established phenomenologically which means that the displacement damage and its consequent defect accumulation behavior prior to annealing (‘incubation phase’) defines to which extent the lattice undergoes an irreversible mechanical deformation immediately after annealing. This ridge formation mechanism assisted by irradiation and moderate annealing constitutes a fine tool to modify the near-surface structure and the local optical properties of LNO and hence it allows one to potentially micromachine new photonic devices.     

Shell effects in quantum dots in tilted magnetic fields

The motion of a few electrons in a three-dimensional harmonic oscillator potential under the influence of a homogeneous magnetic field of arbitrary direction is studied. The ground state of the Fermi system is obtained by minimizing the total energy with regard to the confining frequencies. From this a dependence of the equilibrium shape on the electron number, the magnetic field parameters and the slab thickness is found.     

One- and Two-Dimensional Arrays of Double-Well Optical Traps for Cold Atoms or Molecules

We propose a novel scheme to form one- and two-dimensional arrays of double-well optical dipole traps for cold atoms (or molecules) by using an optical system composed of a binary π-phase grating and a lens illuminated by a plane light wave, and study the relationship between the maximum intensity Imax of each optical well (or the maximum trapping potential Umax for ^85Rb atoms) and the relative aperture β (= α/f) of the lens. We also calculate the intensity gradients of each optical well and their curvatures, and estimate the spontaneous photon-scattering rate of trapped atom in each well, including Rayleigh and Raman scattering rates. Our study shows that the proposed 1D and 2D arrays of double-well traps can be used to prepare 1D and 2D novel optical lattices with cold atoms (or molecules), or form an all-optically integrated atom optical chip, or even to realize an array of all-optical double-well atomic (or molecular) Bose-Einstein condensates by optical-potential evaporative cooling, and so on.