Highly oriented star-like patterns observed on GaSe epilayers grown on Si(111)

Epitaxial lamellar gallium selenide (GaSe) semiconductors have been grown on trench-patterned silicon (Si) substrates by molecular beam epitaxy. An intriguing star-like patterned morphology was identified by atomic force microscopy on these epilayers. This non-trivial feature can be correlated with the accumulation of stacking faults of two concurrent epitaxial domains around self-oriented triangular pits developed earlier on the Si(111) surface by the chemical etching. Crystallographic considerations show how the stars can be formed.     

Low temperature deposition of ITO on organic films by using negative ion assisted dual magnetron sputtering system

In a magnetron sputter type negative metal ion deposition, the influence of positive bias voltage (V_b) on the surface morphology, electrical resistivity, optical transmittance, and microhardness of ITO prepared on organic polycarbonate films has been investigated. In this study, the V_b increased from 0 to 250 V to attract secondary negative In and Sn metal ions, which were produced from ITO target by surface negative ionization with intense Cs ion bombardments. During deposition although reactive oxygen gas was not introduced into the chamber, by adjusting V_b at 100 V, ITO films on polycarbonate substrate with resistivity as low as 6.1×10⁻⁴ Ω cm and transmittance over 90% at 550 nm have been obtained without intentional substrate heating.AFM measurement also shows that surface roughness varied significantly with V_b. However, too intense ion bombardment originated by high V_b (>100 V) condition increased surface roughness and as a result deteriorated the electrical and optical property of ITO films.     

Coupled lateral bending-torsional vibration sensitivity of atomic force microscope cantilever

We study the influence of the contact stiffness and the ration between cantilever and tip lengths on the resonance frequencies and sensitivities of lateral cantilever modes. We derive expressions to determine both the effective resonance frequency and the mode sensitivity of an atomic force microscope (AFM) rectangular cantilever. Once the contact stiffness is given, the resonance frequency and the sensitivity of the vibration modes can be obtained from the expression. The results show that each mode has a different resonant frequency to variations in contact stiffness and each frequency increased until it eventually reached a constant value at very high contact stiffness. The low-order vibration modes are more sensitive to vibration than the high-order mode when the contact stiffness is low. However, the situation is reversed when the lateral contact stiffness became higher. Furthermore, increasing the ratio of tip length to cantilever length increases the vibration frequency and the sensitivity of AFM cantilever.     

现代营销理论演绎

文章对现代营销理论中的4Ps,4Cs,4Rs的理论内涵与应用进行了阐述与分析,并对这三种理论的内在联系进行了研究与探讨,能启迪营销人员在营销的实践工作中把营销理论与实际工作有机地结合起来.     

Differential scanning calorimetric and free volume study of reactive compatibilization by EPM‐g‐MA of poly(trimethylene terephthalate)/EPDM blends

Differential scanning calorimetry (DSC) and positron annihilation lifetime measurements have been carried out to study the effect of the compatibilizer maleic anhydride grafted ethylene propylene copolymer (EPM‐g‐MA) in poly trimethylene terephthalate and ethylene propylene diene monomer (PTT/EPDM) immiscible blends. The DSC results for the blends of 50/50 and 30/70 compositions show two clear glass transition temperatures, indicating that the blends are two‐phase systems. With the addition of compatibilizer, the separation between the two glass transitions decreased, suggesting an increased interaction between the blend components with compatibilizer. At 5 wt % of compatibilizer, the separation between the T_gs reduced in both 50/50 and 30/70 blends. The positron results for the blends without compatibilizer showed an increase in relative fractional free volume, as the EPDM content in the blend is increased. This suggests the coalescence of free volume of EPDM with the free volumes of PTT due to phase separation. However, the effect of compatibilizer in the blends was clearly seen with the observed minimum in free volume parameters at 5% of the compatibilizer, further suggesting that this percent of compatibilizer seems to be the optimum value for these blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 740–747, 2006     

Self-assembled rings of EuBr2 nanostructures

The EuBr₂ nanostructures self-assembled (SA) in ring form are presented in this letter. The atomic force microscopy (AFM) images show rings of ~ 190 to 2500 nm diameter formed on [100] surface. The sample optical response with rings displays an emission band peak (EBP) at 435 nm. The europium absorption bands reveal structural changes and shift toward infrared wavelength. The emission bandwidth of EuBr₂ nanostructures in ring form is narrower than dispersed nanostructures of similar size. To our knowledge, is the first time that there is clear evidence of the arrangement in ring form in the KBr:Eu²⁺ crystal samples.     

Selective nanoshaving of self-assembled monolayers of 2-(4-pyridylethyl)triethoxysilane

Single molecular layers of 2-(4-pyridylethyl)triethoxysilane have been deposited on native oxide surfaces of silicon, with the triethoxysilylethyl groups towards the silicon oxide interface and pyridine at the surface. It is possible to “shave” or mechanically break the molecular bonds at the alkoxy-silane (Si-C) bond using scanning atomic force microscope, leaving large swaths of surface area cut to a depth of 0.64 ± 0.06 nm, exposing the silicon of the alkoxy-silane ligand. Mechanical cleavage of the pyridine ligand alone is also possible, but more difficult to control selectively.     

Microwave dielectric behavior of nanocrystalline titanium dioxide thin films

Dielectric behavior of titania thin films, deposited by DC magnetron sputtering on to borosilicate glass substrates, in the microwave region is reported. Deposition in a 100% pure oxygen DC plasma is demonstrated. The nanocrystalline films showed a crystallite size range between 16 and 50 nm. The crystallite size decreased with increase in film thickness between 150 and 700 nm and increase in rate of deposition. Refractive index decreased with increase in percentage of oxygen in the sputter gas. The dielectric constants were measured using the extended cavity perturbation technique at 8.98, 10.01 and 10.98 GHz. The dielectric constant and loss tangent showed a very small decrease with increase in frequency but exhibited a stronger dependence on processing parameters as well as crystallite size. The dielectric constant peaked at a value of 46 (±0.1) at a frequency of 8.98 GHz with 50% O₂ in the plasma, decreasing above and below it. Similarly, it peaked at a value of 46 (±0.1) for a crystallite size of 40 nm decreasing thereafter. Interestingly, the dielectric constant also showed a maximum at a bandgap of 3.36 eV at the same value. In each case the maximum dielectric constant was accompanied by a minimum in the dielectric loss. The variation in the dielectric properties can be correlated with microstructural changes as evidenced by SEM and AFM images.     

Evolution of ion-induced ripple patterns on SiO2 surfaces

The evolution of nanoscale ripple patterns during sub-keV ion sputtering of thermally grown, fused and single crystalline SiO₂ surfaces has been investigated by means of atomic force microscopy. For all three materials, different dependencies of the ripple wavelength and the surface roughness on the ion fluence have been found. Within the Bradley-Harper model of pattern formation, the observed differences are consistent with different amounts of surface and near-surface mass transport by ion-enhanced viscous flow which might result from different surface energies of the SiO₂ specimens.     

Pairing, Phase Separation, and Deformation in the BEC-BCS Crossover

We prepare a two-component gas of ⁶Li atoms which pair at sufficiently low temperatures. The BEC-BCS crossover is realized by tuning the atomic interactions via a broad Feshbach resonance. We determine the closed-channel molecular component of the pairs as a function of interaction strength by measuring the rate of photoexcitation to a molecular state. The molecular component is sufficiently small that the order parameter of the paired superfluid agrees well with a single-channel model of the crossover. We have also produced a gas with unequal numbers of the two spin components. We observe that this polarized gas phase separates into a paired central core, with the excess unpaired atoms residing outside the core. Remarkably, the real-space distributions deform significantly with increasing polarization.