Magnetic Anisotropy and the Appearance of Stripe Magnetic Domains in Co/Fe Multilayers

Thin Co/Fe multilayers were e-beam evaporated in ultra-high vacuum, keeping constant the Co layer thickness and varying that of Fe in the 0.5÷15 nm range. By increasing the Fe layer thickness, a component of magnetization perpendicular to the film plane rises up, and long and parallel magnetic domains (stripe domains) appear. The phenomenon is explained on the basis of the competition between the magnetoelastic anisotropy induced by stresses at the interfaces, and the shape anisotropy constraining the magnetization in the film plane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tunable Metal‐Enhanced Fluorescence by Stimuli‐Responsive Polyelectrolyte Interlayer Films

In this paper, we report on the tunable metal‐enhanced fluorescence (MEF) of Ag nanostructures. Because of the good MEF properties of the highly dendritic Ag nanostructures, we obtained an increase of up to 25 times for the weak fluorescence of porphyrin molecules (Por^4–). More importantly, by the introduction of a stimulus‐responsive PAA/PDDA multilayer film as an interlayer, the distance between the fluorophores and the Ag nanostructures could be tuned by immersing the substrates into solutions of different ionic strength or pH. The MEF behavior of the composite films could thus be tuned in a controlled manner, because of the distance dependent nature of the MEF effects.

     

直流磁控溅射Si和玻璃衬底Fe/Co多层膜的磁性能比较

对直流磁控溅射Si和玻璃衬底［Co_t/Fe_3t］₅(t=2, 3, 4, 5nm)多层膜的磁性能进行了比较.对于t相同但衬底不同的样品,实验发现饱和磁化强度相差很小,但是矫顽力却相差很大.对矫顽力差异的理论分析表明,多层膜的粗糙度和畴壁类型是引起这种差异的主要原因. 关键词： Fe/Co多层膜 磁性能 矫顽力     

Si／SiNx／SiO2多层膜的光致发光

采用射频磁控溅射法,制备了具有强光致可见发光的纳米Si/SiNx/SiO2多层膜,利用傅立叶红外吸收(FTIR)谱,光致发光(PL)谱对其进行了研究。用260nm光激发得到的PL谱中观察到高强度的392nm(3.2eV)和670nm(1.9eV)光致发光峰,分析认为它们分别来自于缺陷态≡Si-到价带顶和从导带底到缺陷态≡Si-的辐射跃迁而产生的光致激发辐射复合发光。PL谱中只有370nm(3.4eV)处发光峰的峰位会受退火温度的影响,结合FTIR谱认为370nm发光与低价氧化物—SiOx(x<2.0)结合体有密不可分的关系。当SiO2层的厚度增大时,发光强度有所增强,800℃退火后出现最强发光,认为具有较大SiO2层厚度的Si/SiNx/SiO2结构多层膜更有利于退火后形成Si—N网络,能够得到更高效的光致发光。用量子限制-发光中心(QCLC)模型解释了可能的发光机制,并建立了发光的能隙态(EGS)模型。     

Compositional and electrical properties of Cr,Nb, Cr/Nb,CrNbN, and CrN/NbN multilayers grown using the d.c. magnetron sputtering technique

Cr, Nb, Cr/Nb, CrN_x, NbN_x, CrNbN, and (CrN/NbN)_n structures were produced on Si and glass substrates, using the d.c. magnetron sputtering technique. Compositional analysis, based on binding energies of Cr, Nb, and N, was carried out by means of X-ray photoelectron spectroscopy (XPS). Through Auger electron spectroscopy (AES), depth profiles were obtained, allowing to demonstrate the multilayers production. Surface morphological characteristics, as roughness and grain size, were evaluated by atomic force microscopy (AFM), revealing very smooth surfaces, that is a consequence of the deposition parameters used in the synthetization experiments. Finally, for different configurations, conductivity measurements were carried out, revealing the influence of nitrogen content and temperature on electron transport. It was found that substoichiometric nitrides (CrN_0.35 and NbN_0.12) exhibited the highest conductivity, because the nitrogen atoms act as donor of electrons.     

Nanocomposite-based lignocellulosic fibers 1. Thermal stability of modified fibers with clay-polyelectrolyte multilayers

The layer-by-layer (LbL) assembly process of creating highly structured thin films derived from layers of polyelectrolytes and nanoparticles was adopted in this study to modify the surface of lignocellulosic fibers. Aqueous dispersions of clay nanoplatelets were created with ultrasonication and characterized with dynamic light scattering and atomic force microscopy in which confirmed the presence of individual clay nanoplatelets. Film thickness of never-dried clay and poly(diallyldimethylammonium chloride) (PDDA) multilayers was studied with a quartz crystal microbalance with dissipation monitoring (QCM-D). Using identical LbL deposition parameters, a slurry of steam-exploded wood fibers was modified by alternate adsorption of PDDA and clay with multiple rinsing steps after each adsorption cycle. Zeta potential measurements were used to characterize the fiber surface charges after each adsorption step while SEM images revealed that the LbL film masked the cellulose microfibril structure. Using a thermogravimetric analyzer, LbL modified steam-exploded wood fibers were observed to attain increased thermal stability relative to the unmodified material tested in both air and nitrogen atmospheres. Significant char for the LbL clay coated steam-exploded wood suggests the multilayer film serves as a barrier creating an insulating layer to prevent further decomposition of the material. This nanotechnology may have a positive impact on the processing of lignocellulosic fibers in thermoplastic matrices, designing of paper-based overlays for building products, and modification of cellulosic fibers for textiles.     

Development of polyelectrolyte multilayer-coated electrospun cellulose acetate fiber mat as composite membranes

Electrostatic multilayers of chitosan (CHI)/sodium alginate (SA) and CHI/poly(styrene sulfonate) sodium salt (PSS) were alternatively coated on electrospun cellulose acetate (CA) fiber mat. Morphologies of the composite membranes were characterized by scanning electron microscopy. The morphology of the CHI/SA-coated membrane was denser than the CHI/PSS-coated one. The top layers consisted of carboxyl and sulfonic functional groups for SA and PSS layers, respectively. Amino groups of CHI were only presented in slight quantity. X-ray photoelectron spectroscopy (XPS) confirmed the deposition of the amino groups of CHI on the multilayer membrane surface. These composite membranes were characterized for its water permeability where the water flux decreased with an increase in the number of the bilayers. The water flux was in the range of 60 and 40 L m⁻² h⁻¹ for 15 and 25 bilayered membranes, respectively. The sodium chloride (NaCl) solution flux was lower than the pure water flux due to the effect of osmotic pressure, and it decreased with an increase in the NaCl concentration. The rejection of NaCl increased substantially with the number of the bilayers of the polyelectrolytes multilayers. The level of NaCl rejection from this work was in the range of 6% and 15% for 15 and 25 bilayered membranes, respectively.     

Patterned co-culture of primary hepatocytes and fibroblasts using polyelectrolyte multilayer templates

This paper describes the formation of patterned cell co-cultures using the layer-by-layer deposition of synthetic ionic polymers and without the aid of adhesive proteins/ligands such as collagen or fibronectin. In this study, we used synthetic polymers, namely poly(diallyldimethylammonium chloride) (PDAC) and sulfonated polystyrene (SPS) as the polycation and polyanion, respectively, to build the multilayer films. We formed SPS patterns on polyelectrolyte multilayer (PEM) surfaces either by microcontact printing PDAC onto SPS surfaces or vice-versa. To create patterned co-cultures on PEMs, we capitalize on the preferential attachment and spreading of primary hepatocytes on SPS as opposed to PDAC surfaces. In contrast, fibroblasts readily attached to both PDAC and SPS surfaces, and as a result, we were able to obtain patterned co-cultures of fibroblast and primary hepatocytes on synthetic PEM surfaces. We characterized the morphology and hepatic-specific functions of the patterned cell co-cultures with microscopy and biochemical assays. Our results suggest an alternative approach to fabricating controlled co-cultures with specified cell-cell and cell-surface interactions; this approach provides flexibility in designing cell-specific surfaces for tissue engineering applications.     

The scattering and transmission of elastic waves in quasi-two-dimensional planar waveguides with linear defect boundaries

The influence of linear defect boundaries on the transmission and scattering of elastic waves in quasi-two-dimensional wave-guides is studied using the matching method. A linear defect boundary separating two wave-guide crystalline lattice domains is characterised here by a linear chain of defect masses and by modified elastic constants in the boundary, different from their values in the bulk of the domains. In particular a square lattice is considered to model the domains of the two-dimensional planar wave-guide containing the linear defect. The reflection and transmission probabilities, and the total transmission probabilities are calculated numerically and presented for the scattering processes in a variety of cases. We show that the interaction between the localised modes introduced by the defect boundary and the propagating modes of the system leads to Fano resonances. These resonances shift to higher (lower) frequencies for smaller (larger) defect masses, and for the same mass as function of the angle of the incident wave. Other spectral features shown to exist are due to interference effects especially at oblique incidence and when modifying the boundary elastic constants. Received 8 November 1999 and Received in final form 14 January 2000