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1.
Chemical surface passivation of Ge nanowires   总被引:4,自引:0,他引:4  
Surface oxidation and chemical passivation of single-crystal Ge nanowires with diameters ranging between 7 and 25 nm were studied. The surface chemistry differs significantly from that of well-studied monolithic atomically smooth single-crystal substrates. High-resolution Ge 3d XPS measurements reveal that Ge nanowires with chemically untreated surfaces exhibit greater susceptibility to oxidation than monolithic Ge substrates. Multiple solution-phase routes to Ge nanowire surface passivation were studied, including sulfidation, hydride and chloride termination, and organic monolayer passivation. Etching in HCl results in chloride-terminated surfaces, whereas HF etching leads to hydride termination with limited stability. Exposure to aqueous ammonium sulfide solutions leads to a thick glassy germanium sulfide layer. Thermally initiated hydrogermylation reactions with alkenes produce chemically stable, covalently bonded organic monolayer coatings that enable ohmic electrical contacts to be made to the nanowires.  相似文献   

2.
III-V semiconductor surfaces are known to be very reactive in air due to the presence of unsaturated dangling bonds (DBs). Native oxides are highly undesirable in many device applications. Remarkable progress has been made in recent years in the preparation of air-stable surfaces by wet chemical etching. XANES studies have shown that the stability of the passive surface is due to termination of surface DBs through the formation of an ordered overlayer selfassembled in chemical solutions. For a (100) InP surface, saturation of two adjacent DBs is achieved by the formation of In-S-In bridge bonds along the [011] direction. A refined analysis of σ-resonance indicates that XANES data are consistent with a recently proposed (2×2) InP(100)-S structure where the S is located on bridge sites to form twisted short and long dimers. For the GaAs(111) surface, the surface DBs are terminated by monovalent Ga-Cl bonds along the surface normal.  相似文献   

3.
Two classes of binding sites, a single high-affinity site with an association constant of 4·8×106 M−1 and two low-affinity sites with association constant of about 0·05×106 M−1 have been observed in the interaction of Naproxen with bovine serum albumin (BSA). Chemical modification of two tryptophan residues in BSA with 2-hydroxy-5-nitrobenzyl bromide has led to a reduction in the association constant of the high-affinity site by 89% and its number of binding sites by 66% suggesting the involvement of tryptophan residues in the high-affinity site. In contrast, the two low-affinity sites were not affected by the modification. Binding of Naproxen to the low-affinity sites of BSA induces microdisorganisation of the albumin structure leading to conformational changes as evident from fluorescence measurements with 1-anilino-8-naphthalenesulphonic acid as the probe.  相似文献   

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5.
A semiempirical nearest‐neighbor tight‐binding approach, that reproduces the indirect band gaps of elemental semiconductors, has been applied to study the electronic and optical properties of Si and Ge nanowires (NWs). The calculations show that Si‐NWs keep the indirect bandgap whereas Ge‐NWs changes into the direct bandgap when the wire cross section becomes smaller. Also, the band gap enhancement of Si‐NWs showing to quantum confinement effects is generally larger than that of similar‐sized Ge‐NWs, confirming the larger quantum confinement effects in Si than in Ge when they are confined in two dimensions. Finally, the dependence of the imaginary part of the dielectric function on the quantum confinement within two different schemes: intra‐atomic and interatomic optical matrix elements are applied. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2448–2454, 2010  相似文献   

6.
Inorganic-organic polymers with barrier properties against water vapor, excellent electrical data (3, 2, R D>1016 cm, E D up to 400 V/µm) and good adhesion to various substrate materials have been developed. Tailored modifications of these materials provide an excellent protective coating for thin film capacitors. Several mm thick, expensive, encapsulations could be replaced by thin coatings (up to 10 µm). The polymer coating allows the use of thin film chip capacitors in surface-mount technology. As a measure for the efficiency of the coating, the capacitance decrease under controlled humidity has been used. The influence of the material composition, the type of catalyst during sol-gel processing and the curing conditions have been studied. Adhesion and water vapor permeation properties of the polymers and rheological properties of the coating solutions have been investigated. A protective coating is developed, which increases the withstandness of capacitors against humid conditions (90°C, 100% rel. humidity) by a factor of about 30 (compared to uncoated capacitors) and shows no crack formation during thermal cycling.  相似文献   

7.
[reaction: see text] On the basis of reaction rate data, we have proposed a new mechanism for the Baylis-Hillman reaction involving the formation of a hemiacetal intermediate. We have determined that the rate-determining step is second order in aldehyde and first order in DABCO and acrylate. We have shown that this mechanism is general to aryl aldehydes under polar, nonpolar, and protic conditions using both rate data and two isotope effect experiments.  相似文献   

8.
The diagonal elements of the first and second order spinless density matrices have been calculated for the lowest excited1 P and3 P terms of Be, B+ and C++ using wavefunctions at different levels of approximations published in the literature. The analysis of these functions has resulted in a new interpretation of Hund's first rule in terms of an anisotropic screening effect.  相似文献   

9.
Dynamic surface elasticity of solutions of bovine serum albumin (BSA)/sodium polystyrene sulfonate (PSS) complexes has been measured as depending on the age of a surface, polyelectrolyte concentration, and solution pH by the oscillating-ring method. At pH values below the isoelectric point of BSA, the rate of variations in the surface properties increases due to a decrease in the electrostatic adsorption barrier as a result of a reduction in the total charge of the protein/polyelectrolyte complex. Therewith, a local maximum arises in the kinetic dependences of the surface elasticity, this maximum indicating the onset of the breakage of the tertiary structure of the protein in the surface layer. In the pH range corresponding to like charges of the protein and polyelectrolyte, variations in the surface properties slow down. In this case, the BSA/PSS complex is also formed via the interaction of PSS with those domains of globule surface that carry a charge opposite to the total charge of a protein molecule. A higher negative charge of the complex than that of protein globules increases the electrostatic adsorption barrier and decelerates variations in the surface properties. At the same time, the dependences of the surface elasticity on the surface pressure coincide with the dependences for the protein solution. Hence, the polyelectrolyte-protein interaction affects only the adsorption kinetics, while the surface properties in the vicinity of equilibrium are governed by adsorbed protein globules.  相似文献   

10.
The effect of bovine serum albumin on the surface properties of IL-type gemini surfactant ([C10-4-C10im]Br2), have been investigated by surface tension method. The critical micelle concentration (CMC) as a function of BSA concentrations at various temperatures was investigated. The CMC of [C10-4-C10im]Br2 increases with increasing the concentration of BSA as well as the temperature of the system. The interfacial parameters viz; maximum surface excess concentration (Γmax), the minimum area per molecule (Amin), and surface pressure at CMC (Πcmc) were calculated. In addition, thermodynamic parameters of adsorption and micellization were evaluated by using surface tension data. The results indicated that the binding of [C10-4-C10im]Br2 to BSA is spontaneous and exothermic in nature. The process is entropy driven and hydrophobic interactions are the major driving forces.  相似文献   

11.
12.
运用荧光及紫外-可见吸收光谱法研究了胡椒酸丁二醇单酯(简称BPM)与牛血清白蛋白(BSA)的相互作用.实验结果表明,胡椒酸丁二醇单酯与BSA形成基态复合物导致BSA内源性荧光猝灭,猝灭机理主要为静态猝灭和非辐射能量转移,其猝灭速率常数为Kq为1.077×1013L/( mol·s)(25℃)、0.946×1013L/( mol·s)(37℃).利用荧光猝灭反应测得结合常数KA为2.6×106(25℃)、3.4×106( 37℃),结合位点数n为1.30 (25℃)、1.33( 37℃).根据F(o)rster能量转移理论得到结合距离r=2.92nm(25℃)、2.66nm( 37℃)和能量转移效率E=0.45(25℃)、0.43 (37℃).通过热力学参数计算,确定胡椒酸丁二醇单酯与BSA的相互作用是熵增加和吉布斯自由能降低的自发过程,主要作用力是疏水作用力.  相似文献   

13.
Summary The influence of different factors on the spreading of human serum albumin films is studied; factors such as the ionic strength of the spreading solution, nature and concentration of the alcohol used as spreading agent, initial spreading area of the subsolution to which the protein solution was applied and the method for the spreading (direct orTrurnit). The results obtained show that the ideal spreading solution is the buffer ph=5.1,=0.01, containing 0.5% amyl alcohol (v:v). TheTrurnit's method of spreading proteins showed significant advantage over the direct deposit of drops of the protein solutions.  相似文献   

14.
In vacuum, the bare zigzag (zz) edge of graphene is reconstructed into a line of pentagon-heptagon pairs, while the pristine armchair (ac) edge is retained. Our first-principle explorations of graphene edges on three metal surfaces [Cu(111), Co(111), and Ni(111)] indicate an opposite tendency, that is, the pristine zz edge is energetically favorable and the reconstructed ac edge with dangling C atoms is highly stable on Co(111) and Ni(111) surfaces. Insightful analysis shows that passivation of the graphene edge by metal surfaces is responsible for the dramatic differences. Beyond this, the unique edge configuration has a significant impact on the graphene CVD growth behavior.  相似文献   

15.
A new merocyanine dye was synthesized, and its acidity constant was determined by spectrophotometric and chemometrics methods. The interactions of the new cyanine dye with bovine serum albumin (BSA) have been studied by fluorescence and UV absorption spectroscopy at pH 7.40. A visual color change from red to blue was observed by addition of BSA to aqueous solution of the dye. The quenching constants and binding parameters (binding constants and number of binding sites) were determined at different temperatures. The calculated thermodynamic parameters confirmed that the binding reaction is mainly entropy-driven, whereas electrostatic interaction plays major role in the reaction. The displacement experiment confirmed binding of the dye to the subdomain IIA (site 1) of albumin. Moreover, synchronous fluorescence spectroscopy studies revealed the dye induces some local conformational change in BSA. The binding distance, r, between donor (serum albumin) and acceptor (dye) was obtained according to Förster’s theory.  相似文献   

16.
A novel universal approach to cross-linking of protein macromolecules on the surface of magnetite nanoparticles has been developed. The approach is based on protein liability to free-radical modification, leading to the formation of intermolecular covalent cross-links. Free radicals are locally generated on the surface of nanoparticles. Stable coatings of serum albumin 3 nm thick are formed on the surface of magnetite nanoparticles. Using a set of physicochemical methods, it has been proven that stable coatings composed of protein macromolecules are formed around individual nanoparticles. The presence of reactive groups in the protein structure makes it possible to perform subsequent modification of the surface layers-in particular, to graft nonprotein drugs. The approach developed can be used to create superfine systems with desired surface properties for targeted delivery of drugs and biologically active substances.  相似文献   

17.
In this work we report the fabrication and characterization of a label-free impedimetric immunosensor based on a silicon nitride (Si3N4) surface for the specific detection of human serum albumin (HSA) proteins. Silicon nitride provides several advantages compared with other materials commonly used, such as gold, and in particular in solid-state physics for electronic-based biosensors. However, few Si3N4-based biosensors have been developed; the lack of an efficient and direct protocol for the integration of biological elements with silicon-based substrates is still one of its the main drawbacks. Here, we use a direct functionalization method for the direct covalent binding of monoclonal anti-HSA antibodies on an aldehyde-functionalized Si-p/SiO2/Si3N4 structure. This methodology, in contrast with most of the protocols reported in literature, requires less chemical reagents, it is less time-consuming and it does not need any chemical activation. The detection capability of the immunosensor was tested by performing non-faradaic electrochemical impedance spectroscopy (EIS) measurements for the specific detection of HSA proteins. Protein concentrations within the linear range of 10−13–10−7 M were detected, showing a sensitivity of 0.128 Ω μM−1 and a limit of detection of 10−14 M. The specificity of the sensor was also addressed by studying the interferences with a similar protein, bovine serum albumin. The results obtained show that the antibodies were efficiently immobilized and the proteins detected specifically, thus, establishing the basis and the potential applicability of the developed silicon nitride-based immunosensor for the detection of proteins in real and more complex samples.  相似文献   

18.
A modified Harned conductimetric procedure has been used to measure binary diffusion coefficients at 25°C for aqueous sodium and potassium salts of the protein bovine serum albumin (M n BSA; M=Na+ or K+; n=2 to 23). The condition of electroneutrality requires that the BSA ions diffuse at the same speed as the relatively mobile sodium or potassium counterions. Consequently, the protein ions diffuse 3 to 8 times more rapidly than the isoionic protein diffuses. An approximate analysis of counterion-accelerated diffusion of high molecular weight solutes is presented which shows that the increase in diffusivity with the number of counterions is a thermodynamic effect brought about by an increase in the free energy gradient of the solutes.  相似文献   

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20.
In the homogeneous immunoassay of human serum albumin described, a difference in fluorescence lifetime is used along with a small difference in fluorescence intensity to discriminate between the free and the antibody-bound labelled antigen. The immunoassay is based on the use of phase-resolved fluorescence measurements, in which sinusoidally-modulated excitation is combined with phase-sensitive detection to generate time-dependent signals which are integrated over a pi-interval to produce phase-resolved intensities. Texas Red was used as the fluorescent label. Negligible matrix effects were observed from serum, and a comparison of values determined by using the phase-resolved fluoroimmunoassay with values provided by the hospital from which the samples were obtained yielded a correlation coefficient of 0.996.  相似文献   

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