DPPC LB膜的摩擦学行为研究

通过LB技术,以镉离子水溶液为亚相在单晶硅表面制备DPPC不同层数的LB膜,并通过AFM、UMT-2对其表面形貌及摩擦学行为进行考察。摩擦学行为研究发现,DPPC LB膜表现出比花生酸(AA)LB膜更为优异的摩擦学性能。同时,DPPC LB膜的摩擦学性能存在最佳层数。分析认为,DPPC LB膜优异的摩擦学性能与DPPC分子有2个亲水极性基团有关,它可使DPPC分子与亲水基底结合更为牢固,而亚相中金属离子的加入使成膜性能有效提高。     

Influence of Mg²⁺, Ni²⁺, and Cu²⁺ on DNA assembly on HOPG surfaces: atomic force microscopy study

Adsorption of circular DNA onto bare highly oriented pyrolytic graphite (HOPG) surfaces by the addition of Mg²⁺, Ni²⁺, and Cu²⁺ has been investigated by atomic force microscopy (AFM). AFM results revealed that the topography and height of DNA on HOPG surface by the addition of different metal ions are quite different. After the addition of Mg²⁺ for incubation, DNA molecules tend to form many loops on HOPG surfaces, which are derived from the crossover of intramolecular and intermolecular chains. After the addition of Ni²⁺, DNA molecules can form network on HOPG surfaces, and the density of DNA network was significantly increased with increasing DNA concentration. Consequently, dense DNA network can be obtained by using relatively low concentration of DNA and Ni²⁺. As for the addition of Cu²⁺, angular DNA loops composed of flat chains were observed. The observed flat DNA chains with an average height of 0.52 nm can be ascribed to Cu²⁺ insert into the site between bases and phosphate group of DNA inducing denaturation of DNA molecules. This study is very helpful for understanding the interactions of metal ions and DNA molecules, and for constructing various DNA structures on the carbonaceous surfaces. SCANNING 34: 68–75, 2012. © 2011 Wiley Periodicals, Inc.     

AFM nanolithography on a mixed LB film of hexadecylamine and palmitic acid

An evenly mixed Langmuir film of hexadecylamine (HDA) and palmitic acid (PA) was prepared on the air-water interface and transferred to a Si substrate for the fabrication of nano-sized patterns. Vibrational spectrum of the transferred film shows that all acid groups of PAs were deprotonated and amine groups of HDAs were protonated by an acid-base reaction. The effect of mixing ratios in atomic force microscopy anodization lithography on the mixed films was investigated in terms of the line width of the protruded pattern. While the line width fabricated on PA film was 221 nm, the width on the mixed film was reduced to 84 nm under the same lithographic conditions. It is believed that the phenomenon was originated from the mixed structure from the interaction of HDA and PA. The chemical composition difference caused by the presence of ammonium cation in resist resulted in reducing the line width fabricated in the mixed Langmuir-Blodgett film.     

Read/write mechanisms and data storage system using atomic force microscopy and MEMS technology

Information storage system that has a potentially ultrahigh storage density based on the principles of atomic force microscopy (AFM) has been developed. Micro-electro-mechanical systems (MEMS) technology plays a major role in integration and miniaturization of the standard AFM. Its potential application for ultrahigh storage density has been demonstrated by AFM with a piezoresponse mode to write and read information bits in ferroelectric Pb(Zr(x)Ti(1 - x))O3 films. With this technique, bits as small as 40 nm in diameter have been achieved, resulting in a data storage density of simply more than 200 Gb/in2. Retention loss phenomenon has also been observed and investigated by AFM in the piezoresponse mode. Finally, local piezoelectric measurements of PZT films by different processing technologies are discussed in detail.     

A tribological study of kinetically influenced ultrathin Au and Cu metal overlayers grown on dendrimer mediated Si

Evidence is presented here for deposition kinetic energy influences on the wear properties of Au and Cu films deposited by evaporation and sputtering on clean and poly(amidoamine) (PAMAM) dendrimer modified SiO _x substrates. Ramped load nanoscratch tests show increased resistance to wear in the presence of the dendrimer monolayer. Nanoscratch profiles indicate that the critical load to failure (scratch bearing capacity) is increased in the presence of a dendrimer interlayer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis of the wear tracks show that following film failure plowing is the predominant mechanism of wear for sputtered or evaporatively deposited Au. No obvious changes in the wear properties (a pure cutting mechanism) of Cu thin films are observed upon changing the kinetic energy of the incoming metal.     

XPS and XANES characteristics of tribofilms and thermal films generated by two P- and/or S-containing additives in water-based lubricant

Two phosphates were synthesized and their tribological properties as water-soluble lubricant additives were evaluated by using four-ball tester. The micro/nano-scale chemical characteristics of tribofilms and thermal films formed from these additives in different conditions were explored by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectroscopy. The results show that the additives have better anti-wear and friction reducing properties than the oleate solution at higher load. Surface analysis results indicate that tribofilms are mainly composed of absorbed layer and chemical reactant layer, in which phosphorus exists in the form of adsorbed molecule, phosphate or polyphosphate, and sulfur in the form of alkyldisulfide, sulfide and sulfate. As to the thermal films, phosphate (or polyphosphate) and sulfate are detected as the main components. The anti-wear and friction-reducing performances can be ascribed to the formation of films on the metal surface, and the mechanism of the process of molecules adsorption, new compounds production through tribochemical reactions, film formation and destruction.     

Cryo-X-ray analysis-A novel tool to better understand the physicochemical reactions at the bioglass/biological fluid interface

The present study deals with the short-term physicochemical reactions at the interface between bioactive glass particles [55SiO(2)-20CaO-9P(2)O(5)-12Na(2)O-4MgO. mol%] and biological fluid (Dulbecco Modified Eagle's Medium (DMEM)). The physicochemical reactions within the interface are characterized by scanning transmission electron microscopy (TEM) (STEM) associated with Energy-dispersive X-ray spectroscopy (EDXS). Microanalysis of diffusible ions such as sodium, potassium, or oxygen requires a special care. In the present investigation the cryo-technique was adopted as a suitable tool for the specimen preparation and characterization. Cryosectioning is essential for preserving the native distribution of ions so that meaningful information about the local concentrations can be obtained by elemental microanalysis. The bioglass particles immersed in biological fluid for 24 h revealed five reaction stages: (i) dealkalization of the surface by cationic exchange (Na(+), Ca(2+) with H(+) or H(3)O(+)); (ii) loss of soluble silica in the form of Si(OH)(4) to the solution resulting from the breakdown of Si--O--Si bonds (iii); repolymerization of Si(OH)(4) leading to condensation of SiO(2)); (iv) migration of Ca(2+) and PO(4) (3-) to the surface through the SiO(2)-rich layer to form CaO-P(2)O(5) film; (v) crystallization of the amorphous CaO-P(2)O(5) by incorporating OH-- or CO(3) (2-) anions with the formation of three different surface layers on the bioactive glass periphery. The thickness of each layer is approximately 300 nm and from the inner part to the periphery they consist of Si--OH, which permits the diffusion of Ca(2+) and PO(4) (3-) ions and the formation of the middle Ca--P layer, and finally the outer layer composed of Na--O, which acts as an ion exchange layer between Na(+) ions and H(+) or H(3)O(+) from the solution.     

Lateral force microscopy study of Langmuir–Blodgett films of a macrocyclic compound

Langmuir–Blodgett films of 4-phenyl-4-sulfide-11-(1-oxodecyl)-1,7-dithia-11-aza-4-phosphacyclotetradecane, a thiomacrocyclic compound used as a Cu(II) ions sensor, were extracted over mica at several surface pressure values from two subphases: pure water and a 0.01 M Cu(II) aqueous solution. Atomic Force Microscopy and Force Spectroscopy (Lateral Force Microscopy) were used to study both the morphology and the nanomechanical response of Langmuir–Blodgett films. A correlation between extraction pressure and monolayer mechanical properties was observed, so an increase in the extraction pressure of the monolayers corresponds with an increase in the vertical force at which the monolayer breaks while doing lateral force experiments. Experimental data proves that Langmuir–Blodgett extraction technique truly obtains monolayers with different nanotribological properties as a function of the extraction surface pressure. The formation of islands on top of the monolayers was studied and a model mechanism of formation is proposed. A higher friction value was measured on the islands than on the monolayer and friction asymmetry was observed in the latest stage of island formation.     

Biotribological properties of dentures lubricated with artificial saliva

This paper presents the results of tests on the effect of adsorbed films of saliva substitutes on the tribological characteristics of metal alloys based on the example of stainless steel 316LVM and two alloys, Co–Cr–Mo and Ti?6Al–4V. Saliva substitutes were prepared based on animal mucin and xanthan gum dissolved in phosphate buffered saline (PBS). The adsorbed salivary films significantly reduced the coefficient of friction of the tested biomaterials. Low values of coefficient of friction have been achieved during the tests using PBS + mucin. The analysis of wear of tested materials showed lowest values in the process of friction using PBS + mucin + xanthan gum. An IR analysis of the studied surfaces confirmed the presence of wear marks on the adsorbed salivary films.     

氩气浓度对热丝法化学气相沉积纳米金刚石膜的影响

采用热丝化学气相沉积方法,以Ar+CH4+H2混合气体作为气源,通过改变氩气浓度,在单晶硅(100)基片上沉积纳米金刚石膜;采用扫描电子显微镜、原子力显微镜、X射线衍射仪和拉曼光谱仪等分析了纳米金刚石膜的形貌、微结构以及残余应力。结果表明:随着氩气浓度的增大,膜的晶粒尺寸逐渐减小到纳米级;由于晶粒细化导致膜内残余应力由拉应力变为压应力,并且压应力随氩气浓度的增大呈现先增大后减小的趋势;当氩气体积分数为98%时,即在贫氢的气氛中成功获得了平均晶粒尺寸为54 nm、均方根粗糙度约为14.7 nm的纳米金刚石膜。     

Dependence of surface morphology on molecular structure and its influence on the properties of OLEDs

Most organic light-emitting diodes (OLEDs) have a multilayer structure composed of organic layers such as a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL) and an electron injection layer (EIL) sandwiched between two electrodes. The organic layers are thin solid films with a thickness from a few nano meters to a few tenths nano meter, respectively. Surface morphology of an organic thin solid film in OLEDs depends on the molecular structure of the organic material and has an affect on device performance. To analyze the effect of surface morphology of an organic thin solid film on fluorescence and electroluminescence (EL) properties, thin solid films of 4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran (DCM2) and new red fluorophores, (2E,2′E)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis[2-(2-thienyl)acrylonitrile] (ABCV-Th) and (2Z,2′Z)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis(2-phenylacrylonitrile) (ABCV-P) were investigated by atomic force microscopy (AFM). The samples for EL and AFM measurement were fabricated by the high-vacuum thermal deposition (8×10⁻⁷ Torr) of organic materials onto the surface of indium tin oxide (ITO)-coated glass substrate, in which the layer structures of samples for AFM measurement and those for EL measurement were ITO/NPB (40 nm)/red emitters (80 nm) and ITO/NPB (40 nm)/red emitters (80 nm)/BCP (30 nm)/Liq (2 nm)/Al (100 nm), respectively. The analysis based on AFM measurements well supported that the photoluminescence properties and the device performance were very much dependent upon surface morphology of an organic thin layer.     

Sulfate based coatings for use as high temperature lubricants

Films of CaSO₄, BaSO₄, and SrSO₄ were grown with the pulsed laser deposition technique. The high temperature lubricious properties of these films were evaluated and it was found that all three sulfates exhibited a low coefficient of friction (μ ≈ 0.15) at 600°C. X-ray diffraction studies showed the presence of carbonate crystal structures along with the sulfate crystal structures after testing. The carbonate crystal structure is composed of alternating planes of alkali earth atoms and carbonate ions. The layered structure of the carbonates may be important to the lubricating mechanism as the layered structure of the dichalcogenides contributes to their tribological properties. Various observations of the wear region suggest that the starting surface finish of the metal coupon plays a significant role in the tribological mechanism of these materials. Additional composite films containing CaSO₄ were grown with the plasma spray technique. The high temperature friction properties of these films were measured and compared to those of similar films containing CaF₂/BaF₂. Although both types of films exhibited low coefficients of friction at 600°C, analysis of the wear regions did not show the presence of CaSO₄ and CaF₂/BaF₂, respectively. Ca and/or Ba were present, though, suggesting that a new compound is formed in the wear track and that the sulfate and fluoride phases may not be providing the low friction in these composites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Self‐assembled monolayers of DNA on cysteamine modified Au(111) surface: Atomic force microscopy study

The λ‐DNA molecules self‐assemble on cysteamine‐modified gold (111) surface to form flat‐lying self‐assembled monolayers (SAMs). The formation kinetics of such DNA SAMs is studied by atomic force microscopy (AFM). AFM results show that DNA molecules do not arrange themselves on cysteamine‐modified gold (111) surface into a well‐ordered monolayer. It is also found that the surface density of DNA monolayer does not increase as the DNA concentration increases. The high temperature of DNA solution and the immersing in ultrapure water produce some obvious DNA bundles. Whereas divalent cations in DNA solution result in the formation of more compact DNA films. The obtained information may be useful for practical application of the DNA films and further theoretical studies. Microsc. Res. Tech., 2009. © 2009 Wiley‐Liss, Inc.     

Fabrication of self-assembled oligophenylethynylenethiol monolayer for electrochemical glucose biosensor

An electrochemical glucose biosensor was developed using a gold (Au) electrode, which was composed of self-assembled oligophenylethynylenethiol monolayer and glucose oxidase (GOx) structure. Oligophenylethynylenethiol was used as a chemical linker for the immobilization of GOx on Au electrode, which facilitates the transfer of electron produced by enzyme reaction to the Au electrode. The electrical property of self-assembled oligophenylethynylenethiol monolayer was investigated by using cyclic voltammetry (CV). The formation of self-assembled oligophenylethynylenethiol monolayer and GOx layer on Au surface was verified by using atomic force microscopy (AFM) and surface plasmon resonance (SPR). The electrochemical glucose biosensor exhibited a linear relationship between target concentration and oxidation current in the range of 2–30 mM and its detection limit was 2 mM.     

Topographic and phase-contrast imaging in atomic force microscopy

Phase-contrast imaging in the tapping mode atomic force microscopy (AFM) is a powerful method in surface characterization. This method can provide fine details about rough surfaces, which are normally obscured in topographic imaging. To illustrate some of the capabilities of phase-contrast imaging, AFM studies of Pt/Ti/SiO2/Si and Pb(Zr0.52Ti0.48)O3 (PZT) films were carried out. Phase-contrast imaging revealed fine details of their microstructures, including grain boundaries, triple junctions and twinning, which could not be detected by topographic imaging. The studies showed that phase-contrast imaging is capable of providing superior information about surface characteristics when compared to the standard topographic imaging.     

负偏压对含氢类金刚石薄膜性能的影响

为了解决类金刚石(DLC)薄膜与金属基材间的界面结合强度问题,本研究采用直流等离子体增强化学气相沉积(DC-PECVD)技术,以等时长、不同偏压条件在45钢基材上沉积复合DLC薄膜.采用扫描电镜、原子力显微镜观察薄膜形貌;采用拉曼光谱仪分析薄膜成分;采用涂层附着力自动划痕仪测定膜基结合强度.结果表明:制备偏压从-600...     

A Nano- to Macroscale Tribological Study of PFTS and TCP Lubricants for Si MEMS Applications

The reliability and lifetime of cyclic contacting Si MEMS is limited by adhesion and their tribological performance. In this study, the tribological effects of adding a lubricant (tricresyl phosphate, TCP) to a bound self-assembled monolayer (perfluorodecyltrichlorosilane, PFTS) at different length scales were examined using a quartz crystal microbalance (QCM), an atomic force microscope (AFM), a reciprocating microtribometer, and a macroscopic reciprocating tribometer. The results showed that the addition of TCP to a PFTS layer increased the number of cycles possessing low friction and wear by at least a factor of four in the macroscopoic tribometer. Differences in friction response over the range of experimental scales were correlated to contact size and pressure. QCM measurements of TCP on PFTS showed a non-zero slip time, which suggests favorable tribological performance in larger length-scale regimes. This non-zero slip time also may indicate TCP mobility.     

Al、Sn掺杂对于ZnO薄膜微结构及光学特性的影响

采用真空电子束蒸发金属薄膜及后续热氧化技术在石英衬底上分别制备出了ZnO、Al∶ZnO以及Sn∶ZnO薄膜。通过X射线衍射仪(XRD),紫外-可见分光光度计和原子力显微镜(AFM)等分析仪器对比研究了Al、Sn掺杂对ZnO薄膜结晶质量、光学性质及表面形貌的影响。测试结果表明,Al、Sn掺杂可以使薄膜结晶质量得到提高,薄膜应力部分释放,薄膜表面的粗糙度也相应增加,掺杂对薄膜光学带隙的影响在一定程度取决于金属薄膜的氧化程度,氧化充分可以使光学带隙变宽,反之则变窄。     

DLC薄膜的表面形貌及其摩擦学性能研究

以真空蒸发碳离子束辅助镀膜法制备了DLC薄膜，通过原子力显微镜(AFM)和扫描电子显微镜(SEM)观察了该薄膜的表面形貌，对该薄膜的表面形貌对其摩擦学行为的影响进行了研究。研究发现：用真空蒸发碳离子束辅助镀膜的方法制备的类金刚石薄膜表面光滑，颗粒均匀，粒度小，摩擦因数降低；DLC薄膜比弹簧钢片及Ti6Al4V球基体耐磨；DLC薄膜的摩擦学性能在摩擦过程中会进一步改善。     

Tribological Properties of Films Formed by the Reaction of Carbon Tetrachloride with Iron

The tribological properties of halide films grown on iron by reaction with carbon tetrachloride vapor at a temperature of 617 K and a pressure of 1.7 Torr are compared, in ultrahigh vacuum, with FeCl₂ films evaporated onto the surface. It is found that the reactively formed film has a slightly lower limiting friction coefficient than the evaporated layer (~0.06 compared to ~0.08), which may be due either to the diffusion of some carbon into the substrate or the formation of a more oriented layer when this is formed reactively. The major difference between the reactively grown and evaporated film is that the evaporated layer attains the minimum friction when ~40 ? of FeCl₂ has been evaporated, while the reactively formed layer has a minimum friction coefficient when a film of 6±2 ? has been deposited. In the case of the evaporated FeCl₂ film, the growth of second and subsequent layers proceeds before the first layer is complete. It has been shown that the friction coefficient reaches its minimum value after completion of the first monolayer, a process that is complete after the evaporation of ~40 ? of FeCl₂. In the case of the film formed by reaction with CCl₄, the halide film grows directly on the surface implying that the FeCl₂ monolayer thickness is ~6 ?. This value is in good agreement with the layer thickness in bulk ferrous chloride.