FTIR and Raman study of the structural properties and tribological characteristics of collagen

Optical and Quantum Electronics - In the present paper, we propose a compact composite wedge interference structure by combining wedges with different geometry. We use interferential wedges with...     

Effect of the grain size on the formation of a nanophase structure and tribological properties of the friction surface of a ceramic made of partly stabilized zirconia

It is found that the wear of the ZrO₂ + 3 mol% Y₂O₃ ceramics with a grain size of 180 nm in the case of dry friction on steel is smaller by a factor of 20–60 than the wear of a ceramic with an average grain size of 700 nm. It is shown that this is due to the fact that a nanophase structure formed on the friction surface of the ceramic with a grain size of 180 nm consists of ferroelastic nanodomains of the nontransformable T′ phase.     

Bio-inspired dual surface modification to improve tribological properties at small-scale

In miniaturized devices like micro/nano-electro-mechanical systems (MEMS/NEMS), the critical forces, namely adhesion and friction restrict the smooth operation of the elements that are in relative motion. MEMS/NEMS are traditionally made of silicon, whose tribological properties are not good. In this paper, we present an investigation on the approach of dual surface modification of silicon surfaces and their tribological properties at micro-scale. The dual surface modification is a combination of topographical and chemical modifications. As the topographical modification, micro-patterns with varying shapes of pillars and channels were fabricated on Si(1 0 0) wafer surfaces using photolithography method. Chemical modification included the coating of micro-patterns with diamond-like carbon (DLC) and Z-DOL (perfluoropolyether, PFPE) thin films. The surfaces with combined modification were evaluated for their micro-friction behavior in comparison with those of bare Si(1 0 0) flat surfaces and the topographically/chemically modified silicon surfaces. Results showed that the surfaces with dual modification exhibited superior tribological properties. These results indicate that a combination of topographical and chemical modification is very effective in enhancing tribological properties at small-scale. The combined surface treatments such as the ones investigated in the current work could be useful for tribological applications in small-scale devices such as MEMS/NEMS. The motivation for undertaking the dual modification approach comes from an earlier observation made on the significant influence of the surface characteristics of lotus leaf on its micro-friction behavior.     

一种新型肽核酸单体的FTIR,FT-Raman光谱及SERS研究

报道了S-胸腺嘧啶-L-半胱氨酸的FTIR光谱,及其固态、饱和液态的FT-Raman光谱.通过红外与拉曼光谱的结合,对其分子结构中各基团的振动情况进行了较为全面的解析;实验发现,该化合物在银胶上的最佳SERS的浓度为10-4mol·L-1,氨基峰在酸性条件下增强,羧基峰在碱性条件下增强,而其他基团峰随pH值的改变变化不大.依据SERS作用机理和规律,推测S-胸腺嘧啶-L-半胱氨酸在银胶表面的吸附是通过硫原子、羧基、氨基、胸腺嘧啶环和其中的氮原子与银原子配位,且胸腺嘧啶环是倾斜着与银纳米颗粒相吸附;该吸附模型的建立为拉曼光谱更深入研究PNA、多肽及其他生物分子提供了十分重要的信息和有益的参考.     

Correlations between microstructure of plasma-modified gold nanoclusters and their optical properties

Gold nanoclusters with diameters up to 50 nm were grown in sandwich structures consisting in 15 nm of plasma deposited silicon nitride, 1 nm of gold grown by sputtering and 15 nm of plasma deposited silicon nitride (SiN/Au/SiN). Previous to the last step, ammonia plasma treatments of the gold surface were carried out with time as the main variable. The resulting structures were analyzed by high resolution transmission electron microscopy and spectroscopic ellipsometry. As a result of plasma treatments, island-like structures of as-grown gold clusters evolve to near spherical-shape features with decreasing diameter as the plasma treatment time rises. Ellipsometric spectra were modeled based on the Bruggeman effective medium approximation and the influence of size and shape of nanoparticles on the optical properties were calculated.     

The structure and tribological behaviors of CrN and Cr-Ti-N coatings

The Cr-Ti-N coatings with different composition were deposited in a medium frequency magnetron sputtering system on Si (1 1 1) substrates. The structures, surface morphology and wear properties were measured. The binary CrN coatings, formed a single-phase fcc structure with nearly random (1 1 1), (2 0 0) and (2 2 0) orientation, while for the Ti was introduced, coatings show a preferred orientation of (2 0 0). Cr-Ti-N coating shows a much smoother surface than CrN coating. Cr-Ti-N coating with 31.75% Ti content shows the best wear behavior. The excellent tribological properties of this composition coating are corresponding to the solid solution nitride structures.     

Effect of ultrasonic vibration on adhesive enhancement of plasma-modified nickel surface

Poor adhesion of nickel surface limits its further application in the aerospace field. In this study, plasma modification was conducted on the surface of the nickel plate pretreated by sandblasting, and then ultrasonic vibration was applied during the adhesively bonding process of the CFRP(Carbon fibre-reinforced polymer)/Ni joints. The bonding strength of the joints was increased by 65%. The adherend surface and the bonding interface were analyzed from microstructure, element distribution and chemical bonding to study the strengthening mechanism. By the sandblasting, irregular pits were formed on the nickel surface, effectively increasing the surface roughness. The plasma modification could introduce active functional groups including hydroxyl, amino and carbonyl on the nickel surface, which improved the surface wettability macroscopically. However, at a microscopic level, the adhesive with high viscosity and poor fluidity did not form a compact interface with the nickel. The ultrasonic application could promote the filling of the adhesive in irregular micro-scale pits on the surface, thereby strengthening the mechanical anchoring effect. Furthermore, the ultrasonic application produced dynamic impingement at the interface, enhancing the contact between the adhesive and the nickel plate. The adhesive molecules could fully collide and react with the active functional groups introduced on the nickel surface to form more chemical bonds, thus effectively improving the bonding strength of the CFRP/Ni joints.     

Thermal annealing dependence of some optical properties of plasma-modified porous silicon

The photoluminescence and reflectance of porous silicon (PS) with and without hydrocarbon (CH_x) deposition fabricated by plasma enhanced chemical vapour deposition (PECVD) technique have been investigated. The PS samples were then, annealed at temperatures between 200 and 800 °C. The influence of thermal annealing on optical properties of the hydrocarbon layer/porous silicon/silicon structure (CH_x/PS/Si) was studied by means of photoluminescence (PL) measurements, reflectivity and ellipsometry spectroscopy. The composition of the PS surface was monitored by transmission Fourier transform infrared (FTIR) spectroscopy. Photoluminescence and reflectance measurements were carried out before and after annealing on the carbonized samples for wavelengths between 250 and 1200 nm. A reduction of the reflectance in the ultraviolet region of the spectrum was observed for the hydrocarbon deposited polished silicon samples but an opposite behaviour was found in the case of the CH_x/PS ones. From the comparison of the photoluminescence and reflectance spectra, it was found that most of the contribution of the PL in the porous silicon came from its upper interface. The PL and reflectance spectra were found to be opposite to one another. Increasing the annealing temperature reduced the PL intensity and an increase in the ultraviolet reflectance was observed. These observations, consistent with a surface dominated emission process, suggest that the surface state of the PS is the principal determinant of the PL spectrum and the PL efficiency.     

Materials and surface treatments for tribological applications

Understanding wear mechanisms and the consequent optimization of surface treatments require powerful and integrated techniques of surface diagnostics. It is shown that Mössbauer spectroscopy techniques can make original and sometimes determining contributions in different fields of tribology. Examples are presented concerning the characterization and tribological behaviour of both conversion coatings and PVD thin films, as well as the analysis of wear debris produced by sliding couples.     

Evidence of the surface layer in tungstated zirconia

We characterized the structure of tungstated zirconia (WO_x–ZrO₂) by combining X-ray diffraction, Raman spectroscopy and High Resolution Electron Microscopy (HREM) together with molecular simulations. Our results indicate that the structure of this material consists of metastable tetragonal ZrO₂ nanoparticles (<20 nm in diameter) covered by a few-nanometers thick low-crystallinity surface layer formed by tungsten oxospecies (WO_x). Although the X-ray diffraction pattern matched the spectra of the tetragonal ZrO₂ bulk phase the lattice fringes of the ZrO₂ nanoparticles observed by HREM were locally distorted, presumably as a result of the interaction with the surface WO_x layer. The local interplanar distances of the surface layer were close to those present in different bulk tungsten oxocompounds, and its variability was also an indication of the WO_x–ZrO₂ interaction. Molecular simulations corroborated our structural assignment. The results presented here are a direct evidence for the presence of a surface WO_x layer in the case of WO_x–ZrO₂. PACS 68.35.Bs; 81.05.Ys; 82.65.Dp     

Influence of nitrogen ion implantation fluences on surface structure and tribological properties of SiC ceramics in water-lubrication

Nitrogen ions were implanted into SiC ceramics by using ion implantation technology (N⁺-SiC). The surface structure and chemical bonds of N⁺-SiC ceramics were determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and their nanohardness was measured by nanoindenter. The friction and wear properties of the N⁺-SiC/SiC tribo-pairs were investigated and compared with those of SiC/SiC tribo-pairs in water using ball-on-disk tribo-meters. The wear tracks on the N⁺-SiC ceramics were observed by non-contact surface profilometer and scanning electron microscope (SEM) and their wear volumes were determined by non-contact surface profilometer. The results show that the N⁺-SiC ceramics were mainly composed of SiC and SiCN phase and SiN, CC, CN and CN bonds were formed in the implantation layer. The highest hardness of 22.3 GPa was obtained as the N⁺-SiC ceramics implanted at 50 keV and 1 × 10¹⁷ ions/cm². With an increase in nitrogen ion fluence, the running-in period of N⁺-SiC/SiC tribo-pairs decreased, and the mean stable friction coefficient decreased from 0.049 to 0.024. The N⁺-SiC ceramics implanted at 50 keV and 5 × 10¹⁷ ions/cm² exhibited the excellent tribological properties in water. In comparison of SiC/SiC ceramic tribo-pairs, the lower friction coefficient and lower wear rate for the N⁺-SiC/SiC tribo-pairs were acquired.     

Mechanical and tribological properties of Ni/Al multilayers—A molecular dynamics study

Mechanical and tribological properties of multilayers with nanometer thickness are strongly affected by interfaces formed due to mismatch of lattice parameters. In this study, molecular dynamics (MD) simulations of nanoindentation and following nanoscratching processes are performed to investigate the mechanical and tribological properties of Ni/Al multilayers with semi-coherent interface. The results show that the indentation hardness of Ni/Al multilayers is larger than pure Ni thin film, and the significant strength of Ni/Al multilayers is caused by the semi-coherent interface which acts as a barrier to glide of dislocations during nanoindentation process. The confinement of plastic deformation by the interface during nanoscratching on Ni/Al multilayers leads to smaller friction coefficient than pure Ni thin film. Dislocation evolution, interaction between gliding dislocations and interface, variations of indentation hardness and friction coefficient are studied.     

Structural and tribological properties of cluster-assembled CNx films

We report the structural and tribological characterization of nanostructured CN_x thin films produced by the deposition of a supersonic carbon cluster beam assisted by nitrogen ion bombardment. The influence of the deposition parameters on the chemical composition and structure of the films has been systematically studied by X-ray photoelectron spectroscopy, elastic recoil detection analysis, transmission electron microscopy and atomic force microscopy. Depending on the deposition parameters, the films show a structure ranging from amorphous to disordered graphitic with interlinked planes. Nitrogen content depends on the nitrogen ion kinetic energy. The films have a very low density with a high surface roughness. Friction measurements at the nanoscale show a correlation between nitrogen content and mechanical properties of the system. PACS 61.46-w     

Sliding tribological properties of untreated and PIII-treated PETP

Poly(ethylene terephthalate) (PETP) was treated by plasma immersion ion implantation (PIII or PI³) in nitrogen. The surface changes were characterised by XPS and water contact-angle measurements. Sliding tribological properties of untreated and nitrogen PIII-treated PETP against conventional low carbon structural steel S235 were studied under dry and water-lubricated conditions by a pin-on-disc tribometer.XPS results suggested the evolution of surface composition and bonding towards those of amorphous hydrogenated carbon-nitride. Water contact-angle decreased implying increased surface wettability. At a very low Pv factor (0.0075 MPa m s⁻¹) for the nitrogen PIII-treated PETP the dry friction coefficient was smaller than, while the lubricated friction coefficient was similar to, the corresponding value of the untreated variant. At higher Pv factors (near 0.1 MPa m s⁻¹), however, both the dry and lubricated friction coefficients were higher for the treated sample than for the untreated variant, suggesting an increased adhesion component of friction for the nitrogen PIII-treated PETP in this region.     

ZrO2薄膜微观结构和光学性能的研究

无论是在300℃或室温下,用PVD方法淀积的ZrO_2薄膜,达到一定厚度后都出现晶相非均匀性,在基底侧为四方相,空气侧为单斜相.本文给出了ZrO_2薄膜中四方相存在的原因,并用晶体生长过程中的择优生长特性讨论了薄膜柱状体结构的成因,从而解释了薄膜的折射率非均匀性.     

Investigation of the vibrational properties of cubic yttria-stabilized zirconia: A combined experimental and theoretical study

A combined experimental and theoretical investigation into the vibrational properties of cubic 8–9 mol% yttria-stabilized zirconia (YSZ) is presented. Measurements of acoustic phonon dispersion curves have been obtained from inelastic neutron scattering investigations using a triple axis spectrometer, as well as calculations of the vibrational density-of-states (vDOS) using density-functional theory. The present measurements agree closely with, and extend, previously published results. The phonons become broader and decrease in intensity as the Brillouin zone boundary is approached, particularly in the Γ–Δ–X direction. Interestingly, there is evidence of a previously unreported low energy phonon band (8–9 meV) in the Γ–Σ–X direction, which could possibly be related to the stabilization (by yttria doping) of the imaginary mode of cubic ZrO₂ about the X-point. Compared to pure cubic ZrO₂, the vDOS of YSZ are broader and extend to higher frequency. Furthermore, the prominent Zr-related feature in the vDOS of c-ZrO₂ at ≈14 meV is shifted to higher energy in the vDOS of YSZ. This behavior is consistent with the measured dispersion bands (first acoustic branch in the Γ–X direction, about the X-point) of YSZ which is higher in energy by a similar amount relative to that of c-ZrO₂, thus providing support for the structural model considered.     

Adsorption and oxidation of sulfur dioxide on the yttria-stabilized zirconia surface: ab initio atomistic thermodynamics study

The interaction of SO₂ with the yttria-stabilized zirconia (YSZ) (111) and oxygen-enriched YSZ (111) (YSZ+O) surface is investigated using the first-principles method based density functional theory (DFT). It is found that SO₂ is adsorbed either as a molecule or forms SO²⁻₃ species with new SO bonds to a surface oxygen on the YSZ (111) surface. In addition, there exist other species, e.g., SO₃ and SO²⁻₄ on the very active YSZ+O (111) surface. Using the ab initio atomistic thermodynamics method, we present a detailed analysis on the stability of the SO₂YSZ/YSZ+O system as a function of the ambient conditions.     

Laser controlled melting of pre-treated zirconia surface

Laser treatment of pre-prepared zirconia surface is carried out. The pre-prepared surface, prior to laser treatment, consists of 50 μm carbon film and 7% titanium carbide particles, which are imbedded in the carbon film. The microstructural and morphological changes in the laser treated surface layer are examined using optical and scanning electron microscopes, energy dispersive spectroscopy, and X-ray diffraction. The fracture toughness of the laser treated surface is measured and the residual stress formed at the surface vicinity is determined from the X-ray diffraction technique. It is found that the microhardness of the laser treated surface increased slightly due to the dense layer formed at the surface vicinity. However, the laser treatment process reduces the fracture toughness of the surface due to improved surface hardness and the residual stress formed in the surface vicinity.     

Wetting behavior of modified vinylester resins on the surface of UHMWPE materials

A new testing method was used to observe on-line the dynamic wetting course of liquid resins on PE fabric. The measure procedures and data processing were introduced in detail. To aim at some applications of vinylester resins/polyethylene fiber composites, vinylester resins (VRs) were at first modified by three kinds of additives, including elastomer, liquid rubber and isocyanate-terminated prepolymer. Then the wetting behaviors of these modified resins on the surface polyethylene (PE) materials were observed. After they were modified by six kinds of elastomers, the infiltrate-steady-times of these resins on the surface of PE fabric all increased; only the contact angle of natural rubber-modified VR on the surface of PE film decreased. After VRs were toughened by three kinds of liquid rubbers, their wetting velocities all became slower and the contact angles on the surface of PE film all decreased. In addition, VRs were also modified by three kinds of isocyanate-terminated prepolymers, which were the products of different hydroxyl-terminated polymers reacted with methylene bisphenyl isocyanate and whose structures were characterized by means of GPC, DSC and FT-IR, respectively. The wetting state of these modified resins on the surface of PE materials suggested that the interfacial compatibility of modified VRs and PE fabric did not decrease at the same time when the other properties of vinylester resins changed.