Structural,morphological and mechanical properties of niobium nitride thin films grown by ion and electron beams emanated from plasma

The influence of variation in plasma deposition parameters on the structural, morphological and mechanical characteristics of the niobium nitride films grown by plasma-emanated ion and electron beams are investigated. Crystallographic investigation made by X-ray diffractometer shows that the film synthesized at 10?cm axial distance with 15 plasma focus shots (PFS) exhibits better crystallinity when compared to the other deposition conditions. Morphological analysis made by scanning electron microscope reveals a definite granular pattern composed of homogeneously distributed nano-spheroids grown as clustered particles for the film synthesized at 10?cm axial distance for 15 PFS. Roughness analysis demonstrates higher rms roughness for the films synthesized at shorter axial distance and by greater number of PFS. Maximum niobium atomic percentage (35.8) and maximum average hardness (19.4?±?0.4?GPa) characterized by energy-dispersive spectroscopy and nano-hardness analyzer respectively are observed for film synthesized at 10?cm axial distance with 15 PFS.     

Structural and morphological properties of thin ZnO films grown by pulsed laser deposition

The pulsed laser deposition technique was used to produce zinc oxide thin films onto silicon and Corning glass substrates. Homogeneous surfaces exhibiting quite small Root Mean Square (RMS) roughness, consisting of shaped grains were obtained, their grain diameters being 40-90 nm at room temperature and at 650 °C growth respectively. Films were polycrystalline, even for growth at room temperature, with preferential crystallite orientation the (0 0 2) basal plane of wurtzite ZnO. Temperature increase caused evolution from grain to grain agglomeration structures, improving crystallinity. Compressive to tensile stresses transition with temperature was found while the lattice constant decreased.     

Enclosed laser ablation of 20 nm aluminium films using a continuous wave diode laser: II—Theoretical heating considerations and proposed mechanisms

Laser ablation using a 120 W continuous wave diode laser was carried out upon a thin aluminium layer which had been hermetically sealed between two layers of polymer. The results (presented in Part I) have shown that the film could be partially transparentised but with an efficiency which was far less than that seen for a Q-switched laser. In this paper, the thermal effects within the films are analysed and a mechanism by which enclosed surface laser ablation occurs is proposed.     

Structural, elastic constants, hardness, and optical properties of pyrite-type dinitrides (CN2, SiN2, GeN2)

The crystal structures, band structures, elastic constants, hardness, and optical properties of pyrite-type dinitrides (CN₂, SiN₂, and GeN₂) are obtained from the density functional theory using the plane-wave pseudopotential (PWP) method within the local density and generalized gradient approximations. The formation enthalpies for AN₂ (A=C, Si, and Ge) compounds suggest the three structures that are stable. The calculated band structures show the indirect gaps (Γ−R) in CN₂, SiN₂, and GeN₂. The intrinsic hardnesses of AN₂ (A=C, Si, and Ge ) compounds are calculated. Our results show that the cubic CN₂ and SiN₂ are superhard materials. Furthermore, we studied the optical properties such as the complex dielectric function and the electron energy loss spectra.     

激光二极管高效铜微通道冷却器设计

 通过对铜微通道冷却器的散热分析，设计出５层结构的模块式铜微通道冷却器。采用常规的线切割工艺加工，散热通道宽大约200μm，深300μm，各层间用真空钎焊的方法组装。该冷却器对于腔长06mm、宽10mm的线阵激光二极管芯片热阻为0.58℃/W。通过面阵激光二极管封装实验证明，该冷却器可用于10％占空比工作的面阵激光二极管封装。     

Microscopic observation of laser glazed yttria-stabilized zirconia coatings

Thermal barrier coatings (TBCs) are frequently used as insulation system for hot components in gas-turbine, combustors and power plant industries. The corrosive gases which come from combustion of low grade fuels can penetrate into the TBCs and reach the metallic components and bond coat and cause hot corrosion and erosion damage. Glazing the top coat by laser beam is advanced approach to seal TBCs surface. The laser beam has the advantage of forming a dense thin layer composed of micrograins. Plasma-sprayed yttria-stabilized zirconia (YSZ) coating was glazed with Nd-YAG laser at different operating conditions. The surface morphologies, before and after laser treatment, were investigated by scanning electron microscopy. Laser beam assisted the densification of the surface by remelting a thin layer of the exposed surface. The laser glazing converted the rough surface of TBCs into smooth micron-size grains with size of 2-9 μm and narrow grain boundaries. The glazed surfaces showed higher Vickers hardness compared to as-sprayed coatings. The results revealed that the hardness increases as the grain size decreases.     

Theoretical investigation on the electronic structure,elastic properties, and intrinsic hardness of Si2N20

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli （bulk modulus, Young’s mod-ulus, and shear modulus） are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.     

Study of structural,morphological and mechanical properties of PMMA,PVC and their blends

PMMA, PVC and their five blends in different compositions were irradiated by γ -rays of 2 Mrad dose. A comparative study of structural, morphological and mechanical properties of irradiated and non-irradiated samples was carried out. The structural changes that have taken place due to irradiation are seen in the FTIR and X-ray diffraction (XRD) spectra. The ester group is mainly affected in PMMA and the blends. The XRD results have confirmed that the irradiated samples are more amorphous in nature than the non-irradiated ones. The DSC study reveals that some irradiated samples undergo cross-linking, whereas some of them undergo degradation. One of the irradiated blend compositions has become thermally more stable. The SEM study suggests that the irradiated samples have undergone curing. An improvement in the mechanical properties has been observed in some of the irradiated blend compositions.     

Structural and mechanical properties of nano-crystal TiN coatings

The structural and mechanical properties of TiN coatings prepared by ion beam assisted deposition (IBAD) were studied. The coatings have a polycrystal structure with grain size of ～10 nm or less. The hardness of the coatings increases with increasing grain size of TiN crystallites. The coating with grain size of 10.3 nm even has a superhardness of 44.7GPa. The relationship between the hardness and the grain size in the nano-crystalline coatings was discussed on the basis of grain-boundary triple junctions.     

Structural and electrical properties of fluorine doped tin oxide films prepared by spray-pyrolysis technique

Fluorine doped SnO₂ films have been successfully prepared at optimized substrate temperature of 723 K by spray pyrolysis technique. The XRD analysis confirmed that films deposited with F/Sn ratio of 0.05 showed a partial amorphous nature whereas films deposited with F/Sn = 0.10 exhibited tetragonal structure (2 0 0) as the preferred orientation and polycrystalline structure. The lattice constants were found to be a = 0.4750 and c = 0.3197 nm. The theoretically constructed XRD pattern for SnO₂ was used to compare with experimental pattern, the difference between them is discussed. By using SEM analysis, the surface morphology of the films was observed as an effect of the variation of F/Sn ratio. At low temperature, the mobility due to lattice, polar, impurity, grain boundary and neutral scattering was estimated for SnO₂ and the possible scattering mechanisms were assigned to SnO₂:F films using experimentally obtained electrical data. The Mott parameters were determined by applying variable range hopping (VRH) conduction mechanism for SnO₂:F films (F/Sn = 0.05) where band conduction mechanism shifted to VRH conduction at below about 250 K.     

Theoretical investigation on the electronic structure, elastic properties, and intrinsic hardness of Si2N2O

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli (bulk modulus, Young’s mod- ulus, and shear modulus) are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.     

Structural and electronic properties of chiral single-wall copper nanotubes

The structural,energetic and electronic properties of chiral(n,m)(3≤n≤6,n/2≤m≤n)single-wall copper nanotubes(CuNTs)have been investigated by using projector-augmented wave method based on density-functional theory.The(4,3)CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions,whereas the(5,5)and(6,4)CuNTs should be observed in free-standing and tip-suspended conditions,respectively.The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube.Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk.Current transporting states display different periods and chirality,the combined effects of which lead to weaker chiral currents on CuNTs.     

Collimating of diverging laser diode beam using graded-index optical fiber

This paper presents a technique for collimating a diverging beam from a laser diode using graded-index optical fiber. The optical set-up is relatively simple and easy to operate. The results show that laser beam of large divergent angle in the range of 10–35° can be reduced to a fully collimated beam with a divergent angle of less than 0.05°. The theory of the method as well as some experimental results is presented.     

Structural and electrical properties of evaporated Fe thin films

Series of Fe thin films have been prepared by thermal evaporation onto glass and Si(1 0 0) substrates. The Rutherford backscattering (RBS), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and the four point probe techniques have been used to investigate the structural and electrical properties of these Fe thin films as a function of the substrate, the Fe thickness t in the 76-431 nm range and the deposition rate. The Fe/Si samples have a 〈1 1 0〉 for all thicknesses, whereas the Fe/glass grows with a strong 〈1 0 0〉 texture; as t increases (>100 nm), the preferred orientation changes to 〈1 1 0〉. The compressive stress in Fe/Si remains constant over the whole thickness range and is greater than the one in Fe/glass which is relieved when t > 100 nm. The grain size D values are between 9.2 and 30 nm. The Fe/glass films are more electrically resistive than the Fe/Si(1 0 0) ones. Diffusion at the grain boundary seems to be the predominant factor in the electrical resistivity ρ values with the reflection coefficient R greater in Fe/glass than in Fe/Si. For the same thickness (100 nm), the decrease of the deposition rate from 4.3 to 0.3 Å/s did not affect the texture and the reflection coefficient R but led to an increase in D and a decrease in the strain and in ρ for both Fe/glass and Fe/Si systems. On the other hand, keeping the same deposition rate (0.3 Å/s) and increasing the thickness t from 76 to 100 nm induced different changes in the two systems.     

激光能量对激光诱导Cu等离子体特征辐射强度、电子温度的影响

利用Nd:YAG激光(波长1 064 nm,脉宽10 ns)烧蚀金属Cu靶获得等离子体 .改变激光脉冲能量,观测到Cu的原子谱线和离子谱线随激光脉冲能量有不同的变化关系, 但都在330 mJ/pulse时,谱线强度达到最大,随后在330 mJ～370 mJ/pulse间出现一小平台 ,能量继续增加,各谱线强度减小.同时,使用烧蚀Cu靶产生的五条原子谱线(465.11 nm,5 10.55 nm,515.32 nm,521.82 nm,529.25 nm)的相对强度,在局部热力学平衡近似下,利用B oltzmann图的最小二乘法拟合,测定了不同激光能量下Cu等离子体的电子温度.随激光能量的增加,电子温度近似单调地从1.02×104 K上升到1.46×104 K后,反而有所下降.     

Morphologies,microstructures, and mechanical properties of samples produced using laser metal deposition with 316 L stainless steel wire

Laser metal deposition (LMD) with a filler has been demonstrated to be an effective method for additive manufacturing because of its high material deposition efficiency, improved surface quality, reduced material wastage, and cleaner process environment without metal dust pollution. In this study, single beads and samples with ten layers were successfully deposited on a 316 L stainless steel surface under optimized conditions using a 4000 W continuous wave fibre laser and an arc welding machine. The results showed that satisfactory layered samples with a large deposition height and smooth side surface could be achieved under appropriate parameters. The uniform structures had fine cellular and network austenite grains with good metallurgical bonding between layers, showing an austenite solidification mode. Precipitated ferrite at the grain boundaries showed a subgrain structure with fine uniform grain size. A higher microhardness (205–226 HV) was detected in the middle of the deposition area, while the tensile strength of the 50 layer sample reached 669 MPa. In addition, ductile fracturing was proven by the emergence of obvious dimples at the fracture surface.     

Structural,electrical and magnetic properties of (Fe,Co) co-doped SnO2 diluted magnetic semiconductor nanostructures

Nanostructures (NSs) of basic composition Sn_1−xFe_x/2Co_x/2O₂ with x=0.00, 0.04, 0.06, 0.08 and 0.1 were synthesized by citrate-gel route and characterized to understand their structural, electrical and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase rutile type tetragonal structure. The crystallite sizes calculated by using Williamson Hall were found to decrease with increasing doping level. In addition to the fundamental Raman peaks of rutile SnO₂, the other three weak Raman peaks at about 505, 537 and 688 cm⁻¹ were also observed. Field emission scanning electron microscopy studies showed the emergence of structural transformation. Electric properties such as dc electrical resistivity as a function of temperature and ac conductivity as a function of frequency were also studied. The variation of dielectric properties with frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general. Hysteresis loops were clearly observed in M–H curves of Fe and Co co-doped SnO₂ NSs. However, pure SnO₂ nanoparticles (NPs) showed paramagnetic behaviour which vanished at higher values of magnetic field. The grain and grain boundary contribution in the conduction process is estimated through complex impedance plot fitted with non-linear least square (NLLS) approach which shows that the role of grain boundaries increases rapidly as compared to the grain volume with the increase of Fe and Co ions in to system.     

Theoretical study on stability,mechanical properties and thermodynamic parameters of the orthorhombic-A2N2O (A=C,Si and Ge)

The structural stability, mechanical properties and thermodynamic parameters such as Debye temperature, minimum thermal conductivities of orthorhombic-A₂N₂O (A=C, Si and Ge) are calculated by first principles calculations based on density functional theory. The calculated lattice parameters, elastic constants of Si₂N₂O and Ge₂N₂O using PBEsol function are consisted with the experimental data and other calculated values. The full set elastic constants of the orthorhombic-A₂N₂O (A=C, Si and Ge) are calculated by stress–strain method. The mechanical moduli (bulk modulus, shear modulus and Young's modulus) are evaluated by the Voigt–Reuss–Hill approach. The orthorhombic-C₂N₂O exhibits larger mechanical moduli than the other two structures. The hardness of orthorhombic-A₂N₂O (A=C, Si and Ge) is evaluated according to the intrinsic hardness calculation theory of covalent crystal relying on Mulliken overlap population. The results indicate that the orthorhombic-C₂N₂O is a super hard material. Furthermore, the mechanical anisotropy, Debye temperature and minimum thermal conductivity of the orthorhombic-A₂N₂O (A=C, Si and Ge) have been estimated by empirical methods. The orthorhombic-Ge₂N₂O shows the lowest thermal conductivity, which may have useful applications as gas turbine engines and diesel engines.     

硼酸镁晶须增强镁基复合材料的谱学表征与性能研究

用X射线衍射谱分析了Mg2B2O5w/AZ91D镁基复合材料中的物相。研究了固溶处理和时效处理以及固溶处理加人工时效处理对复合材料组织演变的影响及组织与显微硬度之间的关系。结果表明,经过固溶处理后,共晶相的分解使复合材料的硬度值明显下降。时效处理使得复合材料的硬度逐渐增加并在时效处理16h后出现时效峰值201HV。然而随着时效时间的进一步增加,显微硬度值降低。经固溶处理24h,基体中β相基本溶解,形成过饱和的固溶体,接着时效处理8h,β相以弥散形式析出,从而使得复合材料的显微硬度值提高30%;而固溶处理24h及时效处理24h后,β析出相由细小片状的连续析出相向粗大的层片状非连续析出相过渡,使得复合材料的显微硬度下降到183HV。     

Theoretical investigation on the electronic structure,elastic properties,and intrinsic hardness of Si₂N₂O

According to the density functional theory we systematically study the electronic structure, the mechanical prop- erties and the intrinsic hardness of Si2N2O polymorphs using the first-principles method. The elastic constants of four Si2N2O structures are obtained using the stress-strain method. The mechanical moduli (bulk modulus, Young’s mod- ulus, and shear modulus) are evaluated using the Voigt-Reuss-Hill approach. It is found that the tetragonal Si2N2O exhibits a larger mechanical modulus than the other phases. Some empirical methods are used to calculate the Vickers hardnesses of the Si2N2O structures. We further estimate the Vickers hardnesses of the four Si2N2O crystal structures, suggesting all Si2N2O phases are not the superhard compounds. The results imply that the tetragonal Si2N2O is the hardest phase. The hardness of tetragonal Si2N2O is 31.52 GPa which is close to values of β-Si3N4 and γ-Si3N4.