Li Hd

Carbon nitride films synthesized by NH3-ion-beam-assisted deposition

Carbon nitride thin films have been prepared by NH3-ion-beam-assisted deposition with bombardment energies of 200-800 eV at room temperature. These films have been characterized by transmission electron microscopy, Auger electron spectroscopy and x-ray photoelectron spectroscopy for chemical analysis. It was found that the structure of the films varied with the bombardment energy. In the case of 400 eV bombardment, the tiny crystallites immersed on an amorphous matrix were identified to be beta -C3N4. X-ray photoelectron spectroscopy indicated that some carbon atoms and nitrogen atoms form unpolarized covalent bonds in these films.

Formation of β-C3N4 grains by nitrogen-ion-beam-assisted deposition

Abstract Carbon nitride thin films were prepared by nitrogen-ion-beam-assisted deposition. Auger electron spectroscopy shows that the N/C atomic composition ratio increases with increasing current density and decreasing bombarding energy of the nitrogen ion beam. At a bombarding energy of 200 eV and a current density of 0.2 mA cm −2 , a maximum N/C ratio of 0.54 is obtained and crystalline β -C 3 N 4 grains with dimensions of about 0.1 μm are observed by transmission electron microscopy. This film displays a high Knoop hardness of 4450 kgf mm −2 and a resistivity of 10 9 Ω cm.

Anisotropic indentation morphology and hardness of natural ivory

Abstract An investigation of the orientation dependence of indentation morphology and microhardness is reported for natural ivory samples. Indentations exhibit rather different behavior in the three orthogonal planes related to the cylindrical geometry of the tusk, i.e., in the transverse, radial and circumferential planes. For instance, under a load of 50 g, the hardness value in the circumferential plane is about 25% larger than that in the radial plane. This mechanical property may be explained in terms of the special microarchitecture of the hydroxyapatite-like crystals and the collagen fibers in this biological tissue.

Wear and friction properties of laser surface hardened En31 steel

Abstract The surface of En31 steel was treated by CO 2 laser for solid state transformation hardening. The wear and friction characteristics of the treated surfaces were examined and compared with untreated surfaces using the lubricated ring-on-block technique. The microstructures of the laser-hardened tracks and the worn surfaces were studied by SEM. The results indicated that the surface of a single hardened track and the surface with two non-overlapping tracks have better wear and friction properties, as compared with the untreated surfaces. Further, surfaces with non-overlapping tracks were found to have better friction properties than the homogeneous hardened zone of a single track.

IBAD processing of surface coatings and nanocrystalline multi-layers

Abstract Multi-functional ion beam assisted deposition (IBAD) equipment with 8 targets and 4 ion sources has been developed to synthesize coatings and multi-layers of many combinations. DLC, TiN, TiC coatings have been investigated with special attention paid to DLC. It is found that a narrow energy window exists at about 200 eV in order to serve more prominent diamond bondings and diamond-like properties. The surface is hard and smooth with a friction coefficient of less than 0.05. The improvement of the interfacial structure enables DLC coatings on 52100 steel to sustain uniform wear at high wear loads (up to 120 N). Applications of DLC and other coatings in material surface modification are being explored. By alternate sputtering, TiC/Metal multi-layers have been prepared. The individual layers vary in thickness from 1 to 10 nm and the periods vary from 3 to 18 nm. The ceramic phase has been maintained as TiC, whilst Fe, Cr, Nb, Zr, Ni, Cu and Al have been used as the metal phase. The hardness and toughness of these laminated nanocrystalline films have been investigated, the results showing the dependence of the properties on the modulation of the multi-layers as well as on the characteristics of the metal phase.

Disclination loops in Ni-Mo amorphous alloy films induced by ion irradiation

Ni-Mo amorphous films were obtained by 200 keV xenon ion mixing at room temperature to dosages higher than 7*1014 ion cm-2. It was found, for the first time, that when the irradiation dose went up to 7*1015 ion cm-2, many odd lines appeared in the amorphous matrix. After excluding various possible explanations, the authors attribute the observed loops to line defects, i.e., disclinations in amorphous solids. Rich microstructures pertinent to disclination loops are described in detail. Scaling analysis showed that the observed disclinations shared a common fractal dimension in the small length scale. Moreover, approximation of gauge theory in the limit of elastic continuum media enables the authors to account for their anomalous properties successfully.

An icosahedral phase formed during annealing of ion-irradiated Fe-Mo amorphous films

An icosahedral phase has been observed in the Fe-Mo system for the first time. The new icosahedral phase was formed during thermal annealing of ion-irradiated Fe-Mo amorphous films, which were prepared by sputtering from an Fe50Mo50 alloy ingot. The atomic concentration of this phase was determined by in situ energy-dispersive spectra (EDS) to be around Fe40Mo60 which has been proved to be a favourable composition for ion-induced amorphisation in this system.

Self-avoiding magnetic chains

We report a first experimental evidence for the self-avoiding walks in Fe-Cu thin films. Transmission electron microscopy showed that the observed self-avoiding chains result from aggregation of the magnetic Fe particles. Scaling analysis demonstrated that these chains were indeed self-similar structures with fractal dimensions ranging from 1.13 to 1.29. It was found that as the annealing temperature elevated, the fractal dimension of the chains with nearly the same width increased. Rich microstructures pertinent to the self-avoiding magnetic chains are described in detail, and a theoretical attempt based on magnetic interaction is proposed to account for the temperature effect.

Characterizing Hierarchical Structures of Natural Ivory

This paper presents a detailed investigation of the hierarchical and structural organization of the collagen-based aggregates in ivory. Ivory from African elephants is selected as the prototype in this study. A sophisticated architecture composed of collagen fibers and hydroxyapatite-like particles is revealed by optical microscopy, scanning electron microscopy and transmission electron microscopy. X-ray diffraction and TEN with selected area diffraction are employed to analyze the structure. Electron spectroscopy for chemical analysis and infrared absorption spectroscopy give information about the composition and chemical environment of the atoms in ivory. It is found that the structure of ivory has a three-level hierarchical organization, which includes both organic and inorganic materials. In the structure the inorganic material exists inside an organic framework, located outside of the collagen fibrils in the extrafibrillar volume. This inorganic structure has a polycrystalline form. Both the chemical compositions and the chemical environment of the atoms in the hydroxyapatite-like particles in ivory are different from those in natural hydroxyapatite.

The flow characteristics of thick films of conductive inks

SummariesThe resolution of screen printing inks is strongly influenced by the flow characteristics of thick film inks. The printed line resolution is decided by the first stage of the flow of inks. In the drying and firing period, the line resolution decreased due to the existence of second-stage flow, which is caused by the decrease in viscosity due to the increase of temperature, and by the softening and melting of the binder.Some methods are presented to eliminate the phenomenon of second flow.RésuméLa résolution des encres sérigraphiques est influencé fortement par les caractéristiques d’écoulement des feuilles épaisses des encres. La résolution de la ligne d’imprimés est décidée par la première étage d’écoulement des enres. Au cour de la période de séchage et de cuisson; la résolution de la ligne diminue à cause de l’existence d’une deuxième étage d’écoulement provoquée par la diminuation de la viscosité en fonction de la température et par le ramollissement et fusion du liant.On présente quelques méthodes pour éliminer le problème du second écoulement.ZusammenfassungDie Auflösung der Siebdrucke wird stark beenflüßt von des Fleißeigenschaften der dicken Filme der Druckfarben und auch von der Auflösung der Druckzeile von der ersten Stufe der Druckfarbenflie ens bestimmt. Während der Trocken-und Erhitzungzveit, die Druckzeilen-auflösung sich vermindert wegen des zweiten Fließens durch die Viscositätsverminderung bei der Wärmezunahme und der Erweichung und Erschmelzen des Bindermittels.Einige Methoden werden um das Phänomen zweier Fließens zu beisetigen dargestellt.