ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03776.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The role of surface engineering for controlling structural ceramic properties is reviewed. Initially, a perspective of the effects of an unmodified surface state on fracture, adhesion, tribological properties, and degradation is given. Ceramic surface modification techniques including laser, ion, ion‐beam‐assisted deposition, and plasma‐assisted deposition are then discussed with regard to how each non‐equilibrium technique affects bulk and surface properties. The importance of experiments, process and materials characterization, and modeling for understanding changes in localized bonding, chemistry, and structure is emphasized. Although not exhaustive, a broad guide to important literature i

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03777.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Scanning tunneling microscopy (STM) images of the cubic β‐SiC (100) and β‐SiC (111) surfaces are taken after annealing to 1200°C to eliminate the surface oxide. Low‐energy electron diffraction (LEED) patterns of the β‐SiC (111) surface show a 6 √ 3 × 6 √ 3 geometry, while STM images show a 6 × 6 geometry. Contrast reversal is observed as tunneling voltage bias is reversed. SpectroscopicI/Vmeasurements indicate the presence of a graphite layer on the top surface. A model of the surface is proposed where an incommensurate graphite monolayer is grown over a (1 × 1) Si‐terminated β‐SiC (111) surface. This model helps to explain the discrepancy between the 6 √ 3 × 6 √ 3 LEED pattern and the 6 × 6 geometry observed in STM images. Charge transfer between certain carbon atoms and silicon atoms gives rise to the 6 × 6 geom

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03778.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The binding of vapor‐deposited metal and metal oxide films to Al2O3(0001) and fused silica was investigated using thermal desorption spectroscopy combined with mass spectrometric detection of the desorbed species. The experimental value forEd, the activation energy of desorption, is compared withHL, the calculated bond enthalpy value for an adsorbed metal‐surface oxygen bond. For Ga and Ga2O on Al2O3(0001) and fused silica, the calculated value 2HL(Ga‐O) = 200.6 kJ·mol‐1agrees with experimentalEdvalues and indicates that two gallium‐oxygen bonds are broken in the desorption process (Ed= 2HL). For Pb and Sn on Al2O3(0001) and fused silica, the calculated values 3HL(Pb–O) and 3HL(Sn–O) agree with experimentalEdvalues (Ed= 3HL). For Cr adsorbed on Al2O3,HL(Cr–O) = 111.1 kJ·mol‐1is calculated for one Cr‐surface oxygen bond. This value agrees, within experimental error, with Stubican's values for the activation energy of surface diffusion for Cr of 110 ± 12, 121 ± 12, and 119 ± 12 kJ·mol‐1on Al2O3, MgO, and MgAl2O4, respectively. A calculated value of 3HL(Cr–O) = 333.3 kJ·mol‐1agrees within experimental error with literature values for activation energy of volume diffusion of Cr in Al2O3, MgO, and MgAl2O4, Agreement between experiment and theory suggests that in these cases the surface bond breaking process involved in desorption and/or diffusion is described by an integral number of metal‐oxygen bonds similar to those in an appropriately chosen bulk oxide model. This agreement suggests that the binding model may be useful in predicting and/or correlating appr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03779.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The surfaces of highly oriented pyrolytic graphite (HOPG) samples were treated using two different methods, exposure to an energetic oxygen ion beam and immersion in an oxygen ion plasma, and the reactions which occur during treatment were characterized using high‐resolution electron energy loss spectroscopy (HREELS), temperature programmed desorption (TPD), and scanning tunneling microscopy (STM). Both surface treatments result in similar oxidation species. The results of this investigation provide spectroscopic evidence for the presence of semiquinone functionalities on sputtered and oxidized HOPG. STM images are presented to quantify the increase in defect sites after oxygen ion sputtering and to correlate defect site density with reactivit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03780.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

A deposition chamber is described comprising a unique broad‐beam, high‐flux (>2 mA/cm2), low‐energy (<100 eV) molecular and atomic nitrogen source suitable for growth and/or surface modification of ceramic thin films. Atom flux is generated by collisionally neutralizing and dissociating a diatomic nitrogen ion beam impinging a specially shaped surface interposed between the ion source and the substrate to be modified. The dissociation surface functions as a „funnel” to give the resulting neutral beam a tight geometric focus. In addition, our chamber possesses the unique capability of surface analysis at high pressures (mTorr) during thin‐film formation through the use of pulsed time‐of‐flight ion scattering techniques. This allows continuous monitoring (and control) of film stoichiometr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03781.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Positron annihilation techniques have been applied to study the pore diameters and volumes of 11 crystalline and amorphous zeolites. The data, consisting of the number of counts per channel recorded on a multichannel analyzer, were analyzed by means of the POSITRONFIT program. The data were presented as four lifetimes, τ1to τ4, with their associated intensities,I1toI4. The pore volumes reported here were based on a quantum mechanical model. The derived volumes are in reasonable agreement with pore volumes obtained with X‐ray and other data. The intensity of our fourth positron lifetime correlates with Brunauer–Emmett–Teller measurements of the surface area of the powders. These results are consistent with two studies by other

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03782.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Using laser specular reflectance, the optical rms roughnesses (σ0'S) of 42 polycrystalline aluminas (PCA's) were determined. From these conventional experimental results, a nomogram was constructed so that single grazing angle (α) measurements could be used to predict σ0. Subsequently, the nomogram was reassessed using five commercially important PCA's and one single‐crystal sapphire (SC). The outcomes were twofold: that this nomogram was valid for PCA's over the range of 0.28 σ00.10 μm, but that the nomogram was invalid for SC sapphire. When the conventional experimental method was compared with the nomogram method at three different single‐angle values, a 1:1 correspondence was observed for α= 78°, 80°, and 82°. The present noncontact method is advocated for speed and cleanliness, particularly when a quality assurance metho

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03783.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Strength and energy criteria for interface delamination are given for composite systems involving anisotropic fibers. The tensile strength of planar interfaces is measured with a modified laser spallation experiment involving a laser Doppler displacement interferometer. The technique for achieving desired interface properties is demonstrated on an Nb/Al2O3, interface. In the as‐deposited state, the strength is determined to be 0.28 GPa. The interface strength is controlled with sputter‐deposited Cr and Sb interlayers. The strength of Nb/Al2O3interfaces varies from 0.28 to 0.35 GPa when the Cr layer thickness varies from 1 to 50 Å. The strength is reduced to 0.16 GPa with Sb thickness of

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03784.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In a reducing atmosphere, SiO2as an impurity in SiC can react to form SiO and CO gases. Likewise, oxygen in the atmosphere can also lead to the same gaseous species. Experimental data are reported on the rate of weight loss in H2‐H2O atmospheres of porous SiC containing residual SiO2. The amount of residual SiO2was varied by passive oxidation of the porous SiC prior to heating in the reducing atmosphere. The data are compared to a model of active corrosion to determine the mechanism of weight loss and to identify the gas species present in SiC with SiO2as an impurit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1993.tb03785.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY