摘要:

We have studied the lattice recovery by rapid thermal annealing ofSi+-implanted InP using Raman spectroscopy. The crystallinity recovery for different annealing temperatures of samples totally amorphized by the implantation can be monitored by means of their Raman spectra. However, free-charge coupling with the LO mode and possible misorientation of the recrystallized material may alter substantially the first-order Raman spectrum, making it unreliable for a good characterization of the lattice recovery. The study of second-order Raman spectrum overcomes the problems present in the analysis of first-order Raman spectrum and provides suitable criteria to assess the recrystallization of the implanted and annealed samples. After rapid thermal annealing at 875 °C for 10 s, the intensity of the second-order peaks approaches 70&percent; of its value in virgin InP, and third-order Raman peaks are also clearly detected, evidencing the good lattice recovery achieved. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365753

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Microstructural modifications (amorphization, lattice deformation, phase transformations) in alumina induced by implantation of zirconium, copper, or titanium ions and by postimplantation thermal annealings were studied using grazing incidence x-ray diffraction. It was shown that the amount of lattice deformation and the type of damage resulting in the lattice depend on the ion implanted. When zirconium was implanted, the alumina lattice was highly deformed. Amorphization was observed when a high ion dose was implanted. Copper implantation led to the formation of gamma alumina. With titanium ions, very high strain was created and delta alumina was formed. After postimplantation annealings, lattices returned to their equilibrium state through crystallization of alpha alumina and precipitation of oxides of the implanted species(ZrO2, CuOandCuAl2O4,andTiO2). ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365736

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We study the failure of planar random fiber networks with computer simulations. The networks are grown by adding flexible fibers one by one on a growing deposit [K. J. Niskanen and M. J. Alava, Phys. Rev. Lett.73, 3475 (1994)], a process yielding realistic three dimensional network structures. The network thus obtained is mapped to an electrical analogue of the elastic problem, namely to a random fuse network with separate bond elements for the fiber-to-fiber contacts. The conductivity of the contacts (corresponding to the efficiency of stress transfer between fibers) is adjustable. We construct a simple effective medium theory for the current distribution and conductivity of the networks as a function of intra-fiber current transfer efficiency. This analysis compares favorably with the computed conductivity and with the fracture properties of fiber networks with varying fiber flexibility and network thickness. The failure characteristics are shown to obey scaling behavior, as expected of a disordered brittle material, which is explained by the high current end of the current distribution saturating in thick enough networks. For bond breaking, fracture load and strain can be estimated with the effective medium theory. For fiber breaking, we find the counter-intuitive result that failure is more likely to nucleate far from surfaces, as the stress is transmitted more effectively to the fibers in the interior. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365737

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Analytic expressions are derived for the strain field due to a lattice-mismatched quantum wire buried in an infinite medium whose cross-section is composed of any combination of line elements and circular arcs. Expressions for the strain field for rectangular, triangular and circular quantum wires are found confirming published results. For the rectangular wire, useful limiting relations are obtained for the stress components close to the edge of the wire. Good agreement is demonstrated with measurements of lattice spacing reported by Chen &etal; [Appl. Phys. Lett.65, 2202 (1994)] for an In0.2Ga0.8As/GaAs rectangular wire if the indium concentration is assumed to be 24&percent;. The strain field of a single AlGaAs/GaAs crescent-shaped wire, with and without lateral wells, is presented. The lateral wells introduce only minor modifications to the strain distribution when compared to a wire of the same thickness but without lateral wells. For a crescent-shaped quantum-wire stack, it is found that the strain field of each wire is almost independent of other wires in the stack when the wire separation is five times the thickness or more. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365738

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article presents a quantitative determination of static deformation at a nanometer scale of a surface caused by the tip of an atomic force microscope. An analysis of cantilever displacements while in contact with the surface leads to a directly measurable dimensionless parameter which is well sensitive to surface deformation. The method is specifically aimed at stick/slip friction measurements like on layered compounds, likeTiS2or on a relatively rigid surface of an ionic crystal, in this study NaCl [100]. Stick/slip friction images offer a possibility to investigate details of strain-dependent deformation. The observed deformation inTiS2could play an important role in the occurrence of strong stick/slip friction in this and other layered materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366541

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fabry–Perot laser interferometry is used to obtain nanosecond time resolved particle velocity histories of the free surfaces of copper, tantalum, or magnesium disks driven by detonating triaminotrinitrobenzene (TATB)-based charges and of the interfaces between detonating TATB and transparent salt crystals. Detonation reaction zone profiles are measured for self-sustaining detonation waves propagating through various thicknesses of LX-17 (92.5&percent; TATB and 7.5&percent; KelF binder) and pure ultrafine particle size TATB. The experimental records are compared to particle velocity histories calculated with the DYNA2D hydrodynamic code using the ignition and growth reactive flow model. The calculations yield excellent agreement with the experimental records for LX-17 using an unreacted von Neumann spike pressure of 33.7 GPa, a reaction rate law which releases 70&percent; of the chemical energy within 100 ns, and the remaining 30&percent; over 300 additional ns, and a reaction product equation of state fit to cylinder test and supracompression data with a Chapman–Jouguet (C–J) pressure of 25 GPa. The late time energy release is attributed to diffusion controlled solid carbon particle formation. Ultrafine TATB, pressed to a lower density(1.80 g/cm3)than LX-17(1.905 g/cm3),exhibits lower unreacted spike and C–J pressures than LX-17 but similar reaction rates. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365739

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present an analysis of the stability of a dendrite against a small perturbation to the tip velocity. We find that dendritic growth in pure metals and alloys will become unstable above some upper critical undercooling&Dgr;T2*.In alloys above a critical concentration, dendritic growth may also become unstable below a lower critical undercooling,&Dgr;T1*.In the example systems studied, Ni–Cu and Ag–O, the location of these unstable regions shows remarkably close agreement with the onset of spontaneous grain refinement. We obtain values of&Dgr;T2*for Ni and Ag of 195 K and 160 K, respectively, in good agreement with the observed values of 170 K and 133–153 K. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365740

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Properties of physical vapor deposited diamondlike carbon (DLC) films and the migration of hydrogen inH+and4He+ion implanted and hydrogen co-deposited DLC films have been studied. Measurements utilizing Rutherford backscattering spectrometry showed that the films studied have an average mass density of 2.6±0.1g/cm3. The bonding ratiosp3/sp2is typically 70&percent; measured with the electron spectroscopy for chemical analysis technique. Impurities and their depth distributions were deduced from the particle induced x-ray emission and secondary ion mass spectrometry (SIMS) measurements. Distributions of implanted and co-deposited hydrogen were measured by the nuclear resonance reaction1H(15N,&agr;&ggr;)12Cand SIMS. It was found that annealing behavior of implanted H in DLC has a diffusion like character. The obtained diffusion coefficients resulted in the activation energy of 2.0±0.1 eV. It was observed that in H co-deposited DLC films the temperature of H release varied between 950 and 1070 °C depending on the H concentration. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365741

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article we report the results of the scanning tunneling microscope study of the surface morphology of copper films grown by metalorganic chemical vapor deposition from the precursor Cu(tbaoac)2. Films ≈100 nm in thickness were grown by varying the reactor pressure. The images reveal the crucial role of the reactor pressure and growth rate on the morphology and grain growth of the films. Films grown at a low growth rate have a smooth surface with small well connected grains of≈10–40 nm diameter with relatively lower resistivity, while films grown at higher growth rates have rougher surfaces and larger grain sizes of≈10–100 nm diameter with poor connectivity that leads to higher resistivity. The correlation of the morphology with resistivity(&rgr;)and the temperature dependence of&rgr;in the range 300–4.2 K was investigated. Comparison with the&rgr;of pure bulk copper shows that these films have much higher resistivities. A large part of the high resistivity at room temperature arises from an enhanced temperature dependent part of&rgr;and is not due to an enhancement of the residual resistivity alone. The films exhibit deviations from Matthiessen’s rule. From a semi-quantitative analysis of the data using existing theories we could assign the large&rgr;as well as the temperature dependence of&rgr;to grain boundary scattering and surface scattering. However, forT>50K we find that an extra temperature dependent&rgr;term which may be related to enhancement of electron-phonon interactions by the rough film surface is required. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365742

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The growth kinetics of amorphous interlayer (a-interlayer) and formation of crystalline silicide phases in ultrahigh vacuum deposited polycrystalline Er and Tb thin films on (001)Si have been investigated by cross-section transmission electron microscopy. The growth of the amorphous interlayer in both Er/Si and Tb/Si systems was observed to exhibit similar behaviors. The growth was found to follow a linear growth law initially in samples annealed at 190–240 °C. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be 0.5 eV, 15.5 nm, and 0.35 eV, 16 nm in Er/Si and Tb/Si systems, respectively. Crystalline silicides (ErSi2−xorTbSi2−x) were found to form at the amorphous interlayer/Si interfaces in samples after prolonged and/or high-temperature annealing. Simultaneous growth of the a-interlayer and crystalline phase was observed and the growth rate of a-interlayer was faster than the growth of epitaxialErSi2−xandTbSi2−xphases in samples annealed at 270–300 °C in Er/Si and Tb/Si systems, respectively. The competitive growth can be understood from energetic consideration. A high density of recessed amorphous regions were found to form between isolated epitaxial silicide regions which led to uneven silicide/Si interfaces and eventually pinholes in the silicide films at high temperatures. The formation mechanism of rough silicide/Si interface is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365743

出版商:AIP    

年代:1997

数据来源: AIP