摘要:

Positron annihilation spectroscopy on Zn‐doped InP has revealed the presence of a defect with a positron lifetime of ∼330 ps in samples in which the carrier concentration has saturated. This lifetime is attributed to a complex involving vacancies and Zn atoms. A model is proposed in which this complex has a (−/0) level near the bottom of the band gap, and undergoes a large inward lattice relaxation upon the transition to the neutral charge state, causing a reduction in the positron lifetime to ∼281 ps. This model explains the positron annihilation results on annealed samples and at low temperatures, and is supported by Hall effect measurements. The concentration of these complexes is less than 1017cm−3. Therefore, these complexes cannot solely account for the observed discrepancy between the carrier concentration and the Zn concentration in very heavily Zn‐doped InP. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363188

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The microstructural properties of stoichiometric surface and buried Si3N4films, fabricated with15N ion implantation into Si wafers, are studied using the extended x‐ray absorption fine structure (EXAFS) and near‐edge x‐ray absorption fine structure (NEXAFS) spectroscopies. Complementary information about the film composition and structure is provided by nuclear reaction analysis (NRA) and cross‐section transmission electron microscopy (XTEM). The films have been characterized in the as‐implanted state and after annealing in the temperature range 1100–1200 °C. For all the examined films, the N/Si ratio at the peak of the nitrogen profile, as measured by NRA is 1.33, a value that corresponds to stoichiometric nitrides. However, small compositional deviations towards a N‐rich composition are detected by EXAFS in the surface nitrides. The excess nitrogen is also detectable in the NEXAFS spectra, where it introduces a characteristic resonance line superimposed to the absorption edge. Finally, XTEM observations confirm the formation of the nitride layers and reveal different degrees of damage at the Si3N4/Si interface for the low and high energy implantations, respectively. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363189

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The propagation of ultrasonic plane waves through a material can be expressed by a transfer function related to the attenuation and the velocity dispersion. These acoustical parameters are determined from ultrasonic spectroscopy. Experiments were performed on different polymers and for the particular materials we have tested it was observed that amorphous materials can be considered as low‐dispersive media, whereas in semicrystalline materials the velocity dispersion cannot be neglected. These experimental results are compared with those deduced from the Kramers–Kronig relations. These analytical expressions, assuming the causality conditions of every physical system, are verified for different materials proving the validity of our measurements. Other interests of the Kramers–Kronig relations are also discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363190

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The propagation of thermoelastic harmonic waves in bilaminated periodic waveguide is studied in the context of the generalized theory of thermoelasticity. A continuum mixture theory is developed for waves traveling in the direction parallel to the layering. As a result, the problem is transformed into a quasi‐one‐dimensional one. The resulting approximate expressions are found useful in obtaining a qualitative description of the response. The symmetric mode of an exact solution is used to check the validity of the mixture theory. Quasi‐elastic and quasi‐thermal modes are investigated for the cases when the thermal relaxation time is either included or neglected. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363191

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We study by means of numerical simulations the size dependences for sound velocity of model nanostructures. We use molecular dynamics to obtain the zero temperature size dependences of the propagation velocity of mechanical perturbation for rod‐shaped nanostructures with free surfaces. The particles interact with the Stillinger–Weber potential for silicon. We consider the longitudinal sound propagation in the (001) direction only. The bulk limit is reached very quickly and the longitudinal velocity is already independent of the cross section for a nanofiber larger than 40×40 A˚. We also study velocity for structures without free surfaces and the effect of changing the magnitude of the triplet interaction potentials. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363192

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The temperature dependence of the solid solubility [CsCoSi2(B)] and the lattice diffusion coefficient [DCoSi2(B)] of boron in single‐crystalline cobalt disilicide (CoSi2) has been investigated between 450 and 1000 °C. BothCsMCoSi2(B) andDCoSi2(B) are found to be considerably higher than the corresponding quantities in silicon. Using a thermodynamical interpretation, the experimental data show that boron‐doped CoSi2can be described as a regular solution in the dilute limit with an enthalpy of solution of ∼−0.4 eV. The experimental data and theoretical estimates of the excess enthalpy of solution indicate a weak interaction of boron with the silicon and cobalt atoms in CoSi2suggesting that the boron atoms occupy sites in the CoSi2lattice with a small contribution to the Gibbs energy of the solution phase. The diffusion data yield a high mobility of the boron atoms with an activation energy of ∼2.0 eV for the lattice diffusion coefficient which is ∼1.0 eV lower than that reported for the self‐diffusion of Si(Ge) and Co in CoSi2. Boron is a small atom which can occupy interstitial sites in the relatively opened CaF2structure of CoSi2, and it is argued that the diffusion of boron may occur via a mixed process where interstitial/substitutional interchange takes place, including trapping and detrapping of the boron atoms. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363202

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Micrometer‐sized homojunction structures can be formed by applying strong electric pulses, at ambient temperatures, to Li‐doped, floating zonen‐Si. Two such junctions, arranged back to back, act as a transistor, as evidenced by electron‐beam‐induced current and current–voltage measurements. The structures are created during a time ranging from ∼100 ms to a few seconds, depending on the size of the structure. The phenomenon is similar to what was observed earlier in CuInSe2and was explained there by thermally assisted electromigration of Cu. In the case of Si doped with Li we can use secondary‐ion‐mass spectrometry to detect the redistribution of Li after electric‐field application. Such a redistribution is indeed found and corresponds to ann+‐p‐nstructure with thepregion extending at least ∼20 &mgr;m into the bulk of Si. Structures created in Si doped with Li in this way are stable for at least 13 months after their creation. We ascribe this to the large difference between Li diffusivity at the local temperature that is reached during structure formation (∼400 °C; 10−8cm2/s) and at room temperature (∼10−15cm2/s). ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363132

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Finite element (FE) analysis and transmission electron microscopy (TEM) observations have been used to model stress relaxation in InAs quantum dots deposited on (001) GaAs. TEM observations show that these islands are coherently strained and the corresponding strain contrast is simulated using the dynamical electron diffraction contrast theory. The dot strain fields used for the TEM contrast simulations are deduced from FE calculations. These calculations show that elastic stress relaxation mainly occurs at the crest of the island and that the underlying substrate is under tension. That experimental TEM images and simulated images should match shows that the FE method of determination of the dot strain fields is valid (even in the case of microscopic objects), and that the shape of islands can be specified. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363193

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ti and N were implanted into soda lime glass to doses up to 4.5×1017cm−2to reduce solar load and infrared transmission. Analysis of the Ti+N implant distributions by Rutherford backscattering spectrometry and x‐ray photoelectron spectroscopy (XPS) revealed profiles which closely followed each other as designed by the selection of implant energies. XPS, x‐ray diffraction, and selected area electron diffraction in transmission electron microscopy also confirmed the existence of a crystalline B1‐type, cubic TiN layer, 140 nm wide, at doses greater than 9×1016cm−2. Optical measurements showed that the fraction of infrared radiation reflected was increased by almost a factor of 4 compared to an increase of 1.8 in the visible region. The percentage of the total solar energy rejected reached 80% at the highest dose, indicating that the buried TiN layer is highly effective in reducing solar energy transmission. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363194

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The growth and morphology of intermetallic compounds between the solder and substrate play an important role in the solderability and reliability of electronic solder joints. Solder on thin films, as in chip joint, acts as an electrical and mechanical/physical interconnection between the chip and the substrate. We have studied the interfacial reactions between eutectic SnPb (63Sn37Pb, wt%) and Cr/Cu/Au thin films. Our results found here have been compared to the solder reaction on bulk Cu. The eutectic solder has 7° of wetting angle on Cr/Cu/Au thin films rather than 11° on Cu substrate. Sideband around the solder cap was found in both the thin film case and the Cu case. Spalling of Cu6Sn5compound grains occurred in the thin‐film case when the Cu film was consumed but not in the case of bulk Cu. We observed a shape change from hemispherical ‘‘scallops’’ to spheroids before spalling took place. The shape change is assisted by ripening a reaction among the scallops. We have calculated a critical size of the scallop, depending on the Cu film thickness, when the shape change or spalling starts. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363728

出版商:AIP    

年代:1996

数据来源: AIP