摘要:

We have studied the structural properties of Molecular Beam Epitaxy grown thin Co films on &agr;‐sapphire (112¯0) substrates by high resolution x‐ray scattering measurements in the thickness range of 100 A˚ to 5000 A˚. The electron density profile perpendicular to the film plane was determined by x‐ray specular reflectivity measurements. The profile contains information about the total metal film thickness, an oxide layer on top of the film and about the surface and interface roughness. The total metal film thickness was compared with the number of coherently scattering atomic planes by taking radial scans through Bragg peaks parallel to the growth direction. Samples up to 400 A˚ total thickness (out‐of‐plane mosaicity 0.02○) show very strong Laue‐oscillations about the Co (0002)/(111) Bragg peak. Above a total thickness of 400 A˚ the oscillations vanish due to a loss in structural coherence. The combination of specular reflectivity and Bragg scans presents a powerful means to analyze the structural coherence of thin films.

ISSN:0021-8979    

DOI:10.1063/1.353846

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Type‐II (end of range) defects, produced by Ge+implantation, were investigated as possible ‘‘detectors’’ for quantifying nonequilibrium interstitial concentrations following B+implantation into silicon. The type‐II damage was created with a 100 keV (1×1015/cm2) Ge+implant into silicon followed by either a low‐temperature (550 °C) or a high‐temperature (800 °C) anneal. This resulted in the formation of either a layer of point‐defect clusters and small (≤50 A˚ in diameter) dislocation loops or a layer of larger (∼160–400 A˚ in diameter) fully formed dislocations loops. This material was subsequently implanted with 30 keV B+at doses between 7×1013/cm2and 2×1014/cm2. After a final 800 °C anneal, the concentration of atoms bound by the type‐II dislocation loops was measured. Results show that the concentration of interstitials bound by the type‐II dislocation loops increases with increasing B+dose. Relative to control sample values, the net concentration of interstitials trapped as a result of B+implantation varied from 7.0×1013/cm2to 1.8×1014/cm2over the dose range studied. Fully formed loops were also found to be ≥20% more efficient than clusters in trapping the interstitials generated under identical B+implant conditions. The difference is ascribed to the increase in equilibrium point‐defect concentration necessary to stabilize the smaller loops prior to coarsening.

ISSN:0021-8979    

DOI:10.1063/1.353847

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Amorphization of iron by boron implantation was studied by conversion electron Mo¨ssbauer spectroscopy and Rutherford backscattering techniques. The results indicate that the amorphization process depends on the thickness of the sample. After implantation at RT, the amorphous fraction amounting to 0.85 was found for 150 nm thick iron film whereas in the bulk sample this fraction reached only about 0.65. The residual crystalline &agr;‐Fe phase persists in the sample amorphized by B implantation in a wide concentration range corresponding to nominal compositions from Fe90B10to Fe65B35in clear distinction from melt‐spun and sputtered samples.

ISSN:0021-8979    

DOI:10.1063/1.353848

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The distribution of Fe implanted at medium (1–4×1014cm−2) and low (2×1012cm−2) doses into InGaAs and annealed with or without a cap is investigated and the degree of compensation of such implanted regions is assessed. Secondary ion mass spectrometry profiles of low dose implanted Fe reveal a substantial role of the capping layer. Fe concentrations below as well as above the estimated metal vacancy concentration produced by implantation are observed. The effect of the cap strongly depends on the wet chemical surface preparation before insulator deposition. A correlation of the magnitude of the Fe accumulation at the InGaAs surface with defect related photoluminescence intensity is established. On the basis of the substitutional‐interstitial diffusion model the barrier effects of the various caps for host and dopant atoms are analyzed. The best semi‐insulating properties were obtained for plasma enhanced chemical vapor deposition SiO2caped samples using a H2SO4:H2O2:H2O=1:1:125 surface preparation before deposition resulting in a 53% incorporation of Fe. A high electrical activation is proved directly by capacity‐voltage profiles.

ISSN:0021-8979    

DOI:10.1063/1.353797

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The production and annealing of radiation damage in GaSb Ne‐implanted at high energy are studied by transmission electron microscopy and Rutherford backscattering spectrometry in combination with the channeling technique. The anomalous swelling phenomenon of implanted GaSb, previously reported, is found to be related to the formation of voids and microtwins in the crystalline implanted layer. These defects appear when the introduced damage exceeds a critical amount and lead to the formation of a porous polycrystalline GaSb layer, whereas in most other III‐V materials an amorphous layer is formed. Provided the swelling is avoided, there is a good recovery of the lattice upon rapid thermal annealing at 600 °C. Otherwise, a heavily perturbed layer remains, containing voids, dislocations and, at sufficiently high doses, polycrystalline GaSb. From previously published results, it is inferred that the InSb behavior towards radiation damage is similar to that of GaSb.

ISSN:0021-8979    

DOI:10.1063/1.354090

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The depth profiles of10B and11B implanted into amorphous silicon have been analyzed by secondary ion mass spectrometry. Implantation energies between 0.4 and 5.0 MeV were used, and each sample was sequentially implanted with both10B and11B without changing the acceleration voltage but only the field in the mass analyzing magnet. A shift between the two profiles is clearly resolved and has been carefully studied as a function of ion energy. A maximum shift of 3.5% in mean projected range (Rp) is revealed at 0.6–0.8 MeV [Rp(11B)≥Rp(10B)], and for higher energies the ratioRp(11B)/Rp(10B) decreases slowly to a value of ∼1.006 at 5.0 MeV. This reverse shift (heavier isotope penetrates deeper) is attributed to a larger electronic stopping cross section (Se) for10B than for11B at a given energyEwhereSe∼Epandp≥0. The experimental data forRp(11B)/Rp(10B) andRp(11B) are compared with calculations, and it is demonstrated that the variation ofRp(11B)/Rp(10B) with ion energy hinges strongly on theSevsEdependence. A close velocity proportional dependence (p=0.50±0.03) is found to be valid up to ∼300 keV, and thenpdecreases gradually with a maximum inSe(p=0) at ∼2.0 to 2.5 MeV. A semiempirical expression is presented forSeand shown to yield excellent agreement withboththe relative isotope shift and the absolute range values; the deviations are less than 0.2% and 3.0%, respectively.

ISSN:0021-8979    

DOI:10.1063/1.353798

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy, and Raman studies on microstructures of hydrogenated silicon films that were fabricated by diluted‐hydrogen and hydrogen‐atom‐treatment methods are presented. The diluted‐hydrogen samples tend to show a very sharp line shape in the NMR spectra at substrate temperatures higher than 300 °C, and the addition of atomic hydrogen treatment can produce the same NMR spectra at a lower temperature of about 250 °C. The Raman scattering spectra show that the atomic hydrogen treatment creates the microcrystalline phase while the diluted‐hydrogen method produces amorphous phase plus a small quantity of microcrystalline phase. The infrared‐absorption spectra also indicate an increase of SiH2bonding configuration and a hydrogen content reduction when atomic hydrogen treatment is employed. The relation between the origin of the sharp line shape in the NMR spectra and the formation of the microcrystalline phase is also discussed. Together with increase of dark conductivity and reduction of the photo‐to‐dark conductivity ratio, these samples indicate that with appropriate hydrogen incorporation during deposition, and with plasma hydrogen treatment, these films should possess a much more compact structure. These results suggest that the degree of crystallinity of hydrogenated silicon films can be systematically adjusted. A qualitative model based on our experimental data is presented to illustrate the formation procedures of microcrystalline‐phase hydrogenated silicon under the influence of plasma hydrogen and hydrogen dilution.

ISSN:0021-8979    

DOI:10.1063/1.353799

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Using energy‐loss spectroscopy, energy dispersive x‐ray analysis, electron diffraction, and He+‐ion channeling the reaction of Fe during implantation into Si(111) has been investigated at various target temperatures and implantation doses. In samples implanted at 275 °C with 2.8×1017Fe+cm−2a continuous &agr;‐FeSi2layer accompanied by &agr;‐phase precipitates is formed. At 450 °C Fe agglomerates mostly in &agr;‐phase precipitates with only a few being &bgr;‐FeSi2. At 350 °C 1×1017Fe+cm−2produce precipitates electronically close to FeSi2but crystallographically poorly defined. At 4×1017Fe+cm−2a &bgr;‐FeSi2layer is formed at the surface and a 20‐nm‐thick &agr;‐FeSi2one followed by &agr;‐FeSi2precipitates deeper in the volume. Channeling reveals a minimum yield decreasing with dose indicating improved &agr;‐phase crystal quality. A sharp increase at 3.3×1017cm−2indicates an &agr;–&bgr; phase transition. FeSi has not been detected. Precipitates of well defined silicide phases are formed already during implantation. Dose and temperature have a profound influence on the phase formed.

ISSN:0021-8979    

DOI:10.1063/1.353800

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We conducted gas‐gun impact experiments on snow, with initial densities of 100–520 kg m−3and at temperatures from −2 to −23 °C and stress levels of 2–40 MPa. Carbon stress gauges were embedded in the snow to measure shock stress histories and arrival times. The unsteady and complex nature of the shock stresses necessitated the use of finite element and reverberation analysis techniques to determine the shock pressure‐density (P‐&rgr;) relationships for snow. Experimental results indicate that variations in initial snow density are reflected in differences in theP‐&rgr; deformation path. The pressure needed to compact snow to a specific final density increases with lower initial density. Snow deformation was not affected by initial temperature, but was found to be strain rate dependent. Estimated release moduli increased nonlinearly from 50 MPa at a peak compression pressure of about 15 up to 2700 MPa at a peak pressure of about 40 MPa. Calculated stress histories and shock arrival times agreed with measured values within 20%.

ISSN:0021-8979    

DOI:10.1063/1.353801

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The degree of shock energy localization within individual particles and between neighboring particles of different size was explored during shock‐wave consolidation of spherical metal powders. The thermoelectric voltage generated by the passage of a shock wave through a copper powder‐constantan powder interface was recorded. The sizes of the copper and constantan powders were varied between mean diameters of 40 and 98 &mgr;m. Shock‐wave pressures of 5 GPa were applied by flyer plate impact, and the resulting voltage versus time signals were collected with a 10 ns time resolution. In order to analyze the signals, a simulation of the thermocouple system was developed to account for the effects of multiple particle interactions and a slightly nonplanar copper‐constantan interface. The resulting simulated voltage versus time signals are a good match for the observed signals when the size ratio of the copper and constantan particles is less than a factor of 2, and reveal the preferential deposition of energy in smaller particles at the expense of larger particles within the size range examined. The amount of energy localized near particle surfaces was found to be a majority of all the energy, with a significant minority deposited throughout the particle bulk.

ISSN:0021-8979    

DOI:10.1063/1.353802

出版商:AIP    

年代:1993

数据来源: AIP