| 1. |
|
|
| 2. |
- Chen, C. C., et al.
(författare)
-
Different strain relaxation mechanisms in strained Si/Si1-xGex/Si heterostructures by high dose B+ and BF2+ doping
- 2002
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - 0168-583X .- 1872-9584. ; 198:02-jan, s. 57-63
-
Tidskriftsartikel (refereegranskat)abstract
- Strained Si/Si0.8Ge0.2/Si heterostructures are implanted at room temperature with 7.5 keV B+ and 33 keV BF2+ ions to a high dose of 2 x 10(15) ions/cm(2), respectively. The samples are subsequently subjected to three-step anneals (spacer anneal, oxidation anneal and rapid thermal anneal), which are used to simulate a real fabrication process of SiGe-based MOSFET devices. The damage induced by implantation and its recovery are characterized by 2 MeV He-4(+) RBS/ channeling spectrometry. A damage layer on the surface is induced by B+ implantation, but BF2+ ion implantation amorphizes the surface of Si/Si0.8Ge0.2/Si heterostructure. Channeling angular scans along the (110) axial direction demonstrate that the strain stored in the SiGe layer could be nearly completely retained for the B+ implantated and subsequently annealed sample. However, the strain in the BF2+ implanted/annealed SiGe layer has decreased drastically.
|
|
| 3. |
- Lindgren, A. C., et al.
(författare)
-
Characterization of strained Si/Si1-xGex/Si heterostructures annealed in oxygen or argon
- 2002
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:5, s. 2708-2712
-
Tidskriftsartikel (refereegranskat)abstract
- The strained Si/Si1-xGex/Si layer heterostructure heat treated from 700 degreesC to 950 degreesC in Ar (annealing) or O-2-C2H2Cl2 (oxidation) was characterized using high-resolution x-ray diffraction in combination with Rutherford backscattering. Only small changes to the structure are observed up to 800 degreesC, within the resolution limits of diffraction and backscattering. Severe strain relaxation occurs at 950 degreesC and the heterostructure tends to relax more during annealing in Ar than during oxidation in O-2-C2H2Cl2. The strain relaxation is mainly caused by interdiffusion of Si and Ge rather than formation of misfit dislocations. Diffusion of Si interstitials generated during oxidation into the heterostructure is suggested as the cause responsible for the less pronounced interdiffusion of Si and Ge in the oxidized samples.
|
|
| 4. |
- Zhang, Shi-Li, et al.
(författare)
-
Differences between interfacial and surface molybdenum in the formation Of TiSi2
- 2001
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:3, s. 1641-1646
-
Tidskriftsartikel (refereegranskat)abstract
- Backscattering and diffraction results are presented for the effects of an interfacial or a surface Mo layer on the formation of Ti-silicides during solid-state interaction between Ti films and Si substrates. It is shown that the interfacial and surface Mo are fundamentally different in their involvement in the Ti-silicide formation. The interfacial Mo induces the formation of C40 (Mo,Ti)Si-2 at the interface adjacent to the Si substrate already after annealing at 550 degreesC, in agreement with our previous results. Hence, the desired C54 TiSi2 can grow directly on top of the C40 (Mo,Ti)Si-2 at relatively low temperatures as a result of the template effect. The surface Mo is, however, found in a metal-rich silicide presumably (Mo,Ti)(5)Si-3 at 550-600 degreesC, which eventually converts to (Mo,Ti)Si-2 upon annealing at higher temperatures. Underneath this metal-rich silicide lies a fully developed C49 TiSi2 layer. Consequently, the formation of C54 TiSi2 in the presence of surface Mo follows the usual path of the C49-C54 phase transition. This important difference in the participation of Mo in the silicide formation spreads doubts about the validity of using interfacial Mo versus surface Mo to study the dominant mechanism(s) responsible for the enhanced formation of C54 TiSi2.
|
|
| 5. |
- Zhang, Zhibin, et al.
(författare)
-
Different routes to the formation of C54TiSi(2) in the presence of surface and interface molybdenum : A transmission electron microscopy study
- 2002
-
Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 17:4, s. 784-789
-
Tidskriftsartikel (refereegranskat)abstract
- Direct evidence revealing fundamental differences in sequence of phase formation during the growth of TiSi2 in the presence of an ultrathin surface or interface Mo layer is presented. Results of cross-sectional transmission electron microscopy showed that when the Mo layer was present at the interface between Ti films and Si substrates, C40 (Mo,Ti)Si-2 formed at the interface, and Ti5Si3 grew on top after annealing at 550 degreesC. Additionally, both C54 and C40 TiSi2 were found in the close vicinity of the C40 (Mo,Ti)Si-2 grains. No C49 grains were detected. Raising the annealing temperature to 600 degreesC led to the formation of C54 TiSi2 at the expense of Ti5Si3, and the interfacial C40 (Mo,Ti)Si-2 also began to transform into C54 (Mo,Ti)Si-2 at 600 degreesC. When the Mo was deposited on top of Ti, the silicide film was almost solely composed of C49 TiSi2 at 600 degreesC. However, a small amount of (Mo,Ti)(5)Si-3 was still present in the vicinity of the sample surface. Upon annealing at 650 degreesC, only the C54 phase was found throughout the entire TiSi2 layer with a surface (Mo,Ti)Si, on top of TiSi2 Hence, it was unambiguously shown that in the presence of surface versus interface Mo, different routes were taken to the formation of C54 TiSi2.
|
|
| 6. |
- Zhang, Zhibin, et al.
(författare)
-
Formation of C54TiSi(2) on Si(100) using Ti/Mo and Mo/Ti bilayers
- 2002
-
Ingår i: International Journal of Modern Physics B. - 0217-9792. ; 16:1-2, s. 205-212
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of Mo on the formation of C54 TiSi2 on Si (100) substrates is studied using crosssectional transmission electron microscopy. For a Ti/Mo bilayer on Si, the interfacial Mo film reacts with Ti and Si to form C40 (Mo,Ti)Si-2 at 550 degreesC. Crystal grains of metastable C40 TiSi2 and equilibrium C54 TiSi2 are found in the region near the interfacial (Mo,Ti)Si-2 layer due to the template phenomenon. Increasing the temperature to 600 degreesC leads to the growth of C54 TiSi2 throughout the film. No C49 grains can be detected. The findings confirm that the usual sequence for the formation of C54 TiSi2, i.e. the C49 TiSi2 forms first followed by a phase transition to the C54 TiSi2, is altered by the interposed Mo layer. For a Mo/Ti bilayer on Si, the surface Mo layer is found to be present sequentially in (Mo,Ti)(5)Si-3 at 550 degreesC, C49 (Mo,Ti)Si-2 at 600 degreesC and C54 (Mo,Ti)Si-2 at 650 degreesC. The bulk Ti beneath forms the C54 TiSi2 following the usual route through the C49-C54 phase transition. However, this transition is now enhanced, in comparison with the C54 TiSi2 formation with pure Ti, by the C54 (Mo,Ti)Si-2 atop that plays the role as a template precisely as the interfacial C40 (Mo,Ti)Si-2.
|
|
| 7. |
- Zhu, Guoying, et al.
(författare)
-
Environmental cadmium exposure and forearm bone density.
- 2004
-
Ingår i: Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine. - : Kluwer Academic Publishers. - 0966-0844 .- 1572-8773. ; 17:5, s. 499-503
-
Tidskriftsartikel (refereegranskat)abstract
- Environmental exposure to cadmium may give rise to osteomalacia combined with renal dysfunction, so called 'Itai-Itai disease', which was endemic in the heavily polluted area in Japan. The main focus of this study was to investigate whether environmental exposure to cadmium is associated with low bone mass in a population living near a smelter. A total of 790 persons (302 males and 488 females), who were all over 35 years old and resided in areas near a lead, zinc and cadmium smelter and in a control area in southeast China, completed a questionnaire, and bone mineral density was measured by SPA-4 single photon absorptiometry at the radius and ulna. Cadmium content of urine was determined by graphite-furnace atomic absorption spectrophotometry as a measure of dose. The present study shows that forearm bone densities were negatively correlated with urinary cadmium excretion (p < 0.001) and forearm bone density decreased linearly with age (p < 0.001) and urinary cadmium (p < 0.01), suggesting a dose-effect relationship between cadmium dose and bone mineral density. Based on the World Health Organization criteria, (bone mineral density < -2.5 SDs below the normal young adult), the prevalence of osteoporosis in women increased from 34.0% in the control area to 51.9% in the heavily polluted area (p < 0.01) among subjects over 50 years old, and the odds ratio value was 2.09 (95% CI: 1.08-4.03) for the highly polluted area compared with the control area. A striking observation in the study was a marked increase of the prevalence of fracture in the cadmium-polluted area in both sexes. It was concluded that environmental exposure to cadmium is associated with an increased loss of bone mineral density in both gender, leading to osteoporosis and increased risk of fractures, especially in the elderly and in females.
|
|
