The fabrication of silicon nanostructures by local gallium implantation and cryogenic deep reactive ion etching.

We show that gallium-ion-implanted silicon serves as an etch mask for fabrication of high aspect ratio nanostructures by cryogenic plasma etching (deep reactive ion etching). The speed of focused ion beam (FIB) patterning is greatly enhanced by the fact that only a thin approx. 30 nm surface layer needs to be modified to create a mask for the etching step. Etch selectivity between gallium-doped and undoped material is at least 1000:1, greatly decreasing the mask erosion problems. The resolution of the combined FIB-DRIE process is 20 lines microm(-1) with the smallest masked feature size of 40 nm. The maximum achieved aspect ratio is 15:1 (e.g. 600 nm high pillars 40 nm in diameter).

No differences in the incidences of old people's hip fractures between urban and rural populations--a comparative study in two Finnish health care regions in 1989.

In a prospective study, incidences of hip fractures among the aged in urban and rural populations were compared in two health care regions in Finland in 1989. Both the administrative and the more informative functional classification of the municipalities were used. During 1989, a total of 366 patients, aged 55 years and above, who had a permanent place of domicile in either one of the two health care regions, were treated for a fresh hip fracture. In both regions women sustained 80% of the fractures. No significant differences were found in the incidences of hip fractures between the urban and rural populations. However, a significant difference was found in the mean incidence between the towns of the two health care regions (t = 4.228, d.f. = 6, p < 0.01).