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Optimal crystal surface for efficient channeling in the new generation of hadron machines
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Image of FIG. 1.
FIG. 1.

(Color online) Schematic (not to scale) of the application of bent crystal for beam steering. The impact parameter and the impinging angle of beam are shown. The surface roughness of the lateral face of the crystal (parallel to beam direction) is required to be lower than the impact parameter ( for beam halo of LHC) for beam steering using the channelling effect.

Image of FIG. 2.
FIG. 2.

(Color online) AFM pictures of the silicon crystal: (a) just as cut, (b) after etching according to the procedure in Ref. 10, and (c) after chemical etching according to the procedure in Ref. 9. The scrapes due to the blade are visible in the as-cut sample, while they are nearly completely removed after chemical etching. The procedure of etching according to Ref. 10, based on fast and homogeneous oxidation of silicon and subsequent erosion of silicon oxide, allows removal of the surface dead layer without the formation of undesired craters worsening the surface flatness. is more than five times lower with respect to the preparation methodology according to Ref. 9.

Image of FIG. 3.
FIG. 3.

c-RBS spectra on silicon crystal oriented along the [110] direction, after chemical etching, using (a) particles and (b) protons, , IBM geometry, and scattering angle . The dashed spectra refer to random orientation of the crystal. The investigation was carried out down to about 1.5 and deep into the crystal for particles and protons, respectively. For both alpha particles and protons the surface (2.2% and 2%, respectively) is close to the semiempirical value for a perfect crystal (see Ref. 13).


Generic image for table
Table I.

Standard roughness and surface (using particles) of silicon crystals just after cut and after chemical etching. is defined as follows: , where is a height record of an image and is the height average. Results are based on AFM and -RBS analyses are compared with numerical data from Ref. 9.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Optimal crystal surface for efficient channeling in the new generation of hadron machines