Preparation of crystals for channeling University of Ferrara V. Guidi Department of Physics and INFN, Via Paradiso 12, I Ferrara, Italy A. Vomiero INFN Laboratori Nazionali di Legnaro, Viale Università 2, I Legnaro (PD), Italy

To remove organic and metallic impurities, the wafers are degreased in trichloroethylene, acetone, and isopropanol.To remove organic and metallic impurities, the wafers are degreased in trichloroethylene, acetone, and isopropanol. Wafers are cleaned in a solution of water, hydrogen peroxide, and ammonium hydroxide (5:1:1) at 75 °C for 10 min.Wafers are cleaned in a solution of water, hydrogen peroxide, and ammonium hydroxide (5:1:1) at 75 °C for 10 min. A short dipping in diluted hydrofluoric acid (10% in weight).A short dipping in diluted hydrofluoric acid (10% in weight). The wafers are washed in water,hydrogen peroxide and hydrochloric acid (4:1:1) at 75 °C for 10 min.The wafers are washed in water,hydrogen peroxide and hydrochloric acid (4:1:1) at 75 °C for 10 min. Preparation of the samples-1

We attempt the removal of such layer by a wet planar etching (HF,HNO 3,CH 3 COOH). Dicing of the samples by a diamond-blade saw avoiding alignment with major crystalline axes. Dicing of the samples by a diamond-blade saw avoiding alignment with major crystalline axes. Defects are induced by the dicing saw (a surface layer estimated to be as thick as 30  m is rich in stratches, dislocations, line defects and anomalies). Defects are induced by the dicing saw (a surface layer estimated to be as thick as 30  m is rich in stratches, dislocations, line defects and anomalies). Preparation of the samples-2

70 GeV Extraction efficiency for 70-GeV protons. Recent results: (*, strips, 1.8, 2.0, and 4 mm long), results of ; (, “O-shaped” crystals 3 and 5 mm), and of 1997 ( , strip 7mm). Also shown (o) is the Monte Carlo prediction for a perfect crystal with 0.9 mrad bending. Results-1 Example of the bent crystal plate

Results-2 Surface treatment proved to be useful to improve the quality of the extracted beam Images of the 70 GeV protons deflected through mechanically treated and chemically polished crystals Mechanically polished Chemically polished

Study of crystal surface In order to study the optimal procedure to remove defects, we have prepared several Si-samples. some samples have been chemically polished by wet planar etching. some samples have been chemically polished by wet planar etching.

AFM measurements AFM images of the surface of an as-diced Si crystal (left up) and after 40 min chemical etching (left down). Chemical polishing enhances the standard roughness (R a ) (right up), which tends to decrease for longer etching times (right down).

30  m As-cut sample A layer as thick as 30  m is rich in defects 2.0 MeV RBS-channeling  particles spectra

Chemically polished HF 49%, HNO 3 70%, CH 3 COOH 100% (2:15:5) Damage stop 2.0 MeV RBS-channeling  particles spectra

The enhanced yield of the mechanically cut sample (0.5M) with respect to the layer after 30 min of etching (0.5/30C) is attributed to the presence of a more disordered surface structure.

2.0 MeV RBS-channeling proton spectra A lower dicing speed (0.5 mm/min) seems to create a smaller dead layer. A lower dicing speed (0.5 mm/min) seems to create a smaller dead layer. The etched samples exhibit enhanced channeling indication of removal of The etched samples exhibit enhanced channeling indication of removal of the amorphized layer. the amorphized layer.

We understood the physical reasons for such a behavior through characterization of the crystal surfaces. We understood the physical reasons for such a behavior through characterization of the crystal surfaces. Chemical etching improves channeling efficiency and leads to better performance than conventional mechanically treated samples. Chemical etching improves channeling efficiency and leads to better performance than conventional mechanically treated samples. Extraction efficiency of the order of 85% was repeatedly obtained at IHEP Protvino for an impinging intensity as high as protons. Extraction efficiency of the order of 85% was repeatedly obtained at IHEP Protvino for an impinging intensity as high as protons. Conclusions