the si nanowire arrays used in the first part 
 of this study were made using a top - down process by inductively coupled 
 plasma reactive ion etching ( icp - rie ) at cryogenic temperatures . e - beam 
 lithography , e - beam evaporation , and lift - off was used to define a 
 hard - mask with an array of circular ni pads of varying diameter onto 
 a si   wafer . the patterned samples were then loaded into the 
 rie system and cooled to 108 c . etching of the samples 
 was done with a set pressure of 10 mtorr and a strike pressure of 
 30 mtorr . after rie processing , 
 the ni hard mask was removed using 32% hcl and a ( 7:1)-buffered hf 
 dip was done to remove the native oxide of si from the surface . nonideal 
 o2 flow rates caused inhomogeneous lateral etching rates 
 leading to tapered wires , typically with a rounded triangular cross - section 
 corresponding to the higher si { 100 } etching rates . the nanowires were grown in an lpcvd reactor with au colloids dispersed 
 on the substrate as catalyst . a growth pressure of 3 mbar at 515 c 
 under monosilane / hydrogen atmosphere leads to 111-oriented 
 nanowires as described in ref ( 40 ) . such si nanowires of 100 nm diameter were transferred 
 onto the tips of au wires with a diameter of 25 m using 
 the micromanipulation tool , e - beam pt - deposition and ion beam milling 
 in a fei dual - beam fib system ( supporting information ) . all irradiations were performed on a rotatable , heatable , 
 and tilted stage within an ion implanter . the array samples were irradiated 
 up to a total fluence of 5  10 cm ar in three steps , 1  10 cm , 2  10 cm , and 2  10 cm at 100 and 300 kev with an ion flux 
 of less than 2  10 cm h. these irradiations were done at an angle of 45 
 between the ion beam and the substrate normal , while rotating the 
 sample at around 50 rpm . samples were investigated before and after 
 each irradiation with a high - resolution sem in the dual - beam fib system . images 
 were made at an angle of 45 to the substrate normal and aligned 
 to the nanowire arrays . for the reproducible quantitative analysis 
 of the wires , after each irradiation step a semiautomated image analysis 
 protocol was followed ( supporting information ) .
silicon nanowires of various diameters 
 were irradiated with 100 kev and 300 kev ar+ ions on a 
 rotatable and heatable stage . 
 irradiation at elevated temperatures 
 above 300 c retains the geometry of the nanostructure and sputtering 
 can be gauged accurately . 
 the diameter dependence of the sputtering 
 shows a maximum if the ion range matches the nanowire diameter , which 
 is in good agreement with monte carlo simulations based on binary 
 collisions . 
 nanowires irradiated at room temperature , however , amorphize 
 and deform plastically . so far , plastic deformation has not been observed 
 in bulk silicon at such low ion energies . 
 the magnitude and direction 
 of the deformation is independent of the ion - beam direction and can not 
 be explained with mass - transport in a binary collision cascade but 
 only by collective movement of atoms in the collision cascade with 
 the given boundary conditions of a high surface to volume ratio .