The fracture strength of silicon nanowires grown on a [111] silicon substrate by the vapor−liquid−solid process was measured. The nanowires, with diameters between 100 and 200 nm and a typical length of 2 µm, were subjected to bending tests using an atomic force microscopy setup inside a scanning electron microscope. The average strength calculated from the maximum nanowire deflection before fracture was around 12 GPa, which is 6% of the Young's modulus of silicon along the nanowire direction. This value is close to the theoretical fracture strength, which indicates that surface or volume defects, if present, play only a minor role in fracture initiation.

The fracture strength of ZnO nanowires vertically grown on sapphire substrates was measured in tensile and bending experiments. Nanowires with diameters between 60 and 310 nm and a typical length of 2 ñm were manipulated with an atomic force microscopy tip mounted on a nanomanipulator inside a scanning electron microscope. The fracture strain of (7.7 ± 0.8)% measured in the bending test was found close to the theoretical limit of 10% and revealed a strength about twice as high as in the tensile test. From the tensile experiments the Young's modulus could be measured to be within 30% of that of bulk ZnO, contrary to the lower values found in literature.

The electrical properties of vertically aligned silicon nanowires doped by ion implantation are studied in this paper by a combination of electron beam-induced current imaging and two terminal current-voltage measurements. By varying the implantation parameters in several process steps, uniform p-and n-doping profiles as well as p-n junctions along the nanowire axis are realized. The effective doping is demonstrated by electron beam-induced current imaging on single nanowires, and current-voltage measurements show their well-defined rectifying behavior.Semiconductor nanowires are expected to play a critical role in future electronic devices and sensors. 1 To make use of their semiconducting properties, doping is an important issue. Nanowires that form an epitaxial interface and thus are vertically aligned to the substrate are commonly grown by the vapor-liquid-solid (VLS) mechanism in which a metal catalyst forms eutectic droplets at the growing tips of the nanowires. 2 For silicon nanowires, a supply of Si vapor supersaturates these droplets with Si and leads to its precipitation at the liquid-solid (droplet-silicon) interface. Under the gold droplet, the nanowire grows as long as the Si vapor is present. Silicon nanowires reveal p-type conductance when they are grown using the VLS process without adding any dopant on purpose, but the resistivity is rather high (2 Ω cm 3 -400 Ω cm 4 ).Doping can be realized during the gas phase deposition process by adding dopants to the gas mixture in use for the nanowire growth. Dopant incorporation is reported for diborane, 4 trimethylboron, 5 phosphine, 3 and arsenic. 6 By changing the dopant source during growth, p-n junctions can be realized along the axis of the nanowire. 6,7 Little is known on the dopant incorporation mechanism, however. Therefore, it is not obvious to predict the doping concentration for a given process. Also, recent experimental results reveal the growth of a highly doped shell around the nanowire while doping during VLS growth. 8 As an alternative, reproducible and successful doping of nanowires can be achieved via ion implantation. This technique is a standard doping technique in top-down semiconductor manufacturing and offers the advantage to provide for precise control over the total dose of dopants, depth profile, and most importantly works well also for high doping levels of the order of 10 20 -10 21 cm -3 . It has been demonstrated that GaAs can be p-type doped using Zn ions, and Si by the respective use of B and P ions. 10 The latter work presents field effect transistors based on ion-implanted nanowires. However, the demonstration of ion-implanted nanowires acting as devices by themselves is still lacking. Masking selected parts of the sample at different implantation steps, the doping profile can be chosen to be different from nanowire to nanowire. This is an additional advantage over doping during growth, or etching nanowires out of a doped wafer, as for both these methods all nanowires reveal the same doping concentration. This pap...