Mechanical and Electrical Properties of CdTe Tetrapods Studied by Atomic Force Microscopy - eScholarship

Mechanical and Electrical Properties of CdTe Tetrapods Studied by Atomic Force Microscopy Liang Fang 1 , Jeong Young Park 1 , Yi Cui 2 , Paul Alivisatos 2 , Joshua Shcrier 3 , Byounghak Lee 3 , Lin-Wang Wang 3 , and Miquel Salmeron 1 * Molecular Foundry, Materials Science Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720 Chemistry Department, University of California at Berkeley, Berkeley, California 94720 Computational Research Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720 *Author to whom correspondence should be addressed. Electronic mail: mbsalmeron@lbl.gov Abstract The mechanical and electrical properties of CdTe tetrapod-shaped nanocrystals have been studied with atomic force microscopy. Tapping mode images of tetrapods deposited on silicon wafers revealed that they contact the surface with the ends of three arms. The length of these arms was found to be 130 ± 10 nm. A large fraction of the tetrapods had a shortened vertical arm as a result of fracture during sample preparation. Fracture also occurs when the applied load is a few nanonewtons. Compression experiments with the AFM tip indicate that tetrapods with the shortened vertical arm deform elastically when the applied force was less than 50 nN. Above 90 nN additional fracture events occurred that further shorted the vertical arm. Loads above 130 nN produced irreversible damage to the other arms as well. Current-voltage characteristics of tetrapods deposited on gold indicated semiconducting behavior with a current gap of ~2 eV at low loads (<50 nN) and a narrowing to about 1 eV at loads between 60 and 110 nN. Atomic calculation of the deformation suggests that the ends of the tetrapod arms are stuck during compression so that the deformations are due to bending modes. The reduction of the current gap is due to electrostatic effects, rather than strain deformation effects inside the tetrapod.