Studies on electronic structures of semiconductors by atomic force microscopy

We propose a new method of electron spectroscopy. Using an atomic force mic roscope, we have measured attractive forces between a sample and a metal co ated tip with varying applied voltage in dry nitrogen atmosphere. We have t hen plotted the values as a function of the voltage to obtain a force spect rum. The spectra of Si, ZnSe, and diamond show band gap structures which ca n be explained by a charge-transfer model. The spectrum of C-60 single crys tal shows an energy gap of similar to 2.0 eV and a highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) separation of 3.8 eV. These result s are in good agreement with the energy gap and the HOMO-LUMO separation ob tained by electron spectroscopy, respectively. The spectrum of C-60 also re veals the features of density of state, which are in fairly good agreement with those obtained by electron spectroscopy. Application of this method to anthracene and p-terphenyl single crystals allowed us to discuss the natur es of valence and conduction bands. (C) 1999 American Institute of Physics. [S0021-9606(99)70624-0].