Tomoko Miyahara

Single crystal growth of organic semiconductors by the Repeated Solid Solvent Growth Method using melted anthracene as a solvent

We propose a new method of growing single crystals of organic molecular semiconductors, using melted anthracene as a solvent. The method is called the Repeated Solid Solvent Growth Method. Needle-like single crystals of Cu phthalocyanine up to 10 mm in length have been grown by repeated cooling of a glass ampoule which contains the anthracene melt dissolving the molecule. We have found that the crystals tend to grow larger as the procedure is repeated. The crystal growth process is discussed on the basis of the temperature gradient of the growing ampoule.

Studies on electronic structures of semiconductors by atomic force microscopy

We propose a new method of electron spectroscopy. Using an atomic force microscope, we have measured attractive forces between a sample and a metal coated tip with varying applied voltage in dry nitrogen atmosphere. We have then plotted the values as a function of the voltage to obtain a force spectrum. The spectra of Si, ZnSe, and diamond show band gap structures which can be explained by a charge–transfer model. The spectrum of C60 single crystal shows an energy gap of ∼2.0 eV and a highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) separation of 3.8 eV. These results are in good agreement with the energy gap and the HOMO–LUMO separation obtained by electron spectroscopy, respectively. The spectrum of C60 also reveals 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 natures of valence and conduction bands.