Abstract
Electrostatic force microscopy (EFM) can be used for sensing electrical properties of surface. Both simulation and experimental results indicate that the electric force acting on the probe is very depends on the shape and dimensions of the tip. By using a carbon nanotube tip, the lateral spatial resolution of EFM image is demonstrated to be better than 5 nm. For the application on data storage, we demonstrated small bit size (< 35 nm), ultrahigh areal density (~520 Gbit/in^2), low writing voltage (< ±10 V), and short writing time (500 ns) can be achieved by using a conventional conducting probe to inject charges (electrons and holes) in to an ultrathin Nitride-Oxide-Silicon (NOS) structure. From the charge retention behavior at high temperature, we found that decay of trapped charges in ultrathin NOS is mainly vertical process. The charge trapping properties of both electron and hole were further quantitatively determine by variable-temperature high vacuum EFM. From charge retention characteristics at temperatures between 250 °C and 370 °C and assuming thermal emission followed by oxide tunneling is the dominant decay mechanism, we deduced that there are considerable deep trap centers at the nitride-oxide (NO) interface. Besides, the retention behavior of electrons trapped at NO interface is dominated by the temperature dependent thermal emission rate: eth = αT^2exp(-Et/kBT). By contrast, the retention behavior of holes trapped at NO interface is dominated by the temperature independent emission rate: eesc = Aescexp(-Et/kBT). For electron, the interface trap energy and trap density were determined to be about 1.52 eV and 1.46x10^12 cm^2, respectively. For hole, they were about 1.01 eV and 1.08x10^12 cm^2, respectively. Furthermore, the capture cross section of electron was extracted as 4.8x10^-16 cm^2. These results may be useful for ascertaining the origin of trap centers in NOS. Charge patterns on NOS were further used to control the assembly of colloidal nanoparticles. We found that both thiol-terminated gold and CdSe/ZnS core-shell nanoparticles can be assembled on negatively charged patterns, and deduced that these nanoparticles bear positive charges. The assembled gold nanoparticles can form close-packed monolayer at an unprecedented spatial resolution of about 30 nm. Besides, the assembly of the gold nanoparticles is dominated by the electrophoretic (EP) force. By contrast, the dielectrophoretic (DEP) force acting on the CdSe/ZnS nanoparticles may compete with the EP force. Furthermore, nanoparticles with diverse properties can be successively assembled onto different charge patterns on the same surface by repeating the assembly procedure with different nanoparticle colloids. These experimental methods and results would be beneficial for further development of nanoparticle-based applications.