Xinxing Xiao | PubMed Health

PubMed2006

Rapid preparation of crystalline colloidal arrays using a strong electric field dialysis.

We present a simple method for rapid preparation of crystalline colloidal arrays (CCAs) by a strong electric field dialysis (SEFD). This method is based on rapid removing of ionic impurities in colloidal suspensions by applying a strong electric field. In a SEFD process, the negatively charged ions in colloidal suspensions are rapidly driven to the anode, the positively charged ones are rapidly driven to the cathode, and the colloidal particles are withheld in the dialysis tube. It was shown that the colloidal particles aggregated on the wall of the dialysis tube could block the SEFD process, which could be overcome by reversing the direction of the electric field. The purified colloidal particles can self-assemble into a crystalline colloidal array, which has an electrostatically stabilized three-dimensional periodic array of colloidal particles with a characteristic lattice spacing that can be varied by dilution. The reflection spectra show distinct peaks due to diffraction from CCAs. Atomic force microscopy (AFM) image illustrates the non-contacted ordering of the colloidal particles in the CCAs embedded in gels. This indicates the formation of high-quality single CCAs. Using a SEFD method, the preparation time of CCAs can be reduced. This new technique will greatly speed up the process of preparing polymerized crystalline colloidal arrays (PCCAs) into real-world application in the analytical field.

Colloids↗

PubMed2005

Electrical characterization of silicon tips using conducting atomic force microscopy.

The electrical properties of n-doped Si tips have been characterized in conducting atomic force microscopy under various conditions. Si tips with SiO2 layer on them present complex electric properties: which include a larger positive threshold bias, which is different from that of its doped semiconductor material. Silicon tips after removing their SiO2 layer had smaller positive threshold bias; such bias varied with the loading force: smaller loading forces corresponding to larger positive threshold biases, and it remained constant at lower levels for larger loading forces. Humidity of experiments influenced the threshold bias: lower relative humidities (<25%) and larger loading forces were in favor of getting stable threshold bias. The conductance increased remarkably in high relative humidity although it was kept in a narrow range when relative humidity was lower than 40%. Loading force didn't affect the conductance in the examined relative humidity conditions. One advantage of bare silicon tips over commercial conducting ones is that they smaller radius than gold-coated tips; this is in more favor of reaching single molecular electronics.

Electric Conductivity↗