Product Code: ICAL08_N304

Two Recent Advances in Materials Structuring and Diagnostics at the Nanoscale Employing, Ultra Fast, Pulsed Lasers (Invited Presentation - 40 Minutes)
Authors:
Emmanuel Stratakis, Foundation for Reasearch and Technology Hellas & Univ. of Crete, Hellas; Crete Greece
Presented at ICALEO 2008

Bio-mimetic modification of surface properties and development of novel techniques for the study of materials at nanoscale are issues of great interest in current nanotechnology research. Nature inspires us in tailoring special wettability properties of surfaces based on synergetic effects between chemical composition and surface morphology. We have developed a method for preparing stable superhydrophobic and highly water repellent surfaces by irradiating silicon (Si) wafers with femtosecond laser pulses and subsequently coating them with monolayers of chloroalkylsilane. It is possible, by varying the laser pulse fluence on the surface, to achieve control of the wetting properties through a systematic and reproducible variation of roughness at micro- and nano-scale which mimics the dual-scale topography of natural hydrophobic surfaces. The superhydrophobic and self-cleaning properties of these artificial surfaces are compared to that of the lotus (Nelumbo Nucifera) leaves, one of the most hydrophobic surfaces found in nature. Remarkable similarities between the two surfaces were observed, in terms of the water repellence and of self cleaning efficiency. To our knowledge this is the first time such a direct comparison of performance is made and it clearly demonstrates the possibility of designing highly efficient water repellent surfaces. A novel scanning probe technique for imaging of nanometer scale electronic properties of materials, based on conductive atomic force microscopy, complemented with femtosecond laser illumination, is presented. We have successfully implemented this technique to probe the dielectric properties of Si nanowire (NW) oxide which acts as an insulator in transistor gates. In particular, we have investigated the characteristics of leakage currents from nanoscale areas of thermal oxide on core of NWs and compared them to those of planar silicon oxides. It is found that, the interface barrier to electron transit from the semiconductor to the dielectric and the threshold electric field for current flow in Si NWs are quite similar to those in the planar geometry. This is not true for the lowest currents measured which are not uniformly distributed, indicating variations of trap density in the gap of NW oxide. C-AFM combined with multiphoton probing of electronic transitions can reveal electrically active defects in the oxide and serve as a guide to both the clarification of the origin of these defects and to the optimization of growth and processing in order to avoid them. It also introduces a highly versatile tool for nanoscale characterization of single or stacked multiple dielectric structures and of future nanoelectronic devices.