Size Counts...


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Prof. Israel Rubenstein and Dr. Gary Hodes. Smaller and higher

When it comes to size, Dr. Gary Hodes and Prof. Israel Rubinstein of the Materials and Interfaces Department are getting everything under control.

Their research is focusing on controlling the property and size of quantum particles (less than one-millionth of a millimeter) of semiconductors. Semiconductors are the basis of the transistor, which is the fundamental unit in radio, TV, computers, communications and other equipment. Their studies are an important step toward developing a single electron transistor, much smaller than present transistors.

As a result of their research, it emerges that when individual quantum particles are electro-deposited on a metal surface, the surface can act as a kind of template which determines both the direction and size of the particles.

Size is of the essence when it comes to quantum-sized semiconductors. It determines the amount of energy separating the conduction band and the valence band which electrons may occupy, known as the bandgap. Hodes and Rubinstein, in collaboration with Dr. Sidney Cohen of the Chemical Services Unit, and graduate student Boaz Alperson, developed a method to measure the dependence of the bandgap on the size of the quantum particle. The smaller a quantum particle, the wider its bandgap. This property may have great importance for the development of future electroopticaldevices.

How did they do it? Hodes' and Rubinstein's work involves the use of an atomic force microscope; they improved its measuring capability by covering its tip with an electricity-conducting metal.

Using the enhanced atomic microscope, they've succeeded in measuring the width of the bandgap in sing le quantum particles of the semiconductors they deposited. In these measurements, the first of their kind to be carried out at room temperature, the researchers also succeeded in monitoring the transfer of individual electrons into the semiconducting quantum particles.

...and Height Counts, Too

Prof. Israel Rubinstein of the Materials and Interfaces Department, and Prof. Abraham Shanzer of the Organic Chemistry Department, have developed a new technique for building ordered molecular structures. The structures are made from layers of organic molecules arranged in an orderly manner on the top of metal surfaces, and what's holding them together is a metal ion "cement."

The scientists can choose what kind of "building blocks" to use according to their expected chemical reactions. They can mix two or more types of building blocks, which respond differently to chemical reactants.

In this collaborative effort, Rubinstein and Shanzer are also working with Dr. Hagai Cohen of the Chemical Services Unit, and graduate students Anat Hatzor and Tamar Moav. When doing their "construction work," the scientists have already encoded the shape that will emerge after a specific chemical reaction. Therefore, by putting the whole building through a chosen chemical reaction, they're able to break up certain connections in a controlled way.

Using this technique, it's possible to build a complex molecular-scale building whose various wings reach different heights and different shapes, based on the architectural information which has been encoded in the building during its construction process.