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Probing periodic properties of "artificial elements" assembled in a quantum wedge with a low temperature scanning tunneling microscope

D. Chen*, I. B. Altfeder

The Rowland Institute for Science

This is an abstract for a talk to be given at the Fifth Foresight Conference on Molecular Nanotechnology.

An artificial atom¹ can be characterized by the discrete quantum states (QS) of the electrons confined by its boundaries.  The number of occupied QS and their energy spectrum depends on the size of the artificial atom.  With the advanced nano fabrication technology, it is possible to tailor the size of an artificial atom so that the number of occupied QS can be adjusted by unity, hence create a periodic table of "artificial elements", in resemblance to Mendeleev's Periodic Table of  The Elements.

In this paper, we will demonstrate the validity of this concept with  a recent experiment² performed with a low temperature scanning tunneling microscope housed together with a UHV fabrication chamber.  We show that an array of artificial atoms with incremental QS can be realized through the fabrication of a quantum wedge, i.e. a nanoscale wedge whose thickness changes monotonically by discrete atomic planes.   Each atomic layer  increase in  the thickness adds a new QS into the system as a result of the quantum confinement. Thus a quantum wedge is an assembly of artificial atoms with incremental sizes, or "artificial elements".
 
Our quantum wedge is fabricated by the epitaxial growth of Pb on a stepped surface of Si(111).  Tunneling spectroscopy reveals that each slab of equal thickness is associated with a set of QS, and the shift of the energy level of the highest occupied QS (HOQS) between two neighboring slabs is nearly one half of a energy quantization step.  Thus slabs with the even number layers  have their HOQS aligned at one level while those of odd number layers aligned at another.  This two fold repetition of the HOQS gives rise to a binary electron interference fringes when imaged in a conventional constant current mode, showing for the first time a quantum mechanical analog of the classical Fizeau fringes on an optical wedge.

References
[1] M. Kastner, Physics Today, 46(1), 24 (1993)
[2] I. B. Altfeder, K. A. Matveev, and D. M. Chen, Phys. Rev. Lett. 78, 2815 (1997).

*Corresponding Address:
Dongmin Chen, The Rowland Institute for Science,100 Edwin H. Land Blvd. Cambridge, MA 02142, ph: (617)-497-4620, fax: (617)-497-4627, email: chen@risvax.rowland.org
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