CONTENTS - L'Oréal

L’ORÉAL-UNESCO FOR WOMEN IN SCIENCE 2005
L’ORÉAL-UNESCO AWARDS 2005: The Laureates
major impact on the design of quantum computing
devices. In nano-science Professor Koiller has addressed
the fascinating electromechanical behavior of carbon
nanotubes and optical properties of semiconductor
quantum dots.
Professor Koiller has been a Senior Research Fellow of
the Brazilian National Research Council since 1985. Her
publications have appeared in the most prestigious
physics journals. She was the first woman physicist to be
elected full member to the Brazilian Academy of Sciences
and was decorated Comendador da Ordem Nacional do
Mérito Científico of the Presidency of the Republic of Brazil.
Context of the Laureate’s research
Operating in the micro- and macroscopic
worlds
Belita Koiller’s research is in the line of the long tradition
of studying the properties of crystals and controlling
them. Recent progress has been breathtaking, and has
created the transistorized, digital world in which we live,
with cellular telephones, CDs, DVDs, computers, etc.
The first scientists to take an interest in the geometry of
crystals were Hauy and Bravais at the beginning of the
eighteenth century. They recognized that some solids
exhibited very regular and simple forms that one could
perceive with the naked eye. By looking very closely at a
grain of salt, for example, one can see cubes of different
sizes. Other natural crystals, like quartz, display
hexagonal shapes.
Mineralogists analyzed the crystalline state and found
that every crystal has a definite composition, with the
atoms at specific sites: for example, sodium chloride
(table salt) can be viewed as a cubic array with the
chlorine atoms at the corners of a microscopic cube and
the sodium atom at its center. The great progress they
made was to recognize that the macroscopic shape
reproduces the microscopic arrangement of atoms.
The next step was the recognition that atoms were
composed of a positively charged nucleus surrounded by
negatively charged electrons. The heavy nuclei were at the
sites characterizing the crystal while the electrons were
in some cases allowed to move. When they are able to
move, the crystal is a conductor. When the electrons do
not conduct electricity, the material is an insulator. If the
electrons are such that the crystal is a conductor, a
voltage applied across two opposite surfaces of the
crystal induces a flow of electrons, and thus a current.
The microscopic basis of the delicate behavior of
electrons in solids was elucidated by the quantum
physicists in the period between 1930 and 1950.
The semiconductors of the modern world
A semiconductor is a crystal in which some impurities
(dopants) have been introduced to control the conductivity.
Thus semiconductors (poor conductors and poor
insulators) became important when artificial doping
became available: the conductivity and even the (positive
or negative) sign of the current carriers in
semiconductors could be controlled by doping. In 1947,
the transistor - a semiconductor crystal with different