Hisotira de materials scince of thin films

Samer Elatrache V. 17810600 estudiante de CRF

Thin-film technology is simultaneously one of the oldest arts and one of the
newest sciences. Involvement with thin films dates to the metal ages of
antiquity. Consider the ancient craft of gold beating, which has been practiced
continuously for at least four millenia. Gold's great malleability enables it to be
hammered into leaf of extraordinary thinness while its beauty and resistance to
chemical degradation have earmarked its use for durable ornamentation and
protection purposes. The Egyptians appear to have been the earliest practitioners
of the art of gold beating and gilding. Many magnificent examples of
statuary, royal crowns, and coffin cases which have survived intact attest to the
level of skill achieved. The process involves initial mechanical rolling followed
by many stages of beating and sectioning composite structures consisting of
gold sandwiched between layers of vellum, parchment, and assorted animal
skins. Leaf samples from Luxor dating to the Eighteenth Dynasty (1567-1320
B.C.) measured 0.3 microns in thickness. As a frame of reference for the
reader, the human hair is about 75 microns in diameter. Such leaf was
carefully applied and bonded to smoothed wax or resin-coated wood surfaces
in a mechanical (cold) gilding process. From Egypt the art spread as indicated
by numerous accounts of the use of gold leaf in antiquity.
Today, gold leaf can be machine-beaten to 0.1 micron and to 0.05 micron
when beaten by a skilled craftsman. In this form it is invisible sideways and
quite readily absorbed by the skin. It is no wonder then that British gold
beaters were called upon to provide the first metal specimens to be observed
in the transmission electron microscope. Presently, gold leaf is used to decorate
such diverse structures and objects as statues, churches, public buildings,
tombstones, furniture, hand-tooled leather, picture frames and, of course,
illuminated manuscripts.
Thin-film technologies related to gold beating, but probably not as old, are
mercury and fire gilding. Used to decorate copper or bronze statuary, the cold
mercury process involved carefully smoothing and polishing the metal surface,
after which mercury was rubbed into it. Some copper dissolved in the
mercury, forming a very thin amalgam film that left the surface shiny and
smooth as a mirror. Gold leaf was then pressed onto the surface cold and
bonded to the mercury-rich adhesive. Alternately, gold was directly amalgamated
with mercury, applied, and the excess mercury was then driven off by
heating, leaving a film of gold behind. Fire gilding was practiced well into the
nineteenth century despite the grave health risk due to mercury vapor. The
hazard to workers finally became intolerable and provided the incentive to
develop alternative processes, such as electroplating.
The history of gold beating and gilding is replete with experimentation and
process development in diverse parts of the ancient world. Practitioners were
concerned with the purity and cost of the gold, surface preparation, the
uniformity of the applied films, adhesion to the substrate, reactions between
and among the gold, mercury, copper, bronze (copper-tin), etc., process
safety, color, optical appearance, durability of the final coating, and competitive
coating technologies. As we shall see in the ensuing pages, modem
thin-film technology addresses these same generic issues, albeit with a great
compression of time. And although science is now in the ascendancy, there is
still much room for art.