Gold is very likely the first metal discovered by man, more than 11 000 years ago. However, unlike copper (∼9000 BC), bronze (∼3500 BC), and wrought iron (∼2500–3000 BC), gold is too soft for fabrication of tools and weapons. Instead, it was used for decoration, religious artifacts, and commerce. The earliest documented inorganic thin films were gold layers, some less than 3000 Å thick, produced chemi-mechanically by Egyptians approximately 5000 years ago. Examples, gilded on statues and artifacts (requiring interfacial adhesion layers), were found in early stone pyramids dating to ∼2650 BC in Saqqara, Egypt. Spectacular samples of embossed Au sheets date to at least 2600 BC. The Moche Indians of northern Peru developed electroless gold plating (an auto-catalytic reaction) in ∼100 BC and applied it to intricate Cu masks. The earliest published electroplating experiments were ∼1800 AD, immediately following the invention of the dc electrochemical battery by Volta. Chemical vapor deposition (CVD) of metal films was reported in 1649, atmospheric arc deposition of oxides (Priestley) in the mid-1760s, and atmospheric plasmas (Siemens) in 1857. Sols were produced in the mid-1850s (Faraday) and sol-gel films synthesized in 1885. Vapor phase film growth including sputter deposition (Grove, 1852), vacuum arc deposition (“deflagration,” Faraday, 1857), plasma-enhanced CVD (Barthelot, 1869) and evaporation (Stefan, Hertz, and Knudsen, 1873–1915) all had to wait for the invention of vacuum pumps whose history ranges from ∼1650 for mechanical pumps, through ∼1865 for mercury pumps that produce ballistic pressures in small systems. The development of crystallography, beginning with Plato in 360 BC, Kepler in 1611, and leading to Miller indices (1839) for describing orientation and epitaxial relationships in modern thin film technology, was already well advanced by the 1780s (Haüy). The starting point for the development of heterogeneous thin film nucleation theory was provided by Young in 1805. While an historical timeline tracing the progress of thin film technology is interesting of itself, the stories behind these developments are even more fascinating and provide insight into the evolution of scientific reasoning.
In surface science, coverage is the fraction of a surface (i.e., the fraction of a monolayer, ML) that is covered by deposited atoms. Thus, coverage θ = 0.1 ML of a (001)-oriented nickel [Ni(001)] surface (see Sec. III C for definitions of surface crystallography) by copper atoms corresponds to a two-dimensional copper atom density of 1.6 × 1014 atoms/cm2 since the surface atom density of Ni(001) is 1.6 × 1015 atoms/cm2.