interatomic distances may correspond approximately to the wavelengths of X-rays
and may generate a three-dimensional diffraction pattern when radiated with X-rays.
He persuaded Walter Friedrich and Paul Knipping, who had previous experience
with a more powerful X-ray bulb than available to Röntgen and were able to produce
a collimated and narrower primary X-ray beam, to undertake some preliminary
experiments [17, 18]. Using large single crystals of hydrated copper sulphate and
zinc sulphide, they showed that when the beam of X-rays strikes the crystal the
incident beam is scattered in many directions and the resultant diffraction pattern
could be observed using a photographic plate (after it had been developed using
standard photographic reagents). In this experiment the X-rays were not directly
being used as microscope in the manner described earlier by Hooke, but the
observation of a diffraction pattern suggested the possibility of obtaining information about the separations of a regular atomic grid within the crystal [17, 18]. This
required a clearer understanding of the physics responsible for the diffraction process
and the development of mathematical equations which could be used to convert the
diffraction pattern into a model which may give information about the positions of
the atoms. The major obstacle in the pathway leading from the observed diffraction
pattern to the desired crystal structure is known as the phase problem and is
discussed further below.
The interference patterns observed in these experiments supported the characterisation of X-rays as electromagnetic waves with very short wavelengths rather than
as corpuscles. Von Laue with his able coworkers’ demonstration of the phenomenon
of X-ray diffraction proved to be inspirational. Remarkably within the next decade
and even with the interruptions caused by the outbreak of World War I, these initial
observations were developed into an important scientific tool which contributed to
the second scientific revolution. This proved to be an important landmark in modern
science because it enabled chemists, physicists and molecular biologists to obtain a
unique understanding of the fundamental structures of molecules, minerals, metals,
alloys, proteins and enzymes at atomic resolutions. It underpinned what was to
become the zeitgeist of the age, i.e. establishing the structures of molecules leads
to an understanding of their function. More germane to the present volume of
Structure and Bonding, the structural information it provided was used to understand
the principles of chemical bonding and led to the deeper understanding of physical
and chemical properties of important key building blocks of physics, chemistry and
biology. Such an important discovery has of course attracted many scholars, and it is
not possible to summarise all the relevant contributions in a short review. References
[19–27] give more detailed accounts and personal reminiscences. The important
early papers on the diffraction of X-rays have also been collated in two volumes
[25, 26]. My brief summary has drawn extensively on the excellent book by Andre
Authier – Early Days of X-ray Crystallography published in 2013 [21].
Friedrich and Knipping experiments and Laue’s initial interpretation published in
June 1912 had an immediate impact within the scientific community [21]. Max
Planck recalled that scientists in Berlin “felt that a remarkable feat had been
achieved”, and Albert Einstein defined the experiment as “among the most glorious
that physics has seen so far”. Not surprisingly this paper received a good reception
Early History of X-Ray Crystallography
5
and may generate a three-dimensional diffraction pattern when radiated with X-rays.
He persuaded Walter Friedrich and Paul Knipping, who had previous experience
with a more powerful X-ray bulb than available to Röntgen and were able to produce
a collimated and narrower primary X-ray beam, to undertake some preliminary
experiments [17, 18]. Using large single crystals of hydrated copper sulphate and
zinc sulphide, they showed that when the beam of X-rays strikes the crystal the
incident beam is scattered in many directions and the resultant diffraction pattern
could be observed using a photographic plate (after it had been developed using
standard photographic reagents). In this experiment the X-rays were not directly
being used as microscope in the manner described earlier by Hooke, but the
observation of a diffraction pattern suggested the possibility of obtaining information about the separations of a regular atomic grid within the crystal [17, 18]. This
required a clearer understanding of the physics responsible for the diffraction process
and the development of mathematical equations which could be used to convert the
diffraction pattern into a model which may give information about the positions of
the atoms. The major obstacle in the pathway leading from the observed diffraction
pattern to the desired crystal structure is known as the phase problem and is
discussed further below.
The interference patterns observed in these experiments supported the characterisation of X-rays as electromagnetic waves with very short wavelengths rather than
as corpuscles. Von Laue with his able coworkers’ demonstration of the phenomenon
of X-ray diffraction proved to be inspirational. Remarkably within the next decade
and even with the interruptions caused by the outbreak of World War I, these initial
observations were developed into an important scientific tool which contributed to
the second scientific revolution. This proved to be an important landmark in modern
science because it enabled chemists, physicists and molecular biologists to obtain a
unique understanding of the fundamental structures of molecules, minerals, metals,
alloys, proteins and enzymes at atomic resolutions. It underpinned what was to
become the zeitgeist of the age, i.e. establishing the structures of molecules leads
to an understanding of their function. More germane to the present volume of
Structure and Bonding, the structural information it provided was used to understand
the principles of chemical bonding and led to the deeper understanding of physical
and chemical properties of important key building blocks of physics, chemistry and
biology. Such an important discovery has of course attracted many scholars, and it is
not possible to summarise all the relevant contributions in a short review. References
[19–27] give more detailed accounts and personal reminiscences. The important
early papers on the diffraction of X-rays have also been collated in two volumes
[25, 26]. My brief summary has drawn extensively on the excellent book by Andre
Authier – Early Days of X-ray Crystallography published in 2013 [21].
Friedrich and Knipping experiments and Laue’s initial interpretation published in
June 1912 had an immediate impact within the scientific community [21]. Max
Planck recalled that scientists in Berlin “felt that a remarkable feat had been
achieved”, and Albert Einstein defined the experiment as “among the most glorious
that physics has seen so far”. Not surprisingly this paper received a good reception
Early History of X-Ray Crystallography
5