Volume 3 • Issue 4 • 1000e112 J Thermodynam Cat ISSN: 2157-7544 JTC, an open access journal Research Article Open Access Datta, J Thermodynam Cat 2012, 3:4 DOI: 10.4172/2157-7544.1000e112 Editorial Open Access A Century Plus of X-rays Timir Datta* Department of Physics and Astronomy, University of South Carolina, USA *Corresponding author: Timir Datta, Department of Physics and Astronomy, University of South Carolina, USA, Tel: 803-777-2075; E-mail: datta@physics.sc.edu Received September 27, 2012; Accepted September 28, 2012; Published October 03, 2012 Citation: Datta T (2012) A Century Plus of X-rays. J Thermodynam Cat 3: e112. doi:10.4172/2157-7544.1000e112 Copyright: © 2012 Datta T. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. As we approach the last quarter of the celebration of the International Year of Crystallography [1] let me relate some of the excitements and the developments that followed the epochal works conducted in 1912 on both sides of the English Channel. I will conclude with a tip of my Stetson to today’s champions who are keeping the fre brightly lit well into the twenty-frst century. X-ray techniques have played a pivotal catalytic role in catalysis R&D. Te term “catalysis” was introduced by Brezelius in 1835. Later W. Oswald’s defnition -catalyst as an agent that afects the reaction rate without it being consumed in the process joined the lexicon especially, following his Chemistry Nobel prize of 1909. Te story of x-ray in materials starts at the University of Munich. Where, upon learning from Ewald that the particles inside crystals are regularly spaced by a distance of the order of 1/1000 of the wave length of visible light, Max Laue opined, wave nature of x-rays will be confrmed if upon passing a beam thorough a crystal interference patterns can be produced. True Laue learnt about lattice size from Ewald, but he was fully aware that at least since the seventeenth century ideas about internal periodicity in crystalline solids have been on record. For instance Laue knew that in a new year’s pamphlet (1611) Kepler had remarked on the symmetry of snowfakes. NB: Keppler also had the conviction that the geometric solids polyhedrons are the universal building blocks. 1669 Neils Stensen discovered that crystal faces intersect at characteristic angles. Huygen related birefringence of calcite (1690) to a particular 3-dimensional array of ellipsoidal particles. In 1773 Bergman and 1782 Hauy described crystals to be masonry of tiny identical bricks. To accommodate thermal expansion and elasticity, Seeber (1824) replaced the bricks by spherical molecules placed at positions of equilibrium. Hassel’s classifcation of 32 types of crystals in 1830 was followed by Franz Neumann’s (1833) suggestion that crystal symmetries refect internal physics. Also Millerian indices (1839) preceded the development of 14 translational lattices by Bravais (1850). It is likely that most of this was common academic lore. But the technology to physically test these ideas was not yet available. In 1895 Rontgen discovered x-rays serendipitously while researching electrical discharges in vacuum but its nature and the associated wave length was not immediately apparent. When on a skiing expedition Laue discussed the idea with Sommerfeld, Wien and others were prompt of raise doubts; but, shortly Walter Friedrich set up an experiment and forthright succeeded in photographing interference patterns by passing x-rays thru a copper sulfate crystal. With this single epochal observation [2,3] the Munich group resolved a whole array of fundamental questions namely, x-rays are short wavelength (high energy) Maxwellian waves, “atoms” exist and inside crystals they form an ordered lattices. However, it will still be many more decades before the dust of atomicity will settle [4]. In Munich, the tremendous signifcance of the Laue spots must have been clear right away. Because promptly before the publication of the results pertaining to the discovery, Walter Friedrich, Paul Knipping and Max Laue signed a one-page document stating “Te undersigned are engaged since 21 April 1912 with experiments about interference of x-rays passing through crystals”. It was deposited by Sommerfeld on 14 May 1912 [5]. As we know today, wave scattering by lattice determine many solid state properties including all-important band structure. But the physics of X-ray scattering in a crystal a la the Munich group was not quite right. Te description was under constrained. Te Laue-Ewald formula involved three integers each representing the order of interference associated with the three directions of space. Tis full 3-dimensional scheme conjured up an overabundance of spots. Fewer spots were observed in the Laue pattern and missing spots were misinterpreted as “random” gaps in the incident x-ray spectrum. Lucky for us, at the same time on the other side of the English Channel a bright young chap, William Lawrence Bragg was taking his National sciences (physics) degree at Cambridge University. His father William Henry Bragg, physics professor at Leeds was aware of the work at Munich and discussed the results with him. Mathematically gifed Lawrence was intrigued by the absence of spots, the changing of shapes from circular to oval as the pattern moved of incidence and also that the pattern turned six degree when a crystal was rotated by just half that angle. Typically, the angular displacements of non-specular interference spots are determined by trigonometric functions and produce highly nonlinear response [6]. Lawrence then barely 22 years old fgured that the Laue pattern could not be due to three dimensional lattices but a sub-set associated with interference of x-ray wavelets refecting of successive atomic planes. In this specular refection process there are (only) two relevant lengths, the x-ray wave length θ and the inter-plane distance d(klm) where klm are the Miller indices and the scattering angle (θ). Lawrence Bragg derived the appropriate conditions for constructive interference and obtained a simple eponymous equation that relates the order of the interference (n) and the ratio of the lengths with sin (θ); n * [λ/d(klm)] = 2 * Sin(θ). Furthermore based on this equation and the missing spots in the Munich Lawrence was able to deduce that the lattice of ZnS is not simple cubic (SC) as presumed by Laue et al but face centered cubic (FCC). Not coincidentally William Barlow another Englishman was the frst to introduce SC and FCC and the concept of close packing into crystallography (1833). Shortly thereafer Lawrence lef Cambridge to join his father at Leeds. At Leeds their roles can be best described by a phrase from P.W. Anderson (Nobel Physics 1977) “theory on Journal of Thermodynamics & Catalysis J o u r n a l o f T h e r m o d y n a m i c s & C a t a l y s i s ISSN: 2157-7544