Surface and Interface Diffraction
Chris Nicklin is the Principal Beamline Scientist for beamline I07, which will be used to study the structure and morphology of surfaces and buried interfaces using X-ray scattering techniques. Prior to joining Diamond, Chris was a lecturer at the University of Leicester where his research focused on the growth and structure determination of alloy layers and understanding the dynamics of self-assembling nanocrystals. Chris has used both X-ray diffraction techniques and grazing incidence small angle x-ray scattering (GISAXS) to understand these processes at different length scales (atomic – 10 nanometres).
Key Research Areas
Nanoparticle self assembly, structural determination of ordered surface reconstructions, in-situ heterogeneous growth studies, grazing incidence diffraction, grazing incidence small angle x-ray scattering.
Current Research Interests
My main research interests involve determining the atomic arrangement and morphology of a wide variety of two-dimensional structures formed at surfaces and interfaces. Understanding the way this affects the properties and function of the material is a key motivation for this work. Increasingly, important structures are not being formed in clean ultrahigh vacuum (UHV) chambers but in a broad range of environments including high gas pressures, in liquids or at the interface between two solid materials. The power of X-ray scattering is its ability to pass through material in order to probe the interface of interest. The challenge is, therefore, to produce a wide range of environmental chambers that allow measurements to be made in the specific geometries required for interfacial X-ray diffraction or scattering (specifically the requirement for the X-rays to hit the sample at grazing angles to enhance the surface sensitivity).
My interest in surface physics began with my PhD research, which involved measuring valence changes in rare earth elements as their local environment was changed at the surface. I also used resonant photoemission to determine the decay channels in these elements before becoming interested in UHV in-situ surface x-ray diffraction to determine the structure of these and other surfaces with high accuracy. This aspect of my work has recently been used to study more complex surface reconstructions of rare-earth and transition metal alloys (e.g. GdFe2 on Mo(110)).
My research expanded to include the application of X-ray scattering methods to determine the long range order of crystallites formed by self-assembling nanoparticles. This required the development of a small specialist scattering cell that was used to carry out the first GISAXS experiments on the UK beamline (XMaS) at the ESRF. We have been able to ascertain how various parameters affect the quality of the ordering, including unexpected phase changes at low temperatures and the ability to force the particles together in layers formed on a Langmuir trough. Extensions to this work have included monitoring in-situ ligand exchange and the dynamics of aggregation when linker molecules are added.
Surface and interface science faces many challenges in the future and I foresee my research growing in several directions. The next generation of devices based on interfaces (e.g. electronics, magnetic storage etc) will rely on improved control and placement of atoms on a surface or within an interface. One way in which this will be achieved is through the use of patterned or templated substrates to encourage preferential adsorption sites. A range of technologies will contribute to this including direct write nanolithography, magnetic and electric field induced self assembly and strained interface networks. Beamline I07 at Diamond will enable us to determine both the substrate morphology and structures grown on them with high resolution.
- Growth of ultrathin rare-earth films studied by in situ x-ray diffraction, Nicklin CL, Everard MJ, Norris C, Bennett SL, PHYSICAL REVIEW B 70 (23): Art. No. 235413 DEC 2004.
- An ultrahigh-vacuum chamber for surface X-ray diffraction, Nicklin CL, Taylor JSG, Jones N, Steadman P, Norris C, JOURNAL OF SYNCHROTRON RADIATION 5: 890-892 Part 3, MAY 1 1998
- Resonant Photoemission Spectra at the 4f and 5p levels of Tm across the 4d-4f Absorption Threshold, Nicklin CL, Binns C, Mozley S, Norris C, Alleno E, Barthes-Labrousse MG, van der Laan G, PHYSICAL REVIEW B 52 (7): 4815-4822 AUG 15 1995.
- An investigation of the growth and removal of protective antimony caps for antimonide epilayers, S.G. Alcock, M.J. Everard, C.L. Nicklin, J.S.G. Taylor, C.A. Norris and S.L. Bennett, Thin Solid Films, Volume 514, Issues 1-2 , 30 August 2006, 198-203.