Probing surface and interface structure using optics

Abstract

Optical techniques for probing surface and interface structure are introduced and recent developments in the field are discussed. These techniques offer significant advantages over conventional surface probes: all pressure ranges of gas-condensed matter interfaces are accessible and liquid-liquid, liquid-solid and solid-solid interfaces can be probed, due to the large penetration depth of the optical radiation. Sensitivity and discrimination from the bulk are the two challenges facing optical techniques in probing surface and interface structure. Where instrumental improvements have resulted in enhanced sensitivity, conventional optical techniques can be used to characterize heterogeneous adsorbed layers on a substrate, often with sub-monolayer resolution. Nanoscale lateral resolution is possible using scanning near-field optics. A separate class of techniques, which includes reflection anisotropy spectroscopy, and nonlinear optical probes such as second-harmonic and sum-frequency generation, uses the difference in symmetry between the bulk and the surface or interface to suppress the bulk contribution. A perspective is presented of likely future developments in this rapidly expanding field.

Evolution of structural distortion in BiFeO3 thin films probed by second-harmonic generation

“…It works especially well when it comes to surface and interface where different media on each side break the inversion symmetry23, and this technique has been applied to probe many interesting and significant aspects of surface and interface, such as molecular absorption, surface electric states, and magnetic domain structure242526. It has also been engaged in studying the structure and properties of epitaxial grown thin films, such as strain-induced ferroelectric1427, electro-optic response28, surface symmetry, and interfacial enhancement26.…”

Temperature-dependent magnetic second-harmonic generation from Fe nanostructures grown on vicinal W(110)

“…(5) or (6). However, such a contribution would also produce an acentric magnetization loop, which the use of type I extraction of McGilp et al 10,31 would reveal.…”

“…Conventional surface techniques are insensitive to buried nanostructures, but a variety of optical techniques, with their larger penetration depth, can provide useful data. Photon-inphoton-out techniques ("epioptics" 5,6 ), such as optical secondharmonic generation (SHG), which use symmetry to extract the optical response of the interface from the normally dominant bulk response, allow the buried interfacial structure of centrosymmetric materials to be probed through thin capping layers, and magnetic SHG (MSHG) extends this to magnetic interfaces. However, the vast majority of magnetic thin-film systems that have been studied so far are of high surface and interface symmetry, 7 because of the general complexity of the MSHG response and the often poor signal-to-noise ratio (SNR).…”

Optical signatures of thiolate/Cu(110) and S/Cu(110) surface structures

“…7 and 8͒-a versatile and widely used probe belonging to the epioptics family of techniques designed for the study of surfaces and interfaces. 9 RAS has been used to investigate carboxylate/Cu͑110͒ surfaces 1,10-12 and the bonding interaction at this interface. 11 We find that characteristic optical signatures are obtained from thiolate/Cu͑110͒ and S/Cu͑110͒ surface structures, and simulations suggest that a broad optical transition at 3.8 eV is associated with the thiolate/ Cu͑110͒ interface, as a result of the thiolate-Cu bonding.…”