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Resonant Inelastic X-ray Scattering (RIXS) is an x-ray spectroscopy technique used to investigate the electronic structure of molecules and materials. Inelastic X-ray Scattering is a fast developing experimental technique in which one scatters high energy, x-ray photons inelastically off matter. It is a photon-in/photon-out spectroscopy where one measures both the energy and momentum change of the scattered photon. The energy and momentum lost by the photon are transferred to intrinsic excitations of the material under study and thus RIXS provides information about those excitations. The RIXS process can also be described as a Resonant X-ray Raman or Resonant X-ray Emission process. RIXS is a resonant technique because the energy of the incident photon is chosen such that it coincides with, and hence resonates with, one of the atomic x-ray absorption edges of the system. The resonance can greatly enhance the inelastic scattering cross section, sometimes by many orders of magnitude〔W. Schuelke, Electron Dynamics by Inelastic X-Ray Scattering, Oxford University Press, Oxford 2007〕〔F. De Groot and A. Kotani, Core Level Spectroscopy of Solids, CRC Press, 2008〕〔L. Ament, M. van Veenendaal, T. Devereaux, J.P. Hill and J. van den Brink, Resonant Inelastic X-ray Scattering Studies of Elementary Excitations, Rev. Mod. Phys. 83, 705, 2011〕 The RIXS event can be thought of as a two-step process. Starting from the ''initial'' state, absorption of an incident photon leads to creation of an excited ''intermediate'' state, that has a core hole. From this state, emission of a photon leads to the ''final'' state. In a simplified picture the absorption process gives information of the empty electronic states, while the emission gives information about the occupied states. In the RIXS experiment these two pieces of information come together in a convolved manner, strongly perturbed by the core-hole potential in the intermediate state. RIXS studies can be performed using both soft and hard x-rays. ==Features== Compared to other scattering techniques, RIXS has a number of unique features: it covers a large scattering phase-space, is polarization dependent, element and orbital specific, bulk sensitive and requires only small sample volumes: #In RIXS one measures both the ''energy and momentum'' change of the scattered photon. Comparing the energy of a neutron, electron or photon with a wavelength of the order of the relevant length scale in a solid— as given by the de Broglie equation considering the interatomic lattice spacing is in the order of Ångströms—it derives from the ''relativistic energy–momentum relation'' that an x-ray photon has less energy than a neutron or electron. The scattering phase space (the range of energies and momenta that can be transferred in a scattering event) of x-rays is therefore without equal. In particular, high-energy x-rays carry a momentum that is comparable to the inverse lattice spacing of typical condensed matter systems so that, unlike Raman scattering experiments with visible or infrared light, RIXS can probe the full dispersion of low energy excitations in solids. # RIXS can utilize the ''polarization'' of the photon: the nature of the excitations created in the material can be disentangled by a polarization analysis of the incident and scattered photons, which allow one, through the use of various selection rules, to characterize the symmetry and nature of the excitations. # RIXS is ''element and orbital specific'': chemical sensitivity arises by tuning to the absorption edges of the different types of atoms in a material. RIXS can even differentiate between the same chemical element at sites with inequivalent chemical bondings, with different valencies or at inequivalent crystallographic positions as long as the x-ray absorption edges in these cases are distinguishable. In addition, the type of information on the electronic excitations of a system being probed can be varied by tuning to different x-ray edges (e.g., K, L or M) of the same chemical element, where the photon excites core-electrons into different valence orbitals. # RIXS is ''bulk sensitive'': the penetration depth of resonant x-ray photons is material and scattering geometry- specific, but typically is on the order of a few micrometre in the hard x-ray regime (for example at transition metal K-edges) and on the order of 0.1 micrometre in the soft x-ray regime (e.g. transition metal L-edges). # RIXS needs only ''small sample volumes'': the photon-matter interaction is relatively strong, compared to for instance the neutron-matter interaction strength. This makes RIXS possible on very small volume samples, thin films, surfaces and nano-objects, in addition to bulk single crystal or powder samples. In principle RIXS can probe a very broad class of intrinsic excitations of the system under study—as long as the excitations are overall charge neutral. This constraint arises from the fact that in RIXS the scattered photons do not add or remove charge from the system under study. This implies that, in principle RIXS has a finite cross section for probing the energy, momentum and polarization dependence of any type of electron-hole excitation: for instance the electron-hole continuum and excitons in band metals and semiconductors, charge transfer and crystal field excitations in strongly correlated materials, lattice excitations and so on. In addition magnetic excitations are also symmetry-allowed in RIXS, because the angular momentum that the photons carry can in principle be transferred to the electron's spin moment.〔L. Ament, G. Ghiringhelli, M. Moretti Sala, L. Braicovich and J. van den Brink, Theoretical demonstration of how the dispersion of magnetic excitations in cuprate compounds can be determined using resonant inelastic x-ray scattering, Phys. Rev. Lett. 103, 117003 (2009).〕〔L. Braicovich, J. van den Brink, V. Bisogni, M. Moretti Sala, L. Ament, N. Brookes, G. De Luca, M. Salluzzo, T. Schmitt and G. Ghiringhelli, Evidence for Dynamic Phase Separation and High Energy Spin Dynamics in underdoped La2-xSrxCuO4 from Resonant Inelastic X-Ray Scattering, Phys. Rev. Lett. 104, 077002 (2010).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Resonant inelastic X-ray scattering」の詳細全文を読む スポンサード リンク
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