Probing complex heterostructures using hard X-ray photoelectron spectroscopy (HAXPES)

Understanding the Chemical Nature of the Buried Nanostructures in Low Thermal Conductive Sb-Doped SnTe by Variable-Energy Photoelectron Spectroscopy

“…At high kinetic energy (KE), the mean free path of the photoelectron varies with KE following the empirical relation: λ = m (KE) τ , where λ and KE are expressed in Å and eV, respectively. For energies above 1500 eV, up to 10 keV, the best values of m and τ are suggested to be 0.12 (±0.04) and 0.75 (±0.5) . So, eq can be expressed as The intensity ratio Sn 4+ /Sn 2+ was calculated from the deconvoluted experimental spectra.…”

“…For energies above 1500 eV, up to 10 keV, the best values of m and τ are suggested to be 0.12 (±0.04) and 0.75 (±0.5). 40 So, eq 3 can be expressed as…”

Nature of the charge carriers in LaAlO 3 -SrTiO 3 oxide heterostructures probed using hard X-ray photoelectron spectroscopy

“…However noting the importance of this aspect, we try to estimate limits on the relative contribution of the high energy feature to the total spectrum for each type of charge carriers, as follows. First, from the knowledge of the mean free path for inelastic scattering of valence band photoelectrons at 5400 eV photon energies [37] (∼ 7.6 nm) and with the width of the 2DEG found for this sample (see ref- 8), we estimate that ∼ 50% of the total spectral weight in Fig. 2(c) is contributed by the 2DEG at a photon energy of 5400 eV.…”

“…An important aspect of the HAXPES technique is that it provides a large inelastic mean free path [33] and therefore, can probe deep inside the buried interface layers. [8,9,[34][35][36][37] Our present results based on HAXPES measurements clearly indicate that (i) The experimental spectra are almost equally contributed by both the 2DEG at the interface and the bulk charge carriers doped by oxygen vacancies distributed uniformly throughout the STO crystal; (ii) Seemingly both low-energy coherent and highenergy features are present in the valence band spectra of both types of charge distributions, with the 2DEG spectral features having somewhat lower contributions from these high-energy features; (iii) A careful comparison between experiment and theory suggests that the high-energy feature is not due to correlation effects driven by Coulomb interactions within the Ti 3d manifold in either type of charge carriers, indicating that the interface charge carriers are weakly correlated; (iv) Our results, in conjunction with past publications in the literature on bulk oxygendeficient SrTiO 3−δ [25,26,28,[38][39][40][41] and LAO-STO heterostructures [8,32,42] suggest that the high-energy feature in the spectra of bulk-doped charge carriers with as much as 40% of the total spectral weight corresponds to localized in-gap states and is driven by the oxygen vacancy potential; (v) Since the charge carrier density at the interface is much higher than the oxygen vacancy density in the vicinity of the interface [8], the appearance of the weaker high-energy feature in the spectral features of the 2DEG cannot be attributed to the localizing potential of the vacancy. Based on various considerations, we suggest polaron formation as the most likely cause of this high-energy feature in the spectra of the 2DEG; and (vi) The observation of such localized state within the 2DEG and 3D doped carrier suggest substantial reduction of carriers available for transport.…”

Composition, thickness, and homogeneity of the coating of core–shell nanoparticles—possibilities, limits, and challenges of X-ray photoelectron spectroscopy

“…From these observations, a pronounced core–shell structure with an Er-rich shell is indicated for sample A, whereas in sample B, intermixing between Y, Yb, and Er with a slight enrichment of Yb in the near-surface region is consistent with the data. Such spatial distribution of the sensitizer and activator ions enables control of the donor–acceptor interaction and dynamics thereby eliminating or reducing deleterious cross-relaxation between lanthanide dopants and thus fine tuning of the optical properties [ 68 , 69 ]. Additionally, the location of emitting Er 3+ centres in the shell region enables very efficient luminescence resonance energy transfer (LRET) to organic molecules bound to the surface of the UCNPs due to the minimum distance between LRET donors and acceptors.…”