Electronic properties of Cr1−xAlxN thin films deposited by reactive magnetron sputtering

Epitaxial suppression of the metal-insulator transition in CrN

“…We attribute the absence of a phase transition to epitaxial constraints that suppress the shear deformation into the orthorhombic structure, as this would require an instantaneous macroscopic transition of the entire layer. This is in agreement 5,9 and disagreement 6,7 with previous reports on a phase transition in epitaxial CrN. …”

“…3,4 Electronic transport studies report controversial results for CrN, including (i) values for the resistivity ρ at room temperature range over more than two orders of magnitudes, from 1.7×10 -3 to 3.5×10 -1 Ωcm, 3,[5][6][7][8][9][10] even when only considering the most reliable data for single crystal CrN layers; (ii) the temperature dependence of ρ shows metallic behavior with dρ/dT > 0 in some studies, 6,7,11 but an increase in ρ with decreasing temperature in other reports, 3,5,9,12 which has been attributed to the presence of a band gap 5 or carrier localization due to crystalline defects 13 or N-vacancies; 14 (iii) some studies report a discontinuity in ρ(T) at 260-280 K, 3,6,7,14 which is associated with a magnetic and structural phase transition from a paramagnetic NaCl structure at room temperature to a low-temperature antiferromagnetic orthorhombic P nma phase 11,15 with a 0.56-0.59% higher density, 11 and a 25% lower bulk modulus, 16 while other reports show no evidence for a phase transition in the ρ(T)-curves. 5,7,9 Electronic structure calculations suggest that magnetic stress relief couples magnetic ordering with the structural phase transition, 17 and that CrN exhibits a band gap if the Hubbard Coulomb interaction term is sufficiently large. 21 Similarly, the out-of-plane CrN lattice constant, which is determined using a weighted average source wavelength of 0.15418 nm, decreases due to thermal contraction from 0.4180 to 0.4178 nm for 293 and 251 K. This decrease of only 0.05%…”

A Practical Application of X-Ray Spectroscopy in Ti-Al-N and Cr-Al-N Thin Films

“…According to the XPS literature around Cr-Al-N materials (Barshilia et al, 2007;Del Re et al, 2003;Sanjinés et al, 2002), when the peaks are fitted from experimental results, it is necessary to adjust first the N energy band because it is the element that provides greater reliability for XPS, then, take this first adjust as base, the other peaks related to the remaining elements are adjusted. The latter is indispensable due to the characteristic that is present in this kind of insulating materials (films) with respect to the incident signal, avoiding in this way the uncertainties caused for charging and shifts of the Fermi energy.…”

“…5(c) shows the Al2p3/2 spectrum. Four fitting peaks of the Al peak can be deconvoluted in four peaks at 72.8 eV, 73.9 eV, 75.5 eV and 77.3 eV, moreover these peaks are associated to the Al-Al bond, Al-N, Al x -O and Al 2 O 3 with a single bond, respectively (Lindsay et al, 1973;Sanjinés et al, 2002;Briggs & Seah, 1994;Taylor, 1982;Kuo & Tsai, 2000;Barr, 1983;Endrino et al, 2007). The XPS results demonstrate that Cr and the Al atoms have been bonded with N in the forms of nitride.…”

Effect of magnetic disorder and strong electron correlations on the thermodynamics of CrN

“…8 On the other hand in epitaxially stabilized cubic thin films no sign of magnetic ordering has been seen. [9][10][11] Recently Bhobe et al 12 highlighted the importance of electron correlations in CrN based on photoemission spectroscopy. On the theoretical side the concept of magnetic stress has been introduced and used within a local density approximation ͑LDA͒ framework to explain the orthorhombic distortion.…”