Photoluminescence Spectroscopy of Cuprous Oxide: Bulk Crystal versus Crystalline Films

Abstract

Cuprous oxide (Cu2O) crystals and films of 10–65 nm thickness are investigated via electron diffraction, scanning tunneling microscopy (STM), and photoluminescence (PL) spectroscopy at temperature between 100 to 300 K. While the chemical composition and surface morphology of both systems are identical, large differences are found in the optical response. Bulk Cu2O shows pronounced PL peaks at 620, 730, and 920 nm, compatible with the radiative decay of free and bound excitons, whereas broad and asymmetric peaks at 775 and 850 nm are found for Cu2O films grown on Au(111) and Pt(111) supports. The latter represent the PL signature of VO2+ and VO+ defects, being inserted with substrate‐dependent concentrations due to the oxygen‐poor preparation of the Cu2O films. Despite the strong VO signature in PL, all Cu2O samples show p‐type conductance behavior in STM spectroscopy, indicating an abundance of Cu defects in the lattice. The fact that O vacancies still govern the thin‐film PL is explained by a more efficient recombination via VO‐ than Vcu‐emission channels, as the latter requires exciton formation first. Herein, the high sensitivity of low‐temperature PL to probe the defect landscape of dielectrics, being neither reached by photoelectron spectroscopy nor scanning probe techniques is demonstrated.

Fabrication and Wetting Characteristics of Copper Thin Film: An Active Layer for SPR-based Sensor Applications

“…7. The two bands 744 nm (1.67 eV) and 820 (1.55 eV) nm are attributed to oxygen vacancies corresponding to doubly ionized vacancies and single ionized vacancies respectively [50][51]. As for the thin lm of pristine Cu, two PL peaks at about 765 nm (1.62 eV) and 785 nm (1.58 eV) are possibly due to electronic levels Vo + 2 and V Cu respectively.…”

“…vacancies, whereas a shifted and low PL emission at 778 nm (1.59 eV) could be the transformation of Cu to CuO at high temperature treatments [51].…”

Light Emission from Single Oxygen Vacancies in Cu2O Films Probed with Scanning Tunneling Microscopy

“… 31 , 32 Their intensity ratio depends on the hole concentration in the oxide VB, whereby the strong p-type character of Cu 2 O/Au(111) promotes formation of V O2+ defects and leads to a more intense 750 nm peak. 33 Other PL peaks intrinsic to bulk Cu 2 O, especially the free-exciton emission at 620 nm and the V Cu mediated peak at 920 nm, are not detected here because of the finite crystallinity, i.e., the abundance of nonradiative decay channels, in the supported films. 34 In fact, long excitation lifetimes are required to detect the dipole-forbidden Cu 2 O excitons, rendering them invisible in typical nanocrystalline films and powders.…”

“…The spectrum reveals an asymmetric band that can be decomposed into two Gaussians centered at 750 and 850 nm. According to earlier work, they are assigned to the emission from double- (V O2+ ) and single-charged (V O+ ) oxygen vacancies in the lattice. , Their intensity ratio depends on the hole concentration in the oxide VB, whereby the strong p-type character of Cu 2 O/Au­(111) promotes formation of V O2+ defects and leads to a more intense 750 nm peak . Other PL peaks intrinsic to bulk Cu 2 O, especially the free-exciton emission at 620 nm and the V Cu mediated peak at 920 nm, are not detected here because of the finite crystallinity, i.e., the abundance of nonradiative decay channels, in the supported films .…”

“…The PL signature of V O2+ and V O+ complexes in Cu 2 O are peaks at 750 and 850 nm, broadened to 80–100 nm FWHM due to finite sample crystallinity. 33 , 34 , 36 , 37 The underlying decay channels were assigned by density functional theory (DFT) to in-gap resonances at 1.6 and 1.5 eV above the VB top, introduced by V O2+ and V O+ defects, respectively. 38 While V O2+ centers preferentially develop in highly p-type oxides with the VB top pinned to E F , as in our case, any downshift of the VB promotes the formation of single-charged V O+ defects.…”