Weak Field Tuning of Transition-Metal Dopant Hybridization in Solid Hosts

Abstract

Transition-metal (TM)-doped solids are one of the most extensively studied compounds in the fields of catalysis, magnetism, solar cells, etc., due to their tunable optoelectronic properties that stem from TM energy-level hybridization. In this work, the hybridization of the Ni–O bond in TiO2:Ni films was controlled in a stable, reversible manner via surface functionalization with polarized molecules. The Ni-doped TiO2 surface was functionalized with para-benzoic acid groups to modify the electron density distribution within the film. The dopant distribution and elemental composition at the interface are probed via high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy mapping. The effect of the surface modification on the dopant, Ni2+, is studied via surface-sensitive electronic characterization techniques, such as X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy (XAS). The electron density in the valence orbitals of the dopant was observed to be a function of the dipole moment of the para-substituted benzoic acid. The resulting XAS spectra of the Ni2+ after surface modification of TiO2:Ni films were modeled (CTM4XAS) and indicated ligand-dependent symmetry breaking around the Ni2+ at the functionalized interface. Therefore, the modified electron density at the interface due to the polarized molecules is observed to impact the hybridization of the TM dopant energy levels in solid hosts. This phenomenon of adaptive dopant hybridization in a solid host (TiO2) can be exploited to obtain tunable optical responses from TM-doped inorganic phosphors, which have an impact in various fields, such as luminescent displays, solar cells, sensors, telecommunications, counterfeit technologies, and biodetection.

Elucidating the Redox Behavior during Atomic Layer Deposition on Lithium-Ion Battery Cathode Materials

“…High-resolution (HR) XPS measurements were performed for C 1s, O 1s, Al 2p, Li 1s, and M 2p (M = Ni, Co, Mn), at the relevant binding energy ranges for these features. The spectra were processed using CasaXPS , post-processing software. Charge correction was performed by referencing to the adventitious C 1s peak at 284.8 eV.…”

Adsorption of Polarized Molecules for Interfacial Band Engineering of Doped TiO2Thin Films

“…The film roughness, conformality, and optical absorption have been observed to be similar to what has been reported previously. 17 The diffraction pattern of the TiO 2 :Ni 2+ (10 mol %) film indicates that all the major diffraction peaks correspond with the anatase TiO 2 structure (Figure S1a), suggesting the crystalline nature of the doped TiO 2 films. Additionally, X-ray photoelectron spectroscopy (XPS) measurements indicate the presence of Ti, Ni, O, and C elements in the survey spectrum (Figure S1b).…”

“…Optimum Ni doping concentration of 10 mol % was chosen in this study as previous reports show that higher doping concentrations tend to form impurity phases such as NiTiO 3 or NiO. 17,27,28 Dosing of TiO 2 /TiO 2 :Ni 2+ Films. The vapors of BZA ligands were adsorbed onto the surface of pure TiO 2 and TiO 2 :Ni 2+ (10 mol %) films using in situ physical vapor deposition method.…”

“…39,40 The UPS spectrum of TiO 2 :Ni 2+ film confirms a homogeneous Ni distribution based on the overall shift (0.2 eV) toward the Fermi level and slight increase in the intensity of the Ti 3+ defect peak due to the formation of oxygen vacancies upon Ni doping. 17 More importantly, the absence of spectral features in the lower BE region (0−2 eV) indicate that Ni 2+ is substitutionally doped into the host TiO 2 lattice without the formation of impurity phases such as NiTiO 3 , NiO, or metallic Ni. 17,27,41 Next, para-substituted benzoic acid (BZA) molecular dipoles were adsorbed on the surface of the pure TiO 2 and TiO 2 :Ni 2+ (10 mol %) films via in situ vapor deposition to reversibly engineer their band structures.…”

Dipole-Modulated Downconversion Nanoparticles as Label-Free Biological Sensors

“…The surface of the CSNPs was functionalized with biotin using carboxylic acid chemistry 30 instead of capping ligands or cross-linking agents, both of which require complex reaction chemistries. Fourier-transform infrared spectroscopy (FTIR) verified the successful conjugation of biotin to the CSNP surface by exhibiting the presence of a sharp peak at 1686 cm −1 in the spectrum of the functionalized CSNPs, assigned to the stretching vibration of the amide bond (Figure S1B).…”