Interfacial Chemistry with ZnO: In Operando Work Functions in Heterocells

Abstract

Interfacial additives such as oxides may help solve diffusion and nucleation obstacles in heterojunctions of solid-state devices. Healing strategies may rely on them, particularly in ZnO, which has numerous applications, from photovoltaics and sensors to superconductors and batteries as a lithiumphilic interlayer. Here, we show a case study based on in operando cells with two heterojunctions and the ZnO as a dielectric semiconductor. The cells show how the Cu/ZnO surface chemical potentials equalize by forming a more negatively charged region where nucleation of a new phase will likely be facilitated and the dielectric's role in interlaying with negative and positive electrodes. The highly ohmic behavior of the interface, negative electrode (metal)/dielectric, is also analyzed. The advantage of the scanning Kelvin probe (SKP) in studying the surface chemical potentials is demonstrated. Ab initio simulations used density functional theory (DFT) and hybrid functional HS06 to determine the bulk ZnO's band structure and optical properties, including relative permittivities. Aluminum, zinc, copper, and zinc oxide work functions were obtained after simulating the correspondent surfaces and compared with contact potentials obtained with SKP. The study extends hyperbolically into the cell's dimensions to understand all of the interplays of the components. An unexpected long-range equalization of the surface chemical potentials of the three cell constituents away from the interfaces may mirror a metal−insulator−metal plasmonic interaction that can be tailored for solar applications.

Cathodes pinpoints for the next generation of energy storage devices: the LiFePO4 case study

“…Copper and lithium tend to have higher DOS when compared with aluminum, which shows very similar DOS for electrons and holes, explaining its high capacity to deliver a broad range of surface chemical potentials, as pointed out by the authors previously [24,25]. Notably, the conjunction of the highest DOS with a high charge carrier density defines the working chemical potential, which may be severely shifted from the calculated workfunction at null surface potential.…”

“…Conversely to 100% C black (SI, figure S6), as described hereafter, 50 wt.% LFP + 50 wt.% C black aligns its surface chemical potential through the Cu by electron transport in the Cu/50 wt.% LFP + 50 wt.% C black /Al cell. In figures 4(a) and (b), the negatively charged plasmons (solitons) are observed and part of their dynamics [24,25]. The cell transports electrons through the Cu/50 wt.% LFP + 50 wt.% C black surface (figures 4(a)and (b), SI, figures S8(a) and (b)).…”

Cork: Enabler of sustainable and efficient coaxial structural batteries

“…The materials and cells were prepared as described in Supplementary Information SI Materials and Methods [ [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] ]. As shown hereafter, the cork's cell structure is prone to polarize in rod chains, as discussed previously.…”

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Fig. 3 Topography and surface chemical potential characterization of two copper/cork heterojunctions; a to c capacitive tracking measurement CTM and scanning kelvin probe SKP [ 40 ] showing the topography and surface chemical potentials of the Cu-tape and cork of the same heterojunction; The cork shows an impurity charged positively; d surface chemical potential of another Cu-cork-Cu heterojunction showing similar values for the potentials as b and c.

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“…Note : r a = 2 mm; r b = 5 mm; ℓ = 95 mm (SI, 1. Materials and Methods [ [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] ]). …”