Increase In Work Function Research Articles

Unraveling the influence of defects in Janus MoSSe and Janus alloys MoS2(1−x)Se2x

We investigate the effect of structural and substitutional defects in Janus MoSSe and the Janus alloys MoS2(1−x)Se2x by a comprehensive analysis. Distinct Raman signatures are associated with various defect types and densities, mirroring the evolution from MoSe2 to Janus alloys to ideal Janus MoSSe. By the corresponding stoichiometrical and structural changes, the band gap can be tuned from 1.50 eV up to 1.68 eV at room temperature. Electrical characterization in a field effect device uncovers the impact of defects on conductivity, mobility (up to 2.42 × 10−3 cm2 V−1 s−1), and threshold voltages. A decrease of n-type doping of 5.3 × 1011 cm−2 in Janus MoSSe compared to the Janus alloy points towards an increased work function and a reduction of defects. Our findings deepen the understanding of defect physics in 2D Janus materials and pave the way for tailored defect engineering strategies for advanced (opto-)electronic applications.

Enhancement of Catalytic Activity via Inevitable Reconstruction of the Ni-Mo Interface for Alkaline Hydrogen Oxidation.

The inevitable oxidation of nickel-metal-based catalysts exposed to the air will lead to instability and poor reproducibility of a catalytic interface, which is usually ignored and greatly hinders their application for the catalysis of alkaline hydrogen oxidation. The details on the formation of a world-class nickel-based HOR catalyst Ni3-MoOx/C-500 are reported via an interfacial reconstruction triggered by passive oxidation upon air exposure. Interfacial reconstruction, initiated with various Ni-Mo metal ratios and annealing temperature, can fine-tune the Ni-Mo interface with an increased work function and a reduced d-band center. The optimized Ni3-MoOx/C exhibits a record high mass activity of 102.8mA mgNi -1, a top-level exchange current density of 76.5µA cmNi -2, and exceptional resistance to CO poisoning at 1000ppm CO for hours. The catalyzed alkaline exchange membrane fuel cell exhibits a maximum power output of 600mW cm-2 and excellent stability, ranking it as one of the most active non-precious metals HOR catalysts to date.

Characterization of MoS2:Nb sputtered thin films. An application as hole transport layer in Cu2ZnSnS4/Si tandem solar cells

MoS2:Nb films deposited by radio-frequency magnetron sputtering are investigated in view of their application in infrared (IR)-transparent contacts for tandem photovoltaic devices.This material is already known to give a good electrical contact with p-type chalcogenide semiconductors, which are typically grown onto opaque molybdenum metallic contacts and a MoS2 layer spontaneously forms at the back interface during the on-top semiconductor growth. Our study explores a different approach, which involves the direct growth of IR-transparent MoS2:Nb films via sputtering inside complete photovoltaic devices, like Cu2ZnSnS4 (CZTS)-based single junction solar cells and CZTS/Si tandem devices. Films deposited at different sputtering pressures are compared by analysing their microstructure, morphology, chemical composition, optical and electrical properties. The effects of post-deposition sulfurization treatments are also investigated. We find that MoS2:Nb films deposited at around 0.1 Pa exhibit compactness but show a notable sulfur deficit ([S]/[Mo]≈1.4), a significant sub-bandgap optical absorptance and lack of crystallinity. Increasing the Ar pressure to 1 Pa raises the [S]/[Mo] ratio to 2.2, yielding crystalline films with good IR-transparency, although with a porous morphology. Despite 0.5 wt% Nb-doping of the sputtering target, the as-deposited films demonstrate n-type conductivity likely due to uncontrolled impurities and intrinsic defects. Ultraviolet Photoemission Spectroscopy measurements suggest that films’ work function higher than 5 eV can be obtained with a post-deposition sulfurization, making these materials suitable as Hole Transport Layer in photovoltaic applications. A similar increase in work function is expected in the CZTS/MoS2 junctions, since the sputtered MoS2:Nb films undergo a sulfurization process needed to obtain the overlying polycrystalline CZTS absorber.CZTS solar cells produced with sputtered MoS2 and Transparent Conductive Oxides contacts on glass substrates, despite plagued by severe adhesion problems, show the potentiality to give efficiencies comparable to reference devices with standard Mo back contact. Fabrication of CZTS/Si tandem devices on textured silicon bottom cells yields a maximum efficiency of 4.4 %, primarily hindered by the low quality of the CZTS film on textured substrates. Nonetheless, optoelectronic characterizations based on both spectrophotometric and quantum efficiency measurements confirm a good IR transparency of the MoS2-based intermediate contacts and the desired electrical behaviour.

Co-adsorbed self-assembled monolayer enables high-performance perovskite and organic solar cells

Self-assembled monolayers (SAMs) have become pivotal in achieving high-performance perovskite solar cells (PSCs) and organic solar cells (OSCs) by significantly minimizing interfacial energy losses. In this study, we propose a co-adsorb (CA) strategy employing a novel small molecule, 2-chloro-5-(trifluoromethyl)isonicotinic acid (PyCA-3F), introducing at the buried interface between 2PACz and the perovskite/organic layers. This approach effectively diminishes 2PACz’s aggregation, enhancing surface smoothness and increasing work function for the modified SAM layer, thereby providing a flattened buried interface with a favorable heterointerface for perovskite. The resultant improvements in crystallinity, minimized trap states, and augmented hole extraction and transfer capabilities have propelled power conversion efficiencies (PCEs) beyond 25% in PSCs with a p-i-n structure (certified at 24.68%). OSCs employing the CA strategy achieve remarkable PCEs of 19.51% based on PM1:PTQ10:m-BTP-PhC6 photoactive system. Notably, universal improvements have also been achieved for the other two popular OSC systems. After a 1000-hour maximal power point tracking, the encapsulated PSCs and OSCs retain approximately 90% and 80% of their initial PCEs, respectively. This work introduces a facile, rational, and effective method to enhance the performance of SAMs, realizing efficiency breakthroughs in both PSCs and OSCs with a favorable p-i-n device structure, along with improved operational stability.

Accelerating ion diffusion kinetics with an intensified interfacial electric field for efficient hybrid capacitive deionization

The interfacial electric field (IEF) represents a cutting-edge strategy for enhancing ion diffusion kinetics, pivotal in various technological applications. Despite its extensive use, the mechanisms and strategies for regulating IEF remain underexplored. In this study, we enhanced the IEF in a MnO2-x/g-C3N4 (CN) heterostructure by engineering oxygen vacancies in MnO2, which increased the work function difference between MnO2 and CN. The increased work function difference effectively lowers the energy barrier for electron transfer at the heterostructure interface, thereby intensifying the IEF. The enhanced IEF subsequently provides a more potent driving force, facilitating ion movement within the electrode materials during the desalination process. The modified MnO2-x/CN heterostructure demonstrates a notable salt removal capacity of 45.5 mg g−1 and an impressive salt removal rate of 4 mg g−1 min−1, under an operational voltage of 1.2 V in a 500 mg/L NaCl solution. This research not only deepens our understanding of IEF modulation in materials but also sets the stage for the development of high-performance electrodes for hybrid capacitive deionization systems.

Effect of Metal Work Function on Electron Transfer Kinetics in Electrochemical Reactions

The longstanding problem of explaining the observed dependence of the kinetic rates of electrochemical reactions on the work function of the electrode material (metal) is revisited, based on a recent paper.1 It was proposed that this dependence could be explained in terms of the effect of the work function of the metal on the free energies of activation of the forward and backward electron transfer reactions. In this presentation, we will explore details of the proposed mechanism.In essence, the mechanism is based on the effect of work function on the Galvani potential of the metal at any given applied potential. Even though the total electron energy (Fermi level) of an electron in the electrode must be the same, regardless of the metal, when it is at equilibrium with a given electrolyte, the manner in which that energy is partitioned between the effect of work function and the effect of potential is significantly different for different electrode materials. A higher work function leads to more stabilization of an electron in the metal (lower free energy) and, since the total free energy must remain the same, this lower free energy due to work function must be compensated by a more negative Galvani potential.The classical analysis of the effect of a more negative potential is based on the theory that a change in potential has a greater effect on the initial (reactant) free energy than it does on the free energy of the transition state. Consequently, the activation energy of the forward (cathodic) reaction is decreased by some fraction α of the corresponding increase in electron energy in the metal. This type of analysis is generally used to quantify the effect of changes in applied voltage and derive current-voltage relationships. In this paper we extend the analysis to take account of changes in the (Galvani) potential ϕm of the metal due to changes in work function Φm.It is reasonable to assume that a change in ϕm will have a similar effect whether it occurs due to a change in applied voltage or due to a change in the work function of the metal. This implies that an increase in work function with a corresponding negative shift in Galvani potential can lead to a lowering of activation energy and so to faster kinetics. However, we must also consider a possible change in activation energy arising from the decreased electron energy (increased stabilization) due to higher work function. If this caused a change in activation energy it would be expected to be in the opposite direction to the change due to Galvani potential, since it would be expected to lower the initial free energy by a greater amount than that of the transition state.The presentation will consider in detail the interplay of these effects and the consequent implications for modelling electrode kinetics. K. S. R. Dadallagei, D. L. Parr IV, J. R. Coduto, A. Lazicki, S. DeBie, C. D. Haas, and J. Leddy, J. Electrochem. Soc. 170, 086508 (2023)

Spatial and Bidirectional Work Function Modulation of Monolayer Graphene with Patterned Polymer "Fluorozwitterists".

Understanding the electronic properties resulting from soft-hard material interfacial contact has elevated the utility of functional polymers in advanced materials and nanoscale structures, such as in work function engineering of two-dimensional (2D) materials to produce new types of high-performance devices. In this paper, we describe the electronic impact of functional polymers, containing both zwitterionic and fluorocarbon components in their side chains, on the work function of monolayer graphene through the preparation of negative-tone photoresists, which we term "fluorozwitterists." The zwitterionic and fluorinated groups each represent dipole-containing moieties capable of producing distinct surface energies as thin films. Kelvin probe force microscopy revealed these polymers to have a p-doping effect on graphene, which contrasts the work function decrease typically associated with polymer-to-graphene contact. Copolymerization of fluorinated zwitterionic monomers with methyl methacrylate and a benzophenone-substituted methacrylate produced copolymers that were amenable to photolithographic fabrication of fluorozwitterist structures. Consequently, spatial alteration of zwitterion coverage across graphene yielded stripes that resemble a lateral p-i-n diode configuration, with local increase or decrease of work function. Overall, this polymeric fluorozwitterist design is suitable for enabling simple, solution-based surface patterning and is anticipated to be useful for spatial work function modulation of 2D materials integrated into electronic devices.

Electronic structure and properties of activated Al0.5Ga0.5N thin films and nanowires photocathode surface adsorbed with residual gas

To study effect of residual gas in vacuum system on structure and electrical performance of activated AlGaN photocathodes, adsorption models for H2O, CO and CO2 adsorbed on Al0.5Ga0.5N activated surfaces are established and investigated. The results indicate that activated Al0.5Ga0.5N surfaces are not easily adsorbed by residual gases compared to pristine surface. For Al0.5Ga0.5N thin film, H2O and CO exhibit higher affinity for adsorption on Cs/NF3-activated surfaces, while CO2 shows greater tendency to adsorb on Cs-activated surface·H2O, CO and CO2 are most easily adsorbed on Cs/NF3-activated surface for Al0.5Ga0.5N nanowires. Work function of Cs/NF3-activated thin film surface is 2.34 eV, and after adsorbing H2O, CO and CO2, work functions are 1.84 eV, 2.37 eV, and 3.43 eV, respectively. This means that residual gas will increase work function and is harmful to quantum efficiency improvement.

Transition Metal (Cu, Pd, and Ag)-Modified Nb2S2C Monolayer for Highly Efficient Catechol Sensing: A First-Principles Investigation.

Motivated by recent advancements and the escalating application of two-dimensional (2D) gas or molecule sensors, this study explores the potential of the 2D Nb2S2C monolayer for detecting biomolecule catechol (Cc), whose excess concentration is highly dangerous to living beings. We use first-principles density functional theory (DFT) calculations to assess the Cc sensing performance of pure and transition metal (TM = Cu, Pd, Ag)-modified Nb2S2C monolayers. The Nb2S2C monolayer belonging to the new class of synthesized 2D materials, TM carbo-chalcogenides (TMCC), combines distinctive properties from both TM dichalcogenides and TM carbides and exhibits physisorption (-0.66 eV) toward the Cc molecule. Notably, the surface modifications with these TMs significantly enhanced the adsorption energy of Cc. The chemisorption of the Cc molecule on the Pd to Cu-modified monolayer is demonstrated with adsorption energies ranging from -1.09 to -1.3 eV and is due to the robust charge transfer and orbital interactions between the valence orbitals of TMs and Cc. In addition, the modification of the surface by TM leads to an increased work function sensitivity toward the Cc molecule. The study establishes the thermal stability at 300 K and dynamic stability of TM-Nb2S2C through ab initio molecular dynamics (AIMD) simulations and Phonon calculations, respectively. The theoretical estimation of achievable recovery time at 400 and 450 K for Pd and Ag and at 500 K for the Cu-modified Nb2S2C monolayer, respectively, confirms the potential practical application of the sensor for Cc detection. These compelling characteristics position the Nb2S2C monolayer as a promising nanomaterial for detecting Cc molecules in the environment.

Gas adsorption on activated AlGaN photocathode: A first-principle study on charge redistribution, work function variation and emission performance attenuation

AlGaN photocathode has important applications in photoelectronic imaging and vacuum electronic devices. However, The short lifetime of the photocathode results in higher costs of usage. This can be attributed to the decrease in vacuum degree and the adsorption of residual gases. In this study, first-principle study and transmission matrix are utilized to investigate five gases (H2O, CO, CO2, H2, CH4) adsorbed on Cs-activated AlGaN (100) surface. Results suggest that all these five gases are prior to deposit on the surface at low coverage of 0.25 ML with adsorption energy of -2 eV. CO has the highest adsorption possibility with its adsorption energy lower than 0 eV. Significant charge transfer occurs at Cs-gas interface, particularly near the oxygen atoms of oxygen-containing molecules. CO2 and CO exhibit a noticeable increase in work function. The increase in the work function of the H2O adsorption is primarily due to its longer dipole length rather than dipole charge by analysing the surface dipole moment. CH4 and H2 have negligible impact on surface properties. Upon gas adsorption, the electrons on the AlGaN surface flow back to the adatoms, causing the CBM shift towards higher energy and upwards band bending. Combined with the surface electron affinity, the iteration of band structures further explains the increase of work function. The open energy of free electron escaping into the vacuum after CO2 adsorption increases to the level of inactivated surface of 5.55 eV from PBE-D2. This study reveals the mechanism of performance decay of the photocathode and is expected to guide the optimization of packaging technology.

Study on trap sensitivity for single material gate and double material gate nano-ribbon FETs

In this work, the trap sensitivity of single material gate (SMG) and dual material gate (DMG) nano ribbon FETs (NRFETs) are reported using TCAD Sentaurus Device simulator. The trap sensitivity is extracted for Gaussian trap distribution of both acceptor and donor type traps. We have reported the trap sensitivity for the variation in trap concentration, energy peak position, work function of metal gate, and temperature for both the NRFETs. It is realized that trap sensitivity is greater and lesser than 100% for acceptor type trap in SMG and DMG NRFETs, respectively, whereas, such sensitivity is 147% and 123% for donor type trap concentration, respectively. Temperature also shows a significant variation in trap sensitivity for both the NRFETs. The increase in work function leads to the reduction in trap sensitivity for both NRFETs in existence of acceptor and donor trap charges. The maximum sensitivity in trap are 400% and 275% for SMG and DMG NRFETs, respectively, in presence of donor trap concentration. Moreover, the trap sensitivity is very insignificant at high gate bias for donor type trap concentration with wide variation in parameters.

Towards ITER-Relevant CW Extraction at Negative Ion Sources for Fusion

Negative hydrogen or deuterium ion sources for neutral beam injection (NBI) systems used at fusion devices are based on the surface production process at a caesiated low work function converter surface. While producing a stable and globally homogeneous negative ion beam is not an issue, during long pulses typically a pronounced increase in the co-extracted electrons is observed, limiting the pulse length or the achievable performance. This effect is particularly pronounced in deuterium and it is attributed to an increasing work function of the converter surface. In the last years the negative ion source test facilities at IPP Garching, BATMAN Upgrade (using the small prototype source) and ELISE (using a source of the same width but only half the height of the ITER NBI source) have been converted into CW machines, making possible investigating at ITER conditions counter-measures for the increase in the co-extracted electrons. Investigations are performed, mainly at ELISE, on homogenizing and stabilizing the co-extracted electrons by affecting the ion source plasma close to the converter surface by means of biasing (additional) surfaces in the plasma.

Photoswitchable optoelectronic properties of 2D MoSe2/diarylethene hybrid structures

The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe2 with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe2, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe2, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe2 to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe2. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe2/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices.

Impact of the gate work function on the experimental I-V characteristics of MOS solar cells simulated with the Sentaurus TCAD software

In this work, the influence of gate work function on the experimental J-VG characteristics of MOS solar cells was investigated with the aid of the Sentaurus TCAD for 2D numer-ical simulations of TiN/SiOxNy/Si Al/SiOxNy/Si and Al/MgO/Mg/SiOxNy/Si structures aiming at solar cells for en-ergy harvesting applications. The increase of the gate work function led to the increase of the reverse current density as pointed out by the Sentaurus TCAD simulations and by the ex-perimental J-VG characteristics. The work functions of Mg, Al, and un-annealed TiN used in the TCAD simulations were 3.7 eV, 4.1 eV, and 4.4 eV, respectively. It was observed that the onset voltage at 0.5 mA/cm2 in the forward-biasing region was at a lower voltage for TiN (~ - 0.06 V) compared to Al (~ - 0.42 V) and the Al/MgO/Mg stack (~ - 0.47 V). On the other hand, the current density increased steeply in the forward biasing for TiN and Al compared to the Al/ MgO/Mg stack gate and the thin MgO layer between Al and Mg worked as a potential barrier in an opposite direction to the potential barrier of the Mg/Si-OxNy/Si structure, which meant an onset voltage lowering for the Al/MgO/Mg/SiOxNy/Si solar cell. For the Al/MgO/Mg stack, the barrier effect of the MgO layer was fitted as a series re-sistance RS = 100 Ω and an equivalent Al/MgO/Mg work func-tion of 4.15 eV considering a substrate doping NA = 1.2x1016 cm-3 and parallel conductance GP = 0. Also, the experimental JxVG characteristic of the Al/SiOxNy/Si cell was fitted for Al work function of 4.10 eV, a series resistance RS = 100 Ω, a parallel resistance RP = 0.02 Ω (GP = 50 S) and a substrate doping NA = 5.5x1015 cm-3. In this case, the high parallel conductance fitted was attributed to the tunneling through the dielectrics as a pre-dominant effect possibly caused by a high concentration of de-fects in the SiOxNy layer. Finally, the MOS solar cell parameters were relatively lower compared to those of commercial outdoor solar cells, but the power generated by the MOS cells reached the mW range, and the conversion efficiency from light energy into electrical energy was higher (12.7%) than the typical values found for energy-harvesting solar cells.

Phenyltrimethylammonium chloride additive for highly efficient and stable FAPbI3 perovskite solar cells

Formamidinium lead triiodide (FAPbI3)-rich perovskite absorbers have emerged as the frontrunners for the development of perovskite solar cells (PSCs), but pristine FAPbI3 absorber exhibits phase instability because of external stressors during device manufacture and operation. In this work, we systematically study the function of a trace amount of phenyltrimethylammonium chloride (PTAC) additive in FAPbI3-based perovskites. The introduced PTAC have a strong electrostatic interaction with perovskite because of the coordination of electron-rich benzene ring unit and under-coordinated Pb2+, which leads to the decrease of the trap density and the release of the lattice strain. Simultaneously, the increased work function of modulated film optimizes the band alignment, promoting carrier transport and reducing nonradiative recombination, thereby improving the open-circuit voltages and fill factors. Consequently, the modulated PSCs achieve a champion power conversion efficiency of 24.51%, and exhibit much better stability by retaining 90% of their initial efficiency after 1000 hours constant illumination under maximum power point tracking measurement.

Structure evolution and energy band modulation in Ba-doped BiFeO3 thin films

Bi1−xBaxFeO3 (BBFO, x = 0, 0.03, 0.1) thin films were epitaxially grown on SrRuO3-buffered SrTiO3 (001) substrates by pulsed laser deposition. With increasing Ba content, the BBFO thin films show significantly reduced leakage currents but suppressed ferroelectric polarization. X-ray diffraction reciprocal space mappings and Raman spectra indicate a structural evolution from a rhombohedral-like to tetragonal-like phase in the BBFO thin films. Optical absorption and photoelectron spectroscopy measurements demonstrate a modulation of energy band structures in the BBFO thin films. With A-site Ba acceptor doping, the BBFO thin films exhibit a blue-shift of optical bandgap and an increase in work function. The energy positions of conduction and valence bands of the BBFO thin films have been modulated, and the Fermi level shifts down to the center of the forbidden band, but acceptor-doped BFO thin films still show n-type conduction. The presence of extra oxygen vacancies by acceptor doping is supposed to make contribution to conduction behavior. This study provides a method to manipulate the functional properties and gives insights into the physics of Ba doping in BFO thin films.

The Regulation of Photoelectronic Property and Energy State of FAPbI3 Surface Via Ligand Dipole Design

Although the adding multifunction ligand can regulate the perovskite property, the effect of the enhancement depends on the ligand structure. In this paper, the polarity of aromatic ligand is regulated by design strategy — introducing fluorine (F) atom and alkyl chain (R-NH3). Those ligands affect the structure, photoelectric properties and energy state of formamidinium (FAPbI3) perovskite surface. The ligand polarity increases with more F atoms and R-NH3 length, which increases fermi energy and then decreasing band gap and increasing work function (WF). The CF3-PEA/BEA obtains the higher polarity and then increasing WF of the surface system from 6.21 eV to the higher 6.46 eV.

Interplay of Adsorption Geometry and Work Function Evolution at the TCNE/Cu(111) Interface.

The adsorption of organic electron acceptors on metal surfaces is a powerful way to change the effective work function of the substrate through the formation of charge-transfer-induced dipoles. The work function of the interfaces is hence controlled by the redistribution of charges upon adsorption of the organic layer, which depends not only on the electron affinity of the organic material but also on the adsorption geometry. As shown in this work, the latter dependence controls the work function also in the case of adsorbate layers exhibiting a mixture of various adsorption geometries. Based on a combined experimental (core-level and infrared spectroscopy) and theoretical (density functional theory) study for tetracyanoethylene (TCNE) on Cu(111), we find that TCNE adsorbs in at least three different orientations, depending on TCNE coverage. At low coverage, flat lying TCNE dominates, as it possesses the highest adsorption energy. At a higher coverage, additionally, two different standing orientations are found. This is accompanied by a large increase in the work function of almost 3 eV at full monolayer coverage. Our results suggest that the large increase in work function is mainly due to the surface dipole of the free CN groups of the standing molecules and less dependent on the charge-transfer dipole of the differently oriented and charged molecules. This, in turn, opens new opportunities to control the work function of interfaces, e.g., by synthetic modification of the adsorbates, which may allow one to alter the adsorption geometries of the molecules as well as their contributions to the interface dipoles and, hence, the work function.

Studies on the Cooperative Influence of Cr and Mo on the Pitting Corrosion Resistance of Super Austenitic Stainless Steels

The effects of varying Cr and Mo concentrations on the pitting corrosion resistance of super austenitic stainless steels in Cl− solutions were investigated using a combination of immersion experiments, electrochemical measurements, X-ray photoelectron spectroscopy, and first-principles computational simulations. The surface characteristics, impedance, and defect concentration of the passive film were changed, and this eventually resulted in a decrease in the number of pitting pits. Due to a decrease in active sites within the passive film, a delayed beginning of pitting, and the combined effect of MoO42− inhibitors, it was discovered that an increasing Mo concentration slows the rate of pitting extension, resulting in reduced maximum pitting area and depth. Additionally, Mo increased the adsorption energy of nearby atoms, whereas Cr raised the adsorption energy of itself. Interestingly, compared with individual doping, co-doping of Cr and Mo increased work function and adsorption energy, indicating a synergistic impact in enhancing resistance to Cl− corrosion.

Thermal stability, work function and Fermi level analysis of 2D multi-layered hexagonal boron nitride films

Thermal stability and Fermi level analysis of commercial multilayer (ML) and as-grown 10 nm thick hexagonal boron nitride (hBN) films on Cu foil by atmospheric chemical vapor deposition (APCVD) by heating in N2 and air at temperatures ≤900 °C are studied. For all samples, progressive surface oxidation was observed correlating with higher hBN nucleation density. Thermal stability was measured in air from 200 °C to 400 °C (relative humidity ∼65%) where commercial ML and APCVD material degraded; BN peaks begin to be replaced by BO peaks at temperatures >300 °C. It is shown that hBN thermal stability is sensitive to Tgrowth and Cu foil surface preparation methods such as electropolishing (EP). We evaluate as-grown material for different Tgrowth conditions (1000 °C, 1030 °C, 1050 °C and 1060 °C) by ultraviolet photoelectron spectroscopy (UPS) to locate and understand subsequent Fermi level and work function variation, confirming our material is in general n-type, which becomes increasingly so as thermal stability regresses. To this effect, we observe a work function increase of 0.45 eV as BO increases with in-situ anneal temperature. An average electron affinity of 2.13 eV and 1.7 eV is determined for commercial hBN and APCVD material, respectively. Further work is required by material scientists to optimize the material properties of CVD hBN.