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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Electronic and mechanical properties of graphene-germanium interfaces grown by chemical vapor deposition

Epitaxially oriented wafer-scale graphene grown directly on semiconducting Ge substrates is of high interest for both fundamental science and electronic device applications. To date, however, this material system remains relatively unexplored structurally and electronically, particularly at the atomic scale. To further understand the nature of the interface between graphene and Ge, we utilize ultrahigh vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) along with Raman and X-ray photoelectron spectroscopy to probe interfacial atomic structure and chemistry. STS reveals significant differences in electronic interactions between graphene and Ge(110)/Ge(111), which is consistent with a model of stronger interaction on Ge(110) leading to epitaxial growth. Raman spectra indicate that the graphene is considerably strained after growth, with more point-to-point variation on Ge(111). Furthermore, this native strain influences the atomic structure of the interface by inducing metastable and previously unobserved Ge surface reconstructions following annealing. These nonequilibrium reconstructions cover >90% of the surface and, in turn, modify both the electronic and mechanical properties of the graphene overlayer. Finally, graphene on Ge(001) represents the extreme strain case, where graphene drives the reorganization of the Ge surface into [107] facets. From this study, it is clear that the interaction between graphene and the underlying Ge is not only dependent on the substrate crystallographic orientation, but is also tunable and strongly related to the atomic reconfiguration of the graphene–Ge interface.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Non-Faradaic Li + Migration and Chemical Coordination across Solid-State Battery Interfaces

Efficient and reversible charge transfer is essential to realizing high-performance solid-state batteries. Efforts to enhance charge transfer at critical electrode–electrolyte interfaces have proven successful, yet interfacial chemistry and its impact on cell function remains poorly understood. Using X-ray photoelectron spectroscopy combined with electrochemical techniques, we elucidate chemical coordination near the LiCoO 2 –LIPON interface, providing experimental validation of space-charge separation. Space-charge layers, defined by local enrichment and depletion of charges, have previously been theorized and modeled, but the unique chemistry of solid-state battery interfaces is now revealed. Here we highlight the non-Faradaic migration of Li+ ions from the electrode to the electrolyte, which reduces reversible cathodic capacity by ~15%. Inserting a thin, ion-conducting LiNbO 3 interlayer between the electrode and electrolyte, however, can reduce space-charge separation, mitigate the loss of Li+ from LiCoO 2 , and return cathodic capacity to its theoretical value. This work illustrates the importance of interfacial chemistry in understanding and improving solid-state batteries.

Gittleson, Forrest S.↗
DOE OSTI2018

Heat Transfer at Hybrid Interfaces: Interfacial Ligand-to-Nanocrystal Heating Monitored with Infrared Pump, Electronic Probe Spectroscopy

The transfer of thermal energy from the ligand passivating layer to the inorganic core of colloidal nanocrystals is observed using infrared-pump, electronic-probe (IPEP) spectroscopy. Inorganic nanocrystals are excellent model systems for organic-inorganic hybrid interfaces as they have much larger surface-to-volume ratios than bulk solids, which facilitates spectroscopic measurements of weak signals. Such interfaces between disparate materials are challenging to probe by traditional methods. In this work, resonant excitation of the hydrocarbon ligand vibrational absorptions results in a transient red-shift of the CdSe nanocrystal excitonic features consistent with heating, as demonstrated by steady-state absorption measurements, which provide a calibration of the pump-induced temperature rise. The time constant associated with heating ranges from 10 ps to 30 ps depending on the sample morphology, static temperature, input fluence, and environment, all of which are studied in this work. Heat transfer speeds up and the magnitude of nanocrystal heating decreases at higher temperatures. Unlike chemical modulation of electrical conductivity, ligand exchange for several common organic ligands does not dramatically change the interfacial conductivity of the nanocrystal-ligand interface. However, changes in the medium (e.g. solvent) do change the rate of heat outcoupling from the nanocrystal-ligand complex. Lastly, although applied here to nanocrystals to measure interfacial heat transfer, IPEP spectroscopy is readily applicable for any heterogeneous system in which one component has spectrally-isolated phonon modes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Interface Engineering for 25% CdTe Solar Cells

Buffer layers, such as CdS and Mg x Zn 1-x O (MZO), are critical for CdTe and other thin film polycrystalline solar cells. A ternary compound, such as MZO, allows for interface engineering by adjusting composition, bandgap, and doping to manipulate barriers and recombination to enhance thin film efficiencies toward 25%. Here, theoretical studies demonstrate the enormous impact of front interface offset and emitter doping have on device performance. The results reveal it is possible to achieve 25% device efficiency with open-circuit voltage >1 V, even for 10 5 cm/s recombination velocity, provided the interface offsets and doping are properly engineered.

14 SOLAR ENERGY↗
DOE OSTI2019

Dye Nanoaggregate Structures in MK-2, N3, and N749 Dye···TiO 2 Interfaces That Represent Dye-Sensitized Solar Cell Working Electrodes

The working electrode of a dye-sensitized solar cell (DSSC) consists of dye molecules adsorbed onto nanoparticles of a semiconductor such as TiO 2 . A reliable prediction of the DSSC photovoltaic performance of a given dye requires in-depth knowledge about the precise structure of the dye···TiO 2 interface. In this work, X-ray reflectometry (XRR) and grazing-incidence small-angle X-ray scattering (GISAXS) are employed to determine the dye···TiO 2 interfacial structure and associated dye aggregation behavior of three high-performance DSSC dyes, i.e., a metal-free organic dye, MK-2, and the two archetypal ruthenium-based organometallic dyes, N3 and N749 (Black Dye). Results show that all three dyes form nanoaggregates in dye···TiO 2 interfaces. We determine the dye nanoaggregate separations, sizes, distribution densities, and the extent of short-range order within each dye self-assembly in the longitudinal and lateral directions. Dye···TiO 2 composites fabricated using dye solutions of varying concentrations are analyzed. We find that nanoaggregates of the three dyes are separated by several hundred nanometers (158-203 nm) in dye···TiO 2 interfaces that have been fabricated using concentrated dye solutions (0.5 mM or 1.0 mM). MK-2 and N749 dyes also display smaller interparticle separations. Dye nanoparticle diameters are of the order of 156-198 nm, sizes that are comparable to the largest interparticle separations. Thus, no extraneous dye particles can be fitted into gaps between particles, so the dye self-assembly is saturated. Self-assemblies of all three dyes exhibit both lateral and longitudinal short-range order; N3 displays a particularly short coherence length along the TiO 2 surface, with extensive structured disorder along the longitudinal direction. The operation of DSSC working electrodes would therefore seem to be dependent on a dye self-assembly that may exhibit several levels of structural granularity and dye aggregation effects.

14 SOLAR ENERGY↗
DOE OSTI2024

Thermal Transport and Mechanical Stress Mapping of a Compression Bonded GaN/Diamond Interface for Vertical Power Devices

Bonding diamond to the back side of gallium nitride (GaN) electronics has been shown to improve thermal management in lateral devices; however, engineering challenges remain with the bonding process and characterizing the bond quality for vertical device architectures. Here, in this study, integration of these two materials is achieved by room-temperature compression bonding centimeter-scale GaN and a diamond die via an intermetallic bonding layer of Ti/Au. Recent attempts at GaN/diamond bonding have utilized a modified surface activation bonding (SAB) method, which requires Ar fast atom bombardment immediately followed by bonding within the same tool under ultrahigh vacuum (UHV) conditions. The method presented here does not require a dedicated SAB tool yet still achieves bonding via a room-temperature metal–metal compression process. Imaging of the buried interface and the total bonding area is achieved via transmission electron microscopy (TEM) and confocal acoustic scanning microscopy (C-SAM), respectively. The thermal transport quality of the bond is extracted from spatially resolved frequency-domain thermoreflectance (FDTR) with the bonded areas boasting a thermal boundary conductance of >100 MW/m 2 ·K. Additionally, Raman maps of GaN near the GaN–diamond interface reveal a low level of compressive stress, <80 MPa, in well-bonded regions. FDTR and Raman were coutilized to map these buried interfaces and revealed some poor thermally bonded areas bordered by high-stress regions, highlighting the importance of spatial sampling for a complete picture of bond quality. Overall, this work demonstrates a novel method for thermal management in vertical GaN devices that maintains low intrinsic stresses while boasting high thermal boundary conductances.

Raman↗
DOE OSTI2025

Hydration and Restructuring of Polar Polymer Interfaces: Implications in Antifouling and Responsive Materials

Manipulating polymer interfaces is crucial for understanding how structure influences function in applications spanning biofouling prevention to energy storage. Moreover, observing how polymers adapt their microscopic structure to changes in their local environment can reveal essential properties that govern their performance in such applications, providing key insights into how to design more effective interfaces. Here, in this study, a series of “grafting-from” polymer brushes with side chains varying in charge, are probed by sum frequency generation (SFG) and modeled using all-atom molecular dynamics (MD) simulations to elucidate how chemical makeup and charge mediate interfacial restructuring in dry versus hydrated states. Results show that charge, in progressing from nonpolar to cationic to zwitterionic, results in dramatic changes in interfacial structure and overall hydration. While net neutral systems, regardless of bulk phase polarity, show minimal interfacial water structuring, the cationic species exhibits strong bulk water signals from the surface potential. Meanwhile, the polymer brushes themselves restructure in water differently independent of charge, impacting the functional groups that are presented to the aqueous phase. Nonpolar and cationic species for instance undergo a change in alkyl group orientations to accommodate hydrating water molecules, whereas the zwitterionic polymer becomes completely disordered in water. Overall, the structure-based behavior trends presented herein have implications in antifouling applications and responsive material interfaces.

biointerface↗
DOE OSTI2018

Interface Engineering of Earth-Abundant Transition Metals Using Boron Nitride for Selective Electroreduction of CO 2

Two-dimensional atomically thin hexagonal boron nitride (h-BN) monolayers have attracted considerable research interest. In this paper, given the tremendous progress in the synthesis of h-BN monolayers on transition metals and their potential as electrocatalysts, we investigate the electrocatalytic activities of h-BN/Ni, h-BN/Co, and h-BN/Cu interfaces for CO 2 reduction by the first-principles density functional theory. We find that with the h-BN monolayer on the metal, electrons transfer from the metal to the interface and accumulate under the B atoms. By calculating the binding energies of three key intermediates (H, HCOO, and COOH) for hydrogen evolution and CO 2 reduction, we find that H binding on the metal can be significantly weakened by the h-BN monolayer, preventing the hydrogen evolution reaction (HER). However, the binding strength of HCOO is strong on both the metal and h-BN/metal, especially for Ni and Co, promoting the CO 2 reduction channel. On the basis of the free-energy diagrams, we predict that h-BN/Ni and h-BN/Co will have very good electrocatalytic activities for CO 2 reduction to HCOOH, while the competitive HER channel is filtered out by the surface h-BN monolayer. Finally, our study opens a new way for selective electroreduction of CO 2 via the interface engineering of the h-BN/metal system.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Surface Ligands on Energetics at FASnI 3 /C 60 Interfaces and Their Impact on Photovoltaic Performance

Interfacial chemistry and energetics significantly impact the performance of photovoltaic devices. In the case of Pb-containing organic metal halide perovskites, photoelectron spectroscopy has been used to determine the energetic alignment of frontier electronic energy levels at various interfaces present in the photovoltaic device. For the Sn-containing analogues, which are less toxic, no such measurements have been made. Through a combination of ultraviolet, inverse, and X-ray photoelectron spectroscopy (UPS, IPES, and XPS, respectively) measurements taken at varying thickness increments during stepwise deposition of C 60 on FASnI 3 , we present the first direct measurements of the frontier electronic energy levels across the FASnI 3 /C 60 interface. The results show band bending in both materials and transport gap widening in FASnI 3 at the interface with C 60 . The XPS results show that iodide diffuses into C 60 and results in n-doping of C 60 . This iodide diffusion out of FASnI 3 impacts the valence and conduction band energies of FASnI 3 more than the core levels, with the core level shifts displaying a different trend than the valence and conduction bands. Surface treatment of FASnI 3 with carboxylic acids and bulky ammonium substituted surface ligands results in slight alterations in the interfacial energetics, and all surface ligands result in similar or improved PV performance relative to the untreated devices. Finally, the greatest PV stability results from treatment with a fluorinated carboxylic acid derivative; however, iodide diffusion is still observed to occur with this surface ligand.

interfacial energetics↗
DOE OSTI2015

Hydrogenation of CO 2 to methanol: Importance of metal–oxide and metal–carbide interfaces in the activation of CO 2

In this study, the high thermochemical stability of CO 2 makes it very difficult to achieve the catalytic conversion of the molecule into alcohols or other hydrocarbon compounds, which can be used as fuels or the starting point for the generation of fine chemicals. Pure metals and bimetallic systems used for the CO 2 → CH 3 OH conversion usually bind CO 2 too weakly and, thus, show low catalytic activity. Here, we discuss a series of recent studies that illustrate the advantages of metal–oxide and metal–carbide interfaces when aiming at the conversion of CO2 into methanol. CeO x /Cu(111), Cu/CeO x /TiO 2 (110), and Au/CeO x /TiO 2 (110) exhibit an activity for the CO 2 → CH 3 OH conversion that is 2–3 orders of magnitude higher than that of a benchmark Cu(111) catalyst. In the Cu–ceria and Au–ceria interfaces, the multifunctional combination of metal and oxide centers leads to complementary chemical properties that open active reaction pathways for methanol synthesis. Efficient catalysts are also generated after depositing Cu and Au on TiC(001). In these cases, strong metal–support interactions modify the electronic properties of the admetals and make them active for the binding of CO 2 and its subsequent transformation into CH 3 OH at the metal–carbide interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

In Situ Spectroscopic Investigation into the Active Sites for Crotonaldehyde Hydrogenation at the Pt Nanoparticle–Co 3 O 4 Interface

The hydrogenation of crotonaldehyde by platinum nanoparticles supported on cobalt oxide was used as a reaction to probe the effect of the interface between the two materials on the activity and selectivity of the catalyst. Four potential products can be formed by this reaction: propylene, butyraldehyde, crotyl alcohol, and butanol. When Pt nanoparticles are supported on SiO 2 , an inert support, only propylene and butyraldehyde are formed. However, when Pt is supported on cobalt oxide, the alcohols make up roughly 40% of the total activity, indicating that cobalt oxide plays a pivotal role in the reaction, much like other active supports such as TiO 2 . To elucidate the mechanism of alcohol formation, in situ sum frequency generation vibrational spectroscopy (SFG) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) were utilized to probe the reactant adsorption and intermediate formation and the chemical state of the materials under working catalytic conditions. The SFG data indicate that crotonaldehyde adsorbs on the oxide surface, likely through the aldehyde oxygen as well as on the Pt surface through the alkene group. AP-XPS results show that the surface of the Co 3 O 4 support becomes partially reduced under the reaction conditions and Pt exists in its metallic state. Taking these results together, we propose in this paper that the crotonaldehyde adsorbs at reduced oxide surface sites and that this adsorption mode is responsible for the production of alcohol products. A platinum nanoparticle density dependence study was also undertaken to change the abundance of interface sites and study their effect on the reaction. The selectivity between the two alcohol products was altered as a function of the Pt nanoparticle density: higher selectivity toward butanol and lower selectivity toward crotyl alcohol was obtained with increasing density, while propylene and butyraldehyde selectivities were constant with respect to density. Finally, on the basis of the data presented, we propose that butanol is preferentially formed at the metal–oxide interface, while crotyl alcohol is formed at oxide surface sites by reaction with spillover hydrogen.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Determining and Minimizing Resistance for Ion Transport at the Polymer/Ceramic Electrolyte Interface

In this work, we report methods to quantify and minimize the interfacial resistance for Li ion transport, R interface , between a model polymer electrolyte, poly(ethylene oxide) + LiCF 3 SO 3 (PE), and a model Li + -conducting ceramic electrolyte, LICGC from Ohara Corporation. By constructing a PE–ceramic–PE trilayer cell, we found R interface to be very large, 1.2 kΩ·cm 2 at 30 °C, accounting for 66% of the total trilayer cell resistance. When dimethyl carbonate, a loose-binding solvent of Li + , was introduced into the trilayer, R interface decreased to essentially zero. As a result, a composite electrolyte with carbonate plasticizers wherein 40 vol % ceramic particles were dispersed in the polymer showed extraordinary room-temperature conductivity of approximately 10 –4 S/cm, 3 orders of magnitude higher than that of the dry composite electrolyte. Here, this discovery can be used as guidance in designing composite electrolytes to achieve synergistic effects.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Polymers at Liquid/Vapor Interface

Polymers confined to the liquid/vapor interface are studied using molecular dynamics simulations. We show that for polymers which are weakly immiscible with the solvent, the density profile perpendicular to the liquid/vapor interface is strongly asymmetric. On the vapor side of the interface, the density distribution falls off as a Gaussian with a decay length on the order of the bead diameter, whereas on the liquid side, the density profile decays as a simple exponential. This result differs from that of a polymer absorbed from a good solvent with the density profile decaying as a power law. In conclusion, as the surface coverage increases, the average end-to-end distance and chain mobility systematically decreases toward that of the homopolymer melt.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Comparative Analysis of Reactivity of Al and Ga Doped Garnet Solid State Electrolyte at the Interface with Li Metal

Lithium garnet (Li 7 La 3 Zr 2 O 12 , LLZO) based solid electrolytes are leading candidate materials for all-solid-state batteries with lithium metal anodes because of their high ionic conductivity, high mechanical toughness, and superior electrochemical stability. While doping LLZO with Al and Ga increases its ionic conductivity by stabilizing the cubic phase, the impact of dopants on its (electro)chemical stability at the interfaces with Li metal is critical. Here, our study of differences between Al- and Ga-doped LLZO when interfaced with lithium metal using X-ray photoelectron spectroscopy and density functional theory shows a higher propensity of Ga to move across LLZO interface with Li metal and form Ga-Li alloy. Additionally, neutron diffraction reveals loss of cubic phase resulting from the loss of dopant that explains electrochemical behavior differences between Ga- and Al-doped LLZO. Overall, our study reveals the key role of dopant chemistry in enabling stable solid electrolyte materials for all-solid-state batteries.

Klenk, Matthew↗
DOE OSTI2023

Bottlebrush Polymers at Liquid Interfaces: Assembly Dynamics, Mechanical Properties, and All-Liquid Printed Constructs

Bottlebrush polymer surfactants (BPSs), formed by the interfacial interactions between bottlebrush polymers (BPs) with poly(acrylic acid) side chains dissolved in an aqueous phase and amine-functionalized ligands dissolved in the oil phase, assemble and bind strongly to the fluid-fluid interface. The ratio between N BB (backbone degree of polymerization) and N SC (side chain degree of polymerization) defines the initial assembly kinetics, interface packing efficiency, and stress relaxation. The equilibrium interfacial tension (γ) increases when N BB < N SC , but decreases when N BB $\gg$ N SC , correlating to a pronounced change in the effective shape of the BPs from being spherical to worm-like structures. The apparent surface coverage (ASC), i.e., the interfacial packing efficiency, decreases as N BB increases. The dripping-to-jetting transition of an injected polymer solution, as well as fluorescence recovery after photobleaching experiments, revealed faster initial assembly kinetics for BPs with higher N BB . Furhter, Euler buckling of BPS assemblies with different N BB values was used to characterize the stress relaxation behavior and bending modulus. The stress relaxation behavior was directly related to the ASC, reflecting the strong influence of macromolecular shape on packing efficiency. The bending modulus of BPSs decreases for N BB < N SC , but increased when N BB $\gg$ N SC , showing the effect of molecular architecture and multisite anchoring. All-liquid printed constructs with lower N BB BPs yielded more stable structured liquids, underscoring the importance of macromolecular packing efficiency at fluid interfaces. Overall, this work elucidates fundamental relationships between nanoscopic structures and macroscopic properties associated with various bottlebrush polymer architectures, which translate to the stabilization of all-fluidic printed constructs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

The influence of interfaces on properties of thin-film inorganic structural isomers containing SnSe—NbSe₂ Subunits

Inorganic isomers ([SnSe] 1+δ ) m (NbSe₂) n ([SnSe] 1+δ ) p (NbSe₂) q ([SnSe] 1+δ ) r (NbSe₂) s where m , n , p , q , r , and s are integers and m + p + r = n + q + s = 4 were prepared using the modulated elemental reactant technique. This series of all six possible isomers provides an opportunity to study the influence of interface density on properties while maintaining the same unit cell size and composition. As expected, all six compounds were observed to have the same atomic compositions and an almost c-axis lattice parameter of ≈4.90 (5) nm, with a slight trend in the c-axis lattice parameter correlated with the different number of interfaces in the isomers: two, four and six. The structures of the constituents in the ab-plane were independent of one another, confirming the nonepitaxial relationship between them. The temperature dependent electrical resistivities revealed metallic behavior for all the six compounds. Surprisingly, the electrical resistivity at room temperature decreases with increasing number of interfaces. Hall measurements suggest this results from changes in carrier concentration, which increases with increasing thickness of the thickest SnSe block in the isomer. Carrier mobility scales with the thickness of the thickest NbSe₂ block due to increased interfacial scattering as the NbSe₂ blocks become thinner. The observed behavior suggests that the two constituents serve different purposes with respect to electrical transport. SnSe acts as a charge donor and NbSe₂ acts as the charge transport layer. This separation of function suggests that such heterostructures can be designed to optimize performance through choice of constituent, layer thickness, and layer sequence. A simplistic model, which predicts the properties of the complex isomers from a weighted sum of the properties of building blocks, was developed. A theoretical model is needed to predict the optimal compound for specific properties among the many potential compounds that can be prepared.

Alemayehu, Matti B.↗
DOE OSTI2025

Charge Disproportionation at Twisted SrTiO 3 Bilayer Interface Driven by Local Atomic Registry

The interplay of lattice, orbital, and charge degrees of freedom in complex oxide materials has hosted a plethora of exotic quantum phases and physical properties. Recent advances in the synthesis of freestanding complex oxide membranes and twisted heterostructures assembled from membranes provide diverse opportunities for discovery using moiré design with local lattice control. To this end, we designed moiré crystals at the coincidence site lattice condition, providing commensurate structure within the moiré supercell arising from the multiatom complex oxide unit cell. We fabricated such twisted bilayers from freestanding SrTiO 3 membranes and used depth-sectioning-based electron microscopic methods to investigate ordered charge states at the moiré interface. By selectively imaging SrTiO 3 atomic planes at different depths through the bilayer, we clearly resolved the moiré periodic structure at the twisted interface and found that it exhibits lattice-dependent charge disproportionation in the local atomic registry within the moiré supercell. Density functional modeling of the twisted oxide interface predicts that these moiré phenomena are accompanied by a two-dimensional flat band that can drive exceptional electronic phases. Our work provides a robust strategy for controlling moiré periodicity in twisted oxides and paves pathways to exploit the extraordinary functionalities via moiré lattice-driven charge-orbital correlation.

charge disproportionation↗
DOE OSTI2018

Tuning Electronic Structure of Single Layer MoS 2 through Defect and Interface Engineering

Transition-metal dichalcogenides (TMDs) have emerged in recent years as a special group of two-dimensional materials and have attracted tremendous attention. Among these TMD materials, molybdenum disulfide (MoS 2 ) has shown promising applications in electronics, photonics, energy, and electrochemistry. In particular, the defects in MoS 2 play an essential role in altering the electronic, magnetic, optical, and catalytic properties of MoS 2 , presenting a useful way to engineer the performance of MoS 2 . The mechanisms by which lattice defects affect the MoS 2 properties are unsettled. In this work, we reveal systematically how lattice defects and substrate interface affect MoS 2 electronic structure. We fabricated single-layer MoS 2 by chemical vapor deposition and then transferred onto Au, single-layer graphene, hexagonal boron nitride, and CeO 2 as substrates and created defects in MoS 2 by ion irradiation. Here, we assessed how these defects and substrates affect the electronic structure of MoS 2 by performing X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, and scanning tunneling microscopy/spectroscopy measurements. Molecular dynamics and first-principles based simulations allowed us to conclude the predominant lattice defects upon ion irradiation and associate those with the experimentally obtained electronic structure. We found that the substrates can tune the electronic energy levels in MoS 2 due to charge transfer at the interface. Furthermore, the reduction state of CeO 2 as an oxide substrate affects the interface charge transfer with MoS 2 . The irradiated MoS 2 had a faster hydrogen evolution kinetics compared to the as-prepared MoS 2 , demonstrating the concept of defect controlled reactivity in this phase. Our findings provide effective probes for energy band and defects in MoS 2 and show the importance of defect engineering in tuning the functionalities of MoS 2 and other TMDs in electronics, optoelectronics, and electrochemistry.

42 ENGINEERING↗