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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Evidence for In-Plane Electrical Polarization in 3R-β’-In 2 Se 3 Thin Films Grown by Molecular Beam Epitaxy

β-In 2 Se 3 has been identified as a potential ferroelectric. This work describes the growth of β-In 2 Se 3 via molecular beam epitaxy along with a description of its properties, including the search for switchable polarization in 3R-β’-In2Se3. The thin-film morphology, crystal structure, and phase maps of β-In 2 Se 3 on Si(111) and Al 2 O 3 (0001) were evaluated by atomic force microscopy, X-ray diffraction, and Raman spectroscopy as a function of the atomic Se/In flux ratio and growth temperature. Smooth β-In 2 Se 3 thin films were successfully realized on Si(111) at a substrate temperature of 150 °C using a Se/In flux ratio of 5.7, as well as on Al 2 O 3 (0001) at 450 °C using a Se/In flux ratio of 5.5. Scanning transmission electron microscopy (STEM) confirms the 3R polytype of β-In 2 Se 3 in films on both substrates, with a minor disorder associated with the 2H polytype at the interface. Indications of in-plane Se atom displacements characteristic of the 3R-β’-In 2 Se 3 polytype were found by STEM and second harmonic generation analysis in films on Al 2 O 3 (0001), but not in films on Si(111). Furthermore, attempts at electrical polarization switching did not produce compelling evidence for ferroelectricity. Instead, electrical transport measurements demonstrated locally varying anisotropic responses with the applied electric fields along different in-plane directions, with some hysteresis associated with the trapping of charges.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Encapsulation of Monolayer 2D Materials Using Kinetic Energy-Controlled Pulsed Laser Deposition

The integration of monolayer (ML) two-dimensional (2D) materials into next-generation microelectronics, optoelectronics, and sensors is hindered by their sensitivity to environmental exposure. Deposition of additional layers for encapsulation or growth on ML 2D materials by versatile but energetic plasma techniques such as pulsed laser deposition (PLD) has not been considered at the monolayer level because of potential damage caused by hyperthermal species with kinetic energies (KEs) exceeding the threshold displacement energy (TDE) of the ML. Here, we describe a general strategy to understand and mitigate damage during PLD by reducing the incident KE of ablated species below the TDE of the 2D monolayer using background gas collisions. Ion flux diagnostics, combined with in situ Raman spectroscopy of monolayer graphene during PLD of amorphous boron nitride (a-BN) as a dielectric encapsulation layer, show that damage is primarily correlated with fast ions that penetrate the background gas in accordance with Beer’s Law and are often overlooked in ICCD imaging due to the dominance of the bright, delayed plasma luminescence. Significantly, if fast ions are eliminated and a ∼2 nm-thick a-BN layer is “soft landed”, the monolayer graphene is effectively protected from damage by high KE species in the boron nitride plasma plume. Deposited a-BN films display a characteristic dielectric constant of 3.6 at 100 kHz and tunable charge injection properties. Our results enable PLD as a viable option for encapsulation and thin film growth onto ML 2D materials, with implications for both fundamental research and device integration.

2D materials↗
DOE OSTI2026

Dynamics of Radiation Damage Buildup in Ultrathin Hexagonal Boron Nitride Films under Ion Bombardment

Two-dimensional hexagonal boron nitride (hBN) is attractive for several emerging applications. Ion bombardment can be used to modify the hBN properties. However, the understanding of radiation damage buildup in hBN remains limited. Here, we investigate the effects of the dose rate and ion mass on radiation damage buildup by studying 40 nm-thick hBN films bombarded at room temperature with 500 keV 4 He, 15 N, 40 Ar, and 129 Xe ions and comparing with results for ion bombardment of polycrystalline hBN ceramics. Raman spectroscopy is used to quantify damage buildup, and transmission electron microscopy is used for microstructural analysis. Experiments are complemented by molecular dynamics simulations of the formation and evolution of point defects. Lighter ions are found to be more efficient at disordering hBN than heavier ions. This observation points to a critical role of intracascade defect processes. In contrast, a negligible dose rate effect observed suggests limited intercascade defect dynamic annealing processes for these irradiation conditions. These findings provide a fundamental basis for hBN defect engineering.

2D materials↗
DOE OSTI2026

Ultrafast Reactive Laser Sintering of Highly Conductive Garnet-Type LLZTO Solid Electrolytes

Rapid and scalable fabrication of garnet-type solid electrolytes remains a major challenge for the practical deployment of lithium metal batteries. Here, we report reactive laser sintering (RLS) as an ultrafast and potentially scalable strategy for fabricating garnet-type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) solid electrolytes. RLS of LLZTO enables simultaneous reaction and densification, achieving ∼95% relative density while minimizing lithium loss and suppressing secondary phase formation. Compared to conventional furnace sintering, RLS promotes enhanced grain growth and improved densification, leading to improved ionic conductivity (0.36 ± 0.08 mS cm −1 ) while maintaining comparable activation energies for Li + transport. Structural characterization by X-ray diffraction (XRD), Raman spectroscopy, and solid-state 6 Li/ 7 Li NMR confirms the formation of cubic garnet LLZTO with homogeneous microscale elemental distribution. In addition, nanoindentation measurements demonstrate that RLS preserves the mechanical properties of the garnet framework despite ultrafast localized thermal processing. By integrating simultaneous reaction and densification with tunable microstructural control, reactive laser sintering provides a promising manufacturing pathway for high-performance garnet solid electrolytes toward next-generation solid-state batteries.

CO2 laser↗
DOE OSTI2024

Millimeter-Scale Exfoliation of hBN with Tunable Flake Thickness for Scalable Encapsulation

As a two-dimensional (2D) dielectric material, hexagonal boron nitride (hBN) is in high demand for applications in photonics, nonlinear optics, and nanoelectronics. Unfortunately, the high-throughput preparation of macroscopic-scale, high-quality hBN flakes with controlled thickness is an ongoing challenge, limiting device fabrication and technological integration. In this report we present a metal thin-film exfoliation method to prepare hBN flakes with millimeter-scale dimension, near-unity yields, and tunable flake thickness distribution from 1-7 layers, a substantial improvement over scotch tape exfoliation. The single crystallinity and high quality of the exfoliated hBN are demonstrated with optical microscopy, atomic force microscopy, Raman spectroscopy, and second harmonic generation. We further explore a possible mechanism for the effectiveness and selectivity based on thin-film residual stress measurements, density functional theory calculations, and transmission electron microscopy imaging of the deposited metal films. We find that the magnitude of the residual tensile stress induced by thin film deposition plays a key role in determining exfoliated flake thickness in a manner which closely resembles 3D semiconductor spalling. Lastly, we demonstrate that our exfoliated, large-area hBN flakes can be readily incorporated as encapsulating layers for other 2D monolayers. Altogether, this method brings us one step closer to the high throughput, mass production of hBN-based 2D photonic, optoelectronic, and quantum devices.

2D materials↗
DOE OSTI2025

Chemical Vapor Deposition-Grown Hexagonal Boron Nitride and Graphene for Tandem Dielectric Capacitive Polymer Devices

To address the low energy density of polymeric capacitors, this work explores how tandem combinations of antagonistic properties can enhance energy storage. We introduce multilayer architecture integrating chemical vapor deposition (CVD)-grown ≈2 nm hexagonal boron nitride (hBN) and graphene with ferroelectric polyvinylidene fluoride (PVDF) and linear polyetherimide (PEI) layers to suppress leakage paths, reduce loss, and promote Maxwell–Wagner–Sillars polarization. Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and plasma focused ion beam (PFIB) analyses confirm robust material integration. In conclusion, for the tandem device, E BD ≈600 V/μm, while individual layers show lower values (PVDF|Graphene (Gr)|PVDF ≈ 50 V/μm and PEI|hBN|PEI ≈ 275 V/μm), yielding an overall ≈6000% enhancement and demonstrating the effectiveness of the 2D multilayer design.

Chemical vapor deposition (CVD)↗
DOE OSTI2026

2D in-Plane Ordered MXene Nanosheets Derived from (Mo 2/3 Er 1/3 ) 2 AlC Rare-Earth i-MAX for Energy Storage Applications

MXenes have become one of the most versatile families of two-dimensional (2D) materials due to their high conductivity, hydrophilicity, and remarkable electrochemical performance. This has stimulated intense efforts to design and synthesize MXenes, including structurally unique in-plane ordered 2D MXenes called i-MXenes. Here, we have synthesized the quaternary rare earth (RE)-based i-MAX phase (Mo 2/3 Er 1/3 ) 2 AlC using an arc melting method, and the corresponding 2D i-MXene was then obtained through a LiF/HCl soft etching process. Literature studies have shown that Al and the RE element are etched out during the etching process, leading to the formation of pure vacancy-ordered Mo1.33C 2D i-MXene. However, our investigation reveals that upon exposure to a fluorine solution, the i-MAX phase forms RE fluoride impurities, which are challenging to remove through HCl−DI water washing and persist in the final product, resulting in impure Mo 1.33 C@Er i-MXene. These results were confirmed by various characterizations such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning transmission electron microscopy. Although the Mo 1.33 C@Er electrode showed a 24-fold increase in specific capacitance compared to its parent i-MAX phase, it still exhibited a high charge-transfer resistance arising from the insulating nature of RE fluoride byproducts, which adversely influence the overall capacitance behavior of the synthesized 2D Mo 1.33 C@Er i-MXenes. This study contributes to identifying pathways for the preparation of pure 2D i-MXenes from RE-based i-MAX phases and developing improved synthesis methods. With additional process optimization, the 2D i-MXene holds a strong potential for electrochemical energy storage applications. Additionally, the electronic structures of Mo 1.33 C were theoretically studied using first-principles density functional theory calculations, which revealed that pristine Mo 1.33 C is metallic, and this metallic nature is preserved even with −O, −F, and mixed functionalization.

chemical structure↗
DOE OSTI2024

Functionalization of Monolayer MoS 2 with Layered Multimolecular Architectures

Two dimensional van der Waals materials have attracted attention due to their unique properties that arise in the monolayer versus bulk limits. Monolayer MoS 2 has been at the forefront of 2D materials due to its broad applicability in catalysis, photovoltaics, and spintronics. To realize the capabilities of MoS 2 enabled technology, it is necessary to engineer interfaces where charge carriers can be funneled toward or away from the surface. Molecular systems are a versatile strategy to enable this. Ion-linked molecular architectures have been used previously to circumvent difficult and taxing synthetic methods. Here, we demonstrate the growth of metal ion-linked bilayers (ILBs) on monolayer MoS 2 consisting of a first layer spacer (4-mercaptobenzoic acid, MBA) with a Zn(II) ion linked to a fluorophore (BODIPY). Using a combination of Atomic Force Microscopy and Raman spectroscopy, we resolved intrinsic S-vacancies in the MoS 2 lattice via S–H bond breaking of MBA. X-ray Photoelectron Spectroscopy confirmed that Zn(II) acetate can coordinate to carboxylate groups on MBA. Furthermore, with photoluminescence microscopy, we determined that BODIPY emission is observable only in the presence of a metal ion, confirming the growth of a multimolecular ion-linked supramolecular assembly on MoS 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2020

Local Modulation of Single-Atomic Mn Sites for Enhanced Ambient Ammonia Electrosynthesis

Rationally tuning the local structures of single-atomic active sites for the electrocatalytic N 2 reduction reaction (NRR) remains an urgent but worthwhile research topic. Herein, we accomplish the local modulation of single-atomic Mn sites and construct single Mn–O 3 N 1 sites anchored on porous carbon (Mn–O 3 N 1 /PC) by delicately controlling the Mn–O bonding conditions. Furthermore, the constructed structures are confirmed via the combination of atomic-scale imaging, Raman spectroscopy, synchrotron radiation-based soft and hard X-ray absorption spectroscopies, and X-ray photoelectron spectroscopy. The Mn–O 3 N 1 /PC catalyst yields an NH 3 yield rate of 66.41 μg h –1 mg cat. –1 (corresponding to 1.56 mg h –1 mg Mn –1 ) at -0.35 V versus reversible hydrogen electrode, which is about four times that on the control Mn–N 4 /PC catalyst. The enhanced NRR performance is ascribed to its unique geometry and electronic structures, which not only facilitate the adsorption and activation of the N 2 molecule but also lower the free energy change of the potential-determining step.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Identifying the Catalytic Active Site for Propylene Metathesis by Supported ReO x Catalysts

A series of supported ReO x catalysts were investigated that allowed identifying the unique surface anchoring sites on oxide supports responsible for activating the surface ReO 4 sites for propylene metathesis (the catalytic active site). The catalysts were synthesized by incipient-wetness impregnation of aqueous HReO 4 onto the oxide supports (Al 2 O 3 , ZrO 2 , TiO 2 , SiO 2 and CeO 2 ), characterized under dehydrated and propylene metathesis reaction conditions with in situ spectroscopy (Raman, DRIFTS, UV-Vis and NAP-XPS), and chemically probed (CH 3 CH=CH 2 -TPSR, CH 2 =CH 2 /CH 3 CH=CHCH 3 titration and steady-state self-metathesis of propylene to ethylene and 2-butene). The initially calcined supported rhenia species anchor as isolated surface Re 7+ O 4 sites on the oxide supports by reacting with the surface hydroxyls (terminal S-OH, bridged S-OH-S and tricoordinated S 3 -OH) of the oxide supports. The specific oxide support was found to control the number of activated sites (Al 2 O 3 >> ZrO 2 > CeO 2 > TiO 2 > SiO 2 ) and propylene metathesis activity (Al 2 O 3 >> ZrO 2 >> TiO 2 ~ CeO 2 ~ SiO 2 ) revealing that the oxide support action is a potent ligand for the surface ReO x sites. The activation and specific activity of the surface ReO x sites depend on several factors (nature of surface hydroxyls (S 3 -OH > S-OH-S > S-OH), coordination of the oxide support surface cation (ZrO 7 , AlO 6 , CeO 4 ) and electronegativity of the oxide support cation (SiO 2 > Al 2 O 3 > TiO 2 > ZrO 2 > CeO 2 ). No relationships exist between olefin metathesis activity and acid strength of surface Lewis and Brønsted sites. Here, prior studies primarily focused on supported ReO x /Al 2 O 3 and the lack of examination of non-Al 2 O 3 supported rhenia catalysts precluded comparison between efficient and inefficient olefin metathesis catalysts, which prevented identifying the catalytic active site for olefin metathesis by supported ReO x catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ammonia-Assisted Light Alkane Anti-coke Reforming on Isolated ReO x Sites in Zeolite

The conventional reforming produces H 2 with stoichiometric amounts of CO and CO 2 from hydrocarbons. Here, we show that CO x -free H 2 can be produced from ammonia-assisted reforming (ammoreforming) of natural gas liquids (C n H 2n+2 + nNH 3 = nHCN + (2n + 1) H 2 , n = 2 or 3) at the same conditions as the steam reforming. Such a process co-produces HCN, which can be easily separated from H 2 and used as value-added chemicals or for NH 3 recycling through hydrolysis. In addition, the ammoreforming of ethane and propane was realized over the Re-modified HZSM-5 zeolite rather than the traditional Pt-based catalyst for the BMA process (methane ammoreforming). The specific activity of the Re/HZSM-5 catalysts at 650 °C is up to 1 mol H2 /g Re /min (or 180 min –1 ) during ethane ammoreforming. The catalyst is highly coke resistant and shows only slight deactivation with a time-on-stream up to 20 h. Characterization of the fresh and used catalysts by X-ray absorption and Raman spectroscopies suggested that the isolated ReO x site grafted by AlO 4 – tetrahedral in the zeolite framework is responsible for the outstanding catalytic activity and coke resistibility.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

A Bifunctional Ionic Liquid for Capture and Electrochemical Conversion of CO 2 to CO over Silver

Electrochemical conversion of CO 2 requires selective catalysts and high solubility of CO 2 in the electrolyte to reduce the energy requirement and increase the current efficiency. In this study, the CO 2 reduction reaction (CO 2 RR) over Ag electrodes in acetonitrile-based electrolytes containing 0.1 M [EMIM][2-CNpyr] (1-ethyl-3-methylimidazolium 2-cyanopyrolide), a reactive ionic liquid (IL), is shown to selectively (>94%) convert CO 2 to CO with a stable current density (6 mA·cm –2 ) for at least 12 h. The linear sweep voltammetry experiments show the onset potential of CO 2 reduction in acetonitrile shifts positively by 240 mV when [EMIM][2-CNpyr] is added. This is attributed to the pre-activation of CO 2 through the carboxylate formation via the carbene intermediate of the [EMIM] + cation and the carbamate formation via binding to the nucleophilic [2-CNpyr] – anion. The analysis of the electrode–electrolyte interface by surface-enhanced Raman spectroscopy (SERS) confirms the catalytic role of the functionalized IL where the accumulation of the IL-CO 2 adduct between –1.7 and –2.3 V vs Ag/Ag + and the simultaneous CO formation are captured. Furthermore, this study reveals the electrode surface species and the role of the functionalized ions in lowering the energy requirement of CO 2 RR for the design of multifunctional electrolytes for the integrated capture and conversion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Electrochemical Activation of Ni–Fe Oxides for the Oxygen Evolution Reaction in Alkaline Media

The oxygen evolution reaction (OER) is essential to many key electrochemical devices, including H 2 O electrolyzers, CO 2 electrolyzers, and metal−air batteries. NiFe oxides have been historically identified as active for the OER, though they have been less studied in their more commercially relevant bulk oxide forms, such as NiFe 2 O 4 . Past works have demonstrated that the initial starting phase of Ni(Fe) precatalysts can influence their activation to the Ni(Fe)OOH active phase, including the rate and degree of conversion, pointing to the necessity of understanding activation protocols and in situ characteristics of catalyst materials at the device level. In this work, we investigate the characteristics of commercially relevant NiFe bulk oxides (NiFe 2 O 4 and a physical mixture of NiO and γ-Fe 2 O 3 ) during multiple activation procedures. Our results demonstrate that significant performance enhancement is observed for these bulk oxides regardless of the Fe incorporation in the initial form (i.e., atomically or macroscopically integrated), leading to significant performance enhancement (up to 30×) over time on stream. We hypothesize that this activation is due to the formation of NiFeOOH active sites on the surface, supported by in situ cyclic voltammetry and Raman spectroscopy results. We further show that not only the starting material but also the method of activation influences the number of Ni(Fe)OOH active sites formed and suggest that these sites can be quantified from the Ni 2+ to Ni 3+ redox transition using cyclic voltammetry. Broadly, this work demonstrates the necessity of in situ characterization of catalyst materials for cell-level design and testing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Quantifying the Impact of Metal Population Distribution in MFI-Supported Mo Catalysts for Methane Dehydroaromatization

Precise evaluation of intrinsic kinetic behavior in Mo/MFI catalysts for methane dehydroaromatization (MDA) is confounded by variations in Mo dispersion and speciation, which are influenced by metal loading and zeolite acidity. This work advances the utility of H 2 -temperature programmed reduction (H 2 -TPR) for characterizing Mo/MFI catalysts by enabling quantitative comparison of MoO x populations distinguished by reduction behavior and linked to initial catalytic performance. A comprehensive H 2 reduction pathway is established through systematic H 2 - TPR studies varying catalyst composition (1–10 wt % Mo, Si/Al = 15, 40, ∞), supplemented by UV-Raman spectroscopy, X-ray powder diffraction, N 2 physisorption, NH 3 -TPD, and advanced spectroscopic analysis (in situ XAS with principal component analysis/multivariate curve resolution—alternating least squares). Two low-temperature H 2 -TPR regions capture distinct Mo populations undergoing initial Mo(VI)→Mo(IV) reduction: a lower-temperature population (Mo-RI) associated primarily with highly dispersed, anchored MoO x species expected to predominantly reside within MFI channels, and a higher-temperature population (Mo-RII) corresponding to a broader set of MoO x species that becomes increasingly bulk-like/extrazeolitic at higher Mo loading. Quantification of these populations provides practical, kinetically relevant descriptors for comparing initial MDA rates across catalysts with varying Mo loading, Si/Al ratio, and MoO x heterogeneity. Application of lower-temperature Mo-RI estimates to kinetic measurements reveals a minimum threshold of ∼0.12 × 10 –3 mol Mo-RI/g cat , above which initial forward benzene rates normalized to this population converge despite differences in metal loading and zeolite Brønsted acidity. This threshold coincides with a transition toward a common C 2 -mediated benzene-forming regime, as indicated by approach-to-equilibrium analysis of methane-to-ethane, ethane-to-ethylene, and ethylene-to-benzene reaction steps. Above this threshold, normalized initial benzene rates are nearly invariant with increasing Mo-RII/Mo-RI population ratio, indicating that excess Mo-RII populations, including bulk-like/extrazeolitic MoO x domains present at higher loading, do not measurably suppress benzene formation associated with anchored and mostly channel-confined Mo population under the initial-rate conditions examined.

Mo/MFI↗
DOE OSTI2020

Experimental and Computational Studies of Carbon–Carbon Bond Formation via Ketonization and Aldol Condensation over Site-Isolated Zirconium Catalysts

We report here the preparation and investigation of isolated Zr centers supported on a high surface area silica for the conversion of carboxylic acids to internal ketones by ketonic decarboxylation (ketonization) and the aldol condensation of ketones to dimeric enones. Catalysts were synthesized by the grafting of Cp 2 ZrCl 2 on the surface of amorphous silica. The connectivity of Zr was characterized by XRD, UV-vis, and Raman spectroscopy. For the lowest Zr loading, Zr is present predominantly as isolated monomeric species. As the Zr loading is increased, a progressively larger fraction of Zr forms oligomeric species and ZrO nanoparticles. Measurements of catalytic activity show that the turnover frequency for carboxylic acid ketonic decarboxylation reaction and aldol condensation of ketones decreases monotonically with increasing Zr loading. An H/D kinetic isotope effect was not observed over isolated Zr catalysts, suggesting that α-H abstraction is not the rate-determining step, rather C-C bond forming may be rate limiting for both reactions. This conclusion is supported by computational modeling of the reaction mechanism. The proposed catalytic cycle for ketonization proceeds via a β-keto acid intermediate on isolated Zr sites that are always coordinatively saturated with C-C bond formation as the rate-limiting step. C-C bond formation is also rate-determining for aldol condensation, with an apparent activation energy that is in good agreement with the experiment if the resting state is a saturated ≡ZrOH site with two adsorbed ketone molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Isotopic Substitution Reveals the Importance of Aluminate Diffusion Dynamics in Gibbsite (Al(OH) 3 ) Crystallization from Alkaline Aqueous Solution

Understanding molecular-scale factors governing the precipitation of aluminum hydroxides, such as gibbsite, under alkaline conditions is important for the formation of laterite deposits, as well as aluminum processing. However, mechanisms enabling tetrahedral aluminate ions to assemble into octahedral sites of the gibbsite lattice remain unclear. Formation of oligomeric complexes has been hypothesized as a critical intermediate step. Here, we report a study of gibbsite solubility in highly alkaline solutions using deuterium substitution to probe equilibrium and kinetic factors that could affect oligomeric intermediate formation, including the reactivity and the diffusivity of aluminate ions. When substituting sodium hydroxide with sodium deuteroxide, solution analysis shows a nearly 40% and 50% increase in gibbsite solubility in 2.4 and 3.3 mol·kg –1 total sodium solutions, respectively. Raman spectroscopy indicated that monomeric aluminate ions are the predominant species in solution irrespective of deuteration. However, both 27 Al and 23 Na nuclear magnetic resonance (NMR) spectroscopy revealed significant differences in chemical shifts in deuterated solutions, and analysis of 1 H, 23 Na, and 27 Al diffusion coefficients with pulsed-field gradient, stimulated echo NMR spectroscopy shows a decrease in ion diffusivity with increasing total deuterium in solution, consistent with the notion of increasing strength in the hydrogen/deuterium bonding network. In conclusion, because the relative change in 1 H diffusion coefficients are commensurate with the difference in apparent solubility constants, there is evidence for an oligomeric intermediate whose steady-state concentration is maintained by the collision frequency of aluminate ions.

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

Local A-Site Phase Segregation Leads to Cs-Rich Regions Showing Accelerated Photodegradation in Mixed-Cation Perovskite Semiconductor Films

We use hyperspectral photoluminescence microscopy to study compositional heterogeneity and its influence on the stability of mixed-cation (formamindinium (FA) and cesium) FA 1-x Cs x Pb(I 0.9 Br 0.1 ) 3 lead halide perovskites with different Cs contents. We observe substantial microscale heterogeneity in the photoluminescence. By correlating photoluminescence maps with time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging, we show that the redder-photoluminescence regions of the perovskite film are associated with Cs-rich compositions. X-ray diffraction measurement and confocal Raman spectroscopy provide evidence for the presence of d-phase CsPbI x Br 3-x in these regions. Photo-aging tests show that these Cs-rich clusters undergo faster photoluminescence decay than the rest of the film. These observations highlight the importance of local heterogeneities and their influence on the stability of halide perovskite semiconductors being studied for optoelectronics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗