AVS 72 Session 2D-ThP: 2D Materials Poster Session

In this study, we investigated the phase transition behavior of molybdenum disulfide (MoS₂) during and after repeated lithium intercalation and deintercalation cycles, motivated by its potential for energy storage and electronic applications. MoS₂ undergoes a phase transition from the 2H (trigonal prismatic) to the 1T (octahedral) phase upon lithium insertion. After cycling with galvanostatic cycling with potential limitation (GCPL) and using Raman spectroscopy, we confirmed that the 1T phase persisted even after most lithium was removed. Interestingly, a spontaneous reversion of the 1T phase to the 2H phase was observed over time. Raman spectroscopy results showed a significant decrease in 1T phase peaks for cycled MoS2, with the phase converted to 2H after resting periods for several days. Additionally, electrochemical cycling of the cycled MoS₂ flakes revealed lithium potential profiles was comparable to pristine MoS₂, reinforcing the evidence of spontaneous phase reversion. These results demonstrate the metastable nature of the 1T phase and structural evolution of MoS₂ upon and after lithium intercalation cycling. In addition, these findings can provide key insights into the potential strategies of the precise phase control for energy storage and electronic applications, or to synthesize endotaxial structure with distinct quantum states.

Transition metal dichalcogenides (TMDs) are a novel class of quasi-2D materials with potential applications in smaller semiconductor chips, nanoscale piezoelectric biosensing, and more. However, their manufacturing consists of many steps and poses various currently unsolved challenges.

In this study [1], we perform a computational investigation of a TMD manufacturing stage with low-energy plasma-assisted desorption and etching of MoS₂. First, we systematically select an appropriate level of theory and employ a combination of equilibrium and non-equilibrium ab initio molecular dynamics (AIMD) simulations to identify the geometric regions of MoS₂ that exhibit the highest susceptibility to damage induced by plasma particles. We provide energy thresholds for sputtering and investigate their dependence on the incident angle. We show how oxidation and fluorination of MoS₂ into MoS₂O and MoS₂F can lower the sputtering energy thresholds from ~30eV to ~10eV. Such functionalizations expand the energy range where plasma is expected to desorb the target TMD top layer without damaging the metal scaffold. Additionally, the threshold values for MoS₂O and MoS₂F exhibit distinct dependencies on temperature and impact angle, indicating that variation of these parameters could enable precise and selective etching.

We predict a previously unobserved temperature-dependent behavior of the sputtering threshold in MoS₂O at cryo temperatures ~100-200K. We propose a multistage sputtering mechanism to explain this newly observed trend by its connection to threshold sensitivity to impact angle: from ~14eV for a normal θ≈0°impact to ~7eV for a θ≈20°impact. We validate the underlying hypothesis through numerical AIMD simulations. We further demonstrate that the proposed mechanism is not restricted to MoS₂ but is also operative in MoSe₂, WS₂, and WSe₂.

Acknowledgment: This research was supported by the U.S. Department of Energy, Office of Science, Fusion Energy Sciences and Basic Energy Sciences, as part of Microelectronics Science Research Center (MSRC) through the Plasma-enabled 2D Materials project at the Princeton Plasma Physics Laboratory (PPPL), under contract number No. DEAC02-09CH11466.

[1] Yury Polyachenko, Yuri Barsukov, Shoaib Khalid, Igor Kaganovich; J. Phys. Chem. Lett. 2026, 17, 18, 5207–5214 , https://doi.org/10.1021/acs.jpclett.6c00348

Recent progress in neuromorphic computing has highlighted the need for device platforms capable of performing memory and computation in an energy-efficient manner. In conventional von Neumann architectures, the physical separation of memory and processing units causes data-transfer bottlenecks and considerable energy waste, ultimately limiting computational speed. As an alternative approach, memristive devices have attracted attention because their tunable conductance states can emulate synaptic weight modulation. In this work, we demonstrate a low-power neuromorphic system based on gold nanoparticle floating-gate memristors (AuNp-FGMs).

The AuNp-FGM is designed using graphene as the floating gate and MoS₂ as the channel material. By inserting gold nanoparticles between the floating gate and tunneling oxide, a two-terminal memristor structure was fabricated. The device operates within the ±3 V range, and its conductance modulation is governed by changes in the Fermi energy level (E_f) of graphene. Owing to this floating-gate-based charge modulation mechanism, the AuNp-FGM exhibits reliable memory behavior and analog switching characteristics suitable for neuromorphic applications.

The fabricated device shows an on/off ratio exceeding 10⁶, data retention for over 9 hours, and endurance over 80,000 cycles. In addition, the device exhibits low cycle-to-cycle variability, with a Cv of 3.6% measured from 90 cycles, where Cv = σ/μ, σ is the standard deviation, and μ is the mean value. The synaptic update characteristics were further evaluated through multi-level potentiation and depression. For 100-level potentiation using +4 V pulses with a duration of 0.5 s, the non-linearity factor ranges from 0.1 to 0.6. For 100-level depression using −3 V pulses with a duration of 0.2 s, the non-linearity factor ranges from 2.3 to 4.6, measured from 15 devices. Similar modulation behavior was also observed when the number of input pulses was varied to 50, 100, 200, 300, and 400.

To evaluate the applicability of the AuNp-FGM to system-level neuromorphic operation, a neuromorphic array composed of 2 neurons and 32 synapses was constructed. The array was tested using three input patterns: horizontal, vertical, and diagonal. Through 40 learning simulations, the total energy consumption was calculated to be 70 µJ. This corresponds to a 97% reduction in energy consumption compared with previous experiments. These results indicate that graphene/MoS₂-based AuNp-FGM arrays provide a promising platform for low-power neuromorphic systems by combining reliable floating-gate memory characteristics with efficient synaptic weight modulation.

CrPS₄ is a 2D van der Waals material in the ternary transition metal chalcogenide (TTMC) class of compounds. As an A-type antiferromagnetic semiconductor, thin CrPS₄ flakes a few layers thick can display net or zero magnetization depending on whether there is an odd or even number of layers. The combination of 2D magnetic materials such as CrPS₄ with topological insulators such as atomic layer deposition (ALD)-grown alumina has potential as a magnetic tunnel junction in spintronics devices including magnetic RAM, but has seldom been studied to date.

We have analyzed the atomic layer deposition of alumina on mechanically exfoliated CrPS₄ flakes before and after modification with acetylacetone (acacH) at room temperature and at 140 °C. The modifications seem to result in inhibited alumina growth, which was very unexpected considering alumina grows rapidly on most surfaces. In both cases, the alumina grown on the modified CrSP₄ surface may experience a growth delay of over 1 nm [determined by ToF-SIMS depth profiling after 60 cycles of water and trimethylaluminum (TMA) at 130 °C] and a smoother surface compared to alumina grown on the unmodified surface.

The difference in unmodified versus modified alumina growth is likely related to defects which provide nucleation sites for ALD growth. The defects are potentially passivated by the acacH modification. The acac-containing fragments, including Cr(acac)⁺, that indicate a successful modification appear uniformly across the CrPS₄ flakes in ToF-SIMS ion images. Additionally, AFM of the CrPS₄ flakes after these modifications and after alumina ALD reveal a nearly atomically smooth surface, possibly indicating uniform coverage.

The alumina growth could be more efficient on unmodified surfaces because TMA decomposes or builds up at the defects, as we observed clusters of CH^- and AlO₂^- fragments on the CrPS₄ surface by ToF-SIMS that become larger after higher numbers of ALD cycles. This means that the acacH modification could result in a more perfect interface and a better alumina film. This process also has potential applications in area-selective ALD, since alumina growth on CrSP₄ can be slowed with a simple modification, especially when you couple the current findings with the fact that the number of CrPS₄ layers can be controlled by an atomic layer etching (ALE) process.

Phase separation, the spontaneous segregation of a homogeneous mixture into distinct phases with different physical and chemical characteristics, is a fundamental phenomenon in soft matter physics, materials science, and energy-related technologies. Understanding the microscopic dynamics of immiscible fluid systems such as oil-water mixtures is increasingly important for advancing enhanced oil recovery (EOR), chemical processing, and emerging computational material design. In this study, Monte Carlo (MC) simulation techniques were employed to investigate phase separation behavior in mixed oil-water particle systems under varying thermodynamic and spatial conditions. Simulations were performed for particle systems ranging from 500 to 2,500 particles with interval 500 within square simulation domains of side lengths 25–40 units with 5 unit interval. Critical parameters including box size, particle density, interaction strength, and simulation time were systematically analyzed to evaluate their effects on phase evolution and stability. The findings reveal that a system with box size L = 30 and particle number N = 2000 exhibits the clearest and most stable phase-separated structure. Increased particle interactions and larger system sizes significantly enhance the transition from homogeneous dispersion to well-defined phase domains. Furthermore, extended equilibration times improved the sharpness and stability of interfaces, with optimal separation observed at MCstep = 10⁶. The results provide valuable computational insights into molecular-scale phase dynamics, wettability control, and interfacial phenomena. This work demonstrates the growing role of computational modeling and simulation in emerging trends of science and technology, particularly in energy optimization, advanced materials research, and intelligent fluid-system engineering.

Keywords: Oil-water mixture; Phase separation; Monte Carlo simulation; Box size; Particle number

Two-dimensional layered materials are promising candidates for solid-state lubrication because weak interlayer van der Waals interactions can enable low-resistance sliding at micro- and nanoscale contacts. While graphene and transition-metal dichalcogenides have been widely studied in this context, the tribological response of layered tin chalcogenides remains comparatively unexplored. Here, we investigate the nanoscale frictional properties of mechanically exfoliated SnSe and SnSe₂ nanoflakes using atomic force microscopy-based lateral-force microscopy, supported by X-ray photoelectron spectroscopy and first-principles calculations.

SnSe and SnSe₂ flakes were exfoliated onto SiO₂ substrates and measured under ambient conditions using calibrated lateral-force microscopy. Graphene flakes of comparable thickness were measured under the same conditions as a reference solid lubricant. Friction maps and load-dependent lateral-force measurements show that both SnSe and SnSe₂ exhibit low friction coefficients, with values of 0.023 ± 0.004 and 0.027 ± 0.019, respectively, compared with 0.042 ± 0.060 for graphene. These results indicate that Sn-based layered chalcogenides can provide frictional performance comparable to or better than commonly studied two-dimensional lubricants under ambient conditions.

To understand the microscopic origin of the measured friction trends, density functional theory calculations were performed for pristine and oxygen-modified SnSe and SnSe₂ surfaces. Potential-energy-surface calculations indicate that pristine SnSe₂ should possess lower intrinsic sliding barriers than SnSe, consistent with its weaker interlayer interaction. However, XPS analysis reveals the presence of thin native oxide layers on both materials after air exposure. Incorporating oxygen-induced surface distortion into the calculations reverses the predicted friction trend, producing higher sliding barriers for oxidized SnSe₂ than for oxidized SnSe. This result explains the experimentally observed lower friction of SnSe relative to SnSe₂ and highlights the strong influence of surface chemistry on the tribological behavior of two-dimensional materials.

These findings establish SnSe and SnSe₂ as low-friction layered chalcogenides and show that the measured ambient friction response is strongly influenced by native surface oxidation. The intrinsic calculations further suggest that SnSe₂ could exhibit even lower friction when surface oxidation is suppressed, making surface control essential for evaluating its true lubricating potential [1].

[1]. ACS Appl. Nano Mater. 2025, 8, 14713−14719.

Wrinkles and undulations are ubiquitous in two-dimensional (2D) materials. By breaking mirror symmetry, such topographical deformations can enable spin-orbit coupling and Rashba spin splitting, allowing spin precession with important implications for spintronic devices. The Rashba parameter, α_R, is commonly used to quantify the strength of Rashba spin splitting, with larger α_R generally associated with shorter spin-precession lengths. However, using first-principles electronic-structure calculations, we show that α_R can be an inadequate metric for materials with non-parabolic bands and higher-order Rashba spin-orbit interactions. To address this limitation, we propose a new dimensionless metric, L_pr, where L_pr is the spin-precession length and κ is the curvature of undulation. This metric directly captures device-relevant spin-precession behavior and enables more meaningful comparison and ranking of materials by Rashba-effect strength. Finally, using transport calculations, we demonstrate current modulation arising from spin precession in undulated 2D materials and show how this effect can be controlled in realistic device geometries.

The continued evolution of advanced packaging, encompassing high-density substrates, fine-pitch interconnects, microvias, and microBGA architectures, is enabling increasingly complex, high-performance electronic systems. Yet as feature sizes shrink and packaging densities rise, ensuring long-term reliability against corrosion and moisture ingress becomes a critical manufacturing challenge. This creates a compelling need for ultra-thin conformal coatings capable of delivering near-hermetic protection without compromising the dimensional and electrical tolerances demanded by advanced packaging designs.

Atomic Layer Deposition (ALD), introduced in the late 1990s, offers a uniquely precise solution: nanometer-scale films of metals and metal oxides deposited with exceptional conformality and thickness control. However, its broader adoption in electronics manufacturing has historically been limited by elevated processing temperatures incompatible with sensitive substrates and assembled components.

Graphene oxide (GO) has emerged as a promising two-dimensional nanomaterial for drug delivery due to its large surface area, biocompatibility, and versatile surface chemistry. GO can efficiently load therapeutic agents through π–π stacking, hydrogen bonding, and electrostatic interactions, enabling high drug-loading capacity and controlled release. These properties make GO-based nanocarriers attractive for applications in cancer therapy, anti-inflammatory treatments, and multifunctional nanomedicine.

In this work, graphene oxide was investigated as a two-dimensional platform for the loading and delivery of Auranofin (AF), a gold-containing compound originally developed for rheumatoid arthritis and currently attracting significant interest for its anticancer, anti-inflammatory, and redox-modulating properties. In particular, GO nanosheets were employed for the development of AF-based combination systems, including AF–NAC (Auranofin-N-acetylcysteine) and AF-NPX (Auranofin-Naproxen).

The study focused on the physicochemical interactions between GO and the different therapeutic agents, exploiting the high adsorption capability and oxygen-containing functional groups of graphene oxide. The resulting hybrid nanostructures were subjected to comprehensive physicochemical characterization, including UV–Vis spectroscopy, Fourier-transform infrared spectroscopy, dynamic light scattering, zeta potential analysis, and atomic force microscopy, in order to evaluate structural, morphological, and surface properties. In addition, drug-loading efficiency and stability in physiological conditions were assessed to correlate structural features with functional performance. The developed systems were further analyzed in terms of loading efficiency, stability, and potential synergistic effects associated with oxidative stress modulation and anti-inflammatory activity. Special attention was devoted to the AF–NAC system for the investigation of redox-regulation mechanisms, while the AF–NPX formulation was designed to combine the pharmacological activity of Auranofin with the anti-inflammatory properties of Naproxen.

Leveraging the abundance and low cost of anthracite coal, a sustainable and scalable synthesis route is developed to produce graphene quantum dots (GQDs). Through this approach GQDs are collected as powders or slurries and redispersed in common solvents, enabling integration into diverse solution–processed platforms. Briefly, the process involves intercalating naturally sourced anthracite coal with potassium metal and exfoliating it in N-methyl-2-pyrolidone (NMP) to yield reduced GQDs of 2.5-3.5 nm in diameter. This method offers a practical path towards scalability with an isolated yield of ~ 28% GQDs based on the starting anthracite coal mass. Notably, the resulting GQDs feature a 3.4 eV direct bandgap, excitation–dependent photoluminescence, and thermo–optical properties (thermal diffusivity of (6.4 ± 0.3) × 10⁻⁸ m²/s and nonlinear refractive index of −4.69 × 10⁻⁹ cm²/W). These intriguing thermo-optical properties along with improved scalability of the synthesis of GQDs motivate their use in future photothermal and nonlinear optical systems. Overall, this work reframes coal as a sustainable, low-cost precursor for quantum nanomaterials with applications in sensing, energy, and thermal management.

Two dimensional materials provide a powerful platform for surface-site engineering because of their fully exposed atomic planes, tunable defect chemistry, and strong electronic sensitivity which enable precise control of adsorption and catalytic reactivity. The solid carbon materials have emerged as a promising option as these are affordable and have high surface area allowing them to capture small molecules like CO₂ and release it as other chemically valuable products using less heat, particularly when controlled with nitrogen structure. To make carbon capture much cheaper, easier and designing catalyst that generates most controllable active sites, two metal atom system containing main group elements and transition metal elements are paired which will be dispersed on the 2D carbon material. The density functional theory (DFT) is used to investigate Al-Pd dual-atom catalysts system where metal atoms are anchored on defective N-doped graphene as model 2D catalytic surfaces for electrochemical CO₂ reduction. To understand how defect structure and heteronuclear site geometry influence catalysts stability, charge redistribution, and surface intermediates binding, two local coordination environments are examined.

The data obtained from the calculation shows that Al-Pd pair generates an asymmetric active site on the graphene surface which shows cooperative bifunctional role where Al promotes polarization of CO₂ while Pd modulates charge transfer and the binding strength of reaction intermediates. From the electronic structure analysis, including charge redistribution and projected density of states, confirms that both the 2D support and the local coordination environment strongly leads the reactivity of this catalysts system. The free energy analysis and transition state analysis further gives insight into CO₂ reduction selectivity and its competition with hydrogen adsorption.

This work demonstrates how cheap, affordable, versatile, and defect engineered graphene can host atomically dispersed bimetallic sites and how the first principle surface science can guide the design of low-dimensional catalytic 2D materials for carbon conversion.

Selective area van der Waals epitaxy (SAVE) enables site-controlled growth of Bi₂Se₃ on SiOₓ-patterned c-plane sapphire substrates, but the origin of selectivity between exposed sapphire and the surrounding SiOₓ mask remains unclear. Here, we examine three possible contributions to SAVE selectivity: surface wettability, adatom diffusion across the mask, and surface-dependent nucleation.

Contact-angle measurements showed that SiOₓ-coated sapphire remained more wettable and had a higher calculated surface energy than bare sapphire, both before and after UHV annealing. This trend is opposite to that expected if preferential wetting of sapphire were responsible for selective Bi₂Se₃ growth, indicating that macroscopic wettability alone does not explain SAVE selectivity.

To test whether adatom diffusion across the SiOₓ mask contributes to selectivity, patterned samples with different feature spacings were analyzed by atomic force microscopy. A computational AFM analysis workflow was used to estimate average mask coverage across a large set of scans. This metric was used for comparative analysis rather than chemical identification of individual features. No clear relationship between feature spacing and average mask coverage was observed for the feature sizes and shapes measured, weakening a spacing-dependent diffusion model.

Finally, Bi₂Se₃ deposition on unpatterned sapphire and unpatterned SiOₓ-coated sapphire was compared under identical growth conditions. Substantially greater growth was observed on bare sapphire, while the SiOₓ-coated surface remained largely free of deposited material. Together, these results are most consistent with surface-dependent adsorption, desorption, and nucleation behavior as the dominant mechanism underlying SAVE selectivity.

This work was supported by the Coherent / II-VI Foundation and the National Science Foundation Nanomanufacturing of Emerging 2D Materials and Devices REU Program (EEC-2244201).

Two-dimensional transition-metal dichalcogenides (TMDCs) have attracted considerable attention for next-generation electronic and optoelectronic applications because of their tunable electronic structures and van der Waals surfaces. Among them, WSe₂ is particularly promising because of its p-type characteristics and ambipolar transport behavior. However, the microscopic origin of its carrier polarity and the role of surface electronic states remain incompletely understood. Here, we investigate the origin of bipolar transport in nanostructured and bulk WSe₂, with particular emphasis on its surface electronic structure revealed by angle-resolved photoemission spectroscopy (ARPES). ARPES measurements provide direct evidence for pronounced surface electron accumulation (SEA), demonstrating that the near-surface region is heavily n-type, whereas the inner bulk remains lightly p-type. The surface electron concentration reaches approximately 10²⁰ cm⁻³, about four orders of magnitude higher than the bulk hole concentration. This electronic inhomogeneity gives rise to spatially separated bipolar transport, with electrons dominating near the surface and holes governing transport in the bulk, accounting for the observed thickness-dependent conductivity and carrier activation energy. The SEA is attributed primarily to selenium vacancies at the WSe₂ surface, while interactions with ambient molecules can modify or passivate these defects and alter the surface carrier density. These results highlight the crucial role of surface electronic structure in the macroscopic transport properties of WSe₂ and demonstrate the power of photoelectron spectroscopy in disentangling surface and bulk electronic contributions in van der Waals materials.

References

1. Hemanth Kumar Bangolla et al., Nanoscale 18, 5941 (2026).

Two-dimensional (2D) van der Waals (vdW) materials are of interest for a variety of applications ranging from optoelectronics and photocatalysis to energy storage and topological devices. However, vdW materials synthesized using common techniques such as chemical or physical vapor deposition often exhibit a high density of growth-related defects: ranging from grain boundaries and twin defects to pyramidal growth and spiral defects. While pyramidal growth can be minimized through higher growth temperatures, grain boundaries, twin defects, and spiral defects are much harder to overcome. For many applications, especially in electronics and optics, these defects lead to non-radiative recombination, electron scattering, and other undesirable effects. Furthermore, the fabrication of 2D materials into quantum dots (QDs) through bottom-up wet chemistry faces problems with precise location placement and polydispersity in the QDs diameters. This makes the QDs difficult to characterize and is not ideal for most quantum computing and optical setups. Top-down nanofabrication approaches fix this issue but often causes significant damage to the surfaces or edges of the materials. To address these issues, we used selective area van der Waals epitaxy (SAVE) to grow Bi₂Se₃ thin films. SAVE is a technique in which thin films nucleate and grow in defined areas on a wafer. This is done through the use of a patterned mask where growth conditions are selected such that the film will only nucleate inside the exposed pattern.

In this poster, we will describe SAVE growth of Bi₂Se₃ on Al₂O₃ (001) substrates using a SiO₂ mask. The mask was deposited onto a 10x10mm substrate by atomic layer deposition. Patterning of the SiO₂ mask was done through e-beam lithography with dry etching to achieve nano-scale patterned samples with holes of various shapes and sizes. The processed substrates were then loaded into a molecular beam epitaxy chamber for growth of the Bi₂Se₃ film. First, we examine the effects of different substrate temperatures on the selective growth of the Bi₂Se₃ thin films. Second, we will discuss the different growth orientations and processes in the nano-scale features. Third we will investigate the geometric influence of variously shaped patterns on the crystal quality of the selectively grown films.

Two-dimensional (2D) semiconductors have captivated researchers for decades. As scientists continue to investigate the electronic properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), engineers envision a path to augment current silicon technologies using integration. In this investigation, thermal atomic layer deposition (ALD) was used to study a candidate electrical conductor, aluminum zinc oxide (AZO), for electrical contacts to the 2D semiconductor MoS₂. Thermal ALD was chosen for its ability to form conformal films in situations not amendable to line-of-sight deposition, such as recessed edges of a 2D semiconductor layer. Furthermore, only modest temperatures are needed to deposit AZO using supercycles of diethyl zinc and water and of trimethyl aluminum and water. AZO grown with a 20:1 ratio of ZnO:Al₂O₃ yielded the lowest resistivity, and the resistivity was thickness-dependent for films thinner than 50 nm grown on HfO₂/Si. Growth at 175 °C yielded AZO layers with lower resistivity than growth at 150 °C or 200 °C. We used atomic force microscopy to study selectivity of the deposition process on edges of MoS₂. Although prior work showed selective growth of ZnO on the edges of MoS₂[1], we did not observe the same selectively in our study of AZO, possibly due to the use of a higher growth temperature (200 °C vs. 125 °C). Further work will consider the limits of selectivity of AZO deposition and its suitability as an electrical contact to MoS₂.

[1] T. N. Walter et al., Atomic Layer Deposition of ZnO on MoS₂ and WSe₂, Appl. Surf. Sci. 480 (2019) 43.

The development of stable, earth-abundant, and effective electrocatalysts for sustainable hydrogen generation is crucial. Herein, the rational design of MOF-derived B-doped NiCo₂O₄ nanosheets is studied as a bifunctional electrocatalyst for alkaline water splitting. Initially, MOF-derived NiCo₂O₄ nanosheets were directly grown on the Ni foam using a simple hydrothermal technique. Boron impurities then were incorporated into the scaffold structure of NiCo₂O₄ nanosheets using a chemical reduction process. The morphology of the as-deposited nanostructure on Ni foam was studied using scanning electron microscopy. The SEM images confirm the vertically aligned nanosheet formation of MOF-derived B-doped NiCo₂O₄ on Ni foam. An electrochemical water splitting study reveals that the B-doped NiCo₂O₄ electrocatalyst shows enhanced cathodic hydrogen generation reaction and anodic oxygen evolution reaction properties compared to pristine NiCo₂O₄ catalysts. Introduction of a B atom effectively modulates the electronic structure of NiCo₂O₄, which enhances the intrinsic activity. Electrocatalysts display the low overpotential and excellent stability of 75 hours in an alkaline medium. This work provides the groundwork for a unique method of fabricating a strong self-supported and vertically stacked porous structure with plenty of active sites ideal for the inexpensive alkaline electrolyzer.

Polyether ether ketone (PEEK) has emerged as a high performance engineering thermoplastic due to its excellent mechanical strength, thermal stability, chemical resistance, and biocompatibility. However, its relatively low thermal conductivity and limited functional properties restrict its application in advanced electronic, aerospace, and tribological systems. In the present study, Barium Titanate (BaTiO₃) and Graphene Oxide (GO) reinforced PEEK nanocomposite was synthesized to investigate the synergistic influence of ceramic and carbon-based nanofillers on the thermal and microstructural characteristics of the polymer matrix.

The nanocomposite was prepared through Solution Processing and Homogenization of the nanomaterials, ensuring uniform dispersion of the reinforcing phases within the PEEK matrix.

Microstructural characterization was performed using scanning electron microscopy, which revealed a relatively homogeneous distribution of BaTiO₃ particles and GO powder with limited agglomeration. Energy-dispersive X-ray spectroscopy confirmed the presence and elemental distribution of Ba, Ti, C, and O within the composite structure, validating successful incorporation of the reinforcing phases. X-ray diffraction analysis identified the characteristic crystalline peaks of PEEK and BaTiO₃ while also indicating structural interactions between the fillers and matrix.

The thermal behaviour of the proposed nanocomposite was evaluated by STA from 25–1000 °C. The composite retained 98.6% and 95.4% mass at 300 and 500 °C, respectively, indicating excellent thermal stability. Major degradation occurred between 525–625 °C, with the maximum mass-loss rate at approximately 573 °C. The delayed degradation and substantial high-temperature residue are attributed to the synergistic thermal-barrier effects of GO and thermally stable BaTiO₃ reinforcements.

The combined thermal and structural analyses demonstrate that BaTiO₃–GO reinforced PEEK nanocomposites exhibit enhanced thermal performance and stable microstructural characteristics, making them promising candidates for multifunctional applications such as dielectric components, electronic packaging, aerospace structures, insulated bearings, and high temperature engineering systems.

A comprehensive comparison of phonon vibrations in PbS nanosheets (2D) and quantum dots (0D) was conducted using Raman spectroscopy. The nanosheets show strong, distinct Raman peaks in the 200-300 cm^-1 range without resonance enhancement at room temperature. The preferred orientation of PbS nanosheets on their basal plane enables coherent scattering, leading to strong phonon peaks as revealed through our experiments. Although quantum dots lack Raman peaks, surface oxidation improves the Raman signal to be observable at room temperature, but it remains significantly weaker than that from PbS nanosheets. In addition, we used Raman spectroscopy to probe the surface phonons of nanomaterials through structural transitions. The extended phonons in the colloidal 2D PbS nanostructures are not sensitive to organic ligands but can be destroyed with inorganic alloy shells. The enhanced Raman signal enables further study of the phonon physics of colloidal 2D nanostructures, which plays a critical role in the exciton dynamics that underlies hot-carrier cooling, multiple exciton generation, and superfluorescence.

Reference:

https://doi.org/10.1021/acs.jpclett.6c02525

The two-dimensional semiconductor HfSe₂ is a promising candidate for future electronic, optical, and sensing applications due to its moderate bandgap (∼1.1 eV) and the spontaneous formation of a native high-κ dielectric in ambient conditions. In this study, a range of experimental techniques was employed to investigate the intrinsic surface properties of bulk HfSe₂ grown by chemical vapor transport and to directly track oxidation in air. Scanning tunneling microscopy reveals a high defect density across the HfSe₂ surface caused by Se vacancies and impurities, confirmed by XPS, inductively coupled plasma mass spectrometry, and high-resolution Rutherford backscattering spectrometry. Furthermore, XPS highlights the highly reactive nature of the HfSe₂ surface in air, where the formation of HfO_x is detected after a 1 min exposure to air, resulting in changes to the electronic properties, such as the work function and the valence band offset. Understanding the intrinsic surface properties, air stability, and material quality will facilitate the integration of 1T-HfSe₂ in novel devices.

This work was partially supported by the Jonsson School Research Initiative at the University of Texas at Dallas.