Combination Of X-ray Photoelectron Spectroscopy Research Articles

Kinetics and mechanism of surface plutonium oxycarbide formation

Initial studies of plutonium oxycarbide surface films on metal have been reported to slow the rate of metal corrosion in dry conditions. Exploiting this property presents a unique opportunity in the safe storage of this radioactive and toxic material; however, more fundamental work is required. The plutonium, carbon, and oxygen ratio of these surface films is investigated here using x-ray photoelectron spectroscopy (XPS) and is shown to be nonstoichiometric. The origin of the carbon in the formation of surface plutonium oxycarbide films is probed using a combination of XPS, x-ray diffraction, and secondary ion mass spectrometry and is shown to occur from the metal interstitial impurity. The kinetics of plutonium oxycarbide film growth for a specific bulk carbon concentration have been determined.

Direct covalent attachment of fluorescent molecules on plasma polymerized nanoparticles: a simplified approach for biomedical applications.

Polymeric nanoparticles surface functionalised with fluorescent molecules hold significant potential for advancing diagnostics and therapeutic delivery. Despite their promise, challenges persist in achieving robust attachment of fluorescent molecules for real-time tracking. Weak physical adsorption, pH-dependent electrostatic capture, and hydrophobic interactions often fail to achieve stable attachment of fluorescent markers. While covalent attachment offers stability, it often entails laborious multi-step wet-chemistry processes. This work demonstrates that plasma polymerised nanoparticles (PPNs) can directly and covalently attach fluorescent molecules with no need for additional interim treatment processes. For the first time, we provide evidence indicating the formation of covalent bonds between the fluorescent molecules and PPN surfaces. Two model fluorescent molecules, fluorescein isothiocyanate (FITC) and Nile blue (NB), were attached to PPNs in a one-step process. The attached molecules remained on nanoparticle surfaces even after detergent washing, as confirmed by a combination of X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, flow cytometry, and time-of-flight secondary ion mass spectrometry (ToF-SIMS) data. The robust attachment of fluorescent molecules on PPNs ensures their stability and functionality, enhancing the potential of these fluorescently labelled nanoparticles for diagnostic, therapeutic, and imaging applications.

Direct Observation of Morphological and Chemical Changes during the Oxidation of Model Inorganic Ligand-Capped Particles.

Functionalization and volatilization are competing reactions during the oxidation of carbonaceous materials and are important processes in many different areas of science and technology. Here, we present a combined ambient pressure X-ray photoelectron spectroscopy (APXPS) and grazing incidence X-ray scattering (GIXS) investigation of the oxidation of oleic acid ligands surrounding NaYF4 nanoparticles (NPs) deposited onto SiOx/Si substrates. While APXPS monitors the evolution of the oxidation products, GIXS provides insight into the morphology of the ligands and particles before and after the oxidation. Our investigation shows that the oxidation of the oleic acid ligands proceeds at O2 partial pressures of below 1 mbar in the presence of X-rays, with the oxidation eventually reaching a steady state in which mainly CHx and -COOH functional groups are observed. The scattering data reveal that the oxidation and volatilization reaction proceeds preferentially on the side of the particle facing the gas phase, leading to the formation of a chemically and morphologically asymmetric ligand layer. This comprehensive picture of the oxidation process could be obtained only by combining the X-ray scattering and APXPS data. The investigation presented here lays the foundation for further studies of the stability of NP layers in the presence of reactive trace gases and ionizing radiation and for other nanoscale systems where chemical and morphological changes happen simultaneously and cannot be understood in isolation.

Elucidating the synergistic effect of oxygen vacancies and Z-scheme heterojunction in NU-1000/BiOCl-Ov composites towards enhanced photocatalytic degradation of tetracycline hydrochloride.

Although Z-scheme heterojunction composites have been widely studied in photocatalysis, in-depth investigation of oxygen vacancies (Ov) in the Z-scheme photocatalysts is still rare. Herein, an oxygen vacancies modified NU-1000/BiOCl-Ov composite with Z-scheme heterojunction was rationally designed and fabricated. The combination of X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) experiment verified the presence of oxygen vacancies, meanwhile the Z-scheme charge transfer across the heterojunction interface was confirmed in detail by the in situ-XPS, Kelvin probe force microscope (KPFM) studies, ultraviolet photoelectron spectroscopy (UPS), EPR radical capture experiment, as well as density functional theory (DFT) calculation. Importantly, compared to pristine NU-1000 and BiOCl, the optimized NU-1000/BiOCl-Ov composite displayed enhanced photocatalytic performance in the degradation of tetracycline hydrochloride (TCH) under visible light (λ≥400nm). Theoretical calculations reveal that the oxygen vacancies could induce electron redistribution, facilitating the activation of O2 and TCH molecules, thereby promoting the photodegradation efficiency. Moreover, mechanism studies suggested that the synergistic effect of oxygen vacancies and Z-scheme heterojunction could facilitate the effective separation of photogenerated carriers. At last, the degradation routes of TCH were proposed and the toxicity of degradation intermediates was assessed. This work underlines the cooperative functions of oxygen vacancies and Z-scheme heterojunction towards improved photocatalytic performance, which offers new perspectives on the design of metal-organic frameworks (MOFs) composites for efficient photocatalysis.

Improvement of Electrochemical Performance with Cetylpyridinium Chloride for the Al Anode of Alkaline Al-Air Batteries.

Aluminum-air batteries (AABs) are considered among high-power battery systems with various potential applications. However, the strong self-corrosion of Al in alkaline electrolytes negatively affects its Coulombic efficiency and significantly limits their large-scale application. This work presents the use of cetylpyridinium chloride (CPC) as an inexpensive and environmentally benign electrolyte additive in alkaline AABs. Hydrogen evolution test, electrochemical measurement, and surface analysis techniques were used to investigate the inhibition effects of CPC additive for the Al anode. The potentiodynamic polarization data indicated that the effectiveness of the CPC in inhibiting corrosion increased proportionally with higher CPC concentration. The maximum inhibition efficiency of 53.6% was achieved at a CPC dosage of 5 mM. The hydrogen evolution experiment revealed that the rate of hydrogen evolution decreased from 0.789 mL cm-2 min-1 for the pristine NaOH solution to 0.415 mL cm-2 min-1. The combination of X-ray photoelectron spectroscopy (XPS) and ab initio molecular dynamics (AIMD) provides conclusive evidence that CPC may adhere to the surface of Al and create a protective film. These findings indicate that CPC is successful in preventing the self-corrosion of the Al anode. Additionally, the Al anode has improved electrochemical characteristics, including a high specific capacity of 2041 mAh g-1 and a high energy density of 2874 Wh kg-1. This work focuses on the inhibition of self-corrosion of Al and provides novel insights for the design and development of effective additives for AABs.

Exfoliation of Graphene onto Si(111)-7 × 7 under Ultrahigh Vacuum Provides Some Protection against Exposure to Air.

The investigation of graphene as a protective coating for different materials has been an area of active research for well over a decade. However, graphene's ability to protect clean, reconstructed silicon from ambient gases has remained uninvestigated. Here, we describe the use of a clean ultrahigh vacuum transfer method to deposit graphene onto the Si(111)-7 × 7 reconstruction. Using a combination of X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), we confirmed the successful transfer of graphene onto the surface. We then exposed the graphene-protected surface to 120 L of ambient air in the vacuum chamber and found that although the reconstruction is destroyed on unprotected terraces, clean and ordered silicon can be imaged through the transferred graphene. Exposing the sample to ambient air at atmospheric pressure for 2 days produces a strong signature of oxidation in XPS, and STM images revealed that although graphene can still be identified, the regions beneath the graphene appear amorphous. This work demonstrates that graphene provides some protection against the oxidation of Si(111)-7 × 7 by air, but that this protective ability is not sufficient to forestall oxidation during prolonged exposure to atmospheric conditions.

Enhanced Regulation of Selectivity by the Coupling Effects of Surface Acidity and Strain Effects via Precisely Controlling the Location of Pt.

Loading a sensitizer and constructing a rational nanostructure have been reported to be effective approaches for enhancing the catalytic/sensing performance. However, the impact of the precise loading position on the catalytic/sensing performance is always overlooked. Here, we discovered that precisely changing the location of Pt clusters from the outside of Al2O3-ZnO nanocoils (O-PtAlZnNCs) to the inner side of the nanocoils (I-PtAlZnNCs) could change the sensing performance of the sensor from H2S to acetone. Furthermore, precisely loading Pt inside of the confined space led to a high sensing performance and reduced the limit of detection (LOD) of acetone by a factor of 50 times (from 100 to 2 ppb). Combining X-ray photoelectron spectroscopy (XPS), NH3-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ X-ray absorption spectroscopy (XAS), and density functional theory (DFT) simulations, the enhancement of sensitivity and regulation of sensing selectivity are attributed to the coupling effects from enrichment of confined space and Al2O3 acid-base active sites as well as the regulation of electronic structure by location-dominated strain effects. This work not only provides a novel sight to precisely regulate the selectivity and obtain ultrasensitive materials but also serves as a useful instruction for further understanding and precisely designing specific sensors and catalysts with high performance.

Real-time study of the interplay between phase formation and stress evolution at the W1−xSix/a−Si interface

Nanoscale W1−xSix layers with different Si content were deposited by magnetron sputtering on amorphous silicon layers. The structure and stress evolution during deposition were monitored and in real time. Thus, it was possible to disentangle different origins of stress built-up (interface formation, phase formation, grain growth, and texture) on the nanoscale. It was found that the bcc phase with a composition-dependent texture forms at low Si content (less than 10% Si), but only above a critical thickness. At intermediate Si content (13.9% and 16.5% Si), or low Si content and low thicknesses (≲4.5 nm), the β phase with A15 structure and coexisting phases (bcc or amorphous) form, while a single, amorphous phase is observed at high Si content (≳22% Si). An A15 formation driven by impurities (O,C,N) was excluded by combined x-ray photoelectron spectroscopy and x-ray diffraction measurements on a second sample series. calculations of substitutional bcc and A15 W1−xSix alloys support the formation of A15 at higher Si content. The A15-containing interlayer should be taken into account when discussing the superconductivity of W/Si multilayers. The stress evolution during deposition of W1−xSix was correlated with the microstructure evolution, and compared to similar observations for Mo1−xSix. Due to the crystalline phase (bcc/A15) and bcc texture ([111] and [110]) competition, the structure formation of W1−xSix shows a higher complexity. This explains the wide range of stress states (from tensile to compressive) observed after deposition of W1−xSix. Nanoscale W-Si based stress-compensation layers could be employed for tailoring the stress state of nonepitaxial semiconductor devices. Published by the American Physical Society 2024

Silane functionalization of graphene nanoplatelets

The lack of a facile route for the functionalization of highly sp2 hybridized, low oxygen content (<10 atm%, C:O > 9:1) graphene nanoplatelets (GNP) has greatly hindered full exploitation of these materials. Moreover, the highly conductive and paramagnetic properties of GNP can exclude the use of solid-state nuclear magnetic resonance spectroscopy (SS-NMR) and electron paramagnetic resonance spectroscopy (EPR), even at liquid helium temperatures, to prove binding of silane to the GNP surface is successful. Here, three model silanes, 3-Mercaptopropyltrimethoxysilane, 3-Methacryloxypropyltrimethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane were successfully bound to the surface of GNP, each following either a condensation silanization reaction or a pathway dependent on the R-group of each silane. Several techniques were employed, but critically a combination of X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis-mass spectrometry (TGA-MS) in argon and air confirmed successful binding of the silane to the GNP. The approach adopted makes available the pendant R-group on the silane for interaction or reaction with polymers and a route to significantly modifying the properties of polymers and surfaces.

Bimetallic Rh–Pd aerogels as efficient materials for ethanol electrooxidation

This study introduces a series of Rh–Pd bimetallic aerogels Rh75Pd25, Rh50Pd50, and Rh25Pd75 as efficient electrocatalysts for ethanol electrooxidation, crucial for direct ethanol fuel cell technology. The bimetallic Rh–Pd and monometallic Rh and Pd aerogels were synthesized from RhCl3 and PdCl2 as starting materials and sodium borohydride as the reducing agent. A combination of X-ray photoelectron spectroscopy, elemental mapping, and electron microscopy studies of the bimetallic aerogels enable compositional analysis of the materials and provide insight into the porous 3D nanoarchitecture. Importantly, the material performs efficiently as an electrocatalyst on glassy carbon electrodes for the oxidation of ethanol under basic conditions (1.0 M KOH) at onset potentials ranging from −0.59 to −0.64 V (vs. Hg/HgO). Importantly, these materials exhibit high peak current densities of 216 mA/cm2 for the Rh-rich Rh75Pd25 to 536 mA/cm2 for Rh25Pd75, which are significantly higher than reported peak current densities for other Pd-containing electrocatalysts. The 1H and 13C NMR techniques were used to evaluate products for ethanol electrooxidation, with the results indicating selectivity for acetic acid. This demonstrates an enhanced catalytic activity, selectivity to acetic acid vs. CO2, representing a significant step in advancing DEFCs and their broader application in sustainable energy technologies.

On the Strong Binding Affinity of Gold-Graphene Heterostructures with Heavy Metal Ions in Water: A Theoretical and Experimental Investigation.

Minimum energy configurations in 2D material-based heterostructures can enable interactions with external chemical species that are not observable for their monolithic counterparts. Density functional theory (DFT) calculations reveal that the binding energy of divalent toxic metal ions of Cd, Pb, and Hg on graphene-gold heterointerfaces is negative, in contrast to the positive value associated with free-standing graphene. The theoretical predictions are confirmed experimentally by Surface Plasmon Resonance (SPR) spectroscopy, where a strong binding affinity is measured for all the heavy metal ions in water. The results indicate the formation of a film of heavy metal ions on the graphene-gold (Gr/Au) heterointerfaces, where the adsorption of the ions follows a Langmuir isotherm model. The highest thermodynamic affinity constant K = 3.1 × 107 L mol-1 is observed for Hg2+@Gr/Au heterostructures, compared to 1.1 × 107 L mol-1 and 8.5 × 106 L mol-1 for Pb2+@Gr/Au and Cd2+@Gr/Au, respectively. In the case of Hg2+ ions, it was observed a sensitivity of about 0.01°/ppb and a detection limit of 0.7 ppb (∼3 nmol L-1). The combined X-ray photoelectron spectroscopy (XPS) and SPR analysis suggests a permanent interaction of all of the HMIs with the Gr/Au heterointerfaces. The correlation between the theoretical and experimental results indicates that the electron transfer from the graphene-gold heterostructures to the heavy metal ions is the key for correct interpretation of the enhanced sensitivity of the SPR sensors in water.

FeS2/SnS2@C with mosaic-like heterointerface as robust sodium anode

Sodium-ion batteries (SIBs) have been widely researched due to their abundant resource and inherent safety. However, the major challenge for further commercialization of SIBs is the absence of low-priced anode electrodes with high reversible capacity and durability. Herein, a hierarchical heterogeneous structure of FeS2/SnS2@C nanocubes with rich two-dimensional mosaic-like heterointerface and N/S co-doped carbon wrapping is constructed and synthesized, to achieve ultrahigh reversible capacity and long cycling stability as anode of SIBs. Combining x-ray photoelectron spectroscopy, ion diffusion kinetic analysis, and in situ x-ray diffraction, the exquisite hierarchical heterogeneous structure of FeS2/SnS2@C could promote charge/electrons transfer and accelerate ion diffusion kinetics. As expected, the FeS2/SnS2@C anode shows superior reversible capacity (867.5 mA h g−1 at 0.1 A g−1), good rate performance (718.9 mA h g−1 at 5.0 A g−1), and long cycle stability (738.0 mA h g−1 after 1200 cycles at 5.0 A g−1) with Na metal as counter electrode. This work proves that the effectiveness of heterojunction interfaces for promoting Na+ diffusion is highlighted by such capabilities.

Citrate stabilized maghemite hydrosol with controllable MRI contrast: Key role of nanoparticle size

In this study, we have synthetized a series of citric acid stabilized superparamagnetic iron oxide nanoparticles (CA-SPIONs) with different core sizes in an automated chemical reactor with high repeatability of the nanoparticle size and chemical composition. The prepared CA-SPIONs are highly crystalline spherical-shaped particles with the diameters of 3.5 ± 0.7, 6 ± 1, 9 ± 1, and 12 ± 2 nm. The valent state of iron oxide was determined by a combination of X-ray photoelectron spectroscopy, UV–Vis spectroscopy, and Mössbauer studies, which confirmed predominantly maghemite formation. Under normal conditions, these nanoparticles exhibit no coercive force and no hysteresis, while saturation magnetization increases from 2 to 61 emu/g along with the increasing core size. Both longitudinal (r1) and transverse (r2) relaxivities of maghemite hydrosols with different nanoparticle sizes were measured and compared with the same data for the commercial Gd-complex (Gadovist). Magnetic circular dichroism spectroscopy indicated that aggregation occurs in magnetic field, but 9 nm samples slightly aggregate in the fields above 1.0 T, whereas 3.5 nm colloids are stable and do not exhibit aggregation behavior even at 1.5 T. The obtained series were examined in phantom test in clinical 1.5 T MRI scanner, which showed that increasing the particle core size resulted in an enhanced T2 contrast, while T1 contrast declined. Finally, the smallest CA-SPION colloid nanoparticles with the size of 3.5 nm exhibited significant T1 contrast enhancement, comparable with the commercial Gd-complex in water and human plasma as well. The maghemite hydrosol formed by nanoparticles with 3.5 nm size thus has a promising future as a T1 MRI contrast agent.

Copper nanoparticles embedded flexible graphene aerogel for effective capture of iodine vapor

Development of highly efficient and low-cost adsorbents for radioactive iodine vapor is significant but still challenged now. In this work, we reported a novel graphene aerogel (GA-Cu-ED) decorated by zero-valence copper and nitrogen active sites, prepared via a two-step route of hydrothermal reaction and freeze-drying processes. The combination of X-ray photoelectron spectroscopy (XPS) valence imaging and high-resolution transmission electron microscope (TEM) confirms the formation of Cu0 and its uniform distribution. Besides, the good elasticity and ultra-low density of this aerogel were proved. Adsorption experiments indicate that GA-Cu-ED has a high adsorption capacity of 3.76 g/g for gaseous iodine and short adsorption equilibrium time of 90 min. Even after three cycles, this aerogel still shows an almost unchanged adsorption capacity of 3.74 g/g. Meanwhile, this aerogel can be long-term stored under air atmosphere with only slight loss in adsorption performance. In addition, the captured iodine molecules can be tightly bound in this aerogel even after being exposed in air for three days. Mechanism analysis indicates the I-benzene conjugation, I–N charge transfer, and I2–Cu0 chemisorption contribute together to the capture of gaseous iodine. Therefore, our work provides a highly efficient and reliable adsorbent for radioactive iodine vapor, which may be worthy in large-scale application in future.

On-Surface Formation and Chemical Transformations of Indigo Coordination Polymers

Coordination polymers are attractive candidates for miniaturized electronics. With unconventional electronic and magnetic properties posited, they are interesting for multiple applications including magnetic information storage and spintronics. Natural products are appealing to tailor advanced new materials, bearing inherent advantages in biodegradation. Among them, we distinguished indigo, a common natural dye with a distinctive blue color, used as a pigment since antiquity. Motivated by its optical properties and the reported metal complexes [1], we employed it as a molecular building block for the surface formation of coordination polymers with iron.We report on the on-surface formation of extended coordination polymers which controllably feature the cis and the transmonomers of the molecular building block. The reaction products of indigo and Fe were characterized atomically by a combination of state-of-the -art experimental and theoretical techniques. By a combination of X-ray photoelectron spectroscopy and scanning tunneling microscopy (STM), it is found that indigo deprotonates and coordinates with Fe atoms on silver surfaces. We identify unambiguously well-defined coordination polymers composed of (1 dehydroindigo : 1 Fe) repeat units with STM, bond-resolving atomic force microscopy and density functional theory (DFT) simulations. On both Ag(100) and on Ag(111), the trans configuration of dehydroindigo results in N,O-chelation in the polymer chains. On the more inert Ag(111) surface, the molecules undergo thermally induced isomerization from the trans to the cisconfiguration and afford N,N- plus O,O-chelation (see figure). This is enabled by the dehydrogenation and is preferential solely in the environment of the coordination chain on Ag(111). DFT calculations also confirm that the coordination polymers of the cis-isomers on Ag(111) and of the trans-isomers on Ag(100) are energetically favored.Our results demonstrate post-synthetic linker isomerization in interfacial metal-organic nanosystems. Both types of coordination polymers are predicted to be spin-crossover systems and the isomerization is anticipated to have a significant impact on their magnetic properties.

(Battery Student Slam 8 Award Winner) Evaluating Electrodeposited Tin and Antimony-Based Anodes for Sodium-Ion Batteries

The widescale adaption of intermittent renewable energy sources, such as wind and solar, must be accompanied by a grid storage network to store energy when it is abundant and redistribute it as needed for on-demand use. Short-term storage in the form of rechargeable batteries is an attractive avenue for meeting these storage needs. The dominant technology in today’s market, the lithium-ion battery (LIB), is cost-prohibitive due to the need for rare-earth materials. Using the same working principle as LIBs, sodium-ion batteries (NIBs) utilize earth-abundant, low-cost sodium compounds instead of lithium compounds. Tin (Sn) and antimony (Sb) alone are promising anode materials for sodium-ion batteries with high theoretical capacities (847 and 660 mAh/g for Sn and Sb with Na, respectively) relative to current LIB anode chemistry (372 mAh/g) [1,2]. When combined, SnSb has shown to have increased stability relative to Sn or Sb alone [3]. Here, we synthesized Sn-Sb thin films with varied Sn and Sb atomic ratios by co-electrodeposition from a deep eutectic solvent by modifying solution stoichiometry and electrodeposition parameters. Using a combination of X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and energy dispersive X-ray spectroscopy (EDS), phases and compositions of Sn-Sb synthesized by electrodeposition were identified. Once synthesized, we sought to determine the influence of morphology, surface chemistry, and composition on the capacity retention and rate capabilities of Sn and Sb-based anodes in NIBs. An optimized electrode composition was identified using a carbonate-based electrolyte, which resulted in stable capacity retention cycling at a rate of C/2 for 270 cycles.[1] W. T. Jing, C. C. Yang, and Q. Jiang, Journal of Materials Chemistry A, 8, 2913–2933 (2020).[2] S. Megahed and B. Scrosati, Journal of Power Sources, 51, 79–104 (1994).[3] W. P. Kalisvaart, H. Xie, B. C. Olsen, E. J. Luber, and J. M. Buriak, ACS Applied Energy Materials, 2, 5133–5139 (2019).

On-Surface Chemistry: Probing the Presence of Adatoms on Differently Terminated Surfaces by Porphyrin Metalation

Reactive adsorbates in on-surface reactions and in heterogeneous catalysis on different substrates are of emerging importance. This is for the crucial roles they take in reaction pathways and for their decisive influence on reaction kinetics. [1] The thermally activated 2D mobility [2] of reaction precursors and reactive adatoms as well as their spatial and temporal coincidence at reaction sites is of mechanistic importance for many interface-specific reactions. In our work, we use the well-studied metalation reaction of H2-porphyrins to investigate the action of adatoms on metallic and passivated surface substrates. Porphyrin metalation has been established on atomically clean metallic substrates [3] as well as on metal-oxides [4] and metallic surfaces modified by oxygen [5].We perform spectro-microscopy correlation experiments combining X-ray Photoelectron Spectroscopy, Ultraviolet Photoelectron Spectroscopy, Low Energy Electron Diffraction and Scanning Tunnelling Microscopy on Cl- and N terminated Cu(001). Thereby we find extended layers of adsorbate-induced superstructures that have decisive and contrasting impact on the reactivity of the surface, as well as on molecular self-assembly. The O and N termination of Cu facilitates the metalation reaction and self-assembled domains of CuTPP are formed at room temperature. Cl termination on the contrary, fully inhibits the metalation reaction and causes 2HTPP to assemble into small ‘magic’ clusters.

Zeolite-templated carbon synthesized with ion-exchanged FAU-zeolite using alkaline earth metal ions for the selective adsorption of C2 hydrocarbons over C1 hydrocarbon

In this study, zeolite-templated carbon (ZTC) was synthesized using ion-exchanged faujasite-Y (FAU, NaY) zeolites with different alkali earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) to investigate the effects of these metals on the synthesis, characteristics, and C2/C1 hydrocarbon separation performance of ZTC. Thermogravimetric and temperature-programmed desorption of NH3 (TPD-NH3) analyses showed that carbon deposition tends to occur outside the pores because of the increasing number of moderate acid sites as the atomic number increases. In particular, in the case of FAU-ZTC(Ca) synthesized using CaY as the ZTC template, carbon accumulated inside the pores owing to the distribution of the appropriate acid strength, resulting in the highest specific surface area of 2,835 m2/g among the synthesized ZTCs. The combined X-ray photoelectron and Raman spectroscopy results confirm that these defect sites of ZTC act as adsorption sites for large molecules such as C2H4 and C2H6. The isothermal adsorption of CH4, C2H4, and C2H6 showed that FAU-ZTC(Ca) exhibited the highest adsorption capacity ratios of C2H4 and C2H6 to CH4, with a C2H6/CH4 ratio of 5.897 and C2H4/CH4 ratio of 5.288, respectively. The effective pore size ranges affecting the adsorption of CH4, C2H4, and C2H6 determined using linear regression analysis are 0.4 to 0.6 nm for CH4 and 0.6 to 1.1 nm for C2H4 and C2H6. Molecular simulations confirmed that the adsorption energy was maximized by the interaction between the hydrogen atoms of the hydrocarbons and the carbon atoms of ZTC. Furthermore, C2H4 and C2H6 require larger pores than CH4 adsorption because C2H4 and C2H6 prefer to lie horizontally rather than vertically in the pores of the ZTC.

Band alignment and charge transfer mechanisms in the prediction of advanced gate dielectrics for carbon nanotube field-effect transistors

The search for novel gate dielectrics to mitigate interface state density is a pressing concern in the fabrication of high-performance carbon nanotube field-effect transistors (CNT-FETs). In this study, we investigated the feasibility of employing strontium titanate (STO) with an ultra-high dielectric constant as the gate dielectric in CNT-FETs. By combining X-ray photoelectron spectroscopy measurements with first-principles calculations, we determined the band offsets between CNT and STO, as well as between CNT and conventional gate dielectrics such as HfO2 and SiO2. The valence/conduction band offset (VBO/CBO) at the STO/CNT interface is found to be 1.1 eV/1.5 eV, which is the smallest among all studied interfaces, followed by those at HfO2/CNT interface (VBO = 1.3 eV/CBO = 3.4 eV) and SiO2/CNT interface (VBO = 3.6 eV/CBO = 4.5 eV). Moreover, charge transfer at the STO/CNT interface exhibits two orders of magnitude lower values compared to that at HfO2/CNT interface and is also significantly smaller than that at SiO2/CNT interface. This phenomenon can be ascribed to the combined effects of van der Waals forces at the STO/CNT interface and fewer dangling bonds on the STO surface. These findings suggest exceptional compatibility between STO and CNT, making STO highly suitable for high-performance CNT-FETs.

Fe-Doped SrCoOx FET Sensors for Extreme Alkaline pH Sensing.

The accurate measurement of pH in highly alkaline environments is critical for various industrial applications but remains a complex task. This paper discusses the development of novel Fe-doped SrCoOx-based FET sensors for the detection of extreme alkaline pH levels. Through a comprehensive investigation of the effects of Fe doping on the structure, electrical properties, and sensing performance of SrCoOx, we have identified the optimal doping level that significantly enhances the sensor's performance in highly alkaline conditions. With a Fe doping level of 5 mol %, the sensitivity of the sensor improves to 0.86 lg(Ω)/pH while maintaining the response rate. Further increasing the Fe doping to 10 mol % results in a sensor that demonstrates favorable response time, a suitable pH range, and a linear correlation between lg(R) and pH. The combination of X-ray photoelectron spectroscopy and X-ray diffraction analysis provides insight into the regulation mechanisms of Fe doping on the crystal structure, electronic structure, and oxygen vacancy concentration of SrCoOx. Our findings indicate that Fe doping leads to an increase in oxygen vacancy concentration and a decrease in the energy barrier for oxygen ion migration, which contributes to the improved sensing performance of the Fe-doped SrCoOx sensors. Additionally, the study highlights the influence of oxygen vacancy concentration on the electrical properties of SrCoOx. Precise control over the concentration of oxygen vacancies is crucial for optimizing the sensitivity and response speed of SrCoOx FET sensors under extreme alkalinity conditions.