Electron Glass Phase with Resilient Zhang-Rice Singlets in LiCu_{3}O_{3}

LiCu_{3}O_{3} is an antiferromagnetic mixed valence cuprate where trilayers of edge-sharing Cu(II)O (3d^{9}) are sandwiched in between planes of Cu(I) (3d^{10}) ions, with Li stochastically substituting Cu(II). Angle-resolved photoemission spectroscopy (ARPES) and density functional theory reveal two insulating electronic subsystems that are segregated in spite of sharing common oxygen atoms: a Cu d_{z^{2}}/O p_{z} derived valence band (VB) dispersing on the Cu(I) plane, and a Cu 3d_{x^{2}-y^{2}}/O 2p_{x,y} derived Zhang-Rice singlet (ZRS) band dispersing on the Cu(II)O planes. First-principle analysis shows the Li substitution to stabilize the insulating ground state, but only if antiferromagnetic correlations are present. Li further induces substitutional disorder and a 2D electron glass behavior in charge transport, reflected in a large 530 meV Coulomb gap and a linear suppression of VB spectral weight at E_{F} that is observed by ARPES. Surprisingly, the disorder leaves the Cu(II)-derived ZRS largely unaffected. This indicates a local segregation of Li and Cu atoms onto the two separate corner-sharing Cu(II)O_{2} sub-lattices of the edge-sharing Cu(II)O planes, and highlights the ubiquitous resilience of the entangled two hole ZRS entity against impurity scattering.

Achieving environmental stability in an atomically thin quantum spin Hall insulator via graphene intercalation

Atomic monolayers on semiconductor surfaces represent an emerging class of functional quantum materials in the two-dimensional limit - ranging from superconductors and Mott insulators to ferroelectrics and quantum spin Hall insulators. Indenene, a triangular monolayer of indium with a gap of ~ 120 meV is a quantum spin Hall insulator whose micron-scale epitaxial growth on SiC(0001) makes it technologically relevant. However, its suitability for room-temperature spintronics is challenged by the instability of its topological character in air. It is imperative to develop a strategy to protect the topological nature of indenene during ex situ processing and device fabrication. Here we show that intercalation of indenene into epitaxial graphene provides effective protection from the oxidising environment, while preserving an intact topological character. Our approach opens a rich realm of ex situ experimental opportunities, priming monolayer quantum spin Hall insulators for realistic device fabrication and access to topologically protected edge channels.

Room Temperature Ion Beam Synthesis of Ultra-Fine Molybdenum Carbide Nanoparticles: Toward a Scalable Fabrication Route for Earth-Abundant Electrodes

Molybdenum carbides are promising low-cost electrocatalysts for electrolyzers, fuel cells, and batteries. However, synthesis of ultrafine, phase-pure carbide nanoparticles (diameter < 5 nm) with large surface areas remains challenging due to uncontrollable agglomeration that occurs during traditional high temperature syntheses. This work presents a scalable, physical approach to synthesize molybdenum carbide nanoparticles at room temperature by ion implantation. By tuning the implantation conditions, various molybdenum carbide phases, stoichiometries, and nanoparticle sizes can be accessed. For instance, molybdenum ion implantation into glassy carbon at 30 keV energy and to a fluence of 9 × 10¹⁶ at cm^-2 yields a surface η-Mo₃ C₂ with a particle diameter of (10 ± 1) nm. Molybdenum implantation into glassy carbon at 60 keV to a fluence of 6 × 10¹⁶ at cm^-2 yields a buried layer of ultrafine γ'-MoC/η-MoC nanoparticles. Carbon ion implantation at 20 keV into a molybdenum thin film produces a 40 nm thick layer primarily composed of β-Mo₂ C. The formation of nanoparticles in each molybdenum carbide phase is explained based on the Mo-C phase diagram and Monte-Carlo simulations of ion-solid interactions invoking the thermal spike model. The approaches presented are widely applicable for synthesis of other transition metal carbide nanoparticles as well.

Ironsand (Titanomagnetite-Titanohematite): Chemistry, Magnetic Properties and Direct Applications for Wireless Power Transfer

Ironsand is an abundant and inexpensive magnetic mineral resource. However, the magnetic properties of unprocessed ironsand are often inadequate for any practical applications. In this work, the applicability of ironsand for use as a component in a soft magnetic composite for large-scale inductive power transfer applications was investigated. After magnetic separation, the chemical, structural and magnetic properties of ironsand sourced from different locations were compared. Differences observed in the DC magnetic properties were consistent with changes in the chemical compositions obtained from X-ray Absorption Near-Edge Spectroscopy (XANES), which suggests varying the titanohematite to titanomagnetite content. Increased content in titanomagnetite and magnetic permeability correlated well with the total Fe content in the materials. The best-performing ironsand with the highest permeability and lowest core losses was used alongside Mn,Zn-Ferrite particles (ranging from ∼100 μm to 2 mm) to fabricate toroid cores with varying magnetic material loading. It was shown that ironsand can be used to replace up to 15 wt.% of the magnetic materials with minimal impact on the composite magnetic performance, thus reducing the cost. Ironsand was also used as a supporting material in a single-rail wireless power transfer system, effectively increasing the power transfer, demonstrating potential applications to reduce flux leakage.

The Itinerant 2D Electron Gas of the Indium Oxide (111) Surface: Implications for Carbon- and Energy-Conversion Applications

Transparent conducting oxides (TCO) have integral and emerging roles in photovoltaic, thermoelectric energy conversion, and more recently, photocatalytic systems. The functional properties of TCOs, and thus their role in these applications, are often mediated by the bulk electronic band structure but are also strongly influenced by the electronic structure of the native surface 2D electron gas (2DEG), particularly under operating conditions. This study investigates the 2DEG, and its response to changes in chemistry, at the (111) surface of the model TCO In₂ O₃ , through angle resolved and core level X-ray photoemission spectroscopy. It is found that the itinerant charge carriers of the 2DEG reside in two quantum well subbands penetrating up to 65 Å below the surface. The charge carrier concentration of this 2DEG, and thus the high surface n-type conductivity, emerges from donor-type oxygen vacancies of surface character and proves to be remarkably robust against surface absorbents and contamination. The optical transparency, however, may rely on the presence of ubiquitous surface adsorbed oxygen groups and hydrogen defect states that passivate localized oxygen vacancy states in the bandgap of In₂ O₃ .

Water adsorption on vanadium oxide thin films in ambient relative humidity

In this work, ambient pressure x-ray photoelectron spectroscopy (APXPS) is used to study the initial stages of water adsorption on vanadium oxide surfaces. V 2p, O 1s, C 1s, and valence band XPS spectra were collected as a function of relative humidity in a series of isotherm and isobar experiments. Experiments were carried out on two VO₂ thin films on TiO₂ (100) substrates, prepared with different surface cleaning procedures. Hydroxyl and molecular water surface species were identified, with up to 0.5 ML hydroxide present at the minimum relative humidity, and a consistent molecular water adsorption onset occurring around 0.01% relative humidity. The work function was found to increase with increasing relative humidity, suggesting that surface water and hydroxyl species are oriented with the hydrogen atoms directed away from the surface. Changes in the valence band were also observed as a function of relative humidity. The results were similar to those observed in APXPS experiments on other transition metal oxide surfaces, suggesting that H₂O-OH and H₂O-H₂O surface complex formation plays an important role in the oxide wetting process and water dissociation. Compared to polycrystalline vanadium metal, these vanadium oxide films generate less hydroxide and appear to be more favorable for molecular water adsorption.

Observation of Weakened V-V Dimers in the Monoclinic Metallic Phase of Strained VO_{2}

Emergent order at mesoscopic length scales in condensed matter can provide fundamental insight into the underlying competing interactions and their relationship with the order parameter. Using spectromicroscopy, we show that mesoscopic stripe order near the metal-insulator transition (MIT) of strained VO_{2} represents periodic modulations in both crystal symmetry and V-V dimerization. Above the MIT, we unexpectedly find the long-range order of V-V dimer strength and crystal symmetry become dissociated beyond ≈200  nm, whereas the conductivity transition proceeds homogeneously in a narrow temperature range.

How Indium Nitride Senses Water

The unique electronic band structure of indium nitride InN, part of the industrially significant III-N class of semiconductors, offers charge transport properties with great application potential due to its robust n-type conductivity. Here, we explore the water sensing mechanism of InN thin films. Using angle-resolved photoemission spectroscopy, core level spectroscopy, and theory, we derive the charge carrier density and electrical potential of a two-dimensional electron gas, 2DEG, at the InN surface and monitor its electronic properties upon in situ modulation of adsorbed water. An electric dipole layer formed by water molecules raises the surface potential and accumulates charge in the 2DEG, enhancing surface conductivity. Our intuitive model provides a novel route toward understanding the water sensing mechanism in InN and, more generally, for understanding sensing material systems beyond InN.

A soft X-ray spectroscopic perspective of electron localization and transport in tungsten doped bismuth vanadate single crystals

Polarization dependent V L-edge XAS spectra showing anisotropy in the electronic band structure of a W:BiVO₄ single crystal.

Heterojunction synergies in titania-supported gold photocatalysts: implications for solar hydrogen production

The mixed-phase nature of P25 TiO2 (85 % anatase/15 % rutile) plays a key role in the high H2 production rates shown by Au/P25 TiO2 photocatalysts in alcohol/water systems. However, a full understanding of the synergistic charge transfer mechanisms between the TiO2 polymorphs that drive the high rates is yet to be realised. Here, we deconstruct P25 TiO2 into its component phases, functionalise the phases with Au nanoparticles and explore charge transfer in Au/TiO2 systems using EPR spectroscopy. EPR spectroscopy and photocatalytic data provide direct evidence that electrons excited across the rutile band gap move to anatase lattice traps through interfacial surface sites, which decreases electron-hole pair recombination and increases charge carrier availability for photoreactions. In particular, three-phase interfacial sites between Au, anatase and rutile appear to be H2 evolution "hot spots". The results isolate the origin of high photocatalytic H2 production rates seen in Au/P25 TiO2 systems.

Monitoring of NK cell activity and serum LDH in metastatic melanoma patients treated with DTIC and interferon-alpha2a, with or without retinoic acid

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Background: The activity of NK cells, expression of CD69, and serum LDH were evaluated in terms of response to therapy in metastatic melanoma patients. Methods: In phase II clinical study metastatic melanoma (MM) patients were treated with DTIC (800 mg/m2, d1) and IFN-alpha 2a (5×106 IU/m2 s.c., d2–6 (group A, n=25) and 28 patients received the same therapy supplemented with RA, 60 mg/d, d1–10 (group B). Before and after each therapy cycle NK cell activity, CD69+NKcells and LDH were monitored in patients and 39 healthy controls. Results: There is no significant difference in OR (group A 32%, B 21%), in time to progression between groups. NK cell activity was significantly decreased pretherapy in both groups, with a significant increase in the 1st cycle in both groups. NK cell activity did not show significant correlation with OS in group A compared to group B (p=0.445). 20% of patients in group A with pretherapy NK cell cytotoxicity above 30% had better survival from month 3 to 12 of follow-up and a longer maximal survival (1.2 vs. 1.0 year, respectively). In comparison to pre-therapy values, all responding MM patients had a significantly higher increase of CD69 expression on CD56+ NK cells, while the increase was only significantly higher in responders in group B. Analyses of serum LDH level show a significantly higher time and therapy cycle-dependent decrease in group A compared to group B (50% vs. 25%, respectively). However, it is shown that responders in group B had a significantly greater decrease in serum LDH level compared to responders in group B (70% vs. 20%, respectively), if the level after a cycle was evaluated in terms of pretherapy values, as well as a greater decrease if the evaluation in each cycle was done compared to each pretherapy value (35% vs. 20%, respectively). Conclusions: Even though there is no significance in clinical response between patients in group A and B, in agreement with a steady-state pattern of NK cell activity, the fact that only responders in group B had a significant increase in CD69 expression on CD56+ NK cells, as well as the finding that the decrease in serum LDH was significantly greater in patients in group B, implicates favorable imunopotentiating and antitumor effect of RA in the therapy of metastatic melanoma.

No significant financial relationships to disclose.

Pretherapy predictive immunomodulation of NK cell activity and expression of activating and inhibitory receptors in stage IV melanoma patients

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Background: As melanoma (MM) is an immunogenic tumor with poor response to chemotherapy immunomodulating agents are applied in order to potentiate cytotoxic effect of chemotherapy and enhance antitumor immune response. Beside therapeutic benefit of IFN-α and IL-2, 13-cis retinoic acid (RA), as an antiproliferative, differentiating and immunomodulating agent is also investigated. The effect of these agents on NK cells, as main innate immune system effectors, is being investigated. Methods: 35 patients with MM in stage IV prior to therapy and 20 controls were investigated. We evaluated NK activity and the expression of activating (NKG2D and CD161) and inhibitory (CD158a and CD158b) receptors on freshly isolated PBL. Predicitive immunomodulation was performed in 18 h in vitro treated PBL with rh IL-2 (200U/ml), IFN (250U/ml), RA (10−6M), and their combination. Results: Native NK cell cytotoxic activity and expression of NKG2D and CD161 activating receptors on fresh NK cells in MM patients is significantly decreased compared to controls. Predictive treatments with IL-2, IFN, IFN and RA, unlike RA alone, gave a significant increase in NK cell activity of MM patients. Singly, IFN also induced a significant increase in CD161 expression on NK cells in patients. The treatments gave no change in the expression of CD158b, while RA, alone, induced significant decrease in the expression of the inhibitory CD158a antigen. Evaluation of mRNA of transcription molecule IRF-1 shows that it is promptly up-regulated by IFNα, more by IFNα and RA, while single RA has no effect on mRNA induction. Conclusions: Considering that the mechanism of applied immunomodulating agents is continually investigated in order to optimize the dose and schedule of their administration and, also, considering controversial clinical results of RA application, alone, or with IFN, in this study we give novel results that show no significant effect of RA, whereas, IFN-induced increase in NK cell activity of MM patients is for the first time associated with the increase in the expression of NKG2D and CD161 receptors on CD16+NK cells, and not with the decrease in some inhibitory receptors, as the activity of NK cells is regulated by the balance of these two types of signals.

No significant financial relationships to disclose.

Selenium deficiency in Yugoslavia and possible effects on health

New data on Se-deficiency in Yugoslavia are presented. The results include Se contents of soils, cereal crops and garlic grown in the investigated soils, and human serum and scalp hair from several towns and regions in this country. All data indicate a serious Se-deficiency. Analyses of human tissues show a very low Se-status of the Yugoslav population. In some regions, Se contents of garlic, grains and human serum and hair are approaching those in the low-selenium zone in China. It is assumed that the very low Se-status of the human population could be a risk factor for the endemic nephropathy and the urinary tract tumours in endemic areas.