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We report a ternary hybrid photocatalyst architecture with tailored interfaces that boost the utilization of solar energy for photochemical CO2 reduction by synergizing electron and heat flows in the photocatalyst. The photocatalyst comprises cobalt phthalocyanine (CoPc) molecules assembled on multiwalled carbon nanotubes (CNTs) that are decorated with nearly monodispersed cadmium sulfide quantum dots (CdS QDs). The CdS QDs absorb visible light and generate electron‐hole pairs. The CNTs rapidly transfer the photogenerated electrons from CdS to CoPc. The CoPc molecules then selectively reduce CO2 to CO. The interfacial dynamics and catalytic behavior are clearly revealed by time‐resolved and in situ vibrational spectroscopies. In addition to serving as electron highways, the black body property of the CNT component can create local photothermal heating to activate amine‐captured CO2, namely carbamates, for direct photochemical conversion without additional energy input. [ABSTRACT FROM AUTHOR]

We report a ternary hybrid photocatalyst architecture with tailored interfaces that boost the utilization of solar energy for photochemical CO2 reduction by synergizing electron and heat flows in the photocatalyst. The photocatalyst comprises cobalt phthalocyanine (CoPc) molecules assembled on multiwalled carbon nanotubes (CNTs) that are decorated with nearly monodispersed cadmium sulfide quantum dots (CdS QDs). The CdS QDs absorb visible light and generate electron‐hole pairs. The CNTs rapidly transfer the photogenerated electrons from CdS to CoPc. The CoPc molecules then selectively reduce CO2 to CO. The interfacial dynamics and catalytic behavior are clearly revealed by time‐resolved and in situ vibrational spectroscopies. In addition to serving as electron highways, the black body property of the CNT component can create local photothermal heating to activate amine‐captured CO2, namely carbamates, for direct photochemical conversion without additional energy input. [ABSTRACT FROM AUTHOR]

Synthesis of transition metal dichalcogenides (TMDCs) has been achieved through the direct conversion of metal and metal‐oxide films, demonstrating the ability to grow large area thin films with uniform thickness on a variety of substrates and direct control over the growth orientation (horizontal vs vertical) of the TMDC layers. However, the synthesized TMDC films often exhibit small grains and are more defective than their bulk counterparts. This is especially true for 2D telluride films due to the low reactivity between tellurium and transition metals such as W and Mo. In this work, the substrate interactions is examined for WTe2 converted from amorphous WOx thin films grown by atomic layer deposition, on c‐plane sapphire and SiO2 through tellurization at high temperatures. Similar to TMDC telluride MoTe2, the formation of monolayer WTe2 on sapphire is observed, but not on SiO2. However, due to decreased diffusion of W on sapphire compared to Mo, the formation of WTe2 flakes instead of continuous films is observed, providing insight into the role of the specific transition metal during the direct synthesis of TMDC telluride films. [ABSTRACT FROM AUTHOR]

Topological semimetals (TSMs) possess topologically protected surface states near the Fermi level with high carrier densities and high mobilities, holding distinct potential for low-dissipation on-chip interconnects that may outperform current copper interconnects for continued dimensional scaling of CMOS technologies. To translate the exotic properties of TSMs into practical interconnects, developments of high precision synthesis for these emergent semimetals are essential. Here, we report the synthesis of TSM molybdenum diphosphide (MoP2) nanowires with controlled dimensions and crystallinity. By varying the growth temperature in chemical vapor depositions (CVD), we achieve polycrystalline MoP2 as well as single-crystalline MoP2−x nanostructures, which are confined in highly anisotropic forms on crystalline substrates with a miscut angle of 1°. The measured metallic properties, such as room temperature resistivity and temperature-dependent resistance, of the synthesized MoP2 nanostructures show promising dimensional effects for interconnect applications, suggesting potential enhancement of topological surface states in electron transport at reduced dimensions. The demonstration of CVD-grown MoP2 nanowires provides opportunities for careful investigations of design rules for TSMs-based nanoscale interconnects. [ABSTRACT FROM AUTHOR]

The observation of the Higgs boson solidified the standard model of particle physics. However, explanations of anomalies (for example, dark matter) rely on further symmetry breaking, calling for an undiscovered axial Higgs mode1. The Higgs mode was also seen in magnetic, superconducting and charge density wave (CDW) systems2,3. Uncovering the vector properties of a low-energy mode is challenging, and requires going beyond typical spectroscopic or scattering techniques. Here we discover an axial Higgs mode in the CDW system RTe3 using the interference of quantum pathways. In RTe3 (R = La, Gd), the electronic ordering couples bands of equal or different angular momenta4–6. As such, the Raman scattering tensor associated with the Higgs mode contains both symmetric and antisymmetric components, which are excited via two distinct but degenerate pathways. This leads to constructive or destructive interference of these pathways, depending on the choice of the incident and Raman-scattered light polarization. The qualitative behaviour of the Raman spectra is well captured by an appropriate tight-binding model, including an axial Higgs mode. Elucidation of the antisymmetric component is direct evidence that the Higgs mode contains an axial vector representation (that is, a pseudo-angular momentum) and hints that the CDW is unconventional. Thus, we provide a means for measuring quantum properties of collective modes without resorting to extreme experimental conditions.Detection of an axial Higgs mode by quantum pathway interference reveals an unconventional charge density wave phase in RTe3. [ABSTRACT FROM AUTHOR]

The discovery and characterization of two-dimensional (2D) materials beyond graphene has increased dramatically over the past decade with increasingly fine control over the growth dynamics of these materials. MoTe2 represents a model material for studying phase change properties of 2D materials due to small energy differences between its 2H semiconducting phase and 1T′ semimetallic phase. Although some substrates are demonstrated to be better than others for the wafer-scale growth of high quality MoTe2 films, substrate effects on the nucleation and growth of MoTe2 are still not well understood. Here, we grow monolayer MoTe2 by converting MoOx thin films deposited on three different substrates: sapphire Al2O3 (0001), amorphous SiO2, and amorphous AlOx, and examine the early stages of the conversion reaction to elucidate the substrate effects on the nucleation of MoTe2. We observe that the chemical composition of the substrate is more important than the surface topography and crystallinity of the substrate, with high quality monolayer 2H MoTe2 formed on both Al2O3 (0001) and AlOx in contrast to mixed phase 2H/1T′ MoTe2 formed on SiO2, as determined by Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. [ABSTRACT FROM AUTHOR]

Control of surface functionalization of MXenes holds great potential, and in particular, may lead to tuning of magnetic and electronic order in the recently reported magnetic Cr2TiC2Tx. Here, vacuum annealing experiments of Cr2TiC2Tx are reported with in situ electron energy loss spectroscopy and novel in situ Cr K‐edge extended energy loss fine structure analysis, which directly tracks the evolution of the MXene surface coordination environment. These in situ probes are accompanied by benchmarking synchrotron X‐ray absorption fine structure measurements and density functional theory calculations. With the etching method used here, the MXene has an initial termination chemistry of Cr2TiC2O1.3F0.8. Annealing to 600 °C results in the complete loss of F, but O termination is thermally stable up to (at least) 700 °C. These findings demonstrate thermal control of F termination in Cr2TiC2Tx and offer a first step toward termination engineering this MXene for magnetic applications. Moreover, this work demonstrates high energy electron spectroscopy as a powerful approach for surface characterization in 2D materials. [ABSTRACT FROM AUTHOR]

The n-type dopants, Ge and Sn, were implanted into bulk (−201) β-Ga2O3 at multiple energies (60, 100, 200 keV) and total doses of ∼1014 cm−2 and annealed at 1100 °C for 10–120 s under either O2 or N2 ambients. The Ge-implanted samples showed almost complete recovery of the initial damage band under these conditions, with the disordered region decreasing from 130 to 17 nm after 1100 °C anneals. Fitting of secondary ion mass spectrometry profiles was used to obtain the diffusivity of both Ge and Sn, with values at 1100 °C of 1.05 × 10−11 cm s−1 for Ge and 2.7 × 10−13 cm s−1 for Sn for annealing under O2 ambients. Some of the dopant is lost to the surface during these anneals, with a surface outgas rate of 1–3 × 10−7 s−1. By sharp contrast, the redistribution of both dopants was almost completely suppressed during annealing in N2 ambients under the same conditions, showing the strong influence of point defects on dopant diffusivity of these implanted dopants in β-Ga2O3. [ABSTRACT FROM AUTHOR]