Growth Mechanism and Electronic Structure of Zn_3P_2 on the Ga-Rich GaAs(001) Surface

The growth of epitaxial Zn_3P_2 films on III–V substrates unlocks a promising pathway toward high-efficiency, earth-abundant photovoltaic devices fabricated on reusable, single-crystal templates. The detailed chemical, structural, and electronic properties of the surface and interface of pseudomorphic Zn_3P_2 epilayers grown on GaAs(001) were investigated using scanning tunneling microscopy/spectroscopy and high-resolution X-ray photoelectron spectroscopy. Two interesting features of the growth process were observed: (1) vapor-phase P4 first reacts with the Ga-rich GaAs surface to form an interfacial GaP layer with a thickness of several monolayers, and (2) a P-rich amorphous overlayer is present during the entire film growth process, beneath which a highly ordered Zn_3P_2 crystalline phase is precipitated. These features were corroborated by transmission electron micrographs of the Zn_3P_2/GaAs interface as well as density functional theory calculations of P reactions with the GaAs surface. Finally, the valence-band offset between the crystalline Zn_3P_2 epilayer and the GaAs substrate was determined to be ΔE_V = 1.0 ± 0.1 eV, indicating the formation of a hole-depletion layer at the substrate surface which may inhibit formation of an ohmic contact

Imaging 3D Chemistry at 1 nm Resolution with Fused Multi-Modal Electron Tomography

Measuring the three-dimensional (3D) distribution of chemistry in nanoscale matter is a longstanding challenge for metrological science. The inelastic scattering events required for 3D chemical imaging are too rare, requiring high beam exposure that destroys the specimen before an experiment completes. Even larger doses are required to achieve high resolution. Thus, chemical mapping in 3D has been unachievable except at lower resolution with the most radiation-hard materials. Here, high-resolution 3D chemical imaging is achieved near or below one nanometer resolution in a Au-Fe$_3$O$_4$ metamaterial, Co$_3$O$_4$ - Mn$_3$O$_4$ core-shell nanocrystals, and ZnS-Cu$_{0.64}$S$_{0.36}$ nanomaterial using fused multi-modal electron tomography. Multi-modal data fusion enables high-resolution chemical tomography often with 99\% less dose by linking information encoded within both elastic (HAADF) and inelastic (EDX / EELS) signals. Now sub-nanometer 3D resolution of chemistry is measurable for a broad class of geometrically and compositionally complex materials

Support Effect and Surface Reconstruction in In2O3/m-ZrO2 Catalyzed CO2 Hydrogenation

We investigate the chemical and structural dynamics at the interface of In2O3/m-ZrO2and their consequences on the CO2hydrogenation reaction (CO2HR) under reaction conditions. While acting to enrich CO2, monoclinic zirconia (m-ZrO2) was also found to serve as a chemical and structural modifier of In2O3that directly governs the outcome of the CO2HR. These modifying effects include the following: (1) Under reaction conditions (above 623 K), partially reduced In2O3, i.e., InOx(0 < x < 1.5), was found to migrate in and out of the subsurface of m-ZrO2in a semireversible manner, where m-ZrO2accommodates and stabilizes InOxby serving as a reservoir. The decreased concentration of surface InOxunder elevated temperatures coincides with significantly decreased selectivity toward methanol and a sharp increase of the reverse water-gas shift reaction. The reconstruction-induced variation of InOxconcentration appears to be one of the most important factors contributing to the altered catalytic performance of CO2HR at different reaction conditions. (2) The strong interactions and reactions between m-ZrO2and In2O3result in the activation of a pool of In-O bonds at the In2O3/m-ZrO2interface to form oxygen vacancies. On the other hand, the high dispersity of In2O3nanostructures onto m-ZrO2prevents their over-reduction under catalytically relevant conditions (up to 673 K), when bare In2O3is unavoidably reduced into the metallic phase (In0). The relationship between the extent of reduction of In2O3and catalytic performance (CO2conversion, CH3OH selectivity, or yield of CH3OH) suggests the presence of an optimum coverage of surface InOxand oxygen vacancies under reaction conditions. The conventional model that links catalytic performance solely to the coverage of oxygen vacancies appears invalid in the present case. In situ analysis also allows the observation of surface reaction intermediates and their interconversions, including the reduction of CO3∗ into formate, a precursor for the formation of methanol and CO. The combinative ex situ and in situ study sheds light on the reaction mechanism of the CO2HR on In2O3/m-ZrO2-based catalysts. Our findings on the large-scale surface reconstructions, support effect, and the reaction mechanism of In2O3/m-ZrO2for CO2HR may apply to other related metal oxide catalyzed CO2reduction reactions

Discovering hidden material properties of MgCl\u3csub\u3e2\u3c/sub\u3e at atomic resolution with structured temporal electron illumination of picosecond time resolution

\u3cp\u3eA combination of atomic resolution phase contrast electron microscopy and pulsed electron beams reveals pristine properties of MgCl\u3csub\u3e2\u3c/sub\u3e at 1.7 Å resolution that were previously masked by air and beam damage. Both the inter- and intra-layer bonding in pristine MgCl\u3csub\u3e2\u3c/sub\u3e are weak, which leads to uncommonly large local orientation variations that characterize this Ziegler–Natta catalyst support. By delivering electrons with 1–10 ps pulses and ≈160 ps delay times, phonons induced by the electron irradiation in the material are allowed to dissipate before the subsequent delivery of the next electron packet, thus mitigating phonon accumulations. As a result, the total electron dose can be extended by a factor of 80–100 to study genuine material properties at atomic resolution without causing object alterations, which is more effective than reducing the sample temperature. In conditions of minimal damage, beam currents approach femtoamperes with dose rates around 1 eÅ\u3csup\u3e−2\u3c/sup\u3e s\u3csup\u3e−1\u3c/sup\u3e. Generally, the utilization of pulsed electron beams is introduced herein to access genuine material properties while minimizing beam damage.\u3c/p\u3

Discovering hidden material properties of MgCl2 at atomic resolution with structured temporal electron illumination of picosecond time resolution

A combination of atomic resolution phase contrast electron microscopy and pulsed electron beams reveals pristine properties of MgCl2 at 1.7 Å resolution that were previously masked by air and beam damage. Both the inter- and intra-layer bonding in pristine MgCl2 are weak, which leads to uncommonly large local orientation variations that characterize this Ziegler–Natta catalyst support. By delivering electrons with 1–10 ps pulses and ≈160 ps delay times, phonons induced by the electron irradiation in the material are allowed to dissipate before the subsequent delivery of the next electron packet, thus mitigating phonon accumulations. As a result, the total electron dose can be extended by a factor of 80–100 to study genuine material properties at atomic resolution without causing object alterations, which is more effective than reducing the sample temperature. In conditions of minimal damage, beam currents approach femtoamperes with dose rates around 1 eÅ−2 s−1. Generally, the utilization of pulsed electron beams is introduced herein to access genuine material properties while minimizing beam damage

Discovering Hidden Material Properties of MgCl 2

A combination of atomic resolution phase contrast electron microscopy and pulsed electron beams reveals pristine properties of MgCl2 at 1.7 Å resolution that were previously masked by air and beam damage. Both the inter- and intra-layer bonding in pristine MgCl2 are weak, which leads to uncommonly large local orientation variations that characterize this Ziegler–Natta catalyst support. By delivering electrons with 1–10 ps pulses and ≈160 ps delay times, phonons induced by the electron irradiation in the material are allowed to dissipate before the subsequent delivery of the next electron packet, thus mitigating phonon accumulations. As a result, the total electron dose can be extended by a factor of 80–100 to study genuine material properties at atomic resolution without causing object alterations, which is more effective than reducing the sample temperature. In conditions of minimal damage, beam currents approach femtoamperes with dose rates around 1 eÅ−2 s−1. Generally, the utilization of pulsed electron beams is introduced herein to access genuine material properties while minimizing beam damage