Well-defined Facets Research Articles

Facet-Dependent Diversity of Pt-O Coordination for Pt1/CeO2 Catalysts Achieved by Oriented Atomic Deposition.

The surface chemistry of CeO2 is dictated by the well-defined facets, which exert great influence on the supported metal species and the catalytic performance. Here we report Pt1/CeO2 catalysts exhibiting specific structures of Pt-O coordination on different facets by using adequate preparation methods. The simple impregnation method results in Pt-O3 coordination on the predominantly exposed {111} facets, while the photo-deposition method achieves oriented atomic deposition for Pt-O4 coordination into the "nano-pocket" structure of {100} facets at the top. Compared to the impregnated Pt1/CeO2 catalyst showing normal redox properties and low-temperature activity for CO oxidation, the photo-deposited Pt1/CeO2 exhibits uncustomary strong metal-support interaction and extraordinary high-temperature stability. The preparation methods dictate the facet-dependent diversity of Pt-O coordination, resulting in the further activity-selectivity trade-off. By applying specific preparation routes, our work provides an example of disentangling the effects of support facets and coordination environments for nano-catalysts.

(Invited) Unraveling Hot Carrier Transfer Processes in Plasmonic Catalysis

In the last decade, plasmonic nanoantennas have revolutionized light manipulation and control at the nanoscale. Interestingly, generation of hot carriers in metals upon light absorption have opened new pathways for controlling photo(electro)chemical processes and engineering photocatalysts. Yet, fundamental questions remain about the microscopic details of these complex light-matter interactions.We have recently developed a well-controlled platform for micro-scale plasmonic photoelectrochemistry studies that leverages the unique properties of monocrystalline microflakes [1] as well as precise nanofabrication methods. Interestingly, the microflakes exhibit well-defined crystal facets and can bridge the properties of bulk metals with those of nanoscale plasmonic antennas, accessing ultra-thin film dimensions (sub 15-nm) that are challenging for polycrystalline films. By performing careful absorption measurements, we explore the photoelectrochemical performance of these hot carrier micro-scale photoelectrodes for inner- and outer-sphere reactions [2], concurrently comparing them to cm-scale devices [3]. This allows us to unravel the interplay of hot carrier generation and transport at metal-liquid and metal-semiconductor interfaces and identify bottlenecks for charge transfer.[1] Kiani F., Tagliabue G. - High‐Aspect Ratio Au Microflakes via Gap‐Assisted Synthesis – Chemistry of Materials 34 (3), 1278-1288, 2022[2] Kiani F. et al - Transport and Interfacial Injection of d-band Hot Holes Control Plasmonic Chemistry - ACS Energy Letters, 8 (10), 4242-4250, 2023[3] Ma J., Oh K., Tagliabue G. - Understanding Wavelength-Dependent Synergies between Morphology and Photonic Design in TiO2-Based Solar Powered Redox Cells – Journal of Physical Chemistry C, 127 (1), 11-21, 2022

Light-Induced Dynamic Activation of Copper/Silicon Interface for Highly Selective Carbon Dioxide Reduction.

Numerous studies have shown a fact that phase transformation and/or reconstruction are likely to occur and play crucial roles in electrochemical scenarios. Nevertheless, a decisive factor behind the diverse photoelectrochemical activity and selectivity of various copper/silicon photoelectrodes is still largely debated and missing in the community, especially the possibly dynamic behaviors of metal catalyst/semiconductor interface. Herein, through in situ X-ray absorption spectroscopy and transmission electron microscope, a model system of Cu nanocrystals with well-defined facets on black p-type silicon (BSi) is unprecedentedly demonstrated to reveal the dynamic phase transformation of forming irreversible silicide at Cu nanocrystal-BSi interface during photoelectrocatalysis, which is validated to originate from the atomic interdiffusion between Cu and Si driven by light-induced dynamic activation process. Significantly, the adaptive junction at Cu-Si interface is activated by an expansion of interatomic Cu-Cu distance for CO2 electroreduction, which efficiently restricts the C-C coupling pathway but strengthens the bonding with key intermediate of *CHO for CH4 yield, resulting in a remarkable 16-fold improvement in the product ratio of CH4/C2 products and an intriguing selectivity switch. This work offers new insights into dynamic structural transformations of metal/semiconductor junction and design of highly efficient catalysts toward photosynthesis.

Faceted crystal growth of cyclodextrin-oil inclusion complexes

The spontaneous formation of cyclodextrin (CD)-oil inclusion complexes (ICs) and their further growth into patterned crystals present a bottom-up route to the fabrication of periodic macroscopic structure. Although the inclusion processes are well established for the molecules, understanding intermediate structures during the crystal growth and emerging of persistent crystalline order has been lacking. Here we build a hierarchy of oriented micro/nanostructures of CD-oil ICs in solution by choosing different oil guests including several straight-chain alkanes of C12, C14 and C16, oleic acid (OA), glycerol trioleate (TG) and soybean oil (SO), in an attempt to reveal the roles of oil guests in the formation of their crystallites. Remarkably, the ICs tend to grow into clusters and terminate at a certain finite size as long columns or lamella plates with well-defined facets, dependent on the type of oil used. For the first time, we report a non-equilibrium growth of crystallites with surface faceting directed by the guests by means of Arching and Bundling.

Systematic combination of palladium facets and monolayer metal hydroxide nanosheets for promotion of ethanol oxidation reaction

The design of catalyst surfaces that exhibit high activities for ethanol oxidation reaction (EOR) is essential to achieving practical application of direct ethanol fuel cells. Composite catalysts of Pd nanoparticles and metal hydroxide are promising candidates for EOR; however, a guide of catalyst design, including appropriate valence states and interfacial structures between component materials, has not been identified. Herein, we synthesize composite electrocatalysts of cubic and octahedral Pd nanocrystals with well-defined facets and monolayer metal hydroxide nanosheets with an identical structure and different composition containing Ni, Fe and Mn, and systematically elucidate highly active interfacial sites between Pd and metal hydroxides for EOR. Promotion of OH− adsorption by the hydroxide nanosheets enhances the catalytic activities of the Pd nanocrystals and the nanosheet having higher affinity to OH− result in higher EOR performances of the composite catalysts. The improved activities are greater for (111) facet than for (100) facet of the Pd whereas the (100) facet is superior for EOR to the (111) facet for the bare Pd nanocrystals. Our study suggests that combination of the Pd (111) facet and metal hydroxides is favorable for developing highly active electrocatalysts for EOR.

Into the Void: Single Nanopore in Colloidally Synthesized Bi2Te3 Nanoplates with Ultralow Lattice Thermal Conductivity.

Bi2Te3 is a well-known thermoelectric material that was first investigated in the 1960s, optimized over decades, and is now one of the highest performing room-temperature thermoelectric materials to-date. Herein, we report on the colloidal synthesis, growth mechanism, and thermoelectric properties of Bi2Te3 nanoplates with a single nanopore in the center. Analysis of the reaction products during the colloidal synthesis reveals that the reaction progresses via a two-step nucleation and epitaxial growth: first of elemental Te nanorods and then the binary Bi2Te3 nanoplate growth. The rates of epitaxial growth can be controlled during the reaction, thus allowing the formation of a single nanopore in the center of the Bi2Te3 nanoplates. The size of the nanopore can be controlled by changing the pH of the reaction solution, where larger pores with diameter of ∼50 nm are formed at higher pH and smaller pores with diameter of ∼16 nm are formed at lower pH. We propose that the formation of the single nanopore is mediated by the Kirkendall effect and thus the reaction conditions allow for the selective control over pore size. Nanoplates have well-defined hexagonal facets as seen in the scanning and transmission electron microscopy images. The single nanopores have a thin amorphous layer at the edge, revealed by transmission electron microscopy. Thermoelectric properties of the pristine and single-nanopore Bi2Te3 nanoplates were measured in the parallel and perpendicular directions. These properties reveal strong anisotropy with a significant reduction to thermal conductivity and increased electrical resistivity in the perpendicular direction due to the higher number of nanoplate and nanopore interfaces. Furthermore, Bi2Te3 nanoplates with a single nanopore exhibit ultralow lattice thermal conductivity values, reaching ∼0.21 Wm-1K-1 in the perpendicular direction. The lattice thermal conductivity was found to be systematically lowered with pore size, allowing for the realization of a thermoelectric figure of merit, zT of 0.75 at 425 K for the largest pore size.

Well-defined N3 C1 -anchored Single-Metal-Sites for Oxygen Reduction Reaction.

N-, C-, O-, S-coordinated single-metal-sites (SMSs) have garnered significant attention due to the potential for significantly enhanced catalytic capabilities resulting from charge redistribution. However, significant challenges persist in the precise design of well-defined such SMSs, and the fundamental comprehension has long been impeded in case-by-case reports using carbon materials as investigation targets. In this work, the well-defined molecular catalysts with N3 C1 -anchored SMSs, i.e., N-confused metalloporphyrins (NCPor-Ms), are calculated for their catalytic oxygen reduction activity. Then, NCPor-Ms with corresponding N4 -anchored SMSs (metalloporphyrins, Por-Ms), are synthesized for catalytic activity evaluation. Among all, NCPor-Co reaches the top in established volcano plots. NCPor-Co also shows the highest half-wave potential of 0.83 V vs. RHE, which is much better than that of Por-Co (0.77 V vs. RHE). Electron-rich, low band gap and regulated d-band center contribute to the high activity of NCPor-Co. This study delves into the examination of well-defined asymmetric SMS molecular catalysts, encompassing both theoretical and experimental facets. It serves as a pioneering step towards enhancing the fundamental comprehension and facilitating the development of high-performance asymmetric SMS catalysts.

Electrosynthesis of Metal-Organic Framework Films with Well-Defined Facets.

The deposition of metal-organic framework (MOF) films with defined exposed facets is important to enhance the performance of these films for, for example, catalysis or separations. In this work, MOF films with specific exposed facets are electrodeposited anodically on various substrates (e. g. on copper-sputtered Si wafers, copper meshes, copper foams, and polypropylene membranes). The influence of the deposition parameters, including the pH of the solution, current density, concentration of linker, and solvent, on the exposed facets of the deposited MOFs was investigated. The results suggest that precise control over the supersaturation during anodic deposition is a possible strategy for synthesizing MOF crystals with well-defined exposed facets. This approach provides a powerful toolbox for various applications requiring crystal facet control of MOF films.

Spatially and Chemically Resolved Visualization of Fe Incorporation into NiO Octahedra during the Oxygen Evolution Reaction.

The activity of Ni (hydr)oxides for the electrochemical evolution of oxygen (OER), a key component of the overall water splitting reaction, is known to be greatly enhanced by the incorporation of Fe. However, a complete understanding of the role of cationic Fe species and the nature of the catalyst surface under reaction conditions remains unclear. Here, using a combination of electrochemical cell and conventional transmission electron microscopy, we show how the surface of NiO electrocatalysts, with initially well-defined surface facets, restructures under applied potential and forms an active NiFe layered double (oxy)hydroxide (NiFe-LDH) when Fe3+ ions are present in the electrolyte. Continued OER under these conditions, however, leads to the creation of additional FeOx aggregates. Electrochemically, the NiFe-LDH formation correlates with a lower onset potential toward the OER, whereas the formation of the FeOx aggregates is accompanied by a gradual decrease in the OER activity. Complementary insight into the catalyst near-surface composition, structure, and chemical state is further extracted using X-ray photoelectron spectroscopy, operando Raman spectroscopy, and operando X-ray absorption spectroscopy together with measurements of Fe uptake by the electrocatalysts using time-resolved inductively coupled plasma mass spectrometry. Notably, we identified that the catalytic deactivation under stationary conditions is linked to the degradation of in situ-created NiFe-LDH. These insights exemplify the complexity of the active state formation and show how its structural and morphological evolution under different applied potentials can be directly linked to the catalyst activation and degradation.

Fabrication and Characterization of Dielectric ZnCr2O4 Nanopowders and Thin Films for Parallel-Plate Capacitor Applications.

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr2O4 nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr2O4 nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10-4 at a frequency of 1 Hz. Nanoparticulate ZnCr2O4-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process.

In-Situ Measurement of Charge Transfer at Cocatalyst/Semiconductor Interfaces in BiVO4 Particle Photocatalyst

Semiconductor photocatalyst particles are known to transform solar energy to useful chemicals such as H2 or methanol. However, the efficiency of semiconductor photocatalysts often suffers from the quick charge carrier recombination. However, there is no real physical reasons for semiconductors to display this low performance. Multiple strategies have been proposed and applied to modify the semiconductor particles and enhance their solar-to-hydrogen efficiencies. It is often assumed that in semiconductor particles with well-defined crystal facets, the photogenerated charge carriers undergo facet-dependent separation. Thus, a common strategy is to deposit a HER electrocatalyst on ‘electron-selective’ facets and an OER electrocatalyst on ‘hole-selective’ facets. Although this strategy have showed plausible results in previous literatures, a precise understanding of how charge-carrier-selective contacts between the deposited electrocatalyst and semiconductor particles emerge and how the semiconductor photocatalysts are rationally designed is still missing.In this work, we used both ex-situ and in-situ conducting AFM experiments and a new ionomer/catalyst–semiconductor test structures to characterize the charge transfer between semiconductor and deposited electrocatalysts at individual nanoparticle scale. We showed that the presence of the water/electrolyte interface is critical to induce hole selectivity between the CoOx OER cocatalyst and the BiVO4 semiconductor light absorber. We demonstrated that the negative surface charge on the semiconductor is central to induce hole selectivity. The work also demonstrates a facile strategy to control local pH and introduce water using thin-film ionomers for conductive AFM measurements. These new insights can be broadly applied to the rational design of semiconductor photocatalysts for overall water-splitting systems to control charge-carrier selectivity and improve their performance.

Cu Facet-Dependent Elementary Surface Reaction Kinetics of CO2 Hydrogenation to Methanol Catalyzed by ZrO2/Cu Inverse Catalysts.

ZrO2-Cu-based catalysts are active in catalyzing the hydrogenation of CO2 to methanol. Herein, we report Cu facet effects on the catalytic performance of ZrO2/Cu inverse catalysts in CO2 hydrogenation to methanol using various Cu nanocrystals with well-defined Cu morphologies and facets. The ZrO2-Cu interface is the active site, in which the ZrO2-Cu{100} and ZrO2-Cu{110} interfaces exhibit similar apparent activation energies of ∼42.6 kJ/mol, smaller than that of the ZrO2-Cu{111} interface (∼64.5 kJ/mol). Temporal in situ diffuse reflectance infrared Fourier transform spectroscopy characterization results identify the bridge formate hydrogenation as the rate-determining elementary surface reaction under typical reaction temperatures, whose activation energy is similar at the ZrO2-Cu{100} (∼36.3 kJ/mol) and ZrO2-Cu{110} (∼40.5 kJ/mol) interfaces and larger at the ZrO2-Cu{111} interface (∼54.5 kJ/mol). This fundamental understanding suggests Cu facet engineering as a promising strategy to improve the catalytic performance of ZrO2/Cu inverse catalysts for CO2 hydrogenation to methanol.

Elucidating the Role of Capping Agents in Facet-Dependent Adsorption Performance of Hematite Nanostructures.

Organic capping agents are a ubiquitous and crucial part of preparing reproducible and homogeneous batches of nanomaterials, particularly nanocrystals with well-defined facets. Despite studies reporting surface ligands (e.g., capping agents) having a non-negligible role in catalytic behavior, their impact is less understood in contaminant adsorption, an important consideration given their potential to obfuscate facet-dependent trends in performance. To ascribe observed behaviors to the facet or the ligand, this report evaluates the impact of poly(N-vinyl-2-pyrrolidone) (PVP), a commonly utilized capping agent, on the adsorption performance of nanohematite particles of varying prevailing facet in the removal of selenite (Se(IV)) as a model system. The PVP capping agent reduces the available surface area for contaminant binding, thus resulting in a reduction in overall Se(IV) adsorbed. However, accounting for the effects of surface area, {012}-faceted nanohematite demonstrates a significantly higher sorption capacity for Se(IV) compared with that of {001}-faceted nanohematite. Notably, chemical treatment is minimally effective in removing strongly bound PVP, indicating that complete removal of surface ligands remains challenging.

Semiconductor Nanocrystals: Unveiling the Chemistry behind Different Facets.

ConspectusDeveloping next-generation colloidal semiconductor nanocrystals with high-quality optoelectronic properties and precise processability relies on achieving complete mastery over the surface characteristics of nanocrystals (NCs). This requires precise engineering of the ligand-NC surface interactions, which poses a challenge due to the complex reactivity of the multiple binding sites across the entire surface. Accordingly, recent progress has been made by strategically combining well-defined surface models with quantitative surface reactions to advance our understanding and manipulation of NC surface chemistry. Our lab has contributed to this progress by developing a size-dependent shape model of IV-VI NCs, gaining insights into their unique facet-specific chemistry, and developing a systematic ligand modification strategy for target applications. Furthermore, we have created well-defined facets in III-V NCs via a co-passivation strategy, addressing the previously lacking specific shapes.This Account is divided into three parts. First, we discuss the complexities involved in comprehensively understanding the nanocrystal surface structure at the atomistic level. We explain why we focused on well-defined NCs with a large exciton Bohr radius to explore facets, an essential aspect of surface heterogeneity across the entire NC. Second, we present our work on one of the most studied nanocrystals, IV-VI materials, and how facet-specific surface chemistry has led to a meaningful understanding and control of the NC's surface. We discovered a size-dependent facet distribution in IV-VI NCs and suggested facet-specific surface chemistry to improve the photophysical properties of NCs. We further modulate the electronic properties of NC assemblies for efficient optoelectronic applications. Third, we describe our recent success in achieving well-defined facets and their facet-specific chemistry in III-V NCs, which have yet to be explored as much as classical II-VI or IV-VI materials. We explain how controlling the surfaces in III-V NCs has been challenging. We present a precise growth platform for the geometric modulation of NCs, which can be further explored for shape-dependent exciton behavior and surface reactivities.Taken together, we present a compelling case for utilizing facet-specific chemistry as a platform for mechanistic investigation and morphology exploration, which can pave the way for developing high-quality and precisely designed NCs for optoelectronic technologies, unlocking new multidisciplinary applications.

High Thermoelectric Performance in 2D Sb2Te3 and Bi2Te3 Nanoplate Composites Enabled by Energy Carrier Filtering and Low Thermal Conductivity.

Thermoelectrics are an important class of materials with great potential in alternative energy applications. In this study, two-dimensional (2D) nanoplates of the layered chalcogenides, Sb2Te3 and Bi2Te3, are synthesized and composites of the two are investigated for their thermoelectric properties. The two materials, Sb2Te3 and Bi2Te3, were synthesized as hexagonal, 2D nanoplates via a colloidal polyol route. The as-synthesized Sb2Te3 and Bi2Te3 vary drastically from one another in their lateral and vertical dimensions as revealed by scanning electron microscopy and atomic force microscopy. The single crystalline nanoplate nature is deduced by high-resolution transmission electron microscopy and selected area electron diffraction. Nanoplates have well-defined hexagonal facets as seen in the scanning and transmission electron microscopy images. The nanoplates were consolidated as an anisotropic nanostructured pellet via spark plasma sintering. Preferred orientation observed in the powder X-ray diffraction pattern and scanning electron microscopy images of the fractured pellets confirm the anisotropic structure of the nanoplates. Thermoelectric properties in the parallel and perpendicular directions were measured, revealing strong anisotropy with a significant reduction to thermal conductivity in the perpendicular direction due to increased phonon scattering at nanoplate interfaces. All compositions, except that of the 25% Bi2Te3 nanoplate composite, behave as degenerate semiconductors with increasing electrical resistivity as the temperature increases. The Seebeck coefficient is also increased dramatically in the nanocomposites, the highest reaching 210 μV/K for 15% Bi2Te3. The increase in Seebeck is attributed to energy carrier filtering at the nanoplate interfaces. Overall, these enhanced thermoelectric properties lead to a drastic increase in the thermoelectric performance in the perpendicular direction, with zT ∼ 1.26, for the 15% Bi2Te3 nanoplate composite at 450 K.

Impact of Uniform Facets on the Thermodynamics of Ligand Exchanges on Colloidal Quantum Dots

Nanocrystal surfaces play a critical role in dictating their physical and chemical properties. Colloidal semiconductor nanocrystals, or quantum dots, are generally synthesized with insulating aliphatic ligands, but these ligands can be post-synthetically exchanged with other molecular species for a variety of applications. While previous work has investigated the thermodynamics of ligand exchanges on quasi-spherical quantum dots through sensitive isothermal titration calorimetry and 1H NMR measurements, the influence of well-defined crystal facets on the propensity of these ligand exchanges is yet to be explored using these techniques. We studied the exchange of native cadmium carboxylate ligands for zinc chloride ligands on (111) faceted cadmium selenide tetrahedrons and (100) faceted cadmium selenide cubes. From these measurements, we find the unexpected result that the thermodynamics of this ligand exchange between these facets is nearly identical. Further, a modified Ising model was used to fit both the calorimetric and 1H NMR data to extract thermodynamic parameters for the exchange. These simulations suggest that the observed enthalpic differences can be mostly attributed to varying inter-ligand interactions on the (111) and (100) facets.

0641 Difficulty Maintaining Sleep and Sleep Quality mediate the Relationship between Sleep Disturbances and Depression

Abstract Introduction Prior epidemiological research has established the relationship between sleep disturbances and depression. Sleep disturbances are also common prodromal features of and comorbid with depression. However, limitations exist across past studies, including the frequent focus on “sleep disturbances” over well-defined facets of sleep, inattention to mediators, and a lack of focus on special populations. As such, there is a need to delineate the relationship between sleep disturbances and depression across specific facets of sleep, particularly in special populations. The current study examined multiple sleep facets as mediators of the relationship between general sleep disturbances and depression severity in college student athletes. Methods Student athletes (N = 993) from the Pacific Athlete Conference-12 completed the Athlete Sleep Screening Questionnaire-Sleep Difficulty Subscale (ASSQ-SDS) and Patient Health Questionnaire-9 (PHQ-9). Parallel multiple mediator models were conducted to examine whether the relationship between sleep disturbances and depression severity was mediated by sleep duration, sleep quality, sleep onset latency, and difficulty maintaining sleep. Results Using bootstrapping with 5,000 resamples, the indirect effect of sleep disturbances on depression severity was significantly different from zero through sleep quality (indirect effect = .17, SE = .07, 95% CI [.04, .31]) and difficulty maintaining sleep (indirect effect = .12, SE = .03, 95% CI [.06, .19]). Sleep disturbances were associated with sleep quality (b = .29, SE = .01, p < .001) and difficulty maintaining sleep (b = .16, SE = .01, p < .001). Sleep quality (b = .59, SE = .16, p < .001) and difficulty maintaining sleep (b = .78, SE = .17, p < .001) were associated with depression severity. No other mediators reached statistical significance. Conclusion Results demonstrate that perceived sleep quality and difficulty maintaining sleep mediate the relationship between general sleep disturbances and depression severity in college student athletes. Findings suggest that sleep quality and difficulty maintaining sleep may be more impactful on depression than other facets of sleep and may be clinically useful targets of intervention for depression. Support (if any)

Effect of in-plane alignment on selective area grown homo-epitaxial nanowires

In-plane selective area growth (SAG) of III–V nanowires (NWs) has emerged as a scalable materials platform for quantum electronics and photonics applications. Most applications impose strict requirements on the material characteristics which makes optimization of the crystal quality vital. Alignment of in-plane SAG NWs with respect to the substrate symmetry is of importance due to the large substrate-NW interface as well as to obtain nanostructures with well-defined facets. Understanding the role of mis-orientation is thus important for designing devices and interpretation of electrical performance of devices. Here we study the effect of mis-orientation on morphology of selectively grown NWs oriented along the [1 1̅ 1̅] direction on GaAs(2 1 1)B. Atomic force microscopy is performed to extract facet roughness as a measure of structural quality. Further, we evaluate the dependence of material incorporation in NWs on the orientation and present the facet evolution in between two high symmetry in-plane orientations. By investigating the length dependence of NW morphology, we find that the morphology of ≈1 μm long nominally aligned NWs remains unaffected by the unintentional misalignment associated with the processing and alignment of the sample under study. Finally, we show that using Sb as a surfactant during growth improves root-mean-square facet roughness for large misalignment but does not lower it for nominally aligned NWs.

Engineering the Au-Cu2 O Crystalline Interfaces for Structural and Catalytic Integration.

Precise structural control has attracted tremendous interest in pursuit of the tailoring of physical properties. Here, this work shows that through strong ligand-mediated interfacial energy control, Au-Cu2 O dumbbell structures where both the Au nanorod (AuNR)and the partially encapsulating Cu2 O domains are highly crystalline. The synthetic advance allows physical separation of the Au and Cu2 O domains, in addition to the use of long nanorods with tunable absorption wavelength, and the crystalline Cu2 O domain with well-defined facets. The interplay of plasmon and Schottky effects boosts the photocatalytic performance in the model photodegradation of methyl orange, showing superior catalytic efficiency than the AuNR@Cu2 O core-shell structures. In addition, compared to the typical core-shell structures, the AuNR-Cu2 O dumbbells can effectively electrochemically catalyze the CO2 to C2+ products (ethanol and ethylene) via a cascade reaction pathway. The excellent dual function of both photo- and electrocatalysis can be attributed to the fine physical separation of the crystalline Au and Cu2 O domains.

Ultraviolet Exciton-Polariton Light-Emitting Diode in a ZnO Microwire Homojunction.

Low-dimensional ZnO, possessing well-defined side facets and optical gain properties, has emerged as a promising material to develop ultraviolet coherent light sources. However, the realization of electrically driven ZnO homojunction luminescence and laser devices is still a challenge due to the absence of a reliable p-type ZnO. Herein, the sample of p-type ZnO microwires doped by Sb (ZnO:Sb MWs) was synthesized individually. Subsequently, the p-type conductivity was examined using a single-MW field-effect transistor. Upon optical pumping, a ZnO:Sb MW showing a regular hexagonal cross-section and smooth sidewall facets can feature as an optical microcavity, which is evidenced by the achievement of whispering-gallery-mode lasing. By combining an n-type ZnO layer, a single ZnO:Sb MW homojunction light-emitting diode (LED), which exhibited a typical ultraviolet emission at a wavelength of 379.0 nm and a line-width of approximately 23.5 nm, was constructed. We further illustrated that strong exciton-photon coupling can occur in the as-constructed p-ZnO:Sb MW/n-ZnO homojunction LED by researching spatially resolved electroluminescence spectra, contributing to the exciton-polariton effect. Particularly, varying the cross-sectional dimensions of ZnO:Sb wires can further modulate the exciton-photon coupling strengths. We anticipate that the results can provide an effective exemplification to realize reliable p-type ZnO and tremendously promote the development of low-dimensional ZnO homojunction optoelectronic devices.