Low Defect Concentration Research Articles

Investigation of the Reverse Leakage Behavior and Substrate Defects in Vertical GaN Schottky and PIN Diodes

In this work, the effects of the substrate defect density and distribution on the reverse leakage behavior of GaN vertical Schottky diodes and p–i–n diodes are investigated. A direct connection between the reverse leakage behavior of GaN based vertical devices and the dislocation density of the underlying material was determined. The difference in the leakage current for devices on different locations of the wafer can be as high as 6 orders of magnitude (for p–i–n diodes) at −200V, for HVPE substrate with inhomogeneous but predictable defect distributions (GaN substrates with dot-core inversion domain features). For comparison, using HVPE substrates with uniform defect distribution (but with no cores), the p–i–n diodes show much more uniform leakage behavior, varying within only an order of magnitude, and that range fell within the much greater range of that for the inhomogeneous substrates. The substrates with inhomogeneous defect distribution proved to be useful to show the direct correlation. The topography measurements confirmed that the wafers with inhomogeneous defect distribution possess periodically patterned core-centers with higher defect density and larger lattice distortions surrounded by other regions, which have very low defect concentrations. Devices located away from the defective core-centers result in a reduction of the reverse bias leakage by over two orders of magnitude at −10 V for Schottky diodes. Similar trends are also observed in the p–i–n diodes; the devices close to the core centers show the highest reverse leakage (>0.01 A cm−2 at −200V). Devices further away from the core-centers (lower dislocation density) show lower reverse leakage current. Moreover, the p–i–n diodes on regions more than 300 μm away from the core-centers show the best leakage behavior (<10−7 A cm−2 at −200V) of all the devices, outperforming the devices on the substrates with uniform defect distribution (∼10−6 A cm−2 at −200V). The results from this study show that the substrate defect density and distribution play important roles in the device leakage current. X-ray topography is extremely effective for studying defect characteristics underneath individual devices. The use of the wafers with inhomogeneous, but predictable defect density clearly demonstrated the importance of low defect densities for high device performance.

Formula omitted]Silicon-on-insulator for optically interfaced quantum emitters

The coherence of optical emitters in silicon waveguides is impaired by the coupling to the surrounding bath of 29Si nuclear spins. We eliminate this obstacle by fabricating isotopically enriched silicon-on-insulator (SOI) chips. To this end, we use molecular beam epitaxy to grow a 0.4μm thin 28Si layer with a 29Si concentration <0.006% on a 70nm thin SOI seed chip. the resulting layer reveals a high crystalline quality and has a low defect concentration, determined from secondary ion mass spectroscopy, dark field plane-view and cross-view transmission electron microscope images as well as X-ray diffraction. With its low surface roughness, measured by atomic force microscopy, the grown layer is a promising material for the integration of optically interfaced quantum emitters in low-loss nanophotonic waveguides that are free from nuclear spins.

Effects of adding GPLs dispersed at different sonication times on the thermal and electrical conductivities of spark plasma sintered silicon carbide

This study has investigated the effects of adding 1 wt % graphene platelets (GPLs) dispersed at different probe-sonication times such as 1, 2, 4 and 6 h on the microstructure, thermal and electrical conductivities of the spark plasma sintered (SPSed) silicon carbide (SiC) matrix. According to scanning electron microscope (SEM), size measurement and Raman analyses, the dispersion of the GPLs increased, the platelet sizes decreased, and the defect concentrations on the structure of GPLs increased as the sonication time increased. While the size reduction was only around 2–5% up to 2 h sonication time, it increased to 25–30% at the 4 and 6 h sonication times. 2 h sonicated GPLs provided the highest contribution among all GPLs, increasing the thermal and electrical conductivity of the SiC matrix by 24 % and ∼106 times, respectively due to having a combination of large lateral size, good dispersion, and low defect concentration characteristics. Anisotropic effect on thermal and electrical conductivities of GPLs-SiC composites decreased with increasing probe-sonication time since the reduction in platelet size of GPLs led to a decrease in their orientation degree within the matrix microstructure.

Microstructure and Corrosion Behavior of Laser Cladding FeCoNiCrBSi Based High-Entropy Alloy Coatings

High-entropy amorphous alloys designed based on the concept of multi-principal components have the comprehensive advantages of high passivation element content and amorphous structure, and are considered as one of the promising alternative protective materials in extreme marine environments. However, based on the composition of traditional amorphous alloys, the multi-principal design significantly reduces its glass forming ability. In order to improve the glass formation ability of high-entropy amorphous alloys, this study attempts to design Fe19.6Co19.6Ni19.6Cr19.6(B13.72Si5.88)19.6Y2 alloy by microalloying on the basis of traditional FeCoNiCrBSi high-entropy amorphous alloy. The traditional Fe43.6Co6Ni17.4Cr9B17.5Si1.5Nb5 iron-based amorphous alloy was selected as the comparison material. Then, spherical alloy powders were prepared by gas atomization. The amorphous nanocrystalline composite coatings were deposited on the 304 stainless steel by laser cladding technology. The microstructure of the coatings was characterized by scanning electron microscopy and X-ray diffractometer. The corrosion behavior of laser cladding coatings in 3.5 wt.% NaCl solution were investigated in detail. The results show that the Fe43.6Co6Ni17.4Cr9B17.5Si1.5Nb5 powder is composed of FCC, Laves and boride phases. Whereas the Fe19.6Co19.6Ni19.6Cr19.6(B13.72Si5.88)19.6Y2 high-entropy amorphous alloy powder is composed of FCC and boride phases. Due to the remelting and multiple heat treatments during the preparation of the laser cladding coatings, borides were precipitated in both coatings. The microstructure of the two coatings from the bonding area with the substrate to the top layer are plane grains, dendrite, equiaxed grains and amorphous phase, respectively. Fe19.6Co19.6Ni19.6Cr19.6(B13.72Si5.88)19.6Y2 high-entropy amorphous alloy coating exhibits high corrosion potential, passivation film resistance and low corrosion current density in 3.5 wt.% NaCl solution. In addition, the passivation film formed on the coating has higher Cr content and lower defect concentration, showing more excellent corrosion resistance.

Less energy-intensive synthesis of mesoporous multi-oriented graphite microspheres with low defect concentration for advanced potassium-ion battery anodes

Potassium-ion batteries (KIBs) have emerged as prospective alternatives to lithium-ion batteries (LIBs) given the wide availability of K resources and the similar operating voltage. As in the case of LIBs, graphite is regarded as the most promising anode material for KIBs due to high energy density attributed to its low potential plateau and resource abundance. However, the practical use of graphite in KIBs is hindered by poor stability due to huge volume changes during K+ ion insertion-deinsertion. Here, a facile and scalable synthesis method of mesoporous multi-oriented graphite microspheres via pilot-scale spray drying process and less energy-intensive graphitization step is introduced. A high degree of graphitization is achieved even at 1100 °C by virtue of in situ formed Fe nanocrystals within the microsphere that serve as graphitization catalyst. The degree of graphitization can be further improved by selective removal of amorphous carbon by oxidation at 450 °C, which greatly increases the initial Coulombic efficiency and reversible capacity of the graphite microspheres. The synthesized microspheres with the multi-oriented graphite grains and the mesoporous network enable rapid K+ ion insertion-deinsertion, and alleviate stress from volume changes during cycling, thereby exhibiting markedly improved cyclability (247 mA h g−1 after 400 cycles at 0.5C) and rate performance (58 mA h g−1 at 3C) that outperform those of commercial artificial graphite. This study provides a new perspective for designing reliable nanostructured graphite materials for advanced KIB anodes.

Strategies and Methods of Modulating Nitrogen-Incorporated Oxide Photocatalysts for Promoted Water Splitting

ConspectusThe conversion of solar energy to chemicals and the storage of this energy is one of the most promising routes to realizing a “carbon zero” society, for which particulate photocatalytic water splitting to produce hydrogen has been considered to be a clean potential route. For this purpose, many d0 and d10 metal-based nitrogen-incorporated oxide (including nitrogen-doped oxide and oxynitride) semiconductor photocatalysts have been developed as good candidates to harvest major visible regions of solar light and to exhibit suitable energy levels to drive water splitting. Compared to the oxide-type photocatalysts, valence bands of the nitrogen-incorporated oxide can be upshifted in consideration of the lower electronegativity of nitrogen atoms concerning the oxygen atoms.However, a high-temperature nitridation process was needed to introduce nitrogen atoms into the metal oxide lattice. Because of the poor charge balance of the N3– substitution for O2– and the strong reducing effect of the active nitrogen species at high temperature, the nitriding process tends to introduce both anionic vacancy defects as well as low-valent metal ion defects. In addition, the crystal size of (oxy)nitrides synthesized through high-temperature nitridation is generally large, and there is a lack of an effective charge-separation driving force within the bulk of the (oxy)nitrides. Because of the scarcity of surface catalytic sites, the photocatalytic activity of the (oxy)nitrides is rather low.Recently, our group has been devoted to addressing the above key challenges, especially for the d0-metal-based (oxy)nitrides. The new preparation routes and/or methods were carried out to enhance the nitration kinetics for the synthesis of (oxy)nitrides with low-defect concentrations and further fabricate some novel metal (oxy)nitrides. The doping strategies were developed to suppress the generation of low-valent metal ion defects. A one-pot nitridation strategy was developed to construct the type II heterostructures of two metal oxynitrides to enhance their charge separation, and a strategy for the surface modification of metal oxynitrides with inert metal oxides was developed to promote the surface hydrophilicity and the cocatalyst dispersion. In addition, an intimate and strengthened interface between the cocatalyst and the metal oxynitride photocatalyst was achieved by a sequential cocatalyst decoration method, and it was demonstrated that the strengthened interface is beneficial to enhancing the surface charge separation efficiency. Benefitting from these methods and strategies, some novel visible-light-responsive materials have been exploited for promising water splitting, and remarkably improved water splitting performances have been achieved on some typical d0-metal-based (oxy)nitrides regardless of H2/O2-evolving half-reactions and Z-scheme overall water splitting (Z-OWS) reactions. In this Account, we will give a concise summary of these methods and strategies, and the prospects of nitrogen-incorporated oxide photocatalysts for potential water splitting will be examined.

Transparent Colloidal Crystals With Structural Colours

Spatially ordered arrangements of spherical colloids are known to exhibit structural colours. The intensity and brilliance of these structural colours typically improve with colloidal monodispersity, low concentrations of point and line defects and with increasing refractive index contrast between the colloids and the embedding medium. Here we show that suspensions of charge stabilised, fluorinated latex particles with low refractive-index contrast to their aqueous background form Wigner crystals with FCC symmetry for volume fractions between 13 and 40%. In reflection they exhibit both strong, almost angle-independent structural colours and sharp, more brilliant Bragg peaks despite the particle polydispersity and bimodal distribution. Simultaneously, these suspensions appear transparent in transmission. Furthermore, binary AB, A2B and A13B type mixtures of these fluorinated and similarly sized polystyrene particles appeared predominantly white but with clear Bragg peaks indicating a CsCl-like BCC structure and more complex crystals. We characterised the suspensions using a combination of reflectivity measurements and small-angle x-ray scattering, complemented by reflectivity modelling.

Electronically Tunable Transparent Conductive Thin Films for Scalable Integration of 2D Materials with Passive 2D–3D Interfaces

AbstractA novel transparent conductive support structure for scalable integration of 2D materials is demonstrated, providing an electronically passive 2D–3D interface while also enabling facile interfacial charge transport. This structure, which comprises an evaporated nanocrystalline carbon (nc‐C) film beneath nanometer‐thin atomic layer deposited AlOx, is thermally stable and allows direct chemical vapor deposition of 2D materials onto the surface. The combination of spatial uniformity, enhanced charge screening, and low interface defect concentrations yields a tenfold enhancement of MoS2 photoluminescence intensity compared to flakes on conventional Si/SiO2, while also retaining the strong optical contrast for monolayer flakes. Tunneling across the ultrathin AlOx enables facile interfacial charge injection, which is utilized for high‐resolution scanning electron microscopy and photoemission electron microscopy with no detectable charging. Thus, this combination of scalable fabrication and electronic conductivity across a weakly interacting 2D–3D interface opens up new opportunities for device integration and characterization of 2D materials.

Conducting interfaces between LaAlO3 and thick homoepitaxial SrTiO3 films for transferable templates

For the mechanical stability of heterostructure membranes such as LaAlO3 (LAO)/SrTiO3 (STO), which is well-known for two-dimensional electron transport at the interface, a thick template substrate layer is required. However, thick STO films typically suffer from the formation of undesired point defects, mainly due to its cation off-stoichiometry, which results in the insulating interface with LAO. Herein, we report the successful fabrication of a conducting interface between LAO and thick homoepitaxial STO films by pulsed laser deposition. The careful optimization of laser ablation parameters including laser energy density and laser spot size led to stoichiometric 500 nm–thick STO films that have a lattice structure identical to that of bulk single crystals of STO, as confirmed by X-ray diffraction and temperature-dependent Raman spectroscopy. The interface between 4 nm–thick LAO and 500 nm–thick stoichiometric STO films exhibited a metallic behavior at low temperature down to 4 K, implying a low concentration of point defects in the homoepitaxial STO film. Ultimately, a crack-free, millimeter-sized 500 nm–thick STO membrane was successfully fabricated. These results are expected to facilitate the integration of high-quality complex oxide heterostructure membranes with various substrates including silicon, enabling their practical applications.

Silk fibroin induced homeotropic alignment of perovskite crystals toward high efficiency and stability

The photoactive lead halide perovskites with a highly crystalline structure and low trap state density were regarded as the prerequisites for achieving high photovoltaic performance. The perovskite thin films were typically synthesized by simple wet chemistry routes, where the fluctuations in the fabrication readily generate lattice defects and induce stacking faults during the crystal growth. The growth of highly crystalline and low-defect perovskite usually needs complicated synthetical manipulation and well-designed additive engineering. Here in this work, we reported a naturally available protein, silk fibroin (SF), whereby the highly ordered β-sheets component can adequately interact with perovskite intermediates and work as the crystal growth template and trap passivation agent, which induced facile self-assembly of the perovskite crystals with homeotropic alignment structure and low defect concentrations. As a result, the SF incorporated perovskite layer exhibited a much-improved conversion efficiency with charge carrier mobility 1000 times higher than that of pristine film, as well as showed robust stability under various harsh conditions.

Enhancing Thermoelectric Performance of AgSbTe2-Based Compounds via Microstructure Modulation Combining with Entropy Engineering.

Modulation of the microstructure and configurational entropy tuning are the core stratagem for improving thermoelectric performance. However, the correlation of evolution among the preparation methods, chemical composition, structural defects, configurational entropy, and thermoelectric properties is still unclear. Herein, two series of AgSbTe2-based compounds were synthesized by an equilibrium melting-slow-cooling method and a nonequilibrium melting-quenching-spark plasma sintering (SPS) method, respectively. The equilibrium method results in coarse grains with a size of >300 μm in the samples and a lower defect concentration, leading to higher carrier mobility of 10.66 cm2 V-1 s-1 for (Ag2Te)0.41(Sb2Te3)0.59 compared to the sample synthesized by nonequilibrium preparation of 1.83 cm2 V-1 s-1. Moreover, tuning the chemical composition of nonstoichiometric AgSbTe2 effectively improves the configurational entropy and creates a large number of cation vacancies, which evolve into dense dislocations in the samples. Owing to all of these in conjunction with the strong inharmonic vibration of lattice, an ultralow thermal conductivity of 0.51 W m-1 K-1 at room temperature is achieved for the (Ag2Te)0.42(Sb2Te3)0.58 sample synthesized by the equilibrium preparation method. Due to the enhanced carrier mobility, optimized carrier concentration, and low thermal conductivity, the (Ag2Te)0.42(Sb2Te3)0.58 sample synthesized by the equilibrium preparation method possesses the highest ZT of 1.04 at 500 K, more than 60% higher than 0.64 at 500 K of the same composition synthesized by nonequilibrium preparation.

Shining a Hot Light on Emerging Photoabsorber Materials: The Power of Rapid Radiative Heating in Developing Oxide Thin-Film Photoelectrodes

The unique possibilities of rapid thermal processing (RTP) for overcoming two significant challenges in the development of oxide thin-film photoelectrodes are demonstrated. The first is the need to exceed normal temperature limits for glass-based F:SnO2 substrates (FTO, ∼550 °C) to achieve the desired density, crystallinity, and low defect concentrations in metal oxides. Flash-heating of Ta2O5, TiO2, and WO3 photoelectrodes to 850 °C is possible without damaging the FTO. RTP heating-rate dependencies suggest that the emission spectrum of the RTP lamp, which blue-shifts with increasing heating power, can significantly influence the crystallization behavior of wide-bandgap photoelectrodes (≥1.8 eV). The second challenge is avoiding the formation of structural defects, trap states, grain boundaries, and phase impurities, which can be particularly difficult in multinary metal oxides. RTP treatment of α-SnWO4, a promising photoanode material, resulted in an increase in grain size and favorable crystallographic reorientation, culminating in a new performance record.

Effects of the reaction temperature and Ba/Ti precursor ratio on the crystallite size of BaTiO3 in hydrothermal synthesis.

Nanocrystalline BaTiO3 has been prepared by hydrothermal synthesis from titanium isopropoxide and barium hydroxide octahydrate. Reaction conditions including synthesis temperature and Ba/Ti precursor ratio have been explored with the aim of producing BaTiO3 with small crystallites and a low concentration of defects. It has been found that the crystallite/particle size and tetragonality of the BaTiO3 samples increase as the synthesis temperature increases; and the crystallite/particle size of BaTiO3 is also affected by the Ba/Ti precursor ratio. The BaTiO3 sample synthesised using a Ba/Ti precursor ratio of 2 : 1 at a reaction temperature of 120 °C exhibited homogeneous crystallites of the smallest size of 107 nm. Additionally, the Ba/Ti precursor ratio of 2 : 1 with synthesis temperature of 220 °C was found to produce a smaller concentration of defects in BaTiO3.

Monitoring of Dose Dependent Damage in MeV Energy Hydrogen Implanted Silicon by Photo-Modulated Reflectance Measurements

High-energy low-mass proton implantation achieved considerable interest in semiconductor technology, due to much deeper penetration of hydrogen ions into silicon as compared to common dopants, boron, phosphorous, and arsenic. Accordingly, monitoring the accumulation kinetics and stability of proton-implantation induced defects and their influence on the optical and electrical properties of Si achieved increased attention both in technological process control and scientific research. We show that photo-modulated-reflectance (PMR) is effective technique to measure very low defect concentrations in the ppb-ppm range in high energy proton implanted silicon. After ion irradiation, the as-implanted dilute damage structure may lead to long term changes of the defect distribution and the formation of defect compounds due to mobility of point defects at room temperature. Moreover, low-mass hydrogen atoms may move significantly faster at room temperature compared to heavier dopants. We show that PMR is capable to detect differences in implanted proton dose with high sensitivity in a wide dose range, and, on a longer time scale, allows to follow changes in free carrier generation and recombination processes through the measurement of the long term decay of the PMR signal which is related to the sample response based on electro-optic and thermo-optic effects. Our experiments may pave the way toward high precision process control of device structure fabrication which utilizes the high-energy hydrogen implantation step. Also, our aim is to gain insight into the main processes underlying the dose dependent change and long-term decay of the PMR signal in high energy proton implanted Si.

Metal Halide Perovskite Nano/Microwires

Metal Halide Perovskite Nano/MicrowiresMetal halide perovskite nano/microwires (NMWs) are expected as the building blocks for nextgeneration optoelectronic devices. Their well-defined crystal structure, fewer grain boundaries, lower defect concentration, longer photocarrier lifetime, and confined carrier transport endure them a great potential in further optoelectronic applications. More details are presented in article number 2100165 by Meng Wang, Fengren Cao, and Liang Li.

Effect of growth parameters on defect structure and optical properties of ultrathin SnO2 films

Tin oxide films with thicknesses in the range from 5 to 110 nm have been deposited by reactive dc magnetron sputtering of Sn in Ar + O plasma at a low working pressure of 1.0× 10 −3 Torr on glass substrates at different temperatures (150–400 °C). The effect of deposition time, substrate temperature, and oxygen partial pressure on surface morphology , crystallographic structure, optical properties, and photoluminescence characteristics of SnO 2 films has been studied and correlated with their defect structure . The structural transformation from nanocrystalline to polycrystalline of thicker films >40 nm and films were grown at higher temperature is explained based on adatom mobility and uniform substrate coverage. Based on photoluminescence characteristics and transmittance spectra, the 20 nm thick film exhibits the least defect structure and best electronic and optical behaviors. • Ultrathin SnO 2 films (5–20 nm) are successfully grown by DC reactive sputtering. • Effect of scaling down film thickness (down to 5 nm) on physical properties. • Correlation between defect structure and optical properties. • Thinner films are much smoother than the thicker films. • Low structural defect concentration found in 10–40 nm films.

Damage in InGaN/GaN bilayers upon Xe and Pb swift heavy ion irradiation.

350 nm and 550 nm thick InGaN/GaN bilayers were irradiated with different energies (from ∼82 to ∼38 MeV) of xenon (129Xe) ions and different fluences of 1.2 GeV lead (208Pb) ions, respectively. The radiation effects of the swift heavy ions' (SHIs) bombardment were investigated using Rutherford Backscattering Spectrometry in Channeling mode (RBS/C), X-Ray Diffraction (XRD), and micro-Raman spectroscopy. To assess damage profiles, the RBS/C analysis was followed by Monte Carlo simulations using the McChasy code, revealing that InGaN is more susceptible to irradiation damage than GaN. Moreover, the simulations suggest that both randomly displaced atoms (possibly due to partial amorphization) and dislocation loops are formed. The elastic response to radiation was estimated by measuring the expansion of the c-lattice parameter. XRD revealed the presence of strain even in low fluence samples where only a small fraction of the sample volume suffered direct SHI impacts. Micro-Raman suggests that for low defect concentrations, it is dominantly biaxial, while for high defect concentrations, the simultaneous increase of hydrostatic and biaxial occurs. As a driving force of the lattice expansion, we point out the Poisson effect resulting from the pressure exerted by the SHI tracks on the surrounding undamaged crystal structure.

Piezoelectricity in nominally centrosymmetric phases

Compound phases often display properties that are symmetry forbidden relative to their nominal, average crystallographic symmetry, even if extrinsic reasons (defects, strain, or imperfections) are not apparent. Specifically, breaking the macroscopic inversion symmetry of a centrosymmetric phase can dominate or significantly change its observed properties while the detailed mechanisms and magnitudes of the deviations of symmetry breaking are often obscure. Here, we choose piezoelectricity as a tool to investigate macroscopic inversion-symmetry breaking in nominally centrosymmetric materials as a prominent example and measure resonant piezoelectric spectroscopy (RPS) and Resonant Ultrasound Spectroscopy (RUS) in 15 compounds, 18 samples, and 21 different phases, including unpoled ferroelectrics, paraelectrics, relaxors, ferroelastics, incipient ferroelectrics, and isotropic materials with low defect concentrations, i.e., NaCl, fused silica, and ${\mathrm{CaF}}_{2}$. We exclude the flexoelectric effect as a source of the observed piezoelectricity yet observe piezoelectricity in all nominally cubic phases of these samples. By scaling the RPS intensities with those of RUS, we calibrate the effective piezoelectric coefficients using single-crystal quartz as standard. Using this scaling we determine the effective piezoelectric modulus in nominally nonpiezoelectric phases, finding that the ``symmetry-forbidden'' piezoelectric effect ranges from $\ensuremath{\sim}1$ to ${10}^{\ensuremath{-}5}$ pm/V ($\ensuremath{\sim}0.5%$ to $\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}%$ of the piezoelectric coefficient of poled ferroelectric lead zirconate titanate). The values for the unpoled ferroelectric phase are only slightly higher than those in the paraelectric phase. The extremely low coefficients are well below the detection limit of conventional piezoelectric measurements and demonstrate RPS as a convenient and ultrahighly sensitive method to measure piezoelectricity. We suggest that symmetry-breaking piezoelectricity in nominally centrosymmetric materials and disordered, unpoled ferroelectrics is a common phenomenon.

Defect engineering technique for the fabrication of LaCoO3 perovskite catalyst via urea treatment for total oxidation of propane

The low defect content and poor oxygen mobility of perovskite catalysts limit its application in VOC elimination. Herein, we report a strategy involving defect engineering route following an easy urea treatment method to enhance the propane oxidation performance of perovskite catalysts. The constructed LaCoO3-D43 exhibits superior catalytic activity (T90 = 309.3 °C), the T90 value is 150 °C lower than that of LaCoO3, and excellent thermal stability against CO2 and H2O. Experimental results revealed that the urea pyrolysis resulted in the generation of La and O defects and rich surface-active Co species in high-valence states, increasing the utilization of Co active sites. DFT calculations show that the exposed Co surface is conducive to the adsorption and dissociation of oxygen and propane. This work provides a defect engineering strategy to effectively activate perovskite catalysts performance, and can be generalized for the fabrication of other types of perovskite catalysts.

Correlating Reaction Dynamics and Size Change during the Photomechanical Transformation of 9-Methylanthracene Single Crystals.

Photomechanical molecular crystals that expand under illumination could potentially be used as photon-powered actuators. In this study, we find that the use of high-quality single crystals of 9-methylanthracene (9MA) leads to more homogeneous reaction kinetics than that previously seen for polycrystalline samples, presumably due to a lower concentration of defects. Furthermore, simultaneous observation of absorbance and shape changes in single crystals revealed that the dimensional change mirrors the reaction progress, resulting in a smooth expansion of 7 % along the c-axis that is linearly correlated with reaction progress. The same expansion dynamics are highly reproducible across different single crystal samples. Organic single crystals exhibit well-defined linear expansions during 100 % photoconversion, suggesting that this class of solid-state phase change material could be used for actuation.