Single Crystalline Research Articles

Multi‐Stage Optimization of Pore Size and Shape in Pore‐Space‐Partitioned Metal–Organic Frameworks for Highly Selective and Sensitive Benzene Capture

AbstractCompared to exploratory development of new structure types, pushing the limits of isoreticular synthesis on a high‐performance MOF platform may have higher probability of achieving targeted properties. Multi‐modular MOF platforms could offer even more opportunities by expanding the scope of isoreticular chemistry. However, navigating isoreticular chemistry towards best properties on a multi‐modular platform is challenging due to multiple interconnected pathways. Here on the multi‐modular pacs (partitioned acs) platform, we demonstrate accessibility to a new regime of pore geometry using two independently adjustable modules (framework‐forming module 1 and pore‐partitioning module 2). A series of new pacs materials have been made. Benzene/cyclohexane selectivity is tuned, progressively, from 4.5 to 15.6 to 195.4 and to 482.5 by pushing the boundary of the pacs platform towards the smallest modules known so far. The exceptional stability of these materials in retaining both porosity and single crystallinity enables single‐crystal diffraction studies of different crystal forms (as‐synthesized, activated, guest‐loaded) that help reveal the mechanistic aspects of adsorption in pacs materials.

Multi-Stage Optimization of Pore Size and Shape in Pore-Space-Partitioned Metal-Organic Frameworks for Highly Selective and Sensitive Benzene Capture.

Compared to exploratory development of new structure types, pushing the limits of isoreticular synthesis on a high-performance MOF platform may have higher probability of achieving targeted properties. Multi-modular MOF platforms could offer even more opportunities by expanding the scope of isoreticular chemistry. However, navigating isoreticular chemistry towards best properties on a multi-modular platform is challenging due to multiple interconnected pathways. Here on the multi-modular pacs (partitioned acs) platform, we demonstrate accessibility to a new regime of pore geometry using two independently adjustable modules (framework-forming module 1 and pore-partitioning module 2). A series of new pacs materials have been made. Benzene/cyclohexane selectivity is tuned, progressively, from 4.5 to 15.6 to 195.4 and to 482.5 by pushing the boundary of the pacs platform towards the smallest modules known so far. The exceptional stability of these materials in retaining both porosity and single crystallinity enables single-crystal diffraction studies of different crystal forms (as-synthesized, activated, guest-loaded) that help reveal the mechanistic aspects of adsorption in pacs materials.

The Effect of Heat Treatment on the Sol–Gel Preparation of TiO2/ZnO Catalysts and Their Testing in the Photodegradation of Tartrazine

This study aims to synthesize TiO2/ZnO powders and to study the effect of heat treatment on their photocatalytic ability against the Tartrazine anionic dye. The as-obtained powders with the following compositions—90TiO2/10ZnO and 10TiO2/90ZnO (mol%)—were obtained by the sol–gel technique. The prepared gels were annealed at 500 °C and 700 °C and subsequently characterized by XRD, UV–Vis, and SEM methods. The single crystalline phase of TiO2, which has been detected at up to 500 °C is anatase, while for ZnO, it is the hexagonal wurtzite structure. Further increases in the temperature (700 °C) led to the appearance of rutile in the samples. The SEM analysis demonstrated that the binary oxide materials had irregular shaped particles with a tendency to agglomerate. The UV–Vis spectra of the gels exhibited a red shift in the cut-off of the 90TiO2/10ZnO sample compared with pure Ti(IV) butoxide. Photocatalytic tests showed that the investigated samples possessed photocatalytic activity toward Tartrazine. Compared with TiO2, the prepared TiO2/ZnO photocatalysts showed superior properties in the photodegradation of a Tartrazine water solution. The target photocatalysts’ enhanced photocatalytic activities can be explained by their reduced band gap energy, improved surface physicochemical characteristics, separation of photo-induced electron–hole pairs, and lowered recombination rate. Higher photocatalytic activity was observed for powders annealed at 500 °C, with the 10TiO2/90ZnO (mol%) sample exhibiting the highest photocatalytic degradation of the used organic dye.

Triazine-Based Large-Sized Single-Crystalline Two-Dimensional Covalent Organic Framework for High-Performance Lithium-Ion Batteries.

A large-sized single crystalline 2D COFs with excellent crystallinity and stability was prepared through the traditional thermal solvent method. The electrochemical performance can be significantly enhanced using a straightforward hybrid approach that involves in situ growth of the 2D COFs on multi-walled carbon nanotubes (MWCNTs). Both the advantages of COFs and CNTs are mutually enhanced. The single-crystalline feature of the obtained COFs improves the structural integrity and brings excellent chemical and electrochemical stabilities for lithium-ion battery applications. The resultant COF-CNT core-shell hybrids greatly improved the conductivity and demonstrated excellent lithium-ion storage performance with a high capacity of 228 mAh g-1 (0.2 A g-1).

Triazine‐Based Large‐Sized Single‐Crystalline Two‐Dimensional Covalent Organic Framework for High‐Performance Lithium‐Ion Batteries

AbstractA large‐sized single crystalline 2D COFs with excellent crystallinity and stability was prepared through the traditional thermal solvent method. The electrochemical performance can be significantly enhanced using a straightforward hybrid approach that involves in situ growth of the 2D COFs on multi‐walled carbon nanotubes (MWCNTs). Both the advantages of COFs and CNTs are mutually enhanced. The single‐crystalline feature of the obtained COFs improves the structural integrity and brings excellent chemical and electrochemical stabilities for lithium‐ion battery applications. The resultant COF‐CNT core–shell hybrids greatly improved the conductivity and demonstrated excellent lithium‐ion storage performance with a high capacity of 228 mAh g−1 (0.2 A g−1).

High-performance deep-ultraviolet photodetector based on a single-crystalline ϵ-Ga2O3/Sn-doped In2O3 heterojunction

Abstract Metastable ϵ-Ga2O3, with its superior physical properties and high substrate compatibility, demonstrates considerable potential in developing heterojunction deep-ultraviolet photodetectors (DUV PDs). Herein, we fabricate a high-performance DUV PD utilizing a single crystalline ϵ-Ga2O3/ Sn-doped In2O3 (ITO) heterojunction. Under a reverse bias of 15 V, the device exhibits a high responsivity of 506 A/W, an excellent UV/visible rejection ratio of 6.74 × 104, and a fast fall time of 40 ms while maintaining good performance across a broad illumination range of 90–4100 μW cm−2. Moreover, the device can operate in a self-powered mode at zero bias, further verifying the presence of a depletion region within the ϵ-Ga2O3/ITO heterojunction. Our results demonstrate that ϵ-Ga2O3 is promising for high-quality integration on ITO and application in DUV detection, offering new strategic directions for developing high-performance Ga2O3-based DUV PDs.

Epitaxial Orientation-Controlled High Crystallinity and Ferroelectric Properties in Hf0.5Zr0.5O2 Films.

Hafnium-based binary oxides are essential for fabricating nanoscale high-density ferroelectric memory devices. However, effective strategies to control and improve their thin-film single crystallinity and metastable ferroelectricity remain elusive, hindering potential applications. Here, using NdGaO3 (NGO) substrates with four crystalline orientations, we report a systematic study of the structural characterizations and ferroelectric properties of epitaxial Hf0.5Zr0.5O2 (HZO) films, demonstrating orientation-controlled high crystallinity and enhanced ferroelectric properties. HZO films grown on NGO(001) and NGO(110) substrates exhibit relatively low crystallinity and a significant presence of the monoclinic phase. In contrast, HZO films grown on NGO(100) and NGO(010) possess high single crystallinity and a dominant ferroelectric phase. These differences are attributed to the surface symmetry of the NGO substrate, which favors the formation of 4- or 2-fold domain configurations. Moreover, the optimized HZO films exhibit a large polarization (2Pr) of ∼50 μC/cm2, enhanced fatigue behavior up to 1011 cycles, improved retention of 2Pr ∼ 40 μC/cm2 after 10 years, and characteristic polarization switching speeds in the submicrosecond range. Our results highlight the importance of modulating the single crystallinity and ferroelectric phase fraction of HfO2-based films to enhance ferroelectric properties, further revealing the potential of epitaxial symmetry engineering.

Epitaxial (AlxGa1−x−yIny)2O3 alloys lattice matched to monoclinic Ga2O3 substrates

We have epitaxially stabilized a series of monoclinic (AlxGa1−x−yIny)2O3 alloys by careful choice of molecular beam epitaxy growth conditions, which balance alloy growth with suboxide desorption. The films are pseudomorphic to (010) β-Ga2O3 substrates at thicknesses up to 150 nm with compositions ranging from (Al0.01Ga0.83In0.16)2O3 to (Al0.24Ga0.75In0.03)2O3. The absorption edge shifts from approximately 4.62–5.14 eV with coincidently increasing Al and decreasing In mole fractions. J–V measurements reveal an increase in resistivity over four orders of magnitude with a maximum value of 4.2 × 105 Ω-cm for (Al0.17Ga0.76In0.07)2O3, which has nearly identical lattice parameters (both in-plane and out-of-plane) to the underlying β-Ga2O3. Scanning transmission electron microscopy of this sample reveals a mostly uniform and single crystalline film, though we identify areas of non-uniform In incorporation and some γ-phase inclusions. This work demonstrates the feasibility of thick layers lattice-matched to β-Ga2O3 with increased bandgap compared to phase-separation limited (Al,Ga)2O3. These alloys can enable higher bandgap epitaxial dielectrics and high sheet charge density transistors by increasing the conduction band offset with respect to β-Ga2O3.

Step‐Directed Epitaxy of Unidirectional Hexagonal Boron Nitride on Vicinal Ge(110)

Insulating hexagonal boron nitride (hBN) films with precisely controlled thickness are ideal dielectric components to modulate various interfaces in electronic devices. To achieve this, high‐quality hBN with controlled atomic configurations must be able to form pristine interfaces with various materials in devices. However, previously reported large‐scale hBN films with uniform thickness either are polycrystalline or are not suitable for atomically clean assembly via mechanical exfoliation, limiting their applications in device technology. Herein, the large‐scale growth of monolayer (ML) single crystalline hBN films on Ge(110) substrates by using chemical vapor deposition is reported. Vicinal Ge(110) substrates are used for the step‐directed epitaxial growth of hBN, where Ge atomic steps act as the hBN nucleation sites, guiding the unidirectional alignments of multiple hBN domains. Density functional theory calculations reveal that the optimum hydrogen passivations on both hBN edges and Ge surfaces enable the epitaxial coupling between hBN and the Ge step edges and the single crystallinity of the final hBN films. Using epitaxially grown ML hBN films, a few hBN films with controlled stacking orders and pristine interfaces through a layer‐by‐layer assembly process are fabricated. These films function as high‐quality dielectrics to enhance carrier transport in graphene and MoS2 channels.

A Study on the Channel Holes’ Diameter Effects of High-Performance Vertical-Channel Flash Memory Cells

Abstract High-performance vertical-channel flash (HVF) memory cells were fabricated on the single crystalline Si (c-Si) sidewalls of the cylindrical deep wells in c-Si substrate. To investigate the diameter effects of the cylindrical deep wells, namely channel holes, on HVF cells, the channel holes with different diameters, ranging from 65 nm to 260 nm, were made. Memory gate stacks of SiO2/ Al2O3/HfO2/Al2O3/TiN/W were formed by ozone oxidation and then ALD with the deposition thicknesses of 1/5/7/8/2/150 nm, respectively. For the devices with their diameters equal to or greater than 150 nm, their electrical properties, such as Vt, SS, DIBL, and program/erase characteristics, are close. As expected, DIBL and SS become better as the diameter increasing due to better gate control with larger diameter. However, large changes were occurred for the devices with the diameters of 90 nm and 65 nm. A simple model based on cylinder bulk for vertical flash memory devices was presented to obtain an approximate analytical solution for depletion-width and explain our experimental data. For the devices with the diameters of 150 nm, the high On/Off current ratio of 107 and relatively large memory window of 4.5 V were achieved. However, programming/erasing efficiency were degraded with hole diameter decreasing.

Comprehensive study of epitaxial (Nd,Eu,Gd)Ba2Cu3O7−δ films grown on textured templates

We report the successful epitaxial growth and comprehensive study of structural and superconducting properties of (Nd,Eu,Gd)Ba2Cu3O7−δ films with a thickness of up to 1.2 μm prepared by on-axis pulsed laser deposition on SrTiO3 (STO) single crystals as well as on ion-beam-assisted deposition (IBAD) and rolling-assisted biaxially textured substrate (RABiTS)-based metal templates. X-ray diffraction demonstrates the epitaxial quality of the grown films on both single crystalline substrates and metal-based templates. In addition, no significant changes in surface morphology were found with increasing thickness for films on all types of substrates. On all substrates, a T c value of about 89 K was observed, however, significant inhomogeneities indicating small superconducting volume were found for all films on STO. In general, the best transport characteristics over a wide range of magnetic fields and temperatures were observed for thicker films on IBAD-MgO and RABiTS templates, respectively. The J c values at 77 K for the films on IBAD-MgO templates are comparable to YBCO films, but inferior in the low temperature region and high magnetic fields, whereas the films on RABiTS and especially on STO showed much lower J c over the entire temperature and magnetic field range. A maximum pinning force of about 7 GN·m−3 at 65 K was found for the 900 nm thick films on IBAD-MgO template. In addition, the pinning mechanism seems to depend on both temperature and type of substrate. In general, no correlation between local microstructure and transport characteristics was revealed for NEG films on both metal templates.

Enhancement of superconducting properties of grown FeTe0.65Se0.35 single crystals through air annealing

Abstract This work investigates the annealing effects on the superconducting properties of FeTe0.65Se0.35 single crystals. We examine the impact of varying annealing times on the magnetotransport, magnetic, and vortex pinning properties of the single crystals. The structural analysis shows the single crystalline growth of crystals along the c-axis. X-ray photoelectron spectroscopy and Raman spectroscopy results confirm the presence of iron oxides in the annealed samples. Temperature-dependent resistivity and magnetization measurements confirm the superconductivity in the as-grown and annealed samples. However, the as-grown sample shows a broad superconducting transition and low superconducting volume fraction, but after annealing, significant improvement in both is observed. Moreover, the self-field critical current density at 2 K is enhanced by a factor of ~ 4.4 for the optimally annealed sample compared to the as-grown sample. Experimental observations have been analyzed with the theoretical models to understand the effects of annealing on the vortex pinning mechanisms. Further, the specific heat study confirms the bulk superconductivity in the annealed sample compared to the as-grown single crystal. Overall, our study indicates that the superconducting properties vary with the annealing time, and the best results are obtained at an optimum annealing time.

Scintillation properties of multilayered composite scintillators based on the YAG:Ce and TbAG:Ce single crystalline films and GAGG:Ce crystal substrates

This work demonstrates current progress of our group in developing of two- and three-layered composite for radiation monitoring of various components of mixed ionization radiation fluxes based on the epitaxial structures of Ce3+ doped garnet compounds using the Liquid Phase Epitaxy growth technique. These scintillators contain one or two single crystalline films, dedicated for registration of low-penetrating particles, and bulk single crystal substrates used for detection of high-penetrating γ-rays. For creation of two- and three-layered epitaxial structures, the single crystalline films of Ce3+ doped Y3Al5O12, Tb3Al5O12 and Tb2GdAl5O12 garnets were used. The single crystal of mixed Gd3GaxAl5-xO12:Ce garnet with fixed Ga concentrations of x = 2.3 and 3.0 are utilized as substrates. To assess the scintillation properties of these epitaxial structures, the pulse height spectra, light yield and scintillation decay kinetics were measured under excitation by α–particles (239Pu), β-particles (90Sr + 90Y) and γ–rays (137Cs). Finally, the figure-of merit of composite scintillators under study were calculated for selection of the best epitaxial structures for simultaneous registration α– and β-particles and γ–rays.

Structural and Electrochemical Properties of Binary ZnO:Al Nanocomposites as Anode for Lithium-ion Batteries

In conventional lithium-ion batteries (LIBs), carbon compounds are commonly utilised as the anode owing to their great performance, low cost, and abundance. However, due to the limited storage capability of pure carbon materials that restrict further improvement of LIBs, zinc oxide (ZnO) has been one of the promising anode materials to be used as an alternative to strengthen the electrochemical performance of LIBs due to its high theoretical capacity of 987 mAh g-1. This study aims to synthesise ZnO:Al nanowires using the hot-tube thermal evaporation method. Three types of samples are made using this method by varying the concentration of 0 wt% (S1), 3wt% (S2), and 6 wt% (S3) of aluminium (Al) during the Al deposition process. The EDX findings indicated that the sample has a high proportion of zinc (Zn) and oxygen (O), with the S3 sample having the highest Al concentration after being deposited. The most substantial diffraction peak for XRD of all samples was found at (101), exhibiting a single crystalline hexagonal structure with optimum growth direction on the c-axis. For EIS analysis, the S3 sample has the lowest bulk resistance and maximum ionic conductivity. In conclusion, the ZnO sample with 3 wt% of Al as a dopant was selected as the optimum result to synthesise a homogenous surface of ZnO:Al with good crystallinity by using a hot-tube thermal evaporation process and giving the best conductivity in electrochemical performance.

Mutability of Nucleation Particles in Reactive Salt Hydrate Phase Change Materials.

Nucleation particles, solid phases dispersed throughout a medium to decrease the energy barrier for solidification or other reversible phase transitions, are generally selected on the basis of structural or interfacial energy considerations between the host phase and the solid phase that is crystallizing. However, the existence of chemical reactions between the nucleation particles and the host phase can obscure these underlying relationships, thereby complicating the process of selection of active nucleation particle phases. Here, we reveal the origin of nucleation activity of barium-based nucleation particles in the salt hydrate calcium chloride hexahydrate (CCH), a candidate for near room temperature thermal energy storage. We demonstrate that these compounds undergo a series of cation exchange and secondary precipitation reactions, resulting in an assemblage of solid precipitates with some degree of limited solid solution, which collectively dramatically reduce undercooling in CCH, but which obscure the identification of a single crystalline phase primarily responsible for the nucleation of crystalline CCH from the liquid. Importantly, this result illustrates a pathway to harness in situ chemical reactions to generate stable active nucleation particles in reactive phase change materials, which may not be readily synthesized by alternative methods, or which may not be active or remain stable when added in isolation.

Enhanced hydrogen generation from Glycerol: The Role of morphology and structural control in TiO2

In this work, we present the use of hydrothermal strategies to produce hierarchical TiO2 structures (nanoribbons/spherulites) with a rutile single crystalline phase. Using the hydrothermal synthesis, controlling the concentration of Cl- and Sn4+, a high-efficiency system with a rutile crystalline phase was obtained. Using glycerol as a hole-scavenger, promoting the photo(electro)reforming, the prepared photoanodes obtained photocurrent densities of 1.54 mA cm−2 (at 1.23 V vs. RHE) with 0.81 % of applied bias photon-to-current efficiency (ABPE) and photoelectrochemical hydrogen generation of 2.2 mL H2 cm-2h−1, under 1 Sun (AM 1.5G filter, 100 mW cm−2) and longtime stability.

Photoluminescence and Raman spectroscopy of Ce3+ doped Y3Al5O12 single crystalline films grown onto Y3Al5O12 and Lu3Al5O12 substrates

Raman spectroscopy, high spectral resolution luminescence, and X-ray diffraction techniques were employed to study two Ce3+ doped Y3Al5O12 single crystalline films grown by liquid phase epitaxy method onto Y3Al5O12 and Lu3Al5O12 single crystal substrates. Optical spectra were obtained with a micrometer step along the cross-sections of epitaxial structures, allowing excellent differentiation of the film, the transition layer, and the substrate of each sample. X-ray measurements demonstrate the mismatch between the lattice constants of the Y3Al5O12:Ce3+ film and its Lu3Al5O12 substrate, an effect related to different compositions. Consequently, the film grown onto Lu3Al5O12 exhibits higher residual stresses than its counterpart grown onto Y3Al5O12. This was confirmed by a mutual comparison of the Raman bands positions of the films. The luminescence spectra of both samples consist mainly of cerium 5d-4f emission, the intensity of which allows for additional study of epitaxial cross section and estimation of the size of transition layer.

Efficiency of CaZn₂(OH)₆·2H₂O and ZnO nanoparticles in photocatalytic degradation of amoxicillin after multiple cycles

The widespread use of antibiotics has increased their presence in wastewater, largely due to inadequate removal by conventional treatment methods. This highlights a critical need for effective degradation strategies to mitigate environmental and public health risks. This study reports the photocatalytic degradation of amoxicillin (AMX) using calcium zinc hydroxide dihydrate [CaZn2(OH)6·2H2O] (CZ) and zinc oxide (ZnO) nanoparticles (NPs) synthesized by different routes. X-ray diffraction results confirmed the formation of CZ NPs with an 81–95% crystalline phase, while ZnO NPs present a single crystalline phase. The photolysis of AMX under UV-A light (365 nm) was strongly pH-dependent, with degradation rates of 34.7, 5.7, and 4.2% observed at pH 3, 5, and 13, respectively. Maximum adsorption occurred at pH 3, with ZnO achieving 63–83.2% AMX removal and 23.5–47.1% in the case of CZ. The highest overall AMX removal was observed at pH 3, where adsorption dominated the photocatalytic process for both CZ and ZnO. At pH 5 and 13, degradation was primarily driven by photocatalysis in CZ materials, particularly CZ-HT and CZ-SG, while adsorption remained predominant in ZnO. Proton nuclear magnetic resonance analysis indicates benzene ring cleavage in AMX photodegraded by CZ materials. Furthermore, the residues of photodegraded AMX by CZ materials lost antimicrobial activity against Gram-positive and Gram-negative bacteria. Additionally, the reuse of NPs over four cycles maintained consistent degradation performance, highlighting their potential for repeated applications. The comparative analysis of CZ and ZnO NPs superior photocatalytic efficiency of CZ in degrading AMX. This efficiency, along with its potential for repeated use, establish CZ as a promising material for environmental applications aimed at reducing antibiotic contamination and the associated risks of resistance development.

Bismuth-based nanocomposites as potential materials for indoor air treatment

Air pollution is a worldwide health hazard; thus, improving air quality is a demanding need. Photocatalysis is a robust strategy for air treatment. The boosted activity of the photocatalytic system depends on tuning their properties for the particular application. BiOX (X: Cl, I) compounds are emergent photocatalytic systems with numerous advantages for air treatment. However, their optical properties (Eg) and fast recombination of active species (e−/h+) limit their practical applications. In this study, we remark on the properties of BiOX-GO systems for indoor air purification. We use a microwave-activated solvothermal technique to synthesize the nanomaterials (NMs). BiOX NMs exhibit hierarchical 3D structures, crystallinity, and tunable optical absorption properties. BiOX-GO composites present an enhanced visible-light photocatalytic activity due to the electron acceptor capacity of GO and modification of Eg. The indoor air disinfection capacity of the NMs ranked as follows: BiOCl-GO (96.7%) > BiOI-GO (96.2%) > BiOI (89.2%) > BiOCl (79%). The higher efficiency under visible light of BiOCl-GO can be related to the presence of oxygen vacancies, strong oxidation potential, and single crystalline phase of the materials. Due to the abundance and biocompatibility of bismuth-containing compounds, together with their enhanced visible light activity, BiOX become potent candidates for environmentally sustainable remediation technologies.

Novel compositionally disordered (Pb,Sr)WO4 single-crystalline scintillation material for X- and gamma-ray scanners

Heavy, bright, and fast single-crystalline scintillation material (Pb,Sr)WO4 was produced and characterized for the first time. Incongruently melted material was obtained by the solution-melt method under the conditions of spontaneous crystallization. It has a density of 7.3 g/cm3 and an effective charge of Zeff = 71. The scintillation kinetics are characterized by a decay constant of 490 ns, while the light yield of scintillation is measured to be 13 500 ph/MeV, both at room temperature. A fabrication of the new low-temperature melting single crystalline tungstate family’s material opens the door for better and cheaper scintillators for X-ray and γ-ray detectors, in particular for radiographic scanners and medical imaging devices.