Unlocking the Potential of Porous Bi2Te3-Based Thermoelectrics Using Precise Interface Engineering through Atomic Layer Deposition.

Porous thermoelectric materials offer exciting prospects for improving the thermoelectric performance by significantly reducing the thermal conductivity. Nevertheless, porous structures are affected by issues, including restricted enhancements in performance attributed to decreased electronic conductivity and degraded mechanical strength. This study introduces an innovative strategy for overcoming these challenges using porous Bi0.4Sb1.6Te3 (BST) by combining porous structuring and interface engineering via atomic layer deposition (ALD). Porous BST powder was produced by selectively dissolving KCl in a milled mixture of BST and KCl; the interfaces were engineered by coating ZnO films through ALD. This novel architecture remarkably reduced the thermal conductivity owing to the presence of several nanopores and ZnO/BST heterointerfaces, promoting efficient phonon scattering. Additionally, the ZnO coating mitigated the high resistivity associated with the porous structure, resulting in an improved power factor. Consequently, the ZnO-coated porous BST demonstrated a remarkable enhancement in thermoelectric efficiency, with a maximum zT of approximately 1.53 in the temperature range of 333-353 K, and a zT of 1.44 at 298 K. Furthermore, this approach plays a significant role in enhancing the mechanical strength, effectively mitigating a critical limitation of porous structures. These findings open new avenues for the development of advanced porous thermoelectric materials and highlight their potential for precise interface engineering through the ALD.

Nucleation and Layer Closure Behavior of Iridium Films Grown Using Atomic Layer Deposition.

Understanding the initial growth process during atomic layer deposition (ALD) is essential for various applications employing ultrathin films. This study investigated the initial growth of ALD Ir films using tricarbonyl-(1,2,3-η)-1,2,3-tri(tert-butyl)-cyclopropenyl-iridium and O2. Isolated Ir nanoparticles were formed on the oxide surfaces during the initial growth stage, and their density and size were significantly influenced by the growth temperature and substrate surface, which strongly affected the precursor adsorption and surface diffusion of the adatoms. Higher-density and smaller nanoparticles were formed at high temperatures and on the Al2O3 surface, forming a continuous Ir film with a smaller thickness, resulting in a very smooth surface. These findings suggest that the initial growth behavior of the Ir films affects their surface roughness and continuity and that a comprehensive understanding of this behavior is necessary for the formation of continuous ultrathin metal films.

Epitaxial Growth of ß-Ga2O3 Thin Films on Si with YSZ Buffer Layer.

We report the epitaxial growth of (2̅01)-oriented ß-Ga2O3 thin films on a (001) Si substrate using the pulsed laser deposition technique employing epitaxial yttria-stabilized zirconia (YSZ) buffer layers. Epitaxial ß-Ga2O3 thin films possess a biaxial compressive strain on YSZ single-crystal substrates while they exhibit a biaxial tensile strain on YSZ-buffered Si substrates. Post-annealing improves the crystalline quality of ß-Ga2O3 thin films. High-resolution X-ray diffraction analyses reveal that the epitaxial (2̅01) ß-Ga2O3 thin films on Si have eight in-plane domain variants to accommodate the large difference in the crystal structure between monoclinic ß-Ga2O3 and cubic YSZ. The results provide a pathway to integrate epitaxial ß-Ga2O3 thin films on a Si gold standard substrate, which will expand the application scope beyond high-power electronics.

Structural, diffuse reflectance and luminescence study of t-Mg2B2O5 nanostructures.

We report here the structural, reflectance, photoluminescence and thermoluminescence study of t-Mg2B2O5 nanostructures synthesized using optimized combustion method relatively at much lower temperature. The rietveld refinement of X-ray diffraction data confirms single-phase triclinic crystal structure of Mg2B2O5 nanoparticles. The direct band gap determined using diffuse reflectance spectra (DRS) was 5.23 eV, which is contrary to earlier reports quoting Mg2B2O5 as indirect band gap material. To elucidate the nature of band gap in Mg2B2O5, we performed first principle calculations based on full potential linearized augmented plane-wave (FPLAPW) method, predicting the direct band gap of 5.10 eV in t-Mg2B2O5 which is in good agreement with our experimental results. The t-Mg2B2O5 nanoparticles were found to exhibit yellow-reddish photoluminescence peaking at 588 nm, attributed to various defects states. The combustion synthesized Mg2B2O5 nanocrystals exhibited ultraviolet (254 nm) responsive thermoluminescence (TL). TL glow curve of Mg2B2O5 comprises of one dominant peak around 417-428 K and less intense shoulder around 573-589 K which arouse possibility of various trapping sites or defects present in the sample. The TL analysis using general order Kitti's equations was performed to estimate the activation energies of trapping states. Owing to already well-known mechanical and thermal properties, the direct wide band gap nature and UV responsive thermoluminescence of combustion synthesized t-Mg2B2O5 nanostructures can pave way for its use in luminescence-based applications and UV dosimetry. As an additional application of Mg2B2O5, anti-biofilms activity of Mg2B2O5 nanoparticles using pseudomonas aeruginosa bacterial cells was also performed which revealed 91 ± 2.7% inhibition of biofilms formed by P. aeruginosa, respectively, at 100 µg/ml after 24 h of treatment.

Color modulation by selective excitation activated defects and complex cation distribution in Zn1-xMgxAl2O4 nanocrystals.

Complex cation distribution in spinel solid solution, fosters defect generation and permutates the optical properties. To scrutinize the effect on structural properties, viz. the cation distribution and defect states upon substitution of Zn with Mg; and to tune the emission properties, Zn1-xMgxAl2O4 (0.01 ≤ x ≤ 0.30) nanocrystals are synthesized. The nanocrystals show increased inversion and generation of multiple defects, namely zinc vacancies, zinc interstitials, oxygen vacancies and antisite defects with increasing Mg content, which thereby impacts the optical band gap. Pentahedral coordination in addition to tetra- and octahedral coordination of Al has been observed, which infers the presence of oxygen vacancies and dangling bonds. Moire fringes formation has intimated the presence of two or more crystal lattices with higher Mg substitution. Band-to-band and defect-assisted photoluminescence shows the role of multiple defects, especially defect clusters, in deciphering the properties of the resulting crystals. Color change from bluish-white to pink has been achieved depending upon the excitation wavelength and emission mechanism, as proposed through a band model schematic. The presented study may be beneficial for designing the Zn1-xMgxAl2O4 nanocrystals with optimized emission properties.

Defect states and kinetic parameter analysis of ZnAl2O4 nanocrystals by X-ray photoelectron spectroscopy and thermoluminescence.

Defect states in ZnAl2O4 have a significant role in its applicability as a luminescent material. To understand the nature and distribution of defects in its crystal lattice, thermoluminescence (TL) study has been carried out. Excellent TL response is observed from γ- and ultraviolet-irradiated samples at different doses and exposure durations, respectively. Different type of fuels employed in combustion synthesis show a remarkable effect on the trap distribution and hence luminescence properties. Shallow and deep traps are observed in crystals attributed to O- vacancies and F+ centers. The mechanism of trapping, retrapping and recombination have been depicted through schematic band model diagram. X-ray photoelectron spectroscopy indicated the presence of various types of defects specifically AlZn antisite defect, oxygen and zinc vacancies which are further upheld by photoluminescence and Raman spectroscopy. All results when summed up, predict ZnAl2O4 to be a quality material for dosimetry.

Wafer-Scale, Conformal, and Low-Temperature Synthesis of Layered Tin Disulfides for Emerging Nonplanar and Flexible Electronics.

Two-dimensional (2D) metal dichalcogenides have drawn considerable interest because they offer possibilities for the implementation of emerging electronics. The emerging electronics are moving toward two major directions: vertical expansion of device space and flexibility. However, the development of a synthesis method for 2D metal dichalcogenides that meets all the requirements remains a significant challenge. Here, we propose a promising method for wafer-scale, conformal, and low-temperature (≤240 °C) synthesis of single-phase SnS2 via the atomic layer deposition technique. There is a trade-off relationship between the crystallinity and orientation preference of SnS2, which is efficiently eliminated by the two-step growth occurring at different temperatures. Consequently, the van der Waals layers of the highly crystalline SnS2 are parallel to the substrate. Thin-film transistors (TFTs) comprising the SnS2 layer show reasonable electrical performances (field-effect mobility: ∼0.8 cm2 V-1 s-1 and on/off ratio: ∼106), which are comparable to that of a single-crystal SnS2 flake. Moreover, we demonstrate nonplanar and flexible TFTs to identify the feasibility of the implementation of future electronics. Both the diagonal-structured TFT and flexible TFT fabricated without a transfer process show electrical performances comparable to those of rigid and planar TFTs. Particularly, the flexible TFT does not exhibit substantial degradation even after 2000 bending cycles. Our work would provide decisive opportunities for the implementation of future electronic devices utilizing 2D metal chalcogenides.

Copper-Halide Polymer Nanowires as Versatile Supports for Single-Atom Catalysts.

Single-atom catalysts are heterogeneous catalysts with atomistically dispersed atoms acting as a catalytically active center, and have recently attracted much attention owing to the minimal use of noble metals. However, a scalable and inexpensive support that can stably anchor isolated atoms remains a challenge due to high surface energy. Here, copper-halide polymer nanowires with sub-nanometer pores are proposed as a versatile support for single-atom catalysts. The synthesis of the nanowires is straightforward and completed in a few minutes. Well-defined sub-nanometer pores and a large free volume of the nanowires are advantageous over any other support material. The nanowires can anchor various atomistically dispersed metal atoms into the sub-nanometer pores up to ≈3 at% via a simple solution process, and this value is at least twice as big as previously reported data. The hydrogen evolution reaction activity of -18.0 A mgPt -1 at -0.2 V overpotential shows its potential for single-atom catalysts support.

Mechanistic insights into the interaction between energetic oxygen ions and nanosized ZnFe2O4: XAS-XMCD investigations.

The interactions of energetic ions with multi-cation compounds and their consequences in terms of changes in the local electronic structure, which may facilitate intriguing hybridization between O 2p and metal d orbitals and magnetic ordering, are the subject of debate and require a deep understanding of energy transfer processes and magnetic exchange mechanisms. In this study, nanocrystals of ZnFe2O4 were exposed to O7+ ions with an energy of 100 MeV to understand, qualitatively and quantitatively, the metal-ligand field interactions, cation migration and magnetic exchange interactions by employing X-ray absorption fine structure measurements and X-ray magnetic circular dichroism to get deeper mechanistic insights. Nanosized zinc ferrite nanoparticles (NPs) with a size of ∼16 nm synthesized in the cubic spinel phase exhibited deterioration of the crystalline phase when 100 MeV O7+ ions passed through them. However, the size of these NPs remained almost the same. The behaviour of crystal deterioration is associated with the confinement of heat in this interaction. The energy confined inside the nanoparticles promotes cation redistribution as well as the modification of the local electronic structure. Prior to this interaction, almost 42% of Zn2+ ions occupied AO4 tetrahedra; however, this value increased to 63% after the interaction. An inverse effect was observed for metal ion occupancies in BO6 octahedra. The L-edge spectra of Fe and Zn reveal that the spin and valence states of the metal ions were not affected by this interaction. This effect is also supported by K-edge measurements for Fe and Zn. The t2g/eg intensity ratio in the O K-edge spectra decreased after this interaction, which is associated with detachment of Zn2+ ions from the lattice. The extent of hybridization, as estimated from the ratio of the post-edge to the pre-edge region of the O K-edge spectra, decreased after this interaction. The metal-oxygen and metal-metal bond lengths were modified as a result of this interaction, as determined from extended X-ray absorption fine structure measurements. These measurements further support the observation of cation migration from AO4 tetrahedra to AO6 octahedra and vice versa. The Fe L-edge magnetic circular dichroism spectra indicate that Fe3+ ions occupying sites in AO4 tetrahedra and BO6 octahedra exhibited antiferromagnetic-like ordering prior to this interaction. The NPs that interacted with energetic O ions displayed a different kind of magnetic ordering.

Electronic structure and luminescence assets in white-light emitting Ca2V2O7, Sr2V2O7 and Ba2V2O7 pyro-vanadates: X-ray absorption spectroscopy investigations.

Ca2V2O7, Sr2V2O7, and Ba2V2O7 pyro-vanadates were synthesized using a modified chemical precipitation method and annealing. Detailed crystal structure, morphology, electronic structure and optical properties were investigated by XRD, UV-visible absorption, FTIR, Raman, FE-SEM, XANES, and photoluminescence spectroscopy. Rietveld refinement on the XRD patterns of Ca2V2O7, Sr2V2O7, and Ba2V2O7 has confirmed the triclinic structure (space group; P1̄(2)) of the pyro-vanadates. The band gap energy of Ca2V2O7, Sr2V2O7, and Ba2V2O7 is estimated to be ∼2.67 eV, ∼2.97 eV and ∼3.09 eV, respectively. XANES spectra at the Ca L-edge, Sr K-edge and Ba L-edge have confirmed the Ca2+, Sr2+ and Ba2+ ions in the Ca2V2O7, Sr2V2O7 and Ba2V2O7 compounds, respectively. V K-edge XANES spectra have strengthened the presence of sub-pentavalent V ions in all of the pyro-vanadates. O K-edge XANES spectra of Ca2V2O7, Sr2V2O7 and Ba2V2O7 have shown dominating tetrahedral symmetry of the V ions which is also corroborated with the V K-edge XANES. Broad-band emission spectra, ranging from 400 nm to 700 nm, have been observed from the charge-transfer transitions of VO4 tetrahedra. 3T1 → 1A1 and 3T2 → 1A1 transitions, from the VO4 tetrahedra, have provided two distinct emission peaks from the compounds which exhibit a red-shift with the decreasing ionic-radii of alkali-earth metal ions. The mixed compounds, with equal weight proportions, have shown remarkable emission characteristics towards the realization of rare-earth element free white-light-emitting devices.

Atomic-scale investigation of MgO growth on fused quartz using angle-dependent NEXAFS measurements.

The phenomena related to thin film growth have always been interesting to the scientific community. Experiments related to these phenomena not only provide an understanding but also suggest a path for the controlled growth of these films. For the present work, MgO thin film growth on fused quartz was investigated using angle-dependent near-edge X-ray absorption fine structure (NEXAFS) measurements. To understand the growth of MgO, sputtering was allowed for 5, 10, 25, 36, 49, 81, 144, 256, and 400 min in a vacuum better than 5.0 × 10-7 torr. NEXAFS measurements revealed the evolution of MgO at the surface of fused quartz for sputtering durations of 144, 256, and 400 min. Below these sputtering durations, no MgO was observed. NEXAFS measurements further envisaged a systematic improvement of Mg2+ ion coordination in the MgO lattice with the sputtering duration. The onset of non-interacting molecular oxygen on the surface of the sputtered species on fused quartz was also observed for sputtering duration up to 81 min. Angle-dependent measurements exhibited the onset of an anisotropic nature of the formed chemical bonds with sputtering, which dominated for higher sputtering duration. X-ray diffraction (XRD) studies carried out for sputtering durations of 144, 256, and 400 min exhibited the presence of the rocksalt phase of MgO. Annealing at 700 °C led to the dominant local electronic structure and improved the crystallinity of MgO. Rutherford backscattering spectrometry (RBS) and cross-sectional scanning electron microscopy (SEM) revealed a layer of almost 80 nm was obtained for a sputtering duration of 400 min. Thus, these angle-dependent NEXAFS measurements along with XRD, RBS, and SEM analyses were able to give a complete account for the growth of the thin films. Moreover, information specific to the coordination of the ions, which is important in case of ultrathin films, could be obtained successfully using this technique.

XANES, EXAFS and photoluminescence investigations on the amorphous Eu:HfO2.

We report detailed investigations on the local electronic/atomic structure and photoluminescence properties of chemically synthesized Eu:HfO2 powders. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) measurements were performed to analyze the crystal structure, local atomic/electronic structure and luminescence properties of the samples. No crystalline phases were detected with Cu Kα (λ=1.5418Å) based XRD; however, local monoclinic structure was confirmed by the Hf L-edge XANES and EXAFS. O K-edge XANES spectral features could be deconvoluted with doublets and triplets in eg and t2g orbitals, respectively, which ascribed to the local monoclinic structure for all of the samples. Eu M5,4-edge XANES confirmed the pre-dominancy of Eu3+ ions in the HfO2 samples with a fractional amount of Eu2+ ions. PL spectra revealed the electric dipole allowed (5D0-7F0,2,4) emission properties of Eu:HfO2 samples. The orange-red emission is ascribed to the Eu interstitial/surface segregation induced defects.

Free-electron creation at the 60° twin boundary in Bi2Te3.

Interfaces, such as grain boundaries in a solid material, are excellent regions to explore novel properties that emerge as the result of local symmetry-breaking. For instance, at the interface of a layered-chalcogenide material, the potential reconfiguration of the atoms at the boundaries can lead to a significant modification of the electronic properties because of their complex atomic bonding structure. Here, we report the experimental observation of an electron source at 60° twin boundaries in Bi2Te3, a representative layered-chalcogenide material. First-principles calculations reveal that the modification of the interatomic distance at the 60° twin boundary to accommodate structural misfits can alter the electronic structure of Bi2Te3. The change in the electronic structure generates occupied states within the original bandgap in a favourable condition to create carriers and enlarges the density-of-states near the conduction band minimum. The present work provides insight into the various transport behaviours of thermoelectrics and topological insulators.

Modern scientific evidence pertaining to criminal investigations in the Chosun dynasty era (1392-1897 A.C.E.) in Korea.

A guidebook detailing the process of forensic investigation was written in 1440 A.C.E. It outlines the fundamentals and details of each element of criminal investigation during the era of the Chosun dynasty in Korea. Because this old guidebook was written in terms of personal experience rather than on scientific basis, it includes many fallacies from the perspective of modern forensic science. However, the book describes methods to form a scientific basis for the experiments performed. We demonstrate the modern scientific basis for ancient methods to monitor trace amounts of blood and detect lethal arsenic poisoning from a postmortem examination as described in this old forensic guidebook. Traces of blood and arsenic poisoning were detected according to the respective color changes of brownish red, due to the reaction of ferric ions in blood with acetic ions of vinegar, and dark blue, due to the reaction of silver with arsenic sulfide.

(E)-9-(4-Fluoro-styr-yl)-3,3,6,6-tetra-methyl-3,4,5,6,7,9-hexa-hydro-2H-xanthene-1,8-dione.

In the title compound, C25H27FO3, each of the cyclo-hexenone rings adopts a half-chair conformation, whereas the six-membered pyran ring adopts a flattened boat conformation, with the O and methine C atoms deviating by 0.0769 (15) and 0.196 (2) Å, respectively, from the plane of the other four atoms (r.m.s. deviation = 0.004 Å). The C=C double bond adopts an E conformation. The dihedral angle between the benzene and pyran (all atoms) rings is 89.94 (10)°. In the crystal, weak C-H⋯O hydrogen bonds link the mol-ecules into chains running parallel to the b axis.