Transition Band Research Articles

Nanoarchitectonics of Copper Sulfide Nanoplating for Improvement of Computed Tomography Efficacy of Bismuth Oxide Constructs towards Drugless Theranostics

Abstract Triple-negative breast cancer (TNBC) has emerged as one of the dreadful metastatic tumors in women due to complexity, specificity, and high recurrence, resulting in poor therapeutic outcomes and requiring real-time monitoring for improved theranostics. Despite the success as efficient radiosensitizers and computed tomography (CT)-based contrast agents, bismuth (Bi)-based composites suffer from poor colloidal stability, dose-dependent toxicity, and pharmacokinetic shortcomings, leading to poor therapeutic monitoring. In addition, several small molecule-based therapeutics, including nanoparticle-based delivery systems, suffer from several limitations of poor therapeutic delivery and acquired multidrug resistance by cancer cells, depriving the therapeutic needs. To overcome this aspect, this study demonstrates the fabrication of drug-like/drugless nanoarchitectures based on copper sulfide-nanoplated bismuth oxide (Bi2O3@CuS, shortly BC) composites for improved theranostic efficacy against TNBC. These systematically characterized BC nanocomposites exhibited pH-/near-infrared (NIR, 808 nm) light-responsive degradability towards dual modal therapies. Due to the band transition of Cu species, the designed BC composites displayed exceptional photothermal (PTT) conversion efficiency towards localized PTT effects. In addition to pH-/NIR-responsiveness, the internally overexpressed glutathione (GSH)-responsiveness facilitated the release of Cu2+ species for chemodynamic therapy (CDT) effects. To this end, the Bi3+ species in the core could be fully hydrated in the acidic tumor microenvironment (TME), resulting in GSH depletion and reducing CDT-induced reactive oxygen species (ROS) clearance, thereby ablating tumors. The acid-responsive degradability of CuS resulted in the intratumoral enrichment of BC, demonstrating remarkable CT imaging efficacy in vivo. Together, these pH-/NIR-/GSH-responsive biodegradable BC composites could realize the integrated PTT/CDT/CT theranostics against breast carcinoma.

4.8-μm CO-filled hollow-core silica fiber light source

Mid-infrared (MIR) fiber lasers are important for a wide range of applications in sensing, spectroscopy, imaging, defense, and security. Some progress has been made in the research of MIR fiber lasers based on soft glass fibers, however, the emission range of rare-earth ions and the robustness of the host materials are still a major challenge for MIR fiber lasers. The large number of gases provide a variety of optical transitions in the MIR band. When combined with recent advances in low-loss hollow-core fiber (HCF), there is a great opportunity for gas-filled fiber lasers to further extend the radiation to the MIR region. Here, a 4.8-μm CO-filled silica-based HCF laser is reported for the first time. This is enabled by an in-house manufactured broadband low-loss HCF with a measured loss of 1.81 dB/m at 4.8 μm. A maximum MIR output power of 46 mW and a tuning range of 180 nm (from 4644 to 4824 nm) are obtained by using an advanced 2.33-μm narrow-linewidth fiber laser. This demonstration represents the longest-wavelength silica-based fiber laser to date, while the absorption loss of bulk silica at 4824 nm is up to 13, 000 dB/m. Further wavelength expansion could be achieved by changing the pump absorption line and optimizing the laser structure.

Design of highly selective ultrawideband FSS based on deep learning for EMI shielding in 5G bands

Abstract In this paper, a frequency selective surface (FSS) for n41, n78, n257, n258, n260, and n261 bands electromagnetic interference (EMI) shielding is proposed using a deep learning method. The size of the FSS unit cell is 4.8 mm (0.071 λ 0 ), where λ 0 is the wavelength corresponding to the cutoff frequency of the −10 dB stopband where the n41 and n78 bands are located. This FSS exhibits three key characteristics. Firstly, it possesses ultrawideband capability, with a stopband frequency range of 23.922–40.023 GHz and a relative bandwidth reaching 50.4%. Secondly, it effectively shields against electromagnetic radiation in multiple 5 G bands, including n41, n78, n257, n258, n260, and n261. Thirdly, it demonstrates high selectivity, with a very narrow transition band of only 0.405 GHz between the passband and the stopband. To validate the designed FSS, a prototype of this structure was first fabricated for experimentation. The experimental results show that the measured S21 is highly consistent with the simulated S21. Secondly, the unit cell array of FSS is placed above the monopole antenna for co-simulation. It can be observed that after placing the FSS, the intensity of electromagnetic radiation propagating in space is significantly reduced by up to more than 90%. Therefore, the proposed FSS can be effectively applied for EMI shielding in 5 G bands.

FABRICATION AND CHARACTERIZATION OF BISMUTH TELLURIDE THIN FILMS BY THERMAL EVAPORATION TECHNIQUE

An interest in the study of the structural and optical properties of topological insulators, led to the selection of Bismuth telluride thin films. Among the topological insulators, Bismuth telluride is one of the promising materials that exhibit applications in the field of thermoelectric power generation. The films were prepared using the thermal evaporation method under vacuum conditions of [Formula: see text] mbar on glass substrates maintained at a temperature of 120∘C. The thickness of the film samples ranges from 400 Å to 1400 Å. Pure phases of Bi2Te3 with a rhombohedral structure are confirmed using X-ray Diffraction. The crystallite size was calculated using Debye–Scherrer’s formula. Structural morphology and compositions are examined using SEM and EDAX. The UV–Vis study reflects the optical behavior of the thin film samples. The absorption spectra gives the direct and allowed transition band gap of the Bi2Te3 thin film samples for various thicknesses. The band gap decreases with the increase in the thickness of the Bi2Te3 thin films, suggesting that the material has significant absorption towards the visible spectrum. The Photoluminescence (PL) emissions for Bi2Te3 thin film samples of various thicknesses are examined and analysed. Raman study reveals the presence of two active modes.

Compact vertical emitting ring interband cascade lasers for isotope-resolved CO2 sensing

We present a compact vertically emitting ring interband cascade laser (ICL) with low power consumption and the possibility for seamless integration into various CO2 sensing applications. Our devices exhibit desirable performance characteristics in battery-driven handheld devices, including room temperature (20 °C) threshold currents as low as 15 mA, small footprints, and stable single-mode emission, suitable for rapid isotope-resolved CO2 detection. Through epi-down bonding with sub-micron accuracy, we achieved robust integration of substrate-emitting ring ICLs, ensuring reliability and scalability that would be required for mass production. We present comprehensive experimental results validating the efficacy of our approach, including spectral analysis and CO2 sensing capabilities with limits of detection of 24 and 13 ppmv utilizing the 12CO2 P(60) and 13CO2 R(10) transitions in the ν3 fundamental band, respectively. The demonstrated devices hold great promise for a wide range of industrial applications, including environmental monitoring, process control, and atmospheric research, where compact low-power sensors are essential.

Repurposing trityl-substituted triphenylamine-based polyimides for gas separation membranes by blending with a fluorinated polyimide

In the attempt to develop gas separation membranes by reusing polymers with no film-forming ability but with great potential for this purpose, blending has been approached as a simple, time- and cost-effective strategy. Herein, blends of trityl-substituted triphenylamine (TTA)-based polyimides and a fluorinated polyimide (6F-PI) were involved to prepare dense membranes by drop-casting technique. The two blend components involved in variable amounts led to different film morphologies with a strong impact on most blends' properties and gas separation performance. According to optical microscopy, SEM, AFM, and FTIR investigations, the blend series containing hexafluoroisopropylidene (6F) groups in both polyimide components proved to be fully miscible at the molecular levels. When a single 6F-based component was integrated into the blend, the polymers proved to be compatible, but only partially miscible, with a two-phase structure, in which 6F-PI wrapped around the TTA-PI growth fibrillar domains. However, all blends displayed a single glass transition and FTIR bands which do not sum the ones of the polymer components, as well as a high thermal stability, close to that of 6F-PI. Regardless their miscibility level, all blends behaved as classical polyimide films, with good mechanical properties and chemical resistance to corrosive media like acid vapors or basic solutions. The blend composition and diimide structure of TTA-PI little affected the dielectric behavior, unlike the gas separation performance that strongly depended on these characteristics. The higher amount of 6F groups in the miscible blends endowed the membranes with superior permeability and selectivity, allowing in some cases to surpass the trade-off rule. Generally, the gas permeability decreased with the increase of TTA-PI content, with some exceptions. The low intermolecular interfacial interactions promoted by TTA-PI were found to be beneficial to preserve a good selectivity of gas molecules with a small kinetic diameter (He, CO2) though their permeability is lost. The gas permeability changes as a function of the blend composition and structure were mostly due to changes in the solubility coefficient and less from gas diffusion capability, at least for CO2 and N2.

Modulation of optical force by adjusting the distance between three-layer photonic crystal slabs

Optical forces induced by polarization singularities from photonic crystal slabs (PCSs) have gained widely attention in recent years. To enhance the degree of freedom in controlling far-field optical forces, we propose and design a three-layer PCSs structure that simultaneously possesses multiple optical forces with reconfigurability. By modulating the interlayer spacing, the coupling strength between the slabs is regulated, resulting in a band transition from the nodal rings to the nodal ridge, which facilitates the generation of dual polarization vortices. These dual polarization vortices induce multiple phase singularities at their boundaries, leading to multiple optical force singularities, offering the possibility of capturing and dispersing nanoparticles. Interestingly, tuning the spacing among the slabs can transform the converging force into the diverging force at the center, therefore achieving particle screening. This work not only expands the application of nodal ridges to optical force in photonic structures but also provides a feasible approach for the generation of double-ring vortex beam in the nano-optics field.

Measurement and assignment of J = 5 to 9 rotational energy levels in the 9070-9370cm-1 range of methane using optical frequency comb double-resonance spectroscopy.

We use optical-optical double-resonance spectroscopy with a continuous wave (CW) pump and a cavity-enhanced frequency comb probe to measure the energy levels of methane in the upper part of the triacontad polyad (P6) with higher rotational quantum numbers than previously assigned. A high-power CW optical parametric oscillator, tunable around 3000 cm-1, is consecutively locked to the P(7, A2), Q(7, A2), R(7, A2), and Q(6, F2) transitions in the ν3 band, and a comb covering the 5800-6100cm-1 range probes sub-Doppler ladder-type transitions from the pumped levels with J' = 6 to 8, respectively. We report 118 probe transitions in the 3ν3 ← ν3 spectral range with uncertainties down to 300kHz (1 × 10-5cm-1), reaching 84 unique final states in the 9070-9370cm-1 range with rotational quantum numbers J between 5 and 9. We assign these states using combination differences and by comparison with theoretical predictions from a new abinitio-based effective Hamiltonian and dipole moment operator. This is the first line-by-line experimental verification of theoretical predictions for these hot-band transitions, and we find a better agreement of transition wavenumbers with the new calculations compared to the TheoReTS/HITEMP and ExoMol databases. We also compare the relative intensities and find an overall good agreement with all three sets of predictions. Finally, we report the wavenumbers of 27 transitions in the 2ν3 spectral range, observed as V-type transitions from the ground state, and compare them to the new Hamiltonian, HITRAN2020, ExoMol, and the WKMLC line lists.

Updated ultraviolet fluorescence efficiencies of CS: Evidence for model discrepancies in the enhancement of NUV-derived CS abundances in comets

Observations of carbon monosulfide (CS) have a long history serving as a remote proxy for atomic sulfur, and more broadly, one of the sulfur reservoirs in cometary bodies. Recently, systematic discrepancies between NUV- and radio-derived CS abundances have been found to exceed a factor of 2–5, with NUV-derived abundances appearing enhanced for a wide array of comets. Interpretation of cometary CS emission in the ultraviolet has relied on a murky and ill-documented lineage of calculations whose accuracy can be difficult to assess. We report new fluorescence efficiencies of the CS radical, utilizing a rovibrational structure with vibrational states up to v=8 and rotational states up to N=100. The models utilize a new set of band transition rates derived from laboratory electron impact experiments. Benchmark comparisons to IUE observations of C/1979 Y1 (Bradfield) show favorable agreement with the fluorescence models. The present results affirm the accuracy of the historical record of CS abundances derived via ultraviolet CS emission in comets with IUE and HST, but do not explain the consistent enhancement of NUV-derived CS abundances relative to the radio measurements during the same apparitions. Alternative explanations of the factor of 2–5 discrepancy between NUV- and radio-derived CS abundances are discussed, as well as possible connections to sulfur reservoirs in protoplanetary disks. The model code and computed fluorescence efficiencies are made publicly available on the Zenodo service.

Substitutional Cu doping at the cation sites in Ba2YNbO6 toward improved visible-light photoactivity—A first-principles HSE06 study

Artificial photosynthesis holds immense promise for sustainable clean energy harvesting, with recent strides in material engineering with the earth abundant elements enabling efficient utilization of the visible solar spectrum for photoelectrochemical catalytic water splitting. Here, we have investigated the impact of substitutional Cu doping at all three cation sites in Ba2YNbO6 (BYN) using density functional theory calculations at the Heyd-Scuseria-Ernzerhof-06 level. One of the key findings is that the defect formation energy follows the hierarchy Nb > Ba > Y. The presence of an oxygen vacancy (OV) enhances the co-solubility of Cu substitution of Nb, particularly when placed outside the CuO6 unit, while it has a contrary effect for Y substitution. Cu replacement reduces the bandgap as Nb > Y ≫ Ba vis-à-vis pure BYN, while extending it into the visible part of the solar spectrum for Nb and Y replacement cases, albeit with OV causing a slight blue shift to them, without reducing the oxidation state of Cu due to strong charge-delocalization. Cu doping at Y and Nb sites retains the direct band transition character of BYN, a feature removed by OV. While all the bare Cu doped systems exhibit formation of a weak electron polaron, the placement of OV tends to annihilate this except for the system comprising first nearest neighbor placement of an OV relative to the Cu substitution at an Nb site. Notably, Cu doping at the Nb site significantly enhances optical activity, particularly ∼2.0–2.5 eV, resulting in promising candidates for photoelectrochemical catalysts.

First Ab Initio Line Lists for Triatomic Sulfur-Containing Molecules: S2O and S3.

We present in this paper the first room temperature rovibrational line lists for the main isotopologues of disulfur monoxide (S2O) and thiozone (S3) variationally computed from newly developed ab initio potential energy and dipole moment surfaces (PESs and DMSs). S2O and S3 are supposed to be potential candidates for astronomical detection, especially in the Venusian atmosphere where sulfur chemistry plays a major role. Contrary to other stable sulfur-containing species like SO2 or H2S, there is much less experimental data for the short-lived reactive S2O and S3 molecules. Indeed, the infrared spectra of S2O and S3 are quite complicated to analyze without consistent theoretical predictions because they contain both high J (∼100) and a lot of hot band transitions, even at T = 296 K. In this work, we have constructed PESs based on the single-reference coupled cluster approach [CCSD(T)] and including corrections due to the scalar relativistic effects, DBOC, and highly excited Slater determinants. The structure of the excited electronic states of S3 was also discussed. The nuclear-motion Eckart-Watson Hamiltonian expressed in terms of normal-mode irreducible tensor operators was used to compute the energy levels. For line intensity calculation, ab initio DMSs were computed at the CCSD(T)/aug-cc-pV5Z level of the theory. Rotation-vibration patterns in the fundamental bands of S2O and S3 have been simulated taking into account the recent Fourier-transform spectra of S2O recorded at the SOLEIL synchrotron. The present work aims at providing line intensities of S2O and S3 that are missing in the literature as well as new spectroscopic support for atmospheric applications.

Characterization of polycrystalline bulk ferroelectric ZnSnS3 synthesized by hydrothermal method for photovoltaic application

ZnSnS3, a newly theoretically predicted ferroelectric material which shows promising properties for solar cell and photovoltaic applications, was successfully grown in our laboratory by hydrothermal method. The high intensity x-ray diffraction pattern from the (211), (101̅), (200), (210), (310), (320), and (321̅) planes reveal the crystalline character of the trigonal ZnSnS3 phase. The microstructural property and elemental distribution were evaluated using SEM and TEM studies. Diffuse reflectance measurement at room temperature shows a direct bandgap of 2.62 eV along with a high energy direct transition of 3.13 eV. Two broad photoluminescence peaks at various temperatures (4–300 K) were also detected around (2.61–2.73 eV) and (3.04–3.11 eV). The emission characteristics are explained considering the shallow donor level to valence band transitions. Raman study elucidates that the synthesized ZnSnS3 possess a good number of Raman active bands. A phase transition from the ferroelectric to non-ferroelectric phase of ZnSnS3 is observed around 330 °C in DSC and dielectric measurements. The P-E measurement showed that the material is ferroelectric in nature with saturation polarization value of 21.85μC/cm2. The current-voltage characteristics showgood photovoltaic response of the fabricated Ni/ZnSnS3/Ni device in the visible range indicating its application in PV devices and photodetector.

Bond lengths and band strengths of non-equivalent C-H bonds of 2-methyl-1,3-butadiene using density functional theory, Fourier transform IR, and cavity ringdown techniques

The C-H fundamental and overtone spectra (Δυ = 1- 4) of non-equivalent C-H bonds of isoprene (CH2=C(CH3)-CH=CH2) have been obtained using a Fourier transform infrared spectrometer. The C-H vibrational overtone spectra (Δυ = 5, 6) have been recorded using phase shift (PS) and exponential decay cavity ring down (CRD) techniques, respectively at 293 K. Theoretical density functional theory (DFT) calculations of bond lengths, harmonic, and anharmonic frequencies of isoprene and partially deuterated isoprene molecules, as well as computer deconvolution of the bands are used to identify transitions corresponding to non-equivalent C-H bonds. Harmonic frequencies ωe and anharmonicities ωexe are reported for theC-H (a) in plane and C-H (b) out of plane bonds of the methyl group, the single olefinic nonterminal C-H (o), and the four olefinic terminal C-H bonds that are defined in two groups as C-H (cis) and C-H (trans). From the Δυ = 6 peak wavenumbers, correlation functions are used to calculate C-H bond lengths, isolated frequencies, and dissociation energies. Band strengths, oscillator strengths, and transition moments are obtained experimentally for all transitions. The significance of the assigned vibrational transitions and integrated intensities of isoprene for research on Earth's atmosphere and as a potential indicator of life in exoplanets with oxygen-deprived atmospheres is examined.

Numerical Analysis and Design of a High‐Frequency Surface Acoustic Wave Transducer: Influence of Piezoelectric Substrates and IDTs Configurations

ABSTRACTThe development of SAW transducers requires a series of steps ranging from material selection and geometry design to the selection of fabrication techniques for their characterization and validation process. Here, we use the finite element method (FEM) to present a methodology and a detailed analysis of the design of SAW transducers in a delay line configuration. First, we simulate single‐finger and double‐finger configurations with different geometries and designs of IDTs on two piezoelectric substrates, LiNbO in 64 YX and LiNbO 128 YX orientation, to compare the simulation results with the analytical delta model and thereby validate the simulation process, presenting Root Mean Square Error (RMSE) values ranging from 10.79 dB to 16.42 dB. With the above, we performed a comparative analysis to determine the influence of piezoelectric material and IDT configuration by studying a specific transducer design made to operate at a resonance frequency of 97.02 MHz. We compared identical designs on 128 YX and 64 YX orientations of LiNbO with single and double‐finger configurations and added the comparison with the SPUDT configuration. We observed the best results for the single‐finger IDT configuration in 128 YX LiNbO orientation compared to the other variants through its insertion loss level of −7.29 dB, its average sidelobe level of −18.63 dB, and its average transition band slope for the main lobe of 15.09 dB/MHz. The results guide new researchers or students in expanding the use of numerical tools in designing SAW transducers and SAW devices.

Investigation of structural, optical, and magnetic properties of NiFe2O4 for efficient photocatalytic degradation of organic pollutants through photo fenton reactions

Nowadays, water pollution generated from textile effluents is one of the major problems for the human race and ecology. Hence, development of sustainable strategies to lower the water pollution level has become a burning need. In this regard, the present study focuses on the preparation of nano catalyst NiFe2O4 to catalyze the chemical reactions on industrial organic dyes for their fast cleansing from water. By sol-gel auto-combustion technique, NiFe2O4 nanoparticles were synthesized and exposed to thermal process at temperatures of 400, 600, and 800 °C. Highly crystalline phase with spinel cubic structured NiFe2O4 was formed with a crystal size of 18.71 nm, which was confirmed by XRD analysis. The FTIR spectra showed two fundamental absorption bands in the range 597.80–412.59 cm−1, which are the characteristics of tetrahedral M − O and octahedral M − O bond in NiFe2O4. The surface morphology of calcined NiFe2O4 was investigated by scanning electron microscope (SEM). The nanoparticle size analyzer exhibited that the synthesized NiFe2O4 nanoparticles had an average particle size of ∼ 291.3 nm. Three stage decomposition patterns were observed for NiFe2O4, which was analyzed by a temperature programmed STA. Zeta potential analyzer showed that the synthesized sample S1 and S2 were stable in the dispersion medium. Also, NiFe2O4 exhibited optical band gap energies for direct band transitions within the visible spectrum measured to be 1.43–1.45 eV, rendering them effective as photocatalysts under sunlight. The samples showed magnetic measurements by VSM with saturation magnetization, coercivity, remnant magnetization value of 66.81 emu/g, 4.13 Oe and 12.94 emu/g, respectively. The synthesized photocatalyst, NiFe2O4, at 400 °C, significantly degraded three toxic organic pollutants—Methylene blue, Rhodamine B, and Congo Red—under visible light through ‘Photo-Fenton’ reaction mechanisms. Among the three dyes, Methylene Blue exhibited the highest degradation percentage with a rate constant of 0.0149 min−1 and followed pseudo-first-order kinetic model.

Synchrotron radiation far infrared spectrum of the astrophysically significant Ethanol (CH3CH2OH) molecule in the gauche states in the vibrational ground state and other infrared observations

In this communication, the analyses of synchrotron radiation far infrared (FIR) spectrum corresponding to the gauche- (e1ando1) states of Ethyl Alcohol are reported. Detailed assignments have been performed for b-type transitions for K values ranging from 5 to 32 and up to a maximum J value of 50. The assignments confirmed the earlier microwave (MW) and millimeter wave (MMW) spectroscopic results. The transition wavenumbers have been used to determine the term values for the gauche-states involved for all the K and J values for which observation has been made. About 2000 spectral lines have been assigned, including some accurately calculated lines that fall in the MW and MMW regions. Although transitions between the trans-species and gauche species are not allowed in Ethanol, many resonances and level crossings of energy levels cause forbidden transitions. One such system of level crossings between K=10o1 and 12ee00 has been analyzed in detail, and the interaction coefficient determined. The state mixing seems quite strong and causes forbidden transitions (ΔK=0,2,3), including transitions for trans↔gauche, have been found. In addition, many new strong transitions have been assigned, which belong to the trans-species. To extend our work to higher wave numbers to facilitate observations made by the infrared detector on board the James Webb Space Telescope (JWST), the analysis of the torsional fundamental band transitions (around 220cm-1) for o2←e0 and o2←e1 has been taken up. Some of the assignments are discussed here. Lastly, the lower-lying vibrational bands centered around 425cm-1 (CCO– bending mode) and the band at around 800cm-1 (CH3- rocking mode) have been recorded. The CCO bending band shows an unmistakable parallel character for the trans-species. The assignment work on the CCO-bending band is in progress, and the assignments for K=0andK=1(+and-) are included in this report. Accurate term values for the CCO-bending mode could be obtained. The results allowed the determination of the leading rotational constants for the trans-species in the excited vibrational state of the CCO-bending state. The complete known assigned lines of about 16,000 lines for the parent isotopomer and about 650 lines for 13 -C1 and 13−C2 (see graphical abstract) substituted Ethanol isotopomers are gathered in Appendix I and II, respectively. These atlases should be a valuable tool for further energy level analysis and astronomical detection of Ethanol in interstellar space.

Multifunctional cyanoaryl porphyrazine pigments with push-pull structure of macrocycle framing: Photophysics and possible applications

We report the experimental study of fluorescence properties of three porphyrazine derivatives, distinct in the number of fused aromatic rings in aryl groups contained in the macrocycle frame and/or presence of Pd in the macrocycle, in solutions with biological molecules and in methanol-glycerol mixtures. Spectral and lifetime fluorescence analysis has revealed that all three pigments demonstrated two fluorescence transition bands from the first S1 and the second S2 electronic excited states to the ground state S0, and thus followed the anti-Kasha’s rule. Strong dependence of the quantum yield and lifetimes in the S1 → S0 fluorescence band on solution viscosity was observed. A significant increase of the fluorescence decay times and fluorescence intensity with albumin concentration and with presence of other biological molecules in solution was observed as well. A model of the low-laying energy states of porphyrazine derivatives has been developed for elucidation of the fluorescence properties observed, that took into account several radiative and non-radiative relaxation channels in molecular excited states. In particular, the model suggests that the first electronic excited state consists of planar and bent conformations separated by a potential energy barrier and shows a typical molecular-rotor behavior as a function of solution viscosity. Potential applications of the porphyrazine pigments as viscosity sensors and fluorescence probes were considered.

(Invited) High-Density, Flip-Chip Alkali Doping of Graphene and Observation of the Lifshitz Transition

The physical properties of 2D materials can be tuned by doping to extreme charge carrier density, enabling the investigation of phenomena such as superconductivity, charge density waves, band inversion and Lifshitz transitions. For example, it is variably estimated that an electron density of 3.7 − 5.1 × 1014 cm−2 is required in order to induce a Lifshitz transition in monolayer graphene [1,2]. At this charge density, the Fermi surface passes through the hyperbolic saddle point of graphene at the M-pointin the Brillouin zone, where the Fermi surface geometry changes and the density of states diverges at a van Hove singularity. Achieving charge density sufficient to reach the Lifshitz transition has been limited to chemical doping in ultra-high vacuum (UHV) conditions and observation by angle resolved photoemission spectroscopy (ARPES). Integrating experimental methods for charge transport measurements with UHV chemical doping conditions is typically difficult. Field-effect methods including dielectric gating and ionic liquid gating are readily integrated with charge transport measurements, but achieve lower charge carrier density than UHV chemical doping methods.We report here an integrated flip-chip method to dope graphene by alkali vapour in the diffusive regime, suitable for charge transport measurements at ultra-high charge carrier density. We introduce a liquid cesium droplet source into a sealed cavity filled with inert gas (argon) to dope a monolayer graphene Hall bar on a quartz substrate by the process of cesium atom diffusion, adsorption and ionization at the graphene surface (Fig. a). Doping can be monitored by operando ac Hall measurement of longitudinal Rxx and transverse Rxy resistance of graphene (Fig. b). An optical image of a representative graphene Hall bar is shown in Fig. c (scale bar = 100 μm). The measured time dependent Rxx and Rxy during Cs exposure can be used to determine the time dependent electron density n and electron mobility μ.Upon sealing, the flip-chip assembly containing doped graphene is stable in ambient conditions, enabling sample characterization by various means, including non-resonant Raman scattering measurement through the transparent quartz window. Charge transport versus temperature and magnetic field in a variable temperature insert was performed, including Hall measurements to B = 7 T (Fig. d). By these methods, we confirm that flip-chip doping with Cs can be used to achieve charge density exceeding 4 × 1014 cm−2 . The Lifshitz transition is observed via the inversion of cyclotron effective mass, corresponding to sign inversion of the Hall coefficient RH (Fig. d). Employing a third-nearest-neighbour tight binding (3NNTB) calculation, we estimate the Fermi energies and Fermi surfaces corresponding to the charge densities observed by high field magnetotransport (Fig. e). At the Lifshitz transition, the Fermi surface transforms abruptly from that of electron pockets around the K and K' points, to a hole pocket around Γ. Further experimental observations will be discussed.In summary, our findings show that chemical doping, hitherto restricted to ultra-high vacuum conditions, can be applied in a diffusive regime at ambient pressure in an inert gas environment. We anticipate that our flip-chip doping method can be applied to a variety of 2D materials and dopant speciies beyond monolayer graphene and Cs.[1] P. Rosenzweig et al., "Overdoping graphene beyond the van Hove singularity", Physical Review Letters 125, 176403 (2020).[2] A. Zaarour et al., "Flat band and Lifshitz transition in long-range-ordered supergraphene obtained by Erbium intercalation. Physical Review Research 5, 013099 (2023). Figure 1

Pressure induced structural and electronic band transition in CsPbBr3

Cesium lead bromide (CsPbBr3) is a prominent halide perovskite with extensive optoelectronic applications. In this study, we report the pressure modulation of CsPbBr3’s crystal structure and electronic properties at room temperature up to 5 GPa. We have observed a crystal structure transition from the orthorhombic Pnma space group to a new monoclinic phase in the space group P21/c at 2.08 GPa. The structure is associated with ~8% of density jump across the transition boundary. DFT calculations have suggested that the structure transition leads to a change in the electronic band structure, and there is an emergent indirect bandgap at the Pnma-P21/c phase transition boundary at 2.08 GPa. Across the transition boundary, the electronic band gap of CsPbBr3 increased from 2.07 eV to 2.38 eV, which explains its pressure-induced color change. Our study demonstrates the importance of using in-situ crystal structure in the electronic band structure calculations in halide perovskites.

Compact microstrip lowpass filter with wide stopband and sharp transition band using radial stub resonator

This study introduces a compact microstrip lowpass filter that offers a wide stopband and a low transition band. The couple radial stubs are designed for having sharp roll-off. The filter has a −3 dB cut off frequency of 1.6 GHz, with a transition band ranging from 1.6 to 1.7 GHz with attenuation levels of −3 dB and −20 dB, respectively. To ensure a wide stopband, the filter utilizes bended transmission lines with stepped impedance suppressing cells, resulting in a stopband attenuation of 20 dB from 1.7 to 28 GHz. The insertion loss in the passband is less than 0.1 dB, and the overall size of the filter is 0.127 × 0.087 λg2.