Absorption In Region Research Articles

Hyperdoping: doping TiO2 beyond thermodynamic limits using Flash sintering

For the first time, it has been demonstrated that TiO2 optical properties can be improved by doping Fe using flash sintering. Hyperdoped TiO2 (doped with 10 at% Fe) fabricated using flash sintering, exhibited remarkable improvements in optical characteristics. Hyperdoping (exceeding the equilibrium solubility limit), induces charge trap centers or inhibits charge recombination in semiconductors. By employing XPS and UV-Vis spectroscopy, surface species alterations including oxygen vacancies, Ti4+, Ti3+, and optical characteristics were investigated. With varying holding periods, flash sintering unveiled substantial enhancements in optical absorbance and absorption regions by generating Ti3+ and oxygen vacancies. Notably, a 10-second hold time during flash sintering displayed the highest redshift among the investigated samples, indicating superior optical improvement. Oxygen vacancies and Ti3+ increased with decreased holding time during flash, suggesting the influence of flash sintering parameters on forming a metastable phase, signifying the pivotal role of flash sintering's time parameter in modulating material properties.

Effect of Gamma Irradiation (Cesium-137) on the Properties of Chemical Functional Groups from Collagen Extraction of Snakehead Fish Scales (Channa striata)

This study aims to determine the absorption spectrum of the functional groups of snakehead fish scale collagen before irradiation and the effect of the dose of Cesium-137 irradiation on the functional groups in snakehead fish scale collagen. The extraction method used is acid extraction. Measurement of the absorption spectrum of collagen samples from snakehead fish scales using an FTIR spectrophotometer. Samples were irradiated using doses of 10 mGy, 30 mGy and 50 mGy. The results of the functional group values before irradiation produce amide A, amide I, amide II and amide III which fill the absorption area of the functional group. The results of the functional group values produced after irradiation for a dose of 10 mGy produced amide I, amide II and amide III which filled the absorption area. Amide A and amide B do not fill the absorption region at a dose of 10 mGy. Doses of 30 mGy and 50 mGy produced amide A, amide I, amide II and amide III which filled the absorption area. Amide B did not fill the absorption area at doses of 30 mGy and 50 mGy. Amide groups that are not detected or do not meet standard collagen functional group standards can be caused by the chemical composition of the fish scale extraction process.

Impact ionization coefficients and excess noise in Al0.55Ga0.45As0.56Sb0.44 lattice matched to InP

The avalanche multiplication and noise characteristics of Al0.55Ga0.45As0.56Sb0.44p–i–n and n–i–p structures grown lattice matched on InP have been investigated. From measurements undertaken using 530 nm illumination on several devices, the electron (α) and hole (β) impact ionization coefficients have been determined. While α only shows a relatively small increase compared to the higher Al composition alloys of AlxGa1−xAsSb, β is found to increase significantly. Although the β/α ratio is increased to ∼0.125–0.2, higher than the ∼0.003–0.02 seen in the higher-Al alloys, a relatively low excess noise factor of 2.2 was measured in the p-i-n with electron-initiated multiplication of 20. This noise performance is significantly lower than that predicted using a local-field model and comparable to some commercial silicon APDs. This avalanching material with a bandgap of ∼1.24 eV will have the advantages of a smaller band discontinuity with the absorber region and should also operate at a lower voltage.

Effect of radiation defects on grain boundary evolution under shock loading

Grain boundary (GB) failure in tungsten under shock loading after irradiation is a key factor to estimate the performance of tungsten as a plasma facing material in nuclear fusion reactors and as a target in spallation neutron sources. In this work, GB evolution after absorption of different radiation defect clusters under shock loading has been investigated at atomic scale through non-equilibrium molecular dynamics (NEMD) method. Different to the cases without radiation defects, after absorption of interstitial dislocation loops and voids, two mechanisms have been identified for the decrease of critical shock velocity (vc) and the related GB failure. The direct void growth accompanied by appearance of disordered structure around void, from the remaining vacancy cluster which could not be annihilated by compressive stress wave, is the 1st mechanism. In the 2nd mechanism, activation of slip systems, dislocation formation, motion and multiplication, void nucleation and growth dominate the failure process. The higher potential energy and local stress concentration around a defect absorption region in GB are recognized for atomic motion deviations from shock loading direction, resulting in formation of disordered structure, activation of slip system and dislocation multiplication with lower vc under coupling effects of radiation damage and shock loading. These results indicate that under a high dose of radiation damage, GB failure induced by shock loading should be considered seriously in order to estimate the lifetime of tungsten-based plasma facing materials and spallation target materials.

A Full‐Scale Analysis of Absorption Edges in Dye‐Doped Nonlinear Optical Polymers

AbstractA full‐scale analysis of the absorption edges by modified Tauc‐Lorentz models is essential in determining the optical bandgap and Urbach energy of semiconductors, transparent conductors, ionic compounds, and dielectric materials. This technique has not yet been applied to analyzing organic nonlinear optical (NLO) materials. This problem is tackled by preparing high‐quality films of guest–host NLO polymers with a wide thickness range from sub‐micron to 200 microns, allowing accurate measurement of full‐spectral absorption coefficients of NLO materials over four orders of magnitude by the UV‐VIS‐NIR spectroscopy. The Tauc model and a new Monolog–Lorentz model are used to study the optical absorption edge of guest‐host NLO polymers containing various push‐pull chromophores and the dependence of optical bandgap and Urbach edge on the structure and composition of materials is analyzed. The results reveal the critical transition of the Urbach exponential tail to a low energy tail that overlaps with vibrational overtones of materials at the telecom wavelengths. Determining the fundamental absorption region of organic NLO films in this study provides quantitative insight into the research to harness the resonance‐enhanced nonlinear coefficients of materials by operating at the wavelengths near the band edge with the control of optical loss.

CO[formula omitted] collision-induced line parameters for the [formula omitted] band of 12CH[formula omitted] measured using a hard-collision speed-dependent line shape and the relaxation matrix formalism

Ten high resolution Fourier transform spectra of the pentad region near 3.3μm of methane diluted in carbon dioxide at total pressures up to 800 hPa have been recorded at 296.5(5) K. Including a high resolution spectrum of pure methane at low pressure, these spectra have been analyzed using multi-spectrum fitting techniques. The methane lines were modeled using hard-collision speed-dependent line profiles and line mixing was included in the strongest absorption regions, considering the first order Rosenkranz approximation and the relaxation matrix formalism. CO2 broadening and shift coefficients have been measured, together with the speed dependence of broadening. Results obtained using the two line mixing models are intercompared and compared with previous work.

Biophysical features of using a recombination sensor to detect lactate dehydrogenase: sensitivity mechanisms analysis

Background. Most pathologies of the human body (in particular, malignant neoplasms, myocardial hypoxia, liver diseases, etc.) are accompanied by a violation of the integrity of cells in target tissues and the release of intracellular macromolecules into the extracellular environment. Thus, an important diagnostic and prognostic indicator is the level of activity of certain enzymes in blood serum, which are normally intracellular. One of the most promising areas of modern medical electronics and biophysics is the development and optimization of enzyme screening methods in biological fluids. In this study, we aimed to investigate the biophysical characteristics of using a recombination sensor for determining LDH activity in biological fluids. Materials and Methods. Experiments were performed on preparations of standard human blood serum. The reference determination of lactate dehydrogenase activity was carried out photometrically based on the change (decrease) in the concentration of the reduced form of the NADH coenzyme. The passage of the lactate dehydrogenase reaction was experimentally recorded by measuring the photocurrent of a silicon structure with a buried barrier under light irradiation from the region of strong absorption (λ = 532 nm). Results. The biophysical features of the device were studied. The detection of lactate dehydrogenase becomes possible due to the transfer of a hydrogen ion from nicotinamide adenine dinucleotide (NADH) to pyruvate, as a result of which lactate and NAD+ are formed. The effect is explained by the local electrostatic influence on the parameters of the recombination centers in the near-surface bending zone near the silicon surface, which leads to a change in the surface recombination rate. Conclusions. Our approach can be considered as a promising way to develop a highly sensitive method for the detection of lactate dehydrogenase. It has been experi­mentally shown that effective detection is possible in two changes at the surface ben­ding of the deep barrier silicon substrate zone.

Secondary scintillation yield from GEM electron avalanches in - and --isobutane for CYGNO — Directional Dark Matter search with an optical TPC

CYGNO is an international collaboration with the aim of operating a ▪ optical time projection chamber (TPC) for directional Dark Matter (DM) searches and solar neutrino spectroscopy, to be deployed at the Laboratori Nazionali del Gran Sasso (LNGS). A ▪/▪ (60/40) mixture is used, along with a triple Gas Electron Multiplier (GEM) cascade to amplify the ionisation signal. The scintillation produced in the electron avalanches is read out using a scientific complementary metal–oxide–semiconductor (sCMOS) camera. This solution has proven to provide very high sensitivity to interactions in the few ▪ energy range. The inclusion of a hydrogen-based gas will offer an even lighter target, resulting in a more efficient energy transfer in a DM particle collision, and consequently, a lower detection threshold. Additionally, longer track lengths of light nuclear recoils are easier to detect with a clearer direction. However, the addition of such gas will contribute to quenching the scintillation, jeopardizing the TPC performance. In this work, we demonstrate the feasibility of adding 1% to 5% isobutane to the ▪/▪ (60/40) mixture by measuring the respective absolute scintillation yield output. The overall scintillation produced in the charge avalanches is not drastically suppressed by quenching due to the isobutane addition. The presence of Penning transfer from excited He atoms to isobutane molecules increases the number of electrons in the avalanches, partially compensating for the loss of scintillation due to quenching. For the highest applied GEM voltage, the total number of photons produced in the avalanche per ▪ deposited in the absorption region presents a decrease of only a factor of about three, from 2.30(20)×104 to 8.2(4)×103▪, as the isobutane content increases from 0 to 5%. The quantification of the visible component of the scintillation shows that isobutane quenches both visible and ultraviolet (UV) photons emitted by ▪/▪.

A novel recyclable photocatalytic composite TiO2NTs@Bi25FeO40 for tetracycline mineralization

Titanium dioxide nanotubes (TiO2NTs) are prepared by anodizing Ti substrates, which is a good solution to the problem that powdered materials are more difficult to recycle. Hence, a novel recyclable TiO2NTs@Bi25FeO40 (TiO2/BFO) photocatalyst was prepared by anodic oxidation combined with hydrothermal deposition. The photocatalytic ability of TiO2NTs prepared at different factors and Bi25FeO40 compound was evaluated. The TiO2/BFO showed the optimal photocatalytic efficiency, which the removal ratio of tetracycline hydrochloride (TC-HCl) higher than that of TiO2NTs under visible-light irradiation. UV–vis diffuse reflectance spectra (DRS) analysis proved that the band gap of TiO2/BFO was narrower than that of TiO2NTs. The narrow band gap of TiO2/BFO results in a broadening of its light absorption region. Meanwhile, the combination of free radical quenching experiments and EPR measurement showed that ·O2− was the main active radical in the photocatalytic process, and the presence of Bi25FeO40 effectively promoted the generation and transfer of electrons. Mechanistic analysis showed that a unique II-type heterojunction electron transfer structure was formed between TiO2NTs and Bi25FeO40, which promoted the photogenerated electron-hole separation and improved the photocatalytic oxidation activity. The preparation of TiO2/BFO provided a new strategy for synthesizing more efficient and environmentally friendly photocatalyst.

A full wave solver integrated with a Fokker–Planck code for optimizing ion heating with ICRF waves for the ITER deuterium–tritium plasma

Efficient ion heating is crucial for future fusion devices, and the only way to heat ions directly is ion cyclotron resonance heating. Reported here is a full wave solver integrated with a Fokker–Planck code for optimizing ion heating with ion cyclotron range of frequency waves for the International Thermonuclear Experimental Reactor deuterium–tritium plasma. Both the direct absorption of minority ions and the power transfer to bulk ions via collisions are considered, while also accounting for the edge effects on ion absorption near the core. The simulation results show that the appropriate scrape-off layer density profile and parallel wave number lead to enhanced edge coupling and broaden the absorption region with moderate absorption intensity of the minority ions, which is very important for ion heating. More power from the heated ions is transferred to bulk ions than to electrons through collisions in our simulation via optimization, and reducing the total RF power results in a significant increase of the absorbed fraction of bulk ions.

Transformation of Silicate Ions into Silica under the Influence of Acid on the Structure of Serpentinite.

The process of transformation of the silicate components of the crystal lattice structure of chrysotile during its quantitative interaction with aqueous solutions containing various stoichiometrically required amounts of sulfuric acid (SRA H2SO4) calculated with respect to the magnesium content in the composition of chrysotile is investigated. It has been shown by IR spectroscopic, X-ray phase, thermal and chemical methods of investigation and analysis that, with quantitative interactions of chrysotile and sulfuric acid, first of all, the "brucite layer" of the molecular structural structure of chrysotile is exposed to acid at SRA H2SO4 = 0.1-0.3. As a result of ion exchange processes, acidic silanol (≡Si-O-H) or disilanol (=Si=(O-H)2) bonds are formed. These acid groups form one-dimensional silicate chains with transverse bridges (≡Si-O-Si≡), where the angles (Si-O-Si = 180 °C) straighten, which are recorded in the IR spectra in the region of characteristic absorption of 1220-1250 cm-1 silica. The association of the resulting acid groups into silicate chains, dimers, and trimers with transverse bridges, leads to the appearance of colloidal silica particles in the system, which cause some inhibition of the dissolution of layered magnesium hydrosilicate in sulfuric acid solutions containing H2SO4 ˃ 0.3 SRA.

Photo‐Assisted Bifunctional Cathodes with Lower Energy Gap and Broadened Light Absorbing Region for Lithium‐Ion Batteries – Extended Conjugation Through Customization

AbstractHigh‐performance optoelectronic bifunctional cathode materials may simultaneously seize and store solar energy in lithium‐ion batteries to boost their storage capacity. However, such photoactive cathodes with typical intrinsic features are generally limited for UV light applications and offer poor sunlight harvesting which results in lower energy density. Here, the assembly of two oligomers, poly(vat blue 6) (PVB6) and poly(vat blue 6 sulfide) (PVB6S) is reported, through polymerization to extend the conjugated structure of organic optoelectronic small molecules. These oligomers are effectively employed as photo‐assisted bifunctional cathodes for lithium‐ion batteries. The extended conjugated structure narrows the energy gap, promoting exciton dissociation and expanding the light absorption region. PVB6S possesses a narrow energy gap of 1.565 eV, and the discharge‐specific capacity of the battery with PVB6S is enhanced from 203 to 411 mAh g−1 under light illumination, which is approximately twice the original capacity. This demonstrates the extended conjugated structure and charge separation in a cell, which synergistically contributes to the rational design of photo‐assisted bifunctional cathode materials and complementary enhances the performance of lithium‐ion batteries.

Recent Advances in the Field of Amino Acid-Conjugated Aminoferrocenes-A Personal Perspective.

The development of turn-based inhibitors of protein-protein interactions has attracted considerable attention in medicinal chemistry. Our group has synthesized a series of peptides derived from an amino-functionalized ferrocene to investigate their potential to mimic protein turn structures. Detailed DFT and spectroscopic studies (IR, NMR, CD) have shown that, for peptides, the backbone chirality and bulkiness of the amino acid side chains determine the hydrogen-bond pattern, allowing tuning of the size of the preferred hydrogen-bonded ring in turn-folded structures. However, their biological potential is more dependent on their lipophilicity. In addition, our pioneering work on the chiroptical properties of aminoferrocene-containing peptides enables the correlation of their geometry with the sign of the CD signal in the absorption region of the ferrocene chromophore. These studies have opened up the possibility of using aminoferrocene and its derivatives as chirooptical probes for the determination of various chirality elements, such as the central chirality of amino acids and the helicity of peptide sequences.

A novel InGaN-based bidirectional wavelength converter and optical amplifier based on hot electron-induced blue light-emitting device

In this work, the functioning of the Top-Hat Hot-Electron Light Emission and Lasing in a Semiconductor Heterostructure (TH-HELLISH) structure, which is based on InGaN/GaN multiple quantum wells, is investigated to employ it as an optical amplifier and wavelength converter. The heterojunction structure is formed by placing four InGaN quantum wells in the n-type GaN region between the n- and p-type GaN layers. The device with a TH-HELLISH structure was grown on a sapphire (Al2O3) substrate by Metal-Organic Chemical Vapor Deposition (MOCVD) with an indium ratio of 0.16. The TH-HELLISH device was fabricated in Top-Hat HELLISH (THH) geometry with four independent n- and p-channels contacts to create a non-isotropic potential distribution in the heterojunction. The electro-photoluminescence (E-PL) technique was used to obtain light amplification and the converted wavelength. A 370 nm excitation light is absorbed by the TH-HELLISH device, subsequently leading to the emission at 440 ± 1 nm, which fulfills the role of a wavelength converter. It was also observed that TH-HELLISH operates as an optical amplifier with a 1.6-times increase in emission at 370 nm excitation. When the device is illuminated with a wavelength of 370 nm, it is monitored that the threshold electric field decreased from 0.25 kV/cm to 0.18 kV/cm, accompanied by a corresponding decrease in the threshold voltage from 12.5 V to 9.0 V. In addition, the TH-HELLISH device is found to be operated independently of the polarity of the applied voltage, and the absorption and emission regions of the device can be switched by changing the polarity of the applied voltage, therefore behaving as a bi-directional wavelength converter and optical amplifier.

Multicolor lignin-derived carbon quantum dots: Controllable synthesis and photocatalytic applications

The cost-effective, high-performance fabrication of multicolor carbon quantum dots (CQDs) from biomass is critical to its prospective application. Lignin, with its phenylpropane structural unit and abundant functional groups, is a reliable precursor for the formation of high-quality CQDs. Here, CQDs from renewable lignin were successfully prepared via a two-step method, and controllable preparation of CQDs to emit blue, green, yellow, and red fluorescence was achieved by adjusting the N-containing acid dopant. The investigated fluorescence mechanism revealed that the energy bandgap of the lignin-derived CQDs decreased and the emission wavelength redshifted as the graphitization degree and number of C=O surface groups increased. The light absorption region of the Bi7O9I3 photocatalysts modified with blue CQDs to red CQDs gradually broadened in the redshifted direction. In particular, compared with pure Bi7O9I3 (70.9%), the red CQDs-modified Bi7O9I3 (RCQD/BOI) can remove 94.7% of antibiotics within 60 min of light irradiation. The superior photocatalytic activity of RCQD/BOI is attributed to the established internal electric field that accelerates charge transfer and effectively separates the photogenerated e+-h+ inside Bi7O9I3. Furthermore, through radical capture, electron paramagnetic resonance (EPR) experiments validated the photocatalytic mechanism of RCQD/BOI and revealed that h+, O2− and OH are key reactants in the photocatalytic degradation process. This promising and sustainable approach for the synthesis of multicolor lignin-derived CQDs opens the avenue of high-value utilization of biomass resources, green production of CQDs nanomaterials, and efficient development of CQDs-based photocatalysts for wastewater treatment.

Ultrafast evanescently coupled waveguide MUTC-PDs with high responsivity

Novel evanescently coupled waveguide modified uni-traveling carrier photodiodes (MUTC-PDs) employing a thick multi-layer coupling waveguide are reported. To improve the optical-to-electrical (O/E) conversion efficiency, a thick multi-layer coupling waveguide with a gradually increased refractive index from the bottom layer to the absorption layer is utilized. The refractive index profile facilitates the upward transmission of incident light into the absorption region, thereby enhancing the evanescent coupling efficiency. Meanwhile, the coupling waveguide, with a total thickness of 1.75 µm, expands the mode field diameter, thereby reducing the input coupling loss. Additionally, the top layer of the coupling waveguide also serves as the drift layer. This configuration facilitates efficient light absorption within a short PD length, thus ensuring ultrawide bandwidth and high O/E conversion efficiency simultaneously. Without an additional spot size coupler or anti-reflection coating, the measured responsivity is as high as 0.38 A/W for the PD with an active area of 5 × 6 µm2. Meanwhile, an ultrawide 3-dB bandwidth of 153 GHz has been demonstrated.

Rational design by DFT calculations of new metal complexes for photodynamic therapy based on an H2O2-Responsive Ir(III) photosensitizer activatable in physiological environment

A series of complexes based on the structure of an H2O2-responsive Ir(III) phenylpyridine(ppy)-containing complex were designed. The effect of changing the conjugation in the ppy ligands as well as of replacing the Ir(III) metal centre with the isoelectronic Os(II) were evaluated by means of DFT and its time-dependent formulation. The computational exploration of the photophysical properties of all the designed complexes suggest that the character of the low-lying singlet state represent the main factor affecting the region of absorption. In particular, for some of the Ir(III)-based complexes the change of the band character from mixed MLCT/LLCT to almost exclusively LLCT is essential for red-shifting the maximum absorption wavelength together with the destabilization of HOMO thus reducing the HOMO-LUMO energy gap; similarly, the replacement of Ir(III) with Os(II) converts the character of the band to mainly MLCT. The computed spin–orbit coupling constants and the triplet states’ energy confirm that all the designed complexes could, in principle, be able to generate the cytotoxic singlet oxygen under one-photon excitation by energy transfer from the triplet state of the photosensitizer to molecular oxygen, while the production of other types of ROS is precluded, similarly to the reference complex.

Facile fabrication and tunable electronic properties of Azure A chloride/Si heterojunction for photoelectrical application

In this study, the fabrication, structural, and photoelectrical properties of AZACl on Si heterojunction (AZACl/Si HJ) were examined. The morphology of the thin film of AZACl was analyzed using SEM, while XRD studied the crystal structure. The UV spectrophotometer displayed three distinct absorption regions at 194, 260, and 605 nm due to their complex chemical structure. The electrical characteristics of the AZACl/Si HJ were investigated in dark circumstances at various temperatures. The J-V technique was used to derive the diode properties of AZACl/Si HJ. The photoelectric properties of the AZACl/Si HJ, such as photocurrent, sensitivity, and responsivity, were estimated. At - 0.5 V and light irradiance equals 100 mW/cm2, the calculated photocurrent equals 4.76 × 10−5 A/cm2, the sensitivity equals 20, and the responsivity equals 476 × 10−4. These results indicated that the fabricated AZACl/Si HJ exhibits photodiode characteristics.

Probing charge transfer of NiCo2O4/g-C3N4 photocatalyst for hydrogen production

Quantum dots/two-dimensional (0D/2D) semiconductor photocatalysts demonstrate wide solar light absorption region and high charge transfer efficiency. However, the relation between the interfacial electric field and the charge transfer during the photocatalytic hydrogen production process is still unclear. Here, we construct NiCo2O4 quantum dots (QDs) and NiCo2O4 nanoparticles (NPs) anchored with 2D g-C3N4 (CN) to form NiCo2O4-QDs/CN and NiCo2O4-NPs/CN heterojunctions. The hydrogen production rate of CN loaded with NiCo2O4 QDs is about 3 times higher than that of CN loaded with NiCo2O4 NPs. The electric field intensity at the NiCo2O4-QDs/CN interface is calculated to be about 15,600 V cm−2, about 9 times higher than that of NiCo2O4-NPs/CN, which could effectively drive the electrons of CN to flow toward NiCo2O4 QDs, promoting photocarriers separation and hence greatly improving the photocatalytic performance. This work provides a method to understand the relationship between interfacial electric field strength and photogenerated charges of heterostructure photocatalysts.

The morphology of the redshifted 21-cm signal from the Cosmic Dawn

ABSTRACT The spatial fluctuations in the tomographic maps of the redshifted 21-cm signal from the Cosmic Dawn (CD) crucially depend on the size and distribution of the regions with gas temperatures larger than the radio background temperature. In this article, we study the morphological characteristics of such emission regions and their absorption counterparts using the shape diagnostic tool surfgen2. Using simulated CD brightness temperature cubes of the 21-cm signal, we find that the emission regions percolate at stages with the filling factor of the emission regions $\mathrm{FF}_{\rm emi}\gtrsim 0.15$. Percolation of the absorption regions occurs for $\mathrm{FF}_{\rm abs}\gtrsim 0.05$. The largest emission and absorption regions are topologically complex and highly filamentary for most parts of the CD. The number density of these regions as a function of the volume shows the power-law nature with the power-law indexes $\approx -2$ and $-1.6$ for the emission and absorption regions, respectively. Overall, the planarity, filamentarity, and genus increase with the increase of the volume of both emission and absorption regions.