Colloidal quantum dots (QDs) have emerged as a promising light absorber for optoelectronic applications. In this study, we investigate the local atomic structure of undoped and chromium -doped cadmium sulfide QDs using EXAFS spectroscopy to elucidate their local structural alterations and correlations with photoconductive behavior. Synthesized samples are characterized by XRD, TEM, UV-vis and PL spectroscopy. EXAFS and XANES at Cd and Cr K-edge have been used to address both the local atomic and local electronic structure around Cr, Cd, and S which reveals changes in bond lengths, coordination numbers, and local disorder with Cr incorporation. The current-voltage measurements reveal that Cr doping in CdS QDs significantly enhances the photoconductance due to introduction of doping energy levels by Cr within the band gap of CdS facilitating charge carrier generation and transport. These findings contribute to insights of photoconductivity mechanisms and for development of efficient large-scale future optoelectronic devices.

This research explores the structural, dielectric, and electrical transport characteristics of polycrystalline La 2− x Sr x FeMnO 6 compounds with varying strontium concentrations ( x = 0.0, 0.1, 0.2, 0.5, 1.0, 1.5, and 2.0).

Colloidal quantum dots (QDs) have emerged as a promising light absorber for optoelectronic applications. Synthetic control over size of QDs gives tuned structural, optical, and electronic properties. However, introducing dopant atoms into QDs in diverse compositions are long-standing challenge to be tackled. In this study, we investigate the local atomic structure of undoped and chromium (Cr)-doped cadmium sulfide (CdS) QDs using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to elucidate their structural alterations and correlations with photoconductive behavior. The XRD patterns and TEM images reveal the polycrystalline cubic nature of the synthesized QDs. The UV-Vis absorption spectra reveal a red-shift in the absorption edge with increasing Cr doping, indicating the influence of Cr ions on the electronic structure of CdS. PL spectra further show enhanced emission properties, with a noticeable shift in the peaks. EXAFS and XANES at Cd and Cr K-edge have been used to address both the local atomic and local electronic structure around Cr, Cd, and S. This reveals changes in bond lengths, coordination numbers, and local disorder with Cr incorporation. The current-voltage results reveal that Cr doping in CdS QDs significantly enhanced the photoconductance. The doping of Cr ions has introduced new doping energy levels within the band gap of CdS, facilitating charge carrier generation and transport, thus improving the overall photoconducting performance. These findings contribute to the valuable insights of the photoconductance mechanisms in Cr-doped CdS QDs and for development of efficient future optoelectronic devices.

Among Heusler compounds,Ni based alloys have been extensively investigated because they exhibit desirable properties such as high Curie temperatures, which are advantageous for advanced magnetic and spintronic devices.The effect of Al substitution on the magnetic ground state of Ni2MnSn was investigated using the Ni2MnSn0.75Al0.25 Heusler alloy.Temperature-dependent magnetisation measurements identify a second-order paramagnetic to ferromagnetic transition at TC is 734K,followed by a first-order martensitic transformation near 263K,demonstrating strong magnetostructural coupling.Curie Weiss analysis yields a positive Weiss temperature theta CW is 746.4K and an effective magnetic moment of 6.82muB,confirming the predominance of ferromagnetic exchange interactions. The bifurcation between the ZFC and FCW magnetization curves,together with non saturating hysteretic M vs H loops, indicates the coexistence of competing ferromagnetic and antiferromagnetic interactions.Further magnetic investigations establish the formation of an interacting reentrant cluster glass state accompanied by an exchange-bias effect.The observed magnetic behavior is attributed to the modification of Mn Mn exchange interactions induced by Al substitution and the associated atomic disorder,resulting in a complex magnetic ground state.

The presence of magnetic impurities in topological insulators can disrupt their time reversal symmetry and lead to the emergence of an energy gap. This study delves into the energy band structure and the Kondo effect through the introduction of Gadolinium (Gd) magnetic perturbations (at levels of x=0.1,0.16) into a pure Bi2Se3 single crystal. In the case of the Bi1.9Gd0.1Se3 (5%) single crystal, the Kondo effect becomes observable at temperatures below 50 K. However, the unaltered parent and Bi1.84Gd0.16Se3 (8%) exhibit typical metallic behavior. The pure sample displays the highest magnetoresistance (MR) of around 225% and demonstrates quantum oscillations driven by a nontrivial berry phase. The sample doped with 5% Gd undergoes a transition from negative MR to positive MR due to a presence of mixed magnetic state resulting from the opening of a gap at the Dirac point. This gap opening is confirmed through angle-resolved photoemission spectroscopy (ARPES) measurements. The comparison of the parameters obtained from the SdH and ARPES measurements, the reduction in the kF values in the magnetotransport measurements is likely due to the band bending induced by the Schottky barrier. Thermoelectric properties are assessed across all prepared samples. The undoped sample displays the highest Seebeck coefficient and power factor values of -398.02 mu V K-1 and 6.83mWmK-2, respectively, at room temperature. These values are notably high for thermoelectric applications at room temperature.

The polycrystalline La2FeMnO6 has been prepared by the solid-state reaction method. The Rietveld refinement of X-ray diffraction (XRD) data confirms a single-phase double perovskite cubic structure. The vibrational modes have been investigated by the Raman and Fourier transform infrared (FTIR) spectroscopy. The X-ray photoemission spectroscopy (XPS) measurement reveals the presence of mixed valence states of Mn and Fe cations. The dielectric, impedance, modulus, and AC conductivity measurements of La2FeMnO6 have been done over temperature range (125-300 K) and frequencies (1 kHz - 1 MHz). This material exhibits a high epsilon ' (similar to 1826) with a low dissipation factor near room temperature. The NTCR (negative temperature coefficient of resistance) characteristics of both resistivity and impedance showed the semiconducting nature of the sample. Grains and grain- boundaries play important role in the process of electrical conduction. The Cole-Cole plots follow the RC equivalent circuit and verify non-Debye-type relaxation. The value of the exponent 's' suggests the non-overlapping small polaron tunneling (NSPT) process in La2FeMnO6. The NTCR characteristic of this material, with good stability factor, thermistor constant, and sensitivity factor may be useful for NTC-type thermistor.

The domain of single-molecule based electronic devices has grown remarkably over the past decade by utilizing nanotechnology to improve the efficiency of device fabrication. However, most of the single-molecule devices are based on organic materials. Compared with organic molecules, quantum dots (QDs) are excellent owing to their crystalline nature, environmental stability, narrow emission band and quantum yield with tunable electronic and optoelectronic properties. Here, CdS:Fe QDs were synthesized and analyzed to assess their structural, optical, and electronic properties, and subsequently, they were implemented in fabricating single-dot rectifying diodes. EXAFS revealed the average coordination number of the doped Fe element. The ITO/TiO2/CdS:Fe quantum dot heterostructure rectifying diodes were grown by spin coating and were characterized using scanning tunneling microscopy (STM) at room temperature. STM images revealed the distribution of QDs over the substrate, and the spectra revealed the improved rectification behavior with tunneling up to similar to 1000x, revealing their excellent diode functionality. Threshold voltage tuning from 1.62 eV to 0.83 eV indicated the application of these diodes for tunable electronics with low power consumption. Thus, these results indicate the promising use of CdS:Fe QDs for optimized ambient atmosphere rectifying diode applications, opening the way for innovative electronic devices with improved performance and functionality.

X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to study the structural and morphological characteristics of pure and Ni-doped CdS (CdS:Nix) (x = 0-6 atomic %) QDs synthesized via the hydrothermal method. Inductively coupled plasma mass spectrometry (ICP-MS) and EDS measurements have been carried out for quantifying the elemental composition. Due to Ni-doping, the short-range structural disorder causes a significant variation in the intensity of the longitudinal optical (LO) modes of Raman spectra. Optical absorption has been broadened with Ni doping, resulting in a reduction of the band gap from 2.42 eV (for CdS) to 2.36 eV (for CdS:Ni6). Photoluminescence (PL) spectra show various peaks associated with surface defects, near band emission (NBE), sulfur vacancies, photoinduced charge carrier separation, and recombination processes. To investigate the chemical states and valence band spectra of Ni-doped CdS QDs, X-ray photoemission spectroscopy (XPS) has been utilized. To realize their applicability in electronic devices, bilayer heterostructure photodetectors (PDs) have been fabricated on the glass substrate by using CdS:Nix QDs and sol-gel-derived SnO2 (as a charge transport layer), viz., Glass/SnO2/CdS:Nix QD PDs. The performance of the device has been improved with a Ni-doping concentration in CdS QDs. The optimized device has been achieved with high photocurrent (28.2 mA/cm2), high figure-of-merit performance having a responsivity of 2.23 A/W, and detectivity of 2.1 x 1013 Jones at a wavelength of approximately 450 nm under 5 V external bias for CdS:Ni6 QD heterostructure PD. Furthermore, this PD shows good response kinetics and are quite stable over time indicating its operational stability.

Two-dimensional (2D) van der Waals (vdW) materials, including graphene, hexagonal boron nitride (hBN), and metal dichalcogenides (MCs), form the basis of modern electronics and optoelectronics due to their unique electronic structure, chemical activity, and mechanical strength. Despite many proof-of-concept demonstrations so far, to fully realize their large-scale practical applications, especially in devices, wafer-scale single crystal atomically thin highly uniform films are indispensable. In this minireview, we present an overview on the strategies and highlight recent significant advances toward the synthesis of wafer-scale single crystal graphene, hBN, and MC 2D thin films. Currently, there are five distinct routes to synthesize wafer-scale single crystal 2D vdW thin films: (i) nucleation-controlled growth by suppressing the nucleation density, (ii) unidirectional alignment of multiple epitaxial nuclei and their seamless coalescence, (iii) self-collimation of randomly oriented grains on a molten metal, (iv) surface diffusion and epitaxial self-planarization and (v) seed-mediated 2D vertical epitaxy. Finally, the challenges that need to be addressed in future studies have also been described.

Crack formation and its possible prevention or remedy is an important branch of material science, closely related to study of granular materials and soft matter physics. This work reports a study on cracking behaviour in composites of bentonite and Laponite ® in varying proportions. Both components are clays of the montmorillonite group. Our experiments demonstrate that for the particular composition - Laponite ® : bentonite ∼1:1, cracks are totally absent. If either component exceeds the other, cracks develop. This is demonstrated over a range of film thickness. Scanning Electron Microscope (SEM) images of the films at different compositions indicate that at this particular ratio, the much smaller particles of Laponite ® , pack into the spaces between the bentonite platelets perfectly, to form a defect-free smooth film.

An experimental analysis of the Bi0.90Tb0.1Fe0.90Mn0.1O3 system synthesized via the solid‐state method is presented in this report. UV–visible measurements are carried out and a smaller bandgap (i.e., semiconductor‐type behavior) is obtained. The structural phase of the present system is analyzed with X‐ray diffraction and neutron diffraction measurement. Structural‐phase analysis reveals that the system contains two nuclear phases (rhombohedral structure [R3c space group] with orthorhombic [Pn21a space group]). Moreover, also more bending in the bond angle is found, and the existence of a magnetic phase with a nuclear phase for the Bi0.90Tb0.1Fe0.90Mn0.1O3 system is also confirmed by neutron diffraction. The magnetic moment versus temperature (M–T) curve demonstrates that the system's Néel transition temperature is at 568 K. The magnetization data show enhancement in the magnetic property by displaying the weak ferromagnetic‐type behavior at room temperature in the magnetic field versus magnetic moment (M–H) curve as compared to the parent compound. From dielectric measurement, the dielectric constant increases while the loss decreases.

The tunability of structural, optical, electronic, and magnetic properties in semiconductor quantum dots (QDs) makes them promising materials for multiple spintronic and optoelectronic applications. However, controlling the size of QDs to tune these properties is challenging due to their quantum size and high sensitivity to the ambient atmosphere. Here, we demonstrate successfully synthesized tunable Mn-doped cadmium sulfide (0% ≤ Mn ≤ 6%) diluted magnetic semiconductor QDs by hot injection chemical route. XRD and TEM studies confirmed that undoped and Mn-doped CdS QDs are polycrystalline in cubic phase without having any dopant-related signature. The XPS study shows the spin–orbit split due to Mn-doping and the atomic percentage of each element present in the prepared sample has been calculated from XPS data. XANES (X-ray Absorption Near Edge Structure) study shows that the Cd has the same oxidation state (+2) in the undoped and Mn-doped CdS QDs and also Mn has +2 oxidation state in Mn-doped CdS QDs. Extended X-ray Absorption Fine Structure (EXAFS) measurements show local structural disorder in higher doping concentration of Mn. It also shows that due to Mn doping, the coordination number of S in all the Mn-doped samples have the S vacancy compared to undoped CdS. No significant change has been observed in FTIR spectra after Mn doping. Raman spectra exhibits two longitudinal optical (LO) modes at 299 cm−1 and 598 cm−1. The intensity of the first LO peak decreases rapidly and linearly due to local structural and short-range disorder induced with increasing Mn concentration in CdS. UV–Vis spectroscopy reveals non-linear variation of bandgap energy showing the downwards bowing with increasing Mn-doping concentration. PL and TRPL indicate appearance of surface defect states with Mn-doping. TRPL spectra show decrease in decay time due to Mn‐doping. Room temperature ferromagnetism of Mn-doped CdS QDs confirms the diluted magnetic semiconductor behavior, which would play key role in quantum spintronics.

The structural, dielectric, and magnetic properties of Bi0.8Tb0.2Fe0.8Mn0.2O3 have been studied in detail. A structural shift from rhombohedral (space group R3c) to orthorhombic (space group Pn21a + Pnma) phase is observed with doping. The substitution of Mn and Tb gives a very large value of the dielectric constant. It has been demonstrated that the observed spontaneous exchange bias is larger than the conventional exchange bias at room temperature. Moreover, doping reduces the Neel temperature from 643 to 521 K and magnetization increases. Thermoremanent magnetization studies at room temperature show that the system is composed of an interfacial layer of an antiferromagnetic core and a two-dimensional diluted antiferromagnet shell with a net magnetization under the field. Furthermore, the system's reasonable HEB and HC values at room temperature make it intriguing and appealing for a variety of multifunctional devices.

ZnO and CdS nanoparticle (NP) doped with first row transition metal ions showed significant antibacterial activity towards Gram-negative as well as Gram-positive bacteria. While, the antibacterial activity of ZnO NPs was found to be significant in Gram-negative bacteria, the effect was comparatively less pronounced towards Gram-positive bacteria. The activity was found to increase with increasing concentration of the NPs. Doping of ZnO NP with Fe atom resulted in significant reduction in the efficacy its antimicrobial activity. In comparison, CdS quantum dot showed antibacterial activity both in Gram-negative and Gram-positive bacteria. While Co doped CdS particles did not show any modulated antibacterial activity; doping by Fe atom augments it with increasing the dopant concentration. The interaction of anti-diabetic drug chlorpropamide is significantly stronger with bovine serum albumin adsorbed on Fe-doped CdS in comparison with undoped NPs without significant alteration in the protein secondary structure. Present study reveals that the drug binding ability of proteins can be significantly modulated on judicious choice of NP system and also the dopant. The modulation in antimicrobial activity and the drug binding ability of the adsorbed protein was explained on the basis of structural parameters and different physicochemical properties of the doped NP systems.

The tunability of optical, electronic, and magnetic properties in semiconductor quantum dots (QDs) makes them promising materials for multiple optical, spintronic, and optoelectronic applications. While controlling the size of QDs to tune these properties is challenging due to their quantum size and high sensitivity to the ambient atmosphere. Here, we demonstrate successfully synthesized manganese doped cadmium sulfide (0 ≤ Mn ≤ 0.06) diluted magnetic semiconductor quantum dots by hot injection chemical route. The study of structural, optical, electronic, and magnetic properties of the prepared QDs reveals the tuned properties due to doping. Structural-, microstructural- properties and the phase identifications were studied by XRD and TEM, and vibrational properties have been studied by Raman spectroscopy. XRD studies confirmed that undoped and Mn-doped CdS QDs are in cubic polycrystalline phase without any dopant-related peaks. XPS reveals chemical composition and oxidation states of each element. Local structural properties have been studied by XANES and EXAFS. UV–Vis spectroscopy reveals non-linear variation of bandgap energy showing the downwards bowing with increasing Mn-doping concentration. Photoluminescence spectroscopy indicates appearance of surface defect states due to Mn‐doping. Room temperature ferromagnetism of Mn-doped CdS QDs confirms the diluted magnetic semiconductor behavior.

Transport, dielectric and magnetic behaviour of polycrystalline double perovskite Eu 2-x Tb x CoMnO 6 (x = 0.0 and 1.0) have been investigated. Temperature-dependent resistivity follows the variable range and small polaron hopping mechanism. The temperature-dependent dielectric property shows usual frequency-dependent step-like behaviour along with thermally activated relaxor peak in loss curves with colossal dielectric constant near room temperature. The temperature-dependent magnetization for x = 0 and x = 1 samples demonstrates a second order phase transition around 125 K and 113 K respectively. The critical behaviour near the magnetic transition has been systematically investigated. The reliability of critical parameters was verified by the Widom scaling relation and magnetic entropy change calculation. The estimated values of critical parameters are close to the value of the theoretical mean-field model. The appearance of the magnetocaloric effect and giant dielectric constant shows that these materials are interesting for real-life applications.

Observed large magnetoresistance, anomalous Hall effect and no appreciable energy gap at the Dirac point in single crystalline Bi 1.9 Dy 0.1 Te 3 topological insulator.

This paper has demonstrated the role of manganese (Mn) doping in cadmium sulfide (CdS) quantum dots (QDs) and their surface passivation for the fabrication of highly sensitive broadband photodetectors. These photodetectors have been fabricated in a p-n heterojunction geometry using the Mn-doped CdS (CdS:Mn) QDs with TiO2 nanoparticles. The thin film of CdS:Mn QDs has been passivated with lead iodide (PbI2) for faster charge transport and broadening of the spectral response of the device. Our detailed X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS), and Raman spectroscopy indicate a partial PbS formation, which also causes spectral broadening. In addition, this passivation process enables us to enhance the photosensitivity of the device with a spectrally flat response of quantum efficiency throughout the visible range spectrum (350-700 nm). This work also demonstrated that the photosensitivity of the device gradually increases with Mn doping with a faster photoresponse. The highest detectivity of the device was obtained with 4% Mn-doped dots with a value of -3.9 x 10(12) Jones under -0.5 V external bias with a photoresponse time of 0.2 s, indicating its very high detectivity with a fast response.

X‐ray diffraction, Raman spectroscopy, Fourier‐transform infrared (FTIR) spectroscopy, dielectric property, and UV–vis spectroscopy studies of pyrochlore Eu2−xFexTi2O7 have been performed. The X‐ray pattern shows that Eu2−xFexTi2O7 has a pure pyrochlore phase up to x = 0.2. The structural analysis shows a strong distortion of TiO6 octahedral due to the presence of the interstitial anionic vacant site. A significantly increased band intensity of FTIR spectrum with Fe doping suggests the enhanced anionic disorder in the system. The broadening of Raman peaks with increasing x supports the increased disorder in TiO6 octahedral. Dielectric study of Eu2Ti2O7 shows a diffused dielectric transition below 150 K. The dielectric diffusiveness and transition temperature get enhanced with Fe doping due to enhanced anionic distortion. The dielectric constant of Eu2−xFexTi2O7 is also increased on Fe doping. The UV–vis spectrum exhibits a strong absorbance in the UV region and a redshift with Fe doping. The Tauc plot of UV–vis spectrum shows multiple successive valence band edges and the bandgap gets reduced with Fe doping due to the formation of new interbands. Thus, these materials are interesting for people searching for material to be used in tunable electrical and optical devices.