Extrinsic Transitions Research Articles

Experimental and density functional theory studies on some metal oxides and the derived nanoclusters: a comparative effects on human ferritin

A comprehensive investigation into the green synthesis of metal oxide nanoparticles (NPs) has garnered significant attention due to its commendable reliability, sustainability, and environmentally friendly attributes. Green synthesis methods play a crucial role in mitigating the adverse effects associated with conventional approaches employed for nanostructure preparation. This research endeavors to examine the impact of ginger plant extract-assisted green synthesis of metal oxides NPs on the serum ferritin levels of anemic diabetic patients in vitro, focusing specifically on α-Fe2O3 and ZnO NPs. Sixty diabetic volunteers with anemia (35–50 years) and thirty healthy volunteers were enrolled as controls. The assessment was conducted using the VIDAS Ferritin (FER) assay. Photoluminescence (PL) spectroscopy measurements were performed to elucidate the intrinsic and extrinsic transitions of these NPs, affirming the successful formation of α-structured iron oxide. Density functional theory (DFT) calculations were carried out at the B3LYP/6-311++G(d,2p) level of theory to investigate the geometry optimization and molecular electrostatic potential maps of the NPs. Furthermore, TD-DFT calculations were employed to explore their frontier molecular orbitals and various quantum chemical parameters. The binding affinity and interaction types of ZnO and α-Fe2O3 NPs to the active site of the human H-Chain Ferritin (PDB ID: 2FHA) target were determined with the help of molecular docking. Results unveiled the crystalline structure of ZnO and the α-structure of α-Fe2O3. Analysis of the frontier molecular orbitals and dipole moment values demonstrated that ZnO (total dipole moment (D) = 5.80 µ) exhibited superior chemical reactivity, biological activity, and stronger molecular interactions with diverse force fields compared to α-Fe2O3 (D = 2.65 µ). Molecular docking of the metal oxides NPs with human H-chain ferritin provided evidence of robust hydrogen bond interactions and metal-acceptor bonds between the metal oxides and the target protein. This finding could have a great impact on using metal oxides NPs-ferritin as a therapeutic protein, however, further studies on their toxicity are required.Graphical abstract

On the extrinsic Hall-Petch to inverse Hall-Petch transition in nanocrystalline Ni-Co electrodeposits

The Hall-Petch to inverse Hall-Petch (HP-IHP) transition of an electrodeposited nanocrystalline Ni-32at%Co alloy was examined by annealing the as-plated alloy to obtain grain sizes ranging between 18 – 239 nm. We describe this transition as an extrinsic HP-IHP transition (extrinsic to the fabrication process) as opposed to the intrinsic HP-IHP transition observed in materials in their as-plated state (intrinsic to the fabrication process). The extrinsic transition of the Ni-32at%Co alloy took place in the mid-stage of abnormal grain growth, at an average grain size of ∼30 nm. Grain boundary relaxation governs the IHP region and maximum hardness was achieved at initial development of bimodal grain size; meanwhile late-stage abnormal grain growth and further normal grain growth led to the reduction in hardness in the HP region. Segregation of sulfur impurities to grain boundaries, crystallographic orientation and annealed twin development did not have significant contributions to the observed change in hardness.

Atypical behavior of intrinsic defects and promising dopants in two-dimensional WS2

The $2\mathrm{D}\text{\ensuremath{-}}\mathrm{W}{\mathrm{S}}_{2}$ is an emerging material for next-generation electronic and optoelectronic devices. These applications are very sensitive and can be adversely affected by defects incorporated during the sample growth. Using hybrid density functional approach, we carried out a comprehensive study on intrinsic and extrinsic defects in $2\mathrm{D}\text{\ensuremath{-}}\mathrm{W}{\mathrm{S}}_{2}$. All the intrinsic defects and their complexes are found to be deep and self-compensating. S vacancy $({\mathrm{V}}_{\text{S}})$, which has been previously attributed as the source of $n$-type conductivity, turns out to be an electron trap center. We found that ${\mathrm{V}}_{\text{S}}$ gives rise to a suboptical gap, which can be the source of single-photon emitters. Interestingly, hydrogen interstitial $({\mathrm{H}}_{i})$ makes multicenter bond and acts as a shallow donor. In addition, H as adatom (H-ad) also provides shallow donor levels and is the cause of unintentional $n$-type doping. Among the extrinsic defects, halogens and transition metals are found to be promising dopants. While halogens at the S site act as shallow donors, Nb at the W site provides a reasonable shallow acceptor level with low formation energy.

Coupling of Ru and O‐Vacancy on 2D Mo‐Based Electrocatalyst Via a Solid‐Phase Interface Reaction Strategy for Hydrogen Evolution Reaction

AbstractFor most Mo‐based electrocatalysts, the hydrogen evolution reaction (HER) activity depends on their own active structural defects or extrinsic transition metal centers. In this work, in order to combine the advantages of these two different active centers, a solid‐phase interface reaction (SPIR) strategy is proposed, which simultaneously introduces oxygen vacancies (VO) and metal centers (Ru) into the 2D Mo‐based catalyst. Briefly, this SPIR occurs at the interface between MoS2 and RuO2 nanoparticles of the RuO2/MoS2 precursor when overcoming the kinetic barriers at a suitable temperature under an Ar atmosphere. Since the adjacent parts of RuO2 and MoS2 are converted to Ru and MoO2 in situ, a composite system MiSC‐1 containing a large amount of active Ru and VO on MoO2 plane is obtained. Furthermore, theoretical calculations confirm the proposed mechanism of SPIR. MiSC‐1 shows excellent stability and catalytic performance in the HER, with an overpotential value of 12 mV at 10 mA cm−2 in 1.0 M KOH. Additionally, MiSC‐1 exhibits excellent performance in the hydrolysis of ammonia borane. This report will provide a versatile platform for the preparation of a multi‐component catalyst with high total activity as well as the identification of the structural details of the catalysts.

Intrinsic-to-extrinsic transition in fracture toughness through structural design: A lesson from nature

Catastrophic failure of materials and structures due to unstable crack growth could be prevented if fracture toughness could be enhanced at will through structural design, but how can this be possible if fracture toughness is a material constant related to energy dissipation in the vicinity of a propagating crack tip. Here we draw inspiration from the deformation behavior of biomolecules in load bearing biological materials, which have been evolved with a large extensibility and a high breaking strength beyond their elastic limit, and introduce an effective biomimetic strategy to enhance fracture toughness of a structure through an intrinsic to extrinsic (ITE) transition. In the ITE transition, toughness starts as an intrinsic parameter at the basic material level, but by designing a protein-like effective stress–strain behavior the toughness at the system level becomes an extrinsic parameter that increases with the system size without bound. This phenomenon is demonstrated through a combination of numerical simulations, analytic modeling and experiments, and leads to a biomimetic strategy which can be broadly adopted to enhance fracture toughness in engineering systems.

Bimodality in gene expression without feedback: from Gaussian white noise to log-normal coloured noise.

Extrinsic noise-induced transitions to bimodal dynamics have been largely investigated in a variety of chemical, physical, and biological systems. In the standard approach in physical and chemical systems, the key properties that make these systems mathematically tractable are that the noise appears linearly in the dynamical equations, and it is assumed Gaussian and white. In biology, the Gaussian approximation has been successful in specific systems, but the relevant noise being usually non-Gaussian, non-white, and nonlinear poses serious limitations to its general applicability. Here we revisit the fundamental features of linear Gaussian noise, pinpoint its limitations, and review recent new approaches based on nonlinear bounded noises, which highlight novel mechanisms to account for transitions to bimodal behaviour. We do this by considering a simple but fundamental gene expression model, the repressed gene, which is characterized by linear and nonlinear dependencies on external parameters. We then review a general methodology introduced recently, so-called nonlinear noise filtering, which allows the investigation of linear, nonlinear, Gaussian and non-Gaussian noises. We also present a derivation of it, which highlights its dynamical origin. Testing the methodology on the repressed gene confirms that the emergence of noise-induced transitions appears to be strongly dependent on the type of noise adopted, and on the degree of nonlinearity present in the system.

Tuning the electronic band gap of Cu2O via transition metal doping for improved photovoltaic applications

Cu 2 O is a widely known p -type semiconductor with a band-gap value suitable for photovoltaic applications. However, due to its parity-forbidden nature of the first interband transition and high carrier recombination currents, Cu 2 O has failed to reach commercial application. Hybrid density functional theory has been used to study the effect of transition metal dopants on the electronic and optical properties of Cu 2 O . Substitutional transition metal dopants, incorporated on the copper site, allow band-gap tunability by creating a range of defect states in the electronic structure, from shallow levels to deep intermediate bands. The preferred position of the dopants is in the vicinity of copper vacancies, which are naturally found in Cu 2 O and are responsible for its p -type conductivity. Impurity levels created via extrinsic transition metal dopants increase substantially the capacity of Cu 2 O to absorb light, reaching values close to 10%. First row transition metal dopants thus show potential for considerable improvement of the overall photovoltaic performance of Cu 2 O .

Impurity concentration dependent electrical conduction in germanium crystals at low temperatures

A germanium single crystal of 7 N+ purity with a diameter of 45 mm and a length of 100 mm has been grown by the Czochralski method. The structural quality of the crystal has been characterized by Laue diffraction. Electrical conduction and Hall measurements are carried out on samples retrieved from different parts of the crystal along the growth axis. The top part of the crystal exhibits the lowest impurity concentration ($${\sim } 10^{12}\,\hbox {cm}^{-3})$$ that gradually increases towards the bottom ($$10^{13}\,\hbox {cm}^{-3})$$. The crystal is n-type at room temperature and the resistivity shows a non-monotonic temperature dependence. There is a transition from n-type to p-type conductivity below room temperature at which bulk resistivity shows a maximum and dip in carrier mobility. The intrinsic to extrinsic transition region shifts towards room temperature as the impurity concentration increases and it reflects the purity level of the crystal. A similar trend is observed in the boron-implanted high purity germanium (HPGe) crystal at different doping levels. The phenomena can be understood as a result of interplay between a temperature dependent conduction mechanism driven by an impurity band and an intrinsic carrier in Ge crystals having fairly low acceptor concentrations ($${<}10^{12}\,\hbox {cm}^{-3})$$.

Graphene Field-Effect Transistors With High Extrinsic &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${f}_{T}$&lt;/tex-math&gt; &lt;/inline-formula&gt; and &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${f}_{\mathrm{max}}$&lt;/tex-math&gt; &lt;/inline-formula&gt;

In this letter, we report on the performance of graphene field-effect transistors (GFETs) in which the extrinsic transit frequency ( ${f}_{T}$ ) and maximum frequency of oscillation ( ${f}_{\text {max}}$ ) showed improved scaling behavior with respect to the gate length ( ${L}_{g}$ ). This improvement was achieved by the use of high-quality graphene in combination with successful optimization of the GFET technology, where extreme low source/drain contact resistances were obtained together with reduced parasitic pad capacitances. GFETs with gate lengths ranging from $0.5~\mu \text{m}$ to $\text {2}~\mu \text{m}$ have been characterized, and extrinsic ${f}_{T}$ and ${f}_{\text {max}}$ frequencies of up to 34 and 37 GHz, respectively, were obtained for GFETs with the shortest gate lengths. Simulations based on a small-signal equivalent circuit model are in good agreement with the measured data. Extrapolation predicts extrinsic ${f}_{T}$ and ${f}_{\text {max}}$ values of approximately 100 GHz at ${L}_{g}=\text {50}$ nm. Further optimization of the GFET technology enables ${f}_{\text {max}}$ values above 100 GHz, which is suitable for many millimeter wave applications.

Conduction mechanism in vapour transport grown tellurium rich cadmium telluride crystals

Electrical characterisation of vapour transport grown Tellurium rich p-type hexagonal Cadmium Telluride (CdTe) of resistivity 3.954 × 103 Ω cm was carried out. The resistance variation of the grown sample over a wide range of temperature, from 331 K to 771 K, was studied. The electronic conduction behaviour in the investigated CdTe revealed the hopping of carriers among the nearest neighbouring levels and the involved excitonic mechanisms. A characteristic metallic behaviour was identified in the intrinsic to extrinsic transition region, with the signature of optical phonon energy leading to the discrete steps. The dominant transport mechanism within the grown CdTe sample was explored, studying the dependence of mobility of charge carriers with temperature, and was found to be governed by Mott’s variable range hopping model with the density of states independent of energy near the Fermi level. The DSC analysis revealed a reversible phase transition at around 717 K and the result was correlated with prominent variations in resistivity in the intrinsic to extrinsic transition region.

Effects of excess carriers on charged defect concentrations in wide bandgap semiconductors

Unintentional doping and doping limits in semiconductors are typically caused by compensating defects with low formation energies. Since the formation enthalpy of a charged defect depends linearly on the Fermi level, doping limits can be especially pronounced in wide bandgap semiconductors where the Fermi level can vary substantially. Introduction of non-equilibrium carrier concentrations during growth or processing alters the chemical potentials of band carriers and allows populations of charged defects to be modified in ways impossible at thermal equilibrium. We demonstrate that in the presence of excess carriers, the rates of carrier capture and emission involving a defect charge transition level determine the admixture of electron and hole quasi-Fermi levels involved in the formation enthalpy of non-zero charge defect states. To understand the range of possible responses, we investigate the behavior of a single donor-like defect as functions of extrinsic doping and charge transition level energy. We find that that excess carriers will increase the formation enthalpy of compensating defects for most values of the charge transition level in the bandgap. Thus, it may be possible to use non-equilibrium carrier concentrations to overcome limitations on doping imposed by native defects. Cases also exist in which the concentration of defects with the same charge polarity as the majority dopant is either left unchanged or actually increases. This surprising effect arises when emission rates are suppressed relative to the capture rates and is most pronounced in wide bandgap semiconductors. We provide guidelines for carrying out experimental tests of this model.

Ultrahigh-Responsivity, Rapid-Recovery, Solar-Blind Photodetector Based on Highly Nonstoichiometric Amorphous Gallium Oxide

Recently, Ga2O3-based, solar-blind photodetectors (PDs) have been extensively studied for various commercial and military applications. However, to date, studies have focused only on the crystalline phases, especially β-Ga2O3, and the crystalline quality must be carefully controlled because of its strong impact on device characteristics. Based on previous reports, amorphous-semiconductor-based PDs can also be expected to exhibit excellent photodetection characteristics. In this work, amorphous gallium oxide thin films were deposited by radio frequency (RF) magnetron sputtering, and the metal–semiconductor–metal (MSM) PD was fabricated and compared with a β-Ga2O3 film prepared side-by-side as the control sample. The as-sputtered film possessed a high density of defects, including structural disorders, oxygen vacancies, and likely, dangling bonds, resulting in record-high responsivity (70.26 A/W) for a thin-film-type gallium oxide PD due to a high internal gain and the contribution of extrinsic transitions ...

Physical Characterization of Orthorhombic AgInS2 Nanocrystalline Thin Films

Nanocrystalline thin films of AgInS2 were synthesized using an inert gas condensation technique. The grazing incident in-plane x-ray diffraction technique was used to detect the crystal structure of the deposited and annealed thin films. The results confirmed that the as-deposited film shows an amorphous behavior and that the annealed film has a single phase crystallized in an orthorhombic structure. The orthorhombic structure and particle size were detected using high-resolution transmission electron microscopy. The particle size ( $$ P_{\rm{s}}$$ ) estimated from micrograph images of the nanocrystalline films were increased from 6 nm to 12 nm as the film thickness increased from 11 nm to 110 nm. Accordingly, increasing the film thickness up to 110 nm reflects varying the optical band gap from 2.75 eV to 2.1 eV. The photocurrent measurements were studied where the fast rise and decay of the photocurrent are governed by the recombination mechanism. The electrical conductivity behavior was demonstrated by two transition mechanisms: extrinsic transition for a low-temperature range (300–400 K) and intrinsic transition for the high-temperature region above 400 K.

Ultrafast carrier dynamics, band-gap renormalization, and optical properties of ZnSe nanowires

In this paper, we present a comprehensive study of the carrier dynamics and optical properties of ZnSe nanowires (NWs). The transparency of the sample, obtained by the growth of the ZnSe NWs on glass, allowed us to perform transmittance, reflectance, photoluminescence (PL), time-resolved PL, and pump-probe transient absorption spectroscopy on as-grown samples. All measurements were performed at room temperature. Strong light trapping at the band-gap energy has been observed in reflectivity measurements. Fast transient absorption bleaching due to band filling and band-gap renormalization has been observed. The band-gap renormalization has a rise time constant of about 170 fs and a decay time of about 4 ps. Fast transient absorption bleaching is also observed at energies below the band gap, suggesting that intrinsic processes prevail over extrinsic photoinduced transitions in our high-quality NWs. The PL reveals the presence at room temperature of excitonic emission that shows a decay time of 0.5 ns. All of these features indicate that our ZnSe NWs have quality comparable to epitaxial films and can be used for optical devices and nonlinear optics.

Black Phosphorous Thin-Film Transistor and RF Circuit Applications

In this letter, we discuss the design, fabrication, and high-frequency characterization of black phosphorous (BP)based field-effect transistors (FETs) and their circuit applications. We demonstrate BP radio frequency (RF) FETs with an extrinsic transit frequency ~3 GHz and an extrinsic maximum oscillation frequency ~7 GHz. We also demonstrate various BP FET-based RF circuits working in the megahertz range for the first time. We show the design and simulation of BP-based RF amplifier using experimentally obtained scattering parameters, operating at gigahertz frequency with substantial gain. The experimental and simulation results reveal the major performance bottlenecks of these circuits and place BP FET as a promising device candidate for future thin-film nanoelectronic RF systems.

Elasticity of Random Multiphase Materials: Percolation of the Stiffness Tensor

Topology and percolation effects play an important role in heterogeneous materials, but have rarely been studied for higher-order tensor properties. We explore the effective elastic properties of random multiphase materials using a combination of continuum computational simulations and analytical theories. The effective shear and bulk moduli of a class of symmetric-cell random composites with high phase contrasts are determined, and reveal shortcomings of classical homogenization theories in predicting elastic properties of percolating systems. The effective shear modulus exhibits typical percolation behavior, but with its percolation threshold shifting with the contrast in phase bulk moduli. On the contrary, the effective bulk modulus does not exhibit intrinsic percolation but does show an apparent or extrinsic percolation transition due to cross effects between shear and bulk moduli. We also propose an empirical approach for bridging percolation and homogenization theories and predicting the effective shear and bulk moduli in a manner consistent with the simulations.

Size mismatch, grain boundary and bandwidth effects on structural, magnetic and electrical properties of Pr 0.67Ba 0.33MnO 3 and Pr 0.67Sr 0.33MnO 3 perovskites

We have studied the effect of size mismatch on the structural, magnetic and electrical properties of Pr 0.67Ba 0.33MnO 3 (PBMO) and Pr 0.67Sr 0.33MnO 3 (PSMO) perovskites with considerable difference in their variance σ 2 values. Samples were prepared by ceramic route at 1200 °C. Morphological study, microstructure and chemical composition were examined by scanning electron microscopy, EDX analyses and Rietveld structure refinement. Both compounds exhibit single orthorhombic Pnma crystalline phase and with strongly connected and larger grains for PSMO than for PBMO that gives a beginning of single crystal growth in PSMO case. PBMO with higher variance exhibits distinct intrinsic (due to grains) and extrinsic (due to grain boundaries) transitions in the resistivity behaviour, and with higher transition temperatures than those usually reported in the literature. Extrinsic effects, however, are not observed in the lower σ 2 PSMO sample. Both compounds exhibit Curie temperature ( T C) values significantly higher than those reported in the literature, and with higher T C for PSMO due to its larger bandwidth W. The experimental paramagnetic effective moment for PSMO is very close to the theoretical one, whereas there is a significant difference between these moments for PBMO sample, probably due to the considerable size mismatch effect between Pr and Ba, and to the ferromagnetic correlations in the paramagnetic state. Ferromagnetic-metallic regime in the two compounds seems to emanate from the electron-(phonon, magnon) scattering processes with a larger effect for PBMO than that for PSMO, due to the prominent role of the grain boundary in PBMO. Above paramagnetic-insulating transition temperature the data were well fitted by both variable range hopping (VRH) and small polaron hopping (SPH) models giving higher density state, and lower activation energy and Mott temperature T 0 for PSMO than those for PBMO, essentially due to their considerable difference in their variance values.

Enhanced CMR properties of La0.67Ca0.33MnO3 sintered at different temperatures

This article reports the study of the magneto-transport properties of Lanthanum-based colossal magnetoresistive sample, , as a function of temperature. The samples were prepared by the solid state route by sintering at three different temperatures 1100°C, 1250°C and 1350°C; with a view to understand the influence of varying crystallite size on various physical properties. It has been observed that the change in the grain size with the sintering temperature alters the contributions of intrinsic and extrinsic resistances which results in some major effects on the magneto-transport behaviours. The occurrence of intrinsic and extrinsic transitions can be explained well by the consideration of the random network of resistances with two types of resistivities – one more resistive than the other; using time dependent and independent metallic volume fractions, respectively.

Electrodeposition and Thermoelectric Characterization of Bismuth Telluride Nanowires

Bismuth telluride nanowires were electrodeposited from aqueous acidic solutions containing different (20/20 and 20/10 mM) concentration ratios. The polarization plots predicted that combined solutions exhibit more noble reduction potentials than individual solutions. Optimized deposition potentials were obtained from the combined electrolyte polarization plots. An anomalous codeposition behavior caused an increase in Te concentration for depositions in the kinetic region of bismuth telluride; otherwise, decreasing Te concentrations with increased deposition potentials was observed from a composition analysis. X-ray diffraction showed a dominant (110) orientation for nanowires at low deposition potentials. n-Type nanowires were obtained from both electrolytes, while p-type nanowires were only obtained from the 20/10 electrolyte for low Te concentrations. An intrinsic to extrinsic transition was observed for nanowires deposited from the 20/10 electrolyte. The highest measured Seebeck coefficient was and for n- and p-type nanowires, respectively. The Seebeck coefficient dependence on the resistivity and composition of the nanowires is discussed.

220 GHz low‐noise amplifier MMICs and modules based on a high performance 50 nm metamorphic HEMT technology

A metamorphic composite-channel InAlAs/InGaAs based high electron mobility transistor (MHEMT) technology has been developed for active and passive high-resolution imaging applications. The technology features 50 nm gate length in combination with an In content of 80% in the main channel and 53% in the second channel. An extrinsic transit frequency ft of 400 GHz and an extrinsic maximum transconductance gm,max of 1800 mS/mm were measured at a drain voltage of 1 V. Based on this advanced MHEMT technology, coplanar G-band low-noise amplifier (LNA) MMICs were realized, achieving a small-signal gain of more than 15 dB between 192 and 230 GHz together with an average noise figure of 8 dB. Furthermore, mounting and packaging of the monolithic amplifier chips into G-band waveguide modules was accomplished with only minor reduction in circuit performance. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)