Semiconductor Regime Research Articles

Crystal and band structures of N-doped Ti3O5 coatings: Experiments and first-principles calculations

N-doped α-phase Ti3O5 has received limited attention in both theoretical and experimental studies compared to N-doped TiO2. This work focuses on the production and analysis of N-doped Ti3O5 coatings, which can be facilely produced using air-based sputtering. First-principles calculations were employed to investigate the crystal and band structures of N-doped Ti3O5. The results revealed that substitutional nitrogen doping within the investigated range preserved the orthorhombic structure of Ti3O5. As the N-doping concentrations increased, Ti3O5 exhibited a transition from metallic to semiconducting characteristics, confirmed by the density of states and refined band calculations. The calculated bandgaps in the semiconductor regime aligned well with the limited experimental results, demonstrating the pronounced narrowing effect of nitrogen doping. Integrating these calculations with experimental findings enhances the understanding of the crystalline and physical properties of N-doped Ti3O5 coatings.

Syntheses, spectroscopic characterization, and electrical properties of important semiconducting organic compound

This work proposes the synthesis of new azomethine by the reaction of enaminone with an appropriate aldehyde. The new compound was identified by NMR (1H and 13C), and others techniques such as: UV–Vis spectroscopy, Fourier Transform Infra-red spectroscopy (FT-IR) and X-ray diffraction (XRD).The optical data shows the synthesized azomethine exhibit low band gaps. (Eg =2.87 eV). Electrical conductivity study indicates that conductivity of product is in the range of ∼ 10−6 S/cm. . So, it is evaluated that the sample is a typical organic semiconductor as its conductivity increases with increasing temperature and the electronic parameters such as activation energy and room-temperature conductivity are in the regime of semiconductors. It is also found that the dielectric constant and the dielectric loss values increase with temperature and decrease with frequencies.Furthermore, the results obtained in this pioneering study are thoughtfully discussed in the context of existing literature. This study is opening doors to potential applications in chemistry.

Stereolithography of Semiconductor Silver and Acrylic-Based Nanocomposites.

Polymer nanocomposites (PNCs) attract the attention of researchers and industry because of their potential properties in widespread fields. Specifically, electrically conductive and semiconductor PNCs are gaining interest as promising materials for biomedical, optoelectronic and sensing applications, among others. Here, metallic nanoparticles (NPs) are extensively used as nanoadditives to increase the electrical conductivity of mere acrylic resin. As the in situ formation of metallic NPs within the acrylic matrix is hindered by the solubility of the NP precursors, we propose a method to increase the density of Ag NPs by using different intermediate solvents, allowing preparation of Ag/acrylic resin nanocomposites with improved electrical behaviour. We fabricated 3D structures using stereolithography (SLA) by dissolving different quantities of metal precursor (AgClO4) in methanol and in N,N-dimethylformamide (DMF) and adding these solutions to the acrylic resin. The high density of Ag NPs obtained notably increases the electrical conductivity of the nanocomposites, reaching the semiconductor regime. We analysed the effect of the auxiliary solvents during the printing process and the implications on the mechanical properties and the degree of cure of the fabricated nanocomposites. The good quality of the materials prepared by this method turn these nanocomposites into promising candidates for electronic applications.

Excitonic insulators and Gross-Neveu models

We introduce a generalized Gross-Neveu (GN) model to describe the excitonic instabilities in two different systems: a small overlap semi-metal (SM) and a small gap semi-conductor (SMC), both in two (2d) and three-dimensions (3d). We identify the excitonic order parameter (EOP) and obtain the effective potential within the Large $N$ limit approach where the GN model can be exactly solved. We obtain the excitonic insulator (EI) phase diagrams as a function of temperature, chemical potential, overlap between bands and gaps of the system. We show that the EI may undergo first- or second-order thermal transitions depending on the regime whereupon this phase is approached. We also investigate the expected thermodynamic signatures for the specific heat above the fine-tuned excitonic quantum critical point (EQCP), in both 2d and 3d, in the SMC regime. We show that the EQCP is a different kind of critical point since although the EOP vanishes at the EQCP, there is always a finite gap in the SMC regime. We find that for high temperatures, the specific heat might exhibit a scaling behavior in the form $C_V/T \propto T^{(d-z)/z}$, where $d$ is the dimension of the system and $z$ is the dynamical critical exponent. The very low temperature behavior has a dominant exponential thermally activated term due to the presence of a gap that does not vanish at the excitonic transition.

Macroradical enables electrical conduction in epoxy thermoset

A single material combining the unique properties of stable radical moieties with the versatility of the epoxy polymer is presented. Electrical conduction for any material is mostly achieved using metals, metal-organics, or organic conductors with extended π-orbital frameworks. However, in this combined material, intrinsic electronic conduction is enabled into the non-conjugated and amorphous epoxy thermoset. Furthermore, using the classical epoxy-amine curing ensures that only a highly crosslinked network with a rigid topology is formed. This design is a departure from other macroradicals with flexible backbones. The hole mobility of the neat macroradical epoxy thermoset is quantified to be ~3.1 × 10−6 cm2 V−1 s−1, already in the regime of traditional semiconductors. This electronic conduction can only be a result of radical-toradical hopping because the thermoset still retains active radicals after polymerization with a short alkyl amine when measured by electron spin resonance (EPR) spectroscopy. In the scientific literature, the synthesis of macroradicals using the direct approach is scarce. Herein, to obtain the novel radical epoxy monomer, a very mature yet simple amino-epoxide chemistry is employed to prepare a diglycidylamine based on 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl using the direct approach. EPR spectroscopy also reveals that the radical center remained stable even after epoxidation of the precursor. Consequently, this effort offers a change in thinking on how electronic conduction in open shell polymers operates especially on a rigid backbone and paves for a reassessment of the traditional epoxy polymer as enduring materials for frontier applications.

An electronic phase diagram of hole-doped BiCuSeO crystals determined by transport characterization under various growth conditions

Temperature-hole-concentration dependent electronic phase-diagram of BiCuSeO.

A Nanotubular Metal-Organic Framework with a Narrow Bandgap from Extended Conjugation*.

A one‐dimensional nanotubular metal–organic framework (MOF) [Ni(Cu‐H4TPPA)]⋅2 (CH3)2NH2 + (H8TPPA=5,10,15,20‐tetrakis[p‐phenylphosphonic acid] porphyrin) constructed by using the arylphosphonic acid H8TPPA is reported. The structure of this MOF, known as GTUB‐4, was solved by using single‐crystal X‐ray diffraction and its geometric accessible surface area was calculated to be 1102 m2 g−1, making it the phosphonate MOF with the highest reported surface area. Due to the extended conjugation of its porphyrin core, GTUB‐4 possesses narrow indirect and direct bandgaps (1.9 eV and 2.16 eV, respectively) in the semiconductor regime. Thermogravimetric analysis suggests that GTUB‐4 is thermally stable up to 400 °C. Owing to its high surface area, low bandgap, and high thermal stability, GTUB‐4 could find applications as electrodes in supercapacitors.

Consequences of Bi3+ introduction for Pr3+ in PrAlO3

With the intent to comprehend the structure and hence the property changes in the PrAlO3 system, the substitution of Bi3+ for Pr3+ has been attempted. The samples were synthesized by solution combustion synthesis and characterized extensively. X-ray diffraction studies revealed that the rhombohedral perovskite structure was preserved up to 20 mol% substitution of bismuth, beyond which diffraction peaks of the secondary phase of α-Bi2O3emerged. The structural refinements indicated the increment of both a and c lattice dimensions with an increase in bismuth content. The samples had porous morphology, and a mean pore diameter of 22.4 nm, along with a surface area of 100 m2/g, was deduced from BET measurements for the 20 mol% bismuth-substituted sample. FTIR, Raman spectroscopic and electron microscopic analysis reinforced the perovskite structure adopted by the bismuth-substituted samples. Both Pr and Bi in Pr0.80Bi0.20AlO3 existed in the + 3 oxidation state as established from the XPS analysis. The inclusion of bismuth introduced intermediate energy levels within the bandgap, as suggested by the redshift of the absorption edge for the bismuth-substituted samples. As the optical bandgap values were in the semiconductor regime, the application of bismuth-replaced samples as a catalyst for the photodegradation of crystal violet dye solution was demonstrated. The amount of dye degraded increased with an increase in the amount of bismuth in the sample. Additionally, Pr0.80Bi0.20AlO3 catalyzed the reduction of nitroaromatics promoted possibly by the Bi3+/Bi(0) redox couple.

Structural, electronic, optoelectronic and transport properties of LuZnCuAs2 compound: First principle calculations under DFT

We have reported on theoretical insights of LuZnCuAs2 compound from Zintl family using computational code WIEN2k where we optimized unit cell volume at ground state and investigated its structural, electronic, optoelectronic and thermal properties on three different potentials including local density approximation (LDA), generalized gradient approximation (GGA) and generalized gradient approximation plus Tran-Blaha modified Becke-Johnson (GGA + mBJ). The former two suggested a semi-metallic behavior whereas GGA + mBJ showed semiconductor regime with band gap of 0.4 eV. We observed major contribution of 5d-shell of Lutetium (Lu) in density of states (DOS) relative to 3d-shells of Zinc (Zn) and Copper (Cu). We have reported on reflectivity, refractive index, energy loss and absorption of LuZnCuAs2. We also studied thermal behavior of LuZnCuAs2 using BoltzTrap as implemented in WIEN2k code where we calculated its electrical conductivity, Seebeck coefficient, thermal conductivity and the dimensionless figure of merit (ZT).

Strain engineering of the electronic and thermoelectric properties of titanium trisulphide monolayers

The goal of this work is to evaluate the effect of mechanical strain on a number of electronic and thermoelectric properties of TiS3 monolayers. We have used density-functional theory (DFT) calculations at the hybrid HSE06 level to evaluate the response of the electronic band gap and mobilities, as well as the thermopower, the electrical conductivity, the electronic contribution to the thermal conductivity and the power factor. Our calculations indicate that the band gaps can be increased by 44.25%, reaching a value of 1.55 eV from that of the undeformed case of 1.07 eV. The behaviour of HSE06 band gaps agrees well with that calculated at the G0W0 level of theory. We evaluate the variation of electron mobilities with strain and discuss the possible causes of the existent disagreement between experiments and simulations. In addition, our calculations predict small changes in the Seebeck coefficient, whose Sy component can be enhanced by up to 11% with a compression of 5% along the y-axis. On the other hand, the electrical conductivity experiences higher variations, nearly doubling its value from the undeformed case under the semiconductor regime of doping and mechanical deformation. Finally, our predicted power factors can be enhanced by nearly twice under the same conditions by which the electrical conductivity is also improved, indicating that the latter drives the optimisation of the former.

Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet

Giant Gilbert damping anisotropy is identified as a signature of strong Rashba spin-orbit coupling in a two-dimensional antiferromagnet on a honeycomb lattice. The phenomenon originates in spin-orbit induced splitting of conduction electron subbands that strongly suppresses certain spin-flip processes. As a result, the spin-orbit interaction is shown to support an undamped non-equilibrium dynamical mode that corresponds to an ultrafast in-plane N\'eel vector precession and a constant perpendicular-to-the-plane magnetization. The phenomenon is illustrated on the basis of a two dimensional $s$-$d$ like model. Spin-orbit torques and conductivity are also computed microscopically for this model. Unlike Gilbert damping these quantities are shown to reveal only a weak anisotropy that is limited to the semiconductor regime corresponding to the Fermi energy staying in a close vicinity of antiferromagnetic gap.

Strain-induced band modulation and excellent stability, transport and optical properties of penta-MP2 (M = Ni, Pd, and Pt) monolayers.

First principle calculations utilizing density functional theory were carried out to investigate the electronic, transport and optical properties of penta-MP2 (M = Ni, Pd and Pt) monolayer compounds under applied uniaxial and biaxial tensile strains. With an optimum magnitude of applied strain, we found band gap transitions in penta-MP2 monolayers from zero/narrow to the semiconductor regime, wherein band gaps were noticed to be firmly dependent on the applied uniaxial and biaxial tensile strains. In this study, the PBE approach was used primarily to evaluate electronic properties, from where the identified architectures of penta-MP2 with maximum obtained bandgaps under respective optimum strains were assessed through the HSE06 method of calculation for better estimation of band gaps and optical properties. Prior to HSE calculations, we affirmed our assessment for the stability and reliability of the compounds under uniaxial and biaxial strains of up to 15% through phonon spectrum and elastic calculations. A distinct transition was also noted from semiconductor to metal for all compounds after the applied optimum uniaxial and biaxial strains. The optical absorption spectra in all the stretched penta-MP2 compounds reached the order of 106 cm−1, with significant peaks belonging to the IR and visible regions; this indicates promising applications of these materials in high-performance solar energy and good hot mirror materials. The enhanced I–V responses under uniaxial and biaxial tensile strains using the non-equilibrium Green's function (NEGF) approach confirm the usefulness of the strained state of the considered penta-MP2 monolayers. The results show that tuning electronic properties, I–V characteristics and optical properties of stretched penta-MP2 compounds under tensile strain merits significant future applications in optoelectronic devices and as good hot mirror materials.

Atomically thin, large area aluminosilicate nanosheets fabricated from layered clay minerals

Abstract Two-dimensional (2-D) nanosheets, which have dimensions of atomically thin thickness with extremely high aspect ratio, have gathered great attentions due to their interesting properties and potential applications. Especially, some ceramic nanosheets including borides, carbides and sulfides became epitomes of novel functional nanomaterials since they exhibited unique electrical and surface properties distinguished from their bulk forms. In this study, atomically thin nanosheets of aluminosilicate oxides were fabricated via exfoliation of layered clay mineral, mica (muscovite; KAl3Si3O10(OH)2). To overcome the difficulties in exfoliations of large area nanosheets from mica, which has relatively strong interlayer bonding originated from layer charge, polymer assisted wet chemical method were applied. Amphiphilic polymer molecules were successfully intercalated into the ion exchanged muscovite particles to separate each layer. The resulting product possesses nanosheets with micrometer scale lateral sizes. The measured thicknesses of the nanosheets were mainly fell in two groups (1.2–1.7 nm and 2.2–2.7 nm) which correspond to the mono- and di-layer thichnesses of the muscovite with polymer adsorbates, respectively. The FT-IR and Raman results indicated that the adsorption of polymer molecules on the both surfaces of the aluminosilicate nanosheets significantly weaken or even break the interlayer bonding. Contrary to the highly insulating nature of bulk muscovites, the exfoliated nanosheets showed reduced bandgap energy which corresponds to semiconductor regime. The measured optical bandgap of the aluminosilicate ceramic nanosheets was 4.13 eV, which makes this ceramic nanosheet material a potential candidate for various electronic and electro-optic applications including wide bandgap semiconductors and photocatalysts.

Hexagonal thallium nitride in (TlX)2n+1H2n+4 [X = N, P, As; n = 1–5] cluster series: A promising building motif for future smart nanomaterials

A series of inorganic hexagonal cluster motifs from the thallium pnictides, viz., (TlX)2n+1H2n+4 (X = N, P, As; n = 1–5) is investigated under density functional theory. The structure and stability of the hexagonal cluster units toward their growth are exclusively monitored to identify potential hexagonal cluster units for future smart materials especially in the form of nanotube or 2D ultrathin nanomaterials. Apart from the structure and stability, usefulness of the cluster building units is analyzed with various quantum mechanical electronic as well as different spectroscopic (IR and Raman) properties. It appears from the present study that thallium nitride hexagonal cluster units are most promising towards their growth for forming nanotubes or 2D materials in the semiconductor regime of metal-insulator-semiconductor (MIS) parlance.

Electromagnetic metamaterial-inspired band gap and perfect transmission in semiconductor and graphene-based electronic and photonic structures

In this article, at first we propose a unified and compact classification of single negative electromagnetic metamaterial-based perfect transmission unit cells. The classes are named as: type-A, -B and -C unit cells. Then based on the classification, we have extended these ideas in semiconductor and graphene regimes. For type-A: Based on the idea of electromagnetic Spatial Average Single Negative bandgap, novel bandgap structures have been proposed for electron transmission in semiconductor heterostructures. For type-B: with dielectric-graphene-dielectric structure, almost all angle transparency is achieved for both polarizations of electromagnetic wave in the terahertz frequency range instead of the conventional transparency in the microwave frequency range. Finally the application of the gated dielectric-graphene-dielectric has been demonstrated for the modulation and switching purpose.

Dipolar SAMs Reduce Charge Carrier Injection Barriers in n-Channel Organic Field Effect Transistors.

In this work we examine small conjugated molecules bearing a thiol headgroup as self assembled monolayers (SAM). Functional groups in the SAM-active molecule shift the work function of gold to n-channel semiconductor regimes and improve the wettability of the surface. We examine the effect of the presence of methylene linkers on the orientation of the molecule within the SAM. 3,4,5-Trimethoxythiophenol (TMP-SH) and 3,4,5-trimethoxybenzylthiol (TMP-CH2-SH) were first subjected to computational analysis, predicting work function shifts of -430 and -310 meV. Contact angle measurements show an increase in the wetting envelope compared to that of pristine gold. Infrared (IR) measurements show tilt angles of 22 and 63°, with the methylene-linked molecule (TMP-CH2-SH) attaining a flatter orientation. The actual work function shift as measured with photoemission spectroscopy (XPS/UPS) is even larger, -600 and -430 meV, respectively. The contact resistance between gold electrodes and poly[N,N'-bis(2-octyldodecyl)-naphthalene-1,4:5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene) (Polyera Aktive Ink, N2200) in n-type OFETs is demonstrated to decrease by 3 orders of magnitude due to the use of TMP-SH and TMP-CH2-SH. The effective mobility was enhanced by two orders of magnitude, significantly decreasing the contact resistance to match the mobilities reported for N2200 with optimized electrodes.

Analysis of the glass–crystal transformation kinetics by means of the theoretical method developed (TMD) under both non-isothermal and isothermal regimes. Application to the crystallization of the Ag0.16As0.34Se0.50 glassy alloy

This paper analyzes the glass–crystal transformation kinetics of the Ag0.16As0.34Se0.50 glassy semiconductor, both under non-isothermal and isothermal regimes, by means of the theoretical method developed (TMD). The quoted method allows evaluate the characteristic kinetic parameters corresponding to the transformation studied from the experimental data obtained by differential scanning calorimetry (DSC) technique in both regimes. For these regimes, the semiconductor analyzed presents an exothermic peak of crystallization. Following TMD, it has been obtained that the thermal process type is “site saturation”. Moreover, under non-isothermal conditions, it has been found that the crystal growth is three-dimensional, whereas, under isothermal conditions, the crystal growth is one-dimensional. Likewise, the value of the activation energy obtained for the non-isothermal regime is considerably higher than the value of this quantity determined for the isothermal regime, which is an indication that different mechanisms of growth and impingement operate upon non-isothermal crystallization as compared with isothermal crystallization. It is important to indicate that, in both regimes, the experimental curve of the actual volume fraction transformed shows a satisfactory agreement with the theoretical curve corresponding to the considered method, confirming the reliability of this method in order to analyze the transformation kinetics of the Ag0.16As0.34Se0.50 glassy alloy, both in non-isothermal and isothermal regimes.

Understanding the structure and electronic properties of N-doped graphene nanoribbons upon hydrogen saturation

Structures and electronic properties of zigzag graphene nanoribbon (ZGNR) with pyridine (3NV-ZGNR) functionalized by Scandium (Sc) at the edge were studied through quantum chemical calculations in the formalism of density-functional theory (DFT). Pyridine-like nitrogen defects is very crucial for enhancing the Sc atom binding to the defects and is thermodynamically favoured. During Sc decoration of ZGNR there is a shift from 0.35 eV small gap semiconductor regime to that of a metal which can be used for band gap tuning by controlled saturation of Sc. ZGNR decorated with Sc can attract H2. Upon saturation of multiple H2 in quasi-molecular fashion, the metallic character is converted to semiconductors of small gap of 0.10 eV, which are predicted to be interesting materials not only for hydrogen storage but also for their band gap engineered properties.

Study of microstructure and semiconductor to metallic conductivity transition in solid state sintered Li0.5Mn0.5Fe2O4−δ spinel ferrite

Li0.5Mn0.5Fe2O4 ferrite has been prepared by solid state sintering route. XRD pattern showed single phased cubic spinel structure. The samples exhibited typical character of plastoferrite with ring shaped surface microstructure. New feature observed in the present ferrite is the frequency activated conductivity transition from semiconductor to metallic state above 800 K. The increase of conductivity with frequency in the semiconducting regime follows Jonscher power law, while decrease of conductivity in metallic regime obeys Drude equation. The conductivity in semiconductor regime has been understood by hopping mechanism of localized charge carriers among the cations in B sites of cubic spinel structure. At higher temperatures, overlapping of electronic orbitals from neighbouring ions and free particle like motion of lighter Li+ ions among interstitial lattices contributed metallic conductivity. The samples provided evidence of localized nature of the charge carriers at lower temperatures and increasing delocalized character with the increase of measurement temperature. From application point of view, such ferrites behave as semiconductor at low temperature and allow electromagnetic wave to pass through, but transform into a metallic reflector with negative dielectric constant at high temperature.

Charge transport in organic semiconductors: Assessment of the mean field theory in the hopping regime

The performance of the mean field theory to account for charge transfer rate in molecular dimers and charge transport mobility in molecular stacks with small intermolecular electronic coupling and large local electron-phonon coupling (i.e., in the hopping regime) is carefully investigated against various other approaches. Using Marcus formula as a reference, it is found that mean field theory with system-bath interaction and surface hopping approaches yield fully consistent charge transfer rates in dimers. However, in contrast to the dimer case, incorporating system-bath interaction in the mean field approach results in a completely wrong temperature dependence of charge carrier mobility in larger aggregates. Although the mean field simulation starting from the relaxed geometry of a charged molecule and neglecting system-bath interaction can reproduce thermally activated transport, it is not able to characterize properly the role of additional nonlocal electron-phonon couplings. Our study reveals that the mean field theory must be used with caution when studying charge transport in the hopping regime of organic semiconductors, where the surface hopping approach is generally superior.