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VO2 films prepared on amorphous substrates are generally nanocrystalline and have low semiconductor–metal transition (SMT) properties. The current research reported that both the undoped and Nb‐doped VO2 films, composed of differently‐orientated single‐crystalline domains, can be prepared on amorphous quartz substrates through facile annealing of sputtered precursors, with their structures, electric properties, optical properties, and thermochromism being systematically studied. The results showed that the resistance change of the undoped VO2 films across the SMT was ∼3000 times. The SMT critical temperature (Tc) of the sc‐domain VO2 films can be decreased to room temperature by the Nb doping, and the resistance change across the SMT could remain approximately two orders of magnitude higher when the Tc was decreased to 27°C. It was seen that both the semiconductor‐phase undoped and Nb‐doped VO2 films featured defect‐activated conductances, with the Nb donor ionization energy being 0.14–0.17 eV. The absorption coefficients of the VO2 films were obtained by fitting the transmittance and reflectance optical spectra with the Drude‐Lorentz dispersion model, and the Nb doping widened and merged the d|| and π* bands, with both the optical and physical gaps being decreased due to the band widening. The thermochromic performances were also studied, and the result showed that the solar light modulation could remain 90% of the undoped film when the Tc was decreased to 27°C by the Nb doping, so the Nb‐doped VO2 films can be a good candidate for preparing thermochromic energy‐saving coatings. [ABSTRACT FROM AUTHOR]

The 2H‐MoTe2 is a well‐known layered 2D semiconductor that is considered as a promising material for next‐generation microelectronic and optoelectronic devices. Te‐deficiency‐induced defective structures, like Te vacancy and mirror twin boundary (MTB), would be generated at elevated temperatures. However, the temperature‐dependent evolution of such defects and their influence on the macroscopic electrical transport property of 2H‐MoTe2 is unclear. Herein, the semiconductor–metal transition phenomenon in 2H‐MoTe2−x mediated by the evolving disordered MTB network with increasing Te deficiency is reported on. The samples are grown by molecular beam epitaxy, while the Te deficiency is tuned by post‐growth flash annealing in ultra‐high vacuum. Low‐temperature scanning tunneling microscope investigation discloses the medium‐range disorder evolution of the MTB network incorporated in the 2H‐MoTe2, which eventually transforms to an ordered metallic Mo5Te8 metastable phase. The scanning tunneling spectroscopy shows rich in‐gap states localized at the MTBs, which provide a conducting channel in the semiconductor. The ultra‐high vacuum in situ transport measurement shows a gradual decrease of resistance of the sample upon flash annealing from 50 to 480 °C, confirming the influence of Te deficiency on the transport property, which would play an essential role in the device performance and durability. [ABSTRACT FROM AUTHOR]

The 2H‐MoTe2 is a well‐known layered 2D semiconductor that is considered as a promising material for next‐generation microelectronic and optoelectronic devices. Te‐deficiency‐induced defective structures, like Te vacancy and mirror twin boundary (MTB), would be generated at elevated temperatures. However, the temperature‐dependent evolution of such defects and their influence on the macroscopic electrical transport property of 2H‐MoTe2 is unclear. Herein, the semiconductor–metal transition phenomenon in 2H‐MoTe2−x mediated by the evolving disordered MTB network with increasing Te deficiency is reported on. The samples are grown by molecular beam epitaxy, while the Te deficiency is tuned by post‐growth flash annealing in ultra‐high vacuum. Low‐temperature scanning tunneling microscope investigation discloses the medium‐range disorder evolution of the MTB network incorporated in the 2H‐MoTe2, which eventually transforms to an ordered metallic Mo5Te8 metastable phase. The scanning tunneling spectroscopy shows rich in‐gap states localized at the MTBs, which provide a conducting channel in the semiconductor. The ultra‐high vacuum in situ transport measurement shows a gradual decrease of resistance of the sample upon flash annealing from 50 to 480 °C, confirming the influence of Te deficiency on the transport property, which would play an essential role in the device performance and durability.

Two-dimensional electron gas (2DEG) at the (100) KTaO3(KTO) surface and interfaces has attracted extensive interest because of its abundant physical properties. Here, light illumination-induced semiconductor–metal transition in the 2DEG at the KTO surface was investigated. 2DEG was formed at the surface of KTO by argon ion bombardment. The 2DEG prepared with a shorter bombardment time (300 s) exhibits semiconducting behavior in the range of 20~300 K in the dark. However, it shows a different resistance behavior, namely, a metallic state above ~55 K and a semiconducting state below ~55 K when exposed to visible light (405 nm) with a giant conductivity increase of about eight orders of magnitude at 20 K. The suppression of the semiconducting behavior is found to be more pronounced with increasing light power. After removing the illumination, the resistance cannot recover quickly, exhibiting persistent photoconductivity. More interestingly, the photoresponse of the 2DEG below 50 K was almost independent of the laser wavelength, although the photon energy is lower than the band gap of KTO. The present results provide experimental support for tuning oxide 2DEG by photoexcitation, suggesting promising applications of KTO-based 2DEG in future electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Motivated by the wide-band-gap semiconductor properties of Zn-monochalcogenides (Zn-X; X:S, Se and Te), especially for their crucial industrial applications, we use a first-principles approach to investigate the B3 (zinc blende type) to B1 (rock salt type) structural transitions in this series of compounds as a function of pressure and temperature. Under static conditions (i.e., T = 0 K), the transition pressure is found to steadily drop from ZnS to ZnTe via intermediate ZnSe. Our calculations within quasi-harmonic approximation yield negative Clapeyron slopes of the B3–B1 phase boundaries for all the three compounds, where ZnTe has the highest negative slopes. We also present a completely new set of calculations for the thermoelasticity of Zn-X phases in the temperature range 0–1100 K. This article then addresses how the B3–B1 phase transitions can influence the mechanical as well as electronic properties of Zn-X. This phase transition always results in a softening of their elastic constant C12; however, C11 and C44 get stiffened. The same structural transition switches a semiconductor to conductor-type electronically favorable transition, as inferred from their high-pressure electronic structure. Among the three Zn-X compounds, ZnTe becomes the most metallic phase following the B3–B1 transition. Our findings offer a novel explanation for the complete loss of semiconductor property of these monochalcogenides at elevated pressures. [ABSTRACT FROM AUTHOR]

By using first-principles calculations in line with density functional theory, the structural, electronic, optical, elastic and mechanical properties of pure and substituted PbHfO3 have been investigated. Here the substituated elements are Bi, Sn and Tl. To express the effect of substitution, all computations are determined by a generalized gradient approximation and an ultra-soft pseudopotential. In the current research, Bi, Sn, and Tl are substituted at the Pb-site which is preferable to the Hf-site due to the stability of cubic perovskites. According to the structural properties, cubic to pseudo-cubic transition is obvious. Moreover, the decline in band gap is noticed, when specific concentration of impurities (Bi, Sn) atoms are substituated. However, substitution of Tl increases the gap between conduction/valence bands. It is not just the change in band gap that increases or decreases, the nature is also shifted from indirect to direct. Moreover, this behaviour is explained by the different density of states. Since then, a significant alteration in band gap is mainly due to the p-states. As a result, our material is a favourable choice for optoelectronic devices. The changes in electronic characteristics also influence the optical properties including the complex dielectric functions, absorption, reflectivity, loss function, and refractive index. We also explored the elastic constants (Cij), stability criteria, and mechanical attributes like Bulk modulus (B), Young's modulus (Y), shear modulus (G), Poisson's ratio (υ) and anisotropic factor (A). Furthermore, we came to the conclusion that our material is elastically stable, ductile and stiff. [ABSTRACT FROM AUTHOR]

By using first-principles calculations in line with density functional theory, the structural, electronic, optical, elastic and mechanical properties of pure and substituted PbHfO3 have been investigated. Here the substituated elements are Bi, Sn and Tl. To express the effect of substitution, all computations are determined by a generalized gradient approximation and an ultra-soft pseudopotential. In the current research, Bi, Sn, and Tl are substituted at the Pb-site which is preferable to the Hf-site due to the stability of cubic perovskites. According to the structural properties, cubic to pseudo-cubic transition is obvious. Moreover, the decline in band gap is noticed, when specific concentration of impurities (Bi, Sn) atoms are substituated. However, substitution of Tl increases the gap between conduction/valence bands. It is not just the change in band gap that increases or decreases, the nature is also shifted from indirect to direct. Moreover, this behaviour is explained by the different density of states. Since then, a significant alteration in band gap is mainly due to the p-states. As a result, our material is a favourable choice for optoelectronic devices. The changes in electronic characteristics also influence the optical properties including the complex dielectric functions, absorption, reflectivity, loss function, and refractive index. We also explored the elastic constants (Cij), stability criteria, and mechanical attributes like Bulk modulus (B), Young's modulus (Y), shear modulus (G), Poisson's ratio (υ) and anisotropic factor (A). Furthermore, we came to the conclusion that our material is elastically stable, ductile and stiff. [ABSTRACT FROM AUTHOR]

Two-dimensional electron gas (2DEG) at the (100) KTaO3(KTO) surface and interfaces has attracted extensive interest because of its abundant physical properties. Here, light illumination-induced semiconductor–metal transition in the 2DEG at the KTO surface was investigated. 2DEG was formed at the surface of KTO by argon ion bombardment. The 2DEG prepared with a shorter bombardment time (300 s) exhibits semiconducting behavior in the range of 20~300 K in the dark. However, it shows a different resistance behavior, namely, a metallic state above ~55 K and a semiconducting state below ~55 K when exposed to visible light (405 nm) with a giant conductivity increase of about eight orders of magnitude at 20 K. The suppression of the semiconducting behavior is found to be more pronounced with increasing light power. After removing the illumination, the resistance cannot recover quickly, exhibiting persistent photoconductivity. More interestingly, the photoresponse of the 2DEG below 50 K was almost independent of the laser wavelength, although the photon energy is lower than the band gap of KTO. The present results provide experimental support for tuning oxide 2DEG by photoexcitation, suggesting promising applications of KTO-based 2DEG in future electronic and optoelectronic devices.

Pressure dependent physical properties of binary SnS compound have been studied using the density functional theory based methodology. The computed elastic constants reveal that SnS is stable mechanically and is brittle under ambient conditions. With increasing pressure, the compound becomes ductile. The Poisson’s ratio and Cauchy pressure also indicate brittle-ductile transition when pressure increases. The hardness of SnS increases significantly with pressure. The compound possesses elastic anisotropy. The ground state electronic band structure is semiconducting with a small band gap. The band structure becomes metallic under pressure. The bands crossing the Fermi level become more and more dispersive with the increase in pressure while the electronic correlations decrease as pressure is raised. Both the Debye temperature and the phonon thermal conductivity of SnS increase sharply with pressure. The melting temperature of the compound is low. Mixed bonding characteristics are found with ionic and moderate covalent contributions. SnS is a good absorber of ultraviolet light. The reflectivity of the material increases with the increase in the pressure. The reflectivity is nonselective over a wide spectral range. The low energy refractive index is high. The low band gap energy under ambient conditions makes SnS suitable for photovoltaic applications. Non-selective and high reflectivity of SnS indicates that this compound can be used as a coating material to reduce solar heating. Unlike structural anisotropy, the optical anisotropy of SnS is low.

Carbynes have gained highlight due to their unique properties and applications in molecular electronics exhibiting resonant tunnel effect. We studied the electronic transport through a molecular tunnel junction composed of two polyyne-type carbynes separated by distance (4 Å ≥ dn ≥ 2.1 Å) higher than bond length (dn > dC–C) ranging from 0.1 Å based on Density Functional Theory/Non-Equilibrium Green's Function (DFT/NEGF). The frontier molecular orbitals and bond lengths of the polyyne (dC–C ≈ 1.36 Å, dC≡C ≈ 1.26 Å) at 0.0 V become equal to those in cumulene-type carbynes (dC=C ≈ 1.28 Å) at 0.9 V occurring a semiconductor–metal transition for dn < 4 Å. I–V (dI/dV–V) curve presents switching behaviour up to 0.6 V and after a diode behaviour favoured as dn decreases, that is, to 4.0 Å is 3.3 nA (5 nS) while for 2.1 Å is 3750 nA (1500 nS) showing metallic nature. The log(I)–V [log(dI/dV)–V] curve exhibits the behaviour for low bias voltage while the I–dn curve is exhibited for high bias voltage. The exponential expression for G(d) fits perfectly with the Gmax result obtained with DFT/NEGF calculations. Transition Voltage Spectroscopy (TVS) confirms rectangular barrier and direct tunneling for Vd–s < ϕB/e playing a tunneling rule for electronic transport of these 1-D systems. [ABSTRACT FROM AUTHOR]

This paper deals with the study of the physical properties of ZnO/ZnNb 2 O 6 /Nb 2 O 5 composite. X-ray diffraction (XRD) proves the coexistence of hexagonal ZnO, tetragonal Nb 2 O 5 and orthorhombic ZnNb 2 O 6. Scanning electron microscopy (SEM) observations reveals heterogenic distribution of grains with average size of about 456 nm. The dielectric measurements are performed in 20 Hz–1MHz frequency range between 150 °C and 350 °C. Theoretical fit demonstrates that the electric resistivity, associated to grains and grain boundaries, decreases as a function of temperature up to 275 °C. At 275 °C, the composite presents a semiconductor-metal transition, confirmed by the temperature-dependence of DC conductivity. Moreover, the AC conductivity variations suggest that the AC conduction mechanisms are explained by the Quantum-Mechanical Tunneling (QMT) model below 275 °C and the Non-Overlapping Small Polaron Tunneling (NSPT) one above 275 °C. Also, the activation energies, related to dielectric relaxation processes and DC conductivity, are almost equal: E a ~ 0.53eV in the interval 150 °C < T < 275 °C, and E a ~ −0.47eV for T > 275 °C. Moreover, the permittivity variations show the existence of interfacial Maxwell-Wagner-Sillars (MWS) and dipolar polarization. [ABSTRACT FROM AUTHOR]

Pseudobrookite of general formula Pb 0·5 Ba 0·5 Fe 2 O 5 was synthesized by the sol–gel route. X-ray diffraction confirms the orthorhombic Pnma space group of our sample. UV–Vis absorption spectroscopy was used to characterize this material's optical properties. We used the Tauc model and absorption measurements to estimate the direct optical band gap at 3.53 eV. We also calculate the Urbach energy, the optical extinction coefficient, and the refractive index. In addition, the skin depth, optical conductivity, and Cauchy parameters were investigated in relation to the incident photon's wavelength. Electrical conductivity data flow the Jonscher's power law and show that PBFO has two different conducts; Semiconductor behavior in the temperatures region [400 K–520 K]. Then, a metallic trend was detected beyond T S-M = 520 K. The correlated barrier hopping (CBH) model is the appropriate model to describe the conduction process in low temperature range. On the other hand, the conduction is ensured by the non-overlapping small polaron tunneling (NSPT) at high temperature zone. The scaling study shows that the conductivity spectra deviate from Summerfield and Ghosh scaling. The random barrier model (RBM) is employed to correct the Summerfield approach and we note that the conductivity isotherms are combined into a single master curve. The estimated activation energies values from dc-conductivity, hopping frequency and relaxation time are very close. The behavior of dielectric parameters was examined using the Maxwell-Wagner theory of interfacial polarization. The dielectric-relaxation phenomenon is shown by the behaviors of imaginary parts of impedance (Z″) and modulus (M″). The ideal electrical equivalent circuit for simulating the Nyquist curves (i.e. Z′′(Z′)) for our pseudobrookite is (R g + R gb //CPE gb). Finally, the entropy (ΔS), and enthalpy (ΔH) were established as thermodynamic parameters. • Pseudobrookite obtained by sol-gel. • Direct bandgap E g = 3.53 eV. • Dielectric results show two states Semiconductor and metallic. [ABSTRACT FROM AUTHOR]

Abstract The structural, electrical, and magnetic properties of armchair black phosphorene nanoribbons (APNRs) edge-functionalized by transitional metal (TM) elements V, Cr, and Mn were studied by the density functional theory combined with the non-equilibrium Green’s function. Spin-polarized edge states introduce great varieties to the electronic structures of TM-APNRs. For APNRs with Mn-stitched edge, their band structures exhibit half-semiconductor electrical properties in the ferromagnetic state. A transverse electric field can then make the Mn-APNRs metallic by shifting the conduction bands of edge states via the Stark effect. The Mn/Cr-APNR heterojunction may be used to fabricate spin p-n diode where strong rectification acts only on one spin.

Abstract We have studied the electronic structure and the current-voltage (I-V) characteristics of one-dimensional InSe nanoribbons using the density functional theory combined with the nonequilibrium Green’s function method. Nanoribbons having bare or H-passivated edges of types zigzag (Z), Klein (K), and armchair (A) are taken into account. Edge states are found to play an important role in determining their electronic properties. Edges Z and K are usually metallic in wide nanoribbons as well as their hydrogenated counterparts. Transition from semiconductor to metal is observed in hydrogenated nanoribbons HZZH as their width increases, due to the strong width dependence of energy difference between left and right edge states. Nevertheless, electronic structures of other nanoribbons vary with the width in a very limited scale. The I-V characteristics of bare nanoribbons ZZ and KK show strong negative differential resistance, due to spatial mismatch of wave functions in energy bands around the Fermi energy. Spin polarization in these nanoribbons is also predicted. In contrast, bare nanoribbons AA and their hydrogenated counterparts HAAH are semiconductors. The band gaps of nanoribbons AA (HAAH) are narrower (wider) than that of two-dimensional InSe monolayer and increase (decrease) with the nanoribbon width.

High-performance vanadium dioxide (VO 2) thin films with high luminous transmittance and solar modulation ability were successfully fabricated on Zr x O y /glass substrate by pulsed laser deposition. By controlling the growth temperature of the buffer layer, the stoichiometry and crystal structure of Zr x O y buffer layer can be converted from cubic Zr 2 O phase to monoclinic ZrO 2 phase. Through such a transformation, the luminous transmittance (T lum), solar modulation ability (Δ T sol), the transition temperature and the width of thermal hysteresis loop have been tuned without diminishing the thermochromic property. It is found that the insertion of ZrO 2 layer results in a remarkable enhancement of the luminous transmittance and the solar modulation ability when compared to single-layer VO 2 film. The findings in the present work may provide some new strategies for the commercialization of VO 2 films in the field of smart energy-efficient windows. • The ZrO2 film with monoclinic crystal structure was used as the buffer layer in the preparation of high-quality VO2 films by Pulsed Laser Deposition. • The glass/ZrO2/VO2 composite films with impressive photoelectric properties were obtained. [ABSTRACT FROM AUTHOR]

Highlights • Pressure-dependent electronic properties of polycrystalline β -Ag 0.33 V 2 O 5 is investigated for the first time. • An semiconductor-metallic state transition occurs at 4.5 GPa and room temperature. • High temperature/pressure treatment can markedly reduce S-M transition pressure to 1.5 GPa. Abstract The pressure-dependent electronic properties of polycrystalline β -Ag 0.33 V 2 O 5 were investigated and a discontinuous change of electrical resistance is found at around 4.5 GPa, where semiconductive-like decreasing trend before 4.5 GPa and a metallic-like increasing trend after 4.5 GPa with increasing temperature was observed. Furthermore, high temperature/pressure treatment can markedly reduce the semiconductor-metal (S-M) transition pressure to around 1.5 GPa. The results indicate a promising way for engineering the electronic properties of polycrystalline Ag 0.33 V 2 O 5 , and this pressure/temperature induced semiconductor-metal switch may have potential applications in electronics field. [ABSTRACT FROM AUTHOR]

The electronic structure of chair-type biphenylene ribbons is studied within the framework of the Hubbard Hamiltonian in the approximation of static fluctuations. An expression is obtained for the Fourier transform of the Green's functions, whose poles determine the spectrum of elementary excitations. The energy spectrum of biphenylene ribbons indicates that nanoribbons with a width of 6, 9, 12, 15, 18 carbon atoms are in the semiconductor state. Densities of state of electrons of biphenylene ribbons of various widths are presented in comparison with the results of experimental measurements of differential conductance of biphenylene ribbons. It is shown that the width of the band gap decreases exponentially with an increase in the width of the biphenylene ribbon. Ribbons with a width of 21 carbon atoms or more are in the metallic state. [ABSTRACT FROM AUTHOR]

By merging a b i n i t i o calculations and particle-swarm optimization algorithm, we have predicted two new phases of thorium dichalcogenides ThX 2 (X = S, Se and Te) in the F m 3 ¯ m and I 4 / m m m symmetry. The F m 3 ¯ m phase is proved to be the ground-state phase of ThS 2 and ThSe 2 . The calculated enthalpies indicate that the F m 3 ¯ m to P n m a phase transition pressures are about 2.3 GPa and 0.35 GPa for ThS 2 and ThSe 2 , respectively; and the P n m a to I 4 / m m m phase transition pressures are about 37 GPa, 17 GPa and 2 GPa for ThS 2 , ThSe 2 and ThTe 2 , respectively. The phonon dispersion curves and elastic constants suggest that all of the F m 3 ¯ m , P n m a and I 4 / m m m phases are dynamically and mechanically stable. The electronic calculations show that a pressure-induced semiconductor to metal transitions of these three compounds will occur following the P n m a to I 4 / m m m phase transition. Our calculated bulk modulus B 0 and elastic constants C i j of the various phases of these compounds show that the materials become softer one after another from ThS 2 to ThSe 2 and then to ThTe 2 . [ABSTRACT FROM AUTHOR]

While SmS thin films show an irreversible semiconductor-metal transition upon application of pressure, the switching characteristics can be modified by alloying with other elements, such as europium. This manuscript reports on the resistance response of tri-layer SmS/EuS/SmS thin films upon applying pressure and on the correlation between the resistance response and the interdiffusion between the layers. SmS thin films were deposited by e-beam sublimation of Sm in an H2S atmosphere, while EuS was directly sublimated by e-beam from EuS. Structural properties of the separate thin films were first studied before the deposition of the final nanocomposite tri-layer system. Piezoresistance measurements demonstrated two sharp resistance drops. The first drop, at lower pressure, corresponds to the switching characteristic of SmS. The second drop, at higher pressure, is attributed to EuS, partially mixed with SmS. This behavior provides either a well-defined three or two states system, depending on the degree of mixing. Depth profiling using x-ray photoelectron spectroscopy (XPS) revealed partial diffusion between the compounds upon deposition at a substrate temperature of 400 °C. Thinner tri-layer systems were also deposited to provide more interdiffusion. A higher EuS concentration led to a continuous transition as a function of pressure. This study shows that EuS-modified SmS thin films are possible systems for piezo-electronic devices, such as memory devices, RF (radio frequency) switches and piezoresistive sensors.

The electronic structures and transport properties in monolayer blue phosphorene nanoribbons (BPNRs) with transverse electric field have been studied by using density functional theory and nonequilibrium Green's functions method. The results show that the band gaps of BPNRs with both armchair and zigzag edges are linearly decreased with the increasing of the strength of transverse electric field. A semiconductor-metal transition occurs when the electric field strength reaches to 5 V/nm. The Stark coefficient presents a linear dependency on BPNRs widths, and the slopes of both zBPNRs and aBPNRs are 0.41 and 0.54, respectively, which shows a giant Stark effect occurs. Our studies show that the semiconductor-metal transition originates from the giant Stark effect. [ABSTRACT FROM AUTHOR]

We investigate a novel route for synthesis and laser-sintering of VO 2 thin films via solution-based polymer-assisted-deposition (PAD). By replacing the traditional solvent for PAD (water) with propylene glycol, we are able to control the viscosity and improve the environmental stability of the precursor. The solution stability and ability to control the viscosity makes for an ideal solution to pattern simple or complex shapes via direct-write methods. We demonstrate the potential of our precursor for printing applications by combining PAD with laser induced forward transfer (LIFT). We also demonstrate large-area film synthesis on 4 in. diameter glass wafers. By varying the annealing temperature, we identify the optimal synthesis conditions, obtaining optical transmittance changes of 60% at a 2500 nm wavelength and a two-order-of-magnitude semiconductor-to-metal transition. We go on to demonstrate two routes for improved semiconductor-to-metal characteristics. The first method uses a multi-coating process to produce denser films with large particles. The second method uses a pulsed-UV-laser sintering step in films annealed at low temperatures (<450° C) to promote particle growth and improve the semiconductor-to-metal transition. By comparing the hysteresis width and semiconductor-to-metal transition magnitude in these samples, we demonstrate that both methods yield high quality VO 2 with a three-order-of-magnitude transition. [ABSTRACT FROM AUTHOR]

The structural, optoelectronic, elastic and mechanical properties of pure, Ca-, Mg-, and Be-doped SrHfO 3 have been computed with CASTEP code based on density functional theory. The structure of SrHfO 3 remains cubic with 1.40% doping concentration of Ca, Mg and Be whereas it is altered in pseudo-cubic tetragonal at the doping concentration of 4.22% and 7.04%. Reduction in the electronic band gap is observed in all the doping concentrations. For detailed explanation of electronic band gap reduction density of states (DOS), partial DOS and elemental partial DOS have also been computed. DOS plays a very meaningful role in understanding the behavior of band gap at different doping. The impact of dopants on the optical properties of pure SrHfO 3 indicates the increment in refractive index (n), absorption (I), Loss function (L) and extinction coefficient (k) as well. For both cubic and tetragonal structures our compound shows mechanical stability in all doping percentages of Ca, Mg and Be other than the 1.40% of Mg and Be for cubic geometry. Over and above that to examine the mechanical properties of material like ductility and brittleness we have also computed the different characteristics such as Bulk modulus (B), Shear modulus (G), G / B ratio, Cauchy Pressure (CP) and Anisotropic factor (A). Interestingly, the material is purely ductile on all concentrations of Ca, Mg, and Be and shows brittleness only at the doping concentration of 1.40% of Ca. [Display omitted] • The GGA-PBE correlation functional is used to estimate the structural, electronic, optical, elastic and mechanical characteristics of SrHfO 3. • Cubic to pseudo-cubic phase transition is observed. • Band gap is direct in its nature except at 4.22% doping concentration. • Due to approaching trend of compound from semiconductor to conductor, makes it an excellent choice for various photovoltaic applications. • Mechanically SrHfO 3 has stable form, less compressible, ductile in nature and has anisotropic character. [ABSTRACT FROM AUTHOR]

[Display omitted] • The QLs-Al 2 O 3 with different stacking modes show different electronic properties. • The variable electronic properties of QLs-Al 2 O 3 depend on the interlayer charge transfer. • The transferred electrons in QLs-Al 2 O 3 flow from higher potential to lower potential. Two-dimensional (2D) quintuple-layer (QL) Al 2 O 3 with intrinsic out-of-plane polarization exhibit many interesting physical properties. We systematically study the structural and electronic properties of QL-Al 2 O 3 layers using the first-principles calculations. Our results show that polarized QL-Al 2 O 3 is semiconductor with an indirect bandgap. For few QLs-Al 2 O 3 system, its electronic properties can be either semiconductor or metal, depending on the stacking mode of each QL-Al 2 O 3. When the stacked 2QLs-Al 2 O 3 and 3QLs-Al 2 O 3 system possess the same polarization direction, they behave the metallicity with the presence of 2D electron gas and 2D hole gas at two separate surfaces. The metallicity originates from directly interlayer band alignment and from indirectly two-step interfacial charge transfer mechanism with an enhanced surface charge. While for the stacked 2QLs-Al 2 O 3 and 3QLs-Al 2 O 3 system with opposite polarization direction, the disappeared potential difference and interfacial charge transfer make them keep the semiconductor. The revealed semiconductor-metal transition mechanism in stacked QLs-Al 2 O 3 materials is also applicable to other 2D polarized van der Waals materials and heterostructures. [ABSTRACT FROM AUTHOR]

• Elastic, electronic, thermophysical, and optical properties of SnS compound investigated at different pressures. • SnS is mechanically stable in the pressure range 0–20 GPa, and undergoes brittle-ductile transition under pressure. • SnS is a direct band gap semiconductor in the ground state which becomes metallic under pressure. • SnS is a moderately machinable, soft, elastically anisotropic compound with low melting point. • The optical features of SnS are suitable for optoelectronic device applications. Pressure dependent physical properties of binary SnS compound have been studied using the density functional theory based methodology. The computed elastic constants reveal that SnS is stable mechanically and is brittle under ambient conditions. With increasing pressure, the compound becomes ductile. The Poisson's ratio and Cauchy pressure also indicate brittle-ductile transition when pressure increases. The hardness of SnS increases significantly with pressure. The compound possesses elastic anisotropy. The ground state electronic band structure is semiconducting with a small band gap. The band structure becomes metallic under pressure. The bands crossing the Fermi level become more and more dispersive with the increase in pressure while the electronic correlations decrease as pressure is raised. Both the Debye temperature and the phonon thermal conductivity of SnS increase sharply with pressure. The melting temperature of the compound is low. Mixed bonding characteristics are found with ionic and moderate covalent contributions. SnS is a good absorber of ultraviolet light. The reflectivity of the material increases with the increase in the pressure. The reflectivity is nonselective over a wide spectral range. The low energy refractive index is high. The low band gap energy under ambient conditions makes SnS suitable for photovoltaic applications. Non-selective and high reflectivity of SnS indicates that this compound can be used as a coating material to reduce solar heating. Unlike structural anisotropy, the optical anisotropy of SnS is low. [ABSTRACT FROM AUTHOR]

We demonstrate a room temperature semiconductor-metal transition in thin film MoTe2 engineered by strain. Reduction of the 2H-1T' phase transition temperature of MoTe2 to room temperature was realized by introducing a tensile strain of 0.2%. The observed first-order SM transition improved conductance ~10?000 times and was made possible by an unusually large temperature-stress coefficient, which results from a large volume change and small latent heat. The demonstrated strain-modulation of the phase transition temperature is expected to be compatible with other TMDs enabling the 2D electronics utilizing polymorphism of TMDs along with the established materials. [ABSTRACT FROM AUTHOR]

Cobalt nano-ferrite of formula Co 0·4 Fe 2·6 O 4 was successfully prepared by a surfactant-free solvothermal reaction. Powder X-ray Diffraction (PXRD) revealed a cubic spinel structure. Transmission Electron Microscopy (TEM) observations confirmed the presence of agglomerated nanoparticles of two different sizes and shapes. 57Fe Mössbauer Spectrometry (MS) studies suggested a cationic redistribution between tetrahedral and octahedral sites in the spinel lattice. The low-frequency dependence of the dielectric properties is significantly affected by the presence of all polarization phenomena, in particular the interface polarization, on the basis of the phenomenological theory of the Koop model and the Maxwell-Wagner approach. At low frequencies, a linear negative correlation between the imaginary part of the permittivity and the frequency in the logarithm scale is observed. This is attributed to a dc-conductivity process. Furthermore, the electrical modulus analysis shows both Debye and non-Debye dielectric relaxations. The complex impedance plots were analyzed using the equivalent circuit model; grain and grain boundaries effects coexist. In the conductivity spectra, three regions were detected. A single power law and a double power law were separately applied to resolve the grains and grain boundaries effects. This unusual conductivity behavior can be explained by the modification in microstructure as well as the variation in charge carrier mobility. All results were interpreted in terms of microstructure properties and correlated with the cationic distribution within the spinel structure. The close values of activation energies obtained from the impedance, modulus and ac-conductivity in different temperature regions confirmed that the transport is probably due to a hopping mechanism dominated by smaller amount of oxygen vacancies. [Display omitted] • Co 0·4 Fe 2·6 O 4 nanoparticles were prepared by a surfactant-free solvothermal method using benzyl alcohol as solvent. • Microstructure observations and 57Fe Mossbauer spectrometry study explain the electrical conductivity results. • Complex impedance plots highlight the grains and grain boundaries contributions to the dielectric response. • The Co 0·4 Fe 2·6 O 4 material can be classified as a high-k dielectrics suitable for gate dielectric applications. [ABSTRACT FROM AUTHOR]

The motive of this study is to offer a comprehensive evaluation of the structural, elastic, mechanical, anisotropic, electrical and optical characteristics of BaThO 3 under the pressure range of 0 GPa–113 GPa. There is no phase transformation and the structure remains cubic but a diminishment in lattice parameters is observed. The material is found to be mechanically stable, inflexible, rigid and has high resistance to shear stress by computing the various elastic and mechanical (bulk modulus, shear modulus and young's modulus) parameters. The Pugh/Frantsevich ratios, Cauchy pressure, Poisson's ratio, and the Kleinman's parameter have proved the ductility, metallic bond nature and high-pressure endurance of the material. Distinctive anisotropy factors are engaged to verify that a compound is anisotropic. When the electronic band structure (BS) is taken into consideration, a change from wide band gap semiconductor (3.174eV) to narrow band gap semiconductor (1.832eV) and eventually metal (0eV) is seen. The total density of states (TDOS), the partial density of states (PDOS) and elemental partial density of states (EPDOS) have all been estimated in order to investigate the electronic BS. To enforce the relevance of this material, the real ε 1 (ω) and imaginary ε 2 (ω) dielectric functions, absorption I (ω), refractive index n (ω), extinction coefficient k (ω), loss function L (ω), reflectivity R (ω) and real/imaginary conductivity have all been calculated. The static values of ε 1 (ω) and n (ω) increase with applied pressure. Since its absorption spectra are present in the UV range, this is the best material to utilize as a UV filter. Additionally, its high refractive index, absorption, reflectivity, and conductivity make it an excellent component in optoelectronic devices. [Display omitted] • No phase transition is observed and structure remains in cubic. • Different elastic constants have validated the mechanical stability of material. • Material is inflexible, rigid, resistant to shear stress, ductile, and has metallic bonding and high pressure endurance. • BaThO 3 is anisotropic and predicted by four different anisotropy factors. • Semiconductor to metal transition occurred i.e. (3.174eV–0eV). [ABSTRACT FROM AUTHOR]

Using first-principles calculations we show that the electronic properties of multi-layered phosphorene (thickness = 2, 4, and 6 layer) can be modulated by applying normal compressive strains (NCS). A small compressive strain (less than 1.5%) can trigger the direct-to-indirect band gap transition in these systems. With sufficient NCS, a semiconductor-metal transition (SMT) can be obtained, and the critical strain for the SMT gradually reduced with the increase of layer number. The decrease of inter-layer distance and P–P bond length induced by the NCS leads to these transitions. The HSE06 hybrid functional method is used to correct PBE gap. [ABSTRACT FROM AUTHOR]

Novel VO 2 (M)/SnO 2 heterostructured nanorods are prepared by combining the conventional hydrothermal synthesis method and post annealing process. The results reveal that the nanosized SnO 2 particles are not only successfully grown on the surface of the VO 2 nanorods but also uniformly distribute on VO 2 without aggregation. The existence of the SnO 2 nanoparticles inhibits the aggregation during the annealing process and widens the band gap of the VO 2 crystals from 0.75 to 1.7 eV. The two aspects can both improve the optical properties of the VO 2 (M)/SnO 2 composite film. The visible transmittance is up to 35.7% and the IR modulation at 2500 nm is more than 56%, which were much higher than the pure VO 2 (M) film. In addition, the SnO 2 layer could reduce the width of the hysteresis from 17.8 to 10.7 °C caused by Sn-doping and enhance the sensitivity. We believe that the VO 2 (M)/SnO 2 heterostructured coating is a good candidate for smart windows. [ABSTRACT FROM AUTHOR]

VO2 thin films have been successfully deposited on Pt(111)/Ti/SiO2/Si substrate by means of reactive magnetron sputtering technique. The IR reflectance of the as-prepared films exhibited a big contrast (∼50%) between the room temperature (25°C) and high temperature (100°C) owing to the fancy semiconductor-metal transition of VO2 thin film. Nevertheless, the initial resistance was very low and the transition cannot be triggered by the electrical field. Authors believe that the rather poor electrical switching behaviour was connected to the leakage current from the large grain boundaries and pores in the surface of the VO2 thin film. This study may provide insights for VO2 films grown on Pt(111)/Ti/SiO2/Si substrates and suggest that Pt layers can serve as a suitable substrate of VO2 films for optical switching devices but not for electrical switching ones. [ABSTRACT FROM AUTHOR]

Methane (CH4) gas sensing properties of novel vanadium dioxide (VO2) nanostructured films is reported for the first time. The single phase nanostructures are synthesized by pulsed dc-magnetron sputtering of V target followed by oxidation in O2 atmosphere at 550°C. The partial pressure of O2 is controlled to obtain stoichiometric VO2 with the samples showing rutile monoclinic crystalline symmetry and regions of rod shaped nano-architectures. These nanostructured films exhibit a reversible semiconductor to metal transition in the temperature range of 60–70°C. Gas sensing experiments are carried out in the temperature span from 25°C to 200°C in presence of CH4. These experiments reveal that the films respond very well at temperatures as low as 50°C, in the semiconducting state. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline vanadium dioxide (VO2) thin films were grown on glass substrates by using reactive direct current magnetron sputtering and in situ thermal treatments at low preparation temperatures (≤350°C). The VO2 thin films were characterized by grazing-incidence X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy and spectroscopic ellipsometry (SE). The semiconductor-metal transition (SMT) characteristics of the films were investigated by four-point probe resistivity measurements and infrared spectrometer equipped with heating pads. The testing results showed that the crystal structure, morphology, grain size and semiconductor-metal transition temperature (T SMT) significantly changed as the film thickness decreased. Multilayer structures were observed in the particles of thinner films whose average particle size is much larger than the film thickness and average VO2 grain size. A competition mechanism between the suppression effect of decreased thickness and coalescence of nanograins was proposed to understand the film growth and the formation of multilayer structure. The value of T SMT was found to decrease as average VO2 grain size became smaller, and SE results showed that small nanograin size significantly affected the electronic structure of VO2 film. [Copyright &y& Elsevier]

Crystalline vanadium dioxide (VO2) thin films were prepared by annealing amorphous VO2 films which were deposited by atomic layer deposition on a SiO2 substrate. A large influence of the oxygen partial pressure in the annealing ambient was observed by means of in-situ X-ray diffraction. In the range between 1 and 10Pa of oxygen the interesting VO2(R) phase crystallized near 450°C. Between 2 and 10Pa of oxygen, metastable VO2(B) was observed as an intermediate crystalline phase before it transformed to VO2(R). Anneals in inert gas did not show any crystallization, while oxygen partial pressures above 10Pa resulted in oxidation into the higher oxide phase V6O13. Film thickness did not have much effect on the crystallization behavior, but thinner films suffered more from agglomeration during the high-temperature crystallization on the SiO2 substrate. Nevertheless, continuous polycrystalline VO2(R) films were obtained with thicknesses down to 11nm. In the case where VO2(R) was formed, the semiconductor–metal transition was observed by three complementary techniques. This transition near 68°C was characterized by X-ray diffraction, showing the transformation of the crystal structure, by spectroscopic ellipsometry, mapping optical changes, and by sheet resistance measurements, showing resistance changes larger than 2 orders of magnitude between the low-temperature semiconducting state and the high-temperature metallic state. [ABSTRACT FROM AUTHOR]

Phenomenologically, a semiconductor-metal transition is characterized by a sudden change in electrical properties but also in optical behaviours, as a consequence of a change in electron behaviour. The ability to induce a reversible semiconductor-metal transition in a material by varying conditions such as applied temperature or electrical field, results in attractive changes in properties that have fuelled the curiosity of scientists. In this paper, we discuss the interest of such materials exhibiting the reversible semiconductor-metal transition in the development of the next generation of optical Bly-ray discs (BD), the so-called super-resolution near field structure (super-RENS) discs and we show that InSb semiconductor material exhibits huge variations of its optical properties during the optically (thermally)-induced solid-to-liquid change corresponding to a semiconductor-metal transition. First success in the video playback on HDTV (High Definition TeleVision) display from 50 GB (BD capacity ×2) InSb-based super-RENS-ROM discs including a high definition video content with 1920 × 1080 pixels was realized in September 2009 by the super-RENS consortium joining three partners: AIST (National Institute of Advanced Industrial Science and Technology), Mitsubishi Electric Co. and LETI. [ABSTRACT FROM AUTHOR]

The effect of laser and magnetic field on the semiconductor-metal transition in a Cd1-x2Mnx2Te/Cd1-x1Mnx1Te/Cd1-x2Mnx2Te quantum well has been investigated using variational principle in effective mass approximation for smaller Mn composition. The effect of non parabolicity of the conduction band has been included in our calculation. The results are presented and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Ge1Sb2Te4 is one of the most commonly used phase change materials, due to the large optical and electrical contrast between a metastable crystalline phase and the amorphous phase. We use ab initio molecular dynamics to generate an amorphous Ge1Sb2Te4 structure. By analysing the distance distributions, we show that the structure can be analysed in terms of 21% of tetrahedrally coordinated Ge atoms and 79% of 3-fold Ge atoms. These are involved in distorted octahedral shells with bond length correlations that are similar to the a-GeTe structure as a consequence of a Peierls-distortion. The electronic properties are shown to be in reasonable agreement with the experiment with an electronic gap of 0.45eV with. The optical conductivity curve is also in agreement with the experiment, with a maximal conductivity at an energy of ∼3eV. [Copyright &y& Elsevier]

Abstract: We provide a detailed physical discussion of the existence of a quantum critical point (QCP) at the metallization threshold of an almost stoichiometric magnetite, with the critical pressure . A presence of an additional crossover or a critical line separating metallic and semiconducting states is proposed. A connection of the critical behavior to that of a spinless-fermion model with coupling of fermions to the lattice distortion is outlined. [Copyright &y& Elsevier]

Abstract: We demonstrate laser induced semiconductor–metal transition through an abrupt change in diamagnetic susceptibility of a donor at critical concentration in a GaAs/Al x Ga1−x As Quantum Well for finite barrier model in the effective mass approximation using variational principle. We have considered Anderson‘s localization due to the random distribution of impurities in our calculation. The nonparabolicity of the conduction band is also considered. Our results without laser field agree with the earlier theoretical results and also with the recent experimental results. [Copyright &y& Elsevier]

Abstract: Ti-doped ZnO films were deposited onto Corning 7059 glass substrates by simultaneous RF sputtering of Zn and DC magnetron sputtering of Ti. In this work, X-ray diffraction (XRD), electrical resistivity, X-ray absorption spectroscopy (XAS), optical transmission spectrum, and Hall-effect measurements were utilized in order to study the properties of the Ti-doped ZnO films. The resistivities of the ZnO: Ti films were reduced to a value of 3.82×10−3 Ω cm, and a metallic conduction behavior was observed in the ZnO: Ti films with Ti=1.3%. The enhancement of conductivity and the semiconductor–metal transition are likely attributed to the increase in the free carrier concentration, along with the band-gap shrinkage effects caused by Ti doping. [Copyright &y& Elsevier]

Abstract: We demonstrate semiconductor–metal transition through diamagnetic susceptibility of a donor in a GaAs/Al x Ga1− x As quantum well for both infinite and finite barrier models. We have also considered the non-parabolicity of the conduction band in our calculation. Our results agree with the earlier theoretical result and also with the recent experimental result. [Copyright &y& Elsevier]

This study develops a variational approach to calculate the binding energy of a shallow hydrogenic impurity in a n-doped In0.53Ga0.47As/InP single quantum well. Using a proper trial wavefunction, both Schro¨dinger and Poisson equations were solved simultaneously within the effective mass approximation, taking into account finite well barriers, finite temperatures, and different effective masses and dielectric constants along the growth direction. Band bending, screening, and many-body effects were considered and it is found these effects reduce drastically the impurity binding energy and lead to the vanishing of this energy when the 2DEG density reaches a critical value. Our results show that such a vanishing occurs even for very thin quantum wells, contrarily to recent calculations developed for GaAs/AlGaAs quantum wells. [Copyright &y& Elsevier]

Semiconductor–metal transition in a square quantum wire of the GaAs/GaAlAs system is investigated within the effective mass approximation. Vanishing of the donor ionization energy as a function of well width and donor concentration suggests that no transition is possible below a well width of 7 nm. Critical impurity concentrations at which the transition occurs increase with reduction in well width. The effects of Anderson localization and correlation in the Hubbard model are included in a simple way. In general, the critical concentration is one order higher in the square quantum wire system when compared to a quantum well case for lower well widths. When well width is increased it reaches the bulk value in both the cases. The critical concentration is enhanced when a random distribution of impurities is considered. [Copyright &y& Elsevier]