Electrically Tunable Energy Bandgap in Dual-Gated Ultra-Thin Black Phosphorus Field Effect Transistors

The energy bandgap is an intrinsic character of semiconductors, which largely determines their properties. The ability to continuously and reversibly tune the bandgap of a single device during real time operation is of great importance not only to device physics but also to technological applications. Here we demonstrate a widely tunable bandgap of few-layer black phosphorus （BP） by the application of vertical electric field in dual-gated BP field-effect transistors. A total bandgap reduction of 124 meV is observed when the electrical displacement field is increased from 0.10 V/nm to 0.83 V/nm. Our results suggest appealing potential for few-layer BP as a tunable bandgap material in infrared optoelectronies, thermoelectric power generation and thermal imaging.

Calculation on Relation of Energy Bandgap to Composition and Temperature for Ga_xIn_（1－x）As_（1－y）Sb_y

The calculated methods of the compositional dependence of the energy bandgap for Ga_xIn_(1-x)As_(1-y)Sb_y quaternary alloys are discussed in this paper. The dielectric theory of electronegativity and the linearinterpolation method were respectively used to calculate the compositional dependence of the energybandgap for Ca_xIn_(1-x)As_(1-y)Sb_y quaternary alloys. The same formula was deduced from the two schemes.According to the two formulas, we calculate the energy handgap as a function of alloy compositions forGa_xIn_(1-x)As_(1-y)Sb_y quaternary alloys: moreover, the temperature effect was lead into the formulas. Com-paring the calculated values with the measured ones, we found that the calculated method is in good agree-ment with the experimental data for Ga_xIn_(1-x)As_(1-y_Sb_y quaternary alloys.

Tunable Optical Bandgap of Gadolinium Substituted Nickel-Zinc Ferrite Nanoparticles-Effect of Calcination Temperature on Its Optical Parameters

The gadolinium substituted nickel-zinc ferrite nanoparticles of the composition, Ni0.5Zn0.5Gd0.05Fe1.95O4 were prepared using sol-gel method. In order to study the effect of calcination temperature on the optical parameters, the prepared powder was divided into five parts. The first part was taken as the as-prepared sample and the remaining four parts were calcinated at different temperatures, 600°C, 700°C, 800°C & 900°C. The X-ray diffraction patterns revealed the formation of cubic spinel structure with single phase and Fd3m space group. The crystallite size was increased from 11.75 nm to 18.13 nm as the calcination temperature increased from 600 to 900°C whereas as-prepared sample exhibited 17.61 nm. The dislocation density was decreased from 7.243 × 10-3 to 3.042 × 10-3 nm-2 as the calcination temperature increased from 600°C to 900°C. The micro strain was decreased from 10 × 10-4 to 6.452 × 10-4 as the calcination temperature increased from 600°C to 900°C. The characteristic absorbance peaks were obtained at 255.2 nm for the ferrite nanoparticles of as-prepared and calcinated at 600°C and 800°C whereas it was obtained as 252.8 nm for the sample calcinated at 700°C and there was no such characteristic peak in UV-visible range for the sample calcinated at 900°C;it is expected in the below 200 nm region. The optical energy gap was calculated using Kubelka-Munk equation based on Tauc’s plot and found in the range 4.100 eV to 5.389 eV. The lowest energy gap of 4.100 eV exhibited by the sample calcinated at 700°C and the highest energy gap of 5.389 eV by the sample calcinated at 900°C. It is concluded that the tunable band gaps can be obtained with varying calcination temperature.

Role of the Bandgaps on Some Interfacial Phenomena with Ionocovalent Oxides

Many ionocovalent oxide materials are either semiconducting or insulating in nature.One of the most im- portant quantities characterising these materials,therefore,is the bandgap energy.The thermodynamic ap- proaches to the bandgaps of oxides are briefly described and some interracial phenomena with oxides are pres- ented.The standard electrode potentials of oxide electrodes and the heterogeneous catalytic behaviours of the oxides as well as the wetting and adhesion in liquid metal/oxide systems can be closely related to the bandgap energies of the oxides.The interfacial phenomena involving the ionocovalent oxides are associated with the electronic processes.

A Comprehensively Optimized Diagram in (Ga,In) (As,Sb) Reciprocal System

he expressions of the composition space and the dependent properties of the lattice constant, the energy bandgap and the Gibbs energy were presented for the (Ga,In)(As,Sb) quaternary compound semiconductor. On the basis of these expressions, a computer aided analysis system is set up for the design of ⅢⅤ compound semiconductor materials and growth processes. By using this system, a comprehensively optimized diagram is constructed through the projection of the optoelectronic properties (energy bandgap or wave length), in which the composition relations are matched to substrates and the miscibility gaps.

Microscopic Approach of Adhesion and Wetting of Liquid Metal on Solid Ionocovalent Oxide Surface

The adhesion and wetting of non-reactive liquid metals with solid ionocovalent oxides are studied on the basis of the experimental work of adhesion W data obtained with the sessile drop method.An analysis of the experimental W values of different liquid metals on various solid oxides is first performed to evidence the de- pendence of the work of adhesion of a metal/oxide system on the electron density of the metal and on the thermodynamic stability of the oxide.An electronic model is then proposed to describe the microscopic mech- anism of metal-oxide interactions.Based on the model,the contact angle and the work of adhesion of different liquid metals on various solid oxides can be interpreted and estimated,and their correlations to the various physical quantities of the oxides can be easily deduced.The basic consideration of the model is that the adhe- sion between a metal and an oxide is assured by the electron transfer from the metal into the oxide valence band which is not completely filled of electrons at high temperatures,and is enhanced when this electron trans- fer at the metal/oxide interface is intensified.The influence of interface defects on the wetting and adhesion is suggested and discussed.

Preparation of cerium and yttrium doped ZnO nanoparticles and tracking their structural,optical,and photocatalytic performances

Yttrium(Y)and cerium(Ce)co-doped ZnO nanoparticles(NPs)were synthesized via the simple sol-gel auto-combustion route.The effect of Ce and Y doping on the structure,morphology,optical,Zeta potential,and photocatalytic activities of ZnO NPs was examined by Fourier transform infrared(FTIR)spectrometer,X-ray diffraction(XRD),transmission electron microscope(TEM),UV-vis spectrophotometer,and Zetasizer instrument.XRD data show that the fabricated samples crystallize into a hexagonal wurtzite structure.The dopants Y and Ce affect the crystal structure of ZnO NPs.The crystallite size is reduced with the co-doping effect.TEM results confirm the nano-sized particles of the prepared samples.An increase in optical bandgap values from 3.19 eV for x=0.0 to 3.22,3.24,and 3.25 eV for x=0.01,0.03,and 0.05 samples was confirmed by UV-Vis spectroscopy analysis.Y and Ce co-doped ZnO nanoparticles show significant alteration of zeta potential and photocatalytic properties compared to undoped ZnO NPs.Comparatively,undoped ZnO shows better stability in deionized water as compared to Ce-Y doped ZnO NPs and exhibits high photocatalytic activity(degradation rate,97.92%)for methyl orange(MO)degradation.

Impact of La^(3+)substitution on electrical,magnetic,dielectric and optical properties of Ni_(0.7)Cu_(0.1)Zn_(0.2)LaxFe_(2-x)O_(4)(0

The oxalate co-precipitation method was used to synthesize the La3+substituted Ni-Cu-Zn(La-NCZ)nanoferrites having chemical composition Ni_(0.7)Cu_(0.1)Zn_(0.2)LaxFe_(2-x)O_(4)(x=0.015,0.025 and 0.035).DC resistivity study of nanoferrites shows both the conducting and semiconducting behaviour.The room temperature DC electrical resistivity of Ni-Cu-Zn(NCZ)nanoferrites decreases,whereas Curie temperature increases with increasing La^(3+)content.In the temperature range of 30-170℃nanoferrites show p-type semiconducting behavior except x=0.015;thereafter,they show n-type behaviour.The frequency dispersive initial permeability(μi)associated with its real and imaginary(μ’andμ")parts are attributed to the domain wall movement and magnetic spin resonant.Theμi,u’andμ"of La-NCZ nanoferrites are higher than those of pure NCZ nanoferrite.Dielectric constant(ε’),dielectric loss(ε")and AC resistivity(ρAC)of La-NCZ nanoferrites show normal dielectric behaviour.It is found thatε’of NCZ nanoferrites decreases with the increasing content of La3+ions.The bandgap energy of La-NCZ nanoferrites is achieved in the range 1.36-1.70 eV confirming the semiconducting nature of materials.

Enhanced oxygen reduction kinetics by a porous heterostructured cathode for intermediate temperature solid oxide fuel cells

A novel porous heterostructured Nd_(0.8)Sr_(1.2)CoO_(4)±/Nd_(0.5)Sr_(0.5)CoO_(3-δ)(NSC_(214/113))cathode for intermediate tem-perature solid oxide fuel cells(IT-SOFCs)is developed to significantly enhance oxygen reduction reaction(ORR)kinetics.Compared to single-phase materials,the fabricated porous heterostructured NSC 214/113 shows optimized electrochemical properties,including a better conductivity,20 times faster surface oxygen exchange kinetics,and a comparatively lower area-specific resistance(0.065Ωcm^(2) at 800℃).The single cell with Ni-YSZ|YSZ-GDC|NSC_(214/113) configuration exhibits a high peak power density of 1.10 W cm^(−2) at 800℃,superior to other cells reported in literature with similar heterostructured cathodes.Moreover,the underlying mechanism of the ORR performance enhancement is further investigated,revealing that the formation of heterojunction can lead to a narrowed energy bandgap and a decrease of Co oxidation state,which further induce better conductivity,more available electrons and oxygen vacancies to enhance the ORR process.Taken together,our research also provides new insights into potential application of artificial intelligence(AI)method involved in materials in-telligent identification,cell state estimation,system diagnostic and optimization.The revolutionary force of AI,especially in the field of new electrode material development is now advancing in its full swing.More and greater breakthroughs are still expected.

Evidence for structural phase transitions and large effective band gaps in quasi-metallic ultra-clean suspended carbon nanotubes

We report evidence for a structural phase transition in individual suspended metallic carbon nanotubes by examining their Raman spectra and electron trans- port under electrostatic gate potentials. The current-gate voltage characteristics reveal anomalously large quasi-metallic band gaps as high as 240 meV, the largest reported to date. For nanotubes with band gaps larger than 200 meV, we observe a pronounced M-shape profile in the gate dependence of the 2D band （or G＇ band） Raman frequency. The pronounced dip （or softening） of the phonon mode near zero gate voltage can be attributed to a structural phase transition （SPT） that occurs at the charge neutrality point （CNP）. The 2D band Raman intensity also changes abruptly near the CNP, providing further evidence for a change in the lattice symmetry and a possible SPT. Pronounced non-adiabatic effects are observed in the gate dependence of the G band Raman mode, however, this behavior deviates from non-adiabatic theory near the CNP. For nanotubes with band gaps larger than 200 meV, non-adiabatic effects should be largely suppressed, which is not observed experimentally. This data suggests that these large effective band gaps are primarily caused by a SPT to an insulating state, which causes the large modulation observed in the conductance around the CNP. Possible mechanisms for this SPT are discussed, including electron-electron （e.g., Mott） and electron-phonon （e.g., Peierls） driven transitions.

Synthesis and Properties of Novel Polymers Based on PD Electron-withdrawing Unit

In this article, we designed and synthesized a series of 5-（2,6-dimethyl-4H-pyran-4-ylidene）-1,3-diethyl-2-thioxodihydropyrimidine-4,6（1H, 5H）-dione（PD） unit based polymers（PFTDT, CZTDT, PHTDT and THTDT） for the first time. In these polymers, fluorene, 2,7-carbazole, phenothiazine and thiophene are employed as electron-donating groups and PD as electron-withdrawing group. TGA measurements demonstrated that these polymers possess good thermal stability（all above 377 °C）. Very broad absorption spectrum was also obtained from the polymer THTDT（300？850 nm）. CV characterization found that these polymers owned low highest occupied molecular orbital（HOMO） energy levels（？5.39 e V for THTDT, ？5.49 e V for CZTDT and ？5.78 e V for PFTDT） except for PHTDT（？5.17 e V）. The geometry and electronic properties of PFTDT, CZTDT, PHTDT and THTDT were investigated by means of theoretical calculation. All the above advantages demonstrate that PD based polymers could be candidates for electronic devices.