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Recently, the two-dimensional heterostructure is a research hot spot of semiconductor materials, and it has wide application prospects in electronic devices and photocatalysis. In this work, we constructed novel graphene-GaN-graphene (G-GaN-G) sandwich heterostructure, and the electronic and optical properties have been theoretically investigated based on the first principles calculations. The computation results indicate that the heterostructure is most stable when interlayer distance d0 is 3.189 A, and electronic and optical properties of intrinsic GaN and graphene are well preserved. In addition, the effect of vertical and biaxial strain on the G-GaN-G heterostructure is also investigated, we find that strain can effectively regulate the electronic and optical properties. Therefore, the electronic and optical properties of G-GaN-G can be tuned by applying different levels of strain to meet the needs of devices. This study results reveal that the G-GaN-G sandwich heterostructure can be hopefully applied to ultraviolet photodetectors and optoelectronic devices.

Based on the calculation using first-principles, we discussed adjustment for electronic properties of the GaN/graphene/WS2 trilayer vdW heterostructure by doping and biaxial strain. Mg or Se doping can regulate the band gap of the GaN/graphene/WS2 trilayer vdW heterostructure and achieve p-type or n-type dopant in graphene and the trilayer heterostructure system. Band gap decreases with the increase in positive strain, and a p-type Schottky barrier is always maintained. As the negative strain increases, the band gap reaches its maximum at e = − 3% and then gradually decreases. And after |e| ≥ | − 5|%, it changes to an indirect band gap. When |e| ≥ | − 7|%, the Schottky contact type changes from p-type to n-type. Electrons are transferred from GaN layer to graphene and WS2 layer, and transfer increases with the increase in strain from negative to positive. More electrons are transferred to WS2 with positive strain, and more electrons are transferred to graphene with negative strain. The results will provide valuable information for the design of trilayer Schottky devices.

Background Fine-needle aspiration (FNA) of thyroid nodules leads to nearly 25% indeterminate nodules, while BRAFV600E mutation helps to predicting papillary thyroid carcinoma (PTC). However, the clinical validity and utility of the BRAFV600E mutation detected using preoperative FNA samples in a large cohort were rarely reported. Aim To explore the clinical significance of the BRAFV600E mutation on preoperative diagnosis and decision-making in a large FNA cohort in China. Design This was a prospective study of BRAFV600E mutation analysis using an amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) in FNA samples. Patients The study involved 2640 samples from 2307 patients undergoing FNA procedures in a Chinese medical centre. Results A high mutation rate of 86.7% was found in the PTC population. For indeterminate thyroid nodules, the malignant rate of BRAFV600E+ and BRAFV600E- was 87.8% and 39.5% in the Bethesda System for Reporting Thyroid Cytopathology (BSRTC) III, and 88.2% and 31.8% in the BSRTC IV, respectively. A cost-effective diagnostic model combining both BSRTC grading and BRAFV600E mutation status showed the highest sensitivity of 82.9% and specificity of 85.4%. Central lymph node metastasis (CLNM) was independent of the BRAF mutation status and accounted for 34.2% of the patients with PTC. CT values of BRAFV600E of patients with PTMC were significantly lower in young patients and patients with CLNM. Conclusions The combined analysis of cytological results and BRAFV600E mutation is highly recommended in BRAFV600E high-prevalence regions, including China. Prophylactic central neck dissection should be performed in selected patients without regard to the BRAF mutation status.

One of the major challenges that the human beings are facing is the shortage of the fossil fuels. Hydrogen is considered as the most attractive renewable energy because of its abundant high energy density. Semiconductor photocatalytic technology for water decomposition is a promising method for converting sunlight into hydrogen energy, which has attracted considerable attention. Compared with bulk materials, two-dimensional (2D) materials exhibit remarkable photocatalytic properties. In this work, the pristine high-quality hexagonal molybdenum disulfide (MoS2) nanosheets and Ag-doped MoS2 nanosheets were synthesized by hydrothermal method, and the thickness of nanosheets was ranged from 0.9 to 1.1 nm. In addition, the absorption spectra of Ag-doped MoS2 nanosheets increased with the increase of Ag content. What's more, the photocatalytic properties of Ag-doped MoS2 nanosheets were tested, and the results show that Ag-doped MoS2 nanosheets have good stability, high hydrogen production efficiency and strong photocatalytic activity. It is worth mentioning that the photocatalytic hydrogen production rate of Ag-doped MoS2 nanosheets can reach 2695 μmol h−1 g−1. Meanwhile, density functional theory was used to calculate the optical properties, electronic structure of pristine and Ag-doped monolayer MoS2. These calculated results indicate that the absorption intensity of Ag-doped MoS2 in the ultraviolet–visible and visible light region increases significantly, and the conduction band of Ag-doped monolayer MoS2 is downshift compared with pristine MoS2. Therefore, Ag-doped MoS2 can optimize the band structure and promote the absorption of visible light, thereby improving the photocatalytic activity.

GaN/AlN core-shell nanowires (NWs) were synthesized by a Chemical Vapor Deposition (CVD) through two steps method. GaN core nanowire and AlN shell of each core-shell nanowire are uniform and wurtzite hexagonal single crystal structure. The AlN shell epitaxial grow on GaN core nanowire based on gas-solid (VS) mechanism, and they all grow in [001] direction. The PL property of the GaN/AlN core-shell nanowires shows promising application in ultraviolet photoelectric devices.

The electronic structure and optical properties of the sphalerite structures I n x G a 1 − x A s (x = 3.125%, 6.25%, 9.375%, 12.5%) were studied based on the first-principles method of density functional theory. The results demonstrate that the band-gap width of I n x G a 1 − x A s decrease and the optical absorption frequency (absorption edge) emerges an obvious red-shift compared with GaAs due to the existence of impurity energy levels in the material. With the increase in Indium component ratio, the outer electronic hybridization degree of In and As decrease, and the band-gap width of I n x G a 1 − x A s increases. As the component ratio of Indium increases from 6.25% to 9.375%, the band-gap magnitude increases from 0.55 eV to 0.63 eV. In terms of optical properties, the maximum peak values of the real and imaginary parts of dielectric function are 22.6 along [0 0 1] crystal direction and 25.71 along [1 0 0] crystal direction, respectively. The proportion of In component affects the material properties of crystal orientation and make the crystal gradually exhibit noticeable anisotropy. With increase in the proportion of In component, both the static dielectric constant of the material and the maximum peak of the refractive index decreases. In the region of higher energy, the reflection of the doped material is relatively weak for electromagnetic wave, and the average value of refractive index is around 0.7 with a high transmittance characteristic. The results show that the energy loss has a significant peak at the photon energy of 14.9 eV. Therefore, this calculation can provide a reference for the research and application of InGaAs optical detector.

The band structure, electronic, magnetic, and optical properties of g-SiC monolayers doped with alkaline earth metals (Be, Mg, Ca, Sr, and Ba) are calculated by means of first principles based on density functional theory. Although the intrinsic g-SiC monolayer is nonmagnetic, it shows magnetic properties after doping with alkaline earth metals. The magnetic moments are, in the order of the above-named dopants, 1.583 μ B, 1817 μ B, 2.000 μ B, 2.000 μ B, and 2.000 μ B. Charge transfer and the net spin charge occur mainly between the dopant atom and surrounding C atoms. The results show that the conductivity of g-SiC can be greatly improved by doping with alkaline earth metals, a technique that can be applied to the field of semiconductor spintronics. High absorption peaks in the ultraviolet indicate that the material has potential applications in UV optoelectronic devices.

A first-principles projector augmented wave method in the framework of density functional theory is performed to study electronic structures, magnetic and optical properties of Cr-doped GaAs in three different positions. The complex dielectric function, absorption coefficient and electron energy-loss are discussed for optical properties. The results predict that (Ga, Cr)As systems exhibit typical half-metallic properties and stable ferromagnetism when Cr atoms doping in the interior of the supercell, in which deep levels are formed in the forbidden band and reduces the energy gap, increases static dielectric constant greatly and red-shifts the absorption edge obviously. In addition, a smaller magnetic moments from As and Ga atoms are generated by p-d hybridization, and Cr atoms interact antiferromagnetically with As atoms and ferromagnetically with Ga atoms respectively. While the metallic character is observed that Cr atoms are doped on the surface of the supercell.

Based on the first principles of density functional theory , the electronic structure and optical properties of intrinsic monolayer molybdenum disulfide (MoS 2 ) and antimony (Sb)-doped monolayer MoS 2 have been studied, including the formation energy, band structure , state density, differential-charge density and optical properties that have been calculated. These calculated results indicate that the intrinsic monolayer MoS 2, Sb-substituted Mo-doped monolayer MoS2, and Sb-substituted S-doped monolayer MoS2 are all semiconductors with band gaps of 1.68 eV, 1.06 eV, and 1.47 eV, respectively. Thus, doping with Sb can better modify the band structures for MoS2. Moreover, by calculating the differential charge density, it is found that doping with Sb atoms can stimulate more large charge transfers in monolayer MoS2 . More importantly, after Sb doping, the absorption of visible and ultraviolet light by MoS 2 nanomaterials is enhanced. The absorption edge of the Sb-doped MoS 2 system shows a slight redshift. In addition, for the reflectivity of the two doping systems, there are two different reflection peaks in both doping systems, and the peaks are much larger than in the intrinsic MoS 2 . These theoretical results are expected to provide useful guidelines for the design of photoelectron nanodevices based on monolayer MoS 2.

The Ge-doped hexagonal cone-shaped GaN nanorods have been synthesized by the VLS process. The variation of N-rich condition and Ga-rich condition in reaction chamber results in the morphology of the Ge-doped GaN nanorods being hexagonal cone-shaped. The Ge-doped hexagonal cone-shaped GaN nanorods exhibit an excellent emission property with typical turn-on electric field as low as 2.93 V/μm, this indicates that the Ge-doped hexagonal cone-shaped GaN nanorods could be well used in cold cathode electron source applications. The photoluminescence spectrum of the Ge-doped hexagonal cone-shaped GaN nanorods indicates it could be applied in blue-violet and ultraviolet photoelectric devices.

Novel single-crystalline bamboo shoot-shaped gallium nitride (GaN) nanowires were prepared on silicon substrates using Ga2O3 and ammonia (NH3) by chemical vapor deposition (CVD) method. From the view morphology of bamboo shoot-shaped GaN nanowires, it can be seen that the average diameter of sample is 200 nm, and along the axial direction to the tip diameter decreases slowly. The growth mechanism of bamboo shoot-shaped GaN nanowires obeys the vapor-liquid-solid (VLS) mechanism. In addition, field emission tests indicate that the turn on field of bamboo shoot-shaped GaN nanowires is 7.5 V/μm (at the current density of 10 μA/cm2), with field enhancement factor of 646, which is sufficient meets the field emission device and vacuum microelectronic device. Moreover, the photoluminescence (PL) spectrum measurement shows that the main luminescence peak of bamboo shoot-shaped GaN nanowires is at 364 nm (3.41 eV), which indicate the bamboo shoot-shaped GaN nanowires can be used for preparation flexible optoelectronic devices.

We investigated an optical amplifier and router by the aperture nonlinear phase and the phase angle of parametric amplified four-wave mixing in a thermal rubidium vapor. The three-stage optical amplifier has been realized and the total amplified gain is observed up to 10. The router action results from the multi-peaks (multi-pair two-modes) while the cross talk of router can be realized by the opposite dressing shift of composite Autler-Townes splitting.

P-doped GaN NWs in different contents have been synthesized via CCVD. The P-doped GaN NWs present a uniform density and the each nanowire possesses a uniform thickness. The structure of the NWs is single crystalline structure of hexagonal wurtzite. Furthermore, the results from FE test indicate that the turn-on field of the sample with P content of 2.24 at. % is as low as 2.85 V/μm, which presents significant improvement of the FE properties in contrast to pristine GaN NWs.

Based on first-principles calculation, we systematically investigated the electronic structure, charge transfer, and optical properties of the CdO/GaS van der Waals (vdW) heterostructure, and which are effected by applied mechanical strain. Heyd-Scuseria-Ernzerhof (HSE06) is used to accurately calculate the electronic structure, and the results show the CdO/GaS heterostructure is a semiconductor with a direct band gap (1.79 eV), which possess type-II band alignment, and is in favor of the separation of photogenerated carriers and extend their lifetime. The suitable band gap and band edge position of the CdO/GaS heterostructure promise application prospect in photocatalyst for water splitting. The significant advantages of the CdO/GaS heterostructure for photocatalytic performance in whole sunlight spectrum are obtained by applying biaxial strain to the heterostructures.

We present a comprehensive investigation of C60 fullerenes modified g-GaN monolayer (g-GaN/C60 heterostructure) based on density functional theory (DFT). The results show that the g-GaN/C60 heterostructure is most stable when the pentagonal center of C60 molecule is adsorbed above N atom of the g-GaN monolayer. The heterostructure has a narrow direct energy gap 1.02 eV and type-II band alignment, the CBM is dominated by the C 2p orbital of the C60 molecule, as well as the VBM consists of N 2p and Ga 3d orbitals of the g-GaN monolayer. This results in the separation of electrons and holes reducing the complexation of electrons and holes, improving photoelectric conversion efficiency and photocatalytic performance of the g-GaN monolayer. In addition, the broader UV to visible-light absorption spectrum of the g-GaN/C60 heterostructure promises a potential application in photoelectric devices, especially for solar cells. The electronic and photoresponse properties of the g-GaN/C60 heterostructure applied with vertical electric field are more excellent due to better transitions of electrons from the valence band to conduction band.

The adsorption of alkali-metal atoms on GaN nanowires photocathode was investigated by using first principles with density functional theory. The calculation of electronic and optical properties indicates that alkali metal adsorbed GaN nanowires are direct band gap semiconductor, and the band gap of GaN nanowires could be decreased by alkali metal adsorption. A new surface state near the Fermi level results from the Ga, N and alkali metal hybridization, which leads to form a metal electrical conductivity for GaN nanowires. More importantly, alkali metal adsorption can decrease the work function of GaN nanowires. Furthermore, the absorption spectrum of GaN nanowires is red shifted and moves to lower energy side because of alkali metal adsorption. Accordingly, this study will provide the theoretical basis for producing the alkali metal adsorbed GaN photoelectric devices.

Doping can provide hole and electron carriers into g-GaN materials to enhance conductivity and improve photoemission performance of g-GaN-based devices. In this work, we propose 9 × 9 × 1 g-GaN supercell and C, Mg, and S doped g-GaN systems (C and Mg substituting for Ga (CGa and MgGa systems), C and S substituting for N (CN and SN systems)) with different concentrations, and investigate their structural, electronic, electrical, and optical properties in the framework of first-principles calculations. N-type doping is achieved in the CGa and SN g-GaN systems, and p-type doping is achieved in the MgGa and CN g-GaN systems. C substituting for Ga is easier than C substituting for N, and the CGa g-GaN systems are more stability than the CN g-GaN systems. At the ultraviolet of the absorption spectra, the peaks of the doped g-GaN systems blue-shift or red-shift relative to the intrinsic g-GaN, and there are sharp peaks of the doped CGa and SN g-GaN systems at visible range. The work function and the carrier mobility have been modulated by doping and the electrical properties of g-GaN can be tuned effectively, which also promising significant applications in the design of 2D microelectronic devices and the integrated circuit.

Using the first-principles calculation, based on density functional theory, the geometric structures, electronic, magnetic, and optical properties of CO, H2S, and NO toxic gas molecules adsorbed on alkali metals (Li, Na, K, Rb, and Cs) doped g-GaN monolayer have been investigated. The adsorbed systems have induced magnetic property except H2S adsorbed on Na doped g-GaN monolayer, the total magnetic moment of CO, H2S, and NO adsorbed on alkali metals doped g-GaN are 2.0, 2.0, and 1.0 μB, respectively, and the materials are spin semiconductors. The charge transfer mainly occurs between gas molecules, doped atoms, and Ga atoms. The adsorbed behaviors of CO, H2S, and NO adsorbed on intrinsic g-GaN are physisorption, H2S adsorbed on Na doped g-GaN monolayer and NO adsorbed on Li, Na, K, Rb, and Cs doped g-GaN monolayer are chemisorption, while CO adsorbed on alkali metals doped g-GaN monolayer are physisorption. The results show that the adsorptive properties can be enhanced dramatically by doping with alkali metals, and the materials can be used in gas sensor devices and detector devices. In addition, the adsorbed coefficients in ultraviolet and visible indicate the materials promising the application of violet and UV optoelectronic devices.

We report Pt NP coated GaN NWs through CVD method and the fabrication of their field emitters. Pt NPs are attached on the top and surfaces of GaN NWs. With the Pt NP coating, it is found that the turn on field is reduced from 3.3 V μm−1 to 2.7 V μm−1 and the work function is decreased from 4.1 eV to 3.22 eV. In addition, DFT calculation results indicate that higher local electron states, which appear around the Fermi level, are mainly formed from N-2p, Pt-6s, and Pt-5d orbital hybridization, and will provide more electrons to the conduction band at a given operating voltage. Consequently, the field emission performance of GaN NWs can be effectively boosted by adsorbed Pt. Moreover, Pt NP coated GaN NWs are promising for electron emission devices, field emission displays and vacuum nano-electronic devices.

The field emission properties of Ge-dopted GaN nanowires have been investigated in theory and experiment. Ge-doping affecting field emission properties of GaN nanowires has been calculated via the basis of density functional theory (DFT). The results indicate that Ge-doped GaN nanowires have a minimum work function value of 2.37 eV when the impurity concentration is about 4.2 at.%, which is superior for application in cathode material for field emission. In addition, Ge-doped GaN nanowires have been synthesized via CVD method in our experiment. The results indicate: (1) the structure of GaN NWs is wurtzite hexagonal and the growth direction is along [0001]. (2) Ge-doped GaN nanowires possess a lower turn-on field than the pure GaN nanowires, which means Ge-doping can enhance the field emission properties of GaN nanowires, and this is consistent with the theoretical calculation results.

The electronic and optical properties of titanium (Ti) doped gallium nitride (GaN) nanowires (NWs) have been investigated using density functional theory (DFT). The donor states of near the Fermi level are mainly formed by Ti-3d orbital, and Ti-doped GaN NWs' Fermi level has an upshift compared with pure GaN NWs. The doping Ti atoms can decrease work function of GaN NWs. Moreover, the optical properties, including the complex dielectric function, optical refractive index, and absorption coefficient are discussed for radiation up to 25 eV. The results predicate that alloys exhibit a typical metallic property, in which Ti forms deep levels in the forbidden band and reduces energy gap, increases static dielectric constant and obviously red-shifts the absorption edge. The work gives a theoretical guidance for preparation of Ti-doped GaN optoelectronic nanodevices. Keywords: Ti-doped GaN NWs, Work function, Electronic and optical properties

The adsorption behaviors of gas molecules, including CO, NH3, NO, and NO2 on pristine and defective g-GaN, and their adsorption energy, charge transfer, and magnetic moment are investigated using first-principles calculations. The small adsorption energy of all the gas molecules on pristine g-GaN suggests the physisorption characteristics. Among these gas molecules, the binding between NH3 and pristine g-GaN is stronger than the other molecules owing to the hybridization of its frontier orbitals with the 2p orbital of N atoms in pristine g-GaN. To improve the sensing ability of g-GaN, the adsorption behaviours of these gas molecules on g-GaN with Ga and N single vacancies are also examined. All these gas molecules exhibit much larger adsorptions energy on the defective g-GaN than that on the pristine form. For most of the gas molecule adsorption on defective g-GaN, the charge transfer is more significant that in the corresponding gas molecule adsorption on pristine g-GaN. Besides, the magnetisms are found in many gas molecules adsorbed defective g-GaN. Our work not only provides an effective approach to improve the sensing ability of g-GaN but also offers an effective approach for functionalization of g-GaN.

Based on the first-principles, the van der Waals heterostructures of two-dimensional gallium nitride (GaN) and silicon carbide (SiC) stacked graphene respectively have been researched. The G/GaN(SiC) heterostructure not only maintain the electrical properties of monolayer GaN(SiC), also keep the original electrical properties of graphene. Under the applied external electric field, the two heterostructures have their own Schottky contact critical transition points. When Eext > 0.10V/A, both heterostructures are converted to ohmic contacts. In addition, in terms of biaxial strain, these two heterostructures maintain a good p-type Schottky barrier. The difference is that GaN in G/GaN turns into a direct bandgap within the biaxial strain range of −7% ~ −9%, while SiC in G/SiC always keeps the original indirect bandgap. The ohmic contact of G/GaN occurs at e > 7%, while G/SiC occurs at e > 5%. The charge injection of two heterostructures was further explored by analyzing the electrostatic potential under different biaxial strain. We believe that our work will make a significant contribution to future high-power high-voltage devices and Schottky devices.

The electronic and optical characteristics of GaS/g-C3N4 van der Waals (vdWs) heterostructures were studied using density functional theory based on first-principles. The GaS/g-C3N4 vdWs heterostructures with different structural configurations were compared with their formation energies, and their stability was proved by computational molecular dynamics. The stable GaS/g-C3N4 vdWs heterostructures has an indirect band gap semiconductor with a type-I band alignment. Bader charge research demonstrates that GaS is the electron acceptor and g-C3N4 is the electron-donor. The effects of biaxial strain and vertical electric field on electronic and optical properties were analyzed. Both biaxial strain and vertical electric fields can adjust values of band offset and band gaps. Interestingly, when biaxial strain and vertical electric fields are applied, GaS/g-C3N4 vdWs heterostructures has mutual transformation from type-I to type-II band alignment. The type-II band alignment is a feasible scheme in the study of photocatalysis, photocell and photovoltaic. Moreover, the GaS/g-C3N4 vdWs heterostructure with biaxial strain has a strong absorption peak in the visible light region, which is conducive to the photocatalysis of visible light. The results show that the GaS/g-C3N4 vdWs heterostructure has huge application potential in the fields of optoelectronic devices and photocatalysis.

In this paper, electronic and optical properties of GaN/InN core/shell nanowires (CSNWs) have been theoretically investigated through the first principles calculations. The binding energy of In and N atoms on surface of six crystal planes along the [Formula: see text]-axis of GaN nanowires are all negative, which indicate that In and N atoms can be effectively deposited on the surface of GaN nanowires and preparing GaN/InN CSNWs is feasible theoretically. Calculation results of electronic properties indicate that the core/shell ratio and diameter of GaN/InN CSNWs have significant effect on the band structure, bandgap can be effectively adjusted when keeping the number of GaN layers unchanged and changing the number of InN layers. Moreover, with the increase in the number of InN layers, the absorption spectrum of GaN/InN CSNW has significant redshift and few weak absorption peaks appear in the visible light region.

The stability, electronic, and optical behaviours of XSSe/SiC (X = Mo, W) vdWs heterostructures have been investigated by first-principles calculations. The observed XSSe/SiC vdWs heterostructure is semiconductor with indirect bandgap, and it possesses type-II band alignment, which will promote the segregation of photogenerated carriers. In particular, the charge reallocation cause a large potential drop across XSSe/SiC vdWs heterostructure is 5.748 eV (MoSSe/SiC) and 5.849 eV (WSSe/SiC). Charge transfer demonstrates that the XSSe acts as an acceptor, while the SiC acts as a donor. Moreover, the tensile and compressive strain can regulate the band structures of the XSSe/SiC heterostructures from direct band gap to indirect band gap. Meanwhile, the vertical electric field can not change the band type of the XSSe/SiC heterostructures, but can regulate the band gap of the XSSe/SiC heterostructures. Importantly, the XSSe/SiC vdWs heterostructures have many strong peaks in the visible light region, resulting to efficient use of the solar energy. These attractive properties illustrate that the XSSe/SiC vdWs heterostructures are useful for attaining high-efficiency photocatalyst.

The electronic and optical properties of the adsorption of alkali metals (Li, Na, K, Rb, Cs) on graphitic carbon nitride (g-C3N[Formula: see text] were calculated and studied based on the first principles of density functional theory. The results investigate that alkali metals adsorbed g-C3N4 has metallic properties, while intrinsic g-C3N4 was semiconducting. Importantly, the charge density differential investigated the charge transfer discovered between the alkali metal and the g-C3N4 monolayer. Meanwhile, the charges (electrons) transfer from the alkali metals to the g-C3N4 system leading to the increase of most carriers in the g-C3N4 system, reducing the resistance of sensors, which is conducive to sensor detection applications. The work function of g-C3N4 decreased from 4.82 eV to 4.09 eV. Especially, the work function of Cs-adsorbed g-C3N4 is the lowest at 4.09 eV, and the reduction rate is 15.15 %, indicating it easier to emit electrons from an external electric field. Moreover, the absorption spectrum of the alkali metal adsorbed on g-C3N4 in the visible light range shows absorption peaks at 380 nm, 412 nm, 420 nm and 476 nm, which cover the visible light area. Thus, the alkali metals adsorbed g-C3N4 system can be used for visible light catalytic. Adsorption of alkali metals can expand the application of g-C3N4 in optoelectronic devices.

In the original article, Fig. 3 was incorrect. The original article has been updated to display the corrected figure.

The first-principles based on density functional theory are used to calculate the adsorption of gas (CO, NO) molecules on group III (B, Al, Ga, In) atoms adsorbed g-C3N4. It is revealed that the B, Al, Ga, and In-g-C3N4 adsorption systems exhibit magnetic semiconducting behavior, while pristine g-C3N4 is a non-magnetic semiconductor. Next, adsorption of the gas molecules on g-C3N4 was investigated. The results show that the charge transfer amount of NO/g-C3N4 is larger than that of CO/g-C3N4. The CO/g-C3N4 system exhibits non-magnetic semiconductor. However, the NO/g-C3N4 system exhibits magnetic semiconductor behavior. Lastly, adsorption of the gas molecules on III-g-C3N4 was also investigated. It is revealed that all gas molecule adsorbed III-g-C3N4 exhibit a magnetic semiconductor. Interestingly, all the gas/III-g-C3N4, except NO/Al-g-C3N4, NO/Ga-g-C3N4, and NO/In-g-C3N4 systems, can promote the charge (electron) transfer from gas molecule to the III-g-C3N4 system, which is conducive to gas sensing. The absorption spectrums of gas molecules adsorbed III-g-C3N4 systems have many strong visible light absorption peaks. Especially, the absorption peak intensity of NO adsorbed In-g-C3N4 system at 436 nm reached 1.19 × 105 cm−1. Thus, above results indicate that the gas molecules adsorption systems will facilitate design of spintronics, gas sensing and high efficiency photocatalytic device.

The electronic structure and optical properties of the sphalerite structured C u x G a 1 − x A s (x = 3.125%, 6.25% and 12.5%) were studied based on the first-principles method of density functional theory. The results show that the C u x G a 1 − x A s materials exhibit direct band-gaps, from valence band top to guide band low (solid blue line) i.e., 1.30 eV, 0.82 eV, 0.97 eV. It contains impurity levels in the middle, reaching the second transition. The calculated results also show that the energy required for electrons to jump from valence band to impurity levels, i.e., 0.42 eV, 0.36 eV, 0.31 eV. In addition, higher impurity levels resulted from copper doping reduces GaAs band-gaps in a great extent, which is beneficial to the transition and migration of electrons. At the same time, the static dielectric constant and refractive index of the doped system escalate with the increase of Cu doping ratio. Moreover, the absorption spectrum is red-shifted and the absorption of light is enhanced. In the system doped with 6.25% Cu, the electrons in Cu-3d orbital form a strong localization in the energy range of −3.9 eV ~ −1.8 eV. Indeed, the least influence on the complex dielectric function of the [010] is achieved when the ratio of doped Cu decreases to 3.125%, which makes the change of optical properties of the material in this crystal direction smaller than those in [100] and [001] orientations. The C u x G a 1 − x A s transition layer between GaAs devices and copper wires can substantially improve the electrode contact and subsequently the photoelectric characteristics of GaAs photoelectric devices.