Comparison Between Modified Lateral Arm Free Flap and Traditional Lateral Arm Free Flap for the Reconstruction of Oral and Maxillofacial Soft Tissue Defects.

Objective: The traditional lateral arm free flap (tLAFF) has the disadvantages of short vascular pedicle, small vascular diameter, and non-perforator flap. We used a new method to prepare modified LAFF (mLAFF) and evaluate its application value in the repair of oral and maxillofacial soft tissue defects. Methods: The anatomical features of the flap were recorded and compared between the tLAFF group and the mLAFF group. All the flaps in the modified group were perforator flaps. Statistical analysis was performed on the data using ANOVA on SPSS 22.0 statistical software package. Results: Forty-five mLAFFs were prepared as eccentric design rotation repair perforated flap, or multi-lobed or chimeric perforator flaps. Compared with the tLAFF, the vascular pedicle length of the mLAFF was increased, and the outer diameter of the anastomosis was thickened. The damage to the donor site was less. The difference was statistically significant. Conclusion: The mLAFF can effectively lengthen the vascular pedicle length and increase the anastomosis diameter. Perforator LAFFs in the repair of oral and maxillofacial defects have good application value.

Robust half-metallicity in transition metal tribromide nanowires.

One-dimensional (1D) nanowires (NWs) with robust half-metallicity are a rising star in spintronics. Herein, we theoretically investigate the magnetic and electronic properties of 3d transition-metal tribromide NWs, i.e. TMBr3 (TM = Sc, Ti, V, Cr, Co, and Cu). These systems represent repeated TMBr3 motifs with octahedral configuration, and are expected to be synthesized in a nanotube using an established method. Among these NWs, both VBr3 and CuBr3 NWs exhibit a ferromagnetic (FM) ground state, accompanied by sizable magnetocrystalline anisotropic energy, which is dominated by the superexchange coupling between the TM atoms. Strikingly, a half-metallic nature with a magnetic moment of 4.0µB per unit cell is predicted for the VBr3 NW. By combining with a tight-binding model, we demonstrate that the origin behind the half-metallicity is the half-filled e2 orbitals of the V atoms. The Curie temperature is evaluated to be up to 80 K using Monte Carlo simulations, which is comparable to the temperature of liquid nitrogen. We also find that the half-metallic behavior shows a favorable tolerance to the longitudinal elongation of the wire (∼10%). Additionally, a transition from FM semiconductor to half-metal can be realized in the CuBr3 NW through carrier doping. The coexistence of intrinsic high-temperature FM ordering and half-metallicity endows 1D TMBr3 NWs with great promise for spintronic and photoelectron device applications.

Effect of Amidogen Functionalization on Quantum Spin Hall Effect in Bi/Sb(111) Films.

Knowledge about chemical functionalization is of fundamental importance to design novel two-dimensional topological insulators. Despite theoretical predictions of quantum spin Hall effect (QSH) insulator via chemical functionalization, it is quite challenging to obtain a high-quality sample, in which the toxicity is also an important factor that cannot be ignored. Herein, using first-principles calculations, we predict an intrinsic QSH effect in amidogen-functionalized Bi/Sb(111) films (SbNH2 and BiNH2), characterized by nontrivial Z2 invariant and helical edge states. The bulk gaps derived from px,y orbitals reaches up to 0.39 and 0.83 eV for SbNH2 and BiNH2 films, respectively. The topological properties are robust against strain engineering, electric field, and rotation angle of amidogen, accompanied with sizable bulk gaps. Besides, the topological phases are preserved with different arrangements of amidogen. The H-terminated SiC(111) is verified as a good candidate substrate for supporting the films without destroying their QSH effect. These results have substantial implications for theoretical and experimental studies of functionalized Bi/Sb films, which also provide a promising platform for realizing practical application in dissipationless transport devices at room temperature.

Unconventional band inversion and intrinsic quantum spin Hall effect in functionalized group-V binary films.

Adequately understanding band inversion mechanism, one of the significant representations of topological phase, has substantial implications for design and regulation of topological insulators (TIs). Here, by identifying an unconventional band inversion, we propose an intrinsic quantum spin Hall (QSH) effect in iodinated group-V binary (ABI2) monolayers with a bulk gap as large as 0.409 eV, guaranteeing its viable application at room temperature. The nontrivial topological characters, which can be established by explicit demonstration of Z2 invariant and gapless helical edge states, are derived from the band inversion of antibonding states of p x,y orbitals at the K point. Furthermore, the topological properties are tunable under strain engineering and external electric field, which supplies a route to manipulate the spin/charge conductance of edge states. These findings not only provide a new platform to better understand the underlying origin of QSH effect in functionalized group-V films, but also are highly desirable to design large-gap QSH insulators for practical applications in spintronics.

Tunability of the Quantum Spin Hall Effect in Bi(110) Films: Effects of Electric Field and Strain Engineering.

The quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices due to their robust gapless edge states inside insulating bulk gap. However, the currently discussed QSH insulators usually suffer from ultrahigh vacuum or low temperature due to the small bulk gap, which limits their practical applications. Searching for large-gap QSH insulators is highly desirable. Here, the tunable QSH state of a Bi(110) films with a black phosphorus (BP) structure, which is robust against structural deformation and electric field, is explored by first-principles calculations. It is found that the two-monolayer BP-Bi(110) film obtains a tunable large bulk gap by strain engineering and its QSH effect shows a favorable robustness within a wide range of combinations of in-plane and out-of-plane strains, although a single in-plane compression or out-of-plane extension may restrict the topological phase due to the self-doping effect. More interestingly, in view of biaxial strain, two competing physics on band topology induced by bonding-antibonding and px,y-pz band inversions are obtained. Meanwhile, the QSH effect can be persevered under an electric field of up to 0.9 V/Å. Moreover, with appropriate in-plane strain engineering, a nontrivial topological phase in a four-monolayer BP-Bi(110) film is identified. Our findings suggest that these two-dimensional BP-Bi(110) films are ideal platforms of the QSH effect for low-power dissipation devices.

Robust Room-Temperature Quantum Spin Hall Effect in Methyl-functionalized InBi honeycomb film.

Two-dimensional (2D) group-III-V honeycomb films have attracted significant interest for their potential application in fields of quantum computing and nanoelectronics. Searching for 2D III-V films with high structural stability and large-gap are crucial for the realizations of dissipationless transport edge states using quantum spin Hall (QSH) effect. Based on first-principles calculations, we predict that the methyl-functionalized InBi monolayer (InBiCH3) has no dynamic instability, and hosts QSH state with a band gap as large as 0.29 eV, exhibiting an interesting electronic behavior viable for room-temperature applications. The topological characteristic is confirmed by s-pxy band inversion, topological invariant Z2 number, and the time-reversal symmetry protected helical edge states. Noticeably, the QSH states are tunable and robust against the mechanical strain, electric field and different levels of methyl coverages. We also find that InBiCH3 supported on h-BN substrate maintains a nontrivial QSH state, which harbors the edge states lying within the band gap of substrate. These findings demonstrate that the methyl-functionalized III-V films may be a good QSH platform for device design and fabrication in spintronics.

Room Temperature Quantum Spin Hall Insulator in Ethynyl-Derivative Functionalized Stanene Films.

Quantum spin Hall (QSH) insulators feature edge states that topologically protected from backscattering. However, the major obstacles to application for QSH effect are the lack of suitable QSH insulators with a large bulk gap. Based on first-principles calculations, we predict a class of large-gap QSH insulators in ethynyl-derivative functionalized stanene (SnC2X; X = H, F, Cl, Br, I), allowing for viable applications at room temperature. Noticeably, the SnC2Cl, SnC2Br, and SnC2I are QSH insulators with a bulk gap of ~0.2 eV, while the SnC2H and SnC2F can be transformed into QSH insulator under the tensile strains. A single pair of topologically protected helical edge states is established for the edge of these systems with the Dirac point locating at the bulk gap, and their QSH states are confirmed with topological invariant Z2 = 1. The films on BN substrate also maintain a nontrivial large-gap QSH effect, which harbors a Dirac cone lying within the band gap. These findings may shed new light in future design and fabrication of large-gap QSH insulators based on two-dimensional honeycomb lattices in spintronics.

Stanene cyanide: a novel candidate of Quantum Spin Hall insulator at high temperature.

The search for quantum spin Hall (QSH) insulators with high stability, large and tunable gap and topological robustness, is critical for their realistic application at high temperature. Using first-principle calculations, we predict the cyanogen saturated stanene SnCN as novel topological insulators material, with a bulk gap as large as 203 meV, which can be engineered by applying biaxial strain and electric field. The band topology is identified by Z2 topological invariant together with helical edge states, and the mechanism is s-pxy band inversion at G point induced by spin-orbit coupling (SOC). Remarkably, these systems have robust topology against chemical impurities, based on the calculations on halogen and cyano group co-decorated stanene SnXxX'1-x (X,X' = F, Cl, Br, I and CN), which makes it an appropriate and flexible candidate material for spintronic devices.

Novel band structures in silicene on monolayer zinc sulfide substrate.

Opening a sizable band gap in the zero-gap silicene without lowering the carrier mobility is a key issue for its application in nanoelectronics. Based on first-principles calculations, we find that the interaction energies are in the range of -0.09‒0.3 eV per Si atom, indicating a weak interaction between silicene and ZnS monolayer and the ABZn stacking is the most stable pattern. The band gap of silicene can be effectively tuned ranging from 0.025 to 1.05 eV in silicene and ZnS heterobilayer (Si/ZnS HBL). An unexpected indirect-direct band gap crossover is also observed in HBLs, dependent on the stacking pattern, interlayer spacing and external strain effects on silicene. Interestingly, the characteristics of Dirac cone with a nearly linear band dispersion relation of silicene can be preserved in the ABS pattern which is a metastable state, accompanied by a small electron effective mass and thus the carrier mobility is expected not to degrade much. These provide a possible way to design effective FETs out of silicene on a ZnS monolayer.

Tunable electronic and magnetic properties in germanene by alkali, alkaline-earth, group III and 3d transition metal atom adsorption.

We performed first-principles calculations to study the adsorption characteristics of alkali, alkali-earth, group III, and 3d transition-metal (TM) adatoms on germanene. We find that the adsorption of alkali or alkali-earth adatoms on germanene has minimal effects on geometry of germanene. The significant charge transfer from alkali adatoms to germanene leads to metallization of germanene, whereas alkali-earth adatom adsorption, whose interaction is a mixture of ionic and covalent, results in semiconducting behavior with an energy gap of 17-29 meV. For group III adatoms, they also bind germanene with mixed covalent and ionic bonding character. Adsorption characteristics of the transition metals (TMs) are rather complicated, though all TM adsorptions on germanene exhibit strong covalent bonding with germanene. The main contributions to the strong bonding are from the hybridization between the TM 3d and Ge pz orbitals. Depending on the induced-TM type, the adsorbed systems can exhibit metallic, half-metallic, or semiconducting behavior. Also, the variation trends of the dipole moment and work function with the adsorption energy across the different adatoms are discussed. These findings may provide a potential avenue to design new germanene-based devices in nanoelectronics.

Effect of native defects and Co doping on ferromagnetism in HfO2: first-principles calculations.

First-principles calculations of undoped HfO(2) and cobalt-doped HfO(2) have been carried out to study the magnetic properties of the dielectric material. In contrast to previous reports, it was found that the native defects in HfO(2) could not induce strong ferromagnetism. However, the cobalt substituting hafnium is the most stable defect under oxidation condition, and the ferromagnetic (FM) coupling between the cobalt substitutions is favorable in various configurations. We found that the FM coupling is mediated by the threefold-coordinated oxygen atoms in monoclinic HfO(2) and could be further enhanced in electron-rich condition.