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Many optical systems that deal with polarization rely on the adaptability of controlling light reflection in the lithography-free nanostructure. In this study, we explored the Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts at a biaxial hyperbolic film on a uniaxial hyperbolic substrate. This research statistically analyzed and calculated the GH and IF shifts for the natural biaxial hyperbolic material (NBHM). We selected the surface with the strongest anisotropy within the NBHM and obtained the complex beam-shift spectra. By incorporating the NBHM film, the GH shift caused by a transversely magnetic incident-beam on the surface is significantly enhanced compared to that on the uniaxial hyperbolic material. The maximum of GH shift can reach 86λ 0 at about 841 cm-1 when the thickness of NBHM is 90 nm, and the IF shift can approach 2.7λ 0 for a circularly-polarized beam incident on a NBHM of 1700 nm. An increase in spatial-shift was found when a highly anisotropic hyperbolic polariton is excited in hyperbolic materials, where the shift spectra exhibits an oscillating behaviour along with sharp shift peaks (steep slopes). This large spatial shift may provide an alternative strategy to develop novel sub-micrometric optical devices and biosensors.

We investigated the spin angular momentum (SAM) and nonreciprocity of ghost surface polariton (GSP) at the surface of an antiferromagnet (AF) in the normal geometry, where the AF easy axis and external field (H0) both are normal to the AF surface. We found that the dispersion equation is invariant when the inversions of wavevector and external magnetic field, k→−k and H0→−H0, are taken. However, its polarization and SAM are nonreciprocal. The SAM is vertical to the propagation direction of GSP, and consists of two components. We analytically found that the in-plane component is locked to H0, or it is changed in sign due to the inversion of H0. The out-plane one is locked to k since it is changed in sign as the inversion of k is taken. Either component contains an electric part and a magnetic part. Above the AF surface, the two electric parts form the left-handed triplet with the wavevector k, but the two magnetic parts form the right-handed triplet with k. In the AF, the chirality of the SAM changes with the distance from the surface. The SAM is very large on or near the surface and it may be very interesting for the manipulation of micron and nano particles on the AF surface. These are obviously different from the relevant features of conventional surface polaritons. The SAM also is field-tunable.

We investigated surface polaritons in a metamaterial composed of polar-crystal layers and antiferromagnetic layers. In a specific geometry, two surface polaritons were predicted, which are a unique ghost surface polariton (GSP) and surface hybrid-polarization polariton (SHP). The two surface polaritons occupy different segments of one smooth dispersion curve and are magnetically tunable. An external magnetic field along the antiferromagnetic easy axis can bring about the switch or transition between the two surface polaritons and meanwhile performs the necessary condition for the existence of two surface polaritons. In the metamaterial, either surface polariton consists of two branch waves. The branch waves of the GSP are coherent and have the same amplitude and different phases, but those of the SHP are not coherent and have different amplitudes and phases. The main characteristic of the GSP is that its fields oscillate and attenuate with the distance away from the metamaterial surface and exhibit interferent fringes on the plane normal to the surface.

Dyakonov surface polaritons (DSPs) in a single antiferromagnetic (AF) film are investigated in the parallel geometry where the AF anisotropic axis is parallel to the film and no external magnetic field is applied. The analytical dispersion relation is obtained and four surface modes are found, among which one symmetric mode and an anti-symmetric mode are exist in the AF reststrahlen frequency band, and another symmetric and anti-symmetric modes are situated out the reststrahlen band. The existence of symmetric and anti-symmetric modes is caused by the mirror symmetry and finite thickness of the AF film. A pair of modes in the band have magnetostatic limits but the other pair out the band do not. The dispersion properties, field and energy-flux density distributions of each DSP are numerically calculated based on the FeF2 film for various propagating directions and film thicknesses. It is very interesting that the energy flux of each DSP can seriously deviates from its propagation direction, and the largest walk-off angle can reach 200°. In addition, we briefly discuss dispersion properties of Dyakonov odd and even guided modes, they also are symmetric and antisymmetric and have multiple solutions.

A linearly-polarized radiation can be considered as the superposition of two circularly-polarized components with the same propagating direction and opposite spins. We investigated the splitting between the two spin-components in the reflective beam off the antiferromagnetic surface. The gyromagnetism and surface impedance mismatch cause the difference between the spatial shifts of the two spin-components, i.e., the spin-splitting. We analytically achieved the in- and out-plane shift-expressions of either spin-component for two typical linearly-polarized incident beams (i.e., the p- and s-incidences). In the case of no gyromagnetism, we obtained very simple shift-expressions, which indicate a key role played by the gyromagnetism or the surface impedance-mismatch in spin-splitting. Based on a FeF2 crystal, the spin-splitting distance was calculated. The spin-splitting distance is much longer for the p-incidence than the s-incidence, and meanwhile the in-plane splitting distance is much larger than the out-plane one. The gyromagnetism plays a key role for the in-plane spin-splitting and the surface impedance-mismatch is a crucial factor for the out-plane spin-splitting distance. The results are useful for the manipulation of infrared radiations and infrared optical detection.

Magnon transfer torque (MTT) is regarded as capable of manipulating spin by magnons or spin waves only without spatial movement of electrons, which is a key to enrich the toolbox for magnonics. Here using a magnon current through an antiferromagnetic NiO spacer, which can be deep into a magnetic insulator ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG), we demonstrated the perpendicular magnetization of the YIG in a YIG/NiO/Pt heterostructure could be switched. When the thickness of the magnon channel NiO was 1.5 nm, the magnon current could still maintain about $84%$ of the spin current for the YIG/Pt control device, indicating high efficiency of the NiO spacer in transferring magnon torque. Switching the perpendicular magnetization in the YIG/NiO/Pt heterostructures unambiguously verified the effect of magnon transfer torque (MTT), which may advance the development of magnonic memories and logics.

We predicted one Dyakonov surface magnon (DSM) and two Dyakonov magnon polaritons (DSMPs) localized at the antiferromagnet (AF)-air interface. Their concise dispersion equations and necessary conditions of existence were obtained. The DSM is the magnetostatic limit of the first DSMP, which are situated inside the AF reststrahlen frequency band. The second DSMP has no magnetostatic limit and lies outside the frequency band. The specifical frequency ranges occupied by the DSM and DSMPs were analytically found. The DSMPs are hybrid-polarization surface polaritons and the DSM is a hybrid-polarization surface magnetostatic mode. The first DSMP possesses large attenuation constants so that it is highly localized at the surface. Compared with it, the second DSMP exhibits relatively small attenuation constants. According to the features of polarization obtained for either DSMP, we used the TE and TM radiations incident on the AF surface to calculate attenuated total reflection (ATR) spectra, respectively. These ATR spectra not only further prove the existence of the DSMPs but also demonstrate their observability in experiment. However, the DSM should be detected by means of a light-scattering technique.

Three Dyakonov-like polaritons (DLPs) exist at the interface between a hyperbolic material (HM) and a covering medium (CM). Each DLP is a hybridized-polarization surface polariton composed of two evanescent waves on both sides of the interface. We investigated their spin and angular momentum. We analytically found that any DLP carries two spins producing mutually orthogonal spin angular-momentum (SAM) components. The spins and angular-momentum have different features on both sides of the interface, and further differences among the three DLPs are very obvious. For the interface structure formed by hexagonal boron nitride (hBN) and air, the SAM mainly distributes in the air for DLP-I, the SAM is approximately transverse to the propagating direction for DLP-II, and it is surprisingly large in the hBN for DLP-III and can reach several ten times that in the usual situation. There is the spin-k locking for every DLP, but the spin-k locking is different for different DLPs. These properties do not exist for traditional surface polaritons or ordinary evanescent waves. The above unique results can support some potential applications in the fields of nano- and micro-photonics, optoelectronics and mechanics, as well as relevant technologies.

We investigated Goos–Hänchen (GH) and Imbert–Fedorov (IF) shifts of a reflective beam on a twisted bilayer of hexagonal boron nitride (hBN), where a left circularly polarized beam was incident on the surface. Our results demonstrate that the twist angle between the two optical axes plays an important role in obtaining large shifts with a high reflectivity. The GH shift with 10λ 0 is achieved, while the reflectivity is near 100% by tuning the twist angle. The maximum of the IF shift is found in the certain condition satisfied by the reflective coefficients, and the shift strongly depends on the twist angle between the optical axes of the two slabs. The spatial shifts obtained directly from the GH and IF shift definitions were provided, which indicate that the theoretical results from the stationary phase method are believable. These results may open up a new way for developing the nano-optical devices.

The generation of elliptically polarized electromagnetic wave of an antiferromagnetic (AF)/dielectric sandwiched structure in the terahertz range is studied. The frequency and external magnetic field can change the AF optical response, resulting in the generation of elliptical polarization. An especially useful geometry with high levels of the generation of elliptical polarization is found in the case where an incident electromagnetic wave perpendicularly illuminates the sandwiched structure, the AF anisotropy axis is vertical to the wave-vector and the external magnetic field is pointed along the wave-vector. In numerical calculations, the AF layer is FeF2 and the dielectric layers are ZnF2. Although the effect originates from the AF layer, it can be also influenced by the sandwiched structure. We found that the ZnF2/FeF2/ZnF2 structure possesses optimal rotation of the principal axis and ellipticity, which can reach up to about thrice that of a single FeF2 layer.

A tunable terahertz (THz) metasurface (MS) absorber based on the surface phonon polariton (SPhP) is proposed based on a layered structure that consists of a split-silver-ring array followed by a graphene layer, polar crystal layer, and silver layer. A dynamically tunable, polarization-independent, and angle-insensitive MS absorber is numerically investigated at THz frequencies. By changing the Fermi energy of graphene from 0 to 1.0 eV, the state of the absorber can switch between the OFF state (with an absorptivity above 90%) and ON state (with an absorptance below 3%). The switching intensity (SI) of the absorber remains greater than 80% for TE incidence wave with incident angles from 0° to 70° and for TM incidence wave incident angles from 0° to 40° in the frequency range from 2.74 to 3.51 THz. These results should be helpful in guiding the design of THz tunable devices such as optical switches, smart absorbers, and imaging.

Goos–Hänchen (GH) and Imbert–Fedorov (IF) shifts of reflected beams and the effects of two Dyakonov surface magnon polaritons (DSMPs) on these shifts are studied in the Otto configuration with an antiferromagnetic substrate. A modified dispersion equation of the DSMPs is proposed to recognize GH and IF shifts related to the DSMPs. Reflected beam shift spectra are simulated for a F e F 2 substrate. Shift features around the two DSMPs are observed by frequency scanning with a fixed incident angle. The GH-shift amplitude corresponding to either DSMP is situated between the immediately adjacent maximum and minimum of a GH-shift curve. The shift-amplitude maximum of an IF-shift curve corresponds to the relevant DSMP accurately. GH and IF shifts also are given by frequency scanning along dispersion curves.

A polarization-dependent and angle-insensitive absorber based on surface phonon polaritons (SPhPs) is proposed based on a sandwiched layer structure that consists of a patterned α - M o O 3 layer, a dielectric layer, and a gold layer. The absorption remains larger than 95% for TE incidence wave with incident angles from 0° to 30° in the wavelength range from 13.7 to 18.3 µm, which is a broadband absorber. At the same time, the absorption remains larger than 95% for TM incidence wave with incident angles from 0° to 60° in the wavelength range from 11.52 to 11.66 µm, which is a narrowband absorber. It is interesting that the absorber can also be used to fabricate the ideal filter of transverse electric (TE) wave in the wavelength range from 11.52 to 11.66 µm and an ideal filter of transverse magnetic (TM) wave from 15.03 to 18.37 µm. Moreover, one can combine an ideal filter of polarization and a perfect absorber into one single device. The proposed absorber shows promising performance, which has potential applications in sensing, imaging, and detection.

We present a detailed study on the tunable propagation derived from the coupled surface plasmon–phonon polaritons (SPPPs) with the effective medium theory (EMT) in graphene-hBN metamaterials (MMs). Four reststrahlen bands (RBs) are observed, two of which mainly come from the hBN and the others originate from the effect of the graphene. The RBs frequency windows can be adjusted by the chemical potential and the filling ratio. An epsilon-near-zero-and-pole( e NZP )hyperbolic metamaterial (HMM) is detected at the precise frequency, chemical potential and filling ratio where the HMM undergoes a completely inversion of anisotropy. We derive the relative dispersion relation and demonstrate that the propagation of SPPP modes can be regulated by modifying the chemical potential. In addition, the tunability of the graphene-hBN MMs also can be improved by changing the thicknesses of the hBN and the number of graphene sheets. The energy-flux density in the graphene-hBN MM seriously deviates from its wave vector and can be localized at a certain depth. Besides, the ghost SPPP modes with the oscillation-attenuation character are observed at some special conditions through checking the distribution of electric fields. The attenuation total reflection (ATR) measurement is established to examine these SPPP modes. The numerical results show that the observation of each SPPP modes requires different conditions dictated by material parameters and the polarization direction of the incident light.

We theoretically studied the Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of reflective beam at the surface of graphene/hBN metamaterials. The results show that the GH-shift is significantly enhanced and also possesses the large reflectivity when the light beam is incident at the critical angle near the Brewster angle. We found that the IF-shift is the largest when the reflective beam is a special polarized-beam or the reflective coefficients satisfy the conditions |r s | = |r p | and φ s − φ p = 2jπ (j is an integer). By changing the chemical potential, filling ratio and tilted angle, the position and width of frequency windows obtaining the maximum values of shifts can be effectively adjusted. The large and tunable GH- and IF-shifts with the higher reflectivity provide an alternative scheme to develop new nano-optical devices.

We investigated Goos–Hänchen (GH) and Imbert–Fedorov (IF) shifts of the reflective beam from a uniaxial hyperbolic crystal (HC) with a metasurface (MS) that is a subwavelength rectangular-grating layer. Due to the optical axis of this MS normal to that of the HC, this structure is similar to a biaxial HC for the reflective beam. We obtained analytical expressions of reflective beam for any polarized incident light beam and then derived the GH and IF shifts of the relevant reflective beam. Based on the hexagonal boron nitride crystal (hBN), we numerically simulated shift spectra of the reflective beam for differently polarized incident beams. We compared the results obtained from this structure with those for the bulk hBN or MS layer with infinite thickness. We found that the shift spectra from this structure resemble neither those from the bulk hBN nor those from the MS layer so that they are much more complicated than those in the two extreme cases. The effect of the MS coupling with the hBN substrate is very remarkable. First, both the GH and IF shifts are evidently enlarged, especially the IF shift. Second, the shift spectra exhibit oscillation behavior and sharp shift peaks or dips. Finally, the MS brings out the nonreciprocity of the two shifts for the circularly polarized incident beams.

The one-way optical effect in a dielectric/perforated metal/antiferromagnetic (DPMA) sandwich structure in the terahertz range is studied. Theoretical modeling, which is based on the effective medium theory and the transmission matrix method, is conducted. The simulation results show that the one-way effect occurs within a wide frequency range and for various incident angles with a fixed external magnetic field. In addition, this behavior is examined for various DPMA structural characteristics, such as different dielectric materials, film thicknesses, and perforated metal hole sizes and spacings. The developed sandwich structures can aid the design of subminiature optical isolators for application in the terahertz range.

We investigated Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts on a uniaxial hyperbolic crystal, where a circularly-polarized beam was incident on the crystal from the free space. The GH- and IF-shifts were analytically obtained and numerically calculated for the hexagonal boron nitride. Our results demonstrate that the GH- and IF-shift spectra are complicated and completely different in and out the hyperbolic frequency-bands (the reststrahlen bands in the infrared region). At the critical or Brewster angle, concisely analytical expressions of GH-shift was found, which explicitly state the optical-loss dependence of GH-shift at these special angles. We found the GH-shifts are very large at the critical and Brewster angles. It is very necessary to know these effects since hyperbolic materials are usually applied in the nano- and micro-optics or technology fields.

Two Dyakonov-like polaritons (DLPs) were found in the hexagonal boron nitride (hBN). DLP-I lies in the lower reststrahlen band (RB-I) where the hBN is a hyperbolic material, but DLP-II exists in a narrower frequency region where the hBN is an elliptical material, adjacent to the higher reststrahlen band (RB-II). After uniformly considering the DLP electromagnetic fields on the two sides of the hBN surface, we found that the two DLPs are highly confined in the hBN, and even are completely confined in a certain wave-vector. And also, the Poynting vector of either DLP in the hBN seriously deviates from its wave vector and the directional difference outside and inside the hBN dramatically changes with the distance from the surface. The above extraordinary results can support some potential applications in the mid-infrared range, such as high-efficient energy conduction, strictly manipulating infrared-ray direction and infrared-filtering as well as continuous light-splittingfrom micro-meter to nano-meter dimensions.

We theoretically propose a narrowband perfect absorber metasurface (PAMS) based on surface phonon polaritons in the terahertz range. The PAMS has unit cell consisting of a silver biarc on the top, a thin polar-dielectric in the middle and a silver layer at the bottom. The phonon polaritons are excited at the interface between the silver biarc and the polar dielectric, and enhance the absorption of the PAMS. The absorption peak is at 36.813 μm and the full width half maximum (FWHM) is nearly 36 nm, independent of the polarization and incidence angle. The electric fields are located at the split of the biarc silver layer and the quality factor Q is 1150. The FWHM decreases with the decreasing split width. When the thickness of the bottom layer is larger than 50 nm, the narrow band and high absorption are insensitive to the thickness of those layers. The designed absorber may have useful applications in terahertz spectra such as energy harvesting, thermal emitter, and sensing.

The surface plasmonic polariton (SPP) of a transversely-truncated metal/dielectric superlattice (SL) structure has been solved with an approximate method. The effect of inter-layer interfaces in the SL is taken into consideration efficiently in comparison with the effective-medium method. The silver/air and silver/SiO2 SLs with a shorter period are regarded as two specific examples in numerical calculation. A series of separated SPP modes are found and highly localized at the surface, and the highest-frequency mode is the only one also predicated by the effective-medium method. These results obviously show the effect of inter-layer interfaces in the case of short period, whilst the reliability and limitation of the effective-medium method is presented as well. Because the skin depths of the modes are extremely small, the SLs can be used as ideal surface-wave waveguides.

Recent studies have suggested that chemical functionalization is a promising avenue to tailor the band gap of silicene, which plays an important role on widening its application. Here, we propose a new route to functionalize silicene, that is asymmetrically modification of silicene (Janus silicene or X –silicene– Y ), which is produced by co-grafting of two different groups ( X and Y ) on both sides of silicene. By performing density functional theory (DFT) calculations, we demonstrate the stability and electronic properties of X –silicene– Y sheets. The results indicate that chemical functionalization on one side can greatly enhance the chemical reactivity of the opposite side, suggesting the communication between the two adsorbed groups and enhancing the stability of the hybrids. Compared to the pristine silicene with a zero band gap, X –silicene– Y sheets exhibit semiconducting nature with a non-zero band gap, which is dependent on the coverage of X / Y . Our results provide a novel and effective method to engineer the band gap of silicene, which would be useful to design novel silicene-based devices with multiple functions.

Magnetically recyclable materials should be ideal support in photocatalytic system because they permit the photocatalysts to be recovered rapidly and efficiently by applying an external magnetic field such as, MnF2. In this paper, MnF2and SiO2layers constitute a one-dimensional quasiperiodic photonic crystal according to Fibonacci. When the electromagnetic wave irradiates obliquely, the transmission peak moves to higher frequency direction with the angle increasing. Both the number of transmission peaks and the transmission peaks of double-forked structure increase with the increase of structural progression. We also found that the polarization of electromagnetic waves has influence on the transmission properties; TM wave transmission peak half wide is significantly greater than TE wave transmission peak half wide. The band gap near antiferromagnetic (AF) resonance frequency becomes narrow as the intensity of the applied static magnetic field increases. The as-prepared photonic crystal has tremendous potential practical use to eliminate organic pollutants from wastewater.

Novel hierarchical SnO2 hollow nanospindles self-assembled from nanorods have been successfully synthesized via a templating approach under hydrothermal conditions. The influence of the reactant concentration on SnO2 products is investigated in detail. It is found that the interplay of the acidic etching of Fe2O3 templates and controlled hydrolysis of SnCl2 is significant for the formation of the hierarchical SnO2 hollow nanostructures. The evolution process and formation mechanism of the hollow structures with nanorods are analyzed from the angle of nucleation and morphology. Moreover, the electrochemical properties of the hollow structures are also studied by charge–discharge cycling, the result displays that the hierarchical SnO2 hollow nanostructure exhibits much better lithium storage properties with higher reversible capacities and enhanced cyclic capacity retention than the commercial SnO2 nanoparticles.

A new way to increase the sum-frequency generation based on the antiferromagnetic sandwich structure in the THz frequency field is presented. We find that the SF outputs near the higher resonant frequencies are stronger than those near the lower ones and the effect of the dielectric on sum-frequency outputs also is discussed.

Recent studies have shown that two-dimensional nanomaterials can serve as excellent candidates for the support of metal nanoparticles, thus rendering them to have potential applications for developing novel electrocatalysts in the oxygen reduction reaction (ORR). In this work, by performing density functional theory calculations, we investigate the structural and electronic properties of Pt clusters deposited on several defective hexagonal boron nitride (h-BN) sheets as well as their interaction with O that is closely related to the electrocatalytic activity of these composites in ORR. As compared with the pristine h-BN sheet, we find that the binding strength of Pt clusters on defective h-BN sheets is significantly enhanced, which is attributed to their strong hybridization with the sp2 dangling bonds at the vacancy site. Thus, the point defect on h-BN sheets plays a key role on anchoring Pt clusters, ensuring their high stability. More importantly, the interfacial interaction can effectively modify the ...

In the present work, we have investigated the stable configurations, electronic, and magnetic properties of the functionalized boron nitride (BN) nanosheets by NH x (x = 0, 1, and 2) groups by performing comprehensive density functional theory (DFT) calculations. The results indicate that these groups can be stably incorporated into BN nanosheet, resulting in the formation of covalent bonds between these adsorbates and BN sheet. The adsorption energies of the most stable configurations are − 2.80, − 2.42, and − 0.33 eV, respectively, for the adsorption of N, NH, and NH 2 groups on BN nanosheet. The electronic structures of BN nanosheets are found to be effectively modified by these groups due to the introduction of certain impurity states within the band gap of the pristine BN nanosheet, thereby reducing the band gaps in various ways. The relationship between the electronic structures and the configurations of these functionalized BN nanosheets is also addressed by exploring the projected density of states combined with charge transfer analysis. In particular, the attachment of the N and NH 2 groups renders BN nanosheet to exhibit magnetic nonzero magnetic moment, contributed mainly by the N atoms of adsorbates. The present results are expected to open a way to change the electronic and magnetic properties of BN nanosheet, which is helpful to design or develop novel nanodevices based on BN nanosheet.

The reflection and refraction were theoretically investigated for a linearly-polarized wave incident upon the surface of a naturally hyperbolic material. We proposed that this material is uniaxial and possesses two hyperbolic-frequency bands (HB-I and HB-II), whose optical axis is arbitrarily pointed. We paid our attention to reflective and refractive features in the HBs and predicted some extraordinary phenomena. The double reflection was found, where the reflective wave contains a transverse electric branch and a transverse magnetic branch with different amplitudes and phases. The asymmetry of reflection exists and the reflective coefficient abnormally decreases as the incident angle is enlarged. The double refraction inside the material means two refractive branches (the o-wave and e-wave). For the e-wave, there is a special frequency point (SP) in either HB, depending on the orientation of the optical axis. The e-wave and reflective wave exhibit completely different behaviors on the two sides of the SP. The e-wave is a normal refractive wave on the left side of the SP, but it is an evanescent wave on the right side. Its energy-flux seriously deviates from the incident plane and is highly condensed at the inner surface near the SP. It is more interesting that the energy-flux density of the e-wave in the HB-II can even be much larger than that of the incident wave and is opposite in direction on the two sides of the SP, which means an evident radiation-switching effect. The o-wave is a normal refractive wave in the HB-I, but it is an evanescent wave in the HB-II. The above results and conclusions were obtained from the hexagonal boron nitride (hBN). These unique properties may be very useful in optical or optoelectronic technology.

We theoretically investigated the Goos–Hanchen shift (GHS) on the surface of a polar crystal, where a polarized beam was incident on the crystal from any positive permittivity medium. Attention was focused on GHS’s features for the incident-beam frequency lies near or in the reststrahlen band of the crystal. The GHS expressions were obtained for the s- and p-polarized incident beams, respectively. Our results demonstrate that the GHS properties are completely different for differently polarized incidences. The concise expression of GHS was obtained for the crystal with a low optical loss, accompanied by a large GHS in the vicinity of the critical or Brewster angle. In comparison with the optically lossless case, the effect of the loss on the GHS was clearly indicated. Unlike photonic crystals and metamaterials, the crystal used here is a natural material whose interesting frequency range is in the infrared region, and optical loss is much lower. The present GHS can be more easily observed and technically applied because the incident medium above the crystal surface can be any positive permittivity medium. The numerical results were obtained from the interface structure of the ZnS crystal and free space.

We report on a way to obtain a new source in THz frequency field based on sum frequency (SF) generation of an antiferromagnetic film (AFF). The continuous SF output windows versus the infrared signal wave frequencies are shown. We found that the highest SF outputs can be induced when the frequencies of the two signal waves are both situated at the vicinity of the same resonant frequency of AFF. In addition, the incident angles are in the smaller angle regions. An optimum interact length is defined which should be necessary for the choice of AFF thickness in the experiments. Finally, the frequencies of highest SF outputs can be modulated by controlling the external magnetic field strength.

Motivated by the great advance in graphene hydroxide--a versatile material with various applications--we performed density functional theory (DFT) calculations to study the functionalization of the two-dimensional hexagonal boron nitride (h-BN) sheet with hydroxyl (OH) radicals, which has been achieved experimentally recently. Particular attention was paid to searching for the most favorable site(s) for the adsorbed OH radicals on a h-BN sheet and addressing the roles of OH radical coverage on the stability and properties of functionalized h-BN sheet. The results indicate that, for an individual OH radica, the most stable configuration is that it is adsorbed on the B site of the h-BN surface with an adsorption energy of -0.88 eV and a magnetic moment of 1.00 μ(B). Upon adsorption of more than one OH radical on a h-BN sheet, however, these adsorbates prefer to adsorb in pairs on the B and its nearest N atoms from both sides of h-BN sheet without magnetic moment. An energy diagram of the average adsorption energy of OH radicals on h-BN sheet as a function of its coverage indicates that when the OH radical coverage reaches to 60 %, the functionalized h-BN sheet is the most stable among all studied configurations. More importantly, this configuration exhibits good thermal and dynamical stability at room temperature. Owing to the introduction of certain impurity levels, the band gap of h-BN sheet gradually decreases with increasing OH coverage, thereby enhancing its electrical conductivity.

Density functional theory (DFT) calculations were performed on the NO reduction on the silicon (Si)-doped graphene. The results showed that monomeric NO dissociation is subject to a high barrier and large endothermicity and thus is unlikely to occur. In contrast, it was found that NO can easily be converted into N2O through a dimer mechanism. In this process, a two-step mechanism was identified: (i) the coupling of two NO molecules into a (NO)2 dimer, followed by (ii) the dissociation of (NO)2 dimer into N2O + O(ad). In the energetically most favorable pathway, the trans-(NO)2 dimer was shown to be a necessary intermediate with a total energy barrier of 0.464 eV. The catalytic reactivity of Si-doped graphene to NO reduction was interpreted on the basis of the projected density of states and charge transfer.

Recently, doping non-carbon atoms into graphene or carbon nanotube (CNT) has attracted considerable attention due to its effectiveness to change or tailor their electronic and magnetic properties as well as chemical reactivity. In this work, we present a density functional theory study of the recently synthesized phosphorus (P) doped graphene and CNT. Particular attention is paid to studying the effects of P-doping on the structural, electronic, and magnetic properties as well as chemical reactivity of graphene or CNT. The results show that P dopant drastically changes the geometrical structure of graphene or CNT, rendering P and its neighboring C atoms protrude from the sidewall of CNT and graphene. Moreover, P-doping induces localized electronic states into graphene and CNTs, thus modifying the electronic properties by producing n-type behavior. Meanwhile, due to P doping, the graphene and CNT exhibit magnetic nature with spin net moment of 1.02 and 0.99 μB, respectively. In order to evaluate the chemical reactivity of the two nanostructures, their interactions with several gas molecules, including NH3, H2O, O2, NO2, and NO, are further calculated. Our results may be useful not only for deeply understanding the properties of CNTs and graphenes, but also for developing various novel nanodevices.

Recently, the adsorption and dissociation of oxygen molecule on a metal-free catalyst has attracted considerable attention due to the fundamental and industrial importance. In the present work, we have investigated the adsorption and dissociation of O(2) molecule on pristine and silicon-doped graphene, using density functional theory calculations. We found that O(2) is firstly adsorbed on Si-doped graphene by [2+1] or [2+2] cycloaddition, with adsorption energies of -1.439 and -0.856eV, respectively. Following this, the molecularly adsorbed O(2) can be dissociated in different pathways. In the most favorable reaction path, the dissociation barrier of adsorbed O(2) is significantly reduced from 3.180 to 0.206eV due to the doping of silicon into graphene. Our results may be useful to further develop effective metal-free catalysts for the oxygen reduction reactions (ORRs), thus greatly widening the potential applications of graphene.

The effect of magnetic field on the discotic nematic liquid crystalline polymers (LCPs) is analyzed with the extended Doi theory, in which the molecular shape parameter (β) is defined at −1.0. The evolution equation for the probability function of the discotic nematic LCP molecules is solved without any closure approximations. The transition among flow-orientation modes, such as tumbling, wagging, and aligning defined similar to the rodlike LCPs, is strongly affected by the magnetic fields. The new aligning flow-orientation mode observed for the rodlike LCPs under magnetic fields also can be investigated in the lower shear rate region. On the other hand, the effect of magnetic fields parallel to the x- and y-axis on the time-averaged first and second normal stress differences ( , ) are also studied. It can be seen that the shear rate regions of the sign changes of , are completely contrary to those conclusions achieved for the rodlike LCPs. In addition, the absolute values of increase with the magnetic field strength in the lower shear rate range owing to the new aligning flow-orientation mode. Finally, the flow-phase diagram versus β is also discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The magnetically nonlinear optical transmission of the Fabry-Perot resonator tilled with an antiferromagnetic medium is discussed. In a proper incident power range, we find the bistable switches can appear even for a very thin medium film, such as of half-wavelength thickness. All results are based on antiferromagnetic FeF2 medium with far-infrared resonant frequencies.

Second harmonic generation (SHG) from a short-period structure composed of alternating antiferromagnetic (AF) and ionic-crystal layers is investigated, where the generated harmonic waves are situated in the far-infrared range and attributed to the magnetically nonlinear interaction in AF layers. The presence of a kind of appropriate ionic-crystal layers in the structure can support negative refraction for the pumping wave and positive refraction for the SH wave, so the SHG is greatly amplified in the vicinity of each AF resonant frequency. For the composite structure FeF 2 /TlBr, we found that the SH output is about 8 times higher than that of the FeF 2 bulk in the same frequency range.

Recently, the grafting of polymer chains onto nanotubes has attracted increasing attention as it can potentially be used to enhance the solubility of nanotubes and in the development of novel nanotube-based devices. In this article, based on density functional theory (DFT) calculations, we report the formation of trans-polyacetylene on single-walled carbon-doped boron nitride nanotubes (BNNTs) through their adsorption of a series of C(2)H(2) molecules. The results show that, rather than through [2 + 2] cycloaddition, an individualmolecule would preferentially attach to a carbon-doped BNNT via "carbon attack" (i.e., a carbon in the C(2)H(2) attacks a site on the BNNT). The adsorption energy gradually decreases with increasing tube diameter. The free radical of the carbon-doped BNNT is almost completely transferred to the carbon atom at the end of the adsorbed C(2)H(2) molecule. When another C(2)H(2) molecule approaches the carbon-doped BNNT, it is most energetically favorable for this C(2)H(2) molecule to be adsorbed at the end of the previously adsorbed C(2)H(2) molecule, and so on with extra C(2)H(2) molecules, leading to the formation of polyacetylene on the nanotube. The spin of the whole system is always localized at the tip of the polyacetylene formed, which initiates the adsorption of the incoming species. The present results imply that carbon-doped BNNT is an effective "metal-free" initiator for the formation of polyacetylene.

The magnetically optical bi-stability, a third-order nonlinear response, is investigated on an antiferromagnetic (AF) sandwich structure, where an AF film is sandwiched between two dielectric films. The configuration with the AF anisotropy axis and external static magnetic field both in the interfaces and normal to the incident plane is used. The incident wave is taken as a TE wave with its electric component transverse to the incident plane. We find that bistable switches can appear only in a finite frequency range and an incident angle range for a given regime of incident power, which means that there are the critical incident angle and frequency. The power threshold value for the bi-stability increases with the incident angle. In addition, the bi-stability also easily is modulated by the external magnetic field.

Transmission, refraction and absorption properties of an antiferromagnetic/ion-crystal superlattice are investigated. The transmission spectra based on FeF 2 /TlBr superlattices reveal that there exist two intriguing guided modes in a wide stop band. Additionally, FeF 2 /TlBr superlattices possess either the negative refraction or the quasi left-handedness, or even simultaneously hold them at certain frequencies of two guided modes, which require both negative magnetic permeability of antiferromagnetic layers and negative permittivity of ion-crystal layers. Frequency regimes of the guided modes will be dependent on the magnitude of the external magnetic field. Therefore, handedness and refraction properties of the system can be manipulated by modifying the external magnetic field. Absorption spectra exhibit that absorption corresponding to guided modes is noticeable.