We examine the efficacy of Dark-mode plasmonics as a platform for enhanced magneto-optics. Dark-mode of a small particle consists of two co-existing equal-intensity and mutually opposing dipolar excitations. Each of these two opposing dipoles may even resonate at or near the dark-mode frequency , but the net dipole moment vanishes due to the mutual cancelation between the opposing dipoles. We show that application of external magnetic bias may alleviate the intense destructive interference. Furthermore, under external magnetic bias the opposing dark-resonances of a plasmonic particle shift in opposite directions and create a region of extremely sensitive Faraday rotation. We show that the magnetized dark resonance in lossless Ag-like particle may provide more than 20 degrees rotation under magnetic fields of the order of 1-2 Tesla, exhibiting magneto-plasmonic activity that is 2-3 orders of magnitude larger than that observed in conventional plasmonic particle of the same material. 1 Dark modes of an open optical structure can be described as states of excitations that incorporate mutually opposing local dipoles whose far-fields interfere destructively. The net dipolar excitation then vanishes, resulting in a significant reduction of the far-field radiation, and consequently a reduction of the associated radiation damping and bandwidth. 1-8 This, in turn, may trap optical fields in a structure that is inherently coupled to a continuum. More formally, dark modes can be viewed as manifestations of discrete eigenvalues embedded within the continuous spectrum of the associated non-compact scattering operator. Dark modes were suggested as candidates for electromagnetic energy storage, enhanced biological and chemical sensors , and nanoscale waveguides. These modes can be supported by simple structures such as nano-dimers (see, e.g. the "anti-bonding" plasmons in Ref. [ 1]), trimers, 6 clustered nano-rods 3 and spheres. 7,8 In a seemingly unrelated research endeavor, nonreciprocal magneto-optics and its implementation for one-way waveguides, optical isolators and circulators, and Faraday rotators, have been under intensive study. 9-14 Currently the major drawback of nonreciprocal magneto-optics is the requirement for strong magnetic bias B 0. Efforts to reduce B 0 for various applications (e.g. Faraday polarization rotation) in plasmonic structures can be found, e.g. in. 15-17 The work in 15 reports on an experimental evidence for a 2-3 fold enhancement of magneto-optical activity in coated nano-particles. The efforts in 16,17 are limited to graphene metasurfaces. Here we study the effect of bias magnetization on plasmonic particle dark modes, and explore its potential applications as a new platform for non-reciprocal optics. As a simple and physically transparent test-case, we consider the core-shell spherical particle shown in Fig. 1, made of two plasmonic materials with close, but not identical , plasma frequencies. The structure is excited by a linearly polarized local field E L (r) = ˆ zE L e iky. When properly d...

nanotube is observed and the lower side of the wall corresponds to the outside of the nanotube. The thickness of the wall is about 3.3 nm and it consists of many parallel graphene layers. Each layer, however, curves and wrinkles to some extent, indicating lower crystallinity of the present nanotubes than the ones prepared by other methods, such as arc discharge synthesis. It should be noted that this image does not exhibit any clear difference in crystallinity between pure carbon layers (upper half of the wall) and N-doped layers (the lower half). In the case of nanotubes from P-A CVD, their HRTEM images (not shown here) were found to be very similar to the image of Figure 4, and again there was no crystallinity difference between N-doped and undoped multiwalls.In conclusion, this study has demonstrated the fabrication of aligned carbon nanotubes with double coaxial structure of N-doped and undoped multiwalls. It can be determined whether the N-doped layer belongs to the inner or outer multiwalls by changing the sequence of the two-step CVD process. Moreover, the thickness of both the N-doped and pure carbon layers is controllable by changing each CVD period. The use of the AAO film as a template enables us for the first time to precisely control the nitrogen location in N-doped carbon nanotubes. Since nitrogen doping would enhance the electron-conducting properties of carbon nanotubes, the present carbon nanotubes may exhibit excellent performance as field electron emitters. The present technique opens up a novel route for the synthesis of heteroatom-doped carbon nanotubes with double coaxial structure and furthermore this will lead to the production of coaxial heterojunctions (pn, npn, or pnp) by stacking N-and B-doped layers. ExperimentalBy anodic oxidation of an aluminum plate, an AAO film with a channel diameter of 30 nm and a thickness of about 70 lm was prepared. Details are given elsewhere [13]. The resultant AAO film was placed on a quartz boat in a horizontal quartz reactor (inside diameter 55 mm). The reactor temperature was then increased to 800 C under N 2 flow. When the temperature reached 800 C, propylene gas (1.2 % in N 2 ) was passed through the reactor at a total flow rate of 1000 cm 3 (STP)/min. After the 2 h carbon deposition from propylene, the reactor was cooled down to room temperature and the carbon-coated AAO film taken out. In the second step, the carbon-coated film was placed in the reactor again and acetonitrile vapor (4.2 % in N 2 of 500 cm 3 (STP)/min) was allowed to flow over the film at 800 C. The vapor was generated by bubbling N 2 through acetonitrile liquid in a saturator kept at 0 C. This acetonitrile CVD was performed for 5 h. After this two-step sequential CVD process, the doubly coated AAO film was treated with 10 M NaOH solution at 150 C for 6 h to remove the alumina template, thereby liberating the nanotubes from the template AAO film.The carbon-coated AAO films and the corresponding carbon nanotubes were analyzed by X-ray photoelectron spectroscopy (XPS). The samples were...

With innovative modern material-growth methods, a broad spectrum of fascinating materials with reduced dimensions-ranging from single-atom catalysts, nanoplasmonic and nanophotonic materials to two-dimensional heterostructural interfaces-is continually emerging and extending the new frontiers of materials research. A persistent central challenge in this grand scientific context has been the detailed characterization of the individual objects in these materials with the highest spatial resolution, a problem prompting the need for experimental techniques that integrate both microscopic and spectroscopic capabilities. To date, several representative microscopy-spectroscopy combinations have become available, such as scanning tunneling microscopy, tip-enhanced scanning optical microscopy, atom probe tomography, scanning transmission X-ray microscopy, and scanning transmission electron microscopy (STEM). Among these tools, STEM boasts unique chemical and electronic sensitivity at unparalleled resolution. In this Perspective, we elucidate the advances in STEM and chemical mapping applications at the atomic scale by energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy with a focus on the ultimate challenge of chemical quantification with atomic accuracy.

Previous investigations of surface plasmons in Ag largely focused on their excitations in the visible spectral regime. Using scanning transmission electron microscopy with an electron beam of 0.2 nm in conjunction with electron energy-loss spectroscopy, we spectrally and spatially probe the surface plasmons in individual Ag nanoparticles (approximately 30 nm), grown on Si, in the ultra-violet spectral regime. The nanomaterials show respective sharp and broad surface-plasmon resonances at approximately 3.5 eV (approximately 355 nm) and approximately 7.0 eV (approximately 177 nm), and the correlated spectral calculations established their multipolar characteristics. The near-field distributions of the surface plasmons on the nanoparticles were also mapped out, revealing the predominant dipolar nature of the 3.5 eV excitation with obvious near-field enhancements at one end of the nano-object. The unveiled near-field enhancements have potential applications in plasmonics and molecular sensing.