Mass-positioning of Nanodiamonds Using Squeegee Technique

Fluorescent color centers in diamond nanocrystals have recently become the focus of researchers because of their potential applications in quantum information processing, nano-sensing, biomarking, and bioimaging. One of the biggest challenges in working with nanodiamonds is how to position them precisely and efficiently to create strong interaction with nanoscale photonic structures. The most popular methods to position nanodiamonds are spin-coating and transporting via scanning probe microscope tip. On the one hand, spin-coating, where nanodiamonds are randomly located, is not precise; on the other hand, the tip-based technique, where a single nanodiamond is picked and dropped, is tedious and time-consuming. Hence, we suggest a squeegee technique for mass-positioning nanodiamonds relatively precise and fast. We fabricated nanohole arrays in a 100-nm-thick silver film using electron beam and focused-ion-beam lithography techniques. In the scope of study, we found that the optimal nanohole diameter is 125nm. The proposed method for positioning nanodiamonds consists of two stages. First, we located the nanocrystals by sweeping with cleanroom wipers a droplet of a highly concentrated aqueous suspension of nanodiamonds on the fabricated nanohole arrays. Second, nanodiamonds lying outside the nanoholes are washed away by sweeping a water droplet. In order to prove the quality of the technique, we have studied the hole filling ratio using scanning electron microscopy. Our analysis showed that the filling probability is close to 100%. This technique can potentially facilitate our further experiments where nanodiamonds are coupled to nanophotonic structures

Plasmonic waveguides cladded by hyperbolic metamaterials

Strongly anisotropic media with hyperbolic dispersion can be used for claddings of plasmonic waveguides. In order to analyze the fundamental properties of such waveguides, we analytically study 1D waveguides arranged of a hyperbolic metamaterial (HMM) in a HMM-Insulator-HMM (HIH) structure. We show that hyperbolic metamaterial claddings give flexibility in designing the properties of HIH waveguides. Our comparative study on 1D plasmonic waveguides reveals that HIH-type waveguides can have a higher performance than MIM or IMI waveguides

Plasmonic waveguides with hyperbolic multilayer cladding

Engineering plasmonic metamaterials with anisotropic optical dispersion enables us to tailor the properties of metamaterial-based waveguides. We investigate plasmonic waveguides with dielectric cores and multilayer metal-dielectric claddings with hyperbolic dispersion. Without using any homogenization, we calculate the resonant eigenmodes of the finite-width cladding layers, and find agreement with the resonant features in the dispersion of the cladded waveguides. We show that at the resonant widths, the propagating modes of the waveguides are coupled to the cladding eigenmodes and hence, are strongly absorbed. By avoiding the resonant widths in the design of the actual waveguides, the strong absorption can be eliminated

Ultrabright room-temperature single-photon emission from nanodiamond nitrogen-vacancy centers with sub-nanosecond excited-state lifetime

Ultrafast emission rates obtained from quantum emitters coupled to plasmonic nanoantennas have recently opened fundamentally new possibilities in quantum information and sensing applications. Plasmonic nanoantennas greatly improve the brightness of quantum emitters by dramatically shortening their fluorescence lifetimes. Gap plasmonic nanocavities that support strongly confined modes are of particular interest for such applications. We demonstrate single-photon emission from nitrogen-vacancy (NV) centers in nanodiamonds coupled to nanosized gap plasmonic cavities with internal mode volumes about 10 000 times smaller than the cubic vacuum wavelength. The resulting structures features sub-nanosecond NV excited-state lifetimes and detected photon rates up to 50 million counts per second. Analysis of the fluorescence saturation allows the extraction of the multi-order excitation rate enhancement provided by the nanoantenna. Efficiency analysis shows that the NV center is producing up to 0.25 billion photons per second in the far-field

Electron spin contrast of Purcell-enhanced nitrogen-vacancy ensembles in nanodiamonds

Nitrogen-vacancy centers in diamond allow for coherent spin state manipulation at room temperature, which could bring dramatic advances to nanoscale sensing and quantum information technology. We introduce a novel method for the optical measurement of the spin contrast in dense nitrogen-vacancy (NV) ensembles. This method brings a new insight into the interplay between the spin contrast and fluorescence lifetime. We show that for improving the spin readout sensitivity in NV ensembles, one should aim at modifying the far field radiation pattern rather than enhancing the emission rate