Printing techniques using nanomaterials have emerged as a versatile tool for fast prototyping and potentially large‐scale manufacturing of functional devices. Surfactants play a significant role in many printing processes due to their ability to reduce interfacial tension between ink solvents and nanoparticles and thus improve ink colloidal stability. Here, a colloidal graphene quantum dot (GQD)‐based nanosurfactant is reported to stabilize various types of 2D materials in aqueous inks. In particular, a graphene ink with superior colloidal stability is demonstrated by GQD nanosurfactants via the π–π stacking interaction, leading to the printing of multiple high‐resolution patterns on various substrates using a single printing pass. It is found that nanosurfactants can significantly improve the mechanical stability of the printed graphene films compared with those of conventional molecular surfactant, as evidenced by 100 taping, 100 scratching, and 1000 bending cycles. Additionally, the printed composite film exhibits improved photoconductance using UV light with 400 nm wavelength, arising from excitation across the nanosurfactant bandgap. Taking advantage of the 3D conformal aerosol jet printing technique, a series of UV sensors of heterogeneous structures are directly printed on 2D flat and 3D spherical substrates, demonstrating the potential of manufacturing geometrically versatile devices based on nanosurfactant inks.

The magneto-photoluminescence of type-II (ZnMn)Te quantum dots is presented. As a result of the type-II band alignment Aharonov-Bohm (AB) oscillations in the photoluminescence intensity are evident, confirming previous predictions for the suitability of this geometry to control the optical Aharonov-Bohm effect. Moreover, the system demonstrates an interesting interplay between the AB effect and the spin polarization in diluted magnetic semiconductor quantum dots. The intensity of the AB oscillations increases with both magnetic field and the degree of optical polarization, indicating the suppression of spin fluctuations improves the coherence of the system. * isellers@buffalo.edu 2The Aharonov-Bohm (AB) effect describes a phase shift induced upon a charged particle as it moves in a closed trajectory in the presence of a magnetic field [1]. Despite the fact that the AB effect is a property of charged particles it has been shown that for neutral excitons in semiconductor nano-rings, a non-zero electric dipole moment exists [2,3], which is adequate to create AB oscillations. Such behavior results from the inherent differences in confinement potential and effective mass of the particles comprising the exciton, the electron and hole, and leads to different trajectories for each of the charge carriers, resulting in a measurable AB effect. Type-II quantum dots (QDs) have been predicted to be particularly amenable to exhibiting such AB effects because of the enhanced polarization of the electron and hole due to the spatial separation of the carriers in such systems [3,4].In this work we present experimental evidence of AB oscillations i n the magnetophotoluminescence (MPL) of type-II (ZnMn)Te/ZnSe QDs. In this system the hole is strongly confined within the (ZnMn)Te QD while the electron resides in the ZnSe matrix, confined only through coulomb attraction to the hole. Although the AB effect has been observed optically for charged excitons in In(Ga)As QDs [5] and neutral excitons in both Type-II GaAs/InP [6] and Zn(SeTe ) QDs [7,8], and also in capacitance [10] and magnetization measurements [11] in InAs quantum rings, this is the first time such effects have been observed in a diluted magnetic semiconductor (DMS) system. In DMS systems the application of a magnetic field strongly aligns the Mn spins, thus polarizing the emission through the carrier-Mn exchange [12]. At saturation polarization the carrier spins will also be preferentially aligned, significantly reducing the spin disorder in the system [9,10].The samples studied were grown by MBE on (001) GaAs substrates. The GaAs buffer layer was planarized at 580ºC before the temperature was reduced to 300ºC to deposit a ZnSe buffer. The active layers were grown by migration enhanced epitaxy initiated by the growth of several mono-layers of ZnSe followed by the deposition of the (ZnMn)Te QDs. In the sample described here, five 2.6 ML 3 (ZnMn)Te QD layers were grown, separated by narrow (5 nm) ZnSe spacer layers. The QD density of each layer was estimated from atomic for...

We demonstrate coupling to and control over the broadening and dispersion of a mid-infrared leaky mode, known as the Berreman mode, in samples with different dielectric environments. We fabricate subwavelength films of AlN, a mid-infrared epsilon-near-zero material that supports the Berreman mode, on materials with a weakly negative permittivity, strongly negative permittivity, and positive permittivity. Additionally, we incorporate ultra-thin AlN layers into a GaN/AlN heterostructure, engineering the dielectric environment above and below the AlN. In each of the samples, coupling to the Berreman mode is observed in angle-dependent reflection measurements at wavelengths near the longitudinal optical phonon energy. The measured dispersion of the Berreman mode agrees well with numerical modes. Differences in the dispersion and broadening for the different materials is quantified, including a 13 cm-1 red-shift in the energy of the Berreman mode for the heterostructure sample.

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