The use of aluminum for plasmonic nanostructures opens up new possibilities, such as access to short-wavelength regions of the spectrum, complementary metal-oxide-semiconductor (CMOS) compatibility, and the possibility of low-cost, sustainable, mass-producible plasmonic materials. Here we examine the properties of individual Al nanorod antennas with cathodoluminescence (CL). This approach allows us to image the local density of optical states (LDOS) of Al nanorod antennas with a spatial resolution less than 20 nm and to identify the radiative modes of these nanostructures across the visible and into the UV spectral range. The results, which agree well with finite difference time domain (FDTD) simulations, lay the groundwork for precise Al plasmonic nanostructure design for a variety of applications.

Aluminum is abundant, low in cost, compatible with complementary metal-oxide semiconductor manufacturing methods, and capable of supporting tunable plasmon resonance structures that span the entire visible spectrum. However, the use of Al for color displays has been limited by its intrinsically broad spectral features. Here we show that vivid, highly polarized, and broadly tunable color pixels can be produced from periodic patterns of oriented Al nanorods. Whereas the nanorod longitudinal plasmon resonance is largely responsible for pixel color, far-field diffractive coupling is used to narrow the plasmon linewidth, enabling monochromatic coloration and significantly enhancing the far-field scattering intensity of the individual nanorod elements. The bright coloration can be observed with p-polarized white light excitation, consistent with the use of this approach in display devices. The resulting color pixels are constructed with a simple design, are compatible with scalable fabrication methods, and provide contrast ratios exceeding 100:1.RGB | chromaticity | array | electron beam lithography D isplay technologies have been evolving toward vivid, fullcolor, flat-panel displays with high resolution and/or small pixel sizes, higher energy efficiency, and improved benefit/cost ratios. Some of the most popular current technologies are liquid crystal displays (LCD), laser phosphor displays, also known as electroluminescent displays, and light-emitting diode (LED)-based displays. A common characteristic of all color display technologies is the incorporation of various color-producing media, which can be inorganic, organic, or polymeric materials, into the device. These chromatic materials are chosen to produce the fundamental components of the color spectrum in additive color schemes such as the standard red-green-blue (sRGB) when illuminated by an internal light source or when an electrical voltage is applied.Inorganic chromatic materials have the potential to greatly extend the durability and lifetime of color displays. Inorganic nanoparticles have recently begun to be used in color displays in the form of quantum dot LEDs, which have excellent display lifetimes and industry-scalable, size-based, and material-based color tunability (1-3). However, obtaining blue colors from quantum dots has been challenging (4) owing to the requirement of synthesizing nanoparticles in the small size range required to achieve optical transitions in this wavelength range. Au nanoparticles can produce green and red colors based on their surface plasmon resonances (5), but shorter-wavelength hues are quenched because of interband transitions for wavelengths below 520 nm (6). Ag has also been investigated for display applications (7, 8), but although spectral features can be achieved across the visible region the material readily oxidizes (9, 10), requiring additional passivation layers.Al is potentially a highly attractive material for plasmon-based full-spectrum displays. Al is the third most abundant element in the earth's crust, beh...

Abstract:We demonstrate the facile synthesis of high purity aluminum nanocrystals over a range of controlled sizes from 70 nm to 220 nm diameter, with size control achieved through a simple modification of solvent ratios in the reaction solution. The monodisperse, icosahedral and trigonal bipyramidal nanocrystals are air-stable for weeks, due to the formation of a 2-4 nm thick passivating oxide layer on their surfaces. We show that the nanocrystals support sizedependent ultraviolet and visible plasmon modes, providing a far more sustainable alternative to gold and silver nanoparticles currently in widespread use.

Aluminum is an abundant and high-quality material for plasmonics with potential for large-area, low-cost photonic technologies. Here we examine aluminum nanoclusters with plasmonic Fano resonances that can be tuned from the near-UV into the visible region of the spectrum. These nanoclusters can be designed with specific chromaticities in the blue-green region of the spectrum and exhibit a remarkable spectral sensitivity to changes in the local dielectric environment. We show that such structures can be used quite generally for colorimetric localized surface plasmon resonance (LSPR) sensing, where the presence of analytes is detected by directly observable color changes rather than through photodetectors and spectral analyzers. To quantify our results and provide a metric for optimization of such structures for colorimetric LSPR sensing, we introduce a figure of merit based on the color perception ability of the human eye.

Charge transfer introduced by a conductive junction bridging a nanoparticle dimer can have a pronounced effect on the optical properties of the system. We have extended the plasmon hybridization model to include conductive junctions and charge transfer effects. From our model, we are able to derive all the plasmon resonances of the bridged dimer, including the charge transfer plasmon (CTP), and predict their trends when system parameters are varied. In particular, we find that CTP is a result of a sufficiently narrow monopole mode interacting with multipolar (including dipolar) modes. The screening arising from charge transfer induces a blueshift of the hybridized bonding dimer modes and decreases the electric field in the junction. Our model may serve as an important guide for optical properties of bridged nanoparticle aggregates.