At high intensities, light-matter interactions are controlled by the electric field of the exciting light. For instance, when an intense laser pulse interacts with an atomic gas, individual cycles of ...the incident electric field ionize gas atoms and steer the resulting attosecond-duration electrical wavepackets1, 2. Such field-controlled light-matter interactions form the basis of attosecond science and have recently expanded from gases to solid-state nanostructures3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18. Here, we extend these field-controlled interactions to metallic nanoparticles supporting localized surface plasmon resonances. We demonstrate strong-field, carrier-envelope-phase-sensitive photoemission from arrays of tailored metallic nanoparticles, and we show the influence of the nanoparticle geometry and the plasmon resonance on the phase-sensitive response. Additionally, from a technological standpoint, we push strong-field light-matter interactions to the chip scale. We integrate our plasmonic nanoparticles and experimental geometry in compact, micro-optoelectronic devices that operate out of vacuum and under ambient conditions.
We investigated electron-beam lithography with an aberration-corrected scanning transmission electron microscope. We achieved 2 nm isolated feature size and 5 nm half-pitch in hydrogen silsesquioxane ...resist. We also analyzed the resolution limits of this technique by measuring the point-spread function at 200 keV. Furthermore, we measured the energy loss in the resist using electron-energy-loss spectroscopy.
Au nanoparticles with diameters ranging between 15 and 170 nm have been synthesised in aqueous solution using a seed-mediated growth method, employing hydroxylamine hydrochloride as a reducing agent. ...Thiolated polyethylene glycol (mPEG-SH) polymers, with molecular weights ranging from 2100 to 51 000 g mol super(-1), were used as efficient particle stabilising ligands. Dynamic light scattering and zeta potential measurements confirmed that the overall mean diameter and zeta potential of the capped nanoparticles increased in a non-linear way with increasing molecular weight of the mPEG-SH ligand. Electron microscopy and thermal gravimetric analysis of the polymer-capped nanoparticles, with a mean gold core diameter of 15 nm, revealed that the grafting density of the mPEG-SH ligands decreased from 3.93 to 0.31 PEG nm super(-2) as the molecular weight of the ligands increased from 2100 to 51 400 g mol super(-1) respectively, due to increased steric hindrance and polymer conformational entropy with increase in the PEG chain length. Additionally, the number of bound mPEG-SH ligands, with a molecular weight of 10 800 g mol super(-1), was found to increase in a non-linear way from 278 ( sigma = 42) to approximately 12 960 PEG ( sigma = 1227) when the mean Au core diameter increased from 15 to 115 nm respectively. However, the grafting density of mPEG sub(10 000)-SH ligands was higher on 15 nm Au nanoparticles and decreased slightly from 1.57 to 0.8 PEG nm super(-2) when the diameter increased; this effect can be attributed to the fact that smaller particles offer higher surface curvature, therefore allowing increased polymer loading per nm super(2). Au nanoparticles were also shown to interact with CT-26 cells without causing noticeable toxicity.
Single atoms and few-atom nanoclusters are of high interest in catalysis and plasmonics, but pathways for their fabrication and placement remain scarce. We report here the self-assembly of ...room-temperature-stable single indium (In) atoms and few-atom In clusters (2–6 atoms) that are anchored to substitutional silicon (Si) impurity atoms in suspended monolayer graphene membranes. Using atomically resolved scanning transmission electron microscopy (STEM), we find that the symmetry of the In structures is critically determined by the three- or fourfold coordination of the Si “anchors”. All structures are produced without electron-beam induced materials modification. In turn, when activated by electron beam irradiation in the STEM, we observe in situ the formation, restructuring, and translation of the Si-anchored In structures. Our results on In–Si-graphene provide a materials system for controlled self-assembly and heteroatomic anchoring of single atoms and few-atom nanoclusters on graphene.
The nanoscale mechanical properties of live Staphylococcus aureus cells during different phases of growth were studied by atomic force microscopy. Indentation to different depths provided access to ...both local cell wall mechanical properties and whole-cell properties, including a component related to cell turgor pressure. Local cell wall properties were found to change in a characteristic manner throughout the division cycle. Splitting of the cell into two daughter cells followed a local softening of the cell wall along the division circumference, with the cell wall on either side of the division circumference becoming stiffer. Once exposed, the newly formed septum was found to be stiffer than the surrounding, older cell wall. Deeper indentations, which were affected by cell turgor pressure, did not show a change in stiffness throughout the division cycle, implying that enzymatic cell wall remodeling and local variations in wall properties are responsible for the evolution of cell shape through division.
In this work, we use electron energy-loss spectroscopy to map the complete plasmonic spectrum of aluminum nanodisks with diameters ranging from 3 to 120 nm fabricated by high-resolution electron-beam ...lithography. Our nanopatterning approach allows us to produce localized surface plasmon resonances across a wide spectral range spanning 2–8 eV. Electromagnetic simulations using the finite element method support the existence of dipolar, quadrupolar, and hexapolar surface plasmon modes as well as centrosymmetric breathing modes depending on the location of the electron-beam excitation. In addition, we have developed an approach using nanolithography that is capable of meV control over the energy and attosecond control over the lifetime of volume plasmons in these nanodisks. The precise measurement of volume plasmon lifetime may also provide an opportunity to probe and control the DC electrical conductivity of highly confined metallic nanostructures. Lastly, we show the strong influence of the nanodisk boundary in determining both the energy and lifetime of surface plasmons and volume plasmons locally across individual aluminum nanodisks, and we have compared these observations to similar effects produced by scaling the nanodisk diameter.
Understanding plasmon-mediated electron emission and energy transfer on the nanometer length scale is critical to controlling light–matter interactions at nanoscale dimensions. In a high-resolution ...lithographic material, electron emission and energy transfer lead to chemical transformations. In this work, we employ such chemical transformations in two different high-resolution electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and hydrogen silsesquioxane (HSQ), to map local electron emission and energy transfer with nanometer resolution from plasmonic nanoantennas excited by femtosecond laser pulses. We observe exposure of the electron-beam resists (both PMMA and HSQ) in regions on the surface of nanoantennas where the local field is significantly enhanced. Exposure in these regions is consistent with previously reported optical-field-controlled electron emission from plasmonic hotspots as well as earlier work on low-electron-energy scanning probe lithography. For HSQ, in addition to exposure in hotspots, we observe resist exposure at the centers of rod-shaped nanoantennas in addition to exposure in plasmonic hotspots. Optical field enhancement is minimized at the center of nanorods suggesting that exposure in these regions involves a different mechanism to that in plasmonic hotspots. Our simulations suggest that exposure at the center of nanorods results from the emission of hot electrons produced via plasmon decay in the nanorods. Overall, the results presented in this work provide a means to map both optical-field-controlled electron emission and hot-electron transfer from nanoparticles via chemical transformations produced locally in lithographic materials.