We combine theory and experimental studies to investigate the coupling between colloidal quantum dots and randomly generated gold nanoislands. In such devices, the gold nanoislands act as classical antennas, amplifying the light absorbed by the quantum dots. They may thus find applications in detection, sensing, and plasmon-enhanced solar energy conversion. We use the two-dimensional finite-difference time-domain method to demonstrate plasmonic control of the enhancement factor near the island’s plasmon resonance. Furthermore, we experimentally and numerically show how tuning the plasmon resonance to the band gap energy of the quantum dot can lead to a broadening of the quantum dot’s absorption peak. The simulations predict a surprising linear scaling with quantum dot density, which is confirmed by experimental results.

We propose a design for a class of molecular rotors fixed to a semiconductor surface, induced by a moderately intense, linearly polarized laser pulse. The rotor consists of an organic molecule possessing a polarizable headgroup that is attached via a linear component to the surface. The polarization direction in parallel to the surface plane is determined so as to maximize the torque experienced by the molecular headgroup and, hence, the duration of the ensuing rotation, while also controlling the sense of rotation. We find that the molecule continues to rotate for many rotational periods after the laser pulse turns off, before multiple scattering by the potential barrier results in dephasing.

Recent experiments have shown that the efficiency of photoinduced electron transfer from sensitizers (molecules or quantum dots) to semiconductors can be enhanced by coupling the sensitizers to plasmon resonances in metal nanoparticles. Here, we use a model-Hamiltonian approach to show theoretically that there is an optimal coupling between the sensitizer and plasmons that maximizes the electron-transfer efficiency. This optimum results from the competition between electron transfer, plasmon relaxation, and plasmon decoherence. For coupling values that exceed the optimal value, the dynamics of electron transfer from the sensitizer to the semiconductor can be significantly modified due to the sensitizer–plasmon coupling.

We combine experiment, theory, and first-principles-based calculations to study the light-induced plasmon-mediated electron transport characteristics of a molecular-scale junction. The experimental data show a nonlinear increase in electronic current perturbation when the focus of a chopped laser beam moves laterally toward the tip–sample junction. To understand this behavior and generalize it, we apply a combined theory of the electronic nonequilibrium formed upon decoherence of an optically triggered plasmon and first-principles transport calculations. Our model illustrates that the current via an adsorbed molecular monolayer increases nonlinearly as more energy is pumped into the junction due to the increasing availability of virtual molecular orbital channels for transport with higher injection energies. Our results thus illustrate light-triggered, plasmon-enhanced tunneling current in the presence of a molecular linker.

We suggest optical modulation of the dielectric function of a molecular monolayer adsorbed on a metal surface as a potential means of controlling plasmon resonance phenomena. The dielectric function is altered using a laser pulse of moderate intensity and linear polarization to align the constituent molecules. After the pulse, the monolayer returns to its initial state. Time-dependent, optically controlled dielectric function is illustrated by molecular dynamics calculations.

We suggest the combination of single molecule pulling and optical control as a way to enhance control over the electron transport characteristics of a molecular junction. We demonstrate using a model junction consisting of biphenyl-dithiol coupled to gold contacts. The junction is pulled while optically manipulating the dihedral angle between the two rings. Quantum dynamics simulations show that molecular pulling enhances the degree of control over the dihedral angle and hence over the transport properties.

We present a model for strong field coherent control of torsional modes of molecules with a focus on exploring the controllability of molecular torsions subject to dissipative media and understanding how phase information is exchanged between torsional modes and a dissipative environment. Our theory is based on a density matrix formalism, wherein dissipation is accounted for within a multilevel Bloch equation model. Our results point to new and interesting phenomena in wavepacket dissipation dynamics that are unique to torsions and also enrich our general understanding of wavepacket phenomena. In addition, we suggest guidelines for designing torsional control experiments for molecules interacting with a dissipative bath.

We combine photoemission electron microscopy and electromagnetic simulations to describe the surface plasmon polariton dynamics following interaction of an ultrafast optical pulse with a slit coupling structure in a silver film. Through analysis of interference phenomena that lead to photoelectron emission from the silver film, we establish the universal contributions of a nanoscale asperity to the scattered surface field. Our results reveal the important role of surface cylindrical waves within the slit in the excitation of surface plasmon.

We introduce a new paradigm for single molecule devices based on electronic actuation of the internal atom/cluster motion within a fullerene cage. By combining electronic structure calculations with dynamical simulations, we explore current-triggered dynamics in endohedrally doped fullerene molecular junctions. Inelastic electron tunneling through a Li atom localized resonance in the Au–Li@C60–Au junction initiates fascinating, strongly coupled 2D dynamics, wherein the Li atom exhibits large amplitude oscillation with respect to the fullerene wall and the fullerene cage bounces between the gold electrodes, slightly perturbed by the embedded atom motion. Implications to the fields of single molecule electronics and nanoelectromechanical systems are discussed.Keywords: current-induced dynamics; electron scattering; fullerenes; metallofullerenes; molecular electronics; SAMO

We show the possibility of simultaneously aligning molecules and focusing their center-of-mass motion near a metal nanoparticle in the field intensity gradient created by the surface plasmon enhancement of incident light. The rotational motion is described quantum mechanically while the translation is treated classically. The effects of the nanoparticle shape on the alignment and focusing are explored. Our results carry interesting implications to the field of molecular nanoplasmonics and suggest several potential applications in nanochemistry.

The birefringence of a linearly polarized femtosecond laser filament in gases has been previously established. In this work, we report the time-dependent refractive index measurements of the filament based upon the spectral modulation of a weak probe pulse in air and in argon gas at 1 atmospheric pressure. The polarization dependence of the refractive index modulation induced by the delayed molecular alignment and by the electronic Kerr effect is highlighted. A numerical simulation of the refractive indices, which takes into account the molecular alignment, the electronic Kerr non-linearity and the plasma, is in good agreement with the measurements.

We explore the possibility of controlling the orientation of adsorbates, and their adsorption site, through alignment of a beam of gas-phase molecules prior to the surface reaction. To that end, we carry out classical trajectory simulations using ab initio data for the specific example of the I2/Si(100) adsorption reaction. I2 is found to adsorb with the molecular axis roughly parallel to the surface plane independently of the initial alignment. The orientation of the molecule in the surface plane and the adsorption site are controllable through alignment of the gas-phase projectiles. Our results are explained in terms of the surface properties and the reaction dynamics, and the extent to which and way in which they may be generalized is discussed.

We develop a full 3D approach to simulate the optical properties of sharp metal tips that could be quantitatively compared with experiments and provide accurate predictions. Similar to metallic wires, elongated metal tips support a series of extended mode resonances whose properties are largely determined by the tip geometry and are essentially independent of the tip material. For sufficiently long tips, these resonances are energetically well separated from a broader, high-energy feature, whose position and line shape are independent of the tip length but vary strongly with the tip material. The latter is a localized plasmon mode characterized by the hemisphere terminating the tip.