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A central goal in molecular electronics and optoelectronics is to translate tailorable molecular properties to larger materials and to the device level. Here, we present a method to fabricate molecularly cross-linked, self-assembled 2D nanoparticle sheets (X-NS). Our method extends a Langmuir approach of self-assembling gold nanoparticle (NP) arrays at an air-water interface by replacing the liquid sub-phase to an organic solvent to enable cross-linking with organic molecules, and then draining the sub-phase to deposit films. Remarkably, X-NS comprising conjugated oligophenylene dithiol cross-linkers (HS-(C6H4)n-SH, 1 ≤ n ≤ 3) exhibit increasing conductance with molecule length, ~6 orders of magnitude enhancement in UV-Vis extinction coefficients, and photoconductivity with molecule vs. NP contributions varying depending on the excitation wavelength. Finite difference time domain (FDTD) analyses and control measurements indicate that these effects can be modeled provided the local complex dielectric constant is strongly modified upon cross-linking. This suggests quantum hybridization at a molecule–band (q-MB) level. Given the vast number of molecules and nano-building blocks available, X-NS have potential to significantly increase the range of available 2D nanosheets and associated quantum properties.

MnO2 nanosheets and ultraviolet-visible (UV-Vis) absorbance spectroscopy are used to study glucose oxidase (GOx) kinetics. Glucose oxidation by GOx produces H2O2, which rapidly decomposes the nanosheets and reduces their absorption. This direct approach for monitoring glucose oxidation enables simpler, real time kinetics analysis compared to methods that employ additional enzymes. Using this approach, the present study confirms that GOx kinetics is consistent with the Michaelis–Menten (MM) model, and reveals that the MM constant increases by an order of magnitude with increasing buffer concentration. Since larger MM constants imply higher enzyme substrate concentrations are required to achieve the same rate of product formation, increasing MM constants imply decreasing enzyme performance. These results demonstrate the facility of using MnO2 nanosheets to study GOx kinetics and, given the widespread applications of enzymes with buffers, the important sensitivity of enzyme–buffer systems on buffer concentration.

Lock-in amplifiers (LIAs) are commonly used in chemistry laboratories to improve noise-to-signal ratios. Constructing and testing a suitably designed LIA provide undergraduate students with an exce...

The present study demonstrates the ability of excess, weakly amphiphilic n-alkanethiols (n = 4, 12, 18) and solvent composition to tune through a wide range of large-scale, macroscopic architectures formed by alkanethiol-capped Au nanoparticles (NPs). Both the alkanethiols and NPs are significantly hydrophobic species and compete for surface area at an air-water interface. When solutions of the two species are spread on a large (50 cm2) water surface in a Teflon well, a thin film forms and exhibits co-existing macroscopic regions with various distinct NP self-assembled architectures, namely a close packed monolayer, a network phase characterized by micron-sized pores (micropores) surrounded by quasi-linear bundles of nanoparticles, and finally aggregates. We hypothesize that the co-existence of various NP architectures results from fast, non-uniform evaporation across the large water surface. When solutions are instead deposited on a smaller (5 cm2) water surface contained within a Teflon ring to control the water surface curvature and the evaporation rate is slowed, we show for the first time that NPs form macroscopically uniform self-assemblies whose architectures can be tuned from monolayers → monolayers with micropores → extended micropore/NP bundle networks by varying excess alkanethiol concentration and solvent composition. We propose that competition between NPs and excess alkanethiols for water surface area, and alkanethiol self-assembly as well as solvent dewetting play important roles in the formation of the network phase, and discuss a potential mechanism for its formation.

Size-selective precipitation (SSP) is a powerful tool for obtaining monodisperse nanoparticles. Here we report a fast, high yield and tunable SSP procedure via non-solvent addition for producing nearly monodisperse, organic-soluble Au nanoparticles with standard deviations as low as σ < 7%. The addition of excess ligands and judicious choice of ligand head group significantly improve both precipitate yields and nanoparticle monodispersity.

Digital computers use binary states, typically represented by 0 and 5 V, to store and process information at all stages of a calculation. If more states (ideally a continuum) were available in between, density of information could be dramatically increased. Here we show that self-assembled nanoparticle films can feature such continuous state or analogue information storage. Information provided by an arbitrary gate voltage is 'written' by trapping charges in local, gate-modified potentials when films are cooled below 175 K. The information is 'read' using the film's built-in ability to sense charge via Coulomb blockade. Application of a time-dependent, multi-step writing gate voltage generates conductance maps corresponding to multi-valued continuous information. As a proof of concept, we exploit this technique to store 'UT' in Morse code.

Charge transport across a disordered normal-superconductor (DN-S) interface was studied using a macroscopic, molecularly linked Au nanoparticle film as the DN component. Low-temperature conductance versus voltage and magnetic field exhibit zero-bias and zero-field peaks, respectively. Importantly, the latter typically exhibit superimposed oscillations. Such oscillations are rarely seen in other DN-S systems and are remarkable given their robustness in these macroscopic films and interfaces. A number of observations indicate that conductance peaks and oscillations arise due to a 'reflectionless tunnelling' process. Scattering length scales extracted from the data using a reflectionless tunnelling picture are consistent with literature values. Factors resulting in the observation of oscillations in this system are discussed.

Planar tunnel junctions were fabricated by self-assembling 1,1'- ferrocenedicarboxylic acid (FDCA) onto native oxides of thermally deposited aluminum films and subsequently depositing a second aluminum film. Junctions were characterized using Reflection-Absorption Fourier Transform Infrared Spectroscopy (RAIRS) and current-voltage (I-V) spectroscopy. Before deposition of the second aluminum film, RAIRS of FDCA and ferrocenecarboxylic acid (FCA) films revealed COO(-), C=O, and Fc ring stretching modes, indicating that both types of molecules can interact strongly with the oxide and remain intact. After deposition, systems exhibited prominent COO(-) modes and weakened C=O modes, indicating further reaction with aluminum/aluminum oxide. Fc ring modes persisted in FDCA systems but disappeared in FCA systems, suggesting that the second COOH group in the FDCA molecule can act as a protecting group for the ferrocene moiety. Cyclic I-V measurements of FDCA tunnel junction systems revealed very strong ( approximately 10-fold) hysteretic differential conductance switching that was both reversible and stable. Control measurements using as prepared junctions, as well as junctions containing 1,6-hexanedioic acid, 1,9-nonanedioic acid, 1,4-dibenzoic acid, or FCA revealed only very weak ( approximately 10%) differential conductance changes. We attribute FDCA junction switching to barrier profile modifications induced by oxidation/reduction of the functionally protected ferrocene moieties.

Interfaces between disordered normal materials and superconductors (S) can exhibit 'reflectionless tunnelling' (RT)-a phenomenon that arises from repeated disorder-driven elastic scattering, multiple Andreev reflections, and electron/hole interference. RT has been used to explain zero-bias conductance peaks (ZBCPs) observed using doped semiconductors and evaporated granular metal films as the disordered normal materials. Recently, in addition to ZBCPs, magnetoconductance oscillations predicted by RT theory have been observed using a novel normal disordered material: self-assembled nanoparticle films. In the present study, we find that the period of these oscillations decreases as temperature (T) increases. This suggests that the magnetic flux associated with interfering pathways increases accordingly. We propose that the increasing flux can be attributed to magnetic field penetration into S as [Formula: see text]. This model agrees remarkably well with known T dependence of penetration depth predicted by Bardeen-Cooper-Schrieffer theory. Our study shows that this additional region of flux is significant and must be considered in experimental and theoretical studies of RT.

We present a robust, shadow mask method for fabricating break-junctions (BJs). The method uses electromigration and results in devices comprising 100 µm wide gold wires separated by nanogaps. By functionalizing the BJs with alkanedithiols and using electrostatic trapping, we incorporate single gold nanoparticles (NPs) in the gaps with high yield. The resulting single-NP devices exhibit single-electron charging thresholds that can be probed using both voltage and temperature measurements. Both voltage thresholds and thermal activation energies scale with NP size as expected.