Bevan Elliott

Lanthanum Nitride Endohedral Fullerenes La3N@C2n (43≤n≤55): Preferential Formation of La3N@C96

While the trimetallic nitrides of Sc, Y and the lanthanides between Gd and Lu preferentially template C(80) cages, M(3)N@C(80), and while those of Ce, Pr and Nd preferentially template the C(88) cage, M(3)N@C(88), we show herein that the largest metallic nitride cluster, La(3)N, preferentially leads to the formation of La(3)N@C(96) and to a lesser extent the La(3)N@C(88). This is the first time that La(3)N is successfully encapsulated inside fullerene cages. La(3)N@C(2n) metallofullerenes were synthesized by arcing packed graphite rods in a modified Krätschmer-Huffman arc reactor, extracted from the collected soot and identified by mass spectroscopy. They were isolated and purified by high performance liquid chromatography (HPLC). Different arcing conditions were studied to maximize fullerene production, and results showed that yields have a high La(2)O(3)/C dependence. Relatively high yields were obtained when a 1:5 ratio was used. Three main fractions, La(3)N@C(88), La(3)N@C(92), and La(3)N@C(96), were characterized by UV/Vis-NIR and cyclic voltammetry. Unlike other trimetallic nitride metallofullerenes of the same carbon cage size, La(3)N@C(88) exhibits a higher HOMO-LUMO gap and irreversible reduction and oxidation steps.

New M3N@C2n Endohedral Metallofullerene Families (M=Nd, Pr, Ce; n=40–53): Expanding the Preferential Templating of the C88 Cage and Approaching the C96 Cage

Three new families of trimetallic nitride template endohedral metallofullerenes (TNT EMFs), based on cerium, praseodymium, and neodymium clusters, were synthesized by vaporizing packed graphite rods in a conventional Krätschmer-Huffman arc reactor. Each of these families of metallofullerenes was identified and characterized by mass spectroscopy, HPLC, UV/Vis-NIR spectroscopy, and cyclic voltammetry. The mass spectra and HPLC chromatograms show that these larger metallic clusters are preferentially encapsulated by a C(88) cage. When the size of the cluster is increased, the C(96) cage is progressively favored over the predominant C(88) cage. It is also observed that the smaller cages (C(80)-C(86)) almost disappear on going from neodymium to cerium endohedral metallofullerenes. The UV/Vis-NIR spectra and cyclic voltammograms confirm the low HOMO-LUMO gap and reversible electrochemistry of these M(3)N@C(88) metallofullerenes.

The influence of cage size on the reactivity of trimetallic nitride metallofullerenes: a mono- and bis-methanoadduct of Gd3N@C80 and a monoadduct of Gd3N@C84

A reactivity study of the higher TNT EMFs of gadolinium is reported here showing that the reactivity substantially decreases when the fullerene cage gets larger.

Ultra-Sensitive Duffing Behavior of a Microcantilever

We investigate the properties of an electrostatically driven microcantilever exhibiting duffing-like behavior using harmonic detection of resonance. Its potential use as a highly sensitive sensing platform is discussed. We find high sensitivity of this duffing system near its bistability point in a gaseous environment. The response of the higher harmonics of the measured charge on the cantilever induced by an ac voltage that drives the counter electrode is investigated. In particular, we follow the duffing behavior at the higher harmonics (up to the sixth harmonic) as a function of gap distance between the cantilever and counter electrode. To our knowledge, this work represents the first experimental demonstration of sensing a pressure change using the duffing behavior.

Deconvolution of damping forces with a nonlinear microresonator

We report a fully electrical microcantilever device that utilizes capacitance for both actuation and detection and show that it can characterize various gases with a bare silicon microcantilever. We find the motion of the cantilever as it rings down when the oscillating force is removed, by measuring the voltage induced by the oscillating capacitance in the microcantilever∕counterelectrode system. The ringdown waveform was analyzed using an iterative numerical algorithm to calculate the oscillator motion, modeling the cantilever∕electrode capacitance to calculate the electrostatic force. We find that nonlinearity in the motion of the cantilever is not necessarily a disadvantage. After calibration, we simultaneously measure viscosity and density of several gaseous mixtures, yielding viscosities within ±2% and densities within ±6% of NIST values.

Ringdown sensing method

Miniaturization of devices into lab-on-chip designs is a dominating field of current scientific research. While the technology to build these devices is continuing to develop, the practical realization of such devices remain elusive, mainly due to lack of techniques that bridge the macroscopic world to the mechanical motion and/or the electronic signals generated on the micro- or nano-sized scale. Hence, there is an increasing need for sensitive detection techniques that can not only be implemented on such small scale systems but also be integrated with the current CMOS technology. In this regard, a fully electrical microcantilever-based ringdown method will be presented. We show that detection technique can be employed to precisely analyze the composition of gas mixtures. The viscosity and density can be measured simultaneously, which is illustrated for multiple gases yielding viscosities within ± 2% and densities within ± 6% of NIST values.