Jeffrey A. Zimmerman

‘‘Magic number’’ carbon clusters: Ionization potentials and selective reactivity

The ionization potentials (IPs) of several large carbon clusters Cn (n≥48), including the enhanced abundance (‘‘magic number’’) clusters C50, C60, and C70, have been determined by Fourier transform ion cyclotron resonance (FTICR) mass spectrometric charge transfer bracketing experiments. The IPs of C50, C60, and C70 were bracketed by the same two charge transfer compounds, leading to a common value of 7.61±0.11 eV. The IPs of even numbered clusters adjacent to these magic number clusters were found to be lower by as much as 0.5 eV and all clusters between C50 and C200 were determined to have IPs greater than 6.20 eV. The reaction rates of C+60 and C+70 with metallocenes were anomalously slow in comparison to the other large carbon cluster ions. IP and reactivity results suggest that C50, C60, and C70 may indeed have different or more stable structures than neighboring clusters, which supports the hypothesis of closed‐shell, spherical species. The implications of these results for the mechanism of C+n form...

Carbon cluster ion (C+n, 11≤n≤23) reactivity investigated via reaction with naphthalene: Kinetic energy dependence and evidence for long‐lived complexes

Reactions of carbon cluster ions (C+n, 11≤n≤23) with naphthalene have been investigated in a Fourier transform ion cyclotron resonance mass spectrometer (FTICR‐MS). Reactive channels include the formation of adduct ions stabilized by radiative association, three‐body collisions and loss of a hydrogen atom. Radiative association competes favorably with the dissociation of the ion/neutral complex and estimates of the average complex lifetime derived via kinetic modeling range from 28 to 59 (±50%) ms. The reactions have been found to be extremely dependent on the kinetic energy of the cluster ion. This dependency has been exploited to determine the average kinetic energy of the desorbed ions by comparison of reaction product distributions obtained as a function of kinetic energies. Calculated values were on the order of the trapping potential to twice that value (2–4 eV).

Pyrolysis and laser ablation of plasma‐polymerized fluorocarbon films: Effects of gold particles

Plasma‐polymerized fluorocarbon (PPFC) films were analyzed by thermogravimetric analysis (TGA), direct pyrolysis/mass spectrometry, and laser‐ablation/electron‐impact mass spectrometry. Fourier transform mass spectrometry was used to detect products. The films were made by plasma polymerizing tetrafluoroethylene in an argon plasma. Two types of films were studied: with and without fine gold particles incorporated in the PPFC films. TGA showed that gold‐containing films decompose more rapidly and at lower temperature with increasing gold content. Pyrolysis products were determined as a function of temperature. The predominant positive product ions, using 20 eV electron‐impact ionization, were C2F4+, CF3+ and a distribution of higher‐mass unsaturated fluorocarbon species, CnFm+, up to at least n=14 and m≥n+1. The predominant negative ions, formed by electron attachment, were also unsaturated fluorocarbon ions which extended up to 1145 u in mass. These species are different from those observed from polytetra...

Meeting critical gate linewidth control needs at the 65 nm node

With the nominal gate length at the 65 nm node being only 35 nm, controlling the critical dimension (CD) in polysilicon to within a few nanometers is essential to achieve a competitive power-to-performance ratio. Gate linewidths must be controlled, not only at the chip level so that the chip performs as the circuit designers and device engineers had intended, but also at the wafer level so that more chips with the optimum power-to-performance ratio are manufactured. Achieving tight across-chip linewidth variation (ACLV) and chip mean variation (CMV) is possible only if the mask-making, lithography, and etching processes are all controlled to very tight specifications. This paper identifies the various ACLV and CMV components, describes their root causes, and discusses a methodology to quantify them. For example, the site-to-site ACLV component is divided into systematic and random sub-components. The systematic component of the variation is attributed in part to pattern density variation across the field, and variation in exposure dose across the slit. The paper demonstrates our teams success in achieving the tight gate CD tolerances required for 65 nm technology. Certain key challenges faced, and methods employed to overcome them are described. For instance, the use of dose-compensation strategies to correct the small but systematic CD variations measured across the wafer, is described. Finally, the impact of immersion lithography on both ACLV and CMV is briefly discussed.

The formation of large polyaromatic hydrocarbons via carbon cluster ion reactions

Reactions of carbon cluster ions (C+n, 10<n<25) with polyaromatic hydrocarbons (PAHs) and substituted benzenes, studied using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry, provide evidence for the formation of large, highly conjugated PAHs. Product ions consist of adducts formed by radiative association/collisional stabilization and adducts accompanied by the loss of a hydrogen. These two reaction pathways alternate between the even‐ and odd‐numbered cluster ions dependent on reactant neutral employed. Adduct formation continues up to a maximum of five associations and to molecular weights in excess of 900 amu. Collisionally induced dissociation (CID) of product ions produced fragmentation indicative of species with multiply bonded carbon atoms and possibly fullerene‐type structure. Complete dehydrogenation of the adduct ions was possible.

Ionization Potentials and Electron Affinities of Semiconductor Clusters from Charge Transfer Reactions

Publisher Summary Ionization potentials (IPs) and electron affinities (EAs) are among the most important physical properties of small clusters. They can help to indicate both electronic and gross physical structure, if any, possessed by the clusters. Moreover, they can serve as one measure of the transition from individual atomic to bulk behavior. For several years, experiments at the University of Florida have employed Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry to study a number of gas phase ionic processes. The FT-ICR technique is the one mass spectrometry method best suited for obtaining both qualitative and quantitative information about ion/molecule reactions. FT-ICR mass spectrometry has been used to study cluster ions formed directly by laser desorption in the FT-ICR analyzer cell. Given the importance of ionization potentials and electron affinities in understanding cluster properties and given the power of FT-ICR to study ionic reactivities, such chemical reactivity studies of cluster ions, that is, their propensity to undergo charge transfer reactions, have been used to determine important physical properties of clusters. This chapter presents both advantages and disadvantages of the charge transfer bracketing approach.