Characterization of amorphous and nanocrystalline carbon films

Surface contamination by polymer residues has long been a critical problem in probing graphene’s intrinsic properties and in using graphene for unique applications in surface chemistry, biotechnology, and ultrahigh speed electronics. Poly(methyl methacrylate) (PMMA) is a macromolecule commonly used for graphene transfer and device processing, leaving a thin layer of residue to be empirically cleaned by annealing. Here we report on a systematic study of PMMA decomposition on graphene and of its impact on graphene’s intrinsic properties using transmission electron microscopy (TEM) in combination with Raman spectroscopy. TEM images revealed that the physisorbed PMMA proceeds in two steps of weight loss in annealing and cannot be removed entirely at a graphene susceptible temperature before breaking. Raman analysis shows a remarkable blue-shift of the 2D mode after annealing, implying an anneal-induced band structure modulation in graphene with defects. Calculations using density functional theory show that l...

Graphene Annealing: How Clean Can It Be?

▪ Abstract The synthesis of nanocrystalline diamond films from carbon-containing noble gas plasmas is described. The nanocrystallinity is the result of new growth and nucleation mechanisms, which involve the insertion of C2, carbon dimer, into carbon-carbon and carbon-hydrogen bonds, resulting in hetereogeneous nucleation rates on the order 1010 cm−2 s−1. Extensive characterization studies led to the conclusion that phase-pure diamond is produced with a microstructure consisting of randomly oriented 3–15-nm crystallites. By adjusting the noble gas/hydrogen ratio in the gas mixture, a continuous transition from micro- to nanocrystallinity is achieved. Up to 10% of the total carbon in the nanocrystalline films is located at 2 to 4 atom-wide grain boundaries. Because the grain boundary carbon is π-bonded, the mechanical, electrical, and optical properties of nanocrystalline diamond are profoundly altered. Nanocrystalline diamond films are unique new materials with applications in fields as diverse as tribolo...

Nanocrystalline diamond films1

The outstanding properties of SiO2, which include high resistivity, excellent dielectric strength, a large band gap, a high melting point, and a native, low defect density interface with Si, are in large part responsible for enabling the microelectronics revolution. The Si/SiO2 interface, which forms the heart of the modern metal–oxide–semiconductor field effect transistor, the building block of the integrated circuit, is arguably the worlds most economically and technologically important materials interface. This article summarizes recent progress and current scientific understanding of ultrathin (<4 nm) SiO2 and Si–O–N (silicon oxynitride) gate dielectrics on Si based devices. We will emphasize an understanding of the limits of these gate dielectrics, i.e., how their continuously shrinking thickness, dictated by integrated circuit device scaling, results in physical and electrical property changes that impose limits on their usefulness. We observe, in conclusion, that although Si microelectronic devices...

Ultrathin (<4 nm) SiO2 and Si-O-N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits

Core-level binding-energy shifts at surfaces and in solids

By comparing the C 1s photoemission intensities from a clean diamond (111) surface to those obtained from a fluorine-covered surface, we conclude that a single (111) layer of atoms participates in the diamond 2\ifmmode\times\else\texttimes\fi{}1 surface reconstruction. The data interpretation presented does not rely on assuming an electron mean free path, but, in fact provides an independent measurement of its value. For clean diamond (111) a surface core-level peak is observed at 0.80\ifmmode\pm\else\textpm\fi{}0.05 eV lower binding energy than the bulk-C 1s peak at 285.0 eV below ${E}_{F}$. After fluorine exposure a single chemically shifted carbon peak is observed at 1.85\ifmmode\pm\else\textpm\fi{}0.05 eV higher binding energy than the bulk peak, indicating the presence of CF units at the surface.

C 1 s excitation studies of diamond (111). I. Surface core levels

A well-resolved core exciton at the bulk diamond C-$1s$ absorption edge has been observed using high-resolution partial-yield spectroscopy with synchrotron radiation. The obtained excitonic binding energy, 0.19\ifmmode\pm\else\textpm\fi{}0.015 eV, agrees well with a first-principles effective-mass approximation (EMA). This is in sharp contrast to other semiconductors (Si, Ge, and GaAs) where reported excitonic shifts far exceed EMA estimates. In light of these results, one must question whether previous measurements overestimate the core-hole interaction or if they indicate a breakdown of the EMA for core excitons.

Observation of a C-1s core exciton in diamond.

The chemical nature of the adhesive interface between Cr and three polymers has been investigated using synchrotron‐radiation excited photoemission from the polymer carbon 1s core levels. PMDA–ODA polyimide (PI), an important polymer in the electronics industry, was studied along with two simple polymers, PMPO and PVMK, which contain structural fragments of the complicated PI protomer. The carbon 1s spectra were decomposed into distinct peaks which were assigned to specific chemical species and monitored as a function of Cr coverage. Our results confirm that the carbonyl groups on these polymer surfaces are targets for reactive metals during the initial stages of metallization. This initial reaction stage was followed by gradual formation of an electron‐rich, carbidelike, carbon species.

Synchrotron‐radiation excited carbon 1s photoemission study of Cr/organic polymer interfaces

The chemical nature of the adhesive interface between Cr and three polymers has been investigated using synchrotron-radiation-excited photoemission from the polymer carbon and oxygen 1s core levels. Pyromellitic dianhydride--oxydianiline (PMDA-ODA) polyimide, an important polymer in the electronics industry, was studied along with two simple polymers. Poly(methylphenylene oxide) and poly(vinylmethyl ketone) contain structural fragments of the complicated PMDA-ODA polyimide protomer. The core-level spectra were decomposed into distinct peaks which were assigned to specific chemical species and monitored as a function of Cr coverage. Our results confirm that the carbonyl groups on these polymer surfaces are targets for reactive metals during the initial stages of metal deposition. This initial reaction stage was followed by gradual formation of an electron-rich, carbidelike, carbon species.

J. L. Jordan

Papers

C 1 s excitation studies of diamond (111). I. Surface core levels

Observation of a C-1s core exciton in diamond.

Synchrotron‐radiation excited carbon 1s photoemission study of Cr/organic polymer interfaces

High-resolution photoemission study of the interfacial reaction of Cr with polyimide and model polymers

Si(111) surface oxidation: O 1s core-level study using synchrotron radiation