30 research outputs found
Probing the Structure and Chemistry of Perylenetetracarboxylic Dianhydride on Graphene Before and After Atomic Layer Deposition of Alumina
The superlative electronic properties of graphene suggest
its use
as the foundation of next-generation integrated circuits. However,
this application requires precise control of the interface between
graphene and other materials, especially the metal oxides that are
commonly used as gate dielectrics. Toward that end, organic seeding
layers have been empirically shown to seed ultrathin dielectric growth
on graphene via atomic layer deposition (ALD), although the underlying
chemical mechanisms and structural details of the molecule/dielectric
interface remain unknown. Here, confocal resonance Raman spectroscopy
is employed to quantify the structure and chemistry of monolayers
of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on graphene
before and after deposition of alumina with the ALD precursors trimethyl
aluminum (TMA) and water. Photoluminescence measurements provide further
insight into the details of the growth mechanism, including the transition
between layer-by-layer growth and island formation. Overall, these
results reveal that PTCDA is not consumed during ALD, thereby preserving
a well-defined and passivating organic interface between graphene
and deposited dielectric thin films
Fundamental Performance Limits of Carbon Nanotube Thin-Film Transistors Achieved Using Hybrid Molecular Dielectrics
In the past decade, semiconducting carbon nanotube thin films have been recognized as contending materials for wide-ranging applications in electronics, energy, and sensing. In particular, improvements in large-area flexible electronics have been achieved through independent advances in postgrowth processing to resolve metallic <i>versus</i> semiconducting carbon nanotube heterogeneity, in improved gate dielectrics, and in self-assembly processes. Moreover, controlled tuning of specific device components has afforded fundamental probes of the trade-offs between materials properties and device performance metrics. Nevertheless, carbon nanotube transistor performance suitable for real-world applications awaits understanding-based progress in the integration of independently pioneered device components. We achieve this here by integrating high-purity semiconducting carbon nanotube films with a custom-designed hybrid inorganic–organic gate dielectric. This synergistic combination of materials circumvents conventional design trade-offs, resulting in concurrent advances in several transistor performance metrics such as transconductance (6.5 μS/μm), intrinsic field-effect mobility (147 cm<sup>2</sup>/(V s)), subthreshold swing (150 mV/decade), and on/off ratio (5 × 10<sup>5</sup>), while also achieving hysteresis-free operation in ambient conditions
Quantitatively Enhanced Reliability and Uniformity of High‑κ Dielectrics on Graphene Enabled by Self-Assembled Seeding Layers
The full potential of graphene in integrated circuits
can only
be realized with a reliable ultrathin high-κ top-gate dielectric.
Here, we report the first statistical analysis of the breakdown characteristics
of dielectrics on graphene, which allows the simultaneous optimization
of gate capacitance and the key parameters that describe large-area
uniformity and dielectric strength. In particular, vertically heterogeneous
and laterally homogeneous Al<sub>2</sub>O<sub>3</sub> and HfO<sub>2</sub> stacks grown via atomic-layer deposition and seeded by a
molecularly thin perylene-3,4,9,10-tetracarboxylic dianhydride organic
monolayer exhibit high uniformities (Weibull shape parameter β
> 25) and large breakdown strengths (Weibull scale parameter, <i>E</i><sub>BD</sub> > 7 MV/cm) that are comparable to control
dielectrics grown on Si substrates
Probing the Structure and Chemistry of Perylenetetracarboxylic Dianhydride on Graphene Before and After Atomic Layer Deposition of Alumina
Templating Sub-10 nm Atomic Layer Deposited Oxide Nanostructures on Graphene via One-Dimensional Organic Self-Assembled Monolayers
Molecular-scale control over the
integration of disparate materials
on graphene is a critical step in the development of graphene-based
electronics and sensors. Here, we report that self-assembled monolayers
of 10,12-pentacosadiynoic acid (PCDA) on epitaxial graphene can be
used to template the reaction and directed growth of atomic layer
deposited (ALD) oxide nanostructures with sub-10 nm lateral resolution.
PCDA spontaneously assembles into well-ordered domains consisting
of one-dimensional molecular chains that coat the entire graphene
surface in a manner consistent with the symmetry of the underlying
graphene lattice. Subsequently, zinc oxide and alumina ALD precursors
are shown to preferentially react with the functional moieties of
PCDA, resulting in templated oxide nanostructures. The retention of
the original one-dimensional molecular ordering following ALD is dependent
on the chemical reaction pathway and the stability of the monolayer,
which can be enhanced via ultraviolet-induced molecular cross-linking
Imaging Molecular Orbitals of PTCDA on Graphene on Pt(111): Electronic Structure by STM and First-Principles Calculations
International audienceThe adsorption and growth of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on graphene monolayers epitaxially grown on Pt(111) surfaces is studied by a combination of experimental scanning tunneling microscopy (STM) and spectroscopy (STS) measurements and first-principles density functional theory (DFT) calculations. For submonolayer coverage, until the completion of the first layer, PTCDA molecules form a well-ordered herringbone structure with molecules lying flat on the graphene surface weakly coupled to the Pt(111) substrate. High-resolution STM imaging at different sample biases has allowed the identification of intramolecular features that can be related to the original PTCDA frontier orbitals. Theoretical STM calculations, based on local-orbital DFT, have been carried out on the full PTCDA/graphene/Pt(111) system. The comparison of theoretical and experimental STM images has allowed us to ascribe the origin of intramolecular features to the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of the free PTCDA molecules. Moreover, the experimental STS spectra display well-resolved peaks centered at −2.2 and +1.2 eV in excellent agreement with DFT calculations. This study reveals that the growth and electronic structure of PTCDA retain all of the essential electronic features of the molecular layer upon adsorption on this weakly coupled graphene on Pt(111) surface