Enhancing one dimensional sensitivity with plasmonic coupling: erratum.

Our manuscript contained data from unconverged rigorous coupled wave approximation (RCWA) simulations that resulted in incorrect description of minima locations. Here, converged RCWA simulations are presented with corrected minima behavior described. The principle of plasmonic enhancement and its use in ellipsometric test structures is maintained.

Enhancing one dimensional sensitivity with plasmonic coupling.

In this paper, we propose a cross-grating structure to enhance the critical dimension sensitivity of one dimensional nanometer scale metal gratings. Making use of the interaction between slight changes in refractive index and localized plasmons, we demonstrate sub-angstrom scale sensitivity in this structure. Compared to unaltered infinite metal gratings and truncated finite gratings, this cross-grating structure shows robust spectra dependent mostly on the dimension of the smaller line width and pitch. While typical scatterometry simulations show angstrom resolution at best, this structure has demonstrated picometer resolution. Due to the wide range of acceptable specifications, we expect experimental confirmation of such structures to soon follow.

Thickness and rotational effects in simulated HRTEM images of graphene on hexagonal boron nitride.

Recent studies have shown that when graphene is placed on a thin hexagonal boron nitride (h-BN) substrate, unlike when it is placed on a typical SiO2 surface, it can closely approach the ideal carrier mobility observed in suspended graphene samples. This study further examines the epitaxial relationship between graphene and h-BN substrate with high-resolution transmission electron microscopy simulation. Virtual monolayer and multilayer stacks of h-BN were produced with a monolayer of graphene on top, on bottom, and in between h-BN layers, in order to study this interface. Once the simulations were performed, the phase contrast image and Moiré pattern created by this heterostack were analyzed for local and global intensity minima and maxima. In addition, h-BN substrate thickness and rotations between h-BN and graphene were probed and analyzed. The simulated images produced in this work will be used to help understand subsequent transmission electron microscopy images and electron energy-loss studies.

Electronic excitations in graphene in the 1-50 eV range: the π and π + σ peaks are not plasmons.

The field of plasmonics relies on light coupling strongly to plasmons as collective excitations. The energy loss function of graphene is dominated by two peaks at ∼5 and ∼15 eV, known as π and π + σ plasmons, respectively. We use electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope and density functional theory to show that between 1 to 50 eV, these prominent π and π + σ peaks are not plasmons, but single-particle interband excitations.

Enhanced optical second-harmonic generation from the current-biased graphene/SiO2/Si(001) structure.

We find that optical second-harmonic generation (SHG) in reflection from a chemical-vapor-deposition graphene monolayer transferred onto a SiO2/Si(001) substrate is enhanced about 3 times by the flow of direct current electric current in graphene. Measurements of rotational-anisotropy SHG revealed that the current-induced SHG from the current-biased graphene/SiO2/Si(001) structure undergoes a phase inversion as the measurement location on graphene is shifted laterally along the current flow direction. The enhancement is due to current-associated charge trapping at the graphene/SiO2 interface, which introduces a vertical electric field across the SiO2/Si interface that produces electric field-induced SHG. The phase inversion is due to the positive-to-negative polarity switch in the current direction of the trapped charges at the current-biased graphene/SiO2 interface.

Simulation study of aberration-corrected high-resolution transmission electron microscopy imaging of few-layer-graphene stacking.

Graphene is a single layer of carbon atoms arranged in a hexagonal lattice. The high carrier mobility and mechanical robustness of single layer graphene make it an attractive material for "beyond CMOS" devices. The current work investigates through high-resolution transmission electron microscopy (HRTEM) image simulation the sensitivity of aberration-corrected HRTEM to the different graphene stacking configurations AAA/ABA/ABC as well as bilayers with rotational misorientations between the individual layers. High-angle annular dark field-scanning transmission electron microscopy simulation is also explored. Images calculated using the multislice approximation show discernable differences between the stacking sequences when simulated with realistic operating parameters in the presence of low random noise.

Applied physics. Subsurface imaging with scanning ultrasound holography.

Every new microscopic imaging technique reveals hidden features but also new challenges. To capture information about substructure features, especially defects and voids, in the next generation of integrated circuits, higher resolution methods of surface imaging will be required. In his Perspective, Diebold discusses results reported in the same issue by Shekhawat and Dravid in which an acoustic scanning holographic imaging technique has been extended to unprecedented spatial resolution. The method has also been used on biological cells, and the hope is that it can be developed further to obtain detailed information about the depth and elastic properties of buried features.