9 research outputs found
Josephson junction transmission lines as tunable artificial crystals
We investigate one-dimensional Josephson junction arrays with generalized
unit cells as a circuit approach to engineer microwave band gaps. An array
described by a lattice with a basis can be designed to have a gap in the
electromagnetic spectrum, in full analogy to electronic band gaps in diatomic
or many-atomic crystals. We derive the dependence of this gap on the array
parameters in the linear regime, and suggest experimentally feasible designs to
bring the gap below the single junction plasma frequency. The gap can be tuned
in a wide frequency range by applying external flux, and it persists in the
presence of small imperfections.Comment: 9 pages, 5 figure
The Role of Nonlinear Dynamics in Quantitative Atomic Force Microscopy
Various methods of force measurement with the Atomic Force Microscope (AFM)
are compared for their ability to accurately determine the tip-surface force
from analysis of the nonlinear cantilever motion. It is explained how
intermodulation, or the frequency mixing of multiple drive tones by the
nonlinear tip-surface force, can be used to concentrate the nonlinear motion in
a narrow band of frequency near the cantilevers fundamental resonance, where
accuracy and sensitivity of force measurement are greatest. Two different
methods for reconstructing tip-surface forces from intermodulation spectra are
explained. The reconstruction of both conservative and dissipative tip-surface
interactions from intermodulation spectra are demonstrated on simulated data.Comment: 25 pages (preprint, double space) 7 figure
Phase imaging with intermodulation atomic force microscopy
Intermodulation atomic force microscopy (IMAFM) is a dynamic mode of atomic
force microscopy (AFM) with two-tone excitation. The oscillating AFM cantilever
in close proximity to a surface experiences the nonlinear tip-sample force
which mixes the drive tones and generates new frequency components in the
cantilever response known as intermodulation products (IMPs). We present a
procedure for extracting the phase at each IMP and demonstrate phase images
made by recording this phase while scanning. Amplitude and phase images at
intermodulation frequencies exhibit enhanced topographic and material contrast.Comment: 6 pages, 6 page