Distinguishing Quasiparticle-Phonon Interactions by Ultrahigh-Resolution Lifetime Measurements.

We present a determination of quasiparticle-phonon interaction strengths at surfaces through measurements of phonon spectra with ultrahigh energy resolution. The lifetimes of low energy surface phonons on a pristine Ru(0001) surface were determined over a wide range of temperatures and an analysis of the temperature dependence enables us to attribute separate contributions from electron-phonon interactions, phonon-phonon interactions, and defect-phonon interactions. Strong electron-phonon interactions are evident at all temperatures and we show they dominate over phonon-phonon interactions below 400 K.

Experimental Characterization of Defect-Induced Phonon Lifetime Shortening.

We present the first direct experimental measurement of defect-induced lifetime shortening of acoustic surface phonons. Defects are found to contribute a temperature-independent component to the linewidths of Rayleigh wave phonons on a Ni(111) surface. We also characterized the increase in phonon scattering with both surface defect density and phonon wave vector. A quantitative estimate of the scattering rate between phonon modes and surface line defects is extracted from the experimental data for the first time.

2D Helium Atom Diffraction from a Microscopic Spot.

A method for measuring helium atom diffraction with micron-scale spatial resolution is demonstrated in a scanning helium microscope (SHeM) and applied to study a micron-scale spot on the (100) plane of a lithium fluoride (LiF) crystal. The positions of the observed diffraction peaks provide an accurate measurement of the local lattice spacing, while a combination of close-coupled scattering calculations and Monte Carlo ray-tracing simulations reproduce the main variations in diffracted intensity. Subsequently, the diffraction results are used to enhance image contrast by measuring at different points in reciprocal space. The results open up the possibility for using helium microdiffraction to characterize the morphology of delicate or electron-sensitive materials on small scales. These include many fundamentally and technologically important samples which cannot be studied in conventional atom scattering instruments, such as small grain size exfoliated 2D materials, polycrystalline samples, and other surfaces that do not exhibit long-range order.

Electrical DNA Sequence Mapping Using Oligodeoxynucleotide Labels and Nanopores.

Identifying DNA species is crucial for diagnostics. For DNA identification, single-molecule DNA sequence mapping is an alternative to DNA sequencing toward fast point-of-care testing, which traditionally relies on targeting and labeling DNA sequences with fluorescent labels and readout using optical imaging methods. A nanopore is a promising sensor as a complement to optical mapping with advantages of electric measurement suitable for portable devices and potential for high resolution. Here, we demonstrate a high-resolution nanopore-based DNA sequence mapping by labeling specific short sequence motifs with oligodeoxynucleotides (ODNs) using DNA methyltransferase (MTase) and detecting them using nanopores. We successfully detected ODNs down to the size of 11 nucleotides without introducing extra reporters and resolved neighboring sites with a distance of 141 bp (∼48 nm) on a single DNA molecule. To accurately locate the sequence motif positions on DNA, a nanopore data analysis method is proposed by considering DNA velocity change through nanopores and using ensemble statistics to translate the time-dependent signals to the location information. Our platform enables high-resolution detection of small labels on DNA and high-accuracy localization of them for DNA species identification in an all-electrical format. The method presents an alternative to optical techniques relying on fluorescent labels and is promising for miniature-scale integration for diagnostic applications.