Atomic resolution scanning tunneling microscope imaging up to 27 T in a water-cooled magnet

We report the first atomically resolved scanning tunneling microscope （STM） imaging in a water-cooled magnet （WM）, for which extremely harsh vibrations and noise have been the major challenge. This custom WM-STM features an ultra-rigid and compact scan head in which the coarse approach is driven by our newly designed TunaDrive piezoelectric motor. A three-level spring hanging system is used for vibration isolation. Room-temperature raw-data images of graphite with quality atomic resolution were acquired in the presence of very strong magnetic fields, with a field strength up to 27 T, in a 32-mm-diameter bore WM with a maximum field strength of 27.5 T at a power rating of 10 MW, calibrated by nuclear magnetic resonance （NMR）. This record field strength of 27 T exceeds the maximal field strength achieved by the conventional supercon- ducting magnets. Besides, our WM-STM has paved the way to STM imaging using a 45 T, 32-mm-diameter bore hybrid magnet, which is the world＇s flagship magnet, producing the strongest steady magnetic field.

Frequency‑swept feedback interferometry for noncooperative‑target ranging with a stand‑off distance of several hundred meters

Frequency-swept interferometry(FSI)is a powerful ranging method with high precisionand immunity to ambient light.However,the stand-off distance of the current FSIbasedranging system for noncooperative targets is relatively short because the weakecho power cannot provide the needed signal-to-noise ratio(SNR).Here,we reporta ranging method that combines FSI and the laser feedback technique.Comparedwith conventional FSI,the interference between the weak echo signal and the localoscillator occurs in the laser cavity,which enhances the signal spontaneously and thenprovides an improved SNR.In the experiments,the detection limit of the echo poweris less than 0.1 fW,with a 1 mW probe beam.Based on the enhancement from thelaser feedback technique,the system can detect a noncooperative target that is up tohundreds of meters away in space without extra optical amplifiers.On the other hand,a large stand-off distance makes the system sensitive to environmental disturbance,which degrades the ranging precision.To address this issue,an interferometry-basedcompensation device,which is also sensitive to weak echoes from noncooperativetargets,is proposed to monitor the optical-path-length drifts and ensure accurate beatfrequency recognition.Moreover,the device can record distance changes during theintegration time of ranging and track a moving target precisely with improved temporalresolution.Owing to the high sensitivity and the validity of the compensationapproach,the standard deviation in 10 measurements is better than 0.07 mm whentargeting an aluminum sheet at approximately 152 m.Generally,with a large range,high relative precision,and low photon consumption,the novel technical scheme forlaser ranging demonstrates new capabilities that promise to enable a wide range ofapplications,such as large equipment assembly and noncooperative-target tracking.

Sub-molecular features of single proteins in solution resolved with scanning tunneling microscopy

Scanning tunneling microscopy (STM) can be used to image individual biological molecules, such as proteins, in vacuum or air. This requires sample dehydration and thus may not reflect the native state of the molecule. Extensive efforts have been made to image single proteins in solution using STM; however, the images have revealed only round or oval shapes with no sub-molecular details. Here, we present the sub-molecular features of streptavidin proteins under physiological conditions using a homebuilt low-leakage-current and highstability liquid phase STM. The N-lobe, C-lobe, and C-terminal tail of the epidermal growth factor receptor kinase domains were also resolved in solution. Our results demonstrate that the structure, morphology, and dynamics of a protein molecule can be examined under physiological conditions by the STM. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.