Development of a scanning tunneling microscope for variable temperature electron spin resonance

Abstract

Recent advances in increasing the spectroscopic energy resolution in scanning tunneling microscopy (STM) have been achieved by integrating electron spin resonance (ESR) with STM. Here, we demonstrate the design and performance of a home-built STM capable of ESR at temperatures ranging from 1 K to 10 K. The STM is incorporated with a home-built Joule-Thomson refrigerator and a 2-axis vector magnet. Our STM design allows for the deposition of atoms and molecules directly into the cold STM, eliminating the need to extract the sample for deposition. In addition, we adopt two methods to apply radio-frequency (RF) voltages to the tunnel junction, the early design of wiring to the STM tip directly, and a more recent idea to use an RF antenna. Direct comparisons of ESR results measured using the two methods and simulations of electric field distribution around the tunnel junction show that, despite their different designs and capacitive couplings to the tunnel junction, there is no discernible difference in the driving and detection of ESR. Furthermore, at a magnetic field of ∼1.6 T, we observe ESR signals (near 40 GHz) sustained up to 10 K, which is the highest temperature for ESR-STM measurement reported to date, to the best of our knowledge. Although the ESR intensity exponentially decreases with increasing temperature, our ESR-STM system with low noise at the tunnel junction allows us to measure weak ESR signals with intensities in the sub-fA range. Our new design of ESR-STM, which is operational in a large frequency and temperature range, can broaden the use of ESR spectroscopy in STM and enable the simple modification of existing STM systems, which will hopefully accelerate a generalized use of ESR-STM.

Double-Resonance Spectroscopy of Coupled Electron Spins on a Surface

“…The data presented in Figures S3–S6 were measured in a home-built STM based on a commercial cryostat (Janis Research, JDR-250) equipped with two-axis superconducting magnets, which was kept at 0.9 K during the measurement by Joule–Thomson cooling with a small amount of 3 He– 4 He gas. High-frequency transmission cables were installed on the STM systems as described in detail elsewhere. , The single-frequency ESR measurements were performed by using a commercial RF generator (Agilent E8257D). In double-resonance mode, to apply a RF voltage of two frequencies together with a DC bias voltage, the output signals of two RF generators (Agilent E8257D and E8267D) were combined using a power combiner/splitter (Mini-circuits, ZC2PD-K0244+) before combining with a DC bias voltage through a bias tee (SigaTek, SB15D2).…”

“…High-frequency transmission cables were installed on the STM systems as described in detail elsewhere. 27,38 The single-frequency ESR measurements were performed by using a commercial RF generator (Agilent E8257D). In double-resonance mode, to apply a RF voltage of two frequencies together with a DC bias voltage, the output signals of two RF generators (Agilent E8257D and E8267D) were combined using a power combiner/splitter (Minicircuits, ZC2PD-K0244+) before combining with a DC bias voltage through a bias tee (SigaTek, SB15D2).…”

Ferromagnetic Resonance in Two-dimensional van der Waals Magnets: A Probe for Spin Dynamics

“…Moreover, by the mixing of a continuous RF voltage to the STM junction, an rf spin-polarized tunneling current is generated from the magnetic tip, which drives a coherent magnetic precession in a ferromagnetic thin film. Hwang et al report a homebuilt ESR-STM incorporated with a Joule-Thomson refrigerator and a two-axis vector magnet [203]. In addition to the early design of wiring to the STM tip, they apply RF voltages using an antenna (see Fig.…”

Atomic-Resolution Imaging of Micron-Sized Samples Realized by High Magnetic Field Scanning Tunneling Microscopy

“…Scanning tunneling microscopy (STM) has been a powerful tool in studying the atomic structure on material surfaces since its invention [ 1 ]. Traditional STMs are capable of working at room temperature [ 2 , 3 ], in liquid [ 4 , 5 ], at low temperature [ 6 , 7 ], and in ultra-high vacuum conditions [ 8 , 9 ] in order to investigate different physical and chemical properties. With the rapid development of material science, small-sized samples in micron dimension are widely synthesized and studied [ 10 , 11 , 12 ].…”