System and method for performing scanning tunneling microscopy on current-carrying samples
AssigneesUniversity of Maryland, College Park, Government of the United States of America as Represented by the Director, National Security Agency
InventorsTing Xie, Michael Dreyer, Isaak D. Mayergoyz, Robert E. Butera, Charles S. Krafft
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Abstract
A scanning tunneling microscopy based potentiometry system and method for the measurements of the local surface electric potential is presented. A voltage compensation circuit based on this potentiometry system and method is developed and employed to maintain a desired tunneling voltage independent of the bias current flow through the film. The application of this potentiometry system and method to the local sensing of the spin Hall effect is outlined herein, along with the experimental results obtained.
Claims24
A system for studying spin Hall effect in any of a conductive thin film or semiconductor thin film, comprising:
- a test sample formed of one of a conductive thin film or semiconductor thin film, the test sample having a pair of conductive contacts respectively disposed on a pair of longitudinally spaced portions of the test sample;
- a scanning tunneling microscope having a voltage source and a sensing tip spaced from the test sample to define a gap therebetween;
- a current source having an output coupled to a first of the pair of conductive contacts to provide a bias current to the test sample;
- and
- a voltage compensation circuit coupled to the pair of conductive contacts and the voltage source for varying a voltage input to the second of the pair of conductive contacts to provide an input voltage to the test sample compensated to maintain a voltage across the gap that is independent of changes in the bias current.
A method of using a scanning tunneling microscope to study spin Hall effect in any of a conductive thin film or semiconductor thin film, comprising:
- providing a scanning tunneling microscope;
- preparing a longitudinally extended test sample formed of one of a conductive thin film or semiconductor thin film;
- positioning a sensing tip of the scanning tunneling microscope in correspondence with the test sample and spaced therefrom to define a gap therebetween through which a tunneling current will pass;
- connecting an output of a current source to a first portion of the test sample to provide a bias current to the test sample;
- connecting an input voltage that is varied to maintain a voltage across the gap that is independent of changes in the bias current supplied from the current source to a second portion of the test sample, the second portion of the test sample being longitudinally displaced from the first portion;
- maintaining the sensing tip at a selected position;
- applying bias current pulses of selected magnitude from the current source with voltages across the gap of opposing polarity while measuring the tunneling current during a selected time period;
- and
- comparing the measured tunneling current versus time for each polarity of the voltages across the gap.
A method of preparing a scanning tunneling microscope for the study of spin Hall effect in a test sample formed of any of a conductive thin film or semiconductor thin film, the scanning tunneling microscope having a voltage source and a sensing tip configured to be spaced from the test sample to define a gap therebetween, the method comprising:
- providing a current source with an output configured to be coupled to a first longitudinal portion of the test sample to provide a bias current to the test sample;
- and
- providing a voltage compensation circuit coupled to the first longitudinal portion and a second longitudinally displaced portion of the test sample and to the voltage source for varying a voltage input to the second portion of the test sample to provide an input voltage to the test sample compensated to maintain a voltage across the gap that is independent of changes in the bias current.
Dependencies are inferred from the claim text.