SXSPM | Publications | SXSPM Related

Book Chapters

V. Rose, J.W. Freeland, S.K. Streiffer, "New Capabilities at the Interface of X-rays and Scanning Tunneling Microscopy", in Scanning Probe Microscopy of Functional Materials: Nanoscale Imaging and Spectroscopy, S.V. Kalinin, A. Gruverman, (Eds.), Springer, New York (2011), pg 405-432.

The achievement of nanometer spatial resolution with direct elemental selectivity would have a tremendous impact on our ability to probe and understand complex phenomena occurring at the nanoscale. The combination of synchrotron-based X ray spectroscopy with the high spatial resolution of scanning tunneling microscopy (STM) has the potential to help attain this goal. In this chapter we show how synchrotron X-ray-enhanced scanning tunneling microscopy (SXSTM) has evolved from the very early days of photo-assisted STM to become a promising spectroscopy and imaging technique in nanoscience and nanotechnology. The basic principles of SXSTM are discussed accompanied by a presentation of recent experiments.
© Springer Science+Business Media, LLC 2010

Publications in Peer-Reviewed Journals

Nozomi Shirato, Marvin Cummings, Heath Kersell, Yang Li, Benjamin Stripe, Daniel Rosenmann, Saw-Wai Hla, and Volker Rose, “Elemental Fingerprinting of Materials with Sensitivity at the Atomic Limit”, Nano Letters (2014) doi: 10.1021/nl5030613.

By using synchrotron X-rays as a probe and a nanofabricated smart tip of a tunneling microscope as a detector, we have achieved chemical fingerprinting of individual nickel clusters on a Cu(111) surface at 2 nm lateral resolution, and at the ultimate single-atomic height sensitivity. Moreover, by varying the photon energy, we have succeeded to locally measure photoionization cross sections of just a single Ni nanocluster, which opens new exciting opportunities for chemical imaging of nanoscale materials.
© 2014 American Chemical Society

Kangkang Wang, Daniel Rosenmann, Martin Holt, Robert Winarski, Saw-Wai Hla, and Volker Rose, “An easy-to-implement filter for separating photo-excited signals from topography in scanning tunneling microscopy”, Rev. Sci. Instrum. 84, 063704 (2013).

In order to achieve elemental and chemical sensitivity in scanning tunneling microscopy (STM), synchrotron x-rays have been applied to excite core-level electrons during tunneling. The x-ray photo-excitations result in tip currents that are superimposed onto conventional tunneling currents. While carrying important physical information, the varying x-ray induced currents can destabilize the feedback loop causing it to be unable to maintain a constant tunneling current, sometimes even causing the tip to retract fully or crash. In this paper, we report on an easy-to-implement filter circuit that can separate the x-ray induced currents from conventional tunneling currents, thereby allowing simultaneous measurements of topography and chemical contrasts. The filter and the schematic presented here can also be applied to other variants of light-assisted STM such as laser STM.
© 2013 AIP Publishing LLC .

Volker Rose, Kangkang Wang, TeYu Chien, Jon Hiller, Daniel Rosenmann, John W. Freeland, Curt Preissner, Saw-Wai Hla, "Synchrotron X-Ray Scanning Tunneling Microscopy: Fingerprinting Near to Far Field Transitions on Cu(111) Induced by Synchrotron Radiation", Adv. Funct. Mater. 23, 2646 (2013).

Cover article: Volume 23, Issue 20; May 28, 2013
The combination of the high spatial resolution of scanning tunneling microscopy with the chemical and magnetic contrast provided by synchrotron X-rays has the potential to allow a unique characterization of advanced functional materials. While the scanning probe provides the high spatial resolution, synchrotron X-rays that produce photo-excitations of core electrons add chemical and magnetic contrast. However, in order to realize the method's full potential it is essential to maintain tunneling conditions, even while high brilliance X-rays irradiate the sample surface. Different from conventional scanning tunneling microscopy, X-rays can cause a transition of the tip out of the tunneling regime. Monitoring the reaction of the z-piezo (the element that controls the tip to sample separation) alone is not sufficient, because a continuous tip current is obtained. As a solution, an unambiguous and direct way of fingerprinting such near to far field transitions of the tip that relies on the simultaneous analysis of the X-ray-induced tip and sample current is presented. This result is of considerable importance because it opens the path to the ultimate resolution in X-ray enhanced scanning tunneling microscopy.
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

V. Rose, T.Y. Chien, J.W. Freeland, D. Rosenmann, J. Hiller, V. Metlushko, "Spin-dependent synchrotron x-ray excitations studied by scanning tunneling microscopy", J. Appl. Phys. 111, 07E304 (2012).

The ability to position a sharp probe in close proximity to a sample while the surface is illuminated by synchrotron x-rays opens a path to localized spectroscopy and imaging with chemical and magnetic contrast. We have employed a scanning tunneling microscope for the local study of synchrotron x-ray magnetic circular dichroism of micron-sized NiFe rings. Spectra have been obtained by an insulator-coated tip positioned about 200 nm over the sample surface. A negative sample bias is required in order to enhance the dichroism signal at the tip.
© 2012 American Institute of Physics.

M.L. Cummings, T.Y. Chien, C. Preissner, V. Madhavan, D. Diesing, M. Bode, J.W. Freeland, V. Rose, "Combining Scanning Tunneling Microscopy and Synchrotron Radiation for High-Resolution Imaging and Spectroscopy with Chemical, Electronic, and Magnetic Contrast", Ultramicroscopy 112, 22 (2012).

The combination of high-brilliance synchrotron radiation with scanning tunneling microscopy opens the path to high-resolution imaging with chemical, electronic, and magnetic contrast. Here, the design and experimental results of an in-situ synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system are presented. The system is designed to allow monochromatic synchrotron radiation to enter the chamber, illuminating the sample with x-ray radiation, while an insulator-coated tip (metallic tip apex open for tunneling, electron collection) is scanned over the surface. A unique feature of the SXSTM is the STM mount assembly, designed with a two free-flex pivot, providing an angular degree of freedom for the alignment of the tip and sample with respect to the incoming x-ray beam. The system designed successfully demonstrates the ability to resolve atomic-scale corrugations. In addition, experiments with synchrotron x-ray radiation validate the SXSTM system as an accurate analysis technique for the study of local magnetic and chemical properties on sample surfaces. The SXSTM system's capabilities have the potential to broaden and deepen the general understanding of surface phenomena by adding elemental contrast to the high-resolution of STM.
© 2011 Elsevier B.V. Published by Elsevier B.V. All rights reserved.

V. Rose, T.Y. Chien, J. Hiller, D. Rosenmann, R.P. Winarski, "X-ray nanotomography of SiO2-coated Pt90Ir10 tips with sub-micron conducting apex", Appl. Phys. Lett. 99, 173102 (2011).

Hard x-ray nanotomography provides an important three-dimensional view of insulator-coated “smart tips” that can be utilized for modern emerging scanning probe techniques. Tips, entirely coated by an insulating SiO2 film except at the very tip apex, are fabricated by means of electron beam physical vapor deposition, focused ion beam milling and ion beam-stimulated oxide growth. Although x-ray tomography studies confirm the structural integrity of the oxide film, transport measurements suggest the presence of defect-induced states in the SiO2 film. The development of insulator-coated tips can facilitate nanoscale analysis with electronic, chemical, and magnetic contrast by synchrotron-based scanning probe microscopy.
© 2011 American Institute of Physics

V. Rose, J.W. Freeland, "A New Concept for Quantitative Nanoscale Imaging With Magnetic Contrast: Synchrotron X-ray Enhanced Scanning Tunneling Microscopy", Proceedings of 2010 International Conference on Electromagnetics in Advanced Applications (ICEAA 2010), Sydney, Australia, Sept. 20-24, 2010, pp. 201-204 (invited).

The combination of synchrotron x-rays with scanning tunneling microscopy provides a promising new path towards the imaging of nanoscale structures with chemical, electronic, and magnetic contrast. While a scanning probe provides the high spatial resolution measuring x-ray magnetic circular dichroism allows the direct quantification of magnetic moments. This capability has the potential to broaden and deepen the general understanding of nanomagnetism.
© 2010 IEEE

C. Preissner, V. Rose, C. Pitts, "Mechanical Systems for a Synchrotron X-ray Enhanced Scanning Tunneling Microscope", Diamond Light Source Proceedings 1 (2010) e21.

Synchrotron X-ray-enhanced scanning tunnelling microscopy (SXSTM) is a novel technique by which materials can be studied with elemental-sensitive and nanometre-spatial resolution. This poster covers the mechanical engineering design for the prototype SXSTM instrument. System performance and sample handling requirements along with the desire to use existing components constrained the design. The SXSTM needs to be mechanically and acoustically isolated from the environment. In addition, all sample preparations are done in situ, and thus, the sample and SXSTM tips need to be prepared and moved inside the vacuum chamber with a wobble stick. The final design incorporates an Advanced Photon Source-designed vacuum chamber, existing components and commercial parts to provide the user with a robust prototype system to demonstrate the impact of this new technique.
© Cambridge University Press 2013

V. Rose, J.W. Freeland, "Nanoscale chemical imaging using synchrotron x-ray enhanced scanning tunneling microscopy", AIP Conf. Proc. 1234 (2010) 445.

The combination of synchrotron radiation with scanning tunneling microscopy provides a promising new concept for chemical imaging of nanoscale structures. It employs detection of local x‐ray absorption, which directly yields chemical, electronic, and magnetic sensitivity. The study of the tip current in the far field (800 nm tip∕sample separation) shows that insulator‐coated tips have to be considered in order to reduce the background from stray photoelectron. A picture of the different channels contributing to the x‐ray enhanced STM process is proposed. If during electron tunneling the sample is illuminated with monochromatic x‐rays, characteristic absorption will arise, and core electrons are excited, which might modulate the conventional tunnel current and facilitate chemical imaging at the nanoscale.
© 2010 American Institute of Physics

V. Rose, J.W. Freeland, K.E. Gray, S.K. Streiffer, "X-ray-excited photoelectron detection using a scanning tunneling microscope", Appl. Phys. Lett. 92 (2008) 193510.

Detection of x-ray-enhanced electrons emitted by synchrotron radiation with the tip of a scanning tunneling microscope has the potential to open a path to high-resolution microscopy with chemical sensitivity. Nonresonant photoejected electrons typically yield a current background of a few hundred picoamperes at a bare tip. Coating the tip with an insulating boron nitride film can effectively reduce this background. In this configuration, we have quantitatively studied the bias dependent photoelectron collection for tip/sample separations of 400–1600 nm, where quantum mechanical tunneling does not contribute.
© 2008 American Institute of Physics