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Jul 2007

Volume 78, Issue 7, Articles (07xxxx)

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Application of a novel nonperiodic grating in scanning probe microscopy drift measurement

Yuhang Chen and Wenhao Huang

Rev. Sci. Instrum. 78, 073701 (2007); http://dx.doi.org/10.1063/1.2751091 (5 pages) | Cited 4 times

Online Publication Date: 2 July 2007

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A technique based on two-dimensional nonperiodic grating is proposed to quantitatively measure the drift of scanning probe microscopy (SPM) instruments. Cross-correlation image analysis is adopted in determining the drift. The grating, named as zero-reference mark (ZRM), has specially designed codes and arrangement of the elements can be optimized to have maximum ratio of maximum peak to second maximum of the image correlation matrix. Design considerations of ZRM for drift measurement are discussed theoretically. Advantages of applying ZRM are analyzed by numerical simulation. Comparisons between ZRM and periodic grating show that ZRM has a sharper, less ambiguous correlation function. Adopting ZRM is much more insensitive to drift larger than one element width. Measurement sensitivity is improved by almost one order of magnitude. These characteristics of ZRM imply that it is suitable to be severed as a reference mark for SPM drift measurement.
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42.79.Dj Gratings
07.79.-v Scanning probe microscopes and components

Compact x-ray microtomography system for element mapping and absorption imaging

J. M. Feldkamp, C. G. Schroer, J. Patommel, B. Lengeler, T. F. Günzler, M. Schweitzer, C. Stenzel, M. Dieckmann, and W. H. Schroeder

Rev. Sci. Instrum. 78, 073702 (2007); http://dx.doi.org/10.1063/1.2751094 (8 pages) | Cited 4 times

Online Publication Date: 2 July 2007

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We have designed and built a compact x-ray microtomography system to perform element mapping and absorption imaging by exploiting scanning fluorescence tomography and full-field transmission microtomography, respectively. It is based on a low power microfocus tube and is potentially appropriate for x-ray diagnostics in space. Full-field transmission tomography yields the three-dimensional inner structure of an object. Fluorescence microtomography provides the element distribution on a virtual section through the sample. Both techniques can be combined for appropriate samples. Microradiography as well as fluorescence mapping are also possible. For fluorescence microtomography a small and intensive microbeam is required. It is generated using a polycapillary optic. Operating the microfocus tube with a molybdenum target at 12 W, a microbeam with a full width at half maximum lateral extension of 16 μm and a flux of about 108 photons/s is generated. As an example of application, this beam is used to determine the element distribution inside dried plant samples. For full-field scanning tomography, the x-ray optic is removed and the sample is imaged in magnifying projection onto a two-dimensional position sensitive detector. Depending on the sample size, a spatial resolution down to about 10 μm is possible in this mode. The method is demonstrated by three-dimensional imaging of a rat humerus.
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07.85.-m X- and γ-ray instruments
87.59.bd Computed radiography
42.15.Eq Optical system design

Construction of a versatile ultralow temperature scanning tunneling microscope

H. Kambara, T. Matsui, Y. Niimi, and Hiroshi Fukuyama

Rev. Sci. Instrum. 78, 073703 (2007); http://dx.doi.org/10.1063/1.2751095 (5 pages) | Cited 9 times

Online Publication Date: 2 July 2007

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We constructed a dilution-refrigerator (DR)-based ultralow temperature scanning tunneling microscope (ULT-STM) which works at temperatures down to 30 mK, in magnetic fields up to 6 T and in ultrahigh vacuum (UHV). Besides these extreme operation conditions, this STM has several unique features not available in other DR-based ULT-STMs. One can load STM tips as well as samples with clean surfaces prepared in an UHV environment to a STM head keeping low temperature and UHV conditions. After then, the system can be cooled back to near the base temperature within 3 h. Due to these capabilities, it has a variety of applications not only for cleavable materials but also for almost all conducting materials. The present ULT-STM has also an exceptionally high stability in the presence of magnetic field and even during field sweep. We describe details of its design, performance, and applications for low temperature physics.
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07.79.Cz Scanning tunneling microscopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Scanning nonlinear magnetic microscopy

Makoto Endo, Koya Ohara, and Yasuo Cho

Rev. Sci. Instrum. 78, 073704 (2007); http://dx.doi.org/10.1063/1.2752609 (5 pages)

Online Publication Date: 5 July 2007

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Scanning nonlinear magnetic microscopy (SNMM) is introduced as a new microscopic technique for measurement of the distribution of magnetization. The technique is based on the detection of inductance variation in a magnetic material under application of an external alternating magnetic field. The measured inductance thus reflects the nonlinear magnetic response of the material, giving the nonlinear magnetic permeability (μ333) and the direction and magnitude of magnetization. SNMM is demonstrated in application to measurement of the magnetization distribution of a floppy disk.
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75.50.Gg Ferrimagnetics
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Active mechanical noise cancellation scanning tunneling microscope

H. Liu, Y. Meng, H. W. Zhao, and D. M. Chen

Rev. Sci. Instrum. 78, 073705 (2007); http://dx.doi.org/10.1063/1.2755399 (5 pages)

Online Publication Date: 6 July 2007

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We present the design and performance of an active mechanical noise cancellation scanning tunneling microscope (STM). This system features two key parts: a “twin-tip” scanner and an active mechanical noise cancellation algorithm. The twin-tip scanner functions as two independent STMs which share nearly the same mechanical transfer function, allowing both STMs to sense nearly identical background mechanical noise. Based on an adaptive digital signal processing technique, the active mechanical noise cancellation algorithm applies the noise sensed by the first STM to concurrently cancel the noise in the second STM and hence allows the second STM to acquire spectroscopy with a significantly improved signal to noise ratio. This system demonstrates long-term stability of the tip-sample tunnel junction and improved spectroscopy measurement in a mechanically noisy environment.
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07.79.Cz Scanning tunneling microscopes

Application of a charge-coupled device photon-counting technique to three-dimensional element analysis of a plant seed (alfalfa) using a full-field x-ray fluorescence imaging microscope

Masato Hoshino, Toyoaki Ishino, Takashi Namiki, Norimitsu Yamada, Norio Watanabe, and Sadao Aoki

Rev. Sci. Instrum. 78, 073706 (2007); http://dx.doi.org/10.1063/1.2756632 (7 pages) | Cited 1 time

Online Publication Date: 31 July 2007

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A full-field x-ray fluorescence imaging microscope using a Wolter mirror was constructed at Photon Factory BL3C2. White x rays from a bending magnet were used to excite x-ray fluorescence and to enhance the x-ray fluorescence intensity. A photon-counting method using a charge-coupled device was applied to obtain an x-ray fluorescence spectrum at the image plane. The spatial distributions of some specific atoms such as Fe and Zn were obtained from photon-counting calculations. An energy resolution of 220 eV at the Fe Kα line was obtained from the x-ray fluorescence spectrum by the photon-counting method. The newly developed three-dimensional element mappings of the specific atoms were accomplished by the photon-counting method and a reconstruction technique using computed tomography.
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07.85.Tt X-ray microscopes
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Mesoscale scanning probe tips with subnanometer rms roughness

Dewei Xu, Kenneth M. Liechti, and K. Ravi-Chandar

Rev. Sci. Instrum. 78, 073707 (2007); http://dx.doi.org/10.1063/1.2756997 (9 pages) | Cited 9 times

Online Publication Date: 31 July 2007

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Surface smoothness of probe tips is critical for applications, such as measuring surface tension of various liquids, oscillatory hydration forces, and interfacial shear strengths from friction experiments. In this study we establish conditions for fabricating tips with smooth surfaces by controlling the electrochemical polishing process throughout the tip evolution rather than following the current practice of producing tips by the drop-off method. Polishing is conducted under a constant voltage, with the wire immersed below the nominal air/electrolyte interface by no more than one-half of the wire diameter and stopping the etching at different current levels. This process provides a tip radius range of approximately 100 nm to 5 μm for a tungsten wire with a 0.2 mm diameter. Alternatively, the wire can be placed above the nominal air/electrolyte interface but within the meniscus until the current drops to zero. In this case, the tip radii range from 5 to 50 μm. In both cases, atomic force microscopy scans of these tips show that the surface rms roughness is about 0.3 nm.
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07.79.-v Scanning probe microscopes and components
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