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Feb 2002

Volume 73, Issue 2, pp. 241-1098

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back to top MICROSCOPY and IMAGING

Color imaging with a low temperature scanning tunneling microscope

Germar Hoffmann, Jörg Kröger, and Richard Berndt

Rev. Sci. Instrum. 73, 305 (2002); http://dx.doi.org/10.1063/1.1433946 (5 pages) | Cited 23 times

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We report on an improved optical design for detecting light emitted from a scanning tunneling microscope (STM). Using a charge coupled device camera and a grating spectrometer a photon detection efficiency of ≈2.5% at 550 nm is achieved and count rates of up to 5×104 counts/nA/s are observed on a noble metal surface and a W tip. Statistically significant spectra from noble metal surfaces are detected in tens of milliseconds. Thus, new modes of measurement become available, which encompass spectroscopic imaging (acquisition of fluorescence spectra at each point of a STM image), and excitation spectroscopy (acquisition of fluorescence spectra while varying the tip–sample bias). Spectroscopic imaging is used to observe gradual changes of the emission spectra as the STM tip approaches a monoatomic step of Ag(111) on a nanometer scale. Excitation spectroscopy with high resolution in both wavelength and bias voltage is demonstrated for a Ag(111) surface. © 2002 American Institute of Physics.
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07.60.Rd Visible and ultraviolet spectrometers
07.79.Cz Scanning tunneling microscopes
06.20.F- Units and standards

A simple low-dissipation amplifier for cryogenic STM

S. Urazhdin, S. H. Tessmer, and R. C. Ashoori

Rev. Sci. Instrum. 73, 310 (2002); http://dx.doi.org/10.1063/1.1433951 (3 pages) | Cited 5 times

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A current sensitive preamplifier designed for low-temperature scanning tunneling microscopy applications is presented. It combines the dc current measurement necessary for the feedback loop operation with a low noise ac measurement used for spectroscopy. The active device is a high electron mobility transistor which was chosen for its low input capacitance and excellent low-temperature performance. The power dissipation of the transistor can be kept at about 10 μW making it compatible with a variety of cryogenic systems. The ac current sensitivity is about 4 fA/√Hz at 4.2 K. © 2002 American Institute of Physics.
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84.30.Le Amplifiers
07.79.Cz Scanning tunneling microscopes
07.68.+m Photography, photographic instruments; xerography
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
85.30.Tv Field effect devices

Cross-correlation image tracking for drift correction and adsorbate analysis

B. A. Mantooth, Z. J. Donhauser, K. F. Kelly, and P. S. Weiss

Rev. Sci. Instrum. 73, 313 (2002); http://dx.doi.org/10.1063/1.1427417 (5 pages) | Cited 17 times

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A digital image tracking algorithm based on Fourier-transform cross-correlation has been developed to correct for instrumental drift in scanning tunneling microscope images. A technique was developed to eliminate cumulative tracking errors associated with fractional pixel drift. This tracking algorithm was used to monitor conductance changes associated with different conformations in conjugated molecular switch molecules and to trace the diffusion of individual benzene molecules on Ag{110}. Molecular motions have been tracked for up to 25 h (400 images) of acquisition time. © 2002 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation

Simultaneous measurement of spatially separated forces using a dual-cantilever resonance-based touch sensor

Jack V. Phan, Robert Hocken, Stuart T. Smith, and Russell G. Keanini

Rev. Sci. Instrum. 73, 318 (2002); http://dx.doi.org/10.1063/1.1431439 (5 pages)

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A simple device for simultaneously measuring two spatially separated contact forces is described. The device uses a monolithic dual-cantilever touch sensor driven by a piezoelectric PZT actuator. A phase-locking method allows measurement of resonant frequency shifts at constant phase, based on the strain response of a second attached PZT. Calibration and force measurement procedures are developed to extract applied contact forces from the dual-cantilever’s coupled, nonlinear response. Based on a preliminary calibration, the present device exhibits maximum relative measurement error on the order of 6%. Procedures for reducing this error are described. © 2002 American Institute of Physics.
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07.10.Pz Instruments for strain, force, and torque
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Equivalent-time sampling force microscopy using pulse position modulation method

R. A. Said

Rev. Sci. Instrum. 73, 323 (2002); http://dx.doi.org/10.1063/1.1430549 (7 pages)

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This paper presents a homodyne pulse-sampling electrostatic force microscopy technique using a pulse position modulation method for the noncontact measurement of internal voltage waveforms in integrated circuits. The measurement system operates by monitoring the mechanical deflection of a micromachined probe as it responds to electric forces induced by the circuit voltage waveform. Although the mechanical response of typical probes used in such systems is limited to few kHz, measurement of high frequency repetitive waveforms is enabled by applying a high speed sampling pulse signal to the probe with the pulse position modulated at a rate below the probe mechanical resonance. This results in down conversion of the circuit induced electric force harmonics to within the probe mechanical response, thus allowing the measurement of high frequency signals. The proposed technique is modeled using Fourier analysis of the measurement system response, and is demonstrated by the measurement of a 0.8 Mbit/s digital pattern on a CMOS test pad. The performance of the measurement system is analyzed based on obtained measurements and simulated system response. An analysis of the method capabilities shows a measurement sensitivity of 13 mVrms/√Hz. © 2002 American Institute of Physics.
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07.79.-v Scanning probe microscopes and components

Quantitative three-dimensional reconstruction of geometrically complex structures with nanoscale resolution

D. N. Dunn, G. J. Shiflet, and R. Hull

Rev. Sci. Instrum. 73, 330 (2002); http://dx.doi.org/10.1063/1.1430550 (5 pages) | Cited 7 times

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A technique to reconstruct high resolution three-dimensional structural images and chemical maps of geometrically complex features is presented. A focused ion beam microscope is used to collect secondary electron images and secondary ion mass spectroscopy elemental maps as a function of depth in the sample. These images and elemental maps are then used to reconstruct volume images and chemical maps using shape-based interpolative methods with 25 nm lateral resolution and approximately 10 nm depth resolution. From these reconstructions, fundamental parameters such as connectivity, the volume fraction, and surface areas of features of interest can be calculated directly. These techniques open broad new opportunities for understanding three-dimensional structural and chemical relationships in materials research. © 2002 American Institute of Physics.
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68.37.Vj Field emission and field-ion microscopy
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.75.+h Mass spectrometers
42.30.Wb Image reconstruction; tomography
02.60.Ed Interpolation; curve fitting
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