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Aug 2008

Volume 79, Issue 8, Articles (08xxxx)

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Improvement of a dynamic scanning force microscope for highest resolution imaging in ultrahigh vacuum

S. Torbrügge, J. Lübbe, L. Tröger, M. Cranney, T. Eguchi, Y. Hasegawa, and M. Reichling

Rev. Sci. Instrum. 79, 083701 (2008); http://dx.doi.org/10.1063/1.2964119 (7 pages) | Cited 10 times

Online Publication Date: 4 August 2008

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We report on a modification of a commercial scanning force microscope (Omicron UHV AFM/STM) operated in noncontact mode (NC-AFM) at room temperature in ultrahigh vacuum yielding a decrease in the spectral noise density from 2757 to 272 fm/math. The major part of the noise reduction is achieved by an exchange of the originally installed light emitting diode by a laser diode placed outside the vacuum, where the light is coupled into the ultrahigh vacuum chamber via an optical fiber. The setup is further improved by the use of preamplifiers having a bandpass characteristics tailored to the cantilever resonance frequency. The enhanced signal to noise ratio is demonstrated by a comparison of atomic resolution images on CeO2(111) obtained before and after the modification.
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07.79.Lh Atomic force microscopes
42.55.Px Semiconductor lasers; laser diodes
42.81.Qb Fiber waveguides, couplers, and arrays

Confocal laser scanning microscopy using a frequency doubled vertical external cavity surface emitting laser

Elric Esposito, Stefanie Keatings, Kyle Gardner, John Harris, Erling Riis, and Gail McConnell

Rev. Sci. Instrum. 79, 083702 (2008); http://dx.doi.org/10.1063/1.2966395 (6 pages) | Cited 1 time

Online Publication Date: 5 August 2008

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We report on a frequency doubled 980 nm vertical external cavity surface emitting laser for applications in confocal laser scanning microscopy. The beam quality, wavelength flexibility, and low noise characteristics of this compact source make this prolific imaging technique an exemplary tool. Single pass frequency doubling via KNbO3 was demonstrated, yielding 1.8 mW at 490 nm with a near diffraction limited beam quality. Detailed analysis and comparison of the laser performance with the current standard argon ion laser revealed clear advantages of the solid-state source for confocal imaging. Imaging of fluorescein and eGFP labeled biological samples using the attenuated solid-state source provided high-resolution images at lower cost and with improved reliability.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
07.60.Pb Conventional optical microscopes

A silicon metal-oxide-semiconductor field-effect transistor Hall bar for scanning Hall probe microscopy

Akinobu Yamaguchi, Hiromasa Saito, Masayoshi Shimizu, Hideki Miyajima, Satoru Matsumoto, Yoshiharu Nakamura, and Atsufumi Hirohata

Rev. Sci. Instrum. 79, 083703 (2008); http://dx.doi.org/10.1063/1.2968713 (6 pages)

Online Publication Date: 15 August 2008

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We demonstrate successful operation of a scanning Hall probe microscope with a few micron-size resolution by using a silicon metal-oxide semiconductor field-effect transistor (Si-MOSFET) Hall bar, which is designed to improve not only the mechanical strength but also the temperature stability. The Si-MOSFET micro-Hall probe is cheaper than the current micro-Hall probes and is found to be as sensitive as a micro-Hall probe with GaAs/AlGaAs heterostructure or an epitaxial InSb two-dimensional electron gas. This was used to magnetically image the surface of a Sm2Co17 permanent magnet during the magnetization reversal process as a function of an external magnetic field below 1.5 T. This revealed firm evidence of the presence of the inverse magnetic seed as theoretically predicted earlier. Magnetically pinned centers, with a typical size 80 μm, are observed to persist even under a high magnetic field, clearly indicating the robustness of the Si Hall probe against the field application as well as the repetition of the measurement.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
85.30.Tv Field effect devices
81.05.Ea III-V semiconductors
85.75.Nn Hybrid Hall devices
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)

Local potentiometry using a multiprobe scanning tunneling microscope

A. Bannani, C. A. Bobisch, and R. Möller

Rev. Sci. Instrum. 79, 083704 (2008); http://dx.doi.org/10.1063/1.2968111 (6 pages) | Cited 7 times

Online Publication Date: 20 August 2008

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Scanning tunneling potentiometry (STP) is a powerful tool to analyze the conductance through thin conducting layers with lateral resolution in the nanometer range. In this work, we show how a commercial ultrahigh vacuum multiprobe system, equipped with four independent tips, can be used to perform STP experiments. Two tips are gently pushed into the surface applying a lateral current through the layer of interest. Simultaneously, the topography and the potential distribution across the metal film are measured with a third tip. The signal-to-noise ratio of the potentiometry signal may be enhanced by using a fourth tip, providing a reference potential in close vicinity of the studied area. Two different examples are presented. For epitaxial (111) oriented Bi films, grown on a Si(100)-(2×1) surface, an almost constant gradient of the potential as well as potential drops at individual Bi-domain boundaries were observed. On the surface of the Si(111)(math×math)–Ag superstructure the potential variation at individual monoatomic steps could be precisely resolved.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.61.At Metal and metallic alloys
73.61.Cw Elemental semiconductors
73.25.+i Surface conductivity and carrier phenomena
68.55.-a Thin film structure and morphology

Scanning picosecond tunable laser system for simulating MeV heavy ion-induced charge collection events as a function of temperature

Jamie Stuart Laird, Yuan Chen, Leif Scheick, Tuan Vo, and Allan Johnston

Rev. Sci. Instrum. 79, 083705 (2008); http://dx.doi.org/10.1063/1.2965262 (10 pages) | Cited 1 time

Online Publication Date: 26 August 2008

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A new methodology for using scanning picosecond laser microscopy to simulate cosmic ray induced radiation effects as a function of temperature is described in detail. The built system is centered on diffraction-limited focusing of the output from a broadband (690–960 nm) ultrafast Ti:sapphire Tsunami laser pumped by a 532 nm Millennia laser. An acousto-optic modulator is used to provide pulse picking down to event rates necessary for the technologies and effects under study. The temperature dependence of the charge generation process for ions and photons is briefly reviewed and the need for wavelength tunability is discussed. An appropriate wavelength selection is critical for proper emulation of ion events over a wide temperature range. The system developed is detailed and illustrated by way of example on a deep-submicron complementary metal-oxide semiconductor test structure.
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42.62.Cf Industrial applications
07.89.+b Environmental effects on instruments (e.g., radiation and pollution effects)
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
42.79.Hp Optical processors, correlators, and modulators
42.79.Jq Acousto-optical devices

Nondestructive experimental determination of bimaterial rectangular cantilever spring constants in water

David E. Snow, Brandon L. Weeks, Dae Jung Kim, Rajasekar Pitchimani, and Louisa J. Hope-Weeks

Rev. Sci. Instrum. 79, 083706 (2008); http://dx.doi.org/10.1063/1.2969031 (6 pages) | Cited 1 time

Online Publication Date: 27 August 2008

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In order to address the issue of spring constant calibration in viscous fluids such as water, a new method is presented that allows for the experimental calibration of bimaterial cantilever spring constants. This method is based on modeling rectangular cantilever beam bending as a function of changing temperature. The temperature change is accomplished by heating water as it flows around the cantilever beams in an enclosed compartment. The optical static method of detection is used to measure the deflection of cantilever at the free end. Experimentally determined results are compared to Sader’s method and to the Thermotune method most commonly used in cantilever calibrations. Results indicate that the new bimaterial thermal expansion method is accurate within 15%–20% of the actual cantilever spring constant, which is comparable to other nondestructive calibration techniques.
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06.20.fb Standards and calibration

High throughput system for magnetic manipulation of cells, polymers, and biomaterials

Richard Chasen Spero, Leandra Vicci, Jeremy Cribb, David Bober, Vinay Swaminathan, E. Timothy O’Brien, Stephen L. Rogers, and R. Superfine

Rev. Sci. Instrum. 79, 083707 (2008); http://dx.doi.org/10.1063/1.2976156 (7 pages) | Cited 6 times

Online Publication Date: 29 August 2008

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In the past decade, high throughput screening (HTS) has changed the way biochemical assays are performed, but manipulation and mechanical measurement of micro- and nanoscale systems have not benefited from this trend. Techniques using microbeads (particles ∼ 0.1–10 μm) show promise for enabling high throughput mechanical measurements of microscopic systems. We demonstrate instrumentation to magnetically drive microbeads in a biocompatible, multiwell magnetic force system. It is based on commercial HTS standards and is scalable to 96 wells. Cells can be cultured in this magnetic high throughput system (MHTS). The MHTS can apply independently controlled forces to 16 specimen wells. Force calibrations demonstrate forces in excess of 1 nN, predicted force saturation as a function of pole material, and powerlaw dependence of F ∼ r−2.7±0.1. We employ this system to measure the stiffness of SR2+ Drosophila cells. MHTS technology is a key step toward a high throughput screening system for micro- and nanoscale biophysical experiments.
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87.17.Rt Cell adhesion and cell mechanics
87.16.dm Mechanical properties and rheology
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