62 MICROSCOPY
Improving nano-scale imaging
Negative-stiffness vibration isolators can easily support the heavy weight of a combined AFM/ micro-Raman system, and isolate it from low frequency vibrations more effectively than high- performance air tables or active isolation systems. Jim McMahon reports.
Les isolateurs de vibrations à raideur négative peuvent facilement soutenir le poids lourd d’un système micro-Raman combiné à un AFM et l’isoler des vibrations à basses fréquences de façon plus efficace que les tables à air haute performance ou les systèmes d’isolation active. Un article de Jim McMahon.
Schwingungsisolatoren mit negativer Steifigkeit können das hohe Gewicht eines kombinierten RKM- / Raman-Mikroskop-Systems problemlos unterstützen und es von niederfrequenten Schwingungen effektiver isolieren als leistungsstarke Lufttische oder aktive Isolationssysteme. Jim McMahon berichtet.
T
Fig. 1. The MicroView4000 platform, from Nanonics Imaging, is the basis for AFM-Raman Integration.
are susceptible to vibrations from the environment. When measuring a very few angstroms or nanometres of displacement, an absolutely stable surface must be established for the instrument. Any vibration coupled into the mechanical structure of the instrument will cause vertical and/or horizontal noise and bring about a reduction in the ability to measure high resolution features.
he need for precise vibration isolation with scanning probe
microscopy (SPM) and near-field scanning optical microscopy (NSOM) systems is becoming more critical as resolutions continue to bridge from micro to nano. Whether used in academic labs or commercial facilities, SPM and NSOM systems
Traditionally, bungee cords and high-performance air tables have been the vibration isolators most used for SPM and NSOM work. Te ubiquitous passive-system air tables, adequate until a decade ago, are now being seriously challenged by the need for more refined imaging requirements. Bench top air systems provide limited isolation vertically and very little isolation horizontally. Also at a disadvantage are the active isolation systems, known as electronic force cancellation, that use electronics to sense the motion and then put in equal amounts of motion electronically to compensate and cancel out the motion. Active systems are somewhat adequate for applications with lasers and optics, as they can start isolating as low as 0.7Hz, but because they run on electricity they can be negatively influenced by problems of electronic dysfunction and power modulations, which can interrupt scanning.
Lately, the introduction of integrated microscopy systems employing multiple microscopes is enabling more complex optical measurements, but these systems are also much heavier, and there has been little vibration isolation technology available for such
www.scientistlive.com
heavy instrumentation. Air tables, which have been liberally used for optics applications, are not ideal for these nano-scale resolution systems because of their inability to effectively isolate vibrations below 20Hz.
But now, negative-stiffness mechanism (NSM) vibration isolation is quickly becoming the choice for SPM and NSOM systems. Tis includes applications using atomic force microscopy (AFM) integrated with micro-Raman spectroscopy, where negative-stiffness vibration isolation is particularly well adapted. In fact, it is the application of negative-stiffness isolation that has enabled AFMs to be truly integrated with micro- Raman into one combined system. Negative-stiffness isolators can handle the heavy weight of the combined AFM/ micro-Raman system, as well as isolate the equipment from low frequency vibrations, a critical set of factors that high-performance air tables and active systems cannot achieve.
Te integration of AFM with micro-Raman enables a sizable improvement in data correlation between the two techniques and expanded Raman measurement and resolution capabilities. Micro-Raman is a spectroscopic NSOM technique used in condensed matter physics and chemistry to study vibrational, rotational, and other low-frequency modes in a system. It relies on scattering of monochromatic light, usually from a laser in the visible, near infrared or near ultraviolet range. Te laser light interacts with phonons or other excitations in the system, resulting in the energy of the laser photons being
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92