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Renishaw's SEM-Raman system.

Introduction

Renishaw's SEM-Raman system unites two well-established technologies, scanning electron microscopy (SEM) and Raman spectroscopy, resulting in a powerful new technique which allows morphological, elemental, chemical, physical, and electronic analysis without moving the sample between instruments.

SEM

SEM is an established vacuum method of examining and analyzing samples at a variety of magnifications. The recent development of SEMs that can operate at higher pressures (poor vacuum) or with field emission electron guns (FEGs) has extended their suitability to a wider range of samples and applications, such as hydrated and insulating samples, and applications where features as small as 10 A need to be studied.

SEMs have two main imaging modes, secondary electron imaging (SEI) and backscattered electron imaging (BEI)--the former is the principal imaging mode, providing the best spatial resolution, and deriving contrast mainly from surface topography. BEI requires an auxiliary detector and, depending on operational circumstances, derives contrast either from mean atomic number of the substrate, or from topography--specifically line-of-sight to the detector.

Most SEMs are routinely fitted with energy-dispersive X-ray (EDX) analysis equipment, and whilst this has proven a very valuable technique, it yields only elemental information. Furthermore, EDX is rather insensitive to light elements (sodium and below), making the analysis of organic compounds meaningless.

Raman spectroscopy

Laser Raman spectroscopy is an analytical technique that uses light-scattering to identify molecular vibrations in a sample.

Typically, a sample is illuminated using a micrometer-sized laser spot, and the light scattered from the sample is directed into a spectrometer. Most of the light hitting the sample is scattered without change in frequency--Rayleigh scattering. A small proportion, however, transfers energy to the sample, initiating molecular vibrations, and therefore scatters with different frequencies. This process is known as Raman scattering and the differences in frequencies correspond to vibrational energy levels in the sample.

The spectrometer filters out the Rayleigh scattered light (which has lost no energy to the sample), and analyzes the Raman scattered light to produce a Raman spectrum. Thus, a Raman spectrum comprises peaks that are shifted (the Raman shift) from the incident beam frequency by an amount equal to the frequency of the molecular vibrations.

For laboratory applications, micro-sampling is usually achieved using a standard optical microscope for laser light delivery and collection: fiber optic probes are coupled to the spectrometer to allow remote micro-sampling.

SEM-Raman spectroscopy

Renishaw's technology (patents applied for) combines both techniques into one system, so that users can take full advantage of the high spatial resolution afforded by the SEM, and the chemical information revealed by Raman.

Renishaw is the only manufacturer to supply a SEM-Raman system that enables the spectrometer to "see" the same area as the SEM--a micron-scale laser spot projected onto the surface of a sample visible in the SEM image.

Compatibility

Renishaw's SEM-Raman hardware can be fitted to most SEMs without compromising the SEM performance in any way. The nature of Raman spectroscopy means that its performance is unaffected by the SEM environment--high vacuum (HV), low vacuum (LV), environmental (ESEM), and high or low (cryogenic) temperatures.

Structural and chemical analyser for SEM

Renishaw's new structural and chemical analyser enhances the capabilities of SEMs by adding the investigative power of Raman, photoluminescence, and cathodoluminescence spectroscopies.

Now you can determine the chemical, structural, mechanical, and electronic properties of your samples, in addition to the topographical and elemental information, inside the SEM chamber.

* Simultaneous SEM, EDS, and Raman spectroscopy

* Cathodoluminescence and photoluminescenca spectroscopies

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Options and upgrades

Renishaw's Raman microscopes provide chemical information at sub-micrometre spatial resolution with internal calibration and performance validation. Available options include:

* Global Raman imaging

* Multiple excitation wavelengths from 229 nm to 830 nm

* Near excitation accessory to within 10 [cm.sup.-1] of laser

* Hot/cold cells

* XYZ mapping

* Fibre-optic probes

* Automated wavelength switching

* Macro-sampling

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Artefact-free spectra with SynchroScan[TM]

Renishaw's research Raman microscopes are the only commercially available systems that can rapidly provide true artefact-free spectra, over very wide spectral ranges. Renishaw's patented SynchroScan[TM] technology provides computer-controlled extended scanning for even the large wavelength coverage required for photoluminescance spectroscopy. To learn more about how Renishaw's extended scanning can improve your Raman and/or photoluminescenca spectroscopy, ask for our SynchroScan[TM] technical note.

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Raman/AFM/NSOM system

Renishaw plc and Nanonics Imaging Ltd have entered into an agreement for the promotion and sale of a joint Raman/AFM/NSOM system.

This collaboration brings together, for the first time in one commercial system, Raman, AFM and NSOM imaging techniques. The user is able to co-ordinate tip movement with spectrum acquisition, and perform simultaneous and correlated Raman and scanned probe microscopy. All of this is carried out without removing the sample from the micro-Raman spectrometer.

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High power near-IR excitation lasers

Ranishaw plc has expanded its range of lasers with the introduction of the RL785 and RL830, designed for the most demanding spectroscopy applications.

Operating at 785 nm and 830 nm respectively, these compact, low-weight, air-cooled lasers are ideal for Raman and photoluminescence spectroscopy. Their small size makes them perfectly suited to portable and OEM laser-based systems. Features include:

* Frequency stabilisation to < 1 [cm.sup.-1]

* Side band suppression

* High power output ([greater than or equal to] 300 mW)

* Stability of [+ or -] 1%

* Fibre-optic coupling option

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Publication:Laboratory Equipment
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Date:Oct 1, 2003
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