THE HEBREW UNIVERSITY CENTER FOR NANOSCIENCE AND NANOTECHNOLOGY

InVia Raman Microscope


Overview of Technique

InVia Raman microscope is an instrument for materials analysis, including a research-grade optical microscope coupled to a high-performance Raman spectrometer. This new generation Raman microscope offers a powerful non-destructive and non-contact method of sample analysis.

One single instrument (Renishaw InVia Raman) delivers both highly specific discrete analysis and information-rich chemical imaged across the wide range of material types. It is perfect for rapid, non-destructive analysis in life science, materials science, chemistry and physics. The system enables analysis of the samples contained within most transparent containers, and in aqueous solution.

Raman spectroscopy reveals vibrations of molecules and crystals. With this information you can identify substances and also determine other valuable details, such as the level of stress of crystals.

InVia Raman microscope is high-sensitive system enabling high resolution confocal measurements with spatial resolution better than 1 µm.

Our system has excitation laser wavelengths from near infrared to the ultraviolet, with software switching of excitation. The system also includes automated high performance filter and sensitive CCD detector. In addition it is equipped with high and low-temperature attachment.

InVia Raman Microscope has option to choose the polarization of the laser beam. By using the polarizing filters you can select the polarization (normal, circle or linear) of the laser beam. The different Raman scattering response of the sample to different laser polarizations can be useful when assigning the symmetry of the vibrational modes involved.

Features
Research grade microscope. Leica optical microscope is chosen for incorporation with Raman system, ensuring inVia Raman microscope have the high optical efficiency and high stability necessary for rapid, reliable operation.

Resolution. InVia Raman microscope is fitted with two diffraction gratings to satisfy all requirements for spectral resolution, spectral coverage and optimized sensitivity. Precision grating stage is used to ensure accurate and reproducible spectra.

Point mapping is the traditional method of mapping samples, and the most basic form of mapping available on an inVia Raman. Point mapping involves acquiring spectra sequentially from a series of positions on the sample, using software -controlled motorized stage to move the sample between each spectral acquisition.

In addition to manual measurements of points on the sample the system can provide the mapping and imaging capabilities. Rather than just viewing discrete spectra you can create information - rich maps and images that fully illustrate your most complex samples. Using three technologies of Raman System - Point mapping, StreamLine Plus and True Raman Imaging - you can get fully information about your samples.

SynchroScan is patented method for continuous extended scanning. Raman spectra can be obtained over extremely wide ranges.

StreamLine Plus is ultra-fast imaging technique and is the spatial equivalent of Renishaw's SynchroScan method for continuous extended scanning. It produces a seamless rapid data stream. The images are delivered unbelievably quickly.

True Raman imaging technology enables the rapidly determination of the spatial distribution of chemical species. It is ideal for surveying large sample areas, and for studying the spatial variations of samples that change rapidly with time. True Raman imaging directly images Raman - scattered light to reveal chemical distribution.

EasyConfocal optical system offers high spatial resolution less than 1 um. This capability can be used with the optional encoded sample stage to create maps of chemical composition and physical condition from lines, areas and volumes of samples.

Sensitivity. Renishaw's CCD detector is high sensitive detector with ultra-low noise. It is ideal detector for the most demanding Raman spectroscopy applications.

Alignment. The InVia microscope automatically optimizes the optical alignment of each beam path, whether ultraviolet, visible, or near-infrared, and then validates system performance.

Excitation switching. One mouse click can switch between lasers and automatically reconfigure itself, and also optimize its optical alignment to give maximum efficiency.

Basics and Tutorials

Raman spectroscopy is a spectroscopic technique based on the interaction between light and matter in which the light that is inelastically scattered. This process is called the Raman effect, first described by Sir Chandrasekhara Raman in 1922.

In a Raman spectroscopy experiment, photons of a single wavelength are focused onto a sample. Most commonly a laser is used for excitation of a sample as it is a powerful monochromatic source of photons. The photons interact with the molecules in a sample, excite the molecule from the ground state to a virtual energy state, depending on the wavelength of an exciting photon. With Raman spectroscopy, we study the scattered photons.

If the final vibrational state of the molecule is more energetic than the initial state, then the emitted photon will be shifted to a lower frequency in order for the total energy of the system to remain balanced. This shift in frequency is designated as a Stokes shift. If the final vibrational state is less energetic than the initial state, then the emitted photon will be shifted to a higher frequency, and this is designated as an anti-Stokes shift. Raman scattering is an example of inelastic scattering because of the energy transfer between the photons and the molecules during their interaction. A change in the molecular polarization potential - or amount of deformation of the electron cloud - with respect to the vibrational coordinate is required for a molecule to exhibit a Raman effect. The amount of the polarizability change will determine the Raman scattering intensity. The pattern of shifted frequencies is determined by the rotational and vibrational states of the sample.

Photons interacting with molecules most commonly scatter elastically. This is called Rayleigh scattering. Rayleigh scattered photons have the same wavelength as the incident light. However, approximately 1 out of a million photons is inelastically scattered. Spontaneous Raman scattering is typically very weak, and as a result the main difficulty of Raman spectroscopy is separating the weak of inelastically scattered light from the intense Rayleigh scattered laser light. However, modern instrumentation almost universally employs notch or edge filters for laser rejection and spectrographs and CCD detectors.

Not every molecule or functional group exhibits Raman scattering. Factors such as the polarization state of the molecule (which determines the Raman scattering intensity) must be considered. Than greater the change in polarizability of the functional group, then greater the intensity of the Raman scattering effect. This means that some vibrational or rotational transitions, which exhibit low polarizability may not be Raman active. They will not appear in a Raman spectra.

For basic education and principle understanding of Raman Microscope, we kindly ask you use the following web resources:

Equipment Specifications

Renishaw inVia Reflex Spectrometer System for Raman spectral analysis has
Spatial resolution 1 µm
Spectral resolution 0.5 cm-1 in visible region of the spectrum
Excitation wavelengths 355 nm, 457 nm, 514 nm, 785 nm
Laser spot size Continuously variable from 1 to 300 um
Grating stage with dual gratings 2400 lines mm-1 and 1200 lines mm-1
Optical microscope Upright Leica optical microscope allowing confocal measurements with 2.5 um depth resolution
XYZ mapping sample stage Step size 0.1 um
Heating and Cooling Cell -196 C to 600 C
Polarization Circular Polarizer (1/4 wave plate)
Polarization Rotator (1/2 wave plate)
  • Reflection Raman microscopy enables chemical identification of elements and compounds with a spatial resolution of ~1 µm. Raman shifts within 150 cm-¹ of the excitation frequency can be measured at excitation wavelengths of either 488 nm or 785 nm with a spectral resolution of ~1 cm-¹.
  • Spatial maps of Raman intensity over areas as large as several square cm can be made using an automated scan stage.
  • Specialized applications:
  1. polarized Raman
  2. photoluminescence
  3. simultaneous Raman/AFM
  • Objectives: 5x, 10x, 20x, 50x (N.A. 0.75 for Raman imaging), 50x (N.A. 0.45 for Raman imaging, long-working distance).