Laboratory for micro-Raman scattering spectroscopy is equipped with triple Jobin Yvon T 64000 spectrometer (gratings with 1800 grooves/mm), a Coherent Ar- Kr mixed gas ion laser, and a CCD detection system. The set-up contains a confocal microscope and an x-y-z microscope stage. For variable temperature measurements there is a Linkam THMS 600 heating and cooling microscope stage, which allows for the micro-Raman measurements to be performed within the 77 to 900 K temperature range. Another micro-Raman set-up is a TriVista 557 spectrometer. A Konti liquid helium microscope cryostat is also part of this laboratory.


Jobin Yvon T64000 Raman spectrometer

The Jobin Yvon T64000 Raman system is equipped with a triple Jobin Yvon T64000 spectrometer, Coherent mixed Ar⁺/Kr⁺ ion gas laser and CCD detector system. The experimental set-up also includes a confocal microscope and a xyz stage. The Cryovac Konti cooling cryostat for low temperature measurements makes it possible to obtain the micro-Raman spectra within the temperature range from 4 to 300 K. Through appropriate neutral filters of the T64000 system, the laser spot is driven by the mirror combination to the microscope system, which focuses a spot on the sample surface. The confocal microscope permits experiments on small size samples, with improved spatial, lateral and depth resolutions. The light scattered from the sample surface is redirected to the microscope and than orientated by mirrors to the triple monochromator. The spectral dispersed light from the monochromator enters the CCD (Charge Coupled Device) detector.

 
Jobin Yvon T64000 Raman scattering system with Cryovac Konti microscope cryostat.

The T64000 monochromator system consists of a double pre-monochromator (stage 1 and 2, see figure 7) and a spectrograph stages (stage 3 in the same figure). The pre-monochromator is a twin monochromator working in a subtractive mode. It acts as a tunable filter in the spectral range defined by the scanning mechanism and the gratings. The spectrograph stage is used as disperser. The T64000 system can be utilized in a triple additive or in a triple subtractive modes. Its unique optical design allows for easy switching between additive and subtractive modes. An additive mode gives the highest spectral resolution and high linear dispersion, whereas a subtractive mode gives a high stray light rejection and allows for collecting low-frequency Raman spectra down to 5 cm^-1. The optical diagrams for these two modes are shown in figure:

 
Optical diagram of JY T64000 monochro-mator in a triple additive and subtractive mode.
 

In the triple subtractive mode, which is used more often than the additive one, a polychromatic radiation enters the first monochromator through the entrance slit S₁ and is dispersed by the grating G₁. The exit slit of the first monochromator (entrance slit of the 2^nd monochromator) S_i1/2 selects a bandpass between l₁ and l₂. The grating G₂ in the 2^nd monochromator recombines all the dispersed radiations on the exit slit S_i2/3 giving again a polychromatic radiation, but limited to only the spectral range between l₁ and l₂. In that manner, the elastic radiation remains outside this range, which is the main purpose of the pre-monochromator. The polychromatic radiation selected by the pre-monochromator is dispersed by the grating G₃ of the spectrograph and is directed by mirrors to the lateral exit of the spectrograph. The T64000 is equipped with three holographic 1800 grooves/mm gratings defining a mechanical range of 0-950 nm.

The Symphony 1024 x 256 Cryogenic Open Electrode CCD detector, cooled by nitrogen down to 140 K, is mounted in the plane of the exit image of the T64000 monochromator. With an average quantum efficiency of 40% from 200 nm to 900 nm and its relatively flat response, this detector is the optimal choice for general purpose spectroscopic measurements.

Quantum efficiency of CCD

The processes of measurement and acquisition are controlled by a LabSpec software. With regard to the efficiency of its detection, the T64000 system makes it possible to gather weak signals. The exposure time and the accumulation number are chosen in order to obtain the best signal to noise ratio.

System technical specification:

Spectral range: 200 - 950 nm
Precision: ±1 cm^-1 in the range 450 - 850 nm
Gratings: 3 x 1800 grooves/mm
Reproducibility: better than 1 pixel
Step size: 0.00066 nm (with 1800 grooves/mm gratings)
Focal length: 3 x 640 mm (triple additive)
Low frequency: typically 2 – 5 cm^-1 (double filter stage)
Stray light rejection: 10^-14at 20 cm^-1 (514 nm laser)
Resolution: better than 2 pixels of the CCD, i. e. 2 cm^-1 (for 514,5 nm laser)
Dispersion: 17,68 cm^-1/nm (at 600 nm)
 

Jobin Yvon T 64000 system allows for the measurements of high resolution Raman spectra to be made in a relatively short time, which makes it possible that a small content of highly disordered phase in materials be registered, as it is illustrated in the case of anatase TiO₂ or Pr doped CeO₂., see below.
 

TriVista TR557 Raman spectrometer

The TriVista 557 (S&I GmbH) is a triple spectrograph which offers the highest spectral resolution and extreme stray light rejection required for the Raman and photoluminescence  measurements in UV, VIS, and NIR spectral ranges. Its unique optical design (patent pending) allows an easy switching between additive and subtractive modes and it can be easily reconfigured to work as a double or a single spectrometer.

In the heart of the TriVista are industry leading Acton Research Corporation spectrometers. They are known for superb resolution, stray light rejection, excellent imaging and ruggedness. The TriVista can operate from 185 nm to 2.2mm. The spectral resolution can reach 4 picometers in the VIS spectral range (500 nm). The extreme stray light rejection allows Raman spectra to be measured as close as 5 wave numbers from the Rayleigh line.

 

TriVista 557 system (S&I GmbH)

Triple Raman Spectrometer in additive or subtractive mode with Macro- or Micro-Chamber and PTM and CCD detectors.

The TriVista is the most flexible system for scientific use on the market. Nine gratings (three in each stage) with different numbers of grooves per mm (from 300 to 2400 grooves/mm) ensure the collecting of the Raman spectra in different ranges and with different resolutions just by applying software commands. The TriVista 557 model has 500 nm focal length in the first and the second stages and 750 mm in the third stage. It can be used in single, double and triple configurations. A single configuration means all three stages can be used simultaneously and independently for three different experiments to be run at once.  Most often the TriVista is utilized as a double or triple system. In these cases, the light beam sequentially passes through 2 or 3 stages and the gratings of the involved stages coherently move together with very high precision. Two most common reasons for using a double or a triple system instead of a single spectrometer are a high spectral resolution and a high stray light rejection. These two effects can be achieved in different modes of the TriVista operation:

    1. The Additive mode gives a high spectral resolution and high linear dispersion.
    2. The Subtractive mode gives a high stray light rejection.

The TriVista software offers an easy way to switch between additive and subtractive modes just by mouse-clicking. The physical mechanism behind this switch is changing the direction of the grating rotation. In the additive mode both gratings in the first and the second stages synchronously rotate clockwise adding dispersion to each other. In the subtractive mode the grating in the first stage rotates clockwise but the grating in the second stage synchronously rotates counter- clockwise precisely cancelling dispersive action of the grating in the first stage.

As it can be seen from the figure above, in triple configuration the Double monochromator stage is used together with the last stage as a Triple system for Raman spectroscopy. However, it can be also used as an excitation stage for Fluorescence and Photoluminescence and the emission can be detected by the last stage of the system. 

The S&I software was written to obtain an optimized access to all three stages of the TriVista (Fig. 9). It is programmed in "Visual Basic" and runs in co-operation with the Princeton Instruments' WinSpec software package, which is designed to operate a multitude of CCD detector and allow access to exclusive detector functions. The S&I software controls spectrometer functions while the WinSpec is used as a DLL and provides data acquisition and setup functions for multi-channel detectors.

The TriVista spectrometer is equipped with the Princeton Instruments Spec-10: 256 detector (Fig.10), which is a fully integrated spectroscopic CCD system. A choice of industry standard, spectroscopic-format E2V sensors are offered. The Spec-10: 256E incorporates an open electrode sensor which offers a broadband response over a wide spectral region - from 200 to 1050 nm, as can be seen from the quantum efficiency curve in the Fig. 11. The liquid nitrogen cooling of the CCD effectively eliminates dark noise, even for long exposures.
 

Spec-10: 256E CCD Detector	Quantum efficiency of Spec-10: 256E

To simultaneously obtain Stokes and Anti-Stokes Raman spectra (see Fig. 12), the TriVista system is equipped by a laser mask (Fig.13) which can be installed on 1^st , 2^nd, or on both intermediate slits. The laser mask is a very thin metal bar positioned precisely in the middle of the slit which mechanically blocks the laser light. For more versatility, the laser stop mask has 4 options - three bars of different width (150, 300, -600 mm) and the open space to allow the Raman signal to pass unblocked through the intermediate slit. The laser stop mask is set on a sliding strip for changing between 4 options and a precise positioning.

 

Stokes and Anti-Stokes Raman spectra of GeSe2	Sliding Strip with Laser Stop Mask

The Micro-Raman assembly is based on the upright microscope BX51 from Olympus and the Confocal Micro-Raman Interface (CMRI) as an extension for the BX51 to allow for the Micro-Raman Spectroscopy. CMRI is designed to allow direct coupling and fibre coupling for transmission of a laser beam and a Raman signal. Polarisation dependent measurements are possible for both direct coupled and fibre coupled laser beams. The confocal Raman microscope has a spatial resolution on a micron scale.

The TriVista system is equipped with a CCD detector, a confocal microscope, whereas the software-driven XYZ stage makes possible an automated 3D mapping with an auto focus option. For variable temperature measurements under microscope we have supplied Linkam THMSG600 heating/freezing stage which works in temperature range -196° to 600°C, up to 130°C/min heating and temperature stability <0.1°C.
 

X-scan and Y-scan: Raman spectra of the TiO2 at various positions on the sample along x-and y-axes Z-scan: Raman spectra of the Si thin film at various positions on the sample along z-axis

LINKAM THMS600 - System description

The THMS600 is one of the most popular heating and freezing stages used in many applications where high heating/freezing rates and 0.1°C accuracy and stability are needed. The LINKAM THMS600 heating/cooling stage is equipped with a CI94 temperature controller and a LNP94 Liquid Nitrogen Pump.

LINKAM THMS 600 heating/cooling stage	CI94 temperature controller	LNP94 Liquid Nitrogen Pump

Technical data:

• Temperature range -196° to 600°C.

• Up to 130°C/min heating.

• Temperature stability <0.1°C.

• 16 mm X,Y sample manipulation.

• Sample area 22 mm diameter.

• 100 W platinum resistor sensor.

• Light aperture - 2.4mm Ø.

• Silver heating block for high thermal conductivity.

• Direct injection of the coolant into the silver block.

• Single ultra thin lid window - 0.17mm.

• Objective lens working distance - 0.1mm to 4.5mm.

• Water cooled stage body for high temperature work (>300°C).

• Sample side loading without removing the stage lid.

• Can be used with all microscope techniques

• Controlled heating rates of 0.01°C to 130°C/min.

• Controlled cooling rates of 0.01°C    to 100°C/min

• Displays Temperature to 0.01°C

• Hold time 0 - 9999 mins.

• RS232 interface to allow programming by Linksys software.

• A cooling system consists of the 2 Litre dewar and a control unit housing the pump which can be controlled by selecting one of 5 manual pump speeds.

• Recycled dry nitrogen gas is used to purge the sample chamber and upper lid window surface of condensation.

• The precise control of liquid nitrogen flow allows for specific stages controlled cooling rates as fast as 130^OC/min or as slow as 0.1^OC/min.
   

The Linksys 32 software displays the live temperature, active ramp information and allows for the user to have full control of the rate of heating, limit and hold time

Heating Procedure		Cooling Procedure
The dewar with a pump inside should be approximately 2/3 filled with water. The heating is provided using Linksys32 software.		The dewar should be 2/3 filled with liquid nitrogen.The lid must be placed so that the thin capillary tube   is pointing upward. The thin silicon tube carries exhaust nitrogen gas and is used to prevent the blurring of the top of the window on the stage lid.

Stokes and anti-Stokes Raman spectra of TiO2 measured using Linkam stage in the 24 – 600 oC temperature range.

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