Raman Lab Facilities
LabRam Raman system
The LabRam is a new generation of Raman microscope and the instrument of choice for fast, analytical Raman spectroscopy. It is a fully integrated system designed for many applications, such as electronics, chemicals, biomedical products, pharmaceuticals, forensics, environmental samples, polymers and thin films.
The single stage spectrometer takes advantage of the highly sensitive CCD detection system and laser notch filter technology. The two gratings mounted on a translating shaft give complete spectral coverage (200-4000 cm-1) in one hit. Alternatively, sensitivity can be maximised at different excitation laser lines by selecting specifically optimised gratings. The system in our lab is fitted with lasers at 325 nm (He-Cadmium), 458 and 514 nm (Ar-ion), 633 nm (HeNe), and 785 nm (laser diode).
Line scan imaging takes advantage of a 2D CCD detection system. A computer-controlled optical scanner deflects the focused laser beam onto the sample plane as a line. This line is subsequently projected onto the entrance slit of the spectrometer and then imaged onto the CCD. This feature provides simultaneous acquisition of Raman signals from each point of the sample illuminated by the laser scanned line.
For more information, see the technical description from Jobin-Yvon.
Triple additive/subtractive Raman spectrometer
A new triple additive/subtractive Raman spectrometer facility (Jobin-Yvon T64000) was installed in our lab in late 2008. This is the second spectrometer purchased by the MacDiarmid Institute for our laboratory and is available for use by the Institute, the School of Chemical and Physical Sciences and outside clients.
The spectrometer is coupled to a confocal Raman microscope and five different lasers: argon, krypton, helium-cadmium, helium-neon and NIR-solid state. The machine can be used as a single spectrometer with a notch filter, a double subtractive spectrometer (when no notch filters are required) or as a double additive spectrometer (when the instrument acts as a high resolution machine which can resolve atomic line splitting). The spectrometer has both a nitrogen-cooled CCD detector and a photomultiplier (GaAs-cathode).
We have access to (Raman) mapping stages and low temperature conditions - down to 77 K for the microscope and 8 K in the separate closed cycle cryostat.
We operate a state-of-the-art spectroscopic ellipsometer from Beaglehole Instruments, New Zealand. This ellipsometer operates by polarization modulation with an elasto-optic modulator; a method developed by David Beaglehole, Emeritus Professor at Victoria University of Wellington.
A wide wavelength range (196 to 2000 nm) can be used with this instrument. Below 850 nm a photomultiplier is used, in the IR range we make use of a silicon diode or silicon/InGaAs detector and a deuterium light source is available for work in the far UV. A Xe lamp is utilised for the UV to visible range and a quartz-halogen lamp for the visible to IR range.
We currently use the Ellipsometer for projects studying GaN/InN thin films and the optical properties of polymer thin films.
Glass helium bath cryostat
This is a standard helium bath cryostat comprising a glass liquid nitrogen jacket and a glass helium bath that house the stainless steel sample space. The system is designed to make measurements from room temperature to 1.3 K.
The fully evacuated sample space allows excellent isolation of the system from the environment, so very slow warm up can be achieved to ensure thermal equilibrium between the samples and the Rh-Fe thermometer. The sample space has room for three samples, with the contact geometry optimised for low noise four-terminal resistance measurements that are especially useful for measuring the large resistance found in metals and superconductors.
MD4 stainless steel helium cryostat with magnet tail
This MD4 cryostat is fitted with an extension tail that houses the sample, allowing measurements to be carried out when the sample is between the poles of a magnet.
A carbon glass resistance thermometer measures temperatures from room temperature to 1.3 K. Extra care has been taken with this system to use continuous contact leads to avoid voltage noise associated with soldered connections. In this cryostat the sample is immersed directly in liquid helium, resulting in both excellent temperature stability (± 1mK for T < 2.17 K, and ± 3 mK for T > 2.17 K) and very low voltage noise (< 0.1 m V).
This system has been invaluable for measuring the current-voltage characteristics of superconducting thin films in magnetic fields, both parallel and perpendicular to the film plane. A selection of current sources, voltage meters, and electrometers are available for measurements.
Closed cycle cryostat
The closed cycle cryostat is capable of operating from above room temperature to ~10 K. It is equipped with optical ports that are used to make temperature dependent Raman measurements on samples such as high-temperature superconductors and colossal magnetoresistance manganites.
Two separate sets of contact leads are available for temperature-dependent resistance measurements. The first set of leads is optimized for four terminal measurements of low resistance samples, and has the leads thermally anchored to the sample block through metal-coated sapphire pads. The second set of contact leads are useful when the samples have resistance in giga-Ohms or greater, as often found for semiconductors or insulators.
A silicon diode thermometer measures the temperature of the sample block, and if required, a second miniature silicon diode can be attached directly to the sample.
Photoconductivity measurement apparatus
The interface between the optical and electronic properties of semiconductors can be probed through measurement of their photoconductive response. We have developed equipment suitable for performing such measurements, particularly on samples of very high resistance. Mercury or xenon arc lamps, passed through a monochromator are typically used as the light source, particularly for measurements on wide band gap semiconductors that require UV excitation. Both DC and chopped light experiments are possible.
Lasers available for Raman excitation:
- He-Cadmium UV laser (325 nm)
- Blue and green lines of Ar-ion lasers (454 nm to 514 nm)
- Red He-Ne laser (633 nm)
- Near Infrared laser diode (785 nm)
- Krypton laser