Confocal Raman Microscope (CRM-Alpha300 S)

Confocal Raman Microscope (CRM-Alpha300 S)

Instrument Name:

Confocal Raman Microscope (CRM-Alpha300 S)

Manufacturer:

WITec GmbH, Germany

Operating Modes:

Micro Raman Spectroscopy,
Confocal Raman Microscopy,
Atomic Force Microscopy (AFM), Scanning Near-field Optical Microscopy (SNOM)

Excitation Lasers:

1. Frequency doubled Nd:YAG dye laser [maximum power output is 40 mW power at 532 nm]
2. Helium Neon [HeNe] Laser [35 mW output power at 633 nm]

Scan Stage:

The sample scan stage is a linear piezo- driven feedback controlled one with a scan area of 100 x 100 μm2. There is also stepper motor driven large area scan stage of maximum scanning area 25 x 25 mm2.

Detectors:

Single counting photomultiplier tube (PMT) and Peltier cooled charge coupled device (CCD) were used for high sensitive detection of photons.

About the Instrument:

The confocal Raman Microscope, CRM a300 S(WITec GmbH) is the best of its class instrument that combines in a unique way the operations of confocal microscopy, Raman spectroscopy, AFM, and SNOM. This work station has been used for: (i) confocal microRaman spectroscopy and microscopy (Raman spectrum, SERS [air and liquid measurements], Raman spectral imaging), (ii) confocal section analysis, depth scanning in transmission and reflection modes, (iii) atomic force microscopy (contact and acoustic modes), and (iv) aperture scanning near field optical microscopy (SNOM).

The confocal setup reduces unwanted background signals, enhances contrast and provides depth information. Differences in chemical composition, although completely invisible in the optical image, will be apparent in the Raman image and can be analyzed with a resolution down to 200 nm. Its sensitive setup allows for the nondestructive imaging of chemical properties without specialized sample preparation. With AFM, investigation of material properties on the nanometer scale is possible. As SNOM requires only minimal sample preparation if any, it is ideally suited to quickly and effortlessly image the optical properties of a sample with resolution below the diffraction limit. Typical applications are found in nanotechnology, materials research, life sciences and others.

Selected Data:

Evolution of the Raman spectra with number of layers, with 1800 groves/mm grating; (a) the D band is positioned at 1347 cm-1 and the G band is positioned at 1578 cm-1 , without any considerable change with increase in the number of layers and (b) the 2D band whose position undergoes a blue shift from 2686 cm-1 for graphene to 2703 cm-1 for multi-layer graphene along with an increase in FWHM from 32 to 64 cm-1 . The features corresponding to graphite is also included for comparison1.

A) Single spot Raman spectra of (a) Ag-SWNT, (b) Au-SWNT, (c) AuNR-SWNT, (d) pristine SWNTs, and (e) SWNTs treated with heated citrate solution. Traces (d) and (e) are shifted vertically for clarity. Radial breathing mode (RBM) is labeled and the D and G bands are indicated by asterisks (*). The visible emission maxima are marked with their respective wavelengths. Inset (i): the RBM region at a higher resolution. Inset (ii): the Raman spectra of a dropcast film of AuNR, along with the Rayleigh to compare the intensities. (B) TEM image of the Au-SWNT. (C) Raman spectral images of AuNRSWNT, based on the intensities of visible emission in the 595 to 675 nm window. The spots observed away from the nanotube structure are due to shorter nanotubes remaining in the centrifugate or due to the z-axis discrimination of confocal imaging. (D) Light intensity based transmission SNOM image of AuNRSWNT. Inset (i): the three-dimensional view of (B), rotated suitably to show the increased emission. Inset (ii): corresponding topographic image. Raman and SNOM data are acquired with 514.5 nm excitation2

(a) Optical image of the AFM cantilever on a Random Access Memory (RAM)chip sample commonly used in personal computers. The squares marked in different colors, say red, blue and green corresponds to the AFM images labeled (b), (c)& (d) respectively. (e) Topography along the black line in the AFM image(b). (f) Topography along the red line in (d). (g) Non-contact mode AFM image obtained from a standard alumina pattern named Fischer pattern.

Footnotes:

1. Single- and few-layer graphene growth on stainless steel substrates by direct thermal chemical vapor deposition, Robin John, Ashok Reddy, C. Vijayan and T. Pradeep, Nanotechnology, 22 (2010) 165701.
2. Metal-semiconductor transition induced visible fluorescence in single walled carbon nanotube-noble metal nanoparticle composites, Chandramouli Subramaniam, T. S. Sreeprasad, T. Pradeep*, G. V. Pavan Kumar, Chandrabhas Narayana, T. Yajima, Y. Sugawara, Hirofumi Tanaka, Takuji Ogawa and J. Chakrabarti, Phys. Rev. Lett., 99 (2007) 167404.

A detailed description of the instrumentation can be found at : http://www.witec.de/en/home/

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