Analytical Technologies Singapore

Spectroscopy

Horiba Debuts new Raman Microscope for Semiconductor Analyses

HORIBA is pleased to introduce the latest addition to its repertoire, the LabRAM Odyssey Semiconductor system. This pioneering Raman/Photoluminescence microscope derives its foundation from the widely acclaimed LabRAM HR Evolution Confocal Raman Microscope, renowned for its exceptional high resolution capabilities. Noteworthy enhancements include the integration of a sample mounting stage adept at accommodating the prevalent 300 mm wafer size, catering directly to the semiconductor industry’s standard requirements.
 
As compound semiconductors are becoming more complex with a higher number of elements, uniformity assessment on blanket wafers is essential for high quality devices and high yield. The LabRAM Odyssey Semiconductor system will help process engineers qualify the different process steps in a timely manner and with a high level of confidence. With a high spatial resolution mode, the LabRAM Odyssey Semiconductor offers the capability to detect and identify defects and submicron inhomogeneities to understand and give insights about their origin.

The LabRAM Odyssey Semiconductor system includes a 300 mm × 300 mm automated sample stage and an automated objective turret, enabling the acquisition of maps of full wafers of diameter up of 300 mm.  In addition, the DuoScan imaging function permits both variable size laser macrospot for full wafer maps and high spatial submicron step scanning for small area maps.  The range of available excitation lasers, combined with a wide range of spectral detection, from deep UV to near IR, makes the LabRAM Odyssey Semiconductor system a two-in-one Raman and Photoluminescence spectroscopy tool. The “Tilt at midway” autofocus function overcomes possible sample/holder tilt and ensures reliability in uniformity response.

As Raman and Photoluminescence characterisation is moving from the lab to the fab for the emerging 2D materials-based devices, the LabRAM Odyssey Semiconductor system is the perfect tool for metrology technical managers.

NanoRaman Set up with Bioptentiostat for Tip Enhanced Raman Spectroscopy (TERS) Application

The NanoRaman system equipped with LabRAM Evolution being installed locally by Analytical Technologies’ in-house team.

LabRAM Evolution, the world renowned Raman solution for research and analysis. The integral flexibility of the LabRAM HR Evolution makes it the ideal platform for combined with the fully integral nano-Raman for research to TERS (tip enhanced Raman scattering).  

TERS Tip
Raman Microscope

A close up of the integration of a customised environmental chamber and electrochemical cell within a NanoRaman (as shown above) setup designed a sophisticated and versatile experimental configuration to enhance the capabilities of this analytical instrument.

This integrated system is further augmented by the inclusion of a bipotentiostat, a critical component for conducting Tip Enhanced Raman Spectroscopy (TERS) experiments.  

Personalised hands-on guidance and training provided by a HORIBA’s application scientist represents a valuable and tailored educational experience designed to empower researchers, technicians, and users with the skills and knowledge required to make the most effective use of HORIBA’s instruments. 

Another angle of the HORIBA’s LabRAM HR Evolution Setup before the integration of NanoRaman, with HORIBA’s in-house software installed in the computer (right). 

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Shadow Imaging

High-magnification Shadow Imaging is very suitable for visualising particles, droplets and other

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A Steady State Fluorometer Installation

Installation of a steady-state fluorometer equipped with Time-Correlated Single Photon Counting (TCSPC) capabilities and phosphorescence measurement capabilities designed for highly specialised instrument, tailored for advanced research in the field of perovskite materials.

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Photoluminescence Spectroscopy Uncovers Photovoltaic Properties

Fluorescence spectroscopy is the key to new research into photovoltaic materials with the objective of developing more efficient, flexible and less costly solar cells.

​Generally, the better the luminescence of the materials, the better the efficiency of the solar cells, so researchers measure the luminescence of samples to gauge the potential semiconductor properties.
 
A team from Texas A&M University-Central Texas uses photoluminescence to gauge the quality of solar cells, materials that convert light to electricity. The luminescence of a solar cell can indicate the quality of the solar cell crystal. Semiconductors, which are the basis of solar cells, luminesce at a very specific wavelength.

​Generally, the better the luminescence of the materials, the better the efficiency of the solar cells, so researchers measure the luminescence of samples to gauge the potential semiconductor properties.

The research team is trying to develop new materials. Besides silicon, they do some work with mostly thin film photovoltaic materials like cadmium telluride, copper, indium, gallium and selenide.

The team looks at whether a cell is luminescing along with the uniformity of the luminescence. The individual materials should all have the same wavelengths of light and the same distribution.

Sometimes scientists see different spots that have dissimilar wavelengths of luminescence. That tells them the manufacturing process has introduced some level of variability in the photovoltaic materials.

The work encompasses both basic and applied research to want to understand the materials and how to process them so it can be manufactured effectively.

The team is part of a center with the long-term goal to help establish photovoltaic electricity as a major source of energy in the world.

The Texas A&M University group uses a HORIBA MicOS (a fully integrated microscope spectrometer) to do a broad array using photoluminescence across the entire sample. Its aim is to aid in the development of new materials.

The folks at Texas A&M are trying to find those poorer performing parts of the sample to understand it better, for basic research and applied applications. They are trying to understand how to get rid of the variations that are less efficient. Patterning, the deposit of poorly or non-photovoltaic materials, is something they want to eliminate. They do this through photoluminescence by engineering out the poor fluorescing components.

They will get a sample from a collaborator and take a rough scan of it with the MicOS, and do a broad array using photoluminescence across the entire sample. As a result, they have mapped the sample and might see some areas of interest.

If the team identifies one spot on a solar cell that’s more interesting, it can put it in the scanning electron microscope with the HORIBA CLUE (Cathodoluminescence Universal Extension), and zoom in on that area. Then the researchers can do micro-mapping in areas that are interesting to them.

The researchers can do micro-mapping this way in areas that are show unusual photoluminescence. Or they may be trying to understand how to get rid of the variations that are less efficient, like the way the photovoltaic materials were deposited. It lets them look at different ways to eliminate that patterning.

Researchers are trying to identify materials that can be much less expensive than silicon, the historical standard for photovoltaics. They also look for properties of substances that can do what silicon can’t do, like be lightweight, bend, and better integrate with our everyday lives. The paint mentioned earlier can be made on a solar cell on any low-cost material, like plastics and paper.  In labs around the world, novel materials include those made from semiconducting nanoparticles (quantum dots), perovskite crystals, semiconducting polymers, and even biological materials and materials made from plant-based extracts.  All of these are being investigated for better semiconducting properties. 

The key is to understand the efficiencies of the materials. Once achieved, the technology will become more commercial.

The hitch is this – the ability of these photovoltaic materials to convert light into electricity. These paints haven’t reached the efficiency of silicon – yet.

Silicon dominates the market, accounting for about 90 percent of solar cells. The remaining 10 percent is cadmium telluride. But silicon has severe limitations. It’s a poor absorber of light, requiring thick layers to absorb the energy. Researchers like those at Texas A&M are looking for more flexible less expensive alternatives.

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How to choose a Monochromator/Spectrograph

Choose a monochromator/spectrograph based on

  • A system that will allow the largest entrance slit width for the bandpass required.
  • The highest dispersion.
  • The largest optics affordable.
  • Longest focal length affordable.
  • Highest groove density that will accommodate the spectral range.
  • Optics and coatings appropriate for specific spectral range.
  • Entrance optics which will optimize etendue.
  • If the instrument is to be used at a single wavelength in a non-scanning mode, then it must be possible to adjust the exit slit to match the size of the entrance slit image.

Note: f/value is not always the controlling factor of throughput.

For example, the light may be collected from a source at f/1 and projected onto the entrance slit of an f/6 monochromator so that the entire image is contained within the slit. Then the system will operate on the basis of the photon collection in the f/l cone and not the f/6 cone of the monochromator.

What are the criteria for choosing my monochromator?

Top criteria: Dispersion, resolution, bandpass

The dispersion shows the capability to disperse light. It gives the usable bandpass of a monochromator or indicates the spectral range of a spectrograph equipped with a multichannel array detector such as a CCD camera or InGaAs array. Changing the width of the slit aperture can adjust the bandpass.

Spectral resolution is inversely proportional to the linear dispersion of a monochromator. The resolution requirement of the experiment is often the key performance requirement of any application. For narrow structure analysis (resolution better than 0.1 nm in the visible range), large monochromators are the best choice because they offer increased spectral dispersion and thus a higher spectral resolution.

If the application’s most important requirement is to acquire a large spectral range in one shot, small spectrographs are better, as in a process application. In fact, single timonochromators with a focal length below 0.3 m are suitable where most stray light is not considered a major problem.

Laboratory researchers who don’t need high resolution and wide range at the same time, however, should choose larger spectrographs. These users can change gratings (i.e., to a higher or lower groove density) or acquire multiple spectra to achieve complete results.

Second criteria: Accuracy, speed

Monochromators work by scanning through the spectral features of the optical signals, step by step. As a result, the measurement process is generally slower than that of spectrographs with multichannel array detectors that operate in a fixed grating position and directly acquire a full spectrum according to their dispend mainly on the grating motor drive. Instruments with 0.5-m or higher focal length are usually equipped with sine bar mechanisms that give excellent accuracy (better than 0.1 nm) and repeatability (better than 0.01 nm). But the trade-off is speed: It can take several minutes to scan a large spectral range with high spectral resolution in monochromator mode. Smaller devices commonly use direct, or worm drives, because their resolution specifications are lower. In this case, they set the grating position within a few seconds.

Third criteria: Throughput, imaging quality

Most of the time, small monochromators and spectrographs have better throughput than large ones because of their larger numerical apertures (f numbers) and simpler design (often with fewer optical components).

However, the numerical aperture is not the final consideration in optical throughput. The linear dispersion is also important because it defines the input aperture sizes for a particular spectral resolution.

A more useful figure of merit for comparing monochromators for imaging applications is light-gathering capability. Manufacturers of small instruments usually find that to preserve spectral resolution, they can produce only a small image.

Producing a larger image, especially across a large spectral range, is very difficult because of the spatial corrections required.

The commercial introduction of imaging spectrographs has partially corrected the spatial imaging quality issues. These instruments use toroidal gratings or toroidal mirrors to correct for astigmatism in the image plane and to improve image quality, while keeping the numerical aperture at the same level as non-imaging devices. This correction requires complex calculations. The choice of the toroid, the optical incident angles of the device and wavelength optimizations shows the expertise of the manufacturer.

Well-corrected, fixed, compact spectrographs can provide excellent image quality. Some can discriminate three or four spectral channels over a 6-mm-tall focal plane. Interesting axial spectrograph configurations using prisms and lenses also offer excellent image quality over a few hundred nanometers in the visible range.

Some 30-cm or larger imaging spectrographs allow more than 10-channel analysis with a minimized channel overlap.

Final criteria: Stray light, design, focal length

Stray light relates mainly to the quality of the device’s optical components (mirrors and grating). The user is generally not aware of stray light or improper internal reflection, which can produce poor results.

Because of their slit/slit configuration, monochromators have less stray light or reentrant light than do spectrographs, which have no exit slit. However, when the stray light is important in an application, large-focal-length instruments, or double monochromators, are the best choice. Small devices present more risk of stray light than larger ones.

In terms of optical design, most large monochromators/ spectrographs use the asymmetric Czerny-Turner configuration. Smaller instruments tend to use an asymmetric “V” con-figuration as a compromise.

Weighing the trade-offs

No one device can cover all spectroscopic applications. However, a user who carefully analyzes the spectral and performance requirements of an application can weigh the tradeoffs involved in choosing between small- and large-focal-length monochromators and spectrographs.

If you need to analyse a short spectral range at low resolution, you can probably use an inexpensive, compact monochromator or spectrograph. Even if these devices have stray light, chemometric calibration methods can correct it without influencing the results. However, if you need high resolution, accuracy or versatility, large monochromators and spectrographs are often the safest buys. That is why these are generally the best instruments for research or high-technology industries.

HORIBA monochromators specifications

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Fluorescence Spectroscopy w A-TEEM for fast & precise wine authentication

​Wine is a multi-million dollar industry that is susceptible to fraud and the authentication of wines is an important aspect in the industry. Read more to find out how the team at University of Adelaide, South Australia uses fluorescence spectroscopy with A-TEEM, to achieve 100% accuracy in the classification of different wines according to its geographical origin.

Continue reading the rest of the article here.

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