Back-thinned

Figure 1.6. Spectra of solid glassy carbon obtained with a state-of-the-art spectrometer in 1985 (Spex 1403 double monochromator with photon counting PMT) and a multichannel/CCD spectrometer of 1996 (Chromex 250 spectrograph, back thinned silicon CCD) 514.5 nm laser at 50 mW in both cases measurement times and signal/noise ratios (SNR) as shown.

A front-illuminated CCD may be back thinned by ion etching on the side of the silicon wafer opposite the circuit mask. If the silicon is thin enough after... 

With a blunt needle, the tissue is pushed during the advancement until the tip suddenly penetrates and the tissue moves back. Thin membranes and tissue interfaces may generate large differences within a fraction of a millimeter (Figure 4.8). 

Thin-layer chromatography (TLQ is closely related to column chromatography, in that the phases used in both techniques are essentially identical. Alumina and siHca gel are typical stationary phases, and the usual solvents are the mobile phases. There are, however, some distinct differences between TLC and column chromatography. The mobile (liquid) phase descends in column chromatography the mobile phase ascends in TLC. The column of stationary-phase material used in column chromatography is replaced by a thin layer (100 (xm) of stationary phase spread over a flat surface. A piece of window glass, a miCTOscope sUde, or a sheet of plastic can be used as the support for the thin layer of stationary phase. It is possible to prepare your own glass plates, but plastic-backed thin-layer plates are only commercially available. Plastic-backed plates are particularly attractive because they can easily be cut with scissors into strips of any size. Typical strips measure about 1X3 in., but even smaller strips can be satisfactory. 

Back thinning Illumination of the array from the back of the device eliminates the problem of absorption by the polysilicon gates. However, because the film thickness is comparable to the far-red wavelengths, there is often etaloning. Etaloning refers to coherent multiple reflections in the silicon, which results in ripples in the wavelength response, a phenomenon that is considered unacceptable for a Raman system. 

Most recently, a new detector which combines both deep depletion and back-thinning has been produced [157]. In these devices, a proprietary surface treatment is incorporated into production, which effectively eliminates etaloning in the NIR. The NIR performance is compared to alternative CCD devices in Fig. 17. It can be seen from these curves that the back-thinned, deep depletion CCD is the preferred device for NIR-excited Raman spectroscopy. The only drawback to the deep depletion devices is that they tend to be... 

The implementation of so-called back-thinned CCD removes sensitivity limitations of classical front-illuminated and UV-coated CCD. Using this improved technology, the substrates with extremely thin silica layers are back-illuminated and a large increase in quantum efficiency in the UV range up to 0.9 electrons per photon can be achieved. Specific anti-reflection layers on the detector surface produce further enhancement of the detector efficiency for certain spectral bands. 

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