Spectroscopy and Semiconductor Flashcards

Flashcards created from lecture notes.

What is an echelle spectrograph?

An echelle spectrograph disperses light into its correct wavelengths using a diffraction grating. It separates light based on wavelength through diffraction and angular dispersion.

What is the function of multiplex systems?

Multiplex systems collect all wavelengths at the same time instead of dispersing them.

What can silicon be doped with to make an n-type semiconductor?

Phosphorus

When can destructive interference occur for two waves of the same frequency?

One wave is delayed by 1/2 a wavelength.

What does the photocathode do in a PMT?

The photocathode converts absorbed photons into electrons that are emitted from the cathode.

Why does the R955 PMT absorb a wider range of UV light?

The R955 PMT absorbs a wider range of UV lights because its photocathode material is more sensitive to deep UV light, allowing more UV photons to eject electrons

What do dynode chains do in PMTs?

Dynode chains amplify the signal in PMTs through secondary electron emission.

What is one advantage of quartz over glass cuvettes and vice versa?

Quartz is more durable, glass is more cost-effective

What is one advantage of glass over polystyrene cuvettes and vice versa?

Glass is more compatible with a wider range of samples; polystyrene is disposable, so there's less risk of contamination and can be used for larger wavelength ranges

Could a monochromator with a given slit width and effective bandpass be used to fully resolve silver and copper lines based on their wavelengths?

No, because the difference in wavelength (0.67 um) is less than the required resolution (1 um).

Why are there differences in absorption spectra between gas phase and aqueous solutions?

Fewer intermolecular interactions in the gas phase cause differences in how molecules are absorbed and the appearance of peaks because IMFs affect a molecule's energy levels, leading to different absorption spectra.

What are the characteristics of peaks in gas phase vs. aqueous phase?

Gas phase peaks are sharp and thin due to fewer interactions, while aqueous phase peaks are broader/wider due to more molecular interactions with water molecules.

If a diffraction grating is used to detect 532 nm light in the 1st order, what wavelength could also strike the detector due to 2nd order diffraction?

266 nm

What is one advantage of prisms and diffraction gratings for dispersing light?

Prisms bend light based on refractive index variations; diffraction gratings can be chosen based on the experiment and order effects can be corrected for.

If the wavelength that the detector is most sensitive to is changed, will the peak instrument response change?

The peak instrument response will follow because optical filters can adjust what wavelengths are being absorbed.

Why will intensity increase and the peak be sharper when using tungsten lamps?

Because intensity is inversely proportional to the wavelength; intensity will increase and the peak will be sharper, shifted to the left.

Why do photodiodes have an upper wavelength limit?

Photons of longer wavelengths don't have enough energy to excite electrons across the bandgap of the semiconductor.