CCD Detectors in High-Resolution

BiologyJian Guan6-28-2013

Overview• Some Chemistry Concepts• What is CCD?• How does CCD work?• Structure of CCD• Principle of CCD Operation• Pixel Size calculation

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1.12ev

3.55ev

Some Chemistry Concepts

Silicon Crystal

What is CCD?

Willard.S Boyle

George Elwood Smith

How does CCD work?

Structure of CCD

Principles of CCD Operation

Direct detection,

well…

• More than enough

• Damage

• Interference from X-ray

Strongelectro

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Indirect Detection is much more acceptable:Electron energy conversion into light

• high conversion efficiency into visible radiation,

• reasonably short and well-defined decay time of the emitted scintillation,

• phosphor output wavelength matched to CCD sensitivity (which has a maximum at ~700 nm),

• resistance to radiation damage,

• a convenient, reproducible method of depositing a thin layer of phosphor on a flat surface.

P20: zinc cadmium sulphide doped with silver

P43: gadolinium oxy-sulphide doped with terbium

Optical coupling: Lens or Fibre optics

Lens coupling Fibre optics

Readout and analog-to-digital

At the output Stage

The charge in Pixel is transferred to a capacitor

Amplifier and analog-to-digital converter

Convert charge to 12 bits or 16 bits resolution (Digitalization)

Noises

• Dark current noise

• Readout noise

• Spurious events due to X-rays or cosmic rays

Temperature-dependent keep cold

Faster readout, more than one read out node

Software algorithm

Electron diffraction applications

Pixel Size CalculationCalculation of Pixel Size from a CCD Image

Pixel size = Actual pixel size

Magnification

Save CCD image in DM3 file format Get the pixel size information from the Digital Micrograph program

If not:

Apogee AP7p CCDPixel Array: 512 x 512 pixelsArray Dimensions: 12.3 mm x 12.3 mmPixel Dimensions: 24 micron square

For Example

Actual pixel size = Array dimensionPixel arry = 12.3/512 = 24 micron

= 240,000 Angstrom

Magnification = 100,000

Pixel size = Actual pixel size

Magnification = 2.4 Angstrom