AQA · A level Physics

Attosecond tunnelling microscope A-level challenge

Can you get 100%? Use an ultrafast scanning tunnelling microscope to test standard form, electron tunnelling and the spatial spread of an electron wave packet.

Read how an attosecond microscope tracks tunnelling

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Question

8 marks

Answer all parts. Show your working and give units where appropriate.

1(a)

The measured response delay is 500 attoseconds. Express this time in seconds and in femtoseconds.

[2 marks]

1(b)

A conducting tip is brought extremely close to a conducting surface without touching it. A small current is detected. Explain how this current is used to map the surface.

[3 marks]

1(c)

The researchers found that confining tunnelling to a shorter time can cause the electron wave packet to spread over a larger region. The pulse delay gives temporal information, while the tip position and tunnelling current give spatial information. Explain why quoting only the 500-attosecond timing result is not enough to claim atom-scale imaging.

[3 marks]

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