For scanning tunneling microscopy it is generally proposed that that the apex of the tip consist of single atom. For a Pt-Ir tip prepared by mechanical cut the apex atom sometime be of Pt or that of Ir (Though both of them have comparable work functions ). So why it is preferred to use an alloy instead of a tip made of Pt or Ir only.
Let me make a wild guess in this regard, Is there any relation of thermal expansion coefficient or stiffness between the alloy and its compositions ?
The formation of oxide (corrosion) on the tip of Pt/Ir alloy of STM tip is negligible. This prevents the tip–sample gap from being destroyed during STM experiments. Also, this alloy can be easily shaped by chemical etching to produce a fine tip, which is suitable to scan corrugated surfaces.
Mainly it is due to the favouable mechanical properties and high hardness of this particulary alloy which simplifies the preparation of an atomically sharp probe. This is achieved using the cutting/pulling method.
In certain applications where the STM tip is used in a liquid environment (ESTM), the Pt/Ir alloy resists attack from redox reactions.
Other reasons for use of this alloys are:
Doesn't form an oxide when the STM is used in air.
Atomic resultion is possble due to the pz or dz2 states on the tip.
Sources:
http://www.platinummetalsreview.com/pdf/pmr-v4-i1-018-026.pdf
www2.cpfs.mpg.de/~ernst/ernst_da.pdf
https://www.cambridge.org/core/journals/mrs-online-proceedings-library-archive/article/role-of-tip-material-in-scanning-tunneling-microscopy/B32182D2E29CDC6656348326D7AF243F
I fully agree with Alex Gee
In certain applications where the STM tip is used in a liquid environment (ESTM), the Pt/Ir alloy resists attack from redox reactions.
Other reasons for use of this alloys are:
Doesn't form an oxide when the STM is used in air.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Atomic, Molecular and Optical Physics
- Atoms