A phase plate for a charged particle beam system, such as a transmission electron microscope (TEM), is described. The phase plate comprises a support having a through-hole and an elongate member which is magnetisable in a direction along its length and which extends partially across the through-hole and which is narrower than the through-hole.
1. A phase plate for a charged particle beam system comprising:
a support having a through-hole; and
an elongate member which is magnetisable in a direction along its length, which extends only partially across the through-hole and which is narrower than the through-hole,
wherein the elongate member and the support are coated with a conductive layer, the conductive layer being electrically coupled to a ground potential.
2. A phase plate according to claim 1 , wherein the elongate member has a width no more than 1 μm and, optionally, no more than 500 nm.
3. A phase plate according to claim 1 , wherein the elongate member has a width, w, the through-hole has a width, d, wherein d≧20·w.
4. A phase plate according to claim 1 , wherein the through-hole has a diameter or largest dimension, d, and the elongate member has a length, L, such that L≧d.
5. A phase plate according to claim 1 , wherein the through-hole has a midpoint between first and second points on a perimeter of the through-hole, wherein
the elongate member extends from the first point on the perimeter towards the second point without crossing the midpoint.
6. A phase plate according to claim 1 , wherein the through-hole is generally circular.
7. A phase plate according to claim 1 , wherein an arm portion of the support member extends into the through-hole, the arm portion supporting the elongate member.
8. A phase plate according to claim 1 , wherein the elongate member has a thickness of no more than 200 nm and, optionally, no more than 100 nm.
9. A phase plate according to claim 1 , wherein the elongate member has a thickness of at least 5 nm and, optionally, at least 10 nm.
10. A phase plate according to claim 1 , wherein the elongate member comprises nickel, cobalt and/or iron.
11. A phase plate according to claim 1 , wherein the elongate magnetic member has a magnetic flux of 4×10−15 Wb.
12. A phase plate according to claim 1 , wherein the elongate member has a width, w, the through-hole has a width, d, wherein d≧50·w.
13. A phase plate according to claim 1 , wherein the elongate magnetic member has a magnetic flux which is an integer multiple of 4×10−15.
14. A phase plate according to claim 1 , wherein an end of the elongate member is located over the through-hole.
15. A charged particle beam system comprising:
a charged particle beam source;
an objective lens; and
a phase plate according to claim 1 disposed downstream or upstream of the objective lens.
16. A charged particle beam system according to claim 15 , wherein the phase plate is disposed at or near to a back focal plane of the objective lens.
17. A charged particle beam system according to claim 15 , which is operable as a transmission electron microscope and/or which is operable as a scanning electron microscope or a scanning transmission electron microscope.