Structure of Liquid Metal Surfaces: A First Principles Perspective - Metallic Systems: A Quantum Chemist's Perspective - page 138

z

k in

Sample surface

α

k out

β

q z

θ

q

q xy

y

x

(a)

Liquid metal reservoir

Valve

Capillary

Vacuum chamber

x-ray beam

Liquid metal sample Mo sample pan

(b)

FIGURE 5.2 (a). Relection. geometry. in. experimental. x-ray. relectivity. measurement..
The.angles.of.incidence.and.relection.are.respectively.α.and.β;.the.incoming.and.outgoing.
momenta.are. k in .and. k out ,.and.the.wave.vector.transfer.is. q z ..(b).Illustration.of.a.typical.experi-
mental.setup.for.an.x-ray.relectivity.measurement.from.a.liquid.metal.surface,.as.described,.
for.example,.in.Ref..[16].

liquid.Cs.[5].were.itted.better.using.a.layered.surface.density.proile.than.a.mono-
tonic. density. proile.. Ambiguities. in. itting. the. density. proile. were. resolved. with.
subsequent.experiments.on.liquid.Hg.[6],.which.achieved.wave.vector.transfers.up.
to. q z .∼.2.5.Å −1 .and.allowed.resolutions.down.to.that.of.a.single.atomic.layer.needed.
to. discern. deinitely. the. surface. structure.. Further. measurements. were. performed.
on.various.metals,.including.Ga.[7-9],.Hg.[9,10],.and.In.[11],.all.of.which.have.rela-
tively.high.surface.tensions,.as.well.as.alloys.of.Ga:Bi.[12-14]..Subsequently,.mea-
surements. were. made. for. a. eutectic. alloy. of. potassium. and. sodium. [15],. and. for.
the.pure.alkali.metal.K.[16],.both.metal.systems.having.low.surface.tensions..The.
experimental.signature.of.layering.was.the.appearance.of.a.peak.in.the.relectivity.at.