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An instrument to investigate femtochemistry on metal surfaces in real space
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View: Figures


Image of FIG. 1.
FIG. 1.

(Color online) Schematics of combination of fs-laser (left-hand side) with low-temperature STM (right hand side).

Image of FIG. 2.
FIG. 2.

(Color online) Imaging during combined fs laser-STM operation: (a) STM image of 0.03 ML CO on Cu(111), 30 pA, 0.36 V, 6.5 K (b) apparent height along line indicated in (a).

Image of FIG. 3.
FIG. 3.

(Color online) Coupling of laser beam into tunneling gap: (a) top view and side view of the laser beam geometry (blue); the optic holder ring can be moved with the aid of three tube piezos and the zoom-in shows the part of the sample surface that can be reached by the beam and (b) picture of optic holder ring (top) with laser path visualized by a HeNe laser and nitrogen vapor (bottom).

Image of FIG. 4.
FIG. 4.

(Color online) Direction of laser spot into tip-sample region: (a) schematics of shadow effect of tip in laser beamand (b) picture of out coming laser beam; dashed lines indicate tip positions.

Image of FIG. 5.
FIG. 5.

(Color online) Principle of determination of focus size; depth of focus leads to less than 5% deviation at the tip shank as compared to the focus size on the sample.

Image of FIG. 6.
FIG. 6.

(Color online) Principle of measurement: (a) Molecule adsorbed on metal is imaged with STM, (b) STM tip is retracted and moved away from laser beam, then sample is illuminated with light, and (c) same sample region is imaged again by STM.

Image of FIG. 7.
FIG. 7.

(Color online) Thermal expansion of tip: STM image after illuminating tunneling gap with laser light without retraction of tip; position of tip before illumination is indicated by upper cross, lower cross marks approximate middle of the hole created by tip impact; arrow indicates direction of the incoming laser beam; laser beam parameters: 400 nm, in Cu(111) sample, pulses; tunnel parameters: 3.3 pA, mV, .

Image of FIG. 8.
FIG. 8.

Para-chloronitrobenzene adsorbed on Au(111), 5.6 K: (a) molecule (top) and high resolution image of molecule, 61 pA, 97 mV (bottom), (b) large scale image before excitation with laser light; , (c) after excitation with 400 nm light, fluence, pulses, (d) as (b) but with arrows pointing to those molecules or clusters that have diffused (D), reordered , or rotated during excitation (b)–(d) 20 pA, 100 mV.

Image of FIG. 9.
FIG. 9.

(Color online) Para-chloronitrobenzene adsorbed on Au(111), 20 pA, 100 mV, 6 K: (a) before excitationand (b) after excitation with 400 nm, fluence, pulses; circles indicate clusters of three molecules that change from an almost linear arrangement to a triangular one.

Image of FIG. 10.
FIG. 10.

Analysis of fs-induced diffusion of para-chloronitrobenzene on Au(111): number vs. diffusion distance for fluence and pulses, solid line is expected distribution for a two-dimensional random motion.

Image of FIG. 11.
FIG. 11.

(Color online) Calculated temperatures for electrons (main figure) and phonons (inset) on the Au(111) surface in a two temperature model (Ref. 32) for a 40 fs pulse (FWHM) at 500 fs with an absorbed fluence of .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: An instrument to investigate femtochemistry on metal surfaces in real space