Guió Practica STM

7/23/2019 Gui Practica STM

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Microscpia de Efecte Tnel (STM)

CONCEPTES (NANO)TECNOLGICS :

Efecte tnel, Densitat destats, funci de treball

Microscpia efecte tnel

Imatge de resoluci atmica

Transparncies 2,3,4 = definicions i descripci de la tcnica

Transparncia 5, 6 i 7= equip de mesura (STM de docncia)

Transparncia 8 = descripci practica

Es recomana la visualitzaci dels vdeos:https://www.youtube.com/watch?v=WBqUPU8HOB0 (descripci del equip)https://www.dropbox.com/s/mn22apd8akav1ii/STM_PHYWE_animation.mp4?dl=0 (descripcisoftware i funcionament)
https://www.youtube.com/watch?v=WBqUPU8HOB0https://www.dropbox.com/s/mn22apd8akav1ii/STM_PHYWE_animation.mp4?dl=0https://www.dropbox.com/s/mn22apd8akav1ii/STM_PHYWE_animation.mp4?dl=0https://www.youtube.com/watch?v=WBqUPU8HOB0


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la corriente tnel vara en funcin de la densidad de estados DOS (estructura

electrnica) i el BIAS aplicado (f(U)), la funcin de trabajo y la distancia entre los doselementos dzque forman la unin (muestra-punta); siguiendo la dependencia:

A 10.25 nm-1eV-0.5 for fin eV and d in nmA 1.025 nm-1eV-0.5 for fin eV and d in

Metal 1 Metal 2Gap

ExponentialDecay

Electron Wave function ()

VBIAS

rS

Mostra a observarSonda / puntade microscopi


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d ~ 6-10

Bias voltage:mVV range

La punta conductora sha de posicionar a pocs Angstrom (10 ) de la superfcieconductora o semiconductora.Els electrons salten de la punta a la mostra (o vice-versa) generant un corrent tnel de10 pA a 1 nA.

Itnelaugmenta exponencialment en disminuir la distancia (=> til per microscpia) .I disminueix un factor 10 si la distancia dzaugmenta 1 . => molt bona resoluci

vertical


Mostra aobservar

Sonda / puntade microscopi


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http://www.ieap.uni-kiel.de/surface/ag-kipp/stm/stm.htm


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1. Manual approach

1. Press the Advancebutton to move the sample towards the tip.

2. Watch carefully the mirror image of the tip. The tip and its mirror image will approach each other.

3. Always check for the ProbeStatus. While advancing the status light should be orange. If it switches

to red, you advanced too far and your tip is likely to be damaged.

4. When the tip and its mirror image are about to touch, stop further advancing.

2. Automatic final approach1. Switch to the Z-Controller Panel.

2. Set Set point (tunneling current) to 1.00 nA.

3. Set Loop gain (the speed of the feedback loop) to 1000.

4. Set Tip voltage (tipsample-voltage) to 50 mV.

5. Press the Approach button in the approach panel of the measurement software.

OK !!

You have tunnel current

Tip touch !!

Retract or withdraw


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3. ImagingDefine imaging parameters and press START


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Quick buttons for data processing

1. Calculates the distance and signal difference between two points

2. Calculates the distance between two parallel lines.

3. Calculates the angle

4. Creates a new measurement document containing a line cross-section of a Color map or Line View display between two lines

7. Calculates several roughness parameters from the data points in a selected area

8. Removes the effect of a wrong scan plane when the average and plane data filter options do not give satisfactory resul ts.

9. Removes the effect of drift when the average and plane Data filter options do not give satisfactory results

10. The Glitch Filter removes the effect of small defects in the image such as single short glitches in the scan.

11. The Noise filter removes high frequency noise from the image, but applying the filter will also decrease the resolution of the image.

4. Image treatment

Select chart type


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Find atomic terraces on HOPG surface sampleExample parameters: 0.2 nm size, time /line 0.2sec, set point 1.2 nA, Pgain:1000 and Igain:1200.

Atomic resolution on HOPG surface sampleExample parameters: Decrease step by step the imaging area down to 10x10 nm aprox;time/line=0.03sec; Setpoint=1.2nA, P=1200, I=1500

5. Analyse the HOPG sample

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Guió Practica STM