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Fundamentos afm.key

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For Nanotech Class

For Nanotech Class


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    • 1. Atomic Force Microscopy Fundamentals Sebastián Caicedo Dávila EIEE Universidad del Valle Cali-Colombia
    • 2. Background: The STMThe scanning tunneling microscope was developed in 1981 by Gerd Binnigand Heinrich Rohrer (IBM labs in Zürich), based on the quantum tunneleffect 3
    • 3. Background: The STM 4
    • 4. Background: The STMFor this achievement, Binnig and Rohrer received the Nobel Prize inphysics in 1986.The STM work in two modes: 5
    • 5. Background: The STMIn order to work properly, it is necessary to use other physical effects suchas the piezoelectric effect. 6
    • 6. Background: The STMThe STM can achieve resolutions of 0.1nm lateral and 0.01nm in depth.With such resolutions, individual atoms can be imaged andMANIPULATED STM image of Si (111) 7
    • 7. PUBLISHED ONLINE: 22 MARCH 2009 | DOI: 10.1038/NNANO.2009.48ling readout of hydrogen-bonding-based Background: The STMition STM has a variety of applications, which include characterization, Jin He2, Ashley Kibel1,2, Myeong Lee1, Otto Sankey1, Peiming Zhang2 ofdsay1,2,3 * electrical and chemical properties of nanostructures, lithography, etc. has a ubiquitous role in electron transport1,2 ecognition, with DNA base pairing being theple3. Scanning tunnelling microscope images4 s of the decay of tunnel current as a molecu- led apart by the scanning tunnelling micro- ensitive to hydrogen-bonded interactions. Iat these tunnel-decay signals can be used toength of hydrogen bonding in DNA base hat are held together by three hydrogenpair (for example, guanine–cytosine inter-r than junctions held together by two hydro-base pair (for example, adenine–thymine V lar, but less pronounced effects are observed f the tunnelling probe, implying that attrac- pend on hydrogen bonds also have a role inrise of current. These effects provide new aking sensors that transduce a molecular rec-o an electronic signal. ng through an analyte molecule can yield chemi-Given that hydrogen bonds enhance electron tun-vacuum tunnelling9, we have proposed a new -assembled, hydrogen-bonded tunnel junctions ovide good contacts10 and chemical selectivity5,11. feasibility of this approach, we functionalized a Measure of the strength1 |of hydrogenmeasurements. A sharp gold probe, base-pairs using STMnelling microscope (STM) probe with a DNA ht into contact with a monolayer of nucleosides Figure Illustration of the STM bonding in DNA e under 1,2,4-trichlorobenzene (Fig. 1; see (Shuai Chang et al. 2009) functionalized with a thiolated base, is caused to approach a gold (111)y tunnel current set-point (ISP) was established surface functionalized with a monolayer of thiolated nucleosides until the , the servo broken, and the current recorded as desired set-point current (ISP) is obtained, and then retracted while the d away from the surface. Current decay curves tunnel current is recorded. The current–distance curves can be used to 8 drogen-bond molecular junctions are shown in characterize the strength of the hydrogen-bonded interactions. I is the
    • 8. AFM BasicsAFM imaging information is gathered by “feeling” the sample surface witha mechanical probe (cantilever with a sharp -ideally one atom- tip). Whenprobe and sample come to proximity, different kinds of forces come intoaction, and deflect the cantilever: Cantilevers and probes are commonly fabricated of silicon or silicon nitride, due to their elastic properties. 9
    • 9. .spnng force co AFM Basics tpt damping force thp-sample forc e sample whDepending on the distance between the probe and sample surface, the AFM incan work in three modes: Figure 2. The cantilever-tip model (driving force omitted). ★ Non-contact mode Forr glsivIe)tTce ★ Intermittent or tapping mode rep ★ Contact mode de Th sw distance T tip-to-sanple separation) re ev sy )n-contad A. a JtJah foice si fr re Figure 3. Typical tip-sample interaction force vs. distance curve. ch 10 th

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