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urface features whose dimensions rangerom atomic spacing to a tenth of a

millimeter. Current flows through an atomiccale gap between a sharp metallic tip andonducting surface atoms. AFM is notestricted to electrically conducting surfaces.PM uses near field interactions whichliminates the resolution limit. Lateral ranges up to 100um, vertical 10um and lateral andert resolutions can be better than 0.1nm.ample with no excessive height variations.

No sample prep. Vibration free environment.TM and AFM differ in probe material. STMrobe-Tungsten wire. AFM tip-SiO2 or SI3N4nd mounted on a cantilever spring. STMses tunneling current to sense spacingetween the probe and sample surface. AFM-ear field forces between tip and sampleetected by a beam deflection system aresed to sense spacing. AFM-Piezoelectriccanner are ceramics usually lead zirconiumtanate that change dimensions in response

o an applied voltage and conversely, they

evelop an electrical potential in response tomechanical pressure. Maximum scan size in xnd y directions is 100 um and in z is 10 um.

Rhodium Iridium tip or Pt/Ir or gold within 10Angstrom of the sample.

TM-only in air or vacuum.TM has four operational modes-constanturrent, constant height, spectroscopic and

manipulation modes. Constant current mode-he feedback loop controls the scanner

moving up and down to maintain a constantunneling current. The corrugation contouresolves the locations of surface atoms of theample because the LDOS(Local Density of tates) is very sensitive to atom locations isot identical to surface topography, an imageenerated in constant current mode oftenairly accurately depicts the true topography

when scanning is on a scale of a fewanometers. The constant height mode canrovide much higher scanning rates than thatf constant current. It is useful for observingynamic processes in which timing ismportant. The constant height mode can bebtained by turning off the feedback-loop

ontrol. This mode requires that the sampleurface is well leveled without tilt. There islso a risk of crashing the tip onto the sampleurface during scanning. The spectroscopic

mode refers to the operation of recording theunneling current as a function of either tip ample spacing or bias voltage. Thepectroscopic mode is useful for studyingurface properties such as superconductionnd molecular adsorbtion on metal. To recordn STM spectrograph, the tip is stopped at aosition above the sample, and the tunnelingurrent is recorded while changing either the

spacing or bias voltage between the tip andsample.The manipulation mode refers to operationsof relocating or removing atoms on a surface.Can help relocating an adatom i.e. atomattached to the surface by vertical and lateralmanipulation. In vertical manipulation, anadatom is transferred from the surface to theprobe tip, and then is deposited at anotherlocation. The attachment and detachment of the atomto and from the tip is controlled by voltagepulses. In lateral manipulation, an adatomremains adsorbed on the surface and ismoved laterally by the tip when there is aweak bond between the adatom and the tip.This technique has been used for serious aswell as fanciful work.AFM uses a very sharp tip to probe and mapsample topography. The AFM detects near-field forces between the tip and sample,instead of detecting the tunneling current.The short-range forces refer to atomic forces

between atoms when their distance is closeto atomic spacing. The van derWaals forcesare the interactive forces between dipoles of molecules. The dispersion force, a type of vander Waals force between dipoles that arisesfrom thermal fluctuation or electric fieldinduction, is always present betweenmolecules. The van der Waals forces aresignificantly affected by the medium of thegap between tip and sample. For example,when the medium is water rather than avacuum, the forces will be greatly reducedbecause the dielectric constant and refractiveindex of water are closer to those of a solidthan of a vacuum. Electrostatic forces refer tothe interactive forces between the electriccharges of tip and sample. The charges can beeasily trapped at a sample surface and at a tipif they are insulated. Capillary forces areforces resulting from water vaporcondensation between tip and sample. In anair environment, water vapor is likely to forma condensed nucleus there.The operational modes of AFM can be dividedinto Static and Dynamic modes. Static-

cantilever statically deflects to a certaindegree and the feedback loop maintains thisset value of deflection during scanning. In thedynamic modes the cantilever oscillates at adesignated frequency and the feedback looptries to maintain a set value of the amplitudeof oscillation during scanning. Static-tiptouches surface hence only contact type.Dynamic-both contact and non contact type.The most widely used dynamic mode is theintermittent contact mode, tapping mode.The tapping mode reduces possible damage

to sample during scanning and also canprovide information on chemical and physicalproperties of surface other than topography.The cantilever force, proportional to thevertical deflection, will balance with forces onthe tip. The short-range repulsive forceexperienced on the tip apex is most sensitiveto topographic features of a sample. Thus thisshort range force will provide high resolutionimages of topography. Dynamic mode-probetip radius limits the resolution. Regular AFMcantilever has tip radius in the range 10-20nm what is much greater than interatomicspacing on any solid samples. For the tipradius 10 nm and higher effective interactingarea will be at least 100 nm2. As the probescanned over the surface the number of atoms under probe that contributes to theinteraction and to the measured signal willvary with periodicity of the interatomic

spacing on the surface. For the large tipradius (more than 10 nm) this fluctuation areundetectable. Dynamic non contact mode canprovide atomic size resolution in a ultrahighvacuum and with very sharp cantilever's tip.Even though it is more difficult to generate anatomic resolution image with AFM than withan STM.

AFM gives topography, roughness, grain sizeType of signal and how it is collected andprocessed-laser light reflects from flexible

cantilever and detected by position sensitivedetector.

Static mode AFM-Lateral force microscopy ofriction microscopy. When cantilever scansurface in lateral direction the friction forcewill generate lateral force. The angle oftorsion is proportional to the side (lateral)force and can be detected by four quaphotodetector and convert signal to forcecontrast. When moving over a flat surfacewith zones of different firction factors theangle of torsion will be changing in every new

zone . This allows measuring of the locafriction force. If the surface is not absolutelyflat, such interpretation is complicated.Lateral force microscopy can generatetopography contrast. More importantlycontrast can be generated by materialswhose surface properties vary.Focused Ion Beam- Electron solid interactiowhen focused electron beam is incident onspecimen-secondary e, backscattered e, XRays.

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Better choice of liquid metal is Ga, liquid

gallium partially wets heated tungstenfilament and drawn into cone by appliede field. Nearly liquid metal at roomtemperature for minimal heating (stayssuperheated for hours) Low volatility forlong life (up to 1500 hr),Non-reactive toW tip Low energy spread and highangular intensity for excellent probes,Heavy ion for sputtering. Interactionsresulting from ion/solid bombardment:sputtering of ions and neutral particles,

lattice defects-vacancies, interstentials,dislocations, implanted ions, secondarye, no backscattered e.

The Interaction between FIB and thespecimen comes under three headings:

Micro - and nano machining bysputtering of martix atoms from thesurface. This process can be used to milland section the sample.

Sub surface radiation damagesassociated with lattice damages

(vacancies, self-interstitial) and also theGa ions implantation into specimen

Secondary electrons excitations bygenerating of secondary electrons by theincident ion beam;

FIB is an ion beam system that is capableof fast and precise milling of thespecimen material, revealing thestructure under the surface layer, makingcross sections, deposition layers, etc. Theion system produces high resolutionimages as well.

Max sample size 100x50x25mm allowedfor tilt angles in the range -10 to 52 deg.

Ion milling.

FIB assisted Chemical Vapor Dep-Pt, C,Tungsten hexacarbonyl, SiO 2, Al

t deposition damage through coating. Use eeam deposition first then FIB dep to preventurface damage. Sample prep-Mechanicalhinning, Electrochem thinning, Ion milling.

Additional capability of Dual Beam FIB:

End Point MonitorSEM image modes and detectors:

Everhart - Thornley Electron Detector(ETD): SE mode, BSE modeBackscattered electron detector:

A mode, B mode, Z contrast: A + Bmode, topography: A B modeCharge neutralizer

Large Field Detector (LFD) for Low vacuummode;

Gaseous Secondary Electron Detector(GSED) for ESEM modeGaseous Backscattered Electron Detector

(GBSED) for ESEM modeESEM, envirnomental SEM Pressure 130-2600Pa or 1-13 Torr. ESEM allows to study wetsamples, oil bearing or insulating materials.The primary electron beam hits the specimenwhich causes the specimen to emit secondaryelectrons. The electrons are attracted to thepositively charged detector electrode. As theytravel through the gaseous environment,collisions occur between an electron and agas particle results in emission of moreelectrons and ionization of the gas molecules.This increase in the amount of electronseffectively amplifies the original secondaryelectron signal. The positively charged gasions are attracted to the negatively biasedspecimen and offset charging effects. TheThermoelectric Module which is a small wafercomposed of PN semiconductor elements.When current passes through theseelements, one side of the wafer heats and theopposite side cools. When current polarityreverses, the sides of the wafer reversesheating and cooling. This is referred to as thePeltier effect.

FIB systems operate in a similar fashion to ascanning electron microscope (SEM) except,rather than a beam of electrons and, FIBsystems use a finely focused beam of ions(usually gallium) that can be operated at low

beam currents for imaging or high beamcurrents for site specific sputtering or milling.FIB is inherently destructive to the specimen.When the high-energy gallium ions strike thesample, they will sputter atoms from thesurface. Gallium atoms will also be implantedinto the top few nanometers of the surface,and the surface will be made amorphous. Because of the sputtering capability, the FIB isused as a micro- and nano-machining tool, tomodify or machine materials at the micro-

and nanoscale. An FIB can also be used to

deposit material via ion beam inducdeposition. FIB-assisted chemical vadeposition occurs when a gas, such tungsten hexacarbonyl (W(CO)6) introduced to the vacuum chamber andallowed to chemisorb onto the sample. scanning an area with the beam, theprecursor gas will be decomposed intovolatile and non-volatile components; thenon-volatile component, such as tungsten,remains on the surface as a deposition. This isuseful, as the deposited metal can be used asa sacrificial layer, to protect the underlyingsample from the destructive sputtering of thebeam. From nanometers to hundred of micrometers in length, tungsten metaldeposition allows to put metal lines rightwhere needed.

http://en.wikipedia.org/wiki/Sputterhttp://en.wikipedia.org/wiki/Ion_implantationhttp://en.wikipedia.org/wiki/Amorphoushttp://en.wikipedia.org/wiki/Ion_beam_induced_depositionhttp://en.wikipedia.org/wiki/Ion_beam_induced_depositionhttp://en.wikipedia.org/wiki/Chemical_vapor_depositionhttp://en.wikipedia.org/wiki/Chemical_vapor_depositionhttp://en.wikipedia.org/wiki/Tungsten_hexacarbonylhttp://en.wikipedia.org/wiki/Chemisorptionhttp://en.wikipedia.org/wiki/Chemisorptionhttp://en.wikipedia.org/wiki/Tungsten_hexacarbonylhttp://en.wikipedia.org/wiki/Chemical_vapor_depositionhttp://en.wikipedia.org/wiki/Chemical_vapor_depositionhttp://en.wikipedia.org/wiki/Ion_beam_induced_depositionhttp://en.wikipedia.org/wiki/Ion_beam_induced_depositionhttp://en.wikipedia.org/wiki/Amorphoushttp://en.wikipedia.org/wiki/Ion_implantationhttp://en.wikipedia.org/wiki/Sputter