All electrochemical devices rely on the performance of the interfaces between electrolytes and electrodes, at least as much as on the performance of the bulk phases. As a result interfacial studies are growing rapidly in importance. This has only served to emphasize how little is presently understood concerning the fundamental processes at such interfaces."
P.G. Bruce, Solid state Electrochemistry, 1995
To modify the surface of LiMn2O4 micron particles via atomic layer deposition of Chromium oxide coating, in order to increase charge - discharge capacity carried out in a fluidized bed reactor under atmospheric conditions.
1. Identify Probable Precursors for ALD?
2. Temperature for deposition of Chromium (III) oxide?
3. Study the effect of electrochemical data from battery after a pre set charge discharge cycle(s)?
Analytical methods employed: X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM).
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Lithium-ion batteries (LIBs) have found a wide range of applications which include consumer electronics and offer great potential for hybrid electric vehicles (HEVs), plug-in HEVs, pure EVs, and also in smart grids as future energy-storage devices.
LiMn2O4 is envisaged to be the potential replacement for LiCoO2 in Lithium -ion battery as the cathode material. Lithium Manganese Oxide is well known for its high voltage; abundance and environmentally friendliness .But due its quick capacity attributed to (i) spinel dissolution into the electrolyte, (ii) electrolyte decomposition at the high potential regions and (ii) loss of crystallinity during cycling impede and limit it application.
Atomic Layer Deposition
Atomic layer deposition (ALD) was invented by Suntola to enable thin film deposition over large area with good uniformity. Benefits of ALD are many from thickness control at the atomic scale, production of highly conformal films, to low temperature growth, and wide-area uniformity. Due to these advantages, ALD is finding ever more applications. Fig. 1 shows potential applications of ALD .ALD is a surface controlled process where the deposition is controlled by two self-terminating reactions. A schematic presentation of ALD process is presented in Fig 1.
Fig 1 .Potential applications of ALD in various research fields (Kim, Lee et al. 2009)
Fig 2: Schematic representation of Atomic Layer Deposition technique available
At (http://bentgroup.stanford.edu/Research/research_ALD.html , accessed 19/12/2012)
Atomic layer deposition consists of four essential steps: 1) precursor exposure, 2) evacuation or purging of the precursors and any byproducts from the chamber, 3) exposure of the reactant species, and 4) evacuation or purging of the reactants and byproduct molecules from the chamber. For ALD process (in Fig 2) there three key parameters determining the deposition 1) substrate 2) temperature 3) precursor.
Atmospheric Pressure ALD
If ALD could be performed at level greater than atmospheric it would significantly cut the cost associated with equipment of the ALD. Vacuum pumps employed to get the reactants and products through the reactor would no longer be necessary .ALD has been demonstrated ZrO2 ALD using ZrCl4 and O2 and for HfO2 ALD using HfCl4 and O2.
Is the process under which granular solid state particles behave as liquid state when a gas or liquid is passed through them.
Fluidization is one of the best techniques available to disperse and process NPs usually done via upward gas phase. NPs cannot be fluidized individually; they fluidize as very porous agglomerates (Ommen, Valverde et al. 2012).
Fig 3: Illustration of the multistage agglomerate structure obtained by ex-situ analysis. A TEM image of a network of silica NPs. b SEM image of a simple agglomerate or sub agglomerate built up from these networks. C SEM image of complex agglomerate consisting of several sub-agglomerates. (Ommen, Valverde et al. 2012)
Minimum Fluidization Velocity:
Is minimum velocity when solid/mixture in a reactor column behaves as fluid when placed under fluidizing medium.
The minimum fluidization velocity is calculated according to Equation ( Units of operation of chemical engineering . Mcabie and Smith ,pg 177 ) :
Umf : (É¸s.Dp.g.(Ïp-Ïf)Ïµmf3/ 1.75Ï)1/2
É¸s : Spherecity of particles , m .
Dp: Diameter of Particles m.
g : Gravity m/sec2.
Ïp : Density of particles kg/m3
Ïf : Density of fluids kg/m3
Always on Time
Marked to Standard
Ïµmf : Voidage
Interaction of particles and Fluidization.
The main interaction particles in the gas phase are 1.Van der Waals interaction 2. Liquid bridging 3. Electrostatic Interaction (Seville, Willett et al. 2000)
In fluidization Van der Waals are most significant in formation of agglomerates and electrostatic being less relevant but plays important role in force between the agglomerates. Little is known about Capillary bridge influence in fluidization.
Depending on behavior the Fluidization is characterized in to two: (1) Agglomerate Particle Fluidization (2) Agglomerate Bubble Fluidization.
Agglomerate Particle Fluidization
Lack of Bubble, Low min.Fluidization velocity, Large bed Expansion.ex: Aerosil 200, R974, 300 and R972.
Agglomerate Bubble Fluidization
Observance of bubbles at gas velocity much more than minimum fluidization velocity, Less/Limited bed expansion. Ex: Aeroxide TiO2 P25
Fig 4: (a) Agglomerate Particle Fluidization (b) Agglomerate Bubble Fluidization
Fluidization via aeration
The process introducing gas from the bottom of a bed containing particles and increasing the velocity of gas until it the upward drag becomes equal to downward gravitational drag causing the particles to behave like a fluid.
At higher gas velocities, the bed had two layers: a bottom layer with large agglomerates (up to 2 mm in diameter) and a top layer of smaller agglomerates, which fluidized smoothly. Song et al. (2009) reported that by adding coarser particles (e.g., FCC catalyst) to a fluidized bed of NPs improve the fluidization quality: increasing the bed expansion and reducing the elutriation.
Cu/Al2O3 aerogel fine particles were smoothly fluidized at superficial velocities by (Chaouki, Chavarie et al. 1985) greatly in excess of the expected minimum fluidization velocity for such fine powders, because they form stable clusters or agglomerates. These agglomerates fluidized uniformly and expanded in a homogeneous manner, providing a means of dispersing and processing the very high specific surface area nanostructured aerogels. (Morooka et al. 1988) were able to fluidize submicron (20-500 nm) Ni, Si3N4, SiC, Al2O3, and TiO2 particles at high gas velocities ,observing formation of agglomerates and large gas bubbles.
FLUIDIZATION OF NANOPOWDERS USING EXTERNAL ASSISTANCE METHODS
To improve the fluidization behavior of ABF type nanopowders various external assisting fluidization methods have been developed as presence of abundance of bubbles makes the fluidized .These methods include, stirring, sound waves, pulsed flow, centrifugal fields, electric fields, and secondary gas flow from a microjet.
It is carried out by blade stirrer or via large magnetic particles. According to (King, Liang et al. 2008) used a blade stirrer located in the bottom zone of the bed encouraging radial blending of the entire bed which prevents channeling. The blades sweep as close to the edges of the distributor plate as possible to minimize the opportunity for powder to collect along the base of the walls, radial stirring promotes good fluidization behavior for cohesive and difficult to fluidize powders.
Magnetic particles have also been employed to fluidize nanoparticles, (Yu et al. 2005) used magnetic particles excited by an external oscillating magnetic field to stir the bed. Magnetic field to stir the bed; magnetic particles used were large (1-2 mm) and heavy (barium ferrite) and did not fluidize along with the nanopowder, but translated and rotated at the bottom of the column just above the gas distributor. The electromagnetic field was provided by coils located outside the column at the level of the distributor. They found that magnetic stirring enhanced the fluidization of nano agglomerates quite significantly by breaking up clusters of agglomerates and by hindering the formation of bubbles.
Fig 5: Bed expansion ratio and pressure drop for hard agglomerates with and without magnetic excitation. Solid lines the bed expansion ratios and dashed lines the pressure drops. Magnetic field intensity 140G at the center of the field, mass ratio of magnets to NPs 2:1, AC frequency 60 Hz (adopted from Yu et al, 2005). Umf1 minimum fluidization velocity without magnetic excitation; Umf2 minimum fluidization velocity with magnetic excitation.
The above is Fig is shown (Yu et al. 2005) the how the fluidization behavior (pressure drop and bed expansion) of the large (>500 Âµm) SiO2 NP agglomerates, with and without, magnetic excitation, visual observation showed that the.
Without magnetic assistance
Smaller agglomerates were in motion on top but larger agglomerates on the bottom of the bed .There was no bed expansion and the pressure drop was less than bed weight indicating bed wasn't fluidized entirely.
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External magnetic field
Large agglomerates became small due to collisions with the magnetic particles and bed expanded uniformly while pressure drop was close to weight of bed, the entire bed was fluidized.
External Force field generated via sound waves are also being employed to fluidize NPs, (Zhu, Liu et al. 2004) used an external force field generated by sound in order to enhance the fluidization of APF type Aerosil R974 fumed silica NPs. They placed a loudspeaker at the top of the bed. At sound frequencies of 50 or 100 Hz, they obtained a larger bed expansion and also a reduction in the minimum fluidization velocity. However, at frequencies greater than 200 Hz, they observed large ellipsoid-shaped bubbles which do not occur with aeration alone. Guoet al. (2006) also fluidized fumed silica NPs under the influence of an acoustic field. At frequencies below 200 Hz, they found results similar to those of (Zhu, Liu et al. 2004).
A drawback of the use of sound waves produced by a loudspeaker placed at the top of the bed is that just the region close to the free surface can be excited, while larger and heavier agglomeration are mainly present at the bottom of the bed.
Pulsed gas flow
This technique of fluidization was first reported by Rahman (2009) by applying pulsations to gas flow in a fluidized bed ;the fluidization was gravely improved avoiding channeling while minimum fluidization velocity decreased . This technique can be applied to ABF type nanopowders Robert (Ommen, Valverde et al. 2012). Disadvantage is that pulsation can lead to increased elutriation (separation of heavier particles and lighter particles), tough no foreign material needs to be added to the bed.
This technique impose a centrifugal force on nanopowders using a rotating fluidized bed resulting from this centrifugal force fluidization occurs at much higher gas velocities , less entrainment of particles and low beds results in small bubble reducing gas- bypassing .
Fumed silica, alumina, and titania nanopowders have been successfully fluidized in a rotating fluidized bed (Nakamura and Watano 2008). A smooth surface and appreciable bed expansion were obtained when using APF nanopowders, but ABF nanopowders such as Aeroxide titania P25 did not expand significantly due to bubbling.
DC and AC electric fields
Kashyap et al ,( 2008) reported while studying fluidization Tullanox 500 by in a rectangular fluidized bed with a DC electric field. Two electrodes ( Copper sheets ) with opposite polarities, were attached to the parallel walls in the rectangular fluidized bed.The fluidized bed height was found to decrease rather than increase when the DC electric field was applied.
This phenomenon of poor fluidization is attributed to migration NP agglomerates to wall of the cell when DC field is applied (visual observation via high speed camera , Valverde et al. 2008b ) .
Co-flow Cross-flow Mixed flow
Vertical Horizontal Non-uniform
Fig : Sketches of the three different setups used in the alternating electric field enhanced fluidization: a co-flow electric field, b crossflow electric field, c variable electric field ( adopted from Pfeffer ,2012 ).
Tough all the three arrangement encourage bed expansion ,the non uniform arrangement has highest bed expansion and better fluidization as it agitates heavy agglomerates and least effects lighter one avoiding elutriation and also non uniform electric field destabilizes the Gas channels close to gas distributor.
Secondary flows in the form of jets to fluidize micronsized particles carried out with jets pointing upwards, downwards, or horizontally, typically with nozzle sizes of the order of millimeters. Microjets cause turbulent mixing.
Work with micro sized nozzle by Quevedo et al. (2010) and Pfeffer et al. (2008) have reported better fluidization when the nozzle is placed downward pointing near distributor rather than upwards (particles between and the jet and distributor doesn't participate in fluidization ).
Its optimum tool to convert ABF-type behavior into APF-type behavior
Fig :Comparison of the non-dimensional fluidized bed height as a function of gas velocity for conventional and microjet-assisted fluidization of Aerosil R974 (adopted fromPfeffer,2012)
Volmer & Weber Island growth mechanism
The concept of depositing droplets of films rather coating a substrate is known as Volmer - Weber Island growth mode. This mode prevails when the substrate and film are dissimilar along with different crystal structure and chemistry. To encourage an optimum growth the condensing atoms must interact with each more than the substrate.
Through various Microscopic techniques , its known that two are three stages of evolution :
Growth of nuclei to form clusters.
Fig : Volmer -Weber Island growth Fig : SEM image of Islands (Lee, Li et al. 2012) (http://www.tf.uni-kiel.de/matwis/amat/semitech_en/kap_3/backbone/r3_3_2.html, Accessed 19/12/2012)
Recent studies (Shrestha et al, 2010) focusing on the growth mechanism have found that during nucleation phase of ALD platinum thin films and template based platinum nanotubes follow strictly a Volmer - Weber island growth mechanism. Similar results were found (Lee, Li et al. 2012) to while investigating the structure of anistropic pyrolytic carbon .
The Li-ion battery
Since the inception of modern age batteries have played vital role in Mobil and stationary applications such as cell phones, remote controls and lately in EV batteries. The Li-ion and Li-ion-polymer batteries are most advanced in market today B. Scrosat et al,(1995) and S. Megahed et al and B. Scrosati et al .(1995) .
Interaction between alkali-metal-salts and polar polymers is regarded as one amazing discoveries of the last century P.V. Wright,et al (1973) .These exhibition of considerable ionic conductivity by these compounds prompted Armand et al. to make a more detailed electrical characterization , leading to all-solid-state lithium polymer battery concept. Initially Li-metal was used as anode in the secondary Li batteries, and an inorganic intercalation or insertion compound as cathode. The first secondary Li/insertion-compound system was the Li/TiS2 system, was commercialized by Exxon in the mid 1970's.
There are known advantages with using metallic Li as anode in the battery : the redox potential is low so is the weight. Problems are usually corrosion of Li with electrolyte, safety aspects caused by possible short circuiting by the formation of dendrite. Li-ion cells were believed to hold the solution to this problem Plenum, et al, (1980).An insertion electrode usually carbon based replaces the Li metal anode, active lithium is always present as ion rather than as a meta J.S. Xue et al , (1995) .
In complete assembly of Li-ion cell, one of the electrodes contains Li-ions, which are then shuttled reversibly between the electrodes during charge/discharge. A variety of electrodes have been tested over the years P. Novák (1998) but, for commercial, the LiCoO2 electrode has found application.
Fig : The discharge process in a rechargeable Li-ion battery (J. Kim,1998).
Major issues with the Li-ion concept are that Li consumed by secondary reactions cannot be retrieved, and the specific capacity is totally dependent on the amount of Li available for the reversible redox process in the cell. Some of the processes known to lead to capacity loss in Li-ion cells are: Li deposition (in cell over-charge), electrolyte decomposition, active material dissolution, phase changes in the insertion electrode materials, and passive film formation on the electrode and current collector surfaces.
The distinguishing features of today's commercial Li-ion batteries are: D. Abraham,( 2001 )
High operating voltage: a single cell has an average operating potential of approx. 3.6 V, higher Ni-Cd Ni-MH batteries , Pb-acid batteries.
Compact, lightweight, and high energy density
Fast charging potential; batteries can be charged to about 80-90% of full capacity in one hour.
Discharge rate: up to 3C are attainable.
Operating temperature: from -20 to +60..C.
Higher cycle life around 500 cycles.
Low self-discharge: only 8-12% per month.
Non-polluting: does not use toxic heavy metals such as Pb, Cd or Hg.
PROPERTIES OF THE LiMn2O4 SYSTEM
A part of the Li-Mn-O phase-diagram is described in Figure below . It is seen to involve a huge number of structures and tie-lines; which is attributed to the nature of Mn, which can having oxidation states II-VII.Most imperative oxidation state II the most stable Wiksells et al., ( 1963). From a battery viewpoint, the spinel structures of interest in the Li-Mn-O phase-diagram are located within the triangle of the MnO2-LiMn2O4- Li4Mn5O12 tie-lines.
Figure 4.1 A. The Li-Mn-O phase diagram. B. A close-up of the Li2MnO3 -LiMnO2 - ..-MnO2 part of the Li-Mn-O phase diagram. R.J. Gummow, A. de Kock, and M.M. Thackeray, Solid State Ionics, 69 (1994) 59.
Figure 4.2 Part of the unit cell of LiMn2O4 showing the local structure around octahedrally coordinated manganese in an ideal spinel lattice. Mn-O bonds are represented by heavy solid lines; linear chains of manganese ions in neighboring edge-sharing octahedral are indicated by dashed lines.
Causes of decline in capacity
Issues associated and impeding its commercial use: capacity fading, Mn dissolution at high temperature and poor high-rate capability. The capacity fading is primarily due to the following three factors (Thackeray 1997) ,(Li, Zhang et al. 2006) :
Dissolution of Mn3+ : Upon discharge , the concentration of Mn 3+ is at a high level. The Mn 3+ may be disparate at surface accordance to equation (Ning, Wu et al. 2004) :
2Mn3+Solidâ†’ Mn4+solid + Mn2+solution
Mn2+ from this dissolves in the electrolyte solution.
Jahn-Teller effect : Jahn - Teller theorem describes the distortion of ions and molecules that is related to electronic configurations. It occurs after discharge usually on the surface then could spread into the overall composition. Leading to formation of a tetrahedral structure which is low in symmetry and high disorder.
Instability of de-lithiated particles is highly unstable and oxidation of Mn4+ will lead to decomposition of solvents.
Atomic Layer Deposition and Lithium-Ion Battery
In order to increase the application and acceptance for Li-ion batteries, issues such as undesirable reactions (solid electrolyte Interface), poor charge transfer need to be addressed. Researchers believe that Atomic Layer Deposition could provide viable solutions ascribed to its multifunctional capabilities and unique characteristics. ALD can aid in the design of various new LIB components, including anodes, cathodes and electrolytes, but also modify the properties of electrode materials with ultrathin coating films or island growth/deposition (being the objective of this thesis)
Characteristics of ALD as a tool for Cathode material
Characteristics of ALD which are important for viable operation: excellent conformity, atomic scale thickness control, and low growth temperature
Low Growth Temperature
One of main features of ALD is its much lower growth temperature (typically less than 400 Â° C, Meng 2012). In particular, ALD deposits many materials at temperatures below 100 Â° C, even down to RT. Gasser et al. in 1994 conducted the first ALD experiment at RT, depositing SiO2 from Si(NCO) 4 and water. Later in 1997, Luo et al. deposited CdS on ZnSe (100) at RT in an ultra-high-vacuum ALD system using Cd(CH3)2 and H2S as precursors.
Atomic-Scale and Stoichiometric Deposition
Due to its layer-by-layer self-limitation, ALD's other advantage lies in enabling the precise control of the deposited films at the atomic level. GPCs (Growth per cycle ) of ALD are at the level of angstroms (typically less than 2 Å/cycle ,0.2nm per cycle on nanoparticles), jointly determined by the precursors, temperatures, and substrates used . For instance, the GPC for the ALD-Al2O3 of using TMA and water reached the maximum of 1.33 Å/cycle in the range 100-125 Â° C, while GPC values were less at higher or lower temperatures (Meng et al, 2012).
ALD-deposited materials are stoichiometrically close to their theoretic values, although growth temperatures and precursors might exert some influence. Using Rutherford backscattering spectrometry (RBS), for example, Groner et al. demonstrated that the O/Al ratios of the ALD-Al 2 O 3 from TMA and water are close to 1.50 in the temperature range 33-177 Â° C, varying from 1.34 to 1.70.
Excellent Uniformity and Conformality
ALD's unique mechanisms provides excellent uniformity and conformality. Atomic force microscopy (AFM) showed that, for instance, the ALD-Al2O3 on fl at substrates has a surface roughness of 1-3 Å for a deposition in the range 200-560 Å.A much smaller surface roughness of 0.7 Å was even (reported by Lee et al included in the review Meng 2012 ) .
Cathode Surface Modification by ALD
Cathode materials are in direct contact with liquid electrolytes which entail many detrimental side reactions occurring slowly at ambient temperature, consequential in the slow degradation of electrode materials and ultimately, the lowering battery performance. Researchers have attempted substituting partially active elements with alkaline metals and Al to stabilize electrode structures and thereby to enhance cycle ability and thermal stability. However, such substitution often lowered capacity and Li+ diffusion, since the substituents mainly are electrochemically inactive ingredients.
Chen et al. recently categorized the effects of various surface coatings into four classes: (1) higher ionic conductivity; (2) improved performance due to the cathode's modified surface chemistry; (3) HF scavengers that suppress metal dissolution from cathode materials; and, (4) physically protective barriers that impede side reactions between cathode materials and electrolytes.
Chromium oxide Coated on batteries
Amphoteric coatings on LiMn2O4 such as Al2O3, ZnO, ZrO2,MgO published in review article(Li, Zhang et al. 2006) and reported improvement of electrochemical performance. However , the electrochemical performance is affected by oxide coating in terms of conformity ,uniformity, thickness ,specific surface area and crystallinity (S. Lim et al .2008),( Y. S. Jung et al ,2010 ).
Jianqing Zhao et al , 2012 has reported 50 ,300 ALD cycles on LMNO particles facilely deposited (2.9A Ëš per ALD cycle ) improved the cyclicality at elevated temperatures from 25 C to 55 C .Similar results were reported (Beetstra, Lafont et al. 2009) 5 to 28 ALD cycles coating of AL2O3 on LMNO particles.
Chromium oxide coating on LMNO has been reported by (Åžahan, Göktepe et al. 2010)
Coating was carried out on a chromium (III) nitrate aqueous solution along with distilled water and acetic acid to LMNO particles were added. Cyclic performance at room temperature and elevated temperature ( 55 C) were reported
Fig :(a) Cycling performance and (i) the bare LiMn2O4, (ii) 0.5 wt.% Cr2O3- coated LiMn2O4, (iii) 1 wt.% Cr2O3-coated LiMn2O4, (iv) 2 wt.% Cr2O3-coated
LiMn2O4, (v) 3 wt.% Cr2O3-coated LiMn2O4, The applied current density is 148 mA gâˆ’1 (1 C-rate) at room temperature. Li metal was used as the anode
(b) Cycling performances of (a) the bare LiMn2O4 and (b) the 1 wt.% Cr2O3-coated LiMn2O4 at a current level of 1 C (148 mAg âˆ’1)
in the voltage range of 3.5-4.5 V at elevated temperature (55 Â°C).
The conclusion being presented below :
Hence indicating chromium oxide being an effective way to enhance the electrochemical performance.
X-ray Diffractometer ( XRD ) :
Fig: Optical arrangement of a Phillips X-ray Diffractometer (http://www.spec2000.net/09-xrd.htm, 4th SEP,2012)
In a constructive interference when Braggs law is satisfied
2 d sinÎ¸ =n Î»
Where d : distance between equivalent atomic planes,
Î¸ : angle between the incident beam and these planes,
n : an integer
Î»: the wavelength.
The scattered intensity can be measured as a function of scattering angle 2Î¸ . Analysis of the different pattern makes an efficient method for determining the different phases present in the sample. Since the magnitude of the wavelength is same as the interatomic distance and bond length ( 1 Å ) , it serves as the appropriate characterization for crystalline materials.
Transmission Electron Microscopy (TEM):
TEMs use electrons as "light source" and their much lower wavelength makes it possible to get a resolution a thousand times better than with a light microscope objects i.e. to the order of a few angstrom (10-10 m) .
Electrons emitted travel through a light vacuum column of the microscope instead of glass lenses TEM employs electromagnetic lenses to focus the electrons into a very thin beam . The electron beam then travels through the specimen. Depending on the density of the specimen, some of the electrons are scattered. At the bottom of the microscope the unscattered electrons hit a fluorescent screen, which gives rise to a "shadow image" of the specimen with its different parts displayed in varied darkness in accordance to their density. The image is then studied directly by the operator or photographed with a camera.
Fig 7: TEM (ww.nobelprize.org 4th SEP 2012) Fig 8: A TEM image of a specimen under study ( J ruud van Ommen,2009 )
Scanning electron microscope ( SEM ):
The electron gun generated a beam of electrons which travel through a vertical path which is held in a vacuum. The beam passes through lenses focusing on the sample. Once the beam strikes the sample electrons and X-ray are ejected.
Detectors collect these X-rays, backscattered electrons, and secondary electrons and convert them into a signal that produces the final image.
Fig 9 :SEM( http://www.purdue.edu/rem/rs/sem.htm,Acessed :4th SEP 2012) Fig 10 : SEM image of Al nanorods adopted from
Energy-dispersive X-ray spectroscopy (EDS or EDX)
Is an analytical technique used for the elemental analysis or chemical characterization of a sample.The technique is non-destructive and has a sensitivity of >0.1% for elements heavier than C.
The sample is placed in an electron beam, which excites the atoms present in the electrons releasing/generating X rays to release excess energy. The energy of the X-rays is characteristic of the atoms that produced them, forming peaks in the spectrum. Certain elements may have more than one peak associated with them or some peaks from different elements may overlap each other to a certain extent.
As the electron beam can be precisely controlled, ED's spectra from a specific point/particle on the sample, giving an analysis of a few cubic microns of material.
Fig 11 :EDS spectrum of the mineral crust of Rimicaris exoculata (Wikipedia )
Atomic force Microscopy
Fig: AN AFM system (Wikipedia)
They are engaged to measure the height, friction, magnetism of a given sample. Comes under the league of various Scanning probe microscopy, employed usually to understand surface topography .Here probe being a sharp tip which is mounted on a cantilever .The optical lever reflects the laser from the cantilever strikes a position-sensitive photo-detector.