introduction to environmental nanotechnology -...

1

MCC025 MCC025 NanoscienceNanoscienceIntroduction to Environmental Nanotechnology (2)Introduction to Environmental Nanotechnology (2)

(http://fy.chalmers.se/(http://fy.chalmers.se/~fogelstr/GordonYang2006.html)~fogelstr/GordonYang2006.html)

Professor Gordon C. C. YangProfessor Gordon C. C. YangInstitute of Environmental Engineering Institute of Environmental Engineering

National Sun National Sun YatYat--SenSen UniversityUniversityKaohsiung 80424, TaiwanKaohsiung 80424, Taiwan

ee--mailmail:: [email protected]@mail.nsysu.edu.tw

September 2006September 2006

mailto:[email protected]

http://www.chalmers.se/en/

2

NanomaterialsNanomaterials: Preparation, Fabrication, and Characterization: Preparation, Fabrication, and Characterization(September 6, 2006)(September 6, 2006)

In this lecture an overview of various fabrication methods for In this lecture an overview of various fabrication methods for preparing different preparing different nanomaterialsnanomaterials will be briefly presented first. will be briefly presented first. Then an introduction of various methods for characterizing Then an introduction of various methods for characterizing nanomaterialsnanomaterials will be followed so that those unique properties will be followed so that those unique properties of of nanomaterialsnanomaterials for novel applications could be realized.for novel applications could be realized.


3

Introduction Introduction (1)(1)

There are two approaches to the synthesis of There are two approaches to the synthesis of nanomaterialsnanomaterialsand the fabrication of nanostructuresand the fabrication of nanostructures: (1) the : (1) the toptop--downdownapproach and (2) theapproach and (2) the bottombottom--upup approach. Both approaches approach. Both approaches have advantages and disadvantages.have advantages and disadvantages.Attrition or millingAttrition or milling is a typical topis a typical top--down method in down method in preparing preparing nanoparticlesnanoparticles, whereas , whereas chemical precipitationchemical precipitationinvolving the involving the building up of the atom or molecular building up of the atom or molecular constituentsconstituents is ais a typical bottomtypical bottom--up method.up method.LithographyLithography can be considered as a hybrid approach: the can be considered as a hybrid approach: the growth of thin films is bottomgrowth of thin films is bottom--up, whereas etching is topup, whereas etching is top--down. However, down. However, nanolithographynanolithography and and nanomanipulationnanomanipulation are are commonly a bottomcommonly a bottom--up approach. up approach.


4

BottomBottom--up Approach vs. Topup Approach vs. Top--down Approachdown Approach(Source: Unknown)(Source: Unknown)


5

Introduction Introduction (2)(2)

In general, In general, methods for preparing methods for preparing nanomaterialsnanomaterials also can be also can be divided into two categories: physical and chemical.divided into two categories: physical and chemical.

Physical preparation methodsPhysical preparation methods include: (1) vapor include: (1) vapor condensation, (2) physical fragmentation, (3) amorphous condensation, (2) physical fragmentation, (3) amorphous crystallization, and (4) others.crystallization, and (4) others.

Chemical preparation methodsChemical preparation methods include: (1) solinclude: (1) sol--gel synthesis, gel synthesis, (2) chemical precipitation, (3) hydrothermal, and (4) others. (2) chemical precipitation, (3) hydrothermal, and (4) others.


6

Preparation Methods for ZeroPreparation Methods for Zero--Dimensional Dimensional Nanostructures: Nanostructures: NanoparticlesNanoparticles (1)(1)

Both topBoth top--down and bottomdown and bottom--up up appraochesappraoches have been have been developed for the synthesis of developed for the synthesis of nanoparticlesnanoparticles..

TopTop--down approach: down approach: Mechanical attrition produces its Mechanical attrition produces its nanostructures by the structural decomposition of coarser nanostructures by the structural decomposition of coarser grained structures as a result of plastic deformation. For grained structures as a result of plastic deformation. For example, elemental powders of Al and example, elemental powders of Al and ββ--SiCSiC can be can be prepared in a high energy ball mill. The ball milling and rod prepared in a high energy ball mill. The ball milling and rod milling techniques belong tomilling techniques belong to the mechanical alloying the mechanical alloying processprocess, which can be carried out at room temperature. The , which can be carried out at room temperature. The process can be performed on both high energy mills (e.g., process can be performed on both high energy mills (e.g., centrifugal type mill and vibratory type mill) and low centrifugal type mill and vibratory type mill) and low energy tumbling mill.energy tumbling mill.


7

Preparation Methods for ZeroPreparation Methods for Zero--Dimensional Dimensional Nanostructures: Nanostructures: NanoparticlesNanoparticles (2)(2)

BottomBottom--up approach: up approach: Relevant techniques can be further Relevant techniques can be further grouped into two categories grouped into two categories –– thermodynamic equilibrium thermodynamic equilibrium approach and kinetic approach.approach and kinetic approach.

In the In the thermodynamic equilibrium approachthermodynamic equilibrium approach, synthesis , synthesis process consists of (1) generation of process consists of (1) generation of supersaturationsupersaturation, (2) , (2) nucleation, and (3) subsequent growth.nucleation, and (3) subsequent growth.

In the In the kinetic approachkinetic approach, formation of , formation of nanoparticlesnanoparticles is is achieved by either limiting the amount of precursors achieved by either limiting the amount of precursors available for the growth (e.g., molecular beam available for the growth (e.g., molecular beam epitaxyepitaxy), or ), or confining the process in a limited space (e.g., aerosol confining the process in a limited space (e.g., aerosol synthesis and micelle synthesis) .synthesis and micelle synthesis) .


8

BottomBottom--up Approach for Preparation of up Approach for Preparation of NanoparticlesNanoparticles

By homogeneous nucleationBy homogeneous nucleation –– A A supersaturationsupersaturation of growth of growth species must be created. species must be created. The reduction of Gibbs free energy The reduction of Gibbs free energy is the driving force for both nucleation and growth.is the driving force for both nucleation and growth. Without Without supersaturationsupersaturation, , ⊿⊿GGvv is zero and no nucleation would occur. is zero and no nucleation would occur. When When ⊿⊿GGvv is negative, nucleation occurs spontaneously. is negative, nucleation occurs spontaneously. Metallic Metallic nanoparticlesnanoparticles, semiconductor , semiconductor nanoparticlesnanoparticles, and , and many oxide many oxide nanoparticlesnanoparticles can be synthesized through this can be synthesized through this process.process.By By HetrogeneousHetrogeneous nucleationnucleation –– Similar to homogeneous Similar to homogeneous nucleation, there is a decrease in the Gibbs free energy and nucleation, there is a decrease in the Gibbs free energy and an increase in surface or interface energy.an increase in surface or interface energy.By kinetically confined synthesisBy kinetically confined synthesis: e.g., synthesis inside : e.g., synthesis inside micelles or using micelles or using microemulsionsmicroemulsions, aerosol synthesis, , aerosol synthesis, templatetemplate--based synthesis, etc.based synthesis, etc.


9

Preparation Methods for OnePreparation Methods for One--Dimensional Dimensional Nanostructures: Nanostructures: NanowiresNanowires and and NanorodsNanorods

Both topBoth top--down and bottomdown and bottom--up up appraochesappraoches have been have been developed for the synthesis of these developed for the synthesis of these nanomaterialsnanomaterials..

TopTop--down approach: down approach: e.ge.g, lithography;, lithography;BottomBottom--up approach: up approach: (1) spontaneous growth (e.g., (1) spontaneous growth (e.g., evaporation/dissolutionevaporation/dissolution--condensation; stresscondensation; stress--induced induced recrystallizationrecrystallization); (2) template); (2) template--based synthesis (e.g., based synthesis (e.g., electroplating and electroplating and electrophoreticelectrophoretic deposition; conversion deposition; conversion with chemical reaction); and (3) with chemical reaction); and (3) electrospinningelectrospinning


10

Preparation Methods for TwoPreparation Methods for Two--Dimensional Dimensional Nanostructures: Nanostructures: Thin FilmsThin Films

The film deposition involves predominantly heterogeneous The film deposition involves predominantly heterogeneous processesprocesses including including hetrogeneoushetrogeneous chemical reactions, chemical reactions, evaporation, adsorption and deposition on growth surfaces, evaporation, adsorption and deposition on growth surfaces, heterogeneous nucleation and surface growth. Normally, heterogeneous nucleation and surface growth. Normally, film deposition and characterization processes are film deposition and characterization processes are conducted under a vacuum. conducted under a vacuum. Film growth methodsFilm growth methods: (1) : (1) vaporvapor--phase depositionphase deposition (e.g., (e.g., molecular beam molecular beam epitaxyepitaxy, sputtering, chemical vapor , sputtering, chemical vapor deposition) and (2) deposition) and (2) liquidliquid--phase depositionphase deposition (e.g., chemical (e.g., chemical solution deposition, Langmuirsolution deposition, Langmuir--BlodgetBlodget films, selffilms, self--assembled assembled monolayersmonolayers).).


11

Preparation Methods for Metallic and Ceramic Preparation Methods for Metallic and Ceramic NanoparticlesNanoparticles

Metallic Metallic nanoparticlesnanoparticles and ceramic and ceramic nanoparticlesnanoparticles are two are two major types of major types of nanoparticlesnanoparticles of interest by many.of interest by many.

Methods for preparing Methods for preparing metallic metallic nanoparticlesnanoparticles include: (1) include: (1) mechanical fragmentation (e.g., ball milling), (2) reduction mechanical fragmentation (e.g., ball milling), (2) reduction methods (e.g., NaBHmethods (e.g., NaBH44), (3) ), (3) pyrolysispyrolysis, (4) physical methods , (4) physical methods (e.g., vaporization), and (5) physicochemical methods (e.g., (e.g., vaporization), and (5) physicochemical methods (e.g., plasma arcing).plasma arcing).

Methods for preparing Methods for preparing ceramic ceramic nanoparticlesnanoparticles include: (1) include: (1) solid phase reactions (e.g., sintering), (2) gas phase reactionssolid phase reactions (e.g., sintering), (2) gas phase reactions(e.g., chemical vapor deposition), (3) laser ablation, (4) (e.g., chemical vapor deposition), (3) laser ablation, (4) plasma arcing, (5) plasma arcing, (5) pyrolysispyrolysis of organic precursors, (6) liquid of organic precursors, (6) liquid phase reactions (e.g., precipitation), and solphase reactions (e.g., precipitation), and sol--gel synthesis.gel synthesis.


12

Preparation Methods for Preparation Methods for NanosizedNanosized CoreCore--Shell Shell StructuresStructures

CoreCore--shell structure: The formation of shell structure: The formation of the shellthe shell material on material on the surface of grown the surface of grown nanoparticlenanoparticle (i.e., (i.e., the corethe core) is an ) is an extension of particle growth with different chemical extension of particle growth with different chemical composition.composition.Nature of coreNature of core--shell structureshell structure: (1) The core and shell : (1) The core and shell often have totally different crystal structures (e.g., often have totally different crystal structures (e.g., crystalline vs. amorphous); (2) The physical properties of crystalline vs. amorphous); (2) The physical properties of core and shell often differ significantly from one another core and shell often differ significantly from one another (e.g., metallic vs. dielectric); (3) The synthesis processes of (e.g., metallic vs. dielectric); (3) The synthesis processes of cores and shells in each corecores and shells in each core--shell structures are shell structures are significantly different.significantly different.Fabrication methodsFabrication methods: coating, self: coating, self--assembly, vapor phase assembly, vapor phase deposition, etc.deposition, etc.


13

Preparation Methods for Preparation Methods for Carbon Carbon NanotubesNanotubes (1)(1)(Liu, 2006)(Liu, 2006)

There are mainly three techniques to produce carbon nanotubes: (1) arc discharge, (2) laser ablation, and (3) chemical vapor deposition. No matter which method is used, the generation of free carbon atoms and the precipitation of dissolved carbon from catalyst particles are involved. As Fig. 2.1 shows, firstly, metal catalyst particles are formed and then, under high temperature, free carbon atoms diffuse into the surface of the catalyst particles and form metastable carbide particles. Finally, rod-shaped (possibly other shapes as well) carbon tubes grow out of the particle rapidly. The catalyst particles may stay on the supporting substrate or leave the substrate depending on the interaction between the catalyst particles and the substrate.


14

Preparation Methods for Preparation Methods for Carbon Carbon NanotubesNanotubes (2)(2)(Liu, 2006)(Liu, 2006)


15

Sols are dispersions of colloidal particles in a liquid.A gel is a interconnected, rigid network with pores of submicrometer dimensions and polymericchains whose average length is greater than a micrometer.

The term "gel" embraces a diversity of combinations of substances that can be classified in four categories as discussed by Flory (1953): (1) well-ordered lamellar structures; (2) covalent polymeric networks, completely disordered; (3) polymer networks formed through physical aggregation, predominantly disordered; (4) particular disordered structures.

The SolThe Sol--Gel Process Gel Process (1)(1)(Hench and West, 1990)(Hench and West, 1990)


16

Sol-gel processing is a wet chemical route for the synthesis of colloidal dispersions of inorganic and organic-inorganic hybrid materials, particularly oxide and oxide-based hybrids.Sol-gel processing offers many advantages, including low processing temperature and molecular level homogeneity.Typical sol-gel processing consists of (1) hydrolysis:M(OEt)4 + x H2O M(OEt)4-x(OH)x + x EtOHand (2) condensation of precusors:M(OEt)4--x(OH)x + M(OEt)4--x(OH)x

(OEt)4 –x (OH)x -1MOM(OEt)4- -x (OH)x -1 + H2O

The SolThe Sol--Gel Process Gel Process (2)(2)

(Cao, 2004)(Cao, 2004)


17

Precursors can be either metal alkoxides or inorganic and organic salts. Organic or aqueous solvents may be used to dissolve precursors, and catalysts are often added to promote hydrolysis and condensation reactions. In general, hydrolysis and condensation reactions are both multiple-step processes, occurring sequentially and in parallel. Each sequential reaction may be reversible. Condensation results in the formation of nanoscaleclusters of metal oxides or hydroxides, often with organic groupembedded or attached to them. These organic group may be due to incomplete hydrolysis, or introduced as non-hydrolysable organic ligands. Nanoscale clusters’ size and the morphology and microstructure of the final products can be tailed by controlling the hydrolysis and condensation reactions.


(Cao, 2004)(Cao, 2004)


18

Three approaches are used to make sol-gel monoliths:

method 1, gelation of a solution of colloidal powders;

method 2, hydrolysis and polycondensation of alkoxideor nitrate precursors followed by hypercritical dryingof gels;

method 3, hydrolysis and polycondensation ofalkoxide precursors followed by aging and drying underambient atmospheres.


(Hench and West, 1990)(Hench and West, 1990)


19

A silica gel may be formed by network growth from an array of discrete colloidal particles (method 1) or by formation of an interconnected 3-D network by the simultaneous hydrolysis and polycondensation of an organometallicprecursor (methods 2 and 3). When the pore liquid is removed as a gas phase from the interconnected solid gel network under hypercritical conditions (critical-point drying, method 2), the network does not collapse and a low density aerogel is produced. Aerogels can have pore volumes as large as 98% and densities as low as 80 kg/m3.

When the pore liquid is removed at or near ambient pressure by thermal evaporation (called drying, used in methods 1 and 3) and shrinkage occurs, the monolith is termed a xerogel. If the pore liquid is primarily alcohol based, the monolith is often termed an alcogel.




20

The surface area of dried gels made by method 3 is very large (> 400 m2/g), and the average pore radius is very small (< 10 nm). Larger pore radii can be produced by thermal treatment, by chemical washing during aging, or by additions of HF to the sol. The small pore radii can lead to large capillary pressures during drying or when the dried gel is exposed to liquids as described by Laplace's equation.

A dried gel still contains a very large concentration of chemisorbed hydroxyls on the surface of the pores. Thermal treatment in the range 500-800 °C desorbs the hydroxyls resulting in a stabilized gel.




21(Source: Unknown)(Source: Unknown)


22

(http://www.phi.com/genf.asp?ID=281)

Auger Electron Spectroscopy / AES (1)

AES is an analytical technique that uses a primary electron beam to probe the surface of a solid material. Secondary electrons that are emitted as a result of the Auger process are analyzed and their kinetic energy is determined. The identity and quantity of the elements are determined from the kinetic energy and intensity of the Auger peaks. The nature of the Auger process is such that Auger electrons can only escape from the outer 5-50 Å of a solid surface at their characteristic energy. This effect makes AES an extremelysurface sensitive technique. A finely focused electron beam can be scanned to create secondary electron and Auger images, or the beam can be positioned to perform microanalysis of a specific sample feature. Applications include materials characterization, failure analysis, thin film analysis, and particle identification for semiconductor and thin film head manufacturing.


23


Auger Electron Spectroscopy /AES (2)


24


AES---The Auger Process

The Auger effect is named for its discoverer, Pierre Auger, who observed radiationless relaxation of excited ions in a cloud chamber, during the 1920s. Auger electrons are emitted at discrete energies that allow the atom of origin to be identified. The Auger process involves three steps:(1) Excitation of the atom causing emission of an electron;(2) An electron drops down to fill the vacancy created in step 1;(3) The energy released in step 2 causes the emission of an Auger electron.


25


X-ray Photoelectron Spectroscopy (XPS) orElectron Spectroscopy for Chemical Analysis (ESCA)

XPS, also known as ESCA, is the most widely used surface analysis technique because of its relative simplicity in use and data interpretation. The sample is irradiated with mono-energetic x-rays causing photoelectrons to be emitted from the sample surface. An electron energy analyzer determines the binding energy of the photoelectrons. From the binding energy and intensity of a photoelectron peak, the elemental identity, chemical state, and quantity of an element are determined. The information XPS provides about surface layers or thin film structures is of value in many industrial applications including: polymer surface modification, catalysis, corrosion, adhesion, semiconductor and dielectric materials, electronics packaging, magnetic media, and thin film coatings used in a number of industries. Specific applications include: surface elemental and chemical characterization, thin film (<1µm thick) characterization, surface cleanliness, and surface migration of additives or impurities.


26

SIMS (secondary ion mass spectrometry)SIMS (secondary ion mass spectrometry) is a method for is a method for analysinganalysing the elemental and chemical composition of materials, the elemental and chemical composition of materials, in particular their surfaces.in particular their surfaces. The general principle of SIMS The general principle of SIMS analysis is briefly as follows. The material is irradiated withanalysis is briefly as follows. The material is irradiated with a a focused beam of almost focused beam of almost monoenergeticmonoenergetic ions (primary ions). ions (primary ions). The primary ions penetrate the material and transfer their The primary ions penetrate the material and transfer their kinetic energy to the target atoms via a collision cascade. As kinetic energy to the target atoms via a collision cascade. As a a result of the collision cascade, atoms, clusters and molecules result of the collision cascade, atoms, clusters and molecules are emitted from the material (so called sputtering). A fractioare emitted from the material (so called sputtering). A fraction n of the sputtered particles are ionized (secondary ions) and of the sputtered particles are ionized (secondary ions) and therefore possible to analyze with respect to mass to charge therefore possible to analyze with respect to mass to charge ratio. The secondary ion mass spectrum gives information ratio. The secondary ion mass spectrum gives information about the elemental and chemical composition of the material. about the elemental and chemical composition of the material. Since the secondary ions originate only from the 1Since the secondary ions originate only from the 1--5 outermost 5 outermost atomic/molecular layers of the material, the technique is highlyatomic/molecular layers of the material, the technique is highlysurface sensitive.surface sensitive.

(http://www.sp.se)

Secondary Ion Mass Spectrometry / SIMS (1)


27

(Source: Unknown)

Secondary Ion Mass Spectrometry / SIMS (2)


28


SIMS Depth Profiling (Quadrupole Dynamic SIMS/ D-SIMS) (3)

Bombardment of a sample surface with an energetic primary ion beam followed by mass spectrometry of the emitted secondary ionsconstitutes secondary ion mass spectrometry (SIMS). Because secondary ions are either charged positively or negatively, there are two modes of SIMS: +SIMS and –SIMS. In all commercial instruments, these two modes are conducted separately.

Today, SIMS is widely used for analysis of trace elements in solid materials, especially semiconductors and thin films. D-SIMS is capable of detecting trace impurities with a sensitivity of greater than one part per billion. The SIMS ion source is one of only a few to produce ions from solid samples without prior vaporization. The SIMS primary ion beam can be focused to less than 1 μm in diameter. Controlling where the primary ion beam strikes the sample surface provides for microanalysis, the measurement of the lateral distribution of elements on a microscopic scale. During SIMS analysis, the sample surface is slowly sputtered away. Continuous analysis while sputtering produces information as a function of depth, called a depth profile.


29

TOFTOF--SIMSSIMS uses a pulsed primary ion beam to uses a pulsed primary ion beam to desorbdesorb and and ionize species from a sample surface. The resulting ionize species from a sample surface. The resulting secondary ions are accelerated into a mass spectrometer, secondary ions are accelerated into a mass spectrometer, where they are mass analyzed by measuring their timewhere they are mass analyzed by measuring their time--ofof--flight from the sample surface to the detector.flight from the sample surface to the detector. An image is An image is generated by generated by rasteringrastering a finely focused beam across the a finely focused beam across the sample surface.sample surface. Due to the parallel detection nature of Due to the parallel detection nature of TOFTOF--SIMSSIMS, the entire mass spectrum is acquired from , the entire mass spectrum is acquired from every pixel in the image.every pixel in the image. The mass spectrum and the The mass spectrum and the secondary ion images are then used to determine the secondary ion images are then used to determine the composition and distribution of sample surface constituents.composition and distribution of sample surface constituents.


Time-of-Flight Secondary Ion Mass Spectrometry / TOF-SIMS (1)


30


Time-of-Flight Secondary Ion Mass Spectrometry / TOF-SIMS (2)

TOF-SIMS provides spectroscopy for characterization of chemical composition, imaging for determining the distribution of chemical species, and depth profiling for thin film characterization.


31


TOF-SIMS Spectroscopy (3)

In the spectroscopy and imaging modes, only the outermost (1-2) atomic layers of the sample are analyzed. To ensure the analyzed secondary ions originate from the outer surface of the sample, a primary ion dose of less than 1012 ions/cm2 is employed. Below this "static limit," roughly less than one in one thousand surface atoms or molecules are struck by a primary ion. The actual desorption of material from the surface is caused by a "collision cascade" which is initiated by the primary ion impacting the surface. The emitted secondary ions are extracted into the TOF analyzer by applying a potential between the sample surface and the mass analyzer. TOF-SIMS spectra are generated using a pulsed primary ion source (very short pulse of <1 ns). Secondary ions travel through the TOF analyzer with different velocities, depending on their mass to charge ratio (ke = ½ mv2). For each primary ion pulse, a full mass spectrum is obtained by measuring the arrival times of the secondary ions at the detector and performing a simple time to mass conversion.


32


TOF-SIMS Imaging (4)

Chemical images are generated by collecting a mass spectrum at every pi(256 x 256) as the primary ion beam is rastered across the sample surface. The figure to the right shows an example of elemental and molecular imaging. The sample is the cross-section of a time release drug pellet. The map on the left is of the peak intensity at 268 Da, the molecular ion of the drug Metoprolol. The map on the right is of the peak intensity at 23 Dasodium.

xel

for


33


TOF-SIMS Depth Profiling (5)

TOF-SIMS is capable of shallow sputter depth profiling. An ion gun is operated in the DC mode for sputtering, and the same ion gun or a second ion gun is operated in the pulsed mode for data acquisition. Depth profiling by TOF-SIMS allows monitoring of all species of interest simultaneously, and with high mass resolution. The figure to the right shows a TOF-SIMS depth profile of a thin gate oxide acquired in the dual beam mode using a 15 keV Ga+ beam for spectral acquisition and a 1 keV Cs+ beam for sputtering.


34

(http://www.fkf.mpg.de/ga/machines/sims/TOF_SIMS_short.html)

Time Of Flight-Secondary Ion Mass Spectrometry / TOF-SIM (6)

•Determines the chemical composition (spatial-resolved): ppm sensitivity•TOF-SIMS combines static and dynamic SIMS in one machine. •Spatial-resolved Mass Spectrometry: lateral resolution < 100nm, depthresolution: <1nm.

•Secondary electron microscopy (SEM): <100nm. •Parallel mass detection up to high masses. •Mass resolution > 10,000 •Cold sample transfer for volatile materials •Sample cooling to 150K and heating to 900K. •Charge Neutralization: ideal for insulators. •In combination with a preparation chamber (housing LEED, Knudsenevaporators, AES, IRAS, Quadrupole-Masspectrometer, micro balance, facilitiesto clean a surface) the TOF-SIMS apparatus is very flexible and versatile.

•Some possible applications: Defect chemistry, Transport of oxygen in ionicmaterials, Reactions at interfaces, Composition of Quantum dots and theirinterfaces, Multilayer Structures (how sharp are the interfaces?), ProtonConductors, Nano Electronics, Nano Fibers, Cluster, Oxides, Nitrides, Hydrides,HTc superconductors, Composition of molecular monolayers.


35(Stipp et al., 2002)

TOF-SIMS (7)


36(Source: Unknown)

High-Resolution Image Analysis


37

HighHigh--Resolution Transmission Electron Microscopy Resolution Transmission Electron Microscopy (HRTEM)(HRTEM)

A highA high--voltage electron beam passes voltage electron beam passes through a very thin samplethrough a very thin sample, , and the sample areas that do not allow the passage of electrons and the sample areas that do not allow the passage of electrons allow an image to be presented. Due to advances in electronics,allow an image to be presented. Due to advances in electronics,computers, and sample preparation techniques, modern highcomputers, and sample preparation techniques, modern high--voltage instruments voltage instruments have resolution in the 0.1 nm rangehave resolution in the 0.1 nm range; thus it is ; thus it is possible to image heavy atoms in some cases, and possible to image heavy atoms in some cases, and nanoparticlenanoparticlesizes and shapes are easily imaged. sizes and shapes are easily imaged. Sample preparation is crucialSample preparation is crucial, , and usually involves placing very dilute particle suspensions onand usually involves placing very dilute particle suspensions onto to carboncarbon--coated copper grids. Another useful technique is coated copper grids. Another useful technique is imbedding the particle in a solid organic polymer, slicing very imbedding the particle in a solid organic polymer, slicing very thin sections, and passing the electron beam through the sectionthin sections, and passing the electron beam through the section..

(Klabunde, 2001)


38

TEM Images of Nanoiron

(a) NanoscaleNanoscale Fe (x 650,000) (b) Fe (x 650,000) (b) NanoscaleNanoscale Pd/Fe ( x 650,000)Pd/Fe ( x 650,000)

(Yang et al., 2005)

(Particle size range: 50-80 nm)


39

TEM Images of Nanoscale Fe3O4

(a) Naked (b) Chitosan-bound(Chang and Chen, 2005)

(Average particle size: 13.5 nm)


40

TEM Image of Nanoscale Fe3O4

(Mak and Chen, 2005)

(Average particle size: 21 nm)


41

Microemulsified Nanoiron

(a) EDS Pattern (b) TEM Image(Li et al., 2003)


42

Scanning Probe Microscopy (Scanning Probe Microscopy (SPMSPM; also called ; also called Scanning Tunneling Microscopy, Scanning Tunneling Microscopy, STMSTM) and Related ) and Related

Atomic Force Microscopy Atomic Force Microscopy (AFM)(AFM) (1)(1)

Discovery of the SPM technique took place in the 1980Discovery of the SPM technique took place in the 1980’’s. It s. It involves dragging a very sharp needlelike probe across a involves dragging a very sharp needlelike probe across a sample very close to the sample surface. sample very close to the sample surface. For conducting For conducting samplessamples a tunneling current between the sample and probe tip a tunneling current between the sample and probe tip can be monitored and held constant. As the probe can be monitored and held constant. As the probe approaches an elevated portion of the sample, the probe approaches an elevated portion of the sample, the probe moves up and over, and by moves up and over, and by rasteringrastering over an area of the over an area of the sample, a surface map can be produced. With proper sample sample, a surface map can be produced. With proper sample preparation and using a highpreparation and using a high--quality instrument in a quality instrument in a vibrationvibration--free environment, it is sometimes possible to image free environment, it is sometimes possible to image down to atomic resolution. In fact, down to atomic resolution. In fact, it has been possible to it has been possible to probe electronic structure and single atoms by Scanning probe electronic structure and single atoms by Scanning Tunneling Microscopy (STM).Tunneling Microscopy (STM). (Cont(Cont’’d)d)

(Klabunde, 2001)


43

Scanning Probe Microscopy (Scanning Probe Microscopy (SPMSPM; also called ; also called Scanning Tunneling Microscopy, Scanning Tunneling Microscopy, STMSTM) and Related ) and Related

Atomic Force Microscopy Atomic Force Microscopy (AFM)(AFM) (2)(2)

When the When the sample is sample is nonconductingnonconducting, the atomic force , the atomic force (AFM)(AFM)mode can be used, where the probe tip is essentially mode can be used, where the probe tip is essentially touching the surface, and the surface can be mapped by the touching the surface, and the surface can be mapped by the weak interaction force between tip and sample. In the AFM weak interaction force between tip and sample. In the AFM mode, resolution is substantially poorer than for the mode, resolution is substantially poorer than for the tunneling mode. There continues to be developed in this tunneling mode. There continues to be developed in this area, and magnetic mapping is also possible.area, and magnetic mapping is also possible.

(Klabunde, 2001)


44

Scanning Probe Microscopy (SPM)Scanning Probe Microscopy (SPM)------ Scanning Scanning Tunneling Microscopy (STM) and Atomic Force Tunneling Microscopy (STM) and Atomic Force

Microscopy (AFM)Microscopy (AFM) (3)(3) (Sipp et al., 2002)

Atomic force microscopy (AFM), which uses a sharp tip to feel the atomic-scale forces on a sample while the sample is rasteredbeneath it, can make images of the physical properties of a surface, with resolution in x and y of about 2 Å (2×10-10 m) and in z, of a fraction of 1 Å . Images highlight either topography directly (height mode) or slope (deflection mode). For height mode, features are given a false color that is proportional to their height above some baseline so that hills appear light and valleys, dark. For deflection mode, apparent light and shadow on feature edges enhance the roughness of the topography.AFM is excellent for observing colloidal particles, in situ, under air or solution.


45

Atomic Force Microscopy (AFM)Atomic Force Microscopy (AFM)------Deflection Mode Deflection Mode (4)(4)

(Sipp et al., 2002)

(Early Stage) (Middle Stage) (Middle Stage)


46

Powder XPowder X--Ray Diffraction (XRD)Ray Diffraction (XRD)

Although XRD has been useful for crystalline powders for Although XRD has been useful for crystalline powders for several decades, modern improvements in electronics, several decades, modern improvements in electronics, computers, and Xcomputers, and X--ray sources have allowed it to become an ray sources have allowed it to become an indispensable tool for identifying indispensable tool for identifying nanocrystallinenanocrystalline phases as phases as well as crystal size and crystal strain. Other aspects include well as crystal size and crystal strain. Other aspects include small angle Xsmall angle X--ray scattering to characterize particle sizes in ray scattering to characterize particle sizes in nanonano--, micro, micro--, and , and macroscalemacroscale in compressed powders.in compressed powders.

(Klabunde, 2001)


47(Source: http://www.chemistry.ohio-state.edu/~woodward/ch754/powder_diffraction.pdf)


48

XRD Patterns for Various Crystal Forms of TiOXRD Patterns for Various Crystal Forms of TiO22(Yang and Cheng, 2003)(Yang and Cheng, 2003)

Rutile

2θ(degree)

Rel

ativ

e In

ten

sity


49(Source: http://www.chemistry.ohio-state.edu/~woodward/ch754/powder_diffraction.pdf)

Note: B is often calculated relative to a reference solid (with crystallite size > 500 nm) added to the sample: B2 = Bs

2 –Br2.

The Scherrer Formula


50

BrunauerBrunauer--EmmettEmmett--Teller Gas Adsorption Surface Teller Gas Adsorption Surface Area Measurement and Pore Structure AnalysisArea Measurement and Pore Structure Analysis

(BET Method)(BET Method)

Another technique that has been well known for many Another technique that has been well known for many decades is the determination of surface areas of powders decades is the determination of surface areas of powders by by nitrogen gas adsorptionnitrogen gas adsorption at near liquid nitrogen temperature. at near liquid nitrogen temperature. PhysisorptionPhysisorption of a monolayer of Nof a monolayer of N22 allows calculation of allows calculation of surface area, by plotting pressure versus gas uptake. surface area, by plotting pressure versus gas uptake. In In recent years great improvements have allowed not only recent years great improvements have allowed not only rapid surface area determinations but also pore size rapid surface area determinations but also pore size distributions, pore volumes, and in general the ability to distributions, pore volumes, and in general the ability to more thoroughly characterize morphologies and even fractal more thoroughly characterize morphologies and even fractal dimensions.dimensions.

(Klabunde, 2001)


51

NN22--Adsorption/Desorption Isotherms of Adsorption/Desorption Isotherms of NanoironNanoiron

0.0 0.2 0.4 0.6 0.8 1.00

50

100

150

200

250

300

Adsorption Desorption

Volu

me

Adso

rbed

m3 /g

STP

Relative Pressure (P/P0)

(Yang et al., 2004)


52

Determination of the Particle Size from Specific Determination of the Particle Size from Specific Surface AreaSurface Area

SEM Image of Nano-MgO

(1) By nitrogen gas adsorptionBET surface area: 39.8-55.2 m2/g

(2)Assuming all particles are spherical in shape and nonporous, then

dp = 6 * 103 / Sρwhere dp = mean diameter of particles (nm),

S = BET surface area (39.8-55.2 m2/g for nano-MgO),ρ = density of particles (3.58 g/cm3 for MgO)

Thus, dp = 30.4-42.1 nm (This result is in good agreement with the mean diameter measured by SEM, 30-41nm.)


53

Superconducting Quantum Interference Device Superconducting Quantum Interference Device (SQUID) (SQUID) MagnetometryMagnetometry

For magnetic For magnetic nanomaterialsnanomaterials, the very sensitive SQUID , the very sensitive SQUID can can yield information on blocking temperatures, Neel yield information on blocking temperatures, Neel temperatures, temperatures, coercivitycoercivity, saturation magnetization, , saturation magnetization, ferroferro--magnetism, and magnetism, and superparamagnetismsuperparamagnetism.. The device is cooled The device is cooled with liquid helium, and the sample can be studied at near with liquid helium, and the sample can be studied at near liquid helium temperature or up to well above room liquid helium temperature or up to well above room temperature.temperature.

(Klabunde, 2001)


54

Magnetic Hysteresis of Nanoiron

-60 -40 -20 0 20 40 60

-30

-20

-10

0

10

20

30

M

(em

u/g)

H (KOe)

5.0 K 300 K

(Yang et al., 2004)


55

DSCDSC (Differential Scanning (Differential Scanning CalorimetryCalorimetry ) vs. ) vs. TGATGA (Thermal Gravitational Analysis)(Thermal Gravitational Analysis)

100 200 300 400 500

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Wei

ght (

mg)

Temp. (oC)

DSCTGA


56

Differential Scanning Differential Scanning CalorimetryCalorimetry / DSC / DSC (1)(1)

(Klabunde, 2001)

DSC measures the amount of energy (heat) absorbed or released by a sample as it is heated, cooled, or held at a constant temperature. Typical applications include determination of melting point temperature and the heat of melting; measurement of the glass transition temperature; curing and crystallization studies; and identification of phase transformations.

Heating nanostructured materials can lead to crystal growth by amalgamation (exothermic), melting (endothermic), or crystal phase changes (exo- or endothermic). When the nanoparticles are ligated – for example, thiol coatings on gold – chemical reactions and liganddisplacements can occur, which can be exo- or endothermic. By use of DSC, these transformations can be monitored and the extent of exo- or endothermicity determined, which can be very helpful in characterization.


57

Differential Scanning Differential Scanning CalorimetryCalorimetry /DSC /DSC (2)(2)

(http://www.colby.edu/chemistry/PChem/notes/DSCalor.pdf)


58

Fourier Transform Infrared (FTIR) Spectroscopy Fourier Transform Infrared (FTIR) Spectroscopy (1)(1)

Fourier transform infrared (FTIR) spectroscopy is a powerful analytical tool for characterizing and identifying organic molecules. Using the IR spectrum, chemical bonds and the molecular structure of organic compounds can be identified. This provides the user the ability to non-destructively determine the source of organic contaminants in areas such as electrical contacts, metallization lines, magnetic disk drives and die surfaces. Two new advances in FTIR, microbeam technology and attenuated total reflectance (ATR), allow the user to analyze thin films, organic and inorganic, in areas as small as 10-15 microns.

(http://www.calce.umd.edu/general/Facilities/ftir.htm)


59

Bands at 1582, 1474, and 1441 cm-l

are assigned to the aromatic ring C=C stretching vibrations, while bands a t 1245,1155,1126, and 1033 cm-l are assigned to ring C-H in plane bending vibrations. The band a t 1053 cm-l is assigned to a C1-sensitive vibration, and a relatively broad band a t 1294 cm-l is assigned to the C-0 stretching vibration.

(Kung and McBride, 1991)



60(Sun et al., 1998)



61

Raman Spectroscopy Raman Spectroscopy (1)(1)

I is well known that photons interact with molecules to induce transitions between energy states. In Raman spectroscopy, according to the particle theory, a photon is scattered by the molecular system. Most photons are elastically scattered, a process which is called Rayleigh scattering. In Rayleigh scattering, the emitted photon has the same wavelength as the absorbing photon. Raman spectroscopy is based on the Raman effect, which is the inelastic scattering of photons by molecules. The effect was discovered by the Indian physicist, C. V. Raman in 1928. The Raman effect comprises a very small fraction, about 1 in 107, of the incident photons. In Raman scattering, the energies of the incident and scattered photons are different. A simplified energy diagram that illustrates these concepts is given below.


62


(http://carbon.cudenver.edu/public/chemistry/classes/chem4538/raman.htm)


63


The energy of the scattered radiation is less than the incident radiation for the Stokes line and the energy of the scattered radiation is more than the incident radiation for the anti-Stokes line. The energy increase or decrease from the excitation is related to the vibrational energy spacing in the ground electronic state of the molecule and therefore the wave number of the Stokes and anti-Stokes lines are a direct measure of the vibrational energies of the molecule. A schematic Raman spectrum may appear as:



64



In the example spectrum, notice that the Stokes and anti-Stokes lines are equally displaced from the Rayleigh line. This occursbecause in either case one vibrational quantum of energy is gained or lost. Also, note that the anti-Stokes line is much less intense than the Stokes line. This occurs because only molecules that are vibrationally excited prior to irradiation can give rise to the anti-Stokes line. Hence, in Raman spectroscopy, only the more intense Stokes line is normally measured.


65(Sun et al., 1998)


66

Zeta Potential & Point of Zero Charge Determinations Zeta Potential & Point of Zero Charge Determinations (1)(1)

2 4 6 8 10 12 14

-25

-20

-15

-10

-5

0

5

10

Ze

ta p

oten

tial (

mV)

pH

Fe/H2O Fe*/H2O Fe/KNO3(aq) Fe*/KNO3(aq)

(Yang et al., 2004)

(Nanoscale Iron)


67

Point of Zero Charge / PZC Point of Zero Charge / PZC (2)(2)

(Illes and Tombacz, 2004)


68

Point of Zero Charge / PZC Point of Zero Charge / PZC (3)(3)

(Mak and Chen, 2005)


69(Source: Unknown)

Trace Element AnalysisTrace Element Analysis(Mass Spectrometer Detection Limit ~ ppt)


70

Campus ofCampus of

Are you ready to prepare any Are you ready to prepare any nanomaterialsnanomaterials/nanostructures and characterize them?/nanostructures and characterize them?

Be a trained and knowledgeable one first!Be a trained and knowledgeable one first!

introduction to environmental nanotechnology -...

Documents