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CHARACTERIZATION

of NANOMATERIALS

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Overview of the most common nano-

characterization techniques

MAIN CHARACTERIZATION TECHNIQUES:

General Techniques

NMR, IR, UV, CV, etc.,

1.Transmission Electron Microscope (TEM)

2. Scanning Electron Microscope (SEM)

3. Scanning Probe Microscope (SPM)

4. Elemental Analysis (EDS, XPS, ICP)

5. X-ray Powder Diffractometer (XRD)

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1.Transmission Electron

Microscope (TEM)

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Transmission electron microscopy (TEM) is a microscopy

technique in which a beam of electrons is transmitted through

an ultra-thin specimen, interacting with the specimen as it

passes through. An image is formed from the interaction of the

electrons transmitted through the specimen; the image is

magnified and focused onto an imaging device, such as a

fluorescent screen, on a layer of photographic film, or to be

detected by a sensor such as a CCD camera.

The first TEM was built by Max Knoll and Ernst Ruska in 1931,

with this group developing the first TEM with resolution greater

than that of light in 1933 and the first commercial TEM in 1939.

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Energy Filtering TEM(EF-TEM)

High Voltage TEM(HVEM)

Field Emission TEM(FE-TEM)

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High voltage Tank

Field emission Gun

Specimen Holder

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Different contrast of sample

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Electron diffraction is most frequently used in solid state physics and chemistry to

study the crystal structure of solids. Experiments are usually performed in a

transmission electron microscope (TEM), or a scanning electron microscope (SEM

). Selected area (electron) diffraction (abbreviated as SAD or SAED), is a

crystallographic experimental technique that can be performed inside a transmissi

on electron microscope (TEM).

In a TEM, a thin crystalline specimen is subjected to a parallel beam of high

energy electrons. As TEM specimens are typically ~100 nm thick, and the

electrons typically have an energy of 100–400 kiloelectron volts, the electrons

pass through the sample easily.

In this case, electrons are treated as wave-like, rather than particle-like. Because

the wavelength of high-energy electrons is a few thousandths of a nanometer, and

the spacing between atoms in a solid is about a hundred times larger, the atoms

act as a diffraction grating to the electrons, which are diffracted. That is, some

fraction of them will be scattered to particular angles, determined by the crystal

structure of the sample, while others continue to pass through the sample without

deflection. As a result, the image on the screen of the TEM will be a series of

spots—the selected area diffraction pattern, SADP, each spot corresponding to a

satisfied diffraction condition of the sample's crystal structure. If the sample is tilted

, the same crystal will stay under illumination, but different diffraction conditions

will be activated, and different diffraction spots will appear or disappear.

SAED

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Example

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HVEM

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2. Scanning Electron

Microscope (SEM)A scanning electron microscope (SEM) is a type of electron microscope that

produces images of a sample by scanning it with a focused beam of electrons.

The electrons interact with atoms in the sample, producing various signals that

can be detected and that contain information about the sample's surface

topography and composition. The electron beam is generally scanned in a

raster scan pattern, and the beam's position is combined with the detected

signal to produce an image. SEM can achieve resolution better than 1

nanometer. Specimens can be observed in high vacuum, in low vacuum, in dry

conditions (in environmental SEM), and at a wide range of cryogenic or

elevated temperatures.

The most common mode of detection is by secondary electrons emitted by

atoms excited by the electron beam. On a flat surface, the plume of secondary

electrons is mostly contained by the sample, but on a tilted surface, the plume

is partially exposed and more electrons are emitted. By scanning the sample

and detecting the secondary electrons, an image displaying the topography of

the surface is created. Since the detector is not a camera, there is no diffraction

limit for resolution as in optical microscopes and telescopes.

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3. Scanning Probe

Microscope (SPM)

Scanning probe microscopy (SPM) is a branch of microscopy that forms

images of surfaces using a physical probe that scans the specimen. SPM

was founded with the invention of the scanning tunneling microscope in

1981.

Many scanning probe microscopes can image several interactions

simultaneously. The manner of using these interactions to obtain an image

is generally called a mode.

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SPM(Scanning Probe

Microscope)

AFM(Atomic Force

Microscope, SFM)

STM(Scanning Tunneling

Microscope)

(Scanning Force Microsccope)

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Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very

high-resolution type of scanning probe microscopy (SPM), with demonstrated

resolution on the order of fractions of a nanometer, more than 1000 times better

than the optical diffraction limit. The precursor to the AFM, the scanning

tunneling microscope (STM), was developed by Gerd Binnig and Heinrich

Rohrer in the early 1980s at IBM Research - Zurich, a development that earned

them the Nobel Prize for Physics in 1986.

The AFM consists of a cantilever with a sharp tip (probe) at its end that is used

to scan the specimen surface. The cantilever is typically silicon or silicon nitride

with a tip radius of curvature on the order of nanometers. When the tip is

brought into proximity of a sample surface, forces between the tip and the

sample lead to a deflection of the cantilever according to Hooke's law.

Depending on the situation, forces that are measured in AFM include

mechanical contact force, van der Waals forces, capillary forces, chemical

bonding, electrostatic forces, magnetic forces, etc.

Along with force, additional quantities may simultaneously be measured

through the use of specialized types of probes. Typically, the deflection is

measured using a laser spot reflected from the top surface of the cantilever into

an array of photodiodes.

Atomic force microscopy

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4. Elemental

Analysis

(EDS, XPS, ICP)

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1) X-ray photoelectron spectroscopy (XPS)

ESCA(Electron Spectroscopy for

Chemical Analysis)XPS is also known as ESCA (Electron

Spectroscopy for Chemical Analysis), an

abbreviation introduced by Kai Siegbahn's

research group to emphasize the chemical

(rather than merely elemental) information

that the technique provides.

X-ray photoelectron spectroscopy (XPS) is a surface-sensitive

quantitative spectroscopic technique that measures the elemental

composition at the parts per thousand range, empirical formula,

chemical state and electronic state of the elements that exist within a

material. XPS spectra are obtained by irradiating a material with a

beam of X-rays while simultaneously measuring the kinetic energy

and number of electrons that escape from the top 0 to 10 nm of the

material being analyzed.

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XPS is used to measure:

elemental composition of the surface (top 0–10 nm usually)

empirical formula of pure materials

elements that contaminate a surface

chemical or electronic state of each element in the surface

uniformity of elemental composition across the top surface (or

line profiling or mapping)

uniformity of elemental composition as a function of ion beam

etching (or depth profiling)

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2) Energy Dispersive Spectrometer(EDS)

Energy Dispersive X-ray Analysis(EDX, EDXS, XEDS, etc.)

Energy-dispersive X-ray spectroscopy (EDS, EDX, or XEDS), sometimes

called energy dispersive X-ray analysis (EDXA) or energy dispersive X-ray

microanalysis (EDXMA), is an analytical technique used for the elemental

analysis or chemical characterization of a sample. It relies on an

interaction of some source of X-ray excitation and a sample. Its

characterization capabilities are due in large part to the fundamental

principle that each element has a unique atomic structure allowing unique

set of peaks on its X-ray emission spectrum.

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To stimulate the emission of characteristic X-rays from a specimen, a high-energy beam

of charged particles such as electrons or protons (see PIXE), or a beam of X-rays, is

focused into the sample being studied. At rest, an atom within the sample contains

ground state (or unexcited) electrons in discrete energy levels or electron shells bound

to the nucleus. The incident beam may excite an electron in an inner shell, ejecting it

from the shell while creating an electron hole where the electron was. An electron from

an outer, higher-energy shell then fills the hole, and the difference in energy between the

higher-energy shell and the lower energy shell may be released in the form of an X-ray.

The number and energy of the X-rays emitted from a specimen can be measured by an

energy-dispersive spectrometer. As the energy of the X-rays are characteristic of the

difference in energy between the two shells, and of the atomic structure of the element

from which they were emitted, this allows the elemental composition of the specimen to

be measured

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3) Inductively Coupled Plasma (ICP) Emission Spectroscopy

Inductively coupled plasma atomic emission spectroscopy (ICP-AES), also

referred to as inductively coupled plasma optical emission spectrometry (ICP-

OES), is an analytical technique used for the detection of trace metals. It is a

type of emission spectroscopy that uses the inductively coupled plasma to

produce excited atoms and ions that emit electromagnetic radiation at

wavelengths characteristic of a particular element. The intensity of this

emission is indicative of the concentration of the element within the sample.

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5. X-ray Powder Diffractometer

(XRD)

Powder diffraction is a scientific technique using X-ray, neutron, or electron

diffraction on powder or microcrystalline samples for structural characterization of

materials

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Bragg's law (equation)

nl = 2dhkl sinq

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JCPDS : Joint Committee on Powder Diffraction Standards

ICDD : International Center for Diffraction Data

Powder Diffraction File (PDF) #

Program: EVA, ICSD, Pcpdfwin ….

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PCPDFWIN: JCPDS No. or PDF No.

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Example

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Example 4

Hexagonal In2S3

Cubic InSe

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B is the full-width at half maximum