Mekelle University

EIT-M

School of mechanical and industrial

engineering

MSc. Mini project on STM

Submitted by

Ashenafi Atsbeha

EIT-M/PR0230/07

Submitted to

Dr. Areya Werede

And

Mr. Alula G/esas

Submission date

SaturdayJun.13 2015

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Acknowledgement

First of all I would like to thank almighty God for helping me through his various miraculous

ways in completing this task. We are highly obliged to Dr. AREYA WEREDE and

Mr. ALULA G/ESAS.

for guiding me throughout this short assignment paper; giving me direction for my further

learning. I would also like to thank to my class friends for sharing an idea. Finally I would

like to extend our sincere thanks to each and every one who was involved directly or

indirectly in the editing the paper .

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Contents Acknowledgement .................................................................................................................................. 1

Abstract ................................................................................................................................................... 4

Abbreviations .......................................................................................................................................... 5

1. Introduction ..................................................................................................................................... 6

1.1. Operation of STM ................................................................................................................... 6

1.1.1. Two Operation Modes .................................................................................................... 7

2. Instrumentation ............................................................................................................................... 9

2.1. High end resolution ............................................................................................................... 10

2.2. Quantum Tunneling .............................................................................................................. 10

3. Procedure ...................................................................................................................................... 10

3.1. STM Advantages .................................................................................................................. 12

3.2. STM Disadvantages .............................................................................................................. 12

STMs use highly specialized equipment that is fragile and expensive ..................................... 12

4. Application .................................................................................................................................... 12

5. Profile method of STM .................................................................................................................. 13

5.1. Surface Texture and Roughness ............................................................................................ 13

5.2. Measuring of surface roughness. .......................................................................................... 14

6. Pitting corrosion testing ................................................................................................................ 17

Electrochemical testing ............................................................................................................. 17

Potentiostatic methods ...................................................................................................................... 17

Galvanostatic methods ...................................................................................................................... 17

Chemical testing ........................................................................................................................ 17

6.1. Electrochemical testing ......................................................................................................... 17

5.1.1 Potentiokinetic methods ....................................................................................................... 18

5.1.2. Potentiostatic methods ........................................................................................................ 18

5.1.3. Galvanostatic methods ........................................................................................................ 19

6.2. Chemical testing .................................................................................................................... 19

6.2.1. Ferric chloride ............................................................................................................... 20

6.2.2. Redox couples ............................................................................................................... 20

6.2.3. Chemical etchants ......................................................................................................... 20

6.3. Crevice corrosion test ........................................................................................................... 20

6.4. Experimental Procedures. ..................................................................................................... 21

Advantages. ................................................................................................................................... 21

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Disadvantages. .............................................................................................................................. 21

7. Corrosion Immersion Test ............................................................................................................ 22

7.1. Conclusions ................................................................................................................................ 23

References ............................................................................................................................................ 24

Figures pages

Figure 2 working principles of STM....................................................................................................... 7

Figure 3 constant height mode ................................................................................................................ 8

Figure 4 constant current mode ............................................................................................................... 8

Figure 5 Schematic view of an STM ...................................................................................................... 9

Figure 6 a simple scanning tunneling microscope head using a platinum–iridium tip ......................... 11

Figure 7 Schematic representation of current time curve obtained using potentiokinetic method ....... 18

Figure 8 Schematic representation of potential time curve obtained using galvanostatic mothod ....... 19

Figure 9 pitting and crevice corrosion profile ....................................................................................... 21

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Abstract

The invention of scanning tunnelling microscopy help scientist better understand the surface

structure which means this technical solved the fundamental problem in surface physics.

Numerous advantages and versatility of STM make itself become a powerful tool. STM with

tunneling spectroscopy can be used to perform atomically resolved spectroscopy imaging.

Functions such as energy-resolved local density of states (LDOS) mapping, spin-polarized

tunneling imaging, molecular vibrational spectroscopy by inelastic tunneling, and tunneling-

induced photon emission mapping. Furthermore, as a nanofabrication tool, STM also be used

in atom manipulation, local deposition by the decomposition of organometallic gases.

Moreover, STM can be adapted to various environments such as air, ultrahigh vacuum

(UHV), controlled atmospheres and liquid. In the following context, we will introduce both

basic theory of STM and application of STM in nano-device industry.

Common applications include atomic resolution imaging, electrochemical STM, scanning

tunneling spectroscopy (STS), and low-current imaging of poorly conductive samples using

low-current STM. The scanning tunneling microscope (STM) is the ancestor of all scanning

probe microscopes.

Probe tips of STM are usually made from tungsten metal or a platinum-iridium alloy where at

the very end of the tip (called apex) there is one atom of the material.

Pitting and crevice corrosion tests fall into two broad groups: electro-chemical and chemical.

Crevice corrosion occurred in two different locations. A small aluminum rivet was used to

hold an electrical connector onto the plate and this is the first area of crevice corrosion. Later,

the electrical ground connector was moved to underneath the lowest of the fastening bolts as

the crevice corrosion at the initial site lost electrical contact.

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Abbreviations

Ep, ……………………………………….pitting potential

Ecorr… ………………………………….Corrosion potential

CCT,……………………………………...corrosion temperature,

CPT,………………………………………critical pitting temperature,

(STM),…………………………………….Scanning Tunneling Microscope

(STS),……………………………………..scanning tunneling spectroscopy

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1. Introduction

The Scanning Tunneling Microscope (STM) was introduced by G. Binnig and W. Rohrer at

the IBM Research Laboratory in 1982 which was honoured by the Noble Prize in 1986. It has

become widely used as an important instrument for real space analysis in surface science.

The invention of STM help scientist better understand the surface structure which means this

technical solved the fundamental problem in surface physics. From 1986 until now, research

go on improve this advance technical and apply this method into industry innovations of

novel nanometer-scale product. Numerous advantages and versatility of STM make itself

become a powerful tool. STM with tunneling spectroscopy can be used to perform atomically

resolved spectroscopy imaging functions such as energy-resolved local density of states

(LDOS) mapping, spin-polarized tunneling imaging, molecular vibrational spectroscopy by

inelastic tunneling, and tunneling-induced photon emission mapping. Furthermore, as a

nanofabrication tool, STM also be used in atom manipulation, local deposition by the

decomposition of organometallic gases. Moreover, STM can be adapted to various

environments such as air, ultrahigh vacuum (UHV), controlled atmospheres and liquid. In the

following context, we will introduce both basic theory of STM and application of STM in

nano-device industry.

1.1. Operation of STM

The basic idea of the Scanning Tunneling Microscope (STM) is to bring a fine metallic tip in

close proximity (a few Å) to a conductive sample. By applying a voltage between the tip and

the sample a small electric current (0.01nA-50nA) can flow from the sample to the tip or

reverse, although the tip is not in physical contact with the sample. This phenomenon is

called electron tunneling. The exponential dependence of the tunneling current on the tip to

sample distance results in a high vertical resolution. By scanning the tip across the surface

and detecting the current (one can also use the current as a vertical positioning signal for the

tip a map of the surface can be generated with a resolution in the order of atomic distances. It

tunneling current is influenced by the lateral and vertical variation of the electronic state

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density at the surface. The lateral resolution is about 1Å whereas a vertical resolution up to

0.01Å can be achieved. The STM can be used in ultra-high vacuum, air or other

environments.

Common applications include atomic resolution imaging, electrochemical STM, scanning

tunneling spectroscopy (STS), and low-current imaging of poorly conductive samples using

low-current STM. The scanning tunneling microscope (STM) is the ancestor of all scanning

probe microscopes.

Figure 1 working principles of STM

1.1.1. Two Operation Modes

The STM can be operated in two different modes:

Scanning at a constant height (figure 3): the tip is probing the surface in a

straight line. At the same time the tunneling current is recorded.

Scanning with a constant current (figure 4): the tip probes the surface in a way that the

tunneling current is kept constant. The change of the tip height is being recorded.

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i. Constant Height Mode

In this mode the vertical position of the tip is not changed, equivalent to a slow or disabled

feedback. The current as a function of lateral position represents the surface image. This

mode is only appropriate for atomically flat surfaces as otherwise a tip crash would be

inevitable. One of its advantages is that it can be used at high scanning frequencies (up to 10

kHz). In comparison, the scanning frequency in the constant current mode is about 1 image

per second or even per several minutes.

Figure 2 constant height mode

ii. Constant Current Mode

By using a feedback loop the tip is vertically adjusted in such a way that the current always

stays constant. As the current is proportional to the local density of states, the tip follows a

contour of a constant density of states during scanning. A kind of a topographic image of the

surface is generated by recording the vertical position of the tip.

Figure 3 constant current mode

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Figure 4 Schematic view of an STM

2. Instrumentation

The components of an STM include

scanning tip,

piezoelectric controlled height and x,y scanner,

coarse sample-to-tip control,

vibration isolation system, and

Computer.

The resolution of an image is limited by the radius of curvature of the scanning tip of the

STM. Additionally, image artifacts can occur if the tip has two tips at the end rather than a

single atom; this leads to “double-tip imaging,” a situation in which both tips contribute to the

tunneling. Therefore it has been essential to develop processes for consistently obtaining

sharp, usable tips. Recently, carbon nanotubes have been used in this instance.

The tip is often made of tungsten or platinum-iridium, though gold is also used. Tungsten tips

are usually made by electrochemical etching, and platinum-iridium tips by mechanical

shearing.

Due to the extreme sensitivity of tunnel current to height, proper vibration isolation or an

extremely rigid STM body is imperative for obtaining usable results. In the first STM by

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Binnig and Rohrer, magnetic levitation was used to keep the STM free from vibrations; now

mechanical spring or gas spring systems are often used. Additionally, mechanisms for

reducing eddy currents are sometimes implemented.

Maintaining the tip position with respect to the sample, scanning the sample and acquiring

the data is computer controlled. The computer may also be used for enhancing the image with

the help of image processing as well as performing quantitative measurements.

2.1. High end resolution

For an STM, good resolution is 0.1 nm lateral resolution and 0.01 nm depth resolution. The

high resolution of STMs enables researchers to examine surfaces at an atomic level. The

microscopes help scientists get a picture of how the atoms are arranged on a surface, by

looking at the electron density of the surface atoms.

2.2. Quantum Tunneling

STMs are based on the idea of quantum tunneling, when a conducting tip is brought very

close to the surface and a voltage difference between the tip and the surface is applied. When

the voltage difference is applied, electrons can tunnel through the vacuum between the tip

and the surface, causing a tunneling current. Using this principle, STMs work by passing a

sharp wire made of metal over the surface that is to be examined. The tip passes very close to

the surface at the same time that the microscope applies an electrical voltage to the tip. This

creates an image that shows miniscule details on an atomic level.

3. Procedure

First, a voltage bias is applied and the tip is brought close to the sample by coarse sample-to-

tip control, which is turned off when the tip and sample are sufficiently close. At close range,

fine control of the tip in all three dimensions when near the sample is typically piezoelectric,

maintaining tip-sample separation W typically in the 4-7 Å (0.4-0.7 nm) range, which is the

equilibrium position between attractive (3<W<10Å) and repulsive (W<3Å) interactions. In

this situation, the voltage bias will cause electrons to tunnel between the tip and sample,

creating a current that can be measured. Once tunneling is established, the tip's bias and

position with respect to the sample can be varied. If the tip is moved across the sample in the

x-y plane, the changes in surface height and density of states cause changes in current. These

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changes are mapped in images. This change in current with respect to position can be

measured itself, or the height, z, of the tip corresponding to a constant current can be

measured. These two modes are called constant height mode and constant current mode,

respectively.

In constant current mode, feedback electronics adjust the height by a voltage to the

piezoelectric height control mechanism. This leads to a height variation and thus the image

comes from the tip topography across the sample and gives a constant charge density surface;

this means contrast on the image is due to variations in charge density.

In constant height mode, the voltage and height are both held constant while the current

changes to keep the voltage from changing; this leads to an image made of current changes

over the surface, which can be related to charge density. The benefit to using a constant

height mode is that it is faster, as the piezoelectric movements require more time to register

the height change in constant current mode than the current change in constant height mode.

In addition to scanning across the sample, information on the electronic structure at a given

location in the sample can be obtained by sweeping voltage and measuring current at a

specific location. This type of measurement is called scanning tunneling spectroscopy (STS)

and typically results in a plot of the local density of states as a function of energy within the

sample. The advantage of STM over other measurements of the density of states lies in its

ability to make extremely local measurements: for example, the density of states at an

impurity site can be compared to the density of states far from impurities.

Probe tips of STM are usually made from tungsten metal or a platinum-iridium alloy where at

the very end of the tip (called apex) there is one atom of the material.

Figure 5 a simple scanning tunneling microscope head using a platinum–iridium tip

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3.1. STM Advantages

STMs are helpful because they can give researchers a three dimensional profile of a surface,

which allows researchers to examine a multitude of characteristics, including roughness,

surface defects and determining things about the molecules such as size and conformation.

Other advantages of the scanning tunneling microscope include:

It is capable of capturing much more detail than lesser microscopes. This helps

researchers better understand the subject of their research on a molecular level.

STMs are also versatile. They can be used in ultra-high vacuum, air, water and other

liquids and gasses.

They will operate in temperatures as low as zero Kelvin up to a few hundred degrees

Celsius.

3.2. STM Disadvantages

There are very few disadvantages to using a scanning tunneling microscope. The two major

downsides to using STMs are:

STMs can be difficult to use effectively. There is a very specific technique that

requires a lot of skill and precision.

STMs require very stable and clean surfaces,

Excellent vibration control and sharp tips.

STMs use highly specialized equipment that is fragile and expensive

4. Application

STM become a powerful tool to investigate surfaces of conductive materials since it‟s

invented. Recently, through the trend of miniaturization both in magnetic and electronics

devices, such as high-density information storage, high-resolution lithography, and

production of Nano scale integrated chemical systems and electronic devices. So, now, the

development of advanced fabrication and characterization technologies and science for the

nano functional material is become the most important problem in this research area. As we

know, the size of the advance micro devices is shrinking into the nanometer scale, continuing

miniaturization of electronic and mechanical devices has led in recent years to an interest in

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the generation of nanometer-sized structures on surfaces. To achieve this goal, we need to

find an effective and efficient way to resolve the bottleneck of nanotechnology. In this

advance research area, the invention of scanning probe techniques, particularly scanning

tunneling microscopy (STM), has made it possible to modify surfaces at the nanometer scale

and to manipulate even single atoms with the STM tip. STM nanofabrication technique has

potential applications to various technologies. For example, from the effect of single-electron

tunneling, a nanometer-scale SET transistor is become an important candidate technology for

high-speed, low-power large-scale integrated circuit which with tens of thousands of

transistors per chip.

5. Profile method of STM

5.1. Surface Texture and Roughness Regardless of the method of production, all surfaces have their own characteristics, which

collectively are referred to as surface texture. Although the description of surface texture as a

geometrical property is complex, the following guidelines have been established for

identifying surface texture in terms of Well-defined and measurable quantities.

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° Flaws or defects are random irregularities, such as scratches, cracks, holes, depressions,

seams, tears, or inclusions.

° Lay (directionality) is the direction of the predominant surface pattern, usually visible to the

naked eye

° Roughness is defined as closely spaced, irregular deviations on a small scale; it is expressed

in terms of its V height, width, and distance along the surface.

° Waviness is a recurrent deviation from a flat surface; it is A measured and described in

terms of the space between adjacent crests of the waves and height between the crests and

valleys of the waves.

5.2. Measuring of surface roughness. Typically, instruments called surface profilometers are used to measure and record surface

roughness. A profilometer has a diamond

Measuring surface roughness with a stylus. The rider supports the stylus and guards

against damage.

Path of the stylus in surface-roughness measurements (broken line), compared with

the actual roughness profile. Note that the profile of the stylus path is smoother than

that of the actual surface.

Through (f) Typical surface profiles produced by various machining and surface-

finishing processes. Note the difference between the vertical and horizontal scales.

Surface roughness can be observed directly through an optical or scanning tunnelling

microscope. Stereoscopic photographs are particularly useful for three dimensional views of

surfaces and also ca n be used to measure surface roughness.

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Surface roughness is generally characterized by two methods. The arithmetic mean value

(Ra) is based on the schematic illustration of a rough surface, as shown in and is defined as

Where all ordinates a, h, c, . . , are absolute values and n is the number of readings. The root-

mean-square roughness (Rq), formerly identified as RMS) is defined as

STM images of Organic Thin Layers

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Optical-interference microscopes shine a light against a reflective surface and record the

interference fringes that result from the incident and its reflected waves. This technique

allows for a direct measurement of the surface slope over the area of interest. As the vertical

distance between the sample and the interference objective is changed, the fringe patterns

also change, thus allowing for a surface height measurement.

Atomic-force microscopes (AFMS) are used to measure extremely smooth surfaces and even

have the capability of distinguishing atoms on atomically smooth surfaces. ln principle, an

AFM is merely a very fine surface profilometer with a laser that is used to measure probe

position. The surface profile can be measured with high accuracy and with vertical resolution

on the atomic scale, and scan areas can be on the order of 0.1 nm, although smaller areas are

more common.

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6. Pitting corrosion testing

Corrosion tests fall into two broad groups: electro-chemical and chemical. The various

techniques currently in use are described and discussed below, together with emerging

techniques based on the stochastic theory of pitting corrosion.

Common corrosion testing for pitting and crevice corrosions are

Electrochemical testing

Potentiokinetic methods

Potentiostatic methods

Galvanostatic methods

Chemical testing

Ferric chloride

Redox couples

Chemical etchants

6.1. Electrochemical testing

The majority of electrochemical tests for pitting corrosion revolve around the determination

of a pitting potential. There are in fact two potentials which are frequently referred to the pit

nucleation or breakdown potential and the critical pitting. Protection or re passivation

potential these can be defined as follows.

E > stable pits initiate and propagate.

E < no initiation or propagation of pits; pits formed above will eventually re passive below

It is worth noting here that, in the mechanism of pitting, refers to the kinetics of nucleation

(defined here as the formation of a stable pit), whereas the critical potential, is a measure of

the kinetics of re passivation. As such, neither or the potentials relate to the length of the

induction period or to the kinetics of propagation once initiation has occurred. This is a major

drawback in the present system used to characterize pitting corrosion. Nevertheless, these

potentials do provide a useful method for characterizing, on a relative basis, the susceptibility

of a material in a given environment to pit nucleation and re passivation; they have no use

other than this. Actual methods for determining these potentials are given below.

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5.1.1 Potentiokinetic methods

Potentiokinetic techniques as a group determine current as a function of potential (I =f(E)), as

illustrated schematically in Fig. 7

Figure 6 Schematic representation of current time curve obtained using potentiokinetic method

There are three methods by which this relationship can be obtained:

(i) The potentiodynamic method, where there is a continuous change in potential at a fixed rate.

(ii) The quasi-stationary method, where there is a stepwise change of potential at a certain rate.

(iii) The stationary method, where there is a step-wise change of potential which is maintained until a

stable current is established.

These methods are the most commonly used in determining pitting potentials. The higher the

potential, the shorter is that period. When the scan rate is high, pit nucleation only occurs at

potentials where the induction period is very short. There are, however, exceptions to this

rule; if the scan rate is reduced, then the passive film has a longer time to develop, thereby

increasing the resistance of the metal or alloy to pitting corrosion. The most reliable and

consistent method is

5.1.2. Potentiostatic methods

Potentostatic techniques as a group determine current as a function of time at constant

potential (E = constant, I =f(r)) these are perhaps the most reliable methods of determining

and they have been used extensively. In general, they give values more active than the

potentiokinetic and galvanokinetic methods. (This in itself casts doubts on any absolute.

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5.1.3. Galvanostatic methods

Galvanostatic techniques determine the potential as a function of time at constant current (1 =

constant, E = f(r)), as illustrated in Fig. 8. There are two general methods: one that determines

both and one that determines only. These are:

(I) the determination of and by recording E versus t curves at constant current starting from

the corrosion potential

(ii) The determination of by recording E versus T curves at constant current starting from a

fixed potential.

Neither of these techniques is in general use, and there is some doubt as to whether method

(i) gives an accurate value of

Figure 7 Schematic representation of potential time curve obtained using galvanostatic mothod

6.2. Chemical testing

Chemical methods used for assessing resistance to pitting corrosion are based on solutions

containing an activator, which is usually Cl and an oxidizing agent, in definite concentrations.

For this reason such methods cannot be used to predict pitting corrosion resistance in natural

environments, but can only be used to provide a ranking. Such methods, however, are usually

simple and need no complicated electronic apparatus, so that the tests do not need to be

performed by „experts‟. The most common chemical testing methods used are will be

mentioned.

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6.2.1. Ferric chloride

The best known test using ferric chloride as the chemical is ASTM Standard. The test is

straightforward, involving the immersion of the test specimen in a 6%FeCI3 solution for a

reasonable length of time, say 72 h, and measuring the weight loss.

6.2.2. Redox couples

Other chemical accelerated tests involve controlling the potential by means of a redox couple;

many redox couples have been used in this way. Perhaps the best known is

[Fe(CN)6]3/[Fe(CN)6]2 which has been used with additions of NaCI to give a redox potential

of 700 mV versus in neutral and alkaline solutions. In this test, pit nuclei are clearly visible

6.2.3. Chemical etchants

Another chemical test which has been developed involves the use of a series of chemical

etchants. The etchants are glycerol-ethanolic solutions of FeCI3 + AIC13 + L1C1. Using

these solutions it is possible to change the characteristics of attack by varying the

concentration of the components of the solution; it is claimed that tests performed with

chemical etchants reflect the pitting susceptibility of a metal more closely than potentiostatic

tests since the latter do not take into account the cathodic characteristics of the metal.

6.3. Crevice corrosion test

Crevice corrosion is virtually impossible to eliminate from the structure and, since crevice

corrosion occurs more readily than pitting corrosion, it is resistance to crevice corrosion

which is the more important from a practical point of view. As with pitting corrosion there

are electrochemical and chemical tests. These tests for crevice corrosion are discussed in the

pitting corrosion test methods.

In the figure below, both pitting corrosion and crevice corrosion are visible on an aluminum

cover plate. The location of this plate is in the bilge of a boat where it is often covered with

water.

Crevice corrosion occurred in two different locations. A small aluminum rivet was

used to hold an electrical connector onto the plate and this is the first area of crevice

corrosion. Later, the electrical ground connector was moved to underneath the lowest of the

fastening bolts as the crevice corrosion at the initial site lost electrical contact.

21

Pits are present on the surface of the aluminum close to the bolt at the left of the

picture from exposure to water.

Figure 8 pitting and crevice corrosion profile

6.4. Experimental Procedures.

1) All solutions should be of high purity components.

2) Sample finish should be 600 grit.

3) Purge solution for one hour with nitrogen.

4) Immerse test sample one hour prior to start of data collection.

5) Start scan at least 50mV more cathodic than Eoc

6) Scan rate should not exceed 0.6v/hr of 1.6mv/sec.

7) Increase potential to a specified value or a specified current value.

8) To investigate pitting, reverse the scan direction at the potential or current value

specified.

9) Upon reverse scan, stop test at original Eoc.

Advantages.

1. Short term test.

2. Can use actual metals and solutions.

3. Easy interpretation of data.

4. Standardized test so reproducible.

Disadvantages.

1) Destructive test.

2) Data can be dependent on scan rate set for passive metals.

Pit

s Crevice

22

7. Corrosion Immersion Test

Environmental conditions that should be created and the acceleration degree needed usually

identify which laboratory tests should be used. Proper acceleration is obtained by the

following:

Prolonging the exposure to vital conditions which are believed to lead to corrosion

damage. For instance, if a certain vessel is to undergo batch processing with a

chemical for 24 hours, the corrosion exposure in the laboratory should be 240 hours.

Making the conditions more intense in order to boost corrosion rates. This can be

achieved by increasing one or more of the following: pressure, salt concentration, and

temperature or solution acidity.

When the conditions for the environment have been identified and the test has been created,

this should be conducted again several times to verify whether this test meets the acceptable

reproducibility standard.

Generally, immersion tests can be separated into these categories:

Alternate immersion test - This immersion test involves a cyclic procedure that

involves a specimen being immersed for a certain period of time. Then, the specimen

is removed and undergoes drying prior to re-submerging to the cycle. Typically, about

a hundred cycles are completed throughout the test.

Simple immersion test - In this test, small batches of the material are subjected to the

medium under testing, while loss of weight is being gaged for a particular period.

The immersion test remains the most reliable method in terms of screening. It also serves as

the most simple and economical way to determine the most suitable material to protect

against corrosion in certain environments.

23

7.1. Conclusions

We have demonstrated that STM is not a peculiar tool for surface science but a useful

technique for quantitative analysis of local electrical properties in conductor devices with

extremely high spatial resolution. In addition to the profiling methods described above.

Another particular feature of STM is that it controls the probe position by sensing the

tunneling current between the tip and the sample surface. This feature ensures that the STM

can be operated at a definite probe position with respect to the sample surface to

measurement situations. We expect that the STM will contribute to the research and

development of various Nano scale devices is essentially required.

24

References 1. C. J. Chen. Introduction to Scanning Tunneling Microscopy. Oxford University Press,

New

York, 1993.

2. R. Young, J. Ward, and F. Scire. The topografiner: An instrument for measuring

surface

microtopography. Rev. Sci. Instrum. 43, 999-1011 (1972)

3. L. C. Fieldman and J. W. Mayer, Fundamentals of Surface and Thin Film Analysis,

Prentice Hall, Englewood Cli¤, NJ, 1986.

4. Pierre R. Roberge, Ph.D., P.Eng, Corrosion of engineering principle and practices