Dong-Sun Lee / cat - lab / SWU 2012 -Fall version

Chapter 21

Potentiometry

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Electroanalytical techniques

1) Ionics ---- Conductance

2) Electrodics

a) Static (I = 0) --- Potentiometry

b) Dynamic (I 0)

Controlled current --- Coulometric titration

Controlled potential

Stirred solution Controlled potential

Hydrodynamic voltammetry

Amperometry --- Amperometic titration

Quiescent solution Potential scan --- Cyclic voltammetry, Polarography

Small amplitude pulse technique

Differential pulse voltammetry

Square wave voltammetry

Potential step --- Chronoamperometry, Chronocoulometry

Pulse voltammetry, Chronoabsorptometry

Classification of electrochemical methods

1. POTENTIOMETRYMeasure electrical potential developed by an electrode in an electrolyte solution at zero current flow. Use NERNST EQUATION relating potential to concentration of some ion in solution.

2. VOLTAMMETRYDetermine concentration of ion in dilute solutions from current flow as a function of voltage when POLARIZATION of ion occurs around the electrode.POLARIZATION = depletion of concentration caused by electrolysis.If using a dropping mercury electrode, method is termed POLAROGRAPHY.

3. COULOMETRYElectrolysis of a solution and use of Faraday's law* relating quantity of electrical charge to amount of chemical change.[* essentially states that it takes 9.65 x 104 Coulombs of electrical charge to cause electrolysis of 1 mole of a univalent electrolyte species.]

4. CONDUCTIMETRYMeasure conductance of a solution, using INERT ELECTRODES, ALTERNATING CURRENT, AND AN ELECTRICAL NULL CIRCUIT - thereby ensure no net current flow and no electrolysis. The concentration of ions in the solution is estimated from the conductance.

NOTE:Methods 1 and 4,  NO ELECTROLYSIS of solution. Sample recoverable, unaltered by analysis.Methods 2 and 3  must cause ELECTROLYSIS OF THE SAMPLE. http://www.science.uts.edu.au/subjects/91326/Section12/section12.html

Potentiometry

An electroanalytical technique based on the measurement of the electromotive force of an electrochemical cell comprised of a measuring and a reference electrode.

The simplest example of a measuring electrode is a metal electrode whose potential depends on the concentration of the cation of the electrode metal.

Indicator electrode

Electrochemical measuring system.

General Principles

Reference electrode | salt bridge | analyte solution | indicator electrode

Eref Ej E ind

Ecell = Eind – Eref + Ej

Reference cell :

a half cell having a known electrode potential

Indicator electrode:

has a potential that varies in a known way

with variations in the concentration of an analyte

A cell for potentiometric determinations.

1) Saturated calomel electrode (S.C.E.)

Hg(l) | Hg2Cl2 (sat’d), KCl (sat’d) | |

electrode reaction in calomel hal-cell

Hg2Cl2 (s) + 2e = 2Hg(l) + 2Cl–

Eo = + 0.268V

E = Eo – (0.05916/2) log[Cl–]2 = 0.244 V

Temperature dependent

A calomel electrode saturated with KCl is called a saturated

calomel electrode, abbreviated S.C.E.Advantage : using saturated KCl is that [Cl-] does not change if some liquid evaporates.

Reference electrode: maintains a fixed potential :

a half cell having a known electrode potential

Hg2Cl2 Hg22+

+ 2Cl–

Ksp = 1.8 ×10–18

Saturated KCl = 4.6 M KCl

The crystal structure of calomel(Hg2Cl2), which has limited solubility in water (Ksp = 1.8 ×10–18).

Fig. 21-2. Diagram of a typical commercial saturated calomel electrode.

Fig. 21-3. A saturated calomel electrode made from materials readily available in any laboratory.

2) Silver-silver chloride electrode

Ag(s) | AgCl (sat’d), KCl (xM) | |

AgCl(s) + e = Ag(s) + Cl–

Eo = +0.244V

E = Eo – (0.05916/1) log [Cl–]

E (saturated KCl) = + 0.199V (25oC)

3) standard hydrogen electrode (SHE)

The most fundamental reference electrode in electrochemistry. "By definition" its equilibrium potential is considered zero at any temperature, because this electrode was chosen as an arbitrary zero point for electrode potentials. A zero point is needed since the potential of a single electrode cannot be measured, only the difference of two electrode potentials is measurable. All electrode potentials are expressed on this "hydrogen scale." It is a hydrogen electrode with an electrolyte containing unit concentration of hydrogen ions and saturated with hydrogen gas at unit atmosphere pressure. This electrode can be somewhat inconvenient to use because of the need to supply hydrogen gas. Therefore, other reference electrodes (e.g., calomel or silver/silver chloride) are often used instead, but the measured electrode potentials can be converted to the "hydrogen scale." Also called "normal hydrogen electrode." Strictly speaking, one must use unit activity rather than concentration of hydrogen ions and unit fugacity rather than unit pressure of hydrogen gas.

Pt | H2(g, 1.0 atm)|H+(aq, A= 1.0M)

½ H2(g, 1.0 atm) = H+(aq, A= 1.0M) + e Eo = 0.000 V

Voltage Conversions Between Different Reference Scales

If an electrode has a potential of – 0.461V with respect to a calomel electrode, what is the

potential with respect to a silver-silver chloride electrode? What would be the potential with

respect to the standard hydrogen electrode?

Liquid-junction potential

A potential difference between two solutions of different compositions separated by a membrane type separator. The simplest example is the case of two solutions containing the same salt in different concentrations. The salt will diffuse from the higher concentration side to the lower concentration side. However, the diffusion rate of the cation and the anion of the salt will very seldom be exactly the same (see mobility). Let us assume for this example that the cations move faster; consequently, an excess positive charge will accumulate on the low concentration side, while an excess negative charge will accumulate on the high concentration side of the junction due to the slow moving anions. This sets up a potential difference that will start an electromigration of the ions that will increase the net flux of the anions and decrease the net flux of the cations. In steady-sate conditions, the two ions will move at the same speed and a potential difference will be created between the two solutions. This "steady-sate" potential difference seems constant, but this is misleading because it slowly changes as the concentrations between the two solutions equalize. The diffusion process will "eventually" result in equal concentrations of the salt in the two solutions separated by the membrane, and the liquid-junction potential will vanish. For a simple case, the value of the liquid junction potential can be calculated by the so called "Henderson" equation.

Junction potential :

a small potential that exists at the interface between two electrolyte solutions that differ in composition.

Development of the junction potential caused by unequal mobilities of ions.

Mobilties of ions in water at 25oC:

Na+ : 5.19 × 10 –8 m2/sV K+ : 7.62 × 10 –8 Cl– : 7.91× 10 –8

Fig. 21-5. Schematic representation of a liquid junction showing the source of the junction potential, Ej. The length of the arrows corresponds to the relative mobilities of the ions.

Fig 21-4 Diagram of a silver/silver chloride electrode showing the parts of the electrode that produce the reference electrode potential Eref and the juction potential Ej

Liquid junction potential

Cells without liquid junction

Pt/H2(g), HCl/AgCl/Ag

Rare to have this type of cell

Cells with liquid junction

Glass frit

Salt bridge

Develop a potential by differential migration rates of the cation and anion.

Junction potential

HCl(0.1)/HCl(0.01) Ej = 40 mV (H+ faster than Cl– )

KCl(0.1)/KCl(0.01) Ej = –1.0 mV (K+ slower than Cl– )

Usually experimentally determine instrument response

Indicator electrodes

Metallic indicator electrode responds to analyte activity.

Electrode of the first type

Direct equilibrium with analyte

Ag for Ag+, Au for Au3+, etc

Potential described by Nernst equation.

As [M] , E

Note potential linearly related to log of the concentration !

Remember - indicator BY DEFINITION cathode

measurement theoretically under zero-current (steady state)

Electrode of the second type

Indirect equilibrium with analyte

M/MX/X–

Silver/Silver chloride for chloride

also Nernstian response

as [X–] , E

Inert Metallic electrode for Redox systems

Provides a surface for the electrochemistry to occur

Pt, Au, Pd, C

Xn+(aq) + ne = X(s)

Eind = Eo – (0.5916/n) log (1/[Xn+])

AgCl(s) + e = Ag(s) + Cl–(aq)

Eind = Eo – 0.5916 log [Cl–]

A plot of Equation 21-3 for an electrode of the first kind.

A plot of Equation 21-4 for an electrode of the second kind for Cl–.

Indicator electrodes

Indicator electrodes for potentiometric measurements are of two basic types, namely, metallic and membrane.

1) Metallic indicator electrodes :

develop a potential that is determined by the equilibrium position of redox half-reaction at the electrode surface.

First-order electrodes for cations :

A first order electrode is comprised of a metal immersed in a solution of its ions, such as silver wire dipping into a silver nitrate solution. Only a few metals such as silver, copper, mercury, lead , zinc, bismuth, cadmium and tin exhibit reversible half- reactions with their ions and are suitable for use as first order electrodes. Other metals, including iron, nickel, cobalt, tungsten, and chromium, develop nonreproducible potentials that are influenced by impurities and crystal irregularities in the solid and by oxide coatings on their surfaces. This nonreproducible behavior makes them unsatisfactory as first-order electrodes.

Example of first order metallic indicator electrodes

Use of Ag and calomel electrode

to measure [Ag+]

The outer compartment of the electrode is filled with KNO3, so there is no direct contact between Cl- in the inner compartment and Ag+ in the beaker

The reaction at the Ag indicator electrode is

The calomel reference half-cell reaction is

Ag+ + e- Ag(s) E⇌ o+ = 0.799 V

Hg2Cl2(s) + 2e- 2Hg(l) + 2 Cl ⇌ - E_ = 0.241 V

The reference potential is fixed at 0.241V

because the reference cell is saturated with KCl.

The Nernst equation for the entire cell is therefore

Potential of Ag | Ag+ Indicator electrode Potential of S.C.E reference electrode

[Ag+]

E = E+ - E– = {0.799-0.05916 log ( )} - {0.241}1

E = 0.558 – 0.05916 log (1/[Ag+])

Ideally, the voltage changes by 59.16mV (at 25 ) ℃for each factor-of-10 change in [Ag+]

Second-order electrodes for anions

A metal electrode can sometimes be indirectly responsive to the concentration of an anion that forms a precipitate or complex ion with cations of the metal.

Ex. 1. Silver electrode

The potential of a silver electrode will accurately reflect the concentration of

iodide ion in a solution that is saturated with silver iodide.

AgI(s) + e = Ag(s) + I– Eo = – 0.151V

E = – 0.151 – (0.05916/1) log [I–] = – 0.151 + (0.05916/1)pI

2. Mercury electrode for measuring the concentration of the EDTA anion Y4–. Mercury electrode responds in the presence of a small concentration of the stable EDTA complex of mercury(II).

HgY2– + 2e = Hg(l) + Y4– Eo = 0.21V E = 0.21 – (0.05916/2) log ([Y4–] /[HgY2–])

K = 0.21 – (0.05916/2) log (1 /[HgY2–]) E = K – (0.05916/2) log [Y4–] = K +(0.05916 / 2) pY

Ag(s) | AgCl[sat’d], KCl[xM] | | Fe2+,Fe3+) | Pt

Fe3++e = Fe2+ Eo = +0.770V

Ecell = Eindicator – Ereference

= {0.770 – (0.05916/1) log [Fe2+]/[Fe3+]} – {0.222 – (0.05916/1) log [Cl–]}

Inert electrodes Chemically inert conductors such as gold, platinum, or carbon that do not participate, directly, in the redox process are called inert electrodes. The potential developed at an inert electrode depends on the nature and concent-ration of the various redox reagents in the solution.

2) Membrane indicator electrodes

The potential developed at this type of electrode results from an unequal charge buildup at opposing surface of a special membrane. The charge at each surface is governed by the position of an equilibrium involving analyte ions, which, in turn, depends on the concentration of those ions in the solution.

The electrodes are categorized according to the type of membrane they employ :

glass,

polymer,

crystalline,

gas sensor. The first practical glass electrode. (Haber and Klemensiewcz, Z. Phys. Chem, 1909, 65, 385.

Membrane indicator electrodes

Glass membrane pH electrodes

The internal element consists of silver-silver chloride electrode immersed in a pH 7 buffer saturated with silver chloride. The thin, ion-selective glass membrane is fused to the bottom of a sturdy, nonresponsive glass tube so that the entire membrane can be submerged during measurements. When placed in a solution containing hydrogen ions, this electrode can be represented by the half-cell :

Ag(s) | AgCl[sat’d], Cl–(inside), H+(inside) | glass membrane | H+(outside)

E = Eo – (0.05916/1) log [Cl–] + (0.05916/1) log ([H+(outside)]/[H+

(inside)])

E = Q + (0.05916/1) log [H+(outside)]

pH Meter

pH meter is a volt meter that measures the electrical potential difference between a pH electrode and a reference electrode and displays the result in terms of pH value of the sample solution in which they are immersed

Introduction

The pH meter measures the pH of a solution using an ion-selective electrode (ISE) that responds to the H+ concentration of the solution. The pH electrode produces a voltage that is proportional to the concentration of the H+ concentration, and making measurements with a pH meter is therefore a form of potentiometry. The pH electrode is attached to control electronics which convert the voltage to a pH reading and displays it on a meter.

Instrumentation

A pH meter consists of a H+-selective membrane, an internal reference electrode, an external reference electrode, and a meter with control electronics and display. Commercial pH electrodes usually combine all electrodes into one unit that are then attached to the pH meter.

Typical electrode system for measuring pH. (a) Glass electrode (indicator) and saturated calomel electrode (reference) immersed in a solution of unknown pH. (b) Combination probe consisting of both an indicator glass electrode and a silver/silver chloride reference. A second silver/silver chloride electrode serves as the internal reference for the glass electrode. The two electrodes are arranged concentrically with the internal reference in the center and the external reference outside. The reference makes contact with the analyte solution through the glass frit or other suitable porous medium. Combination probes are the most common configuration of glass electrode and reference for measuring pH.

pH Meters

pH meter : A glass combination electrode

E = K – b (0.05916) log ( Ain / Aout)

K : Asymmetry potential

b : electromotive efficiency ( close to 1.00)

A : Activity of hydrogen ion

Composition of glass membranes

70% SiO2

30% CaO, BaO, Li2O, Na2O,

and/or Al2O3

Ion exchange process at glass membrane-solution interface:

Gl– + H+ = H+Gl–

(a) Cross-sectional view of a silicate glass structure. In addition to the three Si│O bonds shown, each silicon is bonded to an additional oxygen atom, either above or below the plane of the paper. (b) Model showing three-dimensional structure of amorphous silica with Na+ ion (large dark blue) and several H+ ions small dark blue incorporated.

Potential of the glass electrode

The potential difference across the glass pH electrode depends on the activity of H+ on each side of the glass membrane.

Em = V1 – V2 = (RT/F)lna1 – (RT/F)lna2

= Easym + 0.05916 log(a1 / a2)

if A1 = constant,

Em = K + 0.05916 loga1

= K – 0.05916 pH

Standardization at pH=7.00 , E = 0 V.

pH 4.00, E= 59.16 mV/pH unit

Potential profile across a glass membrane from the analyte solution to the internal reference solution. The reference electrode potentials are not shown.

Isopotential point

E(mV)

7

pH

100oC 74 mV/pH unit

0oC 54 mV/pH unit

14

500

0

Calibrating a glass electrode 1. Always keep the electrodes in distilled water, saturated KCl solution(3.7M) or buffer when not in

use.

2. Power ON. Switch to “STANDBY” : allow to warm for 30 min.

3. Rinse the electrode thoroughly with distilled water and then with pH 7.00 buffer solution.

Blot with clean tissue.

4. Determine the temperature of the buffer solution with a thermometer.

Adjust “TEMPERATURE” knob on the unit to the temperature.

5. Place the electrode in pH 7.00 (isopotential point) buffer solution.

Rotate the selector switch to “pH”. Wait for a stable display.

By using “CALIBRATION” knob, set the meter to the pH value of the buffer at its measured

temperature. Switch to “STANDBY”

6. Rinse the electrode thoroughly with distilled water and then with pH 4.00 buffer solution.

Blot with clean tissue.

7. Place the electrode in pH 4.00 buffer solution. Rotate the selector switch to “pH”.

Wait for a stable display. Using “SLOPE” knob, set the meter to the pH value of the buffer at its

measured temperature. Switch to “STANDBY”

Calibration of the Meters with pH 7 and pH 2 Buffers

1. Select the pH Mode and set the temperature control knob to 25°C. Adjust the cal 2 knob to read 100%.

2. Rinse the electrode with deionized water and blot dry using a piece of tissue (Shurwipes or Kimwipes are available in the labs).

3. Place the electrode in the solution of pH 7 buffer, allow the display to stabilize and, then, set the display to read 7 by adjusting cal 1. Remove the electrode from the buffer.

4. Rinse the electrode with deionized water and blot dry using a piece of tissue (Shurwipes or Kimwipes are available in the labs).

5. Place the electrode in the solution of pH 2 buffer, allow the display to stabilize and, then, set the display to read 2 by adjusting cal 2. Remove the electrode from the buffer.

6. Rinse the electrode with deionized water and blot dry using a piece of tissue (Shurwipes or Kimwipes, as before).

NOTE - Buffer solution are made available to you in individually labeled 2 oz. bottles. The buffers are to be used in these containers, only! Do not pour them into other containers at any time. After use, cap the bottles so that the buffers can be re-used.

Measuring pH

1. Make sure that the meter is set to the pH Mode and adjust the temperature to 25°C.

2. Place the electrode in the sample to be tested.

3. The pH of the solution appears in the display.

NOTE: Allow the display to stabilize before taking your reading!

4. Rinse the pH electrode and place it back in the storage solution.

Errors that affect pH measurements with glass electrode

1. The alkaline(sodium) error : low readings at pH values greater than 9

2. The acid error : somewhat high when the pH is less than about 0.5

3. Dehydration may cause erratic electrode performance.

4. Variation in junction potential : ~ 0.01 pH unit

5. Error in the pH of the standard buffer : 0.01 pH unit

Cleaning glass electrode :

1. Washing with 6M HCl

2. 20 w/w% aqueous ammonium bifluoride (NH4HF2)

Acid and alkaline errors for selected glass electrodes at 25℃. (From R.G. Bates, Determination of pH, 2nd ed., p. 365.. New York: Wiley, 1973.)

Ion-Selective Electrodes (ISE)

Introduction

An Ion-Selective Electrode (ISE) produces a potential that is proportional to the concentration of an analyte. Making measurements with an ISE is therefore a form of potentiometry. The most common ISE is the pH electrode, which contains a thin glass membrane that responds to the H+ concentration in a solution.

Theory

The potential difference across an ion-sensitive membrane is:

E = K – (2.303RT/nF)log(a)

where K is a constant to account for all other potentials, R is the gas constant, T is temperature, n is the number of electrons transferred, F is Faraday's constant, and a is the activity of the analyte ion. A plot of measured potential versus log(a) will therefore give a straight line.

ISEs are susceptible to several interferences. Samples and standards are therefore diluted 1:1 with total ionic strength adjuster and buffer (TISAB). The TISAB consists of 1 M NaCl to adjust the ionic strength, acetic acid/acetate buffer to control pH, and a metal complexing agent.

ISE (ion selective electrode)

Any electrode that preferentially responds to one ion species.

1. Glass membrane electrode : H+

2. Liquid membrane electrodes

3. Solid state and precipitate electrodes

4. Gas sensing electrodes

5. Enzyme electrodes

Selectivity coefficient

kX,Y = (response to Y) / (response to X)

General behavior of ISE

E = constant (0.05916/nX) log [AX +(kX,Y AY nX nY )]

Instrumentation

ISEs consist of the ion-selective membrane, an internal reference electrode, an external reference electrode, and a voltmeter. A typical meter is shown in the document on the pH meter. Commercial ISEs often combine the two electrodes into one unit that are then attached to a pH meter.

Schematic of an ISE measurement Picture of a commercial fluoride ISE

http://www.chemistry.adelaide.edu.au/external/Soc-Rel/Content/ise.htm

Liquid ISE

Ca ISE

Calcium didecylphosphate dissolved in dioctylphenylphosphonate

[(CH3(CH3)8CH2O)2PO2]2Ca 2[(CH3(CH3)8CH2O)2PO2]– + Ca2+

Diagram of a liquid-membrane electrode for Ca2+.

Comparison of a liquid-membrane calcium ion electrode with a glass pH electrode.

Photograph of a potassium liquid-ion exchanger microelectrode with 125 m of ion exchanger inside the tip. The magnification of the original photo was 400×.

A homemade liquid-membrane electrode.

Solid state crystalline membrane electrode

Migration of F– through LaF3 doped with EuF2.

Example: Fluoride (F-) electrode

Internal ref electrode

Ag/AgCl

Filling soln.

Aqueous NaCl + NaF

Membrane

LaF3 crystal disc

Applications

Electroplating industry, water treatment (fluoridation), toothpaste

Applications of ion selective electrodes

Ion-selective electrodes are used in a wide variety of applications for determining the concentrations of various ions in aqueous solutions. The following is a list of some of the main areas in which ISEs have been used.

Pollution Monitoring: CN, F, S, Cl, NO3 etc., in effluents, and natural waters.

Agriculture: NO3, Cl, NH4, K, Ca, I, CN in soils, plant material, fertilisers and feedstuffs.

Food Processing: NO3, NO2 in meat preservatives.

Salt content of meat, fish, dairy products, fruit juices, brewing solutions.

F in drinking water and other drinks.

Ca in dairy products and beer.

K in fruit juices and wine making.

Corrosive effect of NO3 in canned foods.

Detergent Manufacture: Ca, Ba, F for studying effects on water quality.

Paper Manufacture: S and Cl in pulping and recovery-cycle liquors.

Explosives: F, Cl, NO3 in explosive materials and combustion products.

Electroplating: F and Cl in etching baths; S in anodising baths.

Biomedical Laboratories: Ca, K, Cl in body fluids (blood, plasma, serum, sweat).

F in skeletal and dental studies.

Education and Research: Wide range of applications.

Semi-conductor

Imperfections or impurities in what are normally insulators may give rise to a temperature-dependent conductivity( metallic conductivity decreases with rise in temperature) arising because the highest occupied energy level is very close to an unoccupied level.

Classification specific resistance

semiconductor 10–4 ~ 107 ·m

conductor ~10–8

insulator 1012~1020

Elemental or intrinsic semiconductor : ten nine (99.99999999% purity)

II III IV V VI

B C

Al Si P S

Zn Ga Ge As

Cd In Sn Sb Se

Te

Compounds or extrinsic impurity semiconductor

IV&III or V SiC SiP SiAs SiSb, SiB, SiAl

III&V AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb

II&VI ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe

p-type and n-type semiconductor

Si

Si

Si

Si

Si

Si

SiSi

Si

Complete covalent

bond

SiSi

SiSi

Si

Si

Si

SiSiSi

Al

Displaced by trivalent(acceptor) impurity atom

Si

Si

Si

SiSi

Si P

holeConduction electron

Displaced by pentavalent(donor) impurity atom

carrier

Pure silicon crystal structure

p-type n-type

Diode : electron tube, evacuated glass or metal envelope containing two electrodes, a cathode and an anode. It is used as a rectifier and as a detector in electronic circuits such as radio and television receivers. When a positive voltage is applied to the anode (or plate), electrons emitted from the heated cathode flow to the plate and return to the cathode through an external…

Diode : p-n junction

hole Conduction electron

p n

pp nn

Forward bias

current flow

Reverse bias

No current flow

Depletion region

+ –

–

– +

+

Cathode mark

결핍영역 : 공핍층

Dr. John Bardeen, Dr. Walter Brattain, and Dr. William Shockley discovered the transistor effect and developed the first device in December, 1947, while the three were members of the technical staff at Bell Laboratories in Murray Hill, NJ. They were awarded the Nobel Prize in physics in 1956.

http://www.lucent.com/minds/transistor/ Copyright © 2002 Lucent Technologies. All rights reserved. *

Transistor

An active component of an electronic circuit which may be used as an amplifier, detector, or switch.

A transistor consists of a small block of semiconducting material to which at least three electrical contacts are made.

Transistors are of two general types, bipolar and field effect.

p-n-p type n-p-n type

emitter emitterbase collector collectorbase

C C

E E

Carrier: hole Carrier: conduction electron

B B

TransistorEmiter 와 Collector 사이 Base 에 불순물의 농도에 차이를 두어 Base 속에서 Carrier 를 가속시키는 전기장 ( 전계 ) 를 두어 고주파 특성이 좋아지게 만든 반도체 소자 . 기본적인 반도체 소자로서 Unipolar Transistor 와 Bipolar Transistor 로 나누어지며 , 증폭 , 발진 , 검파 또는 스위치 작용을 함 .

MOS(Metal Oxide Semiconductor)반도체 위에 산화막을 형성하고 그 위에 도선 ( 금속 ) 을 입힌 것으로 ,  N-MOS 와 P-MOS 등이 있음 .

MOS FET(Field Effect Transistor)전기장 ( 전계 ) 효과 TR 중에서 절연막을 산화막으로 형성시킨 절연 게이트형 FET 의 대표적인 것이다 .

FET( 전기장효과 트랜지스터 : 電界效果 Transistor : Field Effect Transistor)전기전도 ( 電氣傳導 ) 에 기여하는 Carrier 의 역할을 전자 또는 정공 ( 正孔 ) 의 어느 하나가 담당하는   Transistor. 전자도 정공도 Carrier 의 역할을 하는 Bipolar 에 대하여 Unipola( 單極 ) Transisor 라고 불리운다 .

FET 는 전기장효과 트랜지스트란 뜻으로 Field Effective Transistor 의 약자이며 생김새는 트랜지스트와 같지만 동작 원리는 일반 트랜지스트의 베이스에 해당하는 게이트 (Gate) 의 전류대신 전압의 크기에 따라 드레인 (Drain) 과 소스 (Source) 간에 흐르는 전류가 크게 변화한다 .

그후 개발된 MOSFET 는 대전력을 취급할 수 있는 관계로 급속히 보급이 확대 되었는데 제조방법에 따라 인헨스먼트 (Enhancement) 형과 디플리션 (Depletion) 형의 두가지가 있다 .

또한 MOSFET 의 전압 , 전류 특성곡선은 5 극 진공관과 비슷하기 때문에

FET 는 진공관의 특성을 많이 가지고 있다

MOSFET 가 가진 좋은 특성은 저전류시의 직선성이 좋고 스위칭 왜율이 낮은 장점과 바이폴라 트랜지스트의 대전류 공급 능력이 우수한 점을 합친

IGBT(Insulated Gate Bi-polar Transistor) 가 개발되어 사용되고 있다 .

Gate 1) 논리회로에서 몇 개의 Transistor 를 조립하여 만든 계수형 회로를 말하며 , 2 진 정보가 입력의 조합에 의해 형성되는 논리 회로 . 2) 반도체 장치에서 MOS  Transistor 에 입력을 가하기 위한 단자로서 Bipolar Transistor 의 Base 에 해당하는 단자 .

EmitterNPN, PNP 등 접합형 Transistor 에서 최초로 신호가 입력되는 반도체 부분 .

Collector접합 Transistor 에서 출력이 나오는 부분 .

Base Material( 기초제 )표면에 회로를 형성시킬 수 있는 비전도성 물질 .

미래의 세상에서는 탄소나노튜브 (carbon nanotube) 가 실리콘 마이크로칩 (silicon microchip) 을 대체할 것으로 보인다 . 2001 년 8 월 26 일판 온라인 버전 나노레터 (Nano Letter) 를 통해 공개된 연구보고서에 따르면 IBM 연구소 부설 T. J. 와슨 연구센터 (T. J. Watson Research Center) 소속의 피에치 에보리스 (Ph. Avouris) 와 브이 데릭 (V. Derycke), 알 마텔 (R. Martel), 제이 아펜절러 (J. Appenzeller) 로 구성된 연구팀은 단일막 탄소나노튜브 (Single wall carbon nanotube ; SWCNTs) 를 사용해서 장효과 트랜지스터 (field effect transister ; FET) 의 활성채널 (active cannel) 을 세계 최초로 제작하는데 성공했다 .

Field effect transistor

Gate

Drain

Source

p channel

MOSFET

n channel

A metal oxide field effect transistor (MOSFET).

(a) Cross-sectional diagram; (b) circuit symbol.

An ion-selctive field effect transistor (ISFET) for measuring pH.

Operation of a field effect transister.

(a) Nearly random distribution of holes and electrons in the base in the absence of gate potential.

(b) Positive gate potential attracts electrons that form a conductive channel beneath the gate. Current can flow through this channel between source and drain.

Operation of chemical-sensing field effect transistor. The transistor is coated with an insulating SiO2 layer and a second layer of SiN4 (silicon nitride), which is impervious to ions and improves electrical stability The circuit at the lower left adjusts the potential difference between the reference electrode and the source in response to changes in the analyte solution, such that a constant drain-source current is maintained.

CO2 gas sensing electrode

Response of a liquid-membrane electrode to variations in the concentration and activity of calcium ion.

Titration of 2.433mmol of chloride ion with 0.1000M silver nitrate.

(a) Titration curve. (b) First-derivative curve. (c) Second-derivative curve.

Apparatus for a potentiometric titration.

Volume of 0.1 N NaOH (mL)

0 5 10 15 20 25

pH

2

4

6

8

10

12

14

Experimental titration curve of 0.1 N HOAc with 0.1 N NaOH ( f = 0.9720).

CAT-Lab/SWU, Dong-Sun Lee

Volume of 0.1 N NaOH (mL)

0 5 10 15 20 25m

V-400

-300

-200

-100

0

100

200

300

Q& A

Thanks

Dong-Sun Lee / CAT / SWU