middle east technical university department of metallurgical and materials engineering prof. dr....

MIDDLE EAST TECHNICAL UNIVERSITY

DEPARTMENT OF METALLURGICAL AND MATERIALS ENGINEERING

Prof. Dr. Macit ÖZENBAŞ

Surface Sciences Research Laboratory

Dept. of Metallurgical and Materials Eng.

Middle East Technical University

Phone : 0-312-210 25 32

Fax : 0-312-210 12 67

E-Mail : [email protected]



Main Activities in the Surface Sciences Research Laboratory :

Production of metallic and ceramic thin films by using different processing techniques such as PVD, CVD, and chemical solution deposition.

Microstructural and property characterization of these thin films by microscopy, diffraction, electrical, magnetic and optical characterization.



The stages of deposition of Se on a nickel substrate.

Tsubstrate = 70ºC

Magnification bar = 2 m



Se islands on sapphire and nickel substrates

Magnification bar = 1 m



Related studies on the formation of thin films :

Crystallization of Amorphous Selenium Thin Films

Adhesion of Thin Films

Amorphous to Crystalline Transition of Selenium Thin Films Deposited onto Aluminum Substrate

Effects of Annealing on Electrical Resistivity of Aluminum Thin Films

Effect of Surface Activation on the Adhesion Behaviour of Metallic Films



SUPERCONDUCTING THIN FILMS

In this study, high Tc superconducting thin films of Y-Ba-Cu-O system have been prepared by resistive evaporation of YF3, BaF2, and Cu powders using either one of two different methods, namely the mixed-powder method and the sequential-deposition method, and a subsequent multi-stage annealing. The substrates employed were polycrystalline -Al2O3 and single crystals of MgO (100), LaAlO3 (100), and SrTiO3 (100).



SEM micrograph of 2 m thick film grown onto -Al2O3 substrate

and annealed in dry oxygen.



Fully-automated measurement unit using four-terminal resistivity measurement technique.



Electrical Resistivity – Temperature behavior of 1 m thick film grown onto -Al2O3 substrate with a 0.15 m Cu buffer layer.



SEM micrograph of the 1 m thick films grown by the sequential-deposition method onto LaAlO3 (100) substrate.



Related studies on superconducting thin films :

Synthesis and Characterization of Superconducting Y-Ba-Cu-O Films Prepared by Sol-Gel Processing

Effect of Ni and Ti Substitution on the Superconducting Properties of YBa2Cu3O7-x System

Characterization of Superconducting Y-Ba-Cu-O Thin Films Prepared by Resistive Evaporation

Characterization of Superconducting Bi-Sr-Ca-Cu-O Films Prepared by Sol-Gel Processing



HOT FILAMENT ASSISTED CHEMICAL VAPOR DEPOSITION OF DIAMOND COATINGS

In this study, the gradual change in crystal structure and morphology of diamond to DLC during growth on Si (111) substrates were examined by HFCVD method. Filament temperature and flow rates were taken as constant in all experiments. C2H5OH/H2 ratio and deposition durations were changed for each sample Cubo-octahedron diamond morphology was observed in the initial stages of deposition. As the growth increased, diamond morphology changed to cauliflower structure.



Schematic drawing of the hot-filament CVD system



SEM micrographs of the diamond particles deposited on Si substrate at 650ºC for 1/2 and 2 hours (ethyl alcohol volume percent : 1 %)



SEM micrographs of the diamond particles deposited on Si substrate at 650ºC for 4 and 6 hours (ethyl alcohol volume percent : 1 %)



SEM micrographs of the diamond particles deposited on Si substrate at 650ºC for 6 hours (ethyl alcohol volume percent : 1 %)



SEM micrographs of the diamond particles deposited on Si substrate at 650ºC for 4 and 6 hours (ethyl alcohol volume percent : 1.3 %)



SEM micrograph of the diamond particles deposited on Si substrate at 650ºC for 4 hours (ethyl alcohol volume percent : 1.6 %)



Nucleation and growth kinetics of low-pressure diamond deposition on a non-reacting surface



FERROELECTRIC THIN FILMS

(COST 514 PROJECT)

In this study, ferroelectric Pb(Zr,Ti)O3 films and powders

were prepared from metal chlorides using sol-gel processing method. For powders; homogeneous precipitation from aqueous solution and for films; dip coating just before precipitation was applied in the presence of urea, (NH2)2CO. Pt-coated Si (111) wafers, Si wafers and -Al2O3 were

employed as substrates.



PZT powder prepared using urea, annelaed at 850ºC for 5 hours having spherical and fine particle size



SEM micrographs of PZT films on PT-coated Si substrates prepared by no urea and urea, annelaed at 850ºC for 5 hours



PZT FILMS ON METAL SUBSTRATES

High toughness of the substrate in some micromechanical applications.To avoid micromachining and brittle silicon structures, metal foils can be used as substrates.High frequency operation, low dielectric loss, low electrical series resistance, etc.The metal should have a high melting point.It should have a similar value of thermal expansion coefficient to PZT.It should have low reactivity with PZT.It should permit good adhesion to PZT.



SEM micrographs of PZT films on stainless steel showing the pyrochlore-perovskite transformation and the

crystallized film



PREPARATION AND PROPERTIES OF Ba1-

xSrxTiO3 FILMS DEPOSITED BY THE SOL-GEL TECHNIQUEBarium strontium titanate [BST : (Ba,Sr)TiO3] has been extensively studied for advanced dynamic random access memory (DRAM) and uncooled infrared detector applications

because of

its high dielectric constant and composition-dependent Curie temperature (from 30 to 400 K).



SEM micrograph of Ba0.8Sr0.2TiO3 film on Pt/Ti/SiO2/Si

substrate (1.3 m thick)



Dielectric properties of BST films on Pt/Ti/SiO2/Si substrates measured at 1

kHzFilm Composition

Thickness

(m)

Capacitance

(nF)

Dielectric Constant

Ba0.8Sr0.2TiO3 1.3

2.5

9.0

4.2

421.0

377.9

Ba0.75Sr0.25TiO3 1.2

1.5

19.0

12.2

820.4

658.5

Ba0.6Sr0.4TiO3 1.8

2.0

14.8

13.3

953.2

938.1



SUB-MICRON PATTERNING OF Pb(Zr0.52Ti0.48)O3 USING SOL-GEL PROCESSING

NSF PROJECT

To pattern piezoelectric ceramics on a variety of substrates

To pattern at the micron length scale

To fabricate micron-sized piezoelectric cantilever sensors

Gravimetric MeasurementsChemical SensingDamping Effects



Current Technology of Patterning Oxide Two steps of forming and patterning

•Uniform deposition by vapor phase techniques (PVD, CVD, MOCVD, RF Sputtering)•Photolithography and post-deposition etching

Disadvantages

•Expensive equipment and clean room environment•Non-uniform etching rates, etch resistant materials•One exposure per structure•Difficulties with sharp geometry



Schematic diagram of the micromolding in capillaries process used in this study

10 m

PZT Lines on Silver Foil

PZT

Silver

10 m

5 m

PZT

Low and high magnification SEM images of a micropatterned PZT net on a silicon substrate after annealing at 600C for 3 h.

SEM image of micropatterned PZT on platinum coated silicon wafer after annealing at 600C for 3 h.

PZT Lines on Silicon Substrate

5 m

Cross-sectional TEM images of micropatterned PZT lines on a silicon substrate: (A) bright field image of one PZT line; (B) dark field image of the same line; and (C) bright field image of an array of lines at low magnification. The insert shows the electron diffraction pattern for the perovskite phase at the zone axis of [011]. The dotted line in (C) corresponds to the interface between PZT lines and the Si substrate. The TEM sample was prepared by ion milling of a cross-sectioned sample that was annealed at 600°C for 3 h.

2 m

Pt Pb Zr

Ti Si Image

EDS of PZT Lines on Platinum coated Silicon Wafer

Electrical Characterization of Patterned PZT

E (kV/cm)

-150 -100 -50 0 50 100 150

Po

lari

zatio

n ( C

/cm

2 )

-100

-50

0

50

100

P-E hysteresis loop of patterned PZT film (2 m line widths) on platinized Si wafer, heat treated at 6000C for 3 hours.

Ferroelectric and dielectric properties of patterned PZT films on platinum coated (100) silicon wafers which were heat treated at 600 C, 3 h.

Pattern Type Ec (kV/cm) Pr (μC/cm2) Dielectrictan δ

at 1 kHz Constant (%)

Different line widths 41.96 38.94 560 5.73

2 μm line widths 52.36 28.66 421 5.14

1 μm line widths 48.40 26.53 426 5.28

E (kV/cm)

-150 -100 -50 0 50 100 150

Po

lari

zatio

n (

C/c

m2 )

-150

-100

-50

0

50

100

150

P-E hysteresis loop of patterned PZT film (2 m line widths) on stainless steel substrates, heat treated at 6000C for 3 hours.

Ferroelectric and dielectric properties of patterned PZT films on stainless steel substrates which were heat treated at 600 C, 3 h.

Pattern Type Ec (kV/cm) Pr (μC/cm2) Dielectrictan δ

at 1 kHz Constant (%)

Different line widths 20.87 12.48 416 5.64

2 μm line widths 19.25 16.22 534 5.12

1 μm line widths 30.00 14.09 363 6.46

PZT Microcantilever



PHOTOCATALYTIC TiO2 THIN FILMS BY CHEMICAL SOLUTION DEPOSITION

In this work, TiO2 thin films were prepared by using sol-gel processing on

soda-lime glass and silicon substrates. Precursor solutions for TiO2 films

were prepared by using the proper amounts of titanium tetraisopropoxide, diethanolamine and ethanol. The resulting alkoxide solution was kept standing at room temperature for hydrolysis reaction for 2 hours. The films were formed on the glass and silicon substrates from the precursor solution by spin coating at 2000 rpm in an ambient atmosphere. These films were dried at 300C for 10 minutes followed by a heat treatment cycle at 500C for 1 hour. The thickness of the TiO2 films was adjusted by repeating the

spin coating cycle before the final heat treatment. Finally, various amounts of polyethylene glycol (PEG) were added to the above solution to observe its effect on the film morphology.



SEM micrographs of TiO2 films deposited on Si substrates by spin coating showing the effect of the addition of PEG to yield pores to increase the photocatalytic activity.

middle east technical university department of metallurgical and materials engineering prof. dr....

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