by santosh reddy epuri - ufdcimages.uflib.ufl.edu · 1 growth of ultrathin samaria films on pt(111)...

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GROWTH OF ULTRATHIN SAMARIA FILMS ON Pt(111)

By

SANTOSH REDDY EPURI

A THESIS PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2013

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© 2013 Santosh Reddy Epuri

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To my family

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ACKNOWLEDGMENTS

I’m grateful to my advisor, Dr. Jason Weaver for his patience and support. I

would like to recognize the valuable contributions of Jin-Hao Zhang towards this

research work. I would like to thank Dr. Andreas Schaefer, William Cartas and other

research group members for their support. I’m also thankful to Dr. Helena Weaver for

agreeing to be on my defense committee. I gratefully acknowledge financial support for

this project provided by the National Science Foundation(NSF), Division of Chemistry,

Chemical Catalysis program through grant number 1026712.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS .................................................................................................. 4

LIST OF FIGURES .......................................................................................................... 6

LIST OF ABBREVIATIONS ............................................................................................. 7

ABSTRACT ..................................................................................................................... 8

CHAPTER

1 INTRODUCTION ...................................................................................................... 9

2 CURRENT STATE OF KNOWLEDGE.................................................................... 12

Ultra Thin Ceria Film on Pt(111) ............................................................................. 12 Ultra Thin Y2O3(111) Films on Pt(111) .................................................................... 14

3 GOALS ................................................................................................................... 15

4 EXPERIMENTAL METHODS ................................................................................. 16

5 RESULTS ............................................................................................................... 18

UHV Treatment ....................................................................................................... 23

Reoxidation ............................................................................................................. 25

6 CONCLUSIONS AND FUTURE WORK ................................................................. 27

LIST OF REFERENCES ............................................................................................... 28

BIOGRAPHICAL SKETCH ............................................................................................ 30

6

LIST OF FIGURES

Figure page 1-1 Rare Earth Consumption (REO) by Application.3 ............................................... 11

2-1 STM images of ceria film grown on Pt(111). ....................................................... 13

2-2 STM images of Y2O3 film grown on Pt(111). ....................................................... 14

5-1 Pt step heights in the presence of Sm2O3.. ......................................................... 18

5-2 LEED and STM images of ~0.6 ML Sm2O3 film grown on Pt(111). .................... 20


5-4 LEED and STM images of ~2.4 ML Sm2O3 film grown on Pt(111).. ................... 22

5-5 Plots of average island diameter and lattice constant ratio with increasing coverage. ............................................................................................................ 22


5-7 LEED and STM images of ~6 ML Sm2O3 film grown on Pt(111). ....................... 23

5-8 LEED and STM images of ~1.5 ML Sm2O3 film grown on Pt(111) followed by annealing in UHV. ............................................................................................... 24

5-9 LEED and STM images of ~2.4 ML Sm2O3 film grown on Pt(111) followed by annealing in UHV. ............................................................................................... 25

5-10 LEED and STM images of ~ 6 ML Sm2O3 film grown on Pt(111) followed by annealing in UHV. ............................................................................................... 25

5-11 LEED and STM images of Re-oxidized Sm2O3 film grown on Pt(111)................ 26

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LIST OF ABBREVIATIONS

AES Auger Electron Spectroscopy

LEED Low Energy Electron Diffraction

PVD Physical Vapor Deposition

REOS Rare Earth Oxides

STM Scanning Tunneling Microscopy

TPD Temperature Programmed Desorption

UHV Ultra High Vacuum

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the

Requirements for the Degree of Master of Science

GROWTH OF ULTRATHIN SAMARIA FILMS ON Pt(111)

By

Santosh Reddy Epuri

May 2013

Chair: Jason F. Weaver Major: Chemical Engineering

The growth of thin films of Sm2O3(111) on Pt(111) has been studied using

scanning tunneling microscopy(STM), low energy electron diffraction (LEED), and auger

electron spectroscopy(AES). The films were grown by physical vapor deposition of

samarium in a 5 X 10−7 Torr oxygen atmosphere. Continuous Sm2O3(111) films were

obtained by post-growth annealing at 1030 K. Furthermore, heating the low coverage

film in UHV causes it to partially reduce to form SmO(100). Re-oxidation of the film

reversed these changes along with improved morphology and ordering of the film.

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CHAPTER 1 INTRODUCTION

The rare earth oxides (REOs) find important applications in the catalysis, lighting

and electronics industries. Catalytic applications of interest include complete and partial

oxidation reactions, oxidative elimination, hydrogenation and dehydrogenation

reactions, coupling reactions and the selective reduction of NO, to name a few. Most

rare earth oxides are thermally stable, as well as chemically active. REOs exhibit

variable valence states along with high oxygen mobility within the oxide lattice. These

properties allow the REOs to actively participate in surface redox reactions whereby

lattice oxygen is exchanged with adsorbed reactants. REOs differ in their selectivity

toward partial vs complete oxidation due to variations in oxygen mobility and the ease of

reduction/oxidation among the REO series. Praseodymia and terbia have the highest

mobility within the REO series and can exist in multiple oxide phases, ranging from

sesquioxide(Ln2O3) to the dioxide(LnO2) including mixed oxide phases such as Pr6O11

and Tb4O7. This ability to switch between multiple oxide phases facilitates oxygen

exchange with adsorbates and promotes complete oxidation of adsorbed reactants by

ceria, praseodymia and terbia. On the other hand, REOs with lower oxygen mobility

exist predominantly in the sesquioxide form and have a tendency towards partial

oxidation of adsorbates.

We’re particularly interested in the oxidative coupling of methane (OCM) reaction

which provides a direct route for producing higher hydrocarbons from methane, and

thus avoiding the sequential steps needed in indirect routes such as CH4 reforming and

Fischer-Tropsch synthesis. One of the principal products of OCM is ethylene which is

used in products as diverse as food packaging, eyeglasses, cars, medical devices,

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lubricants, engine coolants and liquid crystal displays(LCDs). The ability to convert

methane to ethylene is highly attractive from an economic point of view because it has

an estimated market of $160 billion/year. Sesquioxides of certain lanthanides such as

samaria (Sm2O3), which do not form higher oxides, are effective in selectively promoting

CH4 coupling to ethane and ethylene, whereas ceria, praseodymia and terbia exhibit

much lower selectivity for the OCM, and instead tend to completely oxidize methane to

CO2 and H2O. However, the activity of samaria and similar lanthanides is relatively low

for the OCM. The factors which determine reaction selectivity of REOs are understood

only to a limited extent, with most of the model surface science studies focusing on

ceria. These contrasting catalytic properties within the REO series provide us

substantial motivation for pursuing a detailed understanding of their chemical properties.

Such an understanding would be crucial in the successful design of REO-based

catalysts for use in a variety of applications.

Here, we study the growth of Sm2O3 films on Pt(111) surface. We’ve chosen

platinum as substrate because of its thermal stability and high resistance towards

oxidation. Sm2O3 condenses in the bixbyite crystal structure. Bixbyite has a body

centered cubic unit cell with 80 atoms and is of space group Ia-3 symmetry. Sm2O3 has

a lattice parameter a of 10.93 Å.1,2 Sesquioxides like Dy2O3, In2O3, Pr2O3, La2O3 also

exhibit this crystal structure. The bixbyite unit cell can be viewed to consist of 16 fluorite

unit cells with a periodic arrangement of anion vacancies(one-fourth of the anion sites

are vacant). In the bulk, each Sm atom is six-fold coordinated to oxygen atoms. All

oxygen atoms have a tetrahedral coordination to four Sm neighbors. Therefore, similar

to the fluorite structure the (111) planes are expected to be the surfaces with lowest

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energy. The surface unit cell of a bulk-truncated Sm2O3(111) plane is hexagonal with a

surface lattice parameter of 15.6 Å. Sm2O3 is an insulator with a wide band gap of ~4.3

eV.4,5

The studies presented here aim at creating a surface science model system that

will enable studying surface properties of samaria. We show that thin samaria films

adopt a cubic bixbyite structure and the films expose the low energy (111) face. The

films exhibit a crystallographic relationship with the Pt(111) substrate. Using thin films

supported on a metal enabled us to perform scanning tunneling microscopy (STM) and

determine the surface structure of thin samaria films.

Figure 1-1.Rare Earth Consumption (REO) by Application.3

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CHAPTER 2 CURRENT STATE OF KNOWLEDGE

The rare earth elements oxidize with varying strength. Under suitable conditions,

all the rare earth elements form a sesquioxide. The tendency to promote partial or total

oxidation reactions is strongly influenced by the existing oxidation states and oxygen

mobility: While ceria (where 4+ is the most stable oxidation state) is a good catalyst for

total oxidation, samaria (where 3+ is the only stable oxidation state) seems to be the

most effective REO catalyst for oxidative coupling of methane. Despite the high

selectivity of samaria catalysts, the activity is too low for industrial applications.

The first step in the OCM reaction is the activation of methane by the formation of

a methyl radical. Oxides of cerium, praseodymium, terbium with high and multiple

oxidation states actively promote the surface reaction of these CH3 radicals and

transform them finally into CO2. On the other hand, CH3 radicals have less affinity

towards reacting with the surface of samarium sesquioxide resulting in a largely gas

phase reaction of these radicals to form coupling products. A couple of model REO thin

films on Pt(111) have been described in this chapter.

Ultra Thin Ceria Film on Pt(111)

CeO2 ultrathin films were grown on the Pt(111) surface by reactive deposition of

Ce using molecular or atomic oxygen as the oxidizing gas. High-temperature treatments

in O2 produced epitaxial structures with a very good quality in terms of morphology,

stoichiometry, and structure. The cerium oxide films have a very flat morphology with

terraces several tens of nanometers wide. The stoichiometry of the films is mainly CeO2,

and the concentration of Ce3+ ions in the film can be reversibly increased by

temperature treatments. The Ce3+ concentration can be minimized by the use of atomic

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oxygen instead of molecular oxygen as oxidizing gas during the growth. The surface

lattice parameter of the obtained ceria overlayers is smaller than the bulk one at all of

the investigated thicknesses. The defects have been characterized using STM and were

found to be more reactive than the terraces.8

Figure 2-1. STM images of ceria film grown on Pt(111). A) 2ML ceria sample as grown

(2 V, 0.15 nA). B) 0.2ML ceria sample annealed in O2 at 1040K(1V, 0.2 nA). C) Same as panel B (0.5 V, 0.2 nA). D) Sketch of the ceria/Pt system at low coverages with PtO2 islands of different thicknesses either below the ceria islands or on the bare substrate. E) 0.7ML ceria sample annealed in O2 at 1040K measured at two different biases (left 0.3V, 0.1 nA, right 1V, 0.1 nA). F) Atomically resolved images measured on the ceria islands of the sample shown in panels B and C (0.8 V, 0.2 nA). The different kinds of defects are evidenced-oxygen vacancy clusters (triangle, zoom in panel G), surface oxygen vacancies (circle, zoom in panel H), and subsurface oxygen vacancies (dashed circle, zoom in panel I) from Luches et al.6

A B C

D

E

F

G H I

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Ultra Thin Y2O3(111) Films on Pt(111)

Bulk-like yttria films of sub-nanometer thickness were grown on Pt(111). The

films exhibit a Y2O3(111)–1×1 surface with a strict in-plane orientation relationship with

respect to the Pt substrate, thus forming a mono-crystalline film. The surface structure

of the yttria films was determined as the Y2O3(111) bulk truncation. LEED and STM

images showed a large unit cell for the bixbyite structure. Furthermore, Y2O3(111)

surface has been observed to be highly active for adsorption of hydrogen.

Figure 2-2. STM images of Y2O3 film grown on Pt(111). A) Clean Pt(111) substrate. The

inset in A is the LEED (E=60 eV) pattern for the clean substrate. B) ~1.5 ML yttria deposited on Pt(111) at room temperature. This film is subsequently annealed to C) 500 °C, D) 600 °C and E) 700 °C. A 120° angle is drawn in E demonstrating the characteristic edge orientation. The line-profile along the indicated line in E is shown in F. All STM images shown are 25×25 nm2. A ball-and-stick model of a cross-section through the bixbyite structure is shown in G to indicate the layered-structure; red balls and light blue balls correspond to O and Y atoms, respectively from Tao et al.7

A B C

G

F

E D

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CHAPTER 3 GOALS

An essential aim of the project is the preparation of thin samaria films on a well-

defined metal substrate like Pt(111). The films will be grown by physical vapor

deposition(PVD) of the metal in an oxygen ambient. We will characterize the properties

of films prepared in different oxidation states and the thermal stability/phase

transformations of the films using in situ analytical tools like STM, LEED, AES and TPD.

Detailed characterization of the surfaces during thermal reduction/oxidation is important

for determining atomistic processes governing phase transformations. We’ll also be

focusing on the characterization of defect structures by STM, since they are expected to

play an important role in the adsorbate interactions and the phase transformations.

Apart from the pure films, we will also study how alkali doping affects the film properties

like surface structure, thermal stability etc.

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CHAPTER 4 EXPERIMENTAL METHODS

The experiments were performed in an ultra high vacuum (UHV) chamber with a

base pressure in the low 10−10 Torr range. The UHV system is equipped with a RHK

scanning tunneling microscope (STM), OCI low energy electron diffraction (LEED)

optics and Auger Spectrometer.

The Pt(111) crystal was prepared by cycles of Ar+ sputtering (1.5 keV) at 573 K

followed by annealing at 1000 K in UHV until a well-ordered Pt(111) pattern was

observed in low-energy electron diffraction (LEED) and impurities were below the

detection limit of Auger electron spectroscopy (AES). In order to remove minor carbon

contamination, cycles of annealing at 1030 K in 5 × 10-7 Torr of O2 were also performed.

After this procedure a sharp 1X1 pattern was observed for the Pt(111) substrate. STM

images of clean Pt(111) showed terraces with step edges. The step heights measured

were in the range of 1.80-2.00 Å against the reported value of 2.30 Å pointing to an

average error of ~17 %.10

The Pt substrate was held at 600 K, with the samarium metal evaporated from an

electron beam evaporator and with a background O2 pressure of 5 × 10-7 torr. This

partially formed oxide film was then annealed to 1030 K in the same O2 atmosphere for

10 minutes. The rate of evaporation was determined to be approximately 0.3 ML/min for

a flux current of 5 nA from AES.

We define one monolayer (ML) as 3.19 Å thick samaria layer, i.e. the separation

between two equivalent (111) cleavage planes of Sm2O3. All STM images were

recorded in constant current mode at room temperature with platinum-iridium tips. The

large scale STM images were acquired with bias voltages of 0.6 V for low coverage

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films and 1-2 V for thicker films with a tunneling current of 0.3-1 nA. Atomically resolved

images were obtained at bias voltages of 0.6 V, 0.01 V and -1.34 V.

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CHAPTER 5 RESULTS

Three primary modes of thin film growth at a crystal surface are Volmer-

Weber(VW) growth, Frank-van der Merwe(FM) growth and Stranski-Krastanov(SK)

growth. Sm2O3 thin films grow in SK mode on Pt(111). This is basically a layer-plus-

island growth mechanism. Initially, films of Sm2O3 are formed followed by growth

through nucleation and coalescence of Sm2O3 islands.

Figure 5-1 (B), (D) shows step profiles of macroscopic STM images (A), (C). The

Pt step heights with Sm2O3 present measure ~1.80-2.00 Å and are consistent with

those of the clean surface. Therefore, the error in our island height measurements

should range between 15-20 %.

Figure 5-1. Pt step heights in the presence of Sm2O3. A, C are macroscopic STM images of 10 sec(~0.05 ML) and 2 min(~0.6 ML) samaria deposition on Pt(111) followed by annealing in O2. B, D are the line profiles along the indicated lines in A, C respectively. E) Cross-section through the bixbyite structure.

3.19 Å

A B C

D E

2 Å

1.8 Å

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For a (111) oriented Sm2O3 film one may expect step heights of ~3.2 Å because

of the separation between oxygen–samarium–oxygen trilayers in the bixbyite crystal

structure, as is illustrated in figure 5-1 (E). Sm2O3 forms a 1X1 structure at low coverage

and with increasing coverage forms a 3X3 structure which seems to fade at higher

coverages as seen from the LEED images. Also, with increasing coverage the intensity

of Sm spots is increasing while that of Pt spots is decreasing due to decreased electron

scattering from Pt lattice. Thin Sm2O3 films exhibit a crystallographic relationship with

the Pt(111) substrate by exposing the low energy(111) surface.

Figure 5-2 shows the LEED and STM images of the surface after deposition of

~0.6 monolayer(ML) of samaria on Pt(111) substrate followed by post-annealing at 1030

K. The LEED pattern shows Samaria(111)-1X1 structure. Using the Pt(111) diffraction-

pattern as a reference enables us to calculate the ratio of lattice constants as

a*/b*=b/a=1.375. Using the lattice constant ratio, the lattice parameter of the samaria

film is determined as 1.375*2.775 = 3.81 Å. The average height of the islands observed

is ~1 Å while the average depth of the holes is ~0.9 Å. For samaria films with

insufficient thickness to cover the entire surface with a monolayer structure, areas of

pure Pt or Pt covered only with a disordered samaria wetting layer remain exposed. The

average diameter of the islands is ~3.3 nm.



K. The average height of the islands measure ~1.2 Å. The average diameter of the

islands is ~4.1 nm.

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K. The extra spots around samarium in the LEED pattern are most visible at this film

coverage. A preferential crystallographic orientation of the island edges is now

observed. The edges of the islands reveal characteristic structure, typically enclosing

angles of ~120°. Islands measuring heights of 1.2-1.5 Å and 3-3.5 Å are observed.

Island heights of 1.2-1.5 Å should be seen in the context of clean Pt surface having

steps measuring 1.8-2 Å which would approximately add up to the oxygen-samarium-

oxygen trilayer separation height.

Figure 5-2. LEED and STM images of ~0.6 ML Sm2O3 film grown on Pt(111). A) LEED (E=58 eV) pattern for the 2 min(~0.6 ML) deposition of samaria followed by annealing in O2. B, C are macroscopic STM images of the surface. D, E are the line profiles along the indicated lines in C.

The average diameter of the islands is ~6 nm. The atomic resolution of these

islands reveal a imperfect hexagonal structure with voids. The average Sm-Sm distance

1.2 Å

1.5 Å

B C

D E

A

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measured was ~3.2 Å which is in good agreement with 3.81 Å measured using LEED .

These images were scanned at a bias voltage of 0.6 V probing the unfilled states of Sm.

Figure 5-3. LEED and STM images of ~1.5 ML Sm2O3 film grown on Pt(111). A) LEED (E=48 eV) pattern for the 5 min(~1.5 ML) deposition of samaria followed by annealing in O2. B, C are macroscopic STM images of the surface. D) Line profile along the indicated line in C.



K. The LEED pattern shows fading of spots around samarium. The average diameter of

the islands is ~6.3 nm. Atomic resolution of an island show a hexagonal structure

consistent with the observation at a lower coverage. We did not observe any large unit

cell similar to that observed in the case of Y2O3 on Pt(111).7


~6 monolayer(ML) of samaria on Pt(111) substrate followed by post-annealing at 1030

~1.2 Å

A B

D

C

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K. Most of the surface is covered with at least a monolayer of samaria and typical island

heights measure ~3.5 Å.

Figure 5-4. LEED and STM images of ~2.4 ML Sm2O3 film grown on Pt(111). A) LEED (E=58 eV) pattern for the 8 min(~2.4 ML) deposition of samaria followed by annealing in O2. B, C are macroscopic STM images of the surface. D) Atomic resolution of the box shown in C. E) Line profile along the indicated line in C.

Figure 5-5. Plots of average island diameter and lattice constant ratio with increasing coverage.

~2 Å

A

D E

C B

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Figure 5-6. LEED and STM images of ~4.2 ML Sm2O3 film grown on Pt(111). A) LEED (E=52 eV) pattern for the 14 min(~4.2 ML) deposition of samaria followed by annealing in O2. B) Macroscopic STM image of the surface. C) Atomic resolution of one of the islands. D) Line profile along the indicated line in B.

Figure 5-7. LEED and STM images of ~6 ML Sm2O3 film grown on Pt(111). A) LEED (E=56 eV) pattern for the 20 min(~6 ML) deposition of samaria followed by annealing in O2. B) Macroscopic STM image of the surface. C) Line profile along the indicated line in B.

UHV Treatment

At a low coverage of Sm2O3, heating the Sm2O3 film in UHV for 30 min leads to

the formation of a partially reduced new structure. The LEED pattern shows satellite

spots with hexagonal symmetry around the Sm spots as seen in figures 5-8(A) & (B), 5-

9(A). This might be due to the formation of samaria-platinum alloy. Similar observation

~3.5 Å

~1.4 Å

A B C

D

C B A

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has been reported with ceria and platinum.6,11,12 STM images in figures 5-8(C) & 5-9(B)

show the surface cracking up with holes. The atomic resolution of one of these cracks at

a bias voltage of 0.9 mV show a square lattice structure that can be attributed to

SmO(100) as seen in figure 5-9(C). The average Sm-Sm distance measured were 3.1 Å

against an expected value of 3.55 Å.

Figure 5-8. LEED and STM images of ~1.5 ML Sm2O3 film grown on Pt(111) followed by annealing in UHV. A, B are LEED (E=64 eV & 39 eV) patterns for the 5 min(~1.5 ML) deposition of samaria. C) Macroscopic STM image of the surface. D) Atomic resolution of one of the islands on the surface.

There are instances of the co-existence of the hexagonal and square domains as

well as superimposed structures(Moire pattern-square+hexagonal). At a high coverage

of Sm2O3, we did not observe any reduced structure as seen in figure 5-10. One simple

explanation would be that the Sm2O3 layer is sufficiently thick enough so as to not

D

C B A

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expose the beneath SmO layer. One possible inference could be that the Pt-Sm

interface is responsible for this phenomenon.

Figure 5-9. LEED and STM images of ~2.4 ML Sm2O3 film grown on Pt(111) followed by annealing in UHV. A) LEED (E=58 eV) pattern for the 8 min(~2.4 ML) deposition of samaria. B) Macroscopic STM image of the surface. C) Atomic resolution of one of the cracks shown in B.

Figure 5-10. LEED and STM images of ~ 6 ML Sm2O3 film grown on Pt(111) followed by annealing in UHV. A, B are LEED (E=43 eV & 36 eV) patterns for the 20 min(~6 ML) deposition of samaria. C) Macroscopic STM image of the surface.

Reoxidation

Re-oxidation of the reduced surface reverses the change and goes back to the

hexagonal structure of Sm2O3 with changes in the morphology and ordering of the film

as seen in figure 5-11(B). But the most noticeable change is that the islands coalesce

and form larger islands. Typical enclosing angles are ~120o. The atomic resolution of an

island point towards a hexagonal structure as seen in figure 5-11(C).

A B C

A B C

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Figure 5-11. LEED and STM images of Re-oxidized Sm2O3 film grown on Pt(111). A) LEED (E=58 eV) pattern for the 8 min(~2.4 ML) deposition of samaria. B) Macroscopic STM image of the surface. C) Atomic resolution of one of the islands on the surface.

A B C

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CHAPTER 6 CONCLUSIONS AND FUTURE WORK

We have demonstrated that thin samaria films can be grown on Pt(111). The

films exhibit a strict in-plane orientation relationship with respect to the Pt substrate.

Adsorption studies of CO can be conducted on Sm2O3 films of different coverages as

well as on the reduced surface which will help us better understand the nature of the

holes. STM probe could be used to further investigate the surface defects and

vacancies along with their role in surface redox reactions including OCM reaction. The

demonstration of the formation of ordered thin films of samaria on a metal substrate will

allow using this system to investigate the chemical properties of samaria by surface

science techniques.

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LIST OF REFERENCES

(1) Adachi, G.; Imanaka, N. The Binary Rare Earth Oxides. Chem. Rev. 1998, 98, 1479-

1514.

(2) Villars, P.; Calvert, L. In Pearson's handbook of crystallographic data for intermetallic phases; American Society for Metals: 1985; Vol. 3, pp 4764-5000.

(3) Kingsnorth, D. In In Rare Earths: Facing New Challenges in the New Decade; SME Annual Meeting; Society for Mining, Metallurgy, and Exploration (SME): 2010;

(4) Dakhel, A. Dielectric and Optical Properties of Samarium Oxide Thin Films. J. Alloys Compounds 2004, 365, 233-239.

(5) Constantinescu, C.; Ion, V.; Galca, A. C.; Dinescu, M. Morphological, Optical and Electrical Properties of Samarium Oxide Thin Films. Thin Solid Films 2012, 520, 6393-6397.

(6) Luches, P.; Pagliuca, F.; Valeri, S. Morphology, Stoichiometry, and Interface Structure of CeO2 Ultrathin Films on Pt(111). J. Phys. Chem. C 2011, 115, 10718-

10726.

(7) Tao, J.; Batzill, M. Ultrathin Y2O3(111) Films on Pt(111) Substrates. Surf. Sci. 2011, 605, 1826-1833.

(8) Grinter, D. C.; Ithnin, R.; Pang, C. L.; Thornton, G. Defect Structure of Ultrathin Ceria Films on Pt(111): Atomic Views from Scanning Tunnelling Microscopy. J. Phys. Chem. C 2010, 114, 17036-17041.

(9) Dvorak, F.; Stetsovych, O.; Steger, M.; Cherradi, E.; Matolinova, I.; Tsud, N.; Skoda, M.; Skala, T.; Myslivecek, J.; Matolin, V. Adjusting Morphology and Surface Reduction of CeO2(111) Thin Films on Cu(111). J. Phys. Chem. C 2011, 115, 7496-7503.

(10) Zhang, L.; Kuhn, M.; Diebold, U.; Rodriguez, J. Thermal Stability of Ultrathin Cr Films on Pt(111). J Phys Chem B 1997, 101, 4588-4596.

(11) Baddeley, C.; Stephenson, A.; Hardacre, C.; Tikhov, M.; Lambert, R. Structural and Electronic Properties of Ce Overlayers and Low-Dimensional Pt-Ce Alloys on Pt{111}. Phys. Rev. B 1997, 56, 12589-12598.

(12) Essen, J. M.; Becker, C.; Wandelt, K. In In PtxCe1-x Surface Alloys on Pt(111): Structure and Adsorption; Conference - ICSFS-14 -; e-Journal of Surface Science and Nanotechnology: 2009; Vol. 7, pp 421-428.

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(13) Santos, D. M. F.; Saturnino, P. G.; Maccio, D.; Saccone, A.; Sequeira, C. A. C. Platinum-Rare Earth Intermetallic Alloys as Anode Electrocatalysts for Borohydride Oxidation. Catal. Today 2011, 170, 134-140.

(14) Eyring, L. In The binary rare earth oxides; Eyring, L., Gschneidner, K., Eds.; Handbook on the Physics and Chemistry of Rare Earths; Elsevier: 1979; Vol. 3, pp 337-399.

(15) Petit, L.; Svane, A.; Szotek, Z.; Temmerman, W. M. Electronic Structure of Rare Earth Oxides. Rare Earth Oxide Thin Films: Growth , Characterization , and Applications 2007, 106, 331-343.

(16) Unertl, W. In Physical Structure; Holloway, S., Richardson, N., Eds.; Handbook of Surface Science; Elsevier: 1996; Vol. 1, pp 271-360.

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BIOGRAPHICAL SKETCH

Santosh Reddy Epuri was born in Hanamkonda, Andhra Pradesh, India to

Sampath Reddy Epuri and Samatha Epuri. He graduated from FIITJEE Junior College,

Hyderabad in 2007 and received his bachelor’s degree in Chemical Engineering from

the National Institute of Technology(NIT), Warangal in 2011. He enrolled in the master’s

program at the University of Florida, Gainesville in the Fall of 2011. In January 2012, he

started working in Dr.Jason F. Weaver’s group performing surface science research.

by santosh reddy epuri - ufdcimages.uflib.ufl.edu · 1 growth of ultrathin samaria films on pt(111)...

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