Physics chemistry and applications of nanostructures reviews and short notes proceedings of the international conference nanomeeting 2011

Carbon nanotubes, graphene, fullerenes and diamond-like nanostructures have been demonstrated to be of extended research and application interest along with traditional quantum dots and

REVIEWS AND SHORT NOTES

PHYSICS, CHEMISTRY AND APPLICATIONS OF NANOSTRUCTURES

PHYSICS, CHEMISTRY AND

APPLICATIONS OF NANOSTRUCTURES

REVIEWS AND SHORT NOTES

PROCEEDINGS OF INTERNATIONAL CONFERENCE NANOMEETING - 2011

PHYSICS, CHEMISTRY AND

APPLICATIONS OF NANOSTRUCTURES

REVIEWS AND SHORT NOTES Minsk, Belarus, 24 - 27 May 2011

editors Victor E Borisenko

Betarusian State University of Informatics and Radioelectronics, Belarus

S V Gaponenko

6 / Stepanov Institute of Physics,

National Academy of Sciences of Belarus, Belarus

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PHYSICS, CHEMISTRY AND APPLICATIONS OF NANOSTRUCTURES

Reviews and Short Notes to Nanomeeting–2011

Proceedings of the International Conference

INTERNATIONAL CONFERENCE

NANOMEETING-2011

Minsk, Belarus, May 24-27, 2011

ORGANIZERS

Ministry of Education of Belarus

Belarusian State University of Informatics and RadioelectronicsUniversité de la Méditerranée Aix-Marseille II

Nanyang Technological University

Centre National de la Recherche Scientifique

Belarusian Republican Foundation for Fundamental Research

INTERNATIONAL ORGANIZING COMMITTEE

FOREWORD

The Nobel Prize in Physics awarded in 2010 to A K Geim and K S Novoselov

“for groundbreaking experiments regarding the two-dimensional material

graphene” has stimulated an avalanche increase of the practical interest to

carbon based nanostructures It has inevitably influenced the thematic of contributions to the International conference on Physics, Chemistry and Applications of Nanostructures, NANOMEETING-2011 organized in Minsk (Belarus) for the period from May 24 to May 27, 2011 Carbon nanotubes, graphene, fullerenes and diamond-like nanostructures have been demonstrated to

be of extended research and application interest along with traditional quantum dots and quantum wells structures They have, of course, received a special attention and a large place in the Conference program Moreover, two hot topics

“Frontiers of Nanotechnologies and Nanomaterials in Energy Conversion" and

“Nanoelectromagnetics” have been covered within two special thematic sessions The most interesting results have been selected for presentation and discussion at the Conference

This book presents invited reviews and short notes of the contributions to the Conference The papers are arranged within the traditional sections of the previous publications: Physics of Nanostructures, Chemistry of Nanostructures, Nanotechnology and Nanostructure Based Devices, while “Frontiers of

“Nanoelectromagnetics” are presented separately The papers have been mainly preserved in their original form The camera-ready version of the Proceedings was prepared by V L Shaposhnikov and A V Krivosheeva The art design of the book cover belongs to V A Pushkarchuk

The Sponsors who kindly provided the financial support for the Conference are deeply acknowledged

CONTENTS

Foreword vii PHYSICS OF NANOSTRUCTURES

Functionalization of graphene with atomic species (invited) 3

R Larciprete, P Lacovig, S Gardonio, S Lizzit, A Baraldi

Photonic, electronic, and acoustic applications of

nanosilicon (invited) 11

N Koshida, T Ohta, Y Hirano, R Mentek, B Gelloz

Electron energy spectrum and optical phenomena in dense

arrays of Ge quantum dots in Si (invited) 19

A V Dvurechenskii, A I Yakimov

Electric transport properties and critical characteristics of

superconductor/ferromagnet nanostructures (invited) 27

V N Kushnir, S L Prischepa, C Cirillo, C Attanasio

Decay of the second-order population in quantum dots 35

S Mokhlespour, J E M Haverkort

Thermal formation of switching resistivity nanowires in

hafnium dioxide 39

A L Danilyuk, D B Migas, M A Danilyuk, V E Borisenko,

X Wu, N Raghavan, K L Pey

Rabi waves in one-dimensional quantum dot chain: effect of spatially inhomogeneous exciton-photon coupling 43

G Ya Slepyan, Y D Yerchak

Matrix calculations of critical states of superconductor/ferromagnet multilayers 47

V N Kushnir

Molecular dynamics simulation of polymers in nanoconfined

geometries 51

H Eslami

Full density matrix formalism applied to 1D exciton-polariton

transport 54

I G Savenko, E B Magnusson, I A Shelykh

Effective interactions in a hybrid polariton-electron system 58

O Kyriienko, I A Shelykh

An effect of demagnetizing field on the dynamic behavior of

domain walls in ferromagnetic nanowires 62

X.-P Ma, H.-G Piao, J.-H Shim, D.-H Kim, S K Oh, S.-C Yu

Theoretical simulation of electrostatical potential in

semiconductor-vacuum-metal nanostructures 66

L G Il’chenko, V V Lobanov, V V Il’chenko

Mechanical properties of thin films: a new analytical model 70

A A Khrutchinsky, S A Kuten, A L Pushkarchuk, V A Pushkarchuk,

A M Saad, A P Nizovtsev, S Ya Kilin

Surprising thermal effects during growth of carbon nanofibres

via “vapor–liquid–solid” route 81

S P Fisenko, S I Shabunya, V V Martynenko, S A Zhdanok

Influence of carbon nanotubes functionalized with -COOH groups

on the isothermal elastic modulus of water 84

V Korolovych

Raman characterization of self-organized planar graphite

layers on the top of carbon nanotube arrays 87

A Prudnikava, B Shulitski, V Labunov, M Shakerzadeh,

Tan Dunlin, Tay Beng Kang

First principles simulations on dissociative adsorption of methane

molecules upon nickel substrate resulting in a growth of nanotubes 91

Yu F Zhukovskii, E A Kotomin, S Piskunov

The I-V characteristic features of 2D-ordered vertically-oriented

carbon nanowires 95

G Gorokh, D Solovei, I Obukhov

Effect of low-temperature annealing on optical properties of

C 60 and C 70 thin films with nanosized metal overlayer 99

N L Dmitruk, O Yu Borkovskaya, D O Naumenko, I B Mamontova,

V A Pushkarchuk, A P Nizovtsev, A L Pushkarchuk, A B Filonov,

S A Kuten, S Ya Kilin

Maser effect in a Jahn Teller center: single substitutional nitrogen

atom in diamond 110

N A Poklonski, E F Kislyakov, O N Bubel’, S A Vyrko

Thermally stable phosphates filled with micro-sized boron compounds and carbon nanotubes: towards ionizing radiation shielding 114

P P Kuzhir, S A Maksimenko, A O Pliushch, K N Lapko,

A I Lesnikovich, V A Lomonosov, E A Frolova, P V Sedyshev,

V N Shevtsov, A S Kurilin, A G Kurenya, A N Okotrub

Geometrical models for bare boron nanotubes 118

L Chkhartishvili

Catalyst-free synthesis and characterization of boron nitride

nanotubes and whiskers 122

L L Sartinska, A A Frolov, M I Danylenko, I I Timofeeva,

V A Tin’kov

Stability of small boron nitride nanotubes 126

L Chkhartishvili, T Berberashvili, I Murusidze

Uniaxial compressive buckling of boron nitride nanotubes using

molecular dynamics simulation 130

S Ebrahimi-Nejad, A Shokuhfar, A Zare-Shahabadi, A Zolriasatein

Optical properties of silicon nanoclusters embedded in alumina

matrix 134

V L Shaposhnikov, A B Filonov

Band-gap modulation in Si nanowires by strain 138

D B Migas, V E Borisenko, Rusli, Wang Hong

Quantum-chemical analysis of formation energies and migration

barriers of intrinsic point defects in silicon nanowires 142

V Gusakov, J Gusakova, V P Markevich

Polarization-dependent optical properties of porous silicon based

multilayer structures and microcavities 146

A I Efimova, S A Dyakov, A I Bondar, L A Golovan

of Si/Mg 2 Si/Si(111) heterosystems 150

K N Galkin, N G Galkin

RDE and MBE techniques 154

N G Galkin, E A Chusovitin, K N Galkin, T S Shamirsaev,

A K Gutakovski, A V Latyshev

Effect of high pressure sintering temperature on phase composition

and fine structure of nanocrystalline Si 3 N 4 158

V S Urbanovich, A М Makei, L V Sudnik, L V Markova,

G P Okatova, P Klimczyk, L Jaworska

Influence of size effects on growth rate of Si nanowhiskers 162

V V Levdansky, J Smolik, V Zdimal

Synchrotron investigation of Si surface after low energy plasma

treatment in hydrogen and argon 165

S Yu Turishchev, V A Terekhov, E V Parinova, O V Korolik,

A V Mazanik, A K Fedotov

Diffusion of small vacancy clusters and their interaction with

oxygen atoms in silicon 169

V P Markevich, A R Peaker, L I Murin, S B Lastovskii

Excitation energy transfer from semiconductor quantum dots to

cyanine J-aggregates 173

D Savateeva, D Melnikau, V Lesnyak, N Gaponik, Y P Rakovich

Photoinduced long-distant superexchange electron transfer in

nanoscale porphyrin triads with covalently linked acceptors 177

E Zenkevich

Optical properties of cadmium selenide nanocrystals with

cadmium substitution by mercury 181

A Prudnikau, M Artemyev

FRET and non-FRET processes in nanoassemblies «quantum

dot-organic molecule» (bulk experiments and detection of

single objects) 185

E Zenkevich, T Blaudeck, D Kowerko, C von Borczyskowski,

F Cichos

Photoluminescence properties of cadmium selenide quantum dots 189

G Tselikov, V Timoshenko, S Dorofeev

Influence of polar environment on CdSe/ZnS nanocrystals:

Stark effect modelling 192

N Strekal, A Medzvedz, S Maskevich, O Kulakovich, A Orlova,

A Fedorov, A Baranov

Photo-induced processes in CdSe/ZnS quantum dots under

external electric field 196

L I Gurinovich, A P Stupak, S Ya Prislopski, S V Gaponenko,

M V Artemyev

TEM characterization of GaAs nanoislands on Si 200

C Frigeri, S Bietti, C Somaschini, N Koguchi, S Sanguinetti

Optical properties of quantum dots in a tilted wave laser 204

I G Savenko, N Yu Gordeev, O I Rumyantsev, A S Payusov

The anisotropy of electrical properties of InGaAs/GaAs

heterostructures with chains of InGaAs quantum dots 207

O V Vakulenko, S L Golovynskyi, S V Kondratenko

Heavy and light holes states mixing and electroluminescence

intensity increase in p-Al x Ga 1-x As/GaAs 1-y P y /n-Al x Ga 1-x As

nanostructures under uniaxial compression 211

E V Bogdanov, P S Marintsev, N Ya Minina, D E Mironov,

Micromagnetic study of temperature-dependent domain wall

depinning behavior in ferromagnetic nanowires 223

H.-G Piao, X.-P Ma, J.-H Shim, S.-C Yu, S K Oh, D.-H Kim

Dielectric properties of PbZr 0.54 Ti 0.46 O 3 in swift heavy ion tracks

of Si/SiO 2 nanostructures 226

A V Petrov, A A Klimsa, L I Gurskii, E V Telesh, K A Minin,

G Gerlach, G Suchaneck, B Adolphi

nanosized films 230

N A Kalanda, S E Demyanov, L V Kovalev, L I Gurskii,

E V Telesh, D A Kotov, V M Garamus, R Willumeit

of interaction between the components 234

E Ovodok, M Ivanovskaya, D Kotsikau, I Asarko

Structure and electron-energy characteristics of pyrolyzed

polyacrylonitrile monolayer with vacancies 238

I V Zaporotskova, O A Davletova, D I Polikarpov

Probing the structure of nanochannel arrays by electrostatic

force microscopy 241

P Murugaraj, N Kumar, T Jakubov, D E Mainwaring, R Siegele

Irradiation effect on structure and mechanical properties

of nanomaterials 245

R A Andrievski

A ferroelectric phase transition induced by oscillating electric

field in the presence of magnetic field in carbon nanotubes 263

M Belonenko, N Yanyushkina, N Lebedev

Effective medium model for a periodic array of metallic

carbon nanotubes and eigenwaves propagating in a

finite-thickness carbon nanotube slab 267

I Nefedov, S Tretyakov

Towards backward-wave negative-index nonlinear-optical

microdevices 270

A K Popov, S A Myslivets

Precise determination of the atomic structure of a nanotube

by electron diffraction (invited) 274

Ph Lambin

Theoretical simulation of electric properties of CNT-Me and

GNR-Me interconnects 283

Yu N Shunin, Yu F Zhukovskii, N Burlutskaya, S Bellucci

Cylindrical wave method for ideal and doped nanotubes 287

P N D’yachkov, D V Kutlubav, D V Makaev

Enhancement of the infrared absorption by biomolecules

adsorbed on single wall carbon nanotubes 291

G Dovbeshko, O Fesenko, O Gnatyuk, K Yakovkin, M V Shuba,

S A Maksimenko

Terahertz time domain spectroscopy of carbon nanotubes

composite 295

J Macutkevic, R Adomavicus, A Krotkus, G Valusis, A Poddubskaya,

V L Kuznetsov, I N Mazov, I A Simonova

Electrical properties and electromagnetic shielding effectiveness

of epoxy/SWCNT composites 299

V Ksenevich, T Veselova, P Kuzhir, S Bellucci, L Coderoni,

F Micciulla, I Sacco, G Rinaldi

Two-dimensional few cycle optical pulses in semiconductor carbon

nanotubes in the presence of a high-frequency electric field 303

N Yanyushkina, M Belonenko, N Lebedev

Electron beam instability in graphene 307

K Batrakov, V Soroko

First principles study of hydrogen-induced decoupling of epitaxial

graphene from SiC substrates 311

A Markevich, R Jones, S Öberg, P R Briddon

Scattering of the electromagnetic field by a dielectric nanotube

covered by a thin metal layer 315

D Ushakou, A M Nemilentsau, G Ya Slepyan, V V Sergentu

Anisotropy and electromagnetic properties of carbon nanotube

based deformed polymer composites in microwaves 319

D Bychanok, M Shuba, A Poddubskaya, A Pliushch, A Nemilentsau,

M Kanygin, A Kurenya, A Okotrub

CHEMISTRY OF NANOSTRUCTURES

Synthesis and characterization of cadmium phosphide nanocrystals

optically active in the visible to near-infrared 325

S G Hickey, S Miao, C Waurisch, A Eychmüller, B Rellinghaus

New aspects in the hot injection synthesis to provide large scale

high quality quantum dots 329

C Waurisch, L Liebscher, E Sperling, S G Hickey, A Eychmüller

Synthesis of cadmium sulfide coated magnetic nanoparticles 333

E M Semenova, S A Vorobyova, A I Lesnikovich

Optical and electrochemical properties of CdS and CdSe quantum

dots stabilized by polyethylenimine 337

A E Raevskaya, G Ya Grodzyuk, A L Stroyuk, S Ya Kuchmiy,

E A Streltsov, P V Chulkin, S M Rabchynski, G A Ragoisha

Silicate glasses with nanoparticles of CuInSeTe solid solution 341

I V Bodnar, N P Solovei, V S Gurin, A P Molochko

Borosilicate glass with lead selenide nanoparticles 345

G E Rachkovskaya, G B Zakharevich, E E Trusova,

А М Malyarevich, V S Gurin, V V Golubkov

Functionalization of silicon oxide nanostructures via covalent

binding of fluorescein dye molecules 349

T Baumgärtel, H Graaf, C von Borczyskowski, M Ara, H Tada

Magnetic Langmuir-Blodgett films with gluing properties 353

G K Zhavnerko, I V Paribok, V E Agabekov,

Soliman H Al-Khowaiter, Muhanna K A.-Almuhanna

Influence of synthesis conditions on size, morphology and structure

of iron oxides particles 357

A Filipovich, M Ivanovskaya, D Kotsikau, V Pankov

Ultrasound-assisted formation of metal based nanocomposites 361

E V Skorb, D V Andreeva

Optical and electrical conduction properties of polymer-metal

composites with gold and silver nanoparticles 365

A V Kukhta, E E Kolesnik, I N Kukhta, A E Pochtenny,

A V Misevich, I A Milevich, E M Semenova, E Sarantopoulou

Electroless nickel plating on silicate glass sensitized with Sn(II)

M N Nichick, S V Voitekhovich, O A Ivashkevich

UV-excitation 381

E V Frolova, G P Shevchenko, A P Stupak

Synthesis and spectral-luminescent properties of CuI nano-

G Aleksandrova, M Lesnichaya, Ju Myachin, B Trofimov

Hybrid composites based on chitosan/organosilan films and Au

nanoparticles 393

P Boltovets, S Sevostyanov

milling and hot pressing 396

A Zolriasatein, A Shokuhfar, M Ghadimi, S Ebrahimi-Nejad,

R A Khosroshahi, N Nemati

Tribological characteristics of monomolecular organic films 400

A E Salamianski, G K Zhavnerko, N V Karatay

Immersion displacement deposition of copper on porous silicon for

nanostructure fabrication 404

H Bandarenka, S Redko, P Nenzi, M Balucani

Fabrication and investigation of silicon nanoparticles for

applications in ultrasound therapy 408

L A Osminkina, M B Gongalsky, K P Tamarov, A P Sviridov,

R A Galkin, A V Motuzuk, V Yu Timoshenko, A A Kudryavtsev

From vapor-liquid-solid to wet chemically etched silicon nanowires 412

V Sivakov, F Voigt, F Talkenberg, B Hoffmann, G Brönstrup,

M Schreivogel, A Bochmann, M Kulmas, F Voigt, G Bauer,

M Pietsch, S Christiansen

Surface damage effects in ultrasonic cleaning of silicon wafers 416

L Steblenko, D Kalinichenko, A Nadtochiy, A Podolian,

O Korotchenkov

B Lalmi, J P Biberian, B Aufray

Application of nanomaterials in nanomedicine research 433

T Rakovich, A Prina-Mello, A Rakovich, S J Byrne, A Atzberger,

J E McCarthy, Y K Gun'ko, Y Volkov

Fabrication of graphene oxide using local anodic oxidation by

atomic force microscopy 437

Seung-Woong Lee, Bae Ho Park

ZnMgSSe/ZnSe graded-index superlattice waveguide

heterostructures with (Zn)CdSe quantum dot active region

for green laser application 440

A G Vainilovich, E V Lutsenko, V N Pavlovskii, G P Yablonskii,

I V Sedova, S V Sorokin, S V Gronin, S V Ivanov, P S Kop'ev,

Ahmed Alyamani

Nanoporous titania electrochemically formed at low temperatures 444

S Lazarouk, O Kupreeva, T Orekhovskaya, D Sasinovich,

F Arnaud d’Avitaya, N Rochdi

Fabrication of nanopowders of titanium silicides and their use

for water photodecomposition 448

А A Kovalevskii, A S Strogova, V V Tzibylsky

Vicinal Si(111) surfaces as nanotemplates for nanowires growth 451

S I Bozhko, A N Chaika, A M Ionov, D A Fokin, I F Sveklo

Thin film nanostructures prepared with laser ablation of

combined Ni-Pd targets 455

A Bagmut

Synthesis of quaternary TiZrAlN nanocomposite films by reactive

unbalanced magnetron sputtering 458

G Abadias, V V Uglov, S V Zlotski

Microwave-hydrothermal synthesis and photocatalytic activity

of nanodispersed zinc oxide 462

A E Baranchikov, A S Shaporev, V K Ivanov

Cryotreatment effect on the morphology of mesoporous ceria

prepared by sol-gel technique 466

E A Trusova, A A Khrushcheva, I V Zagainov, S V Kutsev,

N S Trutnev

Homogeneous precipitation of sub-10 nm

Ce 1-x R x O 2-δ (R = Pr, Nd, Sm, Eu, Gd, Yb) solid solutions 469

O S Ivanova, A E Baranchikov, V K Ivanov, E A Dolgopolova

Synthesis of Mn-oxides nanostructures and application in catalytic

degradation of dye 472

K A M Ahmed, K Huang

Heating effect during anodic fabrication of porous alumina at

high current densities 475

A A Leshok, P S Katsuba, V B Vysotski

Scanning force microscopy study of human mesenchymal

L V Kukharenko, S A Chizhik, E S Drozd, S V Syroezhkin,

L G Gelis, I V Lazareva, E A Medvedeva

NANOSTRUCTURE BASED DEVICES

Room temperature single electron transistors based on

silicon nanowires (invited) 489

Sun Yongshun, Rusli, Navab Singh

Single-electron transistors fabricated by field-emission-induced

electromigration (invited) 495

Jun-Ichi Shirakashi

A hybrid microresonator with spatially separated mass sensing

and optical detection area (invited) 504

J Kehrbusch, E A Ilin, P Bozek, B Schaaf, E Oesterschulze

Electronic devices using porous anodic aluminum oxide (invited) 512

E Hourdakis, A G Nassiopoulou

Nanosized metal and anodic oxide films with improved optical

features for displays and photonic devices 519

A Smirnov, A Stsiapanau, Abubakar Saddiq Mohammed, Y Mukha,

Ahmed Adnan Hadi, Mohammed Iqbal Dohah

Generation of microplasma from nanopores of zeolite in

semiconductor GaS discharge electronic devices 523

N N Lebedeva, V I Orbukh, E Koç, S Karakose, B G Salamov

Design of photocontrollable polyelectrolyte-based nanoengineered

container systems 527

E V Skorb, D V Sviridov, D G Shchukin, H M Möhwald

A single conical nanochannel in a polymer foil as sensitive

biochemical sensor in an electrochemical cell 531

W Ensinger, M Ali

Nano-pipette probe with separative ion detection 535

T Takami, J Wan Son, Joo-Kyung Lee, Bae Ho Park, T Kawai

Preparation of fine-grained ceramics for varistor application 539

K V Vokhmintcev, E A Trusova, E V Shelekhov, А Е Chalykh,

S A Pisarev

Influence of the submicron layer of the irradiation-induced

defects on the capacitance of silicon pn-diodes 543

N A Poklonski, N I Gorbachuk, A V Ermakova, S V Shpakovski,

V A Filipenia, V A Skuratov, A Wieck

Spin valves with the transport layer of a non-conjugated polymer 547

N V Vorob’eva, A N Lachinov, A A Lachinov

Topology optimization of 1.5 µm all-optical narrow-band light

modulator based on semiconductor nanoheterostructures 550

M V Ermolenko

FRONTIERS OF NANOTECHNOLOGIES AND NANOMATERIALS

IN ENERGY CONVERSION

Nanoscale simulations for energy storage related engineering

problems: the case study of nanoporous carbons under the

nanoscope (invited) 557

R J.-M Pellenq

Quantum dots for bioenergetics: exploration of the energy transfer

from nanocrystals to photosynthetic biological complexes (invited) 566

Advances in nanomaterials for proton exchange membrane fuel cells 588

S Cavaliere, D J Jones, J Rozière

Composite membranes based on SPEEK for polymer electrolyte

membrane fuel cells 592

M Luisa Di Vona, P Knauth, G Auer

Mechanical impulse generated by nanostructured silicon during

its combustion and explosion 596

S K Lazarouk, A V Dolbik, V A Labunov, V C Nguyen, K Pita,

CuO loaded SrTiO 3 nanoparticles: an efficient Pt free

photocatalyst for H 2 evolution from water 604

D N Bui, X L Zhao, S.-Z Kang, J Mu

Visible light photocatalytic activity of chromium-doped zinc

oxide nanoparticles 608

Y Yan, C C Li, X Q Li, S.-Z Kang, J Mu

Thin film layers and multilayer nanostructures for photovoltaic

applications 612

O Goncharova, V Gremenok

Effect of polyelectrolyte on adsorption and photocatalytic properties

of titanium dioxide/polycation modified cellulose fibers 616

PHYSICS OF NANOSTRUCTURES

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INVITED

FUNCTIONALIZATION OF GRAPHENE WITH ATOMIC

SPECIES

R LARCIPRETE

CNR - Institute for Complex Systems, UOS Tor Vergata, Roma, Italy

P LACOVIG, S GARDONIO, S LIZZIT

Elettra - Sincrotrone Trieste S.C.p.A, Trieste, Italy

A BARALDI

Physics Department and CENMAT, University of Trieste, and IOM-CNR, Trieste, Italy

A versatile method to modify the electronic structure and add functionalities to graphene

is to bind foreign atoms to the hexagonal carbon lattice We studied the room temperature chemisorption of oxygen atoms on graphene grown on Ir(111) by using high resolution X-ray photoemission and absorption spectroscopies to determine the adsorption configuration and the chemical structure of the oxidized graphene

1 Introduction

Graphene (GR), a material which combines high electron mobility with atomic thickness, has emerged as a promising candidate for future nanoelectronics [1] Its peculiar semimetallic character with valence and conduction bands crossing

at the Dirac point is mainly incompatible with the semiconducting behavior essential for controlling conductivity in GR based devices Therefore the presence of a gap appears often indispensable This requirement is launching a new approach, alternative to the physical patterning required for the fabrication

of C nanoribbons, that views GR as a macromolecule whose properties can be modified by attaching heteroatoms to the honeycomb scaffold By properly selecting the foreign species, the GR electronic structure as well as its chemical reactivity might be properly adjusted in order to respond to different technological challenges

Among the GR derived materials the most famous is graphane, obtained by bonding H atoms in top position on the C atoms on both sides of GR [2] In perfect graphane H chemisorption changes the sp2 into sp3 hybridization for all C atoms building up a material which is the 2D analog of diamond Density functional theory (DFT) calculations predict that graphane is a wide bandgap material [3], whereas for one side hydrogenated graphene a bandgap of 0.4 eV

has been observed experimentally [4] Very recently the substitution of H with F atoms has lead to the synthesis of fluorographene [5], the thinnest insulator ever produced, which is the 2D material analog of teflon Fluorographene is foreseen

to be more thermally stable than graphane due to the higher strength of the C-F with respect to the C-H bonds Also nitrogen substitutional doping in principle allows the graphene electronic structure to be controlled as N has roughly the same atomic radius, but possesses one electron more than C The extra electrons are expected to induce a n-type behavior of the π conjugated system, and indeed this effect has been observed in N doped GR sheets [6]

A further route for tailoring the GR electronic properties is offered by the functionalization with oxidizing surface groups [7] Fully oxidized GR behaves as an insulator while the loss of oxygen atoms results in a insulator-semiconductor-semimetal transition This means that it is possible to regulate the bandgap with the oxygen content [8] Graphene oxide is usually prepared by wet chemical processing, however efficient and controlled GR oxidation is achieved by exposing its surface to O atoms, which adsorb on the basal plane, at patch edges or in correspondence of unsaturated C-C bonds neighboring C vacancies or point defects Non equivalent adsorption sites lead to different bonding configurations and thus to modified thermal stability of the chemisorbed O atoms

Determining the chemical configuration, bond arrangement and structure of functionalized GR is essential for controlling gap height, transport properties and

to predict chemical and thermal properties In this context surface spectroscopies are unique tools to deepen the know-how on the electronic and chemical structure of the modified graphene Detailed characterizations are optimally carried out on the ordered and extended GR monolayers grown on transition metal surfaces, which show high structural quality with domains typically larger than the terraces of the metal support [9]

In this study we employed high resolution X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) with synchrotron radiation to follow the room temperature adsorption of O atoms on monolayer GR grown on Ir(111)

2 Experimental

The experiments were performed in the ultra high vacuum chamber (base pressure 8×10-11 mbar) of the SuperESCA beamline at the Elettra synchrotron radiation facility (Trieste, Italy) The Ir substrate was prepared by cycles of Ar+ sputtering at 1.5 keV, oxygen treatment between 600-1000 K and flash annealing

at 1473 K The quality of the Ir(111) surface was checked by measuring the Ir 4f7/2 surface core level shift (SCLS) and by monitoring the LEED pattern Graphene was grown by ethylene (C2H4) pyrolysis in several cycles consisting of dosing the molecules (15 L) on the metal surface heated at 623 K followed by a flash annealing to 1423 K Atomic oxygen was produced by a radio frequency plasma source (TECTRA, Gen2) equipped with an ion suppressing grid and an ion trap The oxidation was performed in consecutive steps The atomic source current and the O2 pressure were kept constant at 20 mA and 8×10-6 mbar, respectively The sample was maintained at room temperature and exposed to atomic oxygen for increasing time periods Oxidation was performed with the O source facing the back of the sample to minimize any possible damage by energetic ions Valence band and Ir4f7/2 core level spectra were measured at the photon energy of 130 eV, whereas C1s and O1s spectra were measured at the photon energy of 400 and 650 eV, respectively, with an overall energy resolution ranging from 40 to 150 meV For each spectrum the binding energy (BE) position was calibrated by measuring the Fermi level position of the Ir substrate The measurements were performed with the photon beam impinging at grazing incidence (70°) while the photoelectrons were collected at normal emission Near edge X-ray absorption spectroscopy (NEXAFS) was performed at the C1s threshold in the Auger yield mode, by collecting the electrons at kinetic energy

of 260 eV and at different incidence angles

3 Results and discussion

3.1 Graphene monolayer on Ir(111)

GR growth on Ir(111) was obtained by exposing the hot metal surface to ethylene molecules For this system it has been shown that in the initial stage of the GR growth and at low temperature (T ≤ 970 K) C atoms resulting from the hydrocarbon decomposition organize in dome shaped nanoislands, whose interaction with the Ir substrate takes place only at the cluster edges [10] At high temperature (T >1270 K) island diffusion and coalescence leads to the formation

of the quasi-free-standing graphene layer [11] The process is self-limiting because precursor dissociation is strongly suppressed once the metal surface is fully covered with carbon, so that the GR growth extinguishes after the completion of the first monolayer Fig 1a shows the Ir4f7/2 core level spectra measured on the clean Ir(111) surface and after the growth of the GR monolayer For the clean metal the surface component (S) exhibits a SCLS of -545 meV with respect to the bulk component (B) [12] This value is not appreciably

affected once Ir is covered by GR (SCLS = -535 meV), indicating that the interaction between Ir and GR is very weak [10] The C1s spectrum shown in Fig 1b consists of a single peak with a FWHM of 250 meV, equivalent to that measured on highly oriented pyrolitic graphite (HOPG) [13] The nearly free standing character of the GR layer is further confirmed by the excellent agreement found between the C1s intensity modulation measured for this system

as a function of the emission angle and due to photoelectron diffraction and the intensity modulation function simulated [14] for a flat, free-standing layer of graphene (see the inset in Fig 1b) [15]

Figure 1 High resolution (a) Ir4f 7/2 and (b) C1s core level spectra measured on the GR/Ir(111) interface The Ir4f 7/2 spectrum measured on the clean Ir(111) surface is shown for comparison For all spectra the best fitted curves obtained with Doniach-Šùnnjić functions convoluted with the Gaussians and the spectral components are also shown In the case of Ir4f 7/2 B and S indicate the bulk and the surface components The corresponding best fit parameters are: (bulk) Lorentzian width Γ LB= 200 meV, asymmetry αB =0.15, Gaussian width Γ G = 170 meV and BE= 60.87 eV; (surface) Γ L = 320 meV, αS =0.22, Γ GS= 90 meV and BE= 60.32 eV For the Ir4f 7/2 spectrum measured on the Ir(111) surface only the BE position of S changes slightly to 60.33 eV, while the other parameters remain the same For the C1s: Γ L =130 meV, α=0.093 and Γ G = 165 meV and BE=284.15 eV Inset: stereographic projection of the integrated photoemission intensity modulation [I(θ,φ)–I 0 (θ)]=I 0 (θ), where I 0 (θ) is the average value of each azimuthal scan, as a function of emission angle for scans taken at photon energy of 400 eV [15] The left slice

of the disc is the data; the right part is a calculation of the expected intensity [14]

3.2 Chemisorption of O atoms on GR/Ir(111)

Due to the low adsorption energy of molecular oxygen on sp2 carbon, O functionalization at RT cannot be obtained by exposure to O molecules Since

O2 dissociation occurs only on prismatic (armchair and zig-zag) planes, where the graphitic layers terminate with unsaturated bonds, the GR basal plane can be oxidized at RT exclusively by exposure to atomic O Alternatively, more reactive agents such as O plasma, ozone or acid solutions can be used

The most favorable adsorption site for O atoms interacting with GR is the bridge position over the C-C bonds, resulting in (1,2-ethers) out-of-plane epoxy structures (see Fig 2a) [16] It has been calculated that aligned epoxy clusters generate strain instabilities in the GR lattice which evolves by unzipping the C-C bonds at the basis of the epoxy groups and incorporating etheric O atoms in the

C network [17] Oxygen bonding to unsaturated C atoms at zigzag or armchair edges or neighboring vacancy sites forms semiquinone and carbonyl groups (see Fig 2a) or alternatively results in even more complex configurations as lactones, carboxylates, and anhydrides

In this study we have used high resolution XPS to follow the RT chemisorption of O atoms on the GR surface up to advanced oxidation stages Here we show the results obtained after prolonged exposure (75 min) to atomic oxygen, which for our experimental conditions corresponded nearly to the saturation of O chemisorption

Figure 2 (a) Scheme of different configurations arising for O atoms bonded to a graphene patch: epoxy groups and ethers containing single C-O bonds are represented at the center and on the left

of the patch, respectively, whereas O double bonded to terminal C atoms forming iquinone and semiquinone groups appear at the front and back edges (b) C1s, (c) O1s, and (d) Ir4f 7/2 core

The C1s, O1s and Ir4f7/2 core level spectra measured on the oxidized GR surface are shown in Fig 2 The O1s spectrum shows an intense peak at BE of 531.3 eV and a weak shoulder at lower BE of 529 eV According to the results reported for HOPG [18] and for C nanotubes [19] and in agreement with DFT calculations [18] the former is attributed to oxygen atoms in epoxy structures, while the low BE shoulder contains the contribution of O atoms forming double bonds with C in semiquinone, carbonyl or even in more complex oxidizing groups [18,19] Carbon atoms bonded to epoxy oxygens originate the dominant peak at 285.5 eV in the C1s spectrum, while the broadening of the main sp2 component is due to the presence of disordered regions and vacancies in the honeycomb scaffold The contribution arising from C atoms with double or triple

O bonds is revealed by the spectral intensity at BEs higher than 286.8 eV The formation of C-O-C ethers resulting from epoxy unzipping should manifest with the presence of components shifted by -0.3 ÷ -0.8 eV [20] and ~+1.2 eV [18], with respect to the epoxy peak in the C1s and O1s spectra, respectively We cannot rule out the contribution of small spectral components due to ethers, however their surface density has to be considered not significant because their eventual contribution, which should be evident in the O1s spectrum, cannot be disentangled from the dominant epoxy peak Furthermore, we find that on the GR/Ir(111) surface epoxy structure is stable up to advanced oxidation stages Since the theoretical calculations predicting epoxy instability concerned free standing GR patches, our different findings suggest an effective role of the metal substrate in stabilizing the epoxy structures on top of graphene In this respect the new component appearing at 60.66 eV (SCLS=210 meV) in the Ir4f7/2spectrum measured on the oxidized GR clearly points to a modification of the interaction between GR and the topmost Ir atoms induced by the chemisorbed

oxygen atoms (see Fig 2d)

The modification of the electronic structure in the oxidized GR is evident also in the valence band spectrum measured at normal emission which is compared in Fig 3a to the corresponding spectrum measured on the clean GR/Ir(111) surface The valence band spectrum measured on the Ir(111) surface

is also reported Before oxygen adsorption the π and the σ bands of graphene are clearly observed at 8 and 21 eV, superimposed to the attenuated Ir valence band After oxygen adsorption the O2s feature is observed at ∼25 eV and the σ band appears shifted and strongly damped, due to the modified bonding arrangement and charge distribution in the presence of chemisorbed oxygen As for the π band, it cannot be distinguished from the contribution of O-C-O and C=O bonds occurring mainly between 5 and 10 eV [19], and angle resolved measurements are needed to derive more precise information about the extent of π conjugation

still existing in the oxidized GR Complementary information is provided by the NEXAFS spectra reported in Fig 3b The main figure compares the C-K edge absorption spectra measured at grazing incidence (θinc = 70°) on GR before and after the exposure to O atoms

Figure 3 (a) Valence band spectra measured at normal emission on the clean Ir(111) crystal and on the pristine and oxidized Gr/Ir(111) surface (b) NEXAFS spectra measured at grazing incidence (θ = 70°) on GR/Ir(111) before and after the exposure to oxygen In the inset the NEXAFS spectra measured at normal (θ = 0°) and grazing (θ = 70°) emission on the oxidized GR are compared The narrow peak appearing at 285.5 eV in the pristine spectrum corresponds

to the transition from the C1s core level to the π* states in the conduction band This feature, although strongly broadened and attenuated can be still recognized

in the NEXAFS spectrum of the oxidized GR, indicating that some π conjugation

is still retained in the layer The increased intensity in the σ region with respect

to the pristine GR is likely due to the large number of out of plane O-C-O bonds forming the epoxy structures The transition to states of σ symmetry, strongly depleted at grazing incidence, becomes enhanced in the absorption spectrum measured at normal incidence (θ = 0°) and shown in the inset of Fig 3b The strong angular dependence that emerges from the comparison of the NEXAFS spectra measured at normal and grazing incidence, expresses the presence of a

sp2-like hexagonal structure also in the oxidized GR scaffold, likely in less oxidized domains, with the π and σ orbitals maintaining the same mutual orientation as in the pristine GR

4 Conclusion

The inclusion of foreign atoms in the GR lattice, bonded in top or bridge configurations on to the basal plane or incorporated in the hexagonal network, appears to be a versatile method to modify the electronic structure and add functionalities to this material Identifying the chemical structure of the GR derived materials is of outstanding importance in order to optimize their stability and performances We studied the chemisorption of O atoms on the nearly free-standing GR grown on Ir(111) Results show that up to advanced oxidation stages oxygen prefers to bind in bridge position over the C-C bonds which remain intact in the resulting epoxy structures This behavior attests the structural stability of GR towards the formation of unsaturated vacancies where oxygen incorporation in the lattice would be favored The formation of out of plane C-O-C σ bonds results in a strong depletion of the sp2 character of GR,

although residual regions still behaving as graphitic domains remain in the layer References

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2 D C Elias et al., Science 323, 610 (2009)

3 J O Sofo et al., Phys Rev B 75, 153401 (2007)

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5 R R Nair et al., Small 6, 2877 (2010)

6 D C Wei et al., Nano Lett 9, 1752 (2009)

7 Y Zhu et al., Adv Mater 22, 3906 (2010)

8 I Jung et al., Nano Lett 8, 4283 (2008)

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10 P Lacovig et al., Phys Rev Lett 103, 166101 (2009)

11 S Lizzit et al., Catal Today 154, 68 (2010)

12 M Bianchi et al., New J Phys 11, 063002 (2009)

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INVITED

PHOTONIC, ELECTRONIC, AND ACOUSTIC

APPLICATIONS OF NANOSILICON

N KOSHIDA, T OHTA, Y HIRANO, R MENTEK, B GELLOZ

Graduate School of Engineering, Tokyo Univ of Agri & Tech

2-24-16 Naka-cho, Koganei, 184-8588 Tokyo, Japan

The characteristic photonic, electronic, and acoustic functions of quantum-sized nanosilicon are presented along with the exploration of the device applications Based on the band gap control by appropriate oxidation, the luminescence band can be tuned from red to blue In heavily oxidized samples blue phosphorescence appears Nanosilicon also exhibits an avalanche photoconduction effect Other possible applications of nanosilicon are ballistic electron emitters and thermo-acoustic sound emitters

1 Introduction

Quantum-sized nanosilicon is a wide-gap semiconductor with useful photonic, electronic, and acoustic properties [1] There are many possibilities of the nanosilicon device being an emitter of visible light, ballistic electrons, and acoustic waves Band-gap controllability of nanosilicon is an additional attractive property that will be applicable to tunable photo sensing and photovoltaic conversion Nanosilicon diode with a well-controlled interfacial structure acts as an efficient ballistic electron emitter The complete thermal insulating property of the nanosilicon layer, on the other hand, makes it possible

to generate a significant acoustic pressure without any mechanical surface vibrations We report here the topics of the studies on physical characterizations and applications of nanosilicon

2 Photonics

2.1 Band gap control and blue phosphorescence

It has been confirmed by optical characterizations that the absorption edge of the anodized nanosilicon layer can be tuned from 1.7 to 2.4 eV by high-pressure water vapor annealing (HWA) treatments [2], as shown in Fig 1 The samples in this case were fabricated as self-standing nanosilicon membranes with various thicknesses (from 20 µm to 100 µm) Additional oxidation by rapid thermal oxidation (RTO) shifts the absorption toward the UV region

The luminescence properties of nanosilicon strongly depend on both the band gap and the quality of surface termination, because of its extremely large

surface area For making a quantum confinement effect clear in nanosilicon, the surface oxidation by HWA is very effective Actually, the HWA dramatically enhances the red-band photoluminescence (PL) intensity of nanosilicon (23 % in external quantum efficiency) [3,4] This is due to a significant decrease in non-radiative defects at the interface with relaxed high-quality thin oxide The consequent strong exciton confinement leads to efficient radiative recombination The electroluminescence (EL) was also significantly stabilized [5] after the HWA treatment by which carriers are injected steadily into luminescent nanosilicon dots through tunnel oxides

The further surface oxidation causes a blue shift in the PL band In the sample treated by RTO, the PL spectrum peak appears in the blue region, though there remains a red PL emission peak The spectroscopic behavior of PL dynamics and polarization memory suggests that the blue and red emissions relate to surface oxide and confined excitons, respectively [6] The blue PL shows a fast decay of nanoseconds even at low temperatures, whereas the red one shows a decay of microseconds

Under an appropriate combination of HWA with RTO, the blue PL peak becomes dominant with no red emission, and then a very slow phosphorescence with a decay time of few seconds appears [7], as shown Fig 2 In contrast to the conventional fast blue PL, the decay time reaches 1 s even at room temperature The result of Fourier transform infra-red (FTIR) spectroscopy for the RTO-treated sample indicates that the Si-Hx (x=1, 2, 3) stretching mode peaks disappear and the peaks corresponding to oxidation become apparent When that sample is subjected to HWA, noticeable changes are induced in both the peak position and the peak width of the absorption band representing the asymmetric stretching modes in Si-O-Si bridges [6] The HWA contributes to a significant improvement in oxide quality with a reduction of disorder in the oxide network

As-prepared

HWA

HWA + RTO RTO + HWA

Energy (eV)

Figure 2 Time dependence of blue phosphorescence spectra observed in oxidized nanosilicon

The observed extremely slow transition in the blue emission cannot be explained from the energy band picture The implication is that a molecular-like structure appears in nanosilicon network after RTO+HWA, and that the radiative recombination between discrete energy levels via triplets becomes dominant at low temperatures Note that the phosphorescent sample should be composed of nanosilicon dots with a diameter below 1 nm or less The phosphorescence intensity is almost constant in the range from 4 K to 175 K, while it is quenched through a thermal process with the activation energy of 0.29 eV at higher temperatures The excitation energy dependence of phosphorescence spectra suggests the existence of two excitation processes The broad spectral feature of phosphorescence is due to inhomogeneous broadening resulting from local disorder or different chemical around the emitting centers Possible application of phosphorescence is photon energy transfer from host matrix to doped guest (dye molecules or rare earth elements) Even in fast luminescent nanosilicon layers impregnated with rhodamine B, rhodamine 6G,

or both, energy transfer from red emission to doped dyes was suggested from analyses of the PL polarization memory [8,9] Energy transfer effect has clearly been observed in blue phosphorescent samples doped with dye molecules Rh110 (rhodamine 110) [10] Time-resolved experiments show that the energy transfer

to Rh110 takes place from the blue phosphorescence The ability of oxidized nanosilicon to harvest and transfer absorbed photon energy to a guest is promising for applications in optoelectronics and biology

2.2 Avalanche photoconduction

Controllable band gap of nanosilicon is important from a viewpoint of applications to photo-sensing and photovoltaic conversion Actually, the photoconduction effect has been studied for nanosilicon dot (3.1 nm in mean diameter) diodes under reverse bias voltages The nanosilicon films were fabricated on n-type Si wafers by sequential dry processing based on low-pressure chemical vapor deposition and subsequent thermal oxidation The experimental layer is a kind of nanosilicon-oxide composite

The photoconduction quantum efficiency under an incidence of monochromatic light (: 400 nm) rapidly increased with increasing electric field and reached 2400 % at an electric field of 9×105 V/cm at 77 K [11], as shown in Fig 3 The experimental data on the temperature, electric field, and sample thickness dependencies of the photocurrent suggest that the enhanced quantum efficiency is due to the field-induced avalanche multiplication of photo-excited carriers inside the nanosilicon dot layer Hot electrons are efficiently generated

by tunneling cascade through nanosilicon dot chains [12]

77K 200K 300K

3 Ballistic electron emission

3.1 Operation in vacuum

The hot electron generation in the nanosilicon layer mentioned above implies the possibility of the nanosilicon diode being an electron emitter In fact, when driven in vacuum, the nanosilicon diode uniformly emits quasi-ballistic electrons through the surface electrode [13] Due to the energetic and directional electron emission, this device is applicable to the exposure source for parallel electric beam lithography Actually the experiment was performed on a 1:1 electron imaging system mounted in a vacuum chamber The system was composed of a nanosiicon planar electron source with patterned emission windows, a target wafer, and electric and magnetic fields perpendicular to the target wafer The exposure successfully delineated fine lines with a resolution below 30 nm [14] The periodic submicron patterns were also uniformly delineated over the area of 2.8 mm square by one shot exposure [15] This technique will be useful as a tool of parallel nanofabrication

Another application of the ballistic cathode is a probing source for image pick-up [16] The emitter array was combined with an active-matrix driver circuit and with a high-gain avalanche rushing amorphous photoconductor (HARP) target Prototyped 2/3-inch image sensor showed an extremely high sensitivity with a wide dynamic range and high picture quality under low illumination levels below 0.3 lx The scaling of the image sensor with a sufficient dynamic range was achieved without affect on the sensitivity

3.2 Operation in gases

The the nanosilicon ballistic emitters in atmospheric gases have been demonstrated as a negative ion source in air [17] and a vacuum-ultraviolet (VUV) light generator in Xe gases [18] The former is based on that the mean energy of emitted electrons is close to the most probable electron energy for dissociative attachment of oxygen molecules (O2 + e-→ O + O-

) In the latter case, the electron incidence with 7-8 eV into Xe gas molecules gives rise to direct internal excitation followed by VUV light emission without any impact ionizations The emission spectrum measured under operation in 10 kPa Xe ambient showed peaks at 152 and 172 nm which originate from excimers relaxation The emitted VUV is easily transferred to visible light on a phosphor screen The observed effect is potentially applicable to mercury-free, efficient, and stable flat panel light sources

3.3 Operation in solutions

Another important advantage of the nanosilicon ballistic emitters is their compatibility with the operation in liquids In pure water and aqueous solutions, such emitter acts as a supplier of highly reducing electrons [19,20] leading to the generation of hydrogen gas through direct reduction of H+ ions at the emitting surface with no by-product such as oxygen This effect is also useful for control

of the solution’s electrochemical properties such as the pH value and dissolved

hydrogen content

The above-mentioned activity in solutions is further applicable to thin film deposition by the emitter operation in metal-salt solutions In CuSO4 solution, for instance, thin polycrystalline Cu films are uniformly deposited on the emitting area as shown in Fig 4 This is presumably due to the preferential reduction of Cu2+ ions at the interface [21] It was demonstrated that by using the device with patterned emission line windows, thin Cu nano-wires array can

be fabricated in parallel Multilayered deposition of thin metal films has been demonstrated by sequential emitter operation in different metal-salt solutions This technique is an alternative low-temperature wet process that will be applicable to the deposition of various thin solid films

Figure 4 Single drive of the nanosilicon electron emitter in a CuSO4 solution and optical image of the device surface around the emission area after operation

4 Thermo-acoustic emission

An almost complete thermal insulating property of the nanosilicon layer can be utilized for sound wave emission into air with no mechanical vibrations [22] The device is composed of a thin-film heater electrode, a nanosilicon layer, and

a single-crystalline silicon wafer When an ac or pulsed electrical power is introduced into the heater electrode, a significant sound pressure is generated by

a quick heat transfer in the region within the thermal diffusion length from the