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Fabrication of nano-structured materials and their applications [Elektronische Ressource] / Lindarti Purwaningsih

158 pages
Fabrication of nanostructured materials andtheir applicationsVon der Fakulta¨t fu¨r Mathematik, Informatik undNaturwissenschaften der RWTH Aachen Universityzur Erlangung des akademischen Grades einerDoktorin der Naturwissenschaften genehmigte Dissertationvorgelegt vonMaster of ScienceLindarti Purwaningsihaus Sragen, IndonesiaBerichter: Prof. Dr. Martin Mo¨llerProf. Dr. Joachim P. SpatzTag der mu¨ndlichen Pru¨fung: 12. Januar 2011Diese Dissertation ist auf den Internetseiten der Hochschulbibliothekonline verfu¨gbar.Fabrication of nanostructured materials andtheir applicationsDissertationaccepted by theFaculty of Mathematics, Computer Science, and the Natural Sciencesof the Rheinisch-Westf¨alische Technische Hochschule AachenUniversity, Germany for the degree ofDoctor of Natural SciencesbyMaster of ScienceLindarti Purwaningsihborn in Sragen, IndonesiaReferees: Prof. Dr. Martin Mo¨llerProf. Dr. Joachim P. SpatzOral examination: January 12, 2011This dissertation is available online in the university library.Lindarti PurwaningsihFabrication of nanostructuredmaterials and their applicationsD 82 (Diss. RWTH Aachen University, 2011)Max Planck Institute for Metals ResearchDepartment of New Materials and Biosystems, Stuttgart2011This dissertation is dedicated to my parents:Purwoatmojo & SunartiPeople who believe in education as a way on makinga better life and a better World.ivThe journey of life is to learn...
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Fabrication of nanostructured materials and
their applications
Von der Fakulta¨t fu¨r Mathematik, Informatik und
Naturwissenschaften der RWTH Aachen University
zur Erlangung des akademischen Grades einer
Doktorin der Naturwissenschaften genehmigte Dissertation
vorgelegt von
Master of Science
Lindarti Purwaningsih
aus Sragen, Indonesia
Berichter: Prof. Dr. Martin Mo¨ller
Prof. Dr. Joachim P. Spatz
Tag der mu¨ndlichen Pru¨fung: 12. Januar 2011
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek
online verfu¨gbar.Fabrication of nanostructured materials and
their applications
Dissertation
accepted by the
Faculty of Mathematics, Computer Science, and the Natural Sciences
of the Rheinisch-Westf¨alische Technische Hochschule Aachen
University, Germany for the degree of
Doctor of Natural Sciences
by
Master of Science
Lindarti Purwaningsih
born in Sragen, Indonesia
Referees: Prof. Dr. Martin Mo¨ller
Prof. Dr. Joachim P. Spatz
Oral examination: January 12, 2011
This dissertation is available online in the university library.Lindarti Purwaningsih
Fabrication of nanostructured
materials and their applications
D 82 (Diss. RWTH Aachen University, 2011)
Max Planck Institute for Metals Research
Department of New Materials and Biosystems, Stuttgart
2011This dissertation is dedicated to my parents:
Purwoatmojo & Sunarti
People who believe in education as a way on making
a better life and a better World.iv
The journey of life is to learn...
until we are wise enough to remember...
home.
-Aryani Willems-Contents
Summary 1
General introduction 3
General methods 5
2.1 Lithographies for nanostructure fabrication . . . . . . . . . . . . . . . . . . 5
2.2 Etching process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Wet etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Dry etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Scanning Electron Microscopy (SEM) . . . . . . . . . . . . . . . . . . . . . 9
2.4 Image analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.1 Voronoi diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4.2 Radial Distribution Function (RDF) . . . . . . . . . . . . . . . . . . 14
I Fabrication of nanopillar arrays and their applications 17
3 Introduction 19
3.1 The basic principle of antireflective surfaces . . . . . . . . . . . . . . . . . . 19
3.2 Cellular response to nanoscale topography . . . . . . . . . . . . . . . . . . . 22
3.3 Block copolymer micelle nanolithography (BCML) . . . . . . . . . . . . . . 23
4 Materials & methods 27
4.1 Fabrication of nanopillar arrays for antireflective surface applications . . . . 27
4.1.1 Synthesis of particle seeds inside the micellar cores . . . . . . . . . . 27
4.1.2 Nanoparticle enlargement by electroless deposition using hydroxy-
lamine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.1.3 Reactive Ion Etching (RIE) for the fabrication of high aspect ratio
nanopillars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.2 Synthesis of nanopillar arrays with gold on top for biological applications . 29
4.2.1 Synthesis of gold nanoparticle arrays . . . . . . . . . . . . . . . . . . 29
4.2.2 Light-assisted nanoparticles enlargement . . . . . . . . . . . . . . . . 29
4.2.3 RIE for fabrication of cone-shaped nanopillars . . . . . . . . . . . . 29
vvi Contents
5 Nanopillar arrays 31
5.1 Fabrication of gold nanoparticle etching masks by BCML . . . . . . . . . . 31
5.2 Quartz vs. glass nanopillars . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.3 Influence of the etching parameters on nanopillar profiles . . . . . . . . . . 38
5.4 Silica nanopillar with gold on top . . . . . . . . . . . . . . . . . . . . . . . . 41
6 Applications 47
6.1 Antireflective surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
6.2 Biological application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
7 Conclusions & Outlook 53
II Fabrication of particle and nanopore arrays and their applications 57
8 Introduction 59
8.1 Electrochemical biosensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8.2 Colloidal lithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
9 Materials & methods 65
9.1 Sensor chip fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.2 Colloidal lithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.3 Particle size reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
9.4 Particle removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
9.5 Reactive Ion Etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
10 Fabrication of particle and nanopore arrays 69
10.1 Particle arrays by colloidal lithography . . . . . . . . . . . . . . . . . . . . . 69
10.2 Tunable size of particle mask arrays . . . . . . . . . . . . . . . . . . . . . . 72
10.3 Nanoporous thin gold layers . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
10.4 Deep nanopore arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
11 Application 81
11.1 Electrochemical biosensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
11.2 Functionalization of nanopores . . . . . . . . . . . . . . . . . . . . . . . . . 84
12 Conclusions & outlook 87
III Porous silicon photonic crystal display 89
13 Introduction 91
13.1 Porous silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
13.1.1 Fabrication of porous silicon. . . . . . . . . . . . . . . . . . . . . . . 91
13.1.2 Reflectivity of porous silicon . . . . . . . . . . . . . . . . . . . . . . 93
13.2 Porous silicon photonic crystals . . . . . . . . . . . . . . . . . . . . . . . . . 94
13.2.1 Porous silicons display . . . . . . . . . . . . . . . . . . . . . . . . . . 95Contents vii
14 Materials & methods 97
14.1 Electrochemical etching (first layer - photonic crystal) . . . . . . . . . . . . 97
14.2 Surface modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
14.3 Electrochemical etching (second layer) . . . . . . . . . . . . . . . . . . . . . 98
14.4 Silver impregnation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
14.5 Electrochemical cell experiment . . . . . . . . . . . . . . . . . . . . . . . . . 99
14.6 Reflectivity measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
14.7 Fourier-Transform Infrared spectroscopy . . . . . . . . . . . . . . . . . . . . 100
15 Porous silicon photonic crystal displays 101
15.1 Preparation of porous silicon photonic crystal displays . . . . . . . . . . . . 101
15.2 Performance of photonic crystal display . . . . . . . . . . . . . . . . . . . . 108
16 Conclusions & outlook 111
List of figures 113
Bibliography 123
Acknowledgements 141
IV Appendix 143
Appendix 145
1 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
2 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
3 Computing the total surface area of cone-shaped nanostructures . . . . . . 147Summary
Advances in fabrication of nanostructured materials offer the promise of new multifunc-
tional systems. This is owing to the abundance of novel physical, chemical, and biological
properties that can be exhibited, making nanostructured materials a fundamentally excit-
ing and technologically relevant area of research. By manipulating structure and proper-
ties on the nanometer scale, an extensive range of structural and functional applications
become available. Nanostructured materials can achieve alternate functions (i.e., antire-
flection), in addition to nanoscale manipulations of other entities (e.g., cell attachment
platforms, or biosensors). In this work, the fabrication of nanostructured arrays has been
studied and their utility in a number of applications has been demonstrated. This thesis
is divided into three Parts; each Part details the fabrication and applications of one of the
nanostructure types: nanopillars, ordered nanopores and unordered nanopores.
In Part I, the fabrication and applications of nanopillar arrays are discussed. The fabri-
cation of the nanopillar arrays was investigated on diverse substrates using a combination
ofmethods: blockcopolymermicellelithography(BCML),reactiveionetching(RIE),and
particle enlargement techniques. BCML resulted in ordered gold nanoparticle arrays with
inter-particle spacing which was modified from 50 to 120 nm. The gold nanoparticles sub-
sequently acted as an etching mask during RIE, which removed the surrounding material
resultinginthe’nanopillar’structures. Anintermediatesteptoenlargethegoldnanoparti-
cleswasnecessaryforproducinghigheraspectrationanopillarsandproducinggold-topped
nanopillars (where the initial gold particle was not completely etched away during RIE).
The employment of this combination of techniques, in addition to the different substrate
materials, resulted in a vast variety of nanostructure profiles, e.g., conical structures on
glass and cylindrical structures on quartz. It was determined that the nanopillar struc-
tures were influenced not only by the chemical composition of the substrate, but also the
etching parameters of the RIE.
Ascell-attachmentsurfaces, gold-toppednanopillarswereusedduetotheabilityofgold
tobindcrucialproteinsnecessaryforcellularattachment. Withtheimplementationofsuch
a structure, which can be selectively functionalized to detect or catch certain cell targets
(e.g., cancer cells), versatile medical tools may be produced. As an antireflective surface,
the optical properties of substrates incorporating the nanopillar surfaces were compared
with commercially available unstructured substrates known for their optical properties
®(Suprasil ). The structured substrates were found to have better antireflective properties
compared to the unstructured substrates. Furthermore, the antireflective properties were
determined to depend on the nanopillar spacing, aspect ratio, and cross-sectional shape.
12 Summary
In Part II, the fabrication and applications of ordered nanopore arrays is given. Nano-
pore arrays with a wide range of pore diameters (100-800 nm), inter-pore distances (200
nmto1m),andporedepthsupto200nmweredevelopedusingacombinationofcolloidal
lithography (CL), thin film deposition, and RIE. Several CL methods were investigated
and one was chosen, the lifting up technique, that produced a hexagonal close-packed
array of polystyrene colloid particles. The close-packed particle arrays covered up to four
inches in diameter on the surface of a 200 nm-thick Si N insulating film bonded to a3 4
silicon wafer. The size of the particles was reduced using an oxygen plasma, producing
a separated array. The nanopore structures were initiated upon the deposition of a thin
layerofgoldovertheseparatedarrayofpolystyreneparticles. Theporesthatwereformed
aftertheremovalofthepolystyreneparticleswereextendedintotheSi N layerusingRIE,3 4
resultingindeepnanoporearrays. Theinter-poredistancecouldbeeasilycontrolledbythe
size of the initial particles used to generate the hexagonally close-packed particle arrays.
The nanopore diameters, in addition to being dependent on the initial particle size, were
also a function of the etching time for particle size reduction and the thickness of the gold
layer.
The applications studied for which the deep nanopore arrays may be used include elec-
trochemicalbiosensorsandbioassays. Nanoporearraysworkaselectrochemicalbiosensors
by integrating the redox current generated between the electrodes in each pore resulting
in amplified signal. Short circuits caused by collapse of the gold layer, the rough particle
mask, and the undercut etching are amongst challenges to overcome in the development
of the biosensor. This sensor may be embedded into a circuit produced using standard
silicon-based microtechnology. Here, this was achieved by assembling the nanopore ar-
ray directly onto micropatterns fabricated by conventional photolithography. Gold colloid
particles, due to its easy characterization, was used as a model biological recognition site.
Gold colloid particles were immobilized inside of the pores as a proof of principle that the
nanopore arrays may be used for bioassays. Enhanced selectivity would be possible by
incorporating many different biologically-important molecules.
Finally, in Part III, the feasibility of using a porous silicon photonic crystal to provide
an optical reflection for a display was investigated. Porous silicon was produced by elec-
trochemical etching of silicon. Its refractive index, and therefore the wavelength of light
reflected from its surface, depends on its porosity and on the thickness of the porous sil-
icon layer. To build the display, a silver-impregnated porous-silicon chip was sandwiched
between a sheet of aluminium foil and an indium tin oxide (ITO)-coated glass slide. The
pores were open to an ionic solution (consisting of tetrabutyl ammonium perchlorate and
silver nitrate in acetonitrile) which filled a small gap between the porous silicon and the
ITO layer. Through the ITO-coated glass slide (i.e., the screen), the reflected light from
the porous silicon was visible. An electrochemical cell was produced when a circuit was
created across the porous silicon with the aluminium foil as the anode and the ITO layer
as the cathode. A redox reaction was performed in the cell by applying a voltage through
theelectrodes. Thisreactionoxidizedthesilvermetalintheporesintoitsionandreduced
thesilverionfromthesolutionontotheITO-coatedglassslide, blockingthereflectedlight
from the porous silicon. The reaction was reversible upon changing the applied voltage,
resulting in silver removal from the ITO-coated glass, enhancing the intensity of the re-
flected light. Though complete reversibility was more difficult to demonstrate, the results
established the possibility of using porous silicon for a display.