Cao Z. (Ed.) Thin Film Growth: Physics, materials science and applications

Подождите немного. Документ загружается.

148 Thin ﬁlm growth

we change the azimuthal angles of the ux to mimic the substrate rotation

because the lattice cannot be rotated. The step of increasing and decreasing

this azimuthal angle is the parameter representing the substrate rotation

speed. In this simulation, the rotation speed is xed at 5000 particles per

step. With swing rotation, uniform nanostructured lms can be generated

in our simulation of ballistic sticking of oblique incident particles on seeds

(Ye and Lu, 2007b). The average tilted angle is 53.5 ± 0.3∞ as measured

from the cross-sectional images of the structures, which is very close to the

measurement in experiments. The structure grows at the beginning of the

simulation and then saturates at a later simulation time to a size of 184 ± 21

lattice units when measured from the top-view images. The growth of the

width R of the structures is depicted in Fig. 6.20 as a function of adjusted

simulation time for the swing rotation with different swing angles. From

Fig. 6.20, one can observe that the initial growth exponent is p ª 0.6 for all

the swing angles in the simulations, as shown in the inset of Fig. 6.20. We

believe that the reduction of the exponent p from 1.0 (as in the case of no

substrate rotation) to less than 0.6 is due to the substrate rotation. The global

shadowing affects the saturation of the width R

max

, where the well-separated

structures stop fanning out with an exponent p approaching 0 (Ye and Lu,

2007b). With the global shadowing effect, increasing the swing angles will

reduce the saturation width R

max

, as illustrated in the inset of Fig. 6.20.

6.6 Applications and future trends

The substrate rotation techniques can produce slanted nanorods of uniform

sizes, which enable the fabrication of complex nanodevices, for example,

(a) F = 4.4 ¥ 10

(b) F = 6.4 ¥ 10

6.19 Monte Carlo simulation of swing rotation at f = 90°.

ThinFilm-Zexian-06.indd 148 7/1/11 9:41:20 AM



149Silicon nanostructured ﬁlms grown on templated surfaces

arrays of nano-cantilevers. The arrays of slanted Si nanorods deposited on

templated surfaces have been used to measure the mechanical properties of

these nanorods. The cantilever system of atomic force microscope was used

to measure the response of the Si nanorods when forces are applied to them.

The results have been reported in the literature (Gaire et al., 2005). These

arrays of nanorods provide an ideal system for the study of the mechanical

properties of materials in nanometer size.

When a layer of slanted nanorods is deposited, the substrate can be turned

90∞ to deposit a second layer of slanted nanorods with the same geometry.

This can be continued for many layers. every four layers of these nanorods

can form a complete turn of a square spiral as shown in Fig. 6.21. From the

calculations, these spiral arrays possess a unique optical property where light

with certain wavelengths cannot penetrate through the lm (Toader and John,

2001). A system with this optical property is called a photonic crystal and

it has rich applications in controlling of light. Recently, Si spiral photonic

crystals have been deposited by the swing rotation technique (Ye et al., 2007)

and the ‘PhiSweep’ technique (Summers and Brett, 2008). The properties

of the photonic crystals were tested by optical measurement as well (Ye et

al., 2007). However, in experiments, the Si spiral photonic crystal structures

produced by oblique angle deposition cannot reach the optimized design. For

optimal geometrics of Si spiral photonic crystals, the tilted angle of each arm

Growth exponent p

max

(a.u.)

1.0

0.8

0.6

0.4

0.2

0.0

260

240

220

200

180

160

140

120

100

30 40 50 60 70 80 90

Swing angle f(°)

Growth exponent p

Saturated width R

max

f = 30°

f = 60°

f = 75°

f = 90°

5 ¥ 1 0

Adjusted simulation time t (number of particles)

Width R (a.u.)

400

350

300

250

200

150

100

6.20 Logarithmic plot of the width R as a function of the adjusted

simulation time with different swing angles. R is saturated at a

maximum value R

max

as indicated by the horizontal lines. The inset

is the measurement of the exponent p and the maximum width R

max

for different swing angles. (Source: Ye and Lu, 2007b, reprinted with

permission.)

ThinFilm-Zexian-06.indd 149 7/1/11 9:41:20 AM



150 Thin ﬁlm growth

of the structure should be as large as 65° with respect to the major axis of

the spirals (Toader and John, 2002). A maximum full band gap (about 16%

of the gap center frequency) can be achieved with this optimal Si structure.

Therefore, in the future, the growth condition of the photonic crystals should

be further explored to achieve the optimized photonic crystals. Some other

materials should be tested in order to fabricate the optimized structure.

On smooth surfaces, a layer of nanostructured thin lm consisting of

slanted nanorods has lower refractive index than a continuous lm due to

the porous nature of the lm (Xi et al., 2005). The index can be varied by

changing the orientation of the nanorods. It has been tested that the stacking

of multiple layers of nanostructured thin lms with various refractive indices

has a very low reectance and can potentially be used as an anti-reector in

several applications (Xi et al., 2007). More discussion will be presented later

in this book. Although the layered lms were deposited by oblique angle

deposition at different incident angles, it is reasonable to extend this study

using substrate rotation techniques. We would expect that the anti-reection

lms are much more uniform and the refractive indices are able to be ne

tuned.

In this chapter, we found that the dominant mechanism of fan-out growth

is ballistic sticking that comes from the inter-atomic interactions at the atomic

level. However, Monte Carlo simulation has no real dimension, so a full

1000 nm

(a)

(c)

(b)

(d)

6.21 Square spirals prepared by the swing rotation on W pillars.

(a) and (b) are the top-view and cross-sectional images of the spirals

deposited on the triangular lattice. (c) and (d) are the top-view and

cross-sectional images of the spirals deposited on the square lattice.

(Source: Ye et al., 2005, reprinted with permission.)

ThinFilm-Zexian-06.indd 150 7/1/11 9:41:21 AM



151Silicon nanostructured ﬁlms grown on templated surfaces

picture of the interactions between particles cannot be simulated. Therefore,

molecular dynamics simulation might be able to handle the inter-atomic

interactions. However, the system size in a typical molecular dynamics

simulation is too small for the deposition of atoms on arrays of seeds. It seems

that a multiscale simulation has to be developed for a better understanding

of the effect of ballistic sticking in a large ensemble of atoms. In the present

Monte Carlo simulation model, a simple cubic lattice is used. The extension

of this simulation into other lattice structures should be interesting.

6.7 References

Ablemann L and Lodder C (1997), ‘Oblique evaporation and surface diffusion’, Thin

Solid Films, 305, 1–21.

Amar J G and Family F (1990), ‘Phase transition in a restricted solid-on-solid surface-

growth model in 2+1 dimensions’, Phys Rev Lett, 64, 543–546.

Barabasi A L and Stanley H e (1995), Fractal Concepts in Surface Growth, New York,

Cambridge University Press.

Castez M F and Salvarezza R C (2006), ‘Modeling growth from the vapor and thermal

annealing on micro- and nanopatterned substrates’, Phys Rev E, 73, 011607.

Dew S K, Smy T and Brett M J (1992), ‘Simulation of elevated temperature aluminum

metallization using SIMBAD’, IEEE Trans Commun, 39, 1599–1606.

Gaire C, Ye D-X, Tang F, Picu R C, Wang G-C and Lu T-M (2005), ‘A mechanical testing

of isolated amorphous Si slanted nanorods’, J Nanosci Nanotechnol, 5, 1893–1897.

Geszti O, Gosztola L and Seyfried E (1986), ‘Cross-sectional transmission electron

microscopy study of obliquely evaporated silicon oxide thin lms’, Thin Solid Films,

136, L35–L38.

Gish D A, Summers M A and Brett M J (2006), ‘Morphology of periodic nanostructures

for photonic crystals grown by glancing angle deposition’, Photon Nanostruct, 4,

23–29.

Hashimoto T, Okamoto K, Hara K, Kamiya M and Fujiwara H (1982), ‘Columnar

structure and texture of iron lms evaporated at oblique incidence’, Thin Solid Films,

91, 145–154.

Hawkeye M M and Brett M J (2007), ‘Glancing angle deposition: fabrication, properties,

and applications of micro- and nanostructured thin lms’, J Vac Sci Technol A, 25,

1317–1335.

Horn M W, Pickett M D, Messier R and Lakhtakia A (2004a), ‘Selective growth of sculptured

nanowires on microlithographic lattices’, J Vac Sci Technol, 22, 3426–3430.

Horn M W, Pickett M D, Messier R and Lakhtakia A (2004b), ‘Blending of nanoscale and

microscale in uniform large-area sculptured thin-lm architectures’, Nanotechnology,

15, 303–36.

Imry Y (2002), Introduction to Mesoscopic Physics, 2nd ed, New York, Oxford University

Press.

Jensen M O and Brett M J (2005), ‘Porosity engineering in glancing angle deposition

thin lms’, Appl Phys A, 80, 763–768.

Joannopoulos J D, Meade R D and Winn J N (1995), Photonic Crystals: Molding the

Flow of Light, Princeton, NJ, Princeton University Press.

Johnson M D, Orme C, Hunt A W, Graff D, Sudijono J, Sander L M and Orr B G

ThinFilm-Zexian-06.indd 151 7/1/11 9:41:21 AM



152 Thin ﬁlm growth

(1994), ‘Stable and unstable growth in molecular beam epitaxy’, Phys Rev Lett, 72,

116–119.

Kardar M, Parisi G and Zhang Y C (1989), ‘Dynamic scaling of growing interfaces’,

Phys Rev Lett, 56, 889–892.

Kennedy S R, Brett M J, Toader O and John S (2002), ‘Fabrication of tetragonal square

spiral photonic crystals’, Nano Lett, 2, 59–62.

Kessler D A, Levine H and Sander L M (1992), ‘Molecular-beam epitaxial growth and

surface diffusion’, Phys Rev Lett, 69, 100–103.

Kim J M and Kosterlitz J M (1989), ‘Growth in a restricted solid-on-solid model’, Phys

Rev Lett, 62, 2289–2292.

Krug J and Meakin P (1991), ‘Columnar growth in oblique incidence ballistic deposition:

Faceting, noise reduction, and mean-eld theory’, Phys Rev A, 43, 900–919.

Lakhtakia A and Weiglhofer W S (1995), ‘On light propagation in helicoidal bianisotropic

mediums’, Proc R Soc London Ser A, 448, 419–437.

Leamy H J, Gilmer G M and Dirks A G (1980), ‘The microstructure of vapor deposited

thin lms’, Current Topics in Mat Sci, 6, 309–344.

Liang S and Kadanoff L P (1985), ‘Scaling in a ballistic aggregation model’, Phys Rev

A, 31, 2628–2630.

Limaye A V and Amritkar R E (1986), ‘Theory of growth of ballistic aggregates’, Phys

Rev A, 34, 5085–5090.

Luedtke W D and Landman U (1989), ‘Molecular-dynamics studies of the growth

modes and structure of amorphous silicon lms via atom deposition’, Phys Rev B,

40, 11733–11746.

Lu T-M, Ye D-X, Karabacak T and Wang G-C (2005), ‘Physical self-assembly and

nano-patterning’, Mat Res Soc Symp Proc, 849, KK8.4.1–KK8.4.6.

Malac M, Egerton R F, Brett M J and Dick B (1997), ‘Fabrication of submicrometer

regular arrays of pillars and helices’, J Vac Sci Technol, 17, 2671–2674.

Marsili M, Maritan A, Toigo F and Banavar J R (1996), ‘Stochastic growth equations

and reparametrization invariance’, Rev Mod Phys, 68, 963–983.

Meakin P (1998), Fractals, Scaling and Growth far from Equilibrium, New York,

Cambridge University Press.

Meakin P and Krug J (1990), ‘Columnar microstructure in three-dimensional ballistic

deposition’, Europhys Lett, 11, 7–12.

Meakin P and Krug J (1992), ‘Three-dimensional ballistic deposition at oblique incidence’,

Phys Rev A, 46, 3390–3399.

Mei S-N and Lu T-M (1988), ‘A high ionization efciency source for partially ionized

beam deposition’, J Vac Sci Technol A, 6, 9–11.

Nakhodkin N G and Shaldervan A I (1972), ‘Effect of vapour incidence angles on prole

and properties of condensed lms’, Thin Solid Films, 10, 109–122.

Nieuwenheuzen J M and Haanstra H B (1966), ‘Microfractography of thin lms’, Philips

Tech Rev, 27, 87–91.

Porcu F and Prodi F (1991), ‘Ballistic accretion on seeds of different sizes’, Phys Rev

A, 44, 8313–8315.

Raible M, Linz S J and Hanggi P (2002), ‘Growth instabilities of vapor deposited lms:

atomic size versus deection effect’, Eur Phys J B, 27, 435–442.

Ramanlal P and Sander L M (1985), ‘Theory of ballistic aggregation’, Phys Rev Lett,

54, 1828–1831.

Robbie K and Brett M J (1997), ‘Sculptured thin lms and glancing angle deposition:

growth mechanics and applications’, J Vac Sci Technol A, 15, 1460–1465.

ThinFilm-Zexian-06.indd 152 7/1/11 9:41:21 AM



153Silicon nanostructured ﬁlms grown on templated surfaces

Robbie K, Friedrich L J, Dew S K, Smy T and Brett M J (1995a), ‘Fabrication of thin

lms with highly porous microstructures’, J Vac Sci Technol A, 13, 1032–1035.

Robbie K, Brett M J and Lakhtakia A (1995b), ‘First thin lm realization of a helicoidal

bianisotropic medium’, J Vac Sci Technol A, 13, 2991–2993.

Robbie K, Brett M J and A. Lakhtakia A (1996), ‘Chiral sculptured thin lms’, Nature,

384, 616.

Robbie K, Sit J C and Brett M J (1998), ‘Advanced techniques for glancing angle

deposition’, J Vac Sci Technol B, 16, 1115–1122.

Smilauer P, Wilby M R and Vvedensky D D (1993), ‘Reentrant layer-by-layer growth:

a numerical study’, Phys Rev B, 47, 4119–4122.

Smy T, Vick D, Brett M J, Dew S K, Wu A T, Sit J C and Harris K D (2000), ‘Three-

dimensional simulation of lm microstructure produced by glancing angle deposition’,

J Vac Sci Technol A, 18, 2507–2512.

Stasevich T J, Einstein T L, Zia R K P, Giesen M, Ibach H and Szalma F (2004), ‘Effects

of next-nearest-neighbor interactions on the orientation dependence of step stiffness:

reconciling theory with experiment for Cu(001)’, Phys Rev B, 70, 245404.

Summers M A and Brett M J (2008), ‘Optimization of periodic column growth in glancing

angle deposition for photonic crystal fabrication’, Nanotechnology, 19, 415203.

Suzuki M and Taga Y (2001), ‘Numerical study of the effective surface area of obliquely

deposited thin lms’, J Appl Phys, 90, 5599–5605.

Tang F, Liu D-L, Ye D-X, Zhao Y-P, Lu T-M, Wang G-C and Vijayaraghavan A (2003),

‘Magnetic properties of Co nanocolumns fabricated by oblique-angle deposition’, J

Appl Phys, 93, 4194.

Toader O and John S (2001), ‘Proposed square spiral microfabrication architecture for

large three-dimensional photonic band gap crystals’, Science, 292, 1133–1135.

Toader O and John S (2002), ‘Square spiral photonic crystals: Robust architecture for

microfabrication of materials with large three-dimensional photonic band gaps’, Phys.

Rev. E, 66, 016610.

Tong W M and Williams R S (1994), ‘Kinetics of surface growth: phenomenology,

scaling, and mechanisms of smoothening and roughening’, Annu Rev Phys Chem,

45, 401–438.

Trait R N, Smy T and Brett M J (1993), ‘Modelling and characterization of columnar

growth in evaporated lms’, Thin Solid Films, 226, 196–201.

van Dijken S, Jorritsma L C and Poelsema B (1999), ‘Steering-enhanced roughening

during metal deposition at grazing incidence’, Phys Rev Lett, 82, 4038–4041.

Wong J, Mei S-N and Lu T-M (1987), ‘Al/Si(100) Schottky barrier formation using

nozzle jet beam deposition’, Appl Phys Lett, 50, 679–681.

Xi J-Q, Kim J K and Schubert E F (2005), ‘Silica nanorod-array lms with very low

refractive indices’, Nano Lett, 5, 1385–1387.

Xi J-Q, Schubert M F, Kim J K, Schubert E F, Chen M, Lin S-Y, Liu W and Smart J A

(2007), ‘Optical thin-lm materials with low refractive index for broadband elimination

of Fresnel reection’, Nat. Photonics, 1, 176–179.

Ye D-X and Lu T-M (2007a), ‘Fanlike aggregations on seeds by parallel ballistic ux:

experimental results and Monte Carlo simulations of the growth of three-dimensional

Si structures’, Phys Rev B, 75, 115420.

Ye D-X and Lu T-M (2007b), ‘Ballistic aggregation on two-dimensional arrays of seeds

with oblique incident ux: growth model for amorphous Si on Si’, Phys Rev B, 76,

235402.

Ye D-X, Karabacak T, Lim B K, Wang G-C and Lu T-M (2004), ‘Growth of uniformly

ThinFilm-Zexian-06.indd 153 7/1/11 9:41:21 AM



154 Thin ﬁlm growth

aligned nanorod arrays by oblique angle deposition with two-phase substrate rotation’,

Nanotechnology, 15, 817–821.

Ye D-X, Karabacak T, Picu R C, Wang G-C and Lu T-M (2005), ‘Uniform Si nanostructures

grown by oblique angle deposition with substrate swing rotation’, Nanotechnology,

16, 1717–1723.

Ye D-X, Yang Z-P, Chang A S P, Bur J, Lin S-Y, Lu T-M, Wang R Z and John S (2007),

‘Experimental realization of a well-controlled 3D silicon spiral photonic crystal’, J

Phys D: Appl Phys, 40, 2624–2628.

Ye D-X, Ellison C L, Lim B-K and Lu T-M (2008), ‘Shadowing growth of three-

dimensional nanostructures on nite size seeds’, J Appl Phys, 103, 103531.

Zhao Y-P, Ye D-X, Wang P-I, Wang G-C and Lu T-M (2002a), ‘Fabrication of Si

nanocolumns and Si square spirals on self-assembled monolayer colloid substrates’,

Int J Nanosci, 1, 87–97.

Zhao Y-P, Ye D-X, Wang G-C and Lu T-M (2002b), ‘Novel nano-column and nano-

ower arrays by glancing angle deposition’, Nano Lett, 2, 351–354.

ThinFilm-Zexian-06.indd 154 7/1/11 9:41:21 AM



155

Phase transitions in colloidal crystal

thin films

F. RamiRo-manzano, E. BonEt, i. RodRíguEz

and F. mEsEguER, Centro de tecnologías Físicas, unidad

asociada iCmm-CsiC/uPV, universidad Politécnica de

Valencia, spain

Abstract: this chapter reviews the crystal order of colloidal suspensions as

hard spheres when conned in wedge type cells with at walls. This type of

cell allows the study of colloidal crystal growth transitions between one and

n monolayers.

Key words: colloidal facets, colloidal crystal, connement, phase transitions.

7.1 Introduction

identical objects with rounded surfaces tend to pack in an ordered manner

independently of their size, being either meter size, as occurs for saw tree

trunks or big pipes being transported by lorry, or millimetrical size like

marbles packed in a box. in this case, marbles tend to be packed in close

packed layers each ordered in a triangular symmetry. this is our everyday

experience and nobody is astonished when they see such a neat periodic

distribution of objects. Concerning macroscopic systems, people may

guess that order is a consequence of human inuence. However, this type

of symmetrical distribution also appears for much smaller, submicrometric

size species like colloidal particles, molecules and atoms where human

inuence is less believed. In the former case colloids arrange into colloidal

crystals (Binks, 2006) and opals (sanders, 1964) and in the latter they form

the well-known crystalline structures (sands, 1975) like rock salt, diamond

and other fancy mineral rocks and jewels. the crystallization processes in

minerals appear due mostly to electrical forces, and they have been treated

in a large number of books (Kittel, 1996; Vainshtein, 1981). in the case of

colloidal crystals the crystallization can appear in both charged and also in

non-charged particles, dependent on both the material and the pH value of

the solvent used (Pusey et al., 1989; Holgado et al., 1999).

in this chapter we report the case of non-charged colloids (hard spheres)

where they order in a close packed manner like cannon balls in a pile. Here

it is worth mentioning colloid stability is due to the double layer of ions and

ThinFilm-Zexian-07.indd 155 7/1/11 9:41:41 AM



156 Thin ﬁlm growth

counterions that is governed by the dLVo theory (derjaguin and Landau,

1941; Verwey, 1947). there are two ways non-charged identical microspheres

can be arranged periodically in a box when maximizing the volume fraction

occupied by the spheres. In the rst, particles are ordered in a face centered

cubic (FCC) symmetry, and in the second, particles pack themselves in a

hexagonal close packed (HCP) structure. In both cases the lling fraction

(ff) occupied by the particles represents 74% of the total volume. although

both types of particle ordering would have the same probability, Woodcock

(1997) showed that the FCC arrangement would be favoured over the HCP

one through the use of thermodynamic arguments. Later, míguez et al.

(1997) reported on colloidal suspension of submicrometric particles settled

preferentially in FCC structures. There are other more efcient ways to pack

particles like the Apollonius packing (Duran, 1999). However, it involves

particles of different size and they lead to a quasi fractal ordering (Ramiro-

manzano et al., 2006a).

Colloidal crystals have developed a great deal and at a fast pace in the

last 30 years because they constitute crystallization models of much smaller

species, like atoms and molecules. also in the last ten years colloidal

crystals science and technology have been of great help in developing new

and cutting-edge photonic materials based on devices like photonic crystals

and metamaterials (Joannopoulos et al., 1995; Braun and Wiltzius, 1999;

Blanco et al., 2000). Photonic crystals can be dened as composite materials

with a strong modulation of the refractive index in some spatial directions.

the refractive index modulation produces huge diffraction effects. Light

of certain frequency values is not allowed to travel through it (John, 1987;

Yablonovitch, 1987; Joannopoulos et al., 1997). this is the basic concept

of a photonic bandgap. in this way, colloidal crystals also produce light

diffraction effects, this being the origin of the pretty iridescent colours of

natural opals (sanders, 1964). therefore, colloidal crystals can be considered

as a class of photonic crystals. For many applications using colloidal crystals,

just a few monolayers (mL) are enough to build up the photonic bandgap

(Vlasov et al., 2001). However, as colloidal crystals pack spontaneously in a

FCC lattice showing its (111) facet, their application to photonic crystals is

limited. in fact, the possibility of creating different lattices and facets could

extend dramatically the application range of colloidal crystals (Prasad et al.,

2003; ochiai and sanchez-dehesa, 2001; Fenollosa et al., 2003).

Colloidal crystal thin lms can be achieved through several methods. In

most cases they are processed through self-arrangement of particles driven

by convection (míguez et al., 2002, 2003; Yin et al., 2001; Velikov et al.,

2002; Kitaev and Ozin, 2003), capillarity (Hiemenz and Rajagopalan, 1997;

Knobler and schwartz, 1999; Pan et al., 2006, van duffel et al., 2001;

Wolert et al., 2001), gravitational (míguez et al., 1997; López et al., 1997;

Van Blaaderen et al., 1997), evaporation (Park et al., 1998; Pieranski et al.,

ThinFilm-Zexian-07.indd 156 7/1/11 9:41:41 AM



157Phase transitions in colloidal crystal thin ﬁlms

1983; Pansu et al., 1984), centrifugal (mihi et al., 2006) or electrophoretic

(Holgado et al., 1999) forces. in the vast majority of cases it results in a

thin lm of FCC ordering whose surface shows a triangular symmetry facet

corresponding to the (111) plane (FCC(111) for short). However, strong

connement of particle suspensions promotes new particle orderings as

Pieranski et al. (1983) demonstrated. This connement is generated by two

solid–liquid interfaces in close proximity. However, this phenomenon is not

only restricted to strong connement. Weak connement constituted by two

interfaces, air–liquid and liquid–solid (Prevo and Velev, 2004; mihi et al.,

2006), could also lead to the formation of some of these new orderings.

We consider here only the case of uncharged colloidal particles (i.e. a

hard sphere system). Hard spheres represent the limit of screened colloids

that could be considered unaffected by Coulomb forces. in this chapter

we review how connement in colloidal crystals can produce a manifold

variety of colloidal arrangements. We also show models that give hints

about the evolution dynamics of the crystallization for different connement

restrictions.

7.2 Experimental tools

In this section we explain the design of the connement cell, the colloidal

crystal growth and also their optical characterization. the design of the cell

is rather similar to that used by Lu et al. (2001). Wedge type cells are formed

by two large plates (3 cm large), the substrate plate and the covering plate.

they are made of hydrophilic (treated glass) and hydrophobic (polystyrene)

material, respectively. therefore, in order to achieve large monocrystal areas

of well-isolated facets, a very small wedge angle (≈10

–4

rad) was used. a

6 micrometers thick Mylar lm, attached along only one rim of the slides,

separates the plates. the wedge type cell is obtained by tightening the cell

with several binder clips on the three other sides of the cell (see Fig. 7.1(a)

and 7.1(d)). For thicker samples with many monolayers, we use another

cell design shown in Fig. 7.1(c). in the alternative design the separator

surrounds the entire cell and the plates are bent due to the action of the clips.

Polystyrene particles of different sizes ranging from 245 nm up to 800 nm

in diameter (ikerlat Polymers) were employed. Particles were washed and

rinsed several times with milliQ water. an aqueous suspension of particles

(1 wt%) was introduced through a 2 cm high glass tube (tank) attached to

the inner part of the cell through a small hole (2 mm diameter) drilled on

the glass plate. several drops were put into the small tube, which entered the

cell due to capillary forces. While water leaked out and evaporated, the cell

was subjected to a light ultrasonic vibration to help settle the particles. in

some cases, when particles were of smaller size (245 nm) it was necessary

to apply a light pressure to the feeding glass tube to compensate Brownian

ThinFilm-Zexian-07.indd 157 7/1/11 9:41:41 AM

