Geckeler K.E., Nishide H. (Eds.) Advanced Nanomaterials

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4.5 Epitaxy and Surface Interactions 135

directionally solidiﬁ ed with BA (Figure 4.14 b) shows OsO

- stained darker PI

cylinders, lying in - plane and well oriented along the crystallographic b - axis of

the BA, as reported in the scheme of Figure 4.14 e [275] . The ordered parallel

cylinder structure also extends over regions larger than 50 μ m

. The average

diameter of the PI cylindrical microdomains is approximately 20 nm, while the

average distance between the cylinders is 40 – 50 nm. In both of these examples,

the initial homogeneous solution conﬁ ned between the glass substrates trans-

forms due to the imposed directional solidiﬁ cation of large crystals of BA having

(001) surfaces coexisting with a thin liquid layer near the eutectic composition.

Dropping the temperature further then causes this layer also to directionally

solidify by thickening the preexisting BA crystal with the simultaneous formation

of a thin, metastable vertically oriented lamellar microdomain ﬁ lm (Figure 4.13 b)

[275] . In the case of the PS - b - PMMA, the vertical lamellar structure is vitriﬁ ed

due to the high glass transition temperatures of both blocks. In the case of PS -

b - PI with a low volume fraction of PI block, however, it has been hypothesized

that the vertical lamellar microstructure is transformed into in - plane cylindrical

microstructure due to the interfacial instability of thin lamellae, ﬁ lm thickness,

and preferential wetting of the PI block [275] . Similar ordered microstructures

have been obtained employing other organic crystallizable solvents as AN which

has a melting temperature of 216 ° C, about 100 ° C higher than that of BA [275] .

This process has also been used in combination with thickness effects to achieve

vertically aligned cylinders employing ultrathin ﬁ lms [275] . Cylindrical microdo-

mains, indeed, orient vertically for relatively thin ﬁ lms due to incommensurability

effects, which is similar to what was observed for lamellar diblock copolymers

[276] . A bright - ﬁ eld TEM image of a thinner ﬁ lm (of approximately 20 nm thick-

ness) of PS - b - PI, prepared from a more dilute solution, directionally solidiﬁ ed with

BA and stained with OsO

, is shown in Figure 4.14 c [275] . The dark OsO

- stained

vertically aligned cylindrical PI microdomains are oriented into rows along the

b - axis of the BA crystal and packed in an approximate hexagonal lattice, as shown

in the schematic model of the microstructure reported in Figure 4.14 f [275] . The

aligned vertical cylinders extend over regions larger than 50 μ m

. The FFT power

spectrum in the inset of Figure 4.14 c shows spotlike ﬁ rst reﬂ ections with sixfold

symmetry, indicating approximate hexagonal packing of the cylindrical PI

microdomains.

Various di - and tri - block copolymers with different architecture and properties

such as rubbery – glassy, glassy – glassy, amorphous – crystalline, amorphous – liquid

crystalline, and ABC - type terpolymers have been successfully organized with this

process [275] .

4.5.4

Graphoepitaxy and Other Conﬁ ning Geometries

Graphoepitaxy is a process whereby an artiﬁ cial surface topography of a crystalline

or amorphous substrate inﬂ uences and controls the orientation of the crystal

growth in thin ﬁ lms [277 – 280] . Graphoepitaxy has been used (often in combina-

tion with epitaxy) to obtain high orientation of polymeric crystals onto substrates

136 4 Alignment and Ordering of Block Copolymer Morphologies

constituted by ﬁ lms of other polymers [281 – 285] . For instance, a variety of poly-

mers, including PE, nylons, polyesters, and liquid crystalline polymers, have been

grown in highly oriented form on the oriented surface of poly(tetraﬂ uoroethylene)

( PTFE ) crystals [281] . In the case of PE, the orientation of the crystals is such that

the c - axis lies in the plane of the ﬁ lm and the bc plane of the unit cell is in contact

with the substrate surface [285] . Different orientations, for instance, a ﬁ ber - like

alignment, have been observed for other polymers [285] . This suggests that the

alignment of materials on PTFE ﬁ lms can occur by graphoepitaxial or epitaxial

mechanisms, depending on the materials. In some instances both the lattice

structure and the surface topography of the PTFE ﬁ lms promote the alignment,

so that the two mechanisms can operate in conjunction [285] .

Graphoepitaxy was utilized by Segalman and coworkers [286, 287] to control the

orientation of BC microdomains. The procedure is an example of the combined

top - down and bottom - up approaches to patterning. Segalman ’ s group used topo-

graphically alternating mesa and well patterns fabricated by conventional photoli-

thography and chemical etching techniques to align spherical P2VP microdomains

of a PS - b - P2VP diblock copolymer. A large area single crystal of the P2VP spheres

was obtained on the mesas and wells [286] .

Nanostructures with long - range order were also developed using graphoepitaxy

in combination with BC lithography [288, 289] . Cheng et al . employed a diblock

copolymer of PS - b - PFS, in which the organometallic PFS block provides an excel-

lent (10 : 1) etching contrast in an oxygen plasma [287] . A topographically patterned

silica substrate was fabricated by interference lithography, after which the sub-

strate was used for a templating BC self - assembly. Monolayer ﬁ lms of the BC were

deposited by spin - casting and annealed onto the patterned silica substrate. The

ﬁ lm was then oxidized by etching in an oxygen plasma. Scanning electron micro-

scopy ( SEM ) images of annealed and etched PS - b - PFS ﬁ lms, reported in Figure

4.15 , revealed ordered arrays of PFS spheres in grooves of different widths [288] .

A thin PFS – PS brush layer is present at the groove edge and bottom where the

PFS block wets the silica substrate. This surface - induced thin layer was shown to

drive the ordering of the PS – PFS block copolymer microdomains, and resulted in

PFS spherical microdomains parallel to the groove edges. In the microstructure

with grooves having a width of 240 nm (Figure 4.15 c), and comparable to the

typical block copolymer grain size, a near - perfect alignment of PFS spherical

microdomains was achieved. The microdomain patterns were transferred onto the

underlying silica substrate using a reactive ion etcher ( RIE ) process with a CHF

plasma, so as to create well - ordered arrays of silica posts [288] . The oxidized PFS

domains are perfectly ordered by the guided self - assembly of the BC in the prepat-

terned substrate, and can potentially be useful for fabricating 2 - D photonic crystal

waveguide structures. More recently, other investigations have conﬁ rmed the

general applicability of this approach employing spherical, cylindrical or lamellar

diblock copolymers to yield 2 - D patterns into different lithographic features [35,

36, 38, 290, 291] . However, as the pre - pattern size should be determined by the

grain size of the block copolymers, only patterns with a small periodicity are

applicable. To overcome this problem, graphoepitaxy should be combined with

4.5 Epitaxy and Surface Interactions 137

methods that allow the grain size of the BCs to be increased, which can then in

turn be controlled with the micron size patterns available, for example, from soft

lithography [12] . As discussed in the next sections, the combination of graphoepi-

taxy or epitaxy with directional crystallization provides possible routes to achieve

this result.

Unlike graphoepitaxy, which can be considered to approximate a 1 - D conﬁ ne-

ment of a thin ﬁ lm between (often parallel) solid walls, the 2 - D conﬁ nement of

BCs has been predicted to induce more complicated effects on phase - separation

Figure 4.15 SEM images of annealed and oxygen plasma -

treated PS - b - PFS ﬁ lms on silica gratings with (a) 500 nm - wide

grooves, (b) 320 nm - wide grooves, and (c) 240 nm - wide

grooves. Reproduced with permission from Ref. [288] ;

138 4 Alignment and Ordering of Block Copolymer Morphologies

and morphology orientation [292 – 294] . Recent investigations have conﬁ rmed for

various PS - based diblock copolymers that, in the case of a nonplanar geometry of

conﬁ nements, such as in cylindrical pores, the conﬁ ning of dimensions incom-

mensurable with the copolymer period and the imposed curvature leads to the

production of unusual morphologies [295 – 297] . The self - assembly of asymmetric

diblock copolymers introduced as a melt into nanoporous alumina templates

occurs with an alignment of the cylinders along the pore axis, favored by the

preferential wetting of the pore with the majority block [296] . Furthermore, for

symmetric BCs, concentric lamellae oriented parallel to the long axes of the pores

have been observed, with an overall number of lamellae and forbidden segrega-

tions that are directly dependent on the pore diameter and the preferential wetting

of one block, respectively [296, 297] .

4.5.5

Combination of Directional Crystallization and Graphoepitaxy

The idea of combining graphoepitaxy from a topographical pattern fabricated by

conventional photolithography procedures and the directional crystallization of a

solvent was ﬁ rst introduced by Park et al . [298] . The thin ﬁ lm of the BC was con-

ﬁ ned between crystals of BA, obtained from a directional eutectic crystallization

of the homogeneous BC solution, and the topographic substrate pattern. The

conﬁ nement induced a thickness variation of the BC ﬁ lm, and resulted in the two

different orientations of the microdomains [298] . The patterned substrate was

produced via standard lithographic techniques, and consisted of 30 nm - high,

2 μ m × 2 μ m mesas arranged in a square array with a 4 μ m spacing, as shown in

the schematic diagram of Figure 4.16 a. The square - shaped mesas are made by

selective etching of a thermally grown silicon oxide on a 10 cm wafer. A PS - b - PI

diblock copolymer was directionally solidiﬁ ed with benzoic acid on the patterned

substrate [298] . A low - magniﬁ cation, bright - ﬁ eld TEM micrograph of the OsO

stained BC ﬁ lm is shown in Figure 4.16 b. The prepatterned substrate structure

produces thickness variations in the directionally solidiﬁ ed BC thin ﬁ lms; the ﬁ lms

are thinner on the mesas and thicker in the plateau regions. As described in

Section 4.5.3 (see Figure 4.14 b,c), the directional eutectic solidiﬁ cation produces

an orientation of PI cylinders along the b - axis of the benzoic acid crystal or normal

to the substrate, depending on the thickness [275, 298] .

The BC ﬁ lm directionally solidiﬁ ed on the patterned substrate was then sub-

jected to O

- RIE to selectively remove the cylindrical PI microdomains [298] . A

higher - magniﬁ cation atomic force microscopy ( AFM ) image after O

- RIE, shown

in Figure 4.17 a, reveals the double orientation of the cylindrical PI microdomains.

In the thicker ﬁ lm regions (ca. 50 nm thick), the cylindrical PI microdomains are

well aligned along the b - axis of the BA crystal, with the cylinder axis parallel to the

substrate and to the walls of the mesas. In the thinner ﬁ lm regions (ca. 20 nm

thick), the PI cylinders are hexagonally packed with their cylinder axes perpendicu-

lar to the substrate and with the a

hexagonal lattice direction parallel to b - axis of

BA; that is, along the [10] direction of the square substrate pattern [298] . The SEM

4.5 Epitaxy and Surface Interactions 139

image of Figure 4.17 b shows that the microdomains successively transform from

parallel to vertical when they pass from the plateau into the mesa regions [298] .

The in - plane PI cylindrical microdomains aligned along the b - axis direction of the

BA crystal in the plateau regions transform abruptly into hexagonally packed, verti-

cally oriented cylinders. The cylindrical hole structures on the mesa areas after

- RIE are also shown in Figure 4.17 c, in height - contrast AFM. The vertically

ordered PI cylindrical domains, which appear dark, on the mesa regions are essen-

tially empty. A scheme of this process of directional solidiﬁ cation of the BC,

combined with topographically mediated substrate patterning, is shown in Figure

4.17 d. The BC ﬁ lms conﬁ ned between the top BA crystal and the bottom prepat-

terned substrate undergo thickness variation ( h

and h

), leading to two different

microdomain orientations. Control over the position and orientation of cylindrical

Figure 4.16 (a) Schematic of the

topographically patterned silicon oxide

substrate; (b) Bright - ﬁ eld TEM image of a thin

ﬁ lm of PS/PI block copolymer, directionally

solidiﬁ ed with BA on the prepatterned

substrate. The low - magniﬁ cation image

depicts a typical region larger than 1000 μ m

where the cylindrical PI microdomains are

aligned via directional solidiﬁ cation. The

replicated micron - scale pattern structure is

seen due to the different ﬁ lm thicknesses in

the two types of region. The inset shows the

basis vectors of the cylindrical PI

microdomain lattice and the fast growth

direction of the BA crystal ( b axis).

Reproduced with permission from Ref. [298] ;

140 4 Alignment and Ordering of Block Copolymer Morphologies

domains on the patterned substrate provides nanolithographic templates for

micromagnetics and microphotonics [298] .

4.5.6

Combination of Epitaxy and Directional Crystallization

The method of combination of directional crystallization and epitaxy was intro-

duced by De Rosa et al . [263] . The process is based on the directional solidiﬁ cation

Figure 4.17 (a,c) AFM and (b) SEM images of

a thin ﬁ lm of asymmetric PS - b - PI, directionally

solidiﬁ ed with BA on the prepatterned

substrate and subsequently etched by O

- RIE.

The tapping mode AFM image (panel a)

shows that the cylindrical PI microdomains,

with two different orientations with respect to

the substrate, are well aligned along the fast

growth direction of the BA crystals, as

indicated by the arrow. The square - shaped

mesa regions exhibit vertically oriented,

hexagonally packed PI cylinders. The thicker

matrix regions show the in - plane PI cylinders.

The SEM image reveals that aligned PI

cylinders transform their in - plane to vertical

orientation with respect to the substrate. The

two hexagonal lattice directions of the

vertically ordered PI cylinders are shown in

inset (b). The height mode AFM image on a

mesa region (c) indicates that vertically

ordered cylindrical PI microdomains are

selectively removed by O

- RIE, which appear

dark. Reproduced with permission from Ref.

Physics; (d) Scheme of the orientation of

microdomains of PS - b - PI between the top BA

crystal and the bottom prepatterned

substrate. Reproduced with permission from

4.5 Epitaxy and Surface Interactions 141

of the eutectic solution of a semicrystalline BC in a crystallizable organic solvent

and subsequent epitaxial crystallization of the crystalline block onto the organic

crystalline substrate [263] . The organic substrate (e.g., BA or AN) at a temperature

higher than its melting temperature is a solvent for the BC, and becomes a sub-

strate, when it crystallizes at lower temperatures, for the epitaxial crystallization

of the BC [263 – 265, 299] .

Examples of the ordered microstructures obtained with this method are pro-

vided by PS - b - PEP - b - PE and PS - b - PE semicrystalline BCs containing crystallizable

PE blocks directionally solidiﬁ ed with BA or AN [263 – 265] .

The electron diffraction pattern of PS - b - PEP - b - PE triblock copolymer ﬁ lm direc-

tionally solidiﬁ ed and epitaxially crystallized with BA is shown in Figure 4.18 a

[264] . As in the case of the melt - compatible PE - b - PEP - b - PE (see Figure 4.11 a) [184] ,

the pattern of Figure 4.18 a essentially presents only the 0 kl reﬂ ections of PE,

indicating orientation of the PE crystals similar to that found for the PE - b - PEP - b -

PE triblock copolymer [184] , and for the homopolymer, as shown in Figures 4.10

and 4.12 . The crystalline PE lamellae are oriented edge - on on the substrate surface

with the (100) plane of PE in contact with the (001) plane of BA. The b - and c - axes

of PE are parallel to the b - and a - axes of benzoic acid, respectively.

The bright - ﬁ eld TEM image of the unstained ﬁ lm directionally solidiﬁ ed and

epitaxially crystallized onto BA, reported in Figure 4.18 b [264] , shows the highly

oriented lamellar structure with long thin crystalline lamellae oriented along the

[010]

||[010]

direction. The bright - ﬁ eld image of the same sample after staining

with RuO

, as shown in Figure 4.18 c, indicates that the PS blocks, corresponding

to the darker - stained regions, are organized in parallel cylinders the axes of which

are generally oriented along the elongated direction [010]

||[010]

of the crystal-

line lamellae [264] .

As the order – disorder temperature of PS - b - PEP - b - PE ( > 250 ° C) is much higher

than the crystallization temperature of the PE block (almost 65 ° C) [300, 301] , the

directional crystallization of BA induces the orientation of the cylindrical PS

microdomains along the fast growth direction of the BA crystal ( b - axis) [264] (as

discussed in Section 4.5.3 for amorphous BCs) [275] . Subsequently, epitaxial crys-

tallization of the crystalline PE block onto the BA crystalline substrate induces

molecular orientation of the PE chains, leading to oriented crystalline PE lamellae

in the presence of pre - existing ordered PS cylinders [264] . A schematic model

(Figure 4.18 d) displays the ﬁ nal microstructure generated by a combination of the

directional crystallization and epitaxy. The process induces alignment of the PS

cylinders and PE lamellae along the same direction, resulting in a multilayered

ordering of the PS cylinders [264] .

A different microstructure of the same PS - b - PEP - b - PE is obtained when AN is

used as the crystallizable solvent [265] , due to a different epitaxial relationship

between PE and AN crystals [258] . The selected area diffraction ( SAD ) pattern of

the PS - b - PEP - b - PE ﬁ lm epitaxially crystallized onto AN is shown in Figure 4.19 a

[265] . The pattern exhibits 0 kl reﬂ ections of two sets of PE crystals having two

different orientations [265] , corresponding to the b * c * sections of the PE reciprocal

lattice symmetrically rotated by an angle of almost 70 ° with respect to the a * - axis

of the AN. This angle of 70 ° corresponds to the angle made by the [1 1 0] and

142 4 Alignment and Ordering of Block Copolymer Morphologies

0] directions in the ab - plane of the AN crystal ( a

= 8.65 Å ; b

= 6.04 Å ;

= 11.18 Å ; β = 124.7 ° ; melting temperature of 216 ° C). The c - axis of PE is there-

fore oriented parallel to two equivalent [1 1 0] and [1

0] directions of the AN

crystal, and two sets of PE lamellae oriented edge - on on the AN crystals are pro-

duced, with the (100) plane of PE in contact with the (001) plane of AN (Figure

4.19 b) [265] . The epitaxial relationship between PE and AN crystals can be readily

explained in terms of matching between the b - axis of PE and the inter - row spacing

Figure 4.18 Selected area diffraction pattern

(a), TEM bright - ﬁ eld image of unstained (b)

and stained with RuO

PS - b - PEP - b - PE triblock copolymer

directionally solidiﬁ ed and epitaxially

crystallized onto BA. The dark regions in the

TEM bright - ﬁ eld image of the unstained ﬁ lm

(panel b) correspond to the crystalline PE

phase, which form long lamellae oriented

edge - on, and aligned with the b - axis parallel

to the b - axis of BA. The dark regions in the

TEM bright - ﬁ eld image of the ﬁ lm stained

with RuO

(panel c) correspond to the PS

phase, which form cylinders aligned parallel

to the crystalline lamellae; (d) Schematic

model of the microstructure in thin ﬁ lms of

the PS - b - PEP - b - PE terpolymer directionally

solidiﬁ ed and epitaxially crystallized onto BA.

The directional solidiﬁ cation induces in - plane

cylindrical PS microdomains aligned along the

fast growth direction of BA crystals. The

following epitaxial crystallization of PE blocks

onto the BA crystals induces the formation of

long, thin crystalline PE lamellae in between

the PS cylinders. The PE crystals have their

(100) planes in contact with the (001) plane

of the BA crystal with a

|| c

and b

|| b

Reproduced with permission from Ref. [264] ;

4.5 Epitaxy and Surface Interactions 143

of the (110) plane of AN and a second matching of 2 c of PE with the Bragg distance

of the (110) plane ( d

110

) of AN [258] . Similar lattice matching occurs between PE

and other aromatic substances [258] .

The bright - ﬁ eld TEM image of the unstained ﬁ lm of the PS - b - PEP - b - PE epitaxi-

ally crystallized onto AN (Figure 4.19 c) provides a direct visualization of the crystal-

line PE lamellae that presents a cross - oriented texture. The lamellae having a

thickness of 10 – 20 nm are oriented along the two different [1 1 0] and [1

0] direc-

tions of the AN crystals [265] . A bright - ﬁ eld image of a different region of the same

sample after staining with RuO

(Figure 4.19 d) indicates that the PS blocks (the

darker regions) are organized into a similar, double - oriented pattern [265] .

The directional solidiﬁ cation of the mixture of the terpolymer and AN develops

the orientation of the cylindrical PS microdomains along the fast growth direction

of the AN crystals ( b - axis direction) before crystallization of the PE. The epitaxial

Figure 4.19 (a) Selected area electron

diffraction pattern of a thin ﬁ lm of PS - b - PEP - b -

PE block terpolymer epitaxially crystallized

onto AN; (b) Scheme showing the two

orientations of edge - on PE lamellae onto the

(001) exposed face of the AN crystals. The

(100) plane of PE is normal to the electron

beam and parallel to the (001) face of the AN

crystals. The c - axes of the two sets of PE

crystals are parallel to the [1 0 9] and [1

−

10]

direction of the AN crystal; (c) TEM bright -

ﬁ eld image of an unstained thin ﬁ lm of

PS - b - PEP - b - PE epitaxially crystallized on AN.

The dark regions correspond to the crystalline

PE phase, which forms cross - oriented PE

lamellae standing edge - on; (d) TEM

bright - ﬁ eld image of the ﬁ lm of PS - b - PEP - b - PE

epitaxially crystallized on AN and stained with

RuO

. The dark regions correspond to the PS

phase, which forms a double - oriented

structure similar to that of the PE

microdomains. Reproduced with permission

144 4 Alignment and Ordering of Block Copolymer Morphologies

crystallization induces a high orientation of the molecular chains of the crystalline

phase, resulting in PE lamellae standing edge - on on the substrate surface, oriented

in two directions due to the crystallographic degeneracy. This structure in turn

induces reorganization and reorientation of the pre - existing PS cylinders [265] .

This thin - ﬁ lm process suggests the possibility of creating new 2 - D microdomain

textures via self - assembled semicrystalline BCs using a combination of one or

more crystallizable blocks and various crystalline organic substrates [265] .

The asymmetric PS - b - PE diblock copolymer is an interesting example of crys-

tallization of PE conﬁ ned in PE cylinders formed by self - assembly in the melt

[263, 264] . The electron diffraction pattern of an unstained ﬁ lm of PS - b - PE ﬁ lm

epitaxially crystallized onto BA is shown in Figure 4.20 a. The pattern is similar

to those obtained for the PS - b - PEP - b - PE (Figure 4.18 a) [264] and PE - b - PEP - b - PE

(Figure 4.11 a) [184] epitaxially crystallized onto BA and presents only the 0 kl

reﬂ ections of PE. This indicates that the PE lamellae are oriented edge - on on the

(001) surface of BA, with the (100) plane of PE in contact with the (001) plane

of BA and the b - and c - axes of PE parallel to the b - and a - axes of BA, respectively,

as shown in Figures 4.10 and 4.12 . A bright - ﬁ eld image of a thin ﬁ lm of PS - b - PE

directionally solidiﬁ ed and epitaxially crystallized onto BA and stained with RuO

is shown in Figure 4.20 b [263] . The presence of a very well - ordered array of light -

unstained PE cylinders in the dark - stained PS matrix is apparent [263] . The

cylinders are vertically aligned and packed on a hexagonal lattice, having an

average lattice constant of almost 40 nm. The order extends to large distances

( > 20 μ m).

The PE crystals have been visualized with dark - ﬁ eld imaging, employing the

strong 110 reﬂ ection of PE (Figure 4.20 c). Small rectangular PE crystals are

observed in the dark - ﬁ eld image of Figure 4.20 c (the light regions), well aligned

along the b - axis direction of the BA crystals and packed on a pseudo - hexagonal

lattice, the size and orientation of which are the same as seen in the bright - ﬁ eld

image of Figure 4.20 b [263] . The PE crystals are 7 nm thick and 20 nm long, with

their longest dimension parallel to the [1 1 0] * reciprocal lattice direction [263] .

The size and spacing of PE microdomains observed in bright - and dark - ﬁ eld

images show that there is precisely one crystalline PE lamella centered in each

cylinder, with the b - axis of the lamella oriented parallel to the b - axis of the BA,

conﬁ rming the epitaxy of PE on BA demonstrated by the electron diffraction

pattern (Figure 4.12 a). A scheme of the nanostructure obtained in PS/PE thin ﬁ lm

is shown in Figure 4.20 d [263, 264] .

The same PE - b - PS was also processed with AN to manipulate both molecular

and microstructure orientation [264] . The electron diffraction pattern of an

unstained ﬁ lm is shown in Figure 4.21 a. As in the case of Figure 4.19 a for the

PS - b - PEP - b - PE triblock copolymer, the pattern exhibits the 0 kl reﬂ ections of two

sets of PE crystals in two different orientations, indicating that PE lamellae stand

edge - on on the substrate surface with the c - axes of PE oriented parallel to the

[1 1 0] or [1

0] directions (Figure 4.19 b) [264] . A RuO

- stained bright - ﬁ eld TEM

image of the PS - b - PE diblock copolymer directionally solidiﬁ ed and epitaxially

crystallized onto AN is shown in Figure 4.21 b. Also, in this case the light - unstained