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8 Three-Dimensional Atom Probes (3DAPs)

8 Three-Dimensional Atom Probes (3DAPs)

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Microscopy – Nanoscopy

Fig. 2.39 Simulation of single molecule structure recovery by the diffraction signal from a single

XFEL pulse. (a) Isosurfaces of electron density of the protein chignolin (a protein with 10 amino

acid residues), recovered from 72,000 diffraction patterns of unknown orientation at a scattered

mean photon count (MPC) of 4 × 10−2 per pixel. (b) The molecular model is represented by

the stick figure, with C bonds shown in yellow, N in blue, and O in red. The 1, 2, and 3σ electron

density contours are shown in blue, pink, and red, respectively, with σ denoting the r.m.s. deviation

from the mean electron density. (Reprinted with permission from [2.17]. © 2009 Nature Publishing



Three-Dimensional Atom Probes (3DAPs)


Fig. 2.40 Schematic

illustration of the design of a

3D atom probe (3DAP).

(Reprinted with permission

from [2.105]. © 2001

Materials Research Society)

paths so that the instrument acts as a simple point-projection microscope with a very

high magnification (several million times). The impact of an ion on the detector

directly relates to its original surface position, and by time-of-flight mass spectrometry the nature of the ion is identified. Continued removal of ions produces

a layer-by-layer sectioning of the specimen and generates a full 3D reconstruction

of the element distribution in the material.

An example of detailed, ultrahigh-resolution provided by 3DAP is given in

Fig. 2.41. Upon aging of an Al − 1.9wt% Cu − 0.3wt% Mg − 0.2wt% Ag alloy at

180◦ C for 10 h an -phase plate forms in the alloy with a thickness of 10–13 [111]α

layers corresponding to 3 unit cells of . In addition to the segregation of Ag and

Fig. 2.41 3D atom probe (3DAP) elemental map with a step at the interface of an -phase precipitate formed in an alloy aged at 180◦ C for 10 h. Segregation of Mg and Ag occurs to the precipitate

interface as well as the enhancement of Cu in the vicinity of the step. (Reprinted with permission

from [2.105]. © 2001 Materials Research Society)



Microscopy – Nanoscopy

Mg to the α/ interface, an interface step is apparent. The Cu concentration immediately ahead of the step is higher than in the matrix far from the precipitate. This

indicates a process of redissolution as the precipitate shrinks during the coarsening


In the soft-magnetic nanocrystalline Fe73.5 Si13.5 B9 Nb3 Cu1 alloy, 3DAP studies

[2.104] demonstrated that Cu precipitates (Fig. 2.42) provide nucleation sites for

Fe–Si primary crystallization, most important for the magnetic properties of the

material (see Sect. 8.3).

For thin films and functional multilayers, as, e.g., giant magnetoresistance

(GMR) devices (see Sect. 1.4), the structural and chemical control at the atomic

scale is of importance. 3DAP studies of NiFe/CoFe/Cu/CoFe multilayers (Fig. 2.43)

were performed by the development of appropriate tip preparation techniques. By

these studies the effects of interface roughness and intermixing to properties such

as GMR could be demonstrated (see [2.105]).

Fig. 2.42 3DAP elemental map of Cu of, the melt-spun amorphous Fe73.5 Si13.5 B9 Nb3 Cu1 alloy

which gives rise to a soft-magnetic behavior (see Sect. 8.3) due to nanocrystallization upon annealing at 515◦ C. (a) as quenched; (b) annealed at 400◦ C for 5 min.; (c) annealed at 400◦ C for 60 min.

The data clearly show the nucleation of Cu precipitates as precursors of the Fe–Si nanocrystals.

(Reprinted with permission from [2.104]. © 1999 Elsevier)



Fig. 2.43 (a) 3DAP analysis of a NiFe/CoFe/Cu/CoFe multilayer for giant magnetoresistance

(GMR) devices (see Sect. 1.4). The Ni (green), Co (blue), and Cu (red) atom positions are shown.

Height of the volume ∼35 nm. (b) Magnified view showing individual (111) planes along the

growth direction. (Reprinted with permission from [2.105]. © 2001 Materials Research Society)

2.9 Summary

Microscopical imaging techniques are of outstanding importance for the characterization of nanosystems. The invention of scanning probe microscopy with partially

atomic resolution has very much promoted the progress of nanoscience. A variety

of scanning tunneling microscopes (STMs; where magnetic imaging is basically

reviewed in Sect. 8.1), atomic force microscopes (AFMs), and scanning near-field

optical microscopes (SNOMs) is available for imaging and manipulation. But also

optical far-field stimulated emission depletion (STED) microscopy provides us with

lateral resolution below 10 nm and qualifies for 3D imaging of biological nanosystems. Enormous progress has been achieved in topographic, tomographic, and

analytical transmission electron microscopy by aberration correction techniques.

With the generation of high-intensity and coherent x-ray beams, topographic, chemical, and magnetic imaging by x-rays with some 10 nm resolution have become

feasible and strategies are being developed for imaging the atomic structure of single

molecules. The 3D atomic probe (3DAP) is capable of 3D topographic and chemical

atomic resolution.





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Chapter 3


In this chapter a survey will be given on the variety of “bottom-up” and “top-down”

synthesis techniques for nanostructures focusing first to structures of different

dimensionality such as nanocrystals, nanowires, and nanolayers including shape

control and more complex nanostructures. After the preparation of bulk nanocrystalline systems the synthesis of carbon nanostructures is discussed with a subsequent

overview of nanoporous systems. Finally, the present development of lithography,

which is of outstanding importance for the computer industry, will be presented.

3.1 Nanocrystals and Clusters

3.1.1 From Supersaturated Vapors

In nanosciences the term nanoparticle [3.1] is often used for the entire range from

dimers to entities with 100 nm in diameter. The term cluster is used for small

nanoparticles with less than 104 atoms. For cluster synthesis from supersaturated

vapors classical nucleation theory is employed. Here, the reversible free energy

W (n) = −nkB T ln S + 4π σ




for forming a cluster with n atoms or molecules contains a “bulk” and a “surface”

free energy term where S = p/pe is the ratio of the vapor pressure p and the equilibrium vapor pressure pe at the temperature T and σ and v denote the surface energy

and the volume of a molecule, respectively. From the condition ∂W/∂n = 0 the

critical values n∗ , r∗ , and W(n∗ ) for cluster nucleation can be derived.

Clusters of atoms from supersaturated vapors may be formed by physical cooling,

by supersonic expansion, by gas phase chemical reaction, or by thermal evaporation,

sputtering or laser ablation. Mass spectra of clusters formed by evaporation of the

cluster material and expansion of the carrier gas in an oven source [3.2] are shown in

Fig. 3.1. The predominant cluster sizes of n = 8, 20, 40, etc., are called magic numbers which are governed, e.g., by filling the major electronic shells of the clusters at

H.-E. Schaefer, Nanoscience, DOI 10.1007/978-3-642-10559-3_3,

C Springer-Verlag Berlin Heidelberg 2010



3 Synthesis

Fig. 3.1 Mass spectra

showing the abundance of

potassium clusters from a

supersonic beam of an oven

source as a function of cluster

size n. (Reprinted with

permission from [3.1].

© 1996 Institute of Physics)


Fig. 3.2 Main shapes

observed for small

Au clusters. (a) fcc

cuboctahedron, (b)

icosahedron, (c) regular

decahedron, (d) star

decahedron, (e) marks

decahedron, and (f) round

decahedron. (Reprinted with

permission from [3.4].

© 2001 American Institute of


particular sizes. At larger clusters the magic numbers originate from closing shells

and subshells of icosahedral clusters [3.3]. Small metallic clusters can assume different shapes (Fig. 3.2) depending on the size and environmental conditions such

as ligands or substrates [3.4]. Laser vaporization cluster beams were introduced by

Smalley [3.5] yielding 100 torr pressures with laser powers generating temperatures

of 104 K at the target.

Larger quantities of nanoparticles used for compaction to form nanocrystalline

solids may be prepared by thermal evaporation, sputtering, or laser techniques

(Fig. 3.3) [3.6].

The distribution of the cluster size r follows a log–normal relation

F(r) = √

− ln(r/rM − σ 2 )



2σ 2

2π σ 2 r



originating from the coalescence for the growth of particles, where σ is the width of

the distribution and rM is the most probable radius.


Nanocrystals and Clusters


Fig. 3.3 Synthesis facility with a ultrahigh vacuum (UHV) chamber for production of nanocrystalline materials by materials evaporation in a dilute noble gas atmosphere, crystallite condensation,

and compaction

3.1.2 Particle Synthesis by Chemical Routes

Chemical synthesis permits the manipulation at the molecular level and with

high-compositional homogeneity. Scaling up for economical production of large

quantities of materials may be relatively easy in many systems [3.7]. The nanosized

particles may be precipitated from a supersaturated liquid solution or a coprecipitation of the batched ions to multinary materials. For many applications

(paints, electronic inks, ferrofluids) the agglomeration of the nanoparticles should

be suppressed either by particle charging and electrostatic repulsion or by steric


3 Synthesis

manipulation via surfactants reducing the surface tension. The surfactant molecules

can adsorb unto the particle surface and their lyophilic (solution supporting) chains

extend into the solvent and prevent the particles from agglomeration. Metals and

intermetallics nanocrystallites can be synthesized from aqueous solutions. Noble

metals are prepared from aqueous solutions of salts at adjusted pH. Amorphous particles can be produced by adding, e.g., boronhydride at reaction temperatures below

the glass temperature. In addition, particles of conventionally immiscible alloys as

n-Fe–Cu or n-Co–Cu were prepared by aqueous techniques.

In non-aqueous solutions crystalline metal particles can be prepared such as

nanocrystalline iron (n-Fe) by pyrolysis of Fe(CO)5 in polymers or n-Co, n-Ni, n-Cu

in ethylene glycol. Alloys as n-PdCu were synthesized by reduction of the acetates

or n-Fe/Co by co-reduction of the chlorides with LiBEt3 H in THF, where BEt3 is

triethylboron and THF is tetrahydrofuran.

Nanocrystalline ceramic greenbodies can be sintered at substantially lower temperatures than micrometer-sized powders due to the high interface driving force (see

Fig. 3.4). Ultrafine ceramic particles can be obtained by precipitation from solution

such as 16 nm tetragonal ZrO2 powders from precipitated amorphous hydrous

Fig. 3.4 Isochronal

annealing (ta = 60 min) of

nanocrystalline zirconium

dioxide (n-ZrO2 ). (Top)

Fraction fm of monoclinic

phase (•) and crystallite

diameter d (♦) as determined

from x-ray diffraction.

(Middle) Mass density ρ m

(•) and Vickers hardness

HV(♦). The bulk density of

monoclinic ZrO2 is indicated

(· ·). (Bottom) Mean positron

lifetimes τ¯ of

cluster-condensed n-ZrO2 (•)

and of a specimen compacted

from commercial ZrO2

powder (♦) [3.8]. The

decrease of τ¯ with increasing

annealing temperature

indicates the disappearance of

nanovoids upon sintering

which occurs in n-ZnO2 at

lower Ta than for commercial

ZrO2 powder. (Reprinted with

permission from [3.8].

© 1993 Elsevier)


Nanocrystals and Clusters


zirconia with subsequent hydrothermal treatment. MoC and WC nanopowders with

2 nm primary particles were synthesized by the ambient temperature reduction of

the halides with LiBEt3 H.

The advantage of chemical homogeneity on the molecular scale is used for

the production of WC/Co composites for cutting tool applications from the aqueous precipitation of tris(ethylenediamine) cobalt (II) tungstate, tungstic acids, and

ammonium hydroxides. The extremely fine mixtures of the spray-dried W and Co

salts are reduced with H and reacted with CO in a fluidbed reactor to yield WC/Co

nanophase powder [3.9]. Furthermore, n-Si3 N4 /SiC nanoceramics can be prepared

from a liquid organosilazane precursor [CH3 SiHNH]n (n = 3,4) by laser treatment

[3.10] or pyrolysis [3.11].

One important chemical process for the formation of nanophase ceramics is the

sol–gel process where powder size, morphology, and surface chemistry are controlled simultaneously [3.12]. In this case the precursors for ceramics synthesis

are, e.g., alkoxides or colloidal sols. When using organometallic alkoxide precursors, e.g., Al(OC4 H9 )3 for alumina synthesis, reactions such as hydrolysis and

polymerization are employed to the irreversible sol–gel transition (see Fig. 3.5).

Multicomponent nanophase oxides can be prepared by initially mixing several


For the controlled synthesis of nanoscale particles self-assembled membranes

[3.13] are employed which include micelles, microemulsions (Fig. 3.6), liposomes

(water droplets covered by several layers of phospholipids), and vesicles with diameters down to 3–6 nm. The membrane structure serves as reaction cage to control

supersaturation (nucleation and growth of the particles) and acts as agglomeration


Fig. 3.5 Schematic of the oxide skeleton of a dried gel following the alkoxide solution route.

(Reprinted with permission from [3.12]. © 1996 Institute of Physics)

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