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C: Physical Processes in Nanomaterials and Nanostructures

Local Structure of Nanocrystalline Aluminum Nitride Stevan Mihajlo Ognjanovic, Manfred Zähres, Christian Mayer, and Markus Winterer J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b06610 • Publication Date (Web): 18 Sep 2018 Downloaded from http://pubs.acs.org on September 29, 2018

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The Journal of Physical Chemistry

Local Structure of Nanocrystalline Aluminum Nitride Stevan M. Ognjanović,∗,† Manfred Zähres,‡ Christian Mayer,‡ and Markus Winterer† †Nanoparticle Process Technology and Center for Nanointegration Duisburg-Essen (CENIDE), University Duisburg-Essen 47057 Duisburg, Germany ‡Department of Chemistry and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, 45141 Essen, Germany E-mail: [email protected]

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Abstract The local structure of chemical vapor synthesized (CVS) crystalline AlN nanoparticles is investigated by combining magic angle spinning nuclear magnetic resonance (MAS NMR) and X-ray absorption spectroscopies. Extended X-ray absorption fine structure (EXAFS) data are analyzed by reverse Monte Carlo (RMC) method and X-ray absorption near edge structure (XANES) is interpreted by first principles feff calculations. The measurements show behavior characteristic of partially disordered systems. Nevertheless, combined analysis of the data, supported by Rietveld refinement of X-ray diffraction patterns, leads to the conclusion that the observed behavior is due to the small size (large surface to volume ratios) of the nanoparticles (dXRD < 6 nm) and that highly crystalline wurtzite AlN is formed during the CVS process.

Introduction Aluminum nitride (AlN) is a wide band gap III-V semiconductor with a broad range of applications – from high-power electronic devices 1 and deep UV optoelectronics 2 to phosphors for light emitting diodes (LED) 3,4 and packaging applications 5,6 . The wide applicability of AlN comes from its interesting combination of properties such as high thermal conductivity with a thermal expansion coefficient closely matching that of silicon, high hardness and temperature stability, good piezoelectric properties, wide direct band gap and low dielectric constant. Despite these good properties, wider application of AlN is hindered by its reactivity with oxygen resulting in oxygen substituting nitrogen and subsequent formation of aluminum vacancies. These defects and, more broadly, local structure in general play a significant role in determining the properties of AlN and, therefore, device performance. The local structure of AlN is mostly studied by electron energy loss near edge structure (ELNES) 7–9 , X-ray absorption near edge structure (XANES) 10 and extended X-ray absorption fine structure (EXAFS) spectroscopies 11 focusing on the Al K-edge. Several studies reported on the N K-edge of AlN as well 8,12,13 . These spectroscopic methods are 2


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usually supported by first principle calculations to aid in the interpretation of the measurements 10,13,14 . MacKenzie and Craven 15 , on the other hand, used EELS spectra of different standards to quantify the extent of oxidation for oxide layers more than 10 nm thick. The oxidation mechanism and kinetics in general have been investigated in various environments 16–18 and by different methods 19–22 , including X-ray diffraction (XRD) 18 and electron energy loss spectroscopy (EELS) 23 . Hayashi et al. 24 used magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy to investigate the local structure of hydrated aluminum nitride and reported a mixture of aluminum coordinated with four nitrogen (AlN4 ) and six oxygen (AlO6 ) atoms, whereas Fitzgerald et al. 25 first reported an ‘intermediate’ four coordinated aluminum oxynitride (AlO4 – x Nx ) species in AlON. However, in addition to EELS and XANES/EXAFS,

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Al MAS NMR can also be used to detect metallic Al and other

impurities in AlN 26 , as well as other crystal phases of AlN 27 . The present study combines several experimental methods ( 27Al MAS NMR, EXAFS and XANES at aluminum and nitrogen K-edges) with first principle computations of XANES spectra and Reverse Monte Carlo analysis of EXAFS spectra in order to gain a better understanding of local structure in AlN nanocrystals.

Methods Powder Synthesis Chemical vapor synthesis (CVS) is used to synthesize nanocrystalline aluminum nitride by reacting triethylaluminium (TEAl) and ammonia in the gas phase as previously reported 28 . As synthesized nanoparticles collected on the walls of a thermophoretic particle collector are scraped of and stored in a glove-box. Table 1 lists the sample names as well as the process parameters used for the synthesis of nanoparticles. In addition to the nanocrystals synthesized by the CVS method, commercial micron- (chemPUR, 99 %) and nano-sized (chemPUR, 99 %) AlN powders are used as references. 3



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Table 1: Sample names, process parameters used for their synthesis, average crystallite diameters and lattice parameters obtained by Rietveld refinement of the X-ray diffraction patterns. Sample

Temperature [◦C] Pressure [mbar]

dXRD [nm]

a [Å]

c [Å] ∗

AlN-2.7

1400

10

2.7(1)

3.094(2)

4.98

AlN-2.9

1000

20

2.9(1)

3.104(2)

5.006(5)

AlN-4.2

1400

20

4.2(2)

3.106(1)

5.026(4)

AlN-5.9

1400

100

5.9(1)

3.112(2)

4.995(1)

AlN-12.2

1550

500

12.2(1)

3.1104(3) 4.9851(7) 3.1118(2) 4.9824(4)

nAlN

commercial

22.4(5)

mAlN

commercial

1 nm) into the nanoparticle, causing broadening of the NMR peaks. For quadrupolar nuclei such as

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Zn and

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Al (I = 5/2), a distribution of the EFG causes second-order broad-

ening, a shift to higher fields and, therefore, unidirectional broadening of the NMR feature. Therefore, for the very small nanoparticles synthesized by CVS, the number of atoms that ‘feel’ the surface as an electronic defect (for a nanoparticle of dXRD = 2.7 nm 3/4 of all atoms are within 5 Å of the particle surface) is significant enough to broaden the NMR spectrum, clearly seen as an asymmetry of the AlN4 coordinated atoms. Furthermore, as the relative amount of Al atoms in the vicinity of the particle surface is higher in smaller crystallites, a smaller fraction of atoms have the ordered tetrahedral surroundings and smaller EFG. In other words, as can be seen in figure 2b, showing the ratio of atoms at locations with no EFG (pseudo-Voigt) and large EFG (Czjzek model) as a function of the ratio of the number of atoms in the ‘bulk’ and in the 5 Å (one unit cell) shell, the asymmetry of the AlN4 peak is more pronounced for smaller crystallites. On the other hand, Hayashi et al. 24 did not observe any asymmetry for their ‘ultrafine AlN powder’, even after hydration. However, the much smaller size of our AlN nanocrystals easily explains this discrepancy – while the CVS synthesized crystals are all below 6 nm, 10


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Hayashi et al. 24 used MAS NMR to measure AlN powder containing particles from 10 nm to 100 nm. The commercial, partially oxidized, nano-sized AlN measured alongside the CVS synthesized samples is on the lower end of that 10 nm to 100 nm range (dXRD = 22.2 nm) and already shows very little asymmetry. Nevertheless, since the sample preparation for NMR measurements was not performed under inert atmosphere, as evidenced by the small AlO6 peak around 2 ppm, additional asymmetry can arise from distortions of the crystal lattice due to the onset of oxidation. This is the most likely explanation for deviations from the theoretical line (dashed line) observed in figure 2b, especially for the commercial nano-sized AlN that has significant contributions from AlO4 , AlO5 and AlO6 coordinated Al atoms. On the other hand, due to its larger particle size and, therefore, smaller specific surface area, the commercial micron-sized AlN powder shows no traces of oxygen in coordination with Al atoms even when the sample is prepared in air (figure 2a).

EXAFS Al K-egde EXAFS spectra collected at the CLS are analyzed using the rmcxas software to complement the information on the local structure of AlN obtained by NMR spectroscopy. The best fits, as determined from the residual R values, are based on models using the wurtzite structure. In case of AlN-12.2 sample (figure 3a) the perfect, infinite AlN crystal (using periodic boundary conditions) results in a fit with R = 22.0 % while the models accounting for the surface atoms, including those with oxygen atoms, generates worse results. This suggests that these nanoparticles can be considered as bulk from the point of view of EXAFS analysis, which is, as discussed above for NMR peak asymmetry, in line with results reported by Hayashi et al. 24 and our own measurements. The biggest deviations are seen in the XANES range of the χ(k) (0 Å−1 to 3 Å−1 ) where the dominant contribution to the magnitude of χ(k) is multiple scattering, which is not accounted for in the rmcxas program as already discussed in the Methods section. 11



In Fourier transform space (R-space), the nearest neighbors, at 1.90 Å, and next nearest neighbors, at 2.94 Å, dominate the EXAFS spectrum with only small contributions of more distant atoms. The analysis of the partial pair distribution functions (pPDF), obtained from the RMC analysis and shown in figures 3c and 3d, reveal that the first shell consists of 3.4(5) N atoms at 1.87(2) Å, while the next nearest neighbors are 11(1) Al atoms at 3.04(3) Å (table 3). Even though the models including the surface of the nanoparticle resulted in a worse fit of the χ(k) data, the slightly lower than expected coordination number could be an indirect indication of the influence of the nanoparticle surface. On the other hand, the fit of the AlN-2.9 sample EXAFS spectra improves slightly from R = 24.2 % to R = 22.1 % when surface atoms are included in the starting atomic configuration. However, initial atomic configurations with other crystal structures and various point defects did not improve the fit further. Moreover, no meaningful differences in final R-values are observed when different amorphous and crystalline forms of aluminum oxide, oxide hydroxide or hydroxide are used, most likely due to the small differences in scattering phase and amplitude of oxygen and nitrogen. The phase-corrected Fourier transform of the spectrum (R-space) is shown in figure 4b with two dominant features at 1.88 Å and 2.94 Å. Due to the small size of the AlN-2.9 nanoparticles, already the second shell peak is suppressed compared to the AlN-12.2 spectra and signal corresponding to shells at longer distances is almost within the noise. According to the pPDF analysis, on average 3.1(5) nitrogen atoms surround the Al absorber at a distance of 1.85(1) Å, while the second nearest neighbor shell is formed by 10(1) aluminum atoms at 3.05(2) Å from the Al absorber. Although the coordination number after RMC is lower than the expected 4 and 12 for nitrogen and aluminum for bulk AlN respectively, it matches the coordination number (within the margin of error) for the initial configuration of a 2.9 nm wurtzite AlN cluster (3.6(3) nitrogen and 10.1(8) aluminum atoms). Additionally, models that included randomly distributed vacancies did not improve the χ(k) fit, further reducing the possibility of lower coordination numbers as a consequence of individual atomic defects 12


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1 5

Data RMC Residual

10

D a ta R M C R e s id u a l

5

1 0

| F T ( χ· k 3 ) |

χ·k3

0

-5

5

-10

0 -15 0

2

4

6

8

10

0

-1

k [Å ]

1

2

3

R

(a)

4

5

6

[Å ]

(b)

2 0

2 0 A l- A l ( R M C ) A l- A l ( in itia l)

A l- N ( R M C ) A l- N ( in itia l) 1 5

1 0

1 0

g

1 5

g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5

5

0

0 0

1

2

3

4

5

6

0

1

r [Å ]

2

3

4

5

6

r [Å ]

(c)

(d)

Figure 3: (a) RMC analysis of the Al K-edge spectra of the AlN-12.2 sample using the perfect, infinite wurtzite crystal. (b) Phase corrected Fourier transform of the spectra shown in (a). (c) and (d) Al – Al and Al – N pPDF.

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present in the crystal and supporting the finding that lower coordination numbers are a consequence of the very small particle size. Katsikini et al. 11 used EXAFS to analyze the local structure of epitaxial AlN and found slightly shorter Al – N and Al – Al bond distances which they attributed to oxygen induced defects. However, while oxygen induced defects cannot be excluded in the present study (as observed by the NMR spectra), we observe no change in the Al – Al bond distances compared to the commercial bulk AlN powder. Furthermore, the difference in Al – N bond length distance between the bulk and the smallest CVS synthesized AlN nanoparticles is too small, with regard to the estimated errors, to be meaningfully discussed in more depth. Table 3: Results of the RMC analysis of EXAFS data - mean coordination number, bond distance and mean square displacement of different shells in bulk AlN, AlN-12.2 and AlN-2.9. The initial atomic configurations used are bulk wurtzite for the mAlN and AlN-12.2 samples and wurtzite cluster for the AlN-2.9 sample. Sample mAlN AlN-12.2 AlN-2.9

AlN bulk model

AlN cluster model

Shell

Range [Å]

Al – Al

2.0 – 3.5

Al – N

1.6 – 2.2

3.5(6)

1.88(2)

8(3)

Al – Al

2.0 – 3.5

11(1)

3.04(3)

53(9)

Al – N

1.6 – 2.2

3.4(5)

1.87(2)

11(5)

Al – Al

2.0 – 3.5

10(1) 3.05(2)

42(7)

Al – N

1.6 – 2.2

3.1(5) 1.85(1)

3(1)

N

r [Å]

11.3(12) 3.05(2)

2

σ 2 [10−3 Å ]

N

r [Å]

2

σ 2 [10−3 Å ]

33(7)

XANES The atomic configurations obtained after the RMC analysis (figure 5) are used to calculate the averaged XANES spectra of the different models as well. However, since the rmcxas optimizes the model pPDF, in other words the distances between atoms in the atomic configuration and not the bond angles or coordination geometry, and does not contain an attractive 14


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1 5 D a ta R M C R e s id u a l

D a ta R M C R e s id u a l

1 0

5

1 0

χ· k

3

| F T ( χ· k 3 ) |

0

-5

5

-1 0

0

-1 5 0

2

4

6

k [Å

-1

8

1 0

0

1

2

]

3

R

(a)

4

5

6

[Å ]

(b)

2 0

2 0 A l- A l ( c lu s te r ) A l- A l ( in itia l)

A l- N ( c lu s te r ) A l- N ( in itia l) 1 5

1 0

1 0

g

1 5

g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5

5

0

0 0

1

2

3

4

5

6

0

1

r [Å ]

2

3

4

5

6

r [Å ]

(c)

(d)

Figure 4: (a) RMC analysis of the Al K-edge spectra of the AlN-2.9 sample using the perfect 2.9 nm AlN cluster. (b) Phase corrected Fourier transform of the spectra shown in (a). (c) and (d) Al – Al and Al – N pPDF.

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



Figure 5: A cross-section of the cluster atomic configuration 2.9 nm in diameter with wurtzite structure before (left) and after (right) RMC optimization. Nitrogen atoms are shown in red and aluminum atoms in blue. potential to ‘crystallize’ the nanoparticle, the obtained atomic configurations are not representative of the actual geometric configuration of atoms in the nanocrystals. This means that averaging the XANES spectra, which are very sensitive to both bond distances and bond angles, results in very broadened spectra resembling those of amorphous materials. Nevertheless, XANES calculations of the initial (unrelaxed) atomic configurations resulted in spectra that correspond quite well to the measured data (figure 6). This is especially interesting considering that no additional broadening was introduced into the calculations. Compared to the Al K-edge XANES spectrum calculated for bulk AlN, the spectrum of a nanoparticle with the same wurtzite structure is significantly broadened indicating that the observed broadening is, at least partially, a consequence of the different environments of the absorbing Al atoms near the nanoparticle surface and in the core of the nanoparticle. Additional broadening observed in the measured data could originate from crystal defects present in the actual nanoparticles or species adsorbed or reacted with their surface. Guda et al. 44 reported an intense pre-edge shoulder at 1560.5 eV in Al K-edge XANES spectra of 100 nm AlN particles which they attributed to metallic aluminum in their sample. This was noteworthy as their long-range order studies by X-ray diffraction suggested that the 16


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A lN - 2 .9 A lN b u lk ( F E F F ) A lN c lu s te r ( F E F F )

N o r m a l i z e d µ( E )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 5 5 0

1 5 6 0

1 5 7 0

1 5 8 0

1 5 9 0

1 6 0 0

E n e rg y [e V ]

Figure 6: feff simulated XANES spectra of different initial atomic configurations and the measured spectrum of the AlN-2.9 sample. The calculated spectrum of the bulk model has been offset in ordinate direction for better clarity. nanoparticles contained only comparable amounts of wurtzite and zincblende AlN phases, with no indications of any metallic aluminum. Diffraction patterns of the CVS synthesized samples (see figure 1, for example) show only the reflections characteristic of the wurtzite structure, and, as can be seen in figure 7a, no pre-edge peaks are observed in their XANES spectra. This further supports our findings that the nanoparticles are composed of pure wurtzite AlN. As shown in figure 7a, decreasing the particle size from several microns to a few nanometers results in a shift of the edge position to higher energies. A small edge shift is observed for the AlN-12.2 sample as well, however, the crystallite diameter of 12.2 nm is far too large for any confinement effects to be observed (the Pollmann-Büttner-Kane exciton radius is about 18.0 Å 45 ). This is confirmed by the Brus equation 46 and electron confinement effects are, therefore, excluded as a source of the shift. A possible explanation, supported by FEFF calculations presented in figure S1a in the supporting information, could be the difference in lattice parameters between bulk and nano-sized materials. In addition to the shift of the edge with decreasing particle size, figure 7a shows that the intensity of the white line decreases. In fact, averaging of feff spectra predicts such 17



N K -e d g e P F Y


B u lk A lN A lN - 1 2 .2 A lN - 2 .9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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B u lk A lN A lN - 1 2 .2 A lN - 2 .9

A l K -e d g e T E Y 1 5 6 0

1 5 7 0

1 5 8 0

1 5 9 0

1 6 0 0

4 0 0

E n e rg y [e V ]

4 1 0

4 2 0

4 3 0

E n e rg y [e V ]

(a)

(b)

Figure 7: Al K-edge XANES TEY (a) and N K-edge XANES PFY (b) spectra of commercial micron-sized AlN and CVS synthesized AlN-12.2 and AlN-2.9 samples. The vertical grey line in (a) is a guide to the eye aligned to the maximum of the white line to make the shift of the spectra more apparent. a decrease for a nanoparticle, as can be seen in figure 6. This is, like the XANES broadening, due to effects of the surface of the nanoparticle which broadens the p-density of states (pDOS). However, the relative decrease of the measured white line is greater than that predicted by feff for a pure AlN nanoparticle. Orthogonalized linear combination of atomic orbitals (OLCAO) calculations performed by Mizoguchi 47 and our own feff simulations show (figure S2 in Supporting information) that the white line is mainly composed of Alabsorber p – N s interactions. Therefore, any change in the amount of nitrogen, by presence of nitrogen vacancies or substitution by oxygen for example, would reduce the intensity of the interactions and thereby the white line. The presence of oxygen could induce a further shift in the Fermi level as seen in figure 8 for the hypothetical example of a wurtzite AlO crystal. While this crystal structure is not thermodynamically stable it has been observed during AlN oxidation 11,48 . According to the feff calculations in figure 8, this would shift the Fermi level to higher energy. In other words, the p-states that would normally lead to the relatively intense white line observed in AlN are filled and unable to contribute to the

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E f

F E F F ( A lO ) F E F F ( A lN )

= - 1 0 .4 8 6 e V f

= - 6 .0 2 5 e V


E

p D O S ( A lO ) p D O S ( A lN )

D O S

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-1 0

0

1 0

2 0

E [e V ]

Figure 8: feff XANES simulation of Al K-edge in wurtzite AlN and hypothetical AlO crystals (top) with the corresponding local p-density of states of an Alabsorber atom (bottom). The Fermi levels are plotted with dashed lines.

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XANES spectrum thereby further decreasing the white line intensity. Moreover, any oxygen present, even adsorbed at the surface of the nanocrystal, would decrease the electron density around the absorbing Al atom and, with it the screening of the core hole, shifting the edge to higher energies. Nitrogen K-edge spectra are collected, as already stated, in both partial fluorescence and total electron yields as well. No systematic differences could be observed between them and all the features present in the PFY spectra are present in the TEY spectra as well (not shown). Jones and Woodruff 49 reported that the electron escape depth in metallic Al is 65 Å and 130 Å in aluminum oxide. Therefore, even though the surface-sensitive TEY collects information from depths of up to 130 Å from the surface, it is still not surface-sensitive enough to discriminate between the core and the shell of the CVS synthesized nanocrystals with diameters of up to 12.2 nm. The PFY recorded at the nitrogen K-edge are shown in figure 7b. All the observed features are characteristic of wurtzite AlN, and, similarly to the Al K-edge spectra of the nanoparticles, they are broadened and damped compared to the bulk AlN. However, in line with the feff simulations of AlN with bulk lattice parameters and the lattice parameters obtained from the Rietveld refinement of the AlN-2.9 XRD pattern (figure S1b in Supporting information), no systematic shifts are observed.

Conclusions The local structure of CVS synthesized nanoparticles has been investigated by

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Al MAS

NMR, EXAFS and XANES spectroscopies. The measurements, supported by XRD, confirm that well crystallized wurtzite AlN is obtained from the gas phase synthesis process. Small amounts of aluminum oxide (1 %) are detected by NMR in some samples, and the decrease in the white line intensity hints at the presence of oxygen. Nevertheless, RMC analysis of EXAFS data and feff XANES simulations show that pure wurtzite AlN fits to the measured data the best. Moreover, while asymmetric peaks in NMR and broadened features of the

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XANES spectra might normally indicate the presence of disorder, we have shown that those effects can be related to the effects of the surface which plays a significant role in the very small nanoparticles (dXRD < 6 nm). The influence of the surface on the somewhat larger particles (dXRD > 12 nm) is lower, and they show EXAFS and XANES spectra similar to bulk AlN.

Supporting Information Available Figure S1 shows the feff simulations of aluminum (a) and nitrogen (b) K-edge XANES spectra of a crystal with bulk lattice parameters 29 and lattice parameters obtained from Rietveld refinement of the AlN-2.9 diffraction pattern. A shift of the edge position with the change of lattice parameters can be seen in the case of aluminum edge, but no change is observed for the nitrogen edge. Figure S2 shows the feff XANES simulations of one abosrber atom in the AlN cluster (top) and the corresponding Alabsorber p and N s density of states (bottom). The Fermi level is plotted with a dashed line. By comparing the peak positions in the graphs it is evident that both Alabsorber p and N s density of states contribute to the white line intensity.

Acknowledgement This work was supported by the German Research Foundation (DFG) through project WI 981/13-1. The authors gratefully acknowledge the provision of XAS beamtime at the SGM beamline at the Canadian Light Source and Tom Regier and James Dynes for the support at the beamline.

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References (1) Morkoç, H. Handbook of Nitride Semiconductors and Devices; John Wiley & Sons: Weinheim, Germany, 2009; Vol. 1 Materials Properties, Physics and Growth. (2) Taniyasu, Y.; Kasu, M.; Makimoto, T. An Aluminium Nitride Light-Emitting Diode with a Wavelength of 210 nanometres. Nature 2006, 441, 325–328. (3) Hu, H.; Ji, X.; Wu, Z.; Yan, P.; Zhou, H.; Du, S.; Wu, X.; Gong, G.; Li, C. Synthesis and Photoluminescence of AlN:Mn Hexagonal Maze-like Complex Nanostructure. Mater. Lett. 2012, 70, 34–36. (4) Yang, J.; Wang, T.; Chen, D.; Chen, G.; Liu, Q. An Investigation of Eu2+ -doped CaAlSiN3 Fabricated by an Alloy-Nitridation Method. Mater. Sci. Eng., B 2012, 177, 1596–1604. (5) Xu, Y.; Chung, D.; Mroz, C. Thermally Conducting Aluminum Nitride Polymer-Matrix Composites. Composites Part A 2001, 32, 1749–1757. (6) Kim, W.; Bae, J.-W.; Choi, I.-D.; Kim, Y.-S. Thermally Conductive EMC (Epoxy Molding Compound) for Microelectronic Encapsulation. Polym. Eng. Sci. 1999, 39, 756–766. (7) Eustis, T. J.; Silcox, J.; Murphy, M. J.; Schaff, W. J. Evidence from EELS of Oxygen in the Nucleation Layer of a MBE grown III-N HEMT. MRS Proceedings 1999, 595, F99W3.31. (8) Holec, D.; Rachbauer, R.; Kiener, D.; Cherns, P. D.; Costa, P. M. F. J.; McAleese, C.; Mayrhofer, P. H.; Humphreys, C. J. Towards Predictive Modeling of Near-Edge Structures in Electron Energy-Loss Spectra of AlN-Based Ternary Alloys. Phys. Rev. B 2011, 83, 165122.

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