実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF Experimental Report

25 June 2011

課題番号 Project No.

装置責任者 Name of responsible person

2010A0026

Prof. Yasuhiro Miyake

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Muon States in Nanostructured Carbon Materials

D1 (muon)

実験責任者名 Name of principal investigator

実施日 Date of ExperimentRoderick M. Macrae

26-28 November 2010

所属 Affiliation
Marian University, Indianapolis, USA
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
All samples were of novel carbonaceous materials: (1) graphite platelet nanofibers (column diameter 50-250nm), obtained from Aldrich, (2) nanotube forest materials (provided by group of Kenji Hata, AIST), and (3) two
samples of starch-derived mesoporous carbon (“Starbon”), one nominally “hydrophilic”, the other“hydrophobic” (see below for clarification), provided by James Clark and Peter Shuttleworth at the Green
Chemistry Centre of Excellence at the University of York. All samples were solid powders or flakes as originallyprovided. Approximately 1 g of each sample was available. For µSR experiments, the samples were compressed
into pellets of approximately 2 cm in diameter, enclosed in one layer of 16 micron aluminum foil.

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

New forms of nanostructured and mesostructured carbonaceous materials are expected to find a variety oftechnological uses ranging from nanoengineering [1] to spintronics [2] to ultracapacitors [3,4]. Fundamental
studies of such materials using a probe which can give some local insight into the physical and chemical
properties of the voids are thus of some importance. Muon spin rotation studies have been carried out on
diamond [5,6], graphite [7], amorphous carbon [8], fullerenes [9], and nanotubes [10], and are summarized in therecent review by Cox [11]. While in diamond both bond-centered muonium and interstitial muonium areobserved [5], in graphite the paramagnetic state formed on muon implantation undergoes rapid spin or charge
exchange with the conduction electrons leading to a collapse of the radical line and a temperature-dependent``paramagnetic shift'' in the muon Larmor frequency [7]. Insulating amorphous carbon presumably contains alarge variety of paramagnetic sites (not experimentally resolvable), but was observed by Cox and Davis to have adiamagnetic fraction of around 40% [8]. In single-walled nanotubes MacFarlane and co-workers observed a highfraction (about 40%) of vacuum-like muonium [10]. Fullerenes show distinct states corresponding to muons
stopping respectively inside and outside the cages.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
Though it is evident that µSR methods distinguish clearly between a variety of different bonding types exhibitedby carbonaceous materials, to date there have been no studies in the published literature of muon implantation innanostructured “activated carbon” materials of catalytic importance.
For this preliminary study the method chosen was low transverse field precession measurement to establish thesize of the diamagnetic fraction, together with longitudinal field repolarization measurements to yield an
approximate measure of the distribution of hyperfine coupling constants in the material. The nanotube forest
materials proved to have a density too low for practicable measurements, so measurements focused on thegraphite platelet nanofibers and on the two “Starbon” starch-derived activated carbon materials [12]. Anovernight “disk full” issue led to corruption of all of the LF data on the graphite platelet nanofiber material.
Calibration of signal asymmetry was accomplished through the use of a holmium target. A substantial fraction of
the calibration data set was also corrupted due to the disk problem.
The “hydrophilic” Starbon material is generated by heat
treatment at a lower temperature than the “hydrophobic”
material, and might be expected to be less graphitic incharacter and to retain more of the structural characteristics oftheoriginal

starchmaterial,modified

somewhatbydehydration. This prediction appears to be supported by roomtemperature LF repolarization data (see Figure 1), which show
only a small repolarizing fraction in the hydrophobic sample
and a much larger one in the hydrophilic sample, suggestingthat the latter retains substantial isolated radical-forming
double bond character whereas the former is substantially
Figure 1. LF scans in hydrophilic (filledgraphitized. These preliminary results suggest that muoncircles) and hydrophobic (open circles)

methods can yield insights into the internal bond type“Starbon” catalyst materials.

distribution and reactivity of these materials.

Attempts to measure the temperature-dependence of the repolarization patterns for the Starbon materials wereunsuccessful due to technical issues with the cryostat. (The helium return line had been left open, resulting in thecooling process stalling at 184 K, followed by a slow return to 190 K.)
References[1] Y. Nakayama, S. Akita, New J. Phys. 5, (2003), 128; [2] B. Zhao et al., Appl. Phys. Lett. 80, (2002), 3144; [3] M. D. Stoller etal., Nano Lett. 8, (2008), 3498; [4] MIT LEES laboratory project; see e.g http://lees.mit.edu/lees/posters/RU13_signorelli.pdf; [5] E.
Holzschuh et al., Phys. Rev. A 25, (1982), 1272; [6] B. D. Patterson, Rev. Mod. Phys. 60, (1988), 69; [7] D. P. Hutchinson et al.,Phys. Rev. Lett. 7, (1961), 129; J. Chakhalian et al., Hyperﬁne Interact. 106, (1997), 245; S. F. J. Cox et al., J. Phys.: Condens.
Matter 13, (2001), 2169; [8] E. A. Davis, S. F. J. Cox, 2000 ISIS Annual Report, cited in [11]; [9] E. J. Ansaldo et al., Nature 353,(1991), 121; [10] W.

A. MacFarlane et al., Physica B 289-290, (2000), 589; [11] S. F. J. Cox, Rep. Prog. Phys. 72, (2009),116501; [12] V. Budarin et al., Angew. Chem. Int. Ed. 45, (2006), 3782.

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