Synthesis and Characterization of Magnetic Nanocrystalline

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Ferroelectrics
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Synthesis and Characterization of
Magnetic Nanocrystalline Diamond Films
a
a
Hudson Giovani Zanin , Alfredo Carlos Peterlevitz , Reinaldo
b
a
Francisco Teófilo , Helder Jose Ceragioli & Vitor Baranauskas
a
a
Faculdade de Engenharia Elétrica e de Computação, Departamento
de Semicondutores, Instrumentos e Fotônica – Universidade Estadual
de Campinas, Brazil
b
Departamento de Química –, Universidade Federal de Viçosa, Brazil
Version of record first published: 18 Dec 2012.
To cite this article: Hudson Giovani Zanin , Alfredo Carlos Peterlevitz , Reinaldo Francisco Teófilo ,
Helder Jose Ceragioli & Vitor Baranauskas (2012): Synthesis and Characterization of Magnetic
Nanocrystalline Diamond Films, Ferroelectrics, 436:1, 96-100
To link to this article: http://dx.doi.org/10.1080/10584587.2012.731340
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Ferroelectrics, 436:96–100, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 0015-0193 print / 1563-5112 online
DOI: 10.1080/10584587.2012.731340
Synthesis and Characterization of Magnetic
Nanocrystalline Diamond Films
HUDSON GIOVANI ZANIN,1,∗ ALFREDO CARLOS
PETERLEVITZ,1 REINALDO FRANCISCO TEÓFILO,2
HELDER JOSE CERAGIOLI,1 AND VITOR BARANAUSKAS1
1
Faculdade de Engenharia Elétrica e de Computação, Departamento de
Semicondutores, Instrumentos e Fotônica – Universidade Estadual
de Campinas, Brazil
2
Departamento de Quı́mica – Universidade Federal de Viçosa, Brazil
Magnetic semiconductors are promising materials for electronic applications, because
it is possible to control the quantum state of the electron spin (up or down), providing almost total spin polarization. We present boron-doped nanocrystalline diamond samples
with magnetic properties prepared by chemical vapor deposition process and characterized using X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy,
Raman spectroscopy, scanning electron microscopy and magnetization assays. We believe that ferromagnetic elements were incorporated into the diamond film by diffusion
from stainless steel substrates, during film growth.
Keywords Magnetic diamonds; Boron-doped Nanodiamonds; CVD diamonds; XPS;
EDS; Raman spectroscopy
Introduction
Magnetic semiconductors are promising materials for electronic applications. While traditional (nonmagnetic) electronic devices operation is based on the control of charge carriers
in n-type or p-type semiconductor, in magnetic semiconductors it is also possible to control
the quantum state of the electron spin (up or down), providing almost total spin polarization
[1–4]. Such property, for instance, can be used to construct memory devices that do not
lose their data when the power is turned off.
We present boron-doped nanocrystalline diamond samples with magnetic properties
prepared by Chemical Vapor Deposition (CVD) process. Ferromagnetic elements were
incorporated into the diamond film by diffusion from stainless steel substrates, during film
growth. The CVD process allows the incorporation of magnetic particles concomitantly to
boron incorporation, forming p-type magnetic semiconductor materials. We believe that
this process, compared with ion beam implantation, produces better samples since there is
no need of annealing to reconstruct the damaged path caused by implantation.
The material characterization was performed by Energy Dispersive X-ray Spectroscopy (EDS), Raman spectroscopy, Scanning Electron Microscopy (SEM), X-ray
Received April 18, 2012; in final form July 19, 2012.
∗
Corresponding author. E-mail: [email protected]
96
Magnetic Nanocrystalline Diamond Films
97
Photoelectron Spectroscopy (XPS) and Superconducting Quantum Interference Device
(SQUID).
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Sample Preparation
The diamond films were deposited onto rods of stainless steel (AISI316) substrates, by
Hot-filament-assisted Chemical Vapor Deposition (HFCVD). Tubes of 6 mm in diameter
and 110 mm in length were used as substrates. Prior to deposition, the substrates were
pre-treated by scratching or sandblasting to increase the surface roughness, and cleaned in
isopropyl alcohol during 30 min in an ultra-sonic bath to remove impurities. After cleaning,
the substrates were dipped in a colloidal mixture of diamond dust (0.25 µm in diameter)
dispersed by ultrasonic vibration in n-hexane to increase the concentration of diamond
nucleation centers.
The cylindrical substrate was positioned vertically between two W filaments, parallel
to the axis of the sample. The flow of the feed gas was along the axis of the set-up. During
the deposition process, the substrates were rotated at approximately 4 rpm by magnetic
coupling to an electric motor outside the reactor chamber.
Diamond films were grown from a mixture of ethyl alcohol (C2 H5 OH) vapor diluted
in hydrogen (99.5% vol.) at a total flow rate of 115 standard cubic centimeters per minute
(sccm), regulated by precision mass flow meters, and at a pressure of approximately 20
Torr. The boron doping source was obtained by adding a B2 O3 /water solution to the ethyl
alcohol feed reservoir before starting-up the reactor. The boron–carbon (B/C) concentration
ratio in the feed was 5000 ppm.
The filaments of 272 µm in diameter and 120 mm length were heated by a power
supply with power in the range (400–600) W. In all the experiments, the temperature was
gradually raised to the desired value, maintained constant during the film growth and, at
the end of the experiment, the electric power was suddenly turned off, so favouring the
delamination of the film from the substrate. All the presented results were obtained utilizing
self-sustained diamond samples.
Results and Discussion
Figure 1(A) presents a SEM image of a self-sustained diamond film that was grown on
stainless steel (AISI316) substrate. Average growth rate of 0.5 µm h−1 was achieved,
after long initial nucleation. As one can see in Fig. 1(A), the size of the nanograins is
roughly around 10 nm. Fig. 1(B) shows the Raman spectrum, which is typically of CVD
produced nanodiamond, presenting broad peaks at 1140, 1350, 1480 and 1550 cm−1 that
are signatures of the CVD diamond nanocrystalline structures [5–8].
Figure 2 shows Energy Dispersive X-ray Spectroscopy (EDS) measurements indicating, besides carbon, the presence of Fe, Cr and Ni, which are ferromagnetic elements. Even
though the AISI316 steel substrate does not have magnetic properties, the diamond films
grown on it, have. The ferromagnetic elements, during the deposition, diffused from the
substrate to the growing film.
Figure 3 presents XPS (X-ray Photoelectron Spectroscopy) spectra of the C1s and O1s
lines. The carbon line is adjusted with two components: at 284.6 eV and 286.1 eV binding
energy. While the first, the most intense one, is due to C-C sp3 hybridization of diamond
phase [9], the other component probably results from carbon atoms bonded with oxygen,
such as C-O, found in adsorbed contaminants or joined with hydroxyl [10]. The O1s line is
fitted with two components: at 530.2 eV and at 532.5 eV. Around the first value are found
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98
H. G. Zanin et al.
Figure 1. Typical (A) top-view electron microscopy image of the as-deposited diamond nanocrystalline samples and (B) Raman spectrum of as-deposited nanocrystalline diamond samples.
Figure 2. EDS spectrum of self-supported nanocrystalline diamond sample indicating the concentration of present chemical elements.
Figure 3. XPS spectra of self-supported nanocrystalline diamond sample showing (A) C1s and (B)
O1s lines.
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Magnetic Nanocrystalline Diamond Films
99
Figure 4. Typical magnetisation curve of self-supported nanocrystalline diamond samples.
peaks due oxides as Fe2 O3 , Fe3 O4 and Cr2 O3 [11,12] The other component (at 532.5 eV)
may be associate with H2 O [11]. H2 O was bubbled into reactor chamber during diamond
growth together with ethyl alcohol and also is a common contaminant in vacuum systems.
We observed that delaminated diamond films, grown on stainless steel substrates, were
attracted by magnets. Then we proceed to the evaluation of the self-sustained diamond
samples, utilizing a magnetometer. Figure 4 shows a typical magnetization curve. Based on
the results, we concluded that the magnetization properties of the diamond samples are due
to the Fe, Cr and Ni doping. We understand that these elements diffused from the stainless
steel substrate to the diamond film during the film growth. Since the diamond is transparent
to the X-ray probe of the EDS system, the determination of the doping concentration
profiles throughout the films, employing this technique, is difficult. As revealed by EDS
analysis, Fe, Cr and Ni are present in the diamond films, but these atoms are much larger
than carbon atoms; so, it would be unlikely to find them substitutionally or interstitially in
the lattice. More probably, they are at the grain borders or interstitially.
Conclusions
Self-sustained nanocrystalline diamond films have been prepared using stainless steel
(AISI316) as substrates. EDS results indicated that ferromagnetic elements as Fe and
Cr were transferred from the substrate to the CVD diamond films. XPS showed O 1s line
consisting of two peaks: at 530.2 eV due oxides of Fe and Cr, and, at 532.5 eV, associate
with H2 O. The C 1s XPS spectrum consisted of one intense component at 284.6 eV due
C-C diamond hybridization and other at 286.1 eV, probably due adsorbed contaminants..
Films detached from the substrate show ferromagnetic properties.
Acknowledgments
The electron microscopy work was performed with the JSM-5900 LV microscope of the
LME/LNLS and the XPS with a VSW 100 spectrometer at IFGW – Unicamp. For Robson
Ricardo da Silva of LMD/IFWG- Unicamp for SQUID- magnetometer measurements. The
wish to thanks the Brazilian agencies FAPESP, CAPES and CNPq for financial support.
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