Supporting information for:
Laser desorption Time-of-Flight Mass Spectrometry of atomic switch
memory Ge2Sb2Te5 bulk materials and its thin films
Jan Houška1, Eladia Maria Peña-Méndez2, Jakub Kolář3, Jan Přikryl3, Martin Pavlišta3, Miloslav
Frumar3, Tomáš Wágner3, Josef Havel1,4,*
1
2
Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
Department of Analytical Chemistry, Nutrition and Food Chemistry, Faculty of Chemistry, University of La Laguna, Campus de
Anchieta, 38071 La Laguna,Tenerife, Spain
3
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, 532 10 Pardubice, Czech
Republic
4
Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
*Correspondence to: J. Havel, Department of Chemistry, Faculty of Science, Masaryk University, Kamenice
5/A14, 625 00 Brno, Czech Republic.
E-mail: havel@chemi.muni.cz
1
Characterization of prepared GST:
Microanalysis of the bulk samples and films was carried out by scanning electron microscopy (SEM)
using JSM-5500LV instrument (JEOL Ltd. Tokyo, Japan) with an energy dispersive x-ray (EDX)
microanalyser (IXRF Systems, Austin, TX, USA) operated at 20 kV). The ellipsometric parameters psi,
and delta, , (spectral ellipsometer, Variable Angle Spectroscopic Ellipsometry (VASE); J.A.
Woollam Co., Lincoln, NE, USA) were measured and optical parameters (index of refraction, n,
extinction coefficient, k, thickness, d) calculated in 300-2300 nm spectral region. All the ellipsometric,
transmission, and depolarization data were analyzed simultaneously by WVASE software.
The temperature dependence of the sheet resistance was measured by the Van der Pauw method[1] at an
average heating rate v = 2 K min-1. The thermally treated films were further characterized by
SEM-EDX. Raman spectra were obtained with a Fourier Transformation (FT) micro-Raman
spectrometer (Bruker Biospin, Ettlingen, Germany) using = 785 nm solid-state laser with an output
power of 20 - 36 mW. The resolution of the Raman spectrometer was 1 cm-1. X-ray diffraction (XRD)
microanalysis by scanning electron microscopy of the phase-change material films shows that the
Intensity [a.u.]
material is amorphous (Figs. S1 and S2).
3
2
1
10
15
20
25
30
35
40
45
50
55
60
65

2
Figure S1.
X-ray diffraction (XRD) patterns
Figure S2.
Scanning electron
of amorphous GST films prepared using the
microscope picture of the Ge2Sb2Te5 film and its
conditions listed in Table I, including XRD
surface. The composition of the film and surface
spectra assignment. Curves numbers agree with
droplets is listed in Table II.
sample no. in Table I. The XRD patterns are
obtained from just crystallized films.
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Table I. Parameters of pulsed laser deposition.
Sample no.
Target
composition
Laser energy
(mJ)
Pulse
Laser
Film
frequency
deposition
thickness
time (min)
(Hz)
(nm)
1
Ge2Sb2Te5
300
20
10
190
2
Ge2Sb2Te5
200
20
9
140
3
Ge2Sb2Te5
150
20
10
125
Table II. Thin film prepared by PLD (sample no. 2, Tab I.) with laser pulse duration 30 ns.
Composition
Ge [at. %]
Sb [at. %]
Te [at. %]
Theoretical
22.22
22.22
55.55
Thin film (Fig. S2)
23.81
20.72
55.47
Droplets on surface (Fig. S2)
25.24
20.43
54.33
The thermal properties of the Ge2Sb2Te5 films measured by differential scanning calorimetry
(DSC) provided additional evidence that the films are amorphous with a glass transition
temperature, Tg, in the range of 100-125°C and a crystallization temperature, Tc, with onset
around 175°C, (Fig. S3). Another technique used for probing the amorphous nature of the
phase-change material was Crystallization of the GST films. The results (Fig. S4) also show
changes of resistivity of the film during heating and crystallization of the film. The obtained
values for sheet resistance and crystallization temperature are comparable with those
previously described [2].
25.0
Rs [/sqr.]
Heat Flow Endo Up [mW]
1
25.5
24.5
24.0
23.5
50
100
150
200
250
300
109
108
107
106
105
104
103
102
101
PLD
0
Temperature [°C]
Figure S3.
DSC curve obtained on
50
100 150
200
250 300
T [°C]
Figure S4.
Van der Pauw sheet
PLD film (Sample no. 2, Table I) during
resistance measured on PLD film (Sample
heating. Scan rate is 5 K min-1.
no. 2, Table I) during heating. Scan rate is
2 K min-1.
Micro-Raman spectroscopy was applied to the PLD films (Fig. S5), and vibration bands at 122, 139
cm-1 and a shoulder at 161 cm-1 were identified in the spectra. Although assignment is not easy for
GST, the bands at 131, 147 and 166 cm-1 have been found in GST films [3,4] and they were assigned to
the vibration of particular structural units: 131 cm-1 (GeTe4), 147 cm-1 (Te-Te) and 166 cm-1 (Sb2Te3).
1400
Ge2Sb2Te5 thin film prepared by PLD (sample
no. 2, Tab. I.)
polycrystalline bulk Ge2Sb2Te5 sample
1200
Intensity [a.u.]
1000
Measured by microraman
 =785nm, W=20-36mW
800
600
400
200
0
50
100
150
200
250
300
350
400
Wavenumber [cm-1]
Figure S5.
Micro-Raman spectra of the GST crystalline target and PLD films (no. 2, Table I.).
References
[1] P. M. Hemenger. Measurement of High Resistivity Semiconductors Using the van der Pauw
Method. Rev. Sci. Instrum. 1973, 44, 698.
[2] Y. F. Lai, B. W. Qiao, J. Feng, Y. Le, L. Z. La, Y. Y. Lin, T. A. Tang, B. C. Cai, B. M. Chen.
Nitrogen-doped Ge2Sb2Fe5 films for nonvolatile memory. J. Electron. Mat. 2005, 34, 176.
[3] J. Tominaga, N. Atoda. Jap. J. Appl. Phys. Part 2-Letters Study of the Crystallization of GeSbTe
Films by Raman Spectroscopy. 1999, 38, L322.
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[4] R. Zhao, T. C. Chong, L. P. Shi. Study of the structural transformation of Ge2Sb2Te5 induced by
current pulse in phase change memory. Mat. Res. Soc. Symp. Proc. 2004, 803, 89.
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