On the nature of ionic liquid gating of Nd₂CuO₄ thin films
Recently, ionic liquid gating has been used to modulate the charge carrier properties of metal oxides. The mechanism behind it, however, is still a matter of debate. In this paper, we report experiments on doped and undoped Nd₂CuO₄. We find major resistance drops of the bilayer coupled to observatio...
Gespeichert in:
| Datum: | 2017 |
|---|---|
| Hauptverfasser: | , , , , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2017
|
| Schriftenreihe: | Физика низких температур |
| Schlagworte: | |
| Online Zugang: | http://dspace.nbuv.gov.ua/handle/123456789/129380 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | On the nature of ionic liquid gating of Nd₂CuO₄ thin films / Hasan Atesci, Francesco Coneri, Maarten Leeuwenhoek, Hans Hilgenkamp, Jan M. van Ruitenbeek // Физика низких температур. — 2017. — Т. 43, № 2. — С. 353-359. — Бібліогр.: 50 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-129380 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-1293802018-01-20T03:05:30Z On the nature of ionic liquid gating of Nd₂CuO₄ thin films Atesci, Hasan Coneri, Francesco Leeuwenhoek, Maarten Hilgenkamp, Hans Jan M. van Ruitenbeek К 100-летию со дня рождения И.М. Лифшица Recently, ionic liquid gating has been used to modulate the charge carrier properties of metal oxides. The mechanism behind it, however, is still a matter of debate. In this paper, we report experiments on doped and undoped Nd₂CuO₄. We find major resistance drops of the bilayer coupled to observations of the presence of a considerable Faradeic component in the gate current and of the appearance of charge transfer peaks in the cyclic voltammetry data. This leads us to propose a mechanism of gating based on irreversible electrochemical reactions, likely due to trace amounts of contaminations present in the ionic liquid. This work is therefore in line with previous reports confirming the presence of irreversible electrochemistry in ionic liquid gated electron- doped cuprates. 2017 Article On the nature of ionic liquid gating of Nd₂CuO₄ thin films / Hasan Atesci, Francesco Coneri, Maarten Leeuwenhoek, Hans Hilgenkamp, Jan M. van Ruitenbeek // Физика низких температур. — 2017. — Т. 43, № 2. — С. 353-359. — Бібліогр.: 50 назв. — англ. 0132-6414 PACS: 66.10.–x, 68.15.+e, 82.45.–h http://dspace.nbuv.gov.ua/handle/123456789/129380 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
К 100-летию со дня рождения И.М. Лифшица К 100-летию со дня рождения И.М. Лифшица |
| spellingShingle |
К 100-летию со дня рождения И.М. Лифшица К 100-летию со дня рождения И.М. Лифшица Atesci, Hasan Coneri, Francesco Leeuwenhoek, Maarten Hilgenkamp, Hans Jan M. van Ruitenbeek On the nature of ionic liquid gating of Nd₂CuO₄ thin films Физика низких температур |
| description |
Recently, ionic liquid gating has been used to modulate the charge carrier properties of metal oxides. The mechanism behind it, however, is still a matter of debate. In this paper, we report experiments on doped and undoped Nd₂CuO₄. We find major resistance drops of the bilayer coupled to observations of the presence of a considerable Faradeic component in the gate current and of the appearance of charge transfer peaks in the cyclic voltammetry data. This leads us to propose a mechanism of gating based on irreversible electrochemical reactions, likely due to trace amounts of contaminations present in the ionic liquid. This work is therefore in line with previous reports confirming the presence of irreversible electrochemistry in ionic liquid gated electron- doped cuprates. |
| format |
Article |
| author |
Atesci, Hasan Coneri, Francesco Leeuwenhoek, Maarten Hilgenkamp, Hans Jan M. van Ruitenbeek |
| author_facet |
Atesci, Hasan Coneri, Francesco Leeuwenhoek, Maarten Hilgenkamp, Hans Jan M. van Ruitenbeek |
| author_sort |
Atesci, Hasan |
| title |
On the nature of ionic liquid gating of Nd₂CuO₄ thin films |
| title_short |
On the nature of ionic liquid gating of Nd₂CuO₄ thin films |
| title_full |
On the nature of ionic liquid gating of Nd₂CuO₄ thin films |
| title_fullStr |
On the nature of ionic liquid gating of Nd₂CuO₄ thin films |
| title_full_unstemmed |
On the nature of ionic liquid gating of Nd₂CuO₄ thin films |
| title_sort |
on the nature of ionic liquid gating of nd₂cuo₄ thin films |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2017 |
| topic_facet |
К 100-летию со дня рождения И.М. Лифшица |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/129380 |
| citation_txt |
On the nature of ionic liquid gating of Nd₂CuO₄ thin films / Hasan Atesci, Francesco Coneri, Maarten Leeuwenhoek, Hans Hilgenkamp, Jan M. van Ruitenbeek // Физика низких температур. — 2017. — Т. 43, № 2. — С. 353-359. — Бібліогр.: 50 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT atescihasan onthenatureofionicliquidgatingofnd2cuo4thinfilms AT conerifrancesco onthenatureofionicliquidgatingofnd2cuo4thinfilms AT leeuwenhoekmaarten onthenatureofionicliquidgatingofnd2cuo4thinfilms AT hilgenkamphans onthenatureofionicliquidgatingofnd2cuo4thinfilms AT janmvanruitenbeek onthenatureofionicliquidgatingofnd2cuo4thinfilms |
| first_indexed |
2025-07-09T11:16:19Z |
| last_indexed |
2025-07-09T11:16:19Z |
| _version_ |
1837167839312609280 |
| fulltext |
Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 2, pp. 353–359
On the nature of ionic liquid gating of Nd2–xCexCuO4
thin films
Hasan Atesci1, Francesco Coneri2, Maarten Leeuwenhoek1, Hans Hilgenkamp2,
and Jan M. van Ruitenbeek1
1Huygens-Kamerlingh Onnes Laboratorium, Universiteit Leiden, Postbus 9504, 2300 RA Leiden, The Netherlands
E-mail: ruitenbeek@physics.leidenuniv.nl
2MESA+ Institute for Nanotechnology, University of Twente
P.O. Box 217, 7500 AE Enschede, The Netherlands
Received August 19, 2016, published online December 26, 2016
Recently, ionic liquid gating has been used to modulate the charge carrier properties of metal oxides. The
mechanism behind it, however, is still a matter of debate. In this paper, we report experiments on doped and
undoped Nd2CuO4. We find major resistance drops of the bilayer coupled to observations of the presence of a
considerable Faradeic component in the gate current and of the appearance of charge transfer peaks in the cyclic
voltammetry data. This leads us to propose a mechanism of gating based on irreversible electrochemical reac-
tions, likely due to trace amounts of contaminations present in the ionic liquid. This work is therefore in line
with previous reports confirming the presence of irreversible electrochemistry in ionic liquid gated electron-
doped cuprates.
PACS: 66.10.–x Diffusion and ionic conduction in liquids;
68.15.+e Liquid thin films;
82.45.–h Electrochemistry and electrophoresis.
Keywords: Nd2–xCexCuO4, ionic liquid, conductance, electrochemistry, nanoionics.
Since its discovery in 1986 [1], high temperature super-
conductivity (HTS) in doped Mott-insulator cuprates has
generated much interest [2]. Although the mechanism of
pairing remains illusive [3–6], many of its characteristics
have been firmly established. Cuprate HTS can be either
hole-doped or electron-doped, and typically shows a dome-
shaped phase diagram as a function of chemical doping
[7]. However, chemical doping induces disorder in the
Mott-insulator compound [8], which can be avoided by
electrostatically doping the HTS using an oxide gate die-
lectric [9–12]. Oxide gate dielectrics have successfully
achieved changes in the critical temperature of cuprates
[13]. But, due to the break down electric field [14,15], the
induced charge carrier density is limited to ~ 1013 cm–2,
having only a relatively small influence on the changes on
the conductive properties of the cuprate [16]. This is due to
the fact that the charge carrier density in Mott-insulator
cuprates requires an areal density of up to 1014 cm–2 in
order to go through the phase diagram of HTS cuprates. To
overcome this problem, ionic liquids (ILs) have recently
been used as gate media to generate high carrier accumula-
tion [17,18]. ILs consist entirely of ions, and when a volt-
age is applied across the IL, Helmholtz electric double
layers are formed. These layers consist of ions of one kind
of the IL and the induced charge carriers of the solid and
are separated ~ 1 nm from each other. With IL gating, car-
rier densities of up to 8⋅1014 cm–2 are achievable [17,18],
substantially higher than what is attainable with their con-
ventional dielectric counterparts, making it possible to in-
duce insulator-to-superconductor transitions [19–21].
In this work, we attempt to address two points of inter-
est. Firstly, most of the IL experiments on cuprates have
been done on hole-doped cuprates [19,20,22], whereas for
electron-doped compounds only Pr2–xCexCuO4 and
NdBa2Cu3O7–δ have been tested with ILs [23–25]. Hence,
IL gating on electron-doped cuprate compounds is im-
portant for obtaining a more complete picture of its effects
on cuprates and high-temperature superconductors in gen-
eral. Secondly, there is an increasing number of articles
stating that the effect of IL gating in cuprates and other
oxides is related to electrochemistry [25–30], indicating
that the ideal picture of EDL electrostatics suggested in
some articles [19–21,22] might not be valid.
We have applied the IL gating technique at the
pulsed laser deposition (PLD) grown electron-doped
cuprate of single layers of undoped Nd2CuO4 (NCO)
© Hasan Atesci, Francesco Coneri, Maarten Leeuwenhoek, Hans Hilgenkamp, and Jan M. van Ruitenbeek, 2017
Hasan Atesci, Francesco Coneri, Maarten Leeuwenhoek, Hans Hilgenkamp, and Jan M. van Ruitenbeek
and bilayers of 0.10 Ce doped Nd2–xCexCuO4 ( = 0.10x )
(NCCO) and NCO (NCCO/NCO). We have used a dep-
osition temperature of 820 °C and O2 pressure of
2.5⋅10–1 mbar. The NCO and NCCO targets are ablated
using a laser fluence of ~ 1.2 J/cm–2 and repetition rate
of 4 Hz. The cuprate is grown on substrates formed by a
pristine (LaAlO3)0.3(Sr2TaAlO6)0.7 (001) (LSAT) crystal.
The cuprate and substrate have lattice parameters of 3.94 Å
and 3.87 Å, leading to some epitaxial strain in NC(C)O.
For the reason of lowering the epitaxial strain of the upper
layers, we have grown the bilayers [22,31–33].
By varying the lens and mask positions and the energy
of the laser beam, we can influence the spot size of the
laser beam, while keeping the laser fluence constant at
1.2 mJ/cm–2. We observe that a lower spot size and a low-
er energy leads to a lower growth rate of the compound per
pulse, and is in general more suitable for layer-by-layer
growth. For our system, we find a growth rate of 0.5 Å per
pulse using optimized settings (spot size of 2.2 mm2 and
an energy of 29.3 mJ) for layer-by-layer growth. To moni-
tor the in-situ growth of the cuprate, we have used Refrac-
tive High Energy Electron Diffraction (RHEED) Fig. 1(a).
The intensity of the specular reflected beam shows clear
oscillations for the first unit cells of the compound. The
amplitude of these oscillations quickly dies out, indicating
a transition from layer-by-layer growth to island-like
growth fashion. For the thicknesses of the films we are
interested in, the resulting morphology of the films is char-
acterized by screw dislocations, showing the spiral growth
mode of the cuprate grains Fig. 1(b), and is similar to what
is found for cuprates grown on substrates having lattice
mismatches [34,35].
We have tested a total of 22 samples, where the NCO
single layers have thicknesses varying from 12 to 48 unit
cells, while NCCO/NCO bilayers have bottom layers that
are 24 to 46 unit cells thick and top layers that are 4 to 12
unit cells thick. We show that IL gating has an effect in
lowering the resistance of a bilayer of the compound, and
we argue that this is caused by electrochemical reactions,
likely because of trace amounts of impurities present in the
IL. The results shown in this paper are for a particular
NCCO/NCO bilayer of 20 unit cells thick NCO and 5 unit
cells thick NCCO, and is reproducible for the other sam-
ples, unless stated otherwise.
After PLD deposition, we use photolithography to de-
fine areas on the sample that will be maintained, while the
rest is removed by argon ion milling. In order to decrease
the contact resistance, all of the remaining bilayer is cov-
ered by sputter deposition of Ti/Au, apart from the bilayer
of the channel area. In order to prevent unnecessary leak-
age currents, the substrate surface is then covered by an
insulating photoresist layer, except for the gate electrode
and channel (Fig. 2(a)). The exposed areas are chemically
etched in an oxygen plasma (100 mTorr, 13 W) which re-
moves any residuals of the photolithographic process.
The sample is then placed inside a N2 atmosphere
glovebox (<0.1 ppm O2, H2O), where it is heated to 120 °C to
remove any water on top of the surface. The ionic liquid
bottle containing N,N-diethyl-N-(2-methoxyethyl)-N-me-
thylammoniumbis(trifluoromethyl-sulphonyl)imide (DEME-
TFSI), is kept in the same atmosphere. Before any usage
of the IL, it is preheated at 60 °C for a period of more than
72 hours. With the insertion of a needle in the IL bottle, a
small droplet is formed at the end of the needle, which is
Fig. 1. (Color online) RHEED intensity vs time graph which shows the oscillations of the specular reflected beam for the first few unit
cells of the cuprate, after which the amplitude of the oscillation goes to zero, indicating an island-like growth fashion. The arrow indi-
cates the start of the PLD process, while the asterisks show the instances where the electron beam intensity has been increased manual-
ly (a). The AFM data shows the screw-island growth mode of a typical cuprate film on LSAT. The step heights coincide with half a
unit cell of NC(C)O (1.2 nm) (b).
354 Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 2
On the nature of ionic liquid of gating Nd2–xCexCuO4 thin films
then put on top of the gate electrode and the bilayer chan-
nel area (Fig. 2(b)). Next, the sample is transported to the
insert chamber of the measurement setup, which is flushed
with He gas and pumped several times to remove contami-
nations (O2 and H2O) from the atmosphere of the sample.
We use two Keithley 2400 SourceMeters for the exper-
iments. One SourceMeter is used to measure the four termi-
nal resistance of the channel. To this end, we apply a current
bias between the source and drain electrodes (500 nA),
while limiting the maximum voltage sdV to 250 mV. We
use the other SourceMeter for the application of a gate
voltage gV and monitoring the gate current gI . In order to
limit electrochemical processes influencing carrier doping
of the channel, the maximum gV applied is 2.5 V, which
lies well within the potential window of the liquid [36,37].
Furthermore, the experiments are performed at a suitable
charging temperature of 210 K [21], above the melting
point of DEME-TFSI of 184 K [38].
Our measurement comprises five cycles of two sub
measurements. The first sub measurement is in-situ cyclic
voltammetry (CV) in order to test for possible chemical
reactions in the Au/IL/bilayer system [39]. During the CV,
gI is measured while modulating gV from 0 V to 2.5 V and
back to 0 V again at a scan rate of 5 mV/s. The second sub
measurement records the ( )gI t and four terminal resistance
( )R t characteristics of the channel after switching the gate
voltage from zero to +0.5 V, +1.0 V, +1.5 V, +2.0 V and
+2.5 V for 15 minutes. After the second sub measurement
is finished, the Keithley instruments are reset to zero for
approximately 30 minutes. The relaxation time of the
charges in the IL can be estimated by IL EDLR C , where ILR
is the resistance of the IL, approximated to be in the order
of 109 Ω [40]. The electric double layer capacitance is es-
timated as 2 nF, since the channel area is 1.5⋅10–4 cm–2
and the specific capacitance is 13 µF⋅cm–2. Thus, the RC
time is in the order of seconds, making the waiting time of
30 minutes sufficiently long to cancel any memory effect
of the ions.
The CV data in Fig. 3 indicates the presence of irre-
versible reactions. This is based on the fact the first cyclic
voltammogram does not show any peaks, indicating that
the IL is clean and that no electrochemical reactions take
place in the initial stages of the experiment. The subse-
quent CVs do show peaks, denoted as peaks I (cathodic), II
and III (both anodic). Peak I is located between 1.35 and
1.95 V and indicates an initial reduction. Peak II and III are
located between 1.1 and 1.435 V, and 0.29 and 0.55 V,
respectively. If peak I would be caused by a reversible re-
action, only one anodic peak would be expected. However,
we see two anodic peaks, indicating the oxidation of either
the product(s) or a part of the product(s) of this reduction.
Furthermore, if peaks I and II are part of the same reversi-
ble reaction, the Nernst equation would dictate that for
reversible electrochemistry the difference in potential of
Fig. 2. (Color online) A schematic cross section of the sample. Here, yellow and blue spheres represent TFSI(–) and DEME(+) ions,
respectively. The gate (G), source (S) and drain (D) electrodes are 6 nm (Ti) + 150 (Au) nm thick and are made using photolithography
after deposition of the bilayer. A separator layer (SL) ensures only the bilayer channel at the surface of the NCCO between the source
and drain electrodes is in contact with the ionic liquid droplet. Applying a voltage between the gate and drain electrodes leads to a
charge buildup in the channel (a). A schematic top view of the sample. Except for the large Au gate electrode around the center of the
sample, the Au contacts at the sides of the samples, and the channel area near the center, the whole surface is covered by a hard-baked
photoresist layer. The contacts at the sides are connected to a Hall bar configuration of electrodes on the channel to measure electronic
properties of the channel area of the bilayer, which is freed from photolithographic residuals by oxygen plasma etching. A current is
sent through the source (S) and drain (D) electrodes. In combination with voltage probes placed at one side of the sample, the four-point
resistance of the channel is measured, having an area of 50×300 µm2. The gate electrode, has an exposed area of more than 100 times
the area of the exposed NCCO channel (b).
Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 2 355
Hasan Atesci, Francesco Coneri, Maarten Leeuwenhoek, Hans Hilgenkamp, and Jan M. van Ruitenbeek
the anodic and cathodic peaks lies within 0.059 V [41].
Moreover, one would expect that both peaks are equal in
amplitude. The CV data shows however, that the potential
separation of both peaks (I and II) is 0.27 V < ∆V < 0.51 V,
while the magnitude of peak I is approximately 3 to 10 times
larger than peak II for all CV scans.
The presence of irreversible electrochemistry is further
supported by AFM data. (Fig. 4(a)) shows an image of the
surface of a freshly prepared sample, with structure typical
for island growth of the films. The importance of this ob-
servation is that the edges of the islands expose sites with
higher reactivity, which could act as possible seeding loca-
tions for electrochemical reactions. Before the experiment,
the sample surface topography showed a root mean
squared (rms) roughness value of 0.87 nm (Fig. 4(a)). Af-
ter the IL gating experiments, the surface is altered dramat-
ically, having a substantially higher rms roughness value of
2.35 nm (Fig. 4(b)).
Another argument for electrochemistry is based on our
gate current vs time data. After switching the gate voltage
to the set value at the start of the second sub measurement,
the gate current data shows a rapid initial decrease, fol-
lowed by a slowly decaying function, a typical graph of
which is shown in Fig. 5. In case the charging process is
strictly electrostatic, the total accumulated charge would be
given by = gQ ACV . Here, A is the total NCCO area and
C is the specific capacitance, being equal to 1.5⋅10–4 cm2
and 13 µF⋅cm–2 [42], respectively, making the expected
charge roughly 5 nC for the highest gate voltages used.
The observed charge, calculated as the integral of gI , how-
ever, is typically one to two orders of magnitude higher for
all measurements, suggesting other mechanisms, notably
electrochemical reactions, play a role.
We find that the ( )gI t characteristic cannot be fitted
with only an exponential term, indicative of electrostatic
charging of the bilayer. Rather, we need to add a Faradeic,
diffusive, term with a certain proportionality constant K ,
i.e. ( ) = /I t K t to fit the whole curve, with
= .cAF DK
π
Fig. 3. (Color online) Plots showing 6 CV scans. The first cyclic
voltammogram does not show any peaks and indicates a chemically
pure IL, while the others show peaks increasing in amplitude as a
function of the cycle number. As the number of CV scans increases,
several peaks (I, II and III) start to appear. Peak I is located between
1.35 and 1.95 V and indicates an initial reduction. Peak II and III are
located between 1.1 and 1.435 V, and 0.29 and 0.55 V, respectively.
We observe that the potential separation between peaks I and II is
0.27 V < ∆V < 0.51 V. Furthermore, the amplitude of peak I is a
factor 3 to 10 higher than that of peaks II and III.
Fig. 4. (Color online) AFM images of the surface of the bilayer before (a) and after (b) IL gating experiments. Before the experiments,
the AFM image shows that NCCO has a topography which is island-based. The roughness of the sample is 0.87 nm (a). After the exper-
iments, the surface lost the former characteristics, and has a higher roughness of 2.35 nm (b).
356 Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 2
On the nature of ionic liquid of gating Nd2–xCexCuO4 thin films
Fig. 6. (Color online) ( )R t curve recorded when at = 0t s a gV of 0.5 V is applied. The curve shows a change R∆ , defined as the
difference between R at = 0t s ( 0R ) and the value of the tangent line at = 0t s of R at = 900t s (a). The observed relative change
in R as a function of gate voltage and cycle number at 210 K. The change in R is systematic and becomes larger as gV and the num-
ber of cycles increases (b). Normalized resistance of the NCCO/NCO channel plotted as a function of T for gV = 0 V, +0.5 V, +1.0 V,
+1.5 V, +2.0 V and +2.5 V. The behavior is semiconductor-like, and shows a systematic decrease of the resistance up to a gate voltage
of +2.0 V. However, applying a gate voltage of +2.5 V leads to sample degradation. The inset figure shows the same type of graph for a
film of similar doping which has not been IL gated, showing a critical temperature onset of 12 K (c).
Here, c is the concentration of the substance taking part
in the electrochemical reaction A is the area of the bilayer
surface, F is the Faraday constant, and D is the diffusion
coefficient of the reactive species. We find that the pro-
portionality constant for all of the curves is between
0.04 nA⋅s1/2 < K < 1.4⋅nA⋅s1/2. The large spread in this
parameter is due to the fact that it is gate voltage depend-
ent, where a larger applied gate voltage would lead to
higher gate currents and therefore higher proportionality
constants. If we assume the cations and anions of the IL
are taking part in the reaction, we come to the conclusion
that the desired diffusion constant of the species should be
10–β cm2/s, with β = 14–18. In this calculation, we take an
approximate value for the density of the IL to be 1.5 g/cm–3.
The obtained value of D , however, is many orders of magni-
tude below the expected literature values for DEME-TFSI,
which is 10–β cm2/s, with β = 8.6–10.6 [43,44]. Because of
this difference in diffusion coefficient values, it is not
plausible that the anions and cations of the IL take part in
the irreversible reaction. A more likely scenario is that
trace amount of impurities like hydrogen and oxygen pre-
sent in the IL react with the surface. Indeed, it has been
shown that impurities of hydrogen can lead to major gating
effects in oxides [27,45,46], while oxygen impurities can
lead to either the doping of oxygen [47], or the generation
of oxygen vacancies [28,30,48]. Although it has been
shown that both hydrogenation [49] and (de)oxygenation
[50] are applicable to NCCO, it is not possible to deduce
which of these processes are present in the present system
with our current techniques.
In Fig. 6(a) we show that the resistance R systematical-
ly decreases an amount R∆ when a positive gate voltage is
applied. Here, R∆ is the difference between R at = 0t s
0( )R and the value of the tangent line at = 0t s of R at
= 900t s. In the next figure, the relative change of R is
plotted as a function of cycle number and gV (Fig. 6(b)).
The conductance gains in the first cycle are limited and the
relative change in R is 5% at the highest gV of +2.5 V.
However, as the cycle number is increased, the relative
change in R shows a systematic increase as a function of
both gV and the cycle number, having a relative change
close to 25% at +2.5 V. This clearly shows the irreversibil-
ity of the gating effect, while reversibility is expected in
case the gating would be electrostatic. This behavior is
typical for single-layered channels of NCO as well. We
also observe that the relative change of R is larger for
samples that have been tested with a lower degree of puri-
Fig. 5. ( )gI t curve for a gV of 2.5 V at 210 K. The inset shows
the total accumulated charge Q vs time, calculated by integrating
( )gI t . The total accumulated charge Q exceeds the value that
one would expect for a purely electrostatic charge of the NCCO
layer, i.e. roughly 5 nC.
Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 2 357
Hasan Atesci, Francesco Coneri, Maarten Leeuwenhoek, Hans Hilgenkamp, and Jan M. van Ruitenbeek
fication of IL, again indicating that impurities play a major
role in the effect. In Fig. 6(c) we plot the normalized re-
sistance vs. temperature of the gated bilayer. In this figure,
we observe semiconducting behavior down to 10 K. For
gate voltages up to +2.0 V we observe a systematic de-
crease of the resistance, but no onset of superconductivity,
while a film similar in doping without being gated did be-
come superconductive below 12 K (inset of Fig. 6(c)). The
application of a higher gate voltage ( gV ≅ 2.5 V) leads to
sample degradation.
In summary, we have applied IL gating on the single
layers of NCO and bilayers NCCO/NCO. We observe that
repeated gating leads to the appearance of peaks in the
cyclic voltammogram. These reactions have a substantial
influence in the resistance of the NCCO layer, especially
after a prolonged period of gating, which goes hand in
hand with pronounced distortions of the NCCO surface.
Together with these observations, we see that accumulated
charge in the system that far exceeds the expected electro-
static accumulation. All of these point to the presence of
irreversible electrochemical reactions. The fitting of the
gate current data indicates that these are caused by traces
of impurities in the ionic liquid. With the present tech-
nique of PLD growth of the material and the choice of
substrate, we have found that it is not possible to obtain
layer-by-layer growth, which would help prevent electro-
chemical reactions happening in the compound. This work
confirms previous work done on electron-doped cuprates
of NdBa2Cu3O7–x and Pr2–xCexCuO4. In the former mate-
rial, IL gating has been found to produce oxygen vacan-
cies. In Pr2–xCexCuO4, gate voltages above + 2.5 V lead to
irreversible electrochemical reactions [23]. Similarly, using
gate voltages below + 2.5 V leads to a relatively little gating
effect, not enough to induce a superconducting transition [24].
Acknowledgement
This work is part of the research programme of the
Foundation for Fundamental Research on Matter (FOM,
12PR3047), which is financially supported by the Nether-
lands Organization for Scientific Research (NWO). The
authors also gratefully acknowledge the technical support
from J. Aarts and S. Voltan.
1. J. Bednorz and K.A. Müller, Z. Phys. B 64, 189 (1986).
2. E. Dagotto, Rev. Mod. Phys. 66, 763 (1994).
3. D.J. Scalapino, Phys. Rep. 250, 329 (1995).
4. M.A. Kastner, R.J. Birgeneau, G. Shirane, and Y. Endoh,
Rev. Mod. Phys. 70, 897 (1998).
5. T. Timusk and B. Statt, Rep. Prog. Phys. 62, 61 (1999).
6. J. Orenstein and A.J. Millis, Science 288, 468 (2000).
7. C.H. Ahn, A. Bhattacharya, M. Di Ventra, J.N Eckstein, C.
Daniel Frisbie, M.E. Gershenson, A.M. Goldman, I.H.
Inoue, J. Mannhart, A.J. Millis, A.F. Morpurgo, D. Natelson,
and J.M. Triscone, Rev. Mod. Phys. 78, 1185 (2006).
8. K. Ueno, S. Nakamura, H. Shimotani, H.T. Yuan, N. Kimura,
T. Nojima, H. Aoki, Y. Iwasa, and M. Kawasaki, Nature
Nanotechn. 6, 408 (2011).
9. D. Matthey, S. Gariglio, and J.M. Triscone, Appl. Phys. Lett.
83, 3758 (2003).
10. M. Salluzzo, A. Cassinese, G.M. De Luca, A. Gambardella,
A. Prigiobbo, and R. Vaglio, Phys. Rev. B 70, 214528
(2004).
11. A. Cassinese, G.M. De Luca, A. Prigiobbo, M. Salluzzo, and
R. Vaglio, Appl. Phys. Lett. 84, 3933 (2004).
12. J. Mannhart, J.G. Bednorz, K.A. Miiller, and D.G. Schlom,
Z. Phys. B 83, 307 (1991).
13. J. Mannhart, Supercond. Sci. Technol. 9, 46 (1996).
14. H.C. Lin, P.D. Ye, and G.D. Wilk, App. Phys. Lett. 87,
182904 (2005).
15. Y.H. Wu, M.Y. Yang, and A. Chin, IEEE Electron Dev. Lett.
21, 341 (2000).
16. V.C. Matijasevic, S. Bogers, N.Y. Chen, H.M. Appelboom,
P. Hadley, and J.E. Mooij, Physica C 235, 2097 (1994).
17. H. Yuan, H. Shimotani, A. Tsukazaki, A. Ohtomo, M.
Kawasaki, and Y. Iwasa, Adv. Func. Mater. 19, 1046 (2009).
18. H. Shimotani, H. Asanuma, A. Tsukazaki, A. Ohtomo, M.
Kawasaki, and Y. Iwasa, Appl. Phys. Lett. 91, 082106
(2007).
19. X. Leng, J. Garcia-Barriocanal, S. Bose, Y. Lee, and A.M.
Goldman, Phys. Rev. Lett. 107, 027001 (2011).
20. J. Garcia-Barriocanal, A. Kobrinskii, X. Leng, J. Kinney, B.
Yang, S. Snyder, and A.M. Goldman, Phys. Rev. B 87,
024509 (2013).
21. G. Dubuis, A.T. Bollinger, D. Pavuna, and I. Bozovič,
J. Appl. Phys. 111, 112632 (2012).
22. A.T. Bollinger, G. Dubuis, J. Yoon, D. Pavuna, J. Misewich,
and I. Bozovič, Nature 472, 458 (2011).
23. K. Jin, W. Hu, B. Zhu, D. Kim, J. Yuan, Y. Sun, T. Xiang,
M.S. Fuhrer, I. Takeuchi, and R.L. Greene, Sci. Rep. 6,
26642 (2016).
24. S.W. Zeng, Z. Huang, W.M. Lv, N.N. Bao, K. Gopinadhan,
L.K. Jian, T.S. Herng, Z.Q. Liu, Y.L. Zhao, C.J. Li, H.J. Harsan
Ma, P. Yang, J. Ding, T. Venkatesan, and A. Ariando, Phys.
Rev. B 92, 020503 (2015).
25. L. Zhang, S.W. Zeng, D.Y. Wan, K. Han, L.K. Jian, A.
Ariando, and T. Venkatesan, APS March Meeting (2016).
26. Y. Zhou and S. Ramanathan, J. Appl. Phys. 111, 084508
(2012).
27. H. Ji, J. Wei, and D. Natelson, Nano Lett. 12, 2988 (2012).
28. J. Jeong, N. Aetukuri, T. Graf, T.D. Schladt, M.G. Samant,
and S.S.P. Parkin, Science 339, 1402 (2013).
29. M. Nakano, K. Shibuya, D. Okuyama, T. Hatano, S. Ono, M.
Kawasaki, Y. Iwasa, and Y. Tokura, Nature 487, 459 (2012).
30. K. Ueno, H. Shimotani, Y. Iwasa, and M. Kawasaki, Appl.
Phys. Lett. 96, 252107 (2010).
31. H. Sato, H. Yamamoto, and M. Naito, Physica C 274,
(1997).
32. A. Rüfenacht, P. Chappatte, S. Gariglio, J. Leemann, C.
Fompeyrine, J.-P Locquet, and P. Martinoli, Solid-State
Electron. 47, 2167 (2003).
358 Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 2
http://meetings.aps.org/link/BAPS.2016.MAR.V25.11
On the nature of ionic liquid of gating Nd2–xCexCuO4 thin films
33. Y. Jaccard, A. Cretton, E.J. Williams, J.-P Locquet, E.
Mächler, C. Gerber, T. Schneider, O Fischer, and P.
Martinoli, Proc. SPIE 2158, 200 (1994).
34. B. Prijamboedi and S. Kashiwaya, J. Mater. Sci: Mater.
Electron 17, 483 (2006).
35. L. Luo, M.E. Hawley, C.J. Maggiore, R.C. Dye, R.E.
Muenchausen, L. Chen, B. Schmidt, and A.E. Kaloyeros,
Appl. Phys. Lett. 62, 1993 (1993).
36. E.O. Polat, O. Balci, and O. Kocabas, Sci. Rep. 4, 6484
(2014).
37. J.T. Ye, S. Inoue, K. Kobayashi, Y. Kasahara, H.T. Yuan, H.
Shimotani, and Y. Iwasa, Nature Mater. 9, 125 (2010).
38. T. Sato, G. Masuda and K. Takagi, Electrochimica Acta 49,
3603 (2004).
39. J.F. Rusling and S.L. Suib, Adv. Mater. 6, 922 (1994).
40. H. Yuan, H. Shimotani, J. Ye, S. Yoon, H. Aliah, A.
Tsukazaki, M. Kawasaki, and Y. Iwasa, J. Am. Chem. Soc.
132, 18402 (2010).
41. P.T. Kissinger and W.R. Heineman, J. Chem. Education 60,
702 (1983).
42. T. Tsuchiya, M. Ochi, T. Higuch, K. Terabe, and M. Aono,
ACS Appl. Mater. Interfaces 7, 12254 (2015).
43. K. Hayamizu, S. Tsukuzi, S. Seki, Y. Ohno, H. Miyashiro,
and Y. Kobayashi, J. Phys. Chem. B 112, 1189 (2008).
44. K. Hayamizu, S. Tsukuzi, and S. Seki, J. Chem. Eng. Data
59, 1944 (2014).
45. X. Meng, F. Quenneville, F. Venne, E. Di Mauro, D. Işik, M.
Barbosa, Y. Drolet, M.M. Natile, D. Rochefort, F. Soavi, and
C. Santo, J. Phys. Chem. C 119, 21732 (2015).
46. T. Katase, K. Endo, T. Tohei, Y. Ikuhara, and H. Ohta, Adv.
Electron. Mater. 1, 1500063 (2015).
47. J. Shi, S.D. Ha, Y. Zhou, F. Schoofs, and S. Ramanathan,
Nature Commun. 472, 458 (2013).
48. M. Li, W. Han, J. Jeong, M.G. Samant, and S.S.P. Parkin,
Nano Lett. 13, 4675 (2013).
49. K. Kobayashi, Y. Goto, S. Matsushima, and G. Okada,
J. Mat. Sci. Lett. 10, 523 (1991).
50. W. Jian, S.N. Mao, X.X. Xi, X. Jian, J.L. Peng, T.
Venkatesan, C.J. Lobb, and R.L. Greene, Phys. Rev. Lett. 73,
1291 (1994).
Low Temperature Physics/Fizika Nizkikh Temperatur, 2017, v. 43, No. 2 359
http://dx.doi.org/10.1038/srep06484
Acknowledgement
|