Article
Cite This: Anal. Chem. 2018, 90, 8954−8959

pubs.acs.org/ac

Controlled Deposition Number of Organic Molecules Using Quartz
Crystal Microbalance Evaluated by Scanning Tunneling Microscopy
Single-Molecule-Counting
Eiichi Inami,*,†,‡ Masataka Yamaguchi,† Takayuki Yamaguchi,† Mikio Shimasaki,†and Toyo Kazu Yamada*,†,§†

Department of Materials Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
School of Systems Engineering, Kochi University of Technology, 185 Miyanokuchi, Tosayamada, Kami, Kochi 782-8502, Japan§
Molecular Chirality Research Center, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Downloaded via CHIBA UNIV on August 7, 2018 at 09:15:06 (UTC).
See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information*

ABSTRACT: Precise control of organic molecule deposition
on a substrate is quite important for fabricating singlemolecule-based devices. In this study, we demonstrate
whether a quartz-crystal microbalance (QCM) widely used
for a ﬁlm growth calibration has the ability to precisely
measure the number of organic molecules adsorbed on asubstrate. The well-known Sauerbrey’s equation is extended toformulate the relation between QCM resonant frequency shift
and the number of adsorbed molecules onto the QCM
surface. The formula is examined by QCM measurements ofsublimation of π-conjugated organic molecules and direct
counting of the deposited molecules one by one onto metal
substrates, using ultrahigh vacuum low-temperature scanningtunneling microscopy (STM). It is revealed that the numberof adsorbed molecules evaluated by QCM (NQCM) show good agreement with those counted from the STM images (NSTM)
within the error of ±25%. The results ensure the QCM capability for controlling the deposition number of organic moleculeswith high accuracy, that is, if one needs to deposit 100 molecules on the substrate, QCM control promises deposition of 100 ±25 molecules.
variety of organic molecular ﬁlms supported bysubstrates have been used for molecular electronic
devices, such as electroluminescence, 1−5 photovoltaic
cells,6−12 and ﬁeld-eﬀect transistor.13−15 Some of these devices
are realized by vacuum sublimation,3,4,6,11−13 where the welldeﬁned planar ﬁlm with low defect/impurity concentration isgrown on a substrate. In this method, a quartz-crystal
microbalance (QCM) is used to control the thickness of themolecular ﬁlms. QCM is a thickness-shear-mode acoustic wave
mass-sensitive detector, where the attached foreign mass isobservable through the shift in resonant frequency of theoscillating quartz crystal, as formulated by Sauerbrey.16 To
evaluate the ﬁlm thickness from the measured mass change, theﬁlm density (g·cm−3) is the one key parameter. For QCM
measurement, the sublimated molecules are generally assumed
to cover the whole acoustically active area of QCM surface,forming a uniform ﬁlm with spatially constant density. This
assumption is applicable if the ﬁlm thickness is over a few tensof nanometers since the structure of such thick ﬁlms is almost
bulklike. Therefore, the ﬁlm density can be calibrated bycomparing the attached mass measured by QCM with the ﬁlm
thickness measured by the other techniques.17

A© 2018 American Chemical Society

On the other hand, recent extensive studies on single
molecules on substrates18−25 unveiled exciting novel properties
that motivate us to fabricate high functional molecule-based
devices.26,27 To this end, the sophisticated regulation of themolecular deposition to prepare isolated single molecules or
two-dimensionally ordered ultrathin molecular ﬁlms (including
monomolecular or a few molecular layers) on substrates isquite important. In such low coverage regions, however, thespatially constant ﬁlm density cannot be assumed since themolecular aggregations are aﬀected by the molecule−substrateinterface and the bare ﬁlm surface. Such a surface/interface
causes the change in the separations of monomolecular layers
depending on the layer number.25 Further, under thesubmonolayer coverage regions, the molecules on substrate
do not form ﬁlms but exist as either islands (clusters) or single
molecules, where the ﬁlm density cannot be deﬁned inprinciple. Therefore, thickness control is inadequate toprecisely control deposition of small amounts of molecules.
Received: March 13, 2018
Accepted: June 27, 2018
Published: June 27, 2018
8954

DOI: 10.1021/acs.analchem.8b01118
Anal. Chem. 2018, 90, 8954−8959

Article

Analytical Chemistry

Figure 1. (a) Home-built UHV-LT-STM setup, consisting of three parts: introduction, preparation, and analytical chambers. Samples and tips weremoved between these chambers with transfer rods. (b) Close-up view of the sample preparation chamber, where a quartz-crystal microbalance(QCM), a molecular evaporator, and a sample stage are shown. All point to the center of the chamber. (c) Close-up view of the analytical chamber,where the transfer rod, two cooling shields, and STM are shown. (d) Home-built molecular evaporator using a commercial UHV-ICF70 current
feedthrough, where molecules in an Al2O3 crucible were heated by ﬂowing current through a W ﬁlament. An alumel−chromel thermocouple islocated at the bottom of the crucible to measure the temperature of the crucible. Using the PID control power supply, the crucible temperature wasstabilized during the evaporation.

Alternatively, the number of molecular depositions isimportant and should be varied in a controlled way.
In this article, we demonstrated control of the adsorption
number of single organic molecules on the substrate by using
QCM, whose accuracy was evaluated by direct counting ofdeposited molecules on the substrate one by one, using
ultrahigh vacuum (UHV) low-temperature (LT) scanningtunneling microscopy (STM). Sauerbrey’s equation16 was
extended to relate the number of adsorbed molecules onto the
QCM plate with the resulting QCM frequency shift. The
formula enabled us to control the number of adsorbed
molecules on the substrate without information on the ﬁlm
density. The necessary information regarding the molecules
was only the molar mass. That is, our method needed no
preliminary calibration that is required for the conventional
QCM measurement. The validity of our formula was examined
by QCM measurements of sublimation of π-conjugatedmolecules [iron phthalocyanine (FePc) and metal-freetetraphenylporphine (H2TPP)] and direct STM imaging of
their depositions onto metal substrates [Cu(111) andAu(111)]. Markedly, the number of adsorbed single organic
molecules controlled by QCM on the basis of our formula wasin quite good agreement with that counted from the obtained
STM image within an error of ±25%.

■

Δf = −

2f02(μq ρq )1/2

Δm = −CmΔm(1)

In this equation, Δf Hz is the measured frequency shift; f 0 Hz
is the resonant frequency of the quartz crystal; Δm g·cm−2 isthe mass change per unit area at the QCM surface; μq = 2.947
× 1011 g·cm−1·s−2, the shear modulus of quartz; ρq = 2.468 g·
cm−3, the density of quartz; and Cm = 8.15 × 107 Hz·g−1·cm2,
the sensitivity factor. Under the assumption that the masschange is caused by the adsorptions of homogeneous
molecules with the molar mass of M, Δm can be expressedin terms of the number of adsorbed molecules per unit areanQCM cm−2 as Δm = MnQCM/NA, where NA = 6.02 × 1023
mol−1 is the Avogadro constant. Then, eq 1 can be rewriten as
Δf = −

2f02

M
nQCM = −CnnQCM(μq ρq )1/2 NA(2)In this equation, Cn is the sensitivity factor. Note that eq 2 does
not include the density of adsorbed molecules. Therefore, if wea priori know the M value of the target molecules, Δf can bedirectly converted to nQCM. For example, f 0 of the bare quartz
in our system is 6 MHz (the sensitivity limit of Δf is 0.03 Hz).
Therefore, if the M is assumed as 600 g·mol−1, Cn is evaluatedto be 8 × 10−14 Hz·cm2. In this condition, nQCM = −Δf/Cn (seeeq 2) means that the QCM could have an ability to detect one
organic molecule adsorption per 17 × 17 nm2 area.

METHODS

The principle for measuring the number of adsorbed molecules
by QCM is as follows. According to Sauerbrey,16 mass changes
at the QCM surface are generally expressed by
8955

DOI: 10.1021/acs.analchem.8b01118
Anal. Chem. 2018, 90, 8954−8959

Article

Analytical Chemistry■

introduction chamber28 and then subsequently setting into the
STM stage.

EXPERIMENTAL SECTION
All experiments were performed using a home-built UHV-LTSTM setup (base pressure <8 × 10−9 Pa). Our systemcomprises an introduction, a preparation, and an STM
analytical chamber (see Figure 1a), which are interconnected
for performing substrate cleaning, molecular deposition, andSTM observation without exposing the sample to theatmosphere.
Sample Preparations. Cu(111) and Au(111) were usedas substrates. Both substrates were subjected to several cycles
of Ar+ ion sputtering (1 kV) and annealing [873 K forCu(111), and 800 K for Au(111)] in the preparation chamber,by which cleaned and atomically ﬂat surfaces were obtained. As
test molecules, two types of π-conjugated molecules, FePc and
H2TPP, were used. FePc powder (Aldrich, purity 90%) was
puriﬁed by sublimation at 653 K and by recrystallization at 453
K under the pressure of 10−1 Pa (yield 12%), while the
puriﬁcation was not performed for H2TPP powder. The
molecular powders were then placed into the Al2O3 crucible ina home-built molecular evaporator and were pumped down to10−8 Pa.
Molecular Evaporator. As shown in Figure 1b, theevaporator was set at one of the ports in the preparationchamber pointing toward the center of the chamber. A gate
valve was used as a shutter to separate the evaporator and the
preparation chamber. The evaporator was also connected tothe introduction chamber for exchanging the molecule without
breaking the UHV of the preparation chamber. Figure 1dshows the sketch of the evaporator. A W wire (diameter 0.3mm) was set around the crucible, which was used as a ﬁlament
by ﬂowing current (0−6 A). An alumel−chromel thermocouple was located at the bottom of the crucible. The crucible andthe ﬁlament were shielded by a Cu cylinder to make a crucible
temperature equivalent. Using a proportional-integral-derivative (PID) controller of the power supply, the crucible
temperature during the molecular evaporation could be
precisely controlled (see Supporting Information).
Molecular Deposition. Prior to molecular depositions, thedeposition rates were ﬁrst monitored by QCM (Inﬁcon, 6
MHz, 14 mm diameter, AT-cut quartz crystal with Auelectrode) in the preparation chamber (see Figure 1b). During
the measurement, the QCM head was placed at the center ofthe preparation chamber. After setting the crucible temperature at predetermined values, the QCM resonant frequency f
was measured with the gate valve opened. Following the QCM
measurement, the QCM head was withdrawn, and thesubstrate was alternatively placed at the center of the
preparation chamber to start molecular depositions. During
the deposition, the pressure in the preparation chamber was
about 10−8−10−7 Pa. After molecular depositions, the sample
was quickly set to the STM stage located in the analyticalchamber which was cooled by a UHV-cryostat. Surrounding
the STM, 5 and 80 K cooling shields cut heat radiation. The
sample in the STM stage could be quickly exchanged by
opening doors on the shields with a wobble stick (see Figure
1c).
Sample Characterization. STM measurements were
performed in the constant current mode at 4.7 K withliquid-He and at 78 K with liquid-N2. Electrochemically etched
W-tips (ϕ = 0.3 mm, purity 99.99%) were used for the STM
probe. Each tip was carefully cleaned by annealing in the■

RESULTS AND DISCUSSION
Deposition of Submonolayer FePc on Cu(111). To
check the earlier idea, we compared the number of adsorbed
molecules on substrates between QCM and STM measurement (see the Experimental Section). Figure 2a shows the time

Figure 2. (a) QCM resonant frequency as a function of time during
sublimation of FePc molecules. The red line is a linear ﬁt at constantcrucible temperature of 575.5 K. (b) STM topography image (at 4.7
K) of Cu(111) surface after FePc deposition with the crucible
temperature of 575.5 K for 2 s (60 × 60 nm2, −0.5 V, 200 pA). The
inset is the magniﬁed view, focusing on the single FePc molecules.

dependence of f during sublimation of FePc molecules (M =568.38 g·mol−1). The crucible temperature (Tc) is gradually
increased and is kept at 575.5 K. At the constant Tc, the fdecreases linearly with time (red line in Figure 2a). From theslope (df/dt = −9.82 × 10−2 Hz·s−1), Δf can be simply
obtained by setting the deposition time Δt as Δf = Δt·(df/dt),
and thus, the corresponding nQCM value can also be obtainedby nQCM = −Δf/Cn (see eq 2).
At this crucible temperature (575.5 K), the molecules were
deposited on Cu(111) surface, and then, the surface wasimaged by STM. The Δt was set at 2 s, from which Δf [=Δt·(df/dt)] was obtained as −0.1964 Hz. Therefore, thecorresponding nQCM (=−Δf/Cn) was obtained as 2.55 ×
10−2 nm−2 (see Table 1 for the other parameters). Figure 2b is
the resulting STM image. The FePc molecules were adsorbedon the bare Cu(111) surfaces as single molecules each ofwhich appearers as four-lobed shaped with a center brighter
spot (inset of Figure 2b). From the image, the number ofadsorbed molecules per the STM image area (60 × 60 nm2)
was counted to be NSTM = 123, while NQCM (nQCM × STM
image area) was evaluated as 91.9 (see Table 1). Namely, theobtained NSTM and NQCM showed not perfect, but rather undercontrol with an error [100·(NQCM − NSTM)/NSTM] of about−25%.
Deposition of 1 ML FePc on Cu(111). We also examined
the QCM capability in the higher coverage region.
Experimentally, FePc molecules were deposited on Cu(111)
surface with Tc = 581.0 K for 20 s. Therefore, in a similarmanner as in Figure 2a, the df/dt can be obtained by linear ﬁt
as −1.26 × 10−1 Hz·s−1 (red line in Figure 3a). Subsequently,
the corresponding Δf [=Δt·(df/dt)] and nQCM (=−Δf/Cn)
were also obtained to be −2.52 Hz and 3.27 × 10−1 nm−2,respectively (see Table 1). Here, the obtained nQCM value
indicates that the space where the single molecule can occupy(1/nQCM = 1.75 × 1.75 nm2) is almost comparable with the8956

DOI: 10.1021/acs.analchem.8b01118
Anal. Chem. 2018, 90, 8954−8959

Article

Analytical Chemistry
Table 1. Summary of the QCM and STM Experimental Resultsa
M [g·mol−1]

Cn [Hz·cm2]

Tc [K]Δt [s]

df/dt [Hz·s−1]

Δf [Hz]nQCM [nm−2]

NQCM[/image]

NSTM[/image]error [%]

FePc/Cu(111)568.387.70 × 10−14

H2TPP/Au(111)614.748.32 × 10−14

575.5
581
416.4
416.4

2
20
40
300

−9.82 × 10−2
−1.26 × 10−1
−1.74 × 10−2
−1.87 × 10−2

−0.196−2.520−0.696−5.6102.55 × 10−2
3.27 × 10−1
8.36 × 10−2
6.74 × 10−1

91.9
818.7
301.0
2591.0

123
913
271
2875

−25
−10
11
−10

M is the molar mass, Cn is the sensitivity factor, Tc is the crucible temperature, Δt is the deposition time, df/dt is the changing rate of the QCM
resonant frequency, Δf is the change of the QCM resonant frequency, nQCM is the number of adsorbed molecules per unit area, NQCM is the numberof adsorbed molecules per an STM image evaluated by QCM, and NSTM is the number of adsorbed molecules counted from an STM image. Error
was evaluated from 100·(NQCM − NSTM)/NSTM.
aFigure 3. (a) QCM resonant frequency as a function of time during
sublimation of FePc molecules. The red line is a linear ﬁt at constantcrucible temperature of 581.0 K. (b) STM topography image (at 4.7
K) of Cu(111) surface after FePc deposition with the crucible
temperature of 581.0 K for 20 s (50 × 50 nm2, 1.0 V, 50 pA). The
inset is the magniﬁed view, focusing on the single FePc molecules.

size of single FePc (1.5 × 1.5 nm2). This means that themolecular coverage is around 1 ML. Indeed, the resulting STM
image (Figure 3b) reveals that the Cu(111) surface with 50 ×
50 nm2 area is fully covered with the well-ordered FePc ﬁlms.
From the image, the NSTM is counted to be 913, while NQCM is818.7 (see Table 1), showing again not perfect but rather good
agreement with an error [100·(NQCM − NSTM)/NSTM] of−11%.
Deposition of H2TPP on Au(111). To further verify thereliability of the QCM capability, the same experiments were
performed using a diﬀerent molecule−substrate system. As themolecule, H2TPP (M = 614.74 g·mol−1) was sublimated, andAu(111) was used as the substrate. Figure 4 shows the two setsof experiments (labeled EXP. I and EXP. II). Since the Tc forboth experiments was set at 416.4 K, the slopes of the f (redand blue lines in Figure 4a) showed similar values (df/dt =−1.74 × 10−2 Hz·s−1 for EXP. I, and df/dt = −1.87 × 10−2 Hz·
s−1 for EXP. II). The slight diﬀerence in df/dt values at thesame Tc comes from the experimental error (the details are
discussed later). Meanwhile, to change the molecular coverages, the Δt values were set at 40 s for EXP. I and at 300 s for
EXP. II. Then, the nQCM (=−Δf/Cn) was obtained to be 8.36 ×
10−2 nm−2 for EXP. I and 6.74 × 10−1 nm−2 for EXP. II (seeTable 1 for the other parameters). Because the molecular sizeof single H2TPP is about 1.6 × 1.6 nm2, the coverages (nQCM·
molecular size) were roughly estimated as 0.21 ML for EXP. I
and 1.73 ML for EXP. II.
In this case, the coverage expectations were also reasonablewith the resulting STM images (Figure 4b and c), that is, theH2TPP appeared as single molecules on bare Au(111) surface
for EXP. I (Figure 4b), while the whole surface was covered
with H2TPP for EXP. II (Figure 4c). Similar to the case in

Figure 4. (a) Two sets of QCM resonant frequency as a function oftime during sublimation of H2TPP molecules. Red and blue lines arelinear ﬁts at constant crucible temperature of 416.4 K. (b, c) STM
topography images (at 78 K) of Au(111) surface after H2TPP
deposition for (b) 40 s (60 × 60 nm2, − 1.0 V, 50 pA) and (c) 300 s(62 × 62 nm2, −1.5 V, 20 pA). The crucible temperature is 416.4 K.
The insets in b and c are the magniﬁed views, focusing on the single
molecules.

FePc/Cu(111), the NSTM for both experiments was obtained
from the STM images to be NSTM = 271 for EXP. I and NSTM =2875 for EXP. II. Here, we note that the NSTM for EXP. II was
obtained by doubling the number of H2TPP molecules
counted from the STM image (Figure 4c) since the coverage
estimated from nQCM was around 2 ML. Remarkably, these
NSTM values also showed good correspondence with NQCM =301 for EXP. I and NQCM = 2591 for EXP. II (see Table 1),that is, these errors [100·(NQCM − NSTM)/NSTM] were 11%and −10%, respectively.
Accuracy of QCM Measurements. Table 1 summarizes
our results of QCM and STM measurements. The obtained
NQCM and NSTM are not perfectly ﬁt with an accuracy of one
single molecule, but the numbers are rather good agreements
within an error of ±25%, indicating high reliability of thepresent method. The slight errors less than 25% can be
attributed to the following reasons. First, since the QCM plate
8957

DOI: 10.1021/acs.analchem.8b01118
Anal. Chem. 2018, 90, 8954−8959

Article

Analytical Chemistry

to the conventional QCM system and, thus, possibly becomesa standard technique for sophisticated regulations of themolecular depositions toward high functional molecule-based
devices.

has not been subjected to any cleaning procedures, the surface
should be topographically rough and covered by unknown
impurities, which is clearly diﬀerent from atomically ﬂat/clean
metal substrates [Cu(111) and Au(111)]. Correspondingly,
the molecular adsorption rates should also be diﬀerent
between the QCM surface and the metal substrates. In thecase of the thick molecular ﬁlm, this eﬀect is negligible since alarge fraction of molecules are absorbed mostly onto the preexisting molecules. However, in the case of deposition of asmall amount of molecules, such diﬀerent adsorption rates
aﬀect the number of adsorbed molecules, which may cause thedeviation of NQCM from NSTM. Because of this factor, theadsorption rate of the QCM surface also ﬂuctuates in eachmeasurement since the atomic-scale surface morphology is not
perfectly the same. We consider that this could cause the nonnegligible experimental error, such as diﬀerent df/dt values
obtained even at the same Tc (see Table 1). Direct STM
imaging of the QCM surface before/after molecular sublimation and comparing the QCM measurement will provide
us useful information on this factor, which is one interesting
future work. Second, as mentioned earlier, Sauerbrey’s
equation (eq 1) assumes that the sublimated molecules cover
the whole surface of the QCM plate as a uniform ﬁlm, while
sublimation of a small amount of molecules results in theadsorptions as isolated single molecules and spatiallyinhomogeneous molecular ﬁlm. Since the sensitivity of thefrequency response to a mass deposited is not constant but
depends on the positions on the plate (the sensitivity decreases
with the radial distance from the center of the QCM
surface),29,30 application of eq 1 to the present experiment
may cause the slight deviation of NQCM from the actual value.
For example, as the simple case, we assume that two molecules
are adsorbed on the QCM plate; one is adsorbed at the centerof the plate and another is at the plate edge. In this case, QCM
is sensitive to the former molecule while slightly insensitive tothe latter one. Consequently, NQCM will be smaller than theactual value (NQCM = 2). Third, Sauerbrey’s equation (eq 1)
also assumes that the acoustic impedance (deﬁned as thesquare root of the product of the density and shear modulus of
the ﬁlm) is identical to that of quartz crystal.16,30 In the present
experiment, however, the density and the shear modulus of themolecules are unknown parameters; thereby, the validity of theassumption of eq 1 cannot be conﬁrmed. If the acoustic
impedances of the ﬁlm deviate from that of quartz crystal,
reﬂections of the acoustic wave at the interface disturb thereliability of eq 1. Nevertheless, our experiment demonstrates
that such ambiguous factors cause only slight errors (≤25%),
thereby not so critical that hamper the precise QCM
measurements.

■

ASSOCIATED CONTENT

S Supporting Information*

The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.analchem.8b01118.
Controllability of a crucible temperature duringmolecular evaporation by use of PID controlled power
supply (PDF)■

AUTHOR INFORMATION

Corresponding Authors*E-mail: inami.eiichi@kochi-tech.ac.jp.
*E-mail: toyoyamada@faculty.chiba-u.jp.
ORCID

Eiichi Inami: 0000-0002-2167-8510
Notes

The authors declare no competing ﬁnancial interest.

■

ACKNOWLEDGMENTS
We thank professor Hideki Yorimitsu (Kyoto University) for
providing the sample of H2TPP. This work was supported by
JSPS KAKENHI Grant Number (16K17521, 16K05887,
JP25110011, 17H05353). One of the authors (E. I.) also
acknowledges ﬁnancial support from the Murata Science
Foundation.

■

REFERENCES(1) Tang, C. W.; VanSlyke, S. A.; Chen, C. J. Appl. Phys. 1989, 65,3610−3616.
(2) Coe, S.; Woo, W.-K.; Bawendi, M.; Bulovic, V. Nature 2002, 420,
800.
(3) Van Slyke, S. A.; Chen, C.; Tang, C. W. Appl. Phys. Lett. 1996,
69, 2160−2162.
(4) Kaji, H.; Suzuki, H.; Fukushima, T.; Shizu, K.; Suzuki, K.; Kubo,
S.; Komino, T.; Oiwa, H.; Suzuki, F.; Wakamiya, A.; Murata, Y.;
Adachi, C. Nat. Commun. 2015, 6, 8476.
(5) Tan, Z.-K.; Moghaddam, R. S.; Lai, M. L.; Docampo, P.; Higler,R.; Deschler, F.; Price, M.; Sadhanala, A.; Pazos, L. M.; Credgington,
D.; Hanusch, F.; Bein, T.; Snaith, H. J.; Friend, R. H. Nat.
Nanotechnol. 2014, 9, 687−692.
(6) Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.;
Yan, H. Nat. Energy 2016, 1, 15027.
(7) Tang, C. W. Appl. Phys. Lett. 1986, 48, 183−185.
(8) Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker, R.; Gao,P.; Nazeeruddin, M. K.; Grätzel, M. Nature 2013, 499, 316−319.
(9) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S.
I. Nat. Mater. 2014, 13, 897−903.
(10) Jeon, N. J.; Noh, J. H.; Yang, W. S.; Kim, Y. C.; Ryu, S.; Seo, J.;
Seok, S. I. Nature 2015, 517, 476−480.
(11) Liu, M.; Johnston, M. B.; Snaith, H. J. Nature 2013, 501, 395−
398.
(12) Chen, Q.; Zhou, H.; Hong, Z.; Luo, S.; Duan, H.-S.; Wang, H.H.; Liu, Y.; Li, G.; Yang, Y. J. Am. Chem. Soc. 2014, 136, 622−625.
(13) Kraus, M.; Richler, S.; Opitz, A.; Brutting, W.; Haas, S.;
Hasegawa, T.; Hinderhofer, A.; Schreiber, F. J. Appl. Phys. 2010, 107,
094503.
(14) Zielke, D.; Hübler, A. C.; Hahn, U.; Brandt, N.; Bartzsch, M.;
Fügmann, U.; Fischer, T.; Veres, J.; Ogier, S. Appl. Phys. Lett. 2005,
87, 123508.

■

CONCLUSIONSIn conclusion, accuracy of the number of adsorbed organic
molecules (FePc and H2TPP) controlled by QCM wasevaluated by direct counting of molecules one by one using
STM. We found that the number has an error of ±25%, that is,
if one needs to deposit 100 molecules, QCM promises anaccuracy of deposition of 100 ± 25 molecules on the substrate.
This conclusion remains regardless of the morphologies of theadsorbed molecules on the substrates. Moreover, although thepresent study focused on deposition of pure molecules, themethod can also be applicable for codepositions of diﬀerent
molecules and, thus, can be utilizable in a wide range of ﬁelds.
The present method requires no additional experimental setup
8958

DOI: 10.1021/acs.analchem.8b01118
Anal. Chem. 2018, 90, 8954−8959

Article

Analytical Chemistry(15) Mei, Y.; Loth, M. A.; Payne, M.; Zhang, W.; Smith, J.; Day, C.
S.; Parkin, S. R.; Heeney, M.; McCulloch, I.; Anthopoulos, T. D.;
Anthony, J. E.; Jurchescu, O. D. Adv. Mater. 2013, 25, 4352−4357.
(16) Sauerbrey, G. Eur. Phys. J. A 1959, 155, 206.
(17) Lindner, M.; Schmid, M. Coatings 2017, 7, 9.
(18) Auwä r ter, W.; Seufert, K.; Bischoff, F.; Ecija, D.;
Vijayaraghavan, S.; Joshi, S.; Klappenberger, F.; Samudrala, N.;
Barth, J. V. Nat. Nanotechnol. 2012, 7, 41−46.
(19) Perera, U. G. E.; Ample, F.; Kersell, H.; Zhang, Y.; Vives, G.;
Echeverria, J.; Grisolia, M.; Rapenne, G.; Joachim, C.; Hla, S.-W. Nat.
Nanotechnol. 2013, 8, 46−51.
(20) Schmaus, S.; Bagrets, A.; Nahas, Y.; Yamada, T. K.; Bork, A.;
Bowen, M.; Beaurepaire, E.; Evers, F.; Wulfhekel, W. Nat.
Nanotechnol. 2011, 6, 185−189.
(21) Kawahara, S. L.; Lagoute, J.; Repain, V.; Chacon, C.; Girard, Y.;
Rousset, S.; Smogunov, A.; Barreteau, C. Nano Lett. 2012, 12, 4558−
4563.
(22) Bagrets, A.; Schmaus, S.; Jaafar, A.; Kramczynski, D.; Yamada,T. K.; Alouani, M.; Wulfhekel, W.; Evers, F. Nano Lett. 2012, 12,5131−5136.
(23) Schuler, B.; Fatayer, S.; Mohn, F.; Moll, N.; Pavliček, N.;
Meyer, G.; Peña, D.; Gross, L. Nat. Chem. 2016, 8, 220−224.
(24) Yamada, T. K.; Yamagishi, Y.; Nakashima, S.; Kitaoka, Y.;
Nakamura, K. Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 94,
195437.
(25) Inami, E.; Shimasaki, M.; Yorimitsu, H.; Yamada, T. K. Sci. Rep.
2018, 8, 353.
(26) Joachim, C.; Gimzewski, J. K.; Aviram, A. Nature 2000, 408,
541−548.
(27) Barth, J. V.; Costantini, G.; Kern, K. Nature 2005, 437, 671−
679.
(28) Yamada, T. K.; Abe, T.; Nazriq, N. M. K.; Irisawa, T. Rev. Sci.
Instrum. 2016, 87, 033703.
(29) Ward, M. D.; Delawski, E. J. Anal. Chem. 1991, 63, 886−890.
(30) Buttry, D. A.; Ward, M. D. Chem. Rev. 1992, 92, 1355−1379.

8959

DOI: 10.1021/acs.analchem.8b01118
Anal. Chem. 2018, 90, 8954−8959