Study of Graphene-based 2D-Heterostructure Device Fabricated by All

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES

Article

Study of Graphene-based 2D-Heterostructure Device Fabricated by All-Dry Transfer Process Dung Hoang Tien, Jun-Young Park, K. B. Kim, Naesung Lee, Taekjib Choi, Philip Kim, Takashi Taniguchi, Kenji Watanabe, and Yongho Seo ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b10370 • Publication Date (Web): 15 Jan 2016 Downloaded from http://pubs.acs.org on January 19, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Study of Graphene-based 2D-Heterostructure Device Fabricated by All-Dry Transfer Process Dung Hoang Tien1, Jun-Young Park1, Ki Buem Kim1, Naesung Lee1, Taekjib Choi1, Philip Kim2, T Taniguchi3, K Watanabe3, Yongho Seo1,* 1

Faculty of Nanotechnology & Advanced Materials, HMC, and GRI, Sejong University, Seoul 143-747, South Korea 2

Department of Physics, Harvard University, Cambridge, MA 02138, USA 3

National Institute of Materials Science, Ibaraki 305-0044, Japan ABSTRACT

We developed a technique for transferring graphene and hexagonal boron nitride (hBN) in dry conditions for fabrication of van der Waals heterostructures. The graphene layer was encapsulated between two hBN layers, so that it was kept intact during fabrication of the device. For comparison, the devices containing graphene on SiO2/Si wafer and graphene on hBN were also fabricated. Electrical properties of the devices were investigated at room temperature. The mobility of the graphene on SiO2 devices and graphene on hBN devices were 15,000 and 37,000 cm2V-1s-1, respectively, while the mobility of the sandwich structure device reached the highest value of ~100,000 cm2V-1s-1, at room temperature. The electrical measurements of the samples were carried out in air and vacuum environments. We found that the electrical properties of the encapsulated graphene devices remained at a similar level in both a vacuum and in air, whereas the properties of the graphene without encapsulation were influenced by the external environment.

Keywords: graphene, sandwich structure, mobility, graphene transfer, 2D materials *corresponding authors: [email protected]

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

I. Introduction

Graphene is a promising material for nano-devices with high mobility, but it is strongly influenced by the underlying substrate. When the substrate is SiO2/Si wafer, the quality of graphene on it is limited by scattering from impurities, charged surface states 1, roughness, 2-3 and optical phonons on SiO2 surface

4-5

. Particularly, the inhomogeneity of electron-rich and

hole-rich puddles due to the charged impurity or substrate-induced disorder decreases the mobility

6-8

. Therefore, a suitable substrate should be used for high-quality graphene-based

devices. Recently, hexagonal boron nitride (hBN) has been adopted as a substrate for graphene-based devices, as it has the same crystal structure as graphene and has an atomically smooth surface 9. Graphene on hBN exhibited very high mobility at room temperature (≈ 40,000 cm2V-1s-1)

9-12

. On the other hand, encapsulated graphene (hBN/graphene/hBN)

devices fabricated by the so-called ‘pick-up’ technique

13

showed the highest value of

electrical mobility (≈140,000 cm2V-1s-1) at room temperature. This is because of the graphene layer encapsulated by hBN layers are protected during the fabrication processes. In conventional graphene transfer process, the supporting polymer film has been known to leave residues on the surface of the graphene. These polymer residues may act as scattering sites or doping elements on the graphene layer. In fabricating graphene-based devices, it is very important to avoid residues remaining on the graphene so that the quality of the graphene layer is not deteriorated

14-16

. Until now, the most of heterostructure assembly methods

employs poly (methyl methacrylate) (PMMA) layer as transfer layer

17-19

, and uses solvents

like acetone and chloroform to dissolve the supporting layer 9. It is reported, however, that organic solvents cannot completely remove the polymer layer

20-28

and during the dissolving

process, polymer residue or other contaminants could adhere to the graphene surface, which can cause severe problems for the graphene layer.


Page 3 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In order to fabricate a high-mobility graphene device by avoiding the polymer residue problem as much as possible, we used an all-dry transferring method. In this method, the chosen graphene and hBN layers were transferred to another hBN substrate without using any solvent to dissolve the polymer supporting layers. For the comparison purpose, three kinds of the device were fabricated: graphene on SiO2/Si substrate, graphene on hBN and hBN/graphene/hBN devices, and the electrical properties of the devices were measured. Atomic force microscopy (AFM) was employed to investigate the surface morphology of the devices in both air and vacuum conditions.

II. Experimental details

We used an all-dry method to transfer graphene and hBN in order to fabricate graphene–hBN heterostructure, as depicted in Fig. 1. First, the bottom hBN flake was exfoliated onto silicon wafers coated with 300 nm silicon oxide as the substrate for the devices. High quality single crystals of hexagonal-BN

29

were used for mechanical

exfoliation of the hBN flakes. A polymer multilayer film was formed onto a Si wafer by spincoating (Fig. 1(a)). The polymer multilayer consisted of two layers: a water-soluble layer (poly-vinyl alcohol PVA) and a PMMA, molecular weight 495 K) layer on top. The PMMA layer was the supporting layer to hold the graphene. Then, graphene was exfoliated from commercial graphite (natural Kish graphite, grade 300) on the polymer layer using Scotch tape (Fig. 1(b)). An optical microscope was employed to search and to roughly estimate the thickness of the graphene flake. Graphene with single-layer thickness can be found on the polymer layer with suitable thickness due to the interference effect. The polymer layer with a purple color provided the best contrast to determine the single-layer graphene. Before transfer, the graphene layer thickness was verified by Raman spectroscopy (micro-Raman Renishaw



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

InVia systems). After suitable graphene flakes were selected, the buffer layer PVA was dissolved by DI water (Fig. 1(c)). The PMMA membrane was floated, while the top surface including graphene was kept dry due to its hydrophobicity. In this process, the graphene never contacted the water. The PMMA was placed onto a transparent PDMS (polydimethylsiloxane) stamp. This stamp was attached to a transparent glass slide (Fig. 1(d)), which was clamped onto an arm of a micromanipulator. The manipulator was used to position the graphene flake over a selected hBN flake, and then two flakes were put into contact (Fig.1(e)). By using the micromanipulator, the graphene flake was aligned precisely within a few microns accuracy on the target hBN flake. During the contact, the SiO2/Si substrate was heated to 90oC for around 10 minutes, and then the PDMS layer was retracted. Due to crystallographic similarity between graphene and hBN, the graphene flake adhered more strongly to the hBN than the PMMA and stuck to the target hBN flake (Fig. 1(f)). Meanwhile, the PMMA was retracted together with PDMS.


Page 4 of 27

Page 5 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig.1. All-dry transfer process. (a) Graphene was exfoliated onto PMMA/PVA/Si substrate. (b) The surrounding area was scratched for water to permeate and detach it from the Si wafer. (c) The detached film was floated into water, and raised by a PDMS slab, which was attached to a glass slide. (d) The PDMS slab was inverted and attached to the micromanipulator stage, (e) then aligned above an exfoliated BN flake on Si/SiO wafer. (f) 2

Graphene on hBN remained after the PDMS stamp was retracted.

The top hBN was exfoliated on a PDMS slab separately (See Fig. S2) and then transferred to the graphene on the bottom hBN in order to fabricate the sandwich structure. In this encapsulation process [15], no liquid was used. Similar transfer technique was reported by Kretinin et al.30, but they used a metal ring instead of PDMS stamp. In our method, elastomeric property of PDMS was helpful to apply isotropic pressure on the target substrate, improving the success rate of the transfer. Our method was reliable without respect to the size of graphene and large contact area was provided to reduce the contact resistance, compared with the pick-up technique.13 The transfer techniques, recently reported by Uwanno, et al and Castellanos-Gomez, et al

32

31

are similar to our method. Uwanno, et al explained the

mechanism detaching graphene from PMMA film by the thermal shrinkage of polymers. In our experiment the PDMS and PMMA was tightly attached to the substrate not allowing shrinkage, but the transfer was successful. Goler, et al. 33 also used a PDMS stamp to transfer graphene layer without PMMA layer, but it was difficult to find single-layer graphene due to poor visibility of graphene. All the techniques are based on the elastomeric property of PDMS as a stamp.34 Fig. 2(a) shows an optical image of a graphene flake before it was transferred onto hBN substrate. After the graphene was transferred on the bottom hBN flake (Fig. 2(b)), the top hBN flake was located so as to cover the middle part of the graphene layer (Fig. 2(c)) and leave side parts uncovered for connection to electrical contacts. Raman spectroscopic data confirmed that it was single-layer graphene (Fig. 2(b)). E-beam lithography was used to



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

define the electrode patterns and then evaporation was carried out for depositing metal (1 nm Ti and 80 nm Au) contacts.

Fig.2. (a) Microscopic imaging shows graphene flake on the polymer (PVA/PMMA) multilayer substrate. (b) The selected graphene flake was transferred successfully on the bottom hBN flake. (c) A hBN/graphene/hBN structure was fabricated, where the top hBN layer covered the middle part of the graphene layer and both sides were uncovered. (d) Raman spectrum confirmed that the graphene flake was single layer. (e) Resistance as a function of back gate voltage was measured at room temperature.

The transport characteristics of the devices were measured with two terminals at room temperature in vacuum and air environments. The semiconductor characterization system (Keithley, 4200-SCS) and a lock-in amplifier were employed for accurate electrical measurements. A bias voltage was applied between the source and drain terminals of the graphene channel. The Si substrate was used as a global back-gate, where the bias voltage was used to control the carrier concentration and polarity in the graphene layer. The voltage to the back-gate was swept continuously during the measurements. The output voltage


Page 6 of 27

Page 7 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


between the source and drain was converted to the resistance of the device. Fig. 2(e) shows a representative resistance data as a function of back gate voltage at room temperature, which has a sharp and symmetric Dirac peak confirming its high mobility. The AFM measurements were carried out by using the commercial AFMs (n-Tracer, NanoFocus Inc., SPA300HV, Seiko Instruments Inc.).

III. Results and discussions

There are some models for calculating the mobility of graphene-based devices. The well-known Drude model has been used in many articles to determine the mobility as a function of carrier density 35-38. In this study, we adopted another model proposed by Kim et al.39 to obtain a single value of the mobility. The results are in agreement with those obtained by using other models. According to the model, electronic mobility, µ, of the fabricated device is extracted from following equation:

= +

,

(1)

where Rtot is the resistance of the device, and Rcon is the contact resistance consisting of the graphene section resistance and the metal/graphene contact resistance. Also, n0 is the residual carrier concentration, N geometric factor of the sample, e electron charge (1.6 × 10 ), and n carrier concentration. The geometric factor N is given by N = l/w, where l and w are the length and width of the graphene channel of the device. The relationship between carrier concentration n, back-gate voltage Vg, and Dirac voltage VD is given in the following expression:

( − ) =

!"

,


(2)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

where CBG is the geometric capacitance of the device.

The estimation of CBG of the graphene on SiO2 and graphene on hBN devices and the geometric factors and the mobilities of several samples can be found in the supplementary. Figures 3 show (a) an optical microscopic image of a representative sandwich structure device and (b) its total resistance Rtot versus VG at room temperature in air (black curve) and in vacuum (red curve). As depicted in the Fig. 3(b), the resistance Rtot in vacuum remains almost unchanged compared with that measured in ambient conditions. This is an apparent advantage of the sandwich structure device. From results of fitting the data to Eq. (1), the mobility µ~ 90,000 and 80,000 cm2V-1s-1, and the residual concentrations n0 ≈ 2x1011 and 1.3x1011 cm-2, were estimated in vacuum and air, respectively. The mobility of this device is much higher than the values we obtained from the graphene on SiO2/Si wafer devices (~15,000 cm2V-1s-1) and graphene on hBN devices (~37,000 cm2V-1s-1). The encapsulated graphene device exhibited a high mobility, because the graphene layer was kept intact between two hBN layers during the electrode fabricating process and electrical measurements. The graphene layer was not exposed to the moisture and gas in the ambient environment and was not contaminated by PMMA used for e-beam lithography.

Fig.3. (a) A hBN/graphene/hBN sandwich device with gold electrodes was fabricated. (b) The relationship


Page 8 of 27

Page 9 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


between total resistance Rtot and back-gate bias Vg of the sandwich structure device in ambient condition and vacuum condition at room temperature.

For comparison, the electrical properties of the graphene on SiO2/Si were also measured in air and in vacuum conditions. Fig.4 shows the Rtot versus Vg curve of the device, where the Dirac point shifted clearly from 12 V in vacuum to 23 V in air. The graphene layer became p-doped, as it was exposed to the gas and moisture in the ambient condition [19-35]. The mobility also changed from 1,500 cm2V-1s-1 in vacuum to 1,200 cm2V-1s-1 in air. The residual concentration in vacuum 6.0x10-11cm-2 increased up to 6.4x10-11cm-2 in air, which means that the amount of doping was increased by the ambient condition. When the graphene device is exposed to NO2 gas diluted in a concentration of 1 ppm (flow rate 10-3 mbar⋅l/s), the Dirac point of the device shifted from 0 to 20 V, according to Schedin et al.,

19

. A similar

behavior was found by Suk, et al. 20, but they emphasized the effect of the PMMA residue on electrical properties of the graphene device. According to their results carried out at room temperature, the Dirac peak shifted from 20 (in vacuum) to 40 V (in air) and the conductivity decreased. Our results shown in Fig.4 are almost similar to those other groups, as the PMMA was used for electrode patterning and its residue was left on graphene.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig.4. Rtot was measured as a function of Vg in ambient air and vacuum for the graphene on SiO2 device at room temperature. The inset shows a microscopic image of the device.

On the other hand, the encapsulated graphene devices having bubbles were fabricated, to investigate the effect of the different pressures on the graphene. The relationship of the total resistance Rtot and back-gate bias Vg of the device with bubble was measured in air conditions at room temperature as shown in Fig. 5(a). The curve is symmetric and the Dirac point is at Vg=-2(V). From fitting the above model to the data in Fig. 5(a), the extracted mobility was about 100,000 cm2V-1s-1, which was the highest mobility value we obtained. The electrical measurement of this device was also carried out in a low vacuum (5x10-3 Torr). However, we noticed that the Rtot-Vg behavior of the device became complicated and asymmetric in the vacuum as shown in Fig. 5(b). This complicated behavior originated from the bubble trapped between bottom and top BN layer. The size of the bubble changed, depending on the pressure difference between inside and outside of the bubble. The bubble may contain air, moisture, or other contaminant elements, which caused a doping effect on the graphene channel. The bubble trapped between the graphene layer and bottom hBN flake in the device was observed by AFM as shown in Fig. 5(c). The bubble was big enough to cover the full width of the graphene channel. We speculate that the bubble covered


Page 10 of 27

Page 11 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


region may have different doping density than un-covered region. This spatial inhomogeneity may produce the pronounced double peak structure in Rtot-Vg plat shown in Fig. 5(b). Similar electrical behavior was found in our several sandwich devices. The results are provided in supplementary information of this article.

Fig.5. (a) The relationship between total resistance Rtot and back-gate bias Vg of a sandwich structure device with a bubble in ambient condition at room temperature. The red curve is fitting result. (b) Rtot versus Vg measured at low pressure (5x10-3 Torr) is shown.(c) AFM images show the bubbles trapped between the graphene and the BN layers.

In addition, we found different behavior from another sample where the graphene was attached on the bottom hBN and a bubble was formed in top hBN layer. Previous work also found that the deposition of graphene of hBN resulted in numerous bubbles containing trapped contaminate elements.15 If these bubbles are located in the active parts of graphene devices they cause significant charge inhomogeneity. The Rtot-Vg relationships of the sample



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

were measured in several vacuum conditions. In air, as depicted in the Fig. 6(a), the Rtot-Vg curve had the Dirac point near zero (Vg=-2 V). As the pressure decreased the data shifted to the negative region, and the Dirac peak was lowered. This result was reproduced by repeated measurements. This is attributed to the expanding of the bubble trapped inside the device. In order to explain this behavior, we suggest a model; the trapped gas in the bubble is electrically neutral, but it includes n-doping and p-doping adsorbates. The n-doping adsorbate tends to be adsorbed on the graphene, and the p-doping adsorbate to the hBN side, as shown in Fig. 6(b). While the n-doping effect is increased when the bubble was inflated, the doping effect was mitigated when the bubble shrank. In addition, there could be some other effects, such as deformation of graphene, or gas leaking at the hBN/graphene interfaces.

Fig.6. (a) Rtot versus Vg of a sandwich structure device with a bubble was measured in air and different pressures at room temperature. (b) Schematic diagram shows the bubble structure with doping adsorbates. (c) Optical microscope image shows the device with bubble.


Page 12 of 27

Page 13 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In order to confirm the inflation of the bubbles, AFM topography images of the device were measured in air and in vacuum environments. Figure 7 shows the AFM images and line profiles of a bubble (a) in air conditions and (b) in vacuum level of 5x10-3 Torr, where the bubble was formed at the top hBN layer with 20 nm thickness. From the AFM images and line profiles (c-d) we can see the size and shape of the bubble was changed depending on the pressure outside.

Fig.7. AFM images of the sandwich structure device show the bubbles formed between graphene and hBN layers. Topographic images with 2µm scan size were measured (a) in air and (b) in vacuum (5x10-3 Torr). Inflation of the bubble was confirmed from (c) horizontal line profile and (d) vertical line profile of the topographic images.

It is known that H2O, O2, and NO2 lead to p-type doping of graphene, while ammonia

leads to n-type.40-42 Moisture in air is a dominant p-doping source due to its strong adsorption on surfaces, and O2 and NO2 gases could be additional p-dopants. On the other hand, unexpected n-doping behavior of graphene on hBN was occasionally found even on high quality sample by others.9 The n-doping effect of graphene on clean surface may be related to a charge transfer from substrates. Epitaxy graphene on silicon carbide was found to be n-



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

doped by the substrate, because the Dirac point of graphene shifts below the Fermi level.43 The n-type behavior of graphene on SiO2 was explained by the lower work function of SiO2 substrate (W = 3.03 to 3.41 eV) 44 than that of graphene (Wg = 4.23 to 4.48 eV).45 The deformation of the Dirac peak can be explained by spatial inhomogeneity; long graphene channel was partially laid under a bubble. The part of graphene under the inflated bubble at vacuum is less influenced by the p-doping effect from top layer than the other part without bubble. Thus, two different regions have different positions of Dirac peaks. As they are connected in series, a double-peak structure in Rtot-Vg plot appeared in Fig. 5(b).

IV. Conclusions

A dry method was developed to transfer a graphene layer onto hexagonal boron nitride, and devices with a sandwich structure (hBN/graphene/hBN) were fabricated using this method. We conducted the electrical transport measurements of the devices in different environments. It was found that the encapsulated graphene was less affected by the external gas environment, and exhibited high mobility ~100,000 cm2V-1s-1 at room temperature. The polymer residue and contaminate problems can be significantly reduced by using an all-dry method because no solvent was required to dissolve the polymer supporting layer after transferring. On the other hand, the devices with bubbles trapped between the graphene and hBN layers showed unusual behaviors due to the stretching and doping effects on the graphene. The bubble of 2-dimensional materials can be formed intentionally using artificial deformation of PDMS stamp, and integrated devices having bubbles including dopants can be fabricated. These devices can be utilized as a micro gas pressure sensor, as well as an experimental device used to investigate a band structure deformation by stretching.


Page 14 of 27

Page 15 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ACKNOWLEDGMENT This research was supported by the Basic Science Research Program through the NRF funded by the Ministry of Science, ICT & Future Planning (2013R1A1A1A05005298) and the Priority Research Centers Program (2010-0020207) by the Ministry of Education. Also, this work was supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, industry & Energy (No. 20154030200630).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table Of Contents (TOC)

Supporting Information: calculation of the mobility of the graphene, optical image of hBN exfoliated on PDMS film, and anomalous behavior sandwich structured graphene in vacuum.


Page 16 of 27

Page 17 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References 1.

Ando, T., Screening effect and impurity scattering in monolayer graphene. J Phys Soc Jpn

2006, 75 (7). 2.

Ishigami, M.; Chen, J. H.; Cullen, W. G.; Fuhrer, M. S.; Williams, E. D., Atomic structure of

graphene on SiO2. Nano Lett 2007, 7 (6), 1643-1648. 3.

Morozov, S. V.; Novoselov, K. S.; Katsnelson, M. I.; Schedin, F.; Elias, D. C.; Jaszczak, J. A.;

Geim, A. K., Giant intrinsic carrier mobilities in graphene and its bilayer. Phys Rev Lett 2008, 100 (1). 4.

Fratini, S.; Guinea, F., Substrate-limited electron dynamics in graphene. Phys Rev B 2008,

77 (19). 5.

Chen, J. H.; Jang, C.; Xiao, S. D.; Ishigami, M.; Fuhrer, M. S., Intrinsic and extrinsic

performance limits of graphene devices on SiO2. Nat Nanotechnol 2008, 3 (4), 206-209. 6.

Hwang, E. H.; Adam, S.; Das Sarma, S., Carrier transport in two-dimensional graphene

layers. Phys Rev Lett 2007, 98 (18). 7.

Adam, S.; Hwang, E. H.; Galitski, V. M.; Das Sarma, S., A self-consistent theory for graphene

transport. P Natl Acad Sci USA 2007, 104 (47), 18392-18397. 8.

Martin, J.; Akerman, N.; Ulbricht, G.; Lohmann, T.; Smet, J. H.; Von Klitzing, K.; Yacoby, A.,

Observation of electron-hole puddles in graphene using a scanning single-electron transistor. Nat

Phys 2008, 4 (2), 144-148. 9.

Dean, C. R.; Young, A. F.; Meric, I.; Lee, C.; Wang, L.; Sorgenfrei, S.; Watanabe, K.; Taniguchi,

T.; Kim, P.; Shepard, K. L.; Hone, J., Boron nitride substrates for high-quality graphene electronics.

Nat Nanotechnol 2010, 5 (10), 722-726. 10.

Dean, C.; Young, A. F.; Wang, L.; Meric, I.; Lee, G. H.; Watanabe, K.; Taniguchi, T.; Shepard, K.;

Kim, P.; Hone, J., Graphene based heterostructures. Solid State Commun 2012, 152 (15), 1275-1282. 11.

Taychatanapat, T.; Watanabe, K.; Taniguchi, T.; Jarillo-Herrero, P., Quantum Hall effect and

Landau-level crossing of Dirac fermions in trilayer graphene. Nat Phys 2011, 7 (8), 621-625. 12.

Zomer, P. J.; Guimaraes, M. H. D.; Tombros, N.; van Wees, B. J., Long-distance spin transport

in high-mobility graphene on hexagonal boron nitride. Phys Rev B 2012, 86 (16). 13.

Wang, L.; Meric, I.; Huang, P. Y.; Gao, Q.; Gao, Y.; Tran, H.; Taniguchi, T.; Watanabe, K.;

Campos, L. M.; Muller, D. A.; Guo, J.; Kim, P.; Hone, J.; Shepard, K. L.; Dean, C. R., One-Dimensional Electrical Contact to a Two-Dimensional Material. Science 2013, 342 (6158), 614-617. 14.

Engels, S.; Terres, B.; Epping, A.; Khodkov, T.; Watanabe, K.; Taniguchi, T.; Beschoten, B.;

Stampfer, C., Limitations to carrier mobility and phase-coherent transport in bilayer graphene.

Physical review letters 2014, 113 (12), 126801. 15.

Mayorov, A. S.; Gorbachev, R. V.; Morozov, S. V.; Britnell, L.; Jalil, R.; Ponomarenko, L. A.;

Blake, P.; Novoselov, K. S.; Watanabe, K.; Taniguchi, T.; Geim, A. K., Micrometer-Scale Ballistic



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Transport in Encapsulated Graphene at Room Temperature. Nano Lett 2011, 11 (6), 2396-2399. 16.

Zomer, P. J.; Guimaraes, M. H. D.; Brant, J. C.; Tombros, N.; van Wees, B. J., Fast pick up

technique for high quality heterostructures of bilayer graphene and hexagonal boron nitride.

Applied Physics Letters 2014, 105 (1). 17.

Pirkle, A.; Chan, J.; Venugopal, A.; Hinojos, D.; Magnuson, C. W.; McDonnell, S.; Colombo, L.;

Vogel, E. M.; Ruoff, R. S.; Wallace, R. M., The effect of chemical residues on the physical and electrical properties of chemical vapor deposited graphene transferred to SiO2. Applied Physics

Letters 2011, 99 (12). 18.

Fan, J. Y.; Michalik, J. M.; Casado, L.; Roddaro, S.; Ibarra, M. R.; De Teresa, J. M., Investigation

of the influence on graphene by using electron-beam and photo-lithography. Solid State Commun 2011, 151 (21), 1574-1578. 19.

Schedin, F.; Geim, A. K.; Morozov, S. V.; Hill, E. W.; Blake, P.; Katsnelson, M. I.; Novoselov, K.

S., Detection of individual gas molecules adsorbed on graphene. Nat Mater 2007, 6 (9), 652-655. 20.

Suk, J. W.; Lee, W. H.; Lee, J.; Chou, H.; Piner, R. D.; Hao, Y. F.; Akinwande, D.; Ruoff, R. S.,

Enhancement of the Electrical Properties of Graphene Grown by Chemical Vapor Deposition via Controlling the Effects of Polymer Residue. Nano Lett 2013, 13 (4), 1462-1467. 21.

Ambrosetti, A.; Silvestrelli, P. L., Adsorption of Rare-Gas Atoms and Water on Graphite and

Graphene by van der Waals-Corrected Density Functional Theory. J Phys Chem C 2011, 115 (9), 3695-3702. 22.

Suk, M. E.; Aluru, N. R., Water Transport through Ultrathin Graphene. Journal of Physical

Chemistry Letters 2010, 1 (10), 1590-1594. 23.

Yavari, F.; Kritzinger, C.; Gaire, C.; Song, L.; Gullapalli, H.; Borca-Tasciuc, T.; Ajayan, P. M.;

Koratkar, N., Tunable Bandgap in Graphene by the Controlled Adsorption of Water Molecules.

Small 2010, 6 (22), 2535-2538. 24.

Seitsonen, A. P.; Saitta, A. M.; Wassmann, T.; Lazzeri, M.; Mauri, F., Structure and stability of

graphene nanoribbons in oxygen, carbon dioxide, water, and ammonia. Phys Rev B 2010, 82 (11). 25.

Park, J. H.; Aluru, N. R., Ordering-Induced Fast Diffusion of Nanoscale Water Film on

Graphene. J Phys Chem C 2010, 114 (6), 2595-2599. 26.

Gordillo, M. C.; Marti, J., Effect of Surface Roughness on the Static and Dynamic Properties

of Water Adsorbed on Graphene. J Phys Chem B 2010, 114 (13), 4583-4589. 27.

Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva,

I. V.; Firsov, A. A., Electric field effect in atomically thin carbon films. Science 2004, 306 (5696), 666669. 28.

Wehling, T. O.; Lichtenstein, A. I.; Katsnelson, M. I., First-principles studies of water

adsorption on graphene: The role of the substrate. Appl Phys Lett 2008, 93 (20). 29.

Taniguchi, T.; Watanabe, K., Synthesis of high-purity boron nitride single crystals under

high pressure by using Ba-BN solvent. J Cryst Growth 2007, 303 (2), 525-529. 30.

Kretinin, A. V.; Cao, Y.; Tu, J. S.; Yu, G. L.; Jalil, R.; Novoselov, K. S.; Haigh, S. J.; Gholinia, A.;

Mishchenko, A.; Lozada, M.; Georgiou, T.; Woods, C. R.; Withers, F.; Blake, P.; Eda, G.; Wirsig, A.;


Page 18 of 27

Page 19 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Hucho, C.; Watanabe, K.; Taniguchi, T.; Geim, A. K.; Gorbachev, R. V., Electronic Properties of Graphene Encapsulated with Different Two-Dimensional Atomic Crystals. Nano Lett 2014, 14 (6), 3270-3276. 31.

Uwanno, T.; Hattori, Y.; Taniguchi, T.; Watanabe, K.; Nagashio, K., Fully dry PMMA transfer

of graphene on h-BN using a heating/cooling system. 2d Mater 2015, 2 (4). 32.

Castellanos-Gomez, A.; Buscema, M.; Molenaar, R.; Singh, V.; Janssen, L.; van der Zant, H. S.

J.; Steele, G. A., Deterministic transfer of two-dimensional materials by all-dry viscoelastic stamping.

2d Mater 2014, 1 (1), 1-8. 33.

Goler, S.; Piazza, V.; Roddaro, S.; Pellegrini, V.; Beltram, F.; Pingue, P., Self-assembly and

electron-beam-induced direct etching of suspended graphene nanostructures. J Appl Phys 2011,

110 (6). 34.

Meitl, M. A.; Zhu, Z. T.; Kumar, V.; Lee, K. J.; Feng, X.; Huang, Y. Y.; Adesida, I.; Nuzzo, R. G.;

Rogers, J. A., Transfer printing by kinetic control of adhesion to an elastomeric stamp. Nat Mater 2006, 5 (1), 33-38. 35.

Zhang, Y. B.; Tan, Y. W.; Stormer, H. L.; Kim, P., Experimental observation of the quantum

Hall effect and Berry's phase in graphene. Nature 2005, 438 (7065), 201-204. 36.

Tan, Y. W.; Zhang, Y.; Bolotin, K.; Zhao, Y.; Adam, S.; Hwang, E. H.; Das Sarma, S.; Stormer, H.

L.; Kim, P., Measurement of scattering rate and minimum conductivity in graphene. Phys Rev Lett 2007, 99 (24). 37.

Novoselov, K. S.; Jiang, D.; Schedin, F.; Booth, T. J.; Khotkevich, V. V.; Morozov, S. V.; Geim, A.

K., Two-dimensional atomic crystals. P Natl Acad Sci USA 2005, 102 (30), 10451-10453. 38.

Nomura, K.; MacDonald, A. H., Quantum transport of massless dirac fermions. Physical

review letters 2007, 98 (7). 39.

Kim, S.; Nah, J.; Jo, I.; Shahrjerdi, D.; Colombo, L.; Yao, Z.; Tutuc, E.; Banerjee, S. K.,

Realization of a high mobility dual-gated graphene field-effect transistor with Al2O3 dielectric.

Appl Phys Lett 2009, 94 (6). 40.

Liu, H. T.; Liu, Y. Q.; Zhu, D. B., Chemical doping of graphene. J Mater Chem 2011, 21 (10),

3335-3345. 41.

Ryu, S.; Liu, L.; Berciaud, S.; Yu, Y. J.; Liu, H. T.; Kim, P.; Flynn, G. W.; Brus, L. E., Atmospheric

Oxygen Binding and Hole Doping in Deformed Graphene on a SiO2 Substrate. Nano Lett 2010,

10 (12), 4944-4951. 42.

Romero, H. E.; Joshi, P.; Gupta, A. K.; Gutierrez, H. R.; Cole, M. W.; Tadigadapa, S. A.; Eklund,

P. C., Adsorption of ammonia on graphene. Nanotechnology 2009, 20 (24). 43.

Gierz, I.; Riedl, C.; Starke, U.; Ast, C. R.; Kern, K., Atomic hole doping of graphene. Nano

Lett 2008, 8 (12), 4603-7. 44.

Romero, H. E.; Shen, N.; Joshi, P.; Gutierrez, H. R.; Tadigadapa, S. A.; Sofo, J. O.; Eklund, P. C.,

n-Type Behavior of Graphene Supported on Si/SiO2 Substrates. Acs Nano 2008, 2 (10), 2037-2044. 45.

Bokdam, M.; Khomyakov, P. A.; Brocks, G.; Zhong, Z. C.; Kelly, P. J., Electrostatic Doping of

Graphene through Ultrathin Hexagonal Boron Nitride Films. Nano Lett 2011, 11 (11), 4631-4635.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

Page 20 of 27

Page 21 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


254x190mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

254x190mm (300 x 300 DPI)


Page 22 of 27

Page 23 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig.3. (a) A hBN/graphene/hBN sandwich device with gold electrodes was fabricated. (b) The relationship between total resistance Rtot and back-gate bias Vg of the sandwich structure device in ambient condition and vacuum condition at room temperature. 254x190mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig.4. Rtot was measured as a function of Vg in ambient air and vacuum for the graphene on SiO2 device at room temperature. The inset shows a microscopic image of the device. 254x190mm (300 x 300 DPI)


Page 24 of 27

Page 25 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig.5. (a) The relationship between total resistance Rtot and back-gate bias Vg of a sandwich structure device with a bubble in ambient condition at room temperature. The red curve is fitting result. (b) Rtot versus Vg measured at low pressure (5x10-3 Torr) is shown.(c) AFM images show the bubbles trapped between the graphene and the BN layers. 254x190mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig.6. (a) Rtot versus Vg of a sandwich structure device with a bubble was measured in air and different pressures at room temperature. (b) Schematic diagram shows the bubble structure with doping adsorbates. (c) Optical microscope image shows the device with bubble. 254x190mm (300 x 300 DPI)


Page 26 of 27

Page 27 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


254x190mm (300 x 300 DPI)


Study of Graphene-based 2D-Heterostructure Device Fabricated by All

Recommend Documents