Article pubs.acs.org/cm
Large Area Atomically Flat Surfaces via Exfoliation of Bulk Bi2Se3 Single Crystals Celeste L. Melamed,*,†,‡ Brenden R. Ortiz,‡ Prashun Gorai,†,‡ Aaron D. Martinez,†,‡ William E. McMahon,† Elisa M. Miller,† Vladan Stevanović,†,‡ Adele C. Tamboli,† Andrew G. Norman,† and Eric S. Toberer†,‡ †
National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401, United States
‡
S Supporting Information *
ABSTRACT: In this work, we present an exfoliation method that produces cm2-area atomically flat surfaces from bulk layered single crystals, with broad applications such as for the formation of lateral heterostructures and for use as substrates for van der Waals epitaxy. Single crystals of Bi2Se3 were grown using the Bridgman method and examined with X-ray reciprocal space maps, Auger spectroscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. An indium-bonding exfoliation technique was developed that produces multiple ∼100 μm thick atomically flat, macroscopic (>1 cm2) slabs from each Bi2Se3 source crystal. Twodimensional X-ray diffraction and reciprocal space maps confirm the high crystalline quality of the exfoliated surfaces. Atomic force microscopy reveals that the exfoliated surfaces have an average root-mean-square (RMS) roughness of ∼0.04 nm across 400 μm2 scans and an average terrace width of 70 μm between step edges. First-principles calculations reveal exfoliation energies of Bi2Se3 and a number of other layered compounds, which demonstrate relevance of our method across the field of 2D materials. While many potential applications exist, excellent lattice matching with the III−V alloy space suggests immediate potential for the use of these exfoliated layered materials as epitaxial substrates for photovoltaic development.
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has been performed with a variety of materials10−13 and is relevant in a wide range of fields, including work in photovoltaics such as the recent success by Kim et al. in the epitaxial growth of GaAs on GaAs with a monolayer graphene buffer layer.14 However, these successes in van der Waals epitaxy are often performed on either 2D flakes or substrates grown by chemical vapor transport with small surface areas. There are few demonstrations of 2D materials produced by mechanical exfoliation techniques with surfaces of sufficient crystalline quality and size to serve as substrates with commercial potential and scalability. Here we present an exfoliation method for 2D layered materials that achieves near-perfect surface quality over macroscopic areas. Such surfaces can be repeatedly exfoliated from a source single crystal. We grew single-crystal boules of Bi2Se3 using the Bridgman method and developed exfoliation procedures to yield macroscopic (cm2) slabs of Bi2Se3. The resulting slabs were studied by a combination of diffraction and scanning probe techniques to assess their surface morphology, which reveals high crystalline quality and RMS roughnesses of
INTRODUCTION Since the discovery of remarkable properties in single-layer graphene, research on 2D materials of all types has blossomed, with techniques such as single-layer deposition and solution exfoliation developed to produce these materials.1 The majority of the research has focused on the production of monolayers, due to the unique materials properties resulting from the spatial confinement of a van der Waals-bonded layer. While exfoliation techniques have advanced from the initial adhesive-tape method to producing monolayers with lateral dimensions of ∼500 μm, there are still daunting processing limitations.2 The yield of monolayer-exfoliation methods is often very low, with poor control of orientation and form factor of the resulting flake, and scalability remains uncertain and inconsistent.1 Although most contemporary work focuses on monolayers of 2D materials, there is a rich history of bulk exfoliation of layered materials for other purposes. As far back as the 1960s, researchers used tape and other mechanical methods to cleave off the top of layered crystals for surface studies.3−5 However, these techniques have not been transferred to relevant chemical systems for modern-day applications. One such application is the field of van der Waals epitaxy, which attempts to harness the weakly bonded surfaces of 2D materials to act as buffer layers and relieve lattice mismatch.6−9 van der Waals epitaxy © 2017 American Chemical Society
Received: July 28, 2017 Revised: September 11, 2017 Published: September 12, 2017 8472
DOI: 10.1021/acs.chemmater.7b03198 Chem. Mater. 2017, 29, 8472−8477
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Chemistry of Materials ∼0.04 nm over 20 × 20 μm scans. First-principles calculations were performed to confirm the applicability of this method to other 2D materials systems. This exfoliation method is relevant for applications ranging from fundamental studies of 2D materials to epitaxy of semiconductors to novel heterojunction structures.15−17
exhibited a large amount of cracking, bending, and surface debris due to the soft nature of the material, so we determined that rigid support was necessary to provide a more directed stress profile within the propagating crack tip. Thus, our next method utilized glass slides adhered to each side of a single crystal using double-sided tape. When compressive pressure was applied to one side of the glass, the crystal would reproducibly cleave along the (0001) planes close to the side from which pressure was applied. This cleavage would occur rapidly and propagate across the entire crystal, rather than the slower release associated with the tensile exfoliation discussed above. Critical to this approach is the use of structural support on both sides to avoid deformation and serve as a handle for the exfoliated slab. Inspired by these results, we transitioned to a metallic adhesive in order to produce substrates that are thermally robust. The process of indium-bonded exfoliation is illustrated in Figure S3 and was performed in an argon glovebox. Shavings of indium were placed on glass slides and heated to >200 °C on a hot plate. Once the indium was molten, the (0001) Bi2Se3 single-crystal ingot face was firmly pressed onto the indium and the stack was removed from the heat. The process was repeated on the other side of the crystal ingot to form a symmetric stack of glass−Bi2Se3−glass mechanically bonded with solid indium. To cleave the crystal, gentle compressive, asymmetric pressure was applied to the edge of the top glass slide. This process was repeated multiple times to generate numerous single-crystal slabs from one source crystal. Figure 1b shows the exfoliated square-centimeter slab and the specular nature of its surface as demonstrated with the adjacent ruler. For a 1 mm thick Bi2Se3 crystal, supported indium-bonded exfoliation yields up to 11 atomically flat, single-crystalline, exfoliated slabs with lateral dimensions of 10 mm. Slabs are generally 40−150 μm thick as determined by scanning electron microscopy. For a study of the thickness distribution produced by the indium-bonded method, see ref 24 by Melamed et al. We anticipate that the spread of exfoliated slab thicknesses is due to slight variations in indium coverage and direction of applied pressure for each exfoliation. The solid mechanics associated with this process are nontrivial, as the materials are highly anisotropic and atomic-scale glide is likely present, coupled with macroscopic bending. Studies attempting to exfoliate uniform-thickness slabs are ongoing, leveraging existing techniques such as spalling, which achieved control of spalled layer thickness.25 To verify that the quality of the exfoliated Bi2Se3 slab does not degrade with repeated exfoliation of the original crystal, ω2θ scans were conducted (Figure 2). Two-dimensional diffraction patterns are largely identical across all samples examined, with only slight broadening in χ after six exfoliations, as shown in Figure 2c, d. Only the {0001} family of planes is present in all scans, consistent with the layered crystallography of Bi2Se3. This result demonstrates that the indium-bonded exfoliation process preserves crystallinity even after multiple exfoliation cycles. Once crystallinity of the exfoliated slabs was verified, highresolution reciprocal space maps (RSMs) were performed to further analyze the impact of exfoliation on characteristics such as local strain and macroscopic bending. Figure 3a shows that, before exfoliation, the RSM reveals a full-width at halfmaximum (FWHM) of 216 ± 3 arcsecs for the (0006) peak. This value is an order of magnitude larger than that typically observed in thin-film III−Vs,26 which is attributed to the highly compliant nature of these 2D crystals due to interlayer glide.
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RESULTS AND DISCUSSION Bulk Crystal Growth. Bi2Se3 single crystals have previously been grown by a diverse array of methods; in this work, we chose the Bridgman method, as it has proven to yield largediameter boules (>1 cm).18−20 Experimental details are described in the Experimental Details section. Single-crystal boules (10 mm diameter × 30 mm length) grown by Bridgman were a homogeneous silvery-gray color with neither cracks nor inclusions visible on the boule surface. To facilitate handling and exfoliation, the single-crystal boule was mechanically partitioned along the (0001) plane into smaller ingots, which proved straightforward due to the van der Waals nature of the layered bonding. Figure 1a shows the specular reflection of a ruler on a sectioned single crystal of Bi2Se3. To characterize the atomic structure of the surface, a bulk single crystal with a freshly exfoliated surface was loaded into an ultrahigh vacuum (UHV) chamber for analysis with Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The surface was free of oxygen and carbon, consistent with prior reports for an ideal, Se-terminated cleave.18,21 The lack of oxygen contamination is readily apparent in the AES scan in Figure S1a, but the carbon AES peak can be obscured by Bi, so X-ray photoelectron spectroscopy (XPS, Figure S2) was performed to verify the lack of carbon contamination. LEED data (Figure S1b) exhibits the expected 3-fold rotational symmetry and is crisp and clear, consistent with a high-quality Se-terminated cleave. Exfoliation. A variety of exfoliation strategies for Bi2Se3 were explored. Initial methods, inspired by Jayasena and Subbiah in ref 22, used a sectioning microtome to cleave Bi2Se3 along the (0001) plane. This technique did not yield suitable exfoliated slabs due to scrolling of the exfoliated layer, which yielded tubes rather than sheets, a macroscopic version of the nanoscrolls reported by Liu et al. in ref 23. The next method examined built upon the traditional tape exfoliation of graphene. Tape was adhered to a single crystal and then peeled off, yielding thin slabs of Bi2Se3. The resulting crystals
Figure 1. Images showing (a) a bulk Bi2Se3 crystal and (b) a slab of Bi2Se3 exfoliated using the indium-bonded method. The hightemperature glass handle, which provides structural support during the exfoliation process, is visible in (b). Both crystals show mirror-flat surfaces exhibiting the specular reflection of a ruler with cm markings. Logo used with permission from Colorado School of Mines. 8473
DOI: 10.1021/acs.chemmater.7b03198 Chem. Mater. 2017, 29, 8472−8477
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reference, a typical wafer for thin-film growth after chemicalmechanical polishing exhibits RMS roughness of over an order of magnitude greater than our samples.27 Figure 4 utilizes a heat map spanning 2 nm, the height of two 5-atom steps in the crystal structure of Bi2Se3. Step edges (Figure 5a) are occasionally found by AFM; these exhibit the ∼10 Å height associated with a single 5-atom-thick slab (Figure 5b). To assess the density of step edges, wider-area AFM scans were performed on multiple exfoliated samples. By conducting 15 random 50 μm × 50 μm scans, a step-edge density of 0.014 μm−1 was obtained (Figure S4). Eight of the 15 total 2500 μm2 scans exhibited no step edges at all. The step-edge density was inverted to yield a value of 70 μm, which represents the average distance between each step edge under the assumption that they are parallel. This long terrace width suggests that the propagation of the crack tip during exfoliation was exceptionally well-confined within a given interlayer gap, producing near-atomically flat exfoliated surfaces. Surface Stability. To evaluate the stability of Bi2Se3 surfaces, freshly cleaved single crystals were heated under AsH3 to 550 °C. Samples were analyzed with the previously mentioned AES and LEED systems before and after heat treatment in order to compare results. AES showed no significant loss of Se, nor was there any evidence for replacement of Se by As. LEED showed no change in the crystallinity of the surface. This result suggests that exfoliated Bi2Se3 surfaces have potential for use as substrates for van der Waals epitaxy, which often requires high temperatures. Exfoliation Energy Calculations. To fully understand the applicability of the indium-bonding exfoliation method, firstprinciples density functional theory calculations were performed to compare exfoliation energies of a few layered materials of interest (Figure 6). Computational details are given in the Experimental Details section. The calculated Eexfol for Bi2Se3, In2Se3, and GeS are 22.4, 18.5, and 34.8 meV/Å2. These candidate materials have exfoliation curves and binding energies similar to those of graphite and MoS2 (24.2 and 25.3 meV/Å2, respectively), two well-known layered materials. Wang et al. reported an experimental cleavage energy value of 24.3 meV/Å2 for graphite, which is consistent with our calculation.1 Because all exfoliation energies are comparable, this indicates that the materials studied can all be exfoliated with the indium-bonding method.
Figure 2. 2D XRD scans of the (a) first and (c) sixth Bi2Se3 exfoliated slabs showing the 0001 family of reflections, indicating the slabs retain the single-crystal character of the parent bulk crystal. (b, d) XRD data from (a) and (c), respectively, integrated in χ. This data is consistent with ω-2θ scans of parent Bi2Se3 single crystals.
After exfoliation, reciprocal space maps reveal FWHM values of 226 ± 3 and 360 ± 30 arcsecs for the same peak, which is fairly consistent with the original crystal, with minor degradation associated with the flex of the samples (Figure 3b, c). For the sample region shown in Figure 3c, which exhibits a larger spread in ω, multiple overlapping peaks are observed, suggesting macroscopic domains arising from slight bending in the crystal during the exfoliation process. However, each peak retains a narrow FWHM value, which implies that local crystalline quality is maintained. We expect that increased automation in the exfoliation process will eliminate such bending. Tapping-mode atomic force microscopy (AFM) was conducted to assess surface morphology of exfoliated Bi2Se3 and to ensure repeated exfoliations do not degrade surface quality. Figure 4 shows 20 × 20 μm scans of slabs after (a) one, (b) three, and (c) six exfoliations. These scans exhibit RMS roughnesses of ∼0.04 nm, which is extraordinarily flat. For
Figure 3. Reciprocal space maps on a logarithmic scale of the (0006) peak of a Bi2Se3 sample (a) before and (b, c) after indium-bonded exfoliation. These maps demonstrate that exfoliation only mildly impacts crystalline quality. (b) and (c) were taken on different regions of the same exfoliated sample. The exfoliated peaks remain narrow, with a small amount of broadening introduced by the macroscopic bowing of the sample. Insets show line scans at ω-2θ = 0°, which have FWHM values of 216 ± 3, 226 ± 3, and 360 ± 30 arcseconds, respectively. However, the line scan in (c) consists of two distinct peaks, each with significantly smaller FWHM values (120 ± 20 and 162 ± 7 arcseconds). This suggests that exfoliation causes macroscopic domains due to slight bending in the crystal. 8474
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Figure 4. AFM scans (20 μm × 20 μm) of Bi2Se3 slabs produced from (a) one, (b) three, and (c) six exfoliations showing extraordinarily flat surfaces, with RMS roughnesses of 0.040, 0.039, and 0.043 nm, respectively. The small variations in color are due to noise and are not features on the sample surface. (a) and (c) are the same crystals on which 2D XRD is shown in Figure 2.
is limited by the cost of single-crystal substrates despite exhibiting a solar conversion efficiency of ∼28.8%.28,29 To overcome substrate cost, the photovoltaic industry has investigated a wide variety of complex techniques, such as substrate recycling, epitaxial overgrowth, and metamorphic buffer layers.30−32 An alternative approach toward solving this problem is the use of 2D materials to assist device development. We envision that low-cost exfoliated 2D slabs could be used as lattice-matched substrates for III−V materials (Figure 7). For example, Bi2Se3 is lattice-matched to InP, as shown in Figure 7b. By taking advantage of the weak van der Waals bonding between layers, lattice-matched single-crystal substrates can be produced without costly kerf losses and chemo-mechanical polishing. Several criteria must be satisfied to use 2D materials as substrates for photovoltaics: (i) to minimize minority recombination, single-crystalline domains must be large enough to ensure long minority carrier lifetime; (ii) to minimize generation of nonradiative defects such as threading dislocations in the epitaxial film, a close lattice match between the III−V and the underlying 2D layered material is crucial; and (iii) 2D substrates must be cost competitive. Depending on the materials system in question, single-crystal substrates must also remain stable at the III−V growth
Figure 5. AFM results characterizing the roughness of the exfoliated slabs of Bi2Se3. (a) While the majority of exfoliated slabs have RMS roughnesses < 0.06 nm, occasionally we observe step edges. (b) Step edge in (a) is 1 nm high, consistent with the layered crystallography of Bi2Se3. Specifically, the step edge corresponds to the spacing between van der Waals layers (inset).
Figure 6. Exfoliation energies. van der Waals crystals Bi2Se3, In2Se3, and GeS have similar exfoliation energies to graphite and MoS2, wellknown layered materials that can be exfoliated with relative ease. These calculations consider the energetics as the van der Waals gap is scaled relative to the equilibrium distance, termed the interlayer scaling factor. The exfoliation energy is estimated from the difference between the equilibrium energy (E1.0) and the energy at an interlayer scaling factor of 1.9 (E1.9) and normalized by the number of van der Waals gaps (L) and the surface area (A) within the unit cell. The number in parentheses is the exfoliation energy in meV/Å2.
Figure 7. (a, b) Schematics demonstrating epitaxial relationships between 2D van der Waals materials and III−V films: (a) 2D materials with square or rectangular nets can template (001) zincblende growth while (b) hexagonal nets can template (111) zincblende growth. (c) Such growth would yield low mismatch for a diverse range of III−V compositions. Vertical colored bands show ±0.5% lattice mismatch with GeS (blue), SnS (green), In2Se3 (yellow), and Bi2Se3 (red).
Applicability to III−V Growth. While there are a multitude of potential applications for this exfoliation method, one is the use of lattice-matched 2D materials as substrates for III−V growth. Widespread deployment of GaAs photovoltaics 8475
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temperature. Our indium-bonding exfoliation process produces exfoliated slabs that meet these requirements and are fully compatible with III−V growth chambers, thus providing a path toward low-cost III−V deployment.
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.7b03198. Auger spectroscopy and LEED of a single-crystal Bi2Se3 sample; X-ray photoelectron spectroscopy of a singlecrystal sample; schematic of the indium-bonded exfoliation process; calculated terrace width for six exfoliated samples (PDF)
CONCLUSIONS In summary, we have developed a technique for repeatably producing large-area, atomically flat surfaces from a single 2D source crystal. Bulk single-crystalline Bi2Se3 was grown using the Bridgman method, and an indium-bonded exfoliation method was developed to produce 40−150 μm thick slabs attached to high-temperature glass handles. The crystallinity of these macroscopic (1 cm2) slabs was maintained after exfoliation as determined by 2D XRD and reciprocal space maps. Surface quality was analyzed using AFM, and exfoliated slabs were found to be highly smooth, with RMS roughnesses of ∼0.04 nm in 20 × 20 μm regions after six exfoliations. The long terrace width of 70 μm emphasizes the highly directed crack propagation within the van der Waals gap. Since this exfoliation technique produces substrates fully compatible with III−V growth, one potential revolutionary application for this work is to enable low-cost deployment of III−V photovoltaics.
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*E-mail:
[email protected]. ORCID
Celeste L. Melamed: 0000-0002-3543-1789 Brenden R. Ortiz: 0000-0002-1333-7003 Elisa M. Miller: 0000-0002-7648-5433 Notes
The authors declare no competing financial interest.
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Bridgman Crystal Growth. To prepare feedstock for Bridgman growth, polycrystalline Bi2Se3 precursor was generated by sealing stoichiometric amounts of Bi shot (UMC 99.9999%) and Se shot (Alfa 99.999%) in a cleaned and baked fused silica ampule. The material was heated to 800 °C at a rate of 100 °C/h and held for 24 h at 800 °C, and then it was cooled and powdered. The resulting Bi2Se3 powder was sealed under vacuum in a tapered 10 mm diameter fused silica ampule and placed in a custom Bridgman crystal-growth setup. The ampule was soaked at 850 °C for 24 h and consequently lowered at a rate of 3 mm/h through a temperature gradient of 10 °C/cm. Characterization. ω-2θ scans and reciprocal space maps were conducted using a Bruker D8 Discover equipped with an area detector and a high-resolution PANalytical X’Pert Pro, respectively. X-ray photoelectron spectroscopy (XPS) was performed on a PHI Electronics 5600 setup using Al Kα monochromatic X-rays (1486.7 eV). Tapping-mode atomic force microscopy (AFM) was conducted with an Asylum Research system. An aluminum reflex-coated silicon probe with a 5 N/m force constant and 120 kHz resonant frequency was used, as Bi2Se3 proves to be quite soft. Computational Methods. First-principles density functional theory (DFT) calculations were performed with plane-wave VASP code33,34 to construct the exfoliation curves shown in Figure 6. To account for long-range van der Waals (vdW) interactions in quasi-2D layered materials, we employ the optB86 vdW-corrected functional.35 The structures were relaxed with the vdW-corrected functional using a plane-wave energy cutoff of 340 eV. Previously, we have demonstrated that total energy calculations with the optB86 functional reproduce the lattice parameters and elastic properties such as bulk modulus of quasi2D materials in fairly good agreement with experiments.36 To construct the exfoliation curves (Figure 6), the interlayer distance in the quasi-2D structure was scaled up to mimic the process of pulling the layers of the bulk crystal apart. A scaling factor of unity corresponds to equilibrium. We also scaled down the interlayer spacing to 0.98 of the equilibrium distance to accurately capture the energy well. At a scaling factor of 1.9, we find that the interlayer interactions become negligible, as indicated by the plateauing of the total energies (denoted by E1.9). The total energies with respect to E1.9 are normalized by the number of layers (L) and the surface area (A) in the unit cell and are plotted as a function of the interlayer scaling factor in Figure 6. The exfoliation energy (Eexfol) is calculated as
E1.9 − E1.0 L×A
AUTHOR INFORMATION
Corresponding Author
EXPERIMENTAL DETAILS
Eexfol =
ASSOCIATED CONTENT
S Supporting Information *
ACKNOWLEDGMENTS This work was supported by the U.S. Department of Energy as part of the SuNLaMP program under Contract no. DE-AC3608GO28308 with the National Renewable Energy Laboratory. X-ray photoelectron spectroscopy measurements were funded by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under the same contract number. The authors acknowledge NSF MRI Award CBET-153219 for enabling the scanning probe microscopy in this work. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.
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REFERENCES
(1) Wang, F.; Wang, Z.; Wang, Q.; Wang, F.; Yin, L.; Xu, K.; Huang, Y.; He, J. Synthesis, Properties and Applications of 2D Non-Graphene Materials. Nanotechnology 2015, 26, 292001. (2) Desai, S. B.; Madhvapathy, S. R.; Amani, M.; Kiriya, D.; Hettick, M.; Tosun, M.; Zhou, Y.; Dubey, M.; Ager, J. W.; Chrzan, D.; Javey, A. Gold-Mediated Exfoliation of Ultralarge Optoelectronically-Perfect Monolayers. Adv. Mater. 2016, 28, 4053−4058. (3) Wilson, J.; Yoffe, A. The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties. Adv. Phys. 1969, 18, 193−335. (4) Albrecht, T. R.; Quate, C. F. Atomic resolution imaging of a nonconductor by atomic force microscopy. J. Appl. Phys. 1987, 62, 2599−2602. (5) Kline, G.; Kam, K.; Canfield, D.; Parkinson, B. Efficient and stable photoelectrochemical cells constructed with WSe2 and MoSe2 photoanodes. Sol. Energy Mater. 1981, 4, 301−308. (6) Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H. 2D Materials and van der Waals Heterostructures. Science 2016, 353, aac9439. (7) Koma, A.; Sunouchi, K.; Miyajima, T. Fabrication and Characterization of Heterostructures with Subnanometer Thickness. Microelectron. Eng. 1984, 2, 129−136.
(1) 8476
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Chemistry of Materials (8) Mohanty, D.; Xie, W.; Wang, Y.; Lu, Z.; Shi, J.; Zhang, S.; Wang, G.-C.; Lu, T.-M.; Bhat, I. B. Van der Waals Epitaxy of CdTe Thin Film on Graphene. Appl. Phys. Lett. 2016, 109, 143109. (9) Alaskar, Y.; Arafin, S.; Wickramaratne, D.; Zurbuchen, M. A.; He, L.; Mckay, J.; Lin, Q.; Goorsky, M. S.; Lake, R. K.; Wang, K. L. Towards van der Waals Epitaxial Growth of GaAs on Si using a Graphene Buffer Layer. Adv. Funct. Mater. 2014, 24, 6629−6638. (10) Ohuchi, F.; Shimada, T.; Parkinson, B.; Ueno, K.; Koma, A. Growth of MoSe2 thin films with Van der Waals epitaxy. J. Cryst. Growth 1991, 111, 1033−1037. (11) Kuroda, S.; Minami, K.; Takita, K. Epitaxial Growth of II-VI Semiconductor CdTe on a Layered Material NbSe2. J. Cryst. Growth 2004, 262, 383−387. (12) Loher, T.; Tomm, Y.; Klein, A.; Su, D.; Pettenkofer, C.; Jaegermann, W. Highly Oriented Layers of the Three Dimensional Semiconductor CdTe on the Two Dimensional Layered Semiconductors MoTe2 and WSe2. J. Appl. Phys. 1996, 80, 5718−5722. (13) Samad, L.; Bladow, S. M.; Ding, Q.; Zhuo, J.; Jacobberger, R. M.; Arnold, M. S.; Jin, S. Layer-Controlled Chemical Vapor Deposition Growth of MoS2 Vertical Heterostructures via van der Waals Epitaxy. ACS Nano 2016, 10, 7039−7046. (14) Kim, Y.; Cruz, S. S.; Lee, K.; Alawode, B. O.; Choi, C.; Song, Y.; Johnson, J. M.; Heidelberger, C.; Kong, W.; Choi, S.; et al. Remote Epitaxy through Graphene enables Two-Dimensional Material-based Layer Transfer. Nature 2017, 544, 340−343. (15) Yamada, A.; Ho, K. P.; Akaogi, T.; Maruyama, T.; Akimoto, K. Layered Compound Substrates for GaN Growth. J. Cryst. Growth 1999, 201−202, 332−335. (16) Chen, Z.; Zhao, L.; Park, K.; Garcia, T. A.; Tamargo, M. C.; Krusin-Elbaum, L. Robust Topological Interfaces and Charge Transfer in Epitaxial Bi2Se3/II - VI Semiconductor Superlattices. Nano Lett. 2015, 15, 6365−6370. (17) Mahjouri-Samani, M.; Lin, M.-W.; Wang, K.; Lupini, A. R.; Lee, J.; Basile, L.; Boulesbaa, A.; Rouleau, C. M.; Puretzky, A. A.; Ivanov, I. N.; Xiao, K.; Yoon, M.; Geohegan, D. B. Patterned Arrays of Lateral Heterojunctions within Monolayer Two-dimensional Semiconductors. Nat. Commun. 2015, 6, 7749. (18) Atuchin, V. V.; Golyashov, V. A.; Kokh, K. A.; Korolkov, I. V.; Kozhukhov, A. S.; Kruchinin, V. N.; Makarenko, S. V.; Pokrovsky, L. D.; Prosvirin, I. P.; Romanyuk, K. N.; Tereshchenko, O. E. Formation of Inert Bi2Se3 (0001) Cleaved Surface. Cryst. Growth Des. 2011, 11, 5507−5514. (19) Huang, F.-T.; Chu, M.-W.; Kung, H. H.; Lee, W. L.; Sankar, R.; Liou, S.-C.; Wu, K. K.; Kuo, Y. K.; Chou, F. C. Nonstoichiometric Doping and Bi Antisite Defect in Single Crystal Bi2Se3. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 86, 081104. (20) Deshpande, M. P.; Pandya, N. N.; Parmar, M. N. Transport Property Measurements of Bi2Se3 Crystal Grown by Bridgman Method. Turk. J. Phys. 2009, 33, 139−148. (21) Zhou, W.; Zhu, H.; Yarmoff, J. A. Termination of Single-Crystal Bi2Se3 Surfaces prepared by Various Methods. Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 94, 195408. (22) Jayasena, B.; Subbiah, S. A Novel Mechanical Cleavage Method for Synthesizing Few-Layer Graphenes. Nanoscale Res. Lett. 2011, 6, 95. (23) Liu, P.; Jin, Z.; Katsukis, G.; Drahushuk, L. W.; Shimizu, S.; Shih, C.-J.; Wetzel, E. D.; Taggart-Scarff, J. K.; Qing, B.; Van Vliet, K. J.; et al. Layered and Scrolled Nanocomposites with Aligned SemiInfinite Graphene Inclusions at the Platelet Limit. Science 2016, 353, 364−367. (24) Melamed, C. L.; Ortiz, B. R.; Martinez, A. D.; McMahon, W. E.; Tamboli, A. C.; Norman, A. G.; Toberer, E. S. Single crystalline substrates for III−V growth via exfoliation of bulk single crystals. 44th IEEE PVSC Proceedings; In Press, 2017. (25) Sweet, C. A.; Schulte, K. L.; Simon, J. D.; Steiner, M. A.; Jain, N.; Young, D. L.; Ptak, A. J.; Packard, C. E. Controlled exfoliation of (100) GaAs-based devices by spalling fracture. Appl. Phys. Lett. 2016, 108, 011906.
(26) Ayers, J. The Measurement of Threading Dislocation Densities in Semiconductor Crystals by X-ray Diffraction. J. Cryst. Growth 1994, 135, 71−77. (27) Brightup, S.; Goorsky, M. S. Chemical-Mechanical Polishing for III-V Wafer Bonding Applications: Polishing, Roughness, and an Abrasive-Free Polishing Model. ECS Trans. 2010, 33, 383−389. (28) Ward, J. S.; Remo, T.; Horowitz, K.; Woodhouse, M.; Sopori, B.; VanSant, K.; Basore, P. Techno-economic Analysis of Three Different Substrate Removal and Reuse Strategies for III-V Solar Cells. Prog. Photovoltaics 2016, 24, 1284−1292. (29) Green, M. A.; Emery, K.; Hishikawa, Y.; Warta, W.; Dunlop, E. D. Solar Cell Efficiency Tables (Version 45). Prog. Photovoltaics 2015, 23, 1−9. (30) Lee, K.; Zimmerman, J. D.; Hughes, T. W.; Forrest, S. R. NonDestructive Wafer Recycling for Low-Cost Thin-Film Flexible Optoelectronics. Adv. Funct. Mater. 2014, 24, 4284−4291. (31) Li, Q.; Ng, K. W.; Lau, K. M. Growing Antiphase-Domain-free GaAs Thin Films out of Highly Ordered Planar Nanowire Arrays on Exact (001) Silicon. Appl. Phys. Lett. 2015, 106, 072105. (32) France, R. M.; Dimroth, F.; Grassman, T. J.; King, R. R. Metamorphic Epitaxy for Multijunction Solar Cells. MRS Bull. 2016, 41, 202−209. (33) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. (34) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for ab initio Total-Energy Calculations using a Plane-wave Basis Set. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 11169. (35) Klimes, J.; Bowler, D. R.; Michaelides, A. Chemical Accuracy for the van der Waals Density Functional. J. Phys.: Condens. Matter 2010, 22, 022201. (36) Gorai, P.; Toberer, E. S.; Stevanovic, V. Computational Identification of Promising Thermoelectric Materials among Known Quasi-2D Binary Compounds. J. Mater. Chem. A 2016, 4, 11110− 11116.
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DOI: 10.1021/acs.chemmater.7b03198 Chem. Mater. 2017, 29, 8472−8477
