Limits...
Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors.

Mahjouri-Samani M, Lin MW, Wang K, Lupini AR, Lee J, Basile L, Boulesbaa A, Rouleau CM, Puretzky AA, Ivanov IN, Xiao K, Yoon M, Geohegan DB - Nat Commun (2015)

Bottom Line: The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics.Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns.This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices.

View Article: PubMed Central - PubMed

Affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.

ABSTRACT
The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional crystalline semiconductors as building blocks in next-generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate an approach for the formation of lithographically patterned arrays of lateral semiconducting heterojunctions within a single two-dimensional crystal. Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns. The junctions and conversion process are studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy and device characterization. This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices.

No MeSH data available.


STEM Z-contrast image and elemental imaging of a heterojunction.(a,b) Optical image and corresponding Raman map of a patterned nanosheet on a SiO2 substrate (scale bar, 5 μm). The SiO2 masks (circular discs in a) are removed during KOH etching, and the transfer of the nanosheet onto the TEM grids. (c) Low-magnification Z-contrast image of the nanosheet showing the MoSe2 and MoS2 regions with a finite boundary across the domains (scale bars, 5 nm). (d,e) Fourier filtered images of the atomic resolution Z-contrast images of the MoSe2 and MoS2 (bottom insets in the images) domains with corresponding fast Fourier transform patterns (top insets in the images). (f,g) Surface and line intensity profiles of the squared and line-marked regions in c. (h,i) Low-magnification image of a boundary with its corresponding electron energy loss spectroscopy map showing the sulfur concentration (scale bars, 5 nm).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4525195&req=5

f3: STEM Z-contrast image and elemental imaging of a heterojunction.(a,b) Optical image and corresponding Raman map of a patterned nanosheet on a SiO2 substrate (scale bar, 5 μm). The SiO2 masks (circular discs in a) are removed during KOH etching, and the transfer of the nanosheet onto the TEM grids. (c) Low-magnification Z-contrast image of the nanosheet showing the MoSe2 and MoS2 regions with a finite boundary across the domains (scale bars, 5 nm). (d,e) Fourier filtered images of the atomic resolution Z-contrast images of the MoSe2 and MoS2 (bottom insets in the images) domains with corresponding fast Fourier transform patterns (top insets in the images). (f,g) Surface and line intensity profiles of the squared and line-marked regions in c. (h,i) Low-magnification image of a boundary with its corresponding electron energy loss spectroscopy map showing the sulfur concentration (scale bars, 5 nm).

Mentions: Crystalline structures of the converted and pristine regions as well as their heterojunction boundaries were also studied by atomic resolution Z-contrast STEM. Figure 3a,b shows the optical image and corresponding Raman map of a typical patterned/converted layer transferred onto a grid for STEM imaging (Supplementary Fig. 4; Supplementary Note 4). As shown in Fig. 3c, atomic resolution Z-contrast STEM images are taken at the heterojunction that clearly shows both MoSe2 (Fig. 3d) and MoS2 (Fig. 3e) 2D crystal domains. The line and surface intensity profiles of the selected regions in Fig. 3c are shown in Fig. 3f,g. Likewise, Fig. 3h,i shows a STEM image of a boundary with its corresponding electron energy loss spectroscopy map showing the sulfur content (in green) as a function of position. It is clear that both pristine MoSe2 and converted MoS2 regions lie within the same honeycomb lattice with no grain boundaries—that is, the MoSe2 crystal serves as a template, maintaining the same crystal orientations throughout the whole structure. As can be seen from the STEM image, the interface has a finite width similar to that reported for MoSe2/WSe2 heterojunctions19. The boundary appears to be a MoSxSe1−x ternary alloy with a composition gradient over a distance of several nanometres. The sharpness of the heterojunctions is related to the e-beam lithography and patterning processes used in this work, which can be improved further.


Patterned arrays of lateral heterojunctions within monolayer two-dimensional semiconductors.

Mahjouri-Samani M, Lin MW, Wang K, Lupini AR, Lee J, Basile L, Boulesbaa A, Rouleau CM, Puretzky AA, Ivanov IN, Xiao K, Yoon M, Geohegan DB - Nat Commun (2015)

STEM Z-contrast image and elemental imaging of a heterojunction.(a,b) Optical image and corresponding Raman map of a patterned nanosheet on a SiO2 substrate (scale bar, 5 μm). The SiO2 masks (circular discs in a) are removed during KOH etching, and the transfer of the nanosheet onto the TEM grids. (c) Low-magnification Z-contrast image of the nanosheet showing the MoSe2 and MoS2 regions with a finite boundary across the domains (scale bars, 5 nm). (d,e) Fourier filtered images of the atomic resolution Z-contrast images of the MoSe2 and MoS2 (bottom insets in the images) domains with corresponding fast Fourier transform patterns (top insets in the images). (f,g) Surface and line intensity profiles of the squared and line-marked regions in c. (h,i) Low-magnification image of a boundary with its corresponding electron energy loss spectroscopy map showing the sulfur concentration (scale bars, 5 nm).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525195&req=5

f3: STEM Z-contrast image and elemental imaging of a heterojunction.(a,b) Optical image and corresponding Raman map of a patterned nanosheet on a SiO2 substrate (scale bar, 5 μm). The SiO2 masks (circular discs in a) are removed during KOH etching, and the transfer of the nanosheet onto the TEM grids. (c) Low-magnification Z-contrast image of the nanosheet showing the MoSe2 and MoS2 regions with a finite boundary across the domains (scale bars, 5 nm). (d,e) Fourier filtered images of the atomic resolution Z-contrast images of the MoSe2 and MoS2 (bottom insets in the images) domains with corresponding fast Fourier transform patterns (top insets in the images). (f,g) Surface and line intensity profiles of the squared and line-marked regions in c. (h,i) Low-magnification image of a boundary with its corresponding electron energy loss spectroscopy map showing the sulfur concentration (scale bars, 5 nm).
Mentions: Crystalline structures of the converted and pristine regions as well as their heterojunction boundaries were also studied by atomic resolution Z-contrast STEM. Figure 3a,b shows the optical image and corresponding Raman map of a typical patterned/converted layer transferred onto a grid for STEM imaging (Supplementary Fig. 4; Supplementary Note 4). As shown in Fig. 3c, atomic resolution Z-contrast STEM images are taken at the heterojunction that clearly shows both MoSe2 (Fig. 3d) and MoS2 (Fig. 3e) 2D crystal domains. The line and surface intensity profiles of the selected regions in Fig. 3c are shown in Fig. 3f,g. Likewise, Fig. 3h,i shows a STEM image of a boundary with its corresponding electron energy loss spectroscopy map showing the sulfur content (in green) as a function of position. It is clear that both pristine MoSe2 and converted MoS2 regions lie within the same honeycomb lattice with no grain boundaries—that is, the MoSe2 crystal serves as a template, maintaining the same crystal orientations throughout the whole structure. As can be seen from the STEM image, the interface has a finite width similar to that reported for MoSe2/WSe2 heterojunctions19. The boundary appears to be a MoSxSe1−x ternary alloy with a composition gradient over a distance of several nanometres. The sharpness of the heterojunctions is related to the e-beam lithography and patterning processes used in this work, which can be improved further.

Bottom Line: The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics.Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns.This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices.

View Article: PubMed Central - PubMed

Affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.

ABSTRACT
The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional crystalline semiconductors as building blocks in next-generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate an approach for the formation of lithographically patterned arrays of lateral semiconducting heterojunctions within a single two-dimensional crystal. Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns. The junctions and conversion process are studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy and device characterization. This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices.

No MeSH data available.