The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Mark C. Hersam - One of the best experts on this subject based on the ideXlab platform.
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Ultrahigh Vacuum self assembly of rotationally commensurate c8 btbt mos2 graphene mixed dimensional heterostructures
Chemistry of Materials, 2019Co-Authors: Xiaolong Liu, Itamar Balla, Vinod K Sangwan, Hakan Usta, Antonio Facchetti, Tobin J Marks, Mark C. HersamAbstract:Mixed-dimensional van der Waals heterostructures combine the advantages of nanomaterials with qualitatively distinct properties such as the extended bandstructures and high charge carrier mobilities of inorganic two-dimensional materials and the discrete orbital energy levels and strong optical absorption of zero-dimensional organic molecules. The synergistic interplay between nanomaterials of distinct dimensionality has enabled a variety of unique applications such as antiambipolar transistors, sensitized photodetectors, and gate-tunable photovoltaics. Because the performance of mixed-dimensional heterostructure devices depends sensitively on the buried interfacial structure, it is of great interest to identify materials and chemistries that naturally form highly ordered heterointerfaces. Toward this end, here we demonstrate Ultrahigh Vacuum self-assembly of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) monolayers onto epitaxial MoS2/graphene heterostructures. With molecular-resolution scan...
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Ultrahigh Vacuum Self-Assembly of Rotationally Commensurate C8-BTBT/MoS2/Graphene Mixed-Dimensional Heterostructures
2019Co-Authors: Xiaolong Liu, Itamar Balla, Vinod K Sangwan, Hakan Usta, Antonio Facchetti, Tobin J Marks, Mark C. HersamAbstract:Mixed-dimensional van der Waals heterostructures combine the advantages of nanomaterials with qualitatively distinct properties such as the extended bandstructures and high charge carrier mobilities of inorganic two-dimensional materials and the discrete orbital energy levels and strong optical absorption of zero-dimensional organic molecules. The synergistic interplay between nanomaterials of distinct dimensionality has enabled a variety of unique applications such as antiambipolar transistors, sensitized photodetectors, and gate-tunable photovoltaics. Because the performance of mixed-dimensional heterostructure devices depends sensitively on the buried interfacial structure, it is of great interest to identify materials and chemistries that naturally form highly ordered heterointerfaces. Toward this end, here we demonstrate Ultrahigh Vacuum self-assembly of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) monolayers onto epitaxial MoS2/graphene heterostructures. With molecular-resolution scanning tunneling microscopy and spectroscopy, the resulting C8-BTBT/MoS2/graphene mixed-dimensional heterostructures are found to be rotationally commensurate with well-defined physical and electronic structures. It is further shown that the self-assembled C8-BTBT monolayers are insensitive to the structural defects and electronic perturbations of the underlying MoS2 substrate, which provides significant processing latitude. For these reasons, this work will facilitate ongoing efforts to utilize organic/MoS2/graphene mixed-dimensional heterostructures for electronic, optoelectronic, and photovoltaic applications
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probing intermolecular vibrational symmetry breaking in self assembled monolayers with Ultrahigh Vacuum tip enhanced raman spectroscopy
Journal of the American Chemical Society, 2017Co-Authors: Naihao Chiang, Eric A. Pozzi, Nan Jiang, Mark C. Hersam, Tamar Seideman, George C. Schatz, Lindsey R Madison, Michael R Wasielewski, Mark A Ratner, Richard P Van DuyneAbstract:Ultrahigh Vacuum tip-enhanced Raman spectroscopy (UHV-TERS) combines the atomic-scale imaging capability of scanning probe microscopy with the single-molecule chemical sensitivity and structural specificity of surface-enhanced Raman spectroscopy. Here, we use these techniques in combination with theory to reveal insights into the influence of intermolecular interactions on the vibrational spectra of a N-N′-bis(2,6-diisopropylphenyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI) self-assembled monolayer adsorbed on single-crystal Ag substrates at room temperature. In particular, we have revealed the lifting of a vibrational degeneracy of a mode of PDI on Ag(111) and Ag(100) surfaces, with the most strongly perturbed mode being that associated with the largest vibrational amplitude on the periphery of the molecule. This work demonstrates that UHV-TERS enables direct measurement of molecule–molecule interaction at nanoscale. We anticipate that this information will advance the fundamental understanding of the m...
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Probing Intermolecular Vibrational Symmetry Breaking in Self-Assembled Monolayers with Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy
2017Co-Authors: Naihao Chiang, Eric A. Pozzi, Nan Jiang, Mark C. Hersam, Tamar Seideman, George C. Schatz, Lindsey R Madison, Michael R Wasielewski, Mark A Ratner, Richard P Van DuyneAbstract:Ultrahigh Vacuum tip-enhanced Raman spectroscopy (UHV-TERS) combines the atomic-scale imaging capability of scanning probe microscopy with the single-molecule chemical sensitivity and structural specificity of surface-enhanced Raman spectroscopy. Here, we use these techniques in combination with theory to reveal insights into the influence of intermolecular interactions on the vibrational spectra of a N-N′-bis(2,6-diisopropylphenyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI) self-assembled monolayer adsorbed on single-crystal Ag substrates at room temperature. In particular, we have revealed the lifting of a vibrational degeneracy of a mode of PDI on Ag(111) and Ag(100) surfaces, with the most strongly perturbed mode being that associated with the largest vibrational amplitude on the periphery of the molecule. This work demonstrates that UHV-TERS enables direct measurement of molecule–molecule interaction at nanoscale. We anticipate that this information will advance the fundamental understanding of the most important effect of intermolecular interactions on the vibrational modes of surface-bound molecules
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Ultrahigh-Vacuum Tip-Enhanced Raman Spectroscopy
Chemical reviews, 2016Co-Authors: Eric A. Pozzi, Nan Jiang, Tamar Seideman, Guillaume Goubert, Naihao Chiang, Craig T. Chapman, Michael O. Mcanally, Anne Isabelle Henry, George C. Schatz, Mark C. HersamAbstract:Molecule–surface interactions and processes are at the heart of many technologies, including heterogeneous catalysis, organic photovoltaics, and nanoelectronics, yet they are rarely well understood at the molecular level. Given the inhomogeneous nature of surfaces, molecular properties often vary among individual surface sites, information that is lost in ensemble-averaged techniques. In order to access such site-resolved behavior, a technique must possess lateral resolution comparable to the size of surface sites under study, analytical power capable of examining chemical properties, and single-molecule sensitivity. Tip-enhanced Raman spectroscopy (TERS), wherein light is confined and amplified at the apex of a nanoscale plasmonic probe, meets these criteria. In Ultrahigh Vacuum (UHV), TERS can be performed in pristine environments, allowing for molecular-resolution imaging, low-temperature operation, minimized tip and molecular degradation, and improved stability in the presence of ultrafast irradiation...
Kentaro Kyuno - One of the best experts on this subject based on the ideXlab platform.
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reversible creation and annihilation of a local leakage path in hfo2 geox stacked gate dielectrics a direct observation by Ultrahigh Vacuum conducting atomic force microscopy
Applied Physics Letters, 2006Co-Authors: K Yamamura, Akira Toriumi, Koji Kita, Kentaro KyunoAbstract:By direct observation using Ultrahigh Vacuum conducting atomic force microscopy, it is found that a local leakage path in HfO2∕GeOx stacks created by an electrical stress with a positive tip bias annihilates after applying a reverse tip bias. The creation and annihilation of these paths are repeatable without noticeable degradation. The fact that these paths annihilate by a very small reverse bias suggests that this behavior is caused by local reduction and oxidation in the HfO2 layer.
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evolution of leakage paths in hfo2 sio2 stacked gate dielectrics a stable direct observation by Ultrahigh Vacuum conducting atomic force microscopy
Applied Physics Letters, 2005Co-Authors: Kentaro Kyuno, Koji Kita, Akira ToriumiAbstract:A conducting atomic force microscopy (C-AFM) in Ultrahigh Vacuum (UHV) is used to directly observe the evolution of leakage path in HfO2∕SiO2 stacked gate dielectrics. Thanks to the UHV environment, reproducible results for both positive and negative tip biases are obtained without material formation on the surface, which has been a problem for atmospheric C-AFM. It is found that the density of leakage spots increases exponentially as a function of tip bias and that it is a large factor for leakage current increase.
Masashi Iwatsuki - One of the best experts on this subject based on the ideXlab platform.
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comparative surface studies at atomic resolution with Ultrahigh Vacuum variable temperature atomic force and scanning tunneling microscopes
Microscopy and Microanalysis, 1999Co-Authors: Masashi Iwatsuki, Kazuyuki Suzuki, Shinich Kitamura, M KerskerAbstract:: With the Ultrahigh Vacuum variable-temperature scanning tunneling microscope (UHV-VT-STM), atomic-level observation has been achieved. An Ultrahigh Vacuum atomic force microscope (UHV-AFM) has also been developed, with success in obtaining atom images where observation in noncontact (NC) mode with a frequency modulation (FM) detection method was attempted. Using the FM detection method in the constant oscillation amplitude of the cantilever excitation mode, we have obtained atomic-resolution images of Si(111) 7 x 7 structures and Si(100) 2 x 1 structures and other structures together with STM images in an Ultrahigh Vacuum environment. Also shown here are contact potential difference (CPD) images using the NC-AFM method.
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high resolution imaging of contact potential difference with Ultrahigh Vacuum noncontact atomic force microscope
Applied Physics Letters, 1998Co-Authors: Shinichi Kitamura, Masashi IwatsukiAbstract:An Ultrahigh Vacuum scanning Kelvin probe force microscope (UHV SKPM) utilizing the gradient of electrostatic force, was developed based on an Ultrahigh Vacuum noncontact atomic force microscope (NC-AFM) capable of atomic level imaging, and used for simultaneous observation of contact potential difference (CPD) and NC-AFM images. CPD images of a Si(111) surface with Au deposited, clearly showed the potential difference in phases between 7×7 and 5×2 structures. When Ag was deposited as a submonolayer on the Si(111) 7×7 reconstructed surface, the atomic level lateral resolution was observed in CPD images as well as in NC-AFM topographic images.
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observation of 7 7 reconstructed structure on the silicon 111 surface using Ultrahigh Vacuum noncontact atomic force microscopy
Japanese Journal of Applied Physics, 1995Co-Authors: Shinichi Kitamura, Masashi IwatsukiAbstract:Unlike Ultrahigh Vacuum (UHV) scanning tunneling microscopy (STM), the effectiveness of UHV in UHV atomic force microscopy (AFM) has not been verified. Intensive interaction between tip and sample in UHV often damages the sample surface in the contact mode. Although noncontact (NC) AFM is effective in protecting the sample surface, it has failed to provide atomic-level resolution. We used a stiff silicon cantilever ( ~40 N/m) capable of STM imaging, and succeeded in obtaining the first atomic-resolution images of Si(111)7×7 reconstruction in NC AFM at a tip-sample distance almost equal to that for STM imaging.
Seongju Park - One of the best experts on this subject based on the ideXlab platform.
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effects of step graded alxga1 xn interlayer on properties of gan grown on si 111 using Ultrahigh Vacuum chemical vapor deposition
Applied Physics Letters, 2001Co-Authors: Minho Kim, Hyon Chol Kang, Do Young Noh, Seongju ParkAbstract:We report the growth of high-quality GaN on a Si(111) substrate using a five step-graded AlxGa1−xN (x=0.87–0.07) interlayer between GaN epilayer and AlN buffer layer by Ultrahigh Vacuum chemical vapor deposition. The crack density and the surface roughness of the GaN layer grown on the graded AlxGa1−xN interlayer were substantially reduced, compared to those of GaN grown on an AlN buffer layer. Significant improvement in the structural and optical properties of the GaN layer was also achieved by the use of a graded interlayer. These results are attributed to the decrease of the lattice mismatch between GaN and AlN layer, and the reduction of the thermal stress by the graded interlayer.
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growth of high quality gan on si 111 substrate by Ultrahigh Vacuum chemical vapor deposition
Applied Physics Letters, 2001Co-Authors: Minho Kim, Young Churl Bang, Naeman Park, Cheljong Choi, Tae Yeon Seong, Seongju ParkAbstract:An Ultrahigh Vacuum chemical vapor deposition (UHVCVD) system was employed to grow high-quality GaN on a Si (111) substrate using a thin AlN buffer layer. X-ray diffraction, high-resolution electron microscopy (HREM), and photoluminescence (PL) data indicate that a single crystalline GaN layer with a wurtzite structure was epitaxially grown on a silicon substrate. The full width at half maximum (FWHM) of the x-ray rocking curve for the GaN (0002) diffraction was 16.7 arc min. A cross-sectional HREM image showed an amorphous SiNx layer at the Si/AlN interface, as well as stacking faults and inversion domain boundaries in the GaN epilayer. An intense PL emission line, which is associated with the recombination of the donor bound exciton, was observed at 10 K PL spectra (FWHM=6.8 meV) and a strong band edge emission was obtained (FWHM=33 meV) as well, even at room temperature. These results indicate that high-quality GaN can be grown on Si (111) substrates using a UHVCVD growth method.
Nan Jiang - One of the best experts on this subject based on the ideXlab platform.
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angstrom scale chemical analysis of metal supported trans and cis regioisomers by Ultrahigh Vacuum tip enhanced raman mapping
Nano Letters, 2019Co-Authors: Sayantan Mahapatra, Yingying Ning, Jeremy F Schultz, Junlong Zhang, Nan JiangAbstract:Real space chemical analysis of two structurally very similar components, that is, regioisomers lies at the heart of heterogeneous catalysis reactions, modern-age electronic devices, and various other surface related problems in surface science and nanotechnology. One of the big challenges in surface chemistry is to identify different surface adsorbed molecules and analyze their chemical properties individually. Herein, we report a topological and chemical analysis of two regioisomers, trans- and cis-tetrakispentafluorophenylporphodilactone (trans- and cis-H2F20TPPDL) molecules by high-resolution scanning tunneling microscopy, and Ultrahigh Vacuum tip-enhanced Raman spectroscopy (UHV-TERS). Both isomeric structures are investigated individually on Ag(100) at liquid nitrogen temperature. Following that, we have successfully distinguished these two regioisomeric molecules simultaneously through TERS with an angstrom scale (8 A) spatial resolution. Also, the two-component organic heterojunction has been char...
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probing intermolecular vibrational symmetry breaking in self assembled monolayers with Ultrahigh Vacuum tip enhanced raman spectroscopy
Journal of the American Chemical Society, 2017Co-Authors: Naihao Chiang, Eric A. Pozzi, Nan Jiang, Mark C. Hersam, Tamar Seideman, George C. Schatz, Lindsey R Madison, Michael R Wasielewski, Mark A Ratner, Richard P Van DuyneAbstract:Ultrahigh Vacuum tip-enhanced Raman spectroscopy (UHV-TERS) combines the atomic-scale imaging capability of scanning probe microscopy with the single-molecule chemical sensitivity and structural specificity of surface-enhanced Raman spectroscopy. Here, we use these techniques in combination with theory to reveal insights into the influence of intermolecular interactions on the vibrational spectra of a N-N′-bis(2,6-diisopropylphenyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI) self-assembled monolayer adsorbed on single-crystal Ag substrates at room temperature. In particular, we have revealed the lifting of a vibrational degeneracy of a mode of PDI on Ag(111) and Ag(100) surfaces, with the most strongly perturbed mode being that associated with the largest vibrational amplitude on the periphery of the molecule. This work demonstrates that UHV-TERS enables direct measurement of molecule–molecule interaction at nanoscale. We anticipate that this information will advance the fundamental understanding of the m...
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Probing Intermolecular Vibrational Symmetry Breaking in Self-Assembled Monolayers with Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy
2017Co-Authors: Naihao Chiang, Eric A. Pozzi, Nan Jiang, Mark C. Hersam, Tamar Seideman, George C. Schatz, Lindsey R Madison, Michael R Wasielewski, Mark A Ratner, Richard P Van DuyneAbstract:Ultrahigh Vacuum tip-enhanced Raman spectroscopy (UHV-TERS) combines the atomic-scale imaging capability of scanning probe microscopy with the single-molecule chemical sensitivity and structural specificity of surface-enhanced Raman spectroscopy. Here, we use these techniques in combination with theory to reveal insights into the influence of intermolecular interactions on the vibrational spectra of a N-N′-bis(2,6-diisopropylphenyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI) self-assembled monolayer adsorbed on single-crystal Ag substrates at room temperature. In particular, we have revealed the lifting of a vibrational degeneracy of a mode of PDI on Ag(111) and Ag(100) surfaces, with the most strongly perturbed mode being that associated with the largest vibrational amplitude on the periphery of the molecule. This work demonstrates that UHV-TERS enables direct measurement of molecule–molecule interaction at nanoscale. We anticipate that this information will advance the fundamental understanding of the most important effect of intermolecular interactions on the vibrational modes of surface-bound molecules
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Ultrahigh-Vacuum Tip-Enhanced Raman Spectroscopy
Chemical reviews, 2016Co-Authors: Eric A. Pozzi, Nan Jiang, Tamar Seideman, Guillaume Goubert, Naihao Chiang, Craig T. Chapman, Michael O. Mcanally, Anne Isabelle Henry, George C. Schatz, Mark C. HersamAbstract:Molecule–surface interactions and processes are at the heart of many technologies, including heterogeneous catalysis, organic photovoltaics, and nanoelectronics, yet they are rarely well understood at the molecular level. Given the inhomogeneous nature of surfaces, molecular properties often vary among individual surface sites, information that is lost in ensemble-averaged techniques. In order to access such site-resolved behavior, a technique must possess lateral resolution comparable to the size of surface sites under study, analytical power capable of examining chemical properties, and single-molecule sensitivity. Tip-enhanced Raman spectroscopy (TERS), wherein light is confined and amplified at the apex of a nanoscale plasmonic probe, meets these criteria. In Ultrahigh Vacuum (UHV), TERS can be performed in pristine environments, allowing for molecular-resolution imaging, low-temperature operation, minimized tip and molecular degradation, and improved stability in the presence of ultrafast irradiation...
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conformational contrast of surface mediated molecular switches yields angstrom scale spatial resolution in Ultrahigh Vacuum tip enhanced raman spectroscopy
Nano Letters, 2016Co-Authors: Naihao Chiang, Eric A. Pozzi, Nan Jiang, Mark C. Hersam, Tamar Seideman, Guillaume Goubert, Dhabih V Chulhai, Xing Chen, Xu Chen, Lasse JensenAbstract:Tip-enhanced Raman spectroscopy (TERS) combines the ability of scanning probe microscopy (SPM) to resolve atomic-scale surface features with the single-molecule chemical sensitivity of surface-enhanced Raman spectroscopy (SERS). Here, we report additional insights into the nature of the conformational dynamics of a free-base porphyrin at room temperature adsorbed on a metal surface. We have interrogated the conformational switch between two metastable surface-mediated isomers of meso-tetrakis(3,5-ditertiarybutylphenyl)-porphyrin (H2TBPP) on a Cu(111) surface. At room temperature, the barrier between the porphyrin ring buckled up/down conformations of the H2TBPP-Cu(111) system is easily overcome, and a 2.6 A lateral resolution by simultaneous TERS and STM analysis is achieved under Ultrahigh Vacuum (UHV) conditions. This work demonstrates the first UHV-TERS on Cu(111) and shows TERS can unambiguously distinguish the conformational differences between neighboring molecules with Angstrom-scale spatial resolu...
