yunshen zhou | University of Nebraska Lincoln (original) (raw)
Papers by yunshen zhou
Crystal Growth & Design, 2010
Fast growth of diamond crystals in open air was achieved by combustion synthesis with resonant la... more Fast growth of diamond crystals in open air was achieved by combustion synthesis with resonant laser energy coupling. A premixed C 2 H 4 /C 2 H 2 /O 2 gas mixture was used as precursors for growth of diamond crystals. Through the resonant excitation of the CH 2 wagging ...
Applied Physics Letters, 2011
We developed a process to form transparent interconnections using graphene patterns that were syn... more We developed a process to form transparent interconnections using graphene patterns that were synthesized by laser chemical vapor deposition. The number of graphene layers was tightly controlled by laser scan speed. Graphene patterns were fabricated at a high scan speed of up to 200 μm/s with a single-step process. The process time is about a million times faster than the conventional chemical vapor deposition method. The fabricated graphene patterns on nickel foils were directly transferred to desired positions on patterned electrodes. The position-controlled transfer with rapid single-step fabrication of graphene patterns provides an innovative pathway for graphene-based interconnections.
Applied Physics Letters, 2009
Carbon nanotubes (CNTs) of different alignments, such as surface-bounded and vertically aligned a... more Carbon nanotubes (CNTs) of different alignments, such as surface-bounded and vertically aligned arrays, enable applications in different fields. In this study, controlled growth of CNTs with different alignments was achieved by electrically biasing catalyzed electrodes with different polarities in a laser-assisted chemical vapor deposition process. CNT growth was suggested to be guided by the movement of electrically charged catalyst-nanoparticles under the influence of an external electric field. This discovery provides a convenient approach to control the alignment of CNT arrays for different applications.
Carbon, 2011
Freestanding, two-dimensional (2D), amorphous carbon nanosheets (CNSs) were formed from a precera... more Freestanding, two-dimensional (2D), amorphous carbon nanosheets (CNSs) were formed from a preceramic polymer, poly(phenylcarbyne), through laser ablation using a pulsed Nd:YAG laser. CNSs of several nanometers in thickness and micrometers in size were obtained. The polymer-to-carbon transition was investigated at different laser fluences and target-to-substrate distances. Three different phases, amorphous carbon, ultrathin amorphous CNSs, and thick carbon films, were obtained as the laser fluence increased.
Applied Physics Letters, 2011
Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of high... more Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of highly ordered pyrolytic graphite, using a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Graphene sheets of several nanometers in thickness and micrometers in size were obtained. The laser exfoliation process was investigated at different laser fluences and distances between target and substrate. Three different phases, amorphous carbon, few-layer graphene sheets, and thin graphite films, were obtained as the laser fluence increased. This study reveals an existing route of forming freestanding 2D nanostructures through laser exfoliation.
Applied Physics Letters, 2011
Rapid single-step fabrication of graphene patterns was developed using laser-induced chemical vap... more Rapid single-step fabrication of graphene patterns was developed using laser-induced chemical vapor deposition (LCVD). A laser beam irradiates a thin nickel foil in a CH4 and H2 environment to induce a local temperature rise, thereby allowing the direct writing of graphene patterns in precisely controlled positions at room temperature. Line patterns can be achieved with a single scan without pre- or postprocesses. Surprisingly, the growth rate is several thousand times faster than that of general CVD methods. The discovery and development of the LCVD growth process provide a route for the rapid fabrication of graphene patterns for various applications.
Review of Scientific Instruments, 2008
Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensit... more Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensitivity due to the optical diffraction limit and small interaction cross sections. It has been reported that a highly localized and significantly enhanced electromagnetic field could be generated in the proximity of a metallic tip illuminated by a laser beam. In this study, a tip-enhanced RS system was developed to both improve the resolution and enhance the detection sensitivity using the tip-enhanced near-field effects. This instrument, by combining RS with a scanning tunneling microscope and side-illumination optics, demonstrated significant enhancement on both optical sensitivity and spatial resolution using either silver (Ag)-coated tungsten (W) tips or gold (Au) tips. The sensitivity improvement was verified by observing the enhancement effects on silicon (Si) substrates. Lateral resolution was verified to be below 100 nm by mapping Ag nanostructures. By deploying the depolarization technique, an apparent enhancement of 175% on Si substrates was achieved. Furthermore, the developed instrument features fast and reliable optical alignment, versatile sample adaptability, and effective suppression of far-field signals.
In the rapid growth of nanoscience and technology, organic compounds occupy a prominent position ... more In the rapid growth of nanoscience and technology, organic compounds occupy a prominent position and play comprehensive roles as stabilizers , protective masks [6], templates [7-9], surface modifiers [10], position indicators [11], functional units and building blocks [12-17], and molecular "ink" [18-21], etc. Further more, organic compounds are key components in the design and fabrication of nanomachines and nanodevices. Utilization of organic molecules has allowed prototypes of nanomachines and nanodevices, such as molecular motors [22-26], conductors [27-30], logic gates [31], memories [32], rectifiers [33-36], negative differential resistance devices [37], single electron tunneling devices [38], and gears [39-41], to be developed [42].
![Research paper thumbnail of Self-assembly of N-3-γ-pyridyl Aza[60]fulleroid on Au(111](https://attachments.academia-assets.com/48873981/thumbnails/1.jpg)
](Chinese Science Bulletin, 2005
Self-assembled monolayers of novel C60 derivative, N-3-γ-pyridyl Aza[60]fulleroid (C60Py), on Au(... more Self-assembled monolayers of novel C60 derivative, N-3-γ-pyridyl Aza[60]fulleroid (C60Py), on Au(111) were studied by a scanning tunneling microscope under ultrahigh vacuum (UHV). C60Py molecules were assembled on Au (111) via pyridyl nitrogen-Au interaction. The sole assembly of C60Py molecules on Au (111) only exhibited randoml aggregation of C60Py even the films were annealed at 50 and 105°C. By co-assembling with benzyl mercaptan (BM), the C60PyBM films showed highly dense aggregation, but C60Py assemblies still had disordered structure. After the co-assembled C60Py-BM films were annealed at 50°C, BM molecules were partially desorbed, but the assembly of C60Py remained without obvious change. After the co-assembled C60Py-BM films were further annealed at 105°C, the C60Py monolayers with ordered structure were obtained, while the BM molecules were nearly thoroughly desorbed from the surface. Here, the BM molecules play a key role as a surfactant in the formation of the ordered C60Py monolayer.
Solid State Communications, 2001
A novel salt-derivatived [60]fullerene covalently linking a stable nitroxide is synthesized. The ... more A novel salt-derivatived [60]fullerene covalently linking a stable nitroxide is synthesized. The nanoparticles based on the salt-derivatived [60]fullerene are formed in a facile way through self-assembly. The spectral properties of the sample are studied and the magnetic property is also primarily measured with superconducting quantum interference device. q 2001 Published by
Chemical Physics Letters, 2005
We report a direct observation adopting Ôface-onÕ and Ôedge-onÕ stacking styles in monolayer of a... more We report a direct observation adopting Ôface-onÕ and Ôedge-onÕ stacking styles in monolayer of a novel porphyrin derivative on highly ordered pyrolytic graphite (HOPG) using scanning tunneling microscope (STM). The porphyrin derivative, 5-hydroxyphenyl-10, 15, 20-trikis(4-dodecyloxyphenyl)porphyrinatozinc(II) (ZnDPPOH) is synthesized and assembled on HOPG. In the STM images, we observed two kinds of ordered domains. One consists of ZnDPPOH dimmers, adopting Ôface-onÕ stacking style, the other exhibits a segmented columnar structure, like piled-up ÔarmchairsÕ, lying down on the substrate, adopting an Ôedge-onÕ stacking style. In the latter case, the conjugated and highly delocalized p-systems play key roles in stabilizing the monolayer.
Synthetic Communications, 2002
Chemical Physics Letters, 2004
We report the fabrication of nanoparticle silver oxide thin films by rf magnetron sputtering and ... more We report the fabrication of nanoparticle silver oxide thin films by rf magnetron sputtering and characterization of their nonlinear optical properties. The chemical decomposition and reversibility of AgO x compounds were studied by thermogravimetric analysis, differential scanning calorimetry, and x-ray diffraction. Electron spectroscopy for chemical analysis measurements revealed a 0.5 eV negative binding energy shift from AgO to Ag 2 O phase. The effect of particle plasmon resonance was confirmed by the absorption band shift with increased Ag 2 O particle size. The measured third-order nonlinear susceptibility ( 3 ϭ3.4ϫ10 Ϫ7 esu) and response time ͑27 ps͒ of the Ag 2 O nanoparticles makes it promising for applications in all-optical switching devices and optical data storage systems.
Journal of Physical Chemistry B, 2006
We present the electron transport of pyridyl aza[60]fulleroid oligomers, abbreviated as C 60 NPy,... more We present the electron transport of pyridyl aza[60]fulleroid oligomers, abbreviated as C 60 NPy, which is based on the donor-barrier-acceptor (D-σ-A) architecture, at a single molecular scale using scanning tunneling microscopy. A rectifying effect is observed in the current-voltage characteristics. The theoretical calculation shows that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are well localized either on the Py moiety (donor) or on the C 60 moiety (acceptor), indicating the σ-bridge decouples the LUMO and the HOMO of the donor and the acceptor, respectively. This structure accords well with the unimolecular rectifying model proposed by Aviram and Ratner [Chem. Phys. Lett. 1974, 29, 277]. The mechanism of the rectifying effect is understood by analyzing in detail the electron transport through energy levels of the donor and the acceptor of the C 60 NPy molecules. By directly comparing the experimental conductance peaks and the calculated density of states of the C 60 NPy, we find that the observed rectification is attributed to the asymmetric positioning of the LUMOs and the HOMOs of both sides of the acceptor and the donor of the C 60 NPy molecules with respect to the Fermi level of the electrodes. When a main voltage drop is over the molecule-electrode vacuum junction but a small fraction over the molecule itself, the shift of the energy levels between the donor and the acceptor will be small. This behavior deviates from the original proposal by Aviram and Ratner in which a large shift of the energy level is expected. * Towhomcorrespondenceshouldbeaddressed.
Applied Surface Science, 2006
We reported the design and fabrication of a C 60 derivative with a uracil-like unit (U-C 60 ), to... more We reported the design and fabrication of a C 60 derivative with a uracil-like unit (U-C 60 ), to form a bi-molecular building block with a C 60 derivative with a 2,6-bis (acylamino) pyridine unit (DAP-C 60 ) by complementary trident hydrogen-bonding array. By pre-organizing these two fullerene derivatives in solution, bimolecular blocks were formed via robust and highly directional trident hydrogen-bonding recognition between DAP-C 60 and U-C 60 . Then, the bimolecular blocks were deposited on highly ordered pyrolytic graphite (HOPG). The structure of the monolayer was characterized using a scanning tunneling microscope. Well-ordered monolayer composed of the two fullerene derivatives of DAP-C 60 and U-C 60 was observed and the structure of the monolayer was modeled. #
Crystal Growth & Design, 2010
Fast growth of diamond crystals in open air was achieved by combustion synthesis with resonant la... more Fast growth of diamond crystals in open air was achieved by combustion synthesis with resonant laser energy coupling. A premixed C 2 H 4 /C 2 H 2 /O 2 gas mixture was used as precursors for growth of diamond crystals. Through the resonant excitation of the CH 2 wagging ...
Applied Physics Letters, 2011
We developed a process to form transparent interconnections using graphene patterns that were syn... more We developed a process to form transparent interconnections using graphene patterns that were synthesized by laser chemical vapor deposition. The number of graphene layers was tightly controlled by laser scan speed. Graphene patterns were fabricated at a high scan speed of up to 200 μm/s with a single-step process. The process time is about a million times faster than the conventional chemical vapor deposition method. The fabricated graphene patterns on nickel foils were directly transferred to desired positions on patterned electrodes. The position-controlled transfer with rapid single-step fabrication of graphene patterns provides an innovative pathway for graphene-based interconnections.
Applied Physics Letters, 2009
Carbon nanotubes (CNTs) of different alignments, such as surface-bounded and vertically aligned a... more Carbon nanotubes (CNTs) of different alignments, such as surface-bounded and vertically aligned arrays, enable applications in different fields. In this study, controlled growth of CNTs with different alignments was achieved by electrically biasing catalyzed electrodes with different polarities in a laser-assisted chemical vapor deposition process. CNT growth was suggested to be guided by the movement of electrically charged catalyst-nanoparticles under the influence of an external electric field. This discovery provides a convenient approach to control the alignment of CNT arrays for different applications.
Carbon, 2011
Freestanding, two-dimensional (2D), amorphous carbon nanosheets (CNSs) were formed from a precera... more Freestanding, two-dimensional (2D), amorphous carbon nanosheets (CNSs) were formed from a preceramic polymer, poly(phenylcarbyne), through laser ablation using a pulsed Nd:YAG laser. CNSs of several nanometers in thickness and micrometers in size were obtained. The polymer-to-carbon transition was investigated at different laser fluences and target-to-substrate distances. Three different phases, amorphous carbon, ultrathin amorphous CNSs, and thick carbon films, were obtained as the laser fluence increased.
Applied Physics Letters, 2011
Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of high... more Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of highly ordered pyrolytic graphite, using a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Graphene sheets of several nanometers in thickness and micrometers in size were obtained. The laser exfoliation process was investigated at different laser fluences and distances between target and substrate. Three different phases, amorphous carbon, few-layer graphene sheets, and thin graphite films, were obtained as the laser fluence increased. This study reveals an existing route of forming freestanding 2D nanostructures through laser exfoliation.
Applied Physics Letters, 2011
Rapid single-step fabrication of graphene patterns was developed using laser-induced chemical vap... more Rapid single-step fabrication of graphene patterns was developed using laser-induced chemical vapor deposition (LCVD). A laser beam irradiates a thin nickel foil in a CH4 and H2 environment to induce a local temperature rise, thereby allowing the direct writing of graphene patterns in precisely controlled positions at room temperature. Line patterns can be achieved with a single scan without pre- or postprocesses. Surprisingly, the growth rate is several thousand times faster than that of general CVD methods. The discovery and development of the LCVD growth process provide a route for the rapid fabrication of graphene patterns for various applications.
Review of Scientific Instruments, 2008
Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensit... more Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensitivity due to the optical diffraction limit and small interaction cross sections. It has been reported that a highly localized and significantly enhanced electromagnetic field could be generated in the proximity of a metallic tip illuminated by a laser beam. In this study, a tip-enhanced RS system was developed to both improve the resolution and enhance the detection sensitivity using the tip-enhanced near-field effects. This instrument, by combining RS with a scanning tunneling microscope and side-illumination optics, demonstrated significant enhancement on both optical sensitivity and spatial resolution using either silver (Ag)-coated tungsten (W) tips or gold (Au) tips. The sensitivity improvement was verified by observing the enhancement effects on silicon (Si) substrates. Lateral resolution was verified to be below 100 nm by mapping Ag nanostructures. By deploying the depolarization technique, an apparent enhancement of 175% on Si substrates was achieved. Furthermore, the developed instrument features fast and reliable optical alignment, versatile sample adaptability, and effective suppression of far-field signals.
In the rapid growth of nanoscience and technology, organic compounds occupy a prominent position ... more In the rapid growth of nanoscience and technology, organic compounds occupy a prominent position and play comprehensive roles as stabilizers , protective masks [6], templates [7-9], surface modifiers [10], position indicators [11], functional units and building blocks [12-17], and molecular "ink" [18-21], etc. Further more, organic compounds are key components in the design and fabrication of nanomachines and nanodevices. Utilization of organic molecules has allowed prototypes of nanomachines and nanodevices, such as molecular motors [22-26], conductors [27-30], logic gates [31], memories [32], rectifiers [33-36], negative differential resistance devices [37], single electron tunneling devices [38], and gears [39-41], to be developed [42].
Chinese Science Bulletin, 2005
Self-assembled monolayers of novel C60 derivative, N-3-γ-pyridyl Aza[60]fulleroid (C60Py), on Au(... more Self-assembled monolayers of novel C60 derivative, N-3-γ-pyridyl Aza[60]fulleroid (C60Py), on Au(111) were studied by a scanning tunneling microscope under ultrahigh vacuum (UHV). C60Py molecules were assembled on Au (111) via pyridyl nitrogen-Au interaction. The sole assembly of C60Py molecules on Au (111) only exhibited randoml aggregation of C60Py even the films were annealed at 50 and 105°C. By co-assembling with benzyl mercaptan (BM), the C60PyBM films showed highly dense aggregation, but C60Py assemblies still had disordered structure. After the co-assembled C60Py-BM films were annealed at 50°C, BM molecules were partially desorbed, but the assembly of C60Py remained without obvious change. After the co-assembled C60Py-BM films were further annealed at 105°C, the C60Py monolayers with ordered structure were obtained, while the BM molecules were nearly thoroughly desorbed from the surface. Here, the BM molecules play a key role as a surfactant in the formation of the ordered C60Py monolayer.
Solid State Communications, 2001
A novel salt-derivatived [60]fullerene covalently linking a stable nitroxide is synthesized. The ... more A novel salt-derivatived [60]fullerene covalently linking a stable nitroxide is synthesized. The nanoparticles based on the salt-derivatived [60]fullerene are formed in a facile way through self-assembly. The spectral properties of the sample are studied and the magnetic property is also primarily measured with superconducting quantum interference device. q 2001 Published by
Chemical Physics Letters, 2005
We report a direct observation adopting Ôface-onÕ and Ôedge-onÕ stacking styles in monolayer of a... more We report a direct observation adopting Ôface-onÕ and Ôedge-onÕ stacking styles in monolayer of a novel porphyrin derivative on highly ordered pyrolytic graphite (HOPG) using scanning tunneling microscope (STM). The porphyrin derivative, 5-hydroxyphenyl-10, 15, 20-trikis(4-dodecyloxyphenyl)porphyrinatozinc(II) (ZnDPPOH) is synthesized and assembled on HOPG. In the STM images, we observed two kinds of ordered domains. One consists of ZnDPPOH dimmers, adopting Ôface-onÕ stacking style, the other exhibits a segmented columnar structure, like piled-up ÔarmchairsÕ, lying down on the substrate, adopting an Ôedge-onÕ stacking style. In the latter case, the conjugated and highly delocalized p-systems play key roles in stabilizing the monolayer.
Synthetic Communications, 2002
Chemical Physics Letters, 2004
We report the fabrication of nanoparticle silver oxide thin films by rf magnetron sputtering and ... more We report the fabrication of nanoparticle silver oxide thin films by rf magnetron sputtering and characterization of their nonlinear optical properties. The chemical decomposition and reversibility of AgO x compounds were studied by thermogravimetric analysis, differential scanning calorimetry, and x-ray diffraction. Electron spectroscopy for chemical analysis measurements revealed a 0.5 eV negative binding energy shift from AgO to Ag 2 O phase. The effect of particle plasmon resonance was confirmed by the absorption band shift with increased Ag 2 O particle size. The measured third-order nonlinear susceptibility ( 3 ϭ3.4ϫ10 Ϫ7 esu) and response time ͑27 ps͒ of the Ag 2 O nanoparticles makes it promising for applications in all-optical switching devices and optical data storage systems.
Journal of Physical Chemistry B, 2006
We present the electron transport of pyridyl aza[60]fulleroid oligomers, abbreviated as C 60 NPy,... more We present the electron transport of pyridyl aza[60]fulleroid oligomers, abbreviated as C 60 NPy, which is based on the donor-barrier-acceptor (D-σ-A) architecture, at a single molecular scale using scanning tunneling microscopy. A rectifying effect is observed in the current-voltage characteristics. The theoretical calculation shows that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are well localized either on the Py moiety (donor) or on the C 60 moiety (acceptor), indicating the σ-bridge decouples the LUMO and the HOMO of the donor and the acceptor, respectively. This structure accords well with the unimolecular rectifying model proposed by Aviram and Ratner [Chem. Phys. Lett. 1974, 29, 277]. The mechanism of the rectifying effect is understood by analyzing in detail the electron transport through energy levels of the donor and the acceptor of the C 60 NPy molecules. By directly comparing the experimental conductance peaks and the calculated density of states of the C 60 NPy, we find that the observed rectification is attributed to the asymmetric positioning of the LUMOs and the HOMOs of both sides of the acceptor and the donor of the C 60 NPy molecules with respect to the Fermi level of the electrodes. When a main voltage drop is over the molecule-electrode vacuum junction but a small fraction over the molecule itself, the shift of the energy levels between the donor and the acceptor will be small. This behavior deviates from the original proposal by Aviram and Ratner in which a large shift of the energy level is expected. * Towhomcorrespondenceshouldbeaddressed.
Applied Surface Science, 2006
We reported the design and fabrication of a C 60 derivative with a uracil-like unit (U-C 60 ), to... more We reported the design and fabrication of a C 60 derivative with a uracil-like unit (U-C 60 ), to form a bi-molecular building block with a C 60 derivative with a 2,6-bis (acylamino) pyridine unit (DAP-C 60 ) by complementary trident hydrogen-bonding array. By pre-organizing these two fullerene derivatives in solution, bimolecular blocks were formed via robust and highly directional trident hydrogen-bonding recognition between DAP-C 60 and U-C 60 . Then, the bimolecular blocks were deposited on highly ordered pyrolytic graphite (HOPG). The structure of the monolayer was characterized using a scanning tunneling microscope. Well-ordered monolayer composed of the two fullerene derivatives of DAP-C 60 and U-C 60 was observed and the structure of the monolayer was modeled. #