The Experts below are selected from a list of 30 Experts worldwide ranked by ideXlab platform
Jin Zhang - One of the best experts on this subject based on the ideXlab platform.
-
modulating the charge transfer enhancement in gers using an Electrical Field under vacuum and an n p doping atmosphere
2011Co-Authors: Yabin Chen, Haoli Zhang, Jing Kong, Mildred S Dresselhaus, Jin ZhangAbstract:The modulation of charger-transfer (CT) enhancement in graphene-enhanced Raman scattering (GERS) by an electric Field under different atmospheres is reported. The GERS spectra of cobalt phthalocyanine (CoPc) molecules were collected by in situ Raman measurements under ambient air, vacuum, NH3 atmosphere, and O2 atmosphere, in which the Fermi level of graphene was modulated by an Electrical Field Effect (EFE). The Raman scattering intensities of adsorbed molecules can be tuned to be stronger or weaker as the graphene Fermi level down-shifts or up-shifts under Electrical Field modulation. However, the Raman intensity modulation in GERS is seriously influenced by the hysteresis Effect in graphene EFE, which makes the modulation ability small and shows strong gate voltage sweep rate dependence in ambient air. Fortunately, the hysteresis Effect in graphene EFE can be decreased by performing the measurement under vacuum conditions, and thus the Raman modulation ability in GERS can be increased. Furthermore, compared with the vacuum condition, the Raman modulation ability shows an increase under an NH3 atmosphere, while it shows a decrease under an O2 atmosphere, which is due to the different Fermi level modulation region in different atmospheres. More interestingly, this Raman intensity modulation in GERS shows a hysteresis-like behavior that is the same as the graphene Fermi level modulation under the EFE in a different atmosphere. All these observations suggest that the Raman enhancement in GERS occurs through a charge-transfer (CT) enhancement mechanism and the CT process can be modulated by the graphene EFE. This technique will benefit the study of the basic properties of both graphene and chemical enhancement mechanism in surface-enhanced Raman spectroscopy (SERS).
-
Effect of graphene fermi level on the raman scattering intensity of molecules on graphene
2011Co-Authors: Hua Xu, Haoli Zhang, Jin ZhangAbstract:We studied the modulation of Raman scattering intensities of molecules on graphene by tuning the graphene Fermi level with Electrical Field Effect (EFE). A series of metal phthalocyanine (M-Pc) molecules (M = Mn, Fe, Co, Ni, Cu, Zn), which have different molecular energy levels, were used as probe molecules. The Raman intensities of all these M-Pc molecules become weaker when the graphene Fermi level is up-shifted by applying a positive gate voltage, while they become stronger when the graphene Fermi level is down-shifted by applying a negative gate voltage. However, this Raman intensity modulation only occurs when applying the gate voltage with a fast sweep rate, while it is nearly absent when applying the gate voltage with a slow sweep rate, which is likely due to the arising of the hysteresis Effect in the graphene EFE. In addition, the Raman modulation ability for M-Pc molecules with smaller energy gaps is larger than that with larger energy gaps due to the difference in the energy alignment between g...
Xi Chen - One of the best experts on this subject based on the ideXlab platform.
-
simultaneous Electrical Field Effect modulation of both top and bottom dirac surface states of epitaxial thin films of three dimensional topological insulators
2015Co-Authors: Cuizu Chang, Zuocheng Zhang, Xiao Feng, Jinsong Zhang, Minghua Guo, Yang Feng, Jing Wang, Lili Wang, Xi ChenAbstract:It is crucial for the studies of the transport properties and quantum Effects related to Dirac surface states of three-dimensional topological insulators (3D TIs) to be able to simultaneously tune the chemical potentials of both top and bottom surfaces of a 3D TI thin film. We have realized this in molecular beam epitaxy-grown thin films of 3D TIs, as well as magnetic 3D TIs, by fabricating dual-gate structures on them. The films could be tuned between n-type and p-type by each gate alone. Combined application of two gates can reduce the carrier density of a TI film to a much lower level than with only one of them and enhance the film resistance by 10 000%, implying that Fermi level is tuned very close to the Dirac points of both top and bottom surface states without crossing any bulk band. The result promises applications of 3D TIs in Field Effect devices.
Xiao Feng - One of the best experts on this subject based on the ideXlab platform.
-
simultaneous Electrical Field Effect modulation of both top and bottom dirac surface states of epitaxial thin films of three dimensional topological insulators
2015Co-Authors: Cuizu Chang, Zuocheng Zhang, Xiao Feng, Jinsong Zhang, Minghua Guo, Yang Feng, Jing Wang, Lili Wang, Xi ChenAbstract:It is crucial for the studies of the transport properties and quantum Effects related to Dirac surface states of three-dimensional topological insulators (3D TIs) to be able to simultaneously tune the chemical potentials of both top and bottom surfaces of a 3D TI thin film. We have realized this in molecular beam epitaxy-grown thin films of 3D TIs, as well as magnetic 3D TIs, by fabricating dual-gate structures on them. The films could be tuned between n-type and p-type by each gate alone. Combined application of two gates can reduce the carrier density of a TI film to a much lower level than with only one of them and enhance the film resistance by 10 000%, implying that Fermi level is tuned very close to the Dirac points of both top and bottom surface states without crossing any bulk band. The result promises applications of 3D TIs in Field Effect devices.
Martin Heeney - One of the best experts on this subject based on the ideXlab platform.
-
doping of large ionization potential indenopyrazine polymers via lewis acid complexation with tris pentafluorophenyl borane a simple method for improving the performance of organic thin film transistors
2016Co-Authors: Yang Han, George Barnes, Yenhung Lin, Jaime Martin, Mohammed Alhashimi, Siham Y Alqaradawi, Thomas D Anthopoulos, Martin HeeneyAbstract:Molecular doping, under certain circumstances, can be used to improve the charge transport in organic semiconductors through the introduction of excess charge carriers which can in turn negate unwanted trap states often present in organic semiconductors. Here, two Lewis basic indenopyrazine copolymers with large ionization potential (5.78 and 5.82 eV) are prepared to investigate the p-doping efficiency with the Lewis acid dopant, tris(pentafluorophenyl)borane, using organic thin-film transistors (OTFTs). The formation of Lewis acid–base complex between the polymer and dopant molecules is confirmed via optical spectroscopy and Electrical Field-Effect measurements, with the latter revealing a dopant-concentration-dependent device performance. By adjusting the amount of p-dopant, the hole mobility can be increased up to 11-fold while the OTFTs’ threshold voltages are reduced. The work demonstrates an alternative doping mechanism other than the traditional charge transfer model, where the energy level matchin...
Arif Ul Alam - One of the best experts on this subject based on the ideXlab platform.
-
polymers and organic materials based ph sensors for healthcare applications
2018Co-Authors: Arif Ul Alam, Shruti Nambiar, John T W Yeow, M M R Howlader, Nanxing Hu, Jamal M DeenAbstract:Abstract In this review, we discuss chemical, physical and electrochemical properties of pH-sensitive polymers and organic materials and their sensing mechanisms for healthcare applications. We find that polymers and organic materials, due to their biocompatibility and customizable Electrical and electrochemical properties, can be used in pH sensors as structural, pH-sensitive, and passivation materials. To do so, we first identify the properties and sensing mechanisms for pH-sensitive polymers and organic materials. Different functional groups in the materials determine their chemical properties and are involved in redox reactions for chemical sensing of pH. The transport of charge carriers in the polymers and organic materials is influenced by pH-induced Electrical Field change, which is responsible for physical sensing of pH. Some polymers and organic materials also show hybrid sensing properties, where both functional groups and Electrical Field-Effect contribute to their pH response. Next, we review fabrication technologies for polymers and organic materials, and identify that engineering the materials and new device structures are two possible approaches to improve the sensitivity and reliability of pH sensing devices. We propose that miniaturized sensors can provide enhanced functionality of the sensing materials in constrained spaces. Finally, we present an overview of biocompatible polymers and organic materials for monitoring of pH and pH-related analytes in biological fluids, and for pH-change-triggered drug delivery.