Device applications of low-dimensional semiconductor nanostructures rely on the ability to rationally tune their electronic properties. However, the conventional doping method by introducing impurities into the nanostructures suffers from the low efficiency, poor reliability, and damage to the host lattices. Alternatively, surface charge transfer doping (SCTD) is emerging as a simple yet efficient technique to achieve reliable doping in a nondestructive manner, which can modulate the carrier concentration by injecting or extracting the carrier charges between the surface dopant and semiconductor due to the work-function difference. SCTD is particularly useful for low-dimensional nanostructures that possess high surface area and single-crystalline structure. The high reproducibility, as well as the high spatial selectivity, makes SCTD a promising technique to construct high-performance nanodevices based on low-dimensional nanostructures. Here, recent advances of SCTD are summarized systematically and critically, focusing on its potential applications in one- and two-dimensional nanostructures. Mechanisms as well as characterization techniques for the surface charge transfer are analyzed. We also highlight the progress in the construction of novel nanoelectronic and nano-optoelectronic devices via SCTD. Finally, the challenges and future research opportunities of the SCTD method are prospected.

Introduction of polar azulenes and further functionalization significantly enhance the NLO properties of carbon based materials.

The molecular structures, surface acidity and catalytic activity for NO/NH 3 /O 2 SCR of V 2 O 5-WO 3 /TiO 2 catalysts were compared for two different synthesis methods: co-precipitation of aqueous vanadium and tungsten oxide precursors with TiO(OH) 2 and by incipient wetness impregnation of the aqueous precursors on a reference crystalline TiO 2 support (P25; primarily anatase phase). Bulk analysis by XRD showed that co-precipitation results in small and/or poorly ordered TiO 2 (anatase) particles and that VO x and WO x do not form solid solutions with the bulk titania lattice. Surface analysis of the co-precipitated catalyst by High Sensitivity-Low Energy Ion Scattering (HS-LEIS) confirms that the VO x and WO x are surface segregated for the co-precipitated catalysts. In situ Raman and IR spectroscopy revealed that the vanadium and tungsten oxide components are present as surface mono-oxo O=VO 3 and O=WO 4 sites on the TiO 2 supports. Co-precipitation was shown for the first time to also form new mono-oxo surface VO 4 and WO 4 sites that appear to be anchored at surface defects of the TiO 2 support. IR analysis of chemisorbed ammonia showed the presence of both surface NH 3 * on Lewis acid sites and surface NH 4 + * on Brønsted acid sites. TPSR spectroscopy demonstrated that the specific SCR kinetics was controlled by the redox surface VO 4 species and that the surface kinetics was independent of TiO 2 synthesis method or presence of surface WO 5 sites. SCR reaction studies revealed that the surface WO 5 sites possess minimal activity below ~325 o C and their primary function is to increase the adsorption capacity of ammonia. A relationship between the SCR activity and surface acidity was not found. The SCR reaction is controlled by the surface VO 4 sites that initiate the reaction at ~200 o C. The co-precipitated catalysts were always more active than the corresponding impregnated catalysts. The higher activity of the co-precipitated catalysts is ascribed to the presence of the new surface WO x sites associated surface defects on the TiO 2 support that increase the ammonia adsorption capacity.

Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

No abstract

Redox-active covalent organic frameworks (COFs) are an emerging class of energy storage materials due to their notably abundant active sites, well-defined channels and highly surface areas. However, their poor electrical...

No abstract

The novel stable two-dimensional (2D) monolayers As, Sb, and Bi have attracted much attention for their peculiar semiconducting electronic properties. Tuning the electronic and optical properties of monolayers As, Sb, and Bi is essential to broaden their applications in electronic and optoelectronic devices. Herein, on the basis of the density functional theory (DFT) calculations, we proposed an effective surface charge transfer doping (SCTD) strategy to control the electronic and optical properties of monolayers As, Sb, and Bi. Two types of common p-/n-type surface dopants, that is, tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) and benzyl viologen (BV), were chosen in this work. Our calculations revealed that F4-TCNQ is capable of enhancing the p-type conductivity of the monolayers As, Sb, and Bi because of the charge transfer from the monolayers to F4-TCNQ, while BV could transform the p-type monolayers As, Sb, and Bi into n-type semiconductors because of the injection of electrons from BV to the monolayers. Moreover, the optical property calculations demonstrated that the F4-TCNQ and BV modifications could significantly enhance the optical absorption of monolayers As, Sb, and Bi in the lower light energy regions, yielding potential applications of these semiconductor monolayers in high-efficiency optoelectronic devices as new light absorber materials. Our results unveil that SCTD is an effective way to tune the electronic and optical properties of monolayers As, Sb, and Bi, thus broadening their applications in electronic and optoelectronic devices.