n-Type Field-Effect Transistors Made of an Individual Nitrogen-Doped Multiwalled Carbon Nanotube

1D MXenes: Synthesis, Properties, and Applications

The fascinating properties and versatile nature of 2D MXenes have generated significant interest in the scientific community. This has led to extensive research on expanding these materials into 1D and 0D forms. This review investigates the synthesis, properties, and applications of 1D MXenes, elucidating their potential across various fields. 1D MXenes, including nanowires, nanoribbons, nanorods, and nanotubes, inherit the remarkable properties of their 2D counterparts while also exhibiting unique anisotropic characteristics that enhance their performance in various applications. The review explores various methods for synthesizing 1D MXenes and examines their structural, electronic, and optical properties. The transition from 2D to 1D results in MXenes that offer superior properties, which are advantageous for various next-generation systems. The increased aspect ratio and surface area of 1D MXenes broaden their usage in energy storage, photothermal therapy, oxygen evolution reactions (OER), hydrogen evolution reactions (HER), oxygen reduction reactions (ORR), microwave absorption, filtration membranes, gas sensors, metal detection, etc. The review also addresses the challenges associated with 1D MXenes, such as limited synthesis methods, scalable production, size customization, preservation of structural integrity, and stability. Furthermore, potential opportunities and future directions in the field of 1D MXenes have also been proposed.

Tuning the Defects of Two-Dimensional Layered Carbon/TiO2 Superlattice Composite for a Fast Lithium-Ion Storage

Defect engineering is one of the effective ways to improve the electrochemical property of electrode materials for lithium-ion batteries (LIB). Herein, an organic functional molecule of p-phenylenediamine is embedded into two-dimensional (2D) layered TiO₂ as the electrode for LIB. Then, the 2D carbon/TiO₂ composites with the tuning defects are prepared by precise control of the polymerization and carbothermal atmospheres. Low valence titanium in metal oxide and nitrogen-doped carbon nanosheets can be obtained in the carbon/TiO₂ composite under a carbonization treatment atmosphere of N₂/H₂ gas, which can not only increase the electronic conductivity of the material but also provide sufficient electrochemical active sites, thus producing an excellent rate capability and long-term cycle stability. The prepared composite can provide a high capacity of 396.0 mAh g⁻¹ at a current density of 0.1 A g⁻¹ with a high capacitive capacity ratio. Moreover, a high specific capacity of 80.0 mAh g⁻¹ with retention rate of 85% remains after 10,000 cycles at 3.0 A g⁻¹ as well as the Coulomb efficiency close to 100%. The good rate-capability and cycle-sustainability of the layered materials are ascribed to the increase of conductivity, the lithium-ion transport channel, and interfacial capacitance due to the multi-defect sites in the layered composite.

Structural evolution and dielectric properties of biaxially oriented polyethylene/multiwalled carbon nanotube composite films

In modern power systems, polymer nanocomposite films have been more frequently used as dielectric materials for capacitors. However, the low energy storage density limits its application in more areas. It is a very challenging task to prepare dielectric films with high dielectric constant (ε), high energy storage density, and low dielectric loss (tan δ) at the same time. In this study, one kind of BOPE (biaxially oriented polyethylene) nanocomposite dielectric films with a very small amount of MWCNTs (multiwalled carbon nanotubes) was reported. MWCNTs with a high aspect ratio were used for conductive filler, and the formation of more micro capacitors and interfacial polarization were caused by better dispersibility of MWCNTs in polyethylene matrix by biaxial stretching. The BOPE/MWCNT composite films with high-performance were successfully prepared by achieving the requirements of low content, high dielectric constant and high energy storage density while maintaining the advantages of low dielectric loss of the polymer matrix. The dielectric constant of the BOPE/MWCNT composite films increased from 2.26 to 4.68 with the drawing ratio was 4 × 4 and the content of MWCNTs was 0.6 wt% and the energy storage density was also increased from 1.01 J cm^-3 to 1.29 J cm^-3. From our work, the achievement of low thickness, high energy density and low loss at the same time implied BOPE/MWCNT composite films were promising materials for next-generation film capacitors.

Direct curvature measurement of the compartments in bamboo-shaped multi-walled carbon nanotubes via scanning probe microscopy

Bamboo-shaped multi-walled carbon nanotubes (BS-MWCNTs) have compartmented structures inherently obtained during their catalytic growth, and the curvature of the compartmented structure is known to be determined by the morphology of the metal catalysts. In this study, the inside curvature of the BS-MWCNTs was directly measured through scanning probe microscopy (SPM). The surface of the compartment structures of BS-MWCNTs has discontinuous graphene layers and different frictional force levels depending on the curvature direction. That of the inside curvature can be directly observed through tribological analysis by adding and subtracting the lateral force microscopy images obtained on opposite sides along the axial direction of the BS-MWCNT (diameter of 500 nm). This tells us the direction of the inside curvature of the BS-MWCNT, which was also confirmed by identifying the growth direction of the BS-MWCNTs via scanning electron microscopy. Our demonstration implies that SPM can give the same insight into the structural characterization of nanomaterials that is relatively inexpensive and more user-friendly than currently used methods.

Non-metal sensory electrode design and protocol of DNA-nucleobases in living cells exposed to oxidative stresses

Sensory protocols for evaluation of DNA distortion due to exposure to various harmful chemicals and environments in living cells are needed for research and clinical investigations. Here, a design of non-metal sensory (NMS) electrode was built by using boron-doped carbon spherules for detection of DNA nucleobases, namely, guanine (Gu), adenine (Ad), and thymine (Th) in living cells. The key-electrode based nanoscale NMS structures lead to voids with a facile diffusion, and strong binding events of the DNA nucleobases. Furthermore, the NMS geometric structures would significantly create electrode surfaces with numerous centrally active sites, curvature topographies, and anisotropic spherules. The NMS shows potential as sensitive protocol for DNA-nucleobases in living cells exposed to oxidative stresses. In one-step signaling assay, NMS shows high signaling transduction of Gu-, Ad-, and Th-DNA nucleobases targets with ultra-sensitive and low detection limits of 3.0, 0.36, and 0.34 nM, respectively, and a wide linear range of up to 1 μM. The NMS design and protocol show evidence of the role of surface construction features and B-atoms incorporated into the graphitic carbon network for creating abundant active sites with facile electron diffusion and heavily target loads along with within-/out-plane circular spheres. Indeed NMS, with spherule-rich interstitial surfaces can be used for sensitive and selective evaluation of damaged-DNA to various dysfunctional metabolism in the human body.

Fabrication of heteroatom doped NFP-MWCNT and NFB-MWCNT nanocomposite from imidazolium ionic liquid functionalized MWCNT for antibiofilm and wound healing in Wistar rats: Synthesis, characterization, in-vitro and in-vivo studies

Bacterial biofilm is an obstacle for wound healing because it can affect the epithelialization, development of granular cells, and other regular inflammatory procedures. It plays the role of safeguarding pathogens from antiseptics and antibiotics. In this respect, this research work aims to develop heteroatom (N, F, P/B) incorporated multi-walled carbon nanotubes (MWCNT), such as NFP-MWCNT and NFB-MWCNT, which can maximize the wound healing efficacy via destroying the wound pathogen and biofilms. NFP-MWCNT and NFB-MWCNT were obtained using self-assembling ionic liquids (ILs) such as BMIM-PF₆ and BMIM-BF₄ in an acid-functionalized MWCNT (A-MWCNT) suspension, followed by pyrolysis in a nitrogen atmosphere. The composite formation was established by FTIR, XRD, RAMAN, EDX mapping, and XPS spectroscopy. TEM and SEM analyses confirmed the bamboo stick-like morphology. During this reaction, IL molecules might be cross-linked with A-MWCNT via hydrogen bonding and ionic interaction, with further pyrolysis producing the defects with doping of N, F, P, or B elements. Finally, they were assessed for their antibiofilm activity against typical bacterial strains such as K. pneumoniae, P. aeruginosa, E. coli (Gram-negative), and B. subtilis (Gram-positive), using a quantitative estimation approach. The results revealed greater effectiveness of NFB-MWCNT and NFP-MWCNT, compared to pristine MWCNT. The antibiofilm activity of NFP-MWCNT and NFB-MWCNT was associated with their specific surface chemistry (due to the presence of N, F, P/B heteroatoms), and their nanosize. Moreover, the synthesized material was examined for its wound-healing ability in Wistar rats. The results proved that cells cultured on NFB-MWCNT and NFP-MWCNT displayed exceptional healing ability. The different electronegativity between the heteroatoms creates the surface charge that inhibits the biofilm formation, leading to healing the wounds together with the heteroatom mineral source for mouse fibroblast regeneration and granulation. This is the first study in which the role of different heteroatoms incorporated into MWCNT is examined in the context of antibiofilm-associated wound-healing ability.

Fabrication of N-doped multidimensional carbon nanofibers for high-performance cortisol biosensors

Cortisol is an hormone that regulates blood pressure, glucose levels and carbohydrate metabolism in humans. Abnormal secretion of cortisol can cause various symptoms closely linked to psychological and physical health. In this study, high-performance field-effect transistor (FET)-based biosensors for cortisol detection were fabricated from N-doped multidimensional carbon nanofibers. Nanofiber morphology was controlled by tailoring the pressure conditions during vapor deposition polymerization (VDP). Thereafter, conductive channels of FET were completed by thermal annealing, acid treatment, and antibody attachment. Changes associated with chemical processes were characterized by various instruments. The resulting transducers exhibited a rapid response toward cortisol molecules with accurate selectivity, stable reusability, and high sensitivity. Minimum detection level were as low as 100 aM with a wide linear detection range of 100 aM to 10 nM due to the large surface area of the transducer and a correspondingly high number of antibody labels. The response and applicability of these cortisol biosensors were also assessed using saliva as a test matrix.

3D-Ridge Stocked Layers of Nitrogen-Doped Mesoporous Carbon Nanosheets for Ultrasensitive Monitoring of Dopamine Released from PC12 Cells under K+ Stimulation

3D-ridge nanosheets of N-doped mesoporous carbon (NMCS)-based electrodes are fabricated as ultrasensitive biosensors for in vitro monitoring of dopamine (DA) released from living cells. The large-scale ranges of dense-layered sheets are arranged linearly with a thickness of <10 nm, soft tangled edges, stocked layer arrangements, and tunable mesoporous frameworks with 3D orientations. The intrinsic features of the active interfacial surface of the electrode based on NMCS along with polarized surfaces, dense surface-charged matrices, fast electron transfer, and easy molecular diffusion, are present in the highly active electrode for biosensing applications. The designed electrode based on the NMCS shows high sensitivity and selectivity for DA sensing even in the presence of physiological interference molecules, such as ascorbic acid and/or uric acid, at a low applied potential of 0.25 V versus Ag/AgCl. The large-scale NMCS-based electrode shows low detection limits as low as 10 nmol L^-1 , wide linear range up to 0.5 mmol L^-1 , long-term stability for more than 15 d (relative standard deviation (RSD)= 5.8%), and a low cytotoxicity with high biocompatibility. The findings demonstrated that the NMCS-based electrode is a reliable modified electrode for ultratrace sensitivity of DA, which is secreted normally from dopaminergic cells (PC12) or under a stimulating agent (K⁺ ).

Nitrogen-Doped Carbon for Red Phosphorous Based Anode Materials for Lithium Ion Batteries

Serving as conductive matrix and stress buffer, the carbon matrix plays a pivotal role in enabling red phosphorus to be a promising anode material for high capacity lithium ion batteries and sodium ion batteries. In this paper, nitrogen-doping is proved to effective enhance the interface interaction between carbon and red phosphorus. In detail, the adsorption energy between phosphorus atoms and oxygen-containing functional groups on the carbon is significantly reduced by nitrogen doping, as verified by X-ray photoelectron spectroscopy. The adsorption mechanisms are further revealed on the basis of DFT (the first density functional theory) calculations. The RPNC (red phosphorus/nitrogen-doped carbon composite) material shows higher cycling stability and higher capacity than that of RPC (red phosphorus/carbon composite) anode. After 100 cycles, the RPNC still keeps discharge capacity of 1453 mAh g^-1 at the current density of 300 mA g^-1 (the discharge capacity of RPC after 100 cycles is 1348 mAh g^-1). Even at 1200 mA g^-1, the RPNC composite still delivers a capacity of 1178 mAh g^-1. This work provides insight information about the interface interactions between composite materials, as well as new technology develops high performance phosphorus based anode materials.

High-performance and compact-designed flexible thermoelectric modules enabled by a reticulate carbon nanotube architecture

It is a great challenge to substantially improve the practical performance of flexible thermoelectric modules due to the absence of air-stable n-type thermoelectric materials with high-power factor. Here an excellent flexible n-type thermoelectric film is developed, which can be conveniently and rapidly prepared based on the as-grown carbon nanotube continuous networks with high conductivity. The optimum n-type film exhibits ultrahigh power factor of ∼1,500 μW m⁻¹ K⁻² and outstanding stability in air without encapsulation. Inspired by the findings, we design and successfully fabricate the compact-configuration flexible TE modules, which own great advantages compared with the conventional π-type configuration modules and well integrate the superior thermoelectric properties of p-type and n-type carbon nanotube films resulting in a markedly high performance. Moreover, the research results are highly scalable and also open opportunities for the large-scale production of flexible thermoelectric modules.

Thermoelectric modules can generate electricity directly from heat and have applications to waste heat-energy conversion. Here Zhou et al. have fabricated a thermoelectric module based on an air-stable n-type single-walled carbon nanotube sheet which can reach a high power factor of 1500 μWm⁻¹K⁻².

High performance of nitrogen-modified carbon nanotubes for selective oxidation of allyl alcohol

Nitrogen-modified carbon nanotubes (N-CNT) as a novel heterogeneous catalyst exhibit excellent performance in selective oxidation of allyl alcohol (C₃H₆O).

N-Doped carbon dots: green and efficient synthesis on a large-scale and their application in fluorescent pH sensing

A green and efficient anhydrous method was developed to synthesize nitrogen doped carbon dots (N-CDs) on a large-scale, and the N-CDs exhibited excellent reversible pH-sensitive property.

Study of Microstructure Change of Carbon Nanofibers as Binder-Free Anode for High-Performance Lithium-Ion Batteries

Flexible and binder-free film of N, O-doped carbon nanofibers (CNFs) is the ideal anode for high-energy-density batteries. Here, CNFs flexible films which the N, O dopant give defect in graphite structure results in high specific surface area more than 500 m² g^-1. A flexible film of CNF800 carbonized at 800 °C delivers initial capacities of 2000 and 755 mAh g^-1 at the current densities of 5 and 10 A g^-1, respectively. After 500 cycles, CNF800 remains the capacities of 1251, 865, 702, and 305 mAh g^-1 at 0.5, 1, 5, and 10 A g^-1, respectively. The microstructures of CNFs under various state of charge are studied by HRTEM, XPS, ¹³C NMR, and so forth. The lithiation/delithiation mainly happens to the interlayer of graphite domain of CNFs. The dopants of nitrogen and oxygen involve in lithiation, but much of Li-N is irreversible. The excellent performances of CNFs film can be attributed to the N, O doped structure of graphite domain that has increased the conductivity and lithium storage ability. Further development of N, O doped CNFs may enable practical applications as flexible anode in high-performance lithium-ion batteries.

Controlled n-Type Doping of Carbon Nanotube Transistors by an Organorhodium Dimer

Single-walled carbon nanotube (SWCNT) transistors are among the most developed nanoelectronic devices for high-performance computing applications. While p-type SWCNT transistors are easily achieved through adventitious adsorption of atmospheric oxygen, n-type SWCNT transistors require extrinsic doping schemes. Existing n-type doping strategies for SWCNT transistors suffer from one or more issues including environmental instability, limited carrier concentration modulation, undesirable threshold voltage control, and/or poor morphology. In particular, commonly employed benzyl viologen n-type doping layers possess large thicknesses, which preclude top-gate transistor designs that underlie high-density integrated circuit layouts. To overcome these limitations, we report here the controlled n-type doping of SWCNT thin-film transistors with a solution-processed pentamethylrhodocene dimer. The charge transport properties of organorhodium-treated SWCNT thin films show consistent n-type behavior when characterized in both Hall effect and thin-film transistor geometries. Due to the molecular-scale thickness of the organorhodium adlayer, large-area arrays of top-gated, n-type SWCNT transistors are fabricated with high yield. This work will thus facilitate ongoing efforts to realize high-density SWCNT integrated circuits.

Porous γ-Fe2O3 spheres coated with N-doped carbon from polydopamine as Li-ion battery anode materials

Nitrogen doping has been demonstrated to play a crucial role in controlling the electronic properties of carbon-based composites. In this paper, nitrogen-doped carbon coated γ-Fe2O3 (NC@γ-Fe2O3) composite was successfully fabricated through a facile and high-yield strategy, including a hydrothermal reaction process for porous γ-Fe2O3 and a subsequent coating of nitrogen-doped carbon by using dopamine as precursor. The resulting composite combines the superior properties of porous Fe2O3 and heteroatom-doped conductive carbon layer derived from polydopamine. When used as the anode material of the lithium-ion battery, the as-prepared NC@γ-Fe2O3 composite exhibits excellent lithium storage properties in terms of high capacity, stable cycling performance (869.6 mAh g(-1) at the current density of 0.5 A g(-1) after 150 cycles) and excellent rate capability.

In situ growth of polyphosphazene nanoparticles on graphene sheets as a highly stable nanocomposite for metal-free lithium anodes

A polyphosphazene/GN nanocomposite was readily synthesized by thermal polymerization of hexachlorocyclotriphosphazene with graphene oxide, which exhibits a stable and uniform nanostructure.

One-pot green hydrothermal synthesis of fluorescent nitrogen-doped carbon nanodots for in vivo bioimaging

One-pot green synthesis of fluorescent nitrogen-doped carbon nanodots (CNDs) was developed by hydrothermal treatments of biocompatible polyvinylpyrrolidone (PVP) and glycine. The fluorescent nitrogen-doped CNDs exhibited excellent water solubility, low cytotoxicity, and good salt stability for biological imaging. UV-vis spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) spectroscopy, and Raman spectroscopy were applied to confirm the optical and structural characteristics of the CNDs. Fluorescence of the CNDs was tunable from 417 to 450 nm adjusted by different excitation energy. Fluorescent quantum yield of the CNDs (21.43%) was significantly increased ~47.59% in comparison to that of the CNDs (14.52%) without nitrogen doping by glycine. In the in vivo imaging system (IVIS), fluorescence signal of the nitrogen-doped CNDs was obviously observed in the lungs at 12- and 24-h post-injection. Our work has shown the potential applications of the nitrogen-doped CNDs in fluorescence imaging in vivo.

Nitrogen-doped carbon nanotubes and graphene composite structures for energy and catalytic applications

Substitutional heteroatom doping is a promising route to modulate the outstanding material properties of carbon nanotubes and graphene for customized applications. Recently, (nitrogen-) N-doping has been introduced to ensure tunable work-function, enhanced n-type carrier concentration, diminished surface energy, and manageable polarization. Along with the promising assessment of N-doping effects, research on the N-doped carbon based composite structures is emerging for the synergistic integration with various functional materials. This invited feature article reviews the current research progress, emerging trends, and opening opportunities in N-doped carbon based composite structures. Underlying basic principles are introduced for the effective modulation of material properties of graphitic carbons by N-doping. Composite structures of N-doped graphitic carbons with various functional materials, including (i) polymers, (ii) transition metals, (iii) metal oxides, nitrides, sulphides, and (iv) semiconducting quantum dots are highlighted. Practical benefits of the synergistic composite structures are investigated in energy and catalytic applications, such as organic photovoltaics, photo/electro-catalysts, lithium ion batteries and supercapacitors, with a particular emphasis on the optimized interfacial structures and properties.

A Fe/Fe3O4/N-carbon composite with hierarchical porous structure and in situ formed N-doped graphene-like layers for high-performance lithium ion batteries

A Fe/Fe₃O₄/N-carbon composite consisting of a porous carbon matrix containing a highly conductive N-doped graphene-like network and Fe/Fe₃O₄ nanoparticles was prepared.

Nitrogen-doped electrospun reduced graphene oxide–carbon nanofiber composite for capacitive deionization

A nitrogen-doped electrospun reduced graphene oxide–carbon nanofiber composite was synthesized though electrospinning and ammonia treatment for an electrode for capacitive deionization.

Facile synthesis of nitrogen-doped unzipped carbon nanotubes and their electrochemical properties

N-UCNTs with a high nitrogen level, large surface areas and good crystallinity are synthesized by pyrolysis of an O-UCNTs/melamine composite.

25th anniversary article: Chemically modified/doped carbon nanotubes & graphene for optimized nanostructures & nanodevices

Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real-life applications without precise controllability of the material structures and properties. This invited article to celebrate the 25th anniversary of Advanced Materials reviews the current research status in the chemical modification/doping of carbon nanotubes and graphene and their relevant applications with optimized structures and properties. A broad aspect of specific correlations between chemical modification/doping schemes of the graphitic carbons with their novel tunable material properties is summarized. An overview of the practical benefits from chemical modification/doping, including the controllability of electronic energy level, charge carrier density, surface energy and surface reactivity for diverse advanced applications is presented, namely flexible electronics/optoelectronics, energy conversion/storage, nanocomposites, and environmental remediation, with a particular emphasis on their optimized interfacial structures and properties. Future research direction is also proposed to surpass existing technological bottlenecks and realize idealized graphitic carbon applications.

Hybrid electrolyte Li-air rechargeable batteries based on nitrogen- and phosphorus-doped graphene nanosheets

Nitrogen doped GNSs (N-doped GNSs) and phosphorus doped GNSs (P-doped GNSs) are examined as cathode electrodes for hybrid electrolyte Li-air batteries under basic conditions.

Lanthanum nickel alloy catalyzed growth of nitrogen-doped carbon nanotubes by chemical vapor deposition

CNTs doped with large amounts of nitrogen were produced on a LaNi₅ alloy catalyst by CVD and its growth mechanism discussed on the basis of dissolution and precipitation mechanisms.

Polystyrene/MWCNT/graphite nanoplate nanocomposites: efficient electromagnetic interference shielding material through graphite nanoplate-MWCNT-graphite nanoplate networking

Today, we stand at the edge of exploring carbon nanotube (CNT) and graphene based polymer nanocomposites as next generation multifunctional materials. However, irrespective of the methods of composite preparation, development of electrical conductivity with high electromagnetic interference (EMI) value at very low loading of CNT and (or) graphene is limited due to poor dispersion of these nanofillers in polymer matrix. Here, we demonstrate a novel technique that involves in-situ polymerization of styrene/multiwalled carbon nanotubes (MWCNTs) in the presence of suspension polymerized polystyrene (PS)/graphite nanoplate (GNP) microbeads, for the preparation of electrically conducting PS/MWCNT/GNP nanocomposites with very high (~20.2 dB) EMI shielding value at extremely low loading of MWCNTs (~2 wt %) and GNP (~1.5 wt %). Finally, through optimizing the ratio of PS-GNP bead and MWCNTs in the nanocomposites, an electrical conductivity of ~9.47 × 10(-3) S cm(-1) was achieved at GNP and MWCNTs loading of 0.29 and 0.3 wt %, respectively. The random distribution of the GNPs and MWCNTs with GNP-GNP interconnection through MWCNT in the PS matrix was the key factor in achieving high electrical conductivity and very high EMI shielding value at this low MWCNT and GNP loadings in PS/MWCNT/GNP nanocomposites. With this technique, the formation of continuous conductive network structure of CNT-GNP-CNT and the development of spatial arrangement for strong π-π interaction among the electron rich phenyl rings of PS, GNP, and MWCNT could be possible throughout the matrix phase in the nanocomposites, as evident from the field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) studies.

Enhanced electrochemical performance of FeWO4 by coating nitrogen-doped carbon

FeWO4 (FWO) nanocrystals were prepared at 180 °C by a simple hydrothermal method, and carbon-coated FWO (FWO/C) was obtained at 550 °C using pyrrole as a carbon source. The FWO/C obtained from the product hydrothermally treated for 5 h exhibits reversible capacities of 771.6, 743.8, 670.6, 532.6, 342.2, and 184.0 mAh g(-1) at the current densities of 100, 200, 400, 800, 1600, and 3200 mA g(-1), respectively, whereas that from the product treated for 0.5 h achieves a reversible capacity of 205.9 mAh g(-1) after cycling 200 times at a current density of 800 mA g(-1). The excellent electrochemical performance of the FWO/C results from the combination of the nanocrystals with good electron transport performance and the nitrogen-doped carbon coating.

Charge-selective surface-enhanced Raman scattering using silver and gold nanoparticles deposited on silicon-carbon core-shell nanowires

The deposition of silver (Ag) or gold (Au) nanoparticles (NPs) on vertically aligned silicon-carbon (Si-C) core-shell nanowires (NWs) produces sensitive substrates for surface-enhanced Raman spectroscopy (SERS). The undoped and 30% nitrogen (N)-doped graphitic layers of the C shell (avg thickness of 20 nm) induce a higher sensitivity toward negatively (-) and positively (+) charged dye molecules, respectively, showing remarkable charge selectivity. The Ag NPs exhibit higher charge selectivity than the Au NPs. The Ag NPs deposited on p- and n-type Si NWs also exhibit (-) and (+) charge selectivity, respectively, which is higher than that of the Au NPs. The X-ray photoelectron spectroscopy analysis indicates that the N-doped graphitic layers donate more electrons to the metal NPs than the undoped ones. More distinct electron transfer occurs to the Ag NPs than to the Au NPs. First principles calculations of the graphene-metal adducts suggest that the large electron transfer capacity of the N-doped graphitic layers is due to the formation of a N→Ag coordinate bond involving the lone pair electrons of the N atoms. We propose that the more (-) charged NPs on the N-doped graphitic layers prefer the adsorption of (+) charged dyes, enhancing the SERS intensity. The charge selectivity of the Si NW substrates can also be rationalized by the greater electron transfer from the n-type Si to the metal NPs.