Effect Of Surface Doping Research Articles

Unconventional Surface Doping Effect on the Spin State of an Adsorbed Magnetic Molecule.

Magnetic molecules adsorbed on two-dimensional (2D) substrates have attracted broad attention because of their potential applications in quantum device applications. Experimental observations have demonstrated substantial alteration in the spin excitation energy of iron phthalocyanine (FePc) molecules when adsorbed on nitrogen-doped graphene substrates. However, the underlying mechanism responsible for this notable change remains unclear. To shed light on this, we employ an embedding method and ab initio quantum chemistry calculations to investigate the effects of surface doping on molecular properties. Our study unveils an unconventional chemical bonding at the interface between the FePc molecule and the N-doped graphene. This bonding interaction, stronger than non-covalent interactions, significantly modifies the magnetic anisotropy energy of the adsorbed molecule, consistent with experimental observations. These findings provide valuable insights into the electronic and magnetic properties of molecules on 2D substrates, offering a promising pathway for precise manipulation of molecular spin states.

Surface doping effect on the optoelectronic performance of 2D organic crystals based on cyano-substituted perylene diimides

Compared to organic thin films, organic single crystals offer significant potential in organic phototransistors (OPTs) due to their enhanced charge transport, large surface area, and defect-free nature. However, the development of n-type semiconductors has lagged behind p-type semiconductors. To enhance semiconductor device performance, a doping process can be employed, which typically involves the introduction of charged impurities into the crystalline semiconducting material. Its aim is to reduce the Ohmic losses, increase carrier density, improve transport capabilities, and facilitate effective carrier injection, ultimately enhancing the electrical properties of the material. Traditional doping processes, however, often pose a risk of damaging the structure of single crystals. In this study, we have synthesized novel cyano-substituted chiral perylene diimides, which self-assemble into two-dimensional single crystals that can be used for n-type semiconductor devices. We have employed a surface doping strategy using diethylamine vapor without disrupting the crystal structure. The fabricated devices exhibit significantly higher charge transport properties after doping, achieving a maximum electron mobility of 0.14 cm² V−¹ s−¹, representing an improvement of over threefold. Furthermore, the optoelectronic performance of the doped devices has significantly improved, with the external quantum efficiency increased by over 9 times and the significantly improved response time. These results suggest that our surface doping technology is a promising way for enhancing the performance of 2D organic single-crystal OPTs.

A Lightweight, Zero-Power Intermodulation Sensor Based on the Graphene Oscillator

Wireless sensor networks (WSNs) require a massive number of sensor nodes for data collection and storage, for which the power management and area efficiency of battery-powered sensors may be an issue. In this article, we propose and numerically study a fully passive and lightweight intermodulation sensor based on the reconfigurable graphene field-effect transistors (GFETs) oscillator and passive frequency mixer. The output frequency of the self-powered GFET-based oscillator can be sensitive to the surface doping effect caused by charged surface absorbates, reactive gases, contaminations, or aqueous solutions. In the intermodulation sensor, the low-frequency signals generated by GFET oscillator are mixed with the incident radio frequency (RF) waves, forming the retransmitted and the RF intermodulation signals. Since the intermodulation products do not mess up with the reception signal, the unwanted clutters, self-jamming, and interferences can be effectively suppressed. Our results show that the output frequency of the GFET oscillator can sensitively respond to charged molecules, and such information can be encoded in the backscatter intermodulation signal. We believe that our GFET-based intermodulation sensor may be beneficial for a variety of the Internet of Things (IoTs), remote sensing, and environment monitoring applications.

Wideband mid infrared absorber using surface doped black silicon

Black silicon (BSi) is a synthetic nanomaterial with high aspect ratio nano protrusions inducing several interesting properties such as a very large absorptivity of incident radiation. We have recently shown that heavily doping the BSi in volume enables to significantly enhance its mid-infrared absorptivity and tune its spectral range of interest up to 20 μm. In the present letter, we explore the effect of surface doping on BSi radiative properties and its absorptance in particular since surface doping enables reaching even larger dopant concentrations than volume doping but at more limited penetration depths. We considered 12 different wafers of BSi, fabricated with cryogenic plasma etching on n- and p-type silicon wafers and doped using ion-implantation with different dopant types, dosages, and ion beam energies, leading to different dopant concentrations and profiles. The different wafers radiative properties, reflectance, transmittance, and absorptance are experimentally measured using Fourier transform infrared spectroscopy. We show that doping an n-type BSi wafer with phosphorous with a dose of 1017 atm/cm2 and an energy of 100 keV increases its absorptivity up to 98% in the spectral range of 1–5 μm. We propose a simple phenomenological explanation of the observed results based on the dopant concentration profiles and the corresponding incident radiation penetration depth. Obtained results provide simple design rules and pave the way for using ion-implanted BSi for various applications, such as solar energy harvesting, thermo-photovoltaics, and infrared radiation sensing, where both high absorptance and variable dopant concentration profiles are required.

A DFT + U-D3 Study of the Adsorption of Hydrogen Fluoride and Ethylene Carbonate on the Niobium-Doped (001), (011), and (111) Surfaces of Lithium Manganese Oxide

Cationic doping has been recommended as one of the most effective methods of reducing the number of trivalent manganese (Mn3+) ions that undergo a disproportionation reaction in lithium manganese oxide-based (LiMn2O4) lithium-ion batteries. However, the effect of surface doping on the major LiMn2O4 surfaces and their interactions with the electrolyte components is not yet fully understood. In this work, spin-polarised density functional theory-based calculations [DFT + U-D3 (BJ)] were employed to study the adsorption of the electrolyte components ethylene carbonate (EC) and hydrogen fluoride (HF) onto the Nb-doped major LiMn2O4 (001), (011), and (111) surfaces. During the substitution of niobium for manganese ions in the second surface layers (Nb second ), it was found that the (111) surface stability improves, resulting in an enhanced (111) plane on the morphology. However, replacing the first (Nb first ) as well as both top and sub-surface (Nb both ) layers of Mn atoms in the slabs maintains the same stability trend as in the pure pristine surfaces. Moreover, both adsorbates greatly preferred binding to the surfaces through the Nb instead of Mn atoms, and the largest adsorption energy was calculated for EC on the LiMn2O4 (011) surface doped on the Nb second site and for HF on the LiMn2O4 (111) surface doped on the Nb both site. Furthermore, the EC/HF adsorptions further enhance the stability of the Nb second (111) surface plane. However, minimal charge transfer was calculated for both HF and EC interacting with the pure and Nb-doped surfaces. Our findings are interesting, since exposing the (111) surface promotes the formation of a stable solid electrolyte interface (SEI), significantly reducing Mn dissolution and enhancing the adsorption of EC and HF.

Predicted superior hydrogen evolution activities of MoC via surface dopant

Molybdenum carbides (MoC) are regarded as promising candidates for electrocatalytic hydrogen evolution reaction (HER) as their stabilities, high conductivities. Non-metallic doping is a robust way to enhance the HER activity of MoC in experiments, yet the systematic theoretical study is still lacking. In this work, we investigate the surface doping effect on HER activity of C-terminated γ -MoC(100) by density functional theory (DFT). The thermodynamical stability and realistic catalytic surface of doped surfaces, including mono- and co-doping by three elements (N, P and S) with various doping ratios, are verified by formation energies and surface Pourbaix diagrams, respectively. According to the hydrogen adsorption ability on different coverage and the calculated exchange current densities ( i 0 ) of the doped surfaces, the surfaces doping in range of (P% > 60% and N% > 5%), (60% < N% <85% and P% < 25%), and (60% < N% < 85% and S% < 25%), show larger i 0 ( i 0 > 4 mA/cm 2 ). Especially the N/P co-doping γ -MoC(100), their larger i 0 in greater range enables their promising excellent performance in hydrogen evolution in experiments. The improved HER activities of doped MoC(100) are ascribed to suitable hydrogen adsorption abilities tuned by suitable p z -band centers and the charge redistribution. Our DFT simulations provide more insight and guidance for improving the HER performance of electrode catalysts using non-metallic doping effects. • N/P co-doped MoC(100) at any ratio shows high exchange current density for HER. • N and P doping will downshift p z -band center and tune hydrogen adsorption ability. • The charge redistribution domains the oscillation character of Δ G H in P-doped surfaces.

Effect of surface doping of TiO2 powders with Fe ions on the structural, optical and photocatalytic properties of anatase and rutile

The effect of surface Fe-doping on the structural, photocatalytic, optical properties of polydisperse anatase and rutile TiO2 has been comprehensively studied. The TiO2 surface has been modified by Fe3+ ions through the adsorption from the diluted FeCl3 aqueous solutions. The prepared powders were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, temperature programmed desorption techniques (TPD), Raman and UV–vis spectroscopy. With the adsorption isotherms of Fe3+ ions from FeCl3 aqueous solutions, it was found that adsorption of Fe3+ ions on the anatase surface is twice more efficient compared to that one on the rutile. The XRD and Raman spectroscopy measurements confirmed the monophase structure of the Fe-doped TiO2 with a subtle change in the lattice parameters and O/Ti ratio compared to the undoped counterparts. The red shift of the UV absorption edge has been registered for the Fe-doped anatase resulting in a significant decrease of its bandgap from 3.2 to 2.7 eV. The photocatalytic destruction of organic dye Safranin T over the prepared Fe-doped TiO2 under UV irradiation has been investigated. The influence of various energetically nonequivalent active sites on the surfaces of anatase and rutile on their photoactivity is considered.

Orientation-Dependent Host-Dopant Interactions for Manipulating Charge Transport in Conjugated Polymers.

Molecular orientation plays a critical role in controlling carrier transport in organic semiconductors (OSCs). However, this aspect has not been explored for surface doping of OSC thin films. The challenge lies in lack of methods to precisely modulate relative molecular orientation between the dopant and the OSC host. Here, the impact of molecular orientation on dopant-host electronic interactions by large modulation of conjugated polymer orientation via solution coating is reported. Combining synchrotron-radiation X-ray measurements with spectroscopic and electrical characterizations, a quantitative correlation between doping-enhanced charge carrier mobility and the Herman's orientation parameter is presented. This direct correlation can be attributed to enhanced charge-transfer interactions at host/dopant interface with increasing face-on orientation of the polymer. These results demonstrate that the surface doping effect can be fundamentally manipulated by controlling the molecular orientation of the OSC layer, enabling optimization of carrier transport.

Regulating SnO2 surface by metal oxides possessing redox or acidic properties: The importance of active O2−/O22− and acid sites for toluene deep oxidation

To explore the surface doping effects of metal oxides possessing redox (Cr, Co, Mn) or acidic (In, Bi) properties on SnO2, SnO2 doped by different metal oxides has been designed. All the doping metal oxides disperse finely on the SnO2 support surface, which can improves the reaction activity, obeying the order of 1%Mn/SnO2 > 1%Co/SnO2 > 1%Cr/SnO2 > 1%Bi/SnO2 > 1%In/SnO2 > SnO2. By modifying SnO2 surface with Cr, Co and Mn oxides, both the active surface oxygen (O2− and O22−) and acid sites quantities have been significantly improved, thus resulting in remarkable activity increment. Whereas, by modifying SnO2 surface with In and Bi oxides, only the surface acid sites amount has been improved, hence having limited activity improvement effect. 1%Mn/SnO2 catalyst possesses considerable amount of both types of active sites, thus showing the optimal toluene deep oxidation activity in all the catalysts.

Influence of PVA, PVP and PEG doping on the optical, structural, morphological and magnetic properties of zinc ferrite nanoparticles produced by thermal method

This work demonstrated an in-depth investigation of the effect of surface doping by three different polymers on the synthesis of zinc ferrite nanostructures by a thermal method. The zinc ferrites were doped with 20% concentration by mass of Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and Polyethylene glycol (PEG) to enhance its properties. The X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) confirmed the incorporation of the polymers in the lattice with an obvious increase in the crystallite size, functional groups, spherical morphology, and superparamagnetic behavior respectively. It is noteworthy that the cubic crystalline structure, favorable particle size and magnetic properties of the doped samples gave the NPs a controllable and improved properties for sundry applications in the medical fields such as Hyperthermia and drug delivery with PEG dopant showing a towering leverage on the properties of the ZF with 11% polydispersity Index (PDI).

Effects of Surface Doping of Si Absorbers on the Band Alignment and Electrical Performance of TiO2-Based Electron-Selective Contacts

ABSTRACTWe have investigated the chemical and electrical properties of a thin SiO2/TiO2 stacking layer deposited on n-Si and heavily phosphorus-doped n++ Si substrates to elucidate effects of phosphorus doping of Si absorbers on the band alignment and electrical performance of a SiO2/TiO2 stack-based electron-selective contact deposited on the differently doped Si substrates. From our XPS study, we show a shift of the TiO2 energy levels up to ∼0.13 eV with respect to those of Si as the doping level of Si substrates changes. We also show that the conduction band offset of the SiO2/TiO2 stacking layer at the interface with the n++ Si substrate seems to smaller than that of the SiO2/TiO2 stacking layer at the interface with n-Si substrate. Finally, from our electrical transport measurements, we could conclude that the thinner tunneling barrier, the increased electron density in front of the SiO2 layer in the n++ Si surface, and/or the reduced barrier height by heavy doping, seem to enhance the majority electron transport property of the SiO2/TiO2/n++ Si samples compared to that of the SiO2/TiO2/n-Si samples.

Size-Dependent Asymmetric Auger Interactions in Plasma-Produced n- and p-Type-Doped Silicon Nanocrystals

Nonradiative Auger recombination (AR) tends to dominate carrier dynamics in charged, quantum-confined structures. Consequently, it complicates the practical realization of many semiconductor nanocrystal (NC)-based devices such as light-emitting diodes, photovoltaic cells, and single-photon emitters, in which charged exciton states often occur. To this end, extensive experimental studies on direct band gap NCs have investigated the trion components (both positive and negative) that construct the total AR rate. However, such an analysis has remained elusive for indirect band gap Si NCs. In this study, we investigate AR decay of non-thermal plasma-produced n- and p-type-doped Si NCs. We expand the study over a large NC size range (DNC ≈ 3–8 nm), in which n- and p-type doping is achieved by either a substitutional or surface doping effect, respectively. First, we monitor the AR of charge-neutral multiexcitons by measuring the biexciton lifetime (τXX) as a function of the NC size and doping configuration. We s...

Programmed dielectrophoretic assembly of Pd nanoparticles for conductance control in VO2 nanowires

Recently, hybrid nanodevices consisting of more than one type of nanomaterial, have been an intense research topic as far as science and advanced functionalities of such systems are concerned. However, lack of controlled, scalable and directed assembly techniques for these hybrid systems, particularly the accurate assembly of nanoparticles (NPs) on nanowires (NWs), has resulted in their limited applications. In the present work, a development has been reported using dielectrophoresis (DEP) technique through which a controlled assembly of palladium (Pd) NPs on VO2 NWs has been deposited. Furthermore, modulation in conductivity of VO2 NWs as a function of the NPs density is electrically measured and interpreted through work-function dependent surface doping effect of the Pd NPs on VO2 NWs. This well-controlled and scalable approach to functionalize VO2 NWs by assembling Pd NPs is significant in the view of a huge potential of Pd NPs like sensor applications thus adding functionalities to VO2 NWs. Our approach can be generalized for the large-scale assembly of a variety of NP-NW combination to fabricate advanced functional hybrid devices.

Positive Effect of Surface Doping with Au on the Stability of Pt-Based Electrocatalysts

Corrosion resistance of a transition-metal-rich PtCu3/C oxygen reduction reaction (ORR) catalyst as a representative of Pt alloy-based materials has been significantly improved by doping with small amounts of gold (<1 at. %). Transmission electron microscopy imaging shows near-surface segregation of both platinum and gold with the underlying core consisting predominantly of intermetallic PtCu3. The resulting PtAu skin catalyst shows improved resistance against Cu dissolution, as well as against carbon corrosion if compared to its PtCu3 precursor. Also, it exhibits a much higher Pt and carbon stability than a widely used Pt/C standard. Most importantly, the Au-doped sample shows a substantial improvement in stability at the elevated temperature (60 °C) degradation test (10 000 cycles; 0.4–1.2 VRHE) simulating a real PEM fuel cell environment.

Effect of surface doping on the band structure of graphene: a DFT study

Various techniques, like doping, vacancy creation, strain engineering are tried to open a gap in the bandstructure of graphene and in some cases the gap has opened up. However, when the gap opens up the Dirac cones disappear. Without Dirac cones, graphene loses all its novelty. So opening a gap in graphene, retaining Dirac cones has become a challenging task. We, through first principles study using Density Functional theory, have done band gap tuning investigations. We have succeeded in opening the band gap, retaining the Dirac cones. Surface doping (adsorption) of various elements are tried and finally surface doping of sulfur is found to induce band gap opening in graphene. The Dirac cones are retained and the graphene is now a semiconductor with fast moving massless Dirac Fermions. We are reporting this type of calculations for the first time.

Silicon nanowires: applications in catalysis with distinctive surface property

Over the last few years, silicon nanowires (SiNWs) have come under intensive researches due to their electrical, optical, mechanical, thermal, and chemical properties. On account of their large surface-to-volume ratio and easy modification, composites based on SiNWs have won a special status in the wide application fields. In this review, we summarize the essential aspects of catalytic activities based on SiNWs. An up-to-date overview of SiNW-based catalysts, including various metal-modified-SiNWs as well as hydrogen terminated SiNWs are discussed in detail. In addition, surface doping effect is illustrated to promote the understanding of catalytic activity.

Surface-Doping Effect of InVO4 Nanoribbons and the Distinctive Behavior as Gas Sensors

Indium vanadate (InVO4) gas sensors were fabricated by depositing InVO4 nanoribbons aqueous suspension onto ceramic substrates. Their resistances distinctively increased in the detection of ammonia and propylamine, indicating an n-to-p semiconductor transition. This novel phenomenon of the InVO4-based sensor may be ascribed to the surface doping effect: electrons were trapped by H2O and O2 and produced OH(-) and O2(-) on the InVO4 surface, which resulted in holes overcompensation in the InVO4 valence band. Moreover, the sufficiently large surface-to-volume ratio of these nanoribbons enables fast carrier transfer on the sensor surface. The InVO4 nanoribbons-based sensors had optimum performance at room temperature and enjoyed good restorability. They also had great response to a wide range of target gas concentration, with ultrahigh sensitivities up to 1100% for ammonia and 760% for propylamine.

Optical absorption of polydisperse TiO2: Effect of surface doping by transition metal cations

Optical absorption of polydisperse TiO2: Effect of surface doping by transition metal cations

Particle Size and Structural Control of ZnWO4 Nanocrystals via Sn2+ Doping for Tunable Optical and Visible Photocatalytic Properties

In this work, we report on the microwave-assisted hydrothermal synthesis of Sn2+-doped ZnWO4 nanocrystals with controlled particle sizes and lattice structures for tunable optical and photocatalytic properties. The samples were carefully characterized by X-ray diffraction, transmission electron microscopy, inductive coupled plasma optical emission spectroscopy, UV–vis diffuse reflectance spectroscopy, and Barrett–Emmett–Teller technique. The effects of Sn2+ doping in ZnWO4 lattice on the crystal structure, electronic structure, and photodegradation of methylene orange dye solution were investigated both experimentally and theoretically. It is found that part of the Sn2+ ions were homogeneously incorporated in the ZnWO4 host lattice, leading to a monotonous lattice expansion, and part of Sn2+ ions were expelled at surface sites for decreased crystallinity and particle size reduction. By Sn2+ doping, ZnWO4 nanocrystals showed a significant XPS binding energy shift of Zn 2p, W 4f, and O 1s, which is attributed to the combination of electronegativity between Sn2+ and Zn2+, lattice variation, and particle size reduction. Meanwhile, the BET surface areas were also greatly enlarged from 40.1 to ∼110 m2·g–1. Contrary to the theoretical predictions of the quantum size effect, Sn2+-doped ZnWO4 nanocrystals showed an abnormal band gap narrowing, which can be well-defined as a consequence of bulk and surface doping effects as well as lattice variations. With well-controlled particle size, crystallinity, and electronic structure via Sn2+ doping, the photocatalytic performance of Sn2+-doped ZnWO4 nanocrystals was optimized at Sn2+ doping level of 0.451.

Surface charge transfer doping of germanium nanowires by MoO3 deposition

We report on the surface transfer p-type doping of germanium nanowires (GeNWs) via MoO3 thin film deposition. The GeNWs studied were prepared by a conventional thermal evaporation approach. Electrical property analysis shows that the conductance, hole mobility and concentration were all prominently enhanced after MoO3 thin film coating. Such a remarkable surface doping effect can be attributed to the surface charge transfer at the GeNWs/MoO3 interface, which is verified by in situ XPS analysis of GeNWs as a function of increasing MoO3 coverage. Further hole mobility and concentration evolution study of MoO3/GeNWs reveals that the GeNWs embedded in the MoO3 layer can retain their electrical property after storage in air for 3 months. The generality of the above results suggests that the charge transfer doping via surface deposition has great potential in GeNW-based nanoelectronic devices and may also be applicable to the modulation of other semiconductor nanostructures.