Doping Behavior Research Articles

Modulated wafer-scale WS2 films based on atomic-layer-deposition for various device applications.

Tungsten disulfide (WS2) is promising for potential applications in transistors and gas sensors due to its high mobility and high adsorption of gas molecules onto edge sites. This work comprehensively studied the deposition temperature, growth mechanism, annealing conditions, and Nb doping of WS2 to prepare high-quality wafer-scale N- and P-type WS2 films by atomic layer deposition (ALD). It shows that the deposition and annealing temperature greatly influence the electronic properties and crystallinity of WS2, and insufficient annealing will seriously reduce the switch ratio and on-state current of the field effect transistors (FETs). Besides, the morphologies and carrier types of WS2 films can be controlled by adjusting the processes of ALD. The obtained WS2 films and the films with vertical structures were used to fabricate FETs and gas sensors, respectively. Among them, the Ion/Ioff ratio of N- and P-type WS2 FETs is 105 and 102, respectively, and the response of N- and P-type gas sensors is 14% and 42% under 50 ppm NH3 at room temperature, respectively. We have successfully demonstrated a controllable ALD process to modify the morphology and doping behavior of WS2 films with various device functionalities based on acquisitive characteristics.

Defects and dopant behavior of a medium-dose range implant into heated silicon wafers

Defects and dopant behavior of a medium-dose range implant into heated silicon wafers

Merging Passivation in Synthesis Enabling the Lowest Open-Circuit Voltage Loss for PbS Quantum Dot Solar Cells.

The high open-circuit voltage (Voc ) loss arising from insufficient surface passivation is the main factor that limits the efficiency of current lead sulfide colloidal quantum dots (PbS CQDs) solar cell. Here, synergistic passivation is performed in the direct synthesis of conductive PbS CQD inks by introducing multifunctional ligands to well coordinate the complicated CQDs surface with the thermodynamically optimal configuration. The improved passivation effect is intactly delivered to the final photovoltaic device, leading to an order lower surface trap density and beneficial doping behavior compared to the control sample. The obtained CQD inks show the highest photoluminescence quantum yield (PLQY) of 24% for all photovoltaic PbS CQD inks, which is more than twice the reported average PLQY value of ≈10%. As a result, a high Voc of 0.71V and power conversion efficiency (PCE) of 13.3% is achieved, which results in the lowest Voc loss (0.35eV) for the reported PbS CQD solar cells with PCE >10%, comparable to that of perovskite solar cells. This work provides valuable insights into the future CQDs passivation strategies and also demonstrates the great potential for the direct-synthesis protocol of PbS CQDs.

Pyridine-extended proton sponge enabling high-performance membrane for flow batteries

The development of high-performance and low-cost membrane is of significance towards vanadium flow battery (VFB). The membrane usually suffer from a trade-off challenge between conductivity and selectivity especially in long-term operation of flow battery. Herein, using a proton sponge drived by the proton absorption capacity of extended pyridine groups, a highly ion-selective membrane is fabricated. During acid-assisted doping behaviors, transport nanochannels with highly proton-selective conductivity are constructed based on well-defined nanophase separation structure. The protonated nanochannels display effectively acidic absorption during hydration process for enabling fast proton conduction (a low area resistance of 0.33 Ω cm2) and repelling vanadium ion (a low vanadium ion permeability of 3.04 × 10−10 cm2 s−1). Consequently, prepared membrane with proton sponge exhibits remarkable performance of high energy efficiency of 85.5%, together with excellent chemical durability over 1000 charge-discharge cycles (more than 1100 h) at 120 mA cm−2 in VFB application. These notable properties make prepared membrane as a potential alternative used in large-scale energy storage systems.

Study of an Anti-Doping Education Program in Spanish Sports Sciences Students

A total of 145 students of Physical Activity and Sport Sciences (PASS) from different Spanish universities who took an online anti-doping educational course of the Spanish Anti-Doping Commission (CELAD) answered a questionnaire on their perceptions about doping before, after, and four months later. The results show that the course reduced students' ignorance about the effects of substances on performance and health and increased their moral judgment and feelings against doping. The results are in line with previous research that showed that the moral stance against doping can be improved through educational programs. Online educational interventions can be effective in reducing doping behavior, so their future implementation among ASP can be an effective strategy to reduce doping behavior.

Homovalent cationic Se dopant with noble metal-like activation properties to enhance the sensitivity of SnO2 sensors

A challenge for low-valence cation doping in SnO2 materials is that the sharply elevated baseline resistance is detrimental to sensor stability and the subsequent signal acquisition. In contrast, Homovalent doping has little effect on resistance but the effective homovalent dopant is few. Herein, we find the non-metallic element Se is prone to form cationic SeSn defects in SnO2, which can improve the sensitivity of the SnO2-based sensors with a moderate rise in baseline resistance. The homovalent Se doping make the species and ratio of adsorbed oxygen on Se-doped SnO2 surface basically unchanged after doping. Further experiments and theoretical calculations confirm the sensitization mechanism of Se-doped SnO2 can be attributed to the higher activity of adsorbed oxygen on its surface. Therefore, the sensor based on Se-doped SnO2 can have sufficient sensing-reactions and charge transfer at a temperature close to the maximum value of the baseline resistance, which makes the sensor better to sensitize the target gases requiring high temperature for sensing-reactions. This noble metal-like activation behavior of Se dopant is derived from the easier breaking of Se-O bond compared to Sn-O bond during CO oxidation which provides a new basis for the selection of dopants from the perspective of bond energy.

Enhancing the Performance of N-Type Thermoelectric Devices via Tuning the Crystallinity of Small Molecule Semiconductors.

In the development of high-performance organic thermoelectric devices, n-type materials, especially with small molecule semiconductors, lags far behind p-type materials. In this paper, three small molecules are synthesized based on electron-deficient naphthalene bis-isatin building blocks bearing different alkyl chains with the terminal functionalized with 3-ethylrhodanine unit and studied their aggregation and doping mechanism in detail. It is found that crystallinity plays an essential role in tuning the doping behavior of small molecules. Molecules with too strong crystallinity tend to aggregate with each other to form large crystalline domains, which cause significant performance degradation. While molecules with weak crystallinity can tolerate more dopants, most of them exhibit low mobility. By tuning the crystallinity carefully, organic thermoelectric devices based on C12NR can maintain high mobility and realize effective doping simultaneously, and a high power factor of 1.07 µW m-1 K-2 at 100°C is realized. This delicate molecular design by modulating crystallinity provides a new avenue for realizing high-performance organic thermoelectric devices.

Atmospheric pressure plasma jet treatment of PLA/PAni solutions: Enhanced morphology, improved yield of electrospun nanofibers and concomitant doping behaviour

To obtain uniform and bead-free nanofibers by means of electrospinning is sometimes very challenging, especially for polymers with low solubility, such as for example the intrinsically conducting polymers (ICPs). Recently, atmospheric pressure plasma jet (APPJ) treatment to pre-electrospinning polymer solutions has been found to effectively enhance the electrospinnability of a single polymer type. Here, such an APPJ treatment has been applied for the first time to a blended polymeric solution consisting of polylactic acid (PLA) and polyaniline emeraldine base (PAni EB) as well as its emeraldine salt (ES) form doped by camphorsulfonic acid (CSA). The plasma-induced physical changes of the solutions including pH, conductivity, viscosity and surface tension have been investigated and correlated with the ensuing physicochemical properties of the electrospun nanofibers. To do so, next to the liquid-based characterizations, the nanofibers have been examined by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), water contact angle (WCA) goniometry and uniaxial tensile testing. Results revealed that the pre-electrospinning plasma modification step resulted in a remarkably enhanced nanofiber morphology, deposition yield and mechanical performance of the electrospun nanofibers. Moreover, concomitant doping of PAni EB to PAni ES, as an unexpected side behaviour generated during the plasma treatment without the addition of any protonic acid, was found and further carefully investigated using ultraviolet/visible (UV–Vis) spectrometry. The findings obtained in this work thus enlarge the application range of pre-electrospinning APPJ treatment from single to blended polymeric solutions. Moreover, the recent pioneering discovery revealing the pre-electrospinning APPJ treatment role in enhancing electrospinning has surpassed the sole connotation of improved fiber morphology as new interesting effects are discerned in this study: boosted nanofiber deposition yield and doping capabilities.

Surface tailored Ti-oxo clusters enabling highly efficient organic solar cells

In this work, the hierarchical surface reactivity of a kind of Ti-oxo cluster (TOC) with robust cyclic structure, CTOC, supported by multiple surface ligands, has been initially established. By this method, a series of aromatics (i.e., benzoate for CTOC-Ph, 4-methylbenzoate for CTOC-PhMe and 4-cyanobenzoate for CTOC-PhCN) substituted CTOC-Ars, with identical TOC core have been produced. These CTOC-Ars can be solution-processed into smooth films with order microstructures and optimized semiconducting properties, driven by intermolecular interactions of the aromatics. When using CTOC-Ph as cathode interlayer (CIL) in PM6:BO-4Cl based organic solar cells (OSCs), power conversion efficiencies (PCEs) up to 17.7 % have been achieved, much higher than 15.6 % of those with CTOC CIL. The distinct electron doping behavior with non-fullerene acceptor and higher adsorption energy with the polymer donor has been successfully unraveled, which can enable CTOC-Ph more intimate contact with the photoactive layer and facilitate more efficient charge transport. Moreover, the generality of CTOC-Ars as CIL for efficient OSCs has been confirmed in varied OSC systems, in which high PCEs of 18.4 % can be provided for PM6:L8-BO system.

Atomic-scale study on the dopant distribution in phosphorus and boron-doped Si nanocrystals/SiO2 multilayers

Understanding the distributions and behaviors of dopants in Si nanocrystal are the primary and necessary issues to realize the controllable doping at nanoscale and develop the next generation of optoelectronic devices. This work reports the atomic-scale distributions of phosphorus and boron dopants in Si nanocrystals multilayers. The phosphorus-doped and boron-doped Si nanocrystals/SiO2 multilayers are fabricated by PECVD and subsequently annealed at 1000 °C. It is found that the locations of phosphorus are redistributed after the formation of Si nanocrystals due to the combined effects of formation energy and self-purification. Phosphorus dopants are mainly distributed at the Si nanocrystals surfaces to passivate the dangling bonds, while part of them incorporate into Si nanocrystals lattice sites to provide free electrons. However, boron dopants exhibit different distributions in contrast to phosphorus. The concentration of boron on Si nanocrystals surfaces can reach as high as 40.0 at. %, which forms a dopant-shell covering on Si nanocrystals. Meanwhile, the boron dopant-shell can modify the surface states of Si nanocrystals like Si-oxide related emission centers and dangling bonds, which is responsible for the luminescence properties. Moreover, the boron-aggregations with concentration near 74.8 at. % are appeared inside Si nanocrystals and led to the damage of crystalline lattice.

Adsorption and Sensing of CO2, CH4 and N2O Molecules by Ti-Doped HfSe2 Monolayer Based on the First-Principle

With the continuous emission of greenhouse gases, the greenhouse effect is becoming more and more serious. CO2, CH4, and N2O are three typical greenhouse gases, and in order to limit their emissions, it is imperative that they are accurately monitored. In this paper, the doping behavior of Ti on the surface of HfSe2 is investigated, based on the first-nature principle. Additionally, the parameters of adsorption energy and the transfer charges of Ti−HfSe2 for CO2, CH4, and N2O are calculated and compared, while the sensing characteristics of Ti−HfSe2 are analyzed. The results show that the structure is most stable when Ti is located above the lower-layer Se atom. The CO2 and N2O adsorption systems with large adsorption energies and transfer charges are a chemical adsorption, while the CH4 system is a physical adsorption with small adsorption energies and transfer charges. In addition, Ti−HfSe2 has a good sensitivity and recovery time for CO2 at 298 K, which is feasible for industrial application. All the contents of this paper provide theoretical guidance for the implementation of Ti−HfSe2 as a gas-sensitive material for the detection of greenhouse gas components.

Exploring the relationship between mindset and psychological factors linked to doping

Mindset refers to the way in which one attributes his or her abilities and traits as either ‘fixed’ (e.g., immutable), ‘growth’ (e.g., highly malleable), or somewhere in between. It is possible that mindset may be related to psychological factors linked to doping – such as doping moral disengagement (MD) and doping self-regulatory efficacy (SRE) – though no research as yet has confirmed this. In the present study, 322 student-athletes completed a questionnaire pack measuring mindset and various psychological factors linked to doping. Structural equation modeling provided strong support for all study hypotheses. Specifically, we established: (a) mindset positively predicted doping SRE, (b) mindset negatively predicted doping MD, (c) doping MD positively predicted susceptibility to intentional and inadvertent doping, (d) doping MD negatively predicted anticipated guilt, (e) anticipated guilt negatively predicted susceptibility to intentional and inadvertent doping. In addition, significant negative correlations were found between MSA and doping moral disengagement (r = -.19, p < .01), MSA and susceptibility to inadvertent doping (r = -.11, p < .01), MMC and moral disengagement (r = -.12, p < .05), and MMC and susceptibility to inadvertent doping (r = -.13, p < .05). A significant positive correlation was found between MSA and doping SRE (r = .23, p < .01). Implications of the findings include the potential for early identification of athletes at risk of doping based on their mindset. Future research should look to explore the effectiveness of mindset interventions on reducing transgressive doping attitudes and behaviours.

UV luminescence enhancement of Cu-doped ZnO nanorods grown by hydrothermal treatment

Herein, we studied the effect of Cu doping on the ultraviolet (UV) emission enhancement of ZnO nanorods. ZnO nanorods with different Cu doping concentrations were prepared by hydrothermal method and the Cu doping behavior was investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet visible (UV–Vis) absorption spectroscopy and photoluminescence (PL). XRD patterns confirmed the incorporation of Cu. Compared with pure ZnO, no other phase appears, the intensity of diffraction peaks and the calculated parameters such as lattice constants increase, all of which proved that the doping of Cu is substitutional doping. Doping induces a red-shift in the absorption maximum wavelength of the absorption spectrum, indicating that doping causes attenuation of UV absorption properties. In the PL spectra, the increase of Cu doping concentration makes the UV emission peak enhanced and there is almost no emission peak in the visible region. The UV emission at room temperature can be attributed to the superposition of free and bound excitons, where free excitons dominate and bound excitons are related to the substitution of Cu for Zn. The enhanced UV emission of Cu-doped ZnO materials could lead to the wide application in the field of UV optoelectronic devices.

Understanding the Solution‐State Doping of Donor–Acceptor Polymers Through Tailored Side Chain Engineering for Thermoelectrics

AbstractAmong the molecular doping methods widely utilized to control charge carriers in organic thermoelectric (TE) devices, solution mixing is attractive for the preparation of uniform and thick TE films to obtain high output powers. However, the effects of doping behavior in solution‐state polymers on their film properties are still not well understood, particularly for donor–acceptor (D‐A) polymers, key materials for high‐performance (opto)electronic devices. Here, by preparing three D‐A polymers with engineered side chains, the aggregation effects of D‐A polymers on the doping behavior in the solution and film states are demonstrated. In a less aggregated polymer, mixing the solution with a p‐dopant leads to the Lewis complex formation, which reduces doping efficiency and power factor. However, solution mixing of aggregated polymers induces the formation of ion pairs with the dopant, resulting in power factors that are two orders of magnitude higher at 23.7 µW m−1 K−2. Doping in the film state where aggregation is induced facilitates ion‐pair formation, resulting in smaller deviation in TE properties (power factors = 9.0–16.4 µW m−1 K−2) despite differences in their ordering structures. These results provide an in‐depth understanding of efficient solution‐state doping of D‐A polymers for TEs.

Role of Metallic Adlayer in Limiting Ge Incorporation into GaN.

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth. The role of the adlayer in the incorporation of dopants in GaN is completely unexplored, probably because n-type doping of GaN with Si is relatively straightforward and can be scaled up with available Si atomic flux in a wide range of dopant concentrations. However, a surprisingly different behavior of the Ge dopant is observed, and the presence of atomically thin gallium or an indium layer dramatically affects Ge incorporation, hindering the fabrication of GaN:Ge structures with abrupt doping profiles. Here, we show an experimental study presenting a striking improvement in sharpness of the Ge doping profile obtained for indium as compared to the gallium surfactant layer during GaN-plasma-assisted molecular beam epitaxy. We show that the atomically thin indium surfactant layer promotes the incorporation of Ge in contrast to the gallium surfactant layer, which promotes segregation of Ge to the surface and Ge crystallite formation. Understanding the role of the surfactant is essential to control GaN doping and to obtain extremely high n-type doped III-nitride layers using Ge, because doping levels >1020 cm−3 are not easily available with Si.

Controlled p-Type Doping of MoS2 Monolayer by Copper Chloride.

Electronic devices based on two-dimensional (2D) MoS2 show great promise as future building blocks in electronic circuits due to their outstanding electrical, optical, and mechanical properties. Despite the high importance of doping of these 2D materials for designing field-effect transistors (FETs) and logic circuits, a simple and controllable doping methodology still needs to be developed in order to tailor their device properties. Here, we found a simple and effective chemical doping strategy for MoS2 monolayers using CuCl2 solution. The CuCl2 solution was simply spin-coated on MoS2 with different concentrations under ambient conditions for effectively p-doping the MoS2 monolayers. This was systematically analyzed using various spectroscopic measurements using Raman, photoluminescence, and X-ray photoelectron and electrical measurements by observing the change in transfer and output characteristics of MoS2 FETs before and after CuCl2 doping, showing effective p-type doping behaviors as observed through the shift of threshold voltages (Vth) and reducing the ON and OFF current level. Our results open the possibility of providing effective and simple doping strategies for 2D materials and other nanomaterials without causing any detrimental damage.

Tuning electronic behaviors of WS2 by molecular doping

WS2 has become a hot research topic because of its excellent properties in the fields of chemistry, physics, and material science. We investigate the structural and electronic behaviors of organic molecules adsorbed on the WS2 single-layer using density functional theory. The results observed that organic molecules can inject additional carriers into the WS2 single-layer. Tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) doping achieve p-type doping, while tetrathiafulvalene (TTF) doping can introduce n-type doping behavior. Furthermore, the work function of WS2 can be tuned in the range of 4.05 eV to 5.71 eV after organic molecules doping. Importantly, the doping gap of the TTF-WS2 systems is reduced with the decrease of the applied negative electric field. Especially at − 0.45 V/Å, the doping gap of the TTF-WS2 system is 0.01 eV. It demonstrated that the applied negative electric field can induce effective n-type doping behavior. Therefore, organic molecular doping can regular the electronic behaviors of WS2, which is useful for the design of nanoelectronic devices.

Electron-Phonon Coupling in a Magic-Angle Twisted-Bilayer Graphene Device from Gate-Dependent Raman Spectroscopy and Atomistic Modeling.

The importance of phonons in the strong correlation phenomena observed in twisted-bilayer graphene (TBG) at the so-called magic-angle is under debate. Here we apply gate-dependent micro-Raman spectroscopy to monitor the G band line width in TBG devices of twist angles θ = 0° (Bernal), ∼1.1° (magic-angle), and ∼7° (large-angle). The results show a broad and p-/n-asymmetric doping behavior at the magic angle, in clear contrast to the behavior observed in twist angles above and below this point. Atomistic modeling reproduces the experimental observations in close connection with the joint density of electronic states in the electron-phonon scattering process, revealing how the unique electronic structure of magic-angle TBGs influences the electron-phonon coupling and, consequently, the G band line width. Overall, the value of the G band line width in magic-angle TBG is larger when compared to that of the other samples, in qualitative agreement with our calculations.

Si doping mechanism in MOVPE-grown (100) β-Ga2O3 films

A Langmuir adsorption model of the Si incorporation mechanism into metalorganic vapor-phase epitaxy grown (100) β-Ga2O3 thin films is proposed in terms of the competitive surface adsorption process between Si and Ga atoms. The outcome of the model can describe the major feature of the doping process and indicate a growth rate-dependent doping behavior, which is validated experimentally and further generalized to different growth conditions and different substrate orientations.

Development of Low‐Temperature Doping Process in CdSe‐Nanocrystal Thin Films for Flexible Electronic and Optoelectronic Devices

AbstractAn effective surface‐doping strategy for CdSe nanocrystals (NCs) by examining the size‐dependency of the doping behavior is introduced. A CdSe NC thin‐film transistor (TFT) is fabricated via a doping process with InCl3 treatment followed by an annealing process. Spectroscopic and electronic device characterization reveal that smaller NCs are more effectively doped than larger NCs at all annealing temperatures. This is attributed to the larger specific surface area, where the dopant can be more readily coordinated. The degenerate behavior of a 3.3 nm CdSe‐NC TFT appears at a lower temperature than that of larger NC TFTs. High electron mobility and on‐to‐off current ratio of 1.79 cm2 Vs−1 and 5.2 × 105, respectively are achieved, in a low‐temperature annealing process (150 °C) with 3.3 nm CdSe NCs. This facilitates the fabrication of a flexible CdSe‐NC TFT, which is demonstrated on a polyethylene terephthalate substrate with an Al2O3 dielectric layer using atomic layer deposition. The flexible 3.3 nm CdSe‐NC TFT is successfully fabricated even at 150 °C, with a high on‐to‐off current ratio and low hysteresis at a low operation voltage, which is impossible for larger CdSe‐NC TFTs.