Differential Reflectivity Research Articles

Plexciton Photoluminescence in Strongly Coupled 2D Semiconductor-Plasmonic Nanocavity Hybrid.

Strong plasmon-exciton interaction between two-dimensional transition metal dichalcogenides and a plasmonic nanocavity under ambient conditions has been reported extensively. But the suspicion on whether it has reached a true "strong coupling" is always there because the commonly used dark-field scattering spectroscopy shows a larger spectral splitting and the splitting in the photoluminescence spectra is absent. Here, by using a nanobipyramid-over-mirror to enhance the in-plane vacuum field, we achieve spectral Rabi splitting in both scattering and differential reflection spectra and observe a clear photoluminescence emission of the lower plexciton branch. The established nanocavity offers two polarization-dependent gap plasmon resonances to provide excitation and quantum yield enhancement simultaneously, yielding a total photoluminescence enhancement of 2.1 × 104 times. This allows the acquisition of emission spectra from an individual coupled system regardless of the presence of an uncoupled emitting background in the collection area. The sharp tips of the nanobipyramid lead to a large single-exciton coupling strength up to a few meV. Correlated scattering, differential reflection, and photoluminescence spectra reveal the similarity between the scattering and normalized photoluminescence spectra. These correlative measurements on a single coupled system clear up the suspicions of strong plasmon-exciton interactions and will promote the development of light-emitting plexcitonic devices at room temperature.

Dual-Polarization Radar Characteristics of Tropical Cyclone Tornadic and Nontornadic Supercells

Abstract Landfalling tropical cyclones (TCs) contain highly-sheared environments that are conducive for supercell thunderstorm development. These TC supercells can produce tornadoes, often with little warning. In this study, dual-polarization radar signatures of tornadic and nontornadic TC supercells are examined in the context of known extratropical supercell radar signatures. Prior studies have only presented dual-polarization characteristics of TC supercells using a case study approach. Therefore, this paper aims to create a more comprehensive picture with a larger sample of cases, and an attempt is made to distinguish differences between tornadic and nontornadic TC supercells that may hold operational promise. The environments and characteristic structure of these supercells are notably different from prior conceptual models of supercells developed. Differential reflectivity (ZDR) columns are shallower in TC supercells when compared to their extratropical counterparts. ZDR columns are also less common in TC cases. The ZDR arc is more pronounced in TC supercells, with maximum and mean ZDR values within the arcs being larger. Separation angle between the specific differential phase (KDP) foot and ZDR arc is larger in TC supercells than extratropical supercells. Tornadic TC supercells had significantly stronger low-level mesocyclones than nontornadic TC supercells as measured by normalized rotation (NROT). The observed differences may help operational meteorologists use these signatures more effectively in warning decisions and motive further research into the evolution of dual-polarization signatures in tornadic and nontornadic TC supercells.

Rapid Sampling and Polarimetric Statistics of Lightning With a Phased Array Radar

AbstractPrevious studies of lightning detection by radar mostly consisted of observations with reflector‐antenna systems yielding slow volume scan times. Phased array radars offer much faster scan times that are likely to capture echoes from propagating lightning channels. Rapidly updated range‐height indicator scans were used to observe severe storms that occurred in central Oklahoma with the fully digital S‐band Horus PAR to examine echoes from lightning plasma. Numerous lightning echoes were observed during the sampling period in good spatial and temporal agreement with lightning mapping array detections of very high frequency radiation sources. Statistically, they result in increased horizontal reflectivity factor, deviations in radial velocity and spectrum width, highly variable differential reflectivity and differential phase, and decreases in correlation coefficient. Results presented also highlight the capability of phased array radars to better observe lightning compared to current radars, and aid in the study of storm electrification and lightning physics.

Comparing and Optimizing Four Machine Learning Approaches to Radar-Based Quantitative Precipitation Estimation

To improve radar-based quantitative precipitation estimation (QPE) methods, this study investigated the relationship between radar reflectivity (Z) and hourly rainfall intensity (R) using data from 289 precipitation events in Shanghai between September 2020 and March 2024. Two Z-R relationship models were compared in terms of their fitting performance: Z = 270.81 R1.09 (empirically fitted relationship) and Z = 300 R1.4 (standard relationship). The results show that the Z = 270.81 R1.09 model outperforms the Z = 300 R1.4 model in terms of fitting accuracy. Specifically, the Z = 270.81 R1.09 model more effectively captures the nonlinear relationship between radar reflectivity and rainfall intensity, with a higher degree of agreement between the fitted curve and the observed data points. This model demonstrated superior performance across all 289 precipitation events. This study evaluated the performance of four machine learning approaches while incorporating five meteorological features: specific differential phase shift (KDP), echo-top height (ET), vertical liquid water content (VIL), differential reflectivity (ZDR), and correlation coefficient (CC). Nine QPE models were constructed using these inputs. The key findings are as follows: (1) For models with a single-variable input, the KAN deep learning model outperformed Random Forest, Gradient Boosting Decision Trees, Support Vector Machines, and the traditional Z-R relationship. (2) When six features were used as inputs, the accuracy of the machine learning models improved significantly, with the KAN deep learning model outperforming other machine learning methods. Compared to using only radar reflectivity, the KAN deep learning model reduced the MRE by 20.78%, MAE by 4.07%, and RMSE by 12.74%, while increasing the coefficient of determination (R2) by 18.74%. (3) The integration of multiple meteorological features and machine learning optimization significantly enhanced QPE accuracy, with the KAN deep learning model performing best under varying meteorological conditions. This approach offers a promising method for improving radar-based QPE, particularly considering seasonal, weather system, and precipitation stage differentiation.

An Investigation of Convective Boundary Layer Depth and Entrainment Zone Properties Using Dual-Polarization Radar and Balloon-Borne Observations

Abstract Previous work has shown that differential reflectivity ZDR observations from National Weather Service dual-polarization Doppler weather radars (WSR-88Ds) provide accurate estimates of convective boundary layer (CBL) depth when compared with depth estimates from 0000 UTC rawinsonde observations. We extend this work by launching small rawinsondes, called Windsonds, to study ZDR signals throughout the daytime hours. Results show that it can be difficult to identify CBL depth from ZDR alone when biological scatterers are absent. The exploration of other radar variables leads to the use of azimuthal ZDR variance to help in identifying CBL characteristics. A variable that combines both ZDR and azimuthal ZDR variance, called DVar, allows for improved signal identification using the quasi-vertical profile (QVP) method. Furthermore, the QVP channel width is found to be closely tied to the overall entrainment zone (EZ) structure. Results show that the centers and vertical extents of channels of reduced DVar in QVPs correlate well with sounding-observed CBL depth and EZ depth, respectively, across all stages of CBL development and in both clear and cloud-topped CBLs. The QVP approach tends to fail in identifying CBL and EZ depths when the vertical gradient in moisture above the CBL is small. Additionally, we compare the observed EZ depth to various EZ parameterizations and show that the parameterizations generally underestimate EZ depth. We conclude that the ability of WSR-88Ds to sample the CBL should be leveraged to increase our knowledge of CBL properties. Significance Statement The boundary layer is the lowest layer of Earth’s atmosphere and influences many weather-related phenomena. During the day, sunlight warms the surface and the convective boundary layer (CBL) forms. Even though CBL characteristics are important for accurate weather forecasts, current methods of observing the CBL are severely lacking. This study investigates the potential of using dual-polarization weather radars to expand CBL observations. We also evaluate how well simplified CBL models predict certain CBL characteristics and how they could be improved in the future.

Lightning and Radar Measures of Mixed-Phase Updraft Variability in Tracked Storms during the TRACER Field Campaign in Houston, Texas

Abstract Properties of 7488 thunderstorms are summarized for June–September 2022 during the Tracking Aerosol Convection Interactions Experiment (TRACER) field campaign Houston, Texas, using polarimetric weather radar and VHF 3D Lightning Mapping Array data. Automated tracking of storms linked each instrument’s measurements to a data-defined, time-evolving storm footprint. Within each storm, the depth and magnitude of episodic columns of radar differential reflectivity and specific differential phase quantified the prevalence of updrafts that activated mixed-phase precipitation pathways. Lightning measurements further distinguished the degree of rimed precipitation formation: the fraction of tracks with lightning varied from day to day and cells with lightning had stronger polarimetric columns. Track-level correlation of the lightning flash rate with radar polarimetric measures had substantial spread, showing that lightning provides an additional signal of mixed-phase precipitation processes that can complement future studies of thermodynamic and aerosol controls on cloud microphysics in the Houston region.

Low-temperature transport and relaxation of photo-carriers in TiS2

The investigation of non-equilibrium carrier dynamics in two-dimensional semi-metallic materials, particularly at low temperatures, is crucial for elucidating their fundamental properties, including carrier–carrier interactions and electron–phonon scattering mechanisms. In this study, we examine the behavior of 1T-TiS2, utilizing scanning photocurrent microscopy, bias voltage-adjustable photoresponse measurements, and pump-probe techniques to explore the temperature-dependent transport and relaxation of photo-excited charge carriers. We observe a non-monotonic intrinsic photocurrent in the biased device, with a pronounced peak feature occurring at approximately 25 K, which is corroborated by pump-probe measurements that reveal a similar peak in the magnitude and relaxation time of the differential reflectance as a function of the temperature. Our results highlight the unique carrier dynamics in TiS2, offering valuable insights for the design of TiS2-based optoelectronic devices that can operate effectively across a wide temperature range.

Temporal Associations Between Polarimetric Updraft Proxies and Signatures of Inflow and Hail in Supercells

Recurring polarimetric radar signatures in supercells include deep and persistent differential reflectivity (ZDR) columns, hail inferred in low-level scans, and the ZDR arc signature. Prior investigations of supercell polarimetric signatures reveal positive correlations between the ZDR column depth and cross-sectional area and quantitative characteristics of the radar reflectivity field. This study expands upon prior work by examining temporal associations between supercell polarimetric radar signatures, incorporating a dataset of relatively discrete, right-moving supercells from the continental United States observed by the Weather Surveillance Radar 1988-Doppler (WSR-88D) network. Cross-correlation coefficients were calculated between the ZDR column area and depth and the base-scan hail area, ZDR arc area, and mean ZDR arc value. These correlation values were computed with a positive and negative lag time of up to 45 min. Results of the lag correlation analysis are consistent with prior observations indicative of storm cycling, including temporal associations between ZDR columns and inferred hail signatures/ZDR arcs in both tornadic and nontornadic supercells, but were most pronounced in tornadic storms.

A Numerical Simulation of Convective Systems in Southeast China: A Comparison of Microphysical Schemes and Sensitivity Experiments on Raindrop Break and Evaporation

This study employed version 4.2.2 of the Weather Research and Forecasting (WRF) model for this simulation and applied two microphysics schemes, the Thompson scheme (THOM) and Milbrandt–Yau scheme (MY)—which are widely used in convective simulations—to simulate a mesoscale severe convective precipitation event that occurred in southeastern China on 8 May 2017. The simulations were then compared with dual-polarization radar observations using a radar simulator. It was found that THOM produced vertical structures of radar reflectivity (ZH) closer to radar observations and accumulated precipitation more consistent with ground-based observations. However, both schemes overestimated specific differential phase (KDP) and differential reflectivity (ZDR) below the 0 °C level. Further analysis indicated that THOM produced more rain with larger raindrop sizes below the 0 °C level. Due to the close connection between raindrop breakup, evaporation rate, and raindrop size, sensitivity experiments on the breakup threshold (Db) and the evaporation efficiency (EE) of the THOM scheme were carried out. It was found that adjusting Db significantly changed the simulated raindrop size distribution and had a certain impact on the strength of cold pool; whereas modifying EE not only significantly changed the intensity and scope of the cold pool, but also had great effect on the raindrop size distribution. At the same time, comparison with dual-polarization radar observations indicated that reducing the Db can improve the model’s simulation of polarimetric radar variables such as ZDR. This paper specifically analyzes a severe convective precipitation event in the Guangdong region under weak synoptic conditions and a humid climate. It demonstrates the feasibility of a method based on polarimetric radar data that modifies Db of THOM to achieve better consistency between simulations and observations in southeast China. Since the microphysical processes of different Mesoscale Convective Systems (MCSs) vary, the generalizability of this study needs to be validated through more cases and regions in the future.

Retrieving Estimates of the Storm‐Relative Wind Profile From the Vertical Variation of Hydrometeor Size Sorting Signatures

AbstractRaindrop fall speed increases with raindrop size. Because larger raindrops fall through a given layer of the atmosphere more quickly compared to smaller raindrops, they spend less time in the layer and, therefore, have less time to be acted on and advected by the storm‐relative winds. This results in hydrometeor size sorting which impacts the polarimetric radar variables such as differential reflectivity and specific differential phase . Previous work has shown a strong correlation between the mean storm‐relative wind in the sorting layer and the separation between regions of enhanced and at the bottom of the sorting layer. This study leverages this finding, along with a simple size sorting model, to construct radar‐derived estimates of the storm‐relative wind profile. The radar‐derived “pseudo‐hodographs” are well‐correlated with the magnitude and direction of the corresponding storm‐relative wind profiles. Further, these radar‐derived estimates of the storm‐relative winds are used to calculate estimates of shear and storm‐relative helicity, which also exhibit a strong correlation.

Retrieval of Parameters of Constrained Gamma Raindrop Size Distribution in South China

Abstract Raindrop size distributions (RSDs) retrieved from polarimetric radar observations have proven to be effective for understanding precipitation microphysics. However, the current RSD retrieval scheme from polarimetric radar observations (using radar reflectivity ZHH and differential reflectivity ZDR) in South China has been established for monsoon precipitation only. Using abundant RSD observations from 2D video disdrometers (2DVDs), this study constructs the high-precision shape–slope (μ–Λ) relationships of the constrained gamma (C-G) model for subgroups of ZHH and ZDR for not only monsoon but also premonsoon, typhoon, and dry seasons. The current RSD retrieval is only applicable for precipitation with rain rate: R > 5.0 mm h−1, and total raindrop number concentration: Nt > 1000 m−3. This study expanded the applicability of rain rate and number concentration with R > 0.5 mm h−1 and Nt > 100 m−3. The new retrieval scheme was tested in four typical rainfall cases and provided better accuracy in estimating mass-weighted mean diameters and normalized intercept parameters. The new scheme was also better suited for analyzing precipitation microphysics in South China, which helps to gain a better understanding of microphysics in various types of precipitation in this region.

A Localized Quantitative Precipitation Estimation for S-Band Polarimetric Radar in Taiwan

Abstract A polarimetric radar quantitative precipitation estimation (QPE) to estimate the rain rate R from specific attenuation A has been applied in Taiwan’s operational Quantitative Precipitation Estimation and Segregation Using Multiple Sensors (QPESUMS) system since 2016. A 3-yr (2016–18) drop size distribution (DSD) dataset from an operational Particle Size and Velocity (Parsivel) network was used to derive a localized coefficient as well as the α(K) function in the R(A) scheme for S-band radar, where α is a key parameter in the estimation of A and K is the linear fitted slope of differential reflectivity ZDR versus reflectivity Z. The local drop size distribution data were also used to derive the localized R(Z) and R(KDP) relationships, and the relationships were evaluated using radar observations in heavy rain cases. A synthetic quantitative precipitation estimate combining the localized R(A), R(Z), and R(KDP) relationships is compared to its operational counterpart and showed about 8% reduction in the normalized mean error for the mei-yu cases. Typhoon cases exhibited similar improvements by the localized QPE relationships but showed higher uncertainties than in the mei-yu cases. The higher uncertainties in the typhoon QPE verification were likely due to the stronger winds in typhoons than in the mei-yu events that caused greater mismatches between the radar observations at an altitude and the gauges at the ground. Overall, the results demonstrated advantages of localized radar rainfall relationships derived from the disdrometer data to improve the accuracy of the operational rainfall estimation products. Significance Statement A 3-yr (2016–18) drop size distribution (DSD) dataset from the operational Parsivel network in Taiwan was utilized to localize parameters in the QPE relationships for S-band dual-polarimetric radar. These relationships were evaluated using radar observations in the mei-yu front and typhoon events in Taiwan. The results show that using localized radar rainfall relationships derived from the disdrometer data can enhance the accuracy of the operational rainfall products.

Anisotropic Redox on Pristine Graphene

AbstractChemically modified graphene is an attractive electrode material for electrocatalysis, energy devices, and sensors, whereas pristine graphene is electrochemically passive. The remarkable anisotropic electrochemical nature of graphene is uncovered by π–π interaction, making pristine graphene more active than bare Au. The π–π stacking during redox reaction “dopes” the graphene, disrupting the passivating hydration layer, making it a facile electrochemical electrode. The structure during π–π stacking‐mediated redox of methylene blue (MB) is quantitatively measured by the differential reflectivity of a polarized laser on a ≈100 micron spot. The local redox reaction current varies over fourfold due to the orientation of the ≈10 micron size grains. The mosaic‐grain anisotropy on each spot shows local uniaxial orientation. The redox signal at the optimum orientation is over 2.5‐fold greater than that for bare Au on the same electrode. The redox signal is over fivefold greater at the edges of graphene compared bare Au. Remarkably, the π–π interaction increases chemical stability significantly, leading to negligible photo‐degradation at the approximate absorption wavelength of MB. The exclusive redox activity due to π–π interaction on pristine graphene adds to the toolbox of making exotic opto‐electrochemical electrode materials for electrocatalysis, sensing, and electronics.

Active differential reflection coefficient analysis of differentially-fed antenna array

In this paper, a definition for the active differential reflection coefficient of the differentially-fed antenna array is proposed. Each antenna is fed by the differential port with the equal-amplitude anti-phase signal input. According to the active reflection coefficient of the conventional single-ended antenna array, the active differential reflection coefficient definition of the differential antenna array is given and analyzed. It is derived that the active differential reflection coefficient of the differential port m is half of the active reflection coefficient sum for the single-ended port m + and m −. In addition, the active differential impedance expression is also given. To verify the active differential reflection coefficient, a differential three-element microstrip patch antenna array was designed, fabricated, and measured. The experimental results validate the proposed theoretical analysis. This work will provide a new insight into the differential antenna array.

Phase-Selective Synthesis of Rhombohedral WS2 Multilayers by Confined-Space Hybrid Metal-Organic Chemical Vapor Deposition.

Rhombohedral polytype transition metal dichalcogenide (TMDC) multilayers exhibit non-centrosymmetric interlayer stacking, which yields intriguing properties such as ferroelectricity, a large second-order susceptibility coefficient χ(2), giant valley coherence, and a bulk photovoltaic effect. These properties have spurred significant interest in developing phase-selective growth methods for multilayer rhombohedral TMDC films. Here, we report a confined-space, hybrid metal-organic chemical vapor deposition method that preferentially grows 3R-WS2 multilayer films with thickness up to 130 nm. We confirm the 3R stacking structure via polarization-resolved second-harmonic generation characterization and the 3-fold symmetry revealed by anisotropic H2O2 etching. The multilayer 3R WS2 shows a dendritic morphology, which is indicative of diffusion-limited growth. Multilayer regions with large, stepped terraces enable layer-resolved evaluation of the optical properties of 3R-WS2 via Raman, photoluminescence, and differential reflectance spectroscopy. These measurements confirm the interfacial quality and suggest ferroelectric modification of the exciton energies.

Enhanced thermal stability photophysical properties of photoselective PMMA/ITO nanohybrid films for greenhouse cooling in hot climates

The current research proposed innovative photoselective greenhouse cooling films made from PMMA/ITO nanohybrids, incorporating varying concentrations of Indium tin oxide nanocrystals (ITO NCs) and the fluorescent organic dye Lumogen F Red300, utilizing the solvent casting method. The morphology and structure were examined using transmission electron microscopy (TEM) and X-ray diffraction (XRD), demonstrating good homogeneity and amorphous nature. The impact of different ITO NC concentrations on physical properties was examined through differential scanning calorimetry (DSC), optical absorption, transmission, reflection, fluorescence, and Fourier transform infrared (FT-IR) spectroscopy. Integrating ITO NCs into the PMMA matrix showed enhanced thermal insulation capabilities of PMMA films while maintaining their transparency to photosynthetically active radiation (PAR). Maintaining this balance is crucial because it enables the films to selectively filter and reflect infrared radiation leading to lower greenhouse temperatures while still allowing the essential light needed for plant growth to pass through. This research is particularly significant for Sustainable Development Goals (SDGs) 2 and 13, especially in hot, water-scarce regions, as it protects plants from thermal stress, promotes growth, and supports food security in developing countries.

Change of composition and surface plasmon resonance of Pd/Au core/shell nanoparticles triggered by CO adsorption.

Controlling composition and plasmonic response of bimetallic nanoparticles (NPs) is of great relevance to tune their catalytic activity. Herein, we demonstrate reversible composition and plasmonic response transitions from a core/shell to a bimetallic alloyed palladium/gold NP triggered by CO adsorption and sample temperature. The use of self-organized growth on alumina template film allows scrutinizing the impact of core size and shell thickness onto NP geometry and plasmonic response. Topography, molecular adsorption, and plasmonic response are addressed by scanning tunneling microscopy, vibrational sum frequency generation (SFG) spectroscopy, and surface differential reflectance spectroscopy, respectively. Modeling CO dipolar interaction and optical reflectivity corroborate the experimental findings. We demonstrate that probing CO adsorption sites by SFG is a remarkably sensitive and relevant method to investigate shell composition and follow in real-time Pd atom migration between the core and the shell. Pd-Au alloying is limited to the first two monolayers of the shell and no plasmonic response is found, while for a thicker shell, a plasmonic response is observed, concomitant with a lower Pd concentration in the shell. Above 10-4mbar, at room temperature, CO adsorption triggers the shell restructuration, forming a Pd-Au alloy that weakens the plasmonic response via Pd migration from the core to the shell. NP annealing at 550K, after pumping CO, leads to the desorption of remaining CO and gives enough mobility for Pd to migrate back inside the core and recover a pure gold shell with its original plasmonic response. This work demonstrates that surface stoichiometry and plasmonic response can be tuned by using CO adsorption and NP annealing.

Charge dynamics in the 2D/3D semiconductor heterostructure WSe2/GaAs

Understanding the relaxation and recombination processes of excited states in two-dimensional (2D)/three-dimensional (3D) semiconductor heterojunctions is essential for developing efficient optical and (opto)electronic devices, which integrate van der Waals 2D materials with more conventional 3D ones. In this work, we unveil the carrier dynamics and charge transfer in a monolayer of WSe2 on a GaAs substrate. We use time-resolved differential reflectivity to study the charge relaxation processes involved in the junction and how they change when compared to an electrically decoupled heterostructure, WSe2/hBN/GaAs. We observe that the monolayer in direct contact with the GaAs substrate presents longer optically excited carrier lifetimes (3.5 ns) when compared with the hBN-isolated region (1 ns), consistent with a strong reduction of radiative decay and a fast charge transfer of a single polarity. Through low-temperature measurements, we find evidence of a type-II band alignment for this heterostructure with an exciton dissociation that accumulates electrons in GaAs and holes in WSe2. The type-II band alignment and fast photoexcited carrier dissociation shown here indicate that WSe2/GaAs is a promising junction for advanced photovoltaic and other optoelectronic devices, making use of the best properties of van der Waals (2D) and conventional (3D) semiconductors.

Application of Ce2(WO4)3–ZnO–CuO nanocomposite as active photocatalyst for removal of ciprofloxacin from wastewater

In this study, the synthesis of Ce2(WO4)3/ZnO/CuO nanocomposite (NCs) was carried out using Co-precipitation method. The structural, morphological and spectral confirmation was achieved through X-ray diffraction (XRD), Scanning electron microscopy (SEM), Differential reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR) analysis. The degradation efficiency for photocatalytic degradation of Ciprofloxacin (CF) and band gap value of prepared Ce2(WO4)3/ZnO/CuO nanocomposite was determined by using UV–Visible and DRS analysis. Band gap value for Ce2(WO4)3/ZnO/CuO was found to be 1.39 eV. Effects of different parameters such as contact time, pH, and effect of concentration of catalyst were investigated to optimize degradation conditions. This prepared nanocomposite was used for the degradation of CF and about 91 % degradation efficiency of CF has been achieved at pH 5 within 70 min by irradiation under sunlight and 60 mg concentration of photocatalyst. The EDTA and IPA scavenged photo-generated holes and hydroxyl ions respectively, the decrease in photocatalytic degradation indicates that holes and hydroxyl ions are reactive species in photocatalytic degradation of CF. The value of R2 = 0.99 confirms the validity of Pseudo first order and Langmuir-Hinshelwood kinetic model for the degradation of CF. These results showed a novel method for the preparation of nanocomposite and the efficient degradation of antibiotics and can be applied to industrial manufacture.

Effect of ground-state charge transfer on photoexcited charge transfer in transition metal dichalcogenide heterostructures

We report an experimental investigation on the effect of ground-state charge transfer and its induced electric field on photoexcited charge transfer in van der Waals heterostructures. Two heterostructure samples were fabricated by stacking an undoped WSe2 monolayer with either a Nb-doped or undoped MoSe2 monolayer. While no ground-state charge transfer is expected in the MoSe2/WSe2 heterostructure, the doped holes in the MoSe2:Nb/WSe2 heterostructure can transfer to WSe2, creating a space-charge electric field. By comparing the photoluminescence and time-resolved differential reflectance of the two heterostructures, we find that photoexcited hole transfer from MoSe2 to WSe2 is largely blocked by this field, whereas photoexcited electron transfer from WSe2 to MoSe2 is less affected. These results provide insight into the impact of doping on the charge-transfer performance of van der Waals heterostructures.