Dot Size Research Articles

Interdiffusion Induced Changes in the Absorption Spectra of III-V Quantum Dot Systems

III-V Semiconductor quantum dots (QDs) grown with growth interruption technique do not have uniform group III composition inside the dot. Modelling such as-grown structures requires in-depth knowledge of the composition and potential well profile. In this work, we have developed a three-dimensional analytical model which incorporates strain, as well as the variation of group III composition profile in both lateral and vertical directions inside an as-grown QD in order to quantify the effect of dot size variation on the interband optical absorption spectra of as-grown QD systems. Earlier reports on this subject considered the variation of either the dot height or base to account for the size deviation, which may not be sufficient enough to predict the dot size distribution in realistic systems, where all dimensions are likely to suffer from deviation. Keeping this in mind, Gaussian distribution of dot volume has been adopted here to consider the variations of height and base of QDs in a cumulative way. In our study, we considered InGaAs/GaAs and InGaN/GaN QD systems. The non-uniform distribution of indium inside the as-grown dot leads to a non-rectangular potential well profile, which eventually transforms into a rectangular one after annealing. Through the proposed model, we have investigated the effect of inhomogeneous indium composition and dot size variation on the optical absorption spectra of InGaAs/GaAs and InGaN/GaN as-grown QD systems through Gaussian distribution of dot volume. We have also discussed the effect of size deviation on the full width at half maxima (FWHM) of both as-grown and annealed QD systems. Emphasis has been given to the changes in the conduction and valence band potential profiles due to changes in the morphology inside the dot leading to subsequent changes in the energy levels caused by composition uniformity due to annealing and interdiffusion, thus modifying the nature of absorption spectra.

An Image Processing Approach to Quality Control of Drop-on-Demand Electrohydrodynamic (EHD) Printing.

Droplet quality in drop-on-demand (DoD) Electrohydrodynamic (EHD) inkjet printing plays a crucial role in influencing the overall performance and manufacturing quality of the operation. The current approach to droplet printing analysis involves manually outlining/labeling the printed dots on the substrate under a microscope and then using microscope software to estimate the dot sizes by assuming the dots have a standard circular shape. Therefore, it is prone to errors. Moreover, the dot spacing information is missing, which is also important for EHD DoD printing processes, such as manufacturing micro-arrays. In order to address these issues, the paper explores the application of feature extraction methods aimed at identifying characteristics of the printed droplets to enhance the detection, evaluation, and delineation of significant structures and edges in printed images. The proposed method involves three main stages: (1) image pre-processing, where edge detection techniques such as Canny filtering are applied for printed dot boundary detection; (2) contour detection, which is used to accurately quantify the dot sizes (such as dot perimeter and area); and (3) centroid detection and distance calculation, where the spacing between neighboring dots is quantified as the Euclidean distance of the dot geometric centers. These stages collectively improve the precision and efficiency of EHD DoD printing analysis in terms of dot size and spacing. Edge and contour detection strategies are implemented to minimize edge discrepancies and accurately delineate droplet perimeters for quality analysis, enhancing measurement precision. The proposed image processing approach was first tested using simulated EHD printed droplet arrays with specified dot sizes and spacing, and the achieved quantification accuracy was over 98% in analyzing dot size and spacing, highlighting the high precision of the proposed approach. This approach was further demonstrated through dot analysis of experimentally EHD-printed droplets, showing its superiority over conventional microscope-based measurements.

Anchoring Perovskite-Like Bi4Ti3O12 and Plasmonic Bi on Defect-Rich Yellow TiO2-x for Enhanced Catalytic Activity toward Degradation of Pollutants upon Visible Light.

The efficiency of heterogeneous photocatalytic processes is currently limited due to the fast recombination of photocarriers, poor light absorption, and inefficient surface catalytic characteristics. In this study, defect-rich yellow TiO2-x nanoparticles (abbreviated as D-TiO2) with high surface area and significant absorption in the visible range were integrated with perovskite-like Bi4Ti3O12 to synthesize binary D-TiO2/Bi4Ti3O12 nanocomposites. To overcome the problem of insufficient activity, we integrated the optimized D-TiO2/Bi4Ti3O12 nanocomposite with plasmonic Bi nanoparticles. Significantly, the optimized D-TiO2/Bi4Ti3O12/Bi-2 nanocomposite efficiently removed tetracycline (TC) in 50 min through production of •OH, h+, and •O2- species, whose removal rate promoted 10.6, 3.18, 5.01, and 1.84 compared with the white TiO2 (abbreviated as W-TiO2), D-TiO2, Bi4Ti3O12, and D-TiO2/Bi4Ti3O12 (20%) photocatalysts, respectively. The outstanding performance of the D-TiO2/Bi4Ti3O12/Bi photocatalyst was attributed to its quantum dot size, low resistance for charge migration, increased surface area, oxygen vacancies in D-TiO2, and developed n-n heterojunction among D-TiO2 and Bi4Ti3O12, which accelerated charge transfer and promoted the generation of active species. Furthermore, the stability tests showed that the TC degradation efficiency still reached 96% after four recycles, indicating the remarkable stability of the photocatalyst. Eventually, the biocompatible nature of the treated solution over the optimized photocatalyst was also revealed from an investigation of the growth of lentil seeds.

Numerical study of P3HT-based hybrid solid-state qantum dot solar cells with CdS quantum dots employing different metal oxides using SCAPS-1D

This study presents a comprehensive numerical investigation into solid-state quantum dot solar cells (SSQDSCs) utilizing P3HT poly(3-hexylthiophene) as both a hole transport and absorber layer employing SCAPS-1D simulation software, the research explores the performance of cells composed of FTO (Fluorine-doped Tin Oxide) as the front contact, integrated with different metal oxides (Titanium dioxide (TiO2), zinc oxide (ZnO), and tin dioxide (SnO2), CdS (Cadmium sulfide )quantum dots, P3HT, and Pt (platinum )as the back contact namely Hybrid solar cell. The thickness of each layer is systematically optimized, and the influence of various CdS quantum dots sizes is thoroughly examined. The study also dived into the characterization of interface defects at the P3HT/CdS junction, involving modifications to the electron affinity of P3HT. Additionally, the impact of metal work function variations was also investigated analyzing at each case critical parameters such as open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF), power conversion efficiency (PCE) and quantum efficiency. The results demonstrate that optimization of these parameters has the potential to elevate solar cell efficiency to 18%. These simulation findings offer valuable insights for comparative analysis and a deeper understanding of the challenges encountered in experimental research.

Highly sensitive and selective ratiometric fluorescence and colorimetric detection of Cr(VI) via in situ encapsulation of green/red carbon quantum dots in zeolite

To overcome the limitations arising from non-uniform particle size and solid-state aggregation of carbon quantum dots (CQDs), a novel dual-emissive ratiometric fluorescence probe, GCQDs@SBA-15/RCQDs@SBA-15 (G-RCQDs@SBA-15), has been successfully constructed by simplifying the synthesis process through in situ synthesis of CQDs in SBA-15 to further enhance their optical properties for highly sensitive detection of Cr(VI). The probe G-RCDs@SBA-15, based on green-emission carbon quantum dots (GCQDs) encapsulated in mesoporous molecular sieves SBA-15, provides the response signal, while red-emission carbon quantum dots (RCQDs) encapsulated in SBA-15 serve as an internal reference. The probe exhibits a satisfactory limit of detection (LOD) of 0.336 μM, which is 52 % lower than GCQDs/RCQDs. Importantly, the probe shows superior selectivity in detecting Cr(VI) compared to other metal ions. The fluorescence signal ratio of the probe decreases with increasing Cr(VI) concentration, resulting in a distinct change of fluorescence color from green to red. Based on UV–vis and fluorescence lifetime analysis, Inner filter effect (IFE) is considered the primary potential mechanism for the fluorescence color transition of G-RCDs@SBA-15 following the addition of Cr(VI). G-RCQDs@SBA-15 not only inherits the excellent optical properties of GCQDs and RCQDs but also shows high fluorescence and chemical stability. Considering the sensitive photoconversion properties of G-RCQDs@SBA-15, a smartphone-based laboratory device in combination with RGB analysis software has been used for Cr(VI) detection by directly capturing and analyzing fluorescence images. In addition, the sensing system is validated in the actual lake water samples, exhibiting recoveries from 83.3 % to 96.3 %, indicating its excellent practicality for Cr(VI) detection in real samples.

The effect of laser energy on the size of WS2 quantum dots synthesized by pulsed laser ablation in liquid

The effect of laser energy on the size of WS2 quantum dots synthesized by pulsed laser ablation in liquid

Effects of etching duration on silicon quantum dot size and photoluminescence quantum yield

Abstract The synthesis of silicon quantum dots (SiQDs) via thermal pyrolysis is considered promising due to its cost-effectiveness. The etching process in this method has the potential to control the size of SiQDs precisely and has thus garnered attention. However, there are varying observations regarding the effect of etching duration on SiQD size. Additionally, the impact of dioxonium hexafluorosilicate (DH), a byproduct of the etching process, on the photoluminescence (PL) quantum yield (QY) of SiQDs remains unclear. This study investigates the effect of etching duration on the physical and optical sizes as well as the PLQY of SiQDs. The results indicate that extending the etching duration decreases the physical size of SiQDs, while the optical size initially increases slightly before decreasing. The SiQDs transition through three phases with increasing etching duration: oxidation removal, shallow over-etching, and deep over-etching. Both amorphous silicon (a-Si) in the oxidation removal phase and DH in the deep over-etching phase act as non-radiative recombination centers, thereby reducing the PLQY of SiQDs. Therefore, optimizing the etching duration to achieve the shallow over-etching phase is essential. This study provides new insights into the effects of etching duration on SiQD size and PLQY, aiding in the preparation of higher-quality SiQDs.

Zeolite-decorated black TiOx quantum dots for photocatalytic degradation of organic cationic dyes under LED light irradiation

Defect engineering is a promising strategy to reduce the band gap of semiconductors, enhancing their photocatalytic activity under visible light by introducing intra-bandgap energy states. Among the materials studied, oxygen-deficient black TiOx stands out due to its potential in photocatalytic reduction and hydrogen evolution. However, the valence band edge maximum (VBM) of TiOx is not thermodynamically favorable for the direct oxidation of water to hydroxyl radicals (H2O/•OH). Although the formation of extensive oxygen vacancies is necessary to extend the light absorption of black TiOx to longer wavelengths, a high density of oxygen vacancies (Ov) significantly shortens the diffusion length of charge carriers within the TiOx, leading to increased recombination of electrons and holes (e-/h+), thereby suppressing photocatalytic activity. To overcome these limitations, confining TiOx particles to the quantum dot (QD) size range and constructing heterojunctions with a secondary phase can substantially improve charge carrier separation and photocatalytic performance. In addition to engineering the electronic structure of composite photocatalysts, the preaccumulation of pollutants and their subsequent degradation is an effective strategy. This method decreases the distance between the adsorbed pollutant and the active sites for reactive oxygen species (ROSs) generation, enhancing the efficiency of the photocatalytic degradation process. In this study, we confined TiOx particles to the quantum dot size range by constructing a heterojunction with H-Beta zeolite, which contains defect-induced energy states within its wide band gap. This type of zeolite is particularly effective in adsorbing cationic azo dyes, facilitating pre-accumulation and degradation. The synthesized catalysts were extensively characterized using HRTEM to determine the average size of the TiOx particles and photoluminescence (PL) analysis to investigate charge carrier separation. Our results demonstrated that while TiOx alone showed negligible degradation efficiency, and no •OH were detected, the QD TiOx/Z4 composite achieved complete oxidation of CV by •OH, as confirmed by TOC analysis. The photocatalytic degradation mechanism was proposed based on these experimental findings. These insights could be of significant interest to researchers exploring defective semiconductors for photocatalytic oxidation of organic pollutants in the liquid phase under visible light (LED) irradiation.

Optical Properties of Multilayered Staggered SiGe Nanodots Depending on Si Spacer Growth Temperature

The optical properties of the multilayered staggered SiGe nanodots (NDs) embedded in the Si spacers fabricated at varying Si growth temperatures are clarified in conjunction with the effect of strain by Photoluminescence (PL) and Raman spectroscopy. We found that compressive strain is induced in the SiGe NDs, with higher growth temperatures of the Si spacer resulting in stronger compressive strain. PL spectra indicate that the higher growth temperature leads to a wider bandgap. This transition energy behavior is caused by not only the strain in the SiGe NDs but also the Ge segregation. Furthermore, luminescence from the SiGe NDs was observed along with luminescence originated at the Si/SiGe interface in the SiGe NDs with a small dot size. This phenomenon was caused by the small energy difference of the conduction-band minima between the SiGe NDs and the tensile-strained Si spacers and the small volume of the tensile-strained Si spacers.

On-site monitoring of L-adrenaline neurotransmitter in biological samples by chitosan oligosaccharide derived carbon dots

Carbon quantum dots (CDs) are fascinating fluorescent nanomaterial for spectrofluorimetry sensor applications, owing to the fact of its strong chemical stability, high quantum yield and high photostability. At this instance, we have developed the fluorescent sensing technique to detect the L-adrenaline (L-Adr) by nitrogen-doped carbon quantum dots as a sensing probe. The nitrogen-doped carbon dots was synthesized using chitosan oligosaccharide by hydrothermal method. The synthesized chitosan oligosaccharide derived CDs (COL-CDs) exhibits blue fluorescence under UV light and the size of the carbon quantum dots is 3.39 ± 0.08 nm calculated from HR-TEM image. The hormone called L-Adr found in the human body is crucial for controlling visceral processes. Utilizing the process of photo-induced electron transfer (PET), the previously mentioned COL-CDs have applied to sense the L-Adr. The sensing mechanism have explained clearly using Rehm-Weller equation by calculating ΔG. Tap water, blood serum, urine and adrenaline drug samples employed as real sample for the sensing L-Adr. A reagent free paper-based kit established for the purpose of on-site monitoring L-Adr. The smartphone’s colour picker software used to measure the RGB intensity from the paper-based kit.

Study of dot size effect on electron emission from Si-QDs multiple-stacked structures

We have fabricated diodes with different sized Si quantum dots (QDs) by precisely controlled low-pressure chemical vapor deposition using a pure SiH4 gas and studied the effect of dot size on field electron emission properties of their multiple‒stacked structures. At an applied bias of ∼9 V, the emission current of ∼4.0 nm height dot‒stacks is two orders of magnitude higher than that of ∼5.9 nm height dot‒stacks. These results can be interpreted in terms of an increase in the number of electrons with higher kinetic energy due to the increase in discrete energy levels associated with the reduction in the dot size, which suppresses electron scattering within the dot, and the electric field concentration resulting from the decrease in the curvature of the dot.

Synthesis and Characterization of CdS and Sr-Doped CdS Quantum Dots: Impedance Analysis for Nano-Tuned Electronic Applications

This study reports the synthesis and comprehensive characterization of cadmium sulfide (CdS) and strontium-doped CdS quantum dots (QDs) using a straightforward chemical precipitation method. N, N-Dimethylformamide served as the stabilizing agent, while specific metal precursors facilitated the formation of the nanostructures. The incorporation of strontium into the CdS matrix aimed to enhance the electronic properties of the quantum dots. Energy Dispersive X-ray Analysis (EDAX) confirmed the successful doping of Sr into the CdS QDs. X-ray Diffraction (XRD) analysis verified the high-crystallinity of the synthesized quantum dots, with the mean crystal sizes determined to be 3.18 nm for pure CdS and 3.99 nm for Sr-doped CdS (2mM and 4mM concentrations). Impedance spectroscopy was utilized to study the frequency-dependent electrical properties of the QDs at room temperature, revealing significant variations in impedance with frequency. The results demonstrated that both pure and Sr-doped CdS QDs exhibit capacitive admittance, which is indicative of their potential application in nano-tuned electronic devices. The ability to fine-tune the resonant frequency by controlling the size and doping level of the quantum dots presents a significant advantage for their use in advanced electronic applications. The study highlights the promising application of CdS and Sr-doped CdS quantum dots in the development of high-performance, frequency-tunable nanoscale electronic devices.

Influence of He injection amount on the microstructure of ion irradiated Cr0.8FeMnNi medium entropy alloy compared with 316L stainless steel

In recent years, medium and/or high-entropy alloys (M/HEAs) have attracted attention due to their excellent mechanical properties, positioning them as potential candidates for structural materials in advanced nuclear reactors. This study investigated the effect of He injection amount on the microstructural evolution in Cr0.8FeMnNi MEA and 316L stainless steel. Helium atoms were injected, followed by Fe2+ irradiation. Transmission electron microscopy was used to characterize the irradiation-induced defects. The primary irradiation-induced defects observed across all He injection amounts were black dots; no voids were seen under any irradiation conditions. In He-injected Cr0.8FeMnNi, the number density of black dots was significantly lower than in non-He-injected Cr0.8FeMnNi, while the average size of black dots increased with higher He injection rates. As the He injection amount increased, the binding energy of the self-interstitial atom (SIA) to the He-V complex decreased. This reduction facilitated the nucleation and growth of numerous SIA clusters within the matrix, consequently increasing the number density of black dots. The change in the number density of black dots in Cr0.8FeMnNi was much smaller than that observed in 316L. This could be ascribed to the enhanced self-healing process caused by the diversity of point defects and higher lattice distortion in Cr0.8FeMnNi.

Antimony composition impact on band alignment in InAs/GaAsSb quantum dots

We present a theoretical study of the electronic and excitonic states in InAs/GaAsSb quantum dots. We first center our study on the dependence of the antimony composition in the positioning of conduction- and valence-band alignments in InAs/GaAsSb/GaAs heterostructures. We predict a transition from type I to type II quantum dots at critical composition xc=0.128, which describes well the experimental trend. We discuss the influence of the quantum dot size and antimony composition on the spatial distributions of carriers and the exciton binding energy. We find that the ground state exciton binding energy is always significantly smaller ≃4meV for type II than for corresponding type I quantum dots ≃14meV. Finally, we also predict the excitonic radiative lifetime and find 1 ns for type I and 10 ns for type II quantum dots, in agreement with the existing experimental literature.

Surface structure-based model to calculate thermal and optical properties in nanoscale and quantum dot semiconductors

Surface combination structure was used to design the construction of nano and quantum films, particles, and dots. The created model was applied to tetrahedral semiconductor nanoparticles and quantum dots with a successful performance. It works better than reported experimental data across the whole size range, from the bulk state to the critical size of quantum dots. The model helps to figure out the melting point that changes with the nanosize scale as applied on Si and Sn, which are simple tetrahedral semiconductors, and for CdS and CdSe, which are among II-VI group compounds. It was also used to calculate melting-related parameters such as cohesive energy, Debye temperature, vibrational entropy, and melting enthalpy. The nanosize dependence of the lattice volume and the atom's ionization energy describes the solid surface structure. From the model, an equation was obtained to calculate the energy gaps in Si, CdS, and CdSe particles that are nano- and quantum-dot-sized, and the results are compared to the experimental data that goes with these particles.

Influence of Material Properties on Surface Chemistry Induced Circular Dichroism in Halide Perovskite: Computational Insights.

The chirality transfer phenomenon is attractive for enhancing the optical functionality of nanomaterials by inducing sensitivity to the circular polarization states of photons. An underexplored aspect is how material properties of the achiral semiconductor impact the induced chiroptical signatures. Here we apply atomistic time-dependent density functional theory simulations to investigate the material properties that influence the chiroptical signatures of a lead halide perovskite nanocrystal with a chiral molecule bound to the surface. First, we find that both lattice disorder created by surface strain and halide substitution can increase the chiroptical response of the perovskite quantum dots by an order of magnitude. Both phenomena are attributed to a broadening of the density of the electronically excited states. Second, the intensity of the anisotropy spectra decreases with increasing dot size with a power law decay. Overall, these insights can be used to help guide experimental realization of highly resolvable polarized optical features in semiconducting nanomaterials.

Molecular dynamics simulations on TiO2 quantum dots modified asphalt: Impact of size and concentration of quantum dots

With exceptional solar reflectivity and fluorescent characteristics, TiO2 quantum dots (QDs) modified asphalt has been proposed as an innovative cool pavement technology. However, interaction mechanism and thermodynamic properties of TiO2 QDs modified asphalt at microscale have not been well understood. In this study, electronic and optical properties of TiO2 QDs with varied sizes were investigated based on quantum mechanics (QM) calculations. Moreover, molecular dynamics (MD) simulations were implemented to evaluate mechanical moduli and intermolecular dynamics of TiO2 QDs modified asphalt with different quantum sizes and concentrations. The results from QM calculations unveil that as size of TiO2 QDs rises from 6 Å to 12 Å, energy gap and binding energy of TiO2 QDs decreases by 0.928 eV and 526.38 eV, respectively while density of state (DOS) and absorption coefficient of TiO2 QDs increases. Besides, the results from MD simulations reveal that quantum size imposes significant impact on mechanical moduli of modified asphalt while concentration of TiO2 QDs brings notable influence on interaction between quantum dots and asphalt. Specifically, as concentration of QDs rises from 10 % to 30 %, cohesive energy density (CED) and solubility parameter (SP) of modified asphalt is improved by up to 457 % and 136 %, respectively. With increasing quantum size, bulk modulus, shear modulus, and Young’s modulus of modified asphalt is enhanced by up to 372 %, 206 % and 24 %, respectively. The outcomes of this study provide insights into formula and application of advanced asphalt pavement with TiO2 QDs.

The Impact of the Gain Medium Properties and the Resonator Morphology on the Whispering Gallery Mode Spectrum of Polystyrene Microspheres Coated with AgInS2/ZnS Quantum Dots

The modulation of fluorophore emission by whispering gallery modes (WGMs) in active spherical resonators holds great potential for advanced photonic devices. In the present work, we fabricate and systematically study a series of active WGM resonators based on polystyrene microspheres and heavy metal-free ternary AgInS2/ZnS quantum dots with broad and tunable photoluminescence bands coated on their surface as a gain medium. The variation in the mean size and emission wavelength of the quantum dots allowed us to establish a correlation between their characteristics and the WGM properties, including the resonance peaks intensity profile and the Q-factors. Other aspects such as coupling efficiency, polarization-dependent mode damping, and peak broadening are also discussed. Furthermore, we applied statistical analysis on multiple individual resonators within the batch to calculate the standard deviation of the resonator size and ellipticity. Our study highlights that both the cavity and the gain medium influence the WGM parameters in active spherical resonators.

Continuous flow production of bioactive ceria quantum dots: New paradigms to the effect of process parameters on surface oxygen vacancy tuning

Precisely monitored nucleation-growth kinetics for governing the size, surface chemistry, and sought-after attributes of quantum dots (QDs) for large-scale manufacturing remains a formidable challenge. This study evinces the importance of ultrafast mixing and high heating rates for rapid nucleation, particularly in synthesizing monodispersed QDs with enriched surface defects. Recently, cerium oxide (CeO2) nanostructures have gained prominence in antioxidant therapy owing to the co-existence of Ce3+ and Ce4+. However, current batch processes lack scalability, reproducibility, and control over the reaction kinetics, key for fine-tuning the surface defect-driven properties of CeO2 nanostructures. Addressing this knowledge gap, we demonstrate a unique, sustainable, continuous flow platform that allows simultaneous engineering of surface oxygen vacancies (VO●) and regulates the size of L arginine functionalized CeO2 QDs (VO●-rich l-arg-CeO2 QDs). Introduction of the helical coil reactor regulated by dean vortices yields monodispersed QDs with enhanced Ce3+/Ce4+ratio and VO● at the surface. Through various experimental methodologies, we showed how adjusting temperature, flowrate, and pH enables achieving the desirable size (3 nm), thereby bestowing an optimal surface Ce3+ and VO● fractions, pivotal for size-dictated photo-response, physiochemical properties, and biofunctionality of the QDs. The abundant surface VO● (72 %) entails narrowing of the band gap (∼ 2.5 eV), resulting in unprecedented photothermal response (ΔT = 19.7 ± 0.6 °C) and photoluminescence, features not typically found in defect-free conventional CeO2 nanostructures. With a strategic combination of process parameters, the defect-rich material system displayed excellent biocompatibility (95.6 %), and antioxidant efficacy on human keratinocyte (HaCaT) cells, and long-term stability (ζ = -29±1.5 mV) in suspensions, even after 120 days. This economical, high throughput continuous flow platform for fabricating biofunctionalized VO●-rich l-arg-CeO2 QDs outperforms conventional batch processes, opening numerous possibilities for lab-to-clinic translation in the fight against oxidative stress-related disorders.

Mapping of valley splitting by conveyor-mode spin-coherent electron shuttling

In Si/SiGe heterostructures, the low-lying excited valley state seriously limits the operability and scalability of electron spin qubits. For characterizing and understanding the local variations in valley splitting, fast probing methods with high spatial and energy resolution are lacking. Leveraging the spatial control granted by conveyor-mode spin-coherent electron shuttling, we introduce a method for two-dimensional mapping of the local valley splitting by detecting magnetic field-dependent anticrossings of ground and excited valley states using entangled electron spin-pairs as a probe. The method has sub-μeV energy accuracy and a nanometer lateral resolution. The histogram of valley splittings spanning a large area of 210 nm by 18 nm matches well with statistics obtained by the established but time-consuming magnetospectroscopy method. For the specific heterostructure, we find a nearly Gaussian distribution of valley splittings and a correlation length similar to the quantum dot size. Our mapping method may become a valuable tool for engineering Si/SiGe heterostructures for scalable quantum computing.