Oxygen-terminated Surface Research Articles

Oxygen-Terminated Polycrystalline Boron-Doped Diamond Superhydrophobic Surface with Excellent Mechanical and Thermal Stabilities.

Superhydrophobic surfaces are of great interest because of their remarkable properties. Due to its maximal hardness and chemical inertness, diamond film has great potential in fabricating robust superhydrophobic surfaces. In the present study, an oxygen-terminated polycrystalline boron-doped diamond (O-PBDD) superhydrophobic surface with micro/nano-hierarchical porous structures is developed. The preparation method is very simple, requiring only sputtering and dewetting procedures. The former involves sputtering gold and copper particles onto the hydrogen-terminated polycrystalline boron-doped diamond (H-PBDD) to form gold/copper films, whereas the latter involves placing the samples in an atmospheric tube furnace to form hierarchical pores. By controlling the etching parameters, the wettability of the O-PBDD surface can be adjusted from hydrophilic to superhydrophobic, which is significantly different to the normal hydrophilicity feature of O-termination diamonds. The water contact angle of the obtained O-PBDD surface can reach 165 ± 5°, which is higher than the superhydrophobic diamond surfaces that are reported in the literature. In addition, the O-PBDD surface exhibits excellent durability; it can maintain satisfactory superhydrophobicity even after high-pressure, high-temperature, and sandpaper friction tests. This work provides a new research direction for fabricating robust superhydrophobic materials with diamond film.

Impact of water vapor annealing treatments on Al2O3/diamond interface

Our group developed the first inversion-type p-channel diamond metal–oxide–semiconductor field-effect transistor, which featured normally off properties by employing water vapor annealing treatments for the oxygen-terminated diamond surface. Despite the comprehensive device-grade characterization, the impact of water vapor annealing treatments on the Al2O3/diamond interface has not been investigated in detail. In this work, we fabricated four diamond metal–oxide–semiconductor (MOS) capacitors without and with water vapor annealing treatments for various times of 30 min, 1 h, and 2 h and conducted the cycle capacitance–voltage (C–V) and simultaneous C–V measurements. The large cycle C–V shift existed in the sample without water vapor annealing treatment, whereas it was significantly suppressed by water vapor annealing treatments, indicating the effective passivation of the traps with long time constants. The simultaneous C–V results showed a similar trend that the frequency dispersion of the simultaneous C–V was dramatically reduced with water vapor annealing treatments, and the interface quality of Al2O3/diamond had a slight dependence on the water vapor annealing times. Based on simultaneous C–V measurements, the interface state density (Dit) at an energy level of 0.2–0.6 eV from the valence band edge of diamond was extracted for the different MOS capacitors. The Dit was reduced by one order of magnitude with water vapor annealing treatments, and it almost did not change with the water vapor annealing times. Besides, the flat band voltage shift and effective fixed charge were also dramatically reduced by water vapor annealing. The possible physical reason for the interface improvement by water vapor annealing treatments was discussed.

Fabrication of polycrystalline phosphorus-doped diamond electrodes from red phosphorus.

Polycrystalline phosphorus-doped diamond was fabricated by the quartz-tube-type microwave plasma-assisted chemical vapor deposition method. Significantly, red phosphorus was used as a source of phosphorous, instead of PH3. Phosphorus-doped diamond electrodes with hydrogen-terminated and oxygen-terminated surfaces were investigated for the redox reactions of K3[Fe(CN)6] and [Ru(NH3)6]Cl3. The carrier concentration was estimated as 2.1-5.3 × 1018 cm-3 from electrochemical impedance measurements. Polycrystalline phosphorus-doped diamond shows great promise as chemical electrode materials.

Unveiling interface structure and polarity of wurtzite ZnO film epitaxially grown on a-plane sapphire substrate

Atomic-scale structure properties of the epitaxial growth of the wurtzite ZnO film prepared on an a-plane sapphire (α-Al2O3) substrate have been investigated by using aberration-corrected transmission electron microscopy. The crystallographic orientation relationship of (0001)[1¯1¯20]ZnO//(112¯0)[0001]α-Al2O3 has been determined between the ZnO film and the α-Al2O3 substrate. Two types of oxygen-terminated a-plane α-Al2O3 substrate surfaces have been characterized, which leads to the formation of different heterointerface structures and ZnO domains with opposite lattice polarity. The coalescence of opposite polarity domains results in the appearance of inversion domain boundaries (IDBs) on prismatic planes, and kinks occur on basal planes during the propagation of IDBs within the film. Additionally, the structure of stacking mismatch boundaries in the film with threefold coordinated Zn and O atoms has been resolved. We believe that these findings can be helpful to advance the understanding of the complex propagation of planar defects (e.g., IDBs and stacking faults) in wurtzite films and the interface structure and polarity of wurtzite films on the a-plane sapphire substrate.

Analysis of surface stability of ferrocolumbite from combined DFT – Wulff construction simulations

Ferrocolumbite, a variegated oxide mineral bearing the strategic element niobium, exhibits an array of surface chemical compositions across various cleavage orientations. The complexity of Nb-bearing ores hinders the efficiency of separation processes, necessitating fundamental research to bridge the knowledge gap regarding the surface dominance and properties of the mineral. In this regard, density functional theory (DFT) simulations were performed to determine the stability of different low Miller index surfaces of ferrocolumbite. The thermodynamic Wulff construction theory was then employed to predict the morphology of a ferrocolumbite nanoparticle, taking into account the DFT-calculated surface energies and the symmetries in the ferrocolumbite crystal. Several descriptors, such as ionic atom density and bond length distribution, were partially successful in correlating with surface energies; however, no global correlation could be captured for this complex system. Our findings suggested oxygen-terminated surfaces generally exhibit greater stability than metal or mixed-metal–oxygen-terminated surfaces within a given facet. Based on the Wulff shape prediction, the {110}, {001}, {111}, and {021} facets contribute to >85% of the surface area of the ferrocolumbite particles after comminution. Therefore, a sound conclusion about the adsorption behavior of reagents on ferrocolumbite should include all of these facets. This fundamental research highlights the complex and diverse nature of the ferrocolumbite surface and paves the way for future investigations.

Surface phase diagrams of pristine and hydroxylated barium hexaferrite surfaces from first-principles atomistic thermodynamics

Barium hexaferrite (BHF) is a ferrimagnet, whose hexagonal unit cell presents five iron crystallographic sites along the c-axis. At the nanoscale, BHF nanoparticles grow in the form of platelets, characterized by a low thickness along its principal magnetization axis (c-axis), displaying uniaxial magnetic anisotropy with the easy axis pointing perpendicular to the platelet. This unique property of BHF nanoplatelets has lead to a variety of novel applications, which often require surface functionalization. However, it has been observed that the nanoplatelets display two different surface morphologies depending on the stage/conditions of preparation. To ground these experimental observations, we employ the ab initio thermodynamics framework to perform a systematic investigation of the thermodynamic stability of BHF bulk terminations under a wide range of chemical conditions. We calculate the surface phase diagrams of pristine and hydroxylated bulk terminations along the c-axis. For pristine terminations, two different iron terminated surfaces are preferred: the barium containing 2b termination (Ba-rich conditions) and the 4f2 iron terminated surface (Ba-poor conditions). In the presence of water, the hydroxylated oxygen-terminated surfaces (12k-O) are identified as the most stable ones at Ba-poor conditions and low pH values, whereas the hydroxylated 2b surface is preferred at high pH and Ba-rich conditions.

Work function and energy level alignment tuning at Ti3C2Tx MXene surfaces and interfaces using (metal-)organic donor/acceptor molecules

Two-dimensional MXenes, with ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{T}}_{x}$ being the most prominent member, show properties that make them promising for a manifold of applications, including electrodes in light-emitting diodes, solar cells, and field-effect transistors based on organic semiconductors. In these cases, the work function of MXenes plays an important role in the energy level alignment to the subsequently deposited organic layer, as it determines the electron and hole injection barriers. Therefore, methods for controlling the ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{T}}_{x}$ work function should be developed. We demonstrate that, by using thin layers of (metal-)organic donor/acceptor molecules, the work function of ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{T}}_{x}$ can be tuned over a range of $>3$ eV. This enables tuning the energy level alignment to a subsequently deposited organic semiconductor, all the way from intrinsic Fermi level pinning at the highest occupied molecular energy level (minimal hole injection barrier) to pinning at the lowest unoccupied level (minimal electron injection barrier). Furthermore, it is shown that a predominantly oxygen-terminated surface does not lead to an extraordinary high work function, in contrast to theoretical predictions. The proposed strategy may greatly expand the use of MXenes in conjunction with organic hole and electron transport layers in optoelectronic devices.

Strain Engineering of ZrO2@TiO2 Core@shell Nanoparticle Photocatalysts

TiO2 photocatalysts can provide carbon-capture utilization and storage by converting atmospheric CO2 to green hydrogen, but the efficiency of the current photocatalysts is still too low for economical usage. Anatase TiO2 is effective in transferring the electrons and holes produced by the photoelectric effect to reactants because of its oxygen-terminated surfaces. However, the anatase TiO2 bandgap is 3.2 eV, which requires photons with wavelengths of 375 nm or less to produce electron–hole pairs. Therefore, TiO2 is limited to using a small part of the solar spectrum. Strain engineering has been used to design ZrO2@TiO2 core@shell structures with large strains in the TiO2 shell, which reduces its bandgap but maintains octahedral facets for charge separation and oxygen-terminated surfaces for the catalysis of reactants. Finite element analysis shows that shell thicknesses of 4–12 nm are effective at obtaining large strains in a large portion of the shell, with the largest strains occurring next to the ZrO2 surface. The c-axis strains for 4–12 nm shells are up to 7%. The strains reduce the bandgap in anatase TiO2 up to 0.35 eV, which allows for the use of sunlight with wavelengths up to 421 nm. For the AM 1.5 standard spectrum, electron–hole pair creation in 4 nm thick and 10 nm thick TiO2 shells can be increased by a predicted 25% and 23%, respectively. The 10 nm thick shells provide a much larger volume of TiO2 and use proportionally less ZrO2. In addition, surface-plasmon resonators could be added to further extend the usable spectrum and increase the production of electron–hole pairs many-fold.

Surface termination of the diamond microchannel and single-phase heat transfer performance

The diamond microchannel heat sink (D-MCHS) has extremely ultra-high stability and heat transfer capacity, and the surface modification can further improve the heat dissipation capacity of D-MCHS. In this study, diamond microchannels were modified by three surface termination operations, including oxygen-terminated (OT), hydrogen (HT), and fluorine-terminated surfaces (FT). Referring to the real situation, after the treatment of heat flow, the hydrophobic properties of HT-diamond microchannels decreased and resulted in the increase of surface heat transfer coefficient by 11%. The hydrophilic properties of OT-diamond tend to be stable after being significantly reduced, and the heat transfer coefficient decreased by 7%. FT-diamond was the most stable; its hydrophobicity remained constant after a slight decrease in the initial stage, and the corresponding surface heat transfer coefficient increased by 14%. X-ray photoelectron spectroscopy (XPS) was used to evaluate the surface bonding state of different terminal treatments. The results show that although the F terminal has more stable hydrophobicity, its surface temperature is 5 °C higher than that of the hydrophilic terminal, and the heat transfer coefficient is reduced from 9500 to 6000 W/(m2K), decreasing by nearly 58%.

Metal-organic coordination networks on a titanium carbide MXene: DFT based grand canonical Monte Carlo simulation

The self-assembly of 2D metal–organic networks comprising 1,3,5-tris (pyridyl)benzene (TPyB) molecules and copper atoms on the oxygen-terminated titanium carbide MXene surface was theoretically investigated. We have developed a lattice model of the TPyB-Cu networks on the energetically heterogeneous Ti2CO2(0001) surface. The model based on DFT calculations of the structure and energy of key adsorption complexes and metal–organic structures. Using the grand canonical Monte Carlo method, we have calculated and analyzed adsorption isotherms, structure, potential energy, and heat capacity of the adlayer. Due to steric hindrances in the three-fold Cu-TPyB junction, metal–organic structures consisting of only two-fold Cu-TPyB coordination motifs predominantly emerge on the Ti2CO2(0001) surface: honeycomb (HON), honeycomb filled with Cu3TPyB (HON + Cu3TPyB) and zigzag (ZZ) phases. These phases differ in the local environment of the copper adatoms. Thermal stability of the phases decreases in the following series: ZZ, HON + Cu3TPyB and HON. Self-assembly of these structures offers the opportunity to stabilize and “tune” properties of the single-atom Cu/Ti2CO2(0001) catalyst. We hope that our results will stimulate further experimental studies of hybrid “metal–organic network/MXene” catalysts.

Relationship between ferroelectric polarization and stoichiometry ofHfO2surfaces

We used density functional theory to assess the stability of nonpolar tetragonal $(P{4}_{2}/nmc) \mathrm{Hf}{\mathrm{O}}_{2}(110)$ reconstructed surfaces and the effect of polarization on the stability of the corresponding surfaces of polar orthorhombic $(Pca{2}_{1}) \mathrm{Hf}{\mathrm{O}}_{2}(001)$. The models consisted of nine-formula-unit-thick slabs with two-formula-unit surface unit cells. We determined an oxygen-terminated surface reconstruction to be the most stable surface for the nonpolar ${\mathrm{HfO}}_{2}$ slab, with one oxygen atom per formula unit on both sides of the slab (1.0-O/1.0-O). For the same surface composition, the ferroelectric displacements in the polar orthorhombic slab result in band bending that leads to the migration of charge carriers to the surface (with sign opposite to that of the surface polarization charge) which metallizes the surface to eliminate or reduce the net out-of-plane dipole. Ionic passivation also is effective at screening the polarization charge, which therefore alleviates band bending, leading to stabilization. This is achieved via a nonstoichiometric surface reconstruction, in which the most stable positively polarized side is oxygen-terminated with 1.5 oxygen atoms per formula unit, while the negatively polarized side has one oxygen atom per formula unit (P+:1.5-O/P\ensuremath{-}:1.0-O). This work establishes a link between the stability of the surface reconstruction and the ferroelectric polarization in ${\mathrm{HfO}}_{2}$, which is important for the technological need to control ferroelectric performance at the nanoscale.

Systematic comparison of various oxidation treatments on diamond surface

It is known that surface terminations contribute significantly to diamond properties. As one of the most commonly studied types, oxygen-terminated diamond surface possesses a positive electron affinity (PEA) and hydrophilicity, making it suitable for electronic device fabrication and bioapplications. Various oxidation methods have been reported on diamond, but a systematic comparison is still lacking. Herein, we present a comparative study on the oxidation of microcrystalline diamond powder (DP) and polycrystalline diamond film (PCD) by wet chemical treatments, including various acid mixtures, as well as by dry processes, including O2 plasma and UV ozone. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) results reveal that H2SO4/HNO3 5:1 at 360 °C demonstrates the best oxidation performance on DP and PCD compared to other wet chemical methods, while the PCD treated by O2 plasma exhibits the highest oxygen content among all the treated samples. Besides, the concentration of carbon-oxygen groups on diamond surfaces is found largely determined by oxidation methods. These experimental results can be attributed to the corresponding oxidation mechanism of different treatments and agree well with theoretical simulations. Finally, we investigated the sp2 bonded carbon concentration and surface roughness of oxidized PCD, suggesting the optimized diamond surface cleaning conditions.

Multiple Reaction Pathways for the Oxygen Evolution Reaction May Contribute to IrO2 (110)’s High Activity

Density functional theory calculations in conjunction with statistical mechanical arguments are performed on the rutile IrO2 (110) facet in order to characterize multiple reaction pathways on the surface at the highest active limit (the stoichiometric surface with all metal sites available) and at the lowest active limit (the oxygen-terminated surface). Alternative pathways to the oxygen evolution reaction (OER) are found, with multiple pathways determined at each step of the four proton-coupled electron transfer reaction. Of particular interest is the detailed characterization of a co-adsorption pathway utilizing neighboring, adsorbed O, OH species in order to evolve oxygen; activation energies of this pathway are <0.5 eV and therefore easily surmountable at the high operating potentials of OER. We also determined that surface Ir atoms can potentially participate in deprotonating an OOH* intermediate; the activation energy to this is 0.67 eV on the oxygen-terminated surface. These theoretical findings explain in part the high activity present in iridium oxide catalysts and also provide insight into the mechanistic pathways available on metal oxide catalysts, which may require the concerted interaction of nearest neighbor co-adsorbates to produce chemicals of interest.

The Ti2CO2 MXene as a nucleobase 2D sensor: A first-principles study

MXenes are a recently discovered class of two-dimensional materials, which have been attracting much interest by virtue of their promising biomedical and electronic applications. Here, we report on the results of first-principles calculations, based on density functional theory (DFT) including dispersion, of the adsorption energies and configurations of the five nucleobases, molecules conforming nucleotides in nucleic acids, such as DNA and RNA, on the oxygen-terminated titanium carbide MXene surface (Ti2CO2), chosen as a prototype MXene due to titanium being the most biocompatible transition metal. We find that physisorption is the most likely mechanism of adsorption on the Ti2CO2 (0001) basal surface, with the molecules sitting parallel to the MXene, about 2.5 Å away. The calculated adsorption energies and Bader charge transfer values are moderate, as desired for sensing applications. We find a fair correlation between the adsorption energies and the van der Waals volumes of the nucleobases, hinting towards an adsorption dominated by van der Waals interactions. No structural deformation is observed on the molecules or on the surface. Thus, all of our conclusions support the potential applicability of the Ti2CO2 MXene as a suitable nucleobase sensor.

Achieving high capacitance from porous boron-doped diamond by tuning the surface termination

Porous boron-doped diamond (PBDD) electrode with a high potential window, excellent stability, controllable conductivity, enhanced specific area, and tunable surface termination is a promising electrode material for the candidate. The surface termination of the PBDD electrode is easily tuned by the cyclic voltammetry (CV) scanning process with a positive potential, and an oxygen-terminated (OT) surface is achieved. The OT PBDD electrode exhibits a peak specific capacitance of 20.31 mF cm −2 (38.3% increase compared with the HT PBDD electrode, at 100 mV s −1 ) when 2.4 V (vs. Ag/AgCl) potential is applied, and it further comes to 36.74 mF cm −2 (81.8% increase than the HT PBDD electrode, at 10 mV s −1 ) with a 2.7 V (vs. Ag/AgCl) polarization potential. As the polarization voltage further increases to 3.0 V (vs. Ag/AgCl) or higher, the specific capacitance decrease. The OT PBDD electrode also keeps capacitance retention of 94.8% after 6000 CV cycles at 200 mV s −1 . Moreover, we built up a symmetric device using the OT PBDD as the electrode, which exhibits good electrochemical performance, such as wide potential, high energy density (15.1 Wh kg −1 ), and high power density (4.05 kW kg −1 ). • The PBDD is synthesized via regrowth of diamond nanoparticles in an Ar atmosphere. • The PBDD electrode achieves an oxygen-terminated (OT) surface by anodic polarization. • The OT PBDD device's energy density increases from 7.37 to 15.1 Wh kg −1 after polarization. • The OT PBDD device has the same potential window as the hydrogen-terminated PBDD.

Sensitive Voltammetric Detection of Chloroquine Drug by Applying a Boron-Doped Diamond Electrode

In this research, a boron-doped diamond (BDD) electrode has been explored to detect the chloroquine drug. The electrochemical performance of BDD electrode towards the irreversible anodic response of chloroquine was investigated by subjecting this electrode to the cathodic (−0.5 A cm−2 by 180 s, generating a predominantly hydrogen-terminated surface) and anodic (+0.5 A cm−2 by 30 s, oxygen-terminated surface) pretreatments. The cathodically pretreated BDD electrode ensured a better-defined anodic peak and higher current intensity. Thus, by applying the cathodically pretreated BDD electrode and square-wave voltammetry (SWV), the analytical curve was linear from 0.01 to 0.25 µmol L−1 (correlation coefficient of 0.994), with sensitivity and limit of detection of 12.2 µA L µmol−1 and 2.0 nmol−1, respectively. This nanomolar limit of detection is the lowest recorded so far with modified and unmodified electrodes.

Grinding induced the formation of the heterojunction Bi6O5(OH)3(NO3)5·3H2O/BiOI with improved visible-light photoreactivity

Considering that basic bismuth nitrate Bi6O5(OH)3(NO3)5·3H2O (BBN) with a wide band gap energy (Eg = ~ 3.40 eV) could only respond to UV light, herein, BiOI-coupled BBN (BBN/BiOI) heterojunction at the size of several microns was synthesized by a grinding-assistant ion-exchange strategy. BiOI nanoparticles with relatively uniform diameters in the range of 0.22–0.71 μm attached on the surface of BBN at the size of around 10 μm. BBN/BiOI exhibited significantly enhanced visible-light photocatalytic activity for malachite green (MG, 20 mg/L) degradation at the premium BiOI content with initial I−/Bi3+ molar ratio of 0.8, and the degradation efficiency was increased to 90% from 4% of bare BBN and 44% of BiOI. Especially, the as-prepared BBN/BiOI possessed higher photocatalytic activity than that obtained by solution reaction, which should result from more intimate contact between BiOI and BBN due to mechanical force from grinding, as well as electrostatic attraction between positively charged surface of BBN and oxygen-terminated surface of BiOI. All these are beneficial to transfer and separation of photogenerated carriers, thus improving photo-quantum efficiency. Dissolution behavior of BBN in several dyes’ solution was clarified.

Polarization dependence of ZnO Schottky barriers revealed by photoelectron spectroscopy

In order to answer the question of whether Schottky barriers on polar ZnO surfaces are different at Zn- and O-terminated surfaces, the interface formation of $n$-type ZnO and different high work function metals and metal oxides (Pt, ${\mathrm{PtO}}_{x}$, and ${\mathrm{RuO}}_{2}$) with Schottky barrier heights of up to 1.5 eV has been studied using photoelectron spectroscopy with in situ sample preparation. The experiments are designed to exclude the effects of substrate reduction and consequent Fermi level pinning by high concentrations of oxygen vacancies. Moreover, by including the Zn LMM Auger emission in the analysis, it is demonstrated that an accurate extraction of barrier heights needs to take into account that the screening of the photoelectron core hole can change in the course of contact formation. The polarization dependence of Schottky barriers, which is important for piezotronic applications, is in most cases dominated by the influence of defects. Reducing the influence of defects, up to $\ensuremath{\sim}240$ meV higher Schottky barriers are revealed on oxygen-terminated surfaces. This is opposite to what has been reported in the literature but agrees with the dependence of barrier heights expected for an incomplete screening of the polarization of ZnO by the electrode as for ferroelectric materials.

MXenes and Their Applications in Wearable Sensors.

MXenes, a kind of two-dimensional material of early transition metal carbides and carbonitrides, have emerged as a unique class of layered-structured metallic materials with attractive features, as good conductivity comparable to metals, enhanced ionic conductivity, hydrophilic property derived from their hydroxyl or oxygen-terminated surfaces, and mechanical flexibility. With tunable etching methods, the morphology of MXenes can be effectively controlled to form nanoparticles, single layer, or multi-layer nanosheets, which exhibit large specific surface areas and is favorable for enhancing the sensing performance of MXenes based sensors. Moreover, MXenes are available to form composites with other materials facilely. With structure design, MXenes or its composite show enhanced mechanical flexibility and stretchability, which enabled its wide application in the fields of wearable sensors, energy storage, and electromagnetic shielding. In this review, recent progress in MXenes is summarized, focusing on its application in wearable sensors including pressure/strain sensing, biochemical sensing, temperature, and gas sensing. Furthermore, the main challenges and future research are also discussed.

Real-Space Mapping of Surface-Oxygen Defect States in Photovoltaic Materials Using Low-Voltage Scanning Ultrafast Electron Microscopy.

Ultrathin layers of native oxides on the surface of photovoltaic materials may act as very efficient carrier trapping/recombination centers, thus significantly affecting their interfacial photophysical properties. How ultrathin oxide layers affect the surface and interface carrier dynamics cannot be selectively accessed by conventional ultrafast transient spectroscopic methods due to the deep penetration depth (tens to thousands of nanometers) of the pump/probe laser pulses. Herein, scanning ultrafast electron microscopy (S-UEM) at a low voltage of 1 keV electrons was recently developed at KAUST to selectively map the ultrafast charge carrier dynamics of a few layers on the top surfaces of photovoltaic materials. Unlike high-voltage 30 keV experiments, at 1 keV, the depth of detected secondary electrons (SEs) underneath the surface is significantly reduced 5 times, thus making it possible to visualize the dynamics of charge carrier from the uppermost surface of photoactive layers. More specifically, this new approach has been employed to explore and decipher the tremendous impact of native oxide layers and oxygen defect states on charge carrier dynamics in space and time simultaneously at sub-nanometer levels on several photovoltaic material surfaces, including Si, GaAs, CdTe, and CdZnTe single crystals. Interestingly, the contrast in the SEs time-resolved difference images switched from a dark "energy-loss mechanism" to a bright "energy-gain mechanism" only by removing the layers of surface oxides. Moreover, the charge carrier recombination was estimated and found to be dramatically affected by the native oxide layers. The density functional theory (DFT) calculations demonstrate that the work function of oxygen-terminated Si surface also increases slightly upon optical excitation and makes for less SE intensity, providing another piece of evidence that the origin of the dark contrast observed on these material surfaces should be assigned to the surface oxide formation, mainly oxygen defect states in the band gap and/or work function increment. Our findings provide a new method and pave the way for evaluating the effect of surface morphology and defects, including but not limited to native oxide, on charge carrier dynamics, and interfacial properties of photovoltaic absorber layers.