Understanding the reaction mechanism and kinetics of photocatalytic oxygen evolution on CoOx-loaded bismuth vanadate.

Photocatalytic water splitting for green hydrogen production is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Loading a co-catalyst is essential for accelerating the kinetics, but the detailed reaction mechanism and role of the co-catalyst are still obscure. Here, we focus on cobalt oxide (CoOx) loaded on bismuth vanadate (BiVO4) to investigate the impact of CoOx on the OER mechanism. We employ photoelectrochemical impedance spectroscopy and simultaneous measurements of photoinduced absorption and photocurrent. The reduction of V5+ in BiVO4 promotes the formation of a surface state on CoOx that plays a crucial role in the OER. The third-order reaction rate with respect to photohole charge density indicates that reaction intermediate species accumulate in the surface state through a three-electron oxidation process prior to the rate-determining step. Increasing the excitation light intensity onto the CoOx-loaded anode improves the photoconversion efficiency significantly, suggesting that the OER reaction at dual sites in an amorphous CoOx(OH)y layer dominates over single sites. Therefore, CoOx is directly involved in the OER by providing effective reaction sites, stabilizing reaction intermediates, and improving the charge transfer rate. These insights help advance our understanding of co-catalyst-assisted OER to achieve efficient water splitting.

Linewidth Narrowing with Ultimate Confinement of an Alkali Multipole Plasmon by Modifying Surface Electronic Wave Functions with Two-Dimensional Materials.

This work demonstrates significant line narrowing of a surface multipole plasmon (MP) by modifying the surface electronic wave function with two-dimensional materials (2DMs): graphene and hexagonal boron nitride. This is found in an optical reflectivity of alkali atoms (Cs or K) on an Ir(111) surface covered with the 2DMs. The reduction in reflectivity induced by deposition of the alkali atoms becomes as large as 20% at ∼2 eV, which is ascribed to a MP of a composite of alkali/2DM/alkali/Ir multilayer structure. The linewidth of the MP band becomes as narrow as 0.2 eV by the presence of the 2DM between the two alkali layers. A numerical simulation by time-dependent density functional theory with a jellium model reveals that the density of states of the surface localized state is sharpened remarkably by the 2DMs that decouple the outermost alkali layer from the Ir bulk. Consequently, a local field enhancement of an order of 10^{5} is achieved by ultimate confinement of the MP within the outermost alkali layer. This work leads to a novel strategy for reducing plasmon dissipation in an atomically thin layer via atomic scale modification of surface structure.

Orientational ordering in heteroepitaxial water ice on metal surfaces.

Heteroepitaxial growth of crystalline ice thin films of water on metal substrates under ultrahigh vacuum provides an excellent opportunity to investigate the interior and surface structures of crystalline ice that are closely related to their physicochemical properties. Here we present the spectroscopic studies of the orientational ordering and the surface relaxation of crystalline ice films grown on two representative metal surfaces: Pt(111) and Rh(111). A versatile tool for exploring these structures is sum frequency generation (SFG) vibrational spectroscopy; homodyne detection of SFG signals serves as a good measure of orientational ordering in the interior of crystalline ice films while heterodyne detection enables us to determine the direction of water molecules at the interface with metal substrates, in the interior of crystalline ice films, and at their surfaces. Water molecules on the wetting layer of Pt(111) are preferentially oriented in H-down configuration, and the configuration is passed along into the interior of crystalline ice films. In contrast, water molecules on Rh(111) are adsorbed in a mixture of H-down and H-up configurations, leading to orientationally disordered crystalline ice films. The inter-layer distance at the top of the surface is modulated alternately in accordance with the orientation of molecules hydrogen bonded to the bilayer underneath. Therefore, the molecular orientation also plays an important role in their surface relaxation.

Thickness dependent homogeneous crystallization of ultrathin amorphous solid water films.

The crystallization mechanism and kinetics of amorphous materials are of paramount importance not only in basic science but also in the application field because they are closely related to their thermal stability. In the case of amorphous nanomaterials, thermal stability distinctively different from that of bulk materials often emerges. Despite intensive studies in the past, a thorough understanding of the stability at the molecular level has not been reached particularly on how crystallization processes depend on size and are influenced by their surface and interface. In this article, we report the film-size-dependent crystallization of thermally relaxed nonporous ASW ultrathin films on a Pt(111) surface as a benchmark system of amorphous molecular films. The crystallization processes at the surface and interior of the ASW ultrathin films are monitored simultaneously with thermal desorption and infrared reflection absorption, respectively, as a function of the film thickness. Here, we demonstrate that the crystallization is initiated solely by "homogeneous nucleation" irrespective of the film thickness while the crystallization rate remarkably depends on the thickness; the rate of 5-layer (∼1.5 nm) ASW films is one order of magnitude higher than that of 20-layer (∼6 nm) films. Moreover, we found a clear correlation between the film-thickness-dependent crystallization kinetics and microscopic structural disorder associated with the broad distribution of hydrogen-bond lengths between water molecules.

Enhanced structural disorder at a nanocrystalline ice surface.

Detailed knowledge of the structure and dynamics of the surface of ice particles is of considerable importance for understanding catalytic reactions in the upper atmosphere. Here we report the enhanced structural disorder specific at a nanoscale ice island studied by using heterodyne-detected vibrational sum-frequency generation spectroscopy under ultrahigh vacuum. Ultrathin films of isotopically diluted HOD crystalline ice are grown on Rh(111), whose average height (≥1.4 nm) is controlled by varying the nominal film thickness. The Im χ(2) spectrum of the hydrogen-bonded O-H stretching band shows a bipolar line shape reflecting the orientation-dependent hydrogen bond length alternation in the subsurface of the ice island. The peak splitting and the bandwidth of the bipolar spectrum increase with a decrease in the nominal film thickness. This is ascribed to the significant enhancement of structural disorder at the surface of the ice island as the terrace size is decreased. Temperature dependence of the Im χ(2) spectra of the hydrogen bonded O-H stretching band indicates that the thermal expansivity of the top layer increases upon decreasing the island size. In addition, the stretching frequency of the dangling OD band at the island surface with the average height less than 18 nm shows a systematic blue shift with increasing temperature from 100 to 145 K: this is in stark contrast to thick ice films and bulk ice showing a negligible peak shift at a temperature lower than 180 K. These findings indicate that the anharmonicity of the intermolecular potential at the top layer of the ice island is strongly enhanced upon decreasing its terrace size, providing valuable insights for understanding the properties of ice particles in the outer atmosphere including polar mesospheric clouds.

Singlet fission of amorphous rubrene modulated by polariton formation.

The excited-state dynamics of molecular aggregates are governed by their potential energy landscape that can hardly be controlled artificially. However, it is possible to alter the excited state dynamics by a strong coupling between light and molecules (polariton formation) because it can decouple the electronic and vibrational degrees of freedom. Here, we demonstrate this polaron decoupling effect on the photochemical dynamics in singlet fission (SF) of amorphous rubrene thin films embedded in optical microcavities. The vibronic feature of polariton states in this system is characterized through the analysis of steady state absorption spectra by using the Holstein-Tavis-Cummings model. On the basis of this analysis, we show with time-resolved spectroscopy that the SF rate following a resonant excitation of the lowest energy polariton state is indeed modulated when the cavity photon energy is changed. A numerical simulation by using Fermi's golden rule formula with the vibronic polariton feature successfully accounts for the observed modulation of the SF rate, indicating that the polaron decoupling plays a decisive role in the nonadiabatic dynamics.

Water-Assisted Hole Trapping at the Highly Curved Surface of Nano-TiO2 Photocatalyst.

Heterogeneous photocatalysis is vital in solving energy and environmental issues that this society is confronted with. Although photocatalysts are often operated in the presence of water, it has not been yet clarified how the interaction with water itself affects charge dynamics in photocatalysts. Using water-coverage-controlled steady and transient infrared absorption spectroscopy and large-model (∼800 atoms) ab initio calculations, we clarify that water enhances hole trapping at the surface of TiO2 nanospheres but not of well-faceted nanoparticles. This water-assisted effect unique to the nanospheres originates from water adsorption as a ligand at a low-coordinated Ti-OH site or through robust hydrogen bonding directly to the terminal OH at the highly curved nanosphere surface. Thus, the interaction with water at the surface of nanospheres can promote photocatalytic reactions of both oxidation and reduction by elongating photogenerated carrier lifetimes. This morphology-dependent water-assisted effect provides a novel and rational basis for designing and engineering nanophotocatalyst morphology to improve photocatalytic performances.

Conformational Planarization versus Singlet Fission: Distinct Excited-State Dynamics of Cyclooctatetraene-Fused Acene Dimers.

A set of flapping acene dimers fused with an 8π cyclooctatetraene (COT) ring showed distinct excited-state dynamics in solution. While the anthracene dimer showed a fast V-shaped-to-planar conformational change within 10 ps in the lowest excited singlet state, reminding us of extended Baird aromaticity, the tetracene dimer and the pentacene dimer underwent intramolecular singlet fission (SF) in different manners: A fast and reversible SF with a characteristic delayed fluorescence (FL), and a fast and quantitative SF, respectively. Conformational flexibility of the fused COT linkage plays an important role in these ultrafast dynamics, demonstrating the utility of the flapping molecular series as a versatile platform for designing photofunctional systems.

Effect of Water Adsorption on Carrier Trapping Dynamics at the Surface of Anatase TiO2 Nanoparticles.

Charge carrier trapping plays a vital role in heterogeneous photocatalytic water splitting because it strongly affects the dynamics of photogenerated charges and hence the photoconversion efficiency. Although hole trapping by water at water/photocatalyst interface is the first step of oxygen evolution in water splitting, little has been known on how water adsorbate itself is involved in hole trapping dynamics. To clarify this point, we have performed infrared transient and steady-state absorption spectroscopy of anatase TiO2 nanoparticles as a function of the number of water adsorbate layers. Here, we demonstrate that water molecules reversibly adsorbed in the first layer on TiO2 nanoparticles are capable to trap photogenerated holes, while water in the second layer hydrogen bonding to the first-layer water makes hole trapping less effective.

Disentangling Multidimensional Nonequilibrium Dynamics of Adsorbates: CO Desorption from Cu(100).

Hot carriers at metal surfaces can drive nonthermal reactions of adsorbates. Characterizing nonequilibrium statistics among various degrees of freedom in an ultrafast time scale is crucial to understand and develop hot carrier-driven chemistry. Here we demonstrate multidimensional vibrational dynamics of carbon monoxide (CO) on Cu(100) along hot-carrier induced desorption studied by using time-resolved vibrational sum-frequency generation with phase-sensitive detection. Instantaneous frequency and amplitude of the CO internal stretching mode are tracked with a subpicosecond time resolution that is shorter than the vibrational dephasing time. These experimental results in combination with numerical analysis based on Langevin simulations enable us to extract nonequilibrium distributions of external vibrational modes of desorbing molecules. Superstatistical distributions are generated with mode-dependent frictional couplings in a few hundred femtoseconds after hot-electron excitation, and energy flow from hot electrons and intermode anharmonic coupling play crucial roles in the subsequent evolution of the non-Boltzman distributions.

Cerebral Hyperperfusion after Revascularization Inhibits Development of Cerebral Ischemic Lesions Due to Artery-to-Artery Emboli during Carotid Exposure in Endarterectomy for Patients with Preoperative Cerebral Hemodynamic Insufficiency: Revisiting the "Impaired Clearance of Emboli" Concept.

The purpose of the present study was to determine whether cerebral hyperperfusion after revascularization inhibits development of cerebral ischemic lesions due to artery-to-artery emboli during exposure of the carotid arteries in carotid endarterectomy (CEA). In patients undergoing CEA for internal carotid artery stenosis (≥70%), cerebral blood flow (CBF) was measured using single-photon emission computed tomography (SPECT) before and immediately after CEA. Microembolic signals (MES) were identified using transcranial Doppler during carotid exposure. Diffusion-weighted magnetic resonance imaging (DWI) was performed within 24 h after surgery. Of 32 patients with a combination of reduced cerebrovascular reactivity to acetazolamide on preoperative brain perfusion SPECT and MES during carotid exposure, 14 (44%) showed cerebral hyperperfusion (defined as postoperative CBF increase ≥100% compared with preoperative values), and 16 (50%) developed DWI-characterized postoperative cerebral ischemic lesions. Postoperative cerebral hyperperfusion was significantly associated with the absence of DWI-characterized postoperative cerebral ischemic lesions (95% confidence interval, 0.001-0.179; p = 0.0009). These data suggest that cerebral hyperperfusion after revascularization inhibits development of cerebral ischemic lesions due to artery-to-artery emboli during carotid exposure in CEA, supporting the "impaired clearance of emboli" concept. Blood pressure elevation following carotid declamping would be effective when embolism not accompanied by cerebral hyperperfusion occurs during CEA.

Applications of time-domain spectroscopy to electron-phonon coupling dynamics at surfaces.

Photochemistry is one of the most important branches in chemistry to promote and control chemical reactions. In particular, there has been growing interest in photoinduced processes at solid surfaces and interfaces with liquids such as water for developing efficient solar energy conversion. For example, photoinduced charge transfer between adsorbates and semiconductor substrates at the surfaces of metal oxides induced by photogenerated holes and electrons is a core process in photovoltaics and photocatalysis. In these photoinduced processes, electron-phonon coupling plays a central role. This paper describes how time-domain spectroscopy is applied to elucidate electron-phonon coupling dynamics at metal and semiconductor surfaces. Because nuclear dynamics induced by electronic excitation through electron-phonon coupling take place in the femtosecond time domain, the pump-and-probe method with ultrashort pulses used in time-domain spectroscopy is a natural choice for elucidating the electron-phonon coupling at metal and semiconductor surfaces. Starting with a phenomenological theory of coherent phonons generated by impulsive electronic excitation, this paper describes a couple of illustrative examples of the applications of linear and nonlinear time-domain spectroscopy to a simple adsorption system, alkali metal on Cu(111), and more complex photocatalyst systems.

Ultrafast exciton dynamics in dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene thin films.

Ultrafast dynamics of excitons in organic semiconductors is essential for a deep understanding of the working mechanism of plastic opto-electronic devices. In this work, excited state dynamics in dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene thin films has been studied with femtosecond transient absorption and time-resolved photoluminescence spectroscopy. Upon the excitation with a femtosecond pulse at 400 nm, a broad positive absorption band at 1.5-2.4 eV is observed that contains two components: one decays with a time constant of a few ps and the other with 67 ± 7 ps. Because the decay curve of the latter coincides with that of photoluminescence, the slow decay component is ascribed to the lowest singlet exciton. The former fast decay component is ascribed to mixed states between charge transfer (CT) and Frenkel excitons, because it is accompanied by a feature due to the Stark effect caused by transient charged species: a combination of bleach and positive absorption at hνprobe > 2.4 eV which looks like derivative modulations of the ground state absorption spectrum. A pronounced polarization dependence is observed for the derivative-like features; this is due to anisotropic distributions of the dipole moments formed by the CT excitons. The derivative-like feature changes its shape after the decay of the mixed Frenkel-CT exciton and grows with a pump-probe delay time of up to 1 ns due to a thermal effect. The decay rate of the mixed Frenkel-CT exciton strongly depends on its density because of exciton-exciton annihilation at high density.

Successful carotid stenting of a carotid arterial dissection after straightening the tortuosity using an inflated balloon guiding catheter and the delivery wire of an anchored stent retriever.

The authors present a patient with carotid dissection in a tortuous arterial segment who successfully underwent carotid artery stenting (CAS) by straightening the tortuosity using an inflated balloon guiding catheter (BGC) and a stent retriever (SR). A 56-year-old man was transferred to our institute with right hemiparesis and a National Institutes of Health Stroke Scale score of 9. Magnetic resonance imaging showed left internal carotid artery (ICA) occlusion and ischemic change in the parietal lobe. Emergent angiography revealed tapered extracranial ICA occlusion sugg carotid artery dissection (CAD). CAS was attempted for CAD due to a mismatch of the motor area on clinical imaging. However, several attempts to navigate the stent delivery system over a guidewire failed. Therefore, we deployed a Trevo NXT ProVue SR (3 × 32 mm) in the middle cerebral artery, inflated a BGC, and then pulled on both to straighten the tortuous carotid artery, which resulted in successful navigation of the stent delivery system. The patient's symptoms improved after the recanalization. This case demonstrates the utility of a technique for navigation of a stent delivery system through a tortuous carotid artery in which the tortuosity is straightened by pulling on an inflated BGC and the delivery wire of the SR.

Acute large-vessel occlusion due to an infected thrombus formation induced by invasive sphenoid sinus aspergillosis: illustrative case.

BACKGROUND: The authors describe a rare case of acute large-vessel occlusion due to an infected thrombus formation that was induced by invasive sphenoid sinus aspergillosis. OBSERVATIONS: An 82-year-old man with a history of immunoglobulin G4-related disease and long-term use of steroids and immunosuppressants was admitted to the authors' hospital with severe right hemiparesis. Cerebral angiography revealed occlusion of the left internal carotid artery (ICA). He underwent thrombectomy, resulting in successful recanalization. However, severe stenosis was evident in the left ICA cavernous segment. Pathological analysis of the retrieved thrombus identified Aspergillus. Postoperative magnetic resonance imaging revealed sinusitis in the left sphenoid sinus as a possible source of the infection. The patient's general condition deteriorated during the course of hospitalization due to refractory aspiration pneumonia, and he died 46 days after thrombectomy. Pathological autopsy and histopathological investigation of the left ICA and the left sphenoid sinus showed that Aspergillus had invaded the wall of the left ICA from the adjacent sphenoid sinus. These findings indicate a diagnosis of acute large-vessel occlusion due to infected thrombus formation induced by invasive sphenoid sinus aspergillosis. LESSONS: Pathological analysis of a retrieved thrombus appears useful for identifying rare stroke etiologies such as fungal infection.

Detection of misery perfusion in the cerebral hemisphere with chronic unilateral major cerebral artery steno-occlusive disease using crossed cerebellar hypoperfusion: comparison of brain SPECT and PET imaging.

PURPOSE: In patients with unilateral internal carotid or middle cerebral artery (ICA or MCA) occlusive disease, the degree of crossed cerebellar hypoperfusion that is evident within a few months after the onset of stroke may reflect cerebral metabolic rate of oxygen in the affected cerebral hemisphere relative to that in the contralateral cerebral hemisphere. The aim of the present study was to determine whether the ratio of blood flow asymmetry in the cerebellar hemisphere to blood flow asymmetry in the cerebral hemisphere on positron emission tomography (PET) and single photon emission computed tomography (SPECT) correlates with oxygen extraction fraction (OEF) asymmetry in the cerebral hemisphere on PET in patients with chronic unilateral ICA or MCA occlusive disease and whether this blood flow ratio on SPECT detects misery perfusion in the affected cerebral hemisphere in such patients. METHODS: Brain blood flow and OEF were assessed using (15)O-PET and N-isopropyl-p-[(123)I]iodoamphetamine ((123)I-IMP) SPECT, respectively. All images were anatomically standardized using SPM2. A region of interest (ROI) was automatically placed in the bilateral MCA territories and in the bilateral cerebellar hemispheres using a three-dimensional stereotaxic ROI template, and affected-to-contralateral asymmetry in the MCA territory or contralateral-to-affected asymmetry in the cerebellar hemisphere was calculated. Sixty-three patients with reduced blood flow in the affected cerebral hemisphere on (123)I-IMP SPECT were enrolled in this study. RESULTS: A significant correlation was observed between MCA ROI asymmetry of PET OEF and the ratio of cerebellar hemisphere asymmetry of blood flow to MCA ROI asymmetry of blood flow on PET (r = 0.381, p = 0.0019) or SPECT (r = 0.459, p = 0.0001). The correlation coefficient was higher when reanalyzed in a subgroup of 43 patients undergoing a PET study within 3 months after the last ischemic event (r = 0.541, p = 0.0001 for PET; r = 0.609, p < 0.0001 for SPECT). The blood flow ratio on brain perfusion SPECT in all patients provided 100 % sensitivity and 58 % specificity, with 43 % positive and 100 % negative predictive values for detecting abnormally elevated MCA ROI asymmetry of PET OEF. CONCLUSION: The ratio of blood flow asymmetry in the cerebellar hemisphere to blood flow asymmetry in the cerebral hemisphere on PET and SPECT correlates with PET OEF asymmetry in the cerebral hemisphere, and this blood flow ratio on SPECT detects misery perfusion in the affected cerebral hemisphere.

Endovascular embolization and needle aspiration of a life-threatening cervical hematoma due to a neurofibromatosis type 1-associated arteriovenous fistula: illustrative case.

BACKGROUND: In cases of neurofibromatosis in which the bleeding source is considered strongly related to a neurofibroma, an open surgical approach could risk uncontrollable bleeding from the vascular wall infiltration by neurofibroma. The case of a neurofibromatosis type 1 (NF1)-associated arteriovenous fistula presenting with a life-threatening cervical hematoma that was successfully treated with alternative treatment is described. OBSERVATIONS: A 68-year-old woman diagnosed with NF1 presented with sudden onset of a spontaneous right cervical mass. Neck imaging on admission showed a massive subcutaneous hematoma with tracheal deviation and abnormal vascular structure in the hematoma. Digital subtraction angiography showed that an arteriovenous fistula (AVF) fed from a vertebral artery located within the hematoma cavity was the primary source of bleeding and feeding arteries from the occipital artery to the neurofibroma. Embolization of the cervical neurofibroma, as well as the AVF, was performed to reduce the secondary risk of bleeding, and was accomplished. After endovascular treatment, needle aspiration of the cervical hematoma was performed to reduce the mass effect. LESSONS: When performing open surgery via tissues with neurofibromatosis proliferation, uncontrollable bleeding can occur. Therefore, endovascular embolization and needle aspiration of the hematoma should be considered in this setting.

Toward photochemistry of integrated heterogeneous systems.

This paper begins with describing the excitation mechanisms in surface photochemistry and nuclear dynamics of adsorbate induced by electronic excitation. An illustrative example is Cs adsorbate on a Cu(111) surface. This adsorption system shows drastic changes in the electronic structure with coverage; this allows us to examine different types of electronic excitations that stimulate nuclear motions of Cs. Remarks are made on challenges in photoinduced processes at well-defined surfaces: direct observations of adsorbate-substrate vibrational modes and photoinduced reactions between adsorbates. Then, the paper addresses some issues in more complex systems: metal-liquid interfaces and powdered photocatalysts of metal oxides. Photochemistry and photoinduced nuclear dynamics at metal-liquid interfaces have not been well explored. Studies on this subject may make it possible to bridge the gap between surface photochemistry and electrochemistry. Photocatalysis with powdered catalysts has been extensively studied and is still an active area, but our understanding of the mechanism of photocatalysis is far from satisfactory. Although complicated, the highly integrated systems provide an opportunity to extend our knowledge of surface photochemistry.

Instantaneous vibrational frequencies of diffusing and desorbing adsorbates: CO/Pt(111).

Electronic excitation of metal by intense laser pulses stimulates nuclear motions of adsorbates through nonadiabatic coupling, resulting in diffusion and desorption of adsorbates. These processes take place via precursor states: adsorbates whose vibrational modes with respect to substrate are highly excited. This paper reports the dynamics of precursor states of CO on Pt(111) probed by use of infrared-visible sum frequency generation with phase-sensitive detection, which allows us to obtain the second-order nonlinear susceptibility and thus the vibrational response function. Without pump pulses at 400 nm, the inverse Fourier transformation of the vibrational response function reveals a free induction decay of vibrational polarization of C-O stretching created by a short infrared pulse. The free induction decay is perturbed when an intense 400-nm pump pulse following the infrared pulse is irradiated, because diffusion and desorption of CO are induced by the pump pulse. The time evolution of instantaneous C-O stretching frequency retrieved from the perturbed free induction decay shows a redshift followed by a rapid reverse shift when the fluence of pump pulse is high enough to desorb CO. This indicates that the frustrated modes of CO is first substantially excited and then the parallel momentum of CO is converted to the normal one through mutual collisions, leading to substantial excitation of the external stretching mode of CO.

Intracranial hemorrhage associated with direct oral anticoagulant after clipping for an unruptured cerebral aneurysm: A report of two cases.

Background: Two cases of patients who developed intracranial hemorrhage associated with direct oral anticoagulant (DOAC) use after clipping of an unruptured cerebral aneurysm (uAN) are presented. These cases will help neurosurgeons assess the risks of patients with atrial fibrillation or deep venous thrombosis receiving DOACs who require craniotomy. Case Description: Case 1 was a 65-year-old man on apixaban 10 mg/day who underwent clipping for a left middle cerebral artery uAN. Apixaban was discontinued 72 h before surgery. During surgery, a thin and pial artery bled slightly at 1 point of the frontal lobe, and hemostasis was easily achieved. Computed tomography (CT) 19 h after surgery showed no evidence of intracranial hemorrhage. He was treated with a heparin-apixaban bridge from 29 h to 41 h after surgery. CT showed a left subarachnoid hematoma 24 h later. Case 2 was a 73-year-old woman on dabigatran 110 mg/day who underwent clipping for a right MCA uAN. Dabigatran was discontinued 48 h before surgery. During surgery, a thin and pial artery bled slightly at 2 points of the temporal lobe, and hemostasis was easily achieved. CT 19 h after surgery showed no evidence of intracranial hemorrhage. Dabigatran (110 mg/day) was restarted 29 h after surgery. CT then showed a right subarachnoid hematoma 94 h later, and dabigatran was discontinued, and it was then restarted 38 h later. However, 31 h later, CT showed an additional slight subarachnoid hemorrhage. Finally, she developed a right chronic subdural hematoma. Conclusion: In patients undergoing neurosurgical procedures, discontinuation of DOACs should be individualized based on neurosurgical bleeding risk and patient renal function. Restarting of DOACs could be considered after at least 48 h when hemostasis has been achieved. Bridging of DOACs cannot be recommended.