Single-atom catalysis of carbon monoxide oxidation on metal-oxide surfaces is crucial for greenhouse recycling, automotive catalysis, and beyond, but reports of the atomic-scale mechanism are still scarce. Here, using scanning probe microscopy, we show that charging single gold atoms on oxidized rutile titanium dioxide surface, both positively and negatively, considerably promotes adsorption of carbon monoxide. No carbon monoxide adsorption is observed on neutral gold atoms. Two different carbon monoxide adsorption geometries on gold atoms are identified. We demonstrate full control over the redox state of adsorbed gold single atoms, carbon monoxide adsorption geometry, and carbon monoxide adsorption/desorption by the atomic force microscopy tip. On charged gold atoms, we activate Eley-Rideal oxidation reaction between carbon monoxide and a neighboring oxygen adatom by the tip. Our results provide unprecedented insights into carbon monoxide adsorption and suggest that the gold dual activity for carbon monoxide oxidation after electron or hole attachment is also the key ingredient in photocatalysis under realistic conditions.

Quantum magnetic sensing technology utilizing diamond nitrogen vacancy (NV) color centers exhibits high spatial resolution, sensitivity, and dynamic range. The practical applications of the NV color centers magnetometer are limited by its complex system and large volume. To expand the range of applications, it is necessary to improve the integration level of NV color centers magnetometer while meeting the requirements of high portability and sensitivity. In this article, we designed a portable integrated NV magnetometer and utilized the continuous wave optically detected magnetic resonance (CW-ODMR) method to detect magnetic field. We coupled a micro self-focusing lens with a fiber to create a fiber self-focusing integrated module (FSFI) and bonded a diamond to the other end of the lens. This module was applied to the integrated NV magnetometer. This arrangement ensured uniform intensity of the laser and expanded the irradiation area on the diamond, thereby improving the excitation efficiency of the NV color centers and the number of NV color centers involved in sensing. The magnetometer integrated a microwave antenna module and a fluorescence collection and processing module. The magnetometer was packaged using 3-D printing technology and occupied a volume of 10 cm3. After conducting experimental tests, the sensitivity of the magnetometer was 9.6 nT/Hz1/2, and the photon shot noise limited sensitivity can reach 0.85 nT/Hz1/2. The maximum detection relative error of the dc magnetic field was 0.848%, and the detection bandwidth was 40 Hz. The signal-to-noise ratio (SNR) of the ac magnetic field was 28.107 dB within the detectable bandwidth. The integrated NV magnetometer exhibits excellent performance in detecting magnetic fields and offers strong portability. In various fields, including magnetic anomaly localization, battery current detection, and medical diagnosis, it possesses significant potential for application.

Invisible microstrip defect detection is of great significance for ensuring the reliability of integrated circuits and improving the performance of communication system. In this article, the microwave fields radiated by six typically invisible microstrip defects were experimentally characterized with high accuracy based on quantum wide-field microscope, and the origin of microwave field contrast was theoretically analyzed. In a view of 1400 $\times$ 700 $\mu$ m $^{2}$ , the microwave near-field distribution radiated by invisible microstrip defects was reconstructed with a resolution of 1.63 $\mu$ m/pixel, and the microwave magnetic field detection sensitivity reached 0.7 nT/Hz $^{\mathrm{1/2}}$ . Meanwhile, the causes of microwave field discrepancies were analyzed specifically on the basis of microstrip transmission line theory. It was attributed to the transmission loss and the uneven distribution of induced current arising from variations in geometrical structures. The phenomenon validated the feasibility of detecting invisible microstrip defects utilizing the microwave field intensity distribution. The proposed approach is expected to have applications in microchip design and radio frequency (RF) equipment maintenance, thereby notably improving the practicability of quantum measurement technology.