Oxidizing Hexagonal Boron Nitride into Fluorescent Structures by Photodissociated Directional Oxygen Radical

Abstract

Modifying the wide band gap semiconductor hexagonal boron nitride (hBN) can bring new chances in photonics. By virtue of the solvothermal/hydrothermal oxidation or functionalization, hBN can be converted into fluorescent nanodots. Until now, it has been a big challenge to drily oxidize hBN and turn it into bright fluorescent structures due to its superior chemical stability. Here, we report the oxidation of multilayer hBN into fluorescent structures by ultraviolet (UV, λ = 172 nm) photodissociated directional oxygen radical [O( 3 P)] in a gradient magnetic field. The paramagnetic O( 3 P), produced in a low-pressure O 2 atmosphere, drifts toward hBN and then converts it into boron nitride oxide (BNO) micro/nanometer structures constituted by BO, BO 2 , and O-doped hBN. For a properly oxidized BNO substance, bright and photostable wide-band photoluminescence is realized with nanosecond-scaled lifetimes under the excitation of UV and visible lights.

Photochemically Patterning Graphene in a Highly Efficient, Anisotropic, and Clean Way

“…Table 1 compares v zmax , maximum drift energy W zmax , thermal velocity v T , and thermal energy W T . In a low-pressure atmosphere (20 Pa), the randomly moving H 2 O, OH(X 2 Π), and H(1 2 S) substances collide with the mean free path all in the order of 10 −4 m. 24 Generally speaking, the radicals behave much like a strong wind blowing with their drift energy three orders lower than their molecular thermal energy. This behavior is completely different from the highly dynamic ions of RIE in the electric field.…”

“…Similar to O( 3 P), the OH(X 2 Π) radical is capable of etching hBN at a high speed due to its extremely strong oxidability. 24 As for other materials like tungsten disulfide (WS 2 ), the photochemical oxidation is not to etch but to turn its surface into transparent nanostructures. A wide study should be carried out in detail in order to deeply understand the strong photochemical oxidation and explore its potential applications.…”

“…Even at low oxygen pressure, the instable diamagnetic intermediate of ozone can impair the etching anisotropy by its random motion. 24,25 A few kinds of H 2 O-based etching, either isotropic or anisotropic, have been developed to pattern graphene. 26−30 The paramagnetic hydroxyl radical OH(X 2 Π), a much stronger oxidant photodissociated from H 2 O, is more efficient and anisotropic in the etching process.…”

“…However, the photochemical etching efficiency was extremely low due to severe intermolecular collisions at the pressure of tens of kilopascals. Even at low oxygen pressure, the instable diamagnetic intermediate of ozone can impair the etching anisotropy by its random motion. , …”

“…As common sense, this method is too mild to be applied in the field of etching . To overcome this obstacle, we have developed a magnetic-controlled photodissociated directional radical technique to improve its oxidation intensity and anisotropy in the past few years. ,, Using the paramagnetic oxygen radical O­( 3 P), high-quality graphene microstructures were patterned underneath a shadow mask through irradiation of a xenon excimer lamp (λ = 172 nm) . However, the photochemical etching efficiency was extremely low due to severe intermolecular collisions at the pressure of tens of kilopascals.…”