Hexagonal boron nitride (hBN) has emerged as a critical material for atomic layer passivation due to its unique combination of thermal, chemical, and electrical properties. Its layered structure, analogous to graphene but with an insulating bandgap, makes it an ideal candidate for protecting surfaces and interfaces in advanced electronic and catalytic systems. Unlike encapsulation, which involves fully surrounding a material, passivation with hBN focuses on forming ultrathin protective layers that mitigate degradation mechanisms such as oxidation, diffusion, and charge scattering while preserving the underlying material's functionality.

One of the primary advantages of hBN is its exceptional chemical inertness. The material is highly resistant to oxidation, even at elevated temperatures, making it suitable for protecting reactive surfaces in harsh environments. For instance, transition metals like copper or silver, which are prone to oxidation when exposed to air, can be effectively passivated with a monolayer or few-layer hBN coating. Studies have shown that hBN layers as thin as 2-3 nanometers can suppress oxidation by acting as a diffusion barrier, preventing oxygen molecules from reaching the underlying metal surface. This property is particularly valuable in electronic devices where metal electrodes or interconnects must remain stable over long operational lifetimes.

In addition to oxidation resistance, hBN serves as an effective barrier against atomic or molecular diffusion. Its tightly packed hexagonal lattice structure limits the movement of small atoms and ions, such as hydrogen or lithium, which are common in battery electrodes or catalytic systems. For example, in lithium-ion batteries, hBN-passivated electrodes exhibit reduced side reactions with the electrolyte, leading to improved cycling stability. Similarly, in catalytic applications, hBN layers can prevent the sintering of metal nanoparticles by inhibiting the surface diffusion of metal atoms at high temperatures, thereby maintaining catalytic activity over extended periods.

Charge scattering at interfaces is another critical issue that hBN passivation addresses. In electronic devices, unwanted charge scattering can degrade carrier mobility and overall performance. The atomically smooth surface of hBN minimizes interfacial roughness, leading to reduced scattering rates. When used as a passivation layer in field-effect transistors (FETs), hBN has been shown to preserve high carrier mobility in two-dimensional materials like graphene or transition metal dichalcogenides (TMDCs). For instance, graphene devices passivated with hBN demonstrate carrier mobilities exceeding 100,000 cm²/Vs at room temperature, significantly higher than those with conventional oxide passivation layers. This improvement is attributed to the absence of dangling bonds and charged impurities on the hBN surface, which otherwise act as scattering centers.

The role of hBN in electronics extends beyond passive protection. Its wide bandgap (~6 eV) and high dielectric strength make it an excellent insulating layer in heterostructures. In vertical device architectures, such as tunneling transistors or memristors, hBN passivation ensures clean interfaces with minimal trap states, enabling precise control over charge transport. Moreover, its thermal conductivity, which rivals that of some metals, aids in heat dissipation, reducing thermal degradation in high-power devices. These properties are particularly beneficial in radio-frequency (RF) and optoelectronic applications, where device performance is sensitive to interfacial quality.

Catalysis is another domain where hBN passivation plays a transformative role. In heterogeneous catalysis, the stability of active sites is often compromised by surface poisoning or structural changes under reaction conditions. By depositing ultrathin hBN layers on catalytic surfaces, researchers have achieved enhanced stability without sacrificing activity. For example, platinum nanoparticles passivated with hBN exhibit improved resistance to carbon deposition in hydrocarbon reforming reactions. The hBN layer selectively allows reactant molecules to reach the active sites while blocking larger poisons or sintering-inducing species. This selective permeability stems from the precise interlayer spacing and defect engineering in hBN, which can be tuned to accommodate specific molecular sizes.

The application of hBN passivation is not limited to metals or inorganic materials. Organic semiconductors, which are sensitive to environmental degradation, also benefit from hBN layers. In organic light-emitting diodes (OLEDs) or photovoltaic devices, hBN passivation reduces moisture and oxygen ingress, prolonging device lifetimes. Unlike traditional encapsulation methods that add bulk and rigidity, hBN provides protection without compromising flexibility, making it suitable for wearable or bendable electronics.

Despite its advantages, the implementation of hBN passivation requires precise control over layer thickness and quality. Defects such as grain boundaries or vacancies can compromise its barrier properties, necessitating advanced growth techniques like chemical vapor deposition (CVD) or atomic layer deposition (ALD). Recent advances in scalable synthesis have enabled the production of large-area, defect-free hBN films, paving the way for industrial adoption.

In summary, hexagonal boron nitride serves as a versatile atomic layer passivation material, offering robust protection against oxidation, diffusion, and charge scattering. Its applications span high-performance electronics, energy storage, and catalysis, where interfacial stability is paramount. As synthesis techniques continue to improve, hBN passivation is poised to become a cornerstone in the development of next-generation devices and systems.