Ziwei Wang

Area-selective atomic layer deposition (AS-ALD) is a nanofabrication method delivering atomic layers of patterned films with exceptional precision, but it still relies on vacuum hardware and surface chemistry pretreatments that limit flexibility and throughput. Direct atomic layer processing (DALP) is an ALD-based technique that allows the deposition of single atomic layers in an additive fashion through a micronozzle, with no requirements for vacuum. In this work, we demonstrate DALP deposition of line-patterned TiO2 2–18 nm thin films deposited at temperatures from 80 to 250 °C. We show that the films were locally deposited, with no overspray, with a surface uniformity of 0.03 ± 0.01 nm, and a roughness in the range of 0.23 ± 0.09 nm (80 °C) to 0.57 ± 0.05 nm (250 °C). Moreover, we find that the films undergo a transient growth regime at a low number of cycles, with low nucleation delay (0–11 cycles) and a rapid growth relaxation with decay time-constants τ from 18 to 32 cycles, depending on the temperature. A linear growth regime is achieved after ≈3τ, with values from 0.033 ± 0.001 (250 °C) to 0.052 ± 0.003 (80 °C) nm/cycle. These results show that DALP produces ALD quality TiO2 at ambient pressure and line speeds up to 200 mm/s, providing a high-throughput alternative to inhibitor-based AS-ALD.

Low-symmetry crystals have emerged as a platform for exploring unique light-matter interactions in the form of hyperbolic shear polaritons. These excitations exhibit unique properties such as frequency-dispersive optical axes and asymmetric light propagation and energy dissipation. However, only non-vdW materials have been demonstrated to support hyperbolic shear polaritons, limiting their exotic properties and potential applications. Here, we introduce shear phenomena in low symmetry crystals by demonstrating elliptical and canalized shear phonon polaritons in gypsum, an exfoliable monoclinic sulphate mineral. Our results unveil a topological transition from hyperbolic shear to elliptical shear polaritons, passing through a canalization regime with strong field confinement. We observe a notable slowdown of group velocity, reaching values as low as 0.0005 c . These findings expand the application scope of low-symmetry crystals with the benefits that an exfoliable material provides, such as stronger field confinement, tunability, and versatility for its incorporation in complex photonic devices.

Hydrogen bonding plays a crucial role in biology and technology, yet it remains poorly understood and quantified despite its fundamental importance. Traditional models, which describe hydrogen bonds as electrostatic interactions between electropositive hydrogen and electronegative acceptors, fail to quantitatively capture bond strength, directionality, or cooperativity, and cannot predict the properties of complex hydrogen-bonded materials. Here, we introduce a concept of hydrogen bonds as elastic dipoles in an electric field, which captures a wide range of hydrogen bonding phenomena in various water systems. Using gypsum, a hydrogen bond heterostructure with two-dimensional structural crystalline water, we calibrate the hydrogen bond strength through an externally applied electric field. We show that our approach quantifies the strength of hydrogen bonds directly from spectroscopic measurements and reproduces a wide range of key properties of confined water reported in the literature. Using only the stretching vibration frequency of confined water, we can predict hydrogen bond strength, local electric field, O-H bond length, and dipole moment. Our work also introduces hydrogen bond heterostructures – a class of electrically and chemically tunable materials that offer stronger, more directional bonding compared to van der Waals heterostructures, with potential applications in areas such as catalysis, separation, and energy storage.

Hydrogen bonding plays a crucial role in biology and technology, yet it remains poorly understood and quantified despite its fundamental importance. Traditional models, which describe hydrogen bonds as electrostatic interactions between electropositive hydrogen and electronegative acceptors, fail to quantitatively capture bond strength, directionality, or cooperativity, and cannot predict the properties of complex hydrogen-bonded materials. Here, we introduce a novel approach that conceptualizes the effect of hydrogen bonds as elastic dipoles in an electric field, which captures a wide range of hydrogen bonding phenomena in various water systems. Using gypsum, a hydrogen bond heterostructure with two-dimensional structural crystalline water, we calibrate the hydrogen bond strength through an externally applied electric field. We show that our approach quantifies the strength of hydrogen bonds directly from spectroscopic measurements and reproduces a wide range of key properties of confined water reported in the literature. Using only the stretching vibration frequency of confined water, we can predict hydrogen bond strength, local electric field, O-H bond length, and dipole moment. Our work also introduces hydrogen bond heterostructures - a new class of electrically and chemically tunable materials that offer stronger, more directional bonding compared to van der Waals heterostructures, with potential applications in areas such as catalysis, separation, and energy storage.