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Typical titanium oxide (TiO2) films are transparent in the visible range, allowing for their index of refraction and thickness to be extracted by single-angle spectroscopic ellipsometry (SE) using a Cauchy model. However, TiO2 films grown by atomic layer deposition (ALD) from tetrakis(dimethylamino)titanium (IV) (TDMAT) and H2O at 350 °C absorb in the visible range due to the formation of Ti-O-N/Ti-N bonds. Single-angle SE is inadequate for extracting the optical constants of these films, as there are more unknowns (n, k, d) than measurable parameters (ψ, Δ). To overcome this limitation, we combined SE with transmission (T) measurements, a method known as SE + T. In the process, we developed an approach to prevent backside deposition on quartz substrates during ALD deposition. When applying a B-spline model to SE + T data, the film thicknesses on the quartz substrates closely matched those on companion Si samples measured via standard lithography. The resulting optical constants indicate a reduced refractive index, n, and increased extinction coefficient, k, when compared to purer TiO2 thin films deposited via a physical vapor deposition (PVD) method, reflecting the influence of nitrogen incorporation on the optical properties. 

Abstract This study investigates the presence of titanium oxynitride bonds in titanium dioxide (TiO₂) thin films grown by atomic layer deposition (ALD) using tetrakis dimethyl amino titanium (TDMAT) and water at temperatures between 150 and 350 °C and its effect on the films’ optical and electrical properties. Compositional analysis using X‐ray photoelectron spectroscopy (XPS) reveals increased incorporation of oxynitride bonds as the process temperature increases. Furthermore, depth profile data demonstrates an increase in the abundance of this type of bonding from the surface to the bulk of the films. Ultraviolet‐visible spectroscopy (UV‐vis) measurements correlate increased visible light absorption for the films with elevated oxynitride incorporation. The optical constants (n, k) of the films show a pronounced dependence on the process temperature that is mirrored in the film conductivity. The detection of oxynitride bonding suggests a secondary reaction pathway in this well‐established ALD process chemistry, that may impact film properties. These findings indicate that the choice of process chemistry and conditions can be used to optimize film properties for optoelectronic applications. 

Nonlinear refractive index, n2 , values as high as 1±.1x10 -9 cm 2 /W were measured in atomic layer deposition (ALD) grown TiO 2 nanoscale films, using femtosecond thermally managed Z-scan. The several order of magnitude increase in n 2 is believed due to the incorporation of nitrogen during growth. 

Optical cavities can enhance and control light-matter interactions. This level of control has recently been extended to the nanoscale with single emitter strong coupling even at room temperature using plasmonic nanostructures. However, emitters in static geometries, limit the ability to tune the coupling strength or to couple different emitters to the same cavity. Here, we present tip-enhanced strong coupling (TESC) with a nanocavity formed between a scanning plasmonic antenna tip and the substrate. By reversibly and dynamically addressing single quantum dots, we observe mode splitting up to 160 meV and anticrossing over a detuning range of ~100 meV, and with subnanometer precision over the deep subdiffraction-limited mode volume. Thus, TESC enables previously inaccessible control over emitter-nanocavity coupling and mode volume based on near-field microscopy. This opens pathways to induce, probe, and control single-emitter plasmon hybrid quantum states for applications from optoelectronics to quantum information science at room temperature. 

Abstract Quantum state control of two‐level emitters is fundamental for many information processing, metrology, and sensing applications. However, quantum‐coherent photonic control of solid‐state emitters has traditionally been limited to cryogenic environments, which are not compatible with implementation in scalable, broadly distributed technologies. In contrast, plasmonic nano‐cavities with deep sub‐wavelength mode volumes have recently emerged as a path toward room temperature quantum control. However, optimization, control, and modeling of the cavity mode volume are still in their infancy. Here recent demonstrations of plasmonic tip‐enhanced strong coupling (TESC) with a configurable nano‐tip cavity are extended to perform a systematic experimental investigation of the cavity‐emitter interaction strength and its dependence on tip position, augmented by modeling based on both classical electrodynamics and a quasinormal mode framework. Based on this work, a perspective for nano‐cavity optics is provided as a promising tool for room temperature control of quantum coherent interactions that could spark new innovations in fields from quantum information and quantum sensing to quantum chemistry and molecular opto‐mechanics.