Liquid phase exfoliation has progressed in recent years to become a common method of production for 2D materials. During exfoliation, surfactants can be used to stabilize the nanosheets against reaggregation. Here, using WS2 as a model system, we explore the effect of varying surfactant type and concentration on the yield and dimensions of the exfoliated nanosheets. For ionic surfactants, the mass of nanosheets produced was constant for low surfactant concentrations but decreased sharply for surfactant concentrations above ~10 mM, regardless of surfactant. Very similar surfactant-concentration dependence was observed for both nanosheet length and thickness. Contrary to previous reports, this data implies that the optimum surfactant concentration is not linked to the critical micelle concentration. In addition, we found that surfactant concentrations as low as 0.07 mM yielded stable nanosheet dispersions with zeta potential above 40 mV. By decoupling the exfoliation and stabilization effects of the surfactant, we have shown that it is the (de)stabilization process, rather than the exfoliation process, which links nanosheet concentration, size and thickness to surfactant concentration.

This work is a systematic experimental and theoretical study of the in‐plane dielectric functions of 2D gallium and indium films consisting of two or three atomic metal layers confined between silicon carbide and graphene with a corresponding bonding gradient from covalent to metallic to van der Waals type. k‐space resolved free electron and bound electron contributions to the optical response are identified, with the latter pointing towards the existence of thickness dependent quantum confinement phenomena. The resonance energies in the dielectric functions and the observed epsilon near‐zero behavior in the near infrared to visible spectral range, are dependent on the number of atomic metal layers and properties of the metal involved. A model‐based spectroscopic ellipsometry approach is used to estimate the number of atomic metal layers, providing a convenient route over expensive invasive characterization techniques. A strong thickness and metal choice dependence of the light–matter interaction makes these half van der Waals 2D polar metals attractive for quantum engineered metal films, tunable (quantum‐)plasmonics and nano‐photonics.

Titanium disulfide is a promising material for a range of applications, including lithium-ion battery (LIB) anodes.

Nonlinear frequency mixing (e.g. harmonic generation) and polarization rotation of electromagnetic waves are the foundation of many important and emergent applications, including laser technologies, optical switches, and frequency combs, among others. 1 The current state-ofthe-art for second-order harmonic generation is achieved using a sequence of multiple quantum wells that are designed to enhance transitions resonantly at both fundamental and harmonic frequencies. 2 However, these systems are intrinsically limited to the mid infrared, precluding their operation at frequencies relevant for optical imaging and telecommunications. Therefore, new materials that can achieve large nonlinear optical responses over a broader range of frequencies are needed. Here, we describe near-infrared-to-visible second harmonic generation for two-