Optical photons are ubiquitous in quantum communication and storage applications due to their long coherence times and ease to travel over long distances. On-demand quantum photon sources that may emit single photons as quantum information carriers are especially sought after for quantum-related applications. In this talk, I will present our recent effort in the development of solid-state quantum photon sources based on low-dimensional semiconductor materials. By atomic defect creation [1,2] and local strain field engineering,[3-7] we demonstrate versatile approaches for efficient single photon generation and modulation.

References:

[1] W. Wang et al, ACS Nano, 16, 21240 (2022)

[2] Q. Qian et al. ACS Nano, 16, 7428 (2022)

[3] M. I. B. Utama et al. Nat. Commun. 14, 2193 (2023)

[4] X. Li et al. J. Phys. Chem. C 126, 20057 (2022)

[5] D. J. Morrow et al. Phys. Rev. B 104, 195302 (2021)

[6] W. Wang et al. ACS Photon. 7, 2460 (2021)

[7] L. Peng et al. Nano Lett. 20, 5866 (2020)

Since its discovery, graphene has shown to exhibit remarkable electronic properties.¹ Numerous techniques have been devised to create high-performance devices by manipulating the bandgap in order to enhance their semiconducting properties.²

Doping has proven to be one of the most effective methods for bandgap engineering. Experimental and theoretical studies on graphene doping show the possibility of making p-type and n-type semiconducting graphene by substituting C atoms. Boron and nitrogen have been specifically studied during the last years due to the interesting insulating behavior of h-BN. Boron, nitrogen, and carbon can be atomically mixed to form various semiconducting, hexagonal, layered structures. Experimental and theoretical studies have indicated that BNC nanostructures show semiconducting properties with small bandgaps.^2,3 Low concentrations of borazine rings within the graphene structure can modify graphene’s electronic properties to form a 2D semiconductor material with homogeneous patterns.^4,5The intercalation of hexagonal BN (h-BN) within the graphene lattice has already been successfully achieved, however, segregation of both materials has been the main issue. Recent research has demonstrated that incorporating borazine-like molecules with carbon structures into graphene can result in reduced segregation of h-BN domains.^5,6 Herrera Reinoza et al. demonstrated a notable example by depositing hexamethylborazine onto Ir(111), which yielded numerous boron-nitrogen-carbon (BNC) domains exhibiting low BN segregation and an estimated bandgap ranging between 1.4 and 1.6 eV.⁶

To grow our boron nitride-doped graphene nanomaterial (Figure 1a) we first synthesized graphene via chemical vapor deposition (CVD) by cyclic exposures to 10^-5 mbar of ethylene for 10 minutes with subsequent annealing at 1100 K for 10 minutes. We have successfully doped our graphene by exposing it to hexamethylborazine right after the 3^rd cycle of graphene synthesis. Auger electron spectroscopy depicted in Figure 1b demonstrated the presence of B, C and N in the sample. As depicted in Figure 1c, a bandgap was opened on our BN-doped graphene, forming a semiconductor material.

Transition metal chalcogenides are promising 2D materials due to their unique properties and emerging phenomena such as charge density waves, superconductivity, ferroelectricity and ferromagnetism. Specifically the transition metal trichalcogenides of the form AX₃ (A=Ti, Zr, Hf, X=S, Se, Te ) exhibit a quasi 1-D nature with anisotropic bandstructure which leads to preferential charge transport along the chain direction and minimal edge scattering effects suitable for fabricating high-performance devices. In this study, we examine the surface sensitivity of a high pressure grown Ti-Te transition metal chalcogenide using the chemical vapor transport (CVT) technique and study the surface changes in the sample upon exposure to air. The high-pressure growth results in the formation of silvery mirror-like sheets and nanowhiskers atypical of bulk 1T-TiTe₂ growth, which is usually black and non-reflective. The silvery materials are capable of mechanical exfoliation via the scotch tape method and if left in atmosphere turn a darker color within a few hours. The crystal structure and size of the sheets are examined using X-Ray Diffraction (XRD), transmission electron microscopy (TEM), and select area electron diffraction (SAED). The material adopts a preferential (001) single crystalline nature with monoclinic structure and P2 1/m space group symmetry. Additionally, the SAED patterns show signs of a superlattice formation at the surface of the exposed layer. The local density of states (LDOS) of the in-situ exfoliated sample surface, measured using scanning tunneling spectroscopy (STS), exhibits a metallic to semi-conducting transition, with narrow gap, when exposed to atmosphere, suggesting the surface rapidly decomposes. The STM topography indicates a decrease in surface roughness after exposure to atmosphere reminiscent of ad-layer/s formation at the surface. X-ray photoemission spectroscopy confirms the surface of the exposed sample contains -OH, O₂, -H, H₂O ad-atom species. Stability and reactivity of such layered materials has been a field of interest to researchers lately as these materials have the ability for extreme sensitivity when incorporated into a gas sensor device. In the interest of optical and gas sensing we fabricate simple FET devices and measure the opto-electronic properties while exposing to different wavelengths of light and gases (CO₂, H₂, H₂O, and N₂).