UC Berkeley

Low-dimensional semiconductor nanomaterials, especially focused on one- and two- dimensional nanomaterials have attracted much attention due to their intriguing physical and chemical properties as well as promising prospects for a variety of applications such as electronic and optoelectronic devices, batteries, and sensors for chemical and biological molecules. Recently, intense research has been carried out all over the world on low-dimensional semiconducting nanomaterials. However, many important issues still remain unrevealed and unexplored concerning the direct localized synthesis and the modulation of functionalities by means of structural machining and doping. In order to realize these, development of new methods and tools is needed that would enable precise layout and processing of the nanoscale components into functional building blocks.

In this study, laser-assisted method applied to one- and two-dimensional semiconducting nanomaterials. For one-dimensional semiconducting nanomaterials, the silicon nanowires (SiNWs) and indium nitride nanowires (InN NWs) were grown by the laser-assisted chemical vapor deposition (LACVD) and laser-assisted metal organic vapor phase epitaxy (LAMOVPE) method, respectively. Laser-assisted synthesis provides advantages in controlling process conditions such as growth time and laser irradiation power. To achieve additional controllability of growth direction in the laser-assisted SiNW growth technique, an electrically biased sharp tip was employed. Extending the material space of the laser-assisted method, the LAMOPVE method was introduced to selectively synthesize InN NWs on amorphous silicon substrates and subsequently drive growth via a vapor-liquid-solid (VLS) mechanism with gold nanoparticle (AuNP) catalyst. For two-dimensional layered semiconducting nanomaterials, laser-assisted thinning and patterning enables effective control of the layer thickness and shape, therefore achieving nanoscale fabrication capability. In addition to modulating the optical and electronic properties of two-dimensional layered nanomaterials for on-demand tuning of high performance devices, substitutional p-type laser doping and simultaneously included laser annealing were applied. On-demand fabrication of two-dimensional transition metal dichalcogenides (TMDCs) materials especially, MoS2, laser processing (thinning and patterning) was utilized to fabricate materials by apertured and apertureless near-field scanning optical microscope (NSOM) arrangements. Furthermore, fiber tip-based NSOM processing, micro-Raman spectroscopy and electron spectroscopy were integrated in a TEM apparatus used to in-situ monitor and characterize laser driven nanofabrication. Finally, the localized laser irradiation will also be utilized to drive atomic scale controlled deposition for incorporation of p-type dopant, phosphorus into the TMDCs, including p-type materials of WSe2 and WS2 as well as n-type material of MoS2. The spatial and temporal selectivity of laser-assisted processing enabled optimization the parametric process space. As a result, laser-assisted phosphorus doping controllably produced extraordinary enhancement and decrease of photoluminescence (PL) characteristics on n- and p-type materials, respectively.