Driven by tensile strain, GaAs quantum dots (QDs) self-assemble on In0.52Al0.48As(111)A surfaces lattice-matched to InP substrates. In this study, we show that the tensile-strained self-assembly process for these GaAs(111)A QDs unexpectedly deviates from the well-known Stranski-Krastanov (SK) growth mode. Traditionally, QDs formed via the SK growth mode form on top of a flat wetting layer (WL) whose thickness is fixed. The inability to tune WL thickness has inhibited researchers’ attempts to fully control QD-WL interactions in these hybrid 0D-2D quantum systems. In contrast, using microscopy, spectroscopy, and computational modeling, we demonstrate that for GaAs(111)A QDs, we can continually increase WL thickness with increasing GaAs deposition, even after the tensile-strained QDs (TSQDs) have begun to form. This anomalous SK behavior enables simultaneous tuning of both TSQD size and WL thickness. No such departure from the canonical SK growth regime has been reported previously. As such, we can now modify QD-WL interactions, with future benefits that include more precise control of TSQD band structure for infrared optoelectronics and quantum optics applications.
The emergence of two-dimensional (2D) materials as functional surfaces for sensing, electronics, mechanics, and other myriad applications underscores the importance of understanding 2D material–liquid interactions. The thinness and environmental sensitivity of 2D materials induce novel surface forces that drive liquid interactions. This complexity makes fundamental 2D material–liquid interactions variable. In this review, we discuss the (1) wettability, (2) electrical double layer (EDL) structure, and (3) frictional interactions originating from 2D material–liquid interactions. While many 2D materials are inherently hydrophilic, their wettability is perturbed by their substrate and contaminants, which can shift the contact angle. This modulation of the wetting behavior enables templating, filtration, and actuation. Similarly, the inherent EDL at 2D material–liquid interfaces is easily perturbed. This EDL modulation partially explains the wettability modulation and enables distinctive electrofluidic systems, including supercapacitors, energy harvesters, microfluidic sensors, and nanojunction gating devices. Furthermore, nanoconfinement of liquid molecules at 2D material surfaces arising from a perturbed liquid structure results in distinctive hydrofrictional behavior, influencing the use of 2D materials in microchannels. We expect 2D material–liquid interactions to inform future fields of study, including modulation of the chemical reactivity of 2D materials via tuning 2D material–liquid interactions. Overall, 2D material–liquid interactions are a rich more »
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Anomalous Stranski-Krastanov growth of (111)-oriented quantum dots with tunable wetting layer thickness
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