Publications

AbstractWe systematically investigate the best process conditions that ensure synthesis of different types of one-dimensional cadmium selenide nanostructures with high yield and reproducibility. Through a designed experiment and rigorous statistical analysis of experimental data, models linking the probabilities of obtaining specific morphologies to the process variables are developed. A new iterative algorithm for fitting a multinomial generalized linear model is proposed and used. The optimum process conditions, which maximize the preceding probabilities and make the synthesis process robust (i.e., less sensitive) to variations in process variables around set values, are derived from the fitted models using Monte Carlo simulations.Cadmium selenide has been found to exhibit one-dimensional morphologies of nanowires, nanobelts, and nanosaws, often with the three morphologies being intimately intermingled within the as-deposited material. A slight change in growth condition can result in a totally different morphology. To identify the optimal process conditions that maximize the yield of each type of nanostructure and, at the same time, make the synthesis process robust (i.e., less sensitive) to variations of process variables around set values, a large number of trials were conducted with varying process conditions. Here, the response is a vector whose elements correspond to the number of appearances of different types of nanostructures. The fitted statistical models would enable nanomanufacturers to identify the probability of transition from one nanostructure to another when changes, even tiny ones, are made in one or more process variables. Inferential methods associated with the modeling procedure help in judging the relative impact of the process variables and their interactions on the growth of different nanostructures. Owing to the presence of internal noise, that is, variation around the set value, each predictor variable is a random variable. Using Monte Carlo simulations, the mean and variance of transformed probabilities are expressed as functions of the set points of the predictor variables. The mean is then maximized to find the optimum nominal values of the process variables, with the constraint that the variance is under control.KEY WORDS: Cadmium selenide nanostructuresGeneralized linear modelMultinomialNanotechnologyRobust designStatistical modeling

One-dimensional semiconductors with wurtzite structure, such as GaN, ZnO and CdS nano/microwires, exhibit superior semiconductor, piezoelectric and mechanical properties, making them excellent candidates for novel electronic, opto-electronic devices and integrated systems. More importantly, the coupling between piezoelectric polarization and semiconductor properties (including electric transport and photoexcitation) gives rise to unique and unprecedented physical characteristics and has led to emerging fields of piezotronics and piezo-phototronics. On the basis of the extensive studies in c-axis semiconductor nano/microwires, piezotronics and piezo-phototronics based on a-axis nano/microwires have further been explored and demonstrated recently. We review both the fundamental progresses and developed applications of piezotronics and piezo-phototronics based on a-axis nano/microwires, which further improve the theoretical framework and expand the practical applications of piezotronics and piezo-phototronics in functional nanodevices and nanosystems.

A highly-efficient, lightweight, flexible, piezoelectric lead zirconate titanate (PZT) thin-film nanogenerator is demonstrated by employing the laser lift-off transfer technique and a lateral electrode structure. As reported by K. J. Lee and co-workers on page 2514, this large-area PZT thin-film nanogenerator can convert to the highest output performance from a slight mechanical deformation and provides the feasibility of fully flexible self-powered electronics.

Effectively harvesting ambient mechanical energy is the key for realizing self‐powered and autonomous electronics, which addresses limitations of batteries and thus has tremendous applications in sensor networks, wireless devices, and wearable/implantable electronics, etc. Here, a thin‐film‐based micro‐grating triboelectric nanogenerator (MG‐TENG) is developed for high‐efficiency power generation through conversion of mechanical energy. The shape‐adaptive MG‐TENG relies on sliding electrification between complementary micro‐sized arrays of linear grating, which offers a unique and straightforward solution in harnessing energy from relative sliding motion between surfaces. Operating at a sliding velocity of 10 m/s, a MG‐TENG of 60 cm 2 in overall area, 0.2 cm 3 in volume and 0.6 g in weight can deliver an average output power of 3 W (power density of 50 mW cm −2 and 15 W cm −3 ) at an overall conversion efficiency of ∼50%, making it a sufficient power supply to regular electronics, such as light bulbs. The scalable and cost‐effective MG‐TENG is practically applicable in not only harvesting various mechanical motions but also possibly power generation at a large scale.

Abstract Inorganic lead halide perovskite has become an emerging material for modern photoelectric and electronic nanodevices due to its excellent optical and electronic properties. In view of its huge dielectric and electrical properties, inorganic CsPbBr 3 perovskite is introduced into the piezoelectric nanogenerator (PENG). Based on one‐step electrospinning of solutions containing CsPbBr 3 precursors and polyvinylidene difluoride (PVDF), in situ growth of CsPbBr 3 nanocrystals in PVDF fibers (CsPbBr 3 @PVDF composite fibers) with highly uniform size and spatial distribution are synthesized. The CsPbBr 3 @PVDF composite fibers based PENG reveals an open‐circuit voltage ( V oc ) of 103 V and a density of short‐circuit current ( I sc ) of 170 µ A cm −2 , where the V oc is comparable to the state‐of‐the‐art hybrid composite piezoelectric nanogenerators (PENGs) and the density of I sc is 4.86 times higher than that of lead halide perovskites counterpart ever reported. Moreover, CsPbBr 3 @PVDF composite fibers based PENG exhibits fundamentally improved thermal/water/acid–base stabilities. This study suggests that the CsPbBr 3 @PVDF composite fiber is a good candidate for fabricating high‐performance PENGs, promising application potentials in mechanical energy harvesting and motion sensing technologies.