Jin Liu

Bio: Jin Liu is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Nanowire & Nanogenerator. The author has an hindex of 23, co-authored 37 publications receiving 5600 citations. Previous affiliations of Jin Liu include IBM & Georgia Tech Research Institute.

Direct-current nanogenerator driven by ultrasonic waves

Abstract: We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output. The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. The wave drives the electrode up and down to bend and/or vibrate the nanowires. A piezoelectric-semiconducting coupling process converts mechanical energy into electricity. The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems.

Piezoelectric field effect transistor and nanoforce sensor based on a single ZnO nanowire.

Abstract: Utilizing the coupled piezoelectric and semiconducting dual properties of ZnO, we demonstrate a piezoelectric field effect transistor (PE-FET) that is composed of a ZnO nanowire (NW) (or nanobelt) bridging across two Ohmic contacts, in which the source to drain current is controlled by the bending of the NW. A possible mechanism for the PE-FET is suggested to be associated with the carrier trapping effect and the creation of a charge depletion zone under elastic deformatioin. This PE-FET has been applied as a force/pressure sensor for measuring forces in the nanonewton range and even smaller with the use of smaller NWs. An almost linear relationship between the bending force and the conductance was found at small bending regions, demonstrating the principle of nanowire-based nanoforce and nanopressure sensors.

Nanowire Piezoelectric Nanogenerators on Plastic Substrates as Flexible Power Sources for Nanodevices

Abstract: Research applications in biomedical science and technology usually require various portable, wearable, easy-to-use, and/or implantable devices that can interface with biological systems. Organic or hybrid organic–inorganic microelectronics and nanoelectronics have long been a possibility. However, these devices require a power source, such as electrochemical cells or piezoelectric, thermoelectric, and pyroelectric transducers, to generate or store the electrical energy created through chemical, mechanical, or thermal processes. Finding a suitable power source has remained a major challenge for many devices in bioengineering and medical fields. ZnO is a typical piezoelectric and pyroelectric inorganic semiconducting material used for electromechanical and thermoelectrical energy conversion. Nanostructures of ZnO, such as nanowires (NWs), nanobelts (NBs), nanotubes, nanorings, nanosprings, and nanohelices, have attracted extensive research interest because of their potential applications as nanoscale sensors and actuators. While most of the current applications focus on its semiconducting properties, only a few efforts have utilized the nanometerscale piezoelectric properties of ZnO. Using ZnO NW arrays grown on a single-crystal sapphire substrate, we have successfully converted mechanical energy into electrical energy at the nanoscale. A conductive atomic force microscopy (AFM) tip was used in contact mode to deflect the aligned NWs. The coupling of piezoelectric and semiconducting properties in ZnO creates a strain field and charge separation across the NWs as a result of their bending. The rectifying characteristic of the Schottky barrier formed between the metal tip and the NW leads to electrical current generation. This is the principle behind piezoelectric nanogenerators. The ceramic and semiconducting substrates used for growing ZnO NWs are hard and brittle and cannot be used in applications that require a foldable or flexible power source, such as implantable biosensors. In this Communication, by using ZnO NW arrays grown on a flexible plastic substrate, we demonstrate the first successful flexible power source built on conducting-polymer films. This approach has two specific advantages: it uses a cost-effective, large-scale, wet-chemistry strategy to grow ZnO NW arrays at temperatures lower than 80 °C, and the growth of aligned ZnO NW arrays can occur on a large assortment of flexible plastic substrates. The latter advantage could play an important role in the flexible and portable electronics industry. Various dimensions, shapes, and orientations of ZnO NWs and microwires on flexible plastic substrates have been shown to be capable of producing piezoelectric voltage output, giving a real advantage for energy harvesting using large-scale ZnO NW arrays. The voltage generated from a single NW can be as high as 50 mV, which is large enough to power many nanoscale devices. The ZnO NWs were grown in solution using a synthetic chemistry approach. Figure 1 shows a series of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of typical ZnO NW arrays grown on a conductive plastic substrate. Figure 1a shows a low-resolution, topdown view of the densely aligned NW arrays. The aligned NWs have a uniform diameter of 200–300 nm and a hexagoC O M M U N IC A IO N

ZnO nanobelt/nanowire Schottky diodes formed by dielectrophoresis alignment across au electrodes.

Abstract: Rectifying diodes of single nanobelt/nanowire-based devices have been fabricated by aligning single ZnO nanobelts/nanowires across paired Au electrodes using dielectrophoresis. A current of 0.5 μA at 1.5 V forward bias has been received, and the diode can bear an applied voltage of up to 10 V. The ideality factor of the diode is ∼3, and the on-to-off current ratio is as high as 2000. The detailed IV characteristics of the Schottky diodes have been investigated at low temperatures. The formation of the Schottky diodes is suggested due to the asymmetric contacts formed in the dielectrophoresis aligning process.

Piezoelectric gated diode of a single zno nanowire

Abstract: ) characteristics re-ceived at different levels of deformation were included in the-oretical calculations. The magnitude of the piezoelectric bar-rier dominates the rectifying effect. The rectifying ratio couldbe as high as 8.7:1 by simply bending a NW. The operationcurrent ratio of a straight to a bent ZnO NW could be as highas 9.3:1 at reverse bias. This also shows that the NW can serveas a random access memory (RAM) unit.Figure 1a shows a typical scanning electron microscopy(SEM) image of a well-aligned ZnO NW array. Figure 1bshows a typical transmission electron microscopy (TEM) im-age of a single ZnO NW. The corresponding selected-areaelectron diffraction pattern (Fig. 1c) confirms that the phaseof the NWs is hexagonal wurtzite-structured ZnO. Figure 1dis a high-resolution TEM (HRTEM) image from the outlinedregion indicated in Figure 1b. Figure 1c and d shows that theZnO NWs are single-crystalline and free of dislocations. Thegrowth direction of the ZnO NW was determined to be[0001].In situ

Coaxial silicon nanowires as solar cells and nanoelectronic power sources

Abstract: Solar cells are attractive candidates for clean and renewable power; with miniaturization, they might also serve as integrated power sources for nanoelectronic systems. The use of nanostructures or nanostructured materials represents a general approach to reduce both cost and size and to improve efficiency in photovoltaics. Nanoparticles, nanorods and nanowires have been used to improve charge collection efficiency in polymer-blend and dye-sensitized solar cells, to demonstrate carrier multiplication, and to enable low-temperature processing of photovoltaic devices. Moreover, recent theoretical studies have indicated that coaxial nanowire structures could improve carrier collection and overall efficiency with respect to single-crystal bulk semiconductors of the same materials. However, solar cells based on hybrid nanoarchitectures suffer from relatively low efficiencies and poor stabilities. In addition, previous studies have not yet addressed their use as photovoltaic power elements in nanoelectronics. Here we report the realization of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells. Under one solar equivalent (1-sun) illumination, the p-i-n silicon nanowire elements yield a maximum power output of up to 200 pW per nanowire device and an apparent energy conversion efficiency of up to 3.4 per cent, with stable and improved efficiencies achievable at high-flux illuminations. Furthermore, we show that individual and interconnected silicon nanowire photovoltaic elements can serve as robust power sources to drive functional nanoelectronic sensors and logic gates. These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis, and might find general usage as elements for powering ultralow-power electronics and diverse nanosystems.

Direct-current nanogenerator driven by ultrasonic waves

Abstract: We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output. The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. The wave drives the electrode up and down to bend and/or vibrate the nanowires. A piezoelectric-semiconducting coupling process converts mechanical energy into electricity. The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems.

Recent Progress in Multiferroic Magnetoelectric Composites: from Bulk to Thin Films

Abstract: Multiferroic magnetoelectric composite systems such as ferromagnetic-ferroelectric heterostructures have recently attracted an ever-increasing interest and provoked a great number of research activities, driven by profound physics from coupling between ferroelectric and magnetic orders, as well as potential applications in novel multifunctional devices, such as sensors, transducers, memories, and spintronics. In this Review, we try to summarize what remarkable progress in multiferroic magnetoelectric composite systems has been achieved in most recent few years, with emphasis on thin films; and to describe unsolved issues and new device applications which can be controlled both electrically and magnetically.

Fiber‐Based Wearable Electronics: A Review of Materials, Fabrication, Devices, and Applications

Abstract: Fiber-based structures are highly desirable for wearable electronics that are expected to be light-weight, long-lasting, flexible, and conformable Many fibrous structures have been manufactured by well-established lost-effective textile processing technologies, normally at ambient conditions The advancement of nanotechnology has made it feasible to build electronic devices directly on the surface or inside of single fibers, which have typical thickness of several to tens microns However, imparting electronic functions to porous, highly deformable and three-dimensional fiber assemblies and maintaining them during wear represent great challenges from both views of fundamental understanding and practical implementation This article attempts to critically review the current state-of-arts with respect to materials, fabrication techniques, and structural design of devices as well as applications of the fiber-based wearable electronic products In addition, this review elaborates the performance requirements of the fiber-based wearable electronic products, especially regarding the correlation among materials, fiber/textile structures and electronic as well as mechanical functionalities of fiber-based electronic devices Finally, discussions will be presented regarding to limitations of current materials, fabrication techniques, devices concerning manufacturability and performance as well as scientific understanding that must be improved prior to their wide adoption