Zhuolei Zhang

Hybrid Chalcopyrite–Polymer Magnetoconducting Materials

The search for emerging materials combining magnetic and semiconducting properties has attracted widespread interest in contemporary materials science. Chalcopyrite (CuFeS2), as an earth abundant and nontoxic chalcogenide compound in the I-III-VI2 family, is a promising class of such materials that exhibit unusual electrical, optical, and magnetic properties. However, its successful implementation largely depends on our ability to understand, control and manipulate their structural, transport and spin behavior. Here we show that solution processing monodispersed CuFeS2 quantum dots exhibit a strong coupling among optical, electronic, and magnetic degrees of freedom. The photoresponse and magnetoconductance of CuFeS2 quantum dots are realized under external stimuli. We further exploit a fast and efficient way to achieve an exceptionally large performance in a magneto-optoelectronic hybrid system consisting of magnetic semiconducting CuFeS2 and conducting polymer matrix. The results demonstrate a promising potential of magnetic semiconductor CuFeS2 in the field of spin electronics.

Tunable electroresistance and electro-optic effects of transparent molecular ferroelectrics

A water-based approach grows molecular ferroelectric thin film with tunable electroresistance and electro-optic effect. Recent progress in molecular ferroelectrics (MOFEs) has been overshadowed by the lack of high-quality thin films for device integration. We report a water-based air-processable technique to prepare large-area MOFE thin films, controlled by supersaturation growth at the liquid-air interface under a temperature gradient and external water partial pressure. We used this technique to fabricate ImClO4 thin films and found a large, tunable room temperature electroresistance: a 20-fold resistance variation upon polarization switching. The as-grown films are transparent and consist of a bamboo-like structure of (2,1¯,0) and (1,0,2¯) structural variants of R3m symmetry with a reversible polarization of 6.7 μC/cm2. The resulting ferroelectric domain structure leads to a reversible electromechanical response of d33 = 38.8 pm/V. Polarization switching results in a change of the refractive index, n, of single domains, Δnn=0.3. The remarkable combination of these characteristics renders MOFEs a prime candidate material for new nanoelectronic devices. The information that we present in this work will open a new area of MOFE thin-film technologies.

Rational design of molecular crystals for enhanced charge transfer properties

Here, using solution based self-assembly, we contrast a three-dimensional co-crystal, where a [1]benzothieno[3,2-b][1]benzothiophene (BTBT) based donor and a tetracyanoquinodimethane (TCNQ) based acceptor leads to a mixed stacking sequence with pronounced intermolecular hybridization, with the donor–acceptor bilayer. Despite a comparable increase in conductivity, we observe a co-crystal with unique mechano-pyro-electric coupling properties.

Freestanding Organic Charge-Transfer Conformal Electronics

Wearable conformal electronics are essential components for next-generation humanlike sensing devices that can accurately respond to external stimuli in nonplanar and dynamic surfaces. However, to explore this potential, it is indispensable to achieve the desired level of deformability and charge-transport mobility in strain-accommodating soft semiconductors. Here, we show pseudo-two-dimensional freestanding conjugated polymer heterojunction nanosheets integrated into substrate-free conformal electronics owing to their exceptional crystalline controlled charge transport and high level of mechanical strength. These freestanding and mechanical robust polymer nanosheets can be adapted into a variety of artificial structured surfaces such as fibers, squares, circles, etc., which produce large-area stretchable conformal charge-transfer sensors for real-time static and dynamic monitoring.

Mechanically Strong Polymer Sheets from Aligned Ultrahigh-Molecular-Weight Polyethylene Nanocomposites

Ultrahigh-molecular-weight polyethylene (UHMWPE) is of great interest as a next-generation body armor material because of its superior mechanical properties. However, such unique properties depend critically on its microscopic structure characteristics, including the degree of crystallinity, chain alignment, and morphology. Here, we present a highly aligned UHMWPE and its composite sheets containing uniformly dispersed boron nitride (BN) nanosheets. The dispersion of BN nanosheets into the UHMWPE matrix increases its mechanical properties over a broad temperature range. Experiments and simulation confirm that the alignment of chain segments in the composite matrix increases with temperature, leading to an improvement in mechanical properties at high temperature. Together with the large thermal conductivity of UHMWPE and BN, our findings serve to expand the application spectrum of highly aligned polymer nanocomposite materials for ballistic panels and body armor over a broad range of temperatures.

Author Correction: Tunable two-dimensional interfacial coupling in molecular heterostructures

We regretfully omitted to give credit to a previous figure upon which the surface-tension scheme in Fig. 1b is based. The caption to Fig. 1 should have included the following: “The surface-tension scheme in Fig. 1b is adapted from Fig. 1a in Noh, J., Jeong, S. & Lee, J.-Y. Ultrafast formation of air-processable and high-quality polymer films on an aqueous substrate. Nat. Commun.7, 12374 (2016).”

Chiral Molecular Ferroelectrics with Polarized Optical Effect and Electroresistive Switching

Multifunctional properties of chiral molecules arise from the coexistence of mirror-symmetry-induced stereoisomers and optical rotation characteristics in one material. One of these complex phenomena in these molecules is chiral ferroelectricity, providing the coupling between polarized light and the spatial asymmetry induced dipole moment. Herein we describe the chiral polarization and electroresistance in molecular ferroelectric (R)-(-)-3-hydroxyquinuclidinium chloride thin films with a Curie temperature of 340 K. The high transmittance of chiral ferroelectrics is coupled with polarized light for a linear electro-optic effect, which exhibits angle-dependent optical behaviors. The polarization-controlled conductance imposes a large on/off ratio (∼26.6) of electroresistive switching in molecular ferroelectrics with superior antifatigue endurance.