The large-scale crossbar array is a promising architecture for hardware-amenable energy efficient three-dimensional memory and neuromorphic computing systems. While accessing a memory cell with negligible sneak currents remains a fundamental issue in the crossbar array architecture, up-to-date memory cells for large-scale crossbar arrays suffer from process and device integration (one selector one resistor) or destructive read operation (complementary resistive switching). Here, we introduce a self-selective memory cell based on hexagonal boron nitride and graphene in a vertical heterostructure. Combining non-volatile and volatile memory operations in the two hexagonal boron nitride layers, we demonstrate a self-selectivity of 10 10 with an on/off resistance ratio larger than 10 3 . The graphene layer efficiently blocks the diffusion of volatile silver filaments to integrate the volatile and non-volatile kinetics in a novel way. Our self-selective memory minimizes sneak currents on large-scale memory operation, thereby achieving a practical readout margin for terabit-scale and energy-efficient memory integration.

Synaptic computation, which is vital for information processing and decision making in neural networks, has remained technically challenging to be demonstrated without using numerous transistors and capacitors, though significant efforts have been made to emulate the biological synaptic transmission such as short-term and long-term plasticity and memory. Here, we report synaptic computation based on Joule heating and versatile doping induced metal-insulator transition in a scalable monolayer-molybdenum disulfide (MoS) device with a biologically comparable energy consumption (∼10 fJ). A circuit with our tunable excitatory and inhibitory synaptic devices demonstrates a key function for realizing the most precise temporal computation in the human brain, sound localization: detecting an interaural time difference by suppressing sound intensity- or frequency-dependent synaptic connectivity. This Letter opens a way to implement synaptic computing in neuromorphic applications, overcoming the limitation of scalability and power consumption in conventional CMOS-based neuromorphic devices.

Phase engineering is a breakthrough for various electronic and energy device applications with transition metal dichalcogenides (TMDs). Chemical methods, such as lithium intercalation, are mostly used for phase engineering, which achieves atomically thin flakes and high catalytic performances in several group 6 TMDs including MoS 2 . However, chemical methods cannot be applied to MoTe 2 , a widely investigated group 6 TMD with intriguing semiconducting, topological, and catalytic properties. The lack of modifying MoTe 2 by chemical methods remains a puzzling issue considering the small energy difference between the polymorphs of MoTe 2 . Here, a convectionassisted lithium ion intercalation and phase transition is reported to achieve a vertical heterophase in a MoTe 2 crystal. The vertical heterophase in MoTe 2 reduces the Schottky barrier with metal electrodes down to 66 meV, enhancing the overall ion conductance for electrochemical hydrogen production. Moreover, the weakened adhesion of the 1T' phase layers on the top and bottom surfaces in the vertical heterophase, formed by the intercalation, enables a unique surface tension-driven exfoliation of MoTe 2 flakes. The heterophase chemical engineering suggests a new platform for hybrid catalysts and next-generation electronic devices based on 2D materials.

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Conventional gating in transistors uses electric fields through external dielectrics that require complex fabrication processes. Various optoelectronic devices deploy photogating by electric fields from trapped charges in neighbor nanoparticles or dielectrics under light illumination. Orbital gating driven by giant Stark effect is demonstrated in tunneling phototransistors based on 2H‐MoTe2 without using external gating bias or slow charge trapping dynamics in photogating. The original self‐gating by light illumination modulates the interlayer potential gradient by switching on and off the giant Stark effect where the dz2‐orbitals of molybdenum atoms play the dominant role. The orbital gating shifts the electronic bands of the top atomic layer of the MoTe2 by up to 100 meV, which is equivalent to modulation of a carrier density of 7.3 × 1011 cm–2 by electrical gating. Suppressing conventional photoconductivity, the orbital gating in tunneling phototransistors achieves low dark current, practical photoresponsivity (3357 AW–1), and fast switching time (0.5 ms) simultaneously.