硕士生贺梓萌同学在国际纳米权威期刊Nano Letters上发表论文

      近日，课题组成员张贤同学在刘老师的指导下，以第一作者在国际纳米权威期刊《纳米快报》(Nano Letters，影响因子12.94)上发表题为 “Twist-angle-controlled built-in field reversal enables programmable self-powered photodetection in low-symmetry heterostructures”(通过扭转角控制的内置场反转，可在低对称异质结构中实现可编程自供电光探测)的实验论文。

图：通过扭转角控制的内置场反转，可在低对称异质结构中实现可编程自供电光探测

      二维半导体及其范德华异质结构为光探测提供了有效平台。在这类体系中，原子级锐利的界面和可调控的能带排列有利于实现高效的光生载流子产生、分离和输运。然而，在现有大多数光探测器结构中，界面电荷动力学的调控主要依赖于静电栅控。 该方法通过施加外部电场来重塑能带弯曲和载流子分布，并已被广泛用于偏振敏感光电器件中，以增强横向电学响应。 尽管这种方法有效，但通常需要持续的功率输入来维持非平衡界面电场，从而增强载流子分离。另一类研究则采用更复杂的界面设计，例如引入铁电材料，利用其剩余极化来建立非易失内建电场。 然而，这类结构仍然依赖外部电压脉冲实现极化翻转，从而增加了能耗和操作复杂性。此外，器件疲劳和保持特性退化也可能影响其长期稳定性。 因此，如何实现对界面电场的本征、稳定且低能耗调控，仍然是范德华光探测器领域面临的核心挑战。

      扭转异质结构提供了一条本质上不同的调控路径，其中几何构型本身即可作为界面重构和器件功能调控的控制参数。 与依赖外部电场不同，扭转角能够重新定义原子配准关系和层间轨道耦合，从而实现对界面电荷分布、内建电场和载流子动力学的本征调控。这种由结构定义的调控机制避免了外场驱动方法所带来的高能耗和稳定性问题，为在界面层面直接编程光电响应提供了有前景的策略。对于各向异性过渡金属硫族化合物而言，这一可能性尤其引人关注。其低对称晶体结构使得界面极化电荷和内部电场构型对相对晶格取向高度敏感。 当两个各向异性层发生相对旋转时，各向异性的电荷分布和轨道耦合会有效投影到界面法向方向，从而同时调节界面电场的方向和大小。包括黑磷、 ReS₂ 和 NbOI₂ 在内的代表性体系已经揭示了这种取向依赖的界面物理，并进一步凸显了结构自由度在低对称范德华体系电场工程中的巨大潜力。

      在本研究中，我们以扭转 ReS₂/ReSe₂ 异质结构为模型体系，证明扭转范德华界面的结构自由度可以转化为对界面重构和各向异性电荷动力学的有效调控。我们发现，改变扭转角能够连续重构各向异性晶轴之间的相对取向，从而驱动界面极化电荷及其所产生的内建电场逐步演化。当堆垛构型接近正交取向时，主导的内部电场发生极性反转。这种由几何构型驱动的界面静电势重组进一步重塑了载流子解离过程和各向异性载流子输运行为，并由此编程偏振依赖光响应，获得最高达 5.06 的偏振比。我们的结果表明，扭转角不再只是一个几何描述参数，而可以作为几何可编程光电子学中的功能设计变量，为在低对称范德华异质结构中集成传感、信息编码和安全功能提供了新的可能。

文章链接：https://pubs.acs.org/doi/full/10.1021/acs.nanolett.6c02233

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Twisting Interfaces to Reverse Built-in Fields in van der Waals Photodetectors

Two-dimensional van der Waals heterostructures have transformed the way researchers design photodetectors. By stacking atomically thin semiconductors, it becomes possible to create sharp interfaces, tunable band alignments, and efficient pathways for photogenerated carriers. Yet one central challenge remains: how can the internal electric field that separates photoexcited electrons and holes be controlled without relying on continuous external bias, complex ferroelectric switching, or additional gate structures?

A recent study addresses this question by showing that the answer may lie not in adding another functional layer, but in rotating the existing ones. In twisted ReS₂/ReSe₂ heterostructures, the relative crystallographic orientation between two low-symmetry layers becomes an intrinsic control parameter for interfacial electrostatics. By changing the twist angle, the authors demonstrate a continuous reconstruction of interfacial polarization charges and a reversal of the built-in electric field near the orthogonal stacking configuration. This twist-controlled field reversal enables self-powered photodetection, tunable polarization sensitivity, and hardware-level information encoding.

The work is conceptually important because most van der Waals photodetectors rely on externally imposed fields to improve carrier separation. Electrostatic gates can reshape band bending and carrier distributions, but they require applied voltage and continuous electrical control. Ferroelectric layers can provide nonvolatile internal fields, but they introduce additional material complexity, switching pulses, fatigue, and retention concerns. In contrast, twist angle is a structural degree of freedom: once defined during fabrication, it programs the interface without requiring sustained electrical input. This shifts twist engineering from a tool for band-structure manipulation to a strategy for designing built-in electric fields and device functions.

The authors focus on ReS₂/ReSe₂, a particularly suitable platform because both materials possess low-symmetry crystal structures and pronounced in-plane anisotropy. In such systems, the direction of the Re–Re chains strongly influences optical absorption, carrier mobility, and interlayer coupling. When the two layers are rotated relative to one another, their anisotropic charge distributions and orbital overlaps no longer align. This misalignment reconstructs the interfacial charge landscape and modifies the direction and magnitude of the internal electric field.

Experimentally, devices with twist angles of 0°, 30°, 60°, and 90° were fabricated and characterized. Polarization-resolved Raman spectroscopy confirms the relative crystal orientations, while electrical and optoelectronic measurements reveal a striking evolution of the interfacial response. As the twist angle increases, the open-circuit voltage shifts gradually from positive to negative values, indicating that the built-in electric field does not switch abruptly but evolves through the competition between multiple interfacial dipole contributions. At 90°, the twist-induced dipole becomes dominant and reverses the polarity of the built-in field.

This field reversal has direct consequences for photodetection. Under zero-bias illumination, the 90° device exhibits a photocurrent polarity opposite to that of the other twist configurations and shows a markedly enhanced photocurrent magnitude. The resulting self-powered photoresponse reaches an on/off ratio as high as 10⁵, together with a responsivity of 3.48 A W⁻¹ and a detectivity of 3.76 × 10¹³ Jones. These values are notable because they are achieved through a built-in field programmed by the twist geometry itself, rather than by external biasing.

The study also reveals that twist angle controls not only the magnitude and polarity of the photocurrent, but also its polarization dependence. In the 0° device, where the anisotropic axes of ReS₂ and ReSe₂ are aligned, the photocurrent shows a strong two-lobed polarization pattern with a maximum polarization ratio of 5.06. This reflects the dominant role of the aligned Re–Re chains in guiding anisotropic absorption and carrier transport. As the twist angle increases, this two-lobed response evolves toward a more complex, nearly four-lobed pattern, indicating that interfacial scattering, orbital misalignment, and anisotropic transport pathways increasingly contribute to the photocurrent. Thus, twist angle provides a route to tune between strongly polarization-selective photodetection and multidirectional polarization-sensitive sensing.

A further attractive aspect of the work is the translation of twist-defined device responses into information encoding. By assigning different twist configurations to binary states, the authors demonstrate a hardware-level encoding scheme based on twist-angle-engineered photodetectors. Under zero-bias illumination, 0° and 90° devices can be distinguished by opposite photocurrent polarities and different current magnitudes. Under biased operation, polarization-dependent photocurrent ratios provide an additional decoding mode, in which the analyzer angle functions as a physical key. This illustrates how deterministic structure–property relationships in twisted heterostructures can be used not only for sensing but also for device identification, anti-counterfeiting, and optoelectronic security.

The broader significance of this study lies in its use of geometry as a functional design principle. Twistronics is often associated with moiré bands, correlated electronic states, or excitonic reconstruction. Here, twist angle is instead used to program an internal electric field and device-level photodetection output. This perspective is especially valuable for low-symmetry materials, where crystal orientation and interfacial anisotropy can strongly influence charge separation, recombination, and transport. The work therefore expands the functional scope of twist engineering from electronic structure control to built-in-field engineering and programmable optoelectronics.

Several questions remain for future research. A key challenge will be the scalable fabrication of twist-angle-defined device arrays with precise angular control and high reproducibility. It will also be important to further quantify device-to-device variation, long-term environmental stability, and operational durability under practical illumination and biasing conditions. From a mechanistic perspective, direct nanoscale mapping of interfacial charge redistribution and local electric fields would provide deeper insight into how twist-induced dipoles emerge in low-symmetry heterostructures. Theoretical modeling that incorporates anisotropic orbital overlap, interlayer charge transfer, and exciton dissociation could further strengthen the connection between atomic registry and macroscopic photocurrent.

Despite these open questions, the study provides a compelling demonstration of how structural rotation can be converted into a functional optoelectronic variable. By showing that a 90° twist can reverse the built-in electric field and enable efficient self-powered photodetection, the work highlights a powerful strategy for designing low-power, multifunctional van der Waals devices. More broadly, it suggests that in low-symmetry two-dimensional systems, geometry is not merely a structural parameter—it can be an active information-bearing and field-programming degree of freedom.

In this sense, twisted ReS₂/ReSe₂ heterostructures offer more than another photodetector architecture. They provide a platform in which interfacial electrostatics, anisotropic transport, polarization sensitivity, and information encoding are all governed by the same geometric control parameter. Such a unified structure–function relationship may inspire future developments in self-powered photodetection, polarization-resolved imaging, hardware security, and programmable optoelectronic systems based on low-symmetry van der Waals interfaces.