About

Professor Xi Ling joined the Department of Chemistry and Division of Materials Science & Engineering at Boston University as an assistant professor in September 2016. She completed her postdoctoral research in the Research Laboratory of Electronics at MIT under the guidance of Professors Mildred Dresselhaus and Jing Kong, where she specialized in the chemical vapor deposition (CVD) synthesis of two-dimensional (2D) materials and their heterostructures, as well as materials characterization using spectroscopic techniques. Professor Ling earned her Ph.D. in Physical Chemistry at Peking University in China, working with Professors Jin Zhang and Zhongfan Liu. During her doctoral studies, she discovered the graphene-enhanced Raman scattering (GERS) effect and conducted systematic investigations into this phenomenon. Her research focuses on nanomaterials, structures, and spectroscopy, particularly involving 2D materials and their applications.

Research topics

• Materials science
• Optoelectronics
• Nanotechnology
• Condensed matter physics
• Physics
• Optics
• Chemistry
• Molecular physics
• Chemical physics

Selected publications

• Long-Lived Population Inversion in Resonantly Driven Excitonic Antiferromagnet

  Physical Review Letters · 2025-01-02 · 4 citations

  articleOpen access

  Van der Waals magnets are an emerging material family for investigating light-matter interactions and spin-correlated excitations. Here, we report the discovery of a photo-induced state with a lifetime of 17 ps in the van der Waals antiferromagnet NiPS_{3}, which appears exclusively with resonant pumping at 1.476 eV in the antiferromagnetic state. The long-lived state comes with a negative photoconductivity, a characteristic optical response of population inversion. Our findings demonstrate a promising pathway to potentially achieve long-lived lasing at terahertz frequencies in reduced dimensions.

  PublisherOA PDFDOI

• Mo Atom Rearrangement Drives Layer-Dependent Reactivity in Two-Dimensional MoS2

  ArXiv.org · 2025-09-04

  preprintOpen accessSenior author

  Two-dimensional (2D) materials offer a valuable platform for manipulating and studying chemical reactions at atomic level, owing to the ease of controlling their microscopic structure at the nanometer scale. While extensive research has been conducted on the structure-dependent chemical activity of 2D materials, the influence of structural transformation during the reaction remains largely unexplored. In this work, we report the layer-dependent chemical reactivity of MoS2 during a nitridation atomic substitution reaction and attribute it to the rearrangement of Mo atoms. Our results show that the chemical reactivity of MoS2 decreases as the number of layers is reduced in the few-layer regime. In particular, monolayer MoS2 exhibits significantly lower reactivity compared to its few-layer and multilayer counterparts. Atomic-resolution transmission electron microscope (TEM) reveals that MoN nanonetworks form as reaction products from monolayer and bilayer MoS2, with the continuity of the MoN crystals increasing with layer number, consistent with the local conductivity mapping data. The layer-dependent reactivity is attributed to the relative stability of the hypothetically formed MoN phase which retain the number of Mo atomic layers present in the precursor. Specifically, the low chemical reactivity of monolayer MoS2 is attributed to the high energy cost associated with Mo atom diffusion and migration necessary to form multi-layer Mo lattices in the thermodynamically stable MoN phase. This study underscores the critical role of lattice rearrangement in governing chemical reactivity and highlights the potential of 2D materials as versatile platforms for advancing the understanding of materials chemistry at atomic scale.

  PublisherOA PDFDOI

• Homogenization and Rapid Oxidation of Spiro‐OMeTAD with Ionic Liquids for Efficient Perovskite Solar Cells

  Small · 2025-05-07 · 3 citations

  article

  Abstract Spiro‐OMeTAD is widely recognized as the most effective hole transport layer (HTL) for n‐i‐p perovskite solar cells (PSCs), which typically requires doping with LiTFSI to overcome its low inherent conductivity. However, the doping takes a prolonged oxidation (≈24 h) in an ambient atmosphere, hindering the commercial development. Moreover, the aggregation of LiTFSI leads to poor conductivity and accelerated degradation of the HTL, which are often ignored. This study introduces the long‐chain ionic liquid 1‐octyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (OMIMTFSI) as a multifunctional additive to mitigate the aggregation of LiTFSI and promote the oxidation of Spiro‐OMeTAD simultaneously. The strong electrostatic interactions between OMIM + and LiTFSI, coupled with the dispersion effect of OMIM + in chlorobenzene, effectively hamper the aggregation of LiTFSI, beneficial for uniform doping and enhanced conductivity. The OMIM + also facilitates rapid oxidation of Spiro‐OMeTAD by attracting lone pair electrons from the triphenylamine group. As a result, the power conversion efficiency of PSCs processed in air is significantly improved from 21.48% to 24.04% with enhanced stability, maintaining over 80% of initial values after storing in air for 1360 h or under light and heat treatment for 500 h. This strategy provides valuable insights of designing lithium salt‐doped Spiro‐OMeTAD for efficient and stable PSCs.

  PublisherDOI

• Mo Atom Rearrangement Drives Layer-Dependent Reactivity in Two-Dimensional MoS₂

  Journal of the American Chemical Society · 2025-09-09 · 4 citations

  articleSenior authorCorresponding

  Two-dimensional (2D) materials offer a valuable platform for manipulating and studying chemical reactions at the atomic level, owing to the ease of controlling their microscopic structure at the nanometer scale. While extensive research has been conducted on the structure-dependent chemical activity of 2D materials, the influence of structural transformation during the reaction has remained largely unexplored. In this work, we report the layer-dependent chemical reactivity of MoS2 during a nitridation atomic substitution reaction and attribute it to the rearrangement of Mo atoms. Our results show that the chemical reactivity of MoS2 decreases as the number of layers is reduced in the few-layer regime. In particular, monolayer MoS2 exhibits significantly lower reactivity compared with its few-layer and multilayer counterparts. Atomic-resolution transmission electron microscopy (TEM) reveals that MoN nanonetworks form as reaction products from monolayer and bilayer MoS2, with the continuity of the MoN crystals increasing with layer number, consistent with the local conductivity mapping data. The layer-dependent reactivity is attributed to the relative stability of the hypothetically formed MoN phase, which retains the number of Mo atomic layers present in the precursor. Specifically, the low chemical reactivity of monolayer MoS2 is attributed to the high energy cost associated with Mo atom diffusion and migration necessary to form multilayer Mo lattices in the thermodynamically stable MoN phase. This study underscores the critical role of lattice rearrangement in governing chemical reactivity and highlights the potential of 2D materials as versatile platforms for advancing the understanding of materials chemistry at the atomic scale.

  PublisherDOI

• A novel IgD-FcδR blocker, IgD-Fc-Ig fusion protein, effectively alleviates abnormal activation of T cells the disease progression in systemic lupus erythematosus

  Biochemical Pharmacology · 2025-04-07 · 3 citations

  article
  PublisherDOI

• Sustainable Lignocellulosic Room Temperature Phosphorescent Inks for Intelligent Packaging and Anti-Counterfeiting

  ACS Sustainable Chemistry & Engineering · 2025-05-08 · 7 citations

  article

  Developing sustainable room-temperature phosphorescent (RTP) inks from abundant biomass resources is extremely attractive but remains a significant challenge in the field. Herein, the RTP lignocellulose was facilely prepared by simple immersion of lignocellulose powder in MgCl2 solutions. Compared to untreated lignocellulose, lignocellulose treated with 1 M MgCl2 exhibited a 10.7-fold increase in RTP intensity and a significantly prolonged RTP lifetime of 315.8 ms. The enhanced RTP performance of the treated lignocellulose is attributed to the synergistic effect of enhancing hydrogen bond interactions to suppress non-radiative transitions and narrowing the energy gap to accelerate the intersystem crossing (ISC) rate. Subsequently, the RTP lignocellulose was formulated into environmentally friendly water-based inks for screen printing using poly(vinyl alcohol) (PVA) as the binder, which was applied to the humidity-responsive smart labels in biscuit packaging and RTP anti-counterfeiting with time-resolved and multilevel information encryption. This research provides a new strategy for the development of sustainable RTP inks and prints.

  PublisherDOI

• Atomic substitution approach for electronic non-vdW 2D materials

  2025-03-19

  article1st authorCorresponding

  Atomically thin materials often exhibit extraordinary chemical, optical, electronic, and magnetic properties compared with their bulk 3D counterparts, enabling a variety of applications for next generation electronics and quantum information technologies. While extensive research has been conducted on 2D van der Waals (vdW) materials such as graphene and Transition Metal Dichalcogenides (TMDs), little attention has been given to non vdW materials, which make up most materials in nature. One significant challenge is the lack of an effective synthesis method to access them. In this talk, I will introduce an atomic substitution approach that we have developed to convert vdW layered materials to nanometer thin non vdW materials with tunable thicknesses, desired dimensions, and properties for fundamental physics investigations and nanodevices. As a model system, we will investigate the conversion process from TMDs (e.g. MoS2 and WS2) to corresponding metal nitrides (e.g. MoNx and WNx), characterize the electronic properties of the obtained metal nitrides, and highlight the advantages of this approach in creating new 2D heterostructures as desired building blocks for 2D electronics.

  PublisherDOI

• Downscaling of Non-Van der Waals Semimetallic W₅N₆ with Resistivity Preservation

  ACS Nano · 2025-01-16 · 7 citations

  articleSenior authorCorresponding

  The bulk phase of transition metal nitrides (TMNs) has long been a subject of extensive investigation due to their utility as coating materials, electrocatalysts, and diffusion barriers, attributed to their high conductivity and refractory properties. Downscaling TMNs into two-dimensional (2D) forms would provide valuable members to the existing 2D materials repertoire, with potential enhancements across various applications. Moreover, calculations have anticipated the emergence of uncommon physical phenomena in TMNs at the 2D limit. In this study, we use the atomic substitution approach to synthesize 2D W5N6 with tunable thicknesses from tens of nanometers down to 2.9 nm. The obtained flakes exhibit high crystallinity and smooth surfaces. Electrical measurements on 15 samples show an average electrical conductivity of 161.1 S/cm, which persists while thickness decreases from 45.6 to 2.9 nm. The observed weak gate-tuning effect suggests the semimetallic nature of the synthesized 2D W5N6. Further investigation of the conversion mechanism elucidates the crucial role of chalcogen vacancies in the precursor for initiating the reaction and strain in propagating the conversion. Our work introduces a desired semimetallic crystal to the 2D material library with mechanistic insights for future design of the synthesis.

  PublisherDOI

• Characteristic exciton energy scales in antiferromagnetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>NiPS</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

  Physical review. B./Physical review. B · 2025-04-07 · 5 citations

  articleOpen access

  Two-dimensional antiferromagnets are promising materials for spintronics. The van der Waals antiferromagnet ${\mathrm{NiPS}}_{3}$ has attracted extensive interest due to its ultranarrow exciton feature which is closely linked with the magnetic ordering. Here, we use time-resolved terahertz spectroscopy to investigate photoexcited carriers in ${\mathrm{NiPS}}_{3}$. We identify the onset of interband transitions and estimate the exciton dissociation energy from the excitation wavelength and fluence dependence of the transient spectral weight. Our results provide key insights to quantify the exciton characteristics and validate the band structure for ${\mathrm{NiPS}}_{3}$.

  PublisherOA PDFDOI

• Self‐Catalyzed Chemically Coalescing Liquid Metal Emulsions

  Advanced Science · 2025-04-26 · 6 citations

  articleOpen access

  Abstract Gallium‐based liquid metal alloys (GaLMAs) have widespread applications ranging from soft electronics, energy devices, and catalysis. GaLMAs can be transformed into liquid metal emulsions (LMEs) to modify their rheology for facile patterning, processing, and material integration for GaLMA‐based device fabrication. One drawback of using LMEs is reduced electrical conductivity owing to the oxides that form on the surface of dispersed liquid metal droplets. LMEs thus need to be activated by coalescing liquid metal droplets into an electrically conductive network, which usually involves techniques that subject the LME to harsh conditions. This study presents a way to coalesce these droplets through a chemical reaction at mild temperatures ( T ∼ 80 °C). Chemical activation is enabled by adding halide compounds into the emulsion that chemically etch the oxide skin on the surface of dispersed droplets of eutectic gallium indium (eGaIn). LMEs synthesized with halide activators can achieve electrical conductivities close to bulk liquid metal (2.4 × 10 4 S cm −1 ) after being heated. 3D printable chemically coalescing LME ink formulations are optimized by systematically exploring halide activator type and concentration, along with mixing conditions, while maximizing for electrical conductivity, shape retention, and compatibility with direct ink writing (DIW). The utility of this ink is demonstrated in a hybrid 3D printing process to create a battery‐integrated light emitting diode array, followed by a nondestructive low temperature heat activation that produces a functional device.

  PublisherOA PDFDOI

Recent grants

• MRI: Acquisition of an X-Ray Photoelectron Spectrometer (XPS) for Materials Related Research and Education at Boston University

  NSF · $600k · 2022–2025

• CAREER: Deciphering 2-Dimensional, Crystal-Mediated, Surface-Enhanced Raman Scattering for Quantitative Analysis

  NSF · $679k · 2020–2025

Frequent coauthors

• Jin Zhang

  Jilin University

  92 shared

• Jing Kong

  Beijing Aerospace Flight Control Center

  68 shared

• M. S. Dresselhaus

  Massachusetts Institute of Technology

  49 shared

• Zhongfan Liu

  Beijing National Laboratory for Molecular Sciences

  36 shared

• Shengxi Huang

  Jiangsu University

  35 shared

• Nannan Mao

  IIT@MIT

  33 shared

• Liming Xie

  Inner Mongolia Electric Power (China)

  28 shared

• Yuxuan Lin

  27 shared

Labs

• Ling Group: Nanomaterials, Structures & SpectroscopyPI

Education

• Ph.D., Materials Science and Engineering

  Boston University

  2015

• M.S., Materials Science and Engineering

  University of X

  2010

• B.S., Materials Science and Engineering

  University of Y

  2008

Awards & honors

• NSF Career Award (2020)
• BU Ignition Award, Boston University (2020)
• MSE Innovation Award, Boston University (2017)
• University Provost's Career Development Professorship, Bosto…
• Electrical Engineering and Computer Science (EECS) Rising St…