arXiv subjects

Yueyun Chen

Publications and source records attributed to Yueyun Chen.

5 recordsLinked to original sources

arXiv2026

An Improved Paralyzable Detector Model

Certain radiation detectors are 'paralyzed' with high input count rates. When applied to count rates close to the event discriminator working rate the one-parameter dead time model fails. Here we present a corrected paralyzable detector model accounting for the event discriminator's finite response time. This two-parameter analytical model, when compared to the experimental data from a commercial x-ray detector, gives an improved description of the input and output count rate relations. Furthermore, it can independently determine the discriminator response time and the pulse shaper dead time, critical parameters for understanding a detector's performance. Finally, this model also provides a post-acquisition pile-up correction that greatly reduces artifacts in high-throughput spectra. In some situations, applying this model to optimize the acquisition and post-acquisition correction allows a user to acquire data an order of magnitude faster without compromising accuracy.

physics.ins-det↗

arXiv2025

Mapping Temperature Using Transmission Kikuchi Diffraction

Electronic devices are engineered at increasingly smaller length scales; new metrologies to understand nanoscale thermodynamics are needed. Temperature and pressure are fundamental thermodynamic quantities whose nanoscale measurement is challenging as physical contact inevitably perturbs the system. Here we demonstrate Kikuchi diffraction thermometry (KDTh), a non-contact scanning electron microscope (SEM) technique capable of mapping nanoscale temperatures and pressures. KDTh detects local volumetric lattice changes in crystalline samples by precisely fitting Kikuchi patterns. Temperature changes are deduced using the coefficient of thermal expansion (CTE). We map lattice parameters and temperatures on Joule-heated graphite by rastering a 5.5-nm electron probe across the sample. Our parameter precision is ~0.01% and our temperature sensitivity is 2.2 K/$\sqrt{Hz}$. KDTh offers advanced sensitivity by fitting the entire Kikuchi pattern, even beyond the precision measured in transmission electron microscopy. KDTh can operate in both transmission (transmission Kikuchi diffraction, TKD) and reflection (electron backscatter diffraction, EBSD) modes.

cond-mat.mes-hall↗

arXiv2025

Modification of the scattering mechanisms in bilayer graphene in proximity to a molecular thin film probed in the mesoscopic regime

Quantum coherent effects can be probed in multilayer graphene through electronic transport measurements at low temperatures. In particular, bilayer graphene is known to be susceptible to quantum interference corrections of the conductivity, presenting weak localization at all electronic densities, and dependent on different scattering mechanisms as well as on the trigonal warping of the electron dispersion near the K and K' valleys. Proximity effects with a molecular thin film influence these scattering mechanisms, which can be quantified through the known theory of magnetoconductance for bilayer graphene. Here, we present weak localization measurements in a copper-phthalocyanine / bilayer graphene / h-BN heterostructure that suggest an important suppression of trigonal warping effects in bilayer graphene (BLG), restoring the manifestation of the chirality of the charge carriers in the localization properties of BLG. Additionally, we observe a charge transfer of 3.6$\times$10$^{12}$cm$^{-2}$ from the BLG to the molecules, as well as a very small degradation of the mobility of the BLG/h-BN heterostructure upon the deposition of copper phthalocyanine (CuPc). The molecular arrangement of the CuPc thin film is characterized in a control sample through transmission electron microscopy, that we relate to the electronic transport results.

cond-mat.mes-hall↗

arXiv2024

Measuring Chemical Shifts with Energy-Dispersive X-ray Spectroscopy

Electron microscopy prevalently uses energy-dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) for elemental analysis. EDS and EELS energy resolutions are commonly between 30-100 eV or 0.01-1 eV, respectively. Large solid angle EDS detector technology has increased collection efficiency to enable precision spectroscopy via averaging of 0.02-0.1 eV. This improved precision gives access to chemical shifts; examples are shown in compounds of Al, Ti, and W. EDS can now detect chemical information in a complementary parameter space (accelerating voltage, thickness, atomic number) to that covered by EELS.

cond-mat.mtrl-sci↗

arXiv2024

Unraveling the nature of quasi van der Waals Epitaxy of magnetic topological insulators Cr: (BixSb1-x)2Te3 on a GaAs (111) substrate through coherently strained interface

Quasi van der Waals Epitaxy (qvdWE) has been realized for decades at the interfaces between 3D and 2D materials or van der Waals materials. The growth of magnetic topological insulators (MTI) Cr: (BixSb1-x)2Te3 (CBST) on GaAs (111) substrates for Quantum Anomalous Hall Effect (QAH) is actually one of the examples of qvdWE, which is not well noticed despite the fact that its advantages have been used in growth of various MTI materials. This is distinguished from the growth of MTIs on other substrates. Although the qvdWE mode has been used in many 2D growth on III-V substrates, the specific features and mechanisms are not well demonstrated and summarized yet. Here in this work, we have for the first time shown the features of both coherent interfaces and the existence of strain originating from qvdWE at the same time.

cond-mat.mtrl-sci↗