arXiv subjects

Xiaojie Ni

Publications and source records attributed to Xiaojie Ni.

3 recordsLinked to original sources

arXiv2024

Improving the low-energy muon beam quality of the LEM beamline at PSI: Characterisation of ultra-thin carbon foils

The Low-Energy Muon beamline (LEM) at the Paul Scherrer Institute currently stands as the world's only facility providing a continuous beam of low-energy muons with keV energies for conducting muon spin rotation experiments on a nanometer depth scale in heterostructures and near a sample's surface. As such, optimizing the beam quality to reach its full potential is of paramount importance. One of the ongoing efforts is dedicated to improving the already applied technique of single muon tagging through the detection of secondary electrons emerging from an ultra-thin carbon foil. In this work, we present the results from installing a thinner foil with a nominal thickness of 0.5 $μg~cm^{-2}$ and compare its performance to that of the previously installed foil with a nominal thickness of 2.0 $μg~cm^{-2}$. Our findings indicate improved beam quality, characterized by smaller beam spots, reduced energy loss and straggling of the muons, and enhanced tagging efficiency. Additionally, we introduce a method utilizing blue laser irradiation for cleaning the carbon foil, further improving and maintaining its characteristics

physics.ins-det↗

arXiv2022

Defect Profiling of Oxide-Semiconductor Interfaces Using Low-Energy Muons

Muon spin rotation with low-energy muons (LEμSR) is a powerful nuclear method where electrical and magnetic properties of surface-near regions and thin films can be studied on a length scale of $\approx$\SI{200}{\nano\meter}. In this work, we show the potential of utilizing low-energy muons for a depth-resolved characterization of oxide-semiconductor interfaces, i.e. for silicon (Si) and silicon carbide (4H-SiC). Silicon dioxide (SiO$_2$) grown by plasma-enhanced chemical vapor deposition (PECVD) and by thermal oxidation of the SiO$_2$-semiconductor interface are compared with respect to interface and defect formation. The nanometer depth resolution of μallows for a clear distinction between the oxide and semiconductor layers, while also quantifying the extension of structural changes caused by the oxidation of both Si and SiC.

cond-mat.mtrl-sci↗

arXiv2016

A new muon-pion collection and transport system design using superconducting solenoids based on CSNS

A new muon and pion capture system is proposed for the China Spallation Neutron Source (CSNS), currently under construction. Using about 4\% of the pulsed proton beam (1.6 GeV, 4 kW and 1 Hz) of CSNS to bombard a cylindrical graphite target inside a superconducting solenoid, both surface muons and pions can be acquired. The acceptance of this novel capture system - a graphite target wrapped up by a superconducting solenoid - is larger than the normal muon beam lines using quadrupoles at one side of the separated muon target. The muon and pion production at different capture magnetic fields was calculated using Geant4. The bending angle of the capture solenoid with respect to the proton beam was also optimized in simulation to achieve more muons and pions. Based on the layout of the muon experimental area reserved at the CSNS project, a preliminary muon beam line was designed with multi-purpose muon spin rotation areas (surface, decay and low-energy muons). Finally, high-flux surface muons (10$^8$/s) and decay muons (10$^9$/s) simulated by G4beamline will be available at the end of the decay solenoid based on the first phase of CSNS. This collection and transport system will be a very effective beam line at a proton current of 2.5 $μ$A.

physics.acc-ph↗