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Tian, Xinchun

Publications and source records attributed to Tian, Xinchun.

15 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

In situ TEM measurement of electrical properties of individual BaTiO 3 nanocubes

We report on the measurement of the electrical properties of individual pristine and doped BaTiO 3 nanocubes by using in situ transmission electron microscopy with a two-electrode configuration. The dimensions of the nanocubes tested are between 10 and 20 nm, which rendered their in situ electrical characterization challenging. We characterized 4%Cr and 5%La (atomic percentage) doped BaTiO 3 nanocubes and compared them with the properties of pristine BaTiO3 nanocubes synthesized by the same solvothermal method. We found that the resistance of all three types of nanocubes when displayed in log-scale shows a nearly linear dependence on the applied electric field (R2 ≥ 0.95) over a wide range of electric fields (50–900 kV/cm). Compared with pristine BaTiO 3 nanocubes, the resistance of both 4%Cr and 5%La doped nanocubes showed reduced variation rates with respect to the electric field, with 5%La doping, demonstrating a better reduction in the variation rate. By developing techniques capable of evaluating the properties of individual BaTiO 3 nanocubes, we expect that our work to open the door to the use of BaTiO 3 nanomaterials in the design of future multilayer ceramic capacitors with improved volumetric efficiency and ferroelectrics-enabled nanodevices with advanced functionality.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structural Instability in Electrically Stressed, Oxygen Deficient BaTiO 3 Nanocrystals

The dynamics of oxygen vacancies under external stimuli dominates the performance of many solid-state devices, including capacitors, oxide memristors, anionic conductors, etc. By means of in-situ Transmission Electron Microscopy, we found in BaTiO 3 perovskite nanocrystals that formation of oxygen vacancies due to electrical stressing renders the oxide amorphizable under electron beam illumination, suggesting the presence of a threshold concentration of oxygen vacancy affecting the structural stability of BaTiO 3 crystals upon high energy radiation. In contrast to the structural change, the resistivity of the nanocrystal seems not liable to the amorphization prior to dielectric breakdown at higher voltage bias. Here, we propose that an increase in oxygen vacancy content promotes oxygen mobility in the perovskite structure allowing electron beam induced electric field to modify the local structural and composition. Our in-situ observations reveal the central role of oxygen vacancies in the structural stability of perovskites which is of paramount importance to their applications in extreme environments and suggest a potential new route to micro-processing perovskite oxides using the electron beam via oxygen vacancy management without severely compromising the electric property.

36 MATERIALS SCIENCE↗
DOE OSTI2020

In Situ Transmission Electron Microscopy Study of Conductive Filament Formation in Copper Oxides

The structural and electrical property changes of two types of copper oxides (CuO and Cu 2 O) under voltage bias are studied with in situ transmission electron microscopy (TEM). The phases of different materials are confirmed with electron diffraction. In both types of oxides, dynamic conductive path formation and dissolution are observed. The decrease in resistance of CuO film is found to be accompanied with the formation of Cu 4 O 3 phase where the electric field strength is highest. We also find that the decrease in resistivity of Cu 2 O film is more extensive and occurs in an area depending on the level of current compliance. In conclusion, the physical mechanisms responsible for the observations and their implications for the formation of conducting regions in copper oxide-based memristors are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Direct Observations of Field-Intensity-Dependent Dielectric Breakdown Mechanisms in TiO 2 Single Nanocrystals

One of the main challenges for next-generation electric power systems and electronics is to avoid premature dielectric breakdown in insulators and capacitors and to ensure reliable operations at higher electric fields and higher efficiencies. However, dielectric breakdown is a complex phenomenon and often involves many different processes simultaneously. Here we show distinctly different defect-related and intrinsic breakdown processes by studying individual, single crystalline TiO 2 nanoparticles using in-situ transmission electron microscopy (TEM). As the applied electric field intensity rises, rutile-to-anatase phase transition, local amorphization/melting, or ablation are identified as the corresponding breakdown processes, the field intensity thresholds of which are found to be related to the position of the intensified field and the duration of the applied bias relative to the time of charged defects accumulation. Our observations reveal an intensity-dependent dielectric response of crystalline oxides at breakdown and suggest possible routes to suppress the iniation of premature dielectric breakdown. Hence, they will aid the design and development of next generation robust and efficient solid dielectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2019

In Situ TEM Study of the Amorphous-to-Crystalline Transition during Dielectric Breakdown in TiO 2 Film

Dielectric breakdown of oxides is a main limiting factor for improvement of the performance of electronic devices. Present understanding suggests that defects produced by intense voltage accumulate in the oxide to form a percolation path connecting the two electrodes and trigger the dielectric breakdown. However, reports on directly visualizing the process at nanoscale are very limited. Here, we apply in situ transmission electron microscopy to characterize the structural and compositional changes of amorphous TiO 2 under extreme electric field (~100 kV/mm) in a Si/TiO 2 /W system. Upon applying voltage pulses, the amorphous TiO 2 gradually transformed to crystalline sub-stoichiometric rutile TiO 2-x and the Magnéli phase Ti 3 O 5 . The transitions started fromat the anode/oxide interface under both field polarities. Preferred growth orientation Epitaxial growth of rutile TiO 2-x with respect toon the Si substrate was observed when Si was the anode, while oxidation and melting of the W probe occurred when W was the anode. We associate the TiO 2 crystallization process with the electrochemical reduction of TiO 2 , polarity-dependent oxygen migration, and Joule heating. The experimental results are supported by our phase-field modeling. These findings provide direct details of the defect formation process during dielectric breakdown in amorphous oxides and will help the design of electronic devices with higher efficiency and reliability.

36 MATERIALS SCIENCE↗
DOE OSTI2019

In situ TEM study of the transitions between crystalline Si and nonstoichiometric amorphous oxide under bipolar voltage bias

The electrical responses, either structurally or chemically, at the interface between a SiO 2 thin film and a single crystalline Si substrate are an important research subject in Si-based devices. Dielectric breakdown-induced epitaxial migration of Si into SiO 2 has been reported as a degradation mechanism in field effect transistors (FETs). Here, we show a direct observation of electric field induced conversion of single crystalline Si to nonstoichiometric amorphous oxide starting from the Si/native oxide interface using in situ transmission electron microscopy (TEM). We further show that nanocrystalline Si can form in the amorphous oxide under a voltage bias of reversed polarity. Electron energy loss spectroscopy and energy dispersive X-ray spectroscopy analyses indicate that the observed amorphization process was caused by the oxidation of Si and the recrystallization process was caused by the reduction of nonstoichiometric amorphous silicon oxide. Furthermore, both transitions are a result of field-driven directional migration of oxygen which originally comes from its native oxide layer.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Stress response to CO 2 deprivation by Arabidopsis thaliana in plant cultures

After being the standard plant propagation protocol for decades, cultures of Arabidopsis thaliana sealed with Parafilm remain common today out of practicality, habit, or necessity (as in co-cultures with microorganisms). Regardless of concerns over the aeration of these cultures, no investigation has explored the CO 2 transport inside these cultures and its effect on the plants. Thereby, it was impossible to assess whether Parafilm-seals used today or in thousands of older papers in the literature constitute a treatment, and whether this treatment could potentially affect the study of other treatments.For the first time we report the CO 2 concentrations in Parafilm-sealed cultures of A. thaliana with a 1 minute temporal resolution, and the transcriptome comparison with aerated cultures. The data show significant CO 2 deprivation to the plants, a drastic suppression of photosynthesis, respiration, starch accumulation, chlorophyll biosynthesis, and an increased accumulation of reactive oxygen species. Most importantly, CO 2 deprivation occurs as soon as the cotyledons emerge. Gene expression analysis indicates a significant alteration of 35% of the pathways when compared to aerated cultures, especially in stress response and secondary metabolism processes. On the other hand, the observed increase in the production of glucosinolates and flavonoids suggests intriguing possibilities for CO 2 deprivation as an organic biofortification treatment in high-value crops.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Large-Scale Synthesis of Colloidal Si Nanocrystals and Their Helium Plasma Processing into Spin-On, Carbon-Free Nanocrystalline Si Films

This study describes a simple approach to the large-scale synthesis of colloidal Si nanocrystals and their processing into spin-on carbon-free nanocrystalline Si films. The synthesized silicon nanoparticles are capped with decene, dispersed in hexane, and deposited on silicon substrates. The deposited films are exposed to nonoxidizing room-temperature He plasma to remove the organic ligands without adversely affecting the silicon nanoparticles to form crack-free thin films. We further show that the reactive ion etching rate in these films is 1.87 times faster than that for single-crystalline Si, consistent with a simple geometric argument that accounts for the nanoscale roughness caused by the nanoparticle shape.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Calcination does not remove all carbon from colloidal nanocrystal assemblies

Removing organics from hybrid nanostructures is a crucial step in many bottom-up materials fabrication approaches. It is usually assumed that calcination is an effective solution to this problem, especially for thin films. This assumption has led to its application in thousands of papers. Here in this paper, we show that this general assumption is incorrect by using a relevant and highly controlled model system consisting of thin films of ligand-capped ZrO 2 nanocrystals. After calcination at 800 °C for 12 h, while Raman spectroscopy fails to detect the ligands after calcination, elastic backscattering spectrometry characterization demonstrates that ~18% of the original carbon atoms are still present in the film. By comparison plasma processing successfully removes the ligands. Our growth kinetic analysis shows that the calcined materials have significantly different interfacial properties than the plasma-processed counterparts. Calcination is not a reliable strategy for the production of single-phase all-inorganic materials from colloidal nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Building Materials from Colloidal Nanocrystal Assemblies: Molecular Control of Solid/Solid Interfaces in Nanostructured Tetragonal ZrO 2

We describe in this paper a bottom-up approach to control the composition of solid/solid interfaces in nanostructured materials, and we test its effectiveness on tetragonal ZrO 2 , an inorganic phase of great technological significance. Colloidal nanocrystals capped with trioctylphosphine oxide (TOPO) or oleic acid (OA) are deposited, and the organic fraction of the ligands is selectively etched with O 2 plasma. The interfaces in the resulting all-inorganic colloidal nanocrystal assemblies are either nearly bare (for OA-capped nanocrystals) or terminated with phosphate groups (for TOPO-capped nanocrystals) resulting from the reaction of phosphine oxide groups with plasma species. The chemical modification of the interfaces has extensive effects on the thermodynamics and kinetics of the material. Different growth kinetics indicate different rate limiting processes of growth (surface diffusion for the phosphate-terminated surfaces and dissolution for the “bare” surfaces). Phosphate termination led to a higher activation energy of growth, and a 3-fold reduction in interfacial energy, and facilitated significantly the conversion of the tetragonal phase into the monoclinic phase. Finally, films devoid of residual ligands persisted in the tetragonal phase at temperatures as high as 900 °C for 24 h.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Sulfur in oleylamine as a powerful and versatile etchant for oxide, sulfide, and metal colloidal nanoparticles: Sulfur in oleylamine as a powerful and versatile etchant

Understanding of crystal growth is essential to the design of materials with improved properties. Unfortunately, still very little is understood about the basic growth mechanisms of nanostructures, even in the most established colloidal synthetic routes. Etching is one of the most important mechanisms to consider during particle growth, but it is rarely considered in the syntheses of oxide or chalcogenide nanostructures. Here in this paper, we report that the most common precursor for the synthesis of sulfide nanostructures – the mixture of sulfur and oleylamine – acts as a very powerful etchant for oxide, chalcogenide, and metal nanostructures. Specifically, we discuss its effect on several nanoparticle compositions (PbS, Cu 2 S, Fe 3 O 4 , and Au) and compare it to control conditions in which only oleylamine is present. Our experiments suggest that the etching results from the evolution of H 2 S from the sulfur–oleylamine precursor. We predict that the simultaneous role of this precursor as both etchant and ligand stabilizer will make it a useful tool for the chemical post-processing (e.g., size reduction, focusing of size distributions, faceting) of nanocrystal dispersions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Resonance interaction in LBNE fine-grained-tracker near detector

This talk is devoted to resonance interaction (RES) in the proposed fine-grained tracker detector (FGT) for LBNE experiment. We use fast MC to study the sensitivity of FGT to RES, and use this measurement as a handle to constrain nuclear effects. Similar analysis is performed on NOMAD data for validation and better understanding. Preliminary RES measurement result using NOMAD data will be reported.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Physics sensitivity studies of Fine-Grained Tracker

The reference design of the near detector for the LBNE experiment is a high-resolution Fine-Grained Tracker (FGT). We performed sensitivity studies – critical to constraining the systematics in oscillation searches – of measurements of (1) the absolute neutrino flux, (2) neutrino-nucleon quasi-elastic (QE) and (3) resonance (Res) interactions. In QE and Res emphasis is laid in identifying in situ measurables that help constrain nuclear effects such as initial state pair wise correlations and final state interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

NO$\nu$A Data Acquisition Software System

NO{nu}A is an accelerator-based neutrino oscillation experiment which has a great potential to measure the last unknown mixing angle {theta}{sub 13}, the neutrino mass hierarchy, and the CP-violation phase in lepton sector with (1) 700 kW beam, (2) 14 mrad off the beam axis, (3) 810 km long baseline. The Near Detector on the Surface is fully functioning and taking both NuMI and Booster beam data. The far detector building achieved beneficial occupancy on April 13. This proceeding will focus on the DAQ software system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗