Liquid Nitrogen Temperature Research Articles

Ultrasonic study and molecular dynamics simulation of propylene glycol at pressures up to 1.4 GPa

We report ulsrasonic measurements of the density and bulk modulus of propylene glycol at room temperature and at the temperature of liquid nitrogen up to a pressure of 1.4 GPa. We perform molecular dynamics simulations with two different force fields—COMPASS and Charmm. We show that the COMPASS force field reproduces the experimental data with high accuracy. For this reason we employ this force field to analyze the microstructure and hydrogen bonding in the system. We find that the number of hydrogen bonds does not depend on pressure.

Superconductivity in Li8Au electride

Located at crystal voids, interstitial anion electrons (IAEs) have diverse topologies, which may be tuned to achieve new properties. Elucidating the role of IAEs in electron-phonon coupling (EPC), and using it to design new electride superconductors, leads to the current prediction of superconducting Li8Au at high pressure. We suggest that the occurence of high-temperature superconductivity in electrides requires high-symmetry structures with hydrogen-like cages, an electron acceptor element to balance charges, and isolated IAEs coupled with medium-frequency vibrations. The uniquely designed Li8Au electride has a NaCl-type (B1) lattice, with atomic Au and cubic Li8 cages as bases. Isolated IAEs are formed at the cage centers, with extra charges taken up by Au. These octahedrally coordinated IAEs have a p-orbital-like attribute and are strongly coupled with atomic vibrations in the Li8 cages. The strong EPC in Li8Au results in a calculated Tc of 73.1 K at 250 GPa, which is the highest Tc reported to date for all the electrides. A slight substitutional Pt doping can enhance the Tc of Li8Au to exceed liquid nitrogen temperature.

Effect of cryogenic cycling and above-Tg annealing on the corrosion behavior of Zr-Cu-Ti-Be metallic glass

This work investigates the electrochemical properties of Zr-based Zr35Ti30Cu8.25Be26.75 metallic glass after cryogenic treatment and isothermal annealing above glass transition temperature. Potentiodynamic polarization and electrochemical impedance spectroscopy experiments are used to understand the effect of structural state on the corrosion behavior of Zr-based metallic glass. The metallic glass samples are cycled between liquid nitrogen to room temperature and isothermally held at liquid nitrogen to unravel the effect of cryogenic treatments on the electrochemical properties. The corrosion of cryogenically treated and high temperature annealed samples is compared with the as-cast samples. The results show that holding at liquid nitrogen temperature improves the corrosion resistance of metallic glass compared to cryogenic cycling and the high temperature annealing. These findings are explained based on the changes in structural state of metallic glass.

Structural-Phase Changes of the Fe3C/Fe7C3/P-Phase/Cam Mechanocomposite at Heating

The effect of the action of temperature on the structure and phase composition of anFe3C/Fe7C3/P-phase/Cam composite obtained by mechanosynthesis of Fe–75 at % C has been studied by the methods of X-ray diffraction, Mössbauer spectroscopy, thermogravimetric analysis, and differentialscanning calorimetry. It is shown that the structural and phase changes at heating have a multistage character.In the temperature range 315–400°C crystallization of the paramagnetic P-phase with generation of Fe3Cand/or Fe7C3 occur. In the course of heating to higher temperatures, complete decomposition of carbideFe7C3 (in the range 450–550°C) and partial decomposition of Fe3C (at 600°C and above) are observed. Aftercooling from 800–1000°C the mechanocomposite consists of α-Fe, cementite Fe3C, and graphite. The phasetransformations are accompanied by the processes of composite oxidation with the formation of Fe3O4 oxide and its subsequent reduction. The P-phase is a disorded amorphous carbide Fe1 – xCx, which is characterized by magnetic ordering at the temperature of liquid nitrogen.

The Quality of Frozen Friesian Holstein Semen after Long-Term Storage

Semen cryopreservation is the long-term storage at very low temperatures in liquid nitrogen for future use. This study investigates the quality of frozen Friesian Holstein (FH) semen after long-term storage. Samples of FH semen stored for 25, 20, 15, 10, 5, and 1 years were collected from one of the national centers for artificial inseminations. Frozen semen was stored in containers with liquid nitrogen at -196 ᵒC in a room with a temperature of 20 ᵒC The variables used after thawing were sperm motility, viability, and abnormalities, as well as plasma membrane integrity (IPM) using computer-assisted sperm analysis (CASA), eosin-nigrosine staining, and hypoosmotic swelling (HOS) test, respectively. Data were analyzed by one-way ANOVA and expressed as mean ± SEM. The result showed no significant differences in sperm viability, abnormalities, and IPM. Furthermore, sperm motility was >40%, consistent with the Indonesian standard for frozen bovine semen. CASA analysis showed that all variables of the motility pattern have no significant difference, except linearity (LIN). The Lin of sperm was lower in frozen semen after one and five years than after 20 and 25 years of storage. The overall quality of semen after 25, 20, 15, 10, 5, and 1 years of storage met the standard and was suitable for artificial insemination.

Comparisons and Evaluations of Silicon and Wide Band Gap Devices at Cryogenic Temperature

In this article, the static and dynamic characterizations for semiconductors with different materials, including silicon (Si), silicon carbide (SiC), and gallium nitride (GaN), are evaluated and compared at room temperature and cryogenic temperature (liquid nitrogen temperature). For static characterizations, the on-state resistance and threshold voltage are evaluated. For dynamic characterizations, the turn-on switching loss, turn-off switching loss, and dynamic on-state resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds(on)</sub> ) are evaluated. The results demonstrate that Si and GaN based semiconductors have improved performances with lower on-state resistance and faster switching speed at low temperature operations. For SiC based semiconductors, the on-state resistance increases significantly at cryogenic temperature. The switching speed is reduced dramatically for the evaluated 1.2 kV SiC metal oxide semiconductor field effect transistors (MOSFETs) at cryogenic temperature. This makes it less attractive for cryogenic applications. For the evaluated 650 V and 900 V SiC MOSFETs, the switching speed remains almost unchanged at low temperature. GaN high electron mobility transistor (HEMT) demonstrates a fast turn-on switching speed at low temperature, where the device's <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i> are almost doubled when compared with room temperature. In addition, the dynamic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds(on)</sub> of the evaluated GaN HEMTs also decreases at low temperatures. The evaluation results can serve as guidelines for cryogenic power electronics applications. Meanwhile, the future work for semiconductors cryogenic characterizations is discussed.

Characterization of three washing/decellularization procedures for the production of bioactive human micronized neural tissue (hMINT).

We developed a novel, injectable and decellularized human peripheral nerve-based scaffold, named Micronized Human Neural Tissue (hMINT), designed to be used as a supportive matrix for stem cell transplantation in the context of spinal cord injury (SCI). Human donated sciatic nerves were micronized at liquid nitrogen temperature prior to decellularization using 3 different procedures of various harshness. hMINT were characterized in terms of particle size, DNA, sulfated glycosaminoglycans (sGAG) and growth factors content. To test the biocompatibility and bioactivity of the various preparations, we used a type of mesenchymal stromal cells (MSCs), termed MIAMI cells, which were placed in contact with hMINT to monitor cell attachment by confocal microscopy and gene expression by RT-qPCR in vitro. The content of DNA, sGAG and growth factors left in the product after processing was highly dependent on the decellularization procedure used. We demonstrated that hMINT are biocompatible and promoted the attachment and long-term survival of MIAMI cells in vitro. Finally, combination with hMINT increased MIAMI cells mRNA expression of pro-survival and anti-inflammatory factors. Importantly, the strongest bioactivity on MIAMI cells was observed with the hMINT decellularized using the mildest decellularization procedure, therefore emphasizing the importance of achieving an adequate decellularization without losing the hMINT's bioactivity. The capacity of hMINT/stem cells to facilitate protection of injured neural tissue, promote axon re-growth and improve functional recovery will be tested in an animal model of SCI and other neurodegenerative disorders in the future.

Dependence of Charpy Impact Properties of Fe-30Mn-0.05C Steel on Microstructure

Fe-30Mn-0.05C steel specimens with cold-rolled, partially recrystallized, fine-grained, and coarse-grained microstructures were fabricated by means of 80% cold rolling followed by annealing at 550–1000 °C. The initial and deformed microstructures were characterized, and the Charpy impact properties were tested at room temperature (RT) and liquid nitrogen temperature (LNT). It was found that the Charpy absorbed energy increased with the annealing temperature, while the specimens showed different trends: parabolic increase at RT and exponential increase at LNT, respectively. Compared with the fully recrystallized specimens, those with a partially recrystallized microstructure exhibited lower impact energy, especially at LNT. This was because cracks tended to nucleate and propagate along the recovery microstructure where stress concentration existed. The grain size played an important role in the twinning behavior and impact properties. High Charpy impact energy (~320 J) was obtained in the coarse-grained specimen having the grain size of 42.1 μm at both RT and LNT, which was attributed to the activation of high-density deformation twinning. However, deformation twinning was inhibited in the specimen with the average grain size of 3.1 μm, resulting in limited work hardening and lower impact energy.

Electron Spin Resonance of V4+ Ions in K2O-B2O3-V2O5 Glasses

In the present work the ESR study of potassium borovanadate (K2O-B2O3-V2O5) glasses is reported at room temperature and liquid nitrogen temperature. The spectra at liquid nitrogen temperature is similar to at room temperature except the indusial hyperfine lines are sharper and more intense which might be ascribed to a spin-lattice relaxation effect. The ESR parameters were calculated at room temperature and shows that in-plane π bonding is somewhat covalent and covalency is nearly independent of concentration of K2O. The octahedral site with a tetragonal compression gives g value in the order g׀׀&lt; g&lt; ge(=2.0023). It is observed that the V4+ ions in the present sample exist as VO2+ ions in octahedral coordination with a tetragonal compression and belong to C4v symmetry.

PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion: Further insights by spectroscopic characterization

The present work aims at further investigating a previously studied PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion. High activity and selectivity for propane was proved and the results obtained by NAP-XPS measurements and CO adsorption at liquid-nitrogen temperature (LNT) followed by FT-IR spectroscopy are shown. After reduction, we confirmed the formation of PdZn alloy. At LNT, Pd carbonyl IR band shows a peculiar behavior linked to an intimate interaction between PdZn particles, ZnO and ZrO2. The combined system was characterized as fresh, used and regenerated. On the fresh PdZn/ZrO2+SAPO-34 the characteristic features of the two components do not appear perturbed by the mixing. As for the used system, the absence of Pd carbonyls and the decrease of CO on SAPO-34 Brønsted acid sites are correlated to organic species revealed by ssNMR. Regeneration in oxygen restores catalytic sites, although new Pd2+/Zn2+ carbonyls appear due to ion exchange into SAPO-34 framework.

High ductility CrCoNi medium entropy alloy prepared by liquid nitrogen temperature rolling and short time annealing at moderate temperature

As-cast CrCoNi Medium Entropy Alloy (as-casted MEA) was obtained by vacuum arc melting. The as-casted MEA was rolled 3 times at the temperature of liquid nitrogen (77 K), the sum of the total deformation was 50%. Then, the rolled CrCoNi Medium Entropy Alloy (as-rolled MEA) were annealed with different parameters, the annealing parameters were 923 K/30min, 973 K/30min and 1073 K/30min respectively. The experimental samples were characterized by uniaxial tensile test at room temperature, electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). The tensile test results showed the CrCoNi MEA was deformed by Liquid Nitrogen rolling, the tensile strength increased from 421 MPa to 1312 MPa, but the elongation was only 7.4%. The as-rolled MEA annealed at moderate temperature and short time, the ductility of the CrCoNi was improved significantly. When the as-rolled MEA annealed at 1073 K/30 min, the elongation of CrCoNi increased to 65.3%, while the tensile strength maintained 800 MPa. The EBSD and TEM results showed that the CrCoNi MEA was deformed by Liquid Nitrogen rolling, there were a lot of high density dislocation regions in the alloy. At the same time, a large number of bunches of stacking faults (SFs), intersected SFs and deformation twins (DT) were found in the rolled MEA. The EBSD and TEM results also showed that when the CrCoNi MEA was annealed, a large number of type B and type C annealing twins and 9 R structures were found in the alloy. The growth of annealing twins were achieved by the mechanism of grain boundary migration caused by stacking faults annexation. After annealing, the transformation of FCC→9 R structure was occurred, and the 9 R structure caused more boundary nucleation of annealing twins. The annealing twins and 9 R structure played a key role in improving the ductility of the annealed CrCoNi MEA. Adopt the technology of moderate temperature combining short time annealing process, can effectively control the properties of CrCoNi MEA.

Nanoscale Multimodal Analysis of Sensitive Nanomaterials by Monochromated STEM-EELS in Low-Dose and Cryogenic Conditions.

Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) provides spatially resolved chemical information down to the atomic scale. However, studying radiation-sensitive specimens such as organic-inorganic composites remains extremely challenging. Here, we analyzed metal-organic framework nanoparticles (nanoMOFs) at low-dose (10 e-/Å2) and liquid nitrogen temperatures, similar to cryo-TEM conditions usually employed for high-resolution imaging of biological specimens. Our results demonstrate that monochromated STEM-EELS enables damage-free analysis of nanoMOFs, providing in a single experiment, signatures of intact functional groups comparable with infrared, ultraviolet, and X-ray data, with an energy resolution down to 7 meV. The signals have been mapped at the nanoscale (<10 nm) for each of these energy spectral ranges, including the chemical features observed for high energy losses (X-ray range). By controlling beam irradiation and monitoring spectral changes, our work provides insights into the possible pathways of chemical reactions occurring under electron exposure. These results demonstrate the possibilities for characterizing at the nanoscale the chemistry of sensitive systems such as organic and biological materials.

Low-Temperature Characteristics of a Silicon-Based Sub-THz Detector

Characteristics of a silicon-based sub-THz plasmonic detector are studied in a wide range of temperatures down to that of liquid nitrogen. The temperature dependences of the detector’s sensitivity are obtained and its noise characteristics are studied. The frequency dependence of the sensitivity in the range of 70–120 GHz is measured at room temperature, and its maximum of 25 V/W is reached at 96 GHz. The noise equivalent power of the studied detector is estimated by assuming that Nyquist noise is the main source of noise, and the values of this power vary from 2 × 10−10 W Hz−1/2 at room temperature to 2 × 10−11 W Hz−1/2 at the temperature of liquid nitrogen. The current–voltage characteristics of the sub-THz detector are studied as well. It is found there is a singularity in the differential resistance and sensitivity that depends on the DC voltage applied during the transition from room to nitrogen temperature.

Effect of low-temperature quasihydroextrusion on the structure and physical properties of CuCrZr alloy

The work is devoted to the study of changes in the structural and physical properties of the precipitation-hardened CuCrZr alloy under the influence of low-temperature (77 K) quasihydroextrusion with various degrees of deformation at liquid nitrogen temperature with subsequent aging. Prior to quasihydroextrusion, commercial alloy samples were annealed and quenched from the premelting temperature to obtain a supersaturated solid solution of alloying elements in the copper matrix. After quasihydroextrusion, the microstructure, lattice constant, pole densities, tensile strength and yield strength, microhardness (in different cross-sections of the extrudate), and electrical conductivity of the CuCrZr alloy were studied depending on the degree of deformation by quasihydroextrusion. It is shown that the deformation degree determines the kinetics of decomposition of the supersaturated solid solution and its structure. As a result of extrusion, an anisotropic structure of the matrix and precipitates is formed, which also determines the anisotropy of material properties. Subsequent aging leads to a significant decrease in the anisotropy of properties. With an increase in the deformation degree during extrusion (before aging), a significant monotonous increase in physical and mechanical properties occurs. However, in the range of deformation degrees of 40–50%, an anomalous “jump” of all measured properties and structural parameters is observed. The study proposes a physical mechanism that explains the experimental results. The mechanism is based on the occurrence of two kinetically differently directed processes: dynamic aging and its inhibition due to an increase in the defectiveness of the material. The latter process manifests itself essentially at low temperatures. In general, low-temperature quasihydroextrusion makes it possible to obtain a complex of sufficiently high mechanical and electrical characteristics of the CuCrZr alloy at relatively low degrees of deformation for one extrusion cycle, which is facilitated by low deformation temperature.

Effects of cryo-EM cooling on structural ensembles of biomolecules and their solvation shell.

The recent revolution in cryo electron microscopy (cryo-EM) allows the determination of structures of macromolecular complexes at atomic resolution. Cryo-EM also provides information on structural heterogeneity and ensembles of macromolecules. To obtain cryo-EM images of macromolecules, the samples are first rapidly cooled down to liquid nitrogen temperatures. The rapid cooling prevents ice-crystal formation and preserves some information of the room-temperature ensemble. However, to what extent the ensemble of the macromolecues and of the solvation shell is perturbed by the cooling is currently unknown. To quantify the cooling effects, we first estimated the temperature drop rate by solving the heat equation which suggested rapid cooling within microseconds. Then, we started all-atom explicit-solvent molecular dynamics (MD) simulations of the ribosome from 41 snapshots taken from a room-temperature ensemble with linearly decreasing temperatures at 11 different cooling rates (simulation lengths 0.1-128 ns). In the simulations, we observed that cooling markedly decreased the structural heterogeneity of the cooled ensemble. To investigate if and how this effect depends on the cooling rate, we used Bayesian statistics to test three thermodynamic and kinetic models of the cooling process. A kinetic two-state model improves the prediction of the decrease in heterogeneity compared to the cooling-rate independent thermodynamic model suggesting that kinetic effects contribute markedly. The combination of the estimated temperature drop rate with the kinetic model suggests that small barriers between states (<10 kJ/mol) are overcome during cooling and do not contribute to the heterogeneity of the structural ensemble obtained by cryo-EM. In contrast, conformational states separated by larger barriers are expected to be trapped during plunge-freezing. The obtained parameters for the kinetic model will allow one to quantify the heterogeneity of biologically relevant room-temperature ensembles from cryo-EM structures.

An improved cavitation model with thermodynamic effect and multiple cavitation regimes

Mechanical feed pumps in organic Rankine cycle (ORC) power plants can suffer from cavitation to lose their normal feeding performance or even damage. Cavitation models for organic fluids in ORC systems are lacking presently. Hence, a new cavitation model with thermodynamic effect was proposed. Surface tension-controlled, inertia-controlled, intermediate and heat transfer-controlled cavitation regimes, and two key elements: vapour bubble growth rate and vapour bubble number density are included in the model. A known air or non-condensable gas concentration in the liquid was employed to determine cavitation nuclei number density. The model was coded in ANSYS CFX as user defined model and validated with cavitating flows of organic fluid R114 in a venturi, liquid nitrogen and liquid hydrogen on a tapered hydrofoil and warm water around a hydrofoil NACA 0015 in cavitation tunnels based on visualised cavity length. Two model constants, temperature depression, and minimal cavitation number were correlated to bulk liquid temperature, Reynolds number, and Jakob number. The temperature and pressure profiles of liquid nitrogen and hydrogen on hydrofoil surface were examined against the experimental data. The model was applied to simulate unsteady cavitating flows of organic fluid R245fa in a diaphragm pump. It was shown that the temperature depression and minimal cavitation number cannot be correlated to bulk liquid temperature, Reynolds number and Jakob number. Two model constants can be correlated fairly to Reynolds number. The model underestimates the thermodynamic effect by 43% for R114, 18.6% for liquid nitrogen and 32.6% for liquid hydrogen based on temperature depression. The predicted temperature and pressure profiles on hydrofoil surface agree with the experimental data for liquid nitrogen. The model can produce an expected curve of mean pump flow rate against net positive suction head available.

Extraordinary combination of strength and ductility in an additively manufactured Fe-based medium entropy alloy through in situ formed η-nanoprecipitate and heterogeneous microstructure

The current study investigated the mechanical properties of Fe65Ni15Co8Mn8Ti3Si (at%) medium entropy alloy (MEA), printed by laser-based direct energy deposition (DED) in the room and liquid nitrogen environments. The as-printed microstructure contains various levels of heterogeneities, including different grain sizes, dual-phase microstructure, in situ formed η nanoprecipitate, cellular structure, and elemental segregation generated during the DED process. The impact of each observed heterogeneity on the mechanical properties and the predominant deformation mechanisms were examined. The corresponding MEA revealed a high ultimate tensile strength (UTS) of ∼1.02 GPa, total elongation (TE) of ∼46%, and exceptional cryogenic mechanical properties with a UTS and TE of 1.83 GPa and 40%, respectively. According to microstructural observations, the deformation-induced phase transformation from face-centered cubic (FCC) to body-centered cubic (BCC) is the predominant strengthening mechanism at both room and liquid nitrogen temperatures in addition to solid-solution strengthening and dislocation-mediated plasticity. The non-shearable η nanoprecipitates also enhanced the mechanical properties through precipitation/stacking fault strengthening. Hetero-deformation-induced (HDI) strengthening also occurred in the presence of dual-phase microstructure, cellular microstructure, and elemental segregation in the FCC phase. This upgraded synergy of tensile strength and ductility at liquid nitrogen temperature can be explained through the phase transformation and additional activation of twinned martensite formation, which results in two-step strain-hardening behavior. The presented results expand possibilities for developing DED-processed ferrous HEAs/MEAs to overcome the strength and ductility trade-off at room and liquid nitrogen temperatures.

Revealing spin-valve-like and exchange bias effect in Co3Sn1.9In0.1S2 crystal

We report on sharp spin-valve-like magnetoresistance (MR) below ferromagnetic order (TC), which has not been discussed in the pristine as well as doped crystals. In addition, typical manifestation of exchange bias (EB) effect is also observed by systematic shifts of the loop observed in MR driven by the cooling field. The EB effect appears below a characteristic temperature (TA), below which ferromagnetic and antiferromagnetic phases have been suggested to coexist. As a result of In doping, the sharp spin-valve-like evidence and EB effect over a wide temperature range, which are observed even at much higher temperatures than the liquid nitrogen temperature, suggest the system as a potential candidate for application in topological spintronics.

Nanocrystalline Mn-doped Ni–Cu ferrites with a high cut-off frequency and initial permeability: Suitable for advanced electronic devices and biomedical applications

The microstructural and electromagnetic properties of Mn-doped Ni0.50-xMnxCu0.50Fe2O4 (x = 0.0, 0.10, 0.20, 0.30, 0.40) magnetic nanoparticles are studied. Compositions are produced by the combustion method, and samples prepared from these powders are sintered at different sintering temperatures. The Rietveld refinement of X-ray diffraction (XRD) data confirmed that all compositions have cubic spinel structures with an Fd-3m space group. The average crystallite size is within 8–65 nm measured by different methods. The porosity of the surface, average grain diameter, and grain distribution are measured using optical micrographs. The high cut-off frequency of 10 MHz is observed in the initial permeability as a function of frequency plots. The maximum Curie temperature of 855 K is found for the x = 0 sample. The maximum relative quality factor (2636) and lowest relative loss factor (0.04) are found for x = 0.4. The initial permeability as a function of frequency is also measured at liquid nitrogen temperature (77 K). The “law of approach to saturation (LAS)” is used for magnetization data and the highest saturation magnetization value 61 emu/g is obtained for x = 0.3. The "Jonscher universal power law" fitted the ac electrical conductivity with large dispersion at a higher frequency region and a small polaron hopping model is applicable in this case. The dielectric constant exhibit dispersive behavior at low frequency and follow Koop's as well as Maxwell-Wagner's two-layer models. At 100 Hz the maximum value of the dielectric constant is 2.8 × 105. Nyquist plot representation stated that the electrical conduction mechanism in these ferrites is mainly due to the influence of the grain and grain boundary effects. An electrical equivalent circuit is suggested to explain the impedance analysis. Electric modulus studies confirm the non-Debye type relaxation process of the compositions. Tuning all of the properties specifies that the synthesized magnetic nanoparticles may be an optimistic application for high-frequency electronic devices and biomedical applications.

Near-Threshold Photoemission from Graphene-Coated Cu (110)

The brightness of electron beams emitted from photocathode sources plays a critical role in determining the performance of x-ray free-electron lasers and ultrafast electron-diffraction applications. In order to achieve the maximum brightness, the electrons need to be emitted from a photocathode with the lowest-possible mean transverse energy (MTE). Recent investigations have shown that capping a $\mathrm{Cu}$(110) photocathode with a monolayer of graphene can protect the quantum efficiency (QE) from long-term exposure to varying vacuum conditions. However, there have been no studies that investigate the effects that a monolayer of graphene has on the MTE. Here, we report on measurements of a graphene-coated $\mathrm{Cu}$(110) single crystal near the photoemission threshold for room and liquid-nitrogen temperatures. At room temperature, a minimum MTE of 25 meV is measured at 295 nm. At liquid-nitrogen temperatures, a minimum MTE of 9 meV is measured at the photoemission threshold of 290 nm.