Ultrahigh Vacuum System Research Articles

(U,Th)-He dating of Pleistocene carbonates: Analytical methods and age calculations

The uranium-thorium-helium ((U,Th)-He) dating method applied to calcium carbonate speleothems holds much promise for constraining the timeline of hominin evolution, as well as for palaeoclimatology research beyond the range of U/Th disequilibrium dating. Technical problems are posed by often low U concentrations and the requirement that samples need to be individually removed from the ultrahigh vacuum (UHV) system after helium is extracted from them, to be then analyzed for U, Th content and U series disequilibrium. We describe a low-cost furnace with this capability, constructed from standard UHV components, as well as the methods for subsequent U/Th disequilibrium analysis using multicollector ICP mass spectrometry. We present analytical and numerical solutions to determine (U,Th)-He ages for four conditions that have been encountered: (1) for an age range in which the residual activity ratio (234U/238U) can still be resolved but not that of (230Th/234U) (up to about 3000 ka), (2) for an age range where neither can be resolved (unlimited), (3) for ages up to 1000 ka where both activity ratios may be resolvable, and (4) for cases where (234U/238U) and (230Th/234U) indicate ages < 200 ka but (U,Th)-He systematics point to much older ages.•Helium extraction is carried out using an in-house built vacuum furnace that allows for large sample sizes (20 to 100 mg) of powdered carbonate material wrapped in Cu foil.•U and Th are separated together using Eichrom UTEVAⓇ resin and their isotope abundances are measured together in a single 2-cycle dynamic run using the multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS).•(U,Th)-He ages are calculated using four methods that take into account the U/Th disequilibria.

Reconstruction of Ultra-High Vacuum Mass Spectra Using Genetic Algorithms

In ultra-high vacuum systems, obtaining the composition of a mass spectrum is often a challenging task due to the highly overlapping nature of the individual profiles of the gas species that contribute to that spectrum, as well as the high differences in terms of degree of contribution (several orders of magnitude). This problem is even more complex when not only the presence but also a quantitative estimation of the contribution (partial pressure) of each species is required. This paper aims at estimating the relative contribution of each species in a target mass spectrum by combining a state-of-the-art machine learning method (multilabel classifier) to obtain a pool of candidate species based on a threshold applied to the probability scores given by the classifier with a genetic algorithm that aims at finding the partial pressure at which each one of the species contributes to the target mass spectrum. For this purpose, we use a dataset of synthetically generated samples. We explore different acceptance thresholds for the generation of initial populations, and we establish comparative metrics against the most novel method to date for automatically obtaining partial pressure contributions. Our results show a clear advantage in terms of the integral error metric (up to 112 times lower for simpler spectra) and computational times (up to 4 times lower for complex spectra) in favor of the proposed method, which is considered a substantial improvement for this task.

Activation experiment and spectral response properties analysis of graded-bandgap AlGaAs/GaAs electron-injection cathode

A cesium/oxygen activation experiment was conducted on a gallium-arsenide-based electron-injection cathode in an ultra-high vacuum system connected to a spectral response measuring instrument. Before activation, high-temperature cleaning was performed at 650 °C to obtain an atomically clean surface. The cathode surface impurities before and after the experiment were characterized by X-ray photoelectron spectroscopy. Because of the cathode Ti/Pt/Au electrode properties, the sample could not be cleaned chemically. High-temperature cathode treatment before activation could not remove the oxides completely, which led to a low cathode emission capacity in the photocurrent and spectral response. The experimental quantum efficiency curve was fitted by a two-minima diffusion model, and parameters, such as the electron diffusion length and escape probability, which characterize the cathode performance, were calculated. According to the fitting results, the residual impurities on the cathode surface and the thin emitter layer resulted in a low probability of electron escape, which resulted in a low quantum efficiency.

Increase of the barium ion-trap lifetime via photodissociation

The lifetime of ${\mathrm{Ba}}^{+}$ ions confined in a Paul trap is found, under typical conditions, to be limited by chemical reactions with residual background gas. An integrated ion-trap and time-of-flight mass spectrometer are used to analyze the reactions of the trapped ${\mathrm{Ba}}^{+}$ ions with three common gases in an ultrahigh vacuum system (${\mathrm{H}}_{2}$, ${\mathrm{CO}}_{2}$, and ${\mathrm{H}}_{2}\mathrm{O}$). It is found that the products of these reactions can all be photodissociated by a single ultraviolet laser at 225 nm, thereby allowing the recovery of the ${\mathrm{Ba}}^{+}$ ions and leading to an increase of the effective trap lifetime. For a Coulomb crystal, the lifetime increased from roughly 6 h to 2 days at room temperature. It is suggested that higher enhancement factors are possible in systems with stronger traps. In addition, photodissociation wavelengths for other common trapped-ion systems are provided.

Leakage rate detection of ConFlat seals in aluminum and stainless steel flanges under mechanical loads for quantum optical experiments in space

Several space missions, such as quantum optical experiments or quantum sensors, require ultrahigh vacuum (UHV) systems to perform their experiments and fulfill the scientific mission goals. Most of these experiments use standard ConFlat (CF) flanges for the design of the UHV system. One of the biggest challenges for these vacuum systems during a space mission is the mechanical loads. These loads are applied during launch, stage separation, etc., as a combination of static and dynamic loads. When loads are applied, the UHV system can experience an increased leakage rate, which decreases the vacuum quality. Investigation of the rise of the leakage rate due to static loads is an important step to allow a proper design process of space suitable UHV systems. In this paper, CF DN40 flange connections will be experimentally tested for standard aluminum (AluVaC) and stainless steel (316LN-ESR, 14429-ESU) tubes. Additionally, three different bolt pretension torques of 10, 12.5, and 15 N m are tested and compared. The presented results can be used to improve the design and assembly procedure for future UHV systems, such as the MAIUS (Matter-Wave Interferometry under Microgravity) sounding rocket missions.

Building a Scanning Probe Microscope Using Open Source Control Software and Systems.

A scanning probe microscope (SPM) operating in air and liquid was constructed using an open-source control software running on Linux, a correspondingly developed commercial SPM controller and a commercial STM head. The results are shown for highly oriented pyrolytic graphite (HOPG) and Au(111) substrate surfaces, which are typical samples for SPM measurements. The cost of building the system was much lower than that of commercial products with comparable performance. The system has great scalability, and can be applied to a various environment, such as ultra-high vacuum systems.

Characterization of deuteriated titanium thin film by residual gas analyzer

Titanium thin film was prepared on copper substrate by thermal evaporation method. Gettering property of titanium film for deuterium was studied for different values of temperature, pressure and time. The studies were carried out in an ultra high vacuum system. The substrate was mounted in the vacuum system on a heater whose temperature was controlled by PID controller. The titanium thin film was activated for 1 h at a temperature of 500 °C under vacuum. After activation, during cool down, the vacuum chamber was pressurized at various pressure values of deuterium and left for absorption for various time periods. Comparative studies of the amount of deuterium desorption for various charging pressure and exposure time were studied with the help of residual gas analyzer. Attempts were made to qualify the process of deuteration of the titanium film. The results of these studies are presented in this article.

A simplified analytical model to simulate martensite reorientation and plasticity in shape memory alloy ring couplers

Recent studies on Shape Memory Alloy rings have been undertaken at the European Organization for Nuclear Research (CERN) to develop smart and leak-tight couplers for Ultra High Vacuum systems of particle accelerators. A special thermo-mechanical process (training) is needed to provide SMA rings with proper functional properties, that is to allow thermal mounting, dismounting, and leak tight coupling within a given service temperature window. Low temperature ring expansion is a crucial part of the training process as it gives suitable size, shape recovery properties, and thermal stability range to the SMA element. An analytical model, based on simplified elastic-plastic axisymmetric concepts, has been developed and implemented in a commercial software to simulate isothermal SMA rings expansions. It is particularly useful to predict the final size of a martensitic SMA coupler as a function of the initial dimensions and of the pre-deformation parameters. The effectiveness of the model has been demonstrated by analyzing the stress/deformation field occurring in a wide range of ring geometries for different load cases including martensite reorientation and plasticity. The predictions of the analytical model have been systematically compared with those obtained by axisymmetric finite element (FE) analyses based on elastic-plastic constitutive models and experimental measurements.

Comparison of “Natural” Li Diffusion Behavior on Different Li-Ion Battery Materials

Lithium atoms exhibit “natural” diffusion and intercalation properties on certain materials at room temperature. This effect is used as a screening method of potential anode materials for higher energy and power density for Li-ion batteries as well as quality control tests for fabricated anode. This method requires an ultra-high vacuum system environment with an evaporation source to deposit Lithium thin film on the substrates being tested.Auger electron spectroscopy (AES) is used for measuring the Li-KVV line (peak) at 52 eV on anode materials such as Graphite, Si-Graphite, LTO, and Niobium Oxides. Low energy electron diffraction (LEED) is used for monitoring surface crystallographic variation upon Li deposition and diffusion on some single crystal materials such as HOPG, Si, SiC, CVD Diamond, and LiNbO3. The data analysis indicates that three categories of materials can be distinguished based on their properties. The first is “graphite-like” which has rapid Li diffusion and no changes in crystalline structure. The second is “silicon-like” with no Li diffusion and drastic changes in crystalline structure. The third is “silicon-carbide-like” with some Li “natural” diffusion and no changes in crystalline structure. This testing method is simplifying complexity of the electrochemical system as the cathode and electrolyte are not required for these tests and deliver unique test results of nanoscale Li diffusion characteristics in the fabricated battery anodes before cell assembly not possible with other methods.In addition, the Li Auger peak energy shift indicates ionic and metallic bonding of Li atoms which suggests capabilities of early detection of Li dendrite growth. This method can be used to develop interface materials quicker, reduce dendrite growth, and provide failure analysis of disassembled battery electrodes with degraded performance.

A versatile electrochemical cell for hanging meniscus or flow cell measurement of planar model electrodes characterized with scanning tunneling microscopy and x-ray photoelectron spectroscopy.

We demonstrate the development of a portable electrochemistry (EC) cell setup that can be applied to measure relevant electrochemical signals on planar samples in conjunction with pre- and post-characterization by surface science methods, such as scanning tunneling microscopy and x-ray photoelectron spectroscopy. The EC cell setup, including the transfer and EC cell compartments, possesses the advantage of a small size and can be integrated with standard ultra-high vacuum (UHV) systems or synchrotron end-stations by replacing the flange adaptor, sample housing, and transfer arm. It allows a direct transfer of the pre-characterized planar sample from the UHV environment to the EC cell to conduct in situ electrochemical measurements without exposing to ambient air. The EC cell setup can operate in both the hanging meniscus and flow cell mode. As a proof of concept, using a Au(111) single crystal electrode, we demonstrate the application of the EC cell setup in both modes and report on the post-EC structure and chemical surface composition as provided by scanning tunneling microscopy and x-ray photoelectron spectroscopy. To exemplify the advantage of an in situ EC cell, the EC cell performance is further compared to a corresponding experiment on a Au(111) sample measured by transfer at ambient conditions. The EC cell demonstrated here enables a wealth of future electrocatalysis measurements that combine surface science model catalyst approaches to facilitate the understanding of nano- and atomic-scale structures of electrocatalytic interfaces, the crucial role of catalyst stability, and the nature of low-concentration and atomically dispersed metal (single atom) dopants.

Characterization of Cobalt Phthalocyanine Thin Film on Silicon Substrate Using Spectroscopic Ellipsometry

The cobalt phthalocyanine film (CoPc) was prepared by an ultra-high vacuum system onto a silicon substrate. Structural features and optical properties of the organic semiconductor CoPc has been determined with the use of spectroscopic ellipsometry over the wavelength interval 300–1000 nm. By restricting it to 900–1000 nm the film thickness is determined, and, by the point-by-point fit, the behavior of the dielectric function is established in the entire spectral region. Thus, the optical properties are determined from spectral ellipsometric data using mathematical models based on Gaussian oscillators, which have led to an excellent fit to the experimental data with a relatively low mean square error. Cobalt phthalocyanine was treated as a uniaxial material.

A Cylindrical Triode Ultrahigh Vacuum Ionization Gauge with a Carbon Nanotube Cathode.

In this study, a cylindrical triode ultrahigh vacuum ionization gauge with a screen-printed carbon nanotube (CNT) electron source was developed, and its metrological performance in different gases was systematically investigated using an ultrahigh vacuum system. The resulting ionization gauge with a CNT cathode responded linearly to nitrogen, argon, and air pressures in the range from ~4.0 ± 1.0 × 10−7 to 6 × 10−4 Pa, which is the first reported CNT emitter-based ionization gauge whose lower limit of pressure measurement is lower than its hot cathode counterpart. In addition, the sensitivities of this novel gauge were ~0.05 Pa−1 for nitrogen, ~0.06 Pa−1 for argon, and ~0.04 Pa−1 for air, respectively. The trend of sensitivity with anode voltage, obtained by the experimental method, was roughly consistent with that gained through theoretical simulation. The advantages of the present sensor (including low power consumption for electron emissions, invisible to infrared light radiation and thermal radiation, high stability, etc.) mean that it has potential applications in space exploration.

Local Structure Properties of Hydrogenated and Nonhydrogenated Amorphous In–Ga–Zn–O Thin Films Using XAFS and High-Energy XRD

The strong effect of impurity hydrogen (H) on subgap electronic states in amorphous In–Ga–Zn–O thin-film transistors (a-IGZO TFTs) was confirmed using standard (STD) and ultrahigh-vacuum (UHV) sputtering systems with different base pressures of 10–4 and 10–7 Pa, respectively. However, comprehensive studies of the atomic-scale structure have yet to be reported. We investigated the correlations between the atomic-scale structure, the electronic state, and the impurity hydrogen content in a-IGZO by high-energy X-ray diffraction (HEXRD) coupled with reverse Monte Carlo (RMC) modeling and X-ray absorption fine structure (XAFS) spectroscopy. XAFS probed the distribution of unoccupied electronic states above the Fermi level and the local coordination structure around the In, Ga, and Zn atoms. A possible contribution for H from voids in the a-IGZO films was observed by the HEXRD and RMC configuration models. In contrast, the STD 3% film has many voids, which are occupied by impurity H. The proportion of lower coordinated M-O (M = Zn, Ga, In) structures is increased because of the H in voids. We revealed that this electronic and atomic-scale structure of the a-IGZO TFTs, which results in enhanced TFT characteristics, can be stabilized by the hydrogen-passivated defects resulting from STD sputtering with an optimum oxygen flow rate ratio of 3%.

Atomic-Level Structural Engineering of Graphene on a Mesoscopic Scale.

Structural engineering is the first step toward changing properties of materials. While this can be at relative ease done for bulk materials, for example, using ion irradiation, similar engineering of 2D materials and other low-dimensional structures remains a challenge. The difficulties range from the preparation of clean and uniform samples to the sensitivity of these structures to the overwhelming task of sample-wide characterization of the subjected modifications at the atomic scale. Here, we overcome these issues using a near ultrahigh vacuum system comprised of an aberration-corrected scanning transmission electron microscope and setups for sample cleaning and manipulation, which are combined with automated atomic-resolution imaging of large sample areas and a convolutional neural network approach for image analysis. This allows us to create and fully characterize atomically clean free-standing graphene with a controlled defect distribution, thus providing the important first step toward atomically tailored two-dimensional materials.

A brief overview of 8 m prototype facility of laser interferometer for Taiji pathfinder mission

The 8 m laser interferometer prototype facility is currently being constructed at the Institute of Mechanics, Chinese Academy of Sciences in Beijing, China. It aims to perform laser interferometer experiments and pico-meter precision detection and calibration for Taiji pathfinder mission. The seismically isolated ground and passive vibration isolation are interconnected and the optical benches are stabilized by them, which can form two low-noise testbeds inside a 40 m3 ultra-high vacuum system. An on-ground laser interferometer demonstration used for satellite–satellite tracking will be constructed. In this article, the experimental facility and the employed methods will be described, and the technical details of subsystems will be covered in future papers.

Exploiting the challenges of copper to austenitic stainless steel bimetallic joining by gas tungsten arc welding: A fluid flow perspective

Miscible nature of the material is vital to join dissimilar materials together. The wide range of properties within the single structure requires merging of multiple materials. Hence, sustainable welding technology development to join distinct material with extreme immiscibility such as Cu and SS is emerging as a recent research interest. Because of its requirement in nuclear reactors’ critical components, plan wave linac structures and ultra-high vacuum systems. Gas tungsten arc welding is a well-established commercial process. Hence, a study on optimum weld condition to get better quality of Cu to SS bimetallic joint is advantageous and desirable. However, complex flow nature of the molten Cu and SS is a big challenge. Hence, authors have reviewed and discussed the fluid flow of Cu and SS during gas tungsten arc welding. Which, concludes that the flow characteristics of Cu and SS must be studied through experimental and simulations to set up the favourable weld conditions while joining it with gas tungsten arc welding. The mentioned area of interdisciplinary research and not explored yet about the joint’s mechanical and microstructural properties. The said study can potentially predict what will be the final weld properties well before the metallurgical testing. Moreover, the article enlightens the interdisciplinary research aspect of Cu to SS bimetallic joining.

Automatic mass spectra recognition for Ultra High Vacuum systems using multilabel classification

In Ultra High-Vacuum (UHV) systems it is common to find a mixture of many gases originating from surface outgassing, leaks and permeation that contaminate vacuum chambers and cause issues to reach ultimate pressures. The identification of these contaminants is, in general, done manually by trained technicians from the analysis of mass spectra. This task is time consuming and can lead to misinterpretation or partial understanding of issues. The challenge resides in the rapid identification of these contaminants by using some automatic gas identification technique. This paper explores the automatic and simultaneous identification of 80 molecules, including some of the most commonly present in this kind of environment by means of multilabel classification techniques. The best performance is drawn from a dependent binary relevance method trained by extreme gradient boosting. We obtain a Hamming loss of 0.0145 in the test set. The mean binary AUC for the test set was 0.986, and the minimum test AUC was higher than 0.89. A public interactive web app has been developed to allow vacuum users to test the model with their own data.

In situ XPS investigation of the X-ray-triggered decomposition of perovskites in ultrahigh vacuum condition

X-ray photoelectron spectroscopy (XPS) has been used to investigate the composition of perovskite films upon exposure to different environmental factors, such as moisture, heat, and UV light. However, few research studies have determined that the X-ray itself could cause damage to the perovskite crystals. In this study, the X-ray-induced degradation of CH3NH3PbI3 perovskite films was investigated via XPS within an in situ ultrahigh vacuum system. It is demonstrated that fresh methylammonium lead iodine contains Pb2+ without the initial existence of Pb0. The Pb0 signal was discovered after a few hours of soft X-ray exposure, which indicates that the CH3NH3PbI3 perovskite structure undergoes a decomposition process to form metallic Pb. In addition, the nitrogen content was found to be significantly decreasing in the first hour of X-ray exposure. The discovery of the X-ray-induced chemical state change and the volatile methylamine of perovskite crystals could be further applied as an indicator for the field of X-ray sensors or detectors.

Impact of residual gas on the optoelectronic properties of Cs-sensitized In0.53Ga0.47As (0 0 1) surface

Near-infrared InxGa1-xAs photocathode with better optoelectronic properties is a good candidate for low-light-level (LLL) night-vision system. However, the residual gases in the ultra-high vacuum (UHV) system inevitably affects the stability and photo-emission performance of LLL photoelectric devices such as their quantum efficiency and life-time. In this study, the first-principles calculations were used to investigate the adsorption effect of five different residual gas species, including H2, CH4, CO, H2O and CO2 on Cs-sensitized In0.53Ga0.47As (001) β2 (2 × 4) surface. The study results indicate that CO2 gas molecule is the most easily attached to the Cs-sensitized surface. The adsorption of residual gases leads to the formation of a new dipole pointing from inner Cs atoms to gas molecules. It makes the charge center of the adsorbates escape from the surface, which weakens the interaction between the inner Cs atoms and the clean surface. This results in the increase of the surface work function and degradation of the performance of photoelectric devices. Also, the adsorption of residual gas molecules influences the absorption and reflection coefficients of Cs-sensitized In0.53Ga0.47As (001) β2 (2 × 4) surface.

Development of an ultra-high vacuum system for a cold atom physics rack in space

We present the design and testing of the ultra-high vacuum (UHV) system, which is a key apparatus for the Cold Atom Physics Rack (CAPR) operated on the Chinese Space Station that allows study of ultracold atoms in microgravity. The simulation of the gas flow and experimental tests show that our UHV has a pressure of 3.4×10−9Pa in the science chamber, two orders of magnitude lower than that of the 2D magneto-optical trap (2D-MOT) chamber. Moreover, we demonstrate that the system can not only self-sustain an equilibrium pressure for more than 1 month without power but also restore the desired pressure in the interaction zone. The loss dynamics of the trapped atoms are also measured to assess the performance of the UHV system.