Continuous Flow Cryostat Research Articles

Advances in dry low-temperature scanning probe microscopy system development

Since the beginning of the 21st century, Scanning Probe Microscopy (SPM) has played an increasingly important role in the fields of micro- and nanoscale surface characterization, physical property measurement, and micro/nano fabrication. To provide a more stable operating environment and higher energy resolution for SPM, researchers have developed Low-Temperature Scanning Probe Microscopy (LT-SPM) systems that operate under ultra-high vacuum and low temperature conditions. Currently, most LT-SPM systems achieve temperatures around 4.2 K by supplying liquid helium-4 (<sup>4</sup>He) to continuous flow cryostats or low-temperature Dewars. However, due to the low natural abundance of <sup>4</sup>He and its rising demand, the price of liquid helium has surged dramatically, severely impacting the normal operation of <sup>4</sup>He-based low temperature equipment. To address this issue, dry (cryogen-free) refrigeration technology has emerged as a promising alternative for next-generation low-temperature systems. In this context, the integration of dry refrigeration technology with SPM to construct DRY-LT-SPM systems has become a key research focus in the field of scanning probe instruments.<br>This paper mainly discusses several reported closed-cycle DRY -LT-SPM systems, focusing on aspects such as system design, refrigeration schemes, vibration reduction methods, and overall performance. Finally, the paper summarizes the current challenges and issues faced by DRY -LT-SPM systems and explores potential future developments in this field.

Development of a cryogen-free sub-3K low-temperature scanning probe microscope by remote liquefaction scheme.

We developed a new scheme for cryogen-free cooling down to sub-3K temperature range and ultra-low vibration level. An ultra-high-vacuum cryogen-free scanning probe microscope (SPM) system was built based on the new scheme. Instead of mounting a below-decoupled cryocooler directly onto the system, the new design was realized by integrating a Gifford-McMahon cryocooler into a separate liquefying chamber, providing two-stage heat exchangers in a remote way. About 10 L of helium gas inside the gas handling system was cooled, liquefied in the liquefying chamber, and then transferred to a continuous-flow cryostat on the SPM chamber through an ∼2m flexible helium transfer line. The exhausted helium gas from the continuous-flow cryostat was then returned to the liquefying chamber for reliquefaction. A base temperature of ∼2.84K at the scanner sample stage and a temperature fluctuation of almost within ±0.1 mK at 4K were achieved. The cooling curves, tunneling current noise, variable-temperature test, scanning tunneling microscopy and non-contact atomic force microscopy imaging, and first and second derivatives of I(V) spectra are characterized to verify that the performance of our cryogen-free SPM system is comparable to the bath cryostat-based low-temperature SPM system. This remote liquefaction close-cycle scheme shows conveniency to upgrade the existing bath cryostat-based SPM system, upgradeability of realizing even lower temperature down to sub-1K range, and great compatibility of other physical environments, such as high magnetic field and optical accesses. We believe that the new scheme could also pave a way for other cryogenic applications requiring low temperature but sensitive to vibration.

A high-speed variable-temperature ultrahigh vacuum scanning tunneling microscope with spiral scan capabilities.

We present the design and development of a variable-temperature high-speed scanning tunneling microscope (STM). The setup consists of a two-chamber ultra-high vacuum system, including a preparation and a main chamber. The preparation chamber is equipped with standard preparation tools for sample cleaning and film growth. The main chamber hosts the STM that is located within a continuous flow cryostat for counter-cooling during high-temperature measurements. The microscope body is compact, rigid, and highly symmetric to ensure vibrational stability and low thermal drift. We designed a hybrid scanner made of two independent tube piezos for slow and fast scanning, respectively. A commercial STM controller is used for slow scanning, while a high-speed Versa Module Eurocard bus system controls fast scanning. Here, we implement non-conventional spiral geometries for high-speed scanning, which consist of smooth sine and cosine signals created by an arbitrary waveform generator. The tip scans in a quasi-constant height mode, where the logarithm of the tunneling current signal can be regarded as roughly proportional to the surface topography. Scan control and data acquisition have been programmed in the experimental physics and industrial control system framework. With the spiral scans, we atomically resolved diffusion processes of oxygen atoms on the Ru(0001) surface and achieved a time resolution of 8.3 ms per frame at different temperatures. Variable-temperature measurements reveal an influence of the temperature on the oxygen diffusion rate.

Adapting a continuous flow cryostat and a plate DAC to do high pressure Raman experiments at low temperatures

We present a method for modifying a continuous flow cryostat and a steel plate DAC (Diamond Anvil Cell) to perform high pressure micro-Raman experiments at low temperatures. Despite using a steel DAC with a lower specific heat capacity (∼335 J/kg K), this setup can routinely perform high pressure (∼10GPa) measurements at temperatures as low as 26K. This adaptation is appropriate for varying the temperature of the sample while keeping it at a constant pressure. We determined that the temperature variation across the sample chamber is about 1K using both direct temperature measurements and finite element analysis of the heat transport across the DAC. We present Raman spectroscopy results on elemental selenium at high pressures and low temperatures using our modified setup.

Thermodynamic modeling of continuous flow liquid helium thermostat

Since the discovery of cryogenic superconductivity, liquid helium-based cryogenic superconductivity has been successfully applied in many disciplines. And continuous flow cry-ostats have great importance for the efficient and stable operation of the entire cryogenic system, which can provide a cryogenic working environment for large scale cryogenic applications. In this paper, a thermodynamic model of the liquid helium thermostat is developed based on the principle of continuous flow helium cryostat and the thermodynamic processes between liquid helium and gas helium, using mass conservation, energy conservation and pressure-volume-temperature relationships. The research work can provide theoretical guidance for the stability analysis of continuous flow cryostats, and also has practical value in large-scale cryogenic applications.

Breakthrough instruments and products Janis Research Company, LLC Cryogen free sub-Kelvin ARPES system.

The Janis Research cryogen-free sub-K continuous flow cryostat for angle-resolved photoemission spectroscopy is a convenient multi-functional tool, suitable for a wide range of research applications. In this article, the design and operating principles of the cryostat are described.

A variable-temperature scanning tunneling microscope operated in a continuous flow cryostat.

We present a continuous flow cryostat scanning tunneling microscope (STM) which can be operated at temperatures between 4.9 K and 300 K. A variable temperature insert with 20 mm aperture is installed in the cryostat. A base temperature of 4.9 K at the STM head was achieved with helium exchange gas cooling. By using a novel design of zirconia structure, the size of the STM head was minimized to 9.2 mm in outer diameter. The high compactness and rigidity of the STM head make it less sensitive to vibrations, contributing to the high stability of the tip-sample junction. The drifting rates of the STM at 4.9 K in the X-Y plane and Z direction are 1.96 and 3.05 pm/min, respectively. The performance of the STM was demonstrated by atomically resolved imaging of graphite and NbSe2 without using external vibrational isolation. Furthermore, the dI/dV spectra of NbSe2 were resolved near its critical temperature, illustrating the formation process of the superconducting gap as a function of temperature. This STM is ultrahigh vacuum and strong magnetic field compatible, making it promising for direct application in the extreme conditions involving water-cooled magnets and hybrid magnets.

Design and Experimental Study on Casing Pipe Continuous Flow Cryostat System

Casing pipe continuous flow cryostat system is the subsystems of liquid nitrogen freezing temporary plugging project. It is also an important supporting system which make the cooling uniform, safe and stable. The requirement analysis of cryogenic user have been carried out. The main technical specifications and requirements of the system has been defined. The process flow design and key components design have also been carried out. A verification experimental system has been built. The experimental results show that the design of continuous flow cryostat system is reasonable and the outlet temperature fluctuation is less than 0.3K, which can meet the design requirements.

Ultrafast time-resolved fluorescence at cryogenic temperature.

Time resolved fluorescence at low temperature can be a powerful tool for the study of dynamics and spectroscopy. We have developed a time resolved fluorescence apparatus that provides a time resolution of 45 fs at cryogenic temperature, which is comparable to the best time resolution at ambient temperature. A continuous flow cryostat with a customized vacuum shroud and fluorescence upconversion gating by sum frequency generation were employed. A reflective Cassegrain type microscope objective lens was used to collect and to image the fluorescence to achieve high time resolution. It was demonstrated that time-resolved fluorescence spectra can also be measured directly without the spectra reconstruction at the same time resolution by in situ adjustment of the time delay to compensate the group velocity dispersion. Heat dissipation of the sample holder and the actual temperature of the irradiated volume were estimated by measuring the steady-state emission spectra of prodan solution in two different sample thicknesses, which provides a design consideration for the sample cell. The time-resolved fluorescence spectra of prodan, which undergoes charge transfer in the excited state, were measured at low temperature to demonstrate the capability of the apparatus.

Pressure cell for radio-frequency dielectric measurements at low temperatures.

We present the design, test, and performance of a piston type pressure cell for low-temperature dielectric measurements up to 10 kbar with particular emphasis on the electrical feedthrough for four coaxial cables and four conventional copper wires. The coaxial cables provide proper shielding of the applied test signal; a commercial continuous flow cryostat allows us to minimize the total cable length enabling temperature and pressure-dependent dielectric spectroscopy measurements down to 8 K and up to 5 MHz. We performed open compensation measurements, i.e., background measurements of the response originating from the pressure setup without a sample, to obtain its high frequency characteristics. The stray capacitance of the pressure setup is determined as Cstray = 40 fF, making it possible to measure small single crystals with a weak dielectric response. The proper operation is verified by comparing measurements of a test sample in the pressure setup at ambient pressure and in a standard dielectric spectroscopy setup.

A high-resolution combined scanning laser and widefield polarizing microscope for imaging at temperatures from 4 K to 300 K.

Polarized light microscopy, as a contrast-enhancing technique for optically anisotropic materials, is a method well suited for the investigation of a wide variety of effects in solid-state physics, as, for example, birefringence in crystals or the magneto-optical Kerr effect (MOKE). We present a microscopy setup that combines a widefield microscope and a confocal scanning laser microscope with polarization-sensitive detectors. By using a high numerical aperture objective, a spatial resolution of about 240 nm at a wavelength of 405 nm is achieved. The sample is mounted on a 4He continuous flow cryostat providing a temperature range between 4 K and 300 K, and electromagnets are used to apply magnetic fields of up to 800 mT with variable in-plane orientation and 20 mT with out-of-plane orientation. Typical applications of the polarizing microscope are the imaging of the in-plane and out-of-plane magnetization via the longitudinal and polar MOKE, imaging of magnetic flux structures in superconductors covered with a magneto-optical indicator film via the Faraday effect, or imaging of structural features, such as twin-walls in tetragonal SrTiO3. The scanning laser microscope furthermore offers the possibility to gain local information on electric transport properties of a sample by detecting the beam-induced voltage change across a current-biased sample. This combination of magnetic, structural, and electric imaging capabilities makes the microscope a viable tool for research in the fields of oxide electronics, spintronics, magnetism, and superconductivity.

Construction and 13 C hyperpolarization efficiency of a 180GHz dissolution dynamic nuclear polarization system.

Dynamic nuclear polarization (DNP) via the dissolution method has become one of the rapidly emerging techniques to alleviate the low signal sensitivity in nuclear magnetic resonance (NMR) spectroscopy and imaging. In this paper, we report on the development and 13 C hyperpolarization efficiency of a homebuilt DNP system operating at 6.423T and 1.4K. The DNP hyperpolarizer system was assembled on a wide-bore superconducting magnet, equipped with a standard continuous-flow cryostat, and a 180GHz microwave source with 120mW power output and wide 4GHz frequency tuning range. At 6.423T and 1.4K, solid-state 13 C polarization P levels of 64% and 31% were achieved for 3M [1-13 C] sodium acetate samples in 1:1v/v glycerol:water glassing matrix doped with 15mM trityl OX063 and 40mM 4-oxo-TEMPO, respectively. Upon dissolution, which takes about 15s to complete, liquid-state 13 C NMR signal enhancements as high as 240000-fold (P=21%) were recorded in a nearby high resolution 13 C NMR spectrometer at 1T and 297K. Considering the relatively lower cost of our homebuilt DNP system and the relative simplicity of its design, the dissolution DNP setup reported here could be feasibly adapted for in vitro or in vivo hyperpolarized 13 C NMR or magnetic resonance imaging at least in the pre-clinical setting. Copyright © 2017 John Wiley & Sons, Ltd.

Multipurpose setup for low-temperature conversion electron Mössbauer spectroscopy.

We describe an experimental setup for conversion electron Mössbauer spectroscopy (CEMS) at low temperature. The setup is composed of a continuous flow cryostat (temperature range of 4.2-500 K), detector housing, three channel electron multipliers, and corresponding electronics. We demonstrate the capabilities of the setup with CEMS measurements performed on a sample consisting of a thin enriched 57Fe film, with a thickness of 20 nm, deposited on a silicon substrate. We also describe exchangeable adaptations (lid and sample holder) which extend the applicability of the setup to emission Mössbauer spectroscopy as well as measurements under an applied magnetic field.

Thermohydraulic modelling of a transfer line for continuous flow cryostats

Continuous flow cryostats have to be steadily supplied with the cryogenic cooling agent, e.g. liquid helium (LHe) via a transfer line. The overall setup has to be characterised by a low consumption of the cryogen, determined not only by the cryostat design, but also by the transfer line design. In order to improve the transfer line’s performance, i.e. reducing the evaporation losses a thermohydraulic model has been developed to evaluate different transfer line designs. The presented model is validated by experimental data achieved with a transfer line equipped with built-in pressure sensors. This transfer line has been designed in order to examine the related frictional pressure drop. The developed model allows to examine the impact of the hydraulic and the insulation design on the resulting evaporation losses.

High accuracy computational methods for behavioral modeling of thick-film resistors at cryogenic temperatures

Abstract The aim of this work was to elaborate two-dimensional behavioral modeling method of thick-film resistors working in low-temperature conditions. The investigated resistors (made from 5 various resistive inks: 10 resistor coupons, each with 36 resistors with various dimensions), were measured automatically in a cryostat system. The low temperature was achieved in a nitrogen-helium continuous-flow cryostat. For nitrogen used as a freezing liquid the minimal temperature possible to achieve was equal to −195.85 °C (77.3 K). Mathematical model in the form of a multiplication of two polynomials was elaborated based on the above mentioned measurements. The first polynomial approximated temperature behavior of the normalized resistance, while the second one described the dependence of resistance on planar resistors dimensions. Special computational procedures for multidimensional approximation purpose were elaborated. It was shown that proper approximation polynomials and sufficiently exact methods of calculations ensure acceptable modeling errors.

Cryogenic System for the Integration of a ring-shaped SMB in a Ring-spinning Tester

A liquid nitrogen cryostat has been developed for experiments with a Superconducting Magnetic Bearing (SMB) in a ring spinning machine. The use of an SMB without friction instead of the common friction afflicted twist element is a promising approach leading to increased productivity and material variety. Here, an SMB designed as an axial ring system consisting of a liquid nitrogen (LN2)-cooled high-temperature superconductor ring YBa2Cu3O7-x and a permanent-magnet ring at room temperature is investigated. To assure the high quality of the yarn, the process has strong edge conditions concerning the air moisture and the ambient temperature. To protect the yarn from LN2 temperature, a continuous-flow cryostat was designed, tested, and integrated in the ring spinning tester. The geometric requirements of the spinning process lead to a ring-shaped vessel with a hole in the middle for the rotating spindle. First spinning experiments running at rotations in the range of 20 000 rpm show a reliable operation of the continuous flow cryostat in the SMB-based spinning process. In addition, easy process handling and low LN2 consumption are demonstrated.

Operating parameters of liquid helium transfer lines used with continuous flow cryostats at low sample temperatures

Continuous flow cryostats are used to cool samples to a variable temperature level by evaporating a cryogen, e.g. liquid helium (LHe). For this purpose LHe is usually stored outside the cryostat in a mobile dewar and supplied through a transfer line. In general, the complete setup has to be characterised by the lowest possible consumption of LHe. Additionally, a minimum sample temperature can be favourable from an experimental point of view. The achievement of both requirements is determined by the respective cryostat design as well as by the transfer line. In the presented work operating data, e.g. the LHe consumption during cooldown and steady state, the minimum sample temperature, and the outlet quality are analysed to characterise the performance of a reference transfer line. In addition, an experimental transfer line with built-in pressure sensors has been commissioned to examine the pressure drop along the transfer line, too. During the tests LHe impurities occurred which restricted a steady operation.

Manganese lipoxygenase of F. oxysporum and the structural basis for biosynthesis of distinct 11-hydroperoxy stereoisomers

The biosynthesis of jasmonates in plants is initiated by 13S-lipoxygenase (LOX), but details of jasmonate biosynthesis by fungi, including Fusarium oxysporum, are unknown. The genome of F. oxysporum codes for linoleate 13S-LOX (FoxLOX) and for F. oxysporum manganese LOX (Fo-MnLOX), an uncharacterized homolog of 13R-MnLOX of Gaeumannomyces graminis. We expressed Fo-MnLOX and compared its properties to Cg-MnLOX from Colletotrichum gloeosporioides. Electron paramagnetic resonance and metal analysis showed that Fo-MnLOX contained catalytic Mn. Fo-MnLOX oxidized 18:2n-6 mainly to 11R-hydroperoxyoctadecadienoic acid (HPODE), 13S-HPODE, and 9(S/R)-HPODE, whereas Cg-MnLOX produced 9S-, 11S-, and 13R-HPODE with high stereoselectivity. The 11-hydroperoxides did not undergo the rapid β-fragmentation earlier observed with 13R-MnLOX. Oxidation of [11S-(2)H]18:2n-6 by Cg-MnLOX was accompanied by loss of deuterium and a large kinetic isotope effect (>30). The Fo-MnLOX-catalyzed oxidation occurred with retention of the (2)H-label. Fo-MnLOX also oxidized 1-lineoyl-2-hydroxy-glycero-3-phosphatidylcholine. The predicted active site of all MnLOXs contains Phe except for Ser(348) in this position of Fo-MnLOX. The Ser348Phe mutant of Fo-MnLOX oxidized 18:2n-6 to the same major products as Cg-MnLOX. Our results suggest that Fo-MnLOX, with support of Ser(348), binds 18:2n-6 so that the proR rather than the proS hydrogen at C-11 interacts with the metal center, but retains the suprafacial oxygenation mechanism observed in other MnLOXs.

Pyroelectric properties of the monoclinic rare earth nitrates A 2 Ln(NO3)5·4H2O (A = NH4, Rb; Ln = La, Ce)

Abstract The pyroelectric effect of four isomorphic monoclinic (space group Cc), non-ferroelectric rare earth nitrates A 2 Ln(NO3)5·4H2O (A = NH4, Rb; Ln = La, Ce) was investigated in the temperature range between 100 K and 300 K, using a home-made continuous-flow cryostat for measurements of pyroelectric currents. The symmetry-allowed temperature-dependent change of orientation of the pyroelectric vector p within the mirror plane is unusually large, showing a rotation of p of 148°, 129°, 36° and 40° for (NH4)2La(NO3)5·4H2O, (NH4)2Ce(NO3)5·4H2O, Rb2La(NO3)5·4H2O and Rb2Ce(NO3)5·4H2O, respectively, while changing the temperature from 100 K to 300 K in each case. The pyroelectric coefficients are up to ten times larger than p 3 of tourmaline. In addition, new data of the pyroelectric coefficients of Li2SO4·H2O and BiB3O6 and their temperature dependence are given.

Note: Improved wire-wound heater.

The authors have measured, at cryogenic temperature, the upper limit of the heat transfer in different configurations of a wire-wound heater. We found that the heat transferred has an upper limit of about 15 W/cm(2) and is dependent on the diameter of the wire. In this paper, we present three ways of increasing the heat transferred by this type of heater and its application in different continuous flow cryostats.