Cryogenic Beam Research Articles

Tailoring Lithium Horizontal Deposition for Long-Lasting High-Loading NCA (≥5 mA h cm-2)||Lithium-Metal Full Cells in Carbonate Electrolytes.

We report a design for a synergistic lithium (Li) metal hosting layer for high-loading Li(Ni,Co,Al)O2 (NCA) (≥5 mA h cm-2)||Li-metal full cells in carbonate electrolytes. Based on density functional theory calculations, the hosting layer was designed as a three-dimensional silver/carbon composite nanofiber (Ag/CNF) network with high Li affinity and a platinum (Pt)-coated polypropylene separator with low Li affinity. This design enabled the tailoring of horizontal Li deposition on the Ag/CNF hosting layer. The Li deposition behavior modulated by the hosting layer was thoroughly examined based on the initial Li deposition and cycling behaviors of the Li||Li symmetric cell configuration. Cryogenic focused-ion beam cross-sectional images of the cycled Li anodes clearly demonstrated that dense lithium deposition was enabled by the synergistic hosting layer high-loading NCA (≥5 mA h cm-2)||Li-metal full cells. When the hosting layer was used, the average cycling performance improved by 78.27% under various cycling conditions. Our work demonstrates that the synergistic hosting layer design is a fruitful pathway to accelerate the commercialization of high-energy-density Li-metal batteries in carbonate electrolytes.

Stability of C59 Knockout Fragments from Femtoseconds to Infinity

We have studied the stability of C59 anions as a function of time, from their formation on femtosecond timescales to their stabilization on second timescales and beyond, using a combination of theory and experiments. The C59− fragments were produced in collisions between C60 fullerene anions and neutral helium gas at a velocity of 90 km s−1 (corresponding to a collision energy of 166 eV in the center-of-mass frame). The fragments were then stored in a cryogenic ion beam storage ring at the DESIREE facility, where they were followed for up to 1 minute. Classical molecular dynamics simulations were used to determine the reaction cross section and the excitation energy distributions of the products formed in these collisions. We find that about 15% of the C59− ions initially stored in the ring are intact after about 100 ms and that this population then remains intact indefinitely. This means that C60 fullerenes exposed to energetic atoms and ions, such as stellar winds and shock waves, will produce stable, highly reactive products, like C59, that are fed into interstellar chemical reaction networks.

Thermal Engineering of the Cryogenic Beam Position Monitors for the EIC Hadron Storage Ring

The Electron Ion Collider (EIC) Hadron Storage Ring (HSR) will reuse most of the existing superconducting magnets from the RHIC storage ring. However, the existing stripline beam position monitors (BPM) used for RHIC will not be compatible with the planned EIC hadron beam parameters that include higher intensity, shorter bunches, and some operational scenarios with large radial offsets of the beam in the vacuum chamber. To address these challenges, the existing RHIC stripline BPMs will be decommissioned, and a new BPM design using button pick-ups integrated in a new vacuum interconnect/bellows assembly will be installed adjacent to the decommissioned BPMs.A dedicated analysis of the new BPM housing and button pick-up design has been conducted to assess the thermal effects caused by heat conduction, beam induced resistive wall heating and the RF heating from the BPM signal propagation through the cryogenic cables. This paper reports on the thermal design and analysis results to quantify the heat transfer and temperature distribution that can be expected on the new HSR cryogenic BPM.

Dielectric Behavior and Prolate Growth Patterns of Silicon Clusters SiN with N = 12-30 by Cryogenic Electric Beam Deflection.

We present a comprehensive investigation of the dielectric behavior and geometric structures of cold neutral SiN clusters of intermediate size with N = 12-30 atoms. For this, cryogenic electric beam deflection experiments were carried out for the first time for Si clusters at nozzle temperatures below 30 K. In combination with quantum chemical calculations based on density functional theory and classical trajectory simulations of the rotational dynamics in the electric field, the geometric structures of the clusters are discriminated. Clusters with N < 15 favor a single-capped square antiprism as a nucleus for cluster growth, forming compact geometries in the molecular beam. Starting with 15 atoms, a prolate-like growth is observed. The prolate structures are based on stable building blocks which reappear for numerous sizes throughout the cluster growth. Finally, the transition from prolate to quasi-spherical shapes is shown to take place around Si29/Si30 as predicted theoretically by the literature. The influence of the exchange-correlation functional on the predicted structure and dielectric properties is discussed in detail for some clusters. Relaxation of the electric-dipole moment and therefore quenching of the observed electric response due to vibrational excitation and collisions with the background gas are also considered, which explains deviations between experiment and theory.

Optical deceleration of atomic hydrogen

We demonstrate control over the motional degrees of freedom of a cryogenic hydrogen atomic beam using an accelerating optical lattice. For our method, we load metastable atoms from a cryogenic beam into a moving optical lattice, decelerate the lattice, and observe a commensurate deceleration of the atoms. For this demonstration, hydrogen atoms are decelerated by about 20 m s−1 in a 40 ns slowing cycle, with a peak acceleration of ≈4 m s−2. Since the optical lattice is governed by standard optoelectronics, this technique represents a robust platform for the motional control of hydrogen.

High-precision Ramsey-comb spectroscopy on molecular deuterium for tests of molecular quantum theory

Precision spectroscopy of simple, calculable molecules has become an important tool to compare experiments with theory in an effort to test our understanding of the fundamental laws of physics. For this purpose, we have measured the transition frequency of molecular deuterium () with unprecedented accuracy. We use Ramsey-Comb spectroscopy at deep-ultraviolet wavelengths (201 nm) with a two-photon, Doppler-free interrogation scheme. The resulting transition frequency is kHz. The 1-σ uncertainty of 19 kHz represents an improvement of more than two orders of magnitude compared to the best previous measurement. In this paper, we give an extensive description of our methods and the experimental apparatus that we employed. Particular attention is given to aspects that we recently improved, such as the frequency comb laser system, the method of signal recording, and the cryogenic molecular beam apparatus. In combination with future measurements of the ionisation energy of the EF state, our measurement paves the way for an improved determination of the ground state ionisation and dissociation energy of molecular deuterium.

GRASIAN: towards the first demonstration of gravitational quantum states of atoms with a cryogenic hydrogen beam

At very low energies, a light neutral particle above a horizontal surface can experience quantum reflection. The quantum reflection holds the particle against gravity and leads to gravitational quantum states (gqs). So far, gqs were only observed with neutrons as pioneered by Nesvizhevsky and his collaborators at ill. However, the existence of gqs is predicted also for atoms. The Grasian collaboration pursues the first observation and studies of gqs of atomic hydrogen. We propose to use atoms in order to exploit the fact that orders of magnitude larger fluxes compared to those of neutrons are available. Moreover, recently the q-Bounce collaboration, performing gqs spectroscopy with neutrons, reported a discrepancy between theoretical calculations and experiment which deserves further investigations. For this purpose, we set up a cryogenic hydrogen beam at 6 hbox {K}. We report on our preliminary results, characterizing the hydrogen beam with pulsed laser ionization diagnostics at 243 hbox {nm}.Graphical abstract

Fourth generation cryogenic neutral cluster beam apparatus for studying fundamental properties of metallic clusters.

A cryogenic beam apparatus for studying neutral clusters has been built and tested. The lowest beam temperature reaches less than 9K at a repetition rate of 20Hz. Mechanical decoupling from the refrigerator avoids misalignment during temperature ramping. Adopting a permanent magnet based magnetic deflector eliminates the hysteresis and electric noise of the traditional electromagnet and offers excellent reproducibility of the applied magnetic field. The mass spectrometer can operate in either Mass Spectroscopy Time-Of-Flight mode or Position-Sensitive Time-Of-Flight mode with spatial resolution better than 7μm. Its performance is demonstrated with niobium and cobalt clusters.

A cryogenic, coincident fluorescence, electron, and ion beam microscope.

Cryogenic electron tomography (cryo-ET) combined with subtomogram averaging, allows in situ visualization and structure determination of macromolecular complexes at subnanometre resolution. Cryogenic focused ion beam (cryo-FIB) micromachining is used to prepare a thin lamella-shaped sample out of a frozen-hydrated cell for cryo-ET imaging, but standard cryo-FIB fabrication is blind to the precise location of the structure or proteins of interest. Fluorescence-guided focused ion beam (FIB) milling at target locations requires multiple sample transfers prone to contamination, and relocation and registration accuracy is often insufficient for 3D targeting. Here, we present in situ fluorescence microscopy-guided FIB fabrication of a frozen-hydrated lamella to address this problem: we built a coincident three-beam cryogenic correlative microscope by retrofitting a compact cryogenic microcooler, custom positioning stage, and an inverted widefield fluorescence microscope (FM) on an existing FIB scanning electron microscope. We show FM controlled targeting at every milling step in the lamella fabrication process, validated with transmission electron microscope tomogram reconstructions of the target regions. The ability to check the lamella during and after the milling process results in a higher success rate in the fabrication process and will increase the throughput of fabrication for lamellae suitable for high-resolution imaging.

Direct laser cooling of calcium monohydride molecules

We demonstrate optical cycling and laser cooling of a cryogenic buffer-gas beam of calcium monohydride (CaH) molecules. We measure vibrational branching ratios for laser cooling transitions for both excited electronic states A and B. Furthermore, we measure that repeated photon scattering via the A ← X transition is achievable at a rate of photons s−1 and demonstrate interaction-time limited scattering of photons by repumping the largest vibrational decay channel. We also demonstrate a sub-Doppler cooling technique, namely the magnetically assisted Sisyphus effect, and use it to cool the transverse temperature of a molecular beam of CaH. Using a standing wave of light, we lower the transverse temperature from 12.2(1.2) mK to 5.7(1.1) mK. We compare these results to a model that uses optical Bloch equations and Monte Carlo simulations of the molecular beam trajectories. This work establishes a clear pathway for creating a magneto-optical trap (MOT) of CaH molecules. Such a MOT could serve as a starting point for production of ultracold hydrogen gas via dissociation of a trapped CaH cloud.

(Invited) Atom Probe Tomography: A New Tool For the Analysis of Solid Liquid Interfaces?

Atom probe tomography is an established method for the microsocopic analysis of hard materials, which stands out by combining single-atom sensitivity with a 3D volume reconstruction. The method is based on laser-assisted field evaporation from nanometric emitter tips. In solid state reactions it delivered decisive information to understand the detailed conditions of nucleation and growth of product phases. In recent efforts, we desire to break the materials limitations aiming for application to liquids, softmatter and polymeric materials. To this end, a new instrument has been constructed that joins cryogenic ion beam preparation with a flexible transfer into an atom probe chamber. Meanwhile, we are able to produce nanometric needles from frozen liquids, even from pure water [1]. Studies are performed with aqueous solutions [2], liquids of short alkanes [3], self-assembling monolayers [4]. The talk discusses the field desorption of complex materials and presents time of flight mass spectra and their dependence on field or laser intensity. The complex mechanisms of field desorption from frozen water surfaces are further elucidated by DFT and Monte-Carlo simulation. Finally, by evaluating evaporation probabilities and event correlations, even insight in bonding strength and the stability of molecules in strong electrical fields may be provided.[1] T. M. Schwarz, E. M. Weikum, K. Meng, E. Hadjixenophontos, C. A. Dietrich, J. Kästner, P. Stender, G. Schmitz, Field evaporation and atom probe tomography of pure water tips, Nature Scientific Reports (2020) 10:20271 | (DOI: 10.1038/s41598-020-77130-x[2] T. M. Schwarz, C. A. Dietrich, J. Ott, E. M. Weikum, R. Lawitzki, H. Solodenko, E. Hadjixenophontos, B. Gault, J. Kästner, G. Schmitz, P. Stender, 3D Sub-Nanometer Analysis of Glucose in an Aqueous Solution by Cryo-Atom Probe Tomography, Scientific reports 11 (2021) 11607 (DOI: 10.1038/s41598-021-90862-8)[3] Kuan Meng, Tim Schwarz, Eric Weikum, Patrick Stender, Guido Schmitz, Frozen n-Tetradecane investigated by cryo-Atom Probe Tomography, J. Microsc. Microanal. (2021), 1-11; (DOI:10.1017/S14319276210125)[4] Helena Solodenko, Patrick Stender, Guido Schmitz, “Atom Probe Study of 1-octadecanethiol self-assembled Monolayers on Platinum (111) and (200) surfaces”, J. Microsc. Microanal. (2021), 1–10. (DOI: 10.1017/S1431927621012654)

Measurement of the 2S_{1/2}-8D_{5/2} Transition in Hydrogen.

We present a measurement of the hydrogen 2S_{1/2}-8D_{5/2} transition performed with a cryogenic atomic beam. The measured resonance frequency is ν=770649561570.9(2.0) kHz, which corresponds to a relative uncertainty of 2.6×10^{-12}. Combining our result with the most recent measurement of the 1S-2S transition, we find a proton radius of r_{p}=0.8584(51) fm and a Rydberg constant of R_{∞}=10973731.568332(52) m^{-1}. This result has a combined 3.1σ disagreement with the Committee on Data for Science and Technology (CODATA) 2018 recommended value.

7 T Niobium-Titanium-Based Persistent-Mode Superconducting Magnet for an Electron Beam Ion Source

A high field magnet is a key element of cryogenic electron beam ion sources (EBISs), which are known for generating highly charged ions through the magnetic compression of an electron beam. Herein, we report the design, fabrication, and evaluation of a 7 T niobium-titanium superconducting magnet capable of persistent-mode operation. The magnet was designed using finite element analysis by considering its magnetic, thermal, and mechanical properties. The designed magnet was then fabricated, assembled, and evaluated for various design parameters in a recondensing-type liquid helium cryostat. After several quench trainings, the magnet reached a target magnetic field of 7 T with an operating current of 200 A, a magnetic field uniformity of 0.24%, and an electron beam focusing length of 1.3 m inside the bore. The magnet was successfully operated in the persistent-mode for 9.5 days (228 hours) and achieved a field-decay rate of 0.42 ppm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{h}^{-1}$ </tex-math></inline-formula> . The magnet evaluation results confirm that our superconducting magnet system can be applied to an EBIS to carry out stable and effective electron beam compression.

Deceleration and Trapping of SrF Molecules.

We report on the electrostatic trapping of neutral SrF molecules. The molecules are captured from a cryogenic buffer-gas beam source into the moving traps of a 4.5-m-long traveling-wave Stark decelerator. The SrF molecules in X^{2}Σ^{+}(v=0,N=1) state are brought to rest as the velocity of the moving traps is gradually reduced from 190 m/s to zero. The molecules are held for up to 50ms in multiple electric traps of the decelerator. The trapped packets have a volume (FWHM) of 1 mm^{3} and a velocity spread of 5(1) m/s, which corresponds to a temperature of 60(20)mK. Our result demonstrates a factor 3 increase in the molecular mass that has been Stark decelerated and trapped. Heavy molecules (mass>100 amu) offer a highly increased sensitivity to probe physics beyond the standard model. This work significantly extends the species of neutral molecules of which slow beams can be created for collision studies, precision measurement, and trapping experiments.

CeNTREX: a new search for time-reversal symmetry violation in the 205Tl nucleus

The Cold molecule Nuclear Time-Reversal EXperiment (CeNTREX) is a new effort aiming for a significant increase in sensitivity over the best present upper bounds on the strength of hadronic time reversal (T) violating fundamental interactions. The experimental signature will be shifts in nuclear magnetic resonance frequencies of 205Tl in electrically-polarized thallium fluoride (TlF) molecules. Here we describe the motivation for studying these T-violating interactions and for using TlF to do so. To achieve higher sensitivity than earlier searches for T-violation in TlF, CeNTREX uses a cryogenic molecular beam source, optical state preparation and detection, and modern methods of coherent quantum state manipulation. Details of the measurement scheme and the current state of the apparatus are presented, with quantitative measurements of the TlF beam. Finally, the estimated sensitivity and methods to control systematic errors are discussed.

ENZEL - A cryogenic, retrofittable, coincident fluorescence, electron, and ion beam solution for the cryo-electron tomography workflow.

ENZEL - A cryogenic, retrofittable, coincident fluorescence, electron, and ion beam solution for the cryo-electron tomography workflow.

Spectroscopy on the AΠ1←XΣ+1 transition of buffer-gas-cooled AlCl

Aluminum monochloride (AlCl) has been proposed as an excellent candidate for laser cooling. Here we present absorption spectroscopy measurements on the $A^1\Pi \leftarrow X^1\Sigma^+$ transition in AlCl inside a cryogenic helium buffer-gas beam cell. The high resolution absorption data enables a rigorous, quantitative comparison with our high-level ab initio calculations of the electronic and rovibronic energies, providing a comprehensive picture of the AlCl quantum structure. The combination of high resolution spectral data and theory permits the evaluation of spectroscopic constants and associated properties, like equilibrium bond length, with an order of magnitude higher precision. Based on the measured molecular equilibrium constants of the $A^1\Pi$ state, we estimate a Franck-Condon factor of the $A^1\Pi \leftarrow X^1\Sigma^+$ of 99.88%, which confirms that AlCl is amenable to laser cooling.

Observation of monochromatic and coherent luminescence from nanocavities of GaN nanowall network

Scaling-down the size of semiconductor cavity lasers and engineering their electromagnetic environment in the Purcell regime can bring about spectacular advance in nanodevices fabrication. We report here an unprecedented observation of a coherent Cathodoluminescence from GaN nanocavities (20–100 nm). Incident lower energy (< 15 kV) electron beams excite the band edge UV emission from the walls of the network whereas for higher energies, the emitted photons are spontaneously down converted into NIR and preferentially emerge from the nanocavities. Non-centrosymmetric structure of GaN and its nanowall geometry together facilitate this unique observation which is substantiated by our numerical results. At cryogenic temperatures, an intense and narrow laser-like NIR beam emanates out of the nanocavities. The work promises the possibility of fabrication of very high density (over 108/cm2) cavity lasers that are addressable by simple deflection and tuning of incident electron beams.

Theoretical investigation of laser cooling for [formula omitted] anion by ab inito calculation

A theoretical investigation for the feasibility of laser cooling BN-anion is presented. An ab initio calculation on the three low-lying states Χ2Σ+, Α2Π and Β2Σ+ are performed at the CASSCF/MRCI + Q level. The calculated spectroscopic constants are in good agreement with the available theoretical and experimental data. Radiative properties including Franck-Condon factor, Einstein coefficients and radiative lifetimes are determined. The calculation shows that the transition B2Σ+(v')↔X2Σ+(v'') has highly diagonal FCFs, especially f00 = 0.9898, and enough short radiative lifetimes. A cooling scheme by three laser beams is proposed, which requires one main pumping laser(λ00 = 474.67 nm) and two repumping lasers (λ01 = 514.64 nm, λ12= 514.90 nm). The population dynamics of cooling is investigated with the rate equation approach. The simulation demonstrates that the population does not remain trapped within the intermediate Α2Π state. The resultant scattered photons are about2.5×104, which is expected to stop BN-anion molecule in a cryogenic beam theoretically.

Measurement of the molecular dipole moment and the hyperfine and Λ -doublet splittings of the BΠ13 state of thallium fluoride

We report high-precision measurements on the thallium fluoride $\tilde{J} = 1$ hyperfine manifold of the $B^3\Pi_1$ ($\nu = 0$) state. This state is of special interest because it is central to an optical cycling scheme that is envisioned to play an important role in enhancing the sensitivity of the CeNTREX nuclear Schiff-moment experiment presently under construction. The measurements are made by monitoring the fluorescence induced by narrow-band laser excitation of a cryogenic molecular beam. We use a multipass arrangement of the laser beam to enhance fluorescence. When viewed with a camera, we can spatially resolve images from adjacent passes that approach the molecules from opposing directions. These images yield a sensitive visual method to identify the central frequency of a transition. Coupling these line-center determinations with frequency calibration from an acousto-optic modulator has allowed a more precise determination of the $\tilde{J} = 1$ manifold of hyperfine level splittings. We observe Stark shifts of the $\tilde{J} = 1$ levels and infer a permanent electric dipole moment of 2.28(7) D and $\Lambda$-doublet splittings for the $F_1' = 1/2$ and $F_1' = 3/2$ manifolds of 14.4(9) MHz and 17.4(11) MHz, respectively.