Micro- and Nanotechnology facilities
Altogether nine dilution refrigerators provide the backbone of the low temperature nanophysics research in the LTL. These refrigerators typically provide a 8-30 mK base temperature, which is enough for studies of phase coherent transport in nanostructures and for quantum information processing in superconducting quantum circuits. The dilution refrigerators are in frequent use within EU-funded projects (CARDEQ, IQUOEMS, INFERNOS, GEOMDISS, RODIN, SCOPE).
In the range of temperatures 4.2 – 1.2 K, LTL has a variety of cryostats with different measurement capabilities, ranging from simple DC electrical measurements to involved microwave measurements for noise, cross-correlations, and oscillation in NEMS resonators.
The facilities include a nanodevice production line using e-beam lithography down to 50 nm resolution, operated in a semi-clean environment. The facilities are sufficient for basic samples in mesoscopic physics and for nanocarbon devices. The nanofabrication facilities of LTL supplement the infrastructure at Micronova (Otaniemi, Tietotie 3) in the sense that cleanliness requirements are not as strict, and more non-standard operations are allowed. In this flaxible way, the LTL infrastructure can serve users whose needs are often different from the standard ones. The semi-clean-room equipment also serves many researchers of Aalto University in their work on nanocarbons. Moreover, the fabrication facilities include equipment for heat treatment, critical point drying, and annealing in order to guarantee the best quality of samples before cool down to mK temperatures.
Three nuclear demagnetization cryostats are the flagships of LTL in the microKelvin research. One of them is used for studies of superfluid 3He in international collaboration with researchers especially from EU countries, Japan, and Russia. The second one is employed for unique cooling experiments trying to find new superfluid systems. The third one is a novel dry nuclear demagnetization refrigerator which was constructed in R&D collaboration with BlueFors Cryogenics Ltd. (spin-off company of LTL). This machine provides temperatures down to 0.2 mK and is equipped for nanophysics experiments.
LTL offers low temperature facilities to industrial companies for testing and developing new cryogenic products. These facilities are important for small companies as well as to industry researchers working in cryogenic applications (Aivon, Nanoway, Picowatt, Elekta Neuromag, BlueFors) since the available cryostats allow these LTL infra users to quickly try their ideas in cryogenic environment. New advanced dry dilution refrigerators, CBT temperature sensors and cryogenic amplifiers have been developed within the nationally funded FinCryo-project (TEKES).
Room temperature research facilities are used to characterize samples after fabrication. The equipment include a microRaman setup for local Raman measurements and an atomic force microscope. Using the AFM, surface enhanced Raman can be investigated. In addition, there are setups to measure susceptibility of novel materials at microwave frequencies. These systems are especially for the industrial people who collaborate with the LTL infra researchers on materials issues, for example, on graphene and nanotubes.
The staff of LTL infra offers various training in the area of low temperature physics, cryogenics, micro- and nanofabrication.
The following facilities are available in the LTL semi clean room: electron beam lithography, field emission electron microscope JEOL7100F, DCA UHV e-beam evaporator system with sample stage having angle control and rotation, film deposition system, reactive ion etching, critical point dryer, etc.
Main characteristics: - Minimum temperature in 3He sample: 140 uK (combination of dilution refrigerator and nuclear cooling stage), - Rotation velocity up to 4 rad/s, - Heat leak to sample in rotation: below 25 pW, - Cooldown time to the lowest temperatures: 1-2 weeks, - He boiloff: total 30 liters/day. Instrumentation: - Low temperature NMR for 3He, - Quartz tuning forks for thermometry.
Five dry pulse-tube based dilution refrigerators: Three BlueFors BF-LD250 cryostats, one BF-SD250 and one SD-250 Prototype cryostat. Cryostats are configured for DC and RF measurements. One cryostat is equipped with 9T superconducting magnet. Specifications: - Base temperature: 8-10 mK, - Cooling power mixing chamber @ 100 mK: 250 uW, - Cool-down time to base temperature SD: 18 hrs, - Cool-down time to base temperature LD: 24 hrs, - Mixing chamber diameter: SD Series 150 mm, LD Series 290 mm.
Main characteristics: - Nuclear stage base temperature: 50 µK (Option for cascade nuclear stages with as low as 100 pK nuclear spin temperature), - Hold time below 100 uK for over 1 month, - Continuous base temperature 3 mK (dilution refrigerator), - Cooling power at 10 mK: 15 uW, - Cooldown time to base temperature: about 1 week, - He boiloff total 30 liters/day. Instrumentation: - Low temperature NMR, - Capacitance and susceptibility measurements, - SQUID measurements, - Helium cells (pure 4He, pure 3He, isotope mixtures).
The equipment for sample characterisation include a Micro-Raman spectrometer, scanning electron microscope, atomic force microscope, RF testing equipment, etc.
Based on BlueFors model BF-LD400 dilution refrigerator with 9T superconducting magnet. Characteristics of dilution unit: - Base temperature: 7 mK, - Cooling power mixing chamber @ 100 mK: 550 uW. The experimental cell for liquid 3He (0.6 mol) is embedded inside the top part of the nuclear demagnetization stage. The refrigerator cools3He in the experimental cell down to 0.16mK.
In the range of temperatures 4.2 - 1.2 K, LTL has a variety of cryostats with different measurement capabilities, ranging from simple DC electrical measurements to involved microwave measurements for noise, cross-correlations, and oscillations in NEMS resonators.
Four small 3He/4He dilution refrigerators down to 30-50 mK with approximately 4 hour cool down time. These in-house-build plastic dilution refrigerators provide fast cool down and high throughput in sample characterization.
Quantum Design MPMS XL7. The modular MPMS design integrates a SQUID detection system, a precision temperature control unit residing in the bore of a high-field superconducting magnet, and a sophisticated computer operating system. Easy-to-use software allows full automation of all system parameters. Main characteristics: - Maximum sample size: 9 mm, - Field uniformity: 0.01% over 4 cm, - Temperature range: 1.9-400 K, - Magnetic field: +- 7.0 Tesla.
Main characteristics: - Base temperature: 25 mK (9 mK without microwave cables), - Cooling power at 120 mK: 600 uW, - Cooldown time to base temperature: ~8 hours, - Fully automated gas handling system. Measurement circuitry within an electrically shielded room: 6 input microwave cables (up to 30 GHz) down to mixing chamber, 2 output lines having 2-15 GHz amplifiers at 4K.