1 REFERENCE LEAKS D. Mari, M. Bergoglio INRIM: Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, Torino, Italy

2 Crimped capillaries Permeation leaks Secondary gas flow standards... need calibration by means of Primary standard systems Currently, two types of secondary gas flow standards are primarily available: Geometrical leaks (crimped capillaries...) Permeation leaks - gas flow rates down to mbar L/s - only one value of gas flow is generated - strong temperature dependence - fragility of the leak element - only gases for which permeating materials are available - wide range of gas flow rate is provided, depending on the gas pressure inlet - temperature is not a critical factor; temperature coefficient is lower than 5·10 -3 C -1 - solidity of leak element

3 1. Glass capillaries Five glass capillaries were supplied by Danfoss: nominal gas flow rate values in the range 1x10 -6 mbar L/s - 1x10 -5 mbar L/s at 1 bar referred to vacuum. narrower part of glass capillary Section of narrower part of glass capillary - The glass capillary is connected to a leak detector unit and used, in principle, as a "sniffer" leak detecting device. - The glass is then heated up uniformly using a special burner device. As the glass is heated at a specific point (on and off to prevent closure of the element), the capillary slowly contracts forming the restriction (leak element). - During this procedure helium is blown on top of the glass leak element and nominal leak rate is measured in the leak detector Realization of leak elements

4 2.2 Micro-hole in cupper disk having the same dimension of a CF16 gasket 2.Metal leaks 2.1 Micro-hole in Stainless steel double knife 16 CF flange 2.3 Micro-hole in aluminium disk - Six double CF 16 flanges lowered to 0.8 mm by electro-erosion - Three cupper disks having the same dimension of the CF 16 gasket lowered to 0.4 mm by mechanical process - five aluminium disks lowered to 0.4 mm by mechanical process

5 - RTM SpA, an Italian company leader in the laser technology, realized the micro holes by a Diode-Pumped Solid State laser: short wavelength (532 nm), focused beam diameter of 15 mm, pulse energy in the order of 1 mJ, short pulse duration (nanosecond regime), and a radiation flux density in the processing zone of about 1GW/cm 2. - In the lowered area of flanges/disks, micro-holes having diameters between 5 μm and 20 μm were drilled by laser technology, irradiating the metal surface with a laser beam focused in very small spot able to melt and vaporize the material.

6 on the side where the laser beam pierces, a deposition of material has been observed. At INRIM nanofacilities a Focused Ion Beam (FIB) instrument having micromachining capabilities at the nanometer–micrometer scale was used to remove the material around the hole 2.1 Micro-hole in Stainless steel double knife 16 CF flange Laser beam inlet Laser beam outlet Hole after FIB cleaning (inlet)

7 3. Rectangular channel (supplied by Université de Toulouse) The microsystem consists of series of parallel rectangular microchannels etched by deep reactive ion etching (DRIE) in silicon wafers, and covered with Pyrex plates by anodic bonding Micro-system characteristics : Depth, h= (0.545 ± 0.10) μm Width, W= (50.0 ± 0.3) μm Length, L= (5000 ±10) μm Number of Microchannels: 575

8 4. Nano-holes The nano-holes were supplied by NanoMed labs of Genova University They were drilled by FIB in a silicon nitrate membrane The dimensions of the membranes are: frame dimensions of 5 mm  5 mm, window size 100  m, thickness 200 nm. The membrane is able to stand up to 1 bar of differential pressure

9 5. Fibers Photonic Bandgap Fiber guide light was used as small capillary. The fiber has a hollow core, surrounded by a microstructured cladding formed by a periodic arrangement of 286 holes in silica in a coating of acrylate At INRIM a methodology to cut the fiber was developed: the acrylate coating was removed and the silica was cut by a diamond blade.

10 Geometry characterization of the leak artifacts A 2-D grating was used as reference for the diameters characterization. Grating calibration The pitch p of the grating was measured at INRIM length section (the traceability to SI was obtained through INRIM standards of angle and length) The pitch p of the grating used in our measurements is: p = nm; U(p)=0.023 nm (micro-holes and fibers) A SEM image of the grating by using a magnification x5k and having size 1280x1040 pixel was taken; starting from grating calibration one pixel was determined as equal to (26.17±0.26) nm

11 Hole diameters: A SEM image of each hole was taken, with the same magnification x5k used for SEM image of the grating The diameter of each hole (for both sides of the flange /disk) was determined, starting from 10 profiles obtained by means of an image processing software The thickness of the micro holes was measured by a 1D linear comparator (Moore M3) equipped with a laser interferometer. Measurements were carried out in eight different positions and repeated two times in the lowered area of the flanges/disks. Thickness of the leak artifacts

12 Fittings Each leak element was encased in a suitable fitting to ensure a good tightness (at least lower than mbarL/s) and to be useful for mounting on the various NMIs primary flowmeters. The glass tube 4.2 was sealed by Torr Seal resin in a copper spacer Glass capillary The indium gasket tightness in the piping was checked using a blind spacer (like 4.1) purpose- built and an helium leak detector. The helium signal from detector was lower than mbarL/s…. At the end of the holder 1 a gasket seat was realized in which the indium gasket is allocated and pressed by screw 3.

13 2. Micro-hole in Stainless steel double knife 16 CF flange The tightness of the pipe was checked by a helium leak detector. One side of the artifact was connected directly to helium detector and the other side was closed by a plug. The helium was spread around the piece and the signal from the detector lower than mbarL/s was recorded. The fitting was realized using commercial CF16 and VCR components 3. Micro-hole in cupper disk having the same dimension of a CF16 gasket The fitting was realized using commercial CF16 and VCR components. The tightness ensured a leak lower than mbarL/s.

14 4. Micro-hole in aluminum disk The fitting was realized using a custom INRIM system in conjunction with commercial CF16 and VCR components. The tightness of the pipe was checked: the signal from the helium detector was lower than mbarL/s. 5. Nano hole The membrane was mounted on a copper disk compatible with a copper gasket CF16 and sealed with Torr Seal resin. The fitting was realized using commercial CF16 and KF16 components The tightness ensured a leak lower than mbarL/s.

15 April 2012 to January 2013: The realized leak elements were measured for many gas species and pressures in several National Metrological Laboratories and Universities in a large measurement campaign, both against vacuum and atmosphere. measurements referred to vacuum - inlet pressure: 50, 100, 300, 500, 700, 1000 Pa, 3, 5, 7, 10, 30, 50, 70, 100 kPa (or maximum throughput measurable). -gases: He, N2, Ar, H2 or mixture H2/N2, SF6 measurements referred to atmosphere - inlet pressure (relative) from 2, 5, 10, 50, 100, 150, 200, 250, 300, 350, 400 kPa or more when possible. - gases: He, N2, Ar, R134a, if possible CO2, 1234y, H2 or mixture H2/N2 and SF6. Participating laboratories performed two measurement cycles in the following conditions:

16 Glass capillaryG110-6 mbar 1 bar HeLNE → INRIMno sealing Glass capillaryH110-5 mbar 1 bar HeCMI Flange (stainless steel)A1 11 mmIMT B1 15 mmLNE B2 15 mmGiessen University C1 19 mmCMI A2 11 mm Giessen Universityclogged Al diskE1 8 mmPTB Al diskE2 10 mmINRIM/LNE Cu diskD1 11 mmINRIM Fiber INRIM Nanohole INRIM /Università di Genova Micro-system (rectangular channels) INRIM/ Université de Toulouse RILSAN PA12 INRIM Polycarbonate foils IMT

17 Glass capillary H1- CMI Cupper leak D1- INRIM

18 Aluminium leak E1- PTB Aluminium leak E2- INRIM-LNE

19 Stainless steel leak B1- LNE Stainless steel leak C1- CMI

20 Micro-system (rectangular channels)

21 Thank you for your attention