Lab rtatin n vacuum techniques and thermal imaging Objectives Manually perate a high vacuum system thrugh pump dwn and vent rutines. Learn apprpriate vacuum system terminlgy rughing, backing, freline, gate valve etc. by fllwing instructins during the peratins. Measure residual gas cmpsitin at different pressures during pump dwn. Measure the difference in pump rate f a chamber vented with air versus a chamber vented with N 2. Measure the effect n the cmpsitin f residual gases in a vacuum chamber by heating a tungsten filament until is glws red-ht. Use a thermal camera t image a heated crucible and measure its temperature. Suggested Experiments Recrd the partial pressure f H 2 O, H 2, N 2 and O 2 during the vacuum cnditins at the start f the sessin. Recrding 5 minutes f data shuld be enugh t give yu a high vacuum baseline f the residual gases in the chamber. Start with bth the pumping and prcess chambers under vacuum and the RGA and in gauges switched ff. Yu shuld leave the system in this cnditin at the end f the sessin. Vent the chamber using liquid nitrgen and then pump it t vacuum again. Once yu enter the high vacuum regime yu shuld recrd the pump rates f the different gases in the chamber using the RGA (yu shuld recrd n P A e t n n data fr abut 20-30 minutes). Fit expnential functins f the frm t the partial pressure (P) f each gas (n) as a functin f time (t). Determine A (relative initial partial pressure) and (rate cnstant) and cmpsitin f each f the different gasses in the chamber. Vent the system using air instead f liquid nitrgen. Repeat the pumpdwn experiment again. Cmpare A and fr each f the different gasses n this secnd pump dwn cycle. Are the parameters yu recrd the same r different? Heating the furnace With the Prcess Chamber a lw pressure (~ 10-4 mbar) turn n the pwer surce fr the furnace system. Start at a lw vltage (e.g. < 1 V), and bserve (recrd) what happens t the gas levels within the chamber. Gradually increase the pwer by cntrlling the vltage. Yu will ntice that as the filament gets htter its resistance increases and pwer utput drps. Yu shuld cntinue t gradually (ver a minute) increase the vltage acrss the filament until it glws red-ht. Recrd the current as a functin f vltage. Plt a graph. Dn t g abve 35 A.
Finally, after recrding a few minutes f data at different vltages select a fixed vltage and measure hw lng it takes fr the current t stabilize. Cntinue t check the residual gases in the chamber and the ttal pressure in the chamber. Which gasses are released during the heating prcess? Fllwing heating, ensure cl-dwn time befre venting the chamber and expsing ht surfaces. Cl dwn depends n final temperature reached. Typically 10-20 minutes will suffice but at very high temperatures 30 minutes might be required. Characterizing cil heating Yu shuld characterize the heating f the cil during current flw using a thermal camera Use the camera t measure the temperature f the cil as a functin f current flw, and explre temperature unifrmity acrss the cil. Explain yur findings.
Vacuum system: hints and tips. Study the drawing abve and make sure yu can crrectly identify the different system cmpnents. Yu will need t discuss and cnfirm the cmpnents with yur supervisr and yu will be tested befre yu can cntinue. The vacuum system is shwn schematically in the accmpanying figure. The system is cmpsed f tw chambers; a pump-chamber cnnected t a turb pump, and a prcess chamber cnnected t the pump chamber via a gate valve. The prcess chamber is als pumped t carse vacuum using a rughing pump. Within the prcess chamber, there is a heated filament that can be used t depsit thin films via thermal evapratin. Optical access t the prcess is available via a dr with a glass windw. A residual gas analyzer (RGA) is als cnnected t the pump-chamber. This is used t sample the different gasses in the chamber thrugh measuring their atmic weights and determine their relative partial pressures. There are als tw in gauges, a Pirani-gauge and a backing gauge that are used t recrd the vacuum pressure in different parts f the system. Cautin imprtant infrmatin: At n pint shuld yu ever pen the crystat valve Yu shuld ensure the vent t utside line is intact and functining! Yu shuld nt perate the RGA r in gauge unless the chamber pressure is < 10-4 trr (10-4 mbar) The backing valve shuld nt be clsed fr mre than a few minutes therwise the turb pump will stall The rtary pump shuld always prvide a lw backing pressure fr the turb unless it is being used t rugh (reduce pressure frm atmsphere) the prcess chamber
RGA SOFTWARE Start the RGA sftware by searching n cmputer fr Easy View sftware. Then run graph (trend t fllw pressure). Make sure yu switch the filament n by clicking n the ^^^^ symbl. Select masses: 2 (H 2 ), 18 (water), 28 (CO and N 2 ), 32 (O 2 ) Save data using the Disc icn yu shuld check that yu can save and read the data and plt it in excel befre cntinuing. Nte that when the in gauge is n, H 2 levels will rise in the chamber as the filaments utgas. PUMP-DOWN PROCESS IF ENTIRE SYSTEM IS AT ATMOSPHERIC PRESSURE (Yu shuldn t need t d this) 1 Make sure dr is clsed. 2 Clse red and green valves. 3 Open Gate valve. 4 Clse Rughing valve. 5 Open backing valve. 6 Switch n rughing pump (rtary pump). 7 Switch n turb pump. 8 Wait until Edwards ADD unit (backing gauge) starts t recrd a pressure (abut ne minute). This measures the backing pressure in mtrr. 9 When Pirani gauge pressure is belw 1 mtrr (~10-3 mbar), switch n the in gauge. 10 System is nw under vacuum and ready. VENT PROCESS CHAMBER TO ATMOSPHERIC PRESSURE 1 Clse Gate valve and Rughing valve. 2 Put hse leading frm Red / Green valves int a bucket f liquid nitrgen (r leave in air if vacuum base pressure nt critical). 3 Open Green Valve. 4 Open Red Valve. 5 N 2 (r air) will be sucked int the chamber. 6 Dr can be pened when chamber is at atmsphere. 7 Clse red valve. PUMP-DOWN PROCESS IF PUMP CHAMBER IS UNDER VACUUM AND PROCESS CHAMBER IS AT ATMOSPHERIC PRESSURE 1 Make sure dr is clsed (but nt t tightly).
2 Ensure red valve is clsed. 3 Clse Backing valve. 4 Open Rughing valve. 5 Watch Backing gauge pressure drp (takes abut 1 minute t get a reading). Als watch the Pirani gauge drp t. 6 When pressure f Pirani and backing reaches <100 mtrr (this is the same as ~ 10-1 mbar), clse the Green valve, then clse the rughing valve, then pen the Backing valve. This shuld be dne relatively rapidly. 7 Slwly (ver 20 secnds r s) pen the Gate valve. Start slwly and get faster. 8 Switch n the RGA and in gauges (if needed) and recrd the pressure f the different gasses is the chamber. FLIR A6750sc Thermal Imaging Camera: Hints and tips Check that the camera is cnnected t the PC via the GigE cable. Cnnect the FLIR pwer supply. Switch camera n and wait fr the cld light t cme n (~ 5-6 mins). Open the ResearchIR sftware. G t camera/select t cnnect t the camera (sftware may take a cuple f minutes t find the camera). Chse the apprpriate temperature range: NB: empty means n filter - fr temperatures lwer than 350 C. Fr higher temperatures the ND2 filter must be added t the lens. Select the apprpriate acquisitin frame rate. Set the parameters (NB: can als be dne after recrdings are taken): Emissivity, Distance, Ambient temperature, Fcus the camera using the manual fcus. Set the recrding settings using the tl bx in the ptins alng the tp f the displayed image. Recrd vide r snapshts. Open saved file.
G t tls/ make self viewing file t save the file fr further analysis n any PC. Use the analysis tls alng the left/tp f the displayed image t extract temperature data fr spts, lines r areas f the images. Switch camera ff after use.