Residual Gas Analyzer (RGA) System Controls
At Pioneer Astronautics, I designed and built a control system for a used RGA purchased from eBay. This system needed some work to get back to a running condition. After the RGA was operational, I designed a control system to be able to remotely control pumps, valves, read pressure gauges, and communicate with the turbopump and the RGA remotely using a Raspberry Pi as a cheap PLC. From a power off condition, this system could be powered up, safely pumped down, and mass spectra could be collected from the experiment, all remotely.
RGA control system cabinet
RGA tool with control cabinet below
RGA control software interface developed using CoDeSys
Time-Resolved Photoluminescence (TRPL)
TRPL characterization of films used in organic light-emitting diodes (OLEDs) sheds light on the photophysical processes at work by allowing the measurement of luminescent lifetimes. As exciton (bound electron-hole pairs) densities increase in the material, bimolecular quenching processes become important and can be studied based on the shape of the TRPL curve.
I designed and built a system to measure TRPL using a pulsed nitrogen laser to excite a sample and the amplified output of a photomultiplier tube coupled to an oscilloscope to measure the time-dependent PL signal from the sample. I used an Arduino microcontroller and Python to set the PMT gain, trigger the laser pulse and synchronize it with the oscilloscope, and measure TRPL curves from the oscilloscope. I also designed and built an enclosure with door interlocks to prevent overexposure and damage to the PMT from ambient lighting.
SolidWorks assembly model of TRPL system
TRPL system in operation in the lab
Closeup of sample stage
Steady-State Photoluminescence Quenching (PLQ)
Excitonic states (bound hole-electron pairs) are quenched in organic materials by charge carriers, and the degree of quenching can be measured as a function of injected charge carrier density to learn about the dynamics of excitons and charge carriers in the film.
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I designed and built a piece of equipment to measure the current-dependent PL quenching in single-carrier organic films. A continuous-wave UV laser is used to optically excite the sample, while short current pulses introduce a charge carrier population into the sample, quenching excitons and reducing the steady-state PL. A fiber-coupled spectrometer is used to measure PL during current pulses and compare it to the zero-bias PL, which allows determination of the quenching rate. For this piece of equipment, I wrote a script in Python to automate data collection, communicating with a sourcemeter to bias the sample, collect PL spectra, and output PLQ plots to the user during measurement.
Assembled PLQ system (sample stage on left)
PC and sourcemeter to control current and measure PL
Current-Voltage-Brightness (IVB) Measurement
An IVB measurement is part of a standard LED characterization suite.
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I built this system to measure the light output of an LED during an IV sweep using a flat-plate Si photodiode coupled to the surface of the device. I used an Arduino microcontroller and Python to select one of 8 devices on a substrate, run an IV sweep through a sourcemeter, and simultaneously measure the output current of the photodiode the measure light output. Using a known emission spectrum, my script then calculates and plots a standard set of luminance/power/EQE curves which are displayed to the user.
PC, sourcemeter, current measurement for IVB
OLED is mated to a flat-plate Si photodiode in a dry nitrogen environment to measure current (inset shows the color of this Ir(ppy)3 device)
Laser-cut shadow masks were designed to define specific device areas, shown here with completed devices and a sample holder designed to make contact to individual devcies
Dimensioned drawing of laser-cut shadow mask
OLED device using the same mask
Wavelength-dependent External Quantum Efficiency (EQE)
In a photovoltaic device, EQE is the ratio of the number of charge carriers collected to the number of incident photons. In general, EQE is wavelength-dependent, and many important device properties can be studied through the wavelength dependence of EQE.
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This system uses a Xe arc lamp and a monochrometer to step through a range of wavelengths in the visible range. This light then passes through an optical chopper and is focused onto a PV device. The amplified current output is measured using a lock-in amplifier so that the EQE can be calculated.
EQE setup (look for the green spot on the sample in the lower right)
Watch the system sweep through wavelengths in the visible range for an EQE scan