Non Member State Summer Student Program at ISOLDE

Program at ISOLDE LabVIEW readout of a gauge pressure meter for the VITO beam line. Atomic local studies in Graphene. Diana Sofía Valverde Mendez<dsmendez@princeton.edu> Supervisors: Torben Esmann Mølholt Abel Eduardo Da Silva Fenta August 2016

Program at ISOLDE 1 INTRODUCTION 1 Introduction This document is a brief summary of my contributions to CERN during the NMS summer student program. My stay at CERN took place from the 27 th of June until the 19 th of August. During this time I collaborated in the Solid State Physics section of the nuclear research center ISOLDE. I worked under the primary supervision of Dr. Torben Esmann Mølholt and with Mr. Abel Eduardo Da Silva Fenta as a second supervisor. Because of this I had two independent sets of tasks, so I will divide this report in two sections to address both collaborations individually. 1.1 Pressure Gauge Meter readout for VITO beam line using LabVIEW. The VITO beam line is going to be a low energy isotope implantation system for conducting PAC spectroscopy and other characterization and material deposition techniques at ISOLDE. For this purpose a high vacuum is necessary. In order to measure such vacuum different systems are used to obtain an analogue signal proportional to the pressure in the chamber. Such signal is read by a controlling device and it s then transformed to a pressure value. This type of controlling device is called a gauge meter. Usually in the display of such devices the current pressure is displayed. My project was to program a LabVIEW application to read out such a vacuum gauge meter, live plot the pressure as a function of time and create a log with the measured data for future analysis. Although, I had programming experience in other languages, I had no knowledge of LabVIEW before starting, so this was the first challenge to overcome. I followed the LabVIEW Core 1 Participant Guide to get familiarized with the language, and once I felt confident with the basics I proceeded to understand how the gauge meter s drivers worked and to delve deeper into the language using internet forums and tutorials. This ramping up took close to 2 weeks. Afterwards I proceeded to build a basic prototype of the application. The instrument to read out is a Pfeiffer Vacuum Dual Gauge (model TPG 262). This device has two logging channels which can be read out individually. The first LabVIEW prototype did not take advantage of this feature by measuring both channels with the same control circuit. Therefore after receiving feedback from my supervisor I proceeded to separate both channels and create individual controls for both. This presented a challenge since I had to learn how to keep local state variables in LabVIEW and how to control loops running in parallel. Once this was ready, the following step was to create a log file in Excel that would keep a safe record of the measurements. One of the fundamental steps on building a software application is to guarantee that it is stable and that it will not breakdown during operation, this is of particular interest in scientific instrumentation because the experiments are highly sensitive to correct data storage and manipulation. Regarding this aspect, extensive testing was done to guarantee the applications stability and that warning mechanisms were implemented. As a side project we wished to read a second gauge meter (model TPG 362) also from Pfeiffer Vacuum, the main difference between both devices is that the second one is newer and therefore communicates with the computer through a USB protocol, whereas the TPG 262 communicates with the computer through a serial port. I devoted some time in this task, however I was not able to communicate with the TPG 362 device accordingly. In figure 1 the final version of the application is showed. On the left of the screen the plots presented show how the speed of each channel is modified separately and also the pausing mechanism for both channels. On the right side of the screen the Excel log file generated from the program is shown. Notice that both columns are not the same size because of the different sampling rates and pausing functionality. In figures 2 and 3 the front panel of the application is shown, this consists of 2 tabs, one for setting up the connection with the pressure gauge and the other for live pressure monitoring. The connection setup tab consists of a list with all of the available serial ports and error in and out for both channels. Also it has a reset connection button to change the serial port in use. At the beginning of the 2

Non Member State Summer Student Program at ISOLDE 2 ATOMIC LOCAL STUDIES ON GRAPHENE Figure 1: LabVIEW application and Excel log for reading out a vacuum pressure gauge meter measurement, the user selects the correct serial port in this tab and then starts the application. The pressure monitor tab holds the controls and plots. Each channel is controlled independently through the control panel on the right, the pause button for stopping temporarily the measurements, a clear graph for resetting the channel to zero and a samples per minute knob for regulating the amount of data recorded. Each channel shows a time stamp with the last reset. At the top of the front panel the log controls are found, a log file path is selected here and the log button resets both channels updating the time stamp. Once the measuring has been completed the user presses the log button once again to save the data (The message in the log button changes to save when pressed). There are two warning LEDs in the bottom to let the user know that the connection with the device failed and when the Reset connection is pressed in the Connection setup tab. 2 Atomic local studies on graphene With my second supervisor, my tasks were related to the experiment he is conducting for his PhD thesis. The objective of the project is to understand the interaction between two dimensional materials and adatoms using Perturbed Angular Correlation (PAC). This interaction refers to how the dopant binds to the sample, its spatial configuration and how it alters the electronic structure and properties of graphene. To this effect, graphene samples on different substrates are implanted with radioactive isotopes and are characterized through PAC measurements at ISOLDE. In this facility beam time is shared between many experiments, not only from people working at CERN but from visiting scientists from all around the world. Therefore beam time is scarce and is often limited to a few days. I was lucky to be at CERN during the beam time assigned for one of this project s round of experiments. For this particular beam time, we worked with graphene on 3 different types of substrate: Quartz, SiO and Cu. First the implantation was done with mercury isotopes 197 and 199 into ice in order to collect the isotopes. The ice with the isotopes was melted and then pipette to the surface of the samples. For me to be able to participate actively during the experimental beam time, first I needed to ramp up my knowledge both on the material and on the characterization technique. To do so I was assigned to do bibliographical research on graphene, PAC, nuclear condensed matter physics, hyperfine interactions, and ISOLDE in general. Regarding graphene, I first had to understand its main characteristics and properties. Then I learned about how to modify and tune these characteristics. Because the main concern of this project is to understand how adatoms modify graphene s electronic structure and how they bind to the lattice, I also learned about the state of the art in this particular field. Afterwards I entered a second stage of research in which the information I was gathering was useful for the analysis of results that would result from the beam time. I learned about how working under ambient conditions affect graphene s properties, this was of 3

Program at ISOLDE 2 ATOMIC LOCAL STUDIES ON GRAPHENE Figure 2: Layout and front panel of the application for the TPG 262 connection setup. Figure 3: Layout and front panel for the live pressure monitoring of the gauge meter. 4

Non Member State Summer Student Program at ISOLDE 3 SAFETY AND OTHER CONTRIBUTIONS. Figure 4: Poster on Atomic Local Studies on Graphene presented at summer student session. particular importance because during characterization time, the samples are not in vacuum and it was required to understand whether or not the results of the experiment would be sensible to this. Also I researched about how water interacts with graphene, as will be discussed later in this report the way that the mercury isotopes are implanted in the graphene is through radioactive water placed on top of the surface, therefore when analyzing the results of the experiment, it is important to understand how the water modifies the electronic structure and properties of the sample itself. Before beam time, a lot of preparation has to happen. I got to help in this setup by checking that all of the electrical connections and detectors were working properly for the experiment. Also I helped filling up the recipients with the LN2 necessary for the experiment. During beam time I was only allowed to participate shortly in small tasks because of safety regulations. But by being present during the experimental procedures, such as the implantation and sample manipulation in the glove box, and through my supervisor s explanations I learned a lot. Also I got to observe the manipulation of the beam from the ISOLDE control room and the measurement of PAC spectra. All of the results of my bibliographical research as well as the detailed observations of the experiment gathered during beam time have been recorded in a report which I presented to Mr Fenta. From my involvement in this project I presented a poster in the Summer Student Poster session. See figure 4. 3 Safety and other contributions. Although in this report I only detailed on my contributions to each project, working in a large scientific facility like ISOLDE also involves several hazards that require safety training. For this purpose I attended a radioactive safety training, an electrical safety training and attended two sessions of cryogenic safety training, these enabled me to work in a safe way in the lab and to understand the risks surrounding me. Additionally to my main two projects I also got involved in other tasks inherent to a lab environment. I learned about the other experiments at ISOLDE, got a thorough explanation on how Mössbauer spectroscopy works by overseeing the setup of an offline experiment (We were meant to also participate on beam time for this type of spectroscopy, but it got canceled due to personal circumstances). In addition, I also helped during beam time with a magnetic nanoparticles experiment and learned a lot about experimental work in general. 5

Program at ISOLDE 5 ACKNOWLEDGMENTS 4 Conclusions A LabVIEW application for reading out the Pfeiffer Vacuum TPG 262 Dual Gauge meter was developed and tested for its future implementation in the VITO beam line at ISOLDE. The pressure is plotted as a function of time and the data is logged in an Excel file. Both channels are sampled independently guaranteeing flexibility in their use. A bibliographical study on graphene, and nuclear condensed matter physics was conducted to obtain the necessary background to fully appreciate the experimental time in ISOLDE hall. Further research on how graphene interacts with water and how it is affected by ambient conditions was done. This will help with the analysis of the results obtained during ISOLDE beam time. I participated actively during the beam time, this was a great opportunity to work as a real scientist and learn more about the PAC technique and to also help in the development of the experiment. Some of the tasks included being present during ice implantation/isotope collection, handling the vacuum valves, liquid nitrogen manipulation and aiding with the sample manipulation once taken to the glove box. From this experience a poster was presented in the summer student poster session, this helped divulge the work being done in ISOLDE regarding Solid State Physics. After the poster session I was approached by two people working at CERN with graphene. I got their email and put them in contact with Mr. Fenta. While presenting several other people told me that they had no idea that solid state physics experiments were being performed at CERN. Thus this type of poster sessions help to inform people about what is being done at CERN and expand my professional network for future possible collaborations. As part of the ISOLDE summer program I presented a talk during the weekly ISOLDE group meeting regarding my contributions to the group during my stay and how these experiences related to what I expected from the program. Both this presentation and the poster session were great opportunities to improve my scientific communication skills. Overall I think that my NMS student program at CERN gave me a broader picture of what it is like to be a full time physicist and helped me grow both in a professional and personal level. Particularly meeting people from all over the world and sharing with them lectures and working side by side with them was an amazing experience that can only be found in large international collaborations like CERN. 5 Acknowledgments I wish to express my gratitude to my supervisors for all the help, support and knowledge given to me during this weeks, to ISOLDE and the people working there for receiving me and for providing such interesting projects, to CERN and all the people involved in making this incredible experience happen and to my home university, Universidad de Costa Rica, for giving me the permission to attend this activity and pause momentarily my studies. 6