<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi Aimee,<div class=""><br class=""></div><div class="">I fielded a similar request some years ago from a student user who only wanted to deposit relatively thin (~ few nm) layers of Bi as a seed layer for some 2-D materials synthesis experiments.</div><div class=""><br class=""></div><div class="">During my review at the time, I reached a similar conclusion about potential cross-contamination, but I was also on the verge of a shield change in my open chamber (less restricted materials) evaporator, so I gave it some additional consideration, thinking I could swap the shields out soon after if it looked like the Bi caused a problem. </div><div class=""><br class=""></div><div class="">I also wondered about toxicity, due to some notes about the safety concerns for Bi vapors I found in old thin film deposition guides.</div><div class=""><br class=""></div><div class="">As I dug into it further, I settled on the following additional conclusions:</div><div class=""><br class=""></div><div class="">- Bi is the “heavy metal” least likely to cause heavy metal poisoning issues, and is most dangerous when dealing with its vapors. The evaporator in question is cryopumped, so I confirmed with my cryopump service provider that Bi was not a problem for them, and knew that I’d want to snorkel exhaust the cyropump during subsequent regeneration cycles.</div><div class=""><br class=""></div><div class="">- Bi alloys pretty readily with Ti (see attached phase diagram), and the melting point increases quite nicely with increasing Ti fraction, so I thought a good abatement layer of Ti (50-100 nm) deposited on the chamber immediately after (and before venting, with substrate shutter closed to protect the student samples) would help mitigate any cross-contamination issues quite a bit.</div><div class=""><br class=""></div><div class="">In the end, I let the student try it, and no related issues presented in the aftermath. For a thicker layer of Bi or maybe a different vacuum system configuration, I might have declined the request, but a few nm of Bi and a lot of Ti abatement worked out okay. We weren’t doing much compound semiconductor work on that machine at the time, so your mileage with a similar approach could vary.</div><div class=""><br class=""></div><div class="">Also: when that same student's teammate came by a few weeks later wanting to evaporate bismuth telluride on the same machine, I gave them a firm “no” because Te toxicity didn’t seem like my idea of fun.</div><div class=""><br class=""></div><div class="">Hope this helps in your decision process,</div><div class=""><br class=""><div class="">
<meta charset="UTF-8" class=""><div>-- <br class="">Tim Gilheart, Ph.D.<br class="">Research Scientist - Nanofabrication Cleanroom Manager,<br class="">Shared Equipment Authority (SEA), Rice University<br class="">Cell: 832-341-5488 | Office: 713-348-3159 | <a href="mailto:gilheart@rice.edu" class="">gilheart@rice.edu</a></div>
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<div><img apple-inline="yes" id="7E016FE9-CD3D-46FC-BA64-FAB10DE0B609" src="cid:8B427394-C1EF-448A-825A-4E2E45A26055" class=""></div><div><br class=""><blockquote type="cite" class=""><div class="">On Jun 24, 2022, at 3:43 PM, Price, Aimee <<a href="mailto:price.798@osu.edu" class="">price.798@osu.edu</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta charset="UTF-8" class=""><div class="WordSection1" style="page: WordSection1; caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;"><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Hi everyone,<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">We have had a request to ebeam evaporate Bismuth. We do not have any experience with this material but is a group V and has a relatively low melting point. We have two evaporators and one we strictly limit the materials allowed within, including sources, substrates, and adhesives (none). Our other one is a bit less restricted but we are still very careful about what we allow. An example is that we do allow SiO2 deposition in the less restrictive evaporator. If approved, Bismuth would only be allowed in the less restrictive tool. We are concerned about the low melting point and deposition on the chamber, potentially allowing for redeposition at a later date.<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Does anyone have any experience with Bismuth evaporations? Are there any considerations that you could share? Our main concerns are safety and cross contamination, specifically mobile and deep level traps in compound semiconductors. <o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">We do mostly compound semiconductor work but we do have some Si based devices/structures as well. Below is from Lesker’s website, which generally has terrific information on evaporation and sputter source materials. <o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">(<a href="https://urldefense.com/v3/__https://www.lesker.com/newweb/deposition_materials/depositionmaterials_evaporationmaterials_1.cfm?pgid=bi1__;!!BuQPrrmRaQ!mI63h_8Guu-7k8HK073CzKfATF1rHRCElzW-u0nGPJLzDjFNPtLuuib4HZCEoWp-CAT4aAWhcDBNJjnt5wtE6qPcX2AL4w$" style="color: rgb(5, 99, 193); text-decoration: underline;" class="">https://www.lesker.com/newweb/deposition_materials/depositionmaterials_evaporationmaterials_1.cfm?pgid=bi1</a><o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Melting point: 271C<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">10-8: 330C<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">10-6: 410C<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">10-4: 520C<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Thanks in advance.<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Best,<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Aimee Bross Price<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Manager, Nanofabrication<span class="Apple-converted-space"> </span><o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">The Ohio State University<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Nanotech West Lab<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Institute for Materials Research<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">1381 Kinnear Road<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Suite 100<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Columbus, OH 43212<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class="">614-292-2753<o:p class=""></o:p></div><div style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><o:p class=""> </o:p></div></div><span style="caret-color: rgb(0, 0, 0); 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