Angstrom symbol shows as a box using default font

Welcome to the forum. You did not write your environment and Igor version etc., so I'll assume Igor 9 on Windows for now. What you observe seems about right. The standard font 'Arial' used for EPS does not have the Angstrom symbol as far as I know, so a placeholder is displayed instead. It seems you have already found the solution to this issue. You might also choose more sensible formats such as pdf and svg.

Thank you. Sorry for not saying clearly, my environment is exactly what you said. I have Igor 9 in Macintosh as well. So does it mean now there is no way to use Arial for Angstrom in the eps format? Because I would like to edit those plots in Adobe Illustrator. Thanks!

If you go for Illustrator then you should definitely export to pdf and not eps (svg might also work). There it should work just fine. Also note that you can also make plots pretty nice in Igor itself (I abandoned using Illustrator, Inkscape etc. for 'post-processing' plots a long time ago). :)

I recommend that you execute these commands on Igor's command line to bring up relevant documentation:

tl;dr: Embedding non-ASCII characters in EPS on Windows is one of the most difficult things to do in Igor.

If you provide an example experiment and the command you are using to generate the EPS file we might be able to make suggestions.

Thanks for the advice. I am writing my first paper, so I just start to find a good software that can arrange multiple plots. My data and plots are scattered in different pxp files so I also need to put some efforts on putting plots together :(

The command I used is 

I attach pxp file which contains a plot I made. Thanks for providing help! 

In case you want to prepare the graphs completely within Igor...

1) You can accumulate plots in a single pxp file by exporting the graphs (File -> Save Graph Copy) and merging them into a single experiment file (Hold 'alt' / 'option' while selecting the File menu and choose Merge Experiment). Or you can use one of the scripts here on the website to transfer graphs between experiment files. Here is my implementation:

https://www.wavemetrics.com/code-snippet/quick-graph-transfer-between-e…

2) You can arrange multiple plots by using layouts within Igor itself. Just create a layout in the size of the final combined graph and add the individual graphs into the layout, then arrange them as needed. You can also add text and drawings to the layout if necessary. See here:

3) For individual plots, you should make sure that they have the correct target size (for the journal etc.). I have written a package to help with that:

https://www.wavemetrics.com/node/21562

One general note ... My understanding is that the Angstrom unit should be depreciated in favor of the SI unit scale with nm or pm ... https://www.sizes.com/units/angstrom.htm. Perhaps SAXS still takes exception to this recent guideline.

In additional to the recommendations from @chozo for capturing graphs from multiple experiments, the Igor Pro package SnapIt! is designed to capture a graph from a pxp into its own pxp. https://www.wavemetrics.com/project/SnapIt. Explore also the help in Igor Pro using DisplayHelpTopic "The Browse Expt Button".

Finally, since you are on macOS, I can suggest the two options below as essential tools in my toolbox to create publication-ready, science and engineering graphic layouts ...

* LaTeXiT is a utility designed to typeset LaTeX into PDF/PNG graphics that can be pasted as PICTs onto graphs in Igor Pro. The presumption is that you have LaTeX installed. https://www.chachatelier.fr/latexit/. An equivalent option is to use one or the other of the Igor Pro packages for LaTeX ... LaTex Pictures https://www.wavemetrics.com/project/LaTeXPictures or LaTex to Picture https://www.wavemetrics.com/node/22092.

* Curio is an app designed to layout multiple types of content (e.g. to do story-boarding) as well as much more. https://www.Zengobi.com/.

Using Igor Pro 9.05 on Windows, I first changed your axis text using this command:

I then saved as EPS adding the /EF flag to embed necessary fonts:

This gave me a .eps file that, when opened in Affinity Designer, had the correct Angstrom symbol.

As others have said, learning how to create the entire figure in Igor instead of exporting to Illustrator is likely a wise decision and will save you time in the long run.