Thanks for your comments.
First CHKDSK did not create files containing my lost excel file.
However, I retrieved my file manually from my drive F:
1) I used R-studio demo to list any .xlsx file on my drive F.
2) I have noticed that the .xlsx files that are stored on another drive contain two occurences of the ASCII string:
xl/worksheets/sheet1.xml. I used this pattern as a signature for any .xlsx file .
3) I thus scanned the drive F with the hex editor provided by R-studio demo, and looked for any occurence of this string.
4) I also scanned with the hex editor every xlsx file found in 1).
5) Comparing the adresses obtained in 3) and 4), I could determine which occurences of the string did not belong to an identified file.
6) Then looking closely at the remaining occurences, and comparing the records around them with the structure of a typical .xlsx file edited with the hex viewer, I could find the beginning and the end of each file record.
7) I finally saved these bytes in a new file which opened nicely with Excel.
All this took me 6 hrs.
I guess that all this worked fine because there were not too many xlsx files on my drive and because the file I was looking for was small (10 KB) and not fragmented.
Thanks again for your help