What is the smallest man-made object in earth?

Nanomaterials are by definition in the range of 1-100 nm (10 ^-9 m). This is the size in at least one dimension. There are a number of synthetically created nanomaterials with varied uses.

For example, Nanowires and Nanorods have interesting optical and electrical properties and can be used in optoelectronic systems.

https://en.wikipedia.org/wiki/Nanomaterials

The record for the world's smallest man made object to be photographed is a microscopic sculpture of an elephant made by Jonty Hurwitz in 2015. The amazingly detailed sculpture is a tenth of a millimeter across. Check the below url for amazing images.

https://www.slideserve.com/marcus/importance-properties-of-nanomaterials

https://jontyhurwitz.com/fragile-giant

A recently-made object that is smaller than the microscopic elephant is a snowman built in the nanofabrication facility at the University of Western Ontario (a.k.a. Western University), made of spheres less than one micron (1/1000 of a millimetre) in diameter each, totalling less than 3 microns in height, with added platinum arms and nose and laser-engraved eyes and smile. See http://www.cbc.ca/news/canada/windsor/nonfabrication-western-university-tiny-snowman-1.3911339