This month's cover image is from the featured paper, A homemade atomic force microscope based on a quartz tuning fork for undergraduate instruction by Yingzi Li, Liwen Zhang, Guanqiao Shan, Zihang Song, Rui Yang, Hua Li, and Jianqiang Qian.  DOI: 10.1119/10.1119/1.4941929

Atomic force microscopes are a key tool in nanotechnology that overcome the limitations of optical microscopes and provide imaging capabilities with nanoscale resolution. We have developed an atomic force microscope that uses an inexpensive quartz tuning fork as a micro cantilever. Because of its ease of operation and its open structure, it can be easily customized by students. Due to its low costs, it is possible that every student in the course has access to one setup, allowing all students to obtain deep insights into nanotechnology and to understand the principles of atomic force microscopy.

Papers

Not all counterclockwise thermodynamic cycles are refrigerators by R. H. Dickerson and J. Mottmann.   DOI: 10.1119/1.4945266

A relativistic trolley paradox by Vadim N. Matvejev, Oleg V. Matvejev and Ø. Grøn   DOI: /10.1119/1.4942168

Numerical matrix method for quantum periodic potentials by Felipe Le Vot, Juan J. Meléndez and Santos B. Yuste.   DOI: 10.1119/1.4944706

Time-dependent perturbation theory in quantum mechanics and the renormalization group by J. K. Bhattacharjee and D. S. Ray.   DOI: /10.1119/1.4944701

The principle of relativity and the de Broglie relation byJulio Güémez, Manuel Fiolhais and Luis A. Fernández.   DOI: 10.1119/1.4941569

Ghostly action at a distance: A non-technical explanation of the Bell inequality by Mark G. Alford.    DOI:10.1119/1.4945408

PHYSICS EDUCATION RESEARCH