Polymorph engineering involves the manipulation of material properties through controlled structural modification and is a candidate technique for creating unique two-dimensional transition metal dichalcogenide (TMDC) nanodevices. Despite its promise, polymorph engineering of magnetic TMDC monolayers has not yet been demonstrated. Here we grow FeSe₂ monolayers via molecular beam epitaxy and find that they have great promise for magnetic polymorph engineering. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we find that FeSe₂ monolayers predominantly display a 1T' structural polymorph at 5 K. Application of voltage pulses from an STM tip causes a local, reversible transition from the 1T' phase to the 1T phase. Density functional theory calculations suggest that this single-layer structural phase transition is accompanied by a magnetic transition from an antiferromagnetic to a ferromagnetic configuration. These results open new possibilities for creating functional magnetic devices with TMDC monolayers via polymorph engineering.

BACKGROUND: Cancer is the fourth leading cause of death in adolescents and young adults (AYA) worldwide. Although successful treatment of cancer in AYA has increased in recent years in most of the world, this is not true for many low- and middle-income countries (LMIC) where over 80% of all AYA live. This study investigated the needs of AYA with cancer in parts of Latin America (LATAM) through the perspectives of non-physician health care providers and partners. METHODS: Semi-structured interviews (in Spanish) were conducted with non-physician partners from Mexico, Peru, Central America, and the Caribbean over Zoom. Participants were recruited through previously identified local physicians and international non-physician professionals working in these countries. Transcripts were coded and key themes identified until thematic saturation was reached (Atlas.ti). FINDINGS: Thirty participants representing eight countries were interviewed, providing 1202 min of transcript data. Data were organized into barriers, facilitators, and strategies to improve the delivery of health care for AYA with cancer in LATAM at the patient- (e.g., financial barriers, continued schooling), parent- (e.g., limited medical literacy, advocacy), and hospital-level (e.g., structural barriers, increasing funding). INTERPRETATION: There are many similarities in the barriers and facilitators to AYA care between LATAM and high-income countries (HIC); however, some characteristics are more unique to LATAM, for example, strict age restrictions for pediatric care and abandonment of therapy. As LATAM countries continue to build cancer control programs, there is an opportunity to consider our identified barriers, facilitators, and strategies to address the unique needs of AYA with cancer.