Indirect Band Gap in Scrolled MoS₂ Monolayers

MoS2 nanoscrolls that have inner core radii of ∼250 nm are generated from MoS2 monolayers, and the optical and transport band gaps of the nanoscrolls are investigated. Photoluminescence spectroscopy reveals that a MoS2 monolayer, originally a direct gap semiconductor (∼1.85 eV (optical)), changes into an indirect gap semiconductor (∼1.6 eV) upon scrolling. The size of the indirect gap for the MoS2 nanoscroll is larger than that of a MoS2 bilayer (∼1.54 eV), implying a weaker interlayer interaction between concentric layers of the MoS2 nanoscroll compared to Bernal-stacked MoS2 few-layers. Transport measurements on MoS2 nanoscrolls incorporated into ambipolar ionic-liquid-gated transistors yielded a band gap of ∼1.9 eV. The difference between the transport and optical gaps indicates an exciton binding energy of 0.3 eV for the MoS2 nanoscrolls. The rolling up of 2D atomic layers into nanoscrolls introduces a new type of quasi-1D nanostructure and provides another way to modify the band gap of 2D materials

How the coronavirus gave QR codes a major role in travel

QR codes have become increasingly popular over the last eight months as the COVID-19 pandemic continues across the globe. Many companies are using them as a way to save money on paper products and for contactless assistants. QR codes have also advanced the speed of travel and streamlined hotel check in/out services

Differences in the COVID-19 Pandemic Response between South Korea and the United States: A Comparative Analysis of Culture and Policies

The impact of the COVID-19 pandemic has varied across countries. Some countries controlled the virus relatively well, while others did not. In the United States, almost a million people died. However, South Korea’s death toll is only about 12,000 even though its population is about one-sixth of the United States. What caused the difference? We argue that public compliance to government direction is the primary reason. South Korea’s collective culture valuing communal benefits helped the people conform to government directions, such as mask wearing in public places. By contrast, American people resisted the government policies that restrict individual freedom due to the individualistic culture. In South Korea, historical experiences of relatively frequent national crises led to the rise of defensive nationalism, resulting in national union. However, the United States had relatively fewer national crises, and thus nationalism did not rise. Instead, national division, xenophobia, and hatred toward Asians prevailed in the United States. Besides the cultural differences, differences in national leader’s characteristics, past experiences of public health crisis, and political system also contributed to the different outcomes of the crisis