Semiconductor to Metal to Half-Metal Transition in Pt-Embedded Zigzag Graphene Nanoribbons

The electronic and magnetic properties of Pt-embedded zigzag graphene nanoribbons (Pt–ZGNRs) are investigated using density-functional theory calculations. It is found that Pt–ZGNRs exhibit a semiconductor–metal–half-metal transition as the position of Pt substitutional impurities in the ribbon changes from the center to edge sites. This behavior can be attributed to the interaction between Pt impurities and edge states of ZGNRs, which governs the electron occupation of the edge states. The transition always occurs independent of ribbon width. However, Pt impurity concentration is important for obtaining this transition. Our results demonstrate that Pt–ZGNRs can be used as versatile electronic devices

Clusters for benzene pollution exposure by age at county level.

<p>A local autocorrelation method is used to identify statistically significant hot spots, or cluster areas. High-High areas indicate high values near high values; Low-Low areas indicate low values near low values; High-Low areas indicate high values near low values; Low-High areas indicate low values near high values. (A) age (<14); (B) age (>60). Division 1 is New England; Division 2 is Mid-Atlantic; Division 3 is East North Central; Division 4 is West North Central; Division 5 is South Atlantic; Division 6 is East South Central; Division 7 is West South Central; Division 8 is Mountain; Division 9 is Pacific.</p

Clusters for benzene pollution exposure by income at county level.

<p>Fig. 7 shows High-High areas are high values cluster areas, in which people with low income exposed to higher level of benzene pollution than those with high income. Division 1 is New England; Division 2 is Mid-Atlantic; Division 3 is East North Central; Division 4 is West North Central; Division 5 is South Atlantic; Division 6 is East South Central; Division 7 is West South Central; Division 8 is Mountain; Division 9 is Pacific.</p

Standards of categorization and reference categories for socio-demographic measurements.

<p>*Reference category for comparison based on existing studies in the environmental justice literature.</p><p>**The classification standard for income is detailed in the text.</p

Frequency of <i>OR</i>s greater than 1 by income at the county level in the United States and the nine divisions.

<p>CI: confident interval;</p><p>Percentage was derived by the number of geographic units for low income level divided by the total number of counties at each geographic division.</p

Global Moran's I statistic values by age, race, and educational attainment in the United States and the nine divisions.

<p>* p<0.05.</p

Clusters for benzene pollution exposure by education at county level.

<p>(A): Educational attainment (0–4); (B): Educational attainment (5–8); (C): Educational attainment (9–12). Division 1 is New England; Division 2 is Mid-Atlantic; Division 3 is East North Central; Division 4 is West North Central; Division 5 is South Atlantic; Division 6 is East South Central; Division 7 is West South Central; Division 8 is Mountain; Division 9 is Pacific.</p

Frequency of <i>OR</i>s greater than 1 by age characteristic at the county level in the United States and the nine divisions.

<p>CI: confident interval;</p><p>Percentage was derived by the number of geographic units for each age level divided by the total number of counties at each geographic division.</p

Frequency of <i>OR</i>s greater than 1 by educational attainment at the county level in the United States and the nine divisions.

<p>CI: confident interval;</p><p>Percentage was derived by the number of geographic units for each education level divided by the total number of counties at each geographic division.</p

United States census divisions of urban-designated counties containing 52, 613 tracts used in this study.

<p>The study area focuses on all urban census tracts within the United States, which is further classified into nine divisions. It consists of an aggregate number of 52,613 census tracts within 48 contiguous states and Washington DC.</p