Strukturna i električna svojstva tankih slojeva kalkogenida CuSbTe2, CuSbSe2 i CuSbS2

The ternary chalcogenides CuSbTe2, CuSbSe2 and CuSbS2 were synthesized by the direct fusion technique. The thin films of these compounds were prepared by thermal evaporation under vacuum of about 1.3 mPa (10−5 Torr) and the rate of deposition was 30 nm/min. The structural properties of CuSbTe2, CuSbSe2 and CuSbS2 in powder and thin film forms were investigated by X-ray diffraction (XRD) and transmission electronmicroscopy. Microprobe analysis technique was used to investigate the composition of the three alloys and of their films. The electrical conductivity σ and the thermoelectrical power Q have been measured for all asdeposited and annealed thin films, as a function of temperature in the range from 80 to 500 K. It was found that the electrical conductivity σ, the carrier concentration P, the mobility µ and the thermoelectric power Q increase when increasing the annealing temperature for CuSbTe2, CuSbSe2 and CuSbS2 thin films. The increase of σ, P, µ and Q, and also the decrease of the activation energy ∆E with increasing temperature for the as-deposited CuSbTe2, CuSbSe2 and CuSbS2 thin films, can be attributed to the change in the structure of these films from the amorphous to the crystalline state.Trokomponentne smo kalkogenide CuSbTe2, CuSbSe2 and CuSbS2 pripremili metodom talenja. Tanke smo slojeve tih spojeva pripremali isparavanjem u vakuumu od oko 1.3 mPa, brzinom nanošenja oko 30 nm/min. Strukturna svojstva tih kalkogenida, kako praškova, tako i tankih slojeva, istraživali smo difrakcijom rendgenskog zračenja i prolaznom elektronskom mikroskopijom. Pomoću mikroprobe odredili smo kemijski sastav spojeva i njihovih tankih slojeva. Izmjerili smo električnu vodljivost, σ, i termoelektričnu snagu, Q, svih svježe naparenih i opuštenih legura i njihovih tankih slojeva u ovisnosti o temperaturi u području 80 do 500 K. Električna vodljivost, gustoća nositelja, P, mobilnost, µ, i termoelektrična snaga, Q, povećavaju se ako se tanki slojevi opuštaju na višim temperaturama. Povećanje σ, P, µ and Q, a također smanjenje aktivacijske energije, ∆E, u tankim slojevima CuSbTe2, CuSbSe2 i CuSbS2 tumače se promjenama strukture tih slojeva od amorfnog u kristalinično stanje

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century