<p>The unusual geometry of spiral nanocrystals gives rise to unique optical, electronic, and mechanical properties. In addition, noble metal nanoparticles, such as gold and silver, exhibit strong plasmonic responses, making them highly attractive for applications in sensing, photonics, and biomedicine. Spiral growth of noble metals was demonstrated for gold already over 70 years ago, yet its formation mechanism remains elusive. Here, we extend spiral morphology to silver, with yields of over 90%, that likely originates from the stochastic mismatch of dendrite arms during planar autoaccelerated oriented assembly (AOA). Silver nanoplates (AgNpt) synthesized via H<sub>2</sub>O<sub>2</sub> with 3-mercaptopropionic acid (MPA) ligand form dendrites, leading to nanoribbons, nanospirals or nanoflowers, depending on MPA concentration. Dendrite formation results from MPA coverage-dependent conformational change and decreasing total nanoparticle surface area during H<sub>2</sub>O<sub>2</sub> addition. MPA redistributes preferentially to AgNpt edges due to higher reactivity and surface area decrease, triggering interparticle attraction at a conformation transition coverage, which can be traced by pH profile during MPA adsorption. Rapid 2D oriented assembly launches diffusion-limited AOA, forming dendritic morphology. Occasionally, random arm overlap, caused by building blocks mismatch, represents the point of spiral formation. Necessity of ligand coverage-dependent conformation swich is confirmed by formation of nanospirals using 2-mercaptobenzoic acid (2MBA) ligand, and absence of their formation for all other tested mercaptans. The tailorable AOA onset, controlled by the MPA (or 2MBA) coverage, provides a bottom-up route for twisted nanocrystal synthesis within minutes. Further in-situ experiments would elucidate details of nanospiral formation on atomic scale.</p><p></p>

错误:搜索内容不能为空,请输入英文关键词
错误:关键词超出字数限制,请精简
高级检索

Silver nanospirals via autoaccelerated oriented assembly

  • Rok Mravljak,
  • Aleksandra Kuljanin,
  • Tina Skalar,
  • Boštjan Genorio,
  • Marjan Marinšek,
  • Aleš Podgornik

摘要

The unusual geometry of spiral nanocrystals gives rise to unique optical, electronic, and mechanical properties. In addition, noble metal nanoparticles, such as gold and silver, exhibit strong plasmonic responses, making them highly attractive for applications in sensing, photonics, and biomedicine. Spiral growth of noble metals was demonstrated for gold already over 70 years ago, yet its formation mechanism remains elusive. Here, we extend spiral morphology to silver, with yields of over 90%, that likely originates from the stochastic mismatch of dendrite arms during planar autoaccelerated oriented assembly (AOA). Silver nanoplates (AgNpt) synthesized via H2O2 with 3-mercaptopropionic acid (MPA) ligand form dendrites, leading to nanoribbons, nanospirals or nanoflowers, depending on MPA concentration. Dendrite formation results from MPA coverage-dependent conformational change and decreasing total nanoparticle surface area during H2O2 addition. MPA redistributes preferentially to AgNpt edges due to higher reactivity and surface area decrease, triggering interparticle attraction at a conformation transition coverage, which can be traced by pH profile during MPA adsorption. Rapid 2D oriented assembly launches diffusion-limited AOA, forming dendritic morphology. Occasionally, random arm overlap, caused by building blocks mismatch, represents the point of spiral formation. Necessity of ligand coverage-dependent conformation swich is confirmed by formation of nanospirals using 2-mercaptobenzoic acid (2MBA) ligand, and absence of their formation for all other tested mercaptans. The tailorable AOA onset, controlled by the MPA (or 2MBA) coverage, provides a bottom-up route for twisted nanocrystal synthesis within minutes. Further in-situ experiments would elucidate details of nanospiral formation on atomic scale.