We present a study of a series of n-i-n InAs quantum-dot infrared photodetectors (QDIPs) with unintentionally doped active regions. Different quantum-dot capping layer materials (GaAs, InGaAs, and AlGaAs) are utilized to tune the operating wavelength and modify the QDIP performance. Normal-incidence operation with high detectivity in the mid (3-5 ) and long (8-12 ) wavelength regimes and the potential for multicolor operation is demonstrated.

Assembly of nanometer-scale objects by scanning probe microscope (SPM) as a promising approach for the fabrication of nanoelectromechanical systems (NEMS). This paper describes several techniques for positioning nanoparticles, linking them to form subassemblies, and moving entire subassemblies. These are first steps towards the hierarchical construction of complex nanoassemblies. Results of experiments conducted in ambient air and in liquid environments are presented. Nanomanipulation in liquids opens new research directions involving interactions with single biomolecules, and fine control of forces between tips, particles and surface substrates.

Precise control of the structure of matter at the nanometer scale will have revolutionary implications for science and technology. Nanoelectromechanical systems (NEMS) will be extremely small and fast, and have applications that range from cell repair to ultrastrong materials. This paper describes the first steps towards the construction of NEMS by assembling nanometer-scale objects using a scanning probe microscope as a robot. Our research takes an interdisciplinary approach that combines knowledge of macrorobotics and computer science with the chemistry and physics of phenomena at the nanoscale. We present experimental results that show how to construct arbitrary patterns of gold nanoparticles on a mica or silicon substrate, and describe the underlying technology. We also discuss the next steps in our research, which are aimed at producing connected structures in the plane, and eventually three-dimensional nanostructures.