9.4 Manipulation of single molecules with SPM

Scanning Probe Microscopy (SPM) allows us to manipulate individual atoms and molecules on surfaces. We can move them around, build structures atom-by-atom, and even create molecular switches and motors. It's like playing with LEGO blocks, but at the atomic scale!

SPM techniques enable nanofabrication with incredible precision. We can pattern surfaces, induce chemical reactions, and create tiny devices. This opens up exciting possibilities for building ultra-small electronics, sensors, and machines at the molecular level.

Manipulation Techniques

Moving and Positioning Atoms and Molecules

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  A molecular switch based on the manipulation of 1,3-dichlorobenzene on Ge(001) between two ... View original

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  Mechanical force-induced manipulation of electronic conductance in a spin-crossover complex: a ... View original

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  A molecular switch based on the manipulation of 1,3-dichlorobenzene on Ge(001) between two ... View original

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• 

  Mechanical force-induced manipulation of electronic conductance in a spin-crossover complex: a ... View original

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Top images from around the web for Moving and Positioning Atoms and Molecules

• 

  A molecular switch based on the manipulation of 1,3-dichlorobenzene on Ge(001) between two ... View original

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• 

  Mechanical force-induced manipulation of electronic conductance in a spin-crossover complex: a ... View original

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• 

  A molecular switch based on the manipulation of 1,3-dichlorobenzene on Ge(001) between two ... View original

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• 

  Mechanical force-induced manipulation of electronic conductance in a spin-crossover complex: a ... View original

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• Lateral manipulation involves moving atoms or molecules across a surface by applying a force with an SPM tip
  • Achieved by increasing the interaction strength between the tip and the atom or molecule (adjusting tunneling current or force)
  • Enables precise positioning of individual atoms or molecules on a surface (creating patterns or structures)
• Vertical manipulation refers to transferring atoms or molecules between the tip and the surface
  • Picking up an atom or molecule from the surface with the tip and then placing it back down at a different location
  • Used for assembling 3D structures or moving atoms/molecules to specific sites on a surface
• Single-atom manipulation allows for the controlled movement and positioning of individual atoms using an SPM tip
  • Demonstrated by moving xenon atoms on a nickel surface to spell out "IBM" (1990 experiment)
  • Requires precise control over the tip-sample interaction and careful selection of manipulation parameters

Building Structures Atom-by-Atom

• Atomic-scale assembly involves building structures or devices by precisely positioning individual atoms or molecules
  • Constructing artificial molecules or nanoscale devices with desired properties and functionalities
  • Requires a combination of lateral and vertical manipulation techniques to place atoms/molecules in specific arrangements
  • Examples include creating quantum corrals (circular arrangements of atoms) or molecular switches
• SPM-based manipulation enables bottom-up fabrication at the atomic scale
  • Building structures atom-by-atom or molecule-by-molecule rather than top-down lithographic approaches
  • Allows for the creation of novel structures and devices with atomic precision (nanowires, quantum dots)
• Challenges in atomic-scale assembly include maintaining stability of the assembled structures and scaling up the process for practical applications

Molecular Devices

Switches and Logic Elements

• Molecular switches are molecules that can reversibly change between two or more stable states in response to external stimuli
  • States can differ in their electronic, optical, or magnetic properties
  • Switching can be triggered by light, electric fields, or chemical reactions (photochromic, electrochemical, or pH-sensitive switches)
  • Potential applications in molecular electronics, data storage, and sensing
• SPM can be used to study and manipulate individual molecular switches
  • Probing the switching behavior and stability of single molecules on surfaces
  • Inducing switching by applying voltage pulses or mechanical forces with the SPM tip
• Molecular switches can be used as building blocks for molecular logic elements
  • Implementing Boolean logic operations (AND, OR, NOT gates) using molecular switches
  • Combining multiple switches to create more complex logic circuits or memory devices

Nanoscale Motors and Machines

• Molecular motors are nanoscale machines that convert energy into mechanical motion
  • Inspired by biological motors such as kinesin or ATP synthase
  • Examples include rotaxanes (interlocked molecules with a rotatable component) and catenanes (interlocked ring molecules)
  • Driven by external stimuli such as light, electric fields, or chemical reactions
• SPM can be used to study the motion and operation of individual molecular motors
  • Visualizing the rotation or translation of the motor components
  • Measuring the force and speed generated by the motors
• Potential applications of molecular motors include nanoscale transport, actuation, and energy conversion
  • Controlled drug delivery, nanoscale pumps, or molecular-scale manufacturing
  • Challenges include integrating molecular motors into functional devices and ensuring their stability and efficiency

Nanofabrication Applications

Patterning Surfaces with Atomic Precision

• Nanolithography involves using SPM to create patterns or structures on surfaces with nanometer-scale resolution
  • Replacing conventional lithographic techniques (photolithography) for fabricating smaller features
  • SPM-based lithography can achieve sub-10 nm resolution, enabling the fabrication of ultra-small devices
• Different nanolithography approaches include:
  • Dip-pen nanolithography (DPN): Using an AFM tip coated with molecules to directly write patterns on a surface
  • Local oxidation nanolithography: Using a conductive AFM tip to locally oxidize a surface, creating oxide patterns
  • Nanoshaving: Using an AFM tip to mechanically remove material from a surface, creating patterns or structures
• Nanolithography has applications in fabricating nanoelectronic devices, biosensors, and nanophotonic structures
  • Creating quantum dots, nanowires, or plasmonic antennas with precise dimensions and positions
  • Patterning functional molecules or biomolecules on surfaces for sensor applications

Inducing Chemical Reactions at the Nanoscale

• Controlled dissociation involves using an SPM tip to selectively break chemical bonds in molecules on a surface
  • Applying voltage pulses or mechanical forces to induce dissociation events
  • Enables the modification of individual molecules or the creation of reactive sites on a surface
• SPM-induced dissociation can be used for nanoscale chemical synthesis or surface functionalization
  • Cleaving specific bonds in molecules to create new functional groups or radicals
  • Initiating localized chemical reactions by dissociating precursor molecules on a surface
• Potential applications include creating molecular junctions, fabricating nanoscale devices, or studying chemical reactivity at the single-molecule level
  • Modifying electrode surfaces with functional molecules for molecular electronics
  • Investigating the mechanisms and kinetics of chemical reactions at the nanoscale
• Challenges include controlling the selectivity and efficiency of the dissociation process and understanding the underlying mechanisms