Molecular Electronics

Molecular electronics is an emerging nanotechnology of using individual molecules as a self-contained functional electronic components. In the past several years, molecular wire, diode, switch, transistor, and memory devices have been demonstrated.

We fabricate molecular devices and study underlying physics to understand molecular scale charge transport, specifically about conduction mechanisms, interaction of charge carriers with molecular vibrations, metal-molecule contact effect, energy band structures, etc.

1. Statistical analysis
We emphasize on the statistical analysis of the electronic properties of alkyl molecular devices, since molecular devices tend to have device-to-device nonuniformity due to various reasons and it is sometimes hard to decide the molecular intrinsic "working" devices and "representative devices".

Ref. Tae-Wook Kim et al, “Statistical analysis of electronic properties of alkanethiols in metal-molecule-metal junctions”, Nanotechnology, 18, 315204 (2007) [Abstract & PDF]
Ref. Hyunwook Song et al,“A Statistical Method for Determining Intrinsic Electronic Transport Properties of Self-assembled Alkanethiol Molecular Devices”, Appl. Phys. Lett. 91, 253116 (2007)  
[Abstract & PDF]

2. Molecular configuration dependent charge transprot
We study the charge transport of alkyl self-assembled monolayers using conducting atomic force microscopy. For example, we study "through-bond" vs "through-space" transports as a function of molecular tilt-configuration. With increasing tilt-configuration, the "through-space" transport starts to significantly contribute in the overal charge transport through the molecules.
Also, with increasing tilt-configuration, the transition from direct tunneling to field emission (Fowler-Nordheim) tunneling is enhanced, which is
consistent with a barrier height decrease as affected by the enhancement of the intermolecular through-space transport as molecular tilt.

Ref. Hyunwook Song et al, "Intermolecular Chain-to-Chain Tunneling in Metal-Alkanethiol-Metal Junctions", J. Am. Chem. Soc. (Communication) 129, 3806 (2007) [Abstract & PDF]
Ref. Gunuk Wang et al, "Enhancement of field emission transport by molecular tilt configuration in metal-molecule-metal junction", J. Am. Chem. Soc. 131, 5980 (2009) [Abstract & PDF]

3. Metal-molecule contacts
We study the effect of metal-molecule contacts in the electronic transport properties of molecular junctions, based on the statistical analysis and by using "multi-barrier tunneling" model. We particularly distinguish monothiol vs dithiol contacts to metal electrodes and many other cases.

Ref. Gunuk Wang et al, "Influence of Metal-Molecule Contacts on Decay Coefficients and Specific Contact Resistances in Molecular Junctions", Phys. Rev. B, 76, 205320 (2007)   [Abstract & PDF]
Ref. Gunuk Wang et al, "Effects of Metal-Molecule Contact and Molecular Structure on Molecular Electronic Conduction in Nonresonant Tunneling Regime: Alkyl versus Conjugated Molecules", J. Phys. Chem. C, 112, 13010 (2008)  
[Abstract & PDF]

4. Inelastic electron tunneling spectroscopy (IETS)
We study the inelatic electron tunneling spectroscopy (IETS). This effect is due to transport electrons coupling with molecular vibrations in the molecular junction. It is powerful tool for molecular identity, molecular configuration, etc.

Ref. Hyunwook Song et al, "Vibrational spectra of metal-molecule-metal junctions in electromigrated nanogap electrodes by inelastic electron tunneling”, Appl. Phys. Lett. 94, 103110 (2009)   [Abstract & PDF]    


Polymer Non-volatile Memory Devices

We are doing researches on the non-volatile memory devices using polymer materials. We fabricate polymer memory devices, investigate the memory performances, and understand transport and memory mechanisms.

Ref. Tae-Wook Kim et al, "1 Transistor-1 Resistor Devices for Polymer Non-volatile Memory Applications", Advanced Materials, Early View web published (April 9, 2009) [Abstract & PDF] *It will appear as Inside COVER picture article. 
Ref. Tae-Wook Kim et al, “Resistive Switching Characteristics of Polymer Non-volatile Memory Devices in a Scalable Via-hole Structure”, Nanotechnology, 20, 025201 (2009)  
 [Abstract & PDF]
Ref. Byungjin Cho et al,“Unipolar nonvolatile memory devices with composites of poly(9-vinylcarbazole) and titanium dioxide nanoparticles", Organic Electronics, 10, 473 (2009)
[Abstract & PDF]
Ref. Tae-Wook Kim et al, “Reversible switching characteristics of polyfluorene-derivative single layer film for non-volatile memory devices”, Appl. Phys. Lett. 92, 253308 (2008)
[Abstract & PDF]
Ref. Tae-Wook Kim et al, “Reliable Organic Non-Volatile Memory Device using Polyfluorene-derivative Single Layer Film”, IEEE Elect. Dev. Lett. 29, 852 (2008)
[Abstract & PDF]
Tae-Wook Kim et al, “A direct Metal Transfer method for Cross-bar type Polymer Non-volatile Memory Applications”, Nanotechnology, 19, 405201 (2008)  [Abstract & PDF]