Ambient Pressure Scanning Tunneling Microscopy

Scanning tunneling microscopy (STM) helps us understand the local electronic structure and dynamic species of such surfaces, which is coupled with x-ray photoelectron spectroscopy (XPS) to obtain chemical state information. These techniques are performed at both ambient pressure and ultra-high vacuum.

The research focus is bifurcated into two areas. The first is from a reaction standpoint: systems that are relevant to CO2 hydrogenation to value added products such as methanol. The support materials used for catalytically active metal species have been increasingly recognized of late as contributors to many reaction cycles. Thus, we aim to further understand the role of the supports used (often metal oxides) in this enhancement or stabilization of active species as it pertains to the reduction of carbon dioxide.

  In-situ NAP-STM images of Cu2O/Cu(111) reduction by 10 mTorr CO after 46, 281, 374, 490, 603, 715 and 828 s (A-G). Plot H shows the area of the three species formed during CO reduction. Scale bar = 5 nm. Color corresponds to height. Tunneling conditions: 1.1 V, 0.83 nA

In-situ NAP-STM images of Cu2O/Cu(111) reduction by 10 mTorr CO after 46, 281, 374, 490, 603, 715 and 828 s (A-G). Plot H shows the area of the three species formed during CO reduction. Scale bar = 5 nm. Color corresponds to height. Tunneling conditions: 1.1 V, 0.83 nA

The second area of focus is a more material specific approach. I aim to characterize and elucidate the effects of alkali metals, such as potassium and cesium, which are sometimes added in small amounts to a catalyst to promote a reaction. Little is understood about the way that these metals interact with the material systems and reaction feedstocks.

 

  Figure 2. In-situ STM images of Cu2O reduction by 45 mTorr C  O after 92, 184, 274 s (A to C). Scale bar = 2 nm. Color corresponds to height. Tunneling conditions: 0.9 V, 0.78 nA. Green circle serves as a land mark. Black box indicates formation of a 5-7 ring structure. White arrow points to formation of a Cu island. Black balls in schematic represent oxygen in Cu2O structure. Cu atoms and chemisorbed oxygen atoms are not shown.

Figure 2. In-situ STM images of Cu2O reduction by 45 mTorr CO after 92, 184, 274 s (A to C). Scale bar = 2 nm. Color corresponds to height. Tunneling conditions: 0.9 V, 0.78 nA. Green circle serves as a land mark. Black box indicates formation of a 5-7 ring structure. White arrow points to formation of a Cu island. Black balls in schematic represent oxygen in Cu2O structure. Cu atoms and chemisorbed oxygen atoms are not shown.