256
14 Creating Genetic Materials of Metal Clusters
Au 11 clusters demonstrate Coulomb blockade behavior at low temperature, with
zero-conductance gaps resulting from quantum size effects [263].
Cooperation work in Castleman and Weiss groups presented a study in which they
softly land Al 17
– clusters onto hydroxyl-terminated SAMs using reactivity previously
characterized in the gas phase before imaging the deposited clusters via the STM
technique. Among the reactive Al clusters as discussed in Chap. 6, Al 17
– is unique in
that it exhibits several active sites—one on each face of its structure—in reacting with
water [264]. It was noted that an Al 17
– cluster approaching a hydroxyl group such
as SAM consisting of only hydroxyl-terminated molecules have a high probability
of interacting in this manner to form a chemisorbed product. Further, as a SAM
presents a continuous surface of nucleophiles of which each can donate electrons
to the approaching cluster, it was conjectured the SAMs also profit the link of Al
clusters covalently to the substrate. This is similar to the soft-landing studies that
were performed for the deposition of pre-tethered assemblies onto a surface, as well
as the aforementioned peptide ions onto SAMs where the ions could bind retaining
their charge state [265]. Nevertheless, as Al 17
– and Al 17 neutral clusters have same
structures and free-electron characteristics, the charge of such a deposited species
would be irrelevant when using standard microscopic techniques [266, 267].
This soft-landing of Al clusters extends the novel deposition scheme where fragile
all-metal clusters are deposited in a predictable fashion, and is recognized to display
the important initial states for the bottom-up construction of substrate-supported
clusters. It is worth mentioning in this study there is a well design and implementation of a versatile vacuum suitcase for use in transporting air-sensitive samples (such
as Al clusters) between ultra-high vacuum (UHV) instruments, especially the portability and stability when the sample is transferred into the final vacuum chamber.
This system was easily adaptable to a wide variety of applications involving sample
preparation and analyses where two or more of the procedural steps occur in separate
vacuum chambers. It is important to design such a system with the ease of adaptability
of this transfer device to other vacuum systems.
Besides the STM characterization, there are also some other approaches that have
been applied to the solid-supported metal clusters, for instance, by means of X-ray
photoelectron spectroscopy (XPS). For example, an early work in Cooks group [183]
reported the in situ Raman analysis of surfaces prepared by ion soft landing, on which
surface-enhanced Raman spectroscopy (SERS) effect was noted for crystal violet,
Rhodamine 6G, methyl orange and copper phthalocyanine. Furthermore, imaging
of the modified surfaces was attained utilizing the 2D Raman imaging technique.
The combination of molecular spectral tools of SERS and secondary ion mass spectrometer (SIMS) fitted with in-vacuum sample transport capability facilitates in situ
analysis of such novel surfaces modified by cluster soft landing deposition. It is worth
mentioning that, because of the fingerprint spectra of Raman spectroscopy and the
availability to identify charge transfer between metals and analytes, the in situ Raman
measurements could be applicable to judge the charge state of the soft-landed metal
clusters [268].
14 Creating Genetic Materials of Metal Clusters
Au 11 clusters demonstrate Coulomb blockade behavior at low temperature, with
zero-conductance gaps resulting from quantum size effects [263].
Cooperation work in Castleman and Weiss groups presented a study in which they
softly land Al 17
– clusters onto hydroxyl-terminated SAMs using reactivity previously
characterized in the gas phase before imaging the deposited clusters via the STM
technique. Among the reactive Al clusters as discussed in Chap. 6, Al 17
– is unique in
that it exhibits several active sites—one on each face of its structure—in reacting with
water [264]. It was noted that an Al 17
– cluster approaching a hydroxyl group such
as SAM consisting of only hydroxyl-terminated molecules have a high probability
of interacting in this manner to form a chemisorbed product. Further, as a SAM
presents a continuous surface of nucleophiles of which each can donate electrons
to the approaching cluster, it was conjectured the SAMs also profit the link of Al
clusters covalently to the substrate. This is similar to the soft-landing studies that
were performed for the deposition of pre-tethered assemblies onto a surface, as well
as the aforementioned peptide ions onto SAMs where the ions could bind retaining
their charge state [265]. Nevertheless, as Al 17
– and Al 17 neutral clusters have same
structures and free-electron characteristics, the charge of such a deposited species
would be irrelevant when using standard microscopic techniques [266, 267].
This soft-landing of Al clusters extends the novel deposition scheme where fragile
all-metal clusters are deposited in a predictable fashion, and is recognized to display
the important initial states for the bottom-up construction of substrate-supported
clusters. It is worth mentioning in this study there is a well design and implementation of a versatile vacuum suitcase for use in transporting air-sensitive samples (such
as Al clusters) between ultra-high vacuum (UHV) instruments, especially the portability and stability when the sample is transferred into the final vacuum chamber.
This system was easily adaptable to a wide variety of applications involving sample
preparation and analyses where two or more of the procedural steps occur in separate
vacuum chambers. It is important to design such a system with the ease of adaptability
of this transfer device to other vacuum systems.
Besides the STM characterization, there are also some other approaches that have
been applied to the solid-supported metal clusters, for instance, by means of X-ray
photoelectron spectroscopy (XPS). For example, an early work in Cooks group [183]
reported the in situ Raman analysis of surfaces prepared by ion soft landing, on which
surface-enhanced Raman spectroscopy (SERS) effect was noted for crystal violet,
Rhodamine 6G, methyl orange and copper phthalocyanine. Furthermore, imaging
of the modified surfaces was attained utilizing the 2D Raman imaging technique.
The combination of molecular spectral tools of SERS and secondary ion mass spectrometer (SIMS) fitted with in-vacuum sample transport capability facilitates in situ
analysis of such novel surfaces modified by cluster soft landing deposition. It is worth
mentioning that, because of the fingerprint spectra of Raman spectroscopy and the
availability to identify charge transfer between metals and analytes, the in situ Raman
measurements could be applicable to judge the charge state of the soft-landed metal
clusters [268].