High-Resolution Scanning Tunneling Microscopy Images of Molecular Overlayers Prepared by a New Molecular Beam Deposition Apparatus with Spray-Jet Technique

Abstract

We developed a new molecular beam deposition apparatus using a spray-jet technique for high-quality thin film preparation of nonsublimable molecules. The apparatus was used to deposit chloro[tri-tert-butyl-subphthalocyaninato]boron(III) (TBSubPc) molecules on an Au(111) surface for analysis by low-temperature scanning tunneling microscopy (STM). Highly resolved images, in which tert-butyl groups in a TBSubPc molecule were clearly identifiable, were obtained. The image quality and the resolution of these images compared favorably well to STM images taken on reference samples which were sublimed onto Au (111) from a heated crucible.

Improvement of the inlet system for the spray-jet technique for use in spectroscopic studies and molecular deposition

“…We previously developed a molecular beam apparatus with a spray-jet technique [1][2][3][4][5] that enables us to produce a molecular beam of neutral non-volatile molecules in vacuum from the sprayed mist of a sample solution. The apparatus is intended for use in spectroscopic studies or as a means of molecular deposition.…”

“…The apparatus is intended for use in spectroscopic studies or as a means of molecular deposition. The spray-jet molecular beam apparatus for spectroscopic studies consists of (1) a sample inlet system with an ultrasonic nebulizer, an inlet chamber, and a pulsed nozzle; (2) a set of skimmers; and (3) a high-vacuum chamber equipped with a time-of-flight mass spectrometry (TOFMS) unit, in which pulsed-laser photoionization and mass detection are carried out, while the spray-jet molecular beam deposition apparatus consists of essentially the same component parts as the spray-jet molecular beam apparatus for spectroscopic studies, except that the TOFMS unit is replaced by a ultra-high-vacuum (UHV) chamber equipped with a unit for molecular beam deposition and a unit for transferring a sample plate to a low-temperature scanning tunneling microscope (LT-STM) [4]. From the viewpoint of spectroscopic analysis, the spray-jet technique provides us with different information from those of the supersonic jet technique [6,7], the matrix assisted laser desorption ionization (MALDI) technique [8,9] and the electrospray ionization (ESI) technique [10], while from the viewpoint of molecular deposition, it provides us with a new method of molecular beam deposition [4].…”

“…For spectroscopic studies, we previously used the sprayjet molecular beam apparatus to analyze various sample solutions of non-volatile functional molecules, including a liquid crystal molecule, 4V -n-pentyl-4-cyanobiphenyl (5CB), a naphthalene derivative, 1,5-dihydroxy naphthalene, dye molecules such as 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM), Rhodamine B, and chloro[tri-tert -butyl-subphthalocyaninato]boron(III) (TBSubPc), and dendrimer molecules such as poly(propylene imine) dendrimers with different generations [1][2][3][4][5].…”

“…As for molecular beam deposition, we used the apparatus with an acetone solution of TBSubPc. The deposited overlayer of TBSubPc molecules on an Au(111) surface was then investigated by LT-STM [4]. The spray-jet technique thus enabled us to produce a high-quality molecular beam of which we could spectroscopically characterize the sample molecules or deposit them on a clean surface in vacuum.…”

“…Fig. 1 shows the spray-jet inlet system which consists of an ultrasonic nebulizer (OMRON, NE-U17, 1.6 MHz), an inlet chamber, and a pulsed nozzle (Paker Hannifin, 9-279-900) as previously described [1][2][3][4][5]. In the ultrasonic nebulizer, the generation of a capillary wave on the solution surface leads to the production of a mist of solution, and the atomized droplet size therefore depends on the surface tension and the density of the solution [11].…”