Wave and particle in molecular interference lithography $^{1}$Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria $^{2}$Department of Physics, Faculty of Science, Burapha University, Chonburi 20131, Thailand $^{3}$School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK (Dated: May 28, 2018) The wave-particle duality of massive objects is a cornerstone of quantum physics and a key prop- erty of many modern tools such as electron microscopy, neutron diffraction or atom interferometry. Here we report on the first experimental demonstration of quantum interference lithography with complex molecules. Molecular matter-wave interference patterns are deposited onto a reconstructed $^{Si(111) 7}$×7 surface and imaged using scanning tunneling microscopy. Thereby both the particle and the quantum wave character of the molecules can be visualized in one and the same image. This new approach to nanolithography therefore also represents a sensitive new detection scheme for quantum interference experiments. PACS numbers: 01.55.+b,03.65.-w, 03.65.Ta,03.75.-b The de Broglie wave nature of massive particles has always been an essential ingredient in the conceptual de- velopment of quantum mechanics [1, 2]. First demonstra- tions of the electron wave nature [3, 4] were soon followed by experiments on the diffraction of helium atoms and H$_{2}$ molecules [5] as well as neutrons [6, 7]. The build-up of quantum interference patterns from single particles was shown in particularly nice demonstrations with individ- ual photons [8] and electrons [9, 10]. With the availability of laser and nanofabrication technologies, atom interfer- ometry and coherent lithography have become rapidly developing fields of research [11–14]. Recently, quan- tum interference experiments have also been extended to composite nanoparticles, such as fullerenes [15], He clusters [16] or large fluorinated molecules [17, 18]. Our present demonstration complements these earlier studies as it represents the first realization of quantum interference lithography with molecules. It thereby closes two gaps that so far existed in the field of macromolecule interferometry: On the one hand, previous experiments had not been able to visualize the individual particles that traversed the interferometer. Further, it has also been discussed by several authors that ionizing detectors are inefficient already for medium-sized organic materi- als [19, 20]. Being sensitive to single molecules, our new lithographic interference detection scheme provides, for the first time, the opportunity to visualize both the quantum wave features and the composite particle na- ture of individual molecules in one and the same image and experiment. On the other hand, we show that near- field interferometry is a very natural approach to gen- erating surface-deposited and immobilized nanopatterns with particles that can, in principle, be regarded as func- tional entities by themselves. Our experiment thus oper- ates at the interface between matter-wave interferometry and surface nanoscience. A schematic illustration of the setup is shown in Fig- ure 1. The experiment is sectioned into five differentially pumped vacuum chambers, which comprise three logical compartments: the source, the interferometric nanode- position and the detector. The supplementary vacuum chambers are required for differential pumping as well as for the preparation and transfer of the detection surface. A Knudsen cell at T=1070 K forms the molecular beam which is selected within a transmitted velocity band of Δ v/v = 0 . 05 (FWHM) to account for the fact that dif- ferent velocities correspond to different de Broglie wave- lengths, λ$_{dB}$ = h/mv , and to varying interaction times with the gratings. Two alternative methods have been used for select- ing the molecular speed: First, a gravitational velocity selection scheme exploits the molecular free-fall trajecto- ries in the Earth’s gravitational field. This established method [21, 22] allows to work without any vibrating or rotating element. The interference fringe contrast of the molecular deposit varies, however, with the vertical po- sition on the sample and scattering at the slit edges may spoil the selection quality. Second, interferograms were also recorded using a home-built helical velocity selector which is a minia- turized version of devices known from neutron scatter- ing [23]. Grooves of 300 µ m width were milled along he- lical trajectories into an aluminum cup of 40 mm length. The aspect ratio of length and width of the grooves de- fines the transmitted velocity bandwidth. Their pitch and angular speed defines the center of the distribution. The selector is held by UHV compatible bearings and driven by a motor outside of the chamber. A magneto- fluidic seal allows the mechanical transduction of the ro- tational motion at frequencies in excess of 100 Hz. An acceleration sensor at the mechanical base of the inter- ferometer quantified typical oscillation amplitudes to be as small as 2 nm. This method was chosen for the experiment presented arXiv:1001.0468v1 [quant-ph] 4 Jan 2010 Thomas Juffmann, 1 Stefan Truppe, 1 Philipp Geyer, 1 Andr´ as G. Major, 1,$_{∗}$ Sarayut Deachapunya, 1,2 Hendrik Ulbricht, 1, 3 and Markus Arndt 1