Lars Montelius

Controlled manipulation of nanoparticles with an atomic force microscope

We report on the application of the atomic force microscope (AFM) to manipulate and position nanometer‐sized particles with nanometer precision. The technique, which can be regarded as a nanometer‐scale analogy to atomic level manipulation with the scanning tunneling microscope, allowed us to form arbitrary nanostructures, under ambient conditions, by controlled manipulation of individual 30 nm GaAs particles. A whole new set of nanodevices can be fabricated particle‐by‐particle for studies of quantum effects and single electron tunneling. We also demonstrate a method, based on the AFM manipulation, to determine the true lateral dimensions of nano‐objects, in spite of the tip‐sample convolution.

Improving stamps for 10 nm level wafer scale nanoimprint lithography

The smaller the features on the stamp the more important are the interactions between stamp and polymer layer. A stamp rich in small structures will effectively show a surface area enlargement, which generally leads to adhesion of the polymer to the stamp. This makes a subsequent imprint impossible without troublesome and time-consuming cleaning. The anti-adhesion properties of Si- or SiO2-based stamps can be improved by binding fluorinated silanes covalently to the surface. In this paper, we demonstrate that the deposition procedure as well as the environment during deposition are important with respect to the quality and performance of the molecular layer

Nanoimprint lithography at the 6 in. wafer scale

We demonstrate the nanoimprint lithography (NIL) technique with sub 100 nm resolution, on 6 in. Si substrates. The pattern transfer is performed using a specially designed NIL machine optimized to achieve a very high degree of parallelism between stamp and substrate. The stamp is made with the help of electron beam lithography and Ni electroplating achieving features below 100 nm in size. The nanoimprint process is done in a single layer as well as in a multilayer resist scheme with subsequent O2-plasma etching and metal lift-off.

Local probe techniques for luminescence studies of low-dimensional semiconductor structures

With the rapid development of technologies for the fabrication of, as well as applications of low-dimensional structures, the demands on characterization techniques increase. Spatial resolution is especially crucial, where techniques for probing the properties of very small volumes, in the extreme case quantum structures, are essential. In this article we review the state-of-the-art in local probe techniques for studying the properties of nanostructures, concentrating on methods involving monitoring the properties related to photon emission. These techniques are sensitive enough to reveal the electronic structure of low-dimensional semiconductor structures and are, therefore, able to give detailed information about the geometrical structure, including fabrication-related inhomogeneities within an ensemble of structures. The local luminescence probe techniques discussed in this review article can be divided into four categories according to the excitation source: (i) spatially localized microphotoluminesce...

Ultrasensitive mass sensor fully integrated with complementary metal-oxide-semiconductor circuitry

Nanomechanical resonators have been monolithically integrated on preprocessed complementary metal-oxide-semiconductor (CMOS) chips. Fabricated resonator systems have been designed to have resonance frequencies up to 1.5 MHz. The systems have been characterized in ambient air and vacuum conditions and display ultrasensitive mass detection in air. A mass sensitivity of 4 ag/Hz has been determined in air by placing a single glycerine drop, having a measured weight of 57 fg, at the apex of a cantilever and subsequently measuring a frequency shift of 14.8 kHz. CMOS integration enables electrostatic excitation, capacitive detection, and amplification of the resonance signal directly on the chip.

Size effect on Young’s modulus of thin chromium cantilevers

Thin chromium cantilevers with sub-100nm thickness have been characterized by an atomic force microscope operating in contact mode. A continuous determination of the local mechanical properties at all lengths was accomplished by applying force along the length of the cantilevers. The result show a decrease of the Young’s modulus as the cantilevers get thinner.

Growth of self-assembled InAs and InAsxP1-x dots on InP by metalorganic vapour phase epitaxy

Abstract The formation of self-assembled InAs and InAs x P 1− x dots on InP has been studied, in particular with deposition conditions under which mainly coherent dots are developed. The samples were grown by metalorganic vapour phase epitaxy. Morphological investigations were performed by atomic force microscopy, with the instrument working in the contact mode as well as in the noncontact mode. Surface densities and height distributions were extracted, as a function of growth conditions. In addition, photoluminescence was used for investigations of the optical properties of capped InAs dots, formed under equivalent conditions. Comparisons between the two characterization techniques show a qualitative agreement with respect to the density of dots as well as their size homogeneity. It is also indicated that dots of binary InAs can be formed at deposition temperatures not higher than about 500°C. Elevated deposition temperatures in this process result in an unintentional alloying mechanism due to exchange reactions at the interface, leading to the formation of ternary InAs x P 1− x dots, which can be seen as a simultaneous increase in the energy of the light emission and the average dot size, indicating the widening of the energy gap in the quantum dots, which counteracts the decreased energy quantization in the larger dots formed at higher temperatures.

Fifteen-piconewton force detection from neural growth cones using nanowire arrays.

We used epitaxially grown monodisperse nanowire arrays to measure cellular forces with a spatial resolution of 1 mum. Nerve cells were cultured on the array and cellular forces were calculated from the displacement of the nanowire tips. The measurements were done in situ on live cells using confocal microscopy. Forces down to 15 pN were measured on neural growth cones, showing that this method can be used to study the fine details of growth-cone dynamics.

Large scale nanolithography using nanoimprint lithography

Nanoimprint lithography is a promising technique for fabrication of nanometer-sized structures with an eventual throughput capacity similar to UV-lithography based production of integrated circuits. In this article we address the possibility for wafer scale nanoimprint lithography, and the results presented here are all obtained from 2 in. sized substrate and stamp wafers. Our nanoimprint lithography equipment is described and some of its characteristics are discussed. These include ultrafast imprint cycle times of less than 2 min, good temperature monitoring, and control possibility of the substrate temperature. We show complete results after imprint, removal of remaining resist, and liftoff for 2 in. wafers. Furthermore, in this article the relation between polymer sticking to the stamp applied pressure, stamp depth, etc. is studied in detail.

Fabrication of quantum devices by Ångström-level manipulation of nanoparticles with an atomic force microscope

We describe a technique for the fabrication of lateral nanometer-scale devices, in which individual metallic nanoparticles are imaged, selected and manipulated into a gap between two electrical leads with the tip of an atomic force microscope. In situ, real-time monitoring of the device characteristics is used to control the positions of the particles down to atomic accuracy and to tune the electrical properties of the device during fabrication. Using this technique we demonstrate a nanomechanical switch as well as atomic-scale contacts that are stable at quantized conductance levels on the time scale of hours at room temperature.