Atomic Force Microscope Nanomanipulation Research Articles

Temperature-dependent excited state lifetimes of nitrogen vacancy centers in individual nanodiamonds

Nitrogen vacancy (NV) centers are fluorescent defects widely employed for thermometry, most commonly via temperature-dependent shifts of their optically detected magnetic resonance. Recently, all-optical approaches based on temperature-dependent features of the NV center fluorescence spectrum have also gained traction. Excited state lifetime thermometry is an all-optical technique that has been implemented using other fluorophores but has not previously been demonstrated for NV centers in individual nanodiamonds (NDs). Here, we report temperature-dependent excited state lifetime measurements of NV centers in individual NDs between 300 K and 500 K. We measure a 32 ± 7.0% and 35 ± 8.3% average decrease in the excited state lifetimes of individual NDs on silicon and glass substrates, respectively, over this temperature range. A linear approximation applicable to nearly all measured NDs yields temperature coefficients of −2000 ± 240 ppm/K and −2600 ± 280 ppm/K for NDs on silicon and glass, respectively. In addition to all-optical operation, single-ND excited state lifetime thermometry offers ∼100 ns temporal resolution and utilizes time-correlated single photon counting measurements ideally suited to low emission intensities, a limiting factor for other NV center thermometry techniques above 700 K. We demonstrate that atomic force microscope nanomanipulation can position individual NDs at critical locations on a sample of interest, enabling single-point temperature measurements that combine ∼100 ns temporal resolution and ∼100 nm spatial resolution. This work also has broader implications for other single-ND excited state lifetime sensing applications, where care is required to avoid conflating changes in temperature and other environmental parameters.

Nanomanipulation of Individual DNA Molecules Covered by Single-Layered Reduced Graphene Oxide Sheets on a Solid Substrate.

Nanomanipulation of single DNA molecules has great potential in fundamental genetic research and clinical analysis, and is a good model system for studying the interfacial effects on physiochemical processes, which occur when manipulating the linear DNA molecules with an atomic force microscope (AFM) tip. Here, we demonstrate that AFM nanomanipulation can be carried out on DNA molecules covered by a single-layered reduced graphene oxide sheet. Nanomanipulation, which includes cutting, pushing, and sweeping operations, specific to the covered DNA molecules can be achieved in a well-controlled manner using AFM in the PeakForce Quantitative Nano-Mechanics mode. It was found that the normal force required to cut covered DNA strands is over five times greater than that required for naked strands. This technique provides a distinctive method for the construction of graphene architecture by tailoring the underlying artificial DNA nanostructures.

Directional fluorescence emission from a compact plasmonic‐diamond hybrid nanostructure

AbstractUltracompact directional optical nanoantennas are rapidly gaining popularity yet still challenging tasks to construct at the nanoscale. Here, we experimentally demonstrate unidirectional emission from a fluorescent nanodiamond coupled with a single gold nanorod. Different configurations of the assembled hybrid nanostructures were realized via step‐by‐step atomic force microscope nanomanipulation. The emission patterns can be controlled by adjusting the configurations, i.e., the gold nanorod orientation and separation with respect to the nanodiamond. Numerical simulation results reveal that the unidirectional emission can be ascribed to the interference between the electromagnetic fields produced by the dipole‐like source and the out‐of‐phase dipole induced in the gold nanorod. The proposed hybrid nanostructures remarkably exhibit highly unidirectional emission even when the emitter is positioned up to 50 nm away from the nanorod antenna and present a broad working spectral bandwidth of ∼200 nm. The distinct features of this hybrid structure suggest potential applications for novel nanoscale light sources, sensing, and quantum information. image

Directional side scattering of light by a single plasmonic trimer

AbstractDirectional side scattering of light by individual gold nanoparticles (AuNPs) trimers assembled by the atomic force microscope (AFM) nanomanipulation method is investigated in experiment and theory. The AFM nanomanipulation approach brings an active way to construct ultracompact and effective optical nanoantennas. Different configurations of the trimers are constructed in situ via AFM nanomanipulation. Unidirectional side scattering of light by a single trimer is demonstrated with a broad response bandwidth over 400 nm and directivity up to ∼7.8 dB in experiments. The near‐field plasmon coupling of the AuNPs is simulated with the 3D finite‐difference time‐domain method and the far‐field radiation patterns are calculated by employing near‐field‐to‐far‐field transformation methods. The calculated results are in agreement with the experiments qualitatively. The physical origin is revealed intuitively by employing a simple phenomenological “two‐dipole” model. The unidirectional light scattering is due to the interference between multiple plasmonic resonance modes of the trimers. The study contributes to the understanding of the optical response of complex nanostructures and optimizing nanoantenna performances for practical applications, e.g. increasing the detection efficiency of surface‐enhanced spectroscopy. image

Durable bonding of silica nanoparticles to polymers by photoradiation for control of surface properties

Improvement of superhydrophobic surfaces durability is a critical key for potential commercial applications such as self‐cleaning and ice repellency. In this study, functionalization of silica nanoparticles by photoreactive benzophenone groups was made in order to covalently bond nanoparticles to polymer substrates to obtain durable coatings. Upon ultraviolet irradiation reactive excited triplet benzophenone species are formed enabling them to react with the polymer matrix through hydrogen abstraction. Two matrices were studied: radiation‐curable urethane acrylate and epoxy. The bonding of the particles to the surfaces was evaluated using atomic force microscope nanomanipulation and cross‐section analysis. The results have shown a greater stability of the photoreactive silica nanoparticles. Copyright © 2014 John Wiley & Sons, Ltd.

Damage of DNA ends induced by mechanical force during AFM nano-manipulation

An experimental and statistical study was carried out to explore the effects of mechanical forces on the ends of linear double-stranded DNA (dsDNA) fragments. Mechanical force was applied onto individual DNA molecules during atomic force microscope (AFM)-based picking-up manipulation. By comparing the PCR efficiency of two DNA fragments with primers either at ends or at the inner regions, it was found that the ends of DNA fragments were damaged during picking-up process.

Facilitating the pickup of individual DNA molecules by AFM nanomanipulation with tips mechanically worn on bare mica

The tip is one of the critical factors to improve the efficiency in picking up individual DNA molecules from solid substrates based on atomic force microscope (AFM) nanomanipulation. We found that wearing AFM tips on certain solid substrates in advance to nanomanipulation operation would largely improve the pickup efficiency, which was ascribed to the increasing affinity of the tip to the DNA molecules along with the increase of the tip radius after wearing. It was demonstrated that bare mica was superior to APTES-modified mica to keep the tip clean while wearing, which was crucial for DNA pickup during AFM nanomanipulation.

Atomic Force Microscope Nanomanipulation with Simultaneous Visual Guidance

Atomic force microscopy (AFM) has been used to assemble prototype nanostructures consisting of colloidal nanoparticles. In the standard manipulation protocol, the AFM is used either as a manipulation tool or an imaging tool, but not both at the same time. We developed a new nanomanipulation protocol in which simultaneous visual guidance is obtained during manipulation. As an example, Au nanoparticles were manipulated on a substrate in two steps. First, a nanoparticle is kicked with the z feedback off. This kicking event reduces the static friction. Second, the nanoparticle is dribbled to a target position in tapping mode, and visual guidance is provided by a ghost trace of the nanoparticle. The new manipulation protocol greatly improves efficiency of manipulating small nanoparticles (15 nm in diameter or smaller). Our work highlights the importance and challenges of understanding friction at the nanoscale.

The analytical relations between particles and probe trajectories in atomic force microscopenanomanipulation

Analytical expressions relating the trajectories of spherical nanoparticlespushed by an atomic force microscope tip to the scan pattern of the tip arederived. In the case of a raster scan path, the particles are deflected in adirection defined by the geometries of tip and particles and the spacingb between consecutive scan lines. In the case of a zigzag scanpath, the particles are deflected in a range of directions around90°, also dependingon the parameter b. Experimental results on gold nanoparticles manipulated on silicon surfaces in ambientconditions confirm the predictions of our model.

Enhanced Accuracy of Force Application for AFM Nanomanipulation Using Nonlinear Calibration of Optical Levers

The atomic force microscope (AFM) has been widely used as a nano-effector with a function of force sensing to detect interaction forces between an AFM tip and a sample, thereby controlling the process of the nanomanipulation. However, both the extent and accuracy of force application are significantly limited by the nonlinearity of the commonly used optical lever with a nonlinear position-sensitive detector (PSD). In order to compensate the nonlinearity of the optical lever, a nonlinear calibration method is presented. This method applies the nonlinear curve fit to a full-range position-voltage response of the photodiode, obtaining a continuous function of its voltage-related sensitivity. Thus, interaction forces can be defined as integrals of this sensitivity function between any two responses of photodiode voltage outputs, instead of rough transformation with a single conversion factor. The lateral position-voltage response of the photodiode, a universally acknowledged puzzle, was directly characterized by an accurately calibrated force sensor composed of a tippless piezoresistive microcantilever and corresponding electronics, regardless of any knowledge of the cantilevers and laser measuring system. Experiments using a rectangular cantilever (normal spring constant 0.24 N/m) demonstrated that the proposed nonlinear calibration method restrained the sensitivity error of normal position-voltage responses to 3.6% and extended the force application range.