Monosized (∼4 nm) diamond nanoparticles arranged on substrate surfaces are exciting candidates for single-photon sources and nucleation sites for ultrathin nanocrystalline diamond film growth. The most commonly used technique to obtain substrate-supported diamond nanoparticles is electrostatic self-assembly seeding using nanodiamond colloidal suspensions. Currently, monodisperse nanodiamond colloids, which have a narrow distribution of particle sizes centering on the core particle size (∼4 nm), are available for the seeding technique on different substrate materials such as Si, SiO2, Cu, and AlN. However, the self-assembled nanoparticles tend to form small (typically a few tens of nanometers or even larger) aggregates on all of those substrate materials. In this study, this major weakness of self-assembled diamond nanoparticles was solved by modifying the salt concentration of nanodiamond colloidal suspensions. Several salt concentrations of colloidal suspensions were prepared using potassium chloride as an inserted electrolyte and were examined with respect to seeding on SiO2 surfaces. The colloidal suspensions and the seeded surfaces were characterized by dynamic light scattering and atomic force microscopy, respectively. Also, the interaction energies between diamond nanoparticles in each of the examined colloidal suspensions were compared on the basis of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. From these investigations, it became clear that the appropriate salt concentration suppresses the formation of small aggregates during the seeding process owing to the modified electrostatic repulsive interaction between nanoparticles. Finally, monosized (<10 nm) individual diamond nanoparticles arranged on SiO2 surfaces have been successfully obtained.

Electron spectro-microscopic methods were applied as direct methods of determining the Schottky barrier heights (SBHs) and their spatial distribution for Au-and Ag-Schottky junctions fabricated on an acid-treated oxygen-terminated diamond (001) substrate. Metal layers were formed with two ranges of thickness (3-5 nm for thin layers and 13-100 nm for thick layers) for both Au-and Ag-Schottky junctions. Leading X-ray photoelectron spectroscopy (XPS) core-level peaks of either Au 4f 7/2 or Ag 3d 5/2 for the metal layers and C 1s for diamond were used as measures of the SBH. For the thick-metal samples, spatially resolved XPS measurements were performed over most of the sample surface. It was found that there is a variation in SBH on the order of 0.1 eV for the large ("high barrier") SBH values and that there are several places where the SBHs were rather small ("low barrier" junction). For the thin-metal samples, less variations in SBH were observed. The average SBH of "high barrier" junctions for the thick-metal samples appeared to be slightly (0.1 eV order) larger than that for the thin-metal samples. XPS images of leading metal core levels tuned for the "high barrier" and "low barrier" SBHs were observed. For the thick-Ag Schottky sample, the resulting Ag 3d 5/2 XPS images clearly showed the locations of defective Schottly junctions. It is suggested that the SBHs determined for the thin-metal samples are the average SBHs on the measured surface and that the SBHs determined for the thick-metal samples are the highest SBHs within the measured µm-size metal islands. The presently determined SBHs were compared with previously reported SBHs and reasonable agreement was found. Photoemission electron microscopy (PEEM) images were observed for the thick-Ag Schottky sample and the "low barrier" islands were identified. The methodologies of XPS, XPS imaging, and PEEM used for the thick-metal samples can be applied to any Schottky junction on diamond.

Aluminum nitride (AlN) thin films deposited by reactive radio frequency magnetron sputtering in an Ar/N2 discharge on Si(001) substrates were studied with respect to structure, stress, and piezoelectric properties. In order to optimize the AlN layers for flexural plate wave (FPW) devices, the influence of process pressure and N2 concentration has been evaluated by means of spectroscopic ellipsometry, residual stress measurements, x-ray diffraction, atomic and piezoresponse force microscopy, along with analysis of the piezoelectric charge coefficient d33,f. FPW devices with low compressively stressed (−200 to −300 MPa) AlN layers were prepared and characterized by white light interferometry and Raman measurements. With increasing pressure from 3×10−3 to 8×10−3 mbar, a transition from −840 MPa compressive stress to +300 MPa tensile stress was measured. Increasing the nitrogen concentration from 3.3% to 50% resulted in a change in stress from +150 to −1170 MPa. All films exhibited a high degree of c-axis orientation. A piezoelectric charge coefficient up to d33,f≈−6.8 pC/N was obtained. Furthermore, it is shown that the film surface morphology is also very much dependent on the growth conditions. A model regarding the mean free path of the sputtered particles and the film surface morphology is proposed. The authors show that the optimization of the film stress by means of the nitrogen concentration in the sputter gas mixture is beneficial as the process window is larger

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Diamond is a highly attractive coating material as it is characterized by a wide optical transparency window, a high thermal conductivity, and an extraordinary robustness due to its mechanical properties and its chemical inertness. In particular, the latter has aroused a great deal of interest for scanning probe microscopy applications in recent years. In this study, we present a novel method for the fabrication of atomic force microscopy (AFM) probes for force spectroscopy using robust diamond-coated spheres, i.e., colloidal particles. The so-called colloidal probe technique is commonly used to study interactions of single colloidal particles, e.g., on biological samples like living cells, or to measure mechanical properties like the Young’s modulus. Under physiological measurement conditions, contamination of the particle often strongly limits the measurement time and often impedes reusability of the probe. Diamond as a chemically inert material allows treatment with harsh chemicals without degradation to refurbish the probe. Apart from that, the large surface area of spherical probes makes sensitive studies on surface interactions possible. This provides detailed insight into the interface of diamond with other materials and/or solvents. To fabricate such probes, silica microspheres were coated with a nanocrystalline diamond film and attached to tipless cantilevers. Measurements on soft polydimethylsiloxane (PDMS) show that the manufactured diamond spheres, even though possessing a rough surface, can be used to determine the Young’s modulus from a Derjaguin-Muller-Toporov (DMT) fit. By means of force spectroscopy, they can readily probe force interactions of diamond with different substrate materials under varying conditions. The influence of the surface termination of the diamond was investigated concerning the interaction with flat diamond substrates in air. Additionally, measurements in solution, using varying salt concentrations, were carried out, which provide information on double-layer and van-der-Waals forces at the interface. The developed technique offers detailed insight into surface chemistry and physics of diamond with other materials concerning long and short-range force interactions and may provide a valuable probe for investigations under harsh conditions but also on biological samples, e.g., living cells, due to the robustness, chemical inertness, and biocompatibility of diamond.

A great potential of the use of aluminum nitride (AlN) to enhance the actuation of nanocrystalline diamond (NCD) microelectromechanical system disk resonators is revealed. A disk resonator with a unimorph (AlN/NCD) structure is fabricated by depositing a c-axis oriented AlN on a capacitive NCD disk resonator. The unimorph resonator is piezoelectrically actuated with flexural whispering gallery modes with a relatively large electrode gap spacing, i. e., the spacing which is greater than 1 mu m, although this is not possible for the capacitive NCD disk resonator. This result is explained by a finite element method simulation where the piezoelectric actuation turns out to be more effective than the capacitive actuation when the electrode gap spacing is > 0.8 mu m. The simulation also shows that the electrode gap spacing required for the capacitive actuation to be more effective than the piezoelectric actuation exponentially decreases when the resonator dimension is scaled down for higher frequency operations. Our study indicates that the use of AlN is promising to decrease impedance levels of NCD disk resonators especially for their higher frequency operations