Atoms or pairs of ions picked up by probe tips used in dynamic force microscopy (DFM) can be strongly displaced and even hop discontinuously upon approach to the sample surface. The energy barriers for some of those hops are of the right order of magnitude to explain the rise in energy dissipation commonly observed in DFM measurements at room temperature. The systematic computations reported here can explain the infrequent jumps and very low average energy dissipation observed low temperature in a previous DFM study on a KBr(001) sample. Close to the surface we indeed find new states separated by small energy barriers which account for those phenomena. These energy barriers strongly depend on details of the atomic arrangement in the vicinity of the tip apex.

Microscopic experimental data on the distribution of vacancies created in isolated implantation events are reported for the model system B in Cu. An interstitial-to-substitutional conversion process of the implanted B12 ions is utilized to detect lattice damage. We observe vacancy clouds with well-defined edges and a mean radius of 13.5(9)nm. The radial profile of the local vacancy concentration never exceeds 10−4; it is almost flat in the central region before it falls off rapidly, a behavior which cannot be explained by simple binary-collision computer models.

Lattice sites and annealing behavior of implanted N-12 in semi-insulating ZnSe are investigated by use of beta radiation detected nuclear magnetic resonance (P-NMR). For room-temperature implantation only a small part of the N impurities is found at sites with full T-d symmetry; this fraction is attributed to, substitutional N-Se. Above 500 K the population of this site increases and saturates at a 10 times higher value for T greater than or equal to 950 K. This increase is assigned to the change of initially interstitial N (N-i), isolated or part of a complex, to unperturbed N-Se. An activation barrier E-a = 0.47(5) eV is determined for this process representing an upper limit for the N-i migration energy. We do not observe configurations where N-Se is bound to a diamagnetic partner, like the (V-Se-Zn-N-Se)(+) complex.

B 12 probe nuclei are implanted in amorphous Si and monitored by β-radiation-detected nuclear magnetic resonance (β-NMR). Independently of growth conditions and impurity content, we find the same frequency distribution in a variety of samples. This is interpreted as an intrinsic signature of the amorphous environment while preferential B–H pairing is not observed. Comparing our data with earlier B-NMR11 work, we find the local B configuration to be completely controlled by the incorporation process. In our low-dose implantation experiment, all B is fourfold coordinated and electrically active. This is in contrast to gas-phase doping or high-dose implantation where the threefold coordination prevails.

Spin-polarized, radioactive 12B probe nuclei were implanted in microcrystalline Si with typical grain diameters of ∼10nm. Using β-radiation detected nuclear magnetic resonance (β-NMR) we observed broad, unstructured spectra at room temperature. This broadening is shown to be due to structural disorder. It is not caused by hydrogen or other contaminations of the samples.

A density-matrix-based formalism is presented to extract activation parameters for the reorientational motion of an interstitial B defect in Si, a center created by ion implantation. β-radiation detected nuclear magnetic resonance (β-NMR) data show beginning mobility at T≈240K. At T=410K the signal is lost even though the center is still present. The activation energy for its reorientation in p-type Si is determined to be EA=0.53(2)eV.

Using β-radiation detected nuclear magnetic resonance (β-NMR), we investigated the microscopic behavior of implanted 8Li in nominally undoped ZnSe crystals. From the temperature-dependent amplitudes of high-resolution NMR spectra we conclude a gradual interstitial-to-substitutional site change between 200 and 350K. This is in accordance with earlier emission channeling results. We argue that this conversion proceeds via Lii++VZn2−→LiZn− and involves implantation related Zn vacancies.

Using beta -radiation-detected nuclear magnetic resonance (beta -NMR) in the special form of cross-relaxation spectroscopy we studied the diffusional behavior of implanted B-12 nuclei in Cu single crystals at temperatures T=115-750 K. An extended and completely revised dynamic theory of nuclear cross relaxation is developed to analyze the experimental data. Especially the incorporation of (hitherto neglected) spin-lattice relaxation effects turned out to be an important improvement. Applying this formalism we obtain activation energies of E-a=0.57(5) eV for the migration of interstitial B, the dominating fraction for T less than or similar to 400 K, and of E-a =1.15(10) eV for substitutional B formed at higher temperatures. The previously found direct-exchange mechanism for the diffusion of substitutional B in Cu is confirmed by our analysis.

Recently Grassberger [Physica A 262, 251 (1999)] has shown that the correction to scaling for the conductance of a bond-percolation network on a square lattice is a nonmonotonic function of the linear lattice dimension with a minimum at L = 10, while this anomalous behavior is not present in the site-percolation networks. We perform a high-precision numerical study of the bond-percolation random-resistor networks on the square, triangular, and honeycomb lattices to further examine this result. We use the arithmetic, geometric, and harmonic means to obtain the conductance and find that the qualitative behavior does not change: it is not related to the shape of the conductance distribution for small system sizes. We show that the anomaly at small L is absent on the triangular and honeycomb networks. We suggest that the nonmonotonic behavior is an artifact of approximating the continuous system for which the theory is formulated by a discrete one that can be simulated on a computer. We show that by slightly changing the definition of the linear lattice size we can eliminate the minimum at small L without significantly affecting the large L limit.

β-active probe nuclei are implanted in nominally undoped ZnSe crystals. β-radiation detected nuclear magnetic resonance (β-NMR) studies are described for two different probe nuclei, 8Li and 12B. This way, the implantation behavior of two “opposite”dopants, one acceptor (Li) and one donor (B) can be characterized by the same microscopic technique. Such characterizations are attempted in terms of the structure of intermediate or final lattice sites, defect charge states, or the kinetics of defect reactions and site changes.

Microscopic properties of B in ZnSe are investigated by means of beta-radiation-detected nuclear magnetic resonance (beta-NMR). After implantation of spin-polarized, radioactive B-12 nuclei in nominally undoped ZnSe single crystals at stationary concentrations of similar to 10(8) cm(-3), three different B-defect configurations can be distinguished. First, an unperturbed fraction at cubic lattice sites, identified as substitutional B-Zn(+) by a dipolar linewidth analysis. Second, a smaller part of. "perturbed" probes attributed also to B-Zn(+) but with nearby Se vacancies. And third, a paramagnetic configuration, tentatively assigned to the isolated interstitial B-i(2+) Temperature-dependent measurements shaw a conversion of B-i to B-Zn with an activation energy of E-a = 0.61(3) eV which we attribute to B-i migration. After this annealing stage we find a B-Zn fraction of about 85%, i.e., an excellent ''doping efficiency." A substantial inward relaxation of the nearest: Se and next-nearest Zn atoms around the B-Zn(+) donor is observed and compared with model predictions. [S0163-1829(99)05104-8].

Spin polarized radioactive 12B, 12N, and 8Li probe nuclei are implanted in nominally undoped ZnSe at stationary concentrations ≤ 1010 cm-3. These light dopants, one donor and two acceptors, are characterized by β-radiation detected nuclear magnetic resonance (β-NMR) measurements. The donor 12B and the acceptor 12N show quite similar and rather simple implantation behaviour, the situation is markedly different for the second acceptor 8Li, however. This contrast indicates that in semi-insulating ZnSe the structure of dilute impurities is controlled by individual, element-specific properties.

Optical detection of magnetic resonance (ODMR) and photoluminescence (PL) studies are described for the sulfur-related metastable defect in silicon first reported by Brown and Hall. It is established that its two configurations, $A$ and $B,$ are of triclinic ${(C}_{1})$ symmetry, and the incorporation of a single impurity atom with nuclear spin $I=3/2$ is confirmed directly by resolving its hyperfine structure in each ODMR spectrum. Detailed study of the conversion kinetics indicates the dominant $\stackrel{\ensuremath{\rightarrow}}{A}B$ mechanism under below band-gap excitation to be the result of direct optical excitation, not the result of exciton capture or the energy release accompanying the luminescence. The barrier for thermally activated $\stackrel{\ensuremath{\rightarrow}}{B}A$ return is $0.10\ifmmode\pm\else\textpm\fi{}0.01 \mathrm{eV},$ with no evidence of an intermediate configuration. Stress-induced splittings of the PL are satisfactorily analyzed as the sum of that for a highly localized hole plus that for a shallow Coulombically bound effective-mass electron. A tentative model is proposed involving a substitutional sulfur atom paired with an interstitial copper atom in two different nearby configurations. The low symmetry results from the tendency of the Cu interstitial to go off-center from the tetrahedral interstitial position.

Spin-polarized radioactive 12B and 12N probe nuclei are produced in nuclear reactions and implanted into nominally undoped ZnSe at stationary concentrations ≲ 108 cm−3. The implanted impurities are characterized by β-radiation detected nuclear magnetic resonance (β-NMR) measurements within ∼20 ms after the implantation event. About 85% of the implanted B occupy substitutional Zn-sites after moderate annealing and are immobile there up to at least 950 K. Our first data on N implantation show a substantial fraction reaching cubic lattice sites, essentially without any annealing. We tentatively assign this fraction to unperturbed NSe−.

beta-radiation detected nuclear magnetic resonance measurements are reported on the lattice site of N-12 ions implanted into undoped ZnSe. At 800 K a Larmor resonance is observed indicating the existence of diamagnetic N with full T-d symmetry. From the resonance intensity in ZnSe compared to the reference system N-12 in Cu it is estimated that at 800 K about 40% of the implanted N-12 end up in this highly symmetric site. An unambiguous experimental determination of the precise site is still lacking. Arguments are given, however, that the observed signal corresponds to N-se(-). Searches for quadrupolarly disturbed signals from some of the missing 60% of N-12 in configurations of lower symmetry; e.g., complexes with intrinsic defects, were so far not successful.

The fraction of boron atoms that take up defect-free sites on ion implantation in diamond has been investigated in beta-NMR measurements. Polarized B-12 nuclei were produced in the reaction B-11(d,p)B-12 with 1.5 MeV deuterons and recoil implanted into a diamond Ib sample. Depolarization resonance spectra were measured in an external magnetic field of 1.0 kG at sample temperatures ranging from 300 K to 800 K, showing that the polarised B-12 atoms retain their polarisation on implantation in diamond. The polarization asymmetry at the Larmor frequency yielded a fraction of boron atoms at defect-free tetrahedrally symmetric sites of 12(1)% at 300 K, increasing to 17(2)% at 800 K. The resonance spectra also showed evidence that some of the implanted boron atoms were at low symmetry sites.Measurements after pre-implantation of the diamond sample with 50 - 220 keV Li+ ions showed no significant change of the fraction of boron atoms that are implanted at defect-free symmetric sites in the diamond lattice.

Spin polarized B-12 nuclei were produced in B-11(d,p)B-12 nuclear reaction and recoil implanted into a type Ib diamond sample at doses below 10(11) cm(-2). beta-radiation detected nuclear magnetic resonance spectra were measured directly after implantation at sample temperatures ranging from 300 to 800 K. The polarization asymmetry at the Larmor resonance yielded fractions of boron ions at sites of full tetrahedral symmetry of 12(1)% at 300 K, increasing to 17(2)% at 800 K. It is argued that these boron atoms are incorporated substitutionally by direct replacement collisions during the implantation process, The resonance spectra also showed additional boron at low-symmetry sites. (C) 1997 American Institute of Physics. [S0003-6951(97)01551-9].

Spin polarized, radioactive B-12 probe nuclei are implanted into nominally undoped ZnSe single crystals at stationary concentrations less than or equal to 10(9)/cm(3). From temperature and orientation dependent beta-radiation detected nuclear magnetic resonance measurements we conclude that at T = 800 K about 85% of the implanted B end up as ionized donors at Zn-sites (B-Zn(+)) with unperturbed surroundings. The temperature dependence of the B-Zn signal intensity yields activation parameters for the population of this site. We obtain E-A = 0.61(3) eV and a value of 10(6.0(3))/s for th, pre-exponential factor. B-Zn is immobile up to 950 K within the time window of the beta-decay lifetime.